Moisture evolution, thermal properties and energy consumption of drying spent grain pellets from a blend of some cereals for small scale bio-energy utilization: Modelling and Experimental study

Abstract

A fixed bed convective dryer was used to assess the influence of drying temperature and geometry deformation on moisture and thermo-physical property evolution of solid fraction pellets (spent grain) from wet milling of cereal blends for bio-energy generation for small homes. The aim is to study the physical mechanism of drying the pellets that includes temperature and moisture behaviour, transport phenomena, the response rate to varying process conditions, drying time and energy utilization which can be applied in the development of a fixed bed dryer for drying the pellets at a lower scale. The modified Cranck’s diffusion model was used to study moisture loss by introducing shrinkage. The verification of the model gave the mean absolute error (MAE) for moisture content with shrinkage as 0.0366–0.1500, while for without shrinkage, it was 0.0729–0.1500 for 60–80°C. The effective moisture diffusivity with integrating shrinkage is lower than no-shrinkage though these values varied with drying time. Fitting the moisture ratio with the exponential drying curve equations shows that logarithmic equations were the best model for drying at 60 and 70°C while Henderson and Pabis’s model was better at 80°C isothermal drying. Thermo-physical analysis showed that the average specific heat capacity ranges from 5423.387 to 5198.197 J/kgK while the thermal conductivity ranged from 0.115281 to 0.136882W/mK at 60–80°C. The energy and specific energy consumption ranged from 0.41 to 0.494 kWh and 108.39 to 119.29 MJ/kg. The shrinkage ratios, effective diffusivity and energy and specific energy consumption were empirically presented as a function of moisture, temperature and or air velocity variations with a high degree of association.