Calorific value change of slash as logging residues after biological-drying under humid weather conditions in Japan

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Objectives of this study were to estimate the net calorific value that slash would contain after biological-drying, and to analyze the drying process of slash through drying experiments in a field.To identify the biological drying process in the field, we established slash bags those filled Sugi branches into a wire net bag (15 to 25 branches, 6000.0g to 11173.2g) and continuously scaled weights in the field. Also we piled 3 bags on a ground and established 3 piles. Field experiments, which included weighing each bag twice a day (morning and evening) and measuring temperature inside a pile, were carried out during 31 July 2004 to 4 October 2004. Weather conditions (air temp and humidity, wind velocity, precipitation, solar radiation) are also measured near the field site.Our study site was Kagoshima University Forest in JAPAN with more than 3,000mm annual rain fall.In general a moisture content of slash would reach to the equilibrium moisture content (EMC) which corresponds to each rel … More ative humidity. At 30 degree C, the EMC would be about 15% for 50% humidity and 24% EMC for 80% humidity. Since the average relative humidity in our field was 85% during our experiment, EMC could be estimated 25% to 30%. The EMCs of slash piles were observed 18 to 32% for upper layer pile and 15 to 63% for middle pile in spite of three times typhoon attacks with much rain fall. Through biological drying, it might be possible to decrease the moisture content of slashes reaching to EMC. The slash with lower moisture shows higher calorific heat value and needs lower transporting cost. Fuels with more than 2000kcal/kg could burn spontaneously without any additional fuels. Therefore, slash drying means improving fuel quality both in thermal and economic efficiency.Through 60-days drying, the moisture contents of slash became about one fifth and the calorific heat values increased to twice of initial value. From the results obtained, it might be possible to estimate the EMC of slash in the field from relative humidity. However, drying is essentially expressed as the diffusion process and we would have to model water contents diffusion process.Biological drying (natural drying) of slash would be a reasonable way to improve fuel quality. For a practical application, waterproof top mulching of slash piles might be useful for prevent from rain fall and dewing influence. Less