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The coal/ammonia co-firing technology for thermal power generation is a feasible method to effectively reduce CO 2 emissions. However, the easy formation of NO x is one of the challenges faced by this technology owing to the high nitrogen content in ammonia. This study proposes a novel swirl burner with a scalable dual-channel ammonia pipe, and evaluates the combustion and NO x formation under different extension lengths of the dual-channel ammonia pipe (i.e., 0 m, 0.4 m, 0.8 m, 1.0 m, 1.2 m). The results show that the extension length of the dual-channel ammonia pipe significantly affects the flow, combustion, and NO x formation. When the extension length of the dual-channel ammonia pipe is above 0.8 m, the ammonia stream can completely penetrate the internal recirculation zone into the high CO environment, which contributes to promoting the ammonia pyrolysis and inhibiting the ammonia oxidation to form NO x. NO x emissions significantly decrease from 846 ppm to 146 ppm as the extension length of the dual-channel ammonia pipe from 0 m to 0.8 m, but change slightly as further increases from 0.8 m to 1.2 m. The carbon content in fly ash decreases from 4.53% to 3.40% as the extension length of the dual-channel ammonia pipe increases from 0 m to 1.0 m. Still, it increases from 3.40% to 3.70% as the extension length of the dual-channel ammonia pipe rises to 1.2 m. Overall, it is reasonable to set the extension length of the dual-channel ammonia pipe at 1.0 m in this studied condition, which can obtain low NO x and low carbon content in fly ash. [Display omitted] • A novel swirl burner with a scalable dual-channel NH 3 pipe is proposed. • Effect of NH 3 pipe extension length on combustion and NO x formation is investigated. • NH 3 pipe extension length significantly affects flow, combustion, and NO x formation. • 1.0 m for NH 3 pipe extension length is reasonable with good performance. [ABSTRACT FROM AUTHOR]

Cofiring of coal slime in existing utility boilers is a promising approach to the disposal of coal slime. However, reports about cofiring coal slime with anthracite in the down-fired utility boiler are still few. This work presents a comprehensive study on the combustion characteristics, slagging potential, and NOx emissions of cofiring coal slime and anthracite through lab-scale experiments, numerical simulations, and full-scale industrial measurements in a 600MW down-fired utility boiler. The lab-scale experiments show combustion interactions between anthracite and coal slime, which have both a promotive effect on the ignition of anthracite and inhibitive effect on the combustion and burnout of anthracite. Especially, the inhibitive effect is greater than the promotive effect when the blending ratio of coal slime is above 5%. The addition of coal slime can effectively improve the ash fusion temperature of blended samples. In addition, simulations and full-scale industrial measurements of anthracite cofiring with coal slime are performed in a down-fired utility boiler. The results show that as the blending ratio of coal slime increases, the carbon content in fly ash increases and the boiler efficiency and NOx emissions decrease. A 5% ratio is validated to be a reasonable cofiring ratio of coal slime in the actual operation without no slagging phenomenon. These results provide more insights into the cofiring behavior of coal slime and anthracite and guide the application of blending coal slime in a down-fired boiler. [ABSTRACT FROM AUTHOR]

Based on the pseudo-steady-state approach, the combustion effect of high-reactivity char (i.e., HR-char) on low-reactivity char (i.e., LR-char) is investigated numerically in a hot O 2 /CO 2 atmosphere under two arrangements (LR-LR case : the upstream and downstream particles are LR-char, HR-LR case : the upstream particle is HR-char and the downstream particle is LR-char). This paper is aimed to study the influence of oxygen concentration (from 2% to 30%) and ambient temperature (1300 K, 1400 K, and 1500 K) on the combustion effect under the condition with dominated oxidation reaction and weak gasification reaction, and explain the mechanism in aspects of the temperature, specie concentration, and reaction rate. The numerical results are carefully validated against experimental data published in the literature. The results show that under these studied ambient temperatures, the char-O 2 oxidation-reduction brings a more pronounced effect than the char-CO 2 gasification enhancement for char consumption owning to the dominant role of the char oxidation reaction. The upstream HR-char particle combustion under the HR-LR case produces a higher temperature, lower oxygen, and higher CO 2 atmosphere ahead of the downstream char than under the LR-LR case, which significantly inhibits the downstream LR-char particle combustion. In addition, lower oxygen concentration or higher ambient temperature decreases the difference in temperature, oxygen, and CO 2 between the HR-LR and LR-LR cases ahead of the downstream char, resulting in the lower difference in the downstream LR-char oxidation consumption rate between the HR-LR and LR-LR case. Consequently, the weaker combustion inhibitive effect of the high-reactivity char on the low-reactivity char is observed. The findings shed light on the interaction effects observed during blended coal combustion in O 2 /CO 2 mixtures. • Combustion effect of high-reactivity char on low-reactivity char is investigated. • Effect mechanism is studied with spatially and chemically resolved simulations. • Lower oxygen or higher ambient temperature corresponds to weaker combustion effect. [ABSTRACT FROM AUTHOR]

Stable flame is still one of the challenging issues in the micro-combustors. Besides, the premixed flame may flash back under the large equivalence ratio, and the non-premixed combustion is an effective way to avoid the flame flash-back issue. In this work, a novel non-premixed CH 4 /air micro-combustor with the flame holder, the backward-facing steps and the separated preheating channels is developed to avoid the flame flash-back issue and extend the flame blow-off limits. This paper investigates the influence of two different CH 4 /air injection locations on the flame blow-off limits numerically and profoundly reveals the mechanisms in this micro-combustor. Results show that this novel configuration can considerably anchor the flame without the flame flash-back issue and significantly extend flammability owning to the flow & heat recirculations. Compared with the "Air (out) /CH 4(in) " injection location, the "Air (in) /CH 4(out) " injection location exhibits a comparatively larger size of recirculation, causing a more vital anchorage ability. In addition, after the preheating in the preheating channels, the CH 4 /air mixture of the "Air (in) /CH 4(out) " injection location presents a higher temperature level than that of the "Air (out) /CH 4(in) " injection location. Consequently, compared to the "Air (out) /CH 4(in) " injection location, the larger blow-off limits are attained for the "Air (in) /CH 4(out) " injection location. These results provide new insights into the stable non-premixed flame and give valuable guidance for designing the similar non-premixed micro-combustor. [Display omitted] • A novel CH 4 /air non-premixed micro-combustor is developed. • This novel configuration can anchor the flame without the flame flash-back issue. • Influence of CH 4 /air injection locations on flame blow-off limits is studied. • "Air (in) /CH 4(out) " presents larger recirculation & better heat recirculation. • "Air (in) /CH 4(out) " attains larger blow-off limits than "Air (out) /CH 4(in) ". [ABSTRACT FROM AUTHOR]

The combustion interactions during blended coal combustion affect their combustion characteristics, and the combustion interactions under air–fuel conditions have been well studied. However, oxy–fuel combustion considerably differs from air–fuel firing. Significantly, the char–CO2 gasification reaction under oxy–fuel and high-temperature conditions substantially affects the combustion behaviors, which may influence the combustion interactions. This paper is to study the effect of the char oxidation and gasification reaction competition on comprehensive interactions in O2/CO2 mixture. The results show that under high-temperature and low-oxygen (O2<4%) conditions, an intense gasification reaction is observed. The competition between the char–CO2 gasification and char–O2 oxidation reactions influences the comprehensive interactions during blended chars combustion. As the char–O2 oxidation reaction is strengthened and the char–CO2 gasification reaction is weakened, the comprehensive interactions during blended chars combustion gradually decrease. Moreover, under the competition between the char–CO2 gasification and char–O2 oxidation reactions, only enhancing the char–CO2 gasification reaction or enhancing the char–O2 oxidation reaction weakens the comprehensive interactions. The weaker comprehensive interactions result in the smaller nonadditive behavior of the comprehensive combustion index. The findings shed light on the interaction effects observed during blended chars combustion, which can provide useful information to improve the combustion behaviors of the blended coals in oxy–fuel conditions. [ABSTRACT FROM AUTHOR]

Coal blends are commonly used in thermal power plants and oxy-fuel combustion also attracts great concerns recently. However, little has been done on oxy-fuel combustion of coal blends. In this paper, combustion tests are performed in a drop tube furnace for various coal blends under O 2 /CO 2 mixtures, which are also reproduced numerically. Strong combustion interactions between the parent coals in a blend are observed. The ignition of the low-volatile coal is promoted due to the rapid combustion of the volatiles from the high-volatile coal. However, the char burnout of the low-volatile coal is compromised due to the rapid O 2 consumption by the large amount of volatiles. The interactions under oxy-fuel conditions are more sensitive to the excess O 2 , inlet oxidizer temperature and coal particle size. 1) The increase in the excess O 2 tends to weaken the combustion interactions, in which both the ignition promotion and burnout inhibition effects on the low-volatile coal become less apparent. 2) The increase in the inlet oxidizer temperature further promotes the ignition of the low-volatile coal whereas weakens the burnout inhibition of the low-volatile coal. 3) The effects of reducing particle size on the combustion interactions are similar to those of increasing inlet oxidizer temperature. Since biomass often contains a high volatile content, the findings may shed light on the synergistic effects in oxy-fuel co-combustion of biomass and coal. [ABSTRACT FROM AUTHOR]

Blending coal combustion technology is commonly used in coal-fired power stations, and the combustion interactions (i.e., the ignition promotion and burnout inhibition) during blended coal combustion affect their combustion characteristics. The combustion interactions under conventional air-fuel condition have been well studied. Oxy-fuel firing considerably differs from air-fuel combustion and the combustion interactions of blended coals in O 2 /CO 2 atmospheres have been investigated in our previous research. However, the H 2 O concentration in actual oxy-fuel condition is relatively high, which may influence the combustion interactions. This study further investigates the effect of H 2 O on the combustion characteristics and interactions of blended coals in O 2 /H 2 O/CO 2 atmospheres. The results show that adding H 2 O into the oxy-fuel atmosphere remarkably affects the combustion characteristics with the more notable ignition delay, faster burnout and better comprehensive combustion characteristics (CCI). In addition, the presence of H 2 O strengthens the ignition promotion, the burnout inhibition and the comprehensive interactions, resulting in the more obvious non-additive behaviors of CCI. In O 2 /H 2 O/CO 2 mixtures, enhancing the H 2 O/CO 2 ratio slightly strengthens the ignition promotion, the burnout inhibition, and the comprehensive interactions, which increases the non-additive behaviors of CCI. Furthermore, both of increasing O 2 /H 2 O or O 2 /CO 2 ratios significantly weaken the ignition promotion, strengthen the burnout inhibition and the comprehensive interactions, which increases the non-additive behaviors of CCI. The findings shed light on the interaction effects observed during blended coal combustion in O 2 /H 2 O/CO 2 mixtures, which can provide useful information to improve the combustion characteristics of the blended coals in the real oxy-fuel atmospheres. • Effect of H2O on interactions of blended coals oxy-fuel combustion is studied. • H 2 O increases promotion, inhibition and CCI non-additive behavior in O 2 /H 2 O/CO 2. • Higher H 2 O/CO 2 ratio increases promotion, inhibition, CCI non-additive behavior. • Higher O 2 /H 2 O or O 2 /CO 2 ratios show weaker promotion and stronger inhibition. • Higher O 2 /H 2 O or O 2 /CO 2 ratios present more obvious CCI non-additive behavior. [ABSTRACT FROM AUTHOR]

• Effects of SOFA angles on combustion, NO x and steam parameters are evaluated. • A SOFA angle of 30° is advisable for the novel combustion system. • Significant NO x reduction are achieved while limiting the carbon in the fly ash. A novel combustion system, consisting of moving fuel-lean nozzles from the arches to the front/rear walls, rearranging staged air, and introducing separated over-fire air (SOFA), has been proposed and successfully applied in a 600 MW e Foster Wheeler down-fired boilers to reduce high NO x emissions while limiting the carbon content in the fly ash. This study comprehensively evaluates the effect of SOFA angles on flow, combustion characteristics and NO x emissions for the novel combustion system by numerical simulation and in-situ experiment. The numerical simulation shows in acceptable consistence with the in-situ experiment. The simulated results show that significant NO x reduction is obtained for all five SOFA angles compared to the original combustion system. O 2 and CO concentrations at the furnace outlet, as well as the carbon content in the fly ash decrease significantly with increasing SOFA angle from 0° to 40°. NO x emissions increase slightly and the average temperature at the re-heater entrance changes slightly with the increase of SOFA angle from 0° to 30°. However, with further increasing SOFA angle from 30° to 40°, NO x emissions increase substantially due to the smaller reducing region below the SOFA and the average temperature at the re-heater entrance falls significantly. Taking combustion, NO x and steam parameters into account, a SOFA angle of 30° is advisable. The actual industrial measurements also show that the steam can achieve the designed values when the SOFA angle is set at 30° instead of 40°. Significant NO x reduction (over 50 %) and good performance are attained after adopting the novel combustion technology of 30 °SOFA angle. [ABSTRACT FROM AUTHOR]

The combustion of a biomass with coal may be one of the most effective methods to improve energy utilisation efficiency. This study aims to investigate the combustion characteristics of distillers' grains with bituminous coal using a thermo‐gravimetric analyser. The results demonstrate that increasing the proportion of distillers' grains in coal results in a reduced ignition temperature (Ti) and burnout temperature (Tb), and activation energy (E) in the combustion stage. Therefore, the comprehensive combustion index (CCI) improves. In an O2/CO2 atmosphere, Ti increased by ∼15°C, while Tb did not change much. However, E and CCI declined relative to an O2/N2 atmosphere. Under the O2/CO2 atmosphere, with an increase in O2 concentration from 10 to 40%, Ti changed over a small range, but Tb declined from 745.8 to 641.4°C, while E and CCI improved. As the heating rate rose from 10 to 30°C/min, the values of Ti decreased (from 281.4 to 244.9°C), but the values of Tb increased significantly (from 662.8 to 745.8°C); the value of E reduced, and CCI also improved. This research could provide useful information as a practical reference for heat and power production. [ABSTRACT FROM AUTHOR]

The combination of oxy-fuel and blended-coal combustion may be one of these effective methods to both reduce CO 2 emissions and improve energy utilization efficiency in coal-fired power stations. The aim of this study is to investigate oxy-fuel combustion interactions of blended coals under different conditions using a thermo-gravimetric analyzer. The results show that compared with those in an O 2 /N 2 mixture, the promotive and inhibitive effect and the comprehensive interactions are considerably weaker in an O 2 /CO 2 mixture. In the O 2 /CO 2 mixture, both increasing the O 2 concentration and decreasing the particle size result in decreasing the promotive effect but increasing the inhibitive effect and the comprehensive interactions, which increase the non-additive combustion characteristics. Enhancement of the heating rate increases the promotive effect but decreases the inhibitive effect and the comprehensive interactions, which weaken the non-additive combustion characteristics. Of these factors, the effects of the oxygen concentration and heating rate on comprehensive interactions are greater than that of particle size. This study provides useful information for the design and optimization of thermo-chemical conversion systems of coal blends in the O 2 /CO 2 atmosphere. • Ignition promotion and burnout inhibition exist during blended coal combustion. • Weaker promotion, inhibition and interaction are shown in O 2 /CO 2 than in O 2 /N 2. • Higher oxygen shows weaker promotion, stronger inhibition and interaction. • Smaller particle size shows weaker promotion, stronger inhibition and interaction. • Higher heating rate shows stronger promotion, weaker inhibition and interaction. [ABSTRACT FROM AUTHOR]

Co-incineration of sludge in the existing coal-fired utility boilers is a promising sludge disposal approach, but study on the combustion characteristics and the economic impacts of co-firing sludge in full-scale utility boilers is in absence. In this study, a series of full-scale field experiments and numerical experiments were conducted to study the coal-sludge co-combustion characteristic in a 100 MW coal-fired utility boiler. The effects of sludge blending ratio and moisture content in sludge are concerned. Subsequently, the economic impacts of co-firing sludge is presented. The results demonstrate that the combustion characteristics is acceptable when co-firing 10% sludge. The ignition property and the flame stability are significantly affected when the mass content of co-fired sludge is over 10%. Decreasing the moisture content in sludge is beneficial to the combustion characteristics but the improvements are limited. Co-firing sludge is profitable for power plants as the savings from coal and sludge disposal allowance is quite substantial. Considering both the combustion characteristics and the economic impacts, co-firing 10% sludge with moisture content ranging from 40% to 56% is optimal. The annual profit from co-firing sludge can reach 4.2 million to 5.5 million Chinese yuan (CNY), which is remarkable for the power plant. [ABSTRACT FROM AUTHOR]

A novel combustion system has been applied to a 600 MW e down-fired boiler to reduce NO x emissions without producing an obvious increase in the carbon content of fly ash. The system mainly includes moving fuel-lean nozzles from the arches to the front/rear walls, and re-arranging the staged air, as well as introducing separated-over-fire air (SOFA). This paper evaluates the effects of the SOFA locations (on the arches, on the throat, and on the upper furnace) on the combustion and NO x emissions characteristics using simulations. The numerical results are in good agreement with the measured results. Compared to the original combustion system, significant NO x reduction (approximately 50%) is found for all three SOFA location settings. Taking economic efficiency and NO x emissions into account, the SOFA on the upper furnace is adopted in the actual modification, and no negative effects are observed. [ABSTRACT FROM AUTHOR]

The distribution of air flows and fuel feeds are two crucial operational parameters determining the high-efficiency combustion and low-nitrogen emissions in biomass-fired grate boilers. However, current optimizations primarily focus on air distribution, with limited attention given to fuel feeds optimization. In this study, a three-dimensional integrated model was developed in FLUENT platform for simulating a grate-fired boiler with four feed inlets, in which the DPM model was adopted to track particle information in detail, and the Ergun model was used to account for the flow resistance generated by the thick packed bed, implemented in the form of a UDF code. The reliability of the model was validated through comprehensive on-site experimental data. It was found that key parameters such as temperature and ignition front of char are non-uniformly distributed along the width of the four grates. Specifically, a significant lag in volatiles release and char oxidation occurs near the water-cooled wall on both sides. On this basis, the optimization strategies on improving efficient and low-NO x combustion were proposed by redistributing the biomass fuel from near the sidewalls to the middle sections, and the optimal non-uniform feeding mode along the grate width was found. Results demonstrate that when the mass ratio of fuel between the middle and side grates is 0.30 to 0.20, yielding a maximum overall char burnout ratio of 84.74 %. Additionally, the concentration of NO decreases from 163.2 mg/m3 of uniform feeding mode to 149.4 mg/m3 (at 11 % O 2). These predictions will provide reliable theoretical guidance for enhancing boiler efficiency and reducing NO x emissions in grate-fired boilers. [Display omitted] • An integrated model of grate boiler is developed based on DPM and Ergun models. • Non-uniform characteristics of ignition fronts along grate width are effectively utilized. • Fuel feeds are non-uniformly distributed along the grate width to improve boiler performance. • Optimal material ratio between middle grate and side grate is determined to be 0.3:0.2 [ABSTRACT FROM AUTHOR]

Grate boilers are widely applied in biomass combustion for heat and energy generation. However, grate-firing systems often suffer from low efficiency and high emission. Computational fluid dynamic (CFD) becomes increasingly popular as a flexible method to obtain the detailed combustion behaviors in the furnace, and to optimize the performance of existing grate boilers. This paper presents efforts toward a reliable baseline CFD model for an industrial biomass-fired grate boiler, where the structure of the fuel-bed was sufficiently considered. The combustion performances in the furnace were investigated experimentally and numerically by coupling the fuel bed and freeboard, to clarify the impact of bed structure on the simulation accuracy. Results show that when the bed structure has been taken into account, the predictions are in better agreement with the various measurements, as the deviations between them are all within 10 %. Moreover, the flame center drops, the total heat transferred to the water-cooled walls increases, and the residence time of flue gas is greatly prolonged from 2.76 s to 3.90 s, resulting in a distinct difference of the temperature and species patterns in the freeboard. The simulations will provide valuable theoretical guidance for the accurate modeling of grate-fired boiler. [Display omitted] • A baseline model is proposed for accurate modeling of biomass-fired grate boiler. • Effect of fuel-bed structure on the simulation of grate boiler is clarified in detail. • Bed structure greatly affects the predicted temperature and species patterns. • Flue gas residence time and heat transfer are also highly impacted by bed structure. [ABSTRACT FROM AUTHOR]

Pressurized oxy-coal combustion in conjunction with carbon capture and sequestration is a promising technique for reducing carbon emissions. Biomass is a renewable energy source of zero carbon emissions. Therefore, negative carbon emissions can be achieved with pressurized oxy-biomass combustion, which is an appealing method for carbon peaking and carbon neutralization. NOx is an acidic gas produced from combustion that has the potential to corrode pipelines, demanding strict control. However, the evolution of NOx precursors and NOx formation in pressurized oxy-biomass combustion is still unclear. In this study, the NOx emissions in pressurized oxy-combustion and nitrogen migration characteristics of biomass in a pressurized CO 2 atmosphere were studied in a pressurized fixed bed reactor. The combustion results indicate that as the pressure increases, NO emission decreases while N 2 O formation slightly increases. The pressurized pyrolysis/gasification results show that the release of NH 3 and HCN in CO 2 atmosphere significantly reduces with increasing pressure, while the other-N species are reduced to N 2 by char and CO at high pressure. NH 3 formation peaks at 700 °C while HCN emission increases significantly with increasing temperature. NH 3 yield is considerably higher than HCN yield when the temperature is below 800 °C. The correlation analysis shows that NO formation increases with the increase of the total amount of NH 3 and HCN released in the pyrolysis/gasification process. This study provides new insight into the evidence that the suppression of volatile-N under elevated pressure is one important reason for the decrease of NOx in the pressurized oxy-biomass combustion. [ABSTRACT FROM AUTHOR]

The burner tilt angle has a significant influence on the combustion characteristics of a furnace, but few studies have focused on this topic. In this study, a numerical model was developed and validated to investigate the effect of the burner tilt angle on the combustion and NO X emission characteristics of a 700 MWe pulverized-coal-fired boiler with deep-air-staging technology. The turbulence, heat transfer and chemical reactions in the furnace were reproduced in detail by the model. Deep insight into the effects of burner tilt angle on combustion and NO X emission characteristics was acquired. The results show that the turbulence intensity in the burnout zone of furnace increases as the burner tilt angle increases, leading to a significant increase in the reaction rate of CO combustion. Hence, the level of CO emission is continuously reduced. The char burnout rate changes little with increasing burner tilt angle since the kinetic reaction rate and oxygen diffusion rate increase while the particle residence time decreases. The NO X emission increases as the burner is tilted farther upward because of an enhancement in fuel NO formation and a decrease in NO reburning. This study provides useful guidelines for improving the performance of deep-air-staged tangentially coal-fired boilers. [ABSTRACT FROM AUTHOR]