2 replies to this topic

[Dhanya S Nair]

We have a distillation column which seperates Methyl acetate & water.The column operates under atmospheric pressure.The top product is 97% Methyl Acetate & bottom product is 99.7% Water.The column feed is dilute Methyl Acetate feed.For boil up,steam is directly injected.
We wanted to increase the top product purity to 99.5%.Simulations were carried out & it revealed that operating column under vacuum of 0.65BarA with same feed/steam/distillate rate can yield MA purity of 99.5%.I have observed that requirement of steam is less in vacuum operation.But I expected that steam flow requirement would be more as the latent heat is high in vacuum.Why is the steam flow requirement less in my case for vacuum operation.Please explain.
Generally,How do we decide upon the optimum steam flow to distillation column.

[Fr3dd]

Hi Dhanya,

I'm not sure if I'm understanding you. Unless your mixture has a particular or exceptional behavior in vacuum conditions, I would expect a lower heat requirement since vacuum conditions will lower the boiling points of the components you want to separate, this leading to a decrease of the required heat input in the system.

This is the basic principle in vacuum distillation. I hope this can help you a little.

Regards,

[S.R.Shah]

Vacuum distillation :as it lowers boiling point ;there is may not be change in heat due to phase change.But there may be reduction in sensible heat duty -No phase change.

Other problems,I have encountered that reduction of LMTD for regular coolant such as cooling water increases Heat transfer area Requirement.Sometimes to have larger LMTD and complete condensation more cooler coolants like Chilled water and Brine is used depending on vapor pressure at that vacuum.This also increase costs.