A two-column pressure swing adsorption apparatus and displacement process

Abstract

The application discloses a two-tower series connection pressure swing adsorption device and a displacement process. While ensuring that the product gas quality of difficult-to-adsorb components reaches the quality requirement of high-purity gas, the device can only adopt a first-stage pressure swing adsorption device, so that the yield of the product gas of the difficult-to-adsorb components reaches or exceeds the yield of the product gas of the difficult-to-adsorb components obtained by using the commonly-used second-stage or more-stage pressure swing adsorption device, and the product gas of easy-to-adsorb components with high purity and high yield can be obtained.

Description

Technical Field

[0001] This invention relates to pressure swing adsorption (PSA) gas separation technology, specifically to a two-tower series PSA device and a displacement process. Background Technology

[0002] Pressure Swing Adsorption (PSA) technology has been used in gas separation and purification for over seventy years, and is widely applied in various industries requiring gas separation. Examples include PSA for nitrogen production (separating nitrogen from air), PSA for oxygen production (separating oxygen from air), and PSA for hydrogen production (separating and purifying hydrogen from refinery gas). PSA technology utilizes PSA units. Currently, most PSA units in use, when in adsorption mode, involve the feed gas passing through only one adsorption tower from its entry into the adsorption tower to the acquisition of the target product gas. Additionally, some systems employ multi-stage PSA units. However, multi-stage PSA units are actually two or more PSA units connected in series. An intermediate product gas is obtained through a pre-stage PSA unit, and the target product gas is obtained through a final stage PSA unit. Therefore, in multi-stage PSA units, the feed gas also actually passes through only one adsorption tower.

[0003] Chinese invention patent CN00113035.8 discloses a pressure swing adsorption (PSA) process. This process uses multiple adsorption towers connected in series to maintain a constant amount of adsorbent flowing through the feed gas, while reducing the total amount of adsorbent, resulting in smaller equipment size and lower operating energy consumption. The adsorption process consists of two or more stages, with the direction of the adsorbed gas flow changing back and forth according to a specific pattern. Furthermore, when the depressurized effluent from the adsorption tower flows back into the tower, the distribution of easily adsorbed components within the tower becomes more rational. In this process, the adsorption towers are connected in series by connecting the outlet of the first tower to the outlet of the second tower, the inlet of the second tower to the inlet of the third tower, and the outlet of the third tower to the outlet of the fourth tower, and so on. In addition to series connections, adsorption towers in the adsorption state may also be connected in parallel. Each tower experiences multiple adsorption states, which are continuous. The gas flow direction within the tower needs to be reversed at different adsorption stages. In this method, when the product gas is a difficult-to-adsorb component, the purity of the product gas varies and it is difficult to guarantee a high purity. Furthermore, the product gas flow is discontinuous. In this patent, the adsorbent in the adsorption tower is already saturated or nearly saturated before the pressure is reduced. During the pressure reduction, the gas in the adsorption tower is first discharged into multiple empty tanks, and then pressure is equalized with other adsorption towers. When the gas is discharged into the empty tanks, a large amount of easily adsorbed components will desorb from the adsorbent and be discharged into the empty tanks. When pressure is equalized, a large amount of components discharged into the pressure equalization and boosting adsorption tower are easily adsorbed gases. As a result, the purity of the product gas containing the difficult-to-adsorb component cannot meet the requirements for high-purity gas quality.

[0004] Chinese invention patent CN103695063A discloses a method for concentrating low-concentration methane gas. This method involves concentrating the low-concentration methane gas using a pressure swing adsorption (PSA) process. N (N≥3) adsorption towers are used for adsorption, each containing adsorbent. Within one adsorption cycle, N adsorption stages are performed, with each tower undergoing N-1 series adsorption cycles. After the N towers in series are pressurized in each adsorption stage, the towers that have undergone N-1 adsorption cycles are flushed and replaced, then vacuumed for desorption. The remaining N-1 towers are then pressurized in reverse to the adsorption pressure and undergo adsorption again. This cycle completes one adsorption cycle. In this patent, the adsorption towers are connected end-to-end, and the number of towers simultaneously in series adsorption is the total number of towers minus one. This patent targets easily adsorbed components as the product gas, which can significantly increase the content of these components. Even with low purity of the difficult-to-adsorb components, the easily adsorbed components in the target product can achieve a high yield. However, to ensure high purity of the difficult-to-adsorb components, the yield of the easily adsorbed components in the target product gas will inevitably decrease. The process technology in this patent results in discontinuous gas flows for the easily and difficult-to-adsorbed components, which may cause pressure fluctuations between them. When pressure equalization and counter-pressurization are performed between adsorption towers, the feed gas does not enter any of the adsorption towers, leading to a buildup of feed gas pressure. Furthermore, this patent only allows for one pressure equalization operation and cannot significantly improve the yield of the difficult-to-adsorbed components.

[0005] Chinese invention patent CN102423602A discloses a series adsorption gas separation process that ensures the product gas discharged from the adsorption towers maintains a consistently high concentration. It overcomes the shortcomings of existing technologies where product gas is discharged after only one adsorption tower, resulting in low purity. This process uses at least six adsorption towers working together in a cyclic adsorption process. Simultaneously, each adsorption tower completes one step. The raw material gas enters the first adsorption tower sequentially through a valve, where impurities are adsorbed by the adsorbent to obtain intermediate gas. This intermediate gas then flows out through a valve and into the second adsorption tower, where impurities are adsorbed by the adsorbent to obtain product gas. The product gas then flows out through a valve and enters the next stage. The raw material gas undergoes one adsorption step to obtain intermediate gas, which is then adsorbed again to obtain product gas, resulting in a high purity of the product gas. This patent uses two adsorption towers in series to adsorb easily adsorbed components from the raw material gas, obtaining a product of high purity but difficult-to-adsorb components. However, this technical solution cannot simultaneously guarantee high purity of both easily and difficult-to-adsorb components while achieving extremely high yields for both. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a two-tower series pressure swing adsorption (PSA) device and a displacement process. While ensuring that the product gas quality of the difficult-to-adsorb components meets the requirements for high-purity gas, it can use only a single-stage PSA device to achieve a product gas yield of the difficult-to-adsorb components that meets or exceeds the product gas yield of commonly used two-stage or higher PSA devices in the prior art. At the same time, it can obtain a high-purity, high-yield product gas of easily adsorbed components.

[0007] The objective of this invention is achieved through the following technical solution: a two-tower series pressure swing adsorption device and a displacement process, comprising at least 7 adsorption towers and corresponding valves and fittings, wherein the adsorption towers are connected in series and parallel.

[0008] Each adsorption tower is controlled by 12 valves to switch between various states.

[0009] The lower interface of the adsorption tower is connected to 7 valves, and the upper interface is connected to 5 valves.

[0010] Preferably, the seven valves connected to the lower interface of the adsorption tower include:

[0011] The gas from the outlet of the secondary adsorption tower enters the primary adsorption tower through the primary adsorption inlet valve. The primary adsorption inlet valves of each adsorption tower are connected in parallel through adsorption pipelines.

[0012] The secondary adsorption inlet valve allows the raw gas to enter the secondary adsorption tower. The secondary adsorption inlet valves of each adsorption tower are connected in parallel through the raw gas pipeline.

[0013] The gas from the outlet of the displacement adsorber enters the displacement adsorber through the displacement gas adsorption inlet valve. The displacement gas adsorption inlet valves of each adsorption tower are connected in parallel through displacement pipelines.

[0014] The displacement gas inlet valve allows the displacement gas to enter the displacement adsorber. The displacement gas inlet valves of each adsorption tower are connected in parallel through the displacement gas pipeline.

[0015] The reverse exhaust valve is used to discharge the gas inside the adsorption tower when the adsorption tower is in the reverse depressurization process. The reverse exhaust valves of each adsorption tower are connected in parallel through the reverse pipeline.

[0016] When the adsorption tower is in a vacuum and depressurization state, the gas inside the adsorption tower is discharged from the adsorption tower through the extraction and exhaust valve. The extraction and exhaust valves of each adsorption tower are connected in parallel through extraction pipelines.

[0017] The gas from the outlet of the secondary pressure equalization and depressurization adsorption tower enters the primary pressure equalization and depressurization adsorption tower through the primary pressure equalization and depressurization inlet valve. The displacement gas from the upper interface of the displacement gas adsorption tower can enter the displacement gas boosting adsorption tower through the primary pressure equalization and depressurization inlet valve. The primary pressure equalization and depressurization inlet valves of each adsorption tower are connected in parallel through the pressure equalization pipeline.

[0018] Preferably, the five valves connected to the upper interface of the adsorption tower include:

[0019] The gas in the secondary adsorption tower is discharged into the primary adsorption tower through the secondary adsorption exhaust valve. The secondary adsorption tower and the primary adsorption tower are connected in series through the secondary adsorption exhaust valve and the primary adsorption inlet valve. The secondary adsorption exhaust valves of each adsorption tower are connected in parallel through adsorption pipelines.

[0020] The gas inside the primary adsorption tower is discharged from the adsorption tower through the primary adsorption exhaust valve and discharged into the difficult-to-adsorb component product gas pipeline as the difficult-to-adsorb component product gas. The primary adsorption exhaust valves of each adsorption tower are connected in parallel through the difficult-to-adsorb component product gas pipeline.

[0021] The secondary equalization and depressurization exhaust valve allows gas in the secondary equalization and depressurization adsorption tower to be discharged into the primary equalization and depressurization adsorption tower. The secondary equalization and depressurization adsorption tower and the primary equalization and depressurization adsorption tower are connected in series through the secondary equalization and depressurization exhaust valve and the primary equalization and depressurization inlet valve. The replacement gas from the upper interface of the replacement gas adsorption tower can enter the replacement gas boosting adsorption tower through the secondary equalization and depressurization exhaust valve. The secondary equalization and depressurization exhaust valves of each adsorption tower are connected in parallel through equalization pipelines.

[0022] The gas in the primary pressure equalization and depressurization adsorption tower is discharged into the pressure equalization and boosting adsorption tower through the primary pressure equalization and depressurization vent valve; the primary pressure equalization and depressurization vent valve also serves as the displacement gas adsorption vent valve, through which the gas in the displacement gas adsorption tower is discharged from the displacement gas adsorption tower; the displacement adsorption tower, displacement gas adsorption tower, and displacement gas boosting adsorption tower are connected in series during displacement state through the primary pressure equalization and depressurization vent valve, displacement pipeline, displacement gas adsorption inlet valve, and secondary pressure equalization and depressurization vent valve (or primary adsorption inlet valve); the primary pressure equalization and depressurization vent valves of each adsorption tower are connected in parallel through displacement pipelines;

[0023] The reverse riser valve allows the reverse pressurized gas to enter the adsorption tower that requires reverse pressurization. The reverse riser valves of each adsorption tower are connected in parallel through the reverse riser gas pipeline.

[0024] In addition to providing a two-tower series pressure swing adsorption (PSA) device, this invention further provides a two-tower series PSA displacement process, which is achieved by using the aforementioned two-tower series PSA device:

[0025] In a two-tower series pressure swing adsorption device, when the pressure swing adsorption process is used to separate and purify the gas displacement state, three adsorption towers are connected in series to complete the displacement process.

[0026] In the displacement state, two of the three adsorption towers are connected in series, one end to the other. The adsorption tower upstream in the series connection is the first adsorption tower, and the adsorption tower downstream is the second adsorption tower. The upper interface of the second adsorption tower is then connected to the upper or lower interface of the third adsorption tower, thus realizing the series connection of the three adsorption towers. The series connection method of the first and second adsorption towers is the same as the series connection method when these two adsorption towers are in the adsorption state and the pressure equalization and depressurization state.

[0027] In the displacement state, the first adsorption tower is the adsorption tower being displaced, the second adsorption tower receives the gas components flowing from the first adsorption tower, and the third adsorption tower receives the gas components flowing from the second adsorption tower.

[0028] In the adsorption state, the two adsorption towers are connected in series, end to end. The feed gas enters the first adsorption tower from the lower inlet. The adsorption tower is filled with one or more adsorbents that have a good adsorption effect on easily adsorbed components. For example, carbon molecular sieves are used in pressure swing adsorption nitrogen generators, oxygen molecular sieves are used in pressure swing adsorption oxygen generators, and activated carbon or silica gel with a good adsorption effect on carbon dioxide, or 5A molecular sieve with a good adsorption effect on carbon monoxide, etc., are used in pressure swing adsorption hydrogen generators. After the feed gas comes into contact with the adsorbent bed, the easily adsorbed components are adsorbed by the corresponding adsorbents and removed from the feed gas. The gas is separated from the feed gas. Most of the difficult-to-adsorb components and a small portion of the easily adsorbable components flow out of the first adsorption tower from the upper interface. This adsorption tower is in a secondary adsorption state. The gas flowing out of the adsorption tower in the secondary adsorption state continues to enter the adsorption tower from the lower interface of the second adsorption tower in the adsorption state. Most of the easily adsorbable components contained in the gas are adsorbed by the adsorbent in the adsorption tower. Most of the difficult-to-adsorb components and trace amounts of easily adsorbable components flow out of the adsorption tower from the upper interface of the second adsorption tower. The product gas containing the difficult-to-adsorbable components that meets the quality requirements of high-purity gas is obtained. This adsorption tower is in a primary adsorption state.

[0029] When the adsorption tower is in the adsorption state, the adsorbent inside the tower will exhibit three state zones: the adsorbent bed that has reached saturation adsorption capacity is the saturation zone; the adsorbent bed that has adsorbed some easily adsorbed components but has not yet reached saturation adsorption capacity is the mass transfer zone; and the adsorbent bed that has not yet adsorbed easily adsorbed components is the blank zone. The three state zones are arranged sequentially along the airflow direction. As the adsorption time increases, the three state zones gradually move towards the upper interface of the adsorption tower.

[0030] Within one cycle, each adsorption tower undergoes two adsorption states. The adsorption tower where the feed gas enters directly is in the secondary adsorption state, while the adsorption tower from which the gas exits in the secondary adsorption state enters is in the primary adsorption state. Correspondingly, within one cycle, each adsorption tower undergoes two pressure equalization and depressurization states. Each regenerated adsorption tower first enters the primary adsorption state and then the secondary adsorption state. The pressure equalization and depressurization state after the primary adsorption state is called the primary pressure equalization and depressurization state, and the state after the secondary adsorption state is called the secondary pressure equalization and depressurization state. Before entering the primary adsorption state after the secondary pressure equalization and depressurization state, it must go through three pressure increase states: pressure equalization and pressure increase by replacement gas and one reverse pressure increase. Before entering the secondary adsorption state after the primary pressure equalization and depressurization state, it must go through two reverse pressure increases and one pressure increase state.

[0031] When the mass transfer zone has moved out of the adsorption tower in the secondary adsorption state and into the adsorption tower in the primary adsorption state, the current adsorption state of these two adsorption towers ends. At this time, the mass transfer zone is located at the bottom of the adsorption tower in the primary adsorption state, closest to the lower interface. There is still a large amount of adsorbent in the upper part of the mass transfer zone, which is a blank area. Therefore, it can be ensured that the quality of the product gas of the difficult-to-adsorb component flowing out of the adsorption tower in the primary adsorption state meets the quality requirements of high-purity gas. When the adsorption state ends, the adsorbent bed in the adsorption tower into which the raw gas directly enters has become a saturated zone and no longer has the adsorption function. The gas composition remaining in the voids of the adsorption tower is the same as that of the raw gas and still contains a large amount of difficult-to-adsorb components. If these gases are directly discharged from the device, a large amount of difficult-to-adsorb components will be discharged, and the yield of difficult-to-adsorb components will be greatly reduced. In order to recover this part of the difficult-to-adsorb components, a pressure equalization process is set after the adsorption state ends.

[0032] During the pressure equalization and depressurization phase, the two adsorption towers that were originally in the adsorption phase continue to be connected in series, as they were in the adsorption phase. The difficult-to-adsorb components in the second adsorption tower flow out of the adsorption tower from the upper interface and flow directly into the pressure equalization and depressurization adsorption tower from the upper interface of the adsorption tower in the pressure equalization and depressurization phase. The gas in the voids of the first adsorption tower and the gas desorbed from the adsorbent during the pressure equalization and depressurization phase flow out of the adsorption tower from the upper interface of the first adsorption tower and then flow into the second adsorption tower from the lower interface. The easily adsorbed components are adsorbed by the adsorbent, and the difficult-to-adsorb components flow out of the adsorption tower from the upper interface of the second adsorption tower and flow into the pressure equalization and depressurization adsorption tower from the upper interface of the adsorption tower in the pressure equalization and depressurization phase.

[0033] During pressure equalization, gas from the high-pressure adsorption tower will flow into the low-pressure adsorption tower, causing the pressure in the high-pressure adsorption tower to decrease (this is called pressure equalization depressurization), and the pressure in the low-pressure adsorption tower to increase (this is called pressure equalization boosting). During pressure equalization depressurization, easily adsorbed components adsorbed on the adsorbent will gradually desorb from the adsorbent as the pressure decreases. The desorbed easily adsorbed components will push and follow the gas in the adsorption tower voids towards the upper interface of the adsorption tower. Since the adsorbent in the adsorption tower that was originally in a secondary adsorption state no longer has adsorption capacity, the desorbed easily adsorbed components will flow out of the adsorption tower along with the original gas in the adsorption tower voids. If the adsorption tower that has just finished its secondary adsorption state is used directly to equalize the pressure of the adsorption tower that needs pressure equalization boosting, a large amount of easily adsorbed components will flow into the adsorption tower that needs pressure equalization boosting, which will have a significant impact on the purity of the difficult-to-adsorb components in the product gas.

[0034] During the pressure equalization and depressurization process, the easily adsorbed components entering the second adsorption tower will be adsorbed by the adsorbent in the blank zone. The majority of the gas flowing out from the upper interface of the second adsorption tower consists of difficult-to-adsorb components, along with trace amounts of easily adsorbed components. The quality of this latter part of the gas is equivalent to that of the difficult-to-adsorbed component product gas. This portion of gas flows into the adsorption tower under pressure equalization and depressurization conditions and will not affect the quality of the difficult-to-adsorbed component product gas, thus ensuring that the quality of the difficult-to-adsorbed component product gas meets the requirements for high-purity gas. Simultaneously, since the adsorbent in the first adsorption tower has no adsorption capacity at the end of the adsorption process, all the easily adsorbed components desorbed from the adsorbent in the first adsorption tower will flow into the second adsorption tower. During this process, the easily adsorbed components will push the gas components originally remaining in the voids of the first adsorption tower into the second adsorption tower. At the end of the pressure equalization and depressurization process, the majority of the gas remaining in the voids of the first adsorption tower is easily adsorbed, thus ensuring a high yield of the difficult-to-adsorbed component product gas.

[0035] In the displacement state, the two adsorption towers, originally in the pressure equalization and depressurization state, continue in series, connected end-to-end, as in the pressure equalization and depressurization state. The displacement gas enters the first adsorption tower from its lower inlet. The easily adsorbed components and a small amount of difficult-to-adsorbed components, originally remaining in the adsorption tower's voids, are pushed out of the adsorption tower from bottom to top by the displacement gas from its upper inlet, placing the first adsorption tower in the displacement state. The pushed-out gas then enters the second adsorption tower from its lower inlet. The easily adsorbed components are adsorbed by the adsorbent mass transfer zone and the blank zone, while the difficult-to-adsorbed components and trace amounts of easily adsorbed components flow out of the second adsorption tower from its upper inlet, placing the second adsorption tower in the displacement gas adsorption state. The gas flowing out of the second adsorption tower then flows into the third adsorption tower from either its upper or lower inlet, placing the third adsorption tower in the displacement gas pressurization state. The gas quality inside is equivalent to that of the difficult-to-adsorb component product gas, and will not affect the quality of the difficult-to-adsorb component product gas, thus ensuring that the quality of the difficult-to-adsorb component product gas meets the requirements of high-purity gas. The displacement gas pushes the small amount of difficult-to-adsorb components remaining in the voids of the first adsorption tower after the pressure equalization and depressurization process into the second adsorption tower. After the displacement state, what remains in the voids of the first adsorption tower is the high-purity easily adsorbed component. This part of the easily adsorbed component, as well as the easily adsorbed component desorbed from the adsorbent during the reverse depressurization and vacuum depressurization process, is pressurized by the compressor and used as the easily adsorbed component product gas output device. Since only a small amount of difficult-to-adsorbed component remains in the voids of the first adsorption tower after the pressure equalization and depressurization process, only a small amount of displacement gas is needed to push the difficult-to-adsorbed component out of the first adsorption tower. The pressurization of the displacement gas only consumes a small amount of energy and will not cause a significant increase in the energy consumption of the entire system.

[0036] In the displacement state, adsorption state, and pressure equalization and depressurization state, the airflow direction in the two adsorption towers connected end to end is completely consistent.

[0037] Preferably, the product gas containing easily adsorbed components is used as the replacement gas, and the resulting flow of product gas containing difficult-to-adsorb components is continuous.

[0038] After each adsorption tower completes the desorption and pressurization phases within one cycle, it sequentially goes through the following functional states: primary adsorption, primary pressure equalization and depressurization, displacement gas adsorption, secondary reverse pressurization, secondary adsorption, secondary pressure equalization and depressurization, displacement, reverse pressurization, vacuuming, displacement gas pressurization, pressure equalization and pressurization, and primary reverse pressurization; then it enters the primary adsorption phase again.

[0039] The above states cycle repeatedly to ensure continuous production. The easily adsorbed components discharged from the adsorption tower during reverse depressurization and vacuuming are the easily adsorbed component product gas. Apart from these two processes, there is no easily adsorbed component discharge device during the entire operation, thus ensuring a near 100% yield of the easily adsorbed component product gas.

[0040] Compared with the prior art, the present invention has the following advantages:

[0041] In existing technologies, if the easily adsorbed component is a medium with a small adsorption capacity, in order to obtain a higher yield of the difficult-to-adsorb component while ensuring that the purity of the difficult-to-adsorb component meets the usage requirements, some operating conditions often require the use of two or three stages of pressure swing adsorption devices in series, which also increases the number of adsorption towers. The present invention uses a single pressure swing adsorption displacement device, which sets up a multi-step pressure equalization process and adopts a method of simultaneous adsorption by two adsorption towers. While ensuring the quality of the product gas, it significantly improves the yield, reduces energy consumption and equipment investment, and can simultaneously obtain a high-purity, high-yield product gas of the easily adsorbed component.

[0042] For pressure swing adsorption (PSA) hydrogen extraction devices, under the premise that the purity of the product hydrogen (≥99.999%) and the impurity content (N2≤5ppm, CO≤1ppm, CO2≤1ppm, CH4≤1ppm, H2O≤3ppm) meet the requirements for high-purity hydrogen in GB / T3634.2-2011, the product hydrogen yield is significantly higher than that of existing single-stage PSA hydrogen extraction devices. For example, for methanol cracking gas to purify hydrogen, the existing two-stage PSA devices have a maximum product hydrogen yield of about 94%, while the method in this invention can achieve a product hydrogen yield of over 98.5%. The product hydrogen yield value is obtained as follows: the purity of methanol cracking gas and product hydrogen is analyzed by gas chromatography, and the production of methanol cracking gas and product hydrogen is measured by the volumetric method in Appendix A of GB / T19773-2005. The product hydrogen yield value is then obtained by dividing the product hydrogen production by the amount of hydrogen in the methanol cracking gas. For pressure swing adsorption (PSA) oxygen and nitrogen generators, provided that the oxygen purity (≥90%) and nitrogen purity (≥99.5%) meet the basic parameter requirements in JB / T6427-2015, the unit power consumption for oxygen production and the unit power consumption for nitrogen production are significantly lower than the minimum requirements in JB / T6427-2015; for example, for a product oxygen pressure of 0.2 MPa and a gas production rate of 200 m³ / h... 3 For a PSA oxygen generator with a capacity of [number] m³ / h, the standard specifies a unit oxygen production power consumption of ≤1.0 kW·h / m³. 3 Using the method of this invention, the unit oxygen production power consumption is ≤0.6kW·h / m³. 3 For a product with an oxygen pressure of 0.005 MPa and a gas production rate of 8000 m³ / h... 3 For an axial flow VPSA oxygen generator with a capacity of [number] m³ / h, the minimum power consumption per unit oxygen production in the standard is 0.35 kW·h / m³. 3 Using the method of this invention, the unit oxygen production power consumption is ≤0.25kW·h / m³. 3 For a gas production rate of 3000m³ 3 For a PSA nitrogen generator with a capacity of [number] m³ / h, the standard specifies a unit nitrogen production power consumption of ≤0.43 kW·h / m³. 3Using the method of this invention, the unit nitrogen production power consumption is ≤0.29kW·h / m³. 3 The above unit oxygen production power consumption and unit nitrogen production power consumption values ​​were obtained by measurement and calculation in accordance with the provisions of JB / T6427.

[0043] In the prior art, some pressure swing adsorption displacement devices with relatively high adsorption pressure often require a large number of pressure equalization steps and a corresponding increase in the number of adsorption towers in order to ensure the yield of difficult-to-adsorb components. By adopting the two-tower series pressure swing adsorption device and displacement process provided by the present invention, the number of adsorption towers can be reduced while improving the yield of difficult-to-adsorb component product gas, thereby reducing equipment investment; at the same time, high-purity and high-yield product gas of easily adsorbed components can be obtained. Attached Figure Description

[0044] Figure 1 A schematic diagram of a two-tower series pressure swing adsorption device according to the present invention;

[0045] Figure 2 This is a timing diagram of the two-tower series pressure swing adsorption displacement process in an embodiment of the present invention. Detailed Implementation

[0046] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0047] like Figure 1 As shown, the technical solution of the present invention provides a two-tower series pressure swing adsorption device and a displacement process, including at least 7 adsorption towers and corresponding valves and fittings, wherein the adsorption towers are connected in series and parallel.

[0048] Each adsorption tower is controlled by 12 valves to switch between various states.

[0049] The 12 valves are numbered 1-12. The corresponding adsorption tower code is appended before the number 1-12 to form the valve's complete tag number, such as A1, A2, ..., A12, B1, B2, ..., B12. Valves with the same number have the same function, and their connection methods and functions are as follows:

[0050] There are 7 valves connected to the lower interface of the adsorption tower, namely:

[0051] Gas from the outlet of the secondary adsorption tower enters the primary adsorption tower through the primary adsorption inlet valves A6, B6, ..., G6. The primary adsorption inlet valves of each adsorption tower are connected in parallel through adsorption pipelines.

[0052] Secondary adsorption inlet valves A1, B1, ..., G1 allow the raw material gas to enter the secondary adsorption tower. The secondary adsorption inlet valves of each adsorption tower are connected in parallel through the raw material gas pipeline.

[0053] Displacement gas adsorption inlet valves A4, B4, ..., G4 allow gas from the outlet of the displacement adsorber to enter the displacement adsorber. The displacement gas adsorption inlet valves of each adsorption tower are connected in parallel through displacement pipelines.

[0054] Replacement gas inlet valves A2, B2, ..., G2, through which replacement gas enters the replacement adsorber. The replacement gas inlet valves of each adsorption tower are connected in parallel through replacement gas pipelines.

[0055] The reverse exhaust valves A3, B3, ..., G3 are used to discharge the gas inside the adsorption tower during the reverse depressurization process. The reverse exhaust valves of each adsorption tower are connected in parallel through the reverse pipeline.

[0056] The gas inside the adsorption tower is discharged through the extraction and exhaust valves A12, B12, ..., G12 when the adsorption tower is in a vacuum and pressure reduction state. The extraction and exhaust valves of each adsorption tower are connected in parallel through extraction pipelines.

[0057] The primary equalization and depressurization inlet valves A5, B5, ..., G5 allow gas from the outlet of the secondary equalization and depressurization adsorption tower to enter the primary equalization and depressurization adsorption tower. The replacement gas from the upper interface of the replacement gas adsorption tower can enter the replacement gas boosting adsorption tower through the primary equalization and depressurization inlet valves. The primary equalization and depressurization inlet valves of each adsorption tower are connected in parallel through equalization pipelines.

[0058] There are five valves connected to the upper interface of the adsorption tower, namely:

[0059] Secondary adsorption exhaust valves A7, B7, ..., G7 allow gas in the secondary adsorption tower to be discharged into the primary adsorption tower. The secondary adsorption tower and the primary adsorption tower are connected in series through secondary adsorption exhaust valves and primary adsorption inlet valves. The secondary adsorption exhaust valves of each adsorption tower are connected in parallel through adsorption pipelines.

[0060] Primary adsorption exhaust valves A11, B11, ..., G11 allow the gas inside the primary adsorption tower to be discharged from the adsorption tower as the difficult-to-adsorb component product gas and discharged into the difficult-to-adsorb component product gas pipeline. The primary adsorption exhaust valves of each adsorption tower are connected in parallel through the difficult-to-adsorb component product gas pipeline.

[0061] Secondary equalization and depressurization exhaust valves A8, B8, ..., G8 allow gas in the secondary equalization and depressurization adsorption tower to be discharged into the primary equalization and depressurization adsorption tower. The secondary equalization and depressurization adsorption tower and the primary equalization and depressurization adsorption tower are connected in series through secondary equalization and depressurization exhaust valves and primary equalization and depressurization inlet valves. Replacement gas from the upper interface of the replacement gas adsorption tower can enter the replacement gas boosting adsorption tower through secondary equalization and depressurization exhaust valves. The secondary equalization and depressurization exhaust valves of each adsorption tower are connected in parallel through equalization pipelines.

[0062] The primary equalization and depressurization exhaust valves A9, B9, ..., G9 discharge the gas in the primary equalization and depressurization adsorption tower into the equalization and pressurization adsorption tower. These primary equalization and depressurization exhaust valves also function as exhaust valves for the displacement gas adsorption, discharging the gas from the displacement gas adsorption tower. The displacement adsorption tower, displacement gas adsorption tower, and displacement gas pressurization adsorption tower are connected in series during displacement conditions via primary equalization and depressurization exhaust valves, displacement pipelines, displacement gas adsorption inlet valves, and secondary equalization and depressurization exhaust valves (or primary adsorption inlet valves). The primary equalization and depressurization exhaust valves of each adsorption tower are connected in parallel via displacement pipelines.

[0063] Reverse riser valves A10, B10, ..., G10 allow reverse pressurized gas to enter the adsorption tower requiring reverse pressurization. The reverse riser valves of each adsorption tower are connected in parallel through reverse gas pipelines.

[0064] In addition to providing a two-tower series pressure swing adsorption device, the present invention further provides a displacement process based on the above device, the specific method of which is as follows:

[0065] Taking a 7-tower tower as an example, such as Figure 2 As shown, a cycle can be divided into seven sections and 21 steps. The adsorption towers simultaneously in the adsorption state are identical in each section. Each section contains three steps, and the functional states achieved by different adsorption towers in these three steps are different. All the functional states achieved by the seven adsorption towers in these three steps constitute all the functional states experienced by an adsorption tower in one cycle. The following description, using the first section (steps 1-3) as an example, illustrates the correspondence between different functional states and valves / pipelines.

[0066] Step 1: Adsorption tower A, which has completed its second reverse-up state, and adsorption tower C, which has completed its first reverse-up state, simultaneously enter the adsorption state. Valves A1, A7, C6, and C11 are opened. The raw material gas enters adsorption tower A through valve A1 from the lower port of the first adsorption tower (adsorption tower A). Adsorption tower A enters the second adsorption state, where easily adsorbed components are adsorbed by the adsorbent. Difficult-to-adsorb components (containing trace amounts or small amounts of easily adsorbed components) flow out of adsorption tower A from the upper port of the first adsorption tower and enter adsorption tower C through valve A7, the adsorption pipeline, and valve C6 from the lower port of the second adsorption tower (adsorption tower C). Adsorption tower C enters the first adsorption state, where easily adsorbed components in the gas are adsorbed by the adsorbent. Difficult-to-adsorb components containing trace amounts of easily adsorbed components flow out of adsorption tower C from the upper port of the second adsorption tower and enter the difficult-to-adsorbed component product gas pipeline through valve C11. The gas is then sent out of the pressure swing adsorption unit through subsequent equipment (such as a product gas buffer tank).

[0067] As adsorption towers A and C enter the adsorption state, valves G1 and G7 close, and adsorption tower G (the first adsorption tower) ends its secondary adsorption state; valves B6 and B11 close, and adsorption tower B (the second adsorption tower) ends its primary adsorption state. Simultaneously, adsorption towers G and B maintain their series connection from the adsorption state and are connected to adsorption tower D. The three adsorption towers enter a pressure equalization state, and valves G8, B5, B9, and D9 open. Adsorption tower G enters a secondary pressure equalization and depressurization state, adsorption tower B enters a primary pressure equalization and depressurization state, and adsorption tower D enters a pressure equalization and pressurization state. In the second adsorption tower (adsorption tower B), the easily adsorbed components in the voids and those desorbed from the adsorbent during pressure equalization and depressurization are adsorbed by the adsorbent in the mass transfer zone and the blank zone, containing trace elements. The easily adsorbed components and the difficult-to-adsorb components flow out of adsorption tower B from the upper interface of the second adsorption tower, and flow into adsorption tower D from the upper interface of adsorption tower D through valves B9 and D9. The gas in the void of the first adsorption tower (adsorption tower G) and the easily adsorbed components desorbed from it enter the second adsorption tower (adsorption tower B) from the lower interface through the upper interface of the adsorption tower via valve G8, the pressure equalization pipeline, and valve B5. The easily adsorbed components are adsorbed by the adsorbent in the mass transfer zone and the blank zone. The difficult-to-adsorbed components and trace amounts of easily adsorbed components flow out from the upper interface of the second adsorption tower through valve B9, and flow into adsorption tower D from the upper interface of the adsorbent D through valve D9. When the pressure between adsorption tower G, adsorption tower B, and adsorption tower D reaches equilibrium, the pressure equalization process is completed, and valves G8, B5, B9, and D9 are closed.

[0068] While adsorption towers A and C enter the adsorption state, valve E12 remains open, and adsorption tower E continues to be evacuated and depressurized; valve F3 remains open, and adsorption tower F continues to depressurize in the reverse direction.

[0069] Step 2: Adsorption tower A and adsorption tower C continue to be in a series adsorption state;

[0070] When adsorption tower E finishes its vacuuming and depressurization process, valve E12 closes. Simultaneously, valves G2, G9, B4, B8, E8, or E5 open, and adsorption tower G enters the displacement state, adsorption tower B enters the displacement gas adsorption state, and adsorption tower E enters the displacement gas pressurization state. The displacement gas (easily adsorbed component product gas) enters adsorption tower G from the lower interface of the first adsorption tower (adsorption tower G) via the displacement gas pipeline and valve G2. The gas remaining in the adsorption tower voids after pressure equalization is pushed upwards by the displacement gas and flows out from the upper interface of the first adsorption tower (adsorption tower G), passing through valve G9, the displacement pipeline, and valve B4 from the second adsorption tower (adsorption tower G). B) The gas enters adsorption tower B through the lower inlet. The easily adsorbed components in the gas flowing in from the first adsorption tower are adsorbed by the adsorbent in the mass transfer zone and blank zone of adsorption tower B. The difficult-to-adsorb components flow upward and exit from the upper inlet of the second adsorption tower (adsorption tower B), or flow into adsorption tower E through valve B8 and E8 through the upper inlet of the third adsorption tower (adsorption tower E), or enter adsorption tower E through valve B8, the pressure equalization pipeline, and valve E5 through the lower inlet of the third adsorption tower (adsorption tower E). When the amount of replacement gas flowing into adsorption tower G reaches the set requirement, the replacement process is completed, and valves G2, G9, B4, B8, E8, or E5 are closed.

[0071] As adsorption tower G enters the displacement state, the reverse depressurization process of adsorption tower F is completed, and it enters the vacuum depressurization state. Valve F3 is closed, while F12 is opened. As the pressure inside adsorption tower F decreases, the easily adsorbed components adsorbed on the adsorbent continue to desorb from the adsorbent, or are extracted from the adsorption tower by a vacuum pump through a vacuum tank, or directly extracted from the adsorption tower by a vacuum pump. The extracted easily adsorbed components are pressurized by a compressor and output as easily adsorbed component product gas to the pressure swing adsorption device; adsorption tower D enters the blank waiting state before reverse pressurization.

[0072] Step 3: Adsorption tower A and adsorption tower C continue to be in a series adsorption state;

[0073] When valves B10 and D10 are opened simultaneously, adsorption tower B enters the secondary reverse pressurization state, and adsorption tower D enters the primary reverse pressurization state. The product gas of the difficult-to-adsorb component enters adsorption tower B and adsorption tower D respectively through the reverse rise pipeline via valves B10 and D10 from the upper interface of the adsorption tower. After the pressure in adsorption tower B and adsorption tower D rises to the adsorption pressure, the secondary reverse pressurization state of adsorption tower B is completed, and the primary reverse pressurization state of adsorption tower D is completed. Then, valves B10 and D10 are closed.

[0074] While adsorption towers B and D enter the reverse pressurization state, valve G3 opens, and adsorption tower G enters the reverse depressurization state. After the replacement state is completed, the easily adsorbed components remaining in the gaps of adsorption tower G and the easily adsorbed components desorbed from the adsorbent as the pressure inside the adsorption tower decreases are discharged from the lower interface of adsorption tower G. After being pressurized by the compressor, they are output as easily adsorbed component product gas from the pressure swing adsorption device.

[0075] When adsorption towers B and D enter the reverse pressurization state, valve F12 remains open, and adsorption tower F continues to be evacuated and depressurized; adsorption tower E enters the blank waiting state before equalization and pressurization.

[0076] At this point, the first phase is complete. The valve location numbers and piping for the different adsorption towers in the other six phases to achieve the same functional state are the same as in the first phase. Refer to the descriptions in steps 1-3 for details. Figure 1 The same principle applies to Table 1, and will not be described further here.

[0077] The above are preferred embodiments of the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A two-tower series pressure swing adsorption device, characterized in that: The device includes at least 7 adsorption towers and corresponding valves and fittings, with the adsorption towers connected in series and parallel. Each adsorption tower is controlled by 12 valves to switch between various states; The lower interface of the adsorption tower is connected to 7 valves, and the upper interface is connected to 5 valves. The seven valves connected to the lower interface of the adsorption tower include: The gas from the outlet of the secondary adsorption tower enters the primary adsorption tower through the primary adsorption inlet valve. The primary adsorption inlet valves of each adsorption tower are connected in parallel through adsorption pipelines. The secondary adsorption inlet valve allows the raw gas to enter the secondary adsorption tower. The secondary adsorption inlet valves of each adsorption tower are connected in parallel through the raw gas pipeline. The gas from the outlet of the displacement adsorber enters the displacement adsorber through the displacement gas adsorption inlet valve. The displacement gas adsorption inlet valves of each adsorption tower are connected in parallel through displacement pipelines. The displacement gas inlet valve allows the displacement gas to enter the displacement adsorber. The displacement gas inlet valves of each adsorption tower are connected in parallel through the displacement gas pipeline. The reverse exhaust valve is used to discharge the gas inside the adsorption tower when the adsorption tower is in the reverse depressurization process. The reverse exhaust valves of each adsorption tower are connected in parallel through the reverse pipeline. When the adsorption tower is in a vacuum and depressurization state, the gas inside the adsorption tower is discharged from the adsorption tower through the extraction and exhaust valve. The extraction and exhaust valves of each adsorption tower are connected in parallel through extraction pipelines. The gas from the outlet of the secondary pressure equalization and depressurization adsorption tower enters the primary pressure equalization and depressurization adsorption tower through the primary pressure equalization and depressurization inlet valve. The replacement gas from the upper interface of the replacement gas adsorption tower can enter the replacement gas boosting adsorption tower through the primary pressure equalization and depressurization inlet valve. The primary pressure equalization and depressurization inlet valves of each adsorption tower are connected in parallel through the pressure equalization pipeline. The five valves connected to the upper interface of the adsorption tower include: The gas in the secondary adsorption tower is discharged into the primary adsorption tower through the secondary adsorption exhaust valve. The secondary adsorption tower and the primary adsorption tower are connected in series through the secondary adsorption exhaust valve and the primary adsorption inlet valve. The secondary adsorption exhaust valves of each adsorption tower are connected in parallel through adsorption pipelines. The gas inside the primary adsorption tower is discharged from the adsorption tower through the primary adsorption exhaust valve and discharged into the difficult-to-adsorb component product gas pipeline as the difficult-to-adsorb component product gas. The primary adsorption exhaust valves of each adsorption tower are connected in parallel through the difficult-to-adsorb component product gas pipeline. The secondary equalization and depressurization exhaust valve allows gas in the secondary equalization and depressurization adsorption tower to be discharged into the primary equalization and depressurization adsorption tower. The secondary equalization and depressurization adsorption tower and the primary equalization and depressurization adsorption tower are connected in series through the secondary equalization and depressurization exhaust valve and the primary equalization and depressurization inlet valve. The replacement gas from the upper interface of the replacement gas adsorption tower can enter the replacement gas boosting adsorption tower through the secondary equalization and depressurization exhaust valve. The secondary equalization and depressurization exhaust valves of each adsorption tower are connected in parallel through equalization pipelines. The gas in the primary pressure equalization and depressurization adsorption tower is discharged into the pressure equalization and boosting adsorption tower through the primary pressure equalization and depressurization vent valve; the primary pressure equalization and depressurization vent valve also serves as the displacement gas adsorption vent valve, through which the gas in the displacement gas adsorption tower is discharged from the displacement gas adsorption tower; the displacement adsorption tower, displacement gas adsorption tower, and displacement gas boosting adsorption tower are connected in series during displacement state through the primary pressure equalization and depressurization vent valve, displacement pipeline, displacement gas adsorption inlet valve, secondary pressure equalization and depressurization vent valve, or primary adsorption inlet valve; the primary pressure equalization and depressurization vent valves of each adsorption tower are connected in parallel through displacement pipelines; The reverse riser valve allows the reverse pressurized gas to enter the adsorption tower that requires reverse pressurization. The reverse riser valves of each adsorption tower are connected in parallel through the reverse riser gas pipeline.

2. A two-tower series pressure swing adsorption process, characterized in that: The two-tower series pressure swing adsorption device according to claim 1 is used in the following manner: In the displacement state, two of the three adsorption towers are connected in series, one end to the other. The adsorption tower upstream in the series connection is the first adsorption tower, and the adsorption tower downstream is the second adsorption tower. The upper interface of the second adsorption tower is then connected to the upper or lower interface of the third adsorption tower, thus realizing the series connection of the three adsorption towers. The series connection method of the first and second adsorption towers is the same as the series connection method when these two adsorption towers are in the adsorption state and the pressure equalization and depressurization state. In the displacement state, the first adsorption tower is the one being displaced, the second adsorption tower receives the gas components flowing from the first adsorption tower, and the third adsorption tower receives the gas components flowing from the second adsorption tower. The two adsorption towers, originally in a pressure equalization and depressurization state, continue in series, connected end-to-end. The displacement gas enters the first adsorption tower from the lower inlet, pushing the easily adsorbed components and a small amount of difficult-to-adsorbed components, originally remaining in the adsorption tower's voids, out of the adsorption tower from bottom to top through the upper inlet, thus placing the first adsorption tower in a displacement state. The displaced gas then enters the second adsorption tower from the lower inlet, where the easily adsorbed components are adsorbed in the adsorbent mass transfer zone and blank zone, while the difficult-to-adsorbed components and trace amounts of easily adsorbed components are adsorbed... The adsorbent component flows out of the second adsorption tower from the upper interface, and the second adsorption tower is in the state of displacement gas adsorption. The gas flowing out of the second adsorption tower then flows into the third adsorption tower from the upper or lower interface, and the third adsorption tower is in the state of displacement gas pressurization. The quality of the gas flowing into the third adsorption tower is the same as that of the difficult-to-adsorb component product gas. The displacement gas pushes the small amount of difficult-to-adsorb component remaining in the void of the first adsorption tower after the pressure equalization and depressurization process into the second adsorption tower. After the displacement state is completed, the component remaining in the void of the first adsorption tower is the high-purity easy-to-adsorb component. This part of the easy-to-adsorb component, as well as the easy-to-adsorb component desorbed from the adsorbent during the reverse depressurization and vacuum depressurization process, is pressurized by the compressor and used as the easy-to-adsorb component product gas output device.

3. The two-tower series pressure swing adsorption process as described in claim 2, characterized in that: The product gas containing easily adsorbed components is used as the replacement gas.

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