Abstract: A method and apparatus for controlling pollution and flue gases from a boiler using municipal solid waste as a fuel. The flue gases pass through internal and external economizers before entering a reactor in which the gases are treated with lime or other reactant in slurry form to neutralize the acid components of the flue gases. The heat of the flue gases dries the products of the reaction and the excess reactants so that they may be separated from the flue gas in subsequent separator, which is a baghouse filter. The feed of the reactant to the reactor is modified in accordance with the concentration of acid constituents in the flue gas, and concurrently the operation of the economizers is modified to raise the temperature of the flue gas exiting the economizers when the feed of reactant is increased and vice versa. The temperature of the flue gas is increased by causing the feed water to bypass the external economizer in direct relation to the quantity of reactant fed to the reactor.