JPH079347B2 - Air separation method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an air separation method, and more particularly, to a method for separating and recovering highly pure nitrogen, oxygen and argon from air by a cryogenic separation method. The present invention relates to an improved method capable of recovering the contained component argon in good yield.

[Prior Art] Air separation is generally performed according to the flow shown in FIG. That is, the raw material air A, which has been cooled to near the liquefaction point after removing water and carbon dioxide by a known means, is introduced from the path 1 to the bottom of the main rectification column lower column 2, and the nitrogen having the lowest boiling point is in the lower column 2. After ascending toward the top and roughly separating at this portion, it is sent to the top of the upper column 4 of the main rectification column through the route 3, and further rectified at this part, and then extracted as a product gas from the top of the upper column 4. Be done. On the other hand, the oxygen-rich liquid air separated at the bottom of the lower tower 2 passes through the liquid-air filter 6 from the path 5, is further partially vaporized by the condenser 7a at the top of the argon rectification tower 7, and then is mainly purified through the path 8. It is sent to the upper middle part of the distillation column 4 and separated into nitrogen, argon and oxygen due to the difference in boiling points.
That is, nitrogen rises in the upper column 4 and is separated as product nitrogen in the top direction, oxygen having the highest boiling point is separated as a liquid substance in the lower part of the upper column 4, and the middle part of the upper column 4 has an argon concentration. About 10% argon-rich gas is separated. The high-purity oxygen separated in the lower part of the upper tower 4 may be directly extracted as a liquid substance from the path 10, or as shown in the figure, it is once extracted to the gas-liquid separator 9 and is branched from the path 1 and supplied as raw material air. It is also possible to take out as gaseous oxygen from the path 11 after heat-exchanging and vaporizing. The raw material air that has been cooled by heat exchange is supplied to the bottom of the lower tower either directly or after being split into a path 17.

On the other hand, the argon-rich gas concentrated in the middle part of the upper tower 4 is extracted from the middle part and sent to the argon rectification column 7, and the high boiling point oxygen is circulated to the middle part of the upper column, and at the same time, the low boiling point argon is discharged. Is an upper part and is withdrawn from the path 12 to obtain product argon, and if necessary, further sent to a purified argon column to increase the purity, and then the product is obtained.

[Problems to be Solved by the Invention] The most problematic point in carrying out such an air separation method is the recovery rate of argon. That is, argon contains only a trace amount of about 1% in the air, and the boiling point thereof is close to that of oxygen, so that it is not easy to recover this in a good yield. Further, as described above, argon is concentrated in the middle part of the upper column 4 of the main rectification column and extracted in the direction of the crude argon column. However, depending on the operating conditions of the main rectification column, the rising gas at the extraction position B may be increased. The argon concentration in the medium is not always the maximum. In fact, according to the experiments conducted by the present inventors, the number of stages (height position) indicating the highest argon concentration in the upper column of the main rectification column varies considerably depending on the operating conditions of the main rectification column. For example, Figure 3 shows the results of examining the relationship between the number of stages in the upper column of the main rectification column and the concentration distribution of N ₂ , Ar, and O ₂ when the amount of product oxygen withdrawn was changed, and the solid line shows the steady state. During operation, the broken line is the result when adjusting the amount of oxygen withdrawn from the upper tower.

As is clear from Fig. 3, the gas composition of each stage changes considerably due to the adjustment of the amount of oxygen in the ascending gas in the upper column accompanying the increase / decrease in the amount of oxygen extracted, but at the same time, the number of stages indicating the maximum argon concentration P ₁ and P ₂ also shift slightly up and down. Such a phenomenon similarly occurs when the supply amount or supply temperature of the raw material air is changed.

However, in the past, due to the provision that the plate number position showing the highest argon concentration in the upper tower does not change so much,
After once setting the argon extraction position B and designing the device, no measures were taken to add control while detecting the argon concentration at the extraction position B, and the supply amount and supply temperature of raw material air and product nitrogen The actual situation is to maintain operational stability by keeping the amount of product oxygen extracted as constant as possible. However, it is practically impossible to keep all the operating conditions of the rectification column constant, and the operating conditions fluctuate considerably due to various factors. If so, the argon concentration at the argon-rich gas extraction position B in the middle part of the upper column of the main rectification column fluctuates (decreases as compared with the case of the optimum operating conditions), which in turn adversely affects the argon recovery rate. .

The present invention has been made by paying attention to such a situation, and an object thereof is to always maintain the maximum argon concentration at the argon-rich extraction position B of the upper tower, despite the fluctuation of the operating conditions of the rectification tower. It is intended to provide a control method that can ensure a high level of argon recovery.

[Means for Solving Problems] According to the configuration of the method of the present invention which has been able to achieve the above object, the gas extracted from the middle part of the upper column of the main air rectification column is sent to the argon rectification column to increase the volume. In the air separation method for obtaining pure argon, the liquid oxygen withdrawn from the bottom of the upper column of the main rectification column is vaporized and part of it is returned to the lower part of the upper column, and the upper column is controlled by controlling the returned amount. In order to maximize the argon concentration in the rising gas at the extraction position while detecting the rising gas composition at any position in the upper column of the main rectification column, the rising gas composition in the inside can be adjusted. The gist is to increase the recovery rate of argon by controlling the returned amount of vaporized oxygen.

[Operation and Embodiment] The configuration and operation and effect of the present invention will be described in detail below with reference to the accompanying drawings. FIG. 1 is a schematic flow chart showing an embodiment of the present invention. Since the basic configuration is the same as that of the example of FIG. 2, the same parts are designated by the same reference numerals and the duplicate description thereof will be omitted. The present invention is different from the conventional example and has a characteristic structure in that, as shown in the figure, a thermometer 13 is attached at an appropriate position in the upper column 4 of the main rectification column, and an oxygen gas-liquid separator 9 is provided.
(9a indicates a liquid oxygen evaporator) is branched from the oxygen gas withdrawal path 11 to provide a return path 15 with a control valve 14, the tip of which is connected to the lower part of the upper tower 4, and the thermometer 13 The control valve 14 is connected to the automatic control device 16. Then, in the air separation operation, the opening amount of the control valve 14 is adjusted according to the temperature obtained by the thermometer 13 to control the returning amount of gaseous oxygen as described in detail below, and thereby the argon-rich gas extraction position is adjusted. The control operation is performed so that the argon concentration in B is always the maximum.

That is, as described with reference to FIG. 3, the gas composition in each stage of the main rectification column upper column 4 varies considerably depending on the operating conditions, and accordingly, the number of stages showing the maximum argon gas concentration also varies slightly up and down. On the other hand, in the vertical gas composition separation in the upper tower 4, as shown in FIG. 3, the upper part is nitrogen-rich, the lower part is oxygen-rich, and the middle part is relatively argon-rich. The gas composition at each stage position of the upper tower 4 can be estimated almost accurately by measuring the temperature at a certain stage of the upper tower 4. Further, the gas composition at each stage number position slightly changes depending on the oxygen concentration in the rising gas in the lower portion of the upper tower 4.

The present invention makes good use of such a phenomenon and performs control so that the argon concentration at the argon-rich gas extraction position B becomes maximum. That is, in carrying out the present invention, as shown in FIG. 1, a part of the oxygen gas extracted from the upper column 4 or the path 11 through the gas-liquid separator 9 after being extracted as liquid oxygen is replaced with the upper column 4. A path 15 for returning the gas to the lower part of the upper column 4 is provided, and the composition of the rising gas in the upper column 4 can be adjusted by controlling the amount of the returned gas. Further, a thermometer 13 is attached at an arbitrary position of the upper tower 4, a control valve 14 is provided in the return path 15, and these are connected to an automatic control device 16. Then, the temperature at the position of the number of attached stages in the upper tower 4 is measured by the thermometer 13,
The automatic control device 16 calculates the gas composition and the number of stages position indicating the maximum argon concentration in each stage of the upper tower 4 from the measured values, and the oxygen gas required to match the number of stages position with the argon-rich extraction position B. The return amount is calculated and the opening of the control valve 14 is automatically controlled. That is, as the oxygen content in the ascending gas in the lower part of the upper tower 4 increases or decreases, the plate number position showing the highest argon concentration tends to shift to the lower or upper direction. If such is stored in advance in the automatic control device 16, in the control device 16, after calculating the stage number position showing the maximum argon concentration during the operation based on the temperature obtained by the thermometer 13, the stage number position is calculated. The amount of oxygen gas to be returned to match the argon-rich extraction position B is immediately calculated and calculated, and the signal is the control valve 14
And the opening is adjusted.

As a result, the argon-rich gas extracted in the direction of the crude argon column 7 always shows the highest argon concentration in the upper column 4, which in turn improves the operation efficiency of the crude argon column 7 to bring the argon recovery rate to a high level. Can be kept.

In the example of FIG. 1, the gas composition is estimated from the temperature in the tower to perform the control operation, but this method is changed to the upper tower 4
Of course, it is also possible to directly measure the component composition of the rising gas or the like at an arbitrary number of stages in the inside by gas chromatography or the like, and perform the control operation based on the measured value. Further, in some cases, it can be said that it is also an extremely effective means to make it possible to measure the temperature and gas composition of a plurality of stages in the upper tower 4 and to average the measured values to improve the detection accuracy and control accuracy.

[Advantages of the Invention] The present invention is configured as described above, and by adding a relatively simple control means, the argon concentration at the argon-rich extraction position can be maintained at the maximum level, and the operation efficiency of the argon rectification column can be improved. The improvement made it possible to significantly increase the argon recovery rate.

[Brief description of drawings]

1 is a schematic flow chart showing an embodiment of the present invention, FIG. 2 is a schematic flow chart showing a conventional air separation method, and FIG. 3 shows the relationship between the number of stages in the upper column of the main rectification column and the gas composition. It is a graph shown. 1 ... Raw material air supply path 2 ... Main rectification tower lower tower, 4 ... Main rectification tower upper tower 7 ... Crude argon tower, 13 ... Thermometer 14 ... Control valve, 16 ... Control device

Claims (1)

[Claims] 1. A liquid extracted from the bottom of the main rectification column in an air separation method in which a gas extracted from the middle part of the main rectification column is sent to an argon rectification column to obtain high-purity argon. Oxygen is vaporized and a part of it is returned to the lower part of the upper column, and the rising gas composition in the upper column can be adjusted by controlling the returned amount. While detecting the rising gas composition at an arbitrary position in the air, the amount of vaporized oxygen returned is controlled so that the concentration of argon in the rising gas at the extraction position is maximized, and the argon recovery rate is increased. Separation method.