(66e) Techno-Economic and Environmental Life Cycle Assessments of Hydrocarbon Biofuel from Loblolly Pine

Thermochemical conversion of wood to biofuel via fast pyrolysis is regarded as a promising conversion pathway for producing biofuels. The process involves rapid thermal degradation of wood in the absence of air at a temperature of approximately 500-550^OC with a short residence time of less than 2 seconds. Hydrocarbon biofuel is then produced through catalytic upgrading of the pyrolysis bio-oil product. Drying and size reduction of wood are major contributors to energy consumption of this process. Torrefaction, often referred to as mild pyrolysis, tends to enhance bio-oil properties by reducing water content, minimizing acidity, and reducing size reduction energy. The development of a two-stage fast pyrolysis process that involves a torrefaction pretreatment step prior to pyrolysis was investigated as an approach to minimize the energy consumption associated with size reduction. The impacts of different torrefaction temperatures have on the cost of production of hydrocarbon biofuel as well as the environmental impacts was investigated by carrying out techno-economic analysis (TEA) and life cycle assessment (LCA), respectively, with two-stage processing compared to the one-stage pyrolysis-based processing and to fossil fuels. Effects of the use of renewable co-products such as char and non-condensable gases from pyrolysis to replace fossil energy inputs (natural gas for process heat) to the process are explored in scenario analyses.

Aspen Plus process simulation package was used to model the two stage torrefaction-fast pyrolysis process with catalytic upgrading of pyrolysis bio-oil to hydrocarbon fuel blends. The effect of torrefaction severity on product composition, yield of pyrolysis bio-oil and subsequently yield of hydrocarbon fuel were obtained from the literature.^1-6 The effect of torrefaction on the energy requirement for size reduction was also included in our model based on literature data.⁷ Using these data sources, mass and energy balances were obtained, and used in sizing the equipment, with equipment prices estimated from a number of sources such as the Aspen Economic Process Analyzer, previous works and equipment vendors. A Discounted Cash Flow Rate of Return spreadsheet was used to obtain the gate cost of production, and data obtained from the simulation also served as inputs for the LCA carried out using the LCA software SimaPro 8.0 with greenhouse gas emissions (GHG) as the impact category.

From our model simulations, having a torrefaction step as a pretreatment step prior to fast pyrolysis reduces the cost of bio-oil production from loblolly pine, by reducing energy cost associated with size reduction. Results from the model also show a reduction in GHG emissions associated with the bio-oil production and catalytic upgrading as a result of the torrefaction pretreatment step. The effect of substituting renewable energy (char) for process heat demand rather than natural gas yielded a cost of production decrease from $4.26/gallon hydrocarbon fuel to $4.15/gallon for the one-step pyrolysis-based process. Full results on the TEA and LCA for all scenarios will be presented.

References

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2. Westerhof, R.J. et al. Stepwise fast pyrolysis of pine wood. Energy & fuels 26, 7263-7273 (2012).

3. Jones, S. et al. (National Renewable Energy Laboratory (NREL), Golden, CO., 2013).

4. Vispute, T. Pyrolysis oils: characterization, stability analysis, and catalytic upgrading to fuels and chemicals. (2011).

5. Huber, G.W., Chheda, J.N., Barrett, C.J. & Dumesic, J.A. Production of liquid alkanes by aqueous-phase processing of biomass-derived carbohydrates. Science 308, 1446-1450 (2005).

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