JPH06170144A - Method for recovering high-purity gaseous co or co2 from gaseous mixture - Google Patents

Abstract

(57) [Summary] [Object] To provide means for efficiently recovering highly pure CO or CO ₂ gas from a mixed gas having a low CO or CO ₂ gas concentration. In a method of operating a pressure swing adsorption device in which a plurality of adsorption towers filled with an adsorbent that adsorbs a specific component in a raw material gas are arranged, CO or CO ₂ gas is preferentially selected from the raw material gases as the adsorbent. In addition to the adsorbent to be adsorbed, a pressure equalizing step common to the pressure equalizing step of the other adsorption towers is added to the operation step having the steps of pressurizing, adsorbing, washing and desorbing each adsorption tower. By moving the impurities to the other column in the pressure equalizing step, the amount of cleaning gas is reduced, and the product gas can be used as much, so that the recovery rate can be improved.
Further, by using an adsorbent having a high CO or CO ₂ gas selectivity and abundant CO or CO ₂ adsorption amount,
Highly pure CO or CO ₂ gas can be separated and recovered from a gas having a low CO or CO ₂ concentration in the raw material gas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently recovering a high-purity specific gas from a mixed gas having a low concentration of a target gas for recovery in a raw material gas.

[0002]

2. Description of the Related Art A method for recovering CO gas with high purity will be described below.

For example, as a method for recovering a specific gas component contained in a raw material gas such as various kinds of exhaust gas and synthesis gas,
The target gas is recovered by filling the adsorption tower with an adsorbent that adsorbs only the target components to be recovered, introducing the raw material gas into this adsorbent, and then changing the internal pressure of the adsorption tower by introducing product gas, etc. The method is known as the pressure swing adsorption method.

Here, the higher the purity of the recovered gas, the higher the product value, and various investigations have been conducted for the purpose of improving recovery efficiency and recovery purity.

As a method for separating and recovering high-purity CO gas from a high-concentration CO mixed gas containing CO gas as a main component, such as converter exhaust gas, the improvement of CO gas recovery efficiency is described in Japanese Patent Laid-Open No. HEI-1 -203018, there is a disclosure,
This is because the desorption process after adsorption cleaning is divided into a preliminary desorption process and a main desorption process, and it is overlapped with the operation with other adsorption towers to reduce the waiting time of each tower when switching the operation of multiple adsorption towers. The operation efficiency of the adsorption tower is improved, and as a result, the CO gas recovery efficiency is increased.

On the other hand, regarding the improvement of the purity of the recovered CO gas, it is disclosed in Japanese Patent Publication No. 3-60524 as improving the performance of the adsorbent packed in the adsorption tower, which is generally widely used. The known and used zeolite is loaded with copper chloride to improve the purity of CO gas to be recovered.

[0007]

However, the above-mentioned conventional techniques have the following problems.

Since the adsorbent described in JP-A-1-203018 has a small CO gas adsorption amount per unit adsorbent, the adsorbent gas obtained by the desorption method in which two of the four adsorbents are overlapped is used. It is used in the subsequent washing process to improve the purity.

This method is excellent in ensuring the amount of cleaning gas, but when the concentration of CO gas in the raw material gas is lowered, even if such an operating method is repeated, as described above, Since the amount of CO gas adsorbed is small, there is a problem that it is not possible to secure a sufficient amount of cleaning gas to improve the purity. In addition, in the desorption process, separate vacuum pumps are used for the preliminary desorption and the main desorption, which causes a problem that power consumption increases.

The method disclosed in Japanese Patent Publication No. 3-60524 is effective when the concentration of CO gas in the raw material gas is high, and the optimum adsorption temperature range of the adsorbent is, for example, 60 to
Since the temperature is 70 ° C. and the normal pressure swing method does not raise the temperature to this temperature during adsorption, when the temperature of the target raw material gas is low, a separate gas heating device is required,
The equipment configuration becomes complicated.

The object of the present invention is to solve the drawbacks of the conventional pressure swing adsorption method, and in particular, to provide means for efficiently recovering highly pure CO or CO ₂ gas from a mixed gas having a low CO or CO ₂ gas concentration. To provide.

[0012]

The present invention provides a method for operating a pressure swing adsorption apparatus in which a plurality of adsorption towers filled with an adsorbent for adsorbing a specific component in a raw material gas are arranged. In addition to an adsorbent that preferentially adsorbs CO or CO ₂ gas, an operation process that has steps of pressurizing, adsorbing, cleaning, and desorbing each adsorption tower,
It is characterized in that a pressure equalizing step common to the pressure equalizing steps of other adsorption towers is added.

[0013]

The operation of the present invention will be described with reference to FIG. 6 showing the change with time of the proportion of CO gas and impurities in the adsorption tower and FIG. 7 showing the effect of the pressure equalizing operation.

FIG. 6A shows the case of the conventional method.
(B) shows the case according to the method of the present invention. In the present invention, since the adsorbent packed in the adsorption tower is replaced with a conventional one to have a better selective adsorption performance for CO gas, the CO gas concentration in the raw material gas is 30% or less. Even in the case of low, the amount of CO gas adsorbed by the adsorbent in the adsorption step increases. The CO gas already recovered is used as the cleaning gas in the next cleaning step. As the amount of CO gas is increased, the impurities adsorbed by the adsorbent are cleaned and removed from the adsorbent, and the adsorbent is adsorbed by the adsorbent. The amount of CO gas to be gradually increased, and the purity of CO gas recovered in the next recovery step is improved.

FIG. 7A shows the pressure equalization between one adsorption tower A after the adsorption step and the other adsorption tower B after the desorption / pressure equalization step. Due to this pressure equalization, the impurities in the upper part of the adsorption tower A after the adsorption step are transferred to the upper part or the lower part of the other adsorption tower B, and the cleaning step which is the next step of the adsorption tower A after the adsorption step is completed. It is possible to reduce the amount of cleaning gas.

FIG. 7B shows the pressure equalization between one adsorption tower A after the washing step and another adsorption tower C after the desorption step. Due to this pressure equalization, the adsorption tower A whose cleaning process has been completed
Of impurities in the upper part or the inside of the pipe is transferred to the upper part or the lower part of the other adsorption tower C, and the purity of the recovered CO gas in the recovery step which is the next step of the adsorption tower A after the washing step is increased. Is possible.

[0017]

【Example】

Example 1 An example in which the present invention is applied to recover CO gas by three adsorption towers using a low concentration CO mixed gas such as methanol decomposition gas as a raw material gas will be shown.

FIG. 1 shows a typical gas passage system of an embodiment of the present invention in which three adsorption towers A, B and C are arranged.

The gas passage system includes switching valves A1, B1, C1.
By switching the source gas supply system introduced into each adsorption tower A, B, C and each switching valve A2, B2, C2, the recovered CO gas from each adsorption tower A, B, C is vacuum pump 1 With the recovery system that leads to the product gas holder 3,
Furthermore, by switching the switching valves A5, B5, C5,
A cleaning system in which the recovered CO gas is supplied as a cleaning gas from the product gas holder 3 to the adsorption towers A, B, C by a blower 2 and the product gas system is taken out as a product CO gas in the middle of the cleaning system, and each adsorption tower. The exhaust system from each of the adsorption towers A, B, C has a discharge system for discharging the exhaust gas from A, B, C by switching the switching valves A4, B4, C4.
They are connected by a connection system that is switched by each switching valve A3, B3, C3.

FIG. 2 shows an operation time cycle in each of the adsorption towers A, B and C shown in FIG. As shown in the figure,
The basic process of operation in each adsorption tower A, B, C is through the steps of pressurization, adsorption, washing and desorption.
In the time cycle T1 of 1, the pressure equalization step (equal pressure equalization) is performed before the adsorption tower C is washed during the first pressure equalization (pressure equalization) of the adsorption tower A, and the adsorption tower C after the adsorption step is finished, The gas that has passed through the first pressure equalization step (equal pressure equalization) in the adsorption tower A is connected to the adsorption tower A that is in a depressurized state after the desorption step is completed, and is used for pressurization in the next step. At the end of the first time cycle T1, the adsorption tower C after the washing step and the adsorption tower B after the desorption step are connected to each other, and the pressure is the next step after the adsorption tower B in the desorption step. Used in the process.

In the second time cycle T2 shown in the figure, the adsorption tower A is used as the first pressure equalizing step (pressure equalizing).
The adsorption tower B before the washing step and before the pressurization step is shared, and the adsorption tower A is used as the second pressure equalization step (pressure equalization).
The pressure equalization after cleaning in step 1 and the pressure equalization after desorption in the adsorption tower C are made common.

Further, in the third time cycle T3 in the figure, the adsorption tower B is used as the first pressure equalizing step (pressure equalizing).
In the adsorption tower C, the pressure equalization before the washing step and the pressure equalization before the pressure increase in the adsorption tower C are made common, and as the second pressure equalization step (equal pressure equalization), the pressure equalization after the washing in the adsorption tower B and the adsorption tower A are performed. Common pressure equalization after desorption.

3A to 3D show the adsorption towers A,
It is a figure which shows the gas flow for the operation process of B and C.

FIG. 3 (a) shows the gas flow in the desorption process of the adsorption tower B and the adsorption tower A in the first time cycle T1 in FIG. The gas in the pressure equalization step in the adsorption tower C is sent to the adsorption tower A.

FIG. 3B shows the gas flow in the steps of pressurizing the adsorption tower A, desorbing the adsorption tower B, and cleaning the adsorption tower C in the same first time cycle T1. The recovered CO gas D in the adsorption tower B is sent to the product gas holder 3, and the gas P from the product gas holder 3 is supplied to the adsorption tower C and used for cleaning treatment. Also, the adsorption tower A
Then, the raw material gas F is supplied to the pressurization process before the adsorption process.

FIG. 3C shows the gas flow in the steps of adsorption of the adsorption tower A, desorption of the adsorption tower B, and cleaning of the adsorption tower C in the same first time cycle T1. The raw material gas F is supplied to the adsorption tower A, and the gas P from the product gas holder 3 is supplied to the adsorption tower C and used for cleaning. Then, the recovered CO gas D is recovered from the adsorption tower B.

FIG. 3 (d) shows the gas flow in the same adsorption process of the adsorption tower A in the first time cycle T1 and the pressure equalization step of the adsorption tower B and the adsorption tower C. The raw material gas F is supplied to the adsorption tower A, and the gas for pressure equalization in the adsorption tower C is sent to the adsorption tower B.

In this way, the time cycle of the recovery system having three adsorption towers is divided into three, and in each divided time cycle, the pressure equalizing step shared with other adsorption towers is washed. By placing it before and after the process and transferring the non-target component remaining in the adsorption tower to another tower, the recovery rate as well as the purity of the recovered CO gas can be increased.

FIG. 4 shows that the amount of adsorbent is 60 liters and C
Implemented when the O concentration is 26 vol%, the source gas consisting of H ₂ , CO ₂ , and CH ₄ is supplied at 5 to 15 Nm ³ / Hr, the adsorption pressure is 0.5 kg / cm ² G, and the desorption pressure is 60 Torr. It is a figure which shows the relationship between the amount of cleaning gas and the purity of product CO gas in an example. The horizontal axis of the figure shows the product CO in an operation (comparative example) without using the pressure equalizing step in the present invention.
It represents the ratio when the required cleaning gas amount when the gas purity reaches 99.94% is 100%.

In the conventional example (the method described in JP-A-1-203018), since the CO concentration in the raw material gas is low, C
Since the amount of O gas adsorbed is small, a sufficient amount of cleaning gas cannot be obtained. Therefore, the CO gas purity is limited to 98.6% (indicated by a circle in the figure).

In the method of the present invention, since the amount of CO adsorbed by the adsorbent is large, even if the CO concentration in the raw material gas is low, a sufficient amount of cleaning gas can be secured, and CO gas of high purity can be obtained. Also, by having a pressure equalizing process in the operating process,
For example, when the CO gas purity reaches 99.9%, the amount of cleaning gas can be reduced by about 6% as compared with the method (comparative example) not using the pressure equalizing step. Therefore, the product CO gas amount can be increased by this amount, and the recovery rate can be improved as well as the purity.

As a result, in this embodiment, C in the source gas is
Even if the O concentration is as low as 30% or less, it can be separated and recovered with high purity.

Furthermore, in addition to the preferential adsorption of CO gas, the adsorbent has a static equilibrium adsorption amount of at least 2.5 mmol under the conditions of 20 ° C. and atmospheric pressure. It is desirable to use a gas having an amount of CO gas adsorption of not less than 1 g / g, and if it is less than this, it is difficult to separate and collect CO gas from a low concentration CO mixed gas with high purity.

Example 2 FIG. 5 shows that the adsorbent amount is 1.4 kg and the CO ₂ concentration is 30 vo.
1%, and combustion exhaust gas composed of N ₂ and O ₂ as a raw material gas was supplied at 0.5 to 1.0 Nm ³ / H, and the adsorption and desorption pressures from normal pressure were 50 to 55 Torr. is a diagram showing the relationship between the purity of the cleaned gas quantity and the product CO ₂ gas. Similar to FIG. 4, the horizontal axis of the figure indicates the product CO in the operation (comparative example) without using the pressure equalizing step in the present invention.
₂ Indicates the ratio when the amount of cleaning gas required when the gas purity reaches 99.0% is 100%.

The pressure equalization step is a method of the present invention, even recoveries when applied to CO ₂ gas well, it is possible to obtain a high purity CO _2.

For example, compared with a method (comparative example) in which the pressure equalizing step is not used to reach a CO ₂ gas purity of 99.0%,
The amount of cleaning gas is about 0%. Therefore, product C
The amount of O ₂ gas can be increased by this amount, and the recovery rate as well as the purity can be improved.

Therefore, in this embodiment, CO in the raw material gas is
_{2 Even if the} concentration is as low as about 30%, it can be separated and recovered with high purity.

Further, as the adsorbent, in addition to preferentially adsorbing CO ₂ gas, at least a static equilibrium adsorption amount of 65 c is obtained under the condition of 25 ° C. and atmospheric pressure.
It is desirable to have a CO ₂ gas adsorption amount of c / g or more, and with this amount or less, it is difficult to separate and recover high-purity CO ₂ gas from a low-concentration CO ₂ mixed gas.

[0039]

The present invention has the following effects.

(1) By transferring the impurities to the other column in the pressure equalizing step, the amount of cleaning gas is reduced, and the product gas can be used as much, so that the recovery rate can be improved.

(2) CO or CO ₂ gas selectivity is high,
Moreover, by using an adsorbent that is rich in the amount of CO or CO ₂ gas adsorbed, it is possible to separate and recover high-purity CO or CO ₂ gas from a raw material gas having a low CO or CO ₂ concentration.

[Brief description of drawings]

FIG. 1 is a diagram showing a typical gas passage system of an embodiment of the present invention in which three adsorption towers are arranged.

FIG. 2 is a diagram showing a time cycle in each adsorption tower of FIG.

FIG. 3 is a diagram showing a flow of each gas in FIG.

FIG. 4 is a diagram showing the effect of the present invention in the relationship between the cleaning gas amount and the product CO gas purity.

FIG. 5 is a diagram showing the effect of the present invention in relation to the amount of cleaning gas and the product CO ₂ gas purity.

FIG. 6 is a diagram showing a change over time in the ratio of CO gas or CO ₂ gas and impurities in the adsorption tower.

FIG. 7 is a diagram showing an effect of a pressure equalizing operation.

[Explanation of symbols]

 A, B, C adsorption towers A1 to A5, B1 to B5, C1 to C5 switching valve 1 vacuum pump 2 blower 3 product gas holder

Claims (1)

[Claims] 1. A method for operating a pressure swing adsorption apparatus in which a plurality of adsorption towers filled with an adsorbent for adsorbing a specific component in a raw material gas are arranged, wherein the adsorbent is converted from the raw material gas into CO
Alternatively, an adsorbent for preferentially adsorbing CO ₂ gas is used, and the operation process having the steps of pressurizing, adsorbing, cleaning, and desorbing each adsorption tower is performed in the same operation as the pressure equalization step of other adsorption towers. A method for recovering high-purity CO or CO ₂ gas from a mixed gas, which is characterized by adding a pressure step.