JPH0711382B2 - Liquid air production equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for producing liquid air.

[Conventional technology]

Conventionally, a liquid nitrogen production apparatus and a liquid oxygen production apparatus are known as apparatuses for liquefying gas. These have basically the same configuration, and FIG. 5 illustrates a liquid nitrogen production apparatus.

In the figure, reference numeral 1 is a circulating nitrogen compressor, and nitrogen gas separated from oxygen by an air separation device (not shown) is pressurized by the circulating nitrogen compressor 1 and then enters the cold box A.

In the cold box A, a precooler 2, a Freon cooler 4 receiving cold from the refrigerator 3, a first heat exchanger 5, and a second heat exchanger 6 are provided in order from the inlet side.

The nitrogen gas that has entered the cold box A is cooled by the precooler 2 and the Freon cooler 4 and then further cooled by the first heat exchanger 5 to lower the temperature.

The nitrogen gas discharged from the first heat exchanger 5 is divided into two streams, one of which is adiabatically expanded by the expansion turbine 7 to generate cold, and then precooled at the outlet side of the second heat exchanger 6. It enters the return reline L ₂ that passes through the low temperature portion of the vessel 2 and the heat exchange units 5 and 6, and becomes the circulating nitrogen gas and returns to the suction side of the compressor 1. The remaining nitrogen gas enters the second heat exchanger 6 as it is through the liquefaction line L ₁ passing through the high temperature parts of the precooler 2 and the heat exchangers 5 and 6, and is cooled and liquefied by the circulating nitrogen gas.

This liquid nitrogen is decompressed by the decompression valve 8 and sent to the product tank 10 via the flash bottle 9.

By the way, such an apparatus for producing nitrogen or oxygen can be diverted as it is to an apparatus for producing liquid air, and the liquefaction method of air by this diverting is actually shown in various documents.

[Problems to be Solved by the Invention]

 However, in this case, there were the following problems.

In the air liquefaction process in which the configuration of FIG. 5 is diverted as it is, the air before liquefaction that has exited from the first heat exchanger 5 is
It is liquefied in the second heat exchanger 6 and decompressed by the pressure reducing valve 8.

In this case, since there is a difference in boiling point between oxygen and nitrogen, which are composition components, nitrogen, which is a low-boiling component, is preferentially gasified by the depressurizing action, and the flash bottle 9 is separated into a nitrogen-rich gas component and an oxygen-rich liquid component. Therefore, liquid air having a constant composition cannot be obtained.

Note that, while the operation is continued, the nitrogen component in the circulating air increases due to the nitrogen gas returning from the flash bottle 9 to the circulating compressor 1, and the nitrogen component in the liquid air tends to increase, so that the liquid air has a constant composition. However, since it takes a long time to obtain the product liquid air, the production efficiency is poor and it is not practical.

This is a problem in diverting a known liquid nitrogen or liquid oxygen production apparatus as a liquid air production apparatus, and is one of the reasons why an air liquefaction method is known in the literature but not shown as an actual machine.

Therefore, the present invention provides a liquid air production apparatus capable of efficiently producing liquid air having a constant composition by preventing gasification of liquid air during depressurization to a tank pressure.

[Means for Solving the Problems]

The present invention, at the outlet side of a heat exchanger for cooling and liquefying the raw material air pressurized by a compressor, passes the liquid air discharged from the heat exchanger up to a temperature not higher than the boiling point of the liquid air at the product tank pressure. A subcooler for cooling, a pressure reducing valve for reducing the pressure of the liquid air discharged from the subcooler to the tank pressure, and a part of the liquid air discharged from the supercooler is extracted from the inlet side of the pressure reducing valve. An expansion valve is provided, which is expanded to give cold and serves as a cold source for the subcooler and the heat exchanger.

Further, according to the present invention, on the premise of the above configuration, the raw material air taken out from the liquefaction line passing through the high temperature portion of the heat exchanger is expanded to lower the temperature and returned to the suction side of the compressor via the low temperature portion of the heat exchanger. The return line and the second return line for sending the liquid air, which has been cooled by the expansion valve, to the subcooler and the heat exchanger as a cold source are provided independently of each other.

[Action]

According to the basic configuration of claim 1, the liquid air discharged from the heat exchanger is supercooled by the supercooler to a temperature equal to or lower than the boiling point of the liquid air under the tank pressure, so that the pressure reducing valve does not gasify the liquid air. .

Therefore, liquid air having a constant composition can be efficiently produced.

Further, as in claim 2, the first return line that expands and lowers the temperature of the raw material air and returns it to the suction side of the compressor via the heat exchanger, and the subcooler that cools the liquid air that has been cooled by the expansion valve. By providing the heat exchanger and the second return line for sending as a cold source independently from each other, the expansion pressure by the expansion valve is not regulated by the compressor suction pressure as in the case where these are combined. Since the expansion pressure can be set freely, the degree of supercooling of liquid air can be adjusted.

〔Example〕

 An embodiment of the present invention will be described with reference to FIGS.

First Embodiment (Refer to FIG. 1) In FIG. 1, 11 is an air filter, 12 is a raw material air compressor, 13 is a cooler provided with refrigeration by a refrigerator 14, and 15
Is an adsorption tower.

The raw material air that has passed through the air filter 11 is processed by the raw material air compressor 12 up to the adsorption pressure in the adsorption tower 15, and cooled in the cooler 13 to a temperature suitable for adsorption in the adsorption tower 15, and then the adsorption tower. Entering 15, the carbon dioxide gas and water in the components are adsorbed and removed.

The raw material air exiting the adsorption tower 15 is further pressurized by the circulating air compressor 16 and enters the cold box B, and the precooler 17,
A Freon cooler 19 to which cold is given by a refrigerator 18 and a first and second heat exchangers 20 and 21 pass through a liquefaction line L _{1 in this} order.

Here, the raw material air is divided into two flows on the outlet side of the first heat exchanger 20, one of which is adiabatically expanded by the expansion turbine 22 to generate cold, and then on the outlet side of the second heat exchanger 21, Precooler
It enters the first return line L ₂ passing through the low temperature part of the heat exchangers 17 and 20 and 21, and becomes the circulating air to return to the suction side of the circulating air compressor 16. The remaining air directly enters the second heat exchanger 21 through the liquefaction line L ₁ and is cooled and liquefied by the circulating air.

A subcooler 23 is provided on the outlet side of the second heat exchanger 21 in the cold box B, and the air liquefied in the second heat exchanger 21 passes through the subcooler 23 and a part of the expansion valve After being expanded at 24 to lower the temperature, it returns to the low temperature part of the subcooler 23, and this cold supercools the liquid air.

The supercooled liquid air is depressurized by the pressure reducing valve 25 to the pressure of the product tank 26, and then sent to the tank 26 as a product.

Here, the liquid air discharged from the second heat exchanger 21 is the subcooler.
At 23, it is subcooled to a temperature below the boiling point of liquid air under tank pressure. Specifically, for example, if the tank pressure is
In the case of 3 kg / cm ² G, the boiling point of the liquid air is −179 ° C., so the liquid air is supercooled by the supercooler 23 to −180 ° C. or less.

In this way, the liquid air is supercooled and enters the pressure reducing valve 25, so that gasification of the liquid air does not occur when the pressure is reduced by the pressure reducing valve 25. Therefore, it is necessary to manufacture a product liquid air having a constant composition from the beginning of the operation. You can

On the other hand, the liquid air returned to the subcooler 23 as a cold source is
The second return line L ₃ different from the first return line L ₂ was passed through the low temperature parts of the second heat exchanger 21, the first heat exchanger 20, and the precooler 17, and cold was given to these. After that, it is gasified and released into the atmosphere. Alternatively, the second return line L _{3 is connected} to the adsorption tower 15
It may be connected to the regeneration gas inlet of the above, and the components adsorbed in the adsorption tower 15 may be discharged to be used as a so-called regeneration gas for regenerating the adsorption tower 15.

In this way, it is recommended that the subcooling liquid air that has been chilled by the expansion valve 24 be returned to a line (second return line L ₃ ) that is different from the circulating air that has been chilled by the expansion turbine 22. In this case, the following effects can be obtained.

That is, in the conventionally known device shown in FIG. 5, the gas in the flash bottle 9 is combined with the gas given the cold by the expansion turbine 7 and returned to the return line L ₂ . When this method is applied to the relationship between the supercooling liquid air and the circulating air in the present invention, the supercooling liquid air is merged with the circulating air and returned to the suction side of the circulating air compressor 16.

However, in this case, the pressure at which the expansion valve 24 expands the liquid air is restricted to the compressor suction pressure.

On the other hand, when the circulating air and the subcooling liquid air are individually returned to the first and second both return lines L ₂ and L ₃ which are independent of each other as described above, the expansion in the expansion valve 24 is expanded. The pressure can be freely set regardless of the suction pressure of the compressor 16. Therefore, the degree of supercooling can be freely adjusted according to the product temperature amount and the like.

Second Embodiment (See FIG. 2) Explaining only the differences from the first embodiment, in this second embodiment, instead of the Freon cooler 19 of the first embodiment, first and second heat A heat exchanger 27 similar to the exchangers 20 and 21 is provided between the precooler 17 and the first heat exchanger 20.

Further, two first and second expansion turbines 28 and 29 are provided in parallel in order to secure a cold source which replaces the refrigerator 18 of the first embodiment.

With this configuration, the operation of the device is facilitated because the operation of the refrigerator 18 is relatively troublesome and the refrigerator 18 is unnecessary.

Third Embodiment (Refer to FIG. 3) In the third embodiment, as a combined configuration of the first and second embodiments, in addition to the Freon cooler 19, the first embodiment is further provided.
The heat exchanger 30 is provided in front of the heat exchanger 20, and the first
And a second two expansion turbines 28,29.

By using two expansion turbines with high power recovery efficiency as the cold generating means, the liquefaction power of the entire apparatus can be reduced.

Fourth Embodiment (See FIG. 4) In the first embodiment, a part of the liquid air discharged from the subcooler 23 is expanded by the expansion valve 24 to generate cold, whereas in the fourth embodiment In the example, the liquid air discharged from the second heat exchanger 21 is divided into two streams, one of which is directed to the pressure reducing valve 25 via the supercooler 23, and the other is fed to the expansion valve 24 to be expanded. I have to.

With this configuration, the same operational effect as in the case of the first embodiment can be obtained.

〔The invention's effect〕

As described above, according to the present invention, in order to send the liquefied air cooled by the heat exchanger to the pressure reducing valve by subcooling it to below the boiling point of the liquid air under the tank pressure by the subcooler,
It is possible to prevent gasification of liquid air at the pressure reducing valve.
Therefore, liquid air having a constant composition can be efficiently produced.

Further, as in claim 2, a first return line that expands and lowers the temperature of the raw material air and returns it to the suction side of the compressor via a heat exchanger, liquid air that has been cooled by an expansion valve, and a subcooler. By providing the heat exchanger and the second return line for sending as a cold source independently from each other, the expansion pressure by the expansion valve is not regulated by the compressor suction pressure as in the case where these are combined. Since the expansion pressure can be set freely, the degree of supercooling of liquid air can be adjusted.

[Brief description of drawings]

FIG. 1 is a first embodiment of the present invention, FIG. 2 is a second embodiment thereof,
FIG. 3 is a flow sheet showing the same third embodiment, FIG. 4 is a flow sheet showing the same fourth embodiment, and FIG. 5 is a flow sheet of a conventionally known liquid nitrogen manufacturing apparatus. 16: Circulating air compressor, B: Cold box, 20,2
1 ... Heat exchanger, 23 ... Supercooler, 24 ... Expansion valve, 25 ...
… Pressure reducing valve, 26 …… Tank, L ₁ … Liquefaction line, L ₂ … First return line, L ₂ … Second return line.

Claims (2)

[Claims] 1. At the outlet side of a heat exchanger for cooling and liquefying the raw material air pressurized by a compressor, the liquid air discharged from the heat exchanger is heated to a temperature not higher than the boiling point of the liquid air at the product tank pressure. A subcooler for subcooling, and a pressure reducing valve for depressurizing the liquid air discharged from the subcooler to the tank pressure,
An expansion valve is provided which extracts a part of the liquid air discharged from the subcooler from the inlet side of the pressure reducing valve and expands it to give cold, which serves as a cold source for the subcooler and the heat exchanger. A liquid air manufacturing apparatus characterized by the above. 2. A first return line for expanding a part of the raw material air taken out from a liquefaction line passing through a high temperature part of a heat exchanger to lower the temperature and returning it to a suction side of a compressor via a low temperature part of the heat exchanger. 2. The liquid air according to claim 1, further comprising: a second return line that sends the liquid air, which has been cooled by the expansion valve, to the subcooler and the heat exchanger as a cold source, independently of each other. Manufacturing equipment.