Coal-burning Power Plants Research Articles

Organic aerosol sources in Krakow, Poland, before implementation of a solid fuel residential heating ban

Krakow is a pollution hot-spot in Europe which is thought to be caused mainly by a high use of coal combustion (power plants, residential heating). Here, we quantify the impact of coal burning on air quality in the city of Krakow before the use of solid fuels for residential heating was banned within the city of Krakow. The particulate matter (PM) was collected on 126 24-hour filter samples (January to September, both PM1 and PM10, i.e., with an aerodynamic diameter smaller than 1 μm and 10 μm, respectively) and analyzed with an aerosol mass spectrometer and the sources of the organic aerosol (OA) quantified. Secondary OA (SOA) likely from residential heating was the main contributor to winter-time OA (78 % in PM1, 57 % in PM10) and was composed of equal parts of fossil and non-fossil emissions. Additionally, fresh solid fuel combustion emissions from residential heating contributed to OA during winter (coal combustion OA (CCOA): 12 %, biomass burning OA (BBOA): 3 %). While BBOA contributed substantially to water-soluble OA, COOA was found to be water-insoluble and thus not identified as part of water-soluble OA. Together with the fairly low water-solubility of winter oxygenated OA (WOOA, 29 %), this leads to a low overall water-solubility of organic carbon during winter (35 %). In contrast, spring and summer were characterized by more soluble organic carbon (71 % in PM1, 55 % in PM10) which was dominated by biogenic sources (non-fossil), i.e., fine biogenic secondary oxygenated OA (summer oxygenated OA (SOOA): 35 % in PM1) and coarse primary biological OA (PBOA: 54 % in PM10). Overall, here we provide information on OA's sources needed to evaluate the success of mentioned efforts to improve air quality in Krakow in future studies.

Comparison of two air quality models in complex terrain near sea shore

Air pollution is the most important environmental problem in Zonguldak, Turkey due to excessive coal combustion and thermal power plant emissions. The city center is located on a complex terrain near the Black Sea shore. There exist some previous studies about PM10 pollution in the study area, but none of them is related to the spatial distribution of the pollutant. This air quality modeling study aims to fill this gap in the literature. Firstly, PM10 emission inventory has been prepared for point, line, and area sources for the year 2011. For that period, bituminous coal was the principal fuel for domestic heating in houses and generating electricity in thermal power plants, therefore particulate matter (PM10) was the leading air pollutant. Emission inventory calculations revealed that 2710.2 tons of PM10 have been emitted to the atmosphere from all sources in the study area. Then, the air quality modeling has been performed for PM10 by using two air quality models: AERMOD and CALPUFF. According to the modeling results, the PM10 pollution levels may pose a health threat to the inhabitants of Zonguldak. The maximum PM10 concentrations predicted by the CALPUFF model were higher than that of the AERMOD model. The model predicted values plus background concentration were validated against the PM10 measurements by using fractional bias, index of agreement, geometric mean bias, and geometric mean-variance. According to the model performance analysis, CALPUFF showed slightly better performance as compared to AERMOD.

Assessment of blended coal source fly ashes and blended fly ashes

The availability of traditional siliceous Class F fly ash, produced when burning bituminous coals, is decreasing around the world as many countries begin to switch to renewable energy sources. Existing coal burning power plants are also starting to convert from bituminous to subbituminous coals, which produce calcareous Class C fly ash, or to a blend of the two to reduce emissions and cost. To prolong the availability of siliceous fly ash, suppliers have started distributing blended coal ashes and have also begun to blend siliceous fly ash with other coal combustion products (CCPs), such as calcareous fly ash or bottom ash, or natural pozzolans. A variety of these blended fly ashes were examined in this study and compared to a traditional siliceous fly ash. Although these fly ashes have similar oxide compositions and physical characteristics to a traditional siliceous fly ash, the crystalline and glassy phases present in the fly ash may differ. This can alter cement hydration and result in failure to mitigate expansion due to sulfate attack. In all other performance and durability tests conducted in this study, all fly ashes performed well in cement-based mixtures.

Evaluation of environmental radioactivity in soils around a coal burning power plant and a coal mining area in Barapukuria, Bangladesh: Radiological risks assessment

To study the distributions and potential dispersions of naturally occurring radioactive materials (NORMs: 226Ra, 232Th, and 40K) from coal-based activities (Barapukuria, Bangladesh), we studied a suite of systematically collected surface and sub-surface soil samples by X-ray fluorescence and high purity germanium detector based γ-spectroscopy. The average (range) radioactivities of 226Ra, 232Th, and 40K in the studied soil samples were 80.6 (33.0–118.0), 104.4 (43.0–182.0), and 508.1 (318.3–743.4) Bq.kg−1, respectively, which are significantly higher than the corresponding world average value. No significant fractionations of NORMs were observed between the surface and sub-surface soils, except for 232Th. Along with the anthropogenic origin, several geochemical processes (e.g., weathering, mineralogical dissolution/precipitation, alteration, leaching, differential solubility mediated geochemical mobility etc.) play significant role in NORM distributions. Major-oxide abundances, indices-based calculations, and correlation studies on the measured parameters revealed the natural processes (e.g., geochemical mobility, mineralogical distributions, water logging based differential solubility) responsible for NORM distributions. In terms of mean radium equivalent activity, internal hazard index, and total annual effective dose values, the studied area possesses trivial radiological risks, whereas the values of internal absorbed gamma dose and excess lifetime cancer risk demonstrate significant health hazards. Considering the adverse radiological risks originating from coal-based industrial activities and the long half-lives of NORMs, the present scenario will potentially be deteriorated.

Costs of achieving emission limits in coal-burning power plants under the recent best available techniques regulation amendment: Evidence from national microeconomic data

Emissions limits for coal-burning power plants are gradually being tightened around the world, with additional requirements and consequently significant costs placed on existing power plants. Design that conforms to regulatory requirements require credible estimation of the associated abatement costs. However, the existing methods for estimating abatement costs do not estimate those costs using microeconomic data or take the need to retrofit current abatement technologies into sufficient consideration. Therefore, they fail to calculate the actual costs of compliance accurately and thus are not suitable for assessment of cost proportionality, which is the key principle of regulatory design. This paper introduces a straightforward and innovative methodological approach to quantification of abatement costs that can reflect the real-world situation at an individual power plant and allows assessment of proportionality in meeting emission standards. The approach is based on collection of detailed data at the level of individual plants and on the comparison of costs associated with various levels of emission reduction in defined scenarios. The approach is demonstrated by application to nearly 50% of the installed thermal power capacity of the Czech Republic. The results show that recent European regulations for coal-burning plant emissions incur high abatement costs for most power plants, despite having very little effect in terms of emission reductions.

Preparation of activated coke by carbonization, activation, ammonization and thermal treatment of sewage sludge and waste biomass for SO2 absorption applications

Flue gas desulfurization of coal-burning power plants is imperative to mitigate pollution and acid rain. Use of activated coke as a sulfur dioxide adsorbent is a promising technology, particularly since activated coke can also effectively remove other emissions, such as mercury. In this manuscript, a modified method of ammonia water was used to prepare activated coke for flue gas desulfurization. The feedstock is a blend of sewage sludge and waste biomass, at a mass ratio of 2:1. This material was carbonized prior to activation and ammonization; in some cases, additional thermal treatment was applied. The products were successfully tested for sulfur dioxide adsorption. A graphene model incorporating nitrogen-containing functional groups was used to simulate the sulfur dioxide adsorption process. Thereby, the effects of different ammonia modification concentrations on the physical and chemical properties of activated coke were studied, and the sulfur dioxide adsorption process of nitrogen-containing functional groups (such as pyridine and pyrrole) in activated coke, during flue gas desulfurization, was simulated. This study confirmed that the method of ammonization and heating can introduce nitrogen-containing functional groups on the surface of the activated coke. This greatly improves its chemical properties and, as a result, it markedly improves its SO2 adsorption capacity. It was found through simulation that the doping of nitrogen atoms changes the uniform electrostatic potential distribution and changes the surface polarity. H2O, pyridine functional groups and pyrrole functional groups can promote the adsorption of SO2 on the graphene surface. The pyrrole functional group showed selective adsorption for both SO2 and H2O, but it was predicted to be more effective in adsorbing SO2 than in adsorbing H2O. The pyridine functional group showed no selective adsorption for SO2 and H2O, and it was predicted to be more active in adsorbing SO2 when compared with the pyrrole functional group. The O2 had no effect on the physical adsorption of SO2 on the graphene.

Impact of biopower generation on eastern US forests

Biopower, electricity generated from biomass, is a major source of renewable energy in the US. About ten percent of US non-hydro renewable electricity in 2020 was generated from biomass. Despite significant growth in woody biomass use for electricity in recent decades, a systematic assessment of associated impacts on forest resources is lacking. This study assessed associations between biopower generation, and selected timberland structure indicators and carbon stocks across 438 areas surrounding wood-using and coal-burning power plants in the Eastern US from 2005 to 2017. Timberland areas around plants generating biopower were associated with more live and standing-dead trees, and carbon in their respective stocks, than comparable areas of neighboring plants only burning coal. We also detected an inverse association between the number of biopower plants and number of live and dead trees, and respective carbon stocks. We discerned an upward temporal trajectory in carbon stocks within live trees with continued biopower generation. We found no significant differences related to the amount of MWh biopower generation within the analysis areas. Net impacts of biopower descriptors on timberland attributes point to a positive trend in selected ecological conditions and carbon balances. The upward temporal trend in carbon stocks with longer generation of wood-based biopower may point to a plausibly sustainable contribution to the decarbonization of the US electricity sector.

Potentially Economic Concentrations of Rare Earth Elements and Gold in Power Plant Coal Combustion Products (Far East, Russia)

The distribution of rare earth elements (REE) and gold (Au) in fly ash released during combustion of brown coal from the Pereyaslavskoye (Siberia) and Erkovetskoye (Far East) deposits has been investigated. Coal combustion was carried out in two locations: the boiler unit of the Blagoveshchenskaya coal-fired power plants (CFPP), equipped with an electrostatic precipitator (ESP); and at the Amur Experimental and Technological Complex (ETC) with the aim of separating the combustion products (slag, fly ash, sludge). It was found that in both processes the highest contents of REE (400 and more ppm) and Au (up to 0.29 ppm) are concentrated in fly ash. These characteristics of coals were used as the basis for the author's calculation of the predicted resources of REE and Au under the conditions of the annual operation of firstly one boiler unit, and then five, equipped with an ESP. Further research by the authors will be aimed at improving the degree of recovery of concentrates through the development of technologies at pilot plants such as ETC “Amur”.

Heavy Metal(loid) Body Burden in Environmentally Exposed Children With and Without Internalizing Behavior Problems.

The prevalence of internalizing behavior disorders in children is increasing. Reasons for increasing anxiety and depression include several factors with a less studied consideration being the potential neurotoxic effects of environmental exposures. One group at risk for environmental exposures is children living near coal-burning power plants with coal ash storage facilities. Multivariate logistic regression was used to assess the relationship between metal(loid) exposures and internalizing behaviors in children aged 6-14 years. Metal(loid)s in nail samples were determined by Proton-Induced X-ray Emission and internalizing behavior problems were obtained from the parent ratings on the Child Behavior Checklist. Results indicated that concentrations of metal(loid)s in nails differ between children with internalizing behaviors and without internalizing behaviors. Logistic regression models suggested that exposure to zinc and imputed zirconium were associated with internalizing behaviors in children. However, when a sex-metal(loid) interaction term was included, none of the metal(loid)s were associated with internalizing behaviors indicating a role of sex differences in neurotoxicity with zinc and copper showing effects only for males. In all models, greater exposure to traffic was associated with internalizing behaviors. Zinc has previously been shown to increase risk for mental health problems, while zirconium has received less attention. Out findings indicate that environmental exposures of zinc and zirconium deserve further attention in studies of childhood internalizing disorders.

Study on Strength, Water Stability, Shrinkage, and Microstructure of CFB Slag Modified Cement Stabilized Clay.

Circulating fluidized bed slag (CFBS) is an industrial waste produced by coal combustion in power plants. To explore the application of CFB slag in cement-stabilized bases, this paper studies the influence of different dosage of CFBS on the mechanics, water stability, and shrinkage of cement-stabilized soil using laboratory experiments. The hydration activity and interface morphology of CFBS in cement-stabilized clay were observed using XRD and SEM. The improvement mechanism of CFBS on the performance of cement-stabilized clay was revealed. The results indicated that, compared with cement-stabilized clay, cement–CFBS-stabilized clay exhibited better mechanical and water stability, and significantly inhibited the shrinkage deformation of cement-stabilized clay. When the addition of CFBS was 70%, cement–CFBS-stabilized clay had the best mechanics and durability. Microscopic tests show that CFBS contains more active silicon aluminum oxide, which is easily dissolved and the hydration of which produces more gel products, so the mixture structure is denser, the strength is improved, and water does not easily evaporate; it has the characteristics of micro expansion which compensates for dry shrinkage deformation.

HEAVY METALS AND THEIR IMPACT ON HUMAN HEALTH

Due to the deleterious consequences it is having on a global scale, the presence of heavy metals has become a matter of significant concern. Due to the rapidly expanding agriculture and metal sectors, as well as inappropriate waste management, fertilisers, and pesticides, these inorganic pollutants are being dumped into our water, soil, and environment. Heavy metals interfere with biological functions such as growth, proliferation, differentiation, damage repair, and apoptosis. Multiple industrial, residential, agricultural, medical, and technical applications have resulted in their widespread presence in the environment, generating concerns regarding their possible consequences on human health and the environment. Heavy metals occur naturally and are vital to life, but buildup in organisms can render them hazardous. The most prevalent heavy metals that damage the environment include arsenic, cadmium, chromium, copper, nickel, lead, and mercury. Due to its capacity to travel large distances in the atmosphere, mercury, lead, and cadmium pose the most threat. Mining, industrial output (foundries, smelters, oil refineries, petrochemicals plants, pesticides production, chemical industries), untreated sewage sludge, and diffuse sources such as metal pipelines, traffic, and combustion byproducts from coal-burning power plants are all sources of heavy metals. Mercury, lead, chromium, cadmium, and arsenic have caused human poisoning more frequently than any other heavy metals. Apoptosis, development, proliferation, differentiation, damage healing, and apoptosis are all affected by heavy metals. Instabilities in the genome have been linked to heavy metals like chromium and cadmium, as well as arsenic.

Fly Ash as an Eco-Friendly Filler for Rigid Polyurethane Foams Modification.

There is currently a growing demand for more effective thermal insulation materials with the best performance properties. This research paper presents the investigation results on the influence of two types of filler on the structure and properties of rigid polyurethane foam composites. Fly ash as a product of coal combustion in power plants and microspheres of 5, 10, 15, and 20 wt.%, were used as rigid polyurethane foams modifiers. The results of thermal analysis, mechanical properties testing, and cellular structure investigation performed for polyurethane composites show that the addition of fly ash, up to 10 wt.%, significantly improved the majority of the tested parameters. The use of up to 20 wt.% of microspheres improves the mechanical and thermal properties and thermal stability of rigid polyurethane foams.

CO2 capture and utilization from supercritical coal direct chemical looping combustion power plant – Comprehensive analysis of different case studies

Carbon dioxide utilization has gained much attention as a greenhouse gas (GHG) abatement strategy complementary to carbon dioxide storage. Fossil fuel (including coal) based power plants are the large emitters of carbon dioxide as a single sector. Chemical looping combustion is an inherent CO2 capture technology and can also be used for hydrogen production. The captured CO2 and H2 can be used as reactants for synthesis of various products. Present study explores the carbon dioxide utilization (CDU) from the coal direct chemical looping (CDCL) combustion plant with power and hydrogen co-generation to produce four valuable products as four different cases. These case studies include formic acid (FA), methane, methanol, and dimethyl ether (DME) synthesis plants. The performance of these integrated plants is evaluated based on a comprehensive assessment including energy, exergy, ecological, economic and life cycle (4-E&L) analyses. Levelised cost of the products (LCOP) of CDU plants are estimated and compared. Results of 4-E&L analyses show that the CDCL plant with formic acid synthesis is the most favourable option with 100% CO2 utilization efficiency. At the end, the LCOPs estimated from the proposed CDU integrated CLC based power plant are compared against the LCOPs obtained from two different approaches using hydrogen production from solid oxide electrolysis cell (SOEC). The proposed approach is found to be resulting in less LCOP compared to the other approaches.

Pinch combined with exergy analysis for heat exchange network and techno-economic evaluation of coal chemical looping combustion power plant with CO2 capture

A coal chemical looping combustion (CLC) power plant (600 MW) with CO2 capture was established and validated. The key operation parameters and conditions for the coal chemical looping combustion process were tested and optimized. Heat exchange network (HEN) was established and optimized using the combined pinch and exergy analysis method for matching and integrating different levels or grade energy, from flue gas and exhaust steam waste heat, in coal chemical looping combustion power plant to maximize the energy efficiency output. Followed by conducting a techno-economic evaluation and exergy distribution analysis which showed that the net energy efficiency of the CLC power plant (34.8 %, improved by 1.9 %) is 2.4 % higher than the monoethanolamine (MEA)-based ultra-supercritical coal power plant (32.4 %) with the same CO2 capture ratio (90 %). The CLC power plant also provides a lower cost of electricity (0.088–0.127 $/kWh) and less coal consumption (381 g/kWh), compared to the MEA-based power plant (0.143 $/kWh, 408 g/kWh). The cost and energy penalty of CO2 enrichment and separation are less when compared to traditional MEA-based ultra-supercritical coal power plants due to the intrinsic nature of in-suit CO2 capture, the lower exergy destruction in the chemical looping combustion process, and sufficient energy integration and recovery from HEN.

Utilization of Fly Ash in the Synthesis of Refractory Forsterite-Spinel Ceramics

Forsterite refractory ceramics is utilized in the metallurgical and cement industries as a lining of metallurgical furnaces and rotary kilns for its high refractoriness up to 1850°C and refractoriness under load above 1600°C. Another significant property of forsterite is its coefficient of linear thermal expansion utilized in the electrotechnical industry for ceramic-metal joints. Addition of aluminium oxide into the raw material mixture results in creation of magnesium-alumina spinel (MgO·Al2O3) which improves sintering, thermal shock resistance and mechanical properties in comparison with pure forsterite ceramics. Inexpensive source of aluminium oxide is fly ash. Utilization of fly ash, secondary energetic product of coal-burning power plants, is important for the environment and sustainable development. This paper evaluated properties of fly ash-based forsterite-spinel ceramics in comparison with alumina-based forsterite-spinel ceramics. Forsterite-spinel ceramics was synthesized from olivine, calcined magnesite and fly ash/alumina powders. XRD analysis was used to determine mineralogical composition, thermal analyses were used to determine the behaviour during firing and scanning electron microscopy to determine the morphology of crystal phases. Refractoriness of pyrometric cones, refractoriness under load, thermal shock resistance, coefficient of linear thermal expansion, water absorption, porosity and modulus of rupture were also determined on fired test samples.

Facility for calibrating anemometers as a function of air velocity vector and turbulence

NIST calibrates anemometers as a function of airspeed vector and turbulence intensity (Tu). The vector capability (sometimes called ‘3D’) is particularly important for calibrating multi-hole differential-pressure probes that are often used to quantify pollution emitted by smokestacks of coal-burning electric power plants. Starting with a conventional ‘1D’ wind tunnel, we achieved vector and Tu capabilities by installing translation/rotation stages and removable turbulence generators (grids or flags). The calibration ranges are: yaw angle ±180°; pitch angle ±45°; airspeed 1 m s−1 to 30 m s−1; turbulence intensity 0.07 ⩽ Tu ⩽ 0.25; average data collection rate: 300 points/h at fixed Tu. The system’s expanded uncertainties corresponding to 95% confidence level are: airspeed 0.0045 × |V| + (0.036/|V|)2 where |V| is the magnitude of the airspeed in m s−1; pitch and yaw angles 0.3°; and turbulence intensity 0.03 Tu. The airspeed working standard is a laser Doppler anemometer that is traced to SI unit of velocity via a spinning disk. Calibrations are corrected for blockage by the instrument under test and its supports.

Optimum concentration of fly ash nanoparticles to stabilize CO2 foams for aquifer and soil remediation

Contamination caused by non-aqueous phase liquids (NAPLs) in aquifers and soil is an important challenge that requires effective remediation techniques. One potential approach is through the use of CO2 foams to displace NAPLs from permeable media. CO2 foams generated only by surfactants are not stable enough for the efficient removal of NAPLs contamination. This shortcoming may be alleviated via the use of nanoparticles (NPs)-surfactant mixtures as a stabilizing agent. This work focuses on the evaluation of the optimum concentration of fly ash nanoparticles for stabilizing CO2 foam with the combined action of the surfactant. The performance of this foam is evaluated in remediating a contaminated 41 mm × 36 mm surrogate permeable medium in a microfluidic device. Mixtures of fly ash, a by-product of coal-burning power plants, and alpha-olefin sulfonate (AOS) and lauramidopropyl betaine (LAPB) surfactants are used to generate stable foams. The results show that a 1000 mg/L AOS-LAPB surfactant solution along with 1000 mg/L of fly ash NPs produces the best performance. Formation of deposits in the matrix is observed. These deposits, which are more prominent at higher NP concentrations, appear to adversely affect displacement, displacement efficiency and remediation of the medium. This study demonstrates that using fly ash nanoparticles and optimizing their concentration can effectively stabilize CO2 foams and improve the displacement efficiency for aquifer and soil remediation.

Magnetic Fly Ash as a Chronological Marker in Post-Settlement Alluvial and Lacustrine Sediment: Examples from North Carolina and Illinois

Fly ash consists of mainly silt-size spherules that form during high-temperature coal combustion, such as in steam locomotives and coal-burning power plants. In the eastern USA, fly ash was distributed across the landscape atmospherically beginning in the late 19th century, peaking in the mid-20th century, and decreasing sharply with implementation of late 20th century particulate pollution controls. Although atmospheric deposition is limited today, fly ash particles continue to be resedimented into alluvial and lacustrine deposits from upland soil erosion and failure of fly ash storage ponds. Magnetic fly ash is easily extracted and identified microscopically, allowing for a simple and reproducible method for identifying post-1850 CE (Common Era) alluvium and lacustrine sediment. In the North Carolina Piedmont, magnetic fly ash was identified within the upper 50 cm at each of eight alluvial sites and one former milldam site. Extracted fly ash spherules have a magnetite or maghemite composition, with substitutions of Al, Si, Ca, and Ti, and range from 3–125 µm in diameter (mainly 10–45 µm). Based on the presence of fly ash, post-1850 alluvial deposits are 15–45 cm thick in central North Carolina river valleys (<0.5 km wide), ~60% thinner than in central Illinois valleys of similar width. Slower sedimentation rates in North Carolina watersheds are likely a result of a less agricultural land and less erodible (more clayey) soils. Artificial reservoirs (Lake Decatur, IL) and milldams (Betty’s Mill, NC), provide chronological tests for the fly ash method and high-resolution records of anthropogenic change. In cores of Lake Decatur sediments, changes in fly ash content appear related to decadal-scale variations in annual rainfall (and runoff), calcite precipitation, land-use changes, and/or lake history, superimposed on longer-term trends in particulate pollution.

Haze to electricity: Efficiently harvesting electric energy from air pollutants by construction of bioinspired electron transport chains in light- and heat-driven liquid flow fuel cells

• Construction of bioinspired electron transfer chains for electron transfer. • Ferricyanide and vanadyl screened as efficient electron carriers. • Light-driven fuel cell obtained 1.2 mW/cm 2 at 25 °C fueled with haze pollutants. • Light-driven fuel cell obtained 143 mW/cm 2 at 90 °C fueled with haze pollutants. • About 80% total efficiency for chemical energy to electricity conversion. Inspired by the working principle of naturally-existing photosynthetic and respiratory electron transport chains (ETCs) in phototrophic organisms and living cells, we have constructed artificial ETCs to promote the kinetics of electron transfer thus achieving efficient conversion of haze pollutants to electricity by light- or (photo-thermal) heat-driven liquid flow fuel cells (LFFCs). Ferricyanide (K 3 [Fe(CN) 6 ]) and VO 2 + /VO 2+ with activation by HNO 3 have been screened as efficient anode and cathode mediators to transfer electrons to oxygen. Light-driven LFFC with a CdS@TiO 2 photo-anode achieved a maximal power density ( P max ) of 1.2 mW/cm 2 at room temperature, while heat-driven LFFC made a P max of 142.7 mW/cm 2 at 90 °C. About 80% overall efficiency of haze-to-electricity was obtained. Various wastes including different sugars, lignin, cellulose, urea and even the coal-burning power plant ashes could be converted to electricity, indicating the promising prospect of this technology for application in treatment of organic pollutants coupled with generation of electricity.

The key roles of Fe-bearing minerals on arsenic capture and speciation transformation during high-As bituminous coal combustion: Experimental and theoretical investigations

The conversion of As vapor released from coal combustion to less hazardous solids is an important process to alleviate As pollution especially for high-As coal burning, but the roles of key ash components are still in debate. Here, we used multiple analytical methods across the micro to bulk scale and density functional theory to provide quantitative information on As speciation in fly ash and clarify the roles of ash components on As retention. Fly ash samples derived from the high-As bituminous coal-fired power plants showed a chemical composition of typical Class F fly ash. In-situ electron probe microanalysis (EPMA) was for the first time used to quantify and distinguish the inter-particle As distribution difference within coal fly ash. The spatial distribution of As was consistent with Fe, O, and sometimes with Ca. Grain-scale distribution of As in coal fly ash was quantified and As concentrations in single ash particles followed the order of Fe-oxides > aluminosilicates > unburned carbon > quartz. Sequential extraction and Wagner chemical plot of As confirmed that Fe minerals rather than Al-/Ca-bearing minerals played a vital role in capturing and oxidizing As3+ into solid phase (As5+). Magnetite content in fly ash well-correlated with the increase ratio of As before and after magnetic separation, suggesting magnetite enhanced As enrichment in fly ash. Density functional theory (DFT) indicated that the bridges O sites of octahedral structure on Fe3O4 (111) surface were likely strong active sites for As2O3 adsorption. This study highlights the importance of magnetite on As transformation during bituminous or high-rank coal combustion in power plants and has great implications for developing effective techniques for As removal.