Note: Descriptions are shown in the official language in which they were submitted.
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A GAS HOMOGENIZATION SYSTEM
FIELD OF THE INVENTION
The invention pertains to the field of gas production and conversion to energy
in
downstream applications. In particular, the invention relates to a gas
homogenization
system useful in generating a steady stream of gas of substantially consistent
characteristics.
BACKGROUND
Gasification is a process that enables the conversion of carbonaceous
feedstock, such as
municipal solid waste (MSW) or coal, into a combustible gas. The gas can be
used to
generate electricity, steam or as a basic raw material to produce chemicals
and liquid
fuels.
Possible uses for the gas include: the combustion in a boiler for the
production of steam
for internal processing and/or other external purposes, or for the generation
of electricity
through a steam turbine; the combustion directly in a gas turbine or a gas
engine for the
production of electricity; fuel cells; the production of methanol and other
liquid fuels; as
a further feedstock for the production of chemicals such as plastics and
fertilizers; the
extraction of both hydrogen and carbon monoxide as discrete industrial fuel
gases; and
other industrial applications.
Generally, the gasification process consists of feeding carbonaceous feedstock
into a
heated chamber (the gasifier) along with a controlled and/or limited amount of
oxygen
and optionally steam. In contrast to incineration or combustion, which operate
with
excess oxygen to produce C02, H20, SOx, and NOx, gasification processes
produce a raw
gas composition comprising CO, H2, H2S, and NH3. After clean-up, the primary
gasification products of interest are H2 and CO.
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Useful feedstock can include any municipal waste, waste produced by industrial
activity
and biomedical waste, sewage, sludge, coal, heavy oils, petroleum coke, heavy
refinery
residuals, refinery wastes, hydrocarbon contaminated soils, biomass, and
agricultural
wastes, tires, and other hazardous waste. Depending on the origin of the
feedstock, the
volatiles may include H20, H2, N2, 02, C02, CO, CH4, H2S, NH3, C21-I6,
unsaturated
hydrocarbons such as acetylenes, olefins, aromatics, tars, hydrocarbon liquids
(oils) and
char (carbon black and ash).
As the feedstock is heated, water is the first constituent to evolve. As the
temperature of
the dry feedstock increases, pyrolysis takes place. During pyrolysis the
feedstock is
thermally decomposed to release tars, phenols, and light volatile hydrocarbon
gases while
the feedstock is converted to char.
Char comprises the residual solids consisting of organic and inorganic
materials. After
pyrolysis, the char has a higher concentration of carbon than the dry
feedstock and may
serve as a source of activated carbon. In gasifiers operating at a high
temperature ( >
1,200 C) or in systems with a high temperature zone, inorganic mineral matter
is fused
or vitrified to form a molten glass-like substance called slag.
Since the slag is in a fused, vitrified state, it is usually found to be non-
hazardous and
may be disposed of in a landfill as a non-hazardous material, or sold as an
ore, road-bed,
or other construction material. It is becoming less desirable to dispose of
waste material
by incineration because of the extreme waste of fuel in the heating process
and the further
waste of disposing, as a residual waste, material that can be converted into a
useful
syngas and solid material.
The means of accomplishing a gasification process vary in many ways, but rely
on four
key engineering factors: the atmosphere (level of oxygen or air or steam
content) in the
gasifier; the design of the gasifier; the internal and external heating means;
and the
operating temperature for the process. Factors that affect the quality of the
product gas
include: feedstock composition, preparation and particle size; gasifier
heating rate;
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residence time; the plant configuration including whether it employs a dry or
slurry feed
system, the feedstock-reactant flow geometry, the design of the dry ash or
slag mineral
removal system; whether it uses a direct or indirect heat generation and
transfer method;
and the syngas cleanup system. Gasification is usually carried out at a
temperature in the
range of about 650 C to 1200 C, either under vacuum, at atmospheric pressure
or at
pressures up to about 100 atmospheres.
There are a number of systems that have been proposed for capturing heat
produced by
the gasification process and utilizing such heat to generate electricity,
generally known as
combined cycle systems.
The energy in the product gas coupled with substantial amounts of recoverable
sensible
heat produced by the process and throughout the gasification system can
generally
produce sufficient electricity to drive the process, thereby alleviating the
expense of local
electricity consumption. The amount of electrical power that is required to
gasify a ton of
a carbonaceous feedstock depends directly upon the chemical composition of the
feedstock.
If the gas generated in the gasification process comprises a wide variety of
volatiles, such
as the kind of gas that tends to be generated in a low temperature gasifier
with a "low
quality" carbonaceous feedstock, it is generally referred to as off-gas. If
the
characteristics of the feedstock and the conditions in the gasifier generate a
gas in which
CO and H2 are the predominant chemical species, the gas is referred to as
syngas. Some
gasification facilities employ technologies to convert the raw off-gas or the
raw syngas to
a more refined gas composition prior to cooling and cleaning through a gas
quality
conditioning system.
Utilizing plasma heating technology to gasify a material is a technology that
has been
used commercially for many years. Plasma is a high temperature luminous gas
that is at
least partially ionized, and is made up of gas atoms, gas ions, and electrons.
Plasma can
be produced with any gas in this manner. This gives excellent control over
chemical
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reactions in the plasma as the gas might be neutral (for example, argon,
helium, neon),
reductive (for example, hydrogen, methane, ammonia, carbon monoxide), or
oxidative
(for example, oxygen, carbon dioxide). In the bulk phase, a plasma is
electrically neutral.
Some gasification systems employ plasma heat to drive the gasification process
at a high
temperature and/or to refine the offgas/syngas by converting, reconstituting,
or reforming
longer chain volatiles and tars into smaller molecules with or without the
addition of
other inputs or reactants when gaseous molecules come into contact with the
plasma heat,
they will disassociate into their constituent atoms. Many of these atoms will
react with
other input molecules to form new molecules, while others may recombine with
themselves. As the temperature of the molecules in contact with the plasma
heat
decreases all atoms fully recombine. As input gases can be controlled
stoichiometrically,
output gases can be controlled to, for example, produce substantial levels of
carbon
monoxide and insubstantial levels of carbon dioxide.
The very high temperatures (3000 to 7000 C) achievable with plasma heating
enable a
high temperature gasification process where virtually any input feedstock
including waste
in as-received condition, including liquids, gases, and solids in any form or
combination
can be accommodated. The plasma technology can be positioned within a primary
gasification chamber to make all the reactions happen simultaneously (high
temperature
gasification), can be positioned within the system to make them happen
sequentially (low
temperature gasification with high temperature refinement), or some
combination thereof.
The gas produced during the gasification of carbonaceous feedstock is usually
very hot
but may contain small amounts of unwanted compounds and requires further
treatment to
convert it into a useable product. Once a carbonaceous material is converted
to a gaseous
state, undesirable substances such as metals, sulfur compounds and ash may be
removed
from the gas. For example, dry filtration systems and wet scrubbers are often
used to
remove particulate matter and acid gases from the gas produced during
gasification. A
number of gasification systems have been developed which include systems to
treat the
gas produced during the gasification process.
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These factors have been taken into account in the design of various different
systems
which are described, for example, in U.S. Patent Nos. 6,686,556, 6,630,113,
6,380,507;
6,215,678, 5,666,891, 5,798,497, 5,756,957, and U.S. Patent Application Nos.
2004/0251241, 2002/0144981. There are also a number of patents relating to
different
technologies for the gasification of coal for the production of synthesis
gases for use in
various applications, including U.S. patent Nos. 4,141,694; 4,181,504;
4,208,191;
4,410,336; 4,472,172; 4,606,799; 5,331,906; 5,486,269, and 6,200,430.
Prior systems and processes have not adequately addressed the problems that
must be
dealt with on a continuously changing basis. Some of these types of
gasification systems
describe means for adjusting the process of generating a useful gas from the
gasification
reaction. Accordingly, it would be a significant advancement in the art to
provide a
system that can efficiently gasify carbonaceous feedstock in a manner that
maximizes the
overall efficiency of the process, and/or the steps comprising the overall
process.
As noted above, gas from a gasification system can be exploited for a variety
of
applications such as the conversion of the gas to energy in the form of
electricity or
chemical applications such as fuel cells or chemical feedstock. The equipment,
which is
used to directly convert gas into electricity currently comprises gas turbines
and gas
engines. These machines are designed to function within a very strict range of
characteristics and are often very sensitive to changes in certain gas
characteristics. In
addition to affecting the efficiency of engine operation, a deviation in the
gas
characteristics may even have a negative effect on engine operation. For
example,
changes in the gas characteristics can affect the emissions, efficiency, knock
and
combustion stability, as well as increase the maintenance requirements of the
engine.
Accordingly, these gas-utilizing machines work most effectively when the
characteristics
of the gas are maintained within the specified limits.
The characteristics of the gas produced by a gasification system, such as
chemical
composition, flow rate, temperature, pressure, and relative humidity will
naturally vary
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over time largely due to variations in the feedstock composition and the
reaction
conditions that occur, for example, during the gasification process. Some
characteristics
of the gas will vary on a minute-to-minute basis and some characteristics on a
second-to-
second basis. A steady stream of gas with consistent characteristics will be
produced
only if the gas is allowed to mix thoroughly to ensure a homogeneous gas
composition
and the other characteristics such as temperature, pressure and flow rate are
adjusted.
U.S. Patent No. 6,398,921 describes a gasification process for producing fuel
gas for use
in internal combustion engines for the generation of electricity. Prior to
fueling the
engine, the fuel gas is cleaned, compressed, and stored in a tank for limited
surge storage.
Although the fuel gas is regulated to the inlet pressure required for the
engine, the fuel
gas is not regulated for other characteristics, namely its composition.
Accordingly, there
remains a need for a gas homogenization system, which minimizes variance in
the gas
characteristics (composition, flow rate, pressure, temperature), thereby
rendering a steady
stream of gas of consistent quality required by downstream machinery.
This background information is provided for the purpose of making known
information
believed by the applicant to be of possible relevance to the invention. No
admission is
necessarily intended, nor should be construed, that any of the preceding
information
constitutes prior art against the invention.
SUMMARY OF THE INVENTION
This invention provides a gas homogenization system for homogenizing the
chemical
composition of an input gas and adjusting other characteristics such as flow
rate,
pressure, and temperature of the gas, thereby creating a regulated gas to meet
downstream requirements. This system enables a continual and steady stream of
gas of
defined characteristics to be delivered to downstream applications, for
example, a gas
turbine, engine or other suitable applications.
In particular, the gas homogenization system of the invention provides a gas
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homogenization chamber having dimensions that are designed to accommodate a
gas
residence time sufficient to attain a homogeneous gas of a consistent output
composition.
Other elements of the gas homogenization system are designed and configured
such that
the regulated gas meets the performance requirements of a downstream
application. The
system may also comprise a feedback control system to optimize the energetics
and
output of the process.
An object of the invention is to provide a gas homogenization system. In
accordance
with an aspect of the invention, there is provided a gas homogenization system
for
regulating gas characteristics, comprising: a homogenization chamber
comprising a gas
inlet and a gas outlet; one or more sensing elements associated with the
homogenization
chamber for monitoring one or more characteristics of the gas; one or more
response
elements associated with the homogenization chamber for affecting a change to
the one
or more characteristics of the gas; and one or more process devices
operatively connected
to the one or more response elements for adjusting the one or more
characteristics of the
gas; wherein the homogenization chamber is designed to accommodate a residence
time
sufficient to enable monitoring and regulation of the one or more gas
characteristics.
In accordance with another aspect of the invention, there is provided a gas
homogenization system for regulating gas characteristics, comprising: a
homogenization
chamber comprising a gas inlet and a gas outlet; a gas inlet mechanism in
fluid
communication with the gas inlet of the homogenization chamber, comprising:
one or
more inlet conduits, and one or more sensing elements for monitoring of data
relating to
chemical composition, temperature, flow rate, and pressure parameters of the
gas; a
regulated gas outlet mechanism in fluid communication with the gas outlet of
the
homogenization chamber for directing output of stabilized gas to a downstream
application, the outlet mechanism comprising one or more outlet conduits; one
or more
process devices associated with the system to regulate the chemical
composition,
temperature, flow rate, and pressure parameters of the gas; and one or more
response
elements operatively associated with the one or more process devices for
affecting the
system to optimize the chemical composition, temperature, flow rate, and
pressure
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parameters of the gas; wherein the homogenization chamber is designed to
accommodate
a residence time sufficient to enable monitoring and regulation of the gas
composition,
temperature, flow rate, and pressure.
In accordance with an aspect of the invention, there is provided a process for
converting
an input gas to a regulated gas using the gas homogenization system according
to the
invention, the process comprising the steps of: providing an input gas;
monitoring the gas
within the system for chemical composition, temperature, flow rate, and
pressure by way
of the one or more sensing elements; and providing instructions to the one or
more
response elements for adjusting the one or more process devices to optimize
the chemical
composition, temperature, flow rate, and/or pressure parameters of the gas
thereby
producing a regulated gas that satisfies the requirements of the downstream
application.
BRIEF DESCRIPTION OF THE FIGURES
These and other features of the invention will become more apparent in the
following
detailed description in which reference is made to the appended drawings.
Figure 1A is an illustration of a gas homogenization system, in accordance
with one
embodiment of the invention, where gas is delivered from a single source to a
single
homogenization chamber and then delivered to a single engine by way of a gas
conditioning skid.
Figure 1B is an illustration of a gas homogenization system, in accordance
with one
embodiment of the invention, where gas is delivered from a single source to a
single
homogenization chamber and then delivered to a single engine by way of a
heater, filter
and a pressure regulator valve.
Figure 2 is an illustration of a gas homogenization system, in accordance with
one
embodiment of the invention, where gas is delivered from a single source to a
single
homogenization chamber and then delivered to multiple engines by way of a
heater and a
plurality of filters and pressure regulator valves.
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Figure 3 is an illustration of a gas homogenization system, in accordance with
one
embodiment of the invention, where gas is delivered from a single source to a
single
homogenization chamber and then delivered to multiple engines, each engine
having its
own gas conditioning skid.
Figure 4 is an illustration of a gas homogenization system, in accordance with
one
embodiment of the invention, where gas is delivered from multiple sources to a
single
homogenization chamber and then delivered to multiple engines, each engine
having its
own gas conditioning skid.
Figure 5 is an illustration of a gas homogenization system, in accordance with
one
embodiment of the invention, where gas is delivered to multiple engines from
two
parallel streams, each stream comprising a single source of gas delivered to a
single
homogenization chamber.
Figure 6 is an illustration of a constant-volume homogenization chamber, in
accordance
with one embodiment of the invention.
Figure 7 is an illustration of the design and functionality of a variable-
volume
homogenization chamber, in accordance with one embodiment of the invention.
Figure 8 is an illustration of a homogenization chamber configured as pressure
vessel
and compressor combination, in accordance with one embodiment of the
invention.
Figure 9 is an illustration of a homogenization chamber configured as a double
membrane gas holder, in accordance with one embodiment of the invention.
Figure 10A is an illustration of a homogenization chamber configured as an
absorption-
type gas holder, in accordance with one embodiment of the invention.
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Figure 10B is a cross-sectional view of the absorption-type gas holder showing
the design
of the absorbent material.
Figure 11 is an illustration of a homogenization chamber configured as an
underground
constant volume large diameter pipe, in accordance with one embodiment of the
invention.
Figure 12 is an illustration of a plurality of constant-volume homogenization
chambers
arranged in parallel, in accordance with one embodiment of the invention.
Figure 13 is an illustration of a gas/liquid separator, in accordance with one
embodiment
of the invention.
Figure 14A illustrates a draft induction device configured as a pressure
blower, in
accordance with one embodiment of the invention.
Figure 14B illustrates a draft induction device configured as a vacuum pump,
in
accordance with one embodiment of the invention.
Figure 15 is a flow diagram of a gasification process according to one
embodiment of the
invention.
Figures 16A-D illustrate pressure regulating devices, in accordance with
embodiments of
the invention.
Figures 17A-D present flow regulating devices, in accordance with embodiments
of the
invention.
Figure 18 presents a control valve in accordance with one embodiment of the
invention.
Figures 19A-K illustrate mounting and bracketing devices for the pressure
transmitter, in
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accordance with embodiments of the invention.
Figures 20A illustrates an axial-flow compressor in accordance with one
embodiment of
the invention.
Figures 20B illustrates a reciprocating compressor in accordance with one
embodiment of
the invention.
Figures 20C illustrates a rotary screw compressor in accordance with one
embodiment of
the invention.
Figures 20D illustrates a single stage centrifugal compressor in accordance
with one
embodiment of the invention.
Figures 20E illustrates a two-stage centrifugal compressor in accordance with
one
embodiment of the invention.
Figures 21A illustrates relief valve mechanisms of 1.5"x2" through 3"x4, in
accordance
with embodiments of the invention.
Figures 21B illustrates relief valve mechanisms of 4"x6" through 12"x16", in
accordance
with embodiments of the invention.
Figure 22 is a flow diagram of an integrated system combining an Integrated
Gasification
Combined Cycle (IGCC) power plant and a Liquid Phase Methanol Process
(LPMEOHe)
reactor, in accordance with one embodiment of the invention.
Figure 23 is a flow diagram of an integrated system, in accordance with one
embodiment
of the invention, where Integrated Gasification Combined Cycle (IGCC) power
plant and
Fischer Tropsch (F-T) liquids co-production is used.
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Figure 24 is an illustration of a constant-volume homogenization chamber, in
accordance
with an embodiment of the invention.
Figure 25 is an illustration of a Gas Conditioning System (GCS) and a Gas
Storage Tank
according to one embodiment of the invention.
Figure 26 is a flow diagram of a Municipal Solid Waste (MSW) Plasma
Gasification
Plant according to one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
Definitions
As used herein, the term "about" refers to approximately a +/-10% variation
from the
stated value.
The term "composition of the gas," refers to the entire composition of
chemical species
within a gas. In practice, however, this term will generally be used to
express the species
and concentrations of the chemical constituents that are most relevant to the
downstream
applications. For example, gas composition desirable for a gas turbine will
generally be
described in terms of the amount of nitrogen, carbon monoxide, carbon dioxide,
water
and/or hydrogen in the synthesis gas. The chemical composition may also be
identified
as lacking specific chemical species, i.e. species that would be undesirable
to transfer to
the downstream application, such as a gas being, `free of H2S." The chemical
composition of gas can vary widely, depending on the composition of the
feedstock used
to generate the gas and the manner in which the gasification process, the gas
cleanup and
conditioning were carried out. Depending on the context, which will be
apparent to one
skilled in the art, the composition of the gas will or will not contemplate
trace elements.
The term, "characteristics of the gas," refers to the relevant chemical and
physical
qualities of the gas, including its chemical composition, temperature,
pressure, rate of
flow etc. Depending upon the context, one skilled in the art can appreciate
that it may
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include color, odor, etc.
LHV means low heating value.
HHV means high heating value
As used herein, the term "sensing element" is defined to describe any element
of the
system configured to sense a characteristic of a process, a process device, a
process input
or process output, wherein such characteristic may be represented by a
characteristic
value useable in monitoring, regulating and/or controlling one or more local,
regional
and/or global processes of the system. Sensing elements considered within the
context of
a gasification system may include, but are not limited to, sensors, detectors,
monitors,
analyzers or any combination thereof for the sensing of process, fluid and/or
material
temperature, pressure, flow, composition and/or other such characteristics, as
well as
material position and/or disposition at any given point within the system and
any
operating characteristic of any process device used within the system. It will
be
appreciated by the person of ordinary skill in the art that the above examples
of sensing
elements, though each relevant within the context of a gasification system,
may not be
specifically relevant within the context of the present disclosure, and as
such, elements
identified herein as sensing elements should not be limited and/or
inappropriately
construed in light of these examples.
As used herein, the term "response element" is defined to describe any element
of the
system configured to respond to a sensed characteristic in order to operate a
process
device operatively associated therewith in accordance with one or more pre-
determined,
computed, fixed and/or adjustable control parameters, wherein the one or more
control
parameters are defined to provide a desired process result. Response elements
considered
within the context of a gasification system may include, but are not limited
to static, pre-
set and/or dynamically variable drivers, power sources, and any other element
configurable to impart an action, which may be mechanical, electrical,
magnetic,
pneumatic, hydraulic or a combination thereof, to a device based on one or
more control
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parameters. Process devices considered within the context of a gasification
system, and to
which one or more response elements may be operatively coupled, may include,
but are
not limited to, material and/or feedstrock input means, heat sources such as
plasma heat
sources, additive input means, various gas blowers and/or other such gas
circulation
devices, various gas flow and/or pressure regulators, and other process
devices operable
to affect any local, regional and/or global process within a gasification
system. It will be
appreciated by the person of ordinary skill in the art that the above examples
of response
elements, though each relevant within the context of a gasification system,
may not be
specifically relevant within the context of the present disclosure, and as
such, elements
identified herein as response elements should not be limited and/or
inappropriately
construed in light of these examples.
Unless defined otherwise, all technical and scientific terms used herein have
the same
meaning as commonly understood by one of ordinary skill in the art to which
this
invention belongs.
Overview
The invention provides a homogenization system for homogenizing the chemical
composition of a gas and for adjusting other gas characteristics such as flow
rate,
pressure, and temperature to meet the requirements of downstream applications.
The
resulting output gas stream called the regulated gas is substantially
continual and steady
and has substantially well-controlled characteristics suitable for a
downstream
application.
This invention provides a system comprising one or more chambers of various
sizes and
shapes wherein the primary objective of the chamber is to homogenize the
composition
of a gas to attain a consistent output stream of gas, for example, by reducing
fluctuations
in the concentration of its relevant chemical constituents. The concentration
of chemical
constituents in the output gas will only vary within the range allowable for
the relevant
chemical constituents. The shape of the chamber can range from a standard gas
storage
tank, with fixed or floating roof, down to wide diameter pipe. An important
consideration for the homogenization chamber is its volume which will ensure
that the
gas achieves a critical residence time to enable sufficient homogenization of
its chemical
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constituents. Other considerations include pressure and temperature
(especially
environmental) requirements.
Downstream applications, such as gas engines and gas turbines, can tolerate
only a
limited rate of change and limited overall change of gas characteristics, such
as gas
pressure and the lower heating value (LHV), outside of which the performance,
reliability
or emissions of the application may be affected. Accordingly, it is
advantageous to
stabilize the variance as much as possible to optimize application
performance. The
system of this invention provides the ability to deliver a regulated gas that
only varies
within the rates and ranges allowed by an application, and does so such that
the gas
quality is in a range that the system can produce energy in substantially the
most cost
effective manner possible. Accordingly, in one embodiment, the regulated gas
of the
invention is gas within which the rate of change of the gas LHV and pressure,
and the
overall change of LHV and pressure are within the tolerance limits of a
downstream
application.
Prior to defining the components and process associated with the gas
homogenization
system, a brief overview of the input gas and regulated gas characteristics
are provided
below.
Input Gas Characteristics
The composition of the gas, which will enter the homogenization system of the
invention,
is determined by the gasification process. Adjustments made during the
gasification
process permit the gas to be optimized for specific end-applications (e.g.,
gas turbines for
electricity generation), or optimized for gas generation from different
feedstocks, i.e.,
different sources of carbon, such as coal or municipal solid waste (MSW).
Accordingly,
the composition of the gas can be tailored for particular energy generating
technologies
(for example, for specific gas engines or gas turbines) and, for best overall
conversion
efficiency, according to the different types of feedstock used, by adjusting
the operational
parameters of the gasification process.
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The gas entering the system may be derived from a gasification system.
Examples of
suitable input gases include those derived from a gasifier, a gas conditioning
system
(GCS), a solid residue gas conditioner, and the like. In one embodiment, the
input gas is a
clean gas derived from a H2S scrubber, a HC1 scrubber or an activated carbon
bed.
The gas leaving the gasification system, may be within a defined range of a
target
composition, however, over time the gas may fluctuate in its characteristics
due to
variability in the gasification process such as feedstock composition and feed
rate,
airflow and temperature fluctuations.
Composition and Variances
Typically the main components of the gas as it leaves a gasification system
tend to be
carbon monoxide, nitrogen, carbon dioxide, hydrogen, and water. Much smaller
amounts
of methane, ethylene, hydrogen chloride and hydrogen sulfide may also be
present.
The exact proportions of the different chemical constituents depend on the
type of
feedstock used. For example, gas produced from coal (which is generally
considered to
be a relatively even composition of carbonaceous feedstock compared to
municipal solid
waste), under a specific set of operating conditions, yields about 26% carbon
monoxide,
about 11.5% carbon dioxide, about 28% hydrogen and about 31% water vapour.
Gasification of sub-bituminous coal (which has a composition suitable for
about 23.1
MJ/kg- 25.1% moisture content), under another set of operating conditions,
yields about
18.2%, about 6.9%, about 17.8% and about 15.1%, carbon monoxide, carbon
dioxide,
hydrogen and water, respectively. In fact, there are several different types
of coal,
ranging from peat to lignite (moisture around about 70%, energy content around
about 8-
MJ/kg), to black coal (moisture around about 3% and energy content about 24 -
28MJ/kg) to anthracite (virtually no moisture and energy content up to about
32MJ/kg),
that may each exhibit substantial variability in the gas produced therefrom.
Pressure and Temperature
Similar to the control of gas composition, the pressure and temperature of the
gas can
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also be monitored and controlled in the gasification system in order to
maintain these
parameters within the tolerance limits prescribed by a downstream application.
Despite
these controls, however, fluctuations in both the pressure and temperature of
the gas will
typically occur over time. In the case of pressure, fluctuations may occur on
a per second
basis; and with temperature, on a per minute basis. In one embodiment of the
invention,
the pressure variance limit is selected to be < than about 0.145 psi/second.
Regulated Gas Characteristics
As noted above, the regulated gas exiting the gas homogenization system of the
invention
has substantially stabilized characteristics that meet the specifications of a
downstream
application. Typically, machine manufacturers will provide the requirements
and
tolerances allowed by specific machinery; such gas parameters for a gas engine
or gas
turbine would be known to a person skilled in the art. In one embodiment of
the
invention, a gas engine may require a regulated gas composition LHV to have a
maximum of about 1% change in about 30 seconds. In one embodiment of the
invention,
gas engines can accept gas with HHV as low as about 50BTU/scf, so long as it
contains a
minimum of about 12% Hydrogen. In one embodiment of the invention, the
regulated gas
requires the Wobbe Index (defined as T(degrees R)/sq.rt (specific gravity)) to
be +/- 4%
of the design value for use with turbine engines. In addition, a turbine
engine may also
require a minimum LHV of about 300 Btu/scf and a minimum pressure of about 475
psig.
In one embodiment of the invention, the engine will require a regulated gas
temperature
greater than or equal to the dew point temperature plus about 20 F where
relative
humidity is at a maximum of about 80%.
Gas Homogenization System
As mentioned above, the invention provides a system that collects gas and
attenuates
fluctuations in the chemistry of the gas composition in a homogenization
chamber. Other
elements of the system optionally adjust characteristics of the gas such as
flow rate,
humidity, temperature and pressure to be within ranges that are acceptable to
a
downstream application. The system thereby regulates the characteristics of
the gas to
produce a continual stream of gas with substantially consistent
characteristics for delivery
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to a downstream application, such as a gas engine or a gas turbine. The system
may also
comprise a feedback control system to optimize the energetics and output of
the process.
Figure 1A illustrates a gas homogenization system 1 configured in accordance
with one
embodiment of the invention for the production of a regulated gas. The gas
homogenization system 1 comprises: a chiller 10; a gas/liquid separator 12; a
homogenization chamber 14, to which a relief valve 16 and a pressure control
valve 18
are connected; a gas conditioning skid 20, comprising a gas/liquid separator
22 and a
heater 24; a filter 26; and a pressure regulating valve 28. The regulated gas
may
subsequently be directed through a suitable conduit to an engine 30.
As indicated by the arrows in Figure 1A, a gas enters the homogenization
system 1 at the
chiller 10, where the temperature of the gas is appropriately adjusted. The
gas is then
delivered to the separator 12, by suitable conduit means, where the humidity
of the gas is
regulated. Following this, the gas enters the homogenization chamber 14, by
way of gas
inlet conduit means. Once in the homogenization chamber 14, the gas is mixed
or
blended, resulting in a gas having a stabilized composition. The gas flow rate
and
pressure of the mixed or blended gas are further regulated upon exit of the
mixed or
blended gas from the homogenization chamber. Suitable conduit means then carry
the
mixed or blended gas to the gas conditioning skid 20, where regulation of the
temperature
and humidity of the mixed or blended gas is undertaken. The mixed or blended
gas,
carried by suitable conduit means, is then filtered 26 and regulated for
pressure 28. The
resulting regulated gas, now meeting the desired requirements for a downstream
application, may be directed through suitable conduit means to the engine 30.
Typically, gas will be conveyed from a gasification process to the
homogenization
chamber as it is generated. To ensure a uniform input gas flow rate, a draft
induction
device may also be employed. Similarly, to ensure that factors such as gas
composition,
flow rate, temperature and pressure of the input gas stream are compliant with
the desired
range of target characteristics, the input gas may be monitored by a
monitoring system, as
would be known to the skilled technician, prior to homogenization. Given the
outcome
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of the analysis of these factors, gas may then be directed to the
homogenization chamber.
Figure 1B illustrates a gas homogenization system 100, in accordance with one
embodiment of the invention which is configured for the production of a
regulated gas.
The gas homogenization system 100 comprises a chiller 110; a gas/liquid
separator 112; a
homogenization chamber 114, to which a relief valve 116 and a pressure control
valve
118 are connected; a heater 124; a filter 126; and a pressure regulating valve
128. The
regulated gas may subsequently be directed through a suitable conduit to an
engine 130.
Figure 2 illustrates a gas homogenization system 200 configured in accordance
with one
embodiment of the invention which is configured for the production of a
regulated gas.
The gas homogenization system 200 comprises: a chiller 210; a gas/liquid
separator 212;
a homogenization chamber 214, to which a relief valve 216 and a pressure
control valve
218 are connected; a heater 224; a filter 232; a series of filters 226; and a
series of
pressure regulating valves 228. Thus, the gas is derived from a single source
and the
regulated gas is delivered to a series of engines 230 by way of a single
homogenization
chamber 214.
Figure 3 illustrates a gas homogenization system 300 configured in accordance
with one
embodiment of the invention which is configured for the production of a
regulated gas.
The gas homogenization system 300 comprises: a chiller 310; a gas/liquid
separator 312;
a homogenization chamber 314, to which a relief valve 316 and a pressure
control valve
318 are connected; a series of gas conditioning skids 320, each skid
comprising a
gas/liquid separator 322 and a heater 324; a series of filters 326; and a
series of pressure
regulating valves 328. Thus, the regulated gas is delivered from a single
source to a
series of engines 330 by way of a single homogenization chamber 314 and a
series of gas
conditioning skids 320.
Figure 4 illustrates a gas homogenization system 400 configured in accordance
with one
embodiment of the invention which is configured for the production of a
regulated gas.
The gas homogenization system 400 comprises a series of chillers 410 and a
series of
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gas/liquid separators 412, which feed into a single homogenization chamber
414; a series
of gas conditioning skids 420, each skid comprising a gas/liquid separator 422
and a
heater 424; a series of filters 426; and a series of pressure regulating
valves 428. Thus,
the regulated gas is generated from multiple gas sources and delivered to a
series of
engines 430, by way of a single homogenization chamber 414.
Figure 5 illustrates a gas homogenization system 500 configured in accordance
with one
embodiment of the invention which is configured for the production of a
regulated gas.
The gas homogenization system 500 comprises: two parallel streams of
components
500a and 500b, each stream comprising a chiller 510, a gas/liquid separator
512, a
homogenization chamber 514, a heater 524, and a filter 532. The regulated gas
from the
two streams 500a and 500b are combined and delivered to a series of engines
530 by way
of a series of filters 526, and a series of pressure regulating valves 528.
The above figures relate to exemplary configurations of the gas homogenization
system
and are, therefore, not intended to limit the scope of the invention in any
way. As would
be apparent to a worker skilled in the art, other suitable configurations of a
gas
homogenization system would be useful in producing a regulated gas that
satisfies the
requirements of a downstream application. Accordingly, such configurations are
also
herein contemplated.
1) Homogenization Chamber
As previously mentioned, the gas homogenization chamber of the invention
receives gas
produced from a gasification system and encourages mixing or blending of the
gas to
attenuate fluctuations in the chemical composition of the gas within the
homogenization
chamber. Fluctuations in other gas characteristics, such as pressure,
temperature and
flow rate, can also be reduced during mixing of the gas.
In one embodiment of the invention, the dimensions of the chamber are designed
according to the performance characteristics of an upstream gasification
system and the
requirements of a downstream application, with the objective of substantially
minimizing
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the size of the chamber as much as possible. The gas homogenization chamber is
designed to receive gas from a gasification process and retain the gas for a
certain
residence time to allow for sufficient mixing or blending of the gas in order
to dampen
disturbances and/or fluctuations and achieve a volume of gas with a
substantially
consistent chemical composition.
In one embodiment of the invention, the dimensions of a homogenization chamber
can be
calculated based on the total system response time which includes the process
residence
time between the converter and the analyzer sample probe, plus the total
system response
time for the sample system, analysis and transmission time to a plant control
system
(PCS).
Residence Time
The residence time is the average amount of time that gas remains in the
homogenization
chamber before being directed to a downstream application. The residence time
is
substantially proportional to the response time of the related gasification
system to
dampen the effect of the rate of change of the fluctuations in the
gasification reaction in
order to achieve gas characteristics that fall within accepted tolerance
values. For
example, the gas composition is retained in the homogenization chamber long
enough to
determine whether it falls within the gas composition tolerance allowed for
the particular
downstream application as well as to make any adjustments to the gasification
process to
adjust for the deviance. In this way, the system can affect the rate of change
in gas
characteristics so that upstream controls with fast process lags will be able
to meet the
specifications of a downstream application. In one embodiment, the residence
time is
determined by about 1% maximum change in the lower heating value (LHV) per 30
seconds and a maximum change in pressure of about 0.145psi/second.
Residence time of the gas in the homogenization chamber is determined by the
amount of
variance in the gas characteristics. That is, the smaller the variance in gas
characteristics,
the shorter the residence time required in the homogenization chamber to
correct for this
variance.
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Depending on the different embodiments of the present invention, the residence
time can
vary from less than about one minute to about 20 minutes. In one embodiment,
the
residence time ranges from about 15 to about 20 minutes. In one embodiment the
residence time ranges from about 10 to about 15 minutes. In one embodiment,
the
residence time ranges from about 5 to about 10 minutes. In one embodiment of
the
invention, the residence time ranges from about 3 to about 5 minutes. In one
embodiment of the invention, the residence time ranges from about 1 to about 3
minutes.
In one embodiment of the invention, the residence time ranges from amounts
less than
about one minute.
In one embodiment, the residence time is about 20 minutes. In one embodiment
the
residence time is about 18 minutes. In one embodiment, the residence time is
about 15
minutes. In one embodiment, the residence time is about 13 minutes. In one
embodiment, the residence time is about 10 minutes. In one embodiment, the
residence
time is about 8 minutes. In one embodiment, the residence time is about 6
minutes. In
one embodiment, the residence time is about 4 minutes. In one embodiment, the
residence time is about 3 minutes. In one embodiment, the residence time is
about 2
minutes. In one embodiment, the residence time is about 1 minute. In one
embodiment,
the residence time is less than about 1 minute.
Volume CapacitX
As mentioned earlier, the volume capacity of the homogenization chamber is
related to
the residence time required for a specific downstream application and
fluctuations that
are expected because of heterogeneity of the feedstock. In one embodiment of
the
invention, the variable gas volume ranges from about 0-290 m3. In one
embodiment, the
variable gas volume ranges from about 0-1760 m3. In one embodiment, the
variable gas
volume ranges from about 0-2050 m3. In one embodiment, the variable gas volume
ranges from about 0-30,000 m3. In one embodiment of the invention, the
homogenization
chamber has a maximum capacity of about 290 m3. In one embodiment, the
homogenization chamber has a maximum capacity of about 1800 m3. In one
embodiment
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of the invention, the homogenization chamber has a maximum capacity of about
2300 m3. In one embodiment of the invention, the homogenization chamber has a
maximum capacity of about 30,000 m3.
Design Pressure and Possibilities of Low Pressure and High Pressure
Chambers/Systems
The downstream application selected can directly impact the operating pressure
of the
homogenization chamber. For example, a gas engine will require a gas pressure
of about
1.2-3.0 psig while a gas turbine will require a gas pressure of about 250-600
psig. The
mechanical design pressure of the homogenization chamber is correspondingly
calculated
to accommodate the required operating pressure for a selected application. In
one
embodiment, the homogenization chamber has a mechanical design pressure
suitable for
maintaining the gas pressure for use in a gas engine. In one embodiment, the
homogenization chamber has a mechanical design pressure suitable for
maintaining the
gas pressure for use in a gas turbine. In one embodiment the homogenization
chamber
has a mechanical design pressure of about 5.0 psig. In one embodiment of the
invention,
the homogenization chamber has a mechanical design pressure of about 10.0
psig. In one
embodiment of the invention, the homogenization chamber has a mechanical
design
pressure of about 25.0 psig. In one embodiment of the invention, the
homogenization
chamber has a mechanical design pressure in the range of about 100 to about
600 psig.
One skilled in the art can also appreciate that to meet the requirements of
downstream
applications, such as a gas engine, a lower pressure system would be more
advantageous
than for other applications, such as a gas turbine, where a higher pressure
gas stream
would be more appropriate.
Desi ng Temperature
The homogenization chamber has a mechanical design temperature tolerance that
will
accommodate the gas being contained and the specifications of the downstream
application. Typically, these temperatures will range from about -40 C to
about 300 C.
In one embodiment of the invention, the mechanical design temperature of the
chamber
ranges from about -37 C to about 93 C.
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Type and Shape of Homogenization Chambers
A person skilled in the art will appreciate that the homogenization chamber
can be
formed in a variety of shapes provided functional requirements of the
homogenization
system, discussed above, are satisfied. One skilled in the art will also
appreciate that the
shape and size of the chamber will depend on the gas throughput and residence
time
required for a specific design, as discussed above. Cost and maintenance are
additional
considerations in selecting a type of homogenization chamber.
Different types of homogenization chambers include, but are not limited to
gasometers,
gas holders, variable volume and fixed volume tanks, such as standard fuel
tanks and
surge tanks. Thus, in accordance with one embodiment of the invention, the
homogenization chamber is a standard fuel tank. In accordance with one
embodiment of
the invention, the homogenization chamber is a fixed volume tank such as a
surge tank.
In accordance with one embodiment of the invention, the homogenization chamber
is a
variable volume tank. In accordance with one embodiment of the invention, the
homogenization chamber is a gasometer or gas holder.
With reference to Figure 6, a homogenization chamber 614, in accordance with
one
embodiment of the invention, comprises a fixed-volume tank 600, a gas inlet
640, a gas
outlet 642, a relief gas outlet 644, a drain 646, one or more
pressure/temperature nozzles
648 and one or more level switch nozzles 650. The drain 646 of the tank 600 is
a feature
of the conical bottom drainage system 647, which may be associated with
insulation
means or other suitable means, such as immersion heaters, to prevent freezing
of the
condensate in colder climates. Optionally, the tank 600 comprises fins or
baffles to
enhance mixing of the gas, wherein the selection, shape, number and placement
of which
would be understood by those of skill in the art.
Referring to Figure 7, homogenization chamber 714, in accordance with one
embodiment
of the invention, will now be described. The homogenization chamber 714 (also
known
as a floating roof homogenization chamber), is able to accommodate small
fluctuations in
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pressure. The homogenization chamber 714, comprises a variable volume tank 700
having a gas inlet 751, and a diaphragm 753 connected to a piston 752, which
act
together to increase or decrease the tank volume.
With reference to Figure 8, a homogenization chamber 814, in accordance with
one
embodiment of the invention, will now be described. The homogenization chamber
814
(also known as a pressure vessel), comprises a gas outlet 854 and a gas inlet
856. The
gas inlet is connected to a compressor 858, which functions to compress the
gas prior to
storage in the pressure vesse1800. A worker skilled in the art will readily
understand that
since the gas is compressed prior to storage in the pressure vessel, the
pressure vessel can
be smaller than traditional low pressure tanks.
With reference to Figure 9, a homogenization chamber 914, in accordance with
one
embodiment of the invention, comprises a gas holding chamber 900 connected to
a gas
inlet 968 and a gas outlet 970 and defined by an inner membrane 960 and an
outer
membrane 962. When gas exits the holding chamber 900, a blower 964, associated
with
the outer membrane 962, provides inflation to the region 965 between the
membranes.
When gas is added to the holding chamber 900, a regulator 967, adjusts the
pressure of
the inflated region 965.
Referring to Figure 10A, a homogenization chamber 1014, in accordance with one
embodiment of the invention, will now be described. In this embodiment, the
homogenization chamber 1014 is an absorption type gas holder comprising a
constant
volume tank 1000 having a gas inlet 1072 and a gas outlet 1074. Typically, a
gas
absorption holder occupies less space than a traditional low pressure storage
tank, due to
the high density storage of the absorbent. Figure 10B illustrates a cross
sectional view of
the tank 1000, which acts to absorb gas molecules.
With reference to Figure 11, a homogenization chamber 1114, in accordance with
one
embodiment of the invention, will now be described. In this embodiment, the
homogenization chamber is a pipe with a diameter that is sized to provide the
required
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residence time. The fixed-volume, pipe 1100 comprises a gas inlet means 1180
and gas
outlet means 1182. This embodiment of a homogenization chamber can be
particularly
suited for applications that require minimal residence time for homogenizing
the gas.
Typically, a homogenization chamber of the invention will be located above
ground.
However, it is contemplated that for aesthetic reasons, or in those
jurisdictions which do
not allow above ground containment of fuel, a homogenization chamber may be
located
underground. Thus, in one embodiment, the homogenization chamber is
underground. In
one embodiment, the homogenization chamber is above ground. In one embodiment
of
the invention, the homogenization chamber is positioned such that a portion
thereof is
underground.
It is further contemplated that a homogenization chamber of the invention can
be
configured as a homogenization system with more than one chamber or may be
configured as one or more single homogenization chambers fluidly
interconnected in
parallel. Figure 12 is an illustration of a plurality of fixed-volume,
homogenization
chambers installed in parallel, each homogenization chamber 1214 being
connected to a
single gas inlet manifold 1290 and a single gas outlet manifold 1292. A worker
skilled in
the art will readily appreciate that each of the fixed-volume, homogenization
chamber
used in Figure 12 could be independently selected as one of the above-
mentioned
embodiments, for example, a pressure vessel, a double-membrane gas holder, a
multiple-
absorption type gas holder etc., provided there is a single gas inlet and a
single gas outlet
for the entire system. A worker skilled in the art would be able to ascertain
the suitability
of such designs for a given purpose.
Materials
It is known that gas from a gasification system can be highly toxic and
flammable, and in
most cases will be contained outdoors exposed to various environmental
conditions such
as extreme temperature changes, rain, sun, snow, wind and the like.
Accordingly, a
homogenization chamber will be manufactured from a suitably safe material. Non-
limiting examples of materials include plastics (PVC), steel, composite
materials such as
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fiberglass reinforced plastic or steel, and steel alloys. Gas homogenization
chambers
comprising a combination of these materials are also herein contemplated, as
are metals
comprising suitable internal coatings. Coated metals, for example, can be
useful for
those chambers located underground due to the added environmental protection
provided
by such a coating. Coated metals may also be required to satisfy governmental
regulations.
Gas Monitoring within the Homogenization Chamber
One skilled in the art will appreciate that the gas characteristics of the
input gas will be
monitored during the gas homogenization process in order to determine whether
the gas
meets the downstream requirements and what adjustments are required in order
to satisfy
such requirements. Monitoring of the gas characteristics may occur within the
homogenization chamber or prior to gas delivery to the homogenization chamber.
The
gas monitoring equipment may take the form of sensing elements, response
elements, and
controllers that can monitor and/or regulate the composition, flow rate,
temperature and
pressure of the gas.
The monitoring of the gas characteristics may be part of a process control
system (see
Figure 15 and Control System section provided below). Thus, in one embodiment
of the
invention, a feedback loop can be implemented in which the gas produced is
analyzed in
real-time and the operation of the gasification system is adjusted accordingly
in order to
make the necessary adjustments.
In one embodiment, the homogenization chamber comprises one or more sensing
elements for analyzing gas characteristics such as gas composition,
temperature, flow rate
and pressure, the configuration of each sensing element would be readily
understood by a
worker skilled in the art. For example, temperature can be measured using a
thermocouple, or other temperature sensor format; pressure can be measured
using an
absolute pressure sensor, a gauge pressure sensor, vacuum pressure sensor,
differential
pressure sensor or other pressure sensor; flow rate can be measured using a
flowmeter or
other flow rate sensor; gas composition can be measured using a gas
composition sensor
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based on acoustic properties, or other gas composition sensor as would be
readily
understood.
In one embodiment, a particular sensing element can be configured to measure
multiple
characteristics of the gas, wherein these types of sensors would be readily
understood by
a worker skilled in the art.
In one embodiment, the homogenization chamber further includes one or more
controllers configured to generate instructions for transmission to one or
more response
elements in order to regulate gas characteristics such as gas composition,
temperature,
flow rate and pressure. Response elements contemplated within the present
context, as
defined and described above, can include, but are not limited to, various
control elements
operatively coupled to process-related devices configured to affect a given
process by
adjustment of a given control parameter related thereto. For instance, process
devices
operable within the present context via one or more response elements, may
include, but
are not limited to flow valves, pressure valves, heaters, blowers and the
like.
In one embodiment of the invention, the feedback frequency associated with the
feedback
loop can directly depend on the parameters set by the controller, and possible
rate at
which these parameters can be adjusted within the system. The feedback
frequency can
be variable depending on the conditions being monitored or the feedback
frequency can
be a fixed frequency, or a random frequency.
In one embodiment of the invention, multiple sensing elements are positioned
within the
homogenization chamber in order to provide the capability of gas
characteristic sampling
at different locations within the chamber, thereby providing a means for
evaluation of
homogeneity of the gas therein. Furthermore, one or more redundant sensing
elements
can be positioned within the homogenization chamber in order to ensure
accurate
operation of the one or more sensing elements, for example fault detection. In
addition,
in one embodiment, two or more sensing elements are used to evaluate the same
parameter and the measured value of the parameter is defined as a correlation
between
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the readings determined by the two or more sensing elements.
In one embodiment of the invention, a controller is operatively coupled to one
or more
sensing elements associated with the homogenization chamber in order to
determine
control instructions for modification of one or more parameters associated
with the gas.
For example a controller can comprise one or more of a variety of types of
computing
devices, computers, microprocessors, microcontrollers or other computing
device format
which includes a central processing units (CPU) and peripheral input/output
devices to
monitor parameters from peripheral devices that are operatively coupled to the
controller.
For example the peripheral devices can include the one or more sensing
elements and/or
one or more response elements. These input/output devices can also permit the
CPU to
communicate and control peripheral devices that are operatively coupled to the
controller.
The controller can be operatively coupled to a memory device. For example, the
memory
device can be integrated into the controller or it can be a memory device
connected to the
computing device via a suitable communication link. The memory device can be
configured as an electronically erasable programmable read only memory
(EEPROM),
electronically programmable read only memory (EPROM), non-volatile random
access
memory (NVRAM), read-only memory (ROM), programmable read-only memory
(PROM), flash memory or any other non-volatile memory for storing data. The
memory
can be used to store data and control instructions, for example, program code,
software,
microcode or firmware, for monitoring or controlling the one or more sensing
elements
which are associated with the homogenization chamber and are coupled to the
controller
and which can be provided for execution or processing by the CPU. Optionally,
the
controller also provides a means of converting user-specified operating
conditions into
control signals to control the response elements coupled to the controller.
The controller
can receive user-specified commands by way of a user interface, for example, a
keyboard, a touchpad, a touch screen, a console, a visual or acoustic input
device as is
well known to those skilled in this art.
Control S, s~
In one embodiment of the present invention, a control system, such as that
illustrated at
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Figure 15, may be provided to control one or more processes implemented in,
and/or by,
the various systems and/or subsystems disclosed herein, and/or provide control
of one or
more process devices contemplated herein for affecting such processes. In
general, the
control system may operatively control various local and/or regional processes
related to
a given system, subsystem or component thereof, and/or related to one or more
global
processes implemented within a system, such as a gasification system, within
or in
cooperation with which the various embodiments of the present invention may be
operated, and thereby adjusts various control parameters thereof adapted to
affect these
processes for a defined result. Various sensing elements and response elements
may
therefore be distributed throughout the controlled system(s), or in relation
to one or more
components thereof, and used to acquire various process, reactant and/or
product
characteristics, compare these characteristics to suitable ranges of such
characteristics
conducive to achieving the desired result, and respond by implementing changes
in one
or more of the ongoing processes via one or more controllable process devices.
The control system generally comprises, for example, one or more sensing
elements for
sensing one or more characteristics related to the system(s), processe(s)
implemented
therein, input(s) provided therefor, and/or output(s) generated thereby. One
or more
computing platforms are communicatively linked to these sensing elements for
accessing
a characteristic value representative of the sensed characteristic(s), and
configured to
compare the characteristic value(s) with a predetermined range of such values
defined to
characterise these characteristics as suitable for selected operational and/or
downstream
results, and compute one or more process control parameters conducive to
maintaining
the characteristic value with this predetermined range. A plurality of
response elements
may thus be operatively linked to one or more process devices operable to
affect the
system, process, input and/or output and thereby adjust the sensed
characteristic, and
communicatively linked to the computing platform(s) for accessing the computed
process
control parameter(s) and operating the process device(s) in accordance
therewith.
In one embodiment, the control system provides a feedback, feedforward and/or
predictive control of various systems, processes, inputs and/or outputs
related to the
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conversion of carbonaceous feedstock into a gas, so to promote an efficiency
of one or
more processes implemented in relation thereto. For instance, various process
characteristics may be evaluated and controllably adjusted to influence these
processes,
which may include, but are not limited to, the heating value and/or
composition of the
feedstock, the characteristics of the product gas (e.g. heating value,
temperature, pressure,
flow, composition, carbon content, etc.), the degree of variation allowed for
such
characteristics, and the cost of the inputs versus the value of the outputs.
Continuous
and/or real-time adjustments to various control parameters, which may include,
but are
not limited to, heat source power, additive feed rate(s) (e.g. oxygen,
oxidants, steam,
etc.), feedstock feed rate(s) (e.g. one or more distinct and/or mixed feeds),
gas and/or
system pressure/flow regulators (e.g. blowers, relief and/or control valves,
flares, etc.),
and the like, can be executed in a manner whereby one or more process-related
characteristics are assessed and optimized according to design and/or
downstream
specifications.
Alternatively, or in addition thereto, the control system may be configured to
monitor
operation of the various components of a given system for assuring proper
operation, and
optionally, for ensuring that the process(es) implemented thereby are within
regulatory
standards, when such standards apply.
In accordance with one embodiment, the control system may further be used in
monitoring and controlling the total energetic impact of a given system. For
instance, a a
given system may be operated such that an energetic impact thereof is reduced,
or again
minimized, for example, by optimising one or more of the processes implemented
thereby, or again by increasing the recuperation of energy (e.g. waste heat)
generated by
these processes. Alternatively, or in addition thereto, the control system may
be
configured to adjust a composition and/or other characteristics (e.g.
temperature,
pressure, flow, etc.) of a product gas generated via the controlled
process(es) such that
such characteristics are not only suitable for downstream use, but also
substantially
optimised for efficient and/or optimal use. For example, in an embodiment
where the
product gas is used for driving a gas engine of a given type for the
production of
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electricity, the characteristics of the product gas may be adjusted such that
these
characteristics are best matched to optimal input characteristics for such
engines.
In one embodiment, the control system may be configured to adjust a given
process such
that limitations or performance guidelines with regards to reactant and/or
product
residence times in various components, or with respect to various processes of
the overall
process are met and/or optimised for. For example, an upstream process rate
may be
controlled so to substantially match one or more subsequent downstream
processes.
In addition, the control system may, in various embodiments, be adapted for
the
sequential and/or simultaneous control of various aspects of a given process
in a
continuous and/or real time manner.
In general, the control system may comprise any type of control system
architecture
suitable for the application at hand. For example, the control system may
comprise a
substantially centralized control system, a distributed control system, or a
combination
thereof. A centralized control system will generally comprise a central
controller
configured to communicate with various local and/or remote sensing devices and
response elements configured to respectively sense various characteristics
relevant to the
controlled process, and respond thereto via one or more controllable process
devices
adapted to directly or indirectly affect the controlled process. Using a
centralized
architecture, most computations are implemented centrally via a centralized
processor or
processors, such that most of the necessary hardware and/or software for
implementing
control of the process is located in a same location.
A distributed control system will generally comprise two or more distributed
controllers
which may each communicate with respective sensing and response elements for
monitoring local and/or regional characteristics, and respond thereto via
local and/or
regional process devices configured to affect a local process or sub-process.
Communication may also take place between distributed controllers via various
network
configurations, wherein a characteristics sensed via a first controller may be
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communicated to a second controller for response thereat, wherein such distal
response
may have an impact on the characteristic sensed at the first location. For
example, a
characteristic of a downstream product gas may be sensed by a downstream
monitoring
device, and adjusted by adjusting a control parameter associated with the
converter that is
controlled by an upstream controller. In a distributed architecture, control
hardware
and/or software is also distributed between controllers, wherein a same but
modularly
configured control scheme may be implemented on each controller, or various
cooperative modular control schemes may be implemented on respective
controllers.
Alternatively, the control system may be subdivided into separate yet
communicatively
linked local, regional and/or global control subsystems. Such an architecture
could allow
a given process, or series of interrelated processes to take place and be
controlled locally
with minimal interaction with other local control subsystems. A global master
control
system could then communicate with each respective local control subsystems to
direct
necessary adjustments to local processes for a global result.
The control system of the present invention may use any of the above
architectures, or
any other architecture commonly known in the art, which are considered to be
within the
general scope and nature of the present disclosure. For instance, processes
controlled and
implemented within the context of the present invention may be controlled in a
dedicated
local environment, with optional external communication to any central and/or
remote
control system used for related upstream or downstream processes, when
applicable.
Alternatively, the control system may comprise a sub-component of a regional
an/or
global control system designed to cooperatively control a regional and/or
global process.
For instance, a modular control system may be designed such that control
modules
interactively control various sub-components of a system, while providing for
inter-
modular communications as needed for regional and/or global control.
The control system generally comprises one or more central, networked and/or
distributed processors, one or more inputs for receiving current sensed
characteristics
from the various sensing elements, and one or more outputs for communicating
new or
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updated control parameters to the various response elements. The one or more
computing
platforms of the control system may also comprise one or more local and/or
remote
computer readable media (e.g. ROM, RAM, removable media, local and/or network
access media, etc.) for storing therein various predetermined and/or
readjusted control
parameters, set or preferred system and process characteristic operating
ranges, system
monitoring and control software, operational data, and the like. Optionally,
the
computing platforms may also have access, either directly or via various data
storage
devices, to process simulation data and/or system parameter optimization and
modeling
means. Also, the computing platforms may be equipped with one or more optional
graphical user interfaces and input peripherals for providing managerial
access to the
control system (system upgrades, maintenance, modification, adaptation to new
system
modules and/or equipment, etc.), as well as various optional output
peripherals for
communicating data and information with external sources (e.g. modem, network
connection, printer, etc.).
The processing system and any one of the sub-processing systems can comprise
exclusively hardware or any combination of hardware and software. Any of the
sub-
processing systems can comprise any combination of none or more proportional
(P),
integral (I) or differential (D) controllers, for example, a P-controller, an
I-controller, a
PI-controller, a PD controller, a PID controller etc. It will be apparent to a
person skilled
in the art that the ideal choice of combinations of P, I, and D controllers
depends on the
dynamics and delay time of the part of the reaction process of the
gasification system and
the range of operating conditions that the combination is intended to control,
and the
dynamics and delay time of the combination controller. It will be apparent to
a person
skilled in the art that these combinations can be implemented in an analog
hardwired
form which can continuously monitor, via sensing elements, the value of a
characteristic
and compare it with a specified value to influence a respective control
element to make
an adequate adjustment, via response elements, to reduce the difference
between the
observed and the specified value. It will further be apparent to a person
skilled in the art
that the combinations can be implemented in a mixed digital hardware software
environment. Relevant effects of the additionally discretionary sampling, data
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acquisition, and digital processing are well known to a person skilled in the
art. P, I, D
combination control can be implemented in feed forward and feedback control
schemes.
In corrective, or feedback, control the value of a control parameter or
control variable,
monitored via an appropriate sensing element, is compared to a specified value
or range.
A control signal is determined based on the deviation between the two values
and
provided to a control element in order to reduce the deviation. It will be
appreciated that a
conventional feedback or responsive control system may further be adapted to
comprise
an adaptive and/or predictive component, wherein response to a given condition
may be
tailored in accordance with modeled and/or previously monitored reactions to
provide a
reactive response to a sensed characteristic while limiting potential
overshoots in
compensatory action. For instance, acquired and/or historical data provided
for a given
system configuration may be used cooperatively to adjust a response to a
system and/or
process characteristic being sensed to be within a given range from an optimal
value for
which previous responses have been monitored and adjusted to provide a desired
result.
Such adaptive and/or predictive control schemes are well known in the art, and
as such,
are not considered to depart from the general scope and nature of the present
disclosure.
2) Gas Inlet Mechanism and Upstream Components
Inlet means comprising of one or more conduits is used to carry the gas from
the
gasification system to the homogenization chamber. As noted above, the
upstream
components of the system may optionally include one or more chillers,
gas/liquid
separators, induced draft devices, gas monitoring systems, which may include
temperature and pressure controllers, and control valves.
Conduits
The gas is transferred from the gasification system to the homogenization
chamber of the
invention by way of conduits that are designed to carry the gas at
predetermined
temperatures and pressures. One skilled in the art will appreciate that these
conduits can
take the form of tubes, pipes, hoses, or the like.
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With reference to Figure 1, and in accordance with one embodiment of the
invention, the
gas is transferred to a single homogenization chamber using a single conduit
leading from
a single gasification system. With reference to Figures 4 & 5, and in
accordance with
embodiments of the invention, the gas can also be transferred using multiple
conduits
leading from one or more gasification systems simultaneously to one or more
homogenization chambers. In one embodiment of the invention, multiple gas
conduits
deliver gas from multiple gasification systems to multiple homogenization
chambers.
Chiller and Gas/Liquid Separator
One skilled in the art would appreciate when it would be required to
incorporate one or
more chillers and/or one or more gas/liquid separators into the gas
homogenization
system described herein. Chiller systems are well known in the art and
include, but are
not limited to, shell and tube or plate and frame heat exchangers or other
temperature
modification devices. These systems may employ various cooling fluids, such
as,
cooling water, chilled water, and/or other suitable fluids. Gas/liquid
separators are also
well known in the art, such as the reservoir-type separator illustrated in
Figure 13.
Induced Draft Device
As the gas is typically extracted from the gasification system as it is
generated, the gas
flow is typically non-uniform. When the gasification system is operating at
less than
atmospheric pressure, an induced draft device may convey the gas through the
homogenization chamber. The induced draft device may be located anywhere
preceding
the homogenization chamber. As would be understood in the field, suitable
draft devices
include, but are not limited to blower fans and vacuum pumps, or other
suitable flow
inducing devices. In one embodiment, a pressure blower such as the one in
Figure 14A,
functions similar to a centrifugal pump in that the blades of the blower suck
air into the
middle of the blower and expel air in a radial direction at increased
pressure. In another
embodiment, the vacuum pump shown in Figure 14B is designed similar to a
blower, but
it can operate only when the upstream pressure is substantially a vacuum.
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Gas Monitoring System Preceding the Homogenization Chamber
As discussed above, the gas characteristics of the input gas may be monitored
within the
homogenization chamber or prior to input. In one embodiment, the monitoring
system
may be part of the inlet means and may comprise automated equipment, such as
one or
more sensing elements, capable of providing a detailed assessment of the
characteristics
of the gas. For example, these characteristics can include continuous gas
pressure and
temperature monitoring plus continuous product gas flow rate and composition
monitoring. A worker skilled in the art would readily understand the sampling
devices
required to collect the above information regarding the gas. For example,
temperature
can be measured using a thermocouple, or other temperature sensor format;
pressure can
be measured using an absolute pressure sensor, a gauge pressure sensor, vacuum
pressure
sensor, differential pressure sensor or other pressure sensor; flow rate can
be measured
using a flowmeter or other flow rate sensor; gas composition can be measured
using a gas
composition sensor based on acoustic properties, or other gas composition
sensor as
would be readily understood.
In one embodiment, a particular sensing element can be configured to measure
multiple
characteristics of the gas, wherein these types of sensing elements would be
readily
understood by a worker skilled in the art.
Furthermore, in one embodiment, the monitoring system may include a means for
the
analysis of gas operatively connected with a feedback system as an integrated,
on-line
part of a process control system (see section on Control System provided
above). The
advantages provided by such an integrated on-line gas analysis are finer
tuning
capabilities of process control and enhanced control and homogenization
capabilities for
a variety of applications of the gas.
The gas monitoring system comprises sensing element for monitoring gas
characteristics
thereby determining when characteristics such as gas composition, flow rate,
pressure or
temperature require adjustment. Different types of such sensing elements are
readily
available commercially and include, but are not limited, flow meters,
thermocouples,
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velocity meters, pyrometers, gas sensors, gas analyzers, or other detecting
and measuring
devices.
In one embodiment, for example, once the need to adjust a characteristic, such
as, gas
pressure is detected, a signal is sent to a response element to adjust a flow
valve, which
results in a decrease or increase in gas flow rate into the homogenization
chamber.
Different types of signaling means for generation and transmission of the
signal to a
response element can be used. For example, the signal can be transmitted using
radio
transmission, IR transmission, Bluetooth transmission, wired or wireless
transmission or
other transmission technique as would be readily understood.
In one embodiment of the invention, a controller is operatively coupled to one
or more
sensing element and response elements associated with gas sampling prior to
reaching the
homogenization chamber in order to determine control instructions for
modification of
one or more parameters associated with gas generation. For example a
controller can
comprise one or more of a variety of types of computing devices, computers,
microprocessors, microcontrollers or other computing device format which
includes a
central processing units (CPU) and peripheral input/output devices to monitor
parameters
from peripheral devices that are operatively coupled to the controller. For
example the
peripheral devices can include the one or more sensing elements and/or one or
more
response elements. These input/output devices can also permit the CPU to
communicate
and control peripheral devices that are operatively coupled to the controller.
The
controller can be operatively coupled to a memory device. For example, the
memory
device can be integrated into the controller or it can be a memory device
connected to the
computing device via a suitable communication link. The memory device can be
configured as an electronically erasable programmable read only memory
(EEPROM),
electronically programmable read only memory (EPROM), non-volatile random
access
memory (NVRAM), read-only memory (ROM), programmable read-only memory
(PROM), flash memory or any other non-volatile memory for storing data. The
memory
can be used to store data and control instructions, for example, program code,
software,
microcode or firmware, for monitoring or controlling the one or more sensing
elements
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which are associated with the homogenization chamber and are coupled to the
controller
and which can be provided for execution or processing by the CPU. Optionally,
the
controller also provides a means of converting user-specified operating
conditions into
control signals to control the response elements coupled to the controller.
The controller
can receive user-specified commands by way of a user interface, for example, a
keyboard, a touchpad, a touch screen, a console, a visual or acoustic input
device as is
well known to those skilled in this art.
The gas monitoring system is used to control regulated gas production such
that it
satisfies the general standards of downstream applications. If it does not,
the appropriate
adjustments can be made to the gasification process to bring the gas into
compliance.
Alternatively, or in conjunction with the gas monitoring equipment, the gas
inlet means
may comprise a diverter outlet for releasing non-compliant gas, i.e., gas
which does not
meet the requirements for the downstream application. In this way, non-
compliant gas
will be disposed of through, for example, a diverter which may lead the non-
compliant
gas to a combustor or incinerator, for example, a flare stack as illustrated
at Figures 1-5.
Accordingly, in the event that gas composition diverges excessively from the
requirements of a downstream application, gas can be diverted. In one
embodiment, the
inlet means of the invention includes gas monitoring equipment. In one
embodiment, the
inlet means includes gas monitoring equipment that functions in cooperation
with a
diverter.
Pressure Control System
In some embodiments of the invention, the gas inlet means may further comprise
a
mechanism for controlling the flow rate of the gas into the homogenization
chamber, thus
controlling the pressure of the gas in the chamber. This pressure control
subsystem may
comprise conventional valves or shut off systems known in the art. Several non-
limiting
examples of pressure regulating devices are shown for example in Figures 16A-
D. The
pressure control system responds to signals from the monitoring system and may
control
the flow rate of the gas as well as direct the gas appropriately. In one
embodiment, the
pressure control system includes a valve by which compliant and non-compliant
gas can
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be directed to the homogenization chamber and combustor or incinerator or can
be
relayed to the gasifier of the gasification system, respectively.
As would be understood by the skilled worker, suitable valves for controlling
the flow of
gas are desirable. Figures 17A-D and Figure 18, provide non-limiting examples
of flow
regulating devices and control valves, respectively. Such flow regulating
devices and
valves may increase or reduce the gas flow rate by at least about 10% to about
100%. As
noted above, gas flow rate is monitored and adjusted via a controller. For
example, in
one embodiment of the invention, if the pressure in the system increases to
100%, the
pressure control mechanism can send a signal to the gas blower to adjust the
blower's
revolutions-per-minute (RPM) as required in order to reduce this pressure.
Pressure transmitter mounting and bracketing devices for use with the gas
homogenization system are also herein contemplated and are readily available
commercially. Non-limiting examples of such are provided at Figure 19A-K).
3) Regulated Gas Outlet Mechanism and Downstream Components
The gas homogenization system also comprises an outlet means for transferring
the
regulated gas from the homogenization chamber to downstream applications
(e.g., gas
engines or gas turbines). The outlet means comprises one or more conduits to
carry the
regulated gas from the homogenization chamber to downstream applications. The
system
may optionally include a gas monitoring system, which may include temperature
and
pressure control mechanisms.
Outlet Conduits
The regulated gas is transferred from the homogenization chamber to the
downstream
application by way of regulated gas conduits that are designed to carry the
gas at
predetermined temperatures and pressures. One skilled in the art will
appreciate that
these conduits can take the form of tubes, pipes, hoses, or the like.
With reference to Figure 1, and in accordance with one embodiment of the
invention, the
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regulated gas is transferred from a single homogenization chamber using a
single conduit
to a downstream application. With reference to Figures 2, 3 & 4, and in
accordance with
other embodiments of the invention, the regulated gas can also be transferred
using
multiple conduits from a single homogenization chamber to multiple downstream
applications.
In one embodiment of the invention, multiple homogenization chambers each with
a
corresponding conduit deliver regulated gas to a common downstream application
simultaneously. In one embodiment of the invention, the outlet means includes
multiple
regulated gas conduits delivering regulated gas from multiple homogenization
chambers
to multiple downstream applications.
The recycling of regulated gas is also herein contemplated. Regulated gas
derived from
the homogenization chamber, for example, may be directed to re-enter the
system at
various suitable upstream location of a complete gasification system, via the
use of
appropriate conduit systems, as would be readily understood.
Gas Monitoring System
As already discussed, a monitoring system is used to monitor/control the gas
either prior
to its entry into the homogenization chamber or during its residence in the
homogenization chamber. Similarly, a monitoring system can be used to monitor
the
regulated gas before it is delivered for the downstream application. This can
serve to
confirm and control the characteristics
To this end, the regulated gas outlet means may optionally further comprise
one or more
sensing elements, response elements and/or control devices which monitor
and/or
regulate all or some of the characteristics of the regulated gas (i.e.,
composition, pressure,
flow rate, and temperature). A controller, for example, may act through a
feedback loop
in which the regulated gas is analyzed in real-time and the relevant
adjustments made to
the system. In one embodiment of the invention, the sensing elements analyze
the
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pressure and flow rate of the regulated gas, and from the data analysed via a
controller, a
signal is transmitted to slow down the flow of regulated gas or flare the
excess gas out of
the homogenization chamber. In one embodiment, the sensing elements analyze
the
temperature of the regulated gas and a controller sends a signal to a heater
and/or a chiller
to adjust the temperature of the regulated gas to a temperature suitable for
the
downstream application.
As discussed above the gas monitoring system can comprises one or more
controllers
associated therewith. In one embodiment a controller is associated with the
gas
monitoring system which evaluates the gas within the homogenization chamber
and
another controller is associated with the gas monitoring system which
evaluates the gas
prior to reaching the homogenization chamber. In this configuration the two
controllers
can operate independently and can provide instructions to the one or more
response
elements to which they are connected in order to alter the conditions of the
gas at either
of the locations being monitored. In one embodiment, these two controllers are
operating
in a slave configuration, wherein a master controller is operatively coupled
to these two
controllers and the master controller provides instructions to the two
controllers in order
to enable a more efficient and streamlines adjustment of the characteristics
of the gas at
the monitored locations.
In one embodiment of the invention, the gas monitoring system comprises a
single
controller which is operatively coupled to the one or more sensing elements
and response
elements associated with the with the gas monitoring system which evaluates
the gas
within the homogenization chamber and the gas monitoring system which
evaluates the
gas prior to reaching the homogenization chamber. This configuration can also
provide a
means for efficient and streamlines adjustment of the characteristics of the
gas at the
monitored locations, however in this single controller configuration,
operative connection
with the sensing elements and response elements may be more complex, when
compared
with a master controller and slave controllers configuration.
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Flow and Pressure Re ulg ation
The regulated gas outlet means may further comprise a means for controlling
the flow
rate of the regulated gas from the homogenization chamber and to a downstream
application. Working alternately to, or in conjunction with, the control
system operative
in the inlet means, the pressure of the homogenization chamber may be
controlled. The
pressure control in the outlet means may comprise conventional valves or shut
off
systems known in the art. As discussed above, the flow and pressure control
system
responds to signals from the monitoring system employed to monitor the
characteristics
of the regulated gas as it exits the homogenization chamber. For example, the
control
system may comprise a pressure regulator valve that may be adjusted to control
gas flow
rate and pressure by way of one or more response elements.
Heater and Gas/Liquid Separator
The regulated gas outlet means may further comprise a means for heating the
regulated
gas as it exits the homogenization chamber. One skilled in the art would also
appreciate
when it is advantageous to incorporate a gas/liquid separator into the system
of the
invention.
The operational requirements of a downstream application regarding gas
temperature and
humidity will determine the target temperature that the regulated gas must
meet prior to
transfer to the downstream application. For example, a gas engine will
typically require a
temperature of no more than about 40 C and a relative humidity of no more than
about
80% in order to operate efficiently. Figure 13 provides an illustration of one
embodiment
of a reservoir-type gas/liquid separator. Non-limiting examples of heaters for
use with
the system include shell and tube, electric, glycol water heaters or the like.
A person
skilled in the art will appreciate that the heaters and separators that may be
employed
with the system are readily available commercially.
Filter
Typically downstream applications such as gas engines and gas turbines are
sensitive to
trace elements that may enter the gas during any point of the gas production
process. In
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this regard, the system may comprise one or more filters of an appropriate
pore size to
screen out these potentially interfering contaminants, while substantially
limiting the
impact that the filter has on gas flow rate. In one embodiment, a filter is
associated with
the common header to the engines. In one embodiment, each engine gas train has
its own
filter.
In one embodiment, both of the above-mentioned filtering approaches are used
and may
be configured as a two stage filtering process.
Pressure Re ug lating Valves
The regulated gas outlet device may further comprise pressure regulating valve
device for
controlling the pressure of the regulated gas prior to delivery to the
downstream
application.
Gas Compressor
One skilled in the art will appreciate that a downstream application will
dictate the
specific gas characteristics required for the regulated gas. For example, the
required gas
pressure for the efficient operation of a gas engine will differ from those of
a gas turbine.
As discussed above, a gas turbine will require a relatively high gas pressure.
It is
contemplated, therefore, that in those embodiments requiring a high gas
pressure, a
means for gas pressurization can be included in the homogenization system. Gas
pressurization devices are well known in the art and may include a gas
compressor of a
variety of designs such as axial-flow compressor, reciprocating compressor,
rotary screw
compressor, centrifugal compressor shown in Figures 20 A, B, C, D & E
respectively.
Other implementations include the diagonal or mixed-flow compressor, the
scroll
compressor, or other gas pressurization devices, as would be known to a worker
skilled in
the art.
4) Emergency Exit Port with Control Valve
The pressure control system may additionally comprise one or more emergency
exit ports
with control valves. When gas flow cannot be reduced fast enough, for instance
due to an
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up-stream operational malfunction, or a downstream failure of a gas engine, an
emergency control valve may be opened to release gas through an emergency exit
port.
Two non-limiting examples of relief valves are shown in Figures 21A and B,
respectively.
The emergency valve may be opened rapidly so that no significant change (about
<1%) in
gas pressure may occur. One skilled in the art will appreciate that the
emergency exit
port and corresponding valve may be located at any point in the homogenization
system
of the invention. In one embodiment, the emergency port is located in the
homogenization chamber. In one embodiment, the emergency port is located in
the inlet
means. In one embodiment, the emergency port is located in the outlet means.
Assembly of Gas Homogenization System
The assembly of a gas homogenization system may require the provision of
various
fastening means, connector means, bracketing and/or lifting means, foundation
and/or
anchoring means, grounding lug means, etc. A person skilled in the art will
appreciate
that such means are readily available commercially and their installation well
understood.
Downstream Applications
The system according to the invention is configured to generate a regulated
gas which is
substantially a continual and steady stream of gas having defined
characteristics. This
regulated gas is delivered to one or more downstream applications for
subsequent use
thereof by these one or more downstream applications. For example a downstream
application can be a gas turbine, combustion engine or other suitable
application which
requires a regulated gas for operation thereof.
Combustion Turbine Engine
In one embodiment of the invention, a downstream application is a combustion
turbine
engine which combines 02 with CO and H2 to generate C02, H20 and energy,
wherein
the energy is in the form of heat and pressure. As the gas expands during the
combustion
process, it expands across a multiple stage power turbine to drive an axial
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compressor and a generator in order to generate make electricity. The fuel
gas, namely
the regulated gas, must be pressurized to a sufficient level in order to feed
the gas turbine
as combustion takes place at a pressure approximately equivalent to the
compression ratio
of the combustion turbine.
The regulated gas can be delivered to one or more combustion turbine engines,
and the
regulated gas can be either compressed prior to delivery to an engine or the
entire
gasification process can operated at a predetermined pressure which is
sufficient for
delivery of the regulated gas at the required pressure. The pressure of the
regulated gas
can range from about 100-600 psig depending of the compression ratio of the
particular
combustion turbine engine.
In one embodiment, before entering the fuel system of the combustion turbine
engine, the
regulated gas may be further filtered in order to collect any trace quantities
of particulate
matter that may have been picked up in the processing equipment and piping
associated
with the system.
In one embodiment, a pre-heating system can be employed to pre-heat the cooled
and
compressed fuel gas if desired. A pre-heating system can be configured to use
waste heat
from a gas cooling system located at an alternate location within the system.
For
example, the waste heat can be extracted from upstream in the system for
example when
the gas is cooled after leaving the gasification process. The waste heat may
also be
extracted from downstream in the system and may be recovered from the
turbines. In one
embodiment, the waste heat is extracted from both upstream and downstream of
the
system.
In one embodiment, pre-heating of the regulated gas may be useful where the
gas cooling
system cools the regulated gas to a temperature required by a scrubber, and
that
temperature is below a desirable temperature for the cleaned regulated gas
which is the
fuel gas to be introduced into the combustion chamber of the combustion
turbine engine.
In one embodiment, steam injection can be used in association with some
combustion
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turbines engines in order to control NOx formation and this configuration may
constitute
an alternate to dry emission technology.
Internal Combustion Engine
In one embodiment of the invention, a downstream application is an internal
combustion
engine. An internal combustion engine can produce energy using a process
similar to
that discussed above except that the compressor, combustor and gas turbine are
replaced
by an internal combustion engine. An internal combustion engine may be easier
to utilize
and may be more cost efficient than a turbine, especially for small-scale
gasification
electro-conversion units. Air and auxiliary fuel may be fed to the internal
combustion
engine in a predetermined manner based on the composition of fuel gas, namely
the
regulated gas.
Environmentally attractive low emission internal combustion engine-generator
systems
for gasification systems can be provided to greatly improve efficiency and
pollution
reduction. For example, spark ignition internal combustion engines are
advantageous in
that such engines are less expensive for very small units and are easier to
start and stop
than turbines.
In one embodiment of the invention, in order to facilitate production of a
desired level of
electrical power, particularly during startup, an auxiliary fuel may be used
to power the
internal combustion engine, wherein this auxiliary fuel may be a hydrogen-rich
gas,
propane, natural gas, diesel fuel or the like. The amount of auxiliary fuel
required may
vary depending on the lower heating value of the carbonaceous feedstock being
gasified
and the power requirements for the overall gasification system, for example.
Fuel Cell Technologies
In one embodiment of the invention, a downstream application is a fuel cell.
After
removing contaminants, such as PM, HCL and H2S, at relatively high
temperatures
(SOFC, about 1000 C; MCFC about 650 C), the gas from a gasification system can
be
fed into a gas homogenization system to produce a regulated gas that satisfies
the
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requirements of a high temperature fuel cell (for example, Solid Oxide Fuel
Cell (SOFC)
or Molten Carbonate Fuel Cells (MCFC)). As stringent contaminant limits may
have to
be met in order to prevent the degradation of fuel cell performance, the
upstream Gas
Conditioning System (GCS) configuration may vary to fit the fuel cell
operation
conditions. The gas and oxidant compositions may also need to be adjusted to
optimize
the efficiency or output of a high temperature fuel cell.
Molten carbonate fuel cells (MCFC) contain an electrolyte that is a
combination of alkali
(Li, Na, and K) carbonates stabilized in a LiA1O2 ceramic matrix. Thus, in one
embodiment of the invention, the gaseous input fuel mixture includes carbon
monoxide,
hydrogen, methane, and hydrocarbons, with limits on total hydrocarbons,
particulate
loading, sulfur (in the form of H2S), ammonia, and halogens (e.g., HC1). At
the operating
temperature of about 1200 F (650 C), the salt mixture is liquid and a good
ionic
conductor.
The anode process for an MCFC involves a reaction between hydrogen and
carbonate
ions (C03-) from the electrolyte, which produces water and carbon dioxide
(CO2), while
releasing electrons to the anode. The cathode process combines oxygen and CO2
from the
oxidant stream with electrons from the cathode to produce carbonate ions,
which enter
the electrolyte. If the CO2 content in the fuel gas is insufficient, CO2 can
be recycled from
the emission stream. In one embodiment of the invention, an MCFC produces
excess heat
at a temperature which is sufficiently high to be usable in producing high
pressure steam
that may be fed to a turbine to generate additional electricity. In combined
cycle
operation (steam turbine powered generation and fuel cell power generation),
electrical
efficiencies in excess of about 60% are contemplated for mature MCFC systems.
A solid oxide fuel cell (SOFC) uses a hard ceramic electrolyte instead of a
liquid and
operates at temperatures up to about 1,000 C (about 1,800 F). In this type of
fuel cell, a
mixture of zirconium oxide and calcium oxide forms a crystal lattice, although
other
oxide combinations have also been used as electrolytes. The solid electrolyte
is coated on
both sides with specialized porous electrode materials. At a relatively high
operating
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temperature, oxygen ions (with a negative charge) migrate through the crystal
lattice.
The fuel gas containing hydrogen and carbon monoxide is passed over the anode
while a
flow of negatively charged oxygen ions moves across the electrolyte to oxidize
the fuel.
The oxygen is supplied, usually from air, at the cathode. Electrons generated
at the anode
travel through an external load to the cathode, completing the circuit that
carries the
electrical current.
In one embodiment of the invention, generating efficiencies can range up to
about 60
percent. Like molten carbonate fuel cells, solid oxide cells may require high
operating
temperatures that provide the opportunity for "co-generation," i.e., a
combined heat and
power application using waste heat to generate steam for space heating and
cooling,
industrial processing, or for use in driving a steam turbine to generate more
electricity.
A (high-temperature) fuel cell would consume the hydrogen and (primarily in
SOFCs)
and carbon monoxide from the gas provided by the system. Methane contained in
the fuel
gas would be partially reformed in a high-temperature fuel cell, resulting
again in
hydrogen and carbon monoxide. The gas mixture exiting the fuel cell would
likely still
include useful quantities of methane and carbon monoxide gases. These hot
gases could
be directed into the homogenization system of this invention or diverted to
more heat
exchangers, which could be used for the production of steam that is used in a
reaction
vessel.
Alternatively, and according to one embodiment of the invention, hot but
cleansed gas
can be input to a high temperature hydrogen membrane filtering system to split
the
synthesis gas into two distinct gas streams. One stream is composed of pure
hydrogen
and the other of pure carbon monoxide (CO). In one embodiment of the
invention, carbon
monoxide can either be combusted in a gas-fired boiler to facilitate the
recovery of
carbon dioxide (C02) and the conversion of its potential energy in steam, or
it can be
transported to a compressor and bottled. In one embodiment of the invention,
the
hydrogen (H2) can either be converted into energy in fuel cells or it can be
transported to
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a compressor and then fed into containers holding either/or a graphite nano-
fiber storage
medium or an anhydrous aluminum storage medium, so that the H2 can be safely
stored
or transported.
In one embodiment of the invention, the hydrogen feed line can be provided
from the
high temperature hydrogen membrane filtering system, to fuel cell stacks as a
fuel supply
to them. Fuel cell stacks of this system are typically of the molten carbonate
types that
use hydrogen gas at the anode and CO2 at the cathode to produce electricity.
The carbon
monoxide present in the gas produces extra hydrogen as well as heat (up to
about 1500
F) which can be recovered to produce steam, carbon dioxide and water.
A carbon monoxide line may be provided to direct carbon monoxide from the high
temperature hydrogen membrane filtering system to a conventional gas-fired
boiler. The
gas fired boiler combusts the CO so that CO2 and the potential energy value of
the CO
manufactured by the gasification system may be recovered more cost
effectively.
Some upstream gasification systems will be designed for the input of more than
one fuel
or feedstock into the boiler, thereby providing versatility for increased
amounts of power
generation as required or desirable. Non-limiting examples of additional fuel
sources
include natural gas, as well as the gases obtained from the anaerobic
digestion of organic
wastes (also referred to as biogas).
As would be apparent to those of skill in the art, depending on the specific
electric power
generating device selected, it may be beneficial to include other types of
fuel, in addition
to the gas generated in the gasification system, to maximize the efficiency of
the
electrical generator. Such optional additional fuels, can include natural gas,
oil, and other
conventional hydrocarbon-based fuels. It should be noted that the optional
fuels are not
intended to provide the majority of the BTUs or energy consumed by the
electrical
generators, but instead are included only when they can enhance the overall
efficiency of
the system. Thus, additional fuels are typically not required for use with the
system.
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An alternative configuration, in accordance with one embodiment of the
invention,
employs a gasification system that allows for the use of molten carbonate fuel
cells,
together with the production of CO2 and H20 with greatly reduced emissions of
oxides of
nitrogen, carbon monoxide or unburned hydrocarbons. Here, carbon monoxide is
fed,
along with hydrogen, to fuel cells. These fuel cells may be molten carbonate
or other
types of fuel cells, which consume the carbon monoxide as a valuable fuel.
In one embodiment of the invention, the downstream application includes proton
exchange membrane fuel cell (PEMFC) stacks employing cooled pure hydrogen. As
in
other fuel cells, the chemical energy of the fuel is directly transformed into
electricity.
Electricity is generated via the following electrochemical reactions:
Anode: 2H2 => 4H+ + 4e
Cathode: O2 + 4H+ + 4e => 2 H20
These reactions typically occur at low temperature (for example, <100 C) and
involve
splitting hydrogen into electrons and positive charged hydrogen ions (protons)
at the
platinum catalytic layer of the anode, passing protons through the proton
exchange
membrane (electrolyte) and their electrochemical oxidation at the cathode
catalyst. If the
electrolyte (solid polymer membrane) is saturated with water, a careful
control of the
moisture of the anode and cathode streams is required. Moreover, low
quantities of CO
(for example, levels higher than about 1 ppm) and H2S poison catalyst on the
anode may
affect hydrogen purity requirements.
As would be apparent to a worker skilled in the art, PEMFCs typically generate
more
power for a given volume and weight than other types of fuel cells and
additionally allow
for a rapid start-up. Thus, in accordance with one embodiment of the
invention, the
contemporary efficiency of the PEMFC stacks reach values of about 35-45%.
In one embodiment, a system is configured to allow the use of hydrogen gas to
drive
turbines to generate electricity. This is possible without damage to critical
internal
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components from the high combustion temperature of synthesis gas and results
in greatly
reduced emissions of oxides of nitrogen. In one embodiment, the hydrogen from
the high
temperature hydrogen membrane may be input to a fogger water injection system
where
de-ionized water is added before the combination is burned in a gas turbine or
internal
combustion engine to convert the energy to mechanical force and drive a
generator which
provides electricity. Here, water acts to limit the internal temperatures and
thereby
prevents heat damage to critical internal components. In addition, the fogger
water
injection system makes it possible to operate this invention in locations
and/or at times
when such alternative fuels may not be readily available in quantity. In
addition, the use
of the irrigation fogger may markedly lower nitrous oxide emissions caused by
the high
temperatures of the combustion of synthesis gas and/or alternative fuel mixes.
Polygeneration
In accordance with the invention, the downstream applications may include
polygeneration. Thus, the gas from a gasification system can be fed into a gas
homogenization system to produce a regulated gas that satisfies the
requirements for
polygeneration. Polygeneration involves the co-production of electricity and
synthetic
fuels, which are described in greater detail below, and may be employed in
large scale
Integrated Gasification Combined Cycle (IGCC) plants using coal. The potential
synthetic fuels generated include ethanol, methanol, di-methyl-ether (DME),
and
Fischer-Tropsch (F-T) liquids (diesel, gasoline).
i) Co-production of electricity and methanol
In one embodiment of the invention, a system based on gas derived from a
gasification
system allows for the co-production of electricity and methanol, which can be
used either
as a chemical feedstock or as an energy carrier. As an energy carrier,
methanol has a
number of potential applications. Methanol (MeOH) is potentially a cleaner
alternative
fuel for the future. One attractive possibility is its use in fuel cells for
mobile
applications. Methanol can be easily reformed into hydrogen and is more easily
stored
and transported than hydrogen.
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In one embodiment of the invention, a system configuration combining the
Liquid Phase
Methanol Process (LPMEOHe), and an IGCC power plant is herein contemplated.
Typically this system can reach higher synthesis gas conversion levels in a
single pass
through the reactor and has lower purification costs than a conventional gas
phase
methanol production technology. In addition, such a system can allow for the
production
of high-quality methanol from a wider range of gas compositions and
specifically from
gas mixtures rich in carbon monoxide. In accordance with one embodiment of the
invention, Fig. 22 presents the process flow diagram of a methanol/electricity
co-
production system.
ii) Co-production of electricity and isobutanol
The demand for methyl-t-butyl ether (MTBE) and other tertiary alkyl ethers as
gasoline
additives has attracted attention to alternative pathways for their
production. In one
embodiment of the invention, a system for the synthesis of isobutanol-methanol
mixtures
via CO hydrogenation is contemplated. In one embodiment, the
isobutanol/methanol
mixture formed in isobutanol synthesis can also react jointly over a catalyst
to yield
MTBE.
iii) Co-production of electricity and hydrocarbons
In accordance with one embodiment of the invention, a gasification plant can
co-produce
electricity and Fischer-Tropsch (F-T) fuel liquids. The direct processing of
the gas in the
F-T reaction eliminates the need for an additional step (water-gas shift) to
increase the
H2/CO ratio. The inherent water-gas shift activity possessed by some
catalysts, such as
iron F-T catalysts, allows the direct processing of low-H2/CO-ratio synthesis
gas. The
water-gas shift (WGS) reaction occurs simultaneously with the production of
hydrocarbons during F-T reaction over iron-based catalysts. These two
reactions are:
F-TS: nCO + 2nH2 - (-CH2-)n + nH2O (1)
WGS: CO + H20 - CO2 + H2 (2)
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The relative extents of the F-T and WGS reactions need to be optimized for the
maximum production of hydrocarbons. In one embodiment, the F-T reaction
produces a
large variety of hydrocarbons ranging from light gases to heavy wax (>C20).
Among
others, clean diesel (Cio-C15) and gasoline (C5-C12) can be obtained, which do
not contain
sulfur or nitrogen, have very low contents of aromatics and exhibit a high
Cetane number,
which implies the higher capacity of a fuel to auto-ignite.
In accordance with one embodiment of the invention, Fig. 23 shows an
integrated IGCC
and F-T liquid co-production system.
Chemical Synthesis
The gas obtained from the gasification of carbonaceous feedstock is also a
rich source of
chemicals. In accordance with one embodiment of the invention, gases can be
recombined into liquid fuels, including high-grade transportation fuels, and a
range of
petrochemicals that, in turn, serve as feedstocks in the chemicals and
refining industries.
For example, in contrast to conventional combustion, carbon dioxide exits a
gasifier in a
concentrated stream rather than diluted in a high volume of flue gas. This
allows the
carbon dioxide to be captured more effectively and then used for commercial
purposes or
sequestered.
As noted above, synthesis gas can be used as a building block for chemical
synthesis as
well as a feedstock for the recovery of pure carbon monoxide and hydrogen. The
theoretical CO:H2 ratio is 1 for synthesis of hydrogen, 1 for ethanol
production, 0.5 for
methanol production, and 0.33 for SNG synthesis. The process is very
competitive at a
ratio of 1 but it can be modified to produce different ratios, usually at a
certain increase in
cost. A great number of products can be produced. Non-limiting examples of the
major
products include:
= ethanol (direct from CO/H2 or from methanol)
= mixed alcohols (direct from CO/H2 or from methanol)
= methanol
= SNG via methylation
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= paraffins and olefins, diesel and gasoline (Fischer-Tropsch synthesis)
= benzene, toluene, and xylene (Mobil process from methanol)
= ethylene (Mobil process from methanol)
= ethylene (from CO/H2 via modified Fischer-Tropsch process, i.e., Ruhrchemie)
= ethylene (from FT paraffins via cracking process)
= Hydrogen and carbon monoxide by separation
i) Ethanol
In accordance with the invention, a process for the synthesis of ethanol from
gas is
contemplated. In one embodiment of the invention, the process involves the
catalytic
conversion involving the use of specific catalysts at elevated temperatures.
The
conversion yields a mixture of ethanol, methanol and other higher alcohols and
the target
product (ethanol) can be obtained at 95% purity by distillation.
In one embodiment of the invention, the process involves a fermentation
conversion that
takes place at mild temperatures around 37 C in the presence of specific
bacteria.
CO + 1/2 H20 = 1/6 C2H5OH + 2/3 CO2
H2 + 1/3 CO2 = 1/6 C2H5OH + 1/2 H20
ii) Methanol
In accordance with the invention, a process for the synthesis of methanol from
gas is
contemplated. In one embodiment of the invention, methanol production from gas
involves a catalytic hydrogenation reaction where carbon monoxide and hydrogen
react
to form methanol. This reaction occurs at 50-100 atm and 250-300 C for a high
selectivity of methanol and is known in the art. The reaction is as follows:
CO + 2 H2 ---> CH3OH
The methanol generated can then be further reacted with CO to produce acetic
acid and
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other derivatives used in the manufacture of a variety of consumer products.
In this way,
the methanol produced from synthesis gas in turn acts as a valuable feedstock
for a
variety of other chemicals (e.g., in the manufacture of acetic anhydride,
methyl acetate
and dimethyl terephthalate). The gases processed by the invention may also be
used in
the plastics and fertilizer industries.
Methanol is a clean-burning liquid that can be used to power electricity-
generating
turbines as well as a fuel for automobiles and other vehicles.
iii) Hydrogen
In accordance with the invention, a process for the synthesis of hydrogen from
gas is
contemplated. In one embodiment of the invention, Hydrogen can be derived
commercially from gas in two steps. The synthesis gas is first converted
catalytically
according to the following equation: CO + H2O = CO2 + H2. The second step
purifies the
hydrogen produced from the first step by low temperature separation, pressure-
swing
adsorption, or diffusion.
iv) Carbon Monoxide
In accordance with the invention, a process for the synthesis of carbon
monoxide from
gas is contemplated. In one embodiment of the invention, carbon monoxide can
be
derived commercially from gas using a separation process. The separation
process can be
based on condensation and distillation of carbon monoxide in the liquid phase
at low
temperature or on selective absorption of carbon monoxide.
v) Methane (Substitute Natural Gas or SNG)
In accordance with the invention, a process for the synthesis of methane from
gas is
contemplated. In one embodiment of the invention, gas can be hydrogenated to
methane
(CO + 3H2 = CH4 + H2O) in the presence of specific catalysts. The conversion
can be
carried out in a fluidized bed or a liquid-phase process. The catalysts used
in the
conversion are normally highly selective towards methane and only small
amounts of
higher hydrocarbons are formed.
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vi) Hydrocarbons - Fischer-Tropsch Synthesis
In accordance with the invention, a process for the synthesis of hydrocarbons
from gas is
contemplated. In one embodiment of the invention, the catalytic hydrogenation
of carbon
monoxide with catalysts containing iron, cobalt, or ruthenium produces
hydrocarbons.
The Fischer-Tropsch (F-T) synthesis can provide a wide variety of hydrocarbons
ranging
from methane to gasoline to diesel to waxes.
F-T technology is a well known art in the chemical and refining industries,
most notably
to produce gasoline and diesel fuel from gas produced by coal gasification.
The process
design differences among F-T products are primarily a result of changes to
process
pressure, temperature and use of custom catalysts, to adjust chemical
reactions and
produce the desired product.
Typically, it is not possible for the F-T catalyst to produce a single product
(e.g. ethanol)
with one pass. Therefore, in order to increase the yield of ethanol and in
accordance with
one embodiment of the invention, it is necessary to separate the products
(methanol) by
distillation and re-introduce the methanol with the H2 and CO at the
compression stage.
Several passes are required.
To gain a better understanding of the invention described herein, the
following examples
are set forth. It will be understood that these examples are intended to
describe illustrative
embodiments of the invention and are not intended to limit the scope of the
invention in
any way.
EXAMPLES
EXAMPLE 1:
The following defines characteristics of a homogenization chamber according to
one
embodiment of the invention.
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In one embodiment, a homogenization chamber provides sufficient storage to
allow for
blending of the product gas so short-term variability in gas quality is
substantially
minimized, wherein the homogenization chamber is located outside where it will
be
exposed to snow, rain and wind load.
Functional Requirements
Input gas can be highly toxic and flammable and thus the following required
safety
features can be considered during the design of the homogenization chamber.
For example, the homogenization chamber is designed to meet following
functional
requirements.
Normal / Maximum inlet temperature 35 C / 40 C
Normal operating pressure 3.0 psig
3 3
Normal / Maximum gas inlet flow rate 7200 Nm
/hr / 9300 Nm /hr
Normal / Maximum gas outlet flow rate 7200 Nm3/hr / 9300 Nm3/hr
Relative humidity 60% - 100%
Storage volume of tank 290 m
Operating gas Volume (Range) 0-290 m3
Mechanical design temperature -40 C to 300 C
Mechanical design pressure 5.0 psig
For homogenization chamber design the following two conditions are to be
considered:
(1) Maximum gas outlet flow with no inlet flow
(2) Maximum gas inlet flow with no outlet flow
One embodiment of the gas composition to be stored is defined as follows:
Gas Composition (v/v), Wet basis
CH4 0.03%
CO 18.4%
COz 7.38%
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H2 20.59%
H2S 354 / 666 ppm
H20 5.74%
HC1 5 ppm / 190 ppm
N2 47.85%
In one embodiment of the invention, the homogenization chamber is configured
such that
the following openings are provided.
o One 36" Manhole (Shell)
o One 36" Manhole (Roof)
o One 18" Flange (for gas Inlet)
o One 18" Flange (for gas outlet)
o Four 1" flanged nozzles on the top of the homogenization chamber
o Two 3" flanged nozzles on the top of the homogenization chamber
o Two 4" flanged connections on the top of the homogenization chamber
o Two 6" flanged connections on the top of the homogenization chamber
o One 2" drain at the bottom of the homogenization chamber
In one embodiment of the invention, the homogenization chamber is configured
such that
the following requirements are met.
1) Provision of all the required openings and manhole covers, blank flanges
2) Provision of all required supports for inspection and maintenance platform,
access ladders for inspection.
3) Provision of required lifting hooks and grounding lugs for homogenization
chamber.
In one embodiment of the invention, the homogenization chamber is designed in
consideration of the following environmental conditions.
Elevation above mean sea level - 80 m
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Latitude - 450 24' N
Longitude - 750 40' W
Average atmospheric pressure - 14.5 psia
Maximum summer dry bulb temperature - 38 C
Design summer dry bulb temperature - 35 C
Design summer wet bulb temperature - 29.4 C
Minimum winter dry bulb temperature --36.11 C
Mean wind velocity - 12.8 ft/sec
Maximum wind velocity - 123 ft/sec
Design wind velocity -100 mph/ 160 kph
Prevailing wind direction -Mainly from south and west
Seismic Information - Zone 3
Material of Construction
The material of construction is based on design conditions and gas
composition.
Reliability and Maintainability
Proper access for inspection and maintenance is provided. Homogenization
chamber are highly reliable and all of the gaskets and flanges used are of
appropriate standards to avoid any failure during operation.
Quality Assurance
A quality system that ensures that products meet all requirements is followed.
Each system generally is capable of operating in an industrial environment for
many years, with very high reliability and availability. In one embodiment,
the
system is designed for reliability (including proper de-rating of all
components),
and that a comprehensive system of inspections and tests are conducted to
ensure
and demonstrate compliance with all elements of the specification, including
interface requirements.
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A homogenization chamber will generally be traceable by serial number. Test
data or a Certificate of Conformance, will typically be employed to ensure
that the
equipment meets all aspects of the Requirement Specification.
All test and inspection data are maintained by unit serial number.
EXAMPLE 2:
The following defines characteristics of a homogenization chamber according to
one
embodiment of the invention.
In one embodiment of the invention, a homogenization chamber provides
sufficient
storage to allow for blending of the gas so that short-term variability in gas
quality and
pressure is minimized, wherein the homogenization chamber is located outside
where it
will be exposed to snow rain and wind load.
The homogenization chamber support structure interfaces with a concrete
foundation.
The homogenization chamber is free-standing and the dimensions of the
homogenization
chamber are designed to meet mechanical engineering requirements. The gas
homogenization chamber typically comprises one single tank, which is erected
on-site.
In one embodiment, some water condenses out of the gas, so a bottom drain
nozzle is
included in the design of the homogenization chamber for this purpose. To
assist in
draining the homogenization chamber, it is required that the homogenization
chamber
bottom not be flat, for example the homogenization chamber is configured
having a
conical bottom with a skirt. In one embodiment, traced/insulated drain piping
is used to
form the drain flange. The water within the homogenization chamber gravity
drains to a
floor drain, therefore the homogenization chamber is slightly elevated.
In one embodiment, the homogenization chamber is configured to meet the
following
functional requirements.
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Normal / Maximum Inlet Temperature 35 C / 40 C
Normal / Maximum O eratin Pressure 1.2 psig / 3.0 psig
Normal / Maximum Gas Inlet Flow Rate 7000 Nm3/hr / 8400 Nm3/hr
Normal / Maximum Gas Outlet Flow Rate 7000 Nm3/hr / 8400 Nm3/hr
Relative Humidity 60% - 100%
Storage Volume of Tank 290 m3
Mechanical Design Temperature -40 C to 50 C
Mechanical Design Pressure 5.0 psig
In one embodiment, the material of construction of the homogenization chamber
considers the gas composition given below, wherein corrosion is to be expected
from the
water due to the likely content of HC1, and H2S.
Gas Composition (v/v), Wet basis
N2 47.09%
CO2 7.44%
H2S 20 ppm
H20 3.43%
CO 18.88%
H2 21.13%
CH4 0.03%
HC1 5 ppm
In one embodiment of the invention, the homogenization chamber is configured
such that
the following openings are provided.
o One 36" manhole near the bottom of the homogenization chamber
o One 6" flange at the top for relief
o One 16" flange on the shell for gas inlet
o One 16" flange on the shell for gas outlet
o Six 1" flanges on the shell (2 pressures, 1 temperature, 3 spares)
o One 2" flange at the bottom of the homogenization chamber (drain)
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0 One 1" flanges on the bottom cone for level switches
In one embodiment of the invention, the homogenization chamber is configured
such that
the following requirements are met.
1) Provision of all the required openings and manhole covers, and blind
flanges
for all spare nozzles.
2) Provision of a ladder to the top of the homogenization chamber allowing
safe
access, for example with the integration of a railing, which can lead to the
roof
and relief valve.
3) Provision of required lifting hooks and anchor bolts.
4) Provision of a concrete ring wall.
5) Provision of interior and exterior coatings of the homogenization chamber,
if
required.
6) Provision of insulation and heat tracing of the bottom of the
homogenization
chamber.
7) Provision of a concrete slab.
In one embodiment of the invention, the homogenization chamber is configured
according to the specifications defined at Figure 24.
Materials and Construction
The homogenization chamber is designed and constructed to operate in a harsh
industrial
(waste processing) environment. As mentioned above, the material of
construction is
based on the design conditions and the gas composition. Corrosion from water,
HC1, H2S
is considered during selection of materials of construction.
EXAMPLE 3
The following provides functional requirements for a gas blower according to
one
embodiment of the invention.
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In one embodiment, the gas blower includes a gas cooler and is to be used to
withdraw
gas from a plasma gasification system. The gas blower is configured to provide
adequate
suction through all the equipment and piping as per specifications described
below.
Functional Requirements
Input gas is flammable and will create an explosive mixture with air, thus, in
one
embodiment of the invention all service fluid, i.e. seal purge, is done with
Nitrogen. In
one embodiment of the invention, the blower is operated through a variable
speed drive
(VSD) within the flow range of 10% to 100%.
Engineering of the system will be done with good engineering practice and
following all
applicable provincial and national codes, standards and OSHA guidelines. The
blower is
operated through a variable speed drive (VSD) within the flow range of 10% to
100%.
The gas blower is designed, for example, to meet following functional
requirements.
Normal gas inlet temperature 35 C
Normal gas suction pressure -1.0 psig
Normal gas flow rate 7200 Nm3/hr
Maximum gas flow rate 9300 Nm3/hr
Maximum gas suction temperature 40C
Normal discharge pressure 3.0 psig
Normal discharge temperature (after gas cooler) <35 C
Mechanical design pressure 5.0 psig
Relative Humidity of gas at blower inlet 100 %
Gas Molecular Weight 23.3
Cooling water supply temperature (product gas cooler) 29.5 C
Maximum acceptable gas discharge temperature (after product gas 40 C
cooler)
Turn down ratio 10%
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In one embodiment of the invention, the gas composition drawn through the
system by
the gas blower is defined as follows:
Gas Composition, wet basis(v/v)
CH4 0.03%
CO 18.4%
CO2 7.38%
H2 20.59%
Normal / Max H2S 354 / 666 ppm
H20 5.74%
Normal / Max HC1 5 ppm / 100 ppm
N2 47.85%
To avoid an explosive mixture, in accordance with one embodiment of the
invention, the
blower is configured such that there is minimal to no air intake from the
atmosphere. As
the gas can be toxic and flammable, in accordance with one embodiment of the
invention,
the blower is configured such that there is minimal to no gas leak to the
atmosphere. In
one embodiment of the invention, the blower has a leak-free shaft seal. In one
embodiment, an advanced leak detection system for leak in both directions is
provided.
In one embodiment of the invention, the gas blower is configured such that the
following
requirements are met.
1. Provision of an explosion proof motor with leak-free blower shaft seal.
2. Provision of product gas cooler.
3. Provision of silencer with acoustic box to meet 80 dBA at 1m noise
regulation
requirement.
4. Provision of a common base plate for the blower and motor.
5. Provision of an auxiliary oil pump with motor, and all required
instrumentations
for blower auxiliary system.
6. Provision of all instruments and controls (i.e. low and high oil pressure
switch,
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high discharge pressure and temperature switch, differential temperature and
pressure switch). In one embodiment, all switches shall be CSA approved
discharge pressure gauge, discharge temperature gauge, oil pressure and
temperature gauge. In one embodiment, all instruments shall be wired at common
explosion proof junction box and VFD will be controlled by a pressure
transmitter
installed upstream of the blower.
7. Provision of zero leaks discharge check valve.
8. Provision of equipment safety system to prevent blower from excessive
pressure
/vacuum/ shut off discharge (for example, systems like PRV and recycle line).
Technical Requirements
In one embodiment the blower satisfies the functional requirements of Section
2 and
operate at about 600 Volts, 3 phase, 60 Hz.
Environmental
Product gas blower and product gas cooler may be located outside the building
where it
will be exposed to rain, snow and wind. Thus, in one embodiment, the gas
blower is
configured to withstand the following environmental conditions.
Elevation above mean sea level - 80 m
Latitude - 450 24' N
Longitude - 750 40' W
Average atmospheric pressure - 14.5 psia
Maximum summer dry bulb temperature - 38 C
Design summer dry bulb temperature - 35 C
Design summer wet bulb temperature - 29.4 C
Minimum winter dry bulb temperature --36.11 C
Mean wind velocity - 12.8 ft/sec
Maximum wind velocity - 123 ft/sec
Design wind velocity -100 mph/ 160 kph
Prevailing wind direction - Mainly from south and west
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Seismic Information - Zone 3
Class of Blower
In one embodiment, the blower is configured to work in an environment where
explosive gases may be present in upset conditions. For example, all
instruments
and electrical devices installed on gas pipes or within about 2 meter distance
will
be classified for Class 1, zone 2.
Reliability, Maintainability and Spares
The blower shall be highly reliable. Proper access for inspection and
maintenance
is provided, as is access to isolate and correct faults.
The blower can be operated continuously (24/7). Frequent start/stop operation
of
the blower during process stabilization are contemplated. Gas blower is
capable of
working with high reliability even during frequent start/stop.
Quality Assurance
A quality system that ensures that products meet all requirements will be
followed.
Each system is capable of operating in an industrial environment for many
years,
with very high reliability and availability. In one embodiment, the system is
designed for reliability (including proper de-rating of all components), and
that a
comprehensive system of inspections and tests are conducted to ensure and
demonstrate compliance with all elements of the specification, including
interface
requirements.
Materials and Construction
The material of construction is based on design conditions and gas
composition.
For example, electrical circuit boards, connectors and external components are
coated or otherwise protected to minimize potential problems from dirt,
moisture
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and chemicals. Control panels and switches are of robust construction, and are
designed to be operated by personnel wearing work gloves.
Control Interfaces
Generally, variable speed drive for the motor control is employed. Motor over-
voltage, overload protection etc is included.
Motor status, On/Off operation, speed change is operated and monitored
remotely
through DCS.
EXAMPLE 4:
Working Specification of a Gas Homogenization System
Gas Storage and Gas Heating
In one embodiment of the invention, the cleaned and cooled gas is stored in
the gas
storage tank. The purpose of the gas storage tank is to homogenize its
composition (low
heating value - LHV) and its pressure. The gas is heated on the exit of the
gas storage
prior to the engines to meet engine temperature requirements.
Composition - LHV
In one embodiment, the gas storage provides enough residence time for the gas
to have
better blending to avoid any short term heating value fluctuations. This is
required
because of the varied composition of the waste. With LHV fluctuations, the
engine will
run and produce the electricity, but it may deviate from its threshold
emission limits
because of poor combustion or poor fuel to air ratio.
In one embodiment, the volume of the tank is based on a hold up time of about
2 minutes.
The 2 minute hold up time is designed to meet the gas engine guaranteed norms
on LHV
fluctuation specifications of about 1% LHV fluctuation/30 sec. The residence
time up to
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the gas analyzer (upstream of the gas storage tank) is typically about 30 sec
(including
analysis and feedback). The maximum LHV fluctuation is typically about 10%.
Thus, in
one embodiment, to average this out and get 3% LHV fluctuation, 1.5 min
storage is
provided to meet the upper tolerable limit of the gas engine. Accordingly, the
2 min
storage allows for some margin.
Pressure
In one embodiment, the storage tank is operated at 2.5 to 3.0 psig to meet gas
engine fuel
specification. The exiting gas pressure is maintained constant using a
pressure control
valve. In one embodiment, the gas tank has a design pressure of 5psig, a
relief valve is
installed to handle unusual overpressure scenarios.
The 2 min hold up time described above also provides enough storage to reduce
pressure
fluctuations. In one embodiment, the allowable pressure fluctuation for the
engine is
0.145 PSI/sec. In the case of a downstream failure of a gas engine, a buffer
may be
required (depending on control system response time and 30-35 sec gas resident
time) to
provide time to slow down the process or to flare the excess gas.
Volume Calculation
In one embodiment, cool gas flow entering the storage tank (26C), is at - 8400
Nm3/hr.
That equates to 140 Nm3/min, for 2 min, that is 280 m3 of required storage
volume.
Fixed Volume vs. Variable Volume
In one embodiment, a fixed volume tank is chosen over a variable volume tank
because
pressure fluctuations will not be quick in the process but the possibility of
LHV
fluctuation is there due to the nature of the waste. For example, a variable
volume tank is
typically more useful to absorb flow and pressure fluctuation. However if the
tank is
empty, it will not be helpful in compensating LHV fluctuation. The fixed
volume on the
other hand, is useful for averaging out LHV fluctuation. Also a fixed volume
is typically
more reliable than variable volume in terms of its construction and
maintenance.
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EXAMPLE 5:
Specifications for a Homogenization Chamber
The gas produced from the Plasma Gasification Process (From Plasma
Gasification
Converter) will be processed in the plant to remove unwanted impurities like
acid gases,
heavy metals and particulate matter. In one embodiment, the produced clean and
dry gas
will be utilised in gas engine for power generation. The gas from the
converter will be
neutralized and partially dehydrated prior to use in gas engines. This cleaned
and dry gas
will be stored in a Gas Homogenization Chamber for blending of the gas so that
short-
term variability in gas quality is minimized and constant gas flow is
available for
downstream applications such as a gas engine.
Engine
In one embodiment, the Gas inlet flow rate to the tank is 8200 Nm3/hr (4825
SCFM) at
35C (7950Am3/hr or 4675 ACFM at 1.0 PSIG). In one embodiment of the invention,
the
storage capacity of an homogenization chamber is equivalent to about 15
minutes of
production rate.
Process Requirements
It is expected that fluctuations in gas flow and compositions is mainly due to
change in
material feed rate and composition, airflow fluctuations and temperature
fluctuation
inside the converter. Based on experimental data it is known that each torch
cycle shall be
of approximately 3 minutes. Optimizing cost of gas storage and impact of gas
quality and
flow fluctuations requires gas storage capacity of 3-5 torch cycles (i.e. 10-
15 minute of
production).
Considering 9000 m3/hr of maximum flow rate, storage tank maximum capacity is
2300
m3 while operating capacity shall be 0-2050 m3, in accordance with one
embodiment of
the invention.
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Required gas pressure for gas engine is 2.2psig, so it is necessary to
maintain constant
pressure of 1.5 psig (approx. 105 mbar) inside the gas storage, in accordance
with one
embodiment of the invention.
Typically, water drain system is provided inside the gas storage tank for
wintertime water
vapour condensation.
Process Basis of Design
In one embodiment, gas shall be stored at low pressure that will exclude
storage system
from pressure vessel standard.
Gas compositions
In accordance with one embodiment of the invention, gas composition exiting
Gas
Conditioning System (GCS) is as follows:
Gas compositions (Wet Basis)
Gas Composition (Wet) %
N2 50.414
CO 17.004
H2 18.011
C02 8.809
H20 5.734
H2S <20 ppm
Gas specifications
Lower Flammability Limit: 17.93%
Higher Flammability Limit: 73.26%
Specification Unit Value
Gas Density lb/ft3 0.0536
Gas Molecular Weight Kg/K Mole 24.2
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Gas Viscosity CP 0.0253
Gas Temperature F 95
Gas Relative Humidity % 60
Water Content % 3.3 -5.7
In one embodiment of the invention, the following environmental conditions are
considered.
Environmental Data
Average Elevation above mean sea level : 250 m
Average Atmospheric Pressure : 14.5 psia
Maximum Summer Dry Bulb Temperature : 100.4 F
Design Summer Dry Bulb Temperature : 95 F
Design summer Wet Bulb Temperature : 85 F
Minimum Winter Dry Bulb Temperature : -33 F
Wind Data - Mean Velocity : 12.8 ft/s
- Maximum Velocity : 123 ft/s
- Design Velocity (to ANSI A58.1) : 145 ft/s
Prevailing Wind Direction - Mainly from South and West
Seismic design : TBD
Storage Tank Location and Condition
In one embodiment, the Gas Storage shall be located outdoor, where it shall be
exposed
to rain, snow and sun with condensing environment.
Design ambient temperature : -40F
Snow loading (Extreme snow depth) : 150 cm
Alternatives:
In accordance with different embodiments of the invention, five alternatives
storage
technology selections are provided as follows.
1) Compression of gas followed by storage in a pressure vessel;
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2) Storage of gas in traditional metal tank at low pressure;
3) Storage of gas in a gas holder designed from membrane technology;
4) No gas storage; and
5) Storage of gas in dry seal gas holder.
Considerations for the use of the above storage technologies are provided
below, but are
not intended to limit the scope of the invention in any way.
1) Gas Compression and Storage
After closely reviewing this option, the operating cost of the compressor is
very high. A
gas engine requires gas at low pressure so if gas is compressed it needs to be
decompressed before utilizing it for gas engines. Thus, it requires lots of
operating cost to
compress gas based on compression ratio.
2) Storage in Metal Tanks
Conventional metal storage is an expensive way to store gas at low pressure
unless it is
really required (mainly when it is compressed). Metal storage tanks are either
fabricated
in advance or fabricated on-site (Field erected) based on the size of the
tank. Some
applications require field erected storage tank because of large required
capacity. It is
very important to store gas properly to avoid any fire hazard. Metal storage
tanks are
made from various kinds of metals and metal alloys. Most common metal used is
carbon
steel because it is very cheap, easily available and has good strength. But
for corrosive
fluids various kind of metal alloys are used based on condition and type of
the fluid to be
stored.
Application of Metal Storage Tanks:
(1) Liquid storage;
(2) Storage of liquid or gas at high pressure; and
(3) Small or medium capacity storage even high capacity storage for some
applications, mainly liquid storage.
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Typical benefits of storinggas in a metal stora eg tank:
a) Better pressure control i.e. excessive pressure can be handled precisely
and
safely;
b) Less Instrumentation required;
c) Applicable for Full vacuum conditions if design for service;
d) Better option for wide temperature range; and
e) More reliable from safety point of view.
Disadvantages of Metal Storage at low pressure:
a) Expensive due to large volume; and
b) Pressure fluctuation during filling and emptying of the tank with large
amount of gas.
There are some regulations for storing hydrocarbon that requires hydrocarbon
gases to be
stored in pressure vessel and metallic tanks.
3) Storage in Gas Holders (Double Membrane Technology)
Gas Holders are normally used to store natural gas and bio gas. Gas holders
can typically
store large volume of gas under very low pressure typically less than 14" WG
(0.5 PSIG).
This system includes two durable membranes. The outer membrane is cable
restrained
and remains inflated in a fixed position. An inner membrane moves freely as it
stores or
releases gas generated from the upstream of the storage or released in the
down stream of
the storage. An air handling system maintains a preset operating pressure
between two
membranes. This keeps outer membrane in fixed position regard less of inner
membrane
position. Operating pressure can be changed easily within design range.
While discharging gas from the gas holder a fan provides air to the air
chamber (space
between two membranes). As the gas is added to the holder, an adjustable
pressure relief
valve relieves the pressure between the two membranes allowing gas chamber to
expand.
Applications of the double membrane gas holder:
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(1) Biogas intermediate storage; and
(2) Methane sludge removal in anaerobic process.
Advantages of double membrane gas holder:
1) Reduced installation costs;
2) Easily handle sudden large amount of gas input or withdrawal of the same;
and
3) No regular maintenance required such as painting.
Disadvantage of gas stora eg in a gas holder:
1) Not fit for high pressure application (Max 14" W.G- 0.5PSIG);
2) Not suitable for high temperature applications; and
3) Required more instrumentation and control for pressure control of the tank
(required more relief valves).
4) No Gas Storage
It is important to know the motive of gas storage. For instance if storing gas
that will lead
gas engine feed composition and flow variation is not a consideration. It is
important to
evaluate how much composition variation will occur for an application, how
fast a
control system will react to those variations, how much composition and flow
variation
gas engine can tolerate.
From previous experimentation it was found that there can be significant gas
composition
variation in a process. The gas composition variation is greater than gas
engine
acceptance range, therefore, a homogenization chamber may be used.
Advantages of not storing gas:
1) No capital cost required; and
2) No instrumentation cost.
Disadvantages of not storing gas:
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1) Unstable gas flow at gas engine;
2) Variable gas composition entering gas engine affecting gas engine
performance; and
3) Can not isolate gasification process from gas engine and visa versa.
For some applications, it is recommended to have gas storage to avoid short-
term
variation in gas composition.
It is clear that dry seal type gas storage system can provide constant gas
flow rate and
pressure, besides this it is capable of satisfying required operating
pressure, volume and
temperature conditions.
5) Storage in Gas Holder (Dry Seal)
Dry seal type gas holders are typically a metallic cylinder outside with a
central vent in
the top. Inside the shell a diaphragm is connected to a metal piston to move
diaphragm
upward while filling the gas holder and moving down while withdrawing gas from
the
gas holder. Diaphragm is made up of various materials depending on type of gas
to be
stored.
Applications of the dry seal holder:
1) Steel industries for intermediate gas storage; and
2) Mining and metallurgical industries to buffer the gas for power generation.
Advantages of the dry seal holder:
1) Dry seal gas holders can handle very large volume of gas (up to 30000
m3);
2) Applicable for very large volume input and/or output;
3) Applicable for comparatively high pressure applications (Up to 2000 mm
WG);
4) Low maintenance;
5) 15 to 20 years of service life;
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6) No contaminated water removal before entry;
7) Applicable for wide range of temperatures; and
8) Requires lighter foundation.
Disadvantages of the dry seal holder:
1) Not suitable for very high pressure application (above 2000mm WC); and
2) More instrumentation required for operation.
Functional description of a dry seal homogenization chamber in accordance with
one
embodiment of the invention
A Dry-seal gasholder is designed to have a gross (geometric) volume ranging
from two
hundred cubic meters up to one hundred and sixty-five thousand cubic meters,
whilst
having a working pressure range between fifteen and one hundred and fifty
millibar.
The Dry-seal gasholder is finished with an anti-corrosive treatment to
counteract local
climatic conditions and also any chemical attack from the stored medium. This
anti-
corrosive treatment is fully compatible with the sealing membrane and also the
environment.
The Dry Seal Gasholder has four major elements:
1. The foundation;
2. The main tank;
3. The piston; and
4. The sealing membrane.
Each of these elements can be divided into various sub-elements and associated
accessories.
The Foundation
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A concrete and hardcore base designed to withstand the weight of the steel
gasholder
structure constructed upon it and to withstand dynamic climatic conditions
acting upon
the gasholder etc.
The Main Tank
The main tank is designed to accommodate the design requirements laid down by
the
customer and climatic conditions.
There are three main sub-elements to the tank:
Tank bottom
The tank bottom forms a gas tight seal against the foundation and is "coned
up" to
facilitate drainage to the periphery. The bottom is covered with steel plates.
The outer
annular plates are butt welded against backing strips, whilst the infill
plates are lap
welded on the top side only. Welded to the bottom infill plates
Piston support structure
When the piston is depressurized it rests on a steel framework, which is
welded to the
bottom plates.
Tank shell
The shell of the tank is designed to accommodate the imposed loads and the
general data
supplied by the user. The shell is of butt-welded design and is gas tight for
approximately
40% of its lower vertical height (known as the gas space) at which point the
seal angle is
located. The remaining upper 60% (known as the air space) of the shell has in
it various
apertures for access and ventilation.
Attached to the shell are various accessories:
Staircase tower
For external access to the roof of the gasholder and also incorporates access
to the inside
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of the gasholder via the shell access doors. A locked safety gate is usually
located at the
base of the staircase to prevent any unauthorized access to the gasholder.
Shell access doors
Doors located at pertinent points allowing access into the gasholder from the
external
staircase tower.
Shell vents
Allow air to be displaced from the inside of the gasholder as the piston
rises.
Inlet nozzle
The connection nozzle allowing the stored gas to enter the gasholder from the
supply gas
main
Outlet nozzle
For the export of the stored gas, this nozzle comes complete with an anti-
vacuum grid to
protect the sealing membrane during depressurization. Depending on the
operational
process the inlet & outlet nozzles maybe a shared connection
Shell drains
Allow condensates within the gasholder gas space to drain away in seal pots.
The seal pots are designed to maintain the pressure with the gasholder
Shell manways
Used for maintenance access into the gas space - only used whilst the
gasholder is out of
service.
Earthing bosses
To ensure that the gasholder is safe during electrical storms etc
Volume relief pipes
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Essential fail-safe system to protect the gasholder from over-pressurization
once actuated,
by the piston fender, the volume relief valves allow the stored gas to escape
to
atmosphere at a safe height above the gasholder roof. As the volume relief
valves open
they actuate a limit switch.
Volume relief limit switches
Used to send signals to the control room to confirm the status of the volume
relief valves
Level weight system
A mechanical counter balance system to ensure that the pistons moments are
kept in
equilibrium. The level weights which run up and down tracks located on the
gasholder
shell also actuated limit switches to signal when the gasholder volume has
reached pre-
defined settings.
Level weight limit switches
Used to send signals to the control room to operate import and export valves
etc.
Contents scale
On the gasholder shell is a painted scale displaying the volume of gas stored
within the
gasholder. An arrow painted on an adjacent level weight indicates the current
status. Also
painted on the scale is the location of the piston in relation to the shell
access doors.
Seal angle
Welded to the inside of the shell this angular section is where the sealing
membrane
attaches to the shell.
Tank roof
The roof is designed to withstand the local climatic conditions and the
possibilities of
additional loads such as snow and dust. The roof of the gasholder is of thrust
rafter radial
construction and has a covering of single sided lap welded steel plates. The
roof has
various accessories attached including:
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Center vent
Allows air to enter and exit the gasholder as the storage volume changes.
Roof vents
Small nozzle around the periphery used for the installation of the seal.
Roof manways
Allows access down to the piston fender when the gasholder is full
Circumferential hand railing
Safety hand railing around the outside of the roof.
Radial walkway
For access from the staircase to the center vent etc.
Volume relief valve actuators
Mechanical arms that operate the volume relief valves once the piston fender
reaches a
certain level.
Level weight pulley structures
Steel structures mounting the level weight rope pulleys and rope separators.
Load cell nozzles
For maintenance access to the load cell instrumentation used for volume
recording
purposes.
Radar nozzles
For maintenance access to the radar instrumentation used for volume recording
purposes
and piston level readings.
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Roof interior lighting nozzles
For maintenance access to the gasholders interior lights.
Piston
The gasholder piston moves up and down the inside of the shell as gas enters
and exits
the gasholder. The weight of the piston (less the weight of the level weights)
produces the
pressure at which the gasholder will operate. The piston is designed to apply
an equally
distributed weight to ensure that the piston remains level at all times.
The piston made up of the following sub-elements:
Piston deck
The outer annular area is formed from butt-welded steel plates resting on
steel section
rest blocks. Lap welded steel infill plates form a dome profile to withstand
the gas
pressure in the gas space beneath it. For higher-pressure gasholders the
infill plates are
lap welded on both sides, where as, low-pressure gasholders are only welded on
the
topside. The fully welded piston deck forms a gas tight surface, which rests
on the piston
support structure when the gasholder is depressurized.
The following ancillary items can be found on the piston deck:
Piston manway
Used for maintenance access below the piston into the gas space - only used
whilst the
gasholder is out of service.
Load cell chain receptacle
A receptacle for gathering up the load cell chains as the piston rises.
Piston seal angle
Welded to the outer topside of the annular plates, this angular section is
where the sealing
membrane attaches to the piston.
Level weight rope anchors
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Equally spaced around the periphery of the piston deck are the connections to
which the
level weight ropes are fixed.
Piston fender
The fender is a steel frame structure that is fixed to the piston deck annular
plates and
acts as a support structure for the abutment plates. Access can be gained to
the top of the
piston fender from either the shell access doors or roof manways depending on
the
gasholder volume
Attached to the piston fender are the following items:
Piston walkway
A platform around the top of the piston fender equipped with safety hand
railing - used
for inspection purposes.
Piston ladders
Rung ladders complete with safety loops for access to the piston deck from the
piston
walkway.
Radar reflector plates
Used to bounce the radar signal back to the radar instrument for volume
indication
recording and piston level readings
Abutment plates
Fixed to the outside of the piston fender to form a circumferential surface
for the sealing
membrane to roll against whilst the piston moves during operation.
Piston torsion ring
Around the base of the piston fender is a torsion ring which helps keep the
piston shape
during pressurization. Concrete ballast can be added to the torsion ring to
increase the
weight of the piston and subsequently be a cost effective way to increase the
pressure of
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the gasholder to the required level.
Sealing membrane
The seal rolls from the shell to the abutment surface of the piston and vice
versa
providing the piston with a frictionless self-centering facility. During
depressurization the
seal also provides a gas tight facility that protects the holder from vacuum
damage by
blocking the gas outlet nozzle. During commissioning of the gasholder the
sealing
membrane is set into an operating condition. This setting must be carried out
every time
the gasholder is depressurized.
Technical Specification
Characteristics
Working pressure : 103 mbar ( 2 mbar)
Gross capacity : 2300 m3
Working capacity : 2050 m3 (between 5% & 95% limits)
Shell height : 17185 mm
Inside shell diameter : 17000 mm
Piston stroke : 10200 mm
Net steel weight : 150 tones
Shell Plates : 6 & 8 mm thick butt welded
Seal angle Height : 5435 mm - fabricated from
R.S. section Bottom
Annular row plates : 8 mm thick - butt-welded to
backing strips
Infill plates : 6 mm thick - lap welded on
sides only
Roof Structure Thrust : rafter type - fabricated from
R.S. sections
Annular row plates : 5 mm thick - lap welded one
side only
Infill plates : 4 mm thick - lap welded one
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side only
Piston Height : 5285 mm
Structure : Fabricated from R.S. sections
Annular row plates 8 mm thick -
butt-welded to backing supports
Infill deck plates : 6 mm thick - lap welded one Section
Support structure : Fabricated from R.S. sections
Abutment plates : 4 mm thick
External staircase : Fabricated from R.S. sections
Shell access doors : 3 no. - at various positions above
belt angle
Roof periphery : handrail Fabricated from
R.S. sections
Shell manways : 2 no. diametrically opposite
600 mm diameter
Piston manways : 1 no. - 600 mm diameter
Roof manways : 2 no. diametrically opposite
600 mm Diameter
Fittings
Inlet nozzle : 1 no. - 450 mm diameter
Outlet nozzle : 1 no. - 450 mm diameter c\w anti-
vacuum grid
Shell vents : 32 no.
Shell condensate drains : 6 no. - 50 mm diameter
Volume relief : 2 no. - 200 mm diameter
Roof vents : 8 no. -150 mm diameter
Level weights 3 set each comprising of : 1 no. 5000 kg level weight
1 no. level weight guide
1 no. Guard
2 no. Level weight structures
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2 no. 22 mm diameters plastic
impregnated ropes
2 no. cable sheaves
4 no. jockey pulleys
Limit switches : 4 no. - level weight operated and
set @ 5%, 10%, 90%, & 95% of piston stroke 1 no. - volume relief pipe operated
Load cells : 2 no. - c\w plastic chains
Earthing bosses : 4 no.
Contents scale : Vertical scale painted on side of shell
Example 6:
A Municipal Solid Waste Gasification Plant
This example provides a Municipal Solid Waste (MSW) plant, in accordance with
one
embodiment of the invention, including amongst others a gasification system, a
gas
conditioner and a gas homogenization system.
Process Overview
The raw gas of the gasification system exits the converter and passes through
a
recuperator (heat exchanger). The recuperator cools the gas and the sensible
heat is used
to preheat the process air that will be introduced into the converter. The
cooled gas then
flows into a Gas Conditioning System (GCS), where the gas is further cooled
and cleaned
of particulates, metals and acid gases sequentially. The GCS in this
embodiment
comprises a converter gas conditioner and a solid residue gas conditioner. The
cleaned
and conditioned gas (with desired humidity) is stored in the gas
homogenization chamber
before being fed into gas engines, from which electricity is generated. The
functions of
major components (equipment) in the system are illustrated in the following
sections (see
Table 1), following the sequence that the gas is processed. The equipment
figure and
process diagram of the MSW gasification plant are presented in Figures 25 and
26.
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Table 1: Main Function of Subsystem
Subsystem or equipment Main Function
Recuperator Cool down gas and recover sensible heat
Evaporative Cooler Further cooling down of gas prior to baghouse
Dry Injection System Heavy metal adsorption
Baghouse Particle or dust collection
HCL Scrubber HCL removal and gas cooling/conditioning
Carbon Filter Bed Further mercury removal
H2S Removal System H2S removal and elemental sulfur recovery
Solid residue gas conditioner Slag chamber off-gas cleaning and cooling
Gas Homogenization System Gas storage, homogenization, and humidity
comprising Homogenization control
Chamber (Storage Tank), Chiller
and Gas/Liquid Separator
Gas Engines Primary driver for electricity generation
Flare Stack Burning gas during start-up/shut
down/emergency
Recuperator
In order to recover the gas sensible heat, the raw gas exiting from the
reformer is cooled
by air using a shell-tube type heat exchanger, called a recuperator. The gas
flows through
the tube side and the air passes through the shell side. The gas temperature
is reduced
from 1000 C to 738 C while increasing the air temperature from ambient to 600
C.
Evaporative Cooler (STAGE ONE PROCESSING)
This system drops Gas temperature to 250 C via direct injection of water in a
controlled
manner (adiabatic saturation). This process is also called dry quench in that
there is no
liquid present in the cooling. The water is atomized and sprayed co-currently
into gas
stream. When the water is evaporated, it absorbs the sensible heat from gas
and decreases
the gas temperature to approximately 250 C before it is fed to the baghouse.
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Dry Injection System (STAGE ONE PROCESSING)
Activated carbon has a very high porosity, a characteristic that is conducive
to the surface
adsorption of large molecular species such as mercury and dioxin. Activated
carbon,
stored in a hopper, is pneumatically injected into the input gas stream and
captured in the
baghouse. In this way, the metals and other contaminants are separated from
the gas
stream. Alternatively other materials such as feldspar, lime, and other
sorbents can be
injected into the gas stream to control and capture heavy metals & tars found
in the input
gas stream without blocking it.
Baghouse (STAGE ONE PROCESSING)
Particulate matter and activated carbon with heavy metal on its surface is
removed from
the Gas in the bag-house. In the baghouse, a filter cake is formed with
particulate matter.
This filter cake enhances the particulate removal efficiency of the baghouse.
Heavy
metals like cadmium and lead are in particulate form at this temperature and
are also
collected in the baghouse with very high collection efficiency. When the
pressure drop
across the baghouse increases to a certain set limit, nitrogen pulse-jets will
be used to
clean the bags. The solids falling from the outside surface of the bags are
collected in the
bottom hopper and are sent to the solid residue conditioner for further
conversion or
disposal (see solid residue gas conditioner step below).
HCL Scrubber (STAGE TWO PROCESSING)
The gas exiting from the baghouse (particulate free) is scrubbed in a packed
tower to
remove HC1 in the gas stream by an alkaline solution. Inside the scrubber, it
also
provides enough contact area to cool down the gas to 35 C. The outlet HC1
concentration will reach 5 ppm level. A waste water bleed stream is sent to a
waste water
storage tank for disposal.
Gas Blower (STAGE TWO PROCESSING)
A gas blower is required at this point to provide the driving force for the
gas throughout
the process from the exit of the converter up to the engines. It is located
upstream of the
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mercury polisher because the polisher has a better mercury removal efficiency
under
pressure. The blower is designed using all upstream vessel design pressure
drops. It is
also designed to provide the required pressure for downstream equipment
pressure losses
to have a final pressure of -2.1 to 3.0 psig in the homogenization chamber.
Carbon Filter Bed (STAGE TWO PROCESSING)
The gas pressure is boosted by a blower and further cooled by a water-cooled
heat
exchanger prior to the carbon bed filter which is used as a final polishing
device for
heavy metal in the gas stream. It is also capable of absorbing other organic
contaminants,
such as dioxins from the gas stream if present. The carbon bed filter is
designed for over
99.0% mercury removal efficiency.
H2S Removal System (STAGE TWO PROCESSING)
The Shell Paques Biological technology is selected for H2S removal. First, gas
from the
carbon bed filter passes through a scrubber where H2S is removed from gas by
re-
circulating an alkaline solution. Then, the sulfide containing solution from
the scrubber is
sent to the bioreactor for regeneration of alkalinity. The sulphur recovery
occurs in the
bio-reactor for oxidation of sulphide into elemental sulphur, followed by
filtration of
sulphur, sterilization of sulphur and bleed stream discharge to meet
regulatory
requirements. The H2S removal system is designed for 20 ppm H2S outlet
concentration.
Once the input gas exits the H2S removal system it is then directed to a gas
homogenization system comprising amongst other components a chiller, a
gas/liquid
separator and homogenization chamber.
Solid residue gas conditioner (STAGE ONE PROCESSING)
Ash (may contain activated carbon and metals) from the converter gas
conditioner
baghouse is purged periodically by nitrogen and conveyed to the solid residue
conditioner, where the ash is vitrified. The gas coming out of the solid
residue
conditioner is directed through the solid residue gas conditioner baghouse to
remove
particulates and cooled by a heat exchanger before entering an activated
carbon bed. The
baghouse of the solid residue gas conditioner is also periodically purged
based on
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pressure drop across the system. The solid residue collected in the solid
residue gas
conditioner baghouse is disposed by appropriate means. The combustible gas
exiting
from the solid residue gas conditioner (secondary gas stream) is sent back to
the
converter gas conditioner to fully utilize the recovered energy.
Gas Homogenization System
The gas engine design requires that the gas be of a specific composition range
at a
specified relative humidity. Therefore, once the cleaned gas exits the H2S
scrubber, it is
sub-cooled from 35 C to 26 C using a chiller. This will condense some water
out of the
gas stream. This water will be removed by a gas/liquid separator. This ensures
that the
gas has a relative humidity of 80% once reheated to 40 C (engine requirement)
after the
gas storage prior to being sent to the engines in an embodiment where the
output gas is
used to power an engine. The cleaned and cooled gas enters a homogenization
chamber
(for example, a storage tank) designed to hold approximately 2 minutes of
output from
processing operations, thus blending any variations in "richness" of the gas,
to achieve a
highly consistent gas quality (a regulated gas) flowing to the engines. The
homogenization chamber is operated at 2.2 to 3.0 psig to meet gas engine fuel
specifications. Once the regulated gas exits the homogenization chamber, it is
heated to
the engine requirement and directed to the gas engines.
Gas Engines
Five GE Jenbacher gas engine sets are used to produce electricity based on the
scale of
the plant. Jenbacher gas engine is a type of reciprocating engine. It is
capable of
combusting low or medium heating value gas with high efficiency and low
emissions.
Each gas engine has 1.0 MW capacity. So, the full capacity of electricity
generation is
MW. However, due to the relatively low gas heating value (as compared to fuels
such
as natural gas) the engines have been derated to operate around 700kW at their
most
efficient operating point.
Flare Stack
An enclosed flare-stack will be used to burn gas during start-up, shut-down
and process
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stabilization phases. Once the process has been stabilized the flare stack
will be used for
emergency purposes only. The flare stack should achieve 99.99% destruction
efficiency.
Example 7:
High Level Process Control of Municipal Solid Waste System Comprising a Gas
Homogenization System
This example provides a high level description of a control strategy for a
Municipal Solid
Waste (MSW) plant, according to one embodiment of the invention, which
includes
amongst others a gasification system, a gas conditioner and a gas
homogenization system.
The high level process control includes control of components of the gas
homogenization
system. A two phase approach is used with regard to development and
implementation
of the process control strategy for an MSW plasma gasification plant:
Phase 1: Operation during start-up and commissioning
For start-up and commissioning, a simple front-to-back (or supply-driven)
control
strategy is used where the converter is run at a fixed feed rate of MSW and
process
variations are absorbed by the downstream equipment (engines/generators &
flare). The
plant is operated with a small buffer of excess gas production, requiring a
small
continuous flare. Gas production beyond this normal amount increases the
amount flared
and deficient gas production first eats into this buffer, but may eventually
require
generator power output to be reduced (generators can be operated from 50 -
100% power
output via an adjustable power set point).
The benefits of this control scheme are:
It is less complex. It improves the ability to start-up and commission the
plant, and then
to make use of the operating data to implement more sophisticated control. It
decouples
the back-end from the front-end such that problems with one section of the
plant are less
likely to cascade to the rest of the plant. This increases the uptime and
improves the
ability to troubleshoot and optimize each part of the process. The small
continuous flare
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eliminates the risk of large visible flame at the flare stack which can occur
if the flare is
operated in stop/start mode.
Phase 2: Long-term operating strategy
The long-term control strategy for the MSW plant is to achieve back-to-front
control (or
demand-driven control) where the gas engines/generators at the back-end of the
system
drive the process. The gas engines consume a certain volume/hr of fuel
depending on the
energy content of the fuel gas and the electrical power being generated.
Therefore the
high level goal of the control system is to ensure that adequate MSW/HCF feed
enters the
system and is converted to gas of adequate energy content to run the
generators at full
power at all times, while precisely matching gas production to gas consumption
such that
flaring of gas is eliminated and the electrical power produced per ton of MSW
consumed
is optimized.
A high-level process control schematic for Phase 2 operation is shown in
Figure 15.
Phase 1 operation is a sub-set of the control schematic shown.
Phase 1
Main Process control goals
a) Stabilize the pressure in the gas homogenization chamber (for example, a
storage
tank).
b) Stabilize the composition of the gas being generated.
c) Control pile height of material in the converter lower chamber.
d) Stabilize temperatures in the converter lower chamber.
e) Control temperatures in the reformer.
f) Control converter process pressure.
Description of Goals
a) Stabilize the pressure in the gas homogenization chamber.
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Typically, gas engines are rather intolerant of changes in supply pressure.
The
specifications for Jenbacher engines are as follows:
= minimum pressure = about 150 mbar (2.18 psig)
= maximum pressure = about 200 mbar (2.90 psig)
= allowed fluctuation of fuel gas pressure =+/- 10% (+/- 17.5 mbar, +/- 0.25
psi)
= maximum rate of gas pressure fluctuation = about 10 mbar/sec (0.145 psi/sec)
The engines have an inlet regulator that can handle small disturbances in
supply pressure,
and the holdup in the piping and gas homogenization chamber act somewhat to
deaden
these changes, but this remains by necessity the fastest acting control loop
on the
converter.
The initial Phase 1 pressure control strategy will be based on the operating
premise that
the converter will be run at sufficient MSW feed rate to generate a small
buffer of excess
gas production, which will be flared continuously. Therefore the gas
homogenization
chamber pressure control becomes a simple pressure control loop where the
pressure
control valves in the line from gas homogenization chamber to the flare are
modulated as
required to keep homogenization chamber pressure at the desired set point.
b) Stabilize the composition of the gas beinggenerated.
The gas engines can operate over a wide range of fuel values, provided that
the rate of
change is not excessive. In one embodiment, the allowable rate of change for
LHV is
<1% fluctuations in gas LHV/30 sec. For H2 based fuels, the fuel gas is
adequate with as
little as 15% H2by itself, and the LHV can be as low as about 50 btu/scf (1.86
MJ/nm3).
In one embodiment, the LHV for the gas was in the 4.0 - 4.5 MJ/nm3 range. The
system
volume and gas homogenization chamber greatly simplify the task of stabilizing
the rate
of change by providing mixing of about 2 minutes worth of gas production.
In one embodiment, the gas composition is measured by a gas analyzer installed
in the
inlet of the gas homogenization chamber. Based on this measurement the
controller will
adjust the fuel-to-air ratio (i.e. slightly increase/decrease MSW feed rate)
in order to
stabilize the gas fuel value. Increasing either the MSW or HCF feed relative
to the air
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addition increases the fuel value of the gas. Since this control action has a
fairly long
response time, it will be tuned to only prevent long-term drift, not to
respond to short-
term variation.
While the HCF is by itself a much richer (-2x LHV) fuel source, it is
typically being
added in a 1:20 ratio with the MSW, and is not therefore the dominant player
in terms of
fuel being added to the system. It is uneconomical to add too much HCF to the
system.
HCF therefore is used as a trim and not as a primary control. HCF is ratioed
to the total
feed with the ratio adjusted to stabilize the total C exiting the system in
the gas, as
measured by the gas analyzer. This dampens fluctuations in MSW fuel value.
c) Maintain a stable inventory of material in the converter
A level control system is required to maintain stable pile height inside the
converter.
Stable level control is needed to prevent fluidization of the material from
process air
injection which could occur at low level and to prevent poor temperature
distribution
through the pile owing to restricted airflow that would occur at high level.
Maintaining
stable level also maintains consistent converter residence time.
A series of level switches in the primary gasifier measure pile depth. The
level switches
are microwave devices with a emitter on one side of the converter and a
receiver on the
other side, which detect either presence or absence of solid material at that
point inside
the converter.
The inventory in the converter is a function of feed rate and ram motion (and
to a lesser
degree conversion efficiency. Stage 3 ram sets converter throughput by moving
at a
fixed stroke length and frequency to discharge ash from the converter. Stage 2
ram
follows and moves as far as necessary to push material onto Stage 3 and change
the Stage
3 start-of-stage level switch state to "full". Stage 1 ram follows and moves
as far as
necessary to push material onto Stage 2 and change the Stage 2 start-of-stage
level switch
state to "full". All rams are then withdrawn simultaneously, and a scheduled
delay is
executed before the entire sequence is repeated. Additional configuration may
be used to
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limit the change in consecutive stroke lengths to less than that called for by
the level
switches to avoid excess ram-induced disturbances.
The rams need to be moved fairly frequently in order to prevent over-
temperature
conditions at the bottom of the converter. In addition, full extension ram
strokes to the
end of each stage may need to be programmed to occur occasionally to prevent
stagnant
material from building up and agglomerating near the end of the stage.
d) Stabilize temperatures in the converter lower chamber
In order to get the best possible conversion efficiency, the material is kept
at as high a
temperature as possible, for as long as possible. However, temperatures cannot
go too
high or the material will begin to melt and agglomerate (form clinkers),
which: 1) reduces
the available surface area and hence the conversion efficiency, 2) causes the
airflow in
the pile to divert around the chunks of agglomeration, aggravating the
temperature issues
and accelerating the formation of agglomeration, 3) interferes with the normal
operation
of the rams, and 4) potentially causes a system shut down due to jamming of
the ash
removal screw.
The temperature distribution through the pile will also be controlled to
prevent a second
kind of agglomeration from forming - in this case, plastic melts and acts as a
binder for
the rest of the material.
Temperature control within the pile is achieved by changing the flow of
process air into a
given stage (i.e. more or less combustion). The process air flow provided to
each stage in
the bottom chamber will be adjusted to stabilize temperatures in each stage.
Temperature
control utilizing extra ram strokes may also be necessary to break up hot
spots.
e) Control temperatures in the reformer
Plasma torch power is adjusted to stabilize the reformer exit temperatures at
the design
set point (about 1000 C). This ensures that the tars and soot formed in the
primary
gasifier are fully decomposed. Addition of process air into the reformer also
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the heat load by releasing heat energy with combustion of gas. The flow rate
of process
air is adjusted to keep torch power in a good operating range.
f) Control converter process pressure
Converter pressure is stabilized by adjusting the gas blower's speed. At
speeds below the
blower's minimum operating frequency, a secondary control overrides and
adjusts the
recirculation valve instead. Once the recirculation valve returns to fully
closed, the
primary control re-engages.
Phase 2
For Phase 2 operation, all of the process control goals listed above are
maintained.
However the key new requirements are to eliminate flaring of gas and to
optimize the
amount of electrical power produced per ton of MSW consumed. This requires
that the
flow of gas being produced must exactly match the fuel being consumed by the
engines.
Therefore, back-to-front control (or demand-driven control) must be
implemented where
the gas engines/generators at the back-end of the system drive the process.
In order to stabilize gas flow out of the converter, process airflow into the
converter is
increased. Adjusting the rate of MSW or HCF addition to the system eventually
changes
the gas flow, but with about a 45+ minute residence time and no significant
gasification
reactions taking place at the point of material entry, there is no chance of a
fast response
due to these adjustments (it is expected that significant response may take
about 15
minutes). Adjusting total airflow provides the fastest possible acting loop to
control
pressure. In the short term, because of the large inventory of material in the
converter,
adding more air to the bottom chamber does not necessarily dilute the gas
proportionately. The additional air penetrates further into the pile, and
reacts with
material higher up. Conversely, adding less air will immediately enrich the
gas, but
eventually causes temperatures to drop and reaction rates/gas flow to
decrease.
Total airflow is ratioed to material feed rate (MSW+HCF), so the means of
increasing air
flow is to boost material feed rate. Controller tuning is set such that the
effect of
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increased air is seen immediately. Controller tuning for feed rate is slower,
but the
additional feed eventually kicks in and provides the longer term solution to
stabilizing
gas flow. In one embodiment, temporarily reducing generator power output is
required
depending on system dynamics to bridge the dead time between increasing the
MSW/HCF feed rate and seeing increased gas flow.
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