Effects of the type and proportion of a binder on the quality and combustion of fuel pellets

Experimental research findings are reported on the effects of binders on the density, impact resistance, hardness, vibration durability, hygroscopicity, thermogravimetric and kinetic parameters of thermal oxidation of pellets from sawdust, straw and cardboard. Sodium carboxymethylcellulose (2.5 wt %) and sunflower husk (5 wt %) were used as additives. For comparison, wood pellets without additives or additional components (straw and cardboard) were considered. The use of cardboard increased the pellet density by 10 %. Binders in pellets with cardboard had a marginal effect on density. The use of sunflower husk in blends with straw increased density by 2–9 %. Carboxymethylcellulose increased the impact resistance coefficient and hardness of pellets by 2–55 % compared to pellets without additives. The addition of 5 wt % of carboxymethylcellulose or sunflower husk to pellets with cardboard and with straw contributed to 5–13 % lower hygroscopicity coefficient than that of wood pellets. Composite pellets with binders had up to 2.3 % greater ash residue mass than wood pellets. The lowest values of the activation energy of thermal oxidation were recorded for pellets with 5 wt % of carboxymethylcellulose. They were 8 % and 36 % lower than those of pellets with straw and cardboard, respectively. The use of sunflower husk increased the activation energy. A multi-criteria analysis of mechanical strength and energy characteristics revealed that the most efficient pellets were the ones with cardboard and carboxymethylcellulose. The relative integral efficiency indicator of such fuels was 18 % higher than that of wood pellets. This demonstrates high potential of composite pellets containing cardboard in the energy sector.