Abstract
Sugi (Criptomeria japonica D.Don), Akamatsu (Pinus densiflora Sieb. et Zucc.) and Karamatsu (Larix leptolepis Gordon) bark chips to be used as boiler fuel were divided into three parts: outer bark, inner bark, and adjoining sapwood, and their gross calorific value was determined. The gross calorific values without water were found to be significantly different among the three parts for each species. In order to investigate the reason for the differences, ash contents were measured. When the effect of ash content on calorific value was excluded, the obtained results showed clearly that bark possesses calorific values greater than sapwood. Further investigations on the reason for calorific differences were conducted in terms of differences in elemental and chemical composition. Calorific values of each part were calculated by the use of elemental analysis results, and these values were compared with the ones experimentally measured. Correlation between the two clarified that the superiority of bark to wood in calorific value was derived from its larger carbon content and smaller oxygen content. From a chemical point of view, the superiority was explained by the fact that bark contains less carbohydrate than wood and because carbohydrate was calculated to have the least calorific value of all the chemical components of bark and wood. Furthermore, the superiority was found to be enhanced when net calorific values were compared between bark and wood. Net calorific values as boiler fuel were calculated for Sugi, Akamatsu and Karamatsu bark chips and were shown in relation to practical moisture content at saw mill bark yards.
