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The octagonal tangentially fired boiler can be utilized for burning lignite with high moisture. Co-firing biomass in an octagonal tangential boiler is considered a promising approach. A numerical simulation is carried out in this study to analyze the impact of flue gas recirculation (FGR) and the biomass blending ratio on heat and mass transfer in an octagonal tangentially fired boiler. When the FGR rate increases from 0 to 30%, the maximum temperature in the boiler decreases from 2162.8 to 2106.5 K. Simultaneously, the average temperature of the center longitudinal section decreases from 1589.0 to 1531.9 K. The maximum fluctuation of the outlet flue gas temperature remains within 10.9 K for the four calculated working conditions. Consequently, the efficiency of the boiler is basically unchanged. However, the flue gas temperature at the furnace outlet decreases significantly from 1605.9 to 1491.9 K. When the biomass blending ratio increases from 0 to 20%, the mean temperature of the primary combustion zone decreases from 1600.5 to 1571.2 K. [ABSTRACT FROM AUTHOR]

Cofiring sludge with coal based on existing power plants is a promising method to realize harmless recycling treatment for sludge disposal. However, the influences of sludge addition on NOx emission are still controversial. Moreover, the optimal operating strategies for the cocombustion boiler need further investigations. In this study, the influences of sludge blending ratio, moisture content, sludge inlet position, and air-staging parameter on the combustion characteristics and NOx emission behaviors in a 330-MW boiler were analyzed numerically. The results show that with the increase of sludge blending ratio, the flue gas temperature in the primary zone decreases. The overall burnout ratio declines with the addition of sludge due to the higher ash and moisture contents. Although the sludge contains more N than coal, the NOx emissions in the cofiring case are lower than those in the coal-fired case due to the lower temperature and stronger reducing atmosphere in the primary zone. Reducing the moisture in the sludge is beneficial to the combustion within the furnace. Nevertheless, because of the higher temperature and lower CO concentration within the furnace, the NOx concentration at the furnace outlet increases. For wall-fired boilers, feeding the sludge from the lower burners should be avoided considering the potential surge in NOx emission. When the excess air ratio in the primary zone increases from 0.74 to 0.96, the NOx concentration at the furnace outlet rises by 58%. Hence, although relatively lower excess air ratio in the primary zone could bring adverse impacts on the burnout behaviors, air-staging combustion is still necessary when cofiring sludge in the coal-fired boiler. [ABSTRACT FROM AUTHOR]

The utilization of residual energy of high‐temperature flue gas at the tail of coal‐fired boilers has attracted widespread attention in recent years. The thermal performances of the boiler and system in different split‐flow layouts still need to be analyzed and compared in detail. Thermodynamic models for four different splitting layouts of supercritical carbon dioxide (S‐CO2) Brayton cycles tailored for coal‐fired power plant are built and validated. By performing the process simulations, the effects of splitting ratios on the system thermal performance are comparatively analyzed when the secondary split point and the confluence point are set at different positions. The maximum system efficiency of the two‐split layout with a secondary splitting point at the inlet of the cold side of the high‐temperature recuperator (HTR) can be obtained within a range of secondary split ratio. The maximal and minimal boundaries are determined by the exhaust flue gas temperature and the heat capacity match in the recuperators, respectively. The mass flow rate of the cold stream in the low‐temperature recuperator (LTR) should be kept unchanged by constraining the sum of primary and secondary split ratios, the constant to prevent the cycle efficiency from decreasing dramatically, if the splitting layout with the split point at the outlet of the main compressor (MC) is used. The two‐splitting layout with a secondary splitting point at the inlet of the cold side of the HTR has the best performance by comparing the system efficiencies of different layouts. If there are any improved coupling approaches of the S‐CO2 Brayton cycle and boiler, this paper can provide the reference for the selections of the split ratios. [ABSTRACT FROM AUTHOR]

Very few studies have been reported on the fundamental mechanism analysis the augmentation of heat and mass transfer for the convection and condensation processes in the slit finned tube heat exchanger under dehumidifying conditions. By developing a 3D numerical model for the condensation of the slit finned tube heat exchanger under dehumidifying conditions, the heat and mass transfer characteristics were investigated under different the geometrical and operational parameters. The models neglecting convective mass flux or neglecting the water vapor loss can greatly enlarge the deviations of numerical results with respect to experimental data. The synergy angles are smaller in the windward and leeward sides of slits where the velocity field has a better synergy with both temperature field and the mass field. The slits on the fin not only increase the disturbance of fluid but continuously destroy the developments of thermal and mass concentration boundary layers, greatly enhancing the heat and mass transfer. The latent heat transfer is significantly greater than the sensible heat transfer, which accounts for 71.7% of the total heat transfer rate when inlet velocity is 1 m·s−1 and volume fraction of water vapor is 15%. The increases in the inlet velocity, and the volume fraction of water vapor can enhance the heat and mass transfer coefficient of wet flue gas. Whereas, the increase in inlet velocity can reduce the difference of synergy for the velocity field and the temperature or mass concentration gradient field of different fin tubes. [ABSTRACT FROM AUTHOR]

Elemental mercury (Hg0) emitted from a coal-fired boiler is a serious menace and challenge to humans. Using high-efficiency CeO2/TiO2 catalysts to enhance the conversion from elemental mercury to oxidized mercury is a promising approach to reducing Hg0 emission. However, most of the CeO2/TiO2 catalysts were prepared by impregnation method or coprecipitation method while little attention has been paid to sol–gel method, which has many advantages in material production. In this study, a series of catalysts were synthesized through the sol–gel method to remove the gaseous Hg0 from simulated flue gas. The effect of vanadium (V) on Hg0 removal efficiency and the simultaneous removal of Hg0 and NO were also investigated. The results showed the optimal temperature for Hg0 removal over the CeO2/TiO2 catalysts was 350 °C. The oxidation of Hg0 could be promoted by O2, HCl, and NO, but inhibited by NH3 and SO2. The addition of vanadium could enhance the Hg0 removal performance and the resistance to NH3 and SO2. A synergetic effect was found during the simultaneous removal of Hg0 and NO. The high redox reaction reactivity of Ce4+/Ce3+ and V5+/V4+ should take the credit for the oxidation of Hg0 and the removal of NO. Based upon the performance tests and the characterization experiments of the samples, the detailed mechanisms of the Hg0 and NO removal over the catalysts were proposed. [ABSTRACT FROM AUTHOR]

Coal-fired power plant is the largest anthropogenic mercury source. Active carbon injection technique has been widely used to control the mercury emissions. However, high operation cost limits its development and it is necessary to find other potential mercury sorbents. In this study, raw semi-coke and a series of novel cerium (Ce) modified semi-cokes were synthesized and utilized for removing elemental mercury (Hg0) from simulated flue gas. It is noteworthy that the efficiencies were tested without hydrogen chloride (HCl) in order to evaluate the sorbents efficacy for low-chlorine (Cl) coal. The results show that the modified sorbents exhibited the best performance at 150 °C. The performance of sorbent could be reinforced due to the existence of oxygen (O 2), nitric oxide (NO) and HCl. The adverse effect caused by sulfur dioxide (SO 2) reduced dramatically after Ce modification. The negative impact of ammonia (NH 3) on Hg0 removal in this study could be neglected owing to the tiny concentration of NH 3. Raw semi-coke provided sufficient carbon content, which is favorable to mercury adsorption. As Ce loading increased, the carbon structure changed and the crystal of cerium oxide was formed in the modified semi-coke. The mass fraction of cerium oxide on the sorbent was over 4.4% when the concentration of Ce modification solution was higher than 0.2 mol L−1. The redox reaction activity and the oxygen storage ability of Ce3+/Ce4+ gave a huge boost to the performance of modified semi-coke. The addition of Ce also had an impact on the proportion of oxygen species. Image 1 • Cerium modified semi-cokes were synthesized and utilized for removing elemental mercury (Hg0) from simulated flue gas. • The performance of the sorbent was investigated without HCl to evaluate the removal efficacy for low-Cl coal. • Cerium modification improved Hg0 removal efficiency remarkably. • High Hg0 removal efficiency could be achieved with the simultaneous existence of NO and O 2. [ABSTRACT FROM AUTHOR]

An inherent defect of the operating rotary air preheaters (RAPH) is known as leakage, which seriously hinders the efficient and safe operation of RAPH. It is significant for the estimation of the direct leakage to determine the effects of different structure parameters of sealing sheets and different operation parameters of a RAPH. A direct leakage set-up was built and a three-dimensional numerical model was established to explore the local direct air leaking process of rotary regenerative air preheater and study the effects of geometrical and operational parameters on the leakage. The numerical simulation using the transition k-kl-ω turbulence model was verified by the experimental results. The results show that the local direct air leakage mainly depends on the total pressure difference between the two sides of the seal instead of the one-side pressure. The air leakage can be significantly reduced by narrowing the leakage gap. The increase in the number of sealing sheets can reduce the air leakage own to the increase in the leakage resistance. The increase in the spacing between the adjacent sealing sheets can enlarge the recirculation zone and increase the energy loss of mainstream, greatly reducing the local direct air leakage. Due to the different size recirculation zone formation and streamline curvature induced by sealing sheet, the effect of bending angle on the direct air leakage varies. To obtain lower leakage rate, it is recommended for the rotor of tri-sectional air preheater to pass through flue gas section, secondary-air section, and primary-air section in sequence. [ABSTRACT FROM AUTHOR]

To facilitate the large-scale utilization of high-alkali and -alkaline earth metals (AAEMs) coals in power generation, the ash deposition behaviors of a typical Zhundong coal in oxy-fuel combustion were experimentally investigated using a drop tube furnace. A wall-temperature-controlled ash deposition probe by which the bulk gas temperature could be measured simultaneously was designed and employed in the experiments. The deposition tendencies, ash morphologies, chemical compositions of deposited ash particles were studied respectively under various oxygen concentrations, bulk gas temperatures, probe surface temperatures and probe exposure times. The experimental results revealed that the oxygen concentration had a significant influence on the deposition behavior during oxy-fuel combustion of high-alkali coal. Compared with air case, more fine ash particles were generated during the combustion of Zhundong coal in 21% O 2 /79% CO 2 atmosphere but the deposition tendency was weaker. However, a higher oxygen concentration could aggravate the tendency of ash deposition. The high contents of iron (Fe), calcium (Ca), sulfur (S), and sodium (Na) in Zhundong coal could result in the generations of low-melting point compounds. Calcium in flue gas existed as CaO and was captured prior to SO 3 by the probe surface during the ash deposition process. At the initial 30 min of the ash deposition process, the dark spherical fine ash particles rich in Fe, Na, oxygen (O), and S were largely produced, while in the range of 60–90 min the light spherical fine ash particles with high contents of Ca, barium (Ba), O, and S were generated on the other hand. The deposition mechanisms at different stages were different and the melted CaO (BaO)/CaSO 4 (BaSO 4) would give rise to a fast growth rate of ash deposit. • The ash deposition of high-alkali coal in oxy-fuel combustion was investigated. • Oxygen content, gas and wall temperatures had significant impacts on ash deposit. • Compared to air, more fine ash particles were generated during oxy-fuel combustion. • Low melt point compounds were produced as spherical particles initially. [ABSTRACT FROM AUTHOR]

Abstract: The ever‐growing concern of mercury exhausted from coal‐fired boiler is driving the requirement for using novel catalysts with stable Hg0 removal efficiency. However, the influences of flue gas components on Hg0 removal performance of modified and deactivated catalysts have been seldom investigated previously. The antideactivation ability of modified catalysts is still unclear. In this study, cerium (Ce) and zirconium (Zr) were utilized to modify the honeycomb V2O5–WO3/TiO2 catalysts. Sodium (Na) was doped on the rudimentary and modified catalysts by impregnation method to obtain deactivated catalysts. Elemental mercury removal efficiency of the catalysts was measured using a lab‐scale experimental system under various working conditions. Characterization of the catalysts was conducted to further analyze the mechanism of Hg0 removal process. Physical adsorption plays an important role in Hg0 removal over catalysts in the atmosphere of N2 and O2. The introduction of SO2 has an adverse effect on Hg0 removal because of the competitive adsorption. NO and HCl motivate the Hg0 removal through different mechanisms whereas NH3 has little effect on the removal efficiency. Mars–Maessen mode could be responsible for the excellent Hg0 removal performance and the splendid antideactivation ability of Ce‐modified catalysts. The efficiency of Zr‐modified catalysts is lower due to the decline of vanadium content. [ABSTRACT FROM AUTHOR]

In this article, a two-dimensional incompressible flow of high moisture flue gas in tube banks has been numerically simulated. The flue gas released both sensible and latent heat, and was treated as a combined heat and mass transfer problem. The finite-volume method was used to solve the Navier-Stokes equations, energy conservation equation, and species conservation equation. A simplified model was adopted and modified to account for the condensation phenomena in the flue gas. The influences of number of tube rows, gas velocity, vapor concentration, wall temperature, and tube diameter on heat and mass transfer characteristics were studied. The results analyses were presented by various criterions. [ABSTRACT FROM AUTHOR]

• Effects of oxy-fuel combustion on fouling and slagging issues were investigated. • The influential mechanism of oxygen content on slagging was explored. • Element and mineral species of slag were similar in air and oxy-fuel cases. • Slagging was worse with the increase of flue gas temperature and oxygen content. Zhundong coalfield occupies an important position in Chinese energy resource. However, the high-sodium content has become the hindrance for the safe use of Zhundong coal, leading to severe fouling and slagging issues. Oxy-fuel combustion is a clean combustion technology and beneficial for capturing CO 2. The fouling/slagging mechanisms of Zhundong coal in oxy-fuel combustion were ambiguous and the influences of oxygen content on the slagging behaviors of high-sodium coal have yet to be fully understood. This work employed a drop-tube furnace to explore the effects of flue gas temperature and oxygen content on the fouling and slagging characteristics in oxy-fuel atmosphere, and also conducted the comparison between oxy-fuel and air cases, with the elaboration of mineral constituents, morphologies, and elemental compositions of the deposits. Experimental results showed that the fouling of the high-sodium coal worsened as the flue gas temperature rose from 900 °C to 1200 °C. The element and mineral categories of the slag were similar but the relative contents of the mineral were different between oxy-fuel and air conditions. The diffraction peak of quartz in Wucaiwan slag during oxy-fuel combustion was weaker than that in air, while the condition of Lu'an slag was different. The high sodium content and its compounds promoted the formation of initial layer and the sticky particle surface, worsening the fouling and slagging. More comprehensive understanding of slagging mechanism could be achieved through the present work, which made sense for the optimization of combustion condition and the safe utilization of Zhundong coal. [ABSTRACT FROM AUTHOR]

• Char property was compared between prepared in N 2 and CO 2. • CO 2 -char has much larger specific surface area but lower reactivity. • The differences increases with temperature or Ca content in coal. • Char morphology difference was observed only for high-Ca coal. Oxy-fuel combustion needs recycled flue gas to reduce furnace temperature for material protection. The enhanced CO 2 alters coal devolatilization behavior. Devolatilization (albeit very quick) determines the whole life of coal in furnace, and thus it is essential to clarify the effects of CO 2 gas media on coal devolatilization behavior. However, previous works achieved conflicting results due to operation condition and coal nature differences. The present work attempts to investigate this issue and explore the influence of devolatilization temperature and alkali/alkaline earth metal. For this purpose, five coals with three coal ranks and different mineral compositions were devolatilized within N 2 or CO 2 by using a drop tube furnace under 800−1200 °C. Char produced in CO 2 has much more mesopores and as much as 2.8–8.1 times (depending on coal type) specific surface area than char produced in N 2 , but the combustion reactivity is slightly lower. These differences are due to the additional CO 2 gasification contribution. With increasing devolatilization temperature or inherent Ca content, the impact of CO 2 on devolatilization behavior is more pronounced. Difference in char surface morphology was observed only for high-Ca coal. [ABSTRACT FROM AUTHOR]

[Display omitted] • Plasma ashing method was used to determine the minerals in raw high-alkali coal. • Effects of high SO 2 and H 2 O concentrations on mineral transformation were studied. • The simulation based on the plasma ash was performed under oxy-fuel condition. • The mineral transformation under O 2 /CO 2 and O 2 /RFG conditions were summarized. The study aimed to study the mineral transformation of high-alkali coal to address the ash-related issues in oxy-fuel combustion. However, the traditional ashing method alone is inappropriate to study the mineral transformation at the initial stage of coal combustion due to the high ashing temperature. Hence, both the plasma ashing method (<200 °C) and traditional ashing method (600–1200 °C) were employed in this research to prepare the ash samples for characterization. The plasma ashing method is an efficient way to determine the original minerals in coal because it can consume the organic matter at low temperature. The recirculation of flue gas in oxy-fuel combustion can lead to high SO 2 and H 2 O concentrations, while their influences on mineral transformation need to be clarified. In this work, SO 2 and H 2 O were injected into CO 2 to simulate the recycled flue gas (RFG). Furthermore, the chemical equilibrium calculation was conducted besides multiple experimental tests to acquire more comprehensive information of mineral transformation. The results show that high sodium and calcium contents are determined in these high-alkali coals, and two of them are rich in iron. In O 2 /CO 2 atmosphere, some sodium (e.g. NaCl) volatilizes into the gas phase and the others converts into aluminosilicates (e.g. NaAlSi 3 O 8) during the heating process. The calcium salts (mainly CaCO 3 and CaSO 4) decompose and produce silicates, aluminosilicates, and magnesium silicates. The major iron-containing minerals are identified as FeS, FeS 2 , and Fe 2 O 3. Both FeS and FeS 2 are oxidized into Fe 2 O 3 below 600 °C. Moreover, the kaolinite (Al 2 Si 2 O 5 (OH) 4) in raw coals decomposes at low temperature (<600 °C). In O 2 /RFG atmosphere, the additions of SO 2 and H 2 O enhance the sulfation of AAEMs (alkali and alkaline earth metals) and delay the decomposition of sulfates. The productions of some silicates, aluminosilicates, and magnesium silicates of AAEMs are inhibited to varying degrees, and there could be complicated salts containing sulfur (e.g. hauyne). The transformations of iron-containing minerals are little related to the presences of SO 2 and H 2 O. This work obtained the transformations of main minerals in high-alkali coal under O 2 /CO 2 and O 2 /RFG conditions, which helps to address the ash-related issues. [ABSTRACT FROM AUTHOR]

• Removal efficiencies of 91.4% for NO x and 100% for SO 2 were achieved. • OH radicals in H 2 O 2 /Fe 2 (MoO 4) 3 system were verified by fluorescence test. • The synthesized Fe 2 (MoO 4) 3 catalyst showed satisfactory stability. • A three-step mechanism was developed to interpret the simultaneous removal process. The purification of flue gas has drawn the increasing attention in recent years. In the present study, a novel oxidation-absorption process was proposed for simultaneous removal of NO x and SO 2 from coal-fired flue gas based on the catalytic decomposition of H 2 O 2 over Fe 2 (MoO 4) 3 , in which gaseous pollutants were first oxidized by OH radicals and then absorbed with ammonia solution. The effects of H 2 O 2 dosage, temperature, gas hourly space velocity (GHSV) and flue gas component on simultaneous removal efficiency were systematically investigated. The results indicated that the removal efficiencies of 91.4% for NO x and 100% for SO 2 could be achieved under the optimal conditions. The signal of OH radical was verified by fluorescence test. The OH radicals were essential for NO oxidation and the subsequent NO x removal, while SO 2 was primarily removed in absorption process. Moreover, the presence of SO 2 was favorable for NO x removal, mainly because the existence of SO 2 promoted NO oxidation. X-ray photoelectron spectroscopy (XPS) analysis further confirmed that SO 2 could reduce part of Fe3+ to Fe2+ on catalyst surface, thereby reducing the consumption of H 2 O 2 by Fe3+ and promoting the majority of H 2 O 2 to generate OH. The continuity test revealed that the synthesized Fe 2 (MoO 4) 3 showed satisfactory stability. The surface morphology and crystal structure of the catalyst exhibit negligible change after 15 h of reaction. Products analysis indicated that NH 4 NO 3 and (NH 4) 2 SO 4 were the primary products after removal of NO x and SO 2. A three-step mechanism was preliminarily developed to interpret the simultaneous removal process in H 2 O 2 /Fe 2 (MoO 4) 3 system. [ABSTRACT FROM AUTHOR]

Highlights • Injection positions affect the flow characteristics of RFG in the furnace. • Higher temperature produce lower NO emission under fuel-rich condition. • NO emission reduces 10–30% with RFG introduced from L-nozzle to H-nozzle. • The temperature deviation of tower-type boiler is small. • The nozzle above the burner is preferable for RFG introduction. Abstract Flue gas recirculation (FGR), which is widely adopted to control the steam temperature of ultra-supercritical (USC) double-reheat boiler, significantly affects the temperature distribution, NO x generation, and flue gas temperature deviation in furnace. This study presents a numerical study on the combustion process in a 1000 MW tower-type double-reheat boiler with deep-air-staging. The effect of FGR injection position on the temperature distribution, NO x emission, and gas temperature deviation was studied and discussed under 100% boiler maximum continuous rating (BMCR), 75% turbine heat acceptance (THA), and 50% THA loads. The numerical model was validated by the in-house thermal calculation code and design parameters provided by the boiler manufacturer. The results show that, under the same load, when recirculating flue gas (RFG) is injected into the furnace from the nozzle blow the burner, the burner zone temperature is lower but the NO generation is higher than the case in which RFG is injected from the nozzle above the burner. Compared to the former, NO x emission of the latter reduced by 12.3%, 31.2%, and 33.8% under 100% BMCR, 75% THA, and 50% THA load, respectively. Both the inlet flue gas temperature and the heat flux of the primary superheater decrease when RFG was introduced from the nozzle above the burner. The case in which RFG is injected from the nozzle above the burner was found to be an applicable and effective method to control the NO generation and regulate the steam temperature of the double-reheat boiler. [ABSTRACT FROM AUTHOR]

[Display omitted] • The co-firing of coal and municipal sludge with high moisture content was studied. • The more sludge co-fired, the less NO x emission. • There are higher flue gas temperature and NO x emission at lower moisture content. • Co-firing sludge from the medium-upper burner can reduce the layers of burner. • The shrunk-middle type is the optimum scheme of SA distribution. Using the current coal-fired power plant to treat sludge with large annual production is an efficient sludge treatment method. Nevertheless, the majority of the previous studies concentrated on sludge co-firing with low blending ratio and moisture content in utility boiler. Further analysis and discussion are necessary regarding the impact of sludge with high blending ratio and high moisture content on co-firing performance as well as the potential interactions between high moisture content sludge and coal during the co-firing process. The simulation results of the verified computational fluid dynamic (CFD) model can be regarded as numerical experiments. In the present research, CFD was used to analyze the co-firing characteristics of municipal sludge and coal in a 600 MW tangentially fired utility boiler. The impacts of sludge moisture content, blending ratio, blending strategy, and secondary air (SA) distribution on co-combustion characteristics and NO x emissions were investigated, and their potential synergistic effects were assessed. The co-firing of coal and sludge has little impact on the furnace outlet temperature while potentially lowering NO x emissions, provided that the net calorific value of the feeding of the mixture of sludge and coal is kept constant. The reduction of sludge moisture content can significantly improve co-combustion performance, but it also facilitates NO x production. Blending sludge from the position of the medium-upper burners can reduce the number of layers needed to burn the sludge in practical coal-fired boiler. Furthermore, the SA distribution has a major impact on the furnace outlet flue gas temperature and NO x content. The shrunk-middle type is the optimum scheme for SA distribution. This study contributes to a deeper knowledge of the actual co-firing of sludge and coal in the utility boiler and provides a possible theoretical foundation for the widespread, clean, and effective use of sludge. [ABSTRACT FROM AUTHOR]

• Combination of pilot ignition and air staging for utilizing LCG. • Pilot flame produces H 2 O and NO to facilitate LCG ignition. • NO promotion on CH 4 based LCG is from NO/NO 2 cycle to enhance CH 3 oxidation. • Whether steam exists determines the NO influence on CO based LCG reactivity. Low calorific gas (LCG) is a huge thermal energy resource, but its utilization is poor due to the low reactivity and a tendency of high NO x emission. Present work proposed to combine the pilot ignition and air staging approach, to respectively overcome the difficulty in LCGs ignition and reduce its NO x emission. Experiment and numerical simulation were conducted to explore combustion characteristic of LCG during pilot ignition. Some previous proposed kinetics models for CH 4 or CO combustion were evaluated that whether they capture the NO or H 2 O influence, respectively, within this complex flue gas atmosphere, and the mechanisms were further explored. Adding 0.04 vol% NO reduces the ignition temperature of CH 4 based LCG from 750 to 510 °C under pilot ignition condition. This promotion is via a NO/NO 2 cycle of NO + HO 2 → NO 2 + OH and CH 3 + NO 2 → CH 3 O + NO , to enhance CH 3 oxidation rate by ∼ 30 times. In that cycle, the NO formation (NO 2 consumption) rate is higher than the NO 2 formation (NO consumption), causing only NO but no NO 2 was preserved in flue gas under pilot ignition condition. The effect of adding NO to CO based LCG is dependent on H 2 O presence, where it makes no difference without H 2 O presence, but has an improvement on "moist gas" reactivity. Neither the commonly used kinetics models of CH 4 combustion nor those for CO contained syngas gas can predict reactivity of "dry CO contained LCG" under pilot ignition condition. [ABSTRACT FROM AUTHOR]

• Elliptical rotating flow appears during injection of recirculating flue gas. • FGR technology has a positive impact on burnout rate and NO x emission. • Higher flue gas recirculation ratio shrinks the high-temperature area. • Heat flux peaks occur near the centerline of the left and right walls. • FGR decreases the heat absorption of water-cooled wall. The ultra-supercritical double-reheat boiler has attracted more attention because of high parameters (steam with high temperature and pressure), low pollution and large capacity. However, there are some difficulties in the development of this technology, such as adjusting the reheat steam temperature. In this study, computational fluid dynamics simulation is used to analyze a 660 MW double-reheat tower-type pulverized coal-fired boiler. The influence of flue gas recirculation (FGR) on heat transfer characteristics and combustion process in the furnace (including heating surfaces in the upper parts of the furnace) are evaluated. The user-defined function approach predicates the CO reduction effect on NO x. The results show that the flow at the horizontal section through the centerline of recirculating flus gas nozzles is rotating. The velocity distribution changes into an elliptical rotating flow when FGR ratio is 20%. At higher FGR ratios, the high-temperature area (1565–1700 K) shrinks and both the NO x concentration at the low-temperature superheater outlet and the O 2 concentration in the burner zone descend. The O 2 concentration at the low-temperature superheater outlet first increases and then decreases. In the main combustion zone, the heat flux peak of water-cooled wall is about 330 kW m−2. As FGR ratio increases from 0% to 20%, the rate of heat absorption of water-cooled wall to that of total boiler decreases by 3.50%. These rates for reheater and superheater increase by 2.53% and 2.13%, respectively. [ABSTRACT FROM AUTHOR]

• A novel H 2 O 2 /Fe-Mo catalyst system for removal of SO 2 and NO x was developed. • Satisfactory removal efficiencies were achieved at extremely low H 2 O 2 dosage. • The catalyst with Mo/Fe atomic ratio of 2.0 showed the highest activity. • The roles of Fe and Mo species played in the catalytic process were clarified. In this paper, the simultaneous removal of SO 2 and NO x catalyzed by Fe-Mo mixed oxides at varying Mo/Fe atomic ratios was reported for the first time with the aim of reducing H 2 O 2 consumption and elucidating the roles of Fe and Mo species in the catalytic process. Fe-Mo mixed oxides with varying Mo/Fe atomic ratios were synthesized and the catalytic performances were systematically studied. The catalyst with Mo/Fe atomic ratio of 2.0 exhibited the highest activity, with which removal efficiencies of 89.4 % for NO x and 100 % for SO 2 can be attained at extremely low H 2 O 2 dosage. Products analysis revealed that SO 2 was mainly removed via wet scrubber, while the adequate oxidation resulting from OH radicals was the prerequisite for NO x removal. The redox pair of Fe2+/Fe3+ played a significant role in decomposing H 2 O 2 , while Mo species had double effect on catalytic activity. Higher Mo content resulted in abundant oxygen vacancies and stronger surface acidity, which favored OH formation. However, the excessive Mo content involved severe surface Mo enrichment and remarkably reduced the active sites of Fe species. The H 2 O 2 /Fe-Mo catalyst system showed excellent stability and had a promising prospect for simultaneously removing SO 2 and NO x in coal-fired flue gas. [ABSTRACT FROM AUTHOR]

• Both the sensible heat and latent heat of the humid flue gas are recovered. • The handling capacity of typical liquefied natural gas terminal is considered. • The maximum specific power of the system can reach 74.15 kWh/ton-LNG. • The specific power decreases as the mass flow rate of natural gas increases. This paper proposed a cryogenic power generation system composed of Rankine cycles and direct expansion cycle, aiming at the efficient utilization of flue gas waste heat and liquefied natural gas (LNG) cold energy. Both the sensible heat and latent heat of the humid flue gas are recovered to meet the heat demand of a typical LNG terminal. Performance analysis was conducted to reveal the potential improvement direction and determine the key parameters. Then, parametric study was carried out to evaluate the effects of key design parameters on system performance. Four combinations of working fluids were compared, and the system performance was analyzed at different flow rates of natural gas. Results indicate that the net power output decreases as the condensing temperature of the bottoming Rankine cycle increases, and there exists a volcano-type relationship between the net power output and natural gas expansion pressure. R290/R1150 is the preferred combination of working fluids under the design conditions, and the maximum thermal efficiency, exergy efficiency, and specific power can reach 27.07%, 48.42%, and 74.15 kWh/ton-LNG, respectively. Moreover, the specific power decreases with the increase of LNG flow rate. R1270/R1150 becomes the best combination of working fluids, when the LNG flow rate exceeds 120.28 kg/s. [ABSTRACT FROM AUTHOR]

• Oxygen tends to decrease NO conversion ratio at >650 °C. • The kinetic analysis shows that CO reduces the activation energy of NO reduction. • Ash samples from different ashing methods were studied for NO reduction. • Ash samples of semi-coke are more useful catalysts than those of residual carbon. Semi-coke and residual carbon are potential to serve as reducing agents for NO reduction in deep-staged co-combustion, while the impacts of flue gas components, O 2 and CO, on NO heterogeneous reduction by semi-coke and residual carbon from practical industrial production have yet to be fully understood. The ash originated from different ashing methods, traditional high-temperature ashing method and low-temperature plasma ashing method, has different component distributions, which is also likely to generate important effects on NO reduction. However, the roles of components within various ash samples in NO-CO homogeneous reduction are still unclear. In this paper, the reactivities of various semi-cokes and residual carbon were experimentally studied for NO reduction using a lab-scale fixed-bed reactor. The experimental results indicate that the reactivities of semi-cokes and residual carbon towards NO reduction increase significantly when the temperature is beyond 700 °C, with more than 80% of NO being reduced at >850 °C. The addition of O 2 tends to decrease NO conversion owing to the competition between NO and O 2 for reacting with semi-coke. Carbon monoxide contributes to NO reduction significantly because it can not only reduce NO through the homogeneous reaction between CO and NO, but also lower the activation energy of the heterogeneous NO-char reaction. The interaction effects on NO conversion and apparent activation energy vary with the reaction temperature and CO concentration. In addition, ash samples from semi-coke are more efficient catalysts for NO homogeneous reduction than those of residual carbon. [ABSTRACT FROM AUTHOR]

• SO 3 2− can promote NO 2 absorption efficiency from 30% to more than 90%. • NO 2 will induce a chain reaction leading to rapid oxidation of SO 3 2− in the presence of O 2. • Tetrabutylammonium hydrogen sulfate can stabilize SO 3 2− to improve NO 2 absorption efficiency. • Engineering practice shows that Tetrabutylammonium hydrogen sulfate can increase NO 2 absorption efficiency from 13% to 70%. Under the pre-oxidation condition, NO can be removed simultaneously with SO 2 in the existing wet desulfurization system. NO 2 absorption efficiency in the wet desulfurization system is low, and additives need to be added to achieve efficient removal. In this work, a novel additive was used (tetrabutylammonium hydrogen sulfate, THS) for the simultaneous removal of NO 2 and SO 2. Both lab-scale and pilot-scale experimental systems were employed to study the absorption and removal characteristics of SO 2 and NO 2 , and realize engineering application on a 35 t/h industrial boiler. It has been shown that the NO 2 removal efficiency in a traditional wet desulfurization system is less than 20%. Adding THS can stabilize SO 3 2− and improve the NO 2 removal efficiency. SO 2 can promote the absorption of NO 2 , but O 2 in the flue gas and NO 2 – in the absorption system can inhibit the removal of NO 2. In engineering, THS can increase the NO 2 absorption efficiency from 13% to 70%, which has great application potential. [ABSTRACT FROM AUTHOR]

• Tube temperature show similar distribution characteristics under 100% and 75% loads. • Mass flux of water-cooled wall present negative flow response characteristics. • The FGR nozzle above the burner is preferable to control the steam temperature of the reheater. Flue gas recirculation (FGR) has been widely adopted as the steam temperature regulation method of choice for double-reheat boilers. In this work, the effect of the FGR position on the hydrodynamic characteristics of a double-reheat boiler is studied. Heat flux distributions of the water-cooled wall are determined through combustion simulation, then hydrodynamic characteristics of the boiler are calculated by user-defined program. The hydrodynamic characteristics including working fluid temperature, average tube temperature, fin-tip temperature, and temperature deviation between adjacent loops under 100% boiler maximum continuous rating (BMCR) and 75% turbine heat acceptance (THA) loads were numerically analyzed. The calculation results show that, under 100% BMCR and 75% THA loads, compared with the case that FGR introduced from the nozzle above the burner, the average tube and fin-tip temperatures at the outlet of water-cooled wall are higher, and the temperature deviation between adjacent loops is more significant, when the FGR is introduced from the nozzle below the burner. Therefore, it is suggested in this work that introducing FGR from the nozzle above the burner is safer for water-cooled walls of the 1000 MW double-reheat boiler. [ABSTRACT FROM AUTHOR]