U.S. patent application number 14/002625 was filed with the patent office on 2014-01-16 for systems and methods for carbon dioxide captrue and power generation in low emission turbine systems.
The applicant listed for this patent is Sulabh K. Dhanuka, Richard A. Huntington, Franklin F. Mittricker, Dennis M. O'Dea, Russell H. Oelfke, Omar Angus Sites. Invention is credited to Sulabh K. Dhanuka, Richard A. Huntington, Franklin F. Mittricker, Dennis M. O'Dea, Russell H. Oelfke, Omar Angus Sites.
Application Number | 20140013766 14/002625 |
Document ID | / |
Family ID | 46879960 |
Filed Date | 2014-01-16 |
United States Patent
Application |
20140013766 |
Kind Code |
A1 |
Mittricker; Franklin F. ; et
al. |
January 16, 2014 |
Systems and Methods For Carbon Dioxide Captrue and Power Generation
In Low Emission Turbine Systems
Abstract
Systems, methods, and apparatus are provided for generating
power in low emission turbine systems and separating the exhaust
into rich CO.sub.2 and lean CO.sub.2 streams. In one or more
embodiments, the exhaust is separated at an elevated pressure, such
as between a high-pressure expansion stage and a low-pressure
expansion stage.
Inventors: |
Mittricker; Franklin F.;
(Jamul, CA) ; Dhanuka; Sulabh K.; (Houston,
TX) ; Huntington; Richard A.; (Houston, TX) ;
Sites; Omar Angus; (Spring, TX) ; O'Dea; Dennis
M.; (Somerset, NJ) ; Oelfke; Russell H.;
(Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mittricker; Franklin F.
Dhanuka; Sulabh K.
Huntington; Richard A.
Sites; Omar Angus
O'Dea; Dennis M.
Oelfke; Russell H. |
Jamul
Houston
Houston
Spring
Somerset
Houston |
CA
TX
TX
TX
NJ
TX |
US
US
US
US
US
US |
|
|
Family ID: |
46879960 |
Appl. No.: |
14/002625 |
Filed: |
March 5, 2012 |
PCT Filed: |
March 5, 2012 |
PCT NO: |
PCT/US12/27774 |
371 Date: |
August 30, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61466384 |
Mar 22, 2011 |
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61466385 |
Mar 22, 2011 |
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61466381 |
Mar 22, 2011 |
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61542036 |
Sep 30, 2011 |
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61542031 |
Sep 30, 2011 |
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61542030 |
Sep 30, 2011 |
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61542035 |
Sep 30, 2011 |
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Current U.S.
Class: |
60/783 ;
60/784 |
Current CPC
Class: |
Y02E 20/16 20130101;
F02C 7/00 20130101; Y02A 50/2342 20180101; Y02C 20/40 20200801;
B01D 53/62 20130101; F01N 5/02 20130101; H02K 7/1823 20130101; F02C
3/22 20130101; F01N 3/0857 20130101; F02C 3/24 20130101; Y02C 10/04
20130101; F02C 3/04 20130101; Y02A 50/20 20180101; F05D 2260/61
20130101; F02C 3/34 20130101; F02C 3/20 20130101 |
Class at
Publication: |
60/783 ;
60/784 |
International
Class: |
F02C 7/00 20060101
F02C007/00 |
Claims
1. A power generation system comprising: a first compressor
configured to receive and compress one or more oxidants; a first
combustion chamber configured to receive and combust the compressed
oxidant and at least one first fuel to generate an exhaust stream;
a first expander configured to receive the exhaust stream from the
compressor and generate a gaseous exhaust stream; and a separator
configured to receive and separate the gaseous exhaust stream into
a CO.sub.2 rich stream and a CO.sub.2 lean stream.
2. The system of claim 1, further comprising a second expander
configured to receive and expand the CO.sub.2 lean stream.
3. The system of claim 1, wherein the first expander at least
partially drives the first compressor.
4. The system of claim 2, further comprising a second compressor
configured to receive and compress one or more oxidants and deliver
compressed oxidant to the first compressor.
5. The system of claim 4, wherein the second expander at least
partially drives the second compressor.
6. The system of claim 2, wherein the operating pressure of the
first expander is higher than the operating pressure of the second
expander.
7. The system of claim 1, wherein the first fuel comprises natural
gas, oil, coke, coal, hydrogen, bitumen, or a combination
thereof.
8. The system of claim 1, wherein the oxidant comprises air,
oxygen-enriched air, oxygen, or a combination thereof.
9. The system of claim 1, wherein the separator uses a separation
process selected from hot potassium carbonate separation, molecular
sieve separation, amine separation, membrane separation, adsorptive
kinetic separation, controlled freeze zone separation, or
combinations thereof.
10. The system of claim 1, wherein at least a portion of the
CO.sub.2 rich stream is recycled to the first combustion
chamber.
11. The system of claim 1, further comprising a heat exchanger
configured to transfer heat from the discharge of the first
expander to the lean CO.sub.2 stream.
12. The system of claim 1, further comprising a second combustion
chamber configured to combust one or more oxidants and a second
fuel to heat to the lean CO.sub.2 stream.
13. The system of claim 12, wherein the second fuel comprises
hydrogen.
14. The system of claim 2, further comprising a heat recovery steam
generator configured to use heat from the lean CO.sub.2 stream
exiting the second expander to generate steam.
15. The system of claim 1, further comprising a heat recovery steam
generator configured to use heat from the rich CO.sub.2 stream
exiting the separator to generate steam.
16. The system of claim 1, wherein the first combustion chamber is
further configured to receive high pressure steam.
17. A method for generating power comprising: compressing one or
more oxidants in a first compressor; supplying the compressed
oxidant and at least one first fuel to a first combustion chamber;
combusting the compressed oxidant and the at least one fuel in the
first combustion chamber to generate an exhaust stream; expanding
the exhaust stream in a first expander to generate a gaseous
exhaust stream; and separating the gaseous exhaust stream into a
CO.sub.2 rich stream and a CO.sub.2 lean stream.
18. The method of claim 17, further comprising expanding the lean
CO.sub.2 stream in a second expander.
19. The method of claim 17, further comprising compressing one or
more oxidants in a second compressor and supplying the compressed
oxidant to the first compressor.
20. The method of claim 17, wherein the first fuel comprises
natural gas, oil, coke, coal, other hydrocarbons, hydrogen, or a
combination thereof.
21. The method of claim 17, wherein the oxidant comprises air,
oxygen-enriched air, oxygen, or a combination thereof.
22. The method of claim 18, further comprising operating the first
expander at a pressure higher than that of the second expander.
23. The method of claim 17, wherein the gaseous exhaust stream is
separated using a process selected from hot potassium carbonate
separation, amine separation, molecular sieve separation, membrane
separation, adsorptive kinetic separation, controlled freeze zone
separation, or combinations thereof.
24. The method of claim 17, further comprising recycling at least a
portion of the rich CO.sub.2 stream to the first combustion
chamber.
25. The method of claim 18, further comprising heating the lean
CO.sub.2 stream before expanding the lean CO.sub.2 stream in the
second expander.
26. The method of claim 25, wherein the lean CO.sub.2 stream is
heated in a heat exchanger.
27. The method of claim 25, wherein the lean CO.sub.2 stream is
heated by combusting one or more oxidants and a second fuel in a
second heat exchanger.
28. The method of claim 27, wherein the second fuel comprises
hydrogen.
29. The method of claim 18, further comprising generating steam in
a heat recovery steam generator using heat from the lean CO.sub.2
stream.
30. The method of claim 17, further comprising generating steam in
a heat recovery steam generator using heat from the rich CO.sub.2
stream.
31. The method of claim 17, further comprising injecting the rich
CO.sub.2 stream into a hydrocarbon reservoir.
32. The method of claim 17, further comprising injecting the lean
CO.sub.2 stream into a hydrocarbon reservoir.
33. The method of claim 17, further comprising supplying high
pressure steam to the first combustion chamber.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application 61/542,036 filed Sep. 30, 2011 entitled, SYSTEMS AND
METHODS FOR CARBON DIOXIDE CAPTURE IN LOW EMISSION TURBINE SYSTEMS;
U.S. Provisional Application 61/466,384 filed Mar. 22, 2011
entitled, LOW EMISSION TURBINE SYSTEMS HAVING A MAIN AIR COMPRESSOR
OXIDANT CONTROL APPARATUS AND METHODS RELATED THERETO; U.S.
Provisional Application 61/542,030 filed Sep. 30, 2011 entitled,
LOW EMISSION TURBINE SYSTEMS INCORPORATING INLET COMPRESSOR OXIDANT
CONTROL APPARATUS AND METHODS RELATED THERETO; U.S. Provisional
Application 61/466,385 filed Mar. 22, 2011 entitled, METHODS FOR
CONTROLLING STOICHIOMETRIC COMBUSTION ON A FIXED GEOMETRY GAS
TURBINE SYSTEM AND APPARATUS AND SYSTEMS RELATED THERETO; U.S.
Provisional Application 61/542,031 filed Sep. 30, 2011 entitled,
SYSTEMS AND METHODS FOR CONTROLLING STOICHIOMETRIC COMBUSTION IN
LOW EMISSION TURBINE SYSTEMS; U.S. Provisional Application
61/466,381 filed Mar. 22, 2011 entitled, METHODS OF VARYING LOW
EMISSION TURBINE GAS RECYCLE CIRCUITS AND SYSTEMS AND APPARATUS
RELATED THERETO; U.S. Provisional Application 61/542,035 filed Sep.
30, 2011 entitled, METHODS OF VARYING LOW EMISSION TURBINE GAS
RECYCLE CIRCUITS AND SYSTEMS AND APPARATUS RELATED THERETO; all of
which are hereby incorporated by reference in their entirety.
[0002] This application is related to U.S. Provisional Application
61/542,037 filed Sep. 30, 2011 entitled, SYSTEMS AND METHODS FOR
CARBON DIOXIDE CAPTURE IN LOW EMISSION TURBINE SYSTEMS; U.S.
Provisional Application 61/542,039 filed Sep. 30, 2011 entitled,
SYSTEMS AND METHODS FOR CARBON DIOXIDE CAPTURE IN LOW EMISSION
COMBINED TURBINE SYSTEMS; U.S. Provisional Application 61/542,041
filed Sep. 30, 2011 entitled, LOW EMISSION POWER GENERATION SYSTEMS
AND METHODS INCORPORATING CARBON DIOXIDE SEPARATION; all of which
are hereby incorporated by reference in their entirety.
FIELD OF THE DISCLOSURE
[0003] Embodiments of the disclosure relate to low emission power
generation. More particularly, embodiments of the disclosure relate
to methods and apparatus for carbon dioxide separation and capture
for power generation in low emission turbine systems.
BACKGROUND OF THE DISCLOSURE
[0004] This section is intended to introduce various aspects of the
art, which may be associated with exemplary embodiments of the
present disclosure. This discussion is believed to assist in
providing a framework to facilitate a better understanding of
particular aspects of the present disclosure. Accordingly, it
should be understood that this section should be read in this
light, and not necessarily as admissions of prior art.
[0005] Many oil producing countries are experiencing strong
domestic growth in power demand and have an interest in enhanced
oil recovery (EOR) to improve oil recovery from their reservoirs.
Two common EOR techniques include nitrogen (N.sub.2) injection for
reservoir pressure maintenance and carbon dioxide (CO.sub.2)
injection for miscible flooding for EOR. There is also a global
concern regarding green house gas (GHG) emissions. This concern
combined with the implementation of cap-and-trade policies in many
countries makes reducing CO.sub.2 emissions a priority for those
countries as well as for the companies that operate hydrocarbon
production systems therein.
[0006] Some approaches to lower CO.sub.2 emissions include fuel
de-carbonization or post-combustion capture using solvents, such as
amines. However, both of these solutions are expensive and reduce
power generation efficiency, resulting in lower power production,
increased fuel demand and increased cost of electricity to meet
domestic power demand. In particular, the presence of oxygen,
SO.sub.X, and NO.sub.x components makes the use of amine solvent
absorption very problematic. Another approach is an oxyfuel gas
turbine in a combined cycle (e.g., where exhaust heat from the gas
turbine Brayton cycle is captured to make steam and produce
additional power in a Rankin cycle). However, there are no
commercially available gas turbines that can operate in such a
cycle and the power required to produce high purity oxygen
significantly reduces the overall efficiency of the process.
[0007] Moreover, with the growing concern about global climate
change and the impact of carbon dioxide emissions, emphasis has
been placed on minimizing carbon dioxide emissions from power
plants. Gas turbine power plants are efficient and can have a lower
cost compared to nuclear or coal power generation technologies.
Capturing carbon dioxide from the exhaust of a gas turbine power
plant is expensive for the following reasons: (a) the concentration
of carbon dioxide in the exhaust stack is low, (b) the volume of
gas that needs to be treated is large, (c) the pressure of the
exhaust stream is low, and (d) the amount of oxygen present in the
exhaust stream is large. All of these factors result in a high cost
of carbon dioxide capture.
[0008] Accordingly, there is still a substantial need for a low
emission, high efficiency power generation and CO.sub.2 capture
process.
SUMMARY OF THE DISCLOSURE
[0009] In the low emission power generation systems described
herein, exhaust gases from low emission gas turbines, which are
vented in a typical natural gas combined cycle (NGCC) plant, are
instead separated and recovered. The apparatus, systems, and
methods of the invention combine an open Brayton cycle that uses an
oxidant and hydrocarbon fuel to generate power with a carbon
dioxide separation process. The carbon dioxide separation process
takes place at a pressure between the compressor outlet pressure
and the final expander outlet pressure and results in two exhaust
streams, one carbon dioxide (CO.sub.2) rich and the other CO.sub.2
lean. The rich CO.sub.2 and lean CO.sub.2 streams may be used for
the same or different purposes. Uses for each stream include
injection into hydrocarbon reservoirs for enhanced oil recovery,
generation of additional power, carbon sequestration or storage,
for recycle to the combustion chamber of the turbine to cool the
products of combustion down to the material limitations in the
expander, for sale, or for venting.
[0010] In the systems and methods of the present invention, high
pressure exhaust gases exiting the combustion chamber of a low
emission gas turbine are partially expanded in a first
high-pressure expander, generating power. The exhaust gases exit
the first expander at elevated pressure and are separated into rich
CO.sub.2 and lean CO.sub.2 streams using a CO.sub.2 separation
process. Pressure is maintained on the lean CO.sub.2 stream during
the separation process, which allows further energy extraction from
the lean CO.sub.2 stream in a second low-pressure expander. By
operating the separation process between the two expansion stages
at an elevated pressure, the separation equipment may be downsized
and the effectiveness of the separation process may be
improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The foregoing and other advantages of the present disclosure
may become apparent upon reviewing the following detailed
description and drawings of non-limiting examples of embodiments in
which:
[0012] FIG. 1 depicts a low emission power generation system
incorporating CO.sub.2 separation between two expansion stages.
[0013] FIG. 2 depicts a low emission power generation system
incorporating CO.sub.2 separation and recycle of the rich CO.sub.2
stream.
[0014] FIG. 3 depicts a low emission power generation system
incorporating CO.sub.2 separation and a second inlet
compressor.
[0015] FIG. 4 depicts a low emission power generation system
incorporating CO.sub.2 separation upstream of the expander.
DETAILED DESCRIPTION
[0016] In the following detailed description section, the specific
embodiments of the present disclosure are described in connection
with preferred embodiments. However, to the extent that the
following description is specific to a particular embodiment or a
particular use of the present disclosure, this is intended to be
for exemplary purposes only and simply provides a description of
the exemplary embodiments. Accordingly, the disclosure is not
limited to the specific embodiments described below, but rather, it
includes all alternatives, modifications, and equivalents falling
within the true spirit and scope of the appended claims.
[0017] Various terms as used herein are defined below. To the
extent a term used in a claim is not defined below, it should be
given the broadest definition persons in the pertinent art have
given that term as reflected in at least one printed publication or
issued patent.
[0018] As used herein, the term "natural gas" refers to a
multi-component gas obtained from a crude oil well (associated gas)
and/or from a subterranean gas-bearing formation (non-associated
gas). The composition and pressure of natural gas can vary
significantly. A typical natural gas stream contains methane
(CH.sub.4) as a major component, i.e. greater than 50 mol % of the
natural gas stream is methane. The natural gas stream can also
contain ethane (C.sub.2H.sub.6), higher molecular weight
hydrocarbons (e.g., C.sub.3-C.sub.20 hydrocarbons), one or more
acid gases (e.g., hydrogen sulfide), or any combination thereof.
The natural gas can also contain minor amounts of contaminants such
as water, nitrogen, iron sulfide, wax, crude oil, or any
combination thereof.
[0019] As used herein, the term "stoichiometric combustion" refers
to a combustion reaction having a volume of reactants comprising a
fuel and an oxidizer and a volume of products formed by combusting
the reactants where the entire volume of the reactants is used to
form the products. As used herein, the term "substantially
stoichiometric" combustion refers to a combustion reaction having
an equivalence ratio ranging from about 0.9:1 to about 1.1:1, or
more preferably from about 0.95:1 to about 1.05:1. Use of the term
"stoichiometric" herein is meant to encompass both stoichiometric
and substantially stoichiometric conditions unless otherwise
indicated.
[0020] As used herein, the term "stream" refers to a volume of
fluids, although use of the term stream typically means a moving
volume of fluids (e.g., having a velocity or mass flow rate). The
term "stream," however, does not require a velocity, mass flow
rate, or a particular type of conduit for enclosing the stream.
[0021] Embodiments of the presently disclosed systems and processes
may be used to produce ultra low emission electric power and
CO.sub.2 for enhanced oil recovery (EOR) or sequestration
applications. In EOR applications, CO.sub.2 is injected into or
adjacent to producing oil wells, usually under supercritical
conditions. The CO.sub.2 acts as both a pressurizing agent and,
when dissolved into the underground crude oil, significantly
reduces the oil's viscosity enabling the oil to flow more rapidly
through the earth to a removal well. According to embodiments
disclosed herein, a mixture of compressed oxidant (typically air)
and fuel is combusted and the exhaust gas is expanded in a first
expansion stage to generate power. The exhaust gas is then
separated into rich CO.sub.2 and lean CO.sub.2 streams at elevated
pressure. The lean CO.sub.2 stream may then be expanded again in a
second expansion stage to generate additional power. The rich
CO.sub.2 stream may, in some embodiments, be recycled and mixed
with the oxidant entering the combustion chamber to act as a
diluent to control or otherwise moderate the temperature of the
combustion and exhaust gas entering the succeeding expander. The
combustion may be stoichiometric or non-stoichiometric.
[0022] Combustion at near stoichiometric conditions (or "slightly
rich" combustion) can prove advantageous in order to eliminate the
cost of excess oxygen removal. By cooling the exhaust gas and
condensing the water out of the stream, a relatively high content
CO.sub.2 stream can be produced. While a portion of the recycled
exhaust gas can be utilized for temperature moderation in a closed
Brayton cycle, the remaining portion can be used for EOR
applications and electric power can be produced with little or no
SO.sub.X, NO.sub.X, or CO.sub.2 being emitted to the atmosphere.
For example, the non-recycled stream can be processed to generate a
lean CO.sub.2 stream which can be subsequently expanded in a gas
expander to generate additional mechanical power. The result of the
systems disclosed herein is the production of power and the
production or capture of additional CO.sub.2 at a more economically
efficient level.
[0023] The present invention is directed to systems and methods for
low emission power generation comprising a separation process in
which exhaust gas from a combustion chamber is separated into rich
CO.sub.2 and lean CO.sub.2 streams at an elevated pressure. In some
embodiments, one or both of the rich CO.sub.2 and lean CO.sub.2
streams may be injected into one or more hydrocarbon reservoirs for
enhanced oil recovery (EOR). As used herein, the terms "rich" and
"lean" mean that, of the total amount of CO.sub.2 entering the
CO.sub.2 separation process at least about 51% of that CO.sub.2
exits the separation process via the rich CO.sub.2 stream, with the
remaining CO.sub.2 exiting in the lean CO.sub.2 stream. In some
embodiments, at least about 55%, or at least about 60%, or at least
about 65%, or at least about 70%, or at least about 75%, or at
least about 80%, or at least about 85%, or at least about 90%, or
at least about 95% of the total CO.sub.2 entering the separation
process exits in the rich CO.sub.2 stream.
[0024] In the systems and methods herein, one or more oxidants are
compressed and combusted with one or more fuels in a combustion
chamber. The oxidant may comprise any oxygen-containing fluid, such
as ambient air, oxygen-enriched air, substantially pure oxygen, or
combinations thereof. The one or more oxidants may be compressed in
one or more compressors. Each compressor may comprise a single
stage or multiple stages. In multiple stage compressors, interstage
cooling may optionally be employed to allow for higher overall
compression ratios and higher overall power output. Each compressor
may be of any type suitable for the process described herein, and
is preferably reliable, efficient, and capable of a high
compression ratio. Such compressors include, but are not limited
to, axial, centrifugal, reciprocating, or twin-screw compressors
and combinations thereof. In one or more embodiments, the oxidant
compressor or compressors are axial compressors. The fuel may
comprise natural gas, associated gas, diesel, fuel oil, gasified
coal, coke, naphtha, butane, propane, ethane, methane, syngas,
kerosene, aviation fuel, bio-fuel, oxygenated hydrocarbon
feedstock, bitumen, any other suitable hydrocarbon containing gases
or liquids, hydrogen, or combinations thereof. Additionally, the
fuel may comprise inert components including but not limited to
N.sub.2 or CO.sub.2. In some embodiments, the fuel may be at least
partially supplied by a hydrocarbon reservoir that is benefitting
from enhanced oil recovery via injection of either the rich
CO.sub.2 stream or the lean CO.sub.2 stream or both. The combustion
conditions in the combustion chamber may be lean, stoichiometric or
substantially stoichiometric, or rich. In one or more embodiments,
the combustion conditions are stoichiometric or substantially
stoichiometric. Combustion of the fuel and oxidant can typically
generate temperatures between about 2000.degree. F. and
3000.degree. F. In some embodiments, the combustion chamber
operates at a pressure at or near the output pressure of the
oxidant compressor.
[0025] Combustion of the oxidant and fuel in the combustion chamber
generates an exhaust stream, which is then expanded. The exhaust
stream comprises products of combustion, and its composition will
vary depending upon the composition of the fuel and the oxidant
used. In one or more embodiments, the discharge exhaust stream from
the combustion chamber may comprise vaporized water, CO.sub.2,
carbon monoxide (CO), oxygen, nitrogen, argon, nitrogen oxides
(NO.sub.x), sulfur oxides (SO.sub.x), hydrogen sulfide (H.sub.2S),
hydrocarbons, or combinations thereof. The discharge exhaust stream
may be expanded in one or more expanders. The discharge exhaust
stream entering the expander (or expander system, if more than one
expander is used) is typically at a temperature and pressure
approximately the same as the exit temperature and pressure of the
combustion chamber.
[0026] Each of the one or more expanders may comprise a single
stage or multiple stages. Each expander may be any type of expander
suitable for the process described herein, including but not
limited to axial or centrifugal expanders or combinations thereof.
Each expander is preferably efficient and capable of high expansion
ratios. Expansion of the exhaust stream generates power, which may
be used to drive one or more compressors or electric generators. In
one or more embodiments of the invention, the expander is coupled
to the oxidant compressor via a common shaft or other mechanical,
electrical, or other power coupling, such that the oxidant
compressor is at least partially driven by the expander. In other
embodiments, the oxidant compressor may be mechanically coupled to
an electric motor with or without a speed increasing or decreasing
device such as a gear box or to a steam turbine. When taken
together, the oxidant compressor, combustion chamber, and expander
may be characterized as an open Brayton cycle.
[0027] In one or more embodiments of the invention, at least two
expander stages are employed, with a CO.sub.2 separation process
incorporated between any two of the stages. The first stage is a
high pressure expander that accepts the discharge exhaust gas from
the combustion chamber and outputs the same gases to a CO.sub.2
separation process at a reduced temperature and pressure. While
reduced, the pressure at the outlet of the high pressure expander
is still higher than ambient conditions. For example, the outlet
pressure of the high pressure expander may be greater than about 25
psia, or greater than about 50 psia, or greater than about 75 psia,
or greater than about 100 psia.
[0028] The CO.sub.2 separation process may be any suitable process
designed to separate the pressurized exhaust gases into a rich
CO.sub.2 stream and a lean CO.sub.2 stream. Separating the
components of the exhaust gas allows different components in the
exhaust to be handled in different ways. Ideally, the separation
process would segregate all of the greenhouse gases in the exhaust,
such as CO.sub.2, CO, NO.sub.x, SO.sub.X, etc. in the rich CO.sub.2
stream, leaving the remainder of the exhaust components such as
nitrogen, oxygen, argon, etc. in the lean CO.sub.2 stream. In
practice, however, the separation process may not withdraw all of
the greenhouse gases from the lean stream, and some non-greenhouse
gases may remain in the rich stream. Any suitable separation
process designed to achieve the desired result may be used.
Examples of suitable separation processes include, but are not
limited to, hot potassium carbonate ("hot pot") separation
processes, amine separation, molecular sieve separation, membrane
separation, adsorptive kinetic separation, controlled freeze zone
separation, and combinations thereof. In some embodiments, a hot
pot separation process is used for CO.sub.2 separation. In one or
more embodiments of the invention, the separation process operates
at elevated pressure (i.e., higher than ambient and approximately
the same as the outlet pressure of the high-pressure expander) and
is configured to keep the lean CO.sub.2 stream pressurized.
Maintaining pressure on the lean CO.sub.2 stream in this manner
allows for smaller separation equipment, provides for improved
separation effectiveness, and allows further energy extraction from
the lean CO.sub.2 stream. In some embodiments, the CO.sub.2
separation process is selected and configured to maximize either
the outlet pressure or the outlet temperature, or both, of the lean
CO.sub.2 stream. While the term "CO.sub.2 separator" is used herein
for simplicity in illustrating or describing certain embodiments of
the invention, it should be appreciated that the term is meant to
encompass the entire CO.sub.2 separation process and does not
necessarily refer to a single apparatus or process step.
[0029] In one or more embodiments, the lean CO.sub.2 stream exits
the CO.sub.2 separator at an elevated pressure and is directed to a
second expansion stage, which may be a low pressure expander
configured to receive the pressurized lean CO.sub.2 stream and
output the same gases at approximately ambient pressure. As will be
appreciated by those skilled in the art, each expansion stage
generates power, and the power generated by each expander may be
used to at least partially drive one or more compressors or
electric generators in any configuration, either within the
described system or externally. Conveniently, in one or more
embodiments, the first (high pressure) expander may at least
partially drive a first oxidant compressor. In such embodiments,
the first compressor, combustor, and first expander may be a
packaged gas turbine. In the same or other embodiments, a second
oxidant compressor may be employed to provide further compression
of the oxidant feed to the combustor either before or after the
first compressor, and the second (low pressure) expander may at
least partially drive the second oxidant compressor. In such
embodiments, the first and second compressors, combustor, and first
and second expanders may be a packaged gas turbine. Alternatively,
one expander may be used to drive the oxidant compressor, while
another expander may be used to drive a pipeline or injection
compressor to compress the rich CO.sub.2 stream (or the lean
CO.sub.2 stream) for injection into a reservoir for storage or EOR.
In such configurations, the pipeline or injection compressor may be
located in the vicinity of the power generation systems described
herein.
[0030] Although the CO.sub.2 separation process as described herein
is preferably located between expansion stages, the separation may
alternatively take place prior to the first expansion stage. In
such configurations, the exhaust gas from the combustion chamber is
provided directly to the separator and the separator produces a
rich CO.sub.2 stream and a lean CO.sub.2 stream as described above.
The lean CO.sub.2 stream is then directed to one or more expanders
or expansion stages, and the rich CO.sub.2 stream may also be
expanded or may be treated in a variety of ways described in more
detail below.
[0031] In one or more embodiments, the lean CO.sub.2 stream may
optionally be heated prior to the low pressure expansion stage.
Such heating may be accomplished using any suitable heating device.
For example, one or more heat exchangers or cross exchangers may be
configured to transfer heat to the lean CO.sub.2 stream before the
lean CO.sub.2 stream enters the low pressure expander. The one or
more heat or cross exchangers may be configured to transfer heat
from a variety of sources, such as from the discharge of the first
combustor or from the discharge of the high pressure expander. In
the same or other embodiments, the lean CO.sub.2 stream may be
heated in a second combustion chamber located between the high
pressure and low pressure expansion stages. Use of a second
combustion chamber requires the supply of additional fuel, which
may be the same as or different from the fuel supplied to the first
combustion chamber. In some embodiments, the fuel supplied to and
combusted in the second combustion chamber comprises hydrogen. The
oxidant required by the second combustion chamber may be supplied
via a separate oxidant stream, or there may be sufficient oxidant
in the lean CO.sub.2 stream such that an additional supply of
oxidant is unnecessary. By heating the lean CO.sub.2 stream before
the low pressure expansion stage of the process, power generation
in the low pressure expander may be increased.
[0032] In one or more embodiments, either the lean CO.sub.2 stream
(after expansion) or the rich CO.sub.2 stream, or both, may pass
through one or more heat recovery steam generators (HRSGs). The one
or more HRSGs may be configured to utilize the residual heat in one
or both of the streams to generate steam. The steam generated by
the one or more HRSGs may be used for a variety of purposes, such
as to drive a steam turbine generator in a Rankine cycle, to drive
a steam turbine in mechanical drive service, or for water
desalination. Where the lean CO.sub.2 stream and the rich CO.sub.2
stream are each directed to a HRSG, the steam generated by each
HRSG may be used for the same or different applications. Further,
if any residual heat remains in either or both of the lean or rich
CO.sub.2 streams exiting the one or more HRSGs, the system may
further comprise one or more heat exchangers configured to transfer
that heat to a non-steam working fluid. In such embodiments, the
non-steam working fluid may optionally be used to drive an expander
in a Rankine cycle.
[0033] Each of the rich CO.sub.2 stream and the lean CO.sub.2
streams may be used, wholly or in part, for a variety of
applications, and the two streams may be used for the same or
different applications. For example, at least a portion of the rich
CO.sub.2 stream may be recycled and mixed with the oxidant entering
the combustion chamber or added directly to the combustion chamber
to act as a diluent to control or otherwise moderate the
temperature of the combustion and exhaust gas entering the
succeeding expander. In such instances, the system may be
characterized as comprising a closed Brayton cycle. In the same or
other embodiments, the rich CO.sub.2 stream may be injected into a
hydrocarbon reservoir for enhanced oil recovery (EOR), may be
directed to a reservoir for carbon sequestration or storage. The
rich CO.sub.2 stream may also be sold, vented, or flared. In one or
more embodiments, the lean CO.sub.2 stream may also be used for
EOR. In the same or other embodiments, the lean CO.sub.2 stream may
be sold, vented, or flared.
[0034] The invention may comprise further elements in addition to
the low emission power generation systems and methods described
herein. For example, in some embodiments the systems may further
comprise one or more hydrocarbon reservoirs, injection wells,
and/or compression and pipeline systems configured to increase the
pressure of the rich CO.sub.2 stream and transport the stream for
injection into the hydrocarbon reservoir. In the same or other
embodiments, the systems may further comprise a pipeline system to
convey gas from a hydrocarbon reservoir to the power generation
system for fuel. In the same or other embodiments, the systems may
further comprise an electrical system configured to convey
electricity from an electric generator to at least partially power
one or more compressors within the system or to at least partially
power a pipeline system.
[0035] Referring now to the figures, FIG. 1 illustrates a power
generation system 100 configured to provide separation and capture
of CO.sub.2 after combustion. In at least one embodiment, the power
generation system 100 can have a first compressor 118 coupled to a
first expander 106 through a common shaft 108 or other mechanical,
electrical, or other power coupling, thereby allowing a portion of
the mechanical energy generated by the first expander 106 to drive
the first compressor 118. The first expander 106 may generate power
for other uses as well, such as to power another compressor, an
electric generator, or the like. The first compressor 118 and first
expander 106 may form the compressor and expander ends,
respectively, of a standard gas turbine. In other embodiments,
however, the first compressor 118 and first expander 106 can be
individualized components in a system.
[0036] The system 100 can also include a first combustion chamber
110 configured to combust a first fuel stream 112 mixed with a
compressed oxidant 114. In one or more embodiments, the first fuel
stream 112 can include any suitable hydrocarbon gas or liquid, such
as natural gas, methane, ethane, naphtha, butane, propane, syngas,
diesel, kerosene, aviation fuel, coal derived fuel, bio-fuel,
bitumen, oxygenated hydrocarbon feedstock, or combinations thereof.
The first fuel stream 112 may also comprise hydrogen. The
compressed oxidant 114 can be derived from the first compressor 118
fluidly coupled to the first combustion chamber 110 and adapted to
compress a feed oxidant 120. While the discussion herein assumes
that the feed oxidant 120 is ambient air, the oxidant may comprise
any suitable gas containing oxygen, such as air, oxygen-rich air,
substantially pure oxygen, or combinations thereof. In one or more
embodiments herein, the first combustion chamber 110 operates at a
pressure approximately the same as the discharge pressure of the
first compressor 118. In one or more embodiments, the first
compressor 118, the first combustion chamber 110, and the first
expander 106, taken together, can be characterized as an open
Brayton cycle.
[0037] A discharge exhaust stream 116 is generated as a product of
combustion of the first fuel stream 112 and the compressed oxidant
114 and directed to the inlet of the first expander 106. In at
least one embodiment, the first fuel stream 112 can be primarily
natural gas, thereby generating a discharge 116 including
volumetric portions of vaporized water, CO.sub.2, CO, oxygen,
nitrogen, nitrogen oxides (NO.sub.X), and sulfur oxides (SO.sub.X).
In some embodiments, a small portion of unburned fuel 112 or other
compounds may also be present in the discharge 116 due to
combustion equilibrium limitations. As the discharge stream 116
expands through the expander 106, it generates mechanical power to
drive the first compressor 118 or other facilities, and also
produces a gaseous exhaust stream 122. In one or more embodiments,
the first expander 106 accepts the discharge stream 116 at a
temperature and pressure substantially equivalent to the first
combustion chamber outlet temperature and pressure, and outputs the
same gases at a temperature and pressure that are reduced but still
elevated from ambient conditions.
[0038] The system 100 can also include a CO.sub.2 separation
system. In one or more embodiments, the gaseous exhaust stream 122
is directed to a CO.sub.2 separator 140. The CO.sub.2 separator 140
may employ any of a variety of separation processes designed to
separate the gaseous exhaust stream 122 into a rich CO.sub.2 stream
142 and a lean CO.sub.2 stream 144. For example, the separator 140
may be designed to separate the gaseous exhaust stream using a
chemical separation process, such as hot potassium carbonate ("hot
pot") separation, amine separation, or separation using a solvent
such as a glycol. Other separation processes include physical
separation using membranes, or processes such as adsorptive kinetic
separation or controlled freeze zone separation. In some
embodiments, combinations of the foregoing separation methods may
be used. The rich CO.sub.2 stream 142 may be used for a variety of
downstream applications, such as injection into a hydrocarbon
reservoir for enhanced oil recovery (EOR), carbon sequestration,
storage, sale, or recycle to the first combustion chamber 110 for
use as a diluent to facilitate combustion of the compressed oxidant
114 and the first fuel 112 and increase the CO.sub.2 concentration
in the discharge exhaust stream 116. The rich CO.sub.2 stream 142
may also be vented or flared. In one or more embodiments, the
CO.sub.2 separation process may be configured to maximize the
temperature or the pressure of the lean CO.sub.2 stream 144.
[0039] In one or more embodiments, the lean CO.sub.2 stream 144 may
optionally be used for additional power generation. For example,
lean CO.sub.2 stream 144 may be heated in a heat exchanger 150
configured to transfer heat from the gaseous exhaust stream 122 to
the lean CO.sub.2 stream 144. Upon exiting the heat exchanger 150,
the lean CO.sub.2 stream 144 may then be directed to a second
combustion chamber 130 configured to combust a second fuel stream
132 to add additional heat to the lean CO.sub.2 stream 144. The
second fuel stream may have the same composition as the first fuel
stream 112, or may have a different composition. For example, the
second fuel stream 132 may primarily comprise hydrogen. In one or
more embodiments, the operating pressure of the second combustion
chamber 130 is lower than that of the first combustion chamber
110.
[0040] From the second combustion chamber 110, the reheated lean
CO.sub.2 stream 162 is directed to a second expander 160. The
second expander 160 generally operates at a lower pressure than
that of the first expander 106. For example, in one or more
embodiments the second expander accepts the reheated lean CO.sub.2
stream 162 from the CO.sub.2 separation process at a pressure
higher than ambient and outputs the same gases at approximately
ambient pressure via expanded lean CO.sub.2 stream 164. The power
generated by the second expander 160 may be used for a variety of
purposes, such as to at least partially drive the first compressor
118 or one or more additional compressors (not shown) or to drive
an electric generator. In some embodiments, when either the rich
CO.sub.2 or the lean CO.sub.2 is injected into a reservoir for
storage or EOR, the second expander 160 may be used to drive a
pipeline or injection compressor.
[0041] In one or more embodiments, the expanded lean CO.sub.2
stream 164 may be directed to a heat recovery steam generator
(HRSG) 170 configured to use the residual heat in the expanded lean
CO.sub.2 stream 164 to generate steam 174. The steam 174 may have a
variety of uses, such as for example to generate additional power
by driving a steam turbine generator in a Rankine cycle or for
water desalination. The cooled lean CO.sub.2 stream 172 exiting the
HRSG 170, like the rich CO.sub.2 stream 142, may also be used for a
variety of applications, including EOR, storage, sale, venting, or
flaring.
[0042] Referring now to FIG. 2, depicted is an alternative
configuration of the power generation system 100 of FIG. 1,
embodied and described as system 200. As such, FIG. 2 may be best
understood with reference to FIG. 1. In system 200 of FIG. 2, at
least a portion of the rich CO.sub.2 stream 142 is recycled to the
combustion chamber to achieve a higher concentration of CO.sub.2 in
the working fluid of the power generation system, thereby allowing
for more effective CO.sub.2 separation for subsequent
sequestration, pressure maintenance, or EOR applications. To
accomplish this, the first combustion chamber 110 is adapted to
stoichiometrically combust the incoming mixture of first fuel 112
and compressed oxidant 114. In order to moderate the temperature of
the combustion to meet first expander 106 inlet temperature and
component cooling requirements, a portion of the rich CO.sub.2
stream can be injected into the first combustion chamber 110 as a
diluent. Thus, embodiments of the disclosure can essentially
eliminate any excess oxygen from the working fluid while
simultaneously increasing its CO.sub.2 composition.
[0043] While the recycle loop illustrated in FIG. 2 incorporates
various apparatus, the illustrated configuration is representative
only and any system that recirculates the rich CO.sub.2 stream 142
back to the first combustion chamber 110 to accomplish the goals
stated herein may be used. In one or more embodiments, the rich
CO.sub.2 stream 142 can be sent to a second HRSG 210 in order to
generate a stream of steam 216 and a cooled rich CO.sub.2 gas 212.
The steam 216 can optionally be sent to a steam gas turbine (not
shown) to generate additional electrical power. In such
configurations, the combination of the second HRSG 210 and the
steam gas turbine can be characterized as a closed Rankine
cycle.
[0044] In one or more embodiments, the cooled rich CO.sub.2 gas 212
exiting the second HRSG 210 may be sent to at least one cooling
unit 230 configured to reduce the temperature of the cooled rich
CO.sub.2 gas 212 and generate a cooled recycle CO.sub.2 stream 232.
In one or more embodiments, the cooling unit 230 is considered
herein to be a direct contact cooler (DCC), but may be any suitable
cooling device such as a direct contact cooler, trim cooler, a
mechanical refrigeration unit, or combinations thereof. The cooling
unit 230 can also be configured to remove a portion of condensed
water via a water dropout stream 234. In one or more embodiments,
the cooled rich CO.sub.2 gas 212 can be directed to a blower or
boost compressor 220 fluidly coupled to the cooling unit 230. In
such embodiments, compressed cooled rich CO.sub.2 stream 212 exits
the blower 220 and is directed to the cooling unit 230.
[0045] Further, although the recycle loop shown in system 200 of
FIG. 2 demonstrates 100% recycle of CO.sub.2, it may be desirable
in some circumstances to recycle only a portion of the CO.sub.2 in
the recycle loop to the combustion chamber 110. In such cases, one
or more extraction streams (not shown) may be added to divert a
portion of CO.sub.2 from the recycle loop while the remainder of
the CO.sub.2 is recycled as described herein. The extracted portion
of CO.sub.2 may be withdrawn from the recycle loop via an
extraction stream at a number of locations (not shown), such as
from stream 212, 222, 232, or 242. The extracted CO.sub.2 may be
used for a variety of purposes, such as for EOR, sequestration,
storage, sale, or venting.
[0046] The blower 220 can be configured to increase the pressure of
the cooled rich CO.sub.2 gas 212 before it is introduced into a
recycle compressor 240. In one or more embodiments, the blower 220
increases the overall density of the cooled rich CO.sub.2 gas 212,
thereby directing an increased mass flow rate for the same
volumetric flow to the recycle compressor 240. Because the recycle
compressor 240 is typically volume-flow limited, directing more
mass flow through the recycle compressor 240 can result in a higher
discharge pressure from the recycle compressor 240, thereby
translating into a higher pressure ratio across the first expander
106. A higher pressure ratio generated across the first expander
106 can allow for higher inlet temperatures and, therefore, an
increase in first expander 106 power and efficiency. This can prove
advantageous since the CO.sub.2-rich discharge 116 generally
maintains a higher specific heat capacity. Accordingly, the cooling
unit 230 and the blower 220, when incorporated, may each be adapted
to optimize or improve the operation of the power generation system
200.
[0047] The recycle compressor 240 can be configured to compress the
cooled recycle CO.sub.2 stream 232 to a pressure nominally above
the first combustion chamber 110 pressure, thereby generating the
compressed rich CO.sub.2 recycle stream 242. In at least one
embodiment, a purge stream (not shown) can be tapped from the rich
CO.sub.2 recycle stream 242 and optionally treated in an additional
CO.sub.2 separator (such as one similar to CO.sub.2 separator 140)
or other apparatus (not shown) to capture CO.sub.2. The separated
CO.sub.2 can be used for sales, used in another process requiring
carbon dioxide, and/or compressed and injected into a terrestrial
reservoir for enhanced oil recovery (EOR), sequestration, or
another purpose.
[0048] In some embodiments not depicted herein, high pressure steam
may also be employed as a coolant in the combustion process, either
in place of or in addition to the recycled rich CO.sub.2 stream. In
such embodiments, the addition of steam would reduce power and size
requirements in the recycle loop (or eliminate the recycle loop
altogether), but would require the addition of a water recycle
loop.
[0049] Additionally, in further embodiments not depicted herein,
the compressed oxidant feed to the combustion chamber may comprise
argon. For example, the oxidant may comprise from about 0.1 to
about 5.0 vol % argon, or from about 1.0 to about 4.5 vol % argon,
or from about 2.0 to about 4.0 vol % argon, or from about 2.5 to
about 3.5 vol % argon, or about 3.0 vol % argon. As will be
appreciated by those skilled in the art, incorporating argon into
the compressed oxidant feed may require the addition of a cross
exchanger or similar device between the main compressor and the
combustion chamber configured to remove excess CO.sub.2 from the
recycle stream and return argon to the combustion chamber at the
appropriate temperature for combustion.
[0050] Referring now to FIG. 3, depicted is an alternative
configuration of the power generation system 100 of FIG. 1,
embodied and described as system 300. As such, FIG. 3 may be best
understood with reference to FIG. 1. In system 300 of FIG. 3, a
second compressor 310 is incorporated to provide additional initial
compression of the feed oxidant 120. The second compressor 310 may
be coupled to the second expander 160 through a common shaft 308 or
other mechanical, electrical, or other power coupling, thereby
allowing a portion of the mechanical energy generated by the second
expander 160 to drive the second compressor 310. Pressurized
oxidant stream 312 exits the second compressor and is directed to
the first compressor 118, which in turn further compresses the
oxidant and generates compressed oxidant 114 and directs compressed
oxidant 114 to the first combustion chamber.
[0051] Referring now to FIG. 4, depicted is a simplified
alternative configuration of the power generation system 100 of
FIG. 1, embodied and described as system 400. As such, FIG. 4 may
be best understood with reference to FIG. 1. In system 400 of FIG.
4, the CO.sub.2 separation process is located upstream of the first
expander 106. Accordingly, discharge exhaust stream 116 exits the
first combustion chamber 110 and is supplied directly to the
separator 140. As described above, the separator 140 separates the
discharge exhaust stream 116 into a rich CO.sub.2 stream 142 and a
lean CO.sub.2 stream 144. The rich CO.sub.2 stream 142 may be
further processed, recycled, or used as described in more detail
above. The lean CO.sub.2 stream is expanded in the first expander
106, and the resulting lean CO.sub.2 discharge stream 410 may also
be further processed or used as described in more detail above. For
example, the lean CO.sub.2 discharge stream 410 may be reheated in
a second combustor and expanded again to generate additional power
(not shown).
[0052] While the present disclosure may be susceptible to various
modifications and alternative forms, the exemplary embodiments
discussed above have been shown only by way of example. Any
features or configurations of any embodiment described herein may
be combined with any other embodiment or with multiple other
embodiments (to the extent feasible) and all such combinations are
intended to be within the scope of the present invention.
Additionally, it should be understood that the disclosure is not
intended to be limited to the particular embodiments disclosed
herein. Indeed, the present disclosure includes all alternatives,
modifications, and equivalents falling within the true spirit and
scope of the appended claims.
* * * * *