On the self-heating behavior of upgraded biochar pellets blended with pyrolysis oil: Effects of process parameters

Biochar obtained from biomass pyrolysis is a promising carbon neutral material which can be used in substitution of fossil coal and coke in metallurgical applications. Biochar's mechanical properties improve significantly without compromising reactivity, when upgraded by densification with pyrolysis oil and reheated. However, upgraded biochar pellets use in the industry is limited due to the risks associated with self-heating. This issue must be seriously considered for further industrial production of upgraded biochar pellets. Self-heating oven tests are generally time-consuming and limit the possibility of testing various potential solutions. The aim of this work was both to investigate the self-heating behavior of densified biochar and to possibly substitute the standard oven test with a fast and cost-effective thermogravimetric analysis. This was done by using Response Surface Methodology, where pyrolysis temperature, oil content and treatment temperature were selected as independent variables. By statistical analysis it was possible to understand that self-heating risk can be drastically reduced by upgrading the pellets at high temperatures (i.e. re-heating). In addition, through the analysis of the initial combustion temperature, the maximum weight loss rate and the activation energy considered as responses of the model), it was possible to understand how to predict the results of the self-heating oven tests through thermogravimetric analysis.