Feasibility analysis of a hybrid poplar-based biorefinery in southwestern Washington

Abstract

To mitigate climate change, reduce greenhouse gas (GHG) and particulate emissions, contribute towards energy independence and security, and promote sustainable economic development in the United States (U.S.), cellulosic biofuels have been considered as potential replacement fuels for petroleum-derived fuels. While biofuels offer many environmental and socioeconomic benefits, commercial scale biorefineries are not prominent in the U.S. High feedstock costs and capital investment costs are two of the biggest challenges prohibiting the advancement of commercial scale biofuel production. This study reduced feedstock costs to supply a 250 Gg feedstock capacity cellulosic ethanol biorefinery in western Washington by 22% by incorporating local, low-cost hardwood sawmill residues and hybrid poplar from treated wastewater management ecosystem service with the traditional method of suppling biomass (hybrid poplar) from purpose-grown plantations. The proposed biorefinery is modeled producing 75 megaliters of cellulosic ethanol annually. The proposed biorefinery design, referred to as the Integrated design case, assumes co-location with an adjacent power plant, eliminating the need for an in-house boiler/turbogenerator and wastewater treatment system by using a multi-effect evaporator to evaporate waste streams into combustible syrup for steam production. Two additional design cases are further evaluated for comparison: (1) Non-integrated design case producing 75 megaliters of ethanol annually, and (2) Integrated, Increased Production design case producing 189 megaliters of ethanol annually. Under the Integrated design case, total capital investment is reduced by 38%, installed equipment costs are reduced by 43%, and electricity use is decreased by 64% as compared to the Non-integrated design case. A 38% reduction in total capital investment per liter can be realized by scaling biorefinery ethanol production up to 189 megaliters per year using the integrated design approach. Discounted cash flow rate of return analysis is used to evaluate economic performance and ethanol minimum selling price. Under the most realistic financing scenario, 40% loan and 15% discount rate, the Integrated, Increased Production design case incorporating integrated approaches, including using mixed feedstock supply sources, achieves the lowest minimum ethanol selling price of $0.67/liter, resulting in a 31% reduction in ethanol minimum selling price compared to the Non-integrated design case and a 19% reduction compared to the Integrated design case. Life cycle carbon analysis (quantifying global warming potential (GWP) contribution in CO2 eq. MJ-1) of the Integrated design case is conducted, yielding a 52% reduction in GWP as compared to 2005 gasoline production and use. This study provides a framework for incorporating integrated approaches into biorefinery design using local context to realize economic and environmental gains.