Abstract: An apparatus for reducing the concentration of nitrogen oxides in flue gases produced in a furnace of a combustion unit includes a device for maintaining combustion reactions in the furnace, the combustion reactions resulting in the production of hot gases containing nitrogen oxides, the hot gases flowing mainly upwardly within the furnace, internal heat transfer surfaces within the furnace for recovering heat from the mainly upward flow of hot gases, an introducer for introducing nitrogen oxides reducing agent into the upward flow of hot gases in the furnace, for reducing the concentration of nitrogen oxides in the hot gases, wherein the introducer is integrally connected to the internal heat transfer surfaces, for keeping the temperature of the reducing agent at a sufficiently low temperature level upon introduction thereof into the furnace, and for efficiently mixing the reducing agent with the upward flow of hot gases, and a discharge for discharging flue gases from the furnace.

Abstract: The present invention refers to an improved method and an improved apparatus for reducing the concentration of nitrogen oxides in flue gases produced by the combustion of carbonaceous fuel in combustion units having a furnace with a fluidized bed of solids therein. Hot gases produced within the furnace flow mainly upward within the furnace. Heat is recovered from the hot gases and hot solid material by heat transfer surfaces within the furnace. A nitrogen oxides reducing agent is introduced into the furnace through injection means integrally connected to the heat transfer surfaces, for keeping the temperature of the reducing agent at a sufficiently low temperature level at the introduction thereof and for efficiently mixing it with the mainly upward flowing hot gases.