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To improve the low-load stable combustion capacity of a low-grade coal-fired boiler, this study proposed to reform C-layer secondary air, which was then used to improve the ignition and combustion stability of coal/airflow of a 600 MWe Foster Wheeler down-fired boiler. Cold airflow experiments and industrial measurements were carried out to investigate the influence of the new C-layer secondary air on the aerodynamic and combustion characteristics at low load under different C-layer secondary air ratios and damper openings, respectively. The flow and mixing characteristics of the C-layer secondary air and coal/airflow, the flue gas temperature and NOx, O2, and CO concentration distributions in the furnace at low load were examined. With increase in the C-layer secondary air ratio, the flow range of coal/airflow gradually expanded. The mixing distance first increased and then decreased. At an air ratio of 25%, the mixing distance was the longest. Industrial measurements showed that compared with that at the C-layer secondary air damper opening of 0%, the coal/airflow ignited earlier at 40% (corresponding to the C-layer secondary air ratio of 23.73%), and the flue gas temperature in the furnace increased substantially. At C-layer secondary air damper opening of 0%, 20%, and 40%, carbon content in the fly ash was 4.62%, 5.32%, and 4.20%, respectively. The respective NOx emissions at the furnace exits were 450 mg/Nm3, 378 mg/Nm3, and 427 mg/Nm3, (O2 = 6%). In actual operation, 40% is recommended as the optimal C-layer secondary air damper opening. [ABSTRACT FROM AUTHOR]

On a cold single-phase test stand, the effect of central air on the exit flow field of Babcock, Germany, burner was investigated. Industrial measurements were taken for a 700 MW wall-fired pulverized-coal utility boiler with above burners. Gas temperature, gas composition and concentration in the burner area were measured at 444 MW, 522 MW and 645 MW loads, respectively. Only when the central air mass flow was zero did a center reflux zone exist in the burner outlet area. The steady combustion of faulty coal was aided by early mixing of primary and secondary air, which was made possible by the decreased central air mass flow. At all different loads, the pulverized coal in center region took a long distance to ignite. The temperature in center steadily dropped as central air mass flow decreased, while the temperature in secondary air region gradually rose. Within 1.5 m from the primary air duct outlet, the highest CO concentration was 25 ppm and the highest O2 concentration was close to 21% under all loads. The gas concentration near sidewall was more influenced by load. With all valves opening of burner center air at 30%, the boiler was able to operate safely and stably without oil at a load of 262 MW. The furnace chamber temperature in burner area reached 1056.1 °C. [ABSTRACT FROM AUTHOR]

To address the problem of late ignition and poor burnout of Foster-Wheeler down-fired boilers, this study proposed a new combustion technology, which combines adding on arch secondary air and alternately arranging the fuel-lean coal/airflow (FLCA) and fuel-rich coal/airflow (FRCA). The coal particle trajectories of FLCA and FRCA and overall aerodynamic characteristics in the furnace were studied at FRCA and FLCA ratio (RRL) of 5:5, 7:3, and 9:1. The results showed that even at a low FRCA ratio, the new combustion technology could still effectively ensure the penetration depth of pulverised coal/airflow. At different RRL values, the main airflow from the arch appeared in the near-wall area and could penetrate downwards into the cold ash hopper area. With an increase in the value of RRL, the deflection degree of FLCA towards the furnace wall increased, while that of FRCA decreased. At RRL of 7:3, both the penetration depth and deflection degree of FRCA and FLCA were at a high level, which was conductive to promoting the burnout and recommended in practical applications. [ABSTRACT FROM AUTHOR]

The outlet velocity field of the pulverized coal burner is one of the important factors affecting its operating characteristics. In this article, cold tests were carried out for a new swirl burner with a pre-combustion chamber, and the influence of the air ratio on the outlet velocity field of the burner was studied. Through the cold single-phase test on the 1:3 model test bench, the burner outlet cold air velocities were obtained. The results shown that the formation of the central recirculation zone was mainly affected by the secondary air, a stable central recirculation zone could not be formed when the velocity of secondary air was too low. When the total air of the burner was fixed, the secondary air increased, the length of the central recirculation zone increased, and the mixing speed between different flows increased. When the ratio of the mass flow of the secondary air to tertiary air increased from 26:74 to 85:15, the reflux rate increases 5.5 times, which helped to keep the combustion stable. [ABSTRACT FROM AUTHOR]

To effectively control the flow and combustion of pulverised coal in down-fired boilers and improve their thermal efficiency while ensuring low NOx emissions, on arch secondary air (OASA) combustion technology and a smoke-tracing analysis were proposed. The aerodynamic characteristics of a 300-MWe Foster Wheeler (FW) down-fired boiler with the OASA ratios (ROASA) of 0%, 10%, 20%, and 30%, the flow trajectories and mixing characteristics of OASA, and fuel-rich coal/air flow (FRA) and fuel-lean coal/air flow (FLA) were studied experimentally. For the ROASA of <10%, FRA and FLA flow to furnace centre soon after they are injected into the furnace. OASA and FLA may mix with FRA before ignition. For the ROASA of 20% or higher, FRA and FLA flow to the near-wall area soon after being injected into the furnace. FRA mixes with OASA after ignition. With the increase in ROASA, the mixing distance between OASA and FRA increases first and then decreases. The penetration depth of coal/air flow and furnace airflow fullness increases. For the ROASA of 30%, the dimensionless penetration depth of coal/air flow can exceed 0.7. Furnace dimensionless airflow fullness at all the dimensionless heights can exceed 0.6. In real operation, the recommended ROASA is between 20 and 30%. [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]

• An understanding of the radial air staging method for PC utilization is improved and the key parameter (OFA distribution) is optimized. • Compared to the traditional axial air staging method, for the radial air staging method, the OFA distribution has a greater effect on the heat release from PC particles. • The increased R IO is not conducive to the rapid devolatilization from PC particles, resulting in poorer combustion stability of the boiler. • The increased R IO promotes the oxidation reaction of N released from PC particles, which is detrimental to boiler NO x emission reduction. • The advanced mixture of the OFA with the main airflow facilitates the burnout of the PC particles as the R IO increases. Radial air staging is an innovative method for reducing NO x emissions from coal-fired boilers compared to conventional axial air staging. However, an important issue in using this method is to set the over-fired air (OFA) distribution rationally to achieve good boiler performance. This paper aims to optimize the OFA distribution by evaluating important gas-particle (GP) parameters that influence the pulverized coal (PC) combustion performance. The GP flow experiment is conducted in a laboratory furnace model of a coal-fired boiler with different OFA distributions. The experimental results show that as R IO (Two-level OFA distribution ratio) changes from 0:1 to 1:0, the mixture of the OFA jet and airflow in the main combustion zone is advanced, which is conducive to PC burnout. Meanwhile, the size of the central recirculation zone decreases, resulting in poor PC ignition. It is worth noting that at R IO of 1:0, the central recirculation zone disappears at section y/d = 2.5, indicating that there is no high-temperature flue gas downstream to heat the fresh PC particles, which is extremely unfavorable for the stable combustion of the PC. In addition, at R IO of 0:1, compared to other cases, there are more particles in the central recirculation zone, which promotes the reduction reaction of N element released from PC particles, thus reducing NO x emission. According to the comprehensive evaluation, it is recommended that the R IO of the two-level OFA be set to 1:1 when using radial air staging in a coal-fired boiler. The results provide new insights into the application of the air staging method for efficient and clean PC utilization. [ABSTRACT FROM AUTHOR]

Numerical simulations were conducted to study the effects of the pulverized-coal bias distribution in the primary air on the coal combustion and NOx generation characteristics of a 600-MW down-fired boiler with multiple-injection and multiple-staging combustion technology. The total pulverized-coal in the primary air was kept constant, and the ratio of the pulverized-coal mass flux in the fuel-rich coal/air flow to the total pulverized-coal mass flux (RPR) was set as 60%, 70%, 80%, and 90%. By changing the RPR, the excess air coefficient of the fuel-rich flow was adjusted from 0.700 to 0.467. It was found that numerical simulation results were almost in agreement with cold modeling and in situ experimental results respectively, including the flow fields in the lower furnace at the RPR of 80% and the heating processes for the fuel-rich coal/air flow at the RPR of 90%, which verified the rationality of the numerical model and the grid. The simulation results indicated that the change of RPR has little effect on the symmetry of the flow field in the furnace. With the increase of the RPR from 60 to 90%: (1) the maximum airflow declination angle near the tertiary air slot decreased from 71 to 66°, which indicates that the downward airflow penetration depth gradually decreased; (2) the ignition distance of the fuel-rich coal/air flow decreased from 1.2 to 0.9 m, and the high-temperature area in the furnace hopper decreased and the position gradually moved away from the hopper water walls; (3) the oxygen consumption rate at the initial combustion stage constantly accelerated, and the fuel NOx generation rate under the fuel-rich flow nozzle increased first and then decreased; (4) the NOx emissions at the furnace exit dropped from 778 to 662 mg/m3 at 6% O2, and the carbon in the fly ash decreased from 5.87 to 5.52%. Increasing the RPR reasonably controlled the excess air coefficient of the fuel-rich flow, and realized the high-efficiency combustion in the furnace and the reduction of NOx emissions simultaneously. [ABSTRACT FROM AUTHOR]

The eccentric-swirl-secondary-air combustion technology (ESSACT) is an innovative technology to comprehensively solve high NO x emission and unburned carbon content in fly ash of the down-fired boiler with swirl burners. In this study, a breakthrough idea (i.e. decreasing burner injection angle (θ b)) is proposed to further greatly improve coal burnout of the improved boiler. Using a laser particle dynamic analyzer, the distributions of average and fluctuation velocities of gas/solid (GS) flows, distribution and decay of particle volume flux and jet trajectory of burner primary air in a 1:10 scale model of full-scale furnace at different θ b of 0°, 8°, 15° and 25° are acquired. The effects of θ b on GS flow characteristics (i.e. downward depth of GS flows, recirculation zones below arches and air flow fullness in the lower furnace) in the furnace are intensively studied. As the θ b decreases, the maximum vertical velocity of GS flows increases in the whole lower furnace, and the vertical fluctuation velocity of GS flows and the turbulent intensity and diffusion also increase. With decreasing θ b , maximum recirculation velocity and dimension of recirculation zone below arches both increase continuously, which is conducive to improving ignition and burnout of pulverized coal. Especially, the maximum recirculation velocity with θ b decreasing from 25° to 15° and the dimension of recirculation zone below arches with θ b decreasing from 15° to 8° increase more obviously. With decreasing θ b , the ejection effects of vent air and staged air on GS flows from arches are more effective. In the region below staged air, the maximum particle volume flux for the θ b of 0° and 8° is more than twice that for the θ b of 15° and 25°. As a result, the downward depth of GS flows and air flow fullness in the lower furnace both increase with decreasing θ b. To improve coal burnout of the down-fired boiler applying ESSACT, the θ b is recommended to be set below 8°. Image 1 • A novel low-NO x technology is proposed for a down-fired boiler with swirl burners. • Gas/particle flow characteristics are studied at various burner injection angles. • Recirculation zone and downward depth of flows both increase with decreasing angle. • Particles are more effectively ejected by vent and staged air with decreasing angle. • The burner injection angle is recommended to be set below 8° for the boiler. [ABSTRACT FROM AUTHOR]

• Flow and combustion characteristics of down-fired boiler with central secondary air supply are studied. • Central secondary air ratio that is beneficial to the flow field symmetry and penetration depth is given. • Reasons for the burnout of burner nozzle and the blending proportion limitation of bituminous coal are obtained. • Technical improvement ideas for increasing the blending proportion of bituminous coal are proposed. The existing central secondary air swirl pulverized coal burner and separated secondary air interval arrangement down-fired boiler combustion technology used for the combustion of blended bituminous coal encounter several problems such as burner nozzle burnout, limited proportion of bituminous coal blending under high load, etc. In this study, the effects of central secondary air on the flow, pulverized coal ignition, burnout, and NO x emissions characteristics of a 600-MWe down-fired boiler with the central secondary air combustion technology were studied by the combination of cold-modeling experiments and industrial-scale experiments. Moreover, the reasons for the burnout of the burner nozzle and limited blending proportion of bituminous coal were analyzed and revealed. Cold-modeling experiments showed that with the increase of the central secondary air ratio, the peak value of the dimensionless vertical velocity increases; however, the flow field asymmetry occurs in the furnace when the air ratio increases to 6%. Considering the symmetry of the flow field and the characteristics of the downdraft, the central secondary air ratio is advised to be less than 3.52%. The industrial-scale experiments of burning bituminous coal under 360-MWe load show that the ignition distance of coal/air flow is about 0.10 m for all the cases at 30, 50, and 75% of the central secondary air damper opening, respectively, which reveal that the serious burner nozzle burnout is caused by the premature ignition of the coal/air flow. Under three types of central secondary air damper openings, the NO x emissions at furnace outlet are 333, 329, and 355 mg m−3 @ 6% O 2 , respectively. By considering the flow, combustion, and temperature field characteristics in the furnace, reduction in the central secondary air supply air volume can delay the ignition of the coal/air flow, which provides a new idea and method to achieve a high proportion of bituminous coal blending at rated load. [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]

Measurements were taken for a 600-MWe wall-fired pulverized-coal utility boiler that was retrofitted with centrally fuel rich swirl coal combustion burners and two levels of OFA (over-fire air) technology. Using various swirl air vane angle settings a three-component particle-dynamics anemometer was used to measure flow characteristics in the near-OFA region in the laboratory together with gas temperature and species concentrations in the OFA and burner region in the utility boiler. The results show that, with decreasing swirl air vane angle, the penetrating depth of the jet stream decreases and the divergent angle increases. Flue gas temperature increases as the OFA swirl air vane angle increases from 25° to 45°. The O2 concentration decreases with decreasing swirl air vane angles. After retrofitting, the thermal efficiency of the boiler shows a slight increase in each case of 0.06–0.23%, with the exception of a swirl vane angle of 45°, where the thermal efficiency of the boiler decreases by 0.38%. NOx emissions are reduced when compared with those prior to the retrofitting, with OFA swirl air vane angles of 25°, 35°, 45° and 90° providing reductions of 240, 273, 294 and 319 mg/m 3 (O2 = 6%), respectively. [ABSTRACT FROM AUTHOR]

An experimental study was conducted to show the influence of the primary air velocity on lean coal combustion in a lateral-ignition tiny-oil burner. Using the lateral ignition scheme, a lean-coal ignition experiment was conducted at a coal feed rate of and primary air velocities of 15, 20, 25, and . During firing up with three oil guns in the presence of coal, the gas temperature along the center line increased along the flow of primary air. The gas temperatures on the side of the oil guns () were higher than those on the opposite side (). As the primary air velocity increased, the gas temperature along the center line at the same measurement point decreased while that on the side with the oil guns rose. However, the gas temperature on the opposite side changed only a little. concentrations at the exit of the burner were 1-3%. The burner resistance resulting from the flow and combustion of pulverized coal was 1,300-1,800 Pa. [ABSTRACT FROM AUTHOR]

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]

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]

A burner structure suitable for atmospheric entrained-flow gasifiers using fine ash as feedstock was proposed. The study investigates the impact of the burner structure on the mixing characteristics through 0.75:1 (geometry reduction) single-phase airflow experiments. Additionally, numerical simulations were conducted to study of the gasification process of fine ash in a 10,000 Nm3/h atmospheric entrained flow gasifier. The results indicate that a larger residual temperature near the burner outlet was observed when the diameter of the burner's gasification agents channel was 10 mm or 15 mm, approximately 0.7–0.8. Additionally, the mixing degree of the two airflows at the burner outlet was high, and the distance required for complete mixing was short. When the diameter of the gasification agent channel was 15 mm, the mixed syngas flow velocity was appropriate. This resulted in a maximum temperature of 2500 °C, an 80 % carbon conversion rate, and an outlet effective syngas (CO + H 2) concentration of 62 %. • Novel gasifier and burner structures for fine ash gasification are given. • Fine ash is quickly mixed at the outlet of burner and fully mixed in the center of gasifier. • The highest carbon conversion rate of fine ash entrained-flow gasifier is about 80 %. • Gasification agent channel diameter affects the mixing and gasification characteristics. • The outlet temperature exceeds 1600 °C which satisfies the requirement for liquid slag discharge. [ABSTRACT FROM AUTHOR]

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: 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]

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]

Abstract Removing end surfaces of a multi-channel burner which is the most commonly used burner type in entrained flow gasifiers could ease the risks of burner and cooling screens burning. On an air-particle test facility, experiments were conducted to investigate the influence of the improvements in a 2000 t/d GSP gasifier on the air/particle flow characteristics using a particle dynamics anemometer. For GSP burner and improved GSP burner (IGSP burner), the M-shaped distribution of mean axial velocity appears at the cross-section x/d = 4 and 6, respectively. By removing the end surface, the air and particles first diffusing to the near-wall region under the IGSP burner is delayed resulting in a lower risk that the cooling screen is burned. In IGSP burner, the central recirculation zone is smaller in both radial and axial directions than in GSP burner; removing the end surface could reduce the risk of burner being burned. Industrial-sized experimental results uncovered that in comparison with the prior GSP burner, the heat absorption of the burner support and the four parallel cooling screens for the IGSP burner decreased by 22% and 53%, respectively, which effectively verified the validity of the structural improvement. Highlights • End surfaces at the exit of a multi-channel burner were removed. • Air/particle flow fields under the improved burner were measured in lab-scale. • The influence of the improvements on the air-particle mixture extent was given. • The improvements mitigated high temperature corrosion to cooling screen and burner. [ABSTRACT FROM AUTHOR]

On an air-particle test facility, a particle dynamics anemometer is employed to investigate, in a small-scale gasification chamber for a 2000 t/d GSP gasifier, the influence of burner swirl vane angle (SVA: 16°, 21°, 26° and 31°) on the air/particle flow characteristics. The distributions of three-dimensional air/particle velocity, particle volume flux and particle size were obtained. Further, a novel method was provided to quantify the air-particle mixture extent with dimensionless difference of particle volume concentration. The results show that along the jet flow direction, single peak, double peaks and single peak successively appeared in the profiles of mean axial velocities. As the SVA increased from 16° to 31°, the first appeared peak of mean axial velocities in the near-wall region (300 mm ≤  r  ≤ 352 mm) gradually moved toward the burner; in the region x / d  = 0.3–4, the central recirculation zone expanded. The profile variation of particle volume flux at different SVAs was basically similar to that of air mean axial velocity. In the same cross-sections of x / d  = 1–4, as the SVA increased from 16° to 26°, the air-particle mixture extent in the boundary of peak zone for particle volume flux rose; when the SVA increased to 31°, it reduced. [ABSTRACT FROM AUTHOR]

Considering the excessively deep flame depth existing in a 600 MW down-fired boiler incorporating multiple-injection and multiple-staging technology, 1:20 scale aerodynamic tests were conducted to incrementally improve factors responsible for the deep flame depth. These trials demonstrated that, in all cases, the downward velocity near the wing walls decayed more rapidly than that near the furnace center. Increasing the mass ratio of pulverized coal in fuel-rich flow to that in fuel-lean flow and reducing the secondary air ratio while simultaneously increasing the tertiary air ratio was found to increase the penetration depth. Increasing the distance between adjacent burners, optimally lowering the fuel-rich and fuel-lean flow velocities, and reducing the secondary air velocity all decreased the penetration depth. The comprehensively improved downward airflow depth and air flux into the furnace hopper were reduced by 6.3% and 14.9%, respectively. Cold-state airflow tracing tests were performed in an actual boiler, the improved downward airflow depth reduced apparently, which was consistent with the results from modeling tests. Industrial-scale hot-state experiments determined improved hopper near-wall temperatures of 700–800 °C near the furnace center (values that were lower than those of 800–900 °C near the wing walls). These values were approximately 450 °C less than the prior temperatures at the same location, indicating the flame penetration depth was greatly reduced. [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: 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 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: The influence of the mass flow rate of secondary air on the gas/particle flow characteristics of a double swirl flow burner, in the near-burner region, was measured by a three-component particle-dynamics anemometer, in conjunction with a gas/particle two-phase test facility. Velocities, particle volume flux profiles, and normalized particle number concentrations were obtained. The relationship between the gas/particle flows and the combustion characteristics of the burners was discussed. For different mass flow rates of secondary air, annular recirculation zones formed only in the region of r/d=0.3–0.6 at x/d=0.1–0.3. With an increasing mass flow rate of secondary air, the peaks of the root mean square (RMS) axial fluctuating velocities, radial mean velocities, RMS radial fluctuating velocities, and tangential velocities all increased, while the recirculation increased slightly. There was a low particle volume flux in the central zone of the burner. At x/d=0.1–0.7, the profiles of particle volume flux had two peaks in the secondary air flow zone near the wall. With an increasing mass flow rate of secondary air, the peak of particle volume flux in the secondary air flow zone decreased, but the peak of particle volume flux near the wall increased. In section x/d=0.1–0.5, the particle diameter in the central zone of the burner was always less than the particle diameter at other locations. [Copyright &y& Elsevier]

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 three-component particle-dynamics anemometer is used to measure, in the near-burner region, the influence of the outer secondary air vane angle on the gas/particle flow characteristics of a double swirl flow burner, in conjunction with a gas/particle two-phase test facility. Velocities, particle volume flux profiles and normalized particle number concentrations were obtained. For three different outer secondary air vane angles, annular recirculation zones formed only in the region of r/d = 0.3–0.6 at x/d = 0.1–0.3. With a decreasing outer secondary air vane angle, the peaks of (RMS) root mean square axial fluctuation velocities, radial mean velocities near the wall, RMS radial fluctuation velocities and tangential velocities all increased, and the recirculation increased slightly. There was a low particle volume flux in the central zone of the burner. At x/d = 0.1–1.0, the profiles of particle volume flux had two peaks in the secondary air flow zone and near the wall, and the two peaks increased as the outer secondary air vane angle decreased. In the section x/d = 0.1–0.5, the particle diameter in the central zone of the burner was always less than the particle diameter at other locations. [ABSTRACT FROM AUTHOR]

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]

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]

[Display omitted] • Effect of fuel-lean flow damper opening (FLD) in a down-fired boiler is investigated. • Relation of water-wall and steam temperature in a supercritical boiler is discussed. • On decreasing the FLD, heating of the fuel-rich coal/air flows gradually accelerates. • Specific coal consumption is lowered and energy conversion efficiency is improved. • The optimum NO x emissions and carbon in fly ash are as low as 672 mg/m3 and 4.51%. In-situ trials were carried out to investigate the effects of the fuel-lean coal/air flow damper opening (FLD) on the pulverized-coal combustion and energy conversion efficiency in a 350-MW supercritical down-fired boiler. This boiler was operated with inferior coal, having a high ash content and low calorific value. The influence of combustion in furnace on steam temperature and coal consumption of a supercritical down-fired boiler were discussed innovatively. The experimental results indicate that, as the FLD was decreased from 100% to 25%, heating of the fuel-rich coal/air flow accelerated such that the overall furnace temperature increased and the thermal load gradually focused at the furnace center area. As a result, the maximum temperature of the water-wall in the lower furnace was reduced and the superheating degree rose significantly. Thus the superheated and reheated steam temperatures increased from 550.4 and 545.8 °C to 558.2 and 555.0 °C. Reducing the FLD also lowered the carbon in the fly ash and slag from 8.17% and 7.70% to 4.51% and 3.43%, respectively. Furthermore, the increase of boiler efficiency and the decrease of specific heat consumption both contributed to the reduction of the specific coal consumption, from 354.45 to 340.43 g·(kW·h)−1, thus the energy conversion efficiency of the unit was improved. However, adjustment of the FLD had only a minimal effect on NO x emissions, which remained in the range of 654–672 mg/m3 at 6% O 2. Based on optimizing coal combustion characteristic and economic performance of the unit, an optimal FLD of 25% was recommended. [ABSTRACT FROM AUTHOR]

A novel burner arrangement for entrained-flow pulverized coal gasifier with multiple low-set burners, which burners are arranged to be counter-biased, is proposed aimed at mitigating high-temperature corrosion to the wall. To verify the characteristics of this improvement in an 80,000 Nm3/h fly ash entrained-flow gasifier, experiments were conducted on the model to investigate the impact of six burners being co-biased, opposed and counter-biased on the air/particle flow field by using a particle dynamics anemometer. The results show that, on the horizontal cross-section passing through burner centerlines with co-biased burners, opposed burners and counter-biased burners, the radius of mixing zone is 0.196, 0.16 and 0.174; the ratio of total particle volume flux in the near-wall region to the total particle volume flux in the measurement zone was 76.5%, 26.1% and 57.8%, respectively. On the vertical cross-section above burner outlet, the radius of central recirculation zone with co-biased burners remains to expand to 0.88 while that of counter-biased burners gradually shrinks to 0.33. There is no central recirculation zone under opposed burners; air and particle swirl numbers are close to zero. This study shows that new burner arrangement could ease high-temperature corrosion to gasifier wall and strengthens mixing of burner jets. • A novel multi-burner arrangement for the entrained-flow gasifier was proposed. • Experiment was conducted in a lab-scale fly ash gasifier to verify the improvement. • Air/particle flow fields were measured under three burner arrangements. [ABSTRACT FROM AUTHOR]