Influence of Particle Size and Density on the Hot Surface Ignition of Solid Fuel Layers

Dust layers are present in every industrial facility where solid materials are generated or processed. The emergence of new fuels with still unknown flammability properties generates an increase on the risks related with these facilities that needs to be further studied. Most of these biomasses are susceptible to exothermically react, acting as an ignition source and causing fires and explosions. One of the most common causes of explosions is the ignition of dust layers deposited on the equipment, which could be avoided by a better understanding of the materials. However, the ignitability of these layers depend on several parameters as the particle size and the density of the deposited materials. This paper reports experimental work on hot surface ignition temperatures of layers of different fuels, both biofuels, such as wood or sewage sludge, and fossil fuels, coal and coke. It shows that the common practices that are well-known for fossil fuels cannot be directly extrapolated to new fuels. Unlike fossil fuels, wood-based materials present the same ignition risk in dust and bulk size, so an increase on the particle size does not ensure a safer work space. Furthermore, compacting these materials can increase the ignition risk of these type of layers, contrary to the common practices for fossil fuels storages. These differences point out the need of a complete characterisation of each material to ensure a safe working facility.