In order to avoid perishable characteristics and secure long shelf life of liquid milk, it is mostly converted into more stable derivatives such as butter, cheese, yogurt and milk powder. Amongst them, milk powder contains highest shelf life at ambient conditions and accounts for 76% of global annual trade of milk and milk derivatives. The milk powder production and its qualitative features are often characterized by huge amount of high- and low-grade energy requirements depending upon the number of stages employed for drying, e.g. single, two or three. In the present work, comparative thermodynamic analysis of two- and three-stage milk drying units has been executed. Both the units have been extensively explored on the grounds of parameters such as exergy efficiency (72.01%/43.67%), drying efficiency (67.50%/65.71%), drying chamber efficiency (57.77%/53.51%), exhaust air temperature (346.15 K/353.15 K), overall specific exergy destruction (3081.64 kJ/kg/5006.28 kJ/kg), overall specific exergy consumption (0.74 kWh/kg/1.34 kWh/kg) and sustainability indices (3.57/1.78) so as to establish the fact that the thermodynamic behaviour of two-stage spray dryer was far better than its three-stage counterpart, at the cost of slightly higher specific steam consumption (3.53 kg/kg/2.77 kg/kg).

液态奶为了避免易腐烂的特性并确保较长的保质期，大多将其转化为更稳定的衍生物，如黄油、奶酪、酸奶和奶粉。其中，奶粉在环境条件下的保质期最长，占全球牛奶和牛奶衍生物年贸易量的 76%。奶粉生产及其定性特征通常具有大量的高低级能量需求，这取决于干燥所采用的阶段数，例如单个、两个或三个阶段。在目前的工作中，已经执行了两级和三级牛奶干燥装置的比较热力学分析。这两种装置都基于火用效率 (72.01%/43.67%)、干燥效率 (67.50%/65.71%)、干燥室效率 (57.