Experimental and numerical studies on the explosion severities of coal dust/air mixtures in a 20-L spherical vessel

An experimental investigation was carried out on the influences of dust concentration, particle size distribution and humidity on aluminum dust explosion. Tests were mainly conducted thanks to a 20 L explosion sphere. The effect of humidity was studied by storing the aluminum particles at constant relative humidity until the sorption equilibrium or by introducing water vapour in the explosion vessel. The tested particles sizes ranged from a volume median diameter of 7 to 42 μm and the dust concentrations were up to 3000 g m−3. Among other results, the strong influence of the particle size was pointed out, especially when the Sauter mean diameter is considered. These results stressed the predominance of the specific surface area on the mass median particle diameter. The effect of water on aluminum dust explosion was decoupled: on the one hand, when water adsorption occurs, hydrogen generation leads to an increase of the explosion severity; on the other hand, when the explosion of dried aluminum powder occurs in a humid atmosphere, the inhibiting effect of humidity is put forward. A model based on mass and heat balances, assuming a shrinking core model with chemical reaction limitation, leads to a satisfactory representation of the pressure evolution during the dust explosion.

Experimental investigation and modelling of aluminum dusts explosions in the 20 L sphere

Inhibition of aluminum dust explosion by NaHCO3 with different particle size distributions.

Some myths and realities about dust explosions

Comparison of the explosion characteristics and flame speeds of pulverised coals and biomass in the ISO standard 1 m3 dust explosion equipment

On the basis of a systematic testwork with a number of different dusts, the explosion indices as determined within the 20 l sphere and with the ISO-VDI 1 m 3 vessel have been compared. The repeatability has been assessed and since some systematic deviations appear a refined physical analysis of the explosion processes is developed. It appears in particular that the cube root law supposed to link both vessels is not verified. A striking illustration of this appears when a dust with a significant explosion severity inside the 20 l sphere is not even explosible in the larger vessel. It is strongly suggested that the ignition energy is forcing very significantly the explosion in the smaller vessel inducing several tens of Celsius degrees of preheating. It is shown also that the inner level of turbulence is decreasing very fast in the 20 l sphere during the flame development so that difficult-to-ignite mixtures would tend to burn at a lower combustion rate. It is further demonstrated that the major bias between the chambers can be explained and quantified with these elements. A correlation with the standard 1 m 3 vessel and a grid of interpretation of the data is proposed.

Measuring the violence of dust explosions with the “20 l sphere” and with the standard “ISO 1 m3 vessel”: Systematic comparison and analysis of the discrepancies

Antoinette Accorsi

Papers

Measuring the violence of dust explosions with the “20 l sphere” and with the standard “ISO 1 m3 vessel”: Systematic comparison and analysis of the discrepancies