Physiochemical and leaching characteristics of fly and bottom ash

Bottom ash and fly ash are the by-products of coal in thermal power plants. They are the combustion wastes and contain many elements that may harmful to the environment. The present study investigates the physiochemical, mineral, and leaching characteristics of an Indian coal ash (bottom ash and fly ash). From the characterization of bottom ash and fly ash, it is found that the ash samples are enriched predominantly in silica, alumina, and iron oxides. A series of leaching experiments have been performed to analyze the tracing elements of metal at the different liquid to solid ratio (L/S). The L/S varies from 20:1 to 80:1. From the leaching results of the fly ash and bottom ash data, it is observed that the tracing elements of Mn, Mg, Cr, Zn, Ni, Pb, Fe, and Cu are the most abundant elements, while Hg, Mo, and Co are the least abundant elements.     

Leaching characteristics of bottom ash from thermal power plants

The disposal of coal ash from thermal power plants in India is a challenging task. The objective of the present study was to investigate the leaching characteristics of the bottom ash disposed in ash pond of thermal power plants. A series of leaching experiments have been performed to analyze the tracing elements of metal at different liquid-to-solid ratios (L/S). L/S ratio varies from 20:1 to 80:1. From the experiment, it is observed that the elements Mn, Mg, Cr, Zn, and Cu are present in major concentrations while elements viz. Pb, Fe, Zn, and Co are present in minor concentrations. It is also observed that the leaching characteristics of the bottom ash are affected by the pH of extraction solution and L/S ratio. The minimum leachability of the solution was determined using an ASTM method, whereas the maximum leachability was determined using a TCLP method.     

Assessment of tracing element characteristics of F-type fly and bottom ash mixture

Presently, fly ash–water slurry is transported to ash disposal site at very low solid concentration of approximately 15–20% (by weight), resulting in huge water and energy wastage which leads to several environmental and health problem. The production of a large amount of the toxic metal elements in the ash disposal system of the thermal power plants can pose negative environmental effects on human health and on plants. In the present study, an attempt has been made to investigate the leaching characteristics of fly ash at higher concentrations. The bottom ash was taken as an additive in the proportion of 10, 20, and 30% (by weight) to enhance the leaching characteristics of fly ash. The solid concentration of fly ash suspension was taken in the range of 40 to 60% (by weight). The addition of additive helps to reduce the tracing metal concentration of fly ash. Leaching experiment data show that leachate concentration of all tracing elements present in fly ash reduced maximum with 20% addition of bottom ash (by weight). The present study helps to improve the ash disposal system of the thermal power plant and to minimize the environmental impact.     

Comprehensive characterization of Indian bottom ash: Assessment of its potential utilization

With increased environmental awareness, utilization of bottom ash has become an attractive alternative to disposal. The objective of the present work was to study the environmental impact of bottom ash and to explore the possibility of its potential utilization. Comprehensive characterization of four bottom ash samples collected from different thermal power plants was investigated. Particle size distribution, bulk density, settling characteristics, specific gravity, porosity, permeability, and water-holding capacity etc. were determined for all bottom ash samples. A series of leaching tests was also performed to determine the tracing metal characterization of bottom ash. It is observed that Mn, Mg, Cr, Zn, Ni, and Cu were the most abundant elements while Pb, Mo, Fe, and Co were the least abundant elements. According to the mineral characterization, it is observed that silica (SiO₂) and alumina (Al₂O₃) are primarily present in all samples. Quartz, mullite, and hematite were identified as the mineral phases. The properties of bottom ash give useful information about the utilization of its end use.     

干式烟气脱硫技术进展及其应用前景分析

对国内外有广泛应用前景的几种干式烟气脱硫技术进行了介绍,分析了这些脱硫技术的特点,并针对上海地区电厂燃用高钙低硫煤的实际情况,提出了采用高钙粉煤灰增湿活化脱硫的简易脱硫方法。     

Mineralogy,geochemistry and leachability of ashes produced after lignite combustion in Amyntaio Power Station,northern Greece

The Kozani–Ptolemais–Amyntaio basin constitutes the principal coal field of Greece. Approximately 50% of the total power of Greece is generated by five power stations operating in the area. Pulverized lignite, a bottom ash, and a fly ash sample from the power plant of Amyntaio were subjected to a leaching procedure. The relative mass leached (RML) of three potentially toxic trace elements (Cu, Cr, Ni) was determined by use of AAS. Results indicate that the determined elements are more readily available in fly ash than in bottom ash or pulverized lignite. Mineralogical examination of the samples has revealed that calcite, gypsum, quartz, and feldspar are the constituents of lignite; quartz and calcite are found in fly ash particles; while gypsum, quartz, and calcite are found in bottom ash.     

Impact of heavy metals in Indian fly ashes on its application as soil ameliorant

Coal contains various organic and inorganic substances including trace quantities of the heavy metals. Therefore, the combustion of coals releases some of the ultimately to the environment of some heavy metals elements in the form of their oxides and in a redistribution of these heavy metals in the surface soil and water bodies, particularly in the vicinity of coal-fired power plants. The fly ash and pond ash of different thermal power stations of India were mixed with soil at different doses separately to compare their impact on crop produce and soil. The present study deals with the presence of the heavy metals in the coal ash and its movement through the amendment of coal ash to the soil and crop produce.     

Energy from municipal solid waste: A comparison with coal combustion technology

The conversion of municipal solid waste (MSW) to energy can conserve more valuable fuels and improve the environment by lessening the amount of waste that must be landfilled and by conserving energy and natural resources. The importance of utilizing MSW was recognized in the 1991 U.S. National Energy Strategy, which sought to “support the conversion of municipal solid waste to energy.” One route to utilizing the energy value of MSW is to burn it in a steam power plant to generate electricity. Coal has long been the predominant source of energy for electricity production in the U.S.; therefore, a considerable science and technology base related to coal combustion and emissions control can be, and has been, applied with substantial benefit to MSW combustion. This paper compares the combustion of coal and MSW in terms of fuel characteristics, combustion technology, emissions, and ash utilization/disposal. Co-combustion of coal and MSW is also discussed. MSW issues that can be addressed by research and development are provided.The major environmental issues that designers of MSW combustion systems have had to address are emissions of trace organic compounds, particularly polychlorinated dioxins and furans, and trace elements such as mercury, lead, and cadmium. Emission of trace organics is generally the result of a poorly designed and/or operated combustion system; modern MSW systems use good combustion practices that destroy organic compounds during the combustion process. Proper control of air/fuel mixing and temperature, and avoidance of “quench” zones in the furnace, help to ensure that potentially harmful organics are not emitted. Computer codes and other design and troubleshooting tools that were developed for coal combustion systems have been applied to improve the performance of waste-to-energy systems.Trace element emissions from both coal and MSW combustion result primarily from vaporization of elements during the combustion process. Most of the trace elements that are vaporized condense on fly ash as the combustion products cool downstream of the furnace and can be effectively controlled by using an efficient particulate removal device. However, volatile elements, particularly mercury, are emitted as a vapor. Several mechanisms are available to capture mercury vapor and some are in use. The development of satisfactory control technology for mercury is a topic currently of high interest in coal burning.The potential for leaching of trace elements and organics from MSW residues after disposal raises issues about the classification and management of ash. Results of laboratory leaching tests, especially for lead and cadmium, have not been consistently supported by field experience. Careful interpretation of the available test protocols is needed to make sure that residues are properly managed.Because of the large scale of coal-fired boilers for electricity production, co-firing of MSW with coal in such boilers could consume large quantities of waste. Several short-term demonstrations have shown that co-firing is feasible. The issues involved in co-firing are emissions of trace elements, trace organics, and acid gases; boiler slagging and fouling; and long-term effects, such as corrosion and erosion of boiler tubes.Areas where research and development has contributed to improved MSW combustion include (a) the formation mechanisms of polychlorinated dioxins/furans, especially low-temperature, catalytic mechanisms, (b) methods of combustion air distribution in incinerators that result in better combustion and reduced emission of organic compounds, (c) the use of gas reburning to control NOx and reduce emission of organic compounds, (d) practical methods for removing organic compounds and mercury from MSW flue gas, (e) the performance of electrostatic precipitators in removing MSW fly ash, particularly when co-firing MSW and coal in existing coal-fired boilers, and (f) burning MSW in fluidized beds or of pulverizing refuse-derived fuel and firing it in suspension-fired, pulverized coal boilers.     

Water Holding Capacities of Fly Ashes: Effect of Size Fractionation

Abstract

Water holding capacities of fly ashes from different thermal power plants in Eastern India have been compared. Moreover, the effect of size fractionation (sieving) on the water holding capacities has also been determined. The desorption rate of water held by the fly ash fractions at ambient temperature (25–30°C) has been investigated. The effect of mixing various size fractions of fly ash in increasing the water holding capacities of fly ash has been studied. It is observed that the fly ash obtained from a thermal power plant working on stoker-fired combustor has the highest water holding capacity, followed by the one that works on pulverized fuel combustor. Fly ash collected from super thermal power plant has the least water holding capacity (40.7%). The coarser size fractions of fly ashes in general have higher water holding capacities than the finer ones. An attempt has been made to correlate the results obtained, with the potential use in agriculture.     

Effects on enrichment characteristics of trace elements in fly ash by adding halide salts into the coal during CFB combustion

The effects on enrichment characteristics of trace elements (TEs) in fly ash by adding halide salts into the coal during coal combustion were conducted on a 6 kW_th circulating fluidized bed (CFB) experimental device. Results show that unburn carbon content in fly ash has little relationship with the concentration of TEs namely Hg, As, Pb, Cr and Mn. All the TEs are enriched in fly ash for the raw coal CFB combustion. Concentration of Hg and Mn increases with increasing the addition amount of CaCl₂, NH₄Cl and NH₄Br. As, Pb and Cr enrich in fly ash more strongly when adding more CaCl₂ into the coal while more addition of NH₄Cl and NH₄Br leads to the decrease of their enrichment compared to addition amount of 0.1 wt%. On the whole, putting halide salts into the coal results in the TEs enriched in fly ash, which benefits for TEs removal during the coal combustion. Combining this method with the chemical sequential extraction or thermal treatment of the fly ash will be a promising way to realize the TEs removal and their recovery.     

机械未完全燃烧热损失偏高原因分析及运行中控制措施探讨

结合国产大型火力发电厂锅炉飞灰可燃物偏高的现象,根据设备实际情况和运行经验总结,详细分析了机械未完全燃烧热损失偏高的原因,并提出了降低飞灰可燃物超标问题的措施及方法。     

燃煤电厂飞灰碳含量与PAHs有机污染物吸附量之间相关性研究

以五家燃煤电厂为例,实验分析了飞灰总碳、元素碳、有机碳含量,并与飞灰中多环烃类（PAHs）有机污染物吸附量作了相关分析;此外研究了燃煤排放PAHs与炉前煤中PAHs的关联性,从煤化学、煤燃烧学角度探讨了PAHs的吸附反应机制,提出煤粉燃烧过程中PAHs的一种重要形成机制-未燃碳颗粒及吸附反应机制,指出飞灰中的碳位不仅是PAHs的重要吸附位,同时也是PAHs的重要反应位。     

An assessment of the physical,mineral, and rheological properties of fly ash for stowing in coal mines

With increasing environmental awareness, utilization of fly ash has become an attractive alternate to disposal. The objective of the present study was to investigate the physical, chemical, mineral, and rheological characteristics of fly ash for their potential utilization in stowing operation. The study was conducted with fly ash collected from the ash disposal system of Guru Govind Singh thermal power plant, Ropar, Punjab, India. From the characterization of the fly ash sample, it was found that the ash sample is enriched predominantly in silica; alumina and iron oxides fall under the category of F-type fly ash. The major mineral crystalline phase identified in the ash sample is quartz and mullite. Because of the properties of fly ash, it can be used as a stowing material in coal mines. The data obtained for critical velocity will help design a slurry pipeline system for the hydraulic stowing of fly ash slurry at any concentration and pipe size.     

Comparative studies on fly ash coated low heat rejection diesel engine on performance and emission characteristics fueled by rice bran and pongamia methyl ester and their blend with diesel

In this study, for the first time, fly ash was used as a thermal barrier coating material in a diesel engine. The study consists of three phases. In first phase, biodiesel was prepared in a laboratory scale setup by single step base catalyzed transesterification method. In the second phase, engine combustion chamber elements such as cylinder head, cylinder liner, valves and piston crown face were coated with fly ash, which is a thermal power plant waste, to a thickness of 200 μm by using plasma spray coating method. In third phase, experiments were carried out on fly ash coated single cylinder diesel engine fueled by methyl ester of rice bran, pongamia oil and its blend (20% by volume) with diesel. The test run was repeated on uncoated engine under the same running conditions and the results were compared. An increase in engine power and decrease in specific fuel consumption, as well as significant improvements in exhaust gas emissions (except NOx) were observed for all test fuels used in the fly ash coated engine compared with that of the uncoated engine.     

A comparative study on field scale demonstration of fly ash and pond ash for cultivation of maize-groundnut crops in sequence on a wasteland

In India, the major source of energy is thermal power plants that contribute about 70% of the total energy requirement and produce a huge amount of fly ash per year. The fly ash and pond ash collected from the Ramagundam Super Thermal Power Station, India, were mixed with soil at different doses, 50, 100, and 200 t ha^?1 separately to compare their impact on crop yield and soil characteristics. Ash application had a beneficial effect on the crop yield, apart from reduction in the required doses of chemical fertilizers by half of the recommended doses. Addition of ash resulted in a significant increase in the contents of N, P, K, S, Ca, Mg, and micro-nutrients in maize and groundnut crop produce. The uptake of toxic trace elements (Cu, Zn, Mn, Fe, Pb, and Ni) was below the threshold levels. The residual effect of ash on crop yield and the nutrient composition of the subsequent maize and groundnut crops was also significant. The overall beneficial effect of ash could be attributed to the improvement in the soil. The results indicated that both the ashes could be applied safely for reclamation of uncultivated wastelands and pond ash is found to be better than the fly ash.     

垃圾焚烧飞灰熔融固化炉开发与试验研究

介绍了5000kg/d垃圾焚烧飞灰熔融固化试验炉结构特点,分析研究了垃圾焚烧飞灰化学成分、灰熔点对熔融固化炉炉膛截面热负荷、容积热负荷值的选取以及炉内衬耐火材料抗碱浸蚀抗高温性能的影响因素.对试验装置炉内各点温度变化和随着温度水平提高,炉内阻力减少的原因进行了分析,对飞灰熔融物用722S分光光度计和IRIS1000等离子体发射光谱仪进行浸出毒性鉴别,结果显示检测值均低于浸出毒性鉴别标准.应用数值模拟方法对炉内的速度场、温度场和飞灰颗粒浓度分布进行了计算分析,指出采用单通道送风比双通道送风对飞灰熔融颗粒收集更有利.     

燃煤机组耦合固废焚烧关键技术研究进展

目的  燃煤与固体废弃物混合掺烧不仅可以实现固废的能量回收利用,也是实现燃煤发电的碳减排的路径之一。 方法  文章综述讨论了燃煤电站掺混固废的研究工作,主要介绍了基于目前主流的电站锅炉为反应器开展燃煤与不同固废掺混的燃烧应用与技术发展;从燃料经济性、混合燃料的飞灰特征、污染物排放以及碳税角度评价燃煤掺混固废的燃烧技术发展;最后讨论了直接掺混和间接掺混的技术的特点。 结果  燃煤直接掺混固废燃烧时需要尽可能减少对锅炉运行的影响,特别是气体污染物的排放以及飞灰对换热面的影响和飞灰无害化处置。间接掺混可以避免混合燃料燃烧对炉膛的影响,但是需要较高的硬件成本投资且耦合技术较为复杂。富氧燃烧技术依旧需要对现有锅炉结构优化来提高该技术的适用性。 结论  直接掺混可实现性与成本优于间接掺混,且循环流化床燃料适应广的特点有利于燃煤直接掺混固废燃烧技术的应用,随着基于循环流化床的富氧燃烧技术的发展将更有利于实现火电厂的碳减排。     

The production of ultra-clean coal from Zonguldak bituminous coal by chemical leaching

From run-of-mine coal with an average ash of 50% being produced at Zonguldak coal basin, clean coal with 7% ash can be produced through physical enrichment methods such as jig and heavy media. However, for the production of coal with an ash content of lower than 7%, it is required for the coal to be first ground and then subjected to chemical leaching operation. In this study, chemical leaching tests were performed with aqueous HF, HCL, HNO₃, and citric acid (CA) in order to produce ultra-clean coal (UCC) from Zonguldak bituminous coal. The effects of type of chemical, grain size, temperature, and leaching time in the leaching process were studied. It was observed that UCC with 0.82% ash could be produced from sample coal with 8.84% ash as the result of leaching operation with aqueous HF.     

循环流化床锅炉降低飞灰含碳量研究

介绍了煤指数、床压、床温、流化风量、总风量和一、二次风比例、燃煤粒径对循环流化床锅炉飞灰含碳量的影响,并以某电厂440t/h循环流化床锅炉降低飞灰含碳量的优化调整为例,通过正交试验分析各因素影响情况。试验表明:总风量对锅炉飞灰含碳量的影响相对较大,其次是流化风量,再次是床压。通过调整入炉煤粒径分布,进一步降低飞灰含碳量。试验表明燃煤粒度对锅炉飞灰含碳量影响较大。     

飞灰未燃尽碳对吸附烟气汞影响的试验研究

采用HYDRA AA全自动测汞仪对3个燃煤电厂的飞灰未燃尽碳进行测试,并利用垂直炉试验系统对电厂飞灰吸附烟气汞进行了试验研究.结果表明：不同燃煤电厂飞灰中的未燃尽碳含量不同是由于各电厂不同煤种、不同燃烧工况以及机组的不同参数造成的;同一电厂的飞灰在灼烧后与原灰相比,对烟气汞的吸附效率相差不大;除了飞灰中的未燃尽碳对汞有吸附外,尾矿对汞也有一定的吸附作用;未燃尽碳含量高的飞灰对汞的吸附效率也较高.