Hysys help

[billy1022]

I often get a "consistency error" message when combining 2 streams, one from a preflash and the 2nd downstream of a converged column and compressor operation. The error indicates a difference in calculated molar enthalpies. How can I avoid this error?
thanks

 

[Zoobie]

Sometimes this occurs if you have overspecified your simulation (the usual cause). I have also seen it occur because of some 'buggy' behaviour with the component splitter but I suspect that is more of an isolated case. The other thing you may want to check is the transfer basis for your column. The column operation in HYSYS is treated as a seperate flowsheet and streams are transferred in and out using particular basis for the flash calculations. The default is a P-H flash.

Best Solution: AspenTech technical support. They are the experts and their support system seems to work very well.

 

[MortenA]

The consitency error usually arises from a situation where you have specied a value in a stream thats also calculated by another operation. An example (from my own experience):

I had set up a simualtion of a number of pipesegments connected in series. At some time i must have specified the composition of one of the stream that later on ended up "in the middle" of the string of pipesegment. As long as i didnt change the composition of the very first stream there where no problems. But every time i tried to change the composition (for the inlet stream)- i got a consistency error. The reason why i didnt get the error in the first place was because the compositions were identical (the upstream and the "in the middle" stream! But when i changed it all downstream streams must be the same - but they were specified differently: A consitency error!

On occations it may also occur when the recycle component is added "at the wrong time". If so try to delete your recycle streams and reconnect them again.

Best regards

Morten