September 15-20, 2019
The use of biochar has become increasingly popular over the last decade. The possible applications are vast and range from renewable carbon carrier in industrial and energetic applications to soil amendment and fodder additive. The various applications have different demands on the properties of biochar. These can be influenced by the choice of feedstock, reactor and production conditions. Regardless of production process and application however, achieving a high yield of the solid product is desirable from an economic point of view. The higher the treatment temperature, the more material is devolatilized and the lower is the amount of biochar that remains after pyrolysis . Nevertheless, some properties such as a very high relative carbon content can only be achieved at high temperatures and therefore at the cost of the char yield. Furthermore, it is generally accepted that a higher heating rate leads to a lower char yield and vice versa. Despite this common believe, there is not a large amount of systematic data available, which shows these correlations. Investigations using rapeseed straw as an example show that the heating rate of up to about 5 K/min initially increases the char yield . As the heating rate continues to rise, the mass yield of biochar decreases. Similar results have already been observed in  and . Nevertheless, systematic studies that would allow quantifying the influence of the heating rate on the solid char yield have not been conducted. This study aims to fill this gap.
Using systematic experiments with a thermogravimetric analyzer (TGA), the effects of the heating rate on the solid yield of biomass during slow pyrolysis are investigated. Biomass is a very inhomogeneous feedstock and the influence of the various components not clearly distinguishable from each other. Furthermore, reproducibility is poor, especially given the small amounts typically used in thermogravimetric analyses. Therefore, the experiments are carried out using not only wood as a feedstock, but also pure cellulose and lignin. The latter is often associated with a higher achievable char yield.
During the investigations, the starting materials are pyrolyzed in an inert atmosphere and at different heating rates, all within the regime of slow pyrolysis. The heat treatment temperature is varied between 450 and 700 °C, corresponding to typical conditions in practical biochar production processes. A sufficient holding time helps to minimize the effect of different carbonization degrees on the measurable char yield. Combining the different feedstocks with the pyrolysis conditions creates a broad data basis. This aids the quantification of the change in solid yield that can be achieved by varying the heating rate. After the experiments in the TGA, the resulting biochar is examined under the microscope for optical differences in pore structure and size in order to gain further insights into the influence of the heating rate. The results will further improve the understanding of biomass pyrolysis and optimize the process parameters for biochar production.
Weber, K.; Quicker, P.: Properties of biochar. In: Fuel. 217, 2018, pp 240-261
Zhao, B. et al.: Effect of pyrolysis temperature, heating rate, and residence time on rapeseed stem derived biochar. In: Journal of Cleaner Production. 174, 2018, pp 977-987
Karaosmanoglu, F.; Isigigür-Ergüdenler, A.; Sever, A.: Biochar from the Straw-Stalk of Rapeseed Plant. In: Energy & Fuels. 14, 2000, pp 336-339,
Mermoud, F. et al.: Influence of the pyrolysis heating rate on the steam gasification rate of large wood char particles. In: Fuel. 85, 2006, pp 1473-1482
Markus Lang, Kathrin Weber, and Peter Quicker, "Influence of heating rate on the solid yield of biomass pyrolysis" in "Bio-Char II: Production, Characterization and Applications", Franco Berruti, Western University, London, Ontario, Canada David Chiaramonti, RE-CORD, University of Firenze, Italy Ondrej Masek, University of Edinburgh, Edinburgh, United Kingdom Manuel Garcia-Perez, Washington State University, USA Eds, ECI Symposium Series, (2019). https://dc.engconfintl.org/biochar_ii/66