Selecting the right material for recovery boiler superheaters

The aim of this paper is to examine the selection of superheater materials for recovery boilers. Fireside wastage in recovery boilers is mainly caused by formation of corrosive deposits, typically with aggressive molten alkali phases. Fireside corrosion can also be caused by gaseous components and is then usually associated with a reducing atmosphere. This active oxidation can affect superheater tubes even at temperatures lower than the first melting temperature. There is a wide array of available superheater materials to choose from and a few newer materials to be considered. The operating conditions and deposit properties must be looked at when material selection is done. The material choice has a significant effect to the cost of the recovery boiler, as the selection of the final superheater material can change the price by a factor of 10.