Comparison of Rapid Moisture Content Determination Methods for Wood Chips

Newly developed gravimetric or electric methods may be suitable alternatives to provide a rapid and accurate moisture content determination of wood chips. In total, nine different rapid determination devices were selected for testing including two infrared dryers, four dielectric instruments, two conductivity methods and one time-domain-reflectometry method. Oven drying according to ISO 18134-2 was used as reference. Testing was carried out on different raw materials of wood chips and at different levels of moisture content. On average, the mean measuring deviation from the reference value ranged from -2.6 w-% (± 1.7 w-% SD) to 3.8 w-% (± 4.7 w-% SD). Thereby, best results were obtained with the infrared dryer MA35 for a large range of different moisture contents. In contrast, the electric methods were less accurate but allowed for larger sample sizes. Furthermore, instrument accuracy strongly increased with decreasing moisture content. The high accuracy of the oven drying method could not be reached by any of the tested devices. However, by using a high amount of samples the average moisture content of all measurements approximated the reference value. Therefore, some instruments could be recommended for quality assurance during production.
Proceedings of the 24th European Biomass Conference and Exhibition, 6-9 June 2016, Amsterdam, The Netherlands, pp. 634-638