Note: Descriptions are shown in the official language in which they were submitted.
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
A SYSTEM FOR THE CONVERSION OF COAL TO A GAS OF A
SPECIFIED COMPOSITION
FIEE LD OF THE IN V ENTION
This invention relates to the gasification of coal, and in particular to a
process and
apparatus for the conversion of coal to a gas having a specified composition.
BACKGROUND OF THE INVENTION
Coal of varying gradcs can bc uscd as a primary feedstock for gasification.
This
includes low grade, high sulfur coal, which is not suitable for use in coal-
fired power
generators due to the production of emissions having high sulfur content.
Waste coal
particles and silt that remain after coal has been mined, sorted and washed is
also
useful for gasification. Coal can typically be gasified with oxygen and steam
to
produce so-called "synthesis gas" containing carbon monoxide, hydrogen, carbon
dioxide, gaseous sulfur compounds and particulates. The gasification step is
usually
carried out at a temperature in the range of about 650 C to 1200 C, either at
atmospheric pressure or, more commonly, at a high pressure of from about 20 to
about 100 atmospheres.
There are several different types of coal, each displaying different
properties resulting
from geological history. The degree of coal development is referred to as a
coal's
"rank." Peat is the layer of vegetable material directly underlying the
growing zone
of a coal-forming environment. The vegetable material shows very little
alteration
and contains the roots of living plants. Lignite is geologically very young
(less than
40,000 years). It can be soft, fibrous and contains large amounts of moisture
(typically around 70%) and has a low energy content (8 - 10 MJ/kg). Sub-
bituminous
coal is a coal whose properties range from those of lignite to those of
bituminous coal
and are used primarily as fuel for steam-electric power generation. It may be
dull,
dark brown to black, soft and crumbly at the lower end of the range, to
bright, jet-
black, hard, and relatively strong at the upper end. Sub-bituminous coal
contains 20 to
30 percent inherent moisture by weight. The heat content of sub-bituminous
coal
ranges from 20 to 28 MJ/kg on a moist, mineral-matter-free basis. Black coal
ranges
1
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
from 65-105 million years old to up to 260 million years old. These are
harder,
shinier, less than 3% moisture and can have energy contents up to about 24 -
28MJ/kg. Anthracite contains virtually no moisture and very low volatile
content, so
it bums with little or no smoke. It can have energy contents up to about
32MJ/kg.
Synthesis gas is produced according to the Haber Bosch Process, which was
developed in 1917. This process operates on the basic reforming reaction that
reacts
carbon e.g., coal with steam in a primary reaction to produce hydrogen and
carbon
monoxide. The hydrogen/carbon monoxide ratio of the synthesis gas varies
widely
depending on the nature of the coal feed. However, if one mole of inethane was
reformed with steam, it would produce a synthesis gas that is rich in
hydrogen, e.g.,
three molcs of hydrogen and one mole of carbon monoxide, i.e., a
hydrogen/carbon
monoxide ratio of 3/1. A competing secondary reaction known as the water gas
shiR
reaction also takes place wherein carbon monoxide reacts with steam to form
carbon
dioxide and additional hydrogen. This water gas shift reaction is a secondary
reaction
since high temperature and lower pressure favor the primary reaction.
Because coal often contains sulfur compounds, attempts have been made to
provide
processes for the gasification of coal to produce a clean product fuel gas
wherein the
sulfur is removed from the product fuel gas prior to its use, e.g., in gas
turbines to
generate electricity. In addition, gases from the gasification zone may be
purified to
remove coal dust and fly ash and also many other impurities, e.g., vaporized
ash,
alkali, etc.
Plasma torch technology has been employed in coal gasification processes.
Plasma
torch technology was substantially advanced through the 1960's when new ptasma
generators were developed to simulate the very high temperature conditions
experienced by space vehicles re-entering the Earth's atmosphere. Unlike a
combustion burner flame, a plasma arc torch can be operated in the absence of
oxygen. A plasma arc torch is created by the electrical dissociation and
ionization of a
working gas to establish high temperatures at the plasma arc centerline.
Commercially-available plasma torches can develop suitably high temperatures
for
sustained periods at the point of application and are available in sizes from
about 100
kW to over 6MW in output power.
2
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
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 reactions in the
plasma as
the gas might be neutral (for example, argon, helium, neon), reductive (for
example,
hydrogen, methane, ammonia, carbon monoxidc), or oxidative (for example,
oxygen,
carbon dioxide). In the bulk phase, a plasma is electrically neutral. Thermal
plasma
can be created by passing a gas through an electric arc. The electric arc will
rapidly
heat the gas by resistive and radiative heating to a very high temperature
within
microseconds of passing through the arc. A typical plasma torch consists of an
elongated tube through which the working gas is passed, with an electrode
centered
coaxially within the tube. In one type of such torch, a high direct current
voltage is
applicd across thc gap bctwccn the end of the center electrode as anode, and
an
external electrode as cathode. The current flowing through the gas in the gap
between
the anode and the cathode causes the formation of an arc of high temperature
electromagnetic wave energy that is comprised of ionized gas molecules. Any
gas or
mixture of gases, including air, can be passed through the plasma torcb.
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.
The gas produced during the gasification of coal is usually very hot and
dirty, and
requires further treatment to convert it into a useable product. For example,
wet
scrubbers and dry filtration systems 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.
The integration of a system for gasification of coal with advanced fuel cell
technology
requires a flexible, robust, and continuously operating reforming system that
is
applicable to various coal fuel qualities. Gasification systems incorporating
plasma
technology offer the potential to accept a wide variety of coal feeds,
including coal
3
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
with high sulfur content. The incorporation of partial oxidation conditions
within the
reaction vessel is expected to provide the best gasification configuration, by
optimizing the fuel gas composition, while minimizing energy requirements in
the
reaction vessel.
Syngas 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 syngas
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
scnsitivc to changes in gas characteristics. In addition to affecting the
efficiency of
engine opcration, a deviation in thc gas characteristics may even have a
negative
effect on engine operation. For example, changes in the gas characteristics
can affect
the corrosion protection properties of the lubricating oil in an engine, as
well it can
affect emissions, efficiency, knock and combustion stability. Accordingly,
these
syngas-utilizing machines work most effectively when the characteristics of
the gas
are maintained within the specified limits.
This background information is provided for the purpose of making known
information believed by the applicant to be of possible relevance to the
present
invention. No admission is necessarily intended, nor should be construed, that
any of
the preceding information constitutes prior art against the present invention.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a system for the conversion
of coal to
a gas of a spccificd composition, comprising: a gasification rcaction vessel
comprising one or more processing zones, one or more plasma heat sources; one
or
more coal input means for adding the coal to the gasification reaction vessel
at an
adjustable coal feed rate, one or more process additive input means for adding
process
additives to the gasification reaction vessel at an adjustable process
additive feed rate,
and one or more outlets for the output gas, a solid residue handling
subsystem; a gas
quality conditioning subsystem; an integrated control system comprising:
system
nionitoring means for measuring one or more system parameters to generate
data,
4
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
computing means for collecting and analyzing the data generated by the system
monitoring means, and output means to send appropriate signals to effect
change in
one or more system regulators located throughout the system, wherein the
control
system monitors the one or more system parameters and sends signals to the
appropriate system regulators to effect change in the one or more system
regulators
and thereby produce a product gas of a specified composition.
In one embodiment of the present invention, the gasification system may also
optionally comprise a heat recovery subsystem and/or a product gas regulating
subsystem
BRIEF DESCRIPTION OF THE DRAWINGS
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.
Figures 1 to 4 are schematic diagrams depicting a system for the conversion of
coal
to a gas of a specified composition in accordance with various exemplary
embodiments of the present invention.
Figures 5 to 10 are schematic diagrams depicting various downstream
applications
for the system of Figures 1 to 4.
Figure 11 is a flow diagram depicting monitoring and regulating information
flow
between the system of Figures 1 to 10 and an integrated system control
subsystem
operatively coupled thereto.
Figure 12 is a schematic diagram depicting the integrated system control
subsystem
of Figure 11.
Figure 13 is a schematic diagram depicting exemplary monitoring and regulating
signals respectively received from and transmitted to the system of Figures 1
to 10 by
the integrated system control subsystem of Figure 11.
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Figure 14 is a schematic diagram depicting exemplary monitoring and regulating
access points of the integrated system control subsystem of Figure 11 to
various
devices, modules and subsystems of the system of Figures 1 to 10.
Figures 15 and 16 are schematic diagrams depicting an exemplary cmbodimcnt of
the integrated system control subsystem of Figures 11 to 14 for controlling
inputs to a
plasma gasification vessel of the system of Figures 1 to 10.
Figures 17 to 19 are schematic diagrams depicting various entrained flow
plasma
gasification vessels for use with the systems of Figures 1 to 10.
Figures 20 and 21 arc schematic diagrams depicting various fluidized flow
plasma
gasification vessels for use with the systems of Figures 1 to 10.
Figures 22 and 23 are schematic diagrams depicting moving bed flow plasma
gasification vessels with grate options for use with the systems of Figures 1
to 10.
Figure 24 is a schematic diagram depicting an exemplary heat recovery
subsystem for
use with the systems of Figures 1 to 10.
Figure 25 is a schematic diagram depicting in greater detail, the gas-to-gas
heat
exchanger of Figure 24.
Figure 26 is a schematic diagram depicting in greater detail, the head
recovery steam
generator of Figure 24.
Figure 27 is a schcmatic diagram depicting an optional steam/water treatment
subsystem for treating a steam/water output from the Heat Recovery Steam
Generation system of Figures 1 to 10, and particularly of Figure 2.
Figure 28 is a schematic diagram depicting various data inputs and outputs of
a
plasma gasification process simulation and system parameter optimization and
modeling means, optionally used with the integrated control subsystem of
Figures 11
to 16.
6
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Figures 29 and 30 are schematic diagrams depicting further exemplary heat
recovery
subsystem for use with the systems of Figures 1 to 10.
DETAILED DESCRIPTION OF THE INVENTION
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.
As used herein, the term "about" refers to a +/-10% variation from the nominal
value.
It is to be understood that such a variation is always included in any given
value
provided herein, whether or not it is specifically referred to.
For the purposes of the present invention, the term "syngas" or "synthesis
gas" refers
to the product of a gasification process, and may include carbon monoxide,
hydrogen,
and carbon dioxide, in addition to other gaseous components such as methane
and
water.
As used herein, the term "feedstocks" include, but are not limited to, any
grade of coal
(including low grade, high sulfur coal not suitable for use in coal-fired
power
generators).
The term "solid residue" means the solid by-product of coal gasification. Such
a solid
residue generally coinprises inorganic, incombustible materials present in
carbonaceous materials, such as silicon, aluminum, iron and calcium oxides.
Examples of a solid residue include char, ash and slag.
"Slag" means a non-leachable, non-hazardous, glass-like material that consists
of
inorganic, incombustible material present in carbonaceous materials. In high
temperature conditions (1300 C-1800 C) the mineral matter becomes molten. The
moIten slag forms a glassy substance upon quenching or cooling. This material
is
suitable for a number of commercial uses.
7
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
As used herein, the term "exchange-air" refers to air after it has been heated
using
sensible heat from the hot product gas using a gas-to-air heat exchanger
according to
the present invention.
Referring now to Figures 1 to 10, the present invention provides a coal
gasification
system, generally referred to using the numeral 10, with an integrated control
subsystem 200, an exemplary emhodiment of which is schematically illustrated
in
Figures 11 to 16. The system generally comprises, in various combinations, a
gasification reactor vessel 14 (or converter) having one or more processing
zones and
one or more plasma heat sources, as in 15, a solid residue handling subsystem
16, a
gas quality conditioning subsystem 20, as well as an integrated control
subsystem 200
for managing the overall energetics of the convorsion of coal to energy and
maintaining all aspects of the gasification processes at an optimal set point
(illustratively depicted at Figures 11 to 16). The gasification system may
also
optionally comprise a heat recovery subsystem 18 and/or a product gas
regulating
subsystem 22 (e.g., a homogenization chamber 25 as in the embodiment of Figure
1, a
gas compressor 21 as in the embodiments of Figures 1 and 2, and/or a gas
storage
device 23 as in the embodiment of Figure 4, and the like).
The various embodiments of the coal gasification system 10, with an integrated
control subsystem 200, convert coal to a gas of a specified composition. In
particular,
the present invention provides a system that allows for the efficient
conversion of coal
to a product gas having a composition appropriate for downstream applications.
For
example, if the product gas is intended for use in the generation of
electricity through
combustion in a gas turbine (i.e., ref. 24 in Figures 1 to 7) or use in a fuel
cell
application (i.e., ref. 26 in Figures 4 and 6 to 10), then it is desirable to
obtain
products that can be used as fuel in the respective energy generators.
Altcrnatively, if
the product gas is for use as a feedstock in further chemical processes (i.e.,
option 28
in Figure 4), the composition will be that most useful for a particular
synthetic
application.
With reference to Figures 11 to 16, the integrated control subsystem 200
comprises
system monitoring means 202 for measuring one or more system parameters (e.g.
gas
8
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
composition (%CO, %COz, %H2, etc.), gas temperature, gas flow rate, etc.) and
generating data from the measured system parameter values, as well as
computing
means 204 (schematically illustrated by the exemplary logic boxes 30, 32 and
34 in
Figure 16), for collecting and analyzing the data generated from the system
monitoring means 202 and outputting appropriatc signals to one or more of the
system
regulators 206 (i.e., exemplary regulators 206-1, 206-2, 206-3 and 206-4 of
Figures
15 and 16). The integrated control subsystem 200 manages the energetics of the
conversion of coal to energy and maintains the processes at an optimum set
point, by
monitoring one or more system parameters via monitoring means 202, and sending
signals to the appropriate system regulators 206 to make adjustments as
required to
inaintain ttie reaction set point. Using the control subsystem 200 in
accordance with
the various cmbodimonts of system 10 allows the production of a product gas
having
a specified flow and composition.
With reference to Figure 12, the integrated control subsystem 200, and
particularly the
computing means thereof 204, is generally comprised of one or more processors
208,
one or more monitor inputs 210 for receiving current system parameter values
from
the various monitoring means 202, and one or more regulator outputs 212 for
communicating new or updated system parameter values to the various regulating
means 206. The computing means 204 may also comprise one or more local and/or
remote storage devices 214 (e.g. ROM, RAM, removable media, local and/or
network
access media, etc.) for storing therein various predetermined and/or
readjusted system
parameters, set or preferred system operating ranges, system monitoring and
control
software, operational data, and the like. Optionally, the computing means 204
may
also have access, either directly or via various data storage devices, to
plasma
gasification process siniulation data and/or system parameter optiinization
and
modeling means 216, an exemplary representation of which is provided in Figurc
28.
Also, the computing means 204 may be equipped with one or more graphical user
interface and input peripherals 218 for providing managerial access to the
control
means 200 (system upgrades, maintenance, modification, adaptation to new
system
modules and/or equipement, etc.), as well as various output peripherals 220
for
communicating data and information with external sources (e.g. modem, network
connection, printer, etc.).
9
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
With reference to Figures 11 to 14, the control subsystem 200 of the present
invention
ensures that the gas flow and gas composition from the reaction vessel 14, and
optionally throughout system 10, remains within predefmed tolerances to result
in the
optimuni production of the product gas and of system byproducts (commercial
slag,
gas recovery, steam generation, etc.), irrespective of the composition of
different
grades of coal or any natural variability in sources of the same type of coal.
For
example, there are many different grades of coal that are well known to those
skilled
in the art. Even within a single grade, coal is a complex material that may
exhibit
substantial variability. The control aspects of the present invention
recognize and can
make adjustments to compensate for such variability. The parameters of the
product
gas, such as temperature, flow rate and composition, are nionitored, and the
reactants
arc varicd to maintain the paramctcrs of the product gas within predetermined
tolerances as defined by the end use of the synthesis gas.
The integrated control subsystem 200 of the present invention provides
corrective
feedback by which one or more of the flow rate, temperature and composition of
the
product gas are monitored and corrections made to one or more of the coal
input rate,
the oxygen input rate, the steam input rate and the amount of power supplied
to the
plasma heat sources. The adjustments are based on measured changes in the flow
rate, temperature and/or composition of the product gas in order to ensure
that these
remain within acceptable ranges. In general, the ranges for the flow rate,
temperature
and/or composition of the product gas are selected to optimize the gas for a
particular
downstream application.
In one embodiment, the process of the present invention simultaneously uses
the
controllability of plasma lieat to drive the gasification process, and to
ensure that the
gas flow and composition from the process remains within an acceptable range
even if
the composition of the coal exhibits natural variability. In another
embodiment, the
process allows for the total amount of carbon processed per unit time to be
held as
constant as possible, and utilizes the plasma heat to ensure that the total
heat that
enters and leaves the reaction vessel 14 per unit time is kept within process
limits. The
integrated control subsystem 200 may also be configured to monitor and/or
regulate
processes occurring via any one of the solid residue handling subsystem 16,
the gas
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
quality conditioning subsystem 20, the heat recovery subsystem 18 and/or the
product
gas regulating subsystem 22, as schematically illustred in Figure 14.
The gasification of coal takes place in the gasification reaction vessel 14 of
the
present invention, various exemplary embodiments of which are illustrated in
Figures
17 to 23. The gasification reaction vessel 14, in addition to the one or more
processing
zones and the one or more plasma heat sources 15, also comprises means, as in
36, for
inputting the coal into the gasification reaction vessel 14, as well as means,
as in 38,
for adding one or more process additives, such as steam or oxidant additives,
as
required for maintaining the gasification processes at an optimal set point.
The
gaseous products exit the gasification reaction vessel 14 via one or more
output gas
outlcts, as in 40.
In one embodiment, the application of plasma heat, in conjunction with the
input of
process additives, such as steam and/or oxygen, helps in controlling the gas
composition. The system 10 may also utilize plasma heat to provide the high
temperature heat required to gasify the coal and/or to melt the by-product ash
and
convert it to a glass-like product with commercial value.
Various embodiments of the present coal gasification system 10 also provide
means
for managing the solid by-product of the gasification process. In particular,
the
invention provides a solid residue handling subsystem 16 for the conversion of
the
solid by-products, or residue, resulting from coal-to-energy conversion
processes, into
a vitrified, homogenous substance having low leachability. The solid by-
products of
the gasification process may take the form of char, ash, slag, or some
combination
thereof.
Illustratively, the solid residue handling subsystem 16 comprises a solid
residue
conditioning chamber 42, a plasma heating means 44, a slag output means 46,
and a
controlling means (which may be operatively linked to the overall control
subsystem
200 of the system 10), whereby plasma heat is used to cause solids to melt,
blend and
chemically react forming a dense silicometailic vitreous material that, when
poured
out of the chamber 42, cools to a dense, non-leachable, silicometallic solid
slag. In
particular, the invention provides a solid residue conditioning chamber in
which the
ti
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
solid residue-to-slag conversion is optimized using the integrated control
subsystem to
control the plasma heat rate and solid residue input rate to promote full
melting and
homogenization.
Various embodiments of the present coal gasification system 10 also provide
means
for the recovery of heat from the hot product gas. This heat recovery
subsystem 18
(exemplary embodiments of which are schematically illustrated in Figures 24 to
26,
29, 30) comprises means to transfer the hot product gases to one or more gas-
to-air
heat exchangers 48 whereby the hot product gas is used to heat air or other
oxidant,
such as oxygen or oxygen enriched air. '1'he recovered heat, in the form of
the heated
air (or other oxidant), may then optionally be used to provide heat to the
gasification
process (see Figures 24 and 25), thereby reducing the amount of heat that must
be
provided by the one or more plasma heat sources to drivc the gasification
process.
The recovered heat may also be used in industrial or residential heating
applications.
Optionally, the heat recovery subsystem 18 additionally comprises one or more
heat
recovery steam generators (HRSG) 50 to generate steam which can, for example,
be
used as a process additive in the gasification reaction (see Figures 24 and
26), or to
drive a steam turbine to generate electricity.
Also, as seen in Figures 29 and 30, the heat recovery subsystem 18 may also
include
additional heat recovery subsystems operatively extracting heat from various
other
system components and processes, such as via a plasma heat source cooling
process
53, a slag cooling and handling process 55, GQCS cooling processes 61, and the
like.
The heat recovery system 18 may also comprise a feedback control system, which
may be operatively coupled to the system's overall control subsystem 200, to
optimize the energy trausfer throughout the system 10 (e.g. see Figures 13 and
14).
Various embodiments of the present coal gasification system 10 also provide a
gas
quality conditioning subsystem (GQCS) 20, or other such gas quality
conditioning
means (an exemplary embodiment of which is illustrated in greater detail in
Figure 1),
to convert the product of the coal gasification process to an output gas of
specified
characteristics. The product gas is directed to the GQCS 20, where it is
subjected to a
particular sequence of processing steps to produce the output gas having the
12
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
characteristics required for downstream applications. The GQCS 20 comprises
components that carry out processing steps that may include, for example,
removal of
particulate matter 54 (e.g. via a baghouse or the like), acid gases (e.g. H2S
removal
means 56 and optional HCI removal means, such as an HCI scrubber 57, for
possible
sinall amounts of HCI), and/or heavy metals 58 from the synthesis gas, or
adjusting
the humidity and temperature of the gas as it passes through the system. The
presence
and sequence of processing steps is determined by the composition of the coal
and the
specified composition of output gas for downstream applications. The gas
quality
conditioning system 20 may also comprise an integrated control subsystem,
which
may be operatively linked to the overall integrated control subsystem 200 of
the
system 10, to optimize the GQCS process (e.g., see Figures 13 and 14).
Various embodiments of the present coal gasification system 10 also optionally
provide a means, as in 22, for regulating the product gas, for example, by
homogenizing the chemical composition of the product gas and adjusting other
characteristics such as flow, pressure, and temperature of the product gas to
meet
downstream requirements. This product gas regulating subsystem 22 enables a
continual and steady stream of gas of defined characteristics to be delivered
to
downstream applications, such as a gas turbine 24 or engine, a fuel cell
application
26, and the like.
In particular, the product gas regulating subsystem 22 of the present
invention
provides a gas homogenization chamber 25 (Figure 1) or the like (compressor 21
of
Figures 1, 2, gas storage device 23 of Figure 4, etc.) 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 present product gas
regulation system are designed to meet the gas performance requirements of the
downstream application. The gas regulating system 22 may also comprises an
integrated feedback control system, which may be operatively linked to the
overall
integrated control subsystem 200 of the system 10, to optimize the energetics
and
output of this process (e.g., see Figures 13 and 14)
With reference now to Figures 5 to 10, the person of skill in the art will
understand
that the present system 10 and integrated control subsystem 200, in their
various
13
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
embodiments, may be used in a number of energy generation and conversion
systems
having numerous independent and/or combined downstream applications. For
instance, in the exemplary embodiment of Figure 5, the system 10, an
Integrated
Gasification Combined Cycle (IGCC) system, may produce output energy (e.g.
electricity) by providing both a syngas for use in one or niore gas turbines
24, and
steam, generated by cooling both the syngas and exhaust gas associated with
the gas
turbine 24 via one or more HRSG(s) 50, for use in one or more steam turbines
52.
In the exemplary embodiment of Figure 6, the system 10 combines an Integrated
Gasification Combined Cycle (IGCC) system with a solid oxide fuel cell system
26S,
the latter of which using a hydrogen-rich byproduct of the syngas to produce
energy
(e.g. electricity).
In the exemplary embodiment of Figure 7, the system 10 combines an Integrated
Gasification Combined Cycle (IGCC) system with molten carbonate fuel cell
system
26M, the latter of which, as in Figure 6, using a hydrogen-rich byproduct of
the
syngas to produce energy (e.g_ electricity).
In the exemplary embodiment of Figure 8, the system 10 combines a solid oxide
fuel
cell system 26S, as in Figure 6, with one or more steam turbines 52 activated
by stcam
generated by one or more HRSGs 50 recuperating heat from the syngas and the
fuel
cell output(s).
In the exemplary embodiment of Figure 9, a water-gas shift reactor 59 is added
to the
embodiment of Figure 8 to provide the hydrogen-rich syngas used in the solid
oxide
fuel cell system 26S.
In the exemplary embodiment of Figure 10, the solid oxide fuel cell system 26S
of
Figure 9 is replaced by a molten carbonate fuel cell system 26M.
As will be apparent to the person of skill in the art, the above exemplary
embodiments
of system 10 are not meant to be limiting, as one of skill in the art will
understand that
other such system configurations and combinations can be provided without
departing
from the general scope and spirit of the present disclosure.
14
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Integrated Control Subsystem
As presented briefly above, the present system includes an integrated control
subsystem 200. The control subsystem 200 comprises system monitoring means 202
for measuring one or more system parameters to generate data, computing means
204
(e.g., logic boxes 30, 32, 34 of Figure 16) for collecting and analyzing the
data
generated by the system monitoring means 202, and output means to send
appropriate
signals to effect change in one or more system regulators located throughout
the
system (i.e., regulators 206-1, 206-2, 206-3 and 206-4 of Figures 15 and 16).
The
integrated control subsystem 200 monitors the system parameters and sends
signals to
the appropriate system rcgulators 206 to make real time adjustments to various
operating parameters and conditions as required in response to data obtained
relating
to measured parameters within the system 10. In one embodiment, the integrated
control subsystem 200 provides a feedback control system to manage the
energetics
of the conversion of coal to energy and maintain a reaction set point, thereby
allowing
the gasification processes to be carried out under optimum reaction conditions
to
produce a gas having a specified composition.
The overall energetics of the conversion of coal to gas can be determined and
achieved using the present gasification system. Some factors influencing the
determination of the net overall energetics are: the BTU value and composition
of the
coal, the specified composition of the product gas, the degree of variation
allowed for
the product gas, and the cost of the inputs versus the value of the outputs.
Ongoing
adjustments to the reactants (for example, power for the plasma heat source(s)
15
and/or 44, process additives 38 such as oxygen and steam, perceutage of
sorbent in
the coal) can be executed in a manner whereby the net overall energetics are
asscssod
and optimized according to design specifications.
The control subsystem 200 of the present invention, therefore, provides a
means for
controlling in real time all aspects of the processes to ensure that the
processes are
carried out in an efficient manner, while managing the energetics and
maintaining the
reaction set point within certain tolerances. The real time controller is
therefore
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
capable of simultaneously controlling all aspects of the process in an
integrated
manner.
The composition and flow of product gas from the reaction vessel 14 is
controlled
within predefined tolerances by controlling the reaction environment. The
temperature
is controlled at atmospheric pressure to ensure that the coal that is injected
into the
reaction vessel 14 encounters as stable an environment as possible. The
control
subsystem 200 of this invention provides means to control the amountt of coal,
steam
and oxygen that are fed into the reaction vessel 14.
Operating parameters which may be adjusted to maintain the reaction set point
include coal feed rate, process additive feed rate, power to induction blowers
to
maintain a specified pressure, and power to and position of the plasma hcat
sources
(e.g.., plasma torches 15, 44). These control aspects will be discussed
further having
regard to each parameter.
With particular reference to Figures 13 and 14, and as briefly discussed
above, the
integrated control subsystem 200 may be integrated throughout the system 10 to
monitor, via monitoring means 202, various system parameters, and implement,
via
regulating means 206, various modifications to these paramctcrs to manage the
energetics and maintain each aspect of the process within certain tolerances.
These
parameters, which will be discussed in greater detail below, may be derived
from
processes associated with one or more of the plasma gasification vessel 14,
the solid
residue handling subsystem 16, the plasma heat source(s) 15 and slag
processing heat
source(s) 44, the heat recovery subsystem 18 (e.g. gas-to-air heat exchanger
48 and/or
HRSG 50) and process additive inputs 38 associated therewith, the primary
and/or
secondary feedstock inputs 36, 39 (e.g. carbon-rich additives), the GQCS 20,
the
homogenization chamber 25, and any other processing element or module of the
system 10.
Furthermore, having access to these parameters and access, via the various
local
and/or remote storage devices 214 of computing means 204, to a number of
predetermined and/or readjusted system parameters, system operating ranges,
system
monitoring and control software, operational data, and optionally plasma
gasification
16
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
process simulation data and/or system parameter optimization and modeling
means
216 (e.g. see Figure 28), the integrated control subsystem 200 may further
interact
with the system 10 in order to optimize system outputs.
System monitoring means
A number of operational parameters may be regularly or continuously monitored
using the system monitoring means 202 of the control subsystem 200 to
determine
whether the system 10 is operating within the optimal set point. In one
embodiment
of the invention, means 202 are provided to monitor the parameters on a real
time
basis, thereby providing an instantaneous indicator of whether the system 10
is
operating within the allowed/tolerated variability of the set point.
Parameters that can
be monitored include, but are not limited to, the chemical composition, flow
rate and
temperature of the product gas, the temperature at various points within the
system
10, the pressure of the system, and various parameters relating to the plasma
heat
source(s) 15, 44 (i.e., power and/or position).
'1'he parameters are monitored in real-time and the resulting data are used to
determine
if, for example, there needs to be more steam/oxygen (or other oxidants)
injected into
the system (e.g. via regulating means 206-2), if the coal input rate needs to
be
adjusted (e.g. via regulating means 206-1), or if the temperature or pressure
in any of
the components of the system requires adjustment.
System monitoring means may be located as required in any of the components of
the
GQCS 20, the heat recovery subsystem 18, the solid residue handling means 16,
and
the product gas handling subsystem 22, if such subsystems are present.
Composition ofproduct gas
As discussed previously, if the product gas is intended for use in the
generation of
electricity, then it is desirable to obtain products that can be used as fuel
to power
energy generators. In this case, the optimal energetics are measured by the
efficiency
with which energy may be generated using the gases produced.
17
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
The main components of the output gas as it leaves the reaction vessel 14 are
carbon
monoxide, carbon dioxide, hydrogen, and steam, with lesser amounts of
nitrogen.
Much smaller amounts of methane, acetylene and hydrogen sulfide may also be
present. The proportion of carbon monoxide or carbon dioxide in the output gas
depends on the aniount of oxygen that is fed into the reaction vessel 14. For
example,
carbon monoxide is produced when the flow of oxygen is controlled so as to
prcclude
the stoichiometric conversion of carbon to carbon dioxide, and the process is
so
operated to produce mainly carbon monoxide.
'I'he composition of the product synthesis gas may be optimized for a specific
application (e.g., gas turbines 24 and/or fuel cell application 26 for
electricity
generation) by adjusting the balance between, for example, applied plasma heat
15,
oxidant and/or steam process addiHves 38. Sincc addition of oxidant and/or
steam
process additives during the gasification process affects the conversion
chemistry, it is
desirable to provide means, as in monitoring means 202, for monitoring the
syngas
composition. The above-described inputs of the reactants are varied, e.g. via
regulating means 206, to maintain the parameters of the synthesis gas within
predetermined tolerances that are defined by the end use of the synthesis gas.
Monitoring of the product gas can be achieved using various monitoring means
202
such as a gas monitor and gas flow meter. The gas monitor may be used to
determine
the hydrogen, carbon monoxide and carbon dioxide content of the synthesis gas,
the
value of which is useable in various control steps, as illustratively depicted
by the
exemplary logic boxes 30 and 32 of Figure 16. Composition of the product gas
is
generally measured after the gas has been cooled and after it has undergone a
conditioning step to remove particulate matter.
The product gas can be sampled and analyzed using methods well known to the
skilled technician. One method that can be used to determine the chemical
composition of the product gas is through gas chromatography (GC) analysis.
Sample
points for these analyses can be located throughout the system. In one
embodiment,
the gas composition is measured using a Fourier Transform Infrared (FTIR)
Analyser,
which measures the infrared spectrum of the gas.
18
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
In one embodiment, the parameters of the product gas, such as temperature,
flow rate
and composition, may be monitored via monitoring means 202 located at the
axial
outlet vent 40 of the reaction vessel 14. In another embodiment, sampling
ports may
also be installed at any location in the product gas handling system. As
discussed
previously, regulatuig means 206 are provided to vary the inputs of the
reactants to
maintain the parameters of the product gas within predcterrnincd tolerances as
defined
by the end use of the product gas.
An aspect of this invention may consist in determining whether too much or too
little
oxygen is being added during the gasification process by determining the
composition
of the outlet stream and adjusting the process accordingly. In a preferred
embodiment,
an analyzer, sensor or other such monitoring means 202 in the carbon monoxide
stream detects the presence and concentration of carbon dioxide or other
suitable
reference oxygen rich material.
It will be apparent that other techniques may be used to determine whether
mostly
carbon monoxide is being produced. In one alternative, the ratio of carbon
dioxide to
carbon monoxide may be determined. In another alternative, a sensor may be
provided to determine the amount of oxygen and the amount of carbon downstream
of
the plasma generator, calculating the proportion of carbon monoxide and carbon
dioxide and then making process adjustments accordingly. In one embodiment,
the
values of CO and H2 are measured and compared to target values or ranges. In
another embodiment, the product gas heating value is measured and compared to
target values or ranges.
The person of skill in the art will understand that these and other such
product gas
composition measurements, which may be carried throughout a given embodinient
of
the system 10 via the above or other such monitoring moans 202, may be used to
monitor and adjust, via regulating means 206, the ongoing process to maximize
process outputs and efficiencies, and should thus not be limited by the
examples listed
above and provided by the illustrative system and control subsystem
configurations
depicted in the appended Figures.
19
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Temperature at various locations in system
In one embodiment of the invention, there is provided means, as in monitoring
means
202, to monitor the temperature at sites located throughout the system 10,
wherein
such data are acquired on a continuous or intermittent basis. Monitoring means
202
for monitoring the temperature in the reaction vessel 14, for exainple, may be
located
on the outside wall of the reaction vessel 14, or inside the refractory at thc
top, middle
and bottom of the reaction vessel 14.
Monitoring means 202 for monitoring the temperature of the product gas may be
located at the product gas exit 40, as well as at various locations throughout
the
product gas conditioning system (e.g., within the GQCS 20). A plurality of
tliennocouples can be used to monitor the temperature at critical points
around the
reaction vessel 14.
If a system for recovering the sensible heat produced by the gasificatiorr
process is
employed (such as a heat exchanger or similar technology), as in 18, a
monitoring
means 202 for monitoring the temperature at points in the heat recovery system
(for
example, at coolant fluid inlets and outlets) may also be incorporated. In one
embodiment, a gas-to-air heat exchanger 48, a heat recovery steam generator 50
(HRSG) or both are used to recover heat from the hot gases produced by the
gasification process. In embodiments employing heat exchangers, the
temperature
transmitters are located to measure, for example, the temperatures of the
product gas
at the heat exchanger inlets and outlets. Temperature transmitters are also
provided to
measure the temperature of the coolant after heating in the heat exchanger.
These temperature measurements can be used to ensure that the temperature of
the
product gas as it enters a respective heat exchanger does not exceed the ideal
operating temperature of that device. For example, in one embodiment, if the
design
temperature for a gas-to-air heat exchanger 48 is 1050 C, a temperature
transmitter on
the inlet gas stream to the heat exchanger 4S can be used to control both
coolant air
flow rates through the system and plasma heat power in order to maintain the
optimum product gas temperature. In addition, measurement of the product gas
exit
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
temperature may be useful to ensure that the optimum amount of sensible heat
has
been recovered from the product gas at all heat recovery stages.
A temperature transmitter installed on the air outlet stream to measure the
temperature
of the heated exchange-air ensures that the process is carried out under
conditions that
ensure the process air is heated to a temperature appropriate for use in the
gasification
process. In one embodiment, the coolant air outlet temperature is, for
example, about
625 C, therefore a temperature transmitter installed on the air outlet stream
will
provide data that is used to determine whether adjustments to one or both of
the air
flow rates through the system and torch power in the plasma gasification
vessel 14
(e.g., via regulating means 206-4 of Figures 15 and 16) should be made in
order to
maintain the optimum product gas input temperature, which in turn can be used
to
control the temperature of the coolant air.
According to one embodiment of the invention, the control strategy sets a
fixed set
point for the optimum coolant air output temperature, for example, about 600
C, as
well as a fixed value for the HRSG gas exit temperature, for example, about
235C.
Therefore, according to this embodiment, when the product gas flow is reduced,
the
product gas temperature at the exit of the gas-to-air heat exchanger 48 gets
cooler,
resulting in decreased steam production because the HRSG gas exit temperature
is
also set to a fixed value.
The same concept applies when the airflow through the system is reduced.
According
to one embodiment of the present invention, the exit coolant air temperature
remains
fixed therefore the exit product gas temperature for the gas-to-air heat
exchanger 48 is
hotter, therefore producing more steam in the HRSG 50. However, when airflow
through the system is reduced, product gas flow will consequently also reduce,
so the
increased inlet temperature to the HRSG 50 will only be momentarily high. For
example, if airflow is reduced to 50%, the maximum inlet gas temperature that
the
HRSG 50 would momentarily see is approximately $00 C, which is within the
temperature Iimits of the heat exchanger design.
In one embodiment of the invention, the monitoring means 202 for monitoring
the
temperature is provided by thennocouples installed at locations in the systein
10 as
21
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
required. Such temperature measurements can then be used, as described above,
by
the integrated control subsystem 200, as illustratively depicted by the
exemplary logic
box 34 of Figure 16. The person skilled in the art will understand that other
types of
temperature measurements carried throughout a given embodiment of the system
10,
via the above or other such monitoring meaus 202, may be used to monitor and
adjust,
via regulating means 206, the ongoing process to maximize process outputs and
efficiencies, and should thus not be limited by the examples listed above and
provided
by the illustrative system and control means configurations depicted in the
appended
Figures.
Pressure of system
In one embodiment of the invention, there is provided monitoring means 202 to
monitor the pressure within the reaction vcsscl 14, as well as throughout the
entire
system 10, wherein such data are acquired on a continuous or intermittent
basis. In a
further embodiment, these pressure monitoring means 202 comprises pressure
sensors
such as pressure transducers located, for example, on a vertical vessel wall.
Data
relating to the pressure of the system 10 is used by the control subsystem 200
to
determine, on a real time basis, whether adjustments to parameters such as
plasma
heat source power or the rate of addition of coal are required (e.g., via
regulating
means 206-1 and 206-4 of Figures 15 and 16).
Variability in the amount of coal being gasified may lead to rapid
gasification,
resulting in significant changes in the pressure within the reaction vessel
14. For
example, if an increased quantity of coal is introduced to the reaction vessel
14, it is
likely that the pressure within the vessel 14 will increase sharply. It would
be
advantageous in such an instance to have monitoring means 202 to monitor the
pressure on a continuous basis, thereby providing the data required to make
adjustments in real time, via regulating means 206, to parameters (for
example, the
speed of the induction blower) to decrease the system pressure.
In a further embodiment, a continuous readout of differential pressures
throughout the
complete system 10 is provided, for example, via a number of pressure
monitoring
means 202. In this manner, the pressure drop across each individual component
can
22
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
be monitored to rapidly pinpoint developing problems during processing. The
person
of skill in the art will understand that the above and other such system
pressure
monitoring and control means can be used throughout the various embodiments of
system 10, via the above or other such monitoring means 202, to monitor and
adjust,
via regulating means 206, the ongoing process to maximize process outputs and
efficiencies, and should thus not be limited by the examples listed above and
provided
by the illustrative system and control subsystem configurations depicted in
the
appended Figures.
Rate oj'gas. flow
In one embodiment of the invention, there is provided monitoring means 202 to
monitor the rate of product gas flow at sites located throughout the system
10,
wherein such data are acquired on a continuous or intermittent basis.
The rate of gas flow through the different components of the system will
affect the
residence time of the gas in a particular component. If the flow rate of the
gas
through the reforming region of the gasification reaction vessel 14 is too
fast, there
may not be enough time for the gaseous components to reach equilibrium,
resulting in
a non-optimum gasification process. The person of skill in the art will
understand that
these and other such gas flow monitoring and control means can be used
throughout
the various embodiments of system 10, via the above or other such monitoring
means
202, to monitor and adjust, via regulating means 206, the ongoing process to
maximize process outputs and efficiencies via an integrated control subsystem,
such
as the exemplary control subsystem 200 depicted in Figures 11 to 16.
Computing Means
The control subsystem 200 comprises means for controlling the reaction
conditions
and to manage the chemistry and energetics of the conversion of the coal to
the output
gas. In addition, the control subsystem 200 can determine and maintain
operating
conditions to maintain ideal, optimal or not, gasification reaction
conditions. The
detennination of ideal operating conditions depends on the overall energetics
of the
process, including factors such as the composition of the coal and the
specified
23
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
composition of the product ga.ses_ The composition of the coal may be
homogeneous
or may fluctuate to certain degrees. When the composition of the coal varies,
the
certain system parameters may require continuous or regular adjustment, via
regulating means 206, to maintain the ideal operating conditions.
The integrated control subsystem 200 can comprise a number of elements, each
of
which can be designed to perform a dedicated task, for example, control of the
flow
rate of one of the additives, control of the position or power output of one
of the one
or more plasma heat sources (e.g., 18, 44) of the gasification system, or
control of the
withdrawal of by-product. 'I'he control subsystem 200 can further comprise a
processing system, as in processor(s) 208 of computing means 204.
In one cmbodimcnt, the processing systcm 204 can comprise a number of sub-
processing systems. Each sub-processing system can be configured to implement
a
reaction model that can mimic at least one aspect of the plasma reforming
reactions.
Each reaction model has its own model input and model output parameters and
can be
used to calculate changes of the model output parameters as an effect of
changes to
the model input parameters. Each reaction model can be used to perform an
assessment to help predict changes to the operating conditions of the
gasification
system before affecting any of the control elements of the system. Note that
each
reaction model can only be used within a predetermined range of operating
conditions
where the simulated predictions sufficiently accurately mimic processes of the
(real)
plasma reforming system.
'1'he processing system can further be configured with partial models or a
full model
of the reaction processes of the gasification system. Partial models, topped
by the full
model, can be of enormous complexity and can be used to predict changes to an
ever
increasing number of operating conditions or can be used to expand the range
of
operating conditions within which the model is sufficiently accurate or valid.
The
higher the level of abstraction and completeness of the description of the
reaction
processes, the more powerful the predictions of the processing system.
Increasing
complexity of the full model, however, can affect the utility of the model for
predicting certain effects on the operating conditions of the gasification
system. Their
24
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
usefulness may be limited to predicting effects over short time periods or
small
parameter changes.
Figure 28 provides an exemplary embodiment of such a system model, which may
be
used in conjunction with the integrated control subsystem 200 to define
various
operational parameters, and predicted results based thereon, for use as
starting points
in implementing the variotts processes of system 10. In one embodiment, these
and
other such models are used occasionally or regularly to reevaluate and/or
update
various system operating ranges and/or parameters of the system 10 on an
ongoing
basis. In one embodiment, the NCR HYSYS simulation platform is used and can
consider as inputs, any combination of input chemical composition, thermo-
chemical
characteristics, moisture content, feed rate, process additive(s), etc. The
inodel may
also take provide various optional interactive process optimizations to
consider, for
example, site and coal type specifics, maximization of energy recovery,
minimization
of emissions, minimization of capital and costs, etc. Ultimately, based on the
selected
model options, the model may then provide, for example, various operational
characteristics, achievable throughputs, system design characteristics,
product gas
characteristics, emission levels, recoverable energy, recoverable byproducts
and
optinium low cost designs.
Each reaction model can be implemented exclusively in hardware or in any
combination of software and hardware. A reaction model, as illustrated in
Figure 28,
can be described using any combination of an algorithm, a formula or a set of
formulae that can be processed by the processing system. If the reaction model
is
exclusively implemented in hardware it can become an integral part of the
processing
system.
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 one or more proportional
(P),
integral (I) or differential (D) controllers, for example, a P-controller, an
I-controller,
a PI-controller, a PU controller, a PIU controller etc. lt will be apparent to
a person
skilled in the art that the ideal choice of combinations of P, I, and D
controllers will
depend on the dynamics and delay time of the part of the reaction process of
the
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
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.
Important aspects in the design of the combination controller can be short
transient
periods and little oscillation during transient times when adjusting a
respective control
variable or control parameter from an initial to a specified value. It will be
apparent to
a person skilled in the art that these combinations can be implemented in an
analog
hardwired form that can continuously monitor, via monitoring means 202, the
value
of a control variable or control parameter and compare it with a specified
value to
influence a respective control element to make an adequate adjustment, via
regulating
means 204, 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 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.
Correclive conlrol
In corrective, or feedback, control the value of a control parameter or
control variable,
monitored via an appropriate monitoring means 202, is compared to a specified
value.
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. For example,
when the
output gas exceeds a predetermined H2:CO ratio, a feedback control means, as
in
computing means 204, can determine an appropriate adjustment to one of the
input
variables, such as increasing the amount of additive oxygen to return the
H2:CO ratio
to the specified value. The delay time to affect a change to a control
parameter or
control variable via an appropriate regulating means 206 is sometime called
loop
time. The loop time, for example, to adjust the power of the plasma heat
source, the
pressure in the system, or the oxygen or steam flow rate, can amount to 30 to
60
seconds_
26
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
In one embodiment, the product gas composition is the specified value used for
comparison in the feedback control scheme described above, whereby fixed
values (or
ranges of values) of the amount of CO and H2 in the product gas are specified.
In
another embodiment, the specified value is a fixed value (or range of values)
for the
product gas heating value.
Feedback control is required for all control variables and control parameters
that
require direct monitoring or where a model prediction is satisfactory. There
are a
number of control variables and control parameters of the gasification system
10 that
lend themselves towards use in a feedback control scheme. Feedback schemes can
be
effectively implemented in aspects of the control subsystem 200 for those
control
variables or control parameters that can be directly sensed and controlled and
whose
control does not, for practical purposes, depend upon other control variables
or
control parameters.
Feed forward control
Feed forward control processes input parameters to influence, without
monitoring,
control variables and control parameters. The gasification system can use feed
forward control for a number of control parameter such as the amount of power
that is
supplied to one of the one or more plasma heat sourccs (15, 44). Thc powcr
output of
the arcs of the plasma heat sources (15, 44) can be controlled in a variety of
different
ways, for example, by pulse modulating the electrical current that is supplied
to the
torch to maintain the arc, varying the distance between the electrodes,
limiting the
torch current, or affecting the composition, orientation or position of the
plasma.
The rate of supply of additives that can be provided to the gasification
reactor vessel
14 in a gaseous or liquid modification or in a pulverized form or that can be
sprayed
or otherwise injected via nozzles, for example can be controlled with certain
control
elements in a feed forward way. Effective control of an additive's temperature
or
pressure, however, may require monitoring and closed loop feed back control.
Fuzzy logic control and other types of control
27
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Fuzzy logic control as well as other types of control can equally be used in
feed
forward and feedback control schemes. These types of control can substantially
deviate from classical P, 1, D combination control in the ways the plasma
reforming
reaction dynamics are modeled and simulated to predict how to change input
variables
or input parameters to affect a specified outcome. Fuzzy logic control usually
only
requires a vague or empirical description of the reaction dynamics (in general
the
system dynamics) or the operating conditions of the system. Aspects and
implementation considerations of fuzzy logic and other types of control are
well
known to a person skilled in the art.
It will be understood that the foregoing embodiments of the invention are
exemplary
and can be varied in many ways. Such present or future variations are not to
be
regarded as a departure from the spirit and scope of the invention, and all
such
modifications as would be apparent to one skilled in the art are intended to
be
included within the scope of the following claims.
Gasification Reaction Yessels for Use with This System
With refcrenec now to Figures 1 to 4, and Figures 17 to 23, the present coal
gasification system 10 comprises a gasification reactor vessel 14 having one
or more
processing zones and one or more plasma heat sources, as in 15. The
gasification
reaction vessel 14 also comprises means, as in 36, for inputting the caal into
the
reaction vessel, as well as means, as in 38, for adding one or more process
additives,
such as steam or oxygen/oxidant additives, as required for maintaining the
gasification processes at an optimal set point.
In one embodiment of the present invention, the one or more sources of plasma
heat
15 assist in the coal-to-gas conversion process. In particular, the use of
plasma heat
sources 15, in conjunction with the input of steam and/or oxygen process
additives 38,
helps in controlling the gas composition. Plasma heat may also be used to
ensure the
complete conversion of the offgases produced by the gasification process into
their
constituent elements, allowing reformation of these constituent elements into
the
28
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
product gas having a specified composition. The product gas may then exit the
gasification reaction vessel 14 via one or more output gas outlets 40.
The gasification of coal (i.e., the complete conversion of the coal to a
syngas) takes
place in the gasification rcaction vessel 14, and can proceed at high or low
temperature, or at high or low pressure. A number of reactions take place in
the
process of converting coal to the syngas product. As the coal is gasified in
the
reaction vessel, the physical, chemical, and thermal processes required for
the
gasification may occur sequentially or simultaneously, depending on the
reactor
design.
In the gasification reaction vessel 14, the coal is subjected to heating,
whereby the
coal is dried to remove any residual moisture. As the temperature of the dried
coal
increases, pyrolysis takes place. During pyrolysis, volatile components are
volatilized
and the coal is thermally decomposed to release tars, phenols, and light
volatile
hydrocarbon gases while the coal is converted to char. Char comprises the
residual
solids consisting of organic and inorganic materials.
The resulting char may be further heated to ensure completo conversion to its
gaseous
constituents, leaving an ash by-product that is later converted to slag. In
one
embodiment, the gasification of coal takes place in the presence of a
controlled
amount of oxygen, to minimize the amount of combustion that can take place.
The combined products of the drying, volatilization and char-to-ash conversion
steps
provide an intermediate offgas product. This intermediate offgas gas may be
subjected to further heating, typically by one or more plasma heat sources and
in the
presence of a controlled amount of stcam, to complete the conversion of the
coal to
the syngas. This final step is also referred to as a reformation step.
The one or more plasma heat sources can be positioned to make all the
reactions
happen simultaneously, or can be positioned within the reaction vessel to make
them
happen sequentially. In either configuration, the temperature of the pyrolysis
process
is elevated due to inclusion of plasma heat sources in the reactor.
29
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
The gasification reaction is driven hy heat, which can be fueled by adding
electricity
or fossil fuels (e.g., propane) to heat the reaction chamber or adding air as
a reactant
to drive the exothermic gasification reaction, which provides heat to the
reaction.
Some gasification processes also use indirect heating, avoiding combustion of
the
feed material in the gasification reactor and avoiding the dilution of the
product gas
with nitrogen and excess COZ.
The gasification reaction vessel 14 can he based on one of a number of
standard
reactors known in the art. Examples of reaction vessels known in the art
include, but
are not limited to, entrained flow reactor vessels (Figures 17 to 19), moving
bed
reactors (Figures 22 and 23, fluidized bed reactors (Figures 20 and 21), and
rotary kiln
reactors (not shown), each of which is adapted to accept coal througl- a coal
input
mcans, as in 36. The coal is introduced through one or more inlets that are
disposcd to
provide optimum exposure to heating for complete and efficient conversion of
the
coal to the product gas.
In one embodiment, the gasification reaction vessel 14 is designed to operate
at or
near atmospheric pressure. In another embodiment, the reaction vessel operates
under
pressurized conditions, whereby the gasification reaction is carried out at a
pressure of
between 2 to 10 atm. In yet another embodiment, the reaction vessel operates
under
high pressure whereby the gasification reaction is carried out at a pressure
of up to 30
atm.
The gasification reaction vessel 14 can have a wide range of length-to-
diameter ratios
and can be oriented either vertically or horizontally. The gasification
reaction vessel
will have one or more gas outlet means 40, as well as means for removing solid
residue (e.g., char, ash, slag or some combination thereof) 16, which is
generally an
outlet disposed somewhere along the bottom of the chamber (e.g., slag chamber
42) to
enable the residue to be removed using gravity flow. In one embodiment, the
gasification reaction vessel will use physical transfer means to remove the
solid
residue from the bottom of the vessel. For example, a hot screw (e.g., element
60 of
Figure 20) may be used to convey the ash by-product into the slag processing
chamber 42. Means for processing and handling slag will be discussed in more
detail
later. Note that the slag may also be processed in the same chamber in which
the
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
gasification oceurs (Figures 16 to 19), or in a separate chamber, as in slag
chamber 42
of Figure 20.
According to the present invention, all of the steps for the conversion of
coal to the
syngas product take place in a single chambered reaction vessel.
The design of some gasification reaction vessels 14 is such that the process
for
converting the coal to a syngas may take place in a one-stage process, i_e_,
where all
the steps in the conversion of coal to syngas take place generally in a single
zone
within the vessel. In one such embodiment, it is conceived that the one stage
process
takes place within a single zone in the reaction vessel 14, where all of the
gasification
steps take place in the same zoue. In such a case, the product gas exiting the
gasification rcaction vessel 14 will bc a syngas product.
The design of other gasification reaction vessets 14 is such that the coal to
syngas
conversion process takes place in more than one zone in the chamber, i.e.,
wherein the
gasification and reformation steps are separated to some extent from each
other and
take place in different zones within the vessel.
In one embodiment of the invention, the conversion proccss takes place in two
stages,
first a coal to offgas stage, followed by a offgas to syngas (reformation)
stage. In
such a two stage process, it is conceived that at least two discrete zoncs (a
first zone
for the gasification step and a second zone for the reformation step) within a
single
chambered reaction vessel are required.
in a multi-region gasification reaction vessel, a first, or primary, zone is
used to heat
the coal to dry the coal (if residual moisture is present), extract the
volatile
constituents of the coal, and optionally convert the resulting char to a
gaseous product
and ash, thereby producing an offgas product, while a second zone is used to
apply
plasma heat to assure the complete conversion of the offgas into the syngas
product.
Where two or more distinct zones are used for the gasification of the coal and
the
conversion of offgas to syngas, the product gas exiting the final region of
the
gasification reaction vessel is a syngas.
31
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
In one embodiment, the heat required to drive the gasification of coal is
provided by
heated air. In such an embodiment, the gasification reaction vessel 14
comprises one
or more heated air input means for the introduction of heated air to the
gasification
zone. The heated air input means includes exchange air inlets. These inlets
are
positioned within the reaction vessel to distribute the heated air throughout
the
reaction vessel to initiate and drive the conversion of the coal to a gaseous
product.
With reference to Figures 22 to 23, the reaction vessels 14 depicted therein
could be
considered to encompass multiple zone vessels wherein the gasification
processes
takes place in a first zone 66 and the reformation processes occur within a
second
zone 68 of the vessel 14. Illustratively, the heat required to initiate the
gasification
proccss in the first zone is provided by plasma heat source 70 in the
embodiment of
Figure 23 and by an alternative heat source (e.g., heated air, etc.) in the
embodiment
of Figure 22. In both of these embodiments, a plasma heat source 72 is used in
the
second zone to upgrade the characteristics of the generated gas, in accordance
with a
specified output gas composition, for subsequent processing via the gas output
40.
Referring back to Figures 17 to 23, the person of skill in the art will
understand that
by moving the one or more plasma heat source 15, by adding other plas-na heat
sources, other sources of heat, and the like, the illustrated vessels 14 may
be operated
as single or multiple zone reaction vessels 14 without departing from the
general
scope and spirit of the present disclosure. Furthermore, it will be understood
that the
present coal gasification system 10 with integrated control subsystem 200 may
be
implemented with any of the above or other such gasification vessel
configurations. In
fact, by monitoring one or more direct or indirect process parameters relevant
to the
gasification and/or reformation processes implemented within a given type of
reaction
vessel, whether these processes take place in a single zone or multiple zones
within a
single chamber reaction vessel, the control subsystem 200 of the present
system 10
may be used, via monitoring means 202, to monitor and adjust the ongoing
processes
to maximize, via regulating means 206, process outputs and efficiencies.
Furthen-nore, still referring to Figures 17 to 23, the gasification reaction
vessel
optionally comprises one or more process additive input means 38, which are
provided for the addition of gases such as oxygen, air, oxygen-enriched air,
st0am or
32
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
other gas useful for the gasification process, into the gasification reaction
vessel. The
process additive input means can include air (or oxygen) input ports, steam
input ports
and/or sorbent ports. These ports are positioned within the reaction vessel 14
for the
optimal distribution of process additives throughout the vessel. The addition
of
process additives will be discussed in greater detail later.
Also, in accordance with one embodiment of the present invention, the
gasification
reaction vessel wall is lined with refractory material. The refractory
material can be
one, or a combination of, conventional refractory materials known in the art
which are
suitable for use in a vessel for a high temperature (e.g., a temperature of
about 1100 C
to 1400 C) non-pressurized reaction. Examples of such refractory materials
include,
but are not limited to, high temperature fired ceramics (such as aluminum
oxide,
aluminum nitride, aluminum silicate, boron nitride, zirconium phosphate),
glass
ceramics, chromia refractories and high alumina refractories containing
alumina,
titania, and/or chromia.
As is understood by those of skill in the art, different regions of the
gasification
reaction vessel may be lined with different refractory materials, according to
temperature and corrosion requirements of a particular region. For example, if
slagging is present, it may be advantageous to use a non-wetting refractory
material.
The person of skill in the art will further understand that, although the
ahove
description provides a number of examples of reaction vessel types,
configurations
and materials to be used therefor, other reaction vessel types, configurations
and/or
materials may be used without departing from the general scope and nature of
the
present disclosure.
Plasma Heating Means
Referring now to Figures 1 to 4 and 17 to 23, the system of the present
invention
employs one or more plasma heating means, as in 15, to ensure complete
conversion
of the offgas produced by the gasification process to a product gas having a
specified
composition. Plasma heating means as in 15 may also be optionally provided to
heat
the coal to drive the initial gasification process.
33
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
In one embodiment of the present invention, the one or more plasma heat
sources 15
will be positioned to optimize the offgas conversion to specified product gas.
The
position of the one or more plasma heat sources is selected according to the
design of
the gasification system, for example, according to whether the system employs
a one
stage or two stage gasification process. For instance, in one embodiment that
employs a two stage gasification process, the plasma heat source may be
disposed in a
position relative to the offgas inlet, and pointed in the direction of the
offgas inlet. In
another embodiment that employs a one stage gasification process, the one or
more
plasma heat sources 15 may extend towards the core of the gasification
reaction
vessel. In all cases, thc position of the plasma heat sources is selected
according to
the requirements of the system, and for optimal conversion of the offgas to
the
specified product gas.
Where more than one plasma heat source is used, the position of the heat
sources is
also selected to ensure that there is no conflict between two or more heat
sources, for
example, that no heat source is subjected to direct heat from another or that
there is no
arcing from one plasma heat source to another.
In addition, the location of the one or more plasma heat sources is selected
to avoid
impacting the wall of the reaction vessel with the plasma plume, thereby
avoiding the
formation of "hot spots".
A variety of commercially available plasma heat sources that can develop
suitably
high temperatures for sustained periods at the point of application can be
utilized in
the system. In general, such plasma lieat sources are available in sizes from
about 100
kW to over 6 MW in output powcr. Thc plasma hcat source, or torch, can employ
one,
or a combination, of suitable working gases. Examples of suitable working
gases
include, but are not limited to, air, argon, helium, neon, hydrogen, methane,
ammonia,
carbon monoxide, oxygen, nitrogen, and carbon dioxide. In one embodiment of
the
present invention, the plasma heating means is continuously operating so as to
produce a temperature in excess of about 900 to about 1100 C as required for
converting the offgas to the syngas product.
34
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
In this respect, a number of alternative plasma torch technologies are
suitable for use
in the present system. For example, it is understood that inductively coupled
plasma
torches (ICP) may be employed. It is also understood that transferred arc and
non-
transferred arc torches (both AC and DC), using appropriately selected
electrode
materials, may also be employed. Electrode materials may be selected from, but
are
not limited to, coppar and its alloys, stainless steel and tungsten. Graphite
torches
may also be used. Selection of an appropriate plasma heating means is within
the
ordinary skills of a worker in the art.
In one embodiment, the plasma heat sources 15 are located adjacent to one or
more
air/oxygen and/or steam input ports 38 such that the airloxygen and/or steam
additives
are injected into the path of the plasma discharge of the plasma heat source
15.
In a further embodiment, the plasma heat sources 15 may be movable, fixed or
any
combination thereof.
1'he process of the present invention uses the controllability of plasma heat
to drive
the conversion process and ensure that the gas flow and gas composition from
the
converter remain within predefined tight tolerances. Control of the plasma
heat also
assists in the efficient production of the product gases, irrespective of the
composition
of different coal sources or any natural variability in sources of the same
type of coal.
In one embodiment, the control subsystem 200 comprises regulating means 206 to
adjust the power of the plasma heat sources 15 to manage the net overall
energetics of
the reaction and maintain an optimal set point. In order to manage the
energetics of
the reaction, the power to the plasma heat source 15 may be adjusted to
maintain a
constant gasification system temperature despite any fluctuations in the
composition
of the coal and corresponding rates of feed of steam and air/oxidant.
The control subsystem 200 controls the power rating of the plasma heat source
15
relative to the measured parameters such as the rate at which coal and process
additives are introduced into the gasification reaction vessel 14, as well as
the
temperature of the system as determined by temperature sensors, and other such
nionitoring rneans 202, located at strategic locations throughout the system
10. The
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
power rating of the plasma heat source 15 must be sufficient to compensate,
for
example, for loss of heat in the gasification reaction vessel 14 and to
process the
added coal efficiently.
For example, when the temperature of the reaction vessel 14 is too high, the
control
subsystem 200 may command a drop in the power rating of the plasma heat source
15
(e.g. via regulating means 206-4 of Figures 15 and 16); conversely, when the
temperature of the melt is too low, the control subsystem 200 may command an
increase in the power rating of the plasma heat source 15.
In one embodiment of the invention, the control subsystem 200 comprises
regulating
means 206 to control the position of the torch to ensure the maintenance of
the
optimal high temperature processing zone as well as to induce advantageous gas
flow
patterns around the entire reaction vessel 14.
One or more plasma heat sources, as in 44, are also optionally provided to
ensure
complete processing of the solid residue of the gasification process, as will
be
discussed later.
Coal input means
Still referring to Figures 1 to 4 and 17 to 23, the invention includes means,
as in input
means 36, for introducing coal to the gasification reaction vessel 14. The
input means
36 are located to ensure that the coal is deposited at an appropriate location
in the
reaction vessel for optimum exposure to the gasifying heat source.
In one embodiment, the input means 36 is also provided with regulating means
206
for adjusting the feed rate to ensure that the coal is fed into the reaction
vessel 14 at an
optimum rate for maintaining the gasification reaction at an optimum set
point.
In one embodiment, the control subsystem 200 comprises regulating means 206 to
adjust the rate of coal input to manage the net overall energetics of the
reaction. For
example, the rate of coal addition to the gasification reaction vessel 14 can
be
adjusted to facilitate the efficient conversion of the coal into the product
gases. The
36
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
rate of coal addition is selected to manage the overall energetics of the
system
according to the design specifications of the system 10, while maintaining the
reaction
set point within certain tolerances.
The selection of the input means 36 is made according to the requirements for
feed
dispersion, the operating pressure and the coal particle size. Input means 36
may
include a screw auger, a pneumatic transport system, a plunger system, a ram
system,
a rotary valve system, or a top gravity feed system.
A conditioning process for preparing the coal prior to introduction to the
reaction
vessel may also be utilized. For example, the coal may be pulverized to a size
that
provides the necessary rapid reaction. Generally, the coal should be of a
particle size
of 0.75 inches or smaller. The coal may optionally be fed through a pre-heater
where
it is heated before being fed to the reaction vessel. Such pre-heated
pulverized coal
may be fed to the reaction vessel via heated coal line.
Process additive input means
Still referring to Figures 1 to 4 and 17 to 23, process additives may
optionally be
addcd to the reaction vessel 14 to facilitate efficient conversion of coal
into product
gases. The type and quantity of the process additives are very carefully
selected to
optimize coal conversion while maintaining adherence to regulatory authority
emission limits and minimizing operating costs. Steam input ensures sufficient
free
oxygen and hydrogen to maximize the conversion of decomposed elements of the
input waste into fuel gas and/or non-hazardous compounds. Air/oxidant input
assists
in processing chemistry balancing to maximize carbon conversion to a fuel gas
(minimize free carbon) and to maintain the optimum processing temperatures
while
minimizing the relatively high cost plasma arc input heat. The quantity of
both
additives is established and very rigidly controlled as identified by the
outputs for the
waste being processed. The amount of oxidant injection is very carefully
established
to ensure a maximum trade-off for relatively high cost plasma arc input heat
while
ensuring the overall process does not approach any of the undesirable process
characteristics associated with combustion, and while meeting and bettering
the
ernission standards of the local area.
37
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
For those embodiments having the production of electrical energy as an
objective, it is
advantageous to produce gases having a high fuel value. The production of high
quality fuel gases can be achieved by controlling reaction conditions, for
example, by
controlling the amount of process additives that are added at various steps in
the
conversion process.
The gasification reaction vessel 14, therefore, can include a plurality of
process
additive input ports 38, which may be provided for the addition of gases such
as
oxygen, air, oxygen-enriched air, steam or other gas useful for the
gasification
process. The process additive input means 38 can include air input ports and
steam
input ports. These ports are positioned within the reaction vessel for the
optimal
distribution of process additives through the reaction vessel 14. The steam
input ports
can be strategically located to direct steam into and around the high
temperature
processing zone and into the product gas mass prior to its exit from the
reaction
vessel. The air/oxidant input ports can be strategically located in and around
the
reaction vessel to ensure fill coverage of process additives into the
processing zone.
In one etnbodinient, the control subsystem 200 comprises regulating means 206
to
adjust the reactants to manage the net overall energetics of the reaction. For
example,
process additives may be added to the reaction vessel 14 to facilitate the
efficient
conversion of the coal into product gases. The type and quantity of the
process
additives are very carefully selected to manage the overall energetics of the
system
according to the design specifications of the system, while maintaining the
reaction
set point within certain tolerances. In another embodiment of the invention,
the
control subsystem 200 comprises regulating means 206 to control the addition
of
process additives to maintain an optimal reaction sct point. In another
embodiment of
the control subsystem 200, regulating means 206 are provided to control the
addition
of two or more process additives to maintain the reaction set point. In yet
another
embodiment, regulating means 206 are provided to control the addition of three
or
more process additives to maintain the reaction set point.
In those embodiments comprising a one stage process, i.e., where the
gasification and
reformation steps both take place in a single chamber gasification reaction
vessel 14,
38
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
it is advantageous to strategically locate additive input ports in and around
the
gasification reaction vessel 14 to ensure full coverage of process additives
into the
processing zone. In those embodiments wherein the process takes place in two
stages,
i.e., the gasification and reformation take place in discrete regions within
the system,
it may be advantageous to locate certain additive ports (for exarnple, steain
inputs)
proximal to the region where reformation by the plasma torch, or other such
plasma
heat source 15, takes place.
In a further embodiment, the control subsystem 200 comprises regulating means
206
for adjusting the additive inputs based on data obtained from monitoring and
analyzing the composition of the product gas, via various monitoring means 202
and
computing means 204, whereby these data are used to estimate the composition
of the
feedstock. The product gas composition data may be obtained on a continuous or
intermittent basis, thereby allowing the adjustments to additive inputs such
as air,
steam and carbon-ricb additives to be made on a real-time basis (e.g. via
regulating
means 206-1, 206-2 and 206-3 of Figures 15 and 16). The product gas
composition
data may also be obtained on an intermittent basis.
The control subsystem 200 of the present invention includes a means, as in
regulating
means 206, for introducing the additives into the system when the
concentration of
certain product gases is not at an optimal level according to predetermined
target
levels, as monitored by various monitoring means 202. For example, in the
event that
a gas sensor detects too much carbon dioxide, the control subsystem 200 may
reduce
the delivery of oxidant into the converter to reduce the production of carbon
dioxide
(e.g. via regulating means 206-3 exemplified in Figures 15 and 16).
In one embodiment of the invention, the process is adjusted to produce mostly
carbon
monoxide, rather than carbon dioxide. In order to expedite the production of
carbon
monoxide in such an cmbodiment, the system will include a sensor, analyzer or
other
such monitoring means 202 for determining the amount of oxygen in the gaseous
output stream. If the correct amount of oxygen from steam or air/oxidant
inputs is
used in the gasification process, the product gas will be mainly carbon
monoxide. If
there is too little oxygen, a considerable amount of elemental carbon or
carbon black
may fonn which will ultimately plug up equipment downstream from the reaction
vessel. If there is too much oxygen in the system, too much carbon dioxide,
which has
39
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
essentially no value, will be produced, which is undesirable if the objective
of the
process is to produce a fuel gas. In response to too much carbon dioxide in
the system,
any steam or air/oxidant being injacted is reduced or eliminated by an
appropriate
signal from the control subsystem 200 (e.g. via regulating means 206-2 and/or
206-3
exemplified in Figures 15 and 16).
The conversion of coal into fuel gas within the gasification reaction vessel
14 is an
endothermic reaction, i.e., energy needs to be provided to the reactants to
enable them
to reform into the specified fuel gas product. In one embodiment of the
invention, a
proportion of the energy required for the gasification process is provided by
the
oxidation of a portion of the initial gaseous products or coal within the
reaction vessel
14.
Introduction of an oxidant into the reaction vessel 14 creates partial
oxidation
conditions within the reaction vessel 14. In partial oxidation, the carbon in
the coal
reacts with less than the stoichiometric amount of oxygen required to achieve
complete oxidation. With the limited amount of oxygen available, solid carbon
is
therefore converted into carbon monoxide and small amounts of carbon dioxide,
thereby providing carbon in a gaseous form.
Such oxidation also liberates thermal energy, thereby reducing the amount of
energy
that needs to be introduced into the gasification reaction vessel by the
plasma heat. In
turn, this increased thermal energy reduces the amount of electrical power
that is
consumed by the plasma heat source 15 to produce the specified reaction
conditions
within the reaction vessel 14. Thus, a greater proportion of the electricity
produced by
converting the fuel gas to electrical power in an electric power generating
device (e.g.,
fuel cell application 26, gas turbine 24, etc.) can be provided to a user or
exported as
electrical power, because the plasma heat source 15 requires less electricity
from such
an electric power generating device in a system that employs the addition of
an
oxidant.
'1'he use of oxidant inputs as a process additive therefore assists in
maximizing the
conversion of carbon to a fuel gas and to maintain the optimum processing
teniperatures as required while minimizing the relatively high cost plasma arc
input
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
heat. The amount of oxidant injection is very carefully established to ensure
maximum removal of carbon in gaseous form (CO and C02). Simultaneously,
because the gasification of carbon reactions (combination with oxygen) are
exothermic, substantial quantities of heat are produced. This minimizes the
need for
relatively high cost plasina arc input heat while ensuring the overall process
does not
approach any of the undesirable process characteristics associated with
combustion.
In one embodiment of the invention, the oxidant is air.
Although less fuel gas will be produced within the reaction vessel when
partial
oxidizing conditions exist (because some of the fuel gas or coal is oxidized
to liberate
thermal energy, and thus, less fuel gas is available to an electric power
generating
device), the reduction in electrical consumption by the plasma heat source
offsets a
possible loss in electrical energy production. In one embodiment of the
invention, the
control subsystem 200 comprises means to adjust the addition of process
additives to
maintain an optimal reaction set point (e.g. regulating means 206-2, 206-3 of
Figures
15 and 16).
In one embodiment of the invention, the oxidant additive is selected from air,
oxygen,
oxygen-enriched air, steam or carbon dioxide. In those embodiments using
carbon
dioxide as an oxidizing process additive, thc carbon dioxide may be recovered
from
the product gases and recycled into the process additive stream.
The selection of appropriate oxidizing additive is made according to the
economic
objectives of the conversion process. For example, if the economic objective
is the
generation of electricity, the oxidizing additive will be selected to provide
the optimal
output gas composition for a given energy generating technology. For those
systems
that employ a gas engine to generate energy from the product gases, a higher
proportion of nitrogen may be acceptable in the product gas composition. In
such
systems, air will be an acceptable oxidant additive. For those systems,
however, that
employ a gas turbine 24 to generate energy, the product gases must undergo
compression before use. In such embodiments, a higher proportion of nitrogen
in the
product gases will lead to an increased energetic cost associated with
compressing the
product gas, a proportion of which does not contribute to the production of
energy.
41
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Therefore, in certain embodiments, it is advantageous to use an oxidizer that
contains
a lower proportion of nitrogen, such as oxygen or oxygen-enriched air.
In those embodiments of the present invention that seek to maximize the
production
of electrical energy using the fuel gases produced by the gasification
process, it is
advantageous to minimize the oxidation of the fuel gas that takes place in the
gasification reaction vessel. In order to offset any decrease in the
production of fuel
gas due to partial oxidation conditions, steam may also be used as the
oxidizing
additive. The use of steam input as a process additive ensures sufficient free
oxygen
and hydrogen to maximize the conversion of decomposed elements of the input
coal
into fuel gas and/or non-hazardous compounds.
For those embodiments having the production of electrical energy as an
objective, it is
advantageous to produce gases having a high fuel value. The use of steam as a
process additive is known in the art. The gasification of coal in the presence
of steam
produces a syngas composed predominantly of hydrogen and carbon monoxide.
Those of ordinaty skill in the chemical arts will recognize that the relative
proportions
of hydrogen and carbon monoxide in the fuel gas product can be manipulated by
introducing different amounts of process additives into the converter.
Steam input ports can be strategically located to direct steam into the high
temperature processing zone and/or into the product gas mass prior to its exit
from the
reaction vessel 14.
In one embodiment, there is also provided means for adding sorbent to the
gasification reaction vessel 14. As coal contains sulfur compounds, sorbents
(such as
granulated limestone or dolomite) arc fed into the reaction vessel 14 along
with the
coal to adsorb sulfur released by the coal as it is gasified. The sorbent may
be added
by premixing with the coal before addition to the reaction vessel 14, or it
may be
added through a dedicated sorbent port. The integrated control subsystem 200
may be
used, via appropriate monitoring means 202 and regulating means 206, to
monitor and
adjust sorbent use with the reation vessel 14.
Solid Residue Harndling Subsyslem
42
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Still referring to Figures 1 to 4 and 17 to 23, the present coal gasification
system also
provides means, for managing the solid by-product of the gasification process.
In
particular, the invention provides a solid residue handling subsystem 16 for
the
conversion of the solid by-products, or residue, resulting from coal-to-cnergy
conversion processes, into a vitrified, homogenous substance having low
leachability.
In particular, the invention provides a solid residue handling subsystem 16 in
which
the solid residue-to-slag conversion is optimized by controlling the plasma
heat rate
and solid residue input rate to promote full melting and homogenization. In
one
embodiment, the solid residue handling subsystem comprises a solid residue
conditioning chamber 42 (or slag chamber) having a solid residue inlet, a
plasma
heating means, a slag outlet, optionally one or more ports, and a downstream
cooling
means for cooling and solidifying the slag into its final form. The integrated
control
subsystem 200 of the present invention also comprises regulating means 206 to
regulate the efficient conversion of the solid residue into slag by providing
monitoring
means 202 to monitor temperature and pressure throughout the solid residue
handling
subsystem 16, as well as means to control such operational parameters as the
power to
the plasnia heat source 44 and solid residue input rate.
The solid residue handling subsystem 16 of the present invention is adaptable
to treat
a solid residue stream coming out of any process that converts the coal into
different
fornts of energy. This solid residue is typically in a granular state and may
come from
one or more sources such as the gasification reaction vessel 14 and optionally
the gas
quality conditioning subsystem 20. In all cases, the solid residue is heated
to a
temperature required to convert the solids into a vitrified, homogeneous
substance that
exhibits extremely low leachability when allowed to cool and solidify.
The solid residue handling subsystem 16 therefore ensures that the solid
residue is
brought up to an adequate temperature to melt and homogenize the solid
residue. The
solid residue handling subsystem 16 also promotes the capture of polluting
solids (i.e.,
heavy metals) in the slag, as well as the formation of a clean, homogeneous
(and
potentially commercially valuable) slag product.
43
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
In order to ensure complete processing of the solid residue, the solid residue
handling
subsystem 16 is designed to provide sufficient residence time in the slag
chamber 42.
In one embodiment, the system 16 provides a residence time of at least 10
minutes. In
another embodiment, the solid residue handling subsystem 16 provides a
residence
time of up to 1 hour. In yet another embodiment, the solid residue handling
subsystem
16 provides a residence time of up to 2 hours.
The solid residue, which may take the form of char, ash, slag, or some
combination
thereof, will be removed, continuously or intermittently, from one or more
upstream
processes through appropriately adapted outlets and conveyance means as would
be
known to the skilled worker, according to the requirements of the system and
the type
of by-product being removed. In one embodiment, the solid residue is pushed
into the
slag chamber 42 through a system of hoppers and conveying screws.
The solid residue may be added in a continuous manner, for example, by using a
rotating screw or auger mechanism. For example, in the embodiment of Figure
20, a
screw conveyor 60 is employed to convey ash to a slag chamber 42.
Alternatively, the solid residue can be added in a discontinuous fashion. In
one
embodiment of the invontion, the solid residue input means, attached to the
solid
residue conditioning chamber, may consist of a system of conveying rams. In
such an
embodiment, limit switches are employed to control the length of the ram
stroke so
that the amount of material fed into the vessel with each stroke can be
controlled.
The solid residue input means will further include a control means such that
the input
rate of the solid residue can be controlled to ensure optimal melting and
homogenization of the solid residue material.
In one embodiment, a plasma heat source 44, is employed to heat and melt the
ash
into slag. The molten slag, at a temperature of, for example, about 1300 C to
about
1700 C, may be periodically or continuously exhausted from the slag chamber 42
and
is thereafter cooled to form a solid slag material. Such slag material may be
intended
for landfill disposal. Alternatively, the molten slag can be poured into
containers to
44
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
form ingots, bricks tiles or similar construction material. The solid product
may
further be broken into aggregates for conventional uses.
The solid residue handling subsystem 16, therefore, includes a slag output
means
through which molten slag is exhausted from the slag chamber 42. The output
means
may comprise a slag exit port 46, which is typically located at or near the
bottom of
the chamber 42 to facilitate the natural flow of the molten slag pool out of
the
chamber. The rate at which the molten slag flows out of the slag chamber may
be
controlled in a variety of ways that would be apparent to a person skilled in
the art.
For example, in one embodiment, the temperature differential betwecn the point
closest to the plasma heating means and the exit point may be adjusted to
control the
re-solidification time of the molten slag, e.g., through adjustments in the
volume of
solid residue niaterial allowed to pool in the chamber.
The slag output means may further be adapted to minimize heating requirements
by
keeping the slag chamber 42 sealed. In one embodiment, the output means
comprises
a pour spout or S-trap.
As discussed previously, it may also be advantageous to aim the plume of one
or more
of the plasma heat sources 44 towards the slag pool at, or around, the slag
exit port 46
to maintain thc tcmpcraturc of the moltcn slag and ensure that the slag exit
port 46
remains open through the complete slag extraction period. This practice will
also aid
in maintaining the slag as homogeneous as possible to guard against the
possibility
that some incompletely-processed material may inadvertently make its way out
of the
solid residue handling subsystem 16 during slag extraction.
The molten slag can be extracted from the solid residue handling subsystem in
a
number of different ways as are understood by those of skill in the art. For
example,
the slag can be extracted by a batch pour at the end of a processing period,
or a
continuous pour throughout the full duration of processing. The slag from
either pour
method can be poured into a water bath, where the water acts as a seal between
the
external environment and the gasification system. The slag can also be dropped
into
carts for removal, into a bed of silica sand or into moulds.
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
The walls of the slag chamber 42 are lined with a refractory material that can
be one,
or a combination of, conventional refractory materials known in the art which
are
suitable for use in a chamber for extremely high temperature (e.g., a
temperature of
about 1300 C to 1800 C) non-pressurized reactions. Examples of such refractory
materials include, but are not limited to, chromia refractories and high
alumina
refractorics containing alumina, titania, and/or chromia. Selection of an
appropriate
material for lining the slag chamber is made according to their chemical
composition,
as well as their ability to resist the corrosive nature of the slag, by virtue
of their
highly dense (low porosity) microstructures. Corrosion rates can be decreased
with
lower temperatures or reduced heavy meta[ contamination. It is advantageous to
select a non-wetting refractory material where slagging is present.
A solid residue conditioning chamber is designed for highly efficient heat
transfer
between the plasma gases and the solid residue in melting and homogenizing the
solid
residue. Thus, factors such as efficient heat transfer, adequate heat
temperatures,
residence time, molten slag flow, input solid residue volume and composition,
etc. are
taken into account when designing the solid residue conditioning chamber.
As discussed above, the physical design characteristics of the solid residue
conditioning chamber are determined by a number of factors. These factors
include,
for example, the composition and volume of the solid residue to be processed.
The
solid residue that enters the chamber may be collected from more than one
source
simultaneously. Accordingly, the internal configuration and size of the solid
residue
conditioning chamber are dictated by the operational characteristics of the
input solid
residue to be processed.
Another factor to consider in the design of the solid residue conditioning
chamber is
the residcncc timc rcquircd to cnsurc that the solid residue is brought up to
an
adequate temperature to melt and homogenize the solid residue.
The type of plasma heating means used, as well as the position and
orientation, of the
plasma heating means is an additional factor to be considered in the design of
the
solid residue conditioning chamber. The plasma heating means must meet the
required temperature for heating the solid residue to required levels to melt
and
46
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
homogenize the solid residue while allowing the resulting molten solid residue
to flow
out of the chamber.
The control subsystem 200 of the present invention regulates the efficient
conversion
of solid residue into slag by providing monitoring rneans 202 to monitor the
temperature and optionally pressure at sites locatcd throughout the solid
residue
handling subsystem 16, wherein such data are acquired on a continuous or
intermittent basis. Monitoring means 202 for monitoring the temperature in the
chamber, for example, may be located on the outside wall of the chamber, or
inside
the refractory at the top, middle and bottom of the chamber. The control
subsystem
200 of the present invention also provides regulating means 206 for
controlling
operational parameters such as the power to the plasma heat source 44 ajid
solid
residue input rate.
For example, when the temperature of the melt is too high, the control
suhsystem 200
may command a drop in the power rating of the plasma heat source 44;
conversely,
when the temperature of the melt is too low, the control subsystem 200 may
command
an increase in the power rating of the plasma heat source 44.
In one embodiment, the solid residue handling subsystem 16 can also comprise a
means for recovering heat (e.g. plasma heat source cooling means 53 and slag
cooling
means 55 of Figures 29, 30), which can reduce the amount of waste heat
generated.
Such heat recovery means can include, for example, heat exchangers. In such an
embodiment, the control system can additionally control the operating
conditions of
the heat exchanger. The heat exchanger can have, for example, a number of
temperature sensors, flow control elements, and other such monitoring and
regulating
means 202, 206.
The slag chamber may also include one or more ports to accommodate additional
structural elements/instniments that may optionally be required. For example,
a
viewport that may include a plurality of closed circuit television ports to
maintain
operator full visibility of all aspects of processing, including monitoring of
the slag
exit port 46 for formation of blockages. In another embodiment, the slag
chamber
may include service ports to allow for entry into the chamber for
scrubbing/cleauing,
47
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
maintenance, and repair. Such ports are known in the art and can include
sealable
port holes of various sizes.
Heat recovery Subsystem
Referring now to Figures 1 to 4, 24 to 26, 29, 30, the present coal
gasification system
also provides means, as in 18, for the recovery of heat from the hot product
gas.
This heat recovery subsystem 18 comprises means to transfer the hot product
gases to
one or more gas-to-air heat exchangers 48 whereby the hot product gas is used
to heat
air. The recovered heat (in the form of the heated exchange-air) may then
optionally
be used to provide heat to the gasification process, as specifically
illustrated in
Figures 24 and 25, thereby reducing the amount of heat that must be provided
by the
one or more plasma heat sources 15 required to drive the gasification process.
Tho
recovered heat may also be used in industrial or residential heating
applications.
In another embodiment, the gas-to-air heat exchanger 48 is employed to heat an
oxidant, such as oxygen or oxygen-enriched air, which may then optionally be
used to
provide heat to the gasification process.
Different classes of gas-to-air heat exchangers 48 may be used in the present
system,
including shell and tube heat exchangers, both of straight, single-pass design
and of
U-tube, muldple pass design, as well as plate-type heat exchangers. The
selection of
appropriate heat exchangers is within the knowledge of the skilled worker.
Due to the significant difference in the ambient air input temperature and hot
syngas,
each tube in the gas-to-air heat exchanger 48 preferably has its individual
expansion
bellows to avoid tube rupture. Tube rupture presents a high hazard due to
problems
resulting from air cntcring gas mixture. Tube rupture may occur where a single
tube
becomes plugged and is therefore no longer expanding/contracting with the rest
of the
tube bundle.
In order to minimize the hazard potential from a tube leak, the system of the
present
invention further comprises one or more individual temperature transmitters
associated with the product gas outlet of the gas-to-air heat exchanger 48.
These
48
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
temperature transmitters are positioned to detect a temperature rise resulting
from
combustion in the event of having exchange-air leak into the syngas conduit.
Detection of' such a temperature rise will result in the automatic shut down
of the
induction air blowers which move the coolant air through the heat recovery
system.
Thc gas-to-air heat exchanger 48 is designed to have product gas flow in the
tubes
rather than on the shell side. ln one embodiment, the product gas flows
vertically in a
"once through" design, which minimizes areas where build up or erosion from
particulate matter could occur. In an embodiment, the process air flows
counter-
currently on the shell side of the gas-to-air heat exchanger 48.
Optionally, the lteat recovery subsystein additionally comprises one or inure
heat
recovery steam generators, as in 50, to gcneratc stcam, which can be used as a
process
additive in the gasification reaction, as specifically illustrated in Figures
24 and 26, to
drive a steam turbine 52, or to drive rotating process equipment, such as
induction
blowers. Heat from the product gas is used to heat water to generate steam
using a
heat exchanging means 50, such as a heat recovery steam generator (Figures 1,
3, 4),
or a waste heat boiler (Figure 24). In one embodiment, the steam produced
using heat
from the product gas is superheated steam.
With specific reference to Figures 24 to 26, the relationship between a gas-to-
air heat
exchanger, as in 48, and a heat recovery steam generator, as in 50, is
depicted in
accordance with one embodiment of the invention. The exchange-steam can also
be
used as a process steam additive during the gasification process to ensure
sufficient
free oxygen and hydrogen to maximize the conversion of the coal into the
syngas
product.
Steam that is not used within the conversion process or to drive rotating
process
equipment, may be used for other commercial purposes, such as the production
of
electricity through the use of steam turbines, as in 52, or in local heating
applications
or it can be supplied to local industrial clients for their purposes, or it
can be used for
improving the extraction of oil from the tar sands.
49
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
In one embodiment, the heat recovery steam generator (or HRSG) 50 is located
downstream from the gas-to-air heat exchanger 48. In another embodiment, the
HRSG 50 employed in the present system is a shell and tube heat exchanger. The
HRSG 50 is designed such that the syngas flows vertically through the tubes
and
water is boiled on the shell side.
The gas-to-air heat exchanger 48 and the HRSG 50 are designed with the
understanding that some particulate matter will be present in the product gas.
The
particle size is typically between 0.5 to 350 micron. In one embodiment, the
product
gas velocities here are also maintained at a level high enough for self-
cleaning of the
tubes, while minimizing erosion.
If the temperaturc of the exiting product gas exceeds a predetermined limit,
this may
be an indication that the tubes are starting to plug, at which time the system
should be
shut down for maintenance. The heat exchangers are provided, as required, with
ports
for instrumentation, inspection and maintenance, as well as repair and/or
cleaning of
the conduits.
In an embodiment of the present invention, the system is run intermittently,
i.e.,
subject to numerous start-up and shut down cycles as desired. Therefore, it is
important that the equipment must be designed to withstand repeated thermal
expansion and contraction.
In order to maximize the amount of sensible heat which can be recovered from
the hot
product gases, as well as the heated exchange-air and steam produced by the
heat
recovery system, the conduits between the components is optionally provided
with a
means for minimizing heat loss to the surrounding environment. Heat loss may
be
minimized, for example, through the use of an insulating barrier around the
conduits,
comprising insulating materials as are known in the art, or by designing the
plant to
rn in im ize lengths of conduits.
With reference to Figures 2 and 27, in one embodiment of the present system
10, the
steam recuperated from the outputs of the various steam turbines 52 (e.g. a
steam
turbine operating from steam generated by au HRSG 50 used to cool the syngas
(liue
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
86), a steam turbine operating from steam generated by an HRSG 50 used to cool
a
gas turbine/engine 24 and exhaust gas generated thereby (line 88), or any
combination
thereof), is cooled through an additional heat exchanger 90, which is fed by a
cooling
tower pump or the like. Upon exit from the exchanger 90, the cooled
steam/water is
pumped through a deaerator 92, fed by a soft water source with appropriate
chemicals, to remove air and excess oxygen therefrom, to then be processed
back to
the boiler feed water of the exhaust gas HRSG 50 (line 94), the syngas HRSG 50
(line
96), etc.
As presented above, the present gasification system 10 also comprises an
integrated
control means 200 to optimize the transfer of energy throughout the system,
thereby
managing the energetics of the coal-to-energy conversion. The energetics of
the coal-
to-energy conversion can be optimized using the present system, since the
recycling
of the recovered sensible heat back to the gasification process reduces the
amount of
energy inputs required from extemal sources for the steps of drying and
volatilizing
the coal. The recovered sensible heat may also serve to minimize the amount of
plasma heat required to achieve a specified quality of syngas. Thus, the
present
invention allows for the efficient gasification of coal, wherein the
gasification heat
source is optionally supplemented by air heated using sensible heat recovered
froin
the product gas.
In order to optimize the efficiency of the present invention, the integrated
control
subsystem 200 also provides a means for controlling the conditions under which
the
present process is carried out, as well as the operating conditions of the
system
according to the present invention. These control means, which may be
incorporated
into the overall system control means 200, are provided to monitor one or more
parameters, including, but not limited to, temperature and gas flow rates at
specified
locations throughout the system, and to adjust operating conditions
accordingly, so as
to maintain the system within defined parameters. Examples of operating
conditions
which may be adjusted by the control means, via regulating means 206, include
one or
more of the exchange-air flow rate, the product gas flow rate, the rate of
coal input,
the rate of input of process additives such as steam, and the power to the
plasma heat
sources 15, 44, etc.
51
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
For example, temperature transmitters (and other such monitoring means 202)
may be
installed at specified locations throughout the system 10. The temperature
transmitters may be located to measure, for example, the temperatures of the
product
gas at the gas-to-air heat exchanger inlet and outlet, as well as the
temperatures of the
product gas at the IIRSG inlet and outlet. Temperature transmitters may also
be
provided to measure the temperature of the process air after heating in the
gas-to-air
heat exchanger 48, as well as to measure the temperature of the steam as it
exits the
HRSG 50.
These temperature measurements can be used to ensure that the temperature of
the
syngas as it enters a respective heat exchanger does not exceed the ideal
operating
temperature of that device. For example, if the design temperature for the gas-
to-air
heat exchanger 48 is 1050 C, a temperature transmitter on the inlet gas stream
to the
heat exchanger can be used to control both exchange-air flow rates through the
system
and plasma heat power in order to maintain the optimum syngas temperature. In
addition, measurement of the product gas exit temperature may be useful to
ensure
that the optimum amount of sensible heat has been recovered from the product
gas at
both heat recovery stages.
A temperature transmitter installed on the air outlet stream to measure the
temperature
of the heated exchange-air ensures that the process is carried out under
conditions that
ensure the process air is heated to a temperature appropriate for use in the
gasification
process. In one embodiment, the exchange-air outlet temperature is, for
example,
about 600 C, therefore a temperature transmitter installed on the air outlet
stream will
be used to control one or both of air flow rates through the system and plasma
heat
source power in the plasma reforming chamber in order to maintai the optimum
syngas input temperature, which in turn can be used to control the tcmpcraturc
of the
heated exchange-air.
According to one embodiment of the invention, the control strategy sets a
fixed set
point for the optimum heated exchange-air output temperature, for example,
about
600 C, as well as a fixed value for the HRSG gas exit temperature, for
example, about
235 C. Therefore, according to this embodiment, when the syngas flow is
reduced, the
exit gas temperature of the gas-to-air heat exchanger 48 gets cooler,
resulting in
52
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
decreased steam production because the HRSG gas exit temperature is also set
to a
fixed value.
The same concept applies when the airflow through the system is reduced.
According
to an embodiment of the present invention, the exit exchange-air temperature
remains
fixed therefore the exit product gas temperature for the gas-to-air heat
exchanger 48 is
hotter, therefore producing more steam in the HRSG. However, when airflow
through the system is reduced, product gas flow will consequently also reduce,
so the
increased inlet temperature to the HRSG 50 will only be momentarily high. For
example, if airflow is reduced to 50%, the maximum inlet gas temperature that
the
HRSG 50 would momentarily see is approximately 800 C, which is within the
temperature limits of the heat exchanger design.
In addition, regulating means 206 for controlling an automatic valve for
venting
process air to the atmosphere are also optionally provided and incorporated
into the
overall system control means 200, if more air than required for the
gasification
process is preheated. For example, in some instances it is necessary to heat
more gas
than required for the process due to equipment considerations (e.g., when
starting a
shutdown procedure). In such instances, the excess exchange-air can be vented
as
required.
The system may fnrther comprise means for monitoring one or more of syngas
composition, coal input rate, and process additive input rate (see Figures 15
and 16) in
order to provide additional information as may be required to implement
corrective
procedures to maintain optimum processing conditions. Various such monitoring
means 202 are known in the art and can be employed in the system of the
present
invention.
With reference to Figures 29 and 30, the heat recovery subsystem 18 described
above
may also provide for the cooling of the product gas as required for subsequent
filtering and conditioning steps, namely with regards to the GQCS 20 (e.g.
GQCS
cooling means 61), as well as provide for the cooling of the plasma heat
sources 15,
44 (e.g. source cooling means 53), slag handling and processing means (e.g.
slag
cooling means 55), etc.
53
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Gas Quality Conditioning Subsystem
Referring now to Figures 1 to 4, the present coal gasification system 10 also
provides
a gas quality conditioning subsystem (GQCS) 20, or other such gas conditioning
means, to convcrt the product of the coal gasification process to an output
gas of
specified characteristics.
Passage of the product gas through the GQCS 20 will ensure that the product
gas is
free of chemical and particulate contaminants, and therefore can be used in an
energy
generating system or in the manufacture of chemicals. This conditioning step
can also
be required in those embodiments of the invention that do not have the
generation of
energy or the manufacture of chemicals as an objective. For example, treatment
of
the product gas with the gas quality conditioning subsystem 20 can ensure that
the
product gas can be released through an exhaust mechanism while maintaining
strict
adherence to local emission standards.
In one embodiment, the objective for the gasification system 10 of the present
invention is to produce a fuel gas with specific characteristics (i.e.,
composition,
calorific heating value, purity and pressure) suitable for feeding into a gas
turbine 24
for production of renewable electrical energy. Because the fuel is generated
by the
pyrolysis/gasifleation of coal through the process described herein, there
will exist
certain amounts of waste impurities, particulates and/or acid gases that are
not
suitable to the normal and safe operation of the gas turbines.
The product gas is directed to the GQCS 20, where it is subjected to a
particular
sequence of processing steps to produce the output gas having the
characteristics
required for downstream applications. As briefly presented above, the GQCS 20
comprises components that carry out processing steps that may include, but are
not
limited to, removal of partictilate matter 54, acid gases (e.g. H2S removal
means 56
and optional HCI removal means, such as an HCI scrubber 57, for possible small
amounts of HCI), and/or heavy metals 58 from the synthesis gas, or adjusting
the
humidity and temperature of the gas as it passes through the system. The
presence
and sequence of processing steps required is detennined by the composition of
the
54
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
synthesis gas and the specified composition of output gas for downstream
applications. As presented above, the system 10 also comprises integrated
control
subsystem 200 to optimize the GQCS process.
In one embodiment, under vacuum extraction conditions of the induction fan of
a
gasification system, the hot product gas is continuously withdrawn from the
gasification system through an exit gas outlet(s) 40 of the gasification
system. A gas
transfer means, such as a pipe or other conduit is used to transfer the gas
from the
gasification chamber 14 to the GQCS 20.
It is also contemplated that one or more GQCSs 20 may be used, such as a
primary
GQCS and a secondary GQCS. In this case, the secondary GQCS may be used to
process material such as particulate matter and heavy metals that are removed
from
the gas stream in the primary GQCS. The output gas from the GQCS 20 can be
stored
in a gas storage tank 23 (Figure 4), fed through fiirther processing means
such as a
homogenization chamber 25 (Figure 1) or alternatively, fed directly to the
downstream application for which it was designed (i.e., Figures 2 and 3).
As discussed above, it is advantageous to provide means for cooling the hot
product
gas prior to such a conditioning step. This cooling step may be required to
prevent
damage to heat-sensitive components in the system. In one embodiment, cooling
step
is carried out by the heat recovery subsystem 18, whereby the heat recovered
from the
product gas may also be optionally recovered and recycled for use in the
gasification
process (see Figures 24 to 26).
In another embodiment, the gas from the gasification system is first cooled
down by
direct water evaporation in an evaporator such as quencher (not shown). In yet
another embodiment, cvaporativc cooling towers (dry quench) may be used to
cool
the syngas that enters the GQCS 20 from the gasification system. The
evaporative
cooling tower is capable of cooling the temperature of the syngas from about
740 C to
about 150-200 C. This process may be achieved using adiabatic saturation,
which
involves direct injection of water into the gas stream in a controlled manner.
The
evaporating cooling process is a dry quench process, and can be monitored to
ensure
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
that the cooled gas is not wet, i.e., that the relative humidity of the cooled
gas is still
below 100% at the cooled temperature.
As mentioned above, the GQCS 20 may comprise means, as in 54, for removing
particulate matter from the optionally cooled gas, as well as gaseous
contaminants not
compatible with downstream uses of the product gas, such as combustion in gas
turbines 24 to produce electricity, or as a feedstock 28 in further chemical
production
processes. A particulate removal system 54 is incorporated to remove
particulates
that may be entrained in the fuel gas exiting the converter. Particulate
removal
systems 54 are widely available, and may include, for example, high-
temperature
(ceramic) filters, cyclone separators, a venturi scrubber, an electro filter,
a candle
filter, a crossflow filter, a granular filter, a water scrubber, a fabric
baghouse filter
(Figure 1) and the like, which are well known to practitioners of gas
conditioning.
As is known in the art, particulates can be removed in a number of ways
depending on
particulate size. For example, coarse particles may be removed using a cyclone
separator or filter. Smaller or finer particles may be removed using Wet ESP
or
Baghouse filters (Figure 1). In one embodiment, with as much as 10 g/Nm'
particulate loading it a physical barrier that will remove particulate matter
with 99.9%
efficiency may be required. Wet ESP is driven by an electrostatic field and
may not
be suitable for use with gas streams of high oxygen content without control
mechanisms to trip the current if the oxygen content reaches a particular
level.
In one embodiment, a first particle removal means is used to remove coarse
particles,
and a second particle removal means is used to remove smaller or finer
particles. In
one embodiment, the first particle removal means is a cyclone filter that can
remove
particles larger than 5-10 micron in size. In another embodiment, the second
particle
removal means is a baghouse filter.
Alternative embodiments may change the order of the various gas clean-up steps
to
use more efficiently the characteristics of alternative gas cleaning devices.
However,
depending on the specific particulate removal system employed, it may be
desirable to
cool the fuel gas exiting the reaction vessel 14 before it enters the
particulate removal
system as previously mentioned. The cooling of the fuel gas may be of
particular
56
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
importance if a bag type filter is used for particulate removal, because bag
type filters
are often cellulose or organic polymer-based, and cannot withstand extremely
high
temperatures.
T'he dust is then collected and may be sent back to the gasification reaction
vessel so
that no hazardous, solid wastes are produced or generated in the gas
conditioning
system. Atternatively, the particulate may be directed to the slag reservoir
(see Figure
1) to vitrify the scrubber solids into a non-leachable slag. In some cases,
depending
upon plant considerations and local regulations, solids from the gas clean-up
system
may be sent off-site for safe disposal.
There may also be provided means, as in 58, for removing mercury or other
heavy
metals from the product gas. For example, dry injection systems utilize a
calculated
amount of activated carbon, which is injected in the gas stream with enough
residence
time so that fine heavy metal particles and fumes can adsorb in the activated
carbon
surface. Heavy metals adsorbed on activated carbon can be captured in a
baghouse
filter. Alternatively, a wet ESP system may be used to capture the heavy
metals
adsorbed on activated carbon. In one embodiment of the invention, the heavy
metal
particles adsorbed on activated carbon are captured in a baghouse.
An acid scrubbing system is also an effective technique to capture heavy
metals. This
system requires the passage of the gas containing heavy metals to be passed
through a
packed column with low pH (normally 1-2) solution circulation. Heavy metals
and
heavy metal compounds react with acid to form their stable compounds. With
this
technique the heavy metal concentration in the circulation solution will
increase and
thus treatment of the resulting waste water may be required. In one
embodiment, the
GQCS 20 comprises an acid scrubbing system to remove lieavy iiietals.
In one embodiment, the mercury removal means is provided by an activated
carbon
mercury polisher. An activated carbon filter bed can be used as the final
polishing
device for heavy metal. The product gas is passed through activated carbon bed
that
will adsorb heavy metal (mainly mercury) from the gas stream. Normally
activated
carbon filters are used to achieve above 99.8-99.9 % removal of mercury and
used as
a final polishing device with 7-8 inches of WC pressure drop.
57
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
An acid recovery subsystem 56 is coupled to the gas conditioning system 20, to
recover sulfur or sulfuric acid (from high sulfur coal) and hydrochloric acid
(from
chlorinated hydrocarbons), which may have a marketable value. The acid removal
system 56 may include scrubber systems, acid removal systems, and other
conventional equipment related to sulfur and/or acid removal systems.
The jollowing paragraph will be replaced with new data to be provided
The product gas produced in the coal gasification system will contain acid
gases such
as HCI and H2 S. The concentrations of these acid gases in the product gas
range from
about 0.05 to about 0.5% for HCI, and range from about ] 00 ppm to about 1000
ppm
for H2S. In one embodiment, the expected concentration of HCl is about 0.178 %
and
HZS is about 666 ppm (0.07%). The emission limit for HCI is about 5 ppm while
for
SOz it is about 21 ppm.
Acid gas removal can be achieved by dry scrubbing or wet scrubbing_ The main
components of dry scrubbing are a spray dry absorber and soda ash or lime
powder
injection before baghouse filtration. Normally with dry scrubbing it is
difficult to
achieve more than 99% acid removal efficiency.
If the amount of chlorine is of economically significant size, the chlorine
may be
reclaimed. If chlorine is present in a nuisance amount, it is removed in any
suitable
manner (e.g. water or wet scrubber, activated bauxite adsorption, etc.). The
gas may
be treated to remove components such as chlorine in a gas/liquid scrubber-
contactor.
The greatest advantage of wet scrubbing is a large contact area for heat
transfer and
mass transfer with less pressure drop that will help sub cooling of the gas.
Sodium
hydroxide is the traditional alkaline solution used for wet scrubbing. In one
embodiment, a packed column is used for scrubbing acid gas.
Sulfur compounds are among the first to recombine, either as elemental sulfur,
as
sulfur-oxygen compounds or sulfur-hydrogen compounds. In one embodiment where
the amount of sulfur compounds justifies the cost, a sulfur recovery facility,
as in 76,
is positioned along the conduit at a location, adjacent the heat exchangers,
where a
temperature is reached where the sulfur compounds become stable. The type and
size
58
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
of the sulfur recovery facility 76 depends on the expected amount of sulftir
in the inlet
stream.
If the anticipated amount of sulfur is fairly low, as expected in low sulfur
grades of
coal, an iron filing technique may be used to react sulfur with elemental iron
to
produce iron sulfide. This may be accomplished by circulating iron pcllcts
botween a
compartment in the conduit and a recovery compartment.
For coal that contains a high amount of sulfur, a second-stage liquid washing
process
is used to remove sulfur compounds from the gas. Sulfur may be recovered by
any
suitable technique, depending on the amount of sulfur anticipated in the inlet
stream.
Further downstream, an amine scrubber removes hydrogen sul6de and carbon
dioxide
from the gas stream leaving a stream mainly comprising hydrogcn, carbon
monoxidc
and an inert gas. Such amine scrubbers are known in the art and generally
comprise an
amine process wherein an aqueous solution of monoethanoloamine,
diethanoloamine,
or methyldiethanoloamine is used to remove H2S from the processed gas. Other
methods for recovering sulfur may include, for example, a Claus plant (Figure
1), a
Resox reduction process, a cold plasma hydrogen sulfide dissociation process,
and the
like.
In addition, suitable methods for the removal of sulfur include, for example,
wet
absorption with NaOH or triazine, dry adsorption with Sufatreat, biological
processes
such as Thiopaq, or selective oxidation, including liquid redox (Low CAT). In
one
embodiment, H2S is removed from the synthetic gas using Thiopaq (see Figure
1).
Thiopaq is a two step process in which sour gas is scrubbed with a mild
alkaline
solution (at 8.5 to 9 pH) and the sulfur subsequently recovered (HS- is
oxidized to
elemental sulfur by a biological process). Other methods may include, but are
not
limited to, a moving bed zinc titanate or ferrite adsorption process,
oxidation chemical
reaction processes (e.g. Stretford and SulFerox), and a Selexof acid removal
process,
the latter of which generally involves the use of a physical solvent (e.g.,
polyethylene
glycol dimethyl ether) at high pressures (e.g. 300-1000 psig).
59
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Furthermore, dioxins may be formed at a temperature of 250 -350 C in the
presence
of carbon that will act as catalyst, although plasma gasification conditions
are known
to hinder their formation. For additional minimization of dioxin formation,
quenching
of synthesis gas is normally done in a quencher or spray dryer absorber to
ensure fast
quenching is done between the above temperature range. Activated carbon
injection in
the synthesis gas will absorb dioxin and furan on carbon surface followed by
removal
in baghouse filters.
Demisters or reheaters could also be incorporated for moisture removal and/or
prevention of condensation. Heat exchangers can be included to reheat the fuel
gas to
the inlet temperature required by the downstream power generation equipment. A
compressor can also optionally be included to compress the fuel gas to the
inlet
pressures required by downstream power generation equipment.
In yet another embodiment, a humidity control means can be part of the GQCS
20.
The humidity control means functions to ensure that the humidity of the output
gas is
appropriate for the downstream application employed. For example, a humidity
control means may include a chiller to cool the gas stream and thus condense
some
water out of the gas stream. This water can be removed by a gas/liquid
separator. In
one embodiment such treatment of the gas streain ensures ttiat the gas stream
exiting
from the GQCS 20 has a humidity of about 80% at 26 C. The gas may then be
stored
(e.g., in gas storage device 23).
In another embodiment, the gas processing subsystem can include means for the
recovery of carbon dioxide and/or means for recovery of ammonia. Suitable
means
are known in the art.
The product gas is also sampled for gas chromatography (GC) analyses to
detennine
chemical composition. Sample points for these analyses are spread throughout
the
product gas handling/pollution abatement subsystem.
In one ernbodiment, the control subsystem 200 comprises means to adjust the
operating conditions in the conversion system, including the operating
conditions in
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
the GQCS 20, thereby managing the net overall energetics of the conversion
process,
and maintaining a set point for reaction conditions within a specified range
of
variability during the conversion of coal to a product gas having a specified
chemical
and physical composition. This system can be automated and applied to a
variety of
gasification systems.
The control subsystem 200 may provide the following functions. In one
embodiment,
the control subsystem 200 may sense decrease in efficiency or alternate
functional
deficiency in a process of the GQCS 20 and divert the gas stream to a backup
process
or backup conditioning system. In another embodiment, the control subsystem
200
may provide a means for fine-tuning the steps of the GQCS 20 and providing
minimal
drift from optimal conditions.
The control subsystem 200 of this invention can include monitoring means 202
for
analyzing the chemical composition of the gas stream through the GQCS 20, the
gas
flow and thermal parameters of the process; and regulating means 206 to adjust
the
conditions within the GQCS 20 to optimize the efficiency of processing and the
composition of the output gas. Ongoing adjustments to the reactants (for
example,
activated carbon injection with sufficient residence time, pH control for the
acid gas
scrubber) can be executed in a manner that enables this process to be
conducted
efficiently and optimized according to design specifications.
Suh.ry.etern for Regulating the Product Gas
The present coal gasification system also optionally provides a means, for
regulating
the product gas, for example, by homogenizing the chemical composition of the
product gas and adjusting other characteristics such as flow, pressure, and
temperature
of the product gas to rneet downstream requirements. This product gas
regulating
subsystem 22 enables a continual and steady stream of gas of defined
characteristics
to be delivered to downstream applications, such as a gas turbine 24 or
engine.
As is understood by those skilled in the art, the gasification process may
produce
gases of fluctuating composition, temperature or flow rates. In order to
minimize the
fluctuations in the characteristics of the product gas, there may be provided
a gas
61
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
regulation system 22 in the form of a capturing means useful for delivering to
downstream equipment a product gas having consistent characteristics.
In one embodiment, the present invention provides a gas regulation system 22
that
collects the gaseous products of the gasification process and attenuates
fluctuations in
the chemistry of the gas composition in a homogcnization chambcr 25, or the
like.
Other elements of the system optionally adjust characteristics of the gas such
as flow,
temperature and pressure to fall within ranges that are acceptable to the
downstream
applications. The system thereby regulates the characteristics of the product
gas to
produce a continual stream of gas with consistent characteristics for delivery
to a
downstream application, such as a gas engine or a gas turbine 24.
In particular, the optional product gas regulating subsystem 22 of the present
invention provides a gas homogenization chamber 25 (Figure 1) or the like
(e.g. the
gas compressor 21 of Figures 1 and 2, the gas storage device 23 of Figure 4,
etc.)
having dimensions that are designed to accommodate a residence time sufficient
to
attain a homogeneous gas of a consistent output composition. Other elements of
the
present gas regulation system are designed to meet the gas performance
requiremcnts
of the downstream application. The system also comprises a control subsystem
200 to
optimize the energetics and output of the process.
The composition of the product gas entering the regulation system 22 of the
present
invention, is determined in the gasification process. Adjustments made during
the
gasification process permit the product gas to be optimized for a specific
application
(e.g., gas turbines 24 or fuel cell application 26 for electricity
generation).
Accordingly, the composition of the product gas can be tailored for particular
energy
generating technologies (for example, for specific gas engines or gas turbines
24) and,
for best overall conversion efficiency, according to the different types of
coal and
process additives used, by adjusting the operational parameters of the
gasification
process.
The product gas leaving the gasification system may be within a defined range
of a
target composition, however, over time the product gas may fluctuate in its
62
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
characteristics due to variability in the gasification process such as coal
composition
and feed rate, as well as airflow and temperature fluctuations.
Similar to the control of the composition of the product gas, the flow rate
and
temperature of the product gas can be monitored, for example via monitoring
means
202, and controlled in the gasification systcm, for example via regulating
means 206,
in order to maintain the parameters of the gas within predetermined tolerances
defined
by the end use. Trrespective of these controls, fluctuations in flow rate and
temperature of the product gas, over time, will occur. ln the case of flow
rate, these
fluctuations may occur on a second to second basis; and with temperature on a
per
minute basis.
Conversion of product gas to a gas having a spccificd composition that meets
the
requirements of the particular application equipment, can be effected in the
regulation
system of the present invention. The regulation system comprises one or more
gas
homogenization chambers 25 having a product gas inlet means, a regulated gas
outlet
means, and optionally an emergency exit port.
The product gas homogenization chamber 25 receives the product gas produced
from
a gasification system and encourages mixing of the product gas to attcnuatc
any
fluctuations in the chemical composition of the product gas in the
homogenization
chamber 25. Fluctuations in other gas characteristics, such as pressure,
temperature
and flow rate, will also be reduced during mixing of the product gas.
The dimensions of the chamber are designed according to the performance
characteristics of the upstream gasification system and the requirements of
the
downstream machinery, with the objective of minimizing the size or the chamber
as
much as possiblc. The gas homogenization chamber 25 is designed to receive
product
gas from a gasification process and retain the gas for a certain residence
time to allow
for sufficient mixing of the gas in order to achieve a volume of gas with a
consistent
chemical composition.
The residence time is the amount of time that the product gas remains in the
homogenization chamber 25 before being directed to the downstream equipment.
The
63
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
residence time is proportional to the response time of the related
gasification system
to correct for variances in the fluctuations in the gasification reaction in
order to
achieve a gas composition that falls within accepted tolerance values. For
example,
the gas composition is retained in the homogenization chamber 25 long enough
to
detennine 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 correct for the deviance.
Additionally, residence time of the product gas in the homogenization chamber
25 is
determined by the amount of variance in the product gas characteristics. That
is, the
smaller the variance in product gas characteristics, the shorter the residence
time
required in the homogenization chamber 25 to correct for the variance.
The optional gas regulating subsystem 22 is designed to provide sufficient
residence
time in a homogenization chamber 25. In one embodiment, the gas regulating
subsystem 22 provides a residence time of at least I second. In another
embodiment,
the gas regulating subsystem 22 provides a residence time no more than 2
seconds. In
yet another embodiment, the gas regulatgin subsystem 22 provides a residence
time of
2 to 10 seconds. In yet another embodiment, the gas regulating subsystem 22
provides
a residence time of up to 30 second.
The regulated gas exiting the optional regulation system 22 of the present
invention
will have stabilized characteristics that meet the specifications of the
downstream
application. Typically, machine manufacturers will provide the requirements
and
tolerances allowed by the specific machinery and would be known to the person
skilled in the art.
Use of the Gasification System / The Process
The system according to the present invention gasifies coal, using a process
for
gasification of the coal that generally comprises the steps of passing the
coal into a
gasification reaction vessel 14 where it is heated, dried and volatile
components in the
dried feedstock are volatilized. In one embodiment of the invention, heated
air is used
64
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
to further drive the complete conversion of the resulting char to its gaseous
constituents, leaving an ash by-product. The combined products of the drying,
volatilization and combustion steps provide an offgas that is further
subjected to the
heat from a plasma heat source 15 to convert the offgas to a hot gaseous
product
comprising carbon monoxide, carbon dioxide, hydrogen and steam. Steam and/or
air/oxidant process additives 38 may be optionally added at the gasification
stage
and/or the offgas conversion stage.
In one embodiment of the invention, the process further comprises the step of
subjecting by-product ash to heating by means of a second plasma heat source
44 to
fonn a slag product.
The process of the present invention further comprises the steps of passing
the hot
product gas through a heat exchanging subsystem 18, transferring heat from the
hot
gas to a coolant. In one embodiment, the coolant is air. In another
embodiment, the
coolant is an oxidant selected from oxygen or oxygen-enriched air.
The process of the present invention optionally comprises the steps of passing
the
cooled gas product into a second beat exchanger 18, transferring heat from the
cooled
gas to a coolant that is water to produce a further cooled gas product and
steam.
The process of the present invention maximizes net conversion efficiency by
offsetting the amount of electricity that has to be consumed, for example, to
create the
heat that drives the gasification process, to drive rotating machinery, and to
power the
plasma heat sources 15, 44. For applications having the objective of
generating
electricity, the efficiency is measured by comparing the energy consumed by
the
overall gasification process with the amount of energy generated using the
product
gas (for example, to power gas turbines 24 or in fuel cell technologies 26),
and
through the recovery of sensible heat to generate steam to power steam
turbines 52.
The gasification process can further comprise a corrective (or feedback)
control step
of adjusting one or more of the coal input rate, the product gas flow rate,
the
air/oxidant and/or steam process additive input rate, the pressure of the
system, and
the amount of power supplied to the plasma heat sources based on measured
changes
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
in the flow rate, temperature and/or composition of the product gas. The
feedback
control step thus allows the flow rate, temperature and/or composition of the
product
gas to be maintained within acceptable ranges.
In one embodiment of the present invention, the process further comprises the
step of
pre-heating the coal prior to adding to the gasification reaction vessel 14.
In one embodiment, the gasification process according to the present invention
employs the use of heated air or other oxidant from the gas-to-air heat
exchanger 48
to heat the gasification reaction vessel 14 to a temperature appropriate for
gasifying
coal. In this embodiment, which is typically used at the start-up phase of the
system
10, air is fed into the system, whereby it is heated by plasma heat to provide
a hot
start-up gas that then enters the gas-air heat exchanger 48 to generate heated
air. The
heated air is transferred to the heated air inlet means to heat up the
gasification
reaction vessel 14, such that the entire process can run without the use of
fossil fuels.
'1'he invention will now be described with reference to a specific example. It
will be
understood that the following example is intended to describe an embodiment of
the
invention and is not intonded to limit the invention in any way.
EXA,MPLE
In general, the system of the present invention is used by feeding the coal
along with
the heat from a source such as a plasma heat souree 15, heated air, or any
other heat
source as may be appropriate, into a gasification reaction vessel 14 where the
feedstock is subjected to sufficient heat to allow the gasirication reaction
to take
place.
Heating of the coal results in removal of any residual moisture and
volatilization of
any volatile components, thereby providing a partially oxidized char product.
Further
heating of the partially oxidized char product completely converts the char to
its
gaseous constituents, leaving an ash by-product, which can then be further
heated and
converted to slag.
66
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Extra oxygen may he injected into the gasification reaction vessel to initiate
or to
increase the exothermic reactions that produce carbon monoxide, carbon dioxide
and
carbon particles. The exothermic reactions along with the heat optionally
provided by
the heated process air increase the processing temperature in the gasification
reaction
vessel 14.
In one embodiment, the processing temperature is between about 1000 C to
about
1300 C, although lower and higher temperatures are also contemplated. In one
embodiment of the present invention, the process employs an average
gasification
temperature within the reaction vessel is about 1100 C +/- 100 C.
Refurmuliun
The offgas that is formcd in the gasification reaction vessel 14 is further
heated with a
plasma heat source 15 and optionally treated with steam. These reactions are
mainly
endothermic. In one embodiment of the present invention, the temperature is
maintained in a range that is high enough to keep the reactions at an
appropriate level
to ensure complete conversion to the specified gas product, while minimizing
pollution production. In one embodiment, the temperature range is from about
900 C
to about 1300 C. Appropriate temperature ranges can readily be determined by
the
skilled worker.
The steam that is added in the reformation step acts to ensure formation of a
gas
product having a specified composition, while also reducing the exit
temperature of
the gas. In one embodiment, the exit temperature of the product gas is reduced
to
between about 900 'C and about 1200 C. In another embodiment, the product gas
exit
temperature is reduced to an average temperature of about 1000 C +/- 100 C.
In one cxcmplary embodiment, the amount of coal, oxygen, steam and power to
the
plasma heat sources 15 may be determined on the basis of monitoring the flow
rate of
the exit synthesis gas, the exit temperature of the exit synthesis gas and the
composition of the exit gas.
With specific reference to Figures 15 and 16, the numerical value of the flow
rate of
carbon monoxide and carbon dioxide in the exit gases via lines 100 and 102, is
67
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
inputted into a first processor (illustrated by logic box 30) along with the
numerical
value of the feed rate of coal in line 104 (e.g. obtained via regulating means
206-1).
The first processor 30 estimates the amount of carbon in the gasification
reaction
vessel 14 and adjusts the coal feed rate accordingly.
Output from first proccssor 30, which provides a measure of the numerical
value of
the per cent carbon monoxide and the per cent carbon dioxide is inputted via
line 106
to a second processor (illustrated by logic box 32) along with the numerical
value of
the per cent hydrogen via line 108, and the numerical values of steam (e.g.
via
regulating means 206-2) and oxygen (e.g. via regulating means 206-3) via line
110.
'1'he second processor 32 estimates new oxygen and steam inputs to achieve the
specified gas composition.
Output from the second processor 32 aro inputted into a third processor 34 via
line
112 along with an input representative of the numerical value of the exit gas
temperature via line 114. The third processor 34 computes new plasma heat
source
power (e.g. plasma torch) that outputs as power output (e.g. sent to
regulating means
206-4) via line 116.
Melting of By-Product Ash
In one embodiment of the invention, the solid ash by-product of the char
combustion
step is fiirther optionally processed by melting with a second plasma heat
source 44.
Enough time is allowed when the particles are entrained in the slag pool to
ensure that
all volatiles and carbon are completely removed. As would be appreciated by a
worker skilled in the art, the residence time is a function of the particle
size. The heat
produced by the second plasma heat source 44 homogenizes the slag and allows
it to
be extracted whilc hot. The plasma heat source 44 heats the slag to a
temperature
between about 1100 C and about 1600 C. In one embodiment, to a temperature
is
between about 1400 C and about 1650 C. This manipulation of the temperature
profiles can help to avoid wasting heat and later water to quench the slag in
the
bottom of the gasification reaction vessel 14.
68
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Although the invention has been described with reference to certain specific
embodiments, various modifications thereof will be apparent to those skilled
in the art
without departing from the spirit and scope of the invention as outlined in
the claims
appended hereto.
The following examples have been providcd to compare the gasification of two
low
rank coals, lignite and sub-bituminous coal (see Table 1), to produce syngas
with a
heating value suitable for Integrated Gasification Combined Cycle (IGCC) power
generation.
The following two examples, are provided to demonstrate the operational
parameters
required to provide a syngas suitable for use in an IGCC, wherein the combined
cycle
comprises of one gas turbine (42MW) and one steam turbine. In the present
example,
GE MS6001B Combined Cycle is selected as the targeted model for both cases:
the
net plant power output is about 64MW. According to the present examples, the
overall efficiency of the combined cycle could reach above 45%, much higher
than
traditional coal-fired power plant (30-33%)_
The gasification reaction vessel can either be based on an entrained flow or a
fluidized
bed type reactor. An air separation unit (ASU) will supply 95% oxygen as the
primary
oxidant. Solid residues will be transfonned to slag by a plasma torch at high
temperature. The raw gas coming out from the converter is cooled and scrubbed
before further gas cleaning processes, such as fine particulates and sulfur
removal.
'1'he clean and conditioned syngas will be fed into gas turbine and combusted
to
generate electricity. The high temperature exhausting flue gas is introduced
to a heat
recovery steam generator (HRSG), which supplies steam for steam turbine,
boosting
the capacity of the electricity generation.
Table 1. Lignite and Sub-bituminous coal composition
HHV
Coal type C H 0 N S Moisture
Btu/]b
Lignite 40.6% 6.9% 45.1% 0.6% 0.9% 36% 7000
Sub-bituminous 50.5% 6.2% 35.5% 0.7% 0.3% 25% 8560
69
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
Note: C,H,O... fraction is in term of weight.
Lignite as feedstock
The gasification reaction vessel operates at temperature ranging from 1000 C
to 1100
C, under a pressure ranging from 2 atm to 10 atm. The coal input rate is
controlled at
1309 T/day and pre-dried down to 10% moisture. The oxidant employed is 95%
purity oxygen, provided at an oxidant input rate of about 205 SCFM (463
T/day). The
syngas, after cooling and cleaning, consists of 35.6% Hz and 31.4% CO with
heating
value of 9.1 MJ/m3. The volume flow rate of the dry clean syngas is about
47,323
m3/hr. The cold gas efficiency, taking into account how much energy is
transferred to
syngas from solid fuels, is about 85%.
Sub-bituminous coal as feedstock
The gasification reaction vessel operates at an average temperature of 1100
C, under
a pressure ranging from 2 atm to 10 atm. The coal input rate is controlled at
617 T/day
and pre-dried down to 10% moisture. The oxidant employed is 95% purity oxygen,
provided at an input rate of about 85 SCFM (127 T/day). The syngas, after
cooling
and cleaning, consists of 45.0% H2 and 30.5% CO with heating value of 10.2
MJ/m3.
The volume flow rate of the dry syngas is about 51,400 m3/hr. The cold gas
efficiency
of the gasification system is about 86%.
As indicated, a comparison of the gasification of sub-bituminous coal and
lignite to
produce a gas having a similar heating value, demonstrates that the
gasification of
lignite will consume more oxygen as oxidants and produce less syngas for the
gas
turbine; it means more lignite will be needed to generate the same amount of
electricity than sub-bituminous coal. The cold gas efficiency of lignite as
feedstock is
also lower than that of sub-bituminous as expected. The present examples,
however,
indicate that the prescnt gasification system can be used to convert low rank
coal to a
syngas having a heating value suitable for IGCC power generation.
The disclosure of all patents, publications, including published patent
applications,
and database entries referenced in this specification are specifically
incorporated by
reference in their entirety to the same extent as if each such individual
patent,
CA 02610808 2007-12-03
WO 2006/128286 PCT/CA2006/000882
publication, and database entry were specifically and individually indicated
to be
incorporated by reference.
71
