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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]

Number of down-fired boilers burning bituminous coal or anthracite blended with bituminous coal has exceeded 10% of the total down-fired boilers in China. However, lacking of the industrial-scale research on the performance of down-fired boiler burning bituminous coal or blended coal, which limits the actual operation adjustment. Industrial-scale experiments on a 300-MWe down-fired boiler fueled with bituminous coal and blended coal were performed, which boiler was originally designed to burn low-volatile coal. Without the over-fire air, air-staging combustion can still be realized when the down-fired boiler burning bituminous coal. The combustion performance in the down-fired boiler under different coal varieties was compared. Compared with the anthracite case, flue gas temperature is higher, coal flame fullness is greater, O2 consumption occurs faster and NOx concentration is lower in the primary combustion zone when burning bituminous coal. Strong reducing atmosphere is formed in the primary combustion zone. The NOx emissions are low at a level of 410 mg/m3 at 6% O2 at furnace exit and boiler thermal efficiency reaches 92.590% when burning bituminous coal. The NOx emissions cannot be further reduced by burning blended coal. In addition, the boiler thermal efficiency reduced by 1.108%. Without the over-fire air, compared with burning anthracite or lean coal, the NOx emissions and carbon in fly ash significant reduction by 70% and 90%, respectively, and the boiler thermal efficiency increased when burning bituminous coal. [ABSTRACT FROM AUTHOR]

A key component of a circulating fluidized-bed gasifier is the recycling control device, which is important for stable solid circulation and combustion of particles. In our previous work, a steam–solid ejector was used as a recirculating control device to provide a continuous and stable pressure barrier, which reduced the amount of unburned combustibles in the fly ash. Damage to the ejector nozzle seriously affected the combustion stability and effective syngas concentration. The causes of wear of the nozzle surface were analyzed using a combination of methods. Computational fluid dynamics showed that the radial velocity near the nozzle zone approached 10–12 m/s and obvious erosion appeared on the surface of the nozzle. Scanning electron microscopy and energy-dispersive spectroscopy indicated that the direction of grooves that appeared on the worn nozzle surface was the same as that of the gas–solid flow and that the Ni-based structure of the original material was seriously damaged. [ABSTRACT FROM AUTHOR]

The raw syngas effluent from a fluidized bed gasifier typically contains a large amount of fly ash having a high concentration of carbon, which is undesirable. The present work examined the newly developed entrained-flow gasification technology intended to gasify raw syngas. Simulation of gas–solid flow and reaction behavior in an industrial-scale entrained-flow gasifier applying this new technology was first performed to obtain a better understanding of the particle flow and gasification characteristics. In addition, the devolatilization and heterogeneous reactions of fly ash particles were characterized by thermogravimetric analysis and user-defined function. The predictions from the simulation showed good agreement with the results of in situ experimental measurements. The combustion reaction for raw syngas occurred in the burner jet zone. As the hot gaseous products diffused, gasification reactions dominated the other zones. When burner inclination angle was 0°, 8.5°, and 25.5°, the temperature at the bottom outlet of the gasifier was lower than the ash flow temperature with the value of 1360 °C. Solid slag formed and blocked the outlet. By comparison, this gasifier with the burner inclination angle of 17° could discharge the liquid slag and function as a continuous operation. In this way, the carbon conversion in fly ash reached the maximum value of 87%. [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 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]

In consideration of increasing the tertiary air damper opening of a 600 MWe down-fired boiler with prior multiple-injection multiple-staging technology facilitated the coal burnout, while largely increasing the NO x emissions. Additionally, the flame kernel was greatly moved downwards, thus causing significant temperature variations in the hopper near-wall region and the water wall in the lower furnace was vulnerable to overheating. This work concentrated on the comprehensively improved multiple-injection multiple-staging technology, both 1:20 scale cold aerodynamic tests and industrial experiments were conducted to examine the effects of tertiary air damper opening on flow, combustion, NO x emissions and especially the hopper near-wall temperatures. The aerodynamic tests indicated that, on increasing the tertiary air damper opening from 40 to 70%, all the flow fields exhibit good symmetry. The tertiary air flows downwards along the hopper near-wall region, with a maximum near-wall dimensionless vertical velocity significantly increasing from 0.48 to 0.66, and accordingly, the dimensionless depth of downward airflow increases from 0.744 to 0.846. The industrial experimental results showed that, upon introducing more tertiary air, the ignition distance of fuel-rich coal/air flow shortens from 1.25 to 0.87 m. The coal burnout is enhanced, carbon in fly ash drops from 6.90 to 6.15%, while the NO x emissions slightly increase from 593 to 641 mg/m 3 at 6% O 2 . On reducing the measuring height of hopper near-wall temperature from 9.1 to 3.3 m, the average heating rate increases from 0.44 to 0.63 °C/mm. The increased tertiary air damper opening presents an increasingly obvious cooling effect on the hopper near-wall region, with the temperature reductions around 50 °C, which is conductive to protect the water wall in the lower furnace from overheating. [ABSTRACT FROM AUTHOR]

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

To achieve significant reductions in NO x emissions without increasing the levels of unburnt carbon in the fly ash, a new combustion system was applied to a 300-MW e Babcock & Wilcox (B&W) down-fired boiler installed with swirl burners. The unit featured introduced overfire air (OFA) and decreased outlet area of the inner and outer secondary-air ducts of the swirl burners. Full-scale measurements (adjusting the inner secondary-air vane angle to 35°, 45°, and 55°) revealed that the influence of the high-temperature recirculating region under the arch upon the combustion and NO x emission characteristics of the boiler is greater than that of the high-temperature flue gas entrained by the swirl burner itself. The ignition distance of the coal/air flow is reduced by at least 1.8 m compared with that of the original combustion system. For the inner secondary-air vane angle of 35°, the coal/air flow ignites earlier than for the vane angles of 45° and 55°. The measurements of the gas species concentrations in the zone near the sidewall indicates that at inspection port 1, the coal flame of the burners does not spread across the entire furnace cross-section for all three vane angles; however, for the vane angle of 35° the flame is spread across the entire furnace cross-section at inspection port 2. For this optimal (35°) inner secondary-air vane angle, the NO x emissions and carbon content in the fly ash reached levels of 674 mg/m 3 (6% O 2 ), and 11.4%, respectively, achieving a significant NO x reduction of 51.9% without increasing the levels of unburnt carbon in the fly ash. [ABSTRACT FROM AUTHOR]

[Display omitted] • Combustion method to treat TPC can realize the comprehensive utilization of energy and resources. • TPC has high reaction activity, and its activation energy is lower than semi-coke, lean coal and anthracite, and close to bituminous coal and coke. • The high disordered structure and a looser overall carbon structure of TPC results in low activation energy. • TPC can be used as premium fuel and can replace coal coke, semi-coke, and anthracite. A technical route for large-scale utilization of waste tire pyrolytic char (TPC) by combustion method was proposed. The physical and chemical characteristics and combustion characteristics of TPC were studied and compared with anthracite, semi-coke, bituminous coal, coal char, coal gasification fly ash which have similar chemical compositions. And the material composition of TPC ash was analyzed. The results show that the overall particle size of TPC particles is larger (average particle size is 193.8 μm), and they are formed by bonding fine carbon black particles. The microstructure of TPC particles is different from that of coal and coal char. TPC has a well-developed pore structure, and its specific surface area and pore volume are close to coal char. TPC is composed of a large amount of amorphous carbon, which has a low degree of graphitization and large spacing of aromatic lamellae. TPC carbon has a highly disordered structure, low cross-linked structure strength, and a looser overall carbon structure. The surface functional groups in TPC mainly exist in the form of aromatic carbon and aliphatic carbon, and only a small amount of O = C-O and Π-Π*. The volatiles content of TPC is only 4.36%, but the ignition temperature of TPC is similar to that of lean coal, and the activation energy of TPC is lower than that of anthracite and lean coal, which is caused by the developed pore structure and loose carbon structure. TPC is a high-quality high-calorific value fuel, replacing coal coke and semi-coke as fuel, thereby reducing fossil energy consumption. The ash of TPC can be processed to obtain Zn and white carbon black (SiO 2) raw material, which has high utilization value. The combustion method of TPC can realize its resource utilization and large-scale application. [ABSTRACT FROM AUTHOR]

The pore and chemical structure characteristics of the raw coal and the coal gasification fly ash (CGFA) in an atmospheric pressure circulating fluidized bed gasifier with a gas production capacity of 20000 and 40000 Nm3 h−1 were studied. The results indicated the presence of developed pore structure and high carbon content of the CGFA. The comprehensive fractal dimension method was proposed to analyze the pore structure of the pore section. The comprehensive fractal dimension was found to be > 2.6. The surface of CGFA is rough and porous. When compared to raw coal, the relative content of the CGFA carbon functional group is lower than 20%, and that of aliphatic carbon gets reduced. The interlamellar spacing (0.3489 nm, 0.3501 nm) of the A-filter cake ash (FCAA), A-dry ash (DAA), B-filter cake ash (FCAB), and B-dry ash (DAB) carbon is higher than that of the standard graphite (0.3354 nm), lean coal (0.3468 nm), and anthracite (0.344 nm). Moreover, the carbon structure is loose. The comprehensive results of physical and chemical structure revealed that CGFA showed a good chemical reaction activity and also the value of secondary combustion and gasification as fuel. This study exhibits significance and importance in the field of waste valorization towards a circular economy. [Display omitted] • Pore structure of CGFA was defined via effective fractal dimension. • The pore complexity of sample was analyzed via comprehensive fractal dimension. • The chemical structure of CGFA was described quantitatively. • The gasification activity of the fly ash was defined. [ABSTRACT FROM AUTHOR]

• The combustion and gas emission characteristics of CGFA were studied. • The CGFA lacks fixed carbon secondary combustion stage. • The model-free method and the model method estimate the kinetics parameters. • Determine the best combustion model of the samples. The activation energy of samples was calculated using the model-free method and the model method (typically 46 mechanism functions). The model method is suitable for water scrubbing ash (WSA), and the model-free method is suitable for raw coal (RC), dry ash (DA) and WSA. In the model-free method, the Kissinger method not only guarantees the accuracy of the reduction activation energy E value, but also takes into account the calculation amount of the replacement. The Kissinger method is the better method for the replacement activation energy E value. The average estimated value of DA's E of Kissinger method is 107.89 kJ/mol, which is lower than 143.30 kJ/mol of Yangquan anthracite. The average estimated value of WSA's E is 82.10 kJ/mol, which is slightly higher than that of lean coal (77.54 kJ/mol). It shows that the combustion performance of DA is better than that of Yangquan anthracite, and the combustion performance of WSA is equivalent to that of lean coal. Comprehensive combustion characteristics and gas emission results show that the CGFA has combustibility and utilization value. [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]

• Proposed effective low NO x combustion technology with arch-supplied secondary air. • The flow characteristics of the two-phase flows in the furnace were investigated. • Arch-supplied secondary air increases the downward impulse of the two-phase flow. • Increasing arch-supplied secondary air rate can improved the combustion performance. This study proposes a low NO x combustion method for Foster Wheeler type down-fired boilers. The effectiveness of this technique was validated through laboratory-scale gas-particle two-phase experiments and industrial trials. The flow field characteristics within FW-type boiler furnaces equipped with arch-supplied secondary air injection nozzles were investigated. Furthermore, the application of this technique to a 660 MW subcritical FW-type boiler was examined, focusing on NO x emissions and combustion characteristics. Results demonstrate that optimizing the damper openings for F-layer and arch-supplied secondary air can significantly reduce NO x emissions by over 33 %. Additionally, increasing the mass flow rate of arch-supplied secondary air aids in reducing unburned carbon in fly ash and inducing a downward shift in the flame center within the furnace. [ABSTRACT FROM AUTHOR]

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

Improvements were made to a multi-channel burner, the most commonly used burner type, aimed at mitigating slagging in an industrial entrained flow gasifier for post-processing raw syngas. The novel design is referred to as a fully mixed burner. This research describes investigations of the effect of burner structure on the mixing and gasification characteristics using 1:2.5 (geometry reduction) small-scale airflow experiments and full-size numerical simulations. Experimental results show that, within the multi-channel burner and fully mixed burner, the penetration depths of the external gasifying agent into the raw syngas are 0.04 and 0.8, and the area-averaged temperature difference plateaus at 0.35 and 0.18, respectively. By changing the feeding mode, the fully mixed burner significantly expands the contact area of raw syngas and gasifying agent, so as to enhance the mixing of these two flows. Three-dimensional simulation results show that the whole raw syngas from the multi-channel burner and the full mixed burner is heated to around 1350 °C and 1550 °C, respectively. In the gasifier with the novel burner, the temperature of the near-burner wall and bottom outlet surpass 1500 °C and 1600 °C, respectively. The gasifier's continuous and stable slag tapping is feasible as solid slag would not have blocked the bottom outlet. [Display omitted] • A novel burner was developed based on the multi-channel burner. • Multiple circumferentially distributed spacer nozzles replaced continuous ring channel. • Penetration depth and mixing rate of improved burner leapt in experiments and simulation. • The new design mitigated slagging at bottom outlet and enhanced carbon conversion. [ABSTRACT FROM AUTHOR]

During the gasification process of coal, fine ash (FA) and coarse slag (CS) solid waste are produced, which contain a large amount of residual carbon and ash (mainly SiO 2), resulting in energy waste and environmental pollution. Therefore the main goal of this research is to recover the wasted energy from FA and CS. The investigation of the physicochemical structure, combustion characteristics and SiO 2 properties of entrained flow gasification ash (EFGA) is an important basis for the valorization of EFGA. The physicochemical, combustion characteristics and SiO 2 properties of EFGA in a entrained flow bed of 112,000 Nm3/h gas-forming capacity were investigated, showing that FA and CS undergo different gasification processes, with FA having a more developed pore structure and high specific surface area. FA and CS have different degrees of graphitization, with defects or heteroatoms in FA causing a scattered carbon layer structure with an irregular graphitic carbon crystal structure, and organic molecular functional group fragments forming an indeterminate structure and active sites. The organic molecule functional group fragments constitute an indeterminate structure and active sites. Kinetic analysis shows that the influence of chemical structure on the combustion characteristics of EFGA is higher than that of physical structure. Compared to CS, FA has fewer active sites and a small number of oxygen-containing functional groups, resulting in a weaker combustion reactivity of FA. The combustion activity of EFGA is lower than that of circulating fluidized bed gasification ash and anthracite, making it difficult to be eliminated by direct combustion, although co-combustion is feasible. The specific surface area of SiO 2 prepared by EFGA after acid treatment and calcination is small (<39.7086 m2/g), SiO 2 exists as crystals and the elemental silicon exists mainly in the form of Si–O, O–Si–O and hydrated silicon dioxide Si–O 2 -nH 2 O, which can be used as a raw material for the preparation of silica. • Chemical structure dominates for the combustion performance of EFGA. • Coarse slag has more active centers than fine ash. • Coarse has better combustion performance than fine ash. • SiO 2 in EFGA can be used as high value-added raw materials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Laboratory experiments and industrial trials are conducted for a down-fired boiler. • Effects of air-staging degree (ASD) in furnace of the boiler at low load are studied. • On increasing ASD, the trend of particle diffusion to furnace center area increased. • Maximum value and deviation of water-wall temperature is large at low ASD settings. • Optimum coal consumption and NO x emission are as low as 337.36 g·(kW·h)−1 and 654 mg/m3. Low load operation of down-fired boilers has become the norm such that the comprehensive performances of such boilers at low loads need to be investigated to increase the energy conversion efficiency and reduce carbon and NO x emissions. In this work, cold-model air/particle flow experiments and industrial-scale trials were performed to study the effects of the air-staging degree (ASD) on the air/particle flow, combustion, water wall temperature, energy conversion and NO x emission characteristics of a 350 MW supercritical down-fired boiler at low loads. The experimental conditions are four different combinations of damper openings associated with the secondary-air, tertiary-air and OFA (i.e. 60%/40%/15%, 50%/50%/15%, 35%/70%/15% and 30%/55%/55%), and are referred to as ASD = I, II, III and IV, respectively. The results showed that, as the ASD was increased from I to IV, the injection effect of the secondary-air on the fuel-rich flow was weakened. In addition, the downward diffusion of the air/particle flow toward the furnace center increased, while the particle concentration near water wall decreased and the velocity decay was accelerated. Decreasing the ASD shortened the ignition distance of the fuel-rich flow, reduced the carbon in fly ash and slag and improved the boiler efficiency. At an ASD setting of I, a higher thermal load and increased temperature near the water wall were obtained in the lower furnace. These conditions gave the highest superheated and reheated steam temperatures of 568.1 and 570.7 °C, respectively. As the ASD was increased from II to III, the cooling effect of the tertiary-air reduced the maximum water wall temperature. The reduction, in turn, increased the regulating margin of superheating degree, which raised the steam temperature. Increasing the ASD from I to IV increased the specific coal consumption from 337.36 to 348.12 g·(kW·h)−1, indicating that the energy conversion efficiency of the unit was decreased. Additionally, the NO x emissions at the furnace exit were reduced from 770 to 528 mg/m3 at 6% O 2. On the basis of the present results, an ASD setting of II is recommended to ensure the safe and economical operation of such units while minimizing environmental impact. [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]

The counter-biased burner arrangement has been confirmed to strengthen mixing between burner jets and reduce the risks of firebrick burning in the fly ash entrained-flow gasifier. The burner centerline angle, which represents the bias angle combination of multiple burners, is a critical factor that requires further experimental investigation to boost the air/particle mixture extent in the improved gasifier. In a 1:8-scale model of the 80,000 Nm3/h fly ash entrained-flow gasifier, air/particle flow characteristics under various burner centerline angles (75°, 72°, and 69°) are obtained by a particle dynamics anemometer. The results show that when the burner centerline angles are 75°, 72°, and 69°, the ratio of total particle volume flux in the near-wall region to the total particle volume flux in the measurement zone is 45.9%, 65.3%, and 57.8%; the ratio of the reflux particle quantity in the mixing zone is 0.88:1.27:1. As the burner centerline angle drops from 75° to 69°, the mixing zone radius decreases from 0.275 to 0.174. Simultaneously, the dimensionless difference of particle volume concentration gradually decreases, indicating that lowering burner centerline angle effectively improves the air-particle mixture extent between the burner jets. An optimal burner centerline angle of 69° is recommended. • A novel multi-burner arrangement was applied to fly ash entrained-flow gasifier. • Experimental researches under different bias angle combinations were conducted. • Reducing centerline angle improved the air-particle mixture extent of burner jets. [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]

A fly ash entrained flow gasification process was developed to simultaneously remove and utilize fly ash in the raw syngas coming directly from fluidized and fixed bed gasifiers. The present in situ experiments at a full load of 80,000 Nm3/h showed that, compared to the raw syngas, the effective syngas (CO + H 2) concentration in the purified syngas was slightly decreased, from 72.98% to 72.63%. In contrast, the average mass fraction of carbon in the fly ash was greatly reduced, from 29.5% to below 2%. This gasification process was determined to rapidly heat the entirety of the raw syngas to more than 1285 °C based on fast combustion of a small quantity of the raw syngas and all of the gasifying agent. Thermal analysis showed that the initial gasification temperature of the raw syngas was 1985 °C. Heat loss from the purified syngas was 20.6% of the fuel heat quantity, while the heat loss from unburned combustible gas accounted for 75.1%. Laboratory-scale airflow experiments were also conducted to determine the volume concentration distribution of the gasifying agent at the outlet of a single burner. • A new post-treatment technology for the raw syngas was developed. • The new technology removed and utilized the fly ash simultaneously. • The concentration of CO and H 2 decreased slightly from 72.98% to 72.63%. • The mass fraction of the carbon in the fly ash reduced from 29.5% to below 2%. [ABSTRACT FROM AUTHOR]