This is an air separation process adopting cryogenic air separation units, which mainly produces high-purity nitrogen with liquid oxygen as a by-product. Raw air sequentially passes through air filters, air compressors, cooling towers in the air pre-cooling system, heat exchangers, fractionators, cooling evaporators and rectification units to yield high-purity nitrogen (and high-purity oxygen). The finished gas is then compressed and filled into cylinders or delivered to production lines.