JPH0731001B2 - High-purity nitrogen gas production equipment - Google Patents

Description

The present invention relates to a high-purity nitrogen gas production apparatus.

[Conventional technology]

A conventional nitrogen gas manufacturing apparatus uses an expansion turbine for cooling the refrigerant of a heat exchanger for heat exchange of compressed air compressed by a compressor. By the cold liquefaction separation, low boiling point nitrogen is taken out as a gas, and the rest is stored as oxygen-rich liquid air) and is driven by the pressure of the gas evaporated from it. However, the rotation speed of the expansion turbine is extremely high (tens of thousands of times / minute)
Therefore, it is difficult to follow the load fluctuation, and a specially trained operator is required. Further, since this machine rotates at high speed, it requires high precision in terms of mechanical structure, is expensive, and has a complicated mechanism, which requires specially trained maintenance personnel. That is, since the expansion turbine has a high-speed rotating portion, the above-mentioned various problems occur, and there is a strong demand for the removal of the expansion turbine having such a high-speed rotating portion.

[Problems to be Solved by the Invention]

In order to meet such a demand, the present inventor proposes a high-purity nitrogen gas production apparatus that uses a liquid nitrogen storage tank instead of an expansion turbine, and supplies liquid nitrogen as cold from the liquid nitrogen storage tank to a rectification column. We have already applied (Japanese Patent Application No. 59-41)
No. 23). According to this device, since the expansion turbine is not used, it is possible to eliminate the harmful effect of using the expansion turbine, and moreover, the expansion turbine finely follows the additional fluctuation (change in the amount of product nitrogen gas taken out). Where operation is difficult, in the present invention, since the supply amount of liquid nitrogen can be quickly controlled, the supply amount of liquid nitrogen can be instantly adjusted according to the amount of product nitrogen gas taken out. This also has the effect of preventing the product nitrogen gas from having poor purity. However, when this manufacturing apparatus was actually operated, the product nitrogen gas had poor purity.

The present invention has been made in view of such circumstances, and an object thereof is to provide an apparatus capable of stably producing high-purity nitrogen gas.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the high-purity nitrogen gas production apparatus of the present invention comprises an air compression means for compressing the air taken in from the outside, and carbon gas and moisture in the compressed air compressed by the air compression means. And removing means, heat exchanging means for cooling the compressed air that has passed through this removing means to an ultralow temperature, and a part of the compressed air that has been cooled to an ultralow temperature by this heat exchanging means is liquefied and only nitrogen stored in the bottom is stored. The rectification column to be taken out from the upper side as a gas, the condenser-type partial condenser provided at the upper part of the rectification column, and the stored liquid air at the bottom of the rectification column are used as the cooling for cooling the condenser. A liquid air introduction pipe leading into the partial condenser, a first reflux liquid pipe for guiding a part of nitrogen gas generated in the rectification column into the condenser, and liquefied nitrogen generated in the condenser. Second reflux that returns to the rectification column as reflux Pipe, liquid nitrogen storage means for receiving and supplying liquid nitrogen from outside the apparatus, and an introduction path for guiding the liquid nitrogen in the liquid nitrogen storage means into the rectification column, and the gas introduction path A liquid separator is provided, and a discharge path for discharging the gas separated in the gas-liquid separator is connected to the first reflux liquid pipe.

[Operation] The inventor pursued the cause of the poor purity by actually operating the proposed apparatus which theoretically could not cause the poor purity. As a result, the cause of the poor purity of the product nitrogen gas is that, when liquid nitrogen supplied from the liquid nitrogen storage tank is introduced into the rectification column, a flushing phenomenon occurs depending on the case, and the momentum of the flushing causes the flushing phenomenon to occur. The rectification shelf vibrates, and due to the vibration, the liquid to be treated on the rectification shelf sways and the liquid depth locally changes.In extreme cases, the rectification shelf from the lower rectification shelf to the upper rectification shelf is changed. It was found that the gas that had risen toward the gas-liquid contact port did not come into contact with the liquid in the upper rectification shelf and passed through, resulting in insufficient rectification product gas. Based on this finding, the present inventor provided a gas-liquid separation device in the liquid nitrogen supply path, and if the gas-liquid retention part of the gas-liquid separation device was adjusted to the same pressure as in the rectification column, the gas-liquid separation was performed. The present inventors have reached the present invention by finding that the liquid nitrogen once stored in the apparatus can be gently supplied into the rectification column by its own weight and the occurrence of the above-mentioned flushing phenomenon can be prevented.

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

〔Example〕

FIG. 1 shows 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. The adsorption column 12 is filled with a molecular sieve and serves to adsorb and remove H ₂ O and CO ₂ in the air compressed by the air compressor 9. Reference numeral 8 is a compressed air supply pipe for sending compressed air from which H ₂ O and CO ₂ have been adsorbed and removed. Reference numeral 13 is a first heat exchanger, into which compressed air from which H ₂ O and CO ₂ have been adsorbed and removed by the removing means (adsorption cylinder) 12 is fed. Reference numeral 14 is a second heat exchanger, into which the compressed air that has passed through the first heat exchanger 13 is fed. Reference numeral 15 is a rectification column in which the tower top is connected to the dephlegmator section 21 having the condenser 21a, and the column section 22 is located below the condenser section 21a by the first and second heat exchangers 13 and 14. The compressed air that has been cooled to an ultra-low temperature and is sent through the compressed air supply passage 17 is further cooled, and a part of it is liquefied and stored as liquefied air 18 at the bottom of the tower section 22, and only nitrogen is vaporized in the upper ceiling of the tower section 22. It is supposed to be stored in the department. Reference numeral 23 is a liquid nitrogen storage means (tank), which feeds the internal liquid nitrogen (high-purity product) to the upper side of the tower portion 22 of the rectification tower 15 via the liquid nitrogen introduction passage 24a, Use as a cold source for the compressed air supplied to the inside. The vaporized nitrogen in the liquid nitrogen passing through the liquid nitrogen introduction passage 24a is removed by the vapor-liquid separator 35, and the liquid nitrogen from which the vaporized nitrogen has been removed is removed by the vaporized nitrogen removal passage 36 to a condenser described later.
You will be led to the entrance of 21a. In this case, in the gas-liquid separator 35, the lead-out pipe 36 for leading out the separated gas is in communication with the first reflux liquid passage 21b described later. The rectification tower 15 is divided into a dephlegmator section 21 and a tower section 22.
A part of the nitrogen gas accumulated in the upper part of the tower section 22 is fed into the condenser 21a in the column 21 via the first reflux liquid passage 21b. The inside of the dephlegmator portion 21 is in a reduced pressure state as compared with the inside of the tower portion 22, and the stored liquid air (N ₂ 50 to 70%, O ₂ 30 to
50%) 18 is sent through the pipe 19 with the expansion valve 19a,
It vaporizes and cools the internal temperature to a temperature below the boiling point of liquid nitrogen. Due to this cooling, the nitrogen gas fed into the condenser 21a is liquefied. 25 is a liquid level gauge, and a control valve 26 according to the liquid level of the liquid air in the partial condenser 21
To control the supply amount of liquid nitrogen from the liquid nitrogen storage means 23. The liquid nitrogen produced in the condenser 21a of the dephlegmator 21 is supplied to the upper part of the column part 22 of the rectification column 15 through the second reflux liquid passage 21c, and the liquid nitrogen is supplied. Liquid nitrogen is supplied from the nitrogen storage means 23 through the liquid nitrogen introduction passage 24a, and these are passed through the liquid nitrogen reservoir 21d and the tower portion 22.
It flows downward in the inside, and comes into contact with the compressed air rising from the bottom of the tower portion 22 countercurrently to cool it and liquefy a part thereof. In this process, the high boiling point component in the compressed air is liquefied and accumulated at the bottom of the tower section 22, and the nitrogen gas of the low boiling point component is collected in the tower section.
Collect at the top of 22. 27 is a nitrogen gas take-out passage for taking out the nitrogen gas accumulated in the upper ceiling part of the tower part 22 of the rectification tower 15 as product nitrogen gas. Ultra-low temperature nitrogen gas is introduced into the second and first heat exchangers 14 and 13. It guides and heat-exchanges with the compressed air sent into it to bring it to room temperature and sends it to the main passage 28. In this case, at the uppermost part of the column portion 22 of the rectification column 15, together with nitrogen gas, He (−269 ° C.), H _{2 having} a low boiling point, H ₂
Since (−253 ° C.) and the like easily accumulate, the inlet 27a of the nitrogen gas extraction passage 27 opens at a position lower than the inlet 21e of the first reflux liquid passage 21b as shown in FIG. Only pure nitrogen gas that does not contain H ₂ etc. is taken out as product nitrogen gas. In addition, a shielding plate 21f having a droplet lower hole is provided so as to project obliquely upward from the lower inlet of the first reflux liquid passage 21b so that the mixed gas of He, H _{2 and the} like is not mixed into the product nitrogen gas. ing. Above the condenser 21a, the above-mentioned He
And the gas vent passage 21g for escape of H ₂ or the like to the outside air is provided. 29 indicates the second vaporized liquid air in the dephlegmator 21
A passage 29a for feeding the first heat exchangers 14 and 13 is a pressure-holding valve for the passage 29a. 30 is a back-up passage and a rectification tower 15
In order to make up for the shortage of the product nitrogen gas flowing from the main passage 28 to the main passage 28, the function of evaporating the liquid nitrogen in the liquid nitrogen storage means 23 by the evaporator 31 and constantly supplying a constant amount to the main passage 28, and the air compression system line are provided. It has a function of supplying the entire amount of nitrogen gas consumed when a failure occurs. In this case, the flow rate adjustment in the backup channel 30 is performed by the pressure adjusting valve 37 arranged in the downstream portion of the evaporator 31. An impurity analyzer 32 analyzes the purity of the product nitrogen gas sent to the main passage 28. When the purity is low, the valves 34 and 34a are operated to escape the product nitrogen gas to the outside as shown by arrow B. To act. The chain double-dashed line is a vacuum insulation box.

This apparatus produces product nitrogen gas as follows. That is, the air is compressed by the air compressor 9, the water in the air compressed by the drain separator 10 is removed, and it is cooled by the Freon cooler 11, and then sent to the adsorption cylinder 12 in that state, and the H _{2 in} the air is reduced. Adsorbs and removes O and CO ₂ . Then,
Compressed air from which H ₂ O and CO ₂ have been adsorbed and removed is cooled by the product nitrogen gas or the like fed from the rectification column 15 through the nitrogen gas extraction passage 27. The first and second heat exchangers 13 Then, it is sent to 14, 14 to be cooled to an ultra-low temperature, and then charged into the lower part of the tower section 22 of the rectification tower 15 in that state. Then, the input compressed air, the liquid nitrogen sent from the liquid nitrogen storage means 23 into the tower portion 22 of the rectification tower 15 via the liquid nitrogen introduction passage 24a and the liquid nitrogen overflowed from the liquid nitrogen reservoir 21d. They are brought into contact with each other and cooled, and a part thereof is liquefied and stored as liquid air 18 at the bottom of the tower section 22.
In this process, due to the difference between the boiling points of nitrogen and oxygen (boiling point of oxygen-183 ° C, boiling point of nitrogen-196 ° C), oxygen, which is a high-boiling point component in the compressed air, is liquefied and nitrogen remains as a gas.
Then, the nitrogen remaining in this gas is removed from the nitrogen gas discharge passage.
It is taken out from 27 and sent to the second and first heat exchangers 14 and 13, where it is heated to near room temperature and sent out from the main passage 28 as product nitrogen gas. In this case, since the inside of the column section 22 of the rectification column 15 is at a high pressure due to the compression force of the air compressor 9 and the vapor pressure of liquid nitrogen, the pressure of the product nitrogen gas taken out from the nitrogen gas take-out passage 27 is also high. . Therefore, it is advantageous when this product nitrogen gas is used as a purging gas or the like. Also, since the pressure is so high, a large amount of gas can be transported in a pipe of the same diameter,
When the transportation amount is constant, it becomes possible to use a pipe having a small diameter, and it becomes possible to realize a reduction in equipment cost. Further, nitrogen gas containing a gas having a lower boiling point than nitrogen gas, such as H ₂ and He, accumulates at the top of the tower section 22. This gas flows as an impure gas together with a part of the nitrogen gas into the condenser 21a from the first reflux liquid passage 21b, separates from the liquefied nitrogen gas there, and escapes from the degassing passage 21g to the outside air. At that time, since the inlet 21e of the first reflux liquid passage 21b is located at a position higher than the inlet 27a of the nitrogen gas extraction passage 27, the impure gas such as H ₂ and He is generated in the first reflux liquid passage 21b.
Nitrogen gas containing impure He, H ₂ can be easily entered by the shielding plate 21f that projects obliquely upward from the lower part of the inlet 21e,
The product nitrogen gas is prevented from being mixed and the product nitrogen gas obtained has a high purity. The liquid nitrogen condensed and liquefied on the upper surface of the shielding plate 21f is dripped into the lower rectification shelf 21h from the droplet lower hole at the base of the shielding plate 21f and collected. On the other hand, the liquid air 18 accumulated in the lower part of the tower section 22 of the rectification tower 15 is sent into the dephlegmator section 21 to cool the condenser 21a. By this cooling, the nitrogen gas sent from the upper part of the tower part 22 of the rectification tower 15 to the condenser 21a through the first reflux liquid passage 21b is liquefied and the inside of the tower part 22 of the rectification tower 15 is liquefied. It becomes the reflux liquid, and returns to the tower portion 22 of the rectification tower 15 via the second reflux liquid passage 21c. Then, the liquid air 18 that has finished cooling the condenser 21a
Is vaporized by the passage 29 to the second and first heat exchangers 14,1.
After being sent to 3, the heat exchangers 14 and 13 are cooled, and then discharged into the air. The liquid nitrogen sent from the liquid nitrogen storage means 23 into the tower portion 22 of the rectification column 15 via the liquid nitrogen introduction passage 24a acts as a cold source for liquefying compressed air, and vaporizes itself. And is taken out as a part of the product nitrogen gas from the nitrogen gas taking-out passage 27. In this way, the liquid nitrogen in the liquid nitrogen storage means 23 is not discarded after it has finished its function as a cold source for liquefying compressed air, but is combined with high-purity nitrogen gas that uses compressed air as a raw material. It is commercialized and used without waste.

On the other hand, the liquid nitrogen introduced from the liquid nitrogen storage means 23 to the rectification column 15 is adiabatically expanded by the control valve 26 and is in a gas-liquid mixed state. If it is supplied to the rectification column 15 as it is, it is flushed. Occurs and the nearby rectification shelf 21h vibrates due to the force. In this case, when the liquid to be treated on the rectification shelf shakes and the liquid depth locally changes,
As shown in FIG. 3, the gas-liquid contact hole 2 of the lower rectification shelf 21h
The gas 39 rising from the 1s to the gas-liquid contact hole 21s of the upper rectification shelf 21h passes through without contacting the liquid 38 in the upper rectification shelf 21h, resulting in insufficient rectification product gas. Will come out. On the other hand, as shown in the figure, a liquid nitrogen introduction passage 24 for guiding the liquid nitrogen in the liquid nitrogen storage means 23 to the rectification column 15
If a gas-liquid separator 35 is installed in a, this gas-liquid separator 3
The vaporized nitrogen in the liquid nitrogen is removed by 5 and the above-mentioned flushing is prevented. As a result, only the liquid component of liquid nitrogen is gently supplied to the rectification tower 15 to prevent vibration of the rectification shelf 21h, and a gas passes through the liquid in each rectification shelf 21h.
High-purity nitrogen gas can be obtained. In this case, in the gas-liquid separator 35, a lead-out pipe 36 for leading out the separated gas
Communicates with the first reflux liquid passage 21b, and the reflux liquid passage 21b communicates with the inside of the rectification column. As a result, the internal pressure of the gas-liquid separator becomes equal to the internal pressure of the rectification column, and the liquid nitrogen stored in the gas-liquid separator is gently fed into the rectification column by its own weight from the pipe 24a. The occurrence of the bubbling phenomenon is completely prevented. The vaporized nitrogen removed by the gas-liquid separator 35 is supplied from the passage 36 to the condenser 21a, so that energy is not wasted.

FIG. 4 shows an example in which the inlet 21e of the first reflux liquid passage 21b of FIG. 2 is formed by a pipe 21i. Since the inlet 21e of the pipe 21i protrudes obliquely upward toward the top of the tower 22 and is sufficiently separated from the inlet 27a of the nitrogen gas extraction passage 27, there is no shielding plate 21f shown in FIG. However, the impure gas such as H ₂ and He accumulated at the top of the tower can be effectively condensed by the condenser 21
can lead to a.

FIG. 5 shows a rectification shelf 21h located 3 to 5 steps below the reflux liquid reservoir 21d provided at the outlet of the second reflux liquid passage 21c in FIG.
An example in which a liquid nitrogen reservoir 21k for accumulating the liquid nitrogen from the liquid nitrogen introducing passage 24a is arranged below is shown. In this configuration, even if impurities are mixed in the liquid nitrogen in the liquid nitrogen storage means 23, the liquid nitrogen is sufficiently rectified in the process of passing through the rectification shelf 21h by 2 to 3 steps and is purified. Is improved. For example,
Liquid nitrogen having a purity of O ₂ of 2 ppm has a high purity of O ₂ of 0.2 ppm or less.

〔The invention's effect〕

Since the high-purity nitrogen gas production apparatus of the present invention does not use an expansion turbine, but instead uses an inexpensive liquid nitrogen storage means such as a liquid nitrogen storage tank having no rotating section, the entire apparatus has no rotating section. No breakdown occurs. That is, according to the present invention, by supplying liquid nitrogen as cold, the supply amount (cold amount) of liquid nitrogen can be rapidly changed according to the change in the taken-out amount of product nitrogen gas. It is possible to maintain stable gas purity. In particular, in the present invention, a gas-liquid separator is provided in an introduction path for supplying liquid nitrogen from the liquid nitrogen storage tank to the rectification column, and a derivation path for discharging the liquid separated in the gas-liquid separator is provided in the rectification column. It communicates with the No. 1 reflux liquid pipe. Therefore, the pressure in the gas-liquid separator becomes the same as the pressure in the rectification column, and the liquid nitrogen once stored in the gas-liquid separator is
Due to its own weight, it will be gently supplied into the rectification tower. Therefore, it is possible to prevent the occurrence of a situation in which a bubbling phenomenon occurs at the time of supplying the liquid nitrogen, resulting in poor purity.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a tower top, FIG. 3 is an explanatory diagram of a rectification shelf for vinegar, and FIG. 4 is a block diagram showing a modified example of the tower top. FIG. 5 is a configuration diagram showing a modified example of the liquid nitrogen reservoir. 9 ... Air compressor, 12 ... Removal means, 13,14 ... Heat exchanger, 15 ... Fractionation tower, 19 ... Liquid air intake passage, 19a ...
Expansion valve, 21 ... decompressor section, 21a ... condenser, 21b ... first
Reflux liquid passage, 21c ... second reflux liquid passage, 22 ...
Tower, 23 ... Liquid nitrogen storage means, 24a ... Liquid nitrogen introduction passage, 27 ... Nitrogen gas extraction passage, 35 ... Gas-liquid separator

Claims (1)

[Claims] 1. An air compression means for compressing air taken in from the outside, a removal means for removing carbon dioxide gas and moisture in the compressed air compressed by the air compression means, and a compression through this removal means. A heat exchange means for cooling the air to an ultra low temperature, a rectification tower for liquefying a part of the compressed air cooled to an ultra low temperature by this heat exchange means and collecting it in the bottom part to take out only nitrogen as a gas from the upper side, and this rectification A condenser built-in type condenser provided at the top of the tower, a liquid air introduction pipe that guides the stored liquid air at the bottom of the rectification tower into the condenser as cold for cooling the condenser, and rectification A first reflux liquid pipe for guiding a part of the nitrogen gas generated in the tower into the condenser, and a second reflux liquid for returning the liquefied nitrogen produced in the condenser as a reflux liquid into the rectification tower. Liquid pipe and liquid nitrogen supplied from outside the device The liquid nitrogen storage means to be stored and an introduction path for guiding the liquid nitrogen in the liquid nitrogen storage means into the rectification column are provided with a gas-liquid separator, and the gas-liquid separator is separated. A high-purity nitrogen gas production apparatus, characterized in that a discharge path for discharging gas is connected to the first reflux liquid pipe.