JPS6044587B2 - Totally low pressure air separation method and device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a total low pressure air separation method and apparatus for separating nitrogen, oxygen and argon from air by liquefying and rectifying the air.

This type of conventional technology will be explained with reference to FIG.

The air separation device is composed of a double rectification column consisting of an upper column 3 and a lower column 1, a crude argon column 5 for separating argon, and an expansion turbine 7. A main condenser 2 is installed between the top of the crude argon column 1, a condenser 6 is installed at the top of the crude argon column 5, and rectification is carried out in the lower column 1, upper column and crude argon column 5, respectively. It incorporates multiple shelves (not shown) for storage.

Next, to explain its effect, part of the raw air that has been compressed by the compressor and further cooled by the heat exchanger is transferred to the pipe 1.
It is guided to the expansion turbine 7 through 01 and 102, cooled in the expansion turbine 7, and supplied to the middle part of the upper tower 3 through a pipe 104 for cold heat.

On the other hand, the remaining raw material air is supplied to the bottom of the lower column 1 through pipes 101 and 102, rises inside the column, is condensed in the main condenser 2 at the top of the column, flows down as a reflux liquid, and reaches the top of the tray. It is rectified by making gas-liquid contact with the rising gas. As a result, high-purity nitrogen liquid and gas are obtained at the top of the column, and liquid oxygen is obtained at the bottom of the column. High-purity liquid nitrogen at the top of the lower column 1 is supplied to the top of the upper column 3 through a pipe 110 and an expansion valve 81. Impure liquid nitrogen is piped from a position below the high-purity liquid nitrogen extraction position to pipe 11.
8 and an expansion valve 82 to the middle part of the upper tower 3. Furthermore, the liquid oxygen at the bottom of the tower is divided into two parts, one of which is supplied to the middle of the upper tower 3 through pipes 105, 106 and expansion valve 83, and the other is supplied to the middle of upper tower 3 through pipes 105, 107 and expansion valve 83.
4 is supplied as a refrigerant to the condenser 6 in the top column of the crude argon column 5, where it undergoes heat exchange and is gasified.
08 and is supplied to the middle part of the upper end 3. In the upper tower 3,
The high-purity liquid nitrogen supplied to the top column, and the impure liquid nitrogen and liquid air supplied to the middle column flow down as reflux liquid, and exchange heat with the high-purity nitrogen gas in the lower column 1 in the condenser 2 at the bottom of the column. , condenses nitrogen gas. At the same time, it vaporizes and becomes a rising gas in the upper column 3, and is rectified by making gas-liquid contact on the tray. As a result, high-purity oxygen is obtained at the bottom of the column, and high-purity nitrogen is obtained at the top column, which are taken out and used as product oxygen and product nitrogen. Further, nitrogen-rich gas is taken out as impure nitrogen from the middle part of the upper tower 3 through a pipe 113, and its cold energy is recovered in a heat exchanger and then released to the atmosphere. Then, the gas rising through the lower part of the upper tower 3 flows through the pipe 111.
The crude argon is supplied to the bottom of the crude argon column 4 through the argon column.

The gas supplied to the crude argon column 4 rises inside the column, exchanges heat with the refrigerant liquid air in the condenser 6 at the top of the column, gasifies the liquid air, and condenses itself and flows down as reflux liquid. , it is rectified through gas-liquid contact on a tray. As a result, highly concentrated argon is obtained at the top of the column, which is taken out through pipe 116 and used as a crude argon product. In addition, the reflux liquid is passed from the bottom of the crude argon column 5 through the pipe 112 to the upper column 3.
Returned to Chubu. However, in the above-mentioned conventional technology,
There is a limit to the recovery rate of argon.

The reason for this is that the L/V value (the ratio of the amount of liquid and gas that are in countercurrent contact in the tower) from the middle supply tray to the upper tray of the upper column 3, which supplies the feed air from the expansion turbine 7, is Analysis of actual equipment data has revealed that because of the small size, there is a limit to the argon concentration in the feed gas led to the crude argon column 5. That is, it is well known that in countercurrent contact operation, increasing the L/V value can improve the direct rectification separation efficiency. However, it is difficult to introduce fluid in a droplet-forming state into the expansion turbine 7 due to the hardware aspects of the expansion turbine 7 and the cold generation efficiency, and the temperature at the outlet of the expansion turbine 7 is adjusted so as to be close to the saturation temperature. The reality is that people are driving with this in mind.

For this reason, the gas fluid at the saturation temperature from the outlet of the expansion turbine 7 is directly supplied to the middle part of the upper column 3 of the double rectification column, and the gas amount increases and the L/V value decreases to a certain degree. This was an obstacle to improving distillation efficiency. In view of the above-mentioned points, the present invention aims to provide a completely low-pressure air separation method and apparatus that can improve rectification separation efficiency.

The inventor believes that when operating an expansion turbine, the efficiency is greatly reduced when droplets are generated, and therefore, the outlet temperature is operated close to the saturation temperature, and therefore the double rectifier is operated with gas supplied from the expansion turbine. In view of the conventional technology that the L/V value in the middle part of the upper column is small and the rectification separation efficiency decreases,
By adjusting the amount of gas supplied from the expansion turbine to the middle part of the upper column of the double rectification column, the L/V value can be increased and the rectification separation efficiency can be improved, while the amount of refrigeration that is insufficient in the process can be invented an air separation method and apparatus in which the outlet gas fluid of an expansion turbine can be supplemented by heat exchange and supplied together with feed air to the lower column of a double rectification column.

Hereinafter, a specific example of the present invention will be explained with reference to FIG. In the figure, the same reference numerals as in FIG. 1 indicate the same parts.

Therefore, in the present invention, the piping 101 from the compressor 12 and the switching heat exchanger 11 is branched into two, and one piping 101 is branched into two.
31 to the inlet of the expansion turbine 7, and the other pipe 13
0 to the heat exchanger 9 and from the heat exchanger 9 to the piping 102.
is connected to the lower column 1 of the double rectification column. Then, the piping 132 on the outlet side of the expansion turbine 7 is branched into two, one piping 133 is connected to the middle part of the double rectification column upper tower 3 via the regulating valve 10, and the other piping 134 is connected to the regulating valve 10. is connected to the piping 113 from the upper part of the upper column 3 of the double rectification column, the merging piping 135 is connected to the heat exchanger 9, and the piping 137 is connected from the outlet of the heat exchanger 9 to the switching type heat exchanger. 11, and a pipe 138 from the outlet of the switching heat exchanger 11 is provided. Next, the operation of the present invention will be explained. The raw air compressed and cooled by the compressor 12 and the switching heat exchanger 11 is divided into two parts, one of which is supplied to the lower part of the lower double rectification column 1 through the heat exchanger 9.

The other one is supplied to the expansion turbine 7 through a pipe 131. A part or all of the gas from the outlet of the expansion turbine 7 is guided to the heat exchanger 9 through the control valve 10 and piping 134, 135, and further guided to the switching heat exchanger 11 through the piping 137. 138 and released into the atmosphere. On the other hand, the remaining gas is supplied to the middle part of the double rectification column upper column 3 through the control valve 10 and piping 133, and its supply amount is adjusted according to the amount of product oxygen and crude argon extracted. Next, the rectification separation efficiency of the present invention and the prior art will be specifically compared in Tables 1 and 2 below.

3. , 3- Tables 1 and 2 above assume that the feed air supply amount is constant at 93000 Nd/h, the supply amount to the expansion turbine 7 is constant at 12.9% of the raw air amount, and the expansion turbine 7 In Table 1, the amount of feed from the to the middle part of the upper tower 3 of the double rectification column was set as 0% (with respect to the amount of feed to the expansion turbine 7), and in Table 2, it was set as 50%.

From the above table, L/V in the middle of the upper column 3 of the double rectification column
Compared to the conventional technology, the value of the present invention shown in Table 1 is about 1.
In fact, the results in Table 2 were improved by about 1.34 times.

As a result, the amount of argon recovered using the conventional technology was 424 Nd/h.
On the other hand, the one of the present invention in Table 1 is 507N7
7t'/h, those in Table 2 can be increased to 468Nd/h. In addition, in the case of product oxygen, the value in Table 1 is 14,450 N/h, and the value in Table 2 is 15,040 N/h, and the amount of gas supplied from the expansion turbine 7 to the middle part of the upper column 3 of the double rectification column is adjusted. By doing so, the amount of product oxygen and crude argon extracted can be adjusted and flexible operation can be performed. In the above embodiment, the fluid in the pipe 134 from the expansion turbine 7 is not limited to the impure nitrogen gas pipe 113.

Alternatively, the heat exchanger 9 and the switching type heat exchanger 11 may be integrated.

Figure 3 shows argon (,Ar'), oxygen (02), and nitrogen (N2) in the upper column 3 of the double rectification column according to the prior art and the present invention.
2 is a graph showing the gas composition distribution of each component.

The solid line represents the prior art, the broken line represents the invention shown in Table 1, and the dashed line represents the invention shown in Table 2.

As is clear from this graph, the argon concentration in the feed gas to the crude argon column 5 was 8.54% in the conventional case, 11.38% in the case in Table 1, and 11.38% in the case in Table 2. is found to be concentrated to 9.63%. As described above, in the present invention, part or all of the gas from the expansion turbine is guided to the heat exchanger to cool the feed air, and at the same time, the gas from the expansion turbine is directed to the middle part of the upper column of the double rectification column. Since the supply amount is adjusted according to the amount of product oxygen and argon removed, the L/V value in the middle of the upper column of the double rectification column becomes large, and therefore the rectification separation efficiency increases. and the argon recovery rate is improved.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of the prior art, FIG. 2 is a flow sheet showing a specific example of the present invention, and FIG. 3 is a graph showing the gas composition distribution in the upper column of the double rectification column. 1... Double rectification column lower column, 2... Main condenser, 3...
Dual rectification column upper column, 5... Crude argon column, 6... Condenser, 7... Expansion turbine, 8... Expansion valve, 9...
Heat exchanger, 10... Control valve, 11... Switching type heat exchanger, 12... Compressor.

Claims (1)

[Scope of Claims] 1 Air is compressed and cooled, a part of the raw air is guided to the lower column of the double rectification column, the rest is guided to the upper column of the double rectification column via an expansion turbine, and the air is compressed and cooled. In an all-low-pressure air separation method, in which a mixed gas of oxygen and argon is introduced into a crude argon column from the middle part of the upper column of the distillation column, and separated into argon, oxygen, and nitrogen in the double rectification column and the crude argon column. , a part or all of the fluid on the outlet side of the expansion turbine is combined with the return low-temperature gas generated in the double rectification column to be introduced to heat exchange, and the raw material is led to the double rectification column by the heat exchanger. The feed air is cooled by heat exchange with air, and the amount of the fluid on the outlet side of the expansion turbine supplied to the upper middle part of the double rectification column is determined by the amount of crude argon extracted from the crude argon column, and the amount of crude argon extracted from the double rectification column. A completely low-pressure air separation method that adjusts according to the amount of product oxygen gas removed. 2. A compressor that compresses air and a heat exchanger that cools it;
Equipped with a double rectification tower and a crude argon tower that rectify compressed and cooled raw air and separate it into argon, oxygen, and nitrogen.
In an all-low-pressure air separation device in which a part of the feed air is provided with piping that passes through an expansion turbine and leads to an upper column of a double rectification column, piping from an outlet of the expansion turbine to the upper column of a double rectification column; A communication pipe is installed between the double rectification column and the return low-temperature gas pipe to the heat exchanger, and the amount of fluid supplied from the expansion turbine outlet to the heat exchanger or the double rectification column is connected to the crude argon removal from the crude argon column. A completely low-pressure air separation device that can be adjusted according to the output amount and the amount of product oxygen gas extracted from the double rectification column.