Don´T Gamble with Physical Properties for Simulations

S U C C E E D I N G AT S I M U L AT I O N

Don’t Gamble With Physical Properties For Simulations

Finding good values for inadequate or missing physical property parameters is the key to a successful simulation. And this depends upon choosing the right estimation methods.

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Eric C. Carlson, Aspen Technology, Inc.

hemical engineers use process simulation to perform a variety of important work. This work ranges from calculations of mass- and energy balances of large flowsheets to prediction of the performance of process alternatives that can save millions of dollars. An engineer very quickly can define a complex flowsheet and all the process conditions. Desktop computers now allow rating, sizing, optimization, and dynamic calculations that previously required large mainframe computers. In the past, these simulations were often built by a group of experts, including a physical property expert. Now, simulators such as ASPEN PLUS, ChemCAD III, HYSIM, PRO II, and SPEEDUP are easier to use and more powerful than the standalone programs of the past. Today, a single engineer can set up the basic simulation specifications, including the physical properties, in very little time. Missing or inadequate physical properties, however, can undermine the accuracy of a model or even prevent you from performing the simulation. That some required information is missing is not an oversight in the simulator. After all, for most compounds, physical property parameters are not known for every thermodynamic model or for all temperature or pressure ranges. Models have built-in assumptions and practical limits that should apply. In this article, we will provide practical tips and techniques to help you accurately describe the physical properties needed in a simulation. As an engineer,

you always will have to make assumptions in terms of physical properties, however. The goal of this article is to outline the appropriate assumptions and to provide techniques when properties are...