Abstract: For getting higher efficiency and lower NOx emission, a test to optimize combustion system is conducted in a 1 000 MW bituminous coal-fired boiler in opposed firing pattern. During the test, the gas temperature distribution in furnace is measured, combustion and NOx emission characteristic is studied by varying such factors as type of coal, O2 at economizer exit, mass flow of over fired air (OFA), air damper position of burner and after air port (AAP), combinations of burners and boiler load. It indicates that O2 at economizer exit and mass flow of OFA have great effect on boiler efficiency and NOx emission. It’s better to keep these two parameters at 3.0% and 750 t/h respectively , which can also eliminate slagging on platen superheater. O2 deviation along furnace width can be eliminated by setting outer second air damper of burners in same horizontal row at different proper positions. Unburned carbon in fly ash can be decreased by using design coal, closing outer second air damper of AAP, setting burner’s core air damper at 50% and shutting down one-layer upper row burners at full load if possible. After adjustment, the measured efficiency of boiler is above 94.4% and NOx emission concentration is lower than 300 mg/m 3. They are obviously better than those of boilers in service in China.

Key words: Coal-fired boiler, NOx emission, Opposed firing, Ultra-supercritical