Effect of Aluminum Oxide Additives for Suppressing Clinker Formation in a Co-current Up-flowing Moving Bed Gasifier Fueled by Japanese Cedar Pellets

Abstract

In order to suppress clinker formation in the co-current up-flowing biomass pellet gasifier, first we investigated the reaction processes of mineral matters in Japanese cedar from a fundamental view point. We found that the eutectic point of the CaCO₃-K₂CO₃ system was the dominant factor in clinker formation in the gasifier where the CaCO₃ phase is stable due to a high CO₂ partial pressure. Then we tested an aluminum oxide additive, which is harmless and inexpensive, for pellet preparation and found that it was effective in inhibiting the melt formation in the CaCO3-K2CO3 system. In the CaCO₃-K₂CO₃-Al₂O₃ system where Al₂O₃ coexists, we confirmed that the CaCO₃-K₂CO₃ melt migrates compounds with structures similar to those of complex compounds such as Fairchildite and KAlO₂. The formation of these compounds suppressed the formation of melt together with foaming around 800 °C, and the deformation temperature (DT) was confirmed to be above 1300 °C. By using Japanese cedar pellets with an aluminum hydroxide additive in the Oobae Kuroshio Power Plant and the Uchiko Biomass Power Plant, the average continuous operating hours of 689 hours and 658 hours, respectively, were achieved satisfying the originally planned power generation scheme.