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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]

To achieve low-NO x emission in the coal-fired industrial boiler, the radial air staging method is proposed. The location of the over-fired air (OFA) is an essential parameter as it affects the combustion stability, NO x generation, burnout, and slagging trend. These are related to the gas-particle flow such as the recirculation region, gas mixture, and gas-particle mixture. Therefore, in this paper, taking a coal-fired industrial boiler with radial air staging method as an object, in a cold-modeling furnace, the gas-particle flow characteristics under various OFA locations (L D of 1.29, 1.43, 1.72, and 2.00) are studied. When OFA is radially arranged, the OFA jet diffuses towards the furnace center. As the L D increases, the size of the central recirculation region increases, thereby improving combustion stability. When the L D is 2.00, the mixing of the OFA jet and PCC jet obviously is delayed. Moreover, an increase in L D leads to more returned particles in the furnace center, promoting the reduction reaction of NO x. In addition, as the L D increases from 1.29 to 1.72, the gas-particle mixing uniformity is enhanced, which is beneficial to the uniform temperature distribution. Comprehensively, the L D of 1.43–1.72 is recommended when radial air staging is adopted in coal-fired industrial boilers. • The radial air staging method accelerates the mixing of OFA and the main airflow while reducing the mixing intensity. • With the increase of L D , the obstructing effect by radial OFA on the diffusion of the swirling main airflow is weakened. • The increased L D facilitates gas recirculation in the main combustion zone, which is conducive to stable combustion. • The mixing uniformity of GPF increases with L D in general, promoting the uniformity of temperature distribution. [ABSTRACT FROM AUTHOR]

Industrial pulverized coal boiler (IPCB) usually employ a pre-combustion chamber (PCC) to ensure stable combustion. However, there are potential slagging problems in the PCC, which threaten the safe operation of the boiler. Air-staged combustion technology is an effective method to reduce NO x emission, and different excess air coefficients affect slagging. CFD simulation is an important method for studying slagging in the furnace. In this paper, Using CFD simulation with slagging model embedded by user-defined function, the slagging trends in the PCC are studied under different excess air coefficients. The particles' collision rate (CR), deposition rate (DR), and sticking rate (SR) on the PCC walls are obtained by CFD simulation. As the excess air coefficient in the PCC (α PCC) increases from 0.3 to 1.1, the CR of particles on all walls of PCC (CR PCC) increases exponentially, indicating the abrasion degree on the PCC walls is growing rapidly. In addition, due to the sizeable annular recirculation zone when α PCC = 0.3, the DR of particles on all walls of PCC (DR PCC) and the SR of particles on all walls of PCC (SR PCC) are much larger than those under other conditions, the slagging trend is the worse. As the α PCC increases from 0.3 to 1.1, the slagging trends in the PCC first decrease and then increase. To improve the safety of boiler operation, it is recommended that the α PCC be adjusted between 0.5 and 0.9. • The effect of excess air coefficients (α PCC) on the slagging trends of PCC walls is studied by CFD simulation. • The relationship between the air-staged levels and CR PCC is established. • The entrainment effect of the secondary air on the particles is a crucial factor affecting slagging. • The annular recirculation zone distribution is the main reason for the maximum value of SR PCC at α PCC = 0.3. • The slagging trends first decrease and increase as the α PCC increases from 0.3 to 1.1. [ABSTRACT FROM AUTHOR]

To ensure good combustion stability, industrial pulverized coal-fired boilers normally employ a swirl burner with pre-combustion chamber (PCC). Owing to the high cross-sectional heat load of the PCC, there is potential for slagging, which can affect the safe and stable operation of the boiler, but can be avoided or reduced through the selection of suitable operating parameter values. Here, the effects on the slagging characteristics of PCC of varying the ratio of the inner to the outer secondary air mass flow rates in a swirl burner, R SA , from 0.00 to 0.83 were investigated using a computational fluid dynamics (CFD) simulation approach. The rates of collision, deposition, and sticking were analyzed. The results showed that as the R SA increases, the total collision rate of the pulverized coal particles in the PCC increases, and when R SA = 0.83, the total collision rate in the PCC is about 7 times of that when R SA = 0.00. Further, slagging tends to appear on the wall near the outlet of the PCC, and the degree of slagging in the PCC first decreases and then increases with increasing R SA. The optimum R SA range was found to be 0.22–0.38, which is conducive to the safe and stable operation of industrial pulverized coal-fired boilers. [Display omitted] • The slagging characteristics in the pre-combustion chamber were studied. • The rates of collision, deposition, and sticking were analyzed. • Slagging tends to appear near the exit area of the pre-combustion chamber. • The degree of slagging first decreases and then increases as R SA increases. [ABSTRACT FROM AUTHOR]

Radial air staging is a new air staging method for industrial pulverized coal boilers. In this paper, its impact on the gas-particle flow characteristics of industrial pulverized coal boilers was studied experimentally. The gas-particle flow experiments were carried out on a 1:6 scale boiler platform by a particle dynamics anemometer. The three-dimensional velocities of the gas-particle, average particle size and particle volume flux under different air stoichiometries in the furnace were measured. When the air stoichiometry was 0.2, the burner outlet could not form a stable reflux zone to establish a good combustion process. When the air stoichiometry is greater than 0.8, the maximum particle volume flow is also located near the water wall, increasing the slagging tendency on the wall. The appropriate air stoichiometry range for the new burner was 0.4–0.8. [Display omitted] • Radial air staging was a new air staging method. • Laboratory test and industrial application on the radial air staging were performed. • The appropriate range of air stoichiometry is recommended to be 0.4–0.8. • Anti-slagging and low NO x combustion are realized on industrial boilers. [ABSTRACT FROM AUTHOR]

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]

In this study, a novel swirl burner for industrial pulverized coal boiler was studied by laboratory experiments and industrial application tests. First, a cold flow experiment was carried out on a 1:3 scale model experimental platform. The cold air velocities of burner outlet were measured in detail. Moreover, the influence of the mass flow ratio of the inner and outer secondary air on the shape of the central reflux zone and the reflux rate at the burner outlet was analyzed. It was found that a stable central reflux zone can be formed at the burner outlet. In addition, an industry application test was carried out in a 29 MW hot water boiler. The flue gas temperature at the burner outlet and the composition of exhaust gas were obtained under different operating parameters. The influence of inner and outer secondary air damper opening on burner performance (ignition performance, NO x emission characteristics, stable combustion performance, and anti-slagging performance) was analyzed. The influence of inner secondary air damper opening on burner performance was found to be greater than that of outer secondary air damper opening. The maximum concentration of NO x emission at furnace outlet was 364.9 mg/m3, and low-NO x combustion was achieved for industrial pulverized coal boilers. The minimum load without natural gas support was 3 MW. The load regulation rate was close to 10:1, and low load combustion stability was achieved. During three heating seasons, the normal operation of the boiler was not affected by slagging. • Laboratory experiments and industrial application tests are performed. • Influence of different inner and outer secondary air mass-flow ratio are investigated. • Low NO x combustion is achieved for industrial pulverized coal boilers. • Low load combustion stability is achieved for industrial pulverized coal boilers. [ABSTRACT FROM AUTHOR]

Abstract: Due to the limits of reserves and price for the high rank coal, the low rank coal has been employed as fuel for power generation in China and will be eventually employed in the world. To burn low rank coal, centrally fuel-rich swirl coal combustion burner has been studied in Harbin Institute of Technology. This paper reviews and analyzes the major research results. The work has included both experiments and numerical simulation. The experiments were conducted using small-scale single-phase experimental equipment, a gas/particle two-phase test facility and 200- and 300-MWe wall-fired utility boilers. For the burner, the primary air and glass beads partially penetrate the central recirculation zone and are then deflected radially. At the center of the central recirculation zone, there is high particle volume flux and large particle size. For the burners the local mean CO concentrations, gas temperatures and temperature gradient are higher, and the mean concentrations of O2 and NO x in the jet flow direction in the burner region are lower. Moreover, the mean O2 concentration is higher and the gas temperature and mean CO concentration are lower in the side wall region. Centrally fuel-rich burners have been successfully used in 200- and 300-MWe wall-fired pulverized coal utility boilers. [Copyright &y& Elsevier]

Deep peak shaving requires extremely high requirements for low-load combustion stability of boilers. In this study, a novel swirl burner (NSB) with an eccentric secondary air arrangement was proposed, and the validity and the progressiveness of the NSB in achieving ultra-low-load combustion stability for down-fired boilers (DFBs) were confirmed from laboratory experiments to industrial applications. Firstly, the cold-modelling experiments of gas/particle (GP) two-phase flow characteristics involving two combustion systems (i.e., the DFB with traditional swirl burners (TSBs) and the DFB with NSBs) were performed at an ultra-low load of 90 MW e. Compared with the original boiler with TSBs, the maximum horizontal recirculation velocity and the area of recirculation zone below arches significantly increase for the improved DFB with NSBs. The particle number concentration near furnace center for the improved DFB with NSBs is much higher than that for the original DFB with TSBs. The above two aspects will effectively guarantee timely ignition of anthracite. The downward depth of GP flows and the space utilization ratio of the lower furnace increase, which will be beneficial to promoting volume heat load and heat flux density in primary combustion zone. In addition, full-scale industrial-sized measurements aiming at a 300-MW e DFB improved by NSBs were carried out at ultra-low loads of 100 and 90 MW e. For the original DFB after improved by NSBs, the minimum load for stable combustion without oil support is reduced from 150 to 90 MW e , and the ultra-low-load combustion stability is achieved. For the improved DFB with NSBs, pulverized coal ignition distances for operating burners are about 2 and 2.6 m, respectively, and the signal strength of flame detectors for all operating burners is above 95% at 100 and 90 MW e. The flame fullness and combustion stability are good at the initial combustion stage. At ultra-low loads, furnace negative pressure, superheat steam pressure and oxygen concentration at furnace outlet fluctuate slightly. The temperature at air preheater inlet meets the needs of normal operation of denitrification system, and there is no problem of low temperature corrosion on the surface at flue gas side of air preheater. The unburned carbon in fly ash is about 4%. The maximum concentrations of NO x emission at furnace outlet are 714 and 687 mg/m3 (O 2 = 6%) at 100 and 90 MW e , respectively, and ultra-low emission of NO x after denitrification system is achieved. • A novel swirl burner with an eccentric secondary air arrangement was proposed. • Laboratory and industrial experiments were performed. • Performances of flow, mixture, ignition and combustion are all improved. • Ultra-low-load combustion stability is achieved for the improved down-fired boiler. [ABSTRACT FROM AUTHOR]

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]

Through a gas-particle cold-modeling experiment, the particle dynamic analyzer (PDA) is used to investigate the effects of fuel-lean coal/airflow angle and ratio of oil secondary air to F-layer secondary air on the gas/particle flows characteristics in the furnace of a Foster Wheeler (FW) down-fired boiler with enhanced stable combustion technology. As the fuel-lean coal/airflow angle increases from 10° to 45°, the peak value of the vertical dimensionless velocity of the gas/particle flows gradually increases, and the peak position gradually moves to the near wall region. As the ratio of oil secondary air to F-layer secondary air (the secondary air ratio for short) increased, the peak value of the vertical dimensionless velocity of the gas/particle flows gradually increased and the peak value position of the dimensionless velocity gradually moved towards the near-wall region. In actual operation, for the perspective of performance and safety, the recommended fuel-lean coal/airflow angle and secondary air ratio is 30°and 1:2 respectively. The enhanced stable combustion technology had been applied to two 600 MW FW down-fired boilers, and these boilers can achieve stable operation when burning a wide range of coal quality under the load section from 200 MW to 600 MW. • A Foster Wheeler down-fired boiler retrofitted with novel low-load stable combustion technology is studied by PDA. • Effects of fuel-lean coal/airflow angle and secondary air ratio on the gas/particle flows characteristics were investigated. • The fuel-lean coal/airflow angle of 30° and the secondary air ratio of 1:2 is recommended. • This novel low-load stable down-fired boiler combustion technology is suitable for a wide range of coal quality combustion. [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]

Abstract: Cold airflow experiments on a small-scale burner model, as well as in situ experiments on a centrally fuel-rich swirl coal combustion burner were conducted. Measurements were taken from within a 300 MWe wall-fired pulverized-coal utility boiler installed with eight of centrally fuel-rich swirl coal combustion burners in the bottom row of the furnace during experiments. Various primary air ratios, flow characteristics, gas temperature and gas species concentrations in the burner region were measured. The results of these analyses show that with decreasing primary air ratio, the swirl intensity of air, divergence angles and maximum length and diameter of the central recirculation zone all increased, and the turbulence intensity of the jet flow peaked but decayed quickly. In the burner nozzle region, gas temperature, temperature gradient and CO concentration increased with decreasing primary air ratio, while O2 and NOx concentration decreased. Different primary air ratios, the gas temperatures and gas species concentrations in the side-wall region varied slightly. [Copyright &y& Elsevier]

Abstract: A start-up ignition burner has been proposed to reduce oil fuel consumption during the firing-up process and partial-load operation. To investigate the influence of different excess air ratios on bituminous coal combustion in the start-up ignition burner, full-scale reacting-flow experiments were performed for an experiment setup. The ignition burner was identical to that normally used in an 800 MWe utility boiler. Gas temperature distributions in the burner were obtained for excess air ratios of 0.56, 0.75, 0.98 and 1.14 (corresponding to primary air velocities of 17, 23, 30 and 35 m/s). Coal burnout and the release of C and H were observed at the exit of the burner nozzle. Gases such as O2 and CO were measured at the center of the burner. A change in resistance was obtained within the burner. [ABSTRACT FROM AUTHOR]