Thermo-economic optimisation of industrial milk spray dryer exhaust to inlet air heat recovery

This study reports a thermo-economic design optimisation of an industrial milk spray dryer liquid coupled loop exhaust heat recovery system. Incorporated into the analysis is the ability to predict the level of milk powder fouling over time and its impacts on heat transfer and pressure drop. Focus is given to a finned round tube, a bare round tube and a bare elliptical tube. Modelling results show that spray exhaust heat recovery is economically viable for the considered industrial case study. Based on the results, the best liquid coupled loop heat exchange system uses a finned tube heat exchanger to recover heat from the exhaust air with a face velocity of 4 m/s and 14 tube rows, which gives a net present value of NZ$2.9 million and an internal rate of return of 71%. The developed thermo-economic assessment method has the ability to cater to site specific needs that affect the utility savings and the capital cost for implementing exhaust heat recovery.