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• Proposed effective low NO x combustion technology with arch-supplied secondary air. • The flow characteristics of the two-phase flows in the furnace were investigated. • Arch-supplied secondary air increases the downward impulse of the two-phase flow. • Increasing arch-supplied secondary air rate can improved the combustion performance. This study proposes a low NO x combustion method for Foster Wheeler type down-fired boilers. The effectiveness of this technique was validated through laboratory-scale gas-particle two-phase experiments and industrial trials. The flow field characteristics within FW-type boiler furnaces equipped with arch-supplied secondary air injection nozzles were investigated. Furthermore, the application of this technique to a 660 MW subcritical FW-type boiler was examined, focusing on NO x emissions and combustion characteristics. Results demonstrate that optimizing the damper openings for F-layer and arch-supplied secondary air can significantly reduce NO x emissions by over 33 %. Additionally, increasing the mass flow rate of arch-supplied secondary air aids in reducing unburned carbon in fly ash and inducing a downward shift in the flame center within the furnace. [ABSTRACT FROM AUTHOR]

Abstract: Industrial experiments were performed with a 300-MWe full-scale down-fired boiler. New data is reported for (i) gas temperature distributions within the primary air and coal mixture flows, (ii) gas compositions, such as O2, CO, CO2 and NO x , and (iii) gas temperatures within the near-wall region. The data complements previously-obtained data from the same utility boiler before being modified by declination of the F-tier secondary air. By directing secondary air under the arches, the region where the primary air and pulverized coal mixture is ignited is brought forward within the boiler. Gas temperatures rose in the fuel-burning zone and fell in the fuel-burnout zone. As a result the quantity of unburned carbon in fly ash and the gas temperature at the furnace outlet were both lowered. [Copyright &y& Elsevier]

• A novel low-load stable combustion technology is applied on a 600MWe FW down-fired boiler. • 33% rated load stable combustion without oil support is achieved. • Full-scale industrial measurements are carried out at 200, 240 and 540MWe. • Combustion and NOx formation characteristics at high and low load are contrastively studied. 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, O 2 , 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 (O 2 = 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. [ABSTRACT FROM AUTHOR]

Abstract: Using an IFA300 constant temperature anemometer system, cold air experiments on a scale-model of a down-fired pulverized-coal 300MWe utility boiler with swirl burners were performed to investigate the influence of the staged-air flow ratio on flow characteristics in the furnace. This ratio was increased in incremental steps over the range of 7%–20%. The flame reach of the downward airflow was decreased with the ratio increased. A shallower reach is accompanied by a weaker mixing of vent and staged-air. At lower ratios, mixing is good and thus favors coal combustion but weak mixing at intermediate ratios produces a delay in the mixing point. This is compensated by an increasing recirculation zone under the arch that benefits ignition and the appearance of an upward airflow below the mixing point due to an increasing influence of vent air. At higher ratios still, this upward flowing disturbance is centered higher up in the furnace generated primarily by mixing with staged-air as vent-air mixing weakens. [Copyright &y& Elsevier]

Abstract: Industrial experiments have been performed on a down-fired pulverized-coal 300MWe utility boiler with vent air valve opening of 100% and 40%. The gas temperature distribution along the primary air and coal mixture flow, gas temperature distribution in the furnace, and gas components such as O2, CO, CO2 and NO x in the near-wall region were measured for the first time. The influence of vent air valve opening on coal combustion in the furnace was determined. The results indicate that ignition of the primary air and pulverized-coal mixture is delayed. The position of the gas temperature peak is above the arches. Emission of NO x is up to 2101mg/m3 (at 6% O2 dry) with vent valve opening of 40%. [Copyright &y& Elsevier]