Process for recovering nitrogen in low pressure type air separation apparatus

摘要

In a low pressure type air separation apparatus provided with a reversing heat exchanger for removing water vapor and carbon dioxide gas in feed air, a nitrogen gas taken out of a high pressure column in a duplex type rectification tower is led to an expander for generating subcooling for the air separation apparatus, and the effluent nitrogen gas is obtained under a predetermined pressure by controlling a pressure of the effluent gas from the expander. The effluent nitrogen gas is adjusted to a temperature satisfactory for the inlet temperature conditions for the reversing heat exchanger by passing the effluent nitrogen gas through a heat exchanger, and then is passed through the reversing heat exchanger, whereby the effluent gas from the reversing exchanger is obtained as a product nitrogen gas under a predetermined pressure.