The effect of compaction of the dispersed wood biomass layer on its drying efficiency

The article presents the results of experimental studies of the process of drying a layer of relatively large thickness (up to 100 mm) of woody biomass under conditions of radiation-convective heating. Based on the temperature values recorded in the experiments at the characteristic points of the biomass layer during the drying period, an analysis was made of the influence of the density of the filling of finely dispersed wood (pine shavings, sawdust) on the drying times. It has been established that the compaction of biomass leads to a significant acceleration (by 1.5–2 times, depending on the ambient temperature) of the drying process. A physical model is formulated that describes a complex of heat and mass transfer processes that occur during heating of woody biomass under compaction conditions. It is shown that a 1.7-fold increase in the density of a layer of finely dispersed wood (with an initial thickness of 100 mm) leads to an increase in the layer temperature during the entire drying period by an average of 23%. In order to substantiate the established regularities, an analysis was made of the change in the thermal conductivity of biomass during its compaction using a group of mathematical models of the thermal conductivity of heterogeneous media. The results of the theoretical analysis showed that the increase in the efficiency of biomass drying during its compaction occurs as a result of an increase in the effective thermal conductivity of the layer of crushed woody biomass. The results of the experiments clearly illustrate the possibility of increasing the efficiency of drying dispersed woody biomass without additional costs for optimizing heat and mass transfer processes.