Why does a sudden increase in the pressure of a distillation column lead to an increase in the temperature at the bottom of the column? And why does an increase in pressure result in an increase in the temperature at the top of the column?
Thread Content
I hope the experts on the forum can explain it.
To put it vividly, the higher the pressure, the more vigorously the molecules move, and thus the temperature rises. Also, according to PV=nRT, with all other parameters constant, P and T are directly proportional
Pressure is rising. It means that the saturated vapor pressure inside the tower rises. The corresponding equilibrium saturation temperature (dew point) will rise.
It’s really frustrating: first, an increase in the temperature at the bottom of the tower causes the temperature at the top of the tower to rise as well (the reflux at the top remains unchanged, and so does the reflux in the middle section). As a result, more and more material evaporates from the top of the tower! Since it’s all gas, the amount of distillate at the top increases. With the outlet pipe at the top remaining unchanged, the pressure drop increases, and therefore the pressure at the top of the tower rises!...
It’s not that those who study petrochemical engineering don’t understand it... haha
In a distillation system, pressure is directly proportional to the boiling point of the components; therefore, as the pressure at the top of the tower increases, the temperature at the bottom of the tower becomes equal to the boiling point of the mixture, causing the temperature at the bottom of the tower to rise as well. As for the increase in the top temperature of the tower, it is mainly caused by these three situations: 1. Insufficient cooling capacity of the coolant at the tower top; 2. Excessive heating in the bottom of the tower or at the medium-boiling point, which causes heavier components to rise upward; 3. The presence of non-condensable gases, which affects both the efficiency of the tower and the heat exchange efficiency of the condenser at the tower top. Under normal conditions, as the tower pressure increases, the temperature at the bottom of the tower will certainly rise, but the top temperature may not necessarily increase as long as there is sufficient coolant
It must be the change in temperature that causes the change in pressure