Those who understand distillation towers, come and take a look to help me clear up my doubts
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Reducing the tower pressure lowers energy consumption and improves separation efficiency, but at the same time it reduces the tower’s processing capacity. Is this statement correct?
A decrease in pressure reduces the amount of hot water required in the reboiler, thereby lowering heat consumption; however, it increases the cooling load on the top condenser, as it is more difficult to achieve condensation at lower pressures.
Reducing the pressure in the tower is mainly achieved by controlling the boiling point of the material; this helps to lower the energy consumption of the tower, but it has little impact on the tower’s processing capacity. For example, if a distillation tower has a processing capacity of 10 tons, and it is operating at full capacity with a tower pressure of 10 kPa, a temperature of 160 degrees in the bottom of the tower may be required to achieve good separation results; in such cases, 20 cubic meters of heat transfer oil might be necessary. But when we increase the pressure in the tower to 5 kPa, 130 degrees in the tower bottom should be sufficient, and 15 cubic meters of heat transfer oil will be enough. (The numbers are made up; that’s the reason.)
But whether it is 10 kPa or 5 kPa, our feed volume remains at 10 tons
It depends on the properties of the material; then it is necessary to calculate whether the amount of steam and condensed water required is cost-effective. The processing capacity shouldn’t matter much; what’s important is energy consumption and the protection of the materials.
It’s correct under certain circumstances; such issues cannot be considered in isolation, otherwise it makes no sense. This statement can be applied to substances with relatively similar relative volatilities, such as the distillation separation of propane and propylene. It is not applicable to the separation of multi-component systems with a high relative volatility. For example, the temperature at the top of the tower is around -20 degrees Celsius, while that at the bottom of the tower is around 100 degrees Celsius. When the tower pressure decreases, the recombination of components increases, resulting in a reduced separation efficiency. The entire tower system could also become disrupted. In short, questions without any restrictive conditions cannot be answered.
To be precise, it is reducing the pressure drop across the tray that helps to lower energy consumption, rather than the overall pressure drop of the tower