How are the flow and outlet temperature of circulation determined?

Ring flow is determined by the heat balance of switching heat exchanger (or cooler) according to the requirement of air separation process. Under the condition that the temperature difference between the cold end and the hot end is certain, the larger the circular flow is, the lower the outlet temperature of circulation is; when the outlet temperature of circulation increases, the circular flow tends to decrease.
As for expansion machine, expansion air is composed of circulation air and bypass air. When the cooling loss of the air separation unit is certain, when the outlet of circulation drops to a certain temperature, the circular flow will increase to be equal to the expansion. If we continue to lower the outlet temperature of circulation, it is not allowed that the circulation flow is larger than the expansion. Therefore, there is a allowed minimum outlet temperature of circulation for a certain cold loss. As the cooling loss of the unit decreases, the allowed minimum outlet temperature of circulation will increase. This shows that the determination of the outlet temperature of circulation is related to the cooling loss of the device. The capacity of the unit increases, the cold loss decreases correspondingly, and the temperature of the circulation outlet can increase. Some equipments can be increased from-120℃ to-90℃.
When adding oxygen and nitrogen Liquidators, the cooling amount of pure nitrogen and pure oxygen flowing back will decrease, the cooling amount released by circulation air will increase, and the minimum allowable temperature of circulation air outlet will increase accordingly.
The determination of the outlet temperature of circulation should also consider the actual situation of the length of the cold and hot section of the heat exchanger. With the rise of the outlet temperature of circulation, the length of the cold section relative to the hot section also gradually increases, and the two tend to be equal.