JPS6380821A - Operation for separating gas by variable pressure adsorption - Google Patents

Abstract

PURPOSE:To enhance the concn. and recovery percentage of product gas, by leveling the pressure of an absorbing tower held under negative pressure in a desorbed state and subsequently allowing the product gas to flow in said tower to raise the pressure thereof to a predetermined absorbing pressure. CONSTITUTION:Raw gas is supplied to an absorbing tower 1 and a pressure holding valve 13 is operated to hold absorbing pressure therein to perform an absorbing process, and product gas is discharged from the adsorbing tower 1 to be stored in a product gas tank 4. Next, the pressure of the absorbing tower 1 after finishing the absorbing process and the pressure of an absorbing tower 2 after finishing a desorbing process are leveled and, further, the product gas is allowed to flow in the absorbing tower 2 from the tower top part A to raise the pressure of said tower 2 to adsorbing pressure to prepare for the next absorbing process. The absorbing tower 1 is evacuated by a vacuum pump 11 to be desorbed and, thereafter, the absorbing tower 1 returns to another absorbing process through the pressure leveling process and through the pressure raising process by a product gas. This operation is successively repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method of operating gas separation using pressure swing suction M (hereinafter referred to as PSA). especially.

The present invention relates to a method of operating a PSA for gas separation, in which the product gas pressure is used in the pressure increase step to increase the pressure to the adsorption pressure, thereby improving the product gas concentration and gas recovery rate.

[Prior art] Conventionally, in PSA operation, in order to raise the adsorption tower to four pressures from the regeneration pressure under negative pressure to the adsorption pressure based on atmospheric pressure, (1) pressure equalizing gas was supplied from the top of the adsorption tower (product gas extraction side). , (2) The pressurized raw material gas was introduced into the adsorption tower in this order from the bottom of the adsorption tower (raw material gas supply side). At this time, if there is a large difference between the pressure inside the adsorption tower after introducing pressure equalizing gas and the pressure of the raw material gas, )ruEEK
l. Even if the feed gas supply bt is restricted, the feed gas expands rapidly as it is introduced into the low pressure chamber, and flows through most of the adsorption tower at a high flow rate, from near the center of the adsorption tower to near the top of the adsorption tower. reach. When the pressure is increased in this way, (1) equal pressure gas is produced from the top outlet of the adsorption column in the subsequent adsorption step.

(The raw material gas that has flowed through most of the adsorption tower at a flow rate higher than that due to gas expansion, 0) The raw material gas that has flowed into the adsorption separation from the entrance of the adsorption tower at a flow rate of 1 minute and has effectively contacted all the adsorbents. It flows out.

Therefore, the product gas concentration at the outlet of the adsorption tower is:

(1) High, (Low, 0) High, and the average gas concentration decreases due to the raw material gas flowing through most of the adsorption tower at a large flow rate due to rapid gas expansion.

In the conventional method, the adsorption process must be stopped before the low-FA gas flows out, which results in a short adsorption time, resulting in several problems such as a reduction in the life of the on-off valve and a reduction in the product gas recovery rate. .

[Problems to be Solved by the Invention] The PSA gas separation operation method of the present invention aims to provide an efficient PSA gas separation operation method that avoids rapid raw material gas inflow and gas expansion. Therefore, it is an object of the present invention to provide a PSA operating method that prevents a decrease in the concentration of the product gas, that is, eliminates a region where the concentration of the product gas decreases, thereby improving the average concentration of the product gas. do. In addition, the present invention has two advantages: it lengthens the adsorption time, reduces the frequency of opening and closing the valve, and extends the life of the valve.
The purpose is to provide a SA driving method. A further object of the present invention is to provide a method of operating a PSA gas separation that can increase the recovery rate of product gas.

[Means for Solving the Problems] In order to separate the raw material gas to be separated by pressure fluctuation adsorption, the present invention brings the adsorption column under pressure equalization, increases the pressure in the primary stage, performs the necessary adsorption at a predetermined pressure, and then performs the necessary adsorption in the primary stage. In gas separation operation using pressure fluctuation adsorption, which repeats an adsorption-desorption cycle in which the pressure is lowered to an equal pressure and then increased to a desorption pressure, the pressure of the desorbed adsorption tower under negative pressure is equalized, and then product gas is introduced into the adsorption tower. Gas fraction ll by pressure fluctuation adsorption, which is characterized by increasing the pressure of the gas to a predetermined adsorption pressure! It's a driving method.

[Function] In the PSA method, when gas at adsorption pressure is introduced into the adsorption tower after pressure equalization, rapid expansion occurs due to the pressure difference, and the Q material gas passes through the adsorption tower at a high flow rate. Since the adsorption separation efficiency decreases, it is necessary to supply the raw material gas at approximately the same pressure as the adsorption tower, fill the raw material gas without significantly expanding it, and increase the pressure to the adsorption pressure. but.

When the equalization pressure is a negative pressure, it is impossible to increase the pressure between the equalization IE force and the atmospheric pressure without expanding it with the raw material gas supplied from the booster. In the operating method, the pressure is increased from the equal pressure to an adsorption pressure at which the flow rate into the adsorption tower can be controlled using a product gas that does not require adsorption separation.

In the conventional operation method, when feed gas is introduced into the adsorption tower after it has been desorbed under negative pressure, rapid gas expansion occurs due to the pressure difference, and the feed gas moves through the adsorption tower at a high speed. For passage, the feed gas, still containing the components to be adsorbed, leaves the adsorption column and enters the product gas storage tank.

for that.

The concentration of product gas decreases, and the adsorption separation efficiency decreases.

Therefore, in the PSA gas separation operation method of the present invention, the pressure of the desorbed adsorption tower downstream is equalized with other adsorption towers that have completed adsorption, and the product gas composition is relatively high with the residual gas in the other adsorption towers. By raising the pressure with equal pressure gas close to 100 ml, and then introducing the product gas and raising the pressure of the adsorption tower, it is possible to prevent the product gas from being diluted rapidly by the raw material gas that has passed through the adsorption tower. Therefore, the PSA operating method of the present invention can ultimately improve the concentration of product gas.

The PSA operating method according to the present invention and its characteristics are described in two PSs.
This will be explained using device A as an example and comparing it with the conventional operating method.

Fig. 1 shows the configuration of a two-column PSA device, and Fig. 2 shows an example of pressure change in the two-column PSA during operation of the PSA.

The PSA device includes 1 and 2 adsorption towers filled with adsorbents such as zeolite and activated carbon, 3 to 10 on-off valves, 11 blowers, 12 vacuum pumps, 13 pressure holding valves, 14 product pressure holding tanks, and It has piping connecting these, and also has a control system for managing valve opening and closing, which is omitted in Figure 1.

The product pressure holding tank 14 is a conventional PSA tank for the purpose of smoothing and taking out the production amount of product gas that fluctuates every two hours.
Although it is used for.

This is an essential component in the PSA operating method of the present invention.

In the apparatus configured as described above, the conventional operation method is as follows, for example, as shown in FIG.

(a) Pressure equalization step 1: Connect the adsorption tower 2 that has completed the adsorption step with the adsorption tower 1, which has been left under sufficient vacuum and the adsorbent has been regenerated. ) is introduced into the adsorption tower 1.

At this time, the valve operation is, for example, opening valve 8.9 and closing valves 4, 5, and 6.7. Further, the pressure changes as shown in FIG.

<Exit> Pressurization step: This is a step in which the raw material gas is introduced into the adsorption tower 1 into which the pressure equalization gas has been introduced, and the pressure inside the tower is increased to the target adsorption pressure.

(c) Adsorption step: This is a step in which the raw material gas is introduced into the adsorption tower 1, which has been pressurized to the adsorption pressure, at a flow rate effective for adsorption, and at the same time, the product gas is taken out from the other end. During this time, the adsorption tower 2 continues to regenerate the adsorbent as in the previous step. At this time, the valve operations are 1, for example, valves 3, 4, 8, 10, . and 7 are open, and valve 5°6.9 is closed.

(d) Pressure equalization step 2: The adsorption tower 1, which has completed the adsorption step, and the adsorption tower 2, which has completed the regeneration of adsorption M, are connected, and the pressure equalization step 1
This is a process in which the same operations are performed.

However, the gas flow direction is opposite to pressure equalization step 1, and adsorption tower 1
is reduced in pressure, and the pressure in the adsorption tower 2 is increased. The loop operation is the same as the pressure equalization step 1.

(e) Desorption step: This is a step in which the adsorption tower 1, which has completed adsorption and sent out the semi-finished product gas remaining in the tower to another tower, is depressurized and the adsorbent is regenerated (regeneration). During this time, in the adsorption tower 2, a pressurization J step and a subsequent adsorption step are performed. For example, when the adsorption tower 2 is in a pressure increasing step, valves 3, 5, 9, 10, and 6 are open, and valves 4, 7, and 8 are closed.

In FIG. 2, the solid line indicates the operating process of the adsorption tower 1, and the two-dot line indicates the operating process of the adsorption tower 2. Further, each process shown in the upper part is described for the adsorption tower 1.

With this, one cycle is completed, and the cycle is repeated in sequence.
Product gas is obtained almost continuously.

FIG. 2 is a graph showing the above fluctuations in gas pressure over time t. This graph clarifies the characteristics of the above-mentioned steps more clearly. Therefore, the second
The following is an explanation using a diagram.

First, after the pressure equalization process is completed, valves 3, 4.10 are opened, valves 5, 6, and 8.9 are closed (at this time, in the adsorption tower 2, valve 7 is open and desorbed), and the pump 11 pumps the raw material gas. When supplied, the pressure in the adsorption tower 1 rises (pressurizes) and reaches the adsorption pressure. Thereafter, the valve 8 is opened, and the gas component to be adsorbed and removed is adsorbed by the adsorbent filled in the adsorption tower 1, and the product gas flows out from the top of the tower. The pressure at P in FIG. 2 reaches 3 points (pressure P, ) in the pressure equalizer 81, and is increased to pressure P1 in the pressure increasing step, and enters the adsorption step.

The adsorption tower 1 is desorbed by the pump 12 (pressure equalization step 2 and desorption step in FIG. 2).

The state of the filling gas in the adsorption tower in the step L is as follows:
This will be explained using figures. In the pressure equalization process, a part of the pressure equalization gas remaining in the adsorption tower and having a relatively similar composition to the product gas causes
The pressure of the adsorption tower is increased, and at the end of the pressure equalization step shown in FIG. Therefore, FIG. 3, which shows the filling state of the adsorption tower at the end of the pressure increasing step, is composed of pressure equalization gas and raw material gas. [The feed gas is the gas filled by expansion. 11 is the length of the effective adsorption column for the gas filled by expansion; 1. is the length of the effective adsorption tower for the gas supplied in the adsorption process; 1. <1°.

As mentioned above, in the conventional operation method, in the pressure equalization step 1 and the pressure increase step 2, the adsorption tower 1 is pressurized from a vacuum state by pressure equalization gas or raw material gas. As shown, the pressure equalized gas and the raw material gas are introduced into the adsorption tower, which remains in a low pressure state even after pressure equalization, so they expand within the tower.

In such a situation, where the adsorption column is filled into the adsorption tower while contacting the adsorbent at a high flow rate, even if the raw material gas is supplied at a sufficient flow rate to be effective for adsorption in the adsorption process, the product gas concentration will be as shown in Figure 4. As shown in the figure, it is variable. That is, to explain this in sequence: ■ At first, a product gas with a relatively high gas concentration is obtained because the pressure equalized gas flows out, and ■ Next, the raw material gas expands in the column and reaches the center of the column at a high flow rate. However, as the product gas passes through the short distance from the center of the column to the top of the column at a flow rate effective for adsorption, a product gas with a low gas concentration is obtained. As the distance through which the adsorbent passes becomes longer, a product gas with a higher gas concentration is obtained.After that, the adsorbent breakthroughs (saturates) and the resulting product gas concentration decreases.

Therefore, a sufficiently high gas concentration cannot be obtained unless the adsorption time is shortened to a point before the product gas concentration reaches its minimum point (lowest point, see FIG. 4a). However, if the adsorption time is shortened, the life of the pulp will be shortened, resulting in drawbacks such as a decrease in gas recovery rate. Furthermore, in order to enable adsorption separation even at a high flow rate due to gas expansion, it is necessary to increase the size of the adsorption tower, which has the disadvantage of increasing manufacturing costs, adsorbent costs, etc.

In order to eliminate such drawbacks, the operating method of the present invention is adopted. For example, when the adsorption tower is in a low pressure state after the end of the pressure equalization step 1, according to the example of the apparatus shown in FIG.
．． 8.10 and close valves 4.5 and 6.9, so that the product gas flows from the product tank 14 maintained at the adsorption pressure to the adsorption tower 1, so that it does not expand in the tower even if the raw material gas is supplied. If the pressure is increased with the product gas until the adsorption pressure is reached,
Even when the raw material gas is introduced thereafter, it flows at a flow rate that is effective for adsorption and effectively contacts all the adsorbents, so that the product gas concentration does not decrease.

That is, in the operating method according to the present invention, in the pressure increasing step,
Inside the adsorption tower, gas is supplied from the top of the tower in the following order: - Equal pressure gas, - Gas introduced from the product tank, and - Raw material gas from the entrance of the adsorption tower.
Due to the outflow, the product gas concentration decrease region disappears as shown in the 41st mbkm, and the average product gas concentration increases.

In addition, to obtain the same concentration of product gas, the adsorption time can be lengthened, reducing the frequency of valve switching, extending the valve life and improving the gas recovery rate.

The operating method of the present invention for the two-column PSA gas separation apparatus shown in FIG. 1 will be further explained.

First, in the adsorption step, when valves 3, 4, 8.10 are opened, valves 5, 6.9 are closed, and pump 11 is activated, a passage is created on the left side of adsorption tower 1.

A raw material gas flows into the adsorption tower 1 . Gas is at holding pressure; f?
13, the components to be adsorbed are adsorbed by the adsorbent in the adsorption tower 1, and the product gas flows out from the top of the tower, and the product gas is stored in the product tank 14. Next, valves 4.5, 6.7.10 are closed to equalize the pressure of the adsorption tower 2 where the valve 8.9 step has been completed, and the suction tower 2 is filled with pressure equalization gas and maintained at pressure P. Furthermore, valves 4, 7.8 are closed and valve 9 is opened.

Product gas flows into the adsorption tower 2 from the tower top A, and on the other hand, the adsorption tower 1 is evacuated by a vacuum pump, and the zero-order gas is desorbed.
When the pressure in the adsorption tower 2 reaches the adsorption pressure, the valve 5 is opened, and the pump 11 causes the raw material gas to flow into the adsorption tower 2 from the bottom B, thereby performing an adsorption process. In such a PSA operating method, when gas rapidly flows into the adsorption tower and passes through the adsorption tower with rapid gas expansion, the inflowing gas is purified gas, that is, product gas. There is less chance that unpurified substances will flow out to the product side, and the purity or concentration of the product gas will be increased and improved.

When a PSA gas separation is operated in a conventional manner, the product gas produced has a concentration of
It fluctuates like this. In order to follow this decrease in concentration, 1. With a short adsorption time of -5aFIlh&JJ+(
'Ta<Lfp+,)mlT[1MLjI711. x!
-4? However, in this method, the opening/closing time of the valve is shortened, and the operating efficiency is lowered. On the other hand, in the operating method of the present invention.

As shown in Figure 4, the concentration of the product gas is averaged and 1 As shown in the figure, the density is approximately constant. Furthermore, since the adsorption process takes a long time, the frequency of opening and closing of the valve is reduced, and more efficient operation can be achieved. That is, the fourth
As shown in Figure a, in the conventional operating method, the concentration fluctuates as shown by the dotted line, and furthermore, the average concentration is lower than that in the Jj method of the present invention. On the other hand, in one operating method of the present invention, the concentration of the product gas can be maintained at approximately the highest level as shown in the figure. 1. In the operating method of the present invention, if the adsorption time is unnecessarily long and a breakthrough state is reached, 1
As shown by the dotted chain line, the a degree decreases.

[Effect of the invention] 9. PSA gas separation operation method of the present invention. Firstly.

Improved product gas concentration compared to conventional PSA method [
Second, we were able to provide an operating method for PSA gas separation that improves the gas recovery rate. Third, we were able to open and close valves.

Since we were able to significantly reduce the frequency of switching, we were able to extend the valve life.

Technical effects such as ensuring efficient operation were achieved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one example of a PSA device for carrying out one embodiment of the operating method of the present invention. FIG. 2 is an explanatory diagram showing pressure fluctuations in each adsorption tower in the case of PSA operation using the apparatus shown in FIG. FIG. 3 is an explanatory diagram showing the inflow state in the pressure increasing step of the conventional PSA operating method. FIGS. 4a and 4b are explanatory graphs showing the state of fluctuation in product gas concentration in the conventional operating method and the operating method of the present invention. [Explanation of symbols of main parts] 1.2. ,, Adsorption tower 3-10. ,,opening/closing valve 11,
,,Blower 12, ,It empty pump 13,
,,Pressure valve 14. ,,Product Tank 15,,,Piping Patent Applicant Sumitomo Heavy Industries Co., Ltd. Sub-Agent Patent Attorney Hiroshi Kuramochi (1 other person) 1 Saiful 4-ken -1 → Cyu) (shi) Figure 3 Salt Absorption 11 hours → Figure 4 Work 1 hour -1 → Figure 4 b

Claims (1)

[Scope of Claims] In order to separate the raw material gas to be separated by pressure fluctuation adsorption, the pressure of the desorbed adsorption tower is equalized with another adsorption tower that has completed adsorption, and then the pressure is further increased, and the pressure is lowered to a predetermined pressure. In gas separation operation using pressure fluctuation adsorption, the pressure is lowered to equalization, and then the adsorption-desorption cycle is repeated to increase the desorption pressure. In gas separation operation by pressure fluctuation adsorption, the pressure of the desorbed adsorption tower under negative pressure is equalized, and then, A gas separation operation method using pressure fluctuation adsorption, characterized by introducing product gas and increasing the pressure of an adsorption tower to a predetermined adsorption pressure.