Composition Of Coal Ash Research Articles

Determining the ash composition of coal by X-ray spectrometry

For timely determination of the ash composition in coal, chemical analysis has been replaced by X-ray analysis using a Spectroscan MAX-GV spectrometer at OAO Koks. That permits prompt determination of the ash basicity, which affects the reactivity and hot strength of the coke. The plant’s coal purchases are optimized to stabilize and improve the coke’s CSR and CRI values.

Influence of discard mineral matter on slag–liquid formation and ash melting properties of coal – A FACTSAGETM simulation study

The ash fusion temperature (AFT) profile of a coal is one of the parameters currently widely used in coal marketing and utilization to assess coal ash fusibility and melting characteristics, and to predict the melting behaviour of the coal ash in coal conversion processes. However, the flow temperature of a specific coal source alone does not provide enough insight into the slag formation behaviour at temperatures below the flow temperature. It has been demonstrated that ash flow temperature can be correlated with FACTTM equilibrium calculations, and that such equilibrium calculations provide useful information regarding the phase transitions that take place well below the final ash flow temperature as indicated by a standard AFT analysis.The overall objective of this study is to use the properties of different types of mineral matter and to simulate the effect on slag–liquid formation and ash flow temperature for individual mineral types as well as blends. A thermo-equilibrium simulation approach based on FACTSAGE™ was applied.The slag–liquid flow temperature simulations for coal and individual mineral types compared favourably with the actual measured ash flow temperature and are within the experimental error of an AFT analysis (±30°C). The slag formation of coal showed a more gradual increase in the amount of slag formed over a temperature compared to specific individual mineral types. This can be explained by the ash composition of coal which has a more even distribution of minerals compared to mineral types that have a significantly high SiO2 or CaO content respectively. From this result it is also confirmed that flow temperature properties are non-additive and cannot be calculated from a weighted average principle. It was shown by FACTSAGE™ modelling that the addition of a discard blend to this specific coal source will have no significant effect on the flow temperature of the blend. The FACTSAGE™ modelling showed that the amount of slag–liquid of the ash that was studied is highly dependent on the temperature to which the ash is exposed. For example, the amount of slag–liquid can double by only increasing the operating temperature of a process within a small window of as little as 100°C. This could explain why coal conversion processes such as combustion, and entrained flow gasification, can experience periods of unstable operation despite an apparent constant feed coal quality being observed with very little variation in ash flow temperature. The important parameter is thus not the actual flow temperature, but rather the amount of slag formation at a specific operating temperature.The inability of the standard AFT analysis to reflect changes in ash melting behaviour with relatively small variations in ash composition was highlighted in this study. Even though variation in mineral matter content of the coal blend may have limited or no effect on the actual ash flow temperature, it can significantly change the amount of slag present in the ash bed. The variation in operating temperature can also result in a significant change in slag formation (positive or negative) which is not always reflected by the standard AFT analysis method.It is concluded that FACTSAGETM thermodynamic modelling of ash melting behaviour provides a method to address the shortcomings of the standard AFT determination, which can add significant value and insight towards the improvement of the operational stability of coal conversion processes such as combustion and gasification.

서천화력발전소 매립 석탄재로부터 제조한 다양한 조성비의 지오폴리머와 그 특성의 평가

Pond ash produced from Seochun Power Station was quantitatively characterized to manufacture geopolymers with a range of Si/Al compositional ratios. Mix consistency was kept nearly constant for comparing the compressive strengths of geopolymers. The amorphous composition of coal ash was determined using XRF and quantitative X-ray diffraction. Different mix compositions were used in order to achieve Si/Al ratios of 2.0, 2.5 and 3.0 in the geopolymer binder. Geopolymers synthesized from coal ash with a Si/Al ratio of 3.0 exhibited the highest compressive strength in this study. It was found that geopolymers activated with aluminate produced different microstructure from that of geopolymers activated with silicate. High silica in alkali activators produced the finegrained microstructure of geopolymer gel. It was also found that high compressive strength was related to low porosity and a dense, connected microstructure. The outcome of the reported experiment indicates that quantitative formulation method made it possible to choose suitable activators for achieving targeted compositions of geopolymers and to avoid efflorescence.

Influence of Sewage Sludge Addition on Huainan Coal Ash Fusion Characteristics

The effects of sewage sludge addition on Huainan coal ash fusion characteristics were investigated by X-ray fluorescence (XRF) and X-ray diffraction (XRD). The experimental results showed that the ash chemical composition of Huainan coal ash was rich in SiO2and Al2O3, while the mass fraction CaO in sewage sludge was over 40%. Accordingly, the ash melting temperature of Huainan coal was higher than 1500°C while that of sewage sludge was lower than 1250 °C. The ash melting temperature of coal blending with sewage sludge fell with increasing mass fraction of sewage sludge in the range between 0 and 0.7. The aluminosilicate clay minerals with high fusion temperature contained in Huainan coal can be bond with CaO and iron oxides rich in sewage sludge forming low temperature eutectic system, it led to the reducing fusing temperature of Huainan coal mixing with sewage sludge.

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.

Relationship between coal ash composition and ash fusion temperatures

Coal ash fusion characterization and the ash fusion temperatures (AFTs) are important parameters for coal industry. Previous research has proved that the AFTs are correlated with the chemical composition of coal ash samples. In this paper, a five-component SiO2–Al2O3–CaO–Fe2O3–K2O system is set. The AFTs of 34 synthetic ashes were measured in a carbon atmosphere, and the trends of the AFTs analyzed. Different from other studies, X-ray diffraction (XRD) and scanning electron microscope (SEM) were combined to explore the relationships between the measured AFTs and the mineral composition, morphology and microstructure of ash samples. Furthermore, the effect of the element valence state is also taken into account and X-ray photoelectron spectrometer (XPS) is used to analyze it firstly. The results show that the AFTs decrease with the increasing Fe2O3 content and silica-to-alumina (S/A) ratio. However, for the effect of CaO content, the AFTs reach a minimum value and then increase once again. Furthermore, the AFTs show no significant change as the K2O content varies. At last, all the conclusions found from the synthetic samples are also applicable for the seventeen bituminous coal ashes collected locally and abroad.

Iron Transformation and Ash Fusibility during Coal Combustion in Air and O2/CO2 Medium

Little work has been performed on the transformation of iron and ash fusibility during oxy-coal combustion, which is of great significance to assessing ash deposition propensity. A high-iron bituminous coal was burnt at 1300 °C in a laboratory drop-tube furnace under four conditions: (1) 21 vol % O2/79 vol % N2 (air-firing), (2) 21 vol % O2/79 vol % CO2 (oxy-firing), (3) 27 vol % O2/73 vol % CO2 (oxy-firing), and (4) 32 vol % O2/68 vol % CO2 (oxy-firing). The bulk ash samples were subjected to X-ray fluorescence and Mossbauer spectroscopic analyses. The effects of changing from air combustion to O2/CO2 combustion and the effects of varying the O2 level in O2/CO2 combustion on iron transformation and ash fusibility were investigated. The results show that varying the combustion condition has insignificant effects on the elemental composition of coal ashes but has appreciable effects on the relative proportions of iron combustion products that were identified as hematite, magnetite, and Fe–glass phases. Thi...

EFFECT OF CHEMICAL COMPOSITION ON SINTERING BEHAVIOR OF JINCHENG COAL ASH UNDER GASIFICATION ATMOSPHERE

In order to obtain detailed understanding of coal ash sintering behavior, a series of experiments have been done on the effect of Jincheng coal ash composition on sintering temperature under gasification atmosphere by the pressure-drop technique. The mineral transformations within its sintering temperature range are simulated by the thermodynamic equilibrium calculation module of FactSage to better understand the experiment results. These results show that the sintering temperature decreases initially, and then rises with increasing SiO2. On the whole, the sintering temperatures decrease with increase in Fe2O3, CaO, Na2O, and K2O. Their effects are quite similar, but the degrees are different. As MgO increases, the sintering temperature decreases. However when MgO is increased above a certain limit, the effect of MgO on the sintering temperature is not obvious.

An Evaluation on the Physical and Chemical Composition of Coal Combustion Ash and Its Co-Placement with Coal-Mine Waste Rock

In the last few decades, the utilization of coal to generate electricity was rapidly increasing. Consequently, the production of coal combustion ash (CCA) as a by-product of coal utilization as primary energy sources was increased. The physical and geochemical characteristics of CCA were site-specific which determined by both inherent coal-source quality and combustion condition. This study was intended to characterize the physical, chemical and mineralogical properties of a coal-combustion ash (CCA) from a site specific power plant and evaluate the leachate characteristic of some scenario on the co-placement of CCA with coal-mine waste rock. The physical properties such as specific gravity, dry density, porosity and particle size distribution were determined. Chemically, the CCA sample is enriched mainly in silica, aluminum, iron, and magnesium along with a little amount of calcium and sodium which includes in the class C fly ash category. Moreover, it is found that the mineral phases identified in the sample were quartz, mullite, aragonite, magnetite, hematite, and spinel. Co-placement experiment with mudstone waste rock shows that the CCA, though it has limited contribution to the decreasing permeability, has important contributed to increase the quality of leachate through releasing higher alkalinity. Moreover, addition of CCA did not affect to the increase of the trace metal element in the leachate. Hence, utilization of CCA by co-placement with coal mine waste rock in the dumping area is visible to be implemented.

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.

Prevention of Trace and Major Element Leaching from Coal Combustion Products by Hydrothermally-Treated Coal Ash

The most important structural components of coal ash obtained by coal combustion in “Nikola Tesla A” power plant located near Belgrade (Serbia) are amorphous alumosilicate, α-quartz, and mullite. The phase composition of coal ash can be altered to obtain zeolite type NaA that crystallizes in a narrow crystallization field (SiO2/Al2O3; Na2O/SiO2; H2O/Na2O ratios). Basic properties (crystallization degree, chemical composition, the energy of activation) of obtained zeolites were established. Coal ash extracts treated with obtained ion-exchange material showed that zeolites obtained from coal ash were able to reduce the amounts of iron, chromium, nickel, zinc, copper, lead, and manganese in ash extracts, thus proving its potential in preventing pollution from dump effluent waters.

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.

Characterization of Low-temperature Coal Ash Behaviour under Atmospheric Pressure

The chemical composition of the virgin coal from Korba coal fields,South central India is determined with the help of Fourier transform Infrared spectroscopy. The process of burning of carbon rich coal is carried out from a temperature of 200˚C to 700˚C under atmospheric pressure and controlled air in a muffle furnace. The resultant coals are examined with FTIR. The result shows that the residence time of coal ash at high temperature has considerable influence on the composition of coal ash and little effect on the amount of unburned carbon. With increase of temperature the oxygenated groups are released mainly as H2O and CO, but also as aldehydes, alcohols and acids. The silicate and quartz mineral content remains the same throughout heating.

Mineral and chemical composition of Yanzhou coal and coal ash (China), with volatilisation behaviour to 1000°C

The mineral and chemical composition of the Yanzhou coal and coal ash (China), and the volatilisation behaviour of 16 elements (Al, As, Ca, Cl, Cu, F, Fe, K, Mg, Na, P, Pb, S, Si, Ti, Zn) during gradual heating of this coal (350, 650, 815 and 1000°C) were studied. This high volatile bituminous coal has low moisture and S contents, moderate ash yield, and high calorific value. The coal ashes belong to SiO2–Al2O3–Fe2O3–CaO system abundant in aluminosilicates, as the contents of Fe oxides are significantly higher than the sum of alkaline earth oxides. Some trace elements such as Pb and Zn in coal and Cu, Pb, and Zn in coal ash are slightly enriched in comparison with the Clarke concentrations. The minerals identified in coal (in decreasing order of abundance) are quartz, kaolinite, illite, pyrite+marcasite, calcite, and gypsum, and, to a lesser extent, montmorillonite, dolomite and pyrrhotite. The inorganic phases in coal ash (350–1000°C) are aluminosilicate glass, quartz, destructed clay minerals, mullite, hematite, magnetite, plagioclase, anhydrite and lime. The volatilisation behaviour of elements during coal combustion shows that the emission ratios of the elements volatilised normally increase gradually with increasing temperatures. The elements studied can be divided into four groups according to their volatilisation at the maximum temperature: high volatile Cl>F (86–90%); moderate volatile S>K>Pb>Cu>Zn (24–42%); slight volatile (Mg,As)>Ca>Si (15–17%); and non-volatile elements such as Al, Fe, Na, P and Ti. The reason for the volatilisation behaviour of the above elements is discussed based on their modes of occurrence in coal and coal ash. The results show that significant quantities of elements such as Cl, Cu, F, K, Pb, S and Zn could be volatile during combustion of the Yanzhou coal in TPSs and some of them may be of environmental concern.

Characterization of low-temperature coal ash behaviors at high temperatures under reducing atmosphere

The coal ash obtained at 815 °C under oxidizing atmosphere was further treated at 1300 °C and 1400 °C under reducing atmosphere. The resultant ashes were examined by XRD, SEM/EDX and FTIR. The results show that the residence time of coal ash at high temperatures has considerable influences on the compositions of coal ash and little effect on the amounts of unburned carbon. The amorphous phase of mineral matters increases with the increasing temperature. The FTIR peaks due to presence of different functional groups of minerals support the findings of XRD, and supply additional information of amorphous phase which cannot be detected in XRD. The ash samples generated from a fixed bed reactor during char gasification were also studied with FTIR. The temperatures of char preparation are responsible for the different transformation of minerals during high temperature gasification.

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.

05/02222 Importance of coal ash composition in protecting the boiler against chlorine deposition during combustion of chlorine-rich biomass

05/02222 Importance of coal ash composition in protecting the boiler against chlorine deposition during combustion of chlorine-rich biomass

Formation of SiO and Related Si-Based Materials Through Carbothermic Reduction of Silica-Containing Slag

Silicon based nanoparticulates of various composition and morphology have been produced by smelting reduction method which includes a carbothermic reduction of SiO2–Al2O3–CaO starting materials to SiO vapor at 2073 K and transfer of the vapor with a carrier-gas to cooler surfaces inside the experimental reactor where the nanoparticulates were deposited. The chemical composition of the starting materials was matched to the basic composition of silica-rich coal ash which is considered as a potential source of Si in this study. Special emphasis was placed upon examining the degree of SiO2 reduction from starting materials, purity and morphology of the as-obtained nanomaterials. It is shown that up to 20% of Si can be converted from the silica-based melt into rounded nanoparticles, nanoparticle chains and nanowires containing Si,O and C in variable proportions depending on deposition temperature and gas flow conditions. The diameter of nanoparticulates was estimated to be in the range of 20∼100 nm. The nanoparticles and chains were found to be deposited at lower temperature locations (293∼1320 K) while the nanowires were obtained at higher temperatures (1320∼1570 K). There was a tendency for an increase in Si concentration in order of nanowires, nanoparticles chains and nanoparticles. The carbon concentration, on the contrary, was much higher in nanowires as compared to that in nanoparticles. Although the degree of SiO2 reduction from silica-containing melt to SiO vapor is limited because a part of SiO2 reacts with C producing SiC, its good controllability, high productivity and possibility for processing cheap starting materials make the smelting reduction a very attractive technique for production of silicon based nanostructured materials.