Hot corrosion behaviors of TP347H and HR3C stainless steel with KCl deposit in oxy-biomass combustion

Abstract

Oxy-combustion is one of the most promising technologies for carbon capture and sequestration. When CO2-neutral biomass is burned under oxy-combustion conditions, named “oxy-biomass combustion” a negative CO2 emission can be achieved. However, the high content of potassium and chlorine in biomass results in sever ash deposition and corrosion in air fired furnaces, which are further aggravated in oxy-combustion mode due to the enrichment of corrosive species by flue gas recycle. In this paper, the hot corrosion behaviors and mechanism of two representative materials (TP347H, HR3C) used for superheaters in furnaces are studied. The effects of oxy-combustion atmosphere, KCl deposition, effect of SO2, effect of water vapor, and temperature on the corrosion kinetics at the starting stage are investigated. The corrosion severity of the materials was determined using the weight gain method, and the microstructures and chemical compositions of corrosion layers were characterized by the scanning electron microscopy with energy dispersive spectroscopy, and X-ray diffraction. The results show that the hot corrosion rate is significantly sped up by KCl deposition, more than five times the gas corrosion rate under the same gas composition and temperature. HR3C with higher Cr and Ni contents is more likely to form Cr enrichment on the interface between the corrosion layer and the substrate than TP347H, resulting in stronger resistance to the hot corrosion than TP347H. When the corrosion atmosphere is changed from air-combustion to oxy-combustion, the hot corrosion rate is reduced with a denser Cr oxide film and less metal sulfides. The increase of temperature in the presence of KCl deposition significantly affects the hot corrosion rate, e.g. the corrosion rate at 650 °C is 16 times higher than that at 450 °C. Water vapor and SO2 concentrations have opposite influences on the hot corrosion, respectively. Compared to the dry environment, a high-humidity environment decreases the hot corrosion rate; however, a higher SO2 concentration facilitates the sulfation of KCl deposits, leading to stronger damage to the chromium oxide film and thereby an increased hot corrosion rate.