Techno-Economics and Life Cycle Analysis of Upgrading Woody Biomass to Diesel Blendstock

Woody biomass conversion to transportation fuels have been developed as alternatives to fossil fuel production to reduce greenhouse gas emissions and to increase energy security. Fast pyrolysis, a thermochemical technology, has the potential to offer high efficiencies to produce liquid transportation fuels from woody biomass. Fast pyrolysis involves rapid heating of biomass particles in the absence of air at approximately 500°C and results in non-condensable gases, bio-oil (pyrolysis oil), and char as products. The pyrolysis oil can be upgraded via integrated mild hydrogenation and etherification processes to a high energy density fuel that can be blended with diesel for transportation use. A techno-economic analysis (TEA) and a life cycle analysis (LCA) have been conducted for producing a renewable diesel blendstock by fast pyrolysis and etherification over a mild hydrogenation process as an upgrading pathway. A process simulation was created using Aspen Plus® and for the base case simulations, the fast pyrolysis temperature of 500 °C was assumed. Thermodynamic properties of the hydrogenation and etherification model compounds were estimated using Density Functional Theory (DFT). The feedstock and product compositions and yields for pyrolysis were selected from published literature. The results from the process simulation were used to estimate the capital and operating costs for a plant with a capacity factor of 0.9 and process scale of 2,000 dry metric tons per day of forest residues. For the TEA cash flow, we used the economic assumptions and methodologies in the NREL/PNNL report by Dutta, 2015.Dutta’s capital costs (updated to 2019 U.S. dollars) and operating costs were used wherever appropriate, and new equipment costs were estimated using correlations from Turton, 2012. The discounted cash flow analysis with an internal rate of return of 10% was selected to assess the minimum fuel selling price (MFSP) of diesel fuel blendstock. The well-to-wheel LCA has been conducted using Argonne’s GREET 2019 software to assess environmental sustainability for producing renewable diesel fuel blendstock. The assessed MFSP of renewable diesel fuel blendstock for the base case is $2.99 per diesel gallon equivalent (DGE). The results of the fast pyrolysis temperature effect on the MFSP of diesel fuel blendstock have shown that the MFSP can be reduced to $2.74 per DGE when the fast pyrolysis temperature is decreased to 480 °C. Such a reduction in MFSP is due to the enriched composition of phenols and furans in pyrolysis oils produced at 480 °C. The LCA well-to-wheels analysis indicates that the renewable diesel blendstock would have a 93% reduction in fossil fuel use and a 93% reduction in greenhouse gas emissions relative to petroleum diesel