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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]

A 46 MW pulverized coal industrial boiler with swirl burner had severe slagging and high NOx emission during actual operation. To solve these problems, a full-scale industrial test was carried out. The flue gas temperature and the composition of exhaust gas were obtained under different ratios of secondary and separated secondary air. The results shown that reducing the ratio of secondary and separated secondary air could delay the ignition of pulverized coal and weaken the flame deflection, which was conducive to slowing down the burner slagging problem. However, it will aggravate the erosion of high temperature flue gas on the back wall, and further aggravated the furnace slagging problem. Changing the air ratio couldn't substantially improve the problem of high exhaust temperature. Properly reducing the ratio of secondary and separated secondary air could effectively control NOx emission. When the ratio of secondary and separated secondary air was reduced from 73:27 to 52:48, the NOx emission was reduced by 44.8%. Reducing the ratio of secondary and separated secondary air leaded to the increase of carbon content in fly ash and slag, but the heat loss of exhaust gas was reduced and the thermal efficiency of boiler was increased. [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]

Combustion is an effective method for large-scale utilization of pyrolytic semi-coke (SC), a high order carbon-based solid fuel with low volatile content. The combustion characteristics of SC can be deeply understood through the study of physical and chemical properties. Taking SC as the research object and anthracite (YQ) with similar chemical composition as the control, the activation energy (E) of SC and YQ was calculated respectively by using model-free method and model method (16 typical mechanism functions). The pre-exponential factor (A), the change of enthalpy (ΔH), the change of entropy (ΔS), and the change of Gibbs free energy (ΔG) during the reaction were calculated. As a result, the pore inside of the particle is the main part of the pore structure of SC. The total specific surface area, pore-volume, and fractal dimension of SC are all larger than that of YQ. There is a lot of amorphous carbon in both SC and YQ, and the lattice spacing and graphitization degree of SC is smaller than that of YQ, but the average aromatic carbon lateral size and crystallite volume are much larger than that of YQ. The carbon in SC and YQ mainly exists in the form of aromatic carbon and aliphatic carbon, and the relative content of aromatic carbon in SC and YQ is basically the same. For the model method, the E of SC and YQ calculated by the three-dimensional diffusion (Spherical symmetric) mechanism function is the closest to the E obtained by the model-free method. Different from YQ, the main combustion stage of SC is composed of fixed carbon combustion and CaCO3 decomposition, and basically, no NH3 and HCN are generated. The volatile content of SC, the total specific surface area, and the pore volume in the pore are larger than that of YQ, which results in that the ignition temperature of SC is lower than that of YQ. The E and burn-out temperature of SC are higher than that of YQ due to the lower oxygen-containing functional group content, higher aromatic carbon content, fractal dimension and larger crystallite volume. Comprehensive physical, chemical, and combustion characteristics results show that using SC by combustion is more difficult than YQ. [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]

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]

Waste tire carbon black particles (CBp) are the main pyrolysis products of waste tires (WT), and CBp is difficult to use directly. This work mainly focuses on the physicochemical and combustion characteristics of demineralized CBp (DCBp) to explore the resourceful utilization of CBp resources in large quantities. This work also provides a comprehensive comparison with CBp and other carbon-based solid fuels. The results show that most of the minerals in CBp can be removed by chemical demineralization treatment (Ash content of DCBp <0.11 %). DCBp has a more developed pore structure than CBp. The deashing process affects the degree of loosening and stacking of the graphitic carbon microcrystalline structure, and the relative content of oxygen-containing functional groups in CBp to a minor extent. The deashing process leads to a decrease in the relative strength of the cross-linked stable structure and an increase in the disordered structure of carbon in CBp. The volatile fraction to fixed carbon ratio of DCBp is only 0.0467, and a large number of catalytic alkali metal elements and alkaline earth metal elements are removed in the demineralization process, which makes the early combustion of DCBp more difficult. As the combustion reaction proceeds, the internal pores of the particles are opened, and the micropores and mesopores in DCBp provide a larger surface area for the reaction. In addition, the decrease in the relative strength of the cross-linked stable structure and increases in the disordered structure of carbon can increase the intermolecular collision frequency during the combustion process, thus improving the burnout characteristics of DCBp. The above results indicate that DCBp has the potential to be used as fuel for large-scale resource utilization. [Display omitted] • The chemical demineralization process has little effect on crystal lattice of CBp. • The chemical demineralization process can increase disordered structure of CBp. • The E of DCBp is lower due to the removal of catalytic alkali metal elements. • The A of DCBp is higher than that of CBp. • A and E of demineralized carbon-based solid fuel have kinetic compensation effects. [ABSTRACT FROM AUTHOR]

Due to the good combustion stability, the swirl burner (SB) with a pre-combustion chamber (PCC) is widely used in coal-fired boilers. The swirl blade angle is a key design parameter for the SB with PCC. The differences in flow, combustion, and slagging characteristics are dramatic at various swirl blade angles. Therefore, optimizing the swirl blade angle is necessary to improve the comprehensive performance of the SB with PCC. In this paper, Using CFD, the gas-particle flow, temperature, gas component distribution, and slagging trend in the PCC at swirl blade angles (β) of 50°,55°,60° and 64° in the outer secondary air (OSA) of SB are analyzed. As the β increases, the turbulent mixing of jets in the PCC increases, and more high-temperature flue gas is entrained into the PCC. Besides, the rate of devolatilization and char burnout near the SB nozzle accelerates, which is conducive to enhancing ignition and combustion stability. In terms of slagging on the PCC wall, the slagging trend deteriorates as the β increases. To improve the comprehensive performance of the SB with PCC applied in coal-fired boilers, the β should be set between 55° and 60°. • The comprehensive performance of SB with PCC at different β values is evaluated. • The increasing β is conducive to the turbulent mixing of gas flow. • The ignition and combustion stability are enhanced with the increase of β. • The slagging trend of the PCC wall increases when the β increases. [ABSTRACT FROM AUTHOR]

This paper presents experimental research on cold flow, combustion characteristics, and NO x emissions of a swirl burner with air staging. The aim of the research is to investigate the influence of primary air cone length on the swirl burner performance. Cold flow air experiments on a centrally fuel-rich swirl burner with an over-fire air ratio of 25% were performed, and it was observed that when the dimensionless primary-air cone length (i.e., L p / L i , L p and L i respectively denoting the primary-air cone length in the cold-modeling experiments and inner secondary-air cone length) increases from 0 to 0.75, the diameter and length of the recirculation zone reduces from 0.91 d and 1.51 d to 0.68 d and 0.57 d , respectively. An investigation was conducted in a 0.5 MW laboratory furnace in order to optimize the primary-air cone length of a centrally fuel-rich swirl burner. The flame stability, performance of ignition, and burnout are significantly improved by decreasing the primary-air cone length. The NO x emissions measured at the furnace exit with a cone length L p / L i  = 0 decreased by 50.3% compared to those measured with a cone length L p / L i =  1.0. Based on the evaluation of flame stability, performance of the ignition, burnout, and low NO x emissions, the optimum value of primary-air cone length was observed to be L p / L i  = 0. [ABSTRACT FROM AUTHOR]

To burn anthracite and reduce NO x emissions, a new combustion system was applied to a 300 MW e Babcock & Wilcox (B&W) down-fired boiler that included overfire air (OFA) and a decreased flow area of the inner and outer secondary air ducts of the installed swirl burners. Industrial-scale measurements (adjusting OFA ratios from 15.4% to 22.6%) were conducted to evaluate the overall performance of the retrofitted boiler. The experimental results demonstrated that the new combustion system promoted coal/air flow ignition and combustion stability. When the OFA ratio was less than 19.7%, the influence of the burner secondary air ratio on coal/air flow ignition was greater than that of the recirculation region below the arches. The overall combustion level in the primary combustion zone depended on the oxygen content and the recirculation region in the lower furnace instead of the early or late ignition of the coal/air flow. Oxygen and carbon monoxide concentration measurements in the near-sidewall region revealed that the fullness degree of the coal flame varied under different OFA ratios. Considering both environmental and economic effects, 19.7% was chosen as the optimal OFA ratio, thereby achieving a significant NO x reduction of 47% without increasing carbon content in the fly ash. [ABSTRACT FROM AUTHOR]

Semi-coke is the solid pyrolysis product of low-rank coal, with high carbon content and difficult to ignite and burn out. The blending of semi-coke with bituminous coal can realize a large amount of utilization of semi-coke. In this paper, the combustion, thermal conversion, and kinetic analyses of semi-coke blending with bituminous coal are investigated under oxygen-enriched conditions (30% O 2 atmosphere). Compared with 20% O 2 atmosphere, the ignition and burnout temperatures are reduced by 10, 7, 8, 12, 7 °C and 129, 76, 85, 115, and 152 °C for the semi-coke blending ratios of 0, 30, 50, 70 and 100% under 30% O 2 atmosphere. Oxygen-enriched combustion can effectively decrease the ignition temperature and improve the combustion performance of the mixture. In 30% O 2 and 20% O 2 atmospheres, the synergy effect of the co-combustion process is different. Under the 30% O 2 atmosphere, semi-coke, and bituminous coal have a strong synergistic effect, which can reduce burnout temperature. However, under 20% O 2 atmosphere, the burnout temperature of the mixture will increase. At a higher blending ratio of semi-coke, the effect of oxygen-enriched conditions on co-combustion is greater, and high oxygen concentration will make the interaction of the mixture combustion process more intense. Compared with bituminous coal, the activation energy of the mixture gradually increases with the increase of the blending ratio of semi-coke, and different combustion stages correspond to different mechanism functions, respectively. The research results can provide ideas for the utilization of semi-coke under oxygen-enriched conditions. [Display omitted] • The activation energy of mixture combustion is reduced in 30% O 2 atmosphere. • The co-combustion synergistic effect of mixture is enhanced in 30% O 2 atmosphere. • The increase of semi-coke blending ratio will result in higher activation energy of mixture. • The influence of oxygen-enriched co-combustion is greater under higher semi-coke blending ratio. [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]

A new combustion system has been applied to a 300 MW e down-fired boiler with swirl burners to reduce NO x emissions. The unit provided the introduction of overfire air (OFA) and a decrease in the flow area of the inner and outer secondary air ducts of the swirl burners. Industrial experiments on the retrofitted boiler were performed at different loads. Full-scale measurements of the flue gas temperature distribution in the burner outlet region, the furnace temperature distributions measured by a pyrometer and the local mean gas species concentrations in the region near the sidewall were made at loads of 180, 250, and 300 MW e . The results show that the ignition distance increased with decreasing load, especially as the load decreased from 250 MW e to 180 MW e . At three different loads, the retrofitted coal/air flow could be all ignited in time at a distance in the range of 0.6–1.4 m from the burner outlet. Compared with the original combustion system, the ignition distance of the coal/air flow was significantly reduced at a load of 300 MW e . In addition, at a load of 300 MW e , the temperature of the boiler hopper was much higher than that at loads of 180 MW e and 250 MW e . Compared with the original combustion system, the upper furnace temperature decreased slowly with increasing measurement height at a load of 300 MW e after the retrofit. Measurements of the O 2 and CO concentrations in the region near the sidewall indicate that the fullness degree of the coal flame in the furnace at different loads was different. After the retrofit, the reheat steam temperatures reached the design temperature of 541 °C at loads of 180 MW e and 250 MW e , and the average reheat steam temperatures increased by approximately 13 °C. Compared with the original combustion system, a significant NO x reduction (more than 40%) at different loads was achieved without increasing the levels of unburnt carbon in the fly ash. [ABSTRACT FROM AUTHOR]

[Display omitted] • The combustion performance of CGFA in two oxygen-riched atmospheres is compared. • The emperical optimization of the CGFA oxygen-rich combustion process is analyzed. • 30%O 2 concentration combustion performance of DA is comparable to that of DA blended with 60% bituminous coal in air atmosphere. Coal gasification fine ash (CGFA) has the characteristics of high carbon content, fine-grained, and sizeable annual output, causing environmental pollution and energy waste. Oxygen-enriched combustion is an effective way to solve the CGFA problem. This paper used thermogravimetric to study the effect of thermal conversion, kinetic analysis, and empirical optimization on the combustion process of CGFA in oxygen-enriched atmosphere. The results show that oxygen-enriched combustion of raw coal and CGFA improve ignition, burnout performance, combustion stability, and reduced activation energy. As the O 2 concentration increased from 30 % to 70 %, the activation energy of CGFA increased, but the improvement in combustion performance was not significant. A two-factor analysis of variance was carried out using a generalized linear model to obtain the effects of oxygen concentration, heating rate, and temperature variations on the combustion properties of CGFA, showing that atmosphere, heating rate and temperature variations all had significant effects on the combustion performance of CGFA, but atmosphere and heating rate had a more substantial impact on the combustion performance of CGFA. The combustion performance of raw coal under 30 %O 2 /70 %Ar atmosphere was better than that of CGFA, and the oxygen-enriched combustion (30 %O 2 /70 %Ar) performance of CGFA was comparable to that of CGFA blended with 60 % bituminous coal in air atmosphere. A kinetic model was developed to describe the oxygen-enriched combustion process (R2 > 0.92). The oxygen-enriched conditions of CGFA allow for efficient and clean combustion. [ABSTRACT FROM AUTHOR]

With global green and low-carbon development, carbon emission reduction is imminent. Oxy-fuel combustion technology is considered to be one of the most promising carbon capture and carbon sequestration technologies. In this work, the physical and chemical characteristics and oxy-fuel combustion characteristics of semi-coke (SC) and demineralized semi-coke (De-SC) were studied. The result shows that, compared with 20% O 2 /80% CO 2 , under 30% O 2/ 70% CO 2 atmosphere, the ignition temperature and burnout temperature of De-SC are lower, the maximum combustion rate is higher, and the main combustion process can be clearly divided into homogeneous and heterogeneous combustion stages. Compared with SC, De-SC has a less developed pore structure and lower alkali metal and volatile content, which lead to higher ignition temperatures for De-SC. The demineralization process makes the microcrystalline structure of carbon looser and increases the relative content of oxygen-containing functional groups, which are all beneficial to increasing the reactivity of De-SC. The combustion method of De-SC is mainly the particle surface reaction. Only in the atmosphere of 30% O 2 /70% CO 2 and the heating rate of 30 °C/min the combustion mode of De-SC is on the surface and inside the particles. Under different atmospheres, compared with SC, De-SC has lower activation energy and higher pre-exponential factor. The activation and pre-exponential of De-SC have a kinetic compensation effect. The results of this paper provide a theoretical basis for an in-depth understanding of the application of De-SC under oxy-fuel conditions. • The combustion mode of De-SC is mainly particle surface reaction. • De-SC has lower developed pore structure, alkali metal and volatile content, resulting higher ignition temperature. • A and E have a kinetic compensation effect of SC and De-SC. [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]

[Display omitted] • Combustion performance of CGFA in O 2 /CO 2 is weaker than that in O 2 /Ar. • Increase of oxygen concentration promotes combustion performance of CGFA in O 2 /CO 2. • Combustion kinetic models of different oxygen concentrations are different. • Kinetic model mainly follows the random nucleation model. Coal gasification fine ash (CGFA) has the characteristics of high carbon content, fine-grained, and large annual output, causing environmental pollution and energy wastage. Oxygen fuel combustion is an effective way to solve the CGFA problem. In this paper, the effects of thermal conversion, kinetics and thermodynamics during the oxygen-fuel combustion of CGFA are analysed. The results show that the combustion of CGFA in an oxygen-fuel atmosphere significantly improves its burn-up performance and combustion stability, but the improvement in ignition performance is not significant. an increase in oxygen concentration of more than 30% in an O 2 /Ar atmosphere also improves the activation energy to some extent, but the improvement in combustion performance is not significant. The average activation energy of CGFA under 30% O 2 /70% Ar condition is 104.25 kJ/mol, and its combustion performance is comparable to that of bituminous coal blended gasification ash at 70%. A kinetic model was developed to describe the oxygen-fuel combustion process of FCA, which can be efficiently and cleanly burned under oxygen-fuel conditions and consumed on a largescale. [ABSTRACT FROM AUTHOR]

In order to achieve peaking carbon dioxide emissions and carbon neutrality, a variety of down-fired combustion technologies has been proposed. The existing central air supplied combustion technology (CASCT) used for burning blended bituminous coal faces some serious problems. In order to solve the problem of the wide-range coal combustion in down-fired boiler, this study proposes a novel primary air biased combustion technology (PABCT). The coal gas–solid two-phase flow characteristics and numerical simulation of combustion characteristics under the PABCT and CASCT were compared. The results indicated that compared with the CASCT, under the PABCT, the velocity attenuation in the vertical direction is slower and the airflow diffusion range is smaller below the arch. The attenuation rate of particle volume flux with the downward flow of pulverized coal is slow, and the space utilization rate of the lower furnace is high under the PABCT. The thermal numerical simulation confirms the conclusion obtained from the cold gas–solid two-phase experiment. The PABCT exhibits the characteristics of large undershoot depth of coal/air flow, low temperature in the burner nozzle area, high burnout, low NO x emissions, and slag prevention, thus making it more suitable for wide-range coal combustion from the perspective of furnace flow and combustion. • Primary air biased combustion technology is proposed. • Gas–solid flow characteristics of primary air biased and central air supplied technology are compared. • Space utilization of lower furnace under primary air biased technology primary is high. • Separated secondary air under primary air biased technology has a strong ejection effect. • Primary air biased technology is suitable for wide-range coal combustion of down-fired boiler. [ABSTRACT FROM AUTHOR]

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

[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]

This study proposes changing the inner and outer secondary air ratios (R SA) under sub-stoichiometric (sub- SR) conditions to optimize the burn-out performance and reduce the NO x emissions of a swirl burner. The ignition and combustion characteristics, NO x formation, and the effect of R SA on the carbon and nitrogen conversion processes under sub- SR (SR = 0.85) were investigated via thermal tests carried out in a 0.5 MWe pulverized coal-fired furnace. The fuel-rich flow in the center of the furnace was further rearward than the fuel-lean flow. The pulverized coal burnt rapidly after entering the furnace. The average percentage of unburned carbon was less than 15% in the x/d = 3.5 (x is the axial direction distance, and d is the diameter of the burner) section away from the burner. The N to NO conversion at the beginning of combustion (x/d < 3.5) was effectively suppressed in the swirl burner under sub- SR conditions. The NO reduction reaction almost completely stopped after x/d > 11.5. R SA mainly affected the combustion characteristics and NO x generation characteristics of pulverized coal by changing the degree of air staging at different positions in the furnace. Larger R SA values meant a greater amount of oxygen involved in the early combustion. This accelerated the early burn-out of pulverized coal and the release of elements, increasing NO x emissions. This study recommends R SA values between 0.7 and 1, that the over-fire air (OFA) nozzle be positioned behind the near burner region (x/d > 3.5) for the combustion of bituminous coal to minimize NO x emissions and unburned carbon. [Display omitted] • The fuel-lean gas ignited in advance of the fuel-rich gas. • The conversion process of the percentage of energy loss was obtained. • The conversion process of fuel-N were analyzed. • The combustion effectivity and conversion rate of N to NO with the increase of R SA the under sub- SR. • The recommended R SA range and OFA position were given. [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]

• Industrial experiments of down-fired boiler with bituminous coal under various loads are taken. • The ignition heat of coal/air flow under different coal varieties and loads is given. • Burning bituminous coal has a large furnace flame fullness under the low-load. • Strong combustion stability is determined by the low ignition heat and high furnace temperature under the low-load. • The combustion performances of bituminous coal and anthracite under the low-load are analyzed and compared. The new energy generating capacity is increasing year by year in the electric industry structure, but it is greatly influenced by the natural conditions. Coal-fired power generation unit boilers connected to the grid have the ability of flexible peak-load regulation and long-term low-load operation is required. However, the combustion stability is weak under the low-load when the coal-fired boiler burning anthracite. Down-fired boiler fueled with bituminous coal gradually attract the attention. Ignition and combustion stability, burnout, and NO x emissions are experimentally studied under the various loads on a 300 MW down-fired boiler fueled with bituminous coal, and the results compared with anthracite under the low-load. The ignition distance of the coal/air flow burning bituminous coal is gradually advanced with the reduction of load. And under the corresponding load, the ignition heat of the coal/air flow when burning bituminous coal is more than 37% lower than that burning anthracite. With the reduction of load, the decreasing rate of the overall furnace temperature and the cross-sectional heat load in the primary combustion zone decreases, and the furnace temperature in the primary combustion zone is high under the low-load when bituminous coal is burned. Short ignition distance, low ignition heat and high furnace temperature ensures the strong combustion stability of burning bituminous coal under the low-load. Moreover, under three various loads with burning bituminous coal, the carbon in the fly ash are all less than 1.1%, and the NO x emissions at the furnace exit are 410, 397 and 288 mg/m3 @ 6% O 2 , respectively. [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]

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]

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]

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]

Fuel rich/lean combustion is an important means of reducing NO x in coal-fired boilers. The mass ratio of pulverized-coal in fuel-rich flow to that in fuel-lean flow (MRL) is a key parameter in fuel rich/lean combustion that affects the gas/particle flow characteristics and in turn the coal ignition and NO x formation. In this work, using a 1:40 scale model furnace and a particle dynamics anemometer measurement system, the effects of various MRLs (6:4, 7:3, 8:2 and 9:1) on the gas/particle flow characteristics in a 600 MWe down-fired boiler incorporating multiple-injection and multiple-staging were studied. The results demonstrate that airflows injected from the front-arch burners flow downwards along the front wall and then turn upward in the furnace center zone, forming a U-shaped flow pattern. Increasing the MRL significantly raises the maximum particle volume flux under the fuel-rich flow nozzle, which favors advanced pulverized-coal ignition and improves the fuel rich/lean combustion in the boiler. The velocity decay of the downward gas/particle flow is also accelerated. The particle volume flux in the hopper zone is gradually reduced while the location of the maximum particle volume flux gradually moves away from the hopper declined wall. This scenario avoids the downward flame flushing the furnace hopper and prevents both hopper wall overheating and tube bursts in the actual down-fired boiler. Based on these results, an MRL of 9:1 is recommended as optimal. [ABSTRACT FROM AUTHOR]

In order to achieve peak carbon dioxide emissions and carbon neutrality goals, a higher requirement is put forward for coal type adaptability medium, load stable combustion performance, and pollutant emission for wall-fired boiler with swirl burners. In this work, through industry experiments, the combustion characteristics of a retrofitted wall-firing mode 330 MWe power unit feed with anthracite were investigated. The combustion system was retrofitted employing the centrally fuel-rich (CFR) swirl burner and deeply-staged combustion technology. The experiment data were measured, including flue gas temperature and composition, furnace temperature, and the main operational parameter under high-load (300 MWe), medium-load (230 MWe), and low-load (150 MWe) conditions. The stable combustion of anthracite is achieved at various loads. With the excessive air coefficients of the main combustion region increase, the corresponding second air damper opening increase under high-load condition or over-fire-air damper opening decrease, both the flue gas temperature and heating rate of pulverized coal increase advance the ignition and promote the stable combustion and burn-out of anthracite coal. In the initial combustion stage, the O 2 given into the chamber increase, both O 2 consumption rate and CO concentration decrease, but NO x concentration increases. While in the later stage, both the O 2 and CO concentration tend to become flat. Meanwhile, the O 2 concentration is lower than 2.1%, the CO concentration maintains a relatively high level, and NO x production is inhibited effectively and becomes flat gradually. With the excess air coefficient increase, the temperature in the main combustion region increases, and the difference in furnace temperature between the burn-out region and the main combustion region diminishes. The unburned carbon content in fly ash and exhaust gas temperature decreases, while NO x emission increases. There is little difference for the flue gas temperature distribution in the side-wall region, and the measured O 2 concentration is always higher than 3.5% with the different mass flux of secondary air and over-air-fire. With decreasing load, the NO x emission decreases from the highest 1392.66 to the lowest 958.38 mg/m3 (O 2 6%), and the boiler efficiency improves. Compared with high-load and medium-load, the slagging tendency of the water wall is lower under low-load condition. • Stable combustion of anthracite was achieved under various loads in retrofitted boiler. • The combustion characteristics under deeply-staged technology were studied. • With boiler load decreased, NO x emission decreased, boiler efficiency increased. [ABSTRACT FROM AUTHOR]

• A novel low-load stable combustion technology is applied on a 600MWe FW down-fired boiler. • 33% rated load stable combustion without oil support is achieved. • Full-scale industrial measurements are carried out at 200, 240 and 540MWe. • Combustion and NOx formation characteristics at high and low load are contrastively studied. The randomness and intermittence of solar and wind power generation require coal-fired thermal power boilers that have a low-load stable combustion capacity. This study proposed a novel low-load stable combustion technology in which the oil secondary air flow is arranged parallel to the fuel-rich coal/air flow and participates in pulverised coal combustion during boiler operation. The method was applied to a 600 MWe down-fired boiler manufactured with the technology of Foster Wheeler Corp. Full-scale industrial measurements of furnace flue gas temperature, fuel-rich coal/air flow ignition distance, and distribution characteristics of NOx, O 2 , and CO in the furnace at loads of 200, 240, and 540 MWe were performed. The results showed that the boiler can stably operate without oil support at 240 MWe (40% rated load) and 200 MWe (33% rated load) respectively burning a blended coal of anthracite and lean coal, and blending bituminous coal. At loads of 200, 240, and 540 MWe, the fuel-rich coal/air flow ignition distances were, respectively, approximately 1.4, 1.7, and 1.3 m. NOx emissions at the furnace exit were 406, 407, and 730 mg/Nm3 (O 2 = 6%), and the boiler thermal efficiencies were 92.42%, 92.45%, and 90.58%, respectively. This novel technology presents the characteristics of high efficiency and low NOx emission while realizing low-load stable combustion of down-fired boilers. [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]