Softwood gasification in a small scale downdraft gasifier

Thesis (M.S.)--Humboldt State University, Environmental Systems:\ud Environmental Resources Engineering Option, 2010This thesis is a performance evaluation of a small scale, 11 kilowatt electric, kWe,\ud downdraft gasifier made by Ankur Scientific. According to the US Department of Energy, the potential exists to displace 30% of the United States??? petroleum use by gasifying sustainably harvested biomass which includes forest residues and biomass from\ud forest thinning operations. Transportation costs for this biomass is high, however. One\ud way to minimize these costs is to use small scale, decentralized gasifiers near the harvest\ud sites. Furthermore, the preferred type of gasifier for the small scale is the downdraft\ud gasifier type. A majority of US forests are softwood, and most of the forest derived biomass resource that would be used for gasification is softwood. Historically, however, hardwood has been the preferred fuel for downdraft gasifiers. Therefore, the need exists to evaluate the efficacy of using softwood fuel for downdraft gasification. The softwood fuel used in this evaluation was Douglas fir wood chips. Moisture content, MC, of the fuel is critical to performance, so in this study, the MC of the fuel was varied from 6% to 22%. The survey consisted of three experiments at 6% MC, four at 13% MC, and three at 22% MC. The experimental run times were relatively short; they averaged 2.9 hrs per experiment. The cold gas efficiency of the gasifier was reasonably stable across the three MCs, with an average of 65.7%. Most performance parameters matched those in the literature for various hardwood studies, but the amount of hydrogen produced was lower than all reported values in the literature. The filtration system produced hazardous waste\ud from the sawdust and bag filters. Also, a number of maintenance issues were encountered during the survey which included initial carbon monoxide leaks and\ud mechanical failure of various components of the gasifier. This study showed that softwood gasification is possible, and performance is comparable to hardwood fuel. However, the short run times and maintenance issues encountered reveal that much more\ud research and development are needed if decentralized gasification is to become a feasible option for converting the potential stock of sustainably harvestable US biomass into\ud energy.Indonesia Sugar Group, The Renewable and Appropriate Energy Laboratory at the University of California, Berkele