Method for capturing CO2 from flue gases from district heating plants

Abstract

CO from flue gases from district heating plants burning carbonaceous fuels 2 In a method for recovering aqueous CO2 from a flue gas, the flue gas is compressed and then cooled before being introduced into an absorber 16, and the flue gas is cooled by cooling the aqueous CO2 introduced into the absorber 16. 2 The absorbent solution is made to flow countercurrently to produce lean flue gas, which is removed from the absorber 16 and reheated against the incoming compressed flue gas before being expanded and discharged to the atmosphere, and the rich absorbent is introduced into the regenerator 30 and stripped to produce CO. 2 and removing the lean absorbent from the regenerator 30, introducing the lean absorbent into the absorber 16, the lean absorbent stream being split into two, a first stream which is introduced into the top of the absorbent charge 17 in the absorber 16 and a second stream which is cooled by a thermal fluid received from the district heating plant and returned to the district heating plant, the absorbent thus cooled being introduced into the top of the cooler charge 21 at the top of the absorber, whereby the lean flue gas is cooled and dried before being reheated by fresh incoming compressed flue gas and then expanded and discharged into the environment, and a plant for carrying out said method are disclosed.

Description

[Technical field]

[0001] The present invention relates to the capture of CO2 from CO2-containing flue gases. More particularly, the present invention relates to the capture of CO2 from low temperature flue gases. Typical sources of low temperature flue gases are district heating plants or combined heat and power plants for producing heat and electricity. [Background technology]

[0002] The increasing concentration of CO2 in the atmosphere, which leads to global climate change, is a major concern and puts pressure on the world to stop or at least dramatically reduce the use of fossil fuels and to switch to renewable energy sources. However, due to the rapid increase in global energy demand and the fact that switching from fossil fuels to renewable energy sources will take time and cost, carbonaceous fuels are expected to remain important as an energy source for the next few decades. Carbon Capture and Storage (CCS) is therefore becoming important in reducing global CO2 emissions.

[0003] Many concepts and projects for capturing CO2 have been proposed, but few have progressed from ideas or drawings into actual projects due to the high investment and operating costs of such plants, as well as a lack of political support.

[0004] Most of the proposed projects for CO2 capture are based on post-combustion CO2 capture, where the CO2-containing flue gas is introduced into an absorber where it is brought into intimate contact with a CO2 absorbent to remove or at least substantially reduce the CO2 content of the flue gas before it is released into the environment. The CO2-loaded absorbent is then introduced into a stripper to regenerate the absorbent for reuse, and the captured CO2 is removed for fixation / storage.

[0005] The most commonly proposed sorbents are inorganic sorbents, usually aqueous solutions of potassium carbonate, and organic sorbents, usually aqueous solutions of one or more organic amines or amino acids. Organic sorbents are prone to decomposition during use, especially in the presence of oxygen. Some of the decomposition products of amines known from the operation of such plants are known to be toxic and carcinogenic and may be released to the environment together with the flue gas from which CO2 has been removed. Operation of capture plants using organic sorbents at pressures higher than atmospheric increases the problem of decomposition as the partial pressure of oxygen increases due to compression. Potassium carbonate, on the other hand, is relatively cheap, chemically stable at the operating conditions of capture plants and does not produce toxic or carcinogenic decomposition products.

[0006] The reaction rates and system equilibria for the capture of CO2 in a capture plant depend heavily on the partial pressure of CO2 in the absorber, i.e. in the part of the capture plant where the CO2-containing gas is brought into intimate contact with the absorbent. In addition, the use of high pressure reduces the gas volume, allowing the plant size to be significantly reduced, thus reducing construction costs.

[0007] WO 0048709, granted to Norsk Hydro, relates to a method for capturing CO2 from flue gases from primary power plants, more particularly gas turbine-based power plants. The expanded and cooled flue gases from the gas turbine power plant are recompressed to a pressure of 0.5-3 MPa (5-30 bar), typically 0.7-2 MPa (7-20 bar), cooled, and the compressed gas is introduced into an absorber where it is contacted with an amine absorbent in the absorber of the CO2 capture plant. The CO2-depleted flue gases are reheated by the incoming flue gases, and the gases are expanded in a turbine to provide power for compressing the incoming flue gases. A drawback of this approach is the need for a steam turbine plant and a separate HRSG to fully utilize the heat of the flue gases.

[0008] Flue gases from district heating plants are typically cooled to about 70-50 °C, typically about 60 °C, depending on the actual configuration of the plant, by heating a heat transfer medium circulating in the district heating system and using the recovered thermal energy to generate a hotter heat transfer medium for district heating. Flue gas temperatures below 60 °C are too costly to heat the heat transfer medium to the temperature used for district heating. District heating is often based on waste incineration, which produces flue gases with a dew point of about 60 °C. Thus, the 60 °C flue gases from district heating plants based on waste incineration are substantially water saturated. Flue gases from plants burning other fuels may have a higher or lower dew point.

[0009] US 2021 / 060478 A1 describes a plant and method for CO2 capture at high pressure. Incoming flue gas is introduced into a gas turbine having an external combustion chamber and is used as oxygen-containing gas for burning natural gas in the combustion chamber. Compressed flue gas leaving the combustion chamber is introduced into the CO2 capture section of the plant, but before that, it is heat exchanged with lean CO2 gas leaving the CO2 capture section. After being reheated in the heat exchanger, the lean CO2 gas is expanded and released into the environment.

[0010] Korean Patent Application Publication No. 20170132623(A) relates to an amine-based CO2 capture plant operating at near ambient pressure. According to one embodiment, the CO2-rich gas stream leaving the stripper is introduced into a heat exchanger for preheating water for district heating, after which the gas is further cooled and flashed in a flash tank to separate condensed water from the CO2-rich gas phase, which is further dried and compressed.

[0011] US Patent No. 10227901 (B2) relates to a method of methanation and a power plant with CO2 methanation of CO2 in flue gas from the power plant. Figure 1 contains a principle diagram of the CO2 capture part of the plant, which includes a cooling / scrubbing section at the top of the absorber and the stripper, respectively.

[0012] WO 2017042163 to Capsol-EOP AS describes a plant and method for the capture of CO2 from CO2-containing flue gases, such as flue gases from fossil fuel-burning power plants, where the CO2 is captured at high pressure and measures are implemented to reduce heat losses and corresponding energy costs in order to reduce the costs for CO2 capture. The flue gas is cooled from a typical temperature of flue gas of about 70 to 50 °C, e.g. 60 °C, typically to about 30 °C, before compression in order to reduce the humidity of the flue gas and thereby reduce the compressor work for flue gas compression. The heat of the incoming flue gas at a temperature of about 30 °C and the energy of condensation are usually considered as waste heat and released into the environment.

[0013] The costs of CO2 capture are often considered too high and waste heat is a significant part of the costs. The present invention relates to enabling a CO2 capture plant to return heat energy to an energy plant, such as a district heating plant, to increase the production of hot heat carriers for district heating and therefore increase the energy output from the energy plant. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] International Publication No. 0048709 [Patent Document 2] U.S. Patent Application Publication No. 2021 / 060478(A1) [Patent Document 3] Korean Patent Application Publication No. 20170132623(A) [Patent Document 4] US Patent No. 10227901(B2) [Patent Document 5] International Publication No. 2017042163 Summary of the Invention

[0015] According to a first aspect, the present invention relates to a method for capturing CO2 from flue gas from a district heating plant burning a carbonaceous fuel, wherein the flue gas is compressed and then cooled before being introduced into an absorber, the flue gas is made to flow countercurrently to an aqueous CO2 absorbent solution introduced into the absorber to produce lean flue gas, the lean flue gas is removed from the absorber and reheated by freshly incoming compressed flue gas and then expanded and discharged to the atmosphere, the CO2-absorbed rich absorbent is collected at the bottom of the absorber, removed therefrom and introduced into a regenerator, where the CO2-rich absorbent is stripped to release CO2 in countercurrent flow to steam to produce lean absorbent, and the stripped absorbent is then cooled. The absorbent or lean absorbent is removed from the bottom of the regenerator, the lean absorbent is introduced into the absorber, and the CO2 stripped from the absorbent and steam are removed from the regenerator for further processing and delivery for fixation of CO2, the method being characterized in that the lean absorbent stream is split into two, the first stream being introduced into the top of the absorbent packing in the absorber and the second stream being introduced into the top of the cooler packing at the top of the absorber to cool and dry the lean flue gas, which is then reheated by the newly incoming compressed flue gas and then expanded and discharged into the environment, and the second absorbent stream is cooled by a thermal fluid received from a district heating plant and the thermal fluid thus heated is returned to the district heating plant.

[0016] The flue gas introduced into the bottom of the absorber in countercurrent flow to the aqueous potassium carbonate absorbent is heated because CO2 absorption is an exothermic reaction. The lean flue gas thus heated is in intimate contact with water during heating, so that the lean flue gas leaving the absorber charge is saturated with water. Those skilled in the art will appreciate that when the lean exhaust gas leaving the absorber is cooled, typically from a temperature of about 100°C, a substantial portion of the moisture in the saturated gas will condense, depending on the gas temperature after cooling. Both the energy heat from cooling and the condensation energy are transferred to the heat carrier used to cool the gas, and this energy can be used for other purposes, such as district heating.

[0017] According to a first embodiment, the CO2 stripped from the absorbent and steam are cooled in a CO2 cooler located at the top of the regenerator by countercurrent flow against cooling water, after which the CO2 is removed for further processing and the heat transferred from the CO2 and steam to the cooling water is transferred directly or indirectly to a district heating plant.

[0018] According to another embodiment, the cooling water used to cool the CO2 and steam in the CO2 cooler is water circulating as thermal fluid in the district heating plant, water received from the district heating plant is introduced into the top of the CO2 cooler and used as cooling water, the cooling water thus heated being collected below the cooler and returned to the district heating plant.

[0019] Further according to one embodiment, the cooling water used to cool the CO2 and steam in the CO2 cooler circulates in a loop, the cooling water being cooled in the CO2 cooler heat exchanger by a heat carrier which is received from the district heating plant and circulates back to the district heating plant to transfer heat to the district heating plant.

[0020] According to one embodiment, the second stream of lean absorbent introduced into the top of the cooler packing at the top of the absorber constitutes 10-60%, such as 20-50%, of the total flow rate of lean absorbent introduced into the absorber tower.

[0021] The second stream of lean absorbent may be cooled to a temperature of from 55 to 75°C, for example from 60 to 70°C.

[0022] According to one embodiment, the incoming flue gas to be compressed is water saturated and has a temperature of 50-70°C.

[0023] According to a second aspect, a plant for recovering CO2 from flue gas from a district heating plant burning a carbonaceous fuel comprises a flue gas pipe (1) for introducing the flue gas into a flue gas compressor (6) driven by a motor (7) and / or another drive such as a steam turbine (7), and a compressed flue gas pipe (10) for introducing the compressed flue gas into a heat exchange unit (11), where the compressed flue gas is cooled by a CO2-lean flue gas. 0), a cooled flue gas pipe (15) for taking off the cooled flue gas and introducing it into the absorber tower (16) below the packed section (17), a lean absorbent pipe (18) for introducing lean absorbent at the top of the packed section (17), a lean flue gas pipe (26) connected to the top of the absorber tower (16) for conducting the lean flue gas from the absorber tower (16) to the heat exchange unit (11) to be heated by the compressed flue gas, and a lean absorbent pipe (27) connected to the top of the absorber tower (16) for conducting the lean flue gas from the absorber tower (16) to the heat exchange unit (11) to be heated by the compressed flue gas. a heated lean flue gas pipe (26') for conducting the gas to the lean flue gas expander (8); an expanded lean flue gas pipe (27) for discharging the lean flue gas to the environment; a rich absorbent pipe (19) for conducting the rich absorbent collected at the bottom of the absorber (16) and introducing it into the desorber (30) at the top of the packed stripper section (31); steam pipes (52', 40', 56') for introducing steam into the desorber (30) below the packed stripper section (31); and further The system comprises a CO2 take-off pipe (48) arranged to take out CO2 from the top of the desorption tower (30) for treatment and disposal, and lean absorbent pipes (18, 49) for leading the lean absorbent collected at the bottom of the desorption tower (30) and introducing it into the absorption tower (16), a side draw pipe (18') is arranged to take out a part of the lean absorbent in the lean absorbent pipe (18) and introduce the taken-out absorbent into a cooling water heat exchanger (25') for cooling it with a heat medium received from a district heating plant in a heat medium pipe (3), a heat medium return pipe (3') is arranged to return the heat medium thus heated to the district heating plant, and a cooling medium introduction pipe (23') is arranged to lead the cooled lean absorbent from the heat exchanger (25') and introduce it into the top of the cooler charge (21).

[0024] According to one embodiment, a CO2 cooler cooling water pipe (44) is arranged to introduce cooling water to the top of a CO2 cooler (43) located at the top of the desorber (30) to cool the CO2 and steam by countercurrent flow of water with the CO2 and steam before removing the CO2 through a CO2 removal pipe (48), a CO2 cooler collector plate (42) is arranged below the CO2 cooler (43) to collect used cooling water, and a CO2 cooling water removal pipe (45) is arranged to remove used cooling water from the CO2 cooler collector plate (42), and means are provided for supplying heat of the cooling water in the CO2 cooler cooling water removal pipe (45) to a district heating plant.

[0025] According to a further embodiment, the means for supplying heat to the district heating plant comprises a CO2 cooler heat exchanger (47), a CO2 cooler inlet heat medium pipe (4) arranged to supply a heat medium from the district heating plant to the CO2 cooler heat exchanger (47), a CO2 cooler heat medium return pipe (4') arranged in the CO2 cooler heat exchanger (47) to return the heated heat medium to the district heating plant, a CO2 cooler return pipe (47) arranged to supply hot cooling water to the CO2 cooler heat exchanger (47), and a CO2 cooler cooling water pipe (44) arranged to supply cooling water cooled in the heat exchanger to the top of the CO2 cooler (43).

[0026] According to another embodiment, the cooling fluid received in the CO2 cooler inlet heat transfer medium pipe (4) is water, the CO2 cooler inlet heat transfer medium pipe (4) is connected to the CO2 cooler cooling water pipe, and the CO2 cooler heat transfer medium return pipe (4') is connected to the CO2 cooler cooling water return pipe (45). [Brief description of the drawings]

[0027] [Figure 1] FIG. 2 is a flow diagram of an embodiment of a plant according to the invention. [Diagram 2] FIG. 4 is a flow diagram of another alternative embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] The present invention relates to a method and a plant for CO2 capture optimized for capturing CO2 from incoming flue gas, substantially water-saturated flue gas. A typical source of flue gas is a district heating plant or a combined plant for the production of electricity and heat for district heating. In this specification and in the claims, the expression "district heating plant" or "district heating plant" is used to include both district heating plants and combined plants for the production of electricity and heat for district heating.

[0029] The temperature of the incoming flue gas will typically be greater than 50° C., such as greater than 55° C. or greater than 58° C., and less than 70° C., such as less than 65° C. or less than 62° C., for example about 60° C., depending on the flue gas generating plant and the heat recovery system of the district heating plant which generates the flue gas. At said temperature and ambient pressure the incoming flue gas is substantially water saturated.

[0030] FIG. 1 is a flow diagram showing one embodiment of the present invention. Flue gas is introduced into the CO2 capture plant through a flue gas pipe 1 and optionally into a pretreatment unit 2 where it can be pretreated before being introduced into the plant. Pretreatment can include washing with water to remove particles and / or cooling to adjust the temperature of the incoming gas. However, since the flue gas is washed, water saturated and at the required temperature as above, the pretreatment unit can often be omitted. Flue gas from the CO2 generation plant is usually at near ambient pressure and is introduced into a flue gas compressor 6 either directly from the flue gas pipe or from a pretreatment flue gas pipe 5 which directs the flue gas from the pretreatment unit 2 and is typically compressed to a pressure of 0.5-1.2 MPaA (5-12 bara).

[0031] The flue gas compressor is driven by an electric motor and / or other drive device 7, such as a steam turbine, which is arranged on a common shaft 9 with the flue gas compressor 6 and a CO2 lean flue gas expander 8, described further below. The flue gas introduced to the flue gas compressor 6 is at a higher temperature and is water saturated than normally used, so the work of the compressor 6 must be increased compared to when introduced at 30°C.

[0032] The compressed flue gas is conducted through a compressed flue gas line 10 to a heat exchange unit 11 where the compressed, and therefore heated, flue gas is cooled by heat exchange with the CO2 lean flue gas and the heating medium of the reboiler 57, as will be further explained below.

[0033] The illustrated embodiment of the heat exchange unit has three heat exchangers. The compressed hot flue gas is first introduced into a first flue gas heat exchanger 12 where it exchanges heat with a CO2 lean flue gas. The flue gas leaving the first flue gas heat exchanger 12 is then introduced into a reboiler heat exchanger 13 and then led to a second flue gas heat exchanger 14 where the gas is further cooled by the CO2 lean flue gas.

[0034] The thus cooled compressed flue gas is then led from the heat exchange unit 11 through the cooled flue gas pipe 15 to the bottom of the absorber 16. Typically, the temperature of the cooled compressed flue gas introduced into the absorber 16 is about 100-110°C. In the absorber, the flue gas is made to flow countercurrently to the liquid CO2 absorbent introduced into the top of the packed absorber section 17 through the lean absorbent pipe 18 to ensure intimate contact between the flue gas flowing upwards in the packed section and the CO2 absorbent. Those skilled in the art will understand that the packed absorber section can have several packed sections, typically two or three sections, arranged one on top of the other. The absorbent with absorbed CO2, i.e. the rich absorbent, is collected at the bottom of the absorber 16 and is removed through the rich absorbent pipe 19 and regenerated as further described below. Typically, the temperature of the rich absorbent removed from the absorber 16 is about 105-115°C as it is heated by the exothermic absorption reaction of CO2.

[0035] The flue gas leaving the packed absorber section 17 where CO2 is absorbed (referred to herein as "lean flue gas") typically has a temperature of about 95-105°C and is directed to a cooler packing 21 where it is cooled by flowing countercurrently against cooled CO2 absorbent introduced through a cooled absorbent line 23' to the top of the cooler packing. The cooler packing 21 is typically located near the top of the absorber 16, but may be located in a separate unit. Those skilled in the art will appreciate that the cooler packing may consist of one or more packings, typically 1-3 packings.

[0036] The cooled absorbent introduced to the top of the cooler charge is cooled in the lean absorbent cooler 25 by the aqueous cooling fluid from the home heating system, which is taken from the lean absorbent line 18 in the take-off line 18' and introduced through the inflow heat transfer medium pipe 3 and returned to the home heating plant in the heat transfer medium return pipe 3', and transfers the thermal energy from the lean flue gas cooler 20 to the home heating plant to generate more heat for home heating purposes. The cooled CO2 absorbent is taken from the lean absorbent cooler 25 to the cooled absorbent pipe 23' and introduced to the top of the cooler charge 21. By cooling the CO2 lean flue gas in the cooling section 20, some of the moisture in the lean flue gas is condensed, thus reducing the moisture content in the CO2 lean flue gas. Typically, about 10-60% of the lean absorbent in absorbent line 18 is removed through removal line 18' and cooled in lean absorbent cooler 25, typically from 95-105°C to about 60-70°C.

[0037] The cooled CO2 lean flue gas leaving the lean flue gas cooling section, typically at a temperature of 60-75 ° C, is taken off through the CO2 lean flue gas pipe 26 and firstly introduced into the heat exchange unit 11, where it is first heated in the second flue gas heat exchanger 14, typically to 120-130 ° C, and then introduced into the first flue gas heat exchanger 12, where it is heated by heat exchange with the freshly incoming CO2 rich flue gas. The thus heated CO2 lean flue gas is then typically introduced into the expander 8, at a temperature of about 190-200 ° C, where the lean flue gas is expanded to ambient pressure, whereby it is cooled, typically to about 25-35 ° C, for example 30 ° C, and discharged into the environment through the expanded CO2 lean flue gas pipe 27, preferably a chimney not shown.

[0038] As mentioned above, the CO2 rich absorbent is removed from the bottom of the absorber in the rich absorbent tube 19, pumped by the rich absorbent pump 28 and introduced into the dissorber column 30. The temperature of the rich absorbent introduced into the dissorber column is typically about 105-115°C. A rich absorbent control valve 29 is preferably arranged at the top of the packed stripper section 31 arranged in series to control / reduce the pressure of the rich solvent before it is introduced into the dissorber column 30. Those skilled in the art will appreciate that the packed stripper section can have several packed sections, typically two or three sections, arranged one on top of the other. In the packed stripper section 31, the CO2 is stripped from the liquid absorbent by countercurrent flow of steam introduced from different steam sources below the packed stripper section 31, as described below.

[0039] The CO2 and steam stripped from the absorbent leaving the packed desorber section 31 typically have a temperature of about 100-120°C and flow upwardly through the desorber tower 30 through the lower desorber collector plate 32 and into the packed regenerative cooler section 33 where the steam and CO2 are cooled by countercurrent flow against cooling water. Cooling water, at a temperature of about 90-100°C, is introduced into the top of the packed regenerative cooler section 33 through the regenerative cooler water pipe 34. The cooling water and water condensed in the packed regenerative cooler section 33, having a temperature of about 95-105°C, are collected at the lower desorber collector plate 32, removed through the regenerative cooler water outlet pipe 35, flashed through the regenerative cooler flash valve 36, and introduced into the regenerative cooler flash tank 37.

[0040] The water collected at the bottom of the regenerative chiller flash tank 37 is removed through the regenerative chiller recycle pipe 38, pumped by the regenerative chiller pump 39 into the regenerative chiller pipe 34, and introduced as cooling water into the top of the packed regenerative chiller section.

[0041] The vapor formed by flashing in the regenerator flash tank 37 is removed through the regenerator vapor line 40, compressed in the regenerator vapor compressor 41, and then introduced into the desorber below the packed stripper section 31 as stripping vapor at a temperature of about 140-150°C.

[0042] The steam and CO2 leaving the top of the charged regenerative cooler section 33 continue to flow upwards in the desorber 30 through the CO2 cooler collector plate 42 and are further cooled in the CO2 cooler charged section 43 by countercurrent flow against the cooling water from about 90-100°C to a temperature of about 30°C. The cooling water is introduced into the top of the CO2 cooler charged section 43 through the CO2 cooler cooling water pipe 44. The cooling water is collected on the CO2 cooler collector plate 42, removed through the CO2 cooler water return pipe 45, and pumped by the CO2 cooler cooling water pump 46 to the CO2 cooler heat exchanger 47 where it is cooled by the heat medium received from the district heating plant through the inlet heat medium pipe 4. The heat medium heated in the CO2 cooler heat exchanger is removed through the heat medium return pipe 4' and returned to the district heating plant as a heated heat medium. The water cooled in the CO2 cooler heat exchanger 47 is reintroduced into the CO2 cooler via the CO2 cooler cooling water pipe 44.

[0043] Those skilled in the art will appreciate that the efficiency of steam production from the flash of regenerative cooling water in the regenerative chiller flash tank 37 can be increased by a two-stage flash process in which the aqueous phase leaving the flash tank 37 is flashed into a second flash tank at a second flash valve. In such a two-stage flash process, the vapor phase produced in the second flash tank is compressed in a second regenerative chiller vapor compressor to the same pressure as the vapor phase leaving the regenerative chiller vapor compressor 41 and introduced into the stripping column 30 as additional stripping vapor.

[0044] As mentioned above, the cooling water for cooling the CO2 and steam in the CO2 cooler charge section 43 is cooled in the CO2 cooler heat exchanger 47 by the cooling medium received from the district heating in the CO2 cooler inflow heat medium pipe 4 at a temperature of about 50-70°C, for example about 60°C, and returned to the CO2 generation plant in the CO2 cooler heat medium return pipe 4' at a temperature of about 80-100°C, for example about 90°C, to transfer thermal energy from the CO2 cooler charge section 43 to the CO2 generation plant to generate more heat for domestic heating purposes. Those skilled in the art will understand that the temperature of the inflow heat medium in the CO2 cooler heat medium pipe 4 may vary depending on the district heating plant, and the temperatures shown are the usual range of the temperature of the low-temperature heat medium from such a plant.

[0045] The cooled CO2 and steam are removed from the top of the desorber 30 via CO2 removal line 48 and introduced into modules not shown for drying, compression, and cooling of the captured CO2 before being sent out of the plant.

[0046] Lean absorbent, i.e. absorbent that has been stripped to remove CO2, is collected at the bottom of the desorber 30 from which it is removed through stripped absorbent pipe 49 at a temperature of about 110-120°C, flashed through lean flash valve 50 and introduced into flash tank 51. Liquid collected at the bottom of flash tank 51 at a temperature of about 95-105°C is pumped by pump 54 into lean absorbent pipe 18. A lean absorbent control valve 55 is preferably arranged to control the flow of lean absorbent out of the lean absorbent pump 54.

[0047] Steam is withdrawn from the lean flash tank 51 through the lean flash pipe 52, compressed in the lean flash compressor 53, and introduced as stripping steam at a temperature of about 150 to 200°C through the compressed lean flash pipe 52' into the desorber below the packed section 31.

[0048] A portion of the stripped absorbent collected at the bottom of the desorber 30 is removed through a reboiler pipe 56 and introduced into a reboiler 57, where the stripped absorbent is heated to generate steam, which is introduced into the desorber 30 as stripping steam through a reboiler steam pipe 56'. The reboiler 57 receives high-temperature steam for heating from the reboiler heat exchanger 13 through a reboiler heat pipe 58 at a temperature higher than about 128°C, and the steam used for heating in the reboiler is returned to the reboiler heat exchanger 13 in the form of water through a reboiler water return pipe 59 at a temperature of about 126°C. This heat transfer from the reboiler heat exchanger 13 to the reboiler 57 may be performed by a heat transfer medium other than water, for example, oil.

[0049] Introducing water-saturated flue gas at a higher temperature than previously proposed, for example 50°C to 70°C, typically around 60°C, into the flue gas compressor 6 increases the work of the flue gas compressor 6 compared to the previously proposed temperature of 30°C or less (see, for example, WO2017042163). The increased compressor work requires more power input to the motor 7. However, by compressing the water-saturated flue gas at a relatively higher temperature than previously proposed and allowing the flue gas to be condensed at a higher temperature and pressure, the energy from the condensation can be obtained at a higher temperature. As a result, both the cooling water heat exchanger 25 and the CO2 cooling water cooler 47 can supply high-temperature water to other purposes, such as domestic heating plants, at a temperature higher than 80°C, preferably around 90°C. In addition, the temperatures of both the absorber 16 and the desorber 30 increase. As a result of the increased temperature and, therefore, increased steam flow in the absorber and desorber, the flashing of the lean absorbent in the lean flash tank 51 and regenerator cooler flash tank 37 more efficiently produces the amount of steam required for stripping, which is compressed and returned to the desorber 30 as stripping steam as described above.

[0050] FIG. 2 shows an alternative embodiment of the invention, in which the CO2 is cooled in a cooler 43 by direct contact with a thermal fluid from a district heating plant. The thermal fluid circulating in a district heating system is usually water. According to this embodiment, the CO2 cooler 43 is cooled by direct contact with water from the district heating. Low temperature water, typically at a temperature of 50-70°C, for example about 60°C, is introduced from the heat transfer medium tube 4 to the top of the CO2 cooler 43 and flows counter to the CO2 flowing upwards in the CO2 cooler 43. The water heated by cooling the CO2 is collected on a collector plate 42, taken out via a cooling water tube 45 and pumped into the heat transfer medium return line 4' by a cooling water pump 46. The temperature of the water returned to line 4' is typically about 80-100°C, for example about 90°C.

[0051] Those skilled in the art will appreciate that district heating plants may have energy storage units to store thermal energy when heat production is greater than demand and to supply thermal energy when heat production is less than demand.Heat may be stored as hot water in large, well-insulated tanks or in salt solutions with melting points between 70 and 100°C.

Claims

1. CO from flue gases from district heating plants that burn carbonaceous fuels ２ 1. A method for recovering The flue gas is compressed and then cooled before being introduced into an absorber (16); The flue gas is introduced into the absorber (16) ２ flowing countercurrently to the absorbent solution to produce lean flue gas, which is removed from the absorber (16), reheated by the incoming compressed flue gas, and then expanded and discharged to the atmosphere; CO ２ The rich absorbent having absorbed the CO is collected at the bottom of the absorber (16), removed therefrom, and introduced into a regenerator (30), where the CO ２ The rich absorbent is absorbed by flowing countercurrently to the vapor. ２ to produce lean absorbent, removing the stripped or lean absorbent from the bottom of the regenerator (30), introducing the lean absorbent into the absorber (16), and removing the stripped CO from the absorbent. ２ and steam is taken from the regenerator (30) to produce CO ２ and delivering the resulting mixture to the reaction vessel for deposition of the stream of lean absorbent is split into two, a first stream introduced into the top of the absorbent packing (17) in the absorber (16) and a second stream introduced into the top of the cooler packing (21) at the top of the absorber, whereby the lean flue gas is reheated by the incoming compressed flue gas, and then cooled and dried before being expanded and discharged into the environment; the second absorbent stream is cooled by thermal fluid received from the district heating plant; and The thus heated thermal fluid is directed back to the district heating plant. A method characterized by:

2. CO ２ The CO2 and steam stripped from the absorbent are then pumped through a CO2 regenerator located at the top of the regenerator before being removed for further processing. ２ The CO is cooled in a cooler by countercurrent flow to an aqueous cooling fluid. ２ 2. The method of claim 1, wherein the heat transferred from the steam to the aqueous cooling fluid is transferred directly or indirectly to the district heating plant.

3. The CO ２ In the cooler ２ and the aqueous cooling fluid used to cool the steam is water circulating as a thermal fluid in the district heating plant, and water received from the district heating plant is used as the aqueous cooling fluid to cool the CO ２ 3. The method of claim 2, wherein the aqueous cooling fluid is introduced into the top of a cooler and, having been used and heated, is collected below the cooler and returned to the district heating plant.

4. The CO ２ In the cooler ２ and the aqueous cooling liquid used to cool the steam is circulated in a loop, and the aqueous cooling fluid is CO ２ 3. The method of claim 2, wherein the heat transfer medium is cooled in a cooler heat exchanger by a heat transfer medium received from the district heating plant and circulated back to the district heating plant to transfer heat to the district heating plant.

5. 5. The method of claim 1, wherein the second stream of lean absorbent introduced at the top of the absorber and on top of the cooler packing constitutes 10 to 60%, for example 20 to 50%, of the total flow rate of lean absorbent introduced into the absorber tower.

6. 5. A method according to any one of claims 1 to 4, wherein the second stream of lean absorbent is cooled to a temperature of from 55 to 75°C, for example from 60 to 70°C.

7. 5. A method according to any one of claims 1 to 4, wherein the inlet flue gas to be compressed is saturated with water and at a temperature of from 50 to 70°C.

8. CO from flue gases from district heating plants that burn carbonaceous fuels ２ 1. A plant for recovering a flue gas pipe (1) for introducing said flue gas into a flue gas compressor (6) operated by a motor (7) and / or other driving device such as a steam turbine (7); a compressed flue gas pipe (10) for introducing the compressed flue gas into a heat exchange unit (11), wherein the compressed flue gas is ２ a compressed flue gas pipe (10) cooled by lean flue gas; a cooled flue gas pipe (15) for removing the cooled flue gas and introducing it into an absorber tower (16) below a packed section (17); a lean absorbent pipe (18) for introducing lean absorbent at the top of said packed section (17); a lean flue gas pipe (26) connected to the top of the absorber (16) for conducting the lean flue gas from the absorber (16) to the heat exchange unit (11) so as to be heated by the compressed flue gas; a heated lean flue gas pipe (26') for conducting the heated lean flue gas from the heat exchange unit (11) to a lean flue gas expander (8); an expanded lean flue gas pipe (27) for discharging said lean flue gas into the environment; a rich absorbent pipe (19) for conducting the rich absorbent collected at the bottom of the absorber (16) and introducing it into the desorber column (30) at the top of the packed stripper section (31); a plurality of steam lines (52', 40', 56') for introducing steam into the desorption column (30) below the packed stripper section (31); CO 2 is extracted from the top of the desorption column (30) for further processing and disposal. ２ CO arranged to extract ２ an extraction tube (48); a lean absorbent pipe (18, 49) for leading the lean absorbent collected at the bottom of the desorption tower (30) and introducing it into the absorption tower (16); and a secondary withdrawal pipe (18') arranged for withdrawing a portion of the lean absorbent in the lean absorbent pipe (18) and introducing the withdrawn absorbent into the cooling water heat exchanger (25') for cooling with the heat medium in the heat medium pipe (3) received from the district heating plant, a heat medium return pipe (3') arranged for returning the heat medium thus heated to the district heating plant, and a cooling medium introduction pipe (23') for conducting the cooled lean absorbent from the heat exchanger (25') and introducing it into the top of the cooler packing (21) at the top of the absorber.

9. The CO ２ CO through the extraction pipe (48) ２ Before removing the CO ２ Cooling water is introduced into the top of the cooler (43) to separate the water and the CO ２ and the CO ２ and CO to cool the steam. ２ A cooler cooling water pipe (44) is arranged, and CO ２ A cooler collector plate (42) is provided to collect the used cooling water. ２ It is located below the cooler (43) and ２ The cooling water outlet pipe (45) ２ The CO is arranged to extract used cooling water from the cooler collector plate (42). ２ 9. A plant according to claim 8, wherein means are provided for supplying heat of the cooling water in the cooler cooling water take-off pipe (45) to the district heating plant.

10. The means for supplying heat to the district heating plant comprises CO ２ A cooler heat exchanger (47) is provided, ２ The cooler inlet heat medium pipe (4) carries the CO ２ A cooling device is arranged to supply a heat medium to the cooling device heat exchanger (47), and a CO ２ A cooler heat transfer medium return pipe (4') is connected to the CO ２ The CO ２ A cooler return pipe (47) returns high temperature cooling water to the CO ２ The CO is arranged to supply the cooler heat exchanger (47). ２ A cooler cooling water pipe (44) converts the cooling water cooled by the heat exchanger into CO ２ 10. A plant according to claim 9, arranged to feed the top of the cooler (43).

11. The CO ２ The cooling fluid received in the cooler inlet heat transfer pipe (4) is water, and the CO ２ The cooler inlet heat medium pipe (4) ２ The CO ２ The cooler heat medium return pipe (4') ２ 10. The plant according to claim 9, connected to a cooler cooling water return pipe (45).

12. 5. The method of any one of claims 1 to 4, wherein the second absorbent stream introduced at the top of the cooler packing to cool and dry the lean flue gas has a temperature that is 25 to 45°C lower than the first stream introduced at the top of the absorbent packing.

13. A plant according to any one of claims 8 to 11, wherein the withdrawn lean absorbent is cooled by 25 to 45°C before being introduced into the top of the cooler charge (21).

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