There are generally two types of distillation tower for producing pure oxygen and pure nitrogen at the same time:
1) With auxiliary tower section. It is to add an auxiliary tower at the top of the upper tower, extract a large amount of distillate (dirty nitrogen) at the lower part of the auxiliary tower, and a small amount of steam will further enter the auxiliary tower for separation, and 99.99% pure nitrogen will be obtained at the top. In order to ensure the purity of pure nitrogen, a part of distillate liquid nitrogen is usually extracted from the middle of the lower tower, and the tray is appropriately increased to ensure the purity of pure liquid nitrogen at the top. It is usually used for pure nitrogen and pure oxygen products with a ratio greater than 1.1. The characteristics of this process are relatively simple, but increasing the number of trays will increase the resistance, increase the exhaust pressure of the air compressor, and increase the power consumption.
2) With pure nitrogen tower. It is a separate nitrogen purification tower, which extracts part of nitrogen from the top of the lower tower, and further distills it in the nitrogen purification tower. The purity of nitrogen can reach 99.99%. It is usually used to produce a small amount of high-purity nitrogen. Since this process has low requirements for the nitrogen purity at the top of the lower tower, the lower tower pressure required to ensure the temperature difference of the main cooling tower can also be reduced. At the same time, the number of trays in the upper and lower towers can be reduced, which can further reduce the pressure in the lower tower and reduce the power consumption. However, the process equipment is slightly more complex.
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