Exergy Analysis of a Plate Type Freshwater Generator Used in Marine Vessels

Abstract

The freshwater generation from seawater in marine vessels is outlined. Freshwater is a requirement for human consumption as well as for the operation of onboard machinery. As per the World Health Organization (WHO) guidelines, dissolved solids in the drinking water should be less than 500 mg/litre. Technical water (used for the operation of onboard machinery) will contain less than 2.5 mg/litre of boiler feed water. The submerged plate-type evaporator is mainly used on merchant's vessels in order to produce freshwater. An exergy analysis for utilizing waste heat as a source for a single effect desalination process to meet the freshwater needs is proposed with due consideration to practical aspects. A plate-type freshwater generator installed at the Training Ship of Tolani Maritime Institute, Pune, India, is analyzed. Thermal properties are calculated using a "C" program. The practical approach to exergy analysis of the freshwater generating process is to calculate the total exergy loss, which is then compared with the partial exergy losses in the system in order to establish the impact of the specific process on the overall system efficiency. This exergy study calculates the proportion and the distribution of unavailable work in the evaporator, condenser, and brine section of a plate-type freshwater generator. The exergy efficiency in freshwater generators with plate-type freshwater generators is 64%. Since the exergy losses in the freshwater generator are disclosed, the task of effectively directing efforts in performance and energy conservations is simplified.