Search Results (660)

Despite the shift toward cleaner energy, coal-fired power plants remain a significant source of global energy, generating excess fly ash that accumulates in large stockpiles—often persisting for decades even after the plants are decommissioned. The study investigated the physicochemical properties and suitability of fly ash recovered from seven ash dams for use in cement-based applications. The recovered ash was beneficiated by drying, breaking agglomerates, and sieving to meet specifications for use as a cementitious material. Subsequently, analyses were conducted for particle size, pH, density, loss on ignition, scanning electron microscopy, oxide composition, X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy, and the compressive strength of mortar samples. The results indicate that the samples are Class F fly ashes, containing amorphous aluminosilicates, with a comparable physical, chemical, and mineralogical composition, and that they meet specifications for use in cement-based materials. This remains true despite a slight increase in sulphur-bearing phases in the Kusile ash associated with the plant’s desulfurization technology. Furthermore, the compressive strength results show that, compared with the reference Portland cement mortar, fly-ash-blended mortars exhibit higher strength gain at later ages, indicating good pozzolanic reactivity, though the degree of strength gain depends on each ash’s fineness, amorphous content, and mineralogy. Full article

This study presents a screening-level conceptual, stoichiometric, and scenario assessment of a pathway linking sulfur dioxide (SO₂) capture from coal-fired flue gas to sulfuric acid production and the downstream reaction of sulfuric acid with pretreated scrap aluminum. A regenerable sodium sulfite (Wellman–Lord) capture route, followed by gas polishing and drying, catalytic SO₂ oxidation, controlled SO₃ absorption, acid conditioning, and an Al–H₂SO₄ reactor, is used as the reference configuration. The sulfur balance distinguishes sulfur in coal, ash retention, gaseous SO_x, SO₃/acid mist, absorber inlet and stack slip, captured sulfur, regenerated sulfur, and sulfate purge. Under the central assumptions, 1 t of sulfur in coal yields 0.849 t of recovered sulfur equivalent, 2.599 t of H₂SO₄, 0.477 t of aluminum feed, 2.419 t of anhydrous-equivalent Al₂(SO₄)₃, 4.240 t of commercial aluminum sulfate on a 17 wt% Al₂O₃ basis, and 42.4 kg of H₂ at 80% aluminum conversion. The upstream base-energy screen is 3.3–7.2 GJth and 0.18–0.45 MWhe per tonne of sulfur in coal. Diluting the acid to the selected 0.5–1.0 M aluminum-reaction window and subsequently producing a 17 wt% Al₂O₃ product creates a minimum water-removal load of 21.6–47.6 t and a latent-heat floor of approximately 49–108 GJth/t S. Retail prices are replaced by 2024 customs unit values, and internal-acid-production and sulfuric-acid-opportunity-cost boundaries are evaluated separately. In the central opportunity-cost case, the H₂ value must reach approximately 6.9 USD/kg merely to balance material values before CAPEX, OPEX, energy, purification, transport, and environmental-compliance costs. The Afşin–Elbistan A case is treated as a full-design-throughput illustration based on an historical 18 Mt/y coal requirement, not as a measured current operating average; coal sulfur is tested over 1.0–2.5 wt%. The aluminum step is restricted to cooled and diluted 0.5–1.0 M H₂SO₄ at 40–60 °C, and direct H₂ production from 96 to 98 wt% acid is not assumed. Plant-specific capacity factor, time-matched coal assays, flue-gas flow, oxygen-corrected stack data, reaction kinetics, gas purity, and product quality remain to be verified. The integrated sustainability screening indicates conditional circular-economy potential rather than a demonstrated sustainability advantage: sulfur recovery must be weighed against energy and water demand, sulfate purge and wastewater, diversion of recyclable aluminum from remelting, hydrogen purification, and market-scale product offtake. The pathway therefore remains a research hypothesis requiring experimental validation, process simulation, techno-economic assessment, comparative life-cycle assessment, safety analysis, and market verification. Full article

Reliable full-line monitoring of belt-conveyor idlers remains challenging because large numbers of idlers operate under spatially varying structural stiffness and strong industrial vibration. This study develops an ultra-weak fiber Bragg grating distributed acoustic sensing (UWFBG-DAS) method combined with characteristic energy feature analysis for long-distance idler monitoring. The method makes three main contributions. First, a simplified finite-element model identifies the middle crossbeam as an effective vibration-transmission path and guides the deployment of the sensing array. Second, envelope demodulation and variational mode decomposition (VMD) are employed to isolate the fault-sensitive IMF2 component, whose energy is temporally accumulated and evaluated using a zone-specific self-referencing threshold derived from normal-operation data. Third, the method is validated through field deployment and fault-type classification. Approximately 1.2 km of a sensing cable was deployed in a coal-fired power plant, and identifiable characteristic-energy increases were observed in 9 of 10 idler-replacement tests. For three representative fault types, stratified five-fold cross-validation of 300 samples achieved an overall classification accuracy of 90.3%, with a 95% Wilson confidence interval of 86.5–93.2%. These results demonstrate the feasibility of UWFBG-DAS combined with zone-specific characteristic energy analysis for long-distance idler monitoring under spatially heterogeneous industrial conditions. Full article

Use of fly ash (FA), a by-product of coal-fired power stations, and basic oxygen furnace slag (BOFS), a by-product of steel production plants, in construction applications in Kazakhstan is limited due to their low quality and inherent problematic properties. For example, the concern with using BOFS as an aggregate in concrete is the volume expansion caused by the formation of calcium hydroxide (Ca(OH)₂) or magnesium hydroxide (Mg(OH)₂) in the concrete matrix generated by a chemical reaction between water and free calcium oxide (f-CaO) or free magnesium oxide (f-MgO) in BOFS. This issue can be addressed through geopolymerization and CO₂ curing (mineral sequestration). Moreover, the quality of FA does not meet ASTM Class F FA criteria (coarse particle sizes and low reactivity). This study investigated the physical, mechanical, microstructural, and durability properties of geopolymer mixtures composed of low-quality FA, ground granulated blast-furnace slag (GGBFS), and BOFS aggregates under various curing conditions. Six distinct curing regimes were assessed: air, water, 6 h steam, 12 h steam, 6 h steam combined with 6 h CO₂, and 6 h steam combined with 12 h CO₂ curing. The hardened properties, durability, and microstructural characteristics of geopolymer mixtures were mainly assessed by compressive strength, dielectric constant (DC), drying shrinkage, expansion (1 M NaOH solution and water expansions), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM) images. Test results show that steam curing and combined steam and CO₂ curing significantly enhanced the performance of the mixtures containing BOFS aggregates. The combined steam and CO₂ curing accelerated the mineral sequestration of f-CaO in the BOFS aggregates, increasing the 28-day compressive strength by up to 27.7% and 19.2% (reaching 37.1 MPa) compared to air- and water-cured mixtures (29.1 and 31.1 MPa, respectively). While air (20.0 and 11.7), steam (28.7 and 12.4), and combined steam and CO₂ (23.6 and 12.6) curing at 1-day and 182-day yielded lower DC, water curing (30.5 and 32.2) had higher DC. The extended steam and CO₂ curing times further enhanced compressive strength growth (39.6 MPa) by 36.6% for air-curing and 27.1% for water curing, although curing duration did not significantly affect the dielectric constant. Importantly, the expansion of the BOFS aggregate in both water and 1 M NaOH solution was minimized up to 0.04% under combined curing, mitigating the inherent volumetric instability of the BOFS. Drying shrinkage was also reduced by 0.17% under combined curing conditions. Longer steam and CO₂ curing times reduced variability in dielectric constant, drying shrinkage, and the expansion characteristics. FTIR spectroscopy, SEM image, and XRD analyses confirmed that the mixture’s geopolymerization was more noticeable during the steam and CO₂ curing regimes than during water and air curing regimes. The longer steam and CO₂ curing times promoted extended hydration and the formation of stable carbonate compounds from the BOFS f-CaO, producing a significantly denser and microstructurally stable geopolymer matrix. Full article

Coal ash-slag waste from coal-fired power plants is a high-volume technogenic material whose resource potential is controlled by particle-size heterogeneity, mineralogical composition, and the occurrence modes of valuable elements. This study investigated Au occurrence in ash-slag waste derived from Ekibastuz coal and evaluated gravity–magnetic preconcentration as a diagnostic first stage for separating Au- and Fe-bearing products. The material was characterized by particle-size analysis, X-ray diffraction, chemical analysis, optical and electron-probe microscopy, atomic absorption analysis (AAS), kinetic spectral analysis (KSA), gravity concentration, and magnetic separation. The feed was an aluminosilicate–ferruginous material dominated by mullite, magnetite, quartz, and hematite. In the coarse material, liberated native Au co-reported with heavy Fe-bearing phases: the vibratory spiral concentrate contained 0.99 g/t Au and 39.00% Fe, corresponding to 52.58% Au recovery and 66.49% Fe recovery. The combined spiral and centrifugal concentrates yielded 1.04 g/t Au at 63.22% recovery, representing an approximately eightfold upgrade relative to the 0.13 g/t feed. In contrast, gravity recovery from the finest fraction was approximately 1%, indicating ultrafine, poorly liberated, or matrix-associated Au. KSA gave higher Au values than AAS, reflecting matrix heterogeneity and method-dependent preparation and detection effects rather than analytical superiority. The results support a size-selective gravity–magnetic preconcentration route followed by targeted mineralogical verification and product-specific downstream extraction. Full article

This study develops a management-driven and interpretable framework for identifying the formation of scenario-derived accounting increments in coal-fired power plants. Based on real monthly operational and accounting data from a coal-fired power plant in Guangdong Province in 2024, key management activities, including on-site metering, sampling standardization, coal testing timeliness, and net calorific value testing compliance, were represented as structured management-state variables. A baseline accounting scenario and a management-corrected accounting scenario were constructed, and their difference was defined as a scenario-derived accounting increment. Bootstrap resampling, Monte Carlo simulation, ensemble learning, and CatBoost-based SHAP analysis were integrated to characterize how management states affect parameter admissibility, trigger correction rules, and alter accounting results. Under the random split setting, the Best Stacking model achieved an RMSE of 70.76, an MAE of 39.99, and an R² of 0.999987, and was therefore retained as the primary predictive benchmark. Source-month grouped validation provided an additional internal robustness check, with CatBoost achieving an R² of 0.990007 under the stricter grouped validation setting. CatBoost-based SHAP analysis showed that net calorific value testing compliance was the dominant management-state contributor, with a contribution share of 73.1%, while coal consumption and purchased electricity ranked second and third, indicating that activity-data magnitude amplified the scenario-derived accounting increments once correction rules were triggered. The proposed framework supports whole-process data-quality control and risk-oriented verification governance in carbon accounting. Full article

To alleviate grid peak-shaving pressure from high-penetration renewable energy integration, coupling thermal energy storage (TES) with coal-fired power plants is an effective approach for enhancing operational flexibility. This paper systematically investigates the peak-shaving performance of a coal-fired unit integrated with molten salt storage and heat pump storage systems, focusing on load response characteristics, peak-shaving capability, and the influence of discharge strategies on thermodynamic performance under various rated turbine heat acceptance (THA) conditions. The results indicate that, under identical peak-shaving capacity, the molten salt system exhibits greater storage capacity, which increases with rising THA levels, whereas the heat pump storage capacity remains largely THA-independent. Regarding discharge strategies, replacing high-pressure extraction steam achieves the fastest ramp rate and largest incremental power output, introducing steam into the intermediate-pressure cylinder yields the slowest response but highest round-trip efficiency, and replacing low-pressure extraction steam delivers the smallest peak-shaving capacity and lowest round-trip efficiency. Although TES integration slightly reduces thermal efficiency due to heat exchange losses, this trade-off is justified by significant flexibility improvement, demonstrating clear engineering value for high-renewable grids. Full article

The large-scale disposal of coal fly ash (CFA), coal bottom ash (CBA), and desulfurization gypsum (DG) from coal-fired power plants poses serious environmental challenges, driving the need for high-value utilization strategies. In this study, we propose a synergistic approach to prepare foam glass-ceramics from CFA, CBA, and DG via a sintering-foaming method. The effects of sintering temperature (1200–1230 °C) and DG content (0–5 wt.%) on phase composition, pore structure, and overall material properties were systematically investigated. The optimal sample, obtained at 1220 °C with 2 wt.% DG exhibits outstanding comprehensive performance: a bulk density of 1.0030 g/cm³, porosity of 62.09%, compressive strength of 9.66 MPa, and thermal conductivity of 0.6156 W/(m·K). Additionally, it demonstrates excellent chemical stability, with acid resistance exceeding 96% and alkali resistance over 98%, while the leaching concentrations of heavy metals (Pb, Cr, Cu, Zn) remain far below regulatory limits. Mechanistic analysis reveals a crystallization–foaming coupling effect. At an appropriate DG content (2 wt.%), a synergy is established: bubble formation provides heterogeneous nucleation sites that promote crystal precipitation, while moderate crystallization increases melt viscosity and stabilizes the pore structure. Conversely, excessive DG (3–5 wt.%) reduces melt viscosity, leading to bubble coalescence and rupture, suppressed crystallization, and consequently deteriorated material properties. This work provides a theoretical foundation for the synergistic utilization of multiple power plant wastes and the structure–property regulation of foam glass-ceramics. Full article

In recent years, a sharp increase in coal-based power generation has been observed in a number of countries. Coal-fired thermal power plants remain the main source of harmful emissions in the energy sector of many countries, including Kazakhstan. This creates a strong need for the development of effective methods to reduce pollutant emissions at thermal power plants. The aim of the present study is to perform a numerical investigation of the effectiveness of staged combustion technology with secondary air injection (Over-Fire Air, OFA) applied to three boilers—PK-39, BKZ-160, and BKZ-75—which differ in design, capacity, and furnace configuration. CFD modeling was carried out using the FLOREAN package, adapted to the conditions of the Kazakh energy sector, which relies on high-ash coal (more than 40%) for coal-based power generation. Model validation was performed against experimental data obtained from operating thermal power plants. It was found that air injection through OFA injectors intensifies turbulent mixing, reduces peak temperatures in the main combustion zone, and ensures a more uniform distribution of heat release along the furnace height, thereby suppressing thermal NOx formation. It is shown that the spatial structure of NO concentration fields at the furnace outlet strongly depends on the design features of each boiler. The results demonstrate the high efficiency of staged combustion technology in reducing nitrogen oxide emissions and improving the environmental performance of pulverized-coal boiler units. The obtained results can be used in the design of new and the modernization of existing thermal power plants utilizing coal-based power generation. Full article

Chemical absorption is currently the most mature technology for carbon capture from flue gas in coal-fired power plants. The selection of the amine solution system and process optimization directly determine the energy consumption of carbon capture and are critical to the large-scale implementation of the amine process. In this study, a composite amine solution of N-methyl-diethanolamine-piperazine-water (MDEA-PZ-H₂O) was selected as the CO₂ absorbent. Aspen HYSYS (14.0) software was used to establish a typical process model for CO₂ capture from flue gas in coal-fired power plants. Using single-factor sensitivity analysis, key process parameters in the typical carbon capture process—including amine solution composition, flue gas inlet temperature, lean liquid temperature, and gas-to-liquid ratio—were optimized. Based on the process optimization, this study conducted integrated energy-saving optimization by optimizing the temperature distribution in the absorption tower (achieved through the integration of inter-stage cooling in the absorption tower) and regeneration energy savings (achieved through the coupling of the Mechanical Vapor Recompression (MVR) process). The results indicate that the carbon capture system integrating the inter-stage cooling process with the MVR energy-saving process reduces the energy consumption per unit of carbon captured by 15.15% compared to a typical process system. This demonstrates that the integration of multiple energy-saving processes with the recovery of flue gas and CO₂ waste heat recovery within the system is an effective approach to reducing the energy consumption per unit of carbon capture. Full article

To improve the flexibility and carbon reduction performance of coal-fired power plants, a solar-aided power generation (SAPG) system integrated with parabolic trough collectors and thermal energy storage (TES) was proposed and investigated using a combined Aspen Plus and System Advisor Model (SAM) framework. Two different integration schemes, namely SAPG-1 and SAPG-2, were evaluated under 100%, 75%, and 50% load conditions with a solar multiple of 2 and a TES duration of 6 h. The thermodynamic, economic, and environmental performances of the systems were comprehensively analyzed. The results show that TES significantly improves solar energy utilization, annual solar contribution, and system dispatchability. Compared with SAPG-2, SAPG-1 demonstrates superior thermodynamic and economic performance due to its lower boiler heat demand and more effective feedwater integration. At full load, the solar contribution of SAPG-1 with TES reaches 16.04%, while the annual solar energy production increases to 190.35 GWh with a capacity factor of 21.75%. In addition, TES integration effectively reduces the levelized cost of electricity and shortens the payback period under both CO₂ pricing and non-CO₂ pricing scenarios. The proposed SAPG framework demonstrates considerable potential for enhancing renewable energy utilization, operational flexibility, and economic feasibility in large-scale solar–coal hybrid power generation systems. Full article

This study presents a comprehensive life cycle assessment (LCA) of the modernization of an existing 460 MW coal-fired power unit into a hybrid system incorporating a high-temperature gas-cooled reactor (HTGR). The analysis was conducted from a cradle-to-grave perspective using a functional unit of 1 MWh of net electricity, based on the ecoinvent 3.9 database and the ReCiPe 2016 Midpoint method. The results indicate that the modernized system achieves a global warming potential (GWP) of 18.2 g CO₂-eq/kWh, representing a 93.5% reduction compared to a supercritical coal-fired unit. The largest contribution to the total environmental burden is associated with the upstream uranium supply chain, accounting for approximately 42% of GWP. In contrast, the operational phase exhibits a negative contribution due to the application of environmental credits resulting from the avoidance of emissions related to coal combustion. The findings also confirm a significant improvement in resource efficiency, including reduced primary energy demand and waste generation compared to the reference system. Sensitivity analysis demonstrated the robustness of the results with respect to variations in key economic and thermodynamic parameters, particularly CAPEX (capital expenditures) and operating temperature. Overall, the results suggest that hybrid retrofitting of coal-fired power plants with HTGR technology may serve as a viable transitional pathway supporting the decarbonization of the Polish energy sector. Full article

Coal combustion in large-scale power plants is a major source of atmospheric pollution, including SO₂, NO_x, particulate matter, and the halogen acids HCl and HF. Predicting HCl and HF emissions is challenging due to interactions among fuel composition, fly ash chemistry, combustion conditions, and flue gas dynamics. In this study, artificial neural network (ANN) models are developed from field experiments at the lignite-fired TPP “Kostolac B”. The models incorporate operational parameters (flue gas temperature and flow rate) and fuel/ash characteristics (moisture and total sulphur in coal and CaO content in ash) to estimate HCl and HF emissions. SHAP analysis identified key variables affecting halogen acid release. The developed ANN models achieved satisfactory predictive accuracy, with the test-set performances of RMSE = 2.05 mg/Nm³, R² = 0.80, and MAPE = 18.7% for HCl prediction, and RMSE = 3.23 mg/Nm³, R² = 0.83, and MAPE = 18.7% for HF prediction. SHAP analysis indicated that CaO content in fly ash and coal moisture are the primary drivers of HCl and HF emissions, while operating conditions and coal sulphur content influence emissions through non-linear interaction effects. The proposed ANN-SHAP framework provides a data-driven approach for emission prediction and interpretation, supporting decision-making in emission management. Full article

Carbon dioxide emissions are a major concern for coal-fired power plants. A capture and utilization method is highly demanded. The wastewater generated by a power plant contains a high concentration of Na⁺. Using wastewater salts to absorb carbon dioxide for sodium carbonate production is a promising strategy, as it can achieve carbon capture and utilization and wastewater resource utilization. However, the salt concentration in raw wastewater from coal-fired power plants is generally insufficient to achieve sustainable carbon capture; thus, concentrating the Na⁺ in the wastewater is key. In this study, desulfurization wastewater was investigated as a source of salts. The reverse osmosis (RO) process was selected for salt concentration. As wastewater is significantly complex and unsuitable for direct RO treatment, pre-treatment was conducted. For chemical oxygen demand (COD) removal, Fenton oxidation (49.7%) and electrochemical oxidation (49.3%) achieved better results than microelectrolysis (25.3%). Precipitation showed a strong ability to remove hardness. The removal efficiencies for Mg²⁺ and Ca²⁺ were 99.9% and 99.8%, respectively. It gave 8.6% COD removal as well. Additionally, 89.8% of ammonia was removed by stripping. To further decrease the pollutant concentrations, activated carbon was used for adsorption. RO then concentrated the pre-treated wastewater after nanofiltration. The final level of NaCl was 40.4 g/L after concentration. This was lower than that required to concentrate the water, which contained only NaCl. This is due to the presence of impurities left in the wastewater after pre-treatment. The study reveals that pre-treatment is essential to achieve the desired NaCl concentration in RO with the ultimate goal of CO₂ capture. Full article