Effect of volatility on dust flammability limits for coals, gilsonite, and polyethylene

Abstract

Lean limit concentrations and limestone rock dust inerting requirements were measured in a 20-L chamber for a range of carbonaceous dusts including various ranks of coal, gilsonite, and artificial mixtures consisting of polyethylene and graphite. Although there is some uncertainty in the true yield of volatiles for some of the fossil mineral dusts, especially at flame flux levels, the data show that the combustible volatile content of the carbonaceous dusts is the dominant factor governing their combustion behavior in the dust explosions. The char residues and graphite are essentially inert on the rapid time scale required for flame propagation processes in explosions. The lean flammability limits of the various dusts correspond to invariant combustible volatile concentrations of about 30 to 40 g/m3. Total interting of the dusts occurs when the inert content of the mixture exceeds about 90 to 95 wt pct or, equivalently, when the combustible volatile content is less than 5 to 10 wt pct. The char's role is equivalent to that of the other inert constituents, such as ash and rock dust.