Coal Dewatering Research Articles

Fluidization characteristics of loaded vibrating fluidized bed and dewatering and deashing effect of moist fine-grained coal

ABSTRACT The influence of a thermal vibrating fluidized bed on the dewatering and deashing effect of moist fine-grained coal was investigated by digital image processing and signal analysis methods. Comparative analysis results of the pressure signals of a loaded vibrating fluidized bed indicated that high or low gas velocity and strong or weak vibration conditions easily caused the formation of numerous irregular bubbles and contributed to violent fluctuations in the bed. An interaction between gas velocity and vibration energy was found, with vibration energy being the dominant factor influencing the bubble behavior at low gas velocities. Moreover, at high gas velocities, the advantages arising from vibrations were weakened. Under the condition of f = 20 Hz, A = 2 mm, v = 18 cm⋅s−1, the contact efficiency between the gas – solid two phases was higher, and the pressure fluctuation of the bed became more stable. Under this condition, the ash content of clean coal and the moisture removal rate were 11.76% and 83.54%, respectively. Finally, comparison and analysis of the influence of different parameters on the calorific value of clean coal revealed that the influence of each parameter on heat generation of the selected product was found to be in the following order: f > A > V > T.

Моделирование процесса вибрационного обезвоживания угольной мелочи в технологических системах гидромеханизированных шахт

Introduction. The article discusses the issues of modeling various variants of flow line tunneling technologies based on an analysis of the structure of the tunneling cycle. Materials and methods. As research methods, the authors used: analysis of the structures of the tunneling cycle of continuous mining technologies, mathematical modeling of processes and operations, and industrial testing of options for implementing the proposed technological tunneling systems. Results. Obtained during the implementation of a mathematical model of a high-frequency, low-amplitude process of vibration dehydration of mineral raw materials of small fractions, using fine coal (sludge) as an example, made it possible to determine the optimal parameters of the kinematics of the working body in accordance with the parameters of the source material. Innovative solutions have been proposed for the design of vibration dewatering devices with mechanical and hydraulic high-frequency flexibly adjustable drives. Conclusion. The article summarizes the results of research in the field of modeling and optimization of fine coal dewatering parameters in technological systems of mining enterprises. Options for implementing innovative technical devices for high-frequency, low-amplitude effects on the source material are proposed to increase the efficiency of dehydration. Resume. An analysis of existing means and methods for dewatering rock mass has shown that in relation to the technology of hydromechanized coal mining with its underground dewatering and recycling of process water, the most promising is the use of high-frequency vibration dewatering devices with a mechanical or hydraulic drive. The study of the kinematics of movement of the dewatered rock mass made it possible to determine the optimal values of vibration parameters

Hydrothermal dewatering of low-grade coal: Product evaluation and primary component analysis of ash deposition

The hydrothermal dewatering (HTD) process was carried out using 16 coal samples obtained from several regions in Indonesia. This research aims to identify the dominant parameters that influence ash deposition during coal combustion in a boiler or gasifier due to the HTD process. This research was conducted due to the lack of clear and comprehensive information regarding this issue. Therefore, to understand the effect of HTD on ash deposition, an analysis of the chemical composition of ash and the ash melting temperature (AFT) was carried out. To verify the data obtained from the experimental analysis, statistical methods such as paired sample t-test and primary component analysis were applied to obtain the dominant parameters influencing ash deposition due to HTD. Eight parameters, namely SiO2, Fe2O3, slagging viscosity index (SR), Babcock index (Rs), initial deformation temperature, softening temperature, hemispherical temperature, and fluid temperature under oxidative conditions, have the greatest influence on ash deposition due to the HTD process. Based on the average values of SR and Rs, raw coal and processed coal samples have the same ash deposition trend. On the other hand, based on AFT under oxidation conditions, processed coal has a higher AFT, indicating that the tendency for ash deposition is lower than raw coal. Therefore, the HTD process can be used to improve the quality of low-grade coal. As an implication, low-grade coal, which has not been widely utilized in Indonesia, due to several constraints regarding its characteristics, through the HTD process can be optimized where coal utilization is a bridge towards the use of green energy which is being intensively pursued.

Synergistic improvement of the fine size coal dewatering performance by using binary surfactant mixtures

In this study, gemini surfactants and binary surfactant mixtures were used in order to enhance the dewatering performance of fine size coal particles. Compared to three single gemini surfactants, binary surfactant mixtures presented a better dewatering performance of fine size coal particles, especially the binary surfactant mixture composed of Gemini − 1 surfactant and sodium dodecyl benzene sulfonate (SDBS). Meanwhile, the binary surfactant mixture composed of Gemini − 1 surfactant and sodium dodecyl sulfonate (SDS) was further used in the experimental test as a comparison and showed better dewatering performance than that of the binary surfactant mixture composed of Gemini − 1 surfactant and SDBS. The lowest cake moisture content (20.72 %) was gained when the dosage of Gemini − 1 surfactant and SDS was 400 g/t at the molar ratio of 6 to 7. Surface functional groups of the prepared coal samples were characterized by a Fourier transform infrared spectroscopy (FTIR). Wetting heat values of coal samples before and after adsorbing surfactants were measured by a microcalorimeter. The adsorption capacity of surfactant on coal surface was investigated for studying the difference between three single surfactants and the binary surfactant mixture. Intermolecular interaction calculation and thermodynamics of micellization for the judgment of synergistic effect indicated that the synergistic interaction was formed in the binary surfactant mixture and the binary surfactant mixture of Gemini − 1 surfactant and SDS showed a stronger synergistic interaction. A possible hydrophobic mechanism was supposed that the water molecules were displaced by the binary surfactant mixture for the improvement of hydrophobicity of coal particle surface.

Solvent recovery from solvent-fine coal slurries by filtration and steam stripping

Dewatering of fine coal is a significant industrial challenge with economic and environmental implications. Due to the lack of suitable dewatering technologies, fine coal particles are often discarded to waste impoundments, leading to substantial loss of valuable natural resources while creating environmental problems. The hydrophobic-hydrophilic separation (HHS) process is a unique solution to this problem. In this process, a recyclable solvent is used to simultaneously remove inorganic impurities (ash) and water from a run-of-mine fine coal slurry. A small amount of recyclable oil (or solvent) is added to a fine coal slurry so that the solvent can spontaneously displace the water from the surface of coal particles. The spent solvent is subsequently recovered and recycled in a closed loop. Here, we report the results obtained using two different solvents, i.e., pentane and hexane, to de-ash and dewater ultrafine coal and recover the spent solvent by filtration, followed by steam stripping. Most of the spent solvent can be recovered during the filtration step at 20 psig N₂ and at a 60 s filtration time. The residual solvent left in the cake was then recovered using steam under different conditions. The results showed that the residual solvent concentration could be reduced to <1,400 ppm after 10 s of steam stripping at 150°C and 15 psig.

Role of sodium dodecyl benzene sulfonate in enhancing coal dewatering: Experiments and theoretical calculations

The surface of low-rank coal has many oxygen functionalities, which leads to poor coal slime dehydration. To improve the effect of coal slime dewatering, sodium dodecyl benzene sulfonate (SDBS) was used as accelerator in the coal slime dehydration process. In addition, the mechanism of acceleration was studied using X-ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulations. The results of dehydration experiments showed that adding a certain amount of SDBS into the slurry water was conducive to promoting the removal of water. When the concentration of the SDBS solution was 0.06 g/L, the water content of the filter cake decreased from an initial value of 59.98% to 54.55%. XPS measurements and MD simulations show that the polar groups (sulfonic acid) of SDBS are adsorbed on the oxygen-containing functional groups on the coal surface, thus, exposing the nonpolar groups (alkyl chains) of the molecule to the solution. The calculation of the self-diffusion coefficient (D) of water molecules in the simulated system indicate that the presence of SDBS improves the mobility of water at the coal surface, which is helpful in improving the loss of water from the coal surface, thus, improving its hydrophobicity. Crucially, the results of the MD simulations are consistent with those from experiment. Highlights Addition of a certain amount of SDBS helps to remove moisture from the coal slime. Oxygen-containing functional groups on the coal surface are effectively covered by SDBS. The interaction mechanism of SDBS at coal/water interface was studied by combining experiments and theoretical calculations.

Comparative filtration and dewatering behavior of vitrinite and inertinite of bituminous coal: Experiment and simulation study

The filtration and dewatering of fine clean coal not only ensure industrial water recycle in coal washing plant, but also reduce the moisture of coal product in order to meet the requirements of combustion or coking industry. Fine clean coal is mainly composed by organic matter, and the property difference of different organic matter determines the filtration and dewatering behavior. In this investigation, vitrinite and inertinite were separated from a clean bituminous coal, and the comparative filtration and dewatering behavior of vitrinite and inertinite were conducted. The results showed that inertinite has lower dewatering rate and higher filter cake moisture than vitrinite. The analysis of filter cake structure showed that inertinite particle is easier to be broken into small particles due to the difference of mechanical properties, thus forming more compact filter cake than vitrinite. The analysis of particle surface properties showed that vitrinite is more hydrophobic than inertinite, which makes water easier drained from filter cake. The simulation study showed that the structure of inertinite is more porous than that of vitrinite, and the interaction between inertinite and water is stronger than that between vitrinite and water. This study provides a theoretical basis for improving coal dewatering by selectively improving coal maceral hydrophobicity.

Effect of the degree of polymerization of nonylphenol polyoxyethylene ether on the dewatering of low-rank coal

Effect of the degree of polymerization of nonylphenol polyoxyethylene ether on the dewatering of low-rank coal

In situ synthesis of a multifunctional polymer with a stable core-shell structure for effective dewatering

A multifunctional polymer that was magnetic and had a high water absorption ability was prepared via synthesis of magnetite nanoparticles followed by surface modification and polymerization. The structure and morphology of the multifunctional polymer were characterized by X-ray diffractometer (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive X-ray spectroscope (EDS). The magnetite content and the magnetic property of the multifunctional polymer were analyzed by thermogravimetric analysis (TGA) and superconducting quantum interference device magnetometer (SQUID), respectively. The results suggested that the multifunctional polymer had a stable core-shell structure, a striking temperature-responsive property, and stable magnetic property. Further work was carried out to assess the performance of this multifunctional polymer at a particle size of 0.3–0.45 mm for dewatering of fine coal (<0.25 mm in size). It was found that the multifunctional polymer could give fast kinetics of dewatering and after each cycle, the polymer could be readily separated by simple magnetic separation and then regenerated and reused in next cycle while maintaining the same dewatering performance.

Synergistic effects of surfactant-flocculant mixtures on ultrafine coal dewatering and their linkage with interfacial chemistry

Flocculants are widely used in ultrafine coal dewatering to improve the particles settling rate. However, water entraps inside flocs that consequently increase generated filter cake moisture. In this paper, we report the effectiveness of a chemically enhanced approach to effectively increase particles settling rate and reducing filter cake moisture by taking advantage of the synergistic effect of dewatering chemicals. The effect of the dewatering chemicals on centrifugal dewatering performance, filter cake structure were studied. Applied anionic surfactant did not show a significant effect on dewatering rate and the filter cake structure, but it reduced solid recovery from 89% to 70% and filter cake moisture 19%–13% through strong attribution to decrease in liquid phase surface tension. However, cationic surfactant revealed a slight expansion in solid recovery to 94%, dewatering rate, and the filter cake permeability while there was a decrease in the filter cake moisture to 15% due to the increased coal particles hydrophobicity. Anionic flocculant also improved dewatering rate and filter cake permeability with an increase in solid recovery to 96%, but with the sacrifice of increased filter cake moisture to 24%. Mixed anionic surfactant/flocculant did not show a positive effect on dewatering parameters. However, cationic surfactant-flocculant mixtures led to a higher dewatering rate and solid recovery of 97% with lower moisture (22%) in comparison with single flocculant condition. X-ray Computed Tomography (XCT) results confirmed improved filter cake porosity in the cationic surfactant/flocculant mixture conditions. In agglomerate structure studies, flocculation and agglomeration of ultrafine particles with the cationic surfactant, flocculant, and mixed flocculant-cationic surfactant were observed. Nevertheless, the structure of the agglomerates in the mixed anionic surfactant/flocculant condition was loosened. The financial analysis confirmed using cationic surfactant or its mixture with the flocculant has an economic benefit in comparison with single flocculant condition.

Highly crosslinked 3-D hydrogels based on graphene oxide for enhanced remediation of multi contaminant wastewater

Hydrogels are three dimensional materials with modifying surface which containing more functional groups and it is used in many applications such as hygienic products, agriculture, drug delivery systems, sealing, coal dewatering, food additives and pharmaceuticals. Mostly, it is implemented in biomedical applications like tissue engineering and regenerative medicines, diagnostics, wound dressing, separation of biomolecules or cells and barrier materials to regulate biological adhesions and in biosensors. Herein we report the preparation of aminated guar gum/graphene oxide (AGG/GO) hydrogel using borax as a crosslinker, which has a high surface area with a crosslinked structure for enhanced removal of dyes and heavy metals. The chemical moieties, morphological and structural properties of the AGG/GO hydrogel were examined by Fourier Transform Infrared Spectrometer (FTIR), Scanning Electron Microscope (SEM), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analysis respectively. The swelling properties of hydrogels were demonstrated, followed by viscoelastic studies using rheological analysis found that the material is stable up to an applied frequency of 10 Hz. Interestingly, removal efficiency of the AGG/GO hydrogels for Cu(II), Malachite green, Methylene blue and Rhodamine B dyes were found to be 88, 98, 90, and 75% respectively from aqueous solutions.

Optimization of surfactant-aided coarse coal dewatering process in a pilot-scale centrifuge

Water is a scarce and critical resource for the mineral processing industries and the recycling of the water recovered from different unit operations is possibly the best way to ensure the continued operation of the plants throughout the year. Moreover, the reduction in the product moisture content reduces the cost of transportation and drastically reduces the handling problems. In the present work, the dewatering efficiency of the coarse coal (−13 + 0.5 mm) in a pilot-scale vibratory basket centrifuge was measured and enhanced using surfactants as the dewatering aids, followed by the optimization using statistical analysis. The experiments were conducted considering three variables, i.e. feed rate, feed moisture content and surfactant concentration, using a full factorial design of the experiments. Experimental results were analysed with the help of a statistical software package (Statistica). Regression equations were developed to show the effect of each parameter and their interactions on the residual moisture content. The statistical model developed for the dewatering of coarse coal, using the three variables, was tested and was found to predict the moisture content of product coal with an average error of 5%.

Influence of surfactant for improving dewatering of brown coal: A comparative experimental and MD simulation study

Abstract Experimental method and molecular dynamics (MD) simulations were used to investigate the filtration dewatering process of brown coal in the presence of the surfactant TRITON X-100 (TX-100). A significant reduction in filter cake moisture content was observed upon addition of TX-100 in the dewatering experiments. It was observed that a narrow TX-100 concentration range of below the critical micelle concentration (CMC) was best for dewatering. The enhancement in filtration dewatering characteristics could be attributed to the wetting characteristic changes of the brown coal surface caused by surfactant adsorption, as indicated by measurement of contact angles. Monolayer adsorption of TX-100 at the lignite surface was investigated by MD simulations. The TX-100 molecules repelled water molecules near the coal surface and adsorbed at the water-lignite interface with the ethoxylate closer to the coal surface than the octylphenol. The mobility of water molecules was enhanced in presence of TX-100 according to the results of mean square displacement (MSD) and diffusion coefficient. It was inferred that adsorption of TX-100 resulted in a more hydrophobic brown coal surface, in agreement with the dewatering and contact angle experiments.

Hydrothermal dewatering of low-rank coals: Influence on the properties and combustion characteristics of the solid products

The presence of increased moisture content, low energy density and maximum spontaneous combustion tendency has raised serious environmental issues, which are obstacles to large scale utilization of coals. Hydrothermal dewatering (HTD) is a promising method for upgrading low rank coals (LRCs). The influences of HTD, executed at different temperatures on solid product yield, removal rate of elements, organics and inorganics, and combustion characteristics in LRCs were studied. HTD treatment of LRCs was carried out in 2 L cylindrical autoclave at 200–300 °C for 1 h. For upgraded coals, the inherent moisture and oxygen content decreased significantly while fixed carbon content and calorific value increased. FTIR results indicate the conversion of LRCs near to high-rank coals (HRCs). The organic matter was removed due to loss of Methylene, Methyl groups and O-containing functional groups, whereas inorganic matter was removed mainly in the forms of Fe and Ca-containing minerals. The upgraded coals had higher ignition and burnout temperatures, while their combustion was shifted and delayed toward higher temperature zone. Activation energy of treated coals increased in ignition stage while decreased in combustion segment. Prominent changes were found in coal structure, composition, rank, and combustion characteristics at HTD temperature of 300 °C.

The effect of froth on the dewatering of coals – An oscillatory rheology study

Dewatering of fine coal flotation products is discouraged by the presence of stable coal froth, which is becoming a common problem in coal preparation plants, however, the underpinning mechanism is still unclear. In this study, the dewatering behaviours of fine coal flotation products in both thickening and filtration were investigated and compared with those of coal slurry under the same condition. The mechanism that how coal froth influenced dewatering was investigated by analysing the froth properties using oscillatory rheology in conjunction with the characterization of particle arrangements on the air-water interface using Scanning Electron Microscopy (SEM). It was found that, in the presence of air, particle interactions in coal froth were stronger than those in coal slurry, which was caused by the capillary attractive force between particles on the air-water interface. In addition, particles in coal froth were arranged regularly, while particles in coal slurry were distributed randomly. Strong particle interactions and well organised structures in coal froth made the capillary radii smaller, and as a result, a large amount of froth stabilized on top of water during settling and the final moisture of filter cake was high in filtration.

Ultrafine coal flotation and dewatering: Selecting the surfactants of proper hydrophilic–lipophilic balance (HLB)

ABSTRACT Fine and ultrafine coal (−200 µm) enrichment and its further dewatering processes are more difficult than that of coarser sizes. Utilization of this size fraction, however, is inevitable owing to economic and environmental enforcements. Chemical reagents are widely used in fine coal dewatering to achieve lower cake moistures. Surfactants of the same structures are also used effectively in coal flotation within preparation and coal washing processes. These surfactants contain hydrophilic and lipophilic groups, the ratio of which is known as hydrophilic–lipophilic balance (HLB). Flotation separation efficiency and dewatering performance of hard bituminous coal slimes as well as water recovery characteristics and related entrainment degree during the flotation were investigated using eight various nonionic surfactants of different HLB values. The main motivation of the study is to suggest proper reagent properties by which highest efficiency in both flotation and dewatering can be achieved. This can result in significant economic advantages for industrial processes and also reduce the environmental disadvantages of using chemicals. The flotation separation efficiency of the most lipophilic surfactants (lower HLB) and conventional oily collectors were found to be the highest, while the surfactants with moderate HLB (~10) showed the best filtration performance.

Evaluation of Chemical Reagents to Enhance the Dewatering of Fine Coal

ABSTRACTCoal dewatering of fine coal is one of the major challenges faced by the coal preparation plants. The plant studied in this research is currently producing a fine coal product with 28% moisture and is required to reduce it to below 17% before this fine stream is blended with rest of the clean coal streams. A lot of dewatering aids such as surfactants, flocculants, and superabsorbent polymers are available on the market to enhance the dewatering process. The research was designed to use various dewatering aids to reduce the moisture content of this fine product without decreasing the production rate. Several commercially available chemical reagents were used to enhance the dewatering of this coal product. These reagents were selected in such a way that they could be grouped into different categories depending on their action. The results showed that the surface tension reducing reagents (STR) have a higher capability of moisture reduction than the coal hydrophobicity modifying (CHM) reagents and commonly used in filtration flocculants. Super absorbing polymers used in the dewatering of fine coal were shown to outperform all the other reagents and seem to be suited for this plant dewatering scenario. A cost-benefit analysis is required to make necessary plant modifications if they are to be used there, however, this was not in the scope of this project.

Limit Moisture Content of Coal Concentrate Produced with Industrial Drainers

The process of coal suspension dewatering in centrifuges and pneumatic drainage in vacuum filters and filter presses is theoretically studied. From the condition of equal centrifugal forces and surface tension applied to liquid in a granular layer of the working element of the centrifuge bowl, the analytical relation is obtained to calculate residual concentration of liquid in the treated layer. It is shown that calculation results obtained using the relation, rated data and specifications of industrial drainers agree well. With regard to the equality between the kinetic energy applied by filtration flow in the granular layer to the liquid film in the granules and the work to overcome surface tension forces that keep the film on the surface of the granules, the analytical relation is obtained to calculate residual concentration of a liquid in the layer under pneumatic drainage. The estimates prove realistic nature of the results obtained with the latter relation as well as their agreement with the test and rated data of industrial vacuum filters and filter presses.

Comparative study of low-temperature pyrolysis and solvent treatment on upgrading and hydro-liquefaction of brown coal

Low-temperature pyrolysis (LTP) and solvent treatment (Sol-T) of Yunnan brown coal were conducted for purpose of comparing their effects on upgrading and hydro-liquefaction. Sol-T is effective in both dewatering and deoxygenation of the brown coal. LTP is also effective in dewatering but less effective in deoxygenation, and more extensive cross-linking occurred during LTP than in Sol-T. Sol-T at mild temperatures (less than 200°C) enhances coal conversion and oil yield during hydro-liquefaction, while treatment at above 250°C lowers coal conversion and oil yield. LTP of brown coal is definitely detrimental to its hydro-liquefaction, as both conversion and oil yield are significantly reduced. Thus, Sol-T at mild temperatures is more preferable for upgrading brown coals prior to their use in hydro-liquefaction.

No.29 穏和な溶剤処理による褐炭、泥炭、バイオマスの脱水・改質(研究発表)

No.29 穏和な溶剤処理による褐炭、泥炭、バイオマスの脱水・改質(研究発表)