Strategic valorization of bio-oil distillation sludge via gasification: A comparative study for reactivities, kinetics, prediction and ash deposition

Biomass refinery system is gradually maturing as an emerging technology for waste management and carbon neutral, but bio-oil distillation sludge (DS) as an unexpected product significantly hampers the continuous operation of the system and hazards human health. Herein, we conducted a comparative investigation on the gasification characteristics of bio-oil distillation sludge char (DSc) and walnut shell char (WSc) to explore the clean and efficient strategy for disposal of DS. The biochar was prepared on a fixed bed reactor under two different temperatures (900?degrees C and 1100 degrees C), followed by being gasified on a thermogravimetric analyzer with the purposes of evaluating the gasification behaviors and kinetic evolution. Meanwhile, machine learning approach (back-propagation neural network as an example) and thermodynamic equilibrium simulations were innovatively adopted to predict the gasification performances and ash deposition characteristics, respectively. The results indicated the gasification reactivities for WSc varied with gasification conditions and preparation temperatures, whereas the DSc reactivity was far lower than that of WSc. Gasifying WSc accompanied with the development of porous structures and thus was kinetically fitted by random pore model well. However, the gasification process for DSc was more representative by volume model and grain model. The back-propagation neural network performed an excellent prediction effect on gasifying DSc and WSc under whatever (non-) isothermal conditions, with the correlation coefficients beyond 0.9983. In addition, mineral compositions and ash deposition prediction indicated the presence of potassium and calcium in WSc induced the decreased melting temperatures of ash, and thus severe ash slagging and fouling, while DSc ash, composed of iron and silicon, exhibited flocculent morphology and was difficult to deposit.

Automated summary

This study compares the gasification characteristics of bio-oil distillation sludge char and walnut shell char, and proposes a clean and efficient strategy for disposal of bio-oil distillation sludge. The results show differences in gasification reactivity between the two chars, and machine learning approach proves effective in predicting gasification performance and ash deposition characteristics.