Thermodynamics can be used to describe any process, or system of processes. Of particular interest are the properties of Enthalpy and Gibbs Free Energy. By using these two thermodynamic characteristics together as vectors on a diagram of Free Energy against Enthalpy, it becomes possible to develop optimal process flow sheets that combine the thermodynamics of chemical reactions and the dynamics of physical operations on a single diagram. This concept is also explored in a paper by Baraka Celesin Sempuga (Classification of Chemical Processes: A Graphical Approach using the Heat Engine Concept, Abstract submitted to AICHE in May 2008)

By selecting appropriate operating conditions for a process; such as temperature, pressure and reaction extent; it is possible to find on the G-H diagram the combination of reactions and operations that will allow the process, in its entirety, to be run reversibly, which is to say its change in Entropy will be zero. This would thus allow a flow sheet to be developed that would represent the process performing at its highest efficiency.

Such a flow sheet can provide an important basis for allowing new processes to be developed to minimize its impact on the environment and maximize its productivity and also allow provide a means of identifying the inefficiencies of existing processes and providing a basis for improvement.

The operation of a Gasifier is considered to illustrate the use of the G-H diagram. The primary reaction is the gasification of coal. To provide the heat and work that gasification requires coal is also burned in oxygen. The Water-Gas-Shift reaction is also considered to allow the ratio of Carbon Monoxide and Hydrogen to be adjusted to desired specification. The phase change of liquid water to its vapour phase is also considered which allows for the use of liquid water as a starting feedstock.

Using these ideas one is able to show how to improve the carbon efficiency of a gasification process.