垃圾焚烧飞灰中的重金属污染物处理方法

随着垃圾焚烧技术在各个城市生活垃圾处理中的广泛应用,对生活垃圾焚烧的残余物,主要是飞灰的处理、处置,已成为困扰人们生产生活的重要难题之一。飞灰的处理是控制重金属污染的关键,目前处理垃圾焚烧飞灰中重金属污染物的常用方法有：水泥固化法、化学药剂稳定法、飞灰热处理、化学浸提法等,生物淋滤法是近年新兴起来的金属浸提技术。经处理后的飞灰可进行填埋或资源化利用。因此,着重叙述了当前有关垃圾焚烧飞灰中重金属污染的控制方法与处置技术的研究现状。     

Medium-Sulfur Coal and Fly Ash Resistivity

Electric generating plants burning medium-sulfur coal need a way to predict when ESP performance will be limited by high electrical resistivity of the collected fly ash. The main uncertainty in mathematical predictions of fly ash resistivity lies in the marginal effect of naturally occurring SO₃ vapor in the flue gas. This paper results from a project to expand the data base of SO₃/SO₂ concentrations and fly ash resistivities measured in utility fly ash precipitators. Complete data sets are presented from three plants in the Southern Company electric system. In situ resistivity data are compared with laboratory measurements and with two different mathematical predictions of resistivity based on coal and ash analyses. The revised version of the resistivity predictor gives results in good agreement with resistivity values measured both in situ and in the laboratory.     

粉煤灰在环境工程中的应用

结合改性粉煤灰处理含铅废水的研究成果，系统地阐述了粉煤灰在环境工程领域中的应用，总结了用粉煤灰处理废水的工艺流程和工艺参数，指出了应用中存在的问题和今后研究的重点。     

Conditioning of Fly Ash with Ammonia

This paper presents the results of an investigation of the conditioning of fly ash with ammonia in electrostatic pre-cipitators of power plants operated by the Tennessee Valley Authority. It focuses attention primarily on the mechanisms of conditioning encountered under the particular circumstances available for study. No effect of ammonia on the electrical resistivity of fly ash was evident. Instead, the effect of ammonia appeared to be an enhancement pf the space-charge component of the electric field used for charging and precipitating particles of fly ash. In addition, a second effect appeared to be an increase in the cohesiveness of precipitated ash and a reduction in the quantity of ash reentrained during electrode rapping. Data demonstrating the value of ammonia conditioning for lowering the emission pf fly ash during three precipitator studies are presented. Reasons for the ineffectiveness of ammonia conditioning during a fourth precipitator study are discussed. In conclusion, comments are made about the effects to be expected from ammonia conditioning under circumr stances different from those investigated experimentally, particularly with ammonia as a conditioning agent for fly ash from low sulfur western coal.     

The Effective Collection of Fly Ash At Pulverized Coal-Fired Plants

The relationship between sulfur in coal, boiler exit gas temperature, and the carbon portion of fly ash have a major effect on the electrical properties of fly ash. Whether effective collection of fly ash is obtained by the electrostatic precipitator installation alone or the precipitator—mechanical combination depends primarily on a knowledge of this relationship. Fly ash electrical properties can range from a highly "resistive" to a highly "conductive" state which can appreciably alter the precipitator collection performance. A correlation of coal sulfur and boiler exit flue gas temperature is given to indicate the probability of expecting an optimum voltage—current relationship with different combinations of these factors. Carbon affects the electrical conditioning of fly ash by providing parallel paths of current leakage through the deposited dust layer. Therefore, removal of the carbon particles in a mechanical collector placed before the precipitator can alter the precipitator electrical characteristics.     

Dehalogenation Potential of Municipal Waste Incineration Fly Ash

BACKGROUND, AIMS AND SCOPE: In the first part of this paper the main principles which control the dehalogenation of polychlorinated aromatic compounds on municipal waste incineration fly ash (MWI-FA) have been discussed and the model fly ash of similar dehalogenation activity has been proposed. Even if both systems show comparable dehalogenation properties, the main question concerning the postulated identical reaction mechanism in both cases is left unanswered. The other very important point is to what extent is this dechlorination mechanism thermodynamically controlled. The same problem is often discussed in the literature also for the de novo synthetic reactions. From the data it is clear that metallic copper plays a decisive role in the mechanism of the dehalogenation reaction. Although the results reported in the first part strongly support the idea that copper acts in this dechlorination as the reaction component, in contrast to its generally accepted catalytic behaviour, we believed that additional support for this conclusion can be obtained with the help of a thermodynamic interpretation of the mechanism of the reaction. RESULTS AND DISCUSSION: The pathways of hexachlorobenzene dechlorination on MWI-FA and model fly ash were studied in a closed system at 260-300 degrees C under nitrogen atmosphere. These pathways were the same for both systems, with the following prevailing sequences: hexachlorobenzene --> pentachlorobenzene --> 1,2,3,5-tetrachlorobenzene --> 1,3,5-trichlorobenzene --> 1,3-dichlorobenzene. Thermodynamic calculations were carried out by using the method of minimization total Gibbs energy of the whole system. In the calculations, the following reaction components were taken into account: all gaseous chlorinated benzenes, benzene, hydrogen chloride, a gaseous trimer Cu3Cl3, and also Cu2O and CuCl2 as solid components. The effect of the reaction temperature and the amount of copper and water vapour were considered as well. The effect of reaction temperature was determined from the data calculated for the 500 to 750 K temperature region. The effect of the initial composition was determined for the molar amounts of copper = 0.01-3 moles and water vapour = 0.2 to 3 moles per mole of chlorobenzene isomer CONCLUSIONS: The results of hexachlorobenzene dechlorination by MWI-FA and model fly ash under comparable reaction conditions allow us to conclude that both dechlorinations proceed via the same dechlorination pathways, which can be taken as an evidence of the identical dehalogenation mechanism for both systems. The relative percentual distribution of the dehalogenated products depends on the temperature, but not on the initial amount of water vapour or copper metal. On the other hand, the initial amount of copper substantially affects the conversion of the dehalogenation as well as the molar ratio of Cu3Cl3 to HCl in the equilibrium mixture. Comparison of the experimental with thermodynamic results supports the idea that dehalogenation reactions are thermodynamically controlled. RECOMMENDATIONS AND OUTLOOK: Thermodynamic analysis of the dehalogenation reactions may prove useful for a wide range of pollutants. The calculations concerning polychlorinated biphenyls and phenols are under study.     

Informative Air Pollution Problems in Fly Ash Sintering Plant

A long-term field and laboratory program designed to determine and understand the effects of air pollutants on the performance of electric contact materials has reached the one-year mark. An extensive variety of metals has been exposed at six field environments, for periods up to one year (August 1963 to August 1964). These environments were selected to provide a wide range of air pollutants in typical data processing or process control situations. The program undertakes to determine material degradation as a function of time and environment. The important air pollutants at the field sites are measured regularly, and materials are returned periodically to the laboratory for evaluation using techniques developed specifically for this program. The results of the program to date are presented, and preliminary correlations are drawn.     

Effects of the Basicity on the Comelting Conditions of Municipal Solid Waste Incinerator Fly Ash and Sewage Sludge Ash

Abstract

In this study, the effects of the basicity on the pouring point of the municipal solid waste incinerator fly ash-sewage sludge ash mixture is investigated. Four kinds of sewage sludge ash, which were collected from several primary and secondary sewage treatment plants and were produced by different processes and sludge conditioning alternatives, were used as modifiers. The results indicate that the pouring point of the mixture increased with increasing basicity, within the range of 0.65–1.90. The pouring point is affected by the contents of the mixtures (CaO, SiO₂, Al₂O₃, and the flux). It is suggested that an increase in the CaO content tends to raise the pouring point, whereas an increase in the SiO₂ and/or the Al₂O₃ contents cause as adverse reaction. The prediction equation, obtained by multilinear regression (significant level is 0.05), is as follows: pouring temperature =1189.6 + 4.19CaO-0.96 SiO₂-4.33 Al₂O₃ (R² = 0.91). In general, the pouring point decreased when the basicity was <1. The pouring point apparently increased when the basicity was>1.2. The regression squares for the different basicities were between 0.84 and 0.91. From these relationships, we note that a basicity index of 5 gave the best R² (0.91). From the results of this study, it can be concluded that the modification of the basicity of the fly ash by the addition of sewage sludge ash to lower the pouring point is feasible and leads to a more energy-efficient melting process. In addition, these synthetic slags have a good pozzolanic reactive activity.     

垃圾焚烧飞灰的稳定化处置与资源化利用研究进展

随着垃圾焚烧处理日益广泛的应用，垃圾焚烧飞灰的稳定化处置和资源化利用成为一个亟待解决的问题。文中对垃圾焚烧飞灰的稳定化处置和资源化利用技术分别进行了综合论述，为飞灰的无害化和资源化处理提供参考。     

Fate of Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans in a Fly Ash Treatment Plant

Abstract

To understand the fate of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in a fly ash treatment plant that used the Waelz rotary kiln process (hereafter the Waelz process), the samples of input and output media were collected and analyzed. The most important PCDD/F source in input mass was electric arc furnace (EAF) fly ash, which had a mean PCDD/F content of 18.51 ng/g and contributed more than 99% of PCDD/F input mass, whereas the PCDD/F input mass fractions contributed by the coke, sand, and ambient air were only 0.04%, 0.02%, and 0.000002%, respectively. For the PCDD/F output mass in the Waelz process, the major total PCDD/F contents of 43.73 and 10.78 ng/g were in bag-filter and cyclone ashes, which accounted for approximately 69% and 17%, respectively, whereas those of stack flue gas and slag were 14% and 0.423%, respectively. The Waelz process has a dechlorination mechanism for higher chlorinated congeners, but it is difficult to decompose the aromatic rings of PCDD/Fs. Therefore, this resulted in the accumulation of lower chlorinated congeners. The output/input ratio of total PCDD/F mass and total PCDD/F international toxicity equivalence (I-TEQ) was 0.62 and 1.19, respectively. Thus, the Waelz process for the depletion effect of total PCDD/F mass was positive but minor, whereas the effect for total PCDD/F I-TEQ was adverse overall.     

Control of Fly Ash from Conventional Coal-Fired Utility Boilers

This paper presents a detailed review and critical evaluation of current technologies as applied to fine particulate emissions from coal-fired utility boilers. Quantitative assessments of the capabilities of both conventional and novel air pollution control devices to meet three different performance standards—the present New Source Performance Standard (NSPS) of 0.03 Ib particulate/MBtu heat input, and standards of 0.05 and 0.1 Ib particulate/MBtu are included. Each of the three conventional devices (electrostatic precipitator, fabric filter baghouse, and wet scrubber) is compared and rated with respect to eight different performance categories. This information can be used to determine the relative effectiveness and attractiveness of these three control devices. Novel devices are compared and rated in the same manner, the conclusions from which may provide the research administrator with a guide for the selection of those novel devices which offer the best potential for commercialization.

The major conclusions of the investigation are: (1) The use of conventional scrubbers for fine particulate control on coal-fired utility boilers may no longer be feasible at the new NSPS of 0.03 Ib/MBtu. (2) At the old NSPS (0.1 Ib/MBtu) conventional electrostatic precipitators and baghouses were often competitive. For the new stricter standard, however, the baghouse generally is the more attractive alternative. (3) Novel devices appear to offer almost no hope for this particular application (at a commercial level) between now and 1985 and only little hope before 1990.     

Flow Injection Analysis of MWC Fly Ash Leaching Characteristics

Abstract

A completely mixed batch reactor leaching method utilizing flow injection analysis (the CMBR-FIA method) was developed to study the lead leaching characteristics of municipal waste combustor fly ash. Flow injection analysis (FIA) coupled with atomic absorption spectrophotometry enabled the determination of lead concentrations at one minute intervals. The pH and oxidation-reduction potential of the solution were continuously monitored to characterize the leaching conditions. Automatic titration was used to alter the solution pH to defined endpoints. The CMBR-FIA method offers the ability to immediately observe alterations to the leaching solution, and grants the freedom to study a number of parameters concurrently. The CMBR-FIA method is a rapid and reliable means to investigate leaching characteristics. This paper describes the method and demonstrates its use to monitor the leaching of lead from municipal solid waste combustor fly ash as a function of pH. Soluble lead concentrations are shown to increase quickly with decreasing pH.

A maximum of 50% of the total lead concentration was available in solution at pH 2. This value gradually decreased with time to over 35% of the total.     

Filtration Properties of Fly Ash from Fluidized Bed Combustion

Some of the features of the fluidized-bed combustion (FBC) process have a direct bearing on the particulate properties that most strongly influence filtering pressure drop. A laboratory program was conducted to experimentally determine the relative pressure drop characteristics of ashes from the TVA-EPRI 20-MW bubbling bed, atmospheric pressure FBC (AFBC) pilot plant and six pulverized-coal combustion (PC) units. The combined influences of measured particle and dust cake properties on filtering pressure drop were estimated with existing filtration theories. These theories predict a higher pressure drop for a dust cake produced with the AFBC ash than for one consisting of any of the PC ashes. Laboratory measurements were made of the flow resistance of idealized, simulated dust cakes to confirm these predictions. Field operating data from the fabric filters collecting some of the tested ashes were available to validate the laboratory results. The laboratory and field data show relatively good agreement. The AFBC ash must be treated as a special case for fabric filters, and careful selection of cleaning method and fabric must be made to minimize the inherently high pressure drop characteristics of this ash.     

Zeolite Formation from Coal Fly Ash and Its Adsorption Potential

Abstract

The possibility in converting coal ?y ash (CFA) to zeolite was evaluated. CFA samples from the local power plant in Prachinburi province, Thailand, were collected during a 3-month time span to account for the inconsistency of the CFA quality, and it was evident that the deviation of the quality of the raw material did not have significant effects on the synthesis. The zeolite product was found to be type X. The most suitable weight ratio of sodium hydroxide (NaOH) to CFA was approximately 2.25, because this gave reasonably high zeolite yield with good cation exchange capacity (CEC). The silica (Si)-to-aluminum (Al) molar ratio of 4.06 yielded the highest crystallinity level for zeolite X at 79% with a CEC of 240 meq/100 g and a surface area of 325 m²/g. Optimal crystallization temperature and time were 90 °C and 4 hr, respectively, which gave the highest CEC of approximately 305 meq/100 g. Yields obtained from all experiments were in the range of 50–72%.     

An Assessment of the Significance of Mercury Release from Coal Fly Ash

Abstract

Some mercury (Hg) naturally present in coal is retained in the fly ash remaining after combustion. Concern has been raised regarding the potential for release of this Hg to the environment. The exchange of Hg between fly ash and the atmosphere was measured in the laboratory and in situ at a fly ash landfill. All samples of fly ash used in the laboratory study, with the exception of that derived from lignite-type coal, acted as a sink for atmospheric Hg. Deposition rates were found to increase as air Hg concentrations increased and to decrease with incident light and increased temperature. Addition of water to fly ash samples resulted in re-emission of deposited atmospheric Hg. Deposition was the dominant flux measured in situ at a fly ash landfill. Atmospheric Hg was deposited to all samples collected as part of two demonstration projects using carbon injection for enhanced Hg capture. Hg concentrations of extracts derived using U.S. Environmental Protection Agency Method 1312 (Synthetic Precipitation Leaching Procedure) were ≤14.4 ng/L. Data developed demonstrate that fly ash, including that collected from Hg removal projects, will release little Hg to the air or water, and under certain conditions, absorbs Hg from the air.     

粉煤灰混凝剂用于造纸黑液处理研究

在常温下，用硫酸、盐酸或其混合酸搅拌浸取粉煤灰2h，制得粉煤灰混凝剂。经混合酸处理的3^#粉煤灰混凝剂对造纸黑液混凝效果好，COD去除率为80％，浊度去除率为88％，色度达到2^4。添加了部分硫铁矿渣的6^#混凝剂，COD去除率为86％，浊度去除率可达94％。3^#混凝剂与PY型混凝剂、A12(S04)3、浓H2S04相比，具有去除效率高、运行费用低和以废治废的特点。     

Fly Ash from Electrostatic Precipitators: Characterization of Large Spheres

The body of information contained in this paper is directed towards individuals concerned with the toxicology and physical state of airborne effluents from pulverized coal-fired stationary sources. A flotation/sedimentation technique was used to separate fly ash from power plant clean-up devices into light, medium, and high density fractions. Large spherical particles were selected from each fraction and examined by optical and scanning electron microscopy. Attempts were made to identify pleurospheres (filled hollow spheres) by crushing the spheres in situ under the optical microscope. In no cases were filled spheres observed, suggesting that they are not a common structure in fly ash. Several phenomena which generate hollow spheres are discussed.     

公路周边土壤重金属污染及植物修复

随着中国公路建设迅猛发展,公路周边土壤重金属污染也日趋严重。文中结合近年来国内外的研究情况,以公路土壤污染中的铅、镉、锌、铜、铬等元素为重点,对土壤重金属污染的危害、分布特征及其影响因素,以及相应的植物修复技术等相关研究进行综述。     

Preparation of Calcium Silicate Reagent from Fly Ash and Lime in a Flow Reactor

Abstract

The batch reaction between fly ash and hydrated lime in water to produce high surface area calcium silicates for flue gas desulfurization has been examined extensively. This paper examines the reaction in a flow reactor using two low-calcium fly ashes and introducing gypsum, calcium sulf ite hemihydrate, and calcium chloride as additives to the reaction. The flow system is compared to the batch reaction at similar operating conditions and a segregated flow model is used to approximate flow reactor behavior.

Experiments with calcium chloride and gypsum additives were modeled fairly well by the segregated flow approximation at residence times less than 12 hours. The flow reactor produced low surface area material at longer residence times when gypsum was present. Because the changing solution chemistry affected the batch reaction rate the fly ash and hydrated lime system without gypsum or calcium chloride could not be approximated using batch reaction data. In this case, the flow reactor produced higher surface area product than the batch reactor for a given residence time due to the increased calcium hydroxide availability.