Abstract: A grate assembly for a fluidized bed boiler is provided. A number of parallel sparge pipes extending substantially in the horizontal direction and are provided with devices for supplying fluidizing air from within sparge pipes into a combustion chamber located above the grate assembly. The discharge of coarse material is effected through an aperture system between the sparge pipes into a receiver unit fitted below the grate assembly. At least some of the sparge pipes are provided with a cool medium circulation, wherein at least a part of the cool medium circulation is placed in the sparge pipes at the upper edges thereof, to extend so that it provides a limit to the edge of the aperture system in the upper part of the sparge pipe in the longitudinal direction of the sparge pipe. Devices for supplying fluidizing air comprise a tubular supply channel that is directed from the upper surface of the sparge pipe. The supply channel is provided with air nozzle apertures at its upper part.

Abstract: The invention relates to a method for cooling and cleaning gases containing tar-like or other impurities, and to a reactor. In the method, process gas is first fed into a hot fluidized bed (4), where the tar-like impurities contained in it crack into smaller fractions, whereafter the process gas is passed onward, the fluidized bed material entrained in the process gas is separated from the process gas and returned through the cooler (8) into the fluidized bed and into the process gas stream, whereby the process gas cools under the influence of the cooled fluidized bed material. The reactor comprises a cooler (8) above the fluidized bed (4) and an annular conduit (7) outside the cooler (8), through which conduit the process gas flows into the upper portion of the reactor after the fluidized bed (4).