The effect of the reflux ratio in a distillation column on the column

An increase in the reflux ratio does indeed directly raise the liquid-vapor ratio in the distillation section (the part from the top of the tower to the feed point), as more liquid is circulated back to the top of the tower for re-evaporation. However, the situation is different for the stripping section (the part from the feed point to the bottom of the tower). As the reflux ratio increases, although the amount of liquid returning from the top of the tower increases, at the same time the total volume of the returning fluid also increases due to the condensation of the vapor at the tower top, which results in an increase in the mass flow rate of the liquid in the section below the raw material feed inlet. However, the key point is that although the total amount of liquid increases, since the amount of product taken from the top of the tower (i.e., the distillate) does not increase significantly or remains unchanged, the amount of steam generated from the feed point to the bottom of the tower does not change significantly. This results in a decrease in the liquid-to-vapor ratio (the ratio of liquid flow rate to gas flow rate), because although the amount of liquid increases, the amount of gas does not increase in proportion. In simple terms, an increase in the reflux ratio results in more liquid at the top of the tower, but the amount of gas produced at the bottom does not increase in proportion, which leads to a decrease in the liquid-to-vapor ratio in the stripping section. .

Personally, I feel that discussing this topic from an operational perspective is off-topic unless it is for theoretical design purposes. The distillation in a tower is designed to allow for load adjustments within a certain range, depending on the various operating conditions. During adjustment, the distillation conditions can be modified by referring to the composition levels in the gas/liquid phases; in other words, adjusting the purity of the gas and liquid to meet the required standards is the simplest way to understand this process. If one focuses only on terms such as the stripping section, distillation section, and reflux ratio, the process conditions specified for tower design will be overlooked. These are personal opinions for reference only.

This post was last edited by weilongwu on 2024-8-19 07:44. The fundamental cause of this problem is determined by the TXY diagram.

An increase in the reflux flow rate in the distillation section leads to an increased load on that section, and accordingly, the liquid-to-gas ratio decreases