Aggregation experiments on fine fly ash particles in uniform magnetic field

Aggregation experiments on three fly ash samples in the size range of 0.023-9.314 μm were conducted in a uniform magnetic field. The fly ash particles were produced from combustion of three different bituminous coals. The coals were originated Dongshen, Datong and Xuzhou of China, respectively. A fluidized bed aerosol generator was used to disperse the fly ash particles to generate a constant aerosol. The aerosol particles aggregated when passing through the magnetic field. The variation of particle number concentration caused by particle aggregation was measured in real time by an Electrical Low Pressure Impactor (ELPI). The effects of several parameters, such as particle size, magnetic flux density, particle residence time in the magnetic field, total particle mass concentration and average gas velocity, on particle aggregation were examined. Experimental results indicated that removal efficiencies are the highest for particles with sizes in the middle of the size ranges tested. Increasing magnetic flux density, total particle mass concentration, particle residence time in the magnetic field or by reducing average gas velocity can increase removal efficiencies of single-sized and total fly ash particles. When fly ash particle magnetization reached saturation state, further increase of the magnetic flux density will have no effect on particle aggregation. The single-sized and total particle removal efficiencies of the three fly ashes are different under the same operating conditions. The removal efficiency is the highest for fly ash generated from Dongshen coal, followed by fly ash from Datong coal, and then fly ash from Xuzhou coal. Particle number median diameters decreases with the increase in the total particle removal efficiencies. The model prediction of particle aggregation under high total particle mass concentrations conditions indicated that the single-sized and total particle removal efficiencies will increase greatly with the increase in total particle mass concentration. The model predicted total removal efficiencies of the three fly ash particles are 53%, 43% and 14%, for Dongshen, Datong and Xuzhou coals respectively when total particle mass concentration is 40 g/m³.     

燃煤可吸入颗粒物在磁场中聚并脱除机理

提出了燃煤可吸入颗粒物在均匀磁场中的二元碰撞聚并模型,应用该模型计算了大同烟煤飞灰粒子的聚并系数,在此基础上通过求解聚并动力学方程计算了粒子的聚并脱除效率,并与实验结果进行了对比。数值模拟结果表明,燃煤可吸入颗粒物聚并系数随粒径的增大而增大,粒径差异越大,重力对聚并的加强作用越大;粒径越大,布朗力对聚并的影响越弱;同聚并系数对外磁场强度的变化规律一样,粒子的聚并脱除效率随外磁场的增强而增大,在粒子饱和磁化后,聚并脱除效率达到最大值;延长粒子在磁场中的停留时间以及增大其质量浓度,都可以提高粒子的聚并脱除效率,在质量浓度和停留时间分别为40 g·m-3和1. 2 s时,粒子聚并脱除效率可达44%;数值模拟结果与实验结果相一致。     

Analysis of mechanism on water-reducing effect of fine ground slag, high-calcium fly ash, and low-calcium fly ash

The addition of ultrafine powder (UFP) to concrete can improve the fluidity of concrete, showing a water-reducing effect. The aim of this article was to analyze the water-reducing mechanism of UFP both experimentally and theoretically. Three UFPs—fine ground slag, high-calcium fly ash, and low-calcium fly ash—were chosen for the study. The contrastive experiments were done to investigate the fluidity of mortars with 30%, 45%, 60%, and 75% equivalent cement replaced by fine ground slag, high-calcium fly ash, and low-calcium fly ash, respectively. The results showed the physical and chemical characteristic of the powders, such as their grain morphology, glass phase activities, densities, specific areas, and their grain cumulating conditions, can strongly affect their water-reducing effect.     

Carbon content of fly ash and size distribution of unburnt char particles in fly ash

The type and size of unburnt char particles in 13 fly ash samples were determined microscopically. The samples were collected from a power station fired from an inertinite-rich coal seam. The carbon content of the ash samples ranged from 2.3 to 25.3 wt%. When the carbon content in a fly ash was high, the proportion of coarse char particles, in particular > 10⁶ μm³ particles, was also high. These results suggest that the size distribution of the feedstock coal has a major effect on the carbon content of the fly ash.     

Plerosphere and its role in reduction of emitted fine fly ash particles from pulverized coal-fired power plants

Fine particles (PM_2.5) emitted from the stacks of the coal-fired power plants are of environmental concern since they can easily enter the human respiratory track. The detailed study of the fly ash particles using scanning electron microscope/electron dispersive spectrometry (SEM/EDX) show that fine solid spherical particles (microspheres) are contained by the large cenosphere particles (>50 μm) during the combustion process. The resulting macro particles are known as “plerosphere”, which are typically impregnated by the fine microspheres. The coal-fired power plants’ particle control devices such as the electrostatic precipitators (ESP) and baghouse filters tend to capture the large plerospheres, more efficiently. Therefore, the result of this study suggests that the containment of the microspheres by plerospheres during the coal combustion process can effectively reduce the amount of fine particles and associated elements released into atmosphere.     

粉煤灰空心微珠的研究与应用进展

综述了粉煤灰空心微珠的研究与应用的现状与进展,总结了粉煤灰空心微珠的性质和应用,评述了综合利 用粉煤灰空心微珠的现实意义。     

粉煤灰在油田开发中的应用

本文在对某热电厂粉煤灰的粒度、化学成分、水化性等性能分析的基础上,介绍了一种以粉煤灰为主剂的水井用调剖剂。经室内实验分析和现场应用的效果分析,证明FP-2型粉煤灰类调剖剂的堵水调剖效果好,为粉煤灰的综合利用找出了一条新的应用途径。     

飞灰颗粒与平板表面撞击过程的实验研究

以煤粉锅炉积灰过程为研究背景,在常温常压环境下对飞灰颗粒与平板表面撞击过程进行实验研究,分析飞灰颗粒入射法向速度对颗粒法向反弹速度的影响,以及飞灰颗粒粒径对临界捕集速度的影响。实验结果表明,飞灰颗粒粒径相同时,法向恢复系数随入射法向速度的增大先增大后平缓最后减小,在增大区域具有相当陡的斜率,反映了不同形式的力在不同阶段所占的比重不同;颗粒入射法向速度相同时,法向恢复系数随着颗粒粒径的增大而增大;而临界捕集速度随颗粒粒径的增大而减小。     

Bulk nucleated fine grained mono-mineral glass-ceramics from low-silica fly ash

Cr₂O₃-nucleated fine grained mono-mineral glass-ceramics of augite were produced from low-silica fly ash and additives of SiO₂, Al₂O₃ and MgCO₃, via two steps of heat treatment for nucleation and crystal growth. The starting glass approached the composition of CaMg_0.75Al_0.4Fe_0.1Si_1.75O₆, derived from CaMg_0.75Al_0.5Si_1.75O₆, which belongs to diopside – Ca-Tschermak solid solutions. The influence of Cr₂O₃ (up to 0.75 wt.%) on the development of crystalline phases, the properties and the microstructure of the resultant glass-ceramics crystallized at different temperatures was investigated.     

粉煤灰细粉添加量对多孔莫来石材料的影响

为了提高粉煤灰的资源化利用,在m(漂珠):m(氢氧化铝):m(V2O5):m(AlF3)=45:55:4:3的混合料中分别添加不同量(每100 g混合料分别添加0、5、10、20、30 g)的粉煤灰细粉,以PVA溶液为结合剂,经干料混匀、泥料搅拌、泥料陈腐、挤制成型、1100℃保温2 h烧成制备莫来石试样,然后检测其致...     

粉煤灰的超细粉磨及其性能的研究

在建立的半工业化球磨系统中对多种粉煤灰进行了超细粉磨，探讨了粉磨系统的工艺参数和粉磨电耗，并对超细粉煤灰的颗粒形貌和性能进行了测定和分析。结果表明，利用该系统能够对粉煤灰进行超细粉磨处理，粉煤灰的比表面积可达11000cm^2／g左右，中位粒径可以〈4．0μm，这种超细粉煤灰不仅具有很高的活性，对砂浆和混凝土的工作性也有显著的促进作用，可以减水10％左右，能够用来生产大流动度、大掺量粉煤灰高强砂浆或者混凝土。     

粉煤灰的活性激发与机理研究进展

粉煤灰是燃煤电厂中煤粉燃烧后的固体废弃物,其日益累积不但会占用大量土地资源,还会破坏原有的自然环境,造成严重污染,近年来粉煤灰的处理和资源化利用受到广泛关注。激发粉煤灰的潜在活性是提高粉煤灰综合利用率的关键。对粉煤灰的物理活性和化学活性来源进行了介绍,并对粉煤灰活性的物理激发、水热激发及化学激发技术与激发机理进行了综述,为后续粉煤灰的活化研究和大规模利用提供了参考。不同手段均能激发粉煤灰活性,但采用单一手段激发时存在活化成本高、激发程度低等问题。未来粉煤灰激发技术将朝着多种手段并用的方向发展。     

燃煤飞灰低频下声波团聚的实验研究

通过实验研究了低频下燃煤飞灰的声波团聚。燃煤飞灰气溶胶在声波作用下粒径分布发生明显变化,大量细颗粒团聚产生粗颗粒,气溶胶浓度降低。在147 dB、1400 Hz时,气溶胶总浓度和PM_2.5浓度分别减少了68.4%和75.6%,达到很好的团聚效果。从扫描电镜照片中可以观察到声波团聚过程中产生了粒径大于10 μm的链状团聚体。在声波作用下,气溶胶总浓度随团聚时间呈指数衰减规律降低。实验证明了声波团聚中存在最佳频率,在此频率下团聚效果最好,偏离该值团聚效果急剧降低。另外,实验发现最佳频率随声压级的增大而轻微降低。同时,研究了声压级、停留时间和气溶胶初始浓度等参数对声波团聚的影响。     

Turbulent disruption and agglomeration of fly ash particles in a stirred tank

We have measured the change of size distribution and number concentration of fly ash particles suspended in a stirred tank. Disruption of aggregates is dominant for the dilute suspension (3.3 × 10¹²/m³). On the other hand, agglomeration of particles is dominant for high concentration (8.2 × 10¹³/m³). In both cases, the rapid changes of particle size distributions occur for the initial 2 min and the equilibrium states that the amounts of disruption and agglomeration are in balance have been reached after about 15 min from the starting point of rotation. Also, it has been found that for the intermediate concentration the amounts of agglomeration and disruption are in balance and cancel out each other from the starting point of rotation.     

陶瓷研磨体用于磨制超细粉煤灰的生产实践

山东某公司因地理位置原因,到厂矿渣价格较高,且不能保证稳定供货,影响公司正常生产经营。但该公司周围粉煤灰资源丰富,到厂价格也低。如何在保证水泥质量的前提下,最大限度提高水泥中粉煤灰掺加量,一直是努力的重点。同时,开辟超细粉煤灰在商品混凝土领域的应用,也可为公司增加新的利润增长点。为此,自2017年5月份起,利用一台Φ3.2 m×13 m闲置开路磨进行超细粉煤灰的试生产工作,至2018年4月31日已累计生产比表面积大于650 m2/kg的超细粉煤灰3万余吨,除了本公司生产水泥作混合材使用,还可销售给其他公司,取得了较好的效益,也为超细粉煤灰的球磨机工业化生产探索了一条新的可行的技术路径     

高钙固硫粉煤灰水热条件下元素的溶出机制

试验用比色法和原子吸收法等分析手段系统地研究了粉煤灰 H2O、粉煤灰 NaOH H2O、粉煤灰 Ca(OH)2 H2O3个系统在不同水热条件下Al、Si、Ca元素溶出浓度。结果表明:温度、反应时间和OH-的浓度是影响离子溶出的主要因素;计算了不同粉煤灰 Ca(OH)2 H2O系统在100℃、12h条件下SiO2的溶出率,高钙固硫粉煤灰中SiO2的溶出率高于普通粉煤灰,用SiO2的溶出率可以表征粉煤灰的活性;粉煤灰与Ca(OH)2的水热反应,可能是一个原地化学反应。     

不同颗粒组成粉煤灰对混凝土性能的影响

适当增加含粗颗粒的粉煤灰含量,可以调整胶凝材料颗粒,并能可以改善混凝土的流动性能,但有可能使28 d强度降低;掺用时应兼顾适应性和强度的关系,寻求合理的控制参数。但从远龄期强度看,掺用粉煤灰的混凝土90 d后仍有继续增长的趋势,而且较粗的粉煤灰增长趋势更强劲些,表现出高耐久性的优势。     

Bulk magnetic susceptibility measurements for determination of fly ash presence in concrete

Reproducible measurements of magnetic susceptibility χ_m of laboratory and field extracted concrete core samples were achieved with simple instrumentation. There was a nearly linear relationship between χ_m and the mass of fly ash per unit volume, or its volume fraction. The magnetic response of a given FA was not significantly affected by the process of curing and subsequent evolution of the concrete over two years, or by carbonation of the concrete. Field extracted concrete cores exhibited a wide range of χ_m values. The group of specimens with the highest values of χ_m also had the lowest chloride ion diffusivity, consistent with the presence of admixed FA. Conversely, specimens with nil magnetic response included those from concrete with the highest chloride diffusivity. The magnetic measurements provided reasonable order-of-magnitude indications of FA presence in field extracted cores. However, precise determination of FA content from magnetic measurements of field cores does not appear feasible in the absence of additional information.     

Cd speciation in biomass fly ash particles after size separation by centrifugal SPLITT

The finest particle size fractions (≤25 μm) in four fly ash samples from fluidised bed combustion of three biomass based fuels and a municipal solid waste fuel were size separated using a centrifugal SPLITT fractionation cell. The ashes were separated into different size fractions and the cadmium concentration, partition and speciation in each separated fraction were then investigated in relation to their possible leaching.The fractionation was evaluated by environmental scanning electron microscopy, which also provided indications of the associations between Cd and other main elements on the particles through the use of X-ray fluorescence mapping. The total concentration of Cd in each fraction was determined by AAS analysis which showed different dependences on the ash particle size in the case of biomass or waste fuels. In addition, the speciation of Cd in each fraction, investigated by sequential chemical extractions and X-ray powder diffraction analysis, showed Cd to be present mainly as non-easy leachable forms, i.e. oxide and silicates. A readily leachable fraction was found only in the municipal solid waste fly ashes.     

煤粉炉粉煤灰与循环流化床粉煤灰矿物学性质比较

为了提高粉煤灰的利用率,通过化学成分分析、扫描电子显微镜(SEM)分析、X射线衍射光谱(XRD)分析和核磁共振分析,对煤粉炉和流化床2种粉煤灰的形貌、物相组成和活性进行了表征,研究了2种粉煤灰矿物学性质的差别。试验结果表明:2种粉煤灰在形貌和物相上存在较大的区别。形貌上,煤粉炉粉煤灰中存在大量的玻璃微珠,而流化床粉煤灰由于成灰温度低不存在玻璃微珠;物相上,煤粉炉粉煤灰中存在较大量的结晶类矿物,而流化床粉煤灰多为非晶玻璃态物质。通过核磁共振分析发现煤粉炉粉煤灰中硅氧结构和铝氧结构的聚合度较高,不利于活性组分溶出。