Coal Combustion Products Research Articles

Barium in coal and coal combustion products: Distribution, enrichment and migration

Coal triggering pollution caused by the emission of harmful substances in the process of coal combustion has been paid more and more attention. Barium is a ubiquitous heavy metal element in coal. During coal combustion, Ba in coal has been released into the environment in different forms, and coal-fired products with high Ba content can cause harm to the environment, human health and even pose a serious threat to life. By reviewing the literature, distribution, modes of occurrence, mobility of Ba in coal seams were summarized and studied in this paper. It is expected to provide information for controlling emission of Ba. The content characteristics of Ba in coal in some countries are introduced, and the content gradient of Ba in coal of Chinese different provinces is introduced in detail. And coal with Ba content greater than or equal to 5 times of the world average Ba content, namely, coal containing 750 μg/g Ba is called high Ba coal. Many studies have shown that Ba was extremely enriched in coal in some areas (up to 5,000 μg/g), particularly in the Jurassic coal seams of the Huanglong coalfield in China. There were various types of occurrences of Ba in coal, including witherite, barite, crandallite and other minerals. Meanwhile, Ba can combine with organic matter as well. According to existing studies, the enrichment mechanism of Ba in coal is mainly derived from soil, sediment and seawater erosion, with the later causal minerals Ba carbonate and strontium rhodochrosite being the main carriers of Ba. The migration and transformation pathways of Ba in coal and its combustion products are described. As a medium volatile element, Ba is prone to concentrate in products of coal combustion, particularly those small-grainsize particles in fly ash, which may induce more serious contamination.

Exploring the efficacy of emerging reactivity tests in screening pozzolanic materials

This paper presents the assessment of the reactivity of pozzolans using various emerging reactivity test methods. A wide range of pozzolans representing different classes, including coal combustion products, natural pozzolans and ground glasses, were used in this study. Pozzolans were tested for reactivity quantification in calcite-lime-pozzolan systems in mortar cubes at 40 °C in a modified lime-reactivity test. The existing strength-activity index test, ASTM C311/C618, was modified by producing mortars of portland cement-pozzolan systems at a constant water-to-binder ratio. The bulk electrical resistivity of mortar cubes was measured in both modified lime-reactivity and modified ASTM C311/C618 tests before compressive strength was measured. Select pozzolans were also investigated in pastes using the recently developed R3 heat release test using isothermal calorimetry. The same pastes were then tested for lime consumption by pozzolans using thermogravimetric analysis. The outputs of the modified lime-reactivity test at 7 days are in moderate to strong agreement with the results of other reactivity tests. In mixtures with binders containing portland cement resistivity measurements better differentiate pozzolans based on reactivity; whereas, early-age strength developments are favored by the physical contribution of pozzolans. The resistivity and strength of portland cement-pozzolan mortars in the modified ASTM C311/C618 at 28 days or later and in the modified lime-reactivity test at 7 days are found to be reliable proxies of the reactivity of pozzolans. When strength and resistivity both are jointly considered a sound and balanced quantification of the pozzolanic reactivity is achieved.

Distribution, occurrence mode, and extraction potential of critical elements in coal ashes of the Chongqing Power Plant

Critical metals play an irreplaceable role in supporting the development of the global economy and emerging industries. Their short supply makes the recovery of critical metals from alternative sources, such as coal ash, a research hotspot. In this study, Chongqing Power Plant coal and its combustion products, which are rich in a variety of critical metal elements, were selected for the study. The enrichment, distribution, and occurrence mode of critical elements in the products of coal combustion was studied, and improved sequential chemical extraction procedure, and their extraction potential was proposed and discussed. The results show that the contents of the most critical elements in different coal ashes are generally high in the order of fly ash, slag, and bottom ash. The critical elements Li, Ga, Sr, Zr, Hf, Nb, Ta, and rare earth elements and yttrium (REY) are enriched in fly ash and the contents of Ga, Nb, and REY exceed their respective industrial utilization grades, which have great recovery potential. Lithium, Ga, Nb, Ta, and REY are mainly distributed in small particle sizes in non-magnetic fly ash and occur in aluminosilicate glass, followed by mullite and quartz. Three categories of extractability are proposed: easy-to-extract form, relatively easy-to-extract, and difficult-to-extract forms. Finally, future research should focus on the collaborative extraction of multiple critical elements (such as Li, Ga, Nb, and REY) from coal ash.

FORMULATION AND CHARACTERIZATION OF CERAMIC PARTS FOR COATINGS MADE FROM THE PRODUCTS OF COMBUSTION OF MINERAL COAL

The use of coal as fuel in various industrial processes such as thermoelectric and steel mills generates relevant amounts of waste or by-products, called coal combustion product (CCP’s). Therefore, viable alternatives for the correct disposal or technological applications of this by-product are studied with or without the addition of reinforcement phases in order to reduce the environmental impacts caused. Among these applications, one possible approach is the use of CCP’s for the manufacture of ceramic tiles, since these residues are chemically similar to several ceramics. Therefore, this work aimed to evaluate some physical and mechanical properties of CCP’s to observe the feasibility of manufacturing ceramic parts for coating from the product of coal combustion. The results confirmed the potential and feasibility of using CCP’s to completely compose the ceramic tiles matrix.

Potentially Economic Concentrations of Rare Earth Elements and Gold in Power Plant Coal Combustion Products (Far East, Russia)

The distribution of rare earth elements (REE) and gold (Au) in fly ash released during combustion of brown coal from the Pereyaslavskoye (Siberia) and Erkovetskoye (Far East) deposits has been investigated. Coal combustion was carried out in two locations: the boiler unit of the Blagoveshchenskaya coal-fired power plants (CFPP), equipped with an electrostatic precipitator (ESP); and at the Amur Experimental and Technological Complex (ETC) with the aim of separating the combustion products (slag, fly ash, sludge). It was found that in both processes the highest contents of REE (400 and more ppm) and Au (up to 0.29 ppm) are concentrated in fly ash. These characteristics of coals were used as the basis for the author's calculation of the predicted resources of REE and Au under the conditions of the annual operation of firstly one boiler unit, and then five, equipped with an ESP. Further research by the authors will be aimed at improving the degree of recovery of concentrates through the development of technologies at pilot plants such as ETC “Amur”.

Enrichment and occurrence form of rare earth elements during coal and coal gangue combustion.

Coal ash has emerged as an important alternative source for rare earth elements (REEs). The enrichment and occurrence form of REEs among coal combustion products are of great significance for both technical design and economic evaluation of recovering REEs from the coal ash. Here, the enrichment and occurrence form of REEs in the ash were investigated. Compared with ashes from muffle furnace, coal fly ash (CFA) from power plants involved higher enrichment ratio of REEs, which was explained by the fractionation of coal ashes to concentrate REEs in finer CFA, higher combustion temperature to vaporize more volatile elements, and longer residence time of fly ash to absorb REEs in the gas. In addition, CFA samples were analyzed by sequence chemical extraction procedure (SCEP) and scanning electron microscope with an energy dispersive spectrometer (SEM-EDX), which revealed the important role of aluminum in the occurrence form of REEs compared with Si in aluminosilicates of CFA. This conclusion was further confirmed by thermodynamic equilibrium calculation, which also agreed qualitatively with the observation that REEs mainly existed in the solid phase. Both experimental and computational results of this work provided insights to understand the distribution of REEs in CFA and optimize their extraction processes.

Influence of biomass on multi-component reaction model and combustion products of coal gangue

The effects of biomass on coal gangue combustion characteristics, combustion products and combustion reaction model are studied in this paper. Based on the thermogravimetric experimental data, a multi-component combustion reaction model for coal gangue and biomass was established. The CG combustion reaction mechanism can be well explained by the two-component combustion reaction model. The participation degree of organic matter and inorganic matter is 90% and 10%, respectively. C3P1, C1P1 and C1P3 can be better explained by the five-component combustion reaction model. The reaction model corresponding to PS is a four-component combustion reaction model. Moreover, it is found that the addition of biomass can promote the combustion reaction of coal gangue and the production of gas products using Fourier transform infrared spectroscopy technology. Through combustion, the proportion of F4 mode of Cr, Cd, Pb, Cu, and Ni for CG sample increased from 92%, 60%, 52%, 28% and 60% to 95%, 90%, 82%, 91% and 94%, respectively. The toxicity reduction effect for Cd, Pb, Cu, and Ni is obvious, and the proportion of F4 mode is increased by more than 30%. Compared with other mixed samples, the ash formed by C1P1 is less harmful.

Analysis of technological conditions for the formation and burnout of carcinogenic pahs in boiler flue gases

THE PURPOSE. The necessity of establishing emission standards for highly toxic substances with carcinogenic properties in the context of the implementation of new principles of state regulation of environmental protection activities at energy enterprises is substantiated and confirmed. The analysis of the features of the formation and burnout of carcinogenic polycyclic aromatic hydrocarbons in the flue gases of boilers during the combustion of coals in lowtemperature conditions of the furnace process is carried out. Based on the analysis, the total and partial indicators of the harmfulness of flue gases were calculated in order to assess and predict the overall toxicity of coal combustion products, taking into account the contribution of carcinogenic substances.METHODS. When calculating the overall toxicity of flue gases, a systematic analysis and generalization of experimental data on the content of carcinogenic and non-carcinogenic polycyclic aromatic hydrocarbons in the combustion products of low-power boilers was applied.RESULTS. As a result of the performed study, the contribution of carcinogenic and non-carcinogenic polycyclic hydrocarbons to the overall toxicity of boiler flue gases during the combustion of Azeysky, Mugunsky, Cheremkhovsky and Tugnuy coal was determined. It is shown that substances such as benz(a)pyrene, fluoranthene, pyrene and phenanthrene significantly affect the level of the total indicator of the harmfulness of combustion products from 38.8 to 53.6%.CONCLUSION. The obtained research results can be applied at energy enterprises at the stage of substantiating the introduction of regime-technological and environmental measures in order to develop measures to improve environmental efficiency through technological rationing of carcinogenic emissions.

The Influence of Industrial Waste on the Magnetic Properties of Salt-Affected Soils from Two Soda Ash Manufacturing Sites

The aim of this study was to characterize the impact of soda ash manufacturing on the magnetic properties of soils located in the agricultural landscape in north-central Poland. Two study sites were chosen: Mątwy (SM) and Janikowo (SJ). Highly saline soils with halophyte communities were selected in order to develop an understanding of the relationship between salinization of water–soil interface and the potential contamination risk of the environment. Basic chemical and physicochemical properties of topsoil (0–25 cm) and water (surface and groundwater) samples from five locations were characterized. The characteristics of soil contamination were based on the content of selected metals, magnetic properties and salinity indices. Potential routes of contaminant migration (air and water fluxes) were analyzed. High magnetic anomalies of technogenic origin were revealed in the studied soils. A statistically confirmed relationship between high magnetic susceptibility and the content of selected metals (Co, Ni, Cu, Zn, Ba, Pb and Mn) showed the high utility of magnetometric techniques in soil research (diagnosis of soil transformation and contamination during technogenic impact). Three potential factors influencing contaminant migration were revealed: highly saline ground and surface water, eolian transport of fine-grained mineral fractions from waste ponds and atmospheric deposition of coal combustion products.

Characteristics of emission and light-absorption of size-segregated carbonaceous aerosol emitted from four types of coal combustion at different combustion temperatures

Coal consumed in domestic cooking and heating in rural areas of China is considered as a major source of air pollution. To efficiently represent the emission of coal burnt for residential living at various combustion regimes, four coal samples are selected for combustion experiments in the simulated air state at three different temperatures in a drop-tube furnace system in this study. Size-segregated particulate matter in flue gas from combustion of the four coal samples at different temperatures were collected by a TISCH-type Andersen eight-stage impact sampler operating synchronously with the furnace system. The emission factors of the particulate matter samples show that OC2 and OC3 are the main carbonaceous products of bituminous coal and lignite combustion. It is also found that the particulate matter from lignite flue gas contains EC1 in a large proportion and a small amount of highly-refractory EC2 and EC3 from bituminous coals. Meanwhile, in order to evaluate the light-absorption of organic carbon in particulate matter, the mass absorption cross efficiency (α/ρ) is investigated. The clear-sky radiative transfer model shows that BrC emitted from low-temperature burning leads to even positive top-of-atmosphere radiative forcing at surfaces with an albedo of 0.19. In the 300–700 nm spectral band, the simple forcing efficiency (SFE) of particulate matter sampled significantly decreases as combustion temperature and coal maturity increase. The particulate matter presents a high SFE in the range of 0.4–1.1 μm in terms of particle size.

Effect of effective stress on hydraulic conductivity of bentonite–polymer geosynthetic clay liners to coal combustion product leachates

Experiments were conducted to evaluate the hydraulic conductivity of five geosynthetic clay liners (GCLs) permeated with four synthetic coal combustion product (CCP) leachates (ionic strength = 473–4676 mM). One of the GCLs contained conventional sodium bentonite (Na-B), and the other four GCLs contained a bentonite–polymer (B-P) composites with polymer loading ranging from 0.5 to 12.7% (B-P-0.5–B-P-12.7). Hydraulic conductivity tests were conducted at 20 kPa until reaching hydraulic and chemical equilibrium and then the effective confining stress was increased incrementally from 20 to 100, 250 and 500 kPa. The hydraulic conductivity of B-P GCLs with high polymer loading showed a faster decreasing trend than that of Na-B and B-P GCLs with lower polymer loading as the effective confining stress increased. Additionally, the hydraulic conductivity of GCLs permeated with a synthetic CCP leachate with ionic strength of 473 mM decreased significantly as the effective confining stress increased, whereas the GCLs permeated with an aggressive CCP leachate (e.g. ionic strength = 4676 mM) had limited reduction in hydraulic conductivity at elevated effective confining stress.

Fly Ash as an Eco-Friendly Filler for Rigid Polyurethane Foams Modification.

There is currently a growing demand for more effective thermal insulation materials with the best performance properties. This research paper presents the investigation results on the influence of two types of filler on the structure and properties of rigid polyurethane foam composites. Fly ash as a product of coal combustion in power plants and microspheres of 5, 10, 15, and 20 wt.%, were used as rigid polyurethane foams modifiers. The results of thermal analysis, mechanical properties testing, and cellular structure investigation performed for polyurethane composites show that the addition of fly ash, up to 10 wt.%, significantly improved the majority of the tested parameters. The use of up to 20 wt.% of microspheres improves the mechanical and thermal properties and thermal stability of rigid polyurethane foams.

Shotcrete using ternary binder made from coal combustion products: from lab tests to an application

The paper presents a ternary binder development and its utilization in shotcrete. The binder is made from fluidized bed combustion (FBC) fly ash, siliceous fly ash, and Ca(OH)2 addition, now available under the name Sorfix. XRD and TGA identified ettringite and C-S-H as two main hydration products. In addition, thermodynamic modeling verified robustness in terms of space-filling capabilities when varying input oxide composition.Since alkali-free accelerators produce mostly ettringite in Portland-based systems, a fraction of Portland cement was advantageously replaced with the ternary binder, forming early ettringite as well. Extensive testing led to 45% replacement of Portland cement, following J2 curve for early strength gain used commonly in shotcrete tunnel linings. The shotcrete was successfully tested in a mock-up experiment in a 2 m3 Prague served for the full-scale application, utilizing over 1000 tons of Sorfix and saving over 700 tons of CO2

PROGNOSTIC MODEL OF SUBSURFACE CONTAMINATION CAUSED BY NEW EMBANKMENTS ON THE TERRITORY OF MARITSA EAST COAL MINING COMPLEX – CENTRAL SOUTHERN BULGARIA

One of the many environmental problems resulting from electricity generation in thermal power plants is the release of large amounts of solid wastes (coal combustion products). In the absence of effective eco-friendly disposal practices, this waste is accumulated in the form of coal ash embankments or in the excavated parts of the open-cast mines. The so constituted big landfills and surface impoundments emit leachate emissions containing a wide range of conventional pollutants among which, by definition, sulphate ions (SO4) dominate. Using the computer program VS2DI, a numerical model is developed of the conditions for mass transport of pollutants (using the example of SO4) from the designed new embankments for deposition of non-hazardous industrial solid waste from TPP in the area of the internal embankments of Troyanovo-North open-cast mine, part of the Maritsa East Coal Mining Complex. The scheme of convective-diffusion mass transport is employed, taking into account reversible elimination (sorption-desorption), mechanical dispersion and mixing. On the basis of the developed model, a long-term prognosis (100 years) is made for the extent and the degree of subsurface contamination from the new embankments. Based on the model solutions, the retention capacity of the geological foundation and the risk of groundwater pollution are assessed.

Research Summary on the Processing, Mechanical and Tribological Properties of Aluminium Matrix Composites as Effected by Fly Ash Reinforcement

Fly ash is the main waste as a result of combustion in coal fired power plants. It represents about 40% of the wastes of coal combustion products (fly ash, boiler ash, flue gas desulphurization gypsum and bottom ash). Currently, coal waste is not fully utilized and waste disposal remains a serious concern despite tremendous global efforts in reducing fossil fuel dependency and shifting to sustainable energy sources. Owing to that, employment of fly ash as reinforcement particles in metallic matrix composites are gaining momentum as part of recycling effort and also as a means to improve the specifications of the materials that are added to it to form composite materials. Many studies have been done on fly ash to study composite materials wear characteristics including the effects of fly ash content, applied load, and sliding velocity. Here, particular attention is given to studies carried out on the influence FA content on physical, mechanical, and the thermal behavior of Aluminium-FA composites. Considerable changes in these properties are seen by fly ash refinement with limited size and weight fraction. The advantage of fly ash addition results in low density of composites materials, improvement of strength, and hardness. It further reduces the thermal expansion coefficient and improve wear resistance.

Utilization of waste in nickel ore processing as concrete mixing material

The nickel ore processing process produces nickel slag waste, while in coal-fired power plants, there is waste in the form of fly ash and bottom ash. Fly ash is a product of coal combustion consisting of particulates (fine particles of burned fuel) driven out of a coal-fired boiler along with the flue gases. Incorporating the waste material as a concrete mixture is expected to be an alternative in using materials for concrete mixtures, especially waste materials, to be more useful and reduce environmental pollution. Utilization of waste in the nickel ore processing as a concrete mixture meets the requirements for use as a structural concrete mixture, and this can be seen from the results of testing the compressive strength of concrete produced from all types of mixed compositions producing an average concrete compressive strength of above 17.0 MPa.

Environmentálně rizikové chemické prvky na odkališti Brno-Hády

The studied area is located in Brno-Vinohrady. This location was used for fly ash dumping. Fly ash as a product of coal combustion was deposited there in period from 1967 to 1997 from the in the Červený mlýn and Špitálka heating plants. This material has the ability to absorb pollutants, especially heavy metals in its structure. Elevated concentrations of these elements thus represent a potential environmental risk. The main impulse to have a closer look at this waste dump and the fly ash composition is the planned building of a leisure complex in this area in the near future.The fly ash morphology was investigated by a scanning electron microscope (SEM). The results proved the presence of microspheres. On their surface, heavy metals and other contaminants can be accumulated. The contents of heavy metals were determined in the studied material by atomic absorption spectroscopy (AAS) and X-ray fluorescence (XRF) analysis. Measured values were compared with the limit values of environmental pollution published by the Ministry of the Environment of the Czech Republic and with the results of previous studies from the same place. The limits were exceeded slightly by cobalt (Me = 41.62 ppm; Max = 58.30), and a lot of arsenic (Me = 380.62; Max = 593.35). Amount of arsenic was thus compared with the exposure models, which were created for this location earlier. Its concentration transgressed the line of potential risk for a human organism. The number of radionuclides in the analyzed material by laboratory gamma-ray spectrometry (Me: K = 1.75 %, eU = 6.50 ppm, eTh = 16.75 ppm) was converted to the specific activity of 226Ra (am; Me = 212.40 Bq kg-1) and compared with the limit which is 370 Bq kg-1. Thismethod proved that the deposited material does not contain potentially dangerous amounts of natural radionuclides.Based on the results of this study, especially on the amount of arsenic, the waste dump Brno-Hády represents a potentially dangerous location for the human organism and requires adjustments for possible future utilization as a leisure complex.

Acidity of rainfall samples in close vicinity of coal-fired power plant with wet cooling tower with flue gas injection

The paper presents measurement data concerning the degree of acidification of precipitation collected during a 6-month measurement campaign carried out in an immediate vicinity of a power plant, where the cooling tower was used for discharging flue gases as a product of coal combustion. As reference, data obtained from parallel measurements carried out at a monitoring station considered as city background station were used. High acidity of precipitation was anticipated due to reactions of acid gases contained in the combustion gases with water, which already occur inside the cooling tower. The results have not confirmed this assumption. The pH value of the precipitation samples was significantly higher than the pH of rainwater at the background station located 18 km away from the power plant.

Combustion wastes from thermal power stations and household stoves: A comparison of properties, mineralogical and chemical composition, and element mobilization by water and fertilizers.

Wood and coal combustion generate wastes, which may negatively influence the environment. However, studies concerning coal combustion products serving as soil additives are currently in progress. Hence, this study was conducted to compare properties (mineralogy, metallic element content, and rare earth element content) of combustion wastes of different genesis (ash and soot after wood and coal combustion in households, ash from thermal power stations) and to assess possible risk posed to the soil environment when used as soil additive. This study demonstrated the diversity of chemical and mineralogical features of ashes of household genesis originating from thermal power stations. Ash from household stoves showed a higher concentration of metallic elements (i.e., Zn) compared to those originating from thermal power stations. Antimony (Sb) content in household ash can serve as an indicator of plastic (polyethylene) combustion, which is legally prohibited. Leaching tests using water and common mineral fertilizers showed that ammonium sulfate mobilizes metallic elements (Cu, Zn, Pb) more significantly than potassium nitrate or deionized water. The leaching of metallic elements from household stove's ash certainly excludes the possibility of applying the ash as a soil additive even when the ash contains a source of beneficial elements for plants (i.e., Ca).

Hydraulic conductivity of bentonite-polymer geosynthetic clay liners to coal combustion product leachates

Hydraulic conductivity of seven geosynthetic clay liners (GCLs) to synthetic coal combustion product (CCP) leachates were evaluated in this study. The leachates are chemically representative of typical and worst scenarios observed in CCP landfills. The ionic strength (I) of the synthetic CCP leachates ranged from 50 mM to 4676 mM (TCCP-50, LRMD-96, TFGDS-473, LR-2577, HI-3179 and HR-4676). One of the GCLs contained conventional sodium bentonite (Na–B) and the other six contained bentonite-polymer (B–P) mixture with polymer loadings ranging from 0.5% to 12.7%. Hydraulic conductivity tests were conducted at an effective confining stress of 20 kPa. The hydraulic conductivity of the Na–B GCLs were >1 × 10−10 m/s when permeated with all six CCP leachates, whereas the B–P GCLs with sufficient polymer loading maintained low hydraulic conductivity to synthetic CCP leachates. All the B–P GCLs showed low hydraulic conductivity (<1 × 10−10 m/s) to low ionic strength leachates (TCCP-50, I = 50 mM and LRMD-96, I = 96 mM). B–P GCLs with P > 5% showed low hydraulic conductivity (<1 × 10−10 m/s) up to HI-3179 leachates. These results suggest that B–P GCLs with sufficient polymer loading can be used to manage aggressive CCP leachates.