https://www.mdu.se/

A method that permits the determination of moisture content in biofuel in a fast and representative way is under development. Vie method uses radio frequency waves within the range of 310 MHz to 800 MHz and measures the reflection coefficient in samples with volume of about 0.1 m(3). The influence of sample temperature in the measurements is shown in this study. Two biofuel types were used, with moisture content varying between 31% and 63% and temperature varying between 1 degrees C and 63 degrees C. The data was evaluated with multivariate data analysis. Results show that it is not possible to identify the sample temperature as a principal component in a principal component analysis and partial least squares regression shows no correlation between temperature and the radio frequency data. For the frequency interval and the temperature range studied, it was not possible to detect any influence of sample temperature on moisture content prediction with the radio frequency method.

The aim of this study is to determine the dielectric constant of woody biomass at different water contents and describe its behavior with a dielectric mixing model. The use of the model for determination of water content is also verified. Dielectric constants were calculated from the travel times of electromagnetic waves with a center frequency of 555 MHz through collected biomass samples. The power law, Maxwell-Garnett, and Polder van Santen mixing models were applied to the experimental data. In the models, biomass was considered as a mixture of three phases: a solid solution composed of wood cellular material and bound water, free water, and air. The experimental data was found to be better described by the Maxwell-Garnett model. The use of this model along with an independent validation set for the determination of volumetric water content resulted in a root mean square error of prediction of 0.03 within the investigated volumetric water content range of 0.07-0.29.