| 摘要 |
PURPOSE: To improve the energy efficiency of an air circulation liquefying device by a method wherein after nitrogen compressed at a specified pressure is cooled through indirect heat-exchanger with a process vapor flow, the nitrogen is expanded. CONSTITUTION: High pressure tower supply flows 106 and 510 are rectified to produce high pressure tower region nitrogen of a flow 10 and high pressure coarse liquid oxygen tower bottom liquid of a flow 5. Low pressure tower supply flows 910, 84, 15, and 16 are distilled to produce low pressure tower top nitrogen of a flow 130 and produce low pressure liquid oxygen tower bottom liquid. To meet the requirements of nitrogen reflux and/or a liquid nitrogen product of a process, at least a part of tower top nitrogen from a distillation tower device is compressed to a pressure higher than 200 PSia [1.38 MPa (an absolute pressure)] and preferably to a pressure higher than a nitrogen critical pressure of 492.9 PSia [3.40 MPa (an absolute pressure)]. Thereafter, the nitrogen is expanded immediately after the nitrogen is cooled through indirect heat- exchange with a process vapor flow.
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