A system for separating and purifying CO2

Abstract

The present application provides a method for separating and purifying CO 2 The system can convert the CO in the initial gas 2 It is divided into two parts, and a part of the CO in the initial gas is cooled by four-stage cooling. 2 Condensed into liquid form, and using liquid CO 2 The high pressure and low temperature make it the power of the system ejector after gasification, which reduces the energy consumption of the entire system ejector. Then it is recovered after desulfurization treatment. The other part of CO in the initial gas 2 The process is treated by absorption of lean methanol liquid, and then recovered after step-by-step desulfurization flash distillation. The initial gas purification process only discharges wastewater, and there is no gas external emission link, which realizes the CO 2 Almost completely captured and recovered, and due to the removal of CO 2 The amount of lean methanol liquid is reduced by 30-45%, and the energy consumption for recovering the lean methanol liquid is also reduced by 30-45%. As a result, the diameter of each treatment tower can be reduced, thereby miniaturizing the equipment, reducing investment and land occupation, and having a high value for promotion and application.

Description

Technical Field

[0001] The present invention relates to the technical field of gas purification, and in particular to a system for separating and purifying CO2, and more particularly to a system for separating and purifying CO2 from coal chemical industry gas. Background Art

[0002] The low-temperature methanol washing process is a process for removing acid gas from gas jointly developed by Linde and Lurgi in the 1950s. Its principle belongs to physical absorption. The main features of this process are high gas purification degree, good absorption selectivity, good thermal stability and chemical stability of absorbent methanol, and can absorb multiple components such as CO2, H2S, COS, HCN, etc. in the gas at the same time. This process is widely used in gas purification devices such as hydrogen production, synthetic ammonia, methanol synthesis, coal-to-natural gas, etc., and the gas purification technology of existing large-scale coal chemical plants also mostly adopts the low-temperature methanol washing process.

[0003] The traditional low-temperature methanol washing process has many problems in terms of carbon emissions, energy consumption, and large-scale equipment. For example, the emission of CO2 gas is about 30% to 60% of the total CO2, which can no longer meet the country's development requirements.

[0004] Patent CN103320176A proposes a low-temperature methanol washing method and device with high CO2 yield. The maximum CO2 gas yield can reach 91.2%, but the device still retains the process of regenerating methanol with nitrogen gas.

[0005] Patent CN103418210B proposes a CO2 full capture and H2S enrichment process, which effectively combines the low-temperature methanol washing process and the acidic gas stripping and concentration process, eliminates the nitrogen stripping system and the H2S enrichment tower, does not set up the tail gas washing and venting system, and does not generate tail gas during operation. More than 99.5% of the CO2 gas in the crude synthesis gas is recovered into a high-concentration CO2 product gas. However, the equipment introduces MDEA solution, and in order to achieve full capture of CO2 gas, the circulating amount of methanol is greatly increased, resulting in large-scale equipment, complex process routes, and high operating energy consumption.

[0006] The temperature of liquid CO2 is close to -56.57℃, and its vapor pressure is relatively high, with a minimum of 0.518MPa. The CO2 gas after flash evaporation has higher kinetic energy and a low flash temperature, which is lower than the evaporation temperature of other refrigerants at the same pressure. Evaporation at 0.518Mpa can provide a refrigeration temperature of about -55℃, so it can condense part of the CO2 in the initial gas of almost all coal gasification technologies without the need to provide additional cooling capacity required to liquefy the CO2 in the raw gas.

[0007] Patent CN102971253A proposed a process idea for liquefying and separating CO2, and separated liquid CO2 products, but did not fully utilize the performance of liquid CO2 as an absorbent, nor did it utilize the high-level kinetic energy of liquid CO2 as a jet power. Patent CN104208978B improved the low-temperature methanol washing process based on patent CN102971253A, and designed and utilized the absorbent properties of liquid CO2 and the kinetic energy of high-level liquid CO2, but in terms of process configuration, patent CN104208978B did not systematically consider the energy configuration of the entire process. Only the cooling of condensed CO2 was not enough to support the cooling capacity of the entire process, and it lacked feasibility. Summary of the invention

[0008] In view of the above-mentioned defects or shortcomings in the prior art, the present application aims to provide a system for separating and purifying CO2. By redesigning the purification system, the CO2 gas in the initial gas can be divided into two parts for treatment. One part of the CO2 in the initial gas is condensed into liquid CO2 by condensation, and the high pressure and low temperature of the liquid CO2 are fully utilized. After gasification, it is used as the power of the ejector of the entire system, and then recovered after treatment. The other part of the CO2 in the initial gas is treated by absorption by lean methanol liquid, and then recovered after step-by-step reduced pressure flash evaporation treatment. Since the amount of lean methanol liquid used to remove CO2 is greatly reduced, the energy consumption for recovering the lean methanol liquid is also significantly reduced, so that the diameter of each treatment tower can be reduced at the same time, thereby realizing the miniaturization of the equipment, which has a high value for promotion and application.

[0009] The present application provides a system for separating and purifying CO2, the system comprising:

[0010] A cooling and separation device, used for condensing and separating the initial gas to obtain CO2 liquid a and gas a, comprising a first gas input port connected to the initial gas delivery pipeline, a second liquid output port connected to the flash tower system and used for outputting CO2 liquid a, a third gas output port connected to the absorption tower (C1) and used for outputting gas a, a fourth liquid input port connected to the flash tower system and used for inputting reduced pressure flash CO2 liquid b, and a fifth gas output port connected to the gas inlet end of the CO2 injector and used for outputting gas b formed by evaporation of the CO2 liquid b;

[0011] The absorption tower (C1) is used for the first liquid to absorb CO2 and sulfide in the gas a to produce purified gas and a second liquid, which are respectively connected to the purified gas collection device and the flash tower system through pipelines;

[0012] The flash tower system is used to perform reduced pressure flash evaporation on the second liquid to separate CO2, to obtain gas c and a third liquid, and the third liquid is transported to a sulfide absorption tower (C4) via a pipeline;

[0013] The CO2 ejector is used to extract the gas c and mix it with the gas b and then transport it to the sulfide absorption tower (C4) through a pipeline;

[0014] The sulfide absorption tower (C4) is used to absorb the sulfides in the gas c and the gas b, and the produced CO2 product gas is connected to the CO2 product gas collection device via a pipeline.

[0015] Specifically, the first liquid is a methanol-lean liquid; the second liquid is a methanol-rich liquid that has absorbed CO2 and sulfides, including a sulfur-containing methanol-rich liquid and a sulfur-free methanol-rich liquid; the third liquid is a sulfur-containing semi-lean methanol liquid; after the initial gas passes through the cooling and separation module, about 40% of the CO2 in the initial gas is condensed into CO2 liquid a.

[0016] According to an embodiment of the present application, the cooling and separation device includes a first cooling and separation module, a second cooling and separation module and a liquid CO2 evaporator (E7); the liquid CO2 evaporator (E7) includes a first inlet, a first outlet, a second inlet, and a second outlet; the second inlet is the fourth liquid input port, and the second outlet is the fifth gas output port;

[0017] The output end of the first cooling and separation module is connected to the first inlet, and the input end is the first gas input port;

[0018] The input end of the second cooling and separation module is connected to the first outlet, and the output end includes the second liquid output port and the third gas output port.

[0019] Specifically, the liquid CO2 evaporator (E7) is used to evaporate and gasify liquid CO2 to provide a low-temperature environment to cool the initial gas. The CO2 liquid undergoes a phase change from high pressure to low pressure, from liquid to gas, and can provide a low-temperature environment of about -55°C to cool the initial gas.

[0020] According to an embodiment of the present application, the first cooling and separation module includes an initial gas-purified gas heat exchanger (E1) provided with the first gas input port, an alcohol-water separation tank (V1) connected to the outlet of the initial gas-purified gas heat exchanger (E1), and an ammonia cooler (E2) connected to the first inlet, the other end of the ammonia cooler (E2) is connected to the top of the alcohol-water separation tank (V1), and the bottom of the alcohol-water separation tank (V1) is connected to the alcohol-water distillation tower (C6) through a pipeline through a sewage cooler (E15).

[0021] Specifically, the initial gas delivery pipeline between the initial gas-purified gas heat exchanger (E1) and the alcohol-water separation tank (V1) is connected to the sulfur-free methanol vacuum flash section (C3-3) in the flash tower system; the antifreeze methanol liquid input into the initial gas delivery pipeline by the sulfur-free methanol vacuum flash section (C3-3) is sulfur-free semi-lean methanol liquid, in order to prevent the liquid condensed from the initial gas from freezing in the pipeline and clogging the pipeline, and the alcohol-water separation tank (V1) is used to separate the initial gas and the antifreeze methanol liquid; the initial gas-purified gas heat exchanger (E1) performs primary cooling on the initial gas; the ammonia cooler (E2) performs secondary cooling on the initial gas; the alcohol-water distillation tower (C6) is used to heat and evaporate to separate methanol and water, in preparation for the recycling and regeneration of methanol liquid, and the separated produced wastewater enters the sewage treatment device.

[0022] According to an embodiment of the present application, the second cooling and separation module includes an initial gas fourth-stage cooler (E31) connected to the first outlet and a liquid CO2 separation tank (V2) connected to the other end of the initial gas fourth-stage cooler (E31); the liquid CO2 separation tank (V2) is provided with the third gas output port at the top and the second liquid output port at the bottom.

[0023] According to an embodiment of the present application, the absorption tower (C1) includes a desulfurization section (C1-1), a rough wash section (C1-2), a main wash section (C1-3), and a fine wash section (C1-4) from bottom to top. The lower part of the desulfurization section (C1-1) is connected to the third gas output port via a pipeline, and the bottom is connected to the sulfur-containing methanol medium-pressure flash section (C2-2) in the flash tower system via a pipeline in sequence through a filter (F1), a sulfur-containing methanol cooler (E13), and a pressure reducing valve 1 (K1); the lower part of the rough wash section (C1-2) is connected to the upper part of the desulfurization section (C1-1) and the sulfur-free methanol medium-pressure flash section (C2-3) in the flash tower system via a pipeline. The upper part is connected, and a pressure reducing valve 2 (K2) is provided on the pipeline connecting the lower part of the rough washing section (C1-2) and the upper part of the sulfur-free methanol medium-pressure flash section (C2-3); the lower part of the main washing section (C1-3) is connected to the upper part of the rough washing section (C1-2) through a pipeline through the main washing section methanol cooler (E4) of the absorption tower; the lower part of the fine washing section (C1-4) is connected to the upper part of the main washing section (C1-3) through a pipeline through the methanol ammonia cooler (E3) of the absorption tower, and the top is connected to the purified gas collecting device through the initial gas four-stage cooler (E31) and the initial gas-purified gas heat exchanger (E1) in sequence through a pipeline, and the fine washing section (C1-4) is provided with a pipeline connected to the methanol storage tank (V5).

[0024] Specifically, since the produced purified gas still has a relatively low temperature (-40 to -50°C), it can be further used as a coolant to reduce the energy consumption of refrigeration of the entire system. After analyzing the process route, the purified gas enters the initial gas four-stage cooler (E31) and the initial gas-purified gas heat exchanger (E1) in sequence through the pipeline to cool the initial gas, and then enters the purified gas product collection device, thereby reducing the energy consumption of refrigeration of the entire system.

[0025] The absorption tower (C1) is used to remove CO2 and sulfide in the remaining initial gas from the lean methanol liquid to produce purified gas that meets the standard requirements. In the process of the lean methanol liquid gradually absorbing CO2 and sulfide in the initial gas, the temperature of the lean methanol liquid continues to rise. In order to ensure the good absorbency of the lean methanol liquid, the lean methanol liquid at the bottom of the fine washing section (C1-4) is cooled by the methanol ammonia cooler (E3) of the absorption tower and then enters the main washing section (C1-3), and the lean methanol liquid at the bottom of the main washing section (C1-3) is cooled by the methanol cooler E4 of the main washing section and then enters the rough washing section (C1-2).

[0026] According to an embodiment of the present application, the CO2 injector includes a sulfur-free CO2 injector (J1) and a sulfur-containing CO2 injector (J2), and the second outlet is connected to the air inlet ends of the sulfur-free CO2 injector (J1) and the sulfur-containing CO2 injector (J2) respectively through pipelines;

[0027] The flash tower system comprises a medium-low pressure flash tower (C2), wherein the medium-low pressure flash tower (C2) comprises an effective gas recovery section (C2-1), a sulfur-containing methanol medium-pressure flash section (C2-2), a sulfur-free methanol medium-pressure flash section (C2-3), a sulfur-containing methanol low-pressure flash section (C2-4), and a sulfur-free methanol low-pressure flash section (C2-5);

[0028] The bottom of the effective gas recovery section (C2-1) is connected to the second inlet via a pipeline, and the upper part is connected to the second liquid outlet and the sulfur-containing methanol medium-pressure flash section (C2-2) via pipelines; the bottom of the sulfur-containing methanol medium-pressure flash section (C2-2) is connected to the upper part of the sulfur-containing methanol low-pressure flash section (C2-4) via a pipeline, and the upper part is connected to the pipeline of the initial gas connected to the ammonia cooler (E2) through a circulating CO2 cooler (E16), a gas compressor (M1), a water cooler (E14), and a circulating CO2 cooler (E16); the bottom of the sulfur-free methanol medium-pressure flash section (C2-3) is connected to the upper part of the sulfur-containing methanol low-pressure flash section (C2-4) via a pipeline. A pipeline is connected to the upper part of the sulfur-free methanol low-pressure flash section (C2-5), and the top is connected to the sulfur-containing methanol medium-pressure flash section (C2-2) via a pipeline; the bottom of the sulfur-containing methanol low-pressure flash section (C2-4) is connected to the upper part of the sulfur-containing methanol atmospheric flash section (C3-2) in the flash tower system via a pipeline, and the top is connected to the air inlet end of the sulfur-containing CO2 injector (J2) via a pipeline; the bottom of the sulfur-free methanol low-pressure flash section (C2-5) is connected to the upper part of the sulfur-free methanol atmospheric flash section (C3-4) in the flash tower system via a pipeline, and the top is connected to the air inlet end of the sulfur-free CO2 injector (J1) via a pipeline.

[0029] Specifically, the medium-low pressure flash tower (C2) is used to perform reduced pressure flash evaporation on the methanol-rich liquid that absorbs CO2 and sulfide, and gradually separate CO2 from the methanol-rich liquid.

[0030] According to an embodiment of the present application, the flash tower system includes an atmospheric pressure vacuum flash tower (C3), and the atmospheric pressure vacuum flash tower (C3) includes a sulfur-containing methanol vacuum flash section (C3-1), a sulfur-containing methanol atmospheric pressure flash section (C3-2), a sulfur-free methanol vacuum flash section (C3-3), and a sulfur-free methanol atmospheric pressure flash section (C3-4); the bottom of the sulfur-containing methanol vacuum flash section (C3-1) is connected to the feed inlet of the medium-pressure flash tower feed pump (P3) and the sulfur-containing methanol circulation pump (P4) through a pipeline, and the upper part is connected to the air inlet end of the sulfur-containing CO2 injector (J2) through a pipeline; the medium-pressure flash tower feed pump (P3) The discharge port of the sulfur-containing methanol medium-pressure flash section (C2-2) is connected to the sulfur-containing methanol medium-pressure flash section (C2-2) through a pipeline; the discharge port of the sulfur-containing methanol circulation pump (P4) is connected to the middle of the sulfide absorption tower (C4) through a pipeline through the methanol cooler (E4) of the main wash section of the absorption tower; the bottom of the sulfur-containing methanol atmospheric pressure flash section (C3-2) is connected to the upper part of the sulfur-containing methanol vacuum flash section (C3-1) through a pipeline, the top is connected to the gas outlet end of the sulfur-containing CO2 ejector (J2) through a pipeline, and the upper part is connected to the sulfur-containing methanol low-pressure flash section (C2-4) through a pipeline. The bottom of the sulfur-free methanol vacuum flash section (C3-3) is connected to the feed ports of the supplementary / antifreeze methanol feed pump (P1) and the sulfide absorption tower feed pump (P2) through pipelines, and the upper part is connected to the air inlet end of the sulfur-free CO2 ejector (J1) through pipelines; the discharge port of the supplementary / antifreeze methanol feed pump (P1) is connected to the upper part of the main washing section (C1-3) and the initial gas delivery pipeline between the initial gas-purified gas heat exchanger (E1) and the alcohol-water separation tank (V1) through pipelines; the discharge port of the sulfide absorption tower feed pump (P2) is connected to the lean methanol through a pipeline. The precooler (E5) is connected to the upper part of the sulfide absorption tower (C4); the bottom of the sulfur-free methanol atmospheric pressure flash section (C3-4) is connected to the upper part of the sulfur-free methanol vacuum flash section (C3-3) through a pipeline, the top is connected to the gas outlet end of the sulfur-free CO2 injector (J1) through a pipeline, and the upper part is connected to the bottom of the sulfur-free methanol low-pressure flash section (C2-5) through a pipeline; the gas outlet ends of the sulfur-free CO2 injector (J1) and the sulfur-containing CO2 injector (J2) are merged through a pipeline and connected to the lower part of the sulfide absorption tower (C4) through the initial gas-purified gas heat exchanger (E1).

[0031] Specifically, the atmospheric pressure vacuum flash tower (C3) is used to continue to perform reduced pressure flash evaporation on the methanol-rich liquid that absorbs CO2 and sulfides, and further gradually separate CO2 from the methanol-rich liquid. The separated gas and semi-lean methanol liquid are transported to the sulfide absorption tower (C4) through pipelines. In the sulfide absorption tower (C4), the gas is desulfurized and purified to produce CO2 product gas, and the semi-lean methanol liquid enters the thermal regeneration tower (C5).

[0032] The gas and liquid flashed off under reduced pressure in the atmospheric vacuum flash tower module (C3) both have relatively low temperatures (-40 to -55°C), and can further function as a coolant to reduce the energy consumption of refrigeration in the entire system. After analyzing the process route, the gas flashed off under reduced pressure in the atmospheric vacuum flash tower module (C3) passes through the initial gas-purified gas heat exchanger (E1) to cool the initial gas and then returns to the sulfide absorption tower module (C4). The liquid flashed off under reduced pressure in the atmospheric vacuum flash tower module (C3) passes through the methanol cooler (E4) of the main wash section of the absorption tower to cool the poor methanol liquid in the main wash section (C1-3) and then enters the sulfide absorption tower module (C4).

[0033] According to an embodiment of the present application, the bottom of the sulfide absorption tower (C4) is connected to the middle of the thermal regeneration tower (C5) through a pipeline in sequence through a thermal regeneration tower feed pump (P6), a primary preheater (E6), and a secondary preheater (E10), and the top is connected to the CO2 product gas collection device through a pipeline in sequence through an H2S cooler (E12), the initial gas fourth-stage cooler (E31), and the initial gas-purified gas heat exchanger (E1).

[0034] Specifically, the sulfide absorption tower (C4) also includes a third outlet (C41) and a third inlet (C42), the third outlet (C41) is located higher than the third inlet (C42) and is located above the bottom tower plate in the sulfide absorption tower (C4); the third outlet (C41) is connected to the third inlet (C42) through a pipeline in sequence through the sulfide absorption tower extraction pump (P5) and the sulfur-containing methanol cooler (E13).

[0035] Since the CO2 product gas still has a relatively low temperature (-40 to -50°C), it can also be further used as a coolant to reduce the energy consumption of the entire system's refrigeration. After analyzing the process route, the CO2 product gas is further cooled by the H2S cooler (E12), the initial gas four-stage cooler (E31), and the initial gas-purified gas heat exchanger (E1) before entering the CO2 product gas collection device for storage.

[0036] According to an embodiment of the present application, the bottom of the thermal regeneration tower (C5) is connected to the feed port of the methanol storage tank (V5) through a pipeline in sequence through a thermal regeneration tower bottom extraction pump (P8) and a secondary preheater (E10), and the top is connected to the H2S primary separation tank (V3) through a pipeline through a thermal regeneration tower top condenser (E11); the bottom of the H2S primary separation tank (V3) is connected to the upper part of the thermal regeneration tower (C5) through a pipeline through a thermal regeneration tower top reflux pump (P9), and the top is connected to the H2S secondary separation tank (V4) through a pipeline through the H2S cooler (E12); the bottom of the H2S secondary separation tank (V4) is connected to the upper part of the thermal regeneration tower (C5) through a pipeline, and the top is connected to the H2S recovery device through the initial gas-purified gas heat exchanger (E1) through a pipeline.

[0037] Specifically, the discharge port pipe of the methanol storage tank (V5) is connected to the upper part of the fine washing section (C1-4) in sequence through the absorption tower feed pump (P7), the primary preheater (E6), the lean methanol precooler (E5).

[0038] The thermal regeneration tower (C5) also includes a fourth outlet (C51) and a fourth inlet (C52), wherein the fourth outlet (C51) is located at the bottom of the thermal regeneration tower (C5), and the fourth inlet (C52) is located higher than the fourth outlet (C51), and the fourth outlet (C51) is connected to the fourth inlet (C52) via a pipeline through the thermal regeneration tower reboiler (E8).

[0039] The discharge port of the thermal regeneration tower bottom extraction pump (P8) is also connected to the upper part of the alcohol-water distillation tower (C6) via a pipeline.

[0040] The bottom of the alcohol-water distillation tower (C6) is connected to the sewage treatment device through a sewage cooler (E15) via a pipeline, and the top is connected to the middle of the thermal regeneration tower (C5); the alcohol-water distillation tower (C6) also includes a fifth outlet (C61) and a fifth inlet (C62), the fifth outlet (C61) is located at the bottom of the alcohol-water distillation tower (C6), the fifth inlet (C62) is located higher than the fifth outlet (C61), and the fifth outlet (C61) is connected to the fifth inlet (C62) through a pipeline through an alcohol-water separation tower reboiler (E9).

[0041] According to an embodiment of the present application, a tower plate is provided in the medium-pressure flash distillation section (C2-2) of the sulfur-containing methanol; the bottom of the desulfurization section (C1-1) is connected to the medium-pressure flash distillation section (C2-2) of the sulfur-containing methanol via a pipeline, and the position of the pipeline interface connected to the medium-pressure flash distillation section (C2-2) of the sulfur-containing methanol is lower than the tower plate; the upper part of the effective gas recovery section (C2-1) is connected to the medium-pressure flash distillation section (C2-2) of the sulfur-containing methanol via a pipeline. The medium-pressure flash section (C2-2) of sulfur-containing methanol is connected, and the position of the pipeline interface connected to the medium-pressure flash section (C2-2) of sulfur-containing methanol is lower than the tower plate; the top of the medium-pressure flash section (C2-3) of sulfur-free methanol is connected to the medium-pressure flash section (C2-2) of sulfur-containing methanol via a pipeline, and the position of the pipeline interface connected to the medium-pressure flash section (C2-2) of sulfur-containing methanol is lower than the tower plate; the discharge port of the medium-pressure flash tower feed pump (P3) is connected to the medium-pressure flash section (C2-2) of sulfur-containing methanol via a pipeline, and the position of the pipeline interface connected to the medium-pressure flash section (C2-2) of sulfur-containing methanol is higher than the tower plate; the circulating CO2 cooler (E16) is connected to the medium-pressure flash section (C2-2) of sulfur-containing methanol via a pipeline, and the position of the pipeline interface connected to the medium-pressure flash section (C2-2) of sulfur-containing methanol is higher than the tower plate.

[0042] Specifically, the tower plate is a three-layer tower plate, and the pressure drop of a single-layer tower plate is controlled in the range of 0.5 to 0.8 KPa. The three-layer tower plate can reduce the amount of CO2 gas in the effective gas and maintain the amount of CO2 gas in the range of 10% to 15% without causing too high a pressure drop, thereby increasing the energy consumption of the subsequent compressor to increase the effective gas pressure.

[0043] In summary, the present application discloses a system for separating and purifying CO2. The beneficial effect produced by the above scheme is that, compared with the process of the traditional technology in which all CO2 in the initial gas is treated by methanol absorption, the CO2 in the initial gas of the present application is divided into two parts for treatment. One is to condense about 40% of the CO2 in the initial gas into CO2 liquid a by using a cooling separation device, and obtain the remaining gas a after separation. CO2 liquid a is subjected to reduced pressure flash evaporation to obtain effective gas a and CO2 liquid b, and the high pressure and low temperature characteristics of CO2 liquid b are fully utilized. After evaporation, it becomes CO2 gas b as the power of the system ejector, which reduces the energy consumption of the system ejector. Secondly, lean methanol liquid is used to absorb another part of CO2 in gas a, and then CO2 gas c is evaporated out through step-by-step reduced pressure for recovery. Finally, gas c and gas b are mixed and enter the sulfide absorption tower (C4) for desulfurization to obtain CO2 product gas, thereby realizing CO2 recovery. There is no gas external emission link in the entire treatment process, and the CO2 in the initial gas is almost completely captured and recovered. Moreover, since about 40% of the CO2 in the initial gas is not absorbed and removed by the lean methanol liquid, the amount of lean methanol liquid for removing CO2 is reduced by 30-45%, and the energy consumption for recovering the lean methanol liquid is also reduced by 30-45%. Since the amount of circulating lean methanol liquid is greatly reduced, the diameter of each treatment tower can be reduced, and then the equipment can be miniaturized, which has a high value for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Other features, objects and advantages of the present application will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings.

[0045] Figure 1 This is a schematic diagram of the structure of the gas purification system of this application.

[0046] in,

[0047] C1: absorption tower; C1-1: desulfurization section; C1-2: rough washing section; C1-3: main washing section; C1-4: fine washing section; C2: medium and low pressure flash tower; C2-1: effective gas recovery section; C2-2: medium pressure flash section of sulfur-containing methanol; C2-3: medium pressure flash section of sulfur-free methanol; C2-4: low pressure flash section of sulfur-containing methanol; C2-5: low pressure flash section of sulfur-free methanol; C3: atmospheric pressure vacuum flash tower; C3-1: vacuum flash section of sulfur-containing methanol; C3-2: atmospheric pressure flash section of sulfur-containing methanol; C3-3: vacuum flash section of sulfur-free methanol; C3-4: atmospheric pressure flash section of sulfur-free methanol; C4: sulfide absorption tower; C5: thermal regeneration tower; C6: alcohol-water distillation tower; C41: third outlet; C42: third inlet; C51: fourth outlet; C52: fourth inlet; C61: fifth outlet; C62: fifth inlet.

[0048] E1: initial gas-purified gas heat exchanger; E2: ammonia cooler; E3: methanol ammonia cooler for absorber tower; E31: initial gas fourth-stage cooler; E4: methanol cooler for main wash section of absorber tower; E5: lean methanol precooler; E6: primary preheater; E7: liquid CO2 evaporator; E8: thermal regeneration tower reboiler; E9: alcohol-water separation tower reboiler; E10: secondary preheater; E11: thermal regeneration tower top condenser; E12: H2S cooler; E13: sulfur-containing methanol cooler; E14: water cooler; E15: sewage cooler; E16: circulating CO2 cooler.

[0049] V1: alcohol-water separation tank; V2: liquid CO2 separation tank; V3: H2S primary separation tank; V4: H2S secondary separation tank; V5: methanol storage tank.

[0050] P1: Supplementary / antifreeze methanol feed pump; P2: Sulfide absorber feed pump; P3: Medium-pressure flash tower feed pump; P4: Sulfur-containing methanol circulation pump; P5: Sulfide absorber extraction pump; P6: Thermal regeneration tower feed pump; P7: Absorber feed pump; P8: Thermal regeneration tower bottom extraction pump; P9: Thermal regeneration tower top reflux pump.

[0051] J1: sulfur-free CO2 injector; J2: sulfur-containing CO2 injector; M1: gas compressor; F1: filter; K1: pressure reducing valve 1; K2: pressure reducing valve 2. DETAILED DESCRIPTION

[0052] The present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are only used to explain the relevant invention, rather than to limit the invention. It is also necessary to explain that, for ease of description, only the parts related to the invention are shown in the accompanying drawings.

[0053] The present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0054] Example 1

[0055] like Figure 1 The gas purification system shown mainly includes a cooling separation device, an absorption tower C1, a flash tower system, a sulfide absorption tower C4, a thermal regeneration tower C5, an alcohol-water separation tower C6 and a CO2 ejector.

[0056] Wherein, the flash tower system includes a medium-low pressure flash tower C2 and an atmospheric pressure vacuum flash tower C3; the absorption tower C1 includes a desulfurization section C1-1, a rough washing section C1-2, a main washing section C1-3, and a fine washing section C1-4; the medium-low pressure flash tower C2 includes an effective gas recovery section C2-1, a sulfur-containing methanol medium-pressure flash section C2-2, a sulfur-free methanol medium-pressure flash section C2-3, a sulfur-containing methanol low-pressure flash section C2-4, and a sulfur-free methanol low-pressure flash section C2-5; the atmospheric pressure vacuum flash tower C3, a sulfur-containing methanol vacuum flash section C3-1, a sulfur-containing methanol atmospheric pressure flash section C3-2, a sulfur-free methanol vacuum flash section C3-3, and a sulfur-free methanol atmospheric pressure flash section C3-4, and the CO2 injector includes a sulfur-free CO2 injector J1 and a sulfur-containing CO2 injector J2.

[0057] The cooling and separation device is provided with a first gas input port connected to the initial gas delivery pipeline, a second liquid output port connected to the flash tower system and used for outputting CO2 liquid a, a third gas output port connected to the absorption tower C1 and used for outputting gas a, a fourth liquid input port connected to the flash tower system and used for inputting CO2 liquid b after reduced pressure flash evaporation, and a fifth gas output port connected to the gas inlet end of the CO2 injector and used for outputting gas b formed by evaporation of the CO2 liquid b.

[0058] The cooling and separation device includes a first cooling and separation module, a second cooling and separation module and a liquid CO2 evaporator E7; the liquid CO2 evaporator E7 includes a first inlet, a first outlet, a second inlet and a second outlet; the second inlet is the fourth liquid input port; the second outlet is the fifth gas output port, which are respectively connected to the air inlet ends of the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2 through pipelines.

[0059] Furthermore, the first cooling and separation module includes an initial gas-purified gas heat exchanger E1 provided with the first gas input port, an alcohol-water separation tank V1 connected to the outlet of the initial gas-purified gas heat exchanger E1, and an ammonia cooler E2 connected to the first inlet, the other end of the ammonia cooler E2 is connected to the top of the alcohol-water separation tank V1, and the bottom of the alcohol-water separation tank V1 is connected to the alcohol-water distillation tower C6 through a pipeline through a sewage cooler E15; the initial gas delivery pipeline between the initial gas-purified gas heat exchanger E1 and the alcohol-water separation tank V1 is connected to the sulfur-free methanol vacuum flash section C3-3 in the atmospheric pressure vacuum flash tower C3.

[0060] Furthermore, the second cooling and separation module includes an initial gas fourth-stage cooler E31 connected to the first outlet and a liquid CO2 separation tank V2 connected to the other end of the initial gas fourth-stage cooler E31; the liquid CO2 separation tank V2 is provided with the third gas output port at the top and the second liquid output port at the bottom.

[0061] Furthermore, the lower part of the desulfurization section C1-1 is connected to the third gas outlet via a pipeline, and the bottom is connected to the sulfur-containing methanol medium-pressure flash section C2-2 arranged in the medium-low pressure flash tower C2 via a pipeline in sequence through the filter F1, the sulfur-containing methanol cooler E13, and the pressure reducing valve K1, and the pipeline interface position connected to the sulfur-containing methanol medium-pressure flash section C2-2 is lower than the three-layer tower plate arranged inside the sulfur-containing methanol medium-pressure flash section C2-2; the rough washing section The lower part of C1-2 is connected to the upper part of the desulfurization section C1-1 and the upper part of the sulfur-free methanol medium-pressure flash section C2-3 arranged in the medium-low pressure flash tower C2 through pipelines, and a pressure reducing valve 2 K2 is provided on the pipeline connecting the lower part of the rough wash section C1-2 and the upper part of the sulfur-free methanol medium-pressure flash section C2-3; the lower part of the main wash section C1-3 is connected to the upper part of the rough wash section C1-2 through the main wash section methanol cooler E4 of the absorption tower through a pipeline; the lower part of the fine wash section C1-4 is connected to the upper part of the main wash section C1-3 through the methanol ammonia cooler E3 of the absorption tower through a pipeline, and the top is connected to the purified gas collecting device through the initial gas four-stage cooler E31 and the initial gas-purified gas heat exchanger E1 in sequence through a pipeline, and the fine wash section C1-4 is provided with a pipeline connected to the methanol storage tank V5.

[0062] Furthermore, the bottom of the effective gas recovery section C2-1 is connected to the second inlet via a pipeline, and the upper part is connected to the second liquid output port and the sulfur-containing methanol medium-pressure flash section C2-2 via pipelines, and the pipeline interface connected to the sulfur-containing methanol medium-pressure flash section C2-2 is located below the three-layer tower plate; the bottom of the sulfur-containing methanol medium-pressure flash section C2-2 is connected to the upper part of the sulfur-containing methanol low-pressure flash section C2-4 via a pipeline, and the upper part is connected to the initial gas pipeline of the ammonia cooler E2 through the circulating CO2 cooler E16, the gas compressor M1, the water cooler E14, and the circulating CO2 cooler E16 in sequence, and the upper part of the sulfur-containing methanol medium-pressure flash section C2-2 is connected to the circulating CO2 cooler (E16) The position of the connected pipeline interface is higher than the tower plate; the bottom of the sulfur-free methanol medium-pressure flash section C2-3 is connected to the upper part of the sulfur-free methanol low-pressure flash section C2-5 through a pipeline, and the top is connected to the sulfur-containing methanol medium-pressure flash section C2-2 through a pipeline, and the pipeline interface connected to the sulfur-containing methanol medium-pressure flash section C2-2 is lower than the three-layer tower plate; the bottom of the sulfur-containing methanol low-pressure flash section C2-4 is connected to the upper part of the sulfur-containing methanol atmospheric flash section C3-2 arranged in C3 in the atmospheric pressure vacuum flash tower through a pipeline, and the top is connected to the air inlet end of the sulfur-containing CO2 injector J2 through a pipeline; the bottom of the sulfur-free methanol low-pressure flash section C2-5 is connected to the upper part of the sulfur-free methanol atmospheric flash section C3-4 arranged in C3 in the atmospheric pressure vacuum flash tower through a pipeline, and the top is connected to the air inlet end of the sulfur-free CO2 injector J1 through a pipeline.

[0063] Furthermore, the bottom of the sulfur-containing methanol vacuum flash section C3-1 is connected to the feed ports of the medium-pressure flash tower feed pump P3 and the sulfur-containing methanol circulation pump P4 through pipelines, and the upper part is connected to the air inlet end of the sulfur-containing CO2 injector J2 through a pipeline; the discharge port of the medium-pressure flash tower feed pump P3 is connected to the upper part of the sulfur-containing methanol medium-pressure flash section C2-2 through a pipeline, and the pipeline interface position is higher than the three-layer tower plate; the discharge port of the sulfur-containing methanol circulation pump P4 is connected to the middle part of the sulfide absorption tower C4 through the methanol cooler E4 of the main washing section of the absorption tower through a pipeline; the bottom of the sulfur-containing methanol atmospheric pressure flash section C3-2 is connected to the upper part of the sulfur-containing methanol vacuum flash section C3-1 through a pipeline. The top is connected to the gas outlet of the sulfur-containing CO2 injector J2 through a pipeline; the bottom of the sulfur-free methanol vacuum flash section C3-3 is respectively connected to the feed ports of the supplementary / antifreeze methanol feed pump P1 and the sulfide absorption tower feed pump P2 through a pipeline, and the upper part is connected to the gas inlet end of the sulfur-free CO2 injector J1 through a pipeline; the discharge port of the supplementary / antifreeze methanol feed pump P1 is respectively connected to the upper part of the main washing section C1-3 and the initial gas delivery pipeline between the initial gas-purified gas heat exchanger E1 and the alcohol-water separation tank V1 through a pipeline; the discharge port of the sulfide absorption tower feed pump P2 is connected to the sulfide absorption tower C4 through a lean methanol precooler E5 through a pipeline. The upper part is connected; the bottom of the sulfur-free methanol atmospheric pressure flash section C3-4 is connected to the upper part of the sulfur-free methanol vacuum flash section C3-3 through a pipeline, and the top is connected to the gas outlet end of the sulfur-free CO2 injector J1 through a pipeline; the gas outlet ends of the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2 are merged through a pipeline and connected to the lower part of the sulfide absorption tower C4 through the initial gas-purified gas heat exchanger E1.

[0064] Furthermore, the bottom of the sulfide absorption tower C4 is connected to the middle of the thermal regeneration tower C5 through a pipeline in sequence through the thermal regeneration tower feed pump P6, the first-stage preheater E6, and the second-stage preheater E10, and the top is connected to the CO2 product gas collection device through a pipeline in sequence through the H2S cooler E12, the initial gas fourth-stage cooler E31, and the initial gas-purified gas heat exchanger E1; the sulfide absorption tower C4 also includes a third outlet C41 and a third inlet C42, and the third outlet C41 is located higher than the third inlet C42 and is located above the bottom tower plate in the sulfide absorption tower C4; the third outlet C41 is connected to the third inlet C42 through a pipeline in sequence through the sulfide absorption tower extraction pump P5 and the sulfur-containing methanol cooler E13.

[0065] Furthermore, the bottom of the thermal regeneration tower C5 is connected to the feed port of the methanol storage tank V5 through a pipeline in sequence through the thermal regeneration tower bottom extraction pump P8 and the secondary preheater E10, and the top is connected to the H2S primary separation tank V3 through a pipeline through the thermal regeneration tower top condenser E11; the thermal regeneration tower C5 also includes a fourth outlet C51 and a fourth inlet C52, the fourth outlet C51 is located at the bottom of the thermal regeneration tower C5, the fourth inlet C52 is located higher than the fourth outlet C51, and the fourth outlet C51 is connected to the fourth inlet C52 through a pipeline through the thermal regeneration tower reboiler E8.

[0066] Furthermore, the bottom of the H2S primary separation tank V3 is connected to the upper part of the thermal regeneration tower C5 through a pipeline via the thermal regeneration tower top reflux pump P9, and the top is connected to the H2S secondary separation tank V4 through a pipeline via the H2S cooler E12; the bottom of the H2S secondary separation tank V4 is connected to the upper part of the thermal regeneration tower C5 through a pipeline, and the top is connected to the H2S recovery device through the initial gas-purified gas heat exchanger E1 through a pipeline.

[0067] Furthermore, the discharge port of the thermal regeneration tower bottom extraction pump P8 is also connected to the upper part of the alcohol-water distillation tower C6 via a pipeline.

[0068] Furthermore, the discharge diameter pipeline of the methanol storage tank V5 is connected to the upper part of the fine washing section C1-4 through the absorption tower feed pump P7, the primary preheater E6, and the lean methanol precooler E5 in sequence.

[0069] Furthermore, the bottom of the alcohol-water distillation tower C6 is connected to the sewage treatment device through the sewage cooler E15 via a pipeline, and the top is connected to the middle of the thermal regeneration tower C5; the alcohol-water distillation tower C6 also includes a fifth outlet C61 and a fifth inlet C62, the fifth outlet C61 is located at the bottom of the alcohol-water distillation tower C6, the fifth inlet C62 is located higher than the fifth outlet C61, and the sixth outlet C61 is connected to the fifth inlet C62 through a pipeline through the alcohol-water separation tower reboiler E9.

[0070] Example 2

[0071] Use Figure 1 The gas purification system shown purifies the initial gas produced by coal-to-methanol production. The initial gas pressure is about 3.56 MPa, and the composition is: 43% H2, 19.4% CO, 36.2% CO2, 0.69% H2S and other component gases. The main processing process is as follows:

[0072] The initial gas (temperature of about 30°C) is cooled to about 0°C by the initial gas-purified gas heat exchanger E1, mixed with the sulfur-free semi-lean methanol liquid h for antifreezing from the sulfur-free methanol vacuum flash section C3-3, and then enters the alcohol-water separation tank V1, where the sulfur-free semi-lean methanol liquid i (temperature of about 0°C, pressure of about 3.6MPa) and gas i (temperature of 0°C, pressure of 3.6MPa) are separated.

[0073] The gas i is output from the top of the alcohol-water separation tank V1, mixed with the effective gas c from the sulfur-containing methanol medium-pressure flash section C2-2, and then enters the ammonia cooler E2. After being cooled to -10 to -20°C by the ammonia cooler E2, it enters the liquid CO2 evaporator E7 from the first inlet and is further cooled to -47 to -53°C. At this time, part of the CO2 in the gas i has been condensed into a liquid phase. After being output from the first outlet, it enters the initial gas fourth-stage cooler E31 and is further cooled to -55 to -57°C. The CO2 in the gas i is further condensed, and then enters the liquid CO2 separation tank V2. After separation, CO2 liquid a (temperature of about -53°C, pressure of about 3.55MPa) and gas a (temperature of -53°C, pressure of about 3.55MPa) are obtained.

[0074] The gas a is output from the third gas output port at the top of the liquid CO2 separation tank V2, enters the desulfurization section C1-1 of the absorption tower C1 for desulfurization, and then enters the rough washing section C1-2 and the main washing section C1-3 in sequence to remove most of the remaining CO2 in the gas a, and finally is further processed by the lean methanol liquid of the fine washing section C1-4 to produce a purified gas that meets the requirements, the purified gas temperature is -45 to -55°C, the pressure is about 3.6MPa, the CO2 content is less than 20ppm, and the sulfide content is less than 1ppm. Since the purified gas still has a relatively low temperature and can be used as a refrigerant to provide cooling for the system, the purified gas enters the initial gas four-stage cooler E31 through the pipeline in sequence to perform four-stage cooling on the gas i, enters the initial gas-purified gas heat exchanger E1 to perform one-stage cooling on the initial gas, and then enters the purified gas product collection device. The process is used to purify the lean methanol liquid of gas a from the methanol storage tank V5, which is cooled to about -60°C through the primary preheater E6 and the lean methanol precooler E5, and then enters the upper fine washing section C1-4 of the absorption tower C1, and then enters the main washing section C1-3, the rough washing section C1-2, and the desulfurization section C1-1 in sequence, absorbing CO2 and sulfide step by step. In the process that the lean methanol liquid gradually absorbs CO2 and sulfide in gas a, the temperature of the lean methanol liquid continues to rise. In order to ensure the good absorption of the lean methanol liquid, the lean methanol liquid at about -30°C at the bottom of the fine washing section C1-4 is cooled to about -55°C by the methanol ammonia cooler E3 of the absorption tower, and then enters the main washing section C1-3, and the lean methanol liquid at about -35°C at the bottom of the main washing section C1-3 is cooled to about -45°C by the methanol cooler E4 of the main washing section, and then enters the rough washing section C1-2.

[0075] The sulfur-free semi-lean methanol liquid i is output from the bottom of the alcohol-water separation tank V1 and enters the middle of the alcohol-water distillation tower C6 after passing through the sewage cooler E15. After heating, the methanol in the sulfur-free semi-lean methanol liquid i evaporates and gasifies to form methanol vapor m, which is output from the top of the alcohol-water distillation tower C6 and enters the thermal regeneration tower C5 for regeneration and recycling. The remaining wastewater (temperature of about 110°C and pressure of about 0.15MPa) flows out from the bottom of the alcohol-water distillation tower C6, is cooled by the sewage cooler E15, and enters the sewage treatment device. In order to maintain the temperature stability of the alcohol-water distillation tower C6, the waste water at the bottom of the alcohol-water distillation tower C6 is output from the fifth outlet C61 and heated to 100-120°C through the alcohol-water separation tower reboiler E9, and then returns to the alcohol-water distillation tower C6 from the fifth inlet C62 to heat the sulfur-free semi-lean methanol liquid i from the alcohol-water separation tank V1, thereby promoting the continuous evaporation and gasification of the methanol in the sulfur-free semi-lean methanol liquid i to form methanol vapor, which enters the thermal regeneration tower C5 for methanol regeneration and recycling. The methanol vapor has a temperature of 70-100°C and a pressure of 0.1-0.2MPa, and mainly includes 35-40% methanol and 60-65% water.

[0076] The CO2 liquid a output from the second liquid output port at the bottom of the liquid CO2 separation tank V2 enters the effective gas recovery section C2-1 of the medium-low pressure flash tower C2 through a pipeline, and is subjected to reduced pressure flash evaporation to obtain effective gas a and CO2 liquid b (temperature of about -53°C, temperature of about 1.0MPa). The effective gas a has a temperature of about -35°C and a pressure of about 1.0MPa, including 5-8% H2 and CO, and enters below the three-layer tower plate of the medium-pressure flash section C2-2 of sulfur-containing methanol through a pipeline.

[0077] The lean methanol liquid that absorbs CO2 and sulfide in the absorption tower C1 becomes a methanol-rich liquid a, and the methanol-rich liquid a includes a sulfur-containing methanol-rich liquid c and a sulfur-free methanol-rich liquid d. The sulfur-containing methanol-rich liquid c (temperature of about -25°C, pressure of about 3.6 MPa, CO2 content of 5-8%) output from the bottom of the desulfurization section C1-1 of the absorption tower C1 is successively passed through a filter F1, cooled to -28°C by a sulfur-containing methanol cooler E13, and reduced in pressure to 1.0 MPa by a pressure reducing valve K1, and then enters the sulfur-containing methanol medium-pressure flash section C2-2 below the three-layer tower plate, and is subjected to reduced pressure flash evaporation to obtain a sulfur-containing methanol-rich liquid e (temperature of about -45°C, pressure of about 0.9 MPa) and a gas e (temperature of about -45°C, pressure of about 0.9 MPa). The gas e includes CO2 and sulfide, and is mixed with the effective gas a from the effective gas recovery section C2-1.

[0078] A part of the sulfur-free methanol-rich liquid d (temperature of about -25°C, pressure of about 3.6MPa, CO2 content of 40%) output from the rough washing section C1-2 of the absorption tower C1 enters the desulfurization section C1-1 to continue to absorb sulfides in the gas a, and the other part can be reduced in pressure to 1.0MPa through the pressure reducing valve K2 according to needs and then enter the sulfur-free methanol medium-pressure flash section C2-3. After reduced pressure flash evaporation, sulfur-free methanol-rich liquid f (temperature of about -45°C, pressure of about 0.9MPa) and gas f (temperature of about -45°C, pressure of 0.9MPa, CO2 content of 10%) are obtained. The gas f enters the sulfur-containing methanol medium-pressure flash section C2-2 below the third tower plate and mixes with the effective gas a and gas e therein to obtain effective gas b (temperature of -40 to -45°C, pressure of about 0.9MPa, containing about 55% CO2). After the sulfur-containing semi-lean methanol liquid g After washing and absorbing most of the CO2, effective gas c is obtained (temperature -40 to -50°C, pressure of about 0.9 MPa). The effective gas c is discharged from the top of the sulfur-containing methanol medium-pressure flash section C2-2, enters the circulating CO2 cooler E16 for heat exchange and temperature rise to about -25°C, and then enters the gas compressor M1. After being pressurized to 3.6 MPa by the compressor M1, it enters the water cooler E14 for cooling to about -30°C, and then enters the circulating CO2 cooler E16 again. After being cooled to about -35°C by the circulating CO2 cooler E16, it is mixed with the gas i through a pipeline and enters the ammonia cooler E2 for further cooling. In order to reduce the volume of the compressed effective gas c, at the three-layer tower plate of the sulfur-containing methanol medium-pressure flash section C2-2, the sulfur-containing semi-lean methanol liquid g from the bottom of the sulfur-containing methanol vacuum flash section C3-1 in the atmospheric pressure vacuum flash tower C3 will absorb about 70 to 75% of the CO2 gas in the effective gas b, thereby reducing the amount of CO2 re-entering the gas i and reducing the volume of the effective gas c, which not only improves the CO2 recovery rate but also reduces the power consumption of the compressor M1.

[0079] The sulfur-free methanol-rich liquid f (temperature of about -40°C, pressure of about 1.0MPa, CO2 content of 10%) output from the bottom of the sulfur-free methanol medium-pressure flash section C2-3 enters the sulfur-free methanol low-pressure flash section C2-5, and further decompresses and flashes to produce sulfur-free CO2 gas h1 (temperature of about -45°C, pressure of about 0.6MPa, CO2 content of 35%), which is mixed with the gas b and enters the air inlet end of the sulfur-free CO2 injector J1 as the power gas of the sulfur-free CO2 injector J1, while the sulfur-free methanol-rich liquid h1 (temperature of about -45°C, pressure of about 0.6MPa, CO2 content of 5%) output from the bottom of the sulfur-free methanol low-pressure flash section C2-5 It enters the sulfur-free methanol atmospheric pressure flash section C3-4, and further reduces pressure and flashes to produce sulfur-free CO2 gas h2 (temperature about -50°C, pressure about 0.1MPa), which is then joined with the outlet of the sulfur-free CO2 ejector J1 through a pipeline. The sulfur-free methanol-rich liquid h2 (temperature about -50°C, pressure about 0.1MPa, CO2 content 1-3%) output from the bottom of the sulfur-free methanol atmospheric pressure flash section C3-4 enters the sulfur-free methanol vacuum flash section C3-3, and further reduces pressure and flashes to produce sulfur-free CO2 gas h3 (temperature about -65°C, pressure 0.02MPa The sulfur-free CO2 gas a is mixed with the sulfur-free CO2 gas h1 and the sulfur-free CO2 gas h2 at the outlet of the sulfur-free CO2 injector J1 to obtain the gas h (temperature about -65°C, pressure about 0.02MPa), and the sulfur-free semi-lean methanol liquid h (temperature about -65°C, pressure about 0.02MPa, CO2 content 1-3%) is obtained in the sulfur-free methanol vacuum flash section C3-3. The sulfur-free semi-lean methanol liquid h output from the bottom of the sulfur-free methanol vacuum flash section C3-3 is divided into three parts. The first part is mixed with the initial gas through the supplementary / antifreeze methanol feed pump P1 and then enters the alcohol-water separation tank V1 for antifreeze. The second part enters the main washing section C1-3 through the supplementary / antifreeze methanol feed pump P1 to continue to absorb the CO2 gas in the gas a. The third part enters the upper part of the sulfide absorption tower C4 after passing through the sulfide absorption tower feed pump P2 and the lean methanol precooler E5 to remove the sulfide in the gas d.

[0080] The sulfur-containing methanol-rich liquid e (temperature about -40°C, pressure about 1.0MPa, CO2 content 5%, sulfide <0.5%) output from the bottom of the sulfur-containing methanol medium-pressure flash section C2-2 enters the sulfur-containing methanol low-pressure flash section C2-4 through a pipeline, and a part of the sulfur-containing CO2 gas g1 (temperature about -45°C, pressure about 0.6MPa, CO2 content 10%) is flashed out under reduced pressure and then mixed with the gas b and enters the sulfur-containing CO2 injector J2 as the power gas of the sulfur-containing CO2 injector J2, while the sulfur-containing methanol low-pressure flash section C2-4 output from the bottom of the sulfur-containing methanol low-pressure flash section C2-4 is The output sulfur-containing methanol-rich liquid g1 (temperature about -45°C, pressure about 0.6MPa, CO2 content 3%, sulfide <0.5%) enters the sulfur-containing methanol atmospheric pressure flash section C3-2, further reduces pressure and flashes out part of the sulfur-containing CO2 gas g2 (temperature about -50°C, pressure about 0.1MPa, CO2 content 8%), and merges with the gas outlet end of the sulfur-containing CO2 ejector J2 through a pipeline, while the sulfur-containing methanol-rich liquid g2 (temperature about -50°C, pressure about 0.1MPa, The sulfur-containing CO2 gas g3 (temperature about -65°C, pressure about 0.02MPa) is further flashed under reduced pressure to produce the sulfur-containing CO2 gas g3 (temperature about -65°C, pressure about 0.02MPa) and is extracted by the sulfur-containing CO2 ejector J2, and merges with the sulfur-containing CO2 gas g1 and the sulfur-containing CO2 gas g2 at the gas outlet of the sulfur-containing CO2 ejector J2 to obtain gas g (temperature about -65°C, pressure about 0.02MPa). At this time, the sulfur-containing semi-lean methanol liquid g (temperature about -65°C, pressure about 0.02MPa, CO2 content 2%, sulfide <0.5%) is obtained in the sulfur-containing methanol vacuum flash section C3-1. The sulfur-containing semi-lean methanol liquid g output from the bottom of the sulfur-containing methanol vacuum flash section C3-1 is divided into two parts. The first part enters the sulfur-containing methanol medium-pressure flash section C2-2 above three tower plates to continue to absorb CO2 in the effective gas b, and the second part cools the lean methanol liquid of the main wash section C1-3 through the methanol cooler E4 of the absorption tower main wash section, and then enters the middle part of the sulfide absorption tower C4 for sulfide removal.

[0081] The CO2 liquid b output from the bottom of the effective gas recovery section C2-1 enters the liquid CO2 evaporator E7 from the second inlet, and is depressurized by the liquid CO2 evaporator E7. The CO2 liquid b undergoes a phase change from high pressure to low pressure, and changes from liquid to gas, to obtain gas b (temperature of about -55°C, pressure of about 0.6MPa), which can provide a low-temperature environment of about -55°C to achieve cooling of the gas i. At the same time, after being output from the second outlet, the gas b enters the air inlet ends of the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2 through pipelines, respectively, and serves as the power gas for the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2, thereby reducing the energy consumption of the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2.

[0082] The sulfur-free CO2 gas h and the sulfur-containing CO2 gas g respectively merged at the outlet of the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2 are merged through a pipeline to form a gas c, and the gas c is mixed with the gas b to obtain a gas d. The gas d (temperature is about -55°C, pressure is about 0.1MPa) After being heated by the initial gas-purified gas heat exchanger E1 (the temperature of gas d is about -35°C at this time), it enters the sulfide absorption tower C4 for sulfide removal to purify gas d. The purified gas d is output from the top of the tower sulfide absorption C4. At this time, the gas d has reached the standard for CO2 product gas recovery and utilization (temperature is about -55°C, pressure is about 0.6MPa, CO2 content is 99.99%), but it still has a relatively low temperature and can further play a role as a coolant to reduce the cooling demand and energy consumption of the entire system. Therefore, the H2S-containing gas k1 is cooled by the H2S cooler E12 in turn, the gas i is cooled by the initial gas four-stage cooler E31 for four-stage cooling, and the initial gas is cooled by the initial gas-purified gas heat exchanger E1 for one-stage cooling before entering the CO2 product gas collection device for sealing (temperature is about -20°C, pressure is about 0.6MPa, CO2 content is 99.99%).

[0083] The sulfur-containing semi-lean methanol liquid g and the sulfur-free semi-lean methanol liquid h are combined at the lower part of the sulfide absorption tower C4 to obtain the semi-lean methanol liquid b (temperature of about -40 to -50°C, pressure of 0.1 to 0.3 MPa, CO2 content of 3%, sulfide <0.5%). At this time, the semi-lean methanol liquid b still has a relatively low temperature and can fully utilize the role of the refrigerant to reduce the energy consumption of the system refrigeration. In order to make full use of this part of the energy and further reduce the cooling demand energy consumption of the entire system, the semi-lean methanol liquid b in the sulfide absorption tower C4 is extracted from the third outlet C41, and the sulfur-containing methanol cooler E13 cools the sulfur-rich methanol liquid c output from the bottom of the desulfurization section C1-1, and then returns to the lower part of the sulfide absorption tower C4 from the third inlet C42.

[0084] The semi-lean methanol liquid b (temperature of about -10°C, pressure of 0.1-0.3MPa, CO2 content of 3%, sulfide <0.5%) output from the bottom of the sulfide absorption tower C4 passes through the thermal regeneration tower feed pump P6, the first-stage preheater E6, and the second-stage preheater E10 in sequence for heat exchange (temperature of -5°C, pressure of 0.1-0.3MPa, CO2 content of 3%, sulfide <0.5%) and enters the thermal regeneration tower C5 for sulfide removal to purify the semi-lean methanol liquid b and convert it into lean methanol liquid for repeated use.

[0085] The purified lean methanol liquid (temperature of about 75°C and pressure of about 0.15MPa) is output from the bottom of the thermal regeneration tower C5 and divided into two parts. The first part is cooled to about 25°C by heat exchange in the secondary preheater E10 and then enters the methanol storage tank V5. The second part enters the alcohol-water distillation tower C6 for heating and evaporation and then is output from the top of the alcohol-water distillation tower C6 back to the thermal regeneration tower C5 to heat the semi-lean methanol liquid b, promote the precipitation of sulfide gas in the semi-lean methanol liquid b, make full use of the energy of the alcohol-water distillation tower C6 to heat the lean methanol liquid, and reduce the energy consumption of the thermal regeneration tower reboiler E8.

[0086] When the temperature of the semi-lean methanol liquid b in the thermal regeneration tower C5 drops to a certain level, sulfide gas no longer precipitates. Therefore, part of the lean methanol liquid at the bottom of the thermal regeneration tower C5 is output from the fourth outlet C51 and heated by the thermal regeneration tower reboiler E8 to form a gas-liquid mixture, and then returns to the thermal regeneration tower C5 from the fourth inlet C52 to heat the semi-lean methanol liquid b, thereby promoting the precipitation of sulfide gas in the semi-lean methanol liquid b and ensuring that the sulfide in the semi-lean methanol liquid b is fully removed to form a lean methanol liquid (temperature of about 75°C, pressure of 0.1-0.3MPa, CO2 content of 0.1%, sulfide <0.5%).

[0087] The H2S-containing gas j (temperature of 50°C, pressure of 0.1-0.3MPa, H2S content of 3-8%) output from the top of the thermal regeneration tower C5 is cooled to about 40°C by the thermal regeneration tower top condenser E11 and enters the H2S primary separation tank V3. The condensed liquid in the H2S primary separation tank V3 (temperature of about 40°C, pressure of 0.1-0.3MPa, H2S content of 1%) is output from the bottom and returned to the upper part of the thermal regeneration tower C5 for heating to continue to evaporate the H2S-containing gas j, while the H2S-containing gas k1 (temperature of about 40°C, pressure of 0.1-0.3MPa, H2S content of 1%) output from the top of the H2S primary separation tank V3 is The condensed liquid in the H2S secondary separation tank V4 (temperature is about 25°C, pressure is 0.1-0.3MPa, H2S content is 1%) is output from the bottom and returned to the upper part of the hot regeneration tower C5 for heating to continue to evaporate the H2S-containing gas j, and the H2S-containing gas k (temperature is about 25°C, pressure is 0.1-0.3MPa, H2S content is 3-8%) output from the top of the H2S secondary separation tank V4 is heated to about 30°C by the initial gas-purified gas heat exchanger E1 and enters the H2S recovery device.

[0088] It can be seen from the above embodiments that the present application provides a system for separating and purifying CO2. By designing a new gas purification system, the CO2 gas in the initial gas can be divided into two parts for processing. First, by adopting a four-stage cooling method of an initial gas-purified gas heat exchanger E1, an ammonia cooler E2, a liquid CO2 evaporator E7, and an initial gas four-stage cooler E31, about 40% of the CO2 in the initial gas is condensed into CO2 liquid a by utilizing the low temperature generated by the transformation of CO2's own physical state, and the remaining gas a is obtained after separation. CO2 liquid a is subjected to reduced pressure flash evaporation to obtain effective gas a and CO2 liquid b, and the characteristics of high pressure and low temperature of CO2 liquid b are fully utilized. After evaporation and gasification, it becomes gas b as the power of the ejector of the whole system, which reduces the energy consumption of the ejector of the whole system. Secondly, lean methanol liquid is used to absorb another part of CO2 in gas a, and then gas c is recovered by step-by-step reduced pressure flash evaporation. Finally, the two parts of gas b and gas c are mixed and enter the sulfide absorption tower C4 for desulfurization treatment to obtain CO2 product gas, thereby realizing CO2 recovery. The whole process only has wastewater discharge and no gas external discharge link, which realizes almost complete capture and recovery of CO2 in the initial gas, and is sealed under pressure for easy use. Moreover, since about 40% of CO2 in the initial gas is not absorbed and removed by lean methanol liquid, the amount of lean methanol liquid used for removing CO2 is reduced by 30-45%, and the energy consumption of recovering lean methanol liquid is also reduced by 30-45%. Since the amount of circulating lean methanol liquid is greatly reduced, the diameter of each treatment tower can be reduced, thereby realizing miniaturization of equipment, reducing investment and land occupation, and having high promotion and application value.

[0089] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A system for separating and purifying CO2, characterized in that: The system comprises: A cooling and separation device, used for condensing and separating the initial gas to obtain CO2 liquid a and gas a, comprising a first gas input port connected to the initial gas delivery pipeline, a second liquid output port connected to the flash tower system and used for outputting CO2 liquid a, a third gas output port connected to the absorption tower (C1) and used for outputting gas a, a fourth liquid input port connected to the flash tower system and used for inputting CO2 liquid b obtained by reduced pressure flash evaporation of the CO2 liquid a, and a fifth gas output port connected to the gas inlet end of the CO2 injector and used for outputting gas b formed by evaporation of the CO2 liquid b; The absorption tower (C1) is used for the first liquid to absorb CO2 and sulfide in the gas a to produce purified gas and a second liquid, which are respectively connected to the purified gas collection device and the flash tower system through pipelines; The flash tower system is used to perform reduced pressure flash evaporation on the second liquid to separate CO2 to obtain gas c; The CO2 ejector is used to extract the gas c and mix it with the gas b and then transport it to the sulfide absorption tower (C4) through a pipeline; The sulfide absorption tower (C4) is used to absorb the sulfides in the gas c and the gas b, and the produced CO2 product gas is connected to the CO2 product gas collection device through a pipeline; Wherein, the cooling and separation device comprises a first cooling and separation module, a second cooling and separation module and a liquid CO2 evaporator (E7); the liquid CO2 evaporator (E7) comprises a first inlet, a first outlet, a second inlet and a second outlet; the second inlet is the fourth liquid input port, and the second outlet is the fifth gas output port; the first cooling and separation module comprises an initial gas-purified gas heat exchanger (E1) provided with the first gas input port, an alcohol-water separation tank (V1) connected to the outlet of the initial gas-purified gas heat exchanger (E1), and an ammonia cooler (E2) connected to the first inlet, and the other end of the ammonia cooler (E2) is connected to the top of the alcohol-water separation tank (V1); the second cooling and separation module comprises an initial gas fourth-stage cooler (E31) connected to the first outlet, and a liquid CO2 separation tank (V2) connected to the other end of the initial gas fourth-stage cooler (E31).

2. A system for separating and purifying CO2 according to claim 1, characterized in that: The output end of the first cooling and separation module is connected to the first inlet, and the input end is the first gas input port; The input end of the second cooling and separation module is connected to the first outlet, and the output end includes the second liquid output port and the third gas output port.

3. A system for separating and purifying CO2 according to claim 2, characterized in that: The bottom of the alcohol-water separation tank (V1) is connected to the alcohol-water distillation tower (C6) via a pipeline through a sewage cooler (E15).

4. A system for separating and purifying CO2 according to claim 2 or 3, characterized in that: The top of the liquid CO2 separation tank (V2) is provided with the third gas outlet, and the bottom is provided with a second liquid outlet.

5. A system for separating and purifying CO2 according to claim 4, characterized in that: The absorption tower (C1) comprises, from bottom to top, a desulfurization section (C1-1), a rough wash section (C1-2), a main wash section (C1-3), and a fine wash section (C1-4); the lower part of the desulfurization section (C1-1) is connected to the third gas outlet via a pipeline, and the bottom is connected to the sulfur-containing methanol medium-pressure flash section (C2-2) in the flash tower system via a pipeline in sequence through a filter (F1), a sulfur-containing methanol cooler (E13), and a pressure reducing valve 1 (K1); the lower part of the rough wash section (C1-2) is connected to the upper part of the desulfurization section (C1-1) and the upper part of the sulfur-free methanol medium-pressure flash section (C2-3) in the flash tower system via a pipeline, and the rough wash section is connected to the lower part of the desulfurization section (C1-1) and the upper part of the sulfur-free methanol medium-pressure flash section (C2-3) in the flash tower system via a pipeline, and the rough wash section is connected to the lower part of the desulfurization section (C1-1). A pressure reducing valve 2 (K2) is provided on the pipelines at the lower part of the sulfur-free methanol medium-pressure flash section (C1-2) and the upper part of the sulfur-free methanol medium-pressure flash section (C2-3); the lower part of the main wash section (C1-3) is connected to the upper part of the rough wash section (C1-2) through a pipeline through the main wash section methanol cooler (E4) of the absorption tower; the lower part of the fine wash section (C1-4) is connected to the upper part of the main wash section (C1-3) through a pipeline through the methanol ammonia cooler (E3) of the absorption tower, and the top is connected to the purified gas collecting device through a pipeline in sequence through the initial gas four-stage cooler (E31) and the initial gas-purified gas heat exchanger (E1), and the fine wash section (C1-4) is provided with a pipeline connected to the methanol storage tank (V5).

6. A system for separating and purifying CO2 according to claim 5, characterized in that: The CO2 injector comprises a sulfur-free CO2 injector (J1) and a sulfur-containing CO2 injector (J2), and the second outlet is connected to the air inlet ends of the sulfur-free CO2 injector (J1) and the sulfur-containing CO2 injector (J2) respectively through pipelines; The flash tower system comprises a medium-low pressure flash tower (C2), and the medium-low pressure flash tower (C2) comprises an effective gas recovery section (C2-1), a sulfur-containing methanol medium-pressure flash section (C2-2), a sulfur-free methanol medium-pressure flash section (C2-3), a sulfur-containing methanol low-pressure flash section (C2-4), and a sulfur-free methanol low-pressure flash section (C2-5); The bottom of the effective gas recovery section (C2-1) is connected to the second inlet via a pipeline, and the upper part is connected to the second liquid outlet and the sulfur-containing methanol medium-pressure flash section (C2-2) via pipelines; the bottom of the sulfur-containing methanol medium-pressure flash section (C2-2) is connected to the upper part of the sulfur-containing methanol low-pressure flash section (C2-4) via a pipeline, and the upper part is connected to the pipeline of the initial gas connected to the ammonia cooler (E2) through a circulating CO2 cooler (E16), a gas compressor (M1), a water cooler (E14), and a circulating CO2 cooler (E16); the bottom of the sulfur-free methanol medium-pressure flash section (C2-3) is connected to the upper part of the sulfur-containing methanol low-pressure flash section (C2-4) via a pipeline. A pipeline is connected to the upper part of the sulfur-free methanol low-pressure flash section (C2-5), and the top is connected to the sulfur-containing methanol medium-pressure flash section (C2-2) via a pipeline; the bottom of the sulfur-containing methanol low-pressure flash section (C2-4) is connected to the upper part of the sulfur-containing methanol atmospheric flash section (C3-2) in the flash tower system via a pipeline, and the top is connected to the air inlet end of the sulfur-containing CO2 injector (J2) via a pipeline; the bottom of the sulfur-free methanol low-pressure flash section (C2-5) is connected to the upper part of the sulfur-free methanol atmospheric flash section (C3-4) in the flash tower system via a pipeline, and the top is connected to the air inlet end of the sulfur-free CO2 injector (J1) via a pipeline.

7. A system for separating and purifying CO2 according to claim 6, characterized in that: The flash tower system comprises an atmospheric pressure vacuum flash tower (C3), and the atmospheric pressure vacuum flash tower (C3) comprises a sulfur-containing methanol vacuum flash section (C3-1), a sulfur-containing methanol atmospheric pressure flash section (C3-2), a sulfur-free methanol vacuum flash section (C3-3), and a sulfur-free methanol atmospheric pressure flash section (C3-4); the bottom of the sulfur-containing methanol vacuum flash section (C3-1) is connected to the feed inlet of a medium-pressure flash tower feed pump (P3) and a sulfur-containing methanol circulation pump (P4) through pipelines, and the upper part is connected to the air inlet end of the sulfur-containing CO2 ejector (J2) through a pipeline; the medium-pressure flash tower feed pump The discharge port of (P3) is connected to the medium-pressure flash section (C2-2) of the sulfur-containing methanol through a pipeline; the discharge port of the sulfur-containing methanol circulation pump (P4) is connected to the middle part of the sulfide absorption tower (C4) through a pipeline through the methanol cooler (E4) of the main wash section of the absorption tower; the bottom of the atmospheric pressure flash section (C3-2) of the sulfur-containing methanol is connected to the upper part of the vacuum flash section (C3-1) of the sulfur-containing methanol through a pipeline, the top is connected to the gas outlet end of the sulfur-containing CO2 ejector (J2) through a pipeline, and the upper part is connected to the bottom of the low-pressure flash section (C2-4) of the sulfur-free methanol through a pipeline; The bottom of the flash section (C3-3) is connected to the feed ports of the supplementary / antifreeze methanol feed pump (P1) and the sulfide absorber feed pump (P2) through pipelines, and the upper part is connected to the air inlet end of the sulfur-free CO2 ejector (J1) through pipelines; the discharge port of the supplementary / antifreeze methanol feed pump (P1) is connected to the upper part of the main wash section (C1-3) and the initial gas delivery pipeline between the initial gas-purified gas heat exchanger (E1) and the alcohol-water separation tank (V1) through pipelines; the discharge port of the sulfide absorber feed pump (P2) is connected to the lean methanol precooler (E5) through pipelines. ) is connected to the upper part of the sulfide absorption tower (C4); the bottom of the sulfur-free methanol atmospheric pressure flash section (C3-4) is connected to the upper part of the sulfur-free methanol vacuum flash section (C3-3) through a pipeline, the top is connected to the gas outlet end of the sulfur-free CO2 injector (J1) through a pipeline, and the upper part is connected to the bottom of the sulfur-free methanol low-pressure flash section (C2-5) through a pipeline; the gas outlet ends of the sulfur-free CO2 injector (J1) and the sulfur-containing CO2 injector (J2) are merged through a pipeline and connected to the lower part of the sulfide absorption tower (C4) through the initial gas-purified gas heat exchanger (E1).

8. A system for separating and purifying CO2 according to claim 7, characterized in that: The bottom of the sulfide absorption tower (C4) is connected to the middle of the thermal regeneration tower (C5) through a pipeline through the thermal regeneration tower feed pump (P6), the first-stage preheater (E6), and the second-stage preheater (E10), and the top is connected to the CO2 product gas collection device through a pipeline through the H2S cooler (E12), the initial gas fourth-stage cooler (E31), and the initial gas-purified gas heat exchanger (E1).

9. A system for separating and purifying CO2 according to claim 8, characterized in that: The bottom of the thermal regeneration tower (C5) is connected to the feed port of the methanol storage tank (V5) through a pipeline in sequence through a thermal regeneration tower bottom extraction pump (P8) and a secondary preheater (E10), and the top is connected to the H2S primary separation tank (V3) through a pipeline through a thermal regeneration tower top condenser (E11); the bottom of the H2S primary separation tank (V3) is connected to the upper part of the thermal regeneration tower (C5) through a pipeline through a thermal regeneration tower top reflux pump (P9), and the top is connected to the H2S secondary separation tank (V4) through a pipeline through the H2S cooler (E12); the bottom of the H2S secondary separation tank (V4) is connected to the upper part of the thermal regeneration tower (C5) through a pipeline, and the top is connected to the H2S recovery device through the initial gas-purified gas heat exchanger (E1) through a pipeline.

10. A system for separating and purifying CO2 according to claim 7, characterized in that: The medium-pressure flash distillation section (C2-2) of sulfur-containing methanol is provided with a tower plate; the bottom of the desulfurization section (C1-1) is connected to the medium-pressure flash distillation section (C2-2) of sulfur-containing methanol via a pipeline, and the position of the pipeline interface connected to the medium-pressure flash distillation section (C2-2) of sulfur-containing methanol is lower than the tower plate; the upper part of the effective gas recovery section (C2-1) is connected to the medium-pressure flash distillation section (C2-2) of sulfur-containing methanol via a pipeline, and the position of the pipeline interface connected to the medium-pressure flash distillation section (C2-2) of sulfur-containing methanol is lower than the tower plate; the top of the sulfur-free methanol medium-pressure flash distillation section (C2-3) is connected to the sulfur-containing methanol via a pipeline The medium-pressure flash section (C2-2) is connected, and the position of the pipeline interface connected to the sulfur-containing methanol medium-pressure flash section (C2-2) is lower than the tower plate; the discharge port of the medium-pressure flash tower feed pump (P3) is connected to the sulfur-containing methanol medium-pressure flash section (C2-2) through a pipeline, and the position of the pipeline interface connected to the sulfur-containing methanol medium-pressure flash section (C2-2) is higher than the tower plate; the circulating CO2 cooler (E16) is connected to the sulfur-containing methanol medium-pressure flash section (C2-2) through a pipeline, and the position of the pipeline interface connected to the sulfur-containing methanol medium-pressure flash section (C2-2) is higher than the tower plate.

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