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Colorimetry Applied to Steam-Treated Biomass and Pellets Made from Western Douglas Fir (Pseudotsuga menziesii L.)

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 55(2): 673-678. (doi: 10.13031/2013.41368) @2012
Authors:   P. S. Lam, S. Sokhansanj, X. T. Bi, C. J. Lim
Keywords:   Chemical composition, Color, Douglas fir, Elemental composition, Multi-linear regression, Pelletization, Steam treatment, Torrefaction, Wood pellets

Wood pellets made from sawdust and shavings are white in color and low in ash content. Pellets made from a mix of bark and white wood are darker in color, and bark increases the ash content of pellets. Steam treatment of biomass prior to pelletization improves the durability of pellets. Both wet (steam) and dry thermal (torrefaction) treatments of biomass darken the pellets. The off-color pellets have a lower commercial value than white wood pellets in residential applications. In this research, ground white wood (western Douglas fir, Pseudotsuga menziesii L.) was treated with saturated steam at 200C and 220C for 5 and 10 min. The colors of the treated and untreated powders and pellets were evaluated. The Hunter color coordinates L*, a*, and b* were recorded using a Minolta CM-5 spectrophotometer. Compared to untreated samples, the steam-treated samples became darker; the hues shifted from red to green and from blue to yellow. Multi-linear regression models of three color coordinates with elemental composition of carbon and hydrogen were developed. The values of L*, a*, and b* showed good correlation with percentage of carbon, hydrogen, and oxygen of the samples, with R2 values of 0.97, 0.99, and 0.97, respectively. The developed equations can be useful tools for the bioenergy industry for a quick estimation of fuel properties by a simple color measurement.

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