JPH01290516A - Separation of gaseous co and co2 - Google Patents

Abstract

PURPOSE:To considerably reduce the size of a gas holder usable under ordinary pressure and to separate gaseous CO and CO2 by packing an adsorbent for gaseous CO or CO2 as a gaseous product in the gas holder. CONSTITUTION:In a purge stage, gaseous CO or CO2 as a desired gaseous component adsorbed on an adsorbent such as zeolite in a gas holder is desorbed by evacuation by a purge gas blower and it is sent to a prescribed adsorption tower as purge gas. In a desorption stage, gaseous CO or CO2 is desorbed from an absorbent in the adsorption tower by evacuation by a vacuum pump and it is sent to the gas holder, adsorbed on the adsorbent in the holder and stored. The high adsorbing ability of the adsorbent is utilized and the adsorbent can increase the volume of the gaseous product stored in the gas holder under ordinary pressure by 5-30 times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The second invention relates to a method for separating CO and CO2 gas using the PSA method.

[Conventional technology]

The pressure fluctuation adsorption separation method, so-called PSA method, is a separation method in which only the target gas component is adsorbed on a special adsorbent under pressure, and then the gas component is extracted by reducing the pressure.

The process consists of an adsorption process, a purge process, and a desorption process. The adsorption step is a step in which pressurized raw material gas is fed into an adsorption tower filled with adsorbent to adsorb target gas components, and the remaining adsorbed exhaust gas (off gas) is discharged outside the tower. In the purge process, high-purity target component gas (purge gas) is sent into the tower in order to remove components other than the target component remaining in the tower after the adsorption process and increase the purity of the target gas component. This is a cleaning process.

Subsequently, the pressure inside the column is reduced to release the target component gas from the adsorbent, thereby completing the desorption process. After the desorption process is completed, the adsorption tower returns to the adsorption process and feeds the raw material gas. The first half of the adsorption step may be divided into four steps as a pressurization step.

As shown in Figure 2, the equipment used in this method usually uses 3 to 4 adsorption columns IA, IB, and IC1ID, and each column is used to carry out a different process, and each process is sequentially carried out in the next column. A cyclical system is used. That is, first, the raw material gas and the purge off gas discharged from the fourth adsorption tower are sent to the first adsorption tower IA to perform an adsorption step. The second adsorption tower IB is in the desorption process and is being sucked in by the vacuum pump 2, and this desorption gas is stored in the gas holder 4 as a product gas. The third adsorption tower IC is in a purge process, and purge gas is sent from the gas holder 4 by the blower 3 to perform the purge process.

In the fourth adsorption tower ID, a purge step is further performed, and the gas discharged from the third adsorption tower is sent to clean the inside of the tower.

When each process for all towers is completed, each tower enters the next process. A purge step is carried out in the first column IA, an adsorption step in the second column IB, a desorption step in the third column IC, and a purge step in the fourth column ID. When these processes for all towers are completed, each one enters the next process,
When the process of one cycle is completed, the next cycle starts and these steps are repeated one after another.

By the way, the gas holder 4 is provided to stably supply product gas and to always ensure a constant amount of purge gas to obtain product gas of higher purity. That is, in the first half of the desorption process, a large amount of product gas is released, and in the second half, it becomes extremely small. Therefore, a gas holder 4 is provided as a buffer tank so that a constant amount of product gas and purge gas can always be supplied. -ing

[Problem to be solved by the invention]

However, since this gas holder stores the product gas at normal pressure, it has a large capacity and occupies a large proportion of the total area of the PSA method equipment, resulting in high construction costs. The PSA method is characterized by the fact that it does not use high-pressure equipment, making the entire equipment inexpensive. Using a high-pressure tank as a gas holder reduces the value of this PSA method, and the pressure control equipment, including the compressor, pressure reducing valve, etc. There were problems such as the newly required equipment costs and operating costs such as electricity rising.

[Means to solve the problem]

The present invention was made to solve these problems, and introduced a high-pressure tank while taking advantage of the characteristics of the PSA method, which can be used at normal pressure by filling the gas holder with an adsorbent for product gas. This is a successful miniaturization of the gas holder that achieves the same effect as the previous one.

That is, the present invention provides an adsorption step in which a mixed gas containing a target component, which is either CO or CO
A purge step in which the inside of the tower after the adsorption step is replaced with the target component gas stored in a gas holder; and a desorption step in which the inside of the tower after the purge step is depressurized to desorb and recover the target component from the adsorbent. The present invention relates to a method for separating a CO or CO□ gas by a PSA method, which comprises a step, in which the gas holder is filled with an adsorbent capable of adsorbing the target gas.

The gas holder is I~18 compared to the conventional one. It is sufficient to have a certain capacity. This gas holder may be one for normal pressure, but it must have a structure that allows it to be filled with an adsorbent. The interior of the tower only needs to have a structure that allows the movement of the desorbed gas, and support plates for the adsorbent can be provided in multiple stages as appropriate. The shape of this gas holder is not particularly limited as long as it can store gas, and may be cylindrical or box-shaped. Furthermore, L/D and the like are not particularly limited.

The gas inlet and outlet may be connected at the same location, but if the resistance to gas movement within the column is large, it is preferable to connect them at separate locations.

The adsorbent filled in the gas holder is one that can adsorb the target component gas, that is, the product gas, and may be zeolite or the like.

-i may be the same as that used in the PSA method.

Needless to say, the filling amount is determined according to the set amount of product gas stored in the gas holder.

Such a gas holder may be newly installed, but a simple method is to add one or more adsorption towers and use this as a gas holder.

The equipment used in the separation method of the present invention may be the same as the equipment for the conventional PSA method, except that the gas holder described above is used. Adsorption towers are usually used as a set of 3 to 4 towers, but in some cases, only 2 towers may be used for batch operation.

The raw material gas depends on the type of target product gas, for example -
When separating and obtaining carbon oxide gas, converter gas, methanol decomposition gas, etc. are used, and when separating and obtaining carbon dioxide gas, combustion waste gas from a boiler or the like, hot blast furnace gas from a blast furnace, etc. are used as appropriate.

The operating conditions for the adsorption step in the CO and CO2 gas separation method of the present invention may be the same as conventional ones. In the purge step, conditions such as the amount of purge gas and the speed of purge gas may be the same as conventional ones. After the purge process is completed, the desorption process begins.

In this step, the pressure reduction inside the tower, the air supply rate of the skin gas, etc. may be the same as conventional ones. When the adsorption capacity of the adsorbent in the gas holder decreases, it is activated or replaced. This management can be performed in the same way as for the adsorbent in an adsorption tower.

[Effect]

In the purge step, the target component gas adsorbed on the adsorbent in the gas holder is desorbed under reduced pressure by a purge gas blower and sent as purge gas to a predetermined adsorption tower. On the other hand, in the desorption process, the adsorbent in the gas holder adsorbs and stores the target component gas, which is desorbed from the adsorbent in the adsorption tower and sent under reduced pressure by a vacuum pump.

The method of the present invention utilizes the large adsorption capacity of the adsorbent, and can store 5 to 30 times more gas in the same capacity than when storing at normal pressure.

〔Example〕

An example of an apparatus used in the separation method of the present invention is shown in FIG. As shown in the same figure, this apparatus has an additional buffer adsorption tower 5 with the same capacity as the other adsorption towers and is used as a gas holder, except that the gas holder 4 is removed instead. It is the same as the device. That is, at the lower inlets of the four adsorption towers IA, IB, Ic, and ID, a raw material gas supply pipe 6, a desorption gas withdrawal pipe 7, and a purge gas supply pipe 8 are connected to valves 9 (9a, 9b-') and valves 10, respectively. (10a, 1
0b-), valves 11 (lla, llb...), while an off-gas discharge pipe 12 and a purge-off gas discharge pipe 13 are connected to the upper outlet of each adsorption tower IA, IB, IC1ID via valves 14. (14a, 14b), valve 15
(15a, L5b-=).

The vacuum pump 2 is provided in the middle of the desorption gas drawing pipe 7, which is the same as the device shown in FIG. Moreover, there is no gas holder 4, and a purge gas blower 3 is connected to the vacuum pump 2. The exhaust side of the purge gas blower 3 is also connected to a purge gas supply pipe 8, and a product gas extraction pipe 17 is connected to the middle of the purge gas supply pipe 8. Further, a bypass pipe is provided from the exhaust side of the purge gas blower 3 to the suction side of the vacuum pump 2 via a flow rate control valve 18, and this valve 18 detects the flow rate of gas in the product gas extraction pipe. It is designed to be opened and closed. Further, a flow rate control valve 19 is provided at the base of the header of the purge gas supply pipe 8 to detect the flow rate and open/close the flow rate control valve 19 . A newly installed buff 1 for the gas holder - the lower part of the adsorption tower 5 is a desorption gas drawing pipe 7
A valve 20.2 is provided between the valve 16 of the purge gas supply pipe 8 and the bypass pipe connection part, and a valve 20.2 of the purge gas supply pipe 8 between the connection part on the exhaust side of the purge gas blower 3 and the valve 19.
1. On the other hand, buffer adsorption tower 5
is connected to the base of the raw material gas supply pipe 6 via a pressure control valve 22 . This valve 22 is connected to the buffer adsorption tower 5.
It is opened and closed by detecting the internal pressure of the tower.

An example of a method of implementing the method of the present invention using such an apparatus will be explained. In this example, each column undergoes the following steps in sequence:

In the above, the purge (I) step is a step in which the off-gas from the tower in the purge (II) step is sent, and the purge (
Step n) is a step in which the purge gas is directly fed from the Hesofa adsorption tower.

First, the valves 9a and 14a are opened, and the remaining valves 10a, 11a, and 15a are closed to perform the adsorption process in the first column IA. The raw material gas enters the lower part of the adsorption tower IA from the raw material gas supply pipe 6 through the valve 9a, and the off-gas that has passed through the adsorbent layer is discharged from the upper part of the tower through the valve 14a and the off-gas discharge pipe 12. The second tower IB is in a normal state with all valves closed. The third column IC is in the purge (II) step, and the valves 11C1 and 15C are open, and the valves 9C1, 10C, and 14C are closed. The fourth column ID is in the purge step (N), and the valve 15d is open, and the valves 9d, 10d1, lid, and 14d are closed. The buffer adsorption tower 5 is sucked by a vacuum pump 2 to desorb CO gas, and a part of this gas is drawn out as a product gas, and a part is fed under pressure to a purge gas supply pipe 8 as a purge gas by a purge gas blower 3.

When the adsorption step of the first column IA reaches the second half, the first column IA opens the valve 15a, closes the valve 14a, and releases the off-gas to the valve 15a.
through which it is fed into the second column IB. The second column IB is in a pressurizing process, and valves 9b, 10b, 11b, 14b, and 15b are closed. In the third column IC, valve 10C is opened during the reduced pressure recovery (desorption) process, and valve 9C1 valve 11C1
Valve 14C and valve 15C are closed. The fourth column ID is purged (in the old process, valve lid and valve 15d were opened, and valve 9
d, valve 10d and valve 14d are closed.

The buffer adsorption tower 5 contains CO recovered from the third tower IC.
Gas is fed from the purge gas supply pipe 8 through the valve 21.
O gas is being accumulated. A portion of the adsorbed gas is extracted as product gas.

When the adsorption step in the first column IA is completed, the purge (1) step begins. In the purge (1) step, when the valve 15a is opened and the valves 9a, 10a, 11a and 14a are closed, the purge off gas from the fourth column ID is adsorbed from the purge off discharge pipe 13 through the valve 15d. Tower IA
to go into. The purge off gas from adsorption column IA is discharged to second column IB through valve 15a.

In the second column IB, the adsorption process is carried out, in the third column IC, it is in the solid state, and in the fourth column ID, the purge (n) process is carried out, and the CO gas is discharged from the barafer adsorption column 5, and some of the CO gas is is extracted as a product gas, and a portion is sent to the fourth column ID as a purge gas.

After the purge (1) step of the first column IA is completed, the purge (I
I) Enter the process. In the purge (II) step, the valve 11
a. When the valve 15a is opened and the valves 9a, 10a, 14a and 15d are closed, the purge gas is supplied to the purge gas supply pipe 8.
From there, it passes through valve 11a and enters adsorption tower IA. The purge off gas is discharged to the second column IB through valve 15a.

In the second tower IB, an adsorption step is performed, in the third tower IC a pressurization step, and in the fourth tower ID a reduced pressure recovery step is performed, and in the buffer adsorption tower 5, CO gas is accumulated.

After the purge (II) step of the first column IA is completed, the vacuum recovery step begins. In the reduced pressure recovery process, the valve 10a is opened and the remaining valves 9a, 11a, 14a and 15a are closed. When the vacuum pump 2 is operated, the pressure inside the column is reduced and the target component gas is desorbed. The amount of desorbed gas is large in the first half of the reduced pressure recovery step, as shown by curve 1 which represents the change in the amount of desorbed gas, and by straight line 2 which represents the sum of the amount of product gas extracted and the amount of purge gas. This skin gas is sent to three directions: product gas and purge gas, which are extracted in fixed amounts, and buffer adsorption tower 5, which stores the surplus. At this time, valve 18 and valve 20
is closed and valves 19 and 21 are open. In the second half when the amount of desorbed gas decreases, the valves 16 and 21 are closed, the valve 20 is opened, and the product gas and purge gas are supplied from the buffer adsorption tower 5. In the second tower IB, purge (
In step If), an adsorption step is carried out in the third column IC, a pressurization step is carried out in the fourth column ID, and CO gas is accumulated in the buffer adsorption column 5.

At the end of the vacuum recovery process in the first column IA, the first
Column IA enters a state of rest before the pressurization step and all valves are closed. At this time, the purge (I [) process is performed in the second column IB, the purge (1) process is carried out in the third column IC, the adsorption process is carried out in the fourth column ID, and the CO gas is removed in the buffer adsorption column 5. A release is taking place.

When the reduced pressure recovery process in the first column IA is completed and the pause period is over, the pressurization process begins. In the pressurizing process, valve 9a and valve 10
a, when valve 11a, valve 14a and valve 15a are closed, the fourth
Off-gas from column ID enters through valve 15d and is pressurized. At this time, in the second column IB, a vacuum recovery step is performed, and in the third column IC
A purge step is carried out in , and an adsorption step is carried out in the fourth column ID, respectively, and CO gas is accumulated in the buffer adsorption column 5 .

After the pressurization process to the first column I is completed, the process returns to the adsorption process, the second column IB is pressurized, the third column 1C is a vacuum recovery process,
In the fourth tower ID, a purge process is performed.

After the adsorption process in the first column IA is completed, move on to the purge process,
An adsorption step is carried out in the second column IB, a pressurization step is carried out in the third column IC, and a reduced pressure recovery step is carried out in the fourth column ID, and these steps are sequentially repeated.

Using this method, the gas composition was determined to be CO72% by volume, CO
□ Converter gas of 13% by volume, 14% by volume of N2, Hzl% by volume was used as the raw material gas, and the operating conditions were: vast gas in the adsorption process 15ONm'/l1r (maximum), purge gas ffi
10-40 N m 3/Hr, final tower internal pressure of adsorption step 50 Torr, gas amount of buffer adsorption tower approximately 7 Nm'
Gas separation was performed as follows, and the gas composition was CO99.5% by volume, CO.

A product gas containing 0.4% by volume, 0.1% by volume of N, and 20% by volume of H was obtained.

[Effects of the Invention] According to the method of the present invention, it is possible to significantly reduce the size of the gas holder, which requires a vast area and construction costs in the conventional PSA gas separation method. The required site area will be reduced to about half, and construction costs can be drastically reduced.

[Brief explanation of the drawing]

FIG. 1 shows an example of an apparatus used in the method of the present invention, and FIG. 2 shows an example of an apparatus used in a conventional method in the form of a flow sheet. FIG. 3 is a graph showing changes in the amount of desorption gas produced and the amount of desorption gas used in the desorption process. IA, IB, IC1ID...Adsorption tower 2...Vacuum pump 3...Purge gas blower 5...Pamper adsorption tower (gas holder) 6...Material gas supply pipe 7...Desorption gas drawing pipe 8...Purge gas supply pipe 12...Off gas discharge pipe 13...Purge off gas discharge pipe 17...Product gas discharge pipe Patent applicant Nippon Kokan Co., Ltd. Representative Patent attorney Masahiro Tanaka

Claims (2)

[Claims] (1) An adsorption step in which a mixed gas containing a target component, which is either CO or CO_2, is sent to an adsorption tower and the target component is adsorbed onto the adsorbent packed in the tower; Based on the PSA method, which consists of a purge step in which the inside of the tower is replaced with the target component gas stored in a gas holder, and a desorption step in which the inside of the tower after the purge step is depressurized to desorb and recover the target component from the adsorbent. A method for separating CO or CO_2 gas, characterized in that the gas holder is filled with an adsorbent capable of adsorbing the target component gas. (2) The method for separating CO or CO_2 gas according to claim (1), wherein the adsorption tower is added and one or several of the adsorption towers are used as the gas holder.