Abstract
Metallurgical silicon is produced by carbothermic reduction of quartz in electric arc furnaces using carbon reducers, mostly of fossil origin. The use of charcoal is a relevant alternative to reduce the environmental impact of the metallurgical process. The coal also makes it possible to limit the presence of certain impurities in the silicon and to reduce the overall energy consumption of the process. The main obstacles to its use are its low mechanical strength as well as its cost of production which, in certain contexts, make it difficult to compete with fossil reducers. The aim of this work was to determine the interest properties of a reducing carbon, and to study the influence of the nature of the wood and the operating conditions of the pyrolysis on these properties.A fixed bed pyrolysis pilot reactor, designed specifically for this thesis, has produced charcoal in conditions similar to those encountered in industry. The coals were then characterized according to their yields and physicochemical characteristics. Characterization tests of the mechanical behavior in coal bed - resistance to compression and friability - have been developed. In addition, the CO2 reactivity of the coals was measured by means of a macro-thermogravimetric reactor. The coals were produced from two species of wood of different types, Eucalyptus globulus and Picea abies for three final pyrolysis temperatures - 500, 650 and 800 ° C - and two residence times at the final temperature - 0 and 90 min. -. The influence of the nature of the raw material was also studied through the production of charcoal with four additional species at the temperature of 700 ° C without residence time at the final pyrolysis temperature.Our results show that the nature of wood has a much greater impact on its properties as a reducing agent than the operating conditions of pyrolysis. The apparent density of wood is not a good indicator of the mechanical behavior of charcoal, as is often considered. When the final pyrolysis temperature was increased, the mechanical strength increased and the CO2 reactivity decreased. The impact of residence time at the final pyrolysis temperature on coal properties was negligible, with the exception of coal yield and CO2 reactivity, which decreased with increasing residence time. The work carried out made it possible to determine the optimal pyrolysis operating conditions as well as the most suitable gasoline for the production of a reducing charcoal for the silicon industry.