JP2579180B2 - Stepless pressure equalizing PSA method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an industrial process in which components to be adsorbed in an adsorption process are product gas components, and each of the processes having an adsorption process, a pressure equalization process, a desorption process, and a pressure increase process as basic processes. The present invention relates to a PSA method (pressure fluctuation type adsorption separation method) for separating product gas components by repetition, and more particularly to an improvement in a pressure equalization step at that time.

2. Description of the Related Art A PSA method is known as one of methods for separating an impurity component and a product gas component from a source gas containing impurities. This method is based on an adsorption step, a pressure equalization step, a desorption step, and a pressurization step, and separates a product gas component from a source gas containing impurities by repeating the steps.

The PSA method is divided into two modes depending on whether the component to be adsorbed on the adsorbent is a product gas component or an impurity component.The former mode is one in which the product gas component is added to the adsorbent filled in the adsorption tower. In addition to the adsorption, the impurity component is allowed to pass through.

In this case, the tower A in the high pressure region after the completion of the pressure equalization step is first communicated with the other tower B after the completion of the desorption step to equalize the pressure.

After the pressure equalization, the tower A continuously shifts to the vacuum desorption step and recovers the desorbed gas as a product gas. On the other hand, tower B after pressure equalization
Is usually raised to the adsorption pressure by increasing the pressure with a through gas and preparing for the next pressure equalization step.

Problems to be Solved by the Invention As described above, conventionally, the column A in the high-pressure region after the end of the adsorption step is communicated with another column B to equalize the pressure, and then the column A after the pressure equalization is depressurized. Although the desorbed gas was recovered as a product gas, the pressure after the pressure equalization was as high as about half the adsorption pressure, so that it was inevitable that impurity components were considerably mixed in the product gas.

In order to avoid such disadvantages, it is desirable to lower the pressure after equalization as much as possible. Since the pressure is only about half, in order to further reduce the pressure after equalization, the number of counterparts to be equalized is two,
It must be increased to three towers to increase the number of towers.
For example, if the tower A and the tower to be equalized are two towers B and C, the pressure after the equalization will be about 1/3, and the tower to be equalized with the tower A will be three towers B, C and D. For example, the pressure after equalization is reduced to about 1/4.

However, by increasing the number of columns, the pressure after pressure equalization can be lowered to lower the product recovery pressure, and the purity of the product gas can be increased, but this is extremely disadvantageous in terms of equipment cost and process control.

Therefore, as an alternative to multi-column operation, after the column A in the high-pressure region after the adsorption step is equalized with the other column B, the gas in the initial stage of pressure reduction in the pressure reduction step of the column A is purged out of the system. However, since the pressure after pressure equalization is quite high, about half of the adsorption pressure, the amount of purge gas is large, resulting in loss of product gas components contained in the purge gas. Thus, there is a problem that the product recovery rate decreases.

The present invention has been made in view of the above circumstances, and provides a method of reducing the product recovery pressure by making the pressure equalization step instep.

Means for Solving the Problems The stepless pressure equalizing PSA method of the present invention is characterized in that the component to be adsorbed in the pressure equalization step is a product gas component, and the adsorption step-pressure equalization step-desorption step-pressure increase step is a basic step. In the PSA method in which product gas components are separated and recovered from the raw material gas containing impurities by repeating the respective steps, the column A in the high pressure region after the end of the adsorption step is communicated with another column B, and the equalized gas is removed from the column A. At the same time as sending to the tower B, the product gas component in the equalized gas sent in the tower B is adsorbed, but the non-adsorbed gas is led out,
Thus, the pressure equalizing step is carried out while discharging the non-adsorbed gas out of the system in the tower B to be equalized with the tower A.

 Hereinafter, the present invention will be described in detail.

The method of the present invention comprises a PSA that separates and recovers a product gas component from a raw material gas containing impurities by repeating each of the basic steps including an adsorption step, a pressure equalization step, a desorption step, and a pressure increase step.
This method is applicable when the component to be adsorbed in the adsorption step is a product gas component.

Examples of the source gas containing impurities include gases and combustion gases generated from various furnaces or reactors.
A coke oven gas generated from a coke oven or a gas derived therefrom, an electric furnace, a converter, a blast furnace, a gas generated from a generator, a methanation reaction gas, a gas produced as a by-product thereof, and the like are used. In particular, a coke oven gas or a gas derived therefrom or a gas generated from a blast furnace is important.

The adsorption step is a step of adsorbing the product gas component in the raw material gas to the adsorbent in a pressurized state.

Depending on the composition of the raw material gas, for example, activated carbon, activated carbon fiber, natural zeolite, synthetic zeolite, molecular sieving carbon, silica, alumina, silica-alumina, and carbon coat were applied as the adsorbent to be filled in the adsorption tower. Various adsorbents are used, including porous materials such as silica and / or alumina.

The equalizing step is a step in which the column A in the high-pressure region after the adsorption step is communicated with another column B to equalize the pressure. However, the present invention is different from the conventional method in this step. I will.

The desorption step is a step of recovering the product gas components adsorbed by the adsorbent of the tower A after the pressure equalization under reduced pressure and regenerating the tower A. Decompression includes both an operation of reducing the pressure to atmospheric pressure and an operation of further reducing the pressure to atmospheric pressure or lower. The desorbed gas at the initial stage of depressurization can be purged out of the system or used for increasing the pressure of another column.

The pressure increasing step is a step of increasing the pressure of the column B after the above pressure equalization to the adsorption pressure with a normal through gas.

In the present invention, the equalizing step is performed as follows.

That is, the tower A in the high pressure area after the equalization step is
In addition, the pressure equalizing gas is sent from the tower A to the tower B in communication with the column A, and the product gas component in the sent pressure equalizing gas is adsorbed in the tower B, but the non-adsorbed gas is led out. That is, the pressure equalizing step is performed while discharging the non-adsorbed gas to the outside of the system in the tower B to be equalized with the tower A.

Since the equalizing operation is performed while discharging the equalizing gas sent into the tower B to the outside of the system, the pressure after the equalizing can be arbitrarily set to a pressure close to the atmospheric pressure. For example, if the adsorption pressure is
In the case of 6 kg / cm ² G, the pressure of tower A is increased to 1 kg / cm ² G, 0.8 kg / cm ² G,
It can be set as 0.5kg / cm ² G.

The desorption of the adsorbed components from the column A after the equalizing operation is performed by the column A
May be reduced to atmospheric pressure, and further reduced to an appropriate degree of vacuum using a vacuum pump.

The desorption gas can be entirely a product gas. In order to increase the purity of the product gas, the desorbed gas in the initial stage of depressurization can be purged out of the system, and the remainder can be used as the product gas. Can be significantly reduced, so that the product recovery rate does not significantly decrease.

Function and Effect of the Invention In the present invention, the pressure equalization between the tower A and the other tower B in the high-pressure region after the completion of the pressure equalization step is performed, and the non-adsorbed gas is removed from the system in the tower B to be equalized with the tower A. We go while discharging. In other words, the stepless pressure equalization method is adopted.

By employing this method, the pressure after equalization can be arbitrarily set to a low pressure close to the atmospheric pressure.

For this reason, the product recovery pressure is lowered, and when the process proceeds to the desorption step, product gas can be obtained without significantly lowering the purity.

Further, even when the desorbed gas in the initial stage of the depressurization is purged out of the system, the amount of the purge gas can be significantly reduced, so that the product recovery rate does not significantly decrease.

And, since the product collection pressure can be set low, the gas amount at the time of pressure increase increases, so the effect of depressing the adsorption line of the product gas component in the column works, and the adsorption capacity per unit capacity of the adsorbent increases. Will be.

As described above, in the present invention, the impurity components in the recovered product gas are reduced, and the recovery rate of the product gas component is increased because the adsorption capacity of the adsorbent is increased and the recovery is performed in another column. It does not drop.

In addition, since the number of towers does not increase even if the method of the present invention is adopted, there is no disadvantage in terms of equipment.

 Therefore, the present invention has great industrial significance.

EXAMPLES Next, the present invention will be further described with reference to examples.

Example 1 As a raw material gas, a crude synthetic natural gas obtained by reforming a coke oven gas generated from a coke oven (a gas mainly containing C1 to C4 hydrocarbons and containing H2 or N2 as impurities, CH
(4 content is 60-70vol%) and activated carbon with an average particle size of about 0.8-2.4mm is used as an adsorbent. Adsorption tower: 3 towers Adsorption pressure: 6kg / cm ² G Regeneration pressure: 200torr Product recovery pressure: PSA cycle was performed under the conditions of pressure after pressure equalization to 200 torr space velocity: 100 / h temperature: normal temperature.

The tower A in the high pressure region after the adsorption step was connected to the tower B after the desorption step and sent the equalized gas to the tower B. At this time, the product gas component in the equalized gas was adsorbed in the tower B. The non-adsorbed gas is discharged out of the system while the pressure is maintained, and the pressure of the tower A after the pressure equalization is 0.98 kg / cm ² G, 0.85 kg / cm ² G or 0.51 kg.
/ cm ² G.

For comparison, the equalizing operation of the tower A and the tower B was performed in a closed system without discharging the purge gas from the tower B. The pressure after equalization at this time was 2.2 kg / cm ² G.

 The results are shown in FIG.

FIG. 1 is a graph showing the relationship between product recovery pressure and product gas composition.

From FIG. 1, it can be seen that when the stepless pressure equalization method of the present invention is adopted, the purity of CH4, which is a product, is higher than when a normal one-stage pressure equalization method is adopted, and is an impurity component in the product. H
It is understood that the ratios of 2 and N2 decrease.

Example 2 As a raw material gas, a blast furnace gas (containing N2, H2, CO, etc. as an impurity component and containing CO2 as a product component at 20 vol%) was used.
And a synthetic zeolite used as an adsorbent, the adsorption tower: 3-tower adsorption pressure: 6 kg / cm ² G regeneration pressure: 50 torr product recovery pressure: 0.2kg / cm ² G~50torr space velocity: 100 / h Temperature: normal temperature conditions Performed the PSA cycle.

The tower A in the high pressure region after the adsorption step was connected to the tower B after the desorption step and sent the equalized gas to the tower B. At this time, the product gas component in the equalized gas was adsorbed in the tower B. While adsorbing, the non-adsorbed gas was discharged out of the system, and the pressure of the tower A after equalization was adjusted to 0.2 kg / cm ² G.

 The proportion of CO2 in the recovered product gas was 95 vol%.

For comparison, the equalizing operation of the tower A and the tower B was performed in a closed system without discharging the purge gas from the tower B. The pressure after equalization at this time was 2.0 kg / cm ² G.

The proportion of CO2 in the recovered product gas was 88 vol%, which was inferior to Example 2.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between product recovery pressure and product gas composition in Example 1.

Claims (1)

(57) [Claims] 1. A component to be adsorbed in an adsorption step is a product gas component. By repeating each step including an adsorption step, a pressure equalization step, a desorption step, and a pressure increase step as a basic step, a product gas containing impurities is removed from a product gas. In the PSA method for separating and recovering the components, the column A in the high-pressure region after the end of the adsorption step is communicated with another column B to send the pressure-equalized gas from the column A to the column B. The product gas component inside is adsorbed, but the non-adsorbed gas is led out, so that the equalizing step is performed while discharging the non-adsorbed gas out of the system in the tower A and the counterpart B to be equalized. Stepless pressure equalizing type
PSA method.