Note: Descriptions are shown in the official language in which they were submitted.
CA 02486318 2004-10-29
TO WHOM IT MAY CONCERN:
[00011 Be it known that Jan A. Barynin, residing in Vancouver, British
Columbia,
Canada, and Robert G. Graham, residing in Presque Isle, Michigan, U.S.A., have
invented a new and useful device which is
AN APPARATUS AND METHOD FOR
GASIFYING SOLID ORGANIC MATERIALS
[00021 The invention disclosed and claimed herein deals with an apparatus and
method
for gasifying solid organic materials to convert the chemical energy stored in
such
materials to thermal energy or gaseous products that may serve in biochemical
and/or
chemical synthesis for further product development. More particularly, this
invention
relates to a method for gasifying biomass materials, such as forestry and
agricultural
residues, industrial waste materials such as saw mill pulp and paper products,
hydrocarbon based plastics and the like. This invention also deals with the
apparatus that
is used to convert the chemical energy into thermal energy or gaseous
products.
Specifically, the invention utilizes a novel bottom supported gasification
chamber unlike
those found in the prior art, wherein the feedstock is partially oxidized at
an elevated
temperature in a square or rectangular gasification chamber. The advantages of
using
such gasification chamber are set forth infra, in the discussion. The high
temperature
gases produced by the practice of the invention are essentially void of
particulate solids
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CA 02486318 2004-10-29
and can be utilized to advantage, for example, as the thermal energy source
for a
conventional steam generator or steam boiler, and the like.
BACKGROUND OF THE INVENTION
100031 This invention is directed to an apparatus and method for gasifying
solid organic
materials to convert the chemical energy store in such materials to thermal
energy or
gaseous products that may serve in biochemical and/or chemical synthesis for
further
product development. The novel apparatus specifically relates to a new and
novel
gasification chamber.
100041 It has long been recognized that many industrial and agricultural solid
organic by-
products, such as forestry and agricultural residue, and the like, are a
potential source of
large amount of chemical energy. The substantial increases in the cost of
traditional
fuels, such as fuel, oil and natural gas, which occurred during the 1970's,
have provided
substantial economic incentive to try to develop effective and efficient
techniques for
recovering the energy in these organic by-products, energy that traditionally
was not
recovered to any substantial extent. Such organic materials, frequently
referred to as
"biomass" materials, are now successfully utilized to some extent as fuel in
some very
large industrial systems, for example, in firing the power boiler and the
recovery boiler in
a pulp or paper mill. However the high capital cost that has heretofore been
associated
with biomass energy recovery systems has precluded their successful use in
small or even
medium size energy recovery systems. Medium size energy recovery systems, that
is, of
the size from about 4,000,000 to 8,000,000 BTU/hr., are used in community
centers,
schools, nursing homes, and small industrial and commercial establishments
and, to date,
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biomass fuels have not been satisfactorily utilized as fuel in heating systems
for such
facilities. Among the U.S patents that have issued on inventions relating to
the recovery
of energy from wood chips or similar organic materials are for example, U.S.
Patents,
5,138,957 that issued to Morey, et al. on August 18, 1992; U.S. 4,184,436 that
issued to
Palm, et al. January 22, 1980; U.S. 4,312,278 that issued to Smith, et al. on
January 26,
1982; U.S. patent 4,366,802 that issued to Goodine on January 4, 1983; U.S.
4,321,877
that issued to Schmidt, et al on March 30, 1982; U.S. 4,430,948 that issued to
Schafer, et
al. on February 14, 1984; U.S. 4,593,629 that issued to Pedersen, et al. on
June 10, 1986;
U.S. 4,691,846 to Cordell, et al. that issued on September 8, 1987, and U.S.
patent
4,971,599 that issued to Cordell on November 20, 1990. However, it is not
known that
any of the inventions described in these patents have been successfully
adapted to recover
biomass energy on a cost-effective basis in small and medium size energy
recovery
systems.
[0005] Thus, gasifiers are not new in the art and there are many publications
dealing with
such pieces of equipment and systems in which they are used, but by way of
illustration,
attention can be directed to U.S. Patent 4,691,846 that issued on September 8,
1987 to
Cordell, et aL in which there is described a method and apparatus for
gasifying solid
organic materials in which the system is described in detail with emphasis on
the hopper
and its manner of operation. It should be noted that the gasifier is shown and
described
as a dome-like structure with a bottom feed mechanism for the solid organic
materials,
and an upper exhaust system to remove the gaseous effluent to a secondary
chamber.
[0006] A second disclosure can be found in U.S. 6,120,567 that issued on
September 19,
2000 to Cordell, et al in which there is described a method of gasifying solid
organic
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CA 02486318 2004-10-29
materials and in which a similar apparatus and system as is disclosed in the
`846 patent is
set forth. The 1567 patent is related to the `846 patent. Again, it should be
emphasized
that the gasifier is shown and described as a dome-like structure having a
bottom feed
and an upper exhaust for the gaseous effluent.
[0007] The major concerns with these early devices and systems is that the
primary
gasification chamber cylindrical and is therefore severely limited in the
manner of
construction to accommodate large volumes of through-put without consuming
larger
areas of floor space. Another concern is the need to dump ash on a continuous
basis to
avoid swings in the chemical composition of the producer gas. Moreover, the
gasifier of
the prior art does not have any basins and thus it is impractical to build up
and maintain a
hearth.
SUMMARY OF THE INVENTION
[0008] In accordance with the present invention, there is provided a
relatively simple
method for the recovery of energy from feed stock of forestry and agricultural
residues,
such industrial waste materials such as pulp and paper products, hydrocarbon
based
plastic, and the like, by the gasification of such materials within the
inventive gasifier and
employment of the system disclosed herein. The method, apparatus and system
according to the present invention can be utilized on a cost-effective basis,
due to the
relatively low capital cost of the apparatus, to cleanly and efficiently
recover energy at
medium rates of recovery, and even at very low rates of recovery.
[0009] The apparatus according to this invention utilized a cubic or
hexagonal, vaulted,
bottom supported enclosure, the gasifier wherein the feed stock is partially
oxidized at
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controlled reduced temperatures (less than 1500 degrees F.) in a process in
which it first
gasifies and chars, preferably in a deficiency of oxygen, producing a high
temperature
combustible effluent which may be provided a secondary oxidation in an
oxidizer. The
high temperature effluent from the oxidizer can be utilized as a thermal
energy source,
for example, in an otherwise conventional heat exchanger such as a steam
boiler as a
substitute for the combustion effluent from the fuel oil or gas burner that is
normally
utilized in conjunction with a boiler of such type, or alternatively, the
combustible
effluent from the gasifier may serve as feed stock for upgrading a chemical or
biochemical process.
[0010] During normal operation, the feedstock is mechanically fed to the
gasifier from a
storage hopper by means of screw feeding system, preferable automatically in
response to
the demand for energy from the system. Details of this feeder system design
and its
function is set forth and described in U. S. Patent 6,120,567.
[0011] The gasifier is provided with a hearth that is comprised of a moving
bed of ash on
which the oxidation takes place in form of a burning pile with the fuel feed
entering up
through the hearth through a set or sets of feed cones. The "moving bed of
ash" hearth is
provided with augers for removing ash and non-combustible contaminants, such
as sand,
dirt, stones, rocks and any slag that is formed, from the chamber. The burning
pile is also
used to control the elevation and shape of the "moving bed of ash" hearth.
[0012] While the feed stock oxidation method according to the present
invention has
wide industrial usage, it can also be utilized to particular advantage in
remote regions,
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where winters are long and cold, conventional fuels are expensive, and
occasionally
scarce, because of the long delivery distances from remote major population
centers, and
where biomass feed stocks are plentiful and inexpensive as a result of the
agricultural
and/or forest-base business activities that are frequently conducted in such
regions.
[0013] The essential feature of this invention is a gasifier of cubic or other
hexahedral
shape featuring, respectively, square or rectangular hearth patterns with a
bottom portion,
and a converging upper vaulted, tapered or flat roof. The gasifier features a
"moving bed
of ash" hearth design by which the formed ash and other solids of combustion
residue
accumulates on the bottom of the gasifier floor and thus creates and builds up
and forms
the hearth on which oxidation proceeds.
[0014] In the preferred embodiment, there is at least one trench provided in
the gasifier
floor featuring one or more devices for removal of ash and combustion residues
and for
control of the elevation and shape of the "moving bed of ash" hearth. A most
adaptable
device is an auger. In. an example, there are two trenches, one on either side
of a
centrally located feed cone or feed trough. The ash augers in the trenches
move the ash
towards points of discharge suitably located at the end or bottom of the
trench. The
trenches are connected to a bin or a conveyor of suitable design for further
disposal of the
ash. Alternatively, the control of the "moving bed of ash" hearth level and
the removal of
the ash can be accomplished by a conveyor or conveyors moving across the
entire floor,
or section thereof, from side to side, or end to end of the gasifier as deemed
most suitable
for the dimensions and shape of the "moving bed of ash" hearth, or
alternatively, a set, or
sets, of dump grates can be inserted under the "moving bed of ash" hearth to
facilitate
and control removal of the ash.
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100151 As indicated supra, there is a gasifier with one or several feed cones
arranged
along the centerline of the chamber and protruding above the general elevation
of the
"moving bed of ash" hearth. Each feed cone is serviced by a single, or twin
set, of fuel
feed augers entering vertically, or sloped, from below. Alternatively, for the
"moving
bed of ash" hearth having conveyors moving across its surface, as described in
supra, the
feed is distributed across the chamber floor by the conveyors from a feed bin
attached to
the front of the gasifier, and dragged onto the hearth, or a spreader stoker
may distribute
the feed across the hearth.
[0016] In the gasifier, partial primary oxidation is carried out as a
moderately slow pile
burning or, in the case of multiple feed cones, as multiple pile burnings. The
method is
one in which the combustion is carried out sub-stoichiometrically with the
application of
an oxidizing agent, which typically will be air, oxygen or a mixture hereof,
wherein the
solid organic materials are transferred continuously or intermittently to the
gasifier at a
predetermined rate to maintain a mass of solid organic materials in the
gasifier, and
further wherein the oxidant is continuously added to the gasifier to
continuously gasify
the solid organic materials in the mass, and still further the solid residue
is transferred out
of the gasifier. A preheater may be used to raise the temperature of the
oxidizing agent.
The oxidizing agent is administered through a set or sets of suitable ducts
connected to
nozzles and injection points located within, around and between the feed
cones, and to
row, or rows of nozzles and/or tuyeres in the surrounding walls of the
gasifier.
[0017] As the oxidation proceeds and the temperatures elevate the fuel will
pyrolyze and
gasify. By starving the combustion of oxygen, a "product gas" rich in
combustible
gaseous components is formed. The moderately slow burning will serve to
establish a
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quiet oxidation zone whereby entrainment of particulate matter and fly ash is
minimized.
"Product gas" with a maximum of combustible gaseous components and a minimum
of
particular matter is one key objective of this invention. The "product gas"
may, however,
contain a pyrolytic aerosol or mist of submicron particles or droplets of
liquid tar and
other high molecular weight components that should be eliminated.
[0018] There is provided a recovery and regeneration apparatus (chamber) in
which the
aerosols and other components of the "product gas" under the effect of high
gas
temperature and extended residence time will decompose, separate and/or
convert into
combustible gaseous products thereby enriching the value of the "product gas".
[0019] To further enrich the "product gas", heating the "product gas" to a
temperature
regime in the range of 1800-2200 F by auxiliary means provides certain
residual inert
components in the "product gas" that convert into combustible gaseous products
that
further increase the value of the "product gas". As a means to this end the
recovery and
regeneration apparatus is fitted with a set, or sets, of nozzles for injection
of an oxidizing
agent to quickly raise the temperature to the temperature regime.
[0020] Where "product gas" is the desirable product from said invention, it is
critical to
cool by quenching the "product gas" rapidly to temperatures well below 1400 F
rather
than letting it linger at elevated temperatures as leaving the "product gas"
at elevated
temperatures could lead to a degradation of the value of the "product gas".
The inventive
process can be extended to incorporate a quenching apparatus (not shown)
whereby a
surplus of quenched "product gas" is recycled and used as the quenching
medium,
thereby reducing the "product gas" temperature to 400 F or lower.
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[0021] In the event that "product gas" is not the desired product from the
inventive
process, then essentially all "product gas" is fully oxidized or combusted, so
as to raise
the resulting flue gas temperature to the maximum. This is accomplished by
introducing
an oxidizing medium such as air into the recovery and regeneration chamber. A
heat
exchanger may be used to preheat the air .
[0022] The oxidizer of this invention is preferred to have a cylindrical
configuration to
ensure complete oxidation of the "product gas" and this device is positioned
immediately
downstream of the recovery and regeneration chamber. A heat exchanger may be
located
immediately after the oxidizer. As an example, a natural gas-fired, ceramic
type heat
exchanger would serve in this function.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure IA is a side sectional view of the inventive gasifier
illustrating the central
fuel feed cone, the ash_auger pair within a rectilinear ash hopper, and the
air outlet duct
positioned at the side of the unit.
[0024] Figure I B is a side sectional view of the inventive gasifier
illustrating the central
fuel feed cone, the ash auger pair within a curvilinear ash hopper, and the
air outlet duct
positioned tangentially to the top of the dome.
[0024] Figure I C is a side sectional view of the inventive gasifier
illustrating the central
fuel feed cone, a single ash auger within a curvilinear housing, and the air
outlet duct
positioned tangentially to the top of the dome.
[0025] Figure 2 is a perspective view of the inventive gasification system
illustrating the
fuel storage hopper, the inventive gasifier with a partial cut-away sidewall
showing the
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CA 02486318 2004-10-29
interior of the gasifier unit, the combustion gas recovery and regeneration
chamber, and
the oxidizer.
[0026] Figure 3 is a schematic view of the inventive gasification system
modified to
accommodate increased capacity illustrating an enlarged gasifier, wherein the
gasifier has
been extended in both directions to provide increased output.
[0027] Figure 4 is a perspective view of a feed cone in the shape of a hollow
inverted
truncated pyramid, illustrating tuyere placement on the inner and outer
surfaces of the
feed cone.
[0028] Figure 5 is a perspective view of a feed cone in the shape of a hollow
inverted
truncated cone, illustrating tuyere placement on the inner and outer surfaces
of the feed
cone.
[0029] Figure 6A is a partial side sectional view of the detail portion of Fig
1 A
illustrating a first possible layered sidewall construction consisting of a
steel shell spaced
apart from the refractory lining, the space between the shell and lining
filled with
insulation.
(0030] Figure 6B is a partial side sectional view of the detail portion of Fig
1A
illustrating a second possible layered sidewall construction consisting of a
steel shell
spaced apart from the refractory lining, the open space between the shell and
lining
providing insulation for the shell, and providing a means of cooling the
exterior wall and
preheating air for use within the gasifier unit.
DETAILED DESCRIPTION OF THE INVENTION
CA 02486318 2004-10-29
[00311 Turning now to the specific details of the invention, and with
reference to Figures
2, there is shown a system for practicing the present invention which utilizes
a drive
assembly, indicated generally by reference number 100, a storage hopper
assembly,
indicated generally by reference number 200, a feed assembly, indicated
generally by
reference the number 300, which is driven by the drive assembly 100 and which
feeds
material from the storage hopper assembly 200 into a gasifier 400 wherein
primary
substoichiometric oxidation of the feed material occurs. The un-oxidized or
unburned
portion of the feed material fed into gasifier 400 is withdrawn from the
bottom of the
gasifier 400 and transported away by a clean-out assembly, indicated generally
by
reference number 500 and, in the preferred embodiment of the invention, the
material fed
into the gasifier 400 is only partially oxidized therein. There is provided a
recovery and
regeneration chamber indicated generally by reference number 600 which
receives the
gaseous partially oxidized feed material from gasifer 400, followed by an
oxidizer 700
wherein secondary oxidation, or completion of oxidation, of the partially
oxidized feed
material occurs. The fully oxidized gaseous material from the secondary
oxidation
chamber, or oxidizer 700, may be used as a source of heat energy in a device
which
requires heat energy, and in the preferred embodiment of the present invention
this takes
a form of an otherwise conventional steam boiler, indicated generally by
reference
number 800. However, it is understood that other heat recovery devices may be
substituted for steam boiler 800, including, but not limited to, heat
exchangers and air
turbine systems.
[00321 Alternatively, the partially oxidized gaseous material ("product gas")
withdrawn
from the recovery and regeneration chamber 600 may bypass oxidizer 700 without
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further oxidation to be used as feed for a chemical or biochemical synthesis
to develop
valuable products such as alcohols or other organic derivatives, and in the
preferred
embodiment of the present invention, this takes the form of a conventional
process
routing known in the art, indicated generally also by reference number 800.
[00331 The material which is to be oxidized in the apparatus of Figure 1 is
delivered to
the storage hopper assembly 200 in any suitable manner, for example, manually
from a
pile of such material or by means of a conveyor, not shown, from a self-
unloading truck
body of an appropriate type, also not shown, or in any other suitable manner
known in the
art. In Figure 1, the transfer of the material into the storage hopper
assembly 200 is
indicated by a broad arrow with reference letter M.
[00341 The feed material which is delivered into the storage hopper assembly
200 may be
any of the wide range of solid, organic materials of a type which is
frequently referred to
as waste materials, and suitable materials of this type include coal and coal
tailings,
petroleum coke, wood chips, sawdust, bagasse, news print, plastics, and the
like. They
may also include semi-solid organic materials such as sludges. These materials
are
usually waste by-product materials from various agricultural, forest, or
industrial origins,
and contain substantial amounts of chemical energy that is capable of being
converted to
thermal energy by suitable oxidation processes. Such materials are, however,
difficult to
handle because they are usually moist, almost always soiled, and are non-
uniform or
irregular in shape, and heretofore it has been difficult to efficiently and
effectively
oxidize because of their high moisture content, their non-uniform physical and
chemical
composition, and their frequent contamination with non-gasifiable materials,
such as
sand, dirt, rocks, stones, and other debris.
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[00351 As noted above, the feed material from the storage hopper assembly 200
is
oxidized to a gaseous state in gasifier 400, preferably to a state which is
not fully
oxidized. Referring now to Figure I A, gasifier 400 is defined by four
vertical side walls
401, giving the chamber a square or rectangular cross section and an enclosure
402 which
has an irregularly shaped bottom 403 and which has at its top a roof 404,
which in cross
section may be vaulted, tapered or flat or any combination hereof.
[00361 Wall 401 is made up of a multiplicity of layers. In the preferred
embodiment
(Figure 6A), the innermost layer 405 is an insulating layer of a high-
temperature resistant
type refractory that is capable of withstanding the elevated temperatures that
will develop
within gasifier 400, for example, temperatures in the range of approximately
2300 F to
approximately 2500 F, and that is capable of withstanding the operational
temperature
variations as well as the corrosive, erosive effects of the gaseous materials
produced by
the oxidation of the biomass feed material that is delivered into gasifier
400. Wall 401
may also include an insulating layer 406 on the outside of the wall layer 405
to further
prevent loss of heat through the wall 401 of gasifier 400. As example, the
insulating
layer 406 may be a single layer of insulating firebrick, block insulation, or
blanket
insulation. The outer casing of the wall 401 is a structural layer, or shell
407 of sheet
metal, for example, plate steel, which is airtight and provides the necessary
strength and
rigidity for the wall.
100371 A second embodiment of wall 401 is shown in Figure 6B, wherein
insulating layer
406 is not used, and a vacant layer or space 415 is provided between
refractory innermost
layer 405 and steel shell 407. The air which fills vacant layer 415 acts as an
insulator
between refractory layer 405 and steel shell 407. This warmed air can also be
used as a
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CA 02486318 2004-10-29
source of preheated air for injection into gasifier 400, recovery and
regeneration chamber
600, and /or oxidizer 700.
[0038] The biomass feed material from the storage hopper assembly 200 is
introduced
into gasifier 400 from below gasifier 400 through at least one feed cone 450
located
along the centerline of bottom 403 of gasifier 400. During normal operating
conditions,
as is illustrated in Figure 3, the feed material rises over the top of the
feed cone(s) 450
and it rests on the hearth 410. Hearth 410 is made up of ash and other solid
combustion
residues, until it forms a pile of such material, indicated generally by
reference letter P,
which is the normal or equilibrium condition of gasifier 400. This self-
generated hearth
410 is the "moving ash bed" configuration that is an essential part of this
invention. As
primary oxidation progresses, this bed continues to elevate and the ash must
be removed
at the same rate it is formed to maintain the appropriate fuel pile height.
[0039] The control of pile height and shape is of critical importance for
combustion
control and the release_of gaseous combustibles, i.e., the "product gas". The
shape and
location of feed cone(s) 450 are designed to provide a pile having a generous
depth, and
which has a generally flat upper periphery., This flat, mesa-like upper
surface extends
over 60 to 70 percent of the floor area, generally filling the lower portion
of gasifier 400,
and sharply tapers downward adjacent walls 401. This downward taper, referred
to as the
angle of repose, is dependent upon the type of fuel used. A flat fuel pile is
key to
achieving uniform combustion without bridging. This flat configuration results
in a
uniform pile depth, which in turn results in uniform air pressure within the
pile, thus
minimizing channeling of the pile. Maintaining pile depth is very important.
12 to 18
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CA 02486318 2004-10-29
inches of ash is maintained below the actively burning portion of the pile so
as to prevent
heat damage to feed cone 450 and ash clean-out assembly 500.
[00401 As the feed material in the Pile P in gasifier 400 moves from the
bottom to the
center and top of the mass, it gets hotter and hotter, and volatile components
in such
material and combustion products begin to dissipate from the surface of the
pile, partly
being assisted by the air which is rising through such material. As the feed
material in
the pile P loses more and more of the volatile and pyrolytic ingredients it
will begin to
form high molecular weight carbonaceous derivatives and char until,
eventually, it is
exposed to the full operating temperature inside gasifier 400. This material
moves
generally horizontally outward and then downward toward the outer wall and
lower floor
where it is exposed to further oxidation agents (via tuyere arrays 422, 424,
described
below) for a more complete reaction, at which time all of the organic
constituents of such
feed material will gasify and will pass from gasifier 400 as an incompletely
oxidized
gaseous effluent of combustibles, the effluent leaving gasifier 400 through an
insulated
exit duct 412. The velocity of the effluent above the fuel pile and out the
exit duct will be
low, reducing particulate carryover.
[0041] In Figure 1A, exit duct 412 is positioned so that it vents gasifier 400
through side
wall 401, located adjacent dome 404 and above start-up tuyeres 420 (discussed
below).
In Figure 1B, exit duct 412 is positioned to tangentially intersect the upper
portion of
dome 404. Preferably, side walls 401 are provided in a height which allows any
air-
borne particulate to fall back to pile P rather that exit via duct 412. The
positioning of
exit duct 412 within gasifier 400 can be either as shown in Figure IA or 1B,
may be
sloped or vertical, and is selected to be practical and suitable for the
specific application.
CA 02486318 2004-10-29
100421 The oxidation of the feed material in the pile P proceeds more
satisfactorily if the
amount of feed material in the mass M of feed material is maintained at a
relatively
constant value. Feed rate into gasifier 400 is monitored and controlled by
monitoring and
controlling fuel pile height within gasifier 400. Suitable instrumentation,
not shown, is
provided to control the rate of the delivery of the feed material into
gasifier 400 by the
feed assembly 300 as a function of the elevation of the top of the feed
material in the
height of pile P to maintain such elevation at a substantially constant value,
and thereby
to contain the pile P of feed material at a substantially constant shape
10043] In the preferred embodiment, pile height is monitored using a pair of
infrared light
beam and sensor units 426, 428. Infrared light units 426, 428 are embedded in
side wall
401 such that they are spaced apart and in vertical alignment. Upper infrared
light unit
426 is positioned approximately 12 inches above the desired pile height. Lower
infrared
light unit 428 is positioned at the desired pile height. When the height of
the pile is too
high, an upper infrared beam generated by upper infrared light unit 426 is
interrupted,
and upper infrared light unit 426 sends a signal to a controller which results
in a slowing
of the feed rate (for example, by slowing the rate of turn of the feed auger).
When the
pile height decreases to the extent that a lower infrared beam generated by
the lower
infrared light unit 428 is not interrupted, lower infrared light unit 428
sends a signal to a
controller which results in an increased feed rate.
(0044] Alternative non-intrusive instrumentation may be used to monitor and
control pile
height. Such instrumentation includes, but is not limited to, instrumentation
for
measuring amperage of the vertical feed auger drive, described infra, nuclear
density
gauge technology, or thermocouples.
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10045] A mechanical probe 440 may be employed as an alternative to the
infrared or
nuclear density gauge sensor units, or as a redundant monitoring system along
with those
systems. Mechanical probe 440 is retractable, and consists of an elongate
rigid rod.
Probe 440 has a first end 442 that resides outside gasifier 400, and a second
end 444 that
resides within gasifier 400. Second end 444 terminates in a flat plate or foot
446.
Second end 444 rests upon the upper surface of the pile at a location spaced
apart from
side wall 401, with foot 446 maintaining second end on the surface and
preventing it
from sinking into the pile itself. In the preferred embodiment, probe 440
enters gasifier
400 through a lower portion of the dome (Figures 1 A, 1 B). However, it is
within the
scope of this invention to position probe 440 such that it enters other
portions of the
dome, such as along the vertical centerline of gasifier 400 (Figure 1C). First
end 442 is
provided with a counterweight assembly 448 which maintains foot 446 in contact
with
the pile surface, and also includes sensors which signal changes to fuel feed
rate
depending on the angle of probe 440. The foot 446 may be raised
intermittently,
manually or automatically, to ensure that its level indication is faithful,
and that foot 446
is not embedded in pile P. Retractable probe 440 is preferably formed of
ceramic,
providing a long wearing, heat tolerant apparatus. Alternatively, retractable
probe 440 is
internally cooled by circulating air or water to function satisfactorily in
the high
temperature environment of gasifier 400.
(0046] With primary reference to Figures 1 and 3, there is shown therein that
the feed is
brought to the pile P from the feed bin 200 by the screw conveyor 302 that
will transfer
its load to the pile screw 303, or screws which will enter the primary
oxidizer 400 from
below at a slanted or vertical angle. As an additional alternative means of
controlling
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fuel pile height, a sensor which monitors the electrical load on the motor
that drives pile
screw 303 may be used. Because the electrical load on this motor increases as
pile height
increases due to the increased weight of the pile overlying screw 303, such a
sensor can
be used to monitor pile height and control feed rate.
100471 The storage hopper assembly 200 has an elongate opening 201 in the
bottom
thereof, and the elongate opening 201 is longitudinally aligned, more or less,
with a
horizontal screw member 301 of the feed assembly 300, with the horizontal
screw
member 301 being disposed immediately below the elongate opening 201 of the
storage
hopper assembly 200. The feed assembly 300 may also include a tubular housing
302
which surrounds the horizontal screw member 301, except the portion of the
horizontal
screw member 301 which is in communication with the elongate opening 201 of
the
storage hopper assembly 200. The horizontal screw member 301 of the feed
assembly
300 is rotated by the drive assembly 100, to advance the feed material from
the storage
hopper assembly 200 through the tubular housing 302 to gasifier 400. Feed
assembly
300 includes a second screw member 303, or twin set of screw members 303,
which are
disposed in a vertical orientation and which serve to vertically transfer feed
material from
the end of the horizontal screw member 301 upwardly into gasifier 400. The
portion of
tubular housing 302 about screw member 303 is provided with a greater inner
diameter
than the portion surround screw member 301. Preferably, the horizontal screw
member
301 intercepts the vertical screw member 303 at a location spaced from the
center line of
vertical screw member 303. This configuration allows the feed material being
advanced
by the horizontal screw member 301 to constantly accommodate a change in
direction
and thickness of the passage through which it is traveling, preventing jamming
of the
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CA 02486318 2010-07-19
feed material within the tubular housing'302, a phenomenon which can prevail
if the feed
material is unusually moist or stringy. Screw conveyor 302 and pile screw 303
may both
feature progressive pitch where the diameter, the speed of rotation, and/or
the distance
between the helical flights will progressively increase with each flight in
the direction of
flow.
[0048] The shape of feed cone(s) 450 may be described as that of a tapered
channel
wherein a wide upper opening overlies and is in vertical alignment with a
narrow
opening. More specifically, feed cone 450 is a hollow inverted truncated four
or multi-
sided pyramid, or alternatively, a hollow inverted truncated cone, such that
the wide,
open base overlies a narrowed opening below it. A pyramid-shaped feed cone 450
comprises a square upper opening vertically aligned with circular lower
opening. Pile
screw 303 terminates at lower opening, and lower opening is sized to receive
pile screw
303 therein with minimal clearance. When a conical-shaped feed cone 450 is
employed,
upper opening is circular rather than square. Regardless of peripheral shape,
feed cone
450 is provided with an angled inner surface 456 providing an upwards flaring
and
progressive widening in order to prevent packing of the feed and facilitate
the distribution
of the feed as it reaches the top of the feed cone 450. The angle of inner
surface 456 is
imperative for the formation and shape of the pile P and may range from 35 to
55
degrees, and is selected depending on the type of feed stock being injected
into the
primary oxidizer chamber 400. This angle is a well tested critical requirement
of this
invention. In the preferred embodiment, this angle is 45 degrees. An inner
surface 456
angle of 45 degrees ensures a fuel pile where fuel is distributed evenly in
all sloped
directions, and also generates the desired flat pile surface. Inner surface
19
CA 02486318 2010-07-19
angles which are more, or less, generate peaked or convex pile surfaces. The
angle of the
outer surface 458 of feed cone 450 is less critical, but must be relatively
steep, for
example 60 to 90 degrees to the horizontal, to prevent stagnation of flow or
bridging and
to ensure proper flow of the fuel pile.
100491 The oxidation in gasifier 400 is carried out as a moderately slow pile
burning or,
in the case of multiple feed cones, as multiple pile burnings. In all cases
the oxidation
will be carried out sub-stoichiometrically with the application of an
oxidizing agent,
which typically will be air, oxygen or a mixture thereof. The oxidizing agent
will be
administered through a set, or sets, of suitable ducts or manifolds connected
to nozzles
and injection points located within, around and between the feed cones and to
at least one
array of tuyeres in the surrounding walls 401 of gasifier 400.
[0050] A plenum 460 exists in the hollow vacancy between inner surface 456 and
outer
surface 458 of feed cone 450. Plenum 460 may be a single open space, or
alternatively
may be compartmentalized for example as shown in Figure IA, B, C. Air supply
pipes
provide a source of injection air to plenum 460, which in turn supplies tuyere
arrays
formed in inner 456 and outer 458 surfaces. In the preferred embodiment at
least one set
of tuyeres 466 is provided in inner surface 456, and at least one set of
tuyeres 468 is
provided in outer surface 458. In the most preferred embodiment, at least two
sets of
tuyeres 468 are provided in outer surface 458. Preferably, feed cone tuyeres
466, 468
inject air into pile P in a direction perpendicular to the respective inner
and outer surfaces
456, 458. Alternatively, feed cone tuyeres 466, 468 may be directed generally
horizontally. Air is injected into pile P via feed cone tuyeres 466, 468 at
all times, and air
flow rate is controlled by adjustment of air pressure to these tuyeres.
CA 02486318 2010-07-19
[00511 In the preferred embodiment, there are three tuyere arrays provided in
side walls
401. The first array is a horizontally oriented row of tuyeres referred to as
the lower
perimeter tuyeres 424. Typically, lower perimeter tuyeres are coplanar with
lower
opening of feed cone 450, and inject air into lower and outer portions of pile
P. The
second array is a horizontally oriented row of tuyeres referred to as the
upper perimeter
tuyeres 422. Typically, upper perimeter tuyeres are approximately coplanar
with the
upper edge of feed cone 450, and inject air into outer portions of pile P at
approximately
mid-depth of the pile. The third array is a horizontally oriented row of
tuyeres referred to
as start up tuyeres 420. Start up tuyeres 420 are the uppermost set of side
wall tuyeres,
and are positioned above the outermost peripheral edge of the fuel pile, and
below the flat
fuel pile upper surface or mesa. Start up tuyeres 420 inject air into gasifier
400 only
during initial start up of the unit or during transitory system upsets. Once
fuel pile
combustion is established, start up tuyeres 420 are shut off. In this
preferred
embodiment, only three sets of tuyere arrays in side walls 401 are described.
However, it
is well within the scope of this invention to add additional tuyere arrays,
for example
adjacent the ash removal system 500, as required by the specific application.
100521 Side wall tuyeres 420, 422, 424 can be advantageously formed out of
metal pipe,
for example, 3/4 or 1 1/4 inches in diameter, and these pipes are embedded in
the innermost
layer 405 at the time it is cast, preferably to the extent of approximately
one-half of the
outside diameter of each of the metal pipes. While the metal pipes that make
up the side
wall tuyeres 420, 422, 424 are exposed to the high temperature conditions
existing in
gasifier 400, it is possible to utilize conventional, low-temperature steel
pipe to form such
side wall tuyeres 420, 422, 424 by providing a flow using a blower or other
means, not
21
CA 02486318 2010-07-19
shown, as a coolant, such as air or water, through the flutes when gasifier
400 is
operational to thereby avoid the need for using expensive, special high
temperature alloys
in the construction of such side wall tuyeres 420, 422, 424. Alternatively,
windboxes
may be located along the perimeter inside gasifier to confine the pile to a
tighter area to
maintain optimum air distribution, better combustion, and ash recovery. An
orifice ring
or constriction may be inserted into each pipe to accurately control the
airflow within and
between air nozzles.
[0053] The oxidation of the feed material in gasifier 400 requires a source of
oxygen, and
ambient air has been found to be a suitable source for this purpose. An air
blower of
standard construction is used to provide ambient air to gasifier 400, the air
being
introduced into the interior of the pile P of feed material through the
nozzles and injection
points located within, around and between the feed cones 450 and to the
auxiliary row, or
rows of spaced-apart series of horizontally and or sloped, inward projections,
flutes or
tuyeres 422, 424 in the surrounding walls of gasifier 400. Where necessary,
air nozzles
can be covered with cover plates or caps to avoid back flow and blocking of
the openings
by feed material and ash.
[0054] The moving bed of ash 410, or hearth, of gasifier 400 has a peripheral
shape
defined by an insulated wall 401 and, in the preferred embodiment, the
insulated wall 401
is arranged to define a square or rectangular gasifier 400. Moving bed of ash
410 lies
above bottom 403 of gasifier 400, below the plane defined by lower opening of
feed
cone 450, and is formed of slowly moving solid by-products of combustion. In
this
arrangement, solid incombustibles and ash will accumulate below precombusted
feed
material, and limit precombusted feed material in gasifier 400 from exiting
via clean out
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CA 02486318 2004-10-29
assembly 500. At the same time, any incombustible contaminants that normally
work
their way to the bottom of the pile P as the oxidation process continues will
be able to
accumulate and build up the moving bed 410. Incombustibles may be employed to
take
advantage of the insulating characteristics of said ash and incombustibles.
Excess ash
and incombustibles will collect in the trench(es) 501 which lie below bottom
403 of
gasifier 400. A single trench 501 may be located at the center of the bottom
of gasifier
400, or a pair of trenches may employed so that a trench 501 is provided
adjacent each
respective opposed sides of gasifier 400. As the ash and incombustibles
collect, the
elevation of the moving ash bed 410 rises.
[0055] In the preferred embodiment, the control of elevation and shape of
moving ash
bed 410 is handled by at least one ash auger pair 502 located within trench
501. Each
auger of auger pair 502 is single or double supported, and may be of conical
design or
feature progressive helical flights so as to remove the material in a manner
whereby the
uneven accumulation across the floor and along the auger can be controlled.
Ash auger
pair 502 resides completely within trench 501 such that the augers are closely
adjacent
each other, and so that the upper periphery of the augers are flush with
bottom 403 of
gasifier 400. The augers of ash auger pair 502 counter rotate, that is, rotate
towards each
other, at the same speed.
[0056] Trench 501 is provided in a depth which is approximately the diameter
of an
auger, and is provided in a width that is slightly greater than twice the
diameter of an
auger so that minimal clearance is provided between the augers and trench 501.
Trench
501 may be rectangular in section as shown in Figure 1 A, or may be contoured
to reflect
the shape of the augers as shown in Figure I B. Where there exists potential
for exposure
23
CA 02486318 2004-10-29
to excess temperatures in the trenches, auger pair 502 may be air, water or
oil cooled in
order to properly and safely convey the ash towards the point, or points, of
discharge 504
suitably located in the bottom of the trench 501 at about the middle, or
alternatively at the
end of the trench to wherein they are connected to a bin or a conveyor (not
shown) of
suitable design for further disposal.
(00571 In a second embodiment, the control of elevation and shape of moving
ash bed
410 is handled by a single auger 502' located within trench 501' (Figure I Q.
Auger
502' is single or double supported, and may be of conical design or feature
progressive
helical flights so as to remove the material in a manner whereby the uneven
accumulation
across the floor and along the auger can be controlled. Auger 502' resides
completely
within trench 501' such that auger 502' generally fills trench 501' and so
that the upper
periphery of auger 502' is flush with bottom 403 of gasifier 400. Trench 501'
is identical
in concept to trench 501, scaled to be sized for a single auger.
100581 Probes 506 are used to monitor the level of moving ash bed 410 defined
by the
upper elevation of the accumulated ash. Probes 506 are suitable for
measurement of
differences in characteristics of the ash. As an example of probes 506, there
are used
thermo elements in pairs located one above the other, distanced sufficiently
such that the
level of the moving ash bed 410 will be in between them, and capable of
characterization
by the difference in temperatures and the temperature of the material above
the moving
ash bed 410 while in operation. Said temperature difference will then be the
offset that
will dictate the degree of auger 502 movement required to control the level of
the moving
ash bed 410 between the probes. In this representation, it is assumed that
gasifier 400 is
24
CA 02486318 2004-10-29
equipped with several sets of probes 506 around the perimeter of the chamber
and an
average of probe 506 input data will determine the auger 502 movements.
[00591 To bring gasifier 400 to an operational condition on start up, the feed
assembly
300 is activated to form the pile P of feed material gasifier bottom 403 in
preparation of
development of a "moving ash bed" 410 above bottom 403. The pile P of feed
material is
ignited, for example, manually, wherein a portion 401a of the wall 401 of
gasifier 400 is
removable from the remaining portion of the wall 401 to facilitate the
igniting of the pile
P, and/or to permit the inspection and/or cleaning of gasifier 400 when it is
non-
operational. To facilitate the removal of the removable portion 401a of the
wall 401, the
removable portion 401a may be mounted on a swing-out arm assembly (not shown).
To
facilitate bringing the pile P of feed material up to its normal operating
temperature, fuel
oil or other readily combustible supplemental fuel may be added to it. As an
example,
this may be done manually through the opening provided when the removable
portion
401a is removed.
[00601 While the air disperses up through the pile of feed material P in
gasifier 400, it
will support slow oxidation and progressively enrich the gaseous effluent with
combustible components. Slow oxidation and combustion is facilitated by the
heat
created from the combustion and supported by auxiliary air entering through
start up
tuyeres 420 on the walls 401 and by the radiant heat reflected from the roof
404. Stable
combustion has been established when the pile P of feed material is burning at
the desired
low temperature profile of about 1000 degrees F. During stable combustion,
injected air
from perimeter arrays 422, 424 on walls 401, as well as from feed cone arrays
466, 468,
serve to create the circulation required to maintain uniform heating and
combustion of the
CA 02486318 2010-07-19
pile P and minimize channeling and stratification in the stream of gaseous
combustibles
leaving gasifier 400. Temperature within enclosure 402 of gasifier 400 will
vary
depending on the type of feed material, and will remain oxygen starved. For
example, it
is possible to have an enclosure temperature of 2000 degrees F with no oxygen
present.
100611 The gaseous effluent leaving gasifier 400 leaves through the insulated
exit duct
412 from where it passes into the recovery and regeneration chamber 600, in
effect an
insulated duct, defined by a wall, through which the partially oxidized
gaseous material is
withdrawn from gasifier 400 ("product gas") is given the residence time at
elevated
temperatures. The objective is to increase the cracking and decomposition
leading to the
formation and enrichment of the "product gas" with additional gaseous
combustibles
from high molecular residues, droplets and or solids that may be entrained in
the gaseous
material from gasifier 400. The recovery and regeneration chamber 600 is
fitted with sets
of injection nozzles 606, for delivery of the oxidizing agent, which typically
may be air
or oxygen or a mixture thereof. The nozzles 606 connect to manifolds that may
be in the
shape of ring formed wind boxes all connected through links 604, with
individual
isolation valves 603 and individual airflow measuring devices 602 to a common
duct 601
that receives the oxidizing agent. When ambient air is satisfactory for use as
the oxidant it
may be provided to the common duct 601 by means of a blower 610, of
conventional
design (not shown). The injection nozzles 606 may be grouped to function
individually
or in unison. For example, it may desirable to impart a swirl motion to the
flowing
stream of gaseous combustibles in which event the nozzles 606 are arranged so
as to
point tangentially from the inside surface of the recovery and regeneration
chamber wall,
26
CA 02486318 2010-07-19
without being necessarily perpendicular, onto an imaginary circle, clock- or
anti
clockwise, and thereby promote the desirable swirl motion and resultant
mixing.
10062] With this system of injection nozzles 606 it is possible to add
sufficient oxidizing
agent to partly or completely combust any or all of the gaseous combustibles
in the
stream flowing through the residence chamber 600. By applying a partial, i.e.
a sub-
stoichiometric portion of oxidizing agent, combustion it will be possible to
elevate the
residence temperature promoting the reaction rates of decomposition of said
entrainment.
Alternatively, a complete combustion will be achieved by administrating the
oxidizing
agent in excess of the stoichiometric requirement. As a result the residual
flue gas will be
even hotter which is most desirable when the application of the gasification
process is to
generate, for example, steam or hot water, or as the case may be, hot air for
power
generation via an air turbine driven turbine. The system of injection nozzles
will serve to
apply the minimum excess of oxidizing agent thereby maximizing the flue gas
temperature and the thermal efficiency of the overall system. In this mode,
the recovery
and regeneration section will form the bulk of the oxidation and burn out of
combustibles
leaving little work to be done by the oxidizer, described infra.
[00631 The gaseous effluent leaving recovery and regeneration chamber 600
passes into
oxidizer 700. Oxidizer 700 is defined by an insulated wall and, in the
preferred
embodiment, the insulated wall is arranged to define a oxidizer which is in
the form of a
cylinder whose longitudinal axis is coextensive with the longitudinal axis of
recovery and
regeneration chamber 600. A secondary oxidant may be added to oxidizer 700 to
burn or
completely oxidize gaseous materials flowing into oxidizer 700 via
regenerative chamber
600. Ambient air is satisfactory for use as the secondary oxidant and may be
provided to
27
CA 02486318 2010-07-19
oxidizer 700 by means of a second blower 702, of conventional design.
Preferably, the
second blower 702 is arranged with an air duct 703 and a wind box 704 with its
outlet
705 entering oxidizer 700 in a direction that is tangential to the wall that
defines oxidizer
700. With this arrangement, a swirling or cyclonic action will develop within
oxidizer
700 by virtue of the tangential admission of secondary air through the blower
702, and
solid particles which are carried into oxidizer 700 will be driven to the
outermost portions
of oxidizer 700 by centrifugal force resulting from this swirling action and
maybe
removed from oxidizer 700 by means of a radial port at the bottom of the
oxidizer 700.
Solid particles leaving oxidizer 700 through the radial port may be collected
and taken
away to a storage and disposal location. Sufficient air is added to oxidizer
700 by means
of the second blower 702 to fully oxidize the partially oxidized gaseous
materials
entering oxidizer 700 from the insulated exit of recovery and regeneration
chamber 600.
Preferably excess air is added to oxidizer 700 to prevent excessively high
temperatures
from developing therein.
10064] In a preferred embodiment of the operation of the apparatus according
to the
present invention, the temperature in oxidizer 700 should be limited to no
more than
2800 F. This can be accomplished by utilizing total air added to the system,
including
the air added to gasifier 400 by the air blower, by the air that may be added
by blower
610, and the air that may be added to the oxidizer 700 by the second blower
702, in an
amount which exceeds the stoichiometric equivalent of that required for full
oxidation of
the feed material added to gasifier 400. The fully oxidized, high-temperature
flue gas
exits from oxidizer 700 as an effluent through an insulated duct 710 and
passes into a
heat exchanger such as a steam boiler 800 (not shown). Steam boiler
28
CA 02486318 2004-10-29
800 may be considered to be of conventional construction, and uses the
effluent as the
source of heat for heating water therein as a substitute for the flue gas from
an oil or gas
burner that is usually used in conjunction with such steam boiler 800.
[00651 The recovery and regeneration/oxidizer arrangement may be combined onto
a
single oxidizer compartment sized to provide adequate residence time for
complete burn
out of all combustibles arriving from one or more gasifier(s) 400. In this
arrangement,
the oxidizer compartment can be a horizontal or vertical vessel with an excess
stack on
top and a conical bottom. The conical bottom includes a smelt tap in the event
smelts are
formed and accumulated during operation. Preferably, an auxiliary burner is
inserted in
the recovery and regeneration/oxidizer train to ensure initial ignition of
combustible
gases.
[00661 Side walls 401 of gasifier 400 are provided in a polygonal, preferably
rectangular,
configuration so as to overcome capacity limitations of prior art gasifier
designs.
Specifically, by using linear side walls the gasifier design is easily
expanded. That is,
side-by-side assembly of multiple gasifier units allows accommodation of
increased
volumes of through-put with minimal increased consumption of floor space.
Referring
now to Figure 3, the inventive gasifier 400 is enlarged by extending the
inventive concept
within the apparatus in both directions, providing greater gasifier
throughput. Plural feed
assemblies 300 transport feed material between storage hopper 200 and enlarged
gasifier
400'. Gasifier 400' is provided with plural sets of linearly aligned feed
cones 450, each
set of feed cones 450 corresponding to and in alignment with a feed assembly
300. Plural
ash clean out assemblies 500 are provided. Each ash clean out assembly 500 is
elongated
to extend across the enlarged enclosure 402', and is oriented in a direction
perpendicular
29
CA 02486318 2004-10-29
to that of feed assemblies 300. The number of ash clean out assemblies 500
provided is
sufficient to generally cover the bottom 403' of gasifier 400', and the ash
clean out
assemblies are positioned to extend between adjacent feed cones 450, or to
extend
between outer feed cones 450 and side wall 401'. A single exit duct 412' is
used to
deliver gaseous effluent to downstream components of the system.
Method
[00671 In accordance with the present invention, there is provided a
relatively simple
method for the recovery of energy from feed stock of biomass such as forestry
and
agricultural residues, and from industrial waste materials such as pulp and
paper
products, hydrocarbon based plastic, poultry litter, sludges and the like, by
the sub-
stoichiometric gasification of such materials within the inventive gasifier
400 and
employment of the system described above. The method of using gasifier 400 and
the
system, described above, to gasify solid organic material to produce a gaseous
effluent
and solid residue is as defined in the following method steps:
[00681 Step 1. Provide a supply of fuel. In the preferred embodiment, the fuel
is
solid organic material. The fuel is stored generally adjacent to gasifier 400.
Preferably,
the fuel is stored in a hopper-style level controlled metering bin 200 with an
opening 201
in a lower portion thereof to provide easy distribution of the fuel from
hopper 200.
[00691 Step 2. Transfer fuel from hopper 200 to gasifier 400. Preferably, feed
assembly 300 is provided so that fuel exiting hopper 200 via opening 201 is
transported
CA 02486318 2004-10-29
using a generally horizontal screw member 301 to a generally vertical screw
member
303, and then from screw member 303 into gasifier 400 via an opening the
bottom of
gasifier 400.
[0070] Fuel is transferred to gasifier 400 at a load demand controlled rate
typically within a 50 percent turndown capacity. Use feed cone assemblies 450
adjacent
vertical screw member 303 to direct solid organic material upward and outward
within
gasifier 400 so as to provide a fuel pile within gasifier 400 having a
generally flat upper
surface and of generally constant depth.
[0071] Step 3. Use sensing means to monitor and control pile height within
gasifier 400. During normal operation, the sensing means is used to maintain
the pile at a
generally constant level. In the preferred embodiment sensing means comprises
the pair
of infrared light beam and sensor units 426, 428.
[0072] Step 4. Provide an oxidant to gasifier 400 to aid in generation and
control
of combustion and to provide a gaseous effluent to facilitate partial primary
oxidation of
the fuel in gasifier 400 by partial combustion of those materials. Preferably,
during start
up oxidant is added to gasifier 400 using tuyere array 420. After startup is
complete,
tuyere array 420 is shut off.
[0073] Sidewall tuyere arrays 422, 424 and feed cone tuyere arrays 466, 468
provide oxidant to gasifier 400 during normal operation. Add oxidant gasifier
400 using
sidewall tuyere arrays 422, 424 and feed cone tuyere arrays 466, 468 at a rate
that is
insufficient to fully oxidize the fuel, such that combustion of the fuel is
partial, resulting
31
CA 02486318 2004-10-29
in a gaseous effluent and solid by-products of combustion. Oxidant is
continuously
added to gasifier 400 to continuously partially gasify the fuel in the mass
with the result
that solid by products of combustion including solid residue are accumulated
to form a
supporting moving bed of ash 410 for supporting the fuel within the gasifier
and for
assisting the excess solids to be transferred out of gasifier 400.
[00741 The moving bed of ash 410 supports and maintains the fuel on an upper
surface of the moving bed of ash 410 during oxidation of the solid organic
materials
within the gasifier. The moving bed of ash 410 has a depth which provides
insulation
and protection against heat damage between the oxidizing fuel pile and the
gasifer bottom
403 and its associated assemblies, such as ash clean out assembly 500. The
moving bed
of ash 410 provides quiet removal, and prevents bridging, of the fuel.
[00751 Combustion of the fuel is provided in starved air conditions such that
the
fuel pile has a low (less than 1500 degrees F) temperature profile. The
gasifier
temperature will vary depending on the air-to-fuel ratio as well as the rate
at which the
fuel is combusted.
[00761 Step 5. Remove continuously the solid by-products of combustion and
solid residues from the lower portion of gasifier 400 using ash clean out
assembly 500.
Clean out assembly 500 moves the solid by-products of combustion and solid
residues so
as to aid in fuel pile movement, to aid in aeration of the fuel pile, to aid
in generation and
maintenance of the flat upper surface of the fuel pile, and to transfer excess
accumulations of solid by products of combustion out of gasifier 400,
resulting in the
movement of the moving ash bed hearth.
32
CA 02486318 2004-10-29
100771 Step 6. Provide an effluent path of flow within gasifier 400 for a
first
portion of the gaseous effluent to migrate, mix, and react through the heated
fuel pile.
[00781 Provide a path of flow for any excess solid residue or by-products of
combustion, that is residues and solids which are in excess of the moving bed
of ash 410,
so that these excess solid residue or by-products of combustion are
transferred out of
gasifier 400 using clean out assembly 500. Preferably, material enters and
exits gasifier
400 at generally the same rate so that the optimal height of the fuel pile is
maintained at a
generally constant level.
[00791 Step 7. Direct any gaseous effluent that is generated and transferred
out of
the gasifier 400 via duct 412 to recovery and regeneration chamber 600.
[00801 Step 8.- Add an oxidant to recovery and regeneration chamber 600 to
oxidize other portions of the gaseous effluent not so oxidized, into
additional gaseous
effluent. In the preferred embodiment, this oxidant is air. However, it is
well within the
scope of this invention to use other oxidants, including, but not limited to,
combustion
flue gas. In the preferred embodiment the temperature of the oxidant is
ambient, but the
oxidant may also be preheated if required by the specific application.
[00811 Step 9. Direct all gaseous effluent from recovery and regeneration
chamber 600 to oxidizer 700.
33
CA 02486318 2004-10-29
[00821 Step 10. Add an oxidant to oxidizer 700 to further oxidize any gaseous
effluent not so oxidized, into essentially fully oxidized gaseous effluent,
and transferring
the essentially fully oxidized gaseous effluent out of oxidizer 700. In the
preferred
embodiment, this oxidant is air. However, it is well within the scope of this
invention to
use other oxidants, including, but not limited to, combustion flue gas. In the
preferred
embodiment the temperature of the oxidant is ambient, but the oxidant may also
be
preheated if required by the specific application.
[00831 Step 11. Direct all essentially fully oxidized gaseous effluent from
oxidizer 700 to a heat recovery device 800. In the preferred embodiment, this
devices
comprises a steam boiler. However, it is well within the scope of this
invention to use
other heat recovery devices, including, but not limited to, hot water, hot
oil, or hot air
heat exchangers.
34
