Influence of central coal feed swirl combustion technology on wide-load range performance of burners, based on gas/particle flow characteristics

The minimum stable load of faulty coal boiler is difficult to reach 20 %–30 %, failing to meet the deep peak modulation needs. In this study, a retrofit technology for a central coal feed swirl burner without modifying the secondary air was proposed. A reconstruction scheme was proposed for the existing low NO_x axial swirl burner (LNASB). The gas/particle flow characteristics at the outlet of LNASB and central coal feed swirl burner (CCFSB) under 20 %–100 % load conditions were studied by using the particle dynamic anemometry (PDA). The three-dimensional velocity fields, turbulence intensity distribution, and powder volume flux distribution at the burner outlets were measured. The results indicated that for the LNASB, the swirl number of two-phase flow ranged from 0.03 to 0.15. The burner outlet did not exhibit a recirculation zone, and the pulverized coal accumulated adjacent to the wall of primary air duct. For the CCFSB, the swirl number of two-phase flow ranged from 0.23 to 0.31. The burner's outlet consistently featured a central recirculation zone with a high concentration of pulverized coal. At 100 % load, the recirculation zone extended to a length of 0.9d and a width of 0.34d. At 40 % load, the length remained at 0.9d while the width decreased to 0.24d. At 20 % load, the recirculation zone measured 0.6d in length and 0.32d in width. The application of this technology to the retrofitting of a 350 MW boiler burning faulty coal is expected to reduce the minimum stable load from 47.1 % to 20 %.