Composition Of Coal Ash Research Articles

Role of coal ash morphology and composition in delivery and transport of trace metals in the aquatic environment

Fly ash is predominately the inorganic byproduct of coal combustion for electrical power generation. It is composed of aluminosilicates with Fe, Mg, K, and Ca forming submicron to 100 μm spheres and amorphous particles. During combustion trace elements are incorporated into the heterogenous fine particles that can pose risks to the environment and human health. This study combines optical, rock magnetic, and geochemical analyses of fly ash originating from Appalachian coal to develop an integrated suite of environmental coal ash tracers. The non-magnetic portion of power plant fly ash has higher abundance of clear spheres and clear amorphous particles, combined with enrichment of As, B, Th, Ba, Li, Se, Cd, Pb, and Tl. The magnetic fraction is enriched in opaque and orange spheres and Cu, U, V, Mo, Cr, Ni, and Co. Plerospheres occur in either fraction. We investigated ash-bearing fluvial sediment from Emory-Clinch River system that was impacted by the instantaneous TVA spill in 2008 and Hyco Lake in North Carolina that was contaminated by chronic releases of fly ash since 1964. Five years after the TVA spill, most ash in the riverbed reflects one population with trace element concentrations proportional to percent total ash. This relationship does not hold for As and Se, volatile elements associated with the outer surface of clear spheres, which are affected by river transport. At Hyco Lake, small clear and opaque spheres correlate with trace elements released from storage ponds. The combination of trace elements, fly ash morphology and rock magnetism provides a powerful set of tools to assess the distribution of ash and potential impact on the environment. We conclude that dispersal of fly ash to the aquatic environment, especially small clear and opaque spheres, should be avoided in favor of dry landfills.

Study of the chemical composition of coal and coal ash by X‐ray fluorescence method: A review

Study of the chemical composition of coal and coal ash by <scp>X‐ray</scp> fluorescence method: A review

Development, modelling and optimization of process parameters on the tensile strength of aluminum, reinforced with pumice and carbonated coal hybrid composites for brake disc application

This study focuses on optimizing double stir casting process parameters to enhance the tensile strength of hybrid composites comprising aluminum alloy, brown pumice, and coal ash, intended for brake disc applications. Analytical techniques including X-ray fluorescence, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy were employed to characterize the composite constituents. The Taguchi method was utilized for experimental design and optimization to determine the optimal weight compositions of brown pumice and coal ash, as well as stir casting parameters (stirrer speed, pouring temperature, and stirring duration). Regression analysis was employed to develop a predictive mathematical model for the tensile strength of the hybrid composites and to assess the significance of process parameters. The optimized composite achieved a predicted tensile strength of 186.81 MPa and an experimental strength of 190.67 MPa using 7.5 vol% brown pumice, 2.5 vol% coal ash, a pouring temperature of 700 °C, stirrer speed of 500 rpm, and stirring duration of 10 min. This represents a 52.23% improvement over the as-cast aluminum alloy’s tensile strength. Characterization results revealed that brown pumice and coal ash contain robust minerals (SiO2, Fe2O3, Al2O3) suitable for reinforcing metal matrices like aluminum, titanium, and magnesium. Thermogravimetric and differential thermal analyses demonstrated thermal stability up to 614.01 °C for the optimized composite, making it suitable for brake disc applications.

Melting and Flow Behavior of Coal Ash at High Temperatures Based on SiO2-Al2O3-CaO/Na2O Pseudoternary Phase Diagram.

The entrained-flow gasifier has a better adaptability to various coals. The composition of coal ash is an important factor affecting the high-temperature flow characteristics of molten slag. Based on the SiO2-Al2O3-CaO/Na2O ternary phase diagram, the high-temperature molten flow characteristics of slag located in the main phase regions of feldspar, melilite, diopside, and mullite were investigated by experiments and thermodynamic software calculations. The results indicate that the melting process of ash in the three phase zones is influenced by different factors. It was discovered by infrared spectroscopy analysis that the slag was dominated by Si2O52- ion clusters in the feldspar region. The slag in the diopside region had a slightly higher proportion of simple silicate ion clusters than the slag in the feldspar region, resulting in better fluidity. This is significant for revealing the mechanism of coal ash melting and flowing and guiding industrial coal blending.

Monitoring For Elemental Composition Of Particulate Matter Deposited In Snow Cover Around Coal-Fired Thermal Power Plant (Karaganda, Central Kazakhstan).

Studies on thermal power plant areas with respect to chemical composition of particulate matter deposited in snow cover are limited. This study aims to monitor (2014–2022) particulate load and trace elements associated with the particulate matter distributed around (0.5-4.5 km) the coal-fired thermal power plant in Karaganda. In this study, snow cover was used as an effective scavenger of atmospheric pollutants. Using instrumental neutron activation analysis and atomic absorption spectrometry, the content of 26 elements and Hg, respectively, was determined in the particulate phase of snow. The results showed that particulate load varied from 26 to 1751, with mean of 427 and a background of 47 mg m-2 d-1. Anthropogenic impact caused a significant increase in content of U, Hg, Ta, Zn, Na, Cr, Co, Sr, Rb, Cs, Sc, Ca, Fe, Nd, Ba (2–30 times) in the samples compared to the background. Metal-bearing phases of Zn, Ba, As, U-Ta-Nb were detected through scanning electron microscope. The highest levels of particulate load (169–1032 mg m-2 d-1) and element contents in the samples were localized up to 0.7 km from the thermal power plant. The changes of particulate load and element composition of snow deposits during the monitoring period were connected with temperature, modernization of dust-collecting equipment, composition of coal and fly ash, long-range transport of emissions from other industries. The element content and metal-bearing phases in the particulate phase of snow can be used as markers for identifying emission sources from coal combustion.

Predicting rare earth elements concentration in coal ashes with multi-task neural networks.

The increasing demand for rare earth elements (REEs) makes them a scarce strategic resource for technical developments. In that regard, harvesting REEs from coal ashes-a waste byproduct from coal power plants-offers an alternative solution to conventional ore-based extraction. However, this approach is bottlenecked by our ability to screen coal ashes bearing large concentrations of REEs from feedstocks-since measuring the REE content in ashes is a time-consuming and costly task requiring advanced analytical tools. Here, we propose a machine learning approach to predict the REE contents based on the bulk composition of coal ashes, easily measurable under the routine testing protocol. We introduce a multi-task neural network that simultaneously predicts the contents of different REEs. Compared to the single-task model, this model exhibits notably improved accuracy and reduced sensitivity to noise. Further model analyses reveal key data patterns for screening coal ashes with high REE concentrations. Additionally, we showcase the utilization of transfer learning to improve the adaptability of our model to coal ashes from a distinct source.

Machine learning prediction of pyrolytic sulfur migration based on coal compositions

Understanding the sulfur migration during pyrolysis of coals especially high-sulfur coals is important. However, structural complexity and diversity of coals make it face huge challenge. In this study, a predictive model for morphological sulfur migration was developed using machine learning based on proximate analysis, ultimate analysis, sulfur forms of raw coal, ash composition, and blending ratio of coal. Three algorithms, i.e., Random Forest, XGBoost, and LightGBM were introduced and compared. The results show that six features are sufficient to accurately predict the products (R2 > 0.9, RMSE < 3.01%). LightGBM model has the advantages of better accuracy, generalization, efficiency, and performance, and Hyperopt has a higher upper limit than Grid-search. H content has a significant effect on S content in chars (St,dchar) and increasing H content from 5.0–5.3 wt% facilitates desulfurization. In addition, CaO, K2O and Fe2O3 also have remarkable effects on St,dchar. Higher H and volatile contents have a greater effect on thiophene removal in char. This work can provide a new approach to explore the sulfur migration in coal blending for coking.

Prediction of ash fusion temperatures of municipal solid waste incinerator ash based on support vector regression

The ash fusion temperatures (AFTs) of the municipal solid waste incinerator (MSWI) ash and slags is the main indicator to judge its slagging characteristics. Support vector regression (SVR) algorithm is more appropriate for creating an AFT prediction model than the classic regression method because it can adjust to a wider range of ash sample types in a wider range of areas by avoiding underfitting and overfitting. In this paper, SVR prediction models for the deformation temperature (IDT), softening temperature (ST), hemisphere temperature (HT), and flow temperature (FT) of ash are constructed using the ash chemical composition and AFTs dataset of coal ash and biomass ash and other ash. The AFTs of fly ash, bottom slag, and other ash in the municipal solid waste incinerator are predicted. With average relative errors of 1.98 % and 3.56 % and maximum relative errors of 5.21 % and 5.2 %, respectively, the results demonstrate that ST and FT have greater prediction accuracy. IDT and HT both provide poor predictions, with maximum relative errors of 14.08 % and 9.36 %, respectively, and average relative errors of 10.06 % and 5.95 %, respectively. Additionally, the impact of removing various numbers of outlier samples from training data on prediction accuracy, and the impact of test sample measures, such as ash composition analysis and AFTs determination, on prediction accuracy are analyzed and examined.

Effect of chemical composition of coal ash used to prepare granulated coal ash on the removal of hydrogen sulfide from water.

Granulated coal ash was prepared by mixing coal ash derived from a coal electric power plant and blast furnace cement, to remove hydrogen sulfide from aquatic environment. In this study, we investigate the effects of the composition of the coal ash used to prepare the granulated coal ash on its hydrogen sulfide removal performance. Manganese, magnesium, and calcium contents in the granulated coal ash were found to be the major factors in controlling the rate of hydrogen sulfide removal. The kinetics of hydrogen sulfide removal by the granulated coal ash were expressed as a first-order equation with a rate constant of 0.0081- 0.080 h-1 . The rate constant for hydrogen sulfide removal obtained in this study corelated well with the manganese content in the granulated coal ash. The increasing surface pH attributed to the hydrolysis of calcium and magnesium on the surface of the granulated coal ash slightly increased the hydrogen sulfide removal rate.

Impact of coal quality on power plant and environment: assessment of physiochemical and ash composition of Thar coal from Pakistan

Impact of coal quality on power plant and environment: assessment of physiochemical and ash composition of Thar coal from Pakistan

Effect of preheating Co-firing of biomass and coal on the synergistic reduction of PM and NO source emissions

Co-firing of biomass and coal is a prevalent method in modern thermal power plants to reduce pollutant emissions. This study focuses on the preheating co-firing behavior of coal and biomass to explore the effect of preheating combustion and preheating co-firing on PM (particle matter) and NO source emissions, and different coals were selected to verify the effect of coal rank on this behavior. Coal and biomass were fed into a mixing device through two independent feeders and uniformly mixed before entering the furnace. PM and NO emissions after preheating combustion were measured using an Electrical Low-Pressure Impactor and flue gas analyzer. The results showed that preheating combustion reduced the production of PM1, PM1-10, and NO from coal by 22.30%, 10.75%, and 49.84% respectively, and also reduced the production from biomass by 28.61%, 15.16%, and 53.01% respectively compared to conventional combustion. Preheating co-firing experiments revealed that as the co-firing ratio increases, NO production decreased, but the production of PM1 initially decreased and then increased, reaching a minimum point at a co-firing ratio of 25%. Meanwhile, the lower the rank of the coal, the better the effect of preheating combustion and preheating co-firing, and the ash content and composition of coal also had an impact on the generation of PM1.

Differentiation of Rare Earth Elements in Coal Combustion Products from the Handan Power Plant, Hebei Province, China

As a potential source of REY (rare earth elements and yttrium), coal and its products have attracted much attention. In this paper, we aimed to study the enrichment and differentiation of rare earth elements in fly ash with different particle sizes and promote the full recovery and utilization of rare earth elements in fly ash. Our objective was to focus on the REY concentration in feed coal and its combustion products from the Handan Power Plant. We particularly focused on the distribution of REY in relation to different particle sizes, as well as on the state of occurrence (affinity), by applying stepwise chemical extraction and performing examinations using inductively coupled plasma mass spectrometry (ICP-MS), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results show that the REY content is affected by the mineral composition of coal ash, and REY is more easily enriched in slag and fine ash than coarse ash. In general, the REY content decreased with the decrease in particle size in coarse ash, whereas the REY content increased with the decrease in particle size in fine ash. It was found that the concentration distribution of REY in solid combustion products is as follows: light REY (LREY) &gt; medium REY (MREY) &gt; heavy REY (HREY). This indicates that the enrichment of REY in solid coal products decreases with the increase in atomic number. The results also show that the occurrence state of REY in raw coal and coal ash undergoes no obvious change (residue state &gt; organic/sulfide-bound state &gt; iron–manganese-oxide-bound state &gt; carbonate-bound state &gt; exchangeable state).

Effects of Different Coals for Co-Combustion with Palm Oil Waste on Slagging and Fouling Aspects

ABSTRACT Implementing a co-combustion technology in coal-fired plants using biomass waste is a promising option to alleviate environmental pollution, reduce fuel costs, and minimize waste. The considerable potential of palm oil waste is believed to be able to substitute coal as a raw material in a coal-fired power plant. However, since each coal has different compositions and biomass generally has a high alkali content, the propensity of slagging and fouling during co-combustion needs to be clarified. This research evaluates the co-combustion ash characteristics of different types of coal, which is co-combusted with 25% palm oil biomass waste. The combustion test employs a drop tube furnace, where the produced ash composition and its morphology are investigated using scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction. The results show that the ash melting temperature of the three types of coal mixed with biomass is reduced, although insignificant. Bituminous coal has a low potential for slagging and fouling since SiO2 and Al2O3 dominate the coal ash composition. In addition, lignite coal has low SiO2 and Al2O3 contents but high alkali contents (K and Na). As confirmed by SEM-EDS analysis, probe observations also show that lignite coal co-combustion with empty fruit bunch and frond waste has higher slagging and fouling risks.

Минералого-геохимические свойства углей Мугунского месторождения (Иркутский угольный бассейн)

For the first time, the results of complex mineralogical and geochemical studies of coals of the Mugun lignite deposit of Early-Middle Jurassic age have been obtained. The chemical, phase and microelement composition of coals and coal ash, thermal properties, Raman spectroscopy and isotopic composition of carbon matter have been studied. It has been established that peneplain, characterized by a high degree of laterite-hypergene alteration of rocks, served as a source of terrigenous material for Mugun coals. Many geological, mineralogical, geochemical and technological properties of the studied coals are correlated with the degree of lateritization of the terrigenous admixture.

ВОЛОГА ВУГІЛЛЯ (ОГЛЯД)

The article is devoted to the actual problem of the presence of excessive moisture in coal, which leads to a decrease in its operational properties. The types and properties of moisture in coal have been considered. Mathematical equations and a statistical evaluation of the effect of the maximum moisture content on the quality indicators of coals are given. The relationship between the pore volume and the maximum moisture content in coals of a various degrees of metamorphism has been analyzed. It is shown that safe humidity depends on the grade of coal and on the size class for most coal marks. The effect of moisture on the bulk density of coal concentrates and coal charges has been determined, the changes in moisture during the coal defrosting and preparation for coking have been analyzed, and the effect of moisture on the flowability of coal charges was confirmed. The moisture content in the coal charge significantly affects on the thermal regime of the coke oven battery and on the heat consumption for coking. Moisture also changes the thermal properties of the coal charge during loading: for wet material, the thermal conductivity coefficient is much higher than for the dry material and the water separately. It has been shown that the maximum moisture content depends apon the nature of coal and the degree of its metamorphism, expressed by such indicators as the yield of volatile substances, the reflection of vitrinite, the content of carbon and hydrogen, as well as the calorific capacity. With the transforming of coal from a coarse size class to a fine one, the maximum moisture capacity increases due to an increasing of the specific surface area of coal. The maximum moisture capacity practically does not depend on the coal degree of oxidation and the chemical composition of coal ash. It has been established that the bulk density reaches a maximum for dry coal and decreases to a minimum depending on the size of the pieces at a moisture content of 6-10 %. The classification of coal charges according to moisture index has been developed. An increase of the moisture content in coal leads to a decrease of its grindability and reduces the coal fluidity. An increase of the moisture content of the coal charge leads to an increase of the calorific value of coke oven gas, to the formation of coke of uneven size, to an increase of its porosity and a decrease of mechanical strength, and also leads to a decrease of the service life of coke ovens. Keywords: moisture, coal, coking, preparation scheme, coke oven gas, mathematical equations. Corresponding author D. V. Miroshnichenko, e-mail: dvmir79@gmail.com

The Deposit Formation Mechanism in Coal-Fired Rotary Kiln for Iron Ore Pellet Production: A Review

The deposit-forming problem is one of the main bottlenecks restricting the yield and production benefit of iron ore pellets produced by coal-fired rotary kilns. In order to implement measures to ensure the efficient production of pellets by coal-fired rotary kilns, the mechanism and influencing factors on the deposit formation were reviewed. The pellet powder and coal ash come together to form the material base of the deposit. Meanwhile, the local reducing atmosphere caused by the continued combustion of residual carbon increases the FeO content, resulting in the formation of low-melting-point silicates. Moreover, alkali metal elements in coal ash can also promote liquid phase formation to cause serious deposit aggregation problems. During high-temperature roasting, the liquid phase corrodes the surface of the refractory brick to form the initial deposit, whereafter, it binds the pellet powder and coal ash from the material layer, which causes the deposit to accumulate continuously. The deposit formation of coal-fired rotary kilns is the result of interaction between many factors, which includes the quality of the green pellets, the composition of coal ash, the combustion efficiency of pulverized coal, roasting temperature, FeO content and alkali metal input. Finally, it is recommended that some measures to mitigate deposit formation can be adopted, such as increasing the compression strength of preheated pellets, choosing high-quality raw materials with low alkali metals, improving the combustion of pulverized coal.

Influence of coal ash characteristics on the pretreatment process of fluidized bed cement calcination

A new two-process Portland cement clinker manufacturing equipment was utilized to substitute traditional rotary kilns for emission reduction. Cement raw meal became an intermediate product after calcination in the pretreatment process, and the intermediate product turned into a clinker after the final calcination process. During the pretreatment process, the cement raw meal granulated and CaCO3 decomposition and C2S formation occurred simultaneously. Compositions of coal ash differed with cement raw meal and influenced mineral formation and granulation in the first process. Clinker quality and equipment feasibility were influenced accordingly. Therefore, the influence of coal ash component, content and ash fusion temperature on mineral formation and granulation was investigated. Results showed that high-SiO2/Al2O3 coal ash decreased C2AS formation in the intermediate product. Minor component MgO and alkali oxides had no contribution to C2S formation. SO3 promoted C2S formation and suppressed C2AS formation. Mineral types remained unchanged and mass fraction of granules over 1 mm in intermediate products fluctuated slightly as coal ash content increased. Ash fusion temperatures of coal ash were not directly related to granulation. The pretreatment process was feasible and suggestions for fuel selection were provided from the view of coal ash.

ДОСЛІДЖЕННЯ ТВЕРДИХ ЗАВИСЛИХ РЕЧОВИН У ВОДАХ, ЩО НАДХОДЯТЬ НА ГАСІННЯ КОКСУ

The article is devoted to the results of work for the study of the composition and quantitative content of suspended solids (SS) in the wastewater of coke plants before and after biochemical purification plants (BPP), as well as in other waters involved in the process of coke extinction. The characteristic indicators have been investigated of waters before and after BPP of five coke-chemical enterprises of Ukraine, as well as the chemical composition of suspended solids in water after BPP, etc. It is shown that SS in water after BPP is represented mainly by activated sludge, which is partially oxidized to CO2 when water is supplied to hot coke. The rest activated sludge is returned with water condensate to the settling tank of the extinction tower and, thus, is not emitted into the atmosphere in the form of SS. In addition to sludge, the particles of coke, coal and products of the equipment corrosion are present in the purified water after the BPP and in the water of the extinction tower settling tank. The possibility of the presence of concrete particles is also not excluded. To establish the nature of solid particles, their elemental composition and ash composition has been determined. In particular, it was found that the ash composition of suspended solids from water after BPP quantitatively differs from the both of ash composition of coal concentrates and the composition of concrete. For example, the mass fraction of silicon dioxide in the suspended solids of water after BTH is much lower than in concrete and in ash of coal concentrates. The detected predominance of iron (III) oxide in the composition of SS ash after BPP is explained by the presence in the selected samples of products of the equipment corrosion. Based on our research, it is proposed to make changes in the normative document "Technological standards of permissible emissions of pollutants from coke ovens", namely in chapter IV "Operating conditions of coke ovens" par. 8: to exclude such a normative value as the content of suspended solids in water after BPP, which is submitted for coke extinction. Keywords: water for coke extinction, water after biochemical purification, suspended solids (SS), content, chemical composition, elemental composition, ash composition. Corresponding author A.L. Borisenko, e-mail: zd@ukhin.org.ua

Steam Reforming of Toluene Over Ni/Coal Ash Catalysts: Effect of Coal Ash Composition

Steam Reforming of Toluene Over Ni/Coal Ash Catalysts: Effect of Coal Ash Composition

Characteristics and geological significance of germanium in Taiyuan coal formation of Huainan Coalfield, Anhui, China

HN-1# is the first fully working coring well of the Taiyuan Formation (Ty) in the Huinan Coalfield and exploration studies are currently underway on the associated resources of the coal-bearing strata. The HN-1# well is located in the Fufeng thrust nappe structural belt in the south of the Huainan Coalfield. Three coal samples from the Ty were collected from HN-1# and inductively-coupled plasma mass spectrometry and inductively-coupled plasma atomic emission spectrometry were used to determine the Ge content of each sample. Based on proximate and ultimate analyses, microscopy data, and analyses of the ash products, some important findings were made. The Ty coal samples had a relatively high total sulfur (St,d) content (4.24%), thus the coal was considered to be a lower ranked coal (high volatility bituminous coal), which also had a low coal ash composition index (k, 1.87). Collodetrinite was the main submaceral of the Ty coal. Small amounts of pyrite particles were found in the coal seams of the Ty, while the contents of pyrite and algae in the top and bottom sections of the coal seam were relatively high, which meant that the swampy peat conditions which existed during the formation of the coal seams were affected by seawater; also the degree of mineralization of the coal seam was relatively high, which is consistent with reducing conditions in a coastal environment setting. Atomic force microscopy (AFM) experiments showed that the modes of occurrence of Ge in the Ty coal were mainly those for organic-bound and adsorbed Ge species. The organic carbon isotope values for the Ty coal ranged from − 24.1‰ to − 23.8‰, with an average value of − 24.0‰, which is equivalent to the value for terrestrial plants (average value − 24.0‰). The Ge content of the Ty coal was 13.57 mg/kg. The Ge content was negatively correlated with volatile matter and the ash yield.