Dust cloud characterization and its influence on the pressure-time-history in silos



Using VDI 3673 or NFPA guidelines for venting we distinguish between a homogeneous and inhomogeneous dust distribution in principle. Experiments were conducted in a 12 m3-silo to measure the dust distribution, turbulence and the reduced explosion pressure using three different ways of generating the dust/air mixture: ring nozzles with pressurized dust chambers [1] (homogeneous distribution), [2] pneumatically fed vertically downwards [2] and tangentially [3]. Additionally, the dust feeding rate, the conveying velocity and the ignition position was changed. The reduction of the conveying velocity and therefore the decrease of the RMS turbulence velocity will cause a strong reduction of the explosion pressure and the pressure rate, respectively. The results show that the dust concentration in the pneumatically filled silo is inhomogeneous. However, the RMS turbulence velocity and the reduced explosion pressure for the homogeneous distribution and the vertical filling are of the same order. In comparison, the tangential feeding results in lower values. The calculations for the pneumatical vertical filling according to VDI 3673 guideline (inhomogeneous distribution) underestimate the resulting pressure for small vent areas, but the equations for the homogeneous distribution cover the experimental data.