A journey through space and time in the Godbert-Greenwald furnace: The evolution of a dust cloud particle size distribution.

Minimum Ignition Temperature (MIT) characterizes the ignition sensibility of a dust cloud. This work assesses the role of a standard Godbert-Greenwald furnace in the agglomeration/deagglomeration and fragmentation phenomena. Several organic powders and different dispersion pressures were tested. The average residence time varied from 120 to 330 ms according to the amount of powder injected and the pulse pressure. Entanglement was observed for coarser cellulose particles, while surface cohesion forces characterised the agglomerates of finer cellulose, glucose and ascorbic acid. The latter was characterised by fragmentation, especially at 0.5 and 1 bar(g). Biot, Pyrolysis and Damköhler numbers were used to analyse the effects of cellulose agglomeration and deagglomeration. At 600 K, the pyrolysis is the rate-limiting step, but from 700 K, the external heat transfer becomes the rate-limiting step, which would not happen without agglomeration. Due to the particle size distribution evolution, but also to turbulence and residence time variation, MIT can vary by 50 °C. [ABSTRACT FROM AUTHOR]