2 replies to this topic

[Phani Kanth]

Hi all,

I have a problem when designing the Reboiler for Glycol regeneration using hot oil as a heating medium with BKU type of Heat Exchanger in Aspen Tech EDR(Exchanger Design and Rating V 7.3) programme that was described below:

When this Heat Exchanger run in Rating mode that results two result warnings generated that was

1) "The iteration for the recirculating shellside flow in this kettle reboiler has failed to converge. For
the current estimate of flow in the bundle, including recirculation, 75197 kg/h, the pressure loss in
the tube bundle is 0.021 kgf/cm2, while the driving head due to gravity, which should be equal to
this pressure loss, is 0.023 kgf/cm2. Treat the results with caution."

2)"P21: Stream 2 at pressure 1.35 kgf/cm2 has an unusual value of compressibility, 3.998912,
(calculated from vapor data at the dew point) and/or of molecular weight 130.9253. This may
affect the accuracy of the calculated results."


I had tried to solve these warnings in several time by changing the programme options and some parameters but i was failure to solve these warnings.
for this exchanger we are imported the physical properties from hysys simulation file.may be due to this 2nd warning was generated. So, shall i ignore this warning to move forward steps in thermal design?

Kindly suggest anyone what is fundamental mistake by us for these warnings...!

I'm looking forward for your valuable suggestions.


Regards,
Phani Kanth.

[jcazenave]

The second warning is just that it can be ignored.

The first warning is about convergence and needs to be looked at. It might be ok as 0.002 kgf/cm2 is a small difference but It is difficult to say like that.

Your best option is to contact aspentech support who should be able to help you.

Kind Regards

[Phani Kanth]

Thank you Mr.Jaczenave for your reply.
After several iteration by changing exchangers parameters, finally i sucesseded to clear the first warning,this was generated due to low velocity in tube side that means more numbers tubes for given tube fluid inlet.by decresing the tube bundle ID this was possible.

After this i have one more doubt on this reboilers and currently looking for solution that was How to fix the levels(LL,L,H,HH) in reboiler? and level setting basis. So, I request you and other members in this forum to clear this problem.