The influence of potassium-rich biomass ashes on steel corrosion above 550 °C

The slagging, fouling and high temperature corrosion are major problems in biomass-firing units and lead to heat transfer limitation, bed agglomeration and metal surface degradation. This paper reports the results of the laboratory-scale corrosion studies of selected steel grades (16Mo3, 10CrMo9-10, X10CrMoVNb9-1, X7CrNiNb18-10) under biomass ash deposits. Five biomass ashes (3 agricultural biomass and 2 energy crops) were used for corrosion tests. Selected samples were doped with 0.1 and 0.5% wt. of KCl to simulate salt condensation process occurring in a real boiler. The corrosion experiments were carried out under oxidizing conditions, at 560 degrees C and 610 degrees C for 168 h. To determine the corrosion rate the mass of steel samples were measured after 24, 72 and 168 h. The corrosion products were analysed using SEM-EDS technique. The results showed that oxide scale formation rate determines the overall corrosion mechanism and the influence of ash deposits on steel. For low-chromium steels the oxidation rate is significant and a scale is a protective barrier between the deposit and metal surface limiting further oxidation process. The highest influence of ash on corrosion process was observed for high-chromium steels. However, high-chromium steels show the highest corrosion resistance.