SHAFTWORK TARGETS FOR LOW-TEMPERATURE PROCESS DESIGN

Traditionally, design of low-temperature processes begins with the basic process (reactors and separators). This is followed by the design of the heat exchanger network (HEN), and of the refrigeration system. Pinch analysis (PA) establishes heat load targets for the refrigeration system based on basic process data, bypassing the design of the HEN. However, such targets are incomplete information since the designer still needs to specify a refrigeration system which ultimately requires shaftwork. The present paper extends PA for the design of low-temperature processes to yield shaftwork targets directly from basic process data. This paper therefore bypasses the design of both the HEN and the refrigeration system. The approach combines the principles of PA with exergy concepts. Procedures exist in the literature which provide shaftwork values from refrigeration heat loads. In comparison, the present procedure offers a simpler and a more fundamental approach. It also offers a strong tool for "feel" and understanding, assisting the designer in finding the best HEN and refrigeration system configuration simultaneously. The procedure is demonstrated using an example based on an ethylene process design study.