Chemical Composition Of Coal Ash Research Articles

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.

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

Ash Characteristics and Selected Critical Elements (Ga, Sc, V) in Coal and Ash in Polish Deposits

The chemical composition of coal ash and the content of the critical elements Ga, Sc, and V in coal and ash are examined herein. In this study, lignite and bituminous coal from Polish deposits were used. The coals were subjected to ultimate and proximate analysis; the petrographic composition was determined based on maceral groups. The chemical composition of ash and the content of critical elements were determined using ICP-MS. The obtained results were correlated and Pearson’s linear correlation coefficient was determined. Based on the correlation analysis, the relationship between the chemical composition of ash and the proximate and ultimate analyses was demonstrated. The content of selected critical elements in the tested deposits was lower than the Clarke value in coal. However, in some deposits these contents are much higher in coal ashes. The higher levels of Ga, V, and Sc in the ash are associated with Al2O3. Therefore, it can be stated that ashes can be a potential source of some raw materials. The highest concentrations of critical elements in coal and ash were recorded in the Lublin Coal Basin. Supra-Clarke contents of Ga, V, and Sc were recorded in the Bogdanka coal mine.

Влияния связующего вещества, используемого при прессовании зол для лазерного пробоотбора, на качество аналитических сигналов определяемых элементов

This work is devoted to determining the chemical composition of coal ashes. We used the optical emission spectrometry with inductively coupled plasma and laser sampling as a research method. The aim of the work is to determine the limits of detection (LoDs) and quantitative determination (LoQs) of elements in ashes using polyvinyl alcohol (PVA) and microcrystalline cellulose (MCC) as binders. In this work, analytical signals of Al, Ba, Be, Ca, Cr, Cu, Fe, K, La, Li, Mg, Mn, Na, Ni, P, Pb, S, Sc, Sr, Ti, Y, V, Zr, and Zn were analyzed in tablets obtained from the standard samples ZUK-1, ZUK-2, SG-1A, SG-3, SGD-2A, and SO-1, compacted using PVA and MCC, as well as from binding agents themselves. To obtain compact materials based on fly ash and geological materials, both binders are suitable if their chemical purity is enough for analysis. However, when using both MCC and PVA, some drawbacks were identified. The intensities of analytical lines of the elements were determined lower during the ablation of compact ashes with MCC than with PVA. The signal-background ratio is lower when using MCC as a binder material compared with compacts based on PVA. However, the highest grade PVA according to GOST 10779-78, used in the work, contains an admixture of sodium, about 0.06 w. %, which interferes with quantitative measurements if the sodium content in the sample is comparable to this value, which can be extremely rare in the analysis of fly ashes.

Ranking Coal Ash Materials for Their Potential to Leach Arsenic and Selenium: Relative Importance of Ash Chemistry and Site Biogeochemistry.

The chemical composition of coal ash is highly heterogeneous and dependent on the origin of the source coal, combustion parameters, and type and configuration of air pollution control devices. This heterogeneity results in uncertainty in the evaluation of leaching potential of contaminants from coal ash. The goal of this work was to identify whether a single leaching protocol could roughly group high-leaching potential coal ash from low-leaching potential coal ash, with respect to arsenic (As) and selenium (Se). We used four different leaching tests, including the Toxicity Characteristic Leaching Protocol (TCLP), natural pH, aerobic sediment microcosms, and anaerobic sediment microcosms on 10 different coal ash materials, including fly ash, lime-treated ash, and flue gas desulfurization materials. Leaching tests showed promise in categorizing high and low-leaching potential ash materials, indicating that a single point test could act as a first screening measure to identify high-risk ash materials. However, the amount of contaminant leached varied widely across tests, reflecting the importance of ambient conditions (pH, redox state) on leaching. These results demonstrate that on-site geochemical conditions play a critical role in As and Se mobilization from coal ash, underscoring the need to develop a situation-based risk assessment framework for contamination by coal ash pollutants.

Prediction of correlation between ash fusion temperature of ASTM and Thermo-Mechanical Analysis

Ash problems, such as slagging and fouling, are important because of their negative effect of reducing the heat transfer on the furnace wall and tube in pulverized coal boilers and decreasing the boiler safety. However, slagging has positive effect on gasifier. Slagging is protecting furnace wall and reducing heat loss in gasifier. Slagging and fouling are related to ash deposition, which is determined by the coal-ash fusion temperature, chemical composition of coal ash, and boiler operating conditions et al. The coal-ash fusion temperature is a particularly important factor in slagging and fouling. To measure the ash fusion temperature, the ASTM D1857 test is used, not only by thermal power plants and steelmaking companies in South Korea but all over the world. In this study, the fluid temperature (FT) of ASTM D1857 was predicted by Thermo-Mechanical Analysis (TMA). Three bituminous coals (Glencore, Trafigura, Moolarben) and four sub-bituminous coals (KPU, Berau, Jembayan, PRB) were selected for the TMA tests, wherein T25, T50, T75, and T90 were measured. These four temperatures corresponded to shrinkage levels of 25%, 50%, 75%, and 90%, respectively. The T90 of the bituminous coals and T50 of the sub-bituminous coals were similar to the initial deformation temperature (IDT) of ASTM. The T90 of the bituminous coals was greater than 1300°C, and the T90 of the sub-bituminous coals was ∼1250°C. Two FT-prediction equations—for bituminous coal and sub-bituminous coal—were established according to the T25, T50, T75, and T90 relationships of each coal. The FT-prediction equations indicated an average gap of 71°C in the sub-bituminous coals. For the sub-bituminous coals, the average difference was quite low: ∼23°C. The FT-prediction equations matched the FT of ASTM and are useful for determining the ash fusion temperature in a short time.

Qualitative and chemical characteristics of mineral matter in the selected lignite deposits in light of their suitability for clean coal technologies

An analysis of the variability of ash content and chemical composition of coal ash is crucial when assessing the possibility of using this raw material in clean coal technologies (CCS). The paper focuses on chemical, technological and quality characteristics of ash from the combustion of lignite from Polish deposits. Ash content on a dry ash-free basis for the samples from 9 deposits varies from 1 to 50%. The most commonly observed ash content in the studied samples of lignite is in the range between 10–20%. The measured ash melting temperatures from the collected lignite samples have shown that the sintering, softening, melting and flow temperatures, determined in an oxidizing atmosphere (air), are higher than those determined in a reducing atmosphere. In the majority of Polish lignite deposits, the dominant component of ash was SiO2 , followed by CaO. When evaluating the suitability of coal in energy production, with particular emphasis on the combustion and gasification processes, it is also necessary to study the behavior of ash at high temperatures and the impact of ash on the gasification and combustion facilities. Ash fouling and slagging processes, which are heavily dependent on the ash content, composition, melting point and the content of chlorine, phosphorus and sulfur in coal, have a negative effect on the combustion process.

Influence of coal ash properties on compressive behaviour of FA- and BA-based GPC

This paper presents the results of an experimental study on the behaviour of fly ash (FA) and bottom ash (BA) based geopolymer concretes (GPCs) cured at ambient temperature. A total of 11 batches of coal-ash-based GPCs were manufactured. Axial compression tests were carried out to determine the compressive behaviour and strength development of hardened GPCs. Test parameters included the type, particle size and chemical composition of coal ash, the alkaline liquid to binder ratio and concentration of sodium hydroxide solution. The results indicate that the chemical composition of BA has a pronounced influence on the compressive behaviour of GPCs, with concretes manufactured with BA with a higher silicon dioxide/aluminium oxide ratio developing higher strengths. The results also indicate that milling of the coal ash and the increased calcium oxide content of the BA both lead to significant improvements in the compressive strength of GPCs. It was also found that strength gain of ambiently cured coal-ash-based GPCs continues beyond a concrete age of 28 d and is significantly influenced by the type, particle size and chemical composition of the coal ash and the concentration of sodium hydroxide solution.

Experimental Study on Air-Entraining Capability of Fly Ash Mortar

The applicability of fly ash recently used in Japan was evaluated in this paper. The characteristics of 45 batches of fly ashes obtained in Japan in 2007 are evaluated and the results show that there were large differences in physical characteristics due to the degree of grinding of the coal and the chemical composition of coal ash. The recently evaluatiion method of fly ash in Japan is not considered to be suitable by change of methylene blue color because the chemical characteristics of Ph and ORP (oxidation reduction potential) are defferent in each fly ashes. The results of the measurement of air-entraining content in mortar show that there was a tendency when the air-entraining capability reduced with the increase of the Igloss value, the brain specific surface area value, and the BET specific surface area value. The adsorption character of the air-entraining agent can be expressed approximately by the BET adsorption formula. There was a good correlation between the air-entraining content and the BET specific surface area of fly ash, cement and fine aggregate. The high purity of limestone crushed sand with a low specific surface area is suitable for accurately evaluation for higher specific surface area of fly ash.

Prediction of Coal Ash Fusion Temperature by Least-Squares Support Vector Machine Model

Coal ash fusion temperature (AFT) is one important parameter for coal-fired boiler design and evaluation in a power plant. The relationship between coal AFT and the chemical composition of coal ash is rather complex in nature and makes the modeling of AFT difficult. In this work, a least-squares support vector machine (LS-SVM) model, which was based on a dynamically optimized search technique with cross-validation, is developed to predict the coal ash softening temperature (ST). The accuracy of this LS-SVM model was verified by comparison with the experimental AFT data of different types of coal. Further, the comparison of the present LS-SVM model and the traditional models, for example, multilinear regressions (MLR) and multi-nonlinear models (MNR) as well as the artificial neural network (ANN) models, showed that the LS-SVM model was much better to provide the highest generalized accuracy with the mean squared error of 0.0128 and correlation coefficient of 0.9272. Furthermore, based on the LS-SVM model,...

Influence of the composition of coal ash on its flow temperature and on the CSR and CRI values of the coke produced

Two sets of experimental data characterizing the chemical composition of coal ash, its flow temperature t c, and the CSR and CRI values of the coke from such coal are analyzed. The results indicate that the content of four oxides (SiO2, Fe2O3, CaO, and Na2O) may be used to predict t c and also CSR and CRI in mathematical models. Models of the form y = a(I 4) b , where y = t c, CSR, or CRI and I 4 = SiO2/(Fe2O3 + CaO + Na2O), adequately describe the experimental data within the range considered.

HAZARDOUS WASTE: TVA Spill’s Chemical Legacy

When the holding pond at the Tennessee Valley Authority’s (TVA) Kingston coal-burning power plant broke on the morning of 22 December 2008, it released more than 5.4 million yd3—some 50 years’ worth of accumulation—of coal ash slurry into the neighboring lands and the Emory River. High levels of arsenic and mercury in the spilled slurry could pose serious environmental and human health risks, according to the first peer-reviewed assessment of the chemical contamination from this spill, published 1 August 2009 in Environmental Science & Technology. Scientists have studied the chemical composition of coal ash for decades. They have a general understanding of how coal ash constituents travel through the environment but lack data on how spills translate into long-term human and ecologic health hazards. So environmental scientists Avner Vengosh and Laura Ruhl of the Nicholas School of the Environment at Duke University visited Tennessee in the months after the spill to collect samples of coal ash slurry, sediments, and water from various sites along the Emory and Clinch Rivers, which flow into the Tennessee River, the primary source of drinking water for some 410,000 Tennesseans. Data reported by the Tennessee Department of Environment and Conservation showed the ash contained elevated levels of arsenic and mercury. With time, wrote Vengosh and colleagues, as the mass of slurry begins to dry, these toxic elements might become airborne and pose a health threat to local communities. However, investigating whether this is indeed happening would require long-term air monitoring, says Vengosh. Trace elements including arsenic, selenium, lithium, and boron were measured at elevated levels in a tributary of the Emory that was dammed by the spill and turned into a standing pond. The concentration of dissolved arsenic in this pond was as high as 86 μg/L, whereas unaffected upstream waters contained 0.1–0.4 μg/L. Concentrations of these elements were significantly lower at the downstream Emory and Clinch River sites but were above background concentrations, suggesting that leaching of these toxicants was balanced by massive river dilution. Although dilution improved the water quality, it could not control the deposition of ash in the river sediments. The mercury levels in sediments a couple miles downstream of the spill were almost as high as those in the coal ash itself, around 92–130 μg/kg. Anaerobic bacteria living in these sediments could convert this mercury to its more bioaccumulative and toxic form, methylmercury. Frank Huggins, an environmental chemist at the University of Kentucky, isn’t convinced we yet know the real risk to humans and wildlife. The authors use the word “potential,” he notes. “Sure there is always a lot of potential, but . . . the actual risk is a much more difficult topic to address.” Huggins is just beginning to analyze some samples from the spill site for the TVA. He says complementary and longer-term analyses of the elements, their speciation, and how they behave over time and under different physical conditions in sediments and water will reveal the true hazards. Ecotoxicologist William Hopkins of Virginia Polytechnic Institute and State University says future studies will need to investigate which of the trace elements measured by Vengosh and colleagues are bioavailable to biota in the area as well as the severity of any effects resulting from exposure. Some such investigations have already begun. The TVA recently hired Hopkins as a consultant to begin looking at issues of bioaccumulation and toxicity. Similarly, ecophysiologist Shea Tuberty of Appalachian State University is studying how the spill has affected levels of selenium and other elements in fish tissue, and how that in turn affects fish populations. His preliminary work has established baseline selenium levels in local fish populations that are already close to levels that cause reproductive failure in most aquatic species—possibly the result of decades of selenium leaching from the holding ponds, he says. Vengosh and colleagues agree that much more research is needed to evaluate the long-term environmental and human health effects of the spill. With the support of a new project funded by the National Science Foundation, the Duke team will continue to investigate these effects.

Predicting coal ash fusion temperature based on its chemical composition using ACO-BP neural network

Coal ash fusion temperature is important to boiler designers and operators of power plants. Fusion temperature is determined by the chemical composition of coal ash, however, their relationships are not precisely known. A novel neural network, ACO-BP neural network, is used to model coal ash fusion temperature based on its chemical composition. Ant colony optimization (ACO) is an ecological system algorithm, which draws its inspiration from the foraging behavior of real ants. A three-layer network is designed with 10 hidden nodes. The oxide contents consist of the inputs of the network and the fusion temperature is the output. Data on 80 typical Chinese coal ash samples were used for training and testing. Results show that ACO-BP neural network can obtain better performance compared with empirical formulas and BP neural network. The well-trained neural network can be used as a useful tool to predict coal ash fusion temperature according to the oxide contents of the coal ash.

06/01714 Characterization and quantification of uncertainty in solid oxide fuel cell hybrid power plants: Subramanyan, K. and Diwekar, U. M. Journal of Power Sources, 2005, 142, (1–2), 103–116

The mineralogy of clay-rich mineral matter isolated from a range of Australian bituminous coals has been evaluated in quantitative terms from X-ray powder diffraction (XRD) patterns using a Rietveld-based data processing technique. The chemical composition of coal ash derived from this mineral matter has been calculated and compared to the directly determined composition of the ash prepared from the same coal samples. Although there are some minor differences due in part to uncertainty regarding the actual composition of several minerals, the compositions indicated by the two methods show a relatively high correlation, suggesting that the Rietveld technique provides mineralogical analyses that are consistent with independently determined chemical data. Comparison of the normalised clay mineral percentages from the Rietveld analysis to quantitative interpretations based on a peak intensities in glycolated and heat-treated oriented aggregates of the respective clay fractions also shows a high correlation, confirming mutual consistency of the two different mineralogical analysis methods. Such quantitative mineralogical data are significant to a range of coal exploration, mining and utilization activities, including seam correlation, material handling and ash and slag formation in combustion processes.

05/00081 Petrological and mineralogical characterizations and chemical composition of coal ashes from power plants in Yanzhou mining district, China: Liu, G. et al. Fuel Processing Technology, 2004, 85, (15), 1635–1646

05/00081 Petrological and mineralogical characterizations and chemical composition of coal ashes from power plants in Yanzhou mining district, China: Liu, G. et al. Fuel Processing Technology, 2004, 85, (15), 1635–1646

Petrological and mineralogical characterizations and chemical composition of coal ashes from power plants in Yanzhou mining district, China

The Yanzhou mine district, located southwest of Shandong province, is about 1300 km 2, with the more than 8×10 9 tons of proven reserve sources of coal and 10 big power plants. Up to now, a great amount of coal ashes and waste rocks is stockpiled in the area, and has influenced the environment of the mine area. In this paper, the authors obtained raw coal and ash samples from three power plants; analyzed the enrichment and concentration of trace elements Pb, Zn, Th, Cu, As, V, Cl, and F in coal ashes; and studied petrological and mineralogical characterizations and the chemical composition of coal ashes. The aim of this work is to provide scientific basis for comprehensive utilization and reduction of environmental pollution in the future. On the basis of the study of petrologic, chemical, and trace elements in coal ashes, it was concluded that the ash yield of coals is the residue derived from inorganic and organic matter during incineration and combustion of coal, and the major composition of coal ashes is as follows: crystalline, glassy, and organic matter (incompletely combusted carbon). The main constituents of ashes are SiO 2 and Al 2O 3, with low contents of Fe 2O 3 and CaO, and little amounts of SO 3, P 2O 5, Na 2O, K 2O, and TiO 2. The higher concentration of the compounds is in fly ash, whereas the lower one is in bottom ash. The mass fractions of Pb, Cu, Zn, As, V, and Th were higher in ashes than that in raw coal. The mass fraction of these elements in fly ash is higher than that in bottom ash. Therefore, the smaller the ash particle size is, the higher is the mass fraction of the trace elements Pb, Cu, Zn, As, V, and Th. However, the mass fraction of elements Cl and F is lower in ashes than that in raw coal, and the mass fraction of Cl and F in ashes is positive in the particle size of ashes.

Characteristics of coal ashes in Yanzhou mining district and distribution of trace elements in them

In the process of combustion of coal organic and inorganic materials in it will undergo a complex variation. Part of them will become volatiles and, together with coal smoke, enter into atmosphere, some will remain in micro-particulates such as ash and dust and find their way into atmosphere in the form of solid particles, and the rest will be retained in ash and slag. Coal ashes are the residues of organic and inorganic substances in coal left after coal combustion and the composition of coal ashes is dependent on that of minerals and organic matter in coal. This paper deals with the chemical composition of coal ashes, the distribution of trace elements in them and their petrological characteristics, and also studies the relationship between the yield of coal ashes and the distribution of trace elements. In addition, a preliminary study is also undertaken on the factors that affect the chemical composition of coal ashes. As viewed from the analyses of coal ash samples collected from the Yanzhou mining district, it can be seen clearly that coal ashes from the region studied are composed chiefly of crystalline materials, glassy materials and uncombusted organic matter and the major chemical compositions are SiO2, Al2O3, Fe2O3, and CaO, as well as minor amounts of SO3, P2O5, Na2O, K2O and TiO2. During the combustion of coal, its trace elements will be redistributed and most of them are enriched in coal ashes. At the same time, the concentrations of the trace elements in flying ash are much higher than those of bottom ash, i.e., with decreasing particle-size of coal ashes their concentrations will become higher and higher. So the contents of trace elements are negatively proportional to the particle-size of coal ashes. There has been found a positive correlation between the trace elements Th, V, Zn, Cu and Pb and the yield of coal ashes while a negative correlation between Cl and the yield of coal ashes.

Quantitative X-ray powder diffraction analysis of clay minerals in Australian coals using Rietveld methods

The mineralogy of clay-rich mineral matter isolated from a range of Australian bituminous coals has been evaluated in quantitative terms from X-ray powder diffraction (XRD) patterns using a Rietveld-based data processing technique. The chemical composition of coal ash derived from this mineral matter has been calculated and compared to the directly determined composition of the ash prepared from the same coal samples. Although there are some minor differences due in part to uncertainty regarding the actual composition of several minerals, the compositions indicated by the two methods show a relatively high correlation, suggesting that the Rietveld technique provides mineralogical analyses that are consistent with independently determined chemical data. Comparison of the normalised clay mineral percentages from the Rietveld analysis to quantitative interpretations based on a peak intensities in glycolated and heat-treated oriented aggregates of the respective clay fractions also shows a high correlation, confirming mutual consistency of the two different mineralogical analysis methods. Such quantitative mineralogical data are significant to a range of coal exploration, mining and utilization activities, including seam correlation, material handling and ash and slag formation in combustion processes.

97/00094 Relationship between fusibility and mineral and chemical composition of coal ashes

97/00094 Relationship between fusibility and mineral and chemical composition of coal ashes

Influence of mineral and chemical composition of coal ashes on their fusibility

Influence of mineral and chemical composition of coal ashes on their fusibility