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Low NO x burners and air staging technology are the most economic and effective means of reducing NO x emissions from coal-fired furnaces. However, it is difficult to significantly reduce NO x emissions through air-staged combustion in the furnace without reducing the boiler efficiency. The aim of this work was to study the effect of the inner secondary air cone length of a centrally fuel-rich swirl coal combustion burner on combustion and NOx characteristics using a 0.5 MW laboratory furnace with air-staging. Gas temperature and concentrations of gaseous species (O2, CO, and NO x) were measured in the primary combustion and burnout zones for different inner secondary air cone lengths. It was found that the inner secondary air cone length had significant effects on NO x emissions, unburned carbon content in the fly ash, and ignition performance of the burner. As the inner secondary air cone length increased, the unburned carbon content in the fly ash level increased, NO x emissions decreased, and pulverized-coal ignition occurred later. The optimized results provide an important reference for engineering design. © 2015 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To further reduce the NOx emissions of the down‐fired boiler while improving its low‐load stable combustion capacity, a new low NOx combustion organization mode that utilizes the high velocity parallel oil‐secondary air to improve the pulverized coal combustion process was proposed based on a novel stable combustion technology. We carried out cold airflow experiments under different oil‐secondary air and F‐layer secondary air distributions (mass flow rate ratios of 1:9, 1:3, 2:3) based on a 300 MWe Foster Wheeler down‐fired boiler to study its influence on the flow and mixing characteristics of the coal/airflow. Results show that the mixing between the oil‐secondary air and the fuel‐rich coal/airflow is gradually delayed with the increase of the secondary air distribution. When the secondary air distribution reaches more than 2:3, the oil‐secondary air starts to become the dominant airflow that influences the whole flow field in the furnace. Based on the result of the cold airflow experiment, we carried out industrial measurements under different parallel oil‐secondary air and F‐layer secondary air distributions (4:6, 5:5, 6:4) on a 600 MWe FW down‐fired boiler under the condition of using the high velocity oil‐secondary air. The ignition distance of the fuel‐rich coal/airflow, the flue gas temperature, the O2, CO, and NOx concentrations in the furnace were measured. At the secondary air distribution of 4:6, the ignition distance of the fuel‐rich coal/airflow was about 1.31 m. When the secondary air distribution was increased to 5:5 and 6:4, the ignition was put off, but the pulverized coal/airflow could still catch on fire in time. With the increase of the parallel oil‐secondary air proportion, the flame center in the furnace did not move downward substantially. In three cases, the lowest O2 concentrations in the inspection port area under the burner were all below 1% (peak CO concentration values were all above 28,000 ppm). The pulverized coal all burned in a strong reducing atmosphere. At secondary air distributions of 4:6, 5:5, and 6:4, NOx emissions of the boiler were, respectively, 825.83, 819.48, and 853.86 mg/Nm3 (O2 = 6%). The thermal efficiency was, respectively, 90.09%, 89.16%, and 90.98%. In actual operation, the recommended secondary air distribution is 6:4. [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]

Laboratory experiments and industrial-scale experiments on 300-MW low-volatile coal-fired boiler were performed under deep air staging. Aerodynamic characteristics, gas temperature and concentrations, furnace temperature, and boiler efficiency were measured for various secondary air mass flow rates. Under deep air staging, a steady central recirculation zone forms near the burner nozzle. With a decreasing flow rate, the swirl intensity and maximum axial, radial, and tangential velocities decrease; between X/D=0-0.8, the velocity decay rate decreases, and the relative reverse flow rate decreases. In the early stage, the maximum axial mixing rate decreases; the primary air concentration increases slightly. A decrease in secondary air-box damper opening decreases the gas temperature and its increasing rate, generating a farther ignition position. In the initial stage, the O2 consumption rate and CO concentration increase, while the NOx concentration decreases. In the later stage, O2 concentration remains almost constant below 2%, and the CO concentrations exceed 15 000 ppm, which restrain NOx formation notably. Near the water-cooled wall, flue gas temperature varies slightly, and O2 concentration exceeds 3%. Along radial direction 1.5364 ⩽ R0/D0 ⩽ 1.8708, the O2 concentrations are below 2%, and CO concentrations exceed 6000 ppm. A decreasing damper opening decreases furnace temperature in the primary combustion zone slightly. NOx emission decreases from 833.4 to 769.9 mg/m3 (6% O2), unburnt carbon increases from 5.18% to 6.84%, and boiler efficiency decreases from 91.53% to 90.99%. [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]