(266f) Techno-Economic Analyses and Life Cycle Assessment of Two Stage Fast Pyrolysis for Bio-Oil Production from Wood

Thermochemical conversion of wood to biofuel via fast pyrolysis is regarded as a promising alternative for producing biofuels.  This process involves a quick thermal degradation of wood in the absence of air at a temperature of approximately 500^OC with a short residence time of less than 1 second in the pyrolysis unit. Despite its potential, one of the major drawbacks of this approach for production of biofuels is the process energy intensity. Drying and size reduction of wood are major contributors to energy consumption and the development of a two stage process that involves a torrefaction pretreatment step prior to pyrolysis is being investigated as an approach to minimize the energy consumption associated with the size reduction step. Torrefaction, often referred to as mild pyrolysis, tends to enhance bio-oil properties by reducing water content, minimizing acidity, and increasing heating value.  Previous TEA and LCA works have looked at torrefaction and fast pyrolysis as stand-alone processes.  However, the work reported here investigated a 2-stage process for producing pyrolysis oil.

Aspen Plus process simulation package is used to model the two stage torrefaction-fast pyrolysis process.   The effect of torrefaction severity on composition and yield of pyrolysis bio-oil was included using data from works of Westerhof et al (2012)³,Zheng et al (2012) ⁴, and Jones et al (2009)  ¹ while the work of Phanphanich et al (2011) ²was used for the effect of torrefaction on size reduction energy requirements. Using these data, mass and energy balances are obtained, and then subsequently 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 prepared will be used to obtain the gate cost of production, data obtained from the simulation will also serve as inputs for the Life Cycle Assessment that will be carried out using the LCA software SimaPro.

References

1              Susanne B Jones, Corinne Valkenburg, Christie W Walton, Douglas C Elliott, Johnathan E Holladay, Don J Stevens, Christopher Kinchin, and Stefan Czernik, Production of Gasoline and Diesel from Biomass Via Fast Pyrolysis, Hydrotreating and Hydrocracking: A Design CasePacific Northwest National Laboratory Richland, WA, 2009).

2              Manunya Phanphanich, and Sudhagar Mani, 'Impact of Torrefaction on the Grindability and Fuel Characteristics of Forest Biomass', Bioresource technology,102 (2011), 1246-53.

3              Roel J. M. Westerhof, D. Wim F. Brilman, Manuel Garcia-Perez, Zhouhong Wang, Stijn R. G. Oudenhoven, and Sascha R. A. Kersten, 'Stepwise Fast Pyrolysis of Pine Wood', Energy & Fuels,26 (2012), 7263-73.

4              Anqing Zheng, Zengli Zhao, Sheng Chang, Zhen Huang, Fang He, and Haibin Li, 'Effect of Torrefaction Temperature on Product Distribution from Two-Staged Pyrolysis of Biomass', Energy & Fuels, 26 (2012), 2968-74.