Abstract
A conventional vapor-compression desalting system is analyzed thermodynamically and economically by the concepts of essergy and internal economy. Thermodynamic analysis using the concept of essergy reveals that the low thermodynamic efficiency is inherent to the process even when the pieces of equipment have individual high thermodynamic efficiencies. Economic analysis using the concept of internal economy shows that the decomposition of the system into zones is not totally arbitrary. A closer engineering understanding of the economic effects of the various design variables is permitted. Optimum results, in general, reveal that for the usual rates of electrical energy costs, optimum conditions favor a high thermodynamic efficiency for each of the compressor, evaporator condenser, and main exchanger. Optimum tube diameter, tube length and allowable pressure drops for the main exchanger as a shell-and-tube type may differ appreciably from conventional values. The optimum design depends upon economic factors, which vary from one locality to another. Therefore the specific numerical results given herein may not be applicable to a specific installation but the methods are quite general.