JPH02284621A - Method for recovering high purity gas - Google Patents

Abstract

PURPOSE:To attain efficient purge with a small amt. of purge gas by carrying out purge with gas for desorbing adsorbed useful gas at a high flow rate in the early stage and at a low flow rate in the last stage. CONSTITUTION:Raw gas contg. useful gas such as CO is introduced into an adsorption tower 1 packed with activated carbon supporting copper (I) chloride, etc., and CO is selectively adsorbed. When this adsorbed CO is directly desorbed, gaseous impurities such as CO2 and N2 remaining in the tower 1 are discharged together with the CO and the purity of the CO is lowered. In order to prevent the lowering of the purity, part of the gaseous product is fed into the tower 1 as purge gas to purge the gaseous impurities before desorption. The flow rate of the purge gas is increased in the early stage and reduced in the last stage. Efficient purge is attained with a small amt. of the purge gas and high purity gas can be recovered at a high rate of recovery.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention utilizes the pressure swing adsorption method (hereinafter abbreviated as PSA method) to recover useful gas with high purity from a mixed gas containing the useful gas. It's about how to do it.

(Prior Art) It is well known that there are cryogenic separation methods, absorption methods, and adsorption methods as methods for separating and recovering useful gases from a mixed gas containing them.

Among these, separation technology using PSA has been developed as an adsorption method in recent years.

The PSA method has attracted attention as a method for selectively separating specific component gases from medium or small volumes of raw material gas, and oxygen PSA
Various PSA methods have been developed, such as , nitrogen PSA, and carbon oxide PSA.

As is well known, the PSA method consists of two basic operations: the process of selectively adsorbing useful gases in a mixed gas, and the process of depressurizing and desorbing the adsorbed gases. In between, pressure equalization and purge processes are performed. Combined as necessary. For example, as shown in Japanese Unexamined Patent Publication No. 59-26121 as a method for separating and recovering CO from a mixed gas containing CO, a first adsorption step for removing CO and water and a second adsorption step for separating CO are used. A two-stage PSA method has been proposed.

Furthermore, Japanese Patent Application Laid-Open No. 63-7822 proposes a method for recovering CO in one stage, in which the purge pressure is increased to make the purge process more efficient. ■ Raise the barge temperature. ■ Purge gas amount. It is stated that it is important to increase

(Problem to be solved by the invention) However, as mentioned above, increasing the purge pressure increases the required power, and increasing the amount of purge gas
This is not very preferable as it leads to a decrease in recovery rate.

In view of this problem, the present inventors invented a method for efficiently performing a purge process using a small amount of purge gas.

(Means for Solving the Problems) The gist of the present invention is to provide a method for recovering useful gas from a mixed gas containing useful gas by pressure swing adsorption, in which the mixed gas is passed through an adsorbent to adsorb the useful gas. This method uses the same gas as the component that desorbs the useful gas, purges the gas by increasing the flow rate at the initial stage and decreasing it at the final stage, and then desorbs and recovers the useful gas. This is a collection method.

That is, the present invention is a system that can be applied to a purge step accompanying psA operation, and is not particularly limited to high-purity recovery of CO; however, CO will be specifically explained.

Figure 1 shows the basic cycle of PSA.
Activated carbon carrying copper chloride (1) is generally used as a CO adsorbent. The raw material gas containing CO is introduced into the adsorption tower 1, and GO(a) is selectively adsorbed onto the adsorbent. If the desorption step (1) is entered in this state (a), the impurity gas (b) (CO2, N2, etc.) remaining in the adsorption tower will be discharged together, reducing the purity of CO.

Therefore, before entering the desorption step (1) using the vacuum pump 2, a part of the product gas is flowed into the adsorption tower as a purge gas, and the purge step (a) in which impurity gas in the adsorption tower is washed out increases the purity of the product gas. It is necessary for Since the purge gas is used by recycling the product gas, it is important to carry out the purge step with as little purge gas as possible in order to increase the recovery rate of the product gas.

The present invention is characterized in that, in the purge step (a), the purge gas is not flowed at a uniform flow rate, as shown in a typical example in FIG. .

The present inventors manufactured a transparent acrylic adsorption tower, flowed a colored gas, and varied the flow rate pattern of the purge gas to investigate the replacement status of the impure gas and the purge gas. As a result, we found that the most preferable method is to flow a large amount in the early stage and reduce the flow rate in the final stage.

If the initial flow rate is low, it will simply mix with impure gas and the replacement will not proceed well, so initially a small amount of purge gas is used to drive out the impure gas, and then the impure gas remaining in the gap between the adsorbents is driven out by piston flow. It was found that this method can perform the purge process effectively with the least amount of purge.

Based on this model test result, the actual GO-PSA
The effects of the present invention when fractionally purifying CO from converter gas using the apparatus will be explained based on the following examples.

(Example) Table 1 shows the recovery rate of product gas purity when various flow patterns of purge gas were changed. I have actually confirmed that the method of flushing a lot at the beginning and reducing it at the end is the most effective method with the least amount of purging.

(Effects of the Invention) According to the present invention, since the purge process is efficiently performed with a small amount of purge gas, there are significant effects such as the ability to separate high purity gas at a high recovery rate.

[Brief explanation of drawings]

Figures 1 (A), (4) and (2) are diagrams showing the basic operation cycle of the PSA, and Figures 2 (A) and (() are diagrams showing examples of purge gas flow patterns according to the present invention. 1...Adsorption tower 2...Vacuum bomb and 4 other people (A) (T) Engineering Adsorption tower: 21 empty pump (A) Time

Claims (1)

[Scope of Claims] 1. A method for recovering useful gas from a mixed gas containing useful gas by pressure swing adsorption method, which includes: passing the mixed gas through an adsorbent to adsorb the useful gas; and a component that desorbs the adsorbed useful gas. Using the same gas, purge is performed by increasing the flow rate of the gas at the beginning and decreasing it at the end,
A method for recovering high-purity gas, characterized by recovering useful gas by subsequent desorption.