JPS6157550B2 - - 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 the inventors of the present invention have also conducted intensive studies, particularly regarding expansion turbines, in order to meet this demand. 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 introduced into a switching heat exchanger 6 through a conduit 5, and cooled by the return gas separated and purified in a rectification column 8. , moisture, carbon dioxide, etc. contained in the air are removed. This air flows through conduit 7
It is guided to the lower column of the rectification column (hereinafter simply referred to as the lower column) 8b. The air thus introduced into the lower column 8b becomes a rising gas, while it is brought into contact with the reflux liquid (nitrogen-rich liquid) obtained by condensation at the top of the lower column 8b, and undergoes crude rectification. In addition to obtaining liquid nitrogen-rich gas, the reflux liquid has an oxygen component of about
The result is 30-40% oxygen-enriched liquid air. The liquid air crudely rectified as described above in the lower column 8b is introduced into the liquid air subcooler 10 through a pipe 9 and cooled, and then passed from the pipe 11 to the upper column of the rectification tower (hereinafter simply referred to as You will be led to the middle part of 8a (called the upper tower). Further, the nitrogen-rich liquid stored at the top of the lower column 8b is introduced into the liquid air supercooler 10 through the pipe 12 and cooled, and then passed through the pipe 13.
from there 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. Thereafter, it is sent to an expansion turbine 17 via a regulating valve 16. Approximately 0.32Kg/cm ² G in expansion turbine 17
The air, which has been expanded and obtained the necessary cooling by extracting external work by an atmospheric suction type load blower, is blown into the lower tower 8a through the conduit 18. However, when this air is extracted from the lower column 8b as a nitrogen-rich gas, it is introduced into the impure nitrogen line 21 without being blown into the upper column 8a. The oxygen, nitrogen, and impure nitrogen thus separated and purified in the upper column 8a are transferred to conduits 19, 20, and 21, respectively.
The air is extracted from the air and sent to the switching heat exchanger 6, where it undergoes heat exchange with the raw material air as described above to recover the temperature to room temperature, and then is taken out as a product.
In particular, the oxygen is pressurized from the conduit 22 by a compressor not shown, and then recovered as product oxygen. The system diagram shown in FIG. 2 shows another conventional method, and the feature of this conventional method is that when the external mechanical energy generated when driving the expansion turbine 17 is recovered, power generation is used instead of the load blower 17a. The main point is that it is directly connected to the machine 17b to recover power. However, the reduction in the power consumption unit (hereinafter referred to as O ₂ unit) for obtaining product oxygen for the expansion turbine 17 in each of the conventional processes described above has a limit in the following points. This is because power is saved not directly by reducing the turbine capacity itself, but by the very inefficient indirect method of energy conversion and recovery.
Furthermore, the reduction in O ₂ basic unit due to an increase in oxygen yield is not considered at all. Therefore, the present inventors conducted various studies on the possibility of efficiently reducing the O ₂ basic unit. In other words, the cooling required to maintain the thermal balance of the air separation system is Q (kcal/h), and the expansion turbine 1
7, the flow rate, adiabatic head, and efficiency are respectively expressed as E(N
m ³ /h), Δiad (kcal/Nm ³ ), and η (%), these variables must satisfy the following equation. Q=E・△iad・η/100...(1) In equation (1), Q is almost uniquely determined once the production amount of the equipment is determined. On the other hand, the O ₂ basic unit is directly influenced by the flow rate E of the expansion turbine 17, and reducing E leads to a reduction in the O ₂ basic unit. The reason for this is explained below. Also, as shown in Fig. 5, Fig. 4 shows the vapor-liquid equilibrium line and rectification operation line of the upper column. If the amount of raw air supplied to the lower tower is A, and the amount of gas extracted to the expansion turbine is E, then (A-E) is the gas V ₁ rising up the lower tower, and the main evaporator converts liquid oxygen into It is evaporated and used to produce rising gas _V2 at the bottom of the upper column. As shown in Figure 4, in the lower part of the upper column, rectification is performed according to the operating line a and the equilibrium line, so the rectification conditions are better when the operating line a is away from the equilibrium line, and the O ₂ source is The units will get better. Operation line a
The slope of is the descending liquid volume L ₂ at the bottom of the upper tower and the rising gas volume V ₂
Therefore, in order to improve _{the O 2 consumption} rate, _{L 2 /} V ₂ should be made smaller. This is primarily to reduce the flow rate E of the expansion turbine 17. In the present invention, as a means for achieving this, the inlet pressure of the expansion turbine 17 is
By increasing △iad, we succeeded in effectively reducing the flow rate E of the expansion turbine while ensuring the necessary cooling Q for the device. After passing the gaseous air or gaseous nitrogen from the lower tower through the reheating circuit of the main heat exchanger through the circulation heat exchanger and raising the temperature,
The gist is that the pressure is increased by applying it to a load blower of an expansion turbine, and the pressurized air is further cooled by passing through the circulation heat exchanger before being introduced into the expansion turbine. The configuration and effects of the present invention will be explained below based on the drawings of the embodiments. However, the embodiments below are merely representative examples, and the embodiments can be implemented with appropriate changes in accordance with the spirit of the above and below. Needless to say. FIG. 3 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 FIGS. 1 and 2, respectively, and the same components are designated by the same reference numerals. and the explanation thereof will be omitted. The following description will focus on the characteristic configuration of this embodiment. A portion of the rising air or nitrogen in the lower tower 8b is transferred to the conduit 1
After being extracted from the heat exchanger 4, it was introduced into the reheat circuit 15 of the switching heat exchanger 6, and after adjusting the intermediate temperature of the switching heat exchanger 6, it was passed through the circulation heat exchanger 25 and raised to room temperature. Thereafter, by applying the load blower 17a of the expansion turbine 17 to recover the external mechanical energy generated by the turbine drive, the expansion turbine 17 is further compressed and the pressure is increased. Then, after cooling the pressurized air by passing it through an aftercooler 24 and a circulation heat exchanger 25,
It is introduced into the expansion turbine 17. Therefore, since the air pressure on the inlet side of the expansion turbine 17 is increased by the recovery of the mechanical energy as compared to the conventional method, the heat drop Δiad caused by the adiabatic expansion also increases accordingly. As a result, the turbine flow rate E
can be reduced within a range that satisfies equation (1), so as mentioned above, the rectification effect in the upper column 8a is enhanced and the product oxygen yield is increased. Furthermore, the expansion turbine 17 can also be made smaller.
Therefore, due to these synergistic effects, the O ₂ consumption rate can be significantly reduced. Also, as shown in the diagram, the lower tower 8
Since the rising air from inside b is appropriately heated by the circulation heat exchanger 25 before being introduced into the load blower 17a, it does not particularly hinder the operation of the load blower 17a, and the air passing through the load blower 17a The subsequent pressurized air or nitrogen can be water-cooled in the aftercooler 24, and together with the temperature lowering effect by the circulation heat exchanger 25, the temperature characteristics of the air supplied to the expansion turbine 17 are maintained appropriately. However, installation of the aftercooler 24 is not necessarily required depending on operating conditions. (Example) An example in which the conventional method shown in FIGS. 1 and 2 and the method of the present invention shown in FIG. 3 are applied to an oxygen production apparatus with a production scale of 10,000 Nm ³ is shown below.

【table】

[Table] As is clear from Table 1, the turbine flow rate E in the conventional method and conventional method was approximately 20% (turbine flow rate/feedstock air amount) ratio, but in the method of the present invention, it was approximately 14%. As a result, calculations show that the O ₂ consumption rate of the expansion turbine is reduced by about 4.5% compared to the conventional method, and by about 2.1% compared to the conventional method. Therefore, it is clear that according to the method of the present invention, running costs can be significantly reduced and product oxygen can be produced at a lower cost. As mentioned above, when the aftercooler 24 is disposed between the outlet side of the load blower 17a and the circulation heat exchanger 25, the cost of cooling water for cooling the aftercooler will increase. Since this increase is only about 5 to 10% of the above-mentioned reduction in O ₂ unit power, the effect of reducing running costs is sufficient even if an aftercooler is provided. The air separation method of the present invention is configured as described above, but the key point is that the expansion turbine is driven by a so-called pressure booster turbine system, and the turbine flow rate is actively reduced within a range that can maintain the cooling of the equipment. It has become possible to increase the rectification effect, that is, the product oxygen yield. Therefore, high-purity product oxygen can now be produced at a lower cost due to significant savings in running costs based on the O ₂ consumption reduction effect of expansion turbines. 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]

1 and 2 are system diagrams showing the conventional oxygen production method, FIG. 3 is a system diagram illustrating the oxygen production method according to the present invention, and FIG. 4 is an X-Y diagram of the upper column. FIG. 5 is an explanatory diagram of the gas-liquid state during rectification. 6... Switching type heat exchanger, 8a... Rectification column upper column,
8b... Fractionation column lower column, 17... Expansion turbine, 1
7a... Load blower, 25... Circulating heat exchanger.

Claims (1)

[Claims] 1. Feed air cooled by heat exchange with low-temperature return gas in the main heat exchanger is introduced into the lower column of the rectification column and separated into oxygen-enriched liquid air and nitrogen-rich gas, and the gases rise in the lower column. After extracting a portion of the air or gaseous nitrogen and adjusting the intermediate temperature through the reheat circuit of the main heat exchanger, it is introduced into an expansion turbine that generates the refrigeration necessary for operation and is expanded to perform external work. Therefore, in an air separation method that establishes thermal equilibrium in the system, the gaseous air or gaseous nitrogen that has passed through the reheating circuit is passed through a circulation heat exchanger to raise its temperature, and then passed through the load blower of the expansion turbine. An air separation method characterized in that the pressurized air is pressurized, and the pressurized air is further cooled by passing through the circulation heat exchanger and then introduced into the expansion turbine.