The raw air is passed through an air filtration system to remove dust and mechanical impurities, and the filtered air is compressed by a multi-stage turbocompressor with an intercooler to the required pressure for the process. The compressed air is cooled and cleaned by two layers of cooling water in an air cooling tower of small air separation unit. Chemical impurities in the compressed air that are soluble in water are also absorbed by the falling cooling water cleaning. The remaining impurities in the air, such as water vapor, carbon dioxide, nitrous oxide and potentially harmful hydrocarbons, are adsorbed as they pass through two adsorbers equipped with molecular sieves. This part of the process does not differ from the conventional process.
The dry purified air exiting the molecular sieve purification unit is cooled to near condensing temperature into the pressure tower by the returning dirty nitrogen and product gas in the main heat exchanger unit of small air separation unit. The cooling of the cryogenic air separation process is generated by the nitrogen circulation system. Nitrogen from the top of the pressure tower and the turbine expander is reheated in the main heat exchanger, compressed by a nitrogen cycle compressor, and cooled in an after-compressor cooler. One stream from the medium pressure stage is further compressed in a turbine booster directly braked by the turbine expander, cooled by the booster aftercooler and then cooled in the main heat exchanger, and then expanded by the turbine expander into the gas-liquid separator, where the gas nitrogen is reheated and returned to the inlet side of the circulating compressor and the liquid nitrogen is sent to the top of the low pressure tower of small air separation unit.
