Particle Size Distribution Of Ash Research Articles

Experimental study of fly ash precipitation in a model electrostatic precipitator with discharge electrodes of different design

The study was inspired by the need to replace the spiked band electrode with another one which would display a higher mechanical strength and a longer service life and would be able to provide similar electric field parameters and similar precipitation efficiency as does the spiked band electrode. A major objective of the study was to investigate the influence of the physicochemical properties (chemical composition, particle size distribution and resistivity) of the fly ash on the collection efficiency. For this purpose, three electrodes with a difference in design were tested. The fly ash was produced by a pulverized-fuel boiler fired with bituminous coal and a lignite-fired fluidized-bed boiler of which flue gas was used. The experiments were carried out under laboratory conditions with a single-stage electrostatic precipitator test facility. The chamber of the experimental setup was made of Plexiglas, with a length of 2 m, a height of 0.45 m and an interelectrode spacing of 0.4 m. The results (gathered in tables and plotted in figures) show how the corona electrode geometry, the physicochemical properties and resistivity influence the collection efficiency under experimental conditions. The highest collection efficiency was obtained with a pipe and double-spike electrode. In the course of the experiment, the N EHD parameter was established, which is a dimensionless electrohydrodynamic characteristics value, used to describe the dominance of either electrohydrodynamic or viscous forces in a nonconductive fluid .

Oxidation of organic pollutants in incineration flue gas by a fluidized palladium catalyst

The catalytic oxidation of trace organic compounds generated from waste incineration is usually carried out by a fixed-bed reactor. However, the performance of a fluidized catalyst reactor is seldom studied. This work investigated the destruction removal efficiency (DRE) of benzene, toluene, ethylbenzene, xylene (BTEX), and polycyclic aromatic hydrocarbons (PAHs) generated from waste incineration under different operating conditions by a fluidized palladium catalyst. The investigated conditions included different fluidized velocities and the effects of heavy metals, acid gas, and water vapor. Experimental results showed that the fluidized-catalyst reactor was very effective for destroying BTEX and PAHs and capturing particles. When the feedstock contained heavy metals, Pb and Cd inhibited the oxidation of organic compounds, but Cr did not. Because the feedstock contained sulfur and chloride (PVC), the palladium catalyst was poisoned and deactivated. The presence of water vapor also decreases the DRE of BTEX and PAHs. Moreover, the particle size distribution of fly ash and heavy metals after the catalyst reactor became smaller by comparing the mass size distribution of fly ash and the elemental size distribution of heavy metals (Pb, Cr, Cd) before and after the fluidized-catalyst reactor.

Formation of fine particles from residual oil combustion: Reducing nuclei through the addition of inorganic sorbent

The potential use of sorbents to manage emissions of ultrafine metal nuclei from residual oil combustion was investigated by using an 82-kW-rated laboratory-scale refractory-lined combustor. Without sorbent addition, baseline measurements of the fly ash particle size distribution (PSD) and chemical composition indicate that most of the metals contained in the residual oil form ultrafine particles (∼0.1 μm diameter). These results are consistent with particle formation via mechanisms of ash vaporization and subsequent particle nucleation and growth. Equilibrium calculations predict metal vaporization at flame temperatures and were used to define regions above the dew point for the major metal constituents (iron [Fe], nickel [Ni], vanadium [V], and zinc [Zn]) where vapor-phase metal and solidphase sorbents could interact. The addition of dispersed kaolinite powder resulted in an approximate 35% reduction in the ultrafine nuclei as determined by changes to the PSDs as well as the size-dependent chemical composition.

Effect of particle size distribution of fly ash–cement system on the fluidity of cement pastes

This paper investigates the effect of particle size distribution of fly ash–cement system on the fluidity of the cement pastes using class F fly ash collected from the hopper attached to an electrostatic precipitator when the burning conditions and types of coal are changed at a coal-fired power plant. The unburned carbon content of fly ashes used in the experiment is less than 1.5%. To prevent the unburned carbon in fly ashes from affecting the fluidity of the pastes, polycarboxylic acid plasticizer with more saturation amount is added into the pastes for experimentation. The particle size distribution of fly ash–cement system is analyzed using n value of Rosin–Rammler function and the n value is derived with a nonlinear least squares fitting method. As the result, it is shown that the fluidity increases as the particle size distribution becomes wider, i.e., as n value gets smaller.

Properties and microstructure of sintered incinerator bottom ash

The fraction of incinerator bottom ash with a particle size less than 8 mm produced at a commercial municipal solid waste incinerator was wet milled, dried, compacted and sintered at a range of temperatures to form ceramic materials. The effects of milled ash particle size distribution, powder compaction pressure and sintering temperature were investigated, and the materials formed characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis (TG/DTA). The main minerals present in the milled ash were quartz (SiO 2) and calcite (CaCO 3). Sintered densities of materials produced from ash milled to 95% less than 27 μm increased from 1.38 to 2.63 g/cm 3 on increasing the sintering temperature from 1020 to 1080 °C. Firing above 1080 °C caused a rapid decrease in density and sample expansion. The principal crystalline phase present in the high-density material was diopside (CaMgSi 2O 6). This work shows that a significant fraction of incinerator bottom ash can be processed to form sintered materials with properties controlled by ash particle size distribution and sintering conditions.

On trimodal particle size distributions in fly ash from pulverized-coal combustion

Combustion-generated fine particles, defined as those with aerodynamic diameters less than 2.5 μm, have come under increased regulatory scrutiny because of suspected links to adverse human health effects. Whereas classical theories regarding coal combustion suggest that mechanisms of ash vaporization and fragmentation lead to bimodal ash particle size distributions (PSDs), this paper presents experimental results supporting other existing hypotheses that three distinct ash modes may be more appropriate. This paper focuses on the existence and generality of a central mode, between approximately 0.7 and 3.0 μm diameter. This central mode is presumably caused by fragmentation mechanisms, but is still important from a health perspective, because a large portion is contained within the 2.5 μm particle size fraction. Presented here are experimental results from two different laboratory combustors and one industrial boiler, all burning pulverized coals. Use of a variety of particle-sampling and size classification methods, including electrical mobility, time-of-flight, and inertial (low-pressure impaction) methods, confirms that the central mode is not an artifact of the particle-sampling and -sizing methods used. Results from the combustion of 10 different coals consistently show that this central mode is significant for both high-and low-rank coals. Size-segregated elemental distributions of calcium, iron, and aluminum provide additional insight into mechanisms of formation of each mode. Field tests show that the central mode can be the major contributor to fine particle emissions leaving an electrostatic precipitator (ESP). The new experimental results presented here are interpreted in the light of complementary existing data and available theories from the literature.

A mathematical model of ash formation during pulverized coal combustion

A mathematical model of ash formation during high-rank pulverized coal combustion is reported in this paper. The model is based on the computer-controlled scanning electron microscope (CCSEM) characterization of minerals in pulverized coals. From the viewpoint of the association with coal carbon matrix, individual mineral grains present in coal particles can be classified as included or excluded minerals. Included minerals refer to those discrete mineral grains that are intimately surrounded by the carbon matrix. Excluded minerals are those liberated minerals not or at least associated with coal carbon matter. Included minerals and excluded minerals are treated separately in the model. Included minerals are assumed to randomly disperse between individual coal particles based on coal and mineral particle size distributions. A mechanism of partial-coalescence of included minerals within single coal particles is related to char particulate structures formed during devolatilization. Fragmentation of excluded minerals, which is important particularly for a coal with a significant fraction of excluded minerals, is simulated using a stochastic approach of Poisson distribution. A narrow-sized sample of an Australian bituminous coal was combusted in a drop-tube furnace under operating conditions similar to that in boilers. The particle size distribution and chemical composition of experimental ash were compared to those predicted with the model. The comparisons indicated that the model generally reflected the combined effect of coalescence of included minerals and fragmentation of excluded minerals, the two important mechanisms governing ash formation for high-rank coals.

The implication of mineral coalescence behaviour on ash formation and ash deposition during pulverised coal combustion

In modelling the fate of minerals of pulverised coal in coal-fired boilers, ash formation is a primary step that decides ash particle size distribution and composition. Frequently, two extreme schemes have been used regarding mineral coalescence behaviour within individual char particles, i.e. no coalescence and full coalescence. However, their implications on ash deposition and thermal performance have not been investigated. In the present paper, the implications of coalescence of included minerals on ash character and subsequent ash deposition are demonstrated by means of an ash formation model and an ash deposition model. The simulated results in a cylindrical furnace for an Australian bituminous coal indicate that ash deposition and thermal performance are significantly influenced by the coalescence behaviour of included minerals.

Effect of urea on fly ash PCDD/F concentrations in different particle sizes

The effect of urea as an inhibitor for reducing polychlorinated dibenzo- p-dioxin and dibenzofuran (PCDD/F) concentrations in flue gases was studied in a pilot scale plant, together with the effect on the particle size distribution of these compounds. Total PCDD/F concentrations decreased by a maximum of 74%, the decrease being greatest for the most highly (octa-) chlorinated isomers. The PCDD/F reduction affected all the particle size classes when an adequate amount of urea was used (1% of the fuel input), which indicates that inhibition, unlike formation, is independent of the fly ash particle size distribution.

Estimation of required parameters for detection of small smoke plumes by lidar at 1.54 μm

Parameters of eyesafe lidar at 1.54 μm for detection of small plumes of smoke from burning wood or oil have been evaluated. It was assumed that a diode-pumped solid-state Er:glass laser at 1.54 μm or a Nd:YAG laser with a Raman cell or optical-parametric oscillator is used as a light source and that detection of backscattered light is performed with an avalanche photodiode. Ash and soot particle size distributions were taken from experiments. A backscattering coefficient at 1.54 μm for various source of smoke was estimated. In computing the laser energy, range between lidar and smoke, receiver optics diameter, fuel mass burned in unit time, fire source radius, laser pulse duration and visibility were varied. Results of the computations enabled estimation of the required laser energy, which ranges from 0.05 to 1400 mJ depending on the parameters.

Numerical Calculations on Condensation/Coagulation of PbO and Fly Ashes in a Vertical-type Small Size Incinerator

This study is about numerical calculations on condensation and coagulation of hazardous metallic species which are important physical phenomena in an incinerator. Lead oxide(PbO), one of major metallic species produced in the combustion process, is selected for the study. Governing equations are three moment forms of the General Dynamic Equation and a vapor balance equation made by adding the effect of condensation and coagulation to the well-known convective diffusion equation. These differential equations, expressed in dimensionless variables, are solved using the finite differenced method. Temperature and velocity fields considering the gravitational force, number concentration of metal vapors, and ash particle size distribution are selected as the factors influencing the result of total aerosol size distribution.

Selenium in onions grown in media amended with coal fly ashes collected with differing efficiencies

A study was conducted to learn if the extent of selenium uptake by onions grown on coal fly ash-amended growth media would be influenced by the particle size distribution of the fly ash. Two fly ashes having differing percentages of finely sized particles were used as plant growth amendments at percentages in the media to yield equal concentrations of selenium. Selenium concentrations in the harvested onion bulbs were found to be independent of fly ash particle size distribution.

Development of Fly Ash Quality Control System.

In order to effectively utilize fly ash as reproduction resources, it is necessary to qualify physical and chemical properties of fly ash and to collect an evaluated quality of ash by selection and storage. So a fly ash qualify control system capable of measuring and analyzing the component and the particle size distribution of ash in onstream was developed and a demonstration plant is now installed on site. This quality control system consists of an automatic sampling system, a residual carbon content analyzer, an elementary composition analyzer, a quality evaluation equipment and the like, and is capable of operating automatically. This paper introduces its quality evaluation technique in this system and the result of its effectively demonstration test as well as the state of operating machines.

Effect of content and particle size distribution of high-calcium fly ash on the rheological properties of cement pastes

The Theological properties of high-calcium fly ash cement pastes were investigated. An increase both in yield value and plastic viscosity with fly ash content was found. It was also observed that the pastes became more fluid with the higher fly ash fineness. A more important relation was shown between the fine fractions (< 24 mm) content and the degree of fluidity rather than that of specific surface area vs. fluidity.

Studies on Separation Characteristics of Hexavalent Chromium from Aqueous Solution by Fly Ash

Abstract Hexavalent chromium has been separated from an aqueous solution by fly ash. The particle size distribution and physical properties of fly ash have been illustrated. It is observed that the percent removal of Cr6 + by fly ash is affected by its concentration in aqueous solution, temperature, particle size, and pH. Better separation is obtained at acidic pH and at higher temperature. Particle size has a nonsignificant effect on separation. The reaction kinetics of separation follows first-order kinetics more satisfactorily at higher temperature.

A multifrequency laboratory investigation of attenuation and scattering from volcanic ash clouds

Interest in remote monitoring of volcanic activity has increased in the last several years partly as a result of several powerful eruptions and partly as a result of satellite-borne spectrometers with thermal IR bands with which to monitor the physical makeup and effects of the volcanic inputs to the atmosphere. The authors consider the first wide-bandwidth laboratory experiments intended to improve our understanding of the spectral response of volcanic ash important for remote sensing of volcano eruption ejecta, making comparisons between data from the laboratory of ash suspensions and Mie theory for scattering and attenuation from spheres. Described are the experimental configuration, the sample preparation techniques and the results obtained. The results indicate a general sphere-like behavior of the ash, however the levels indicate effective radii that lie at the extremes of the actual particle size ranges. The data presented are unique in their multispectral character as well as their control over ash particle size distributions. They should be useful in the process of selecting appropriate remote sensing datasets and for improving models for retrieving estimates of particle size distribution, concentration, total mass of ash ejected, cloud drift, and fall-out rate from that data. They should also be useful for designing and assessing performance of ash hazard sensors for flying aircraft.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of the occurrence and composition of iron compounds on ash formation, composition, and size in pilot-scale combustion of pulverized coal and coal-water slurry fuels

Two coals, Beulah (North Dakota) lignite and Elk Creek (West Virginia) high-volatile A bituminous, were burned in both pulverized coal and coal-water slurry fuel forms to study the effect of the modes of occurrence and composition of iron compounds in the coal on the particle size distribution and composition of ash. The slurry preparation process appeared to cause a significant reduction in the particle size distribution of pyrite in the lignite, relative to the pulverized coal. This in turn caused a change in the dominant mechanism of ash formation. In the Beulah pulverized coal, pyrite fragmentation is the major process, forming submicrometer- or micrometer-sized iron oxide particles

Effect of fuel particle and droplet size distribution on particle size distribution of char and ash during pilot-scale combustion of pulverized coal and coal-water slurry fuels

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffect of fuel particle and droplet size distribution on particle size distribution of char and ash during pilot-scale combustion of pulverized coal and coal-water slurry fuelsSharon Falcone Miller and Harold H. SchobertCite this: Energy Fuels 1993, 7, 4, 520–531Publication Date (Print):July 1, 1993Publication History Published online1 May 2002Published inissue 1 July 1993https://doi.org/10.1021/ef00040a013RIGHTS & PERMISSIONSArticle Views306Altmetric-Citations15LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (4 MB) Get e-Alerts Get e-Alerts

Effect of mineral matter particle size on ash particle size distribution during pilot-scale combustion of pulverized coal and coal-water slurry fuels

The objective of this work was to investigate the effect of the particle size distribution (PSD) of mineral matter in coal on the particle size distribution of ash produced during firing of two coals in pulverized coal and coal-water slurry forms. The coals used in this work were Beulah (North Dakota) lignite and Elk Creek (West Virginia) high volatile A bituminous coal. Combustion experiments mere performed in a pilot-scale 316 MJ/h down-fired unit with 20% excess air. The dominant mechanism of ash formation in the Beulah pulverized coal was fragmentation of mineral particles, specifically pyrite, resulting in a finer ash particle size distribution than that of the original mineral matter (62% reduction in d 50 of mineral matter)

Ash particle size and composition evolution during combustion of synthetic coal and inorganic mixtures

To develop methods to predict and mitigate ash deposition problems, a firm understanding of the fundamental mechanisms of ash formation and deposition must be obtained. The first step to understanding the mechanisms of ash deposition is to determine how the initial inorganic constituents in the coal are transformed to produce intermediate species. To avoid some of the complexities involved in coal minerals, simplified, precisely formulated model mixtures consisting of a synthetic coal organic matrix and minerals and inorganic species were prepared, t ~ Mineral inclusions in the synthetic coal were limited in order to isolate specific chemical and physical transformations during combustion under controlled conditions in a laminar flow furnace. Char and ash products were analyzed to determine their chemical and physical characteristics. Although these model mixtures were not exhaustive representations of real coal, they provided a system which could be used to determine the effect of gas temperature and coal inorganic composition on the particle size and composition of specific ash types. Two calcium, silica, and sulfur synthetic coal systems were prepared: one system having calcium in the mineral form as 10-/zm calcite (Ca [min.]-Si-S), and the other having calcium associated in a simulated organic association as ironically dispersed calcium acetate (Ca[org.]-Si-S). A third system consisted of sodium, silica, and sulfur, with the sodium being associated as sodium benzoate simulating an organic association (Na[org.]-Si-S). Silica, in all three systems, consisted of 10-/.Lm quartz that was associated within the synthetic coal particles. Sulfur was extraneously added to the model mixtures in an elemental form and was also included in the organic polymer in very small amounts. The calcite particles were added to the organic matrix during polymerization to allow for their incorporation into the synthetic coal particles. The mineral grains associated with coal particles can be described as being included. The organic matrix consisted of a furfuryl alcohol polymer. The purpose of the Ca -S i -S and Na-S i -S systems was to demonstrate the differences in interactions between included quartz and 1) Ca that is mineral bound as included calcite, 2) Ca that is organically bound or dispersed on an ionic level within the organic matrix, and 3) Na that is organically bound. Reactions involving Ca, Si, and S during combustion are of particular interest when burning low-sulfur and calcium-rich western U.S. subbituminous coals, since calcium sulfate and calcium silicate phases play important roles in the formation of convective pass ash deposits. The effect of temperature on the particle size and composition distribution of ash produced from included calcite and quartz and organically associated calcium and included quartz are of specific interest, as are the reactions of sulfur oxides with the available calcium oxide. The Na (org.)-Si-S system adds another dimension to the role of organically associated elements in the formation of ash, especially with regard to the formation of low melting point Na sulfates and Na silicates on the surface of quartz particles. Quartz was chosen instead of clay (aluminosilicate) as the silicate material to test reactions with the calcium and sodium because lower viscosity and lower melting point liquid phases will form alkali// alkaline earth elements reacting with silica. Lower viscosity liquid phases usually lead to more severe fouling deposits.