Abstract: The existing faulty coal-fired boiler has a minimum stable combustion load rate of 50%, making it challenging to meet deep peak shaving demands. Previous research has primarily focused on reducing NO_x emissions rather than achieving stable combustion at low loads. Most experimental conditions are set at full load, thus lacking studies on low-load conditions. To address the insufficient deep peak shaving capability of faulty coal-fired boiler, a novel low-load stable combustion technology has been developed. This technology retains the original burner's secondary air structure. By incorporating central powder feeding, introducing swirling gap air, and optimizing the premixing section and flared outlet, it can achieve stable combustion at a minimum load rate of 30% solely through its own recirculation zone. This technology was applied to LNASB burners of a 350 MW faulty coal-fired boiler, resulting in a low-load stable combustion LNASB burner （SLNASB）. Through laboratory gas-particle phase experiments, the effect of gap air mass flow on the gas-particle flow of SLNASB was analyzed at 30% boiler load. The experimental results showed that gap air could regulate the shape and size of recirculation zone. When the gap air mass flow was 66% of the inner secondary air mass flow, the recirculation zone formed a large ring with a length of 1.0d and a diameter of 0.48d. The zone boundary was 0.075d from the central axis （where d is the outer second exit diameter）. At 44% gap air flow, the recirculation zone became central, with a length of 0.7d and a diameter of 0.60d. At 22% and 0 gap air flow, the recirculation zone turned into a small ring, with lengths of 0.5d and diameters of 0.24d and 0.32d, respectively. The total recirculation ratio for 66%, 44%, 22% and 0 gap air flow were 0.74, 0.55, 0.29 and 0.38, respectively, with swirl numbers of 0.872, 0.934, 0.784 and 0.512, and gas/particle diffusion angles of 37.8°/36.3°, 38.4°/36.6°, 35.1°/32.0° and 36.0°/35.4°, respectively. In the radial range of r=0~50 mm, the axial velocity of 66% and 44% gap air flow was lower than that of 22% and 0. At 22% gap air flow, the tangential velocity decayed more rapidly. For the same x/d （where x is the distance from the measuring point to the outer）, the radial velocity with no gap air was greater than with it, and the negative value range was smaller. After x/d=0.1, the turbulence intensity peak at 66% and 44% gap air flow was higher than the other two conditions. As the gap air flow decreased, the turbulence kinetic energy at the same position gradually increased. The turbulence kinetic energy dissipation rate at 0 gap air flow was lower than with it. Under different conditions, the particle concentration is higher near the burner center region and lower at the periphery. At 66% gap air flow, there was significant particle recirculation in the x/d=0.3~0.7 range, with the recirculation starting point close to the burner center. At 44% gap air flow, central region particle recirculation occurred in the x/d=0.5~0.7 range. At 0 gap air flow, the peak position was near r/d=0.15, with high concentration particles at the edge of primary air, and obvious particle recirculation in the x/d=0.1~0.3 range. At 22% gap air flow, there was no significant particle recirculation.