Deep cooling nitrogen production has a history of nearly a hundred years, and the process flow is constantly improving. Pressure swing adsorption nitrogen production is a technology developed in recent decades and widely accepted by the market. This article compares the differences between the two in terms of processes, costs, operations, and product types, and draws relevant conclusions. 1. The typical process flow of cryogenic nitrogen production: The entire process consists of air compression and purification, air separation, and liquid nitrogen vaporization. The compressed and purified air enters the air compressor after being cleaned of dust and mechanical impurities through an air filter, compressed to the required pressure, and then sent to the air cooler to reduce the air temperature. Then enter the air drying purifier to remove water, carbon dioxide, acetylene, and other hydrocarbons from the air. Air separation: The purified air enters the main heat exchanger in the air separation tower and is cooled to saturation temperature by the reflux gas (product nitrogen, waste gas). It is then sent to the bottom of the distillation tower to obtain nitrogen gas at the top of the tower. The liquid air is then throttled and sent to the condensation evaporator for evaporation. At the same time, some of the nitrogen gas sent by the distillation tower is condensed. Part of the condensed liquid nitrogen is used as the reflux liquid of the distillation tower, and the other part is used as the liquid nitrogen product to exit the air separation tower. The exhaust gas from the condensation evaporator is reheated by the main heat exchanger to about 130K and enters the expansion and refrigeration unit to provide cooling capacity for the air separation tower. A portion of the expanded gas is used for regeneration and cooling of the molecular sieve, and then discharged into the atmosphere through a silencer. Liquid nitrogen vaporization: The liquid nitrogen from the air separation tower enters the liquid nitrogen storage tank for storage. During maintenance of the air separation equipment, the liquid nitrogen in the storage tank enters the vaporizer and is heated before being sent to the product nitrogen pipeline. Cryogenic nitrogen production can produce nitrogen with a purity of 99.999%. 2. Main Equipment Introduction: Air Filter: In order to reduce the wear and tear of the mechanical movement surface inside the air compressor and ensure air quality, air must first pass through the air filter to remove dust and other impurities before entering the air compressor. At present, air compressors mostly use coarse efficiency filters or medium efficiency filters for air intake. Air compressors: According to the working principle, air compressors can be divided into two categories: volumetric and velocity compressors. At present, air compressors mostly use reciprocating plug type air compressors, centrifugal air compressors, and screw type compressed air coolers: they are used to reduce the temperature of compressed air before entering the air drying purifier and air separation tower, avoid significant fluctuations in the inlet temperature, and can analyze most of the moisture in the compressed air. Usually, nitrogen water coolers (consisting of a water cooling tower and an air cooling tower: the water cooling tower cools the circulating water with the exhaust gas from the air separation tower, and the air cooling tower cools the air with the circulating water from the water cooling tower) and Freon air coolers are used. Air drying purifier: Compressed air still contains a certain amount of water, carbon dioxide, acetylene, and other hydrocarbons after passing through the air cooler. Deposition of frozen water and carbon dioxide in the air separation tower can block channels, pipelines, and valves. Acetylene accumulation in liquid oxygen poses a risk of explosion, and dust can wear and tear the operating machinery. In order to ensure the long-term safe operation of the air separation unit, specialized purification equipment must be installed to remove these impurities. The most commonly used methods for air purification are adsorption and freezing. At present, molecular sieve adsorption method is widely used in small and medium-sized nitrogen production plants in China.
