Particle Size Distribution Of Ash Research Articles

Effects of alkaline extraction on behavior of rare earth elements in coal ashes.

The effects of alkaline extraction on the behavior of rare earth elements in coal ashes were investigated in the present study. Independent variables are the concentration of extractant and particle size of coal ashes. Sodium hydroxide was used as an extractant, and the molarity of the solvents varied from 1.0 to 7.0M. The coal ashes used here were fly and bottom ashes. Fly and bottom ashes were classified into four samples by particle size, with each categorized at both 45 and 300µm. The particle size distribution and crystalline characteristics of coal ashes, leaching, and the contents of rare earth elements in coal ashes after alkaline extraction were investigated, and the effects of independent variables on the content of rare earth elements in coal ashes were discussed. The test results showed that the dissolution of amorphous phase in coal ashes mainly occurred when the molarity was not more than 3M, while dissolution and precipitation such as geopolymerization and the formation of zeolite occurred simultaneously when the molarity was more than 5M. The dissolution and formation of precipitates such as geopolymer in the present study affected the variation of the rare earth element contents in the ashes. Besides, the ashes being smaller in size was more favorable for an increase in the rare earth elements in coal ashes.

Assessment of atmospheric air pollution in Dnipro city as a result of dust entrainment from the ash-disposal areasof Prydniprovsk TPP

Purpose. The purpose of this work is to assess the pollution of atmospheric air in Dnipro city as a result of dust entrainment from the ash-disposal areas of Prydniprovsk TPP. The methods. Assessment of atmospheric air pollution in the city of Dnipro as a result of dust entrainment from the ash-disposal areas of Prydniprovska TPP was carried out as follows: physical and chemical characteristics of the stored fly ash were determined; specific dust entrainment from the surface of dry beaches of ash-disposal areas under the most favorable conditions was determined; mathematical modeling of the spread of atmospheric air pollution of Dnipro city by suspended particles was carried out using UPCAP "ECO Center"program; a comparative assessment of dust entrainment reduction due to the gradual processing of the deposited fly ash was carried out. Findings. Almost 100% of the total mass of ash consists of particles smaller than 80 μm, the content of particles smaller than 10 and 2.5 μm is 27.7 and 8.2%, respectively. The main chemical compounds contained in ash are silicon dioxide, aluminum oxide, iron (III) oxide and carbon. The gross entrainment of substances in the form of suspended fine-grained solid particles from the surface of the dry beaches of the Prydniprovska TPP ash-disposal facilities is 18,654 tons per year. The area of atmospheric air pollution of Dnipro city by suspended particles is about 850 km2 and covers Samarskyi, Sobornyi, partly Industrialnyi and Shevchenkivskyi Districts. As a result of the implementation of a waste-free technology for the processing of fly ash with the utilization of the iron-containing fraction, the area of pollution can be reduced by 13.5 times up to 63 km2, the contamination zone in this case will cover underpopulated part of Samarskyi District of the city of Dnipro. Scientific novelty. A refined dependence of the particle size distribution of the mature Prydniprovsk TPP fly ash particles was determined for the further assessment of potential dust entrainment. For the first time, modeling of the distribution of fine-grained particles of fly ash of the Prydniprovsk TPP in the atmospheric air of the city of Dnipro was carried out, taking into account meteorological conditions, conditions of dust formation and particle size distribution. Practical implementation. The results of the research can contribute to reducing the level of atmospheric air pollution in the city of Dnipro. This will improve the quality of life of the local population and protect the natural environment from negative impacts. Research results can also be a basis for the development and implementation of technological solutions for the waste-free processing of stored fly ash with marketable products obtaining.

Measurements and Prediction of Ash Deposition in a Cyclone-Fired Boiler Operating under Variable Load Conditions

Measurements of ash deposition rates were made between the secondary superheater and reheater sections of a 450 MW cyclone-fired lignite boiler as the operational load varied from 33 to 100%. Significant reductions in deposition rates with a decrease in operational load were observed. To uncover the causative mechanisms behind these observations, operational data from the power plant were used to carry out computational fluid dynamic (CFD) simulations of the boiler. After ascertaining that the gas temperatures and velocities at various sections within the boiler were being represented adequately, decoupled simulations of the ash deposition process on the deposit probe were carried out using a finely resolved boundary layer mesh. Fly ash particle size distribution (PSD) and its concentration for the decoupled calculations were determined from stand-alone cyclone barrel simulations. The ash partitioning (mass %) between the fly ash and slag was found to be ~50:50, which was in line with previous field observations, and it did not vary significantly across different cyclone loads. The predicted PSD of the deposit ash was concentrated in the size range 10–30 microns, which was in agreement with cross-sectional images of the deposit obtained from the measurements. At lower loads, sharp variations in the deposition rates were predicted in the gas temperature range 950–1150 K. The particle kinetic energy—particle viscosity-based capture methodology utilized in this study in conjunction with appropriate ash compositions, ash viscosity models and gas temperature estimates can help estimate slagging propensities at different loads reasonably well in these systems.

Reduction of aerodynamic resistance of inertial-vacuum ash collector

THE RELEVANCE of the research topic is due to the existence of an environmental problem associated with harmful emissions into the atmosphere. The most highly efficient are electrostatic precipitators and fabric filters (~90-99.5% capture). Against the background of these devices, inertial one’s lag behind both in terms of their catching efficiency and the catching spectrum of the ash particle size distribution. The research carried out in the article is aimed at creating such an inertial apparatus that would have both minimal resistance and high efficiency. PURPOSE. Consider the possibility of reducing aerodynamic resistance by changing the design of the device, namely, by increasing the diameter of the inlet pipe in the inertial-vacuum ash collector. Consider a number of other ways to further reduce the aerodynamic drag of the apparatus. To identify the prospects and assessment of capital costs for the reconstruction of the ash collector. METHODS. When solving the problem, the method for calculating the dynamics of a dispersed flow in an inertial-vacuum ash collector, implemented by the MFD, was used. RESULTS. The article describes the relevance of the topic, considers the results of a numerical calculation. The calculation of the influence of boundary conditions, which include the flow rate at the inlet, thermal and hydraulic parameters of the flow of exhaust gases at the inlet to the ash catcher, in relation to the desired pressure drop across the apparatus, as well as the collection efficiency, was made. This article describes the process that results in a change in the hydraulic characteristics along the flow part of the IVAC. CONCLUSION. A change in the design of the apparatus leads to a decrease in the resistance of the IVAC, while these changes are extremely sensitive to the effect on the degree of purification. Calculations have shown that this method justifies itself in terms of reducing resistance. The pressure drops ranges from 279.8-1273 mm. water. pr. The convergence of the iterative calculation, taking into account the quality of the grid, provides flexibility, is achieved by fewer iterations, but the time spent on the calculation does not decrease.

Measurement of Fly Ash Particle Size Distribution Using Lensless Digital In-Line Holography

Abstract We propose the use of a lensless digital in-line holography setup for the measurement of particle size distribution (PSD) of fly ash obtained from wet electrostatic precipitators of different power plants. The fly ash samples were prepared by spreading the ash nonuniformly over a glass slide. A number of holograms corresponding to distinct regions of the glass slide were recorded and reconstructed. The particle sizes in each reconstructed image were estimated using a circular Hough transform–based edge detection algorithm. PSDs in the range of 10 to 90 μm were obtained. A numerical scheme to extend the measurement range below 10 μm is discussed. The performance of the proposed method is compared with the laser particle-size analyzer and conventional hydrometer. The experimental results indicate that the performance of the proposed method is similar to the hydrometer, with lower experimental and time complexity.

Characterization, risk assessment, and potential utilization of fly ash from PLTSa Merah Putih at Bantargebang, Bekasi, Indonesia

Municipal solid waste incineration (MSWI) has been adopted in Indonesia to reduce the volume and mass of municipal solid waste. However, as a by-product of waste combustion, fly ash generation cannot be avoided. It can cause an environmental problem if not managed properly. Hence, this study aims to investigate the characteristics of fly ash generated from Indonesia’s first waste-to-energy incineration pilot plant and its potential utilization. Fly ash was characterized using X-Ray fluorescence (XRF), BET surface area measurement, pore size distribution (PSD), scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS), and X-ray diffraction (XRD). The characterization results showed that calcium was predominant, around 28%, followed by titanium, silica, iron, and aluminum, with values of 7.10%, 5.70%, 4.40%, and 4.30%, respectively. These results demonstrated that MSW incineration fly ash was classified as a very active high-calcium fly ash. The surface structure of fly ash was flaky and complex, with some irregular material. The particle size distribution of fly ash shows that the diameters of most particles were nearly 12 μm. The specific surface area of fly ash was 3.06 m2/g, the total-pore volume was 0.01 cm3/g, and the average pore size was 11.82 nm. In addition, the environmental risk assessment was evaluated using the toxicity characteristic leaching procedure (TCLP). TCLP concentrations of heavy metals, including arsenic, barium, beryllium, cadmium, chromium hexavalent, copper, lead, mercury, nickel, selenium, and zinc, were lower than the regulatory level, indicating a low environmental risk. Therefore, it has great potential for utilization as a paving block mixture material.

Improving the properties of metakaolin/fly ash composite geopolymers with ultrafine fly ash ground by steam-jet mill

The particle size distribution and shape of fly ash (FA) are important factors affecting the properties of geopolymers. In this study, a steam-jet mill was used to optimize the fineness and properties of FA as a replacement for metakaolin (MK) in the production of geopolymers. The structural changes of FA by different grinding processes were observed by particle size analysis and SEM. As the treatment frequency increased, the particle size of FA decreased and the particles changed from spherical to irregular shape. XRD, FT-IR, SEM, EDS and LF-NMR were used to reveal the hydration mechanism of geopolymers with different treatment processes and FA substitution ratios and to investigate their mechanical properties. The results showed that the small particle size and irregular shape of the FA had high activity and excellent filling effect. After 28 days, the compressive strength of B-F30 (20% substitution MK and 30 Hz treatment) was 67.80 MPa, which was similar to that of A (0% substitution MK) at 66.36 MPa. FA crushed by the steam-jet mill allows optimization of the pore structure and further increases the compressive strength of geopolymers. This provides an effective way to prepare high-performance geopolymers using solid waste.

Analysis of the synergistic effect of particle size of compound mineral admixtures on the hydration properties and porosity of Portland cement under low-temperature conditions

The mechanical properties of cement matrix composites can be severely affected at low temperatures, limiting the environment in which they can be used. To ameliorate this problem, the addition of silica fume and fly ash to the matrix is an effective method. This study used silica fume and flew ash as composite admixtures mixed with Portland cement to characterize the heat of hydration, mechanical properties, and microstructure of the composite cementitious materials. The test results show that the particle size distribution of fly ash and silica fume can influence the hydration reaction rate and the whole hydration process. By adjusting the particle size of the admixtures, the structural loosening and strength attenuation of the concrete caused by low temperatures can be improved. At low temperatures, when cement hydration is low, the coarser the particle size, the better the gradation between silica fume and fly ash and the better the filling of the pores. In addition, the specific surface area of silica fume was fixed at 19.1m 2 /g, and the correlation between fly ash particle size intervals in mineral admixtures was strongest in (30~40μm), (40~50μm) on the total porosity. Silica fume in the (>0.4μm) and (0.25~0.4μm) particle size intervals had the strongest correlation with porosity. Finally, a prediction model between the particle size interval of the mineral admixture and the total porosity of the concrete under standard and low temperature curing conditions was established. • The admixture effectively fills micro-pores • Methods for improving the strength of cementitious materials at low temperatures • The particle size distribution affects the rate of hydration and the hydration process • The hydration rate can be increased by improving the particle size of the admixture.

Impact of PM10 Particles on the Measurement Error of SO2 Electrochemical Gas Sensor

To address the problems of poor measurement accuracy and long service life of SO2 electrochemical gas sensors when used in thermal power plant areas, fly ash emitted from a thermal power plant in China was used as the research object. Based on the analysis of the morphological characteristics of fly ash particles, theoretical calculations were used to obtain the settling speed of fly ash particles and the amount of fly ash deposited at different times, and then the impact of fly ash on the measurement error of a SO2 electrochemical gas sensor was investigated by experimental tests. The research results show that the particle size distribution of fly ash is 2–11 μm, the average settling speed of fly ash particles is 1.34 × 10−3 m/s, and the deposition amount of fly ash on the surface of the sensor inlet film is 0.95 mg per day. The deposition time of fly ash affects the sensor measurement error, and the longer the deposition time, the larger the sensor measurement error, which is due to the reduction of gas diffusion area S and diffusion coefficient K in the sensor caused by fly ash deposition. Fly ash deposition has a greater impact on the sensor when measuring low concentration gases. The higher the gas concentration, the lower the measurement error, because the higher the gas concentration, the faster the gas reaches the working electrode area and the higher the effective SO2 concentration detected in the limited response time. When using SO2 electrochemical sensors in environments with high concentrations of fly ash or dust, it is recommended to install dust-proof devices (such as air-permeable filter membranes with a pore size of less than 4 μm) and regularly clean the deposited fly ash, which can improve the accuracy of the sensor measurement and extend the service life.

Rare earth elements and other critical elements in the magnetic fraction of fly ash from several Polish power plants

Fly ash is a promising alternative source of many critical raw materials, including rare earth elements. According to the EU report, the demand for these metals is set to grow due to the economic growth of the developing countries, along with the development of new innovative technologies. A geochemical analysis showed that the overall content of critical and excessive elements in fly ash from several Polish power plants was higher than in the magnetic fraction. However, the outlook coefficient values for magnetic concentrates were higher than for ashes. Ashes and the magnetic fraction from brown coals seem to be the most promising source of REY recovery. The separation of fine-size grades from the analyzed ashes does not have a significant impact on REY concentration in the obtained products. A microanalysis showed that iron spinels were enriched in Co, Cu, Ni, Mn, Mo, and Zn. The concentration of these metals in magnetic concentrates insignificantly exceeded the world average value of fly ash. The sample with the highest heavy metal enrichment factor also had the highest Fe enrichment factor. The phase composition of the magnetic fraction was dominated by: magnetite, hematite, magnesioferrite, and other iron spinels with Mn and Al substitutions. The chemical composition of ferrospheres was determined using energy dispersive spectroscopy (EDS) together with the SEM technique, and was then linked to their morphology. It was concluded that the impact on the enrichment efficiency and thus the composition of the magnetic fraction had: the diversity of morphological structures of iron spinels, the presence of AlSi glass interlayers, the presence of substitutions in the magnetite crystal structure as well as the ash particle size distribution.

Numerical Analysis on Reduction of Ultrafine Particulate Matter by a Kaolin Additive during Pulverized Coal Combustion

Adding additives into the furnace is an effective way to reduce particulate matter (PM) formed during coal combustion. However, a numerical model that can predict the performance of additives on PM reduction is still lacking. In this work, a numerical framework, which contains the submodels for ash formation and ash–additive interactions, was developed to predict the ash particle size distribution with and without kaolin additives. The model fully considers the physical–chemical reaction process between the combustion gaseous products (alkali metal vapor) and the Si-/Al-based adsorbent particles. The simulation results are validated by experimental measurements of PM formed during the combustion of high-sodium Zhundong coal on a lab-scale furnace. Given the typical conditions of the lab-scale furnace, adding 3% (by weight) kaolin reduces the mass yield of PM0.3 by 33.35% but has no obvious influence on PM>1. On the basis of a time-scale analysis, we show that the chemical adsorption of the mineral precursors is the dominant mechanism for PM reduction. The influences of the kaolin particle size and dosage on PM reduction are evaluated. The PM reduction efficiency quickly increases and then enters into a plateau as the kaolin mass ratio increases. When a certain critical value is reached, a further increase of the addition ratio has a negligible effect on PM reduction. The critical kaolin mass ratio is 4.1% for 2.1 μm of kaolin and quadratically increases to 4.9% for 21.3 μm of kaolin. Increasing the kaolin size, in contrast, has a negative impact on PM reduction. On the basis of the simulation results, it can be concluded that there exists an optimal condition for PM1 reduction by kaolin addition. The numerical framework developed in the current work can help to quickly find the optimal addition strategy under different additive/coal properties, combustion temperatures, and atmospheres.

Development of a New Sensor Module for an Enhanced Fuel Flexible Operation of Biomass Boilers

The heterogeneity of biogenic fuels, and especially biogenic residues with regard to water and ash content, particle size and particle size distribution is challenging for biomass combustion, and limits fuel flexibility. Online fuel characterization as a part of process control could help to optimize combustion processes, increase fuel flexibility and reduce emissions. In this research article, a concept for a new sensor module is presented and first tests are displayed to show its feasibility. The concept is based on the principle of hot air convective drying. The idea is to pass warm air with 90 °C through a bulk of fuel like wood chips and measure different characteristics such as moisture, temperatures and pressure drop over the bulk material as a function over time. These functions are the basis to draw conclusions and estimate relevant fuel properties. To achieve this goal, a test rig with a volume of 0.038 m3 was set up in the laboratory and a series of tests was performed with different fuels (wood chips, saw dust, wood pellets, residues from forestry, corn cobs and biochar). Further tests were carried out with conditioned fuels with defined water and fines contents. The experiments show that characteristic functions arise over time. The central task for the future will be to assign these functions to specific fuel characteristics. Based on the data, the concept for a software for an automated, data-based fuel detection system was designed.

Modelling Particle Size Distribution of Residual Fly Ash from Pulverized Biomass Combustion

The present work aims to develop a simple model for describing the particle size distribution (PSD) of residual fly ash from pulverized biomass combustion. The residual ash formation was modelled considering the mechanism of fragmentation and coalescence. The influences of particle shape and stochastic fragmentation on model description of the PSD of the fly ash were investigated. The results showed that biomass particle shape has a great influence on the model prediction, and a larger fragmentation number is required for cylindrical particles than that for spherical particles to get the same PSD of fly ash, and the fragment number of the particles increases with the shape factor increasing. For pulverized biomass with a wide size distribution, the model predicted ash PSD considering the stochastic fragmentation is very similar to that assuming uniform fragmentation. It implies that the simple model assuming uniform fragmentation is applicable for predicting fly ash size distribution in practical processes where biomass particles have a wide range of sizes. For the fuel with a narrower initial PSD, the stochastic fragmentation model generally predicts a coarser PSD of the residual ash than assuming uniform fragmentation. It means the stochastic fragmentation is of great influence to be considered for accurate description of ash formation from the fuel with a narrow PSD.

Influence of Particle Morphology of Ground Fly Ash on the Fluidity and Strength of Cement Paste.

The grinding process has become widely used to improve the fineness and performance of fly ash. However, most studies focus on the particle size distribution of ground fly ash, while the particle morphology is also an important factor to affect the performance of cement paste. This article aims at three different kinds of ground fly ash from the ball mill and vertical mill, and the particle morphology is observed by scanning electron microscopy (SEM) to calculate the spherical destruction (the ratio of spherical particles broken into irregular particles in the grinding process of fly ash), which provides a quantification of the morphology change in the grinding process. The fluidity of cement paste and the strength of cement mortar are tested to study the relation of spherical destruction and fluidity and strength. The results show that the spherical destruction of ground fly ash in a ball mill is more than 80% and that in a vertical mill with a separation system is only 11.9%. Spherical destruction shows a significant relation with the fluidity. To different addition of ground fly ash, the fluidity of cement paste decreases with the increase of spherical destruction. To the strength of cement paste, particle size distribution and spherical destruction are both the key factors. Therefore, spherical destruction is an important measurement index to evaluate the grinding effect of the fly ash mill.

Effect of Fly Ash with Different Particle Size Distributions on the Properties and Microstructure of Concrete

Fly ash has become an important component of concrete as a supplementary cementitious material. Fly ash, as an admixture in concrete, has a great impact on the improvement of concrete properties and utilization of resources. In this work, fly ashes with different particle size distributions (S. Tsivilis, Andersen, normal and F distributions) were selected to prepare concrete. The relationships among the particle size distribution of the fly ash, compressive strength, hydration, pore structure and microstructure of the concrete were studied. The results showed that the compressive strength of the concrete increased at 28 d with fly ashes with the S. Tsivilis and F distributions. Moreover, the porosity of the concrete at 28 d was reduced, and the pore structure of the concrete was improved. The early compressive strength of the concrete increased with the fly ash with a normal distribution. The second hydration heat release rate of the concrete with fly ashes with a normal distribution and an F distribution was obviously faster. In addition to the Andersen distribution, other distributions of fly ash had obvious improvement effects on the pore structure of the concretes. High-performance concrete can be made from fly ash with different particle sizes, which avoids the need for ultrafine grinding with a high energy consumption and high-cost chemical excitation processes.

Characterization and utilization of coal fly ash: a review

Fly ash is a by-product, obtained mainly from thermal power plants, composed of silicon dioxide (SiO2) and aluminum oxide (Al2O3). Other oxides present in fly ash include iron (III) oxide (Fe2O3), calcium oxide (CaO), magnesium oxide (MgO) and so on. It may also contain some trace elements such as arsenic (As), zinc (Zn), lead (Pb), selenium (Se), gallium (Ga) and germanium (Ge) and some lesser amount of rare-earth elements. The particle size of fly ash normally ranges from 0.01 to 200 μm. Such variability in the particle size distribution of fly ash could influence the modification of fly ash into many useful products such as zeolites, geopolymers and other composite materials. The physical, chemical and mineralogical characteristics of fly ash combined with its easy availability make this an attractive raw material for various applications. In order to explore the potential use of fly ash, it is essential to look deeply into its characteristic properties. This review meticulously studies the characterization of fly ash by different modern techniques, including X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, thermogravimetric test, energy-dispersive X-ray spectroscopy, differential scanning calorimetry, secondary ion mass spectroscopy and Raman spectroscopy and attempts to correlate the same with its potential applications.

Gypsum-Cement Composites Based on Volcanic Ash

The studies’ results to determine the gypsum, ash and Portland cement components proportions, which would ensure a decrease in the specific binder consumption, as well as the ash grain composition’s effect on the properties of the gypsum cement pozzolan composite, are presented. It was revealed that the use of volcanic ash together with Portland cement in gypsum concrete composites allows reducing gypsum consumption by up to 50% without a significant decrease in strength characteristics. At the same time, the developed gypsum concrete composites have increased water resistance. The influence of the ash particle size distribution on the strength properties of the composite is ambiguous; in the compositions with a high ash content it is advisable to use larger fractions, and with a content of less than 50% ash in the composite, - the small fractions. To study the parameters’ effect of the dispersed reinforcement with basalt fibers on the properties of a gypsum-cement composite, an experiment with such a second-order composite rotatable plan as regular hexagon was conducted. It was found that the maximum values ​​of optimization parameters are observed in the central area of ​​the plan with and . The compressive strength of a fiber gypsum cement pozzolan composite increases by 1.15-1.18 times, when bending, by 1.56-1.72 times with respect to the strength of the initial matrix.

Enhancement on mechanical and durability performances of binary cementitious systems by optimizing particle size distribution of fly ash

Fly ash is a well-known supplementary cementitious material that is the by-product of coal-fired thermal power plants. The contribution of fly ash to the enhancement of the mechanical and durability properties of cementitious materials has been documented in concrete technology for many years. In this study, to allow superior mechanical and durability properties, fly ash-based mixtures have been produced after optimization of particle size distribution (PSD) of Class F and Class C fly ash according to the formula of Fuller–Thompson. Different distribution modulus values ranging from 0.3 to 0.6 were used to achieve ideal PSD in accordance with the Fuller–Thompson equation. 30% of F- and C-class fly ash by weight of cement were used to replace with cement in cementitious composites by optimizing PSD with help of air jet sieve. The recommended optimization technique improved the 7-, 28- and 90-day compressive and flexural strength results of mortars. Compressive and flexural strength tests and rapid chloride permeability test of cement-based systems incorporating fly ash up to 15% replacement ratio with optimized PSD at 90-days exhibited better results than those of plain samples owing to the filler effect.

Mineral Distribution in Pulverized Blended Zhundong Coal and Its Influence on Ash Deposition Propensity in a Real Modern Boiler Situation.

This study aims to explore the mechanism under which ash deposition propensity is improved by coal blending in a real modern boiler situation. In this paper, Zhundong coal (ZD), from northwestern China, known to have a heavy ash deposition problem in boilers, was blended with Jincheng anthracite (JC), which has a high ash fusion temperature (AFT). The density composition of the coal blend, which reflects the mineral distribution in pulverized coals, was found to change during the intergrinding process. The higher rank coal JC was found to be more concentrated in its lower and highest density fractions. The variances in the chemical composition among density fractions in the pulverized coal blend were found greatly narrowed as compared with the parent coals. AFT results indicate that the ash melting behavior in the coal blend (ZD/JC = 50:50) varies with density, which is confirmed by corresponding slag contents calculated with FactSage 7.1. Particle size distributions of the density fractions in ZD, JC, and the coal blend were determined with a laser particle analyzer. The size distribution of ash particles in each density fraction was estimated according to the char morphology, which is deduced from the ash content and coal particle size distribution. Minerals in the lowest density fractions will form ash with a particle size of around 2 μm. Included minerals in the medium density fractions will form ash particles with size related to its ash content, and excluded minerals will undergo slight fragmentation and have a ash particle size similar to the corresponding coal particles. A comprehensive comparison between ash volume, ash particle size, and softening temperature indicates that ash deposition propensity of the coal blend is improved not only because of an apparent increase in AFT but also because of an apparent decrease in the total volume of ash particles possibly arriving on the deposition surface.

Insight of particulate arsenic removal from coal-fired power plants

Arsenic is easily volatilized as vapors during coal combustion and predominantly transferred into particulate forms. The removal of particulate arsenic together with fine fly ash particles is essential to control arsenic emission during coal combustion. In this study, fly ashes and different size fraction samples (PM2.5, PM10, and PM20) were collected or prepared from four Chinese coal-fired power plants, with objectives of studying the arsenic distribution and speciation in fly ash, and understanding the retention relationship between the removal of ash particles and particulate arsenic. The results demonstrated that the concentration of arsenic of the first two ESP (electrostatic precipitator) hoppers was at similar level, then followed by a substantial increase in the rear hoppers. And the particle size distribution of fine fly ash particles from various ESP systems presented essentially similar trend. Furthermore, particulate arsenic was mainly present as arsenates probably through the interactions between arsenic vapors and accessory Ca/Fe/Al-minerals. Arsenic associated with calcium compounds tended to be enriched in coarse particles, while arsenic bound with Fe/Al-compounds was enriched in fine particles. Meanwhile, arsenic associated with calcium sulfate compounds was easier to be captured by ESP compared to calcium silicate-bound arsenic. The interactions between arsenic vapors and various accessory minerals not only affected the size distribution characteristics of particulate arsenic, but also had a great effect on its removal efficiency of ESP. Specifically, based on the ash resistivity calculation, arsenic-bearing fine particles with certain amount of Fe had suitable conductivity and favored the capture of particulate arsenic by ESP.