ali2u,
I had a bad copy of HYSIS and couldn't get it to perform with any stability on my operating system. Two months later we finally got it running. So if you have having problems with it running consistantly complain loud and often... My problem was in March 2002, so hopefully the software company has gotten that problem sorted out....
Hysis is a less expensive tool than SIMSCI packages, but works.... I prefer SIMSCI products, but use both.
Simulation is hard to learn, akin to learning to speak a foriegn language, it takes time and is frustrating. Find someone who knows how to use the product and then schedule a hour or two a week with them to help you out. When stuck, spend an hour looking at the reference material and then call for assistance. Most effective use of time and resources...
Also if you understand the basic principals of the process, the modeling effort is easier. That is, having a complete heat and material balance of the process is a great start....