doi:10.3850/978-981-08-7724-8_10-05

ABSTRACT

The main objective of this work was the determination of the near-laminar and turbulent free flame speeds, and explosion enhancement factors of dust-air explosions in fire balls of approximately up to 1 m in diameter. Such information could find immediate application in the more effective design of dust-explosion protection systems in industry. In many respects, this work was a feasibility study and an evaluation of the capability of the proposed measurement techniques in delivering reliable data. Dust-air mixtures were exploded in a 1 m³ industry standard vessel for the determination of explosion indices of dusts. Maize starch, phenolic resin, pulverised coal, biscuit flour and dried skimmed milk powders were tested. The tests were carried out under turbulent conditions of variable rms turbulent velocity, which was controlled by the ignition delay time from the onset of dust injection. The flame speeds and the K_st values were measured at increasing ignition time delays and hence decreasing levels of turbulence, and were extrapolated to their laminar values (limit values at infinite time delay). A methodology was developed for dealing with problem of dust settlement, and other areas where further work is needed (such as the ignition mechanism) were identified. The laminar flame speeds and K_st values for 5 dusts tested are reported. Maximum enhancements factors of up to 4 with regard to the laminar K_st value were recorded in the ISO vessel, and up to about 6 with regard to the flame speed.

Keywords: Dust explosion, Flame speed, Laminar.

© 2011 CPD Unit, University of Leeds