Heat losses in distillation design

[Jobst]

Hi All,

I'm doing preliminary design on a few pretty small packed columns (max diameter ~300 mm, min diameter ~150 mm, heights no more than 7 m).

Aside from being a bit uneasy about how the 150 mm column will work mechanically/hydraulically, I'm unsure how to account for/treat heat losses. Are there any general rules of thumb as to how to proceed with looking at this? I'd be concerned about operation with for example excessive subcooling in reflux drums/column bases, or condensation in overhead lines before it's really wanted (i.e. for vapour feeds).

I have access to HYSYS but have never used the heat loss models before so don't really know what I'm doing there. I will have a bit of a play with dummy heat losses in the form of coolers on various lines to see what it does to my operation but a general treatise on the topic would be a nice starting point.

Before anyone tells me, I have already ordered Distillation Design by Kister

 

[gr2vessels]

Jobst,
It is a simple heat transfer process at the shell surface, a combination of convection and radiation, but for your purpose you can use a generic 'conductance' to calculate the rate of heat loss. It depends on the outside air temperature and moisture, wind velocity, shell surface roughness and if it is painted or not, then it depends on the shell material for heat conductivity between the internal hot fluid and external air.
This small calculation is typical for insulation calculations, to establish the type and thickness of insulating material to minimize the heat loss of your column (ask your local friendly insulator for those two or three formulas he is using to earn his money). Occasionally, I am using my own little book of insulation 'secrets', to calculate the required thickness of a typical insulation on a column worth perhaps millions...
Cheers,
gr2vessels