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Background: Thermal pretreatment of biomass ranges from simple (nondestructive) drying to more severe treatments that cause devolatization, depolymerization and carbonization. These pretreatments have demonstrated promise for transforming raw biomass into feedstock material that has improved milling, handling, storage and conversion properties. In this work, southern pine material was pretreated at 120, 180, 230 and 270°C, and then subjected to pyrolysis tests in a continuous-feed bubbling-fluid bed pyrolysis system. Results: High pretreatment temperatures were associated with lower specific grinding energies, higher grinding rates and lower hydrogen and oxygen contents. Higher pretreatment temperatures were also correlated with increased char production, decreased total acid number and slight decrease in the oxygen content of the pyrolysis liquid fraction. Conclusion: Thermal pretreatment has both beneficial and detrimental impacts on fast pyrolysis conversion of pine material to bio-oil, and the effect of thermal pretreatment on upgrading of pyrolysis bio-oil requires further attention.

Background: In this work the impact of grinding and chopping on the rheological properties of four switchgrass materials (panicum virgatum) is investigated, comparing physical characterization to previously published feeding performance in bulk equipment in a high-tonnage facility, in which chopped materials exhibited dramatically better handling performance than corresponding ground materials. Results: Physical characterization included sieve analysis, automated digital image analysis of particle size and shape distributions, microscopy of particle microstructure, shear tests using two different sizes of ring shear testers, flow tests in a custom hopper with an adjustable outlet, and uniaxial compression and spring back tests. Shear tests failed to demonstrate consistent statistically significant differences between the shear strengths of the chopped and ground materials subjected to uniaxial compression. However, in laboratory-scale hopper flow tests, the chopped materials exhibited substantially better flow performance than the ground materials, in agreement with the previously published bulk handling tests. Conclusion: Chopped switchgrass materials exhibit substantially better flowability properties in large-scale bulk equipment and in laboratory-scale hopper feeding tests; however, shear tests were not able to reliably predict the flowability properties of bulk switchgrass particles, likely because uniaxial-compression shear tests do not capture the effects of compressibility and elasticity in multi-dimensional flow streams.

The thin layer drying of pine forest residues consisting of bark, needles, leaves, and chips was experimentally conducted at air temperatures of 40, 50, 60, 70, and 80oC. Physical and chemical properties of fractionated forest residues were determined to evaluate its fuel properties. The experimental data obtained from thin layer drying study were fitted with Lewis, Page, and Henderson and Pabis equations to evaluate the drying behavior of the forest residues. Among the three drying models, the Henderson and Pabis model fitted well with the experimental drying data at the tested temperatures (40, 50, 60, 70, 80oC), achieving R2 values of0.992, 0.994, 0.997, 0.989, and 0.983, respectively. The drying constant k for the forest residues was increased with increase in drying air temperature and was correlated in the form of a second order regression equation. The thin layer drying data developed from this study will be useful for designing low temperature dryers for forest residues.

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