1. Nitrogen production from cryogenic air separation:
Cryogenic air separation is a traditional method of nitrogen production, which has a history of nearly several decades. It uses air as raw material, compresses, purifies, and then uses heat exchange to liquefy air into liquid air. The liquid air is mainly a mixture of liquid oxygen and liquid nitrogen. The boiling point of liquid oxygen and liquid nitrogen is different (at 1 atmosphere, the boiling point of the former is - 183 C, and the latter is - 196 C). Nitrogen is separated by distillation of liquid air. The cryogenic air separation nitrogen machine is complex, covers a large area, has a high capital construction cost, a large one-time investment in equipment, a high operating cost, a slow gas production (12-24 hours), high installation requirements and a long period. The investment scale of PSA units with the same specifications is 20%-50% lower than that of cryogenic air separation units for equipment under 3 500 Nm3/h, including comprehensive equipment, installation and infrastructure. The cryogenic air separation nitrogen machine is suitable for large-scale industrial nitrogen production, while the medium and small-scale nitrogen production is not economical.
2. Nitrogen production from molecular sieves by air separation (PSA or PSA):
In the nitrogen machine below 3000Nm3/h, it is quite competitive and more and more welcomed by small and medium-sized nitrogen users. PSA nitrogen production has become the preferred method for small and medium-sized nitrogen users. Because, using air as raw material, carbon molecular sieve as adsorbent, using pressure swing adsorption principle, using carbon molecular sieve to selectively adsorb oxygen and nitrogen to separate nitrogen and oxygen, commonly known as PSA nitrogen production. This method is a new nitrogen production technology developed rapidly in the 1970s. Compared with the traditional nitrogen production method, the process is simple, highly automated, fast gas production (15-30 minutes), low energy consumption, product purity can be adjusted in a larger range according to user needs, easy operation and maintenance, low operating cost, and strong adaptability of the device.
3. Nitrogen production by membrane air separation (hollow fiber membrane separation):
Using air as raw material, oxygen and nitrogen are separated by different permeation rates of gases with different properties such as oxygen and nitrogen under certain pressure. Compared with other nitrogen machines, it has the advantages of simpler structure, smaller volume, no switching valve, less maintenance, faster gas production (<3 minutes), convenient capacity increase, etc. It is especially suitable for medium and small nitrogen users whose nitrogen purity is less than 99.5%, and has the best function-price ratio. When the purity of nitrogen is above 98%, the price of PSA nitrogen machine is 15% higher than that of PSA nitrogen machine of the same specification.