Abstract: A three-dimensional gas–solid two-phase model was developed for a 660MW coal-fired unit equipped with a NaHCO₃ dry injection system under deep peak-regulation conditions. The Realizable k-ε turbulence model and discrete phase model were employed to investigate the effects of injection velocity, median particle size, and lance arrangement on particle transport. Particle coverage ratio and dimensionless distribution standard deviation at the outlet characteristic section were used as evaluation indices. The relative errors between the simulated and measured pressure drops were 4.11% and 7.95% at 35% and 100% loads, respectively. Increasing the injection velocity from 5 to 40 m·s^-1 produced only minor changes in particle coverage. Particle sizes of 1–10 μm resulted in coverage ratios above 37%, whereas the coverage ratio decreased to 21.47% at 100 μm. The center-dense lance arrangement increased the coverage ratio from 25.54% to 33.04% and reduced the dimensionless distribution standard deviation from 2.803 to 1.999. Therefore, particle-size control and lance-arrangement optimization are more effective than simply increasing the injection velocity.