Calibration of new dust dispersion systems in 1 m3 standard dust explosion vessel for fibrous biomass testing

Biomass is considered as an alternative fuel for partial/complete replacement of coal in power generation. The data on coal, agricultural and chemical dusts explosion properties are available in the literature but reliable data on fibrous biomass is not available. This is because the standard C-tube dispersion system in the 1m3 dust explosion vessel does not allow fibrous biomass to flow. In this paper alternative dust dispersion systems (Rebound nozzle, Hemispherical dispersion cup and Spherical grid nozzle) were designed and calibrated against the standard dispersion system using non-fibrous and fibrous dusts. The criterion for the calibration was the achievement of same Pmax, Kst, mass burned (%), flame speed and spherical flame propagation. The ignition delay and inlet air valve off timing were varied using gas explosions to achieve the same turbulence levels in the vessel that produced similar results as with standard system. The calibrated conditions for the rebound nozzle were; 0.70s ignition delay and 0.75s valve off timing and for spherical grid nozzle were; 0.50s ignition delay and 0.65s valve off timing. All of the injection systems with an external store of the dust were problematic with fibrous dust and would only pass fibrous dusts milled to <63µm and were not suitable for the practical dusts with sizes up to 1mm that are in current use in power stations burning pulverised biomass. The alternative was to place the dust inside the vessel and to disperse it using a blast of compressed air and the hemispherical cup was developed for this purpose. The hemispherical dispersion cup produced reliable results at 0.60s ignition delay and 0.65s valve off timing with gas explosions. The dust explosion tests using the hemispherical dispersion cup produced the same results for Pmax and proportion of injected mass burned (%) but had lower values of Kst and flame speed and the flame propagation was shown to not be spherical.