Supply chain and process emissions impact of torrefaction to enable biomass use in large power plants versus raw biomass use in small power plants

Thesis (M.S.)--Humboldt State University, Environmental Resources Engineering,\ud Energy, Technology, and Policy, 2014The purpose of this study is to determine if electricity from torrefied biomass causes fewer greenhouse gas (GHG) emissions than electricity currently produced with raw biomass in Humboldt County. Torrefaction is an emerging woody biomass pre-treatment option that enables replacement of coal in large-scale power plants. This study quantifies emissions per unit energy produced (g CO2e kWhe-1) and per unit mass utilized (g CO2e BDT-1) for two electricity generation pathways, termed raw biomass and torrefied biomass. The raw biomass pathway represents business as usual, to which the torrefied biomass pathway is compared. The biomass fuel for both pathways is timber harvest waste. To estimate total GHG impact, CO2, CH4 and N2O emissions and credits for all processes from waste harvest to power production are calculated for both pathways and compared. Total emissions for the raw biomass pathway are -370 ?? 920 g CO2 e kWhe-1, versus -240 ?? 810 g CO2e kWhe-1 for the torrefied biomass pathway, with uncertainty expressed as one standard deviation. Because consumption of biomass fuel offsets large alternative disposal emissions, the pathway that consumes more biomass fuel achieves lower net emissions. Emissions per BDT of forestry waste utilized were calculated to be -330,000 ?? 180,000 g CO2 e BDT-1 for the raw biomass pathway and -360,000 ?? 76,000 g CO2 e BDT-1 for the torrefied biomass pathway. On a per mass basis, combustion emissions in the torrefied pathway offset less of the savings from avoided emissions than in the raw biomass pathway. The difference between the business-as-usual raw biomass pathway and the prospective torrefied biomass pathway represents an opportunity to develop lower-emission biomass fueled energy systems on a per BDT utilized basis that also emit less than the cleanest current fossil fuel power plants, 290 g CO2 e kWh-1 (Moomaw et al., 2011), on a per kWh basis. Further research on alternative waste disposal practices and emissions is necessary to refine uncertainty estimates for this study. This study recommends that further torrefaction pretreatment research be completed to encourage development of the technology