US20140196499A1

US20140196499A1 - Stripper overhead heat integration system for reduction of energy consumption

Info

Publication number: US20140196499A1
Application number: US13/740,531
Authority: US
Inventors: Sanjay Kumar Dube; David James Muraskin
Original assignee: Alstom Technology AG
Current assignee: General Electric Technology GmbH
Priority date: 2013-01-14
Filing date: 2013-01-14
Publication date: 2014-07-17

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.

Description

TECHNICAL FIELD

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 (CO₂) removal from a gas stream and, more specifically, relates to a CAP CO₂removal process and system having a heat integration system for the reduction of energy consumption.

BACKGROUND

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 (CO₂), 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.
Moreover, in CAP processing the CAP stripper functions to separate a water/ammonia/CO₂solution absorbed in the water wash column. The ammonia is returned to the CO₂absorber for capture of CO₂, 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.
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

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.
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 CO₂with 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 CO₂and 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.
The above described and other features are exemplified by the following figures and in the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the figures, which are exemplary embodiments, and wherein the like elements are numbered alike:

FIG. 1 is a schematic diagram (Prior Art) generally depicting an ammonia based CO₂removal system;

FIG. 2 is schematic diagram depicting an ammonia based CO₂removal system including a refrigerant loop, according to an embodiment; and

FIG. 3 is schematic diagram depicting another embodiment of the CO₂removal system disclosed herein including refrigerant loop and slip stream.

DETAILED DESCRIPTION

FIG. 1 is a schematic representation of an example of a prior multi-stage absorber chilled ammonia based CO₂removal system 100. The system 100 comprises a CO₂absorption stage comprising a CO₂absorber 101 arranged to allow contact between a gas stream, such as a flue gas, to be depleted of CO₂or purified and an absorption liquid comprising ammonia. Thus, a gas stream from which CO₂is to be removed is fed to the CO₂absorber 101 via line 102. In the CO₂absorber 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 CO₂absorber 101 via line 103. In the CO₂absorber 101, CO₂from 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 CO₂(CO₂rich absorption liquid) exits the CO₂absorber 101 via line 104 and enters an absorption liquid regenerator unit 111 where CO₂is separated and released from the used absorption liquid. The separated CO₂exits the absorption liquid regenerator unit 111 via line 112 and the regenerated absorption liquid is recycled to the CO₂absorber 101. Gas depleted in CO₂then exits the CO₂absorber 101 via line 105.
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 CO₂absorption 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 CO₂which leaves the CO₂absorber 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 CO₂absorber 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 CO₂and reduced ammonia levels exits the contaminant absorber 106 via line 109.
The second absorption liquid enriched with ammonia, CO₂and other contaminants may be recycled via an absorption liquid regenerator unit 110, wherein ammonia, CO₂and 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.
The stripper 110 offgas stream, generally comprising ammonia, CO₂and other low boiling point contaminants, could be fed to the absorption liquid regenerator unit 111 or typically fed to the CO₂absorber 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 CO₂absorber 101.
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.
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).
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 CO₂removal 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.
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.
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.
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 CO₂occurs 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 CO₂is absorbed therein.
Thus, the stream 12 exiting the absorber and entering the NH₃ 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 % CO₂, e.g., about 1½ mol % CO₂(thus depleted in CO₂, as described above; it is noted that particular values described herein can vary depending upon, e.g., the CO₂capture efficiency and so forth). The temperature of stream 12 is typically between about 5° C. and about 10° 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.
Stream 16 entering typically near the top of the water wash column 220 comprises an absorption liquid for absorption of NH₃from the gas, comprising primarily water, substantially no CO₂or a low amount of CO₂(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° C. and about 15° C., and the temperature of stream 16 exiting the heat exchanger 52A is typically about 5° 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).
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.
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 CO₂. Typically, the temperature of stream 24 entering the water wash column at fourth inlet 22 is about 5° 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° C. and about 10° 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° C. and about 10° 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° C. and thereby recirculated back to the water wash column 220.
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 % CO₂, e.g., about 1 mol % CO₂, which exits the water wash column 220, as shown in FIG. 2.
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 CO₂capture 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.
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, CO₂, dissolved oxygen, argon and nitrogen at a typical temperature of between about 5° C. to about 8° 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.
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.
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° C. and about 220° 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 CO₂wash 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 CO₂wash, e.g., CO₂product cooler.
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.
Stream 46 is a gas stream comprising ammonia, CO₂and water having a temperature of between about 60° C. and about 190° C., and more typically about 110° 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° C. and about 130° 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° C. to about 70° 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° C. to about 190° C., and so forth. Thus, the temperature of stream 46 is correlated to the pressure of the stripper 240.
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° C. to between about 40° C. to about 130° C., more specifically about 70° C. Heat exchanger 54 is a condenser typically operating at about 40° C. to about 130° 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, CO₂and 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, CO₂and 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, CO₂and 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 CO₂absorber. 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.
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° 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° C. and about 220° 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.
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, CO₂and water at about the pressure of the stripper 240. The temperature of stream 78 is typically between about 70° C. and about 220° C.
Referring now to FIG. 3, the carbon dioxide (CO₂) 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, CO₂and 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

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 CO₂) and electrical consumption. For example, simulations have shown a specific energy consumption reduction from 3.2 GJ/ton CO₂to 2.3 GJ/ton CO₂is possible with the proposed heat integration design including refrigeration loop.
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.
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.
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.
Further advantages include the ability to employ an independent stripper-regenerator loop.
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.
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.
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.

Claims

What is claimed is:

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 CO₂with 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 CO₂and 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° C. and about 190° C., and the condensed stream exiting the first heat exchanger is at a temperature between about 40° C. and about 130° 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).