Joint examination of fuel-related measures for the improvement of corn cob combustion properties

The aim of this paper is the production of a high-quality corn cob pellet which satisfies ISO 17225-6 requirements and addresses the ash melting behavior through additives kaolin and magnesium oxide. The effects of additives on the (1) physico-mechanical properties and (2) ash melting behavior of pellets were investigated. Before statistically analyzing the effect of additives on the mechanical durability and bulk density, pelletizing was conducted in two experimental series (full factorial design). In series 1, moisture content (18-20 wt. %), additive type (kaolin or MgO), and additive content (0-2 wt. %) were varied; in series 2, binding agent content (2-4 wt. %), additive type (kaolin or MgO), and additive content (0-2 wt. %) were varied, whereas moisture content was kept constant at 20 wt. %. The effect of additives on ash melting behavior was pre-evaluated: (1) in a laboratory scale, (2) using thermodynamic equilibrium calculations, and (3) fuel indices. Results show that without a binder, only pellets with MgO can reach durability threshold class B (≥96 wt. %) from ISO 17225-6, whereas using a binder, the mean value of all pellets complies with the durability class A (≥97.5 wt. %). Results of pre-evaluation tests are in agreement regarding kaolin but not regarding MgO. Experimental results show that corn cob ash starts sintering >800 °C, melt consisting primarily of K, Si, and O, and both additives prevent sintering. FactSage predicts K sorption in the ash using kaolin, and molar (Si + P + K)/(Mg + Ca + Al) ratio predicts the improvement of ash behavior with both additives.