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Aspen Based Stripper Model


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#1 drdave

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Posted 07 April 2007 - 11:07 AM

Hello All, rolleyes.gif

This is the case of CO2 stripper modeling on Aspen plus.

Ammonia & CO2 containing aqueous solution (AKA ammonium carbonate liquor, AC liquor)is the feed to the stripper as sketched in file attached.Actual plant operation shows erratic behaviour of CO2 vent with high temperature ( >100deg_C / Specified= 45 deg_C)& high ammonia content. This erratic condition can be corrected with low temperature AC feed liquor at 112~115 deg_C(Specified is 140 deg_C).

Actual operation simulation gets converged in the temperature range of 112 ~120 deg_C but on higher temperature,It indicates "not converged try better temperature & composition" but there is no more further clarification.

Can you please elaborate the reasons for "Non convergence" at higher temperature? for stripper model.

The following are further points which are not confirmed on simulation run(i.e. simulation shows reverse than mentioned below):

1] More ammonia loss from top bed (Top bed is washer bed to remove traces of NH3)

2] Heavy CO2 slip from tower sump to system.

Thanks in advance.

D R Dave

Attached Files



#2 joerd

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Posted 09 April 2007 - 09:15 AM

There are a few things I can think of:
1) maybe your condenser is too small
2) maybe you have a foaming problem in your stripper
3) maybe your AC is not clean

Non-convercenge of a column is often caused by trays "drying up" during the calculation. This is due to the way you spec the column constraints. They may be difficult to achieve given the feed composition, or downright infeasible. Try fixing the bottoms draw rate, for example, and see if you can get the column to converge. Very often, the intermediate/unconverged solution of the column gives a clue to what is going on.

#3 drdave

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Posted 10 April 2007 - 11:09 AM

Thanks Jored.

Let me clarify further.
1] The model mentioned has no condenser.
2] System has been observed almost foam-free despite composition given is prone to such trouble.
3] AC liquor is clean. Passivation air is effective to form sheathing. Less corrosion crunch.

In fact, Simulation makes result available which is erratic indicated by
A] releasing NH3 with CO2 vent (not desirable)
B] CO2 leakage with sump out .
C] Density & temperatures are not meeting as specified with respect to both varibles (ie flowsheet & result variables)

Here, Can I get sure tips to resolve as specified OR reasons to deviations with specified?

I have tried to give an elaborate sketch herewith.

DR Dave

Attached Files






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