DEAR Cryogenic air separation unit.The lower tower needs a larger reflux ratio to ensure the quantity and purity of pure liquid nitrogen, and then it is sent to the upper tower as reflux liquid. In this process, the unit cooling capacity of the expanded refrigerant is higher, and the expansion capacity is smaller on the premise of compensating the same cooling loss.Swirl plate. It consists of several swirling trays with metal structure. This kind of structure has little resistance and will not be damaged. It has been used as an improved one for quite a long time. But the heat transfer effect is not as good as packed tower. Sieve tray tower. The drenching tray with larger diameter and spacing is adopted. Both nitrogen and water pass through the screen. Because the water cooling tower does not work continuously and stably, the cooling effect is not ideal, so it is no longer used.DEAR Cryogenic air separation unit.The gas in the channel does not switch, so a higher flow rate can be adopted in the design to improve the heat transfer coefficient, and the heat transfer temperature difference of the cross section is not limited by the self cleaning condition. In order to reduce the loss of incomplete recovery of cooling capacity at the hot end, the temperature difference at the hot end is still small (2 ~ 3 ℃).
DEAR Cryogenic air separation unit.For the oxygen generator with switching heat exchanger process, in order to achieve the self removal of water and carbon dioxide, the amount of nitrogen in the waste gas is relatively large, so as to ensure the non freezing condition. Therefore, the amount of pure gas nitrogen product is less, which can only reach 1.3 times of the gas oxygen production at most.Low temperature liquid evaporator has atmospheric type and steam water bath type. The atmospheric evaporator is composed of finned evaporation tubes, which are placed in parallel in several groups and have a large volume. With the flow of low temperature liquid, the surface of evaporation fin will be frosted gradually. The frost should cover the evaporator surface.But this point in the actual operation of the pipe network, if not careful operation is difficult to achieve. The correct way is as follows: before the shutdown, remove the short pipe (made of stainless steel) behind the vent valve (50 ~ 100 mm), and clean it with chloroalkane solvent to prevent combustible materials in the pipe;
The liquid oxygen absorbs the latent heat of condensation released by the gas nitrogen with higher temperature and evaporates. So it is called "condensing evaporator". Condensing evaporator is an important heat exchange equipment in distillation system. Its working quality is related to the power consumption and normal production of the whole air separation unit. Therefore, it is necessary to correctly operate and maintain the condensing evaporator.DEAR Cryogenic air separation unit.In the plate type 6000m3 / h air separation plant, the air flow is only 33000m3 / h, while the annular flow is 5200m3 / h, resulting in air liquefaction at the cold end of the switching heat exchanger. When the circulating flow is reduced to 3400m3 / h, the gas distribution of each unit is reasonable, and the liquefaction phenomenon disappears. In addition, it is also related to the performance of liquid air subcooler, liquid nitrogen subcooler and liquefier.For high and medium pressure units, the cooling capacity is relatively rich, and the increase of expansion capacity does not affect the distillation. Therefore, the extraction amount of argon fraction can reach 25% - 28% of the processing air volume, and the extraction rate of argon can reach 60%. The highest argon extraction rate of molecular sieve purification unit is 87%.
