Distillation column pressure control issue
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Dear colleagues, I would like to seek your advice regarding the choice of pressure control method for the tower tops. Our company has started a new project with a production capacity three times that of the previous plant; as a result, the diameter of the vapor lines at the tops of two or three towers is around 30 inches (750 mm). If a vapor line at the top of the tower along with a control valve is used, isn’t the size of the control valve too large? I wonder if any of you who work in the marine industry have experience with actual methods for controlling tower top pressure? Thank you!
Regarding this issue alone, ensuring the pressure at the top of the tower means controlling the flow rate of the rising gas. When the volume of the flowing liquid remains constant, there must also be a corresponding balanced amount of mass and heat transfer for the rising gas; this is a process parameter that is determined during design. Therefore, to ensure that distillation proceeds stably, continuously, and normally, it is necessary to control it in accordance with the design parameters.
A vapor line at the top of the tower is used, along with a control valve – why is a control valve needed?
The size of the vapor stream at the top of the tower is large; if a control valve is used to regulate the pressure of this vapor stream, a very large control valve will be required, which increases costs!
Hello, thank you for your reply. What I mean by my question is, for distillation columns with a large vapor phase size at the top, what pressure control method should be chosen.
It should be possible to adjust it using a thermal bypass, with the control valve located on the thin gas pipeline.
In such situations, there are two ways to resolve the issue: 1. As one of the users upstairs suggested, use a thermal bypass method to control the pressure; avoid using the control method you mentioned, which involves creating a bottleneck. Although thermal bypass control is not as sensitive as the \"critical\" method, the difference is not significant depending on the condensation method used at the top of the tower. 2. Do not install the control valve directly on the exhaust pipe at the top of the tower; instead, it can be placed on the exhaust pipe of the reflux tank behind the condenser. By treating the top of the tower, the condenser, and the reflux tank as a single system, the exhaust pipe will become smaller after extensive condensation, eliminating the need for a large control valve.
The control valve is added to regulate the pressure inside the tower.
It was already clearly explained on the seventh floor: the condensation has caused a pressure drop, and a bypass valve is added to the reflux tank for control
Firstly, this is a distillation tower, which is equipped with a condenser at its top. If all of the gaseous material at the top of the tower is condensed, a condenser coolant is typically used to control the tower pressure; if there is still gaseous material being removed, then the amount of material taken out is controlled in order to regulate the tower pressure. The point where the gaseous material is removed is usually located at the top of the reflux drum downstream of the condenser, and at this location the size of the extraction line is small, allowing for the use of a suitable type of control valve.
Generally, there is reflux at the top of the tower; the vapor from the top of the tower usually enters the reflux drum after being cooled by air or water. Therefore, installing a control valve directly on the vapor stream at the top of the tower is not beneficial for either air cooling or water cooling. The current practice is to install a control valve on the vapor outlet line at the top of the reflux drum in order to regulate the pressure in the column.