Corrosion of Heat Transfer Materials by Potassium-Contaminated Ilmenite Bed Particles in Chemical-Looping Combustion of Biomass

Abstract

This study discusses the potential corrosion of boiler materials in chemical-looping combustion (CLC) of biomass. The CLC of biomass has the potential to negative CO2 emission in heat and power production. Biomass fuels, however, typically contain compounds of alkali metals, especially potassium and chloride, which may lead to the corrosion of heat-transfer surfaces in the reactors. The influence of potassium-contaminated ilmenite bed material deposits on the corrosion of seven heat transfer materials used in the air and fuel reactors in CLC was studied using one-week lab-scale experiments. Samples with KCl and without any deposit were used as references. After the exposure, the cross-sectional surfaces of the metals were analyzed with SEM/EDX. The results suggested that potassium-contaminated ilmenite might lead to minor corrosion of all studied materials under the oxidizing conditions simulating the air reactor, i.e., 700 °C and dry air. Under reducing fuel reactor conditions, i.e., 450 °C and 550 °C and 50/50 CO2/H2O, corrosion was observed on ferritic steels, especially in the presence of HCl and with KCl deposit. In contrast, samples with uncontaminated and potassium-contaminated ilmenite deposits did not significantly differ from the samples without any deposit. Minor corrosion of ferritic steels was observed at 450 °C, while at 550 °C, the corrosion was more significant. The results suggested that ferritic steels are not suitable for the fuel reactor. Austenitic and nickel-based alloys did not corrode under the test conditions used in this work.

Keywords

• chemical looping combustion
• ilmenite
• corrosion
• heat transfer