Coal Combustion By-products Research Articles

Water Adsorption Isotherms on Fly Ash from Several Sources.

In this study, horizontal attenuated total reflection (HATR) Fourier-transform infrared (FT-IR) spectroscopy was combined with quartz crystal microbalance (QCM) gravimetry to investigate the adsorption isotherms of water on fly ash, a byproduct of coal combustion in power plants. Because of composition variability with the source region, water uptake was studied at room temperature as a function of relative humidity (RH) on fly ash from several regions: United States, India, The Netherlands, and Germany. The FT-IR spectra show water features growth as a function of RH, with water absorbing on the particle surface in both an ordered (ice-like) and a disordered (liquid-like) structure. The QCM data was modeled using the Brunauer, Emmett, and Teller (BET) adsorption isotherm model. The BET model was found to describe the data well over the entire range of RH, showing that water uptake on fly ash takes place mostly on the surface of the particle, even for poorly combusted samples. In addition, the source region and power-plant efficiency play important roles in the water uptake and ice nucleation (IN) ability of fly ash. The difference in the observed water uptake and IN behavior between the four samples and mullite (3Al2O3·2SiO2), the aluminosilicate main component of fly ash, is attributed to differences in composition and the density of OH binding sites on the surface of each sample. A discussion is presented on the RH required to reach monolayer coverage on each sample as well as a comparison between surface sites of fly ash samples and enthalpies of adsorption of water between the samples and mullite.

Prediction of Consolidation and Shear Behavior of Fly Ash–Soil Mixtures Using Mixture Theory

AbstractFly ash is the most generated coal combustion by-product (CCP) and causes the most substantial disposal issues. The current practice of landfilling these materials is costly and ultimately ...

Mineralogical, Microstructural and Thermal Characterization of Coal Fly Ash Produced from Kazakhstani Power Plants

Coal fly ash (CFA) is a waste by-product of coal combustion. Kazakhstan has vast coal deposits and is major consumer of coal and hence produces huge amounts of CFA annually. The government aims to recycle and effectively utilize this waste by-product. Thus, a detailed study of the physical and chemical properties of material is required as the data available in literature is either outdated or not applicable for recently produced CFA samples. The full mineralogical, microstructural and thermal characterization of three types of coal fly ash (CFA) produced in two large Kazakhstani power plants is reported in this work. The properties of CFAs were compared between samples as well as with published values.

Flue gas desulfurization gypsum as a chemical amendment to reduce the concentrations of phosphorus and suspended solids in liquid manure

PurposeAnimal liquid manure contains large amounts of phosphorus (P), which is susceptible to runoff losses when manure is surface-applied on farms as a soil amendment. Even very small quantities of P can have a large impact on waterways and lead to eutrophication. Previous studies have shown that flue gas desulfurization (FGD) gypsum, a coal combustion by-product, can reduce P losses from runoff in soils. Therefore, the authors hypothesize that FGD gypsum could reduce nutrients in liquid manure prior to field applications. The purpose of this paper is to evaluate the effect of FGD gypsum to reduce P and suspended solids (SS) concentrations in liquid manure, also determining its proper rate(s) and minimum time of reaction.Design/methodology/approachThe experimental design was completely randomized with three replicates. Each plot was constituted by a polyvinyl chloride (PVC) column (1 m height and 0.15 m diameter). Dairy liquid manure and FGD gypsum rates (0, 0.62, 1.25 and 2.5 mgl−1) were added to the PVC columns and manually shaken for two minutes. Sampling was performed at 0.35, 0.65 and 0.95 m depths after 0 (immediately after shaking), 4, 8, 16 and 24 hours. Amount of phosphorus was determined by a colorimetric method and solids concentration by mass difference.FindingsFGD gypsum reduced P concentrations in the liquid manure after four hours of reaction. The most effective rate was 0.62 mgl−1at a 0.35 m depth. FGD gypsum increased SS concentrations in depth in all treatments.Originality/valueThere are growing concerns regarding the fate of nutrients, especially phosphorus, from land application of animal waste. The results indicated that treating liquid manure in the settling tanks with FGD gypsum before field application can be particularly useful on farms where surface-manure is applied, reducing potential losses of P following manure applications, and consequently the eutrophication risk to waterways.

Plant uptake of major and trace elements from soils amended with a high-calcium dry flue gas desulfurization by-product

Coal combustion by-products (CCBs) are a potentially valuable source of essential plant nutrients, but CCBs also frequently contain trace elements. The objective of this greenhouse study was to evaluate the effects of soil and application rate of a high-calcium (Ca) dry flue gas desulfurization (DFGD) by-product on Bermudagrass (Cynodon dactylon L.) growth and plant tissue and soil composition. Surface horizons of two soils with contrasting texture were mixed with a high-Ca DFGD by-product at rates of 0, 2.5, 5, 10, and 15Mgha−1. Bermudagrass was allowed to grow in the soils for 119days. Concentrations of plant nutrients and selected trace elements were determined in soil and plant tissue. Plant dry matter and tissue concentrations of Ca, Mg, B, Se, Rb, and U increased as DFGD application rate increased. Concentrations of Mehlich-3-extractable soil P, Ca, Mg, S, Na, Fe, and B and strong-acid-extractable V and Hg increased with increasing application rate. Soil pH increased with application rate and electrical conductivity was only greater than that in the control at the 15Mgha−1 application rate after 119days. The DFGD by-product used in this study can be beneficially reused as a soil amendment provided soil pH and plant tissue Se concentrations are closely monitored.

Effects of Coal Fly Ash Particulate Matter on the Antimicrobial Activity of Airway Surface Liquid.

Background:Sustained exposure to ambient particulate matter (PM) is a global cause of mortality. Coal fly ash (CFA) is a byproduct of coal combustion and is a source of anthropogenic PM with worldwide health relevance. The airway epithelia are lined with fluid called airway surface liquid (ASL), which contains antimicrobial proteins and peptides (AMPs). Cationic AMPs bind negatively charged bacteria to exert their antimicrobial activity. PM arriving in the airways could potentially interact with AMPs in the ASL to affect their antimicrobial activity.Objectives:We hypothesized that PM can interact with ASL AMPs to impair their antimicrobial activity.Methods:We exposed pig and human airway explants, pig and human ASL, and the human cationic AMPs β-defensin-3, LL-37, and lysozyme to CFA or control. Thereafter, we assessed the antimicrobial activity of exposed airway samples using both bioluminescence and standard colony-forming unit assays. We investigated PM-AMP electrostatic interaction by attenuated total reflection Fourier-transform infrared spectroscopy and measuring the zeta potential. We also studied the adsorption of AMPs on PM.Results:We found increased bacterial survival in CFA-exposed airway explants, ASL, and AMPs. In addition, we report that PM with a negative surface charge can adsorb cationic AMPs and form negative particle–protein complexes.Conclusion:We propose that when CFA arrives at the airway, it rapidly adsorbs AMPs and creates negative complexes, thereby decreasing the functional amount of AMPs capable of killing pathogens. These results provide a novel translational insight into an early mechanism for how ambient PM increases the susceptibility of the airways to bacterial infection. https://doi.org/10.1289/EHP876

The investigation of fly ash based asphalt binders using atomic force microscope

Atomic Force Microscope (AFM) is a relatively new technique for investigation of construction materials. In this study AFM was used to investigate the interaction of asphalt binder with fly ash. Fly ash is a coal combustion byproduct of electric power utilities having pozzolanic properties and commonly used in Portland cement concrete. In this study, an investigation was made by using different types of fly ash with two types of asphalt binders such as PG 58-28 and PG 64-28. Asphalt microstructure is divided into four subgroups such as Saturates, Aromatics, Resins and Asphaltenes (SARA). These four phases can be distinguished by the atomic force microscope. The interaction of these phases affected by introducing fly-ash was investigated and correlation with rheological properties was observed.

Effects of ammonium nitrate encapsulated with coal combustion byproducts on nutrient accumulation by corn and rye

ABSTRACTAmmonium nitrate is a fertilizer and an explosive. Encapsulation of ammonium nitrate (NH4NO3) with coal combustion byproducts (fly ash or flue gas desulfurization gypsum) reduces the explosiveness of NH4NO3. A field study was conducted to determine the effects of encapsulated NH4NO3 on corn (Zea mays L.) and rye (Secale cereal L.) yield and accumulation of nitrogen (N), arsenic (As), cadmium (Cd), iron (Pb), copper (Cu), manganese (Mn), and zinc (Zn). Nitrogen rates were 56 and 112 kg ha−1. Yields and concentrations of N and metals in corn grain, ear-leaf, and stover and in rye shoots were not affected by N source. Increased N rate resulted in increased corn ear-leaf, grain, and stover N, ear-leaf Cu, Mn, and Zn, and rye shoot yield, Cu, and Zn. For both species, metal levels did not exceed normal ranges. Coal byproduct-encapsulated NH4NO3 is as effective as non-encapsulated NH4NO3 for corn or rye production, without increasing plant metal concentrations above normal levels.

STRENGTH AND PERMEABILITY CHARACTERISTICS OF ROAD BASE MATERIALS BLENDED WITH FLY ASH AND BOTTOM ASH

The Philippines has an extensive road network which handles most of its passenger andfreight movements. Large volumes of aggregate embankment materials of good quality are required toprimarily support these transport infrastructures, and this poses threat to the environment. Coal combustionby-products (CCPs) are seen to be its potential alternative mainly due to its vast production and disposalproblems in the country. Representative samples of class C fly ash and bottom ash were gathered togetherwith conventional road base materials. Fly ashes were substituted to act as fines; whereas, bottom ashsubstitutions were varied at different mixture ratios of 0%, 20%, 40%, 60%, 80%, and 100% of fineaggregates. Index properties (i.e. specific gravity, Atterberg limits, and maximum and minimum indexdensities), compaction characteristics, unsoaked and soaked California Bearing Ratios (CBR), and hydraulicconductivities were obtained for all the blends in order to produce empirical relationships with varyingbottom ash content. Results show that the optimum strength can be produced at a blend of 100% bottom ash.However, permeability tests show a considerable decline in hydraulic conductivity with the addition of coalashes to the typical aggregates. Thus, proper drainage must be carefully applied to these blendedembankment materials so as to avoid substantial ingress of water.

Nowoczesne palniki cyklonowe dla zwiększenia elastyczności kotłów pyłowych

In this paper, the concept, as well as a model pilot cyclone burner are presented and discussed in order to provide a solution for both combustion and gasification of solid fuels (e.g. pulverized coal). The burner design allows to operate it as a separate structure or a part of an existing pulverized-fuel boiler. In the latter case, the cyclone burner increases the flexibility and dynamics of the power generation system, as well as boiler thermal output. The burner also provides the conditions for the reduction of boiler technological minimum without the necessity to ignite boiler startup burners, and also enables the realization of treatment and processing (e.g. the vitrification) of coal combustion by-products. The proposed solution can also become an interesting technological option aimed at the retrofitting and modernization of old 200 MW PC-based power generation facilities within the Framework Program “Power 200+. Revitalization and restoration of power on the basis of 200 MW power units”.

Investigating Amorphous Composition Mix Design Performance and Properties of Fly Ash-Based Geopolymer

Identifying viable replacement for Ordinary Portland Cement (OPC) is part of the effort to limit CO2 emission during its production. Fly ash-based geopolymer composites have emerged as a sustainable and promising replacement product with proven comparable binding properties, coupled with superior characteristic in some area, when compared to OPC. However, fly ash being a by-product of coal combustion, remains unfavourable in industry application due to its deferring composition dependent on the type of coal feedstock, resulted in inconsistent mechanical and chemical properties produced. In order to overcome this shortcoming, a unified method to evaluate fly ash at the amorphous composition level is required. This study aims to tackle this challenge by establishing a framework to effectively identify relationship among the fly ash amorphous content and identifying an optimum proportion of alkaline activator in order to optimise its full potential in geopolymer concrete or mortar production. This is achieved by utilising XRF and Q-XRD analyses on geopolymer specimen’s amorphous compositions and evaluate their respective compressive strength through laboratory testing. A number of testing variants are carried out including curing regime, alkaline activator concentrations, presence of mechanical activation and deferring water content are investigated.

Geopolymerization of Coal Ash to Produce Cementless Binders

The main objective of this study was to evaluate geopolymer concrete made from coal combustion by-products, disposed of in landfills, as a potential substitute for the ordinary Portland cement (OPC), which is responsible for 5-8% of the total CO~2~ emissions in the world. In this study, a coal fly ash sample from the Carolinas was used in a chemical process known as geopolymerization to produce a \geopolymer binder. The developed geopolymer binder could competently substitute the OPC binder in regular concrete applications. An experimental design program was conducted to optimize parameters of the geopolymerization affecting the strength of the final cementless concrete product. Mortar and concrete samples were made to compare the strength of geopolymer with OPC concrete. The results showed that the compressive strength of geopolymer-based products were more than 6700 psi for mortars and 5750 psi for concrete samples, which could effectively compete with OPC concrete. This paper presents the results of the experiments and discusses the effectiveness of the produced cementless binder.

Development and testing of a model for simulating weathering and trace elements release from fixated scrubber sludge utilized in abandoned coal mine reclamation site

In this paper we present the first approximation to a fully coupled model for simulating chemical reactions between engineered coal combustion byproducts (specifically fixed scrubber sludge-FSS) and ambient groundwater. If FSS is placed at a mine site as a hydrologic barrier over pyritic refuse, it would interact with acidic mine water at the bottom and soil water at the top of the FSS. A coupled reactive transport model was developed for simulating reactions at the exposed edges of the FSS over long time frames. In our modeling, emphasis was placed on the release and fate of toxic trace elements such as arsenic, boron, barium, and zinc, which are commonly present in FSS. The parameters associated with dissolution of trace element hosts were calibrated and optimized using data from column leachate experiments on core samples extracted from a reclaimed abandoned mine land site in Indiana. In an effort to evaluate the leaching potential of these trace elements, reactive transport simulations were conducted and compared with historical chemistry data. The model successfully reproduced many characteristics observed in the field, such as initial rises in the concentrations of arsenic, boron, and zinc, following by continuous decline toward steady state by the end of simulation. Also, simulation results indicated that the weathering rate was slightly higher at the top of the FSS where it is in contact with ambient soil water than at the bottom of the FSS. While the preliminary modeling results are promising, comparisons between model calculations and historical data point to the fact that there must be other sources or mechanisms that accommodate rapid releasing of trace elements. Further model development will require explicit inclusion of mechanisms for sorption/desorption of the potentially toxic elements.

Physical and Chemical Properties of Coal Bottom Ash (CBA) from Tanjung Bin Power Plant

The objective of this study is to determine the physical and chemical characteristics of Coal Bottom Ash (CBA) obtained from Tanjung Bin Power Plant Station and compare them with the characteristics of natural river sand (as a replacement of fine aggregates). Bottom ash is the by-product of coal combustion during the electricity generating process. However, excess bottom ash production due to the high production of electricity in Malaysia has caused several environmental problems. Therefore, several tests have been conducted in order to determine the physical and chemical properties of bottom ash such as specific gravity, density, particle size distribution, Scanning Electron Microscopic (SEM) and X- Ray Fluorescence (XRF) in the attempt to produce sustainable material from waste. The results indicated that the natural fine aggregate and coal bottom ash have very different physical and chemical properties. Bottom ash was classified as Class C ash. The porous structure, angular and rough texture of bottom ash affected its specific gravity and particle density. From the tests, it was found that bottom ash is recommended to be used in concrete as a replacement for fine aggregates.

Synthetic Zeolites Derived from Fly Ash as Effective Mineral Sorbents for Diesel Fuel Spill Remediation

AbstractDevelopment of an effective sorbent for diesel fuel spill remediation remains an important challenge in the field of synthesis due to the potential capacity of sorbents to efficiently purify contaminated sites. Fly ash, a coal combustion by-product, was used as a raw material to synthesize two inexpensive zeolites (SZ-1 and SZ-2) for oil spill remediation using an alkali fusion approach prior to hydrothermal treatment. The sorbents were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and N2 adsorption/desorption. Diesel fuel sorption was used to examine the potential capacity of the synthetic zeolites to sorb oil and other petroleum products. Diesel fuel viscosity and density were determined at room temperature using a viscometer and a pycnometer, respectively. The synthetic zeolites exhibited a higher diesel fuel sorption capacity than fly ash. The SZ-1 zeolite sorbed approximately 1.43 g·g−1 and SZ-2 sorbed approximately 1.9 g·g−1. The sorption was mainly a physical process and mesopore filling seemed to play the dominant role. Sorbent textures were, therefore, vital for the sorption of petroleum products.

Leaching behavior of trace elements in coal spoils from Yangquan coal mine, Northern China

The long-term dumping of coal waste piles has caused serious environmental problems. Release of trace elements (including rare earth elements, REEs) from coal spoils gobs was investigated at Yangquan coal mine, Shanxi Province, China. X-ray diffraction (XRD) was used to analyze the mineral composition of the coal spoils. The minerals of the coal-spoil samples are mainly kaolinite and quartz, with a minor proportion of pyrite. The batch and column tests were employed to simulate the leaching behavior of trace elements from coal spoils. Elements V, Cr, Zn, As, Pb, and Cd are highly enriched in all coal spoils. The coal spoils also have elevated levels of Ga, Ge, Se, Sn, Hf, and Th. The leachate of coal spoils, fried coal spoils and CSFGM (coal spoils fire gas mineral) samples are acidic, with the pH values ranging between 3.0 and 6.6. The released elements with high concentrations (over 100 μg/L) include Fe, Mn, Co, Ni and Zn, while moderately-released elements are Cu, Se, Mo and As. A high content of heavy metals in batch-test leachate with CSFGM indicates an increased mobility of heavy metals in coal spoil combustion byproduct. Within the first hour washing with the electrolyte solution, a rapid rise of common cations, trace elements, and REEs content, as well as a drop of pH value, in effluent was observed. An increased leaching velocity favors the release of trace elements from coal spoils. In addition, the pulse input of precipitation led to more elements to be released than continuous leaching.

Fire-resistant panels composed only of combustion by-products

The reuse of two wastes from coal combustion in the manufacture of panels to be used as building materials or in the protection of metal structures against fire was analysed in this study. The panels were composed of 100% coal combustion by-products. The wastes used were fly ashes and flue gas desulfurisation gypsum from the combustion of coal in a Spanish power plant. The gypsum was previously calcined for 6 h at 150°C. Different mixtures of gypsum and fly ash were tested. The mixtures were kneaded with water until a homogeneous paste was achieved, with which moulds were filled. After 28 d at ambient temperature, the panels were subjected to different physical (density, pH and humidity), mechanical (compressive strength and surface hardness) and fire-resistance tests. Moreover, leaching tests were applied to the fly ash and gypsum. The results obtained were evaluated with the requirements established in some European standards for commercial gypsum products. The fire resistance of the panels under study was found to be higher than that of commercial gypsum and they also showed good mechanical properties.

Resolution of rare earth element interferences in fossil energy by-product samples using sector-field ICP-MS

The supply and price of rare earth elements (REEs) have become a concern to many countries in the world, which has led to renewed interest in exploration and recovery of REEs from secondary or waste sources. Potential high REE waste sources that are of particular interest are coal mining, preparation, combustion, and other fossil energy by-products, including those from natural gas production. In this work, we have examined a set of five solid samples from the treatment of produced and flowback water containing elevated concentrations of barium. In order to confirm the correct concentrations of Eu, we studied these materials using sector field inductively coupled plasma mass spectrometry (SF-ICP-MS), which is capable of resolving species of nearly identical masses, including Eu and BaO. While the use of quadrupole inductively coupled plasma mass spectrometry (Q-ICP-MS) for the REE analysis of most geological sample matrices should pose no problem, the presence of large amounts of Ba, as encountered in water treatment solids from natural gas produced and flowback samples may require SF-ICP-MS for accurate determination of all REEs.

Migration and Emission Characteristics of Trace Elements in a 660 MW Coal-Fired Power Plant of China

Trace elements (TEs) emitted from coal-fired power plants have caused widespread concern. The onsite investigation of TEs emission from a Chinese 660 MW pulverized coal (PC) boiler equipped with selective catalytic reduction (SCR), electric submersible pump (ESP), wet flue gas desulfurization (WFGD), and wet electrostatic precipitator (WESP) was conducted by using U.S. Environmental Protection Agency Method 29. Simultaneous sampling of the coal, bottom ash, ESP ash, flue gas, and by-products from WFGD and WESP processes was performed. Results show that TEs mass balance rates for the entire system, furnace and each air pollution control device (APCD), are in the acceptable range of 70–130%, which confirms the validity and reliability of the field test data. The studied TEs are mainly distributed in bottom and ESP ash with the ratios of 2.11–12.15% and 87.83–97.83%, respectively, while little amounts of them exist in WFGD, WESP, and the stack. Coal combustion by-products such as bottom ash and gypsum have little influence on soil from the perspective of TEs while more attention should be paid to Ni, Zn, and Cd in the ESP ash. Waste water from WFGD should be treated carefully especially for Cr and Mn. WESP wastewater has no influence on groundwater except for Mn, Ag, and Sb. Zn, Ni, and Sb prefer to enrich in ESP ash while accumulation of Mn occurs in bottom ash. Ba is enriched in both bottom and ESP ashes. ESP has great removal efficiency for TEs with the value exceeding 99.87%. Both WFGD and WESP are capable of capturing TEs, which results in the overall removal rate across ESP + WFGD + WESP of more than 99.90%. TEs concentration in the flue gas emitted from the stack is extremely low with the range of 0.00–1.33 μg/m3. The ultralow-emission (ULE) coal-fired power plant equipped with SCR + ESP + WFGD + WESP has good effects on TEs emission control.

Assessment of the phytoremediation potential and an adaptive response of Festuca rubra L. sown on fly ash deposits: Native grass has a pivotal role in ecorestoration management

Fly ash (FA) is a coal combustion by-product of thermal power plants, and has been recognized as a great environmental and health hazard worldwide. The establisment of a permanent green cover on fly ash deposits is essential and can be achieved by sowing the native plant species that should be crucial for stability and resilience of an ecosystem. Improved understanding of species’ response to unfavorable properties of fly ash provides key insight into the decision about ecorestoration practice and management. Therefore, long-term research based on the assessment of the phytoremediation potential and adaptive response of Festuca rubra L. (red fescue) sown on the fly ash deposits at the thermoelectric power plant ‘Nikola Tesla-A’ in Obrenovac (Serbia) was the main concern. Field research was carried out on the passive FA lagoons (L3—the lagoons 3 years old and L2—the lagoons 11 years old) and in the Botanical Garden ́́Jevremovać́ in Belgrade (CS—control site). The physico-chemical properties of soil and fly ash were determined by using standard soil analyses. The element concentrations in soils, fly ash and plants were determined by using ICP-OES. Chlorophyll a fluorescence parameters were measured by using the Plant Stress Meter. Pigments, phenolics and malonyldialdehide contents (MDA) in leaves were measured spectrophotometrically and the total antioxidant capacity in plant leaves was determined by using DPPH free radical. Site-dependent variations were observed for all the parameters examined. FA contains alkaline pH, high electrical conductivity (EC) and low total nitrogen (N) coupled with toxic elements i.e. As and B as well as deficiency of Mn and Zn. Improvement of the physico-chemical characteristics of FA over time is reflected in the increased values of higroscopic water (HW), silt, clay, the amount of adsorbed bases (S), total adsorption capacity (T) and the reduced concentrations of total and available As, B, Cu, Zn and Mn (except available As content) indicating favorable fly ash conditions. F. rubra is an excluder plant, it retains a larger content of As, Cu, Mn and Zn in roots than in leaves and with extensive root system it can provide good fly ash stabilization, i.e. this species has a great potential in phytoremediation of FA. Furthermore, results show that F. rubra sown on the FA deposits has a high amount of MDA and reduced values of chlorophyll a fluorescence parameters (Fm, Fv, Fv/Fm, Fm/Fo), chlorophylls (Chl a, Chl a+b) and total carotenoids (Tot Carot) indicating high oxidative stress and lower efficiency of photosynthesis. However, in spite of toxic concentrations of As and B and low content of Cu, Mn and Zn in the leaves, this species has high potential to activate adaptive mechanisms, such as increased biosynthesis of anthocyanins, phenolics, ascorbic acid and total radical scavenging activity. Taken together, F. rubra possesses high adaptive capacity to perform functional ecorestoration on fly ash deposits. These findings indicate that F. rubra can be identified as a vital element for large-scale reclamation purpose.