Effect of temperature on corrosion of furnace walls in a waste wood fired boiler

Abstract

One way of reducing the furnace wall corrosion is to lower the temperature of the wall by reducing the boiler pressure. To test this, four coupons of 16Mo3 were exposed in the furnace wall of a waste wood fired boiler for 1075 h. The temperatures of the samples were individually controlled in the range 280–410°C. The corrosion rates and corrosion mechanism were investigated. The deposits were analysed by XRD and SEM/EDS. The corrosion fronts were studied by focused ion beam milling (FIB)/EDS. The environment was modelled by Thermo-Calc. The amount of potassium and chlorine in the deposit decreased with decreasing temperature. The FIB sections showed a distinctive iron chloride layer at the corrosion front, with an outer layer of iron oxide. The corrosion rate decreased with decreasing metal temperature, but the boiler pressure needs to be reduced to a low level to achieve this, which is not beneficial for the electrical efficiency and therefore not a viable way of reducing corrosion.

Keywords:

• High temperature corrosion
• Microscopy of cross-section corrosion
• Biomass
• Chlorine induced attack
• Thermodynamic modelling
• 16Mo3
• Waterwalls

Acknowledgements

We greatly appreciate Mattias Mattson, Vattenfall Research and Development AB, for the valuable help in this project. This work was financed by Vattenfall Research and Development AB and by the KME Materials Technology Consortium, which consists of power plant manufacturers, energy and materials companies and the Swedish Energy Authority.