Cryogenic air separation nitrogen production uses air as raw material, which is compressed, purified and heat exchanged to liquefy gas air into liquid air. Liquid air is mainly a mixture of liquid oxygen and liquid nitrogen. Liquid oxygen and liquid nitrogen have different boiling points and are separated by distillation to obtain nitrogen.
1.Air compression and purification
The air passes through the air strainer to remove dust and mechanical impurities, then enters the air compressor, compresses to the required pressure, and then goes to the air cooler to reduce the air temperature. It then enters the air drying purifier to remove moisture, carbon dioxide, acetylene and other hydrocarbons from the air.
2.Air separation
The purified air enters the main heat exchanger in the air separation column, and is cooled to the saturation temperature by the reflux gas (production nitrogen gas, waste gas), and is sent to the bottom of the distillation column. The nitrogen is obtained from the top of the column. After throttling, the liquid air is sent to the condensing evaporator for evaporation. At the same time, part of the nitrogen from the refining column is condensed. One part of the condensed liquid nitrogen is used as the reflux of the rectifying column, and the other is used as the reflux liquid of the rectifying column, and some of them are taken out of the air separation column as liquid nitrogen products.
The exhaust gas from the condensing evaporator is reheated to about 130K through the main heat exchanger, and then enters the expander for expansion and refrigeration, thus providing cooling capacity for the air separation column. Part of the expanded gas is used for regeneration and cold blowing of molecular sieve, and then discharged to the atmosphere through the muffler.
3.Vaporization of liquid nitrogen
The liquid nitrogen from the air separation column enters the liquid nitrogen storage tank for storage. During the maintenance of the air separation unit, the liquid nitrogen in the storage tank enters the vaporizer and is heated, and then sent to the product nitrogen pipeline. The nitrogen with purity of 99.999% can be produced by the above process of low temperature and high purity nitrogen.
