(106b) Modelling of a Solar-Thermal Reactor for Biomass Fast Pyrolysis

Solar thermochemical conversion can provide carbon-free processes for biomass to fuels and chemicals. Biomass fast pyrolysis is an endothermic process that requires fast heating rates (>300 ^oC) and high heat flux at temperatures up to 600 ^oC. Concentrated solar thermal energy is an ideal option to meet these requirements. A computational Eulerian-Eulerian model is used to simulate and investigate fast pyrolysis of switch grass biomass in a solar parabolic trough receiver/reactor equipped with a novel gas-separation system. The separator controls the effect of tar-cracking reactions and achieves high separation efficiency compared to other gas-solid separation methods such as the U-separator and the cyclone. The study assumes an average heat flux concentrated along the receiver/reactor. Pyrolysis reaction was represented as a single global first order Arrhenius type reaction with volatiles separated into condensable (bio-oil) and non-condensable gas (NCG) products. The drying of moisture of the switch grass was represented as a mass transfer process in which the liquid water is converted to vapour.

The mechanism of solid-gas separation, residence time, devolatilization efficiency and product yield has been presented in this model. The separation efficiency achieved by the conical deflector was over 99%, this was found to correlate with experimental separator conducted by Huard et. al. (2010). The gas residence time distribution was within 1-2 s; this is within the range of residence time recommended for fast pyrolysis. The product composition had a bio-oil yield of >50% with minimal NCG. The range of yields was compared with similar models and experiments using different reactors. This work presents a new and energy efficient approach to demonstrate the potentials of solar thermal systems for biomass fast pyrolysis.