ARS | Publication request: Use of dielectric spectroscopy for pelleted biofuels characterization

Submitted to: Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE)
Publication Type: Proceedings
Publication Acceptance Date: May 26, 2008
Publication Date: June 30, 2008
Citation: Trabelsi, S., Lewis, M.A. 2008. Use of dielectric spectroscopy for pelleted biofuels characterization. Proceedings of the American Society of Agricultural and Biological Engineers International (ASABE).

Interpretive Summary: Dielectric spectroscopy is the study of dielectric properties (electrical characteristics) of materials and their variation with frequency or wavelength. Dielectric properties are electrical properties that determine how materials interact with electric fields such as those of high-frequency and microwave electromagnetic energy. Therefore, the dielectric properties of materials determine how rapidly they will heat in microwave ovens and lower radio-frequency dielectric heating equipment. Dielectric properties are also important in low power applications, such as the rapid measurement of moisture content in grain and other commodities. Biofuels represent an attractive alternative source of energy to fossil fuels. Moisture content of solid biofuels is a determinant factor in pricing, optimum combustion conditions, and storage management. This paper discusses the measurement of dielectric properties across broad ranges of frequency for pine pellets prepared as a biofuel. The moisture contents of the pine pellets are determined from the dielectric properties and compared with moisture contents determined by standard methods. Moisture contents by this rapid, nondestructive measurement were determined with standard error of about 0.4% moisture content. Bulk densities of the pine pellets were also determined simultaneously with a standard error of about 0.02 grams per cubic centimeter. The dielectric method presented in this paper is nondestructive, does not require contact with the material and can be used for real-time characterization of solid biofuels. The data are of interest to engineers and scientists working on biofuels applications. The new method offers promise for the monitoring of moisture and bulk density in biofuels processing and utilization and can improve the energy efficiency in such applications.

Technical Abstract: A microwave dielectric method for nondestructive instantaneous determination of bulk density and moisture content of pine pellets is presented. The method is based on measurement of dielectric properties, and , at microwave frequencies. Bulk density was determined from a complex-plane representation of the dielectric properties and does not require moisture content and temperature to be known. Moisture content was determined from measured and independent of bulk density with a density-independent calibration function. The standard error of calibration for bulk density was about 0.02 g/cm3 and that of moisture content was about 0.4%. Keywords. Dielectric properties, pine pellets, microwave frequencies, free space, bulk density, moisture content.