One of the main impeding factors in achieving national biofuel production targets is the establishment of a sustainable biomass feedstock supply system. One option for preserving and enhancing biomass quality, reducing storage and transportation costs and for attaining uniformity among feedstock is to pre-treat the biomass by a process known as torrefaction. Torrefaction is a thermochemical pre-treatment which results in a solid product with a reduced moisture content, enhanced energy density, improved hydrophobicity and microbial degradation resistance, and increased brittleness.

Ajay Shah, Iowa State University, Ames, USA, and colleagues carried out a techno-economic analysis of a production-scale torrefaction system and quantified the effects of changes in feedstock moisture content, temperature, plant operating window, and initial capital investment in terms of energy and cost. Results indicated that the energy required for the torrefaction process increased and energy efficiency decreased with increasing moisture contents. However, both of these energy metrics exhibited a decreasing trend with increasing process temperature. To be cost effective and sustainable, a production-scale torrefaction system needs to be integrated with other large-scale biomass preprocessing or upgrading processes at a central facility.

The output from this analysis provides clear guidance on the opportunities and costs associated with production-scale torrefaction of biomass as a feedstock intermediate.

• Techno-economic analysis of a production-scale torrefaction system for cellulosic biomass upgrading,
  A. Shah, M. J. Darr, D. Medic, R. P. Anex, S. Khanal, D. Maski,
  Biofuels, Bioproducts and Biorefining 2011.
  DOI: 10.1002/bbb.336