The major challenge to using agricultural biomass feedstocks as a coal substitute in utility applications is that it not only requires special handling and processing equipment but it is also severely limited in the percentage of co-firing possibilities. However, the torrefaction process has the ability to improve these properties. Combined with densification, torrefaction can significantly increase the energy density and handling properties of agricultural materials and also make them essentially water-proof. To date, torrefaction efforts have been mainly directed to woody biomass. On the other hand, agricultural biomass based torrefaction has attracted limited attention.
This research program is intended to address the knowledge and understanding gap for the industrial production and use of torrefied agricultural biomass materials. This will be completed by developing and demonstrating feasibility of producing high quality torrefied densified products using a broad range of agricultural based feedstocks. Those agricultural based feedstocks will need to have suitable characteristics (such as durability, grindability and hydrophobicity) for storage, handling and transportation and suitable fuel specifications for large scale utility applications. This report is related to the first phase of multi-phased research program and focuses on assessing feedstocks and torrefaction performance. A broad range of agricultural-based feedstocks including willow, miscanthus, switchgrass, wheat-straw, corn-stover, sorghum, bagasse, canola-residue, olive-residue, and sunflower-husks were investigated for their physical and chemical fuel characteristics including bulk density, grinding characteristics, particle size distribution, ultimate and proximate analysis, ash composition and structural composition. Evaluation of torrefaction behavior of the feedstocks was carried out at different torrefaction conditions (temperature and time) using both Thermo Gravimetric Analyser and diverse torrefaction reactor configurations at laboratory scale - rotary drum, fluidized bed and a fixed bed. A literature survey on the impact of washing on the fuel related qualities of agricultural feedstocks was performed.
Keywords: Biomass, Agricultural biomass, torrefaction, chemical analyses, physical analyses, grinding, sizing, ash composition, structural analysis (lignin, hemi-cellulose, cellulose, extractives), thermogravimetric analysis, washing.