Note: Descriptions are shown in the official language in which they were submitted.
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
A HORIZONTALLY-ORIENTED GASIFIER WITH LATERAL TRANSFER
SYSTEM
FIELD OF THE INVENTION
This invention pertains to the field of carbonaceous feedstock gasification
and in
particular, to a horizontally-oriented gasifier with a lateral transfer
system.
BACKGROUND OF THE INVENTION
Gasification is a process that enables the conversion of carbonaceous
feedstock, such as
municipal solid waste (MSW) or coal, into a combustible gas. The gas can be
used to
generate electricity, steam or as a basic raw material to produce chemicals
and liquid
fuels.
Possible uses for the gas include: the combustion in a boiler for the
production of steam
for internal processing and/or other external purposes, or for the generation
of electricity
through a steam turbine; the combustion directly in a gas turbine or a gas
engine for the
production of electricity; fuel cells; the production of methanol and other
liquid fuels; as
a further feedstock for the production of chemicals such as plastics and
fertilizers; the
extraction of both hydrogen and carbon monoxide as discrete industrial fuel
gases; and
other industrial applications.
Generally, the gasification process consists of feeding carbonaceous feedstock
into a
heated chamber (the gasifier) along with a controlled and/or limited amount of
oxygen
and optionally steam. In contrast to incineration or combustion, which operate
with
excess oxygen to produce CO2, H20, SO,, and NOx, gasification processes
produce a raw
gas composition comprising CO, H2, H2S, and NH3. After clean-up, the primary
gasification products of interest are H2 and CO.
Useful feedstock can include any municipal waste, waste produced by industrial
activity
and biomedical waste, sewage, sludge, coal, heavy oils, petroleum coke, heavy
refinery
residuals, refinery wastes, hydrocarbon contaminated soils, biomass, and
agricultural
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
wastes, tires, and other hazardous waste. Depending on the origin of the
feedstock, the
volatiles may include H20, Hz, Nz, 02, CO2, CO, CH4, H2S, NH3, C21-16,
unsaturated
hydrocarbons such as acetylenes, olefins, aromatics, tars, hydrocarbon liquids
(oils) and
char (carbon black and ash).
As the feedstock is heated, water is the first constituent to evolve. As the
temperature of
the dry feedstock increases, pyrolysis takes place. During pyrolysis the
feedstock is
thermally decomposed to release tars, phenols, and light volatile hydrocarbon
gases while
the feedstock is converted to char.
Char comprises the residual solids consisting of organic and inorganic
materials. After
pyrolysis, the char has a higher concentration of carbon than the dry
feedstock and may
serve as a source of activated carbon. In gasifiers operating at a high
temperature ( >
1,200 C) or in systems with a high temperature zone, inorganic mineral matter
is fused
or vitrified to form a molten glass-like substance called slag.
Since the slag is in a fused, vitrified state, it is usually found to be non-
hazardous and
may be disposed of in a landfill as a non-hazardous material, or sold as an
ore, road-bed,
or other construction material. It is becoming less desirable to dispose of
waste material
by incineration because of the extreme waste of fuel in the heating process
and the further
waste of disposing, as a residual waste, material that can be converted into a
useful
syngas and solid material.
The means of accomplishing a gasification process vary in many ways, but rely
on four
key engineering factors: the atmosphere (level of oxygen or air or steam
content) in the
gasifier; the design of the gasifier; the internal and external heating means;
and the
operating temperature for the process. Factors that affect the quality of the
product gas
include: feedstock composition, preparation and particle size; gasifier
heating rate;
residence time; the plant configuration including whether it employs a dry or
slurry feed
system, the feedstock-reactant flow geometry, the design of the dry ash or
slag mineral
2
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
removal system; whether it uses a direct or indirect heat generation and
transfer method;
and the syngas cleanup system. Gasification is usually carried out at a
temperature in the
range of about 650 C to 1200 C, either under vacuum, at atmospheric pressure
or at
pressures up to about 100 atmospheres.
There are a number of systems that have been proposed for capturing heat
produced by
the gasification process and utilizing such heat to generate electricity,
generally known as
combined cycle systems.
The energy in the product gas coupled with substantial amounts of recoverable
sensible
heat produced by the process and throughout the gasification system can
generally
produce sufficient electricity to drive the process, thereby alleviating the
expense of local
electricity consumption. The amount of electrical power that is required to
gasify a ton of
a carbonaceous feedstock depends directly upon the chemical composition of the
feedstock.
If the gas generated in the gasification process comprises a wide variety of
volatiles, such
as the kind of gas that tends to be generated in a low temperature gasifier
with a "low
quality" carbonaceous feedstock, it is generally referred to as off-gas. If
the
characteristics of the feedstock and the conditions in the gasifier generate a
gas in which
CO and H2 are the predominant chemical species, the gas is referred to as
syngas. Some
gasification facilities employ technologies to convert the raw off-gas or the
raw syngas to
a more refined gas composition prior to cooling and cleaning through a gas
quality
conditioning system.
Utilizing plasma heating technology to gasify a material is a technology that
has been
used commercially for many years. Plasma is a high temperature luminous gas
that is at
least partially ionized, and is made up of gas atoms, gas ions, and electrons.
Plasma can
be produced with any gas in this manner. This gives excellent control over
chemical
reactions in the plasma as the gas might be neutral (for example, argon,
helium, neon),
3
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
reductive (for example, hydrogen, methane, ammonia, carbon monoxide), or
oxidative
(for example, oxygen, carbon dioxide). In the bulk phase, a plasma is
electrically neutral.
Some gasification systems employ plasma heat to drive the gasification process
at a high
temperature and/or to refine the offgas/syngas by converting, reconstituting,
or reforming
longer chain volatiles and tars into smaller molecules with or without the
addition of
other inputs or reactants when gaseous molecules come into contact with the
plasma heat,
they will disassociate into their constituent atoms. Many of these atoms will
react with
other input molecules to form new molecules, while others may recombine with
like
atoms. As the temperature of the molecules in contact with the plasma heat
decreases all
atoms fully recombine. As input gases can be controlled stoichiometrically,
output gases
can be controlled to, for example, produce substantial levels of carbon
monoxide and
insubstantial levels of carbon dioxide.
The very high temperatures (3000 to 7000 C) achievable with plasma heating
enable a
high temperature gasification process where virtually any input feedstock
including waste
in as-received condition, including liquids, gases, and solids in any form or
combination
can be accommodated. The plasma technology can be positioned within a primary
gasification chamber to make all the reactions happen simultaneously (high
temperature
gasification), can be positioned within the system to make them happen
sequentially (low
temperature gasification with high temperature refinement), or some
combination thereof.
The gas produced during the gasification of carbonaceous feedstock is usually
very hot
but may contain small amounts of unwanted compounds and requires further
treatment to
convert it into a useable product. Once a carbonaceous material is converted
to a gaseous
state, undesirable substances such as metals, sulfur compounds and ash may be
removed
from the gas. For example, dry filtration systems and wet scrubbers are often
used to
remove particulate matter and acid gases from the gas produced during
gasification. A
number of gasification systems have been developed which include systems to
treat the
gas produced during the gasification process.
4
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
These factors have been taken into account in the design of various different
systems
which are described, for example, in U.S. Patent Nos. 6,686,556, 6,630,113,
6,380,507;
6,215,678, 5,666,891, 5,798,497, 5,756,957, and U.S. Patent Application Nos.
2004/0251241, 2002/0144981. There are also a number of patents relating to
different
technologies for the gasification of coal for the production of synthesis
gases for use in
various applications, including U.S. patent Nos. 4,141,694; 4,181,504;
4,208,191;
4,410,336; 4,472,172; 4,606,799; 5,331,906; 5,486,269, and 6,200,430.
Prior systems and processes have not adequately addressed the problems that
must be
dealt with on a continuously changing basis. Some of these types of
gasification systems
describe means for adjusting the process of generating a useful gas from the
gasification
reaction. Accordingly, it would be a significant advancement in the art to
provide a
system that can efficiently gasify carbonaceous feedstock in a manner that
maximizes the
overall efficiency of the process, and/or the steps comprising the overall
process.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a horizontally-oriented
gasifier with
lateral transfer system. In accordance with an aspect of the invention, there
is provided a
horizontally-oriented gasifier comprising a horizontally-oriented gasification
chamber
having one or more feedstock inputs, one or more gas outlets and a solid
residue outlets;
a chamber heating system; one or more lateral transfer units for moving
material through
the gasifier during processing; and a control system for controlling movement
of the one
or more lateral transfer units.
In accordance with another aspect of the invention, there is provided a
process for
converting a feedstock to an off-gas and ash, comprising the steps of:
a) establishing three regional temperature zones in an
horizontally-oriented
gasifier; wherein a first zone has a temperature which promotes drying, a
second zone has a temperature which promotes volatization and a third
zone has a temperature which promotes char-to-ash conversion;
5
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
b) providing carbonaceous feedstock to the first zone and maintaining the
carbonaceous feedstock at the first zone for a period of time to obtain a
substantially dried reactant material;
c) passing the substantially dried reactant material to the second zone for
a
period of time such that volatile components of the dried reactant material
are volatilized to form off-gas;
d) passing residual char from the second zone to the third zone for period
of
time such that the char is converted to additionally off-gas and ash.
This invention provides a horizontally-oriented gasifier with lateral transfer
system that
enables extraction of volatiles throughout the various stages of gasification
of
carbonaceous feedstock to be optimized. Feedstock is introduced at one end of
the
gasifier and is moved through the gasifier during processing by one or more
lateral
transfer units. The temperature at the top of the material pile generally
increases as
gasification proceeds through drying, volatilization and char-to-ash
conversion (carbon
conversion) with the simultaneous production of CO and CO2. A control system
obtains
information from measurable parameters such as temperature and pile height or
profile
and manages the movement of each lateral transfer unit independently.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the invention will now be described, by way of example only, by
reference to the attached Figures, wherein:
Figure 1 is a schematic of a horizontally-oriented stepped floor gasifier of
the invention,
detailing the feedstock input, gas outlet, ash outlet and lateral transfer
system.
Figure 2 is a flow diagram showing the different regions of the gasifier in
general terms.
Figure 3 is a representation of the gasification processes occurring in
Regions 1, 2 and 3
of one embodiment of the gasifier.
6
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Figure 4 is a cross-sectional view through one embodiment of the gasifier,
detailing the
feedstock input, gas outlet, ash outlet, lateral transfer system, additive
ports and access
ports.
Figure 5 is a central longitudinal cross-sectional view through the embodiment
of the
gasifier illustrated in Figure 4, detailing the thermocouples and process
additive ports.
Figure 6 is a perspective view of the embodiment of the gasifier illustrated
in Figures 4
and 5.
Figure 7 illustrates a view of the outside of the embodiment of the gasifier
illustrated in
Figures 4 to 6 detailing the external elements of the lateral transfer system.
Figure 8 illustrates a portion of a lateral transfer unit of the gasifier
illustrated in Figures
4 to 6.
Figure 9 illustrates a bottom view of the lateral transfer unit illustrated in
Figure 8.
Figure 10 illustrates an alternative embodiment of the lateral transfer unit
illustrated in
Figure 8.
Figure 11 is a perspective view of one embodiment of the gasifier, detailing
the feedstock
input, gas outlet, ash outlet, ram enclosure and access ports.
Figure 12 is a side view of the gasifier illustrated in Figure 11 detailing
the air boxes, ash
can and dust collector.
Figure 13 is a central longitudinal cross-sectional view through the gasifier
illustrated in
Figures 11 and 12, detailing the feedstock input, gas outlet, ash outlet,
lateral transfer
system, thermocouples and access ports.
7
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Figure 14 illustrates a cross sectional view of the gasifier of Figures 11 to
13 detailing the
air boxes, ram fingers and ash extractor screw.
Figure 15 illustrates a close-up cross sectional view of Figure 14 detailing
the air boxes,
ram fingers, ash extractor screw and serrated edge of step C.
Figure 16 is a sectional view of the gasifier of Figures 11 to 12 detailing
the refractory.
Figure 17 details the air box assembly of Step A and B of the gasifier
illustrated in
Figures 11 to 16.
Figure 18 illustrates a cross sectional view of the Step C air box of the
gasifier illustrated
in Figures 11 to 16.
Figure 19 illustrates a side view of the outside of the gasifier of Figures 11
to 16 detailing
the Step C air box and ash screw extrator.
Figure 20 illustrates a cross sectional view of the gasifier of Figures 11 to
16 detailing an
air box.
Figure 21 illustrates a cross sectional view of the gasifier of Figures 11 to
16 detailing the
sealing of the upstream edge of the air box with a resilient sheet sealing
between the
carrier ram and the air box top plate.
Figure 22 details the dust seal of the multiple-finger carrier ram of the
gasifier illustrated
in Figures 11 to 16.
Figure 23 showing the dust removal system of one embodiment of the gasifier
illustrated
in Figures 11 to 16 detailing the dust pusher, dust can attachment, shutter,
operator
handle and chain mechanism.
8
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Figure 24 details the ram enclosure of the gasifier illustrated in Figures 11
to 16 detailing
a portion the lateral transfer unit structure.
Figure 25 details the multiple-finger carrier ram setup at Step 1 of the
gasifier illustrated
in Figures 11 to 16.
Figure 26 is an illustration detailing the level switch locations in one
embodiment of the
invention.
Figure 27 is an illustration detailing two reactant material pile profiles for
the gasifier of
Example 2, according to an embodiment of the invention.
Figure 28 is an illustration of the thermocouple for an embodiment of the
invention,
detailing the deflector.
Figure 29 is an illustration of the gasifier of Example 2 coupled to a gas
reformulating
chamber.
Figure 30 is an alternative view of the gasifier of Example 2 coupled to a gas
reformulating chamber.
Figure 31 is a cross sectional view of the gasifier of Example 2 coupled to a
gas
reformulating chamber detailing one plasma torch.
Figure 32 is schematic showing the converter of Figures 29 to 31 incorporated
into power
plant.
DETAILED DESCRIPTION OF THE INVENTION
9
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Definitions
As used herein, the term "sensing element" is defined to describe any element
of the
system configured to sense a characteristic of a process, a process device, a
process input
or process output, wherein such characteristic may be represented by a
characteristic
value useable in monitoring, regulating and/or controlling one or more local,
regional
and/or global processes of the system. Sensing elements considered within the
context of
a gasification system may include, but are not limited to, sensors, detectors,
monitors,
analyzers or any combination thereof for the sensing of process, fluid and/or
material
temperature, pressure, flow, composition and/or other such characteristics, as
well as
material position and/or disposition at any given point within the system and
any
operating characteristic of any process device used within the system. It will
be
appreciated by the person of ordinary skill in the art that the above examples
of sensing
elements, though each relevant within the context of a gasification system,
may not be
specifically relevant within the context of the present disclosure, and as
such, elements
identified herein as sensing elements should not be limited and/or
inappropriately
construed in light of these examples.
As used herein, the term "response element" is defined to describe any element
of the
system configured to respond to a sensed characteristic in order to operate a
process
device operatively associated therewith in accordance with one or more pre-
determined,
computed, fixed and/or adjustable control parameters, wherein the one or more
control
parameters are defined to provide a desired process result. Response elements
considered
within the context of a gasification system may include, but are not limited
to static, pre-
set and/or dynamically variable drivers, power sources, and any other element
configurable to impart an action, which may be mechanical, electrical,
magnetic,
pneumatic, hydraulic or a combination thereof, to a device based on one or
more control
parameters. Process devices considered within the context of a gasification
system, and to
which one or more response elements may be operatively coupled, may include,
but are
not limited to, material and/or feedstrock input means, heat sources such as
plasma heat
sources, additive input means, various gas blowers and/or other such gas
circulation
devices, various gas flow and/or pressure regulators, and other process
devices operable
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
to affect any local, regional and/or global process within a gasification
system. It will be
appreciated by the person of ordinary skill in the art that the above examples
of response
elements, though each relevant within the context of a gasification system,
may not be
specifically relevant within the context of the present disclosure, and as
such, elements
identified herein as response elements should not be limited and/or
inappropriately
construed in light of these examples.
As used herein, the term, "reactant material" can mean feedstock, including
but not
limited to partially or fully processed feedstock.
As used herein, the term "(carbonaceous) feedstock" can be any carbonaceous
material
appropriate for gasifying in the present gasification process, and can
include, but ia not
limited to, any waste materials, coal (including low grade, high sulfur coal
not suitable
for use in coal-fired power generators), petroleum coke, heavy oils, biomass,
sewage
sludge, sludge from pulp and paper mills and agricultural wastes. Waste
materials
suitable for gasification include both hazardous and non-hazardous wastes,
such as
municipal waste, wastes produced by industrial activity (paint sludges, off-
spec paint
products, spent sorbents), automobile fluff, used tires and biomedical wastes,
any
carbonaceous material inappropriate for recycling, including non-recyclable
plastics,
sewage sludge, coal, heavy oils, petroleum coke, heavy refinery residuals,
refinery
wastes, hydrocarbon contaminated solid waste and biomass, agricultural wastes,
tires,
hazardous waste, industrial waste and biomass. Examples of biomass useful for
gasification include, but are not limited to, waste or fresh wood, remains
from fruit,
vegetable and grain processing, paper mill residues, straw, grass, and manure.
As used herein, the term, "input" denotes that which is about to enter or be
communicated to any system or component thereof, is currently entering or
being
communicated to any system or component thereof, or has previously entered or
been
communicated to any system or component thereof. An input includes, but is not
limited
to, compositions of matter, information, data, and signals, or any combination
thereof. In
respect of a composition of matter, an input may include, but is not limited
to, influent(s),
11
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
reactant(s), reagent(s), fuel(s), object(s) or any combinations thereof. In
respect of
information, an input may include, but is not limited to, specifications and
operating
parameters of a system. In respect of data, an input may include, but is not
limited to,
result(s), measurement(s), observation(s), description(s), statistic(s), or
any combination
thereof generated or collected from a system. In respect of a signal, an input
may include,
but is not limited to, pneumatic, electrical, audio, light (visual and non-
visual),
mechanical or any combination thereof. An input may be defined in terms of the
system,
or component thereof, to which it is about to enter or be communicated to, is
currently
entering or being communicated to, or has previously entered or been
communicated to,
such that an input for a given system or component of a system may also be an
Output in
respect of another system or component of a system. Input can also denote the
action or
process of entering or communicating with a system.
As used herein, the term "output" denotes that which is about to exit or be
communicated
from any system or component thereof, is currently exiting or being
communicated from
any system or component thereof, or has previously exited or been communicated
from
any system or component thereof. An output includes, but is not limited to,
compositions
of matter, information, data, and signals, or any combination thereof. In
respect of a
composition of matter, an output may include, but is not limited to,
effluent(s), reaction
product(s), process waste(s), fuel(s), object(s) or any combinations thereof.
In respect of
information, an output may include, but is not limited to, specifications and
operating
parameters of a system. In respect of data, an output may include, but is not
limited to,
result(s), measurement(s), observation(s), description(s), statistic(s), or
any combination
thereof generated or collected from a system. In respect of a signal, an
output may
include, but is not limited to, pneumatic, electrical, audio, light (visual
and non-visual),
mechanical or any combination thereof. An output may be defined in terms of
the system,
or component thereof, to which it is about to exit or be communicated from,
currently
exiting or being communicated from, or has previously exited or been
communicated
from, such that an output for a given system or component of a system may also
be an
input in respect of another system or component of a system. Output can also
denote the
action or process of exiting or communicating with a system.
12
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Overview of the System
Referring to Figure 1, this invention provides a horizontally-oriented
gasifier (2000)
having one or more feedstock input(s) (2004), one or more gas outlet(s) (2006)
and a
solid residue (ash) outlet (2008). Material enters the gasifier (2000) via the
one or more
feedstock input(s) (2004) and is moved through the gasifier (2000) during
processing by
one or more lateral transfer units (2010) which is controlled by a control
system.
The invention provides a horizontally-oriented gasifier (2000) comprising a
lateral
transfer system to facilitate the extraction of gaseous molecules from
carbonaceous
feedstock. In particular, the invention provides a gasifier in which the
gasification
process is facilitated by sequentially promoting drying, volatilization and
char-to-ash
conversion (carbon conversion). This is accomplished by allowing drying to
occur at a
certain temperature range prior to moving the material to another region and
allowing
volatilization to occur at another temperature range, prior to moving the
material to
another region and allowing char-to-ash conversion to occur at another
temperature
range. Accordingly, as the material in the gasifier is moved from the feed
area towards
the solid residue end by one or more lateral transfer units (2010) it goes
through different
degrees of drying, volatization and char-to-ash conversion (carbon
conversion).
To facilitate movement of reactant material, the individual lateral transfer
units (2010)
can be controlled independently or a group of two or more lateral transfer
units (2010)
can be controlled in a coordinated manner.
Thus, each area in the horizontally-oriented gasifier experiences temperature
ranges and
optional process additives (2019) (such as air, oxygen and/or steam) that
promote a
certain stage of the gasification process. In a pile of reactant material, all
stages of
gasification are occurring concurrently, however individual stages are favored
at a certain
temperature range.
13
CA 02651352 2012-01-19
By physically moving the material through the gasifier, the gasification
process can be
facilitated by allowing as much drying as energetically efficient to occur
prior to raising
the temperature of the material to promote volatilization. The process then
seeks to allow
as much volatilization as energetically efficient to occur prior to raising
the temperature
of the material to promote char-to-ash conversion (carbon conversion).
As illustrated in Figures 2 and 3, the horizontal expansion of the
gasification process
achieved by use of the invention facilitates the gasification process by
regionally
promoting one or more of the stages (drying, volatization and char-to-ash
conversion) of
the gasification process in response to the characteristics of the reactant
material at that
particular location in the gasifier.
Theoretically, the conditions in the gasifier at any location could be
optimized in
response to the character of the reactant material at that particular
location. A practical
embodiment of this concept, however, is to segregate the gasifier into a
finite number of
regions optimized in response to the general or average reactant material
characteristics
of a larger area. For example, the gasifier could therefore be segregated into
two, three,
four or more regions depending on the characteristics of the feedstock. To
facilitate
understanding, the discussion below describes segregating the gasifier into
three regions.
The invention, however, is not limited to a gasifier having three regions.
Although as discussed above the processes of gasification are occurring in a
continuous
and concurrent manner throughout the gasifier, the gasifier can be notionally
divided into
regions. In the three region embodiment:
Region I: Promotes Drying of the Material
Referring to Figure 3, Region I would be the area between lines 310 and 320.
Feedstock
is delivered into the gasifier at Region I. The normal temperature range for
this region
(as measured at the bottom of the material pile) lies between about 300 and
900 C. The
major process here is that of drying which occurs predominantly at the top and
in middle
14
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
of the pile of material and at a temperature above about 100 C. In addition,
some
volatilization and some char-to-ash conversion (carbon conversion) occurs in
this region.
Region II: Promotes Volatilization of the Material
Referring to Figure 3, Region II would be the region between lines 320 and
330. The
material pile has a bottom temperature range between about 400 and 950 C. The
main
process occurring in Region II is that of volatilization with the remainder of
the drying
operation as well as a substantial amount of char to ash conversion (carbon
conversion).
Region III: Char-to-Ash Conversion (Carbon Conversion)
Referring to Figure 3, Region III would be the region between lines 330 and
340. The
Region III temperature range lies between about 500 and 1000 C. Although, in
one
embodiment in order to avoid agglomeration of the ash, the maximum temperature
in this
region does not exceed about 950 C. The major process in Region III is that of
carbon
conversion with a lesser amount (the remainder) of volatilization. By this
time the
moisture from the reactant material has been removed. By the end of this
region, the
majority of the solid residue is ash.
In one embodiment, the ash from Region III is translocated into an ash
collection
chamber. Appropriate ash collection chambers are known in the art and
accordingly, a
worker skilled in the art having regard to the requirements of the system
would readily
know the size, shape and manufacture of an appropriate ash collection chamber.
In one embodiment, the ash will be translocated into a water tank for cooling,
from which
the gasifier residue is transmitted through a conduit, optionally, under
control of a valve,
to a point of discharge.
In one embodiment, the ash is translocated into a solid residue conditioning
conversion
chamber for the conversion of ash-to-slag.
15
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Horizontally-oriented Gasifier
Referring now to Figure 1, the gasifier (2000) comprises a horizontally-
oriented
gasification chamber (2002) having a feedstock input (2004), gas outlet (2006)
and ash
(solid residue) outlet (2008). The gasifier further comprises a lateral
transfer system
having one or more lateral transfer units (2010) for transporting solid
material through
the gasification chamber.
In one embodiment, the number of lateral transfer units in a particular
gasifier is
dependent on the path length reactant material must travel and the distance
reactant
material can be moved by each lateral transfer unit and is a compromise
between
minimizing the magnitude of process disturbances caused by each discrete
transfer and
mechanical complexity, cost, and reliability.
During processing, feedstock is introduced into the chamber (2002) at one end;
hereafter
referred to as the feed end, through the feedstock input (2004) and is
transported from the
feed end through the various regions in the gasification chamber towards the
ash (solid
residue) outlet (2008) or ash end. As the feed material progresses through the
chamber, it
loses its mass and volume as its volatile fraction is volatilized to form off-
gas and the
resulting char is reacted to form additional off-gas and ash.
Due to this progressive conversion, the height of the material (pile height)
decreases from
the feed end to the ash end of the chamber and levels off when only solid
residue (ash)
remains.
In one embodiment, the off-gas escapes through the gas outlet (2006) into, for
example, a
gas refinement chamber where it can undergo further processing including
plasma heat-
dependent processing or into a storage chamber or tank. The solid residue
(ash) is
transported through the ash outlet (2008) to, for example, an ash collection
chamber or a
solid residue conditioning chamber for further processing.
16
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
In one embodiment, the gasifier has a stepped floor having a plurality of
floor levels or
steps. Optionally, each floor level is sloped. In one embodiment the floor
level is sloped
between about 5 and about 10 degrees.
In one embodiment of the step-floor gasifier, the individual steps (floor
levels) correlate,
at least in part, with the individual regions discussed above, with each
region or step
having conditions optimized for different degrees of drying, volatilization
and carbon
conversion. For convenience, the uppermost step will be referred to as step A;
the next
step will be referred to as step B, etc. Corresponding lateral transfer units
will be
identified with the same letter, i.e. lateral transfer unit A or ram A
services step A, lateral
transfer unit B or ram B services step B.
In the three step embodiment, there is an upper step or step A (2012), middle
step or step
B (2014) and a lower step or step C (2016).
The feedstock is fed onto the upper step (step A) (2012). The normal
temperature range
for this step (as measured at the bottom of the material pile) lies between
300 and 900 C.
Step B is designed to have a bottom temperature range between 400 and 950 C to
promote volatilization with the remainder of the drying operation as well as a
substantial
amount of char-to-ash conversion (carbon conversion).
Step C temperature range lies between 500 and 1000 C. The major process in
Step C is
that of char-to-ash conversion (carbon conversion) with a lesser amount (the
remainder)
of volatilization.
In one embodiment, movement over the steps is facilitated by the lateral
transfer system
with each step optionally being serviced by an independently controlled
lateral transfer
unit.
17
CA 02651352 2012-01-19
Design Considerations for the Chamber
The chamber of a gasifier is designed to provide a sealed, insulated space for
processing
of the feedstock into off-gas and to allow for passage of off-gas to
downstream process
such as cooling or refining or other and optionally for removal of ash for
subsequent
further processing. Such processing of the feedstock is facilitated by a
design that
promotes the introduction of process additives, such as hot air and/or steam,
into the
reactant material throughout the gasifier and enables control of the pile
height of the
reactant material and its movement through the gasifier without disruption or
bridging.
The design may optionally provide for access to the interior of the gasifier
for inspection,
maintenance and repair.
A gasifier is designed to accomplish extraction of volatile compounds from the
carbonaceous feedstock. Thus, factors such as heat transfer, gas flow, mixing
of process
additives, among others, can be taken into account when designing the shape of
the
gasifier. The use of computer modeling can facilitate the optimization of
gasifier design.
Appropriate computer modeling systems and simulators are known in the art and
include
the Chemical Process Simulator as detailed in U.S. Patent 6,817,388.
In one embodiment, in addition to using the Chemical Process Simulator, flow
modeling
of the gasifier can be performed to ensure proper mixing of process inputs,
and to ensure
that kinetic effects are not significant.
The physical design characteristics of the gasifier are determined by a number
of factors.
These factors include, for example, the chemical composition and physical
characteristics
of the feedstock to be processed including moisture content, particle size,
hardness and
flow characteristics; system throughput; required conversion efficiency
(residence time);
desired gasifier geometry (Lid ratio); material transport characteristics;
mixing
characteristics (solid and gas); gas superficial velocity and additive
distribution among
others. The internal configuration and size of the gasification chamber are
dictated, in
18
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
part, by the operational characteristics through analyses of the input waste
stream to be
processed.
As discussed above, the feedstock is introduced into the gasifier via the
feedstock input
(2004) and moves through the gasification chamber during processing. This
movement is
achieved, wholly or in part, by the use of a lateral transfer system.
In one embodiment, to facilitate reactant material transfer, when designing
the gasifier
the dynamics of reactant material transfer through the gasifier can be
considered such that
the risk of bridging, obstruction of reactant material flow by various
instrumentations or
by resistance from downstream reactant material or by wall friction can be
reduced or
eliminated.
During processing, air as a source of oxygen is introduced into the chamber.
Optionally,
the method of injecting air can be selected to facilitate an even flow of air
into the
gasification chamber, prevent hot spot formation and/or improve temperature
control.
The air can be introduced through the sides of the chamber, optionally from
near the
bottom of the chamber, or can be introduced through the floor of the chamber,
or through
both.
Also to be considered in the design of the gasifier is the position,
orientation and number
of the process additive inputs. The process additives can optionally be
injected into the
gasifier at locations where they will ensure most efficient reaction to
achieve the desired
conversion result.
In one embodiment, the floor of the gasification chamber is perforated to
varying degrees
to allow for introduction of process additives, such as air at the base of the
material pile.
In one embodiment, the side-walls of the chamber slope inwards towards the
bottom to
achieve a small enough width for good air penetration from the sides while
still having
19
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
the required volume of material. The slope angle can optionally be made steep
enough to
assure that the material will drop towards the bottom of the chamber during
processing.
In one embodiment, the gasification chamber is a steel weldment with
connection
features for feedstock input, air and steam input, gas output and ash removal.
In one embodiment, the gasification chamber is tubular.
In one embodiment, the roof or upper portion of the gasification chamber is
designed to
optimize flow and residence time of gas throughout the gasification chamber.
The roof
portion can be flat, domed, half-cylindrical or another practical
configuration that
promotes the flow of gas through the gasification chamber.
In one embodiment, the gasification chamber of the invention is a horizontal
vessel with
its cross-section optionally including a semi-circular dome or arched roof and
optionally
with a tapered lower section.
Materials
The gasification chamber is a partially or fully refractory-lined chamber with
an internal
volume sized to accommodate the appropriate amount of material for the
required solids
residence time. The refractory protects the gasification chamber from the high
temperature and corrosive gases and minimizes unnecessary loss of heat from
the
process. The refractory material can be a conventional refractory material
well-known to
those skilled in the art and which is suitable for use for a high temperature
e.g. up to
about 1100 C, un-pressurized reaction. When choosing a refractory system
factors to be
considered include internal temperature, abrasion; erosion and corrosion;
desired heat
conservation/limitation of temperature of the external vessel; desired life of
the
refractory. Examples of appropriate refractory material include high
temperature fired
ceramics, i.e., aluminum oxide, aluminum nitride, aluminum silicate boron
nitride,
zirconium phosphate, glass ceramics and high alumina brick containing
principally,
silica, alumina, chromia and titania. To further protect the gasification
chamber from
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
corrosive gases the chamber is, optionally, partially or fully lined with a
protective
membrane. Such membranes are known in the art and, as such, a worker skilled
in the art
would readily be able to identify appropriate membranes based on the
requirements of the
system and, for example, include Sauereisen High Temperature Membrane No 49.
In one embodiment, the refractory is a multilayer design with a high density
layer on the
inside to resist the high temperature, abrasion, erosion and corrosion.
Outside the high
density material is a lower density material with lower resistance properties
but higher
insulation factor. Optionally, outside this layer is a very low density foam
board material
with very high insulation factor and can be used because it will not be
exposed to
abrasion of erosion. Appropriate materials for use in a multilayer refractory
are well
known in the art.
In one embodiment, the multilayer refractory comprises an internally oriented
chromia
layer; a middle alumina layer and an outer insboard layer.
The wall of the chamber can optionally incorporate supports for the refractory
lining or
refractory anchors. Appropriate refractory supports and anchors are known in
the art.
Lateral transfer system
Design Objectives
Material is moved through the gasification chamber in order to promote
specific stages of
the gasification process (drying, volatilization, char-to-ash conversion). To
facilitate
control of the gasification process, material movement through the
gasification chamber
can be varied (variable movement) depending on process requirements. This
lateral
movement of material through the gasifier is achieved via the use of a lateral
transfer
system comprising one or more lateral transfer units. Movement of reactant
material by
the lateral transfer system can be optimized by varying the movement speed,
the distance
a lateral transfer unit moves and the when multiple lateral transfer units are
used, the
sequence in which the plurality of lateral transfer units are moved in
relation to each
21
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
other. The one or more lateral transfer units can act in a coordinated manner
or
individual lateral transfer units can act independently. In order to
facilitate control of the
material flow rate and pile height the individual lateral transfer units can
be moved
individually, at varying speeds, at varying movement distances, at varying
frequency of
movement.
By strictly regulating the movement of the one or more lateral transfer units,
the reactant
pile can obtain the desired profile such that both wall friction and back
pressure imposed
by reactant material sitting on downstream stages is reduced or eliminated.
The lateral transfer system must be able to effectively operate in the harsh
conditions of
the gasifier and in particular must be able to operate at high temperatures.
Moreover, the
high temperature environment and abrasive nature of the feedstock demands that
the
lateral transfer system be robust.
In embodiments in which the hot air is supplied through the floor of the
gasifier, the
lateral transfer design can be a compromise between assurance of motion versus
degradation of processing by blocking air-flow.
Lateral Transfer Units
The individual lateral transfer units comprise a moving element and a guiding
element or
alignment element. It would be apparent to a worker skilled in the art that
the moving
element can be equipped with appropriate guide engagement elements.
The moving element can include, but is not limited to, a shelf / platform,
pusher ram or
carrier rams, plow, screw element, conveyor or a belt. The rams can include a
single ram
or multiple-finger ram.
In one embodiment, the gasifier design will allow for the use of a single ram
or multiple-
finger ram.
22
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
In one embodiment, a multiple-finger ram is used when minimum interference
with gas
flows is desirable during operation of the rams.
In the multiple-finger ram designs, the multiple-finger ram may be a unitary
structure or a
structure in which the ram fingers are attached to a ram body, with individual
ram fingers
optionally being of different widths depending on location. The gap between
the fingers
in the multiple-finger ram design is selected to avoid particles of reactant
material from
bridging.
In one embodiment, the individual fingers are about 2 to about 3 inches wide,
about 0.5
to about 1 inch thick with a gap between about 0.5 to about 2 inches wide.
In one embodiment, the moving element is "T-shaped".
In certain embodiments in which the system operates at very high temperatures,
cooling
can optionally be provided for the moving elements. In one embodiment using a
ram or
shelf, cooling within the ram or shelf can be provided. Such cooling could be
by fluid
(for example, air or water) circulated inside the ram or shelf from outside of
the chamber.
In one embodiment, the plow has folding arms which can be withdrawn when the
plow is
retracted.
In one embodiment, the conveyor is a belt or flighted chain conveyor.
The moving element is constructed of material suitable for use at high
temperature. Such
materials are well-known to those skilled in the art and can include stainless
steel, mild
steel, or mild steel partially protected with or fully protected with
refractory.
23
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
The guide elements can be located in the interior of the gasifier or be
internally mounted.
Alternatively, the guide elements can be located exterior to the gasifier or
be externally
mounted.
In embodiments in which the guide elements are interior or internal mounted,
the lateral
transfer system can be designed to prevent jamming or debris entrapment.
In embodiments in which the guide elements are located exterior to the
gasifier or are
externally mounted, the gasifier includes at least one sealable opening
through which the
moving element can enter the gasification chamber.
The guide element can include one or more guide channels located in the side
walls of the
gasifier, guide tracks or rails, guide trough or guide chains.
The guide engagement members can optionally include one or more wheels or
rollers
sized to movably engage the guide element. In one embodiment, the guide
engagement
member is a sliding member comprising a shoe adapted to slide along the length
of the
guide track. Optionally, the shoe further comprises at least one replaceable
wear pad.
In one embodiment, the lateral location of the moving element is provided only
at the
point at which the moving element enters the gasification chamber, with
alignment
elements ensuring that the moving element is held angularly aligned at all
times thereby
eliminating the need for complex, accurate guide mechanisms.
In one embodiment, the alignment element is two chains driven synchronously by
a
common shaft. The chains are optionally individually adjustable to facilitate
proper
alignment.
In one embodiment, the lateral transfer system can be a movable shelf /
platform in which
material is predominantly moved through the gasifier by sitting on top of the
shelf /
24
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
platform. A fraction of material may also be pushed by the leading edge of the
movable
shelf / platform.
In one embodiment, the lateral transfer system can be a carrier ram in which
material is
predominantly moved through the gasifier by sitting on top of the carrier ram.
A fraction
of material may also be pushed by the leading edge of the carrier ram.
In one embodiment, the lateral transfer system can be a pusher ram in which
material is
predominantly pushed through the gasifier. Optionally, the ram height is
substantially the
same as the depth of the material to be moved.
In one embodiment, the lateral transfer system can be a set of conveyor
screws.
Optionally, the conveyor screws can be set in the floor of the chamber thereby
allowing
material to be moved without interfering with air introduction.
Power to propel the lateral transfer system is provided by a motor and drive
system and is
controlled by actuators.
The individual lateral transfer units may optionally by powered by dedicated
motor and
have individual actuators or one or more lateral transfer units may be powered
by a single
motor and shared actuators.
Basically any controllable motor or mechanical turning device that can provide
accurate
control of the lateral transfer system can be used to propel the lateral
transfer system.
Appropriate motors and devices are known in the art and include electric
motors, motors
run on syngas, steam, gases, gasoline, diesel or micro turbines.
In one embodiment, the motor is an electric variable speed motor which drives
a motor
output shaft selectably in the forward or reverse directions. Optionally, a
slip clutch
could be provided between the motor and the motor output shaft. The motor may
further
comprise a gear box.
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Movement of the lateral transfer system can be effected by a hydraulic system,
hydraulic
rams, chain and sprocket drive, or a rack and pinion drive. These methods of
translating
the motor rotary motion into linear motion have the advantage that they can be
applied in
a synchronized manner at each side of a unit to assist in keeping the unit
aligned and thus
minimizing the possibility of the mechanism jamming.
In one embodiment, the use of two chains per ram keep the rams angularly
aligned
without the need for precision guides.
The externally mounted portions or components of the lateral transfer unit is
optionally
housed in an unsealed, partially sealed or sealed enclosure or casing. The
enclosure may
further comprise a removable cover to allow for maintenance. In one
embodiment, the
enclosure may have a higher internal pressure than the interior of the
gasification
chamber; this may be achieved by the use of nitrogen.
Chamber Heating System
The gasification process requires heat. Heat addition can occur directly by
partial
oxidation of the feedstock or indirectly by the use of one or more heat
sources know in
the art.
In one embodiment, the heat source can be circulating hot air. The hot air can
be
supplied from, for example, air boxes, air heaters or heat exchangers, all of
which are
known in the art.
In one embodiment, hot air is provided to each level by independent air feed
and
distribution systems. Appropriate air feed and distribution systems are known
in the art
and include separate air boxes for each step level from which hot air can pass
through
perforations in the floor of each step level to that step level or via
independently
controlled spargers for each step level.
26
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
In one embodiment, each floor level has one or more grooves running the length
of
individual steps. The grooves being sized to accommodate hot air and/or steam
pipes.
The pipes optionally being perforated on their lower third to half to
facilitate the uniform
distribution of hot air or steam over the length of the step. Alternatively,
the sparger pipes
can be perforated towards the top of the pipes.
In one embodiment, the heat source can be circulating hot sand.
In one embodiment, the heat source can be an electrical heater or electrical
heating
elements.
In order to facilitate initial start up of the gasifier, the gasifier can
include access ports
sized to accommodate various conventional burners, for example natural gas,
oil/gas or
propane burners, to pre-heat the chamber. Also, wood/biomass sources, engine
exhausts,
electric heaters could be used to preheat the chamber.
Process Additive Inputs
Process additives may optionally be added to the gasifier to facilitate
efficient conversion
of feedstock into specified gases. Steam input can be used to ensure
sufficient free
oxygen and hydrogen to maximize the conversion of decomposed elements of the
input
feedstock into product gas and/or non-hazardous compounds. Air input can be
used to
assist 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 cost of input heat.
Optionally, other additives may be used to optimize the process and thereby
improve
emissions.
The invention, therefore, can include one or more process additive inputs.
These include
inputs for steam injection and/or air injection. The steam inputs can be
strategically
located to direct steam into high temperature regions and into the product gas
mass just
27
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
prior to its exit from the gasifier. The air inputs can be strategically
located in and around
the gasifier chamber to ensure full coverage of process additives into the
processing zone.
In one embodiment, the process additive inputs are located proximal to the
floor of the
gasifier.
In one embodiment, the process additive inputs located proximal to the floor
are half-pipe
air spargers trenched into the refractory floor. Such air spargers may be
designed to
facilitate replacement, servicing or modification while minimizing
interference with the
lateral transfer of reactant material. The number, diameter and placement of
the air holes
in the air spargers can be varied according to system requirements or lateral
transfer
system design.
In one embodiment, the process additive inputs are located in the floor of the
gasifier.
Such process additive inputs are designed to minimize plugging by fine
particles or be
equipped with an attachment to prevent plugging. Optionally, the process
additive inputs
can include a pattern of holes through which process additives can be added.
Various
patterns of holes can be used depending on system requirements or lateral
transfer system
design. In choosing the pattern of the airholes, factors to consider include
avoiding high
velocity which would fluidize the bed, avoiding holes too close to gasifier
walls and ends
so that channeling of air along refractory wall is avoided, and ensuring
spacing between
holes was no more than approximately the nominal feed particle size (2") to
ensure
acceptable kinetics.
In one embodiment, airhole pattern is arranged such that operation of the
lateral transfer
unit does interfere with the air passing through the airholes.
In one embodiment in which a multiple-finger ram is used, the pattern of the
airholes is
such that when heated the airholes are between the fingers (in the gaps) and
are in arrow
pattern with an offset to each other. Alternatively, the airhole pattern can
also be hybrid
28
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
where some holes are not covered and others are covered, such that even
distribution of
air is maximized (ie. areas of floor with no air input at all are minimized).
In one embodiment, the pattern of holes facilitates the even distribution of
process
additives over a large surface area with minimal disruption or resistance to
lateral
material transfer.
In one embodiment, the process additive inputs provide diffuse, low velocity
input of
additives.
In embodiments in which hot air is used to heat the chamber additional
air/oxygen
injection inputs may optionally be provided.
Service Ports
In one embodiment, the gasification chamber can further comprise one or more
ports.
These ports can include service ports (2020) to allow for entry into the
chamber for
maintenance and repair. Such ports are known in the art and can include
sealable port
holes of various sizes.
In one embodiment, access to the inside of the gasifier is provided by a
manhole at one
end which can be closed by a sealable refractory lined cover during operation.
In one embodiment, further access is available by removing one or more air
boxes.
The gasifier can optionally include a flanged lower section which is connected
to a
flanged main section of the gasification chamber to facilitate opening of the
gasification
chamber for refractory inspection and repair.
Ash Removal System
29
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
The residual solids (ash) after gasification is complete can optionally be
removed from
the gasifier and passed to a handling system. The gasifier may therefore
optionally
include a controllable solids removal system to facilitate solid residue or
ash removal.
In one embodiment, the controllable solids removal system comprises a ram
mechanism
to push the ash out of the chamber.
In one embodiment, the controllable solids removal system consists of a system
of
conveying rams. Optionally, the length of the ram stroke can be controlled so
that the
amount of material fed into a solid residue processing chamber with each
stroke can be
controlled.
In a further embodiment of the invention, the controllable solids removal
system may
comprise of a controllable rotating arm mechanism.
As the material is processed and is moved from region to region in the
gasifier the heat
generated within the pile can cause melting which will result in agglomeration
of the ash.
Agglomerated ash has been shown to cause jamming in drop port type exits. The
invention therefore can optionally comprise a means for breaking up ash
agglomerates.
In one embodiment, in order to ensure that any agglomerations do not create
jamming at
the exit from the chamber, a screw conveyor concept is used to extract the ash
from the
gasifier. The ram motion will push the ash into the extractor and the
extractor will pull
the ash out of the gasifier and feed it into an ash conveyor system. Rotation
of the
extractor screw breaks up agglomerations before the ash is fed into the
conveyor system.
This breaking up action can be enhanced by having serrations on the edge of
the extractor
screw flights.
Control
30
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
In one embodiment of the present invention, a control system may be provided
to control
one or more processes implemented in, and/or by, the various systems and/or
subsystems
disclosed herein, and/or provide control of one or more process devices
contemplated
herein for affecting such processes. In general, the control system may
operatively
control various local and/or regional processes related to a given system,
subsystem or
component thereof, and/or related to one or more global processes implemented
within a
system, such as a gasification system, within or in cooperation with which the
various
embodiments of the present invention may be operated, and thereby adjusts
various
control parameters thereof adapted to affect these processes for a defined
result. Various
sensing elements and response elements may therefore be distributed throughout
the
controlled system(s), or in relation to one or more components thereof, and
used to
acquire various process, reactant and/or product characteristics, compare
these
characteristics to suitable ranges of such characteristics conducive to
achieving the
desired result, and respond by implementing changes in one or more of the
ongoing
processes via one or more controllable process devices.
The control system generally comprises, for example, one or more sensing
elements for
sensing one or more characteristics related to the system(s), processe(s)
implemented
therein, input(s) provided therefor, and/or output(s) generated thereby. One
or more
computing platforms are communicatively linked to these sensing elements for
accessing
a characteristic value representative of the sensed characteristic(s), and
configured to
compare the characteristic value(s) with a predetermined range of such values
defined to
characterise these characteristics as suitable for selected operational and/or
downstream
results, and compute one or more process control parameters conducive to
maintaining
the characteristic value with this predetermined range. A plurality of
response elements
may thus be operatively linked to one or more process devices operable to
affect the
system, process, input and/or output and thereby adjust the sensed
characteristic, and
communicatively linked to the computing platform(s) for accessing the computed
process
control parameter(s) and operating the process device(s) in accordance
therewith.
31
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
In one embodiment, the control system provides a feedback, feedforward and/or
predictive control of various systems, processes, inputs and/or outputs
related to the
conversion of carbonaceous feedstock into a gas, so to promote an efficiency
of one or
more processes implemented in relation thereto. For instance, various process
characteristics may be evaluated and controllably adjusted to influence these
processes,
which may include, but are not limited to, the heating value and/or
composition of the
feedstock, the characteristics of the product gas (e.g. heating value,
temperature, pressure,
flow, composition, carbon content, etc.), the degree of variation allowed for
such
characteristics, and the cost of the inputs versus the value of the outputs.
Continuous
and/or real-time adjustments to various control parameters, which may include,
but are
not limited to, heat source power, additive feed rate(s) (e.g. oxygen,
oxidants, steam,
etc.), feedstock feed rate(s) (e.g. one or more distinct and/or mixed feeds),
gas and/or
system pressure/flow regulators (e.g. blowers, relief and/or control valves,
flares, etc.),
and the like, can be executed in a manner whereby one or more process-related
characteristics are assessed and optimized according to design and/or
downstream
specifications.
Alternatively, or in addition thereto, the control system may be configured to
monitor
operation of the various components of a given system for assuring proper
operation, and
optionally, for ensuring that the process(es) implemented thereby are within
regulatory
standards, when such standards apply.
In accordance with one embodiment, the control system may further be used in
monitoring and controlling the total energetic impact of a given system. For
instance, a a
given system may be operated such that an energetic impact thereof is reduced,
or again
minimized, for example, by optimising one or more of the processes implemented
thereby, or again by increasing the recuperation of energy (e.g. waste heat)
generated by
these processes. Alternatively, or in addition thereto, the control system may
be
configured to adjust a composition and/or other characteristics (e.g.
temperature,
pressure, flow, etc.) of a product gas generated via the controlled
process(es) such that
such characteristics are not only suitable for downstream use, but also
substantially
32
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
optimised for efficient and/or optimal use. For example, in an embodiment
where the
product gas is used for driving a gas engine of a given type for the
production of
electricity, the characteristics of the product gas may be adjusted such that
these
characteristics are best matched to optimal input characteristics for such
engines.
In one embodiment, the control system may be configured to adjust a given
process such
that limitations or performance guidelines with regards to reactant and/or
product
residence times in various components, or with respect to various processes of
the overall
process are met and/or optimised for. For example, an upstream process rate
may be
controlled so to substantially match one or more subsequent downstream
processes.
In addition, the control system may, in various embodiments, be adapted for
the
sequential and/or simultaneous control of various aspects of a given process
in a
continuous and/or real time manner.
In general, the control system may comprise any type of control system
architecture
suitable for the application at hand. For example, the control system may
comprise a
substantially centralized control system, a distributed control system, or a
combination
thereof. A centralized control system will generally comprise a central
controller
configured to communicate with various local and/or remote sensing devices and
response elements configured to respectively sense various characteristics
relevant to the
controlled process, and respond thereto via one or more controllable process
devices
adapted to directly or indirectly affect the controlled process. Using a
centralized
architecture, most computations are implemented centrally via a centralized
processor or
processors, such that most of the necessary hardware and/or software for
implementing
control of the process is located in a same location.
A distributed control system will generally comprise two or more distributed
controllers
which may each communicate with respective sensing and response elements for
monitoring local and/or regional characteristics, and respond thereto via
local and/or
regional process devices configured to affect a local process or sub-process.
33
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Communication may also take place between distributed controllers via various
network
configurations, wherein a characteristics sensed via a first controller may be
communicated to a second controller for response thereat, wherein such distal
response
may have an impact on the characteristic sensed at the first location. For
example, a
characteristic of a downstream product gas may be sensed by a downstream
monitoring
device, and adjusted by adjusting a control parameter associated with the
converter that is
controlled by an upstream controller. In a distributed architecture, control
hardware
and/or software is also distributed between controllers, wherein a same but
modularly
configured control scheme may be implemented on each controller, or various
cooperative modular control schemes may be implemented on respective
controllers.
Alternatively, the control system may be subdivided into separate yet
communicatively
linked local, regional and/or global control subsystems. Such an architecture
could allow
a given process, or series of interrelated processes to take place and be
controlled locally
with minimal interaction with other local control subsystems. A global master
control
system could then communicate with each respective local control subsystems to
direct
necessary adjustments to local processes for a global result.
The control system of the present invention may use any of the above
architectures, or
any other architecture commonly known in the art, which are considered to be
within the
general scope and nature of the present disclosure. For instance, processes
controlled and
implemented within the context of the present invention may be controlled in a
dedicated
local environment, with optional external communication to any central and/or
remote
control system used for related upstream or downstream processes, when
applicable.
Alternatively, the control system may comprise a sub-component of a regional
an/or
global control system designed to cooperatively control a regional and/or
global process.
For instance, a modular control system may be designed such that control
modules
interactively control various sub-components of a system, while providing for
inter-
modular communications as needed for regional and/or global control.
34
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
The control system generally comprises one or more central, networked and/or
distributed processors, one or more inputs for receiving current sensed
characteristics
from the various sensing elements, and one or more outputs for communicating
new or
updated control parameters to the various response elements. The one or more
computing
platforms of the control system may also comprise one or more local and/or
remote
computer readable media (e.g. ROM, RAM, removable media, local and/or network
access media, etc.) for storing therein various predetermined and/or
readjusted control
parameters, set or preferred system and process characteristic operating
ranges, system
monitoring and control software, operational data, and the like. Optionally,
the
computing platforms may also have access, either directly or via various data
storage
devices, to process simulation data and/or system parameter optimization and
modeling
means. Also, the computing platforms may be equipped with one or more optional
graphical user interfaces and input peripherals for providing managerial
access to the
control system (system upgrades, maintenance, modification, adaptation to new
system
modules and/or equipment, etc.), as well as various optional output
peripherals for
communicating data and information with external sources (e.g. modem, network
connection, printer, etc.).
The processing system and any one of the sub-processing systems can comprise
exclusively hardware or any combination of hardware and software. Any of the
sub-
proces sing systems can comprise any combination of none or more proportional
(P),
integral (I) or differential (D) controllers, for example, a P-controller, an
I-controller, a
PI-controller, a PD controller, a PID controller etc. It will be apparent to a
person skilled
in the art that the ideal choice of combinations of P, I, and D controllers
depends on the
dynamics and delay time of the part of the reaction process of the
gasification system and
the range of operating conditions that the combination is intended to control,
and the
dynamics and delay time of the combination controller. It will be apparent to
a person
skilled in the art that these combinations can be implemented in an analog
hardwired
form which can continuously monitor, via sensing elements, the value of a
characteristic
and compare it with a specified value to influence a respective control
element to make
an adequate adjustment, via response elements, to reduce the difference
between the
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
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.
In corrective, or feedback, control the value of a control parameter or
control variable,
monitored via an appropriate sensing element, is compared to a specified value
or range.
A control signal is determined based on the deviation between the two values
and
provided to a control element in order to reduce the deviation. It will be
appreciated that a
conventional feedback or responsive control system may further be adapted to
comprise
an adaptive and/or predictive component, wherein response to a given condition
may be
tailored in accordance with modeled and/or previously monitored reactions to
provide a
reactive response to a sensed characteristic while limiting potential
overshoots in
compensatory action. For instance, acquired and/or historical data provided
for a given
system configuration may be used cooperatively to adjust a response to a
system and/or
process characteristic being sensed to be within a given range from an optimal
value for
which previous responses have been monitored and adjusted to provide a desired
result.
Such adaptive and/or predictive control schemes are well known in the art, and
as such,
are not considered to depart from the general scope and nature of the present
disclosure.
Control Elements
Sensing elements contemplated within the present context, as defined and
described
above, can include, but are not limited to, temperature sensing elements,
position sensors,
proximity sensors, pile height sensors and means for monitoring gas.
In one embodiment, the gasifier further comprises a temperature sensor array
comprising
one or more removable thermocouples. The thermocouples can be strategically
placed to
monitor temperature at points along each stage and at various heights at each
stage.
36
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Appropriate thermocouples are known in the art and include bare wire
thermocouples,
surface probes, thermocouple probes including grounded thermocouples,
ungrounded
thermocouples and exposed thermocouples or combinations thereof.
In one embodiment, individual thermocouples are inserted into the chamber via
a sealed
end tube (thermowell) which is then sealed to the vessel shell, allowing for
the use of
flexible wire thermocouples which are procured to be longer than the sealing
tube so that
the junction (the temperature sensing point) of the thermocouple is pressed
against the
end of the sealed tube to assure accurate and quick response to temperature
change (see
Figure 28).
Optionally, to prevent material from getting blocked by the thermocouple tube
the end of
the sealed tube cap can be fitted with a deflector. In one embodiment, the
deflector is a
square flat plate, with bent corners that contact the refractory and are in-
line with reactant
material flow to slip-stream particles over the thermowell (see Figure 28).
In addition, the invention may comprise devices for monitoring the exit of
gas. In one
embodiment this can include a gas composition monitor and gas flow meter.
By measuring process temperatures throughout the material pile, gas phase
temperatures
above the pile, and by measuring resultant off-gas flowrate and analyzing off-
gas
composition, the amount of air injected can be optimized to maximize
efficiency and
minimize undesirable process characteristics and products including slagging
of ash,
combustion, poor off-gas heating value, excessive particulate matter and
dioxin/furan
formation thereby meeting or bettering local emission standards. Such
measurements can
be taken during initial start-up or initially testing of the gasifier,
periodically or
continually during operation of the gasifier and may optionally be taken in
real time.
In one embodiment, the gasifier can optionally comprise a pressure sensor or
monitor
within the gasifier.
37
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
The gasifier can further comprise level switches or monitors to assess pile
height.
Appropriate level switches, sensors and monitors are known in the art. In one
embodiment, the level instrumentation comprises point-source level switches.
In one embodiment, the level switches are microwave devices with an emitter on
one side
of the chamber and a receiver on the other side, which detects either presence
or absence
of solid material at that point inside the gasification chamber.
A worker skilled in the art would readily be able to determine the appropriate
placement
of level switches, sensors and monitors such that the desired reactant
material pile profile
can be obtained.
In one embodiment, the gasifier further comprises proximity or position
sensors.
Response elements contemplated within the present context, as defined and
described
above, can include, but are not limited to, various control elements
operatively coupled to
process-related devices configured to affect a given process by adjustment of
a given
control parameter related thereto. For instance, process devices operable
within the
present context via one or more response elements, may include, but are not
limited to
elements controlling chamber heating, elements controlling process additives
and
elements controlling lateral transfer system movement.
Control System for the Lateral Transfer System
A level control system is required to maintain stable pile height inside the
gasifier. Stable
level control prevents fluidization of the reactant material from process air
injection
which could occur at low level and to prevent poor temperature distribution
through the
pile owing to restricted airflow that would occur at high level. Maintaining
stable level
also maintains consistent gasifier residence time by keeping the volume of
reacting
material constant.
38
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Optionally, a series of level switches in the gasifier measure pile depth. The
level
switches are optionally microwave devices with a emitter on one side of the
chamber and
a receiver on the other side, which detects either presence or absence of
solid material at
that point inside the gasifier.
The lateral transfer units move as necessary to ensure that pile height is
controlled at the
desired level. To accomplish this in embodiments in which the lateral transfer
units
comprise rams, the rams move in a series of programmed step of which there are
several
key control parameters including: specific ram movement sequence, ram speed,
ram
distance, and ram sequence frequency.
In general, rams move out to a set point distance, or until a controlling
level switch is
tripped; either at the same time or in a pre-determined sequence. The level
switch control
action can be based on a single switch, tripping either empty or full, or may
require
multiple switches tripping, empty or full, or any combination thereof.
Afterwards, the
rams move back to end the cycle, and the process is repeated. There is an
optional delay
between cycles as required by the process and residence time requirements of
the gasifier.
To ensure efficient movement of material in the stepped-floor embodiments, the
sequencing of lateral transfer unit movement can be optimized by starting at
the lowest
level of the gasifier, creating a pocket, then filling it from the step above
before the lateral
transfer unit's moving element is retracted to prevent pull back of the pile
and then
repeating up the steps.
In one embodiment, the ram sequencing comprises the lowest ram is extended
first; the
middle ram is then extended which pushes material down onto the lowest ram
filling the
void created by that rams movement; the lowest ram is then retracted; the
upper ram is
then extended filling the void at the back of the middle ram; the middle ram
is then
retracted; new material dropping from the feed port fills any void on the top
ram and the
top ram is retracted. Optionally, all of these motions can be controlled
automatically and
independently by the control system in response to system instrumentation
data.
39
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
In one three-step embodiment, the gasifier throughput is set by adjusting the
volumetric
feed rate into the gasifier. The level control system then controls the
lateral transfer
unit's moving elements as needed to control level of the pile on each step on
aim, which
includes controlling the rate of ash discharge from the gasifier.
In one three-step embodiment, the Step C lateral transfer unit's moving
element sets
gasifier throughput by moving a fixed length in relation to location indicator
or guide
point and frequency to discharge ash from the gasifier. The Step B lateral
transfer unit's
moving element follows and moves as far as necessary to translocate material
onto Step
C and change the Step C start-of-stage level switch state to "full". The Step
A lateral
transfer unit's moving element follows and moves as far as necessary to push
material
onto Step B and change the Step B start-of-stage level switch state to "full".
All lateral
transfer units' moving elements are then withdrawn simultaneously, and a
scheduled
delay can be executed before the entire sequence is repeated. Additional
configuration
may be used to limit the change in consecutive stroke lengths to less than
that called for
by the level switches to avoid excess lateral transfer unit-induced
disturbances.
Optionally, full extension of the lateral transfer unit's moving element to
the end of each
step may need to be programmed to occur occasionally to prevent stagnant
material from
building up and agglomerating near the end of the step.
Temperature Control
In order to get the best possible conversion efficiency, the temperatures in
the gasifier
and temperature distribution through the pile can be stabilized and
controlled.
Temperature control within the pile can be achieved by changing the flow of
process air
into a given region or step. The process air flow provided to each step in the
bottom
chamber can be adjusted to stabilize temperatures in each step. Optionally,
temperature
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
control utilizing extra lateral transfer unit's moving element may also be
necessary to
break up hot spots and to avoid bridging.
In one embodiment, temperature control within the pile is achieved by changing
the flow
of process air into a given step (ie. more or less combustion). For example,
the process
air flow provided to each step in the gasifier may be adjusted by the control
system to
stabilize temperatures at step. Temperature control utilizing extra ram
strokes may also
be used to break up hot spots and to avoid bridging.
In one embodiment, the air flow at each step is pre-set to maintain
substantially constant
temperature ranges and ratios between steps. For example, about 36% of the
total air flow
may be directed to Step A, about 18 % to Step B, and about 6% to Step C, the
remainder
being directed to an attached gas reformulating chamber (e.g. 40% of total air
flow).
Alternatively, air input ratios may be varied dynamically to adjust
temperatures and
processes occurring within each step of the gasifier and/or reformer.
Downstream Options
The gasifier of the invention can be adapted for a variety of applications
including waste
disposal and syngas production. The gasifier can therefore be a component of a
larger
system depending on the application.
In one embodiment, the gasifier is adapted for waste disposal applications and
is in
gaseous communication with a flare stack fitted with appropriate pollution
abatement
devices.
In one embodiment, the gasifier is a component of a syngas generating system
and
comprises a cyclonic oxidizer, a gas refinement system or a gas reformulating
system.
In one embodiment, the gasifier is a component of a hazardous treatment
facility.
41
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Cyclonic oxidizer, a gas refinement system or a gas reformulating system
utilize a plasma
heat source to refine the off-gas.
EXAMPLES
Example 1
Referring to Figures 4 to 10, in one embodiment, the gasifier (2100) comprises
a
refractory-lined horizontally-oriented gasification chamber (2102) having a
feedstock
input (2104), gas outlet (2106), a solid residue outlet (2108), and various
service (2120)
and access ports (2122). The gasification chamber (2102) has a stepped floor
with a
plurality of floor levels (2112, 2114 and 2116). Each floor level is sloped
between about
5 and about 10 degrees. Each floor level has a series of additive inputs
(2126) located in
the side walls proximal to the floor level to allow for the addition of oxygen
and/or
steam.
Movement through the steps is facilitated by the lateral transfer system. In
this example,
Figures 4 to 9, the lateral transfer system comprises a series of moving shelf
units (2128,
2130, 2132) in which material is predominantly moved through the gasifier by
sitting on
top of the shelf with a small fraction of material being pushed by the leading
edge of the
shelf. As shown, each floor level is serviced by a moving shelf unit (2128,
2130, 2132)
mounted on an external frame (2134). Corresponding sealable openings in the
gasification chamber walls allow for entry of each moving shelf. Thus the
moving shelf
units (2128, 2130, 2132) are capable of moving material along floor levels
(2112, 2114,
2116) respectively at a controlled rate. The distance individual shelves
travel across their
respective step is controlled by an externally mounted controller. The ability
to control
the start and the stop point for each push allows for control of pile height
through the
gasification chamber. In normal operation, after material has been moved as
required, the
shelf may be fully or partially withdrawn from the chamber; for example, the
shelf may
be withdrawn just out of the processing region but still inside the
refractory, to permit
processing gas to be introduced from the bed of the chamber. This is
particularly
applicable to the final processing zone where the material is more dust-like
and needs to
42
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
be fluidized by multiple gas introduction points from the floor of the
chamber.
Withdrawal of the shelf also avoids unnecessary heating of the shelf and loss
of heat from
the process.
The externally mounted controller is a gearhead synchronous motor (2156)
coupled to the
moving shelf by means of roller chains (2166). Start and stop points for
moving shelf
motion is remotely controlled by a process computer. Speed and frequency of
motion is
also controlled by the computer.
Referring now to Figures 8, 9 and 10, each moving shelf unit comprises an
externally
mounted guide portion (2136), moving element or shelf (2138) having guide
portion
engagement members, externally mounted drive system and an externally mounted
controller. The externally mounted portions of the moving shelf units is
housed in a
sealed enclosure (2139). The enclosure further comprises a removable cover to
allow for
maintenance.
Referring to Figures 8 and 9, the guide portion comprises a pair of generally
parallel
elongated tracks (2140(a), 2140(b)) mounted on the frame (shown in part)
(2134). The
angle of the individual tracks corresponding in general to the slope of the
corresponding
step. Each of the tracks has a substantially rectangular cross-section. The
moving element
comprises an elongated rectangular block (2144) sized to slidably move through
the
corresponding sealable opening in the chamber wall.
Referring to Figure 10, the leading edge of the elongated rectangular block is
substantially perpendicular to the floor of the gasification chamber. The
leading lower
edge of the elongated rectangular block that contacts the refractory (2146) of
the chamber
is sharp to reduce the risk of riding up on top of the material and jamming
the
mechanism. The sharp leading edge is designed to be effectively self-
sharpening. As it
is sliding flat against the refractory floor there will be a slight wearing of
the bottom
surface of the shelf (2128), thus tending to sharpen the forward edge. The
shelf is
43
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
designed to be easily removable for maintenance that could include replacement
of the
endpiece or grinding of the fixed end.
The elongated rectangular block is adapted to sealingly engage the chamber
wall and has
substantially smooth parallel faces such that it is possible to obtain sealing
against each
face to prevent material egress and air ingress during normal process
operation, and also
to control hazardous gas escape during abnormal situations. The seal is
located at the
inside face of the refractory and is resiliently held against the sliding
faces of the shelves.
This minimizes material escape and gas leakage and precludes the likelihood of
jamming
of a shelf. The seals (2148) are designed to be easily replaceable during
operation and
are manufactured from stainless steel.
As shown in Figure 10, the moving shelf further comprise a scraper (2150) to
remove
material from the shelf as it is withdrawn (or partially withdrawn) from the
chamber. The
scraper is a one-piece sheet metal part fixed to outside frame and is designed
to be readily
replaceable during operation.
The elongated rectangular block (2144) is mounted on substantially parallel
brackets .
Each bracket having at least two guide engagement members (2154). The guide
engagement members illustrated in Figure 8 are rollers sized to movably engage
the track
(2140(a) or 2140(b)).
Power to propel the elongated rectangular block along the tracks is supplied
by a
externally mounted electric variable speed motor (2156) which drives a motor
output
shaft (2158) selectably in the forward or reverse direction allowing for
extension and
retraction of the elongated rectangular block at a controlled rate. A slip
clutch is provided
between the motor (2156) and the motor output shaft (2158). The motor further
comprise
a gear box. Two driver sprocket gears (2160) are mounted on the motor output
shaft. The
driver sprockets (2160) and corresponding driven sprockets (2162) mounted on
an axle
(2164) operatively mesh with chain members (2166) which are secured by
brackets
44
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
(2168) to the elongated rectangular block (2144).
The ram stroke is controlled by proximity and limit switches so that the
amount of
material fed into the chamber with each stroke is controlled. A switch is also
used to
verify the start position of the rams and length and speed is then controlled
by a variable
frequency drive in the motor controller.
Example 2
Referring to Figures 11 to 25, in one embodiment the gasifier (2200) comprises
a
refractory-lined horizontally-oriented gasification chamber (2202) having a
feedstock
input (2204), gas outlet (2206), a solid residue outlet (2208), and various
service (2220)
and access ports (2222). The gasification chamber (2202) is a refractory-lined
steel
weldment having a stepped floor with a plurality of floor levels (2212, 2214
and 2216).
The solid residue outlet is equipped with an ash extractor comprising an
extractor screw
(2209) which will pull the ash out of the gasifier and feed it into an ash
conveyor system.
Referring to Figure 16, the refractory is a multilayer design with a high
density chromia
layer (2402) on the inside to resist the high temperature, abrasion, erosion
and corrosion,
a middle, high density alumina layer with medium temperature resistance and
insulation
factor (2404) and an outer very low density insboard material with very high
insulation
factor (2406) that can be used because it will not be exposed to abrasion of
erosion. The
refractory lines the metal shell (2408) of the gasification chamber.
Each level or step has a perforated floor (2270) through which heated air is
introduced.
To avoid blockage of the air holes during processing, the air hole size is
selected such
that it creates a restriction and thus a pressure drop across each hole. This
pressure drop
is sufficient to prevent waste particles from entering the holes. The holes
are tapered
outwards towards the upper face to preclude particles becoming stuck in a
hole. In
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
addition, the movement of the lateral transfer units may dislodge any material
blocking
the holes.
The air feed for each level or step is independently controllable. Independent
air feed and
distribution through the perforated floors (2270A, 2270B, 2270C) of each step
is
achieved by a separate air box (2272, 2274, and 2276) which forms the floor at
each step.
Referring to Figures 17 and 18, to reduce the risk of stress-related failure
or buckling of
the air box, several features are included. The material for the perforated
top plate (2302)
of the air boxes is an alloy that meets the corrosion resistance requirements
for the
system. The perforated top sheet (2302) is relatively thin, with stiffening
ribs and
structural support members (2304) to prevent bending or buckling.
To minimize stress on the flat front, top and bottom sheets of the boxes,
perforated webs
is attached between both sheets. To allow for thermal expansion in the boxes
they are
attached only at one edge and are free to expand at the other three edges.
Referring to Figures 17, the fixed edge of the Step A & B boxes (2272 and
2274) is also
the connection point of the input air piping (2278) thus, the connection
flange (2280) will
be at high temperature and must be sealed to the cool wall of the gasifier. A
shroud
concept is used. The hot air box (2272) and pipe (2278) are attached to one
end of the
shroud and the other end of the shroud (2282) is connected to the cool
gasifier (2200). A
temperature gradient will occur across the length of the shroud (2282), thus
there will be
little or no stress at either connection. The space between the shroud (2282)
and the
internal duct of the air box (2272) is filled with insulation to retain heat
and to ensure the
temperature gradient occurs across the shroud. When the air box 2270A,(2272)
is in its
operating location in the chamber the top plate opposite to the air connection
is extended
beyond the air box to rest on a shelf of refractory. This provides support to
the air box
when operating and also acts as a seal to prevent material from falling below
the air box.
At the same time it allows free movement to allow for expansion of the air
box.
46
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
Referring to Figure 21, the downstream edge of the air box can be dealt with
in the same
way. The upstream edge of the air box is sealed with a resilient sheet sealing
(2306)
between the ram and the air box top plate (2302).
Connection to the hot air supply piping is via a horizontal flange such that
to enable
removal of an air box requires only the flange to be disconnected to permit
the removal to
take place.
The third step air box (2276) is inserted from below and uses the shroud
concept for
sealing and locating the box to the gasifier (2200). The general arrangement
of the third
step air box is shown in Figure 19.
Sealing against dust falling around the edges of the third stage box is
achieved by having
it set underneath a refractory ledge at the edge of the second stage. The
sides can be
sealed by flexible seals protruding from below recesses in the sides of the
refractory.
These seals sit on the top face of the box, sealing between the walls and the
box. The
downstream edge of the air box is dust sealed to the side of an extractor
trough using a
flexible seal.
To permit removal of the third stage air box, the hot air pipe connection is
vertical.
Movement through the steps is facilitated by lateral transfer system.
Referring to Figures
24 to 25, in this Example, the lateral transfer system comprises a series of
multiple-finger
carrier rams (2228, 2230, 2232), with a single multiple-finger carrier ram
servicing each
step. The system of carrier rams further allows for the control of the height
of the pile at
each step and the total residence time in the chamber. Each carrier ram is
capable of
movement over the full or partial length of that step, at variable speeds.
Referring to Figure 24, each carrier ram unit comprises an externally mounted
guide
portion, a multiple-finger carrier ram, externally mounted drive system and an
externally
mounted controller.
47
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
The multiple-finger carrier ram is a structure in which fingers (2328) are
attached to a
ram body (2326), with individual fingers being of different widths depending
on location.
The gap between the fingers in the multiple-finger carrier design is selected
to avoid
particles of reactant material from bridging. The individual fingers are about
2 to about 3
inches wide, about 0.5 to about 1 inch thick with a gap between about 0.5 to
about 2
inches wide.
The air box airhole pattern is arranged such that operation of the rams does
interfere with
the air passing through the airholes.
The multiple-finger carrier ram has independent flexibility built-in so that
the tip of each
finger (2328) can more closely comply with any undulations in the air box top
face. This
compliance has been provided by attaching the fingers (2328) to the ram body
(2326)
using shoulder bolts, which do not tighten on the finger. This concept also
permits easy
replacement of a finger.
The end of the ram finger is bent down to ensure that the tip contacts the top
of the air in
the event that the relative locations of the ram and airbox change due, for
example, to
expansions. This feature also lessens any detrimental effect on the process
due to air
holes being covered by the ram, the air will continue to flow through the gap
between the
ram and air box.
Referring to Figures 24 and 25, the guide portion comprises a pair of
generally
horizontal, generally parallel elongated tracks (2240(a), 2240(b)) (not shown)
mounted
on a frame. Each of the tracks has a substantially L-shaped cross-section. The
moving
element comprises a ram body (2326) and a series of elongated, substantially
rectangular
ram fingers (2328) sized to slidably move through corresponding sealable
opening in the
chamber wall. The ram fingers are constructed of material suitable for use at
high
temperature.
48
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
The ram fingers are adapted to sealingly engage the chamber wall to avoid
uncontrolled
air from entering the gasifier, which would interfere with the process or
could create an
explosive atmosphere. It is also necessary to avoid escape of hazardous toxic
and
flammable gas from the chamber, also, excessive debris escape is undesirable.
Gas
escape to atmosphere is prevented by containing the ram mechanisms in a sealed
box.
This box comprises a nitrogen purge facility to prevent formation of an
explosive gas
mixture within the box. Debris sealing and limited gas sealing is provided for
each finger
of the ram. The sealing is in the form of a flexible strip (2308) pressing
against each
surface of each finger of the rams, see Figure 22.
Leakage of debris is monitored by means of windows in the sealed box and a
dust
removal facility is provided to facilitate the removal of debris. This removal
can be
accomplished without breaking the seal integrity of the ram box, see Figure
23.
The dust removal facility (2310) comprises a metal tray (2312) having a dust
outlet
(2314) equipped with a shutter (2316) and attachment site (2318) for a dust
can (2332),
and a manual-operated, chain (2320) driven dust pusher (2322). Dust is pushed
to the
outlet (2314) by the pusher (2322) when the operator handle (2324) is used.
Power for moving the rams is provided by electric motors which drive the ram
via a
gearbox and roller chain system (as described in Example 1). Briefly, power to
propel
the rams along the tracks is supplied by a externally mounted electric
variable speed
motor (2256) which drives a motor output shaft (2258) selectably in the
forward or
reverse direction allowing for extension and retraction of the ram at a
controlled rate. A
position sensors (2269) transmit ram position information to the control
system. Two
driver sprocket gears (2260) are mounted on the motor output shaft. The driver
sprockets
(2260) and corresponding driven sprockets (2262) mounted on an axle (2264)
operatively
mesh with chain members (2266) which are secured by brackets (2268) to the
elongated
rectangular block (2244).
49
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
The motors are controlled by the overall control system which can command
start and
stop position, speed of movement and frequency of movement. Each ram is
controlled
independently. There is a tendency for the material on top of the ram to be
pulled back
when the ram is withdrawn. This tendency is dealt with by appropriately
sequencing the
ram strokes.
Example 3
Referring to Figure 26, in the embodiment of the invention described in
Example 2 a
staggered ram sequence control strategy can be implemented to facilitate
movement of
the rams. A summary of an exemplary ram sequence is as follows:
1. Ram C (2232) move fixed distance (with adjustable setpoint), creating a
pocket at
the start of Step C (2216).
2. Ram B (2230) follows as soon as Ram C (2232) passes a trigger distance
(trigger
distance has adjustable setpoint). Ram B pushes/carries material to
immediately
fill the pocket at the start of Step C (2216). Feedback control is to stroke
as far as
necessary to block level switch C (2217), or minimum setpoint distance if
already
blocked, or maximum setpoint distance if blocking does not occur. At the same
time as Ram B (2230) is filling the pocket at the start of Step C (2216), it
is
creating a pocket at the start of Step B (2230).
3. Ram A (2228) follows as soon as Ram B (2228) passes a trigger distance. Ram
A
(2228) pushes/carries material to immediately fill the pocket at the start of
Step B
(2214). Feedback control is to stroke as far necessary to block level switch B
(2215), or minimum setpoint distance if already blocked, or maximum setpoint
distance if blocking does not occur. At the same time as Ram A (2228) is
filling
the pocket at the start of Step B (2214), it is also creating a pocket at the
start of
Step A (2212). This typically triggers the feeder to run and fill the gasifier
until
level switch A (2213) is blocked again.
4. All rams reverse to home position simultaneously.
50
CA 02651352 2008-11-05
WO 2007/131241
PCT/US2007/068413
The reactant material profile obtained by such a sequencing strategy is show
in Figure 27
(Profile B).
51
