I have problems with the operation of the distillation tower; I seek advice from experts
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I know that the pressure in a distillation column is caused by two factors. The first is an excessive amount of vapor at the bottom of the column, and the second is too much gas phase at the top of the column. If the pressure at the top rises, I can increase the amount of product taken from the top of the column and reduce the reflux. With less reflux, there will be more heavy components at the top of the column, which will surely lead to an increase in temperature. And if the temperature at the top of the column is high, won’t the pressure also be high? It’s so confusing; it seems that the temperature at the top of the tower, whether it’s high or low, has little to do with pressure
I believe that the pressure in a distillation tower is generated by the vaporization of the material. The increase in tower top pressure is simply due to an increased heating rate, which leads to a greater amount of gasification ； The low-boiling-point substances recovered from the top of the tower in small quantities result in an increased reflux flow; this reflux flow contains low-boiling-point substances that re-enter the reactor, leading to secondary vaporization and further increases in pressure. To reduce the top pressure of the tower, the first step should be to decrease the heating rate; secondly, increasing the draw rate can be employed. However, this will result in a short-term increase in the top temperature of the tower, as well as an increase in the content of heavier components in the extracted product. It is also possible to increase the reflux rate while reducing the heating rate (in other words, by decreasing the amount of product taken out, which helps maintain the purity of the extracted material); the cooling effect of the reflux can be used to suppress the amount of gasification. In this case, the tower top temperature may rise for a short period of time, and this control method requires more time. 【The short-term rise in temperature is due to the decrease in pressure, which lowers the boiling point of the material and increases its vaporization rate; not only does the boiling point of low-boiling substances drop, but that of the heavier components as well, leading to an increase in the temperature at the top of the tower.】 Of course, it is also possible to adjust this by changing the feed rate to the bottom of the tower; (when the temperature at the bottom of the tower is high, it is not advisable to increase the feed rate, as this will further increase the pressure)
So, when the temperature at the top of the tower rises, does the pressure at the top increase or decrease?
The short-term rise in temperature is due to the decrease in pressure, which lowers the boiling point of the material and increases its vaporization rate. Expert, with an increase in vaporization rate, wouldn’t the pressure rise again, thereby causing a further rise in temperature?
Or could you help me explain this issue? Our supervisor said that by reducing backflow, the heavier components at the top of the tower will rise, which will increase the temperature at the top of the tower and decrease the pressure in it. ； The pressure will decrease, is it because of the reduction in the light components at the top of the tower?
You can look it up online on Douding.com under 【Training Content for Job Requirements】. The explanation inside is quite clear.
The second floor explained it in great detail; it’s a kind person.
Adjusting the control requires a process and cannot be done immediately; it depends on the extraction rate and the liquefaction speed of the condenser. With rapid liquefaction, the volume of the material vapor decreases quickly, causing the pressure to drop as well. A decrease in pressure leads to an increase in the amount of material that vaporizes; the entire process is dynamic. The overall trend for the pressure at the top of the tower is downward, and it takes some time to adjust until the temperature at the bottom of the tower drops (this works in conjunction with reducing the heating rate), resulting in a decrease in the amount of material that vaporizes and stabilization of the pressure at the top of the tower.
The operation of a distillation tower relies on balance. It takes a process. It is not possible to derive general rules from the dynamic phenomena at a particular moment after the balance has been disrupted. All the indicators are closely related to each other. The more indicators that are adjusted, the more chaotic it becomes. In the end, I couldn’t even figure out the pattern myself. In short, one must remain calm and restore balance.
It can be explained as follows: by reducing the reflux, the product output increases. As a result, less material and energy accumulate inside the tower, so the tower pressure decreases. At the same time, due to the reduced reflux, the concentration of heavier components at the top of the tower increases, which leads to the product at the top not meeting the required standards~~