Nickel speciation of residual oil fly ash and ambient particulate matter using X-ray absorption spectroscopy

The chemical speciation of Ni in fly ash produced from approximately 0.85 wt % S residual (no. 6 fuel) oils in laboratory (7 kW)- and utility (400 MW)-scale combustion systems was investigated using X-ray absorption fine structure (XAFS) spectroscopy, X-ray diffraction (XRD), and acetate extraction [1 M NaOAc-0.5 M HOAc (pH 5) at 25 degrees C]-anodic stripping voltammetry (ASV). XAFS was also used to determine the Ni speciation of ambient particulate matter (PM) sampled near the 400-MW system. Based on XAFS analyses of bulk fly ash and their corresponding acetate extraction residue, it is estimated that > 99% of the total Ni (0.38 wt %) in the experimentally produced fly ash occurs as NiSO4.xH2O, whereas > 95% of the total Ni (1.70 and 2.25 wt %) in two fly ash samples from the 400-MW system occurs as NiSO4.xH2O and Ni-bearing spinel, possibly NiFe2O4. Spinel was also detected using XRD. Acetate extracts most of the NiSO4.xH2O and concentrates insoluble NiFe2O4 in extraction residue. Similar to fly ash, ambient PM contains NiSO4.xH2O and NiFe2O4; however, the proportion of NiSO4.xH2O relative to NiFe2O4 is much greater in the PM. Results from this and previous investigations indicate that residual oil ash produced in the 7-kW combustion system lack insoluble Ni (e.g., NiFe2O4) but are enriched in soluble NiSO4.xH2O relative to fly ash from utility-scale systems. This difference in Ni speciation is most likely related to the lack of additive [e.g., Mg(OH)2] injection and residence time in the 7-kW combustion system.     

Nickel and sulfur speciation of residual oil fly ashes from two electric utility steam-generating units

Representative duplicate fly ash samples were obtained from the stacks of 400- and 385-MW utility boilers (Unit A and Unit B, respectively) using a modified U.S. Environmental Protection Agency (EPA) Method 17 sampling train assembly as they burned 0.9 and 0.3 wt % S residual (No. 6 fuel) oils, respectively, during routine power plant operations. Residual oil fly ash (ROFA) samples were analyzed for Ni concentrations and speciation using inductively coupled plasma-atomic emission spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, and X-ray diffraction (XRD). ROFA deionized H2O extraction residues were also analyzed for Ni speciation using XAFS and XRD. Total Ni concentrations in the ROFAs were similar, ranging from 1.3-1.5 wt%; however, stack gas Ni concentrations in the Unit A were 0.990 microg/Nm3 compared with 0.620 microg/Nm3 for Unit B because of the greater residual oil feed rates employed at Unit A to attain higher 400-MW load conditions with a lower heating value oil. Ni speciation analysis results indicated that ROFAs from Unit A contain approximately 3 wt % NiSO4 x xH2O (where x is assumed to be 6 for calculation purposes) and appoximately 4.5 wt% of a Ni-containing spinel compound, similar in composition to (Mg,Ni)(Al,Fe)2O4. ROFAs from Unit B contain on average 2 wt% NiSO4 x 6 H20 and 1.1 wt% NiO. XAFS and XRD analyses did not detect any nickel sulfide compounds, including carcinogenic nickel subsulfide (Ni3S2) (XAFS detection limit is 5% of the total Ni concentration). In addition, XAFS measurements indicated that inorganic sulfate and organic thiophene species accounted for > 97% of the total S in the ROFAs. Unit A ROFAs contained much lower thiophene proportions because cyclone-separated ROFA reinjection is employed on this unit to collect and reburn the larger carbonaceous particles.     

Characterization of Fine Particulate Matter Produced by Combustion of Residual Fuel Oil

ABSTRACT

Combustion experiments were carried out on four different residual fuel oils in a 732-kW boiler. PM emission samples were separated aerodynamically by a cyclone into fractions that were nominally less than and greater than 2.5 |j.m in diameter. However, examination of several of the samples by computer-controlled scanning electron microscopy (CCSEM) revealed that part of the PM_2.5 fraction consists of carbonaceous cenospheres and vesicular particles that range up to 10 |j.m in diameter. X-ray absorption fine structure (XAFS) spectroscopy data were obtained at the S, V, Ni, Fe, Cu, Zn, and As K-edges and at the Pb L-edge. Deconvolution of the X-ray absorption near edge structure (XANES) region of the S spectra established that the dominant molecular forms of S present were sulfate (26-84% of total S) and thiophene (13-39% of total S). Sulfate was greater in the PM_2.5 samples than in the PM₂₅₊ samples. Inorganic sulfides and elemental sulfur were present in lower percentages. The Ni XANES spectra from all of the samples agreed fairly well with that of NiSO₄, while most of the V spectra closely resembled that of vanadyl sulfate (VO?SO₄?xH₂O). The other metals investigated (i.e., Fe, Cu, Zn, and Pb) also were present predominantly as sulfates. Arsenic was present as an arsen-ate (As⁺⁵). X-ray diffraction patterns of the PM_2.5 fraction exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca, etc.) superimposed on broad peaks due to amorphous carbons. All of the samples contain a significant organic component, with the loss on ignition (LOI) ranging from 64 to 87% for the PM_2.5 fraction and from 88 to 97% for the PM_2.5+ fraction. Based on ¹³C nuclear magnetic resonance (NMR) analysis, the carbon is predominantly condensed in graphitic structures. Aliphatic structure was detected in only one of seven samples examined.     

The effect of metal catalysts on the formation of polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran precursors

The catalytic effects of copper and iron compounds were examined for their behavior in promoting formation of chlorine (Cl₂), the major chlorinating agent of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), in an environment simulating that of municipal waste fly ash. Formation of Cl₂ occurred as a result of a metal-catalyzed reaction of HCl with O₂. Catalytic activity was greatest at a temperature of approximately 400 °C, supporting a theory of de novo synthesis of PCDDs and PCDFs on fly ash particles downstream of waste combustion.     

Speciation and mobility of cadmium in straw and wood combustion fly ash

Two fly ashes from biomass combustion have been analysed regarding cadmium speciation and mobility. A fly ash from straw combustion contained 10 mg Cd/kg dry matter, and around 50% of the cadmium was leachable in water. The possible main speciation of cadmium in this fly ash was CdCl2. When adding this fly ash to agricultural soil a threat for groundwater contamination and plant uptake is existing. A fly ash from wood chip combustion had 28.6 mg Cd/kg dry matter. In this fly ash, the cadmium was bound more heavily, with only small amounts of cadmium leached in mild extractants. A possible speciation of cadmium in this fly ash was as oxide or as CdSiO3. Long-term effects and accumulation of cadmium could be a problem when adding this fly ash to agricultural or forest soils.     

Fly and bottom ashes from biomass combustion as cement replacing components in mortars production: Rheological behaviour of the pastes and materials compression strength

In the present research mortar pastes obtained by replacing a commercial cement with the equivalent mass of 5, 10, 20 and 30 wt.% of fly ash or bottom ash from fir chips combustion, were prepared and rheologically characterized. It was observed that the presence of ash modifies their rheological behaviour with respect to the reference blend due to the presence, in the ashes, of KCl and K₂SO₄ which cause precipitation of gypsum and portlandite during the first hydration stages of the pastes. Hydrated materials containing 5 wt.% of ash display compression strength and absorption at 28 d of same magnitude as the reference composition; conversely, progressive increase of ash cause a continuous decline of materials performances. Conversely, samples tested after 180 d display a marked decline of compression strength, as a consequence of potassium elution and consequent alkali-silica reaction against materials under curing.     

Continuous CO2 capture and MSWI fly ash stabilization, utilizing novel dynamic equipment

Novel dynamic equipment with gas in and out continuously was developed to study the capture capacity of CO₂. Municipal solid waste incineration (MSWI) fly ash has a high capture rate of CO₂ in CO₂-rich gas. Fly ash can sequester pure CO₂ rapidly, and its capacity is 16.3 g CO₂/100 g fly ash with no water added and 21.4 g CO₂/100 g fly ash with 20% water added. For simulated incineration gas containing 12% CO₂, the capture rate decreased and the capacity was 13.2 g CO₂/100 g fly ash with no water added and 18.5 g CO₂/100 g fly ash with 20% water added. After accelerated carbonation, the C and O contents increased, indicating CO₂ capture in the fly ash; CO₂ combines with Ca(OH)₂ to form CaCO₃, which increased the CaCO₃ content from 12.5 to 54.3%. The leaching of Pb markedly decreased from 24.48 to 0.111 mg/L.     

粉煤灰协同微波-Fenton氧化法处理活性艳蓝KN-R染料废水

以粉煤灰联合微波-Fenton氧化工艺处理活性艳蓝KN-R生产废水,考察了粉煤灰投加量及吸附时间对处理效果的影响,并通过正交实验对微波-Fenton工艺参数进行了优化。实验结果表明,粉煤灰絮凝吸附与微波-Fenton氧化具有协同效应;在粉煤灰投加量为40 g/L,搅拌吸附时间为20 min,滤液pH值为4,Fe2＋和H2O2投加量分别为3.6 mmol/L和0.15 mol/L,微波功率为200 W,辐射反应时间为4 min的优化条件下,染料废水的处理效果最好,COD和色度的去除率分别达到90.90%和99.98%。     

SGA对垃圾焚烧飞灰中重金属的固化性能研究简

根据EPA 1311、HJ/T 299-2007、HJ/T 300-2007和HJ 557-2009等国内外不同标准,研究了深圳某垃圾焚烧发电厂垃圾焚烧飞灰的浸出毒性,探讨了六硫代胍基甲酸（sixthio guanidine acid,SGA）、二甲基二硫代氨基甲酸盐（sodium dimethyl dithio carbamate,SDD）和Ca（OH）₂浓度对垃圾焚烧飞灰中重金属的固定性能的影响。研究结果表明,随着浸提液pH的降低,该厂焚烧飞灰中大部分金属元素的浸出量增大,焚烧飞灰浸出液中的Cd、Ni、Pb和Zn浓度分别超过国家危险废物鉴别标准（GB5085.3-2007）规定值的4.75倍、1.47倍、6.72倍和2.20倍,属于危险废弃物,必须进行稳定化处理。当固化剂SGA加入量为0.1 mol/kg时,稳定化后的重金属浸出浓度已经低于危险废物鉴别标准,且对Cd、Cr、Cu和Pb的固化性能优于SDD和Ca（OH）₂;当固化剂SGA、SDD和Ca（OH）₂加入量为0.5 mol/kg时,稳定化后的焚烧飞灰重金属浸出浓度均低于国家危险废物鉴别标准（GB 5085.3-2007）中的规定值。与SDD和Ca（OH）₂相比,SGA对垃圾焚烧飞灰中重金属的固化处理更具有优势。     

Natural and anthropogenic environmental nanoparticulates: Their microstructural characterization and respiratory health implications

A wide range of environmental particulate matter (PM) both indoor and outdoor and consisting of natural and anthropogenic PM was collected by high volume air filters, electrostatic precipitation, and thermophoretic precipitation directly onto transmission electron microscope (TEM) coated grid platforms. These collected PM have been systematically characterized by TEM, energy-dispersive X-ray spectrometry (EDS) and scanning electron microscopy (SEM). In the El Paso, TX, USA/Juarez, Mexico metroplex 93% of outdoor PM₁ is crystalline while 40% of PM₁ is carbonaceous soot (including multiwall carbon nanotubes (MWCNTs) and multiconcentric fullerenes) PM. Multiply-replicated cytotoxicity (in vitro) assays utilizing a human epithelial (lung model) cell line (A549) consistently demonstrated varying degrees of cell death for essentially all PM which was characterized as aggregates of nanoparticulates or primary nanoparticles. Cytokine release was detected for Fe₂O₃, chrysotile asbestos, BC, and MWCNT PM while reactive oxygen species (ROS) production has been detected for Fe₂O₃, asbestos, BC, and MWCNT aggregate PM as well as natural gas combustion PM.Nanoparticulate materials in the indoor and outdoor environments appear to be variously cytotoxic, especially carbonaceous nano-PM such as multiwall carbon nanotubes, black carbon, and soot nano-PM produced by natural gas combustion.     

Removal of SO2 and NOX from Stack Gas by Reaction with Calcium Hydroxide Solids

Previous workers have shown that simultaneous SO₂/NO_X removal can be obtained in a dry scrubbing system with Ca(OH)₂ promoted by an additive such as NaOH, and that fly ash and product recycle improve the reactivity of the solids toward SO₂. To test SO₂/NO_X removal with fly ash and product recycle, bench-scale experiments with a packed bed reactor were performed at bag filter conditions. The most reactive solid for NO_X removal was prepared by slurrying Ca(OH)₂ with fly ash, CaSO₃, and NaOH. The best conditions for NO_X removal were the greatest temperature (125°C) and greatest concentrations of SO₂ (1500 ppm) and O₂ (20 percent). At the best conditions, NO_X removed in 1 hour was 3-4 moles per 100 moles Ca(OH)₂, compared to 5-10 moles SO₂ removed per 100 moles Ca(OH)₂. The best SO₂ removal was obtained at the highest relative humidities/lowest temperatures (55% RH/ 65°C) with solids prepared by slurrying Ca(OH)₂ with fly ash and NaOH. At these conditions, SO₂ removed In 1 hour was 60-80 moles per 100 moles Ca(OH)₂, compared to 0.5 to 1 moles NO_X removed per 100 moles Ca(OH)₂.     

Oxygen-18 study of high-temperature air oxidation of SO2

The oxygen-18 enrichment in sulfates formed at high temperatures (475–500°C) by platinum-catalyzed air oxidation of SO₂ to SO₃ in humidified air, was found to be several parts per thousand higher than in the air oxygen, SO₂, or water vapor from which the sulfates were formed. Variation of the δ¹⁸O in the sulfates showed little dependence on variation of the δ¹⁸O in the water vapor. The mechanism of sulfate formation involved isotopic exchange between the air oxygen and water vapor, isotopic exchange between the water vapor and SO₂, and formation of the hydrate, H₂SO₄· 3H₂O.When Fe₂O₃ or V₂O₅ was heated in mixtures of air, water vapor, and SO₂, some of the SO₂ was analytically oxidized (via SO₃ formation) to sulfate of relatively high δ¹⁸O and the remainder to chemisorbed sulfate of relatively low δ¹⁸O. Charcoal and fly ash (containing unburned carbon and basic oxides) reacted with the SO₂ to yield chemisorbed sulfates of relatively low δ¹⁸O.     

Characterisation of particulate matter and gaseous emissions from a large ship diesel engine

Composition of exhaust from a ship diesel engine using heavy fuel oil (HFO) was investigated onboard a large cargo vessel. The emitted particulate matter (PM) properties related to environmental and health impacts were investigated along with composition of the gas-phase emissions. Mass, size distribution, chemical composition and microphysical structure of the PM were investigated. The emission factor for PM was 5.3 g (kg fuel)^?1. The mass size distribution showed a bimodal shape with two maxima: one in the accumulation mode with mean particle diameter D_P around 0.5 μm and one in the coarse mode at D_P around 7 μm. The PM composition was dominated by organic carbon (OC), ash and sulphate while the elemental carbon (EC) composed only a few percent of the total PM. Increase of the PM in exhaust upon cooling was associated with increase of OC and sulphate. Laser analysis of the adsorbed phase in the cooled exhaust showed presence of a rich mixture of polycyclic aromatic hydrocarbon (PAH) species with molecular mass 178–300 amu while PM collected in the hot exhaust showed only four PAH masses.Microstructure and elemental analysis of ship combustion residuals indicate three distinct morphological structures with different chemical composition: soot aggregates, significantly metal polluted; char particles, clean or containing minerals; mineral and/or ash particles. Additionally, organic carbon particles of unburned fuel or/and lubricating oil origin were observed. Hazardous constituents from the combustion of heavy fuel oil such as transitional and alkali earth metals (V, Ni, Ca, Fe) were observed in the PM samples.Measurements of gaseous composition in the exhaust of this particular ship showed emission factors that are on the low side of the interval of global emission factors published in literature for NO_x, hydrocarbons (HC) and CO.     

Predicting Extents of Mercury Oxidation in Coal-Derived Flue Gases

Abstract

The proposed mercury (Hg) oxidation mechanism consists of a 168-step gas phase mechanism that accounts for interaction among all important flue gas species and a heterogeneous oxidation mechanism on unburned carbon (UBC) particles, similar to established chemistry for dioxin production under comparable conditions. The mechanism was incorporated into a gas cleaning system simulator to predict the proportions of elemental and oxidized Hg species in the flue gases, given relevant coal properties (C/H/O/N/S/Cl/Hg), flue gas composition (O₂, H₂O, HCl), emissions (NO_X, SO_X, CO), the recovery of fly ash, fly ash loss-on-ignition (LOI), and a thermal history. Predictions are validated without parameter adjustments against datasets from lab-scale and from pilot-scale coal furnaces at 1 and 29 MW_t. Collectively, the evaluations cover 16 coals representing ranks from sub-bituminous through high-volatile bituminous, including cases with Cl₂ and CaCl₂ injection. The predictions are, therefore, validated over virtually the entire domain of Cl-species concentrations and UBC levels of commercial interest. Additional predictions identify the most important operating conditions in the furnace and gas cleaning system, including stoichiometric ratio, NO_X, LOI, and residence time, as well as the most important coal properties, including coal-Cl.     

Characterization of fine particulate matter produced by combustion of residual fuel oil

Combustion experiments were carried out on four different residual fuel oils in a 732-kW boiler. PM emission samples were separated aerodynamically by a cyclone into fractions that were nominally less than and greater than 2.5 microns in diameter. However, examination of several of the samples by computer-controlled scanning electron microscopy (CCSEM) revealed that part of the PM2.5 fraction consists of carbonaceous cenospheres and vesicular particles that range up to 10 microns in diameter. X-ray absorption fine structure (XAFS) spectroscopy data were obtained at the S, V, Ni, Fe, Cu, Zn, and As K-edges and at the Pb L-edge. Deconvolution of the X-ray absorption near edge structure (XANES) region of the S spectra established that the dominant molecular forms of S present were sulfate (26-84% of total S) and thiophene (13-39% of total S). Sulfate was greater in the PM2.5 samples than in the PM2.5+ samples. Inorganic sulfides and elemental sulfur were present in lower percentages. The Ni XANES spectra from all of the samples agreed fairly well with that of NiSO4, while most of the V spectra closely resembled that of vanadyl sulfate (VO.SO4.xH2O). The other metals investigated (i.e., Fe, Cu, Zn, and Pb) also were present predominantly as sulfates. Arsenic was present as an arsenate (As+5). X-ray diffraction patterns of the PM2.5 fraction exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca, etc.) superimposed on broad peaks due to amorphous carbons. All of the samples contain a significant organic component, with the loss on ignition (LOI) ranging from 64 to 87% for the PM2.5 fraction and from 88 to 97% for the PM2.5+ fraction. Based on 13C nuclear magnetic resonance (NMR) analysis, the carbon is predominantly condensed in graphitic structures. Aliphatic structure was detected in only one of seven samples examined.     

Impact of Free Calcium Oxide Content of Fly Ash on Dust and Sulfur Dioxide Emissions in a Lignite-Fired Power Plant

Abstract

Emitted pollutants from the Agios Dimitrios lignite-fired power plant in northern Greece show a very strong linear correlation with the free calcium oxide content of the lignite ash. Dust (fly ash) emissions are positively correlated to free calcium oxide content, whereas sulfur dioxide (SO₂) emissions are negatively correlated. As a result, at present, the Agios Dimitrios Power Plant operates very strictly within the legislative limits on atmospheric particulate emission. In the present study, the factors to be considered in assessing the impact of lignite combustion on the environment are presented and evaluated statistically. The ash appears to have a remarkable SO₂ natural dry scrubbing capability when the free calcium oxide content ranges between 4 and 7%. Precipitator operating problems attributable to high ash resistivity can be overcome by injecting sulfur trioxide to reduce the ash resistivity, with, of course, a probable increase in operating costs.     

Immobilization and volume reduction of heavy metals in municipal solid waste fly ash using nano-size calcium and iron-dispersed reagent

This study was conducted to examine the synthesis and application of novel nano-size calcium/iron-based composite material as an immobilizing and separation treatment of the heavy metals in fly ash from municipal solid waste incineration. After grinding with nano-Fe/Ca/CaO and with nano-Fe/Ca/CaO/[PO₄], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash). Heavy metals in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized, respectively. Additionally, scanning electron microscopy combined with energy-dispersive X-ray spectrometry (SEM-EDS) observations indicate that the main fraction of enclosed/bound materials on treated fly ash includes Ca/PO₄-associated crystalline complexes. After nano-Fe/Ca/CaO/[PO₄] treatment, the heavy metal concentrations in the fly ash leachate were much lower than the Japan standard regulatory limit for hazardous waste landfills. These results appear to be extremely promising. The addition of a nano-Fe/Ca/CaO/PO₄ mixture with simple grinding technique is potentially applicable for the remediation and volume reduction of fly ash contaminated by heavy metals.

Implications: After grinding with nano-Fe/Ca/CaO and nano-Fe/Ca/CaO/[PO₄], approximately 30 wt% and 25 wt% of magnetic fraction fly ash were separated. The highest amount of entrapped heavy metals was found in the lowest weight of the magnetically separated fly ash fraction (i.e., 91% in 25% of treated fly ash), whereas heavy metals either in the magnetic or nonmagnetic fly ash fractions were about 98% and 100% immobilized. These results appear to be very promising, and the addition of nano-Fe/Ca/CaO/PO₄ mixture with simple grinding technique may be considered potentially applicable for the remediation and volume reduction of contaminated fly ash by heavy metals.     

Emission characteristics for co-combustion of leather wastes,sewage sludge,and coal in a laboratory-scale entrained flow tube furnace

Four different mixed fuels consisted of leather waste, coal, and sewage sludge were combusted in a lab-scale entrained flow fluidized bed furnace. The influence of blending ratio on emission characteristics of SO₂, NO_x, HCl, particulate matter (PM), heavy metals, and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) was studied. Results showed that the mixing of coal with sewage sludge had a complex effect on the emission characteristics. On the one hand, with more sewage sludge blending in the mixed fuel, the acid gas pollutant (SO₂, NO_x) decreased a lot, and the recovery of volatile heavy metals (Cd, Pb) increased at the same time. Furthermore, the leaching toxicity of Cr in the fly ash and bottom ash went down below the national standard with the adding of sewage sludge. On the other hand, the mixing of sewage sludge which consisted of more ash content resulted in the increase of the PM emission. Moreover, the high content of Cu and chlorine in the sewage sludge can promote the formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) when the fuel 3 and 4 were combusted. Most importantly, the concentration of toxic PCDD/Fs in the flue gas produced from fuel 3 and fuel 4 was successfully controlled down below 0.20 ng I-TEQ/Nm³ by the active carbon.

     

Microscale air quality impacts of distributed power generation facilities

The electric system is experiencing rapid growth in the adoption of a mix of distributed renewable and fossil fuel sources, along with increasing amounts of off-grid generation. New operational regimes may have unforeseen consequences for air quality. A three-dimensional microscale chemical transport model (CTM) driven by an urban wind model was used to assess gaseous air pollutant and particulate matter (PM) impacts within ~10 km of fossil-fueled distributed power generation (DG) facilities during the early afternoon of a typical summer day in Houston, TX. Three types of DG scenarios were considered in the presence of motor vehicle emissions and a realistic urban canopy: (1) a 25-MW natural gas turbine operating at steady state in either simple cycle or combined heating and power (CHP) mode; (2) a 25-MW simple cycle gas turbine undergoing a cold startup with either moderate or enhanced formaldehyde emissions; and (3) a data center generating 10 MW of emergency power with either diesel or natural gas-fired backup generators (BUGs) without pollution controls. Simulations of criteria pollutants (NO₂, CO, O₃, PM) and the toxic pollutant, formaldehyde (HCHO), were conducted assuming a 2-hr operational time period. In all cases, NO_x titration dominated ozone production near the source. The turbine scenarios did not result in ambient concentration enhancements significantly exceeding 1 ppbv for gaseous pollutants or over 1 µg/m³ for PM after 2 hr of emission, assuming realistic plume rise. In the case of the datacenter with diesel BUGs, ambient NO₂ concentrations were enhanced by 10–50 ppbv within 2 km downwind of the source, while maximum PM impacts in the immediate vicinity of the datacenter were less than 5 µg/m³.

Implications: Plausible scenarios of distributed fossil generation consistent with the electricity grid’s transformation to a more flexible and modernized system suggest that a substantial amount of deployment would be required to significantly affect air quality on a localized scale. In particular, natural gas turbines typically used in distributed generation may have minor effects. Large banks of diesel backup generators such as those used by data centers, on the other hand, may require pollution controls or conversion to natural gas-fired reciprocal internal combustion engines to decrease nitrogen dioxide pollution.     

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.