Improving the energy effectivity of biomass drying for utilisation in energy systems by combining convective and contact drying

The article deals with reducing the energy consumption of biomass drying before combustion in energy plants. The combination of traditionally used convective hot air drying and less applies contact drying is analyzed. To determine the basic drying characteristics, the experiments on a contact dryer and a convective hot air dryer were carried out with wet wood chips. A heat balance model of a system with serial connection of a convective air dryer and a contact dryer was compiled. In the model, the utilization of condensation heat from the waste vapor leaving contact drying to preheat the drying air for convective drying was considered. Based on these results, the system could be optimized to achieve the lowest energy consumption, drying time, and dryer sizing. This solution can significantly improve the energy efficiency of drying moist biomass before combustion from 3.29 and 2.76 MJ per kg of evaporated water for only convective drying and only contact drying, respectively, to 1.48 or 1.33 MJ per kg of evaporated water, depending on the order of the dryers in their connection.