BIOMASS GASIFICATION SYSTEMS HAVING
CONTROLLABLE FLUID INJECTORS
BACKGROUND OF THE INVENTION
[0001] The subject matter disclosed herein relates generally to gasification
systems, and more particularly, to biomass gasification systems having controllable
injection nozzles.
[0002] Gasification is a process that has become ubiquitous in various industries
and applications for conversion of a lower, less readily usable type of fuel into a
higher form of fuel. For example, biomass gasification systems are utilized in a
variety of types of power plants to pyrolytically convert biomass via heating with air
or oxygen to generate producer gas composed of gases such as carbon monoxide,
carbon dioxide, hydrogen, methane, and nitrogen. This producer gas is then utilized
to make methanol, ammonia, and diesel fuel through known commercial catalytic
processes. In such a way, various forms of organic waste, such as wood, coconut
shell fibers, alcohol fuels, and so forth, may be gasified for use in the production of
electricity for a variety of downstream applications.
[0003] Unfortunately, many current biomass gasification systems generate
producer gas with high levels of undesirable particulates, such as tar. Accordingly,
prior to use in a power generation system, the producer gas needs to be cleaned to
generate a gas mixture with the desired composition. The incorporation of cleaning
components, such as scrubbers and filters, for removing these undesirable particulates
can add cost and complexity to the biomass gasification system, thus reducing its
efficiency. Accordingly, there exists a need for biomass gasification systems capable
of generating relatively clean producer gas while overcoming these drawbacks.
BRIEF DESCRIPTION OF THE INVENTION
[0004] Certain embodiments commensurate in scope with the originally claimed
invention are summarized below. These embodiments are not intended to limit the
scope of the claimed invention, but rather these embodiments are intended only to
provide a brief summary of possible forms of the invention. Indeed, the invention
may encompass a variety of forms that may be similar to or different from the
embodiments set forth below.
[0005] In a first embodiment, a biomass gasification system includes a reactor
adapted to gasify a biomass feedstock to thermally convert the biomass feedstock into
producer gas are provide. The reactor includes an enclosure disposed about a biomass
gasification chamber. The enclosure includes an inlet, an outlet, and a pair of side
walls disposed between the inlet and the outlet. The reactor also includes a plurality
of fluid injectors disposed along a length of the side walls and adapted to inject fluid
into the gasification chamber. The biomass gasification system also includes a
control system communicatively coupled to the plurality of fluid injectors and adapted
to independently control each fluid injector of the plurality of fluid injectors to
independently control a flow of fluid through each fluid injector.
[0006] In a second embodiment, a biomass gasification system includes a reactor
adapted to gasify a biomass feedstock in a biomass gasification chamber to thermally
convert the biomass feedstock into producer gas. A plurality of nozzles are disposed
along a length of the reactor and adapted to inject air and/or oxygen into the biomass
gasification chamber. The biomass gasification system also includes a control system
adapted to determine an approximate location of a combustion zone in the gasification
chamber and to selectively deactivate each nozzle of the plurality of nozzles not
capable of injecting air and/or oxygen into the combustion zone.
[0007] In a third embodiment, a method includes the step of receiving data
corresponding to an operational parameter of a biomass gasification process or a
power generation system that receives producer gas from the biomass gasification
process. The method also includes activating, based on the received data, a subset of
a plurality of air and/or oxygen injectors disposed along a length of a biomass gasifier
and about a biomass gasification chamber. The method further includes controlling
an air delivery system to supply the activated subset of the plurality of air and/or
oxygen injectors with air and/or oxygen for injection into the biomass gasification
chamber.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] These and other features, aspects, and advantages of the present invention
will become better understood when the following detailed description is read with
reference to the accompanying drawings in which like characters represent like parts
throughout the drawings, wherein:
[0009] FIG. 1 is a block diagram of an embodiment of a biomass gasification
system including a biomass gasifier having a plurality of controllable fluid injectors;
[0010] FIG. 2 is a diagram of an embodiment of a biomass gasifier having a
plurality of fluid injectors and an embodiment of an air delivery system capable of
selectively delivering air to the air injection nozzles;
[0011] FIG. 3 illustrates an embodiment of a method for selectively activating a
plurality of controllable fluid injectors based on an operational parameter of a biomass
gasification process;
[0012] FIG. 4 illustrates an embodiment of a method for selectively activating a
plurality of controllable fluid injectors based on a type of feedstock utilized in a
biomass gasification process;
[0013] FIG. 5 illustrates an embodiment of a method for selectively activating a
plurality of controllable fluid injectors based on a detected tar content of a producer
gas generated in a biomass gasification process; and
[0014] FIG. 6 illustrates an embodiment of a method for selectively activating a
plurality of controllable fluid injectors based on an operational parameter of an engine
located in a power generation system downstream of a biomass gasification chamber.
DETAILED DESCRIPTION OF THE INVENTION
[0015] One or more specific embodiments of the present invention will be
described below. In an effort to provide a concise description of these embodiments,
all features of an actual implementation may not be described in the specification. It
should be appreciated that in the development of any such actual implementation, as
in any engineering or design project, numerous implementation-specific decisions
must be made to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that such a
development effort might be complex and time consuming, but would nevertheless be
a routine undertaking of design, fabrication, and manufacture for those of ordinary
skill having the benefit of this disclosure.
[0016] When introducing elements of various embodiments of the present
invention, the articles "a," "an," "the," and "said" are intended to mean that there are
one or more of the elements. The terms "comprising," "including," and "having" are
intended to be inclusive and mean that there may be additional elements other than the
listed elements.
[0017] As described below, provided herein are fuel conversion systems including
thermal conversion devices having a plurality of controllable fluid injectors that inject
air and/or oxygen into a chamber of the thermal conversion device. These
controllable fluid injectors may be disposed in a variety of systems and devices, such
as various types of gasification systems typically found in industrial equipment,
power plants, or other applications. For example, in certain embodiments, the
controllable fluid injectors may be incorporated into a reactor, such as a biomass
gasifier of a biomass gasification system, to inject air and/or oxygen into a
gasification chamber. That is, the controllable fluid injectors may be included in a
biomass gasification system capable of converting biomass into a higher, potentially
more useful, type of fuel. For instance, the biomass gasification system may gasify
biomass, for example, pyrolytically via heating with air or oxygen, to generate
producer gas having varying concentrations of gases such as carbon monoxide, carbon
dioxide, hydrogen, methane, and nitrogen, as well as particulate matter of various
sizes.
[0018] The controllable fluid injectors described herein facilitate this conversion of
biomass into producer gas by injecting air and/or oxygen into a combustion zone of a
biomass gasification chamber. The controllability of the fluid injectors may enable
the selective activation and deactivation of subsets of the plurality of fluid injectors.
The embodiments described herein may offer distinct advantages over traditional
biomass gasification systems that typically do not include controllable fluid injectors.
For example, such embodiments may enable activation of subsets of the fluid
injectors that are capable of injecting air and/or oxygen into the combustion zone and
deactivation of subsets of fluid injectors that are less suitable for injecting fluid into
the combustion zone. As such, embodiments of the biomass gasifier configurations
illustrated and described herein may render a single biomass gasifier suitable for use
with a variety of types of feedstock, which may be associated with different
combustion and pyrolysis zone lengths. However, it should be noted that the
illustrated configurations of the controllable fluid injectors are merely exemplary and
are not intended to constrain or limit forms which the fluid injectors may take; other
sizes, shapes, and configurations are also within the scope of the disclosed fluid
injectors.
[0019] Turning now to the drawings, FIG. 1 illustrates a biomass gasification
system 10 that is capable of thermally converting biomass into a more useful gaseous
form of fuel (i.e., a fuel form that can be economically utilized with high energy
recovery levels) and, subsequently, to clean and cool the gaseous fuel produced via
the thermal conversion process. To that end, the illustrated biomass gasification
system 10 includes a feedstock preparation unit 14, a biomass gasifier 16, a cleaning
and cooling subsystem 18, and a power generation system 20. The cleaning and
cooling subsystem 18 includes a cyclone 22, a first scrubber 24, a second scrubber 26,
a third scrubber 28, a blower 30, a flare 32, and a filter unit 34. Various conduits are
provided that couple these components of the biomass gasification system 10
together, thereby enabling fluid flow between the components, as described in detail
below.
[0020] During operation of the biomass gasification system 10, biomass 36, is
utilized as a natural energy source to generate a more readily usable fuel form, such as
producer gas. To that end, the biomass 36 may take the form of any natural or
organic material having a molar energy content. For example, the biomass 36 may
include one or more of alfalfa straw, bean straw, barley straw, coconut shell, coconut
husks, corn cobs, corn fodder, cotton stalks, peach pits, peat, prune pits, rice hulls,
safflower, sugarcane, walnut shell, what straw, wood blocks, wood chips, or any other
suitable organic feed material.
[0021] During operation, the biomass 36 is introduced into the biomass gasifier 16
through the feedstock preparation unit 14, where the biomass 36 may be appropriately
processed as desired. Depending on the form of the incoming biomass 36, the
feedstock preparation unit 14 may resize or reshape the biomass 36, for example, by
chopping, milling, shredding, pulverizing, briquetting, or palletizing the biomass 36.
In some embodiments, the feedstock preparation unit 14 may reduce the biomass 36
via densification to a uniformly dimensioned fungible fuel that is sized and shaped to
maximize the efficiency of the gasifier 16. In other embodiments, the feedstock
preparation unit 14 may receive the biomass 36 as a uniform fuel source and may
further process the fuel to customize the processed feedstock 44 for compatibility with
the gasifier 16 (e.g., by reducing or increasing moisture content). In instances in
which the biomass 36 is partially or completely dried, the feedstock preparation unit
14 may emit a dryer exhaust 46 as part of the drying process.
[0022] Once prepared, the processed feedstock 44 and air or oxygen 48 are input
into a biomass gasification chamber 50 of the gasifier 16 via inlet 52. In the chamber
50, the biomass-derived feedstock 44 is gasified with the air or oxygen 48 to generate
a producer gas with varying concentrations of gases such as carbon monoxide, carbon
dioxide, hydrogen, methane, and nitrogen. In particular, the producer gas may be
generated by partially combusting the biomass-derived feedstock 44 at an elevated
temperature (e.g., approximately 1000° C). That is, gasification in the biomass
gasifier 16 is performed with a surplus of feedstock 44 such that the feedstock 44 is
incompletely combusted. The foregoing feature may offer advantages over complete
combustion processes by forcing the generation of desirable partial combustion
products (e.g., carbon monoxide and hydrogen) while substantially reducing or
eliminating the generation of undesirable full combustion byproducts (e.g., nitrogen,
water vapor, surplus of oxygen). These desirable partial combustion products, as well
as less desirable tar and dust, are produced via reaction of carbon dioxide and water
vapor through a layer of heated feedstock-derived charcoal. Therefore, as described
in detail below, the gasifier 16 is operated to reduce the biomass-derived feedstock 44
to charcoal and, subsequently, to convert the charcoal to produce carbon monoxide
and hydrogen, which, due to their energy rich nature, may be further converted to
useful fuel sources such as methanol, ammonia, and diesel fuel via known catalytic
processes.
[0023] It should be noted that the biomass-derived feedstock 44 may be converted
to these higher fuel sources in a variety of suitable types of biomass gasifiers.
Specifically, in the embodiments illustrated herein, the thermal conversion process is
performed in a downdraft style gasifier, but the illustrated gasifier 16 is not intended
to constrain or limit other forms the gasifiers may take during implementation. For
example, embodiments of the present invention are compatible with various types of
gasifiers, such as downdraft style gasifiers, updraft style gasifiers, crossdraft gasifiers,
and so forth. As appreciated by one skilled in the art, the gasifier type chosen for a
given gasification system may be dictated by features of the biomass in its final fuel
form, such as its size, moisture content, and ash content. For example, in
embodiments in which the feedstock 44 may include substantial amounts of tar or
dust, a downdraft gasifier may be chosen due to its relative insensitivity to the dust
and tar content of the fuel as compared to updraft or crossdraft systems.
[0024] Turning now to the operation of the illustrated gasifier 16, the chamber 50
includes a drying zone 54, a pyrolysis zone 56, a combustion zone 58, and a reduction
zone 60. It should be noted that the zones are shown as distinct areas of the chamber
50 merely for explanatory purposes but, as appreciated by one skilled in the art, the
operational zones would likely exist on a continuum in which the occurring thermal
and chemical reactions of one zone often mix with those of the adjacent zones.
Further, depending on operational factors, such as the type of biomass 36 being
utilized, the respective lengths of each of the zones may differ. As described below,
features of the presently disclosed embodiments may render a single gasifier 16
suitable for use with a variety of types of biomass 36 utilized as the feed because air
and/or oxygen may be selectively injected into the gasification chamber 50 at
locations suitable for the given type of biomass 36 being utilized.
[0025] After the biomass-derived feedstock 44 enters the drying zone 54, the
moisture content of the feedstock 44 may be reduced from an elevated level (e.g., 10-
30%) to a desired level (e.g., 6-10%). In addition to moisture removal in the drying
zone 54, the feedstock 44 may also be subjected to reductions in organic acid content.
As the dried feedstock 44 flows downstream through the gasifier 16 in the direction
indicated by arrows 62 to the pyrolysis zone 56, the feedstock 44 is thermally
decomposed at a temperature (e.g., approximately 280-500°C) that is generally lower
than the gasification temperature, typically producing substantial amounts of tar and
gases, such as carbon dioxide. The relative amounts of charcoal, tar, and chemicals
produced in the pyrolysis zone 56 may depend on the operating conditions within the
gasifier 16 (e.g., the temperature at which the pyrolysis occurs) as well as the
chemical composition of the feedstock 44. Nevertheless, a condensable hydrocarbon
is produced in the relatively low temperature pyrolysis zone 56 regardless of the type
of feedstock 44 utilized.
[0026] When the decomposed feedstock 44 reaches the combustion zone 58,
additional air and/or oxygen 64 is injected into the biomass gasification chamber 50
via a plurality of fluid injectors 66 disposed along a length of a pair of side walls 68 of
the biomass gasifier 16. That is, the plurality of fluid injectors 66 are disposed at a
variety of locations along the side walls 68, thus enabling the controlled injection of
air at a variety of lengthwise locations along the length of the gasification chamber
50. In the disclosed embodiments, the fluid injectors 66 are described as injecting air
into the gasification chamber 50. However, it should be noted that the fluid injectors
66 may be adapted to inject air, oxygen, or a combination of air or oxygen with any
other suitable gas into the gasification chamber 50. For example, in many
embodiments, the air 64 may include inert gases, such as argon and nitrogen, in
addition to oxygen or water vapors.
[0027] In the illustrated embodiment, a control system 67 controls the supply of air
to the plurality of fluid injectors 66 via an air delivery system 69. The control system
67 is capable of exhibiting independent control over the air supply to each of the fluid
injectors 66 to control the location or locations along the length of the gasifier 16 at
which the air 64 is injected into the gasification chamber 50. For example, the control
system 67 may concurrently activate the supply of air from the air delivery system 69
to the fluid injectors 66 in the desired locations along the length of the gasifier 16, and
deactivate the supply of air from the air delivery system 69 to the fluid injectors in
less desirable locations. In this way, the control system 67 may enable injection of air
at selected lengthwise locations along the side walls 68 of the gasifier 16. The
foregoing feature may render the biomass gasifier 16 suitable for use in a variety of
applications that would typically require separate gasifiers. For example, a gasifier
designed for gasification of a sawdust feed may have a substantially longer pyrolysis
zone 56 than a gasifier designed for gasification of a wood chip feed. Therefore, the
optimal lengthwise location of the fluid injectors along the side walls for the sawdust
gasifier would typically be located below the optimal location of the fluid injectors for
the wood chip gasifier since it is desirable for the air to be injected into the
combustion zone. However, since the plurality of fluid injectors 66 in presently
disclosed embodiments are controllable, a suitable subset of the fluid injectors 66 may
be activated for any given application depending, for example, on the type of biomass
feed being utilized, thus reducing or eliminating the need for multiple gasifiers.
[0028] In the illustrated embodiment, in the combustion zone 58, a primary
reaction between the carbonized fuel produced in the pyrolysis zone 56 and the
injected air produces carbon dioxide in a substantially exothermic reaction (i.e., C +
0 2 -> C0 2) . That is, the carbon content of the produced charcoal is partially
combusted with oxygen supplied by the fluid injectors 66 to yield carbon dioxide and
heat. Concurrently, a secondary reaction takes place between the hydrogen in the fuel
and the oxygen in the injected air 64, thereby producing steam (i.e., 2H2 + 0 2 ->
2H20 ) in an endothermic reaction that utilizes a portion of the heat produced in the
primary reaction. The heat produced in the primary reaction is substantially greater
than the heat absorbed in the secondary reaction, thus rendering the overall process
occurring in the combustion zone 58 exothermic. As previously mentioned, the
overall combustion process occurring in the combustion zone 58 is incomplete and is
designed to occur with a surplus of fuel.
[0029] The products of this partial combustion (i.e., carbon dioxide, steam, and the
uncombusted, partially decomposed pyrolysis products) are exposed to a charcoal bed
at an elevated temperature, sparking a series of high temperature chemical reactions in
the reduction zone 60. The predominant heat reactions occurring in the reduction
zone 60 include a Boudouard reaction (i.e., C + C0 2 <-> 2CO), which is forced to
favor the substantially endothermic formation of carbon monoxide due to the high
temperatures (e.g., approximately 800-1000°C) in the reduction zone 60, and a Water
Gas reaction (i.e., C + H20 -> CO + H2), which is also substantially endothermic.
Together, these endothermic reduction reactions lower the temperature of the gas
flowing through the reduction zone 60. However, slightly exothermic reactions, such
as the production of methane from carbon and hydrogen (i.e., C + 2H2 -> CH4) also
occur in the reduction zone. Still further, operational conditions may be chosen such
that additional desired reactions also take place in the reduction zone 60. For
example, a Water Shift reaction (i.e., C0 2 + H2 -> CO + H20 ) may be catalyzed to
achieve a desired hydrogen content of the producer gas and, more specifically, to
adjust the hydrogen to carbon monoxide (H/CO) ratio of the producer gas to an
appropriate level for the downstream application. Accordingly, at an outlet 70 of the
gasifier 16, a producer gas indicated by arrow 7 1 is routed to conduit 72 for
transmission to the cleaning and cooling subsystem 18.
[0030] As appreciated by one skilled in the art, the composition of the producer
gas 7 1 is subject to considerable variations and depends on factors such as the
biomass type, operational parameters of the gasifier 16, and so forth, and may include
varying concentrations of gases such as carbon monoxide, hydrogen, methane, carbon
dioxide, and nitrogen. For example, in instances in which air instead of oxygen is
injected via fluid injectors 66, the producer gas 7 1 may include a greater volumetric
concentration of nitrogen. Still further, the temperature of the producer gas 7 1 at the
outlet 70 of the gasifier 16 may be between approximately 300°C and approximately
400°C. However, the producer gas 7 1 is subject to considerable variations in
temperature based on biomass type and operational conditions. For example, in
gasifiers 16 in which the operational flow velocity through the gasifier 16 exceeds the
desired air flow rate, the temperature of the producer gas 7 1 may be higher than
desired (e.g., greater than approximately 500°C).
[0031] Concurrent with the flow of producer gas 7 1 through the outlet 70 of the
gasifier 16, hot ash exits the gasifier 16 via an ash extraction system 74. The hot ash
may be derived from the mineral content of the fuel that remains in oxidized form
after the combustion zone 58. The ash extraction system 74 receives the hot ash
generated during the biomass gasification and contains the hot ash for subsequent
removal from the biomass gasifier 16. If desired for the given application, one or
more heat exchangers may be placed in the ash extraction system 74 to cool the hot
ash via convection.
[0032] Whereas the hot ash remains in the ash extraction system 74 for removal,
the producer gas 7 1 flows through conduit 72 to the cyclone 22. The cyclone 22 is a
dry filter that may be operated to remove dust and other particles from the producer
gas 71. For example, the cyclone 22 may be used to filter out particles equal to or
greater than approximately 5 micrometers. In some embodiments, approximately 60
to 65 percent of the producer gas 7 1 may comprise particles greater than 60
micrometers in size; therefore, the cyclone 22 may remove a large number of particles
from the producer gas 7 1.
[0033] After filtering in the cyclone 22, the producer gas 7 1 flows through a
conduit 76 to the first scrubber 24 where the filtered producer gas 7 1 is cleaned, for
example, by removing tar and entrained gases, such as hydrogen cyanide. In
particular, within the first scrubber 24, fines and tar may be separated from the
producer gas 7 1 with clean water, as indicated by arrow 78, to produce a stream of
black water 80 that exits a bottom portion of the first scrubber 24 and is directed to a
black water processing system located within a water treatment unit 81. The scrubbed
producer gas 71 exits the first scrubber 24 and is transferred to the second scrubber 26
via conduit 82.
[0034] In the second scrubber 26, additional fines, tar, and gases may be removed
with clean water 84. As before, the fines and tar may be separated from the producer
gas to produce a second stream of black water 86 that may exit a bottom portion of
the second scrubber 26 and be directed to a black water processing system located
within the water treatment unit 81. In some embodiments, the water treatment unit 81
may include a series of flash tanks that subject the black water 80 and 86 to a series of
pressure reductions to remove dissolved gases and to separate and/or concentrate the
fines. The separated fines may be recycled and used in the feedstock preparation unit
14 to provide additional biomass 36 for the biomass gasifier 16 if desired.
[0035] The scrubbed producer gas exiting the second scrubber 26 flows through
conduit 88 to the third scrubber 28, which may be a chilled water scrubber. In the
third scrubber 28, the producer gas may be cooled with chilled water 92 that flows
into the third scrubber 28, exchanges heat with the hot producer gas, and subsequently
flows back to a chilled water tank 93 where the water is cooled for recirculation. The
cooled producer gas flows through conduit 94 to the blower 30. The blower 30 is
operated to pull the producer gas 7 1 from the biomass gasifier 16 through the gas
cleaning and cooling subsystem 18. If desired, an excess portion of the producer gas
may be burned by flare 32.
[0036] The unburned portion of the producer gas flows from the blower 30 to the
filtering unit 34. The filtering unit 34 includes one or more filter elements configured
to extract particulates from the producer gas. The cleaned and filtered producer gas is
routed from the gas cleaning and cooling subsystem 18 to the power generation
system 20, where the producer gas may be utilized to produce power. For example,
the power generation system 20 may include a gas engine that combusts the producer
gas 1 with air 98 to produce power 100 for a downstream application. For example,
the power 100 may be used to directly operate other systems and/or to provide power
to a utility grid. During combustion, the gas engine may produce engine exhaust 102,
which may be used to dry the biomass 36 in the feedstock preparation unit 14 in some
embodiments.
[0037] FIG. 2 is a diagram of an embodiment of the biomass gasification system
10 that may be used to generate producer gas 7 1 in accordance with the presently
disclosed embodiments. The biomass gasification system 10 includes the biomass
gasifier 16 that converts the biomass feedstock 44 into the producer gas 7 1 via
pyro lytic heating with air or oxygen. To that end, the biomass gasifier 16 includes the
plurality of fluid injectors 66 disposed lengthwise along the side walls 68 of the
gasification enclosure in a flow direction from the gasifier inlet to the gasifier outlet in
the flow direction. In the depicted embodiment, the fluid injectors 66 are shown as
perpendicular to the gasifier walls. However, in other embodiments, the fluid
injectors 66 may be angled with respect to the walls of the gasifier, for example, as
shown in FIG. 1. In the illustrated embodiment, the plurality of fluid injectors 66
includes a first subset 104 of fluid injectors 66 including fluid injectors 106 and 108; a
second subset 110 of fluid injectors 66 including fluid injectors 112 and 114; and a
third subset 116 of fluid injectors 66 including fluid injectors 118 and 120. However,
it should be noted that in certain embodiments, each fluid injector 106, 108, 112, 114,
118, and 120 may represent a single injector or a plurality of injectors distributed
about the gasification chamber 50. In addition, in certain embodiments, additional
numbers of subsets as well as additional numbers of fluid injectors within a given
subset other than the illustrated quantities may be provided. Still further, it should be
noted that although in the illustration of FIG. 2, the fluid injectors are shown on a
single side of the gasification chamber 50, as would be understood by those skilled in
the art, presently disclosed embodiments may include fluid injectors disposed about
the circumference of the gasifier.
[0038] As described above, air/oxygen is supplied to the plurality of fluid injectors
66 (e.g., 106, 108, 112, 114, 118, and 120) by the air delivery system 69. The
illustrated air delivery system 69 includes an air source set 122 including independent
air/oxygen sources 124, 126, and 128, and a flow controller set 130 including
independent flow controllers 132, 134, and 136. Each of the components of the air
delivery system 69 is controlled by the control system 67 that includes control and
processing circuitry 138 and memory 140. The memory 140 may include any suitable
type of memory, including but not limited to read only memory (ROM), random
access memory (RAM), magnetic storage memory, optical storage memory, or a
combination thereof.
[0039] During operation of the biomass gasification system 10, the control
circuitry 138 is capable of independently controlling air/oxygen flow associated with
each of the air sources 124, 126, and 128 by independently controlling the flow
controllers 132, 134, and 136. For example, in the illustrated embodiment, the air
source 124 and the flow controller 132 may be concurrently operated to activate or
deactivate the flow of air to the first subset of fluid injectors 104. When the first
subset 104 of fluid injectors 104 is activated, the fluid injectors 106 and 108 receive
air flowing along an airflow path from the air source 124 and through the flow
controller 132, and air 142 and 144 is injected into the gasification chamber 50.
Similarly, the airflow path including the air source 126 and the flow controller 134
supplies the fluid injectors 112 and 114 with air 146 and 148 that is injected into the
gasification chamber 50. Likewise, air 150 and 152 is supplied to the fluid injectors
118 and 120 from the airflow path that includes the air source 128 and the flow
controller 136.
[0040] As described in detail above, the biomass feedstock 44 and the air/oxygen
48 are injected into the biomass gasifier 16 and flow in direction 62 through the
drying zone 54, the pyrolysis zone 56, the combustion zone 58, and the reduction
zone 60 to produce the producer gas 71. As also described above, the plurality of
fluid injectors 66 may be independently controlled to optimize the production of the
producer gas 7 1 based on a variety of operational parameters, such as the type of
feedstock 44 being utilized in the given process. For example, the plurality of fluid
injectors 66 may be independently controlled such that additional air/oxygen is
injected only into the approximated combustion zone 58 associated with the given
biomass gasification process (i.e., for the particular biomass 36 and feedstock 44).
For further example, the plurality of fluid injectors 66 may be independently
controlled such that air/oxygen is injected only into a bottom portion of the
combustion zone 58 (e.g., an approximate bottom quarter or half of the combustion
zone).
[0041] For instance, in one embodiment, the feedstock 44 may be wood chips, and
the combustion zone 58 may begin at approximately the lengthwise location indicated
by dashed line 154. In this embodiment, the first, second, and third subsets of fluid
injectors 104, 110, and 116 may all be activated since all the fluid injectors 106, 108,
112, 114, 118, and 120 inject air into the combustion zone 58 that begins at dashed
line 154. If air injection is only desired in a bottom portion of the combustion zone
58, however, only the third subset 116 of fluid injectors may be activated for use with
the wood chip feed.
[0042] In another embodiment, the feedstock 44 may be sawdust, and the
combustion zone 58 may begin at approximately the lengthwise location indicated by
dashed line 156. In this embodiment, the first subset of fluid injectors 104 may be
deactivated since the fluid injectors 106 and 108 are located at a lengthwise location
along the side walls 68 that is not suitable for injection of air into the combustion zone
58 that begins at dashed line 156. The second subset 110 and/or the third subset 116
of fluid injectors may then be activated, depending on whether injected air/oxygen is
desired throughout the combustion zone 58 or only in a bottom portion thereof. It
should be noted that the illustrated and described embodiments are merely exemplary,
and in additional embodiments, any subset of the plurality of fluid injectors 66 may be
independently controlled to inject air/oxygen at a desired lengthwise position along
the side walls 68 of the biomass gasifier 16.
[0043] FIG. 3 illustrates an embodiment of a method 158 that may be implemented
by the control system 67 to selectively activate the plurality of controllable fluid
injectors 66 based on an operational parameter of a biomass gasification process. The
method 158 includes receiving an operational parameter of the biomass gasification
process (block 160) and, based on the received parameter, determining desired subsets
of the fluid injectors 66 for activation (block 162). For example, as previously
described, the operational parameter may be the type of biomass 36 and feedstock 44
being utilized, and the activated subsets of fluid injectors 66 may be the fluid injectors
capable of injecting air and/or oxygen into the approximate combustion zone 58
associated with the type of biomass 36 and feedstock 44. Further, the method 158
includes controlling the air delivery system 69 to inject air and/or oxygen into the
gasification chamber 50 through the activated fluid injectors 66 (block 164).
[0044] FIG. 4 illustrates an embodiment of a method 166 that the control system
67 may utilize when the operational parameter is the type of biomass 36 and feedstock
44. The method 166 includes receiving data corresponding to the biomass and
feedstock type (block 168) and determining an approximate length of the pyrolysis
zone corresponding to that feedstock type (block 170). The pyrolysis zone length
may be utilized to determine the approximate length of the combustion zone 58 (block
172) and its corresponding location along the side walls 68 of the biomass gasifier 16.
The lengths of the pyrolysis and combustion zones may be determined, for example,
based on user input, prior knowledge of previous gasification processes, automatically
computed by the control system, based on a mathematical model, and so forth.
Subsequently, the fluid injectors 66 capable of injecting air/oxygen into the
combustion zone 58 (or the desired portion of the combustion zone 58) may be
identified (block 174), and the unidentified fluid injectors 66 may be deactivated
(block 176).
[0045] FIG. 5 illustrates an embodiment of a method 178 that may be implemented
by the control system 67 to control the fluid injectors 66 based on a detected tar
content of the producer gas 71. Specifically, the method 178 includes receiving data
corresponding to the tar content of the producer gas 7 1 (block 180), which may be
acquired, for example, via a sensor located at the outlet 70 of the biomass gasifier 16.
The method 178 proceeds by determining whether the tar content present in the
producer gas 7 1 is below a predetermined limit (block 182). For example, the
predetermined limit may be a limiting percentage of the producer gas 7 1 by weight or
volume that is allowed to be tar. If the tar content is below the predetermined limit,
the tar content of the producer gas 7 1 is monitored. However, if the tar content
exceeds the predetermined limit, the control system 67 identifies one or more fluid
injectors 66 that may be contributing to the excessive tar content in the producer gas
7 1 (block 184) and deactivates the identified fluid injectors 66 (block 186). Data
corresponding to the tar content of the producer gas 7 1 may then be received (block
180), and the process may be repeated until the tar content is below the predetermined
limit.
[0046] FIG. 6 illustrates an embodiment of a method 188 that the control system
67 may implement to control the plurality of fluid injectors 66 when the received
operational parameter is a parameter of a component of the power generation system
20. For example, in certain embodiments, the control system 67 may receive data
corresponding to an operational parameter of an engine (block 190) and exhibit
selective control over the plurality of fluid injectors 66 based on the engine parameter.
For example, in some embodiments, as the power output of the engine changes, the
air intake into the biomass gasifier 16 may also change, and the ash removal grate
speed may be adjusted to maintain a desired air to fuel ratio at the inlet of the biomass
gasifier 16. As such, the residence time of the feedstock 44 flowing through the
biomass gasifier 16 changes, and the change in the flow rate of the feedstock through
the gasification chamber 50 is determined by the control system (block 192).
[0047] The determined change in the flow rate of the feedstock 44 through the
biomass gasifier 16 may be utilized by the control circuitry 138 to determine a
corresponding change in the approximate locations of the pyrolysis and combustion
zones 56 and 58 in the gasification chamber 50 (block 194). Here again, the control
system 67 may then selectively control the plurality of fluid injectors 66 to ensure that
air/oxygen is being injected into the gasification chamber at the desired locations
along the length of the side walls 68 of the gasifier 16. For example, in the illustrated
method 188, the control system 67 adjusts the activated subsets of fluid injectors 66 to
exclude the injectors that are not capable of injecting air/oxygen into the desired
portion of the combustion zone 58 (block 196).
[0048] In the illustrated methods, the control system 67 controls the plurality of
fluid injectors 66 based on parameters such as the tar content of the producer gas 71,
the type of biomass 36 or feedstock 44, or an operational parameter of an engine of
the power generation system 20. However, it should be noted that these embodiments
are merely exemplary, and the control system logic employed in a particular biomass
gasification system 10 may be subject to considerable implementation- specific
variations. That is, the control system 67 may utilize various operational or process
specific parameters to independently control the plurality of fluid injectors 66, not
limited to the specific parameters described herein.
[0049] This written description uses examples to disclose the invention, including
the best mode, and also to enable any person skilled in the art to practice the
invention, including making and using any devices or systems and performing any
incorporated methods. The patentable scope of the invention is defined by the claims,
and may include other examples that occur to those skilled in the art. Such other
examples are intended to be within the scope of the claims if they have structural
elements that do not differ from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from the literal language
of the claims.
CLAIMS:
1. A biomass gasification system, comprising:
a reactor configured to gasify a biomass feedstock to thermally convert the
biomass feedstock into producer gas, wherein the reactor comprises:
an enclosure disposed about a biomass gasification chamber, wherein
the enclosure comprises an inlet, an outlet, and side walls disposed between
the inlet and the outlet; and
a plurality of fluid injectors disposed along a length of the side walls
and configured to inject fluid into the gasification chamber; and
a control system communicatively coupled to the plurality of fluid injectors
and configured to independently control each fluid injector of the plurality of fluid
injectors to independently control a flow of fluid through each fluid injector.
2. The biomass gasification system of claim 1, wherein the fluid
comprises air, oxygen, or a combination thereof.
3. The biomass gasification system of claim 1, wherein the plurality of
fluid injectors comprises a plurality of subsets of fluid injectors, and wherein each
fluid injector within a subset of fluid injectors is configured to be activated and
deactivated concurrent with the activation and deactivation of each other fluid injector
in the subset.
4. The biomass gasification system of claim 1, wherein the control
system is configured to selectively control each fluid injector based on an operational
parameter of the reactor.
5. The biomass gasification system of claim 4, wherein the operational
parameter comprises a type of the biomass feedstock, an approximate length of a
pyrolysis zone of the gasification chamber, an approximate length of a combustion
zone of the biomass gasification chamber, an operational parameter of an engine that
receives the producer gas from the reactor, a tar content of the producer gas, or a
combination thereof.
6. The biomass gasification system of claim 1, comprising an air delivery
system configured to supply the plurality of fluid injectors with air, oxygen, or a
combination thereof.
7. The biomass gasification system of claim 6, wherein the air delivery
system comprises an air source, an oxygen source, a flow controller, or a combination
thereof.
8. The biomass gasification system of claim 1, comprising a cyclone
configured to separate particulates from the producer gas.
9. The biomass gasification system of claim 1, comprising a scrubber
system configured to clean the producer gas.
10. The biomass gasification system of claim 1, comprising a power
generation system configured to receive the producer gas and to utilize the producer
gas to generate at least one of methanol, ammonia, and diesel fuel.
11. A method, comprising:
receiving data corresponding to an operational parameter of a biomass
gasification process or a power generation system that receives producer gas from the
biomass gasification process;
activating, based on the received data, a subset of a plurality of air and/or
oxygen injectors disposed along a length of a biomass gasification chamber; and
controlling an air delivery system to supply the activated subset of the
plurality of air and/or oxygen injectors with air and/or oxygen for injection into the
biomass gasification chamber.
12. The method of claim 10, wherein the operational parameter comprises
a type of biomass feedstock utilized in the biomass gasification process.
13. The method of claim 10, wherein the operational parameter comprises
an approximate length of a pyrolysis zone of the biomass gasification chamber.
14. The method of claim 10, wherein the operational parameter comprises
an approximate length of a combustion zone of the biomass gasification chamber.
15. The method of claim 10, wherein the operational parameter comprises
an operational parameter of an engine.
16. The method of claim 10, wherein the operational parameter comprises
a tar content of a producer gas produced in the biomass gasification process.
17. The method of claim 10, wherein the activated subset of the plurality
of air and/or oxygen injectors is capable of injecting air and/or oxygen into a
combustion zone of the biomass gasification chamber.
18. The method of claim 10, wherein controlling the air delivery system
comprises activating an air and/or oxygen source and a flow controller corresponding
to each of the air and/or oxygen injectors included in the subset.
19. The method of claim 10, comprising deactivating, based on the
received data, a second subset of the plurality of air and/or oxygen injectors disposed
along the length of the biomass gasification chamber.
20. The method of claim 18, comprising controlling the air delivery system
to deactivate an air and/or oxygen source and a flow controller corresponding to each
of the air and/or oxygen injectors included in the second subset.
21. A biomass gasification system, comprising:
a reactor configured to gasify a biomass feedstock in a biomass gasification
chamber to thermally convert the biomass feedstock into producer gas, wherein a
plurality of nozzles are disposed along a length of the reactor and configured to inject
air and/or oxygen into the biomass gasification chamber; and
a control system configured to determine an approximate location of a
combustion zone in the gasification chamber and to selectively deactivate each nozzle
of the plurality of nozzles not capable of injecting air and/or oxygen into the
combustion zone.