ABSTRACT This study investigates the surface characteristics of Yongshengyuan (YSY) low-rank coal, a material known for its flotation challenges, employing a suite of analytical techniques such as Zeta potential analysis, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction phase analysis (XRD), and X-ray photoelectron spectroscopy (XPS). The flotation performance of low-rank coal was evaluated using three distinct surfactants (sodium petroleum sulfonate, hexadecyl dimethyl ammonium bromide, methyl oleate) in conjunction with 3# oil (base oil). The experimental results demonstrate that all surfactants enhance the flotation efficiency of low-rank coal, with the combination of sodium petroleum sulfonate and methyl oleate with 3# oil proving most effective. Comprehensive analyses of AFM, Zeta potential, contact angle and wetting heat of coal sample pre and post-application of the compound reagent, reveal that the surfactant preferentially interacts with the polar hydrophilic sites on the YSY low-rank coal surface. This interaction diminishes the presence of oxygen-containing functional groups on the coal surface, increases the ratio of hydrophobic groups, enhances the coal’s hydrophobicity, and consequently bolsters the flotation efficiency of the low-rank coal.

ABSTRACT This study investigated the performance of aggloflotation, a novel hybrid process that combines oil agglomeration and flotation, for the beneficiation of lignite coal from Sivas/Gemerek, Türkiye. The effects of critical process parameters, including depressant (sodium silicate) dosage, collector (kerosene) dosage, frother (methyl isobutyl carbinol) dosage, pulp pH, and solid-liquid ratio, were systematically evaluated. The optimum conditions were determined to be 250 g/t sodium silicate, 250 g/t kerosene, 200 g/t methyl isobutyl carbinol, pH 4, and a solid-liquid ratio of 10%. Under these conditions, the aggloflotation process achieved a yield of 80.92%, a combustible recovery of 91.35% and an ash content of 8.65%. Compared to conventional flotation and oil agglomeration, aggloflotation significantly outperformed both, particularly in reducing ash content while maintaining high recoveries. The process demonstrated efficiency in treating fine and ultrafine coal particles, addressing a significant challenge in the beneficiation of low-rank coals. These results suggest that aggloflotation offers a promising, efficient, and environmentally friendly solution for the cleaning of low-rank coals, with potential implications for enhancing coal utilization in energy production.

ABSTRACT The moisture content of flotation clean coal products is a critical factor influencing their calorific value, making dewatering research vital for the efficient utilization of coal. In this study, cationic polyacrylamide (CPAM) was employed as a high molecular weight flocculant and filter aid to investigate the mechanisms by which the anionic sodium dodecyl sulfate (SDS), cationic dodecyltrimethylammonium bromide (DTAB), and nonionic polyoxyethylene lauryl ether (Brij L23) affect the dewatering of flotation clean coal. The influence of these surfactants on the dewatering performance of flotation clean coal in conjunction with CPAM was examined through filter aid experiments, density functional theory, zeta potential measurements, agglomeration of flotation clean coal particles, and Nuclear Magnetic Resonance (NMR) analysis. The results indicated that DTAB and SDS exhibited a larger positive electrostatic potential compared to Brij L23, demonstrating stronger electrostatic adsorption on the molecules of flotation clean coal. However, the -OSO3 groups in SDS interacted more strongly with the molecules of flotation clean coal than the tertiary amine groups in DTAB. The ether and hydroxyl groups in Brij L23 interacted weakly with the molecules of flotation clean coal. The surfactants increased the compactness and structural complexity between particles within the flocs, leading to an increase in the fractal dimension of the flocs. Additionally, the surfactants enlarged the pores within the filter cake of flotation clean coal, which was beneficial for the removal of moisture.

ABSTRACT Pyrolysis is highly regarded as a means to produce smokeless briquettes. This study investigated the effects of torrefaction and fast pyrolysis on the physicochemical and combustion characteristics of coal and biocoal briquettes. Biocoal briquettes were prepared with coal dust and rice husks using cassava starch gel as a binder, whereas no biomass was used for coal briquettes. The feedstocks were compacted in a briquetting machine and then dried in a solar dryer before pyrolysis in a muffle furnace fitted with a vacuum system. The proximate compositions were derived from thermogravimetric analysis (TGA), and the calorific values were calculated. The combustion characteristics were determined through thermogravimetry (TG-DTG) analysis. The functional groups were analyzed via Fourier transform infrared (FTIR) spectroscopy. The results revealed that biocoal briquettes with coal-to-rice husk ratios of 50:50 and 60:40, which were subjected to torrefaction for 30 min at 200°C, had the same volatile matter content (12%), but differed in other properties. The pyrolyzed coal briquette exhibited the highest flammability and combustion indices. Furthermore, some transmittance peaks shifted to lower or higher frequencies. This study demonstrates that the the properties of pyrolyzed briquettes are influenced by the pyrolysis temperature, feedstock and blending ratio.

ABSTRACT This study investigates the impact of various solvents on the static stability and flow characteristics of waste-activated carbon (WAC)-based coal-water slurry for co-gasification. Using the Euler–Euler method, we analyze slurry stability both in stationary conditions and during flow in a horizontal pipeline. Results show that glycerin offers the highest stability during slurry preparation, while acetonitrile provides the lowest. Solvents like glycerin, propanol, and formamide improve stability compared to water. In static conditions, glycerin’s stable height change rate is nearly 0, while acetonitrile peaks at 4.09. During the flow, glycerin-based slurry maintains a stable height of 40 mm with no accumulation, while acetonitrile retains only 88% of its height. The solid volume fraction difference for glycerin slurry is minimal (0.011), whereas acetonitrile slurry shows a much larger difference (0.7). However, glycerin slurry has the highest pressure drop (129 mWc/100 m), indicating higher energy consumption during transportation. This study highlights how solvent viscosity and density influence slurry properties and introduces a numerical approach for predicting slurry stability in preparation and transport.

ABSTRACT Screening is indispensable process, which is extensively used in coal separation on a global scale. In traditional screening, material stratification is difficult to achieve, which leads to a poor screening effect. In this study, balls are added under the elastic screen surface to increase the screen amplitude and promote the loose stratification of materials. The screen surface motion characteristics, the changes of the material layer on the screen, the material distribution characteristics under the screen, and the screening efficiency are studied by means of vibration tests, high-speed dynamic recording, and screening tests. The experimental results show that when 2-ball additional excitation is applied, the highest screening efficiency of 79.45% is reached, the elastic screen surface can produce a large amplitude of up to 24.77 mm, the screen surface deformation is larger, the material layer is looser, material migration is faster, and the screening effect is better. The main screening area of the material is the second sections of the screening surface, and the screening efficiency of fine particles is mainly affected by the screening efficiency of complex excitation screening. With the increase of the screening surface length, the screening effect of complex excitation elastic screening becomes better.

ABSTRACT Efficient separation of residual carbon and ash in coal gasification fine slag is of great significance for clean utilization of coal, resource conservation, and environmental protection. In this study, a novel corona charging approach was proposed to enhance particle charging and improve the electrostatic separation efficiency of coal gasification fine slag. A multiphysical model was established to investigate the coupling effects of the electrostatic field, gas flow field, and particle charging behavior. The results showed that, under the effect of positive DC corona on particle charging, the electric field voltage was positively correlated with the charge-to-mass ratio (CMR) of the particles. As the particle size increased, their charge amount increased, while the CMR decreased. The inlet gas velocity obviously affects the charging time of particles, resulting in a decrease in the average CMR with increasing gas velocity. Comparative experiments revealed that implementing corona charging promoted the decarbonization efficiency and carbon recovery efficiency (REC) by 17.99% and 23.66%, respectively, significantly improving the electrostatic separation of carbon and ash particles in coal gasification fine slag.

ABSTRACT Based on the multi-domain fractal theory, the distribution characteristics of each granularity level of coal particles during hydrophobic flocculation were analyzed. The fractal dimension of fine-grained increased from 1.07 to 1.33, indicating that the particle size distribution range was wide, and the internal difference was significant. The fractal dimension of middle-grained decreased from 2.71 to 2.03, showing that the particle size growth noticeable and the morphology of flocs tended to be regular. The fractal dimension of the coarse-grained changes slightly around 2.90, demonstrating that the flocs had a relatively stable spatial structure under the dynamic balance of fragmentation and reaggregation. By introducing the fractal dimension of each granularity level into the flocculation kinetic equation, the conservation relationship between the median particle size and the standard deviation of the floc was quantified, and the analysis of the particle distribution characteristics of the hydrophobic flocculation system at any time was realized.

ABSTRACT High-temperature coal tar pitch (HCTP) serves as a crucial precursor for high-quality carbon materials, while solid particle (SP) characteristics significantly influence the properties of the pitch. This study explores the compositional differences of SPs across various sizes to facilitate their effective separation. We employed ultrasonic graded centrifugation to isolate seven SP types of different sizes and analyzed their properties using SEM, SEM-EDS plane scanning, laser particle size analysis (LPSA), organic element analysis (EA), FT-IR, ICP-MS, and XRD. Our results reveal distinct variations in the SP distribution by particle size. As the particle size decreases, the proportion of particles in the 1–100 μm range decreases, while ultrafine particles (0.01–0.1 μm) become more prevalent. The carbon content in SPs initially increases and then decreases with smaller particle sizes, reaching a peak in medium-sized particles. Non-carbon impurities such as Si, S, Zn, Pb, Ca, Fe, and inorganic ash are concentrated in larger particles (SP1–SP2) and smaller particles (SP6–SP7). Notable inorganic compounds like PbS, ZnS, and FeS are found across all sizes, whereas SiO2 and CaCO3 are restricted to larger particles (SP1–SP2). Furthermore, smaller particles exhibit greater specific surface areas and pore volumes.