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Abstract: An OFA (over-fire air) program and matched measures supporting efficient-combustion are proposed for the FW (Foster Wheeler)-type down-fired boiler, where the OFA is supplied from the arches of the boiler. A gas/solid cold test was conducted at a scale of 1:15, using a two-dimensional laser phase Doppler analyzer to measure parameters in the model furnace, such as the two-phase gas/solid flow velocity, fluctuation velocity, particle size, particle volume flux and particle number concentration. The effects of the OFA ratio on the gas/solid flow characteristics in the furnace were investigated. With an increase in the OFA ratio, the jet depth of the fuel-rich flow decreased. For an OFA ratio of 25%, the jet depth of the fuel-rich flow was much less than that for other OFA ratios, and the residence time of the gas/solid flow in the lower furnace was shorter. An increase in the OFA ratio can increase the penetration depth and allow fuller mixing with the upward airflow, while an OFA ratio that is too great will hinder the upward flow back to the burner nozzle region. An OFA ratio of 20% is considered appropriate for the proposed OFA technical scheme. [Copyright &y& Elsevier]

A new overfire air (OFA) technology was proposed by the authors for a Foster Wheeler down-fired boiler, and a small-scale cold experimental system for a 660-MWe unit was established. The velocity field distribution was measured in the furnace to study the characteristics of single-phase flow in the furnace at different OFA nozzle angles. The furnace temperature and distributions of the O2 concentration and NO concentration at different OFA nozzle angles were simulated using Fluent 6.3.26, and the average temperature of the furnace outlet, the O2 and NO x concentrations and carbon content in the fly ash were calculated. As the OFA nozzle angle increased, the vertical penetration depth of OFA increased and the horizontal penetration depth of OFA gradually decreased. The carbon content in the fly ash and NO x concentration initially rose and then fell at the furnace outlet, and they were lowest when the OFA angle was set at 20°. Thus, according to the findings of this article, an optimized OFA angle of 20° was chosen. [ABSTRACT FROM AUTHOR]

Abstract: A new over-fire air (OFA) program, which called arch-supplied OFA, is proposed for Foster Wheeler (FW) type down-fired boiler in this paper. The OFA nozzles are setting on arches near the furnace center and emitting OFA flow into the furnace at an inclined angle. Cold airflow experiments were conducted to determine the effect of the OFA ratio on the aerodynamic field in a small-scale furnace modeled for a 660-MWe down-fired boiler. As the OFA ratio increases, the penetration depth of the OFA flow increases in the level direction and the turning point from downward to upward of the OFA flow moves to the furnace center. At the same time, the velocity of the F-tier airflow decreases and its ability to bring the arch-injected airflow to deeper positions weakens and the turning point from downward to upward of the F-tier airflow moves to the wall. When the OFA ratio is 20%, the OFA flow could penetrate to the furnace center in the level direction and mix with the upflowing gas completely, while the arch-injected airflow have sufficient travel distance and enough residence time in the lower furnace. Thus, considering the penetration depth of arch-injected flow in the vertical direction and the OFA flow in the level direction, an OFA ratio of 20% is recommended for the new OFA arrangement according to the present work. [Copyright &y& Elsevier]

Abstract: Industrial experiments were performed for a retrofitted 660-MWe full-scale arch-fired boiler. The ignition position of the primary air/fuel mixture flow, furnace temperature and flue gas component after the air heater were measured with different anthracite ratios at loads of 660- and 380-MWe. As the ratio of anthracite increased, the gas temperature decreased in the fuel-burning zones of the C4 and C6 burners, indicating a farther ignition position of the primary fuel/air flow under the arches, the gas temperature of the lower furnace decreased while that of the upper furnace increased, NO x emissions decreased while both the exhaust gas temperature and carbon content in fly ash increased, and the boiler efficiency decreased. At the rated load, an anthracite ratio of 35% was optimal for economical efficiency. At low load, the negative gas pressure fluctuated remarkably, which led to unstable combustion in the furnace. To ensure safe and stable operation of the boiler, a mass ratio of anthracite of 25% is advisable. [Copyright &y& Elsevier]

Abstract: Industrial experiments were performed for a retrofitted 660MWe 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 330MWe. 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 660MWe 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%. [Copyright &y& Elsevier]

Abstract: Air-surrounding-fuel is a well-known concept used within tangential and wall-fired boilers. Here, we report for the first time on industrial experiments performed to study the effects of this concept on a 660 MWe full-scale down-fired boiler. Data are reported for the gas temperature distributions along the primary air and coal-mixed flows, furnace temperatures, gas compositions, for example O2, CO and NO x , and gas temperatures in the near-wall region. The influence of concentration control valve (CCV) opening on combustion and NO x emission in the furnace were determined. The results show that the flame stability, temperature distribution, unburnt carbon are influenced by both concentration ratios and fuel-rich flow velocities. As CCV opening increases, NO x emissions decrease from 2594 mg/m3 to 1895 mg/m3. Considering altogether economic benefits and environmental protection issues, 30% is the optimal value for the CCV opening. [ABSTRACT FROM AUTHOR]

Abstract: We measured various operational parameters of a 200-MWe, wall-fired, lignite utility boiler under different loads. The parameters measured were gas temperature, gas species concentration, char burnout, component release rates (C, H and N), furnace temperature, heat flux, and boiler efficiency. Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has two ring recirculation zones that start in the secondary air region of the burner. With increasing secondary air flow, the air flow axial velocity increases, the maximum values for the radial velocity, tangential velocity, and turbulence intensity all increase, and there are slight increases in the air flow swirl intensity and the recirculation zone size. With increasing load gas, the temperature and CO concentration in the central region of burner decrease, while O2 concentration, NO x concentration, char burnout, and component release rates of C, H, and N increase. Pulverized-coal ignites farther into the burner, in the secondary air region. Gas temperature, O2 concentration, NO x concentration, char burnout and component release rates of C, H, and N all increase. Furthermore, CO concentration varies slightly and pulverized-coal ignites closer. In the side wall region, gas temperature, O2 concentration, and NO x concentration all increase, but CO concentration varies only slightly. In the bottom row burner region the furnace temperature and heat flux increase appreciably, but the increase become more obvious in the middle and top row burner regions and in the burnout region. Compared with a 120-MWe load, the mean NO x emission at the air preheater exits for 190-MWe load increases from 589.5mg/m3 (O2 =6%) to 794.6mg/m3 (O2 =6%), and the boiler efficiency increases from 90.73% to 92.45%. [Copyright &y& Elsevier]

Abstract: Turbulence intensities at the exit of a centrally fuel rich (CFR) burner were measured employing a probe with hot-film sensors. In addition, using glycol as a smog tracer, optical images of the highlighted primary airflow were taken with a CCD camera and contrast-enhanced by computer. Profiles of the interface between primary and secondary air were obtained from which fractal dimensions (FDs) of the primary air boundary were estimated. Results indicate that FDs of this air boundary are in the range of 1.10–1.30 depending on burner conditions. As the FD and mean turbulence intensities of the primary air boundary have uniform distributions, they can be used to analyze coal combustion and NO x formation characteristics of the burner. When either decreasing the outer secondary air vane angle or increasing either the inner secondary air vane angle or total mass flow rate of the secondary air, the burner swirl number increases which subsequently shows up as an increase in the FD and mean turbulence intensities of the primary air boundary. Increasing the ratio of the mass flow rate of inner to outer secondary air decreases the burner swirl number, but increases the FD and mean turbulence intensities of primary air boundary. [Copyright &y& Elsevier]

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]

Abstract: We measured various operational parameters of a 200-MWe, wall-fired, lignite utility boiler under various outer secondary air vane angles. The parameters measured were gas temperature, gas species concentrations, char burnout, and component release rates (C, H and N). Cold air experiments of a single burner were conducted in the laboratory. A double swirl flow pulverized-coal burner has a single ring recirculation zone that forms in the secondary air region in the burner. By decreasing vane angles, maximum values of radial velocity, tangential velocity and turbulence intensity all increase. Moreover, swirl intensity of air flow and recirculation zone size increase. Concomitantly, in the central region of the burner, decreasing the vane angles of outer secondary air increases gas temperatures, CO concentrations, char burnout and component release rates of C, H, and N, while O2 and NO x concentrations decrease, and an early ignition of pulverized-coal occurs. Meanwhile, in the secondary air region of the burner, conditions are similar except that NO x mean concentrations are reversed showing instead an increase. In the side wall region, gas temperatures increase, O2 and NO x concentrations decrease, but CO concentrations vary only slightly. [Copyright &y& Elsevier]

Abstract: Industrial experiments were performed on a down-fired pulverized-coal 300MWe utility boiler with swirl burners. Gas temperature, concentrations of gas components (O2, CO, CO2 and NO x ) in the burning region and carbon content in the fly ash were measured with outer secondary-air vane angles of 25°, 32.5° and 50°. Results indicate that with increasing vane angle, NO x emission and boiler efficiency decrease. Overall evaluation boiler efficiency and NO x emission, the vane angle of 32.5° is optimum. Using an IFA300 constant-temperature anemometer system, cold air experiments on a quarter-scaled burner model were also carried out to investigate the influence of various outer secondary-air vane angles on the flow characteristics in the burner nozzle region. No central recirculation zone appeared for vane angles of 25° and 32.5°. Most of the pulverized-coal was ignited in the external recirculation zone. For vane angles of 45° and 55°, a central recirculation zone could be observed, and air flow rigidity and axial velocities decreased rapidly. [Copyright &y& Elsevier]

The corrosion tests of Inconel 740 H in supercritical water were carried out at 600–700 °C and 25 MPa. The weight gain elevated with the rise in exposure time and temperature. The oxidation kinetics follows parabolic law in all cases. The temperature has an enhanced impact on oxide phase composition. Cr 2 O 3 was the major oxide phase and the oxides containing Ti, Ni Co, Fe or Nb were also detected at different temperatures. A marked experiment was performed in H 2 16O/16O 2 and subsequently in H 2 16O/18O 2. The oxygen isotope profile showed that oxidation proceeded by outward chromium transport. The related mechanism was discussed. [Display omitted] • Corrosion test of Inconel 740 H in supercritical water was performed at 600–700 °C. • Temperature has a great impact on oxide phase composition. • Isotope profile shows that oxidation occurred by outward metal transport. [ABSTRACT FROM AUTHOR]