Determining the melting behaviour of ashes from incineration plants via thermal analysis

The ash behaviour comprises one major obstacle towards the efficient utilization of municipal solid wastes, (MSW), in incineration plants. The presence of large amounts of inorganic constituents such as alkali and alkali earth metals, chlorine, sulfur and zinc increase significantly the ash reactivity and lead to severe ash-related problems such as fouling, slagging, corrosion and erosion during their thermal treatment. In this paper, the melting behaviour of various ash fractions originating from the incineration of MSW is studied using simultaneous, (DSC/TG), thermal analysis methods. The produced results provide the basis for improved modelling of the ash behaviour during the incineration of MSW. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fly ash with high sulphate and chloride content: solidification and stabilisation using hydraulic lime

This paper examines the solidification/stabilisation treatment of two fly ash samples from a Municipal Solid Waste (MSW) incineration plant using a lime-pozzolan binder. The two examined fly ash samples were characterised by a high chloride and sulphate content and by a significant concentration of heavy metals. The effective development of hydrate phases during hydration of hydraulic lime-fly ash mixtures allows us to stabilise numerous pollutants in hardened pastes. The release of pollutants into the leachants is limited and decreases with the curing period of the pastes.     

垃圾焚烧中氯化物对重金属Pb迁移转化特性的影响

采用管式炉和模拟垃圾对垃圾中氯化物对重金属Pb迁移转化特性的影响进行了研究,使用ICP-AES(美国EPA消解方法)、SEM、EDS和XRD等对重金属浓度、灰渣表面形貌、成分和灰渣X射线衍射物相等进行了分析。结果表明,氯化物含量的增加使得Pb生成更多易挥发性物质,从而向飞灰迁移分布,但有机氯PVC的影响比无机氯NaCl的大。无机氯NaCl和有机氯PVC对焚烧中Pb迁移转化作用机理不同,NaCl易与Pb反应生成PbCl2,而PVC与Pb反应除了生成PbCl2外,还生成了Pb(ClO4)2、PbCl2O4和PbO2。同时焚烧温度和停留时间也是焚烧中Pb迁移分布的两个主要影响因素。     

垃圾焚烧飞灰中重金属的热稳定化条件及机理

研究了生活-农业混合型垃圾焚烧飞灰与单一生活垃圾焚烧飞灰（简称混合型飞灰与单一型飞灰）热处理过程中的重金属挥发特性与稳定化效果，并结合FT-IR、XRD检测手段对稳定化机理进行了探讨。结果表明，单一型飞灰中重金属的挥发性普遍高于混合型飞灰，垃圾源氯含量对重金属的挥发性有明显影响。飞灰中Mn、Cr不易挥发，Zn、Cu较易挥发，Pb、Cd挥发性很强，热处理温度超过1 000 ℃时挥发率都超过50%。800 ℃为相对最优的热处理温度，兼顾了热处理过程重金属稳定化与抑制挥发。800 ℃以上时飞灰形成了稳定的硅酸盐结构体系，是重金属热处理后难以浸出的主要机理。     

煤催化气化工艺中碱金属腐蚀刚玉质耐火材料的实验研究

针对煤催化气化反应器设计中遇到的材料问题,采用碳酸钾及催化气化工况富含碱金属气化灰渣为实验原料,进行了碱金属腐蚀刚玉质耐火材料的实验研究。着重考察了有氧空气气氛和无氧还原性气氛、反应温度、反应时间、碱金属存在形态对腐蚀行为的影响,并结合SEM-EDX、XRD、核磁Al谱等表征手段,研究了反应前后碱金属和刚玉质耐火材料的成分、物相及结构变化。结果表明,碱金属对耐火材料腐蚀行为受反应的温度、气氛、时间及碱金属存在形态等因素影响较大。分析表明,有氧空气气氛下腐蚀尤为严重的原因是,原料中存在的钾与刚玉耐火材料发生化学反应生成新的钾的铝酸盐物相,且其含量随温度升高、反应时间延长而增加。     

垃圾焚烧氯对重金属迁移特性的影响

在管式反应炉上，通过加入有机氯（PVC）和无机氯（NaCl）研究了垃圾焚烧时氯对重金属迁移特性的影响。结果表明，在低温下，氯对重金属的挥发几乎没有影响，只有在较高的反应温度下氯才会对重金属的挥发特性产生影响，且垃圾焚烧过程中氯的存在使重金属更易向飞灰或烟气中迁移，垃圾中有机氯对重金属迁移特性的影响要大于无机氯。氯的存在会显著改变分布在飞灰和烟气或底渣和飞灰之间的重金属的分布特性。     

煤灰在不同耐火砖表面的润湿性与侵蚀性研究

通过观察煤灰柱在耐火材料表面随温度升高的形态变化和接触角的变化,来判断煤灰在耐火材料表面的润湿性;用扫描电镜(SEM)和能谱分析(EDS)等方法对煅烧煤灰过程中煤灰对耐火材料的侵蚀和渗透进行了观察测试,就渣样的形貌、耐火材料横断面的扫描图像及其元素变化进行了分析。结果表明,温度是影响煤灰在耐火材料表面润湿性和侵蚀性的重要因素;不同耐火材料的抗煤灰侵蚀不同,主要取决于耐火材料的组成和结构,其中结构致密度尤其重要;煤灰对耐火材料的侵蚀其实就是煤灰与耐火材料中各矿物元素互相侵蚀与渗透的结果,在侵蚀过程中还伴随着各种化学反应来抑制或促进侵蚀;煤灰在耐火材料表面的润湿性与煤灰对耐火材料的侵蚀性基本上表现出一致性。     

Fly ASH Reactivity. Formation of hydrate phases

In this study the process of hydration of fly ash, produced by a municipal solid waste (MSW) incinerator, is examined in water and in a solution enriched with Ca(OH)₂. The examined fly ash samples are characterized by a high content of alkaline chlorides and anhydrite and by remarkable amounts of heavy metals. Investigations using differential thermal analysis/thermogravimetry (DTA/TG) and X-ray diffractometry (XRD)show particular kinetics of the formation of the ettringite phase. The development of such a hydrated phase is much more intense in the presence of an excess of Ca(OH)₂so as to consume the ‘free’ sulphate in the case of the more reactive fly ash. Experimental results from thermal analysis and X-ray diffractometry show the presence of different hydrated phases during the interaction between fly ash and aqueous solution. The analytical determinations, related to the aqueous solution, point out an interesting decrease in concentration of metals Pb, Zn and Cr(VI), relating to the middle period of the interaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

Observation of nano copper in waste heat boiler fly ashes

Fly ashes collected from waste heat boilers in the incineration process may possess representative chemical structure of toxic metals during incineration and their changes in the quench process at 1125–553 K and 503–493 K, respectively. Note that copper may play an important role in catalytic formation of dioxins during incineration. Speciation of copper in the fly ashes has, therefore, been studied by X-ray absorption spectroscopy in the present work. About 24% of nano copper in the fly ash was observed by least-squares-fitted XANES (X-ray absorption near edge structural) spectroscopy. Sintering of the fly ash at 1423 K for 30 min led to a reduction of the nano CuO content to 8%.     

垃圾焚烧飞灰颗粒的微观形态特征及能谱研究

利用SEM/EDX，观察了垃圾焚烧飞灰颗粒的微观形态特征，探讨了其主要组成元素及其质量分数。实验结果表明，飞灰颗粒形态多样化，其中以不规则形状聚合体居多，球形体、絮状集合体相对较少，少数颗粒为棒状集合体。球形飞灰颗粒很少有重金属分布，不规则形状聚合体或絮状集合体的表面易分布重金属。从飞灰颗粒表面、内部组成元素的质量分数来看，Si、Ca、Al为主要元素。飞灰颗粒表面、内部有重金属Pb、Cu等分布，局部测定点其质量分数可高达16.2%和14.5%。     

固体添加剂对垃圾掺烧污泥焚烧飞灰高温过程中重金属挥发特性的影响

在研究垃圾与污泥掺烧后焚烧飞灰中重金属浸出特征的基础上,重点研究了飞灰在1 000 ℃条件下高温处置过程中重金属(Cu、Zn 、Pb、Cd)随不同停留时间的挥发特性及添加剂(CaO、Al₂O₃、SiO₂、高岭土、粉煤灰)对重金属转化与挥发特性的影响。研究结果表明,飞灰中重金属Zn、Pb、Mn含量较高,Ni的含量较低,而毒性较大的Cd达到29.4 mg/kg。浸出液中七种金属都满足危险废物鉴别标准(GB5085.3-1996),并且重金属的浸出浓度受浸取时间及浸取液pH值影响较大。在同样的高温处置条件下,焚烧飞灰中不同重金属的挥发特性有较大的差别。其中,Pb表现出易挥发的特性,其挥发率超过80%,而Cu挥发性较小,其挥发率小于30%。综合来看,飞灰中重金属的挥发性大小依次为Pb>Cd>Zn>Cu。飞灰中添加Al₂O₃和高岭土可以抑制Cd的挥发,添加Al₂O₃后Pb的挥发率有所减少,添加SiO₂、CaO、高岭土、粉煤灰均使Zn的挥发率降低,而对Cu的挥发率没有抑制作用,这与飞灰中高Cl含量及各痕量元素化合物对固体添加剂活性位选择性的竞争吸附有关。     

Characteristics of major dioxin/furan congeners in melted slag of ash from municipal solid waste incinerators

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in slag of fly ash from three municipal solid waste (MSW) incinerators were analyzed to observe any changes in characteristics and distribution of their congeners by melting process. Actual concentration and Toxic Equivalent (TEQ) concentration profiles of 17 major congeners of PCDDs/PCDFs for gas, fly ash and melted slag were compared. The distributions of PCDDs/PCDFs in different streams macroscopically showed similarities with the generally known profiles for emission gas from a municipal waste incinerator. The total concentrations of PCDDs/PCDFs in off-gas and fly ash have been known to be a function of incineration conditions and of air pollution control device utilization; however, their normalized distributions were independent of such conditions. The concentrations of PCDDs/PCDFs in the melted slag of fly ash were not related to the concentrations of PCDDs/PCDFs congeners in fly ash but were rather a function of the melting furnace type and operation. The total amount of PCDDs/PCDFs in the melted slag of fly ash contained almost 150–27,000 times less dioxin than that in fly ash, however, the TEQ of dioxin in the slag was reduced by 435–43,500 times, which could enable them to be utilized as recycled construction materials. In normalized TEQ concentration profiles of 17 congeners of PCDDs/PCDFs, the ratio of PCDFs to PCDDs changed from 1.32 to 2.19 by melting, which showed relatively higher portion of furans left in melted slag than those in fly ash. By comparing reduction ratios of different congeners, PCDDs (dioxins) were relatively easier to destruct than PCDFs (furans) during melting process. The most difficult congener to destruct could be octa-chlorinated dibenzofuran (OCDF) among major congeners. For slag cooling methods, dioxin concentration in TEQ of slow cooled slag by air was four times higher than that of fast cooled slag by water. Thus cooling by water is more appropriate with the added beneficial effect of producing granules/particles, which can be utilized as roadbed materials.     

Analyse des molecules organochlorées piegées dans la matrice minérale des REFIOM

Analysis of the chloroorganic trapped in the mineral matrix of fly ash. Incineration is often considered as the most efficient process for urban waste destruction. Although it is a rather clean technique, it is often suspected to be the source of severe pollutions such as metal pollution or dioxin and furan emissions. In order to reduce hazardous emissions, various operating furnace parameters can be controlled, like gas residence time, flame temperature and excess air flow rate, among others. According to European regulations, incineration fly ash corresponds to class I disposal landfills, which demonstrates that it is considered as a toxic waste. The aim of this work was to develop a non equilibrium plasma process in order to study the behaviour of chloroorganics trapped on fly ash by on-line mass spectrometric analysis. The identification of the desorption of chloroorganics trapped within the mineral matrix presents juridical and scientific aspects. This study shows the existence of chemical reactions between the excited species produced from the plasma and the molecules desorbed from the mineral matrix of fly ash during the plasma treatment through the chemical analysis of the gaseous effluent. Special emphasis was put on the physicochemical properties of fly ash (composition of mineral matrix, particles size…)     

Hydration Behaviour of Mixtures of Cement and Fly Ash with High Sulphate and Chloride Content

DTA/TG thermoanalytical investigations and X-ray diffractometry were carried out which demonstrate the effect of MSW fly ash on the hydration reactions of pozzolanic cement. The MSW fly ash has high content of calcium sulphate, alkali chlorides and heavy metals. During the first curing period the calcium aluminate reacts with the sulphate to form ettringite. In that period also the presence of syngenite is noted in the pastes. With the growth of the fly ash content of the mixture there is a lengthening of the period in which the hydration reactions of the calcium silicates are inhibited. Subsequently with the progress of hydration in the pastes the CSH phase develops and the formation of calcium chloroaluminate phase is observed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydration behaviour of a lime-pozzolan cement containing MSW incinerator fly ash

A lime-pozzolan cement was used to make pastes containing different quantities of MSW fly ash. After setting, the pastes were cured in water at room temperature from 1 h to 260 days. The hydration characteristics and the nature of the hydration products of the various pastes were studied by simultaneous TG/DSC thermal analysis and X-ray diffractometry. The MSW fly ash was found to induce a slowing of the hydration process in lime-pozzolan pastes, and after some days an evident acceleration of hydration reactions occurred. Sulphate and chloride in the MSW fly ash yield hydration products forming a cementitious matrix.The author is grateful to D. Calabrese for assistance with the thermal and XRD analyses.     

城市生活垃圾焚烧体系化学热力学平衡分析

采用化学热力学平衡分析方法，分析城市生活垃圾焚烧体系污染物的排放特性。主要计算了聚氯乙烯（PVC）及典型城市垃圾焚烧过程氯元素的化学平衡组成及其浓度，同时研究了脱氯剂对PVC及垃圾中氯转化的影响。计算结果表明，PVC热态反应的主要产物是HCl气体，在加入脱氯剂后温度低于600℃时，脱氯剂对HCl的脱除作用很明显；城市生活垃圾热解和燃烧过程中在温度超过600 ℃，垃圾中的有机氯和无机氯都将转化为HCl气体，而此时脱氯剂失去效果。由计算结果得到控制HCl生成，消除二口恶英污染物的生成反应工艺条件。     

无电镀镍复合镀层耐蚀性质研究

研究无电镀镍镀层加入钻石微粒或PTFE微粒的均匀分散相 ,所得之复合镀层在 3.5%NaCl水溶液中的电化学分析 ,浸渍试验与临雾试验 ,皆显示复合镀层之耐蚀性低于不含微粒之无电镀镍镀层 .由SEM ,AES ,XRD ,EPMA分析镀层微观组成 ,复合镀层之磷含量分布呈差异性变化 ,磷量较多区域为微阴极 ,磷量较少区域为微阳极 ,复合镀层存在众多微电池组合 ,容易引起电化学伽凡尼腐蚀 ,造成复合镀层耐蚀性降低 ,当镀层微粒含量增加时 ,微粒的惰性保护效果超过微电池效应 ,复合镀层的耐蚀性质才能提高     

Evaluation of a mixed chelator as heavy metal stabilizer for municipal solid‐waste incineration fly ash: Behaviors and mechanisms

This paper compares the stabilization performances of three dithiocarbamate and three phosphate chemical stabilizing agents, selects the best agents from each group, combines them as a mixed heavy metal stabilizer for municipal solid‐waste incineration (MSWI) fly ash, and investigates the effectiveness of the mixed chelator in stabilizing heavy metals in MSWI fly ash from southwest China. The mechanism of stabilization is also analyzed. Results indicate that piperazine dithiocarbamate can stabilize Cd, Cu, and Ni effectively, while sodium dihydrogen phosphate can stabilize Pb better. With the addition of the mixed chelator (2% sodium dihydrogen phosphate and 1% piperazine dithiocarbamate), all the targeted heavy metal concentrations in the leachate were below the standards for pollution control on municipal solid waste landfill sites in China. The stabilizing agents combined with the heavy metals in fly ash could not generate insoluble crystals; however, the heavy metals could combine with the agents' effective groups, generating flocs in the pores or on the surfaces of the fly ash and offering significant densification. The mixed chelator could transfer heavy metals from unstable fractions to stable fractions, so the leaching of heavy metals from the fly ash was greatly decreased.     

不同反应气氛下准东高钠煤中钠的迁移转化与积灰特性

为了获得循环流化床工艺下不同反应气氛对准东高钠煤中钠的迁移转化与积灰特性的影响,在0.4t/d循环流化床实验装置上开展了相同床温(950℃)下的新疆沙尔湖高钠煤的气化(还原性气氛)与燃烧(氧化性气氛)实验研究。结果表明,气化和燃烧气氛下飞灰与积灰中Na主要以NaCl的形式存在;气化比燃烧更容易将Na、Cl固留在底渣和飞灰中,相应的进入气相中的Na、Cl更少;燃烧气氛下,部分NaCl会被烟气中的SO_2硫化,生成稳定性更高的Na_2SO_4并冷凝在飞灰和积灰棒表面,燃烧过程中产生的飞灰粒径更细,积灰更严重;沙尔湖煤燃烧与气化过程中存在HCl对金属壁面的腐蚀。     

燃煤电厂异相凝并飞灰重金属淋滤特性

采集了燃煤电厂的异相凝并后飞灰，分析了其物理化学特性。并通过淋滤实验研究了飞灰中重金属As、Se、Pb的环境稳定性。结果表明，凝并飞灰的粒径峰值为138.04 μm，而粉煤灰为60.26 μm；凝并后细颗粒凝聚成了较大的颗粒；凝并飞灰中重金属As、Se、Pb含量均高于同工况下粉煤灰中的含量，且后序脱硫环节所产生石膏中重金属的含量有所下降；批淋滤实验研究结果表明，凝并飞灰中的重金属浸出能力受淋滤液的pH值影响较大，温和环境和碱性条件抑制了As的浸出，酸性和碱性条件抑制了Se的浸出，而碱性条件抑制了Pb的浸出。柱淋滤实验研究结果表明，在酸性溶液和水溶液中，凝并飞灰的重金属浸出能力均受到了抑制。