4 replies to this topic

[arvind]

Hi all,

I need little help regarding design a thermosyphon reboiler,

the feed is naptha entering in thermo. at sat. temp. say rate 12500 lb/ hr and its 80% of mass is getting vapourised ( i. e 10000 lb/hr vapour + 2500 lb/hr liq. ) and feed this mixture to the column the operating pressure is 10 barg, plz anyone help me for designing of line sizing for the two phase flow of liquid and vapour which is feeding to the column. plz give me equation to decide diameter.


waiting for u r reply

arvind

[arvind]

Hi arvind,
at you operating pressure u must know your vapor as well as liquid densities,then calculate the total volumetric flow rate from mass flow rates u have specified and with the velocities u prefer to keep in these pipes will give u the cross section or dia of pipe.

Hope this helps.
Regards,
pankaj.

Pankaj,

Thanks for your reply but I amwaiting for the design calculation point of view,

which shows the std. velocity to take ( is it base on erosion velocity ? like in two phase flow line calculation ? )

and also the pressure drop consideration as well

ok, can you give me the the formulas for the resultant flow rate calculation, mean flow rate ?

arvind

[Roger Susan]

This may be a bit of a useless answer for you. But with out knowing your circumstance if you can get access to the modelling tool HTRI which is pretty much a process industry standard software for modelling heat exchangers it does all that stuff for you.

Expensive but if you deal with Heat exchangers often it is certainly worth while.

HTFS is also a modelling program but not sure if it does reboiler piping.

Generally you have to get pressure drop and static head balanced so that it drives the liquid through reboiler back into column. Vaporisation will reduce fluid overall density (2 phase) and help with the static head difference (liquid into and 2 phase out of and hence less head out of reboiler) and size the line so that pressure drop does not take you above this difference. (do not forget the reboiler pressure drop). The key is the 2 phase pressure drop and that is not easy to calculate. That why I chicken out and use software. If you cannot, you will have to be conservative and use highest pressure drop calculation given by any of the 2 phase correlations.

[fcontrer]

arvind:


Check it:

http://www.distillat...m/technical.htm

"Properly Design Of Thermosyphon Reboiler".

http://www.distillat...al/053__abs.htm

Its Free.

Frank.