Water content measurement in woody biomass : using dielectric constant at radio frequencies

Abstract: The will for replacement of fossil fuels increased the use of woody biomass as fuel in heating and power plants. An important parameter for the use woody biomass as fuel is the water content of biomass as it influences the heating value and thereby the combustion control and pricing. Currently, water content is determined using the gravimetric method by drying samples  in an oven. This method is neither fast nor representative, as the water content can vary largely in different parts of the container which raised the need to develop sensors that are able to measure water content of biomass on-line and in a representative way.This thesis presents results from studies on the measurement of water content of woody biomass with radio frequency. Included are the study on the influence of temperature in the measurements, the use of dielectric mixing models to explain the dielectric behavior of woody biomass and the application of the measurement principle to full-scale. It was found that varying temperature between 1 and 62 °C did not influence the prediction of water content in biomass. It was possible to explain the behavior of the dielectric constant of woody biomass with a model with physical basis using empirically obtained parameters. Application of the principle to full-scale had positive results but larger prediction error than laboratory-scale measurements.