(57t) Influence of Flammable Solvent Spray on Dust Explosibility

An investigation was performed on the influence of flammable solvent spray (ethanol, isopropanol, toluene, acetone, hexane and heptane) on the maximum explosion pressure (P_max), maximum rate of pressure rise ((dP/dt)_max), and minimum explosible concentration (MEC) of two combustible dusts (lycopodium and brown coal). Experiments were performed in a standard 20-liter sphere using a 10-J spark ignition source with a 60-ms time delay. The experimental procedures were in accordance with European standards EN 14034-1, 2 & 3 for MEC, P_max and (dP/dt) _max, respectively.

It was generally found that the explosion severity of a solvent spray-dust hybrid mixture was higher than that of dust alone, but lower than the explosion severity of solvent. The addition of a flammable solvent to a dust-air mixture increases the maximum explosion pressure to some extent and significantly increases the maximum rate of pressure rise, even though the concentration of the flammable solvent is below its lower flammability limit. The results also confirm that a hybrid spray-dust mixture explosion is possible, even when dust and spray concentrations are lower than their respective minimum explosible concentration and lower flammability limit. It can be deduced from the findings that the explosion properties of a single substance cannot be used to accurately estimate explosion severity or ignition sensitivity when substances are combined in different states.

Although similar findings have been established for hybrid gas-dust mixtures, experimental investigation on the influence of solvent spray-dust mixtures has not been previously performed. This research has direct application to many industrial processes such as pharmaceutical fluidized-bed spray granulation.