Characteristics of hydrogen sulfide formation in pulverized coal combustion

Low excess air combustion and two-stage combustion are currently being attempted as a means of reducing NOx emission from the boiler in pulverized coal-fired power plants. However, a strong reducing atmosphere is formed in the region between burners and air ports in the case of two-stage combustion. This atmosphere promotes the formation of hydrogen sulfide (H2S), which causes sulfidation corrosion at the boiler wall. The control of H2S formation and the prevention of corrosion are important in power plants. In this study, the characteristics of H2S formation in two-stage combustion were investigated using a test furnace for pulverized coal combustion. H2S was formed in the case of H2 coexistence. The H2S concentration was affected by the fuel ratio and the sulfur content in coal. The H2S concentration is very low below a H2 concentration of about 2%, above which the H2S concentration has a strong correlation with that of H2. Furthermore, it was found that after the release of sulfur has finished, H2S and SO2 reach equilibrium concentrations in accordance with the equation SO2 + 3H2 = H2S + 2H2O.