Abstract: The present invention provides a method and an apparatus for predicting and calculating an amount of harmful oxide such as NOx contained in an exhaust gas from a reference concentration of harmful oxide, which is previously determined by a type of fuel supplied to a fluidized bed combustor, an amount of change of an air ratio and an amount of change of a gas residence time to the conditions of a specific air ratio and gas residence time in the combustor, and injecting a treatment agent such as NH.sub.3 in an amount optimum to the predicted amount into an exhaust gas. With this arrangement, an amount of harmful oxide in the exhaust gas can be securely lowered to a target value.

Abstract: A method of and apparatus for detecting an abnormality of a fluidized bed boiler is characterized in that an abnormality of the fluidized bed boiler is detected on the basis of a physical quantity related to a condition change of a gas existing in a space defined by a pressure vessel and the fluidized bed boiler accommodated within the pressure vessel.