Dehydrator Reboiler Heat Requirement

[zdas04]

I took a vessel design class in 1981 and I made a marginal note in my book that "it takes 6,500 BTU to cook 1 lbm of H2O from the glycol" of an atmospheric reboiler on a TEG dehydrator. I've been using that number for nearly 30 years without questioning it. Today I had to figure a reboiler capacity and wondered where that number came from. The steam tables get me much closer to 1,000 BTU/lbm (based on the change in enthalpy) than 6,500. I could accept 25% efficiency and get 4,000 BTU/lbm, but I'm having a hard time justifying the 6,500 BTU/lbm that I've used forever.

Can anyone explain it, or should I just not rely on my un-footnoted marginal notes from earlier decades?

David

 

[katmar]

David, I think you might have better luck with this question in one of the chemical engineering or petroleum engineering groups. It is more a process question than a heat transfer question.

I have no experience of TEG Regenerators, but in general you would have to supply more heat than just the latent heat of the top product because of reflux. As far as I can see TEG Regenerators run with low reflux ratios, so 6,500 BTU/lbm sounds high but you will definitely need more than 1,000 BTU/lbm.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[zdas04]

Katmar,
I think you are right. I've started a new thread (thread798-254864) in Chemical process engineering. Anyone who would like to comment, please follow the link and do it there. Thank you.

David