Comparing Pyrolysis Gases and Dusts Explosivities: A Clue to Understanding Hybrid Mixtures Explosions?

During the explosion of an organic dust cloud, the following steps are usually encountered: particle heating; its devolatilization/pyrolysis; and, then, a homogeneous combustion of the pyrolysis gases. In order to highlight the influence of the pyrolysis step in such explosions, experiments have been carried out on wheat starch powders and their pyrolysis gases. The maximum rate of pressure rise of the gases reaches 2830 bar s(-1) whereas it remains lower than 400 bar s(-1) for the starch at the same fuel equivalence ratio. Such a difference can be explained by the predominance of the pyrolysis step, but also, to a lesser extent, by changes in the initial turbulence level of the suspension. A model based on the flash pyrolysis mechanisms of cellulosic compounds and their combustion has been developed to represent the evolution of the explosion pressure of such powders. Applications to the case of gas/dust hybrid mixtures are also discussed.