Carbon dioxide separator

Abstract

The present invention relates to a carbon dioxide separation apparatus (10), comprising an absorber (20) and a desorber (30), wherein the absorber (20) has a gas inlet (21) for a gas to be purified and a gas outlet (22) for a purified gas, the absorber (20) has an absorption solvent inlet (23) and a solution outlet (24), the desorber (30) has at least a first solution inlet (31), an absorption solvent outlet (32), a warm solvent inlet (33), and a carbon dioxide outlet (34), and the solution outlet (24) is connected to the first solution inlet via a first solution connection (40). a first solution connection (40) having a first heat exchanger (41); an absorption solvent outlet (32) connected to an absorption solvent inlet (23) via an absorption solvent connection (50), the absorption solvent connection (50) having the first heat exchanger (41) so that heat of the solvent flow is transferred to the solution flow; the absorption solvent connection (50) having a branch point (51) to a warm solvent connection (52), the warm solvent connection (52) being connected to the warm solvent inlet (33), the warm solvent connection having a second heat exchanger (53).

Description

[Technical field]

[0001] The present invention relates to an apparatus for separating carbon dioxide from a gas, in particular from an off-gas. [Background technology]

[0002] In order to reduce anthropogenic climate change, the release of carbon dioxide into the atmosphere is increasingly avoided. Instead, attempts are being made to separate the formed carbon dioxide and then convert it or send it to storage. A typical process for this purpose involves scrubbing the off-gas with a basic solution, for example an amine solution, at about 25 ° C to 50 ° C. This amine solution acts as a solvent in which the carbon dioxide dissolves. The solution containing the carbon dioxide is then heated and, in a desorption step, the carbon dioxide is converted back into the gas phase. This restores the solvent and also obtains a pure carbon dioxide gas stream. The carbon dioxide gas stream can then be sent for storage, for example purely illustratively, or fed to a methanol synthesis.

[0003] WO 2010 / 086039 discloses a process and apparatus for separating carbon dioxide from the off-gas of a fossil fuel power plant.

[0004] China Patent Publication No. 111203086 discloses a CO2 separation system with low energy consumption and low emissions.

[0005] WO 2014 / 077919 discloses an apparatus and process for removing acid gases from a gas stream and regenerating an absorption solution.

[0006] US Patent Application Publication No. 2017 / 0197175 discloses an energy efficient process for extracting acid gases from a gas stream.

[0007] WO 2013 / 013749 discloses heat recovery in the adsorption-desorption process.

[0008] WO 2019 / 232626 discloses post-combustion CO2 separation with heat recovery.

[0009] US Patent Application Publication No. 2021 / 0220771 discloses post-combustion carbon dioxide separation with heat recovery.

[0010] China Utility Model No. 208786105 discloses carbon dioxide separation with heat recovery.

[0011] US Patent Application Publication No. 2014 / 0127119 discloses a carbon dioxide absorbent.

[0012] US Pat. No. 5,145,658 discloses the recovery of reaction heat from an alkaline scrubbing solution for removing acid gases.

[0013] US Pat. No. 3,563,696 discloses the removal of carbon dioxide from a gas mixture.

[0014] WO 2004 / 080573 discloses the regeneration of aqueous solutions from gas absorption processes.

[0015] US Patent Application Publication No. 2014 / 0374105 discloses a process for removing carbon dioxide from a gas.

[0016] All plants for separating CO2 have in common that energy must be supplied for the re-release of the CO2 from the solution. For this purpose, high and therefore relatively valuable levels of heat are employed. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] International Publication No. 2010 / 086039 [Patent Document 2] China Patent Application Publication No. 111203086 [Patent Document 3] International Publication No. 2014 / 077919 [Patent Document 4] US Patent Application Publication No. 2017 / 0197175 [Patent Document 5] International Publication No. 2013 / 013749 [Patent Document 6] International Publication No. 2019 / 232626 [Patent Document 7] US Patent Application Publication No. 2021 / 0220771 [Patent Document 8] China Utility Model No. 208786105 Specification [Patent Document 9] US Patent Application Publication No. 2014 / 0127119 [Patent Document 10] U.S. Pat. No. 5,145,658 [Patent Document 11] U.S. Pat. No. 3,563,696 [Patent Document 12] International Publication No. 2004 / 080573 [Patent Document 13] US Patent Application Publication No. 2014 / 0374105 Summary of the Invention [Problem to be solved by the invention]

[0018] An object of the present invention is to provide a carbon dioxide separation device in which the entire adsorption / desorption process is energetically optimized. [Means for solving the problem]

[0019] This object is achieved by a carbon dioxide separation device having the features of claim 1. Advantageous developments are evident from the dependent claims, the following description and the drawings.

[0020] The carbon dioxide separation device according to the invention comprises an absorber and a desorber. In the absorber, the gas to be purified of carbon dioxide is introduced and the carbon dioxide from the gas phase is transferred to the liquid phase by contact with a solvent, usually an amine solution. This forms a solution of the solvent in which the carbon dioxide is dissolved and may be bound. This solution is transferred into a desorber, where the carbon dioxide is re-ejected from the solution, so that the solvent is recovered and reused in the absorber. A carbon dioxide gas stream is obtained as well, which can be sent for further use. This basic principle has already been used in many variants.

[0021] The absorber has a gas inlet for the gas to be purified and a gas outlet for the purified gas. The gas to be purified can be, for example, off-gas from the combustion of a fossil fuel. The purified gas can then be mainly nitrogen with only a small amount of residual carbon dioxide, the proportion of oxygen being significantly reduced by the combustion process. The purified gas can then be released, for example, to the atmosphere without emitting significant amounts of the greenhouse gas carbon dioxide. The absorber typically comprises one or more mass transfer elements arranged between the gas inlet and the absorption solvent inlet. The mass transfer elements also serve to improve the contact between the liquid and gas phases, in particular to increase the surface area of ​​the liquid phase. Such mass transfer elements are known to those skilled in the art and can be, for example, bubble cap trays, random packings, or structured packings.

[0022] The absorber further comprises an absorption solvent inlet and a solution outlet. The absorption solvent inlet is typically located at the top of the absorber and the solution outlet is located at the bottom of the absorber. Thus, the gas inlet is typically located at the bottom and the gas outlet at the top, whereby the gas and solvent flow countercurrently through the absorber.

[0023] The desorber comprises at least a first solution inlet, an absorption solvent outlet, a hot solvent inlet, and a carbon dioxide outlet. The solution outlet of the absorber is connected to the first solution inlet of the desorber via a first solution conduit. The first solution conduit comprises a first heat exchanger. This heats the solution stream flowing through the first solution conduit, so that the carbon dioxide present in the solution can be re-emitted in the desorber. The absorption solvent outlet of the desorber is connected to the absorption solvent inlet of the absorber via an absorption solvent conduit. The solvent in the desorber with a significantly reduced carbon dioxide content flows back to the absorber via the absorption solvent conduit. The absorption solvent conduit also comprises a first heat exchanger. This transfers the heat of the solvent stream in the absorption solvent conduit to the solution stream. The absorption solvent conduit comprises a branch to a hot solvent conduit. In this way, a substream of the solvent stream is diverted and made to flow into the hot solvent conduit. The hot solvent conduit is connected to the hot solvent inlet. The hot solvent conduit comprises a second heat exchanger. This allows for the introduction of additional energy into the overall system. The desorber typically comprises one or more mass transfer elements located above and below the first solution inlet. The mass transfer elements also serve to improve the contact between the liquid and gas phases, in particular to increase the surface area of ​​the liquid phase. Such mass transfer elements are known to those skilled in the art and can be, for example, bubble cap trays, random packing, or structured packing.

[0024] According to the invention, a third solution conduit branches off from the first solution conduit between the absorber and the first heat exchanger. The end of the third solution conduit, where the solution stream re-emerges from the third solution conduit, is fluidly connected to the first solution conduit downstream of the first heat exchanger or absorber. The third solution conduit comprises a fourth heat exchanger in which the solution stream from the third solution conduit is heated. The fourth heat exchanger and the gas inlet are connected via a gas conduit, whereby the gas to be purified is passed through the fourth heat exchanger before it is allowed to flow into the absorber. The gas to be purified is typically supplied at a temperature between 100 ° C and 200 ° C, for example 150 ° C, corresponding to the temperature produced by the upstream process. In absorbers, where temperatures between 30 ° C and 40 ° C are customary, a heat exchanger for cooling is usually necessary. However, the heat thus produced is often no longer usable, since it is produced at such a low level. Direct heat transfer allows energy to be transferred directly to the solution stream, which is thus brought to, for example, 100° C.-110° C. and thus to the temperature level of the desorber. The energy provided in the second heat exchanger, which is typically derived from a higher value energy source, usually steam, can thus be at least partially saved.

[0025] In a further embodiment of the invention, the first solution conduit comprises an evaporator downstream of the first heat exchanger. The evaporator, also known as a vacuum vessel, ensures that the solution of the solution stream heated in the first heat exchanger can expand and thus partially evaporate. The liquid phase of the solution stream is thus separated from the gas phase of the solution stream in the evaporator. The liquid phase is forced to flow into the desorber via the first solution conduit. The desorber further comprises a steam inlet and the evaporator comprises a steam outlet. The steam outlet of the evaporator and the steam inlet of the desorber are connected to a gas-solution conduit for displacing the gas phase. It is particularly preferred if the steam inlet is arranged in the lower region of the desorber. This optimizes the energy management of the entire process.

[0026] In a further embodiment of the invention, the end of the third solution conduit, where the solution stream re-emerges from the third solution conduit, is connected to an evaporation device, so that a vacuum can be created here in the same way as for the heated solution stream in the first solution conduit, and the gas phase can be separated from the liquid phase.

[0027] In a further embodiment of the invention, the gas conduit comprises a raw gas purifier, which is particularly preferably configured to remove sulphur oxides.

[0028] In a further embodiment of the invention, the second solution conduit branches off from the first solution conduit between the absorber and the first heat exchanger. The second solution conduit leads directly to the top of the desorber. In this context, directly should be understood to mean that there is no heat exchanger or the like. A (flow control) valve may be arranged here. Thus, the carbon dioxide-containing solution is itself used to cool the gas stream coming out of the desorber. This results in that the heat supplied from the first and second heat exchangers into the desorbing means remains in the desorbing means and in the solvent and is not released to the cooling medium.

[0029] In a further embodiment of the invention, a fourth solution conduit branches off from the first solution conduit between the absorber and the first heat exchanger. The end of the fourth solution conduit, where the solution flow re-emerges from the fourth solution conduit, is connected to the first solution conduit downstream of the first heat exchanger or the absorber. The fourth solution conduit comprises a fifth heat exchanger. The fifth heat exchanger is connected to the second heat exchanger in such a way that the heat exchange medium cooled in the second heat exchanger is made to flow into the fifth heat exchanger. This allows maximum heat energy to be obtained from the heat exchange medium, usually steam, which in turn reduces the total energy demand.

[0030] In a further embodiment of the invention, the end of the fourth solution conduit, where the solution stream re-emerges from the fourth solution conduit, is connected to an evaporation device, so that a vacuum can be created here in the same way as for the heated solution stream in the first solution conduit, and the gas phase can be separated from the liquid phase.

[0031] In a further embodiment of the invention, the carbon dioxide outlet is connected to a first carbon dioxide compressor. The first carbon dioxide compressor is connected to a first carbon dioxide heat exchanger for recooling the carbon dioxide heated by compression. This is typical, since both the storage of carbon dioxide and its further processing, for example to produce methanol, require carbon dioxide at higher pressures. For this purpose, it is customary to connect several carbon dioxide compressors and carbon dioxide heat exchangers in series in a cascade to perform staged compression with intermediate cooling of the carbon dioxide in each case. A fifth solution conduit branches off from the first solution conduit between the absorber and the first heat exchanger. The end of the fifth solution conduit, where the solution stream re-emerges from the fifth solution conduit, is connected to the first solution conduit downstream of the first heat exchanger or absorber. The fifth solution conduit comprises a first carbon dioxide heat exchanger. This allows the thermal energy generated by the compression of the carbon dioxide to be utilized in the process. If several carbon dioxide heat exchangers are present, they are preferably integrated in parallel in the fifth solution conduit.

[0032] In a further embodiment of the invention, the end of the fifth solution conduit, where the solution stream re-emerges from the fifth solution conduit, is connected to an evaporation device, so that a vacuum can be created here in the same way as for the heated solution stream in the first solution conduit, and the gas phase can be separated from the liquid phase.

[0033] In a further embodiment of the invention, the pressure of the solvent in the second heat exchanger is 0.2 bar to 5 bar higher than the pressure in the desorber at the absorption solvent outlet. The second heat exchanger can therefore achieve a higher outlet temperature, since the increase in pressure allows the temperature to increase up to the boiling temperature at the corresponding pressure. This in turn has the consequence that the solvent has a higher temperature at the absorption solvent outlet and therefore flows into the first heat exchanger at a higher temperature. This makes it possible to make said exchanger more compact or to achieve a higher starting temperature of the loaded solution stream from the first heat exchanger. The latter in turn leads to a more efficient stripping of carbon dioxide from the solution.

[0034] The pressure of the solvent in the second heat exchanger is the result of the device. There are two exemplary and preferred embodiments of the specific regulation of the pressure through the device. In a first exemplary and preferred embodiment of the present invention, the second heat exchanger is located at least 1 m below the absorption solvent outlet, whereby the pressure in the second heat exchanger is generated by the hydrostatic pressure of the liquid column of the solvent, so that the pressure of the solvent in the second heat exchanger is 0.2 bar to 5 bar higher than the pressure in the desorber at the absorption solvent outlet. In a second exemplary and preferred embodiment of the present invention, a first pump for generating a corresponding positive pressure is located upstream of the second heat exchanger, so that the pressure of the solvent in the second heat exchanger is 0.2 bar to 5 bar higher than the pressure in the desorber at the absorption solvent outlet.

[0035] In another embodiment of the invention, a pressure reducing means, such as a control valve, an aperture plate, or a tube constriction, is placed between the second heat exchanger and the desorber. The pressure reducing means establishes / maintains a desired positive pressure in the second heat exchanger on the gas / vapor side. This allows to prevent evaporation in the second heat exchanger as well, if necessary.

[0036] It is preferred if the first solution inlet is located in the central region of the desorber.

[0037] The carbon dioxide separator according to the invention will be explained in more detail below with reference to an embodiment shown in the drawing. [Brief description of the drawings]

[0038] [Figure 1] First Exemplary Embodiment [Diagram 2] Second Exemplary Embodiment [Diagram 3] Third Exemplary Embodiment DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] FIG. 1 shows a first exemplary embodiment of a carbon dioxide separator 10 of the invention. The carbon dioxide separator 10 is used, for example, to separate carbon dioxide from an off-gas stream, which enters at a gas inlet 21 and leaves again at a gas outlet 22 with a significantly reduced amount of carbon dioxide. In the absorber 20, this gas stream is countercurrently contacted with a solvent, usually an amine solution, to incorporate the carbon dioxide into a solution. This solution leaves the absorber at a solution outlet 24 and is pumped through a first solution conduit 40 via a second pump 46. The first solution conduit 40 comprises a first heat exchanger 41 in which the solution stream is heated by a solvent stream from an absorption solvent conduit 50. Downstream of the first heat exchanger 41 is arranged an evaporator 42, which is able to convert part of the solution into a gas phase. The liquid phase of the solution stream is conveyed further through the first solution conduit 40 and conveyed, for example, by a third pump 47 through the first solution inlet 31 into the desorber 30. Gas formed in evaporator 42 is forced through vapor outlet 43 into gas solution conduit 44 and through that conduit into desorber 30 via vapor inlet 35. Vapor inlet 35 is preferably located at the lower end or bottom of desorber 30.

[0040] In the desorber 30, the carbon dioxide is thermally removed from the solution and exits through the carbon dioxide outlet 34. This carbon dioxide stream can then be fed, for example, to further reaction or storage. The solvent from which the carbon dioxide has been removed collects at the bottom of the desorber 30 and is fed to the absorption solvent conduit 50 through the absorption solvent outlet 32. The solvent stream donates its thermal energy to the solution stream in the first heat exchanger 41. For example, a fourth pump is used to pump the solvent stream through the third heat exchanger 55 and into the absorber through the absorption solvent inlet 23.

[0041] The side stream is split off from the solvent stream in absorption solvent conduit 50 at branch 51 and passed through hot solvent conduit 52 via second heat exchanger 53 and returned into desorber 30 through hot solvent inlet 33, specifically in vapor form or as a vapor / liquid mixture. The energy required to strip carbon dioxide from the solution is supplied to the system via second heat exchanger 53.

[0042] Furthermore, a third solution conduit 60, which comprises a fourth heat exchanger 61, branches off from the first solution conduit 40. The third solution conduit 60 leads at its end to the evaporator 42. The energy transferred to the solution stream in the fourth heat exchanger 61 is derived from the gas stream to be purified of carbon dioxide. The fourth heat exchanger 61 is then connected to the gas inlet 21 of the absorber 20 via a gas conduit 25 in order to transfer this gas stream into the absorber 20. The gas conduit 25 further comprises a raw gas purifier 26, in which SO x is removed and the gas stream is brought to the correct temperature for absorption of carbon dioxide in absorber 20.

[0043] 2 shows a second exemplary embodiment, which differs from the first exemplary embodiment in that a fourth solution conduit 62 is additionally present, directing a substream of the solution stream into the evaporator 42 via a fifth heat exchanger 63. The energy for heating the solvent stream in the fifth heat exchanger 63 is derived from the heat exchange medium already cooled in the second heat exchanger 53, so that the residual heat of the heat exchange medium is efficiently utilized.

[0044] 3 shows a third embodiment. In addition to the second exemplary embodiment, it also includes a carbon dioxide compressor 36 connected to the carbon dioxide outlet 34, and a carbon dioxide heat exchanger 37 connected to the carbon dioxide compressor 36. To utilize the heat generated by compression and released in the carbon dioxide heat exchanger 37, the carbon dioxide separator 10 includes a fifth solution conduit 64 that passes a subsidiary stream of the solution stream through the carbon dioxide heat exchanger 37 and into the evaporator 42. [Explanation of symbols]

[0045] 10 Carbon dioxide separator 20 Absorber 21 Gas inlet 22 Gas outlet 23 Absorption solvent inlet 24 Solution outlet 25 Gas Pipes 26 Raw Gas Purifier 30 Detachable device 31 First solution inlet 32 Absorption solvent outlet 33 Hot solvent inlet 34 Carbon dioxide outlet 35 Steam inlet 36 Carbon Dioxide Compressor 37 Carbon Dioxide Heat Exchanger 40 First solution conduit 41 First heat exchanger 42 Evaporation device 43 Steam outlet 44 Gas solution conduit 45 Second solution conduit 46 Second Pump 47 Third Pump 50 Absorption solvent conduit 51 Branch 52 High temperature solvent conduit 53 Second Heat Exchanger 54 First Pump 55 Third Heat Exchanger 60 Third solution conduit 61 Fourth Heat Exchanger 62 Fourth solution conduit 63 Fifth Heat Exchanger 64 Fifth solution conduit

Claims

1. A carbon dioxide separation apparatus (10), comprising an absorber (20) and a desorber (30), the absorber (20) comprising a gas inlet (21) for a gas to be purified and a gas outlet (22) for a purified gas, the absorber (20) comprising an absorption solvent inlet (23) and a solution outlet (24), the desorber (30) comprising at least one first solution inlet (31), an absorption solvent outlet (32), a high temperature solvent inlet (33), and a carbon dioxide outlet (34), said solution outlet (24) being connected to said first solution inlet (31) via a first solution conduit (40), said first solution conduit (40) comprising a first heat exchanger (41), said absorption solvent outlet (32) being connected to said absorption solvent inlet (23) via an absorption solvent conduit (50), said absorption solvent conduit (50) comprising said first heat exchanger (41), whereby heat of the solvent stream is transferred to the solution stream, said absorption solvent conduit (50) comprising said first heat exchanger (41), In a carbon dioxide separation apparatus (10) having a hot solvent inlet (50) including a branch (51) to a hot solvent conduit (52), the hot solvent conduit (52) being connected to the hot solvent inlet (33), and the hot solvent conduit including a second heat exchanger (53), a third solution conduit (60) branches off from the first solution conduit (40) between the absorber (20) and the first heat exchanger (41), and an end of the third solution conduit (60) is connected to the first heat exchanger (41) or the absorber (20). a third solution conduit (60) connected to the first solution conduit (40) downstream of a third solution conduit (20), the third solution conduit (60) comprising a fourth heat exchanger (61), the fourth heat exchanger (61) and the gas inlet (21) being connected via a gas conduit (25), whereby the gas to be purified is passed through the fourth heat exchanger (61) before the gas to be purified is made to flow into the absorption unit (10).

2. 2. The carbon dioxide separation apparatus (10) of claim 1, characterized in that the first solution conduit (40) comprises an evaporator (42) arranged downstream of the first heat exchanger (41), the evaporator (42) separates a liquid phase of the solution stream from a gas phase of the solution stream, the liquid phase being passed through the first solution conduit (40) into the desorber (30), the desorber (30) comprising a vapor inlet (35), the evaporator (42) comprising a vapor outlet (43), the vapor outlet (43) and the vapor inlet (35) being connected to a gas solution conduit (44) for transferring the gas phase.

3. 3. The carbon dioxide separator (10) of claim 2, wherein the end of the third solution conduit (60) is connected to the evaporator (42).

4. The carbon dioxide separation device (10) according to any one of claims 1 to 3, characterized in that the gas conduit (25) comprises a raw gas purifier (26).

5. The carbon dioxide separation apparatus (10) of claim 4, characterized in that the raw gas purifier (25) is configured to remove sulfur oxides.

6. 6. The carbon dioxide separation apparatus (10) according to claim 1, characterized in that a second solution conduit (45) branches off from the first solution conduit (40) between the absorber (20) and the first heat exchanger (41), the second solution conduit (45) leading directly to an upper portion of the desorber (30).

7. 7. The carbon dioxide separation apparatus (10) according to claim 1, characterized in that a fourth solution conduit (62) branches off from the first solution conduit (40) between the absorber (20) and the first heat exchanger (41), an end of the fourth solution conduit (62) is connected to the first solution conduit (40) downstream of the first heat exchanger (41) or the absorber (20), and the fourth solution conduit (62) comprises a fifth heat exchanger (53), the fifth heat exchanger (63) being connected to the second heat exchanger (53) such that a heat exchange medium cooled in the second heat exchanger (53) is made to flow into the fifth heat exchanger (63).

8. The carbon dioxide separation apparatus (10) of claim 7 in conjunction with claim 2, wherein the end of the fourth solution conduit (62) is connected to the evaporator (42).

9. 9. The carbon dioxide separation apparatus (10) according to any one of claims 1 to 8, characterized in that the carbon dioxide outlet (34) is connected to a first carbon dioxide compressor (36), which is connected to a first carbon dioxide heat exchanger (37), a fifth solution conduit (65) branches off from the first solution conduit (40) between the absorber (20) and the first heat exchanger (41), an end of the fifth solution conduit (65) is connected to the first solution conduit (40) downstream of the first heat exchanger (41) or the absorber (20), and the fifth solution conduit (65) comprises the first carbon dioxide heat exchanger (37).

10. The carbon dioxide separation apparatus (10) of claim 9 in conjunction with claim 2, characterized in that the end of the fifth solution conduit (65) is connected to the evaporator (42).

11. 11. The carbon dioxide separation apparatus (10) according to any one of claims 1 to 10, characterized in that the pressure of the solvent in the second heat exchanger (53) is 0.2 bar to 5 bar higher than the pressure in the desorber (30) at the absorption solvent outlet (32).

12. 12. The carbon dioxide separation apparatus (10) according to claim 11, characterized in that the second heat exchanger (53) is located at least 1 m below the absorption solvent outlet (32), whereby the pressure of the solvent in the second heat exchanger (53) is 0.2 bar to 5 bar higher than the pressure in the desorber (30) at the absorption solvent outlet (32), since pressure is generated by the hydrostatic pressure of the solvent.

13. 12. The carbon dioxide separation apparatus (10) according to claim 11, characterized in that a first pump (54) for generating a positive pressure is arranged upstream of the second heat exchanger (53), so that the pressure of the solvent in the second heat exchanger (53) is 0.2 bar to 5 bar higher than the pressure in the desorber (30) at the absorption solvent outlet (32).

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