PR and SRK equations in HYSYS
Thread Content
Question: When performing simulations in HYSYS using PR and SRK as the basis, the feed stream to the operating unit is divided into – and + branches by a \"cutter\". Why does this happen, and how should such simulations be carried out? Waiting online for answers; hope everyone can help. Last edited by snowlee on 2008-1-31 12:21.]
For example, the property calculation of the feed material uses the PR equation, while the property calculation of the feed material in the operating unit uses the SRK equation. HYSYS is not capable of using both equations simultaneously to simulate the properties of the same material; it is necessary to use a \"cutter\" – the properties are calculated once for the upstream part of the material and once for the downstream part. A computer isn’t a human brain.:)
Oh, I see. Then how should I make the adjustments? Re-enter the logistics for the unit operations following the cutter?
It is sufficient to adjust the physical properties of the feed and those of the feed in the operating unit to match the same equation of state.
Generally, when different components are processed using different units or when operating conditions change, it becomes necessary to use a different thermodynamic method – which is why Cutter was introduced. This is consistent with the approach used in Aspen Plus’ Section; therefore, there is no need to adjust any other parameters – simply changing the thermodynamic method, that is, changing PR to SRK.
In Hysys, a flowsheet can have only one EOS. You can create another Sub Flowsheet, select SRK, and specify the P and H values for the fluid stream being transferred between them
Previously, it was not necessary to use sub-processes; one could simply set BASIS-1 as WILSON and BASIS-2 as NRTL, with all feed streams also using the WILSON equation from BASIS-1. Only the phase separator in the simulation would use the NRTL equation from BASIS-2, and that was also acceptable