An economic analysis of bio-energy options using thinnings from overstocked forests

The economic feasibility of producing bio-fuels and ultimately bio-energy by utilizing thinnings from overstocked forests is examined. Large areas of forest in the western US are severely overstocked with small diameter trees, and as such, pose extreme risk for catastrophic wildfires. Physical removal of such small diameter trees, or forest “thinning,” is the best solution to the wildfire problem, and represents a potential raw material for the production of bio-fuels. Production of (1) wood pellets, (2) bio-oil, and (3) methanol all represent potential conversion pathways which would utilize unmerchantable forest thinnings as the feedstock. Wood can also be directly combusted, either in conjunction with another fuel such as coal or on its own to generate steam and electricity. This study examines the potential for accomplishing both forest wildfire reduction and the generation of energy using a single integrated pathway. The economic effects of thinning scale, thinning duration, and distance to end-use markets are quantified. Co-firing of thinnings with coal is currently found to be the most viable option for transportation distances of less than 500 km. Beyond 300 km transportation distance, pelletization, fast pyrolysis, and methanol synthesis become increasingly cost competitive for different ranges of thinning yield and duration. Bio-energy options are economically preferable to landfill or open burning disposal of thinned biomass; however, revenue from bio-fuels will not cover the cost of thinning. Results for a range of thinning scenarios are visualized using technology maps.