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.     

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.     

Generation of PCDD/F in Fly Ash from Municipal Solid Waste Incinerators

Abstract

Fly ash from municipal solid waste incinerators (MSWIs) has been characterized in terms of polychlorinated dibenzyl-p-dioxin and polychlorinated dibenzofuran (PCDD/F) content. Increasing values of PCDD/Fs have been found to correlate with decreasing temperatures of sampling points in flue gas treatment lines of the plants, confirming other researchers’ findings about temperature as the major controlling parameter for the PCDD/F formation. Measured PCDD/F ratios show that de novo synthesis is the dominant formation mechanism. The increasing trends of particulate-bound PCDD/Fs can be explained not only through the dominant de novo synthesis process but also considering the adsorption of gaseous PCDD/Fs on fly ash deposits, even outside the typical de novo synthesis temperature ranges. The effective role of a post-combustor unit, imposed by Italian law to destroy PCDD/Fs, also needs to be carefully reconsidered.     

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.     

Vitrification Process for Treatment of Sewage Sludge and Incineration Ash

ABSTRACT

Vitrification processes, in which the operating temperature is higher than the melting point of the silica compounds contained in sewage sludge that turns into slag, are studied in this paper. The dried sludge and the incineration ash are injected into a furnace with auxiliary fuel and flux. The flux is the material used to control basicity of the ash content. Crushed limestone is used as the flux in this test. Almost all ashes in the sludge are vitrificated into slag. The flow of molten slag from the tap is smooth. After the slag is treated, it can be used as wall tile, interlocking tile, insulating material, and slag wool. This technology conforms to resource recycling.     

Leaching Dynamics Studies of Municipal Solid Waste Incinerator Ash

Abstract

An assessment of the short- and long-term hazards from municipal solid waste incinerator (MSWI) ash is made through the elemental analysis of 40 to 50 elements in the ash and leachates produced by several leaching procedures. The ash was analyzed using neutron activation analysis (NAA) and x-ray fluorescence (XRF). The leachates were analyzed using NAA and inductively-coupled plasma atomic emission spectroscopy (ICP). The leaching dynamics of an ash monofill were modelled with a series of extractions using simulated acid rain. An initial spike of the metals Ag, Ba, Be, Cr, Cu, Mo, Pb, Sr, and Zn in the leachates appears to be the greatest hazard posed by MSWI ash monofills. The elements As, Cd, Cu, Hg, Pb, S, and Zn were identified as potential long term hazards utilizing a sequential extraction procedure which approximates the total amount of the elements available over the lifetime of the monofill.

The pH of the resulting leachate is the single greatest factor governing the concentration of metals in solution, more important than the concentration of the element in the ash. These results are applied to an assessment of the suitability of the Toxicity Characteristic Leaching Procedure (TCLP) in measuring leaching potential of an MSWI ash monofill.     

Determination of Baghouse Performance from Coal and Ash Properties: Part II

Baghouse performance at utility coal-fired power plants is determined by baghouse design, operating procedures, and the characteristics of the ash that is collected as a dustcake on the fabric filter. The Electric Power Research Institute has conducted laboratory research to identify the fundamental variables that influence baghouse performance. A database was assembled including measured characteristics of coal and dustcake ash, and data describing operating parameters and performance of full-scale and pilotscale baghouses. Predictions of performance can be based on physical characteristics of the ash to be filtered (discussed in Part I of this article), as well as chemical characterizations of the ash, or empirical correlations with the alkali content of the source coal The effects of design and operational variables can be included in these predictions. Baghouse performance can be optimized by exercising proper operating practices and by selecting a filtering fabric and cleaning method matched to the cohesivity of the ash to be collected.     

Determination of Baghouse Performance from Coal and Ash Properties: Part I

Baghouse performance at utility coal-fired power plants is determined by baghouse design, operating procedures, and the characteristics of the ash that is collected as a dustcake on the fabric filter. The Electric Power Research Institute has conducted laboratory research to identify the fundamental properties of dustcake ash that influence baghouse performance. A database was assembled including measured characteristics of dustcake ash and data describing operating parameters and performance of full-scale and pilot-scale baghouses. Semi-empirical models were developed that describe the effects of particle morphology, particle size, ash cohesivity and ash chemistry on filtering pressure drop and particulate emissions. Cohesivity was identified as the primary ash characteristic affecting baghouse performance. Predictions of performance can be based on physical or chemical characterizations of the ash to be filtered. Part II of this article will discuss the effects of ash and coal chemistry, and baghouse design and operation on performance.     

Geotechnical Engineering Properties of Incinerator Ash Mixes

Abstract

The incineration of solid waste produces large quantities of bottom and fly ash. Landfilling has been the primary mode of disposal of these waste materials. Shortage in landfill space and the high cost of treatment have, however, prompted the search for alternative uses of these waste materials. This study presents an experimental program that was conducted to determine the engineering properties of incinerator ash mixes for use as construction materials. Incinerator ash mixes were tested as received and around optimum compacted conditions. Compaction curves, shear strength, and permeability values of fly ash, bottom ash, and their various blends were investigated. Bottom ash tends to achieve maximum dry density at much lower water content than does fly ash. The mixes displayed a change in their cohesion and friction angle values when one of the two mix components was altered or as a result of the addition of water. The permeability of bottom ash is quite comparable to that of sand. The permeability of fly ash lies in the range of those values obtained for silts and clays. A 100% bottom ash compacted at the optimum water content has a lower density value and yields a higher friction angle and cohesion values than most construction fills. This would encourage the use of bottom ash as a fill or embankment material because free drainage of water will prevent the buildup of pore water pressures.     

Latent Hydraulic Reactivity of Blended Cement Incorporating Slag Made from Municipal Solid Waste Incinerator Fly Ash

Abstract

The reactivity of cement pastes made by blending Portland cement with slag from municipal solid waste incinerator (MSWI) fly ash was investigated to assess the potential of recycling MSWI fly ash slag. The slag, prepared by melting MSWI fly ash at 1400 °C for 30 min, was pulverized and ground, then blended with ordinary Portland cement (OPC), using various substitution levels to make slag-blended cement (SBC). The pozzolanic reactivity of the ecocement was then characterized by determining variations in the compressive strength, degree of hydration, microstructure, speciation, and mineralogical crystalline phases. The results suggest that the strength of the pastes at an early age decreased with increasing substitution levels, whereas the strength at a later age of the tested pastes (with substitution levels less than 10%) outperformed OPC paste because of typical SBC properties. The development of strength at a later age was also confirmed by X-ray diffraction and scanning electron microscopy techniques. This implies that active silica (Si) and alumina (Al) react with the hydration product, calcium hydroxide (Ca(OH)₂), to form calcium silicate hydrate (C-S-H), which contributed to strength development at a later age by the filling up of pores in the SBC pastes. The pozzolanic activity of the SBC pastes indicates that it is suitable for use as a substitute for OPC in blended cement.     

Refinery Sludge Treatment/Hazardous Waste Minimization Via Dehydration and Solvent Extraction

Abstract

The patented Carver-Greenfield (C-G) Process®, a combination of dehydration and solvent extraction treatment technologies, has a wide range of uses in separating hydrocarbon solvent-soluble hazardous organic contaminants (indigenous oil) from sludges, soils, and industrial wastes. As a result of this treatment, the products from a C-G Process facility are: ? Clean, dry solids which are typically suitable for disposal in nonhazardous landfills;

? Water which is treatable in an industrial or Publicly Owned Treatment Works (POTW) wastewater treatment facility;

? Extracted indigenous oil containing hydrocarbon soluble contaminants which may be recycled or reused or disposed of at less cost because its volume is smaller than the original waste feed.

The C-G Process was demonstrated on spent oily drilling fluids as part of the U.S. Environmental Protection Agency Superfund Innovative Technology Evaluation (SITE) Program. This paper summarizes the use of the C-G Process for economical treatment and minimization of hazardous refinery wastes, reviews the SITE program results, and describes extending the C-G Process technology to treatment of other wastes. Estimated treatment costs are presented.     

Sorption and Biodegradation of Vapor-Phase Organic Compounds with Wastewater Sludge and Food Waste Compost

ABSTRACT

To test the possible use of composted food waste and wastewater sludge as biofilters to treat gas-phase volatile organic compounds (VOCs), batch experiments were conducted with an isolated strain that could degrade aromatic compounds under aerobic conditions. A benzene and trichloroethylene (TCE) mixture was used as the gas-phase pollutant in experiments with composted food waste, sludge, and soil. Under aerobic conditions, benzene was degraded as a primary substrate and TCE was degraded cometabolically, with water contents varying from 6 to 60% (volume of water added/volume of solid). Optimal water content for VOC removal was 12% for the soil, 36% for the composted food waste, and 48% for the sludge.

The extent of VOC sorption and biodegradation at the optimal water content was different for each material. With the same initial VOC concentration, more VOCs were removed by sorption onto the composted food waste and the sludge, while less VOCs were biodegraded in comparison with the results using soil. The reason the biodegradation in the soil was greater may be partly attributed to the fact that, due to less sorption, the aqueous-phase concentration of VOCs, which microorganisms could utilize as a carbon source or cometabolize, was higher. We also speculate that the distribution of microorganisms in each medium affects the rate of biodegradation. A large number of microorganisms were attached to the composted food waste and sludge. Mass transfer of VOCs and oxygen to these microorganisms, which appear to have been heterogeneously distributed in clusters, may have been limited, resulting in hindered biodegradation.     

拟建窑河洼电厂灰场对地下水环境的影响评价

在对淮南市窑河洼区环境水文地质调研基础上,对拟建窑河洼电厂灰场及邻区的浅层地下水环境质量现状进行了模糊数学评价。基于地下水水质模型,以F^-作为模拟因子,对地下水F^-浓度变化进行了数值模拟,对其5a后的污染范围和程度进行了预测评价。结果表明,模型较为可靠、合理,灰场建成后对场区及邻区地下水环境质量的短期影响不大,这为电厂灰场选址决策及电厂灰场建设后,可能引起地下水污染的范围和程度预测提供了科学依据。     

Hydration properties of eco-cement pastes from waste sludge ash clinkers

Three types of hydraulic cements have been developed by incorporating sludge ash from a primary sewage treatment plant and a water purification plant, as well as slag from steelworks (ferrate), as a partial replacement for clay, silica, alumina, and iron oxide in raw cement meal. The raw meal for the pre-determined recipes was prepared by heating it to 1400 degrees C for 6 hr in a clinkerization process, using a simulated incinerator and smelter. The major components of ordinary Portland cement, C3S, C2S, C3A, and C4AF, were all found in the clinkers. Of the three types of eco-cements, the eco-cement A paste was most similar to ordinary Portland cement in terms of composition and compressive strength development, while the eco-cement B paste showed early strength development. The differential thermal analysis species analyses indicated that the hydrates in the eco-cement pastes were mainly calcium hydroxide and CSH gels, like those found in ordinary Portland cement paste. Moreover, the degree of hydration, as determined by nuclear magnetic resonance, increased in all eco-cement pastes with an increasing curing age. The results indicate that it indeed is feasible to use sludge ash and ferrate to replace up to 20% of the mineral components of raw materials for cement.     

Release of Mercury Vapor from Coal Combustion Ash

Abstract

The long-term stability of Hg in coal combustion byproducts (CCBs) was evaluated at ambient and near-ambient temperatures. Six CCB samples with atypically high levels of total Hg were selected for study assuming a greater potential for release of measurable amounts of Hg vapor. The samples selected included two fly ash samples from U.S. eastern bituminous coal, two fly ash samples from South African low-rank coal, one fly ash from Powder River Basin (PRB) subbituminous coal blended with petroleum coke, and one PRB subbituminous coal fly ash incorporated with flue gas desulfurization material.

Air scrubbed of Hg was passed through compacted 100-g aliquots of each sample at 1 mL/min and vented to a gold-coated quartz trap to collect released Hg vapor. The samples were maintained at ambient and near-ambient (37 °C) temperatures. All samples released low-picogram levels of Hg after 90 days. No pattern was evident to link the total Hg content to the rate of release of Hg vapor. An average of 0.030 pg Hg/g CCB/day was released from the samples, which equates to 2.2 x 10^-8 lb Hg/ton CCB/year. If this were applied to a coal-fired power plant production of 200,000 tons of fly ash per year, there would be a maximum potential release of 0.0044 lb, or 2.00 g, of Hg per year. Experiments are continuing to determine long-term vapor release of Hg from CCBs. All samples have been set up in duplicate at ambient temperature with an improved apparatus to reevalu-ate results reported in this article.     

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.     

Laboratory Evaluations of the Thermal Degradation Properties of Toxic Organic Materials in Sewage Sludge

Laboratory thermal decomposition studies were performed to evaluate potential emissions from sewage sludge incinerators. Precisely controlled thermal decomposition experiments were conducted on sludge spiked with mixtures of hazardous organic compounds, on mixtures of pure compounds without sludge, and on unspiked sludge. Experiments were conducted in nitrogen and air atmospheres with gas phase reaction times of 2.0 seconds over the temperature range 300°C-1000°C.

It was found that sludge inhibited the decomposition of moderately stable spiked contaminants but accelerated the decomposition of the most stable components. This effect was attributed to radical scavengers produced by the sludge matrix at lower temperatures which then decomposed at higher temperatures. A multiple hearth simulation study suggested that most of the organic material present In the sludge matrix is vaporized within the upper hearths that are held at lower temperatures and may consequently escape from such incinerators undestroyed. A number of stable byproducts resulted from the sludge decomposition that may be of environmental concern.     

造纸厂废碱液污染土的环境岩土工程研究

分析了我国造纸厂废碱液的组成成分，受污染土的环境岩土工程特性和污染机理，介绍了污染土地区的岩土工程勘察内容，评价以及一些主要的治理措施。     

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.