Corrosion in recycled wood combustion - theory and solutions

The use ofwaste-derived fuels, such as recycled wood, is a good and sustainable way toproduce heat and electricity, minimize the use of fossil fuels and increase theuse of renewable energy. Besides, waste-based fuels are relatively cheap andwidely available. However, this trend is not totally trouble-free because ofalkali metals, heavy metals, and chlorine, which waste-based fuels typicallycontain in higher shares than coal and oil. These-ash forming elements increasethe tendency of high-temperature corrosion and fouling of heat transfersurfaces. In recycled wood firing, alkali chlorides are present in combinationwith heavy metals, and the corrosion starting temperature may be considerablylower than with virgin wood combustion. In practice, this means that corrosionissues might be present in furnace walls, low-temperature superheaters, andeconomizers.

In boiler design, thekey parameter is the composition of the fuel or fuel mixture. This specifiesthe final steam temperature, the layout of the boiler and material solutions. Understandingthe corrosion phenomena enables the most cost-effective boiler design andmaterial selection. Severalstudies have been made and a more detailed understanding has been gained duringthe recent years when combating high-temperature corrosion issues related torecycled wood combustion and heavy metal induced corrosion. The main findingsare summarized in this article and some solutions to minimize unscheduledboiler shutdowns and to maximize boiler capacity, are presented.