Soot formation during oxy-steam-reforming of biomass pyrolysis volatile matters: validation of a chemical model

The conversion of solid biomass into fuel gas can be carried out by gasification. Biomass pyrolysis is the first step, and produces volatile matters (VMs) that consist of permanent gases and tars. Their noncatalytic conversion into syngas in a few seconds can be carried out at high temperatures, typically 1200 °C. This complex process involves three main types of reactions: (i) thermal cracking, (ii) the reaction with water vapor called steam reforming, and (iii) in certain cases reactions with oxygen for oxy-steam reforming. The VM conversion operation is known to have a major drawback: the formation of soot, sometimes in very large quantities. In this paper, pilot-scale experiments are carried out on the conversion of reconstituted VM under increasingly complex thermochemical conditions: cracking, steam reforming, and oxy-steam reforming. The soot yield is always superior to 0.5 g/g of tar. A numerical model is then proposed in order to describe the different situations. The model predicts accurately the quantities of soot formed in all situations, along with the composition of the gas phase. The effects of H2O and O2 addition on soot formation are identified using the validated model.