Liquid oxygen self-cyclic adsorption can be divided into three types according to different heat sources of thermal siphon evaporator:
1) use the gas and nitrogen of the lower tower as the heat source. The liquid oxygen in the thermal siphon evaporator (plate or tube type) is partly evaporated due to the condensation and heat release of gas and nitrogen, forming the self-circulation of liquid oxygen. According to information introduction, the cycle rate of liquid oxygen can reach more than 6 times, so that the content of acetylene and other hydrocarbon in liquid oxygen can meet the explosion-proof requirements through adsorption.
Condensate liquid nitrogen can flow back into the lower tower, or be sent to the top of the upper tower after throttling. The advantage of this type is that it can be used as auxiliary condensing evaporator, which has no influence on the rectification condition of the tower, and the heat transfer coefficient is relatively high. In order to overcome the resistance of circulation circuit, its position is lower than that of main condensing evaporator. Its disadvantage is that due to the small heat transfer temperature difference, the required heat transfer area is relatively large, which is about more than 10% of the total area of the condensing evaporator. This type has been adopted at home and abroad at present.
2) Since then, saturated air of switching heat exchanger has been used as heat source. After the air is heated and condensed, it goes back to the bottom of the tower. Its advantage is that the heat transfer temperature difference of the thermal siphon evaporator is relatively large, and under the condition that the circulation rate of liquid oxygen is also 6, the required heat transfer area can be several times smaller. The disadvantage is that when the liquid empty goes back to the tower, the purity of the liquid empty at the bottom will decrease, which will have some influence on the rectification working condition of the tower.
3) use the inflated overheated air as the heat source. It makes the liquid oxygen in the thermal siphon evaporator partly evaporate, forming the liquid oxygen self-cyclic adsorption, and its cycle rate can also meet the requirements.
The advantage of this kind of heat source is that the heat transfer temperature difference is large, and the expansion air after the thermal siphon evaporator enters the upper tower in a nearly saturated state, which is beneficial to the rectification. The disadvantage is that the air side of the thermal siphon evaporator has no phase change, the heat transfer coefficient is small and the required heat transfer area is relatively large. In addition, it increases the pressure after the expansion machine and reduces the enthalpy drop in the expansion machine. For the same refrigerating capacity, the expansion should be increased.
