U.S. patent application number 16/378986 was filed with the patent office on 2019-08-01 for system and method for biomass combustion.
The applicant listed for this patent is Morgan State University. Invention is credited to Seong W. LEE.
Application Number | 20190234611 16/378986 |
Document ID | / |
Family ID | 65998120 |
Filed Date | 2019-08-01 |
United States Patent
Application |
20190234611 |
Kind Code |
A1 |
LEE; Seong W. |
August 1, 2019 |
SYSTEM AND METHOD FOR BIOMASS COMBUSTION
Abstract
Disclosed is a system and method for the combustion of biomass
material employing a swirling fluidized bed combustion (SFBC)
chamber, and preferably a second stage combustion carried out in a
cyclone separator. In the combustion chamber, primary air is
introduced from a bottom air box that fluidizes the bed material
and fuel, and staged secondary air is introduced in the tangential
direction and at varied vertical positions in the combustion
chamber so as to cause the materials in the combustion chamber
(i.e., the mixture of air and particles) to swirl. The secondary
air injection can have a significant effect on the air-fuel
particle flow in the combustion chamber, and more particularly
strengthens the swirling flow, promotes axial recirculation,
increases particle mass fluxes in the combustion chamber, and
retains more fuel particles in the combustion chamber. This process
increases the residence time of the particle flow. The turbulent
flow of the fuel particles and air is well mixed and mostly burned
in the combustion chamber, with any unburned waste and particles
being directed to the cyclone separator, where such unburned waste
and particles are burned completely, and flying ash is divided and
collected in a container connected to the cyclone separator, while
dioxin production is significantly minimized if not altogether
eliminated. The system exhaust is directed to a pollutant control
unit and heat exchanger, where the captured heat may be put to
useful work.
Inventors: |
LEE; Seong W.; (Ellicott
City, MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Morgan State University |
Baltimore |
MD |
US |
|
|
Family ID: |
65998120 |
Appl. No.: |
16/378986 |
Filed: |
April 9, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15056179 |
Feb 29, 2016 |
10253974 |
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16378986 |
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62121843 |
Feb 27, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F23G 2207/30 20130101;
F23G 5/46 20130101; F23G 2202/10 20130101; F23G 2203/50 20130101;
F23C 10/20 20130101; F23G 2200/00 20130101; F23G 5/50 20130101;
F23G 2207/102 20130101; F23G 2206/10 20130101; F23G 2207/101
20130101; F23G 2209/262 20130101; F23G 5/30 20130101; F23G 5/444
20130101 |
International
Class: |
F23C 10/20 20060101
F23C010/20; F23G 5/46 20060101 F23G005/46; F23G 5/44 20060101
F23G005/44; F23G 5/30 20060101 F23G005/30; F23G 5/50 20060101
F23G005/50 |
Claims
1. A system for fluidized bed combustion, comprising: a combustion
chamber, said combustion chamber further comprising: a primary air
distribution and delivery system configured to provide vertical
airflow through said combustion chamber; and a secondary air
distribution and delivery system configured to provide a plurality
of vertically displaced, horizontally aligned, tangential airflows
in said combustion chamber; and a biomass feeder in communication
with an interior of said combustion chamber and positioned to
deliver biomass material to said interior of said combustion
chamber at a location above said primary air distribution and
delivery system and below said secondary air distribution and
delivery system.
2. The system of claim 1, further comprising a cyclone separator
positioned downstream from said combustion chamber.
3. The system of claim 2, said cyclone separator having an air
inlet configured to receive flue gas from said combustion chamber
and fresh air from an air delivery system that supplies air to said
primary air distribution and delivery system and said secondary air
distribution and delivery system.
4. The system of claim 2, further comprising a heat exchanger
positioned downstream from said combustion chamber, wherein said
heat exchanger is in thermal communication with a thermal energy
conversion device.
5. The system of claim 1, further comprising a mobile chassis,
wherein said combustion chamber is mounted on said mobile
chassis.
6. The system of claim 1, further comprising a monitoring and
control system, said monitoring and control system further
comprising: a gaseous emissions monitor configured to detect levels
of particular matter and noxious emissions in flue gas from said
combustion chamber; and a processor having computer executable code
configured to: receive data from said gaseous emission monitor;
compare data received from said gaseous emissions monitor to alert
levels of an amount of particulate matter and noxious gases in
system flue gas; and in response to a determination that said
amount of particulate matter or noxious gases in system flue gas
exceed said alert levels, direct a control signal to at least said
secondary air distribution and delivery system to vary airflow
through said secondary air distribution and delivery system.
7. The system of claim 1, wherein said secondary air distribution
and delivery system further comprises a plurality of vertically
displaced, horizontally aligned sets of air injection nozzles.
8. The system of claim 7, wherein each set of air injection nozzles
comprises a plurality of nozzles evenly spaced around an internal
circumference of said combustion chamber.
9. The system of claim 8, wherein each air injection nozzle further
comprises a first branch extending radially through a wall of said
combustion chamber, and an internal branch configured at 90.degree.
to said first branch.
10. The system of claim 9, wherein said first branch comprises an
inlet, an air inlet channel extending from said inlet to an
interior, circular chamber, an interior flow channel extending from
said circular chamber in a direction parallel to but not collinear
with said air inlet channel, and a nozzle outlet extending at
90.degree. from said interior flow channel and having a reducing
diameter as said nozzle outlet extends from said interior flow
channel.
11. The system of claim 8, wherein said system further comprises at
least three of said sets of air injection nozzles.
12. A method for fluidized bed combustion, comprising the steps of:
providing a combustion chamber, said combustion chamber further
comprising: a primary air distribution and delivery system
configured to provide vertical airflow through said combustion
chamber; and a secondary air distribution and delivery system
configured to provide a plurality of vertically displaced,
horizontally aligned, tangential airflows in said combustion
chamber; providing a biomass feeder in communication with an
interior of said combustion chamber and positioned to deliver
biomass material to said interior of said combustion chamber at a
location above said primary air distribution and delivery system
and below said secondary air distribution and delivery system;
directing biomass from said biomass feeder to said combustion
chamber; directing a vertical primary airflow into said combustion
chamber and multiple, vertically displaced tangential airflows into
said combustion chamber to create a swirling fluidized bed of
biomass particles in said combustion chamber; and maintaining a
biomass feed rate from said biomass feeder, a primary airflow rate
from said primary airflow, and a secondary airflow rate from said
tangential airflows sufficient to maintain a combustion efficiency
of at least 90%.
13. The method of claim 12, further comprising: providing a
monitoring and control system, said monitoring and control system
further comprising: a gaseous emissions monitor configured to
detect levels of particular matter and noxious emissions in flue
gas from said combustion chamber; and a processor having computer
executable code configured to: receive data from said gaseous
emission monitor; compare data received from said gaseous emissions
monitor to alert levels of an amount of particulate matter and
noxious gases in system flue gas; and in response to a
determination that said amount of particulate matter or noxious
gases in system flue gas exceed said alert levels, direct a control
signal to at least said secondary air distribution and delivery
system to vary airflow through said secondary air distribution and
delivery system; and modifying airflow through said secondary air
distribution and delivery system to maintain combustion efficiency
in said combustion chamber of at least 90%.
14. The method of claim 12, wherein said biomass has a moisture
content of less than 35%.
15. The method of claim 12, further comprising the step of
directing flue gas from said combustion chamber to a cyclone
separator.
16. The method of claim 15, further comprising the step of directed
flue gas from said cyclone separator to a heat exchanger in thermal
communication with a thermal energy conversion device.
17. The method of claim 16, further comprising the step of
directing flue gas from said heat exchanger to an exhaust system.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 15/056,179 entitled "SYSTEM AND METHOD FOR
BIOMASS COMBUSTION" filed with the U.S. Patent and Trademark Office
on Feb. 29, 2016, now U.S. Pat. No. 10,253,974 issued on Apr. 9,
2019, which is based upon and claims benefit of copending U.S.
Provisional Patent Application Ser. No. 62/121,843 entitled "Method
and Design of the Ultra-Clean Mobile Combustor for Waste Biomass
and Poultry Litter Disposal," filed with the U.S. Patent and
Trademark Office on Feb. 27, 2015 by the inventor herein, the
specification of which is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] This invention relates to systems and methods for fluidized
bed combustion, and more particularly to a fluidized bed combustion
system and method optimized for burning biomass wastes and poultry
litter in an environmentally-friendly manner.
BACKGROUND OF THE INVENTION
[0003] The consolidation and industrialization of the poultry
industry over the last 50 years has resulted in highly concentrated
regional poultry operations. Traditionally, farmers managed the
manure or litter associated with poultry production by spreading it
on fields. However, as the industry consolidated, operations became
highly regionally concentrated, and cropland diminished, this waste
disposal method became less viable. For example, in the
Maryland-Delaware region, 523 million chickens are now produced
annually, generating approximately 42 million cubic feet of chicken
waste each year, such that chickens outnumber people in the region
by as much as 400 to 1. This high concentration of waste causes
eutrophication (e.g. nitrogen, phosphorus), particularly along the
shores of the Chesapeake Bay, the largest estuary system in the
United States, creating an urgent need for efficient, clean,
environmentally friendly chicken waste disposal approaches.
[0004] The United Nations and The U.S. Federal Government have
identified agriculture as the biggest user of water and a major
polluter of water. In fact, agriculture has been identified as the
single largest source of pollutants for rivers, lakes, and
estuaries in the U.S. The industrialization of agriculture has
resulted in such high concentrations of animal waste that
conventional disposal methods are no longer adequate or viable
(e.g. spreading on fields). Thus, there is an urgent need for
environmentally safe and economically viable approaches to
disposing of agricultural waste. This need in combination with
global demand for clean, low-cost, renewable energy has fueled
interest in biomass-to-energy conversion technologies, including
for use in disposing of high concentrations of animal waste, which
approach becomes even more appealing given recently implemented
regulations that prohibit the use of chicken litter as fertilizer
on significant acreage. However, due to the low energy density of
biomass, the economics of biomass-to-energy operations have been
challenging (i.e., fuel collection and transportation costs can be
high relative to energy density; high moisture content adds to
transportation costs and reduces burn efficiencies). Thus, there
remains a need for solutions that can reduce the cost of converting
biomass to energy and/or increase the efficiency of the combustion
process.
[0005] Fluidized bed combustion systems are often used for burning
biomass fuel. Most of the existing fluidized bed combustion
apparatus known to the inventor have only a single level secondary
injection of air in the fixed tangential direction to facilitate a
turbulent or swirling flow, as shown in U.S. Pat. No. 5,105,917 to
Harada et al., and in U.S. Pat. No. 8,161,917 to Yang et al., the
specifications of which are incorporated herein by reference in
their entireties. Certain systems disclose multiple secondary air
supply ports, such as the system shown in European Patent
Publication No. 0 458 967 A1. Still other systems disclose methods
for incinerating waste using a two-level swirling flow fluidized
bed without tangential flow for suppressing re-synthesis of dioxins
produced during incineration and the removal of a suspended
particulate material, such as the system disclosed in International
PCT Publication No. WO/2010/010630. The specifications of each of
the foregoing references are incorporated herein by reference in
their entireties. However, widespread commercial acceptance of such
prior systems has been lacking, due to an inability to reach
sufficiently high combustion efficiencies and minimization of
noxious emissions. Thus, there remains a need in the art for
fluidized bed combustion systems and methods capable of efficiently
and cleanly disposing of biomass materials.
SUMMARY OF THE INVENTION
[0006] Disclosed is a system and method for ultra-clean and
preferably mobile combustion, particularly configured for burning
biomass and poultry litter in an environmentally friendly manner
(i.e., so as to reduce emissions of pollutants), which system and
method provides high combustion efficiency using equipment of
compact design and that is easy to operate.
[0007] In accordance with certain aspects of an embodiment of the
invention, the system carries out preferably a two-step combustion
process, namely, a first stage combustion carried out in an
advanced swirling fluidized bed combustion (SFBC) chamber, and a
second stage combustion carried out in a cyclone separator. In the
combustion chamber, primary air is introduced from a bottom air box
that fluidizes the bed material and fuel, and staged secondary air
is introduced in the tangential direction and at varied vertical
positions in the combustion chamber so as to cause the materials in
the combustion chamber (i.e., the mixture of air and particles) to
swirl. The secondary air increases the residence time of the
particle flow. The turbulent flow of the fuel particles and air is
well mixed and mostly burned in the combustion chamber. Any waste
and particles that remain unburned in the combustion chamber are
directed to the cyclone separator, where such unburned waste and
particles are burned completely, and flying ash is divided and
collected in a container connected to the cyclone separator, while
dioxin production is significantly minimized if not altogether
eliminated. The collected ash and char may optionally be used as
fertilizer. The system exhaust, in the form of high temperature
flue gas, is directed to a pollutant control unit and heat
exchanger, where the captured heat may be put to useful work, such
as by generating steam for delivery to a turbine, powering a
Sterling engine, or such other energy generation devices as may be
apparent to those skilled in the art, or for direct heating of
process materials, such as water, feed stock (for drying the same),
or the like, or such other direct heat application processes as may
be apparent to those skilled in the art.
[0008] The system and method set forth herein have the potential to
significantly improve the economics of biomass-to-energy
operations, by dramatically improving the efficiency of the
combustion process while reducing capital and operating costs. The
single chamber design in comparison to the classic combustor system
with multiple chambers contributes to lower capital costs. This
novel system yields a more efficient burn rate and less solid and
gaseous waste than conventional systems for biomass waste
disposal.
[0009] Relative to other biomass combustion systems, the system and
method disclosed herein is expected to have a higher electrical
output, lower capital cost, lower maintenance costs, and greater
flexibility regarding fuel sources and conditions. Thus, the system
and method set forth herein has the potential to significantly
improve the economics of biomass-to-energy operations. In a
particularly preferred embodiment, a system and method operating in
accordance with the disclosure herein would have a commercial
electrical power rating of 50 MWe, would carry a capital cost of
$3,000-$3,200 per kW, and would carry operating and maintenance
costs of $15-$20/ton of feed, thus offering a clean, high
efficiency, and affordable method to dispose of biomass and poultry
litter while generating energy.
[0010] In accordance with certain aspects of an embodiment of the
invention, a system for fluidized bed combustion is disclosed
comprising a combustion chamber, the combustion chamber further
comprising: a primary air distribution and delivery system
configured to provide vertical airflow through the combustion
chamber; and a secondary air distribution and delivery system
configured to provide a plurality of vertically displaced,
horizontally aligned, tangential airflows in the combustion
chamber; and a biomass feeder in communication with an interior of
the combustion chamber and positioned to deliver biomass material
to the interior of the combustion chamber at a location above the
primary air distribution and delivery system and below the
secondary air distribution and delivery system.
[0011] In accordance with further aspects of an embodiment of the
invention, a method for fluidized bed combustion is disclosed,
comprising the steps of: providing a combustion chamber, the
combustion chamber further comprising: a primary air distribution
and delivery system configured to provide vertical airflow through
the combustion chamber; and a secondary air distribution and
delivery system configured to provide a plurality of vertically
displaced, horizontally aligned, tangential airflows in the
combustion chamber; providing a biomass feeder in communication
with an interior of the combustion chamber and positioned to
deliver biomass material to the interior of the combustion chamber
at a location above the primary air distribution and delivery
system and below the secondary air distribution and delivery
system; directing biomass from the biomass feeder to the combustion
chamber; directing a vertical primary airflow into the combustion
chamber and multiple, vertically displaced tangential airflows into
the combustion chamber to create a swirling fluidized bed of
biomass particles in the combustion chamber; and maintaining a
biomass feed rate from the biomass feeder, a primary airflow rate
from the primary airflow, and a secondary airflow rate from the
tangential airflows sufficient to maintain a combustion efficiency
of at least 90%.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The numerous advantages of the present invention may be
better understood by those skilled in the art by reference to the
accompanying drawings in which:
[0013] FIG. 1 is a schematic view of a system for burning biomass
in accordance with certain aspects of an embodiment of the
invention.
[0014] FIG. 2 is a close-up, cross-sectional view of a combustion
chamber used in the system of FIG. 1.
[0015] FIG. 3 is a top, cross-sectional view of the combustion
chamber of FIG. 2.
[0016] FIG. 4 is a side view of primary airflow nozzles for use in
the combustion chamber of FIG. 2.
[0017] FIG. 5 is a cross-sectional view a secondary airflow nozzles
for use in the combustion chamber of FIG. 2.
[0018] FIG. 6 is a top, cross-sectional view of a cyclone separator
used in the system of FIG. 1.
[0019] FIG. 7 is a flowchart depicting a method for burning biomass
in accordance with certain aspects of an embodiment of the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] The following description is of a particular embodiment of
the invention, set out to enable one to practice an implementation
of the invention, and is not intended to limit the preferred
embodiment, but to serve as a particular example thereof. Those
skilled in the art should appreciate that they may readily use the
conception and specific embodiments disclosed as a basis for
modifying or designing other methods and systems for carrying out
the same purposes of the present invention. Those skilled in the
art should also realize that such equivalent assemblies do not
depart from the spirit and scope of the invention in its broadest
form.
[0021] FIG. 1 shows a schematic view of a system for burning
biomass in accordance with certain aspects of an embodiment of the
invention, including a combustion chamber 100, air delivery system
(shown generally at 200), a cyclone separator 300, a heat exchanger
400, and exhaust system 500. Optionally, the entire system may be
housed on a mobile chassis (not shown) so that the system may be
moved from site to site for processing of biomass at the site of
production or collection of the biomass.
[0022] Combustion chamber 100 includes a generally cylindrical
housing having preferably a metal exterior and a refractory layer
on an interior surface of the metal exterior. A primary air
distribution and delivery system 110 is provided in the bottom of
the combustion chamber 100, and receives high pressure air from air
delivery system 200, in turn directing that air toward the top of
the combustion chamber in order to vertically distribute the
biomass/fuel and diffuse particles throughout the column in the
combustion chamber 100. Moreover, secondary air distribution and
delivery system 130 includes multiple, vertically displaced rows of
nozzles, discussed in greater detail below, which nozzles are
configured to provide controllable, multi-angle air-injection at
multiple, distinct vertical levels within combustion chamber 100 to
provide a swirling flow in the column, which in turn maximizes
combustion throughout the combustion chamber 100.
[0023] A fuel feeder 102 is provided adjacent combustion chamber
100, and may be provided, by way of non-limiting example, a hopper
for receiving biomass, poultry litter, and other materials that
might be used for fuel in the combustion chamber 100, and a
delivery mechanism 103, such as a feed screw, configured to deliver
such biomass/fuel from fuel feeder 102 to combustion chamber 100.
Such biomass/fuel is delivered into combustion chamber 100 at a
point above primary air distribution and delivery system 110, and
below secondary air distribution and delivery system 130. The solid
biomass/fuel is supplied tangentially into the combustion chamber
100, such that no bed material is required. The airflow from the
primary air distribution and delivery system 110 and from the
secondary air distribution and delivery system 130 act as both
particle fluidizers and combustion oxidizers. The multiple levels
of nozzles of secondary air distribution and delivery system 130
provide extended swirl flow along with additional air (e.g., oxygen
supply). This configuration retains particles in the combustion
zone, reducing unburned particles and thus minimizing residual
material. The extended swirling flow generated by the system
results in vigorous particle-to-wall collisions, which increases
the residence time and combustion efficiency of fuel particles in
the combustion zone.
[0024] A natural gas feed 104 is preferably positioned to feed
natural gas into combustion chamber 100 above primary air
distribution and delivery system 110. Natural gas is preferably
used only to initiate the burn at startup in order to achieve the
initial biomass ignition. Further, monitoring and control subsystem
160 is provided, which preferably includes temperature and pressure
sensors 162 within combustion chamber 100, one or more particulate
matter (PM) meters and emissions probes 164 capable of monitoring
both levels of particulates and gaseous emissions (including NOx,
SOx, CO, and CO.sub.2), which sensors and probes are readily
commercially available such that their specific configuration is
not addressed further here. Likewise, those skilled in the art will
recognize that additional process control accessories may be
provided as may be suitable for a particular installation.
Monitoring control subsystem 100 is also in electrical
communication with, and thus is configured to provide control
signals to, delivery mechanism 103 from fuel feeder 102 (e.g., by
controlling a motor driving a feed screw of delivery mechanism 103)
to control the amount of biomass/fuel delivered to combustion
chamber 100, to a blower 112 to control the amount of air delivered
through primary air distribution and delivery system 110 and
through secondary air distribution and delivery system 130, and
preferably to valves 114 to allow independent control of the amount
of air delivered through such systems 110 and 130 with respect to
one another. Alarm levels may be established for monitored data,
which alarm levels are preferably set by a person using data
processing equipment 166 responsible for configuring the system. As
an alarm relay is activated, the monitoring and control subsystem
160 is configured to decrease the fuel feeding rate through
preferably a variable speed controller, reducing such feed rate to
a point necessary to have the particulate matter levels below the
set alarm relay levels. Likewise, monitoring and control subsystem
160 controls the amount of air delivered through primary air
distribution and delivery system 110 and through secondary air
distribution and delivery system 130 (through control of blower 112
and valves 114 in air delivery system 200) so as to control the
burn rate in combustion chamber 100. All of these factors may be
controlled so as to maintain the safest possible burn rate so as to
maintain emissions within a desired range and so as to ensure a
maximum efficiency in biomass combustion is maintained.
[0025] With continued reference to FIG. 1, exhaust from combustion
chamber 100 is directed to a cyclone separator 300. As will be
discussed in further detail below, any waste and particles that
remain unburned in combustion chamber 100 are directed to the
cyclone separator 300, where such unburned waste and particles are
burned, and flying ash is divided and collected in a container
connected to the cyclone separator, while dioxin production is
significantly minimized if not altogether eliminated. The collected
ash and char may optionally be used as fertilizer. The system
exhaust, in the form of high temperature flue gas, is directed from
cyclone separator 300 to a heat exchanger 400 and an exhaust system
500 including a pollutant control unit. Heat captured by heat
exchanger 400 may be put to useful work through use of any thermal
energy conversion device 420 as may be deemed appropriate for a
given installation by persons of ordinary skill in the art, such as
by way of non-limiting example by generating steam for delivery to
a turbine, powering a Sterling engine, or such other energy
generation devices as may be apparent to those skilled in the art,
or for direct heating of process materials, such as water, feed
stock (for drying the same), or the like, or such other direct heat
application processes as may be apparent to those skilled in the
art.
[0026] FIG. 2 provides a front, cross-sectional view of combustion
chamber 100, while FIG. 3 provides a top, cross-sectional view of
combustion chamber 100. As shown in FIGS. 1-3, combustion chamber
100 includes a primary air box 116 that receives primary air from
blower 112, and directs such primary air to primary air
distribution and delivery system 110. Primary air distribution and
delivery system 110 directs primary air into combustion chamber
100, where such primary air receives natural gas through natural
gas feed 104 and biomass/fuel from delivery mechanism 103, both
igniting the biomass as it enters combustion chamber 100 and
causing it to flow upward in combustion chamber 100. As such
biomass flows upward through combustion chamber 100, it encounters
secondary air distribution and delivery system 130, which in turn
comprises two or more airflow manifolds 132, each of which receives
air from air delivery system 200. Each airflow manifold 132 directs
secondary air to a plurality of secondary air injection nozzles 134
positioned around an interior circumference of combustion chamber
100. In a particularly preferred embodiment, four air injection
nozzles 134 are provided at a common height on the interior of
combustion chamber 100, and are spaced evenly along the interior
circumference of combustion chamber 100 at that common height. The
secondary air injection nozzles 132 control the direction of the
injected secondary air into combustion chamber 100, injecting such
secondary air at various angles so as to cause the particles and
air in combustion chamber 100 to achieve a swirling effect so as to
increase combustion of the biomass in combustion chamber 100.
[0027] As best shown in the top, cross-sectional view of FIG. 3,
air nozzles 132a may be provided along an exterior of combustion
chamber 100 that receive secondary air from airflow manifolds 132,
and deliver such secondary air to each secondary air injection
nozzle 134. Each secondary air injection nozzle 134 has a first
branch that extends radially through both an exterior metal layer
150 of combustion chamber 100 and an internal refractory layer 152
lining an interior of combustion chamber 100. An interior branch of
each air injection nozzle 132 is arranged at approximately
90.degree. to each respective first branch so as to position the
outlet of secondary air injection nozzle 134 to direct secondary
air tangentially along the interior of refractory layer 152 of
combustion chamber 100, in turn creating a swirling effect on the
interior of combustion chamber 100.
[0028] As shown in the side view of primary air distribution and
delivery system 110 of FIG. 4, the primary air distribution and
delivery system 110 includes a plurality of primary nozzles 120,
which nozzles 120 are particularly configured to maximize air
distribution at the bottom of combustion chamber 100. Each nozzle
120 has a rounded, semi-circular head 121, a cylindrical branch 122
extending downward from head 121, and an outwardly extending lower
branch 123 that has a widening diameter as it extends from
cylindrical branch 122 to base portion 124, which base portion 124
comprises the widest diameter d for each nozzle 120. Base portion
124 receives air directly from primary air distribution and
delivery manifold 125, which extends horizontally along the bottom
portion of combustion chamber 100, receiving air from primary air
box 116. In certain configurations, a plurality of manifolds 125
may extend horizontally across the bottom of combustion chamber 100
so as to provide even distribution of nozzles 120 across the full
width of combustion chamber 100.
[0029] With continued reference to FIG. 4, horizontally extended
outlets 126 are positioned on each cylindrical branch 122, and
upwardly angled outlets 127 are positioned on each lower branch
123, for feeding air from primary air distribution and delivery
system 100 into combustion chamber 100. In a particularly preferred
embodiment, each primary nozzle 120 includes four horizontally
extended outlets 126 and four upwardly angled outlets 127. In a
prototype construction implementing the system and methods
described herein (described in greater detail below), a total of 24
outlets 126 were provided, each having a diameter d of 1/8 inch. In
an embodiment of the invention, openings formed by horizontally
extended outlets 126 and upwardly angled outlets 127 comprise 2% of
the overall surface area of the primary air distributors.
[0030] Similarly, and with reference to the cross sectional view of
secondary air injection nozzles 134 of FIG. 5, both the shape and
axial position of secondary air nozzles 134 are important to
providing proper air and material flow within combustion chamber
100. More particularly, secondary air injection nozzles 134
function to change the direction of the supplied secondary air so
as to cause a swirling flow condition inside of combustion chamber
100. As mentioned above, sets of preferably four, evenly
circumferentially spaced secondary air injection nozzles 134 are
provided at at least two, and preferably three, distinct heights on
the interior of combustion chamber 100. In the prototype
construction described above, the bottom-most set of secondary air
injection nozzles 134 were positioned 34 inches from the bottom of
the combustion chamber and primary air distribution manifold 125,
with the subsequent higher sets of secondary air injection nozzles
134 each evenly spaced 10-11 inches above the next-lowest set. In
any configuration, the position and number of secondary air
injection nozzles will generally be determined by the height of the
combustion chamber 100 above air box 116, with horizontally aligned
sets of secondary air injection nozzles 134 being positioned
equidistant to one another. It has been found that at least three
horizontal sets of secondary air injection nozzles 134 are most
preferred in order to ensure that an optimal biomass material
residence time is maintained for the biomass particles undergoing
combustion. The higher the number of second air injection nozzles
134, the higher the oxygen supply into the combustion chamber 100,
which in turn increases the swirling effect on the fluidized bed
and a resulting high combustion efficiency above 90%. Each
secondary air injection nozzle 134 includes inlet 135 that receives
secondary air from an airflow manifold 132. Inlet 135 opens into
inlet channel 136, which in turn directs secondary air into a
centrally located, circular chamber 137. An interior flow channel
138 extends from chamber 137, and at a distal end directs the
airflow through nozzle outlet 139, which outlet 139 extends at
generally 90.degree. to a flow axis of both inlet channel 136 and
interior flow channel 138, in turn introducing air into combustion
chamber 100 in a tangential direction so as to cause swirling air
flow. This configuration has been found to provide a swirling air
flow from the secondary air injection into combustion chamber 100,
which in turn forms the particle suspension layer and dilution zone
within combustion chamber 100. Through adjustment of the secondary
air injection through secondary air injection nozzles 134
configured in this manner, the axial position of the particle
suspension layer within combustion chamber 100 can be closely
controlled.
[0031] The resulting strong swirling air flow field in combustion
chamber 100, in combination with the interaction of centrifugal
forces and gravity on the particles in combustion chamber 100,
cause larger particles to be kept in combustion chamber 100 for a
significant amount of time, in turn contributing to high combustion
efficiency and extremely low emissions. The swirling particle flow
in combustion chamber 100 can be described by stochastic trajectory
modeling (STM), and the diffusion-kinetics model can be used for
predicting fuel materials depletion during the combustion process
to describe the residence time of particles in combustion chamber
100, which modelling techniques are known to those of ordinary
skill in the art. These techniques may, in turn, be used to control
biomass feed rate and airflow through primary air distribution and
delivery system 110 and secondary air distribution and delivery
system 130 to effect residence time and the overall combustion
process in combustion chamber 100. By way of non-limiting example,
in the exemplary prototype construction described below, biomass
material residence time in combustion chamber 100 would preferably
be in the range of 2-5 seconds with combustion temperatures of
1400-1700.degree. F.
[0032] FIG. 6 is a top, cross-sectional view of the cyclone
combustor 300, having an air inlet 302 that receives flue gas from
combustion chamber 100 and fresh air from air delivery system 200.
The high temperature flue gas directed to cyclone combustor 300 may
contain unburned carbon particles. As shown in FIG. 6, fresh air is
added into the flue gas before it enters the cyclone combustor 300.
In this configuration, the unburned carbon particles and oxygen in
the fresh air will burn again in the cyclone combustor 300. In
addition to re-burning the unburned carbon, the cyclone combustor
300 functions as a particle separator in which the coarse particles
will fall down to a particle collector. The flue gas is therefore
preliminarily cleaned through the cyclone, before it is passed on
to heat exchanger 400 and exhaust system 500.
[0033] As mentioned above, heat exchanger 400 may be employed to
put heat captured from the flue gas from combustion chamber 100 to
useful work. For example, such heat exchanger 400 may be used to
produce electricity through employment of a Sterling engine or
through steam generation to drive a turbine. Moreover, heat
exchanger 400 may be used for direct heating of water, for drying
of materials (including drying of biomass material that is to be
processed through combustion chamber 100 before its introduction
into combustion chamber 100), or for heating of spaces for workers,
consumers, livestock, or the like.
[0034] After heat exchanger 400, the flue gas may be directed to
exhaust system 500, which may include (by way of non-limiting
example) a filter bag or other filter housing, and an exhaust stack
or exhaust gas pool of standard configuration.
[0035] The foregoing system may be used to process a wide variety
of biomass material, including (by way of non-limiting example)
poultry litter, municipal solid waste, agricultural waste, algae
waste, biomedical hazard waste, and the like. Moreover, sawdust,
wood chips, wood pellets, switch grass, dried leaves, corn husks,
rice shells, and such other biomass materials as may be selected by
those skilled in the art may similarly be processed by the
foregoing system to produce high heat and energy.
[0036] The foregoing system may be particularly well suited to
processing of poultry litter. While total poultry litter production
on a given poultry farm will determine feed rate of materials to
combustion chamber 100, in a particularly preferred configuration,
poultry litter may be directed to combustion chamber 100 at a feed
rate of 40-60 lb/hr. Operating at a schedule of 20 hours/day, 6
days/week, and 52 weeks/year, such a feed rate can process
approximately 300,000 pounds of poultry litter each year. In
processing such poultry litter (as well as other biomass
materials), it will be important to monitor and regulate moisture
of the feedstock to ensure proper combustion in combustion chamber
100. Particularly for poultry litter, a desired practical moisture
level is between 15% and 35%, and above this range, pre-drying will
be required for combustion to proceed efficiently in combustion
chamber 100. Of course, feedstock may certainly have a lower
moisture content and achieve proper combustion in combustion
chamber 100, such that an overall operational target is for
moisture content of any biomass material to be generally below
35%.
[0037] In accordance with certain aspects of the invention, a
method for processing biomass material may comprise the steps shown
in FIG. 7. At step 702, biomass feedstock is provided having a
moisture content that is general less than 35%. In the event that
such biomass has a moisture content higher than 35%, predrying of
such biomass material should be carried out to reduce the moisture
content. Next, at step 704, such biomass material is introduced
into a combustion chamber 100 of a biomass combustion system
configured as detailed above. As the biomass material is being
introduced into combustion chamber 100, as noted at step 706, a
vertical primary airflow is directed into combustion chamber 100,
while multiple, vertically displaced tangential airflows are
introduced into combustion chamber 100, so as to create a swirling
fluidized bed of the biomass particles in combustion chamber 100,
with the biomass particles being combusted at a combustion
efficiency of at least 90%. At step 708, flue gas from the
combustion chamber is directed to a cyclone separator configured as
above, where any unburned waste and particles that were unburned in
the combustion chamber are burned completely, and flying ash is
divided and collected in a container connected to the cyclone
separator, while dioxin production is significantly minimized if
not altogether eliminated. The collected ash and char may
thereafter optionally be used as fertilizer. Next, at step 710, the
system exhaust (in the form of high temperature flue gas) is
directed to a heat exchanger, and at step 712 the heat captured
from the heat exchanger is put to useful work, such as by
generating steam for delivery to a turbine, powering a Sterling
engine, or other such other energy generation devices as may be
apparent to those skilled in the art, or for direct heating of
process materials, such as water, feed stock (for drying the same),
or the like, or such other direct heat application processes as may
be apparent to those skilled in the art. Finally, at step 714, the
flue gas is directed from the heat exchanger to the exhaust system
with significantly reduced noxious emissions, and more particularly
having NO.sub.x of less than 80 ppm, SO.sub.x of less than 20 ppm,
CO.sub.2 of less than 2%, and particulate matter content of less
than 3 lb/MM Btu.
Example 1
[0038] A lab-scale prototype of the system described above was
designed and built by the Lee Research Group at The Center for
Advanced Energy Systems and Environmental Control Technologies
(CAESECT) at Morgan State University in Baltimore, Md. The lab
prototype system can process 11-24 lb/hr of pre-dried poultry
litter with high combustion efficiency (over 96%) without
co-combustion or bed materials. The poultry litter was burned in a
well-controlled environment at a temperature low enough
(1,400-2,100.degree. F.) to avoid formation of nitrogen oxides, but
high enough to avoid agglomeration and slagging in the ash.
Milestones for efficiency, ultra-clean emissions, and particular
matter were set as follows: NO.sub.x (30-80 ppm), SO.sub.x (15-20
ppm), CO.sub.2 (1.5-2.0%), and particulate matter (2.0-2.5 lb/MM
Btu). The residual fly ash (i.e., phosphate P.sub.2O.sub.5 and
potassium, K.sub.2O) is a high value fertilizer. The results
produced from the prototype configuration indicate improved
performance characteristics over other combustion technologies, as
shown in Table 1 below.
TABLE-US-00001 TABLE 1 Comparison of System with Other Combustion
Technologies System According to Aspects of the Stoker* BFBC* CFBC*
Invention Firing Capacity Small/ Small/ Medium/ Small/ Medium
Medium Large Medium Combustion =80% 80-90% 85-94% Above 95%
Efficiency (%) SO.sub.x Removal None Sorbent Sorbent in Optional in
combustor in bed bed/ freeboard NO.sub.x Emissions High Low Very
low Very low Ash Form Bottom Bottom Bottom Fly ash ash ash ash
Combustion 1,300 850-950 850-1000 850-1,250 Temperature Primary Air
100 100 >80 10-50 Fraction (%) Mean Gas- None 0.2 0.5-1.0 1-5
Particle Slip Velocity (m/s) Turbulence in None Good Excellent
Excellent Combustor *Stoker-Fired Combustor, BFBC--Bubbling
Fluidized Bed Combustor (FBC), CFBC--Circulating FBC, SFBC
[0039] In order to achieve the foregoing benefits, the prototype
system was configured as detailed in Table 2 below:
TABLE-US-00002 Combustor Dimensions Component Description Units
(in) Units (cm) 1 Combustor Outer Diameter (d.sub.cod) 15.12
38.4048 2 Combustor Internal Diameter (d.sub.cid) 13.72 34.8488 3
Refractory Material Thickness (t.sub.r) 0.7 1.778 4 Fuel Feeder
Diameter (d.sub.f) 2.9 7.366 5 Primary Air Inlet Diameter (d.sub.p)
3.5 8.89 6 Secondary Air Inlet Diameter (d.sub.s) 0.46 1.1684 7
Total Combustor Height (H) 74 187.96 8 Air Box Height (H.sub.a) 13
33.02 9 Combustion Chamber Height (H.sub.c) 61 154.94
[0040] The prototype configuration was provided one primary port
and 12 secondary ports. The primary air was injected from the
bottom of the chamber. The heights of secondary air nozzles were
34, 45 and 55.5 inch respectively. The feeding rate for the
prototype configuration was 11-24 lb/hr. The air flow rate for
primary air was 49-110 cfm, and for secondary air was 6-16 cfm. The
temperature during poultry litter combustion was between
1,400-2,100.degree. F., which achieved up to 97% combustion
efficiency. The measured emissions from the combustion chamber were
0-23 ppm NOx, 0-19 ppm SOx, 0-1.7% CO2, and particular matter of
0.45-1.19 lb/MM Btu, achieving a combustion efficiency of up to
97%.
[0041] A system and method implemented in accordance with the above
disclosure provides significant opportunity for the clean disposal
of biomass with the added advantage of power generation. The total
number of farms in the U.S. producing poultry products, including
broilers, breeders and egg layers is estimated at 99,700. Of this
total, approximately 30,000 broiler farms account for 95% of
broiler production in the U.S., with 6%-7% of broiler production
generated in the Delaware-Maryland-Virginia region, with 2,700
broiler farms. The U.S. accounts for 20% of the world's broiler
production, while European Union countries account for 12% (60% of
U.S.). The current projections for both the small scale farm unit
and a large scale regional unit configured as described above would
generate energy to the grid that is currently estimated to be able
to pay back the capital cost in 3.5 years. This does not include
any environmental credits/funding, or the value of cost for
bio-waste disposal.
[0042] Longer-term markets would include any agricultural industry
where biomass is generated and must be disposed of in a clean,
cost-efficient manner (including, by way of non-limiting example,
pork and meat production industries, rice husk bio-mass, and post
algal processed (oil-extracted) biomass). In addition, algae is an
interesting source of bio-energy for its concentration of oil.
Currently, after oil extraction, the remaining algal biomass can be
dried and "pelletized" and used as fuel that is burned in
industrial boilers and other power generation sources. The system
and method described herein may be suitable to decrease costs of
generating energy from the spent algal biomass, increasing the
market potential for the technology.
[0043] Moreover, the system and method described herein are
believed to provide significant improvement over conventional
direct combustion technologies. For example, for bubbling fluidized
bed combustion, high pressure air is fed through the bottom of the
boiler with lower fluidization velocity which causes a bubbling
effect and allows most of the bed material to be retained in the
lower furnace. For circulating fluidized bed combustion,
high-pressure air suspends the bed material and fuel particles,
which can rise up the chamber into the cyclone. Heavy particles
will fall into the cyclone hopper and be returned to the furnace to
be used again. For swirling fluidized bed combustion, secondary air
ports provide a swirling flow environment for combustion in an
effort to increase the particle residence time and reduce unburned
particles. However, the system and method employed in accordance
with the invention provides multiple levels of secondary air
injection nozzles, with optimized configurations for both primary
air injection nozzles and secondary air injection nozzles, which
features optimize the ability to control the combustion process and
achieve higher combustion efficiencies (with resulting lower
noxious emissions) than such previously known systems. As
demonstrated in the initial test results (above), the system and
method disclosed herein 1) provides efficient burning at controlled
temperatures which reduces NO.sub.x and particulate emissions, 2)
supplies sufficient secondary air and extended swirling air to burn
fuels in the upper part of combustion chamber with high efficiency,
3) mixes fuel and combustion air quickly and uniformly, and 4)
provides large gas-particle slip motion which prolongs particle
residence time and allows a reduction in chamber size and thus the
cost of the system.
[0044] Having now fully set forth the preferred embodiments and
certain modifications of the concept underlying the present
invention, various other embodiments as well as certain variations
and modifications of the embodiments herein shown and described
will obviously occur to those skilled in the art upon becoming
familiar with said underlying concept. It should be understood,
therefore, that the invention may be practiced otherwise than as
specifically set forth herein.
* * * * *