Professionally I work at BPT and focus on creating value adding App for Process Simulation. You can find more info on those on the BPT website. Below are posts that should help HYSYS, PetroSIM and UNISIM users alike in their day to day challenges to produce accurate yet fast models efficiently.

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Monday, 30 March 2015

Did you know series: When using Lee-Kesler Enthalpies with the PR EOS, you get better enthalpies AND ASME steam enthalpies for water as a bonus

The vast majority of Aspen HYSYS simulation cases is using the Peng Robinson equation of state. The default enthalpy method when you select to use the Peng Robinson EOS is the enthalpy of the EOS itself. And that is what the majority is using. This is typically not a conscious selection, it is just that people go with the default. To use Lee Kesler enthalpies in version V8.x should be self evident, it is on the same page where you select the EOS. If you still use V7.3, then you should go to the Parameters tab after selecting the EOS, there you can choose the enthalpy method.

You really should go for Lee Kesler enthalpies. I do not have hard evidence in this post (literature comparisons or so), but even a quick search on the internet will yield literature references that confirm this. There are also conversations I had with users that are a pretty good indicator. Some people emphasise the benefits for cryogenic systems, others recommend Lee-Kesler more generally. There is also some recent work I did on modelling turbo expanders that clearly showed that the Lee-Kesler enthalpies matched vendor performance data much better.

And, there is a little bonus that is probably not so well known: When you select Lee Kesler enthalpies, HYSYS will look at your stream composition and if it is all water, it will use the ASME steam tables. Even at standard conditions, the error on PR EOS duties is about 3.5% and this grows worse as you go to higher pressures. So, if only for this, selecting Lee Kesler Enthalpies is a good thing to do.

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