Energy and exergy analyses of a solar assisted milk powder spray dryer

In the current study a detailed thermal analysis of a solar assisted spray dryer has been presented. Various methods and strategies were used to analyse and estimate the effect of process improvements from optimal evaluation models (Inversion Temperature) to heat exchanger optimization (Pinch Analysis). The spray dryer was a Buchi B-290 design with a two-fluid nozzle, having a main air flow rate of 0.01 kgs􀀀 1 and varying nozzle tips to adjust droplet diameters. A solar air heater was designed and developed as a preheater to split the heating power consumption into 0.768 kW (electrical heater) and 0.327 kW (SAH). Addition of polystyrene sheets on the sides of the solar air heater, reduced heat losses from 4.9 to 2.27 W.m􀀀 2 K􀀀 1. Using solar air heater, the ratio of electrical energy input to energy used in the spray drying reduced from 2.68 to 1.69, thus contributed 30 % to the overall energy input. The exergy analysis revealed that the maximum improvement potential exists in the condenser (0.233 kW) followed by the spray drying chamber (0.294 kW), the electric heater (0.152 kW), and the solar air heater (0.097 kW). The study provided a comprehensive thermal analysis helpful during the design optimization of spray drying processes when integrating with solar energy.