Calcite or Kaolinite Addition for Mitigating Bed Agglomeration during Combustion and Steam Gasification of Potassium-Rich Agricultural Residues with Olivine as the Bed Material

Effects of calcite or kaolinite as additives for mitigating bed agglomeration arising from potassium (K)-rich agricultural residues with olivine sand were studied in a bubbling fluidized bed under both combustion and steam gasification conditions. The effectiveness of each type of additive was evaluated by comparing the particle size distributions (PSDs) of the bed particle samples collected from each test with additives to those without. Calcite was found to significantly inhibit agglomeration under steam gasification. The anti-agglomeration mechanism of calcite is ascribed to the stronger reactivity of Ca than K with olivine sand, which prevents the formation of sticky K-rich layers on olivine. In comparison, such an anti-agglomeration effect of calcite was found to be insignificant under combustion conditions owing to the much less agglomeration severity under combustion conditions without any additive. In contrast, the addition of kaolinite augmented the agglomeration process under both atmospheres because it introduces reactive silica into the bed through phase transformation, the presence of which alters the agglomeration into a rapid melting-induced mechanism over that of coating-inducement.