Combustion and NO_x emission characteristics of a retrofitted down-fired 660MW_e utility boiler at different loads

Industrial experiments were performed for a retrofitted 660MW_e full-scale down-fired boiler. Measurements of ignition of the primary air/fuel mixture flow, the gas temperature distribution of the furnace and the gas components in the furnace were conducted at loads of 660, 550 and 330MW_e. With decreasing load, the gas temperature decreases and the ignition position of the primary coal/air flow becomes farther along the axis of the fuel-rich pipe in the burner region under the arches. The furnace temperature also decreases with decreasing load, as does the difference between the temperatures in the burning region and the lower position of the burnout region. With decreasing load, the exhaust gas temperature decreases from 129.8°C to 114.3°C, while NO_x emissions decrease from 2448 to 1610mg/m³. All three loads result in low carbon content in fly ash and great boiler thermal efficiency higher than 92%. Compared with the case of 660MW_e before retrofit, the exhaust gas temperature decreased from 136 to 129.8°C, the carbon content in the fly ash decreased from 9.55% to 2.43% and the boiler efficiency increased from 84.54% to 93.66%.