JP2579179B2 - Pressure fluctuation adsorption separation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pressure fluctuation for separating a specific component from a raw material gas whose composition and flow rate fluctuates by repeating each of the basic steps of an adsorption step, a regeneration step, and a pressure increase step. The present invention relates to an adsorption separation method.

2. Description of the Related Art As one of methods for separating an impurity component and a target product gas component from a source gas containing impurities, a pressure fluctuation type adsorption separation method (PSA method) is known. In this method, a product gas component is separated from a raw material gas containing impurities by repeating an adsorption step-regeneration step-pressurization step as a basic step.

The above-mentioned pressure fluctuation type adsorption separation method is classified into the following two modes depending on whether the adsorbent adsorbs a target product gas component or an impurity component.

A method in which the product gas component is adsorbed on the adsorbent filled in the adsorption tower, the impurity component is allowed to pass through, and then the product gas component is recovered by pressure reduction in the regeneration step.

A method in which impurity components are adsorbed by the adsorbent filled in the adsorption tower, and product gas components are passed through and collected.

In the conventional pressure fluctuation type adsorption separation method, the adsorption step is performed in one column. At this time, the adsorption operation is usually performed until immediately before the component to be adsorbed in the raw material gas breaks through.

Incidentally, JP-A-59-147620 and JP-A-61-146317 disclose a method in which the adsorption step is performed in two columns.
In any case, the first column is separated from the second column before the adsorbed component breaks through in the first column, and the source gas is introduced into the second column.

Problems to be Solved by the Invention However, the conventional method of performing the adsorption step in one column is as follows.
Although no problem occurs when the composition and flow rate of the source gas are constant, various problems are encountered when the composition and flow rate of the source gas fluctuate.

In other words, when the amount of the component to be adsorbed in the source gas increases, the component to be adsorbed may break through the adsorption tower when a certain amount of the source gas is supplied to the adsorption tower. Unless the adsorbed component is mixed in the passing gas, the product gas is lost if the adsorbed component is a product gas and the recovery rate is reduced.If the adsorbed component is an impurity component, the product gas is lost. Purity decreases. On the other hand, the appearance of a large amount of adsorbent is disadvantageous in terms of tower installation cost and adsorbent cost, and the excess adsorbent portion adsorbs components that should originally pass through, so it is adsorbed by adsorbent. When recovering the component, the proportion of the other component in the component to be adsorbed increases.

Further, even when the amount of the component to be adsorbed in the raw material gas is reduced, the component that should originally pass through is adsorbed to the excess adsorbent portion. The proportion of components will increase.

Similarly, in the method in which the above-mentioned adsorption step is performed in two columns, no problem occurs when the composition and the flow rate of the source gas are constant, but when the composition and the flow rate of the source gas fluctuate, the first column is not used. In this case, it is difficult to separate the first column from the second column before the adsorbed component breaks down and introduce the raw material gas into the second column. If the amount of the adsorbed component in the raw material gas increases, the first column breaks. If the amount of the components to be adsorbed in the raw material gas is reduced, or the excess adsorbent portion in the first column is adsorbed, the components to be passed are adsorbed, and the conventional adsorption step is performed in one column. The same problems occur as in the case of the system.

Such a problem always occurs when a gas continuously generated from a furnace or a reactor is treated in a line, and a fundamental solution is strongly demanded.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems when a specific component is separated from a raw material gas having a variable composition or flow rate in a pressure fluctuation adsorption separation method.

Means for Solving the Problems In the pressure fluctuation type adsorption separation method of the present invention, a specific component is separated from a raw material gas whose composition and flow rate fluctuates by repeating each of the basic steps of an adsorption step, a regeneration step and a pressure increase step. In the pressure fluctuation type adsorption separation method, the adsorption step is performed by connecting two pre-pressurized adsorption towers in series, and the first adsorption tower is configured such that the components to be adsorbed in the raw material gas are at the lower limit of the fluctuation range. The second adsorption tower is set so as not to break through regardless of the fluctuation width of the component to be adsorbed in the raw material gas. The same operation is performed by using the adsorption tower as a first adsorption tower and using another pre-pressurized adsorption tower as a second adsorption tower.

 Hereinafter, the present invention will be described in detail.

The pressure fluctuation type adsorption separation method of the present invention separates a specific component from a raw material gas whose composition and flow rate fluctuates by repeating respective steps including an adsorption step, a regeneration step, and a pressure increase step as basic steps.

This method has the following two aspects as described in the section of the prior art, and the present invention can be applied to either of the aspects, but the particular aspect is important.

A method in which the product gas component is adsorbed on the adsorbent filled in the adsorption tower, the impurity component is allowed to pass through, and then the product gas component is recovered by pressure reduction in the regeneration step.

A method in which impurity components are adsorbed by the adsorbent filled in the adsorption tower, and product gas components are passed through and collected.

The adsorption step is a step of adsorbing either the product gas component or the impurity component from 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.

In the regeneration step, the components adsorbed by the adsorbent in the adsorption step are collected under reduced pressure (when product components are adsorbed) or discharged (when impurity components are adsorbed), and the column is washed. It is. 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. Prior to the pressure reduction, a pressure equalization step with another column is often provided.

The pressure increasing step is a step of increasing the pressure of the adsorption tower with the product gas. The pressure can be increased by a raw material gas, an exhaust gas, a cleaning gas or the like instead of or together with the product gas.

Examples of the raw material gas whose composition and flow rate fluctuate include gas and combustion gas generated from various furnaces or reactors.For example, coke oven gas generated from a coke oven or gas derived therefrom, electric furnace, converter, A gas generated from a blast furnace or a generating furnace, a methanation reaction gas, or a gas produced as a by-product thereof is used. Particularly, coke oven gas or gas derived therefrom is important.

In the present invention, the adsorption step is performed by connecting two adsorption towers, which have been pre-pressurized, in series. in this case,
The first adsorption tower always breaks through even if the component to be adsorbed in the source gas is at the lower limit of the fluctuation range, and the second adsorption tower does not depend on the fluctuation range of the component to be adsorbed in the source gas. Set to prevent breakthrough.

For the columns other than the column in the adsorption step, the regeneration step and the pressure increasing step are respectively performed in parallel.

In the following adsorption step, the same operation is performed using the second adsorption tower as the first adsorption tower and the other pre-pressurized adsorption tower as the second adsorption tower.

Next, the operation and effect of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram showing the relationship between the amount of adsorbed component per unit time and the adsorption line in the tower. The upper block diagram shows the case where the adsorbed component in the raw material gas reaches the upper limit of the fluctuation range. ,
The lower block diagram shows the case where the component to be adsorbed in the source gas has the lower limit of the fluctuation range. FIG. 1 shows a case where the component to be adsorbed is CH4.

In FIG. 1, the new first tower is equivalent to the old second tower immediately before. l is a fluctuation range (upper limit-lower limit width of fluctuation), Feed is a flow of a source gas, and Thr. is a flow of a passing gas.

In FIG. 1, the hatched portion indicates a state in which the component to be adsorbed is adsorbed on the adsorbent.

The hatched area on the right of the new first tower is the portion adsorbed in the old second tower, and the hatched area on the upper right of the new first and new towers is the new first tower and new two tower. It is the portion that is newly adsorbed when the raw material gas is supplied by connecting the eyes in series.

In the first new tower, the component to be adsorbed in the raw material gas is always passed even if it is at the lower limit of the fluctuation range. The second adsorption tower does not break through regardless of the fluctuation range of the component to be adsorbed in the raw material gas. That is, the fluctuation range of the component to be adsorbed in the raw material gas is exclusively absorbed in the second new tower.

For the convenience of the description below, the component to be adsorbed is a product gas component,
Taking the case where the passing component is an impurity component as an example, in the first new tower, since the product components in the raw material gas are in a breakthrough state, all of the adsorbents in the first new tower absorb the product gas components. , And the risk of adsorbing impurity components that should pass through is minimized. As a result, the product components adsorbed in the new first column are most efficiently recovered with high purity. Then, the product gas component that has passed without being adsorbed in the first new tower is also adsorbed in the second new tower, and this new second tower becomes a new first tower (new new first tower) in the next stage. In addition, there is no loss of product gas components.

As described above, in the present invention, the adsorption is most effectively performed without losing the product gas component, and the control of the PSA cycle can be easily performed, even if the target gas is a raw material gas whose composition and flow rate fluctuate.

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

Example 1 When four adsorption towers were used, and two of them connected in series were in the adsorption step, one of the remaining two towers was in the regeneration step, and the other was in the pressure step. It formed a suction pressure: 6 kg / cm ² G regeneration pressure: 110Torr product recovery pressure: 1kg / cm ² G~110torr space velocity: 200 / h temperature: was performed the pressure swing adsorption separation process at ambient temperature conditions.

In this case, of the two towers connected in series in the adsorption step, the first tower must always break through even if it is the lower limit of the fluctuation range of the CH4 concentration in the feed gas, and the second tower has the fluctuation width The switching timing was set by a timer so as not to break through even at the upper limit (so that the fluctuation range of the CH4 concentration in the raw material gas is exclusively absorbed in the second column).
Further, the second column was set to be the first column in the adsorption step in the next stage.

As a raw material gas, a crude synthetic natural gas obtained by reforming a coke oven gas generated from a coke oven was used, and as an adsorbent, activated carbon having an average particle size of about 0.8 to 2.4 mm was used.

 The results are shown in FIG.

Comparative Example 1 Example 1 was repeated except that three adsorption towers were used, and one of the towers was in the adsorption step, the other was in the regeneration step, and the remaining one was in the pressure step. The pressure fluctuation type adsorption separation method was carried out under the same conditions as described above.

In this case, the switching timing of the tower in the adsorption step was set by a timer so as to be switched immediately before the product gas breaks through.

 The results are shown in FIG.

The meanings of the abbreviations in FIGS. 2 and 3 are as follows.

Time: Elapsed time _{(h) Feed Gas CH 4 (} vol%): CH4 concentration in the raw material gas _{(vol%) Thr.Gas CH 4 (} vol%): CH4 concentration (vol%) of the passing gas Dep.Gas CH ₄ yield (%): CH4 recovery rate of product gas (%) Dep.Gas N ₂ (vol%): N2 concentration in product gas (vol%) As shown in FIG. 2, the present invention (Example 1) According to), the CH4 concentration in the source gas is 4% at the upper and lower limits.
It can be seen that the CH4 concentration in the passing gas, the CH4 recovery rate of the product gas, and the N2 concentration in the product gas are all extremely stable despite the fluctuation.

On the other hand, according to the conventional method in which the adsorption step is performed in one column (Comparative Example 1), as shown in FIG.
4 It can be seen that when the concentration fluctuates, the CH4 concentration in the passing gas, the CH4 recovery rate of the product gas, and the N2 concentration in the product gas all fluctuate accordingly.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing the relationship between the load of the adsorbed component per unit time and the adsorption line in the tower. The upper block diagram shows that the adsorbed component in the raw material gas reached the upper limit of the fluctuation range. If
The lower block diagram shows the case where the component to be adsorbed in the source gas has the lower limit of the fluctuation range. FIG. 2 is a graph showing experimental results in Example 1. FIG. 3 is a graph showing experimental results in Comparative Example 1.

Claims (3)

(57) [Claims] In a pressure fluctuation type adsorption separation method in which a specific component is separated from a raw material gas whose composition and flow rate fluctuates by repeating respective steps including an adsorption step, a regeneration step, and a pressure increase step as a basic step, the adsorption step is performed in advance. The two adsorption towers are connected in series, and the first adsorption tower always breaks through even if the component to be adsorbed in the raw material gas has the lower limit of the fluctuation range.
The second adsorption tower is set so as not to break through regardless of the fluctuation width of the component to be adsorbed in the raw material gas. In the following adsorption step, the second adsorption tower is replaced with the first adsorption tower. A pressure fluctuation type adsorption separation method, wherein the same operation is performed as a second adsorption tower while using another pre-pressurized adsorption tower as a tower. 2. The pressure fluctuation adsorption separation method according to claim 1, wherein the component to be adsorbed in the adsorption step is a product gas component. 3. The pressure fluctuation type adsorption separation method according to claim 1, wherein the component to be adsorbed in the adsorption step is an impurity component.