High O2 Concentrations Research Articles

Characteristics of OH formation during single coal particle ignition and volatile combustion in O2/N2 and O2/CO2 atmospheres

The behaviors of volatile combustion and ignition of lignite coal were assessed on a concentrating light heating platform using hydroxyl-Planar laser-induced fluorescence (OH-PLIF) over a range of 21–60% O2 in both N2 and CO2 diluent gases. The results indicated that when the O2 concentration was below 40%, substituting CO2 for N2 delayed the ignition delay time (tign). This was evident as no ignition occurred in the 21% O2/CO2 mixture, and a nearly 1.0 s difference in tign emerged when substituting CO2 for N2 in 30% and 40% air atmospheres. Additionally, the weaker flame luminosity and the shorter volatile flame duration time (tvol) were also observed in O2/CO2 compared with that in O2/N2. Correspondingly, a significantly lower OH signal intensity was observed in O2/CO2 compared to O2/N2, which was primarily due to physical and chemical effects of CO2. Firstly, the higher heat capacity and lower diffusion rate of O2 in O2/CO2 leads to a lower volatile release rate and decreasing flame temperature, as evidenced by the closer proximity of the flame front to the coal particle surface. The lower flame temperature and volatile release rate would reduce the number of hydrocarbon molecule (RH) and the reaction rate of RH→hydrocarbon radical (R) + H, leading to a decrease in the concentration of OH radical from the reaction: H + O2→OH + O. Secondly, CO2 participates directly in H + OH + three-body (M)→H2O + M reaction, competing with the primary OH formation pathway, H + O2→OH + O, for H radicals, thus suppressing the OH generation. However, when O2 concentration exceeded 40%, the tign was shorter in O2/CO2 by about 1.2–1.4 s than in O2/N2 with the same O2 concentration. Simultaneously, compared to the O2/N2, similar flame luminosity and tvol were observed in the O2/CO2. An obvious increase in OH intensity was also observed in O2/CO2. With higher O2 concentrations in the O2/CO2, the absorption and emission radiation characteristics of CO2, increased O2 diffusivity and the decreased specific heat capacity in the O2/CO2 gas mixture, synergistically facilitate temperature rise and volatile release, which promotes the generation of RH, and then increases the H concentration due to the reaction RH→R + H. This would lead to a substantial increase in concentration of OH produced by the reaction H + O2→OH + O, which was detected by OH-PLIF.

Recovery of elemental sulfur direct from nonferrous flue gas by a low-temperature Claus process with H2S as the interim reducer

Direct reduction of high concentrations of SO2 from flue gases with oxygen to produce elemental sulfur (S8) is a promising pathway, that can realize sulfur resource recycling economically and storage avoiding the expensive SO2 pre-separation procedure. However, the process is significantly restricted by the O2 oxidation in flue gas and the traditional reducing gases can hardly work efficiently because of the excessive consumption by O2. In this study, we developed a low-temperature Claus process (LTCP) to reduce SO2 to S8 in the presence of O2 (5 vol%), and the interim production of H2S was employed as the reducer carrier, which can be efficiently re-produced by the reaction of S8 with H2 or CO thereafter. Results indicated that LTCP exhibited 97.2% S8 yield with the stoichiometric ratio at 150 °C and 5 vol% of oxygen content, which were both far higher than those for H2 or CO as the reducing gases at 350 °C. Further increasing the SO2 to H2S ratios to 1:1, almost 100% of H2S can be used to selectively reduce SO2 by Claus reaction at lower temperatures, and the slip H2S can be completely suppressed. As the catalyst and the temporary storage for S8 deposit, Al2O3 shows the best performance compared with other supported metal oxide and sulfide catalysts, and the sulfur capacity even achieves 432 mg(S)/g(Cat) with only 15% breakthrough. Meanwhile, LTCP also demonstrates excellent off-line temperature-swing regeneration performance, and part of the recovered S8 can be readily used to produce H2S. These promising results can officiously resolve the intractable problem of O2 oxidation and enable sulfur recovery directly from any nonferrous smelting and other flue gases with high concentrations of SO2.

Kinetic modeling of IG-110 oxidation in inert atmosphere with low oxygen concentration for innovative high-temperature gas-cooled reactor applications

ABSTRACT The oxidation behavior of IG-110, a graphite core component, was investigated at temperatures ranging from 400 to 1000°C in a 10 ppm Ar/O2 flow to simulate the oxidation process between the graphite core component and helium coolant with low O2 concentrations employed in advanced High-Temperature Gas-cooled Reactors (HTGRs). The results reveal that IG-110 undergoes significant mass loss at temperatures above 700°C, resulting in total mass changes of −1.5%, −5.3%, and −9.0% at 700, 800, and 1000°C, respectively, during a 10-hour oxidation period. No significant mass loss is observed below 600°C. To understand the oxidation mechanism of IG-110 under low O2 concentrations, we propose a kinetic model as the current chemical kinetic-controlled model does not fully explain the oxidation behavior observed in our research. Our analysis shows lower estimated reaction rates compared to studies at higher O2 concentrations; the activation energy values exhibit good agreement. The proposed kinetic model sheds light on the oxidation mechanism of IG-110 under 10 ppm Ar/O2 flow. This study provides new insights into the oxidation behavior of graphite core components in HTGRs and highlights the importance of controlling the O2 concentration in the helium coolant to prevent severe degradation of SiC-matrix fuel compacts.

Quasi-open Cu(I) sites for efficient CO separation with high O2/H2O tolerance.

Carbon monoxide (CO) separation relies on chemical adsorption but suffers from the difficulty of desorption and instability of open metal sites against O2, H2O and so on. Here we demonstrate quasi-open metal sites with hidden or shielded coordination sites as a promising solution. Possessing the trigonal coordination geometry (sp2), Cu(I) ions in porous frameworks show weak physical adsorption for non-target guests. Rational regulation of framework flexibility enables geometry transformation to tetrahedral geometry (sp3), generating a fourth coordination site for the chemical adsorption of CO. Quantitative breakthrough experiments at ambient conditions show CO uptakes up to 4.1 mmol g-1 and CO selectivity up to 347 against CO2, CH4, O2, N2 and H2. The adsorbents can be completely regenerated at 333-373 K to recover CO with a purity of >99.99%, and the separation performances are stable in high-concentration O2 and H2O. Although CO leakage concentration generally follows the structural transition pressure, large amounts (>3 mmol g-1) of ultrahigh-purity (99.9999999%, 9N; CO concentration < 1 part per billion) gases can be produced in a single adsorption process, demonstrating the usefulness of this approach for separation applications.

Hydrochemical Characteristics and Controlling Factors of Shallow and Deep Groundwater in the Heilongdong Spring Basin, Northern China

Heilongdong Spring Basin (HSB) is located in a semi-arid region in northern China. In the past few decades, it has been influenced by anthropogenic activities. Currently, there is a lack of information about the impact on the hydrogeochemistry and groundwater quality of different aquifers. To address this concern, the present study used conventional hydrochemical diagrams, stable isotope analysis and multivariate statistical techniques to analyze hydrochemical characteristics and controlling factors of shallow and deep groundwater in the study area. The results showed that all groundwater samples were weakly alkaline. The shallow groundwater (SGW) was mainly composed of SO4-Ca and SO4·HCO3-Ca·Mg water types with high TDS values. However, the predominant water types of deep groundwater (DGW) were HCO3-Ca·Mg and HCO3·SO4-Ca·Mg types with relatively low TDS. The large majority of shallow groundwater had poor water quality, which was influenced by natural factors and anthropogenic activities, characterized by high concentrations of SO42−, NO3−, and Cl−. In contrast, the overall water quality of deep groundwater was good, mainly controlled by the natural background. Nonetheless, a few karst groundwater samples of DGW in runoff areas exhibited close hydraulic connections with SGW samples and presented contamination to a certain degree. Our research results provide a scientific basis for the utilization and protection of groundwater in different aquifers in northern China.

Mechanisms on the inhibition of alkali-silica reaction in supersulfated cement

The supersulfated cementitious system gains increasing popularity for lowering carbon emissions of the construction industry. However, the alkali-silica reaction (ASR) behavior of this sulfate-rich cement is still unclear. This study first reports the characteristics and suppressing mechanisms of ASR in supersulfated cement (SSC). The results show that nearly no ASR-induced expansion is found in the SSC even if 100% glass aggregates are used, while the expansion ratio of the traditional OPC is twenty times higher than the SSC. In the SSC, the further hydration of unreacted slag during the ASR test refines the pore size and enhances the compressive strength of the matrix. Meanwhile, the consumption of the alkali ions in the pore solution during the formation of N-A-S-H gel reduces the concentration of the alkali ions and the contact possibility with the aggregates. The high bulk electrical resistance of the SSC can mitigate the diffusion of alkali ions from the external solution to the mortar. Moreover, the higher Al/Si ratio of C-A-S-H in the SSC than C–S–H in the OPC system results in a higher adsorption capacity of Na+ due to the more negatively charged surface, reducing the concentration of alkali ions in the pore solution. Furthermore, the high concentration of SO42− in the pore solution of SSC can inhibit the diffusion of OH−. As a result, the low-carbon SSC system would be a promising cementitious material to mitigate the ASR risk.

Hydrochemical Characteristics and Controlling Factors in Wudu River Basin of Guizhou Province

TheWudu River is a typical mining-type watershed in the karst mountainous area of western Guizhou Province. Based on the collection of the main stream, tributaries, spring water, and mine water samples in Wudu River Basin, the hydrochemical characteristics and control factors of Wudu River Basin were studied using Gibbs diagram, Piper diagram, and mathematical statistics analysis, and the solute contribution rate of different sources was calculated. The results revealed that the pH value of the water in the Wudu River Basin ranged from 7.87 to 8.52, with an average of 8.14. The TDS values ranged from 135 to 243 mg·L-1, with an average of 191.7 mg·L-1. The major cations in natural river and spring water were Ca2+ and Mg2+, the major anion was HCO3-, and the hydrochemical type was HCO3-Ca. However, owing to the influence of mining activities, the major cations in some tributaries were Ca2+ and Na+, and the hydrochemical types transitioned to HCO3·SO4-Ca and HCO3·SO4-Ca·Na. The ion components of river water in Wudu River Basin were affected by mine water discharge and cation exchange, carbonate rock weathering, silicate rock weathering, and agricultural fertilization. The high concentration of SO42- and Na+in mine water was the primary source of SO42- and Na+in the tributaries of the Wudu River. The method for calculating chemical material balance showed that the contribution rate of carbonate rock weathering ranged from 44.12% to 86.92%, with an average of 74.32%. The contribution rate of mining activities ranged from 3.28% to 37.07%, with an average of 11.61%. Carbonate rock weathering was the main controlling factor of hydrochemical components in the Wudu River Basin; meanwhile, mining activities also had a certain impact on river water chemistry but they showed spatial heterogeneity. The average contribution rates of atmospheric precipitation, silicate rock weathering, agricultural activities, and domestic sewage were 3.75%, 4.67%, 2.85%, and 2.81%, respectively, which had a limited impact on the hydrochemical components of the basin.

Amine Adsorbents Stability for Post-Combustion CO2 Capture: Determination and Validation of Laboratory Degradation Rates in a Multi-staged Fluidized Bed Pilot Plant.

Alternative to current liquid amine technologies for post-combustion CO2 capture, new technologies such as adsorbent-based processes are developed, wherein material lifetime and degradation is important. Herein a robust method to determine degradation rates in a laboratory setup is developed, which was validated with a continuous multi-staged fluidized bed pilot plant designed to capture 1 ton CO2 per day. An amine functionalized polystyrene adsorbent showed very good agreement between the experimental 1000-hour laboratory degradation rates and 2200 hours of degradation in a pilot plant. This validates how laboratory experiments can be extrapolated for sorbent screening and for scale-up. Resulting, the oxidative degradation in the desorber at high temperatures (120 °C) and low O2 concentrations (150 ppmv) is 3 times higher compared to the adsorber at low temperatures and high O2 (56 °C, 7 vol %). Laboratory degradation experiments can hence be used to further optimize process operations to limit degradation or screen for potential new adsorbents.

Arsenic removal from coal-fired flue gas by metal oxides modified wood chips coke: Experimental and DFT study

Coal-fired power plant is one of the main anthropogenic arsenic emission sources, where gaseous As2O3 is the main form in the flue gas to the atmosphere. In this work, a series of metal salt impregnated wood chips coke (Me-BC) were developed for As2O3 removal from flue gas, which selected BC with low cost and high arsenic removal potential as the carrier and modified by metal nitrate through impregnation and pyrolysis to load active components. The results indicate that As2O3 removal performance of the Me-BC obeys Fe-BC-0.15 > BC > Al-BC-0.15 > Ca-BC-0.15 > K-BC-0.15 under the basic flue gas composition (N2 + O2 + CO2) at 150℃, with the highest As2O3 removal capacity (141.5 μg/g) and efficiency (92.9%) for Fe-BC-0.15 compared to 92.4 μg/g, 60.7% of the BC. The arsenic removal ability of Fe-BC firstly increases and then decreases as Fe(NO3)3 impregnation concentration increases with its maximum value at 0.15 mol/L. Generally, the NO has a significant inhibitory effect on the arsenic removal of Fe-BC-0.15 due to consumption of surface active oxygen species by or the competitive adsorption between NO and As2O3. Low-concentration SO2 complete with As2O3 for the adsorption on active sites while high-concentration SO2 will promote SO3 and Oβ formation which benefits for As2O3 capture. Overall, Oɑ and Oβ and C-O play an important promoting role in the arsenic removal by adsorbents. DFT calculations indicates that C-O have strongest adsorption energy for As2O3 among oxygen-containing functional groups. The adsorption of SO2 and NO on naked BC and BC-O is easier than As2O3. Both Fe2O3 and BC play an important role in the arsenic removal process by Fe-BC-0.15.

Groundwater recharge processes in the Lake Chad Basin based on isotopic and chemical data

The Lake Chad Basin is Africa’s largest endorheic basin. Because water supply for the rural population and most of the urban population depends on groundwater, assessment of groundwater recharge is crucial. Recharge sources for the upper Quaternary aquifer are precipitation, rivers, and swamps. Using water chemistry, and environmental (18O, 2H, 3H) and carbon (14C) isotopes, recharge processes can be assessed and groundwater ages roughly estimated. For this purpose, more than 1,000 samples from groundwater, surface water and precipitation were analysed for hydrochemistry and environmental stable isotopes. Furthermore, 3H measurements and 14C values of dissolved inorganic carbon for groundwater from the northeastern part of the Basin are included in the evaluation. The environmental isotope distribution shows recent recharge from precipitation north of Lake Chad (Kanem Region), where very low 3H values indicate occurrence before the 1960s bomb peak. Focused recharge from fresh river water is typical for Salamat Region in south Chad and the Komadugu Yobe wetlands between Nigeria and Niger. Slightly high δ-values in water occur in the Waza Logone area between Chad and Cameroon. Groundwater along the Lake Chad shore and the Bahr el Ghazal corridor show high δ-values (δ18O –0.78 to 7.45‰, δ2H –13.6 to 30.8‰). Recharge is caused by surface water that undergoes evaporative processes before percolation. Groundwater ages of 600–4,150 years, estimated from 14C analyses combined with high SO4 concentrations, along the Bahr el Ghazal indicate that recharge was caused by residuals of the Mega Lake before it dried out completely.

Advantages and limitations of a high-throughput analytical method using an automated enzymatic assay to quantify the glutathione in grape juice

Glutathione is a tripeptide, present in plants and other organisms in free (GSH) and dimer (GSSG) forms, known for its antioxidant activity. A high-throughput, economical method was developed to measure the total glutathione (TG) concentration in grape juice, using an enzymatic assay (EA), based on the reaction of thiol with 5,5′-dithio-(2-nitrobenzoic acid) (DTNB) in the presence of glutathione reductase enzyme. This method was automatised to allow high-throughput measurements in the concentration range of 1–100 mg L−1. GSH and GSSG were also quantified separately using the UHPLC-MS/MS method. The two methods (EA and UHPLC-MS/MS) gave comparable results in grape juice (R2 =0.97), where the concentrations of SO2 were low (<100 mg L−1). The sample preparation is a critical step in the quantitative analysis of glutathione given the high reactivity of GSH. In this work, ascorbic acid and SO2, commonly used in oenology, were tested as protecting agents at different concentration. The results given by the EA method could be altered by the reaction of SO2 and DTNB, however this effect was observed only at high concentration of SO2 (1 g L−1). Ascorbic acid at a 2.5 mg L−1 concentration protected the sample well, without interfering with the analysis, and allowed for storage for up to four months at − 20 °C.

Sources of antimony contamination and its migration into water systems of Xikuangshan, China: Evidence from hydrogeochemical and stable isotope (H, O, S, and Sr) signatures

The Xikuangshan (XKS) mine was selected for a comprehensive Sb-related hydrogeochemical study because of its significant Sb contamination in water systems. Hydrochemical data, specifically multi-isotope (H, O, S, and Sr) data, were conducted to elucidate the primary sources and migration processes of Sb responsible for water system contamination. At the XKS Sb mine, water is near-neutral to alkaline and is characterized by high concentrations of SO42− and Sb. Sb occurs as Sb(OH)6− (the dominant species) in these oxidized waters. The hydrochemistry is mainly controlled by carbonate dissolution and silicate weathering. δ2HH2O and δ18OH2O values indicate that the infiltration recharge of mine water and mining activities regulate the migration of Sb in groundwater. δ34SSO4 and δ18OSO4 values indicate that dissolved SO42− and Sb primarily come from stibnite oxidation, bacterial SO42− reduction has either not occurred or is extremely weak, and the reductive dissolution of Fe (III) hydroxides does not significantly affect Sb migration in water. The 87Sr/86Sr ratios further indicate that the discharge of solid mine wastes leaching and smelting water is a crucial source of Sb contamination in groundwater. In addition, the relationship between δ34SSO4 and δ87Sr values suggests the complexity of the contamination source and migration of Sb in water. Finally, a robust conceptual hydrogeochemical model was developed using isotopic tools in combination with detailed hydrogeological and hydrochemistry characterization to describe the contamination source and migration of Sb in water systems at the XKS Sb mine.

Study on Nitrogen Injection Fire Prevention and Extinguishing Technology in Spontaneous Combustion Gob Based on Gob-Side Entry Retaining.

Under the gob-side entry retaining mining mode with roof cutting and pressure relief (GERRC), the gob and retained roadway section are interconnected to create an open area. Owing to the increased airflow, the coal remnants in the gob are more prone to spontaneous combustion. This study aimed to investigate the distribution of oxygen concentration within a gob and identify optimal parameters for nitrogen injection. The engineering context was the "110 method" introduced in the 1201 working face of the South Five mining area at Daxing. Computational fluid dynamics simulation software was used to analyze the effects of various nitrogen injection treatment parameters on the overall performance of the gob, including their impact on oxygen distribution. The simulation results showed that air leakage within the gob primarily originates from the working face adjacent to the intake roadway, as well as gaps within the retained roadway. The increased air leakage causes the high O2 concentration range in the gob to expand, and the retained roadway section is connected to an area with a high concentration of oxygen near the working face, which increases the risk of residual coal spontaneous combustion. The results show that the optimal nitrogen injection conditions for inerting and reducing the risk of spontaneous combustion within the gob require an injection quantity of 500 m3/h, with the injection point located at a depth of 60 m. With these parameters, the range of the oxidation zone was significantly reduced. To monitor the O2 concentration and temperature change curves in the gob during the project implementation, a bundle tube monitoring system was used, considering the actual mining situation. By varying the nitrogen injection spacing and quantity, we found that injecting nitrogen at a spacing of 30 m and at a quantity of 500 m3/h effectively placed most areas of the gob in the suffocation zone, reducing the risk of spontaneous combustion of residual coal. The accuracy of the simulation was verified. The study offers valuable insights into improving safety in coal mines and reducing spontaneous combustion incidents, providing important reference significance for fire prevention and control.

Assessment Vertical and Spatial Distribution of SO2 Concentration over Baghdad City (Case Study at 2022)

Abstract One of the most important issues at the present time in developed and developing countries alike is air pollution. Sulfur dioxides consider one of important gases pollutant that product from fossil fuel combustion such as oil and coal. It is considered one of the principal air pollutants that has contributed to premature deaths and respiratory illnesses. Globally SO2 also has a high spatial and temporal variability because of its short atmospheric residence time. In this study reanalysis data of SO2 concentration values is download from ERA5 website (fifth generation ECMWF reanalysis for global climate and weather) for months (Jan., April, July and Oct.) from year 2022, and for 8-height levels from ground surface to 5000 meter, for all area of Baghdad province, other atmospheric parameter also download such as boundary layer height BLH and wind and direction. Results show high values of SO2 in January relative to other months and the smallest values is in July at all 8-levels nearly. Spatial Speed and direction given opposite relation with SO2 concentration, while most high concentration of SO2 in located in Baghdad city center and area around because its represent the sources of pollutant.

The Influence of Sulfur Dioxide Concentration on Antioxidant Activity, Total Polyphenols, Flavonoid Content and Individual Polyphenolic Compounds in White Wines during Storage

Wines represent a rich source of bioactive compounds, especially polyphenolic compounds, which mostly contribute to the antioxidant activity. Sulfur dioxide (SO2) has mostly been used as a preservative in winemaking to prevent oxidation during storage. The aim of this paper is to evaluate the changes in SO2 levels and the influence of sulfur dioxide addition at seven different concentrations on the antioxidant activity (detected by DPPH-2,2-diphenyl-1-picrylhydrazyl and the ABTS Trolox equivalent antioxidant capacity methods), total polyphenols, flavonoid content and individual polyphenolic compounds (determined by the HPLC high-performance liquid chromatography method) of white wines during 5 months of storage. The assayed sulfur dioxide concentrations show a decreasing tendency with time, with a final decrease of more than 50% in comparison with the start of the experiment. Between the first and second measurements, the average decrease in sulfur dioxide was 16%. In the following interval, it was found that the maximum decline in SO2 was 26%. The changes in SO2 levels cannot be considered statistically significant. At the same time, we observed a decreasing tendency in the TPC content during storage. The antioxidant activity determined by the DPPH method at the beginning of the experiment ranged from 116.75 up to 270.62 mg·L−1, while the antioxidant activity increased with sulfur dioxide concentration. The AA detected by the ABTS method displayed a decreasing tendency during storage. In the case of the TFC content, we observed a significant influence of sulfur dioxide on the concentration. No addition or addition of high SO2 concentrations negatively influenced the flavonoid content in the samples. During storage, we observed a highly variable content of phenolic compounds in relation to SO2 addition. The most abundant compounds were chlorogenic acid, caffeic acid and epigallocatechin.

Impact of nitrogen and sulfur fertilizers on leaching behavior of heavy metals from aquifer sediments to groundwater

BackgroundThe groundwater of the Bathinda district of Punjab is contaminated with heavy metals, nitrate (NO3), and sulfate (SO4) exceeding the BIS limits for drinking water in many areas. The article attempts to understand the role of fertilizers, nitrate and sulfate, in the mobilization of heavy metals from the aquifer minerals. MethodHeavy metal mobilization from aquifer sediments was studied through batch experiments using artificial groundwater (AGW) with varying concentrations of NO3 and SO4. For actual field conditions, column experiments were conducted with artificial groundwater containing 50 ppm NO3 as mobile phase and 1 ml/minute flow rate. The leached metal ions from the sediments were analyzed with ICP-MS. Significant findingsIt was found that compared to the AGW without NO3 and SO4, the heavy metal mobilization potential of AGW with NO3 and SO4 was significantly enhanced. The presence of nitrate significantly influenced the leaching of Cr, Co, Ni, Zn, and Hg, moderately affected the mobilization of As, and least impacted the mobilization of Fe, Mn, Cu, Cd, Pb, and U. An increase in leaching of Cr, Mn, Ni, Zn, As, and U was observed with the increase in SO4 concentration from 0 to 400 ppm, however, drastic reduction was observed with SO4 concentration of 500 ppm indicating high concentration of SO4 is posing an inhibitory action. The concentration of Cr, Fe, Co, Ni, Cu, Zn, Se, and Pb were significantly positively correlated indicating similar processes driving the mobilization of these metals. To reduce the mobilization of toxic heavy metals from the aquifer sediments, the NO3 and SO4 from the wastewater and agricultural run-off should be removed/reduced to the extent possible through optimized fertilizer usage, use of organic fertilizers, and treating the wastewater before discharging in the environment.

Influence of Central Air on Flow and Combustion Characteristics and Low-Load Stabilization Performance of a Babcock Burner

On a cold single-phase test stand, the effect of central air on the exit flow field of Babcock, Germany, burner was investigated. Industrial measurements were taken for a 700 MW wall-fired pulverized-coal utility boiler with above burners. Gas temperature, gas composition and concentration in the burner area were measured at 444 MW, 522 MW and 645 MW loads, respectively. Only when the central air mass flow was zero did a center reflux zone exist in the burner outlet area. The steady combustion of faulty coal was aided by early mixing of primary and secondary air, which was made possible by the decreased central air mass flow. At all different loads, the pulverized coal in center region took a long distance to ignite. The temperature in center steadily dropped as central air mass flow decreased, while the temperature in secondary air region gradually rose. Within 1.5 m from the primary air duct outlet, the highest CO concentration was 25 ppm and the highest O2 concentration was close to 21% under all loads. The gas concentration near sidewall was more influenced by load. With all valves opening of burner center air at 30%, the boiler was able to operate safely and stably without oil at a load of 262 MW. The furnace chamber temperature in burner area reached 1056.1 °C.

Effect of the Fe2O3@TiO2 core-shell structure on CO catalytic oxidation and SO2 poisoning resistance

The core-shell Fe2O3@TiO2 and FeTiOx mixed oxide catalysts were prepared to explore the effect of the core-shell structure on the catalytic oxidation of CO under a high concentration of SO2. The core-shell structure helped inhibit the sintering of nanoparticles and enabled Fe2O3@TiO2 to share a larger specific surface area, pore size and more active chemisorbed oxygen species than FeTiOx, promoting the CO catalytic performance. FeTiOx and Fe2O3@TiO2 reached 84% and 96% conversion efficiency in the flue gas containing 1000 ppm CO at 300 °C. When SO2 was added to the flue gas, the CO conversion efficiency of FeTiOx dropped to about 10% after 5 h, while Fe2O3@TiO2 still achieved 60% CO conversion efficiency. The TiO2 shell of Fe2O3@TiO2 reacted with SO2 to protect the inner active sites from exposure to SO2, while the FeTiOx surface without shell protection was deposited by ferric sulfate and deactivated. Although the amount of sulfate on Fe2O3@TiO2 was larger than that on FeTiOx, the poor thermal stability of titanic sulfate made it decompose more easily than ferric sulfate. Therefore, the core-shell structure showed a critical role in promoting the resistance to SO2-poisoning of Fe2O3@TiO2 in CO catalytic oxidation.

Effect of the primary oxidizer stream jet velocities on the ignition and combustion characteristics of pulverized coal under MILD oxy-coal combustion conditions

MILD oxy-coal combustion technology is a prospective technology with the potential for CO2 capture and storage, and it is characterized by the intense flue gas recirculation to preheat the fuel and to dilute the oxidizer due to the oxidizer or fuel jet with high velocity. The effect of the primary oxidizer stream jet velocities ranging from 1.7 m/s to 11.2 m/s on the coal ignition and combustion characteristics were experimentally investigated on a flat flame pulverized coal burner at various oxygen concentrations of 5%-21% and gas temperatures of 1473–1873 K under O2/CO2 and O2/N2 atmospheres. The coal flame images were recorded by the digital camera, and the flame structure evolution and ignition delay times of coal particles were analyzed at different primary oxidizer stream jet velocities and hot coflow conditions. The coal combustion radiation spectrum was monitored by an optical fiber spectrometer and the coal particle temperatures were derived with the two-color pyrometry. The results showed that the bright yellow soot flame gradually disappeared with the decrease of O2 concentration when CO2 replaced N2. The difference of ignition delay times between O2/CO2 atmosphere and O2/N2 atmosphere decreased from 2.8 ms to 0.2 ms when the primary air jet velocity increased from 1.7 m/s to 11.2 m/s at 1473 K and 5% O2. This meant the elevated jet velocity was beneficial to offset the delayed effect of the physicochemical properties of CO2 on coal ignition. The peak coal particle temperature increased by 68 K at 1873 K and 5% O2 under O2/CO2 atmosphere with the highest jet velocity owing to the accelerated diffusion of O2 into coal particle stream. Moreover, a dimensionless coal particle temperature parameter η was proposed to characterize the variation of the peak coal particle temperature caused by the improved heat transfer and mass transport between the coflow and coal particles under high jet velocity. The maximum value of η was 1.053 at 1873 K and 21% O2 under O2/CO2 atmosphere with the jet velocity of 11.2 m/s, indicating the increased jet velocity had the predominant effect on the increase of peak particle temperature at high gas temperature and O2 concentration.

An assessment of China's joint prevention and control policy on sulfur dioxide emissions reduction: A spatial econometric analysis

Sulfur dioxide (SO2) is a typical pollutant that affects human health, climate, and environmental and ecological conditions. China has been experiencing high concentrations of SO2, particularly in urban areas, since the 1990s. In 2010, a “joint prevention and control” (JPC) policy was issued to address air pollution problems and strengthen the regulation of SO2 emissions. This study aimed to describe the mitigation effects of this policy on SO2 emissions in 116 Chinese cities from 2003 to 2017. We applied global and local Moran's I indices to confirm the presence of significant spatial autocorrelation in SO2 emissions and constructed four spatial models to assess the effect of the JPC policy in reducing SO2 emissions and its transmission mechanism. We found that the policy decreased SO2 emissions by 1.89 × 104 tons, SO2 intensity by 1.70 tons per km2, and SO2 per capita of 158.49 tons per 10,000 people in each city, on average, all of which are significant changes. The empirical results also show that population growth, economic structure, and environmental protection significantly decrease SO2 emissions. Finally, we recommended policies to encourage regional cooperation under the JPC policy, with the aim of promoting further reductions in SO2 emissions.