A carbon capture system and a method for carbon capture

Abstract

A carbon capture system (1) comprising an absorption unit (3), a desorption unit (5), a solvent capable of absorbing / desorbing carbon dioxide, a solvent heating unit (10), and a heat pump system (20) comprising a refrigerant recirculation flow line (22), and in refrigerant flow line order, a condenser (21), a depressurization section (24), an evaporator (25), and a compression section (26a, 26b), wherein the condenser (21) is arranged to transfer heat to the solvent heating unit (10). The heat pump system (20) further comprises a desuperheating heat exchanger (30) arranged at a point between the compression section (26a, 26b) and the condenser (21) with reference to the refrigerant flow line order, the desuperheating heat exchanger (30) being arranged to transfer heat from a refrigerant in the refrigerant recirculation flow line (22) to a desuperheating fluid flow (43a, 43b) arranged to flow to and from the desuperheating heat exchanger (30).

Description

A CARBON CAPTURE SYSTEM AND A METHOD FOR CARBON CAPTURETECHNICAL FIELD

[0001] The present disclosure relates to a carbon capture system and a method for carbon capture.BACKGROUND ART

[0002] Post Combustion Carbon Capture (PCCC) is an energy intensive process, but one that is essential in order to decarbonize other energy intensive industrial processes, such as power production from natural gas or other fossil fuels, cement and steel production, various petrochemical or oil refining processes, or waste incineration.

[0003] In a typical PCCC process, a flue gas containing carbon dioxide, COz, is contacted in an absorber column with a COz-absorbing solvent, such as an aqueous amine solution, removing the CO2 from flue gas. The COz-rich solvent is then regenerated in a second column, a desorber. In the desorber the rich solvent is distributed onto a packed structure and circulated downwards in the desorber, thereby desorbing CO2 from the solvent. Gaseous CO2 is allowed to leave at the top of the desorber. In a dedicated reboiler, nearby the desorber, heat is applied to (re)boil lean solution leaving the desorber, so to generate stripping vapour, which vapour is supplied at the desorber bottom and allowed to flow upwards across the packed structure in the desorber. The fraction of stripping vapour that has not condensed along the packing is mixed with gaseous CO2. The lean solvent, containing lesser amounts of CO2, is recycled from the bottom of the desorber back to the top of the absorber, typically allowing heat transfer between the lean and rich solvent streams, to repeat the process.Various heat integration solutions may be applied in order to reduce the net import of thermal energy required to regenerate the solvent.

[0004] The thermal energy required at the reboiler is typically provided by (utility) steam provided at a pressure level that depends on the required desorber operating pressure. There are different ways of obtaining utility steam. It may for example be extracted from the parent plant (e.g. from / between turbine stages of a power or cogeneration plant) or be generated by recovering heat from the production process, if suitable high temperature heatis available (e.g. hot gas streams in cement plants). Steam may also be generated with dedicated heating utilities, such as high temperature heat pumps (HTHPs), electric boilers, etc. The most energy efficient solution for providing utility steam depends on the characteristics of the parent plant, and on the case-specific characteristics.

[0005] In applications where steam is not directly generated to operate the production process, no utility steam can be directly withdrawn when adding a PCCC system. A clear example is the cement industry. Steam for the PCCC system could then be generated by a mix of high temperature heat recovery from the production process, if available, internal PCCC plant open-circuit heat pumping and / or dedicated energy utilities

[0006] HTHPs are the most promising candidates for efficiently electrifying the PCCC plant regeneration process, and especially for applications lacking steam from the parent plant. The profitability and energy efficiency of HTHPs and the carbon capture system comprising such a HTHP depend on the associated investment costs, electricity prices, and on the HTHP energy efficiency.SUMMARY OF THE INVENTION

[0007] Post Combustion Carbon Capture (PCCC) is an energy intensive process, but one that is essential in order to decarbonize other energy intensive industrial processes, such as power production from natural gas or other fossil fuels, cement and steel production, various petrochemical or oil refining processes, or waste incineration. It is an object of the present disclosure to provide an energy efficient PCCC system. A further object is to provide a method for energy efficient carbon capture.

[0008] The invention is defined by the appended independent patent claims. Nonlimiting embodiments emerge from the dependent patent claims, the appended drawings and the following description.

[0009] According to a first aspect there is provided a carbon capture system comprising an absorption unit provided with a flue gas inlet and a flue gas outlet, a desorption unit provided with a carbon dioxide outlet, a solvent capable of absorbing carbon dioxide at a lower temperature and desorbing carbon dioxide at a higher temperature, a recirculation arrangement for recirculating the solvent between the absorption unit and the desorption unit via lean solvent and rich solvent lines, and a solvent heating unit arranged to heat solvent containing carbon dioxide so as to desorb carbon dioxide from the solvent. The carboncapture system comprises a heat pump system comprising: a refrigerant recirculation flow line, and in refrigerant flow line order, a condenser, a depressurization section, an evaporator, and a compression section, wherein the condenser is arranged to transfer heat to the solvent heating unit, wherein the heat pump system further comprises a desuperheating heat exchanger arranged at a point between the compression section and the condenser with reference to the refrigerant flow line order, the desuperheating heat exchanger being arranged to transfer heat from a refrigerant in the refrigerant recirculation flow line to a desuperheating fluid flow arranged to flow to and from the desuperheating heat exchanger.

[0010] The desuperheating fluid can be either a process fluid of the carbon capture plant or another fluid flow requiring heating, e.g. district heating water flow.

[0011] The carbon capture system may be arranged to contact incoming flue gas with the solvent in the absorption unit at a temperature allowing the solvent to absorb carbon dioxide from the flue gas, forming a rich solvent, feed flue gas from which carbon dioxide has been absorbed through the flue gas outlet, feed the rich solvent to the desorption unit via the rich solvent line and heat the rich solvent so as to desorb carbon dioxide from the rich solvent, forming a lean solvent. The lean solvent may be transported to the absorption unit via the lean solvent line. The released carbon dioxide may be fed through the carbon dioxide outlet of the desorption unit. The system comprises the heating unit arranged to heat solvent (lean / rich / intermediate solvent) containing carbon dioxide so as to provide stripping vapour for desorption of carbon dioxide in the desorption unit. The heating unit makes the solvent slightly leaner than at a point of extraction from / in the desorption unit, but the vast majority of desorption takes place in a packing in the desorption unit.

[0012] In the heat pump system, the recirculating refrigerant is evaporated, heated, and compressed. A high-temperature and high-pressure medium exits the compression section and the desuperheating heat exchanger (DSH) desuperheats the compressed refrigerant, possibly down to saturated conditions. After heat exchange in the condenser, the refrigerant is depressurized and entered into the evaporator to complete the heat exchange cycle. In a rough example, the refrigerant, for example HFO (hydrofluoro-olefin), would operate with low-pressure level at 2 bar, intermediate-pressure level at 6 bar and high-pressure level at 18 bar and consequently a high-temperature around 128 °C. Some refrigerants, such as hydrocarbons, would operate with low-pressure level at 1 bar, intermediate-pressure level at 3 bar and high-pressure level at 9 bar. Ammonia is also another refrigerant of interest,however limited by a lower critical temperature than the abovementioned example, and higher operation pressures.

[0013] By using a DSH, as defined above, it is possible to limit the maximum temperature at which the solvent used in the carbon capture process is exposed to when exchanging heat with the refrigerant in the condenser, hence reducing its thermal degradation. . The refrigerant is cooled in the DSH before entering the condenser. The heat transferred from the refrigerant to the desuperheating fluid flow arranged to flow from the DSH may be used for heating of other parts of the carbon capture system or to heat a fluid in a heating system external of the carbon capture system, i.e. there is heat recovery. This is required to reuse the high temperature heat from the DSH, hence maintaining the heat pump energy efficiency.

[0014] The profitability of heat pump systems depends on the associated investment costs, electricity prices, and very importantly on the heat pump system energy efficiency, typically expressed by the heating Coefficient of Performance (COP), which is defined as the ratio of useful heat provided by the heat pump system and corresponding heat pump system electricity consumption. The maximum achievable COP is mostly dependent on the heat pump system operating temperature levels (refrigerant evaporation and condensation temperatures), on the thermo-physical properties of the selected refrigerant, and on the heat pump system cycle configuration.

[0015] If there is a direct contact between the condenser and the solvent heating unit, meaning the condenser is or is integrated with the solvent heating unit, there is no intermediate steam circuit between the condenser and the heating unit. By means of the DSH, the maximum temperature of the refrigerant entering into the condenser may be reduced to minimize / reduce thermal degradation of the solvent in the condenser / heating unit (depending on refrigerant temperature at the compression section discharge and solvent characteristics).

[0016] Heating units, reboilers, may be of the kettle type, so they accept an overflow of liquid that is slightly heated and that is returned to the desorption unit sump or directly sent to a lean / rich heat exchanger arranged in the lean solvent / rich solvent lines. Specific plate reboilers can also be used instead of the kettle type, with different hydraulic considerations to ensure solvent circulation.

[0017] The depressurization section of the heat pump system may include one or more pressure reducing members, such as throttling valves, expanders, ejectors, thermal compressors, a flash vessel, etc.

[0018] At least a portion of the desuperheating fluid flow may comprise a process fluid stream arranged to circulate in the carbon capture system.

[0019] Such process fluid stream from the carbon capture system may include e.g. a fluid stream from the desorption unit, a fluid stream from a heat exchanger arranged to heat flue gas before entering the absorption unit, etc.

[0020] The process fluid stream may be arranged to circulate from and to the desorption unit.

[0021] The process fluid may be water from a water wash section arranged in the desorption unit. The process fluid may be exited / entered at an upper or lower portion of the desorption unit.

[0022] At least a portion of the desuperheating fluid flow from the desuperheating heat exchanger may be arranged to heat refrigerant in the heat pump system at a point between the condenser and the evaporator with reference to the flow line order.

[0023] Such a point may be a flash vessel heat exchanger arranged along the refrigerant flow line.

[0024] In one embodiment the condenser may be integrated with the solvent heating unit.

[0025] In such case, there is a direct contact between the solvent heating unit and the condenser and no intermediate circuit between these components. The condenser is arranged to transfer heat directly to the solvent heating unit, i.e. the condenser is the solvent heating unit. The system may then supply for, as discussed above, a reduced solvent thermal degradation.

[0026] In an alternative embodiment, the condenser is arranged to be in heat exchangeable connection with the solvent heating unit via an intermediate fluid flow.

[0027] At least a portion of the intermediate fluid flow may be a process fluid stream arranged to circulate in the carbon capture system.

[0028] By using such process fluid stream / vapor in the intermediate fluid flow to transfer heat from the condenser to the heating unit instead of using a fluid flow external tothe carbon captures system, there is an energy efficient improvement, i.e. an increase in the COP of the system.

[0029] The process fluid flow may be e.g. a fluid stream from the desorption unit, a fluid stream from a heat exchanger arranged to heat flue gas before entering the absorption unit, etc.

[0030] The carbon capture system may further comprise a solvent recirculation flow line arranged to recirculate solvent from and back to the desorption unit, wherein the solvent heating unit may be arranged to heat solvent flowing in the solvent recirculation flow line.

[0031] In such a configuration the solvent heating unit is arranged outside the desorption unit. The solvent recirculation flow line may be arranged to recirculate solvent from and back to the desorption unit at a bottom section thereof.

[0032] The solvent recirculation flow line may comprise a depressurizer arranged to reduce the pressure of the solvent before it reaches the heating unit and a pressurizer arranged to increase the pressure of the solvent after it has been heated in the heating unit and before it flows back into the desorption unit.

[0033] Such (lean) solvent recirculation may be used to increase solvent vapor pressure from heating unit pressure to desorption unit pressure. The pressurizer may here e.g. be a centrifugal blower

[0034] The heat pump system may comprise a refrigerant heat exchanger that may be arranged at a point upstream of the desuperheating heat exchanger and downstream of the evaporator with reference to the refrigerant flow line order.

[0035] The compression section of the heat pump system may comprise at least a first and a second compression stage arranged in series.

[0036] The compression section may comprise at least two compression stages / stages of compression, the compression stage being arranged to increase the pressure of the refrigerant. The essential function of a multi-stage compression section is to increase the overall pressure from input to output, one stage at a time. A compression stage may be any form of compression stage. Multiple stages of compression are more efficient in their ability to compress the refrigerant to the final output than the performance capability of only a single stage, also by allowing different refrigerant flow rates in each stage.

[0037] The compression section comprises at least a first and second compression stage arranged in series. The compression section may comprise at least two or at least three or atleast four compression stages arranged after each other with reference to the refrigerant flow line order. The number of compression stages used is mostly dictated by the selected compression technology, refrigerant and the temperature lift given by the available heat source and the required heating temperature.

[0038] The last compression stage of the compression section, with reference to the refrigerant flow line order, may be a high-pressure compression stage. The other compression stage(s) of the compression section may be lower-pressure compression stages. A high- pressure / medium-pressure / low-pressure compression stage is a qualitative measure of the pressure level and is dependent on the refrigerant operating pressure range. For the same temperature lift between heat source and heat sink (in one example a temperature lift from 65°C to 125°C), different refrigerants can be used, each with a different operating pressure range.

[0039] The refrigerant heat exchanger may be arranged upstream of the second compression stage and downstream of the first compression stage, with reference to the refrigerant flow line order.

[0040] Its role is to increase the refrigerant temperature at the suction of the second compression stage, hence, the compression stage discharge temperature. If there are more than two compression stages in the series of compression stages in the heat pump system, the heat exchanger may be placed between any two of the compression stages. The compression stage / one of the compression stages arranged upstream of the refrigerant heat exchanger is the second compression stage. The compression stage / one of the compression stages arranged downstream of the refrigerant heat exchanger is the first compression stage.

[0041] Placing the superheating, the refrigerant heat exchanger, downstream of the first compression stage and upstream of the second compression stage, can be beneficial for improving the COP. If there are three or more compression stages in the compression section, the heat exchanger should preferably be placed between the two last compression stages, as seen in the refrigerant flow line order, to increase the COP benefit. By heating the refrigerant, by means of the refrigerant heat exchanger, the mass flow rate of refrigerant flowing in the second compression stage is reduced, to provide the same heating load at the condenser, while the compression specific power consumption (kWh / kg refrigerant compressed) and the refrigerant flow rate at the first compression stage might increase. The magnitude of thesechanges and their combined effect, potentially positive for increasing the COP, depend mostly on selected refrigerant, compression section design and operating conditions.

[0042] The heat exchanger provides for vapor / gas with higher temperatures at the compressor discharge and so reduces the refrigerant flow rate required to be compressed for a given amount of process heating provided at the condenser / reboiler.

[0043] For a simulated case with two compression stages and a heat exchanger placed between the two compression stages, using refrigerant R1233zd(e) at relevant operating conditions for Post Combustion Carbon Capture plants, the COP is found to improve by approx. 5%, as compared to a heat pump system with two compression stages but no refrigerant heat exchanger between the stages. The size of the COP improvement may depend on the refrigerant used, the cycle configuration and operating conditions (condensation pressure, intermediate pressure, evaporation pressure).

[0044] The heat exchanger may be placed as far downstream as possible in the compression section, with reference to the refrigerant flow line order, i.e. as high as possible in pressure-level. Thereby, the suction temperature of the last compression stage may increase.

[0045] Increasing the number of compression stages in the compression section could increase the COP, but may result in higher investment cost, footprint and operational complexity.

[0046] The heat source fluid flow arranged to flow to and from the refrigerant heat exchanger and transfer heat to the refrigerant could be a suitable external heat source, such as e.g. a particularly high temperature flue gas, such as above 100 °C, from a plant in which the carbon capture system arranged for removing carbon dioxide from a flue gas is integrated. In this case the refrigerant heat exchanger may be considered an external heat exchanger.

[0047] Alternatively, the heat source fluid flow arranged to flow to and from the refrigerant heat exchanger and transfer heat to the refrigerant may be an internal warm / hot fl uid / gas, such as for example a redirected portion of said refrigerant flowing in the refrigerant flow line. In such case, the heat exchanger may be considered an internal heat exchanger.

[0048] Using only one compression stage with a heat exchanger arranged upstream of this compressor stage, the refrigerant can be made to enter superheated into the compression stage, thereby avoiding the risk of formation of liquid refrigerant during the compression. The amount of superheating is often no more than what is needed to avoid that effect.

[0049] The refrigerant heat exchanger of the heat pump system may further be connected to the refrigerant flow line at a point between the condenser and the evaporator with reference to the flow line order, such that at least a portion of the refrigerant flow is directed towards the refrigerant heat exchanger, so as to form at least a portion of a heat source fluid flow arranged to flow to and from the refrigerant heat exchanger.

[0050] In this case, the refrigerant heat exchanger is being heated with an internal heat source and is an internal heat exchanger. Preferably, the refrigerant downstream or immediately downstream of the heat pump condenser is directed towards the heat exchanger as the heat source. The heat exchanger may be connected to the refrigerant flow line at a point between the condenser and the depressurization section.

[0051] The depressurization section may comprise at least a first pressure reducing member, and wherein the refrigerant heat exchanger may be connected to the refrigerant flow line at a point between the condenser and the at least a first pressure reducing member with reference to the refrigerant flow line order.

[0052] The pressure reducing member may be a throttling valve, an expander, ejector, thermal compressor etc. The refrigerant heat exchanger may be connected to the refrigerant flow line at a point between the condenser and the pressure reducing member, with reference to the refrigerant flow line order. The pressure reducing member reduces pressure and consequently temperature of the refrigerant, thereby reducing the potential for superheating of refrigerant at compression stage suction via the refrigerant heat exchanger.

[0053] The depressurization section may comprise at least a first pressure reducing member and a flash vessel arranged downstream the first pressure reducing member and upstream the evaporator, with reference to the refrigerant flow line order, wherein the flash vessel further may be connected to the refrigerant flow line at a point between the evaporator and the desuperheating heat exchanger with reference to the refrigerant flow line order, allowing a portion of the refrigerant flow to flow from the flash vessel to the point between the evaporator and the desuperheating heat exchanger.

[0054] The flash vessel may be arranged downstream the first pressure reducing member and upstream a second pressure reducing member, with reference to the refrigerant flow line order.

[0055] In the flash vessel, the refrigerant flow downstream the first pressure reducing member separates into a gas phase at the flash vessel top and a liquid phase at the flashvessel bottom. Gaseous refrigerant from the flash vessel is allowed to flow to the refrigerant flow line at a point before or after the heat exchanger with reference to the refrigerant flow line order. Liquid refrigerant from the flash vessel may be circulated to the pressure reducing member arranged downstream the flash vessel and upstream of the evaporator.

[0056] When the flash vessel is used, a synergy with the refrigerant heat exchanger may be that the flashed gas mixes with superheated vapor before or after the refrigerant heat exchanger, reducing the suction temperature of the compression stage arranged downstream the refrigerant heat exchanger.

[0057] A flash vessel heat exchanger may be arranged in association with the flash vessel, wherein the flash vessel heat exchanger may be arranged to heat liquid refrigerant in or from the flash vessel by transferring heat to the refrigerant in the refrigerant recirculation flow line from a flash vessel heat source flow arranged to flow to and from the flash vessel heat exchanger.

[0058] At least a portion of the flash vessel heat source flow may be a process fluid stream arranged to circulate in the carbon capture system.

[0059] The heat source for the flash vessel heat source flow may be from various parts of the plant in which the system is integrated. The heat source may e.g. be from a first cooling step of desorber overhead vapor or from a desorber water wash stream. The purpose with the flash vessel heat exchanger associated with the flash vessel is to reduce the amount of refrigerant circulating in the compression stage(s) and the evaporator of the heat pump system. The flash vessel heat exchanger associated with the flash vessel may enhance the heat pump system. The refrigerant pressure in the flash vessel may be adjusted to increase the amount of heat provided by the heat source, so as to maximize the COP increase. In one example, with a R1233zd(e) refrigerant, a COP increase of 6% is predicted.

[0060] At least a portion of the flash vessel heat source flow may comprise at least a portion of the desuperheating fluid flow.

[0061] That the flash vessel is associated with a heat exchanger is here meant that the flash vessel may comprise an internal heat exchanger or be connected to an external heat exchanger arranged downstream of the flash vessel. With an external heat exchanger part of the liquid refrigerant leaving the flash vessel bottom is vaporized, and at a position in the refrigerant flow line it is mixed with vapour leaving the flash vessel top.

[0062] The heat pump system may further comprise a subcooler arranged at a point between the condenser and the depressurization section with reference to the refrigerant flow line order, the subcooler being arranged to transfer heat from refrigerant in the refrigerant recirculation flow line to a subcooling fluid flow arranged to flow to and from the subcooler.

[0063] By including a subcooler (SC) in the heat pump system at a point between the condenser and the depressurization section with reference to the refrigerant flow line order, high pressure hot refrigerant can be used to provide useful process heating to the carbon capture system, before the refrigerant is being sent to the heat exchanger. The "high pressure" depends on the refrigerant used. The temperature may in one example be about 125 °C.

[0064] At least a portion of the subcooling fluid flow may be a process fluid stream arranged to circulate in the carbon capture system.

[0065] At least a portion of the desuperheating fluid flow is arranged to heat a fluid in a heating system external of the carbon capture system.

[0066] Alternatively, or in addition, wherein at least a portion of the desuperheating fluid flow is arranged to heat a fluid forming part of the carbon capture system.

[0067] According to a second aspect there is provided a method for operating a carbon capture system described above, the method comprising: heating, in the heating unit, the solvent containing carbon dioxide so as to release carbon dioxide from said solvent, operating the heat pump system so as to provide heat to the heating unit via the condenser, feeding the desuperheating fluid flow to the desuperheating heat exchanger so as to transfer heat from the refrigerant flowing in the refrigerant recirculation flow line to the desuperheating fluid flow.BRIEF DESCRIPTION OF THE DRAWINGS

[0068] Fig. 1 shows a simplified sketch of an example of a carbon capture system. The system comprising an absorption unit with a flue gas inlet and outlet, a desorption unit, a recirculation arrangement for recirculating carbon dioxide absorbing solvent between the absorption unit and the desorption unit, a solvent heating unit, and a heat pump system with a condenser arranged to transfer heat to the solvent heating unit.

[0069] Fig. 2 shows part of the carbon capture system of Fig. 1 with a more detailed view of the heat pump system. The heat pump system comprising a refrigerant flow line with recirculating refrigerant, and in refrigerant flow line order, a condenser (arranged to be in connection with the solvent heating unit), a depressurization section, an evaporator, a compression section, and a desuperheating heat exchanger. The heat pump system further comprises a refrigerant heat exchanger, a subcooler and a flash vessel (with internal heat exchanger).

[0070] Fig. 3 shows the system of Fig. 2, wherein the flash vessel is provided with an external heat exchanger instead of an internal heat exchanger.

[0071] Fig. 4 shows the system of Fig. 2, and a process fluid stream arranged to circulate in the carbon capture system. The process fluid stream being arranged to be in heat exchangeable connection with the refrigerant at a few points in the heat pump system.

[0072] Fig. 5 shows the system of Fig. 2, wherein the heat pump system further comprises a solvent recirculation flow line arranged to recirculate solvent from / to the desorption unit, wherein the solvent heating unit is arranged to heat solvent flowing in the solvent recirculation flow line.

[0073] Fig. 6 shows the carbon capture system of Fig. 5, wherein the condenser is arranged to be in heat exchangeable connection with the solvent heating unit via an intermediate fluid flow.DETAILED DESCRIPTION

[0074] In Fig. 1 is illustrated an example of a carbon capture system 1. Such a system 1 may be arranged for removing carbon dioxide from a flue gas 2a. The system may comprise an absorption unit 3 provided with a flue gas inlet 3a at a bottom portion thereof. The absorption unit 3 may have a lean COz-absorbing solvent inlet 3c. The flue gas 2a may for example be obtained from power production from natural gas or other fossil fuels, cement and steel production, various petrochemical or oil refining processes, or waste incineration. Before the flue gas 2a is entered into the absorption unit 3, there may be an initial flue gas treatment step. This initial step may comprise a Direct Contact Cooler (DCC) 4 where the flue gas 2a is cooled and dried in a packed structure fully wetted, so that the flue gas is also water washed, e.g. for reducing SOx concentration.

[0075] The solvent is capable of absorbing carbon dioxide at a lower temperature and desorbing carbon dioxide at a higher temperature. The solvent may for example be an amine- based absorbing solvent, such as an amine solution (e.g., containing one single organic amine (monoethanolamine, diglycolamine, methyldiethanolamine, amphetamine, diammonium phosphate, piperazine, etc.) or be a blend of two or more organic amines), a solution of amino acids, or an aqueous solution of inorganic alkaline compounds (e.g., ammonia or potassium carbonate).

[0076] COz-containing flue gas 2a is allowed into counter-current contact with the CO2- absorbing solvent in the absorption unit 3 at a temperature allowing the solvent to absorb carbon dioxide from the flue gas, forming a rich solvent. The absorption unit 3 may comprise an exit 3b at a top portion of the absorption unit for exiting of treated flue gas 2b.

[0077] The system may comprise a desorption unit 5 with a carbon dioxide outlet 5a at a top portion thereof. A recirculation arrangement may be arranged for recirculating the solvent between the absorption unit 3 and the desorption unit 5 via lean solvent 7 and rich solvent lines 6. A rich solvent line 6 may be arranged between a bottom portion of the absorption unit 3 and an upper portion of the desorption unit 5, allowing rich solvent containing absorbed CO2 to flow from the absorption unit 3 to the desorption unit 5. The desorption unit 5 may be arranged to heat the rich solvent so as to desorb carbon dioxide from the rich solvent, forming a lean solvent, and to discharge CO2 through the carbon dioxide outlet 5a of the desorption unit 5. A lean solvent line 7 may be arranged between a bottom portion of the desorption unit 5 and an upper portion of the absorption unit 3, allowing lean solvent from which the CO2 has been separated to flow from the desorption unit to the absorption unit. The arrangement may comprise one or more lean / rich solvent heat exchanger 8 and solvent condenser (not illustrated).

[0078] A heating unit 10, which may be a reboiler, is arranged to heat the lean / rich / intermediate solvent by heat exchange, so as to provide stripping vapour for desorption of carbon dioxide in the desorption unit 5. The heating unit 10 may be arranged externally of the desorption unit (as illustrated in Fig. 1) or may be an integrated part of the desorption unit (not illustrated).

[0079] The thermal energy required at the solvent heating unit 10 is typically provided by (utility) steam, provided at a pressure level that depends on the required desorption unit 5 operating pressure. There are different ways of obtaining utility steam and the most energyefficient solution for providing utility steam depends on the characteristics of the parent plant into which the present carbon capture system 1 has been incorporated, and on the casespecific characteristics. Steam could be generated by a mix of internal system heat pumping and with dedicated energy utilities. Dedicated heating utilities would always be needed to a certain extent, as internal steam generation cannot cover the whole heating unit heating demand.

[0080] In this carbon capture system 1, a heat pump system 20 is used for reducing the amount of electricity required for steam generation. The profitability of the heat pump system depends on the associated investment costs, electricity price, and very importantly on their energy efficiency, typically expressed via the heating Coefficient of Performance (COP), defined as the ratio of useful heat provided by the heat pump system and corresponding compression electricity consumption. The maximum achievable COP is mostly dependent on the heat pump system operating temperature levels (refrigerant evaporation and condensation temperatures), on the thermos-physical properties of the selected refrigerant, and on the heat pump system cycle configuration.

[0081] The present heat pump system 20 comprises, see e.g. Fig. 2, a condenser 21 arranged to transfer heat to the solvent heating unit 10. The heat pump system 20 also comprises a refrigerant flow line 22 with recirculating refrigerant, and in refrigerant flow line order, the condenser 21, a de-pressurization section 24, an evaporator 25, and a compression section 26. The heat pump system 20 further comprises a desuperheating heat exchanger 30, see any of Figs 2-6. The desuperheating heat exchanger (DSH) is arranged to be in heat exchangeable connection with a desuperheating fluid flow 43a, 43b arranged to flow to and from the DSH. The DSH 30 may be arranged at a point between the compression section 26 and the condenser 21 with reference to the refrigerant flow line order. In the DSH heat is transferred from the refrigerant in the refrigerant recirculation flow line 22 to the desuperheating fluid flow 43a, 43b.

[0082] The DSH 30 desuperheats the compressed refrigerant, possibly down to saturated conditions. The refrigerant is cooled somewhat in the DSH 30 to a temperature below a critical temperature of the condenser 21, before entering the condenser. Heat transferred from the refrigerant to the desuperheating fluid flow 43b arranged to flow from the DSH 30 may be used for heating of other parts of the carbon capture system, such as to heat refrigerant in the heat pump system 10 at a point between the condenser 21 and theevaporator 25, with reference to the flow line order (see Figs 5 and 6 where this flow is used in a flash vessel heat exchanger 29a), or to heat a fluid in a heating system external of the carbon capture system.

[0083] This carbon capture system 1 may supply for a reduction of the overall system power consumption, i.e. an increase in the COP of the system. This can be done, as described above, by transferring heat from the refrigerant to the desuperheating fluid flow 43a 43b arranged to flow from the DSH 30 to heat of other parts of the carbon capture system or to heat a fluid in a heating system external of the carbon capture system (not illustrated), i.e. there is heat recovery. This provides for an energy efficient carbon capture system.

[0084] In addition, a process fluid stream 32, 61, 62 arranged to circulate in the carbon capture system can be used as the desuperheating fluid flow 43a, 43b, instead of using a fluid stream external to the carbon capture system. By using such process fluid stream / vapor in the DSH 30, the heat pump system condenser load reduces but not the total amount of thermal energy provided to the process in the form of stripping vapor, so the amount of lean vapor to be evaporated and recompressed reduces, resulting into lower power consumption.

[0085] The process fluid stream 32, 61, 62 (see Figs 4-6) arranged to circulate in the carbon capture system may include e.g. a fluid stream 32 from / to the desorption unit 5, a fluid stream 62 from / to a heat exchanger 80 arranged to heat flue gas before entering the absorption unit, a fluid stream 61 from / to a condenser 60 arranged to cool the carbon dioxide exiting the desorption unit 5 through the carbon dioxide outlet 5a (see Fig. 4), etc.

[0086] The process fluid stream 32 may be arranged to circulate from and to the desorption unit 5 (see Figs 4-6), and may e.g. be water from a water wash section 33 arranged in the desorption unit 5, which may be re-entered into the desorption unit 5 at a position upstream of the water wash section 33, see Fig. 4. In the DSH 30 a fraction of the fluid stream may be evaporated and re-entered into the desorption unit 5 below the desorber packing, while the still liquid fraction is re-entered into the desorption unit 5 at a position upstream of the water wash section 33, see Fig. 4. Thereby, useful use of the desuperheating can be made, i.e. generating stripping vapor to be reintroduced at the desorber bottom so to reduce the amount of heating required at the heating unit.

[0087] The heated water from the water wash (WW) section 33 or Direct Contact Cooler (DCC)-WW section is an interesting mid-temperature heat source. Process water flowing downwards from the desorption WW / DCC-WW section may be collected. In many plants, thiswater stream temperature is above 90 °C. Water can be collected below / downstream of the WW / DCC-WW section with a tray and used to provide heat at an intermediate pressure level to the recirculating refrigerant. By using this warm water to evaporate some of recirculating refrigerant in the refrigerant flow line, the amount of cooling needed at a cooler at the upper portion of the desorption unit 5 could be decreased, as cooled water is re-entered into the desorption unit 5 upstream of the water wash section 33 via the process fluid stream 32. The amount of water (and to a lesser extent its temperature) collected after / downstream of the desorber WW / DCC-WW section determines the maximum amount of heat transferrable at the DSH, when the whole water stream is evaporated.

[0088] The DCC unit 4 pump-around water stream is the only warm stream that is rapidly available as soon as there is a flue gas circulating during a plant start-up. Therefore, it can be used as heat source if the heat pump system 20 is to be used to start-up the system without support from additional external heating system (e.g. electro-boiler). The temperature and flow rate of DCC water are project specific, so it is not possible to decide beforehand whether it would always be used as heat source for the heat pump system 20 during operation. At least it may be used to kick-start the carbon capture system 1.

[0089] The process fluid stream 32, 61, 62 may, hence, be used as a heat sink for the DSH and the amount of (stripping) vapor to be generated at the solvent heating unit 10 may then be reduced, resulting in a reduced heat pump system condenser duty.

[0090] The DSH 30 may be of indirect contact type, wherein the desuperheating fluid flow 43a, 43b used to cool the superheated refrigerant vapor / gas does not come into direct contact with each other. Superheated refrigerant vapor / gas may be supplied to one side of the heat exchanger and a cooling medium may be supplied to the other side. As the superheated refrigerant vapor / gas passes through the desuperheating heat exchanger, heat is exchanged by the refrigerant and gained by the cooling medium.

[0091] In Figs 2-4 there is shown a direct contact between the condenser 21 and the solvent heating unit 10, i.e. the condenser 21 is integrated with the solvent heating unit 10. In such system, the heat pump system may supply for a minimized solvent thermal degradation. By means of the DSH 30, the maximum temperature of the refrigerant entering into the condenser 21 may be reduced to possibly minimize / reduce thermal degradation of the solvent in the condenser 21 / heating unit 10 (depending on refrigerant temperature at the compression section discharge and solvent characteristics).

[0092] In an alternative embodiment, the condenser 21 is arranged to be in heat exchangeable connection with the solvent heating unit 10 via an intermediate fluid flow 63, see Fig. 6. At least a portion of the intermediate fluid flow 63 may be a process fluid stream arranged to circulate in the carbon capture system 1. Such process fluid stream may be, as discussed above, e.g. a fluid stream from / to the desorption unit 5, a fluid stream from / to a heat exchanger arranged to heat flue gas before entering the absorption unit, etc. By using such process fluid stream / vapor in the intermediate fluid flow to transfer heat from the condenser 21 to the solvent heating unit 10 instead of using a fluid flow external to the carbon captures system, there is an energy efficient improvement, i.e. an increase in the COP of the system.

[0093] The carbon capture system 1 may comprise a solvent recirculation flow line 70, Figs 5-6, arranged to recirculate solvent from and back to the desorption unit 5. The solvent heating unit 10 is then arranged to heat solvent flowing in the solvent recirculation flow line 70. In such a configuration the solvent heating unit 10 is arranged outside the desorption unit 5. The solvent recirculation flow line 70 may be arranged to recirculate solvent from and back to the desorption unit 5 at a bottom section thereof. In the solvent recirculation flow line 70 is arranged a depressurizer 73, which is arranged to reduce the pressure of the solvent before it reaches the solvent heating unit 10, and a pressurizer 71 arranged to increase the pressure of the solvent after it has been heated in the solvent heating unit 10 and before it flows back into the desorption unit 5. Such (lean) solvent recirculation may be used to increase solvent vapor pressure from heating unit pressure to desorption unit pressure. The pressurizer 71 may here e.g. be a centrifugal blower

[0094] The heat pump system 20 may comprise a refrigerant heat exchanger 27, see Figs 2-4, that may be arranged at a point upstream of the DSH 30 and downstream of the evaporator 25 with reference to the refrigerant flow line order.

[0095] The compression section may comprise first and second compression stages 26a, 26b arranged in series. The number of compression stages 26a, 26b in the compression section may be two or more, such as three of four compression stages (not illustrated). The refrigerant heat exchanger 27 may then be arranged at a point upstream the last compression stage 26b of the compression section with reference to the refrigerant flow line order. If the compression section 26 comprises two compression stages 26a, 26b the refrigerant heat exchanger may be arranged between the two compression stages, as illustrated in Fig. 2. Therefrigerant heat exchanger 27 may be arranged upstream of the last / second compression stage 26b and downstream of the first compression stage 26a, as seen in the refrigerant flow line order. The refrigerant heat exchanger 27 is arranged to heat the refrigerant by transferring heat from a heat source in the form of a heat source fluid flow 40 arranged to flow to and from the refrigerant heat exchanger 27. The refrigerant heat exchanger 27 is thus configured to transfer heat from the heat source fluid flow 40 to the refrigerant.

[0096] The refrigerant may for example be one of or a mixture of synthetic refrigerants, such as HFCs, HFOs, HCFOs (e.g. R245fa, R-134a, R1224yd(Z), R1233zd(E), R1336mzz(Z)), and natural refrigerants, such as hydrocarbons and others (e.g. R290, R600, R601a, R601, R718).

[0097] The evaporator 25 may be connected to a heat source 50. This heat source may be external to the carbon capture system 1, and may be heat recovered from a warm stream in the plant / system in which the carbon capture system 1 has been incorporated.Alternatively, the heat source for the evaporator 25 may be a heat source internal to the carbon capture system 1, such as any of the process water streams used in a water wash in the absorption unit 3 or in the DCC 4.

[0098] The refrigerant heat exchanger 27 may be arranged upstream of the last compression stage 26b. Its role is to increase the refrigerant suction temperature, hence the compression discharge temperature. The refrigerant heat exchanger 27 provides higher temperatures at the compressor discharge and so reduces the refrigerant flow rate for a fixed amount of heating provided at the condenser / solvent heating unit. Such a configuration may increase the COP.

[0099] As shown in Fig. 2, the refrigerant heat exchanger 27 may be an internal heat exchanger connected to the refrigerant flow line 22 at a point between the condenser 21 and the evaporator 25 or between the condenser and the depressurization section 24, such that at least a portion of the refrigerant flow is directed towards the refrigerant heat exchanger, so as to form the heat source fluid flow. Refrigerant downstream or immediately downstream of the heat pump condenser 21 may be directed towards the refrigerant heat exchanger as the heat source fluid flow.

[0100] The depressurization section 24 may comprise a pressure-reducing member 24a, such as a throttling valve, arranged at a point between the condenser 21 and the evaporator25 with reference to the refrigerant flow line order, see Fig. 2. The refrigerant heat exchanger27 may then be connected to the refrigerant flow line at a point between the condenser 21and the pressure-reducing member 24a with reference to the refrigerant flow line order. How much of the refrigerant that is directed towards the refrigerant heat exchanger 27 from the condenser 21 may be controlled by means of a control valve, such as a three-way control valve 72. If less than 100% of the refrigerant is directed towards the refrigerant heat exchanger 27, part of the refrigerant goes to the refrigerant heat exchanger and part of the refrigerant is directed directly towards the evaporator 25. If 100% of the recirculating refrigerant goes through the refrigerant heat exchanger 27 and then to the evaporator 25, highest possible compression stage suction temperature at the last compression stage 26b can be obtained.

[0101] The depressurization section 24 may also comprise a flash vessel 29, which may be arranged at a point between the first pressure-reducing member 24a and the evaporator 25 with reference to the refrigerant flow line order, see Fig. 2. A second pressure reducing member 24b may be arranged downstream the flash vessel 29, with reference to the refrigerant flow line order. After the first pressure-reducing member 24a, the refrigerant would naturally split into vapour and liquid phases, in equilibrium with each other. The flash vessel 29 is used to split refrigerant flow, with vapour stratifying at the vessel top and liquid at the vessel bottom. The flash vessel 29 may be connected to the refrigerant flow line 22, at a point upstream (see Figs 4 and 5) or downstream (see Figs 2 and 3) the refrigerant heat exchanger 27, with reference to the refrigerant flow line order. The flashed vapour mixes with superheated vapor before or after the heat exchanger 27, causing a reduction of the last compression stage suction temperature.

[0102] The flash vessel 29 may be operating at an intermediate pressure level between the refrigerant evaporation and condensation pressures. It may be beneficial to supply heat to the refrigerant at this mid-pressure / temperature level if available, to evaporate more refrigerant at this mid-pressure level, which reduces the refrigerant flow circulating across the lower pressure / evaporation level, accordingly. The flash vessel 29 may be associated with a flash vessel heat exchanger 29a, 34 arranged to heat liquid refrigerant in or from the flash vessel 29 by transferring heat from a heat source in the form of a flash vessel heat source flow 42a, 42b. The flash vessel heat exchanger may be an internal heat exchanger 29a, see Fig. 4. An alternative configuration, see Fig. 3, is to connect the bottom of the vessel with an external flash vessel heat exchanger 34.

[0103] The heat pump system 20 may further comprise a subcooler 31 being in heat exchangeable connection with a subcooling fluid flow 44 arranged to flow to and from thesubcooler, see Figs 2 and 3. In the subcooler, heat is transferred from the refrigerant to the fluid in the subcooling fluid flow 44. The subcooler may be arranged at a point between the condenser 21 and the evaporator 27 with reference to the refrigerant flow line order.

[0104] By including a subcooler (SC) 31 in the heat pump system 20, high pressure hot refrigerant can be used to provide useful process heating, before being sent to the heat exchanger 27 for providing superheating. Subcooling further reduces the refrigerant temperature after the condenser 21, hence lowering the temperature of hot liquid refrigerant into the heat exchanger 27 to potentially achieve lower temperature upstream of the compression stage / at compression stage suction.

[0105] If there is a subcooler 31 in the heat pump system 20, the flash vessel 29 may be connected at a point after the subcooler with reference to the refrigerant flow line order.

[0106] The process fluid stream 32, 61, 62, Fig. 4, may constitute at least a portion of the flash vessel heat source flow 42a, 42b. The process fluid stream 32, 61, 62 may further constitute at least a portion of the flash vessel heat source flow arranged to flow to and from the flash vessel heat exchanger 29a, as shown in Fig. 4. A possible design to provide heat exchange in the flash vessel with process fluid stream is to make the process fluid circulate into piping submerged in the liquid refrigerant contained in the vessel. Thereby, more refrigerant in the vessel may be evaporated.

[0107] The subcooling fluid flow 44 (Figs 2 and 3) arranged to flow to and from the subcooler 31 may be a rich solvent flow flowing in a rich solvent line 6 arranged between the absorption unit 3 and the desorption unit 5, see Fig. 1. Thereby rich solvent may be heated in the subcooler before being entered into the desorption unit 5.

[0108] In one embodiment, rich solvent from a lean / rich solvent heat exchanger 8 arranged on the rich solvent line 6 and the lean solvent line 7 may be directed to the subcooler 31 via the rich solvent line.

[0109] Providing any amount of heat to the rich solvent by the subcooler 31 could result into less stripping vapor required at the desorption unit bottom, so lower reboiler duty and consequently lower refrigerant flow, thus higher COP.

[0110] In one example, based on the heat pump system 20 illustrated in Fig. 2, but without a subcooler, the recirculating refrigerant used in the refrigerant flow line 22, here exemplified with R1233zd(E), undergoes the following pressure and temperature changes.Starting at the condenser 21, refrigerant exiting the condenser may have a temperature of 127°C, in the flash vessel 29 the temperature becomes 76 °C and the pressure 6 bar, refrigerant entering the evaporator 25 may have a temperature of 40 °C and a pressure of 2 bar, refrigerant exiting the evaporator 25 may have a temperature of 47 °C and a pressure of 1.9 bar, refrigerant exiting the first compression stage 26a may have a temperature of 84 °C and a pressure of 6 bar, refrigerant exiting the refrigerant heat exchanger 27 may have a temperature of 122 °C, refrigerant exiting the last compression stage 26b may have a temperature of 167 °C and a pressure of 18.5 bar, and refrigerant exiting the desuperheating heat exchanger 30 and entering the condenser 21 may have a temperature of 129 °C.

Claims

CLAIMS1. A carbon capture system (1) comprising: an absorption unit (3) provided with a flue gas inlet (3a) and a flue gas outlet (3b), a desorption unit (5) provided with a carbon dioxide outlet (5a), a solvent capable of absorbing carbon dioxide at a lower temperature and desorbing carbon dioxide at a higher temperature; a recirculation arrangement for recirculating the solvent between the absorption unit (3) and the desorption unit (5) via lean solvent and rich solvent lines (6, 7), a solvent heating unit (10) arranged to heat solvent containing carbon dioxide so as to desorb carbon dioxide from said solvent, a heat pump system (20) comprising: a refrigerant recirculation flow line (22), and in refrigerant flow line order, a condenser (21), a depressurization section (24), an evaporator (25), and a compression section (26a, 26b), wherein the condenser (21) is arranged to transfer heat to the solvent heating unit (10), wherein the heat pump system (20) further comprises a desuperheating heat exchanger (30) arranged at a point between the compression section (26a, 26b) and the condenser (21) with reference to the refrigerant flow line order, the desuperheating heat exchanger (30) being arranged to transfer heat from a refrigerant in the refrigerant recirculation flow line (22) to a desuperheating fluid flow (43a, 43b) arranged to flow to and from the desuperheating heat exchanger (30).

2. The carbon capture system (1) of claim 1, wherein at least a portion of the desuperheating fluid flow (43a, 43b) comprises a process fluid stream (32, 61, 62) arranged to circulate in the carbon capture system (1).

3. The carbon capture system (1) of claim 2, wherein the process fluid stream (32) is arranged to circulate from and to the desorption unit (5).

4. The carbon capture system (1) of any of the preceding claims, wherein at least a portion of the desuperheating fluid flow (43b) from the desuperheating heat exchanger (30) is arranged to heat refrigerant in the heat pump system (20) at a point between the condenser (21) and the evaporator (25) with reference to the flow line order.

5. The carbon capture system (1) of any of the preceding claims, wherein the condenser (21) is integrated with the solvent heating unit (10).

6. The carbon capture system (1) of any of claims 1-4, wherein the condenser (21) is arranged to be in heat exchangeable connection with the solvent heating unit (10) via an intermediate fluid flow (63).

7. The carbon capture system (1) of claim 6, wherein at least a portion of the intermediate fluid flow (63) is a process fluid stream (32, 61, 62) arranged to circulate in the carbon capture system (1).

8. The carbon capture system (1) of any of the preceding claims, further comprising a solvent recirculation flow line (70) arranged to recirculate solvent from and back to the desorption unit (5), wherein said solvent heating unit (10) is arranged to heat solvent flowing in said solvent recirculation flow line (70).

9. The carbon capture system (1) of claim 8, wherein the solvent recirculation flow line (70) comprises a depressurizer (73) arranged to reduce the pressure of the solvent before it reaches the heating unit (10) and a pressurizer (71) arranged to increase the pressure of the solvent after it has been heated in the heating unit (10) and before it flows back into the desorption unit (5).

10. The carbon capture system (1) of any of the preceding claims, wherein the heat pump system (20) further comprises a refrigerant heat exchanger (27) arranged at a point upstream of the desuperheating heat exchanger (30) and downstream of the evaporator (25) with reference to the refrigerant flow line order.

11. The carbon capture system (1) of any of the preceding claims, wherein the compression section (26a, 26b) of the heat pump system (20) comprises at least a first and a second compression stage (26a, 26b) arranged in series.

12. The carbon capture system of claim 10 and 11, wherein a refrigerant heat exchanger (27) is arranged at a point upstream of the second compression stage (26b) and downstream of the first compression stage (26a) with reference to the refrigerant flow line order.

13. The carbon capture system (1) of any of claims 10-12, wherein the refrigerant heat exchanger (27) further is connected to the refrigerant flow line (22) at a point between the condenser (21) and the evaporator (25) with reference to the flow line order, such that at least a portion of the refrigerant flow is directed towards the refrigerant heat exchanger (27) so as to form at least a portion of a heat source fluid flow (40) arranged to flow to and from the refrigerant heat exchanger (27).

14. The carbon capture system (1) of any of claims 10-13, wherein the depressurization section (24) comprises at least a first pressure reducing member (24a, 24b), and wherein the refrigerant heat exchanger (27) is connected to the refrigerant flow line (22) at a point between the condenser (21) and said at least a first pressure reducing member (24a, 24b) with reference to the refrigerant flow line order.

15. The carbon capture system (1) of any of the preceding claims, wherein the depressurization section (24) comprises at least a first pressure reducing member (24a, 24b) and a flash vessel (29) arranged downstream the first pressure reducing member (24a) and upstream the evaporator (25), with reference to the refrigerant flow line order, wherein the flash vessel (29) is further connected to the refrigerant flow line (22) at a point between the evaporator (25) and the desuperheating heat exchanger (30) with reference to the refrigerant flow line order, allowing a portion of the refrigerant flow (41a, 41b, 41c) to flow from the flash vessel (29) to the point between the evaporator (25) and the desuperheating heat exchanger16. The carbon capture system (1) of claim 15, wherein the flash vessel (29) is arranged downstream the first pressure reducing member (24a) and upstream a second pressure reducing member (24b), with reference to the refrigerant flow line order.

17. The carbon capture system (1) of claim 15 or 16, wherein a flash vessel heat exchanger (29a, 34) is arranged in association with the flash vessel (29), wherein the flash vessel heat exchanger (29a, 34) is arranged to heat liquid refrigerant in or from the flash vessel (29) by transferring heat to the refrigerant in the refrigerant recirculation flow line (22) from a flash vessel heat source flow (42a, 42b) arranged to flow to and from the flash vessel heat exchanger (29a, 34).

18. The carbon capture system (1) of claim 17, wherein at least a portion of the flash vessel heat source flow (42a, 42b) is a process fluid stream arranged to circulate in the carbon capture system (1).

19. The carbon capture system (1) of claim 18, wherein at least a portion of the flash vessel heat source flow (42a, 42b) comprises at least a portion of the desuperheating fluid flow (43a, 43b).

20. The carbon capture system (1) of any of the preceding claims, wherein the heat pump system (20) further comprises a subcooler (31) arranged at a point between the condenser (21) and the depressurization section (24) with reference to the refrigerant flow line order, the subcooler (31) being arranged to transfer heat from refrigerant in the refrigerant recirculation flow line (22) to a subcooling fluid flow (44) arranged to flow to and from the subcooler.

21. The carbon capture system (1) of claim 21, wherein at least a portion of the subcooling fluid flow (44) is a process fluid stream arranged to circulate in the carbon capture system (1).

22. The carbon capture system (1) of any of the preceding claims, wherein at least a portion of the desuperheating fluid flow (43a, 43b) is arranged to heat a fluid in a heating system external of the carbon capture system.

23. The carbon capture system (1) of any of the preceding claims, wherein at least a portion of the desuperheating fluid flow (43a, 43b) is arranged to heat a fluid forming part of the carbon capture system.

24. Method for operating a carbon capture system (1) according to any of the above claims, the method comprising:- heating, in the solvent heating unit (10), the solvent containing carbon dioxide so as to desorb carbon dioxide from said solvent,- operating the heat pump system (20) so as to provide heat to the solvent heating unit (10) via the condenser (21), - feeding the desuperheating fluid flow (43) to the desuperheating heat exchanger (30) so as to transfer heat from refrigerant in the refrigerant recirculation flow line (22) to the desuperheating fluid flow (43).

Images