CN100436989C - Method for preparing high purity oxygen using full low pressure air separation plant - Google Patents

Abstract

The invention provides a combined operation method for producing high-purity oxygen by using a full low-pressure air separation device. The operation method can ensure the purity of other air separation products while improving the oxygen purity. The specific operation method is as follows: adjust the oxygen output of the product, the amount of air entering the tower, and the opening of the valve for sending the liquid air from the lower tower to the upper tower, so that the oxygen of the air separation product can be reduced by 5% to 25%, and the amount of air entering the tower can be increased by 2% to 10%. , the liquid air increment from the lower tower to the upper tower is 5% to 35%; under the above operating conditions, the oxygen purity can be increased by 0.1 to 0.4 percentage points, and the argon fraction remains at the normal value. The invention has the advantages of not only improving the purity of the oxygen product to meet the requirement of high-purity oxygen, but also taking into account the purity of the nitrogen and argon products. At the same time, the operation adjustment range is small, which has little impact on the operating conditions of the air separation unit and has strong operability.

Description

A method for producing high-purity oxygen with full low-pressure air separation unit

technical field

The invention belongs to the technical field of oxygen production, and in particular provides a method for producing high-purity oxygen with a full low-pressure air separation device.

Background technique

With the continuous improvement of steelmaking production requirements and the further deepening of pure steel technology research, the requirements for high-purity oxygen products (nitrogen content <15ppm) continue to increase. In addition, the market demand for high-purity liquid oxygen is also expanding. However, the flow design of existing large-scale air separation plants can only produce oxygen products with a purity of about 99.6%. If a further purification method is adopted, the product cost is high and the output is small, which is difficult to meet the needs of large-scale industrial production.

Therefore, through the optimized research on the high-purity oxygen technology of the existing full low-pressure air separation unit, the existing air separation unit can directly produce high-purity oxygen (purity above 99.9%), and can produce continuously and stably, which is the solution to the contradiction between demand and supply. best solution.

At present, the oxygen, nitrogen, and argon products in large-scale industrial gases are generally extracted by full low-pressure rectification. The more advanced processes and equipment used in large-scale air separation units mainly include:

1. The upper tower adopts structured packing instead of the sieve plate tower;

2. Argon is produced by full rectification;

3. Processed air is purified at room temperature, using molecular sieve pressure swing adsorption (PSA) or temperature swing adsorption (TSA) technology;

4. DCS is used for process detection, control, optimization and load tracking adjustment;

5. Adopt the latest internal compression process and the process of expanding air into the lower tower to achieve the purpose of reducing energy consumption and investment.

The product purity of a typical cryogenic rectification air separation plant is generally: oxygen > 99.6%, nitrogen > 99.99%, argon > 99.999%. This plan is based on the above air separation process to formulate high-purity oxygen production operations.

The means of high-purity oxygen production technology analysis include the following:

1. Establish the mathematical model of the air separation distillation system;

2. Complete the simulation calculation of the distillation process and the whole process;

3. Under various working conditions, compare and analyze the simulated calculation results with the actual operation, and propose a feasible high-purity oxygen production plan and operation adjustment method.

In general, there are two ways to improve the purity of oxygen products:

(1) Reduce product oxygen output and improve product oxygen purity.

When the nitrogen output is constant, the adjustment of the product oxygen should reduce the oxygen output from 100% to 95%-70%, and the oxygen purity should be increased by 0.1-0.4 percentage points. As shown in Figure 1: As the oxygen product output decreases, the oxygen purity continues to increase. The figure shows the changing laws of liquid oxygen and gaseous oxygen products respectively. Simultaneously, the purity changes of nitrogen and argon products are shown in Fig. 2 and Fig. 3 . Figure 2 shows the relationship between nitrogen and oxygen depletion, with the nitrogen purity decreasing as the oxygen product depletion varies. Figure 3 shows that the argon content in the argon fraction drops significantly as the production of oxygen product decreases.

(2) Increase the amount of processing air and improve the oxygen purity of the product

Adjust the opening of the guide blades of the air compressor so that the air volume entering the tower increases by 2% to 10% compared with the design working condition. When the output of oxygen and nitrogen products remains unchanged, the oxygen purity of the product increases by 0.1% to 0.4%. Slightly decreased; the oxygen content in the argon fraction increased and the argon content decreased. As shown in Figure 4: As the amount of processing air increases, the oxygen purity continues to increase. The figure shows the changing rules of liquid oxygen and gaseous oxygen products respectively. Figure 5 shows that the nitrogen purity decreases with the change of the amount of processing air. The change trends of liquid nitrogen and gaseous nitrogen products are shown in the figure respectively. Figure 6 shows that the argon content in the argon fraction decreases significantly as the amount of processing air changes, and the figure shows the relationship between the argon content and the amount of processing air.

The above two methods can increase the purity of the oxygen product by 0.1 to 0.4 percentage points, but have an impact on the purity of other products: the purity of the nitrogen product has decreased, and the purity of the argon fraction has decreased significantly.

Contents of the invention

The object of the present invention is to: provide a kind of method of producing high-purity oxygen with full low-pressure air separation unit, this operation method takes into account the purity of other air separation products while improving the purity of oxygen products. The specific operation method is as follows:

(1) Reduce the oxygen output of the product, and simultaneously increase the amount of liquid space sent from the lower tower to the upper tower;

When the nitrogen output remains unchanged, lower the opening of the oxygen outlet valve of the product to reduce the oxygen output by 5% to 30%. An increase of 0.1 to 0.4 percentage points. As shown in Figure 7 to Figure 9. Figure 7 shows that with the continuous reduction of the oxygen product and the increase of the empty volume of the reflux liquid sent to the tower, the purity of the oxygen product increases. Figure 8 shows that the argon content in the argon fraction increases with the continuous reduction of the oxygen product and the increase of the reflux liquid space sent to the tower. Figure 9 shows that with the continuous reduction of the oxygen product and the increase of the reflux liquid space sent to the tower, the purity of the product argon is continuously improved.

(2) Increase the amount of processing air, and at the same time increase the amount of liquid air sent from the lower tower to the upper tower.

Keep the output of oxygen and nitrogen products unchanged, adjust the opening of the guide vane of the air compressor to increase the air volume entering the tower by 2% to 10%, and at the same time adjust the reflux liquid volume of the upper tower to increase it by 5% to 35%. When the oxygen purity increases by 0.2 to 0.4 percentage points, the reduction of the argon fraction slows down, as shown in Figures 10 to 12. Figure 10 shows that with the increase of the air volume, the air volume of the reflux liquid sent to the upper tower increases at the same time, so that the oxygen purity is continuously improved. Figure 11 shows that: with the increase of the air volume, the volume of the reflux liquid sent to the upper tower increases simultaneously, which increases the argon content in the argon fraction. The starting point of calculation in the figure is - 5% increase of air, 10% increase of liquid air. Figure 12 shows that with the increase of the air volume and the increase of the reflux liquid space sent to the upper tower, the argon purity is continuously improved.

(3) Reduce the oxygen output, increase the amount of processing air and increase the amount of liquid air sent from the lower tower to the upper tower at the same time.

Adjust the valve opening of the product oxygen, air entering the tower, and the reflux liquid air of the upper tower, so that the oxygen of the air separation product is reduced by 5% to 35%, the air entering the tower is increased by 2% to 10%, and the reflux liquid air of the upper tower is increased by 5%. ~35%. Under the above operating conditions, the oxygen purity increases by 0.1 to 0.4 percentage points, and the purity of the argon product meets the requirements.

The present invention has the advantages of: aiming at the production of high-purity oxygen by the full low-pressure air separation unit, the operation scheme proposed through analysis and calculation not only improves the purity of the product oxygen, but also takes into account the purity requirements of the product nitrogen and argon. At the same time, the operation adjustment range is small, which has little impact on the operating conditions of the air separation unit and has strong operability.

Description of drawings

Fig. 1 is the air separation oxygen output-oxygen purity figure of the present invention.

Fig. 2 is the air separation oxygen output-nitrogen purity figure of the present invention.

Fig. 3 is the air separation oxygen output-argon purity figure of the present invention. The figure shows the relationship between argon content and oxygen loss.

Fig. 4 is an air separation process air volume-oxygen purity diagram of the present invention.

Fig. 5 is an air separation process air volume-nitrogen purity diagram of the present invention.

Fig. 6 is a diagram of air volume-argon fraction content for air separation processing in the present invention.

Fig. 7 is the relationship diagram of air separation oxygen production-liquid space-oxygen purity in the present invention. The calculation starting point in the figure is - 15% reduction of oxygen, 12% increase of liquid air. The figure shows the change law of gaseous oxygen product purity, oxygen production and liquid space.

Fig. 8 is a relationship diagram of air separation oxygen production-liquid space-argon fraction in the present invention. The calculation starting point in the figure is - 15% reduction of oxygen, 12% increase of liquid air. The figure shows the change rules of argon content, oxygen production and liquid space in the argon fraction.

Fig. 9 is the relationship diagram of air separation oxygen production-liquid space-refined argon purity. The calculation starting point in the figure is - 15% reduction of oxygen, 12% increase of liquid air. The figure shows the change rules of refined argon purity, oxygen production and liquid space.

Fig. 10 Air separation processing air volume-liquid air volume-oxygen purity relationship diagram. The starting point of calculation in the figure is - 5% increase of air, 10% increase of liquid air. The figure shows the change law of gaseous oxygen product purity and processing air volume and liquid air volume.

Fig. 11 Relation diagram of air volume-liquid air volume-argon fraction in air separation process. The starting point of calculation in the figure is - 5% increase of air, 10% increase of liquid air. The figure shows the change law of the argon content in the argon fraction and the amount of processing air and liquid air.

Fig. 12 Relation diagram of air volume-liquid air volume-refined argon in air separation process. The starting point of calculation in the figure is - 5% increase of air, 10% increase of liquid air. The figure shows the change law of the purity of refined argon and the amount of processing air and liquid air.

Detailed ways

The operation plan has passed the operation inspection of the air separation unit, and the oxygen purity reaches 99.9%, which meets the requirements of high-purity oxygen production.

Table 1 is the calculation data of ^60000Nm3 air separation plant under different operating conditions.

Table 1 Prediction of product purity in combination operation

working conditions Air Increment% Oxygen reduction % Liquid air increment % Oxygen purity % Nitrogen purity % Refined argon purity% 1 5 10 10 99.95 99.994 - 2 5 10 20 99.94 99.991 - 3 5 10 30 99.92 99.988 - 4 2 10 30 99.82 99.995 99.997

5 2 12 30 99.85 99.994 99.998 6 2 12 25 99.86 99.995 99.999 7 3 12 30 99.88 99.992 99.999 8 3 12 28 99.89 99.992 99.999 9 3 12 27 99.90 99.993 99.999

Claims (2)

1, the full low pressure air separation unit of a kind of usefulness is produced the method for high purity oxygen, and it is characterized in that: guarantee the combination operation of other space division product purity in the time of the production high purity oxygen, concrete operation method is as follows:

Adjust product oxygen outlet valve aperture, make oxygen yield reduce 10%～12%, adjust simultaneously and go up tower backflow liquid air valve, make the liquid air amount increase by 10%～30%, the argon cut remains on normal value;

Perhaps, adjust the air compressor machine guide vane opening, make entering tower air capacity increase by 2%～5%, adjust simultaneously and go up tower backflow liquid air amount, make it to increase at 10%～30% o'clock, the argon cut remains on normal value;

2, produce the method for high purity oxygen according to the full low pressure air separation unit of the described usefulness of claim 1, it is characterized in that: reduce oxygen yield, and increase the processing air capacity, tower returns the liquid air amount of tower under improving simultaneously, and concrete operation method is as follows:

Adjust product oxygen, advance the tower air, go up the valve opening of tower backflow liquid air, make space division product oxygen decrement 10%～12%, advancing the tower air increases by 2%～5%, and last tower is served tower liquid air increment 10～30%; The argon cut remains on normal value under above operating condition.

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