Bench-Scale Pyrolysis of Wood Pellets

Past work has demonstrated the feasibility of pyrolyzing biomass and condensing the resulting vapor to form a low quality combustible liquid. The product, often termed pyrolysis oil, bio-oil, or bio-crude, can be refined to a transportation grade fuel. Because the pyrolysis process is comparatively simple, we speculate that a mobile pyrolysis system might be able to process the biomass at the site of harvest, generating a dense liquid for transportation. This would be expected to result in improved transportation economics compared to transporting the raw biomass fuel. This technology is being considered for northern New Mexico forests that are presently managed by periodic thinning efforts with little utilization of the products. We have designed a bench-scale system and pyrolyzed biomass pellets, which function in these tests as surrogate material for the forest trimmings. The system features controllable furnace temperatures, augur feed, gas recirculation, and multi-stage condensation. We have analyzed gases, chars, and liquids resulting from various operating conditions and report product quantities and qualities through various standard chemical methods. Good liquid mass yields of over 50% of the original material are typically found, with varying product quality and quantity depending on the operating temperature. Our results suggest the current configuration gives better yields and functions more optimally at pyrolysis temperatures around 525°C. For a practical system, combustion of the non-condensable fuel gases may be able to replace the electrically heated furnace used in these tests.