| 摘要 |
PROBLEM TO BE SOLVED: To recover reflux liquid required for high-pressure distillation at high recovery percentage, by supplying fluid abundant in liquefied nitrogen as the reflux liquid of a low-pressure tower, and discharging oxygen and nitrogen separated in a low-pressure tower, heating it by the heat exchange with material air, and recovering them as oxygen gas and nitrogen gas. SOLUTION: Nitrogen gas for boosting introduced into an expansion turbine 12 is lowered in temperature, depressurized by adiabatic expansion to generate cold required for process, and is led to a condensing evaporator 13 provided at a low-pressure middle part 7b through a path 45, evaporates the falling liquid flowing down within the low-pressure tower 7, also liquefies itself into liquefied nitrogen, and passes through a path 46. The nitrogen gas is depressurized into 3.7 kgf/cm<2> abs with a valve 47a, joins the path 30 for liquefied nitrogen returning from a high-pressure tower 5, and is led into the apex of the low-pressure tower 7. What is more, the pressure of the expansive nitrogen gas coming out of the expansion turbine 12 is set, so that the temperature difference between the boiling-point temperature of the falling liquid in the condensing evaporator 13 and the liquefaction temperature of the expansive nitrogen gas may come to the specified temperature. |
