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KDON-350/800 ASU adopts a complete low-pressure process, with detailed process description as follows:
Feed air is sucked into the air filter from the atmosphere, where the contents of dust and other mechanical impurities are being removed, before entering an oil-free air compressor, and through two stage compression, it is pressurized up to a pressure of ~0.7MPa (Gauge); upon being cooled in the after-cooler, it enters the pre-cooling unit where it is pre-cooled to a temperature of 5~10ºC, before being inlet to a switch-over molecular sieve adsorption unit, where the contents of moisture, CO2, hydrocarbons in the air are being adsorbed. Molecular sieve adsorption unit is made up of two vessels filled with molecular sieve: when one vessel is working, the other is being regenerated in an electrical heater for its molecular sieve by the waste nitrogen from the cold box.
The purified air, except that a small portion is used as bearing gas for airshaft expansion turbine, all the rest enters the cold box for air separation. In the main heat exchanger, it is cooled by gas refluxes (pure oxygen, pure nitrogen, & waste nitrogen, etc.) Part of air being withdrawn from the middle level of the main heat exchanger, enters expansion turbine for expansion and refrigeration. A major part of the expanded air thru expanding in the sub-cooler, is cooled by the oxygen in the LP column before sending to LP column. The remaining small part goes by-pass directly into the waste-nitrogen circuit, and then discharged out of cold box after being re-heated. Rest of the process air is continuously cooled in the main heat exchanger to reach close to liquefied air temperature before entering the MP column.
In the MP column, the air is being initially separated into nitrogen and oxygen enriched liquefied air. GAN is being condensed and liquefied in the main condenser, and meantime LOX at the low-pressure side of the main condenser is being vaporized. Part of LIN is used as MP column reflux, the remaining LIN is drawn from top of the MP column, and through liquefied air LIN subcooler, it is subcooled with pure nitrogen and waste nitrogen and throttled before being sent to top of the LP column. Liquefied air after being sub-cooled and throttled is being sent to middle level of the LP column as reflux.
Oxygen production is drawn at the lower level of the LP column, and thru expansion air sub-cooler and main heat exchanger reheating, it is then delivered out of the column. Waste nitrogen is drawn at the upper level of the LP column, and after being reheated in the sub-cooler and main heat exchanger, it is then delivered out of the column, with some part used as the regeneration gas for the molecular sieve adsorbers. Pure nitrogen is delivered at the top of the LP column, and thru reheating in the liquefied air / liquefied nitrogen subcooler and the main heat exchanger, it is delivered out of the column.
Oxygen out of the distillation column is pressurized by the oxygen compressor up to a specified pressure before being delivered to the end-user.
KDON-350/800 Air Separation Plant