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

Lorenzo Riva,Alessandro Cardarelli,Geir Johan Andersen,Therese Videm Buø,Marco Barbanera,Pietro Bartocci,Francesco Fantozzi,Henrik Kofoed Nielsen

doi:10.1016/j.fuel.2020.118395

Lorenzo Riva, Alessandro Cardarelli + Show 6 more

Open Access

https://doi.org/10.1016/j.fuel.2020.118395

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Abstract

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.

Highlights

Greenhouse Gases (GHG) should be reduced implementing not a single but many possible sustainable solutions [1]
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
The self-heating behavior of biochar pellets with pyrolysis oil as binder are tested by both UN test and thermogravimetric analysis (TGA)

Summary

Introduction

Greenhouse Gases (GHG) should be reduced implementing not a single but many possible sustainable solutions [1]. The industrial production of thermally treated biochar pellets with pyrolysis oil has been further investigated It is still not very clear how densification and addition of pyrolysis oil may increase the risk of self-heating, which is the tendency of certain porous fuels to undergo spontaneous exothermic reactions, in absence of any external ignition, at relatively low temperatures and in an oxidative atmosphere [14]. The method is based on heating the sample in an isothermal oven test, where volumes, temperatures and test times are fixed Using this test it is possible to scale up the results to larger volumes and understand if a material can be stored and shipped safely [20]. A new approach to couple thermal analysis and oven test to analyze selfheating is proposed This solution might facilitate the self-heating assessment of treated biochar pellets with a reduction of costs, easing their potential industrial production and application

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