Experimental investigations on ignition sensitivity of hybrid mixtures of oil shale dust and syngas

Hybrid mixtures of a combustible dust and flammable gas are usually encountered in many process industries. Ignition sensitivity parameters of such mixtures are critical to assess the possibility for accident to happen in industry. The work of this paper investigates the ignition sensitivity of the main four kinds of oil shale dusts of China and related dust/syngas hybrid mixtures. The experiments were carried out on the standardized 20-L spherical vessel, Hartmann apparatus and 1-m3 explosion vessel. Comparing the results with that of bituminous coal, it was found that the ignition sensitivities of oil shale dusts are generally weaker than that of selected bituminous coal. Results show that the presence of syngas would significantly increase the ignition sensitivity of the hybrid mixtures. With the increasing of syngas contents (below its lower explosion limit) in the mixtures, the minimum ignition energy (MIE) and the minimum explosion concentration (MEC) decrease sharply. For example, the MIE of oil shale from Fushun and Huadian was observed to decrease from 16 J, 10 J to 1.25 mJ and 0.98 mJ, and the MEC dropped from 280 g/m3, 250 g/m3 to 50 g/m3, 50 g/m3. When the syngas content is increased to 3% in volume, the influence of oil shale volatile content on MIE and MEC can be ignored for the four shale samples. The limiting oxygen concentration (LOC) has been investigated systemically in a 1-m3 explosion vessel. It has been found that the LOC of oil shale dust from Longkou is 17% in volume, while the hybrid of 2% syngas and 350 g/m3 of dust revealed the lowest LOC of 16% when nitrogen was used as the inert.