Combustion Fly Ash Research Articles

Material- and Site-Specific Partition Coefficients for Beneficial Use Assessments.

Partition coefficient (Kd) values available in the literature are often used in fate and transport modeling conducted as part of beneficial use risk assessments for industrial byproducts. Because element partitioning depends on soil properties as well as characteristics of the byproduct leachate, site-specific Kd values may lead to more accurate risk assessment. In this study, contamination risk to groundwater of beneficially reused byproducts was assessed using batch leaching tests on waste to energy bottom ash and coal combustion fly ash. Leachates were equilibrated with eight different soils to obtain the waste-soil-specific Kd,exp values for the metals of interest. The Kd,exp values were used as inputs in the Industrial Waste Management Evaluation Model to demonstrate the degree to which Kd estimates affect risk assessment outcomes. Measured Kd,exp values for the most part fell within the large range of Kd values reported in the literature, but IWEM results using default Kd values for some types of soils resulted in overestimated risk compared to those derived from Kd,exp values. Modeled concentration at the receptor location was much lower for some elements for those soils with high concentrations of iron and aluminum.

Detection Improvement of Unburned Carbon Content in Fly Ash Flow Using LIBS with a Two-Stage Cyclone Measurement System

Fly ash contents can be considered as a basis for optimal and stable boiler combustion control and fly ash quality control in power plant, especially the unburned carbon in fly ash. The real-time and quantitative measurement of contents in fly ash was studied using a constructed two-stage cyclone measurement system and detected using laser-induced breakdown spectroscopy(LIBS) technique. The surrounding gas effect, such as CO2 effect on unburned carbon content, was studied comprehensively in this paper. The CO2 effect was eliminated using this proposed combination method of two-stage cyclone measurement system and LIBS with 1ns pulse-width laser according to the efficient gas-particle separation and the controlled laser-induced plasma processes of particle flow. The quantitative analysis was improved using the plasma temperature correction method with the intensity ratio of the emission pair from magnesium as a plasma temperature indicator. The measurement of unburned carbon content in fly ash with temperature correction method presented the concordant results analyzed by chemical analysis method. It is demonstrated the feasibility and improved detection ability for the real-time measurement of fly ash contents in power plant.

The effect of peat and wood fly ash on the porosity of mortar

Fluidized bed combustion fly ash (FBCFA), notably different from regular (coal) fly ash, is a promising industrial side stream to be used as a supplementary cementitious material (SCM). Peat and wood are important sources of biomass for energy production in Nordic countries and generate formidable amounts of un-used ash yearly. Two FBCFAs from the co-combustion of peat and wood, fly ash from coal combustion, and limestone filler were used to replace 10 wt%, 20 wt%, and 40 wt% of cement in mortar specimens. The compressive strength, porosity, water absorption, water vapor permeability, and drying shrinkage of the mortars were measured and compared. It was found that in almost all properties FBCFAs outperformed un-reactive limestone filler. Compared to coal fly ash, FBCFAs produced mortars with comparable compressive strength although with higher porosity, water absorption, and water vapor permeability.

Fly ash as low cost and environmentally friendly filler and its effect on the properties of mix asphalt

Abstract In the countries where the energy industry is based mainly on coal, the management of the waste generated in the process of its combustion (fly ash) is a serious problem. The article presents the properties of mix asphalt where the traditional limestone filler was replaced by fly ash in 25%, 50% and 75%. Two kinds of ashes were used for the tests: class F and class C; these ashes were characterized in terms of chemical composition, mineralogy and grain size. In total, the tests were carried out for 7 types of mix asphalt: reference AC 11 S and 6 mixes with lime-ash filler. Bulk density of an mix asphalt, maximum density of a mix, air voids content, indirect tensile strength and water and frost resistance for obtained mix asphalt were determined. For the samples with fly ash addition, the air voids ranged from 1.2% to 1.6% in the case of class F and from 1.3% to 2.8% in the case of class C fly ash. Water and frost resistance was 96%–104% and 102%–104%, respectively for the samples with the addition of class F and class C fly ash. The results indicate that both classes of fly ash can be applied as the alternative mineral filler, since the air voids as well as resistance to water and frost of the obtained mix asphalt met the standards.

The products of a high temperature reaction of fly ash with lime and soda

A composition of coal combustion fly ash depends on a coal composition and conditions of a combustion process. The main components are SiO2 and Al2O3. An amount of Al2O3 in coal combustion fly ash is relatively high, about 30–40%, and for this reason, the fly ash could be potentially used as a raw material source for alumina production. There are several ways to get alumina. The fly ash could be acid leached or sintered with a suitable additive. One of the possible sintering processes is lime-soda sinter process. The article deals with products of lime-soda sinter process of the fly ash produced from brown coal in Czech thermal power plant. The phase composition of sintered material was determined by X-ray diffraction analysis (XRD). The presence of sodium aluminate and dicalcium silicate was confirmed.

A porous geopolymer based on aluminum-waste with acoustic properties

Paval, a solid waste stream from the aluminum industry, is used as a pore generation agent in geopolymers. Paval was mixed with coal combustion fly ash, as a geopolymeric precursor, and activated with alkaline solution with the aim of obtaining porous geopolymers to be used as noise barriers. Both geopolymeric and pore generation reactions happen simultaneously. Aluminum from Paval can react with water and OH¯ from the geopolymerization activating solution, producing hydrogen. The hydrogen gas released generates a highly porous material. The influence of the fly ash-paval proportion and the setting temperature on open porosity, compressive strength and noise-absorbing properties were evaluated. To better understand these influences, the setting time, volume expansion and mineral composition were also studied. The obtained results showed that a higher Paval content (fly ash-Paval ratio 50:50) and setting temperature (70 °C) produced a lower setting time and higher volume expansion, increasing the open porosity and improving acoustic properties, but reducing the compressive strength. The material manufactured under these conditions showed similar amorphous phase content to the non-porous geopolymers made without Paval. On the other hand, the obtained materials did not raise environmental concerns in a normalised leaching test.

Feasibility of coal combustion fly ash alone and in combination with gypsum and green manure for reclamation of degraded sodic soils of the Indo‐Gangetic Plains: A mechanism evaluation

AbstractThe disposal of coal combustion fly ash (FA) generated from thermal power plants is a worldwide problem. However, its low bulk density and presence of calcium and iron–aluminium sesquioxide make it a prospective ameliorant alternative to gypsum for amending degraded sodic soils. A field experiment consisting of eight treatments with variable doses of FA and gypsum along with green manure (GM) was conducted for evaluating the amelioration mechanism by measuring changes in pH, exchangeable sodium percentage, zeta (ζ) potential, and properties of meso‐aggregates (0.5–2.0 mm). The results showed that compared with control, FA significantly reduced ζ‐potential, bulk density, and pH. The GM with FA further decreased ζ‐potential and increased hydraulic conductivity. The hydrolysis of iron and aluminium sesquioxide, present in FA, functioned to lower soil pH, whereas the reduction in exchangeable sodium percentage is attributed to bioavailable Ca (27.4%). A lower FA application rate produced better crop yields. FA 2.5% (w/w) alone, compared to the FA 5% (w/w), resulted in higher yield of rice (1.96 tonnes ha−1), whereas 25% gypsum requirement (25GR) + FA 2.5% (w/w) and 25GR + FA 2.5% (w/w) + GM provided wheat yield on par with 50% gypsum requirement (50GR). The study identifies that where gypsum is scarce, the recommended amendment is 25GR + FA 2.5% or 25GR + FA 2.5% + GM when applied for sodic soil to achieve a similar yield response to standard 50GR. If gypsum is unavailable, a one‐time application of FA 2.5% (w/w) alone will improve the productivity of degraded sodic soils corresponding to more exchangeable calcium and organic carbon, which were found to be higher for meso‐aggregates (0.5–2.0 mm).

Fluidized bed combustion fly ash as filler in composite polyurethane materials

Fly ash (FA) is a waste material having great potential as modifier of mechanical and thermal properties in polyurethane (PUR) technology. There are very few reporting the use of fluidized bed combustion (FBC) FA in the production of PUR foams. In this work, authors have used the as received FBC FA as an additive to PUR rigid foams. The composite materials containing 5, 10, 15, and 20 wt% of FA were obtained by hand mixing and casting method. Microscopic observations of both unmodified and composite foams showed a well formed, cellular structure of the rigid foam. The cell structure was uniform; most of the cells were closed, which was an important parameter influencing thermal insulation properties of PUR materials. FA was uniformly distributed within PUR matrix and placed between cells. When the content of FA in composite foams increased, cells’ dimensions decreased, which suggested that FA particles acted as nucleation sites during the foam formation process. The absorption bands presented in IR spectrum of PUR foam confirmed the presence of urethane bonds in the unmodified foam material. The IR spectrum of as-received FA reconfirmed the crystalline phases recognized by XRD analysis, which were anhydrite, quartz, lime, calcite and aluminosilicate. No additional bands were observed which suggested that no chemical bonding between PUR matrix and FA particles occurred in the composite foam. The incorporation of FA into the PUR matrix, up to 10 wt%, improved the mechanical performance of the composite materials, when compared to unmodified PUR foam. Such a tendency suggested the occurrence of interfacial interactions between polymer matrix and FA particles, as well as the uniform distribution of the filler within PUR material. For all the materials analyzed, the addition of FA to PUR foam reduced both carbon content and the gross calorific value. The addition of FA improved the thermal stability of the PUR foam material (barrier effect of the FA prevented the release of gases from the foam structure).

Oxy-Coal Combustion Fly Ashes: Leachability of Inorganic Trace Contaminants

The leachability and speciation of inorganic trace contaminants of oxy-coal combustion fly ash from a 20 MWth oxy-pulverized coal combustion (oxy-PCC) demonstration plant have been evaluated. Colle...

Effect of Mechanical Activation of Fluidized Bed Fly Ash on Geopolymer Properties

This paper is focused on the elucidation of mechanical activation effect of circulating fluidized bed combustion fly ash (Amgalan Thermal Station, Mongolia) on mechanical properties of geopolymers. Fluidized bed fly ash was mechanically activated for 15-120 minutes with a vibratory mill. The effect of mechanical activation was quite visible on the particle size reduction and on the degree of amorphization.Geopolymer samples were prepared from the raw and milled fluidized bed fly ashes by alkaline activation. Chemical activation was performed with 10M sodium hydroxide solution, as well as solutions containing a mixture of sodium silicate and sodium hydroxide with a weight ratio of 2:1. The geopolymer cubic specimens were cured at 70°C for 24 hrs and their 7 days uniaxial compressive strength was measured. After curing and drying, the bulk density, water absorption and apparent porosity of geopolymer samples were evaluated.X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and thermogravimetry-differential thermal analysis (TGA-DTA) have been used for the structural characterization of the CFA and the resulting geopolymers. The highest compressive strength of 32.4 MPa was achieved for the fly ash milled for 30 minutes and activated with the solution containing the sodium silicate and 10M sodium hydroxide at a weight ratio of 2:1. Non-milled CFA based geopolymers showed the compressive strength of 16.2 MPa after activation with the same solution. Mechanical activation resulted in an increase in the reactivity of the fluidized bed fly ash and that enhances the geopolymerization reactions.

Occurrence and recovery potential of rare earth elements in Finnish peat and biomass combustion fly ash

Rare earth elements (REEs) are highly important in the modern society as a result of their wide use in various fields of industry. Their high supply risk and increase in demand has led to classification as critical materials, and consequently, new resources for REEs are being prospected widely. Coal fly ash has been suggested as a possible secondary resource for REEs, but very little information is available regarding REE occurrence in biomass or peat derived fly ash.In this paper, fly ash samples from commercial power plants using peat and biomass as fuel were studied for REEs. The average concentration of REEs was 530 ppm, with up to 920 ppm in one fly ash. Five out of seven fly ashes were identified promising for profitable REE recovery according to outlook coefficients of >0.7 and critical REE content of >30%. Four fly ashes were found to exhibit medium REE enriched distributions, whereas three fly ashes displayed light REE enriched distributions. These enriched distribution patterns, as well as the observed Gd, Ce, Eu, La, and Y anomalies in the patterns, are proposed to originate mainly from the granitic bedrock at the fuel source. Additionally, positive correlation between REEs and iron was found, indicating REE association with iron minerals.

Influence of low calcium fly ash on compressive strength and hydration product of low energy super sulfated cement paste

This research aims to explore the effects of low calcium Class F fly ash (FFA) as an alumina supplier on the compressive strength and hydration products of an ecological super-sulfated cement (SSC) with fluidized bed combustion (CFBC) fly ash (CFA) as a crucial activator. Experimental results showed that partial replacement of ground granulated blast furnace slag (GGBFS/slag) by FFA in range of 10–30 wt% significantly improved the compressive strength of hardened eco-SSC paste. Microstructural examination using scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM/EDS), X-ray diffraction (XRD), thermogravimetric and derivative thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) spectroscopy obviously proved that the main hydration products of the hardened paste were ettringite/monosulfate (AFt/AFm) and calcium aluminum silicate hydrate (C-A-S-H). Increase in FFA resulted in higher degree of AFt/AFm precipitation and C-A-S-H with lower Ca:(Si + Al) ratio.

Effects of fly ash properties on carbonation efficiency in CO2 mineralisation

CO2 mineralisation by industrial wastes is a promising option for mitigating carbon emissions safely and permanently with low material cost. But there is still absence of a detailed understanding on how fly ash properties affect the carbonation reactions. To fill this knowledge gap, five coal combustion fly ashes, Beijing (BJ), Wuhai (WH), Hazelwood (HW), Yallourn (YA) and Loy Yang (LY) ashes, from China and Australia were selected for carbonation studies. Experiments were performed in a batch reactor at 40 and 140 °C with 20 bar initial CO2 pressure, 200 g/L solid to liquid ratio, 450 rpm stirring rate to compare the carbonation performance of the five fly ashes and the effect of fly ash properties on carbonation reactions. Then BJ, YA and HW ashes were then selected for further study in a wide temperature range (40–220 °C) because of their higher CO2 sequestration capacity than the other two ashes. Quantitative X-ray diffractometry (XRD) with Rietveld refinement was used to characterize the crystalline and amorphous phases in fresh and carbonated fly ashes. Scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) were used to characterize morphological and elemental properties of fresh and carbonated fly ash samples. Compared to LY and WH ashes, BJ, YA and HW ashes displayed much higher CO2 sequestration capacity due to the higher fraction of reactive Ca/Mg-bearing crystalline phases, including lime (CaO) and portlandite (Ca(OH)2) in BJ ash, periclase (MgO) and srebrodolskite (Ca2Fe2O5) in YA ash, and periclase and brucite (Mg(OH)2) in HW ash. Compared to YA and WH ashes, BJ ash displayed faster kinetics of carbonation reactions because the reactant phases of BJ ash were mainly Ca-bearing phases which have higher reactivity with CO2 than Mg-bearing phases. Also, particle size and morphological analyses indicated that the reacted particles displayed a lower porosity and pore area than the fresh sample due to the new precipitates not only depositing on the active surface, but also filling the pores of the fly ash particles, which was responsible for the reduced kinetics with time.

Mineralogy and Geochemistry of Feed Coals and Combustion Residues from Tunbilek and Seyitmer Coal-Fired Power Plants in Western Turkey

This study focuses on the enrichment of elements in feed coal (FC) and combustion residues, namely, fly ash (FA) and bottom ash (BA) samples, picked up from the Tuncbilek and Seyitomer coal-fired power plants in western Turkey. The FCs in both plants have generally similar mineralogical compositions, although siderite and dolomite are more prominent in Tuncbilek and feldspar and pyrite are more abundant in Seyitomer. Minerals in the FA from both power plants are mainly quartz, hematite, magnetite, anhydrite, and mullite. Along with quartz, the Fe-oxides are dominant phases in the BA samples. Accessory minerals in the FCs, FAs, and BAs, such as chromite and pentlandite, were identified by combined scanning electron microscopy-energy dispersive X-ray analysis. Significant enrichments of Cr and Ni were detected in FCs, FAs, and BAs from both power plants. These enrichments are probably associated with pyrite, chromite, and pentlandite. Mercury was also significantly enriched in the Seyitomer FA, owing to Hg retention by chars and anhydrite. The Hg and Cl concentrations of char samples from FAs of both power plants indicate that Hg and especially Cl concentrations are much higher than those in the FCs.

Geopolymerization enhanced hydrothermal synthesis of analcime from steel slag and CFBC fly ash and heavy metal adsorption on analcime

ABSTRACTThis work is focused on crystal phase transition of solid wastes and functional application of crystal analcime in waste water purification, which provide a new environment-friendly route. In this paper, analcime was synthesized from steel slag and Circulating fluidized bed combustion (CFBC) fly ash (CFA) by hydrothermal method enhanced via geopolymerization (non-crystallized process). Then the analcimes were used for the removal of heavy metal ions (Pb2+, Cu2+) in aqueous solutions. Both the raw materials and products were characterized by XRF, XRD, FT-IR, SEM-EDS, and TEM. The results showed that non-crystallized process reduced the time of hydrothermal reaction and promoted the purity of analcime. The adsorption kinetics of analcime were all well fitted the pseudo-second-order model, and adsorption isotherms were well described by the Langmuir model. The maximum adsorption capacity of analcime for Pb2+ and Cu2+ were around 75.76, and 21.83 mg/g, respectively. The preference order observed for adsorption is Pb2+ > Cu2+.

Pre-processing of coal combustion fly ash by classification for enrichment of rare earth elements

Fly ash from the combustion of coal shows potential as a source of valuable metals like the rare earth elements (REEs). These are present in the fly ash at low concentrations. Thus, simple dry pre-processing methods that can produce REE-enriched fractions from the fly ash could improve the feasibility of subsequent extraction processes. The performed air classification experiments with a coal combustion fly ash showed a certain size dependence of the REE concentrations. In the different size fractions the REEs were enriched or depleted. Thereby, the different groups of REEs showed differences in their behavior. In the finest size fraction all REEs were enriched by a factor of 1.05 to 1.65. In contrast, in the coarsest size fraction and in the second finest size fraction all REEs were depleted (0.63 to 0.78 and 0.58 to 0.92). In the medium size fraction the concentrations were close to those in the fly ash and in the second largest size fraction the light REEs (La, Ce, Pr, Nd and Sm) were enriched by a factor of 1.19 to 1.35, while the concentrations of the other REEs were similar as in the fly ash. Thus, air classification shows some potential as a simple dry pre-processing step for the separation of REE-enriched fractions from the bulk of a coal fly ash.

Concreto autocompactante con altos contenidos de subproductos de la combustión de carbón

El concreto autocompactante (CAC) se ha considerado como un gran logro en la tecnología del concreto debido a sus grandes ventajas como la auto-compactabilidad. Para tener esta propiedad el concreto fresco debe demostrar una alta fluidez, resistencia a la segregación y una buena cohesión. Con el propósito de evaluar estas propiedades, además de utilizar un subproducto de la combustión del carbón como la ceniza volante (CV) y la escoria de parrilla (E) se prepararon varias mezclas de concreto autocompactante remplazando el cemento en un 35% y 50% de cada una de estas adiciones. A los cuales se les evaluaron sus propiedades, tanto en estado fresco como en endurecido, las propiedades en estado fresco fueron evaluadas mediante el flujo de asentamiento, el embudo en V y la caja en L, en estado endurecido se evaluaron propiedades mecánicas (resistencia a la compresión, tracción indirecta y flexión) y de permeabilidad (succión capilar, absorción y porosidad y resistencia a cloruros). Todos los CAC mostraron buenaspropiedades en estado fresco y desarrollaron a los 28 días de curado resistencias a la compresión en un rango de 34 y 48 MPa. Los resultados muestran que el empleo de subproductos de la combustión del carbón pueden ser incorporados en la elaboración de CAC.

Gold Nanoparticle Conjugated Water Soluble Multiwall Carbon Nanotubes

The poor solubility and dispersibility of carbon nanotubes in both aqueous and organic solvents restrict their applications in biological science. Herein, a simple and cheap method for synthesizing and purification of water soluble multiwall carbon nanotubes from coal combustion fly ash and characterization of this water soluble multiwall carbon nanotubes after conjugation with gold nanoparticles has been described.

Use of Computed Tomography for the Evaluation of Autoclaved Aerated Concrete Structure

This paper deals with the use of computed tomography (CT) images and analytical software for the nondestructive evaluation of the texture of autoclaved aerated concrete (AAC) with 20% fluidized bed combustion fly ash as a substitute for quartz sand. The samples of AAC, made in the laboratory with the same composition but different ways of curing in the fresh stage (before autoclaving), were subjected to observation of the differences in the texture of the silicate matrix, such as inhomogenity, defects, and pore size distribution. The curing conditions with limited drying resulted in formation of larger, locally-connected pores and additional cracking after autoclaving, which led to a decrease in compressive strength up to 1.32 MPa, compared to samples cured in conditions that allowed complete drying reaching 1.95-1.96 MPa. Also there were problems identified related to imperfect laboratory preparation of the samples, such as agglomeration of individual mixture compounds and larger air void formation, due to the absence of vibrating, cracking and weak spots formation. CT provided sufficient contrasting images for consequent software evaluation of pore size distribution, however a higher resolution of the images is needed for determination of pores smaller than 0,125 mm.

Fly ash based geopolymeric foams using silica fume as pore generation agent. Physical, mechanical and acoustic properties

The aim of this work is the development of a porous geopolymeric foam with sound absorbing properties using silica fume as the pore generation agent. The samples were manufactured using a coal combustion fly ash as source material for the geopolymerization reaction, an alkaline solution as activating solution and silica fume as pore forming agent. Three parameters were studied: silica fume proportion (0, 20 and 40 wt%), activating solution (potassium silicate and potassium hydroxide) and setting temperature (40 and 70 °C). Once the samples were prepared, the experimental study of the most important physical, mechanical and acoustic features were carried out. The increase in the proportion of silica fume in the mixture and setting temperature produced a reduction in setting time and a raise of open void porosity, reducing the compressive strength at 28 days up to a half but increasing the sound absorption. The influence of activating solution in open porosity and sound absorbing properties was not very important.