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The eccentric-swirl-secondary-air combustion technology has been confirmed to comprehensively solve high NO x emission and poor coal burnout for down-fired boilers with swirl burners. The influence of vent-air inclination angle (β v), a critical factor that affects coal burnout, on gas/particle flow characteristics is investigated to further decrease unburned combustible in fly ash. Gas/particle two-phase flow experiments under different β v (i.e., 10°, 20°, 28°, 40° and 50°) are performed by using a particle dynamic analyser in a 1:10-scale model of the full-scale improved boiler. With increasing β v , the under-arch recirculation zone and the recirculation velocities of gas/particle flows continuously increase. In the staged air region, the vertical velocities of gas/particle flows near water-cooled wall for β v of 40° and 50° are still as high as 2–4 m/s, however, the vertical velocities of gas/particle flows basically decay to negative values for smaller β v of 10° and 20°. At furnace section Y/Y 0 from 0.220 to 0.369, the vertical fluctuation velocities of gas/particle flows near water-cooled wall for β v of 40° and 50° are significantly higher than those with β v of 10°, 20° and 28°, and the particle volume flux at the same horizontal position X/X 0 constantly increases with increasing β v. Furthermore, the downward ejection ability of vent air to gas/particle flows from burners continuously improves, and the downward depth of gas/particle flows and the space utilization ratio of lower furnace both increase with increasing β v. The appropriate inclination angle of vent air for the improved boiler varies from 40° to 50°. Image 1 • A novel high-efficiency low-NO x technology is applied to a down-fired boiler with swirl burners. • Gas/particle flow characteristics at different vent-air inclination angles are investigated. • With increasing angle, recirculation zone and downward depth of gas/particle flows increase. • Primary air is more effectively ejected by under-arch air with increasing inclination angle. • The appropriate inclination angle of vent air for the improved boiler varies from 40° to 50°. [ABSTRACT FROM AUTHOR]

• 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]

In this paper, based on the MIMSC (multi-injection and multi-stage combustion) technology, new burner arrangement and air distribution parameter settings were proposed for a 300-MW subcritical down-fired boiler originally using MBEL (Mitsui Babcock Energy Limited) combustion technology. Numerical simulations were conducted to study the influences of the secondary-tertiary air proportion on the airflow mixing effect in the furnace, the ignition and pulverized coal combustion characteristics. The airflow mixing effect in the furnace is characterized by the size of the dimensionless vertical velocity decay area (V da) and the fluctuation of the maximum vertical velocity decay curve (V dc). During the research, the sum of the secondary and tertiary air rate remained constant, and the secondary air rate was set to 30.54%, 33.54%, 36.54%, 39.54%, and 42.54%. It was found that under the condition of using new type burner, with the secondary air rate increased from 30.54% to 42.54%, the ignition distance of pulverized coal decreased from 1.30m to 0.84m, the dimensionless penetration depth decreased from 1.46 to 1.27, and the NO x emission and carbon in the fly ash decreased first and then increased. The variation of V dc showed the following regulation. At the secondary air rate of 30.54% to 33.54%, increasing the secondary air rate decreased the fluctuation amplitude. While at the secondary air rate of 39.54% to 42.54%, increasing the secondary air rate increased the fluctuation amplitude. Only at the secondary air rate of 36.54%, V dc in the tertiary air mixing area was smooth. When V dc was smooth, V da was small at 0.043, the carbon in fly ash at the furnace outlet was the lowest at 4.19%, and the NO x emission was low at 675.9 mg/m3 at 6% O 2. An optimal secondary air rate of 36.54% is recommended. For the subsequent design of burner structure and parameters, it is suggested that V dc in the tertiary air mixing area should be smooth. [ABSTRACT FROM AUTHOR]

Effects of adjusting the inner-secondary-air damper opening among 100%, 70%, and 50% on the flow, combustion, and NO x emissions of a 600-MWe down-fired boiler incorporating multiple-injection and multiple-staging technology were investigated. Both 1 : 20-scale aerodynamic tests and industrial experiments were conducted. The small-scale tests showed that symmetric flow patterns formed in all cases, and the velocities of boundary and outer secondary air decayed more quickly than the velocity of inner secondary air. As the inner-secondary-air damper opening decreased from 100% to 50%, the average dimensionless depth of downward airflow reduced from 0.830 to 0.788 while the horizontal velocity in the recirculation zone increased. Industrial experiments demonstrated that, as the inner-secondary-air damper opening decreased from 100% to 50%, the heating rate of fuel-rich coal/air flow increased from 572 to 687°C/m, the corresponding ignition distance shortened from 1.36 to 1.11 m, and the hopper near-wall temperature decreased by approximately 50°C. Carbon in fly ash decreased from 7.31% to 6.93%, and NO x emissions rose from 343 to 371 ppm at 6% O2. The boiler efficiency improved from 89.78% to 89.92%. An inner-secondary-air damper opening of 70% is more reasonable than 50% and 100% considering the ignition distance, carbon in fly ash, and NO x emissions. Copyright © 2017 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To alleviate the over-temperature of water-wall and increase the energy conversion efficiency of supercritical down-fired boilers, cold-model air/particle flow experiments and in-situ trials were performed to investigate the effects of the secondary-air distribution wall-side deflection coefficient (w s) on air/particle flow and combustion characteristics. As w s increased from 0 to 0.33, the amount of air/particle flow diffused toward water-wall and the corresponding particle concentration both decreased, while the velocity decay was accelerated. At a w s of 0.16, due to prior ignition of fuel-rich flow and a longer flame stroke in lower furnace, the carbon in fly ash and slag were lowest. As w s increased, the thermal load was gradually focused at the furnace center, and the maximum value and deviation of water-wall temperature in lower furnace decreased. Consequently, the temperatures of superheated and reheated steam respectively increased from 542.7 °C to 543.9 °C–560.2 °C and 560.1 °C, respectively. Furthermore, increasing w s from 0 to 0.28 decreased the specific coal consumption from 346.29 to 341.09 g (kW h)−1, indicating the energy conversion efficiency was improved. However, adjusting w s had only a minimal effect on NO x emissions. A w s of 0.28 is recommended to optimize the water-wall temperature, pulverized-coal burnout, and economic performance. [Display omitted] • Laboratory and industrial experiments are combined performed for a down-fired boiler. • The wall-side deflection coefficient of secondary-air distribution (w s) is proposed. • On increasing w s , maximum value and deviation of water-wall temperature is lowered. • Specific coal consumption is reduced and energy conversion efficiency is improved. • The optimum carbon in fly ash and NO x emissions are as low as 4.92% and 654 mg/m3. [ABSTRACT FROM AUTHOR]

Numerical simulations are carried out to investigate the influence of burner nozzle–organization–mode (N–O–M) on flow field distribution and combustion characteristics of a 300‐MWe subcritical down‐fired boiler. Three typical N–O–Ms respectively designed with Mitsui Babcock Energy Limited (MBEL), fuel‐lean coal/air flow down‐setting (FD), and multi‐injection multistaging combustion (MIMSC) technology are studied, plus industrial‐size measurements on the original MBEL boiler. Vertical velocity attenuation index (η) and maximum dimensionless penetrating depth (γ) are introduced to estimate the transfer effect and penetrating capacity of pulverized coal/air flow. Results uncover that under the N–O–M based on MBEL technology, flow field and temperature field are deflective. η is 9.257. Under N–O–Ms based on FD and MIMSC technology, flow field and temperature field present obvious symmetry. η respectively are 4.365 and 2.921. γ are correspondingly about 0.8 and 1.36. Carbon content in fly ash and NOx emissions at furnace outlet are lowest (5.77% and 735.21 mg/m3 (O2 = 6%)) under the N–O–M with MIMSC technology. The bigger the η is, the worse penetrating characteristics of coal/air flow is, resulting in poor burnout of pulverized coal. Therefore, MIMSC technology is recommended for the boiler improvement, and η should be taken into account in the design of new down‐fired boiler N–O–Ms. [ABSTRACT FROM AUTHOR]