Nitrogen production by cryogenic air separation is a traditional method for nitrogen production, which has a history of several decades. It takes air as raw material, compresses and purifies it, then liquefies air into liquid air by heat exchange. Liquid air is mainly a mixture of liquid oxygen and liquid nitrogen. According to the different boiling points of liquid oxygen and liquid nitrogen (the boiling point of the former is - 183 ℃, the latter is - 196 ℃), the liquid air is distilled and separated into nitrogen.

The cryogenic air separation nitrogen plant is complex, with large floor area, high infrastructure cost, high one-time investment, high operation cost, slow gas production (12-24 h), high installation requirements and long cycle. Considering the factors of equipment, installation and infrastructure, the investment scale of PSA equipment with the same specification for equipment below 3500nm3 / h is 20% - 50% lower than that of cryogenic air separation unit. Low temperature nitrogen separation unit is suitable for large-scale industrial nitrogen production, but small and medium-sized nitrogen production is not economical.