Experimental measurement of particle size effects on the self-heating ignition of biomass piles: Homogeneous samples of dust and pellets

Biomass can become an important fuel source for future power generation worldwide. However biomass piles are prone to self-heating and can lead to fire. When storing and transporting biomass, it is usually in the form of pellets which vary in diameter but are on average around 7 mm. However, pellets tend to break up into smaller particles and into dust down to the mu m size. For self-heating, size of particles is known to matter in thin layers but the topic is poorly studied for biomass piles. This work presents an experimental study on the self-heating ignition behaviour of different particle sizes of wheat biomass. We study for the first time homogeneous samples from the dust scale to pellet diameter size, ranging from diameters of 300 mu m to 6.5 mm. Experiments are done in an isothermal oven to find minimum ignition temperatures as a function of sample volume. The results are analysed using Frank-Kamenetskii theory. For the homogeneous biomass samples studied, we show that particle diameter variation does not bring a large change in self-heating ignition behaviour. The present work quantifies the size effects on biomass ignition and helps address the safety problems of biomass.