The agglomeration characteristics of olivine-and potassium (K)-rich grape marc or silicon (Si)-rich wheat straw were studied in a laboratory-scale fluidized reactor and compared under air combustion, steam gasification, or CO 2 gasification atmospheres at temperatures relevant to a dual fluidized bed gasifier. Agglomeration with grape marc is found to be induced mostly by the formation of adhesive K-rich layers onto the olivine, a process that is significantly augmented in a steam atmosphere compared to that in the air or CO 2 . The formation of an initial Krich outer layer, which is caused by the mere physical attachment of K-species onto the olivine surface, facilitated the formation of an inner layer. This inner layer exhibits chemical reactions between grape marc ash and olivine, with the ash elements involved in the chemical reactions differing between combustion and steam gasification environments. Agglomeration with a wheat straw is most significant under air combustion conditions and depends primarily on the temperature rather than on the atmosphere.

Interactions between olivine or silica sand and potassium (K)-rich grape marc or silicon (Si)-rich wheat straw were studied in a fixed-bed reactor under combustion, steam, or a CO 2 gasification atmosphere. This study focused on the effects of atmosphere composition, feedstock, and bed material type on the thermochemical aspects of agglomeration. The agglomeration extent of grape marc with olivine as the bed material under air and steam atmospheres is significantly less than with silica sand. The presence of CO 2 , compared to that of O 2 or steam, was found to promote the reaction between K and olivine by facilitating the production of reactive silica from olivine carbonization. The use of olivine promotes the release of K by more than 10% compared with silica. No significant differences were observed in the agglomeration extent of wheat straw in its interaction with either olivine or silica sand. Nevertheless, olivine alters the agglomeration mechanism of wheat straw to become "melting-induced" from "coatinginduced" in a silica bed.

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.