JPH069644B2 - Gas separation method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a gas for adsorbing a target component in a mixed gas to an air-adhesive using an adsorption method and taking this out as a high-purity product gas to the outside of the system. Regarding separation method.

2. Description of the Related Art As a method for separating a component of interest in a mixed gas, there are generally a rectification method, an absorption method, an adsorption method, a membrane method and the like. Of these, the adsorption method is used to adsorb the target component in the mixed gas to the adsorbent to separate it from the non-target component, and the product gas is obtained by desorbing and recovering this, which is the CO gas from the byproduct gas of the steelworks. It is being applied to separation, etc.

As the adsorbent used in the adsorption method, an adsorbent having a selective adsorption property with respect to the target component is used.

To increase the selective adsorption of the adsorbent, a known adsorbent,
For example, various improvements have been made such as supporting a metal salt on activated carbon.

However, in the above adsorption method, the concentration of the target component in the recovered gas rises up to the adsorption limit of the target component determined by the adsorbent used, pressure, and temperature, but beyond that, the target component becomes constant. , No further rise.

For this reason, if the component of interest in the mixed gas is not highly purified and its utility value is high, for example, when CO gas is recovered as a synthetic chemical raw material from the converter gas, which is one of the by-product gases at steel mills, CO The CO gas having the desired purity cannot be recovered by simply adsorbing the gas on the adsorbent and desorbing the gas.

As a countermeasure against this, as shown in FIG. 3, high-purity CO gas is supplied into the adsorption tower in which the CO gas is adsorbed, non-target component gas remaining in the adsorption tower is purged, and then the inside of the adsorption tower is depressurized. As a result, a method for separating useful components in a converter gas for recovering the CO gas adsorbed on the adsorbent with high purity (Japanese Patent Laid-Open No. Sho 60-96).
59-26121) or as shown in FIG. 4, the raw material gas is supplied until the concentration of the easily adsorbed component at the outlet of the adsorption tower reaches the concentration of the easily adsorbed component at the inlet of the adsorption tower, and then the vacuum desorption with the adsorption tower is completed. The gas is introduced from the former adsorption tower to the latter adsorption tower, and the former adsorption tower is reduced in pressure to atmospheric pressure or close to atmospheric pressure by a depressurizing step, and then depressurized adsorption is performed. While introducing the product gas into the tower to purge the hard-to-adsorb components, the gas flowing out from the upper part of the adsorption tower is pressurized to the adsorption tower into which the gas generated in the depressurization step is introduced, and the adsorption tower after the purging step is completed. A method for purifying carbon monoxide from a mixed gas containing carbon monoxide by using an adsorption method in which the easily adsorbed components adsorbed on the adsorbent are desorbed and the product gas is recovered by exhausting to below atmospheric pressure. Kaisho 60
-5012) has been proposed.

The former has a low CO yield because the gas containing impure CO gas remaining inside after the adsorption is purged by blowing in high-purity CO gas.

In the latter case, the exhaust gas is discharged from the upper part of the adsorption tower in the raw material gas adsorption step, and the exhaust gas contains a large amount of easily adsorbed components. This is because the gas generated in the depressurization process and the purging process of the other adsorption towers is introduced into the adsorption tower where the product is recovered by vacuuming from the lower part of the adsorption tower, and therefore the high residual gas remaining in the adsorption tower after the completion of the recovery process. This is because the concentration of the easily adsorbed component is pushed up to the upper part of the adsorption tower, and the concentration of the easily adsorbed component becomes higher in the upper part in the adsorption tower. Therefore, when the raw material gas is next supplied to the adsorption tower, the gas containing a large amount of easily adsorbed components is discharged. Therefore, the yield is low.

OBJECT OF THE INVENTION An object of the present invention is to improve the yield of a target component when recovering the target component in a mixed gas as a product gas.

In a method for separating a target component by supplying a raw material gas to an adsorption column filled with an adsorbent having a selective adsorption product for the target component, in order to improve the yield of recovering a high-purity target component as a product gas, It depends on how low the amount of the component of interest contained in the exhaust gas released to the outside can be suppressed.

In order to suppress the amount of the target component contained in the exhaust gas to a low level, the concentration distribution of the target component in the gas phase of the target tower at the time of exhaust gas emission is required, and the concentration of the target component at the outlet side of the adsorption tower immediately before the exhaust gas discharge is reduced. It is necessary to.

Therefore, a method of investigating the concentrations of the target components of the offgas in the raw material gas adsorption step, the offgas in the purge step, and the gas remaining in the adsorption tower after recovery, and charging the above three kinds of offgas into the adsorption tower after the recovery step has been completed As a result of various studies, this invention was brought about.

That is, the off gas at the time of the raw material gas adsorption step where the target component has the lowest concentration among the above three kinds of off gases is charged from the outlet side of the adsorption tower after the completion of the recovery step in countercurrent to the raw material gas supply. Therefore, it is possible to reduce the concentration of the target component of the gas phase on the outlet side of the adsorption tower, and further to make the target component in the exhaust gas discharged outside the system before charging the adsorption tower extremely low. We propose a gas separation method that makes it possible.

Configuration of the Invention The present invention is a method for supplying a raw material gas to an adsorption column filled with an adsorbent having a selective adsorption property for a target component to concentrate and separate the target component, wherein two adsorption columns are used as a pair and one of the adsorption columns is used. In No. 1, the raw material gas is supplied from the lower part of the adsorption tower, and then the concentration operation is performed, and in the other adsorption tower 2, the total amount of off-gas generated at the time of supplying the raw material to the adsorption tower 1 is supplied from the upper part of the adsorption tower, and then the adsorption tower 1 The total amount of off-gas generated during the concentration operation of is supplied from the lower part of the adsorption tower to collect the target component in the off-gas,
A gas separation method in which exhaust gas mainly containing non-focused components is released immediately before the end of the concentration operation in the adsorption tower 1.

A gas separation method in which the operations described above are set as one cycle and the functions of the adsorption tower 1 and the adsorption tower 2 are switched alternately for each cycle.

Two adsorption towers and one gas storage tower are used. In one adsorption tower 1, after the raw material gas is supplied from the lower part of the adsorption tower, a part of the gas in the adsorption tower is released to reduce the pressure. A concentration operation for purging the inside of 1 with a high-purity component of interest is performed, and the entire amount of off-gas generated when the raw material is supplied to the adsorption tower 1 is stored in the gas storage tower. The entire amount is supplied from the upper part of the adsorption tower, the off gas stored in the gas storage tower is further supplied from the upper part of the adsorption tower, and then the entire amount of the off gas generated during the purging is supplied from the lower part of the adsorption tower. The gas separation method in which the exhaust gas mainly containing non-focused components is discharged immediately before the end of the concentration operation in the adsorption tower 1.

A gas separation method in which the operations described above are set as one cycle and the functions of the adsorption tower 1 and the adsorption tower 2 are switched alternately for each cycle.

Is.

In the present invention, the off gas generated when the raw material is supplied is
It is supplied directly to the upper part of the other adsorption tower or once housed in the gas storage tower, and the off-gas generated during the concentration operation is supplied to the lower part of the adsorption tower, which has the effect that the upper part of the adsorption tower has a low concentration, This is because when the exhaust gas is released immediately before the end of the concentration operation, the outflow of the component of interest can be suppressed low.

Next, the details of the present invention will be described using CO as a raw material gas.
The case of separating and collecting gas will be described.

Process diagram of FIG. 1 is shall apply in the case of carrying out the invention described above, for example, the synthetic zeolite was filled as an adsorbent, the adsorption in the column maximum pressure 3 kg / cm ^3, as the lowest pressure 0.2 kg / cm ³ A raw material gas (CO 74.2%, N ₃ 25.8%) is fed into the tower 1, and off-gas I generated during the adsorption step is supplied to the adsorption tower 2 from the top of the tower where product recovery is completed, and further generated during the depressurization step. The offgas II and the offgas III generated in the purging step using the product CO gas as the purging gas were both supplied to the adsorption tower 2 from the lower part of the tower, and the exhaust gas was discharged from the upper part of the adsorption tower 2 immediately before the completion of the purging step.

A high-purity CO gas is separated in the adsorption tower 1 and all the off gas containing CO is supplied to the adsorption tower 2 with the above series of steps as one cycle.

Next, while the product CO gas is being recovered from the adsorption tower 1, the adsorption tower 2 that is adsorbing the off gas is filled with the raw material gas, and the CO separation and recovery step is performed by the adsorption tower 2 to complete the product C.
The O gas is separated, and the other adsorption tower 1 is used for the off-gas adsorption step during that time, and the product CO gas is recovered from the adsorption tower 2 in the first cycle.

The above CO gas separation and recovery cycle is performed by the absorption tower 1 and the adsorption tower 2.
Can be continuously produced by carrying out alternately.

The concentration of off gas in the CO gas separation and recovery process is as follows.

The average CO concentration of the offgas I when the raw material gas was supplied to the adsorption tower 1 from the lower part of the tower was 20%. Further, the average CO concentration of the offgas II in the depressurization process subsequent to the raw material gas adsorption process is 35%, and the offgas III generated in the next purging process is
The average CO concentration was 77%. Further, CO in the exhaust gas discharged from the adsorption tower 2 reached a low concentration of 14%.

The step diagram of FIG. 2 is shall apply in the case of carrying out the invention, the synthetic zeolite was filled as an adsorbent, the adsorption tower in the column maximum pressure 3 kg / cm ^3, as the lowest pressure 0.2 kg / cm ³ The raw material gas (co74.2%, N ₃ 25.8%) is fed into the column 1, the offgas I generated during the adsorption step is stored in the gas storage tower, and the offgas II generated during the depressurization step is adsorbed from the upper portion of the tower 2 To the adsorption tower 2 from the top of the tower, and offgas III generated in the purging step from the bottom of the adsorption tower to the adsorption tower 2 immediately before the purging step is completed. The exhaust gas is discharged from the upper part of the adsorption tower 2.

A high-purity CO gas is separated in the adsorption tower 1 by using the above series of steps as one cycle, and the off gas containing CO is all supplied to the adsorption tower 2. Then, the product CO gas separation and recovery is repeated in the same manner as the embodiment of FIG.

The concentration of off-gas in the above embodiment is as follows.

When the raw material gas was supplied to the adsorption tower 1 from the lower part of the tower, the average CO concentration of the offgas I stored in the gas storage tower was 7.5%. Further, the average CO concentration of the offgas II in the depressurization process subsequent to the raw material gas adsorption process was 9.4%, and the average CO concentration of the offgas III generated in the next purging process was 21.1%. In addition, the CO in the exhaust gas discharged from the adsorption tower 2 is 1
The concentration was as low as 0.8%.

Next, this invention method according to the above-described embodiment and the conventional method I and the fourth method shown in FIG. 3 performed using the same source gas as the invention method.
Compared with the conventional method II shown in the figure, CO purity in product gas, C
The O yield was investigated. The results are shown in Table 1.

As a result, although the product purities are almost the same, the yields of the present invention are high at 93.8% and 95.7%, but the conventional method is 78.0%.
It can be seen that both are low below.

EFFECTS OF THE INVENTION As described above, the present invention uses two adsorption towers to supply a raw material gas to one adsorption tower to perform concentration operation of a component of interest in the raw material gas, and to another adsorption tower above. The off gas generated during the concentration operation is supplied and adsorbed so that the upper part of the tower has a low concentration, and the target component in the exhaust gas discharged to the outside of the system is made as low as possible to improve the product gas yield. Can be planned.

[Brief description of drawings]

FIG. 1 and FIG. 2 are process drawings in the practice of this invention, and FIG.
FIG. 4 and FIG. 4 are process diagrams according to the conventional method.

Claims (4)

[Claims] 1. In a method of supplying a raw material gas to an adsorption column filled with an adsorbent having a selective adsorption property for a target component to concentrate and separate the target component, two adsorption columns are used as a pair, and one adsorption column 1 is used. Then, after supplying the raw material gas from the lower part of the adsorption tower, the concentration operation is performed, and in the other adsorption tower 2, the total amount of off-gas generated at the time of supplying the raw material to the adsorption tower 1 is supplied from the upper part of the adsorption tower 1 and then in the adsorption tower 1. The entire amount of off-gas generated during the concentration operation is supplied from the lower part of the adsorption tower, the target component in the off-gas is collected, and the exhaust gas mainly containing the non-target component is released immediately before the end of the concentration operation in the adsorption tower 1. A gas separation method characterized by the above. 2. In a method for supplying a raw material gas to an adsorption column filled with an adsorbent having a selective adsorption property for a target component to concentrate and separate the target component, two adsorption columns are used as a pair, and one adsorption column 1 is used. The raw material gas is supplied, the concentration operation and the recovery operation are performed at the same time, and the target component in the off-gas generated from the adsorption tower 1 is collected at the other adsorption tower 2 to collect the exhaust gas mainly containing the non-target component. The gas separation method characterized in that the operation of releasing just before the end of the concentration operation is alternately performed by switching the functions of the adsorption tower 1 and the adsorption tower 2 for each cycle. 3. A method of supplying a raw material gas to an adsorption tower filled with an adsorbent having a selective adsorption property for a target component to concentrate and separate the target component, using two adsorption towers and one gas storage tower. In the other adsorption tower 1, after supplying the raw material gas from the lower part of the adsorption tower, a part of the gas in the adsorption tower is released to reduce the pressure, and the adsorption tower 1 in that state is further purged with a high-purity component of interest. Then, the entire amount of off-gas generated when the raw material is supplied to the adsorption tower 1 is stored in the gas storage tower, and in the other adsorption tower 2, the entire amount of off-gas generated during the depressurization is supplied from the upper part of the adsorption tower, and the gas storage is further performed. The off-gas contained in the tower is supplied from the upper part of the adsorption tower, and then the entire amount of the off-gas generated during the above-mentioned purging is supplied from the lower part of the adsorption tower to collect the target component in the off-gas and mainly the non-target component exhaust gas. The adsorption tower Gas separation method characterized by releasing immediately before and concentration termination. 4. In a method of supplying a raw material gas to an adsorption column filled with an adsorbent having a selective adsorption property for a target component to concentrate and separate the target component, two adsorption columns and one gas storage column are used. In the adsorption tower 1, raw material gas supply, concentration operation, and recovery operation are performed, and in the other adsorption tower 2, the target component in the offgas generated from the adsorption tower 1 is collected, and the non-target component is the main exhaust gas. The gas separation method, wherein the operation of releasing the adsorbent 1 just before the end of the concentration operation of the adsorption tower 1 is alternately performed by switching the functions of the adsorption tower 1 and the adsorption tower 2 for each cycle.