An accurate and fast method for moisture content determination

Abstract

Moisture content (M) is an important quality parameter of wood chips, strongly influencing the net calorific value as received, and consequently the price of fuel chips. The oven-drying method, the current standard for determining M, is slow and may sometimes not be concluded before the sampled lot is combusted. This increases the risk of inefficient combustion and reduces the value of M determination. A fast and reliable method for determining M would therefore be valuable. The Metso MR Moisture Analyzer (Metso), which measures M by means of magnetic resonance, was compared with the oven-drying method. M measurements were carried out using one machine in Sweden and one in Canada for a total of six different biomass materials, where M ranged from 17–65% on a total weight basis. On average the Metso overestimated M by 0.23 percentage points (not significant) for the machine in Sweden and significantly underestimated M by 1.84 percentage points for the one in Canada. The results for repeatability of measurements showed that 95% of the measurements were within ±1.53 percentage points of the mean for the machine in Sweden and within ±1.91 percentage points of the mean for the machine in Canada. The samples are measured in standardized containers of 0.8 litres, which limits the length of the wood chips that can be measured to 10 cm without further sample preparation. The Metso is easy to use and a single measurement requires 120 seconds, allowing quick M measurement even if multiple samples are needed.