U.S. patent application number 17/832247 was filed with the patent office on 2022-09-22 for systems and methods for oxidation of hydrocarbon gases.
The applicant listed for this patent is 8 Rivers Capital, LLC. Invention is credited to Jeremy Eron Fetvedt, Brock Alan Forrest, Peter Michael McGroddy.
Application Number | 20220298965 17/832247 |
Document ID | / |
Family ID | 1000006381078 |
Filed Date | 2022-09-22 |
United States Patent
Application |
20220298965 |
Kind Code |
A1 |
Forrest; Brock Alan ; et
al. |
September 22, 2022 |
SYSTEMS AND METHODS FOR OXIDATION OF HYDROCARBON GASES
Abstract
The present disclosure relates to systems and methods wherein a
dilute hydrocarbon stream can be oxidized to impart added energy to
a power production system. The oxidation can be carried out without
substantial combustion of the hydrocarbons. In this manner, dilute
hydrocarbon streams that would otherwise be required to undergo
costly separation processes can be efficiently utilized for
improving the power production system and method. Such systems and
methods particularly can utilize dilute hydrocarbon stream
including a significant amount of carbon dioxide, such as may be
produced in hydrocarbon recovery process, such as enhanced oil
recovery or conventional hydrocarbon recovery processes.
Inventors: |
Forrest; Brock Alan;
(Durham, NC) ; Fetvedt; Jeremy Eron; (Raleigh,
NC) ; McGroddy; Peter Michael; (Durham, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
8 Rivers Capital, LLC |
Durham |
NC |
US |
|
|
Family ID: |
1000006381078 |
Appl. No.: |
17/832247 |
Filed: |
June 3, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15492376 |
Apr 20, 2017 |
11359541 |
|
|
17832247 |
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62325752 |
Apr 21, 2016 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F01K 7/16 20130101; F05D
2240/35 20130101; F01K 25/103 20130101; F02C 7/10 20130101; F02C
1/04 20130101; F05D 2260/20 20130101; F02C 3/34 20130101; F05D
2260/61 20130101; F02C 3/30 20130101 |
International
Class: |
F02C 3/34 20060101
F02C003/34; F01K 25/10 20060101 F01K025/10; F02C 1/04 20060101
F02C001/04; F02C 7/10 20060101 F02C007/10; F01K 7/16 20060101
F01K007/16; F02C 3/30 20060101 F02C003/30 |
Claims
1-26. (canceled)
27. A method for heating a stream, the method comprising:
compressing a stream comprising CO.sub.2 to form a compressed
stream comprising CO2.sub.; firstly, heating the compressed stream
comprising CO.sub.2 in a recuperator heat exchanger with heat
withdrawn from a stream of combustion products arising from
combustion of a first fuel source; and secondly, heating the
compressed stream comprising CO.sub.2 with heat obtained by
oxidizing, without substantial combustion, a second fuel source
that is a dilute hydrocarbon stream, said oxidizing being carried
out separate from the combustion of the first fuel source.
28. The method of claim 27, wherein the concentration of
hydrocarbons in the dilute hydrocarbon stream is below the lower
explosive limit (LEL) of the hydrocarbons.
29. The method of claim 27, wherein the hydrocarbons in the dilute
hydrocarbon stream are catalytically oxidized.
30. The method of claim 27, wherein the compressed stream
comprising CO.sub.2, after being firstly and secondly heated, is
passed through a combustor wherein the first fuel is combusted with
oxygen to form the stream of combustion products.
31. The method of claim 30, wherein the stream of combustion
products is expanded in a turbine to produce power before being
passed to the recuperator heat exchanger.
32. The method of claim 27, wherein the dilute hydrocarbon stream
is added to the compressed stream comprising CO.sub.2 before the
compressed stream comprising CO.sub.2 is input to the recuperator
heat exchanger.
33. The method of claim 32, wherein the hydrocarbons in the dilute
hydrocarbon stream are oxidized within the recuperator heat
exchanger.
34. The method of claim 32, wherein the hydrocarbons in the dilute
hydrocarbon stream are oxidized in a further heat exchanger.
35. The method of claim 27, wherein the dilute hydrocarbon stream
is combined with the compressed stream comprising CO.sub.2 in the
recuperator heat exchanger.
36. The method of claim 27, wherein the dilute hydrocarbon stream
is input to an oxidation reactor.
37. The method of claim 36, wherein a reaction stream exiting the
oxidation reactor is input to the recuperator heat exchanger.
38. The method of claim 36, wherein a reaction stream exiting the
oxidation reactor is input to a turbine for power production.
Description
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates to systems and methods
whereby various gas streams may be oxidized for energy production.
A gas stream more particularly may include hydrocarbons and one or
more diluents. Energy produced via oxidation may be imparted, for
example, to a power production system or method.
BACKGROUND
[0002] Many industrial processes result in gaseous streams that
include a content of hydrocarbon materials that are combustible. In
many instances, such streams may include hydrocarbons as well as
one or more further material that may be considered to contaminate
or otherwise dilute the hydrocarbons and thus limit their
usefulness. Carbon dioxide is an example of a further material that
is frequently found comingled with hydrocarbon gases, particularly
in various aspects of the petroleum industry. For example, raw
natural gas produced from geologic formations often includes a
significant content of carbon dioxide. Conversely, carbon dioxide
withdrawn from geologic formations often includes a significant
content of hydrocarbon gases. Still further, production gases that
are recovered in enhanced oil recovery (EOR) methods often comprise
a mixture of hydrocarbon gases and carbon dioxide.
[0003] Combination gas streams, such as the examples noted above,
typically require specific processing in order to separate the
components--i.e., to provide a substantially pure hydrocarbon
stream that may be suitable for combustion and/or to provide a
substantially pure carbon dioxide stream that may be suitable for
use in EOR, or sequestration, or for other end uses. It thus would
be useful to have further options for utilizing
hydrocarbon-containing streams.
SUMMARY OF THE DISCLOSURE
[0004] In one or more embodiments, the present disclosure can
provide systems and methods useful for power production. In
particular, the systems and methods can be configured for
processing of a dilute hydrocarbon stream such that the
hydrocarbons in the stream are oxidized without substantial
combustion and thusly impart added energy to the power production
cycle.
[0005] In one or more embodiments, the present disclosure can
provide a method for power production comprising:
[0006] combusting a carbonaceous fuel with oxygen in a combustor in
the presence of a recycle CO.sub.2 stream to form a combustion
product stream comprising CO.sub.2;
[0007] expanding the combustion product stream in a turbine to
produce power and form a turbine exhaust stream;
[0008] cooling the turbine exhaust stream in a recuperator heat
exchanger;
[0009] removing any water present from the cooled turbine exhaust
stream to form the recycle CO.sub.2 stream;
[0010] compressing at least a portion of the recycle CO.sub.2
stream;
[0011] optionally diverting a portion of the recycle CO.sub.2
stream and combining the diverted portion with the oxygen prior to
said combusting;
[0012] passing the compressed recycle CO.sub.2 stream back through
the recuperator heat exchanger such that the compressed recycle
CO.sub.2 stream is heated with heat withdrawn from the turbine
exhaust stream;
[0013] inputting a dilute hydrocarbon stream under conditions
wherein the hydrocarbons in the dilute hydrocarbon stream are
oxidized without substantial combustion; and
[0014] directing the heated, compressed recycle CO.sub.2 stream to
the combustor.
[0015] In one or more further embodiments, the method for power
production can be further defined in relation to one or more of the
following statements, which can be combined in any number and
order.
[0016] The dilute hydrocarbon stream can be input such that the
hydrocarbons are oxidized within the recuperator heat exchanger or
a further heat exchanger configured for heat exchange with one or
both of the recycle CO.sub.2 stream and the oxygen.
[0017] The dilute hydrocarbon stream can be combined with the
compressed recycle CO.sub.2 stream before said passing step.
[0018] The dilute hydrocarbon stream can be combined with the
compressed recycle CO.sub.2 stream in the recuperator heat
exchanger.
[0019] The dilute hydrocarbon stream can be combined with the
compressed recycle CO.sub.2 stream in a further heat exchanger.
[0020] A portion of the recycle CO.sub.2 stream can be diverted and
combined with the oxygen to form a diluted oxygen stream, and the
dilute hydrocarbon stream can be combined with the diluted oxygen
stream.
[0021] The diluted oxygen stream combined with the dilute
hydrocarbon stream can be passed through the recuperator heat
exchanger or a further heat exchanger wherein the hydrocarbons in
the dilute hydrocarbon stream are oxidized.
[0022] The dilute hydrocarbon gas is a product of an enhanced oil
recovery process.
[0023] In one or more embodiments, the present disclosure can
provide a method for power production comprising: [0024] carrying
out a closed or semi-closed Brayton cycle wherein: [0025] CO.sub.2
is used as a working fluid; [0026] a carbonaceous fuel is used as a
first fuel source and is combusted to heat the working fluid; and
[0027] a recuperator heat exchanger is used to re-capture heat of
combustion; and [0028] adding a dilute hydrocarbon stream to the
closed or semi-closed Brayton cycle as a second fuel source,
wherein hydrocarbons in the dilute hydrocarbon stream are oxidized
without substantial combustion to provide additional heat.
[0029] In one or more embodiments, the present disclosure can
provide a method for processing of a waste stream comprising:
[0030] providing a waste stream comprising one or more hydrocarbons
and one or more diluents; [0031] inputting the waste stream into a
closed or semi-closed Brayton cycle such that the hydrocarbons in
the waste stream are oxidized without substantial combustion.
[0032] In one or more embodiments, a method for power production
can comprise carrying out a closed or semi-closed power production
cycle wherein: CO.sub.2 is circulated as a working fluid that is
repeatedly compressed and expanded for power production; a first
fuel source is combusted in a combustor to heat the working fluid
after the working fluid is compressed and before the working fluid
is expanded for power production; and a recuperator heat exchanger
is used to re-capture heat of combustion for heating of the working
fluid. The method further can comprise heating the working fluid
with heat that is formed outside of the combustor using a second
fuel source, said heating being in addition to the re-captured heat
of combustion, and said second fuel source being a dilute
hydrocarbon stream that is oxidized without substantial combustion
to provide the heat that is formed outside of the combustor.
[0033] In one or more further embodiments, the method for power
production can be further defined in relation to one or more of the
following statements, which can be combined in any number and
order.
[0034] The concentration of hydrocarbons in the dilute hydrocarbon
stream can be below the lower explosive limit (LEL) of the
hydrocarbons.
[0035] Hydrocarbons in the dilute hydrocarbon stream can be
catalytically oxidized.
[0036] The method particularly can comprise the following steps:
the first fuel is combusted with oxygen in the combustor in the
presence of the CO.sub.2 working fluid to form an exhaust stream;
the exhaust stream from the combustor is expanded in a turbine to
produce power and form a turbine exhaust stream; the turbine
exhaust stream is cooled in the recuperator heat exchanger; the
turbine exhaust stream exiting the recuperator heat exchanger is
purified to remove at least water from the working fluid; at least
a portion of the working fluid is compressed in a compressor; at
least a portion of the compressed working fluid is passed back
through the recuperator heat exchanger such that the compressed
working fluid is heated with heat withdrawn from the turbine
exhaust stream; and the heated, compressed working fluid is
recirculated to the combustor.
[0037] The dilute hydrocarbon stream can be added to the working
fluid after the working fluid is compressed in the compressor and
before the working fluid is passed back through the recuperator
heat exchanger.
[0038] The hydrocarbons in the dilute hydrocarbon stream can be
oxidized within the recuperator heat exchanger.
[0039] The hydrocarbons in the dilute hydrocarbon stream can be
oxidized in a further heat exchanger configured for heat exchange
with one or both of the working fluid and an oxygen stream
providing the oxygen to the combustor.
[0040] The dilute hydrocarbon stream can be combined with the
compressed working fluid in the recuperator heat exchanger.
[0041] A portion of the compressed working fluid can be combined
with oxygen to form a diluted oxygen stream, and wherein the dilute
hydrocarbon stream is combined with the diluted oxygen stream.
[0042] The diluted oxygen stream combined with the dilute
hydrocarbon stream can be passed through the recuperator heat
exchanger wherein the hydrocarbons in the dilute hydrocarbon stream
are oxidized.
[0043] The diluted oxygen stream combined with the dilute
hydrocarbon stream can be passed through a further heat exchanger
wherein the hydrocarbons in the dilute hydrocarbon stream are
oxidized.
[0044] The dilute hydrocarbon stream can be input to an oxidation
reactor.
[0045] A reaction stream exiting the oxidation reactor can be input
to the recuperator heat exchanger.
[0046] A reaction stream exiting the oxidation reactor is input to
a further turbine for power production.
[0047] A portion of the turbine exhaust stream can be input to the
oxidation reactor so as to be included in the reaction stream that
is input to the further turbine.
[0048] The dilute hydrocarbon stream can be a product of an
enhanced oil recovery process.
[0049] In one or more embodiments, the present disclosure can
provide a system for power production comprising:
[0050] a power production unit configured for carrying out a closed
or semi-closed Brayton cycle, said unit including a combustor
configured for combustion of a carbonaceous fuel in the presence of
a recycle CO.sub.2 stream; and
[0051] one or more inputs configured for input of a dilute
hydrocarbon stream to a component of the unit other than the
combustor.
[0052] In some embodiments, a power production system can comprise:
a power production unit configured for carrying out a closed or
semi-closed power production cycle, said power production unit
including: a combustor configured for combustion of a first fuel in
the presence of a compressed CO.sub.2 working fluid; a turbine
configured for expanding the compressed CO.sub.2 working fluid to
provide an expanded CO.sub.2 working fluid; a compressor configured
for compressing the expanded CO.sub.2 working fluid to provide the
compressed CO.sub.2 working fluid; a recuperator heat exchanger
configured for transferring heat from the expanded CO.sub.2 working
fluid leaving the turbine to the compressed CO.sub.2 working fluid
leaving the compressor; and one or more inputs configured for input
of a dilute hydrocarbon stream to a component of the power
production unit other than the combustor.
[0053] In one or more further embodiments, the power production
system can be further defined in relation to one or more of the
following statements, which can be combined in any number and
order.
[0054] The input can be configured for input of the dilute
hydrocarbon stream into the recuperator heat exchanger.
[0055] The power production system can further comprise a second
heat exchanger, and the input can be configured for input of the
dilute hydrocarbon stream into the second heat exchanger.
[0056] The input can be configured for input of the dilute
hydrocarbon stream into a line comprising the CO.sub.2 working
fluid.
[0057] The input can be configured for input of the dilute
hydrocarbon stream into the line downstream of the recuperator heat
exchanger and upstream of the compressor.
[0058] The power production system further can comprise an
oxidation reactor, and the input can be configured for input of the
dilute hydrocarbon stream into the oxidation reactor.
[0059] The oxidation reactor can be a catalytic oxidation
reactor.
[0060] The oxidation reactor can be configured for output of a
reaction stream that is input to the recuperator heat
exchanger.
[0061] The oxidation reactor can be configured for receiving a
portion of the expanded CO.sub.2 working fluid upstream of the
recuperator heat exchanger.
[0062] The power production system further can comprise a second
turbine configured for receiving a reaction stream from the
oxidation reactor.
BRIEF SUMMARY OF THE FIGURES
[0063] Having thus described the disclosure in the foregoing
general terms, reference will now be made to accompanying drawings,
which are not necessarily drawn to scale, and wherein:
[0064] FIG. 1 is a flow diagram for a power production plant
according to embodiments of the present disclosure wherein a dilute
hydrocarbon stream can be input to various elements of the power
production plant;
[0065] FIG. 2 is a flow diagram for a power production plant
according to embodiments of the present disclosure wherein a dilute
hydrocarbon stream is input to a recycled working fluid stream;
[0066] FIG. 3 is a flow diagram for a power production plant
according to embodiments of the present disclosure wherein a dilute
hydrocarbon stream is input to a supplemental heat exchanger;
[0067] FIG. 4 is a flow diagram for a power production plant
according to embodiments of the present disclosure wherein a dilute
hydrocarbon stream is combined with a diluted oxidant stream;
[0068] FIG. 5 is a flow diagram for a power production plant
according to embodiments of the present disclosure wherein a dilute
hydrocarbon stream is input to a catalytic reactor;
[0069] FIG. 6 is a flow diagram for a power production plant
according to embodiments of the present disclosure wherein a dilute
hydrocarbon stream is input to a turbine exhaust stream downstream
from a turbine and upstream from a heat exchanger; and
[0070] FIG. 7 is a flow diagram for a power production plant
according to embodiments of the present disclosure wherein a dilute
hydrocarbon stream is input to a catalytic reactor with a turbine
exhaust stream and then expanded through a secondary turbine.
DETAILED DESCRIPTION
[0071] The present invention now will be described more fully
hereinafter. This invention 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 invention to those skilled in
the art. As used in this specification and the claims, the singular
forms "a," "an," and "the" include plural referents unless the
context clearly dictates otherwise.
[0072] In one or more embodiments, the present disclosure provides
systems and methods for power production wherein a dilute
hydrocarbon stream is oxidized without substantial combustion to
add energy for power production. The systems and methods allow for
low cost, efficient utilization of streams that would otherwise be
required to undergo expensive and time-consuming separation to
provide useful materials (e.g., a purified stream of the
hydrocarbons and/or a purified stream of one or more diluents).
[0073] A dilute hydrocarbon stream as used herein is understood to
mean a stream that comprises greater than trace amounts of one or
more hydrocarbons and at least one diluent. The dilute hydrocarbon
stream can comprise a concentration of hydrocarbons that is
suitable to provide the desired level of heating via oxidation of
the hydrocarbons. The concentration of the hydrocarbons in the
dilute hydrocarbon stream is limited only in that the dilute
hydrocarbon stream comprises hydrocarbons in an amount that is
below the lower explosive limit (LEL). In particular, the dilute
hydrocarbon concentration in the stream can be below the LEL after
the dilute hydrocarbon is mixed with a recycle CO.sub.2 stream as
further described herein.
[0074] A hydrocarbon present in the dilute hydrocarbon stream
preferably is in a gaseous state. Non-limiting examples of
hydrocarbons that may be present include C.sub.1 to C.sub.10
compounds. Preferably, the dilute hydrocarbon stream comprises
C.sub.1 to C.sub.4 compounds; however, C.sub.5 to C.sub.10
compounds may be present, particularly when the dilute hydrocarbon
stream will be subject to pressurization. In specific embodiments,
the dilute hydrocarbon stream comprises at least methane. In some
embodiments, the dilute hydrocarbon stream comprises natural
gas.
[0075] A diluent present in the dilute hydrocarbon stream can be
any material that serves to dilute the hydrocarbon concentration to
be within the range noted above. In specific embodiments, the
diluent can comprise CO.sub.2. Other non-limiting examples of
diluents that may be present include nitrogen, water, H.sub.2S, and
oxygen. In some embodiments, the diluent can comprise predominately
CO.sub.2 (i.e., greater than 50% by volume of the diluent being
CO.sub.2), and the diluent specifically can comprise about 60% by
volume or greater, about 75% by volume or greater, about 80% by
volume or greater, about 90% by volume or greater, about 95% by
volume or greater, about 98% by volume or greater, about 99% by
volume or greater, about 99.5% by volume or greater, or about 99.8%
by volume or greater CO.sub.2. For example, the diluent can
comprise about 60% by volume to about 99.9% by volume, about 75% by
volume to about 99.8% by volume, or about 80% by volume to about
99.5% by volume CO.sub.2.
[0076] The dilute hydrocarbon stream can come from any source,
including industrial waste, reaction products, hydrocarbon
production streams (e.g., from a natural gas well or oil well) and
the like. If desired, a hydrocarbon stream from such source can be
specifically diluted through addition of CO.sub.2 (or other
diluent) to the hydrocarbon stream. For example, a waste stream can
comprise hydrocarbons in a concentration above the LEL, and such
stream may be used according to the present disclosure through
addition of further diluent. Further to the above, CO.sub.2
withdrawn from natural formations often include a content of
natural gas or other mixture of gaseous hydrocarbons. In some
embodiments, a dilute hydrocarbon stream can arise from enhanced
oil recovery (EOR), such as in methods described in U.S. Pat. No.
8,869,889 to Palmer et al., the disclosure of which is incorporated
herein by reference. EOR methods typically result in a production
stream comprising a mixture of materials that must be separated to
provide useable streams of substantially pure materials. When
CO.sub.2 is used in EOR, the produced materials specifically must
be treated to separate CO.sub.2 from the hydrocarbon products. In
the aforementioned patent to Palmer et al., a mixture of CO.sub.2
and hydrocarbons may be used as part of the fuel source in an
associated power production method. In such methods, the combined
CO.sub.2 and hydrocarbon mixture is directed to a combustor where
it is combusted, typically along with a stream of substantially
pure hydrocarbon fuel. Such method requires a purpose-built
combustor capable of combusting lower BTU-content fuels, is limited
to using only streams with a specified hydrocarbon centration (in
order to maintain flame stability in the combustor), and is limited
in the total flowrate of CO.sub.2-rich hydrocarbons that can be
processed in a single plant. Further, because the relative
concentrations of the components of such stream of CO.sub.2 and
gaseous hydrocarbons from EOR can undergo significant fluctuations,
such methods are hindered in that it is difficult to achieve a
substantially constant flame temperature in the combustor.
[0077] Currently, significant energy and expense is required to
separate hydrocarbons from CO.sub.2. In the case of raw natural gas
production, the dilute hydrocarbons produced from the field are
typically dried, distilled to remove longer chain hydrocarbons
(natural gas liquids, or NGLs), sweetened via removal of H.sub.2S
and other impurities, and sent through an absorber tower to scrub
out the CO.sub.2. The cleaned natural gas is then sent into the
pipeline for downstream consumption, such as by power production,
and the clean CO.sub.2 is vented, sequestered, and/or utilized
(e.g., for further EOR). When CO.sub.2 is used for EOR, the portion
of the injected CO.sub.2 that is produced along with the produced
oil often contains a small amount of gaseous hydrocarbons that must
be separated in order to enable reinjection of the CO.sub.2 into
the formation. This CO.sub.2-rich hydrocarbon gas must be separated
from produced oil and similarly dried and distilled to remove any
NGLs. This gas must then be recompressed for reinjection into the
field. These processes require a large amount of energy and
consumables, leading to high capital expenses and operating
expenses for the process.
[0078] The systems and methods of the present disclosure allow for
low cost, efficient use of dilute hydrocarbon streams to add energy
to existing power production systems and methods. For example, the
dilute hydrocarbon streams can be input to a system and method
wherein a carbonaceous fuel is combusted to produce heat to a
stream that may or may not be pressurized above ambient pressure.
The dilute hydrocarbon stream likewise can be applied to one or
more systems wherein a working fluid is circulated for being
repeatedly heated and cooled and/or for being repeatedly
pressurized and expanded. Such working fluid can comprise one or
more of H.sub.2O, CO.sub.2, and N.sub.2, for example.
[0079] The systems and methods of the present disclosure can
overcome problems in the field by extracting the heating value of
the entrained hydrocarbons of a dilute hydrocarbon stream without
combustion. Instead, the inherent conditions of the high
temperature power production systems and methods can be utilized to
facilitate thermal oxidation of these hydrocarbons in the dilute
hydrocarbon stream. For example, oxidation can occur in a heat
exchanger. This allows the existing power cycles to utilize these
dilute hydrocarbon streams with minimal modification of the
process, to utilize significantly higher flow rates of these
streams, and to simplify the overall cycle by eliminating certain
equipment and the need for external sources of heat.
[0080] Utilization of CO.sub.2 (particularly in supercritical form)
as a working fluid in power production has been shown to be a
highly efficient method for power production. See, for example,
U.S. Pat. No. 8,596,075 to Allam et al., the disclosure being
incorporated herein by reference, which describes the use of a
directly heated CO.sub.2 working fluid in a recuperated oxy-fuel
Brayton cycle power generation system with virtually zero emission
of any streams to the atmosphere. It has previously been proposed
that CO.sub.2 may be utilized as a working fluid in a closed cycle
wherein the CO.sub.2 is repeatedly compressed and expanded for
power production with intermediate heating using an indirect
heating source and one or more heat exchangers. See, for example,
U.S. Pat. No. 8,783,034 to Held, the disclosure of which is
incorporated herein by reference. Thus, in some embodiments, the
dilute hydrocarbon stream can be used an input to a closed or
semi-closed Brayton cycle to increase the efficiency of power
production via such cycle.
[0081] Further examples of power production systems and methods
wherein a dilute hydrocarbon stream as described herein can be used
are disclosed in U.S. Pat. No. 9,068,743 to Palmer et al., U.S.
Pat. No. 9,062,608 to Allam et al., U.S. Pat. No. 8,986,002 to
Palmer et al., U.S. Pat. No. 8,959,887 to Allam et al., U.S. Pat.
No. 8,869,889 to Palmer et al., and U.S. Pat. No. 8,776,532 to
Allam et al., the disclosures of which are incorporated herein by
reference. As a non-limiting example, a power production system
with which a dilute hydrocarbon stream may be used can be
configured for combusting a fuel with O.sub.2 in the presence of a
CO.sub.2 circulating fluid in a combustor, preferably wherein the
CO.sub.2 is introduced at a pressure of at least about 12 MPa
(e.g., about 12 MPa to about 60 MPa) and a temperature of at least
about 400.degree. C. (e.g., about 400.degree. C. to about
1,200.degree. C.), to provide a combustion product stream
comprising CO.sub.2, preferably wherein the combustion product
stream has a temperature of at least about 800.degree. C. (e.g.,
about 1,500.degree. C.). Such power production system further can
be characterized by one or more of the following:
[0082] The combustion product stream can be expanded across a
turbine with a discharge pressure of about 1 MPa or greater (e.g.,
about 1 MPa to about 7.5 MPa) to generate power and provide a
turbine discharge steam comprising CO.sub.2.
[0083] The turbine discharge stream can be passed through a
recuperator heat exchanger unit to provide a cooled discharge
stream.
[0084] The cooled turbine discharge stream can be processed to
remove one or more secondary components other than CO.sub.2
(particularly any water present and/or SO.sub.x and/or NO.sub.x) to
provide a purified discharge stream, which particularly may be a
recycle CO.sub.2 stream.
[0085] The recycle CO.sub.2 stream can be compressed, particularly
to a pressure wherein the CO.sub.2 is supercritical.
[0086] The supercritical CO.sub.2 can be cooled to increase the
density (preferably to at least about 200 kg/m.sup.3) of the
recycle CO.sub.2 stream.
[0087] The high density recycle CO.sub.2 stream can be pumped to a
pressure suitable for input to the combustor (e.g., as noted
above).
[0088] The pressurized recycle CO.sub.2 stream can be heated by
passing through the recuperator heat exchanger unit using heat
recuperated from the turbine discharge stream.
[0089] All or a portion of the pressurized recycle CO.sub.2 stream
can be further heated with heat that is not withdrawn from the
turbine discharge stream (preferably wherein the further heating is
provided one or more of prior to, during, or after passing through
the recuperator heat exchanger) prior to recycling into the
combustor.
[0090] The heated pressurized recycle CO.sub.2 stream can be passed
into the combustor.
[0091] In one or more embodiments, a power production system
suitable for input of a dilute hydrocarbon stream as described
herein can be configured for heating via methods other than through
combustion of a carbonaceous fuel (or in addition to combustion of
a carbonaceous fuel). As one non-limiting example, solar power can
be used to supplement or replace the heat input derived from the
combustion of a carbonaceous fuel in a combustor. Other heating
means likewise can be used. In some embodiments, any form of heat
input into a CO.sub.2 recycle stream at a temperature of
400.degree. C. or less can be used. For example, condensing steam,
gas turbine exhaust, adiabatically compressed gas streams, and/or
other hot fluid streams which can be above 400.degree. C. may be
utilized.
[0092] In one or more embodiments, a power production plant may
include some combination of the elements shown in FIG. 1 (although
it is understood that further elements may also be included). As
seen therein, a power production plant 10 (or power production
unit) can include a combustor 100 configured to receive fuel from a
fuel supply 50 (e.g., a carbonaceous fuel) and oxidant from an
oxidant supply 60 (e.g., an air separation unit or plant (ASU)
producing substantially pure oxygen). A plurality of fuel supply
lines (52, 54) are illustrated; however, only a single fuel supply
line may be used, or more than two fuel supply lines may be used.
Likewise, while only a single oxidant line 62 is illustrated, a
plurality of oxidant lines may be used. The fuel is combusted in
the combustor with the oxidant in the presence of a recycle
CO.sub.2 stream. The combustion product stream in line 102 is
expanded across a turbine 110 to produce power with a combined
generator 115. Although the combustor 100 and turbine 110 are
illustrated as separate elements, it is understood that, in some
embodiments, a turbine may be configured so as to be inclusive of
the combustor. In other words, a single turbine unit may include a
combustion section and an expansion section. Accordingly,
discussion herein of passage of streams into a combustor may also
be read as passage of streams into a turbine that is configured for
combustion as well as expansion.
[0093] Turbine exhaust in line 112 is cooled in a heat exchanger
120, and water (in line 132) is separated in separator 130 to
produce a substantially pure recycle CO.sub.2 stream in line 135.
If desired, part of the stream of substantially pure CO.sub.2 may
be withdrawn from the plant and/or diverted to other parts of the
plant (e.g., for cooling the turbine). The recycle CO.sub.2 stream
is compressed in a multi-stage compressor. As illustrated, the
multi-stage compressor includes a first stage 140, a second stage
160, and an intercooler 150. Optionally, one or more further
compressors or pumps may be added. The compressed recycle CO.sub.2
stream in line 165 is passed back through the heat exchanger 120 to
the combustor 100. As illustrated (and as further discussed below),
a dilute hydrocarbon stream 170 can be introduced into the power
production cycle. The stream 170 is shown generally as one or more
inputs configured for input of the dilute hydrocarbon stream to a
component of the power production unit 10. This is illustrated by
the solid arrow on the right margin of FIG. 1. The dilute
hydrocarbon stream 170 specifically may be excluded from being
input to the combustor 100.
[0094] Within the power production cycle as discussed above, the
recycle stream in one or both of line 135 and line 165 (consisting
of predominantly clean CO.sub.2) can be divided into an export
CO.sub.2 fraction, a diluting CO.sub.2 fraction, and a recycle
CO.sub.2 stream. The ratio of the CO.sub.2 divided into the
diluting CO.sub.2 fraction is determined by what is needed to mix
with the substantially pure oxygen from the ASU and provide the
combustion oxidant with the desired O.sub.2/CO.sub.2 ratio. The
dilute hydrocarbon stream 170 can be mixed directly with the
recycle CO.sub.2 stream (e.g., with the stream in line 135 and/or
line 165 and/or a side stream taken from line 135 and/or line 165).
The amount of the recycle CO.sub.2 stream used in this mixture is
sufficient to maintain the necessary mass flow through the recycle
circuit and depends on the mass flow of the dilute hydrocarbon
stream (this also provides a mechanism to handle changes in the
flow rate of the dilute hydrocarbon streams). The remainder of the
CO.sub.2 from the turbine exhaust stream becomes export CO.sub.2
fraction that will be cleaned and sent to a pipeline for downstream
utilization or sequestration.
[0095] The export CO.sub.2 fraction and diluting CO.sub.2 fraction
streams may be compressed and pumped together in the typical
operation of the power cycle (i.e., may be compressed and pumped in
any manner of combinations depending on the final use of the export
CO.sub.2 fraction). In one embodiment, these streams may be sent to
a CO.sub.2 purification unit (for example, using refrigeration and
distillation) to remove excess O.sub.2 and any inert materials and
generate a stream of high purity CO.sub.2 at the desired pressure.
The diluting CO.sub.2 fraction is then sent to be mixed with
incoming O.sub.2 to form the high pressure oxidant needed in the
combustor. In another embodiment, the diluting CO.sub.2 fraction
can be sent directly to O.sub.2 mixing without this impurity
removal being required. The export CO.sub.2 fraction is sent to a
pipeline for downstream sequestration or utilization.
[0096] In one embodiment, the recycle CO.sub.2 stream can be mixed
with the dilute hydrocarbon stream 170 prior to compression and
pumping to the combustor input pressure (e.g., about 300 bar in
some embodiments). As illustrated in FIG. 2, a dilute hydrocarbons
from hydrocarbon source 171 flows through line 172 and is input to
line 135. As such, the dilute hydrocarbon in line 171 is input to
the line 135 comprising the recycle CO.sub.2 working fluid
downstream of the recuperator heat exchanger 120 and upstream of
the compressor 140 and/or the compressor 160. This can be done
separately from the export CO.sub.2 fraction and the diluting
CO.sub.2 fraction to prevent contamination of these streams by
hydrocarbons and other non-CO.sub.2 species present in the dilute
hydrocarbon stream 170. This can be accomplished using either
entirely separate rotating equipment or using separate wheels of
the same rotating equipment, as would be feasible in an integrally
geared compressor. The mixed dilute hydrocarbon/recycle CO.sub.2
stream (now at a pressure of about 300 bar and at a temperature
slightly above ambient temperature) is then sent to the primary
heat exchanger train 120 to be heated against the turbine exhaust
stream in line 112. Unless otherwise indicated, other elements
illustrated in FIG. 2 are as described in relation to FIG. 1.
[0097] As the stream is heated through the heat exchanger train 120
to a temperature near that of the turbine exhaust, hydrocarbons
input via the dilute hydrocarbon stream 170 undergo thermal
oxidation without substantial combustion. The thermal oxidation
takes place without substantial combustion in that the conditions
do not allow for formation of a sustained flame. Thus, the absence
of substantial combustion does not necessarily exclude any
combustion from occurring, and a small percentage (e.g., less than
5% by volume) of the hydrocarbon compounds provided via the dilute
hydrocarbon stream may combust while substantially all (e.g., at
least 95% by volume) of the hydrocarbon compounds provided via the
dilute hydrocarbon stream instead undergo thermal oxidation. In
some embodiments, thermal oxidation may take place in the complete
absence of any combustion of the hydrocarbon compounds provided via
the dilute hydrocarbon stream. This thermal oxidation may occur in
the primary recuperator heat exchanger and/or may occur in a
separate heat exchanger that is dedicated to facilitating these
reactions. In some embodiments, thermal oxidation can occur within
dedicated passages of the recuperator heat exchanger.
[0098] These oxidation reactions are enabled by the fact that the
power cycle combustor operates with an excess of O.sub.2, leading
to residual O.sub.2 being present in the recycle CO.sub.2 stream at
a substantially small concentration but at a high partial pressure.
For example, the recycle CO.sub.2 stream in line 135 and/or line
165 may have an O.sub.2 concentration of about 0.01% by volume to
about 10% by volume, about 0.1% by volume to about 8% by volume, or
about 0.2% by volume to about 5% by volume. In the presence of this
O.sub.2, entrained hydrocarbons (as well as other diluent species,
such as H.sub.2S) input to the recycle CO.sub.2 stream from the
dilute hydrocarbon stream begin to oxidize within the channels of
the power cycle heat exchangers as they are progressively
heated.
[0099] The mixture of the recycle CO.sub.2 stream with the dilute
hydrocarbon stream is preferably controlled such that the total
hydrocarbon content of the mixture is below the lower explosive
limit (LEL), which can vary based upon the specific mixture of
compounds present. Thus, in some embodiments, the mixture of the
dilute hydrocarbon stream and the recycle CO.sub.2 stream can have
a minimum hydrocarbon concentration of at least 0.1% by volume, at
least 0.5% by volume, at least 1% by volume, or at least 2% by
volume, and the mixture of dilute hydrocarbon stream and the
recycle CO.sub.2 stream can have a maximum hydrocarbon
concentration that is less than the LEL, as noted above. As a
non-limiting example, a mixture comprising predominately CO.sub.2
and methane may have a maximum methane content of less than 5% by
volume (e.g., about 0.01% by volume to 4.95% by volume).
[0100] It is understood that conditions for combustion require the
combination of an ignition source with both of a fuel and an
oxidant in a sufficient ratio. When the fuel concentration is below
the LEL, the fuel to oxidant ratio is insufficient for combustion.
Examples of LEL values for various hydrocarbons are as follows
(with all percentages being on a volume basis): butane (1.8%);
carbon monoxide (12.5%); ethane (3.0%); ethanol (3.3%); ethylene
(2.7%); gasoline (1.2%); methane (5.0%); methanol (6.7%); and
propane (2.1%). Based upon known LEL values, it is possible to
calculate the LEL of a substantially pure hydrocarbon fuel as well
as a mixed hydrocarbon fuel to ensure that that the hydrocarbon
concentration is below the overall LEL for the particular material
or materials being mixed with the recycle CO.sub.2 stream. Since
the concentration of hydrocarbons in this mixed stream is so dilute
(i.e., being below the LEL of the mixture), "combustion" does not
occur. This process simply oxidizes the hydrocarbons to CO.sub.2
and water and produces sensible heat for the recycle CO.sub.2
stream, thereby allowing the high grade heat of the turbine exhaust
to be further preserved and used downstream in the heat exchanger.
This additional heat also reduces the need for sources of low-grade
heat used to optimize the power cycle recuperative heat exchanger
train. Namely, it may not be necessary to scavenge heat from the
ASU main air compressor and/or the hot gas compression cycle as
non-turbine derived heat sources.
[0101] The turbine exhaust in line 112 from this process is cooled
in the primary heat exchanger 120 as in a typical power production
cycle configuration, such as shown in FIG. 1; however, it is then
sent to a modified direct-contact cooler that has been upgraded to
remove any SO.sub.x and/or NO.sub.x species arising from the dilute
hydrocarbon stream (e.g., sulfate or sulfite species formed by
oxidation of sulfur containing compounds, such as H.sub.2S and/or
nitrate or nitrite species formed by oxidation of nitrogen). An
exemplary process in this regard is described in U.S. Pat.
application Ser. No. 15/298,975, filed Oct. 20, 2016, the
disclosure of which is incorporated herein by reference. The
cleaned turbine exhaust is then split into the diluting CO.sub.2
fraction, the export CO.sub.2 fraction, and the recycle CO.sub.2
stream, and the process repeats with additional dilute hydrocarbon
stream being input to the power cycle.
[0102] In some embodiments, the recycle CO.sub.2 stream and the
dilute hydrocarbon stream can be mixed within the primary heat
exchanger train once the recycle CO.sub.2 stream has been heated to
an appropriate temperature to facilitate the oxidation reactions.
Alternatively (or in combination), the recycle CO.sub.2 stream and
the dilute hydrocarbon stream can be mixed within a further,
separate heat exchanger. This can prevent these reactions from
occurring in the lower temperature portions of the heat exchanger
train where the temperature may be insufficient to provide for the
oxidation reaction to occur. Accordingly, the recycle CO.sub.2
stream may be input to the heat exchanger at a first temperature
section, and the dilute hydrocarbon stream may be input to the heat
exchanger at a second, higher temperature section wherein the
temperature of the recycle CO.sub.2 stream is sufficient to
facilitate oxidation of the hydrocarbon compounds in the dilute
hydrocarbon stream. As an example, in FIG. 3, an optional, second
heat exchanger 167 (or supplemental heat exchanger) is illustrated.
A side stream 166 taken from line 165 directs a portion of the
recycle CO.sub.2 stream through the second heat exchanger 167 to be
heated by oxidation of the dilute hydrocarbon stream in line 172
that is input to the second heat exchanger 167 and is received from
hydrocarbon source 171. The heated stream of recycle CO.sub.2
stream is then input to the recuperator heat exchanger 120.
[0103] In some embodiments, the dilute hydrocarbon stream can be
introduced into the oxidant stream, which is formed of a mixture of
oxygen and the diluting CO.sub.2 fraction, at an appropriate
location within the primary heat exchanger (or alternatively a
separate, dedicated heat exchanger) such that the temperature of
the combined stream is sufficient to sustain the oxidation
reactions. Using the oxidant stream can serve to increase the rate
(and decrease the required residence time) of these reactions due
to the higher partial pressure of oxygen present in such stream
relative to the partial pressure of oxygen in the recycle CO.sub.2
stream. For example, referring to FIG. 4, a diluting CO.sub.2
fraction in line 165a is taken from line 165 and mixed with oxidant
in line 62 from the oxidant source 60 to form a diluted oxidant
stream (e.g., with an O.sub.2/CO.sub.2 ratio of about 5/95 to about
40/60 or about 10/90 to about 30/70). The diluted oxidant stream
may be heated by passage through the heat exchanger 120 against the
cooling turbine discharge stream in line 112. All or a portion of
the dilute hydrocarbon stream thus may be input to the diluted
oxidant stream prior to or during passage through the heat
exchanger 120. As illustrated in FIG. 4, dilute hydrocarbon from
dilute hydrocarbon source 171 is passed through line 172 for input
to the diluted oxidant stream in line 62 downstream from the point
where CO.sub.2 is added in line 165a.
[0104] In some embodiments, a portion of the oxidant stream may be
introduced into the mixture of the dilute hydrocarbon stream and
the recycle CO.sub.2 stream either upstream of or within the
primary heat exchanger train (or alternatively a separate,
dedicated heat exchanger). Such addition can serve to increase the
partial pressure of oxygen and increase the rate of the oxidation
reactions.
[0105] In some embodiments, a catalyst may be used in the area of
the heat exchanger with oxidation is to occur in order to
facilitate the oxidation reactions and ensure complete oxidation.
As a non-limiting example, commonly used water gas shift catalysts
(e.g., various metal oxides, such as Fe.sub.2O.sub.3,
Cr.sub.2O.sub.3, and CuO) may be used. Similarly, other catalysts
adapted to reduce the partial pressure of O.sub.2 that is required
in the mixed recycle CO.sub.2 stream and dilute hydrocarbon stream
may be used.
[0106] In addition, catalyzed oxidation can be carried out in a
dedicated reactor that is separate from the primary heat exchange
unit 120. As illustrated in FIG. 5, an optional oxidation reactor
180 can be used, and all or part of the dilute hydrocarbon stream
can be input directly to the oxidation reactor. In particular,
dilute hydrocarbon from dilute hydrocarbon source 171 is passed
through line 172 to oxidation reactor 180 wherein the dilute
hydrocarbon is oxidized to produce heat. Further, optionally,
oxidant can be taken from line 62 (or directly from oxidant source
60) in stream 62a and can be input to the oxidation reactor 180.
The oxidation of the dilute hydrocarbon stream in the oxidation
reactor 180 can produce a reaction stream 182 that can have a
chemistry substantially comprised of CO.sub.2 and H.sub.2O (with a
possible negligible amount of residual hydrocarbons). The reaction
stream 182 would be expected to be increased in temperature as a
result of the oxidation reaction, and the so-heated reaction stream
can be input to the heat exchanger 120 at the appropriate
temperature interface. In some embodiments, a portion of the
recycle CO.sub.2 stream (e.g., from one or both of lines 135 and
165) may be added to the dilute hydrocarbon stream and/or the
reaction stream 182. As seen in FIG. 5, CO.sub.2 in line 165b
(taken from line 165) can be input to the line 172 with dilute
hydrocarbon via line 165b' and/or to the reaction stream 182 via
line 165b''. Such additions can be useful for regulating the
temperature of the oxidation reaction in the oxidation reactor 180
and/or regulating the temperature of the reaction stream 182 itself
before introduction to the primary recuperative heat exchanger
train 120. In this manner, the dilute hydrocarbon stream can
essentially be used as a low grade heat source that may be
considered to be "external heat" for addition to the recuperative
heat exchanger 120 that can add to or replace other sources of
external heating, such as utilizing heat recuperation from the ASU
and/or a hot gas recompression cycle. Such a manner of operation
can be useful to improve efficiency by reducing the UA requirements
of the power cycle recuperative heat exchanger train while
providing additional CO.sub.2 for export and further offsetting
fuel demand at the power cycle combustor.
[0107] In some embodiments, the dilute hydrocarbon stream may be
mixed with the turbine exhaust stream so that oxidation of the
hydrocarbons can "super-heat" the turbine exhaust stream. As
illustrated in FIG. 6, dilute hydrocarbon from dilute hydrocarbon
source 171 can be input through line 172 directly to the turbine
exhaust in line 112 upstream from the heat exchanger 120. This can
serve to increase the amount of heat available for recuperation by
the recycle CO.sub.2 stream upon passage through the heat exchanger
120. Oxidant from the oxidant stream 62 may be input to the turbine
exhaust stream in such embodiments depending upon the residual
oxygen concentration in the turbine exhaust and the chemistry of
the dilute hydrocarbon stream 170. Such optional embodiment is
illustrated in FIG. 6 wherein oxidant in line 62b is passed from
line 62 (or directly from oxidant source 60) to the turbine exhaust
line 112. Although oxidant line 62a is shown entering turbine
exhaust line 112 upstream of the point where the dilute hydrocarbon
in line 172 is input, it is understood that the oxidant line 62a
may enter the turbine exhaust line 112 downstream of the point
where the dilute hydrocarbon in line 172 is input, or the oxidant
line 62a may connect directly to the line 172 for mixture with the
dilute hydrocarbon prior to entry to turbine exhaust line 112.
[0108] In further, optional embodiments, as illustrated in FIG. 7,
a portion of the turbine exhaust in line 112 can be diverted in
line 112a to an oxidation reactor 190 (which may include one or
more catalysts as noted above) to be combined with dilute
hydrocarbon delivered in line 172 from dilute hydrocarbon source
171. Further, optionally, oxidant from oxidant source 60 may be
input to the oxidation reactor 190. The line 112a can be configured
to divert a portion of the expanded CO.sub.2 working fluid upstream
of the recuperator heat exchanger 120 and downstream from the
turbine 110. The reaction product stream in line 192 exiting the
oxidation reactor 190 will be elevated in temperature above the
temperature of the turbine exhaust in line 112 and can be further
expanded across a further turbine 195 (i.e., a secondary turbine or
a supplemental turbine) for added power generation. The turbine
exhaust in stream 197 can be re-combined with the turbine exhaust
in line 112 prior to entry to the recuperative heat exchanger 120,
may be utilized for other purposes, or may be exhausted.
[0109] In any of the embodiments described herein, the dilute
hydrocarbon stream may be supplemented with another fuel in order
to accommodate changes in the flow rate or composition of the
dilute hydrocarbon stream. For example, a content of natural gas
may be mixed with the dilute hydrocarbon stream.
[0110] The presently disclosed systems and methods are beneficial
for the integration of a high efficiency power production system
with low BTU fuels without necessitating changes to the basic
nature of the equipment utilized (e.g., the combustor and/or
turbine). The ability to utilize dilute hydrocarbon streams in this
manner without the requirement for upgrading provides significant
economic and process advantages, such as reducing or eliminating
GPU requirements and/or increasing CO.sub.2 recovery.
[0111] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing description. Therefore, it is to be understood that the
invention is not to be limited to the specific embodiments
disclosed and that modifications and other embodiments are intended
to be included within the scope of the appended claims. Although
specific terms are employed herein, they are used in a generic and
descriptive sense only and not for purposes of limitation.
* * * * *