JPS6244189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] This invention relates to a high purity nitrogen gas production apparatus.

[Conventional technology]

The electronic industry uses extremely large amounts of nitrogen gas. Therefore, it is desired to supply nitrogen gas at low cost, and in order to meet this demand, the PSA method has been introduced, and nitrogen gas has been manufactured and supplied using this method. Figure 1 shows a nitrogen gas production device using this PSA method. In the figure, 1 is an air intake port, 2 is an air compressor, 3 is an aftercooler, 3a is a cooling water supply path, and 4 is an oil-water separator. 5 is a first adsorption tank, 6 is a second adsorption tank, V ₁ and V ₂ are air-operated valves, and air compressed by the air compressor 2 is sent into the adsorption tank 6 by valve action. V ₃ and V ₄ are vacuum valves, and the interior of the adsorption tank 6 is brought into a vacuum state by the action of the vacuum pump 6a. 6b is a cooling pipe that supplies cooling water to the vacuum pump 6a, 6c is a silencer, and 6d is its exhaust pipe. V ₅ , V ₆ , V ₇ and V ₉ are air operated valves. 7 is a product tank, which is connected to the adsorption tanks 5 and 6 through a pipe 8. 7a is a product nitrogen gas extraction pipe, 7b is an impurity analyzer, and 7c is a flow meter.

This nitrogen gas production device compresses air with an air compressor 2, cools the compressed air with an aftercooler 3 attached to the air compressor 2, and removes condensed water with a separator 4. valve
It is sent to the adsorption tanks 5 and 6 via V ₁ or V ₂ . The two adsorption tanks 5 and 6 each have a built-in carbon molecular sieve for oxygen adsorption, and compressed air is alternately fed into these adsorption tanks 5 and 6 every minute by a pressure swing system. . In this case, the adsorption tanks 5 and 6 to which compressed air is not fed are brought into a vacuum state by the action of the vacuum pump 6a. That is, the air compressed by the air compressor 2 enters one of the adsorption tanks 5, and the carbon molecular sieve adsorbs and removes the oxygen therein, and converts it into nitrogen gas, which passes through the valves _V5 ,
It is sent into the product tank 7 through V ₇ and V ₉ , and is passed through the pipe 7a.
taken from. At this time, the other adsorption tank 6 is
Air from the air compressor 2 is shut off by closing the valve _V2 , and the interior is evacuated by the vacuum pump _6a by opening the valve V4. As a result, the oxygen adsorbed on the carbon molecular sieve is removed by suction and the carbon molecular sieve is regenerated. In this way, nitrogen gas is alternately sent from the adsorption tanks 5 and 6 to the product tank 7, and product nitrogen gas is continuously obtained.

[Problem that the invention seeks to solve]

The above-mentioned nitrogen gas production apparatus produces nitrogen gas by utilizing the characteristic of the carbon molecular sieve that selectively adsorbs oxygen, and therefore can obtain nitrogen gas at low cost. However, as mentioned above, compressed air is sent alternately to the two adsorption tanks 5 and 6 every minute, and at the same time, the inside of the other adsorption tank is vacuumed, which requires a large number of valves. The disadvantage is that the operation is complicated and failures are likely to occur frequently. Therefore, the reality is that two sets of two adsorption tanks 5 and 6 must be provided, and one set must be kept as a spare. Therefore, it also has the disadvantage of high equipment costs.

On the other hand, conventional cryogenic liquefaction nitrogen gas production equipment uses an expansion turbine to cool the heat exchanger for cooling the compressed raw air compressed by the compressor, and uses the liquid accumulated in the rectification tower to cool the compressed raw air. It is powered by the pressure of gas evaporated from air (low boiling point nitrogen is extracted as a gas through cryogenic liquefaction separation, and the remainder accumulates as oxygen-rich liquid air). However, the rotation speed of expansion turbines is extremely high (tens of thousands of rotations/minute), and load fluctuations (amount of product nitrogen extracted <<
Since it is difficult to perform follow-up operation for fluctuations in the demand quantity, the purity of the product varies when the load fluctuates. Furthermore, since this device rotates at high speed, it requires high precision in its mechanical structure, is expensive, and has the disadvantage that specially trained personnel are required due to the complicated mechanism. That is, since the expansion turbine has a high-speed rotating section, the above-mentioned problems arise, and there has been a strong desire to eliminate the expansion turbine having such a high-speed rotating section.

[Means for solving problems]

This invention provides air compression means for compressing air taken in from the outside, removal means for removing carbon dioxide and moisture from the compressed air compressed by the air compression means, and compressed air that has passed through the removal means. A nitrogen gas production system equipped with a heat exchange means that cools air to an ultra-low temperature, and a rectification column that liquefies a portion of the compressed air cooled to an ultra-low temperature by this heat exchange means, stores it inside, and extracts only nitrogen as a gas from the upper side. The apparatus includes a liquid nitrogen storage means for receiving and storing liquid nitrogen from outside the apparatus, and a liquid nitrogen storage means for storing the liquid nitrogen supplied from outside the apparatus, and a liquid nitrogen storage means for converting the liquid nitrogen in the liquid nitrogen storage means into cold heat generated from a cold heat generation expander to generate cold heat for liquefying compressed air. A first introduction path that continuously leads to the heat exchange means as a source, and nitrogen gas taken out as a gas from the rectification column through the heat exchange means and heat exchanged with the compressed air to raise the temperature of the product. a nitrogen gas extractor for producing nitrogen gas; a liquid nitrogen evaporator; a second introduction path for introducing liquid nitrogen from the liquid nitrogen storage means to the liquid nitrogen evaporator; The gist of the present invention is to provide a high-purity nitrogen gas production apparatus including a guide path for guiding nitrogen gas as product nitrogen gas into the nitrogen gas extraction path.

That is, the high-purity nitrogen gas production apparatus of the present invention uses the heat of vaporization of liquid nitrogen to cool the compressed air sent to the heat exchange means, liquefies and separates a part of the compressed air in the rectification column, and converts it into nitrogen. Since the nitrogen gas is retained as a gas and extracted as a product nitrogen gas, an expansion turbine is not required, and the disadvantages such as variation in purity caused by the expansion turbine during load fluctuations can be avoided, and nitrogen gas can be obtained at a low cost. You will be able to do this. Also, unlike the PSA system, it does not require a large number of valves, so there are fewer failures. Furthermore, since the apparatus of the present invention is equipped with a backup system line consisting of a liquid nitrogen evaporator, a second introduction path, and a guide path, even when the system is malfunctioning, the liquid nitrogen storage means can be connected to the backup system line. The product can be gasified by supplying liquid nitrogen to the product.
Therefore, stable supply of product gas can be realized.
Furthermore, since this device uses the liquid nitrogen storage means as a liquid nitrogen supply source for both the rectification column line and the backup line, it is possible to save equipment costs and installation space.

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

〔Example〕

FIG. 2 shows an embodiment of the invention. In the figure, 9 is an air compressor, 10 is a drain separator, 11 is a fluorocarbon cooler, and 12 is a set of two adsorption cylinders. The adsorption cylinder 12 is filled with a molecular sieve and functions to adsorb and remove H ₂ O and CO ₂ from the air compressed by the air compressor 9. 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 adsorption column 12 is sent. 14 is a second heat exchanger, into which the compressed air that has passed through the first heat exchanger 13 is sent. Reference numeral 15 denotes a liquid nitrogen storage tank that receives liquid nitrogen from outside the device and stores it.The liquid nitrogen inside is sent to the second heat exchanger 14 through the first introduction path pipe 16, and the liquid nitrogen is transferred to the second heat exchanger 14. It exchanges heat with the compressed air sent into the exchanger 14, and then into the first heat exchanger 13, where it also exchanges heat with the compressed air sent into the first heat exchanger 13 and is vaporized. It's getting old. The liquid nitrogen vaporized by the first heat exchanger 13 is sent into a main pipe (takeout path) 17.

The rectification column 18 takes in compressed air cooled to an extremely low temperature (approximately -170°C) from the bottom through the first and second heat exchangers 13 and 14, and in the process of raising it, oxygen in the compressed air is removed. (boiling point -183°C) is liquefied, dropped and stored at the bottom, and nitrogen (boiling point -196°C) is stored in the upper part in a gaseous state and discharged from there. 18a is a first guide pipe, which is a part of the main pipe 17, and guides the ultra-low temperature nitrogen gas discharged from the upper part of the rectification column 18 to the second and first heat exchangers 14 and 13. , exchanges heat with the compressed air sent there to bring it to room temperature and send it into the main pipe 17. Reference numeral 18b denotes a rectification column pipe, which is installed at the top of the rectification column 18 to transfer the liquid air accumulated at the bottom of the rectification column 18 (liquid nitrogen, the main component of which is liquid oxygen, to a considerable extent) into the rectification column 18.
It is guided to a meandering pipe 18d that communicates with the atmosphere through a pipe 8c, where it is vaporized, and serves to cool the pipe 18d to a temperature below the boiling point of liquid nitrogen. 18c is a second guide pipe that sends the liquid nitrogen that has been cooled in the pipe 18d to the second and first heat exchangers 14 and 13. Heat exchange between the second and first heat exchangers 14 and 13 (heat exchanger 1
The liquid nitrogen that has finished cooling the compressed air in the first heat exchanger 13 is vaporized and discharged from the first heat exchanger 13 as shown by the arrow. Reference numeral 19 denotes a backup system line, which includes a liquid nitrogen evaporator 20, a second introduction path pipe 30a for supplying liquid nitrogen from the liquid nitrogen storage tank 15 to the liquid nitrogen evaporator 20, and the liquid nitrogen evaporator 2.
A guide pipe 30b that sends the nitrogen gas vaporized at 0 to the main pipe 17, this guide pipe 30
It consists of a pressure regulating valve 30c provided at b. The pressure regulating valve 30c opens when the pressure on the secondary side (use side) falls below the set pressure.
Alternatively, the opening degree of the valve is adjusted to maintain the pressure on the secondary side at the set pressure. In the backup system line M19, when the pressure inside the main pipe 17 decreases due to a breakdown in the rectification column line or a significant increase in the demand for product nitrogen gas, the pressure regulating valve 30c is opened. Therefore, liquid nitrogen flows from the liquid nitrogen storage tank 15 to the liquid nitrogen evaporator 20 and is vaporized, and the resulting vaporized nitrogen gas flows into the main pipe 17 as product nitrogen gas. The first and second heat exchangers 13 and 14 and the rectification column 18 are housed in a vacuum cold box shown by a dashed line and are vacuum insulated. When the rectification column 18 is vacuum insulated in this way, the accuracy of rectification is improved, and the effect of improving the purity of the product nitrogen gas can be obtained. This will be explained with reference to FIG. That is, FIG. 3a shows a partially enlarged view of the rectification column 18, in which 18e is a rectification shelf, 18g is liquid air, 18h is a vaporized gas, 1
8f indicates the wall surface of the rectification column. In this state, if the rectification column 18 is not vacuum insulated, the temperature of the liquid air near the rectification column wall 18f will change to curve a in FIG. 3b due to heat intrusion from the rectification column wall 18f. As the temperature increases as shown in Figure 3, the concentration of oxygen gas in the vaporized gas reaches curve a in Figure 3c. It becomes higher as shown. That is, this increases the amount of impure oxygen in the vaporized gas, resulting in poor rectification efficiency. On the other hand, if the rectification column 18 is vacuum insulated,
Since the heat intrusion from the rectification column wall 18f is reduced, the temperature of the liquid air near the rectification column wall 18f does not become very high as shown by curve b in FIG. 3b.
Therefore, almost no oxygen evaporates, and the oxygen gas concentration in the vaporized gas becomes significantly lower as shown by curve b in FIG. 3c. Therefore, rectification efficiency improves. In other words, by providing vacuum insulation, the purity of the product nitrogen gas obtained is significantly higher than in the case without vacuum insulation. In addition, in this way, the rectification tower 18
By vacuum insulating the system, a secondary effect can also be obtained, which is that the start-up from a rest state to steady operation becomes faster. This is because the thermal insulation material has almost no heat capacity and the loss of cooling and heat is extremely small compared to the normal pressure insulation method.

This device produces product nitrogen gas in the following manner. That is, air is compressed by an air compressor 9, moisture in the compressed air is removed by a drain separator 10, and cooled by a fluorocarbon cooler 11. In this state, the air is sent to an adsorption column 12 filled with molecular sieve. , H ₂ O in air and
Adsorbs and removes CO ₂ . Then, the compressed air from which H ₂ O and CO ₂ have been adsorbed and removed is sent to the first heat exchanger 13 and the second heat exchanger 14 to be cooled to an ultra-low temperature, and then passed from the lower part of the rectification column 18 to the rectification column 18. send it inside. Then, the oxygen in the air is liquefied by utilizing the difference in boiling point between nitrogen and oxygen (the boiling point of oxygen is -183°C, the boiling point of nitrogen is -196°C), and the nitrogen is taken out as a gas and transferred to the first heat exchanger 13. The nitrogen gas is fed into the tank, heated to near room temperature, and taken out from the main pipe 17 as nitrogen gas. In this case, the liquid nitrogen in the liquid nitrogen storage tank 15 acts as a cold source for the first and second heat exchangers 13 and 14, and is vaporized and sent into the main pipe 17, and is then vaporized into the rectification column. It is combined with the nitrogen gas in the air obtained from step 18 and taken out as a product nitrogen gas. The product nitrogen gas thus obtained is of ultra-high purity.

As described above, according to this high-purity nitrogen gas production device, compressed air is cooled using the heat of vaporization of liquid nitrogen, and is sent to the vacuum-insulated rectification column 18 to separate oxygen, etc., and produce nitrogen. The nitrogen gas is removed and combined with liquid nitrogen (in gaseous form), which serves as a cooling source, to produce nitrogen gas, which eliminates the above-mentioned disadvantages caused by expansion turbines and is extremely inexpensive and highly pure. of liquid nitrogen can be obtained.

That is, the vacuum-insulated rectification column 18
By setting with high precision, it becomes possible to obtain nitrogen gas with a purity of 99.999% without any variation in purity. On the other hand, PSA nitrogen gas production equipment can only produce nitrogen with a purity of 99.3% at most, and cryogenic liquefaction separation equipment that uses an expansion turbine has fluctuations in purity when the load fluctuates. In addition, this high-purity nitrogen gas production equipment can be used in cases where the rectification column line cannot cope with a significant increase in the demand for product nitrogen gas, or when a malfunction occurs in the rectification column line. When nitrogen gas cannot be obtained, the backup system line 19 is activated and the liquid nitrogen storage tank 1 is
5 is directly vaporized in the evaporator 20 and then flows into the main pipe 17 as product nitrogen gas. This prevents the occurrence of a decrease in the purity of the product nitrogen gas when demand increases significantly, and the problem of product nitrogen gas supply. Stagnation is avoided and product nitrogen gas can be constantly and stably supplied, which is a major feature. Furthermore, since this device uses one liquid nitrogen storage tank 15 as a storage tank for both the rectification column line and the backup system line, it is possible to significantly reduce equipment costs and at the same time save installation space for the liquid nitrogen storage tank 15. This is also a major feature, as it can be made smaller and the entire device can be made more compact.

As described above, according to the high-purity nitrogen gas production apparatus of the present invention, high-purity nitrogen gas can be obtained in a stable state, so it can be directly used in the electronic industry. And this gas does not contain carbon dioxide (it is removed in the manufacturing equipment)
Therefore, there is no need to separately equip an adsorption tank for carbon dioxide gas. Furthermore, a large amount of nitrogen gas can be obtained by simply supplying a small amount of liquid nitrogen. That is, according to the high-purity nitrogen gas production apparatus of the present invention, 100Nm ³ (gas equivalent) from the liquid nitrogen storage tank 15
By sending 1000 Nm 3 of liquid nitrogen into the heat exchangers 13 and 14, 1000 Nm ³ of product nitrogen gas can be obtained. In this way, with this production equipment, by supplying only a small amount of liquid nitrogen, 10 times as much product nitrogen gas can be obtained. Therefore, extremely cheap nitrogen gas can be obtained. In addition, compared to nitrogen gas production equipment using the PSA method or the conventional cryogenic liquefaction separation method that uses an expansion turbine, the equipment is simple and inexpensive, and it does not require a large number of valves. High reliability. It also eliminates the need for special personnel due to the expansion turbine.

In addition, in FIG. 2, the second and first heat exchangers 14 and 13 are heated with liquid nitrogen in the liquid nitrogen storage tank 15.
Although an example is shown in which the vaporized liquid nitrogen is led to the main pipe 17 and combined with the product nitrogen gas after being cooled, it may be appropriately released into the atmosphere as shown in FIG. In this case, the liquid nitrogen is not effectively utilized, so the cost of the product nitrogen gas becomes somewhat high.

Figure 5 shows another embodiment.

That is, in this high-purity nitrogen gas production apparatus, the first guide pipe 18a is provided with an oxygen adsorption column 27a containing a built-in adsorbent that selectively adsorbs oxygen and carbon monoxide at extremely low temperatures. Since the other parts are substantially the same as the apparatus shown in FIG. 3, the corresponding parts are given the same reference numerals and the explanation thereof will be omitted.

As the adsorbent, for example, synthetic zeolite 3A, 4A or 5A (Molecular Sieve 3A, 4A, 5A, manufactured by Union Carbide) having a pore diameter of 3 Å, 4 Å or 5 Å is used. As shown in Figure 6, these synthetic zeolites 3A, 4A, and 5A have excellent resistance to oxygen and carbon monoxide at extremely low temperatures (although not shown in Figure 6, they show curves similar to the O ₂ curve in the same figure). It has selective adsorption properties. Therefore, the impurities in the nitrogen gas obtained from the upper part of the rectification column 18 are removed, and the purity of the product nitrogen gas is further improved. In addition, in this device, the nitrogen gas generated by vaporizing the liquid nitrogen in the liquid nitrogen storage tank 15 also passes through the oxygen adsorption column 27a in the same way as the nitrogen gas obtained from compressed air. Even when the nitrogen gas is mixed with impure oxygen and carbon monoxide, the purity of the resulting nitrogen gas product does not decrease. In this case, since the amount of impure oxygen and carbon monoxide in the ultra-low temperature nitrogen gas introduced into the oxygen adsorption column 27a has already reached a low level after passing through the rectification column 18, the amount of oxygen and carbon monoxide to be adsorbed is The amount is tiny. Therefore, only one adsorption column is required, and zeolite regeneration once a year is sufficient.

In addition, the rectification column 18 used in each of the above examples
It goes without saying that similar effects can be obtained by using other types of rectification columns instead.

〔Effect of the invention〕

As described above, the high-purity nitrogen gas production device of the present invention does not use an expansion turbine, but instead uses a liquid nitrogen storage means such as a liquid nitrogen storage tank that does not have any rotating parts, so the entire device has no rotating parts. There will be no failures at all. In addition, unlike the PSA system, it does not have a large number of valves, so valve-related failures do not occur.Furthermore, since the expansion turbine is a high-speed rotating device, it can closely follow load fluctuations (changes in the amount of product nitrogen gas taken out). Although operation is difficult, the device of this invention uses a liquid nitrogen storage tank instead of an expansion turbine, and uses liquid nitrogen as a cooling source whose supply amount can be finely adjusted, making it possible to closely follow load fluctuations. , it becomes possible to produce nitrogen gas with stable and extremely high purity. In particular, the device of this invention
Liquid nitrogen is supplied from the liquid nitrogen storage means to the heat exchange means, and since this introduction path is independent from the rectification column line, it is possible to control only heat transfer, and pressure fluctuations within the rectification column can be controlled. It has the advantage of being able to be driven without having to take this into account. Furthermore, since the high-purity nitrogen gas production device of the present invention is equipped with a backup line that operates when the device malfunctions,
A stable supply of product nitrogen can be achieved. Furthermore, this device uses one liquid nitrogen storage means for both the rectification column line and the backup system line, so it is possible to significantly reduce equipment costs, and at the same time, it is possible to save a lot of equipment costs. The installation space for the liquid nitrogen storage means can be reduced, and the entire device can be made more compact, which is a major feature.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of a conventional example, Fig. 2 is a configuration diagram of an embodiment of the present invention, Fig. 3 is an explanatory diagram of improvement of rectification effect by vacuum insulation, and Fig. 4 is a modification of Fig. 2. FIG. 5 is a block diagram of another example, and FIG. 6 is a characteristic curve diagram of a synthetic zeolite used therein. 9...Air compressor, 12...Adsorption cylinder, 13,1
4... Heat exchanger, 15... Liquid nitrogen storage tank, 17...
... Main pipe, 18 ... Rectification column, 19 ... Backup system line, 20 ... Liquid nitrogen evaporator, 3
0a...Second introduction pipe, 30b...Guide pipe, 30c...Pressure control valve.

Claims (1)

[Claims] 1. Air compression means for compressing air taken in from the outside, removal means for removing carbon dioxide and moisture from the compressed air compressed by this air compression means, and cooling the compressed air that has passed through this removal means to an ultra-low temperature. In a nitrogen gas production device equipped with a cooling heat exchange means and a rectification column that liquefies a part of the compressed air cooled to an ultra-low temperature by the heat exchange means and stores it inside and extracts only nitrogen as a gas from the upper side, A liquid nitrogen storage means that receives liquid nitrogen from outside the device and stores it, and a liquid nitrogen storage means that continuously uses the liquid nitrogen in the liquid nitrogen storage means as a cold source for liquefying compressed air in place of the cold heat generated from the cold heat generation expander. Nitrogen gas taken out as a gas from the rectification column is passed through the heat exchange means and heat exchanged with the compressed air to raise the temperature and convert it into product nitrogen gas. a liquid nitrogen evaporator; a second introduction path for guiding the liquid nitrogen in the liquid nitrogen storage means to the liquid nitrogen evaporator; A high-purity nitrogen gas production device comprising a guide path for guiding gas into the nitrogen gas extraction path.