Experimental Study on Combustion Characteristics and NOx Emissions in a 600 MWe Utility Boiler: Influence of Coal Mill Operating Modes

ABSTRACT The large‐scale integration of renewable energy into the grid poses significant challenges to the safe and stable operation of power systems, necessitating the transformation of coal‐fired power into a dual‐role energy source that provides both base support and system flexibility. Reliable maximum output from coal‐fired units is essential to support the power system. Previous studies have primarily focused on optimizing operational parameters; however, mill malfunctions or overloading shutdowns often lead to mismatched coordination and combustion imbalances, thereby constraining the maximum output of units. This article takes the 600 MWe wall‐fired boiler as the research object and conducts industrial tests on different coal mill operation modes under 600 MWe load. Results indicate that under the nonconventional ABCEF and ABCDE‐II coal mill operation schemes, the ignition of pulverized coal corresponding to burners A1 and A2 is delayed by approximately 0.05–0.08 m compared to the conventional ABDEF operation scheme, but stable combustion requirements are still met. Compared with the ABDEF scheme, the ABCEF scheme results in increases of 12.75°C in flue gas temperature, 0.8% in unburned carbon content in fly ash, and 59.09 mg/m 3 in NOx emissions, whereas the desuperheating water flow is reduced by 31.7 t/h. The flue gas temperature under the ABCDE‐II scheme is similar to that of the ABDEF scheme, but the NOx concentration at the air preheater outlet is 69 mg/m 3 higher. Overall, the boiler unit can achieve safe and stable operation at maximum output under various coal mill operation schemes. This study provides valuable insights for achieving maximum output under nonconventional mill operation conditions in wall‐fired boilers.