Industrial measurement of combustion and NOx formation characteristics on a low-grade coal-fired 600MWe FW down-fired boiler retrofitted with novel low-load stable combustion technology

The randomness and intermittence of solar and wind power generation require coal-fired thermal power boilers that have a low-load stable combustion capacity. This study proposed a novel low-load stable combustion technology in which the oil secondary air flow is arranged parallel to the fuel-rich coal/air flow and participates in pulverised coal combustion during boiler operation. The method was applied to a 600 MWe down-fired boiler manufactured with the technology of Foster Wheeler Corp. Full-scale industrial measurements of furnace flue gas temperature, fuel-rich coal/air flow ignition distance, and distribution characteristics of NOx, O₂, and CO in the furnace at loads of 200, 240, and 540 MWe were performed. The results showed that the boiler can stably operate without oil support at 240 MWe (40% rated load) and 200 MWe (33% rated load) respectively burning a blended coal of anthracite and lean coal, and blending bituminous coal. At loads of 200, 240, and 540 MWe, the fuel-rich coal/air flow ignition distances were, respectively, approximately 1.4, 1.7, and 1.3 m. NOx emissions at the furnace exit were 406, 407, and 730 mg/Nm³ (O₂ = 6%), and the boiler thermal efficiencies were 92.42%, 92.45%, and 90.58%, respectively. This novel technology presents the characteristics of high efficiency and low NOx emission while realizing low-load stable combustion of down-fired boilers.