The effect of heating rate, particle size and gas flow on the yield of charcoal during the pyrolysis of radiata pine wood

Charcoal derived from sustainable grown wood is a potential source of fuel and reductant for iron and steel making and a potential way to decrease the net CO2 emissions from the steelmaking industry. However a modern charcoal making process is likely to be required to supply the iron and steel industry with the required amount of charcoal to make significant difference to greenhouse gas emissions. The design of such a process requires fundamental knowledge on the effect of process variables on charcoal formation and yield during pyrolysis. The effect of biomass heating rate, purging gas flow and particle size on the yield of charcoal from pine wood was quantified in a series of pyrolysis experiments using a thermo-gravimetric apparatus. Temperature-time curves obtained during the heating of biomass showed the pyrolysis reactions became exothermic at about 350 degrees C. Increasing the flow of inert carrier gas through the biomass sample resulted in a decrease in charcoal yield and a faster rate of biomass decomposition. At zero gas flow the charcoal yield is independent of particle size. As gas flow through the sample is increased the yield of charcoal is increasingly dependent on increasing particle size. Increasing the wood heating rate from 0.11 to 10 degrees C/min, resulted in decreased charcoal yield. The period of fast biomass decomposition shifted to higher temperatures and the start of decomposition occurred at higher temperatures. These results indicate that low temperature reactions of charcoal formation are favoured by low heating rates and the initial charcoal acts as a catalyst for primary biomass decomposition. Lower heating rates are also associated with increased retention of pyrolysis vapours in the biomass which results is increased production of secondary charcoal and increased charcoal yield. (C) 2019 Elsevier Ltd. All rights reserved.