Design optimization of fluidized bed pyrolysis for energy and exergy analysis using a simplified comprehensive multistep kinetic model

In this paper, a simplified comprehensive multistep kinetic mechanism for fast pyrolysis was integrated with secondary and homogeneous reactions to evaluate the energy and exergy of the process. The kinetic mechanism was implemented in a two-dimensional multifluid model, which was able to reproduce experimental product yields and compositions. The results showed that the energy and exergy yields of noncondensable gas increased with temperature, while those of char decreased. The bio-oil energy and exergy yields were maximized at 500 °C. The results also showed that cellulose had the highest bio-oil energy and exergy yields, while lignin extraction with low Lig-O had superior energy and exergy efficiencies. A higher feeding rate was found to result in considerably higher energy and exergy efficiencies, and the recycled char was sufficient to supply heat for the reactor at a biomass feeding rate of ≥1.5 kg/h for all fluidization velocities. A capacity rate parameter was proposed for a sustainable pyrolysis reactor with high biomass conversion and performance. This model provides a useful reference for reactor scale-up and optimization.