The Capture of Heavy Metals from Incineration Using a Spray Dryer Integrated with a Fabric Filter Using Various Additives

ABSTRACT

This study investigated the effects of feedstock additives [polyvinyl chloride (PVC) and NaCl] and spray dryer additives (SiO₂, CaCl₂, NaHCO₃) on heavy metal and fly ash removal efficiencies, and on particle size distribution of heavy metals. A spray dryer with an integrated fabric filter was used as an air pollution control device (APCD). Removal efficiencies for fly ash and heavy metals were greater than 95 and 90%, respectively. When additives of PVC or NaCl were used, the concentration of heavy metals distributed in fly ash apparently varied when the particle diameter was <1 μm. Although the effects of the additives SiO₂, CaCl₂, and NaHCO₃ on the elemental size distribution of Cr were insignificant, these additives did slightly increase concentrations of Cd, Zn, and Pb partitioning in coarser particles (>1μm).     

The capture of heavy metals from incineration using a spray dryer integrated with a fabric filter using various additives

This study investigated the effects of feedstock additives [polyvinyl chloride (PVC) and NaCl] and spray dryer additives (SiO2, CaCl2, NaHCO3) on heavy metal and fly ash removal efficiencies, and on particle size distribution of heavy metals. A spray dryer with an integrated fabric filter was used as an air pollution control device (APCD). Removal efficiencies for fly ash and heavy metals were greater than 95 and 90%, respectively. When additives of PVC or NaCl were used, the concentration of heavy metals distributed in fly ash apparently varied when the particle diameter was <1 microm. Although the effects of the additives SiO2, CaCl2, and NaHCO3 on the elemental size distribution of Cr were insignificant, these additives did slightly increase concentrations of Cd, Zn, and Pb partitioning in coarser particles (>1 microm).     

Leaching characteristics of stabilized/solidified fly ash generated from ash-melting plant

This study was designed to elucidate the leaching characteristics of stabilized/solidified (S/S) fly ash generated by ash-melting. For this study, pH-dependent leaching tests, sequential extraction procedures, and column leaching tests were carried out. The pH-dependent leaching test results for Pb, Cu, and Zn showed that the heavy metal concentrations in the high-pH range were lower than the predicted values for hydroxide and carbonate. During sequential extraction, Cu and Pb were principally distributed in the S/S ashes' organic matter fraction in the chelating agent, suggesting that metals bind to the chelating agent. The percentage of the water-soluble fraction for Pb and Cu was low (<0.2 %). The fly ashes treated with a chelating agent and cement had low leachability potential for metals in the high-pH range. Column tests for S/S fly ashes showed that two leaching stages were distinguishable: one for short time, corresponding to faster metal leaching, and another for the leaching rate. Kinetic speciation was then applied to data obtained from column leaching tests. The first-order reaction/diffusion model showed a better fit for Ca, Pb, and Cu, suggesting that the initial dissolution of soluble compounds, such as metal chloride, was controlled by the first-order reaction (surface wash off). Subsequently, insoluble compounds such as hydroxide or carbonate might penetrate into the porous matrix by diffusion.     

Edaphological characteristics of unweathered and weathered fly ashes from Gondwana and lignite coal

Naturally weathered and unweathered samples of fly ashes produced from Gondwana and lignite coals were characterized for their edaphological properties. The particle size distribution in these fly ashes varied widely, and the percentage of [Formula: see text] size particles governed their water holding capacity. All fly ashes were noncoherent in the dry state and had lower particle density than quartz and mulite. The fly ashes were low in available N, but were sufficient in available P, K, Ca, Mg, S, Cu, Fe, Mn, Zn and B. Among the fly ashes, unweathered lignite fly ash was the richest source of K, Ca, Mg, S and Fe, while weathered lignite fly ash had the highest amounts of Mn, Zn and B. The pH of the fly ashes was closely related to the ratio of exchangeable Ca to exchangeable Al. The fly ashes were high in soluble salt, but were poor in cation exchange capacity. As an amendment to correct soil pH, the fly ashes had a poor buffering capacity. Weathering decreased the total Fe, available S and exchangeable Na percentages, but increased the organic C content of the fly ashes. Invariably, an excess of soluble salts and exchangeable Na could limit plant growth on fly ash dumps. Toxic levels of B and Al existed in only some fly ashes.     

A Model to Predict the System Performance of an Electrostatic Precipitator for Collecting Polydisperse Particles

Abstract

This paper presents a model for predicting the performance of an electrostatic precipitator (ESP) for collecting polydisperse particles. The particle charge was obtained by modifying Cochet’s charge equation; the particle size distribution was approximated by a lognormal function; and then the statistic method of moments was employed to obtain a set of the first three moment equations. The continuous evolution of the particle size distribution in an ESP is easily taken into account by the first three moment equations. The performance of this model was validated by comparing its predictions with the existing data available in the literature. Effects of the particle size distribution on the ESP performance were examined, and the results indicated that both overall mass and number efficiencies are lower for inlet particles with a larger mass median diameter and a higher geometric standard deviation. The methodology introduced may be applied to develop design criteria and determine optimal operating conditions of an ESP for improving the collection efficiency of the submicron particles.     

Heavy metal leaching from coal fly ash amended container substrates during Syngonium production

Coal fly ash has been proposed to be an alternative to lime amendment and a nutrient source of container substrates for ornamental plant production. A great concern over this proposed beneficial use, however, is the potential contamination of surface and ground water by heavy metals. In this study, three fly ashes collected from Florida, Michigan, and North Carolina and a commercial dolomite were amended in a basal substrate. The formulated substrates were used to produce Syngonium podophyllum Schott 'Berry Allusion' in 15-cm diameter containers in a shaded greenhouse. Leachates from the containers were collected during the entire six months of plant production and analyzed for heavy metal concentrations. There were no detectable As, Cr, Hg, Pb, and Se in the leachates; Cd and Mo were only detected in few leachate samples. The metals constantly detected were Cu, Mn, Ni, and Zn. The total amounts of Cu, Mn, Ni, and Zn leached during the six-month production period were 95, 210, 44, and 337 microg per container, indicating that such amounts in leachates may contribute little to contamination of surface and ground water. In addition, plant growth indices and fresh and dry weights of S. podophyllum 'Berry Allusion' produced from fly ash and dolomite-amended substrates were comparable except for the plants produced from the substrate amended with fly ash collected from Michigan which had reduced growth indices and fresh and dry weights. Thus, selected fly ashes can be alternatives to commercial dolomites as amendments to container substrates for ornamental plant production. The use of fly ashes as container substrate amendments should represent a new market for the beneficial use of this coal combustion byproduct.     

Comparison of CaO’s effect on the fate of heavy metals during thermal treatment of two typical types of MSWI fly ashes in China

Both grate and fluidized bed incinerators are widely used for MSW incineration in China. CaO addition for removing hazardous emissions from MSWI flue gas changes the characteristics of fly ash and affects the thermal behavior of heavy metals when the ash is reheated. In the present work, two types of MSWI fly ashes, sampled from both grate and fluidized bed incinerators respectively, were thermal treated at 1023–1323 K and the fate of heavy metals was observed. The results show that both of the fly ashes were rich in Ca and Ca-compounds were the main alkaline matter which strongly affected the leaching behavior of heavy metals. Ca was mostly in the forms of Ca(OH)₂ and CaCO₃ in the fly ash from grate incinerator in which nascent fly ash particles were covered by Ca-compounds. In contrast, the content of Ca was lower in the fly ash from fluidized bed incinerator and Ca was mostly in the form of CaSO₄. Chemical reactions among Ca-compounds caused particle agglomeration in thermal treated fly ash from grate incinerator, restraining the heavy metals volatilization. In thermal treated fly ash from fluidized bed incinerator, Ca was converted into aluminosilicates especially at 1323 K which enhanced heavy metals immobilization, decreasing their volatile fractions as well as leaching concentrations. Particle agglomeration hardly affected the leaching behavior of heavy metals. However, it suppressed the leachable-CaCrO₄ formation and lowered Cr leaching concentration.     

Stabilization of APC Residues from Waste Incineration with Ferrous Sulfate on a Semi-Industrial Scale

Abstract

A stabilization method for air pollution control (APC) residues from municipal solid waste incineration (MSWI) involving mixing of the residue with water and FeSO₄ has been demonstrated on a semi-industrial scale on three types of APC residues: a semidry (SD) APC residue, a fly ash (FA), and an FA mixed with sludge (FAS) from a wet flue gas cleaning system. The process was performed in batches of 165-175 kg residue. It generates a wastewater that is highly saline but has a low content of heavy metals such as Cd, Cr, and Pb. The stabilized and raw residues have been subject to a range of leaching tests: the batch leaching test, the pH-static leaching test, the availability test, and the column test. These tests showed that the stabilized residues have remarkably improved leaching properties, especially with respect to Pb but also with respect to Cd, Cu, and Zn. The release of Pb was reduced by a factor of 250-36,000.     

A New Method to Assess Mercury Emissions: A Study of Three Coal-Fired Electric-Generating Power Station Configurations

Abstract

U.S. Environmental Protection Agency (EPA) Method 7473 for the analysis of mercury (Hg) by thermal decomposition, amalgamation, and atomic absorption spectroscopy has proved successful for use in Hg assessment at coal-fired power stations. In an analysis time of ～5 min per sample, this instrumental methodology can directly analyze total Hg—with no discrete sample preparation—in the solid matrices associated with a coal-fired power plant, including coal, fly ash, bottom ash, and flue gas desulfurization (FGD) material. This analysis technique was used to investigate Hg capture by coal combustion byproducts (CCBs) in three different coal-fired power plant configurations. Hg capture and associated emissions were estimated by partial mass balance. The station equipped with an FGD system demonstrated 68% capture on FGD material and an emissions estimate of 18% (11 kg/yr) of total Hg input. The power plant equipped with low oxides of nitrogen burners and an electrostatic precipitator (ESP) retained 43% on the fly ash and emitted 57% (51 kg/yr). The station equipped with conventional burners and an ESP retained less than 1% on the fly ash, emitting an estimated 99% (88 kg/yr) of Hg. Estimated Hg emissions demonstrate good agreement with EPA data for the power stations investigated.     

Sulfidation treatment of molten incineration fly ashes with Na2S for zinc, lead and copper resource recovery

The present study focuses on the conversion of heavy metals involved in molten incineration fly ashes to metal sulfides which could be thereafter separated by flotation. The sulfidation treatment was carried out for five molten incineration fly ashes (Fly ash-A to Fly ash-E) by contacting each fly ash with Na(2)S solution for a period of 10 min to 6h. The initial molar ratio of S(2-) to Me(2+) was adjusted to 1.20. The conversion of heavy metals to metal sulfides was evaluated by measuring the S(2-) residual concentrations using an ion selective electrode. The formation of metal sulfides was studied by XRD and SEM-EDS analyses. In the case of Fly ash-A to Fly ash-D, more than 79% of heavy metals of zinc, lead and copper was converted to metal sulfides within the contacting period of 0.5h owing to a fast conversion of metal chlorides to metal sulfides. By contrast, the conversion of about 35% was achieved for Fly ash-E within the same contacting period, which was attributed to a high content of metal oxides. Further, the S(2-) to Me(2+) molar ratio was reduced to 1.00 to minimize Na(2)S consumption and the conversions obtained within the contacting period of 0.5h varied from 76% for Fly ash-D to 91% for Fly ash-C. Finally, soluble salts such as NaCl and KCl were removed during the sulfidation treatment, which brought about a significant enrichment in metals content by a factor varying from 1.5 for Fly ash-D to 4.9 for Fly ash-A.     

Determination of polychlorinated dibenzo-p-dioxins and dibenzo-furans in solid residues from wood combustion by HRGC/HRMS

PCDD/PCDF were determined in solid samples from wood combustion. The samples included grate ashes, bottom ashes, furnace ashes as well as fly and cyclone ashes. The solid waste samples were classified into bottom and fly ash from native wood and bottom and fly ash from waste wood. For each of the four classes concentration distribution patterns from individual congeners, the sums of PCDD/PCDF and the international toxicity equivalents (I-TEQ) values are given. The I-TEQ levels of fly ash from waste wood burning can be approximately up to two thousand times higher than the values from fly ashes of natural wood. The I-TEQ levels in bottom ashes from waste wood combustion systems are as low as the corresponding ashes from the combustion of native wood. Grate ash samples from waste wood combustion systems with low carbon burnout show high levels of PCDD/PCDF.     

Extraction of heavy metals from MSW incinerator fly ash using saponins

An extraction process with saponins was evaluated for removing heavy metals from MSW (municipal solid waste) incinerator fly ashes. Two different fly ashes, A and B, were treated on a laboratory scale with three triterpene-glycoside type of saponins, M, Q, and T, in the pH range 4-9. The results were compared with those of the HCI and EDTA treatment. The treatment with saponins extracted 20-45% of Cr from the fly ashes. Saponins were also effective in extracting Cu from fly ash A attaining 50-60% extraction. Saponin T extracted 100% of Pb from fly ash A at pH around 4. The extraction of Zn with the saponin treatment was similar to that of the HCl treatment. Further, Cr, Cu, Pb, and Zn were fractionated by sequential extraction to investigate the effect of saponins on each fraction. Extraction behavior of other elements during the saponin treatment was also studied. The leaching test on the residues received after the saponin treatment showed that the fly ashes were successfully detoxified to meet the landfilling guideline.     

水泥对垃圾焚烧飞灰的固化处理试验研究

对垃圾焚烧飞灰的化学成分、重金属物质的含量及浸出浓度进行测试分析.结果表明,飞灰中Pb和Cr等重金属物质浸出量超过浸出毒性标准,因而被认为是危险废物,必须进行固化处理.还考察了水泥对焚烧飞灰中重金属物质固化的效果,研究表明当飞灰掺量适当时,重金属物质的固化效果良好.重金属物质通过物理固封、替代,沉淀反应和吸附等形式可固化进水泥水化产物结构中.     

Dechlorination and destruction of PCDDs/PCDFs in fly ashes from municipal solid waste incinerators by low temperature thermal treatment

Dechlorination and destruction characteristics of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/PCDFs) in fly ashes from commercial-scale municipal solid waste incinerators by low temperature thermal treatment using a laboratory-scale heating system were investigated. Experiments were carried out in reducing atmosphere at temperatures of 300 degrees C, 450 degrees C and 600 degrees C respectively, for the treatment time of 1h and 3h. Concentrations of PCDDs/PCDFs in raw fly ashes ranged from 35.5 to 107.3 microg kg(-1) (1.5-3.4 microg TEQ kg(-1)) and treated fly ashes ranged from 0.34 to 45.3 microg kg(-1) (0.012-1.63 microg TEQ kg(-1)). Concentrations of PCDDs/PCDFs in fly ashes treated at the different temperatures and times were observed to decrease with increase of treatment temperature and time by dechlorination or destruction. The distribution of octa- and hepta-chlorinated congeners were decreased and tetra-, penta- and hexa-chlorinated congeners were increased at 300 degrees C and 450 degrees C, but the distribution of octa- and hepta-chlorinated congeners were increased and tetra-, penta- and hexa-chlorinated congeners were again decreased at 600 degrees C. Total destruction efficiencies of PCDDs/PCDFs in fly ashes showed above 95% at the treatment temperature of 450 degrees C for 3h. However, removal efficiency of each congener in fly ashes varied, especially, 2,3,7,8-TeCDD and 1,2,3,7,8-PeCDD in fly ash A increased. And the dechlorination and destruction characteristics of PCDDs/PCDFs in fly ash A and B was different due to difference in contents of Ca-compounds and metal oxides such as CuO and PbO in fly ashes.     

A Federal Tax on Energy

Abstract

In this investigation, the collection efficiency of particulate emission control devices (PECDs), particulate matter (PM) emissions, and PM size distribution were determined experimentally at the inlet and outlet of PECDs at five coal-fired power plants. Different boilers, coals, and PECDs are used in these power plants. Measurement in situ was performed by an electrical low-pressure impactor with a sampling system, which consisted of an isokinetic sampler probe, precut cyclone, and two-stage dilution system with a sample line to the instruments. The size distribution was measured over a range from 0.03 to 10 µm. Before and after all of the PECDs, the particle number size distributions display a bimodal distribution. The PM_2.5 fraction emitted to atmosphere includes a significant amount of the mass from the coarse particle mode. The controlled and uncontrolled emission factors of total PM, inhalable PM (PM₁₀), and fine PM P(M_2.5) were obtained. Electrostatic precipitator (ESP) and baghouse total collection efficiencies are 96.38–99.89% and 99.94%, respectively. The minimum collection efficiency of the ESP and the baghouse both appear in the particle size range of 0.1–1 µm. In this size range, ESP and baghouse collection efficiencies are 85.79–98.6% and 99.54%. Real-time measurement shows that the mass and number concentration of PM₁₀ will be greatly affected by the operating conditions of the PECDs. The number of emitted particles increases with increasing boiler load level because of higher combustion temperature. During test run periods, the data reproducibility is satisfactory.     

Cork stoppers as an effective sorbent for water treatment: the removal of mercury at environmentally relevant concentrations and conditions

The technical feasibility of using stopper-derived cork as an effective biosorbent towards bivalent mercury at environmentally relevant concentrations and conditions was evaluated in this study. Only 25 mg/L of cork powder was able to achieve 94 % of mercury removal for an initial mercury concentration of 500 μg/L. It was found that under the conditions tested, the efficiency of mercury removal expressed as equilibrium removal percentage does not depend on the amount of cork or its particle size, but is very sensitive to initial metal concentration, with higher removal efficiencies at higher initial concentrations. Ion exchange was identified as one of the mechanisms involved in the sorption of Hg onto cork in the absence of ionic competition. Under ionic competition, stopper-derived cork showed to be extremely effective and selective for mercury in binary mixtures, while in complex matrices like seawater, moderate inhibition of the sorption process was observed, attributed to a change in mercury speciation. The loadings achieved are similar to the majority of literature values found for other biosorbents and for other metals, suggesting that cork stoppers can be recycled as an effective biosorbent for water treatment. However, the most interesting result is that equilibrium data show a very rare behaviour, with the isotherm presenting an almost square convex shape to the concentration axis, with an infinite slope for an Hg concentration in solution around 25 μg/L.     

Screening of heavy metal containing waste types for use as raw material in Arctic clay-based bricks

In the vulnerable Arctic environment, the impact of especially hazardous wastes can have severe consequences and the reduction and safe handling of these waste types are therefore an important issue. In this study, two groups of heavy metal containing particulate waste materials, municipal solid waste incineration (MSWI) fly and bottom ashes and mine tailings (i.e., residues from the mineral resource industry) from Greenland were screened in order to determine their suitability as secondary resources in clay-based brick production. Small clay discs, containing 20 or 40% of the different particulate waste materials, were fired and material properties and heavy metal leaching tests were conducted before and after firing. Remediation techniques (washing in distilled water and electrodialytical treatment) applied to the fly ash reduced leaching before firing. The mine tailings and bottom ash brick discs obtained satisfactory densities (1669–2007 kg/m³) and open porosities (27.9–39.9%). In contrast, the fly ash brick discs had low densities (1313–1578 kg/m³) and high open porosities (42.1–51. %). However, leaching tests on crushed brick discs revealed that heavy metals generally became more available after firing for all the investigated materials and that further optimisation is therefore necessary prior to incorporation in bricks.     

Metals leachability from medical waste incinerator fly ash: A case study on particle size comparison

This paper presents the results from a study of metals leachability of medical waste incinerator fly ash in Japan on the basis of particle size. Sequential extraction and Toxicity Characteristic Leaching Procedure (TCLP) analysis were carried out in order to quantify the leaching amount of metals in each categorized particle size. Sequential extraction was also subjected to identify the preference of binding matrix of metals. The results of sequential extraction showed an increase both exchangeable and carbonate associated chromium concentrations in the bigger particle size fractions. Likewise, concentrations of carbonate matrix of arsenic and tin tended to increase in the bigger particle size fractions. In contrast, exchangeable associated cadmium as well as both exchangeable and carbonate matrices of barium were found higher in the smaller particle size fractions. However, no correlation was found in Kendal-tau correlation analysis between particle size of the ash and metals leachability of the TCLP.     

Trace metal emissions from co-combustion of refuse derived and packaging derived fuels in a circulating fluidized bed boiler

Energy recovery from refuse derived fuels (RDF) and packaging derived fuels (PDF) is one option in integrated waste management. Nine RDF and PDF co-combustion tests with peat and coal in a circulating fluidized bed boiler were carried out in this work. Heavy metal emissions in flue gas and fly ash were measured. Multivariate data analyses were used to find out the most important parameters affecting metal emissions in the flue gas.

The results showed that total heavy metal emissions were low. Although RDF and PDF had more heavy metals than peat and coal, the multivariate data analysis showed that an increase of the RDF or PDF share in the fuel mixture up to 20% did not correlate directly with the metal emissions in the flue gas. Distribution of Cd, Cu, Zn and Sn between flue gas and fly ash correlated with each other. Injection of limestone to bind sulphur and chlorine did not have a significant effect on heavy metal emissions in the flue gas. Heavy metals concentrated on the fly ash, but all fly ashes passed the EPA-TCLP tests.     

Effect of NOx Control Processes on Mercury Speciation in Utility Flue Gas

Abstract

The speciation of Hg in coal-fired flue gas can be important in determining the ultimate Hg emissions as well as potential control options for the utility. The effects of NO_x control processes, such as selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR), on Hg speciation are not well understood but may impact emissions of Hg. EPRI has investigated the reactions of Hg in flue gas at conditions expected for some NO_x control processes. This paper describes the methodology used to investigate these reactions in actual flue gas at several power plants. Results have indicated that some commercial SCR catalysts are capable of oxidizing elemental Hg in flue gas obtained from the inlets of SCR or air heater units. Results are affected by various flue gas and operating parameters. The effect of flue gas composition, including the presence of NH₃, has been evaluated. The influence of NH₃ on fly ash Hg reactions also is being investigated.