U.S. patent application number 12/238671 was filed with the patent office on 2010-04-01 for convective section combustion.
This patent application is currently assigned to AIR PRODUCTS AND CHEMICALS, INC.. Invention is credited to Mark Daniel D'Agostini, Kevin Boyle Fogash, Reed Jacob Hendershot, Jeffrey William Kloosterman, Aleksandar Georgi Slavejkov.
Application Number | 20100077945 12/238671 |
Document ID | / |
Family ID | 41426183 |
Filed Date | 2010-04-01 |
United States Patent
Application |
20100077945 |
Kind Code |
A1 |
Hendershot; Reed Jacob ; et
al. |
April 1, 2010 |
CONVECTIVE SECTION COMBUSTION
Abstract
An oxy/coal combustion system and method include a furnace
arranged and disposed to receive and combust a first solid fuel to
form a combustion fluid, a convective section having one or more
inlet devices, the convective section arranged and disposed to
receive and combust a second fuel in the presence of the oxygen,
and one or more heat exchangers arranged and disposed to exchange
heat with the combustion fluid.
Inventors: |
Hendershot; Reed Jacob;
(Breinigsville, PA) ; Slavejkov; Aleksandar Georgi;
(Allentown, PA) ; D'Agostini; Mark Daniel;
(Ebensburg, PA) ; Fogash; Kevin Boyle;
(Wescosville, PA) ; Kloosterman; Jeffrey William;
(Allentown, PA) |
Correspondence
Address: |
AIR PRODUCTS AND CHEMICALS, INC.;PATENT DEPARTMENT
7201 HAMILTON BOULEVARD
ALLENTOWN
PA
181951501
US
|
Assignee: |
AIR PRODUCTS AND CHEMICALS,
INC.
Allentown
PA
|
Family ID: |
41426183 |
Appl. No.: |
12/238671 |
Filed: |
September 26, 2008 |
Current U.S.
Class: |
110/345 ;
110/214; 110/263 |
Current CPC
Class: |
Y02E 20/344 20130101;
F23C 9/003 20130101; F23C 2201/101 20130101; Y02E 20/34 20130101;
F23C 2201/401 20130101; F23L 7/007 20130101; F23C 6/047
20130101 |
Class at
Publication: |
110/345 ;
110/214; 110/263 |
International
Class: |
F23B 80/00 20060101
F23B080/00; F23B 10/00 20060101 F23B010/00; F23J 15/00 20060101
F23J015/00 |
Claims
1. An oxy/fuel combustion system comprising: a furnace arranged and
disposed to receive and combust a first fuel with oxygen to form a
combustion fluid, the first fuel provided from a first solid fuel
source; a convective section having an inlet device, the convective
section arranged to receive the combustion fluid from the furnace
and disposed to receive a second fluid, the second fluid converted
from a second fuel, the second fuel being a solid fuel; and one or
more heat exchangers in the convective section arranged and
disposed to transfer heat from the combustion fluid to a heat
exchange medium.
2. The system of claim 1, wherein the inlet device is arranged and
disposed to receive the oxygen.
3. The system of claim 1, wherein the inlet device is recessed from
the convective section.
4. The system of claim 1, further comprising a solid fuel
conversion mechanism selected from the group consisting of a
fluidized bed, a gasifier, a combustor, an additional burner, a
micronizing pulverizer, and combinations thereof, wherein the solid
fuel conversion mechanism is arranged and disposed to convert the
second solid fuel into at least a portion of the second fluid.
5. The system of claim 1, wherein the first fuel includes coal.
6. The system of claim 1, wherein the second fluid includes
micronized coal.
7. The system of claim 1, wherein the second fluid includes a
volatilized fuel.
8. The system of claim 5, wherein the volatilized fuel is generated
by mixing the second fuel with a recycled flue gas.
9. The system of claim 1, wherein the conversion mechanism is a
gasifier arranged and disposed for the oxygen to oxidize the second
fuel.
10. The system of claim 9, wherein the gasifier is a slagging
gasifier.
11. The system of claim 1, wherein the conversion mechanism is a
combustor.
12. The system of claim 1, wherein the first fuel is a solid
fuel.
13. The system of claim 1, wherein the first solid fuel source is
arranged and disposed for providing the second solid fuel
source.
14. The system of claim 1, further comprising a conversion
mechanism selected from the group consisting of a fluidized bed, a
gasifier, a combustor, an additional burner, a micronizing
pulverizer, and combinations thereof, the conversion mechanism in
communication with the first solid fuel source thereby converting
the first fuel prior to the first fuel being received by the
furnace.
15. The system of claim 1, further comprising water cooled tubes
bounding a convective combustion zone corresponding with the inlet
devices, wherein the water cooled tubes provide heat transfer
protecting at least one of the one or more of the heat
exchangers.
16. The system of claim 1, further comprising a control system
arranged and disposed for modifying the flow rate of the second
fluid.
17. An oxy/fuel combustion method comprising: providing a furnace
and a convective section, the furnace in fluid communication with
the convective section; providing a first fuel from a first solid
fuel source; receiving the first fuel in the furnace; combusting
the first fuel in the furnace thereby producing a combustion fluid;
receiving the combustion fluid in the convective section;
converting a second fuel into a second fluid, the second fuel being
a solid fuel; receiving the second fluid in a convective section;
and transferring heat from the combustion fluid to a heat exchange
medium.
18. The method of claim 17, further comprising converting the
second fuel to the second fluid by a fluidized bed.
19. The method of claim 17, further comprising converting the
second fuel to the second fluid by a gasifier.
20. The method of claim 17, further comprising converting the
second fuel to the second fluid by a combustor.
21. The method of claim 17, further comprising converting the
second fuel to the second fluid by an additional burner.
22. The method of claim 17, further comprising converting the
second fuel to the second fluid by a micronizing pulverizer.
23. The system of claim 1, further comprising controlling the flow
rate of the second fluid by a control system.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Application is related to application Ser. No. ______,
entitled "OXY/FUEL COMBUSTION SYSTEM WITH LITTLE OR NO EXCESS
OXYGEN", Attorney Docket No. 07228 USA, filed contemporaneously
with this Application on Sep. 26, 2008, assigned to the assignee of
the present disclosure and which is herein incorporated by
reference in its entirety, application Ser. No. ______, entitled
"COMBUSTION SYSTEM WITH STEAM OR WATER INJECTION", Attorney Docket
No. 07238 USA, filed contemporaneously with this Application on
Sep. 26, 2008, assigned to the assignee of the present disclosure
and which is herein incorporated by reference in its entirety,
application Ser. No. ______, entitled "COMBUSTION SYSTEM WITH
PRECOMBUSTOR", Attorney Docket No. 07255 USA, filed
contemporaneously with this Application on Sep. 26, 2008, assigned
to the assignee of the present disclosure and which is herein
incorporated by reference in its entirety, application Ser. No.
______, entitled "OXY/FUEL COMBUSTION SYSTEM WITH MINIMIZED FLUE
GAS RECIRCULATION", Attorney Docket No. 07257 USA, filed
contemporaneously with this Application on Sep. 26, 2008, assigned
to the assignee of the present disclosure and which is herein
incorporated by reference in its entirety, application Ser. No.
______, entitled "OXY/FUEL COMBUSTION SYSTEM HAVNIG COMBINED
CONVECTIVE SECTION AND RADIANT SECTION", Attorney Docket No. 07247
USA, filed contemporaneously with this Application on Sep. 26,
2008, assigned to the assignee of the present disclosure and which
is herein incorporated by reference in its entirety, application
Ser. No. ______, entitled "PROCESS TEMPERATURE CONTROL IN OXY/FUEL
COMBUSTION SYSTEM", Attorney Docket No. 07239 USA, filed
contemporaneously with this Application on Sep. 26, 2008, assigned
to the assignee of the present disclosure and which is herein
incorporated by reference in its entirety, and application Ser. No.
______, entitled "COMBUSTION SYSTEM WITH PRECOMBUSTOR", Attorney
Docket No. 07262Z USA, filed contemporaneously with this
Application on Sep. 26, 2008, assigned to the assignee of the
present disclosure and which is herein incorporated by reference in
its entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure is directed to a combustion system.
In particular, the present disclosure is directed to a combustion
system configured for solid fuel combustion in the convective
section of the combustion system.
BACKGROUND OF THE DISCLOSURE
[0003] In known systems, gas and/or oil have been used for
reburning combustion fluid downstream of furnaces to control
NO.sub.x emissions. Gas and/or oil have an unreliable supply
(especially in winter) costs can vary widely; they may have
problems with firing dual fuels; and they may reduce efficiency of
a system due to hydrogen content thereby increasing water vapor of
combustion fluids. This reburning of combustion fluid has been used
for decreasing NO.sub.x emissions produced by reaction of nitrogen
in combustion air (thermal NO.sub.x) and oxidation of nitrogen
chemically bound in coal (fuel NO.sub.x).
[0004] In the reduction of NO.sub.x emissions, known systems have
provided finely divided, micronized particles of coal for
reburning. Known systems include a furnace (or a radiant section)
and a convective section. These systems focus on reducing NO.sub.x
emissions emanating from the system and have not, therefore,
adequately provided for efficient transfer of heat (at least in
part) in the convective section of the systems.
[0005] Oxy/fuel systems generate high combustion temperatures
requiring heat release to be distributed to ensure high superheat
temperatures and high efficiency. Known systems use recycled flue
gas (RFG) to transfer heat from the furnace to the convective
section. Using RFG to distribute heat increases the complexity of
the flue gas handling system, the size of the convective section,
and/or the size of the boiler. Thus, it increases the overall
capital and operating costs of the systems. Since oxy/fuel system
have a lower mass flux than air/fuel system (due to the removal of
N.sub.2) and, therefore, a higher heat release and temperature, it
is desirable to remove a larger percentage of the available heat
generated in the furnace of the oxy/fuel system to the convective
section thereby resulting in a controlled temperature in the
convective section while controlling the temperature and heat
release in the furnace.
[0006] Therefore, there is an unmet need to provide a method,
system, and apparatus for reburning fuels other than oil and/or
gas, for the purpose of controlling heat release and temperature
within the system, and/or withstanding the increased heat in the
convective section while minimizing the use of FGR.
SUMMARY OF THE DISCLOSURE
[0007] According to an embodiment, an oxy/fuel combustion system
includes a furnace arranged and disposed to receive and combust a
first fuel to form a combustion fluid, the first fuel provided from
a first solid fuel source, a convective section having an inlet
device, the convective section arranged to receive the combustion
fluid from the furnace and disposed to receive a second fluid, the
second fluid converted from a second fuel, the second fuel being a
solid fuel, and one or more heat exchangers in the convective
section arranged and disposed to transfer heat from the combustion
fluid to a heat exchange medium.
[0008] According to another embodiment, an oxy/fuel combustion
method includes providing a furnace and a convective section, the
furnace in fluid communication with the convective section,
providing a first fuel from a first solid fuel source, receiving
the first fuel in the furnace, combusting the first fuel in the
furnace thereby producing a combustion fluid, receiving the
combustion fluid in the convective section, converting a second
fuel into a second fluid, the second fuel being a solid fuel,
receiving the second fluid in a convective section, and
transferring heat from the combustion fluid to a heat exchange
medium.
[0009] The present disclosure allows for harnessing of energy in
the convective section of a combustion system, thereby enabling
transfer of heat to a heat exchange fluid, and increasing the heat
content of the fluid.
[0010] Another advantage of the present disclosure is that fuel is
burned not only in the furnace section, but also in the convective
section of a combustion system.
[0011] Yet another advantage of the present disclosure is use of
synthetic air (CO.sub.2 mixed with O.sub.2) and/or substantially
pure O.sub.2 in a combustion system to combust fuel, while
minimizing the use of RFG.
[0012] Still yet another advantage of the present disclosure is the
ability to use a single source of fuel in the furnace as a primary
fuel and the convective section as a secondary fuel.
[0013] Still yet another advantage of the present disclosure is
increased heat transfer surface temperature control in the
convective section.
[0014] Still yet another advantage of the present disclosure is
increased control of the heat transfer fluid temperatures in the
convective section (e.g. the superheat steam temperature).
[0015] Further aspects of the method and system are disclosed
herein. The features as discussed above, as well as other features
and advantages of the present disclosure will be appreciated and
understood by those skilled in the art from the following detailed
description and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 illustrates a schematic view of an exemplary
embodiment of a combustion system according to the disclosure.
[0017] FIG. 2 illustrates a schematic view of another exemplary
embodiment of a combustion system according to the disclosure.
[0018] FIG. 3 illustrates a schematic view of yet another exemplary
embodiment of a combustion system according to the disclosure.
[0019] FIG. 4 illustrates a schematic view still yet another
exemplary embodiment of a combustion system according to the
disclosure.
[0020] FIG. 5 illustrates a schematic view of a further exemplary
embodiment of a combustion system according to the disclosure.
[0021] Wherever possible, the same reference numbers will be used
throughout the drawings to represent the same parts.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0022] The present disclosure now will be described more fully
hereinafter with reference to the accompanying drawings, in which a
preferred embodiment of the disclosure is shown. This disclosure
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete and will fully convey the scope of the
disclosure to those skilled in the art.
[0023] The present disclosure relates to enhanced generation of
heat and balanced distribution of heat generation within a
combustion system 102 by combusting fuel in both a furnace 104 and
a convective section 106. The combustion is specifically applied to
solid fuel combusted to produce a combustion fluid 118.
[0024] As used herein, the term "solid fuel" and grammatical
variations thereof refers to any solid fuel suitable for combustion
purposes. For example, the disclosure may be used with many types
of carbon-containing solid fuels, including but not limited to:
anthracite, bituminous, sub-bituminous, and lignitic coals; tar;
bitumen; petroleum coke; paper mill sludge solids and sewage sludge
solids; wood; peat; grass; and combinations and mixtures of all of
those fuels. As used herein, the term "oxygen" and grammatical
variations thereof refers to an oxidizer having an O.sub.2
concentration greater than that of atmospheric or ambient
conditions. As used herein, the term "oxy/coal combustion" and
grammatical variations thereof refers to coal combustion in oxygen,
the term "air/coal combustion" and grammatical variations thereof
refers to coal combustion in air, the term "oxy/fuel combustion"
and grammatical variations thereof refers to fuel combustion in
oxygen, and the term "air/fuel combustion" and grammatical
variations thereof refers to fuel combustion in air. As used
herein, the term "combustion fluid" and grammatical variations
thereof refers to a fluid formed from and/or mixed with the
products of combustion, which may be utilized for convective heat
transfer. The term is not limited to the products of combustion and
may include fluids mixed with or otherwise traveling through at
least a portion of combustion system. Although not so limited, one
such example is flue gas. As used herein, the term "recycled flue
gas" and grammatical variations thereof refers to combustion fluid
exiting the system that is recirculated to any portion of the
system. As used herein, the term "flue gas recycle" and grammatical
variations thereof refers to a configuration permitting the
combustion fluid to be recirculated. Although various embodiments
illustrate flames in particular locations, it will be appreciated
that flames may be present, but not necessarily required to be
present, in any place where combustion occurs.
[0025] FIG. 1 illustrates an exemplary embodiment of the present
disclosure. In FIG. 1, combustion system 102 includes furnace 104
arranged and disposed to receive a first fuel 110 to form a
combustion fluid 118, a convective section 106 downstream of
furnace section 104 arranged and disposed to receive combustion
fluid 118 from furnace 104 and arranged and disposed to receive a
second fluid 105, and one or more heat exchangers 120 arranged and
disposed to transfer heat from combustion fluid 121 to a heat
exchange medium (not shown).
[0026] As illustrated in FIG. 1, some embodiments further include a
solid fuel conversion mechanism configured to convert solid fuel to
a form that can be combusted in convective section 106. In other
embodiments, solid fuel conversion mechanism is configured to
combust (or partially combust) the solid fuel producing second
fluid 105 which is transported to convective section 106. As used
in the present disclosure, the term solid fuel conversion mechanism
refers to systems for chemically or physically affecting a fuel.
For example, the oxidation or reduction of a fuel would be a
chemical conversion and the gasifying of a fuel would be physical
conversion. These conversions may be performed in the solid fuel
conversion mechanism.
[0027] As illustrated, furnace 104 is in fluid communication with
convective section 106. In this embodiment, furnace 104 is arranged
and disposed to receive first fuel 110 at a windbox 114 proximal to
a general combustion zone 116. Furnace 104 is configured to combust
first fuel 110 thereby producing combustion fluid 118 that is fed
to convective section 106 of combustion system 102. As will be
appreciated, among other components, windbox 114 and the general
combustion zone 116 are merely exemplary and may be reconfigured or
replaced with other furnace components or other mixing
mechanisms.
[0028] FIG. 1 depicts convective section 106 as a part of
combustion system 102. However, more than one furnace 104 and/or
convective section 106 of the same combustion system or a separate
combustion system may be used. In addition, furnace 104 and/or
convective section 106 may be in fluid communication with other
types of systems. Convective sections may be included in combustion
fluid path 118, 121, and/or 122 as needed to improve the efficiency
of combustion system 102. However, in other embodiments, convective
section 106 may be a convective section to another combustion
system, a portion between furnace 104 and convective section 106,
or a portion after the convective section. As illustrated in FIG.
1, three inlet devices 112 in convective section 106 are arranged
and disposed to receive oxygen 107 from oxygen source 108. In one
embodiment, inlet devices 112 are arranged and disposed for
combustion by including burners. Oxygen 107 may be mixed (for
instance in a mixing chamber preceding inlet devices 112, in the
solid fuel conversion mechanism, or in convective section 106) with
second fluid 105 provided to convective section 106 in inlet
devices 112. As will be appreciated, air or other fluids may be
used as a carrier fluid to transport second fluid 105 to the point
where the second fluid 105 may be mixed with oxygen 107. Only one
inlet device 112 in convective section 106 is required, but
additional inlet devices 112 and/or additional heat exchangers 120
are contemplated.
[0029] As illustrated in FIG. 1, convective section 106 includes a
plurality of heat exchangers 120. As will be appreciated,
convective section 106 may include fewer or more heat exchangers
120. Heat exchangers 120 may include any number of primary
superheaters, any number of secondary superheaters, any number of
reheaters, any number of economizers, or combinations thereof. As
depicted in FIG. 1, one heat exchanger 120 is a secondary
superheater (upstream from a primary superheater) and another heat
exchanger 120 is the primary superheater (downstream from the
secondary superheater). Additional heat exchangers 120 (not shown
in FIG. 1) may be included. Other heat exchangers 120 may be
economizers, reheaters, or additional superheaters.
[0030] Referring to FIG. 1, the solid fuel conversion mechanism is
a fluidized bed 113. In other embodiments (as described below), the
solid fuel conversion mechanism may be an external reaction chamber
213 (see FIG. 2), a micronizing pulverizer 313 (see FIG. 3), a
combustor, a burner, other similar devices, or combinations
thereof. As illustrated in FIG. 1, first fuel 110 from solid fuel
source 109 is fed to fluidized bed 113 after being crushed in a
primary crusher 115. In the embodiments illustrated by FIGS. 1, 2,
and 3, first fuel 110 and/or other fluids being transported may be
transported by any method as would be appreciated by those skilled
in the art. For example, solid fuel may be transported by a carrier
gas, mechanical systems, and/or pneumatic systems. Upon exiting
primary crusher 115, first fuel 110 (having been crushed)
preferably is of an ambient temperature or about 80.degree. F.
(about 27.degree. C). In the embodiment illustrated by FIG. 1,
fluidized bed 113 performs at least partial devolatilization of
first fuel 110 (having been crushed) thereby forming second fluid
105, which is volatilized. As illustrated in FIG. 1, the at least
partial devolatilization of first fuel 110 relies upon a hot
combustion fluid 121 fed from downstream of a first heat exchanger
120 and two inlet devices 112 and upstream from a second heat
exchangers 120 and another inlet device 112. As will be
appreciated, other sources of hot fluids (not necessarily hot
combustion fluids) and inlet devices located in other areas may be
included.
[0031] Referring again to FIG. 1, hot combustion fluid 121 is used
to produce fluid 105, a relatively low heating value gaseous fuel.
In this embodiment, hot combustion fluid 121 may be about
1675.degree. F. (about 913.degree. C.) prior to being mixed with
first fuel 110 at ambient conditions in a 1:1 mass ratio in
fluidized bed 113 to achieve a final temperature of about
1000.degree. F. (about 538.degree. C,). Upon first fuel 110 being
converted by fluidized bed 113, first fuel 110 (in part) is
volatilized to form second fluid 105 and fed to inlet devices 112.
The remaining portion of first fuel 110 includes partially
devolatilized solid fuel, which is fed to furnace 104. In other
embodiments, second fluid 105 is produced by converting a second
fuel that is not the same fuel as first fuel 110. The second fuel
is provided by a second fuel source.
[0032] As illustrated in FIG. 1, in an embodiment, partially
devolatilized first fuel 110 may be fed to a pulverizer 124 prior
to being fed to furnace 104. However, in other embodiments,
pulverizer 124 may be omitted. In the embodiment illustrated by
FIG. 1, partially devolatilized first fuel 110 exiting fluidized
bed 113 is cooled by combustion fluid 122 fed from the end of
combustion system 102. Combustion fluid 122 may have a lower
temperature and may also be used as a transport fluid to transport
the partially devolatilized first fuel 110 to furnace 104. As will
be appreciated, combustion fluid 122 may also be exhausted from
combustion system 102 and/or collected.
[0033] FIG. 2 illustrates another exemplary embodiment of the
present disclosure. Combustion system 102 as disclosed in FIG. 2 is
similar to combustion system 102 as disclosed in FIG. 1 primarily
except that it includes external reaction chamber 213 as the solid
fuel conversion mechanism. External reaction chamber 213 may be for
partial fuel oxidation (for example, with a gasifier) or for
complete fuel oxidation. In one embodiment, the solid fuel
conversion mechanism may be a slagging gasifier such as, for
example, a slagging cyclone. The type of gasifier is selected to
provide the ability to achieve relatively long solid particle
residence times and withstand high gas temperatures, thus promoting
efficient gasification and/or combustion of the first fuel 110 with
minimal carbon residue.
[0034] As illustrated in FIG. 2, external reaction chamber 213 may
convert coal from the solid to a gaseous fuel 203 through partial
oxidation. Using external reaction chamber 213 may result in a
higher heating value than using fluidized bed 113 and may not
require combustion fluid 118 to transport gaseous fuel 203 to inlet
devices 112. As used herein, the term heating value refers to the
heat that is released when a specific volume or mass is combusted.
For example, natural gas has a heating value of about 1000 BTU/scf
(standard cubic foot) while CO and H.sub.2 are a little more than
300 BTU/scf. In general, a higher heating value fuel is easier to
combust and provides more heat. The exception is H.sub.2, it has a
low heating value but is fairly easy to combust. As illustrated in
FIG. 2, the heat available in convective section 106 may not be
limited based upon the volatility of first fuel 110 used.
[0035] In addition, the higher heating value of the gaseous fuel
203 may result in more stable combustion in the convective section
106. In one embodiment, the gasifier is included and provides
sources of energy in the form of chemical sources (i.e. partially
combusted fuel such as CO and others) and thermal sources (above
ambient temperatures). In some cases, it may be valuable to extract
heat from the reacted stream before injection into convective
section 106. The heat extraction from reaction chamber 213 or
transfer piping may be integrated into the overall steam cycle. In
this embodiment, for higher efficiency, inlet devices 112 are
burners with oxygen 107 injected to facilitate more efficient
combustion. In the illustrated embodiment, combustion fluid 122
exiting the convective section 106 is fed to external reaction
chamber 213 to temper the gas temperature 203 before transport. In
the illustrated embodiment, much like may be done in furnace 104,
slag 201 may be separated in the reaction chamber and captured.
[0036] FIG. 3 illustrates another exemplary embodiment of the
present disclosure. Combustion system 102 as disclosed in FIG. 3 is
similar to combustion system 102 as disclosed in FIG. 1 primarily
except that it includes micronizing pulverizer 313 as the solid
fuel conversion mechanism. The depicted micronizing pulverizer 313
is fed first fuel 110 from primary crusher 111. In the embodiment
illustrated in FIG. 3, primary crusher 111 is arranged and disposed
to separate first fuel 110. Generally, first fuel 110 is separated
based upon the size of the particles of first fuel 110. As will be
appreciated, various techniques may be used to separate first fuel
110. In the embodiment illustrated by FIG. 3, first fuel 110 that
is below a predetermined particle size is fed to micronizing
pulverizer 313. The remaining first fuel 110 is fed to furnace 104.
In other embodiments, first fuel 110 may be split in other ways
understood by those skilled in the art. In the embodiment
illustrated by FIG. 3, micronizing pulverizer 313 is arranged and
disposed to further pulverize first fuel 110 so that about 80% to
100% of first fuel 110 exiting the micronizing pulverizer 313 (the
micronized solid fuel or second fluid 301) is at a size of less
than about 45 micrometers. Specifically, the embodiment illustrated
in FIG. 3 results in between 80% and 100% of second fluid 301 being
less than 44 micrometers. Second fluid 301 may burn relatively
easily and may be used in convective section 106. As illustrated in
FIG. 3, second fluid 301 is fed to inlet devices 112 and
combusted.
[0037] FIG. 4 illustrates an exemplary embodiment of the present
disclosure. As illustrated in FIG. 4, inlet devices 112 are in
convective section 106; however, convective section 106 includes
recesses 111 that contain inlet devices 112. As illustrated in FIG.
4, inlet devices 112 are positioned within chambers forming
recesses 111, aligning the edge of convective section 106. As
illustrated in FIG. 4, second fluid 105 (but could be second fluid
203 or second fluid 301) is introduced at a point in convection
section 106 proximal to inlet device 112. At this point, second
fluid 105 and oxygen 107 are injected into the chamber to achieve
stable combustion. In other embodiments, oxygen 107 may be part of
second fluid 105 and not provided independently to the chamber. In
yet other embodiments, to minimize peak flame temperatures from
inlet devices 112, oxygen 107 and second fluid 105 staging may be
used. Staging refers to mixing the fuel or oxidizer at several
locations instead of all at once. This has the effect of lowering
the peak flame temperature. In these embodiments, oxygen 107 may be
mixed with second fluid 105 in chamber 111, before chamber 111, or
staged so that a portion of oxygen 107 is mixed with convective
section 106.
[0038] In addition, injection of second fluid 105 may be
substantially bounded by oxygen 107 and/or a flue gas recycle
stream to provide a thermal radiation buffer to protect heat
exchangers 120 in convection section 106. Such injection may be
controllably provided so as to better handle changes in conditions
in convective section 106. As further protection, a region
immediately bounding a convective combustion zone (i.e. the
combustion zone in convective section 106) near inlet devices 112
may include a heat sink, such as water cooled tubes 501 (see FIG.
5), recycled flue gas, or refractory that can handle high heat
fluxes and protect heat exchangers 120 of convective section 106
from the intense flame radiation (see FIG. 5). Alternatively, the
heat injection may be accomplished by combusting second fluid 105
before injection into system 102 and then injecting the hot
combustion products (see FIG. 2). In further embodiments, as
illustrated in FIG. 5, the system may controllably vary flow rates
to one or all inlet devices 112 to improve efficiency or may
controllably vary flow rates of fluid in the water tubes to better
protect the heat exchangers. For example, valves 503 and a control
system 505 may be included to modify the flow of any fluid, for
example, oxygen, flue gas, flue gas mixed with oxygen, and/or fuel.
In addition, sensors for monitoring physical conditions, such as
thermocouples for monitoring temperature, may be included in system
102 and utilized by the control system.
[0039] FIG. 4 shows this combustion occurring immediately before
entry into convective section 106, but the combustion may also take
place further away from the convection section and may even occur
in a centralized location as shown in FIG. 2. The arrangement
illustrated in FIG. 4 may protect inlet devices 112 from combustion
fluid, which may be corrosive, erosive, and/or oxidative.
Additionally, recesses 111 may be cooled to maintain inlet devices
112 at a desired temperature, which may be below the temperature of
convective section 106. Similar to the above features, these
features may be controlled for improved efficiency.
[0040] FIG. 5 illustrates combustion system 102 configured in a
manner similar to the configuration of FIGS. 1 through 3; however,
in FIG. 5, combustion system 102 includes water cooled tubes 501
bounding the convective combustion zone corresponding with inlet
devices 112. As illustrated in FIG. 5, water cooled tubes 501 are
arranged and disposed to transfer heat produced by combustion of
the mixture of the second fluid and oxygen 107 to a heat exchange
medium (not shown). The heat exchange medium may be water, for
example.
[0041] In the embodiments illustrated by FIGS. 1 through 5, the
position of inlet devices 112 exemplary and may be modified based
upon heat duty required for the different parts of the steam
cycle.
[0042] Arranging water cooled tubes 501 around the convective
combustion zone corresponding with inlet devices 112 or extracting
heat from the solid fuel conversion mechanism may also modify the
heat distribution within combustion system 102. The heat duty
transferred from furnace 104 may be reduced by the amount of duty
transferred by water cooled tubes 501 and the heat transferred from
the fuel conversion mechanism.
[0043] Increasing flow in one or more inlet device 112 and/or
decreasing flow in one or more inlet devices 112 shifts some of the
firing duty from furnace 104 to convection section 106. Such
shifting may change the heat and material balance for the
combustion system 102. In other embodiments, the positions and
arrangements of inlet devices 112 illustrated by FIGS. 1 through 5
can be combined to increase efficiency. For example, one inlet
device 112 may be recessed (similar to the embodiment illustrated
by FIG. 4), while another inlet device 112 may have water cooled
tubes 501 nearby (similar to the embodiment illustrated by FIG. 5),
and/or while another inlet device 112 may be positioned without
being recessed and without having water cooled tubes 501 nearby
(similar to the embodiments illustrated by FIGS. 1 through 3).
Additionally, fewer or more inlet devices 112 may be included. As
will be appreciated, to maximize efficiency, multiple tests on
combustion system 102 and/or modeling of combustion system 102 may
be performed thereby providing design parameters with improved
efficiency. Such design parameters may involve other combinations
of these.
EXAMPLES
[0044] In the embodiments illustrated by FIGS. 1 through 5, three
inlet devices are shown. The position of these inlet devices
represent different possible locations within the convection
section. The placement of the inlet devices depends upon the heat
duty required for the different parts of the steam cycle. A heat
and material balance was performed using the coal described in
Table 1 to determine a possible firing rate split for the different
locations of inlet devices. Table 1 details the analysis of a
typical high volatile bituminous coal used in the example.
TABLE-US-00001 TABLE 1 Coal Analysis Coal Characteristics for a
Typical High Volatile Bituminous Coal Proximate Analysis, H.sub.2O
2.5 wgt % Volatile Matter 37.6 Fixed Carbon 52.9 Ash 7 Ultimate
Analysis, H.sub.2O 2.5 wgt % C 75 H 5 S 2.3 O 6.7 N 1.5 HHV, BTU/lb
13000
[0045] In this example, the fuel source for the inlet devices in
the convective section were assumed to contain 50% of the volatiles
from the coal and 18.8% of the total heating value of the coal. In
this example, the combined oxidant and fuel carrier gas stream
consisted of 80% O.sub.2 and 20% CO.sub.2. The convective section
fuel injection was split 10%, 65%, and 25% between the inlet
devices, respectively along the flow path of the combustion fluid.
The temperature was estimated at about 2900.degree. F. (about
1593.degree. C.) exiting the furnace, 2400.degree. F. (about
1316.degree. C.) between the first two inlet devices, and
1950.degree. F. (about 1066.degree. C.) between the second and
third inlet devices, and 670.degree. F. (about 354.degree. C.)
after the final inlet device. Due to the low level of flue gas
recycle, the average convective section temperature was higher than
that available with a traditional system design. This higher
temperature led to a greater temperature difference driving force
for heat transfer which therefore lowered the heat transfer surface
area required in the convective section for similar duty.
[0046] The burners and heat injection in the convective section may
be used in a steady-state or transient condition. For example, the
inlet devices may be used mainly in a start-up mode to bring the
steam conditions to the requirements of the steam process as soon
as possible. This is especially important for a combustion system
designed to operate using large amounts of flue gas recycle to
achieve the proper heat distribution within the system. During
start-up before sufficient flue gas recycle is available, the inlet
devices in the convection section may be used to achieve the proper
convective section heat transfer.
[0047] While the disclosure has been described with reference to a
preferred embodiment, it will be understood by those skilled in the
art that various changes may be made and equivalents may be
substituted for elements thereof without departing from the scope
of the disclosure. In addition, many modifications may be made to
adapt a particular situation or material to the teachings of the
disclosure without departing from the essential scope thereof.
Therefore, it is intended that the disclosure not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include
all embodiments falling within the scope of the appended
claims.
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