Abstract
The present study investigates the initial corrosion behaviour of HVAF-sprayed NiCr, NiAl and NiCrAlY coatings in two different environments, O2 + H2O and O2 + H2O + KCl at 600 °C for up to 168 h in order to evaluate the possibility of utilizing such coatings in biomass- and waste-fired boilers. SEM/EDX analysis showed that all coatings displayed a protective behaviour in O2 + H2O. Upon addition of KCl (O2 + H2O + KCl), the corrosion behaviour of the NiCr coating drastically changed as it formed a thick oxide layer and displayed major chlorine diffusion down to the substrate. The NiCrAlY coating displayed a significantly better corrosion resistance with only minor oxide formation. The NiAl coating exhibited a protective behaviour similar to when exposed in the absence of KCl indicating that a thin protective oxide has formed on the coating surface. The performance of the NiAl and NiCrAlY coatings is promising for future studies with long-term exposures in more corrosive environments such as in a biomass- and waste-fired boiler.
Highlights
IntroductionIn today’s society, renewable and more CO2 neutral fuels (compared to fossil fuels) are becoming increasingly important
In today’s society, renewable and more CO2 neutral fuels are becoming increasingly important
To be able to compete with the electricity production from fossil fuels, more corrosion-resistant materials are needed for the heat exchangers in a biomassand waste-fired boiler
Summary
In today’s society, renewable and more CO2 neutral fuels (compared to fossil fuels) are becoming increasingly important. The main reasons behind the severe corrosivity are the large amounts of alkali chlorides and HCl(g) in the flue gas released during combustion This results in economic problems for the boiler operators since the maintenance costs are greatly increased. To be able to compete with the electricity production from fossil fuels, more corrosion-resistant materials are needed for the heat exchangers (especially superheaters) in a biomassand waste-fired boiler. This improvement needs to be balanced against the overall economy of the plant, not leading to greatly increased costs
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