JPH0367726B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for separating and recovering a gas rich in specific gas components from a mixed gas by the PSA method, in particular,
The present invention relates to a method for separating and recovering a gas rich in high-calorie components from a mixed gas consisting of non-combustible components or low-calorie components and high-calorie components using the PSA method.

Conventional technology One method for producing combustible _{gas that can be used as city gas is to react liquefied petroleum gas or methanol, whose main component is C4H10 ,} with water vapor at high temperatures to decompose it into _CH4 . Attempts have been made to produce enriched reformed gas.

Since this reformed gas contains a relatively large amount of CO ₂ as a result of the decomposition reaction, it lacks a calorific value and cannot be used as city gas. In order to make this reformed gas usable as city gas, it is necessary to remove as much CO ₂ from this gas as possible.

As another method for producing gas with combustibility that can be used as city gas, attempts have been made to obtain gas having a calorific value equivalent to that of natural gas from coke oven gas.

In JP-A-61-255994 and JP-A-61-255995 filed by the present applicant, non-combustible components such as coke oven gas such as CO ₂ and N _{2 and H 2 ,} CO, hydrocarbons, etc. PSA from raw material gas consisting of combustion components and
This method mainly separates and removes non-combustible components and CO. JP-A-60-197793, also filed by the present applicant, discloses that C1 to C4 hydrogen is produced by adding CO-rich generator gas to coke oven gas and causing the reaction in the presence of a catalyst. CO ₂ is removed from the obtained gas using an alkaline cleaning method, or CH ₄ is generated by reacting CO ₂ and H ₂ in the presence of a catalyst, and finally non-combustible components and low-calorie components are removed using the PSA method. It shows how to do this.

As a method for removing and recovering acidic gases such as CO ₂ from natural gas, Japanese Patent Publication No. 1525/1983 describes a pressure swing method using carbon molecular sieves with an average pore diameter of approximately 3 Å as an adsorbent. A method is shown in which the amount of desorbed gas from the beginning of the desorption process reaches 70% of the total amount of desorbed gas and is recycled into raw material gas.

In the PSA method described in the above-mentioned publication, a vacuum regeneration method (a method in which the adsorption tower is kept in vacuum during regeneration and the adsorbed components are desorbed from the adsorbent for regeneration) is adopted as the method for regenerating the adsorbent. ing.

In general, in the PSA method, in addition to the vacuum regeneration method, a normal pressure regeneration method, that is, a method in which the adsorbent is regenerated at normal pressure using a part of the product gas, is also adopted as necessary. For example, JP-A-58
Publication No. 159830 describes a method for removing acidic gases such as carbon dioxide from natural gas using the PSA method. A method of desorption by reducing the pressure to atmospheric pressure is also disclosed.

Problems to be Solved by the Invention In general, the vacuum regeneration method has the advantage of high product recovery rate because it does not require regeneration gas.
Since a vacuum pump is used, there are disadvantages in that the equipment cost is high and the power consumption for operating the vacuum pump is large.

On the other hand, the normal pressure regeneration method does not require a vacuum pump, which is advantageous in terms of equipment costs and electricity costs, but because the product gas is used for regeneration, the recovery rate of the product gas is low. be. For example, as in Comparative Example 2 described below, H ₂ 7%, CH ₄ 68
%, CO ₂ When performing a PSA cycle using a carbon molecular sieve with an average pore size of 4 Å as an adsorbent, the product used as cleaning gas can be removed by using the atmospheric regeneration method. Since gas is lost, the CH ₄ recovery rate is lower than the CO ₂ in the product.
When the content is 3.7%, it remains at 80%, and the
If you try to reduce the CO ₂ content to around 3%, even more CH ₄
Recovery rate decreases.

An increase in the product recovery rate even by 1% has great significance from an industrial perspective, and if the product recovery rate can be increased even in the normal pressure regeneration method, it would be extremely advantageous from an industrial perspective.

Note that the method described in Japanese Patent Publication No. 1525/1983 recycles approximately 70% of the total amount of reduced pressure gas (desorption gas) in the reduced pressure regeneration process, so the amount of raw material gas processed is small, and the amount of processed material is reduced. If you want to increase it, you have to increase the scale of the momentum device, which is a disadvantage, and the cases to which this method can be applied are limited.

In view of this situation, the present invention has been made with the object of providing a PSA method that can increase the product recovery rate even though the atmospheric pressure regeneration method is employed.

Means for Solving the Problems The separation and recovery method using the PSA method of the present invention is based on the PSA method.
In separating and recovering a gas rich in specific gas components from a mixed gas using the method, the following steps are taken: a carbon-based adsorbent is used as the adsorbent, the adsorbent is regenerated at normal pressure and by steam injection, and the entire process is carried out at the steam temperature. or a temperature close to that temperature.

The present invention will be explained in detail below.

The method of the invention is applicable to mixed gases of various compositions. As a mixed gas, for example, an electric furnace,
Gases obtained from converters, blast furnaces, generating furnaces, coke ovens, etc., combustion gases, various reaction gases or by-product gases thereof, natural gas, and the like can be cited. It can also be applied to intermediate gases that are once purified by other methods.

In particular, it is suitable for the purpose of separating and recovering a gas rich in high-calorie components from a mixed gas consisting of non-combustible components or low-calorie components and high-calorie components,
A typical example of such a mixed gas is:
Examples include raw material gases containing CH ₄ as a main component and CO ₂ .

A specific example of a raw material gas containing CH ₄ as a main component and CO ₂ is, for example, reformed gas produced by reacting liquefied petroleum gas with water vapor at high temperatures and decomposing it. The exit gas composition of this reformed gas is, for example, H ₂ 7% CH ₄ 68% CO ₂ 25%. If the CO ₂ content in this outlet gas can be reduced to a few percent or less, it will have the combustibility to be used as city gas.

Similarly, reformed gas is produced when methanol is decomposed by reacting with water vapor at high temperatures.

Specific examples of raw material gases containing _{CH 4} as the main component and CO ₂ include
Natural gas, coke oven gas, including _{C2H6 ,} CO2 _, etc.
Alternatively, gases obtained by adding CO-rich generator gas to coke oven gas and causing the mixture to react in the presence of a catalyst may also be mentioned.

The method of the present invention can be applied not only to the purpose of removing CO ₂ from the raw material gas mainly composed of CH ₄ and containing CO ₂ as described above, but also to the purpose of separating H ₂ from coke oven gas.

As the adsorbent, a carbon-based adsorbent is suitable for the purpose of the present invention, considering that it can be regenerated with steam. Among carbon-based adsorbents, carbon molecular sieves, especially carbon molecular sieves with average pore diameters of about 3 Å to about 5
Å's carbon molecular sieve is highly practical.

When carrying out the PSA method, a plurality of columns are used, and for each column, the steps of increasing the pressure → adsorption process → reducing the pressure → regeneration process are performed cyclically. For example, one column may be in an adsorption step while another column is in a regeneration step. The pressure increase and pressure reduction steps include a pressure equalization step. The number of towers is often 2 to 6 towers.

The pressure increase step is a step in which the pressure of the column after the regeneration step described below is equalized as necessary, and then the pressure is increased to a predetermined pressure using raw material gas, product gas, or rest gas obtained in the pressure reduction step described below. be.

The adsorption step is a step in which a raw material gas is supplied to the column whose pressure has been increased in the previous step to mainly adsorb a specific component (for example, CO ₂ ). Other components in the source gas are passed through. The adsorption operation is performed to absorb specific components (e.g.
Adsorption operation is performed until just before the CO ₂ ) breakthrough, or for a certain period of time after the breakthrough, depending on the product gas specifications.

The pressure reduction step is a step in which the pressure of the tower after the adsorption step is equalized as required, and then lowered to atmospheric pressure. Through this step, certain components (eg, CO ₂ ) and other adsorbed gases adsorbed on the adsorbent are partially desorbed. The rest gas produced at this time can be used in the pressure increasing step mentioned above, or can be used for chemical synthesis or other purposes, or can be discarded.

The regeneration step is a step of regenerating the adsorbent packed in the tower that has been reduced to atmospheric pressure.

In the present invention, this adsorbent is regenerated at normal pressure by blowing steam. The appropriate steam temperature ranges from over 100°C to about 130°C or lower; below 100°C, adsorption performance is inhibited by condensation of water vapor. On the other hand, if the water vapor temperature is too high, it will not only be disadvantageous in terms of thermal energy, but also the adsorption capacity of the adsorbent will decrease, resulting in even the components to be adsorbed being passed through.

Since the adsorbent is regenerated using steam, performing the adsorption step at room temperature is disadvantageous in terms of PSA operation time and thermal efficiency. Therefore, in the present invention, not only the regeneration process but also the entire process is performed at or near the steam temperature.

By carrying out the above regeneration step, cleaning of the specific components adsorbed on the adsorbent is completed.
By increasing the pressure of the column, the specific components in the raw material gas can be adsorbed again.

Effect As mentioned earlier, each column undergoes a pressurization process →
The adsorption step→pressure reduction step→regeneration step is carried out, and after the regeneration step is completed, the pressure increase step is resumed and the subsequent steps are repeated. The above process operations are performed cyclically using multiple towers. That is, a program is set up so that while one process is being performed in one tower, another process is being performed in another tower.

In the method of the present invention, the advantages of the normal pressure regeneration method remain intact, and since the adsorbent is regenerated using steam, there is no consumption of product gas used for regeneration.
A high product recovery rate can be maintained.

Example Next, the present invention will be further explained with reference to Examples.

_Example 1 A reformed gas obtained by reacting liquefied petroleum gas containing _C4H10 as a main component with steam at a temperature of 400°C in the presence of a catalyst, or reacting methanol with steam at a temperature of 400°C in the presence of a catalyst. Using a gas having the same composition as the reformed gas obtained by the reaction, 7% _H2 , 68% _{CH4 ,} 25% CO2, a PSA cycle was carried out for 10 minutes per cycle under the following conditions.

Adsorption tower Three-column adsorbent Carbon molecular sieve with average pore diameter of 4 Å Space velocity 200/hr Temperature 110°C Adsorption pressure 6 Kg/cm ² G Regeneration pressure Normal pressure cleaning gas (injected under normal pressure after completion of pressure reduction)
Amount of steam cleaning gas at a temperature of 110℃ 10g/・Adsorbent PSA pattern adsorption (raw material gas supply) Depressurization (equal pressure) Depressurization (to atmospheric pressure) Cleaning (using steam) Pressure increase (pressure equalization) Pressure increase (product gas used) Above PSA The CH ₄ recovery rate when carrying out was 84.7
%, and the CO ₂ content in the product was 3.0%.

FIG. 1 shows the results when this PSA cycle was repeated continuously.

(See Figure 1) From Figure 1, it can be seen that according to the present invention, both the CH ₄ recovery rate and the CO ₂ content in the product are stable, and continuous industrial operation is possible.

Comparative Example 1 A PSA cycle was carried out in the same manner as in Example 1, except that washing was not performed and the operation was performed at room temperature.

The CH ₄ recovery rate at this time was 88.7%, and the CO ₂ in the product
The content was 12.6% and separation of CO ₂ was virtually impossible.

Comparative Example 2 A PSA cycle was carried out in the same manner as in Example 1, except that the product gas was used as the cleaning gas, the temperature was set to room temperature, and the regeneration was performed under the following conditions.

Cleaning gas (introduced under normal pressure after completion of pressure reduction) Product gas Cleaning gas amount (product gas used) 3.6/・Adsorbent At this time, the CH ₄ recovery rate was 80.1%, and the CO ₂ in the product
The content was 3.7%.

Note that increasing the tower temperature further reduces the CH ₄ recovery rate.

Comparative Example 3 A PSA cycle was carried out in the same manner as Comparative Example 2 except that zeolite with an average pore diameter of 5 Å was used as the adsorbent.

The CH ₄ recovery rate at this time was 77.0%, and the CO ₂ in the product
The content was 5.0%.

Effects of the Invention The separation and recovery method using the PSA method of the present invention not only has the advantages of the normal pressure regeneration method (the advantage of not requiring equipment and operating costs for a vacuum pump), but also regenerates the adsorbent using steam. Therefore, there is no need to use product gas as a cleaning gas. Therefore, a high product recovery rate can be maintained and the upper limit of the product recovery rate in conventional atmospheric pressure regeneration methods can be overcome.

Increasing the product recovery rate by even 1% has great industrial significance, and the fact that the present invention has made it possible to increase the product recovery rate even in the normal pressure regeneration method brings great benefits from an industrial perspective. It is something that brings.

[Brief explanation of drawings]

FIG. 1 is a graph showing the results when the PSA cycle in Example 1 was continuously repeated.

Claims (1)

[Claims] 1. When separating and recovering a gas rich in specific gas components from a mixed gas by the PSA method, a carbon-based adsorbent is used as an adsorbent, and the adsorbent is regenerated at normal pressure by steam injection. A separation and recovery method using the PSA method, which is characterized in that the entire process is carried out at or near steam temperature. 2. The separation and recovery method according to claim 1, wherein the carbon-based adsorbent is a carbon molecular sieve. 3. The separation and recovery method according to claim 1, which is a method for separating and recovering a gas rich in high-calorie components from a mixed gas consisting of non-combustible components or low-calorie components and high-calorie components. 4 Increase the steam temperature from over 100℃ to 130℃.
2. The separation and recovery method according to claim 1, wherein the steam injection is carried out at a temperature set at a temperature lower than 100%.