Capacitance Sensing of Moisture Content in Fuel Wood Chips

Moisture content of wood chips is an important factor to be known in their utilization as a biomass material. Several moisture measuring instruments are available in the market, but for most of these instruments, some sort of sample preparation is needed that involves sizing, grinding, and weighing. The samples in this process are usually destroyed, and the measurement involves considerable time and labor. The standard methods of oven drying and Karl Fisher also fall in the destructive and laborious category. In this paper, estimation of moisture content of hardwood chips, from the measurement of certain electrical properties of a parallel-plate capacitor, holding the samples of these materials between them at two radio frequencies, is presented. The wood chip samples tested were in the moisture range of 3%-50%. The standard error of prediction was 2.0, and the prediction accuracies were better for the samples with moisture contents below 25%. The construction and performance of a prototype moisture sensing instrument working on these principles is briefly described. This method being nondestructive and rapid would be useful in the biofuel industry.