Novel method for hybrid gas-dust cloud ignition using a modified standard minimum ignition energy device

Abstract

Hybrid dust-gas explosions are a persistent problem in the process industries because of their low ignition energy and serious consequences. The probability of ignition of a hybrid dust-gas mixture is quantified by its minimum ignition energy (MIE). This study aims at improving the MIE measurement of hybrid dust-gas systems using a modified Kühner MIKE3 MIE apparatus. The modification includes an add-on device in order to purge the Hartmann tube with the gas of the hybrid mixture before the dust dispersion and ignition attempt. This ensures the gas composition in the Hartmann tube is the same as that of the gas used for dispersing the dust.In this study, the MIE for a hybrid system consisting of Pittsburgh Pulverized Coal (PPC), methane and air was examined. MIE testing was conducted for the two cases: case (a) followed the ASTM E2019-03 standard procedure, while case (b) applied a pre-dispersion purge of the Hartmann tube with the methane-air mixture. In addition, this hybrid system MIE study was conducted with two different particle sizes of PPC, having equivalent polydispersity. Certified cylinders consisting of methane (1, 2, and 3 vol %) blended with ultra-high purity (UHP) air (21.00% oxygen and 79.00% nitrogen) were used.Significant differences in the MIE values of the hybrid dust-gas system were found between the two cases for both particle sizes. The hybrid MIE values obtained with a pre-dispersion purge of the Hartmann tube were found to be lower than those without the purge (which is the most common testing approach); while a smaller particle size also resulted in a lower hybrid MIE. Additionally, it was found that for experiments with or without pre-dispersion purge, and for both particle sizes, the greater the methane concentration, the lower the MIE.This study proves that many of the previous hybrid MIE studies in the Hartmann tube are non-conservative. Future studies should be conducted by including a pre-dispersion purge in the testing procedure. This work lays the foundation for improving the existing ASTM E2019-03 or developing a standalone standard for hybrid dust-gas system MIE testing.