JPH01176415A - Production of enriched gas by psa method - Google Patents

Abstract

PURPOSE:To prevent fluctuation of the flow rate of a gaseous product by utilizing the gaseous product as boosting gas and recirculating the gaseous product of the same flow rate as the boosting gas to a gaseous raw material at a time for nonutilizing the boosting gas or utilizing it for boosting of the other tower being equalized in pressure. CONSTITUTION:A gaseous raw material (f) is sent to an adsorption tower 1a and impure components are adsorbed and a gaseous product (p) is taken out and one part (p') thereof is sent to an adsorption tower 1b and boosting being equalized in pressure is performed. Then the adsorption tower 1b is successively raised in pressure with one part (p') of the gaseous product and, on the other hand, an adsorption tower 1c having been finished in pressure equalization is decompressed with a vacuum pump 2 and rest gas (r) is discharged to the outside of the system. Furthermore when boosting of the adsorption tower 1b has been finished, one part (p') of the gaseous product of the same flow rate as the boosting gas is sent to a gas holder 3 via a recycle gas line and recycled together with the gaseous raw material.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to the production of useful components by adsorption and removal of impurity components from a raw material gas containing useful components as main components and impurity components using the PSA method (pressure fluctuation adsorption separation method). A method for producing a product gas rich in CO2, in particular, by adsorbing and removing CO2 from a raw material gas mainly composed of CH4 and containing CO2 by the PSA method.
The present invention relates to a method for producing H4-rich gas.

Conventional technology In order to produce gas with combustibility that can be used as city gas, liquefied petroleum gas or methanol containing C:4H10 as a main component is reacted with water vapor at high temperature to decompose it.
Attempts have been made to produce reformed gas rich in H4.

This reformed gas contains a relatively large amount of C as a result of the decomposition reaction.
Since it contains O2, it does not generate enough heat as it is,
It cannot be used as high calorie city gas. In order to make this reformed gas usable as high-calorie city gas, C
O2 must be removed as much as possible.

It is often necessary to remove CO2 not only from the above-mentioned reformed gas for city gas but also from gas containing CO2.

Generally, as a method for removing CO2 from a raw material gas containing CO2, an alkaline cleaning method is known in which the raw material gas is brought into contact with an aqueous solution of an alkali such as sodium carbonate or potassium carbonate.

For example, Japanese Patent Laid-Open No. 60-197 filed by the present applicant
No. 793 discloses that CO-rich generator gas is added to coke oven gas and then reacted in the presence of a cobalt catalyst to generate CO.
A method is disclosed in which 1-C4 hydrocarbons are produced and the resulting gas is then washed with alkali to remove CO2 contained in the gas.

As a method for removing CO2 from gas containing CO2,
In addition to the above alkaline cleaning properties, the PSA method is also known.

Among those using the PSA method, one worth noting is Japanese Patent Publication No. 1525/1983.

In other words, the publication states that when removing and recovering acidic gases such as CO2 from natural gas, adsorption and desorption are performed by the PSA method using carbon molecular sieves with an average pore diameter of 3λ as an adsorbent. A method of recycling up to 70% of the total amount of desorption gas into raw material gas is shown.

Problems to be Solved by the Invention: However, among the methods of removing CO2 from gas containing CO2, the method of removing CO2 by alkaline cleaning requires a large-sized device and requires a large amount of thermal energy to heat and regenerate the alkali. There are disadvantages such as:

In this respect, the method of removing CO2 using the PSA method is advantageous in that the device is compact and control and maintenance are easy.

However, in the PSA method, a portion of CH4 is also adsorbed by the adsorbent along with CO2, so CH4 is mixed into the reduced pressure gas generated in the depressurization process, and the CH4 recovery rate is inevitably reduced by that amount. In experiments conducted by the present inventors, when a PSA cycle was carried out using the reformed gas of Example 1 described later as a raw material gas, the CH4 recovery rate was limited to 89%.

In addition, there is a considerable amount of C in the CO2-rich gas that is the rest gas.
) (The inclusion of 4 means that this rest gas can be used for other purposes (
For example, it was a hindrance to reusing it as liquefied carbon dioxide.

The method described in Japanese Patent Publication No. 62-1525 attempts to overcome the above-mentioned problems caused by the PSA method.
Since 0% of the gas is recycled, the amount of raw material gas that can be processed is small, and in order to increase the amount of gas that can be processed, the scale of the momentum device must be increased, so there is still room for further improvement from an industrial perspective. .

Therefore, the present inventors have proposed to further improve the method described in Japanese Patent Publication No. 62-1525 by using the PSA method to obtain carbon dioxide from a raw material gas containing rCH4 as the main component and CO2.
In producing CH4-rich gas by removing O2,
■ Use a zeolite-based adsorbent with an average pore diameter of approximately 5 Å or more as the adsorbent packed in the adsorption tower;
℃ or higher; and (1) in the depressurization step in which the pressure in the column is reduced from a predetermined pressure to atmospheric pressure to vacuum after the adsorption step is completed, the pressure must be maintained at a temperature of 50° C. or higher from the start of the depressurization operation.
A method for producing rich methane gas, characterized by feeding back the reduced pressure gas that reaches a certain pressure in the range of 0±200 Torr, excluding the part used for pressure equalization, to the adsorption tower. Headline, already filed for patent application 1986-18
A patent application has been filed as No. 5670.

According to this method, the recovery rate of CH4 is increased to the maximum, and the amount of reduced pressure gas fed back before the adsorption tower is kept to the minimum necessary, so the throughput of raw material gas can be maintained at a high level.

However, in this method, since the product gas is used to raise the pressure of the adsorption tower after pressure equalization to the adsorption pressure, the amount of product gas decreases during the time required for this pressure increase.

However, when using this product gas as high-calorie city gas, it is necessary to adjust the calorific value by adding a small amount of liquefied petroleum gas to increase the heat. Since it is necessary to adjust the amount of heat enhancer added each time there is a change in the temperature, the operation becomes cumbersome.

To level out this fluctuation, it is necessary to install a buffer tank corresponding to the fluctuation and extract a certain amount of product gas from that tank, but such countermeasures are disadvantageous from an industrial standpoint. The next challenge was to find a more fundamental solution.

The present invention aims to provide a suitable method for solving such problems.

Means for Solving the Problems The method for producing enriched gas by the PSA method of the present invention is to produce PSA from a raw material gas containing useful components as main components and impurity components.
In producing a product gas rich in useful components by adsorbing and removing impurity components by the method, the product gas is used as a booster gas, and when the booster gas is not used, the same amount of product gas as this booster gas is added to the raw material gas. It is characterized in that it is returned to the recycle line or used to boost pressure in other columns during pressure equalization, thereby keeping the product gas flow rate constant at all times.

In this case, "the product gas is used as a booster gas, and
When the pressurized gas is not used, the product gas at the same flow rate as the pressurized gas is returned to the recycle line for raw material gas, or used to boost pressure in other columns during pressure equalization, thereby keeping the product gas flow rate constant at all times. , and ``In the depressurization process in which the pressure of the base is reduced from a predetermined pressure to atmospheric pressure to vacuum after the completion of the adsorption process, the depressurized gas that reaches a certain degree of vacuum after the start of the depressurization operation is consumed as pressure equalizing gas. It is particularly preferable to return the reduced pressure gas, except for the fraction, to the recycle line to feedstock gas.

The present invention will be explained in detail below.

As the raw material gas, a very wide range of gases can be used as long as they are mainly composed of useful components and contain impurity components. (Note that "useful components" and "impurity components" have subjective meanings such as "component of interest" and "component of non-concern," and do not mean that they are industrially useful or unnecessary.) , the useful component is CH4, and the impurity component is CO
The reformed gas obtained by reacting raw material gas No. 2, for example, liquefied petroleum gas or methanol with steam at high temperature, is important.

A typical example of such a reformed gas is a 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, 25% H, 7% CH4H% CO2.If the CO2 content in this exit gas can be reduced to about 5% or less, it will have the combustibility to be used as high-calorie city gas. will have the following. This is because the calorific value can be adjusted by adding a small amount of liquefied petroleum gas to increase the heat.

Further, it is also possible to use mm of reformed gas obtained by reacting methanol with water vapor at high temperature and decomposing it.

In the present invention, in the depressurization process in which the pressure of the column is reduced from a predetermined pressure to atmospheric pressure to vacuum after the adsorption process is completed, the reduced pressure gas that reaches a certain degree of vacuum after the start of the depressurization operation is consumed as pressure equalizing gas. It is desirable to return the reduced-pressure gas excluding the remaining gas to the recycle line for raw material gas.

“A certain degree of vacuum” refers to the type of raw material gas, the type of adsorbent,
Although it cannot be defined unconditionally as it varies depending on other PSA operating conditions, the above-mentioned reformed gas obtained by reacting liquefied petroleum gas or methanol with steam at high temperature is used as the raw material gas, and as an adsorbent to fill the adsorption tower. For example, when using a zeolite adsorbent with an average pore diameter of about 5A or more, the pressure is 500±200 Torr after the start of the pressure reduction operation.
The reduced pressure gas reaching a certain pressure in the range (in particular 500±l 00 Torr) is returned to the recycle line to feed gas. However, when the gas at the beginning of pressure reduction is used for pressure equalization with other columns, this pressure equalization portion is excluded from the feedback portion.

In this case, it is important to determine the limit between the amount to be fed back and the amount to be removed from the system as rest gas, based on a "certain degree of vacuum" (in the above example, a certain pressure in the range of 500±200 Torr). When the pressure is higher than this degree of vacuum, the proportion of the product gas component (CH4 in the above example) in the rest gas increases, and the recovery rate of the product gas decreases by that amount. On the other hand, if the pressure is lower than this degree of vacuum, a considerable amount of the impurities in the reduced pressure gas (C02 in the above example) will be returned to the adsorption tower, reducing productivity and reducing the throughput. If you try to increase the size, the device will become larger.

In the present invention, the product gas is used as a pressurizing gas, and when the pressurizing gas is not used, the product gas at the same flow rate as the pressurizing gas is returned to the recycle line for raw material gas, or used to pressurize other columns during pressure equalization. Make sure to use it. By doing this, the product gas always has a constant flow rate, so when adding an additive to the product gas, the amount of the additive added can be kept constant, which greatly simplifies management. .

In addition, when using the above-mentioned reformed gas obtained by reacting liquefied petroleum gas or methanol with steam at high temperature as the raw material gas, the adsorbent and temperature conditions described below should be selected or set as the adsorbent and temperature conditions. is advantageous.

That is, as the adsorbent, it is desirable to use a zeolite-based adsorbent having an average pore diameter of about 58 or more, and the object of the present invention cannot be fully achieved with an adsorbent having an average pore diameter of 4A. The preferred average pore size range is about 5λ to about 1OA
It is. The zeolite-based adsorbent exhibits an effect of completely desorbing adsorbed CH4 when the degree of vacuum is increased in the pressure reduction step.

In other words, it is an adsorbent that has good ``cutting'' against CH4, and this point is also different from carbon molecular sieve, which has poor ``cutting''.

Further, it is desirable to use the above-mentioned adsorbent and to perform the treatment while maintaining the raw material gas at a temperature of 80°C or higher, particularly 100 to 130°C.

This is because if the temperature is below 80°C, it is difficult to increase the CH4 recovery rate to the targeted 99%.

In this way, using a specific zeolite adsorbent and
Performing the PSA operation under the above temperature conditions is also advantageous in terms of dehumidification. In other words, even if the raw material gas contains water, a balance can be maintained between the ability to adsorb water and the ease of desorption, and dehumidification can be performed simultaneously during the PSA operation. Therefore, there is no need to provide a special process for dehumidification.

Function Next, the function of the present invention will be explained by taking as an example a case where a raw material gas in which the useful component is CH4 and the impurity component is CO2 is used.

FIG. 1 is a curve showing the amount of reduced pressure gas of CH4 and CO2 in the pressure reduction step. The horizontal axis is the pressure, and the vertical axis is the amount of pressure reduction. The solid line is the integral value, and the dotted line is the differential value.

Since the composition of the depressurized gas is rich in CH4 at the beginning of depressurization, this amount is used to raise the pressure of other columns if necessary.

As the degree of pressure reduction approaches atmospheric pressure, the ratio of CH4 and CO2 in the reduced pressure gas reverses, and CO2 becomes larger. However, CH4 is still included so much that it cannot be ignored.

When the degree of pressure reduction is further increased to below atmospheric pressure, the amount of CO2 desorbed increases, but the amount of CH4 in the reduced pressure gas becomes negligible.

When the degree of vacuum is further increased, the desorption of CO2 becomes minimal,
Adsorbent regeneration is complete.

The pressure reduction process is carried out from the pressure immediately after the adsorption process to atmospheric pressure to 40T.
In the example in Figure 1 where the vacuum is reduced to orr, after pressure equalization,
It can be understood that it is most efficient to feed back the gas desorbed during the pressure reduction period up to 500 Torr before the adsorption tower, and to remove the gas desorbed during the pressure reduction period from 500 Torr to 40 Torr as rest gas.

FIG. 2 shows an example of a PSA cycle and the flow rate of product gas corresponding to the cycle.

FIG. 3 is a diagram showing the flow of gas when the PSA cycle of FIG. 2 is carried out. (1) is an adsorption tower, (
It consists of three towers: 1a), (tb), and (1c). (2) is a vacuum pump, (3) is a recycled gas holder, (4)
is a recycled gas compressor. f is the raw material gas, p is the product gas, po is a part of the product gas, r is the rest gas, and C is the flow of the recycled gas. i and ii are channels.

In Fig. 3 (a), gas f
+c is being sent and adsorption is being carried out in the column (1a). The pressure equalization gas is sent from the column (IC) to the column (1b), and a part of the product gas p' is also sent to the column (1b), and pressure increase during pressure equalization has begun.

In Fig. 3 (b), while the recycled gas C is being recycled into the raw material gas f, the gas f is fed into the column (1a).
+c is being sent and adsorption is being carried out in the column (1a). In the column (1b), pressure is subsequently increased using part of the product gas p° as pressurizing gas. Reduced pressure gas is led out from the column (IC) where pressure equalization has been completed, and the reduced pressure gas is sent to the recycle gas line through channel i until atmospheric pressure and through channel ii until a certain degree of vacuum below atmospheric pressure. is,
The vacuum desorption portion exceeding the degree of vacuum is discharged to the outside of the system as rest gas r.

In FIG. 3 (c), gas f
+c is being sent and adsorption is being carried out in the column (1a). Pressurization has been completed in the column (1b). Tower (1c)
Then, vacuum depressurization is performed, and the decompressed gas is discharged outside the system as rest gas r. At this stage, the product gas p is not used for pressure increase, so a part of the product gas p' (product gas equivalent to pressure increase) is returned to the recycle gas line.

When a PSA cycle is carried out using three columns as shown in FIGS. 2 and 3, the flow rate of the product gas fluctuates as shown in FIG. 2 (b) when the product gas is only used as pressurizing gas.

However, in the present invention, the product gas is used as the pressurizing gas, and when the pressurizing gas is not used, the product gas at the same flow rate as the pressurizing gas is returned to the recycle line for the raw material gas, or is used for pressurizing other columns during pressure equalization. Since the product gas is used, the flow rate of the product gas is as shown in FIG. 2 (c), and the flow rate is always constant.

According to the present invention, even if the product gas is used for pressurization and recycling in other columns, the product gas used for pressurization and recycling is only circulated within the system and is not lost.
There is no risk that the recovery rate of product gas will decrease.

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

Example 1 - 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. As a gas with the same composition as the reformed gas obtained by
A PSA cycle was performed according to FIGS. 2 and 3 under the conditions of 500/hr and a temperature of 100-110°C.

The initial reduced pressure gas was used as equalization gas, the middle reduced pressure gas was returned to the raw material gas recycle line via a recycle gas holder, and the latter reduced pressure gas was disposed of as rest gas.

The product gas is used as the pressurizing gas, and when the pressurizing gas is not used, the product gas at the same flow rate as the pressurizing gas is returned to the raw material gas recycling line via the recycling gas holder, or used to pressurize other columns during pressure equalization. I did it like that.

CH4 recovery rate when performing the above PSA was 99.1%
Product gas, initial reduced pressure gas, when performing the above PSA,
Mid-term decompression gas (feedback gas), late decompression gas (
The composition of the rest gas) is shown in Table 1, and the composition of the raw material gas is also shown in Table 1.

Table 1 (values are capacity %) Note 1. Moisture in the raw material gas is 40℃, f3kg/cm"
G saturation.

Note 2. Moisture in the product gas is -45°C in terms of dew point (0.083 mitHg as water vapor partial pressure) Effects of the Invention If the PSA cycle is carried out by the method of the present invention, the recovery rate of useful components in the raw material gas will be extremely high. This is extremely advantageous industrially.

Furthermore, since the amount of useful components transferred into the rest gas is extremely small, there is no problem when reusing this rest gas for other purposes.

In addition, since the amount of reduced pressure gas fed back to the raw material gas recycling line is kept to the minimum necessary, the throughput of raw material gas can be maintained at a high level, or the apparatus can be made more compact.

Furthermore, in the present invention, since the flow rate of the product gas is always constant, when additives are added to the product gas to produce the final product gas (for example, the product gas is methane-rich gas, liquefied gas is added as a heat enhancer). (When adjusting the calorific value by adding petroleum gas), the amount of the additive added can be kept constant, which greatly simplifies management.

Therefore, the present invention has great industrial significance as a method for producing enriched gas by the PSA method.

[Brief explanation of the drawing]

FIG. 1 is a curve showing the amount of reduced pressure gas of CH4 and CO2 in the pressure reduction step. The horizontal axis is the pressure, and the vertical axis is the amount of pressure reduction. The solid line is the integral value, and the dotted line is the differential value. FIG. 2 shows an example of a PSA cycle and the flow rate of product gas corresponding to the cycle. FIG. 3 is a diagram showing the flow of gas when the PSA cycle of FIG. 2 is carried out. (1), (1a), (1b), (lc)-adsorption tower, (2
)...Vacuum pump, (3)...Recycle gas holder, (4)...Recycle gas compressor, f...Source gas, p.
... Product gas, P゛... Part of product gas, r... Rest gas, C... Recycled gas Figure 1 Figure 3 (a) p Figure 3 (b)

Claims (1)

[Scope of Claims] 1. In producing a product gas rich in useful components by adsorbing and removing impurity components from a raw material gas containing useful components as a main component and containing impurity components by the PSA method, the product gas is used as a pressurizing gas. At the same time, when the pressurized gas is not used, the product gas at the same flow rate as the pressurized gas is returned to the recycle line for raw material gas, or used to pressurize other columns during pressure equalization, thereby keeping the product gas flow rate constant at all times. A method for producing enriched gas by the PSA method, which is characterized by: 2. The production method according to claim 1, characterized in that a raw material gas in which the useful component is CH4 and the impurity component is CO2 is used. 3. The production method according to claim 2, wherein the raw material gas in which the useful component is CH4 and the impurity component is CO2 is a reformed gas obtained by reacting liquefied petroleum gas or methanol with steam at high temperature. . 4. When producing a product gas rich in useful components by adsorbing and removing impurity components from a raw material gas that is mainly composed of useful components and also contains impurity components using the PSA method, after the adsorption process is completed, the pressure of the column is changed from a predetermined pressure to atmospheric pressure. In the depressurization process, in which the pressure is reduced to vacuum through the start of the depressurization operation, the reduced pressure gas that reaches a certain degree of vacuum after the start of the depressurization operation, excluding the part that is consumed as pressure equalization gas, is returned to the recycle line to the raw material gas, and The product gas is used as a pressurizing gas, and when the pressurizing gas is not used, the product gas at the same flow rate as the pressurizing gas is returned to the recycle line for raw material gas, or used to pressurize other columns during pressure equalization, thereby reducing the product gas flow rate. A method for producing enriched gas by the PSA method, characterized by: keeping constant constant at all times. 5. The production method according to claim 4, characterized in that a raw material gas in which the useful component is CH4 and the impurity component is CO2 is used. 6. The production method according to claim 5, wherein the raw material gas in which the useful component is CH4 and the impurity component is CO2 is a reformed gas obtained by reacting liquefied petroleum gas or methanol with steam at high temperature. . 7. A patent claim characterized in that the reduced pressure gas that reaches a certain pressure in the range of 500±200 Torr after the start of the pressure reduction operation, except for the part consumed as pressure equalization gas, is returned to the recycle line for raw material gas. The manufacturing method described in Scope Item 5. 8. Use a zeolite adsorbent with an average pore diameter of about 5 Å or more as the adsorbent packed in the adsorption tower, and
6. The manufacturing method according to claim 5, characterized in that the treatment is carried out while maintaining the temperature at a temperature of .degree. C. or higher.