JPS6146748B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for liquefying and separating air,
In particular, the present invention relates to a method for economically producing high-purity product oxygen by separating air using a completely low-pressure system. By liquefying air and rectifying it, N ₂ , O ₂ ,
Air liquefaction separation equipment that separates Ar, etc. is in operation in various fields. This type of air liquefaction separation equipment pressurizes the raw air etc. according to the operating conditions.
Since it is necessary to perform pressure reduction operations, it is essential to install equipment such as compressors and expansion turbines. Air liquefaction separation equipment generally has a large capacity and increases operating power costs, so in order to reduce the production cost of product oxygen, it is necessary to improve rectification efficiency and save operating power costs as much as possible. There is a strong industrial demand for this, and in order to meet this demand, the inventors of the present invention have conducted intensive studies, particularly regarding compressors for compressing product oxygen. A conventional high-purity oxygen production method (hereinafter simply referred to as an oxygen production method) using total low-pressure air separation is mainly carried out according to a system diagram as shown in FIG. In the following explanation, the switching type heat exchanger is an example of the "main heat exchanger" described in the claims, and is also applicable to, for example, a heat exchanger having a switching type adsorber on the inlet side. . In FIG. 1, raw air is supplied through an air filter 1, and an air compressor 2
After being compressed and pressurized to kg/cm ² G, it is cooled in an aftercooler 3. Then from the conduit 5 to the switched heat exchanger 6
The air is introduced into the air and is cooled by the return gas separated and purified in the rectification column 8, and moisture, carbon dioxide, etc. contained in the air are removed. This air passes through a conduit 7 to a rectification column lower column (hereinafter simply referred to as a lower column) 8b.
guided by. The air thus introduced into the lower column 8b becomes a rising gas, and is crudely rectified by being brought into contact with the reflux liquid (nitrogen-rich liquid) obtained by condensation at the top of the lower column 8b. In addition to obtaining liquid nitrogen rich in liquid nitrogen, the reflux liquid has an oxygen content of about 30% at the bottom of the lower column 8b.
~40% oxygen enriched liquid air. The liquid air crudely rectified as described above in the lower column 8b is introduced into the liquid air supercooler 10 through the pipe 9 and cooled.
From pipe 11 to the upper tower of the rectification tower (hereinafter simply referred to as the upper tower)
You will be led to the middle of 8a. Further, the nitrogen-rich liquid stored at the top of the lower column 8b is introduced into the liquid air supercooler 10 through a pipe 12 and cooled, and then guided through a pipe 13 to the upper part of the upper tower 8a. On the other hand, a part of the gaseous air rising in the lower column 8b is extracted from the conduit 14 and then introduced into the reheat circuit 15 of the switching heat exchanger 6, to adjust the intermediate temperature of the switching heat exchanger 6. rear,
It is sent to an expansion turbine 17 via a regulating valve 16.
The air, which has been expanded to about 0.32 Kg/cm ² G in the expansion turbine 17 and obtained the necessary cooling by extracting external work, is blown into the upper tower 8a through the conduit 18. However, this air is transferred to the lower tower 8 as nitrogen-rich gas.
When the nitrogen is extracted from the upper column 8a, it may be introduced into the impure nitrogen line 21 without being blown into the upper column 8a. The high-purity oxygen component, high-purity nitrogen component, and impure nitrogen component thus separated and purified in the upper column 8a are extracted in gaseous form through conduits 19, 20, and 21, respectively, and sent to the switching heat exchanger 6, as described above. By exchanging heat with raw material air, the product is recovered to room temperature and then taken out as a product. In particular, oxygen is introduced into the compressor 30 through the conduit 22 and pressurized to, for example, about 30/cm ² G. Afterwards, it is recovered as product oxygen. In contrast, the present inventors have been conducting various studies on the possibility of efficiently reducing the power for pumping product oxygen with respect to the compressor 30 in the conventional process described above. This is based on the technical guideline that if the product oxygen can be pressurized in advance without using a separate compressor, that is, without consuming power, the power consumption of the compressor 30 can be effectively reduced. The present invention was completed as a result of intensive research to develop such a non-powered pressure boosting means. However, the air separation method of the present invention is as follows:
The high-purity liquid oxygen component extracted from the lowermost part of the upper column of the rectification column is introduced in liquid form into an evaporator located further below the lowermost part, while the high-purity liquid oxygen component extracted from the lower column of the rectification column A part of the gaseous air is introduced into the heat exchanger installed in the evaporator to vaporize the high-purity liquid oxygen component and liquefy itself, and the vaporized oxygen component is sent to the switching heat exchanger while being liquefied. The key point is that the air is returned to the lower column of the rectification column. The configuration and effects of the present invention will be explained below based on the drawings of the embodiments, but the embodiments below are merely representative examples, and may be implemented with appropriate changes in accordance with the spirit of the above and below. Needless to say. FIG. 2 shows a system diagram of the all-low-pressure air separation method of the present invention. The basic configuration is the same as that of the conventional example shown in FIG. is omitted. The following description will focus on the feature of this embodiment. An evaporator 31 is disposed below the lowest bottom part 8'a of the upper column 8a, and the lower part of the evaporator 31 and the lowest bottom part 8'a are connected by a conduit 32, and the lowermost part of the evaporator 31 is A conduit 33 extending from the bottom 31a is connected to the upper tower 8a via a circulation pump 34 and an adsorber 35.
A conduit 36 extending from the top of the evaporator 31 is connected to the switching heat exchanger 6. Furthermore, a reboiler 37 is provided in the evaporator 31.
The upper part of the heat exchanger 37 is connected to a branch pipe 38 from the gas air extraction pipe 14, and the lower part of the heat exchanger 37 and the lower column 8a are connected by a pipe 39. . In the oxygen production process configured in this way, the liquid oxygen remaining at the bottom of the upper column 8a is transferred to the conduit 32.
During this time, potential energy ΔH (ΔH is the water head difference between the liquid oxygen upper surface L ₁ in the upper column 8a and the liquid oxygen upper surface L ₂ in the evaporator 31) is generated. Boost the pressure by the corresponding amount. On the other hand, the gaseous air extracted from the lower column 8b is supplied to the heat exchanger 37 from the branch conduit 38.
Through heat exchange, the liquid oxygen in the evaporator 31 is vaporized and liquefied itself. That is, in order to evaporate liquid oxygen at high pressure, air, which has a higher liquefaction point than nitrogen, is used. The liquid oxygen vaporized in this way (hereinafter referred to as vaporized oxygen) is extracted from the conduit 36 and passes through the switching heat exchanger 6 and then the compressor 3.
0, but the supply pressure at this time is higher than in the conventional case. That is, in the conventional process, vaporized oxygen that is evaporating near the liquid level _L1 in the upper column 8a is simply extracted from the conduit 19 and supplied to the compressor 30 as shown in FIG. In the process, as described above, the liquid oxygen vaporization capacity in the evaporator 31, which can be called the liquid oxygen evaporation section in the upper column 8a, increases by an amount corresponding to the potential energy ΔH, so that the vaporized oxygen transported in the conduit 36 increases by an amount corresponding to the potential energy ΔH. The pressure is higher than the pressure of vaporized oxygen transported in conduit 19 shown in FIG. Therefore, the power consumption in the compressor 30 can be reduced accordingly. The liquid oxygen that is not in a vaporized state in the evaporator 31 is extracted from the conduit 33 by the circulation pump 34, and then introduced into the adsorber 35 to restore purity, vaporized, and returned to the bottom of the upper column 8a. . Therefore, the amount of rising gas in the upper column 8a does not change, and the rectification conditions in the upper column 8a do not deteriorate compared to the conventional process, so a sufficient yield can be maintained, especially for product oxygen. . On the other hand, the air liquefied in the reboiler 37 is transferred to the conduit 39.
However, since the amount of rising gas in the lower column 8b decreases by the liquefied amount, the lower column 8
As for b, there is a concern that the rectification conditions may deteriorate somewhat. However, in this case, the yield of product nitrogen is only slightly reduced and the yield of product oxygen is not affected at all. Therefore, in the process of the present invention whose main purpose is to recover product oxygen, 8
There is no problem with sending it back to B. Example: The conventional method shown in Fig. 1 and the method of the present invention shown in Fig. 2 were applied to an oxygen production apparatus with a production scale of 10000 Nm ³ and a recovered oxygen pressure of 30 Kg/cm ² G, and the power for pumping product oxygen was compared. The results shown in Table 1 were obtained.

[Table] As is clear from Table 1, calculations show that the method of the present invention reduces the power consumption unit by about 9% compared to the conventional method. Therefore, it is clear that the method of the present invention can be expected to significantly reduce running costs and produce oxygen product at a lower cost. The air separation method of the present invention is configured as described above, but the point is that the vaporized oxygen introduced into the product oxygen pressure-feeding compressor can be self-pressurized in advance, so that the power consumption of the compressor can be reduced accordingly. It became possible,
High-purity product oxygen can now be produced at a lower cost. Furthermore, by reducing the power required to operate the air separation device, it is possible to achieve so-called energy saving, so in today's world where there is a strong demand for energy saving, the industry plays a major role in this aspect.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing a conventional oxygen production method, and FIG. 2 is a system diagram illustrating an oxygen production method according to the present invention. 6... Switching type heat exchanger, 8a... Rectification column upper column,
8b... Lower rectification column, 17... Expansion turbine, 3
0...Compressor for pressure-feeding product oxygen, 31...Evaporator,
34... Circulation pump, 35... Adsorption device, L ₁ , L ₂
...Liquid oxygen surface.

Claims (1)

[Claims] 1 The raw air, which has been cooled by heat exchange with the low-temperature return gas in the main heat exchanger, is introduced into the lower column of the rectification column and crudely rectified into oxygen-rich liquid air and nitrogen-rich liquid air. Air and rich liquid nitrogen are introduced into the upper column of the rectification column to separate and purify them into high-purity oxygen components, high-purity nitrogen components, and impure nitrogen components, and each is extracted from the bottom, top, and upper part of the upper column of the rectification column. After that, it is sent to the main heat exchanger where it undergoes temperature recovery by exchanging heat with the feed air and is then taken out as a product.At the same time, a part of the gaseous air rising inside the column is extracted from the lower column of the rectification column and sent to the main heat exchanger. In the air separation method, the air is passed through a reheating circuit of a heat exchanger and then introduced into an expansion turbine for expansion to perform external work, thereby establishing thermal equilibrium in the system. The high-purity liquid oxygen component extracted from the bottom bottom of the rectification column is introduced in liquid form into an evaporator located further below the bottom bottom, while a part of the gaseous air extracted from the lower column of the rectification column is is introduced into the heat exchanger installed in the evaporator to vaporize the high-purity liquid oxygen component and liquefy itself, and the vaporized oxygen component is sent to the main heat exchanger, while the liquefied air is sent to the bottom of the rectification column. An air separation method characterized by returning the air into the tower.