Coal Ash Samples Research Articles

Crystallization of Coal Ash Slags at High Temperatures and Effects on the Viscosity

The principle aim of this paper is to understand the crystallization of coal ash slags and the effects on the viscosity by means of high temperature viscosity measurements, in combination with FactSage modeling, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Four coal ashes with the fusion temperatures between 1130 and 1470 °C applied in entrained flow gasifiers in China were prepared for this study. The thermodynamic modeling was carried out using FactSage 6.2 software to predict the composition of homogeneous liquid slag systems as well as heterogeneous slag systems. It can be concluded that the viscosity of coal ash samples is closely related to the phases at high temperatures. The viscosity increases significantly until the mass percentage of the solid phases reaches a certain value (15.15–33.82%). For the coal ash samples enriched in Al2O3 and SiO2 with high AFT, mullite is the first solid phase forming in the liquid slag above 1600 °C, followed by quartz, anorthite, and ferro-cordi...

Beneficiation of coal pond ash by physical separation techniques

In this study, investigations to develop a beneficiation process for separating coal pond ash into various products were undertaken. To this end, coal pond ash samples with different particle size ranges were tested in terms of their washability characteristics in a float-and-sink analysis. It was found that coal pond ash was heterogeneous in nature consisting of particles that varied in terms of their size and composition. However, it can be made more homogenous using a gravity separation method. Therefore, the possibility of separating coal pond ash was tested on standard equipment typically used for gravity concentration. To increase the separation efficiency, coal ash was separated according to the size of the particles and each size fraction was tested using equipment appropriate for the corresponding sizes. A hindered-settling column and a shaking table were tested for their ability to treat the 1.19 × 0.074 mm size fraction, and a Falcon concentrator was evaluated for its ability to treat the -0.074 mm size fraction. The results showed that various marketable products, such as lightweight aggregate, sand and high-carbon fuel, can be recovered from coal pond ash using simple physical separation techniques.

Elemental analysis of coal and coal ASH by PIXE technique

Coal and coal ash samples were characterized by particle induced X-ray emission spectroscopic technique. Sixteen elements, namely K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, As, Rb, Sr, Y and Pb were quantified in this study. Elements like K, Ca, Ti and Fe were present as major elements, whereas, other elements like V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Rb, Sr and Pb were present in trace level. The enrichment ratio of different ash samples with respect to coal were also estimated and discussed.

Determination of uranium concentrations and its activity ratios in coal and fly ash from Philippine coal-fired thermal power plants using ICP-MS and TIMS

Abstract The specific activity of 238U as a technologically enhanced naturally occurring radioactive material (TENORM) in feed coal, bottom and fly ash samples from four major coal-fired thermal power plants in the Philippines have been measured using high-resolution gamma-ray spectroscopy system equipped with a high-purity germanium (HPGe) detector. The uranium concentration has been determined from same samples using inductively coupled plasma mass spectrometry (ICP-MS). There was a good correlation between the measured uranium using both methods and has been estimated to be 0.98. Uranium from coal, bottom and fly ash samples were chemically separated and activity ratio (234U/238U) and 235U/238U ratio was measured using a thermal ionization mass spectrometer (TIMS). The highest concentration of uranium was found in fly ash and lowest was for feed coal. Uranium isotopic composition plays an important role in studying its biogeochemical behavior and is a good tracer on the sources of uranium in the environment.

Speciation of Trace and Major Elements from Coal Combustion Products of Serbian Power Plants (I)—“Kostolac A” Power Plant

In order to examine association patterns and pollution potential of trace and major elements from coal ash, six composite samples of fresh, filter fly, and aged dump coal ash from “Kostolac A” power plant located 100 km from Belgrade, the Serbian capital, were subjected to the sequential extraction procedure. Five extractants were applied (in the following order): distilled water, 1 M ammonium acetate, 0.2 M ammonium oxalate/0.2 M oxalic acid, an acidic solution of H2O2, and 6 M HCl. Obtained concentrations were statistically analyzed and associations of trace and major elements were established.

Effect of lime addition on slag fluidity of coal ash

The ash fusibility temperature (AFT) and slag fluidity of three different coal ash samples through addition of CaO with different amounts were studied. Especially the variation of temperature at critical viscosity was examined at different viscosities. The results show that the fusibility temperatures of coal ashes decrease and then increase with increasing addition amount of CaO, which is consistent with the change of liquids temperature with CaO content calculated by FACTsage. Slag viscosity also decreases with increasing amount of CaO addition above the temperature of critical viscosity ( T cv). The temperature of critical viscosity firstly decreases with increasing addition of CaO, and then reaches a minimum value when the content of CaO is around 15%. FCATsage was employed to calculate the liquid composition at the temperature of critical viscosity. It indicates that high content of FeO of liquid leads to the low temperature of critical viscosity.

Radioactivity of coals and ashes from Catalagzi coal-fired power plant in Turkey

The Çatalağzı coal-fired power plant (CFPP) is the Turkish CFPP that uses the hard coals produced in Zonguldak, located in the West Black Sea region of the country. Gamma-ray spectrometry was used to determine (226)Ra, (232)Th and (40)K contents in pulverised coal, bottom ash and fly ash samples. The natural radionuclide concentrations in pulverised coal ranged from 29 to 61 Bq kg(-1) for (226)Ra, from 32 to 55 Bq kg(-1) for (232)Th and from 229 to 414 Bq kg(-1) for (40)K. The fly ash fraction gave concentrations ranging from 80 to 98 Bq kg(-1) for (226)Ra, from 64 to 85 Bq kg(-1) for Th and from 754 to 992 Bq kg(-1) for (40)K, respectively. The enrichment factors from coal to fly ashes are 1.7, 2.24 and 2.6 for (232)Th, (226)Ra and (40)K, respectively. Therefore, it is advisable to monitor the environmental impact of the power plant.

226Ra, 232Th and 40K radionuclides enhancement rate and dose assessment for residues of lignite-fired thermal power plants in Turkey

A total of 77 coal, slag and fly ash samples collected from six thermal power plants were measured by gamma-ray spectrometry. The average (226)Ra activity concentrations in coal, slag and fly ash were measured as 199.8±16.7, 380.3±21.8 and 431.5±29.0 Bq kg(-1), respectively. The average (232)Th activity concentrations in coal, slag and fly ash were measured as 32.0±2.4, 74.0±9.0 and 87.3±9.8 Bq kg(-1), respectively. The average (40)K activity concentrations in coal, slag and fly ash were found to be 152.8±12.1, 401.3±25.0 and 439.0±30.2 Bq kg(-1), respectively. The radium equivalent activities of samples varied from 147.6±8.5 to 1077.4±53.3 Bq kg(-1). The gamma and alpha index of one thermal power plant's fly ash were calculated to be 3.5 and 5 times higher than that of the reference values. The gamma absorbed dose rates were found to be higher than that of the average Earth's crust. The annual effective dose of residues measured in four thermal power plants were calculated higher than that of the permitted dose rate for public, i.e. 1 mSv y(-1).

Application of Three-phase Foam Technology for Spontaneous Combustion Prevention in Longdong Coal Mine

According to the status of 7312-2 light-face in Longdong Coal Mine, the technology of three-phase foam and its application were studied. The three-phase foam and its extinction theory are particularly introduced in this paper. The primary form of coal ash and yellow mud samples were received by analysis with instrument Laser Partical Sizer, and the coal ash was determined as the experimental material. With experiments of the proportion of ash and water and performance of foaming agent, the optimum proportion is 1:4, and the performance of foaming agent is best when the critical micelle concentration is 0.7%. Continuously, through matching experiments with foaming agents, No.3 and No.6 foaming agents were selected finally, and matching proportion was 1:1. Based on the practice of 7312-2 light-face, the process flow of three-phase foam and its primary technical parameters were designed. The monitoring results of the concentration of CO and temperature show that the effect of the three-phase foam for extinction is outstanding.

Natural radionuclides from coal fired thermal power plants – estimation of atmospheric release and inhalation risk

Coal, bottom ash and fly ash samples were collected from three different coal-fired thermal power plants in India and subjected to gamma spectrometry analysis for natural radioactivity contents. The results of present study show that fly ash and bottom ash contains two to five times more natural radionuclides than feed coal. None of the fly-ash and bottom ash samples had radium equivalent activities and external hazard index values more than 370Bq kg -1 and unity respectively. However the absorbed dose rate at 1m above the ash pond was 79.19nGyh -1 (average of 3 plants) higher than the global average value of 55nGyh -1 . The corresponding annual external effective dose is estimated to be 0.68mSvy -1 , which is also more than that (0.46mSvy -1 ) in areas of natural background radiation. The 5th percentile, 95th percentile and mean values for total inhalation risk arising from radionuclides (Ra 226 ,T h 228 ,P b 210 and Nat-U) were found to be 3.83 × 10 −9 , 6.50 × 10 −8 and 2.08 × 10 −8 respectively. In India, the rapid increase in thermal generation capacity and at the same time a deterioration of the quality of coal with increased ash content resulted in huge quantity of fly ash and bottom ash of varying properties. The coal contains naturally occurring primordial radionuclide thus the use of coal as a heat source for electric power generation will result in the emission of a variety of natural radioactive elements into the environment. The trace elements in coal that are naturally radioactive are uranium (U), thorium (Th), and their decay products, including radium (Ra) and radon (Rn). Thus coal fired power plant is a major contributor towards the Technologically Enhanced Natural Radiation (TENR) as it results in generation of huge amounts of fly ash and bottom ash containing natural radionuclides. Indian coal used in power plants generally has high ash content and is of lower quality (Mathur et. al., 2003). Presently about 110 million tonnes of coal-ash is generated in India from more than 70 thermal power plants (Sarkar et. al., 2005). By the year 2012 this is predicted to increase to 170 million tonnes per annum (Rajamane, 2003). Thus, fly ash and bottom ash are significant sources of exposure to the naturally occurring radionuclides that affect especially the population in the vicinity of industrial areas. In India, the major portion of fly ash produced goes for disposal in ash ponds and landfills; and a small fraction of it is utilized in construction material (taking advantage of its cementitious or binding characteristic) or as soil amendment (mainly because of its high alkalinity). The openly dumped fly ash poses radiation hazard due to the leachability of radionuclides into the ground water stream ultimately contaminating the drinking waters. The disposal and even the utilization in construction work also leads to exposure to radiation doses to the personals in vicinity. Therefore it is necessary to characterize and quantify the natural radioactivity content in fly ash and bottom ash for subsequent evaluation of the associated environmental and biological risks. The feed coal used in power plants contains various elements, minerals and organic constituents. Upon burn up the elements tend to get enriched in the ashes. Radionuclides which are normally found in the coals get enriched into the ashes after burn up. The concentration of most radioactive elements in

Yielding Conditions for Fiber Materials from Coal Ash Slag

In this study, we focused on optimizing a part of the furnace and operating conditions of the fiber yielding system from fused coal ash to expand ash utilization for building materials; promotion of ash use is desirable because slag inhibits the elution of toxic heavy metals, such as Hg, Pb and As, to undetectable levels, making the fibers safe to use. In particular, the fiber materials from coal ash slag are expected to be used as thermal insulators and acoustic materials. We designed a coal ash fusing furnace which is suitable for the fiber manufacturing and recovery process. To manufacture fiber materials which are both safe and homogeneous, the slag viscosity had to be stabilized to approximately 1 Pa·s at the slag-tapping hole of the furnace. However, the slag temperature at 1 Pa·s was too high to measure. Thus, we estimated the slag temperature at 1 Pa·s using Riboud’s and Urbain’s expressions. To control the slag viscosity and temperature, CaCO3 addition to coal ash was effective. When the basicity (CaO/SiO2(wt%/wt%)) of the coal ash sample was 0.98, the fused slag temperature at 1 Pa·s was estimated as 1563 °C. Then, we verified that to yield 1 Pa·s fusing slag from 120 kg/h coal ash, the necessary fuel quantity of the coal ash fusing furnace was 40 kg/h coal and 4 m3N/h LPG.

Natural radionuclide emission from coal-fired power plants in the southwestern of Turkey and the population exposure to external radiation in their vicinity

To evaluate the effect of radionuclide emission on the environment from Yataǧan, Yeniköy and Kemerköy coal-fired power plants which are located in southwestern Anatolia of Turkey, the concentrations of natural radionuclides such as 226Ra, 232Th and 40K in coal, bottom ash and fly ash samples, have been measured, as well as the concentration of the same radionuclides in surface soils. The dose rate arises from the total radioactivity content of soil that the people living by the power plants are exposed to be assessed additionally. The average activity concentrations of 226Ra for Yataǧan CPP is 80 ± 22 Bq kg–1 ranging from 56 to 131 Bq kg–1, for Yeniköy CPP is 138 ± 20 Bq kg–1 ranging from 115 to 189 Bq kg–1, for Kemerköy CPP is 238 ± 80 Bq kg–1 ranging from 134 to 356 Bq kg–1 in coal; average activity concentrations of 226Ra in fly ash and in bottom ash for above-mentioned power plants are 334 ± 60 Bq kg–1 ranging from 291 to 481 Bq kg–1, 461 ± 33 Bq kg–1 ranging from 398 to 511 Bq kg–1, 815 ± 254 Bq kg–1 ranging from 316 to 1260 Bq kg–1, 276 ± 51 Bq kg–1 ranging from 222 to 349 Bq kg–1, 285 ± 69 Bq kg–1 ranging from 213 to 409 Bq kg–1, 743 ± 234 Bq kg–1 ranging from 366 to 1098 Bq kg–1, respectively. The radionuclides activity concentrations of surface soil in the vicinity of coal-fired power plants are 32 ± 9 Bq kg–1 (18–53 Bq kg–1) for 226Ra, 37 ± 16 Bq kg–1 (17–89 Bq kg–1) for 232Th, 455 ± 165 Bq kg–1 (203–794 Bq kg–1) for 40K relevant to Yataǧan CPP; 42 ± 30 Bq kg–1 (9–168 Bq kg–1) for 226Ra, 32 ± 14 Bq kg–1 (6–74 Bq kg–1) for 232Th, 365 ± 151 Bq kg–1 (117–937 Bq kg–1) for 40K relevant to Yeniköy and Kemerköy CPP. As a result, average dose rates in the vicinity of coal-fired power plants have been calculated to be 56 ± 16 nGy h–1 ranging from 30 to 100 nGy h–1 for Yataǧan CPP, 54 ± 22 nGy h–1 ranging from 15 to 126 nGy h–1 for Yeniköy and Kemerköy CPP. To sum up, the natural radionuclide activity concentrations of burnt coal and ashes thrown out from these three power plants are quite high relative to the world average UNSCEAR[ 1 ] data. In addition, the average 226Ra, 232Th and 40K activity concentration values of surface soil samples and the calculated gamma dose rates in the vicinity of power plants were located within the worldwide intervals reported by UNSCEAR,[ 30 ] with some local differences.

Effect of Coal Ash Composition on Ash Fusion Temperatures†

The ash fusion temperatures (AFTs) of coal mineral matter at high temperature are important parameters for all gasifiers. Experiments have been conducted in which mixtures of selected coal ashes and SiO2, Al2O3, CaO, Fe2O3, and MgO were subjected to the standard test for ash fusibility. The computer software package FactSage has been used to calculate the liquidus temperatures of coal ash samples and the proportions of the various phases present as a function of temperature. The results show that the AFTs of coal ash samples first decrease with increasing CaO, Fe2O3, and MgO contents, then reach a minimum value, before increasing once more. However, for the effect of S/A ratio, its AFTs are always increased with increasing S/A ratios. The measured AFTs all show variations with mixture composition that correlated closely with liquidus temperatures for the appropriate pseudoternary phase diagrams. The liquidus and AFTs generally showed parallel compositional trends but are displaced from each other because ...

Accurate determination of naturally occurring radionuclides in Philippine coal-fired thermal power plants using inductively coupled plasma mass spectrometry and γ-spectroscopy

Abstract There is an increased interest in measuring naturally occurring radioactive materials (NORM) like coal, fly ash considering health hazards caused by naturally occurring radionuclides. This paper presents activity concentration (AC) of 226 Ra, 228 Ra, 232 Th, 238 U and 40 K in feed coal, bottom and fly ash samples from Philippines coal-fired thermal power plants using inductively coupled plasma mass spectrometry (ICP-MS) and high-purity germanium gamma spectroscopy (HPGe γ-spectroscopy). Coal, bottom and fly ash samples were digested using a microwave oven with a mixture of HNO 3 , HClO 4 and HF. Uranium ( 238 U) and thorium ( 232 Th) ACs were also analyzed from samples using ICP-MS. A good correlation was found for the measurement of U and Th using both techniques ( R 2 = 0.97 and 0.94 respectively). ICP-MS measurements showed the highest AC of 232 Th and 238 U in fly ash and lowest for feed coal samples. With HPGe γ-spectroscopy measurements, highest AC (in Bq kg − 1 ) of 226 Ra, 228 Ra, 228 Th and 40 K, were noticed in fly ash followed by bottom ash and feed coal. ICP-MS method is rapid for the measurement of uranium and thorium in comparison to γ-spectroscopy as secular equilibrium is not required. Activity concentrations of bottom and fly ash samples were found to be within the reported values worldwide and below the International Atomic Energy Agency recommended values for regulatory control.

Chemical Composition and Some Trace Element Contents in Coals and Coal Ash from Tamnava-Zapadno Polje Coal Field, Serbia

The chemical compositions and trace element contents (Zn, Cu, Co, Cr, Ni, Pb, Cd, As, B, Hg, Sr, Se, Be, Ba, Mn, Th, V, U) in coal and coal ash samples from Tamnava-Zapadno polje coal field in Serbia were studied. The coal from this field belongs to lignite. This high volatility coal has high moisture and low S contents, moderate ash yield, and high calorific value. The coal ash is abundant in alumosilicates. Many trace elements such as Ni > Cd > Cr > B > As > Cu > Co > Pb > V > Zn > Mn in the coal and Ni > Cr > As > B > Cu > Co = Pb > V > Zn > Mn in the coal ash are enriched in comparison with Clarke concentrations.

Arsenic concentration in porewater of an alkaline coal ash disposal site: Roles of siderite precipitation/dissolution and soil cover

The geochemical behavior of As in porewaters of an alkaline coal ash disposal site was investigated using multilevel samplers. The disposal site was in operation from 1983 until 1994 and was covered with 0.3–0.5 m thick soils in 2001 when this study was initiated. Sequential extraction analyses and batch leaching experiments were also performed using the coal ash samples collected from the disposal site. The results suggest the important roles of siderite (FeCO 3) precipitation/dissolution and soil cover, which have been ignored previously. Arsenic levels in the porewater were very low (average of 10 μg L −1) when the site was covered with soil due to coprecipitation with siderite. The soil cover enabled the creation of anoxic conditions, which raised the Fe concentration by the reductive dissolution of Fe-(hydr)oxides. Because of the high alkalinity generated from the alkaline coal ash, even a small increase in the Fe concentration (0.66 mg L −1 on average) could cause siderite precipitation. When the soil cover was removed, however, an oxidizing condition was created and triggered the precipitation of dissolved Fe as (hydr)oxides. As a result, the dissolution of previously precipitated As-rich siderite caused higher As concentration in the porewater (average of 345 μg L −1).

Prediction of Chinese Coal Ash Fusion Temperatures in Ar and H2 Atmospheres

The ash fusion temperatures (AFTs) of 21 typical Chinese coal ash samples and 60 synthetic ash samples were measured in Ar and H2 atmospheres. The computer software package FactSage was used to cal...

Utilization of zeolites synthesized from coal ash for methylene blue removal from water

The adsorption of methylene blue from aqueous solution was carried out using zeolites synthesized from coal ash as low-cost adsorbents. The coal ash sample was converted to zeolites by hydrothermal treatment using different synthesis parameters. The materials were characterized by physical-chemical analysis, XRD and SEM studies. The adsorption isotherms can be fitted by Freundlich model. The values of the adsorption capacity of adsorbents were similar for adsorbents. Kinetic studies indicate that the adsorption follows pseudo-second-order kinetic model.

Concentration of Major and Trace Elements in the Miocene Lignite from the Çanakkale-Çan Coalfield

This study focuses on major and trace element concentrations of three lignite samples, of which two are from the working lignite seam and one from a feed coal to Çan thermal power plant. The Çanakkale-Çan lignite deposit is currently being mined by open-cast mining methods despite its high sulfur content. The production lignites are mainly consumed by Çan fluidized-bed thermal power plant with 2 × 160 MW capacity and less domestic heating and industrial factories around Çan. Major oxide compositions of the coal ash samples imply that the more abundant oxides are SiO2 and Al2O3 and less CaO and Fe2O3. Trace element concentrations in the samples on whole-coal basis show that three samples analyzed were enriched in V, and also concentrations of B, Sc, Sn, Th, Tl, and U in one sample that exceed the range values of most world coals.

A new method for identifying the modes of particulate matter from pulverized coal combustion

Knowledge of the modality of the size distribution of particulate matter (PM) from pulverized coal combustion is of great significance from the viewpoint of exposure and risk assessment. Mass or number size distributions are usually used in modality analyses, but sometimes the central particle mode fails to be detected due to overlapping. This work provides a new method for identifying particle modes using mass fraction size distributions of the aluminum (Al). Five Chinese pulverized coals of different ranks were burnt in a laboratory drop tube furnace at 1673 K. The produced PM was size segregated by a low pressure impactor and subjected to elemental composition analysis by X-ray fluorescence (XRF). Particle mass size distributions, mass fraction size distributions of the Al and sulfur (S) were obtained for all the particle samples. The mass size distributions of four coal ash samples all show three distinct particle modes, with a central mode at approximately 2 µm, while the mass size distribution of the LPS coal ash sample only indicates two particle modes. However, the mass fraction size distributions of the Al for all ash samples, including the LPS coal ash sample, generally show three particle modes. The obscurity of the central mode in the mass size distribution of the LPS coal ash sample is expected to be a consequence of the merging of it into the coarse mode. The formation of the central mode is attributed to the more pronounced heterogeneous condensation or adsorption of vaporized species on fine residual ash particles, whose origins are still unclear at present. This is further confirmed by examination of the mass fraction size distributions of the S. These results show that mass fraction size distributions of the Al seem to be more effective in identifying particle modes and their size boundaries than particle mass size distributions.