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The deep cryogenic air separation technology is a method that separates the main components (nitrogen, oxygen and argon) in the air through low temperatures. It is widely used in industries such as steel, chemical, pharmaceutical and electronics. With the increasing demand for gases, the application of deep cryogenic air separation technology is also becoming more and more widespread. This article will thoroughly discuss the production process of deep cryogenic air separation, including its working principle, main equipment, operation steps and its application in various industries.

Overview of Cryogenic Air Separation Technology

The basic principle of cryogenic air separation is to cool the air to extremely low temperatures (generally below -150°C), so that the components in the air can be separated according to their different boiling points. Usually, the cryogenic air separation unit uses air as the raw material and goes through processes such as compression, cooling, and expansion, finally separating nitrogen, oxygen, and argon from the air. This technology can produce high-purity gases and, by precisely regulating process parameters, meet the strict requirements for gas quality in different industrial fields.

The cryogenic air separation unit is divided into three main parts: air compressor, air pre-cooler, and cold box. The air compressor is used to compress the air to a high pressure (usually 5-6 MPa), the pre-cooler reduces the temperature of the air through cooling, and the cold box is the core part of the entire cryogenic air separation process, including the fractionation tower, which is used to achieve gas separation.

Air compression and cooling

Air compression is the first step in cryogenic air separation, mainly aiming to compress the air at atmospheric pressure to a higher pressure (usually 5-6 MPa). After the air enters the system through the compressor, its temperature will increase significantly due to the compression process. Therefore, a series of cooling steps must be carried out to reduce the temperature of the compressed air. Common cooling methods include water cooling and air cooling, and a good cooling effect can ensure that the compressed air does not cause unnecessary burden on the equipment during subsequent processing.

After the air is preliminarily cooled, it enters the next stage of pre-cooling. The pre-cooling stage usually uses nitrogen or liquid nitrogen as the cooling medium, and through heat exchange equipment, the temperature of the compressed air is further reduced, preparing for the subsequent cryogenic process. Through pre-cooling, the temperature of the air can be reduced to close to the liquefaction temperature, providing necessary conditions for the separation of the components in the air.

Low-temperature expansion and gas separation

After the air is compressed and pre-cooled, the next key step is low-temperature expansion and gas separation. Low-temperature expansion is achieved by rapidly expanding the compressed air through an expansion valve to normal pressure. During the expansion process, the temperature of the air will drop significantly, reaching the liquefaction temperature. Nitrogen and oxygen in the air will start to liquefy at different temperatures due to their boiling point differences.

In the cryogenic air separation equipment, the liquefied air enters the cold box, where the fractionation tower is the key part for gas separation. The core principle of the fractionation tower is to utilize the boiling point differences of different components in the air, through gas rising and falling in the cold box, to achieve gas separation. The boiling point of nitrogen is -195.8°C, that of oxygen is -183°C, and that of argon is -185.7°C. By adjusting the temperature and pressure in the tower, efficient gas separation can be achieved.

The gas separation process in the fractionation tower is very precise. Usually, a two-stage fractionation tower system is used to extract nitrogen, oxygen, and argon. First, nitrogen is separated in the upper part of the fractionation tower, while liquid oxygen and argon are concentrated in the lower part. To improve the separation efficiency, a cooler and re-evaporator can be added in the tower, which can further precisely control the gas separation process.

The extracted nitrogen is usually of high purity (above 99.99%), widely used in metallurgy, chemical industry, and electronics. Oxygen is used in medical, steel industry, and other high-energy-consuming industries that require oxygen. Argon, as a rare gas, is usually extracted through the gas separation process, with high purity and widely used in welding, smelting, and laser cutting, among other high-tech fields. The automated control system can adjust various process parameters according to actual needs, optimize production efficiency, and reduce energy consumption.

In addition, the optimization of the deep cryogenic air separation system also includes energy-saving and emission control technologies. For example, by recovering the low-temperature energy in the system, energy waste can be reduced and the overall energy utilization efficiency can be improved. Moreover, with the increasingly strict environmental regulations, modern deep cryogenic air separation equipment is also paying more attention to reducing harmful gas emissions and enhancing the environmental friendliness of the production process.

Applications of deep cryogenic air separation

Deep cryogenic air separation technology not only has important applications in the production of industrial gases, but also plays a significant role in multiple fields. In the steel, fertilizer, and petrochemical industries, deep cryogenic air separation technology is used to provide high-purity gases such as oxygen and nitrogen, ensuring efficient production processes. In the electronics industry, the nitrogen provided by deep cryogenic air separation is used for atmosphere control in semiconductor manufacturing. In the medical industry, high-purity oxygen is crucial for patients’ respiratory support.

In addition, deep cryogenic air separation technology also plays an important role in the storage and transportation of liquid oxygen and liquid nitrogen. In situations where high-pressure gases cannot be transported, liquid oxygen and liquid nitrogen can effectively reduce volume and lower transportation costs.

Conclusion

The deep cryogenic air separation technology, with its efficient and precise gas separation capabilities, is widely applied in various industrial fields. With the advancement of technology, the deep cryogenic air separation process will become more intelligent and energy-efficient, while enhancing the purity of gas separation and production efficiency. In the future, the innovation of deep cryogenic air separation technology in terms of environmental protection and resource recovery will also become a key direction for industry development.

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Email :anna.chou@hznuzhuo.com