Search Results (30)

Coal serves as a cornerstone and stabilizer for China’s energy security; utilizing it in a clean and efficient manner aligns with the current national energy situation. The moisture content of coal is a crucial factor affecting its calorific value and separation efficiency. Therefore, enhancing the drying rate while simultaneously reducing the moisture content in coal is essential to improve separation efficiency. This paper primarily investigates the drying and separation characteristics of wet fine coal particles within a gas–solid fluidized bed system. A hot gas–solid fluidized bed was employed to study the particle fluidization behavior, heat–mass transfer, and agglomeration drying properties under varying airflow temperatures. The results indicate that as the airflow temperature increases, the minimum fluidization velocity tends to decrease. Additionally, with an increase in bed height, the particle temperature correspondingly decreases, leading to weakened heat exchange capability in the upper layer of the bed. Faster heating rates facilitate rapid moisture removal while minimizing agglomeration formation. The lower the proportion of moisture and magnetite powder present, the less force is required to break apart particle agglomerates. The coal drying process exhibits distinct stages. Within a temperature range of 75 °C to 100 °C, there is a significant enhancement in drying rate, while issues such as particle fragmentation or pore structure collapse are avoided at elevated temperatures. This research aims to provide foundational insights into effective drying processes for wet coal particles in gas–solid fluidized beds. Full article

In order to improve the durability of loess-based composite coal gangue porous planting concrete (LCPC), the effects of fly ash and slag powder content on the durability and microstructure of LCPC were studied. In this paper, fly ash and slag powder were mixed into LCPC, and freeze-thaw cycle and dry-wet cycle tests were carried out. The compressive strength, dynamic elastic modulus, and mass change were used as evaluation indices to determine the optimal mix ratio for LCPC durability. Scanning electron microscopy (SEM) was performed, and the experimental design was carried out with the water–cement ratio, fly ash, and slag powder content as variables. The microstructure characteristics of LCPC were analyzed. The results show that the maximum number of freeze-thaw cycles can reach 35 times and the maximum number of dry-wet cycles can reach 50 when 5% fly ash and 20% slag powder are used. With an increase in the water-cement ratio, the skeleton of the loess gradually became complete, and its structure became more compact. In the micro-morphology diagram, the mixed fly ash and slag powder particles are not obvious, but with an increase in dosage, the size of the cracks and pores gradually decreases. The incorporation of fly ash and slag powder can play a positive role in the durability of LCPC and improvement of its microstructure. The results of this study are crucial for improving the application performance of ecological restoration, soil improvement, and long-term stability of structures, and can provide a scientific basis for the sustainable development of environmentally friendly building materials. Full article

In practical coal preparation processes, influenced by mining methods and mechanization levels, the proportion of fine and even ultrafine pulverized coal continues to increase. However, due to the small particle size, significant inter-particle interactions, and the low efficiency of conventional physical separation techniques, the efficient deashing of fine coal remains a significant technical challenge. Consequently, in the face of growing demand for fine coal processing, efficient and mature dry separation technologies are still lacking. To address this issue, a pulsating circulating airflow separation device was designed and developed in this study to deash and desulfurize pulverized coal with a particle size of less than 1 mm. The effects of gas velocity and pulsating airflow frequency on the deashing performance were investigated. Using Design-Expert software (version 13), an optimized formula for deashing efficiency was established, and the optimal operating parameters were evaluated. The separation results demonstrated that under the optimal conditions of fluidization, the number N = 1.2 and pulsating airflow frequency f = 2.375 Hz, the standard deviation of ash segregation (σ_ash) reached 25%, and the ash content in the cleaned coal was reduced from 37.28% to 22.32% in the cleaned sample. Furthermore, the sulfur content decreased significantly from 0.971% in the raw coal to 0.617% in the cleaned coal, indicating effective desulfurization. In addition, the concentrations of other harmful elements in the raw coal were also reduced to varying degrees. These findings demonstrate that the application of pulsating airflow can effectively enhance ash and sulfur removal from pulverized coal particles smaller than 1 mm. This approach offers a novel and promising method for the dry beneficiation of fine coal particles. Full article

During the extraction and utilization of coal resources, a large amount of CO₂ and coal-based solid wastes (CBSW), such as coal gangue, are generated. To reduce the carbon and waste emissions, an effective approach is to mineralize the CO₂ with the CBSW and then backfill the mineralized materials into the goaf area. However, efficient CO₂ mineralization is challenging due to the low reactivity of coal gangue. To this end, mechanical activation was used for the modification of coal gangue, and the mechanical activation mechanism of coal gangue was revealed from a microcosmic perspective by dry powder laser particle size testing (DPLPST), X-ray diffractometer (XRD) analysis, Fourier-transform infrared spectrometer (FTIR) analysis, and scanning electron microscopy (SEM). The results showed that compared with the unground coal gangue, the average particle size of coal gangue after 0.5 h, 1 h, and 1.5 h milling decreases by 94.3%, 95%, and 95.3%, respectively; additionally, the amorphous structures of the coal gangue after milling increase, and their edges and corners gradually diminish. After the pressure mineralization of coal gangues with different activation times, thermogravimetric (TG) analysis was performed, and the CO₂ mineralization effect of the mechanically activated coal gangue was explored. It is found that the carbon fixation capacity of the coal gangue after 0.5 h, 1.0 h, and 1.5 h mechanical activation is increased by 1.18%, 3.20%, and 7.57%, respectively. Through the XRD and SEM, the mechanism of CO₂ mineralization in coal gangue was revealed from a microcosmic perspective as follows: during the mineralization process, alkali metal ions of calcium and magnesium in anorthite and muscovite are leached and participate in the mineralization reaction, resulting in the formation of stable carbonates such as calcium carbonate. Full article

The paper analyzes the processes of emission and dispersion of particulate contaminants from a large point source emitter: a hard coal-fired power plant. Reference is made to the European Green Deal and its main objective of reducing anthropogenic particulate and greenhouse gas emissions. CHPP, Krakow Combined Heat and Power Plant, Poland, as described in the article, has a strong impact on the mechanisms that shape the microclimatic factors of the Krakow agglomeration. This combined heat and power plant provides heat and electricity for the city, while simultaneously emitting significant amounts of suspended particulate matter into the atmosphere. Due to the adverse impact of non-conventional energy sources on the natural environment and the increasing effects of climate warming, radical changes need to be implemented. The HYSPLIT (Hybrid Single-Particles Lagrangian Integrated Trajectories) model was used to track the movement of contaminated air masses. A 5-day episode of increased hourly concentrations of PM2.5 particulate matter contamination was selected to analyze the backward trajectories of air mass displacement. From 15 August 2022 to 19 August 2022, high 24-h particulate matter concentrations were recorded, measuring around 20 µg/m³. The HYSPLIT model, a unique tool in the precise identification of point sources of pollution and their impact on the air quality of the region, was used to analyze the influx of polluted air masses. A 5-day episode of increased hourly concentrations of PM2.5 pollutants was selected for the study, with values of approximately 20 µg/m³. It was found that low-pressure systems over the North Atlantic brought wet and variable weather conditions, while high-pressure systems in southern and eastern Europe, including Poland, provided stable and dry weather conditions. The simulation results were verified by analyzing synoptic maps of the study area. The image of the displacement of contaminated air masses obtained from the HYSPLIT model was found to be consistent with the synoptic maps, confirming the accuracy of the applied model. This means that the HYSPLIT model can be used to create maps of contaminant dispersion directions. Consequently, it was confirmed that modeling using the HYSPLIT model is an effective method for predicting the displacement directions of particulate contamination originating from coal combustion in a combined heat and power plant. Identifying circulation patterns and front zones during episodes of increased contaminant concentrations is strategic for effective weather monitoring, air quality management, and alerting the public to episodes of increased health risk in a large agglomeration. Full article

Gas–solid separation fluidized bed is an efficient and clean coal separation technology with a good separation effect for coal particles. However, there is a lack of systematic research on the complex motion behavior of the feeding particles in gas–solid separation fluidized beds. In this study, the separation kinetics of non-spherical single feeding particles in the fluidized bed are examined. The particle sphericity coefficient Φ is introduced to characterize the morphology of irregular coal particles, and the drag coefficient for the feeding particles is modified to verify the suitability of the non-spherical particle drag model for gas–solid fluidized bed separation. After optimization and correction, a ρ_S.sus (the bed density when single feeding particles are suspended in the gas–solid separation fluidized bed) prediction model is obtained. When the prediction accuracy of the ρ_S.sus prediction model is 90%, the confidence degree is 85.72%. This ρ_S.sus of the single non-spherical feeding particle prediction model highlights a direction for improving the separation effect, provides a theoretical basis for the industrialization of gas–solid fluidized bed, and promotes the process of dry fluidized separation. Full article

The application of coal technologies for energy generation leads to high pollutant emissions. Thus, governmental and international organizations have created new programs and laws for monitoring emissions. Recently, the government of Kazakhstan has introduced regulations for the measurement of emissions produced by factories and power plants. However, the requirements and Corecommendations for the monitoring methods have not been defined. Therefore, this article addresses the problem and focuses on determining the measurement errors made by optical SGK510 and electrochemical POLAR devices used for coal power plants. The hypothesis is based on the fact that there are currently no systems for monitoring probe drying, and its implementation is expensive. The main methods are analyzed, namely their operation, taking into account the presence of water particles in samples, and the possibility of using adjustment coefficients is considered. The main pollutants chosen for analysis are CO, NO, NO₂, NO_x, SO₂, and O₂. Using the Broich–Pagan test, homoscedasticity was determined, and the Fisher test showed the possibility of using tuning coefficients. The data for the optical method were compared to measurements taken using Inspector 500. The error for SO₂ determination was 7.19% for NO, 44.0985% for NO₂, 733.26% for NO_x, 7.39% for O₂, 2.75% for CO, 60.81%. The comparison between SGK510 and POLAR demonstrated the following errors: for CO—1.5%, for NO_x—82.4405%, for SO₂—41.17%, for O₂—11.61%. According to the Fisher criteria analysis of the optical method, only SO₂ and CO values measured by SGK510 in comparison to Inspector 500 had close similarity, while others demonstrated high deviations. The significance tests were carried out by Fisher’s, t-test, and ANOVA methods. For the electrochemical measurement, only CO values had close similarity. In the future, methods will be proposed to improve the accuracy of the system while reducing maintenance costs, as well as cleaning sampling systems. The multicomponent analysis application for accuracy improvement with the exhaust gas humidity, temperature, and flow consideration was recommended as a possible solution. Full article

Coal fly ash (CFA), a by-product of coal combustion, is a valuable raw material for various applications. However, the heterogeneous nature of the composition and properties of CFA provides challenges to its effective usage and utilisation. This study investigates the thermal behaviour of the fly ashes of lignite (FA1) and brown coal (FA2) and their fractions obtained by dry aerodynamic separation. Thermal analysis techniques, including thermogravimetry (TG), differential scanning calorimetry (DSC), and evolved gas analysis (EGA), were used to characterise the behaviour of the fly ash fractions while heating up to 1250 °C. The results reveal distinct differences in the thermal behaviour between ash types and among their different size fractions. For the FA1 ashes, the concentration of calcium-rich compounds and the level of recrystallisation at 950 °C increased with the decrease in particle size. The most abundant detected newly formed minerals were anhydrite, gehlenite, and anorthite, while coarser fractions were rich in quartz and mullite. For the FA2 ashes, the temperature of the onset of melting and agglomeration decreased with decreasing particle size and was already observed at 995 °C. Coarser fractions mostly remain unchanged, with a slight increase in quartz, mullite, and hematite content. Recrystallisation takes place in less extension compared to the FA1 ashes. The findings demonstrate that the aerodynamic separation of fly ashes into different size fractions can produce materials with varied thermal properties and reactivity, which can be used for specific applications. This study highlights the importance of thermal analysis in characterising fly ash properties and understanding their potential for utilisation in various applications involving thermal treatment or exposure to high-temperature conditions. Further research on advanced separation techniques and the in-depth characterisation of fly ash fractions is necessary to obtain materials with desired thermal properties and identify their most beneficial applications. Full article

The Upper Hunter Valley is a major coal mining area in New South Wales (NSW), Australia. Due to the ongoing increase in mining activities, PM10 (air-borne particles with an aerodynamic diameter less than 10 micrometres) pollution has become a major air quality concern in local communities. The present study was initiated to quantitatively examine the spatial and temporal variability of PM10 pollution in the region. An earlier paper of this study identified two air quality subregions in the valley. This paper aims to provide a holistic summarisation of the relationships between elevated PM10 pollution in two subregions and the local- and synoptic-scale meteorological conditions for spring and summer, when PM10 pollution is relatively high. A catalogue of twelve synoptic types and a set of six local meteorological patterns were quantitatively derived and linked to each other using the self-organising map (SOM) technique. The complex meteorology–air pollution relationships were visualised and interpreted on the SOM planes for two representative locations. It was found that the influence of local meteorological patterns differed significantly for mean PM10 levels vs. the occurrence of elevated pollution events and between air quality subregions. In contrast, synoptic types showed generally similar relationships with mean vs. elevated PM10 pollution in the valley. Two local meteorological patterns, the hot–dry–northwesterly wind conditions and the hot–dry–calm conditions, were found to be the most PM10 pollution conducive in the valley when combined with a set of synoptic counterparts. These synoptic types are featured with the influence of an eastward migrating continental high-pressure system and westerly troughs, or a ridge extending northwest towards coastal northern NSW or southern Queensland from the Tasman Sea. The method and results can be used in air quality research for other locations of NSW, or similar regions elsewhere. Full article

To promote the sustainable exploitation of open-pit coal resources, waste is used as backfill material to realize the comprehensive utilization of solid waste mine resources. We proposed a mining method that is a combination of the highwall mining and filling mining methods. Cemented paste backfill (CPB) samples were prepared with high-clay-mineral-content marl particles as aggregate and normal Portland cement, sulfoaluminate cement and gypsum as cementing materials. The physical and mechanical properties and microstructural evolution of CPB with different binder ratios under wetting–drying cycles were measured. The results showed that the CPB with 0–3 wetting–drying cycles underwent shear and tensile coalescence, and that with 4–10 cycles underwent shear coalescence. The unconfined compressive strength (UCS) and elastic modulus (EM) decreased exponentially with increasing number of wetting–drying cycles but decreased exponentially and cubically with increasing porosity, respectively. The EM is more sensitive to gypsum content than the UCS. CPB deterioration was divided into an initial deterioration stage and a secondary deterioration stage. The evolution curve of the total damage variable presents an ‘S’ shape, with an initial damage stage, an accelerated damage expansion stage, a decelerated damage expansion stage and an end damage stage. The research results provide a basis for improving the recovery rate of resources under highwall conditions, and the extensive utilization of stripping materials, and promote the coordinated development of coal resource exploitation and environmental protection. Full article

Flip-flow vibrating screens (FFVSs) effectively tackle the challenges posed by the dry deep-screening of wet, fine, low-grade bituminous coal, thereby facilitating advancements in the thermal coal preparation process. The tensile lengths of the screen panels not only influence the service lives of the screen panels but also play a pivotal role in determining the screening performance of the FFVSs. To investigate the effect of the screen-panel tensile length on the screening performance of an FFVS, this study constructs a dual-mass flip-flow screening test rig. The experimental results reveal that when the fine-particle content and the external water content in the feed of low-grade bituminous coal are 55% and 16%, respectively, the most favorable tensile length of the screen panels is 2 mm. With a fine-particle content of 55% in the feed of low-grade bituminous coal and an increase in the external water content from 4% to 20%, the screening efficiency of the FFVS initially decreases and then increases. Notably, low-grade bituminous coal with 16% external water content poses the most challenging screening conditions. Furthermore, when the external water content of the low-grade bituminous coal is 16% and the fine-particle content in the feed increases from 25% to 55%, the screening efficiency of the FFVS gradually improves. Full article

Ultrafine, highly active coal gasification slag (HCGS) was produced via a sustainable, green dry-ball-milling method. Coal gasification fine slag (CGS), a potential environmental pollutant, was used as a new source of rubber filler without pre-treatment, enabling waste utilisation. HCGS was added to styrene-butadiene rubber (ESBR) composites, and the effects of HCGS and the filler content on the mechanical and thermal stabilities of SBR were evaluated. The procedure conforms to important green metrics, requiring no solvent or additional reagent, or solvent-assistance for product collection. HCGS reduced the scorch time (t₁₀) and curing time (t₉₀) of the filled ESBR composites relative to those of pure SBR and improved the mechanical parameters. The tensile strength at 50 phr reached 10.91 MPa, and the tear strength at 90 phr reached 64.92 kN/m, corresponding to 9.4- and 3.92-fold increases relative to that of SBR filled with HCGS, respectively. HCGS exerted a reinforcing effect on ESBR, comparable to that of commercial carbon black (CB) N330. HCGS improves the binding between rubber molecules and filler particles and captures the rubber chain, thereby limiting its movement. HCGS is potentially applicable as a CB substitute in the rubber industry, with environmental and economic benefits in the disposal of CGS. Full article

Coal bottom ash is used globally in various applications in the construction industry to reduce its negative environmental impacts. In this study, the potential utilization of lignite bottom ash from four power plants in Greece in concrete manufacturing was evaluated through granulometric, chemical, and mineralogical analyses. The particle-size distribution of bottom ash obtained from dry sieving resembles that of sand, making bottom ash suitable for replacing fine aggregates in the production of concrete. Its chemical composition, determined with selective point analyses energy dispersive spectroscopy (EDS), reveals high amounts of silica and alumina indicating pozzolanic properties, and high calcium contents suggesting hydraulic/cementitious character. Mineralogical characterization, obtained from powder X-Ray diffraction analyses (XRD), displays the prevalence of amorphous matter, calcite, quartz, aluminosilicate minerals, and portlandite, implying a beneficial pozzolanic and hydraulic activity in concrete manufacturing. Full article

A wet electrostatic precipitator (WESP) has much higher capture rate for fine particulate matter, PM_2.5, than a traditional dry type electrostatic precipitator does. In order to make full use of existing dust removal equipment and reduce the emissions of smoke and dust to zero, a combination of chemical coagulation and humidification coagulation is proposed using a WESP. The results show that the addition of chemical coagulant can promote the coagulation of coal-fired dust particles. After the addition of pectin (PG), the median diameter of dust particles increases from 28.19 μm to 45.28 μm. Water vapor humidification can promote the coagulation of dust particles. When the water vapor injection rate increases from 0 kg/h to 3.2 kg/h, the median diameter of dust particles increases from 28.19 μm to 36.45 μm. The synergistic effect of the coagulant and water vapor can enhance the chemical coagulation effect; when 1.0 × 10⁻² g/L PG and 3.2 kg/h water vapor synergize, the collection efficiency reaches 98.17%, and when 1.0 × 10⁻² g/L polyacrylamide (PAM) and 3.2 kg/h water vapor synergize, the collection efficiency reaches 96.68%. Both chemical coagulation and water vapor humidification can promote the condensation of coal dust, which is beneficial to improve the efficient capture of fine particles using WESP. Full article

In this experiment, the influence of coal gangue as the admixture on the performance of dry-mixed mortar was studied, and the results were analyzed by XRD and SEM. The effects of different ways of crushing, particle size distribution, coal gangue, cement, admixture, and water content on the water retention, consistency, and 7 d compressive strength of dry-mixed mortar were investigated. The results show that the optimum content of hammer crushing of coal gangue through 3 mm sieve and cement is 83% and 17% of the total mass (W/W), respectively, the admixture content of 1# compound is 0.2 g/kg, and the amount of water is in the range of 194~200 mL/kg. At this time, the consistency can reach 91.5 mm, the water retention rate can reach 92.11%, and the 7 d compressive strength can reach 10.6 MPa, which meets the requirements of dry-mixed mortar for ordinary plastering and masonry mortar (GB-T 25181-2019). Full article