Electrostatic Precipitator Fly Ash Research Articles

Physicochemical Properties of Fe-Bearing Phases from Commercial Colombian Coal Ash

High amounts of coal combustion products, such as fly ash and bottom ash, are generated every year; however, only 64% are used, which means that a significant part is landfilled despite containing valuable materials such as ferrospheres, which may be used as catalysts, substituting critical raw materials (e.g., platinoids). In commercial coals, pyrite contents are reduced as a pre-combustion S-emissions control measure, so low amounts of ferrospheres are expected in the respective ashes. However, given the large amounts of ash being generated from these coals, it may provide a reliable source of catalysts, with ferrospheres being easily recovered via magnetic separation. Several studies have been conducted regarding these morphotypes; however, there is a lack of investigation considering the ash derived from highly beneficiated coals and the variations with location and time. In this study, bottom ash, economizer grits, and fly ash samples from a Portuguese power plant burning Colombian commercial coal were fractionated using ferrite (Fe-MC fraction) and Nd (Nd-MC fraction) magnets, and a multi-technique approach was used to assess their properties (magnetic parameters, particle size distribution, mineralogy, particle morphology, microtexture, and chemical composition). The Fe-MC presented higher Fe concentrations (up to 44 wt.% Fe2O4) than the Nd-MC (up to 7 wt.% Fe2O4). Once it was a sequential process, Nd magnets essentially collected Fe-bearing aluminosilicate glass, and Fe-bearing minerals were residual when compared to the Fe-MC, where magnetite, magnesioferrite, hematite, and maghemite accounted for up to 30 wt.%. Among the Fe-MC, the sample collected from electrostatic precipitator fly ash (ESP FA), despite having a lower yield, presented higher Fe concentrations than the ones from bottom ash and economizer grits, which was related to the mode of occurrence of Fe-bearing phases: in the Fe-MC from ESP FA, discrete ferrospheres predominated, while in the remaining Fe-bearing phases, they were often embedded in aluminosilicate glass. All Fe-MC samples showed an increase of Fe-substituting elements (e.g., Mn and Ni) and their concentration tended to increase with decreasing particle size along with Fe. The integrated study of cross-sections enabled the identification of oxidation rims, martitization aspects, and the co-existence of hematite and magnesioferrite.

Integrative Study Assessing Space and Time Variations with Emphasis on Rare Earth Element (REE) Distribution and Their Potential on Ashes from Commercial (Colombian) Coal

The increasing demand for rare earth elements (REEs), which is associated with their economic importance and the supply risk, has motivated the research for alternative secondary sources of these elements. Coal and coal combustion ash have been pointed out as promising REE raw materials. This research seeks to understand REE fractionation, from feed coals to ashes, considering seasonal variations, and to assess the trends within the ash fractions that can be used for further beneficiation processes. Colombian commercial feed coals, combustion ashes, and their respective fractions were sampled from a Portuguese power plant and were characterized via petrographical, mineralogical, and chemical analyses. The total REE concentrations in the feed coals studied range between 6.97 and 23.15 ppm, while, in the ashes, they vary from 159.9 to 266.6 ppm. Fly ash (FA) from electrostatic precipitator (ESP) presented higher concentrations than the bottom (BA) and economizer (ECO) ashes. Furthermore, REEs and the LREE/HREE ratio increased slightly towards the back rows of the ESP. In the feed coals, the REEs are significantly correlated with ash, and they occur in micrometric phosphate minerals intermixed with clays. In the ashes, the REEs were mostly detected in micrometric particles, with P and Al-Si as the major components. The results from the fractioned samples show that the REEs were enriched in the fine (<25 µm) and nonmagnetic fractions of the ESP FA. A single trial combining sieving and magnetic separation enabled the attainment of a REE recovery of 53%, and a final enrichment factor of 1.25. Coal combustion ashes and their respective size fractions are promising REE raw materials; however, the REE oxide concentrations are below the economical cutoff of 1000 ppm.

Fly ash from coal combustion: Dependence of the concentration of various elements on the particle size

The dependence of the distribution of various elements on the particle size of coal combustion fly ash is of special interest for use of the fly ash in ultrafine cement, or for recovery of valuable elements from fly ash. Therefore, electrostatic precipitator fly ash from a coal fired power plant was split into particle size classes with mass median diameters of 2.2 µm, 5.4 µm, 9.7 µm, 19 µm and 43 µm by means of an air classifier. The size dependence for the elements Al, As, Ba, Br, Ca, Ce, Cl, Co, Cr, Cu, Fe, Ga, Ge, Hg, K, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Rb, S, Sb, Se, Si, Sn, Sr, Ta, Ti, Th, Tl, U, V, W, Y, Yb, Zn, Zr, and for total carbon, was determined. For several components a considerable dependence of the concentration on the particle size was observed, which can be approximated by power functions. Substantially higher concentration with decreasing particle size was found for total carbon, As, Cu, Ga, Ge, Hg, Sn, Pb, Tl, V and Zn, whereas the concentration of the main mineral components Si, Al, Fe, Ca, K, Na, Mg, Mn and Ti was slightly lower in the fine particles. The increased concentrations have to be considered for critical elements like Pb and Cu when air classified ultrafine fly ash is used in ultrafine cement. Air classification might also be an important pre-processing step in a recovery process for trace elements like Ga, Ge and V.

Grate-Fired Biomass Combustion Plants Using Forest Residues as Fuel: Enrichment Factors for Components in the Fly Ash

The aim of this work is to investigate the enrichment factors for various nutrients and heavy metals in the fly ash from grate-fired combustion plants using forest residues as fuels. Sustainable energy production requires recycling of the ash on the soil to close the nutrient cycles. The coarser bottom ash which is discharged from the boiler usually contains lower amounts of heavy metals compared to the fly ash which is separated from the off-gas. The discharge of the finest fly ash to landfill sites serves to remove the unwanted heavy metals from the cycle. For this purpose, the enrichment of these components in the finest fly ash should be maximized. At the same time the enrichment of the nutrients in the fine fly ash should be minimal. The enrichment of the components in the electrostatic precipitator fly ash of three biomass combustion plants was determined. The enrichment of the critical heavy metals Cd, Pb and Zn in the fly ash was higher than the values reported in one study but less than values calculated from the data presented in another study. Further investigations would be required to clarify this deviation. Thereby additional data on the furnace operation conditions e.g. combustion temperature should be included. The enrichment of most nutrients (Ca, Mg and PO43−) in the fly ash was low. For K the enrichment in the fly ash was higher resulting in notable K losses to the fly ash.

The influence of electrodialytic remediation on dioxin (PCDD/PCDF) levels in fly ash and air pollution control residues

Fly ash and Air Pollution Control (APC) residues collected from three municipal solid waste incinerators in Denmark and Greenland were treated by electrodialytic remediation at pilot scale for 8–10 h. This work presents for the first time the effect of electrodialytic treatment on polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF), and how these levels impact on the valorization options for fly ash and APC residue.PCDD/PCDF levels in the original residues ranged between 4.85 and 197 ng g−1, being higher for the electrostatic precipitator fly ash. The toxic equivalent (TEQ) varied ten fold, ranging 0.18–2.0 ng g−1 I-TEQ, with penta and hexa-homologs being most significant for toxicity.After the electrodialytic treatment PCDD/PCDF levels increased in the residues (between 1.4 and 2.0 times). This does not mean PCDD/PCDF were synthesized, but else that soluble materials dissolve, leaving behind the non-water soluble compounds, such as PCDD/PCDF. According to the Basel Convention, PCDD/PCDF levels in these materials is low (<15 μg WHO-TEQ kg−1) and the fly ash and APC residue could eventually be valorized, for instance as construction material, provided end-of-waste criteria are set and that a risk assessment of individual options is carried out, including the end-of-life stage when the materials become waste again.

Incorporation of treated municipal solid waste incineration electrostatic precipitator fly ash as partial replacement of Portland cement: Effect on early age behaviour and mechanical properties

The use of municipal solid waste incineration (MSWI) electrostatic precipitator fly ash (ESPFA) as partial replacement of cement was studied in this work in order to provide a method to assess its potential reactivity in presence of cement. Thermal fly ash (TFA) and ground sand (GS), respectively pozzolanic and chemically inert materials, were also used as partial replacement of Portland cement in order to understand the effects of ESPFA on cementitious materials properties. In this study, cement pastes were designed keeping the sulphate content constant. Isothermal calorimetry was used to characterize the early-age behaviour. The results showed the influence of the mix design of cement pastes. Compressive strength tests, mercury intrusion porosimetry, thermogravimetry, and calorimetric measurements were carried out on mortars and cement pastes containing one of the three mineral additions. ESPFA had a chemically inert behaviour but the strength and thermogravimetric analyses showed their physical effect. The high specific surface of ESPFA actually leads to relatively good activity coefficient and enhanced portlandite formation. The leaching of calcium, chromium, lead and zinc was studied by tests at controlled pH. Results showed that ESPFA do not affect durability. Moreover, the concentrations of heavy metals in the leaching solution were lower than allowed concentrations.

Full-scale study on halloysite fireside additive in 230 t/h pulverized coal utility boiler

The paper presents slagging and fouling properties of ashes when hard coal was fired in a pulverized coal-fired boiler (230 t/h capacity) and the change of fouling indices of resulting fly ash when halloysite fireside additive was used. During reported full-scale study the pulverized coal-fired boiler was fired with hard coal with the addition of pulverized halloysite injected directly into furnace through the designed spray-nozzles in the upper part of boiler furnace. Chemical analysis of fuel properties and collected from the ESP (electrostatic precipitator) fly ash samples was carried out to obtain the following information:•determine chemical properties of coal and its ash produced during combustion in order to determine its propensity for slagging versus reference study conducted without the use of additive•identify the slagging and fouling indicators when halloysite additive was used.The tests results are intended to determine the effectiveness of the pulverized halloysite injection to the furnace in terms of reducing slagging and fouling of heating surfaces, in particular the evaporator and convective section of the boiler. The required halloysite feeding is determined by comparing the change in chemical composition (ash modification effectiveness) between fly ashes produced in the reference and test case so as it is corrected according to the fuel slagging properties (fuel slagging index).

Field Application of Accelerated Mineral Carbonation

Globally, coal-fired power plants are the largest industrial source of carbon dioxide (CO2). CO2 emissions from flue gas have potential for direct mineralization with electrostatic precipitator fly ash particles in the field. Demonstration scale accelerated mineral carbonation (AMC) studies were conducted at the Jim Bridger Power Plant, a large coal fired power plant located in Wyoming, USA. AMC produces kinetically rapid conditions for increased rates of mineralization of CO2, sulfur dioxide (SO2) and mercury (Hg) on fly ash particles. Control and AMC reacted fly ash particles were investigated for: change in carbon (expressed as CaCO3), sulfur (expressed as SO42−), and mercury (Hg) contents; topology and surface chemical composition by scanning electron microscope/energy dispersive X-ray spectroscopy analysis; chemical distribution of trace elements; and aqueous mineral solubility by the toxicity characteristic leaching procedure. Results of the AMC process show an increase in C, S, and Hg on AMC fly ash particles suggesting that multiple pollutants from flue gas can be removed through this direct mineral carbonation process. Results also suggest that the AMC process shifts soluble trace elements in fly ash to less leachable mineral fractions. The results of this study can provide insight into potential successful field implementation of AMC.

Mercury Speciation and Distribution in a 660-Megawatt Utility Boiler in Taiwan Firing Bituminous Coals

Mercury speciation and distribution in a 660-MW tangential-fired utility boiler in Taiwan burning Australian and Chinese bituminous coal blends was investigated. Flue gases were simultaneously sampled at the selective catalytic reduction (SCR) inlet, the SCR outlet, the electro-static precipitator (ESP) outlet, and the stack. Samplings of coal, lime, bottom ash/slag, fly ash, and gypsum slurry were also conducted. Results indicated that flue gases at the inlet to SCR contained a great potion of particle-bound mercury (Hgp), 59–92% of the total mercury. Removal of mercury was not observed for the SCR system. However, repartitioning of mercury species across the SCR occurred that significantly increased the portion of elemental mercury (Hg0) to up to 29% and oxidized mercury (Hg2+) to up to 33% in the SCR outlet gas. Overreporting of Hgp at the inlet of SCR may cause the observed repartitioning; the high ammonia/nitric oxide circumstance in the SCR unit was also speculated to cause the mercury desorption from ash particles and subsequent reentrance into the gas phase. ESP can remove up to 99% of Hgp, and wet flue gas desulfurization (FGD) can remove up to 84% of Hg2+. Mercury mass balances were calculated to range between 81 and 127.4%, with an average of 95.7% wherein 56–82% was in ESP fly ash, 8.7–18.6% was retained in the FGD gypsum, and 6.2–26.1% was emitted from the stack. Data presented here suggest that mercury removal can be largely enhanced by increasing the conversion of Hg0 into Hgp and Hg2+.

Studies on Speciation Changes and Mass Distribution of Mercury in a Bituminous Coal-Fired Power Plant by Combining Field Data and Chemical Equilibrium Calculation

Transformation of mercury compounds in combustion flue gas and overall mercury mass balance in a typical bituminous coal-fired power plant were studied. Upon decreasing temperature and interaction with flue gas components, oxidized mercury increased across an electrostatic precipitator. A major fraction of particulate mercury was removed in the electrostatic precipitator, and oxidized mercury was removed in wet flue gas desulfurization. Hg was mainly speciated into elemental form in the stack emission. The measurement of mercury in a real facility and equilibrium calculation showed that coal composition, operating conditions, and flue gas components were the major factors affecting mercury emission and speciation. A reliable overall Hg mass balance was obtained from the field measurement. Mercury mainly entered from coal, and lime/limestone feeding was distributed in electrostatic precipitator fly ash (57.6−64.3%), gypsum (4.5 −12.9%), effluents (0.5−1.9%), and stack emission (15.2−27.0%). Further, the ma...

Association of the Sites of Heavy Metals with Nanoscale Carbon in a Kentucky Electrostatic Precipitator Fly Ash

A combination of high-resolution transmission electron microscopy, scanning transmission electron microscopy, and electron energy-loss spectroscopy (HRTEM-STEM-EELS) was used to study fly ashes produced from the combustion of an eastern Kentucky coal at a southeastern-Kentucky wall-fired pulverized coal utility boiler. Fly ash was collected from individual hoppers in each row of the electrostatic precipitators (ESP) pollution-control system, with multiple hoppers sampled within each of the three rows. Temperatures within the ESP array range from about 200 degrees C at the entry to the first row to < 150 degrees C at the exit of the third row. HRTEM-STEM-EELS study demonstrated the presence of nanoscale (10 s nm) C agglomerates with typical soot-like appearance and others with graphitic fullerene-like nanocarbon structures. The minute carbon agglomerates are typically juxtaposed and intergrown with slightly larger aluminosilicate spheres and often form an ultrathin halo or deposit on the fly ash particles. The STEM-EELS analyses revealed that the nanocarbon agglomerates host even finer (< 3 nm) metal and metal oxide particles. Elemental analysis indicated an association of Hg with the nanocarbon. Arsenic, Se, Pb, Co, and traces of Ti and Ba are often associated with Fe-rich particles within the nanocarbon deposits.

Environmental assessment of elements and polyaromatic hydrocarbons emitted from a Canadian coal-fired power plant

A detailed assessment of elements was carried out at a power plant rated at approximately 760 MW of electricity using western Canadian subbituminous coal. The concentrations of elements of environmental concern (As, Cd, Cr, Hg, Ni, and Pb) in milled coals, ashes, stack-emitted materials. Speciation of As, Cr, and Ni were determined. The polyaromatic hydrocarbons (PAHs) emitted from the stack were also measured. The rates of input of elemental input for As, Cd, Cr, Hg, Ni, and Pb were 28, 0.94, 230, 0.44, 44, and 88 kg/day, respectively; of which only 0.16, 0.01, 0.40, 0.27, 0.15, and 0.04 kg/day, respectively, were stack emitted. The total stack emission of toxic elements is 1.02 kg/day, with Cr being the highest contributor to this group with 0.4 kg/day. However, Hg at 0.27 kg/day has the highest percentage rate of emission at about 60%, while Cd has the lowest at about 1%. The electrostatic precipitator (ESP) removes a significant portion of the elements indicated by their relative enrichment (RE) ratios greater than 0.7. The results show that most of the elements in milled coal are low compared to world coals and other Canadian milled coals. Mercury is mostly (∼ 81%) emitted as gaseous elemental mercury (GEM), with 19% as reactive gaseous mercury (RGM). Particulate mercury is very low and averages about 0.1% of the total mercury at this station. Most of the arsenic in the milled coal is primarily associated with pyrite or as arsenate in its less toxic form of As+5 (> 95%). In both bottom and fly ashes, more than 95% of the total arsenic is present as As+5. Chromium in the milled coal and bottom ash is mostly non-toxic (Cr+3). The more toxic Cr+6 comprise less than 5% of the total Cr in the ESP fly ash and the stack-emitted ash. Nickel in milled coal and ashes is in the form of non-toxic Ni+2, predominantly in coordination with oxygen. The emitted PAHs include acenapthene, fluorene, 2-methyl-fluorene, phenathrene, anthracene, fluoanthene, and pyrene; which are emitted from stack at the combined rate of 3.6 g/day. The concentrations of elements of environmental concern (As, Cd, Hg, Ni, and Pb) emitted to the atmosphere by the power plant in the zone of maximum impact at ground level are lower than those listed in the Health Guidelines of the USEPA and Canadian National Air Pollution Surveillance. This is based on stable meteorological conditions, down wind from the power plant for a maximum distance of 3 km.

Ash chemistry and mineralogy of an Indonesian coal during combustion: Part II — Pilot scale observations

This paper reports on combustion experiments carried out in a pilot scale furnace as a follow-up to research previously carried out using a drop-tube furnace to investigate the combustion behaviour of an Indonesian coal, in particular the effects of additives on ash chemistry, mineralogy and ash deposit formation. Combustion experiments were carried out in a pilot scale furnace to test the effectiveness of bauxite addition in reducing ash build-up. Samples collected from deposits on the slagging panels and fouling probe tubes, electrostatic precipitator fly ash, the furnace ash and tunnel ash were fully characterized using various analytical techniques. Experimental results substantiated earlier drop-tube observations suggesting that the use of raw coal with an addition of 3 wt.% bauxite would appear to offer the best performance with respect to slagging and fouling propensity in comparison to use of the raw coal alone. Observations on the reduction in glass content resulting from the addition of bauxite during PSF test runs support the earlier findings of the drop-tube tests. The reduction in glass content found in the slagging panel and fouling probe samples is comparable to that found in ash formation experiments conducted at 1400 °C despite the observed differences in mineralogy. Although deposits are still likely to form as indicated by the PSF runs they appear to be more friable and hence amenable to removal by conventional methods such as frequent soot blowing. These findings demonstrate how the results of laboratory experiments can be combined with those of pilot scale trials to provide data for full-scale trials on the effects of additives in the remediation of ash problems associated with the firing low-rank coals.

Characteristics and composition of fly ash from Canadian coal-fired power plants

Fly ashes were collected from the electrostatic precipitator (ESPs) and/or the baghouse of seven coal-fired power plants. The fly ashes were sampled from power plants that use pulverized subbituminous and bituminous feed coals. Fly ash from bituminous coals and limestone feed coals from fluidized-bed power plant were also sampled. The fly ashes were examined for their mineralogies and elemental compositions. The fly ashes from pulverized low sulfur coals are ferrocalsialic, those from high sulfur coals are ferrosialic and the fly ashes from the fluidized bed coals are ferrocalcic. The concentrations of As, Cd, Hg, Mo, Ni, and Pb in fly ash are related to the S content of the coal. Generally, those feed coals with a high S content contain higher concentrations of these elements. The concentrations of these elements are also greater for baghouse fly ash compared to ESP fly ash for the same station. The S content of fly ash from high S coal is 0.1% for pulverized ESP fly ash and 7% for baghouse fly ash from the fluidized bed, indicating that most of the S is captured by fly ash in the fluidized bed. The baghouse fly ash from the fluidized bed has the highest content of Cd, Hg, Mo, Pb, and Se, indicating that CaO, for the most part, captures them. Arsenic is captured by calcium-bearing minerals and hematite, and forms a stable complex of calcium or a transition metal of iron hydroxy arsenate hydrate [(M 2+) 2Fe 3(AsO 4) 3(OH) 4·10H 2O] in the fly ash. Most elements in fly ash have enrichment indices of greater than 0.7 indicating that they are more enriched in the fly ash than in the feed coal, except for Hg in all ESP ashes. Mercury is an exception; it is more enriched in baghouse fly ash compared to ESP. Fly ash collected from a station equipped with hot side ESP has a lower concentration of Hg compared to stations equipped with cold side ESP using feed coals of similar rank and mercury content. Fly ash particles from fluidized bed coal are angular and subangular with cores of quartz and calcite. The quartz core is encased in layer(s) of calcium-rich aluminosilicates, and/or calcium/iron oxides. The calcite core is usually encased in an anhydrite shell.

Speciation of Chromium in Feed Coals and Ash Byproducts from Canadian Power Plants burning Subbituminous and Bituminous Coals

The chromium species in the feed coals and ash byproducts from seven Canadian coal-fired power plants were examined using Cr X-ray absorption near-edge spectroscopy. Chromium in the Canadian feed coals is always found as Cr{sup 3+} but generally has a dual occurrence, as Cr{sup 3+} is distributed to varying degrees between the clay mineral illite and a poorly crystallized chromium oxyhydroxide phase associated with the organic fraction. In two subbituminous feed coals from Alberta, chromium is present largely as Cr{sup 3+}/illite, whereas in two other such coals, it is present predominantly as CrOOH. Chromium in a low-sulfur bituminous feed coal from Alberta is found mostly as Cr{sup 3+}/illite, whereas for feed coals from Nova Scotia with high sulfur contents, chromium is distributed between both Cr{sup 3+}/illite and CrOOH. Very little chromium was found in the limestone used in a fluidized-bed combustor. The chromium species in most bottom ash samples from all seven combustion units is predominantly, if not entirely, Cr{sup 3+} associated with aluminosilicate phases. Chromium speciation for subbituminous electrostatic precipitator fly ash is mostly Cr{sup 3+}, but in some cases, it is slightly lessand varies by sampling location at the plant. Chromium in fly ash from the combustion ofmore » bituminous feed coals is predominantlyCr{sup 3+}. A unique species of chromium found in one feed coal and an unrelated fly ash is metallic chromium, similar to that in stainless steel. The occurrence of this form of chromium in these materials indicates contamination from machinery, such as the coal milling machine or possibly wearing down of stainless steel parts by the coal or ash. The observation of this unexpected contamination demonstrates the power and usefulness of X-ray absorption fine-structure spectroscopy for speciation determination. 35 refs., 6 figs., 4 tabs.« less

Speciation of Arsenic in Feed Coals and Their Ash Byproducts from Canadian Power Plants Burning Sub-bituminous and Bituminous Coals

The arsenic species in the feed coals and ash byproducts from seven Canadian power plants (including one with a fluidized-bed combustor) that were burning local sub-bituminous and bituminous coals with sulfur contents in the range of 0.30−3.5 wt % have been examined using As X-ray absorption fine structure (XAFS) spectroscopy. The feed coals can be grouped based on their contents of arsenic associated with pyrite (As/pyr) and as As3+ and As5+ (arsenate) species. The arsenic species in sub-bituminous feed coals with low sulfur (0.22−0.38 wt %) and arsenic (1.6−2.2 mg/kg) contents consist of ∼50% As3+ and ∼50% As5+, whereas those with moderate sulfur (0.50 wt %) and arsenic (3.63 mg/kg) contents consist of 84% As/pyr, 7% As3+, and 9% As5+. In bituminous feed coal with low sulfur (0.40 wt %) and arsenic (4.39 mg/kg) contents, the arsenic speciation consists of 34% As/pyr, 12% As3+, and 54% As5+, and for those with high sulfur (2.60−3.56 wt %) and arsenic (54−84 mg/kg) contents, it consists of 77%−82% As/pyr and 18%−23% As5+. The bottom ash produced from sub-bituminous feed coals with low sulfur and arsenic contents consists of 10%−20% As3+ and 80%−90% As5+, and for moderate sulfur (0.50 wt %) and arsenic (3.63 mg/kg), the arsenic speciation consists of 5% As/pyr, 10% As3+, and 85% As5+ as arsenate. For bituminous feed coals with low sulfur and arsenic contents, the bottom ash is entirely As5+, whereas for coals with high sulfur and arsenic contents, the bottom ash consists of 10%−15% As3+ and 85%−90% As5+; and for the fluidized-bed combustor, the bottom ash is entirely As5+ arsenate. The species of arsenic in fly ash from sub-bituminous and bituminous coals are mostly arsenate (As5+), possibly in part incorporated in the glass matrix, and remains the same for coarse- and fine-grained electrostatic precipitator (ESP), baghouse, and stack-emitted ashes. The only difference between the ESP and baghouse fly ash is the higher amount of crystalline arsenates in the hopper fly ash. Neither the sulfur content nor the pyrite content of the feed coal seems to influence the speciation of arsenic, because virtually all of the arsenic in fly ash samples from high-sulfur coal is in the form of arsenate (As5+). However, arsenic (mostly as As5+) in these fly ashes is found to be very surface-enriched, because the amount measured by XPS decreases from >3 wt % to <0.8 wt % in the first few atomic layers. The presence of stable calcium or transition-metal iron hydroxyl arsenate hydrate [(M2+)2Fe3(AsO4)3(OH)4·10H2O] complexes, as determined by X-ray diffractometry, in the fly ash produced from high-sulfur/pyrite feed coals indicates that some of the arsenic might be captured by calcium and iron compounds.

Petrology of subbituminous feed coal as a guide to the capture of mercury by fly ash—influence of depositional environment

The mercury and maceral content of subbituminous feed coals burned at six Canadian power plants was measured and compared to the mercury and carbon content of corresponding fly ashes. The fly ashes were collected from electrostatic precipitator (ESP) pollution controls used at the power plants. Four feed coals from the Upper Cretaceous to Tertiary age Scollard Formation were deposited in freshwater depositional environment and contain 35–44% inertinite. Two feed coals from the Upper Cretaceous age Horseshoe Canyon Formation were deposited in a brackish water environment and contain 14% inertinite. The data show that abundant inertinite equates to more unburned carbon in ESP fly ash, and to enhanced capture of mercury in cold-side ESP fly ash. This indicates that the inertinite content of a coal seam may be indicative of the percentage of unburned carbon and the percentage of mercury captured by a cold-side ESP.

Emission of polycyclic aromatic hydrocarbons from medical waste incinerators

This study was conducted on two batch-type medical waste incinerators (MWIs), including the one with a mechanical grate (MG-MWI) and the other with a fixed grate (FG-MWI) for the disposal of general medical waste and special medical waste, respectively. Both incinerators shared the same air-pollution control devices which were installed in series, including one electrostatic precipitator (ESP) and one wet scrubber (WSB). In addition to the investigated emissions of polycyclic aromatic hydrocarbons (PAHs) from both types of MWIs, the PAH removal efficiencies of air-pollution control devices were also included. In this study, the GC/MS technique was used to analyze the concentrations of 21 PAH species contained in the stack flue gas, ESP fly ash, WSB effluent, and incinerating ash. Results show that total-PAHs (i.e., the sum of 21 PAH species) in stack flue gas were dominated by LM-PAHs (i.e., two- to three-ringed PAHs), but in incinerating ash, ESP fly ash and WSB effluent we found that they were dominated by MM-PAHs (i.e., four-ringed PAHs) and HM-PAHs (i.e., five- to seven-ringed PAHs) for both types of MWIs. The above results due to air-pollution control devices used in both types of MWIs had much higher removal efficiencies on both MM-PAHs and HM-PAHs (>78%) than on LM-PAHs (<5%). The emission factors of total-PAHs for MG-MWI (=252,000 μg/kg-waste) were lower than FG-MWI (=856,000 μg/kg-waste), which was probably due to more complete combustion involved in the combustion process of the former than the latter. Nevertheless, the above two emission factors were found consistently higher than the only municipal waste incinerator that was located in the same city (=871 μg/kg-waste, respectively). The above results warrant the need for seeking better technologies for disposing medical waste in the future.

Influence of the electrostatic precipitator and the flue gas temperature on concentrations of organic compounds

In the scope of 3 measurement series samples were taken simultaneously at five different locations of an incineration facility: boiler flue gas at approx. 560 – 610 °C and approx. 430 – 470 °C before an electrostatic precipitator (EP); flue gas before EP at approx. 280 – 300 °C; flue gas behind EP at approx. 280 – 300 °C; EP fly ash. The main reason for these investigations was to determine at which flue gas temperatures different organic compounds increase or rather decrease.

Influence of the electrostatic precipitator on concentrations of organic compounds in flue gas

In the scope of 11 measurement series at two combustion facilities the flue gas before and behind an electrostatic precipitator (EP) as well as the EP fly ash was sampled simultaneously and analyzed for several organic compounds. For polychlorinated dibenzofurans (PCDF) and dibenzo(p)dioxins (PCDD), polychlorinated biphenyls (PCB) and benzenes (PCBz), polychlorinated phenols (PCPh) and polycyclic aromatic hydrocarbons (PAH) formation as well as destruction was observed. The PCDF/D homologeous groups show a reproducible increase/decrease pattern.