KETTLE REBOILER BAFFLE SELECTION AND SPACING

[a1j2]

I am trying to design a Kettle Reboler for a Demethanizer where the liquid entering will have to raise its temperature by around 15C due to the flasing of almost 3% of its mass. The liquid composition is Methane, Ethane and Propane (basically).

The heat experts that I have consulted are confused about the fact of raising the temperature on a kettle reboiler since they have used them in propane refrigeration services where the "boiling" of the propane is done in isothermal conditions, while here I am needing to raise the temperature to flash some of the methane.

The heat experts do not know how to deal with the temperature increase along the tlenght of the U tube bundle. They have shown me only temperature profiles on the vertical axis and keep talking about "recirculation in the vertical axis but nothing about the "recirculation" on the longitudinal axis> they also do not know how to calculate the temperature increase of the liquid along the longitudinal axis. Additionally they say they do not believe HTRI progfam for those calculations...

Hence, if anyone can provide me some ideas, certainly a will appreciate that very very much.

Kind Regards

 

[sshep]

A conventional kettle reboiler generally has liquid entering at the bottom and vapor leaving at the top. The liquid feed is often piped to enter at more than one location to avoid any chance of bundle interferance with incoming liquid. Due to the mixing and crossflow geometry in the boiling pool, it does not seem easy (or important) to quantify any longitudinal temperature gradient. Opportunity for vertical quantification is possible because of the liquid head and vertical flow of vapor in the pool.

Because of the mixing assumption used in sizing, your question seems to be along the lines of asking for a temperature profile in a CSTR- the assumptions used in the engineering model preclude obtaining the profile which you desire. I also think you are adding additional complexity where it is not needed. This is my opinion, others may see it differently.

best wishes,
sshep

 

[pipehead]

There are no baffles in in kettle reboiler. You just need to design enough space above the tubes to disengauge and keep the vapor line large enough to overcome hydraulics. You may need multiple vapour outlets too like sshep said on inlets..

 

[25362]

Vol 3 of Ludwig's Applied process design for chemical and petrochemical plants deals with kettle reboilers in a manner that may be of help in your design.