Chilled ammonia process carbon capture system with refrigeration system and heat pump

Abstract

A refrigerated ammonia carbon capture system using a first working fluid (preferably ammonia) and a heat pump system using a second working fluid (preferably water) are coupled via an evaporator. The heat from the working fluid in the refrigeration system is used to evaporate the working fluid in the heat pump system, allowing waste heat from the refrigerated ammonia carbon capture system to be used to obtain high-temperature, high-pressure steam. Steam extraction is configured for use in the reboiler of the refrigerated ammonia carbon capture unit, eliminating the need for steam upgrading and additional equipment for generating high-temperature, high-pressure steam.

Description

Technical Field

[0001] This disclosure relates to a cryogenic ammonia carbon capture system configured to utilize low-temperature waste heat via a cascaded heat pump system, the cascaded heat pump system comprising at least a first heat pump system using a first working fluid and a second heat pump system using a second working fluid different from the first working fluid. The disclosed embodiments include a cascaded heat pump system wherein the first heat pump system includes a first evaporator configured to heat and evaporate the first working fluid (i.e., ammonia) by heat exchange with a refrigeration system of the cryogenic ammonia carbon capture unit, and the second heat pump system includes a second evaporator configured to heat and evaporate a second working fluid (i.e., water) by heat exchange with the first working fluid, the second heat pump system being configured to heat and compress the second working fluid to obtain vapor at a temperature and pressure suitable for use in a reboiler of the cryogenic ammonia carbon capture unit, the reboiler acting as a condenser for the second heat pump system without any additional heat transfer. Background Technology

[0002] The need to reduce carbon dioxide emissions has become a major concern in averting global warming. The accelerated increase in atmospheric carbon dioxide concentration is attributed to the increasing use of fuels such as coal, oil, and natural gas, which release billions of tons of carbon dioxide into the atmosphere each year.

[0003] Numerous technologies have been developed to reduce emissions from industrial plants, particularly carbon dioxide (CO2) emissions. CO2 capture means separating CO2 from the remaining flue gas from industrial plants, rather than releasing it into the atmosphere. Several methods can be used to capture CO2 from coal-fired plants. Post-combustion technologies separate CO2 from flue gas after a conventional combustion process. The main advantage of this technology is that the combustion process at the power plant remains unchanged, allowing the process to be implemented in existing power plants. A process using ammonia as a solvent and operating at low temperatures (2°C–10°C), also known as cryogenic ammonia carbon capture (CAP), has been developed. This process offers several advantages, including: i) low cost and high availability of the required solvent, ii) a chemically stable solution, iii) regeneration under medium pressure, and iv) high CO2 carrying capacity.

[0004] WO2006022885 discloses the use of refrigerated ammonia to capture carbon dioxide. The purpose of this process is to absorb carbon dioxide at low temperatures, particularly in the temperature range of 0°C to 20°C, preferably 0°C to 10°C. The corresponding cooling task is typically assigned to cooling facilities, such as cooling water or refrigeration systems. The actual configuration depends on the actual availability of cooling facilities, their capacity, and the supply temperature.

[0005] First, the flue gas entering the refrigerated ammonia process is treated in a reactor to remove contaminants, and then cooled in multiple heat exchangers. The cooled flue gas enters a CO2 capture section, which consists of an absorber and a desorber operating at high pressure (typically 21 bar). The flue gas enters the bottom of the absorber and comes into countercurrent contact with a lean CO2 stream from the bottom of the desorber and into the top of the absorber. This lean CO2 stream consists primarily of water and ammonia, containing a small amount of carbon dioxide. The carbon dioxide in the flue gas is absorbed by the ammonia in the absorber. The low temperature in the absorber prevents ammonia evaporation and enhances the mass transfer of CO2 into the solution. According to WO2006022885, more than 90% of CO2 can be captured from the flue gas.

[0006] The purified gas stream exits from the top of the absorber, while the CO2-rich stream exits from the bottom and is pumped to a heat exchanger for heating before being sent to the desorber. Inside the desorber, CO2 is separated from the solution and exits the top of the desorber as a relatively clean and high-pressure stream. According to WO2006022885, a condenser is installed at the top of the desorber to separate water vapor and ammonia contained in the CO2 stream and recycle them back to the desorber. The lean CO2 stream exits the bottom of the desorber and is directed to an air cooler, then to the top of the absorber to absorb CO2 from the flue gas. The desorption reaction is endothermic, and the energy required depends largely on the composition of the CO2-rich stream entering the desorber. The heat required for desorption is typically provided by a steam pressure of approximately 8 bar absolute and a temperature of 175°C.

[0007] As mentioned earlier, the refrigerated ammonia carbon capture process generates waste heat, which needs to be discharged into a cooling or refrigeration system. On the other hand, the CAP process also requires heat to support the desorption reaction. In many cases, the CAP's main unit is not configured to supply heat and cooling to the CAP system. Therefore, to make the CAP as independent as possible, an electrically driven heating and cooling system needs to be added to the system. However, this solution implies additional complexity, higher costs, and undesirable CO2 emissions.

[0008] Therefore, improved systems and methods for operating the refrigerated ammonia carbon capture process to address the complexity, cost, and CO2 emissions of current technologies would be beneficial and would be popular in this technology. Summary of the Invention

[0009] In one aspect, the subject matter disclosed herein relates to a refrigeration system for ammonia-based carbon capture (CAP) process incorporating a heat pump, wherein the waste heat of this refrigeration system is used to evaporate a fluid (i.e., water), which can be compressed to a higher pressure / temperature level, up to a value that enables the supply of heat to the desorber of the CAP. Therefore, the object of this disclosure is to “upgrade” a portion of the waste heat from the CAP to provide the heating required in the ammonia-based refrigeration process. Specifically, the disclosed solution is capable of generating the steam heat required for desorption in the CAP. Attached Figure Description

[0010] When considered in conjunction with the accompanying drawings, the embodiments disclosed in this invention and their many accompanying advantages will become better understood by referring to the following detailed description, thereby readily providing a more comprehensive understanding of them, wherein:

[0011] Figure 1 A process flow diagram is shown that combines the refrigeration system with a heat pump in a cryogenic ammonia carbon capture system according to an exemplary embodiment. Detailed Implementation

[0012] Reference will now be made in detail to one embodiment of this disclosure, which is interpreted by way of explanation rather than limitation thereof. Figure 1 As shown in the figure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this disclosure without departing from its scope or substance. Throughout this specification, references to “an embodiment”, “an embodiment”, or “some embodiments” mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the disclosed subject matter. Therefore, the phrases “in one embodiment”, “in an embodiment”, or “in some embodiments” appearing in various places throughout the specification do not necessarily refer to the same embodiment. Furthermore, in one or more embodiments, a particular feature, structure, or characteristic may be combined in any suitable manner.

[0013] When describing the elements of various implementation schemes, the articles “a,” “an,” “the,” and “the” are intended to refer to one or more of the elements present. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that additional elements may exist in addition to those listed.

[0014] refer to Figure 1 A block diagram is shown showing the combination of a multi-stage refrigeration system 50 and a steam heat pump system 10 in a refrigerated ammonia carbon capture system (hereinafter referred to as CAP system) 30 according to the present invention.

[0015] The CAP system 30 includes multiple reboilers 31 and multiple coolers 32, 32', 32'', for example, a first cooler 32 that typically operates at a higher temperature, usually between 35°C and 45°C, a second cooler 32' that operates at an intermediate temperature, and a third cooler 32'' that typically operates at a lower temperature, usually between 20°C and 27°C. Heat from the coolers is transferred through pipeline Q. P Q P ', Q P ''Recycle.

[0016] The multi-stage refrigeration system 50 consists of three refrigeration thermodynamic cycles 50', 50'', and 50''', which carry away the low-temperature waste heat Q generated from the CAP system 30. P The working fluid (preferably ammonia) is compressed to a higher pressure and temperature, and ultimately exchanges heat Q with water in the evaporator 11 of the heat pump system 10 in the condenser 59 at the end of the refrigeration system 50. A The condensation system consists of three interconnected heat cycles 10', 10'', and 10'''. Figure 1 The number of refrigeration thermodynamic systems and the number of cycles are given in an explanatory manner, but it will be apparent to those skilled in the art that both the number of refrigeration thermodynamic systems and the number of cycles can vary independently of each other depending on the operating parameters of the CAP system 30, the working fluid, and the possible auxiliary heat sources and / or heat loads connected to the system, as will be disclosed below.

[0017] For more details, see the reference. Figure 1 Heat Q from CAP system 30 PThe vapor flow from the evaporator 51 is delivered to the refrigeration system 50, which evaporates the working fluid of the first refrigeration thermodynamic cycle 50' of the refrigeration system 50 from the liquid phase to the gas phase at a first temperature and pressure. The vapor flow from the evaporator 51 is directed to the compressor 52' ​​driven by the electric motor 53' to be compressed to a second temperature and pressure higher than the first temperature and pressure. The compressed flow is directed to the economizer 55', where it mixes with a flow expanding in the valve 56'', which originates from the second refrigeration thermodynamic cycle 50'' operating at a higher temperature and pressure. The liquid from the economizer 55' is directed to the expansion valve 56' and the evaporator 51, while the vapor flow at the second temperature and pressure is directed to the compressor 52'' of the second refrigeration thermodynamic cycle 50'' driven by the electric motor 53'' to be compressed to a third temperature and pressure higher than the second temperature and pressure. The compressed flow is directed to the economizer 55'' of the second refrigeration thermodynamic cycle 50'', where it mixes with a flow expanding in valve 56''' from the third refrigeration thermodynamic cycle 50''', which operates at a higher temperature and pressure. This mixed flow is directed to expansion valve 56'' and the economizer 55' of the first refrigeration thermodynamic cycle 50'', while the vapor flow at the third temperature and pressure is directed to compressor 52''' of the third refrigeration thermodynamic cycle 50''', driven by electric motor 53''', to be compressed to a fourth temperature and pressure higher than the third temperature and pressure. Then, as will be described below, the compressed flow is directed to condenser 59 for condensation, and subsequently to expansion valve 56''' of the third refrigeration thermodynamic cycle 50''' and the economizer 55'' of the second refrigeration thermodynamic cycle 50'''.

[0018] Still referencing Figure 1 A portion of the flow from compressor 52' ​​of the first refrigeration thermodynamic cycle 50' may optionally be directed to evaporative condenser unit 57', which exchanges heat with a mixed flow of flue gas condensate and makeup water from the CAP to remove excess heat from the first refrigeration thermodynamic cycle 50' via a portion of the condensate vapor flow. Evaporative condenser unit 57' has two functions: discharging unwanted excess heat from an optional district heating unit 58 installed downstream of the refrigeration system 50, as described below, and concentrating flue gas condensate from the CAP to reduce the load on the wastewater treatment plant.

[0019] In addition, always refer to Figure 1The second refrigeration cycle 50'' (or other refrigeration cycles of the refrigeration system 50) may be equipped with a district heating unit 58, which receives a portion of the compressed flow from the compressor 52'' to distribute excess heat from the second refrigeration cycle 50'' to other locations / systems, i.e., residential users, via an insulated pipe system. Due to space requirements, the evaporator-condenser unit 57 and the district heating unit 58 can be omitted from the refrigeration system 50 by releasing the discharged heat into the atmosphere. Therefore, the district heating unit 58 can provide additional financial revenue according to the system requirements of this disclosure.

[0020] With the aid of condenser unit 59, a certain amount of heat Q can be exchanged between refrigeration system 50 and heat pump system 10 through evaporator 11 of the first heat pump 10' of heat pump system 10. A Within the evaporator 11, the working fluid (preferably water) of the heat pump system 10 evaporates at a first heat pump temperature, higher than the temperature of the third refrigeration thermodynamic cycle 50''', and is subsequently directed to a compressor 12' driven by an electric motor 13', to be compressed to a second heat pump temperature and pressure higher than the first heat pump temperature and pressure. The compressed vapor stream is directed to an economizer 15', where the compressed stream mixes with the stream expanding in the expansion valve 16'' of the second heat pump 10'' operating at a higher temperature and pressure, and is subsequently directed to the expansion valve 16' and returned to the evaporator 11, while the vapor stream at the second heat pump temperature and pressure is directed to the compressor 12'' of the second heat pump 10'', driven by the electric motor 13'', to be compressed to a third heat pump temperature and pressure higher than the second heat pump temperature and pressure. The compressed flow is directed to the economizer 15'' of the second heat pump 10'', where it mixes with the expanded flow in the expansion valve 16''' of the third heat pump 10''', which operates at a higher temperature and pressure, and is subsequently directed to the expansion valve 16'' and the economizer 15'' of the first heat pump 10', while the vapor flow at the temperature and pressure of the third heat pump is directed to the compressor 12''' of the third heat pump 10''', driven by the electric motor 13''', to be compressed to a fourth heat pump temperature and pressure higher than the third heat pump temperature and pressure. As will be described below, the compressed flow is then directed to the temperature-regulating condenser 17 and the CAP reboiler 31 (in... Figure 1 In this system, the reboiler 31 is represented as part of the heat pump system 10 and the CAP system 30 (and is connected via a pipeline 31') for condensation, and after being collected in the condensate receiver unit 19, it is directed to the expansion valve 16''' of the third heat pump 10''' and the economizer 15'' of the second heat pump 10'''.

[0021] Specifically, the heat obtained by the heat pump system 10 through the CAP reboiler 31 is exchanged with the CAP system 30, thereby achieving the purpose of the present invention to provide heat to the CAP system 30 without the need for an additional electrically driven heating and cooling system, thus reducing the complexity, cost and carbon dioxide emissions of the system.

[0022] Optionally, the steam heat pump system 10 includes various steam input / output transmission devices 11', 11'', 11''', 14', 14'', 14''', 17', and 18', operating at different temperatures and pressures depending on the main unit's conditions and requirements. Specifically, the steam input reduces the steam generation compression power. On the other hand, if there are low-pressure steam users, the generated steam can be delivered to these users, and the steam output can provide additional financial revenue. If the low-pressure steam can be generated by combustion in other ways, this can save fuel consumption.

[0023] refer to Figure 1 Steam output conduction devices 11', 11'', 11''', and 17' can be installed: from the inlet of compressor 12' to the outlet of expansion valve 16' of the first heat pump 10' and / or from the inlet of compressor 12'' to the outlet of expansion valve 16'' of the second heat pump 10'' and / or from the inlet of compressor 12''' to the outlet of expansion valve 16''' of the third heat pump 10''' and / or from the outlet of compressor 12''' to the inlet of condensate receiver 19, connected in parallel with temperature-controlled condenser 17 and CAP reboiler 31. Superheating (SH) of the steam flow is achieved through heat transfer from subcooling (SC) of the liquid flow from the economizer. Superheated steam is typically required to address heat losses to the corresponding steam users in the steam pipeline.

[0024] The steam input transfer device 14' may optionally be arranged along a recirculation line that connects the outlet of the subcooled section of the economizer 15' to the inlet of the suction cylinder 15 of the compressor 12' in the corresponding heat pump 10', and this line is connected in parallel with the line that passes through the expansion valve 16' and the evaporator 11.

[0025] The steam input transfer device 14'' can optionally be arranged along a recirculation line connecting the outlet of the subcooled section of the economizer 15'' to the inlet of the economizer 15'' of the compressor 12'' in the corresponding heat pump 10'', and this line is connected in parallel with the line passing through the expansion valve 16''. Finally, two additional steam input transfer devices 14''', 18' can be arranged along a line downstream of the condensate receiver unit 19 according to this disclosure. Specifically, the steam input transfer device 14''' connects the outlet of the condensate receiver 19 to the inlet of the economizer 15'' of the second heat pump 10'', and is connected in parallel with the line passing through the expansion valve 16''', while the steam input transfer device 18' is arranged along a line connecting the outlet of the condensate receiver 19 to the outlet of the compressor 12''' of the third heat pump 10''' (along which a pump is required).

[0026] While various aspects of the invention have been described with reference to specific embodiments, it will be apparent to those skilled in the art that numerous modifications, variations, and omissions are possible without departing from the spirit and scope of the claims.

Claims

1. A refrigerated ammonia carbon capture system (30) comprising a refrigeration system (50) and a heat pump system (10), the heat pump system (10) comprising a plurality of thermal cycles (10', 10'', 10'''), each heat pump operating at a temperature and pressure higher than that of an upstream heat pump, wherein the refrigeration system (50) is coupled to the heat pump system (10) via an evaporator (11), wherein heat from the refrigeration system (50) is used to evaporate the working fluid of a low-temperature thermal cycle (10') of the heat pump system (10), the thermal cycle (10', 10'', 10''') being configured to use water as the working fluid to obtain high-temperature, high-pressure steam, thereby providing heat to the refrigerated ammonia carbon capture system (30).

2. The cryogenic ammonia carbon capture system (30) according to claim 1, wherein the cryogenic ammonia carbon capture system (30) comprises: The CO2 capture section comprises an absorber and a desorber, wherein the absorber is configured to absorb carbon dioxide from a CO2-poor solution consisting mainly of water and ammonia, and the desorber is configured to separate CO2 from the solution. A condenser is disposed on top of the desorber to separate water vapor and ammonia contained in the CO2 stream and recycle them to the desorber. The thermal cycle (10', 10'', 10''') is configured to use water as the working fluid to obtain high-temperature, high-pressure steam, thereby providing heat to the desorber of the refrigerated ammonia carbon capture system (30).

3. The refrigerated ammonia carbon capture system (30) according to claim 1 or 2, wherein the refrigeration system (50) comprises a plurality of refrigeration thermodynamic cycles (50', 50'', 50'''), each refrigeration thermodynamic cycle operating at a temperature and pressure higher than that of the upstream refrigeration thermodynamic cycle.

4. The refrigerated ammonia carbon capture system (30) according to claim 3, wherein one or more heat exchangers are coupled to any one of the plurality of refrigeration thermodynamic cycles (50', 50'', 50''') to provide heat to external services.

5. The refrigerated ammonia carbon capture system (30) according to claim 4, wherein the external service includes district heating.

6. The refrigerated ammonia carbon capture system (30) according to any one of the preceding claims, wherein one or more heat exchangers are coupled to any one of the plurality of heat cycles (10', 10'', 10''') to provide heat to an external service.

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