From in-situ coal to fly ash: a study of coal mines and power plants from Indiana

This paper presents data on the properties of coal and fly ash from two coal mines and two power plants that burn single-source coal from two mines in Indiana. One mine is in the low-sulfur (<1%) Danville Coal Member of the Dugger Formation (Pennsylvanian) and the other mines the high-sulfur (>5%) Springfield Coal Member of the Petersburg Formation (Pennsylvanian). Both seams have comparable ash contents (11%). Coals sampled at the mines (both raw and washed fractions) were analyzed for proximate/ultimate/sulfur forms/heating value, major oxides, trace elements and petrographic composition. The properties of fly ash from these coals reflect the properties of the feed coal, as well as local combustion and post-combustion conditions. Sulfur and spinel content, and As, Pb and Zn concentrations of the fly ash are the parameters that most closely reflect the properties of the source coal.     

Characterization of fly ash from a power plant and surroundings by micro-Raman spectroscopy

Fly ash samples were collected from a Portuguese power plant that burns low-sulphur coals from South Africa, U.S.A., Colombia, and Australia. The fly ashes were collected from the hoppers of the economizers, air heaters, electrostatic precipitators, and from the stack. The power plant air monitoring system was also sampled. The fly ash characterization was conducted by micro-Raman spectroscopy (MRS). The micro-Raman spectroscopic analysis permitted an efficient identification and characterization of different inorganic and organic materials present in fly ash: quartz, hematite, magnetite, calcite, glass, aluminium and calcium oxides, and different types of organic constituents.The study of the structural evolution of the unburned carbon/char material during their path through the power plant, though the use of Raman spectra and Raman parameters reveal that despite the high temperatures they reached, these materials are still structurally disordered. However, a structural evolution occurs in the char from the economizer up to the electrostatic precipitators where the char is structurally more disordered.The different features of the Raman spectra observed for carbon particles collected from the stack, together with the high range of variation of the Raman parameters, confirm the existence of different carbon particles in the stack, i.e., char and others (probably soot).The filters from the surroundings contain a variety of carbon particles with Raman parameters different from the ones obtained in the fly ash hoppers and stack. These are diesel particles as indicated by the values of W_D1, FWHM_D1, FWHM_G, W_G and ID1/IG obtained.     

Impact of co-combustion of petroleum coke and coal on fly ash quality: Case study of a Western Kentucky power plant

Petroleum coke has been used as a supplement or replacement for coal in pulverized-fuel combustion. At a 444-MW western Kentucky power station, the combustion of nearly 60% petroleum coke with moderate- to high-sulfur Illinois Basin coal produces fly ash with nearly 50% uncombusted petroleum coke and large amounts of V and Ni when compared to fly ash from strictly pulverized coal burns. Partitioning of the V and Ni, known from other studies to be concentrated in petroleum coke, was noted. However, the distribution of V and Ni does not directly correspond to the amount of uncombusted petroleum coke in the fly ash. Vanadium and Ni are preferentially associated with the finer, higher surface area fly ash fractions captured at lower flue gas temperatures. The presence of uncombusted petroleum coke in the fly ash doubles the amount of ash to be disposed, makes the fly ash unmarketable because of the high C content, and would lead to higher than typical (compared to other fly ashes in the region) concentrations of V and Ni in the fly ash even if the petroleum coke C could be beneficiated from the fly ash. Further studies of co-combustion ashes are necessary in order to understand their behavior in disposal.     

采煤对浅层地下水环境的影响及矿井水生态利用分析

黄河流域中上游矿区煤?水矛盾突出,煤炭开采对地下水环境造成一定的破坏。基于此,以鄂尔多斯盆地北部侏罗纪煤田榆神府矿区为研究区,在野外调查、数据分析、室内测试的基础上,分析研究区矿井水的量质特征,揭示煤炭高强度开采对地下水环境的影响,并开展矿井水生态利用研究。结果表明:研究区矿井富水系数在0.23~2.28,平均为0.91,评估2020年区内矿井排水量高达4.70亿m3,受采掘活动影响,浅埋煤层开采区地下水位下降趋势明显;区内矿井水出现不同程度的污染组分超标现象,主要超标指标为化学需氧量(COD)、Na+、SO₄ 2?、溶解性总固体(TDS),未处理的矿井水外排将会污染区内地下水环境;研究区浅层地下水超限的水质指标主要为NO₃-N,与矿井水超限水质指标差别较大,反映出浅层地下水水质受采矿活动影响较小;提出矿井水浅层回灌和矿井水生态灌溉2种模式开展研究区矿井水的生态利用,矿井水回灌对矿井水中的溶解性有机碳、色度具有较好的去除效果,回灌后出水满足Ⅲ类地下水限值;浅埋煤矿矿井水具有作为矿区生态修复灌溉用水的较好潜力,中深埋煤矿和深埋煤矿矿井水不适宜作为灌溉用水。研究结果为我国西部煤矿区水资源保护和生态修复提供重要依据。      

Sulfur and carbon isotope geochemistry of coal and derived coal-combustion by-products: An example from an Eastern Kentucky mine and power plant

The isotopic compositions of S (δ³⁴S) and C (δ¹³C) were determined for the coal utilized by a power plant and for the fly ash produced as a by-product of the coal combustion in a 220-MW utility boiler. The coal samples analyzed represent different lithologies within a single mine, the coal supplied to the power plant, the pulverized feed coal, and the coal rejected by the pulverizer. The ash was collected at various stages of the ash-collection system in the plant. There is a notable enrichment in ³⁴S from the base to the top of the coal seam in the mine, with much of the variation due to an upwards enrichment in the δ³⁴S values of the pyrite. Variations in δ³⁴S and in the amount of pyritic S in the coal delivered to the plant show that there was a change of source of coal supplied to the plant, between week one and week two of monitoring, supporting a previous study based on metal and sulfide geochemistry for the same plant. The fly ash has a more enriched δ³⁴S than the pulverized coal and, in general, the δ³⁴S is more enriched in fly ashes collected at cooler points in the ash-collection system. This pattern of δ³⁴S suggests an increased isotopic fractionation due to temperature, with the fly ash becoming progressively depleted in ³⁴S and the flue gas S-containing components becoming progressively enriched in ³⁴S with increasing temperatures. Substantially less variation is seen in the C isotopes compared to S isotopes. There is little vertical variation in δ¹³C in the coal bed, with δ¹³C becoming slightly heavier towards the top of the coal seam. An 83–93% loss of solid phase C occurs during coal combustion in the transition from coal to ash owing to loss of CO₂. Despite the significant difference in total C content only a small enrichment of 0.44–0.67‰ in ¹³C in the ash relative to the coal is observed, demonstrating that redistribution of C isotopes in the boiler and convective passes prior to the arrival of the fly ash in the ash-collections system is minor.     

Mobility of heavy metals from coal fly ash

The mobility of Cd, Co, Cu, Ni, Pb, Sb, and Zn from six different coal-fired power plant fly ashes that show a wide compositional range was examined using a sequential extraction procedure in order to assess their mobility when these wastes are ponded or landfilled. The extraction sequence was as follows: (1) water extractable, (2) cation exchangeable (CH₃COONH₄ at pH 7), (3) surface oxide-bound cations (CH₃COONH₄ at pH 5), (4) Fe oxide-bound cations (HONH₃Cl), and (5) residual (HF, HCl, HNO₃, 211). The heavy metal contents in the extraction solutions were determined by anodic (Cd, Cu, Pb, Sb, and Zn) and cathodic (Ni and Co) stripping voltammetry. The results reveal differences in the total contents of the selected trace elements among the fly ash samples, which must be related to differences in coal composition and combustion technology. The extractable fraction under natural conditions ranges from 1.5 to 36.4 percent of the total element content. Cadmium, Co, Cu, and Zn show the highest extractable fraction (10.8–18.9 percent on average). Cadmium is the most easily water-extractable element, while Co, Cu, and Zn increase their mobility as the severity of the extraction increases. Cobalt, Ni, Pb, and Zn are mainly associated with the surface oxide-bound and Fe oxide-bound fractions. Nickel, Pb, and Sb have low mobility potentials (5.3–6.6 percent as extractable fraction), but Sb presents a relatively high water-extractable fraction.     

Progression in sulfur isotopic compositions from coal to fly ash: Examples from single-source combustion in Indiana

Sulfur occurs in multiple mineral forms in coals, and its fate in coal combustion is still not well understood. The sulfur isotopic composition of coal from two coal mines in Indiana and fly ash from two power plants that use these coals were studied using geological and geochemical methods. The two coal beds are Middle Pennsylvanian in age; one seam is the low-sulfur (< 1%) Danville Coal Member of the Dugger Formation and the other is the high-sulfur (> 5%) Springfield Coal Member of the Petersburg Formation. Both seams have ash contents of approximately 11%. Fly-ash samples were collected at various points in the ash-collection system in the two plants. The results show notable difference in δ³⁴S for sulfur species within and between the low-sulfur and high-sulfur coal. The δ³⁴S values for all sulfur species are exclusively positive in the low-sulfur Danville coal, whereas the δ³⁴S values for sulfate, pyritic, and organic sulfur are both positive and negative in the high-sulfur Springfield coal. Each coal exhibits a distinct pattern of stratigraphic variation in sulfur isotopic composition. Overall, the δ³⁴S for sulfur species values increase up the section in the low-sulfur Danville coal, whereas they show a decrease up the vertical section in the high-sulfur Springfield coal. Based on the evolution of δ³⁴S for sulfur species, it is suggested that there was influence of seawater on peat swamp, with two marine incursions occurring during peat accumulation of the high-sulfur Springfield coal. Therefore, bacterial sulfate reduction played a key role in converting sulfate into hydrogen sulfide, sulfide minerals, and elemental sulfur. The differences in δ³⁴S between sulfate sulfur and pyritic sulfur is very small between individual benches of both coals, implying that some oxidation occurred during deposition or postdeposition.The δ³⁴S values for fly ash from the high-sulfur Springfield coal (averaging 9.7‰) are greatly enriched in ³⁴S relative to those in the parent coal (averaging 2.2‰). This indicates a fractionation of sulfur isotopes during high-sulfur coal combustion. By contrast, the δ³⁴S values for fly-ash samples from the low-sulfur Danville coal average 10.2‰, only slightly enriched in ³⁴S relative to those from the parent coal (average 7.5‰). The δ³⁴S values for bulk S determined directly from the fly-ash samples show close correspondence with the δ³⁴S values for SO₄^− 2 leached from the fly ash in the low-sulfur coal, suggesting that the transition from pyrite to sulfate occurred via high-temperature oxidation during coal combustion.     

Risk assessment of bottom ash from fuel oil power plant of Italy: mineralogical,chemical and leaching characterization

The main aim of the present study is to contribute to the field of environmental research by providing new data on bottom ash samples derived from an oil power plant located in Southern Italy. To achieve this purpose, the mineralogical and chemical properties of representative bottom ash samples were investigated through the integrated employment of different analytical techniques, i.e., X-ray powder diffraction, scanning electron microscopy, X-ray fluorescence and atomic absorption spectrometry. The obtained experimental results show that quartz, alunogen, rhomboclase and potassium hydrogen silicate are the major crystalline phases of all the analyzed samples. Furthermore, the revealed main ash constituents are SiO₂ and SO₃, with low contents of Fe₂O₃ and Al₂O₃, and little amounts of CaO, Na₂O, K₂O, MgO, P₂O₅ and TiO₂. Among the trace elements, very high amounts of heavy metals, i.e., V, Cr, Ni, La, Pb and Mo, were detected. The comparison of the obtained heavy metal abundance data with those reported in the literature highlights significant differences. Leaching test evidenced V, Ni and Cr values that make these ashes a potential contamination source for groundwater quality and for soil, nearby the ash disposal landfills area. All the obtained findings show that these materials are highly harmful for the human health, with a greater extent for the heavy metal concentrations.     

An approach to the ecological characterization of arid and semiarid basins

A morphometric study of 61 sub-basins of the River Segura basin (SE Spain) enables us to attribute ecological processes in streams of these arid and semiarid watersheds to altered patterns of discharge resulting from human activity. Methods used are compared to other, commonly used limnological indexes.     

Analysis of influence of the power plant ash storage yard on groundwater environment

The fluoride contained in the filter liquor produced by fly ash in the thermal power plant which takes the coal as fuel can lead to groundwater pollution. Therefore, it is of great significance to study the migration characteristics of the pollutants in groundwater, in order to control and prevent the groundwater fluoride pollution. By adopting the numerical modeling method, this paper takes the ash-storage yard of Shahe Power Plant in Xingtai City as an example, to study the characteristics of fluoride migration in phreatic water, and establish a two-dimensional groundwater flow and water quality model on the basis of the hydrogeological condition analysis in this study area. Meanwhile, based on the Vmodflow software, the migration regulation of the fluoride in groundwater has been simulated. Because the phreatic aquifer of this area belonging to the Shahe alluvial-diluvial sediments and with a coarse lithology as well as high permeability, the migration and diffusion ability of the fluoride in this area is relatively strong. It turns out that the longest migration distance in 5 years is 892 m and that within 8 years is 1 515 m.     

Geochemical studies to delineate topsoil contamination around an ash pond of a coal-based thermal power plant in India

In the present study, an attempt was made to delineate soil contamination around the ash pond of a coal-based thermal power plant. The topsoil in the study area was found to be contaminated to varying degrees from ash disposal. The soil drawn from various profiles was largely contaminated by ash fall out, predominantly in the prevalent wind direction. Pb, Zn, Cu, Ni, Co, Mn, Cr, V and Ba were found to be enriched in the topsoil around the ash pond with respect to the crust as well as the background, while Mn, V, Cr, Co and Ni were enriched compared to their maximum permissible concentrations prescribed for agricultural soils. These observations have been further strengthened from the contamination index map and lognormal distribution pattern of the elements. As a consequence of this contamination, many of the important physicochemical properties of topsoil in the direction of the wind have been modified significantly.Electronic Supplementary Material Supplementary material is available in the online version of this article at     

富拉尔基热电总厂粉煤灰敏感性指标的试验研究

以富拉尔基热电总厂粉煤灰为研究对象，对其与水和温度有关的各项敏感性指标－渗透稳定性、软化特性、冻融强度损失和冻胀性进行了试验研究。     

测井曲线判识构造软煤技术预测煤与瓦斯突出

基于构造软煤与硬煤的物性差异,分析构造软煤分层在测井曲线上的响应特征;根据煤层段测井曲线的形态特征,将揭露区钻孔测井曲线初步判识的结果同钻孔邻近巷道煤壁观测的结果进行对比、验证,形成了一套测井曲线判识构造软煤技术。利用该技术获取了研究区的构造软煤资料,对研究区的煤与瓦斯突出危险性区域进行了预测。     

The occurrence of gold in fly ash derived from high-Ge coal

We present the first data on the mode of occurrence of Au in fly ashes from the Wulantuga and Lincang power plants in China, which burn high-Ge coal. Gold occurs as fine-grained drop-like particles with a size of n*0.01–0.2 μm on the surface of the glass globules. These features of the Au particles are proof for Au condensation from the gas phase and deposition on the surface of fly ash in the cooler zone of the electrostatic precipitator and baghouse filter.     

粉煤灰对低质量浓度铀的吸附研究

简单介绍了粉煤灰的基本性质、吸附特性和处理废水的机理。根据粉煤灰的物理和化学吸附特性,研究了其对低质量浓度铀溶液吸附效果,分析了吸附容量及影响因素。实验表明,t=0～76h时,铀的质量浓度急速下降,吸附效果明显,最大时吸附量可达到82%。随着吸附的进行,溶液pH值增大,而溶液中Fe^3＋、∑Fe则在减少。     

Measurement of parameters impacting methane recovery from coal seams

Summary This paper describes the behaviour of coalbeds as gas reservoirs and discusses the results of a study carried out to establish the effect of release of methane on gas flow behaviour of coal. Experimental work consisted of microscopy, establishing adsorption/desorption isotherms, and monitoring changes in the volume of coal matrix with increasing and decreasing gas pressure. Micrographs obtained using small pieces of coal indicated that coal is made up of blocks, containing matrix and pores, separated by microfractures. This confirms the dual porosity model of coal structure with a primary porosity, and a fracture/cleat porosity-physical model used in coalbed methane simulators developed recently. Isotherms suggested that for the samples tested, a major part of the gas is released only after pressure falls below 600 psi, and this is primarily due to desorbing gas. Results of the volumetric strain experiments indicated that there is an increase in matrix volume with increase in gas pressure, in spite of matrix compressibility. Adsorption, therefore, induces swelling of the matrix. With decrease in gas pressure from 1000 psi to atmospheric, the matrix volume shrunk by 0.5%. These experimental results were inputted in a reservoir model and simulation runs made to determine the effect of pore volume and matrix shrinkage compressibilities on gas production. Over a five year period 60% more gas was produced when matrix shrinkage was used as an input parameter.Editor's note: The units used in this paper are generally used by the Gas Research Institute and are found in most oil and gas publications. Conversions of the more important units are: 1 MMCFD 28 300 m³/day; 1 MSCFD 28.3 m³/day; 100 psi 0.68 MPa; 100 ft²/lb 46.87 m²/kg; 1 ft 0.3048 m; 1 acre 0.40 hectare.     

某电厂贮灰坝失稳过程及破坏机制研究

运用非饱和土土力学理论分析了某电厂贮灰坝失稳过程,揭示了该贮灰坝的失稳和破坏机制。分析表明,随着子坝挡水历时的增加,积水不断下渗,浸润线逐渐抬高,非饱和区域相应减少,坝体中受此影响的部位的孔隙水压力也随之不断增高,抗剪强度不断降低。此过程发展到一定程度,则导致贮灰坝产生破坏和滑动。上述分析清楚地诠释了干滩长期消失会使贮灰坝的稳定性遭受巨大威胁的原因。其研究结果可为贮灰坝、尾矿坝在类似工况下的稳定性评价和预测预报提供借鉴。     

Hydrogen from coal gasification: An economical pathway to a sustainable energy future

Although hydrogen is the most abundant element in the universe, it does not occur naturally in large quantities or high concentrations on Earth. Hydrogen must be produced from other compounds such as fossil fuels, biomass, or water and is therefore considered an energy carrier like electricity. Gasification of carbonaceous, hydrogen-containing fuels is an effective method of thermal hydrogen production and is considered to be a key technology in the transition to a hydrogen economy. However, for gasification to play a major role during the transition period, capital and operating cost must be reduced and reliability and performance must be improved.Analyses show that hydrogen produced from coal-based gasification can be competitive with production from natural gas provided the cost of natural gas remains above $4/10⁶ Btu and the high reliability of gasification-based processes can be demonstrated. But for coal to be considered in a carbon-constrained environment, the cost of natural gas would have to be greater than $5.50/10⁶ Btu. The development of advanced technologies, however, offers the potential for significant reductions in capital costs, improved thermal efficiencies, and increased reliability. If these advanced technologies are capable of achieving their goals, the cost of producing hydrogen from coal could be reduced by 25–50%, even with the capture and sequestration of CO₂. With these reductions, the cost of natural gas would have to be less than $2.50/10⁶ Btu to compete, a scenario that is very unlikely to occur in the future. This potential cost reduction provides considerable impetus for continuing research and development in the production of hydrogen from coal.     

Assessment of greenhouse gas emissions from coal and natural gas thermal power plants using life cycle approach

The importance of mitigation of climate change due to greenhouse gas (GHG) emissions from various developmental and infrastructure projects has generated interest at global level to reduce environmental impacts. Life cycle assessment may be used as a tool to assess GHG emissions and subsequent environmental impacts resulting from electricity generation from thermal power plants. This study uses life cycle approach for assessing GHG emissions and their impacts due to natural gas combined cycle (NGCC) and imported coal thermal power plants using the IPCC 2001 and Eco-Indicator 99(H) methods in India for the first time. The total GHG emission from the NGCC thermal power plant was 584 g CO₂ eq/kWh electricity generation, whereas in case of imported coal, it was 1,127 g CO₂ eq/kWh electricity generation. This shows that imported coal has nearly ~2 times more impacts when compared to natural gas in terms of global warming potential and human health as disability-adjusted life years from climate change due to GHG emissions such as carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O).     

Effect of some additives on synthesis of zeolite from coal fly ash

Hydrothermal conversion of fly ash into zeolites was conducted and the effects of the addition of sodium halide and waste solutions produced after zeolitization of fly ash, as well as the adjustment of the Si/Al ratio prior to synthesis process on the formation and cation exchange capacity (CEC) of zeolite product were evaluated. Both the addition of NaCl and NaF ameliorated the crystallinity and CEC of synthesized zeolite, but NaF had a better improvement effect. Na⁺ was considered to enhance the crystallization of zeolite, while F⁻ favored the dissolution of fly ash. The type of zeolite formed depended on the Si/Al ratio of the starting material prior to the nucleation and crystallization of zeolite. The adjustment of the Si/Al ratio of fly ash by addition of Na₂SiO₄ and Al(OH)₃ changed the type and CEC of zeolite. Waste solutions contained large amount of Si and little Al due to the formation of a zeolite named NaP1 in zeolite terminology with the Joint Committee of Powder Diffraction Standard (JCPDS) code of 39-0219. The alkalinity decreased largely. As a result, the CEC value of zeolite products synthesized with waste solution as alkali source decreased. The supplementation of new alkali to adjust the alkalinity of waste solution could enhance the CEC of synthesized product. It was concluded that: (1) addition of sodium halide and adjustment of the Si/Al ratio prior to synthesis can improve the quality of zeolite; (2) waste solutions produced following the zeolitization of fly ash can be reused as an alkali source in the activation of fly ash; zero-emission of waste solution in the synthesis of zeolite from fly ash is possible.