Study of Chemical Process Structures for Process Synthesis
STUDY OF CHEMICAL PROCESS STRUCTURES FOR PROCESS SYNTHESIS Hiroshi OAKI and Masaru ISHIDA Research Laboratory of Resources Utilization, Tokyo Institute of Technology, Yokohama227 Whenthermodynamic characteristics of processes are represented by a vector on the (JH, TqJS) diagram, the processes may be classified into six types: heating, separation, refrigeration, heat source, mixing, and refrigerant. Based on this classification, which is quite appropriate to process synthesis, the analogy between chemical reactions and physical operations is discussed. Since a chemical process system is considered to be an isolated system, the criterion for those processes to constitute a process system is examined and a new criterion based on the dissipation factor, D=T0JS/JH9 is proposed. It is shown that there are only six basic patterns for the combination of processes to makeup a process system. Whenan endergonicprocess and an exergonic one constitute a process systemand the former process is carried out with the help of the latter, the exergy transformation between these two processes becomes an important factor. The concept of the ideality index is introduced and the relationship between this ideality index and the dissipation factor Dis discussed. state to another2\ we mayevaluate the changes in Introduction enthalpy, AH, and entropy, AS, for each process. In chemical engineering, the process has usually Then we may describe thermodynamic character- been classified according to the type of equipment or istics of the process by a vector on the {AH, TQAS) operations such as heat generation, heat transfer, diagram shown in Fig. 1. distillation, absorption, extraction, and so on8>11). In this diagram, the enthalpy change is chosen as Such classification is suitable for equipment design abscissa and the entropy change multiplied by the calculations.
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