Method of maintaining low emissions of nitrogen oxides in combustion in a fluidized bed irrespective of the bed height, and power station in which the method is implemented

摘要

Method and arrangement for combustion of fuel in a fluidized bed 10. A fluidized bed is supplied with fuel for combustion, energy released during the combustion is recovered by means of steam tubes 12a, 12b arranged in and downstream of the fluidized bed, the bed height varies on changes in the amount of power extracted so that the steam tubes are covered or not covered by the bed. The content of nitrogen oxides formed during combustion is reduced by thermal reduction using a reduction agent which is sprayed into the flue gases downstream of the fluidized bed. One or more uncooled zones 15, free of steam tubes, are arranged in the fluidized bed, alternately with the steam tubes. When an uncooled zone is not covered by the bed material, a reduction agent is sprayed into essentially uncooled flue gas in the region of said uncooled zone.