Ageing effect on ignition sensitivity of lignocellulosic dust

As the use of biomass as a carbon-neutral energy source increases, so does the need for storage facilities, especially for those that are highly seasonal. Consequently, the stored materials may be subject to a natural ageing process before they are used. Such ageing can modify the deflagration parameters of the materials since it can reduce hygroscopicity, increase stiffness and brittleness and change chemical composition in terms of cellulose, hemicellulose and lignin contents. Hydrothermal treatment is a process that accelerates the ageing of wood and lignocellulosic materials. In this work, several lignocellulosic powders from industrial processes were subjected to accelerated ageing to investigate their influence on flammability properties. Grape marc, cork flour, olive pomace, wood dust and lignocellulosic residues from processing waste were selected based on their morphology, chemical characterization and lignin/cellulose content. Based on literature data, ageing conditions in terms of temperature and humidity were chosen to reproduce naturally aged materials. In this study, the effects of ageing on the minimum ignition energy (MIE) and combustion/pyrolysis behaviour were investigated by chemico-physical screening and thermogravimetric analysis and differential scanning calorimetry (TGA and DSC) in an inert and oxidative atmosphere. Results showed how ageing can change the risk of ignition. For example, the MIE of grape marc decreases, while wood-based samples do not ignite after ageing. The decrease in the case of grape pomace is consistent with the decrease in lignin content and moisture. At the same time, passivation of the particle surface could explain the behaviour of the wood samples.