An arrangement in a recovery boiler having a furnace for combusting waste liquor and a flue gas duct comprising vertical flue gas channels, at least part of which is provided with heat recovery units for recovering heat from flue gases. The heat recovery units have a width of substantially the width of the flue gas duct, whereby downstream of the furnace the first flue gas channel is provided with a superheater. In addition to the superheater, the first flue gas channel is provided with one of following heat recovery units: an economizer, a boiler bank, or a reheater. The superheater and a second heat recovery unit are located one after the other in horizontal introduction direction of the flue gas, so that in a flue gas channel the flue gas flows in the vertical direction downwards and heats the superheater and the second heat recovery unit simultaneously
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