A circulating fluidized bed boiler having improved reactant utilization. The circulating fluidized bed boiler includes a circulating fluidized bed having a dense bed portion; a lower furnace portion adjacent to the dense bed portion; and an upper furnace portion, wherein the dense bed portion of the circulating fluidized bed boiler is maintained below the stoichiometric ratio (fuel rich stage) and the lower furnace portion is maintained above the stoichiometric ratio (fuel lean stage), thereby reducing the formation of NOx.; a reactant to reduce the emission of at least one combustion product in the flue gas; and a plurality of secondary air injection ports downstream of the circulating fluidized bed for providing mixing of the reactant and the flue gas in the furnace above the dense bed, wherein the amount of reactant required for the reduction of the emission of the combustion product is reduced. In a preferred embodiment, the circulating fluidized bed boiler may further include a return system for returning carry over particles from the flue gas to the circulating fluidized bed.