fractionation
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What is the difference between top cold reflux and top circulating reflux?
The temperature of the circulating reflux is slightly higher; essentially, it is the return flow of the liquid phase after cooling. The cold reflux, on the other hand, is the reflux of the gas phase after cooling, and its temperature is generally lower than that at the top of the tower. The temperature of the circulating reflux is usually similar to that of the reflux at the top of the tower. In general, cold reflux has a greater impact on the gas-liquid equilibrium compared to circulating reflux.
Both reflux systems can control the temperature at the top of the tower. The top circulation is used during normal production; it serves to remove the excess heat from the distillation tower and to control the temperature at the top, thereby ensuring that the dry point of the crude gasoline meets the required standards. Cold reflux is used only in emergency situations, such as when the slurry circulation is interrupted and there is a risk of overpressure in the distillation tower
More or less, there’s not much difference. Both recirculations are used to control the top temperature. It’s just that there is a sequence to the adjustments, mainly due to considerations of thermal balance.
The differences are quite significant; there are variations in terms of composition, quantity, and usage!
Cold reflux is used for controlling the top temperature during normal startup and shutdown operations; it is typically applied to gasoline products as an abnormal operation method for regulating the tower top temperature. Circulating reflux is used as a normal control method for the tower top product, with the medium being top circulation oil.
Both are set by controlling the temperature of the fractionation tower; the amount of top reflux is relatively large, and the temperature is around 100 degrees. The top reflux helps to establish a vapor-liquid equilibrium at the top of the tower, thereby ensuring that the dry point of the crude gasoline at the tower top meets the required standards. The temperature of the cold reflux is around 25 degrees, and it is used to assist the top reflux in controlling the temperature at the top of the tower; its usage amount is relatively small. At the same time, unqualified crude gasoline is used for reprocessing.