Abstract
Moisture content is one of the most important parameters related to the quality of wood chips that affects both the calorific and economic value of fuel chips. For industrial applications, moisture content needs to be detected quickly. For this purpose, various indirect moisture content measurement methods (e.g., capacitance, NIR, microwave, ECT, X-ray CT, and nuclear MR) have been investigated with different results in the past. Nevertheless, determining wood chip moisture content in real time is still a challenge. The main aim of this article was therefore to analyze the dielectric properties of wood chips at low frequencies (10 kHz–5 MHz) and to examine the possibility of using these properties to predict wood chip moisture content and porosity. A container-type probe was developed for this purpose. The electrical capacitance and dissipation factor of wood chips with different moisture content was measured by an LCR meter at 10 kHz, 50 kHz, 100 kHz, 500 kHz, 1 MHz, and 5 MHz frequencies. Wood chip porosity was also measured using a gas displacement method. Linear models for moisture content and porosity prediction were determined by backward stepwise linear regression. Mathematical model was developed to better understand the physical relationships between moisture content, porosity, and electrical capacitance. These models were able to predict the moisture content of observed quantities of wood chips with the required accuracy (R2 = 0.9–0.99). This finding opens another path to measuring the moisture content and porosity of wood chips in a relatively cheap and fast way and with adequate precision. In addition, principal component analysis showed that it is also possible to distinguish between individual wood chip fraction sizes from the information obtained.
Highlights
Moisture content (MC) is undoubtedly one of the most important parameters of the quality of wood chips, e.g., [1,2,3,4,5,6] and many others
Based on our results presented in this paper and this comparison, it can be stated that measuring the electrical properties of wood chips at lower frequencies is undoubtedly a promising method to predict their MC fast and with adequate precision
It was found that dielectric properties obtained at low frequencies (10 kHz–5 MHz) from parallel plate capacitor inserted in container-type probe can be used for the sufficiently accurate prediction of wood chip moisture content and porosity
Summary
Moisture content (MC) is undoubtedly one of the most important parameters of the quality of wood chips, e.g., [1,2,3,4,5,6] and many others. It affects both the calorific and economic value of fuel chips. Moisture is one of the basic natural characteristics of wood, its determination is a challenge, especially in real time, e.g., [10,11]. Oven drying is a standard and standardized [4,7,16,17,18,19] method, many authors [2,4,5,6,12,13,15,16,17] point out its disadvantages: the method is destructive, slow, and labor consuming, with potential sources of errors including mainly sampling errors or sample size, and it cannot be used for real-time
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