CN1042215C - Oxygen Generation Process Using Pressure Swing Adsorption Separation - Google Patents

Abstract

In order to provide a pressure-swing-adsorption oxygen production process which can maintain the product recovery at a high level while enhancing the oxygen productivity and reducing the unit power consumption, a pressure recovery step is carried out in which communication is provided between an outlet end of an adsorption column which has completed an adsorption step and an outlet end of an adsorption column which has completed a regeneration step, and in which gas remaining in the adsorption column which has completed the adsorption step is collected within the adsorption column which has completed the regeneration step; and simultaneously with the pressure recovery step, a gas mixture which has approximately the same composition as feed gas mixture is introduced into at least one of the adsorption column which has completed the adsorption step and the adsorption column which has completed the regeneration step through the inlet end thereof.

Description

Oxygen Generation Process Using Pressure Swing Adsorption Separation

The present invention relates to an oxygen generation method using a pressure swing adsorption separation method, and more specifically, relates to a pressure swing adsorption method using an adsorbent that selectively adsorbs nitrogen, from a mixed gas mainly composed of oxygen and nitrogen, such as air Oxygen method that produces around 90% purity.

The pressure swing adsorption oxygen generation method (hereinafter referred to as the oxygen PSA method) is widely used in the process of processing a mixed gas mainly composed of oxygen and nitrogen, such as air, to generate concentrated oxygen. This oxygen PSA method uses zeolite that selectively adsorbs nitrogen as an adsorbent, and uses a device (oxygen PSA device) equipped with a plurality of adsorption towers filled with zeolite, which basically operates at a higher pressure by repeatedly alternating each adsorption tower Concentrated oxygen is continuously produced by the adsorption process and the regeneration process operated at lower pressure.

In such an oxygen PSA device, oxygen is concentrated and separated from air by utilizing the high selective adsorption characteristics of zeolite for nitrogen, but oxygen and argon have approximately the same adsorption characteristics for zeolite, so the oxygen obtained by separation and concentration contains argon, So its maximum concentration is about 95%.

On the other hand, as a condition for using oxygen, when using oxygen to cut metal, if the oxygen concentration does not reach about 99.5%, there will be problems in cutting speed and cutting surface. In addition, when medical oxygen is used in hospitals, the Pharmacopoeia Law It is stipulated that the oxygen concentration must be above 99.5%. When electric furnace steelmaking is used, the oxygen concentration should be below 95%. In addition, in most oxygen-consuming departments, an oxygen concentration of about 90% is sufficient, so the scope of application of the oxygen PSA method is very wide. Because of this, an oxygen concentration of around 90% is sufficient, but in sectors where a large amount of oxygen is consumed, various improvements have been made to the PSA method in order to obtain cheaper oxygen.

As the focus of improving the performance of the oxygen PSA method, two points can be cited, that is, in order to miniaturize the device, increase the oxygen production amount of the unit adsorbent used; in order to reduce the power consumption and increase the oxygen recovery rate of the product.

As mentioned above, the oxygen PSA method has an adsorption step and a regeneration step as basic steps, but in order to increase the oxygen recovery rate, a pressure recovery step and a repressurization step are added to these basic steps. In addition, in order to replace the pressure recovery process, a co-current decompression process is also carried out, and the concentrated oxygen remaining in the adsorption tower is used as a product or cleaning gas, and in order to increase the oxygen production amount of the unit adsorbent, it can also be used in In the regeneration process, part of the product gas is used for purge operation to promote the nitrogen desorption of the adsorbent. This cleaning operation is to reduce the partial pressure of the easily adsorbed components in the gas phase by supplying a part of the product gas from the product outlet end in the stage of reducing the internal pressure of the adsorption tower through decompression, and promote the method of nitrogen gas analysis. It involves the process of normal pressure regeneration and vacuum regeneration.

In order to improve the performance of the oxygen PSA method, the method in the past is such as the method described in Japanese Patent Application Publication No. 63-144104. In the pressure recovery process, two adsorption towers are connected to each adsorption tower (product gas) Outlet) and the lower part (raw material gas inlet) simultaneously carry out the pressure equalization process of gas recovery (up and down simultaneous pressure equalization). At this time, more gas can be recovered, but in the adsorption tower on the gas receiving side, relatively concentrated oxygen gas is recovered to the upper part of the tower, while air or gas with more nitrogen content than air is recovered to the lower part of the tower. For this reason, when this method is used, the product recovery rate is high, but the oxygen generation per unit adsorbent becomes low.

In addition, the method described in Japanese Patent Application Laid-Open No. 63-144103 is to connect two towers in the same manner as above in the pressure equalization process, and recover gas from the upper and lower parts of the tower at the same time, but at this time, the lower pipeline uses a vacuum exhaust. The gas pipeline is used to discharge part of the recovered gas from the lower part to adjust the recovery amount from the lower part of the tower. When using this method, compared with the above method, there is not only the problem that the product recovery rate is not too high due to the reduction of the gas recovery amount, but also the pressure boost caused by the recovery in the receiving side tower is small, so in the subsequent pressurization process The amount of oxygen necessary for oxygen pressurization increases, and the adsorption pressure of the tower decreases in the adsorption process for generating oxygen.

That is to say, in the oxygen PSA method, because maintaining a high product recovery rate and increasing the oxygen production per unit of adsorbent is an alternative requirement, a process method that can achieve the coexistence of the two has not been developed yet.

Therefore, the object of the present invention is to provide a pressure swing adsorption oxygen generation method that can maintain a high product recovery rate, increase the oxygen production rate, and reduce the power consumption rating.

In order to achieve the above object, the pressure swing adsorption oxygen generation method of the present invention is an oxygen generation method using a pressure swing adsorption separation method, wherein a plurality of adsorption towers filled with zeolite adsorbents are alternately and sequentially repeated at higher pressures respectively The adsorption process carried out under the atmosphere and the regeneration process carried out below the atmospheric pressure (101KPa), thereby separating oxygen and nitrogen from the mixed gas mainly composed of oxygen and nitrogen to generate oxygen, is characterized in that after the above adsorption process is completed, The outlet end of the adsorption tower is connected with the outlet end of the adsorption tower after the above-mentioned regeneration process is completed, so that the residual gas in the adsorption tower after the adsorption process is completed is recovered in the adsorption tower after the regeneration process is completed, so as to carry out the pressure recovery process, At the same time, the above-mentioned mixed gas is introduced into the adsorption tower from at least one inlet port of the adsorption tower after the adsorption process and the adsorption tower after the regeneration process.

In addition, the present invention is also characterized in that the adsorption tower that introduces the above-mentioned mixed gas is the adsorption tower after the regeneration step is completed, by introducing the above-mentioned mixed gas at about atmospheric pressure (101KPa) to carry out a pressurization process, after the primary pressurization process is completed. While a part of the product oxygen is supplied from the outlet end in the adsorption tower, the mixed gas of about atmospheric pressure (101KPa) is continuously introduced from the inlet end to carry out the secondary pressurization process. The adsorption tower that introduces the above mixed gas is the adsorption tower after the adsorption process is completed. The above-mentioned mixed gas is introduced at a pressure approximately equal to that of the adsorption process, and vacuum exhaust is simultaneously performed from the inlet port during the pressure recovery process of the adsorption tower after the above-mentioned adsorption process.

Figure 1 shows a system diagram of an example of an oxygen PSA unit.

Fig. 2 shows a flowchart of the first embodiment of the present invention.

Fig. 3 shows a flowchart of a second embodiment of the present invention.

Fig. 4 shows a flowchart of a third embodiment of the present invention.

Fig. 5 shows a flowchart of a fourth embodiment of the present invention.

Hereinafter, the present invention will be described in further detail in combination with the illustrated embodiments.

At first, Fig. 1 represents an example of the oxygen PSA plant that is used to implement the method of the present invention, shows that there are three adsorption towers A, B, C that are respectively filled with adsorbent zeolite, from the mixed gas air that is main component with oxygen and nitrogen A three-tower oxygen PSA device for separating and producing oxygen.

This oxygen PSA device has the above-mentioned three adsorption towers A, B, C and the blower 1 that boosts the raw material air to a specified pressure and sends it to the above-mentioned adsorption tower, the vacuum pump 2 that vacuum-exhausts the above-mentioned adsorption tower, temporarily stores the The product storage tank 3 for the product oxygen exported from the tower, the flow control valves 4 and 5 for controlling the gas flow during the regeneration process and the pressurization process, and the flow regulating valve 6 for controlling the supply of product oxygen, and the adsorption process for switching each adsorption tower , multiple automatic valves 11, 12, 13, 14, 15, 16, 17 (for the valves attached to each adsorption tower, corresponding to each adsorption tower A, B, C, add a, b, c) And the air introduction pipe 18 that is used to introduce the air of atmospheric pressure (101KPa) state into the adsorption tower.

The above-mentioned oxygen PSA device is a device that opens and closes the above-mentioned multiple automatic valves in a prescribed order to continuously generate oxygen. For example, by repeating the 9 processes shown in FIG. The oxygen and nitrogen are separated to produce the product oxygen.

Hereinafter, the first embodiment of the method for generating oxygen according to the present invention will be described in conjunction with the process diagram shown in FIG. 2 using the above-mentioned nitrogen PSA device.

First of all, process 1 is to switch adsorption tower A to the adsorption process, adsorption tower B to the pressure recovery process after the regeneration process is completed, and adsorption tower C to the state of the pressure recovery process after the adsorption process is completed. In the adsorption tower A Separation of oxygen and nitrogen.

That is to say, use the blower 1 to introduce the feed air boosted to a predetermined pressure, such as 106KPa, into the adsorption tower A, and the nitrogen in the air is adsorbed on the zeolite filled in the tower and separated from the oxygen. The product is exported in oxygen form.

In addition, for the adsorption tower B whose internal pressure is lower than the atmospheric pressure (101KPa) and the adsorption tower C whose internal pressure is higher, the pressure recovery of the outlet ports of the two is connected to each other, and the flow regulating valve 5 (see Figure 1) is used to adjust the adsorption. The gas flow in the tower C is introduced into the adsorption tower B from the outlet side, and at the same time, the air in the atmospheric pressure state is sucked in from the inlet side of the adsorption tower B through the air introduction pipe 18 . Thus, in the adsorption tower B, the oxygen-rich gas in the adsorption tower C is recovered to the outlet side of the adsorption tower B, and at the same time, the primary pressurization of the raw material air is introduced from the inlet side of the adsorption tower B without pressurization by the blower 1 process.

In process 2, adsorption tower A continues to carry out the adsorption process of receiving pressurized raw material air from the lower part of the tower and generating product oxygen from the top of the tower, while adsorption tower B carries out the second process of receiving a part of product oxygen generated from adsorption tower A from the top of the tower. pressurization process. In addition, the adsorption tower C is subjected to a vacuum regeneration process in which the gas in the tower is exhausted by the vacuum pump 2 to reduce the pressure in the tower and analyze the nitrogen adsorbed on the adsorbent.

In step 3, adsorption tower A continues to perform the adsorption process, and adsorption tower B continues to perform the secondary pressurization process, and finally pressurize to the pressure during the adsorption process, that is, approximately the same pressure as the adsorption pressure. The adsorption tower C is exhausted with a vacuum pump 2, and when it reaches a higher degree of vacuum, it is vacuum exhausted while receiving a part of the product oxygen generated from the adsorption tower A from the top of the tower at the same time, which is in the so-called exhaust cleaning state (cleaning and regeneration process) ).

In process 4, adsorption tower A is in the same pressure recovery process as adsorption tower C in process 1, adsorption tower B is in the same adsorption process as adsorption tower A in process 1, and adsorption tower C is in the same adsorption process as adsorption tower C in process 1. The same primary pressurized state of column B. Hereinafter, in step 5, adsorption tower A is in the vacuum regeneration step, adsorption tower C is in the secondary pressurization step, and in step 6, adsorption tower A is in the state of cleaning and regeneration step.

In addition, in operation 7,8,9, adsorption tower C is in the state of adsorption tower A in operation 1-3, adsorption tower A is in the state of adsorption tower B, and adsorption tower B is in the state of adsorption tower C, and operation 9 ends After that, return to the state of process 1.

In this way, each adsorption tower performs steps 1 to 9, and returns to step 1 from step 9 to continuously generate oxygen. If the cycle time is 60 seconds, the time of each process is usually: 5-10 seconds for processes 1, 4, and 7, 10-15 seconds for processes 2, 5, and 8, and 40-45 seconds for processes 3, 6, and 9. Second. In addition, the pressure of each process is usually about 101KPa for adsorption pressure, 26.7KPa for vacuum recovery pressure, 106KPa for the final pressure in the primary pressurization process, and about 101KPa for the final pressure in the secondary pressurization process.

As shown in this embodiment, in the pressure recovery process, through the outlets of the adsorption tower with a higher pressure in the tower after the adsorption process is completed and the adsorption tower with a lower pressure in the tower after the regeneration process than atmospheric pressure (101KPa) The ends of the adsorption tower are connected to each other, and the upper gas of the adsorption tower after the adsorption process is recovered from the top to the adsorption tower after the regeneration process is completed, and the air in the state of atmospheric pressure (101KPa) is sucked from the lower part of the adsorption tower. The oxygen-rich gas in the adsorption tower is recycled to the adsorption tower after the regeneration process is completed, and the adsorption tower can be pressurized efficiently at the same time.

That is to say, the adsorption tower after the regeneration process must be pressurized to a pressure close to the adsorption pressure as much as possible in the above-mentioned primary pressurization process and secondary pressurization process before entering the next adsorption process, but as above As mentioned above, in the primary pressurization process, while the oxygen-rich gas is recovered to the upper part of the adsorption tower after the regeneration process is completed, by sucking air from the lower part of the tower, the amount of recovered gas can reach a necessary sufficient amount. , while fully increasing the pressure in the adsorption tower. Therefore, the pressure in the adsorption tower entering the secondary pressurization process using a part of the product oxygen can be made higher than before, and the amount of product oxygen used can be reduced.

By reducing the amount of product oxygen used for the above pressurization, the adsorption operation of the adsorption tower in the adsorption step can be performed in a stable state, and the production of product oxygen can be increased. In addition, the air sucked into the adsorption tower in the primary pressurization process is the air with the same composition as the raw material mixture, and because the air does not pass through the blower 1, it is sucked into the adsorption tower by the pressure difference between the negative pressure in the tower and the atmospheric pressure (101KPa). In the adsorption tower, there is no need to pass through the compression power brought by the blower 1. In addition, compared with the use of the blower, the amount of air actually processed is increased compared with the past, so it is expected to reduce the power cost and increase the output of product oxygen.

Fig. 3 shows a flowchart of Embodiment 2 of the present invention. Compared with the above-mentioned embodiment 1, in the secondary pressurization process operation, continue to inhale air until the pressure in the tower is close to atmospheric pressure (101KPa). In addition, in the following embodiments, the same parts as those in the above-mentioned embodiment 1 will not be described in detail again.

That is to say, operation 1 is the same as above-mentioned embodiment 1, and adsorption tower A receives the feed air from blower 1, enters the adsorption operation that produces product oxygen, adsorption tower B carries out the pressure recovery operation after completion of the regeneration operation, and adsorption tower C performs adsorption In the pressure recovery process after the process is completed, the adsorption tower B recovers the oxygen-rich gas from the outlet side of the adsorption tower C to the outlet side, and at the same time it is still in the state of a pressurization process in which air is sucked in from the inlet side through the air inlet pipe 18 .

Process 2 is that the adsorption tower A continues to perform the adsorption process, the adsorption tower B performs the secondary pressurization process, and the adsorption tower C performs the vacuum regeneration process of discharging the gas in the tower through the vacuum pump 2. At this time, in the adsorption tower B, it is received from the top of the tower. Part of the product is oxygen, and air is also sucked in from the lower part of the tower. Therefore, in the adsorption tower B, the product oxygen in the upper part of the tower and the air in the lower part of the tower are used for secondary pressurization.

In process 3, adsorption tower A continues the adsorption process, and adsorption tower B continues the secondary pressurization process, but in this adsorption tower B, according to the pressure inside the tower, it is possible to stop sucking air from the lower part of the tower and only receive products from the top of the tower Oxygen for pressurization. In addition, while the adsorption tower C receives part of the product oxygen from the top of the tower, it performs a cleaning and regeneration process of vacuum exhaust.

Hereinafter, in the same manner as above-mentioned embodiment 1, in operation 4, carry out the same pressure recovery process as adsorption tower C in operation 1 in adsorption tower A, carry out the same adsorption process as adsorption tower A in operation 1 in adsorption tower B, Adsorption tower C performs the same primary pressurization as adsorption tower B in process 1; in process 5, adsorption tower A performs a vacuum regeneration process, adsorption tower C performs a secondary pressurization process, and in process 6, adsorption tower A performs cleaning Regeneration process. And in operation 7,8,9, adsorption tower C is in the state of adsorption tower A in operation 1～3, and adsorption tower A is in the state of adsorption tower B, and adsorption tower B is in the state of adsorption tower C, after operation 9 finishes , and return to process 1.

As shown in this embodiment, even in the secondary pressurization process, until the pressure in the tower reaches close to atmospheric pressure (101KPa) by continuing to suck in air, the amount of air suction is more than that of the above-mentioned embodiment 1, so the pressure required can be reduced. The amount of product oxygen, and further increase the production of product oxygen. In addition, in the secondary pressurization process, the pressure at which the suction of air is stopped may be close to the atmospheric pressure, but it is usually about 80.0-93.3KPa.

Fig. 4 shows the flow chart of the embodiment of the present invention 3, compared with above-mentioned embodiment, during pressure recovery process, will continue to introduce raw material air to the adsorption tower of recovery gas discharge side after adsorption process completes (operation 1,4,7 ).

Like this, by introducing raw material air to the adsorption tower that enters the pressure recovery process after the adsorption process, the pressure in the adsorption tower can be maintained at the adsorption pressure, and the nitrogen analysis on the adsorbent can be suppressed, so it is possible to prevent nitrogen from being mixed into the adsorption tower. The upper part is recovered into the gas in the adsorption tower after the regeneration process is completed, and the adsorption tower on the receiving side can be fully pressurized.

Fig. 5 shows the flow chart of embodiment 4 of the present invention, compared with above-mentioned embodiment 1, when carrying out pressure recovery, release recovery gas from the adsorption tower top of the recovery gas discharge side after adsorption process finishes, also will simultaneously from tower bottom Simultaneously start vacuum exhaust (steps 1, 4, 7). As a result, there is no idle time for the vacuum pump, which is expected to improve efficiency.

In addition, in the present invention, various embodiments can be combined for implementation, and the number of adsorption towers used is not limited to 3, and it is also applicable to the form of using 2 or more adsorption towers.

In addition, the adsorbent can use zeolite that preferentially adsorbs nitrogen in a large amount compared with oxygen, such as MS-5A, MS-10X, MS-13X, and mordenite. In addition, zeolite in which ions are exchanged for metals in zeolite can also be used. Zeolite with a fine-pore size that sufficiently absorbs nitrogen at an adsorption rate, etc.

In addition, the mixed gas mainly composed of oxygen and nitrogen is not limited to air, and a mixed gas of any composition can be used. In this case, the above-mentioned air introduction pipe may be connected to a place where the raw material mixed gas is generated or a storage tank.

Hereinafter, using the device with the structure shown in above-mentioned Fig. 1, carry out the operation method shown in the above-mentioned embodiments 1-4 and the above-mentioned up-and-down simultaneous pressure equalization method of the conventional examples, and illustrate the implementation results of measuring the oxygen generation amount and the oxygen recovery rate.

The inner diameter of the adsorption tower is 155mm x 1.6m high, and the adsorbent uses 1.6mm particles of molecular sieve 5A. The operating conditions were set at an adsorption pressure of 106KPa and a vacuum regeneration pressure of 26.7KPa. In addition, the cycle time is 60 seconds, the process corresponding to the process 1 is 5 to 10 seconds, the process corresponding to the process 2 is 10 to 15 seconds, and the process corresponding to the process 3 is 40 to 45 seconds. The experimental results are shown in Table 1.

Table 1 Oxygen production oxygen concentration Oxygen recovery rate Example 1 1.00Nm ³ /h 93% _O2 56% Example 2 1.10Nm ³ /h 93% _O2 56% Example 3 0.95Nm ³ /h 93% _O2 53% Example 4 1.15Nm ³ /h 93% _O2 56% Past example 0.9Nm ³ /h 93% _O2 54%

As mentioned above, using the pressure swing adsorption type oxygen generation method of the present invention, in the primary pressurization process, since the raw material gas or the mixed gas with the composition of the raw material gas is introduced into the adsorption tower, it can prevent the regeneration process from being completed. Nitrogen gas flows into the final adsorption tower, and the adsorption tower can be fully pressurized at the same time, which can reduce the amount of product oxygen used for pressurization and increase the production of product oxygen.

In particular, by sucking the raw gas or a mixed gas having approximately the same composition as the raw gas into the adsorption tower after the regeneration process without using a pressurizing means such as a blower, the power cost can be saved compared with the processing capacity.

In addition, when the raw material gas is air, since the air in the adsorption tower is sent in at atmospheric pressure (101KPa), the raw material can be supplied without a blower, therefore, the oxygen recovery rate can be significantly improved substantially.

Claims (5)

1. A method of generating oxygen by a pressure swing adsorption separation method by alternately and sequentially repeating an adsorption process in which a plurality of adsorption towers filled with a zeolite adsorbent are respectively operated at a pressure higher than that of other adsorption towers, and, A regeneration process operated at a pressure lower than 101 KPa whereby oxygen and nitrogen are separated from a mixed gas mainly composed of oxygen and nitrogen to produce oxygen, The method is characterized by: Make the outlet end of the adsorption tower after the completion of the adsorption process communicate with the outlet end of the adsorption tower after the completion of the regeneration process, so that the residual gas in the adsorption tower after the completion of the adsorption process is recovered in the adsorption tower after the completion of the regeneration process Carry out the pressure recovery process, and at the same time introduce the mixed gas into the adsorption tower from any one or two inlet ports of the adsorption tower after the adsorption process and the adsorption tower after the regeneration process. 2. The method for producing oxygen by pressure swing adsorption separation method according to claim 1, characterized in that, the adsorption tower for introducing the mixed gas is the adsorption tower after the regeneration process is completed, and the process is carried out by introducing the mixed gas under the pressure of 101KPa. One pressurization process. 3. The method for producing oxygen by pressure swing adsorption separation method according to claim 2, characterized in that, in the adsorption tower after the completion of the primary pressurization process, a part of product oxygen is supplied from the outlet end, and at the same time, 101Kpa is continuously introduced from the inlet end The mixed gas of the pressure is subjected to the secondary pressurization process. 4. The method for producing oxygen by pressure swing adsorption separation method according to claim 1, characterized in that, the adsorption tower into which the mixed gas is introduced is the adsorption tower after the adsorption process is completed, and the mixed gas is produced at the same pressure as the adsorption process. is imported. 5. The method for producing oxygen by pressure swing adsorption separation method according to claim 1, characterized in that the adsorption tower after the adsorption process is vacuum exhausted from the inlet port simultaneously during the pressure recovery process.

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