Overall characterization of cork dust explosion.

Explosibility and ignitability studies of air/cork dust mixtures were conducted in a near-spherical 22.7 L explosibility test chamber using pyrotechnic ignitors and in a furnace of 1.23 L. The suspension dust burned as air-dispersed dust clouds and the uniformity of the dispersion inside the chamber was evaluated through optical dust probes. The range of tested particle sizes went from a mass median diameter of 47.4 to 438.3 microm and the covered dust cloud concentration was up to 700-800 g/m(3). Measured explosion parameters included minimum explosible concentration, maximum explosion pressure, maximum rate of pressure rise and minimum autoignition temperature. The effect of dust particle size on flammability was evaluated and it was found that the minimum explosible concentration is around 40 g/m(3) and it is relatively independent of particle size below 180 microm. Maximum explosion pressure of 7.2 bar and maximum rate of pressure rise of 179 bar/s were detected for the smallest tested sizes. The limitations on the rates of devolatilization of the solid particles became rate controlling at high burning velocities, at high dust loadings and for large particle sizes. The effect of initial pressure on the characteristic parameters of the explosion was studied by varying the initial absolute pressure from 0.9 bar to 2.2 bar, and it was found that as initial pressure increases, there is a proportional increase of minimum explosion limit, maximum explosion pressure, and maximum rate of pressure rise. The influence of the intensity of the ignition energy on the development of the explosion was evaluated using ignition energies of 1000 J, 2500 J and 5000 J, and the experimental data showed that the value of 2500 J is the most convenient to use in the determination of minimum explosion concentration. The behavior of the cork dust explosion in hybrid methane air mixtures was studied for atmospheres with 2% and 3.5% (v/v) of methane. The effect of methane content on the characteristic parameters of the explosions was evaluated. The conclusion is that, the hazard and explosion danger rise with the increase of methane concentration, characterized by the reduction of the minimum dust explosion concentration. The minimum autoignition temperature obtained with the thermal ignition tests was 540 degrees C and the results have shown that this value is independent of particle size, for particles with mass median diameters below 80 microm.