Measurement of Self-Heating of Biomass Pellets using Isothermal Calorimetry

Abstract: Self-heating in storage facilities of biomass pellet can lead to spontaneous combustion. This has resulted in many fires over the years, causing both financial and environmental losses.In order to assess the risk for spontaneous combustion of biomass pellets during storage, it is important to know how prone the fuel is to self-heating, i.e. to determine its reactivity. This thesis presents experimental work performed to develop a sensitive screening test procedure for biomass pellets, using isothermal calorimetry for direct measurement of the heat production rate. This method can be used to compare the reactivity of different biomass pellets. This could be useful for e.g. facility owners to gain better knowledge of their fuels propensity for self-heating and thereby facilitate safer storage.The screening test procedure can also be used for research purposes. Experiments have been performed with 31 different biomass pellet batches to investigate how the pellet composition, origin, etc. influence the reactivity of the pellets. The results from these experiments clearly show a significant difference in reactivity between different types of pellets. The results indicate that pine/spruce mix pellets are significantly more reactive than all other types of pellets tested, and that pellets consisting of 100 % pine are more reactive than pellets consisting of 100 % spruce. Pellets produced from winery wastes, straw, or eucalyptus, have low reactivity compared to pellets consisting of pine and/or spruce. The reactivity of the pellets was shown to be reduced by either introducing certain types of anti-oxidants into the pellets or by extracting lipids from the raw material of pellets.The screening test procedure is already being used today by some facility owners for assessing their fuels propensity for self-heating. The procedure is also one of the suggested test methods in “ISO/CD 20049 Solid biofuels — Determination of self-heating of pelletized biofuels”.