|Thermodynamic Process Synthesis, Using Simple Thermodynamic Tools to Assess and Design Processes |
Chemistry and Chemical Biology
|David Glasser, University of Witwatersrand, Johannesburg, South Africa|
1:00 PM, 601 CoRE
A chemical plant can in principle be viewed as an isolated entity. In order for this entity to operate it has to satisfy a mass balance, an energy balance and its entropy production must be not less than zero. This latter condition can be re-written in terms of a Gibbs Free Energy and this is shown to be a work balance inequality for the plant that has to be satisfied in order for the plant to operate. Thus making a plant operate successfully often becomes an exercise in how to put work into the plant. On the other hand putting in too much work becomes a source of inefficiency.
These ideas are illustrated by examining a methanol production plant. It is shown that this plant can be viewed as a heat engine that is needed to supply the work needed to make the plant run. Furthermore it is shown that this work is not sufficient to make a commercial plant operate and the extra work is added via compression.
The big advantage of the new approach is that one is now able to examine a plant at a very high level using only simple thermodynamic data, without needing all the detail of a normal design. One can then make decisions about the plant flow-sheet at very early stage of a project or alternatively identify the sources of inefficiencies in current plants that in the case of the methanol plant lead to increased carbon dioxide emissions. This thus becomes a very powerful systems tool for looking at flow-sheets in an integrated fashion.