THE CHARACTERIZATION OF SOLID RESIDUES FROM PFBC BOILERS

PFBC is one of the two important advanced fossil fuel technologies, no w available. It permits the combustion of fossil fuels with extremely low emissions, while also achieving high electrical conversion efficie ncies. However, relatively little is known about the ash characteristi cs, despite the existence of several demonstration units. This study l ooks at bed and cyclone ash from two of these boilers, the Spanish PFB C plant at Escatron, in Spain, and the Tidd plant in Brilliant, Ohio. In particular, these ashes are examined using both conventional and so me newly developed techniques in order to determine their chemical spe ciation. This work confirms the ashes have extremely low free lime con tents (1% or less), and extremely low elemental carbon. More surprisin gly, the existence of significant amounts of dolomite in the cyclone a shes from the Tidd plant has been demonstrated, and significant quanti ties of other calcium compounds (i.e. silicates, ferrites etc.) have a lso been shown in the bed ashes from the Spanish plant. One other inte resting observation is the presence of low levels of sulphides in the ashes from the Escatron unit, and its total absence from the Tidd unit which used dolomite rather than calcitic limestone. These results als o clearly indicate that ashes from PFBC plants are likely to be signif icantly easier to dispose of in landfills than AFBC ashes, and should have considerably better potential for use in cementitious application s.