Content
1.1 Pressure swing adsorption separation process
1.2 Membrane separation process
1.3 Cryogenic distillation process
1.3.1 Internal compression and external compression process
1.3.2 Structured packing
1.3.3 Full distillation to produce argon without hydrogen
2. Summary
1. A brief introduction and analysis of air separation process
We live in the atmosphere, and air is the gas we rely on for survival, because the air contains about 21% oxygen, nitrogen accounts for about 78%, and the remaining 1% is carbon dioxide and other gases. Nitrogen is the most commonly used gas in chemical process flow, mainly used as a protective gas, because the chemical properties of nitrogen are stable and it is difficult to participate in chemical reactions.
1.1 Pressure swing adsorption separation process
Pressure swing adsorption is a process of separating various gases in the air by different adsorption efficiencies of molecular sieves. The air separation process mainly separates oxygen and nitrogen in the air. Pressure swing adsorption will have a balance process. If the gas is not completely adsorbed on the molecular sieve, the oxygen and nitrogen in the air will continue to be adsorbed on the molecular sieve until a balance state is reached.
1.2 Membrane separation process
Membrane separation is a newly developed new process for separating air. This process technology mainly uses the principle of different solubility and diffusion coefficients of gas molecules on the membrane for separation. When the mixed gas passes through the membrane, due to the difference in solubility of different gas molecules on the membrane, when there is a pressure difference on both sides of the membrane, different gas molecules will gather on both sides of the membrane, thereby separating different gases.
1.3 Cryogenic distillation process
The cryogenic distillation process is realized by using different boiling points of different gases. Under low temperature conditions, the boiling points of oxygen and nitrogen are different. The low temperature pressurization process technology is used to distill and separate oxygen and nitrogen in the air to obtain higher purity gas. With the continuous development of cryogenic distillation technology, different processes have emerged according to different production conditions, mainly internal compression and external compression process distillation, structured packing distillation and full distillation without hydrogen to produce argon distillation.
1.3.1 Internal compression and external compression process
At present, there are two main forms of gas pressurization, one is external compression and the other is internal compression. Usually, the process of producing gas in the air separation unit is carried out at room temperature. Therefore, the external compressor should be pressurized to the required pressure. Under reduced pressure, the boiling point of the gas will decrease. For the principle of internal compression, the liquid product in the distillation tower is mainly increased in pressure by a pump, and then enters the main pipeline through a heat exchanger. The main difference between the two methods is that external compression is reduced in pressure by a compressor, and internal compression is pressurized by a hydraulic pump. The internal compression process has low operating costs, simple equipment maintenance, high safety factor, and convenient operation.
Structured packing is a new process technology developed in recent years, with the following advantages: ① Low energy consumption and continuous heat exchange. Structured packing can form a layer of liquid film on the surface of the reflux liquid,and the resistance of gas flow will also be reduced. Since there are different pipelines for the transportation of gas and liquid respectively, heat exchange will be carried out continuously, thereby reducing the resistance of the packing tower and ultimately reducing energy consumption. ② It has a high separation efficiency for oxygen, nitrogen and argon. After using structured packing, the pressure in the tower will decrease. As the pressure in the tower decreases, the separation efficiency of the tower will gradually increase. ③ It can be changed and operated in a wide range. After adopting structured packing,the gas and liquid are connected continuously, resulting in a reduction in the liquid holding capacity of the tower itself,which can withstand changes in a larger load range and is easy to operate.
1.3.3 Full distillation hydrogen-free argon production
Full distillation hydrogen-free argon production technology is a new process technology, and there are already many such devices in large domestic chemical companies. This process technology is divided into two steps. The first step is to remove oxygen from the gas by hydrogenation to obtain crude argon, and then use low-temperature distillation to remove nitrogen to obtain high-purity argon. This process technology has the advantages of easy operation, simple process flow, and high product purity. Since this process uses hydrogen, the safety factor of the process is reduced, resulting in poor process reliability.
2.Summary
Air is an inexhaustible resource. Nitrogen and oxygen in the air are important raw materials in chemical processes. The separation of gases in the air is of great significance to the development of the chemical industry. The development of any industry will move towards a more enterprise-oriented, technological and professional direction. Each enterprise should reasonably choose the separation process according to its actual situation, improve production quality, reduce production costs and maximize economic benefits under the premise of ensuring production safety. At present, there are still many problems with these three air separation process technologies, and the process needs to be further optimized to achieve efficient separation of air.
