A gas purification method

Abstract

The present application provides a gas purification method to remove CO from the initial gas. 2 It is divided into two parts, and a part of the CO in the initial gas is condensed 2 Condensed into liquid form, and using liquid CO 2 The characteristics of high pressure and low temperature, the CO produced by evaporation 2 The gas is then used as the power of the system ejector, reducing the energy consumption of the entire system ejector. It is then recovered after desulfurization treatment. The other part of the CO in the initial gas 2 The lean methanol liquid is absorbed and then flash evaporated to produce CO 2 Gas, two parts CO 2 After the gases are mixed, they are recycled through desulfurization treatment. The initial gas purification process only discharges wastewater, and there is no external gas discharge 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%, so that the diameter of each treatment tower can be reduced, thereby realizing the miniaturization of the equipment, which has a high value of promotion and application.

Description

Technical Field

[0001] The invention relates to the technical field of gas purification, and in particular to a coal chemical gas purification method. 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 -55C°, 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 deficiencies in the prior art, the present application aims to provide a gas purification method, which divides the CO2 in the initial gas into two parts for treatment. A 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 of lean methanol liquid, and then recovered after step-by-step reduced pressure flash evaporation treatment. The initial gas purification process only has wastewater discharge and no gas emission link, thereby achieving almost complete capture and recovery of CO2 in the initial gas. Moreover, since the amount of lean methanol liquid used to remove CO2 is greatly reduced, the energy consumption of 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 achieving miniaturization of the equipment, and having a high value for promotion and application.

[0009] The present application provides a gas purification method, comprising the following steps:

[0010] Cooling the initial gas to obtain CO2 liquid a and gas a, wherein the CO2 liquid a has a temperature of -50 to -58°C and a pressure of 1.6 to 6 MPa; the gas a has a temperature of -50 to -58°C and a pressure of 1.6 to 6 MPa;

[0011] Washing gas a with a lean methanol liquid to obtain a purified gas and a methanol-rich liquid a, wherein the purified gas has a temperature of -45 to -55°C and a pressure of 1.6 to 6 MPa; the methanol-rich liquid a has a temperature of -20 to -30°C and a pressure of 1.6 to 6 MPa;

[0012] Flash distill CO2 liquid a under reduced pressure to obtain effective gas a and CO2 liquid b, wherein the effective gas a has a temperature of -30 to -40°C and a pressure of 0.8 to 1.6 MPa; the CO2 liquid b has a temperature of -50 to -58°C and a pressure of 0.8 to 1.6 MPa;

[0013] Evaporating CO2 liquid b to obtain gas b, wherein the temperature of the gas b is -50 to -58°C and the pressure is 0.1 to 0.8 MPa;

[0014] Flash distillation of methanol-rich liquid a under reduced pressure to obtain semi-lean methanol liquid b and gas c, wherein the semi-lean methanol liquid b has a temperature of -40 to -55°C and a pressure of 0.1 to 0.8 MPa; the gas c has a temperature of -60 to -65°C and a pressure of <0.1 MPa;

[0015] Mixing gas b and gas c to obtain gas d, wherein the temperature of gas d is -50 to -60°C and the pressure is 0.1 to 0.8 MPa;

[0016] The gas d is desulfurized to obtain a CO2 product gas having a temperature of -50 to -60°C and a pressure of 0.1 to 0.8 MPa.

[0017] Specifically, the initial gas is cooled step by step in sequence by using 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), and the condensed liquid is separated by using a liquid CO2 separation tank (V2) to obtain CO2 liquid a and gas a, wherein the CO2 liquid a includes CO2, H2, and CO;

[0018] The gas a is washed and purified by using lean methanol liquid from a methanol storage tank (V5) after being cooled to -60°C by a primary preheater (E6) and a lean methanol precooler (E5), absorbing sulfides and carbides in the gas, and finally obtaining purified gas and methanol-rich liquid a, wherein the methanol-rich liquid a includes sulfur-containing methanol-rich liquid c and sulfur-free methanol-rich liquid d;

[0019] The CO2 liquid a enters the effective gas recovery section (C2-1) of the medium-low pressure flash tower (C2), and is subjected to reduced pressure flash evaporation to obtain effective gas a and CO2 liquid b; the effective gas a includes CO2, H2, and CO;

[0020] The sulfur-containing methanol-rich liquid c and the sulfur-free methanol-rich liquid d are flashed under reduced pressure by a medium-low pressure flash tower (C2) and a normal pressure vacuum flash tower (C3) to obtain a sulfur-containing semi-lean methanol liquid g and a gas g, and a sulfur-free semi-lean methanol liquid h and a gas h, respectively; the sulfur-containing semi-lean methanol liquid g and the sulfur-free semi-lean methanol liquid h are mixed to obtain the semi-lean methanol liquid b; the gas g and the gas h are mixed to obtain the gas c;

[0021] After passing through a sulfur-free CO2 injector (J1) and a sulfur-containing CO2 injector (J2), the gas b and the gas c are mixed to obtain a gas d;

[0022] The gas d is desulfurized in the sulfide absorption tower (C4) to obtain CO2 product gas, which enters the CO2 product collection device for storage.

[0023] According to the technical solution provided in the embodiment of the present application, the methanol-rich liquid a includes a sulfur-containing methanol-rich liquid c and a sulfur-free methanol-rich liquid d, and the reduced pressure flash evaporation of the methanol-rich liquid a includes the following steps:

[0024] Flash distill the sulfur-containing methanol-rich liquid c under reduced pressure to obtain a sulfur-containing methanol-rich liquid e and a gas e, wherein the sulfur-containing methanol-rich liquid e has a temperature of -35 to -50°C and a pressure of 0.8 to 1.6 MPa; the gas e has a temperature of -40 to -50°C and a pressure of 0.8 to 1.6 MPa;

[0025] Flash distill the sulfur-free methanol-rich liquid d under reduced pressure to obtain a sulfur-free methanol-rich liquid f and a gas f, wherein the sulfur-free methanol-rich liquid f has a temperature of -35 to -50°C and a pressure of 0.8 to 1.6 MPa; the gas f has a temperature of -40 to -50°C and a pressure of 0.8 to 1.6 MPa;

[0026] The effective gas a, the gas e and the gas f are mixed to obtain an effective gas b, wherein the effective gas b has a temperature of -35 to -45°C and a pressure of 0.8 to 1.6 MPa.

[0027] Specifically, the sulfur-containing methanol-rich liquid c and the sulfur-free methanol-rich liquid d are respectively subjected to medium-pressure flash evaporation in a medium-low pressure flash tower (C2) to obtain sulfur-containing methanol-rich liquid e and gas e, and sulfur-free methanol-rich liquid f and gas f, respectively; the effective gas a, the gas e, and the gas f are mixed below the three tower plates of the sulfur-containing methanol medium-pressure flash section (C2-2) to obtain an effective gas b.

[0028] According to the technical solution provided in the embodiment of the present application, the sulfur-containing methanol-rich liquid e is flash evaporated under reduced pressure to obtain a sulfur-containing semi-lean methanol liquid g and a gas g, wherein the sulfur-containing semi-lean methanol liquid g has a temperature of -60 to -65°C and a pressure of <0.1 MPa; the gas g has a temperature of -60 to -65°C and a pressure of <0.1 MPa;

[0029] Flash distill the sulfur-free methanol-rich liquid f under reduced pressure to obtain sulfur-free semi-lean methanol liquid h and gas h, wherein the sulfur-free semi-lean methanol liquid h has a temperature of -60 to -65°C and a pressure of <0.1 MPa; the gas h has a temperature of -60 to -65°C and a pressure of <0.1 MPa;

[0030] The sulfur-containing semi-lean methanol liquid g and the sulfur-free semi-lean methanol liquid h are mixed to obtain the semi-lean methanol liquid b; the gas g and the gas h are mixed to obtain the gas c.

[0031] Specifically, the sulfur-containing methanol-rich liquid e is flashed at low pressure, normal pressure and vacuum in sequence to obtain sulfur-containing semi-lean methanol liquid g and gas g; the sulfur-free methanol liquid f is flashed at low pressure, normal pressure and vacuum in sequence to obtain sulfur-free semi-lean methanol liquid h and gas h.

[0032] According to the technical solution provided in the embodiment of the present application, cooling the initial gas to obtain CO2 liquid a and gas a includes the following steps:

[0033] The initial gas is cooled to -5 to 5°C using an initial gas-purified gas heat exchanger (E1);

[0034] The sulfur-free semi-lean methanol liquid h and the initial gas are mixed and separated to obtain the sulfur-free semi-lean methanol liquid i and the gas i, wherein the sulfur-free semi-lean methanol liquid i has a temperature of -5 to 5°C and a pressure of 1.6 to 6 MPa; the gas i has a temperature of -5 to 5°C and a pressure of 1.6 to 6 MPa;

[0035] Use an ammonia cooler (E2) to cool the gas i to -10 to -20°C;

[0036] The gas i is cooled to -47~-53℃ in three stages by using liquid CO2 evaporator (E7);

[0037] The gas i is cooled four-stage to -55~-57℃ by the initial gas four-stage cooler (E31) to obtain CO2 liquid a and gas a.

[0038] Specifically, the purified gas, the CO2 product gas, the gas d and the gas k are used to perform primary cooling on the initial gas through an initial gas-purified gas heat exchanger (E1);

[0039] The sulfur-free semi-lean methanol liquid h is used to absorb the moisture in the initial gas, which can not only absorb and remove the moisture in the initial gas, but also prevent the moisture from condensing into ice in the pipeline to block the pipeline;

[0040] Using an alcohol-water separation tank (V1) to separate the sulfur-free semi-lean methanol liquid i and the gas i;

[0041] The liquid CO2 evaporator (E7) is used to reduce the pressure and gasify the CO2 liquid b to perform three-stage cooling on the gas i, so that the liquid CO2 evaporator (E7) uses the physical state change of the CO2 liquid itself to cool the gas i, thereby reducing the refrigeration energy consumption of the system;

[0042] The gas i is subjected to four-stage cooling using the purified gas and the CO2 product gas to obtain CO2 liquid a and gas a, and then the CO2 liquid a and gas a are separated using a liquid CO2 separation tank (V2).

[0043] According to the technical solution provided in the embodiment of the present application, the CO2 liquid b is evaporated by the liquid CO2 evaporator (E7) to obtain the gas b.

[0044] Specifically, after passing through 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, which can provide a low-temperature environment of about -55°C to achieve cooling of the gas i. At the same time, gas b can also be used as a 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).

[0045] According to the technical solution provided in the embodiment of the present application, the processing process of the effective gas b includes the following steps:

[0046] The effective gas b is washed with the sulfur-containing semi-lean methanol liquid g to obtain an effective gas c, wherein the effective gas c has a temperature of -40 to -50°C and a pressure of 0.8 to 1.6 MPa;

[0047] Compressing the effective gas c to 1.6-6 MPa;

[0048] The effective gas c and the gas i are mixed.

[0049] Specifically, in order to reduce the volume of the compressed 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) is used to absorb most of the CO2 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), thereby realizing the recycling and utilization of the effective gas c without generating external waste.

[0050] According to the technical solution provided in the embodiment of the present application, the treatment process of the semi-lean methanol liquid b comprises the following steps:

[0051] Cooling the sulfur-containing methanol-rich liquid c with the sulfur-containing semi-lean methanol liquid b;

[0052] Heating the sulfur-containing semi-lean methanol liquid b to obtain lean methanol liquid and gas j, wherein the lean methanol liquid has a temperature of 70 to 80° C. and a pressure of 0.1 to 0.3 MPa; the gas j has a temperature of 50 to 70° C. and a pressure of 0.1 to 0.3 MPa;

[0053] Cooling and separating the gas j step by step to obtain a gas k containing H2S, wherein the gas k has a temperature of 20 to 30°C and a pressure of 0.1 to 0.3 MPa;

[0054] Cooling the initial gas with the gas k;

[0055] The gas k is recovered.

[0056] Specifically, the sulfur-containing semi-lean methanol liquid g and the sulfur-free semi-lean methanol liquid h both enter the sulfide absorption tower (C4) to purify and wash the sulfides in the gas d, and finally produce a standard CO2 product gas that can be recycled;

[0057] 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 sulfur-containing semi-lean methanol liquid b; at this time, the sulfur-containing 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. After analyzing the process route, the sulfur-containing semi-lean methanol liquid b can be cooled by the sulfur-containing methanol cooler (E13) and then returned to the sulfide absorption tower (C4), and then enter the thermal regeneration tower (C5) for heating to reduce the solubility of the sulfur-containing semi-lean methanol liquid b, thereby continuously evaporating and precipitating the sulfide-containing gas j, so that the sulfur-containing semi-lean methanol liquid b is gradually depleted and becomes a lean methanol liquid, thereby realizing the recycling of the lean methanol liquid;

[0058] The evaporated gas j is cooled and separated step by step in the H2S primary separation tank (V3) and the H2S secondary separation tank (V4) to obtain the H2S-containing gas k, which enters the H2S recovery device to achieve H2S recovery.

[0059] According to the technical solution provided in the embodiment of the present application, the following steps are also included:

[0060] Heating the sulfur-free semi-lean methanol liquid i to obtain sulfur-free semi-lean methanol vapor m and wastewater, wherein the methanol vapor m has a temperature of 70 to 100° C. and a pressure of 0.1 to 0.2 MPa;

[0061] The methanol vapor m is cooled to obtain a methanol-lean liquid.

[0062] Specifically, the sulfur-free semi-lean methanol liquid i is heated in the alcohol-water distillation tower (C6) to allow methanol to evaporate continuously from the sulfur-free semi-lean methanol liquid i and enter the thermal regeneration tower C5 for regeneration and recycling, while the wastewater enters the sewage treatment device.

[0063] According to the technical solution provided in the embodiment of the present application, the gas i is cooled in four stages and the initial gas is cooled in one stage in sequence using the purified gas and the CO2 product gas.

[0064] Specifically, since the purified gas and the CO2 product gas still have a relatively low temperature (the temperature is -45 to -60°C), they can further function as a coolant to reduce the energy consumption of the entire system refrigeration. After analyzing the process route, the CO2 product gas is sequentially cooled by the initial gas four-stage cooler E31 for four-stage cooling of gas i, and by the initial gas-purified gas heat exchanger (E1) for one-stage cooling of the initial gas, and then enters the CO2 product gas collection device for storage; the purified gas is sequentially cooled by the initial gas four-stage cooler (E31) for four-stage cooling of gas i, and by the initial gas-purified gas heat exchanger (E1) for one-stage cooling of the initial gas, and then enters the purified gas product collection device.

[0065] According to the technical solution provided in the embodiment of the present application, the initial gas is cooled in one stage using the gas d.

[0066] Since the gas d still has a relatively low temperature (about -50 to -60°C), it can further function as a coolant to reduce the energy consumption of the entire system refrigeration. After analyzing the process route, the gas d enters the sulfide absorption tower (C4) after the initial gas is cooled in one stage by the initial gas-purified gas heat exchanger (E1).

[0067] In summary, the present application discloses a gas purification method. The beneficial effect produced by the above scheme is that, compared with the process in which all CO2 gas in the initial gas is treated by methanol absorption in the traditional technology, 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 cooling, and obtain the remaining gas a after separation. The CO2 liquid a is subjected to reduced pressure flash evaporation to obtain effective gas a and CO2 liquid b, and the CO2 liquid b is converted into gas b after evaporation and gasification. The second is to use lean methanol liquid to absorb another part of the CO2 in the gas a, and then gradually reduce the pressure and flash evaporation to obtain gas c for The two parts of gas b and gas c are finally mixed and desulfurized to obtain CO2 product gas, thereby realizing CO2 recovery. There is no external gas emission link in the entire 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, thereby realizing the miniaturization of the equipment, which has a high value for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] 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.

[0069] Figure 1 This is the gas purification process flow chart for this application.

[0070] in,

[0071] 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: first outlet; C42: first inlet; C51: second outlet; C52: second inlet; C61: third outlet; C62: third inlet.

[0072] 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.

[0073] V1: alcohol-water separation tank; V2: liquid CO2 separation tank; V3: H2S primary separation tank; V4: H2S secondary separation tank; V5: methanol storage tank.

[0074] 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.

[0075] 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

[0076] 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.

[0077] The present application will be described in detail below with reference to the accompanying drawings and in combination with embodiments.

[0078] like Figure 1 The gas purification process flow chart shown mainly includes an absorption tower C1, a medium-low pressure flash tower C2, an atmospheric pressure vacuum flash tower C3, a sulfide absorption tower C4, a thermal regeneration tower C5, an alcohol-water fractionation tower C6 and a CO2 ejector, wherein 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.

[0079] The initial gas-purified gas heat exchanger E1 is connected to the upper part of the alcohol-water separation tank V1 through a pipeline. The top of the alcohol-water separation tank V1 is connected to the liquid CO2 separation tank V2 through an ammonia cooler E2, a liquid CO2 evaporator E7, and an initial gas quaternary cooler E31 in sequence through a pipeline. The bottom is connected to the alcohol-water distillation tower C6 after passing through the sewage cooler E15 through a pipeline.

[0080] The top of the liquid CO2 separation tank V2 is connected to the lower part of the desulfurization section C1-1 disposed in the absorption tower C1 through a pipeline, and the bottom is connected to the middle part of the effective gas recovery section C2-1 disposed in the medium- and low-pressure flash tower C2 through a pipeline;

[0081] Furthermore, the bottom of the desulfurization section C1-1 is connected to the sulfur-containing methanol medium-pressure flash section C2-2 arranged in the medium-low pressure flash tower C2 through a pipeline in sequence through a filter F1, a sulfur-containing methanol cooler E13, and a 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 lower part of the rough washing 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 arranged in the medium-low pressure flash tower C2 through a pipeline, and the rough washing 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 arranged in the medium-low pressure flash tower C2 through a pipeline. A pressure reducing valve 2 K2 is provided on the pipelines at the lower part of the 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 middle part of the rough wash section C1-2 through a pipeline via 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 via 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.

[0082] Furthermore, the bottom of the effective gas recovery section C2-1 is connected to the gas inlet ends of the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2 respectively through a pipeline through the liquid CO2 evaporator E7, and the upper part is connected to the sulfur-containing methanol medium-pressure flash section C2-2 through a pipeline, 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; 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 through a pipeline, and the upper part is connected to the initial gas pipeline of the ammonia cooler E2 through a pipeline in sequence through a circulating CO2 cooler E16, a gas compressor M1, a water cooler E14, and a circulating CO2 cooler E16; 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 is connected to the medium-pressure flash section C2-2 of the sulfur-containing methanol through a pipeline at the top, and the pipeline interface connected to the medium-pressure flash section C2-2 of the sulfur-containing methanol is located below 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 pressure flash section C3-2 arranged in C3 of the atmospheric pressure vacuum flash tower through a pipeline, and 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 pressure flash section C3-4 arranged in C3 of the atmospheric pressure vacuum flash tower through a pipeline, and is connected to the air inlet end of the sulfur-free CO2 injector J1 through a pipeline.

[0083] 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.

[0084] 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 first outlet C41 and a first inlet C42, the first outlet C41 is located higher than the first inlet C42 and is located above the bottom tower plate in the sulfide absorption tower C4; the first outlet C41 is connected to the first inlet C42 through a pipeline in sequence through the sulfide absorption tower extraction pump P5 and the sulfur-containing methanol cooler E13.

[0085] 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 second outlet C51 and a second inlet C52, the second outlet C51 is located at the bottom of the thermal regeneration tower C5, the second inlet C52 is located higher than the second outlet C51, and the second outlet C51 is connected to the second inlet C52 through a pipeline through the thermal regeneration tower reboiler E8.

[0086] 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.

[0087] Furthermore, the discharge port of the thermal regeneration tower bottom extraction pump P8 is also connected to the upper part of the alcohol-water separation tower C6 via a pipeline.

[0088] 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.

[0089] 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 third outlet C61 and a third inlet C62, the third outlet C61 is located at the bottom of the alcohol-water distillation tower C6, the third inlet C62 is located higher than the third outlet C61, and the third outlet C61 is connected to the third inlet C62 through a pipeline through the alcohol-water separation tower reboiler E9.

[0090] According to Figure 1 The gas purification process flow chart shown in the figure 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:

[0091] 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.

[0092] 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 and is further cooled to -45 to -55°C. At this time, part of the CO2 in the gas i has been condensed into a liquid phase. Then, it enters the initial gas four-stage cooler E31 to be further cooled to -55 to -58°C, and the CO2 in the gas i is further condensed. Then, it enters the liquid CO2 separation tank V2, and is separated to obtain CO2 liquid a (temperature -55 to -58°C, pressure about 3.55MPa) and gas a (temperature -55 to -58°C, pressure about 3.55MPa).

[0093] The gas a is output from 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 turn 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 turn 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 collection device (the purified gas temperature at this time is about -40°C). 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, while 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.

[0094] 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 (the wastewater temperature is about 40°C at this time). 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 third 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 third 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 methanol in the sulfur-free semi-lean methanol liquid i to form methanol vapor m which enters the thermal regeneration tower C5 for methanol regeneration and recycling. The methanol vapor m 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.

[0095] The CO2 liquid a output from 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 -50 to -58°C, temperature about 1.0MPa). The effective gas a has a temperature of about -35°C and a pressure of about 1.0MPa, including 5 to 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.

[0096] 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.

[0097] 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 about 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 -35 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 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.

[0098] 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 gas 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.

[0099] 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.

[0100] The CO2 liquid b output from the bottom of the effective gas recovery section C2-1 is depressurized by the liquid CO2 evaporator E7, and the CO2 liquid b undergoes a phase change from high pressure to low pressure, 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, the gas b is divided into two parts, which are mixed with the sulfur-containing CO2 gas g1 and the sulfur-free CO2 gas h1 through pipelines and then enter the air inlet ends of the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2, and serve 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.

[0101] The sulfur-free CO2 gas h and the sulfur-containing CO2 gas g which are respectively combined at the gas outlet of the sulfur-free CO2 injector J1 and the sulfur-containing CO2 injector J2 are combined through a pipeline to form a gas c. The gas c is mixed with the gas b to obtain a gas d (temperature of about -55°C, pressure of about 0.1MPa). The gas d is heated by the initial gas-purified gas heat exchanger E1 (at this time, the temperature of the gas d is about -35°C) and enters the sulfide absorption tower C4 to remove the sulfide to purify the gas d. The purified gas d is output from the top of the tower sulfide absorption tower C4. At this time, the gas d has reached C The O2 product gas recycling standard (temperature of about -55°C, pressure of about 0.6MPa, CO2 content of 99.99%), but still has a relatively low temperature, can be further used as a coolant to reduce the cooling demand energy consumption of the entire system, so the H2S-containing gas k1 is cooled by the H2S cooler E12, the gas i is subjected to four-stage cooling by the initial gas four-stage cooler E31, and the initial gas is subjected to one-stage cooling by the initial gas-purified gas heat exchanger E1 before entering the CO2 product gas collection device for storage (temperature of about -20°C, pressure of about 0.6MPa, CO2 content of 99.99%).

[0102] 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 first 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 second inlet C42.

[0103] 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.

[0104] 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.

[0105] 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 second 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 second 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%).

[0106] 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.

[0107] It can be seen from the above embodiments that the present application provides a gas purification method, which divides the CO2 in the initial gas 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. The 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 entire system ejector, thereby reducing the energy consumption of the entire system ejector. Second, the lean methanol liquid is used to absorb another part of the gas a The CO2 is separated and then gas c is recovered by step-by-step pressure reduction and flash evaporation. Finally, the two parts of gas b and gas c are mixed and enter the sulfide absorption tower C4 for desulfurization to obtain CO2 product gas, thereby realizing CO2 recovery. The entire process only discharges wastewater and there is no external gas emission link. The CO2 in the initial gas is almost completely captured and recovered, and is sealed under pressure for easy utilization. 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, thereby realizing miniaturization of the equipment, which has a high value of promotion and application.

[0108] 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 gas purification method, characterized in that: The following steps are involved: Cooling the initial gas to obtain CO2 liquid a and gas a, wherein the CO2 liquid a has a temperature of -50 to -58°C and a pressure of 1.6 to 6 MPa; the gas a has a temperature of -50 to -58°C and a pressure of 1.6 to 6 MPa; Washing gas a with a lean methanol liquid to obtain a purified gas and a methanol-rich liquid a, wherein the purified gas has a temperature of -45 to -55°C and a pressure of 1.6 to 6 MPa; the methanol-rich liquid a has a temperature of -20 to -30°C and a pressure of 1.6 to 6 MPa; Flash distill CO2 liquid a under reduced pressure to obtain effective gas a and CO2 liquid b, wherein the effective gas a has a temperature of -30 to -40°C and a pressure of 0.8 to 1.6 MPa; the CO2 liquid b has a temperature of -50 to -58°C and a pressure of 0.8 to 1.6 MPa; Evaporating CO2 liquid b to obtain gas b, wherein the temperature of the gas b is -50 to -58°C and the pressure is 0.1 to 0.8 MPa; Flash distillation of methanol-rich liquid a under reduced pressure to obtain semi-lean methanol liquid b and gas c, wherein the semi-lean methanol liquid b has a temperature of -40 to -55°C and a pressure of 0.1 to 0.8 MPa; the gas c has a temperature of -60 to -65°C and a pressure of <0.1 MPa; Mixing gas b and gas c to obtain gas d, wherein the temperature of gas d is -50 to -60°C and the pressure is 0.1 to 0.8 MPa; Desulfurizing gas d to obtain CO2 product gas, wherein the CO2 product gas has a temperature of -50 to -60°C and a pressure of 0.1 to 0.8 MPa; The cooling of the initial gas to obtain CO2 liquid a and gas a comprises the following steps: The initial gas is cooled to -5 to 5°C using an initial gas-purified gas heat exchanger (E1); Mixing the sulfur-free semi-lean methanol liquid h and the initial gas, and obtaining the sulfur-free semi-lean methanol liquid i and the gas i after separation, wherein the sulfur-free semi-lean methanol liquid i has a temperature of -5 to 5°C and a pressure of 1.6 to 6 MPa; the gas i has a temperature of -5 to 5°C and a pressure of 1.6 to 6 MPa; Use an ammonia cooler (E2) to cool the gas i to -10 to -20°C; The gas i is cooled to -45~-55℃ in three stages by using liquid CO2 evaporator (E7); The gas i is cooled four-stage to -50 to -58°C using an initial gas four-stage cooler (E31) to obtain the CO2 liquid a and the gas a.

2. A gas purification method according to claim 1, characterized in that: The methanol-rich liquid a comprises a sulfur-containing methanol-rich liquid c and a sulfur-free methanol-rich liquid d, and the reduced pressure flash evaporation of the methanol-rich liquid a comprises the following steps: Flash distill the sulfur-containing methanol-rich liquid c under reduced pressure to obtain a sulfur-containing methanol-rich liquid e and a gas e, wherein the sulfur-containing methanol-rich liquid e has a temperature of -35 to -50°C and a pressure of 0.8 to 1.6 MPa; the gas e has a temperature of -40 to -50°C and a pressure of 0.8 to 1.6 MPa; Flash distill the sulfur-free methanol-rich liquid d under reduced pressure to obtain a sulfur-free methanol-rich liquid f and a gas f, wherein the sulfur-free methanol-rich liquid f has a temperature of -35 to -50°C and a pressure of 0.8 to 1.6 MPa; the gas f has a temperature of -40 to -50°C and a pressure of 0.8 to 1.6 MPa; The effective gas a, the gas e and the gas f are mixed to obtain an effective gas b, wherein the effective gas b has a temperature of -35 to -45°C and a pressure of 0.8 to 1.6 MPa.

3. A gas purification method according to claim 2, characterized in that: Flash distill the sulfur-containing methanol-rich liquid e under reduced pressure to obtain sulfur-containing semi-lean methanol liquid g and gas g, wherein the sulfur-containing semi-lean methanol liquid g has a temperature of -60 to -70°C and a pressure of <0.1 MPa; the gas g has a temperature of -60 to -70°C and a pressure of <0.1 MPa; Flash distill the sulfur-free methanol-rich liquid f under reduced pressure to obtain sulfur-free semi-lean methanol liquid h and gas h, wherein the sulfur-free semi-lean methanol liquid h has a temperature of -60 to -70°C and a pressure of <0.1 MPa; the gas h has a temperature of -60 to -70°C and a pressure of <0.1 MPa; The sulfur-containing semi-lean methanol liquid g and the sulfur-free semi-lean methanol liquid h are mixed to obtain the semi-lean methanol liquid b; the gas g and the gas h are mixed to obtain the gas c.

4. A gas purification method according to claim 1, characterized in that: The CO2 liquid b is evaporated by the liquid CO2 evaporator (E7) to obtain the gas b.

5. A gas purification method according to claim 3, characterized in that: The processing process of the effective gas b comprises the following steps: The effective gas b is washed with the sulfur-containing semi-lean methanol liquid g to obtain an effective gas c, wherein the effective gas c has a temperature of -40 to -50°C and a pressure of 0.8 to 1.6 MPa; Compressing the effective gas c to 1.6-6 MPa; The effective gas c and the gas i are mixed.

6. A gas purification method according to claim 3, characterized in that: The treatment process of the semi-lean methanol liquid b comprises the following steps: Cooling the sulfur-containing methanol-rich liquid c with the sulfur-containing semi-lean methanol liquid b; Heating the sulfur-containing semi-lean methanol liquid b to obtain lean methanol liquid and gas j, wherein the lean methanol liquid has a temperature of 70 to 80° C. and a pressure of 0.1 to 0.3 MPa; the gas j has a temperature of 50 to 70° C. and a pressure of 0.1 to 0.3 MPa; Cooling and separating the gas j step by step to obtain a gas k containing H2S, wherein the gas k has a temperature of 20 to 30°C and a pressure of 0.1 to 0.3 MPa; Cooling the initial gas with the gas k; The gas k is recovered.

7. A gas purification method according to claim 1, characterized in that: The following steps are also included: Heating the sulfur-free semi-lean methanol liquid i to obtain methanol vapor m and wastewater, wherein the methanol vapor m has a temperature of 70 to 100° C. and a pressure of 0.1 to 0.2 MPa; The methanol vapor m is cooled to obtain a methanol-lean liquid.

8. A gas purification method according to claim 1, characterized in that: The purified gas and the CO2 product gas are used to sequentially perform four-stage cooling on the gas i and one-stage cooling on the initial gas.

9. A gas purification method according to claim 1, characterized in that: The initial gas is subjected to primary cooling using the gas d.

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