Agricultural waste pulverised biomass: lean flammability and flame speed as a measure of reactivity

There is very little information on the combustion properties of pulverised biomass, particularly for agricultural wastes. This makes burner design and optimization difficult and also has implications on fire and explosion hazard protection, both in storage, milling and particle transport to burner. A modified Hartmann dust explosion tube was employed to determine the Minimum Explosible Concentration (MEC) and the flame speed for three Pakistani agricultural wastes: bagasse, rice husk and wheat straw. The MEC was influenced by the particle size distribution and there was a strong linear correlation between the MEC and the sum of the ash and moisture content of these and other biomasses. Comparison of the results was made with more conventional pulverized biomass. Peak flame speeds were approximately 2.5 m/s. The lean limits for these pulverised agricultural waste biomasses were comparable to pulverised wood but much leaner than those for coal and hydrocarbon fuels, which indicate that these biomasses are highly reactive.