燃煤过程中微量元素砷和硒形态转化的热力学平衡模拟

砷和硒是煤中的易挥发有毒微量元素。由于砷和硒在燃煤烟气中的浓度极低以及实验条件的限制，目前化学热力学平衡分析已成为预报烟气中砷和硒等有毒元素形态分布的主要理论分析方法，本文综述了热力学平衡分析方法应用于砷和硒在燃煤过程中形态转化和平衡分布等方面的研究进展，首先用于热力学平衡分析的是含有砷或硒一种微量元素和煤中主量元素及氯元素的简单体系，并假设烟气中只有理想气体组成的气相和纯凝聚相的理想模型。然而是否考虑砷和硒与其他微量、主量或次量元素的相互作用，砷和硒所有可能存在的反应，以及在熔融相砷和熔融物的结合会严重地影响模型的预报结果，因此，目前热力学平衡体系已发展成为包括砷和硒在内的多个微量元素和煤中所有主量、次量元素，以及包括熔融相在内的非理想多相复杂体系。     

燃煤二氧化硫释放和钙基脱硫剂的反应特性

我国是以煤炭为主要能源的国家。煤中通常含有硫,硫燃烧后生成的SO_2是影响环境质量的最主要污染源之一。国家新颁布的《锅炉大气污染物排放标准》增加了关于燃煤SO_2控制限值的条款,因此降低燃煤SO_2排放是一项很重要的课题。 一、硫在煤中的存在形态和含量 煤中的硫以各种不同的形态存在,一般可分为可燃硫和不燃硫二类。不燃硫主要是硫酸盐硫(S_(I.Y)),通常是石膏,有时还含有绿矾(FeSO_4·7H_2O)等。可燃硫包括有机硫(S_(YJ))和无机硫(S_(LT))。有机硫的分子结构可表示为C_xH_yS_z。可燃硫中无机硫主要是黄铁矿,有些煤含有少量的元素硫和方铅矿(PbS)、闪锌矿(ZnS)等。我国的煤含硫量各地差别较大,通常在0.3％～6.5％之间。全国平均在1.68％左右。 二、SO_2的释放规律     

燃煤电厂静电除尘器协同控制汞排放

对燃煤电厂静电除尘设备协同控制汞排放影响因素展开深入研究,主要分析除尘器前后烟气中汞形态浓度的变化情况、除尘器内部飞灰对烟气汞的吸附及SCR脱硝反应器对除尘器脱汞的影响。采用安大略法和Lumex汞分析仪分别对我国8家电厂烟气、煤和灰中汞含量进行了测试,并对某电厂SCR反应器前后飞灰汞含量进行了测试对比。     

粉煤灰的处理和利用

燃煤发电厂每年排出大量由煤的灰分形成的各种煤灰渣——粉煤灰、炉渣和熔渣,其中绝大部分是从煤燃烧后的烟气中收捕下来的细灰,我们称之为粉煤灰。 粉煤灰是我国当前排量较大、较集中的工业废渣之一。现阶段我国年排渣量已达三     

用数值模拟方法研究含硫颗粒物生成过程

为了研究不同燃烧条件对燃煤中含硫颗粒物生成的影响,利用数值分析方法模拟炉膛煤燃烧。通过改变燃烧环境温度、进口氧气所占总气体摩尔比,分析得到的碳烟(soot)颗粒、SO2和CO2等主要物质浓度场。模拟结果能够很好地反映炉膛内各物质生成趋势和历程。生成的碳烟颗粒中富集煤中一部分硫元素,燃烧后期未被氧化的碳烟颗粒是燃煤烟气含硫颗粒物的一个重要来源。进口O_2摩尔比从0.1~0.5时碳烟颗粒迅速被氧化,出口处产生含硫碳烟颗粒物减少。在1 200~1 600 K范围内,温度增高不利于碳烟颗粒的生成,来源于碳烟颗粒的含硫颗粒物也就逐渐减少。     

同位素稀释质谱法测定粉煤灰标准参考物质中痕量铅

煤是重要的能源之一,我国又是以煤为主要能源的国球。研究和防治燃煤对环境的污染是非常重要的课题。粉煤灰是热电厂、钢铁厂和供热中心等排出而又广泛存在的污染物质。铅是有毒元素之一,准确测定其含量,这对作环境评价和粉煤灰的再资源化都是十分必要的。标准参考物质既能用来校准仪器,提高分析质量,又能检查和校对新建立的分析方法,促进测试技术的提高。国外50年代就开展了这项工作。近些年来我国对此也十分重视,相继     

燃煤钙基固砷剂的影响因素研究

利用电石渣、CaCO3、CaCO3·Ca(OH)3和Ca(OH)2作为燃煤钙基固砷剂,通过正交试验研究了固砷剂种类、固砷剂用量、燃烧温度及煤粒径对固砷效果的影响.结果表明,燃烧温度是影响燃煤固砷的最显著因素,最佳为1 050℃;钙基固砷剂中CaCO3和电石渣的固砷效果最好,其次是CaCO3·Ca(OH) 2,Ca(OH) 2的固砷效果最差;钙基固砷剂用量按Ca、S摩尔比计量为2.0、煤粒径为160～200目时,钙基固砷剂具有较好的固砷效果,而且具有固砷固硫的双重作用.     

土壤固相吸附砷的研究进展

砷是一种常见的有毒元素,土壤砷污染与修复问题已引起世界范围的广泛关注。土壤原位修复是消除土壤砷污染的有效方法,其中砷在土壤固相上的吸附也是近年来的研究热点。土壤固相广泛存在于土壤中,并具有表面积大和表面电荷等理化性质,它可通过与砷酸根阴离子发生表面配位反应,形成内外层配位体等方式来固定土壤中的砷,以降低金属离子的迁移能力和有效性,是一种有效的原位减轻砷污染的方法。文中简单介绍了砷污染的现状、危害和赋存状态,重点介绍了铁铝锰的氧化物和氢氧化物、粘土矿物、有机质等土壤固相对砷的吸附机理及其影响因素,旨在更好地掌握砷的吸附行为。     

Ⅱ、渤海湾的悬浮物和沉积物的中子活化分析

一、序言测定海水、海水中的悬浮物以及海底的沉积物中微量元素的浓度,可以为评价海洋的污染情况和研究污染元素的迁移转化规律提供重要依据。悬浮物和沉积物的特点是:(1)基体成分复杂,对于待分析元素易产生干扰,因此要求分析方法分辨率高;(2)海水中悬浮物的总量很少,故要求分析方法取样量要小,而且最好对同一份样品可以做多元素测定;(3)样品中     

污泥焚烧中Cd形态转化的热力学平衡模拟

采用热力学平衡分析方法,结合典型污泥成分和焚烧条件预测了污泥焚烧过程中重金属Cd的转化和迁移规律。模拟计算中考虑了主量矿物质与Cl、S对Cd的形态转化的影响。研究结果表明,污泥焚烧过程中,在低温的条件下Cd主要以固体碳酸盐形式存在,随着温度升高,碳酸盐分解为固态CdO,随后有气态Cd(OH)2、Cd和CdO生成,并且在较高温度主要以气态Cd存在。焚烧体系中,矿物质SiO2对Cd的形态转化影响大于其他矿物质,SiO2能与Cd结合生成稳定的CdSiO3,从而可有效抑制含Cd气态污染物的排放。焚烧体系中Cl较易与Cd结合形成CdCl2而导致Cd的挥发,Cl含量的增加促进了Cd在焚烧体系中的挥发。在低温阶段,Cd易与S结合形成固态硫酸盐,抑制了金属的挥发;在高温阶段,金属的形态转化基本不受S的影响,但是可以影响气态金属Cd的生成温度。根据污泥在不同焚烧温度、Cl含量、S含量条件下Cd的不同产物形态,可以对Cd的污染进行有效控制。     

Ruminant uptake of nickel and other elements from industrial air pollution in the Norwegian-Russian border area

Concentrations of the elements aluminium, arsenic, cadmium, chromium, cobalt, copper, lead, mercury, nickel, selenium and zinc in liver, and of nickel in kidneys, were studied in reindeer, moose and sheep from South Varanger in eastern Finnmark and comparable districts in western Finnmark, Norway. The study included samples from 31 reindeer, 10 moose and 10 sheep from Jarfjord (South Varanger); 31 reindeer, 27 moose and 15 sheep from Pasvik (South Varanger); and 40 reindeer, 16 moose and 15 sheep from western Finnmark. Levels of arsenic, copper, nickel and selenium were much higher in reindeer from one or both areas in South Varanger than in reindeer from western Finnmark. Levels of chromium, cobalt and zinc were also significantly higher in South Varanger reindeer than in reindeer from the reference area. Within South Varanger the highest levels of these elements were invariably found in the Jarfjord area. For the other elements studied hepatic levels in South Varanger were similar to or lower than in western Finnmark. Also in moose, higher levels of nickel and of selenium (Jarfjord only) were found in the South Varanger samples than in samples from western Finnmark. In sheep, on the other hand, levels in South Varanger samples were similar to levels in western Finnmark for all the elements studied. Comparing the results with reports on pollution of air and vegetation, it was concluded that for all the elements showing higher levels in reindeer and moose from South Varanger compared to the reference areas, the effect most probably was a result of atmospheric transport of industrial pollution from the nearby Russian towns Nikel and Zapoljarnij. The geographical and interspecies differences within the South Varanger samples support this conclusion.     

Susceptibility of different yeast species to environmental toxic metals

The purpose of the study reported here was to investigate the relative resistance of yeast species to various metallic and metalloid ions, with a view to gaining more knowledge on this subject, as resistant species may become dominant in habitats contaminated with the relevant metals. Saccharomyces cerevisiae, Candida albicans and Candida tropicalis were grown in media containing different concentrations of mercury (as HgCl(2)), cadmium (as CdCl(2)), lead (as Pb(CH(3)COO)(2)), arsenic (as Na(2)HAsO(4)) and selenium (as Na(2)SeO(3)) for various intervals. Invariably, the two Candida species turned out to be more resistant to all the metals studied than S. cerevisiae. The metal showing the highest toxicity for these species was mercury, with cadmium being the second, lead, the third and arsenic and selenium being the least toxic elements. Strains showing resistance to mercury were isolated, even in the case of S. cerevisiae.     

Emission inventory and sources of polycyclic aromatic hydrocarbons in the atmosphere at a suburban area in Taiwan

The application of a chemical mass balance air pollution model to ambient measurements of polycyclic aromatic hydrocarbons (PAHs) is presented. Sixteen air samples were collected at seven sites in a suburban area in Taiwan and analyzed for the concentration of 21 compounds between July 2001 and September 2001. Each ambient sample was evaluated for the PAH contribution from six sources (heavy oil combustion, natural gas combustion, coal combustion, diesel combustion, vehicles and municipal solid waste incinerator). Average predictions agree well with the emission inventory. By this method, the average contributions are 49%, 14%, 22%, 12%, and 2% from vehicles, heavy oil combustion, natural gas combustion, coal combustion and diesel combustion at these seven receptors. By far, vehicles are the major PAH emission sources and municipal solid waste incinerator is a minor contributor. The calculated result of particulate PAHs is compared with that of total (gaseous and particulate) PAHs. The estimate based on total PAHs is better than the estimate based on particulate PAHs only. Contributions of eight low reactive PAHs for the same emission sources and receptors were calculated. Atmospheric reactivity seems not a problem for source apportionment in this study.     

The application of regenerable sorbents for mercury capture in gas phase

Mercury is a well-known toxic element, and flue gas streams emitted from coal-fired utilities are one of the largest anthropogenic sources of this element. This study briefly reviews the proposed technologies for reducing mercury emissions from coal combustion, focusing on an emerging process which involves the use of regenerable sorbents and especially those loaded with noble metals. Among the mercury species formed during coal combustion, elemental mercury is the most difficult to remove from the flue gases due to its low reactivity and insolubility in water. The widespread interest in using regenerable sorbents with metals is due to their ability to retain elemental mercury. With this technology, not only can efficiencies of 100 % be reached in the retention of elemental mercury but also a way to avoid the generation of new wastes loaded with mercury. This study considers the main aspects that must be taken into account when developing effective regenerable sorbents for mercury capture, with special attention to sorbents containing noble metals. The characteristics of this process are compared with those of other processes in a more advanced state of development.     

health effects associated with increased use of coal

The increased use of coal projected under the National Energy Plan has raised fears of increased morbidity and mortality related to fossil fuel combustion products. The evidence for adverse health effects from the major emissions of coal combustion is considered, as well as the basis for predictions of an increase in morbidity and mortality. It can be concluded that with presently available control technology, no detectable adverse health effects will be observed associated with increased coal combustion. It is further concluded that a reduction in energy supply, or a large increase in energy cost leading to reduced energy supply to lower socio-economic groups will cause far more demonstrable adverse health effects than increased coal utilization.     

PAH and soot emissions from burning components of medical waste: examination/surgical gloves and cotton pads

This is a laboratory investigation on the emissions from batch combustion of representative infectious ("red bag") medical waste components, such as medical examination latex gloves and sterile cotton pads. Plastics and cloth account for the majority of the red bag wastes by mass and, certainly, by volume. An electrically heated, horizontal muffle furnace was used for batch combustion of small quantities of shredded fuels (0.5-1.5 g) at a gas temperature of approximately 1000 degrees C. The residence time of the post-combustion gases in the furnace was approximately 1 s. At the exit of the furnace, the following emissions were measured: CO, CO2, NOx, particulates and polynuclear aromatic compounds (PACs). The first three gaseous emissions were measured with continuous gas analyzers. Soot and PAC emissions were simultaneously measured by passing the furnace effluent through a filter (to collect condensed-phase PACs) and a bed of XAD-4 adsorbent (to capture gaseous-phase PACs). Analysis involved soxhlet extraction, followed by gas chromatography-mass spectrometry (GC-MS). Results were contrasted with previously measured emissions from batch combustion of pulverized coal and tire-derived fuel (TDF) under similar conditions. Results showed that the particulate soot) and cumulative PAC emissions from batch combustion of latex gloves were more than an order of magnitude higher than those from cotton pads. The following values are indicative of the relative trends (but not necessarily absolute values) in emission yields: 26% of the mass of the latex was converted to soot, 11% of which was condensed PAC. Only 2% of the mass of cotton pads was converted to soot, and only 3% of the weight of that soot was condensed PAC. The PAC yields from latex were comparable to those from TDF. The PAC yields from cotton were higher than those from coal. A notable exception to this trend was that the three-ring gas-phase PAC yields from cotton were more significant than those from latex. Emission yields of CO and CO2 from batch combustion of cotton were, respectively, comparable and higher than those from latex, despite the fact that the carbon content of cotton was half that of latex. This is indicative of the more effective combustion of cotton. Nearly all of the mass of carbon of cotton gasified to CO and CO2 while only small fractions of the carbon in latex were converted to CO2 and CO (20% and 10%, respectively). Yields of NOx from batch combustions of latex and cotton accounted for 15% and 12%, respectively, of the mass of fuel nitrogen indicating that more fuel nitrogen was converted to NOx in the former case, possibly due to higher flame temperatures. No SO2 emissions were detected, indicating that during the fuel-rich combustion of latex, its sulfur content was converted to other compounds (such as H2S) or remained in the soot.     

The effect of coal combustion flue gas components on low-level chlorine speciation using EPA method 26A

U.S. Environmental Protection Agency (EPA) Method 26A is the recommended procedure for capturing and speciating halogen (X2) and hydrogen halide (HX) stack emissions from combustion sources. Previous evaluation studies of Method 26A have focused primarily on hydrogen chloride (HCl) speciation. Capture efficiency, bias, and the potential interference of Cl2 at high levels (> 20 ppm [microgram/m3]) and NH4Cl in the flue gas stream have been investigated. It has been suggested that precise Cl2 measurement and accuracy in quantifying HX or X2 using Method 26A are difficult to achieve at Cl2 concentrations < 5 ppm; however, no performance data exist to support this. Coal contains low levels of Cl, in the range of 5-2000 ppmw, which results in the presence of HCl and Cl2 in the products of combustion. HCl is the predominant Cl compound formed in the high-temperature combustion process, and it persists in the gas as the products of combustion cool. Concentrations of Cl2 in coal combustion flue gas at stack temperatures typically do not exceed 5 ppm. For this research, bench-scale experiments using simulated combustion flue gas were designed to validate the ability of Method 26A to speciate low levels of Cl2 accurately. This paper presents the results of the bench-scale tests. The effect of various flue gas components is discussed. The results indicate that SO2 is the only component in coal combustion flue gas that has an appreciable effect on Cl2 distribution in Method 26A impingers, and that Method 26A cannot accurately speciate HCl and Cl2 in coal combustion flue gas without modification.     

Electromigration of arsenic and co-existing metals in mine tailings

The aim of this study was to investigate the feasibility of enhanced electrokinetic remediation technology for controlled leaching and collection of labile arsenic fractions from mine tailings. Direct current was applied to tailings for 20 d using ammonium oxalate and sodium hydroxide as enhancement solutions. Migration of arsenic was observed, resulting in 63-71% removal near the cathode but only 6-17% overall removal in the entire tailings matrix in 20 d. However, significant migration of arsenic towards the anode and accumulation in a collection well near the anode was observed, especially under alkaline conditions. Thus, treatment time and consumption of chemicals could probably be reduced by installing specific collection or adsorption zones near the anode. A relationship between electrokinetic mobility of arsenic and other elements and their extractability in sequential extraction tests was established, indicating that dissolution or desorption of the elements and thermodynamic conditions (pH and Eh gradient) played a bigger role in the electrokinetic removal process than electromigration of soluble ions.     

State of energy consumption and CO2 emission in Bangladesh

Carbon dioxide (CO2) is one of the most important gases in the atmosphere, and is necessary for sustaining life on Earth. It is also considered to be a major greenhouse gas contributing to global warming and climate change. In this article, energy consumption in Bangladesh is analyzed and estimates are made of CO2 emission from combustion of fossil fuel (coal, gas, petroleum products) for the period 1977 to 1995. International Panel for Climate Change guidelines for national greenhouse gas inventories were used in estimating CO2 emission. An analysis of energy data shows that the consumption of fossil fuels in Bangladesh is growing by more than 5% per year. The proportion of natural gas in total energy consumption is increasing, while that of petroleum products and coal is decreasing. The estimated total CO2 release from all primary fossil fuels used in Bangladesh amounted to 5072 Gigagram (Gg) in 1977, and 14 423 Gg in 1995. The total amounts of CO2 released from petroleum products, natural gas, and coal in the period 1977-1995 were 83 026 Gg (50% of CO2 emission), 72 541 Gg (44% of CO2 emission), and 9545 Gg (6% CO2 emission), respectively. A trend in CO2 emission with projections to 2070 is generated. In 2070, total estimated CO2 emission will be 293 260 Gg with a current growth rate of 6.34% y . CO2 emission from fossil fuels is increasing. Petroleum products contribute the majority of CO2 emission load, and although the use of natural gas is increasing rapidly, its contribution to CO2 emission is less than that of petroleum products. The use of coal as well as CO2 emission from coal is expected to gradually decrease.     

Analysis and discussion on formation and control of primary particulate matter generated from coal-fired power plants

Particulate matter (PM) has been becoming the principal urban pollutant in many major cities in China, and even all over the world. It is reported that the coal combustion process is one of the main sources of PM in the atmosphere. Therefore, an investigation of formation and emission of fine primary PM in coal combustion was conducted. First, the sources and classification of coal-fired primary PM were discussed; then their formation pathways during the coal combustion process were analyzed in detail. Accordingly, the emission control methods for fine particles generated from coal-fired power plants were put forward, and were classified as precombustion control, in-combustion control, and postcombustion control. Precombustion control refers to the processes for improving the coal quality before combustion, such as coal type selection and coal preparation. In-combustion control means to take measures for adjusting the combustion conditions and injection of additives during the combustion process to abate the formation of PM. Postcombustion control is the way that the fine PM are aggregated into larger ones by some agglomeration approaches and subsequently are removed by dust removal devices, or some high-performance modifications of conventional particle emission control devices (PECDs) can be taken for capturing fine particles. Finally, some general management suggestions are given for reducing fine PM emission in coal-fired power plants.

ImplicationsThe analysis and discussions of coal properties and its combustion process are critical to recognizing the formation and emission of the fine primary PM in combustion. The measures of precombustion, in-combustion, and postcombustion control based on the analysis and discussions are favorable for abating the PM emission. Practically, some measures of implementation do need the support of national policies, even needing to sacrifice economy to gain environmental profit, but this is the very time to execute these, and high-performance PECDs, especially novel devices, should be used for removing fine PM in flue gas.