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

The anions of precipitants played a leading role in the formation of catalytic phase while the cations decided the stability of hydroxyl group and further altered the morphology of catalysts. That was why the ammonium and sodium hydroxide possessed the similar hydroxyl group and amorphous MnFe composition, they still presented the different surface structure features. The coupling behavior of active precursors under different precipitants was the root cause of internal motivation of catalytic properties. [Display omitted] • Anion and cation of precipitant served in phase transition and structure features. • Reactants activation of precipitants acted as the inherent motivation of activity. • Precipitant affected the catalyst intrinsic activity deeply by kinetic analysis. • Possible inductive mechanism model of three precipitants on catalyst was proposed. Herein, the inductive strategy of three precipitants on dual transition metal MnFeO x catalysts for low-temperature NH 3 -SCR reaction was investigated in detail. The results showed that the anions of precipitants played the leading role in the formation of catalytic phase, in which carbonate induced the transfer of Mn precursor from MnCO 3 to the ultimate Mn 2 O 3 phase while that of hydroxyl from Mn 3 O 4 to Mn 5 O 8 phase. Iron coupling would alter the original transition behavior of manganese due to an internal synergistic effect. Furthermore, the cations decided the stability of hydroxyl groups on ammonium and sodium hydroxide precipitants, leading to the difference of morphology in catalysts. The activity results suggested that MnFe-ammonium carbonate (denoted as AC) catalyst possessed the higher catalytic efficiency than other catalysts, with over 90% NO conversion achieved from 75 to 225 °C. The abundant Mn4+ and Fe3+ and strong surface acidity of MnFe-AC catalyst were in favor of the redox circle and the adsorption of NH 3. Both activation energy and TOF, relied on the amount of acid, confirmed that the precipitants had an effect on the intrinsic catalytic activity of the catalysts such as energy barrier and reaction rate. Transient reaction further revealed that both E-R and L-H mechanisms co-existed on all catalysts, while E-R mechanism contributed more during the SCR process. On this basis, the possible inductive mechanism model of three precipitants on MnFeO x catalyst was proposed. [ABSTRACT FROM AUTHOR]

CGFA recycling process using NaOH-HCl hydrothermal treatment. [Display omitted] • Successful harmless treatment and resource utilization of residual carbon in CGFA. • The physicochemical evolution of residual carbon improves its combustion behavior. • Hydrothermal treatment improves the residual carbon's combustion characteristics. • DA-N and DA-NC properties are similar to lean coal and anthracite, respectively. Coal gasification fine ash (CGFA) is difficult to handle, which makes its effective utilization difficult. This study modified a typical CGFA sample, referred to as dry ash (DA), by using a NaOH-HCl hydrothermal process and analyzed the physicochemical properties of the carbon residue after treatment. The evolution of the physicochemical properties and the effect of this evolution on the combustion characteristics of the sample were investigated in detail. It was determined that the loss on ignition (LOI) significantly increased after DA was subjected to NaOH-HCl hydrothermal treatment. The carbon skeleton of the residual carbon was also modified, with a higher degree of looseness and a lower degree of cross-linking. At the same time, the specific surface area of the carbon particles and the content of surface C C bonds increased. This was beneficial for improving the combustion reaction activity of the treated sample. It is worth noting that compared with DA, DA-NC (samples obtained after DA was hydrothermally treated with NaOH) exhibited an LOI increase of 27.98 %, an ash removal rate of 48.32 %, and an S BET as high as 354.09 m2/g. Proximate analysis and thermogravimetric analysis further showed that NaOH-HCl hydrothermal treatment effectively increased the residual carbon content of the sample and reduced the activation energy required for combustion. The comparable combustion characteristics of DA-N and DA-NC (samples obtained after DA was hydrothermally treated with NaOH-HCl) with coal demonstrated their value as fuels. This work demonstrates that DA can be successfully modified into high calorific value solid fuel by NaOH-HCl hydrothermal treatment, which is beneficial for realizing the large-scale resource processing of CGFA. Moreover, the evolution of the physical and chemical properties of the residual carbon during the treatment process leads to a significant improvement in combustion characteristics. [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]

• 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]

[Display omitted] • Sm-doping strengthened NH 3 -SCR activity and SO 2 tolerance over MnFeO x catalyst. • Enhanced NO 2 cooperated with increased NH 3 (ads) to cause "Fast SCR" reaction. • Sm induced Fe serving as sacrificial sites to preferentially react with SO 2. • Mechanism model for improving activity and SO 2 tolerance with Sm was proposed. The development of catalysts with high NH 3 -SCR activity in the presence of SO 2 was urgent for non-electric industries to control NO x emission at low temperature. Herein, a series of Sm-doping MnFeO x catalysts were synthesized through a typical PEG-assisted co-precipitation method and applied for low-temperature NH 3 -SCR process. SmMnFe-0.1 catalyst significantly broadened the activation temperature window and yielded almost 100% NO conversion from 75 to 200 °C, simultaneously, the NO removal efficiency still maintained at about 90% in the presence of SO 2 and H 2 O. The characterization results confirmed that Sm could optimize the dispersity of active components and enlarge the surface area of catalyst. Furthermore, strong interaction among active ions facilitated more oxygen vacancies and accelerated NO oxidizing to NO 2 , further cooperating with abundant adsorbed NH 3 , leading to cause "Fast SCR" reaction. Both catalysts were dominated by the E-R mechanism despite MnFeO x catalyst also obeyed the L-H pathway. Particularly, the intense redox circles between Sm and Mn inhibited the electron transferring from SO 2 to Mn ions, and induced Fe species serving as sacrificial sites along with Sm to preferentially react with SO 2 , resulting in an excellent SO 2 tolerance, and the possible mechanism model was proposed. [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]

• 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]

[Display omitted] • CuO modified CeFe catalysts were prepared via wet impregnation method. • CuO could improve de-NO x and CO oxidation activities for CeFe catalyst. • CuO could increase surface acidity, Ce3+/(Ce3+ + Ce4+) ratio and surface adsorbed oxygen of CeFe catalyst. • Reaction mechanism model of CuO over CeFe catalyst for NH 3 -SCR and CO oxidation was proposed. Nitrogen oxides (NO x) and carbon monoxide (CO) coexisted in numerous industrial waste gases. And selective catalytic reduction of NO x with ammonia (NH 3 -SCR) and CO catalytic oxidation were considered as the effective technologies for simultaneous elimination of NO x and CO, respectively. However, an efficient bifunctional catalyst was crucial for achieving simultaneous removal of NO x and CO. Herein, we developed a series of Cu-modified CeFe catalysts for simultaneous removal of NO x and CO. The results demonstrated that 5Cu-CeFe catalyst presented the best catalytic performance, achieving approximately 81% NO x removal efficiency and nearly 99% CO conversion rate at 200 °C under a gas houely space velocity of 90,000 h−1. The XPS analysis demonstrated that copper oxides played a critical role in promoting the formation of Ce3+ and O β , thereby facilitating the NH 3 -SCR catalytic performance and CO catalytic oxidation. Moreover, the copper oxide modification of CeFe catalyst attained a trade-off between the surface acidity and redox ability, resulting in improving adsorption and activition capacity of the reactant gases. In situ DRIFTS experiments revealed that the NH 3 -SCR process primarily obeyed the Eley-Rideal (E-R) pathway over both CeFe and 5Cu-CeFe catalysts, while Langmuir-Hinshelwood (L-H) pathway hardly participated in NH 3 -SCR process. The presence of Cu+–CO species and surface lattice oxygen was crucial for CO oxidation, and both Mars-van Krevelen (M−K) and L-H pathways might be involved in the CO catalytic oxidation process over 5Cu-CeFe catalyst. [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]

[Display omitted] • Mn and/or Ce doping on blast furnace slag-derived zeolite X catalysts were firstly synthesized. • Mn-Ce/X catalyst had the highest NO conversion and the best N 2 selectivity. • Mn-Ce/X catalyst had higher Mn4+/Ce3+, stronger acidity and excellent redox ability. • NH 2 NO and NH 4 NO 2 intermediates on Mn-Ce/X catalyst prevented the generation of N 2 O. Several Mn and/or Ce oxides on blast furnace slag-derived (BFS-derived) zeolite X catalysts were prepared to investigate their low-temperature NH 3 -SCR performance. It was found that Mn-Ce/X catalyst had the highest NO conversion of nearly 98% at 250 °C and excellent N 2 selectivity of nearly 100% during 75–175 °C. The co-addition of Ce and Mn could inhabit the growth of crystal grains, resulting in the increase of surface area and the generation of Mn-Ce double active sites. Besides, high concentration of Mn4+ and Mn3+ could promote oxidation of NO to NO 2 accelerating the "fast-SCR" reaction and high concentration of Ce4+ could form more oxygen vacancies on Mn-Ce/X catalyst. In addition, the Mn-Ce/X catalyst had large acid amount and high redox ability owing to the co-existed Mn-Ce double active sites on zeolite catalyst and the co-effect of Mn-Ce oxides and zeolite X. Furthermore, the decomposition of NH 4 NO 3 species on Mn/X catalyst led to the low N 2 selectivity at higher temperature. While NH 2 NO and NH 4 NO 2 intermediates on Mn-Ce/X catalyst played a vital part in NH 3 -SCR reaction and prevented the generation of N 2 O, and Mn-Ce/X catalyst provided more Mn-Ce active sites for the reaction between NO 3 – species and gaseous NO, accelerating SCR catalytic reaction. [ABSTRACT FROM AUTHOR]

• Synergistic interaction of Sm and Fe enhanced Pb-resistance of Mn-Ce/AC catalyst. • Sm and Fe co-doping alleviated the damage of Pb species to catalyst structure. • Surface acidity and redox ability of Mn-Ce/AC catalyst were protected by Sm and Fe from lead. • NH 3 -SCR reaction on catalysts after Pb poisoning followed L-H and E-R mechanism. A novel anti-Pb poisoning Sm and Fe co-doped Mn-Ce/AC catalyst was prepared by impregnation method for low-temperature NH 3 -SCR of NO reaction. Maintaining the excellent low-temperature activity of Mn-Ce/AC catalyst, Sm and Fe co-doping remarkably enhanced the catalyst's Pb-resistance with NO conversion up to 77%. Sm and Fe co-doped poisoning-catalysts exhibited large specific surface area and pore volume, and the crystallinity of the MnO x and CeO x reduced. The redox properties and surface acidity of the lead poisoned SmFeMnCe/AC catalyst were effectively retained, which could promote NO oxidation and NH 3 activation, further benefiting the SCR reaction. In situ DRTFTS results indicated that the low-temperature NH 3 -SCR mechanism of all poisoned catalysts followed both L-H mechanism and E-R mechanism, and the L-H mechanism was dominated. On the one hand, the extraordinary lead resistance of Sm weakened the damage of lead species on the physicochemical properties of the catalyst; on the other hand, the high oxidation properties and surface acidity of Fe enhanced the catalytic activity of the poisoned catalyst. Finally, a possible synergistic mechanism model of Sm and Fe co-doping on Mn-Ce/AC catalyst against Pb-poisoning was proposed. [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]

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