DUST EXPLOSION VENTING - INVESTIGATION OF THE SECONDARY EXPLOSION FOR VESSEL VOLUMES FROM 0.3 M(3) TO 250 M(3)

By means of the obtained experimental results it is now possible to assess the probable damage potential of a secondary dust explosion due to fire and blast effects in the vicinity of vented vessels for most practically relevant cases. As empirical equations the results were included in the new VDI-guideline 3673. Tests have been carried out for vessel volumes from 0.3 m3 to 250 m3, static bursting pressures between 100 mbar and 500 mbar and scaled ven, areas F/V2/3 of 0.08 up to 0.39. The combustible material in most of the cases was cornstarch (only few tests with wheatflour). According to the optimum explosion effects in the closed vessel, the mass of material was 0.5 kg/m3 up to 1.5 kg/m3. K(St)-values of 100 bar m s-1, 200 bar m s-1 and 300 bar m s-1 have been studied by ignition time variation. The ignition source was located at the centre or at the closed end of the vessel (in a few cases at the vented area). Pressure development inside the closed and vented vessel were studied as a function of the time intervals between dust injection, ignition and initiation of disc bursting. By applying pressure transducer the explosion and blast pressure development in the environment of the vented vessel was measured as well as cloud formation and flame propagation outside the vented vessel using video and high speed cameras or ionization gauges. In a large number of tests with identically chosen experimental parameters it could be shown that two different types of secondary explosions, which differ in respect to their peak pressure by a factor of three to four, dominate the venting event.