Prediction of biomass corrosiveness over different coatings in fluidized bed combustion

Abstract

Energy production in biomass fired boilers is increasing rapidly due to the advantages of CO2 neutrality and renewability, however damaging agents present in biomass composition accelerates power plant components corrosion. This study evaluates the influence of the biomass burned in fluidized bed combustion processes on high-temperature corrosion, by means of thermodynamic equilibrium modelling, considering those reactions occurring between the combustion atmosphere and different protective coatings (isFeAl, isNiAl and isSiCrAl). Fuels composition and operating conditions from a 10 kW BFB boiler were introduced as input data to improve the performance of the model. Representative samples from agricultural waste, industrial wood and forestry wood waste were selected for evaluation. Results showed industrial wood waste as highly damaging for most coatings studied, with high risk of salt stickiness, deposits formation and release of acidic gases. The elevated volatiles percentage together with significant ash content determined might lead to a major ash components release to the gas phase, available to later condense in the metals surfaces. Silication of alkali and deposited alkali chlorides were the dominant corrosion mechanisms observed for most cases. An increase in alloys corrosion resistance was detected through the model when nickel or chromium was present, showing isSiCrAl as the most resistant. However, alloys protection exhibited significant variations depending upon the biomass burned, thus materials selection should consider the compatibility with conditions for its final use. Thermodynamic modelling, based on real conditions and fuels composition, provides a useful tool to identify key factors for protective coatings design when employing new waste fuels.