Energy and exergy analysis of a milk powder production system

•Geothermal energy assisted milk powder production line was studied thermodynamically.•The first study on exergy analysis of a milk powder production line.•The overall energy and exergy efficiencies were calculated as 85.4 and 57.45%, respectively.•The evaporator, has the highest exergy destruction rate with 333.6kW, needs a detailed assessment. Milk has been consumed since time immemorial because of its unique nutritional properties and produced almost 816million tonnes in the year of 2016. Due to its highly perishable characteristic, milk is processed into more stable milk products such as cheese, yoghurt, and butter and milk powder. Among them, milk powder is distinctive for its longer shelf life and can be stored at ambient temperature. The other advantages of milk powder are less volume requirement during its transportation and higher selling price. Therefore, it is widely used in many food products such as ice cream, bakery products, and sausages. According to a recent study on the statistics from Food and Agriculture Organization, world production of whole dried milk was 3,597,015 tonnes in 2014: Oceania 36.5%, Americas 36.1% and Europe 24.1% of the World production. Milk powder production is a process that requires high energy, especially for evaporation. Recently, reducing energy use has been gaining importance by increasing energy and exergy efficiency. Conventional energy analysis is performed based on the First Law of Thermodynamics. Unlike from the First Law, the Second Law or exergy analysis (defined as useful work) has appeared in the literature, while this analysis not only assesses quantity but also quality of energy. In this study, exergy analysis of a milk powder production system, mainly includes 3 processes (pasteurization, evaporation and spray drying) which will be presented. The aim of the study is to apply a thermodynamic analysis including comprehensive exergy analysis by using different performance parameters such as exergy efficiency, improvement potential rate, sustainability index, relative irreversibility and exergetic factor for the milk powder production system. As a result, exergetic efficiencies of the system components were found in the range of 9–83%. The overall energy and exergy efficiencies of the whole milk powder production system were calculated as 85.4 and 57.45%, respectively. Additionally, it was found that the evaporator and the heater have a higher impact in improvement actions.