Two-stage pressure swing vacuum adsorption system and method for biogas purification

Abstract

The invention discloses a two-stage pressure swing vacuum adsorption system and method for biogas purification, and relates to the technical field of gas separation and purification and carbon capture. The system comprises a desulfurizing tower, a dewatering tower, a primary pressure swing adsorption system, a vacuum system and a secondary pressure swing adsorption system, the desulfurization tower and the water removal tower are used for converting to-be-treated biogas into mixed gas of CH4 and CO2; the first-stage pressure swing adsorption system and the second-stage pressure swing adsorption system are used for carrying out two-step purification on the mixed gas and respectively comprise adsorption towers with the same number, and each adsorption tower can sequentially and circularly carry out adsorption, pressure equalizing, vacuum desorption, pressure boosting and final pressure boosting operation; the vacuum system is used for assisting each adsorption tower in the primary pressure swing adsorption system to perform vacuum desorption operation. According to the system and the method, CH4 in the biogas can be purified to 99% or above, the high-standard requirements of vehicle fuel gas or incorporation into a natural gas pipeline network and the like are met, meanwhile, energy consumption is reduced, economical efficiency is improved, and gradient utilization of energy and efficient carbon capture are further achieved.

Description

Technical Field

[0001] The present invention belongs to the technical fields of gas separation and purification technology and carbon capture technology, and particularly relates to a two-stage pressure swing vacuum adsorption system and method for biogas purification. Background Art

[0002] Biogas is produced by the anaerobic fermentation of organic biomass, such as food waste, industrial and agricultural waste, and animal manure. Biogas contains approximately 50%-70% methane (CH4) and 20%-40% carbon dioxide (CO2), with the rest being small amounts of impurities such as hydrogen sulfide (H2S) and water. After simple purification steps, biogas can be directly used for combustion and internal combustion engine power generation. However, the high content of carbon dioxide in the raw gas results in low calorific value and effective utilization rate for combustion and power generation. If biogas is purified and further decarbonized and upgraded, methane product gas with a methane purity of up to 98%-99% can be produced, which not only increases the calorific value of the raw gas but also can be used as a substitute for fossil natural gas, directly input into the natural gas pipeline or prepared as vehicle fuel, while reducing carbon emissions. Therefore, using industrial technology to remove CO2 from biogas to improve the purity of methane is a necessary stage for the efficient utilization of biogas.

[0003] Traditional carbon capture technologies (such as chemical absorption method, membrane separation method) face problems such as high energy consumption, complex equipment, and expensive operating costs in practical applications. Pressure swing adsorption (PSA) has become a research hotspot in the field of carbon capture due to its unique advantages. The PSA technology selectively adsorbs and desorbs gases by regulating pressure changes, without the need for a thermal regeneration process, with relatively low energy consumption. In addition, it also has characteristics such as simple process, flexible operation, and strong adaptability. The two-stage pressure swing vacuum adsorption technology significantly improves the performance of the traditional single-stage PSA system by optimizing the adsorption-desorption cycle process. Through hierarchical adsorption, vacuum-enhanced desorption, and material co-optimization, it breaks through the bottlenecks of single-stage PSA in terms of energy efficiency, recovery rate, and adaptability, and is particularly suitable for carbon capture scenarios of low-concentration, multi-impurity industrial tail gases.

[0004] In summary, existing carbon capture technologies have problems in terms of recovery rate, economy, adaptability, etc. to varying degrees, which seriously restricts the large-scale construction of the system. The technical advantages and industrialization potential of two-stage pressure swing adsorption can be coupled with a vacuum system, making it one of the key technical paths to achieve a low-cost, high-reliability carbon capture system. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects in the prior art and provide a two-stage pressure swing vacuum adsorption system and method for biogas purification.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] In a first aspect, the present invention provides a two-stage pressure swing vacuum adsorption system for biogas purification, which includes a desulfurization tower, a water removal tower, a first pressure swing adsorption system, a vacuum system, and a second pressure swing adsorption system connected in sequence;

[0008] The desulfurization tower and the water removal tower are used to convert the biogas to be treated into a mixed gas of CH4 and CO2; the first pressure swing adsorption system and the second pressure swing adsorption system are used to purify the mixed gas in two steps, and each includes an equal number of adsorption towers. Each adsorption tower can sequentially perform adsorption, pressure equalization, vacuum desorption, pressure boosting, and final pressure boosting operations in a cycle; the vacuum system is used to assist each adsorption tower in the first pressure swing adsorption system to perform vacuum desorption operations.

[0009] Preferably, the first pressure swing adsorption system includes a first adsorption tower, a second adsorption tower, a third adsorption tower, a fourth adsorption tower, and a fourth gas storage tank;

[0010] The outlet of the water removal tower is divided into four branches and is respectively connected to a first stop valve, a second stop valve, a third stop valve, and a fourth stop valve; the first stop valve is communicated with the bottom air inlet of the first adsorption tower, and the product gas outlet at the top of the first adsorption tower is communicated with the fourth gas storage tank through a fifth stop valve; the second stop valve is communicated with the bottom air inlet of the second adsorption tower, and the product gas outlet at the top of the second adsorption tower is communicated with the fourth gas storage tank through a sixth stop valve; the third stop valve is communicated with the bottom air inlet of the third adsorption tower, and the product gas outlet at the top of the third adsorption tower is communicated with the fourth gas storage tank through a seventh stop valve; the fourth stop valve is communicated with the bottom air inlet of the fourth adsorption tower, and the product gas outlet at the top of the fourth adsorption tower is communicated with the fourth gas storage tank through an eighth stop valve;

[0011] The product gas outlet of the first adsorption tower is respectively connected to the product gas outlet of the second adsorption tower through a pipeline provided with a first pressure balance valve, to the product gas outlet of the third adsorption tower through a pipeline provided with a fourth pressure balance valve, and to the product gas outlet of the fourth adsorption tower through a pipeline provided with a fifth pressure balance valve; the product gas outlet of the second adsorption tower is respectively connected to the product gas outlet of the third adsorption tower through a pipeline provided with a second pressure balance valve, and to the product gas outlet of the fourth adsorption tower through a pipeline provided with a sixth pressure balance valve; the product gas outlet of the third adsorption tower is connected to the product gas outlet of the fourth adsorption tower through a pipeline provided with a third pressure balance valve.

[0012] Preferably, the vacuum system includes a vacuum pump, a first gas storage tank, a pressure regulating valve, and a second gas storage tank connected in sequence through pipelines;

[0013] The bottom first-stage CO2 gas outlets of the first adsorption tower, the second adsorption tower, the third adsorption tower and the fourth adsorption tower are respectively communicated with the inlet of a vacuum pump through pipelines provided with a first pressure regulating valve, a second pressure regulating valve, a third pressure regulating valve and a fourth pressure regulating valve.

[0014] Preferably, the secondary pressure swing adsorption system includes a fifth adsorption tower, a sixth adsorption tower, a seventh adsorption tower, an eighth adsorption tower, a third gas storage tank and a fifth gas storage tank;

[0015] The outlet of the second gas storage tank is divided into four branches and is respectively connected to a ninth stop valve, a tenth stop valve, an eleventh stop valve and a twelfth stop valve; the ninth stop valve is communicated with the bottom gas inlet of the fifth adsorption tower, and the top product gas outlet of the fifth adsorption tower is communicated with the fifth gas storage tank through a thirteenth stop valve; the tenth stop valve is communicated with the bottom gas inlet of the sixth adsorption tower, and the top product gas outlet of the sixth adsorption tower is communicated with the fifth gas storage tank through a fourteenth stop valve; the eleventh stop valve is communicated with the bottom gas inlet of the seventh adsorption tower, and the top product gas outlet of the seventh adsorption tower is communicated with the fifth gas storage tank through a fifteenth stop valve; the twelfth stop valve is communicated with the bottom gas inlet of the eighth adsorption tower, and the top product gas outlet of the eighth adsorption tower is communicated with the fifth gas storage tank through a sixteenth stop valve;

[0016] The product gas outlet of the fifth adsorption tower is respectively connected to the product gas outlet of the sixth adsorption tower through a pipeline provided with a seventh pressure balance valve, connected to the product gas outlet of the seventh adsorption tower through a pipeline provided with a tenth pressure balance valve, and connected to the product gas outlet of the eighth adsorption tower through a pipeline provided with an eleventh pressure balance valve; the product gas outlet of the sixth adsorption tower is respectively connected to the product gas outlet of the seventh adsorption tower through a pipeline provided with an eighth pressure balance valve and connected to the product gas outlet of the eighth adsorption tower through a pipeline provided with a twelfth pressure balance valve; the product gas outlet of the seventh adsorption tower is connected to the product gas outlet of the eighth adsorption tower through a pipeline provided with a ninth pressure balance valve;

[0017] The bottom second-stage CO2 gas outlets of the fifth adsorption tower, the sixth adsorption tower, the seventh adsorption tower and the eighth adsorption tower are respectively communicated with the third gas storage tank through pipelines provided with a fifth pressure regulating valve, a sixth pressure regulating valve, a seventh pressure regulating valve and an eighth pressure regulating valve.

[0018] Preferably, the first adsorption tower, the second adsorption tower, the third adsorption tower, the fourth adsorption tower, the fifth adsorption tower, the sixth adsorption tower, the seventh adsorption tower and the eighth adsorption tower have the same structure.

[0019] Preferably, a plurality of perforated plates and / or wire meshes are installed inside each adsorption tower. The perforated plates are located in the upper part, and the wire meshes are located in the lower part. Adsorption materials are placed on both the perforated plates and the wire meshes. The perforated plates are spaced apart from each other and from the wire meshes, and each perforated plate and wire mesh can completely cover the cross-section of the tower cavity where they are located.

[0020] Preferably, the open top of the cylinder body of each adsorption tower is detachably connected to the head through a flange, and a gasket for sealing is installed at the connection.

[0021] Preferably, support angles, reinforcing ribs and PTFE gaskets are also provided at the bottom inside each adsorption tower. A plurality of the support angles are evenly installed at the bottom of the bed for structural support, and PTFE gaskets for anti-corrosion are provided on the surfaces. A plurality of the reinforcing ribs are arranged on the inner wall of the tower to enhance the strength of the tower body.

[0022] Preferably, a plurality of legs are evenly provided at the bottom of each adsorption tower. A guard plate is provided at the connection between the top of the leg and the adsorption tower, and the bottom is stably supported on the ground through a leg seat.

[0023] In a second aspect, the present invention provides a method for biogas purification using the two-stage pressure swing vacuum adsorption system for biogas purification described in the first aspect, which is as follows:

[0024] S1. The biogas to be purified is sequentially treated by a desulfurization tower and a water removal tower to become a mixed gas of CH4 and CO2, and then enters the first-stage pressure swing adsorption system. The first adsorption tower, the second adsorption tower, the third adsorption tower and the fourth adsorption tower in the first-stage pressure swing adsorption system cycle through S11 - S14 to preliminarily purify the mixed gas, which is as follows:

[0025] S11. Open the first stop valve and the fifth stop valve. The mixed gas enters the first adsorption tower through the first stop valve for adsorption, and the obtained first-stage product gas is stored in the fourth gas storage tank through the fifth stop valve. At the same time, the gases in the second adsorption tower and the fourth adsorption tower are respectively pressurized and equalized by opening the sixth pressure balance valve, and the gas in the third adsorption tower is vacuum desorbed by opening the third pressure regulating valve.

[0026] Subsequently, close the sixth pressure balance valve and the third pressure regulating valve, open the first pressure balance valve, so that the first adsorption tower performs a final pressurization operation on the second adsorption tower while adsorbing. At the same time, open the seventh stop valve, so that the first-stage product gas from the fourth gas storage tank purges the bed layer of the third adsorption tower. At the same time, open the fourth pressure regulating valve and the vacuum pump to vacuum desorb the gas in the fourth adsorption tower.

[0027] After the adsorption in the first adsorption tower ends, close the first stop valve, the fifth stop valve, the seventh stop valve and the first pressure balance valve, open the second stop valve and the sixth stop valve, and the mixed gas enters the second adsorption tower through the second stop valve for adsorption. The obtained primary product gas is stored in the fourth gas storage tank through the sixth stop valve. At the same time, the gas in the first adsorption tower and the third adsorption tower are respectively equalized and pressurized by opening the fourth pressure balance valve, and the fourth adsorption tower maintains vacuum desorption.

[0028] Subsequently, close the fourth pressure balance valve, the fourth pressure regulating valve and the vacuum pump, open the second pressure balance valve, and make the second adsorption tower perform a final pressure boosting operation on the third adsorption tower while adsorbing. At the same time, open the eighth stop valve, and make the primary product gas from the fourth gas storage tank purge the bed layer of the fourth adsorption tower. At the same time, open the first pressure regulating valve and the vacuum pump, and perform vacuum desorption on the gas in the first adsorption tower.

[0029] After the adsorption in the second adsorption tower ends, close the second stop valve, the sixth stop valve, the eighth stop valve and the second pressure balance valve, open the third stop valve and the seventh stop valve, and the mixed gas enters the third adsorption tower through the third stop valve for adsorption. The obtained primary product gas is stored in the fourth gas storage tank through the eighth stop valve. At the same time, the gas in the second adsorption tower and the fourth adsorption tower are respectively equalized and pressurized by opening the sixth pressure balance valve, and the first adsorption tower maintains vacuum desorption.

[0030] Subsequently, close the sixth pressure balance valve, the first pressure regulating valve and the vacuum pump, open the third pressure balance valve, and make the third adsorption tower perform a final pressure boosting operation on the fourth adsorption tower while adsorbing. At the same time, open the fifth stop valve, and make the primary product gas from the fourth gas storage tank purge the bed layer of the first adsorption tower. At the same time, open the second pressure regulating valve and the vacuum pump, and perform vacuum desorption on the gas in the second adsorption tower.

[0031] After the adsorption in the third adsorption tower ends, close the third stop valve, the seventh stop valve, the fifth stop valve and the third pressure balance valve, open the fourth stop valve and the eighth stop valve, and the mixed gas enters the fourth adsorption tower through the fourth stop valve for adsorption. The obtained primary product gas is stored in the fourth gas storage tank through the eighth stop valve. At the same time, the gas in the first adsorption tower and the third adsorption tower are respectively pressurized and equalized by opening the fourth pressure balance valve, and the second adsorption tower maintains vacuum desorption.

[0032] Subsequently, close the fourth pressure balance valve, the second pressure regulating valve, and the vacuum pump, and open the fifth pressure balance valve to perform a final pressure boost operation on the first adsorption tower while the fourth adsorption tower is adsorbing; meanwhile, open the sixth stop valve to allow the primary product gas from the fourth gas storage tank to purge the bed layer of the second adsorption tower; meanwhile, open the third pressure regulating valve and the vacuum pump to perform vacuum desorption on the gas in the third adsorption tower.

[0033] After the adsorption in the fourth adsorption tower is completed, close the fourth stop valve, the eighth stop valve, the sixth stop valve, and the fifth pressure balance valve.

[0034] S2. The mixed gas of CH4 and CO2 preliminarily purified by the first pressure swing adsorption system is stored in the first gas storage tank, pressurized by a pressure regulating valve and then enters the second gas storage tank, and then enters the second pressure swing adsorption system; the fifth adsorption tower, the sixth adsorption tower, the seventh adsorption tower, and the eighth adsorption tower in the second pressure swing adsorption system cycle through S21 - S24 to perform deep purification on the preliminarily purified mixed gas, specifically as follows:

[0035] S21. Open the ninth stop valve and the thirteenth stop valve. The mixed gas enters the fifth adsorption tower through the ninth stop valve for adsorption, and the resulting product gas CH4 is stored in the fifth gas storage tank through the thirteenth stop valve; meanwhile, the gas in the sixth adsorption tower and the eighth adsorption tower is respectively boosted and equalized in pressure by opening the twelfth pressure balance valve, and the gas in the seventh adsorption tower is desorbed by opening the seventh pressure regulating valve.

[0036] Subsequently, keep the seventh adsorption tower in desorption state, close the twelfth pressure balance valve and open the seventh pressure balance valve to perform a final pressure boost operation on the sixth adsorption tower while the fifth adsorption tower is adsorbing; meanwhile, open the eighth pressure regulating valve to desorb the gas in the eighth adsorption tower and store it in the third gas storage tank.

[0037] S22. After the adsorption in the fifth adsorption tower is completed, close the ninth stop valve, the thirteenth stop valve, and the seventh pressure balance valve, open the tenth stop valve and the fourteenth stop valve. The mixed gas enters the sixth adsorption tower through the tenth stop valve for adsorption, and the resulting product gas CH4 is stored in the fifth gas storage tank through the fourteenth stop valve; meanwhile, the gas in the fifth adsorption tower and the seventh adsorption tower is respectively equalized in pressure and boosted by opening the tenth pressure balance valve, and the eighth adsorption tower remains in desorption state.

[0038] Subsequently, keep the eighth adsorption tower in desorption state, close the tenth pressure balance valve and open the eighth pressure balance valve to perform a final pressure boost operation on the seventh adsorption tower while the sixth adsorption tower is adsorbing; meanwhile, open the fifth pressure regulating valve to desorb the gas in the fifth adsorption tower and store it in the third gas storage tank.

[0039] After the adsorption in the sixth adsorption tower ends, close the tenth stop valve, the fourteenth stop valve and the eighth pressure balance valve, open the eleventh stop valve and the fifteenth stop valve, and the mixed gas enters the seventh adsorption tower through the eleventh stop valve for adsorption. The resulting product gas CH4 is stored in the fifth gas storage tank through the fifteenth stop valve. At the same time, the gases in the sixth adsorption tower and the eighth adsorption tower are respectively equalized and pressurized by opening the twelfth pressure balance valve, and the fifth adsorption tower remains in desorption.

[0040] Subsequently, the fifth adsorption tower remains in desorption, close the twelfth pressure balance valve and open the ninth pressure balance valve, so that while the seventh adsorption tower is adsorbing, it performs a final pressurization operation on the eighth adsorption tower. At the same time, open the sixth pressure regulating valve to desorb the gas in the sixth adsorption tower and store it in the third gas storage tank.

[0041] After the adsorption in the seventh adsorption tower ends, close the eleventh stop valve, the fifteenth stop valve and the ninth pressure balance valve, open the twelfth stop valve and the sixteenth stop valve, and the mixed gas enters the eighth adsorption tower through the twelfth stop valve for adsorption. The resulting product gas CH4 is stored in the fifth gas storage tank through the sixteenth stop valve. At the same time, the gases in the fifth adsorption tower and the seventh adsorption tower are respectively pressurized and equalized by opening the tenth pressure balance valve, and the sixth adsorption tower remains in desorption.

[0042] Subsequently, the sixth adsorption tower remains in desorption, close the tenth pressure balance valve and open the eleventh pressure balance valve, so that while the eighth adsorption tower is adsorbing, it performs a final pressurization operation on the fifth adsorption tower. At the same time, open the seventh pressure regulating valve to desorb the gas in the seventh adsorption tower and store it in the third gas storage tank.

[0043] After the adsorption in the eighth adsorption tower ends, close the twelfth stop valve, the sixteenth stop valve, the seventh pressure regulating valve and the eleventh pressure balance valve.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] A) Through the two-stage pressure swing vacuum adsorption process, the present invention can increase the methane (CH4) concentration in biogas from the initial 50%-70% to 99%, meeting the standards for vehicle fuel gas (such as Bio-CNG) or direct incorporation into the natural gas pipeline network.

[0046] B) In the desorption stage of pressure swing vacuum adsorption, a vacuum pump is used for suction, enabling the adsorbent (such as activated carbon, molecular sieve) to rapidly release CO2 under low pressure. Compared with the traditional high-pressure desorption process, the energy consumption is reduced. At the same time, the two-stage adsorption cycle design can extend the service life of the adsorbent, reducing the comprehensive operating cost.

[0047] C) The purified CO2 removed can reach a concentration of over 98%, which can be directly used for agricultural gas fertilizers, food processing, or carbon capture and storage (CCUS), realizing the low-carbon circular utilization of the entire biogas industrial chain. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic connection diagram of the system of the present invention;

[0049] Figure 2 It is a sectional view of the adsorption tower;

[0050] Figure 3 It is a top view of the adsorption tower.

[0051] In the figure: 1 - desulfurization tower; 2 - water removal tower; 3 - pressure regulating valve; 11 - first adsorption tower; 12 - second adsorption tower; 13 - third adsorption tower; 14 - fourth adsorption tower; 15 - vacuum pump; 21 - fifth adsorption tower; 22 - sixth adsorption tower; 23 - seventh adsorption tower; 24 - eighth adsorption tower; 31 - first gas storage tank; 32 - second gas storage tank; 33 - third gas storage tank; 34 - fourth gas storage tank; 35 - fifth gas storage tank; 41 - first stop valve; 42 - second stop valve; 43 - third stop valve; 44 - fourth stop valve; 45 - ninth stop valve; 46 - tenth stop valve; 47 - eleventh stop valve; 48 - twelfth stop valve; 51 - first pressure regulating valve; 52 - second pressure regulating valve; 53 - third pressure regulating valve; 54 - fourth pressure regulating valve; 55 - fifth pressure regulating valve; 56 - sixth pressure regulating valve; 57 - seventh pressure regulating valve; 58 - eighth pressure regulating valve; 61 - fifth stop valve; 62 - sixth stop valve; 63 - seventh stop valve; 64 - eighth stop valve; 65 - thirteenth stop valve; 66 - fourteenth stop valve; 67 - fifteenth stop valve; 68 - sixteenth stop valve; 71 - first pressure balance valve; 72 - second pressure balance valve; 73 - third pressure balance valve; 74 - fourth pressure balance valve; 75 - fifth pressure balance valve; 76 - sixth pressure balance valve; 77 - seventh pressure balance valve; 78 - eighth pressure balance valve; 79 - ninth pressure balance valve; 80 - tenth pressure balance valve; 81 - eleventh pressure balance valve; 82 - twelfth pressure balance valve; 101 - head; 102 - support angle; 103 - stiffener; 104 - perforated plate; 105 - gasket; 106 - PTFE gasket; 107 - cylinder; 108 - wire mesh; 109 - flange; 110 - guard plate; 111 - leg; 112 - leg seat. DETAILED DESCRIPTION OF THE INVENTION

[0052] The present invention will be further described and explained below in conjunction with the drawings and specific embodiments. The technical features of each embodiment in the present invention can be combined correspondingly without conflict.

[0053] AsFigure 1 As shown in the figure, a two-stage pressure swing vacuum adsorption system for biogas purification provided by the present invention mainly includes a desulfurization tower 1, a water removal tower 2, a first-stage pressure swing adsorption system, a vacuum system, and a second-stage pressure swing adsorption system. Among them, the desulfurization tower 1 and the water removal tower 2 are used to convert the biogas to be treated into a mixed gas of CH4 and CO2; the first-stage pressure swing adsorption system and the second-stage pressure swing adsorption system are used to purify the mixed gas in two steps. The first-stage pressure swing adsorption system and the second-stage pressure swing adsorption system respectively include an equal number of adsorption towers, and each adsorption tower can sequentially cycle through adsorption, equal pressure, vacuum desorption, pressure boosting, and final pressure boosting operations; the vacuum system is used to assist each adsorption tower in the first-stage pressure swing adsorption system to perform vacuum desorption operations.

[0054] During actual use, the biogas to be purified is connected to the inlet of the desulfurization tower 1 through a pipeline. The outlet of the desulfurization tower 1 is connected to the inlet of the water removal tower 2 through a pipeline. The outlet of the water removal tower 2 enters the first-stage pressure swing adsorption system through a pipeline. The first-stage pressure swing adsorption system is used to preliminarily purify the biogas. The gas preliminarily purified by the first-stage pressure swing adsorption system enters the vacuum system. The vacuum system is used to create a vacuum environment at the outlet end of the first-stage pressure swing adsorption system. Subsequently, the gas enters the second-stage pressure swing adsorption system. The second-stage pressure swing adsorption system is used to further purify the gas to 99%, which is convenient for industrial applications.

[0055] As a preferred embodiment of the present invention, the first-stage pressure swing adsorption system mainly includes a first adsorption tower 11, a second adsorption tower 12, a third adsorption tower 13, a fourth adsorption tower 14, and a fourth gas storage tank 34. The connection methods of each component will be specifically described below.

[0056] In the first-stage pressure swing adsorption system of this embodiment, the outlet of the water removal tower 2 is divided into four branch pipelines. The first branch is connected to the inlet of the first stop valve 41, the second branch is connected to the inlet of the second stop valve 42, the third branch is connected to the inlet of the third stop valve 43, and the fourth branch is connected to the inlet of the fourth stop valve 44. The outlet of the first stop valve 41 is connected to the bottom gas inlet of the first adsorption tower 11 through a pipeline. The top product gas outlet of the first adsorption tower 11 is connected to the inlet of the fourth gas storage tank 34 through a pipeline provided with a fifth stop valve 61. Similarly, the outlet of the second stop valve 42 is connected to the bottom gas inlet of the second adsorption tower 12 through a pipeline. The top product gas outlet of the second adsorption tower 12 is connected to the inlet of the fourth gas storage tank 34 through a pipeline provided with a sixth stop valve 62. The outlet of the third stop valve 43 is connected to the bottom gas inlet of the third adsorption tower 13 through a pipeline. The top product gas outlet of the third adsorption tower 13 is connected to the inlet of the fourth gas storage tank 34 through a pipeline provided with a seventh stop valve 63. The outlet of the fourth stop valve 44 is connected to the bottom gas inlet of the fourth adsorption tower 14 through a pipeline. The top product gas outlet of the fourth adsorption tower 14 is connected to the fourth gas storage tank 34 through a pipeline provided with an eighth stop valve 64.

[0057] In the primary pressure swing adsorption system of this embodiment, first pressure balance valves 71, second pressure balance valves 72, third pressure balance valves 73, fourth pressure balance valves 74, fifth pressure balance valves 75, and sixth pressure balance valves 76 are respectively provided between the first adsorption tower 11, the second adsorption tower 12, the third adsorption tower 13, and the fourth adsorption tower 14 for the pressure equalization process. Specifically as follows:

[0058] A pipeline connecting the first adsorption tower 11 and the fifth shut-off valve 61 and a pipeline connecting the second adsorption tower 12 and the sixth shut-off valve 62 are connected through a pipeline provided with the first pressure balance valve 71; a pipeline connecting the first adsorption tower 11 and the fifth shut-off valve 61 and a pipeline connecting the third adsorption tower 13 and the seventh shut-off valve 63 are connected through a pipeline provided with the fourth pressure balance valve 74; a pipeline connecting the first adsorption tower 11 and the fifth shut-off valve 61 and a pipeline connecting the fourth adsorption tower 14 and the eighth shut-off valve 64 are connected through a pipeline provided with the fifth pressure balance valve 75. Similarly, a pipeline connecting the second adsorption tower 12 and the sixth shut-off valve 62 and a pipeline connecting the third adsorption tower 13 and the seventh shut-off valve 63 are connected through a pipeline provided with the second pressure balance valve 72; a pipeline connecting the second adsorption tower 12 and the sixth shut-off valve 62 and a pipeline connecting the fourth adsorption tower 14 and the eighth shut-off valve 64 are connected through a pipeline provided with the sixth pressure balance valve 76. A pipeline connecting the third adsorption tower 13 and the seventh shut-off valve 63 and a pipeline connecting the fourth adsorption tower 14 and the eighth shut-off valve 64 are connected through a pipeline provided with the third pressure balance valve 73.

[0059] During actual use, the primary product gas can enter the adsorption towers through the fifth shut-off valve 61, the sixth shut-off valve 62, the seventh shut-off valve 63, and the eighth shut-off valve 64 from the fourth gas storage tank 34 respectively to purge the residual gas in the bed layer. The first adsorption tower 11, the second adsorption tower 12, the third adsorption tower 13, and the fourth adsorption tower 14 are respectively connected to the first pressure regulating valve 51, the second pressure regulating valve 52, the third pressure regulating valve 53, and the fourth pressure regulating valve 54 for the vacuum desorption process of the primary CO2 gas.

[0060] As a preferred embodiment of the present invention, the vacuum system mainly includes a vacuum pump 15, a first gas storage tank 31, a pressure regulating valve 3, and a second gas storage tank 32. The connection methods of each component will be specifically described below.

[0061] In the vacuum system of this embodiment, the primary CO2 gas outlet at the bottom of the first adsorption tower 11 is connected to the inlet of the vacuum pump 15 through a pipeline provided with a first pressure regulating valve 51. The primary CO2 gas outlet at the bottom of the second adsorption tower 12 is connected to the inlet of the vacuum pump 15 through a pipeline provided with a second pressure regulating valve 52. The primary CO2 gas outlet at the bottom of the third adsorption tower 13 is connected to the inlet of the vacuum pump 15 through a pipeline provided with a third pressure regulating valve 53. The primary CO2 gas outlet at the bottom of the fourth adsorption tower 14 is connected to the inlet of the vacuum pump 15 through a pipeline provided with a fourth pressure regulating valve 54. The outlet of the vacuum pump 15 is connected to the inlet of the first gas storage tank 31 through a pipeline. The outlet of the first gas storage tank 31 is connected to the inlet of the pressure regulating valve 3 through a pipeline. The outlet of the pressure regulating valve 3 is connected to the inlet of the second gas storage tank 32 through a pipeline. The outlet of the second gas storage tank 32 enters the secondary pressure swing adsorption system through a pipeline.

[0062] During actual use, the gas at the outlet of the primary pressure swing adsorption system enters the second gas storage tank 32 after passing through the vacuum system, and then starts the secondary pressure swing adsorption process through the secondary pressure swing adsorption system. That is to say, the primary CO2 gas is desorbed and stored in the first gas storage tank 31 through the vacuum pump 15. The pressure regulating valve 3 is connected to its outlet and is used for pressure regulation of the inlet of the secondary pressure swing adsorption.

[0063] As a preferred embodiment of the present invention, the secondary pressure swing adsorption system mainly includes a fifth adsorption tower 21, a sixth adsorption tower 22, a seventh adsorption tower 23, an eighth adsorption tower 24, a third gas storage tank 33, and a fifth gas storage tank 35. The connection modes of each component will be specifically described below.

[0064] In the secondary pressure swing adsorption system of this embodiment, the gas outlet of the second gas storage tank 32 is divided into four branch pipelines. The first branch is connected to the inlet of the ninth shut-off valve 45, the second branch is connected to the inlet of the tenth shut-off valve 46, the third branch is connected to the inlet of the eleventh shut-off valve 47, and the fourth branch is connected to the inlet of the twelfth shut-off valve 48. The outlet of the ninth shut-off valve 45 is communicated with the bottom gas inlet of the fifth adsorption tower 21 through a pipeline, and the top product gas outlet of the fifth adsorption tower 21 is communicated with the inlet of the fifth gas storage tank 35 through a pipeline provided with a thirteenth shut-off valve 65. The outlet of the tenth shut-off valve 46 is communicated with the bottom gas inlet of the sixth adsorption tower 22 through a pipeline, and the top product gas outlet of the sixth adsorption tower 22 is communicated with the inlet of the fifth gas storage tank 35 through a pipeline provided with a fourteenth shut-off valve 66. The outlet of the eleventh shut-off valve 47 is communicated with the bottom gas inlet of the seventh adsorption tower 23 through a pipeline, and the top product gas outlet of the seventh adsorption tower 23 is communicated with the inlet of the fifth gas storage tank 35 through a pipeline provided with a fifteenth shut-off valve 67. The outlet of the twelfth shut-off valve 48 is communicated with the bottom gas inlet of the eighth adsorption tower 24 through a pipeline, and the top product gas outlet of the eighth adsorption tower 24 is communicated with the inlet of the fifth gas storage tank 35 through a pipeline provided with a sixteenth shut-off valve 68.

[0065] During actual use, CH4 enters the fifth gas storage tank 35 for storage through the thirteenth shut-off valve 65, the fourteenth shut-off valve 66, the fifteenth shut-off valve 67, and the sixteenth shut-off valve 68, and can be utilized resourcefully.

[0066] In the secondary pressure swing adsorption system of this embodiment, seventh pressure balance valves 77, eighth pressure balance valves 78, ninth pressure balance valves 79, tenth pressure balance valves 80, eleventh pressure balance valves 81, and twelfth pressure balance valves 82 are respectively provided between the fifth adsorption tower 21, the sixth adsorption tower 22, the seventh adsorption tower 23, and the eighth adsorption tower 24 for the secondary pressure equalization process. Specifically as follows:

[0067] Between the pipeline connecting the fifth adsorption tower 21 and the thirteenth stop valve 65 and the pipeline connecting the sixth adsorption tower 22 and the fourteenth stop valve 66, communication is achieved through a pipeline provided with a seventh pressure balance valve 77; between the pipeline connecting the fifth adsorption tower 21 and the thirteenth stop valve 65 and the pipeline connecting the seventh adsorption tower 23 and the fifteenth stop valve 67, communication is achieved through a pipeline provided with a tenth pressure balance valve 80; between the pipeline connecting the fifth adsorption tower 21 and the thirteenth stop valve 65 and the pipeline connecting the eighth adsorption tower 24 and the sixteenth stop valve 68, communication is achieved through a pipeline provided with an eleventh pressure balance valve 81. Similarly, between the pipeline connecting the sixth adsorption tower 22 and the fourteenth stop valve 66 and the pipeline connecting the seventh adsorption tower 23 and the fourteenth stop valve 66, communication is achieved through a pipeline provided with an eighth pressure balance valve 78; between the pipeline connecting the sixth adsorption tower 22 and the fourteenth stop valve 66 and the pipeline connecting the eighth adsorption tower 24 and the sixteenth stop valve 68, communication is achieved through a pipeline provided with a twelfth pressure balance valve 82. Between the pipeline connecting the seventh adsorption tower 23 and the fifteenth stop valve 67 and the pipeline connecting the eighth adsorption tower 24 and the sixteenth stop valve 68, communication is achieved through a pipeline provided with a ninth pressure balance valve 79.

[0068] In the two-stage pressure swing adsorption system of this embodiment, the secondary CO2 gas outlet at the bottom of the fifth adsorption tower 21 is connected to the inlet of the third gas storage tank 33 through a pipeline provided with a fifth pressure regulating valve 55, the secondary CO2 gas outlet at the bottom of the sixth adsorption tower 22 is connected to the inlet of the third gas storage tank 33 through a pipeline provided with a sixth pressure regulating valve 56, the secondary CO2 gas outlet at the bottom of the seventh adsorption tower 23 is connected to the inlet of the third gas storage tank 33 through a pipeline provided with a seventh pressure regulating valve 57, and the secondary CO2 gas outlet at the bottom of the eighth adsorption tower 24 is connected to the inlet of the third gas storage tank 33 through a pipeline provided with an eighth pressure regulating valve 58. The outlet of the third gas storage tank 33 is connected to the outside through a pipeline provided with a control valve, facilitating its application in the industrial field.

[0069] During actual use, the final product gas enters the fifth gas storage tank 35 for recovery through the thirteenth stop valve 65, fourteenth stop valve 66, fifteenth stop valve 67, and sixteenth stop valve 68; the tail gas enters the third gas storage tank 33 through the fifth pressure regulating valve 55, sixth pressure regulating valve 56, seventh pressure regulating valve 57, and eighth pressure regulating valve 58, and at this time, available high-purity CH4 and CO2 gases are obtained. Specifically, the fifth adsorption tower 21, sixth adsorption tower 22, seventh adsorption tower 23, and eighth adsorption tower 24 are respectively connected to the fifth pressure regulating valve 55, sixth pressure regulating valve 56, seventh pressure regulating valve 57, and eighth pressure regulating valve 58 for the gas vacuum desorption process, and finally CO2 is stored in the third gas storage tank 33.

[0070] As a preferred embodiment of the present invention, the structures of the first adsorption tower 11, the second adsorption tower 12, the third adsorption tower 13, the fourth adsorption tower 14, the fifth adsorption tower 21, the sixth adsorption tower 22, the seventh adsorption tower 23 and the eighth adsorption tower 24 are the same. In this embodiment, the structure of the above-mentioned adsorption tower is as shown in Figure 2 and 3 shown as follows:

[0071] As shown in Figure 2 shown, a plurality of perforated plates 104 (two in the present embodiment shown in Figure 2 shown) and / or wire meshes 108 (one in the present embodiment shown in Figure 2 shown) are installed inside each adsorption tower. The perforated plate 104 is located in the upper part inside the adsorption tower, and the wire mesh 108 is located in the lower part inside the tower. Adsorption materials are placed on both the perforated plate 104 and the wire mesh 108. The adjacent perforated plates 104 are arranged at intervals, and there is also an interval between the lowermost perforated plate 104 and the wire mesh 108. Each perforated plate 104 and wire mesh 108 can completely cover the cross-section of the tower cavity where they are located. In actual use, a perforated plate 104 with a suitable round hole diameter can be selected according to the type and size of the adsorption material. The top openings of the cylinders 107 of each adsorption tower are detachably connected to the heads 101 through flanges 109, which is convenient for filling and replacing the adsorbent. A gasket 105 is installed at the connection between the cylinder 107 and the head 101 to ensure the sealing performance. At the bottom inside each adsorption tower, there are also support angles 102, reinforcing ribs 103 and PTFE gaskets 106 to ensure the firmness and stability of the tower and the internal components of the tower. A plurality of support angles 102 are evenly installed at the bottom of the bed for structural support, and a PTFE gasket 106 for anti-corrosion is provided on the surface. A plurality of reinforcing ribs 103 are arranged on the inner wall of the tower to enhance the strength of the tower body. A plurality of legs 111 are evenly provided at the bottom of each adsorption tower. A guard plate 110 is provided at the connection between the top of the leg 111 and the adsorption tower, and the bottom is stably supported on the ground through a leg base 112.

[0072] As shown in Figure 3 shown, it is a top view of the adsorption tower. The head 101 and the cylinder 107 are connected by three flanges 109 installed at equal distances to ensure airtightness.

[0073] Based on the above two-stage pressure swing vacuum adsorption system for biogas purification, the present invention also provides a biogas purification method, which is specifically as follows:

[0074] S1. The biogas to be purified is sequentially processed through the desulfurization tower 1 and the water removal tower 2 to become a mixed gas of CH4 and CO2, and then enters the first pressure swing adsorption system. In the first pressure swing adsorption system, the first adsorption tower 11, the second adsorption tower 12, the third adsorption tower 13, and the fourth adsorption tower 14 sequentially complete the steps of adsorption, pressure equalization, vacuum desorption, purging, pressure boosting, and final pressure boosting to ensure the continuity and integrity of the cycle. Continuous CO2 is produced through the system cycle and stored in the third gas storage tank 33.

[0075] That is to say, in actual use, the first pressure swing adsorption system cyclically performs steps S11 to S14 to preliminarily purify the mixed gas. The specific operation process of the mixed gas in the first pressure swing adsorption system is as follows:

[0076] S11. Open the first stop valve 41 and the fifth stop valve 61. At this time, the second stop valve 42, the third stop valve 43, and the fourth stop valve 44 are all in the closed state. The mixed gas enters the first adsorption tower 11 through the first stop valve 41 for adsorption, and the obtained primary product gas is stored in the fourth gas storage tank 34 through the fifth stop valve 61. At the same time, the gases in the second adsorption tower 12 and the fourth adsorption tower 14 are respectively boosted and equalized in pressure by opening the sixth pressure balance valve 76, and the rest of the pressure balance valves are all in the closed state. The gas in the third adsorption tower 13 is subjected to vacuum desorption by opening the third pressure regulating valve 53.

[0077] After the above steps are completed, close the sixth pressure balance valve 76 and the third pressure regulating valve 53, and open the first pressure balance valve 71 to perform the final pressure boosting operation on the second adsorption tower 12 while the first adsorption tower 11 is adsorbing. At the same time, open the seventh stop valve 63 to allow the primary product gas CH4 from the fourth gas storage tank 34 to purge the bed layer of the third adsorption tower 13 to blow out the excess CO2 in the third adsorption tower 13 and improve the purity and yield. At the same time, open the fourth pressure regulating valve 54 and the vacuum pump 15, and the rest of the pressure regulating valves are all in the closed state to perform vacuum desorption on the gas in the fourth adsorption tower 14.

[0078] S12. Similarly, after the adsorption of the first adsorption tower 11 is completed, close the first stop valve 41, the fifth stop valve 61, the seventh stop valve 63, and the first pressure balance valve 71, and open the second stop valve 42 and the sixth stop valve 62. The mixed gas enters the second adsorption tower 12 through the second stop valve 42 for adsorption, and the obtained primary product gas is stored in the fourth gas storage tank 34 through the sixth stop valve 62. At the same time, the gases in the first adsorption tower 11 and the third adsorption tower 13 are respectively equalized in pressure and boosted by opening the fourth pressure balance valve 74, and the fourth adsorption tower 14 remains under vacuum desorption.

[0079] After the above steps are completed, close the fourth pressure balance valve 74, the fourth pressure regulating valve 54 and the vacuum pump 15, and open the second pressure balance valve 72, so that the second adsorption tower 12 performs a final pressure boost operation on the third adsorption tower 13 while adsorbing. At the same time, open the eighth shut-off valve 64, so that the primary product gas from the fourth gas storage tank 34 purges the bed layer of the fourth adsorption tower 14. At the same time, open the first pressure regulating valve 51 and the vacuum pump 15 to perform vacuum desorption on the gas in the first adsorption tower 11.

[0080] S13. Similarly, after the adsorption of the second adsorption tower 12 is completed, close the second shut-off valve 42, the sixth shut-off valve 62, the eighth shut-off valve 64 and the second pressure balance valve 72, and open the third shut-off valve 43 and the seventh shut-off valve 63. The mixed gas enters the third adsorption tower 13 through the third shut-off valve 43 for adsorption, and the obtained primary product gas is stored in the fourth gas storage tank 34 through the eighth shut-off valve 64. At the same time, the gas in the second adsorption tower 12 and the fourth adsorption tower 14 are respectively equalized and pressurized by opening the sixth pressure balance valve 76, and the first adsorption tower 11 maintains vacuum desorption.

[0081] After the above steps are completed, close the sixth pressure balance valve 76, the first pressure regulating valve 51 and the vacuum pump 15, and open the third pressure balance valve 73, so that the third adsorption tower 13 performs a final pressure boost operation on the fourth adsorption tower 14 while adsorbing. At the same time, open the fifth shut-off valve 61, so that the primary product gas from the fourth gas storage tank 34 purges the bed layer of the first adsorption tower 11. At the same time, open the second pressure regulating valve 52 and the vacuum pump 15 to perform vacuum desorption on the gas in the second adsorption tower 12.

[0082] S14. Similarly, after the adsorption of the third adsorption tower 13 is completed, close the third shut-off valve 43, the seventh shut-off valve 63, the fifth shut-off valve 61 and the third pressure balance valve 73, and open the fourth shut-off valve 44 and the eighth shut-off valve 64. The mixed gas enters the fourth adsorption tower 14 through the fourth shut-off valve 44 for adsorption, and the obtained primary product gas is stored in the fourth gas storage tank 34 through the eighth shut-off valve 64. At the same time, the gas in the first adsorption tower 11 and the third adsorption tower 13 are respectively pressurized and equalized by opening the fourth pressure balance valve 74, and the second adsorption tower 12 maintains vacuum desorption.

[0083] After the above steps are completed, close the fourth pressure balance valve 74, the second pressure regulating valve 52 and the vacuum pump 15, and open the fifth pressure balance valve 75, so that the fourth adsorption tower 14 performs a final pressure boost operation on the first adsorption tower 11 while adsorbing. At the same time, open the sixth shut-off valve 62, so that the primary product gas from the fourth gas storage tank 34 purges the bed layer of the second adsorption tower 12. At the same time, open the third pressure regulating valve 53 and the vacuum pump 15 to perform vacuum desorption on the gas in the third adsorption tower 13.

[0084] After the adsorption in the fourth adsorption tower 14 ends, close the fourth stop valve 44, the eighth stop valve 64, the sixth stop valve 62, and the fifth pressure balance valve 75.

[0085] S2. The mixed gas of CH4 and CO2 preliminarily purified by the first pressure swing adsorption system is stored in the first gas storage tank 31 to supply gas to the second pressure swing adsorption system. The mixed gas in the first gas storage tank 31 enters the second gas storage tank 32 after being pressurized by the pressure regulating valve 3, and then enters the second pressure swing adsorption system. The fifth adsorption tower 21, the sixth adsorption tower 22, the seventh adsorption tower 23, and the eighth adsorption tower 24 in the second pressure swing adsorption system sequentially complete the steps of adsorption, pressure equalization, vacuum desorption, purging, pressure boosting, and final pressure boosting to ensure the continuity and integrity of the cycle. Except for the absence of the purging step, the remaining steps are the same as those of the first adsorption system.

[0086] That is to say, in actual use, the second pressure swing adsorption system cyclically performs steps S21 to S24 to deeply purify the preliminarily purified mixed gas. The specific operation process of the mixed gas in the second pressure swing adsorption system is as follows:

[0087] S21. Open the ninth stop valve 45 and the thirteenth stop valve 65. At this time, the tenth stop valve 46, the eleventh stop valve 47, and the twelfth stop valve 48 are all in the closed state. The mixed gas enters the fifth adsorption tower 21 through the ninth stop valve 45 for adsorption, and the obtained product gas CH4 is stored in the fifth gas storage tank 35 through the thirteenth stop valve 65. At the same time, the gas in the sixth adsorption tower 22 and the eighth adsorption tower 24 is respectively pressurized and equalized by opening the twelfth pressure balance valve 82, and the remaining pressure balance valves are in the closed state. The gas in the seventh adsorption tower 23 is desorbed by opening the seventh pressure regulating valve 57, and the remaining pressure regulating valves are in the closed state. Since the pressure at the valve is relatively low, the gas in the adsorption tower can be desorbed.

[0088] After the above steps are completed, the seventh adsorption tower 23 remains desorbed, close the twelfth pressure balance valve 82 and open the seventh pressure balance valve 77, so that the fifth adsorption tower 21 performs the final pressure boosting operation on the sixth adsorption tower 22 while adsorbing. At the same time, open the eighth pressure regulating valve 58 to desorb the gas in the eighth adsorption tower 24 and store it in the third gas storage tank 33.

[0089] S22. Similarly, after the fifth adsorption tower 21 finishes adsorption, close the ninth cut-off valve 45, the thirteenth cut-off valve 65, and the seventh pressure balance valve 77, open the tenth cut-off valve 46 and the fourteenth cut-off valve 66. The mixed gas enters the sixth adsorption tower 22 through the tenth cut-off valve 46 for adsorption, and the produced gas CH4 is stored in the fifth gas storage tank 35 through the fourteenth cut-off valve 66. At the same time, the gas in the fifth adsorption tower 21 and the seventh adsorption tower 23 are respectively equalized and pressurized by opening the tenth pressure balance valve 80, and the eighth adsorption tower 24 remains in desorption.

[0090] After the above steps are completed, the eighth adsorption tower 24 remains in desorption. Close the tenth pressure balance valve 80 and open the eighth pressure balance valve 78 to make the sixth adsorption tower 22 perform a final pressure boost operation on the seventh adsorption tower 23 while adsorbing. At the same time, open the fifth pressure regulating valve 55 to desorb the gas in the fifth adsorption tower 21 and store it in the third gas storage tank 33.

[0091] S23. Similarly, after the sixth adsorption tower 22 finishes adsorption, close the tenth cut-off valve 46, the fourteenth cut-off valve 66, and the eighth pressure balance valve 78, open the eleventh cut-off valve 47 and the fifteenth cut-off valve 67. The mixed gas enters the seventh adsorption tower 23 through the eleventh cut-off valve 47 for adsorption, and the produced gas CH4 is stored in the fifth gas storage tank 35 through the fifteenth cut-off valve 67. At the same time, the gas in the sixth adsorption tower 22 and the eighth adsorption tower 24 are respectively equalized and pressurized by opening the twelfth pressure balance valve 82, and the fifth adsorption tower 21 remains in desorption.

[0092] After the above steps are completed, the fifth adsorption tower 21 remains in desorption. Close the twelfth pressure balance valve 82 and open the ninth pressure balance valve 79 to make the seventh adsorption tower 23 perform a final pressure boost operation on the eighth adsorption tower 24 while adsorbing. At the same time, open the sixth pressure regulating valve 56 to desorb the gas in the sixth adsorption tower 22 and store it in the third gas storage tank 33.

[0093] S24. Similarly, after the seventh adsorption tower 23 finishes adsorption, close the eleventh cut-off valve 47, the fifteenth cut-off valve 67, and the ninth pressure balance valve 79, open the twelfth cut-off valve 48 and the sixteenth cut-off valve 68. The mixed gas enters the eighth adsorption tower 24 through the twelfth cut-off valve 48 for adsorption, and the produced gas CH4 is stored in the fifth gas storage tank 35 through the sixteenth cut-off valve 68. At the same time, the gas in the fifth adsorption tower 21 and the seventh adsorption tower 23 are respectively pressurized and equalized by opening the tenth pressure balance valve 80, and the sixth adsorption tower 22 remains in desorption.

[0094] After the above steps are completed, the sixth adsorption tower 22 remains in desorption. The tenth pressure balance valve 80 is closed and the eleventh pressure balance valve 81 is opened, so that the eighth adsorption tower 24 performs a final pressure boost operation on the fifth adsorption tower 21 while adsorbing. At the same time, the seventh pressure regulating valve 57 is opened, and the gas in the seventh adsorption tower 23 is desorbed and stored in the third gas storage tank 33.

[0095] After the adsorption of the eighth adsorption tower 24 ends, the twelfth stop valve 48, the sixteenth stop valve 68, the seventh pressure regulating valve 57, and the eleventh pressure balance valve 81 are closed.

[0096] The system and method of the present invention can purify CH4 in biogas to more than 99%, meet high-standard requirements such as vehicle fuel gas or being incorporated into the natural gas pipeline network, reduce energy consumption, improve economy, and further achieve cascaded utilization of energy and efficient carbon capture.

[0097] The embodiments described above are only a preferred solution of the present invention, but it is not intended to limit the present invention. Those of ordinary skill in the relevant technical field can still make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all technical solutions obtained by adopting equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A two-stage pressure swing vacuum adsorption system for biogas purification, characterized in that, It includes a desulfurization tower (1), a water removal tower (2), a primary pressure swing adsorption system, a vacuum system, and a secondary pressure swing adsorption system that are connected in sequence. The desulfurization tower (1) and the water removal tower (2) are used to convert the biogas to be treated into a mixed gas of CH4 and CO2; the primary pressure swing adsorption system and the secondary pressure swing adsorption system are used to purify the mixed gas in two steps, each including the same number of adsorption towers, and each adsorption tower can sequentially cycle through adsorption, equalization, vacuum desorption, boosting, and final boosting operations; the vacuum system is used to assist each adsorption tower in the primary pressure swing adsorption system in vacuum desorption operations.

2. The two-stage pressure swing vacuum adsorption system for biogas purification according to claim 1, wherein The primary pressure swing adsorption system includes a first adsorption tower (11), a second adsorption tower (12), a third adsorption tower (13), a fourth adsorption tower (14), and a fourth gas storage tank (34). The outlet of the water removal tower (2) is divided into four branches and is respectively connected to a first stop valve (41), a second stop valve (42), a third stop valve (43), and a fourth stop valve (44); the first stop valve (41) is communicated with the bottom air inlet of the first adsorption tower (11), and the product gas outlet at the top of the first adsorption tower (11) is communicated with the fourth gas storage tank (34) through a fifth stop valve (61); the second stop valve (42) is communicated with the bottom air inlet of the second adsorption tower (12), and the product gas outlet at the top of the second adsorption tower (12) is communicated with the fourth gas storage tank (34) through a sixth stop valve (62); the third stop valve (43) is communicated with the bottom air inlet of the third adsorption tower (13), and the product gas outlet at the top of the third adsorption tower (13) is communicated with the fourth gas storage tank (34) through a seventh stop valve (63); the fourth stop valve (44) is communicated with the bottom air inlet of the fourth adsorption tower (14), and the product gas outlet at the top of the fourth adsorption tower (14) is communicated with the fourth gas storage tank (34) through an eighth stop valve (64). The product gas outlet of the first adsorption tower (11) is respectively connected to the product gas outlet of the second adsorption tower (12) through a pipeline provided with a first pressure balance valve (71), to the product gas outlet of the third adsorption tower (13) through a pipeline provided with a fourth pressure balance valve (74), and to the product gas outlet of the fourth adsorption tower (14) through a pipeline provided with a fifth pressure balance valve (75); the product gas outlet of the second adsorption tower (12) is respectively connected to the product gas outlet of the third adsorption tower (13) through a pipeline provided with a second pressure balance valve (72), and to the product gas outlet of the fourth adsorption tower (14) through a pipeline provided with a sixth pressure balance valve (76); the product gas outlet of the third adsorption tower (13) is connected to the product gas outlet of the fourth adsorption tower (14) through a pipeline provided with a third pressure balance valve (73).

3. A two-stage pressure swing vacuum adsorption system for biogas purification according to claim 2, characterized in that, The vacuum system includes a vacuum pump (15), a first gas storage tank (31), a pressure regulating valve (3), and a second gas storage tank (32) that are connected in sequence through pipelines. The bottom first-stage CO2 gas outlets of the first adsorption tower (11), the second adsorption tower (12), the third adsorption tower (13), and the fourth adsorption tower (14) are respectively connected to the inlet of the vacuum pump (15) through pipelines provided with a first pressure regulating valve (51), a second pressure regulating valve (52), a third pressure regulating valve (53), and a fourth pressure regulating valve (54).

4. A two-stage pressure swing vacuum adsorption system for biogas purification according to claim 3, characterized in that, The secondary pressure swing adsorption system includes a fifth adsorption tower (21), a sixth adsorption tower (22), a seventh adsorption tower (23), an eighth adsorption tower (24), a third gas storage tank (33), and a fifth gas storage tank (35); The outlet of the second gas storage tank (32) is divided into four branches and is respectively connected to a ninth stop valve (45), a tenth stop valve (46), an eleventh stop valve (47), and a twelfth stop valve (48); the ninth stop valve (45) is connected to the bottom gas inlet of the fifth adsorption tower (21), and the top product gas outlet of the fifth adsorption tower (21) is connected to the fifth gas storage tank (35) through a thirteenth stop valve (65); the tenth stop valve (46) is connected to the bottom gas inlet of the sixth adsorption tower (22), and the top product gas outlet of the sixth adsorption tower (22) is connected to the fifth gas storage tank (35) through a fourteenth stop valve (66); the eleventh stop valve (47) is connected to the bottom gas inlet of the seventh adsorption tower (23), and the top product gas outlet of the seventh adsorption tower (23) is connected to the fifth gas storage tank (35) through a fifteenth stop valve (67); the twelfth stop valve (48) is connected to the bottom gas inlet of the eighth adsorption tower (24), and the top product gas outlet of the eighth adsorption tower (24) is connected to the fifth gas storage tank (35) through a sixteenth stop valve (68); The product gas outlets of the fifth adsorption tower (21) are respectively connected to the product gas outlet of the sixth adsorption tower (22) through a pipeline provided with a seventh pressure balance valve (77), to the product gas outlet of the seventh adsorption tower (23) through a pipeline provided with a tenth pressure balance valve (80), and to the product gas outlet of the eighth adsorption tower (24) through a pipeline provided with an eleventh pressure balance valve (81); the product gas outlet of the sixth adsorption tower (22) is respectively connected to the product gas outlet of the seventh adsorption tower (23) through a pipeline provided with an eighth pressure balance valve (78), and to the product gas outlet of the eighth adsorption tower (24) through a pipeline provided with a twelfth pressure balance valve (82); the product gas outlet of the seventh adsorption tower (23) is connected to the product gas outlet of the eighth adsorption tower (24) through a pipeline provided with a ninth pressure balance valve (79); The bottom second-stage CO2 gas outlets of the fifth adsorption tower (21), the sixth adsorption tower (22), the seventh adsorption tower (23), and the eighth adsorption tower (24) are respectively connected to the third gas storage tank (33) through pipelines provided with a fifth pressure regulating valve (55), a sixth pressure regulating valve (56), a seventh pressure regulating valve (57), and an eighth pressure regulating valve (58).

5. A two-stage pressure swing vacuum adsorption system for biogas purification according to claim 4, characterized in that, The structures of the first adsorption tower (11), the second adsorption tower (12), the third adsorption tower (13), the fourth adsorption tower (14), the fifth adsorption tower (21), the sixth adsorption tower (22), the seventh adsorption tower (23) and the eighth adsorption tower (24) are the same.

6. The two-stage pressure swing vacuum adsorption system for biogas purification according to claim 5, characterized in that, A number of perforated plates (104) and / or wire meshes (108) are installed inside each adsorption tower. The perforated plates (104) are located in the upper part, and the wire meshes (108) are located in the lower part; adsorption materials are placed on both the perforated plates (104) and the wire meshes (108). The perforated plates (104) are arranged at intervals with each other, and the perforated plates (104) and the wire meshes (108) are arranged at intervals with each other. Each perforated plate (104) and wire mesh (108) can completely cover the cross-section of the tower cavity where they are located.

7. A two-stage pressure swing vacuum adsorption system for biogas purification according to claim 5, characterized in that, The top openings of the cylindrical bodies (107) of each adsorption tower are detachably connected to the heads (101) through flanges (109), and gaskets (105) for sealing are installed at the connection points.

8. A two-stage pressure swing vacuum adsorption system for biogas purification according to claim 5, characterized in that, Support angles (102), reinforcing ribs (103) and PTFE gaskets (106) are also provided at the bottoms inside each adsorption tower; a number of the support angles (102) are evenly installed at the bottom of the bed for structural support, and PTFE gaskets (106) for anti-corrosion are provided on the surfaces; a number of the reinforcing ribs (103) are arranged on the inner wall of the tower to enhance the strength of the tower body.

9. A two-stage pressure swing vacuum adsorption system for biogas purification according to claim 5, characterized in that, A number of legs (111) are evenly provided at the bottoms of each adsorption tower; a guard plate (110) is provided at the connection between the top of the leg (111) and the adsorption tower, and the bottom is stably supported on the ground through a leg base (112).

10. A biogas purification method using the two-stage pressure swing vacuum adsorption system for biogas purification according to claim 4, characterized in that, Specifically as follows: S1. The biogas to be purified passes through the desulfurization tower (1) and the water removal tower (2) in sequence, and becomes a CH4 and CO2 mixed gas, and then enters the first-stage pressure swing adsorption system; the first adsorption tower (11), the second adsorption tower (12), the third adsorption tower (13) and the fourth adsorption tower (14) in the first-stage pressure swing adsorption system cycle through S11 to S14 to preliminarily purify the mixed gas. Specifically as follows: S11. Open the first cut-off valve (41) and the fifth cut-off valve (61), the mixed gas enters the first adsorption tower (11) through the first cut-off valve (41) for adsorption, and the obtained first-stage product gas is stored in the fourth gas storage tank (34) through the fifth cut-off valve (61); at the same time, the gases in the second adsorption tower (12) and the fourth adsorption tower (14) are respectively boosted and equalized in pressure by opening the sixth pressure balance valve (76), and the gas in the third adsorption tower (13) is vacuum desorbed by opening the third pressure regulating valve (53); Subsequently, close the sixth pressure balance valve (76) and the third pressure regulating valve (53), open the first pressure balance valve (71), so that the first adsorption tower (11) performs a final pressure boost operation on the second adsorption tower (12) while adsorbing; at the same time, open the seventh cut-off valve (63), so that the first-stage product gas from the fourth gas storage tank (34) purges the bed of the third adsorption tower (13); at the same time, open the fourth pressure regulating valve (54) and the vacuum pump (15) to vacuum desorb the gas in the fourth adsorption tower (14); After the adsorption in the first adsorption tower (11) ends, close the first stop valve (41), the fifth stop valve (61), the seventh stop valve (63) and the first pressure balance valve (71), open the second stop valve (42) and the sixth stop valve (62), and the mixed gas enters the second adsorption tower (12) through the second stop valve (42) for adsorption. The obtained primary product gas is stored in the fourth gas storage tank (34) through the sixth stop valve (62). At the same time, the gases in the first adsorption tower (11) and the third adsorption tower (13) are equalized and pressurized respectively by opening the fourth pressure balance valve (74), and the fourth adsorption tower (14) maintains vacuum desorption. Subsequently, close the fourth pressure balance valve (74), the fourth pressure regulating valve (54) and the vacuum pump (15), open the second pressure balance valve (72), so that the second adsorption tower (12) performs a final pressure boost operation on the third adsorption tower (13) while adsorbing. At the same time, open the eighth stop valve (64), so that the primary product gas from the fourth gas storage tank (34) purges the bed layer of the fourth adsorption tower (14). At the same time, open the first pressure regulating valve (51) and the vacuum pump (15) to perform vacuum desorption on the gas in the first adsorption tower (11). After the adsorption in the second adsorption tower (12) ends, close the second stop valve (42), the sixth stop valve (62), the eighth stop valve (64) and the second pressure balance valve (72), open the third stop valve (43) and the seventh stop valve (63), and the mixed gas enters the third adsorption tower (13) through the third stop valve (43) for adsorption. The obtained primary product gas is stored in the fourth gas storage tank (34) through the eighth stop valve (64). At the same time, the gases in the second adsorption tower (12) and the fourth adsorption tower (14) are equalized and pressurized respectively by opening the sixth pressure balance valve (76), and the first adsorption tower (11) maintains vacuum desorption. Subsequently, close the sixth pressure balance valve (76), the first pressure regulating valve (51) and the vacuum pump (15), open the third pressure balance valve (73), so that the third adsorption tower (13) performs a final pressure boost operation on the fourth adsorption tower (14) while adsorbing. At the same time, open the fifth stop valve (61), so that the primary product gas from the fourth gas storage tank (34) purges the bed layer of the first adsorption tower (11). At the same time, open the second pressure regulating valve (52) and the vacuum pump (15) to perform vacuum desorption on the gas in the second adsorption tower (12). S14. After the adsorption in the third adsorption tower (13) ends, close the third stop valve (43), the seventh stop valve (63), the fifth stop valve (61) and the third pressure balance valve (73), open the fourth stop valve (44) and the eighth stop valve (64), and the mixed gas enters the fourth adsorption tower (14) through the fourth stop valve (44) for adsorption. The obtained primary product gas is stored in the fourth gas storage tank (34) through the eighth stop valve (64); meanwhile, the gases in the first adsorption tower (11) and the third adsorption tower (13) are respectively boosted in pressure and equalized in pressure by opening the fourth pressure balance valve (74), and the second adsorption tower (12) maintains vacuum desorption; Subsequently, close the fourth pressure balance valve (74), the second pressure regulating valve (52) and the vacuum pump (15), open the fifth pressure balance valve (75), and make the fourth adsorption tower (14) perform a final pressure boost operation on the first adsorption tower (11) while adsorbing; meanwhile, open the sixth stop valve (62), and make the primary product gas from the fourth gas storage tank (34) purge the bed layer of the second adsorption tower (12); meanwhile, open the third pressure regulating valve (53) and the vacuum pump (15) to perform vacuum desorption on the gas in the third adsorption tower (13); After the adsorption in the fourth adsorption tower (14) ends, close the fourth stop valve (44), the eighth stop valve (64), the sixth stop valve (62) and the fifth pressure balance valve (75); S2. The mixed gas of CH4 and CO2 preliminarily purified by the first-stage pressure swing adsorption system is stored in the first gas storage tank (31), boosted in pressure by the pressure regulating valve (3) and then enters the second gas storage tank (32), and then enters the second-stage pressure swing adsorption system; the fifth adsorption tower (21), the sixth adsorption tower (22), the seventh adsorption tower (23) and the eighth adsorption tower (24) in the second-stage pressure swing adsorption system cycle through S21 - S24 to perform deep purification on the preliminarily purified mixed gas, specifically as follows: S21. Open the ninth stop valve (45) and the thirteenth stop valve (65), and the mixed gas enters the fifth adsorption tower (21) through the ninth stop valve (45) for adsorption. The obtained product gas CH4 is stored in the fifth gas storage tank (35) through the thirteenth stop valve (65); meanwhile, the gases in the sixth adsorption tower (22) and the eighth adsorption tower (24) are respectively boosted in pressure and equalized in pressure by opening the twelfth pressure balance valve (82), and the gas in the seventh adsorption tower (23) is desorbed by opening the seventh pressure regulating valve (57); Subsequently, the seventh adsorption tower (23) maintains desorption, close the twelfth pressure balance valve (82) and open the seventh pressure balance valve (77), and make the fifth adsorption tower (21) perform a final pressure boost operation on the sixth adsorption tower (22) while adsorbing; meanwhile, open the eighth pressure regulating valve (58) to desorb the gas in the eighth adsorption tower (24) and store it in the third gas storage tank (33); S22. After the adsorption in the fifth adsorption tower (21) ends, close the ninth stop valve (45), the thirteenth stop valve (65) and the seventh pressure balance valve (77), open the tenth stop valve (46) and the fourteenth stop valve (66), and the mixed gas enters the sixth adsorption tower (22) through the tenth stop valve (46) for adsorption. The resulting product gas CH4 is stored in the fifth gas storage tank (35) through the fourteenth stop valve (66); meanwhile, the gases in the fifth adsorption tower (21) and the seventh adsorption tower (23) are respectively equalized and pressurized by opening the tenth pressure balance valve (80), and the eighth adsorption tower (24) remains in desorption. Subsequently, the eighth adsorption tower (24) remains in desorption. Close the tenth pressure balance valve (80) and open the eighth pressure balance valve (78) to enable the sixth adsorption tower (22) to perform a final pressure boost operation on the seventh adsorption tower (23) while adsorbing; meanwhile, open the fifth pressure regulating valve (55) to desorb the gas in the fifth adsorption tower (21) and store it in the third gas storage tank (33). S23. After the adsorption in the sixth adsorption tower (22) ends, close the tenth stop valve (46), the fourteenth stop valve (66) and the eighth pressure balance valve (78), open the eleventh stop valve (47) and the fifteenth stop valve (67), and the mixed gas enters the seventh adsorption tower (23) through the eleventh stop valve (47) for adsorption. The resulting product gas CH4 is stored in the fifth gas storage tank (35) through the fifteenth stop valve (67); meanwhile, the gases in the sixth adsorption tower (22) and the eighth adsorption tower (24) are respectively equalized and pressurized by opening the twelfth pressure balance valve (82), and the fifth adsorption tower (21) remains in desorption. Subsequently, the fifth adsorption tower (21) remains in desorption. Close the twelfth pressure balance valve (82) and open the ninth pressure balance valve (79) to enable the seventh adsorption tower (23) to perform a final pressure boost operation on the eighth adsorption tower (24) while adsorbing; meanwhile, open the sixth pressure regulating valve (56) to desorb the gas in the sixth adsorption tower (22) and store it in the third gas storage tank (33). S24. After the adsorption in the seventh adsorption tower (23) ends, close the eleventh stop valve (47), the fifteenth stop valve (67) and the ninth pressure balance valve (79), open the twelfth stop valve (48) and the sixteenth stop valve (68), and the mixed gas enters the eighth adsorption tower (24) through the twelfth stop valve (48) for adsorption. The resulting product gas CH4 is stored in the fifth gas storage tank (35) through the sixteenth stop valve (68); meanwhile, the gases in the fifth adsorption tower (21) and the seventh adsorption tower (23) are respectively pressurized and equalized by opening the tenth pressure balance valve (80), and the sixth adsorption tower (22) remains in desorption. Subsequently, the sixth adsorption tower (22) remains in desorption, the tenth pressure balance valve (80) is closed, and the eleventh pressure balance valve (81) is opened, so that the eighth adsorption tower (24) performs a final pressure boost operation on the fifth adsorption tower (21) while adsorbing; at the same time, the seventh pressure regulating valve (57) is opened, and the gas in the seventh adsorption tower (23) is desorbed and stored in the third gas storage tank (33). After the adsorption of the eighth adsorption tower (24) ends, the twelfth stop valve (48), the sixteenth stop valve (68), the seventh pressure regulating valve (57), and the eleventh pressure balance valve (81) are closed.

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