Measurement of Moisture Distribution in a Biomass Silo Through Electrical Capacitance Tomography

The moisture distribution in stored biomass is a key factor in the self-heating and spontaneous combustion of biomass fuels. Measurement of moisture distribution in biomass fuels is thus essential for the safe operation of biomass-fired power plants. As a noninvasive imaging technique, electrical capacitance tomography (ECT) is proposed to measure the moisture distribution in stored wood pellets. The moisture distribution in different shapes and locations is measured on a laboratory-scale silo. Tomographic reconstruction algorithms are applied to obtain a visual representation of the moisture distribution. The relationship between the moisture content and effective permittivity of wood pellets is experimentally established. Experimental results demonstrate that ECT is capable of measuring the wet area ranging from 4% to 93% with a relative error of ±8%. The centroid position of the moisture distribution is measured with a relative error of ±5%. Meanwhile, the measured moisture content of the wet area has a relative error of ±10% over the range of 7.7%~16.4%.