Gas-particle flow and combustion performance of prototype and enhanced burners under minimum stable load: From laboratory to industrial scale

The operational frequency of coal-fired units undertaking deep peak-shaving loads has significantly increased, with stable combustion under ultra-low loads emerging as a critical challenge for grid security. This study conducts the first systematic comparison of a prototype low-NOx swirl burner (L-D) with two enhanced variants (L-A, L-C) under 180MWe conditions (27% rated load). A hybrid approach, combining 1:4.5 lab-scale cold-flow experiments and full-scale industrial tests on a 660 MWe wall-fired boiler operating at minimum stable load without auxiliary fuel, was employed. Key findings are demonstrated: the recirculation zone of L-C was the longest (0.63 nozzle diameters), with a peak reflux ratio exceeding 60 % at axial positions of x/d = 0.3–0.4. Stronger axial velocity decay and radial diffusion were observed in L-A than in L-D, whereas L-C maintained a more concentrated particle distribution. The calculated swirl numbers were 0.584 for L-C, 0.495 for L-A, and 0.440 for L-D. Ignition distances were measured as 1.36 m for L-C, 1.47 m for L-A, and 2.39 m for L-D. NO_x emissions from L-C exceeded 1600 mg·m^-3 (6% O₂) at 1.2 m from the burner outlet, while incomplete combustion in L-A led to CO concentrations reaching 11,196 ppm in near-wall regions. This integrated lab-industrial investigation bridges the experimental gap for sub-30 % load operations and establishes design-performance correlations for deep peak-shaving retrofits.