Energy parameters of corn drying in a hot air dryer powered by exhaust gas waste heat: An optimization case study of the food-energy nexus

Abstract

This paper presents the energy parameters of corn drying in a convective crop dryer powered by exhaust gas waste heat. The empirical study was applied for drying 1,500 g batch size of an indigenous variety of maize grains (corn kernels). The study considered the impact of the drying air temperature and velocity on the energy indices (total and specific energy consumption, electric and thermal energy demand), drying rate, of the crop dryer, and the moisture diffusion coefficient of the studied samples. Tests were run at varying drying air temperatures (50, 55, and 60 °C) and air velocities (1.0, 1.5, and 2.0 m/s). Results obtained show that the drying parameters had a noticeable influence on the rates of heat transfer and moisture diffusion in the maize samples. The average drying rates varied between 0.83 and 1.4 g/min, whereas drying duration ranged from 305 to 515 min. The thermal efficiency of the drying process ranged from 4.23% to 8.07%. Its values had a direct relationship with the drying air temperature and an inverse relationship with the drying air velocity. The specific energy consumption, which varied between 129.95 and 227.63 kWh/kg increased with increasing air temperature and velocity. Drying air temperature had an inverse effect on the values of the electric energy consumption of the dryer system at constant air velocity. The maximum and minimum thermal energy values were obtained as 97.12 and 55.4 kW-hr, respectively. The activation energy and moisture diffusion coefficient values were in the range of 31.75 to 41.05 kJ/mol and 5.77×10−11 to 1.11×10−10 m2/s, respectively for the studied drying conditions. Prospects for commercial applications as well as recommendations for additional studies were stated.