If the hole has nothing to do with the process itself it is probably an access for inspection, cleaning, equipment or airing. PS: Destillation column in oil refinery or another of the multitudes of applications a destillation column might have?
At the bottom of distillation column .there is a baffle to make to compartment (once through reboiler).
But in the baffle there is a hole.
What is purpose of that hole
It's very hard to know without a picture or drawing. Usually the baffle is there to ensure there is adequate feed to the reboiler. When the column is shut down you want the area behind the baffle to be able to drain out. That is the only instance I can imagine without seeing some more information.
Sump baffles are often used for thermosyphon reboilers to keep a constant head/flow to the reboiler. However, from what I've seen, normally the column downcomer usually empties into the reboiler side, not the product side. Is your drawn downcomer location correct?
The hole might have been a modification later on if someone determined there wasn't enough vapor disengagement time on the reboiler side. Drilling a large hole lower effectively lowers the entire baffle height.
Is your liquid level normally maintained above or below the hole?
Yes, this is for a once through type reboiler - the 2phase product from the reboiler enters the product sump in the column bottom, and part of it flows out through the underflow baffle to mix with fresh feed coming from the last tray above. The resulting flash vapor goes up to the bottom tray through the chimney and the resultant liquid mix goes to the reboiler. The purpose of this mixing is to reduce the vapor fraction of the transfer line stream ( ie product leaving the reboiler) at a specified upper limit in order to reduce the risk of 2phase slugging in the transfer line.
Thank you georgeverghese
But we are mixting cold liquid with hot liquid (reboiler inlet liquid is cold and product side liquid is hot) so it will not reduce mixing.i think it will promote
Georgeverghese, if I am understanding you, the baffle is for maintaining a colder inlet temp to the reboiler than if it were unbaffled to avoid excessive vapor generation/slug flow. What, then, is the purpose of the hole? Its existence increases the reboiler inlet temp and resulting vapor fraction. Is it to just maintain level as an equalizer, or does the hole serve to recoup some of the energy loss that would occur if the reboiler liquid outlet were 100% removed in the product stream (i.e. if the hole weren’t there)?
Yes agree with your point
t will increase the reboiler inlet temperature that's why effeciency decrease (we cannot assume reboiler is A therotical plate
The underflow of hot liquid through this perforated baffle results in an increase in feed temp to the reboiler due to the mixing of colder fresh feed from the last tray with the hot product in the product sump. Due to preflashing of this mix in the reboiler feed sump in the column, the vapor fraction of the reboiler recirc stream in the transfer line is decreased.
The flowrate of the recirc pump is set such that, at the max flow load in the column bottoms, the desired vapor fraction in the reboiler hot return transfer line is achieved. This means a certain amount of underflow is derived through this perforated baffle. There is an option in Simsci Pro-II in the column unit operation that simulates the once through type reboiler with incredible ease.
Ok
But it is thermoshipon reboiler .
How we can fix the flow rate ?
Due to pre flashing reboiler feed density may increase and chances of heavy accumulation in the reboiler and problem in thermo shiponing
