Field test corrosion experiments in Denmark with biomass fuels Part I Straw firing

In Denmark, straw and other types of biomass are used for generating energy in power plants. Straw has the advantage that it is a "carbon dioxide neutral fuel" and therefore environmentally acceptable. Straw combustion is associated with corrosion problems which are not encountered in coal-fired plants.

The type of corrosion attack can be directly ascribed to the composition of the deposit and the metal surface temperature. A series of field tests have been undertaken in the various straw-fired power plants in Denmark, namely Masnedø, Rudkøbing and Ensted. Three types of exposure were undertaken to investigate corrosion: a) the exposure of metal rings on water/air cooled probes, b) the exposure of test tubes in a test superheater, and c) the exposure of test tubes in existing superheaters.

Thus both austenitic steels and ferritic steels were exposed in the steam temperature range of 450-600°C. The corrosion rates were assessed by precision measurements of material loss and internal corrosion. The corrosion products and course of corrosion for the various steel types were investigated using light optical and scanning electron microscopy.

Corrosion mechanisms are discussed in relation to temperature and deposit composition.