Regarding the effect of cold reflux in the catalytic stabilizer on the top pressure of the tower
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How does the catalytic stabilizer overhead cold reflux affect the tower top pressure? We all know that increasing the refrigerant return flow leads to an increase in the pressure at the top of the stabilizer. But how exactly does this affect things? I don’t understand! In my opinion, the increase in tower top pressure is related to the amount of cold reflux introduced. When the gas-liquid equilibrium at the top of the stabilizer is maintained, a cold reflux with a temperature much lower than that of the fluid is introduced; initially, the amount of cooling of the gas phase at the top of the tower is less than the amount of vaporization of the cold reflux in that gas phase, causing the pressure at the top of the stabilizer to rise. As the amount of cold reflux increases and exceeds their equilibrium limit, the amount of vapor that condenses at the top of the tower is greater than the amount that vaporizes due to the cold reflux, resulting in a decrease in the vapor load at the top of the tower. In this case, shouldn’t the pressure at the top of the tower also decrease? The fact is that the greater the amount of cold reflux introduced at the top of the tower, the higher the pressure at the top of the tower becomes. Please advise… Thank you!
From what you said, I still don’t quite understand. In my personal view, once the cold reflux is sent back, it vaporizes, and as a result the pressure surely increases. The simplest way to understand this is that the cold reflux vaporizes
As the amount of cold reflux increases and exceeds their equilibrium limit, the amount of vapor that condenses at the top of the tower is greater than the amount that vaporizes due to the cold reflux, resulting in a decrease in the vapor load at the top of the tower. In this case, shouldn’t the pressure at the top of the tower also decrease?
If the amount of cold reflux is excessively high, the amount of vapor that condenses at the top of the tower will exceed the amount that vaporizes due to the cold reflux, resulting in a decrease in the vapor load at the tower top. Initially, the pressure at the top of the stabilizer will drop; however, as most of the liquid hydrocarbons after cooling enter the lower part of the stabilizer and gradually vaporize, the pressure at the top of the tower will rise sharply, leading to a pressure surge in the tower.
I basically understand what you mean, but in actual production, the top temperature remains within a certain range; therefore, the reflux ratio also cannot be too high. If the cold reflux is increased indefinitely, the situation you described could occur, as an excessively low top temperature would result in nothing meeting the required standards
It’s just my personal opinion; I’m not sure if it’s correct, so I’d like to discuss it with everyone.
First, you need to understand the meanings of the terms dew point and bubble point. The liquid used for reflux is one at its dew point temperature (40 degrees); when it is introduced at the top of the tower (where the temperature is 100 degrees), it will inevitably vaporize completely. The more liquid that is introduced, the greater the amount of vaporization that occurs (it’s not possible to reduce the temperature at the top to below 40 degrees), and as a result, the pressure increases
I basically understand it now: the equilibrium limit corresponds to a relatively low temperature, around 40 degrees roughly. The operating temperature is usually above this value; therefore, during normal production, the more cold reflux that is introduced, the faster the pressure rises.