Partitioning and transformation behavior of toxic elements during circulated fluidized bed combustion of coal gangue

A study on toxic elements behaviors from a 330 MW coal gangue circulated fluidized bed co-combustion power plant equipped with electrostatic precipitators (ESPs) was performed. Simultaneous sampling of feed coal, bottom ash, fly ash and flue gas were implemented. Sequential chemical extraction was taken to investigate the transformation behaviors of toxic elements. The relative distribution and partitioning behavior of toxic elements in the power plants were analyzed systemically. The toxic elements can be divided into two groups, Cluster one, whereby high volatile tendencies are represented by As, Cd, Cu, Pb, Se and Sn which have a volatilization ratio more than 20% and are mainly enriched in fly ash. These elements are primarily associated with sulfide minerals. Cluster two, represented by Co, Cr, Mn and V, have low volatilization rate (≤5%) and are equally distributed between bottom ash and fly ash. In addition, Bi, Ni and Zn may be located between Cluster one and Cluster two. The variation of modes of occurrence of toxic elements could lead to the difference of transformation behaviors during the combustion of feed coal. Most toxic elements transformed and partitioned into other fractions from Fe-Mn oxides during combustion.