Aspen errors using radfrac for absorber

[zouhour]

Hi,

I'm simulating an absorption chiller into Aspen 7.3 and I used radfrac for modeling the absorber. The simulation leads to these errors.

Block: ABSORBER Model: RADFRAC
*** SEVERE ERROR
A VAPOR FEED/PUMPAROUND TO THE BOTTOM STAGE IS REQUIRED WHEN
"QN=0" IS SPECIFIED IN "COL-SPECS"; REQUIRED FEED/PUMPAROUND
HAS ZERO FLOW.


Block: SOLBPHX Model: HEATX
* WARNING
UNABLE TO MEET AREA SPEC - MINIMUM APPROACH TEMPERATURE REACHED
CALCULATED AREA IS LESS THAN SPECIFIED AREA

Could you help me please.

[shuwana]

Hello Zouhour

when u r modelling the absorber u must have two feeds
1. from the bottom, the gas/vapor stream from which the absorption is to be carried out
2. from the top, the absorbing liquid

u can send me screen shot of your model; i think i can help

regards
Shuwana

Hi,

I'm simulating an absorption chiller into Aspen 7.3 and I used radfrac for modeling the absorber. The simulation leads to these errors.

Block: ABSORBER Model: RADFRAC
*** SEVERE ERROR
A VAPOR FEED/PUMPAROUND TO THE BOTTOM STAGE IS REQUIRED WHEN
"QN=0" IS SPECIFIED IN "COL-SPECS"; REQUIRED FEED/PUMPAROUND
HAS ZERO FLOW.


Block: SOLBPHX Model: HEATX
* WARNING
UNABLE TO MEET AREA SPEC - MINIMUM APPROACH TEMPERATURE REACHED
CALCULATED AREA IS LESS THAN SPECIFIED AREA

Could you help me please.

[juncruz]

In my chiller absorption simulation using NH3 as the refrigerant, NH3 is fed to the bottom as vapor. Water is fed to stage 1. The absorber is radfrac with total condenser with a small distillate rate, no reboiler. Equilibrium calculation and standard convergence. This distillate is then mixed with the bottom product in a mixer. No pumparound. This works for me.