System for preparing liquefied natural gas by utilizing marsh gas

Abstract

The utility model belongs to the technical field of energy recycling, and particularly relates to a system for preparing liquefied natural gas by utilizing marsh gas. According to the utility model, NH3 and H2S gases are removed by utilizing the water washing device and the alkali washing device, so that the heat consumption of the device is reduced, then the CO2 content is reduced to be below 20ppm by utilizing the vacuum pressure swing adsorption decarbonization component and the amine liquid deacidification component, the heat consumption of the device is greatly reduced while the CO2 removal precision is met, and then water in the gases is removed by utilizing the dehydration device, so that the energy consumption of the device is reduced. The methane content in the prepared natural gas reaches 99% or above, the combustion heat value of biogas is greatly increased, the process is mature, and stable and continuous production can be achieved.

Description

Technical Field

[0001] This utility model belongs to the field of energy recovery and utilization technology, specifically relating to a system for producing liquefied natural gas from biogas. Background Technology

[0002] Biogas is a biomass energy source rich in methane, but it is also a greenhouse gas. It has been under research for some time, but the small production scale and high CO2 content of biogas have led to limitations in economic models for biogas recovery and utilization, such as high investment, high operating costs, and long payback periods, thus restricting the development of the biogas recovery and utilization industry.

[0003] Biogas mainly contains CH4 (50%-70%) and carbon dioxide (CO2 (30%-50%), with the relative content of these two components depending primarily on the properties of the organic matter feedstock and parameters such as temperature and pH of the bioreactor system. Biogas also contains small amounts of other compounds, such as N2, H2O, O2, H2S, and NH3 from urea hydrolysis. Biogas, after purification, contains 97%-99% CH4. To use it as fuel, harmful gases such as NH3 and H2S must first be removed, and secondly, the CO2 content should be reduced as much as possible to increase its calorific value. my country's biogas industry started relatively late. As a major agricultural country, a large amount of biogas remains unutilized; therefore, biogas purification technology has significant future market potential. Utility Model Content

[0004] This utility model provides a system for producing liquefied natural gas from biogas. The system includes an ammonia removal device, a desulfurization device, a CO2 adsorption device, a dehydration device, and a liquefaction device connected in sequence by a gas pipeline.

[0005] The ammonia removal device is connected to a biogas intake assembly.

[0006] This invention relates to a system that purifies biogas to obtain natural gas and further liquefies the natural gas to obtain liquefied natural gas (LNG). For biogas containing harmful gases such as NH3 and H2S, NH3 and H2S can cause damage to metal pipes and valves in the system and also cause subsequent components such as adsorbents and molecular sieves to fail. Therefore, an ammonia removal device and a desulfurization device are first used to remove NH3 and H2S, and then a CO2 adsorption device and a dehydration device are used to remove CO2 and water from the raw gas to increase the calorific value of the gas. Finally, the purified natural gas is liquefied to obtain LNG that can be used directly.

[0007] Furthermore, the ammonia removal device includes a water washing tower for washing the raw gas with water; the desulfurization device includes a desulfurization tower for washing the raw gas with alkaline solution.

[0008] Furthermore, the desulfurization device also includes an alkali regeneration tank for storing and regenerating alkali solution, and a plate and frame filter for filtering sulfur.

[0009] In this application, since NH3 has high solubility, water washing is used to remove NH3 from the raw gas, which is simple to operate and low in cost. H2S removal is achieved by alkaline washing, which involves a wet alkaline desulfurization-regeneration-sulfur recovery process to remove H2S from the raw gas. In the desulfurization tower, the raw gas that has had NH3 removed by the ammonia removal device comes into contact with the alkaline solution, and H2S is removed by acid-base neutralization. The raw gas with H2S removed is then passed into the subsequent CO2 adsorption device. The sulfur-rich alkaline solution is mixed with fresh alkaline solution in the alkaline regeneration tank, and after oxidation and regeneration, elemental sulfur is obtained. The sulfur particles (elemental sulfur) generated during the regeneration process form sulfur foam through flotation. The liquid containing sulfur foam is passed into a plate and frame filter to filter out the sulfur solids. The liquid without sulfur is then passed back into the desulfurization tower to remove H2S from the raw gas.

[0010] Furthermore, the drain outlet on the water washing tower is connected to the alkali regeneration tank in the desulfurization tower.

[0011] In this application, the drain outlet of the water washing tower is connected to the alkaline regeneration tank in the desulfurization tower. The NH3 in the water discharged from the water washing tower can be used to remove H2S, and the ammonia-containing liquid that should be treated as wastewater can be utilized. This not only reduces the cost of desulfurization, but also eliminates the need to treat the ammonia-containing liquid.

[0012] Furthermore, the CO2 adsorption device includes a vacuum pressure swing adsorption assembly for removing carbon dioxide, and an amine deacidification assembly for further removing carbon dioxide.

[0013] Furthermore, the number of vacuum pressure swing adsorption components is 6.

[0014] Furthermore, the amine deacidification assembly mainly includes an amine absorption tower.

[0015] In this application, a vacuum pressure swing adsorption (VPSA) module and an amine deacidification module are used to remove CO2 from the feed gas. The VPSA module is a gas separation technology based on the selective adsorption characteristics of adsorbents, achieving efficient separation of CH4 and CO2 through periodic pressure changes and vacuum desorption. The composition and separation principle of the VPSA module are prior art and will not be described in detail here. However, the biogas to be treated in this application has a relatively high CO2 content. After passing through the VPSA module, the CO2 content in the feed gas can be reduced from 44 mol% to 3 mol%. Further CO2 removal is required using an amine deacidification module. After further removal by the amine deacidification module, the CO2 content in the feed gas can be reduced to below 20 ppm. The composition and separation principle of the amine absorption tower in the amine deacidification module are prior art and will not be described in detail here. In addition, upstream of the CO2 adsorption unit, NH3 and H2S have been removed by the ammonia removal unit and the desulfurization unit. There are basically no components in the raw gas that would cause the adsorbent in the VPSA module to deteriorate or become ineffective. After the raw gas passes through the VPSA module, the CO2 content in it has been greatly reduced, which makes the load on the amine deacidification module lower and can reduce the amount of amine liquid to replenish, thus saving costs.

[0016] Furthermore, the dehydration device includes two dehydration towers that alternately perform an adsorption dehydration process and an adsorption dehydration capacity regeneration process.

[0017] Furthermore, the dehydration tower is equipped with a molecular sieve for adsorbing moisture.

[0018] Furthermore, the dehydration device also includes a heater for heating the gas to regenerate the molecular sieve.

[0019] Furthermore, the dehydration tower is equipped with a raw material gas inlet pipe, a regenerated gas outlet pipe, a raw material gas outlet pipe, and a regenerated gas inlet pipe;

[0020] The raw material gas inlet pipe and the regenerated gas outlet pipe are located on one side of the molecular sieve, and the raw material gas outlet pipe and the regenerated gas inlet pipe are located on the other side of the molecular sieve.

[0021] The raw material gas inlet pipe is connected to the outlet pipe of the amine deacidification component; the regenerated gas outlet pipe is connected to the inlet pipe of the amine deacidification component.

[0022] The regenerated gas inlet pipe is connected to the heater; the raw material gas outlet pipe is connected to the heater and the liquefaction device respectively.

[0023] In this invention, two dehydration towers are used to remove moisture from the raw gas. Each dehydration tower utilizes a molecular sieve to adsorb moisture from the raw gas. As the dehydration towers are used, the moisture adsorbed by the molecular sieve gradually increases, and its adsorption activity decreases, requiring regeneration of the molecular sieve. In the dehydration device of this application, the raw gas is fed into one dehydration tower for moisture removal, while the other dehydration tower regenerates its adsorption and dehydration capacity. The regeneration process includes hot blowing and cold blowing. First, hot blowing is performed. Hot blowing refers to the process where, after the raw gas has been dehydrated in the dehydration tower and purified into directly usable natural gas, most of it enters the liquefaction unit for liquefaction. A small portion of the natural gas is heated by a heater and then enters the dehydration tower for molecular sieve regeneration through the regeneration gas inlet pipe. The gas used for molecular sieve regeneration is referred to as regeneration gas. After entering the dehydration tower, the regeneration gas passes through the molecular sieve, where heat evaporates the moisture on the molecular sieve and carries it away, before it enters the amine deacidification component for further processing. Then, cold blowing is performed. Cold blowing means that the regeneration gas that was introduced into the heater is introduced into the regeneration gas inlet pipe into the dehydration tower without starting the heater to heat it, so that the molecular sieve is cooled down in preparation for the next adsorption. After that, the regeneration gas enters the amine deacidification component for reprocessing.

[0024] After passing through the dehydration unit, the methane content in the raw gas reaches over 99%. After liquefying the gas using a liquefaction unit, it can be used as a liquefied natural gas product.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] This invention utilizes a water washing device and an alkaline washing device to remove NH3 and H2S gases, reducing the heat consumption of the device. Then, a vacuum pressure swing adsorption decarbonization component and an amine deacidification component are used to reduce the CO2 content to below 20ppm, which meets the CO2 removal accuracy while greatly reducing the heat consumption of the device. Finally, a dehydration device is used to remove water from the gas, so that the methane content in the produced natural gas reaches more than 99%, which greatly improves the calorific value of the biogas. The process is mature and can be used for stable and continuous production. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the apparatus for producing liquefied natural gas from biogas according to this utility model.

[0028] Figure 2 This is a schematic diagram of the dehydration device in this utility model.

[0029] The components include: 1. Biogas intake assembly; 2. Ammonia removal device; 21. Water washing tower; 3. Desulfurization device; 31. Desulfurization tower; 32. Alkali regeneration tank; 33. Plate and frame filter; 4. CO2 adsorption device; 41. Vacuum pressure swing adsorption assembly; 42. Amine deacidification assembly; 5. Dehydration device; 51. Dehydration tower; 511. Molecular sieve; 512. Raw gas intake pipeline; 513. Raw gas outlet pipeline; 514. Regenerated gas outlet pipeline; 515. Regenerated gas intake pipeline; 52. Heater; and 6. Liquefaction device. Detailed Implementation

[0030] To enable those skilled in the art to better understand the present invention, the technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. It should be noted that the following detailed descriptions are exemplary and are only some embodiments of the present invention, not all embodiments.

[0031] Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this utility model.

[0032] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. The experimental materials used in the embodiments of this utility model are all conventional experimental materials in the art and are commercially available. Experimental methods not specifying detailed conditions are performed according to conventional experimental methods or the operating instructions recommended by the supplier.

[0033] like Figure 1 As shown, a system for producing liquefied natural gas from biogas includes an ammonia removal unit 2, a desulfurization unit 3, a CO2 adsorption unit 4, a dehydration unit 5, and a liquefaction unit 6 connected in sequence via a gas pipeline. In the system provided in this application, the ammonia removal unit 2 and the desulfurization unit 3 first remove NH3 and H2S, then the CO2 adsorption unit 4 and the dehydration unit 5 remove CO2 and water from the raw gas to increase its calorific value. Finally, the purified natural gas is liquefied to obtain a directly usable liquefied natural gas product.

[0034] In one embodiment of this application, the biogas intake assembly 1 includes a raw material gas blower, in which the raw material biogas is pressurized and enters the ammonia removal device 2.

[0035] In one embodiment of this application, the ammonia removal device 2 is configured as a water washing tower 21. Since NH3 has high solubility in water, water washing is used to remove NH3 from the raw material gas, which is simple to operate and low in cost. The raw biogas is pressurized by a raw material gas blower and enters the water washing tower 21, where NH3 is removed by the demineralized water stream. The ammonia-containing wastewater is recycled to absorb NH3 before being discharged outside the tower for treatment. The water washing tower 21 is equipped with instruments and valves to automatically control the water circulation volume and the water circulation pump flow rate, and to regulate the liquid level.

[0036] In one embodiment of this application, the desulfurization device 3 is configured as a desulfurization tower 31, an alkali regeneration tank 32, and a plate and frame filter 33 connected in sequence, with the plate and frame filter 33 connected to the desulfurization tower 31. This embodiment uses a wet alkali desulfurization-regeneration-sulfur recovery method to remove H2S from the raw gas. In the desulfurization tower 31, the raw gas after NH3 removal by the ammonia removal device 2 comes into contact with the alkali solution, and H2S is removed by acid-base neutralization. The raw gas without H2S is then passed into the subsequent CO2 adsorption device 4. The sulfur-rich alkali solution is mixed with fresh alkali solution in the alkali regeneration tank 32, and after oxidation and regeneration, elemental sulfur is obtained. The sulfur particles (elemental sulfur) generated during the regeneration process form sulfur foam through flotation. The liquid containing sulfur foam is passed into the plate and frame filter 33 to filter out the sulfur solids. The liquid without sulfur is then passed back into the desulfurization tower 31 to remove H2S from the raw gas.

[0037] In another embodiment of this application, the drain outlet of the water washing tower 21 is connected to the alkaline regeneration tank 32 in the desulfurization tower 31. The NH3 in the water discharged from the water washing tower 21 can be used to remove H2S, and the ammonia-containing liquid that should be treated as wastewater can be utilized. This not only reduces the cost of desulfurization, but also eliminates the need to treat ammonia-containing wastewater.

[0038] In one embodiment of this application, the CO2 adsorption device 4 includes a vacuum pressure swing adsorption (VPSA) assembly 41 for removing carbon dioxide and an amine deacidification assembly 42 for further removing carbon dioxide. The number of VPSA assemblies is six, and the amine deacidification assembly 42 is configured as an amine absorption tower. The VPSA assembly is a gas separation technology based on the selective adsorption characteristics of adsorbents. It achieves efficient separation of CH4 and CO2 through periodic pressure changes and vacuum desorption. The composition and separation principle of the VPSA assembly are prior art and will not be described in detail in this application. However, for the biogas to be treated in this application, its CO2 content is relatively high. After passing through the VPSA assembly, the CO2 content in the raw gas can be reduced from 44 mol% to 3 mol%. Further CO2 removal is required using the amine deacidification assembly 42. After further removal by the amine deacidification assembly 42, the CO2 content in the raw gas can be reduced to below 20 ppm. The composition and separation principle of the amine absorption tower in the amine deacidification assembly 42 are prior art and will not be described in detail in this application. In addition, upstream of the CO2 adsorption unit 4, NH3 and H2S have been removed by the ammonia removal unit 2 and the desulfurization unit 3. There are basically no components in the raw gas that would cause the adsorbent in the VPSA component to deteriorate or become ineffective. After the raw gas passes through the VPSA component, the CO2 content in it has been greatly reduced, resulting in a lower load on the amine deacidification component 42, which can reduce the amount of amine liquid replenished to save costs.

[0039] In one embodiment of this application, the dehydration device 5 includes two dehydration towers 51 that alternately perform an adsorption dehydration process and an adsorption dehydration capacity regeneration process, and a heater 52 for heating gas to regenerate the molecular sieve 511; the molecular sieve 511 for adsorbing water is provided in the dehydration towers 51. The dehydration tower 51 is equipped with a raw material gas inlet pipe 512, a regenerated gas outlet pipe 514, a raw material gas outlet pipe 513, and a regenerated gas inlet pipe 515. The raw material gas inlet pipe 512 and the regenerated gas outlet pipe 514 are located on one side of the molecular sieve 511, while the raw material gas outlet pipe 513 and the regenerated gas inlet pipe 515 are located on the other side of the molecular sieve 511. The raw material gas inlet pipe 512 is connected to the outlet pipe of the amine deacidification component 42. The regenerated gas outlet pipe 514 is connected to the inlet pipe of the amine deacidification component 42. The regenerated gas inlet pipe 515 is connected to the heater 52. The raw material gas outlet pipe 513 is connected to both the heater 52 and the liquefaction device 6. The dehydration tower 51 is a device that uses the molecular sieve 511 to adsorb moisture from the raw material gas. As the dehydration tower 51 is used, the amount of moisture adsorbed by the molecular sieve 511 gradually increases, and the adsorption activity decreases. At this point, the molecular sieve 511 needs to be regenerated. When the dehydration device 5 in this application is working, the raw gas is introduced into one of the dehydration towers 51 for moisture removal, while the other dehydration tower 51 is regenerated for adsorption and dehydration capacity. The regeneration process includes hot blowing and cold blowing. First, hot blowing is performed. Hot blowing means that after the raw gas is dehydrated by the dehydration tower 51, it has been purified into natural gas that can be used directly. Most of the natural gas will enter the liquefaction device 6 for liquefaction, and a small part of the natural gas will be heated by the heater 52 and then enter the dehydration tower 51 for regeneration through the regeneration gas inlet pipe 515 for the regeneration of the molecular sieve 511. Here, the gas used for the regeneration of the molecular sieve 511 is called regeneration gas. After the regeneration gas is introduced into the dehydration tower 51, it passes through the molecular sieve 511, and the heat evaporates the moisture on the molecular sieve 511 and carries away the moisture, which then enters the amine deacidification component 42 for reprocessing. Afterwards, cold blowing is performed. Cold blowing means that the regeneration gas that is introduced into the heater 52 is not started for heating, but is introduced into the regeneration gas inlet pipe 515 to the dehydration tower 51 to cool down the molecular sieve 511 in preparation for the next adsorption. Then the regeneration gas enters the amine deacidification component 42 for reprocessing.

[0040] In one embodiment of this application, the raw gas after passing through the dehydration device 5 has a methane content of over 99%, and can be used as liquefied natural gas (LNG) after liquefaction. The dehydration device 5 is equipped with a nitrogen compressor, a nitrogen expander, a plate-fin heat exchanger, and a nitrogen cryogenic unit. After being pressurized by the compressor and nitrogen expander, the nitrogen gas sequentially enters the plate-fin heat exchanger, the nitrogen cryogenic unit, and is cooled stage by stage. Then, the nitrogen expander depressurizes and cools the gas, and finally, the gas exchanges heat with natural gas at the plate-fin heat exchanger to liquefy natural gas (LNG) product.

[0041] A specific usage process of this utility model is as follows:

[0042] 1) Removal of NH3

[0043] The biogas is pressurized to 0.02 MPa in the raw gas blower and enters the water washing tower. NH3 is removed by the demineralized water stream. The ammonia-containing wastewater is recycled to absorb NH3 and then discharged outside the tower for treatment. The water washing tower is equipped with instruments and valves to automatically control the water circulation volume and the water circulation pump flow rate, and to regulate the liquid level.

[0044] 2) Removal of H2S

[0045] After exiting the water washing tower, the gas enters the desulfurization tower and comes into contact with the alkaline solution to remove H2S. The sulfur-rich alkaline solution is mixed with fresh alkaline solution in the alkaline solution regeneration tank. The sulfur-containing foamy liquid enters the plate and frame filter to filter out the sulfur solids. The lean solution is returned to the desulfurization tower. The desulfurization tower is equipped with an alkaline solution buffer tank that automatically controls the liquid level.

[0046] 3) Vacuum pressure swing adsorption (VSA) unit for CO2 removal

[0047] The desulfurized gas is pressurized to 0.7 MPa by the desulfurized gas compressor and enters the vacuum pressure swing adsorption unit, which reduces the CO2 content in the raw gas from 44 mol% to 3 mol%.

[0048] The specific process for CO2 removal in a vacuum pressure swing adsorption (PSA) unit is as follows:

[0049] 3.1) Adsorption process: Selective adsorption occurs under the action of the adsorbent. When the mass transfer front of the adsorbed impurity (called the adsorption front) reaches the reserved section at the bed outlet, the raw material gas inlet valve and product gas outlet valve of the vacuum pressure swing adsorption assembly are closed to stop adsorption. The vacuum pressure swing adsorption assembly will then switch to the isobaric depressurization step.

[0050] 3.2) Isobaric process: Gas enters from one vacuum pressure swing adsorption (VSA) module at a higher pressure into another VSA module at a lower pressure. This process not only reduces the pressure within the VSA modules but also recovers the gas. This process involves multiple consecutive isobaric processes.

[0051] 3.3) Emission Process: After depressurization, switch to the emission step. This step reduces the pressure to approximately 0.2 barg in the opposite direction to adsorption. The adsorbed carbon dioxide begins to desorb from the adsorbent.

[0052] 3.4) Vacuum Process: After the emission process, the vacuum pressure swing adsorption (VSA) unit switches to the vacuum process. The vacuum pump operates in the opposite direction to adsorption to apply a vacuum to the VSA unit, resulting in complete desorption of CO2 from the adsorption bed.

[0053] 3.5) Isopressurization process: After the vacuum process, switch to the isopressurization process. This step corresponds to isodepressurization. It not only repressurizes the vacuum pressure swing adsorption (VSA) unit but also recovers the product gases. This step involves multiple consecutive equal repressurizations.

[0054] 3.6) Final pressurization process: After the initial pressurization process, the pressure of the vacuum pressure swing adsorption (VSA) assembly did not approach the adsorption pressure. Therefore, to maintain system pressure stability, the VSA assembly was pressurized by the product gas through a pressure regulating valve.

[0055] 4) CO2 removal in the amine deacidification unit

[0056] The feed gas after passing through VPSA enters the decarbonization gas compressor and is pressurized to 5 MPa. It then enters the amine absorption tower to contact with the amine liquid and absorb the remaining CO2 in the feed gas. At this time, the CO2 in the gas is less than 20 ppm.

[0057] The 61°C rich amine solution exiting the tower exchanges heat with a 115°C lean amine solution in the rich-lean-lean-solid heat exchanger. The 93°C rich amine solution then enters the amine regeneration tower, while the 83°C lean amine solution goes to the amine absorption tower. In the amine regeneration tower, CO2 gas is separated and discharged externally. The lean amine solution at the bottom of the tower enters the reboiler for heating before returning to the rich-lean-lean-solid heat exchanger. The lean amine solution is then pumped back to the amine absorption tower for recycling, with instruments and regulating valves automatically controlling the tower's liquid level and the lean amine pump's flow rate.

[0058] 5) Dehydration

[0059] The decarbonized gas enters the dehydration tower to remove 0.3 mol% of water.

[0060] The dehydration tower consists of two towers, which are automatically controlled by a programmable valve to work alternately. One tower performs adsorption, and the dehydrated biogas is sent to the liquefaction unit; at the same time, the other tower performs regeneration, which includes hot blowing and cold blowing. Hot blowing is performed first, in which a stream of regeneration gas is separated and heated to 220°C by a regeneration gas heater, causing the water in the adsorbent to be discharged. During cold blowing, the regeneration gas at 53°C cools down the dehydration tower to prepare for the next adsorption. Both hot and cold blowing regeneration gases are circulated into the decarbonization gas compressor at the front end of the amine deacidification unit.

[0061] 6) Natural Gas Liquefaction

[0062] After dehydration, the raw gas enters the liquefaction unit, where the methane content is over 99%. After being liquefied by a plate-fin heat exchanger, it becomes liquefied natural gas.

[0063] The liquefaction unit uses nitrogen as a refrigerant. Nitrogen gas at 0.02 MPa is pressurized to 0.73 MPa by a nitrogen compressor, then to 1.13 MPa by the compression end of a nitrogen expander, enters a plate-fin heat exchanger to -9°C, enters a nitrogen cryogenic compressor to -37°C, enters a plate-fin heat exchanger to -79°C, and is expanded to 0.034 MPa and -155.5°C by the expansion end of the nitrogen expander before entering the plate-fin heat exchanger to provide the cooling capacity required for natural gas liquefaction.

Claims

1. A system for producing liquefied natural gas from biogas, characterized by, The system includes an ammonia removal device (2), a desulfurization device (3), a CO2 adsorption device (4), a dehydration device (5), and a liquefaction device (6) connected in sequence by a ventilation pipeline. The ammonia removal device (2) is connected to a biogas intake assembly (1); The ammonia removal device (2) includes a water washing tower (21) for washing the raw gas with water; the desulfurization device (3) includes a desulfurization tower (31) for washing the raw gas with alkaline solution. The CO2 adsorption device (4) includes a vacuum pressure swing adsorption assembly (41) for removing carbon dioxide. The dehydration device (5) includes two dehydration towers (51) that alternately carry out the adsorption dehydration process and the adsorption dehydration capacity regeneration process.

2. The system for producing liquefied natural gas using biogas according to claim 1, wherein, The desulfurization device (3) also includes an alkali regeneration tank (32) for storing and regenerating alkali solution, and a plate and frame filter (33) for filtering sulfur.

3. The system for producing liquefied natural gas using biogas according to claim 2, wherein, The drain outlet of the water washing tower (21) is connected to the alkali regeneration tank (32) in the desulfurization tower (31).

4. The system for producing liquefied natural gas using biogas according to claim 1, wherein, The CO2 adsorption device (4) also includes an amine deacidification component (42) for further removal of carbon dioxide.

5. The system for producing liquefied natural gas using biogas according to claim 1, wherein, The number of vacuum pressure swing adsorption components (41) is 6.

6. The system for producing liquefied natural gas using biogas according to claim 1, wherein, The dehydration tower (51) is equipped with a molecular sieve (511) for adsorbing moisture.

7. The system for producing liquefied natural gas using biogas according to claim 6, wherein The dehydration device (5) also includes a heater (52) for heating the gas to regenerate the molecular sieve (511).

8. The system for producing liquefied natural gas using biogas according to claim 6, wherein, The dehydration tower (51) is equipped with a raw gas inlet pipe (512), a regenerated gas outlet pipe (514), a raw gas outlet pipe (513), and a regenerated gas inlet pipe (515). The raw material gas inlet pipe (512) and the regenerated gas outlet pipe (514) are located on one side of the molecular sieve (511), and the raw material gas outlet pipe (513) and the regenerated gas inlet pipe (515) are located on the other side of the molecular sieve (511). The raw material gas inlet pipe (512) is connected to the outlet pipe of the amine deacidification component (42); the regenerated gas outlet pipe (514) is connected to the inlet pipe of the amine deacidification component (42); the regenerated gas inlet pipe (515) is connected to the heater (52); and the raw material gas outlet pipe (513) is connected to the heater (52) and the liquefaction device (6) respectively.

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