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To solve the problem of high NOx emission of 600‐MWe boilers in power plants, we established a cold gas–solid modeling testbed scaled by 1:5 for two‐channel overfire air (OFA). A phase‐Doppler anemometer was used to measure the characteristics of the outlet flow field of the two‐channel OFA under different OFA rates. We also verified the industrial feasibility of this testbed under loads of 300 and 600 MWe. The influence of the OFA rate on the divergence angle of the outlet jet was small: When the OFA rate was increased from 15% to 35%, the divergence angle only increased by 2.2°. The attenuation of the axial velocity of the outlet jet increases with increasing OFA rate. For OFA rates of 15% and 25%, the jet penetration depth was between 1.5d and 2.5d (where d is the cone diameter of the OFA model in the cold‐flow experiments). When the OFA rate was 35%, the jet penetration depth was between 2.5d and 3.5d. The jet maintained about 17% O2 concentration at 1.4 m (about 11d) in the furnace under different boiler loads, and the concentration of emitted NOx increased with decreasing load. Based on these findings, we propose the use of two‐stage OFA: The jet at the outlet of the first‐stage OFA ports should have a larger jet‐divergence angle, and the other stage should have a larger jet‐penetration depth to realize full mixing with the flue gas and to ensure high burnout and low NOx emission. [ABSTRACT FROM AUTHOR]

To enhance the rapid switching ability of the boiler load and reduce NOx emissions, a new combustion system was implemented in a 600‐MWe wall‐fired boiler with swirl burners. This system included two levels of overfire air (OFA) and low NOx combustion technology. Industrial tests were conducted at 300‐, 450‐, and 600‐MWe loads before and after the retrofitted. These tests included measuring flue gas and furnace temperatures with thermocouples and analyzing local gas concentrations using a gas analyzer. The research results indicate that under conditions where the OFA ratio exceeds 30%, the burner exhibits good ignition performance at different loads. At the 600‐MWe load, the nitrogen oxides (NOx) emissions were reduced by 55% compared to before the retrofit. After the retrofit, the flame center inside the furnace of different loads was located at the height of 33.36 m, the first and second‐stage cooling water quantities were slightly higher, the reheat cooling water quantity was greatly reduced after the retrofit, and contributes to the boiler's safe operation. Under different load conditions after the retrofit, the gas temperature near the sidewall was below 850°C, and the O2 concentration near the sidewall was above 5%, effectively suppressing sidewall high‐temperature corrosion and slagging. [ABSTRACT FROM AUTHOR]

For realizing higher boiler efficiency and lower NO x emissions at a half load of a 600-MWe utility boiler, a novel approach is proposed for various coal feed rates. In this study, at 50% of the full load, industrial-size experiments were conducted at various coal feed rates with measurements of local gas temperatures and species concentrations (in the burner region and near-wall region, respectively), the carbon content of the fly ash, the carbon content of the slag, and the NO x emissions. The pulverized-coal ignition positions of two burners at low loads were at 0.2–0.3 m from the burner nozzle outlet; hence, satisfactory ignition performance was realized. At larger coal feed rates of mill A, both the ignition performance and the NO reduction performance improved. The unburnt carbon in the fly ash decreased monotonically and the carbon in the slag increased monotonically, with settings from 50%:50%–36%:64% (namely, changing the coal-feed rate pair of the middle and bottom mills from 50%:50%–43%:57%–36%:64%). • A breakthrough idea is proposed to increase bottom mill coal feed rate. • Industrial-size experiments were performed for four settings. • Combustion, NO x emissions and boiler thermal efficiency varied greatly among them. • An appropriate parameter setup was recommended for boilers at low load. [ABSTRACT FROM AUTHOR]