Application of exergy analysis to the dairy industry: A case study of yogurt drink production plant

This work was aimed at undertaking a detailed exergy analysis of an industrial-scale yogurt drink production plant using actual operational data. Exergy efficiency and exergy destruction rate of each subcomponent of four main subsystems of the plant, including steam generation, above-zero refrigeration, milk reception, pasteurization, and standardization, and yogurt drink production lines were derived independently. This analysis was performed to quantify thermodynamic inefficiencies of all subcomponents of the plant in order to identify the breakthrough points for further energy savings. An effort was also made to compute the quantity of exergy destruction in processing a given amount of pasteurized yogurt drink. The results indicated that the highest exergy destruction rate occurred in the boiler & compressor combination of steam generator, followed by ice-water tank & agitator combination in the above zero refrigeration system. The specific exergy destruction of pasteurized yogurt drink was determined as 442 kJ/kg according to the mass allocation method. The steam generator had the highest contribution to the specific exergy destruction of pasteurized yogurt drink, followed by yogurt drink production, above-zero refrigeration, and milk reception, pasteurization, and standardization lines, respectively. In general, the current survey can be an important step for future improvements of dairy processing plants from the sustainability and productivity viewpoints. This study clearly showed the effectiveness of exergy analysis for determining irreversibilities and losses occurring in dairy processing plants in order to improve their thermodynamic performances.