Influence of blade angle in the outer secondary air for swirl burner on the flow, combustion, and slagging characteristics in the pre-combustion chamber under the air-staged condition

Due to the good combustion stability, the swirl burner (SB) with a pre-combustion chamber (PCC) is widely used in coal-fired boilers. The swirl blade angle is a key design parameter for the SB with PCC. The differences in flow, combustion, and slagging characteristics are dramatic at various swirl blade angles. Therefore, optimizing the swirl blade angle is necessary to improve the comprehensive performance of the SB with PCC. In this paper, Using CFD, the gas-particle flow, temperature, gas component distribution, and slagging trend in the PCC at swirl blade angles (β) of 50°,55°,60° and 64° in the outer secondary air (OSA) of SB are analyzed. As the β increases, the turbulent mixing of jets in the PCC increases, and more high-temperature flue gas is entrained into the PCC. Besides, the rate of devolatilization and char burnout near the SB nozzle accelerates, which is conducive to enhancing ignition and combustion stability. In terms of slagging on the PCC wall, the slagging trend deteriorates as the β increases. To improve the comprehensive performance of the SB with PCC applied in coal-fired boilers, the β should be set between 55° and 60°.