Full-process biogas liquefaction and carbon dioxide co-production system

Abstract

The invention discloses a whole-process biogas liquefaction and carbon dioxide co-production system which comprises a feed gas pretreatment module, an outlet of the feed gas pretreatment module is connected with a carbon-rich system and a carbon-poor system, and a gas chromatograph sensor Q is arranged at the outlet of the feed gas pretreatment module; after the collected biogas is desulfurized and dehydrated by the feed gas pretreatment module, the components of the biogas are detected by the gas chromatograph sensor Q, the biogas enters the carbon-rich system or the carbon-poor system according to the characteristics of the components, efficient carbon dioxide separation and gas liquefaction of the biogas are completed in the carbon-rich system, and gas liquefaction is completed in the carbon-poor system. According to the invention, efficient separation and liquefaction treatment of biogas with different components and biogas at different stages can be realized, and the resource utilization efficiency and adaptability under diversified raw materials and complex working conditions are improved.

Description

Technical Field

[0001] The present invention relates to biogas liquefaction technology, and particularly to a full-process biogas liquefaction and carbon dioxide co-production system. Background Art

[0002] At present, biogas liquefaction and carbon dioxide capture technologies face challenges under complex raw material conditions and full-process conditions. The proportions of methane and carbon dioxide in biogas produced by different raw materials through fermentation vary greatly, and the ratio of methane to carbon dioxide also changes dynamically at different stages during the fermentation process of the same raw material. Traditional processes have certain limitations in adapting to multiple working conditions, reducing energy consumption, and improving resource utilization efficiency, and are difficult to meet the requirements of diversified biogas liquefaction and carbon dioxide capture. In the patent CN202010091218.8 (a mixed refrigerant biogas pressurized liquefaction system and its working method) previously disclosed by Wang Yong et al., a biogas pretreatment unit, a secondary membrane separation unit, a mixed refrigerant refrigeration cycle unit, and a CO2 rectification and purification unit are provided to achieve efficient desulfurization, dehydration, and filtration of biogas. The secondary membrane separation unit can separate biogas into a high-purity CH4 stream and a CO2-rich stream, and produce liquid CH4 and food-grade liquid CO2 through pressurized liquefaction and rectification processes. However, it still has deficiencies in terms of adaptability and process efficiency. First, the secondary membrane separation unit and the pressurized liquefaction process of the system cannot get rid of the dependence on the ratio of methane and carbon dioxide in biogas raw materials, and it is difficult to cope with the multi-condition of dynamic changes in methane and carbon dioxide during the fermentation process of different raw materials and cannot efficiently separate and liquefy the biogas components at different stages of the full process, resulting in poor applicability. Second, there is a 5% - 10% loss of raw gas in the secondary membrane separation, resulting in a low resource utilization rate. Summary of the Invention

[0003] Object of the Invention: The object of the present invention is to provide a full-process biogas liquefaction and carbon dioxide co-production system, which can achieve efficient separation and liquefaction treatment of biogas with different components and at different stages, and improve resource utilization efficiency and adaptability under diversified raw materials and complex working conditions.

[0004] Technical Solution: A full-process biogas liquefaction and carbon dioxide co-production system of the present invention includes a raw gas pretreatment module. The outlet of the raw gas pretreatment module is connected to a carbon-rich system and a carbon-poor system, and a gas chromatograph sensor Q is arranged at the outlet of the raw gas pretreatment module.

[0005] After the collected biogas is desulfurized and dehydrated by the raw gas pretreatment module, the gas chromatograph sensor Q detects the biogas components and selects to enter the carbon-rich system or the carbon-poor system according to the component characteristics. The efficient separation of carbon dioxide and gas liquefaction of biogas are completed in the carbon-rich system, and gas liquefaction is completed in the carbon-poor system.

[0006] Further, if the proportion of carbon dioxide content in the biogas after desulfurization and dehydration is greater than that of methane content, the biogas after desulfurization and dehydration enters the carbon-rich system;

[0007] If the proportion of carbon dioxide content in the biogas after desulfurization and dehydration is less than that of methane content, the biogas after desulfurization and dehydration enters the carbon-lean system.

[0008] Further, the carbon-rich system includes a membrane separation carbon dioxide removal module, a biogas liquefaction module, a nitrogen removal and recovery module, and a BOG reliquefaction module connected in sequence along the gas flow direction. The biogas after desulfurization and dehydration is stabilized in the membrane separation carbon dioxide removal module and then passes through the first-stage membrane module and the second-stage membrane module in sequence. The permeate carbon dioxide is discharged, and a part of the retentate methane is compressed and sent back to the buffer tank as recycle gas to improve the methane recovery rate. Another part is used as product gas and enters the biogas liquefaction module and the nitrogen removal and recovery module. After nitrogen expansion precooling, heavy hydrocarbon separation, and nitrogen expansion deep cooling, nitrogen is removed and recovered and then input into the methane storage tank in liquid form. The BOG generated in the methane storage tank is sent to the BOG reliquefaction module and then refrigerated and liquefied again, thus completing the efficient separation of carbon dioxide and methane liquefaction;

[0009] The carbon-lean system includes a biogas liquefaction module, a nitrogen removal and recovery module, and a BOG reliquefaction module connected in sequence along the gas flow direction. The biogas after desulfurization and dehydration directly enters the biogas liquefaction module and the nitrogen removal and recovery module after absorbing a small amount of carbon dioxide in the carbon dioxide absorption tower. After nitrogen expansion precooling, heavy hydrocarbon separation, and nitrogen expansion deep cooling, nitrogen is removed and recovered and then input into the methane storage tank in liquid form. The BOG generated in the methane storage tank is sent to the BOG reliquefaction module and then refrigerated and liquefied again, thus completing the efficient methane liquefaction.

[0010] Further, the raw gas pretreatment module includes a first gas flow regulating valve, a filter, a first gas compressor, a first gas water cooler, a second gas compressor, a second gas water cooler, a sulfur-containing gas pre-absorption tower, a heater, a hydrolysis tower, a second gas flow regulating valve, a third gas water cooler, a sulfur-containing gas fine absorption tower, a first steam-water separator, and a drying tower connected in sequence along the gas flow direction. The outlet of the first steam-water separator is also connected with a first steam trap.

[0011] Further, the membrane separation carbon dioxide removal module includes a third gas flow regulating valve, a pressure reducing valve, a raw gas buffer tank, and a first-stage membrane separation unit connected in sequence along the gas flow direction;

[0012] The outlet of the first-stage membrane separation unit is divided into two paths, one path is connected to the inlet of the first-stage vacuum buffer tank, and the other path is connected to the inlet of the bubbling humidifier;

[0013] The outlet of the first-stage vacuum buffer tank successively has a first-stage vacuum unit, a first-stage vacuum pump circulating water tank, and a first-stage plate heat exchanger along the gas flow direction; among them, the outlet of the first-stage plate heat exchanger is connected to the inlet of the first-stage vacuum unit;

[0014] The outlet of the bubbling humidifier successively has a second steam-water separator and a second-stage membrane separation group along the gas flow direction; among them, the outlet of the second steam-water separator is also connected to a second steam trap;

[0015] The outlet of the second-stage membrane separation group is divided into two paths, one path is connected to the inlet of the second-stage vacuum buffer tank, and the other path is connected to the inlet of the first methane storage tank.

[0016] Further, the outlet of the second-stage vacuum buffer tank successively has a second-stage vacuum unit and a second-stage vacuum pump circulating water tank along the gas flow direction;

[0017] The outlet of the second-stage vacuum pump circulating water tank is divided into two paths, one path is connected to the inlet of the second-stage vacuum unit through a second-stage plate heat exchanger, and the other path is connected to the inlet of the raw gas buffer tank through a third gas compressor;

[0018] The outlet of the first methane storage tank successively has a fifth gas flow regulating valve and a fourth gas compressor along the gas flow direction;

[0019] The outlet of the fourth gas compressor is connected to the biogas liquefaction module.

[0020] Further, the biogas liquefaction module includes a third gas flow regulating valve. The outlet of the third gas flow regulating valve is connected to the inlet of the carbon dioxide absorption tower. The outlet of the carbon dioxide absorption tower is connected to the hot-end inlet 34a of the first LNG heat exchanger. The hot-end outlet 34b of the first LNG heat exchanger is connected to the inlet of the heavy hydrocarbon separator. The outlet of the heavy hydrocarbon separator is connected to the hot-end inlet 36a of the second LNG heat exchanger. The hot-end outlet 36b of the second LNG heat exchanger is connected to the inlet of the nitrogen stripping tower. The outlet of the nitrogen stripping tower is connected to the hot-end inlet 38a of the third LNG heat exchanger. The hot-end outlet 38b of the third LNG heat exchanger is connected to the inlet of the first gas throttle valve. The outlet of the first gas throttle valve is connected to the inlet of the second methane storage tank. The outlet of the second methane storage tank is connected to the inlet of the sixth gas flow regulating valve;

[0021] The cold-end outlet 34e of the first LNG heat exchanger is successively connected with a fifth gas compressor, a fourth gas water cooler, a sixth gas compressor, and a fifth gas water cooler along the gas flow direction; among them, the outlet of the fifth gas water cooler is connected to the hot-end inlet 34d of the first LNG heat exchanger;

[0022] Further, the hot end outlet 34c of the first LNG heat exchanger is divided into two paths, one path is connected to the inlet of the seventh gas flow regulating valve, and the other path is connected to the inlet of the eighth gas flow regulating valve;

[0023] The outlet of the seventh gas flow regulating valve is connected to the cold end inlet 36f of the second LNG heat exchanger through the first turbine expander;

[0024] The outlet of the eighth gas flow regulating valve is connected to the hot end inlet 36d of the second LNG heat exchanger. The hot end outlet 36c of the second LNG heat exchanger passes through the second turbine expander and the ninth gas flow regulating valve and is connected to the cold end inlet 38c of the third LNG heat exchanger. The cold end outlet 38d of the third LNG heat exchanger is connected to the cold end inlet 36f of the second LNG heat exchanger. The cold end outlet 36e of the second LNG heat exchanger is connected to the cold end inlet 34f of the first LNG heat exchanger.

[0025] Further, the nitrogen removal and recovery module includes a nitrogen-methane separation column, an eleventh gas flow regulating valve, and a third gas throttle valve;

[0026] The inlet of the nitrogen-methane separation column is connected to the biogas liquefaction module, and the outlet of the nitrogen-methane separation column is connected to the inlet of the third gas throttle valve through the eleventh gas flow regulating valve.

[0027] Further, the BOG re-liquefaction module includes a fourth LNG heat exchanger, a tenth gas flow regulating valve, and a second gas throttle valve;

[0028] The hot end inlet 42a of the fourth LNG heat exchanger is connected to the biogas liquefaction module. The hot end outlet 42b of the fourth LNG heat exchanger is connected to the inlet of the tenth gas flow regulating valve. The inlet of the second gas throttle valve is connected to the biogas liquefaction module. The outlet of the second gas throttle valve is connected to the cold end inlet 42c of the fourth LNG heat exchanger. The cold end outlet 42d of the fourth LNG heat exchanger is connected to the biogas liquefaction module.

[0029] Beneficial effects: Compared with the prior art, the remarkable technical effects of the present invention are as follows:

[0030] It is applicable to the dynamic changes in the proportions of methane and carbon dioxide during the fermentation processes of different raw materials. It can achieve the liquefaction and recovery of methane and carbon dioxide under different gas component stages through process flow changes. The system has good adaptability and avoids the high requirements for the raw material gas component ratio in the traditional mixed refrigerant system.

[0031] The collaborative design of the rich carbon system and the lean carbon system can adapt to the full process conditions of biogas treatment, efficiently complete gas separation and liquefaction, and solve the pain points that the traditional process cannot optimize the gas components in different stages of biogas fermentation.

[0032] The system design reduces energy consumption. Through the nitrogen removal and recovery module and the BOG re-liquefaction module, it improves the resource utilization efficiency. In contrast, the mixed refrigerant refrigeration cycle system used in Wang Yong's patent in the background technology relies on a complex refrigeration cycle and has relatively high energy consumption.

[0033] The system allows biogas raw gas with different components to enter the corresponding rich-carbon system or lean-carbon system after passing through the raw gas pretreatment module. After passing through the membrane separation carbon dioxide removal module or the carbon dioxide absorption tower, the gas then enters the biogas liquefaction module, the nitrogen removal and recovery module, and the BOG re-liquefaction module in sequence. Thus, efficient carbon dioxide separation and methane liquefaction are achieved, minimizing the loss of methane components in the raw gas and avoiding the problem of resource waste.

[0034] The system has strong process flexibility. Through the multi-stage coupling process of membrane separation, liquefaction, and nitrogen removal and recovery modules, it can dynamically adjust the treatment strategy according to the gas component ratio and is applicable to various gas source conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic structural diagram of a full-process biogas liquefaction and carbon dioxide co-production system of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] The technical solution of the present invention will be introduced in detail below in combination with the specific embodiments and the drawings in the specification.

[0037] Such as Figure 1As shown in the figure, the full-process biogas liquefaction and carbon dioxide co-production system of the present invention involves the following components: the first gas flow regulating valve 1, the filter 2, the first gas compressor 3, the first gas water cooler 4, the second gas compressor 5, the second gas water cooler 6, the sulfur-containing gas pre-absorption tower 7, the heater 8, the second gas flow regulating valve 9, the hydrolysis tower 10, the third gas water cooler 11, the sulfur-containing gas fine absorption tower 12, the first steam-water separator 13, the first steam trap 14, the drying tower 15, the third gas flow regulating valve 16, the pressure reducing valve 17, the raw material gas buffer tank 18, the first-stage membrane separation unit 19, the first-stage vacuum buffer tank 20, the first-stage vacuum unit 21, the first-stage vacuum pump circulating water tank 22, the first-stage plate heat exchanger 23, the bubbling humidifier 24, the second steam-water separator 25, the second-stage membrane separation unit 26, the second-stage vacuum buffer tank 27, the second-stage vacuum unit 28, the second-stage vacuum pump circulating water tank 29, the second-stage plate heat exchanger 30, the third gas compressor 31, the fourth gas flow regulating valve 32, the carbon dioxide absorption tower 33, the first LNG heat exchanger 34, the heavy hydrocarbon separator 35, the second LNG heat exchanger 36, the nitrogen stripping tower 37, the third LNG heat exchanger 38, the first gas throttle valve 39, the second methane storage tank 40, the sixth gas flow regulating valve 41, the fourth LNG heat exchanger 42, the tenth gas flow regulating valve 43, the nitrogen-methane separation tower 44, the third gas throttle valve 45, the fifth gas compressor 46, the fourth gas water cooler 47, the sixth gas compressor 48, the fifth gas water cooler 49, the seventh gas flow regulating valve 50, the first turbine expander 51, the eighth gas flow regulating valve 52, the second turbine expander 53, the ninth gas flow regulating valve 54, the second gas throttle valve 55, the first methane storage tank 56, the fifth gas flow regulating valve 57, the fourth gas compressor 58, the second steam trap 59, the eleventh gas flow regulating valve 60, the temperature sensor T, the pressure sensor P, the flow sensor M, and the gas chromatograph sensor Q.

[0038] The full-process biogas liquefaction and carbon dioxide co-production system of the present invention includes a raw material gas pretreatment module. The outlet of the raw material gas pretreatment module is connected to a rich carbon system and a lean carbon system. A gas chromatograph sensor Q is provided at the outlet of the raw material gas pretreatment module. The system detects the biogas components through the gas chromatograph sensor to achieve split treatment. After the collected biogas is desulfurized and dehydrated by the raw material gas pretreatment module, the gas chromatograph sensor Q detects the biogas components and selects to enter the rich carbon system or the lean carbon system according to the component characteristics. The efficient separation of carbon dioxide from biogas and gas liquefaction are completed in the rich carbon system, and gas liquefaction is completed in the lean carbon system.

[0039] The carbon-rich system includes a membrane separation carbon dioxide removal module, a biogas liquefaction module, a nitrogen removal and recovery module, and a BOG re-liquefaction module, which are connected in sequence along the gas flow direction. After desulfurization and dehydration, the biogas is stabilized in the membrane separation carbon dioxide removal module and then passes through the first-stage membrane component and the second-stage membrane component in sequence. The permeate gas carbon dioxide is discharged, and a part of the retentate gas methane is compressed and sent back to the buffer tank as recycle gas to improve the methane recovery rate. Another part enters the biogas liquefaction module and the nitrogen removal and recovery module as product gas. After nitrogen expansion precooling, heavy hydrocarbon separation, and nitrogen expansion deep cooling, nitrogen is removed and recovered and then input into the methane storage tank in liquid form. The BOG generated in the methane storage tank is sent to the BOG re-liquefaction module and then refrigerated and liquefied again, thus completing the efficient separation of carbon dioxide and methane liquefaction.

[0040] The carbon-poor system includes a biogas liquefaction module, a nitrogen removal and recovery module, and a BOG re-liquefaction module, which are connected in sequence along the gas flow direction. After desulfurization and dehydration, the biogas directly enters the biogas liquefaction module and the nitrogen removal and recovery module after absorbing a small amount of carbon dioxide in the carbon dioxide absorption tower. After nitrogen expansion precooling, heavy hydrocarbon separation, and nitrogen expansion deep cooling, nitrogen is removed and recovered and then input into the methane storage tank in liquid form. The BOG generated in the methane storage tank is sent to the BOG re-liquefaction module and then refrigerated and liquefied again, thus completing the efficient liquefaction of methane.

[0041] The raw gas pretreatment module includes a first gas flow regulating valve 1, a filter 2, a first gas compressor 3, a first gas water cooler 4, a second gas compressor 5, a second gas water cooler 6, a sulfur-containing gas pre-absorption tower 7, a heater 8, a second gas flow regulating valve 9, a hydrolysis tower 10, a third gas water cooler 11, a sulfur-containing gas fine absorption tower 12, a first steam-water separator 13, a first steam trap 14, and a drying tower 15. The specific connection method is as follows:

[0042] The first gas flow regulating valve 1 is connected to the inlet of the filter 2. The outlet of the filter 2 is connected to the inlet of the first gas compressor 3. The outlet of the first gas compressor 3 is connected to the inlet of the first gas water cooler 4. The outlet of the first gas water cooler 4 is connected to the inlet of the second gas compressor 5. The outlet of the second gas compressor 5 is connected to the inlet of the second gas water cooler 6. The outlet of the second gas water cooler 6 is connected to the inlet of the sulfur-containing gas pre-absorption tower 7. The outlet of the sulfur-containing gas pre-absorption tower 7 is connected to the inlet of the heater 8. The outlet of the heater 8 is connected to the inlet of the hydrolysis tower 10. The outlet of the hydrolysis tower 10 is connected to the inlet of the second gas flow regulating valve 9. The outlet of the second gas flow regulating valve 9 is connected to the inlet of the third gas water cooler 11. The outlet of the third gas water cooler 11 is connected to the inlet of the sulfur-containing gas fine absorption tower 12. The outlet of the sulfur-containing gas fine absorption tower 12 is connected to the inlet of the first steam-water separator 13. The outlet of the first steam-water separator 13 is connected to the inlet of the drying tower 15. Among them, the outlet of the first steam-water separator 13 is also connected to the inlet of the first steam trap 14. The outlet of the drying tower 15 is respectively connected to the inlets of the third gas flow regulating valve 16 in the rich carbon system and the fourth gas flow regulating valve 32 in the lean carbon system.

[0043] After the biogas is generated, the first gas flow regulating valve 1 is opened to allow the gas to enter the system. It passes through the filter 2, whose function is to prevent dust or solid particles from entering the compressor and causing wear and blockage. After the gas flows out of the filter 2, it successively enters the first gas compressor 3, the first gas water cooler 4, the second gas compressor 5, and the second gas water cooler 6, and the gas pressure increases. To prevent the sulfur-containing gas in the biogas from affecting the subsequent liquefaction process, the pressurized gas enters the sulfur-containing gas pre-absorption tower 7 to remove most of the H2S, and then enters the heater 8. After being heated to a certain temperature, the gas enters the hydrolysis tower 10. After the organic sulfur COS is hydrolyzed into H2S, the second gas flow regulating valve 9 is opened to allow the biogas to enter the third gas water cooler 11. The cooled biogas enters the sulfur-containing gas fine absorption tower 12 for further desulfurization. The desulfurized biogas enters the first steam-water separator 13 for dehydration, and the separated condensed water is discharged from the first steam trap 14. The biogas flows out from the outlet of the first steam-water separator 13 and enters the drying tower 15 to adsorb the remaining moisture. The pressurized gas after desulfurization and dehydration meets the conditions for entering the subsequent process.

[0044] The membrane separation carbon dioxide removal module includes a third gas flow regulating valve 16, a pressure reducing valve 17, a raw material gas buffer tank 18, a first-stage membrane separation group 19, a first-stage vacuum buffer tank 20, a first-stage vacuum unit 21, a first-stage vacuum pump circulating water tank 22, a first-stage plate heat exchanger 23, a bubbling humidifier 24, a second steam-water separator 25, a second steam trap 59, a second-stage membrane separation group 26, a second-stage vacuum buffer tank 27, a second-stage vacuum unit 28, a second-stage vacuum pump circulating water tank 29, a second-stage plate heat exchanger 30, a third gas compressor 31, a first methane storage tank 56, a fifth gas flow regulating valve 57, and a fourth gas compressor 58. Among them, the first-stage membrane separation group 19, the first-stage vacuum buffer tank 20, the first-stage vacuum unit 21, the first-stage vacuum pump circulating water tank 22, and the first-stage plate heat exchanger 23 constitute the first-stage membrane module, and the second-stage membrane separation group 26, the second-stage vacuum buffer tank 27, the second-stage vacuum unit 28, the second-stage vacuum pump circulating water tank 29, and the second-stage plate heat exchanger 30 constitute the second-stage membrane module. The specific connection method is as follows:

[0045] The outlet of the third gas flow regulating valve 16 is connected to the inlet of the pressure reducing valve 17, the outlet of the pressure reducing valve 17 is connected to the inlet of the raw material gas buffer tank 18, and the outlet of the raw material gas buffer tank 18 is connected to the inlet of the first-stage membrane separation group 19. The outlet of the first-stage membrane separation group 19 is divided into two paths, one path is connected to the inlet of the first-stage vacuum buffer tank 20, and the other path is connected to the inlet of the bubbling humidifier 24.

[0046] The outlet of the first-stage vacuum buffer tank 20 is connected to the inlet of the first-stage vacuum unit 21, the outlet of the first-stage vacuum unit 21 is connected to the inlet of the first-stage vacuum pump circulating water tank 22, and the outlet of the first-stage vacuum pump circulating water tank 22 is connected to the inlet of the first-stage plate heat exchanger 23. Among them, the outlet of the first-stage plate heat exchanger 23 is connected to the inlet of the first-stage vacuum unit 21.

[0047] The outlet of the bubbling humidifier 24 is connected to the inlet of the second steam-water separator 25, and the outlet of the second steam-water separator 25 is respectively connected to the inlet of the second steam trap 59 and the second-stage membrane separation group 26. The outlet of the second-stage membrane separation group 26 is divided into two paths, one path is connected to the inlet of the second-stage vacuum buffer tank 27, and the other path is connected to the inlet of the first methane storage tank 56.

[0048] The outlet of the second-stage vacuum buffer tank 27 is connected to the inlet of the second-stage vacuum unit 28, and the outlet of the second-stage vacuum unit 28 is connected to the inlet of the second-stage vacuum pump circulating water tank 29. The outlet of the second-stage vacuum pump circulating water tank 29 is divided into two paths. One path is connected to the inlet of the second-stage plate heat exchanger 30, and the outlet of the second-stage plate heat exchanger 30 is connected to the inlet of the second-stage vacuum unit 28. The other path is connected to the inlet of the third gas compressor 31, and the outlet of the third gas compressor 31 is connected to the inlet of the raw gas buffer tank 18. The outlet of the first methane storage tank 56 is connected to the inlet of the fifth gas flow regulating valve 57, and the outlet of the fifth gas flow regulating valve 57 is connected to the inlet of the fourth gas compressor 58. The outlet of the fourth gas compressor 58 is connected to the biogas liquefaction module.

[0049] If the gas after desulfurization, dehydration and pressurization is detected by the gas chromatograph sensor Q and the proportion of carbon dioxide in the gas is much larger than that of methane, the third gas flow regulating valve 16 is opened to allow the gas to enter the pressure reducing valve 17, whose function is to ensure the separation efficiency and extend the service life of the membrane. The first-stage CO2 permeate gas generated by the first-stage membrane separation group 19 enters the first-stage vacuum buffer tank 20. After stabilization, the CO2 permeate gas enters the first-stage vacuum unit 21. The pressurized CO2 permeate gas enters the first-stage vacuum pump circulating water tank 22 and is cooled and then output as the CO2 product gas. The circulating water in the first-stage vacuum pump circulating water tank 22 is cooled by the first-stage plate heat exchanger 23 and then enters the first-stage vacuum unit 21 to provide cooling for it, aiming to ensure the stability of the system and extend the equipment life. The biogas after stabilization enters the first-stage membrane separation group 19, and the first-stage CH4 retentate gas generated enters the bubbling humidifier (24). The humidified first-stage CH4 retentate gas enters the second steam-water separator 25 for dehydration. The separated condensed water is discharged from the second steam trap 59 and then enters the second-stage membrane separation group 26, the second-stage vacuum buffer tank 27, the second-stage vacuum unit 28, the second-stage vacuum pump circulating water tank 29, and the second-stage plate heat exchanger 30 in sequence to complete the gas separation and treatment at the second stage. The treated second-stage CO2 permeate gas enters the third gas compressor 31. The pressurized second-stage CO2 permeate gas enters the raw gas buffer tank 18 again. The second-stage CH4 retentate gas enters the first methane storage tank 56. When the biogas liquefaction module is started, the fifth gas flow regulating valve 57 is opened and the gas enters the fourth gas compressor 58. The pressurized gas enters the hot end inlet 34a of the first LNG heat exchanger 34.

[0050] The biogas liquefaction module includes a third gas flow regulating valve 32, a carbon dioxide absorption tower 33, a first LNG heat exchanger 34, a heavy hydrocarbon separator 35, a second LNG heat exchanger 36, a nitrogen stripping tower 37, a third LNG heat exchanger 38, a first gas throttle valve 39, a second methane storage tank 40, a sixth gas flow regulating valve 41, a fifth gas compressor 46, a fourth gas water cooler 47, a sixth gas compressor 48, a fifth gas water cooler 49, a seventh gas flow regulating valve 50, a first turbine expander 51, an eighth gas flow regulating valve 52, a second turbine expander 53, a ninth gas flow regulating valve 54. The specific connection method is as follows:

[0051] The outlet of the third gas flow regulating valve 32 is connected to the inlet of the carbon dioxide absorption tower 33. The outlet of the carbon dioxide absorption tower 33 is connected to the hot end inlet 34a of the first LNG heat exchanger 34. The hot end outlet 34b of the first LNG heat exchanger 34 is connected to the inlet of the heavy hydrocarbon separator 35. The outlet of the heavy hydrocarbon separator 35 is connected to the hot end inlet 36a of the second LNG heat exchanger 36. The hot end outlet 36b of the second LNG heat exchanger 36 is connected to the inlet of the nitrogen stripping tower 37. The outlet of the nitrogen stripping tower 37 is connected to the hot end inlet 38a of the third LNG heat exchanger 38. The hot end outlet 38b of the third LNG heat exchanger 38 is connected to the inlet of the first gas throttle valve 39. The outlet of the first gas throttle valve 39 is connected to the inlet of the second methane storage tank 40. The outlet of the second methane storage tank 40 is connected to the inlet of the sixth gas flow regulating valve 41. The cold end outlet 34e of the first LNG heat exchanger 34 is connected to the inlet of the fifth gas compressor 46. The outlet of the fifth gas compressor 46 is connected to the inlet of the fourth gas water cooler 47. The outlet of the fourth gas water cooler 47 is connected to the inlet of the sixth gas compressor 48. The outlet of the sixth gas compressor 48 is connected to the inlet of the fifth gas water cooler 49. The outlet of the fifth gas water cooler 49 is connected to the hot end inlet 34d of the first LNG heat exchanger 34.

[0052] The hot end outlet 34c of the first LNG heat exchanger 34 is divided into two paths. One path is connected to the inlet of the seventh gas flow regulating valve 50, and the other path is connected to the inlet of the eighth gas flow regulating valve 52.

[0053] The outlet of the seventh gas flow regulating valve 50 is connected to the inlet of the first turbine expander 51. The outlet of the first turbine expander 51 is connected to the cold end inlet 36f of the second LNG heat exchanger 36.

[0054] The outlet of the eighth gas flow regulating valve 52 is connected to the hot-end inlet 36d of the second LNG heat exchanger 36. The hot-end outlet 36c of the second LNG heat exchanger 36 is connected to the inlet of the second turbine expander 53. The outlet of the second turbine expander 53 is connected to the inlet of the ninth gas flow regulating valve 54. The outlet of the ninth gas flow regulating valve 54 is connected to the cold-end inlet 38c of the third LNG heat exchanger 38. The cold-end outlet 38d of the third LNG heat exchanger 38 is connected to the cold-end inlet 36f of the second LNG heat exchanger 36. The cold-end outlet 36e of the second LNG heat exchanger 36 is connected to the cold-end inlet 34f of the first LNG heat exchanger 34. The cold-end outlet 34e of the first LNG heat exchanger 34 is connected to the inlet of the fifth gas compressor 46.

[0055] If the gas after desulfurization, dehydration and pressurization is detected by the gas chromatograph sensor Q and the proportion of methane in the gas is much larger than that of carbon dioxide, the fourth gas flow regulating valve 32 is opened to allow the gas to enter the carbon dioxide absorption tower 33. The purpose is to adsorb most of the small amount of carbon dioxide contained in the gas. After flowing out of the carbon dioxide absorption tower 33, the gas enters the hot-end inlet 34a of the first LNG heat exchanger 34 to release heat. To prevent equipment blockage and improve liquefaction efficiency, the gas after releasing heat flows out of the hot-end outlet 34b of the first LNG heat exchanger 34 and enters the heavy hydrocarbon separator 35. After removing the heavy hydrocarbons, it enters the hot-end inlet 36a of the second LNG heat exchanger 36. The gas after releasing heat flows out of the hot-end outlet 36b of the second LNG heat exchanger 36 and enters the nitrogen stripping tower 37. The purpose is to optimize the product gas quality and reduce the equipment load. The nitrogen-containing gas separated enters the nitrogen-methane separation tower 44 in the nitrogen removal and recovery module. The methane gas and nitrogen gas flowing out are discharged as product gas. The nitrogen-free gas separated by the nitrogen stripping tower 37 enters the hot-end inlet 38a of the third LNG heat exchanger 38. The gas after releasing heat flows out of the hot-end outlet 38b of the third LNG heat exchanger 38 and enters the first gas throttle valve 39. The gas after pressure reduction and temperature reduction is liquefied and enters the second methane storage tank 40 to complete the liquefaction process.

[0056] To improve the heat exchange efficiency, the nitrogen gas after absorbing heat flows out of the cold-end outlet 34e of the first LNG heat exchanger 34 and then enters the fifth gas compressor 46, the fourth gas water cooler 47, the sixth gas compressor 48, and the fifth gas water cooler 49 in sequence. The pressurized nitrogen gas enters the hot-end inlet 34d of the first LNG heat exchanger 34.

[0057] The gas after releasing heat flows out from the hot-end outlet 34c of the first LNG heat exchanger 34 and separately enters the seventh gas flow regulating valve 50 and the eighth gas flow regulating valve 52, enabling nitrogen to enter the first turbine expander 51 and the hot-end inlet 36d of the second LNG heat exchanger 36 respectively. The purpose is to improve the refrigeration efficiency and reduce energy consumption. The cooled gas flows out from the hot-end outlet 36c of the second LNG heat exchanger 36 and enters the second turbine expander 53 and the second gas throttle valve 55 respectively. After the expansion is completed, the ninth gas flow regulating valve 54 is opened, and the low-temperature gas enters the cold-end inlet 38c of the third LNG heat exchanger 38. After releasing the cold quantity, the gas flows out from the cold-end outlet 38d of the third LNG heat exchanger 38 and enters the cold-end inlet 36f of the second LNG heat exchanger 36 together with the gas flowing out from the first turbine expander 51. After releasing the cold quantity, it flows out from the cold-end outlet 36e of the second LNG heat exchanger 36 and enters the cold-end inlet 34e of the first LNG heat exchanger 34 to complete the cycle.

[0058] The nitrogen removal and recovery module includes a nitrogen stripping tower 37, a nitrogen-methane separation tower 44, an eleventh gas flow regulating valve 60, and a third gas throttle valve 45. The specific connection method is as follows: the outlet of the nitrogen stripping tower 37 is connected to the inlet of the nitrogen-methane separation tower 44, the outlet of the nitrogen-methane separation tower 44 is connected to the inlet of the eleventh gas flow regulating valve 60, and the outlet of the eleventh gas flow regulating valve 60 is connected to the inlet of the third gas throttle valve 45.

[0059] To reduce the heat load of the nitrogen stripping tower, the cooled gas enters the nitrogen stripping tower 37 to achieve the preliminary separation of nitrogen. The gas after preliminary separation enters the nitrogen-methane separation tower 44 for in-depth separation. Subsequently, nitrogen and methane flow out from the nitrogen-methane separation tower 44 as product gases, completing the removal of the nitrogen component in the biogas.

[0060] The BOG re-liquefaction module includes a fourth LNG heat exchanger 42, a tenth gas flow regulating valve 43, and a second gas throttle valve 55. The specific connection method is as follows: the outlet of the sixth gas flow regulating valve 41 is connected to the hot-end inlet 42a of the fourth LNG heat exchanger 42, the hot-end outlet 42b of the fourth LNG heat exchanger 42 is connected to the inlet of the tenth gas flow regulating valve 43, the inlet of the second turbine expander 53 is connected to the inlet of the second gas throttle valve 55, the outlet of the second gas throttle valve 55 is connected to the cold-end inlet 42c of the fourth LNG heat exchanger 42, and the cold-end outlet 42d of the fourth LNG heat exchanger 42 is connected to the cold-end inlet 38c of the third LNG heat exchanger 38.

[0061] The liquefied methane stored in the second methane storage tank 40 will generate BOG after a period of time. After a certain amount of BOG is generated, the sixth gas flow regulating valve 41 is opened, and the overflowing BOG gas enters the hot end inlet 42a of the fourth LNG heat exchanger 42. The cooled gas flows out from the hot end outlet 42b of the fourth LNG heat exchanger 42 and enters the tenth gas flow regulating valve 43. The expanded gas flows out as a liquid CH4 product gas.

[0062] The working process of the full-process biogas liquefaction and carbon dioxide co-production system of the present invention is as follows:

[0063] Step (a): After the biogas fermentation device produces biogas, the first gas flow regulating valve 1 is opened to allow the biogas to enter the filter 2. After filtering out the impurities in the biogas, the biogas sequentially enters the first gas compressor 3, the first gas water cooler 4, the second gas compressor 5, and the second gas water cooler 6. The pressurized biogas enters the sulfur-containing gas pre-absorption tower 7 to remove most of the H2S, and then enters the heater 8. After being heated to a certain temperature, the biogas enters the hydrolysis tower 10. After the organic sulfur COS is hydrolyzed into H2S, the second gas flow regulating valve 9 is opened to allow the biogas to enter the third gas water cooler 11. The cooled biogas enters the sulfur-containing gas fine absorption tower 12 for further desulfurization. The desulfurized biogas enters the first steam-water separator 13 for dehydration. The separated condensed water is discharged from the first steam trap 14, and the biogas flows out from the outlet of the first steam-water separator and enters the drying tower 15 to adsorb the remaining moisture.

[0064] Step (b): After the desulfurized and dehydrated biogas is detected by the gas chromatograph sensor for its gas composition, if the proportion of carbon dioxide content is greater than the proportion of methane content, the third gas flow regulating valve 16 is opened, and the biogas enters the carbon-rich system. The desulfurized and dehydrated biogas enters the pressure reducing valve 17. The biogas after pressure reduction enters the raw material gas buffer tank 18 to initially stabilize the gas flow. The stabilized biogas enters the first-stage membrane separation unit 19, and the generated first-stage CO2 permeate gas enters the first-stage vacuum buffer tank 20. The stabilized CO2 permeate gas enters the first-stage vacuum unit 21. The pressurized CO2 permeate gas enters the first-stage vacuum pump circulating water tank 22 and is cooled and output as a CO2 product gas. The circulating water in the first-stage vacuum pump circulating water tank 22 is cooled by the first-stage plate heat exchanger 23 and then enters the first-stage vacuum unit 21 to provide cooling for it.

[0065] Step (c): The stabilized biogas enters the first-stage membrane separation unit 19, and the generated first-stage CH4 retentate gas enters the bubbling humidifier 24. The humidified first-stage CH4 retentate gas enters the second steam-water separator 25 for dehydration. The separated condensed water is discharged from the second steam trap 59, and then successively enters the second-stage membrane separation unit 26, the second-stage vacuum buffer tank 27, the second-stage vacuum unit 28, the second-stage vacuum pump circulating water tank 29, and the second-stage plate heat exchanger 30 to complete the gas separation and treatment at the second stage. The treated second-stage CO2 permeate gas enters the third gas compressor 31. The pressurized second-stage CO2 permeate gas enters the raw material gas buffer tank 18 again. The second-stage CH4 retentate gas enters the first methane storage tank 56. When the biogas liquefaction module is started, the fifth gas flow regulating valve 57 is opened, and the gas enters the fourth gas compressor 58. The pressurized gas enters the hot end inlet 34a of the first LNG heat exchanger 34.

[0066] Step (d): After the biogas after desulfurization and dehydration is detected by the gas chromatograph sensor for its gas composition, if the proportion of its carbon dioxide content is less than the proportion of its methane content, the third gas flow regulating valve 32 is opened, and the biogas enters the lean carbon system. The biogas after desulfurization and dehydration enters the carbon dioxide absorption tower 33. The decarbonized biogas enters the hot end inlet 34a of the first LNG heat exchanger 34. The gas after releasing heat flows out from the hot end outlet 34b of the first LNG heat exchanger 34 and enters the heavy hydrocarbon separator 35. After removing the heavy hydrocarbons, it enters the hot end inlet 36a of the second LNG heat exchanger 36. The gas after releasing heat flows out from the hot end outlet 36b of the second LNG heat exchanger 36 and enters the nitrogen stripping tower 37. The separated nitrogen-containing gas enters the nitrogen-methane separation tower 44. The flowing-out methane gas and nitrogen gas are discharged as product gas. The nitrogen-free gas separated by the nitrogen stripping tower 37 enters the hot end inlet 38a of the third LNG heat exchanger 38. The gas after releasing heat flows out from the hot end outlet 38b of the third LNG heat exchanger 38 and enters the first gas throttle valve 39. The gas after pressure reduction and temperature reduction is liquefied and enters the second methane storage tank 40.

[0067] Step (e): The nitrogen gas that has absorbed heat flows out from the cold-end outlet 34e of the first LNG heat exchanger 34 and then successively enters the fifth gas compressor 46, the fourth gas water cooler 47, the sixth gas compressor 48, and the fifth gas water cooler 49. The pressurized nitrogen gas enters the hot-end inlet 34d of the first LNG heat exchanger 34, and the gas after releasing heat flows out from the hot-end outlet 34c of the first LNG heat exchanger 34 and respectively opens the seventh gas flow regulating valve 50 and the eighth gas flow regulating valve 52 to make the nitrogen gas enter the first turbine expander 51 and the hot-end inlet 36d of the second LNG heat exchanger 36 respectively. The cooled gas flows out from the hot-end outlet 36c of the second LNG heat exchanger 36 and enters the second turbine expander 53 and the second gas throttle valve 55 respectively. After the expansion is completed, the ninth gas flow regulating valve 54 is opened, and the low-temperature gas enters the cold-end inlet 38c of the third LNG heat exchanger 38. The gas after releasing cold flows out from the cold-end outlet 38d of the third LNG heat exchanger 38 and enters the cold-end inlet 36f of the second LNG heat exchanger 36 together with the gas flowing out from the first turbine expander 51. After releasing cold, it flows out from the cold-end outlet 36e of the second LNG heat exchanger 36 and enters the cold-end inlet 34e of the first LNG heat exchanger 34 to complete the cycle.

[0068] Step (f): The cooled gas flows out from the hot-end outlet 36c of the second LNG heat exchanger 36 and enters the second turbine expander 53 and the second gas throttle valve 55 respectively. The gas that has expanded and cooled flows out from the second gas throttle valve 55 and enters the cold-end inlet 42c of the fourth LNG heat exchanger 42. The gas after releasing cold flows out from the cold-end outlet 42d of the fourth LNG heat exchanger 42 and enters the cold-end inlet 38c of the third LNG heat exchanger 38.

[0069] Step (g): The gas after pressure reduction and cooling is liquefied and enters the second methane storage tank 40. After it stabilizes, the tenth gas flow regulating valve 43 is opened, and the overflowing BOG gas enters the hot-end inlet 42a of the fourth LNG heat exchanger 42. The cooled gas flows out from the hot-end outlet 42b of the fourth LNG heat exchanger 42 and enters the second gas throttle valve 55. The gas after expansion flows out as liquid CH4 product gas.

[0070] The present invention realizes natural gas liquefaction and BOG gas reliquefaction by using nitrogen expansion refrigeration technology, and efficiently captures carbon dioxide through membrane separation technology. Through the carbon-rich and carbon-poor system diversion strategy, it takes into account the efficiency of the whole-process liquefaction of biogas and the economy of carbon dioxide capture, and significantly improves the efficiency of comprehensive resource utilization.

[0071] The biogas treatment solution that combines a rich-carbon system with a lean-carbon system can adapt to the characteristics of different biogas raw materials and fermentation stages, make full use of resources, reduce power consumption, improve efficiency, provide an economical and efficient solution for biogas resource utilization and carbon dioxide capture, and has significant energy-saving and emission-reduction effects and application prospects.

[0072] The biogas treatment solution of the present invention combines a rich-carbon system with a lean-carbon system, focuses on the efficient utilization of biogas resources and carbon dioxide capture, and is applicable to the biogas liquefaction and carbon dioxide capture requirements under multiple working conditions and the whole process.

[0073] The following is an explanation in combination with the specific operating parameters during the normal operation of a biogas liquefaction system using nitrogen expansion refrigeration:

[0074] Taking the operation of the carbon-enriched system as an example, the 0.1Mpa, 40℃ biogas passes through the first gas flow regulating valve 1, the filter 2, the first gas compressor 3, the first gas water cooler 4, the second gas compressor 5, and the second gas water cooler 6, and then the biogas is pressurized to 5Mpa, 40℃, and passes through the sulfur-containing gas fine absorption tower 12, the first steam-water separator 13, the first steam trap 14, and the drying tower 15. Then, it enters the pressure reducing valve 17, and the gas expands to 0.5Mpa, 20℃, and then the gas passes through the raw gas buffer tank 18 and enters the primary membrane separation group 19, among which the 0.05Mpa, 20℃ CO2 permeate gas flows into a vacuum unit 21 and passes through a vacuum pump circulating water tank 22, and is pressurized to 0.1Mpa, 21℃ as CO2 product gas output, and the 0.4Mpa, 20℃ CH4 The retentate gas enters the bubbling humidifier 24, and the humidified CH4 retentate gas enters the second steam-water separator 25 for dehydration, and then the CH4 retentate gas at 0.4Mpa and 20°C enters the secondary membrane separation group 26, among which the CO2 permeate gas at 0.04Mpa and 20°C flows into the second-stage vacuum unit 28 and passes through the second-stage vacuum pump circulating water tank 29, and then is pressurized to 0.1Mpa and 20°C and flows into the third gas compressor 31, and the gas pressurized to 0.5Mpa and 22°C again flows into the raw gas buffer tank 18, and the CH4 retentate gas at 0.3Mpa and 20°C enters the first methane gas storage tank 56. After the biogas liquefaction module is started, the fifth gas flow regulating valve 57 is opened to allow the gas to flow into the fourth gas compressor 58, and the gas pressurized to 5Mpa and 42°C is merged into the biogas liquefaction module. The combined gas at 5 MPa and 40°C passes through the first LNG heat exchanger 34, the heavy hydrocarbon separator 35, the second LNG heat exchanger 36, the nitrogen stripping tower 37, and the third LNG heat exchanger 38 in sequence to be cooled to 5 MPa and -130°C, and then flows into the first gas throttle valve 39 to be expanded to 0.12 MPa and -160°C. The expanded gas enters the second methane storage tank 40. After a period of time, the BOG gas overflowing at 0.12 MPa and -155°C enters the fourth LNG heat exchanger 42 to be cooled to 0.12 MPa and -160°C for reliquefaction.

[0075] In the nitrogen expansion refrigeration cycle, the nitrogen that has absorbed heat flows out from the cold end outlet 34e of the first LNG heat exchanger 34 at 0.1 Mpa and 30 °C, and then enters the fifth gas compressor 46, the fourth gas water cooler 47, the sixth gas compressor 48, and the fifth gas water cooler 49 in sequence, and is pressurized to 5 Mpa and 50 °C. The pressurized nitrogen enters the hot end inlet 34d of the first LNG heat exchanger 34. The gas after releasing heat is divided into two paths. One path of the gas passes through the first LNG heat exchanger 34, the seventh gas flow regulating valve 50, and the first turbine expander 51 in sequence to cool the gas to 0.1 Mpa and -170 °C. The other path of the gas passes through the first LNG heat exchanger 34, the eighth gas flow regulating valve 52, the second LNG heat exchanger 36, and the second turbine expander 53 in sequence to cool to 0.1 Mpa and -165 °C, and then enters the third LNG heat exchanger 38 to absorb heat to 0.1 Mpa and -150 °C, and then converges with the first path to jointly provide cooling capacity for the second LNG heat exchanger 36 and the first LNG heat exchanger 34, absorb heat to 0.1 Mpa and 30 °C, and then enter the fifth gas compressor 46, the fourth gas water cooler 47, the sixth gas compressor 48, and the fifth gas water cooler 49 in sequence to complete the refrigeration cycle.

Claims

1. A full-process biogas liquefaction and carbon dioxide co-production system, characterized by: It includes a raw gas pretreatment module, the outlet of which is connected to a carbon-rich system and a carbon-depleted system, and a gas chromatograph sensor Q is provided at the outlet of the raw gas pretreatment module; After the collected biogas is desulfurized and dehydrated by the raw gas pretreatment module, the gas chromatograph sensor Q detects the biogas composition and selects to enter the carbon-rich system or the carbon-lean system according to the component characteristics. The carbon dioxide of the biogas is efficiently separated and the gas is liquefied in the carbon-rich system, and the gas liquefaction is completed in the carbon-lean system.

2. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 1 is characterized in that: If the proportion of carbon dioxide in the biogas after desulfurization and dehydration is greater than the proportion of methane, the biogas after desulfurization and dehydration will enter the carbon-rich system; If the proportion of carbon dioxide in the biogas after desulfurization and dehydration is less than the proportion of methane, the biogas after desulfurization and dehydration will enter the carbon-depleted system.

3. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 1 is characterized in that: The carbon-enriching system comprises a membrane separation carbon dioxide removal module, a biogas liquefaction module, a nitrogen removal and recovery module and a BOG reliquefaction module which are sequentially connected along the gas flow direction. After the biogas after desulfurization and dehydration is stabilized in the membrane separation carbon dioxide removal module, it passes through the first section membrane assembly and the second section membrane assembly in sequence. The permeate gas carbon dioxide is discharged, and a part of the permeate gas methane is compressed and sent back to the buffer tank as circulating gas to improve the methane recovery rate. The other part enters the biogas liquefaction module and the nitrogen removal and recovery module as product gas, and is precooled by nitrogen expansion, separated from heavy hydrocarbons, and deep cooled by nitrogen expansion. After the nitrogen is removed and recovered, it is input into the methane storage tank in liquid form. The BOG generated in the methane storage tank is sent to the BOG reliquefaction module and is refrigerated and liquefied again, thereby completing efficient carbon dioxide separation and methane liquefaction. The carbon-depleted system comprises a biogas liquefaction module, a nitrogen removal and recovery module and a BOG reliquefaction module which are sequentially connected along the gas flow direction. The biogas after desulfurization and dehydration directly enters the biogas liquefaction module and the nitrogen removal and recovery module after absorbing a small amount of carbon dioxide in a carbon dioxide absorption tower. After nitrogen expansion precooling, heavy hydrocarbon separation, nitrogen expansion deep cooling, nitrogen removal and recovery, the biogas is input into a methane storage tank in liquid form. The BOG generated in the methane storage tank is sent to the BOG reliquefaction module and is refrigerated and liquefied again, thereby completing efficient methane liquefaction.

4. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 1 is characterized in that: The raw gas pretreatment module comprises a first gas flow regulating valve (1), a filter (2), a first gas compressor (3), a first gas water cooler (4), a second gas compressor (5), a second gas water cooler (6), a sulfur-containing gas pre-absorption tower (7), a heater (8), a hydrolysis tower (10), a second gas flow regulating valve (9), a third gas water cooler (11), a sulfur-containing gas fine absorption tower (12), a first steam-water separator (13), and a drying tower (15), which are sequentially connected along the gas flow direction, wherein the outlet of the first steam-water separator (13) is also connected to a first steam trap (14).

5. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 3 is characterized in that: The membrane separation carbon dioxide removal module comprises a third gas flow regulating valve (16), a pressure reducing valve (17), a raw gas buffer tank (18), and a primary membrane separation group (19) which are sequentially connected along the gas flow direction; The outlet of the primary membrane separation group (19) is divided into two paths, one of which is connected to the inlet of a vacuum buffer tank (20), and the other is connected to the inlet of a bubbling humidifier (24); The outlet of the first vacuum buffer tank (20) is provided with a vacuum unit (21), a vacuum pump circulating water tank (22), and a plate heat exchanger (23) in sequence along the gas flow direction; wherein the outlet of the first plate heat exchanger (23) is connected to the inlet of the first vacuum unit (21); The outlet of the bubbling humidifier (24) is provided with a second steam-water separator (25) and a secondary membrane separation group (26) in sequence along the gas flow direction; wherein the outlet of the second steam-water separator (25) is also connected to a second steam trap (59); The outlet of the secondary membrane separation group (26) is divided into two paths, one of which is connected to the inlet of the second-stage vacuum buffer tank (27), and the other is connected to the inlet of the first methane gas storage tank (56).

6. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 5 is characterized in that: The outlet of the second-stage vacuum buffer tank (27) is provided with a second-stage vacuum unit (28) and a second-stage vacuum pump circulating water tank (29) in sequence along the gas flow direction; The outlet of the second-stage vacuum pump circulating water tank (29) is divided into two paths, one of which is connected to the inlet of the second-stage vacuum unit (28) via the second-stage plate heat exchanger (30), and the other is connected to the inlet of the raw gas buffer tank (18) via the third gas compressor (31); The outlet of the first methane gas storage tank (56) is provided with a fifth gas flow regulating valve (57) and a fourth gas compressor (58) in sequence along the gas flow direction; The outlet of the fourth gas compressor (58) is connected to the biogas liquefaction module.

7. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 3 is characterized by: The biogas liquefaction module comprises a third gas flow regulating valve (32), the outlet of the third gas flow regulating valve (32) is connected to the inlet of a carbon dioxide absorption tower (33), the outlet of the carbon dioxide absorption tower (33) is connected to the hot end inlet 34a of a first LNG heat exchanger (34), the hot end outlet 34b of the first LNG heat exchanger (34) is connected to the inlet of a heavy hydrocarbon separator (35), the outlet of the heavy hydrocarbon separator (35) is connected to the hot end inlet 36a of a second LNG heat exchanger (36), and the hot end outlet 34b of the first LNG heat exchanger (34) is connected to the inlet of a heavy hydrocarbon separator (35). The hot end outlet 36b of the NG heat exchanger (36) is connected to the inlet of the nitrogen stripping tower (37), the outlet of the nitrogen stripping tower (37) is connected to the hot end inlet 38a of the third LNG heat exchanger (38), the hot end outlet 38b of the third LNG heat exchanger (38) is connected to the inlet of the first gas throttle valve (39), the outlet of the first gas throttle valve (39) is connected to the inlet of the second methane storage tank (40), and the outlet of the second methane storage tank (40) is connected to the inlet of the sixth gas flow regulating valve (41); The cold end outlet 34e of the first LNG heat exchanger (34) is connected to a fifth gas compressor (46), a fourth gas water cooler (47), a sixth gas compressor (48), and a fifth gas water cooler (49) in sequence along the gas flow direction; wherein the outlet of the fifth gas water cooler (49) is connected to the hot end inlet 34d of the first LNG heat exchanger (34).

8. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 7 is characterized in that: The hot end outlet 34c of the first LNG heat exchanger (34) is divided into two paths, one of which is connected to the inlet of the seventh gas flow regulating valve (50), and the other is connected to the inlet of the eighth gas flow regulating valve (52); The outlet of the seventh gas flow control valve (50) is connected to the cold end inlet 36f of the second LNG heat exchanger 36 via the first turbine expander (51); The outlet of the eighth gas flow regulating valve (52) is connected to the hot end inlet 36d of the second LNG heat exchanger (36), the hot end outlet 36c of the second LNG heat exchanger (36) is connected to the cold end inlet 38c of the third LNG heat exchanger (38) through the second turbine expander (53) and the ninth gas flow regulating valve (54), the cold end outlet 38d of the third LNG heat exchanger (38) is connected to the cold end inlet 36f of the second LNG heat exchanger (36), and the cold end outlet 36e of the second LNG heat exchanger (36) is connected to the cold end inlet 34f of the first LNG heat exchanger (34).

9. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 3 is characterized in that: The nitrogen removal and recovery module comprises a nitrogen-methane separation tower (44), an eleventh gas flow regulating valve (60), and a third gas throttle valve (45); The inlet of the nitrogen-methane separation tower (44) is connected to the biogas liquefaction module, and the outlet of the nitrogen-methane separation tower (44) is connected to the inlet of the third gas throttle valve (45) via the eleventh gas flow regulating valve (60).

10. The full-process biogas liquefaction and carbon dioxide co-production system according to claim 3, characterized in that: The BOG reliquefaction module comprises a fourth LNG heat exchanger (42), a tenth gas flow regulating valve (43), and a second gas throttle valve (55); The hot end inlet 42a of the fourth LNG heat exchanger (42) is connected to the biogas liquefaction module, the hot end outlet 42b of the fourth LNG heat exchanger (42) is connected to the inlet of the tenth gas flow regulating valve (43), the inlet of the second gas throttle valve (55) is connected to the biogas liquefaction module, the outlet of the second gas throttle valve (55) is connected to the cold end inlet 42c of the fourth LNG heat exchanger (42), and the cold end outlet 42d of the fourth LNG heat exchanger (42) is connected to the biogas liquefaction module.

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