Main system composition of gas separation equipment

The low-pressure gas separation equipment is composed of four main systems: air compression system, impurity purification and heat exchange system, refrigeration system and liquefaction rectification system. The corresponding mechanical equipment includes air turbine compressor, air cooling tower, turbine expander and fractionation tower. The working principle of the low-pressure gas separation equipment is based on the liquefaction cycle and rectification theory. The incoming air is first compressed and cooled by the air cooling tower of the turbine compressor to a pressure of 0.5 MPa and a temperature of about 303k, and then enters the switching heat exchanger (E1 and E2). The two heat exchangers can remove water and carbon dioxide in the air and conduct heat exchange. The air is cooled to a temperature close to the liquefaction temperature (101K) and then sent to the lower tower, Part of the air is extracted from the lower tower and sent to the heat exchanger (E2) for heating. The heated air joins with a small amount of cold air from the lower tower and enters the turbine expander for adiabatic expansion to generate the required cooling capacity, which is then sent to the upper tower for rectification. The remaining air is preliminarily rectified in the lower column. Liquefied air containing 38% oxygen is obtained at the bottom, pure liquid nitrogen containing 99.99% nitrogen is obtained at the top of the lower tower, and dirty liquid nitrogen containing about 95% nitrogen is obtained at the middle. Liquefied air, pure liquid nitrogen and dirty liquid nitrogen are respectively extracted from the lower column and depressurized to about 0.05 MPa through the throttle valve, and then sent to the upper column as reflux liquid. Here, the second deep low-temperature rectification is carried out to obtain high-purity oxygen containing 99.6-99.8% oxygen at the bottom of the upper column. It flows through the heat exchanger (E4, E2, E1) to exchange heat with the air, and is discharged out of the column after being heated to atmospheric temperature. High purity nitrogen with 99.999% nitrogen is obtained at the top of the upper column, and sewage nitrogen with about 96% nitrogen is obtained at the middle of the upper column. All of them are reheated to atmospheric temperature by heat exchangers (E3, E4, E2, E1) and then discharged to the unit.