High-temperature corrosion of water-wall tubes in oxy-combustion atmosphere

Abstract

Oxy-combustion is one of the most promising technology for CO2 capture in coal-fired power plants. However, under oxy-combustion conditions, the concentrations of acid gas species are significantly increased due to the introduction of the flue gas recycle, which aggravates the high-temperature corrosion of heat exchanger materials in boilers. In this study, the early-stage high-temperature corrosion (0–16 h) of two representative water-wall tube materials (20G, 12Cr1MoV) is experimentally tested in a lab-scale furnace with the simulated oxy-combustion atmosphere. The effects of material, temperature, CO2, H2O, SO2, H2S and CO atmospheres on high-temperature corrosion behaviors is investigated. The micro-morphologies and compositions of corrosion layers are characterized by scanning electron microscope with energy dispersive X-ray spectra (SEM-EDS) and X-ray diffraction (XRD). Kinetic analysis shows that the high concentration of CO2 accelerates high-temperature corrosion of water wall materials. In the simulated oxy-fuel combustion atmosphere (CO2/O2/SO2), the mass gain rate can be enhanced by 10%–30% compared to the conventional air combustion atmosphere (N2/O2/SO2), and the major composition of oxide scale is magnetite. In a reducing oxy-fuel atmosphere (CO2/CO/SO2/H2S), the major components of oxide scale are magnetite and ferrous sulfide. The high concentration of moisture in the atmosphere accelerated the corrosion rate by 10–30%. For both model alloys, the corrosion kinetics obey the parabolic law. Water-wall tube material 12Cr1MoV appears superiority in corrosion resistance compared with 20G material.