Lower flammability limits of hybrid mixtures containing 10 micron coal dust particles and methane gas

Mixtures of combustible dust and flammable gas pose an increased explosion risk in processing equipment due to reduced flammability limits over the dust and gas alone. Although correlations have been proposed based on experimental testing for predicting the flammability limits of hybrid mixtures from those of the dust and gas, none appear to be applicable across a range of fuel mixtures. The objective of this work is to use computational fluid dynamics to explore the lower flammability limits of 10 mu m coal dust particles and methane gas under laminar, free-flame conditions, and to compare the limits to the experimentally determined mixing rules. This comparison gives an understanding of the baseline behaviour upon which different fuel mixtures, equipment geometry, and various operational conditions can be added in the future. The results from the computational model suggest that Le Chatelier's Law, which proposes linear mixing between the dust and gas limits, is applicable for the small particles studied. Bartknecht's curve, which proposes wider flammability limits than linear, appeared to be overly conservative, while new relations that predict narrowing of the limits did not appear to delineate flammable mixtures under the conditions investigated. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.