Experimental combustion characteristics and NOx emissions for a 600-MWe utility boiler after the retrofitted: Effects of load variation

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 degrees C, and the O-2 concentration near the sidewall was above 5%, effectively suppressing sidewall high-temperature corrosion and slagging.