Reflux temperature

If the reflux temperature is too low, it will result in excessive load after cooling, which is not conducive to energy savings and cost reduction； On the contrary, excessively high temperatures make it difficult to control the top temperature of the tower, which hinders timely and effective adjustment operations.

Reflux provides the conditions for gas-liquid phase contact; the reflux rate and the temperature of the reflux returning to the column directly affect the overall thermal balance of the column, thereby influencing the quality of the distillation process. In a catalytic fractionation tower, the amount of reflux and the temperature of the reflux returning to the tower are determined by the overall thermal balance of the tower. As the temperature conditions within the tower change, appropriately adjusting the amount of reflux at the tower top and the reflux temperature is a means of maintaining temperature equilibrium at the top of the tower, thereby achieving the goal of controlling product quality. During normal adjustment, the focus is on adjusting the temperature of the reflux returning to the tower.

What temperature is appropriate for controlling the temperature of the return fluid? Some factories keep it around 75°C, while others keep it at 50°C? Why is the difference so big?

A high reflux temperature increases the load on the top of the tower, resulting in product flash points that do not meet the specifications. Excessively high temperatures, especially with light fluids, can also cause cavitation and vacuum conditions in the pumps

The methods of condensation cooling at the top of the tower are divided into primary condensation and secondary condensation. The former uses cold reflux, while the latter uses hot reflux. The reflux temperature of the latter is higher than that of the former.

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The reflux temperature is typically set at 40°C. A lower reflux temperature yields better separation results, while a higher reflux temperature results in relatively poorer separation performance. In particular, reducing the temperature after air cooling will **lower the pressure at the top of the tower, thereby significantly improving the separation efficiency. Supercooling control is recommended, but it isn’t necessary to go too low

This post was last edited by microchen on 2012-2-24 at 14:20. 1. The cold reflux temperature is determined relative to the dew point temperature of the product at the top of the tower; generally, as long as it is lower than this dew point temperature, it can be considered cold reflux (of course, this is related to pressure as well). 2. The function of reflux is to remove heat from the top of the tower, thereby enabling liquid phase reflux within the tower. The heat removed at the tower top is mainly latent heat; for reflux, the reflux temperature has a very minor impact on separation accuracy. 3. The different temperatures of the reflux tank depend primarily on the phase equilibrium within that tank; to prevent excessive loss of light components, a lower temperature is usually required. 4. If there are no light components present, it doesn’t matter if the temperature is higher, as long as the product at the top of the tower is cooled to a safe temperature before being sent to the storage area (or elsewhere). The advantage of this is that it reduces the heat exchange area required for air or water cooling at the top of the tower, thereby saving on investment costs. 5. Additionally, for some distillation towers, an excessively low reflux temperature can be detrimental to the distillation process, as it causes the uppermost trays in the tower to function as heat exchange surfaces, reducing the efficiency of those trays. (It is best for the liquid phase reflux in the tower to occur around the saturation temperature, as this facilitates the mass transfer process.)