Air separation method of air separation plant
The main components of air are oxygen, nitrogen, argon, carbon dioxide and some other gases and impurities. They exist in the air in the form of molecules, in large numbers, and have never stopped moving irregularly. There are three main methods for mixing them together and separating them uniformly: cryogenic, adsorption and membrane separation.
The cryogenic air separation unit has the advantages of stable operation, low maintenance cost, simple operation, large output adjustment range and high product quality, and can produce liquid as a backup product.
liquid nitrogen
The principle of low temperature air separation method is that according to the different boiling points of each component in the air, through pressure precooling and purification, use the maximum cooling capacity provided by the turbine to liquefy, and then rectify to obtain the required liquid oxygen, oxygen, nitrogen, liquid Nitrogen and other noble gases. The specific principle is that the purified air is cooled to the condensation temperature in the cold box, and then enters the rectification tower for rectification. As rising gas, the fluid descending from the top of the tower undergoes heating and mass exchange. The cryogenic liquid absorbs heat and begins to evaporate. The nitrogen component vaporizes first, and the higher temperature gas condenses, releasing the heat of condensation. When the gas condenses, the oxygen component is condensed first. This process continues until the gas and liquid reach equilibrium. At this time, the nitrogen component decreases due to the evaporation of the liquid phase, and the oxygen concentration in the liquid phase increases due to the condensation of the gas into the liquid phase. At the same time, due to the condensation of the gas phase, the oxygen component decreases, and nitrogen in the liquid phase enters the gas phase, so that the nitrogen concentration in the gas phase increases. Repeating the above process many times, the nitrogen concentration in the gas phase increases, and the liquid oxygen concentration also increases. Therefore, after a lot of evaporation and condensation, the whole rectification process can be completed, and the oxygen and nitrogen in the air can be separated.
The cryogenic separation of the air separation unit can produce gaseous and liquid oxygen, nitrogen, argon and other products at the same time, and the extraction rate is high. The maintenance cost of the equipment is extremely low, and it can run continuously for 2 years without downtime (multiple XLA units have been running continuously for 15 years, no need for large heating and no replacement of molecular sieve and alumina). The service life of the valve is nearly 20 years, and the service life of the adsorbent can be up to more than eight years in normal operation (with usage records). The price of the adsorbent is very cheap, and the cost of the whole set of equipment is less than 1%.
