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Comparation of Different types of Metallurgical type medium and large air separation equipment

In recent years, the demand for air separation products in the steel industry has become more and more diversified, and many users need not only oxygen, but also high-purity nitrogen and argon, and even other rare gases. Due to the application of a large number of new steel technology and new equipment, various kinds of nitrogen for protection, nitrogen for sealing, nitrogen for replacement, and nitrogen safety are more and more, and the amount of nitrogen used has increased significantly, even exceeding the amount of oxygen used. In order to improve the quality of steel and alloy steel needs, steel blowing argon and furnace refining, vacuum degassing and other argon volume has risen. Other users require air separation equipment not only to provide a large number of gas products but also to provide a reasonable amount of liquid products. Some of the metallurgical air separation equipment to meet their product specifications of the process can be used both the traditional external compression process, but also the new internal compression process, according to customer demand for its selectivity is also greater.

Therefore, the choice of process for metallurgical air separation equipment, and which process type to use, is generally based on customer preferences, energy consumption and investment, and other comprehensive factors to determine. This paper focuses on the analysis of metallurgical air separation equipment for several process types and their respective characteristics, for reference.

99.6 High Purity Oxygen Plant主图
99.6 High Purity Oxygen Plant主图

Characteristics and comparison of typical processes

Metallurgical air separation oxygen product extraction rate is similar, the nitrogen product mainly depends on the distillation effect of the primary distillation tower, and the more gas phase feed (the greater the proportion of gas phase), the better the distillation effect of the lower tower. So the three processes under the tower distillation effect of the outer compression process are the best, the inner compression process is the second, and the worst since the pressurization process.

General metallurgical air separation equipment for nitrogen demand is small, but the amount of liquid nitrogen in the lower tower will affect the top of the upper tower reflux, affecting the reflux ratio of the upper tower, thus affecting the extraction rate of argon, so the extraction rate of self-pressurization is lower than that of external compression argon. At the same time, due to the external compression expansion of air into the upper tower, resulting in the reduction of the reflux ratio of the upper tower, resulting in the extraction rate of argon products from the external compression process being lower than the argon products from the internal compression.

So for metallurgical air separation, the expansion air into the upper tower and the lower tower nitrogen extraction rate is the main factor affecting the extraction rate of argon products, in addition, the size of the liquid ratio will also significantly affect the extraction rate, especially for argon products, the amount of liquid products, the extraction rate of argon products will be significantly reduced, the proportion of liquid products generally does not exceed 10%, with a small medium-pressure booster does not exceed 15% (part of the de-liquefaction (The cold end temperature difference will be expanded).

China cryogenic liquid oxygen plant

The characteristics and choices of the three process types are as follows.

1. Self-pressurization process

a conventional self-pressurization process: can be suitable for oxygen pressure 0 ∽ 1.5 bar (G), if the oxygen pressure is high, the air compressor pressure should also be raised accordingly (positive flow air and product oxygen heat transfer liquefaction, liquefied most of the unattended distillation to the upper tower, the lower tower of the distillation effect is poor).
b with external pressure since the booster process: the purpose of this process is to improve the pressure of oxygen out of the cold box, so as to improve the oxygen through the inlet pressure, so that oxygen pressure to reduce energy consumption, can save energy; but with argon products, the number of argon products will be reduced, while the number of nitrogen products can not be met when the demand is large.

2. External compression process

a conventional external compression air separation equipment process: due to high pressure and high-temperature oxygen fire, so the oxygen pressure is generally below 3.0MPa (G); at present, piston oxygen compressors and oxygen turbine compressors are very mature, so there is no problem in safety and stability. The advantage of the conventional external compression process is low energy consumption, low investment, and the need for medium-pressure nitrogen can be pumped through the lower tower pressure nitrogen, pressurized to reach the required pressure. However, it produces fewer liquid products, for the liquid product requirements of large users can not meet.
b large amount of liquid outside the compressed air separation equipment process: this process is suitable for liquid volume requirements are larger, the use of increased small air booster (discharge pressure 14bar (G), divided into two shares into the main heat exchanger), or increase the small circulating nitrogen compressor (similar to nitrogen cycle), when the liquid product up to 15 ∽ 20%, and the number of liquid products less than 3000Nm³ / h when more reasonable, otherwise energy consumption too high.

3. Internal compression process

a low-pressure oxygen compression process: oxygen pressure is low, in 0.2 ~ 1.2MPa (G), the use of a low-pressure oxygen compression process, the advantage is not to invest in a piston oxygen compressor or oxygen turbine compressor (the pressure is too low may not be able to do), can produce liquid products about 15%, the pressure is higher when the energy consumption will be higher, not economic.

b medium-pressure oxygen compression process: the process is the conventional internal compression process (pressure 45 bar below, choose the booster does not pump, pressure to the end, so that the machine efficiency, the booster energy consumption is low; pressure 45 bar above, choose the pump, the model is a good choice, mainly and machine efficiency and investment) its argon extraction rate of up to 85%, liquid products up to 20%, medium-pressure nitrogen, you can go down the tower Pumping pressure nitrogen (low-pressure nitrogen volume small priority down the tower pumping pressure nitrogen, pumping pressure nitrogen volume when pumping dirty liquid nitrogen to supplement the upper tower reflux liquid) and then nitrogen pressurization to obtain, can save part of the energy consumption, its suitable for medium-pressure oxygen, medium-pressure nitrogen product specifications, nitrogen volume can be used nitrogen cycle. Its advantage is better safety and stability, but the comprehensive energy consumption and investment are higher, of course, this process is less used in the metallurgical industry.

Industrial Oxygen Concentrator supplier

Comparison of internal compression and external compression processes

The following is a comparison of air separation equipment in terms of stable operation, plant safety, departmental machine configuration, operation and maintenance, floor space, product extraction, liquid products, comprehensive energy consumption, etc.

Stable operation: in the internal compression process, the air compressor and booster run at the same time, and the air separation equipment operates normally; requires stable oxygen back pressure to ensure that the main heat exchanger heat exchange is perfect and the stability of air separation working conditions.

However, in actual production, especially in some steel enterprises oxygen pressure fluctuates frequently and substantially, resulting in unstable air separation operating conditions, difficult operation, and high requirements; while the outer compression oxygen turbocompressor is not affected by this.

Device safety: the safety of the internal compression process is mainly to prevent the precipitation of hydrocarbons in liquid oxygen (low-temperature solid acetylene carbon-hydrogen triple bond instability, will automatically break, carbon-hydrogen separation, the release of energy, the occurrence of micro-explosions, the danger in the main cooling and high-pressure plate type, take room temperature adsorption treatment, but can not adsorption of impurities will continue to enter the main cooling in the form of solids, the accumulation of blockage, the impact of the need to stop and heat treatment ); and the safety aspect of the external compression process is the high-temperature oxygen fire hazard in the compression process of the oxygen compressor, taking the discharge of liquid oxygen to discharge low(hydrocarbons, nitrous oxide, carbon dioxide, and water (will generate tens of thousands of volts of static electricity) to prevent the accumulation of solids blocking the main cooling).

Departmental machine configuration: internal compression investment is much higher than external compression, currently external compression can be completely localized, while internal compression is the main part of the machine and also depends on imports (domestic Shaanxi drum and Shaanxi drum can also, efficiency booster is slightly lower, air compressor efficiency is similar), the investment is much higher, but the operation of these parts of the machine is reliable, continuous operation for a long time.

Operation and maintenance: the internal compression process can provide high-pressure oxygen without an oxygen compressor, while in the external compression process, the higher the oxygen pressure, the higher the requirements for the oxygen compressor, and the more difficult to manufacture and maintain the oxygen compressor.

In terms of floor space: the air booster in the internal compression process can reduce the floor space whether it is set up alone or in conjunction with the main air compressor; the oxygen compressor in the external compression process requires a safe distance and covers a larger area.

Product extraction: the extraction rate of oxygen from the outer compression is higher than the inner compression because the fractionation efficiency of the primary distillation tower of the outer compression is higher than the inner compression, but the extraction rate of argon from the inner compression is higher than the outer compression (the outer compression has expanded air into it so that the reflux ratio of the upper section of the upper tower is reduced).

Liquid products: internal compression than the traditional external compression to be higher, but with booster (pressurized to about 14 bar, divided into two strands into the fractionation tower) of the external compression process to produce liquid and internal compression is similar, and lower investment and energy consumption.

Comprehensive energy consumption: the energy consumption of internal compression is higher than that of external compression, external compression mainly has the energy consumption of oxygen production and external pressure delivery, and the energy consumption of internal compression is divided into the energy consumption of oxygen production and internal pressure delivery, then the energy consumption of oxygen production is the same, while the energy consumption of pressure delivery is about 30% higher than that of external compression, and the comprehensive energy consumption is also higher than the corresponding part.

Compared with the external compression process, the internal compression process not only has the loss of heat transfer, but also the additional energy loss of compound heat, so the internal compression energy consumption is higher than the external compression. The inner compression process required airflow and the pressure of the optimal curve is as follows (heat exchanger temperature difference is certain, to the air booster energy consumption is the minimum) (in fact, the inner compression process air separation needs to be selected for high-pressure heat exchanger investment (and integral temperature difference) and booster operating energy consumption trade-off).

Air Separation Psa Oxygen Generator from China factory
Air Separation Psa Oxygen Generator from China factory

Conclusion

For the metallurgical industry, if the pressure of oxygen products is less than 3.0MPa (G), and the size of the air separation equipment is below 8000Nm³/h generally chooses external compression (oxygen compressor selected piston oxygen compressor) process, the process has the advantages of simple process, flexible operation, saving investment, occupying an area of small, and the use of internal compression flow process when the air booster can not do due to the small amount.

For the metallurgical industry, oxygen product pressure is generally less than 3.0MPa (G), and the scale of air separation equipment in the 8000Nm³ / h ~ 80000Nm³ / h scale, when the user's liquid product sales market is not good, the general choice of external compression (oxygen compressor using oxygen turbocompressor) process, the process has a simple process, flexible operation, the advantages of saving investment; and when the user of argon product requirements higher, the user's local liquid product sales market is better, or higher requirements for safety, and high requirements for floor space, should choose the oxygen compression process.

For oxygen pressure lower than 0.2 ~ 1.2MPa (G), the output of 8000Nm³ / h or more users, from saving investment, simple operation, and other factors should choose the oxygen compression process.

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