ABsorber Column Convergence (it's NOT)

[Ian Ednie]

This simulation has 3 components: Air, Water, and Ammonia. Because Ammonia is only available in CoolProp property set, that's the one I used I entered Air and Water in CoolProp, too. And my Property Package (obviously) is CoolProp.

Inlet gas, at bottom of the Absorber, is .97 mole fraction air, .03 ammonia (0 water), 0.92 lbmol/hr. Inlet liquid, at top of the column, is water (no air, no ammonia), 4.1 gpm. Tied appropriate outlet streams to appropriate spots in the column, but it doesn't converge.

Any suggestions?

Thanks!!!

[Daniel Medeiros]

Can you attach the simulation file?

[Ian Ednie]

Here it is.

[Daniel Medeiros]

There's a problem with the CoolProp property package in the current release. The fix will be available in the next one. In the meantime, use this simulation with normal ChemSep compounds. I also added a function to quickly replace compounds added to the simulation by others in the 'unselected' list. I used it to replace compounds in your simulation without losing mass balance data. This will also be available in the next release.

Regards
Daniel

[Ian Ednie]

As I looked back over the problem definition, I noticed that gas inlet flows were in SCFM, not SCFH. So the inlet gas flow should 55.5 lbmol/hr, not 0.92.

I still can't get the column to converge.

Revised simulation file is attached.

[Gregor Reichert]

The selected Property Package "PengRobinson" has a general problem to calculate a mixture of Ammonia/Water even with ChemSep components. Please use a different PP like "PengRobinson/LeeKesler" which gives at least some results.

But be aware that this system will not be able to calculate realistic results. Ammonia and water are reacting with each other by producing NH4+ and OH- ions. You would need to model this system by either an electrolyte model or an activity coefficient model like NRTL with adjusted interaction parameters.
The electrolyte model is not working in a way yet to be able to calculate this. For NRTL you would need to regress interaction parameters by yourself.

Gregor

[Daniel Medeiros]

I sent him the simulation with the PR property package, Gregor. He had originally selected the CoolProp PP. I was in a hurry and only checked the convergence of the column.

[vernet]

Hello, I am very interested in your discussion because I am working on this subject. We try to parameter an ammonia/water absorption cycle working between 160°C at the boiler and -65°C at the evaporator.
It is true that in the absorber there is a chemical reaction with the association of water and ammonia. But that is not the only thing. You have to know that there is also the reaction of condensing ammonia. Then the resulting energy is the summ of ammonia/water association chemical energy and ammonia condensing energy. Both are dependant on pressure, temperature and molar solution fraction between water and ammonia.

[sarah shbeeb]

Hello, I am trying to build a co2 capture unit on DWSIM where there is an absorber and a distillation process. I am having trouble in running the absorber unit and I've tried changing many parameters. I keep getting different types of error and I can't seem to fix them. Attached is what I have done so far;

please advise