Discussion Central

1.  Modeling/Designing an Extract Cooler

Posted 06-15-2017 16:18

I am looking for advice on approaching a problem I've been given at work.

We have an extractive cooler. Hot gas and a liquor solution is sent counter-current through a plate tower. The gas has a contaminant in it that needs to be removed. As the gas is being cooled, to below the dew point of the contaminant, it condenses and dissolves into the liquor solution. Because this involves both a heat exchange and liquid-liquid extraction in one unit, how do I approach it? Mass and energy balances? How do i construct the energy balance, a term for latent heat of condensation and another balance for the dissolution into the solution?

Ultimately I need to be able to answer the question, "if we put in another extractive cooler with similar parameters what would the concentration of the contaminant be at the outlet of the second cooler"

I imagine you will want to know more details, please feel free to ask and I will provide.
Thank you!

Sahil Azeez
Process Engineer
Algoma Steel


2.  RE: Modeling/Designing an Extract Cooler

Posted 06-16-2017 09:22
What you are describing is an absorber tower, nothing to do with liquid-liquid extraction. Any of the commercial steady state process simulators should be able to do this easily. I wouldn't recommend trying to do this from scratch by yourself.

The only problem you may encounter is with the mixture thermodynamics. All the major simulator companies have experts in this area and provide consulting for free for customers.

Companies you should consider are Aspen Technology located in MA, they market Aspen+ and Hysis, and Simulation Sciences located in CA, they market PRO/II. There are several smaller companies that probably could handle this as well.

If this is a one time thing you can hire them to do it for you or you could consider a short or long term lease of their software. Both have websites. I suggest you call them to discuss your problem and see what they can do for you.

John Braccili
Wallingford, PA

3.  RE: Modeling/Designing an Extract Cooler

Posted 06-16-2017 10:37
Many years ago I had a similar problem and did not have access to a simulator.  I used an article by the revered expert James Fair, entitled (I believe) "Designing Direct Contact Coolers and Condensers", and I solved the equations manually.  If you have a simulator, use that but if not, locate the article and apply the equations.

Barry Juran PE
Philadelphia PA
Chemical Process Engineer and Sr. Biopharm Specialist

4.  RE: Modeling/Designing an Extract Cooler

Posted 06-19-2017 00:15

It doesn't sound like you have a liquid-liquid extraction.  It sounds more like you are using a liquid to absorb a component from a gas stream in a standard tray column.  Since you are working with a gas and not true vapor-liquid equilibrium, this would be an absorption problem involving Kga values.  This involves heat transfer, heat of solution, heat capacity, liquid and gas concentration values, and diffusion values, so it gets complicated.  I would use Aspen Ratefrac to model this problem, since hand calculations would be very difficult.


Harold Reed, M.S.

Sirius Technical Services Contract Engineer

For Evonik Corporation

Process Technology and Engineering, Americas


5.  RE: Modeling/Designing an Extract Cooler

Posted 06-19-2017 08:00
Thank you @John Braccili@Barry Juran  and @Harold Reed. You're absolutely right, I should view it as an absorber, as the primary method of removal is absorption. The removal via saturation and condensation is secondary. I'm not sure why they're calling them coolers then...

Barry, thank you for the excellent article reference, although this is fairly complicated to do by hand, I will have some idea of what's happening in the background of the simulation software I'll be using.

Thank you all and will try this out in ASPEN.

Sahil Azeez
Process Engineer
Essar Steel Algoma
Mississauga ON