Method and system for purification of co by pressure swing adsorption

Abstract

The application provides a method and system for purifying CO by pressure swing adsorption. The method is applied to a pressure swing adsorption system comprising at least two adsorption beds filled with adsorbent. In the equalization stage, the equalization gas from at least one of the adsorption beds in a high pressure state is divided into two streams and input into corresponding adsorption beds in a low pressure state. The gas phase outlets corresponding to the two streams are located at different positions on the corresponding adsorption beds to flush the non-target gas in the dead space of the adsorption beds. By using the method of the application, the impurity components in the dead space of the tower bottom and the pipeline can be reduced in the equalization stage, and the purity of the product gas is improved.

Description

Technical Field

[0001] This application relates to the field of pressure swing adsorption (PSA) technology, and in particular to a method and system for purifying CO using PSA. Background Technology

[0002] CO is an important basic chemical raw material, used to prepare acetic acid, acetic anhydride, oxalate esters, ethylene glycol, oxalic acid, dimethylformamide, dimethyl carbonate, formic acid, etc., and for the further synthesis of TDI and MDI from phosgene. Pure CO required for chemical synthesis can be separated and extracted from various CO-containing gas mixtures. Industrially available CO feedstocks include natural gas and petroleum-derived syngas, water gas, semi-water gas, and tail gases from steel mills, calcium carbide plants, and yellow phosphorus plants. Pressure Swing Adsorption (PSA) technology is widely used in the chemical industry for CO purification.

[0003] In conventional pressure swing adsorption (PSA) CO purification processes, the equalization step connects the tops of the high-pressure and low-pressure towers to achieve pressure equilibrium. However, existing equalization processes typically face several problems. Firstly, to avoid fluidization during equalization, a relatively long equalization time is usually required. Secondly, the dead space at the bottom of the tower and in the pipelines contains a large amount of impurity gas, resulting in an undesirable concentration gradient distribution. Thirdly, after the displacement step, the undisplaced impurities in the dead space at the bottom of the tower and in the pipelines are extracted during the subsequent vacuuming step and carried into the product gas, thus affecting the purity of the product gas. This is especially problematic when the purity requirements for the product gas are very stringent, where impurities in the dead space become a significant concern. Summary of the Invention

[0004] To address the aforementioned problems, one objective of this invention is to provide a method for purifying CO using pressure swing adsorption (PSA) to reduce impurities in the dead spaces at the bottom of the column and in the pipeline during the pressure equalization stage, thereby improving the purity of the product gas. A second objective of this invention is to provide a system for purifying CO using PSA to prevent the retention of impurities in the dead spaces at the bottom of the column and in the pipeline.

[0005] The first aspect of this invention provides a method for purifying CO using pressure swing adsorption. To achieve the above objective, the technical solution adopted by this invention is as follows:

[0006] A method for purifying CO using pressure swing adsorption (PSA) is applied to a PSA system comprising at least two adsorption beds, each filled with adsorbent. During the pressure equalization stage, a pressure-equalizing gas from at least one adsorption bed under high pressure is split into two streams and introduced into corresponding adsorption beds under low pressure.

[0007] The gas phase outlets corresponding to the two airflows are located at different positions on the adsorption bed to flush out non-target gases in the dead space within the adsorption bed.

[0008] As one of the preferred options, the two airflows are respectively input to the same position within the adsorption bed, which is under low pressure.

[0009] As one of the preferred solutions, the two airflows are respectively input to different positions within the adsorption bed, which is under low pressure.

[0010] As a preferred embodiment, the adsorption bed is provided with gas phase outlets at the top and bottom when under high pressure, and with a gas phase inlet at the top when under low pressure; wherein,

[0011] The pressure-equalizing gas is simultaneously input from the top and bottom of the adsorption bed under high pressure to the top of the corresponding adsorption bed under low pressure.

[0012] As one preferred embodiment, the ratio of the equalizing gas output from the bottom of the adsorption bed to the total output equalizing gas is greater than 0% and not higher than 80%.

[0013] As a preferred embodiment, the adsorption bed is provided with gas phase outlets at the top and bottom when under high pressure, and with gas phase inlets at the top and bottom when under low pressure; wherein,

[0014] The equalizing gas is input from the top of the adsorption bed under high pressure to the top of the corresponding adsorption bed under low pressure, and at the same time, the equalizing gas is input from the bottom of the adsorption bed under high pressure to the bottom of the corresponding adsorption bed under low pressure.

[0015] As one of the preferred embodiments, the ratio of the equalizing gas output from the bottom of the adsorption bed to the total amount of equalizing gas output is greater than 0% and not higher than 90%.

[0016] As one of the preferred embodiments, in the pressure equalization stage, at least one pressure equalization gas in the adsorption bed under high pressure is divided into two streams and input into the corresponding adsorption bed under low pressure. The time taken for each input is greater than 0 seconds and not greater than 60 seconds.

[0017] As one of the preferred solutions, each adsorption bed sequentially undergoes a cycle of adsorption, pressure equalization, displacement, reverse release, vacuuming, pressure equalization and pressure increase, and final pressurization.

[0018] A second aspect of the present invention also provides a method for purifying CO by pressure swing adsorption (PSA), applied to a PSA system comprising at least two adsorption beds, each filled with adsorbent. During the pressure equalization stage, the pressure-equalizing gas from at least one of the adsorption beds under high pressure is split into two streams and respectively introduced into the corresponding adsorption beds under low pressure and into a gas holder; wherein...

[0019] The gas phase outlets corresponding to the two airflows are located at different positions on the adsorption bed to flush out non-target gases in the dead space within the adsorption bed.

[0020] A third aspect of the present invention also provides a system for purifying CO by pressure swing adsorption, for implementing the CO purification method by pressure swing adsorption as provided in the first and second aspects of the present invention.

[0021] Compared with the prior art, this application has the following advantages:

[0022] This invention proposes a method for purifying CO using pressure swing adsorption (PSA), applied to a PSA system comprising at least two adsorption beds, each filled with adsorbent. During the pressure equalization stage, the equalizing gas from at least one adsorption bed under high pressure is split into two streams and input into corresponding adsorption beds under low pressure. The gas phase outlets corresponding to the two streams are located at different positions on the respective adsorption beds to flush out non-target gases from the dead space within the adsorption beds.

[0023] This invention proposes a method for purifying CO using pressure swing adsorption (PSA), applied to a PSA system comprising at least two adsorption beds, each filled with adsorbent. During the pressure equalization stage, the equalizing gas from at least one adsorption bed under high pressure is split into two streams and input into the corresponding adsorption bed under low pressure and a gas holder, respectively. The gas phase outlets corresponding to the two streams are located at different positions on the respective adsorption beds to flush out non-target gases from the dead space within the adsorption beds.

[0024] By adopting the two technical solutions described above in this application, each adsorption bed undergoes a pressure equalization rise and pressure equalization fall stage. For this adsorption bed, during the pressure equalization fall stage, the adsorption bed at a higher pressure is connected to the adsorption bed to be adsorbed at a lower pressure, reducing the pressure of this adsorption bed while simultaneously increasing the pressure of the adsorption bed to be adsorbed, preparing it to enter the adsorption stage. After the pressure equalization is completed, the pressures of the two beds are the same. During the process of balancing the pressures of the two beds, the pressure equalization gas in this adsorption bed flows bidirectionally, which not only achieves rapid pressure equalization and makes the gas flow between the two towers more uniform, but also reduces the pressure of this adsorption bed during the pressure equalization process, causing some CO in this adsorption bed to desorb and enter the adsorption bed to be adsorbed from different height directions together with the pressure equalization gas. This flushes away non-target gases (or impurity components) in the dead space of the tower bottom and pipelines in this adsorption bed, effectively reducing the residual impurity gases in the dead space and improving the purity of the product gas.

[0025] The system provided in this embodiment of the invention has the same advantages over the prior art as the pressure swing adsorption method for purifying CO described above, and will not be repeated here. Attached Figure Description

[0026] To more clearly illustrate the technical solution of this application, the drawings used in the description of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the pressure equalization path of the pressure swing adsorption method for purifying CO according to an embodiment of this application;

[0028] Figure 2 This is a schematic diagram of another pressure equalization path of the pressure swing adsorption method for purifying CO described in one embodiment of this application;

[0029] Figure 3 This is a schematic diagram of another pressure equalization path of the pressure swing adsorption method for purifying CO described in one embodiment of this application.

[0030] Explanation of reference numerals in the attached figures:

[0031] 1. Raw material gas pipeline; 2. Adsorption tail gas pipeline; 3. Displacement tail gas pipeline; 4. First equalization pipeline; 5. Second equalization pipeline; 6. Product gas pipeline; 7. Backflow gas pipeline; 8. Displacement gas pipeline. Detailed Implementation

[0032] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0033] It should be noted that in related technologies, the main components of the CO-containing gas mixture include at least CO2, CO, CH4, N2, and H2, as well as various impurity components such as H2O and sulfides. These gas components have different adsorption capacities on the adsorbent, and CO's adsorption capacity lies between that of CO2 and CH4. Therefore, the pressure swing adsorption (PSA) process for purifying CO typically includes two treatment steps: a pretreatment step to remove components with stronger adsorption capacity than CO, such as CO2, H2O, and sulfides; and a post-treatment step to remove components with weaker adsorption capacity than CO, such as N2, CH4, and H2, which are distilled off from the top of the adsorption tower as light components, while the adsorbed CO is extracted from the bottom as a heavy component as the product gas.

[0034] It should also be noted that the specific steps in the post-processing process include adsorption, pressure equalization, displacement, reverse release, vacuuming, pressure equalization boost, and final pressurization. The pressure equalization stage involves connecting the tops of the high-pressure tower and the low-pressure tower to achieve pressure equilibrium. Many of the problems mentioned in the background of this invention exist in this pressure equalization stage.

[0035] It is understood that the CO purification method proposed in this invention refers to the purification of CO-containing raw gas (or semi-finished gas) entering the post-processing stage. It has already removed impurities such as CO2, H2O and sulfides. The main components of the raw gas are CO, CH4, N2 and H2.

[0036] Please refer to Figure 1-3 The diagram shown illustrates the principle framework of a pressure swing adsorption (PSA) method for purifying CO. Figure 1 , Figure 2 and Figure 3 The different equalization paths during the equalization phase are shown. Please refer to... Figure 1 and Figure 2 This invention provides a method for purifying CO by pressure swing adsorption, applied to a pressure swing adsorption system with at least two adsorption beds, each filled with adsorbent. In the pressure equalization stage, the pressure equalization gas in at least one of the adsorption beds under high pressure is split into two gas streams and input into the corresponding adsorption beds under low pressure. The gas phase outlets corresponding to the two gas streams are located at different positions on the respective adsorption beds to flush out non-target gases in the dead space within the adsorption beds.

[0037] Specifically, pressure swing adsorption (PSA) technology utilizes the different affinities and adsorption capacities of adsorbents to separate different gas components. An adsorption bed is a device used to adsorb and separate target components, typically filled with adsorbents such as activated carbon, molecular sieves, activated alumina, and others. The appropriate adsorbent can be selected based on specific application requirements and separation objectives. "At least two adsorption beds" refers to a two-tower PSA system (consisting of two adsorption towers) or a multi-tower PSA system (consisting of more adsorption towers) to purify CO from the feed gas. The operating states of each adsorption bed can be sequentially performed according to a pre-set time sequence for adsorption, desorption, and other operations. This time sequence control can be achieved through valves and a control system. Figure 1 Four adsorption towers are shown as an example.

[0038] Specifically, each adsorption bed undergoes a series of cyclical process steps in one cycle, including adsorption, pressure equalization, convective release, displacement, reverse release, vacuuming, pressure equalization and boosting, and final pressurization. Each adsorption bed performs different steps simultaneously. At any given time, one or more adsorption beds are in any one of the cyclical stages of adsorption, pressure equalization, displacement, reverse release, vacuuming, pressure equalization and boosting, or final pressurization. Regardless of the number of adsorption beds used, these process steps are executed alternately to achieve a continuous and stable CO adsorption and desorption process. The timing arrangement of each adsorption bed can be adjusted according to process design, operational requirements, and the number of adsorption towers; this paper does not impose specific limitations on this. It is worth noting that when one or more adsorption beds are in the pressure equalization stage (pressure equalization and pressure equalization and boosting), a corresponding adsorption bed will be connected to an adsorption bed in the pressure equalization or boosting stage. That is, when one adsorption bed experiences pressure reduction, another adsorption bed experiences pressure increase, thus simultaneously achieving pressure equalization across the 2N towers.

[0039] The following text uses two adsorption beds as an example, referring to the adsorption bed under high pressure as the high-pressure tower and the adsorption bed under low pressure as the low-pressure tower, to illustrate the pressure swing adsorption method for CO purification of the present invention. For pressure swing adsorption purification processes with more adsorption beds, please refer to the above.

[0040] During the pressure equalization stage, the pressure equalization gas in the high-pressure tower is divided into two streams and input into the low-pressure tower respectively. This can be understood as establishing a first pressure equalization pipeline 4 and a second pressure equalization pipeline 5 to connect the two towers, giving the pressure equalization gas more flow paths and enabling multidirectional flow in different directions. The high-pressure tower has two gas phase outlets. When the pressure in the high-pressure tower decreases, some of the CO adsorbed on the adsorbent desorbs, making CO part of the pressure equalization gas and output through the gas phase outlets. Since the gas phase outlets are located at different positions in the high-pressure tower, they provide more channels and paths, allowing the pressure equalization gas containing CO (hereinafter referred to as pressure equalization gas) to flow through different spatial areas in the high-pressure tower before flowing into the low-pressure tower. This also takes into account non-target gases in the dead space at the bottom of the high-pressure tower and in the pipeline. The pressure equalization gas carries away the gas in the dead space, effectively reducing the residual impurity gas in the dead space and helping to improve the purity of the product gas.

[0041] It is understandable that each adsorption bed undergoes the following process steps in one cycle: adsorption, pressure equalization, displacement, reverse release, vacuuming, pressure equalization and pressure increase, and final pressurization. That is, in the pressure equalization stage, the current adsorption bed acts as a high-pressure tower, while the low-pressure tower acts as the adsorption bed to be adsorbed. Similarly, in the pressure equalization stage, the previous high-pressure tower returns to a low-pressure state, that is, the current adsorption bed becomes a low-pressure tower, while the adsorption bed to be adsorbed returns to a high-pressure state, that is, the adsorption bed to be adsorbed becomes a high-pressure tower, and the above pressure equalization stage is repeated.

[0042] In some embodiments, some or all of the gas phase outlets in each adsorption bed can serve as gas phase inlets; that is, when converted to a low-pressure tower, the original gas phase outlets become gas phase inlets to receive the equalizing gas output from the gas phase outlets of another adsorption bed. The gas phase outlets and their corresponding gas phase inlets can be connected via equalizing pipelines. It is understood that the gas phase outlets in each adsorption bed may not serve as gas phase inlets; they can have separate gas phase inlets connected to their corresponding gas phase outlets via additional equalizing pipelines.

[0043] Thus, in one operating cycle, the pressure-equalizing gas flow from the high-pressure towers in the two adsorption beds flows to the other low-pressure tower through the first pressure-equalizing pipeline 4 and the second pressure-equalizing pipeline 5. Since each adsorption bed has both high-pressure and low-pressure states, each adsorption bed exists as a high-pressure tower and a low-pressure tower at different times. Therefore, each adsorption bed is equipped with two gas phase outlets, and each gas phase outlet is configured to output pressure-equalizing gas. This takes into account the non-target gases in the dead space at the bottom of each adsorption bed and in the pipeline. The pressure-equalizing gas carries away the gas in the dead space, effectively reducing the residual impurity gas in the dead space of each adsorption bed and helping to improve the purity of the product gas.

[0044] It is understood that non-target gases refer to the non-adsorbed phase gases in the adsorption bed that were not adsorbed by the adsorbent. Specifically, after adsorption, a certain amount of impurities such as H2, N2, O2, and CH4 remain in the adsorption bed besides CO. After the displacement stage, a portion of the space at the bottom of the adsorption bed or in the pipeline cannot be displaced, resulting in the continued presence of impurities in that space. If these impurities are not removed or discharged, they not only affect the effectiveness of subsequent adsorption stages but can also be drawn into the product gas during the subsequent vacuuming step, affecting the purity of the product gas.

[0045] In this way, the multi-directional flow of the equalizing gas, flowing from different locations in the high-pressure tower to the low-pressure tower simultaneously, shortens the equalization time, reduces the production cycle, and improves production efficiency and output. Simultaneously, the desorbed CO is flushed away by the equalizing gas, removing impurities from the dead space within the high-pressure tower, reducing residual impurities and improving the purity of the product gas in the subsequent vacuuming step. By diverting the equalizing gas to the low-pressure tower, the gas flow path during the equalization process is more rational, resulting in a more uniform pressure balance between the two towers. Furthermore, the removal of impurities from the dead space in the high-pressure tower reduces the formation of concentration gradients within the tower, enhancing the equalization effect. This allows the adsorbent in the adsorption bed to more uniformly adsorb and desorb the target gas (CO), strengthening the adsorbent's adsorption capacity and improving the stability and adsorption efficiency of the entire process.

[0046] In summary, the pressure swing adsorption method for purifying CO provided in this embodiment of the invention has advantages such as simple operation, high efficiency, and good purification effect. It is suitable for the purification needs of CO gas in industrial production, especially when the purity requirements of the product gas are high. This method can effectively achieve efficient separation and purification of CO.

[0047] As a specific explanation of this embodiment, taking a single adsorption bed as an example, the specific process steps for each cycle in pressure swing adsorption are as follows:

[0048] Adsorption stage: The feed gas enters the adsorption bed through the feed gas pipeline 1. Under a certain pressure, the adsorbent in the adsorption bed rapidly adsorbs CO. Weakly adsorbed components such as CH4, N2 and H2 are distilled out from the top through the adsorption tail gas pipeline 2 as light components.

[0049] Pressure equalization stage: This adsorption bed (acting as a high-pressure tower at this time) is connected to the adsorption bed at a lower pressure (acting as a low-pressure tower at this time) through the first pressure equalization pipeline 4 and the second pressure equalization pipeline 5 to reduce the pressure of this adsorption bed and at the same time increase the pressure of the adsorption bed to be adsorbed. After the pressure equalization is completed, the pressure of the two beds is the same. Then the adsorption bed to be adsorbed can be introduced with pressurizing gas and finally pressurized with the distillate gas of this adsorption bed to prepare for adsorption.

[0050] Replacement stage: Part of the CO product gas is introduced into the adsorption bed through the replacement gas pipeline 8 to perform forward replacement flushing of the adsorption bed, so as to replace the non-target gas remaining on the adsorbent. The replaced non-target gas is output through the replacement tail gas pipeline 3.

[0051] Reverse release stage: CO is desorbed and the product CO is released in reverse from the bottom of the adsorption bed through the reverse release pipeline 7;

[0052] Vacuuming stage: When the pressure inside the adsorption bed drops to near atmospheric pressure, the adsorption bed is evacuated. The pressure of the adsorption bed is further reduced by the power of the vacuum pump. The extracted gas is product gas CO, which is output through product gas pipeline 6.

[0053] Pressure equalization stage: The pressure of this adsorption bed (which is now a low-pressure tower) is equalized with that of the adsorption bed at a higher pressure (which is now a high-pressure tower). The principle and steps are the same as those of the pressure equalization stage, but the gas flow direction is reversed.

[0054] Final pressurization: Part of the adsorbed distillate gas is used to pressurize the adsorption tower in reverse, raising the pressure to the adsorption pressure.

[0055] It is understandable that after the final pressurization is completed, the adsorption stage will be restarted to complete one cycle for each adsorption bed.

[0056] To reiterate, in some embodiments, a forward release stage can be set between the equalization stage and the replacement stage. In the forward release stage, the programmable valve on the upper part of the adsorption bed can be opened to release the pressure of the adsorption bed in the forward direction. The forward-released gas flows out of the return gas cabinet through the top.

[0057] It is worth mentioning that during the replacement stage, the replacement exhaust gas usually contains a high level of CO. A pre-adsorption step can be added in the middle of the pressure equalization stage to recover CO.

[0058] Please refer to it again. Figure 1 As mentioned above, a portion of the gas phase outlet in each adsorption bed can serve as a gas phase inlet. In some embodiments, the two gas streams are respectively input to the same location within the corresponding adsorption bed under low pressure. That is, the pressure-equalizing gas in the high-pressure tower is transported from different gas phase outlets through the first pressure-equalizing pipeline 4 and the second pressure-equalizing pipeline 5 to the same gas phase inlet in the low-pressure tower; in other words, the low-pressure tower shares the same gas phase inlet for receiving the two gas streams. In this embodiment, when the gas phase outlet of the same adsorption bed is used as a gas phase inlet, only one of the two gas phase outlets needs to serve as a gas phase inlet to receive the pressure-equalizing gas transported from the two gas phase outlets of the other adsorption bed.

[0059] Specifically, during the pressure drop equalization stage, gas phase outlets are provided at the top and bottom of both the high-pressure tower and the low-pressure tower. One gas stream exits from the bottom gas phase outlet of the high-pressure tower, and the other gas stream exits from the top gas phase outlet of the high-pressure tower. Both gas streams are input into the same gas phase outlet of the low-pressure tower, at which point the gas phase outlet of the low-pressure tower that receives the gas stream serves as the gas phase inlet. In some embodiments, the two gas streams can be input into the gas phase outlet at the top of the low-pressure tower; in some embodiments, the two gas streams can be input into the gas phase outlet at the bottom of the low-pressure tower.

[0060] Preferably, the top and bottom of the adsorption bed (high-pressure tower) under high pressure are respectively provided with gas phase outlets, and the top gas phase outlet of the adsorption bed (low-pressure tower) under low pressure serves as a gas phase inlet; the pressure equalizing gas is simultaneously input from the top and bottom of the high-pressure tower to the top of the low-pressure tower. In this embodiment, the top of the high-pressure tower is connected to the top of the low-pressure tower, allowing the pressure of the two towers to quickly reach equilibrium. At the same time, the bottom of the high-pressure tower is connected to the top of the low-pressure tower, making the flow of the pressure equalizing gas between the two towers more uniform. Furthermore, during the pressure equalization process, the gas pressure in the high-pressure tower decreases, CO in the adsorbent desorbs and flows to the bottom, and the pressure equalizing gas can enter the low-pressure tower through the bottom, thereby achieving the replacement and flushing of impurities in the dead space at the bottom of the high-pressure tower.

[0061] Please refer to it again. Figure 2 As mentioned above, all gas phase outlets in each adsorption bed can serve as gas phase inlets. In some embodiments, the two gas streams are respectively input to different locations within the corresponding low-pressure adsorption beds. That is, the pressure-equalizing gas in the high-pressure tower is transported from different gas phase outlets through the first pressure-equalizing pipeline 4 and the second pressure-equalizing pipeline 5 to different gas phase inlets in the low-pressure tower. In other words, the low-pressure tower receives the two gas streams at different gas phase inlets. In this embodiment, when the gas phase outlets of the same adsorption bed are used as gas phase inlets, the two gas phase outlets can respectively serve as gas phase inlets to receive pressure-equalizing gas transported from the two gas phase outlets of another adsorption bed.

[0062] Specifically, during the pressure drop equalization stage, gas phase outlets are provided at the top and bottom of both the high-pressure tower and the low-pressure tower. One gas stream exits from the bottom gas phase outlet of the high-pressure tower, and the other gas stream exits from the top gas phase outlet of the high-pressure tower. Both gas streams are input into the two gas phase outlets of the low-pressure tower, at which point both gas phase outlets of the low-pressure tower serving as gas phase inlets. In some embodiments, the upper gas stream can be input into the top gas phase outlet of the low-pressure tower, and the lower gas stream can be input into the bottom gas phase outlet of the low-pressure tower; in other embodiments, the upper gas stream can be input into the bottom gas phase outlet of the low-pressure tower, and the lower gas stream can be input into the top gas phase outlet of the low-pressure tower.

[0063] Preferably, the top and bottom of the adsorption bed (high-pressure tower) under high pressure are respectively provided with gas phase outlets, and the top and bottom gas phase outlets of the adsorption bed (low-pressure tower) under low pressure are respectively used as gas phase inlets; the pressure equalizing gas is input from the top of the high-pressure tower to the top of the low-pressure tower, and simultaneously input from the bottom of the high-pressure tower to the bottom of the low-pressure tower.

[0064] In this embodiment, the top of the high-pressure tower is connected to the top of the low-pressure tower, which allows the pressure of the two towers to be quickly balanced. At the same time, the bottom of the high-pressure tower is connected to the bottom of the low-pressure tower, making the flow of the pressure-equalizing gas between the two towers more uniform. During the pressure equalization process, the gas pressure in the high-pressure tower decreases, CO in the adsorbent desorbs and flows to the bottom, and the pressure-equalizing gas can enter the low-pressure tower through the bottom. The pressure-equalizing gas is used to replace and flush the impurities in the dead space at the bottom of the high-pressure tower.

[0065] Preferably, when the equalizing gas is simultaneously input from the top and bottom of the high-pressure tower to the top of the low-pressure tower, the ratio of the equalizing gas output from the bottom of the corresponding adsorption bed to the total output equalizing gas is greater than 0% and not higher than 80%; when the equalizing gas is input from the top of the high-pressure tower to the top of the low-pressure tower, and simultaneously from the bottom of the high-pressure tower to the bottom of the low-pressure tower, the ratio of the equalizing gas output from the bottom of the corresponding adsorption bed to the total output equalizing gas is greater than 0% and not higher than 90%. The total output equalizing gas can be understood as the sum of the contents of the equalizing gas output from the two gas phase outlets of this adsorption bed, that is, all the equalizing gas output from the adsorption bed. Ensuring that the ratio of the equalizing gas output from the bottom gas phase outlet to the total equalizing gas is within a specified range can usually be achieved by controlling the valve opening of the programmable valves on the first equalizing pipeline 4 and / or the second equalizing pipeline 5 in the control system. The control system can adjust the flow rate of the bottom gas phase outlet as needed, thereby affecting the ratio between the bottom output equalizing gas and the total equalizing gas.

[0066] Specifically, the programmable valve can be a regulating valve, which is a device used to control the flow rate of fluids. The flow rate of gas can be adjusted by adjusting its valve opening.

[0067] When equalizing gas is simultaneously input from the top and bottom of the high-pressure tower to the top of the low-pressure tower, it means that the proportion of equalizing gas output from the bottom to the total equalizing gas should be between 0% and 80%, and not zero; when equalizing gas is input from the top of the high-pressure tower to the top of the low-pressure tower, and simultaneously input from the bottom of the high-pressure tower to the bottom of the low-pressure tower, it means that the proportion of equalizing gas output from the bottom to the total equalizing gas should be between 0% and 90%, and not zero.

[0068] Based on the expertise and years of practical experience of this invention, it has been found that compared to Method 1, where the equalizing gas is simultaneously input from the top and bottom of the high-pressure tower to the top of the low-pressure tower, Method 2, where the equalizing gas is input from the top of the high-pressure tower to the top of the low-pressure tower and simultaneously from the bottom of the high-pressure tower to the bottom of the low-pressure tower, has relatively independent flow paths for the two gas streams. The gas residence time in the bottom region is relatively short, the mixing degree is relatively low, and the degree of impurity replacement and flushing in the bottom region is relatively low. Therefore, the proportion of gas discharged from the bottom can be appropriately higher under this method. Thus, in Method 1, when the equalizing gas is input from the bottom of the high-pressure tower to the top of the low-pressure tower, the gas flows upward against gravity, and the equalizing gas residence time at the bottom is longer, resulting in a relatively high mixing degree. When the equalizing gas is input from the bottom of the high-pressure tower to the top of the low-pressure tower, the proportion of equalizing gas output from the bottom can be appropriately lower, not only achieving rapid pressure equalization but also helping to remove impurities from the dead zones at the bottom, thus improving the overall effect of the adsorption bed.

[0069] Furthermore, during the pressure equalization stage, at least one pressure-equalizing gas in the adsorption bed under high pressure is split into two streams and input into the corresponding adsorption bed under low pressure, with the time taken for each input being greater than 0 seconds and not greater than 60 seconds. In this embodiment, providing the pressure-equalizing gas with more channels and paths not only flushes out non-target gases in the dead space within the adsorption bed but also increases the pressure equalization velocity, promoting uniform gas distribution within the bed and helping to reach the pressure equalization state more quickly. This shortens the entire process cycle, eliminates the need for additional energy consumption to maintain gas flow and pressure balance during the pressure equalization process, improves production efficiency and output, and reduces energy consumption and production costs.

[0070] Please refer to it again. Figure 3 In another approach, unlike approaches one and two described above, the equalizing gas output from the bottom of the high-pressure tower in both gas streams does not need to be input into the corresponding low-pressure tower. Instead, a portion of the equalizing gas is used as flushing gas to wash away non-target gases in the dead space within the adsorption bed before being directly discharged from the adsorption bed and flowing into the gas holder. In this approach, the technical measures employed by the present invention are as follows:

[0071] A method for purifying CO by pressure swing adsorption is applied to a pressure swing adsorption system with at least two adsorption beds, each filled with adsorbent. In the pressure equalization stage, the pressure equalization gas in at least one of the adsorption beds under high pressure is split into two gas streams and respectively introduced into the corresponding adsorption beds under low pressure and the gas holder. The gas phase outlets corresponding to the two gas streams are located at different positions on the corresponding adsorption beds to flush out non-target gases in the dead space within the adsorption beds.

[0072] It should be understood that the content of the equalizing gas used as flushing gas should be lower than the content of the equalizing gas output from the bottom in Method 1 and Method 2. It can be flexibly selected based on factors such as the total amount of raw material gas, the target amount of purified gas, purification cost and process budget. This embodiment of the invention does not impose specific limitations.

[0073] As a specific explanation of this embodiment, based on the methods provided in Method 1 and Method 2 above, it provides some specific implementable principles and implementation steps. This embodiment can arbitrarily combine various features without conflicting with each other. Further descriptions of specific features, structures, or characteristics related to this embodiment can be found in other relevant parts of this disclosure (e.g., the arrangement of the gas phase inlet, the working sequence of the adsorption bed, the flow path of the equalizing gas, etc.). These specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. This embodiment will not elaborate further.

[0074] The method provided by the present invention will be illustrated below with specific examples.

[0075] Example 1:

[0076] The mixed gas contains 40% hydrogen, 30% carbon monoxide, 20% carbon dioxide, and 7.2% nitrogen, with the remainder being methane, water, and other trace amounts of harmful CO2. In the pretreatment stage, the raw gas undergoes pressurization, dehydration, desulfurization, deoxygenation, and decarbonization. The raw gas, now free of CO2 and impurities, enters the post-treatment stage. In the post-treatment stage, the gas undergoes the following steps in the adsorption tower: adsorption, two pressure equalization cycles (method 1), forward discharge, displacement, reverse discharge, vacuuming, a second top-bottom pressure equalization rise, pre-adsorption, a first top-bottom pressure equalization rise, and final pressurization. Each pressure equalization cycle lasts 50 seconds, and the gas discharged from the bottom during pressure equalization accounts for 5% of the total pressure equalization gas volume.

[0077] One method involves the equalization of pressure during the pressure drop phase, where equalization gas is simultaneously introduced into the top of the low-pressure tower from the top and bottom of the high-pressure tower in two separate gas streams.

[0078] Example 2:

[0079] The mixed gas contains 40% hydrogen, 30% carbon monoxide, 20% carbon dioxide, and 7.2% nitrogen, with the remainder being methane, water, and other trace amounts of harmful CO2. In the pretreatment stage, the raw gas undergoes pressurization, dehydration, desulfurization, deoxygenation, and decarbonization. The raw gas, now free of CO2 and impurities, enters the post-treatment stage. In the post-treatment stage, the gas undergoes the following steps in the adsorption tower: adsorption, two pressure equalization cycles (method 1), forward discharge, displacement, reverse discharge, vacuuming, a second top-bottom pressure equalization rise, pre-adsorption, a first top-bottom pressure equalization rise, and final pressurization. Each pressure equalization cycle lasts 40 seconds, and the gas discharged from the bottom during pressure equalization accounts for 15% of the total pressure equalization volume.

[0080] One method involves the equalization of pressure during the pressure drop phase, where equalization gas is simultaneously introduced into the top of the low-pressure tower from the top and bottom of the high-pressure tower in two separate gas streams.

[0081] Example 3:

[0082] The mixed gas contains 40% hydrogen, 30% carbon monoxide, 20% carbon dioxide, and 7.2% nitrogen, with the remainder being methane, water, and other trace amounts of harmful CO2. In the pretreatment stage, the raw gas undergoes pressurization, dehydration, desulfurization, deoxygenation, and decarbonization. The raw gas, now free of CO2 and impurities, enters the post-treatment stage. In the post-treatment stage, the gas undergoes the following steps in the adsorption tower: adsorption, two pressure equalization cycles (method 1), forward discharge, displacement, reverse discharge, vacuuming, a second top-bottom pressure equalization rise, pre-adsorption, a first top-bottom pressure equalization rise, and final pressurization. Each pressure equalization cycle lasts 30 seconds, and the gas discharged from the bottom during pressure equalization accounts for 30% of the total pressure equalization volume.

[0083] Example 4:

[0084] The mixed gas contains 40% hydrogen, 30% carbon monoxide, 20% carbon dioxide, and 7.2% nitrogen, with the remainder being methane, water, and other trace amounts of harmful CO2. In the pretreatment stage, the raw gas undergoes pressurization, dehydration, desulfurization, deoxygenation, and decarbonization. The raw gas, now free of CO2 and impurities, enters the post-treatment stage. In the post-treatment stage, the gas undergoes the following steps in the adsorption tower: adsorption, two pressure equalization cycles (method 1), forward discharge, displacement, reverse discharge, vacuuming, a second top-bottom pressure equalization rise, pre-adsorption, a first top-bottom pressure equalization rise, and final pressurization. Each pressure equalization cycle lasts 25 seconds, and the gas discharged from the bottom during pressure equalization accounts for 50% of the total pressure equalization volume.

[0085] Example 5:

[0086] The mixed gas contains 40% hydrogen, 30% carbon monoxide, 20% carbon dioxide, and 7.2% nitrogen, with the remainder being methane, water, and other trace amounts of harmful CO2. In the pretreatment stage, the raw gas undergoes pressurization, dehydration, desulfurization, deoxygenation, and decarbonization. The raw gas, now free of CO2 and impurities, enters the post-treatment stage. In the post-treatment stage, the gas undergoes the following steps in the adsorption tower: adsorption, two pressure equalization cycles (method two), forward discharge, displacement, reverse discharge, vacuuming, a second top-bottom pressure equalization rise, pre-adsorption, a first top-bottom pressure equalization rise, and final pressurization. Each pressure equalization cycle lasts 35 seconds, and the gas discharged from the bottom during pressure equalization accounts for 20% of the total pressure equalization gas volume.

[0087] Method 2 involves the equalization of pressure during the equalization phase, where one stream of gas is introduced from the top of the high-pressure tower to the top of the low-pressure tower, while another stream is introduced from the bottom of the high-pressure tower to the bottom of the low-pressure tower.

[0088] Example 6:

[0089] The mixed gas contains 40% hydrogen, 30% carbon monoxide, 20% carbon dioxide, and 7.2% nitrogen, with the remainder being methane, water, and other trace amounts of harmful CO2. In the pretreatment stage, the raw gas undergoes pressurization, dehydration, desulfurization, deoxygenation, and decarbonization. The raw gas, now free of CO2 and impurities, enters the post-treatment stage. In the post-treatment stage, the gas undergoes the following steps in the adsorption tower: adsorption, two pressure equalization cycles (method two), forward discharge, displacement, reverse discharge, vacuuming, a second top-bottom pressure equalization rise, pre-adsorption, a first top-bottom pressure equalization rise, and final pressurization. Each pressure equalization cycle lasts 25 seconds, and the gas discharged from the bottom during pressure equalization accounts for 60% of the total pressure equalization gas volume.

[0090] Comparative example:

[0091] The feed gas contains 40% hydrogen, 30% carbon monoxide, 20% carbon dioxide, and 7.2% nitrogen, with the remainder being methane, water, and other trace amounts of harmful components. After pressurization, the feed gas undergoes dehydration, desulfurization, deoxygenation, and decarbonization. The feed gas, now free of CO2 and impurities, enters the post-treatment process. In the post-treatment process, the feed gas undergoes the following steps in the adsorption tower: adsorption, two pressure equalization drops using method three, forward release, displacement, reverse release, vacuuming, a second top pressure equalization rise, pre-adsorption, a first top pressure equalization rise, and final pressurization. Each pressure equalization drop lasts 40 seconds.

[0092] Method three involves all the pressure equalization gas being fed from the top of the high-pressure tower to the top of the low-pressure tower during the pressure equalization stage.

[0093] Experimental test:

[0094] This invention uses Examples 1 to 6 as test examples, combined with comparative examples, and conducts standardized experimental tests on the test examples and comparative examples according to GB / T35995-2018 "National Standard for Carbon Monoxide". Hydrogen was used as a representative impurity component in the product gas to evaluate the hydrogen content and purity in the product gas. The results are shown in Table 1.

[0095] Table 1 shows the performance test results of the product gas extracted from the experimental example and the comparative example.

[0096]

[0097] Table 1

[0098] As shown in Table 1, adding top and bottom equalization paths to the same adsorption bed can effectively reduce the residual impurity gas in the dead space within a shorter equalization time, thereby reducing the concentration of impurity components in the product gas and improving its purity. In the bottom equalization path, further increasing the total amount of equalization gas output from the bottom can further remove impurity components from the dead space at the bottom of the adsorption bed, reducing the amount of impurity components carried into the product gas. When the total amount of equalization gas output from the bottom reaches a certain level, further increasing the total amount of equalization gas output from the bottom will not further improve the replacement and cleaning capacity of impurity components, but this portion of equalization gas belongs to the equalization stage and will not affect the product gas yield. Furthermore, in the bottom equalization path, when using method one for equalization, the total amount of equalization gas output from the bottom is less than when using method two, yet it still has a high replacement and rinsing capacity, helping to remove impurities from the bottom dead zone area and improving the overall effect of the adsorption bed.

[0099] Thus, by adopting the technical solution of this application, each adsorption bed will undergo a pressure equalization rise and pressure equalization fall stage. For this adsorption bed, in the pressure equalization fall stage, the adsorption bed at a higher pressure is connected to the adsorption bed to be adsorbed at a lower pressure, reducing the pressure of this adsorption bed and simultaneously increasing the pressure of the adsorption bed to be adsorbed, so that the adsorption bed to be adsorbed is ready to enter the adsorption stage. After the pressure equalization is completed, the pressure of the two beds is the same. In the process of balancing the pressure of the two beds, the pressure equalization gas of this adsorption bed flows bidirectionally, which not only achieves rapid pressure equalization and makes the gas flow between the two towers more uniform, but also reduces the pressure of this adsorption bed during the pressure equalization process, causing some CO in this adsorption bed to desorb and enter the adsorption bed to be adsorbed from different height directions together with the pressure equalization gas. This can flush out non-target gases (or impurity components) in the dead space of the bottom of the tower and pipeline in this adsorption bed, effectively reducing the residual impurity gas in the dead space and improving the purity of the product gas.

[0100] Another aspect of the present invention provides a system for purifying CO by pressure swing adsorption, for realizing the CO purification method by pressure swing adsorption as described above.

[0101] The above system embodiments are basically similar to the method embodiments, so the description is relatively simple. For relevant details, please refer to the description of the method embodiments.

[0102] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0103] It should also be noted that, in this document, the terms "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations, nor should they be construed as indicating or implying relative importance. Moreover, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, article, or terminal device that comprises a list of elements includes not only those elements, but also other elements not expressly listed, or elements inherent to such a process, method, article, or terminal device.

[0104] The above provides a detailed description of the method and system for purifying CO using pressure swing adsorption (PSA). Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of these embodiments are merely illustrative and should not be construed as limiting the scope of this application. Furthermore, those skilled in the art will recognize that various modifications and variations in implementation methods and application scope may occur based on this application. It is neither necessary nor possible to exhaustively list all possible implementation methods here, but any obvious changes or modifications derived therefrom remain within the protection scope of this application.

Claims

1. A method for purifying CO using pressure swing adsorption, characterized in that, In a pressure swing adsorption (PSA) system comprising at least two adsorption beds, each filled with adsorbent, during the pressure equalization phase, the equalizing gas from at least one adsorption bed under high pressure is split into two streams and input into the corresponding adsorption bed under low pressure; wherein... The gas phase outlets corresponding to the two airflows are located at different positions on the adsorption bed to flush out non-target gases in the dead space within the adsorption bed. Under high pressure, the adsorption bed has gas phase outlets at both the top and bottom; under low pressure, the adsorption bed has a gas phase inlet at the top. The pressure-equalizing gas is simultaneously input from the top and bottom of the adsorption bed under high pressure to the top of the corresponding adsorption bed under low pressure. The ratio of the equalizing gas output from the bottom of the adsorption bed to the total output equalizing gas is greater than 0% and not higher than 80%.

2. The method for purifying CO by pressure swing adsorption according to claim 1, characterized in that, The two airflows are respectively input into the same position within the adsorption bed, which is under low pressure.

3. The method for purifying CO by pressure swing adsorption according to claim 1, characterized in that, The two airflows are respectively input to different positions within the adsorption bed, which is under low pressure.

4. The method for purifying CO by pressure swing adsorption according to claim 1, characterized in that, Each adsorption bed undergoes a cyclical process of adsorption, pressure equalization, displacement, reverse release, vacuuming, pressure equalization and pressure increase, and final pressurization.

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