燃煤痕量元素转化、排放及控制的研究进展

综述了煤燃烧过程中痕量元素转化、排放规律及实用的控制技术,重点介绍了当前最受关注的汞排放控制技术,并反映了量子化学在燃煤痕量元素研究中的最新应用。分析了燃煤痕量元素研究存在问题及发展方向。     

燃煤飞灰颗粒物中元素分布规律的研究

利用ICP-AES光谱仪和TOC总碳分析仪对不同粒级下的飞灰颗粒进行了元素测定,对元素分布规律的形成原因进行了分析.分析结果表明:煤经旋流燃烧器燃烧而未经过除尘设备的飞灰中300目以下小颗粒含量较高.随着燃烧温度的升高,大颗粒的含碳量增加,小颗粒的含碳量减少,元素Al、Mg、Cr在各个粒级中含量变化不大,Ti、Ba、V在大于280目的小颗粒中含量有下降趋势,其他大部分痕量元素在大于300目的小颗粒中得到富集.     

我国不粘—弱粘煤 煤岩组分及其性质研究

本研究选择我国种府煤、焦坪煤和灵武煤三处不粘——弱粘煤。首先研究了其煤岩组分组成及特点，结果得出3种煤的惰性组分含量均在30％以上，属于高惰性组分煤。然后通过仔细地手选分离，分出了纯度较高的镜煤、高煤、暗煤和丝煤4种宏观煤岩组分。借助于溶剂抽提、工业分析、元素分析、FTIR分析、GC、GC-MS分析等方法研究了各样品的抽提率、族组分组成、煤质特征、分子结构特征、官能团特征及生物标志物；进而测定了各种组分的HGI，而且通过煤矿试验和煤岩分析研究了不同粒级煤粉中煤岩组分的分布规律。     

煤燃烧过程中微量元素铬、铅的迁移转化规律研究

通过化学逐级提取法等手段,研究了煤中铬、铅在燃烧过程中的迁移转化规律及其环境稳定性,掌握了其在燃烧产物中的形态和分布,为开展燃煤电厂灰渣中重金属污染的防治工作提供了依据。     

国外动态

炭黑尾气中多环烃及痕量元素的含量 Environ.Sci.＆Technol.,14[3],(1980). 油炉法炭黑生产污染大气,主要是产生大量炭黑粉尘、CO、烃类及硫化物等污染物造成的。但是,由于油炉法炭黑生产过程系天然气燃烧和重质芳香烃高温裂解过程,因而也是向大气排放多环烃和痕量元素的潜在性的污染源。表1炭黑     

燃煤电厂砷排放控制技术研究进展

对煤中砷的赋存状态及煤在燃烧后砷的转化行为进行了分析,并分别从煤的物理洗选、抑制煤中砷元素的挥发、气态砷吸附剂和污控设备协同脱砷等方面,重点论述了国内外对燃煤电厂砷排放控制的最新研究进展。同时提出了控制砷排放的新思路,为今后脱砷技术的进一步研究指明了方向。     

ICP—AES法测定粉煤灰和植物中痕量元素

粉煤灰和植物中痕量元素的测定可用比色法、原子吸收法、原子荧光法、等离子发射光谱法、X 光荧光法、中子活化法等。原子吸收分光光度法具有灵敏度高、检测限好的特点,但测量范围窄,一般只有2—3个最级,每次只能测定一个元素,测定过程中化学干扰比较严重。X 光荧光法准确度高,     

无火焰石墨炉原子吸收法测定电厂废水中的痕量元素

电厂废水中含有一些有害金属元素,虽然浓度低(多数在几十PPb左右),但废水排放量大。测定其中痕量元素,在电厂环境保护工作中具有重要意义。我们在检测电厂废水时,选用了无火陷石墨炉原子吸收法。此法根据原子蒸气能吸收该元素特征波长的现象,将试样的一部分     

煤燃烧过程中金属元素迁移特性

利用ICP-AES光谱仪对原煤、飞灰和底灰中铝、钾、钙、镁、铁、锰、锌、铜、硒、铬、砷等11种元素的含量进行了分析;对上述元素在煤燃烧过程中的迁移挥发特性进行了讨论,结果是钙、锰、铁挥发性较小,主要沉积在底灰中,而锌、铜挥发性较大,其他元素属于中等挥发性。     

电除尘器内部粒子运动及分布数学模型仿真研究

对电除尘器除尘过程中粉尘粒子运动及其分布规律进行研究,用数学的方法构建了一个比较完整的数学模型。通过设定合适的边界条件,采用差分法对所建立的数学模型进行求解,并借助功能强大的数值计算和绘图工具软件Matlab将电除尘器中复杂的粉尘粒子运动进行数值仿真,力求清晰地描述除尘过程中粒子的运动状态和分布规律。研究表明,电除尘器中粉尘粒子在横断面上的浓度分布大致符合指数函数的分布规律,靠近收尘极板的浓度值高于电晕线附近的浓度值,这说明数学模型能够真实地反映电除尘中粉尘粒子的运动规律。     

Impact of the use of waste on trace element concentrations in cement and concrete.

The results of model calculations carried out to identify and quantify the input pathways of trace elements into cement and concrete and to estimate the extent to which trace element concentrations in cement may change due to waste utilization are presented. As expected, primary raw materials represented the most important input pathway for trace elements into cement, but the contribution from wastes was not negligible. The use of waste led to a slight increase of the concentrations of cadmium, antimony and zinc in cement. For cobalt, lead and vanadium, this increase was less distinct and for all other trace elements considered, the effect of the use of wastes on trace element concentrations in cement could not be demonstrated clearly. The trace element content of concrete was governed by the aggregates for most elements considered. However, for arsenic, cadmium, lead and zinc, both cement and the additive coal fly ash contributed noticeably to the total trace element concentration in the concrete.     

Element associations in ash from waste combustion in fluidized bed

The incineration of MSW in fluidized beds is a commonly applied waste management practice. The composition of the ashes produced in a fluidized bed boiler has important environmental implications as potentially toxic trace elements may be associated with ash particles and it is therefore essential to determine the mechanisms controlling the association of trace elements to ash particles, including the role of major element composition. The research presented here uses micro-analytical techniques to study the distribution of major and trace elements and determine the importance of affinity-based binding mechanisms in separate cyclone ash particles from MSW combustion. Particle size and the occurrence of Ca and Fe were found to be important factors for the binding of trace elements to ash particles, but the binding largely depends on random associations based on the presence of a particle when trace elements condensate in the flue gas.     

Leachate from land disposal of coal fly ash

The results of large-scale lysimeter tests in which two pulverized coal fly ashes (PCFA) have been exposed to natural weather conditions for up to seven years are presented and compared with those of laboratory leaching tests. Laboratory column leaching tests on PCFA show good reproducibility, and comparisons between lysimeter and laboratory leaching results are promising for several salt ions and trace elements in the leachate when expressed in terms of the leachate to solids ratio (L/S). A long-term disposal strategy which takes into account the largely insoluble nature of PCFA is suggested.     

Trace element partitioning in ashes from boilers firing pure wood or mixtures of solid waste with respect to fuel composition,chlorine content and temperature

Trace element partitioning in solid waste (household waste, industrial waste, waste wood chips and waste mixtures) incineration residues was investigated. Samples of fly ash and bottom ash were collected from six incineration facilities across Sweden including two grate fired and four fluidized bed incinerators, to have a variation in the input fuel composition (from pure biofuel to mixture of waste) and different temperature boiler conditions. As trace element concentrations in the input waste at the same facilities have already been analyzed, the present study focuses on the concentration of trace elements in the waste fuel, their distribution in the incineration residues with respect to chlorine content of waste and combustion temperature.Results indicate that Zn, Cu and Pb are dominating trace elements in the waste fuel. Highly volatile elements mercury and cadmium are mainly found in fly ash in all cases; 2/3 of lead also end up in fly ash while Zn, As and Sb show a large variation in distribution with most of them residing in the fly ash. Lithophilic elements such as copper and chromium are mainly found in bottom ash from grate fired facilities while partition mostly into fly ash from fluidized bed incinerators, especially for plants fuelled by waste wood or ordinary wood chips. There is no specific correlation between input concentration of an element in the waste fuel and fraction partitioned to fly ash. Temperature and chlorine content have significant effects on partitioning characteristics by increasing the formation and vaporization of highly volatile metal chlorides. Zinc and cadmium concentrations in fly ash increase with the incineration temperature.     

Chemical changes in different types of coal ash during prolonged,large scale,contact with seawater

In this study, we followed the chemical changes occurring in coal ash exposed to prolonged (300 days), large scale, contact with running seawater. Four major components (Al, Ca, Mg, Fe) and seven minor and trace elements (Cd, Cr, Cu, Mn, Zn, Pb, Hg) were measured in four coal ash types: fly and bottom ash freshly obtained from coal-fired power plant, and old ash (crushed and blocks) recovered from the sea after 3-5 years contact with seawater. Changes occurred in the chemical composition of the coal ash along the experiment: Fe increased in fresh ash, Al increased in old ash and Ca increased in all ash types except old ash blocks. Cu and Hg decreased in fresh fly ash while Cr increased, Cd decreased in all ash types except bottom ash, and Mn decreased in bottom ash. Most of the changes occurred in the fresh fly ash, and not in the old ash, indicating equilibrium after prior exposure to seawater. In addition, more changes occurred in fresh fly ash than in bottom ash, emphasizing the differences between the two ash types. While the changes in the concentrations of the major elements may be an indication of the integrity of the ash matrix, the only elements of environmental significance released to the environment were Hg and Cd. However, calculated seawater concentrations were much lower than seawater quality criteria and therefore the coal ash was considered suitable for marine applications concerning seawater quality.     

Characterization and Leaching of Coal Fly Ash

Physical characteristics, chemical composition and leaching behaviour of a waste fly ash from a coal-fired power station are reported. Particle size distribution was studied by the following techniques: sedimentation in a liquid medium; sedimentation in an air flow; and Fraunhofer diffraction of a laser beam. Results obtained by the different methods are in good agreement. Mineralogical content and chemical composition were determined by X-ray diffraction, electronic microprobe and X-ray fluorescence. Acid leaching of the samples was investigated, using the following strong acids in sequence: HCl+ HNO₃, H₂F₂, HClO₄. Analysis of leachates by atomic absorption shows trace metals In, Tl, Ge, Cu, Ga, Pb, Ni, Co, Mn, Cd, Zn, Cr.In this work fly ashes from a Spanish power plant are characterized according to the type of particles, size distribution and chemical composition by means of physical methods. Three particle size fractions are leached by acids and analysis of trace elements in the leaching liquor is carried out. The concentration of trace metals is somewhat higher in the particles of smallest size.     

PHYSICO-CHEMICAL CHARACTERIZATION AND LEACHING OF DESULPHURIZATION COAL FLY ASH

Fly ash produced by coal combustion using two types of desulphurization process were studied: a conventional pulverized coal boiler equipped with lime injection (PCL ash), and a circulating fluidized bed combustion boiler with limestone injection (CFBC ash). The ashes were characterized completely: granulometry, morphology, mineralogy, chemical composition and behaviour to water contact. Both PCL ash and CFBC ash present similar features: fine granulometry, presence of anhydrite phase and sulphate content. However, PCL ash also shows lots of spherical particles, unlike CFBC ash, and a much higher lime content, due to the lower desulphurization rate in PC boilers. Unlike CFBC ash, most of the trace elements in PCL ash show an inverse concentration–particle size dependence. Leachates obtained from both samples are rich in soluble salts [CaSO₄and Ca(OH)₂] and arsenic and selenium are prevented from solubilizing by high lime content. In wetted PCL ash, the formation of ettringite crystals stabilizes calcium and sulphate ions. Simultaneously, arsenate, selenate and chromate anions are trapped in the crystal. CFBC ash does not really harden because the lime content is too low. However, the leached selenium concentration is cut down in wetted CFBC ash samples.     

Study of Pollution of the Plitvice Lakes by Water and Sediment Analyses

The process of eutrophication in form of intense plant growth has been observed in some lakes and water streams at the Plitvice Lakes National Park in central Croatia. Here we investigate whether this phenomenon is a consequence of anthropogenic pollution or due to naturally produced organic matter in the lakes. We applied chemical analysis of water at two springs and four lakes (nutrients, dissolved organic carbon (DOC), trace elements) and measurements of surface lake sediments (mineral and organic fraction analyses, trace elements) in four different lakes/five sites. The chemical composition of water does not indicate recent anthropogenic pollution of water because the concentrations of most trace elements are below detection limits. The concentrations of DOC and nutrients are slightly higher in the area of increased eutrophication-plant growth. Also the content of organic matter in the sediment is at the highest level in areas with highest C/N ratio indicating that the organic fraction of this sediment is mainly of terrestrial origin. There is no significant difference among the trace element concentration in the upper segment of all cores, deposited approximately during last 50 years when higher anthropogenic influence is expected due to development and touristic activity, and the lower part of the cores, corresponding to the period approximately 100–200 years before present. The content of trace elements and organic matter in sediments decreases from the uppermost lake downstream. According to our results there is no indication of recent anthropogenic pollution in water and sediment. Higher concentrations of DOC in water as well as phosphorus and some other elements in the lake sediment can be a consequence of input of natural organic matter to the lake water.     

Long-term anaerobic digestion of food waste stabilized by trace elements

The purpose of this study was to examine if long-term anaerobic digestion of food waste in a semi-continuous single-stage reactor could be stabilized by supplementing trace elements. Contrary to the failure of anaerobic digestion of food waste alone, stable anaerobic digestion of food waste was achieved for 368 days by supplementing trace elements. Under the conditions of OLR (organic loading rates) of 2.19-6.64 g VS (volatile solid)/L day and 20-30 days of HRT (hydraulic retention time), a high methane yield (352-450 mL CH(4)/g VS(added)) was obtained, and no significant accumulation of volatile fatty acids was observed. The subsequent investigation on effects of individual trace elements (Co, Fe, Mo and Ni) showed that iron was essential for maintaining stable methane production. These results proved that the food waste used in this study was deficient in trace elements.     

废水厌氧处理系统微量金属生物有效度及影响因素

介绍了废水厌氧处理系统中微量金属营养元素生物有效度的概念,分析了影响微量金属营养元素生物有效度的诸多因素。厌氧生物处理系统存在微量金属营养元素并不等于存在微量金属营养元素生物有效度;对厌氧生物处理系统进行微量金属营养元素生物有效度的检定是非常必要的;微生物的螯合作用对微量金属营养元素生物有效度起非常重要的作用;微量金属营养元素必须直接加入反应器内才能充分保证其生物有效度。