U.S. patent application number 11/610876 was filed with the patent office on 2008-06-19 for system and method for low emissions combustion.
This patent application is currently assigned to GENERAL ELECTRIC COMPANY. Invention is credited to Ahmed Mostafa Elkady, Andrei Tristan Evulet.
Application Number | 20080141645 11/610876 |
Document ID | / |
Family ID | 39399990 |
Filed Date | 2008-06-19 |
United States Patent
Application |
20080141645 |
Kind Code |
A1 |
Evulet; Andrei Tristan ; et
al. |
June 19, 2008 |
SYSTEM AND METHOD FOR LOW EMISSIONS COMBUSTION
Abstract
A turbine system comprises a compressor for compressing air to
generate a compressed flow, an air separation unit for receiving
and separating at least a portion of the compressed flow into
oxygen and a low-oxygen stream, a combustor for receiving and
combusting at least a portion of the low-oxygen stream, a portion
of the compressed flow and a fuel to generate a high temperature
exhaust gas, and a turbine for receiving and expanding the high
temperature exhaust gas to generate electricity and a reduced
temperature low-NOx exhaust gas.
Inventors: |
Evulet; Andrei Tristan;
(Clifton Park, NY) ; Elkady; Ahmed Mostafa;
(Clifton Park, NY) |
Correspondence
Address: |
GENERAL ELECTRIC COMPANY;GLOBAL RESEARCH
PATENT DOCKET RM. BLDG. K1-4A59
NISKAYUNA
NY
12309
US
|
Assignee: |
GENERAL ELECTRIC COMPANY
SCHENECTADY
NY
|
Family ID: |
39399990 |
Appl. No.: |
11/610876 |
Filed: |
December 14, 2006 |
Current U.S.
Class: |
60/39.12 ;
60/39.5; 60/783 |
Current CPC
Class: |
Y02E 20/18 20130101;
F02C 6/08 20130101; Y02E 20/16 20130101; F02C 3/22 20130101; F02C
6/10 20130101 |
Class at
Publication: |
60/39.12 ;
60/39.5; 60/783 |
International
Class: |
F02G 3/00 20060101
F02G003/00; F02C 7/00 20060101 F02C007/00 |
Claims
1. A turbine system comprising: a compressor for compressing a
first stream of air to generate a compressed flow; an air
separation unit for receiving and separating a second stream of air
into oxygen and a low-oxygen stream; a combustor for receiving and
combusting at least a portion of said low-oxygen stream, a portion
of said compressed flow and a fuel to generate a high temperature
exhaust gas; and a turbine for receiving and expanding said high
temperature exhaust gas to generate electricity and a reduced
temperature low-NOx exhaust gas.
2. A turbine in accordance with claim 1, wherein said low-oxygen
stream has less than about 20% by volume of oxygen.
3. A turbine in accordance with claim 1, wherein said low-oxygen
stream has less than about 15% by volume of oxygen.
4. A turbine in accordance with claim 1, wherein said low-NOx
exhaust gas has a NOx level of less than about 30 ppm.
5. A turbine in accordance with claim 1, wherein said low-NOx
exhaust gas has a NOx level of less than about 10 ppm.
6. A turbine in accordance with claim 1, wherein said low-NOx
exhaust gas is directed to a HRSG for the generation of steam and a
reduced temperature exhaust gas.
7. A turbine in accordance with claim 6, wherein said steam is
directed to a bottoming cycle for the generation of additional
electricity.
8. A turbine in accordance with claim 6, wherein said reduced
temperature exhaust gas is split into a first portion that is
directed to a carbon dioxide capture system and a second portion
that is directed to said compressor for compression along with said
first stream of air.
9. A turbine in accordance with claim 6, further comprising a heat
exchanger, wherein said second portion and said low-oxygen stream
are directed into said heat exchanger for heat exchange
therebetween.
10. A turbine system comprising: an air separation unit for
separating air into oxygen and a low-oxygen stream; a compressor
for compressing air and at least a portion of said low-oxygen
stream to generate a mixed compressed flow; a combustor for
receiving and combusting at least a portion of said mixed
compressed flow and a fuel to generate a high temperature exhaust
gas; and a turbine for receiving and expanding said high
temperature exhaust gas to generate electricity and a reduced
temperature low-NOx exhaust gas.
11. A turbine system in accordance with claim 10, wherein said
compressor comprises at least a first-stage compressor section and
a second-stage compressor section.
12. A turbine system in accordance with claim 11, wherein said
low-oxygen stream is directed into said second-stage compressor
section for mixing with a compressed flow from said first-stage
compressor section.
13. A turbine system in accordance with claim 11, further
comprising an intercooler, wherein said low-oxygen stream is
directed into said intercooler for mixing with a compressed flow
from said first-stage compressor section to produce a mixed flow
that is directed to said second-stage compressor section.
14. A turbine system in accordance with claim 10, wherein said
low-NOx exhaust gas is directed to a HRSG for the generation of
steam and a reduced temperature exhaust gas.
15. A turbine system in accordance with claim 14, wherein said
steam is directed to a bottoming cycle for the generation of
additional electricity.
16. A turbine system in accordance with claim 14, wherein said
reduced temperature exhaust gas is split into a first portion that
is directed to a carbon dioxide capture system and a second portion
that is directed to said compressor for compression along with said
air.
17. A turbine system comprising: a compressor for compressing air
to generate a compressed flow; an air separation unit for receiving
and separating at least a portion of said compressed flow into
oxygen and a low-oxygen stream; a combustor for receiving and
combusting at least a portion of said low-oxygen stream, a portion
of said compressed flow and a fuel to generate a high temperature
exhaust gas; and a turbine for receiving and expanding said high
temperature exhaust gas to generate electricity and a reduced
temperature low-NOx exhaust gas.
18. A turbine system in accordance with claim 17, further
comprising a mixer for receiving and mixing said compressed flow
and said low-oxygen stream prior to introduction into said
combustor.
19. A gasification system comprising: an air separation unit for
separating air into oxygen and a low-oxygen stream; a gasifier for
reacting said oxygen and a carbonaceous feedstock to produce a
syngas; a syngas processing system for converting said syngas to a
purified combustible fuel; and a gas turbine system comprising: a
compressor for compressing air to generate a compressed flow; a
combustor for receiving and combusting at least a portion of said
low-oxygen stream, at least a portion of said compressed flow and
at least a portion of said purified combustible fuel to generate a
high temperature exhaust gas; and a turbine for receiving and
expanding said high temperature exhaust gas to generate electricity
and a reduced temperature low-NOx exhaust gas.
20. A gasification system in accordance with claim 19, wherein said
compressor comprises at least a first-stage compressor section and
a second-stage compressor section.
21. A gasification system in accordance with claim 20, wherein said
low-oxygen stream is directed into said second-stage compressor
section for mixing with a compressed flow from said first-stage
compressor section.
22. A gasification system in accordance with claim 20, further
comprising an intercooler, wherein said low-oxygen stream is
directed into said intercooler for mixing with a compressed flow
from said first-stage compressor section to produce a mixed flow
that is directed to said second-stage compressor section.
23. A gasification system in accordance with claim 19, wherein said
low-oxygen stream has less than about 20% by volume of oxygen.
24. A gasification system in accordance with claim 19, wherein said
low-oxygen stream has less than about 15% by volume of oxygen.
25. A gasification system in accordance with claim 19, wherein said
low-NOx exhaust gas has a NOx level of less than about 30 ppm.
26. A gasification system in accordance with claim 19, wherein said
low-NOx exhaust gas has a NOx level of less than about 10 ppm.
27. A gasification system in accordance with claim 19, wherein said
low-NOx exhaust gas is directed to a HRSG for the generation of
steam and a reduced temperature exhaust gas.
28. A gasification system in accordance with claim 27, wherein said
steam is directed to a bottoming cycle for the generation of
additional electricity.
29. A gasification system in accordance with claim 27, wherein said
reduced temperature exhaust gas is split into a first portion that
is directed to a carbon dioxide capture system and a second portion
that is directed to said compressor for compression along with said
air.
30. A gasification system comprising: an air separation unit for
separating air into oxygen and a low-oxygen stream; a gasifier for
reacting said oxygen and a carbonaceous feedstock to produce a
syngas; a syngas processing system for converting said syngas to a
purified combustible fuel; and a gas turbine system comprising: a
compressor for compressing air and at least a portion of said
low-oxygen stream to generate a compressed flow; a combustor for
receiving and combusting said compressed flow and at least a
portion of said purified combustible fuel to generate a high
temperature exhaust gas; and a turbine for receiving and expanding
said high temperature exhaust gas to generate electricity and a
reduced temperature low-NOx exhaust gas.
31. A method of reducing emissions comprising the steps of:
producing a low-oxygen stream; producing a compressed air stream;
combusting at least a portion of said low-oxygen stream, a portion
of said compressed air stream, and a fuel to produce a high
temperature exhaust gas; expanding said high temperature exhaust
gas to generate electricity and a low-NOx exhaust gas.
32. A method of reducing emissions in accordance with claim 31,
further comprising the steps of: utilizing said low-NOx exhaust gas
to generate steam and a reduced temperature exhaust gas.
33. A method of reducing emissions in accordance with claim 32,
further comprising the steps of: directing a first portion of said
reduced temperature exhaust gas to a carbon dioxide removal system;
and compressing and mixing a second portion of said reduced
temperature exhaust gas with said air stream to produce a
low-oxygen compressed flow.
Description
BACKGROUND
[0001] The invention relates generally to gasification and
combustion technologies and more specifically to methods and
apparatus for low emissions combustion.
[0002] Integrated gasification combined cycle (IGCC) systems are a
promising technology for power generation as they offer the
possibility of producing electricity from abundant fuels such as
coal biomass, pet coke, municipal waste and other fuel feedstock,
with reduced emissions. An IGCC system typically includes an air
separation unit (ASU), a gasification system and a gas turbine
combined cycle system. Pressurized high purity oxygen is produced
in the ASU and sent to gasifier. In the gasifier, fuel feedstock
reacts with the oxygen in the presence of steam to produce syngas
rich in carbon monoxide (CO) and hydrogen (H2). Syngas containing
hydrogen is combusted in the combustor of the gas turbine combined
cycle system. Current syngas combustors are diffusion burners and
steam is usually used as a diluent to reduce thermal nitrogen oxide
(NOx) formation. Using steam as a diluent in syngas combustion puts
a limitation on the maximum turbine inlet temperature that can be
achieved thus limiting the maximum efficiency.
[0003] Some of the challenges currently faced in commercializing
IGCC systems for power generation include high capital cost
compared to other power generation technologies such as pulverized
coal plants. To improve the overall efficiency of the IGCC system,
several integration schemes of the various subsystems are being
explored. Some of these include supplying the steam required for
syngas cleanup and combustion diluent from the heat recovery steam
generator (HRSG) of the gas turbine system as well as compressing
the air required for ASU using the compressor of the gas
turbine.
[0004] Accordingly, there is still a need for further integration
of the various sub systems of the IGCC system to increase the
overall efficiency and a need for developing combustion
technologies that allow higher turbine inlet temperatures without
correspondingly increasing thermal NOx formation.
BRIEF DESCRIPTION
[0005] A turbine system comprises a compressor for compressing air
to generate a compressed flow, an air separation unit for receiving
and separating at least a portion of the compressed flow into
oxygen and a low-oxygen stream, a combustor for receiving and
combusting at least a portion of the low-oxygen stream, a portion
of the compressed flow and a fuel to generate a high temperature
exhaust gas, and a turbine for receiving and expanding the high
temperature exhaust gas to generate electricity and a reduced
temperature low-NOx exhaust gas.
DRAWINGS
[0006] These and other features, aspects, and advantages of the
present invention will become better understood when the following
detailed description is read with reference to the accompanying
drawings in which like characters represent like parts throughout
the drawings, wherein:
[0007] FIG. 1 is a schematic illustration of one embodiment of the
instant invention.
[0008] FIG. 2 is a schematic illustration of another embodiment of
the instant invention.
[0009] FIG. 3 is a schematic illustration of another embodiment of
the instant invention.
[0010] FIG. 4 is a schematic illustration of another embodiment of
the instant invention.
[0011] FIG. 5 is a schematic illustration of another embodiment of
the instant invention.
[0012] FIG. 6 is a schematic illustration of another embodiment of
the instant invention.
[0013] FIG. 7 is a schematic illustration of another embodiment of
the instant invention.
[0014] FIG. 8 is a schematic illustration of another embodiment of
the instant invention.
[0015] FIG. 9 is a schematic illustration of another embodiment of
the instant invention.
[0016] FIG. 10 is a graphical illustration of NOx data for varying
levels of oxygen content at a combustor inlet.
[0017] FIG. 11 is a graphical illustration of NOx data for varying
levels of oxygen content at a combustor inlet and at various
combustor flame temperatures.
DETAILED DESCRIPTION
[0018] A turbine system 10 comprising a compressor 12, a combustor
14, a turbine 16 and an air separation unit (ASU) 18, is shown in
FIG. 1. As used herein, the term ASU means any system or subsystem
that can take in air and issue an oxygen stream and a low-oxygen
stream and optionally a nitrogen stream. As used herein, the term
oxygen stream means a stream consisting of greater than about 80%
by volume of oxygen, while the term low-oxygen stream means a
stream consisting of less than about 20% by volume of oxygen.
[0019] Air 20 is compressed within compressor 12 to produce a
compressed flow 22. A second stream of air 24 is introduced within
ASU 18 to produce an oxygen (02) stream 26 and a low-oxygen stream
28. At least a portion of the low-oxygen stream 28 and at least a
portion of the compressed flow 22 are directed to combustor 14 for
combustion with a fuel 30 to produce a high-pressure, high
temperature exhaust gas 32. The high temperature exhaust gas 32 is
directed to turbine 16 for expansion and generation of electricity
via generator 34 and a reduced temperature low-NOx exhaust gas 36.
As used herein, the term low-NOx exhaust gas means an exhaust gas
having less than about 30 parts per million (ppm) of NOx, and
typically less than about 20 ppm and often less than about 10 ppm.
In fact, in some embodiments, the NOx level can be as low as 5 ppm
and less. The low-oxygen stream 28 dilutes the overall oxygen
content within the combustor 14, thereby lowering the peak
combustion temperature and decreasing the NOx production. Air 20,
without the dilution from the low-oxygen stream 28, typically has
an oxygen content of about 21%. With the addition of all or a
portion of the low-oxygen stream 28 into the combustor, the oxygen
content of the combined combustion air is less than about 21% and
typically between about 10% to about 20%, and often between 15% to
about 18%. Additionally, the NOx production is also reduced due to
the reduced partial oxygen pressure in the combustion flame.
[0020] In another embodiment of the invention 50, the low-oxygen
stream 28 is directed to a compressor 51 and is compressed along
with air 20 to produce a mixed compressed flow 52, as shown in FIG.
2. The mixed compressed flow 52 is directed to combustor 14 for
combustion with fuel 20 to produce high-pressure, high temperature
exhaust gas 32. The high temperature exhaust gas 32 is directed to
turbine 16 for expansion and generation of electricity via
generator 34 and a reduced temperature low-NOx exhaust gas 36. In
one embodiment of the invention, the compressor 51 comprises a
first-stage compressor section 54 and a second-stage compressor
section 56. In one embodiment, the low-oxygen stream 28 is directed
into second-stage compressor section 56 for mixing with a
compressed flow 58 from first-stage compressor section 54. In yet
another embodiment of the invention, an optional intercooler 60
receives and mixes the low-oxygen stream 28 and the compressed flow
58 to produce a mixed stream 62 that is directed to second-stage
compressor section 56 for compression to produce mixed compressed
flow 52. This embodiment is particularly attractive because several
commercial gas turbine systems, for example the GE LMS 100,
currently utilize a multi-stage compressor and an intermediate
intercooler making retrofit applications both desirable and
practical to implement.
[0021] In another embodiment of the invention 100, the compressed
flow 22 is split into two streams a first portion 102 and a second
portion 104, as shown in FIG. 3. The first portion 102 of
compressed flow 22 is directed to ASU 18 to produce oxygen stream
26 and low-oxygen stream 28. The second portion 104 is directed to
an optional mixer 106 where the second portion 104 is mixed with
the low-oxygen stream 28 to form a mixed flow 108. The mixed flow
108 is then directed to combustor 14 for combustion with fuel 30.
(Alternatively, the second portion 104 and the low-oxygen stream 28
are directed into combustor 14.) In this embodiment, the system
advantageously uses only one compression cycle to compress both the
air directed to the combustor 14 and the air directed to the ASU
18, thereby saving capital investment, operating and maintenance
expenses, and limiting the overall footprint of the system.
[0022] In another embodiment of the invention 200, the oxygen
stream 26 is directed to a gasifier 202 where it is reacted with a
carbonaceous feedstock 204 to produce a syngas 206, as shown in
FIG. 4. A portion 208 of oxygen stream 26 can be split off and
otherwise utilized, for example, portion 208 could be captured,
stored or transported. Syngas 206 is then directed to a syngas
processing system 210 for converting the syngas 206 to a purified
combustible fuel 212. The purified combustible fuel 212 is directed
into combustor 14 for combustion with the mixed flow 108. This
embodiment provides the advantage of applying the low NOx solution
to existing gasification systems. Most gasification systems include
an ASU as a standard component of the system, so system integration
would be straightforward.
[0023] In another embodiment of the invention 300, the compressor
12 comprises a first stage compressor 302 and a second stage
compressor 304, as shown in FIG. 5. Air 305 is directed to first
stage compressor 302 for generating a compressed stream 306 that is
directed to ASU 18. Second stage compressor 304 receives air 20 and
generates compressed stream 22 that is directed to mixer 106 for
mixing compressed stream 22 with low-oxygen stream 28.
[0024] In another embodiment of the invention 400, the low-oxygen
stream 28 is directed into second stage compressor 304 and is
compressed along with air 20 to produce a mixed compressed flow
402, as shown in FIG. 6. The mixed compressed flow 402 is directed
to combustor 14 for combustion with the purified combustible fuel
212 to produce high-pressure, high temperature exhaust gas 32. The
high temperature exhaust gas 32 is directed to turbine 16 for
expansion and generation of electricity via generator 34 and a
reduced temperature low-NOx exhaust gas 36. In yet another
embodiment of the invention, an optional intercooler 310 receives
and mixes the low-oxygen stream 28 and at least a portion of the
compressed stream 306 to produce a mixed stream 312 that is
directed to second-stage compressor section 304 for compression to
produce mixed compressed flow 402.
[0025] In another embodiment of the invention 500, the embodiment
discussed in relation to FIG. 1 is further modified to include an
Exhaust Gas Recirculation (EGR) circuit, as shown in FIG. 7. The
low-NOx exhaust gas 36 produced by turbine 16 is directed to a Heat
Recovery Steam Generator (HRSG) 502 for the generation of steam 504
and a reduced temperature exhaust gas 506. The steam 504 is
typically directed to a steam turbine bottoming cycle (not shown)
for the generation of additional electricity. The reduced
temperature exhaust gas 506 is directed to a flow-splitting device
508 for splitting the reduced temperature exhaust gas 506 into at
least a first portion 510 and a second portion 512. In one
embodiment, the first portion 510 is directed to a carbon dioxide
capture system 514 for the removal and isolation of carbon dioxide
contained within the stream. In one embodiment, the first portion
510 is between about 50% to about 80% of the reduced temperature
exhaust gas 506.
[0026] The second portion 512 of reduced temperature exhaust gas
506 is directed, typically via a pump 516, to a water removal
system 518, for example a condenser, to remove any excess water and
produce a low-oxygen, low-water stream 520. In one embodiment, the
second portion 512 is between about 20% to about 50% of the reduced
temperature exhaust gas 506. The low-oxygen, low-water stream 520
is directed into compressor 12 for compression along with air 20 to
produce a low-oxygen compressed flow 522. The NOx formation within
combustor 14 is significantly reduced as compared to prior art
systems as the combustor 14 is receiving multiple streams with a
reduced oxygen content, low oxygen compressed flow 522 and
low-oxygen stream 28. The NOx formation is reduced because of the
reduced partial oxygen pressure in the combustion flame and the
lower temperature of the flame compared to combustion of
atmospheric air. Additionally, carbon dioxide capture is made
significantly easier in this system as the first portion 510 of
reduced temperature exhaust gas 506 has a lower volumetric flow and
a higher carbon dioxide content making the capture and isolation of
the carbon dioxide much more efficient with a smaller overall
system footprint. In one embodiment 600, low-water stream 520 is
directed into a heat exchanger 602 along with low-oxygen stream 28
for heat exchange therebetween as the temperature of the low-water
stream 520 is reduced prior to entry into compressor 12 and the
temperature of low-oxygen stream 28 is raised prior to entry into
combustor 14, as shown in FIG. 8.
[0027] In another embodiment of the invention 700, the embodiment
discussed in relation to FIG. 5 is further modified to include an
Exhaust Gas Recirculation (EGR) circuit, as shown in FIG. 9. The
low-oxygen, low-water stream 520 is directed into compressor 12 for
compression along with air 20 to produce a low-oxygen compressed
flow 522.
[0028] FIG. 10 is a graphical illustration of NOx reduction
(corrected to 15% oxygen by volume) demonstrated in certain
experiments plotted against the oxygen level at the inlet of the
combustor maintained at a fixed flame temperature of about
2900.degree. F. As shown from the data, a significant reduction in
NOx occurs as the oxygen content in the combustion air changes from
the standard 21% by volume to 14% by volume. As demonstrated from
these experiments, a NOx reduction of about 80 percent is measured
at the 14% oxygen content level as compared to the baseline level
of 21% oxygen content.
[0029] FIG. 11 is another graphical illustration showing the NOx
levels in ppm (corrected to 15% oxygen by volume) demonstrated in
certain experiments plotted against the oxygen level at the
combustor inlet for three different flame temperatures, about
2600.degree. F., about 2800.degree. F., and about 3000.degree. F.
As shown from the data, a significant reduction in NOx levels
occurs as the oxygen content in the combustion air changes from the
standard 21% by volume to about 16% by volume and less. As shown,
for all three flame temperatures, the NOx levels at 16% by volume
of oxygen are less than about 10 ppm and in one case less than 5
ppm, providing a significant reduction in NOx levels from the
baseline.
[0030] While only certain features of the invention have been
illustrated and described herein, many modifications and changes
will occur to those skilled in the art. It is, therefore, to be
understood that the appended claims are intended to cover all such
modifications and changes as fall within the true spirit of the
invention.
* * * * *