Impact of high-velocity primary air on combustion and NO_x emission performance of a novel swirling W-shaped boiler: A numerical simulation combined with industrial experiment verification

The research object in this study is a W-shaped boiler with swirl burners (i.e. swirling W-shaped boiler), which is enhanced by multiple ejection and staged combustion technology (MESCT). Through the method of numerical simulations combined with industrial experiment verification, the influence of greatly increasing the primary air velocity (PAV) on the combustion and NOx emission characteristics is deeply explored. The results show that, as the PAV raises from 20 to 31 m/s, the high-temperature recirculation zone (HTRZ) under the arch expands, which effectively promotes the ignition of pulverized coal (PC) airflow and balances the inhibition effect of ignition on account of the reduction of PC concentration. At the same time, the flame center in the primary combustion zone moves down and the flame fullness increases. With the increase of PAV, the oxidizing atmosphere in the prophase of PC ignition is strengthened, and the formation of NOx is increased. The PAV increases from 20 to 31 m/s, and the combustible component of fly ash decreases significantly from 8.97% to 5.35%, with a decrease of about 40%. However, the NOx emission concentration increases only by 8.5% from 672 to 729 mg/m3 (O2 = 6%). Compared with the traditional swirling W-shaped boiler, when the improved W-shaped boiler with a PAV of 31 m/s, the combustible component of fly ash and NOx emission concentration are reduced by 51.8% and 43.4%, respectively.