The role of equilibrium thermodynamics in process synthesis

The role of classical thermodynamics in generating design options in a systematic way is emphasised. Two thermodynamic approaches to solving this problem, the pinch and exergy methods, are compared. It is demonstrated that both approaches are based on analysis of exergy losses within a designed system. The difference is that in pinch analysis knowledge of exergy losses precedes design, while the latter allows us to establish energy targets prior to design. In conventional exergy analysis, losses may be evaluated only after the configuration of the process has been chosen. As a result, the conventional exergy approach remains trial-and-error. In order to overcome this limitation, this paper proposes a new exergy-based approach to generating design alternatives. A special graphic presentation of exergy balance around the ideal processes, where exergy losses are nil, allows us to generate alternatives with predetermined targets in a systematic way. In the next design step, real processes with the same structure as the selected ideal ones are identified. The final solution is carried out through optimization of a superstructure embedding the limited number of real process alternatives.