System and method for biogas purification co-production of lng and co2

Abstract

The application discloses a biogas purification system for co-production of LNG and CO2 and a method thereof, which comprises a desulfurization unit, one side of the desulfurization unit being connected with a first-stage pressurization unit, one end of the first-stage pressurization unit being connected with a PSA unit through a pipeline; a second-stage pressurization unit being connected with one end of the PSA unit, and one end of the second-stage pressurization unit being provided with a fine decarbonization and dehydration unit for removing impurities and liquefying LNG, one end of the fine decarbonization and dehydration unit being connected with a cold box unit; and a CO2 pressurization unit being connected with the PSA unit in communication through a pipeline; the application can remove carbon dioxide in the biogas without a membrane separation method, has high removal efficiency, and has smaller investment cost compared with the membrane separation; after removal, the carbon dioxide can be recycled and reused, resource waste is reduced, and the income effect of the device is improved.

Description

Technical Field

[0001] This invention specifically relates to a system and method for biogas purification and co-production of LNG and CO2. Background Technology

[0002] As biogas projects gradually develop towards large and medium-sized scales, liquefying biogas using natural gas liquefaction technology and supplying it to surrounding LNG refueling stations and urban residents is one way to achieve short-distance transportation and commercial application of biogas. However, biogas contains a large amount of CO2, which brings great difficulties to liquefaction. It is usually necessary to remove CO2 from the feed gas, which not only requires complex carbon removal processes but also wastes the abundant carbon resources in the biogas.

[0003] Existing technology patent number CN111256431B discloses a mixed refrigerant biogas pressurized liquefaction system and its working method. The biogas is desulfurized, dehydrated and filtered by the biogas pretreatment unit and then pressurized. After passing through a two-stage membrane separation unit, high-purity CH4 stream and CO2-rich biogas stream are obtained. After pressurized liquefaction and distillation, pressurized liquid CH4 and food-grade liquid CO2 are obtained.

[0004] Existing technology patent number CN112358899A discloses a system and method for producing liquefied natural gas from biogas, and a liquefaction device. The liquefaction device is used to liquefy biogas after it has been treated by the pretreatment device to obtain liquefied natural gas and tail gas. The liquefaction device includes a tail gas outlet, which is connected to the inlet of the desorption channel.

[0005] The existing technology 1 uses membrane separation to separate carbon dioxide from biogas. However, the equipment is expensive to invest in and has been damaged, resulting in high maintenance costs and making it unsuitable for the operation of biogas liquefaction plants with long design lifespans. The solution provided by technology 2 has a relatively complex overall process flow and only liquefies natural gas, without effectively recovering and utilizing the separated carbon dioxide, resulting in resource waste. Therefore, we propose a system and method for biogas purification and co-production of LNG and CO2. Summary of the Invention

[0006] The purpose of this invention is to provide a system and method for biogas purification and co-production of LNG and CO2, in order to solve the problems mentioned in the background art.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a system for biogas purification and co-production of LNG and CO2, comprising:

[0008] The desulfurization unit is connected to a primary booster unit on one side, and a PSA unit is connected to one end of the primary booster unit via a pipeline.

[0009] A secondary pressurization unit is connected to one end of the PSA unit, and one end of the secondary pressurization unit is equipped with a fine decarbonization and dehydration unit for removing impurities from LNG and liquefying it. One end of the fine decarbonization and dehydration unit is connected to a cold box unit.

[0010] The CO2 booster unit is connected to the PSA unit via a pipeline, and one end of the CO2 booster unit is equipped with a CO2 dehydration unit for dehydrating CO2, and one end of the CO2 dehydration unit is connected to a CO2 liquefaction unit.

[0011] Preferably, the fine decarbonization and dehydration unit includes a first fine decarbonization tower, a second fine decarbonization tower, a third fine decarbonization tower, a first heater, a first cooler, and a first separator. The first fine decarbonization tower is internally connected to the secondary pressurization unit for adsorption. One end of the second fine decarbonization tower is connected to the first fine decarbonization tower, and the other end of the second fine decarbonization tower is connected to the first heater for heating. The first heater is connected to the third fine decarbonization tower through a pipe for hot blowing regeneration. The third fine decarbonization tower is connected to the first separator through the first cooler for gas-liquid phase separation.

[0012] Preferably, the top of the first separator is provided with a first delivery pipe connected to the PSA unit to allow the gas phase portion to return, and the bottom of the first separator is provided with a second delivery pipe to discharge the liquid phase portion.

[0013] Preferably, the CO2 dehydration unit includes a first drying tower, a second drying tower, a pre-drying tower, a second heater, a second cooler, and a second separator. One end of the first drying tower is connected to the CO2 pressurization unit, and the lower end of the first drying tower is connected to the CO2 liquefaction unit via a pipe for liquefaction. The upper end of the pre-drying tower is connected to the CO2 pressurization unit, and the lower end of the pre-drying tower is connected to the second heater, the output port of the second heater is connected to the second drying tower, the upper part of the second drying tower is connected to the second cooler via a pipe for cooling, and the output port of the second cooler is connected to the second separator via a pipe for gas-liquid phase separation.

[0014] Preferably, the top of the second separator is provided with a third conveying pipe for inputting the gas phase portion to the CO2 pressurization unit, and the bottom of the second separator is provided with a fourth conveying pipe for discharging the liquid phase portion.

[0015] Preferably, the cold box unit output port is connected to a loading unit, and one side of the loading unit is connected to the CO2 liquefaction unit via a pipe.

[0016] A method for biogas purification and co-production of LNG and CO2 includes the following steps:

[0017] Step A: Biogas originates from fermentation, is pressurized by a blower, and enters the desulfurization unit to remove hydrogen sulfide;

[0018] Step B: After being pressurized by the first-stage pressurization unit, it enters the PSA unit for CO2 adsorption, and then is pressurized again by the second-stage pressurization unit, and then enters the fine decarbonization and dehydration unit to remove CO2, H2O and Hg to below the standard value to produce LNG;

[0019] Step C: The qualified LNG is cooled by passing it into the cold box unit, and then loaded onto trucks for transportation via the loading unit;

[0020] Step D: The CO2 desorbed from the PSA unit in step B is sent to the CO2 booster unit for pressurization, then introduced into the CO2 dehydration unit for dehydration, and after dehydration, it enters the CO2 liquefaction unit for liquefaction and cooling, and then sent to the loading unit for loading and transportation.

[0021] Preferably, the dewatering step in step B of the fine decarbonization and dewatering unit is as follows:

[0022] Step B1: Biogas from the secondary booster unit enters the first purification tower for adsorption, reducing the CO2, H2O, and Hg content in the biogas to below the standard value, and then is transported to the cold box unit through pipeline;

[0023] Step B2: The regenerated gas is sent to the second fine stripping tower for cold blowing, then to the first heater for heating, and after heating, it is sent to the third fine stripping tower for hot blowing regeneration. The H2O and CO2 adsorbed in the adsorbent are desorbed by heating and then sent to the first cooler for cooling. After cooling, it is sent to the first separator for separation.

[0024] Step B3: The separated gas phase is returned to the PSA unit through the first delivery pipe, and the liquid phase is discharged through the second delivery pipe.

[0025] Preferably, the specific steps of the CO2 dehydration unit in step D are as follows:

[0026] Step D1: The desorbed gas from the PSA unit is introduced into the first drying tower for adsorption, and then introduced into the CO2 liquefaction unit for liquefaction.

[0027] Step D2: The regenerated gas enters the pre-drying tower for cold blowing, then enters the second heater for heating, and then enters the second drying tower for hot blowing regeneration. After regeneration, it enters the second cooler for cooling, and finally passes through the second separator for gas-liquid phase separation.

[0028] Step D3: The gas phase is returned to the PSA unit through the third delivery pipe, and the liquid phase is discharged through the fourth delivery pipe.

[0029] Preferably, in step D2:

[0030] After passing the hot-blowing regeneration in the second drying tower, the regenerated gas is sent to the second heater for heating, and then sent to the second cooler for cooling after hot-blowing regeneration in the pre-drying tower.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] This invention removes carbon dioxide from biogas without the need for membrane separation, achieving high removal efficiency and lower investment costs compared to membrane separation. After removal, the carbon dioxide can be recycled and reused, reducing resource waste and improving the profitability of the device. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the present invention;

[0034] Figure 2 This is a schematic diagram of the decarbonization and dehydration unit structure of the present invention;

[0035] Figure 3 This is a schematic diagram of the CO2 dehydration unit structure of the present invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] Please see Figures 1-3 This invention provides a technical solution: a system for biogas purification and co-production of LNG and CO2, comprising:

[0038] Desulfurization unit 1, one side of which is connected to a first-stage booster unit 2, and one end of the first-stage booster unit 2 is connected to a PSA unit 3 through a pipeline. The PSA unit 3 is an adsorption mechanism that adsorbs CO2, H2O and Hg impurities.

[0039] The secondary pressurization unit 4 is connected to one end of the PSA unit 3, and one end of the secondary pressurization unit 4 is equipped with a fine decarbonization and dehydration unit 5 for removing impurities and liquefying LNG, which facilitates the removal of impurities. At the same time, this process involves the recycling of the adsorbent, because after the adsorbent adsorbs a certain amount of impurities, it needs to go through a regeneration step to remove the adsorbed impurities from the adsorbent in order to maintain its adsorption capacity. One end of the fine decarbonization and dehydration unit 5 is connected to the cold box unit 6.

[0040] The CO2 booster unit 8 is connected to the PSA unit 3 via a pipeline. One end of the CO2 booster unit 8 is equipped with a CO2 dehydration unit 9 for dehydrating CO2, and the other end of the CO2 dehydration unit 9 is connected to a CO2 liquefaction unit 10, which facilitates the recycling and reuse of liquefied CO2 and reduces the waste of resources.

[0041] Preferably, the fine decarbonization and dehydration unit 5 includes a first fine decarbonization tower 51, a second fine decarbonization tower 52, a third fine decarbonization tower 53, a first heater 54, a first cooler 55, and a first separator 56. The first fine decarbonization tower 51 is internally connected to the secondary pressurization unit 4 for adsorption. One end of the second fine decarbonization tower 52 is connected to the first fine decarbonization tower 51, and the other end of the second fine decarbonization tower 52 is connected to the first heater 54 for heating. The first heater 54 is connected to the third fine decarbonization tower 53 through a pipe for hot blowing regeneration. The third fine decarbonization tower 53 is connected to the first separator 56 through the first cooler 55 for gas-liquid phase separation, which facilitates better decarbonization and dehydration.

[0042] Preferably, the top of the first separator 56 is provided with a first delivery pipe 520 connected to the PSA unit 3 to allow the gas phase portion to return, facilitating the recycling of the removed impurities, and the bottom of the first separator 56 is provided with a second delivery pipe 521 to discharge the liquid phase portion.

[0043] Preferably, the CO2 dehydration unit 9 includes a first drying tower 91, a second drying tower 92, a pre-drying tower 93, a second heater 94, a second cooler 95, and a second separator 96. One end of the first drying tower 91 is connected to the CO2 pressurization unit 8, and the lower end of the first drying tower 91 is connected to the CO2 liquefaction unit 10 through a pipe to liquefy CO2 and improve the recovery effect of CO2. The upper end of the pre-drying tower 93 is connected to the CO2 pressurization unit 8, and the lower end of the pre-drying tower 93 is connected to the second heater 94. The output port of the second heater 94 is connected to the second drying tower 92. The second drying tower 92 is connected to the second cooler 95 through a pipe for cooling, and the output port of the second cooler 95 is connected to the second separator 96 through a pipe for gas-liquid phase separation.

[0044] Preferably, the top of the second separator 96 is provided with a third delivery pipe 912 for inputting the gas phase portion to the CO2 pressurization unit 8, and the bottom of the second separator 96 is provided with a fourth delivery pipe 913 for discharging the liquid phase portion.

[0045] Preferably, the cold box unit 6 has an output port connected to a loading unit 7, and one side of the loading unit 7 is connected to the CO2 liquefaction unit 10 through a pipe, which facilitates transportation and recycling.

[0046] A method for biogas purification and co-production of LNG and CO2 includes the following steps:

[0047] Step A: Biogas originates from fermentation, is pressurized by a blower, and enters desulfurization unit 1 to remove hydrogen sulfide;

[0048] Step B: After being pressurized by the first-stage pressurization unit 2, it enters the PSA unit 3 for CO2 adsorption, and then is pressurized again by the second-stage pressurization unit 4, and then enters the fine decarbonization and dehydration unit 5 to remove CO2, H2O and Hg to below the standard value to produce LNG.

[0049] Step C: The qualified LNG is introduced into the cold box unit 6 for cooling, and then loaded onto trucks for transportation through the loading unit 7;

[0050] Step D: The CO2 extracted from PSA unit 3 in step B is sent to CO2 booster unit 8 for pressurization, then passed into CO2 dehydration unit 9 for dehydration, and after dehydration, it enters CO2 liquefaction unit 10 for liquefaction and cooling, and then is sent to loading unit 7 for loading and transportation.

[0051] Preferably, the dewatering step in step B of the fine decarbonization and dewatering unit 5 is as follows:

[0052] Step B1: Biogas from the secondary booster unit 4 enters the first purification tower 51 for adsorption, reducing the CO2, H2O, and Hg content in the biogas to below the standard value, and then is transported to the cold box unit 6 through pipeline;

[0053] Step B2: The regenerated gas is sent to the second fine stripping tower 52 for cold blowing, and then sent to the first heater 54 for heating. After heating, it is sent to the third fine stripping tower 53 for hot blowing regeneration. The H2O and CO2 adsorbed in the adsorbent are heated and desorbed, and then sent to the first cooler 55 for cooling. After cooling, it is sent to the first separator 56 for separation.

[0054] Step B3: The separated gas phase is returned to the PSA unit 3 through the first delivery pipe 520, and the liquid phase is discharged through the second delivery pipe 521.

[0055] Preferably, the specific steps of the CO2 dehydration unit 9 in step D are as follows:

[0056] Step D1: The desorbed gas from PSA unit 3 is introduced into the first drying tower 91 for adsorption, and then introduced into the CO2 liquefaction unit 10 for liquefaction.

[0057] Step D2: The regenerated gas enters the pre-drying tower 93 for cold blowing, and after cold blowing, it is passed into the second heater 94 for heating, and then enters the second drying tower 92 for hot blowing regeneration. After regeneration, it enters the second cooler 95 for cooling, and finally passes through the second separator 96 for gas-liquid phase separation.

[0058] Step D3: The gas phase portion returns to PSA unit 3 through the third delivery pipe 912, and the liquid phase portion is discharged through the fourth delivery pipe 913.

[0059] Preferably, in step D2:

[0060] After passing the hot blowing regeneration in the second drying tower 92, the regenerated gas is sent to the second heater 94 for heating, and after heating, it is sent to the second cooler 95 for cooling via hot blowing regeneration in the pre-drying tower 93.

[0061] The system operation process is described as follows:

[0062] Main processes of natural gas liquefaction:

[0063] After fermentation, the biogas is pressurized by a blower to 0.5–5 kPa.G and 40°C, then saturated with water and sent to desulfurization unit 1 to remove 20 kPa.G of hydrogen sulfide and reduce the H2S content to ≤0.1 ppm. It then enters primary pressurization unit 2, where it is pressurized to 0.6 MPa.G and 40°C before entering PSA unit 3. PSA unit 3 adsorbs CO2 from the biogas, reducing the CO2 content to below 300 ppm. After passing through secondary pressurization unit 4 at 4.1 MPa.G, it enters fine decarbonization and dehydration unit 5, where the CO2, H2O, and Hg contents are reduced to standard values: CO2 ≤50 ppm, H2O ≤1 ppm, Hg ≤0.01 μg / m3. Finally, it enters cold box unit 6, where it is cooled to -162°C before being loaded onto trucks for transport.

[0064] The CO2 separated in PSA unit 3 enters CO2 pressurization unit 8 and is pressurized to 2.6 MPa.G. It then enters CO2 dehydration unit 9 to dehydrate the CO2. After dehydration, the CO2 enters CO2 liquefaction unit 10 to be cooled and liquefied before entering loading unit 7 for loading and transportation.

[0065] Process flow of fine decarbonization and dehydration unit 5:

[0066] Taking the normal adsorption of decarbonization and dehydration tower 51, the cold blowing of decarbonization and dehydration tower 52, and the hot blowing of decarbonization and dehydration tower 53 as examples, valves not mentioned in the description are closed by default.

[0067] Biogas from the secondary booster unit 4 enters the decarbonization and dehydration tower 51 through pipelines 501 and F1 for normal adsorption, reducing the CO2, H2O, and Hg content in the biogas to below standard values. It then flows through F4 and pipeline 504 to the cold box unit 6. Regenerated gas enters the decarbonization and dehydration tower 52 through pipelines 507, 508, and F17 for cold blowing. The regenerated gas after cold blowing in the decarbonization and dehydration tower 52 then enters the regenerated gas heater 54 through F8, pipelines 510 and 511 for further heating. The regeneration gas, heated to approximately 220°C, enters the decarbonization and dehydration tower 53 via pipes 513, 514, and F10 for hot blowing regeneration. After the H2O and CO2 adsorbed in the adsorbent are desorbed by heating, the gas enters the regeneration gas cooler 55 via pipes 516 and 518 for cooling, and then enters the regeneration gas separator 56 via pipe 519 for separation. The gas phase is returned to the PSA unit for adsorption via the first conveying pipe 520, and the liquid phase is discharged via the second conveying pipe 521.

[0068] In this unit, decarbonization and dehydration towers 51 to 53 switch between adsorption, hot blowing, and cold blowing.

[0069] CO2 Dehydration Unit 9 Process:

[0070] The desorbed gas from the PSA unit enters the CO2 dehydration unit 9 through pipe 901. The following description takes the normal adsorption of drying tower 91 and the regeneration of drying tower 92 as an example. Valves not mentioned in the description are closed by default.

[0071] The desorbed gas from the PSA unit enters the drying tower 91 for normal adsorption via pipes 901 and F19. The adsorbed CO2 is then sent to the CO2 liquefaction unit 10 for liquefaction via pipe F21 and pipe 904. The regeneration gas enters the pre-drying tower 93 via pipes 903 and F23 for cold blowing, and then enters the CO2 regeneration gas heater 94 via pipe 906 for heating to 180°C. After that, it enters the drying tower 92 via pipes 907, 908, and F24 for hot blowing regeneration. The regeneration gas after hot blowing regeneration in the drying tower 92 enters the CO2 regeneration gas cooler 95 via pipes 910, 909, and F26 for cooling, and then enters the CO2 regeneration gas separator 96 via pipe 911 for gas-liquid phase separation. The gas phase portion flows into pipe 901 via the third conveying pipe 912, and the liquid phase portion is discharged via the fourth conveying pipe 913.

[0072] After the drying tower 92 passes the hot-blowing regeneration test, the regenerated gas undergoes cold-blowing regeneration through pipelines 901, 902, and F20. The cold-blown regenerated gas then enters the CO2 regenerated gas heater 94 through pipelines 907, 908, and F24 and is heated to 180°C. After that, it undergoes hot-blowing regeneration of the pre-drying tower 93 through pipeline 906. The regenerated gas after hot-blowing regeneration of the pre-drying tower 93 enters the CO2 regenerated gas cooler 95 through pipelines 914, 909, and F28 for cooling. After that, it enters the CO2 regenerated gas separator 96 through pipeline 911 for gas-liquid phase separation. The gas phase portion flows into pipeline 901 through the third conveying pipe 912, and the liquid phase portion is discharged through the fourth conveying pipe 913.

[0073] The drying towers 91 and 92 in this unit switch between adsorption and regeneration.

[0074] The main processes of this system are all executed by computer control, involving few human operations and a high degree of automation.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A system for biogas purification and co-production of LNG and CO2, characterized in that, include: A desulfurization unit (1) is connected to a first-stage booster unit (2) on one side, and a PSA unit (3) is connected to one end of the first-stage booster unit (2) through a pipeline. A secondary pressurization unit (4) is connected to one end of the PSA unit (3), and one end of the secondary pressurization unit (4) is provided with a fine decarbonization and dehydration unit (5) for removing impurities from LNG and liquefying it. One end of the fine decarbonization and dehydration unit (5) is connected to a cold box unit (6). The CO2 booster unit (8) is connected to the PSA unit (3) via a pipeline. One end of the CO2 booster unit (8) is equipped with a CO2 dehydration unit (9) for dehydrating CO2, and one end of the CO2 dehydration unit (9) is connected to a CO2 liquefaction unit (10).

2. The system for biogas purification and co-production of LNG and CO2 according to claim 1, characterized in that: The fine decarbonization and dehydration unit (5) includes a first fine decarbonization tower (51), a second fine decarbonization tower (52), a third fine decarbonization tower (53), a first heater (54), a first cooler (55), and a first separator (56). The first fine decarbonization tower (51) is internally connected to the secondary pressurization unit (4) for adsorption. One end of the second fine decarbonization tower (52) is connected to the first fine decarbonization tower (51), and the other end of the second fine decarbonization tower (52) is connected to the first heater (54) for heating. The first heater (54) is connected to the third fine decarbonization tower (53) through a pipe for hot blowing regeneration. The third fine decarbonization tower (53) is connected to the first separator (56) through the first cooler (55) for gas-liquid phase separation.

3. The system for biogas purification and co-production of LNG and CO2 according to claim 2, characterized in that: The first separator (56) has a first delivery pipe (520) at the top end that is connected to the PSA unit (3) to allow the gas phase portion to return, and a second delivery pipe (521) at the bottom end of the first separator (56) to discharge the liquid phase portion.

4. The system for biogas purification and co-production of LNG and CO2 according to claim 1, characterized in that: The CO2 dehydration unit (9) includes a first drying tower (91), a second drying tower (92), a pre-drying tower (93), a second heater (94), a second cooler (95), and a second separator (96). One end of the first drying tower (91) is connected to the CO2 pressurization unit (8). The lower end of the first drying tower (91) is connected to the CO2 liquefaction unit (10) through a pipe for liquefaction. The upper end of the pre-drying tower (93) is connected to the CO2 pressurization unit (8). The lower end of the pre-drying tower (93) is connected to the second heater (94), and the output port of the second heater (94) is connected to the second drying tower (92). The second drying tower (92) is connected to the second cooler (95) through a pipe for cooling. The output port of the second cooler (95) is connected to the second separator (96) through a pipe for gas-liquid phase separation.

5. A system for biogas purification and co-production of LNG and CO2 according to claim 4, characterized in that: The second separator (96) is provided with a third delivery pipe (912) at the top for inputting the gas phase portion to the CO2 booster unit (8), and a fourth delivery pipe (913) at the bottom for discharging the liquid phase portion.

6. A system for biogas purification and co-production of LNG and CO2 according to claim 4, characterized in that: The cold box unit (6) has an output port connected to a loading unit (7), and one side of the loading unit (7) is connected to the CO2 liquefaction unit (10) via a pipe.

7. The method for biogas purification and co-production of LNG and CO2 according to claim 1, characterized in that: Includes the following steps: Step A: Biogas originates from fermentation, is pressurized by a blower, and enters the desulfurization unit (1) to remove hydrogen sulfide; Step B: After being pressurized by the first-stage pressurization unit (2), it enters the PSA unit (3) for CO2 adsorption, and then is pressurized again by the second-stage pressurization unit (4), and then enters the fine decarbonization and dehydration unit (5) to remove CO2, H2O and Hg to below the standard value to produce LNG; Step C: The qualified LNG is introduced into the cold box unit (6) for cooling, and then loaded onto a vehicle for transport through the loading unit (7); Step D: The CO2 extracted from the PSA unit (3) in step B is sent to the CO2 pressurization unit (8) for pressurization, and then introduced into the CO2 dehydration unit (9) for dehydration. After dehydration, it enters the CO2 liquefaction unit (10) for liquefaction and cooling, and then is sent to the loading unit (7) for loading and transportation.

8. A method for biogas purification and co-production of LNG and CO2 according to claim 7, characterized in that: In step B, the dewatering step of the fine decarbonization and dewatering unit (5) is as follows: Step B1: Biogas from the secondary booster unit (4) enters the first purification tower (51) for adsorption, reducing the CO2, H2O and Hg content in the biogas to below the standard value, and then is transported to the cold box unit (6) through pipeline; Step B2: The regenerated gas is sent to the second fine stripping tower (52) for cold blowing, and then sent to the first heater (54) for heating. After heating, it is sent to the third fine stripping tower (53) for hot blowing regeneration. The H2O and CO2 adsorbed in the adsorbent are heated and desorbed, and then sent to the first cooler (55) for cooling. After cooling, it is sent to the first separator (56) for separation. Step B3: The separated gas phase is returned to the PSA unit (3) through the first delivery pipe (520), and the liquid phase is discharged through the second delivery pipe (521).

9. A method for biogas purification and co-production of LNG and CO2 according to claim 7, characterized in that: The specific steps of the CO2 dehydration unit (9) in step D are as follows: Step D1: The desorbed gas from the PSA unit (3) is introduced into the first drying tower (91) for adsorption, and then introduced into the CO2 liquefaction unit (10) for liquefaction. Step D2: The regenerated gas enters the pre-drying tower (93) for cold blowing, and after cold blowing, it is passed into the second heater (94) for heating, and then enters the second drying tower (92) for hot blowing regeneration. After regeneration, it enters the second cooler (95) for cooling, and finally passes through the second separator (96) for gas-liquid phase separation. Step D3: The gas phase is returned to the PSA unit (3) through the third delivery pipe (912), and the liquid phase is discharged through the fourth delivery pipe (913).

10. A method for biogas purification and co-production of LNG and CO2 according to claim 9, characterized in that: In step D2: After passing the hot blowing regeneration in the second drying tower (92), the regenerated gas is sent to the second heater (94) for heating, and after heating, it is sent to the second cooler (95) for cooling via hot blowing regeneration in the pre-drying tower (93).

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