(745a) The Selection and Optimization of Heat Carrier Materials to Maximize Liquid Yields and Heat Recovery in Auger Pyrolyzers

Auger pyrolysis reactors are a promising technology in the future of commercial pyrolysis processes. Advantages of auger pyrolyzers over traditional fluidized bed pyrolyzers include the minimal requirement of an inert gas and the lack of sensitive hydrodynamic bed conditions. Additionally, auger pyrolyzers have the flexibility of different modes of heat transfer such as conventional indirect heating or directing heating via heat carrier materials to provide higher heat transfer rates. To mitigate the risk upon scale-up, a better understanding and optimization is required of auger pyrolyzer heat carrier materials. This work focuses on the selection of heat carrier materials and their ability to be recycled within the auger pyrolyzer for maximum product yields and energy recovery.

A twin-screw, lab-scale auger reactor was used to pyrolyze up to 1 kg/hr of red oak at 515°C for all trials. The effect of heat transfer properties on pyrolysis product yields was evaluated for several heat carrier materials. Stainless steel shot, silicon carbide, and sand were investigated. High liquid yields of ~65 wt. % were achieved. Sand was then chosen to further evaluate and optimize heat carrier parameters such as mass flow ratios, particle size, and long-term performance. Two sizes of sand deemed fine (250-600 µm) and coarse sand (600-1000 µm) were evaluated at heat carrier to biomass ratios of up to 20:1. The sand was then recycled at up to 5 recycles producing consistent yields of bio-oil (~60 wt. %), char (~17 wt. %) and gas (~18wt %). Regeneration of the heat carriers was found to be required trial to both remove any carbon residue and maximize heat recovery. The results from this work suggest that the selection and optimization of heat carrier for auger pyrolyzers is important in reaching high liquid yields, while minimizing processing costs attributed to attrition rates and heat recovery.

*Funding for this project was provided by Phillips 66 Company.