Numerical simulation on H2S distribution characteristics of tangentially coal-fired boiler under wide loads

Abstract

Air staged combustion reduces NOx emissions, but increases the H2S concentration in primary combustion zone. The excessive H2S concentration near the furnace wall is an important factor that aggravates the high-temperature corrosion of the water-cooled wall. With large-scale renewable power integrated into the grid, the demand for flexible peak-shaving operation of traditional thermal power units has increased. The H2S concentration distribution near the furnace wall under different boiler loads deserves attention. Hence, the influence of different operating parameters of tangentially coal-fired boiler on H2S concentration distribution near the furnace wall was investigated by orthogonal test. A supercritical 600 MW tangentially coal-fired boiler was selected to establish a numerical model. The L16(45) orthogonal numerical conditions was designed to cover four boiler loads, including 100% BMCR, 75% THA, 50% THA and 35% BMCR. A user-defined SOx generation model was employed to calculate the H2S concentration distribution inside the furnace. The release of fuel sulfur and mutual transformation of sulfur components were considered. At the same time, the model included a multiple surface reaction model for describing the heterogeneous reaction between coke and O2/CO2/H2O, and the ratio of the gasification rate to the consumption rate for char particle was calculated. The results show that the high H2S concentration areas are mainly located below the bottom burner that on operation and between the top burner and SOFA nozzle. The main reason for the high H2S concentration in the latter area is that the tangential circle of flue gas increases gradually along the furnace height. The orthogonal analysis indicates that the average H2S concentration in the key area of the furnace wall under 35% BMCR load is 364 μL/L, which is significantly lower than that under the other loads. In addition, the impact of operating parameters on the H2S concentration in key areas follows the order of boiler load > primary air rate > excess air coefficient of main combustion zone > imaginary tangent circle diameter > vertical swing angle of burner.

Keywords

• tangentially coal-fired boiler
• wide load
• h2s distribution
• orthogonal analysis
• numerical simulation