JPH10281641A - Method and equipment for separating air - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce loss caused by the vaporization of liquefied air by introducing the liquefied air decompressed by adiabatic expansion through an expansion turbine in the limit of not vaporizing to the lower tower of a refining tower, in air separation using air separating equipment having a main heat exchanger and an air refrigerating cycle. SOLUTION: The air being compressed by a circulating air compressor 31 from the air pressure of 0.1-1.0 MPa at a previous stage to 3.0-6.0 MPa is chilled to -170 deg.C passing through a first circulating heat exchanger 32, a refrigerator 33, a second circulating heat exchanger 34 and a third circulating heat exchanger 35 and liquefied. Thereafter, the air is introduced into the lower tower of the refining tower decompressed by a Joule-Thomson expansion valve decompressing the liquefied air by the adiabatic expansion through an expansion turbine 39 in advance. Therefore, as the expansion of the liquefied air is accompanied by the work of driving the turbine, further drop of the temperature is enabled and the loss caused by the partial vaporization of the liquefied air can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air separation method and an air separation equipment, and more particularly to an air separation method and equipment in which a part of air is liquefied by using an air refrigeration cycle separately from a main heat exchanger. The present invention relates to a method and equipment for reducing loss due to vaporization of liquid air when introducing air liquefied in the air refrigeration cycle to a lower column of a rectification column.

[0002]

2. Description of the Related Art An air separation method for producing liquid nitrogen or liquid oxygen from air, in other words, an air separation method for separating air into nitrogen and oxygen is a method for producing oxygen for private use or for products in a wide range of fields such as steelmaking, chemical and electronic industries. Widely used as a means for producing nitrogen and nitrogen. Various researches and developments have been conducted on such air separation methods with the aim of improving separation efficiency, lowering running costs, and improving operational stability. Show
Although it is almost completed and matured, there is still room for improvement from a practical viewpoint.

FIG. 1 is a flow chart showing a molecular sieve type air separation method developed under such a situation. The raw material air passes through an air filter 1, a raw material air compressor 2, a cooler 3, etc., and is supplied with air at a desired pressure and temperature (hereinafter, referred to as air).
Compressed air) and is led to a molecular sieve adsorber (impurity component adsorption unit) 6. The molecular sieve adsorber 6 shown in the figure is a two-pair one-switching type. In the adsorber 6, the moisture, carbon dioxide gas, hydrocarbon gas and the like in the compressed air are almost completely removed by the adsorption action of zeolite or the like. Is done. The compressed air led out of the adsorber 6 through the pipe 6a is led to the main heat exchanger 7 where it is cooled to near the liquefaction point by heat exchange with return gas to be described later. Is introduced to

The compressed air introduced into the lower tower 8a is
The distillation separation proceeds while being cooled in the process of ascending in the column a. A low-boiling nitrogen-rich liquid (liquid nitrogen) 9 or a nitrogen-rich gas is taken out from the upper portion of the lower column 8a, while the high-boiling point is obtained in the lower portion. Is stored (hereinafter sometimes referred to as a coarse distillation step). The upper nitrogen-rich gas is led through line 13 to the main condenser 8b, where it is liquefied and descends along line 14 to return to the upper part of the lower column 8a. A part of the nitrogen-rich liquid in the upper part of the lower tower 8a is led to the top of the upper tower 8c through the line 15 through the supercooler 12.

On the other hand, the oxygen-rich liquid 10 is supplied to a pipe 25
Through the supercooler 12 to the middle stage of the upper tower 8c.
From the middle stage of the lower tower 8a, liquid nitrogen in the middle stage of the rough distillation step is led to the upper stage of the upper tower 8c through the pipe 11 through the supercooler 12. As described above, the low-temperature liquid nitrogen and oxygen-rich liquid introduced from the middle, upper, and top portions of the upper tower 8c and descending in the upper tower 8c undergo mass transfer with the gas rising in the upper tower 8c. As a result, rectification proceeds.

By repeating these steps, high-purity nitrogen gas is purified at the top of the upper tower 8c, while high-purity liquid oxygen is stored at the lower part of the upper tower 8c. 17, is returned to the main heat exchanger 7 as the above-mentioned return gas, and exchanges heat with the compressed air derived from the adsorber 6 to utilize the cold. Be commercialized as.
Alternatively, liquid nitrogen which is liquefied in the main condenser 8b and led to the upper part of the lower tower 8a or liquid oxygen stored in the lower part of the upper tower 8c may be taken out as liquids and commercialized.

Further, from a position slightly lower than the upper part of the upper tower 8c, crude nitrogen gas is extracted through a pipe line 20, and is returned from the subcooler 12 through the main heat exchanger 7 as a return gas by heat exchange. After utilizing the cold, the extracted gas after the heat exchange is sent to the adsorber 6 through the heater 29 for regeneration, and is used for the regeneration.

At this time, a part of the compressed air purified by the adsorber 6 is branched before being introduced into the main heat exchanger 7, and is separated via a pipe 30 into an air refrigeration cycle 4.
Will be introduced. The compressed air introduced into the air refrigeration cycle 4 is compressed by an air circulation compressor 31, cooled by a first circulation heat exchanger 32, a refrigerator 33, and a second circulation heat exchanger 34, and partially expanded by an expansion turbine. After adiabatic expansion at 36, the third circulating heat exchanger 35, the second circulating heat exchanger 3
4. Returning to the air circulating compressor 31 via the first circulating heat exchanger 32, forming an air refrigeration cycle. The remaining air leaving the second circulation heat exchanger 34 (the remaining air not sent to the expansion turbine 36) exchanges heat with the low-temperature air from the expansion turbine 36 in the third circulation heat exchanger 35. To cool and liquefy. The liquefied air is then reduced to the operating pressure of the lower tower 8a by the Joule-Thomson expansion valve 37 and introduced into the lower tower 8a.

[0009]

As a result of the study by the present inventors, in the above-described air separation equipment, the air liquefied in the third circulating heat exchanger 35 is decompressed by the Joule-Thomson expansion valve 37. However, at the time of this decompression, 5
It was found that 10% to 10% of the liquefied air had been vaporized. That is, while 5 to 10% of the liquid produced in the air refrigeration cycle 4 is once liquefied, the lower rectification tower 8a
Before being introduced into the rectification column, it is again cooled and liquefied during the above-mentioned process in the rectification column. Such a situation is inefficient from the viewpoint of separation efficiency, running cost and the like. The present invention has been made in view of such circumstances, and an object of the present invention is to provide an air separation method and an air separation facility that reduce loss due to vaporization of liquefied air caused by use of a Joule-Thomson expansion valve 37. It is something to offer.

[0010]

SUMMARY OF THE INVENTION The air separation method according to the present invention, which can solve the above-mentioned problems, is characterized in that the air separation is performed using an air separation facility having a main heat exchanger and an air refrigeration cycle. It is characterized in that air liquefied in the air refrigeration cycle is decompressed to the extent that it is not vaporized by adiabatic expansion through an expansion turbine and introduced into the lower column of the rectification column.

Further, the air separation equipment according to the present invention is an air separation equipment having a main heat exchanger and an air refrigeration cycle, wherein an expansion turbine is provided at a portion where the air liquefied in the air refrigeration cycle is introduced into the lower tower of the rectification tower. It is characterized by having been provided.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the air refrigeration cycle 4, the compressed air before entering the circulating air compressor 31 is 0.5 to 0.5.
Although the pressure is about 1.0 MPa, it is compressed by the compressor 31 to about 3.0 to 6.0 MPa. Thereafter, through the third circulating heat exchanger 35 and the like, -170
The liquid is cooled to about ℃ and liquefied, and the pressure is reduced again to about 0.5 to 1.0 MPa by a Joule-Thomson expansion valve and introduced into the lower tower 8a of the rectification column. Although the temperature of the liquefied air slightly decreases due to the adiabatic expansion through the Joule-Thomson expansion valve, according to studies by the present inventors, the temperature range that decreases during the adiabatic expansion is about 3 to 4 ° C. It was found that a part (about 5 to 10%) of the liquefied air was vaporized due to a vaporization factor (pressure reduction) that exceeded the temperature reduction.

As described above, partial vaporization of the liquefied air is inefficient, and if the temperature of the liquefied air can be further reduced when the liquefied air is introduced into the lower column of the rectification column, the loss due to the vaporization Can be reduced. The present inventors have proposed that the liquefied air is not reduced by adiabatic expansion through a Joule-Thomson expansion valve, but by adiabatic expansion performed through an expansion turbine, when the liquefied air is introduced into the lower column of the rectification tower by adiabatic expansion. Have been found that the temperature can be further reduced, and the present invention has been completed.

That is, if the decompression of the liquefied air is performed by adiabatic expansion through an expansion turbine, unlike the adiabatic expansion through a Joule-Thomson expansion valve, the liquefied air involves the work of moving the turbine during expansion, so that the temperature is further increased. Therefore, the loss due to the partial vaporization of the liquefied air can be reduced.

[0015]

EXAMPLE An experiment was performed using an air refrigeration cycle as schematically shown in FIG. In the experiment, nitrogen (purity 9
9.9%), the flow rate, temperature and pressure of nitrogen at each of the points A to K in FIG. 2 were adjusted as shown in Table 1, and the expansion turbine 39 was used in the introduction path to the lower tower of the rectification tower. L when done
The situation of liquid nitrogen at the point was investigated. For comparison, the situation where a Joule-Thomson expansion valve was provided instead of the expansion turbine 39 was also examined. Table 2 shows the results at both L points.
Shown in

[0016]

[Table 1]

[0017]

[Table 2]

When a Joule-Thomson expansion valve is employed, the temperature of liquid nitrogen at point L is -176.3 ° C.,
At this time, about 6% of liquid nitrogen had been vaporized. On the other hand, when the expansion turbine was employed, the temperature at the point L was -178.2 ° C., and at this time, the liquid nitrogen was not vaporized. By adopting the expansion turbine in this way,
It was possible to reduce the loss of a part of liquid nitrogen vaporizing. Since liquid nitrogen has a lower boiling point than liquid oxygen, the effect of the above experiment (suppression of vaporization) obtained when using liquid nitrogen is more pronounced when using liquefied air in which liquid nitrogen and liquid oxygen are mixed. It should surely be demonstrated.

[0019]

As described above, according to the present invention, when introducing liquefied air from the air refrigeration cycle to the lower tower of the rectification tower, an expansion turbine is provided at the introduction portion, and adiabatic expansion through the expansion turbine is performed. The loss of liquefied air being partially vaporized can be reduced.

[Brief description of the drawings]

FIG. 1 is an overall flowchart for explaining a conventional air separation method and air separation equipment.

FIG. 2 is a schematic diagram of an air refrigeration cycle used in Examples.

[Description of Signs] 1 air filter 2 raw material air compressor 3 cooler 4 air refrigeration cycle 6 molecular sieve adsorber 7 main heat exchanger 8 rectification tower 8a lower tower 8b main condenser 8c upper tower 9 nitrogen rich liquid 10 oxygen rich Liquid 12 Subcooler 29 Regeneration heater 31 Air circulation compressor 32 First circulation heat exchanger 33 Refrigerator 34 Second circulation heat exchanger 35 Third circulation heat exchanger 36 Expansion turbine 37 Joule-Thomson expansion valve

Claims (2)

[Claims] When air is separated using an air separation facility having a main heat exchanger and an air refrigeration cycle, the air liquefied in the air refrigeration cycle is decompressed by adiabatic expansion through an expansion turbine and is then discharged to the rectification column. An air separation method characterized by being introduced into a tower. 2. An air separation facility having a main heat exchanger and an air refrigeration cycle, wherein an expansion turbine is provided at a portion where the air liquefied in the air refrigeration cycle is introduced into a lower tower of the rectification tower. Separation equipment.