Radiological characteristics of pulverized fly ashes produced in Turkish coal-burning thermal power plants

The objective of this study is to determine radiological characteristics of pulverized fly ash (PFA) collected from the 15 coal-burning thermal power plants (TPPs) in operation by means of gamma spectrometric technique and to assess the radiological impacts from the utilization of PFA samples examined as filling and cover material in earthwork applications. Also, the annual effective doses received by workers handling PFA and members of the public living in a house near the PFA pile/landfill were estimated using methods specified in the Radiation Protection 122. The activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K measured in PFA samples were tabulated for each TPP. The activity results show that Turkish PFA may have relatively high natural radioactivity content, depending on its origin reaching in the case of Kangal PFA 2720 Bq kg⁻¹ of ²²⁶Ra. The values of external exposure indexes (radium equivalent activity index and gamma index) calculated for PFA samples are within the recommended safety limits. As well, the highest mean total annual effective doses estimated as 7.3 × 10⁻⁵ Sv y⁻¹ for workers and 1.5 × 10⁻⁴ Sv y⁻¹ for members of the public are significantly lower than the annual limit of 1.0 × 10⁻³ Sv y⁻¹.     

Characterization of spinel and magnetospheres of coal fly ashes collected in power plants in the former USSR

Six samples of magnetospheres, recovered by magnetic separation from fly ashes, collected from power plants with high temperature boilers in the former USSR, were investigated by combination of instrumental techniques. The phase and chemical compositions, morphology and microstructure of magnetospheres have been studied by optical microscopy, scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM/EDX), X-ray diffraction (XRD), Mössbauer spectroscopy. Iron in magnetospheres mainly occurs as Fe-spinels, hematite, and iron bearing glass. Structural formulas of spinels promising for catalysis applications were calculated on the base of obtained results. The magnetospheres have been characterized mainly as core-shell nanocomposites from spinel, hematite and quartz crystals in glass matrix divided in high-silica and high-ferrous glasses. The mechanism of magnetospheres formation was proposed.     

Determination of selenium by ICP-MS and HG-ICP-MS in coal, fly ashes and sorbents used for flue gas cleaning

The determination of selenium in solid materials related with the use of coal for energy production was evaluated by two methods; ICP-MS and HG-ICP-MS. Coals, fly ashes and various solids used as sorbents in gas cleaning processes (kaolin, limestone, alumina, metal oxide mixtures and activated carbons), were the materials analysed. In several of these materials, selenium could be determined by either method with similar results. However in coal, fly ashes and some activated carbons, the use of a HG-ICP-MS is necessary in order to avoid interferences. The results obtained by both methods in samples whose selenium content ranges from μg g⁻¹ to mg g⁻¹, are discussed. In general, good (±2-4%) to excellent (±1-2%) agreement between the reference and the obtained concentrations was achieved in the analysis of the certified and reference samples, the relative standard deviation being lower than 10% in all cases.     

Fine particle and trace element emissions from an anthracite coal-fired power plant equipped with a bag-house in China

Fine particle and trace element emissions from energy production are associated with significant adverse human health effects. In this investigation, the fine particles and trace elements emitted from the combustion of pulverized anthracite coal at a 220 MW power plant were determined experimentally in the size range from 30 nm to 10 μm with 12 channels. The particulate size distributions and morphological characteristics before and after the bag-house were evaluated. The uncontrolled and controlled emission factors of particles are compared with the calculated values from the US Environment Protection Agency, AP-42. Size-classified relative enrichment factors of As, Hg, Se, Cd, Cr, Cu, Al, V, Zn, Mn, Fe were obtained. Relative distributions of trace elements between bottom ash, fly ash and flue gas are determined by mass balance method. The bag-house collection efficiencies of particles and trace elements in the particulate phase are obtained. Finally, the controlled and uncontrolled emission factors of elements of different particulate size fractions are obtained, which will provide useful information for PM_2.5 and PM₁₀ emission inventory development, toxic and hazardous pollutant emission estimates and emission standards established for metal-based pollutants from a pulverized coal-fired boiler.     

A novel robust dynamic method for NOx emissions prediction in a thermal power plant

NOx is a harmful by-product of coal-fired boilers, and accurate prediction of NOx emissions in the outlet of a boiler is essential for environmental protection. In recent years, data-driven models have been widely studied and applied in this area. However, dynamic characteristics are ignored by many existing models, leading to sub-optimal performance. Besides, outliers that occur in the operation data have adverse effects on the efficacy of these prediction models. To address these issues, this paper presents a novel method for predicting NOx concentration via integrating a robust dynamic probabilistic approach and the long short-term memory (LSTM). First, mutual information (MI) is applied to determine the input variables. Subsequently, a robust probabilistic method is proposed to extract dynamic latent features considering outliers. On this basis, the generated latent variables are further utilized to train the LSTM-based model, with which the intrinsic relation between inputs and NOx values are obtained. Based on the application to a 660 MW thermal power plant, the superiority of the proposed method is demonstrated in terms of high prediction accuracy.     

Corrosion behavior of metallic alloys in molten chloride salts for thermal energy storage in concentrated solar power plants: A review

Recently, more and more attention is paid on applications of molten chlorides in concentrated solar power (CSP) plants as high-temperature thermal energy storage (TES) and heat transfer fluid (HTF) materials due to their high thermal stability limits and low prices, compared to the commercial TES/HTF materials in CSP-nitrate salt mixtures. A higher TES/HTF operating temperature leads to higher efficiency of thermal to electrical energy conversion of the power block in CSP, however causes additional challenges, particularly increased corrosiveness of metallic alloys used as containers and structural materials. Thus, it is essential to study corrosion behaviors and mechanisms of metallic alloys in molten chlorides at operating temperatures (500–800 °C) for realizing the commercial application of molten chlorides in CSP. The results of studies on hot corrosion of metallic alloys in molten chlorides are reviewed to understand their corrosion behaviors and mechanisms under various conditions (e.g., temperature, atmosphere). Emphasis has also been given on salt purification to reduce corrosive impurities in molten chlorides and development of electrochemical techniques to in-situ monitor corrosive impurities in molten chlorides, in order to efficiently control corrosion rates of metallic alloys in molten chlorides to meet the requirements of industrial applications.