在深度冷冻法中，主要的分离过程是在双级精馏塔中进行的。该塔由上、下两塔

In the deep freezing method, the main separation process is carried out in a two-stage rectification tower. The tower consists of upper and lower towers and the condensing evaporator between the towers. The air entering the bottom of the lower tower has been partially liquefied under the temperature and pressure conditions there. Since the boiling point of liquid nitrogen is lower than that of liquid oxygen, the liquefied gas at the bottom of the lower tower is oxygen-enriched liquid air, and the oxygen content is generally 30% to 40%. The operating pressure of the lower tower should be higher than that of the upper tower to make the condensation temperature of nitrogen at the top of the lower tower higher than the boiling temperature of liquid oxygen at the bottom of the upper tower (see p-V-T relationship). Therefore, the heat in the condensing evaporator is transferred from the tube to the tube and has a certain heat transfer temperature difference. The condensing evaporator simultaneously plays the role of condensing the top of the lower tower and heating the bottom of the upper tower. The air passes through the multi-layer tray rectification from the bottom to the top, which gradually increases the concentration of the volatile component nitrogen and condenses into liquid nitrogen in the condensing evaporator tube. A part of the liquid nitrogen is used as the reflux liquid in the lower tower; a part is collected in the liquid nitrogen tank and used as the reflux liquid at the top of the upper tower after decompression. The oxygen-enriched liquid air at the bottom of the lower tower enters the middle of the upper tower through a throttle valve, and contacts the gas evaporated by the condensing evaporator in counter current. As a result, the oxygen content in the downstream liquid increases continuously from top to bottom, and finally accumulates between the tubes of the condensing evaporator, and the oxygen content can reach more than 99%, and the product oxygen is continuously evaporated and drawn out of the tower. The top of the upper tower is the product nitrogen, and the concentration can also reach more than 98%. The temperature of the product oxygen and product nitrogen leaving the rectification tower are very low, and the input air can be cooled by a heat exchanger. <br>Because the boiling point of argon is between the boiling points of nitrogen and oxygen, it is not possible to obtain pure nitrogen and pure oxygen at the same time using a two-stage rectification tower. If the argon-enriched gas is extracted as the raw material for argon extraction at the appropriate part in the middle of the upper tower, the concentration of product nitrogen and oxygen can be increased. Neon and helium with a lower boiling point accumulate on the liquid nitrogen, which can be extracted as a raw material for extracting neon and helium. Krypton and xenon with relatively high boiling points are accumulated in the liquid oxygen and gas oxygen at the bottom of the upper tower, and can be extracted as raw materials for krypton and xenon extraction. <br><br>The molecular sieve adsorption method is based on the different adsorption of molecular sieve to nitrogen and oxygen. After the air passes through the molecular sieve bed, the composition of the adsorption phase and the gas phase will change to achieve the purpose of separation. Because the adsorption phase has a high nitrogen content, it flows out of the gas The oxygen content is higher. When the adsorption column is long enough, oxygen of a certain purity can be prepared, and the molecular sieve can be regenerated by desorption under reduced pressure

In deep freezing, the main separation process is performed in a two-stage distillation tower. The tower consists of condensate evaporators between the top and lower towers. The air entering the bottom of the lower tower has been partially liquefied under temperature and pressure conditions there. Because the boiling point of liquid nitrogen is lower than the boiling point of liquid oxygen, the liquefied gas at the bottom of the lower tower is oxygen-rich liquid air, the oxygen content is generally 30% to 40%. The operating pressure of the lower tower should be higher than that of the upper tower so that the condensation temperature of nitrogen at the top of the lower tower is higher than the boiling temperature of liquid oxygen at the bottom of the upper tower (see p-V-T relationship). So that the condensate evaporator heat from the tube to the pipe, and has a certain heat transfer temperature difference. The condensate evaporator also acts as condensation at the top of the lower tower and heating the upper tata bottom. The air is distilled from the lower down to the lower tower by a multi-layered tower plate, which gradually increases the concentration of volatile component nitrogen and condenses into liquid nitrogen in the condensate evaporator tube. Part of the liquid nitrogen in the lower tower as a reflux liquid, part of the collection in the liquid nitrogen tank, after decompression as the upper tower top reflux. Oxygen-rich liquid air at the bottom of the lower tower enters the middle of the upper tower through a throttle valve and comes into contact with the gas countercurrent sofhei evaporating from the condensate evaporator. Thus, the oxygen content in the lower liquid from top to bottom increased, and finally accumulated in the condensate evaporator pipe, oxygen content can reach more than 99%, and constantly evaporate the product oxygen in this and lead out of the tower. The top of the tower is derived from the product nitrogen, the concentration can also reach more than 98%. The oxygen and nitrogen of the product sidontium are very low and the inlet air can be cooled by the heat exchanger.<br>Since the boiling point of radon is between nitrogen and oxygen boiling point, pure nitrogen and pure oxygen cannot be obtained at the same time by using the two-stage distillation tower. If the appropriate part of the upper tower is pumped out of the rich argon gas as the raw material for lifting, the concentration of nitrogen and oxygen in the product can be increased. The lower boiling point of argon and helium accumulate on the liquid nitrogen and can be extracted as a raw material for lifting argon and helium. The higher boiling point of radon, radon is accumulated in the bottom of the upper tower liquid oxygen and gas oxygen, can be extracted as a raw material for lifting radon, radon.<br><br>Molecular sieve adsorption method Based on the different adsorption force of nitrogen and oxygen by molecular sieve, the composition of the adsorption phase and the gas phase will change to achieve the purpose of separation, because the adsorption phase has a higher nitrogen content, so the oxygen content of the outflow gas is higher. When the adsorption column is long enough, a certain purity of oxygen can be produced, and the molecular sieve can be regenerated by means of de-appatising deattachment.

In the deep freezing process, the main separation process is carried out in a two-stage distillation column. The tower consists of the upper and lower towers and the condensing evaporator between them. The air entering the bottom of the lower tower has been partially liquefied under the temperature and pressure conditions. As the boiling point of liquid nitrogen is lower than that of liquid oxygen, the liquefied gas at the bottom of the lower tower is oxygen rich liquid air, with an oxygen content of 30% - 40% generally. Only when the operating pressure of the lower tower is higher than that of the upper tower can the condensation temperature of nitrogen at the top of the lower tower be higher than the boiling temperature of liquid oxygen at the bottom of the upper tower (see p-V-T relationship). Thus, the heat in the condensing evaporator is transferred from the inside of the tube to the inter tube, and there is a certain heat transfer temperature difference. The condensation evaporator plays the role of condensation at the top of the lower tower and heating at the bottom of the upper tower. The air passes through the multi-layer tray distillation from bottom to top in the lower tower, which makes the concentration of volatile component nitrogen gradually increase, and condenses into liquid nitrogen in the condensing evaporator tube. Part of liquid nitrogen is used as reflux liquid in the lower tower; part of liquid nitrogen is collected in the liquid nitrogen tank and used as reflux liquid on the top of the upper tower after decompression. The oxygen rich liquid air at the bottom of the lower tower enters the middle part of the upper tower through the throttle valve and contacts with the gas evaporated from the condensing evaporator in reverse flow. Thus, the oxygen content in the downflow liquid increases continuously from top to bottom, and finally accumulates in the condenser evaporator pipe. The oxygen content can reach more than 99%, and the product oxygen is continuously evaporated here and led out of the tower. The top of the upper tower leads out the product nitrogen, with a concentration of more than 98%. The temperature of product oxygen and product nitrogen out of distillation tower is very low, and the input air can be cooled by heat exchanger.<br>Since the boiling point of argon is between that of nitrogen and oxygen, pure nitrogen and pure oxygen can not be obtained by using two-stage distillation tower at the same time. If the rich argon gas is extracted from the middle part of the upper tower as the raw material, the concentration of nitrogen and oxygen in the product can be increased. Neon and helium with lower boiling point accumulate on liquid nitrogen and can be extracted as raw materials for neon and helium extraction. Krypton and xenon with higher boiling point are accumulated in liquid oxygen and gas oxygen at the bottom of upper tower, and can be extracted as raw materials for krypton and xenon extraction.<br>The molecular sieve adsorption method is based on the different adsorption capacity of the molecular sieve for nitrogen and oxygen. After the air passes through the molecular sieve bed, the composition of the adsorption phase and the gas phase will change to achieve the purpose of separation. Because the nitrogen content of the adsorption phase is high, the oxygen content of the outflow gas is high. When the adsorption column is long enough, oxygen of certain purity can be produced, and the molecular sieve can be regenerated by means of decompression desorption<br>