Main content area

Life cycle assessment of a corn stover torrefaction plant integrated with a corn ethanol plant and a coal fired power plant

Kaliyan, Nalladurai, Morey, R. Vance, Tiffany, Douglas G., Lee, Won F.
Biomass and bioenergy 2014 v.63 pp. 92-100
biocoal, biomass, business enterprises, carbon dioxide, coal, corn, corn stover, electricity, energy, ethanol, gasoline, greenhouse gas emissions, greenhouse gases, heat, life cycle assessment, power plants, steam, torrefaction, water content, Midwestern United States
A life cycle assessment (LCA) study was conducted to understand and assess potential greenhouse gas (GHG) emissions reduction benefits of a biomass torrefaction business integrated with other industrial businesses for the use of the excess heat from the torrefaction off-gas volatiles and biocoal. A torrefaction plant processing 30.3 Mg h−1 of corn stover at 17% wet basis (w.b.) moisture content was modeled. The torrefaction plant produced 136,078 Mg y−1 of biocoal at 1.1% w.b. moisture content and 28.1 MW of excess heat energy in the torrefaction off-gas volatiles. At the torrefaction plant gate, the life-cycle GHG emission for the production of biocoal (including corn stover logistics emissions) is 11.35 g MJ−1 carbon dioxide equivalent (dry basis) (i.e., 229.5 kg Mg−1 carbon dioxide equivalent of biocoal at 1.1% w.b. moisture content). The excess heat from the torrefaction plant met 42.8% of the process steam needs of a U.S. Midwest dry-grind corn ethanol plant producing 0.38 hm3 y−1 of denatured ethanol, which results in about 40% reduction in life-cycle GHG emissions for corn ethanol compared to gasoline. Co-firing 10%, 20%, and 30% (energy basis) of biocoal at a coal-fired power plant reduced the life-cycle GHG emissions of electricity generated by 8.5%, 17.0%, and 25.6%, respectively, compared to 100% coal-fired electricity. A sensitivity analysis showed that adding a combined heat and power (CHP) system at the torrefaction plant to meet 100% electricity demand of the torrefaction plant (2.5 MW) could further reduce the GHG emissions for biocoal, corn ethanol, and co-fired electricity.