Primary energy and exergy analysis of a spray dryer for the application of industrial effluents: a case study

This study presents a mathematical model based on the mass, energy, and exergy balance of the spray dryer with a direct and hybrid heat recovery system. The spray drying system is an energy-intensive process; thus, an insight of exergy analysis helps improve overall system performance by reducing the irreversibilities in the spray drying system. An industrial case study illustrates the proposed exergy-based model. Besides, the exergetic parametric analysis is carried out by varying the slurry feed flow rate, the temperature of hot gases, solid content in the feed, and dead state temperature to determine the best operating conditions at minimum irreversibility in the drying system. The highest exergy efficiency of the spray dryer with a hybrid heat recovery system is 49.9% at 10 degrees C dead state temperature. In comparison, the direct heat recovery system has the lowest one (19.17%) at the drying air temperature of 500 degrees C. The exergy input is directly proportional to the mass flow rate of hot air/gases, thus, observed to be lower at a 70% recirculation ratio of exhaust air/gases. The improvement potential for direct and hybrid heat recovery systems is obtained in the range of 580-666 kJ/s and 740-700 kJ/s, respectively, showing the drying process has vast potential for improving the exergetic performance. Moreover, the hybrid energy recovery system is found to be more sustainable.