Experimental and theoretical study of heat and mass transfer in a continuous, vertical and coaxial pyrolysis reactor for high porosity biochar production

Abstract

The development of a high porosity biochar production facility to meet an industrial need requires a detailed knowledge of the thermochemical phenomena of pyrolysis. The main challenge of this work is the production of biochar with a high porosity in large quantities, and producing a residual gas that can be used for drying biomass. Two complementary tools have been here developed and operated: a patented prototype and a designing numerical model. The model was developed in parallel with tests on the prototype and a characterisation phase of the various materials involved in the pyrolysis process in order to increase the correspondence between numerical model and experimental results. The model is used to predict, depending on the geometry chosen, the temperature in the pyrolysis zone, the heating rate and residence time corresponding to the applied biomass flow rate, as well as the biochar and gas mass yields.This study demonstrated the ability of the experimental plant to produce a high porosity biochar with a specific surface of 200m2.g-1 in the best case and a constant carbon content around 90% on dry basis due to the separation of the partial oxidation and pyrolysis zones. Following a material characterisation phase and a customisation of the parameters of the Arrhenius formalism adapted to pine bark, the numerical model shows a strong correspondence in terms of temperatures, biochar yield and thermochemical kinetics with the experimental observations from the prototype.