Low-temperature methanol washing system and method based on pre-co2 separation and high-h2s partial pressure desulfurization

Abstract

The application discloses a low-temperature methanol washing system and method based on preposed CO2 separation and high H2S partial pressure desulfurization. The system comprises a raw material gas pretreatment unit, a preposed high-pressure CO2 liquefaction separation unit, a high partial pressure desulfurization and decarburization unit, a liquid CO2 decompression evaporation and cold quantity recovery unit, a carbon dioxide product desulfurization unit, a methanol regeneration unit and a methanol distribution and temperature control optimization system. By arranging the CO2 condensation separation before desulfurization and adopting segmented methanol circulation and independent control, the desulfurization efficiency is greater than or equal to 99.9%, the CO2 content in the high-pressure absorption raw material gas is reduced by 20%-65%, the lean methanol circulation amount is reduced by 15%-35%, the sulfur-containing rich methanol amount is reduced by 20%-50%, the system energy consumption is reduced by 12%-31%, and the total sulfur content of the exhaust gas is less than or equal to 3.0 ppm. The method provided by the application has the advantages of great operation flexibility, safety and reliability, high product purity and high recovery rate, and is high in energy saving and environmental protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas purification, in particular to a low-temperature methanol washing system and method based on pre-CO2 separation and high-H2S partial pressure desulfurization, which is particularly suitable for coal chemical synthetic gas purification with high carbon dioxide content. BACKGROUND

[0002] The low-temperature methanol washing process is widely used in the field of coal chemical industry to remove acid gases (CO2, H2S, etc.) in synthetic gas. The traditional process usually adopts the sequence of desulfurization followed by decarburization, which has the following technical defects:

[0003] 1. Limited desulfurization efficiency: The partial pressure of H2S in the desulfurization section of the high-pressure absorption tower is low, and the solubility of H2S in methanol is limited, making it difficult to improve the desulfurization efficiency, thus requiring more methanol for desulfurization;

[0004] 2. Large amount of sulfur-rich methanol circulation: The partial pressure of CO2 in the desulfurization section of the high-pressure absorption tower is high, so a large amount of CO2 is absorbed by the sulfur-rich methanol, which already has a large circulation amount, resulting in more CO2 dissolved in the sulfur-rich methanol, and high regeneration energy consumption;

[0005] 3. Complex control of sulfur content in CO2 products and tail gas: The amount of sulfur-containing CO2 products and tail gas produced from sulfur-rich methanol is higher, and the demand for sulfur-free rich methanol will be higher to effectively control the sulfur content in the out-of-bound area to meet the standard;

[0006] 4. Insufficient production of high-pressure CO2 products: Since a larger amount of CO2 component is absorbed by sulfur-rich methanol in the desulfurization section of the high-pressure absorption tower, the CO2 content in the raw material process gas after desulfurization is reduced, and the liquefied CO2 from condensation is also proportionally reduced.

[0007] In the prior art, CN114963692A proposes a method for directly condensing and separating CO2, but does not involve process sequence optimization; CN118925474B uses multi-stage condensation, but CO2 separation is located after desulfurization, which does not effectively reduce the desulfurization tower load; CN221333461U achieves ultra-low temperature condensation, but requires the addition of methanol to prevent CO2 solidification, increasing system complexity; CN120079222A proposes mixing process gas with methanol before condensation and separation, but the condensation treatment before desulfurization is only used to prevent blockage and does not significantly optimize desulfurization efficiency; CN220413278U uses liquid CO2 refrigeration, but does not involve high-H2S partial pressure desulfurization, sulfur-rich methanol circulation, and temperature control.

[0008] Therefore, existing technologies still suffer from problems such as insufficient CO2 product output, limited desulfurization efficiency, large methanol circulation volume, and high system energy consumption. There is an urgent need to develop a new technology solution that can fundamentally optimize the process flow, improve desulfurization efficiency, and reduce energy consumption. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a low-temperature methanol washing system and method based on pre-CO2 separation and high H2S partial pressure desulfurization.

[0010] To achieve the above objectives, the present invention employs the following technical solution: a low-temperature methanol washing system based on pre-CO2 separation and high H2S partial pressure desulfurization, comprising:

[0011] The feed gas pretreatment unit is used for preliminary cooling and dehydration of the feed process gas, including a feed gas tube heat exchanger I and a methanol-water separator arranged in sequence.

[0012] A pre-high pressure CO2 liquefaction and separation unit is connected downstream of the raw gas pretreatment unit, and includes a raw gas cooler, a raw gas coil heat exchanger II, and a carbon dioxide condenser tube side arranged in sequence.

[0013] The high partial pressure desulfurization and decarbonization unit is connected downstream of the pre-high pressure CO2 liquefaction separation unit and includes a high pressure absorption tower, which is divided into a carbon dioxide gas-liquid separation section, a desulfurization section and a decarbonization section; wherein the carbon dioxide gas-liquid separation section of the high pressure absorption tower is located before the desulfurization section.

[0014] The liquid CO2 pressure-reducing evaporation and cold energy recovery unit is connected downstream of the pre-high pressure CO2 liquefaction and separation unit, and includes a first-stage liquid CO2 pressure-reducing valve, a medium-pressure CO2 flash tank, a second-stage liquid CO2 pressure-reducing valve, and the shell side of a carbon dioxide condenser.

[0015] The carbon dioxide product desulfurization unit is connected downstream of the liquid CO2 vacuum evaporation and cold energy recovery unit, and includes a high-pressure carbon dioxide product tower. The bottom of the high-pressure carbon dioxide product tower is equipped with a medium-pressure CO2 flash tank, and the upper part is a high-pressure CO2 absorption section.

[0016] The methanol regeneration unit includes a methanol coiled heat exchanger III, a medium-pressure flash tower, a hydrogen sulfide concentration tower, a methanol circulation pump I, a methanol coiled heat exchanger II, a thermal regeneration tower, a methanol-water separator, and a circulating gas compressor; the medium-pressure flash tower contains a sulfur-free rich methanol medium-pressure flash tank and a sulfur-containing rich methanol medium-pressure flash tank; the hydrogen sulfide concentration tower is divided into a lower H2S concentration tower and an upper H2S concentration tower.

[0017] The methanol distribution and temperature control optimization system includes an independent desulfurization-rich methanol circulating pump, a flow ratio control system, and a desulfurization-rich methanol cooler located between the desulfurization section and the decarbonization section of the high-pressure absorption tower. The outlet temperature and ratio are controlled by adjusting the frequency of the desulfurization-rich methanol circulating pump and the desulfurization-rich methanol cooler.

[0018] Furthermore, the shell-side inlet of the feed gas coiled tube heat exchanger I is connected to the feed gas pipeline, and the outlet is connected to the methanol-water separator pipeline. The liquid phase outlet of the methanol-water separator is connected to the feed inlet pipeline in the middle of the methanol-water separation tower, and the gas phase outlet is connected to the tube-side inlet of the feed gas cooler via a pipeline. The tube-side outlet of the feed gas cooler is connected to the shell-side inlet pipeline of the feed gas coiled tube heat exchanger II. The shell-side outlet of the feed gas coiled tube heat exchanger II is connected to the tube-side inlet pipeline of the carbon dioxide condenser. The tube-side outlet of the carbon dioxide condenser is connected to the inlet pipeline of the carbon dioxide gas-liquid separation section of the high-pressure absorption tower. The bottom liquid phase outlet of the carbon dioxide gas-liquid separation section is sequentially connected to the first-stage liquid CO2 pressure reducing valve and the inlet pipe of the medium-pressure CO2 flash tank. The top gas phase outlet of the medium-pressure CO2 flash tank is sequentially connected to the fourth pressure reducing valve and the inlet pipe of the circulating gas compressor. Its bottom liquid phase outlet is sequentially connected to the second-stage liquid CO2 pressure reducing valve and the shell-side inlet pipe of the carbon dioxide condenser. The shell-side outlet of the carbon dioxide condenser is connected to the bottom gas phase inlet pipe of the high-pressure CO2 absorption section of the high-pressure carbon dioxide product tower. Its bottom liquid phase outlet is sequentially connected to the sixth pressure reducing valve and the inlet pipe of the upper middle section of the H2S concentration tower of the hydrogen sulfide concentration tower.

[0019] Furthermore, the tube side outlet of the raw material gas coiled heat exchanger II, the low-temperature exhaust gas outlet at the top of the hydrogen sulfide concentration tower, and the low-temperature and high-pressure carbon dioxide product gas outlet at the top of the high-pressure carbon dioxide product tower are sequentially connected to the tube side of the raw material gas coiled heat exchanger I, as well as the purified gas pipeline, the exhaust gas pipeline, and the high-pressure carbon dioxide product gas inlet, respectively.

[0020] Furthermore, the lean methanol liquid phase inlet at the top of the decarbonization section of the high-pressure absorber is connected to the outlet pipe of the methanol coiled heat exchanger II. The sulfur-free rich methanol outlet at the bottom is connected to the sulfur-free rich methanol inlet of the methanol coiled heat exchanger III, and sequentially connected to the desulfurized rich methanol circulating pump, the desulfurized rich methanol cooler, the flow proportional controller, and the liquid phase inlet pipe at the top of the desulfurization section. The sulfur-containing rich methanol outlet at the bottom of the desulfurization section is connected to the sulfur-containing rich methanol inlet pipe of the methanol coiled heat exchanger III. The sulfur-free rich methanol outlet of the methanol coiled heat exchanger III is sequentially connected to the first pressure reducing valve and the sulfur-free rich methanol medium-pressure flash tank via pipes. The sulfur-containing rich methanol outlet of the methanol coiled heat exchanger III is sequentially connected to the second pressure reducing valve and the sulfur-containing rich methanol medium-pressure flash tank via pipes.

[0021] Furthermore, the gas phase outlet of the sulfur-free rich methanol medium-pressure flash tank is connected to the inlet pipe of the circulating gas compressor, and the liquid phase outlet is connected to the top inlet pipe of the high-pressure CO2 absorption section of the high-pressure carbon dioxide product tower via the third pressure reducing valve, and to the top inlet pipe of the hydrogen sulfide concentration tower via the fifth pressure reducing valve. The gas phase outlet of the sulfur-containing rich methanol medium-pressure flash tank is connected to the inlet pipe of the circulating gas compressor, and the liquid phase outlet is connected to the middle inlet pipe of the hydrogen sulfide concentration tower via the sulfur-containing methanol pressure reducing valve. The outlet of the circulating gas compressor is connected to the raw material gas pipeline via a pipeline.

[0022] Furthermore, the liquid phase outlet at the bottom of the upper column of the H2S concentration tower is sequentially connected to the methanol circulating pump I, the shell side of the methanol coiled heat exchanger II, the shell side of the methanol coiled heat exchanger III, and the liquid phase inlet pipe at the top of the lower column of the H2S concentration tower. The liquid phase outlet at the bottom of the lower column of the H2S concentration tower is sequentially connected to the tube side of the methanol coiled heat exchanger I and the feed inlet at the top of the thermal regeneration tower via pipes. The nitrogen pipeline is connected to the gas phase inlet at the bottom of the lower column of the H2S concentration tower via a pipeline.

[0023] Furthermore, the top gas phase outlet of the thermal regeneration tower is connected to a sulfuric acid-containing gas pipeline via a pipe, and the bottom liquid phase outlet is connected in sequence to the shell side of methanol coiled tube heat exchanger I and the inlet of methanol circulating pump II. The outlet of methanol circulating pump II is divided into two paths: one path is connected to the inlet pipeline of the tube side of methanol coiled tube heat exchanger II, and the other path is connected to the upper feed inlet of methanol water separator and the raw material gas pipeline via pipes respectively. The top gas phase outlet of methanol water separator is connected to the lower feed inlet pipeline of thermal regeneration tower, and the bottom liquid phase outlet is connected to a water pipeline via a pipe.

[0024] The low-temperature methanol washing method is as follows:

[0025] The process gas is introduced into the pre-high pressure CO2 liquefaction and separation unit before desulfurization. The temperature of the process gas is reduced to -25℃ to -45℃ through multi-stage cooling. The gas then enters the carbon dioxide gas-liquid separation section of the high pressure absorption tower to condense and separate liquid CO2. Methanol absorption is not introduced during the CO2 liquefaction and separation process.

[0026] The liquid CO2 separated at the bottom of the carbon dioxide gas-liquid separation section is depressurized to 1.2-2.5 MPa by the first-stage liquid CO2 pressure reducing valve and then enters the medium-pressure CO2 flash tank for depressurization flash evaporation to recover effective gas;

[0027] The liquid CO2 separated from the bottom of the medium-pressure CO2 flash tank is depressurized to 0.6-1.2 MPa through a two-stage liquid CO2 pressure reducing valve and then enters the shell side of the carbon dioxide condenser for depressurized evaporation and cooling.

[0028] The high-pressure CO2 gas generated by flash evaporation in the shell side of the carbon dioxide condenser is sent to the bottom of the high-pressure carbon dioxide product tower and flows from bottom to top. It comes into counter-current contact with the sulfur-free methanol liquid from the sulfur-free rich methanol medium-pressure flash tank at the top of the tower to carry out desulfurization.

[0029] The process gas after liquefying and separating CO2 at the top of the carbon dioxide gas-liquid separation section is sequentially sent to the desulfurization section and decarbonization section of the high-pressure absorption tower for purification.

[0030] After the sulfur-free rich methanol from the bottom of the decarbonization section of the high-pressure absorption tower is cooled by the desulfurized rich methanol cooler, its temperature drops to -35℃ to -8℃.

[0031] The operating range of the flow ratio controller after the independent desulfurization methanol-rich circulating pump located between the desulfurization section and the decarbonization section of the high-pressure absorption tower is controlled between 0.5 and 0.8.

[0032] Furthermore, the operating pressure of the high-pressure carbon dioxide product tower is 0.6-1.2 MPa, and its bottom gas phase inlet is directly connected to the gaseous high-pressure CO2 outlet of the shell side of the carbon dioxide condenser.

[0033] Furthermore, the methanol in the desulfurization section and the decarbonization section are transported through independent circulation systems, and the methanol circulation volume in the desulfurization section is 50% to 80% of that in the conventional process.

[0034] Furthermore, the CO2 content in the process gas separated from the top of the carbon dioxide gas-liquid separation section of the high-pressure absorption tower is reduced by 20%-65%, and the H2S partial pressure is increased by 11%-48%.

[0035] Furthermore, the system's total energy consumption is reduced by 12%-31%, and the total sulfur content in the exhaust gas is less than 3 ppm.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. Increased high-pressure CO2 product output: The CO2 liquefaction and separation of the pre-high-pressure CO2 liquefaction and separation unit is completed before the desulfurization process. Compared with the pre-high-pressure CO2 liquefaction and separation unit, the CO2 content in the raw gas entering the high-pressure CO2 liquefaction and separation unit is 10%-18% higher, which can increase the output of its high-pressure CO2 product by 9.2%-17.4%.

[0038] 2. Significantly improved desulfurization efficiency: Pre-CO2 separation increases the H2S content in the feed gas entering the desulfurization unit, resulting in an 11%-48% increase in its partial pressure. Under higher H2S partial pressure operating conditions, its solubility in methanol can be increased by 10%-45%, and the amount of sulfur-rich methanol produced in the desulfurization section is reduced by 10%-45%. The high-pressure desulfurization efficiency is increased from 99.5% in the traditional process to over 99.9%.

[0039] 3. Significantly reduced energy consumption: Pre-CO2 separation reduces the amount of CO2 in the feed gas entering the desulfurization unit by 20%-65% and increases the partial pressure of H2S by 11%-48%, thereby reducing the system's demand for lean methanol by 15%-35% and reducing total energy consumption by 12%-31%.

[0040] 4. Methanol Distribution and Temperature Control Optimization: The circulating pump, flow controller, and rich methanol cooler installed between the desulfurization and decarbonization sections can jointly control the temperature of the sulfur-free rich methanol sent to the top of the desulfurization section and the ratio of its flow rate to that of the sulfur-free rich methanol sent to the medium-pressure flash tower by adjusting the frequency of the circulating pump and the outlet temperature of the rich methanol cooler. This reduces the amount of sulfur-containing rich methanol compared to the traditional process, to 50% to 80%. Consequently, the demand for sulfur-free rich methanol used to absorb H2S in the hydrogen sulfide concentration tower also decreases year-on-year, and the total sulfur content in the tail gas is reduced from 10 ppm in the traditional process to 1-3 ppm.

[0041] 5. Reduced investment costs: Compared with traditional processes, the amount of raw gas entering the high-pressure absorption tower is reduced by 10% to 16%, the amount of lean methanol circulating in the decarbonization section of the high-pressure absorption tower is reduced by 15% to 35%, and the amount of sulfur-free rich methanol circulating in the desulfurization section is reduced by 20% to 50%, which reduces the size of equipment in the system. For example, the diameter of the high-pressure absorption tower can be reduced by 5% to 10%. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the process flow of the system of the present invention.

[0043] In the diagram, 1. Feed gas coiled tube heat exchanger I; 2. Methanol-water separator; 3. Feed gas cooler; 4. Feed gas coiled tube heat exchanger II; 5. Carbon dioxide condenser; 6. Desulfurized rich methanol circulating pump; 7. Desulfurized rich methanol cooler; 8. Flow proportional controller; 9. High-pressure absorption tower; 10. Carbon dioxide gas-liquid separation section; 11. Desulfurization section; 12. Decarbonization section; 13. Methanol coiled tube heat exchanger III; 14. First pressure reducing valve; 15. Sulfur-free rich methanol medium-pressure flash evaporator; 16. Second pressure reducing valve; 17. Sulfur-containing rich methanol medium-pressure flash evaporator; 18. Medium-pressure flash tower; 19. Hydrogen sulfide concentration tower. 20. Lower column of H2S concentration tower; 21. Upper column of H2S concentration tower; 22. Methanol circulating pump I; 23. Methanol coiled tube heat exchanger II; 24. Thermal regeneration tower; 25. Methanol coiled tube heat exchanger I; 26. Methanol circulating pump II; 27. High-pressure carbon dioxide product tower; 28. High-pressure CO2 absorption section; 29. ​​Medium-pressure CO2 flash tank; 30. Methanol-water separator; 31. Primary liquid CO2 pressure reducing valve; 32. Third pressure reducing valve; 33. Fourth pressure reducing valve; 34. Sulfur-containing methanol pressure reducing valve; 35. Fifth pressure reducing valve; 36. Sixth pressure reducing valve; 37. Secondary liquid CO2 pressure reducing valve; 38. Circulating gas compressor. Detailed Implementation

[0044] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0045] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0046] The present invention will now be described in further detail with reference to the accompanying drawings:

[0047] See Figure 1 , Figure 1The schematic diagram of the present invention illustrates a low-temperature methanol washing system and method based on pre-CO2 separation and high H2S partial pressure desulfurization, mainly comprising: a feed gas coiled heat exchanger I1; a methanol-water separator 2; a feed gas cooler 3; a feed gas coiled heat exchanger II4; a carbon dioxide condenser 5; a desulfurized rich methanol circulating pump 6; a desulfurized rich methanol cooler 7; a flow proportional controller 8; a high-pressure absorption tower 9; a carbon dioxide gas-liquid separation section 10; a desulfurization section 11; a decarbonization section 12; a methanol coiled heat exchanger III13; a first pressure reducing valve 14; a sulfur-free rich methanol medium-pressure flash evaporator 15; a second pressure reducing valve 16; and a sulfur-containing rich methanol medium-pressure flash evaporator 17. 7; Medium-pressure flash distillation tower; 18; Hydrogen sulfide concentration tower; 19; Lower tower of H2S concentration tower; 20; Upper tower of H2S concentration tower; 21; Methanol circulation pump I; 22; Methanol coiled tube heat exchanger II; 23; Thermal regeneration tower; 24; Methanol coiled tube heat exchanger I; 25; Methanol circulation pump II; 26; High-pressure carbon dioxide product tower; 27; High-pressure CO2 absorption section; 28; Medium-pressure CO2 flash tank; 29; Methanol-water separator; 30; First-stage liquid CO2 pressure reducing valve; 31; Third-stage pressure reducing valve; 32; Fourth-stage pressure reducing valve; 33; Sulfur-containing methanol pressure reducing valve; 34; Fifth-stage pressure reducing valve; 35; Sixth-stage pressure reducing valve; 36; Second-stage liquid CO2 pressure reducing valve; 37; Circulating gas compressor; 38.

[0048] The feed gas from the coal gasification unit is combined with methanol and circulating gas from methanol circulating pump II26 and circulating gas compressor 38, and then enters the shell side of feed gas coil heat exchanger I1 through a common pipeline. Methanol is injected into the feed gas to prevent the moisture in the feed gas from freezing when cooled below zero degrees. The cold source of feed gas coil heat exchanger I1 is the low-temperature purified gas from the top of the downstream high-pressure absorption tower 9, the cold exhaust gas from the top of the hydrogen sulfide concentration tower 19, and the cold carbon dioxide product gas from the top of the high-pressure carbon dioxide product tower 27. The raw gas is reheated in the raw gas coil heat exchanger I1 and then sent out of the boundary area. After being cooled and partially condensed by the raw gas coil heat exchanger I1, the raw gas enters the methanol-water separator 2 for gas-liquid separation. The liquid phase at the bottom enters the middle of the methanol-water separator 30, and the gas phase at the top of the tank enters the tube side of the raw gas cooler 3 for cooling and condensation. The cold source is an externally supplied refrigerant shared with the traditional low-temperature methanol wash. The cooled and condensed raw gas enters the shell side of the raw gas coil heat exchanger II4 and is cooled by the low-temperature purified gas from the top of the high-pressure absorption tower 9. Then it enters the tube side of the carbon dioxide condenser 5. The cold source is the low-temperature liquid carbon dioxide from the secondary liquid CO2 pressure reducing valve 37 in the shell side of the carbon dioxide condenser 5. After the liquid carbon dioxide is depressurized, its bubble point temperature can be reduced to -60℃. Its vaporization process will absorb a large amount of heat, thereby realizing the condensation of a large amount of carbon dioxide gas components in the raw gas into liquid carbon dioxide in the tube side of the carbon dioxide condenser 5.

[0049] The raw material gas, after being further cooled and condensed, enters the carbon dioxide gas-liquid separation section 10 for gas-liquid separation. The liquid carbon dioxide at the bottom is depressurized by the first-stage liquid CO2 pressure reducing valve 31 and enters the medium-pressure CO2 flash tank 29. The light component impurities collected from the top, mainly consisting of effective gas, CO2 gas and a very small amount of sulfur-containing compounds, are sent to the circulating gas compressor 38 to recover the effective gas components. The high-purity liquid carbon dioxide obtained at the bottom of the tank is sent to the shell side of the carbon dioxide condenser 5 after passing through the second-stage liquid CO2 pressure reducing valve 37.

[0050] The high-pressure carbon dioxide gas from the shell outlet of the carbon dioxide condenser 5 enters the bottom of the high-pressure carbon dioxide product tower 27 and flows from bottom to top. It comes into countercurrent contact with the sulfur-free methanol liquid from the sulfur-free rich methanol medium-pressure flash tank 15 at the top of the tower for desulfurization. The sulfur-containing rich methanol liquid at the bottom is sent to the hydrogen sulfide concentration tower 19 for depressurization and regeneration.

[0051] After carbon dioxide removal, the raw gas enters the bottom of the desulfurization section 11 of the high-pressure absorption tower 9. Simultaneously, sulfur-free rich methanol from the decarbonization section 12, pressurized by the desulfurization rich methanol circulation pump 6 and cooled by the desulfurization rich methanol cooler 7, enters the top of the desulfurization section 11. Under gravity, it flows downwards and fully contacts the raw gas in the high-pressure, low-temperature environment of the tower, absorbing all sulfur-containing compounds and some carbon dioxide. The desulfurized raw gas then enters the bottom of the decarbonization section 12, while the sulfur-containing rich methanol at the bottom of the desulfurization section 11 is sent to the methanol coil. Meanwhile, the low-temperature lean liquid from the outlet of the methanol coiled tube heat exchanger II23 enters the top of the decarbonization section 12. Similarly, the cooled methanol flows from top to bottom under gravity and comes into full contact with the feed gas in the high-pressure and low-temperature environment inside the tower to absorb all or most of the carbon dioxide. The decarbonized feed gas is purified gas. The low-temperature purified gas is taken out from the top of the decarbonization section 12. The sulfur-free rich methanol at the bottom of the decarbonization section 12 is sent to the methanol coiled tube heat exchanger III13, and part of it is returned to the top of the desulfurization section 11.

[0052] Sulfur-free and sulfur-containing rich methanol are cooled by methanol coil heat exchanger III13 and reduced in pressure by first pressure reducing valve 14 and second pressure reducing valve 16, respectively, and then enter sulfur-free rich methanol medium-pressure flash tank 15 and sulfur-containing rich methanol medium-pressure flash tank 17. Under the low temperature and medium pressure environment of the flash tank, the purpose of desorbing as little carbon dioxide as possible and desorbing as many effective gases (hydrogen and carbon monoxide) as possible is achieved. The gas at the top of the sulfur-free and sulfur-containing rich methanol medium-pressure flash tanks, as well as the recovered gas from the top of the medium-pressure CO2 flash tank 29, are combined and then returned to the raw material gas after being pressurized by the circulating gas compressor 38.

[0053] The liquid at the bottom of the sulfur-free rich methanol medium-pressure flash tank 15 is depressurized by the third pressure reducing valve 32 and the fifth pressure reducing valve 35, and then enters the top of the high-pressure CO2 absorption section 28 and the top of the upper column of the hydrogen sulfide concentration tower 19, respectively. The liquid at the bottom of the sulfur-containing rich methanol medium-pressure flash tank 17 is depressurized by the sulfur-containing methanol pressure reducing valve 34 and then enters the middle of the upper column of the hydrogen sulfide concentration tower 19. The liquid at the bottom of the upper column 21 of the H2S concentration tower is collected, pressurized by the methanol circulation pump I22, and then passes sequentially through the methanol coil heat exchanger II23 and the methanol coil. After desorption and heating in heat exchanger III13, the methanol returns to the top of the lower column 20 of the H2S concentration tower. Nitrogen gas is introduced from the bottom of the tower, while the liquid phase at the bottom is reheated by methanol coil heat exchanger I25 and finally sent to the upper feed inlet of the thermal regeneration tower 24. In the above process, the sulfur-free rich methanol is depressurized and then undergoes carbon dioxide desorption and methanol cooling in the upper column 21 of the H2S concentration tower. The desorbed carbon dioxide gas merges with the gas from the top chimney plate of the lower column 20 of the H2S concentration tower and then passes through the upper column 21 of the H2S concentration tower. The sulfur-free, rich methanol extracted from the top of column 21 of the H2S concentration tower flows downwards within the tower due to gravity, making full counter-current contact with the gas inside the tower to absorb the sulfur-containing components in the gas, ensuring that the sulfur content in the exhaust gas meets the standards. Simultaneously, the sulfur-rich methanol, after being depressurized, begins to flow downwards in the middle of the tower for carbon dioxide desorption and methanol cooling. After flowing to the bottom chimney plate, it passes sequentially through methanol coiled tube heat exchanger II23 and methanol coiled tube heat exchanger III13, where it is supplied with... While cooling, the gas undergoes a phase change as its temperature rises. It then enters the top of the lower column 20 of the H2S concentration tower, where gas and liquid separate. The gas passes through the chimney plate and enters the bottom of the upper column 21 of the H2S concentration tower. The liquid flows from top to bottom and comes into full counter-current contact with the nitrogen from the bottom of the lower column 20 of the H2S concentration tower. Carbon dioxide is extracted from the methanol solution, and a small amount of sulfur-containing gas is also vaporized or extracted here. All of the above gases eventually enter the bottom of the upper column 21 of the H2S concentration tower through the chimney plate at the top of the lower column 20 of the H2S concentration tower.

[0054] The feed to the upper part of the thermal regeneration tower 24 is a methanol solution heated by the methanol coil heat exchanger I25, while the feed to the lower part is methanol vapor drawn from the top of the methanol-water separator 30. The gas drawn from the top of the tower flows into a sulfuric acid-containing gas pipeline and is sent out of the boundary area. The lean methanol drawn from the bottom of the tower is first cooled by the methanol coil heat exchanger I25, and then pressurized by the methanol circulation pump II26. A small portion is used as antifreeze and introduced into the feed gas pipeline, and a small portion is introduced as feed into the upper feed inlet of the methanol-water separator 30. The majority of the remaining lean methanol passes through the methanol coil heat exchanger I25. After I23 is fully cooled, it is used as the main lean methanol solution and fed into the top of the high-pressure absorption tower 9. In the thermal regeneration tower, all the acidic gases in the feed are distilled off from the top of the tower by heating and distillation. The bottom of the tower yields a completely regenerated lean methanol solution, which is then pressurized and cooled before being used as the main lean methanol solution in the high-pressure absorption tower. At the same time, in the methanol-water separation tower 30, methanol and water are separated by heating and distillation to achieve dehydration. The methanol vapor obtained from the top of the tower is sent to the thermal regeneration tower 24, while the water obtained from the bottom of the tower is sent out of the boundary area via a water pipe.

[0055] The above analysis demonstrates the ingenious design of a low-temperature methanol washing system based on pre-CO2 separation and high H2S partial pressure desulfurization. This system achieves a high degree of synergistic integration between a multi-stage carbon dioxide separation and purification unit and a staged desorption and cooling unit for the methanol solution. The system is characterized by simple operation, flexible load adjustment, and safe and reliable operation. It can simultaneously and effectively remove carbon dioxide and sulfuric acid-containing gases, and can complete the separation, purification, and pressurization of carbon dioxide under extremely low energy consumption. The system ultimately produces a high-purity, high-recovery purified gas product and supports continuous operation. This overall technical solution is highly economical and applicable to coal chemical production and energy-saving technologies.

[0056] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

[0057] Example 1

[0058] The feed gas used in this embodiment has the following volumetric composition: 52.41% hydrogen, 0.54% carbon monoxide, 46.13% carbon dioxide, 0.21% sulfur-containing compounds, and the remainder being nitrogen and other inert gases. The pressure is 5.5 MPa, the temperature is 40°C, and the flow rate is 312,158 Nm³. 3 / h.

[0059] A low-temperature methanol washing system and method based on pre-CO2 separation and high H2S partial pressure desulfurization specifically includes the following steps:

[0060] 1. The feed gas from the coal gasification unit, after being combined with methanol and circulating gas from methanol circulating pump II26 and circulating gas compressor 38, enters the shell side of the feed gas coil heat exchanger I1 via a common pipeline. Its cold source is the low-temperature purified gas from the top of the downstream high-pressure absorption tower 9, the cold exhaust gas from the top of the hydrogen sulfide concentration tower 19, and the cold carbon dioxide product gas from the top of the high-pressure carbon dioxide product tower 27. These cold gases are reheated to 32°C in the feed gas coil heat exchanger I1 before being sent out of the boundary area. The feed gas, after being cooled and partially condensed by the feed gas coil heat exchanger I1, is at -14°C and enters... Methanol-water separator 2 performs gas-liquid separation. The liquid phase at the bottom enters the middle of methanol-water separator 30, while the gas phase at the top enters the tube side of feed gas cooler 3 for cooling and condensation. The cold source is an externally supplied refrigerant shared with traditional low-temperature methanol washing. The cooled and condensed feed gas enters the shell side of feed gas coil heat exchanger II4, where it is first cooled by the low-temperature purified gas from the top of high-pressure absorption tower 9. Then, it enters the tube side of carbon dioxide condenser 5, where the cold source is the low-temperature liquid carbon dioxide from the secondary liquid CO2 pressure reducing valve 37. Finally, the low-temperature liquid carbon dioxide in the shell side of carbon dioxide condenser 5 is cooled to -34°C.

[0061] 2. The raw material gas, after being further cooled and condensed, enters the carbon dioxide gas-liquid separation section 10 for gas-liquid separation. The liquid carbon dioxide at the bottom is reduced to 1.9 MPa by the first-stage liquid CO2 pressure reducing valve 31 and then enters the medium-pressure CO2 flash tank 29. The light component gas collected from the top is sent to the circulating gas compressor 38 to recover the effective gas components. The high-purity liquid carbon dioxide obtained at the bottom of the tank is reduced to 1.0 MPa by the second-stage liquid CO2 pressure reducing valve 37 and then sent to the shell side of the carbon dioxide condenser 5. The high-pressure carbon dioxide gas at the outlet enters the bottom of the high-pressure carbon dioxide product tower 27 and flows from bottom to top. It comes into countercurrent contact with the sulfur-free methanol liquid from the sulfur-free rich methanol medium-pressure flash tank 15 at the top of the tower for desulfurization. The sulfur-containing rich methanol liquid at the bottom is sent to the hydrogen sulfide concentration tower 19 for depressurization and regeneration.

[0062] 3. The raw gas, after pre-removal of carbon dioxide, enters the bottom of the desulfurization section 11 of the high-pressure absorption tower 9. At the same time, the sulfur-free rich methanol from the decarbonization section 12 is pressurized by the desulfurization rich methanol circulation pump 6 and cooled by the desulfurization rich methanol cooler 7 before entering the top of the desulfurization section 11. In the tower, all the sulfur-containing compounds and some carbon dioxide in the raw gas are absorbed. The desulfurized raw gas enters the bottom of the decarbonization section 12, while the sulfur-containing rich methanol at the bottom of the desulfurization section 11 is sent to the tube side of the methanol coiled heat exchanger III 13. Meanwhile, the low-temperature lean liquid from the outlet of the tube side of the methanol coiled heat exchanger II 23 enters the top of the decarbonization section 12. Similarly, all or most of the carbon dioxide in the raw gas is absorbed in the tower. The decarbonized raw gas is purified gas. The low-temperature purified gas is extracted from the top of the decarbonization section 12. Part of the sulfur-free rich methanol at the bottom of the decarbonization section 12 is sent to the tube side of the methanol coiled heat exchanger III 13, and part is returned to the top of the desulfurization section 11.

[0063] 4. After being cooled by the methanol coil heat exchanger III13 and reduced to 1.5 MPa by the first pressure reducing valve 14 and the second pressure reducing valve 16, the sulfur-free and sulfur-containing rich methanol enter the sulfur-free rich methanol medium-pressure flash tank 15 and the sulfur-containing rich methanol medium-pressure flash tank 17, respectively. They are flashed in the low temperature and medium pressure environment of the flash tank. The gas from the top of the sulfur-free and sulfur-containing rich methanol medium-pressure flash tanks and the recovered gas from the top of the medium-pressure CO2 flash tank 29 are combined and then returned to the raw material gas after being pressurized by the circulating gas compressor 38.

[0064] 5. The liquid at the bottom of the sulfur-free rich methanol medium-pressure flash tank 15 is depressurized by the third pressure reducing valve 32 and the fifth pressure reducing valve 35, and then enters the top of the high-pressure CO2 absorption section 28 and the top of the upper column of the hydrogen sulfide concentration tower 19, respectively. The liquid at the bottom of the sulfur-containing rich methanol medium-pressure flash tank 17 is depressurized by the sulfur-containing methanol pressure reducing valve 34 and then enters the middle of the upper column of the hydrogen sulfide concentration tower 19. The liquid at the bottom of the upper column 21 of the H2S concentration tower is collected, pressurized by the methanol circulation pump I22, and then passes through the methanol coil heat exchanger in sequence. After desorption via heat exchanger II23 and methanol coiled tube heat exchanger III13, the methanol returns to the top of the lower column 20 of the H2S concentration tower. Nitrogen gas is introduced from the bottom of the tower, while the liquid phase at the bottom is reheated via methanol coiled tube heat exchanger I25 and finally sent to the upper feed inlet of the thermal regeneration tower 24. In the above process, sulfur-free rich methanol undergoes carbon dioxide desorption and methanol cooling in the upper column 21 of the H2S concentration tower after depressurization. The desorbed carbon dioxide gas reacts with the gas from the top chimney of the lower column 20 of the H2S concentration tower. After the gases from the plates converge, they are extracted through the gas phase outlet at the top of the upper column 21 of the H2S concentration tower. The sulfur-free, rich methanol at the top of the upper column 21 absorbs the sulfur-containing components in the gas within the tower to ensure that the sulfur content in the exhaust gas meets the standards. At the same time, the sulfur-containing rich methanol undergoes carbon dioxide desorption and methanol cooling in the tower after depressurization. After flowing to the bottom chimney plate, it passes through the methanol coiled tube heat exchanger II23 and methanol coiled tube heat exchanger III13 in sequence. While being provided with cooling, its own temperature rises and undergoes a phase change. It then enters the top of the lower column 20 of the H2S concentration tower, where gas-liquid separation occurs. The gas passes through the chimney plate and enters the bottom of the upper column 21 of the H2S concentration tower. The liquid flows from top to bottom and comes into full counter-current contact with the nitrogen from the bottom of the lower column 20 of the H2S concentration tower. The carbon dioxide in the methanol solution is extracted, and a small amount of sulfur-containing gas is also vaporized or extracted here. All of the above gases finally enter the bottom of the upper column 21 of the H2S concentration tower through the top chimney plate of the lower column 20 of the H2S concentration tower.

[0065] 6. The feed to the upper part of the thermal regeneration tower 24 comes from the methanol solution heated by the methanol coil heat exchanger I25, while the feed to the lower part comes from the methanol vapor collected from the top of the methanol-water separator 30. The gas collected from the top of the tower is collected into the sulfuric acid-containing gas pipeline and sent out of the boundary area. The lean methanol collected from the bottom of the tower is first cooled by the methanol coil heat exchanger I25, and then pressurized by the methanol circulation pump II26. A small portion is used as antifreeze and is introduced into the raw material gas pipeline, and a small portion is introduced as feed into the upper feed port of the methanol-water separator 30. The majority of the remaining lean methanol passes through the methanol coil heat exchanger. After being fully cooled, II23 is used as the main lean methanol solution and fed into the top of the high-pressure absorption tower 9. In the thermal regeneration tower, all the acidic gases in the feed are distilled off from the top of the tower by heating and distillation. The bottom of the tower yields a completely regenerated lean methanol solution, which is then pressurized and cooled before being used as the main lean methanol solution in the high-pressure absorption tower. At the same time, in the methanol-water separation tower 30, methanol and water are separated by heating and distillation to achieve dehydration. The methanol vapor obtained from the top of the tower is sent to the thermal regeneration tower 24, while the water obtained from the bottom of the tower is sent out of the boundary area via a water pipe.

[0066] In this embodiment, the obtained carbon dioxide product gas has a chemical purity of 99.26%, a recovery rate of 57.12%, a cooling consumption of 4178 kW, a methanol loss of 43 kg / h, and a steam consumption of 15.1 t / h.

[0067] Example 2

[0068] A low-temperature methanol washing system and method based on pre-CO2 separation and high H2S partial pressure desulfurization is disclosed. The feed gas composition used in this study is as follows: hydrogen 52.62%, carbon monoxide 0.73%, carbon dioxide 44.68%, sulfur-containing compounds 0.34%, and the remainder being nitrogen and other inert gases. The pressure is 5.6 MPa, the temperature is 40℃, and the flow rate is 312158 Nm³. 3 / h.

[0069] In addition, the condensation temperature of the feed gas coil heat exchanger I1 is -16°C, the condensation temperature of the carbon dioxide condenser 5 is -36°C, the first-stage liquid CO2 pressure reducing valve 31 is set to 1.8 MPa, the second-stage liquid CO2 pressure reducing valve 37 is set to 0.96 MPa, and the other conditions are the same as in Example 1.

[0070] In this embodiment, the obtained carbon dioxide product gas has a chemical purity of 99.38%, a recovery rate of 56.81%, a cooling consumption of 3829 kW, a methanol loss of 42 kg / h, and a steam consumption of 14.3 t / h.

[0071] Example 3

[0072] A low-temperature methanol washing system and method based on pre-CO2 separation and high H2S partial pressure desulfurization is disclosed. The feed gas composition used in this study is as follows: hydrogen 47.12%, carbon monoxide 14.13%, carbon dioxide 38.05%, sulfur-containing compounds 0.52%, and the remainder being nitrogen and other inert gases. The pressure is 3.9 MPa, the temperature is 40℃, and the flow rate is 657548 Nm³. 3 / h.

[0073] In addition, the condensation temperature of the feed gas coil heat exchanger I1 is -14°C, the condensation temperature of the carbon dioxide condenser 5 is -35°C, the first-stage liquid CO2 pressure reducing valve 31 is set to 1.9 MPa, the second-stage liquid CO2 pressure reducing valve 37 is set to 1.05 MPa, and the remaining conditions are the same as in Example 1.

[0074] In this embodiment, the obtained carbon dioxide product gas has a chemical purity of 99.23%, a recovery rate of 45.25%, a cooling consumption of 6016 kW, a methanol loss of 43 kg / h, and a steam consumption of 15.5 t / h.

[0075] Example 4

[0076] A low-temperature methanol washing system and method based on pre-CO2 separation and high H2S partial pressure desulfurization is disclosed. The feed gas composition used in this study is as follows: hydrogen 54.51%, carbon monoxide 0.82%, carbon dioxide 44.28%, sulfur-containing compounds 0.26%, and the remainder being nitrogen and other inert gases. The pressure is 3.9 MPa, the temperature is 40℃, and the flow rate is 657548 Nm³. 3 / h.

[0077] In addition, the condensation temperature of the raw gas coil heat exchanger I1 is -15°C, the condensation temperature of the carbon dioxide condenser 5 is -36°C, the first-stage liquid CO2 pressure reducing valve 31 is set to 1.8 MPa, the second-stage liquid CO2 pressure reducing valve 37 is set to 0.95 MPa, and the remaining conditions are the same as in Example 1.

[0078] In this embodiment, the obtained carbon dioxide product gas has a chemical purity of 99.35%, a recovery rate of 53.62%, a cooling consumption of 6835 kW, a methanol loss of 44 kg / h, and a steam consumption of 16.2 t / h.

Claims

1. A low-temperature methanol washing system based on pre-CO2 separation and high H2S partial pressure desulfurization, characterized in that, include: The raw material gas pretreatment unit is used to pre-cool and dehydrate the raw material process gas, including a raw material gas coil heat exchanger I (1) and a methanol-water separator (2) arranged in sequence. A pre-pressurized CO2 liquefaction and separation unit is connected downstream of the raw gas pretreatment unit, including a raw gas cooler (3), a raw gas coil heat exchanger II (4), and a carbon dioxide condenser (5) arranged in sequence. The high partial pressure desulfurization and decarbonization unit is connected downstream of the pre-high pressure CO2 liquefaction separation unit and includes a high pressure absorption tower (9), which is divided into a carbon dioxide gas-liquid separation section (10), a desulfurization section (11) and a decarbonization section (12). The carbon dioxide gas-liquid separation section (10) of the high-pressure absorption tower (9) is located before the desulfurization section (11); The liquid CO2 pressure-reducing evaporation and cold energy recovery unit is connected downstream of the pre-high pressure CO2 liquefaction separation unit and includes the shell side of the first-stage liquid CO2 pressure reducing valve (31), the medium-pressure CO2 flash tank (29), the second-stage liquid CO2 pressure reducing valve (37), and the carbon dioxide condenser (5). The carbon dioxide product desulfurization unit is connected downstream of the liquid CO2 vacuum evaporation and cold energy recovery unit, including a high-pressure carbon dioxide product tower (27), with a medium-pressure CO2 flash tank (29) built into the bottom of the high-pressure carbon dioxide product tower (27) and a high-pressure CO2 absorption section (28) at the top. The methanol regeneration unit includes a methanol coiled heat exchanger III (13), a medium-pressure flash tower (18), a hydrogen sulfide concentration tower (19), a methanol circulation pump I (22), a methanol coiled heat exchanger II (23), a thermal regeneration tower (24), a methanol coiled heat exchanger I (25), a methanol circulation pump II (26), a methanol-water separator (30), and a circulating gas compressor (38). The medium-pressure flash tower (18) has a built-in sulfur-free rich methanol medium-pressure flash tank (15) and a sulfur-containing rich methanol medium-pressure flash tank (17). The hydrogen sulfide concentration tower (19) is divided into a lower H2S concentration tower (20) and an upper H2S concentration tower (21). The methanol distribution and temperature control optimization system includes an independent desulfurized methanol-rich circulating pump (6), a flow proportional controller (8), and a desulfurized methanol-rich cooler (7) located between the desulfurization section (11) and the decarbonization section (12) of the high-pressure absorption tower (9). The outlet temperature and proportion are controlled by adjusting the frequency of the desulfurized methanol-rich circulating pump (6) and the desulfurized methanol-rich cooler (7).

2. The system according to claim 1, characterized in that: The shell-side inlet of the raw gas coiled tube heat exchanger I (1) is connected to the raw gas pipeline, and the outlet is connected to the methanol-water separator (2). The liquid phase outlet of the methanol-water separator (2) is connected to the feed inlet pipeline in the middle of the methanol-water separation tower (30). The gas phase outlet is connected to the tube-side inlet of the raw gas cooler (3) via a pipeline. The tube-side outlet of the raw gas cooler (3) is connected to the shell-side inlet pipeline of the raw gas coiled tube heat exchanger II (4). The shell-side outlet of the raw gas coiled tube heat exchanger II (4) is connected to the tube-side inlet pipeline of the carbon dioxide condenser (5). The tube-side outlet of the carbon dioxide condenser (5) is connected to the inlet pipeline of the carbon dioxide gas-liquid separation section (10) of the high-pressure absorption tower (9). The carbon dioxide gas-liquid separation section (10) The bottom liquid phase outlet is connected in sequence to the inlet pipe of the first-stage liquid CO2 pressure reducing valve (31) and the medium-pressure CO2 flash tank (29). The top gas phase outlet of the medium-pressure CO2 flash tank (29) is connected in sequence to the inlet pipe of the fourth pressure reducing valve (33) and the circulating gas compressor (38). Its bottom liquid phase outlet is connected in sequence to the shell-side inlet pipe of the second-stage liquid CO2 pressure reducing valve (37) and the carbon dioxide condenser (5). The shell-side outlet of the carbon dioxide condenser (5) is connected to the bottom gas phase inlet pipe of the high-pressure CO2 absorption section (28) of the high-pressure carbon dioxide product tower (27). Its bottom liquid phase outlet is connected in sequence to the sixth pressure reducing valve (36) and the middle inlet pipe of the upper H2S concentration tower (21) of the hydrogen sulfide concentration tower (19).

3. The system according to claim 2, characterized in that: The tube side outlet of the raw gas coil heat exchanger II (4), the low-temperature exhaust gas outlet at the top of the hydrogen sulfide concentration tower (19), and the low-temperature and high-pressure carbon dioxide product gas outlet at the top of the high-pressure carbon dioxide product tower (27) are sequentially connected to the tube side of the raw gas coil heat exchanger I (1), as well as the purified gas pipeline, the exhaust gas pipeline, and the high-pressure carbon dioxide product gas inlet.

4. The system according to claim 3, characterized in that: The top lean methanol liquid phase inlet of the decarbonization section (12) of the high-pressure absorption tower (9) is connected to the outlet pipe of the tube side of the methanol coiled heat exchanger II (23). The bottom sulfur-free rich methanol outlet is connected to the sulfur-free rich methanol inlet of the tube side of the methanol coiled heat exchanger III (13), and is connected in sequence to the desulfurization rich methanol circulation pump (6), the desulfurization rich methanol cooler (7), the flow ratio controller (8) and the top liquid phase inlet pipe of the desulfurization section (11). The bottom sulfur-containing rich methanol outlet of the desulfurization section (11) is connected to the sulfur-containing rich methanol inlet pipe of the tube side of the methanol coiled heat exchanger III (13). The sulfur-free rich methanol outlet of the tube side of the methanol coiled heat exchanger III (13) is connected in sequence to the first pressure reducing valve (14) and the sulfur-free rich methanol medium-pressure flash tank (15) through pipes. The sulfur-containing rich methanol outlet of its tube side is connected in sequence to the second pressure reducing valve (16) and the sulfur-containing rich methanol medium-pressure flash tank (17) through pipes.

5. The system according to claim 4, characterized in that: The gas phase outlet of the sulfur-free rich methanol medium-pressure flash evaporator (15) is connected to the inlet pipe of the circulating gas compressor (38). The liquid phase outlet is connected to the top inlet pipe of the high-pressure CO2 absorption section (28) of the high-pressure carbon dioxide product tower (27) via the third pressure reducing valve (32), and to the top inlet pipe of the upper tower of the hydrogen sulfide concentration tower (19) via the fifth pressure reducing valve (35). The gas phase outlet of the sulfur-containing rich methanol medium-pressure flash evaporator (17) is connected to the inlet pipe of the circulating gas compressor (38). The liquid phase outlet is connected to the middle inlet pipe of the upper tower of the hydrogen sulfide concentration tower (19) via the sulfur-containing methanol pressure reducing valve (34). The outlet of the circulating gas compressor (38) is connected to the raw material gas pipeline through a pipeline.

6. The system according to claim 5, characterized in that: The bottom liquid phase outlet of the upper column (21) of the H2S concentration tower is connected in sequence to the methanol circulating pump I (22), the shell side of the methanol coiled heat exchanger II (23), the shell side of the methanol coiled heat exchanger III (13), and the top liquid phase inlet of the lower column (20) of the H2S concentration tower. The bottom liquid phase outlet of the lower column (20) of the H2S concentration tower is connected in sequence to the tube side of the methanol coiled heat exchanger I (25) and the upper feed inlet of the thermal regeneration tower (24) through a pipeline. The nitrogen pipeline is connected to the gas phase inlet at the bottom of the lower column (20) of the H2S concentration tower through a pipeline.

7. The system according to claim 6, characterized in that: The top gas phase outlet of the thermal regeneration tower (24) is connected to a sulfuric acid-containing gas pipeline via a pipe, and the bottom liquid phase outlet is connected in sequence to the shell side of the methanol coiled heat exchanger I (25) and the inlet of the methanol circulating pump II (26). The outlet of the methanol circulating pump II (26) is divided into two paths: one path is connected to the inlet pipe of the tube side of the methanol coiled heat exchanger II (23), and the other path is connected to the upper feed port of the methanol water separator (30) and the raw material gas pipeline via pipes. The top gas phase outlet of the methanol water separator (30) is connected to the lower feed port pipe of the thermal regeneration tower (24), and the bottom liquid phase outlet is connected to a water pipeline via a pipe.

8. A low-temperature methanol washing method using the system described in any one of claims 1-7, characterized in that, Includes the following steps: Before desulfurization, the raw process gas enters the pre-high pressure CO2 liquefaction separation unit. The temperature of the process gas is reduced to -25℃ to -45℃ through multi-stage cooling. It then enters the carbon dioxide gas-liquid separation section (10) of the high pressure absorption tower (9) to condense and separate liquid CO2. The CO2 liquefaction separation process does not introduce methanol absorption. The liquid CO2 separated at the bottom of the carbon dioxide gas-liquid separation section (10) is reduced to 1.2-2.5 MPa by the first-stage liquid CO2 pressure reducing valve (31) and then enters the medium-pressure CO2 flash tank (29) for pressure reduction flash evaporation to recover effective gas; The liquid CO2 separated from the bottom of the medium-pressure CO2 flash tank (29) is reduced to 0.6-1.2 MPa by the secondary liquid CO2 pressure reducing valve (37) and then enters the shell side of the carbon dioxide condenser (5) for pressure-reduced evaporation and cooling. The high-pressure CO2 gas generated by the flash evaporation in the shell side of the carbon dioxide condenser (5) is sent to the bottom of the high-pressure carbon dioxide product tower (27) and flows from bottom to top. It comes into countercurrent contact with the sulfur-free methanol liquid from the sulfur-free rich methanol medium-pressure flash tank (15) at the top of the tower to carry out desulfurization. The process gas after liquefying and separating CO2 at the top of the carbon dioxide gas-liquid separation section (10) is sequentially sent to the desulfurization section (11) and decarbonization section (12) of the high-pressure absorption tower (9) for purification. The sulfur-free rich methanol from the bottom of the decarbonization section (12) of the high-pressure absorption tower (9) is cooled by the desulfurized rich methanol cooler (7) until its temperature drops to -35°C to -8°C. The operating range of the flow ratio controller (8) after the independent desulfurization methanol-rich circulating pump (6) located between the desulfurization section (11) and the decarbonization section (12) of the high-pressure absorption tower (9) is controlled between 0.5 and 0.

8.

9. The low-temperature methanol washing method according to claim 8, characterized in that: The operating pressure of the high-pressure carbon dioxide product tower (27) is 0.6-1.2 MPa, and its bottom gas phase inlet is directly connected to the gaseous high-pressure CO2 outlet of the shell side of the carbon dioxide condenser (5).

10. The low-temperature methanol washing method according to claim 8, characterized in that: The methanol in the desulfurization section (11) and the decarbonization section (12) are transported through independent circulation systems, and the methanol circulation volume in the desulfurization section (11) is 50% to 80% of that in the conventional process.

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