Understanding Off-Gassing of Biofuel Wood Pellets Using Pellets Produced from Pure Microcrystalline Cellulose with Different Additive Oils

Abstract

Fuel wood pellets have the tendency of undergoing self-heating and off-gassing during storage and transportation. Self-heating can lead to spontaneous combustion and cause fires while toxic gasses such as carbon monoxide and some volatile organic compounds released due to off-gassing are a human health and environmental hazard. Previous research suggests that the self-heating and off-gassing of wood pellets are as a result of the oxidation of wood extractives. The aim of this study was to identify the extractives, i.e., fatty and resin acids that are responsible for the emissions of carbon monoxide, carbon dioxide and methane from wood pellets by testing the off-gassing tendencies of pellets produced from synthetic microcrystalline cellulose and different additive oils. The additive oils were intentionally selected to represent different types of wood extractives (mainly fatty and resin acids) and they included: tall oil, pine rosin, linseed oil and coconut oil. The highest mean concentrations of carbon monoxide, carbon dioxide and methane were recorded from cellulose pellets with added linseed oil. The concentrations of carbon monoxide and methane for the other four pellet types were negligible and there was no carbon dioxide emission. Pellets with added linseed oil had high off-gas emissions due to the high content of unsaturated fatty acids compared to other pellet types.

Off-Gassing and Oxygen Depletion in Headspaces of Solid Biofuels Produced from Forest Residue Biomass

“…They obtained different extractive contents in these experiments by extracting sawdust with acetone and adding oils with different unsaturated fatty acid contents (linseed oil and tall oil) and unequivocally showed that unsaturated fatty acids in pine pellets are one of the main causes of gas emissions and oxygen loss in the headspace of stored wood pellets. This finding is also confirmed by the results of other studies [21,25,27,31].…”

“…It was found in studies conducted by other authors that the O 2 concentration decreased with the emission of harmful gases during the storage and transport of wood pellets in enclosed spaces. Since oxygen is consumed in the autooxidation processes, its concentration decreases with the incubation time [25]. Along with the presence of CO, this is another factor that poses a threat to the lives of people staying in poorly ventilated rooms and cargo bays where wood pellets are stored [20,43].…”

“…This results in oxygen depletion in the room, which poses an additional threat to human health and life. The amount of emitted gas depends on the temperature, relative humidity, headspace volume, oxygen level, storage method, accessible pellet surface, type of material from which the pellets are made and extractive content [22][23][24][25][26][27][28][29]. The autooxidation process is exothermic, so gas is emitted with heat release, resulting in pellet self-heating and increasing the danger of self-ignition and fire.…”

Lignin Use in Enhancing the Properties of Willow Pellets

“…The authors noted that this could be due to the saturation of these extractives in the pellets compared to the limited amount of oxygen available in the testing apparatuses [65]. Comparatively, an additional study from Siwale et al [66] examined the CO production from cellulose pellets containing these lipophilic extractives and reported that pellets containing linseed oil were the only pellets to produce a significant amount of CO [66].…”