A heat exchanger for heating a fluid in an incineration plant, comprising at least one heat exchanger component wherein the side in contact with the flue gas has an oxide layer comprising an -Al.sub.2O.sub.3 which protects the heat exchanger component against corrosion caused by corrosive compounds entrained or comprised by the flue gas.

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

An integrated steam generator/steam superheater apparatus is disclosed. The disclosed apparatus can be used in a process, such as an ammonia synthesis process, to cool an ammonia converter effluent process gas and to generate superheated steam. The integrated apparatus includes a steam superheater portion wherein hot process gas is used to generate superheated steam by heat transfer to saturated steam. The apparatus also includes a steam generator portion wherein the process gas is used to generate saturated steam by heat transfer to water. Both the superheater and the steam generator are integrated into a single unit, without intervening pluming, etc., thereby saving space and equipment.