Fragmentation of dolomite bed material at elevated temperature in the presence of H_2O & CO_2: Implications for fluidized bed gasification

摘要

With the aims of improving the understanding of the use of dolomite bed materials in a fluidized bed (FB) gasifier, dolomite primary fragmentation behaviors and mechanisms at elevated temperatures were thoroughly investigated by means of quantitative analysis of particles production, size distribution, and particles shape (in terms of HS circularity and convexity). Crystalline Glanshammar and amorphous Sala dolomites of different original particle sizes (300-350 mu m, 350-500 mu m, and 500-1000 mu m) were treated under various conditions, such as temperatures of 650,750, and 950 degrees C and gas conditions of N-2, N-2 & steam, and H2O & CO2. Crystalline Glanshammar dolomite exhibited severe fragmentation, while amorphous Sala dolomite only fragmented slightly. Fragmentation mechanisms were proposed for amorphous and crystalline dolomite. In case of the Glanshammar dolomite, the release of H2O trapped in the crystal lattices and trace level of CO2 at structure defects, contributed to 10% and 55% of the primary fragmentation, respectively. The presence of CO2 can significantly mitigate the fragmentation of crystalline Glanshammar dolomite, which is probably either due to the prevention of CO2- dissociation at the defects or filling of cations by interchanging CO2- with the dolomite, consequently, allowing for a stabilization of dolomite structure. The analysis shows that elutriation in fluidized bed gasifier can be reduced significantly when either using amorphous Sala dolomite as bed material or treatment of the Glanshammar dolomite in the presence of CO2 before its utilization in a fluidized bed.