Influence of pyrolysis conditions and the nature of the wood on the quality of charcoal as a reducing agent

The production of charcoal for metallurgical applications requires careful selection of the wood and control of the pyrolysis conditions to ensure acceptable charcoal quality. The main properties of charcoal to be considered are density, mechanical strength, and reactivity. In this study, charcoal was produced from two types of wood commonly used in the industry, Eucalyptus globulus (eucalyptus) and Picea abies (spruce), in a pilot scale pyrolysis fixed bed reactor at three temperatures (500, 650 and 800 degrees C) and two solid residence times (0 and 90 min). The yields, composition, apparent density, true density, porosity, carbon structural ordering, friability, compressive strength and CO2 reactivity of the resulting charcoals were analyzed. A new method to test compressive strength was applied to a charcoal bed. Our results show that the nature of the wood has a much greater impact on these values than the pyrolysis operating conditions. Wood apparent density is not a good indicator of the mechanical behavior of charcoal. Despite its higher density, eucalyptus charcoal showed lower mechanical stability than spruce charcoal independently of the pyrolysis conditions. When the final pyrolysis temperature was increased, the mechanical strength, porosity of the charcoal increased and CO2 reactivity decreased. The impact of solid residence time during pyrolysis on the charcoal properties was negligible except for CO2 reactivity, which decreased with an increase in residence time.