Note: Descriptions are shown in the official language in which they were submitted.
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D D~scription
SYS TE~ FOR BU~N. TNG B IOM~S S
TO PRODUCE HOT ~A.
Technical Field
This invention relates to the field o~
power plants and more specifically to a system
~or prducing hot gas to pwoer a trubine, or for
a ~ossil booster or incinerator.
Backgrol~nd A~t
Developing alternative sources of ~uel has
become an increasing concern both
environmentally and economically. Traditional
~ossil fuels are becoming rare and expensive.
Burning them, often has a negative impact on
the environment.
In an ef~ort to solve the problems
associated with traditonal fossil fuels,
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attention has been directed toward burning
biomass to fuel a ~urbine system. Biomass, in
the form of sawdust, has proven to be a viable
option for fueling turbine systems.
A turbine system consists generally of a
combustion chamber for burning fuel in the
presence of compressed air provided by an air
compressor gas generator, a turbine into which
high pressure combustion gas flows, expands and
produces power to drive the air compressor, and
an electrical generator which is powered by the
power turbine.
When designing a system to burn wood,
several issues must be addressed. Wood
combusts at a substantially higher temperature
than traditional fossil ~uels. The life and
ef~ectiveness of the turbine will be
substantially af~ected by high temperatures and
ash, a byproduct o~ burning wood. Further, the
abrasiveness of sawdust and the combustion of
sawdust must be considered when ~eeding the
sawdust into the combustion chamber.
Several systems have been developed for
burning wood to produce power. Typical of the
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art are those devices disclosed in the
following U.S. Patents:
Pat. No. Inventor(~) Issue Date
2,735,266 G.H. Atherton Feb. 21, 1956
4,409,786 Hamrick et al. Oct. 18, 1983
5,341,637 Hamrick Aug. 30, 1954
The '266 patent teaches a portable, self
contained power plant for converting wood waste
to electrical energy. A chamber is utilized to
burn and pyrolize wood on a grate to form
combustible products which are in turn injected
into a second combustion chamber for complete
combustion. The system generates a relatively
low amount of energy due to low wood burning
rates inherent with burning on a grate or pile.
Further, the system does not provide a
suf~icient means for removing ash from the
combustion gas. Also, a control system is not
provided ~or controlling various aspects o~ the
system during operation thereo~.
The '786 and '637 patents teach wood
burning systems for fueling a turbine. Each
system is designed to generate a large amount
of energy. The '786 patent does not teach a
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control system suf~icient for commercial
operation o~ the system. The systems taught in
both patents teach combustors wherein the
biomass is fed into the combustor ~rom the top
or proximate the top. Combustion o~ wood
particles is inef~icient with this
con~iguration because the larger particles move
out of the combustion zone, due to gravity,
be~ore they entirely combust. Further, the
feediny system disclosed in both patents is not
sufficient ~or commercial application.
Moreover, with the design of the '637
combustion chamber, slag is prone to collect on
the walls of the chamber. Also, the combustion
15- chamber and cyclone filter design o~ the '637
patent tend to ~oster pressure drops. Further,
the control system disclosed in the '637 patent
does not provide ~or environmental concerns.
Therefore, it is an object of the present
invention to provide a system ~or burning
biomass to produce hot gas which includes a
~eeding system such that the system can be used
commercially.
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It is another object of the present
invention to provide a system for burning
biomass which includes a more efficient and
smaller combustor and cyclone ~ilter.
It is yet another object of the present
invention to provide such a system which
combusts the biomass more efficiently.
Moreover, it is an object of the present
invention to provide a system for burning
biomass to produce hot gas which includes a
control system for monitoring and controlling
environmentally damaging gas within the exhaust
gas.
Summary
Other objects and advantages will be
accomplished by the present invention which
provides a system for burning biomass to
produce hot gas for powering a turbine. The
system o~ the present invention includes a wood
processing system, a combustor, a cyclone ash
separator, a gas generator, a turbine and a
control system. The wood processing system
-
-
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serves to process, dry and prepare the biomass
for injection into the combustor. The biomass
is injected into the bottom of the combustor.
Combustion o~ the biomass takes place in the
combustor. The resultant combustion gas enters
the cyclone ash separator ~or removal o~ ash
from the combustion gas. The combustion gas
exits the cyclone ash separator via a duct. An
air bypass assembly permits the injection of
bypass air into the stream of the combustion
gas at t~e exit of the cyclone. The combustion
gas and bypass air enter the turbine, where
they expand to power the turbine which drives
an electrical generator.
Rrief Description of the Drawinas
The above mentioned features of the
invention will become more clearly understood
from the following detailed description o~ the
invention read together with the drawings in
which:
Figure 1 illustrates the biomass burning
system of the present invention;
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Figure 2 illustrates the wood processing
system of the present invention;
Figure 3 illustrates an alternate
embodiment o~ the sawdust preparation system of
the present invention;
Figure 4 illustrates an enlarged view of
the combustor and cyclone;
Figure 4A illustrates an in~ector region
for a combustor to accommodate the use of very
fine particulate fuel.
Figure 5 is a top view of the vanes and
vane actuator at the lower end of the
combustor;
Figure ~ is an alternate embodiment of the
air bypass assembly;
Figure 7 is a block diagram of the control
system for the system for burning biomass of
the present invention; and,
Figure 8 illustrates the major CCP input
and output signals and controller functions.
Description of the Preferred Embodiments
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A system ~or burning biomass to produce
hot gas to power a turbine incorporating
varlous features of the present invention is
illustrated generally at 10 in Figure 1. It
will be noted that although a system for
providing hot gas to power a turbine is
described herein, it is not intended to limit
the system to this particular use and can be
utilized as a hot air source ~or a fossil power
plant booster or an incinerator.
The system for burning biomass 10 is
designed to provide an improved wood processing
system. Further, the system provides an
improved manner ~or injecting the biomass into
the combustor 14. Moreover, an extensive
control system 22, shown in Figure 7, is
provided ~or monitoring and controlling various
aspects o~ the system 10, as well as exhausts
and byproducts o~ the system 10.
The system for burning biomass 10 of the
present invention generally includes a biomass
(typically wood sawdust~ processing system 12
(shown in Figure 2), a combustor 14, a cyclone
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.
ash separator 16, a gas generator 18 (including
both a gas generator turbine 20 and a
compressor 21), a power turbine 19, an
electrical generator 17 (shown in Figure 1),
and a control system 22 (shown in Figure 7).
The power turbine 19 is coupled to the
generator 17 through a gear box 123 and a brake
125.
Referring to Figure 2, the wood processing
system 12 includes a reclaiming system 26, a
sawdust preparation system 28, a storage unit
30 and a pressurized lock vessel assembly 32.
The reclaiming system 26 includes a dump hopper
34 into which the sawdust is dumped. The
sawdust is fed ~rom the dump hopper 34, by a
reclaimer 35, onto a drag conveyor system 36
including a first 130, second 131 and third
drag conveyor 132. The first conveyor 130
includes a magnet 38 at its terminal end ~or
removing iron and other ferrous metals ~rom the
sawdust. The second and third conveyors 131,
132 are used to divert biomass into aspirator
bins 40A, 40B. In the pre~erred embodiment,
_
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the drag conveyor system 36 is designed to
convey a maximum of ten tons per hour. The
drag conveyor system 36 feeds the sawdust into
a destoner or aspirator 40 (A and B) which
removes rocks, bark, bottles and other
remaining debris, From the destoner/aspirator
40, the sawdust is fed pneumatically into the
sawdust preparation system 28. The sawdust
preparation system 28 consists of two or more
parallel paths to obtain the desired flow rate
of biomass ~uel.
In the preferred embodiment, the
(e.g.,sawdust) biomass preparation system 28
includes at least one air swept pulverizer 42A
(and preferably a second air swept pulverizer
42B) which serves to pulverize, dry and
classify the sawdust in one efficient
operation. The air swept pulverizers 42A, 42B
can be operated in an ambient pressure mode or
high pressurized mode. The ambient pressure
mode has ~he advantage of being able to blend
differen~ types o~ ~uels with di~ferent
moisture content prior to combustion. The high
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pressurized mode has the advantage of
processing only wet sawdust outside o~ the
combustor thereby eliminating the potential
explosion problem. Additionally, the process
directs to the combustor all wood fuel
ingredients including the wood alcohol vapors
lost in the unpressurized system. In the wood
processing system 12 depicted in Figure 2, two
air swept pulverizers 42A, 42B are utilized and
they are operated in the ambient pressure mode.
The sawdust enters the air swept pulverizers 42
at approximately ~orty-~ive weight percent
water in a ~luidized air stream from the
aspirators 40A, 40~3. The sawdust is dried in
the air swept pulverizers 42 to approximately
20 weight percent water. In the preferred
embodiment, turbine exhaust air ~rom the system
lO is pulled through the pulverizers 42 to dry
the biomass and each air swept pulverizer 42
pulverizes and dries 9,300 pounds per hour at
300 horsepower using 13,940 (ACFM) actual cubic
~eet per minute o~ 600~F turbine exhaust air.
Drying air dampers 61 ~eed drying air into the
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pulverizers 42. Each air swept pulverizer 42
processes 9,300 pounds per hour o~ sawdust at
45 weight percent moisture to approximately
6,480 pounds per hour of wood fuel at 20 weight
percent moisture. The preferred air swept
pulverizer 42 is a Jacobson air swept
pulverizer, model number 48-H.
Radial materials fans 43A, 43B are used to
pull drying air (47) and biomass fuel which is
being dried in the pulverizers 42A, 42B through
the drying system and forces the air through
cyclones 44A, 44B. The fluidized transfer
process greatly increases the efficiency o~ the
drying process. An elevated loop in the
~luidized transport ducts 41A, 41B totally
eliminates the possibility of introducing any
high mass objects such as stones and metals
into the biomass fuel pulverizers 42A, 42B.
Cyclones 44A, 44B are in communication
with each of the air swept pulverizers 42A,
42B, and the biomass fuel from the pulverizers
42A, 42B is fed into the cyclones 44A, 44B by
the materials fans 43A, 43B. The lower end of
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the cyclones 44A, 44B define rotary feeders
46A, 46B which pass the biomass into a
pneumatic conveyor 48.
The pneumatic conveyor 48 moves the
biomass into the top of a storage cyclone 30.
The biomass is discharged from the bottom of
the cyclone 30 into a live bin 52. Inclined
drag conveyors could also be used in the place
of the pneumatic conveyor to fill the live bin
52. The live bin 52 has a reversing cross
auger and eight feed augers 51 that will move
the fuel dust to one of two lock vessels 56A,
56B .
The pressurized fuel dust ejector assembly
32 includes one or two pressurized lock vessels
56A, 56B which communicate in a parallel manner
to the charging vessel 57. Each lock vessel
56A, 56B can be cross-charged with compressed
air from the other and topped off with
mechanical compressed air before it is
connected to the charging vessel 56. This
eliminates pressure surge in the feed system
and pressure surges in the gas compressor
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14
system. Again the charge vessels are
repressurized before ~eeding the biomass into
the charging vessel 57. An auger 58 at the
bottom o~ the charging vessel 57 typically
meters out biomass at 1-3.54 pounds per second
into the pressurized combustor 1~. Compressed
air ~rom the compressor 21 is input to a high
temperature and pressure blower 59 which is
used to boost the ~uel dust conveying air which
discharge~ into the combustor 14. Plant
compressed air is used to activate rubber
vibrator jets 49 on the side o~ the lock
vessels 56A, 56B and the walls o~ the charge
vessel 57. These jets ~luidize the ~uel dust
so i~ does not bridge or plug the holes in the
ejector lock vessels 56A, 56B and/or the charge
vessel 57. The charge vessel 57 also has a
centerline-mounted rotating mechanical and air
jet brldge breaker 50 that keeps the ~uel dust
in a ~luidized state so that it moves to the
discharge auger 58 without bridging or rat
holing in the charge vessel.
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,
In an alternate e~bodiment, the lock
vessels 56A, 56B and the charge vessel 57 are
equipped with internal rotating vessels and a
fixed bridge breaking screw auger to move the
fuel out o~ the lock vessels into the charge
vessel 57 and to break the bridge in the charge
vessel and move the fuel dust through a
metering screw so that it can be pneumatically
injected into the combustor.
The wood processing system 12 further
includes a manually fillable receptacle 60
positioned at the ~ront end of the pneumatic
conveyor 48. The receptacle 60 provides a
location for manually loading fuel dust or
additives to the system. A second receptacle
(not shown) can be positioned at the augers 51
as a convenient location to add additives when
such are used to control the ash problem
related to burning sawdust.
Pneumatically feeding of biomass (e.g.,
sawdust) from the aspirator bins 40A, 40B and
metering augers to the pulverizers 42A, 42B ,
and pneumatically conveying the biomass fuel
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16
dust to the live bin 52 with materials fan 45
reduces the temperature o~ the drying air ~rom
the turbine to 250~ or less eliminating the
possibility of explosion o~ fuel dust in the
pulverizers, their cyclones 44A, 44B, the live
bin fan 45 and the live bin cyclone 30. The
dust discharged ~rom the pulverizer cyclones
44A, 44B and live bin cyclone 30 is recycled to
a bag house 47 through a rotary lock 46 back
into the conveyor line 48 by ~an 43.
In an alternate embodiment, shown in
Figure 3, the sawdust preparation system 28
includes the use of a pressurized air swept
pulverizer system 162. In the embodiment
shown, two air swept pulverizer systems 162 are
utilized in a parallel manner (as in Figure 2)
to ~eed into one high pressure and high
temperature cyclone 171. It will be noted that
one or more than one air swept pulverizer
system 162 can be utilized. Each air swept
pulverizer system 162 includes a biomass surge
hopper 163, a ~irst isolation valve 164, a lock
hopper 165, a second isolation valve 166, a
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charge hopper 167, a metering screw 168, an air
swept pulverizer ~eed hopper 169 and an air
swept pulverizer 170. The biomass surge hopper
163 receives the processed sawdust ~rom the
destoner or aspirator gO (see Figure 2). The
sawdust moves through the ~irst isolation valve
164 and into the lock hopper 165 where the
sawdust is pressurized and raised in
temperature. In the preferred embodiment, the
sawdust is pressurized to 125 psi and brought
to a temperature o~ 150~F. The sawdust moves
through the second isolation valve 166 into the
charge hopper 167. In the pre~erred
embodiment, the sawdust is maintained at the
same pressure and brought up to 200~F. The
metering screw 168 meters the sawdust into the
air swept pulverizer ~eed hopper 169 which
~eeds the sawdust into the air swept pulverizer
110 a~ a rate o~ 5 tons/hour at 45 weight
percent water. The sawdust is dried and
pulverized in the air swept pulverizer 170.
Pre~erably, the sawdust is dried with hot air
~rom the compressor 21 (see Figure 1). In the
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18
preferred embodiment, ducts 197, 198 are in
communication with the combustor duct 25 to
feed air into the pulverizers 170.
From the air swept pulverizer system(s)
162, the wood fuel is fed into a high pressure,
high temperature cyclone 171, where the wood
fuel 152 is separated from the gas.
Pre~erably, the cyclone 171 is held a~ 350~F
and 125.5 psi. The high temperature air is
exhausted through the top of the cyclone 171
and is injected into the combustor 14 via the
port 95 to increase power and BTU input. The
wood fuel 152 exits through the lower end of
the cyclone 171 through a high temperature
rotary air lock 172 and enters a pneumatic feed
line 173. Primary air 150 from a conveying air
line 174 i5 fed into the rotary air lock 172 to
mix with the wood fuel 152. In the pre~erred
embodiment, the rotary air lock 172 is held at
605~F and a pressure dif~erential o~ 0.5 psi
and ~he conveying air line 174 is at 126.5 psi
and delivers air into the rotary air lock 172
a~ a temperature of 605~F and a rate o~ 2-4
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pounds/sec. The wood fuel 152 and primary air
150 are fed into the bottom of the combustor 14
via the pneumatic air line 173. In the
preferred embodiment, the air 150 and wood fuel
152 mixture is delivered at a temperature of
500~F and a pressure of 126 psi; the air 150 is
delivered at a rate of 8 pounds/second and the
wood fuel 152 at a rate of 1-5 pounds /second
at 20 weight percent water.
In the preferred embodiment, the primary
air 150 is fed from the air compressor 21 which
delivers the air at 600~F and a pressure of 125
psi. A booster fan 175 mounted in a pressure
vessel 176 is utilized to boost the pressure
and temperature of the primary air 150 before
it enters the conveying air line 174.
It is advantageous to use the pressurized
alr swept pulverizer system because there is no
dry fuel handling. This decreases the
potential fire problem, and all volatile
organic compounds are burned. Further, this
system offers better fuel efficiency and
emissions control and added power. Moreover,
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less capital equipment is required to process
the sawdust.
The combustor 14, shown clearly in Figure
4, is a pressure balanced bottom ~uel feed
combustor. The combustor 14 includes an outer
shell 66, a combustor lining 68 defining a
network of openings 71 and annular slots 70, an
annulus 72 between the outer shell 66 and the
combustor lining 68, a bottom fuel injector 74,
a gas burner 78, and a commercial gas burner
controller 190. The outer shell 66 defines a
port 95 at a lower end thereo~. During
operation o~ the system 10, the port 95
receives secondary and tertiary air 128 from
the air compressor 21, which i9 powered by the
gas generator turbine 20. A check valve 24
(~igure 1) is included in the air vent 25 to
the combustor 14 at port 95 to prevent back
~10w from the combustor 14 such that damage to
the compressor 21 is prevented. Also, a
pressure relie~ valve 6~ i8 in communication
with the duct 25 ~or relieving pressure in the
system. Further, an alternate embodiment
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21
includes a steam injector 134 to inject steam
into the tertiary air 128 of the annulus 72 of
the combustor 14 and/or the annulus 98 of the
cyclone 16. Steam is injected to boost turbine
power after reaching 90~ of achievable power by
using wood fuel only. In the preferred
embodiment, the outer shell 66 is fabricated
from 0.5 in. thick carbon steel or the
equivalent and the inside of the outer shell 66
is insulated with 3" thick fiber~raxTM
insulation retained by a 0.078" stainless steel
floating liner.
The bottom fuel injector 74 injects the
wood fuel 152 from the wood processing system
12 into the bottom of the combustor 14. The
fuel is metered into the pneumatic line
entering the fuel injector 74 by the metering
screw 58. Bottom injection of fuel into the
combustor 14 increases residence time of the
fuel in the combustor 14 and reduces the
required energy for injection. Bottom
injection also prevents accumulation of
unburned, ashes and slag inside the combustor
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14. In the preferred embodiment, the
combustion zone at the orifice of the fuel
injector 74 is lined with a refractory casting
of Andalucast LCV (FSS-1151) cured to 650~F.
The lower end of the combustor 14 is
configured to promote thorough burning of the
wood fuel 152 fed into the combustor 14.
Generally, the lower end of the combustor 14
includes a refractory cone 80 and a secondary
air flow controller 178, shown in Figure 5, for
controlling the air 128 flowing from the
combustor annulus 72 into the re~ractory cone
section 153. The refractory cone 80 serves to
accumulate and radiate heat to stabilize
initial combustion. In the preferred
embodiment, the control of the secondary air
flow 128 is accomplished by a plurality of
movable vanes 179 which are controlled by a
vane actuator 180, shown generally in Figure 4.
For applications that may involve the use
of very fine particulate (dust) fuel, it may be
necessary to have means for initiating
combustions. An embodiment of such a fuel
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injector 74 ' iS illustrated in Figure 4A. In
this embodiment, a liquid fuel line 75 is
disposed within the lower end of the combustor
14 to convey fuel to a nozzle 76 positioned
proximate the cone 80. This fuel line 75 is
protected from extreme the incoming regular
~uel 152 with a barrier 77. The liquid fuel is
ignited in any normal manner at the nozzle 76
to raise the temperature of the dust of regular
~uel to initial combustion temperature.
Thereafter, the liquid ~uel ~low can be
terminated.
A top view of the vanes 179 is shown in
Figure 5. The vanes 179 encircle the exit of
the fuel injector 74. Each of the vanes 179
pivots relative to one end such that the vanes
179 can be maneuvered to control air flow
therethrough. As shown in Figure 5, the vanes
are positioned in a fully open position thereby
permittlng a maximum air flow. Controlling the
amount of secondary air 128 flowing into the
lower end o~ the combustor 14 controls both the
secondary air 128 to wood fuel 152 ratio and
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24
the flame temperature in the re~ractory section
153 of the combustor and promotes swirling of
the wood fuel 152 ~or a more thorough
combustion o~ the wood ~uel 152. The degree of
opening between the vanes 179 is achieved with
the actuator 180 which either draws the vanes
closer or separates them via the connecting
linkage 181.
The combustor ~iner 68 defines a plurality
o~ spaced annular slots 70, as shown in Figure
4. The annular slots 70 permit cooling-
dilution air 129 ~lowing in the annulus 72 to
enter into the combustion zone 122 ~or
supporting combustion throughout the combustor
14 and controlling the ~lame and gas
temperature. In the preferred embodiment, the
combustor liner 68 is manufactured from 0.125
in. thick INCONEL 625, 309 SST or 310 SST.
Cooling-dilution air 129 circulates within the
annulus 72 to cool the combustor llner 68.
Pre~erably, the combustor liner 68 is cooled to
below the ash slagging temperature such that
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26
bypass assembly 104 are provided proximate the
exit of the cyclone ash separator 16. In the
preferred embodiment, the outer shell 94 oi~ the
cyclone 16 ls fabricated from carbon steel or
the equivalent. The annulus 98 o:E the cyclone
16 is in communication with the annulus 90 of
the communication pipe 84 which ls in
communication with the annulus 72 of the
combustor 14. Cooling-dilution air 129 is
circulated in the annulus 98 between the outer
shell 94 and the cyclone liner 96 from the
combustor annulus 72. The cooling-dilution air
129 flows around the cyclone liner 96 to cool
the cyclone liner 96 and keep the ~iner 96
below slagging temperature. Further, the
circulating air serves to cool the outside
shell 94 of~ the cyclone 16 to reduce thermal
losses.
The ash collector 100 is located at the
lower end of the cyclone liner 96 and defines
two ash lock hoppers 106, 108 for receiving and
holding the ash collected. Each ash lock
hopper 106, 108 defines a discharging valve 109
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the generator break 125 and emergency shutdown
button in the control room. The relief valves
127 are operated by the system pressure.
The air bypass asse~mbly 104 permits and
controls the flow of air 128 (air flowing in
the annulus 98 of the cyclone 16) combining
with the cleaned combustion gas 126 as the gas
126 exits the cyclone 16 through the duct 110.
In the embodiment shown in Figure 4, the air
bypass assembly 104 includes a fixed sleeve
182, a control sleeve 185 and an outlet pipe
184. The fixed sleeve 182 is de~ined by the
first end of the duct 110 exiting the cyclone
16. The fixed sleeve 182 encircles the outlet
pipe 184 in a m~nne~ such that an annular space
186 is defined therebetween. The annular space
186 is unobstructed at the upper end thereof.
The ~ixed sleeve 182 supports the lower end o~
the outlet pipe 184 such that it is retained
within the fixed sleeve 182. Further, the
fixed sleeve 182 defines a plurality of
openings 183 at an upper portion thereof, as
shown in Figure 1. The control s~eeve 185 is
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,
29
annularly received by an outer surface of the
fixed sleeve 182 proximate the plurality of
openings 183 and defines a plurality of
openings 187 which correspond to the openings
183 defined by the fixed sleeve 182, as shown
in Figure 1. The control sleeve 185 rotates to
control the flow of air 128 flowing from the
annulus 98 of the cyclone 16 through the upper
portion of the annular space 186 dei~ined
between the fixed sleeve 182 and the outlet
pipe 184. This air 128 combines with the
combustion gas 126 exiting the upper end of the
outlet pipe 184. In the preferred embodiment,
the control sleeve 185 rotates in a limited
manner, in one direction to fully block the
openings 183 of the fixed sleeve 182 and in the
opposing direction to reveal partially or fully
the openings 183 of the ~ixed sleeve 182
there~y controlling the flow rate of the
tertiary air or cooling-dilution air 129. The
lower end of outlet pipe 184 defines a
plurality of vents 188. Air ~lowing in the
lower portion of the annular space 18 6 serves
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to cool the outlet pipe 184 and exits through
the vents 188 into the entrance of the outlet
pipe 184 to combine with the cleaned combustion
gas 126.
In an alternate embodiment shown in Figure
6, the air bypass assembly 104 includes a
casing 112 sealed around the first end of the
duct 110 and a pressure controlled bypass flow
valve 114. The first end o~ the duct 110
de~ines a plurality o~ openings 116 open to the
casing 112. When the valve 114 is opened, air
~rom the cyclone annulus 98 flows into the
casing 112, through the plurality o~ openings
116 and into the duct 110 and combines with the
cleaned combustion gas 126. In the pre~erred
embodiment, the bypass ~low valve 114 is
manufactured ~rom SST 309 or an equivalent
~aterial.
The flame temperature and cyclone exit air
temperature are monitored and controlled with
excess air by modulating the bypass flow. The
bypassed air 128 is directed into the cyclone
exit vortex to decrease cyclone pressure loss
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31
and to increase cyclone e~iciency during
operation o~ the system.
In an alternate em~odiment (see Figure 1),
a steam injector 118 is in communication with
the duct llO to inject steam into the stream o~
cleaned combustion gas 126 and bypassed air for
added power. In an alternate embodiment, steam
injectors 134 (see Figure 4) are utilized to
inject steam into the secondary air 128 at the
lower end o~ the combustor 14 and the lower end
o~ the cyclone 16.
To begin operation o~ the system 10, the
gas generator 18 is rotated at low speed with a
hydraulic starter (not shown) to create a
gentle dra~t and purge the system 10. Natural
gas, oil or LPG is injected into the bottom o~
the combustor 14, through the starter ~uel
inlet or gas burner 78, and ignited by a high
temperature electrical spark to warm the
combustor 14 and cyclone 16 and preheat the
re~ractory cone 80. During initial start up
and idle the gas burner 78 is utilized and is
controlled via the commercial gas burner
CA 022~8~79 1999-01-1~
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.
32
controller 190 which includes a gas pressure
control 192 and an air flow control 194.
The gas generator 18 is accelerated by the
starter engine, and sawdust fuel 152 injection
is started. After the sawdust fuel 152 i8
ignited and the speed of the gas generator
turbine 20 is increased by a combination of
energy input from the starter engine and the
progressively increased combustion rate, the
natural gas ~uel/oil is turned off. When the
gas generator 18 reaches a self-sustaining
energy balance speed, the starter engine is
turned of~. Pre~erably, the sawdust fuel feed
rate i8 3.5 lb/sec with 2 - 4 lb/sec primary
air.
Secondary and tertiary air 128 are
supplied from the compressor 21 and function to
support combustion and control ~lame and gas
temperature. The air 128 enters the combustor
via the port 95 at the bottom o~ the combustor
14. In one embodiment, the air enters the port
95 at a rate o~ 121.5 lb/sec, a temperature of
600~F and a pressure of 125 psi with a density
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33
o~ 0.318 ft3/sec. The secondary air 128 ~lows
through the vanes 179 at the lower end of the
combustor 14 and enters the re~ractory section
153. The secondary air 128 flowing through the
vanes 179 serves two main ~unctions: to swirl
the wood ~uel 152 as it feeds into the
re~ractory section 153; and to control the
flame temperature in the refractory section
153. The vanes 179 are con~igured such that as
lo the air/wood ~uel mixture enters the re~ractory
section 153 it establishes a swirling action
such that the wood fuel 152 is retained within
the re~ractory section 153 for an extended
period to encourage more thorough heating of
the wood fuel 152, ultimately encouraging
combustion o~ all wood ~uel 152. The
conditions in the re~ractory section 153 are
below stoichiometric conditions such that
complete combustion does not take place in the
re~ractory section 153.
The majority of the tertiary air 130
enters the combustion zone 154 just above the
refractory 80 through a network o~ holes and/or
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34
slots 71 dei~ined by the combustor liner 68 to
complete combustlon in a super stoichiometric
condition. The amount o~ air :Eed into the
combustion zone 122 is such that the oxygen
content is above stoichiometry. The surface
temperatures inside the combustor liner 68 are
about 1400~F maximum due to cooling by the
cooling-dilution air 129 which is at
approximately 640~F. Surf~ace temperatures of
the outside of the combustor liner 68 are
approximately 910~F while the insulated outer
wall of~ the outer shell 66 is about 269~F. The
resulting outside ambient air is about 100~F.
The primary air 150 for injection with the
wood :Euel 152 comes directly ~rom the
compressor 21. When utilizing the sawdust
preparation system shown in Figure 2, the air
iB fed through a booster f~an. The sawdust i~uel
152 enters ~rom the bottom o~ the pressurized
charge vessel assembly 32 and is carried by the
primary air 150 to the bottom oi~ the combustor
14 where it is injected. When utilizing the
sawdust preparation system depicted in Figure
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,
3, the booster ~an 175, mounted in a pressure
vessel 176, is utilized to boost the pressure
and temperature of the primary air 150 be~ore
it is ultimately delivered to the bottom o~ the
combustor 14.
Combustion temperatures inside the
re~ractory section 153 at the bottom o~ the
combustor 14 reach approximately 2200~F (~or a
short period o~ time, e.g., less that 1 sec.)
and decrease along the combustor as the
cooling-dilution air 129 ~lows into the
combustion zones through the combustor annular
slots 70. The cooling of the inner wall o~ the
combustor liner 68 by the cooling-dilution air
129 ~low prevents slag ~ormation and residue
inside the combustor liner wall. The
temperature o~ the combustion gas cools to
1600~F maximum as it turns into the
communication pipe 84 joining the combustor 14
and the cyclone 16.
Particulates are separated ~rom the
combustion gas 125 in the cyclone ash separator
16 and are ultimately collected at the bottom
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.
in the second ash lock hopper 108. Clean
combustion gas 126 exits at the top of the
cyclone 16 at a maximum temperature of 1580~F,
at 70 lb/sec and at 122 psi. As it exits, the
clean combustion gas 126 is mixed with diverted
air 128 from the air bypass assembly 104 and
then is routed to the turbine 20 via the duct
110, at a pressure o~ approximately 122 psi and
a temperature of 1350~F.
The use of the bypass air allows the
combustor volume to be reduced. The lower air-
gas flow rate through the co~bustor 14 and the
cyclone 16 decreases ash carry over and allows
the design o~ a more e~icient cyclone 16.
This ~eature reduces the ash grains per cubic
foot in the turbine exhaust by 50%.
The gas generator 18 utilized in the
system 10 has a split shaft to allow the gas
generator turbine 20 and power turbine 19 to
rotate at di~ferent revolutions per minute. In
the pre~erred embodiment, the gas generator 18
is a modi~ied commercial gas turbine with a
special center section and automatic check
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37
valves 121 to allow off-board firing without
blowback. These automatic check valves 121
reduce the pressure drop between the compressor
discharge and the turbine inlet, as well as
reducing compressor air back-pressure for easy
start of the gas generator.
Upon entering the gas generator turbine
20, the combustion gas 126 expands to produce
work. The gas generator turbine 20 powers the
air compressor 21 via a drive shaft. The power
turbine 19 drives the electrical generator 17
which is linked to any suitable electrical
power transmission line. The power in excess
of that required to drive the biomass burning
system 10 is supplied to the outside user.
There~ore, a load rejection device is not
needed due to the internal use of electrical
power in the biomass burning system 10 and
specifically in the wood drying process and the
use of a special brake between the turbine gear
box 123 and generator 17. I~ the generator 17
should be disconnected ~rom the power grid or
lose its field, the central control system 136
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would automatically stop the biomass fuel dust,
open the pressure relief valves 127 and apply a
caliper brake 125 to prevent a generator
overspeed.
Steam is injected (as at 118) to boost
turbine power a~ter reaching 90% of achievable
power by using wood fuel only.
Re~erring to ~igure 7, the control system
22 includes a com~ustion control processor
(CCP) 136 which is utilized to monitor and
control the biomass burning system 10. The CCP
136 is a distributed process controller that
regulates the combustion process and monitors
the combustion gas 125 and cleaned combustion
gas 126. In the pre~erred embodiment, the
distributed process controller is a Bristol
Babcock 3335 DPC. The purpose o~ the control
system 22 is to monitor functions ~rom the
biomass burning system 10, a generator
20-- instrument package (GIP) 140, a turbine
instrument package (TIP) 138 and a continuous
emissions monitor (CEM) 142, and to use these
inputs to provide a safe and e~icient control
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39
o~ the biomass burning system 10 and to
instruct the speed tachometer 146 and power
controller 148. In the preferred embodiment,
the GIP is an Allen Bradley line
synchronization module, the TIP is manu~actured
by General Electric (model number 7LM1500
GD102), and the CEM is an EPI 410.
Figure 8 illustrates the major CCP input
and output signals and controller ~unctions.
Each are labeled according to the various
elements o~ the system.
The biomass burning process includes the
wood processing and the combustion process.
Selected conditions within the wood processing
system 12, the combustor 14, the cyclone 16 and
the gas generator 18 are monitored by the CCP
136. Within the wood processing system 12, the
temperature o~ the hot exhaust ~or drying and
the dryer inlet and outlet air temperatures are
monitored. Moisture monitors 63 are located
throughout the wood processing system 12 to
monitor the moisture o~ the wood ~uel 152 as it
is processed ~or use.
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In the combustor 14, the temperature of
the combustion zone 122 is monitored, and
pre~erably the first 154, second 156, fourth
158 and ~ifth zones 160 are individually
monitored. Moreover, the temperature at the
entrance of the first combustion zone 154 and
the temperature at the exit of the first zone
154 are specifically monitored. ~n the
preferred embodiment, the temperatures at these
various locations are measured with high
temperature thermocouples, type S (as at 211 ln
Figure 4). The temperature o~ the combustor
122 liner walls is controlled by modulating the
cyclone bypass valve 185 to flow the proper
amount o~ cooling-dilution air 129 through the
combustor cooling annulus 72. The position of
the cyclone bypass vlave 185 is controlled by
the CCP 136.
The temperature of the pneumatically ~ed
~uel 152, the temperature o~ the primary air
150 a~ter the cooler and a~ter water injection,
and the temperature o~ the secondary air 128
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before and a~ter steam injection are monitored,
pre~erably, wlth type K thermocouples.
Also, the mass flow, the ~uel ~eed rate
and pressure in the injection line 173 are
monitored. Pre~erably, the mass ~low rate is
measured with a Kurz mass flow monitor. The
injection line ~uel ~eed rate is measured with
a pressure transmitter. The ~eed rate o~ ~uel
is a ~unction o~ the revolutions per minute
(RPM) of the injector screw. The pressure at
the exit of the combustor 1~, the pressure
across the pneumatic ~eed booster and the
compressor 21 air ~low into the combustor 1
are monitored, pre~erably, with pressure
transmitters. Further, the temperature o~ the
combustion gas 125 entering the cyclone and the
cleaned combustion gas 126 exiting the cyclone
are monitored.
In the gas generator 18, the temperature
o~ the gas entering and leaving the compressor
21, the temperature o~ the gas entering the gas
generator turbine 20, the temperature o~ the
gas leaving the power turbine 19, the ~low rate
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o~ air flowing in the gas generator air vent 25
and the pressure at the exit of the compressor
2~ are also monitored with similar transducers
Further, the gas generator speed and the power
turbine speed are monitored and, in the
preferred embodiment, the load of the turbine
19 is also monitored such that the control
system 22 can maintain the turbine 19 at a
constant speed with a variable load. a more
rapid response is provided when both the speed
and the load are monitored.
The generator instrument package (GIP) 140
and the turbine instrument package (TIP) 138
function as industrial systems maintaining the
turbine 19 and generator 18 ~unctions and
monitor certain aspects of the generator 18 and
the turbine 19, respectively, such as
vibration, lube oil pressure and temperature,
power turbine and gas generator RPM, generator
20_ volts, amps etc. The GIP 140 and TIP 138
provide controls ~or shutting down the system
when preestablished limits have been passed.
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The continuous emissions monitor ( CEMS )
142 controls emissions, regulates combustion
and provides environmental reporting.
Speci~ically, the continuous emissions monitor
142 monitors the level o~ carbon monoxide,
particulates, and NOX in the turbine exhaust
gas. The CEMS controls emlssions by monitoring
the exhaust carbon monoxide level and
regulating the combustor air via the CCP. The
controls are implemented to control the level
o~ CO when it exceeds EPA standards.
The in~ormation from the biomass burning
system lO, the gas generator 18, the GIP 140,
the TIP 138 and the CEMS 142 is utilized to
instruct the speed and power controllers 146,
148 such that the biomass burning system 10
operates in a sa~e and e~icient manner.
Speci~ically, the CCP 136 uses a so~tware
program to control the steam injector 118 at
the exit of the cyclone 16, the steam injectors
134 at the combustor 14 and the cyclone 16 when
utilized, the vane actuator 180 ~or controlling
the ~low o~ the secondary air 128 into the
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combustor 14, the fuel feed injector 74, ~he
gas burner controller 190, the air bypass
assembly 104 and the thermal relie~ valve, 102,
The CCP 136 outputs a current which provides a
pressure signal to the vane actuator 180. The
air bypass assembly 104 is set according to the
system power level. The thermal relief valve
102 is interlocked with the distributed process
controller and is opened with a key switch
electro-pneumatic system.
The speed of the power turbine 19 is
controlled in one o~ two manners depending upon
whether the system 10 is linked to an outside
system or not. When the biomass burning system
10 is connected to the outside transmission
line, the speed is controlled by the 60 cycle
balance of the transmission line. However,
when the system 10 is connected to an internal
load, the speed of the power turbine 19 and the
gas generator 18 are under the control o~ the
combustion control processor 136. a mechanical
speed governor is utilized as a control loop
independent of the combustion control processor
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136 for controlling the speed of the gas
generator 18 in the event of a control system
22 failure. The bypass valves 121 are opened
and closed during the start cycle according to
compressor RPM and compressor discharge
pressure schedule, and closed and opened during
the shut down process to prevent compressor
stalls and surges. These valves 121 are
controlled by the CCP 136.
From the foregoing description, it will be
recognized by those skilled in the art that a
system for burning biomass to produce hot gas
offering advantages over the prior art has been
provided. Speci~ically, the system for burning
biomass provides an improved manner for
injecting the wood fuel 152 or biomass into the
combustor lg. Further, the control system
includes an air bypass assembly 104 for
iniecting air into the stream of the combustion
gas 126 to control the combustion process. The
use of the bypass assembly 104 permits the use
of smaller cyclone 16, increases the efficiency
of the cyclone filter and controls slagging and
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46
emissions. Also, a thermal relle~ valve 102 is
included for rapid cooling of the gas generator
turbine 20 and the combustor 14.
While a pre~erred embodiment has been
shown and described, it will be understood that
it is not intended to limit the disclosure, but
rather it is intended to cover all
modi~ications and alternate methods falling
within the spirit and the scope o~ the
invention as de~ined in the appended claims.
