Life-Cycle Energy and GHG Emissions of Forest Biomass Harvest and Transport for Biofuel Production in Michigan

Abstract

High dependence on imported oil has increased U.S. strategic vulnerability and prompted more research in the area of renewable energy production. Ethanol production from renewable woody biomass, which could be a substitute for gasoline, has seen increased interest. This study analysed energy use and greenhouse gas emission impacts on the forest biomass supply chain activities within the State of Michigan. A life-cycle assessment of harvesting and transportation stages was completed utilizing peer-reviewed literature. Results for forest-delivered ethanol were compared with those for petroleum gasoline using data specific to the U.S. The analysis from a woody biomass feedstock supply perspective uncovered that ethanol production is more environmentally friendly (about 62% less greenhouse gas emissions) compared with petroleum based fossil fuel production. Sensitivity analysis was conducted with key inputs associated with harvesting and transportation operations. The results showed that research focused on improving biomass recovery efficiency and truck fuel economy further reduced GHG emissions and energy consumption.

Development of economic and environmental metrics for forest-based biomass harvesting

“…The primary goal of the LCA is to evaluate energy consumption and GHG emissions from forest harvesting operations in Michigan, U.S. System boundary defines the scope for LCA and is illustrated in Figure 2. Harvesting activities include cutting standing trees from the stump, processing them into typical log length (e.g., 2.54 m), and then transporting the processed logs to forest landings [14] (Figure 2). Activities from "upstream" inputs of the biomass feedstock production are excluded from this study.…”

“…Activities from "upstream" inputs of the biomass feedstock production are excluded from this study. These "upstream" activities may include reforestation and landscape carbon stock changes due to direct and indirect land use change [14]. We also excluded inputs for "downstream" activities of producing, distributing and end use of biofuels.…”

“…For the purpose of this study, a green tonne is at 50% moisture content wet basis [14]. Since no byproducts were considered, the environmental impacts were assigned to bioethanol, the primary product.…”

“…These material and energy inputs included fossil fuel, major machinery used to harvest wood (e.g. harvesters, forwarders), and lubricants and other inputs during machine fabrication, maintenance and large process equipment replacing [14]. The global warming potential (GWP) was established to measure a particular chemical's propensity to cause global climate change represented by carbon dioxide equivalents (CO 2eq ) over different time horizons [17].…”

“…Previous LCAs of biofuel produced from various biomass feedstocks focused on environmental performance of producing and supplying feedstocks [7,[10][11][12][13][14], without paying much attention on economic viability. Moreover, the evaluation of harvesting/forwarding activities was mostly based on the assumption of employing cut-to-length harvester/forwarder only [12] or whole tree harvesting system only [13].…”