U.S. patent application number 13/740531 was filed with the patent office on 2014-07-17 for stripper overhead heat integration system for reduction of energy consumption.
This patent application is currently assigned to ALSTOM TECHNOLOGY LTD.. The applicant listed for this patent is ALSTOM TECHNOLOGY LTD.. Invention is credited to Sanjay Kumar Dube, David James Muraskin.
Application Number | 20140196499 13/740531 |
Document ID | / |
Family ID | 51164126 |
Filed Date | 2014-07-17 |
United States Patent
Application |
20140196499 |
Kind Code |
A1 |
Dube; Sanjay Kumar ; et
al. |
July 17, 2014 |
STRIPPER OVERHEAD HEAT INTEGRATION SYSTEM FOR REDUCTION OF ENERGY
CONSUMPTION
Abstract
A stripper heat integration system includes a first heat
exchanger; a second heat exchanger; and a refrigerant loop
comprising a refrigerant and configured for flow of the refrigerant
therein. The refrigerant loop is in communication with the first
heat exchanger and the second heat exchanger. The stripper heat
integration system further includes a compressor located in the
refrigeration loop, and configured to compress the refrigerant
prior to the refrigerant entering the second heat exchanger. The
first heat exchanger and the second heat exchanger are in fluid
communication with a stripper, and the stripper heat integration
system is configured for use with a carbon capture system, to
reduce energy consumption of the carbon capture system.
Inventors: |
Dube; Sanjay Kumar;
(Knoxville, TN) ; Muraskin; David James;
(Knoxville, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ALSTOM TECHNOLOGY LTD. |
Baden |
|
CH |
|
|
Assignee: |
ALSTOM TECHNOLOGY LTD.
Baden
CH
|
Family ID: |
51164126 |
Appl. No.: |
13/740531 |
Filed: |
January 14, 2013 |
Current U.S.
Class: |
62/617 |
Current CPC
Class: |
B01D 2257/504 20130101;
Y02C 10/12 20130101; Y02C 20/40 20200801; B01D 2252/103 20130101;
B01D 2252/102 20130101; B01D 2259/65 20130101; Y02C 10/06 20130101;
B01D 53/1475 20130101; B01D 53/1425 20130101 |
Class at
Publication: |
62/617 |
International
Class: |
F25J 3/06 20060101
F25J003/06 |
Claims
1. A stripper heat integration system comprising: a first heat
exchanger; a second heat exchanger; a refrigerant loop comprising a
refrigerant and configured for flow of the refrigerant therein, the
refrigerant loop in communication with the first heat exchanger and
the second heat exchanger; and a compressor located in the
refrigeration loop, configured to compress the refrigerant prior to
the refrigerant entering the second heat exchanger; wherein the
first heat exchanger and the second heat exchanger are in fluid
communication with a stripper, and the stripper heat integration
system is configured for use with a carbon capture system, to
reduce energy consumption of the carbon capture system.
2. The stripper heat integration system of claim 1, wherein the
first heat exchanger is a condenser and the second heat exchanger
is a reboiler.
3. The stripper heat integration system of claim 1, wherein the
refrigerant is selected from the group consisting of water,
ammonia, hydrocarbons, and a combination thereof.
4. The stripper heat integration system of claim 2, wherein the
condenser is configured to receive the refrigerant and reduce
temperature.
5. The stripper heat integration system of claim 4, wherein the
compressor is configured to receive the reduced temperature
refrigerant, compress the refrigerant, and increase pressure of the
refrigerant, wherein the refrigerant thereafter condenses in the
reboiler.
6. The stripper heat integration system of claim 2, wherein
operating temperature of the reboiler is greater than operating
temperature of the condenser.
7. The stripper heat integration system of claim 1, further
comprising a recirculating slip stream exiting and entering the
stripper.
8. The stripper heat integration system of claim 1, wherein the
system is part of a chilled ammonia process (CAP) system.
9. The stripper heat integration system of claim 7, wherein the
system comprises a third heat exchanger.
10. A method of recovering heat duty from a stripper comprising:
contacting in a first heat exchanger a gas stream comprising water,
ammonia and CO.sub.2 with a liquid refrigerant of a refrigerant
loop, wherein the gas stream is sent to the first heat exchanger
from a stripper overhead section of the stripper, and the
refrigerant loop comprises the refrigerant and is in communication
with the first heat exchanger and a second heat exchanger; and
after the contacting, obtaining from the first heat exchanger a
condensed stream comprising, water, ammonia and CO.sub.2 and at a
temperature less than the temperature of the gas stream entering
the first heat exchanger; wherein the first heat exchanger and the
second heat exchanger are in fluid communication with the
stripper.
11. The method of claim 10, wherein the gas stream entering the
first heat exchanger is at a temperature between about 60.degree.
C. and about 190.degree. C., and the condensed stream exiting the
first heat exchanger is at a temperature between about 40.degree.
C. and about 130.degree. C.
12. The method of claim 10, wherein the first heat exchanger is a
condenser and the second heat exchanger is a reboiler.
13. The method of claim 10, wherein the refrigerant is selected
from the group consisting of water, ammonia, hydrocarbons, and a
combination thereof.
14. The method of claim 12, wherein the condenser receives the
liquid refrigerant and vaporizers the liquid refrigerant to form a
vaporized refrigerant.
15. The method of claim 14, comprising compressing the vaporized
refrigerant with use of a compressor to increase pressure and
compress the vaporized refrigerant.
16. The method of claim 11, comprising recirculating a slip stream
into and out of the stripper.
17. The method of claim 11, comprising recovering the stripper heat
duty in a chilled ammonia process (CAP).
Description
TECHNICAL FIELD
[0001] The present disclosure generally relates to reducing energy
consumption of a carbon capture process and system, such as a
chilled ammonia process (CAP) and system for carbon dioxide
(CO.sub.2) removal from a gas stream and, more specifically,
relates to a CAP CO.sub.2 removal process and system having a heat
integration system for the reduction of energy consumption.
BACKGROUND
[0002] Energy used in the world can be derived from the combustion
of carbon and hydrogen-containing fuels such as coal, oil, peat,
waste and natural gas. In addition to carbon and hydrogen, these
fuels contain oxygen, moisture and contaminants. The combustion of
such fuels results in the production of a gas stream containing the
contaminants in the form of ash, carbon dioxide (CO.sub.2), sulfur
compounds (often in the form of sulfur oxides, referred to as
"SOx"), nitrogen compounds (often in the form of nitrogen oxides,
referred to as "NOx"), chlorine, mercury, and other trace elements.
Awareness regarding the damaging effects of the contaminants
released during combustion triggers the enforcement of even more
stringent limits on emissions from power plants, refineries and
other industrial processes. There is an increased pressure on
operators of such plants to achieve near zero emission of
contaminants. However, removal of contaminants from the gas stream,
such as a flue gas stream, requires a significant amount of
energy.
[0003] Moreover, in CAP processing the CAP stripper functions to
separate a water/ammonia/CO.sub.2 solution absorbed in the water
wash column. The ammonia is returned to the CO.sub.2 absorber for
capture of CO.sub.2, and water is returned to the water wash column
for ammonia capture. The ability to recover the stripper overhead
energy into a power plant steam cycle is based upon the
availability of suitable extraction and return locations along with
the economic justification of such streams. In general, for
example, a Pulverized Coal (PC) plant steam cycle can have several
locations for integrations of the steam condensate when considering
the stripper overhead temperatures. Without recovery of heat from
the stripper overhead, heat is wasted thereby resulting in high
specific steam consumption.
[0004] Accordingly, there exists a need for systems and processes
for recovering and efficiently utilizing stripper overhead heat
duty in carbon capture systems, particularly in CAP
applications.
SUMMARY
[0005] According to aspects illustrated herein, there is provided a
stripper heat integration system. The system comprises a first heat
exchanger; a second heat exchanger; and a refrigerant loop
comprising a refrigerant and configured for flow of the refrigerant
therein. The refrigerant loop is in communication with the first
heat exchanger and the second heat exchanger. The stripper heat
integration system further comprises a compressor located in the
refrigeration loop, and configured to compress the refrigerant
prior to the refrigerant entering the second heat exchanger. The
first heat exchanger and the second heat exchanger are in fluid
communication with a stripper, and the stripper heat integration
system is configured for use with a carbon capture system, to
reduce energy consumption of the carbon capture system.
[0006] According to another aspect illustrated herein, there is
provided a method of recovering heat duty from a stripper. The
method comprises contacting in a first heat exchanger a gas stream
comprising water, ammonia and CO.sub.2 with a liquid refrigerant of
a refrigerant loop, wherein the gas stream is sent to the first
heat exchanger from a stripper overhead section of the stripper,
and the refrigerant loop comprises the refrigerant and is in
communication with the first heat exchanger and a second heat
exchanger. The method further comprises, after the contacting,
obtaining from the first heat exchanger a condensed stream
comprising, water, ammonia and CO.sub.2 and at a temperature less
than the temperature of the gas stream entering the first heat
exchanger, wherein the first heat exchanger and the second heat
exchanger are in fluid communication with the stripper.
[0007] The above described and other features are exemplified by
the following figures and in the detailed description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Referring now to the figures, which are exemplary
embodiments, and wherein the like elements are numbered alike:
[0009] FIG. 1 is a schematic diagram (Prior Art) generally
depicting an ammonia based CO.sub.2 removal system;
[0010] FIG. 2 is schematic diagram depicting an ammonia based
CO.sub.2 removal system including a refrigerant loop, according to
an embodiment; and
[0011] FIG. 3 is schematic diagram depicting another embodiment of
the CO.sub.2 removal system disclosed herein including refrigerant
loop and slip stream.
DETAILED DESCRIPTION
[0012] FIG. 1 is a schematic representation of an example of a
prior multi-stage absorber chilled ammonia based CO.sub.2 removal
system 100. The system 100 comprises a CO.sub.2 absorption stage
comprising a CO.sub.2 absorber 101 arranged to allow contact
between a gas stream, such as a flue gas, to be depleted of
CO.sub.2 or purified and an absorption liquid comprising ammonia.
Thus, a gas stream from which CO.sub.2 is to be removed is fed to
the CO.sub.2 absorber 101 via line 102. In the CO.sub.2 absorber
101, this gas stream is contacted with an absorption liquid
comprising ammonia, for example, by bubbling the gas stream through
the absorption liquid or by spraying the absorption liquid into the
gas stream. The absorption liquid comprising ammonia is fed to the
CO.sub.2 absorber 101 via line 103. In the CO.sub.2 absorber 101,
CO.sub.2 from the gas stream is absorbed in the absorption liquid,
for example, by formation of carbonate or bicarbonate of ammonium,
either in dissolved or solid form. Used absorption liquid
containing absorbed CO.sub.2 (CO.sub.2rich absorption liquid) exits
the CO.sub.2 absorber 101 via line 104 and enters an absorption
liquid regenerator unit 111 where CO.sub.2 is separated and
released from the used absorption liquid. The separated CO.sub.2
exits the absorption liquid regenerator unit 111 via line 112 and
the regenerated absorption liquid is recycled to the CO.sub.2
absorber 101. Gas depleted in CO.sub.2 then exits the CO.sub.2
absorber 101 via line 105.
[0013] As further shown in FIG. 1, the system 100 also comprises an
ammonia absorption stage for removing ammonia present in the gas
stream after processing the CO.sub.2 absorption stage. The ammonia
absorption stage comprises a contaminant absorber 106. The
contaminant absorber 106 is arranged to allow contact between the
gas stream depleted of CO.sub.2 which leaves the CO.sub.2 absorber
101 via line 105 and a second absorption liquid, which contains no
ammonia or a low concentration of ammonia. The second absorption
liquid is fed to the contaminant absorber 106 via line 107. In the
contaminant absorber 106, contaminants, including ammonia,
remaining in the gas stream when it leaves the CO.sub.2 absorber
101 are absorbed in the second absorption liquid. Used absorption
liquid containing absorbed ammonia leaves the contaminant absorber
106 via line 108. A gas stream depleted of CO.sub.2 and reduced
ammonia levels exits the contaminant absorber 106 via line 109.
[0014] The second absorption liquid enriched with ammonia, CO.sub.2
and other contaminants may be recycled via an absorption liquid
regenerator unit 110, wherein ammonia, CO.sub.2 and other
contaminants can be separated from the absorption liquid. The
absorption liquid regenerator unit 110 may generally be a stripper,
in which the absorption liquid is heated at a temperature at which
lower boiling point components may be transferred to the gas phase
to form a stripper offgas stream, while higher boiling point
components remain in the liquid phase and may be recycled for use
as absorption liquid. The stripper 110 may be heated using high,
medium or low pressure steam depending on the stripper operating
pressure.
[0015] The stripper 110 offgas stream, generally comprising
ammonia, CO.sub.2 and other low boiling point contaminants, could
be fed to the absorption liquid regenerator unit 111 or typically
fed to the CO.sub.2 absorber 101, as shown in FIG. 1. The
absorption liquid regenerator unit 111 generally operates at high
pressures, such as a range of 10-20 bar or higher. The absorption
liquid regenerator (stripper) 110 typically operates at a lower
pressure as the stripper overhead flows to the CO.sub.2 absorber
101.
[0016] In contrast to prior CAP systems and processes, and as
further described below with respect to FIGS. 2 and 3, embodiments
disclosed herein employ the use of a refrigerant loop, which can
recover stripper overhead duty and use this heat duty in the
stripper reboiler in lieu of steam. Thus, the inventors have
determined how to recover energy from the stripper overhead to
reduce energy consumption of the overall system in terms of both
specific steam and electrical consumption. Accordingly, the
inventors have determined how to improve upon and/or replace, e.g.,
the steam cycle shown in stripper 110, and thereby reduce the
energy consumption of the overall system. Moreover, the refrigerant
loop 210 can be internal to the overall system as shown in FIG.
2.
[0017] As will be explained in further detail below, according to
embodiments, the inventors have determined how to use, e.g., a
continuous refrigerant loop to eliminate prior steam requirements.
For example, by using the refrigerant loop described herein between
a first heat exchanger (condenser) and a second heat exchanger
(reboiler), and which is in fluid communication with a stripper,
refrigerant liquid may flow into the condenser, be evaporated and
then compressed, sent to the reboiler with an increased pressure
where it condenses in the reboiler, becomes liquid again and can be
recycled back to the condenser. As a result of such processing,
energy can be captured and prior requirements for steam supply
could be eliminated. Thus, according to embodiments, the inventors
have determined how to replace some need for steam supplied to the
reboiler with use of the herein described loop configurations.
Thus, it has been determined how to, e.g., transfer energy from
steam into electrical energy (see compressor 72 of FIGS. 2 and
3).
[0018] Referring now to FIG. 2, schematically depicted therein is a
system 200 including a refrigerant loop or cycle 210, and for use
in an overall carbon capture system, such as a CAP system for
CO.sub.2 removal from a gas stream. Thus, embodiments disclosed
herein employ a stripper overhead heat integration system 230
comprising the refrigerant loop or cycle 210 for the reduction of
energy consumption, as described in further detail herein.
[0019] It is also noted that while a CAP system and process are
primarily referred to herein, the various embodiments also apply to
other carbon capture systems, such as amine based carbon capture
systems, and so forth. Additionally, embodiments are particularly
attractive for, e.g., combined power plant (CCPP) gas applications
due to high stripper steam consumption, as well as Pulverized Coal
(PC) plant applications, among other applications.
[0020] The exemplary system 200 shown in FIG. 2 comprises a water
wash column 220 in fluid communication with a stripper 240. It is
noted that while FIG. 2, as well as FIG. 3, sets forth examples
including various components, such as water wash column 220 and
stripper 240, other components could also be included in the
systems described herein.
[0021] As illustrated in FIG. 2, system 200 includes the water wash
column 220 defining a first inlet 10 for receiving stream 12 for
treatment in the interior of water wash column 220, and a second
inlet 14 for receiving stream 16. The stream 12 is a gas stream
coming from an absorber (not shown) of an overall CAP system. In
the absorber (not shown), absorption of CO.sub.2 occurs using a
scrubbing medium, such as ammonium carbonate/bicarbonate/carbonate
containing ionic solution. As the gas, e.g., a flue gas, flows
upwardly in the absorber column, the gas contacts a scrubbing
solution including dissolved ammonium carbonate and ammonium solids
that flow in a countercurrent direction to the gas, and the
CO.sub.2 is absorbed therein.
[0022] Thus, the stream 12 exiting the absorber and entering the
NH.sub.3 water wash column 220 comprises typically between about
5,000 parts per million (ppm) to about 20,000 ppm ammonia, e.g.,
about 10,000 ppm to about 12,000 ppm ammonia, about 5 mol % to
about 10 mol % oxygen, e.g., about 6 mol % to about 7 mol % oxygen,
about 85 mol % nitrogen, argon, water and about 1 mol % to about 2
mol % CO.sub.2, e.g., about 11/2 mol % CO.sub.2 (thus depleted in
CO.sub.2, as described above; it is noted that particular values
described herein can vary depending upon, e.g., the CO.sub.2
capture efficiency and so forth). The temperature of stream 12 is
typically between about 5.degree. C. and about 10.degree. C. and
the pressure is atmospheric pressure, or greater depending upon the
process and type of plant, e.g., plants other than CCPP and PC,
industry where pressure may be up to 10 bar. In the water wash
column 220, it is therefore desired to recover this ammonia and
reduce the ammonia vapor from the stream 12.
[0023] Stream 16 entering typically near the top of the water wash
column 220 comprises an absorption liquid for absorption of
NH.sub.3 from the gas, comprising primarily water, substantially no
CO.sub.2 or a low amount of CO.sub.2 (e.g., about 0.1 mol %), and
similarly substantially no ammonia or a low concentration of
ammonia (e.g., about 0.1 mol %). The stream 16 enters the water
wash column 220 at second inlet 14 via heat exchanger 52A, as
illustrated in FIG. 2. The temperature of stream 16 entering the
heat exchanger 52A is typically between about 10.degree. C. and
about 15.degree. C., and the temperature of stream 16 exiting the
heat exchanger 52A is typically about 5.degree. C. Thus, in heat
exchanger 52A the temperature of stream 16 is reduced prior to this
stream being returned to the water wash column 220. The pressure of
stream 16 is about 2 bars as the water wash column 220 typically
operates at atmospheric pressure and an increased pressure can
therefore employed to overcome column height, and so forth. The
water wash column 220 can also operate at higher pressure depending
on the CAP application (e.g., plants other than CCPP and PC,
industry where pressure may be up to 10 bar).
[0024] The water wash column 220 also defines a third inlet 18 for
receiving water stream 20, which may be generally characterized as
clean make up water for the system to be supplied as needed because
some water generally may be depleted or lost as a result of system
processing.
[0025] The water wash column 220 further defines a fourth inlet 22
for receiving stream 24 of recirculation loop 26 that assists in
scrubbing out and removing ammonia from the stream 12 entering the
water wash column 220. Stream 24 entering the water wash column 220
at inlet 22 comprises primarily water, about 1.5 molar ammonia and
a low amount of CO.sub.2. Typically, the temperature of stream 24
entering the water wash column at fourth inlet 22 is about
5.degree. C. and at about the pressure of the water wash column
220. By the heat of absorption, the temperature of stream 24
increases to between about 8.degree. C. and about 10.degree. C. as
this stream enters the water wash column 220. Accordingly, as shown
in FIG. 2, recirculation loop 26 also comprises the stream 24
subsequently exiting a first discharge outlet 28 of the water wash
column 220, resulting in stream 24 now being at the referenced
elevated temperature of between about 8.degree. C. and about
10.degree. C. Stream 24 is then pumped through pump P52 to heat
exchanger 52B where heat is removed by refrigeration resulting in
stream 24 exiting heat exchanger 52B at a reduced temperature of
about 5.degree. C. and thereby recirculated back to the water wash
column 220.
[0026] Water wash column 220 also defines a second discharge outlet
32 for discharging liquid stream 30, described in further detail
below with respect to the operation of the stripper 240, and a
third discharge outlet 34 for clean stream 36 typically comprising
about 200 ppm ammonia (e.g., between about 10 and 1000 ppmv), and
about 0.3 to about 2 mol % CO.sub.2, e.g., about 1 mol % CO.sub.2,
which exits the water wash column 220, as shown in FIG. 2.
[0027] The water wash column 220 further comprises a lower section
A and an upper section B, and it is noted that although the water
wash column 220 is shown and described as having the referenced
number of sections, inlets and outlets as described herein, the
present disclosure is not limited in this regard as water wash
columns having any number of suitable sections or stages, inlets,
and/or outlets may be employed. The water wash column 220 is
typically a packed column that employs water to absorb ammonia from
the gas stream. Accordingly, the intent is to remove ammonia from
the gas stream, for example a flue gas stream, prior to that stream
exiting the CO.sub.2 capture plant and going through a chimney to
the atmosphere. In the water wash column 220, desired temperatures
can be maintained using heat exchangers and a chiller. Ammonia is
thus removed from the entering stream 12 resulting in the capture
of ammonia in exiting liquid stream 30 (ammoniated water), which is
sent to stripper 240 to separate out the ammonia from the
water.
[0028] More specifically, liquid stream 30 exiting the water wash
column 220 at water wash column second discharge outlet 32
comprises primarily water, about 0.5 to about 3 molar ammonia,
e.g., about 1.5 molar ammonia, CO.sub.2, dissolved oxygen, argon
and nitrogen at a typical temperature of between about 5.degree. C.
to about 8.degree. C., and operating at about the pressure of the
water wash column 220. The second discharge outlet 32 for stream 30
is in fluid communication with the first stripper inlet 38. Stream
30 passes through heat exchanger 51, which is used to raise the
temperature of that stream, and then into the first stripper inlet
38 for entering the stripper 240. It is noted that the elevated
temperature of stream 30 entering the stripper 240 is dependent
upon operating conditions, such as pressure and temperature of the
stripper 240.
[0029] As further shown in FIG. 2, a pump P51 is located in the
line for stream 30 to increase the pressure of stream 30 to
substantially about the pressure of the stripper 240. The pressure
of stream 30 entering heat exchanger 51 is dependent upon the
pressure of the stripper 240. For example, if the stripper pressure
is about 2 bars, then stream 30 can be pumped via pump P51 to
between about 3 to about 4 bars to overcome additional pressure
drop, and so forth. As a further example, if the stripper 240 is
operating at a higher pressure of about 15 bars, then the pressure
of stream 30 can be increased via pump P51 to about 17 bars, or
higher to overcome additional pressure drop of the system.
[0030] A portion of liquid stream 30 entering the stripper 240
exits the bottom of the stripper 240 via stripper first outlet 40
as lean stream 42, which comprises primarily water, and a low
amount of ammonia, such as between about 0.01 and 0.3 molar
ammonia, e.g., about 0.05 molar ammonia, typically at an elevated
temperature of between about 80.degree. C. and about 220.degree.
C., and at a typical pressure of between about vacuum to about 15
bars. Stream 42 then passes through heat exchanger 51, as shown in
FIG. 2, where this stream can be used to preheat stream 30 entering
heat exchanger 51. Stream 42 is then returned to the water wash
column 220 as stream 16 after passing through heat exchanger 52A
where it is further cooled. Accordingly, the stripper first outlet
40 is in fluid communication with the water wash column second
inlet 14. A side stream 42' can be taken off of stream 42 exiting
heat exchanger 51, as shown in FIG. 2, and sent to a CO.sub.2 wash
for further processing. The constituents, temperature and pressure
of the side stream 42' are thus the same or substantially the same
as stream 42. As further shown in FIG. 2, side stream 42' passes
through pump P37 wherein the pressure is increased to substantially
the pressure of the CO.sub.2 wash, e.g., CO.sub.2 product
cooler.
[0031] As further shown in FIG. 2, in addition to the stripper
first inlet 38 and stripper first outlet 40, the stripper 240 also
defines a stripper second outlet 44 for stream 46 exiting typically
the top of the stripper 240, and stripper third outlet 48 for
stream 50 exiting the lower portion of the stripper 240.
[0032] Stream 46 is a gas stream comprising ammonia, CO.sub.2 and
water having a temperature of between about 60.degree. C. and about
190.degree. C., and more typically about 110.degree. C. The
pressure of stream 46 exiting stripper second outlet 44 is
typically about the pressure of the stripper 240, for example,
vacuum to about 15 bars. It is noted that the temperature of stream
46 is dependent upon the pressure of the stripper 240. For example,
if the stripper 240 is operating at a pressure of between about 2
bars to about 5 bars, then the temperature of stream 46 is
typically between about 110.degree. C. and about 130.degree. C. As
further examples, if the pressure of the stripper 240 is operating
at a vacuum pressure, then the temperature of the stream 46 is
about 60.degree. C. to about 70.degree. C. Similarly, if the
stripper 240 is operating at a higher pressure of about 15 bars,
then the temperature of stream 46 also will be higher, such as
about 180.degree. C. to about 190.degree. C., and so forth. Thus,
the temperature of stream 46 is correlated to the pressure of the
stripper 240.
[0033] Stream 46 enters heat exchanger 54 at heat exchanger 54
first inlet 52 where the gas stream 46 is cooled therein to a
temperature considered low enough to capture energy of the system,
but not too low as to form solids that could result in plugging.
For example, stream 46 can be cooled from about 60-190.degree. C.
to between about 40.degree. C. to about 130.degree. C., more
specifically about 70.degree. C. Heat exchanger 54 is a condenser
typically operating at about 40.degree. C. to about 130.degree. C.
where the afore-referenced cooling takes places resulting in stream
55 exiting the heat exchanger 54 first outlet 56 at a reduced
temperature. Thus, stream 55 is a mixed vapor/liquid stream
comprises ammonia, CO.sub.2 and water, now condensed and at a
reduced temperature. As further shown in FIG. 2, stream 55 then
enters separator V05 at separator first inlet 58 to separate the
liquid and vapor. Accordingly, vapor stream 63 comprising ammonia,
CO.sub.2 and water exits typically at the top of separator V05, and
liquid stream 60 exits the separator V05 typically at the bottom as
a liquid recycle stream comprising ammonia, CO.sub.2 and water.
Stream 60 can enter the stripper 240 via stripper second inlet 62,
as shown in FIG. 2. While not shown in FIG. 2, stream 60 also could
be recycled back to the CO.sub.2 absorber. Thus, flexibility is
achievable with the present design as the amount of this recycle
stream sent to the stripper 240 and/or absorber can be varied
depending upon the processing needs.
[0034] A liquid refrigerant stream 64 of refrigeration loop 210
enters the heat exchanger 54 via second inlet 66 to assist in the
afore-referenced cooling of stream 46 and capturing of heat
duty/reduction of energy consumption. Thus, in stream 64 a suitable
refrigerant in liquid form enters the heat exchanger 54 at
typically at temperature approach of about 10.degree. C. with
respect to stream 55. Examples of suitable refrigerants include,
but are not limited to, water, ammonia, hydrocarbons, combinations
thereof, and so forth. The selection of the refrigerant can be
based on the refrigerant properties, which are compatible
with/closely match the stripper 240, and are desirable therefore.
Regarding the pressure of the liquid refrigerant stream 64, it is
noted that the pressure of the refrigerant will vary depending upon
the refrigerant employed. For example, if ammonia is employed as
the refrigerant, the pressure may be between about 20 bars to about
100 bars depending upon the stripper operating conditions. However,
if water is employed, the pressure may be significantly less. The
liquid refrigerant stream 64 uses heat from gas stream 46 also
entering the heat exchanger 54, which is at the afore-described
elevated temperature, thereby vaporizing the refrigerant. Thus,
evaporation of the liquid refrigerant occurs as a result of passing
through heat exchanger 54. The vaporized refrigerant 70 exits the
heat exchanger 54 at heat exchanger second outlet 68 and is then
compressed (e.g., via compressor 72) to increase the pressure such
that it can enter the heat exchanger 53 (reboiler) first inlet 74
and condense in the heat exchanger 53 (reboiler) thereafter exiting
the heat exchanger 53 first outlet 76 and returning to the heat
exchanger 54 (condenser) to complete the loop. It should be noted
that the condensed refrigerant from the heat exchanger 53 is
typically at a higher pressure and the pressure may be reduced by
using a control valve before returning it to the heat exchanger 54
to provide the desired refrigerant temperature. A refrigerant
separator could be employed after the control valve to separate
refrigerant liquid and vapor (not shown). It is desired to increase
the pressure by compression such that the saturation pressure is
increased to substantially the conditions required in heat
exchanger 53 (reboiler) of the refrigerant loop 210. Accordingly,
heat exchanger 53 (reboiler) of the recirculation loop shown in
FIG. 2 will operate at a higher temperature, such as typically
between about 70.degree. C. and about 220.degree. C., than heat
exchanger 54 (condenser). Compression of the refrigerant in the
refrigerant loop 210 is conducted to attain the higher saturation
temperature requirements of the heat exchanger 53 (reboiler) and
once this high saturation temperature is reached, the stream
condenses, releases heat to meet and maintain temperature
requirements of the heat exchanger 53 (reboiler), thereby boiling
off process liquids. The compressed liquid refrigerant is
thereafter returned to the heat exchanger 54 to evaporate/vaporize
and complete the refrigerant cycle 210 again. It is noted that
energy reduction is dependent on the specific value of steam which
varies by location, and the processing parameters are dependent on,
e.g., refrigerant selection and stripper operating conditions.
[0035] As further shown in FIG. 2, the stripper 240 also includes a
recirculation loop wherein heat exchanger 53 (reboiler) also
defines a heat exchanger 54 second outlet 77 for discharge a
portion of the vapor from heat exchanger 53 (reboiler) back to the
stripper 240 via stream 78 entering the stripper 240 at stripper
inlet 80. Stream 78 comprises a mixture of ammonia, CO.sub.2 and
water at about the pressure of the stripper 240. The temperature of
stream 78 is typically between about 70.degree. C. and about
220.degree. C.
[0036] Referring now to FIG. 3, the carbon dioxide (CO.sub.2)
removal system 205 illustrated in FIG. 3 is similar to that of FIG.
2, but includes a slip stream 90 and an additional heat exchanger
(heat exchanger 94). Thus, like elements have been assigned like
reference numbers. In FIG. 3, refrigeration loop 210 cycles between
heat exchanger 94 and heat exchanger 54, as shown in FIG. 3. Slip
stream 90 comprises ammonia, CO.sub.2 and water, and exits stripper
discharge outlet 92 from the stripper 240 passing through the heat
exchanger 94 and entering the stripper 240 at stripper inlet 96.
Slip stream 90 is at a lower temperature, typically at a
temperature between the temperature of the heat exchanger 53 and
the heat exchanger 54, and at a pressure of about the pressure of
the stripper 240. Accordingly, compression of the refrigerant in
the refrigerant loop 210 to attain the requirements of heat
exchanger 53 are not required, and thus the power of the compressor
72 can be reduced. The power of the compressor 72 can be reduced
by, e.g., lowering the condensing pressure of the refrigerant with
the system of FIG. 3. Thus, as shown in FIG. 3, and in contrast to
the embodiment shown in FIG. 2, in lieu of the refrigeration loop
210 cycling into and out of heat exchanger 53, steam condensate can
enter and exit heat exchanger 53 from a regenerator (not shown) of
the overall system. It is further noted that that slip stream 90
will typically have a lower temperature than stream 50 and
therefore will employ lower compressor ratio and associated power
consumption. The specific processing parameters will vary depending
upon, e.g., the refrigerant and stripper operating conditions.
EXAMPLE
[0037] The inventors have expended significant amounts of effort in
performing computer simulations using sophisticated modeling
techniques to achieve a surprising reduction in energy consumption.
Simulations were conducted regarding embodiments disclosed herein
using the referenced refrigerant loop cycle in comparison to prior
systems, such as shown in FIG. 1. Simulations have demonstrated the
ability to reduce energy consumption in terms of both specific
steam (GJ/ton CO.sub.2) and electrical consumption. For example,
simulations have shown a specific energy consumption reduction from
3.2 GJ/ton CO.sub.2 to 2.3 GJ/ton CO.sub.2 is possible with the
proposed heat integration design including refrigeration loop.
[0038] A further advantage of embodiments disclosed herein is the
ability to employ an internal refrigerant loop to recover stripper
overhead duty and use this heat duty in the stripper reboiler in
lieu of steam there by resulting in reduced energy consumption. The
refrigeration loop includes the use of a refrigerant compressor to,
e.g., increase the refrigerant condensing pressure of the process.
As explained above according to embodiments, liquid can be drawn
from the stripper 240 and the stripper 240 overhead heat compressed
and condensed against this liquid to reduce refrigerant compressor
72 power. Some heat also could be provided by steam condensate from
the regenerator reboiler system.
[0039] Another advantage includes possible elimination of large
cooling water demand, cooling tower system(s), and/or low pressure
steam extractions, to cool the stripper overhead stream.
[0040] Still further advantages include elimination of the need for
a double loop cooling water system for stripper condensers of some
capture systems which are employed to avoid plugging, and therefore
reduction of the number of streams and equipment. For example,
according to embodiments, low pressure steam and large amounts of
steam condensate/cooling water for cooling the stripper overhead
can be eliminated.
[0041] Further advantages include the ability to employ an
independent stripper-regenerator loop.
[0042] Moreover, elimination of a dedicated steam extraction source
from a power plant steam cycle to operate the stripper for some
capture systems results in an improved and less costly approach to
the supply of energy to the capture system.
[0043] While the components of the systems set forth herein are
described as having various numbers of inlets and outlets, the
present disclosure is not limited in this regard as the components
described herein may have any number of suitable inlets and/or
outlets, as well as pumps, valves and so forth, without departing
from the broader aspects disclosed herein. Similarly, while
reference is herein made to various locations, such as top, bottom,
and so forth, the present disclosure is not limited to exact
locations, as the various lines and streams disclosed herein can
enter/exit at other locations. Still further, it will be
appreciated that the embodiments shown in FIGS. 2 and 3 could
include other components, such as control valves, vapor/liquid
separators, pumps, and so forth.
[0044] While the invention has been described with reference to
various exemplary embodiments, it will be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted for elements thereof without departing from the
scope of the invention. In addition, many modifications may be made
to adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
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