Drying is a fundamental procedure in many technological processes. This unit operation reflects primarily the diffusivity of liquids (e.g. water) within the porous matrix of materials. The drying of residual biomasses is an important issue in regions where agricultural or agro-industrial activities may provide significant amounts of this kind of materials as residual products to be used as renewable solid fuels. For drying, combustion and gasification of biomasses, internal fluid diffusivity is a most important aspect. We have used an uncomplicated method based on drying kinetics for the determination of relative diffusivity of water in woody biomasses (Ulate-Segura and Mata-Segreda, 2014*). Every material shows a specific drying curve that depends on its chemical and physical characteristics. Observed results can be registered as mass - time data (m vs. t). There is an initial linear relationship (constant -dm/dt) due to the evaporation of water covering the solid that behaves as free liquid. This period will last for as long as the rate of liquid arrival from inside the material to the surface equals the rate of evaporation. Once the system achieves the critical condition tc - xc (where x is the extent of drying at the time t), the drying rate decreases as the process takes place. In this stage the rate of drying is dependent on factors other than the intrinsic liquid volatility. It is reasonable to state that fluids diffuse faster in porous materials with high xc values, allowing the use of this parameter as relative measure of liquid diffusivity. 14 Samples of wood sawdust were analyzed. xc Values observed were between (0,21 ± 0,01) and (0,41 ± 0,02). Also, the data allow the calculation of other parameters that can be useful to decide the suitability of use of a specific woody biomass as solid fuel. One is the apparent specific surface area through which the evaporation of water takes place. Another useful piece of information derived from the measurements is the energy cost involved during drying that can be easily obtained from duration of the drying and performance of the moisture analyzers. *Ulate-Segura, D. G.; Mata-Segreda, J. F., Int. J. Renew. Energy Biofuels 2014, DOI: 10.5171/2014.970016.

Drying kinetics as a convenient method to determine relative diffusivity of water in woody biomasses

249th National Meeting (2015)

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