JPH073309B2 - Oxygen gas production method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing oxygen gas which can produce highly pure oxygen gas easily.

[0002]

2. Description of the Related Art Oxygen gas has hitherto been produced by using an air separation device to separate nitrogen and oxygen by utilizing the difference in boiling points between them. Further, in the above air separation device, in order to generate the cold required for the liquefaction separation of air, an expansion turbine is provided and the Joule-Thomson effect due to adiabatic expansion is utilized.

[0003]

However, since the expansion turbine has an extremely high rotation speed (tens of thousands of revolutions / minute), it is difficult to perform fine follow-up operation with respect to load fluctuations (changes in the amount of product oxygen gas taken out). is there. That is, it is difficult to immediately and accurately change the rotation speed of the expansion turbine according to the change in the amount of product oxygen gas taken out, and it is difficult to constantly cool the compressed air, which is the raw material for producing oxygen gas, to a constant temperature. The purity of the product oxygen gas obtained varied, and low purity products were frequently produced, resulting in a low purity of the product oxygen gas overall.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an oxygen gas production method capable of coping with load fluctuations while keeping the purity of the obtained product oxygen gas constant.

[0005]

In order to achieve the above object, the oxygen gas production method of the present invention is a method for producing oxygen gas by cryogenic liquefaction separation of air, which is required for cryogenic liquefaction separation of air. A configuration in which a certain amount of the cold amount is constantly applied by the cold generated by the expander, and the balance is applied by the cold of the liquid oxygen itself supplied from outside the deep liquefaction separation system and stored in the storage tank. Take

Next, the present invention will be described in detail based on embodiments.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an air separation device used in an embodiment of the present invention. In the figure, 9 is an air compressor, 10
Is a drain separator, 11 is a Freon cooler, and 12 is a set of two adsorption tubes, which are filled with molecular sieves (which exhibit excellent adsorption ability at low temperature) to alternately adsorb and regenerate. . That is, while one adsorption cylinder 12 adsorbs and removes H ₂ O and CO ₂ in the air compressed by the air compressor 9 and further cooled by the freon cooler 11,
The other adsorption column 12 regenerates the adsorbent. Reference numeral 7 is a first heat exchanger, and the compressed air from which the H ₂ O and CO ₂ have been adsorbed and removed by the adsorption cylinder 12 is sent through the compressed air supply pipe 8. The compressed air sent into this is cooled to an ultra-low temperature by the heat exchange action of the first heat exchanger 7. Reference numeral 13 is a rectification tower, and 15 is a lower tower thereof. In the first heat exchanger 7, the condenser 17 generates compressed air which is cooled to an ultra-low temperature by the cold heat generated by the expansion turbine 31 or the like and is sent through the pipe 8. And then countercurrently contacted with the reflux liquid flowing down and distilled to be stored as oxygen-rich liquid air 18 at the bottom,
Only nitrogen is kept in the gaseous state at the top. Reference numeral 14 is an upper tower of the rectification tower 13, in which the condenser 17 is arranged. A part of the nitrogen gas accumulated in the upper portion of the lower column 15 in the rectification column 13 is fed into the condenser 17 through the pipe 24 and liquefied, and then is passed through the pipe 25 and is stored in the liquid nitrogen reservoir 26 of the lower column 15 in the liquid nitrogen reservoir 26. It is designed to be fed as a reflux liquid. Is the upper tower 14, has become depressurized than inside the lower tower 15, the stored liquid air in the bottom of the lower column _{15 (N 2: 50~70%,} O 2: 30
~ 50%) 18 passes through the pipe 21 and the heat exchanger 21a
It is cooled by the expansion valve 20 and is adiabatically expanded by the expansion valve 20 and fed, and the nitrogen component, which is a low boiling point component thereof, is vaporized and the oxygen component is stored in a liquid state at the bottom. A liquid level gauge 19 controls the opening and closing of the expansion valve 20 according to the amount of liquid air at the bottom of the lower tower 15. Reference numeral 28 denotes a second introduction pipe for extracting the nitrogen content (purity not so high) accumulated in the upper part of the upper tower 14 as waste nitrogen gas, and guiding the waste nitrogen gas to the first heat exchanger 7. The cold air cools the raw material air to an ultralow temperature, and the waste nitrogen gas that has completed the heat exchange is discharged into the atmosphere as indicated by arrow A. In the lower part of the upper tower 14, liquid oxygen is fed from the liquid oxygen storage tank 23 as a cold source through the first introduction path pipe 23a, and together with the liquid oxygen generated in the upper tower 14, a built-in condenser. It is designed to cool 17. Liquid oxygen is externally supplied to the liquid oxygen storage tank 23 from a tank truck or the like via a pipe 27. Reference numeral 27a is a variable opening valve provided on the introduction path pipe 23a and is controlled by the liquid level gauge 22a. That is, the variable opening degree valve 27a is used for the upper tower 14
The opening of the liquid oxygen 22 is adjusted by the liquid level gauge 22a according to the liquid level of the liquid oxygen 22 accumulated at the bottom of the inside, and the opening becomes large when the liquid level of the liquid oxygen 22 falls below a predetermined height. Then, the flow rate of liquid oxygen from the liquid oxygen storage tank 23 is increased, and conversely, when the liquid level rises above a predetermined height, the opening becomes smaller and the flow rate of liquid oxygen is decreased to set the liquid level of liquid oxygen 22 to a predetermined level. It is designed to be held at the height of. Numeral 29 takes out nitrogen gas accumulated in the upper part of the lower tower 15 and removes the first heat exchanger 7
It is a second introduction path pipe to guide. Both the second introduction path pipe 29 and the second introduction path pipe 28 can be integrated in that the nitrogen gas in the rectification column 13 is guided to the heat exchange means 7. Reference numeral 30 is a pipe for taking out the waste nitrogen gas fed into the first heat exchanger 7 through the second introduction pipe 29 from the middle of the first heat exchanger 7, and the taken-out waste nitrogen gas is expanded by the expansion turbine. Send to 31. This expansion turbine 31 is a known one, and adiabatically expands the taken-out waste nitrogen gas to generate cold heat, which is merged with the waste nitrogen gas flowing through the inside of the second introduction pipe 28 to be extremely heated. It is designed to be cooled and fed again to the first heat exchanger 7. 32 is a liquid oxygen take-out pipe, one end of which is open above the bottom of the upper tower 14,
The liquid oxygen staying at the bottom of the pump is delivered to the liquid oxygen pressurizing pump 33. The pressurizing pump 33 pressurizes oxygen in a liquid state up to a predetermined pressure, and as shown in FIG.
And place the compression part 127 at the bottom of the liquid oxygen leak prevention part 1.
It is configured by attaching via 28. More specifically, as shown in FIG. 3, the motor support 1
25, a main shaft 135 is provided through the centers of the liquid oxygen leak prevention unit 128 and the compression unit 127, and the main shaft 135 is connected to the rotary shaft 126a of the motor 126 via the coupling 136, and inside the motor support 125. Is rotatably supported by a bearing 137 provided on the bearing cover 137a and a bearing 138 provided at the tip of the compression unit 127. 140 is a sleeve. The compression unit 127 includes two spiral impellers 1 attached to the main shaft 135.
The upper and lower stages 46 are attached to each other, and a casing for accommodating them is provided. The rotation of the main shaft 135 causes liquid oxygen to pass through the central suction port 146 of the impeller 146.
A is sucked in from a and discharged from a discharge port 146b on the outer periphery in a pressurized state. That is, by rotating the impeller 146, liquid oxygen is sucked from the suction nozzle 148, first the impeller 146 of the first stage pressurizes, and then the pressurized fluid is added by the impeller 146 of the second stage through the passage 147. It is adapted to pressurize the liquid oxygen to a predetermined pressure. The liquid oxygen leak prevention portion 128 surrounds the outer circumference of the main shaft 135 with a sleeve 150, and further, a labyrinth 151 and a labyrinth cover 152 are provided on the outer circumference of the sleeve 150 so that the liquid oxygen leaks from the compression portion 127 and the motor support 125. I try not to reach inside and cause an explosion. In this respect, the inside of the motor support base 125 is airtightly divided into three parts so that leaked oxygen does not reach the motor side. Reference numeral 153 denotes an oxygen discharge pipe, which discharges liquid oxygen in a vaporized state so that it does not reach the motor side even if liquid oxygen leaks from the leak prevention portion 128. In FIG. 1, 34 is an oxygen transport pipe, which is configured to deliver the liquid oxygen pressurized by the pressure pump 33 to the first heat exchanger 7 via the second heat exchanger 21a. Reference numeral 35 is a product oxygen gas extraction pipe for sending the product oxygen gas, which has reached room temperature, from the first heat exchanger 7 to the outside of the system.

Reference numeral 36 is a backup system line, which opens the valve 36a when the air compression system line fails, evaporates the liquid oxygen in the liquid oxygen storage tank 23 by the evaporator 37, and sends it to the pipe 35 to supply oxygen gas. Make sure the supply of is not stagnant. The alternate long and short dash line indicates a vacuum cold storage box. This vacuum cool box blocks heat from the outside and further improves the purification efficiency.

The present invention uses the above apparatus to produce a product oxygen gas as follows. That is, air is compressed by the air compressor 9, water in the air compressed by the drain separator 10 is removed and cooled by the Freon cooler 11, and then sent to the adsorption cylinder 12 in that state to remove H _{2 in} the air.
O and CO ₂ are adsorbed and removed. Then, the compressed air from which H ₂ O and CO ₂ have been adsorbed and removed is sent to the first heat exchanger 7 to be cooled to an ultralow temperature, and in that state, it is introduced into the lower column 15 of the rectification column 13. Then, this input compressed air,
The overflowed liquid nitrogen from the liquid nitrogen reservoir 26 is brought into contact with the liquid nitrogen countercurrently to liquefy a part of the liquid nitrogen and the liquid air 1
Collect as 8. In this process, due to the difference between the boiling points of nitrogen and oxygen (oxygen boiling point −183 ° C., nitrogen boiling point −196 ° C. in the standard state), oxygen, which is a high boiling point component in compressed air, is liquefied and nitrogen remains as a gas. Remain. Then, the nitrogen gas remaining as this gas is taken out from the second introduction path pipe 29 and sent to the first heat exchanger 7, and when it is heated up to about -140 ° C., taken out from the pipe 30 to the expansion turbine 31. Send out. In this case, the expansion turbine 31
The nitrogen gas sent to the above is adiabatically expanded by the expansion turbine 31 to generate cold heat, and in that state, it merges with the waste nitrogen gas sent from the upper tower 14 through the second introduction path pipe 28 to cool, The heat exchanger 7 exchanges heat with the compressed air sent into the heat exchanger 7 and cools it to an ultralow temperature. On the other hand, the oxygen-rich liquid air 18 accumulated at the bottom of the lower tower 15 is further cooled in the second heat exchanger 21a, and then sent into the upper tower 14 in the form of spray by the pipe 21 with the expansion valve 20. It In the upper tower 14, the liquid air 18 fed in this way vaporizes the nitrogen component due to the difference in boiling point and shifts it to the upper part, liquefying oxygen and causing it to flow downward, and accumulate as liquid oxygen 22 at the bottom. The liquid oxygen take-out pipe 32 collects the liquid oxygen 2 accumulated at the bottom.
2 is taken out, pressurized by the liquid oxygen pressurizing pump 33, then heat-exchanged by the second and first heat exchangers 22a, 22 and sent to the take-out pipe 35 as room temperature product oxygen gas. In this way, highly pure oxygen gas is produced.

In particular, according to the present invention, even if the demand amount of the product oxygen gas changes, it is possible to promptly respond to the fluctuation of the demand while keeping the purity constant, which is the greatest feature. That is, when the demand amount of the product oxygen gas rapidly increases, the retention amount of the liquid oxygen 22 in the upper tower 14 decreases,
As a result, the liquid level becomes lower than the predetermined height. As a result, the liquid level gauge 22a immediately detects the liquid level and the valve 27
Increase the opening of a. As a result, a large amount of liquid oxygen is supplied from the liquid oxygen storage tank 23 into the upper tower 14, and the liquid level of the liquid oxygen 22 in the upper tower 14 rises to a predetermined height. When the demand for product oxygen gas decreases, the reverse operation is performed. In this way, by constantly controlling the liquid level of the liquid oxygen 22 to a predetermined height, the amount of reflux liquid generated in the condenser 17 becomes appropriate, and the entire device operates properly. Therefore, an appropriate amount of product oxygen gas can be delivered from the pipe 35 according to the demand amount without changing the purity.

As described above, according to the present invention, not only can oxygen gas of high purity be produced, but also the expansion turbine 31
By controlling the supply amount of liquid oxygen from the liquid oxygen storage tank 23 with the liquid level gauge 22a and the valve 27a while keeping the cooling capacity of the device constant, the oxygen gas generation amount is increased / decreased and the product oxygen gas demand amount is increased. You will be able to respond smoothly to fluctuations.
Moreover, in the present invention, the product oxygen gas is delivered in a pressurized state for the purpose of smooth delivery of the product oxygen gas and convenience of use on the consumption side. However, the pressurization is performed in a gaseous state. Instead, since it is performed in a liquid state, the pressurization efficiency is high, and pressurization can be performed with a small amount of power. That is, since 1 mole of gas has a large volume of 22.4 liters, a large-scale device is required to pressurize it. However, since the volume of liquid is smaller than that of gas, the pressurization is relatively high. It's easy. In particular, oxygen has a strong activity, and in a gas state, it reacts with the lubricating oil of the pressure pump and explodes immediately.In a liquid state, such a situation can be prevented, and the seal of the pump is more liquid than a gas. It is easier and easier to carry out.

In each of the above embodiments, the liquid level gauge 22a is used.
The opening degree of the opening degree variable valve 27a is controlled by means of the above. However, instead of the opening degree variable valve 27a, an opening / closing valve that opens and closes may be used, and opening / closing of the opening / closing valve may be controlled by the liquid level gauge 22a. Good.

[0013]

As described above, according to the present invention, in the method of producing oxygen gas by cryogenic liquefaction separation of air, a certain amount of refrigeration required for cryogenic liquefaction separation of air is generated by the expander. Since the cold oxygen is always applied and the rest is applied by the cold of the liquid oxygen itself supplied from outside the deep liquefaction separation system and stored in the storage tank, the following effects are obtained. That is, the expander, which is difficult to switch the operating speed quickly, always operates at a constant speed to keep its cooling capacity constant, and the required cooling fluctuation based on the demand fluctuation can be met by the liquid oxygen from the liquid oxygen storage tank. Control the supply amount of.
This makes it possible to increase or decrease the amount of oxygen gas generated and smoothly respond to changes in the demand amount of product oxygen gas. That is, the above-described configuration solves the disadvantage of the expansion turbine system that cannot quickly respond to demand fluctuations, and makes use of the advantage of the expansion turbine system that the product cost is low (the cost of transporting liquid oxygen is unnecessary). (Inexpensive late-night power can be used, especially by operating the expansion turbine).

[0014]

[Brief description of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a plan view of a pressurizing pump.

FIG. 3 is a cross-sectional view of a pressure pump.

[0015]

[Explanation of symbols]

 7 1st heat exchanger 9 Air compressor 12 Adsorption cylinder 13 Oxygen rectification column 22 Liquid oxygen 22a Liquid level gauge 23 Liquid oxygen storage tank 23a 1st introduction path pipe 27a Variable opening valve 28,29 2nd introduction path Pipe 31 Expansion turbine 35 Product oxygen gas extraction pipe

Claims (1)

[Claims] 1. A method for producing oxygen gas by cryogenic liquefaction separation of air, wherein a certain amount of the amount of refrigeration required for cryogenic liquefaction separation of air is constantly applied by the cold generated by an expander,
A method for producing oxygen gas, characterized in that the remaining portion is filled with the cold of the liquid oxygen itself supplied from outside the cryogenic liquefaction separation system and stored in the storage tank.