Management of Solid Residues

Abstract

Solid residues produced in fluidized bed boilers are different from those produced in pulverized-coal-fired boilers, where ash melts at high-flame temperature forming spherical cenosphere. The coal ash in fluidized bed combustors, on the other hand, does not melt due to its low combustion temperature. So, ash particles are non-spherical and do not usually contain cenosphere. This gives fluidized bed ash substantially higher surface area and hence higher reactivity than fused ash from pulverized coal combustion. When limestone is used in a circulating fluidized bed (CFB) furnace to control the emission of SO2, the solid residue contains a large amount of unslaked calcium oxide and calcium sulfate, along with the coal ash. Thus, the amount of solid waste produced by a fluidized bed boiler with limestone addition is 50–100 % greater than that produced by a pulverized-coal-fired boiler without a flue gas desulfurization unit.