[2026 Distillation Technology] Adjustment of Distillation Column Process Parameters and Influencing Factors (5)
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『5』How is the top temperature adjusted in distillation operations? The top temperature of the tower is an important factor determining the quality of the product at the tower top. With the column pressure remaining constant, an increase in the top temperature leads to an increase in the content of heavier components in the product at the top of the column, resulting in a decline in its quality.
There are mainly two methods for adjusting the tower top temperature: one is to keep the reflux flow rate constant and adjust the reflux temperature； One method is to fix the reflux temperature and adjust the reflux flow rate.
As production facilities become increasingly large, methods for adjusting the reflux volume have been widely adopted to ensure production stability. The specific adjustment methods are as follows: ① Control the top temperature using the backflow rate. The reflux flow increases and the top temperature decreases; this control method is commonly used when the tower top is a total condenser. ②When the refrigerant used at the tower top undergoes a phase change during heat transfer, the top temperature can be controlled through cascade regulation of the evaporation pressure of the refrigerant and the top temperature. As the evaporation pressure decreases, the corresponding evaporation temperature also drops, resulting in a decrease in the top temperature. This method can change the reflux flow rate when the top condenser is a fractional condenser ； When there is subcooling in the tower top condenser, it can also be used to adjust the reflux temperature. ③When there is no phase change in the refrigerant at the top of the tower during heat transfer, the top temperature can be controlled through cascade control of the refrigerant flow rate and the top temperature. As the flow rate increases, the maximum temperature decreases. This method can change both the reflux rate and the reflux temperature. ④Adjust the top temperature using the heat exchange area of the top condenser. Raising the refrigerant level increases the heat exchange area and lowers the top temperature. This method can change both the reflux rate and the reflux temperature. ⑤When the material concentration in the distillation section is high, the temperature at the top of the column can be adjusted using the temperature difference between two plates. The temperature difference increases, the amount of reflux liquid rises, and the top temperature decreases.