JPH0760051A - Separation of gas from mixed gas - Google Patents

Abstract

PURPOSE:To make the capacity of a compressor small so as to contrive the reduction of initial cost and of power charge by a method wherein the gas left unpenetrated into a gas separation membrane module is conducted into a pressure recovery vessel provided in the process previous to the compressor, the high pressure energy of the unpermeated gas is converted into mixed gas and its converting manipulation is continuosly effected. CONSTITUTION:After pressure application, a material mixed gas is introduced into a gas separation membrane module 1 to pass therethrough a specific gas component of the mixed gas. To accomplish this, a process A is provided to introduce the material mixed gas into the module 1 after applying pressure directly to the mixed gas by a compressor 2 and a process B is provided to introduce the material mixed gas under pressure into the module 1 after raising the pressure of the mixed gas in a pressure recovery vessel 3 or 17 by the gas left unpermeated. By subjecting the mixed gas to the processes A and B alternately or partially in a duplicate manner, the gas separation is continuously effected. As a result, the cost of the compressor and the power charge for driving the compressor can be substantially reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas separation system which uses a gas separation membrane module such as a hollow fiber when a specific gas is selected and taken out from a mixed gas.

[0002]

2. Description of the Related Art There are various methods for separating or removing gas. For example, as a typical example of separating oxygen, nitrogen, etc. from air, there is a deep-cooling air separation method, or recently for small-to-medium scale separation. There is an adsorption method represented by the PSA method, which is rapidly increasing, and more recently, because the performance of various polymer membranes that selectively permeate a specific gas from a mixed gas has improved. Membrane separation methods using these polymer membranes have been actively commercialized.

Membrane separation does not involve a phase change such as cryogenic separation, so that it can be separated with a small energy consumption,
Further, since it is not separated by using a chemical reaction, it has been said that there is an advantage that it is extremely easy to reduce the size and weight.

Indeed, as shown in FIG. 2, the mixed gas is
For example, in this example, the pressure is increased by the compressor 2 through the air / mixed gas inlet adjusting valve 12, separated by the hollow fiber module 1 into oxygen and nitrogen, which is an extremely simple system and device configuration. .

Therefore, in order to improve the separation performance and efficiency, it is necessary to separate a gas having a higher pressure and a larger capacity, and therefore, it is required to increase the pressure and capacity of the compressor 2. It

That is, the gas permeation amount Q through the separation membrane is

[0007]

[Equation 1]

Here, P is the gas permeation coefficient of the membrane, l is the membrane thickness, P _{1 is} the pressure on the gas supply side of the membrane, P _{2 is} the pressure on the gas permeation side of the membrane, A is the membrane area, and t is the time.

As can be seen from the equation, it is necessary to increase the pressure when a large amount of gas is separated on an industrial scale.

However, the initial cost of the compressor in the membrane separation system is extremely high, accounting for about half of the total cost.

In terms of running cost, the electric cost of the electric motor for driving the compressor occupies most of the present system.

Further, there are problems such as vibration and noise of the compressor, a lubricating oil system, etc., which is a major obstacle in industrially utilizing the membrane separation system on a large scale.

For example, to give an example, assume that FIG. 2 shows an example in which oxygen is recovered from air in the atmosphere and the remaining nitrogen is diffused into the atmosphere.

Mixed gas, "air" components and conditions, etc. 1
An example is as follows. Oxygen is about 21%, residual gas such as nitrogen is about 79%, and the pressure at the mixed gas inlet adjusting valve 12 is about 1.5 kg / cm ² G. Inflow rate is about 300N
m ³ / Hr. Is.

As described above, in order to further improve the gas separation performance and efficiency, the pressure of the mixed gas is set to about 20 kg in the compressor 2.
/ Cm ² and more pressure is G, in a hollow fiber module 1, the oxygen is transparent gas, it was possible to obtain a pressure of about 2 kg / cm ² G.

On the other hand, the residual gas does not pass through the hollow fiber.
Therefore, there is almost no pressure drop, and about 18 kg / cm
²G Met. This nitrogen has no purpose to be used and is wasted
Had been released to.

Therefore, the effective utilization of the pressure energy that is held is awaited. Also, about 18 kg / cm ²
It is dangerous to discharge a large amount of high-pressure gas called G into the atmosphere, and it was necessary to attach a decompression device.

On the other hand, as an example of an open technique as a device for reducing the operating cost of a membrane separation system, Japanese Patent Laid-Open No. 2-90
914 can be seen.

In this example, in order to further improve the separation performance of the membrane, pressurization and depressurization exhaust are alternately performed to improve the separation performance.

However, in this system, in the operation of the actual machine, it is necessary to add new depressurized exhaust energy for sucking the gas in the module in order to sufficiently perform the depressurized exhaust. It cannot be said that it will be effectively utilized.

[0021]

As described above, in order to achieve separation performance and efficiency on a larger scale in the case of performing gas separation in a membrane separation system, high pressure and large capacity are industrially achieved. I have to stand.

On the other hand, therefore, in the conventional system in which a large amount of gas is made to have a high pressure by a large-capacity compressor, the initial and running costs of the compressor itself are very high, and the environment such as vibration and noise is high. There is a problem that the problem will be highlighted.

Furthermore, the gas to be recovered is naturally used,
The permeated gas, that is, the recovered gas, can be obtained at a pressure suitable for use due to the pressure drop at the time of permeation, while the residual gas has almost no pressure drop due to the non-permeation and has a high pressure. The residual gas had to be decompressed once and then discarded, and it was wasteful that not only the loss of high-pressure energy held by the residual gas but also the equipment cost such as that required by the decompressor could not be ignored. .

[0024]

Means for Solving the Problems The above problems have been solved by the means described in the claims.

[0025]

According to the present invention, (1) by using a high-pressure impervious gas to pressurize a mixed gas as a raw material, the pressure boosting width of the compressor is reduced by the amount of pressurization, and the capacity of the compressor is reduced. Can be greatly reduced, that is, the initial cost can be greatly reduced.

(2) According to the above method, the electricity cost of the electric motor of the compressor can be greatly reduced.

(3) Further, since the pressure of the high-pressure residual gas can be effectively utilized in this system to reduce the pressure, the original pressure reducing device can be eliminated.

[0028]

FIG. 1 shows an embodiment of the present invention.

The mixed gas, "air", enters the mixed gas inlet regulating valve 12 and has a pressure of about 1.5 kg / cm ² G.

The flow rate is 300 Nm ³ / Hr. The gas component is about 21% oxygen and about 79% residual gas.

First of all, when the operation is started, the mixed gas (air) enters the low pressure air supply port 6 through the mixed gas inlet adjusting valve 12, and the No. (1) Enter the mixed gas chamber 18-1 of the pressure recovery unit (cylinder) 3.

In this state, the non-permeate gas is not introduced into the non-permeate gas chamber 19-1 and the pressure is almost atmospheric pressure.

Therefore, the air is mixed gas outlet adjusting valve 13
It is pressurized up to about 20 kg / cm ² G by the compressor 2 through -1.

Next, the oxygen as the permeating gas enters the hollow fiber module 1 and is used as oxygen gas through the permeating gas exhaust port 11 and further through the permeating gas outlet adjusting valve 16, the oxygen concentration at that time. Is about 90% and the flow rate is
About 56 Nm ³ / Hr. The pressure was about 2 kg / cm ² G.

Although the oxygen could be obtained by permeating through the hollow fiber module 1, the pressure drop due to permeation was about 18 kg / cm ² G.

On the other hand, air enters the hollow fiber module 1 and the non-permeated gas, that is, oxygen, is discharged from the non-permeated gas exhaust port 10, the nitrogen concentration at that time is about 97%, and the flow rate is about. 244 Nm ³ / Hr. , Pressure is about 18k
It was g / cm ² G.

The reason why the pressure of nitrogen is high is that the pressure drop is extremely small because it is not permeated by the hollow fiber module 1.

In this system example, the system uses oxygen, and nitrogen is an excess gas.

Therefore, the nitrogen having passed through the non-permeate gas exhaust port 10 passes through the non-permeate gas inlet adjusting valve 15-1, the high pressure air supply port 9-1, and the No. 1) It is introduced into the impervious gas chamber 19-1 of the pressure collector (cylinder) 3.

At this time, the impermeable gas inlet adjusting valve 15-2
The mixed gas inlet adjusting valve 12-1, the mixed gas outlet adjusting valve 13-1, and the impermeable gas outlet adjusting valve 14-1 are closed.

Therefore, the nitrogen of high pressure "18 kg / cm ² G" introduced into the impervious gas chamber 19-1 pushes the float type piston 4 and the mixed gas chamber 18-1 already introduced.
Approximately 10 kg / c by pressurizing low-pressure "atmospheric pressure" air inside
At m ² , the mixed gas outlet adjusting valve 13-1 is opened and discharged to enter the compressor 2.

On the other hand, another series No. No. 2 pressure recovery device (cylinder) 17 The operation opposite to 1 is performed. That is, No. One series is the impervious gas chamber 19-1
When the air is pressurized with the high pressure nitrogen of No. The two series of mixed gas inlet adjusting valves 12-2 are open, air enters the mixed gas chamber 18-2, and the mixed gas outlet adjusting valve 1
After 3-2, it enters the compressor 2.

Of course, no. Although it is mixed with one series of pressurized air and enters the compressor 2, it is controlled by a regulating valve so that the pressurized side does not flow backward to the low pressure side.

Impermeable gas chambers 19-1 and 19-2 whose pressurization has been completed
The nitrogen is discharged by opening the non-permeable gas outlet adjusting valves 14-1 and 14-2.

As described above, the No. 1 series and No. A control program is incorporated so that the two series operate alternately in batch.

By the above series of operations, at the time of start-up, the pressure of the mixed gas is about 1.5 kg / cm ²
It is necessary to increase G up to 20 kg / cm ² G, which consumes a large amount of power, but other than that, the pressure of the non-permeable gas can be effectively used, and the power consumption is saved by about 40%. I knew it would be done.

Moreover, at startup, the compressor 2
As long as peak capacity is secured by operating the standby machine of
The subsequent operation is the increased pressure applied to the compressor, that is, ΔP₂
= 20-10-10kg / cm²Can be set with the rating for G
Therefore, the conventional compressor's rating, that is, ΔP ₁= 2
0-1.5 = 18.5 kg / cm²Greater than G
It can be miniaturized.

In this system example, the pressure recovery device is described as two series, but of course, three series, four series and a plurality of series are extremely effective and are appropriately designed depending on the operating conditions.

Further, No. 1 pressure recovery device (cylinder)
3 and No. 2 The unpermeated gas whose pressure is reduced by the pressure recovery device (cylinder) 17 becomes a low pressure gas of about 1.5 kg / cm ² G, and is safely discharged to the atmosphere from the unpermeated gas outlet adjusting valves 14-1, 2 Therefore, no special decompression device is required.

In the present embodiment, the example of the hollow fiber is shown as the gas separation membrane module, but the present invention is not limited to this, and for example, spiral type, plate and fin type, etc. Even in this, the same action and effect are produced.

[0051]

As described above, the pressure recovery system of the present invention has the following main effects. That is, (1) the size of the compressor can be reduced, and the cost of the compressor, which occupies a large amount in the membrane separation system, can be significantly reduced.

(2) By greatly reducing the amount of pressure boosted by the compressor, the electricity cost for driving the compressor, which occupies a large amount in the running cost of the membrane separation system, can be greatly reduced.

(3) On the other hand, environmental problems such as noise and vibration of the compressor can be eliminated together with the miniaturization.

(4) Further, in order to improve the performance of the membrane separation system, increase the efficiency, and popularize it on a large scale, it is necessary to increase the pressure and the capacity as described in the problems of the conventional method of the present invention. However, even if the system of the present invention is used for high pressure and large capacity, it is not necessary to increase the size of the compressor in proportion to it, and the larger the scale, the more remarkable the effect.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a conventional method.

[Explanation of symbols]

 1 Hollow fiber module 2 Compressor 3 No. 1 Pressure recovery machine (cylinder) 4 Float type piston 5 Seal 6-1 Low pressure air supply port 6-2 Low pressure air supply port 7-1 High pressure exhaust port 7-2 High pressure exhaust port 8-1 Low pressure exhaust port 8-2 Low pressure exhaust Port 9-1 High-pressure air inlet 9-2 High-pressure air inlet 10 Non-permeate gas exhaust port 11 Permeate gas exhaust port 12-1 Mixed gas inlet adjustment valve 12-2 Mixed gas inlet adjustment valve 13-1 Mixed gas outlet adjustment valve 13-2 Mixed gas outlet adjusting valve 14-1 Unpermeated gas outlet adjusting valve 14-2 Unpermeated gas outlet adjusting valve 15-1 Unpermeated gas inlet adjusting valve 15-2 Unpermeated gas inlet adjusting valve 16 Permeate gas outlet adjusting valve 17 No. 2 Pressure recovery device (cylinder) 18-1 Mixed gas chamber 18-2 Mixed gas chamber 19-1 Impermeable gas chamber 19-2 Impermeable gas chamber

Claims (1)

[Claims] 1. A method for separating a gas from a mixed gas, wherein a raw material mixed gas is pressurized and then introduced into a gas separation membrane module to allow a specific gas component in the mixed gas to pass through the gas separation membrane module. Directly pressurizing the raw material mixed gas to be introduced into the gas separation membrane module, and then step A of introducing the raw material mixed gas into the gas separation membrane module and pressurizing and then pressurizing the raw material mixed gas with the gas that has not permeated the gas separation membrane module. A method for gas separation from a mixed gas, which comprises a step B to be introduced, and the steps A and B are alternately or partially overlapped to continuously separate the gas.