JP2002372367A - Air separator for gas product and its cold heat utilizing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air separator for a gas product in which cold heat of LNG can be utilized effectively. SOLUTION: In an air separator comprising a means for supplying material air, a main heat exchanger, a rectifying column for separating the components and an LNG heat exchanger, and in its cold heat utilizing method, a gas product taken out from the rectifying column is heated by the main heat exchanger, nitrogen gas in the gas product is passed through the LNG heat exchanger in order to recover cold head and then passed again through the main heat exchanger in order to exchange heat thus producing a gas product. High purity nitrogen gas or nitrogen gas having a low content of oxygen is passed through the LNG heat exchanger and the pressure thereof is preferably higher than that of LNG.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air separation apparatus for mainly producing gas products and a method for utilizing the cold energy thereof, and more particularly, to a method for producing a gas product from raw air by utilizing the cold energy of liquefied natural gas (hereinafter, LNG). The present invention relates to an air separation apparatus for producing gas products such as nitrogen and oxygen, and a method for compensating for refrigeration loss using the apparatus.

[0002]

2. Description of the Related Art In an air separation apparatus which has been conventionally operated for producing gas products, an expansion turbine is used to compensate for a loss at a hot end of a heat exchanger and heat intrusion.
It is necessary to compress air or nitrogen gas to a predetermined pressure to generate cold.

FIG. 3 is a diagram for explaining the structure and operation of a conventional air separation device. As shown in FIG. 1, the raw air filtered by the suction filter 1 is supplied to an air compressor 2.
After being compressed to about 0.5MPa, the rear cooler 3
And unnecessary components such as water and carbon dioxide contained in the adsorption tower 4 are removed. These constitute a means for supplying raw air.

Next, the raw material air enters the main heat exchanger 5 and, as described later, is cooled to near the boiling point by exchanging heat with low-temperature nitrogen gas or oxygen gas extracted from the rectification column. It is introduced into the high-pressure rectification column 6. The raw material air introduced into the high-pressure rectification column 6 gradually increases the nitrogen concentration by gas-liquid contact with the reflux liquid nitrogen while ascending in the column, and becomes high-purity nitrogen gas at the top. The nitrogen gas that has reached the top is introduced into the condenser 8 and is condensed into liquid nitrogen by heat exchange with liquid oxygen at the bottom of the low-pressure rectification column 7, and a part thereof is used as a reflux liquid of the low-pressure rectification column 7. It is fed to the top of the low pressure column, partly as reflux, to the top of the high pressure rectification column 6.

[0005] The reflux liquid used in the high-pressure rectification column 6 comes into contact with air while descending from the top of the high-pressure rectification column 6 to increase the oxygen concentration, and as a liquid air having a high oxygen concentration from the bottom. It is withdrawn and supplied to the middle part of the low-pressure rectification column 7. The liquid air further increases the oxygen concentration while descending the low-pressure rectification column 7 and stays at the bottom as high-purity liquid oxygen.

As products, high-purity oxygen gas is supplied from the bottom of the low-pressure rectification column 7 and high-purity nitrogen is supplied from the low-pressure rectification column 7.
, Or from the top of the high-pressure rectification column 6, refluxed to the main heat exchanger 5, and heat-exchanged with the raw air as described above to warm it to near the atmospheric temperature, Supplied as gas products. After low-purity nitrogen gas is extracted from the upper part of the low-pressure rectification column 7 and heated in the main heat exchanger 5, it is used as exhaust gas for the regeneration gas of the adsorption tower 4 or for producing cold water. Released to the atmosphere.

In the air separation apparatus for producing the gas product shown in FIG. 3, it is usually necessary to constantly generate refrigeration in order to compensate for the loss at the hot end of the heat exchanger and the intrusion heat. For this reason, a part of the raw material air from which the pressurization, cooling, and moisture and carbon dioxide gas have been removed is passed through a booster 9 and a rear cooler 10 to be compressed and cooled, and then cooled using an expansion turbine 11. Then, it is charged into the upper part of the low-pressure rectification column 7.

[0008]

[0007] LNG is an environment-improving energy, and its introduction has been promoted from the viewpoint of alternative energy to petroleum. With this, technology for effectively utilizing the cold energy of LNG has been developed. Practical application has been promoted to an air separation device for producing liquid nitrogen and liquid oxygen (for example, JP-A-2000-65470 and JP-A-6-11254).

[0009] As an example of utilizing the cold heat of LNG, LNG
It is constructed relatively close to the NG receiving terminal and recovers a large amount of LNG cold, more than 20 t / h supplied from the receiving terminal, to efficiently produce liquid products of nitrogen and oxygen. There are large air separation units. In this case, nitrogen gas produced by the apparatus or nitrogen gas having a low oxygen content is used as a recovery medium, and these nitrogen gases are liquefied by heat exchange with LNG, and are liquefied at the hot end of the heat exchanger. It is supplied to the main body of the air separation device in order to compensate for loss and heat intrusion. However, when utilizing the cold energy of LNG in a large-scale air separation device, it is difficult to modify the existing device because the process of recovering the cold energy is complicated.

On the other hand, an LNG satellite base has been constructed for the local supply of city gas in remote areas. LNG is transported to this satellite base by lorry, etc., but it is smaller than the LNG receiving base and typically stays at about 1 to 5 t / h, so it is vaporized by an air-heated vaporizer. At present, the cold heat of LNG is not effectively used.

As described above, the refrigeration required mainly in the air separation apparatus for producing gas products is generated by expanding compressed and cooled air or nitrogen gas with an expansion turbine, and the refrigeration of LNG is generated. There were no cases of use. This is because although air separation equipment that mainly produces gas products requires less refrigeration than when producing liquid products, there is a simple means to compensate for the refrigeration with the cold heat of LNG. This is because it has not been developed and requires complicated equipment, and the economic effect of utilizing the cold heat of LNG has been poor.

The present invention has been made in view of such a situation, and it is possible to effectively use the cold heat of LNG even in an air separation device that mainly produces gas products. It is an object of the present invention to provide an air separation device capable of reducing the power consumption required for producing gas products, and a method of utilizing the cold energy thereof.

[0013]

SUMMARY OF THE INVENTION The gist of the present invention is the following (1) air separation device for gas products and (2) and (3) a method for utilizing cold heat by the air separation device. (1) A means for supplying raw air, a main heat exchanger for exchanging heat between the supplied raw air and the extracted gas product, and selectively taking in the raw air cooled by the main heat exchanger. A rectification column for separating composition components, an LNG heat exchanger for recovering the cold of natural gas, a means for flowing nitrogen gas of gas products from the main heat exchanger to the LNG heat exchanger, and an LNG heat exchanger An air separation device for producing a gas product, comprising a means for flowing nitrogen gas from a gas to a main heat exchanger. (2) A main heat exchanger that exchanges heat between the supplied raw air and the extracted gas product, and a rectification column that takes in the raw air cooled by the main heat exchanger and selectively separates constituent components. A method for utilizing cold energy by an air separation device for producing a gas product, wherein an LNG heat exchanger for recovering the cold energy of natural gas is provided on the outlet side of the device, and the gas product extracted from the rectification column is provided. Is heated in the main heat exchanger by heat exchange with raw material air, and then nitrogen gas is
A method for utilizing the cold energy of an air separation device, wherein cold heat is recovered through an NG heat exchanger, and then heat-exchanged with raw air through the main heat exchanger to produce a gas product. (3) A main heat exchanger that exchanges heat between the supplied raw air and the extracted gas product, and a rectification column that takes in the raw air cooled by the main heat exchanger and selectively separates constituent components. A method for utilizing cold energy by an air separation device for producing a gas product, wherein an LNG heat exchanger for recovering the cold energy of natural gas is provided on the outlet side of the device, and the gas product extracted from the rectification column is provided. Is heated by heat exchange with the raw air in the main heat exchanger, then nitrogen gas is branched out of the gas product and a part thereof is passed through the LNG heat exchanger to recover cold heat. A method for utilizing the cold energy of an air separation device, wherein the method is combined with nitrogen gas which is taken out and passed through a main heat exchanger.

In the above method (3), it is desirable that the nitrogen gas branched through the main heat exchanger is compressed to a predetermined pressure and / or cooled to a predetermined temperature and then passed through the LNG heat exchanger. In addition, when merging with the nitrogen gas taken out from the rectification column, it is desirable to cool the nitrogen gas from which the cold heat has been recovered through the LNG heat exchanger to a predetermined temperature.

In the above-mentioned methods (2) and (3) of utilizing cold energy,
The nitrogen gas passed through the NG heat exchanger is a high-purity nitrogen gas or a nitrogen gas having a low oxygen content, and preferably has a pressure higher than the LNG pressure.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION In the air separation device of the present invention, an LNG heat exchanger for recovering cold heat of LNG at the outlet of the device, means for flowing gas from the main heat exchanger to the LNG heat exchanger,
And means for flowing gas from the LNG heat exchanger to the main heat exchanger are provided, and the gas product taken out of the rectification tower is heated to near atmospheric temperature through the main heat exchanger, and nitrogen gas is From the main heat exchanger to the LNG heat exchanger, cool the nitrogen gas to a low temperature by recovering the cold heat of the LNG, introduce the cooled gas product again into the main heat exchanger, and It is characterized by supplying cold air to

By adopting such an apparatus configuration, even in an air separation apparatus that mainly produces gas products,
Necessary refrigeration can be obtained from the cold heat of LNG without using an expansion turbine by using equipment that is simpler than the expansion turbine device.

As specific equipment, it is necessary to newly install an LNG heat exchanger and a means for flowing gas products between the main heat exchanger and the LNG heat exchanger. Some modifications are required. However, such a modification can be easily applied to a device already in operation.

Further, as shown in FIG. 2, which will be described later, a new means for flowing gas products between the main heat exchanger and the LNG heat exchanger is provided. Is made to flow between the LNG heat exchanger and the branch point, the modification in the main heat exchanger becomes unnecessary.

In recovering the cold energy of the LNG, the nitrogen gas used for the cold energy recovery in consideration of the flammability of the LNG is a high-purity nitrogen gas or a nitrogen gas having a low oxygen content. Here, the nitrogen gas having a low oxygen content corresponds to a low-purity nitrogen gas extracted from the upper part of the low-pressure rectification column 7 shown in FIGS. 1 and 2 described later.

Further, in consideration of an emergency leak inside the heat exchanger, nitrogen gas compressed to a pressure higher than the pressure of LNG is generally used. For this reason, when the nitrogen gas introduced into the LNG heat exchanger via the main heat exchanger is lower than the pressure of LNG, it is necessary to pressurize the nitrogen gas. Therefore, it is desirable to provide a nitrogen gas compressor. .

In the case where a branch point is provided in the nitrogen gas flowing means in the air separation device, the nitrogen gas obtained by collecting the cold heat of the LNG is merged with the nitrogen gas before passing through the main heat exchanger. Since it may be necessary to control the temperature of the nitrogen gas in advance, it is desirable to provide an adjusting means such as an expansion turbine.

If the LNG passed through the LNG heat exchanger still has a surplus available cold, for example, if the LNG has a cold of about -50 ° C. at the LNG temperature, this cold will be transferred to Freon or brine. Can be recovered. Therefore, LN
It is desirable to provide a brine cooler or the like also in the lower process of the G heat exchanger, and use the recovered cold heat for precooling the raw material air in the air separation device or cooling argon in the argon purification device.

In the method for utilizing cold energy of the present invention, by appropriately combining the above-mentioned cold energy recovery, the present invention is not limited to an air separation device for gas products, but may be combined with a small-scale vaporization device used at a satellite base, for example. In addition, it is possible to sufficiently and reliably recover the cold heat of LNG, and it is possible to effectively reduce the power consumption required for producing gas products.

According to the method of utilizing cold energy of the present invention,
Since nitrogen gas is used as a gas product for recovering NG cold energy, and the pressure of the nitrogen gas is maintained at or above the LNG pressure, safety at the time of recovering cold energy can be sufficiently ensured. .

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The effects of the method of utilizing cold energy of the present invention will be specifically described based on Embodiments 1 and 2. (Embodiment 1) FIG. 1 is a view showing an example of the configuration of an air separation apparatus for producing a gas product to which the method of utilizing cold energy of the present invention is applied. The supply of the raw material air is made 50,000 Nm ³ / h from the atmosphere, introduced into the air compressor 2 and compressed to 0.5 MPa, and then guided to the rear cooler 3 to produce cooling water or cold water produced by exhausted nitrogen gas. After cooling with brine or the like (not shown), moisture and carbon dioxide in the raw material air were removed in the adsorption tower 4.

The raw air is heat-exchanged with the low-temperature nitrogen gas or oxygen gas (detailed conditions will be described later) extracted from the high-pressure rectification tower 6 and the low-pressure rectification tower 7 in the main heat exchanger 5. It was cooled to -170 ° C and introduced into the high-pressure rectification column 6.

In the high-pressure rectification column 6, oxygen-enriched liquid air was selectively separated at the bottom, and nitrogen gas was separated at the top. Then, the oxygen-enriched liquid air extracted from the bottom of the high-pressure rectification column 6 was introduced into the intermediate portion of the low-pressure rectification column 7. On the other hand, the nitrogen gas withdrawn from the top of the high-pressure rectification column 6 is branched, a part is taken out as a product, a part is introduced into the condenser 8, and the liquid oxygen separated at the bottom of the low-pressure rectification column 7 is separated. After being condensed and liquefied by the reaction, it was branched and introduced into the top of the high-pressure rectification column 6 and the top of the low-pressure rectification section 7 as a reflux liquid.

The nitrogen gas taken out from the top of the high-pressure rectification column 6 as a product is in a state of 1,250 Nm ³ / h and a pressure of 0.45 MPa. After being heated to the vicinity, the LNG heat exchanger 12
The cold of G was recovered and cooled to -140 ° C.

Thereafter, the cooled nitrogen gas is introduced into the central part of the main heat exchanger 5 and is heated again to near the atmospheric temperature by heat exchange with the raw material air, so that the cold heat of the LNG is reduced by the refrigeration of the air separation device. And then taken out as product gas.

Further, from the top of the low-pressure rectification column 7, nitrogen gas was supplied at 10,000 Nm ³ / h and a pressure of 0.3 MPa.
Oxygen gas was discharged from the bottom at 10,000 Nm ³ / h and at a pressure of 0.3 MPa.
It was taken out in a state of 00 Nm ³ / h and a pressure of 0.4 MPa.

Similarly, these gases are heated to near the ambient temperature by exchanging heat with the raw air in the main heat exchanger 5, and oxygen gas and nitrogen gas are supplied to a product booster (not shown) if necessary. And then supplied as product gas. The exhausted nitrogen gas was released to the atmosphere after being used as a regeneration gas for the adsorption tower 4 and for producing cold water.

On the other hand, the LN introduced into the LNG heat exchanger 12
G had an inlet side of 500 kg / h, a pressure of 0.3 MPa, and a temperature of −160 ° C., but was heated to −60 ° C. by heat exchange with nitrogen gas. Here, care was taken to keep the pressure of the nitrogen gas at 0.3 MPa or more, so that no flammable components were mixed into the nitrogen gas side and sufficient safety was ensured.

A brine cooler 13 is provided in a lower process of the LNG heat exchanger 12, and the excess cold heat of LNG is exchanged with the brine to heat it to around the ambient temperature.
Can be supplied as The low-temperature brine obtained by recovering the excess cold heat of the LNG can be used for pre-cooling the raw material air and the like.

Considering the effects of the first embodiment, the energy required for producing gas products in an air separation device of the same scale, that is, the basic unit of electric power for producing oxygen gas, has a separation energy of 0.40 kWh / in Nm ^3, cold energy content is 0.04kWh / Nm ^3, become 0.44kWh / Nm ³ in total (rEFRIGERATION VOL.57, see No.652 p106~112). According to the result of the first embodiment, since 0.04 kWh / Nm ³ of the cooling energy is reduced by using the LNG cold heat, the power consumption is reduced by about 9%.

It should be noted here that the supply amount of LNG is converted to 600 Nm ³ / h, and the supply amount of raw air is 50,000 Nm
^Although it was a very small amount of about 1% compared to ³ / h, LNG originally had energy of about 850 kW / t-LNG. According to the result of the first embodiment, a reduction of about 400 kW at 500 kg / h was made. ,
The reduction effect is about 800 kW / t-LNG, which means that 90% or more of the original energy is recovered. Therefore, if the method of utilizing cold energy of the present invention is applied, efficient L
It was confirmed that the use of NG cold energy could be achieved. (Embodiment 2) In the above-described embodiment 1, nitrogen gas of 1,250 Nm ³ / h and pressure of 0.45 MPa was taken out from the top of the high-pressure rectification column 6 to recover LNG by cold heat. The removal of nitrogen gas from the top of the high pressure rectification column is limited in equipment, especially in air separation equipment for producing liquefied argon.

Further, in Example 1, the nitrogen gas from which the cold heat of LNG was recovered was introduced again into the center of the main heat exchanger, but such a gas was supplied to the main heat exchanger of the operating air separation device. The introduction part is not provided, and in order to apply the cold heat utilization method of the present invention, the main heat exchanger needs to be modified or replaced. Therefore, in the second embodiment, a case will be described in which the main heat exchanger of the operating air separation device does not need to be modified or replaced.

FIG. 2 is a diagram showing another example of the configuration of an air separation apparatus for producing a gas product using the cold energy utilization method of the present invention. In the configuration example shown in FIG. 2, a branch point B is provided in the flow path of the nitrogen gas on the outlet side of the main heat exchanger 5, and LN
A distribution means up to the G heat exchanger 12 is provided. At the same time,
A branch point A is provided in the flow path of the nitrogen gas on the inlet side of the main heat exchanger 5 in the air separation device, and a flow means from the LNG heat exchanger 12 to the branch point A is provided.

Further, it is desirable to provide a nitrogen gas compressor 14 and a rear cooler 15 in the flow means from the branch point B to the LNG heat exchanger 12. Further, it is desirable to provide an expansion turbine 16 in the flow means from the LNG heat exchanger 12 to the branch point A in order to adjust the temperature of the nitrogen gas.

The nitrogen gas taken out from the top of the low-pressure rectification column 7 merges with the nitrogen gas sent out from the expansion bin 16 at the branch point A, is introduced into the main heat exchanger 5, and is mixed with the raw air and heat. After being exchanged, the temperature was increased to near the atmospheric temperature, and then branched at point B on the outlet side. Some of the branched nitrogen gas is
If necessary, the pressure was increased to a predetermined pressure by a product booster (not shown), and then supplied as product nitrogen gas.

The other part of the nitrogen gas, which is branched, is set to a flow rate of 1,250 Nm ³ / h, pressurized to 0.4 MPa by the nitrogen compressor 14, cooled to 35 ° C. by the rear cooler 15, and subjected to LNG. Introduced to the heat exchanger. LN introduced into LNG heat exchanger
G is 500kg / h (about 600Nm ³ / h), pressure 0.3MPa, temperature -160
° C, and the heat exchanged nitrogen gas was cooled to -140 ° C. This nitrogen gas is adjusted to −175 ° C. by expanding it in the expansion turbine 16, and from the branch point A to the main heat exchanger 5.
Was merged with the nitrogen gas on the entry side.

On the other hand, LNG exiting the LNG heat exchanger 12 is
Heated to -90 ° C by heat exchange with nitrogen gas. L
A brine cooler 13 is provided in a lower process of the NG heat exchanger 12,
The excess cold heat of LNG was heated to near ambient temperature by heat exchange with brine, and then supplied as NG.

By adopting the above configuration, when applying the method of the present invention, installation of the LNG heat exchanger 12 and
Distribution means from branch point B to LNG heat exchanger and LN
The existing apparatus can be applied only by modifying the piping relating to the flow means from the G heat exchanger to the branch point A.

In the second embodiment, if necessary, a nitrogen compressor
14. A new rear cooler 15 and expansion turbine 16 are required, and the amount of nitrogen gas introduced into them is 1,250 Nm ³ / h
Compared to 50,000 Nm ³ / h of raw material air volume, it is 2.5% small amount, so it can be handled with small-scale equipment.

Further, even if the power consumption of the nitrogen compressor 14 is required, it can be predicted that the power consumption is limited to about 100 kW, and in the second embodiment, the power consumption can be reduced by 300 kW.
In other words, by using the cold energy of LNG efficiently by simple equipment modification, the basic unit required for gas oxygen production can be reduced from 0.44 kWh / Nm ³ to 0.41 kW / Nm ³ and reduced by 7%. Was.

In the description of the second embodiment, the air separation apparatus for producing only oxygen gas and nitrogen gas as gas products has been described. However, the same method can be applied to the production of liquefied argon. It is possible to reduce the power consumption per unit of production.

[0047]

According to the air separation device and the method for utilizing the cold energy of the present invention, even in the air separation device for producing a gas product, the cold energy of LNG can be effectively used. It is possible to reduce the power consumption required for manufacturing products.

More specifically, the cold energy corresponding to the cold energy of the air separator for producing the gas, that is, the cold heat corresponding to the loss of the hot end of the heat exchanger and the heat of intrusion, is reduced to about 1% of the amount of the raw material air by L.
By covering the amount of NG, it is possible to reduce the power consumption unit required for producing oxygen gas by 5% or more. In addition, the LNG amount with respect to the raw material air amount corresponds to the processing scale of a satellite base having a small-scale vaporizer that could not effectively utilize the cold heat of LNG in the past,
Combination with such a small-scale LNG vaporizer is also possible.

Further, since the amount of LNG is small and the amount of nitrogen gas for recovering the cold of LNG is also small compared to the amount of raw air, the air separation apparatus of the present invention and the method of utilizing the cold thereof are applied. The modification of the equipment of the above can be made small and simple. For this reason, the present invention can be easily applied to a device currently in operation, and is effective in reducing the power consumption.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of an air separation device for producing a gas product to which the method of utilizing cold energy of the present invention is applied.

FIG. 2 is a diagram showing another example of the configuration of an air separation device for producing a gas product using the cold heat utilization method of the present invention.

FIG. 3 is a diagram for explaining a configuration of a conventional air separation device and its operation.

[Explanation of symbols]

 1: Absorption filter 2: Air compressor 3: Rear cooler 4: Adsorption tower 5: Main heat exchanger 6: High pressure rectification column 7: Low pressure rectification column, 8: Condenser 9: Booster, 10 : Rear cooler 11: Expansion turbine, 12: LNG heat exchanger 13: Brine cooler, 14: Nitrogen compressor 15: Rear cooler, 16: Expansion turbine A, B: Branch point

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Atsushi Miyamoto 2-6-6 Chikushinmachi, Sakai-shi, Osaka F-term in Air Water Corporation (reference) 4D047 AA08 AB01 AB02 CA07 DA17

Claims (6)

[Claims] 1. A means for supplying raw air, a main heat exchanger for exchanging heat between the supplied raw air and a taken-out gas product, and taking and selecting raw air cooled by the main heat exchanger. A rectification column that separates the constituent components in an efficient manner, an LNG heat exchanger that recovers the cold of natural gas,
An air separation apparatus for producing a gas product, comprising: means for flowing nitrogen gas out of a gas product to an NG heat exchanger; and means for flowing nitrogen gas from an LNG heat exchanger to a main heat exchanger. 2. A main heat exchanger for exchanging heat between a supplied raw material air and a taken-out gas product, and a main heat exchanger for taking in the raw material air cooled by the main heat exchanger and selectively separating composition components. A method for utilizing cold energy by an air separation device having a distillation tower and producing a gas product, wherein an LNG heat exchanger for recovering the cold energy of natural gas is provided on the outlet side of the apparatus, and the LNG heat exchanger is taken out from the rectification tower. The gas product is heated by heat exchange with the raw air in the main heat exchanger, and then nitrogen gas of the gas product is passed through the LNG heat exchanger to recover cold heat, and then passed through the main heat exchanger again. A method for utilizing the cold energy of an air separation device, wherein heat is exchanged with raw material air to produce a gas product. 3. A main heat exchanger for exchanging heat between the supplied raw material air and the extracted gaseous product, and a precision heat exchanger for taking in the raw material air cooled by the main heat exchanger and selectively separating composition components. A method for utilizing cold energy by an air separation device having a distillation tower and producing a gas product, wherein an LNG heat exchanger for recovering the cold energy of natural gas is provided on the outlet side of the apparatus, and the LNG heat exchanger is taken out from the rectification tower. The gas product is heated by heat exchange with the raw air in the main heat exchanger, then the nitrogen gas is branched out of the gas product, a part of the gas product is passed through the LNG heat exchanger, and the cold heat is recovered. A method for utilizing the cold energy of an air separation device, wherein the nitrogen gas is taken out of a column and is combined with nitrogen gas before passing through a main heat exchanger. 4. The nitrogen gas passed through the LNG heat exchanger is a high-purity nitrogen gas or a nitrogen gas having a low oxygen content, and has a pressure higher than a natural gas pressure. 4. A method for utilizing cold energy by the air separation device according to 2 or 3. 5. The air separation apparatus according to claim 3, wherein the nitrogen gas branched through the main heat exchanger is compressed to a predetermined pressure and / or cooled to a predetermined temperature and passed through an LNG heat exchanger. How to use cold heat. 6. The air separation apparatus according to claim 3, wherein the nitrogen gas from which the cold energy has been recovered by passing through the LNG heat exchanger is cooled to a predetermined temperature and combined with the nitrogen gas extracted from the rectification column. How to use cold heat.