Multi-tower vacuum pressure swing adsorption (VPSA) process control method and system therefor

Abstract

A multi-tower vacuum pressure swing adsorption (VPSA) process control method, in which a blower, a vacuum pump and at least three adsorption towers are provided, wherein each tower sequentially undergoes a loop of adsorption, pressure equalization depressurization, evacuation, and pressure equalization repressurization, and gas discharged during pressure equalization depressurization is used by another adsorption tower to implement pressure equalization repressurization. The method comprises: setting the number of adsorption towers to be n, and equally dividing one adsorption cycle into n time periods, wherein n-2 time periods are used for adsorption, one time period is used for adsorption and pressure equalization depressurization, and the other time period is used for evacuation and pressure equalization repressurization; and a vacuum pump performing evacuation and desorption on the plurality of adsorption towers in turn according to this time sequence. The control method has a simple process and a high adsorbent utilization rate.

Description

Control method and system of multi-tower VPSA process TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial pressure swing adsorption gas separation and purification, in particular to a control method of multi-tower VPSA process. BACKGROUND

[0002] VPSA technology is a physical adsorption that uses the selective adsorption characteristics of solid adsorbents for different gas components to obtain high-purity product gas through a variable pressure adsorption process by relying on the molecular force between the adsorbent and the adsorbate molecules. VPSA technology is widely used in the fields of chemical industry, medicine and environmental protection (waste incineration, industrial oxygen-enriched combustion and wastewater treatment, etc.). A VPSA system mainly consists of a blower, a vacuum pump, a program-controlled valve, an adsorption tower and a buffer tank. The working principle is that raw air is pressurized by a blower into an adsorption tower, adsorbed by an adsorbent, and the separated gas is discharged from the top outlet of the adsorption tower, thereby producing product gas with high purity. When the adsorbent is adsorbed to a certain extent and reaches a saturation state, the pressure is balanced by a program-controlled valve, and then a vacuum pump is used to perform vacuum desorption to discharge the previously adsorbed gas, so as to regenerate the adsorbent. The working conditions of the VPSA system change frequently, and the pressure changes in a cycle of tens of seconds from positive pressure adsorption to vacuum desorption, mainly including adsorption, pressure equalization and pressure reduction, vacuum pumping, pressure equalization and pressure increase, and final pressure increase. The current adsorption tower pressure equalization operation is performed by the pressure equalization valve at the top of the tower. During this period, the adsorption tower cannot maintain adsorption, and the utilization rate of the adsorbent is low. Therefore, two or more adsorption towers are usually provided to always maintain some adsorption towers in adsorption, and multiple adsorption towers are alternately repeated to produce oxygen and regenerate, thereby realizing continuous adsorption separation.

[0003] Invention patent CN1175474A discloses a multi-tower negative pressure swing adsorption gas separation method. The working program of the adsorption tower during operation includes five steps of adsorption, pressure equalization and pressure reduction, negative pressure pumping, pressure equalization and pressure increase, and final pressure increase. A negative pressure buffer tank is connected to the desorption gas main pipe to make the vacuum pumping step continuous in the entire process. When working, the number of adsorption towers in the adsorption state is the total number of adsorption towers minus 2. Although this process can improve the utilization rate of the adsorbent to a certain extent, it still needs to be improved.

[0004] The patent CN115770462A discloses a system and method for recovering carbon dioxide from flue gas, which comprises an air inlet pipe, an air outlet pipe, a pressure equalization pipe, a vacuum pipe one, a vacuum pipe two, a vacuum pump one, a vacuum pump two and at least three adsorption towers. The adsorption towers are sequentially circulated in the states of adsorption, first pressure equalization and pressure reduction, second pressure equalization and pressure reduction, third pressure equalization and pressure reduction / vacuum desorption and flushing pressure increase. Although the control method of the process can keep the VPSA device in the process of multiple towers adsorbing at the same time and a single tower being in the process of vacuumizing, thereby improving the utilization efficiency of molecular sieve, the process is complex, the system is complex, the equipment investment is large, and the process is difficult to popularize and apply.

[0005] SUMMARY

[0006] In view of the above technical problems, the present application provides a control method for a multi-tower VPSA pressure swing adsorption process. The control method is simple in program and high in utilization rate of adsorbent.

[0007] In order to achieve the purpose of the application, the technical scheme adopted by the present application is:

[0008] A control method for a multi-tower VPSA pressure swing adsorption process, characterized in that it comprises a blower, a vacuum pump and at least three adsorption towers, and a single adsorption tower sequentially performs circulation of adsorption, pressure equalization and pressure reduction, vacuumizing and pressure equalization and pressure increase, and the gas released during pressure equalization and pressure reduction is used for another adsorption tower to complete pressure equalization and pressure increase.

[0009] Assuming that the number of adsorption towers is n, one adsorption cycle is evenly divided into n time periods, in which n-2 time periods are used for adsorption, one time period is used for adsorption and pressure equalization and pressure reduction, and the other time period is used for vacuumizing and pressure equalization and pressure increase; and the vacuum pump performs vacuumizing and desorption on multiple adsorption towers in turn according to the time sequence.

[0010] The control method of the present application keeps the system in the state of only single-tower vacuumizing in each time period.

[0011] According to the control method for a multi-tower VPSA pressure swing adsorption process of claim 1, the time for each pressure equalization and pressure reduction and pressure increase is 1-5s.

[0012] Preferably, when the adsorption tower is in pressure equalization and pressure increase, the connecting pipeline with the vacuum pump is in an open state. The high pressure difference of the connecting pipeline of the adsorption tower and the vacuum pump is used to quickly and fully flush the adsorption tower, so that the gas pressure in the tower is balanced within a few seconds, the pressure equalization is realized quickly, and the production efficiency is improved.

[0013] Further preferably, the pressure of the adsorption tower after pressure equalization and pressure reduction during oxygen enrichment is-20-10Kpa, and the pressure after pressure equalization and pressure increase is-10--30Kpa.

[0014] Further preferably, the pressure of the adsorption tower after pressure equalization and pressure reduction is -10-0 Kpa, and the pressure after pressure equalization and pressure increase is -10--30 Kpa when the flue gas is separated to recover carbon dioxide.

[0015] The application also provides a system for controlling the multi-tower VPSA pressure swing adsorption process, which comprises an air inlet main pipe, a pressure equalization main pipe, an upper air outlet main pipe, a lower air outlet main pipe, a blower, a vacuum pump and at least three adsorption towers, the top of each adsorption tower is connected to the upper air outlet main pipe through an upper air outlet pipe, the bottom of each adsorption tower is connected to the lower air outlet main pipe through a lower air outlet pipe, the upper air outlet pipe is connected to the pressure equalization main pipe through a pressure equalization pipe, the blower is connected to the air inlet of the air inlet main pipe, the lower air outlet pipe is connected to the air inlet main pipe through an air inlet pipe, and the air outlet main pipe is provided with the vacuum pump; the upper air outlet pipe, the lower air outlet pipe, the pressure equalization pipe and the air inlet pipe are all provided with a program-controlled valve.

[0016] The application has the following advantages:

[0017] 1. The VPSA pressure swing adsorption process control method of the application divides multiple adsorption towers into time periods and performs the cycle of adsorption, pressure equalization and pressure reduction, vacuum pumping and pressure equalization and pressure increase in a rolling manner, and uses one vacuum pump to sequentially and alternately perform vacuum pumping and desorption on multiple adsorption towers in time periods. After the process flow is distributed in time, the vacuum pump and each adsorption tower are alternately and seamlessly connected in vacuum pumping and desorption, the pressure equalization time can be controlled within a few seconds, the entire system is always in the state of multiple towers adsorbing and single tower vacuum pumping, and the molecular sieve utilization efficiency is effectively improved.

[0018] 2. The application connects each adsorption tower through the pressure equalization main pipe and connects each adsorption tower and the vacuum pump through the lower air outlet main pipe, so that adsorption tower one is connected to adsorption tower two that has completed vacuum pumping, and adsorption tower two is connected to the lower air outlet main pipe that is being pumped, the high pressure difference between the adsorption tower and the lower air outlet main pipe is used to quickly and fully flush the adsorption tower, the gas pressure in the adsorption tower after pressure equalization is balanced, the adsorption tower gas pressure of 50 Kpa can be quickly equalized to close to 0 Kpa within a few seconds, the recovery of the remaining gas in adsorption tower one and the impurity flushing of adsorption tower two are quickly achieved, and the production efficiency of the device is improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Fig. 1 is a three-tower VPSA oxygen production process flow chart of Example 4.

[0020] Fig. 2 is a four-tower VPSA oxygen production process flow chart of Example 5.

[0021] Fig. 3 is a five-tower VPSA CO2 recovery process flow chart of Example 6.

[0022] Figure 4 is a process flow diagram of the six-tower VPSA recovery of CO2 of Example 7.

[0023] Figure 5 is a process flow diagram of the boiler flue gas CO2 recovery of Example 8.

[0024] Figure 6 is an air internal circulation flow diagram of the VPSA applied to central air conditioning of Example 9.

[0025] The reference signs are: T1-T8: adsorption tower 1-adsorption tower 8; A1-A4: program-controlled valve A1-program-controlled valve A4; L1: upper exhaust main pipe; L2: equalizing main pipe; L3: air inlet main pipe; L4: lower exhaust main pipe; L5: upper exhaust pipe; L6: lower exhaust pipe; L7: equalizing pipe; L8: air inlet pipe. DETAILED DESCRIPTION

[0026] In order to more clearly and specifically describe the technical scheme of the present application, the present application will be further described by relevant examples. The following examples are only used to specifically illustrate the implementation method of the present application, and do not limit the protection scope of the present application.

[0027] Example 1

[0028] A control method of a multi-tower VPSA pressure swing adsorption process, comprising a blower, a vacuum pump and at least three adsorption towers, a single adsorption tower sequentially performs adsorption, equalizing pressure and pressure reduction, vacuum pumping and equalizing pressure and pressure increase, the gas released during equalizing pressure and pressure reduction is used for another adsorption tower to complete equalizing pressure and pressure increase.

[0029] Assuming that the number of adsorption towers is n, one adsorption cycle is equally divided into n time periods, wherein n-2 time periods are used for adsorption, one time period is used for adsorption and equalizing pressure and pressure reduction, and another time period is used for vacuum pumping and equalizing pressure and pressure increase; the vacuum pump sequentially performs vacuum pumping and desorption on multiple adsorption towers in the time sequence.

[0030] The system maintains a state of only single-tower vacuum pumping in each time period.

[0031] Example 2

[0032] Based on the example 1, the present example is characterized in that:

[0033] The time for each equalizing pressure and pressure increase is 1-5 seconds.

[0034] When the adsorption tower is in equalizing pressure and pressure increase, the connecting pipeline with the vacuum pump is in an open state.

[0035] Example 3

[0036] As shown in Figures 1-4, a system for controlling a multi-tower VPSA pressure swing adsorption process includes an air inlet manifold L3, an equalization manifold L2, an upper exhaust manifold L1, a lower exhaust manifold L4, a blower, a vacuum pump, and at least three adsorption towers, the top of each of the adsorption towers being connected to the upper exhaust manifold L1 through an upper exhaust pipe L5, the bottom of each of the adsorption towers being connected to the lower exhaust manifold L4 through a lower exhaust pipe L6, the upper exhaust pipe L5 being connected to the equalization manifold L2 through an equalization pipe L7, the blower being connected to an air inlet of the air inlet manifold L3, the lower exhaust pipe L6 being connected to the air inlet manifold L3 through an air inlet pipe L8, and the vacuum pump being provided on the air inlet manifold L3; and a programmable valve being provided on each of the upper exhaust pipe L5, the lower exhaust pipe L6, the equalization pipe L7, and the air inlet pipe L8.

[0037] Example 4

[0038] Process control for oxygen production in three adsorption towers

[0039] Operation process of a single adsorption tower:

[0040] a. Adsorption (A): open the programmable valves A1 and A3, and close the programmable valves A2 and A4, air is sent into the adsorption tower for adsorption separation to produce oxygen, and the oxygen-rich gas is discharged from the top of the tower through the upper exhaust pipe L5 into a product tank.

[0041] b. Equalization and pressure reduction (ED): open the programmable valve A2, and close the programmable valves A1, A3, and A4, air supply is stopped, and the remaining gas in the adsorption tower is discharged into the adsorption tower with equalization and pressure increase through the equalization pipe L7.

[0042] c. Adsorbent regeneration (V): open the programmable valve A4, and close the programmable valves A1, A2, and A3, vacuum is started, nitrogen adsorbed by the adsorbent is discharged to the atmosphere through the lower exhaust pipe L6, and the adsorbent is regenerated.

[0043] d. Equalization and pressure increase (ER): open the programmable valves A2 and A4, and close the programmable valves A1 and A3, the remaining gas in the adsorption tower is recovered through the equalization pipe L7, and the pressure difference provided by the lower exhaust manifold L4 is used to achieve rapid equalization within 1-3 seconds.

[0044] After equalization and pressure reduction, the pressure of the adsorption tower is -20-10 Kpa, the pressure for vacuum desorption is -50--30 Kpa, and the pressure after equalization and pressure increase is -10--30 Kpa. After equalization and pressure increase, the programmable valves A1 and A3 are opened, and the programmable valves A2 and A4 are closed, the gas in the product tank is quickly recharged to the adsorption tower, the final charging and pressure increase are achieved, the pressure instantaneously rises to 50 Kpa, and the second round of adsorption is started.

[0045] The single oxygen production cycle is divided into 3 time periods, the first time period is adsorption, the second time period is adsorption and equal pressure drop, and the last time period is vacuum pumping and equal pressure rise; the vacuum pump is used to pump and analyze the 3 adsorption towers in turn according to the time sequence.

[0046] Table 1: Three-tower VPSA process control timing table

[0047] The opening and closing of each program-controlled valve realizes the flow control of Table 1. The VPSA oxygen production process of the three-tower system has two adsorption towers adsorbing simultaneously and one adsorption tower being pumped in each time period. Since the equal pressure time is only 1-3 seconds, the total time of each time period is more than 10 seconds, and the equal pressure almost does not occupy the time in the time period, therefore, the adsorption time of the whole process accounts for nearly 66%, and the adsorbent utilization rate is high.

[0048] Example 5

[0049] Oxygen production flow control of four adsorption towers

[0050] The operation flow of a single adsorption tower is the same as that of Example 4.

[0051] The single oxygen production cycle is divided into 4 time periods, the first two time periods are adsorption, the third time period is adsorption and equal pressure drop, and the last time period is vacuum pumping and equal pressure rise; the vacuum pump is used to pump and analyze the 4 adsorption towers in turn according to the time sequence, and the adsorption time of the whole process accounts for nearly 75%.

[0052] Table 2: Four-tower VPSA process control timing table

[0053] Example 6

[0054] CO2 recovery flow control of five adsorption towers

[0055] Operation flow of a single adsorption tower:

[0056] a. Adsorption (A): Open program-controlled valves A1 and A3, and close program-controlled valves A2 and A4. Send the industrial flue gas into the adsorption tower for CO2 adsorption and separation. The waste gas after adsorption is discharged from the top of the tower through the upper discharge pipe L5.

[0057] b. Equal pressure drop (ED): Open program-controlled valve A2, and close program-controlled valves A1, A3 and A4. Stop the gas inlet, and discharge the remaining gas in the adsorption tower into the adsorption tower for equal pressure rise through the equal pressure pipe L7.

[0058] c. Regeneration of adsorbent (V): open the program-controlled valve A4, close the program-controlled valves A1, A2 and A3, start vacuumizing, and the CO2-rich gas adsorbed by the adsorbent is discharged into the product buffer tank through the lower discharge pipe L6 for further purification.

[0059] d. Equalization and pressure increase (ER): open the program-controlled valves A2 and A4, close the program-controlled valves A1 and A3, and the remaining gas in the adsorption tower under equalization and pressure reduction is recovered through the equalization pipe L7. During the process, the program-controlled valve A4 is opened, and the lower discharge main pipe L4 provides a pressure difference to achieve rapid equalization within 1-5 seconds.

[0060] The pressure of the adsorption tower after equalization and pressure reduction is -10-0 Kpa, the gas in the gap space of the adsorbent of the adsorption tower is discharged during equalization, and carbon dioxide starts to be desorbed in small amounts. The pressure for vacuumizing and desorption is -50--30 Kpa, and the pressure after equalization and pressure increase is -10--30. After equalization and pressure increase, the program-controlled valves A1 and A3 are opened, the program-controlled valves A2 and A4 are closed, the blower sends air to the adsorption tower, and the pressure rapidly rises to 50 Kpa, starting the second round of adsorption cycle.

[0061] The single CO2 recovery process is evenly divided into 5 time periods, the first 3 time periods are adsorption, the 4th time period is adsorption and equalization and pressure reduction, and the last 1 time period is vacuumizing and equalization and pressure increase; the vacuum pump performs vacuumizing and desorption on the 5 adsorption towers in turn according to the time sequence.

[0062] Table 3: Control timing table of five-tower VPSA process

[0063] The flow control of Table 3 is realized by opening and closing of each program-controlled valve. The CO2 recovery process of the five-tower system has 4 adsorption towers adsorbing simultaneously and 1 adsorption tower vacuumizing in each time period. Since the equalization time is only 1-3 seconds, the total time of each time period is more than 10 seconds, which almost does not occupy the time in the time period. Therefore, the adsorption time of the entire process accounts for nearly 80%, and the utilization rate of the adsorbent is high.

[0064] Example 7

[0065] CO2 recovery flow control of six adsorption towers

[0066] The operation flow of a single adsorption tower is the same as that of Example 6.

[0067] The single CO2 recovery process is evenly divided into 6 time periods, the first 4 time periods are adsorption, the 5th time period is adsorption and equalization and pressure reduction, and the last 1 time period is vacuumizing and equalization and pressure increase; the vacuum pump performs vacuumizing and desorption on the 6 adsorption towers in turn according to the time sequence, and the adsorption time of the entire process accounts for 83%.

[0068] Table 4 Six-tower VPSA process control timing table

[0069] Similarly, according to the production size, the number of adsorption towers is selected, and a 7-9 tower VPSA system can be used for large-scale production, and one adsorption tower is always kept in vacuum pumping, and the remaining towers are all in adsorption, and the adsorption time of the nine towers accounts for nearly 90%.

[0070] Example 8

[0071] A large amount of flue gas is generated when a coal (gas) boiler burns, and the flue gas contains 8-10% carbon dioxide. When C02 in the flue gas is separated and recovered, the control process of the application can save a large amount of adsorbent and reduce the construction investment of the engineering device. The process flow chart is shown in Figure 5.

[0072] The flue gas after desulfurization, denitrification and dust removal contains about 8-10% CO2, and when CO2 is recovered, a 9-tower VPSA process is used. The operation process is as follows: first, the flue gas is pressurized to above 10KP and sent to the PSA process, after removing the water in the flue gas, it is sent to the VPSA process for CO2 separation. CO2 is extracted by a vacuum pump and sent to a product buffer tank, and the adsorbent is regenerated. The CO2 gas in the product buffer tank contains a small amount of non-condensable gas, which is sent to a compressor for pressurization and temperature control to liquefy CO2, and the non-condensable gas is discharged. Liquid CO2 is sent to a CO2 storage tank.

[0073] Carbon dioxide capture adsorbents in combustion flue gas: silica gel, activated carbon, molecular sieve (13X, Na-y, SAPO-56, SAPO-35, SAPO-17).

[0074] Example 9

[0075] As shown in Figure 6, the VPSA pressure swing adsorption system of the application can also be applied to the air internal circulation of central air conditioning. The low-temperature air in the room is sent to the VPSA system by an air extractor, and the CO2 gas is separated and discharged by the adsorbent, and the low-temperature air without CO2 is sent back to the room. The low-temperature air without CO2 can also be used as an air source and sent back to the central air conditioner for further refrigeration, which helps to save energy.

[0076] The embodiments only express the specific implementation of the application, which is described in more detail and in more detail, but it cannot be understood as a limitation on the scope of the patent of the application. It should be noted that for ordinary skilled in the art, without departing from the concept of the application, a number of modifications and improvements can be made, which are within the scope of protection of the application.

Claims

1. A method of controlling a multi-column VPSA pressure swing adsorption process, characterized by: The system comprises a blower, a vacuum pump and at least three adsorption towers, each of the adsorption towers is sequentially subjected to adsorption, pressure equalization and pressure reduction, vacuumizing and pressure equalization and pressure increasing, the gas released during the pressure equalization and pressure reduction is used for another adsorption tower to complete the pressure equalization and pressure increasing; The number of the adsorption towers is n, one adsorption cycle is equally divided into n time periods, n-2 time periods are used for adsorption, one time period is used for adsorption and pressure equalization and pressure reduction, and another time period is used for vacuumizing and pressure equalization and pressure increasing; the vacuum pump is used to vacuumize and resolve the adsorption towers in turn according to the time sequence.

2. The method of claim 1, wherein: The time for each pressure equalization and pressure reduction and pressure equalization and pressure increasing is 1-5s.

3. The method of claim 2, wherein: When the adsorption tower is subjected to pressure equalization and pressure increasing, the connecting pipeline with the vacuum pump is in an open state.

4. The method of claim 3, wherein: The pressure of the adsorption tower after the pressure equalization and pressure reduction during the oxygen enrichment is-20-10Kpa, and the pressure after the pressure equalization and pressure increasing is-10--30Kpa.

5. The method of claim 3, wherein the method further comprises: determining a pressure differential between the first and second towers; and adjusting the pressure differential between the first and second towers. The pressure of the adsorption tower after the pressure equalization and pressure reduction during the flue gas separation and carbon dioxide recovery is-10-0Kpa, and the pressure after the pressure equalization and pressure increasing is-10--30Kpa.

6. A system for implementing the control method of the multi-column VPSA process according to any one of claims 1 to 5, characterized in that: The system comprises an air inlet main pipe, a pressure equalization main pipe, an upper air outlet main pipe, a lower air outlet main pipe, a blower, a vacuum pump and at least three adsorption towers, the top of each of the adsorption towers is connected to the upper air outlet main pipe through an upper air outlet pipe, the bottom of each of the adsorption towers is connected to the lower air outlet main pipe through a lower air outlet pipe, the upper air outlet pipe is connected to the pressure equalization main pipe through a pressure equalization pipe, the blower is connected to the air inlet of the air inlet main pipe, the lower air outlet pipe is connected to the air inlet main pipe through an air inlet pipe, and the vacuum pump is arranged on the air outlet pipe; the upper air outlet pipe, the lower air outlet pipe, the pressure equalization pipe and the air inlet pipe are all provided with a program-controlled valve.

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