Clean Coal Ash Research Articles

Study on the differential effects of various hydrocarbon oil components on coal slime flotation performance

ABSTRACT To investigate the impact of different collectors on the surface forces of coal particles due to variations in their molecular structures and properties, this paper utilizes Materials Studio software to simulate a water-coal adsorption system. The aim is to explore the wetting behavior and mechanisms of different hydrocarbon oil components on coal surfaces. Through flotation experiments, the flotation efficiency and applicability of different hydrocarbon oils as collectors are evaluated. The influence of nine types of hydrocarbon oil collectors on the flotation performance of coal slime is examined, revealing the impact patterns of different hydrocarbon oil collectors on the hydrophobicity of coal samples. This provides a theoretical basis for the compounding of different collectors and the variability in flotation efficiency among various alkane collectors. The study found that n-tetradecane achieved a flotation yield of 70.88% at a pulp concentration of 80 g/L, while n-eicosane had the lowest clean coal ash content of 8.31%. XRD and contact angle analyses indicated that an appropriate increase in carbon chain length enhances flotation yield and reduces ash content, but excessively long carbon chains decrease selectivity, affecting the yield.

Particle Properties and Flotation Characteristics of Difficult-to-Float Lean Coal

The flotation effect of lean coal is crucial for its clean utilization. Therefore, the flotation characteristics of difficult-to-float lean coal were studied. The analysis results of the feed properties showed that the ash content of the feed was high and the particle size was very fine. The minerals in the gangue mainly included sericite, kaolinite, quartz, white mica, and other substances. After flotation, the functional groups of the coal particles in the tailings decreased, and the absorption peak intensity weakened. Furthermore, the results of multi-factor flotation experiments showed that the dosages of the collector and the frother were significant factors affecting the yield of clean coal. The clean coal yield gradually increased with an increase in the two factors. The ash content of the clean coal increased with an increase in the frother dosage. Within the range of feed concentrations used in this work, the feed concentration was not a significant factor affecting the clean coal’s yield and ash content. Prediction models for the clean coal yield and ash content were proposed. Under optimized experimental conditions, the clean coal yield and the flotation perfection index were 72.15% and 46.63%, respectively, indicating a good flotation effect.

Preparation of Bio-Based microemulsion collector and its flotation performance for coal slime

Cardanol polyoxyethylene ether (CPE) is a green bio-degradable surfactant. Herein, we used CPE as an emulsifier to prepare a new environmentally friendly and high-efficiency bio-based microemulsion collector (HE-BMC) for coal slime flotation. The phase behavior studies showed that the single-phase microemulsion (SPM) area proportion was the largest at the mass ratio of CPE-12 to n-pentanol of 1.2. The dilution integrity study results demonstrated that the microemulsion collector average particle size was stabilized at nearly 30 nm when the mass ratio of SACS to n-dodecane was greater than 6: 4, with water content higher than 20 %. Based on the above research, the relationship model between the microemulsion collector size and the component contents was constructed using the mixture design method. Consequently, the optimal formulation for HE-BMC was obtained and consisted of 24.75 % CPE-12, 20.62 % n-pentanol, 27.69 % n-dodecane, and 26.94 % water, with an average size of 25.83 nm. The physical properties study results elucidated that HE-BMC has good daily storage and transportation as well as better dispersibility in water. The particle size in water was 2.28 μm when the cumulative particle size distribution reached 90 %. The flotation test results revealed that the HE-BMC yielded 3.91 % more clean coal than n-dodecane while maintaining a similar clean coal ash content. However, the dosage of HE-BMC was only 41.67 % of that required for n-dodecane. Furthermore, long flame coal slime flotation utilizing HE-BMC could be achieved without the need for adding frother.

Investigating the Influence of Froth Image Attributes on Clean Coal Ash Content: A Novel Hybrid Model Employing Deep Learning and Computer Vision Techniques for Prediction Exploration

Investigating the Influence of Froth Image Attributes on Clean Coal Ash Content: A Novel Hybrid Model Employing Deep Learning and Computer Vision Techniques for Prediction Exploration

Modelling and comparison of fine coal beneficiation with water-only cyclone and spiral

ABSTRACT In this study, a three-level Box-Behnken design of experiments combined with response surface methodology used to investigate the effects of some parameters of a water-only cyclone (WOC), spiral and WOC-spiral circuit. The actual data collected from the tests were used to construct the empirical models representing clean coal ash and yield as process responses to the independent variables. The significance test of model fit for clean coal ash and yield were performed using analysis of variance (ANOVA). The results showed that ash content and yield of the clean coal models were significant. The results showed that WOC produced coal with lower ash content, the spiral products resulted in higher yields. It was observed that the WOC-spiral circuit achieved higher yield at equivalent ash contents.

Cleaning of fine-grained lignite by two-stage hydrophobic flocculation using different waste oils

ABSTRACT In this study, the conditions for obtaining clean coal from fine-grained lignite suspensions by two-stage hydrophobic flocculation using different waste oils were investigated. Waste vegetable oil, waste hydraulic oil and waste engine oil were chosen as bridging liquids for hydrophobic flocculation tests. During the studies, sodium silicate was used as the dispersant. Acetone was used at each stage to clean the floc obtained from the agglomeration process. The ash content (%) and combustible recoveries (CR, %) of the floc obtained at the end of each experiment were determined. In addition, contact angle (θ) and calorific values (kcal/kg) were measured and the results were evaluated in detail. At the end of the cleaning stages, low ash clean coal was obtained with a very high combustible recovery. In addition, it was observed that the calorific values increased considerably from 5128 to 5772,5558 to 6304 and 5447 to 5732 using waste vegetable oil, waste hydraulic oil and waste engine oil, respectively.

Study on the effect of flow field optimization on flotation efficiency

ABSTRACT With the help of computational fluid dynamics (CFD) methodology, the Eulerian model was used for numerical simulation of XFD type flotation machine. By altering the flow field pattern, analyzing the internal flow characteristics of the flotation machine in terms of velocity field and turbulivity, and optimizing its structure, the relationship between turbulence intensity and turbulent energy dissipation rate in the flotation machine is investigated. The findings demonstrate that altering the flow field pattern enhances the turbulence in the flotation machine’s mixing zone, enhances the velocity distribution of the three-phase fluid at the bottom of the flotation tank, and fosters bubble-particle contact, collision, and adhesion. This can successfully reduce the clean coal ash content.

Prediction of Clean Coal Ash Content in Coal Flotation through a Convergent Model Unifying Deep Learning and Likelihood Function, Incorporating Froth Velocity and Reagent Dosage Parameters

This study successfully achieved high-precision detection of the clean coal ash content in the coal froth flotation domain by integrating deep learning with the likelihood function. Methodologically, a novel data processing and prediction framework was established by combining a deep learning Keras neural network with the likelihood function from probability statistics. The SIFT algorithm was utilized to extract key feature points and descriptors from the images, and keypoint matching and mean-shift clustering algorithms were employed to accurately obtain information on foam motion trajectories and velocities. For parameter optimization, the maximum likelihood estimation was applied to find the optimal parameter estimates of the likelihood function, ensuring enhanced model accuracy. By incorporating the optimized likelihood function parameters into the Keras deep neural network, an efficient prediction model was constructed for the dosage of flotation reagents, froth velocity, and clean coal ash content. The model’s evaluation involved six performance metrics. The experimental results were highly significant, with R2 at 0.99997%, RMSE at 0.04458%, MAE at 0.00170%, MAPE at 0.02329%, RRSE at 0.00994%, and MAAPE at 0.00067%.

Deep correlation and precise prediction between static features of froth images and clean coal ash content in coal flotation: An investigation based on deep learning and maximum likelihood estimation

This research combines deep learning with sophisticated likelihood analysis to achieve precise detection of clean coal ash content in the domain of froth flotation through image acquisition and processing. The utilization of maximum likelihood estimation method establishes a robust correlation between static features of froth images and clean coal ash content, while the application of the BFGS algorithm efficiently searches for optimal parameter estimates. Furthermore, a deep neural network model is constructed using Keras to accommodate multi-feature and hybrid data inputs. The model's performance is rigorously evaluated using metrics such as mean squared error, mean absolute error, and root mean squared error. Experimental results demonstrate remarkable accuracy, with the mean squared error, mean absolute error, and root mean squared error on the test set being 0.003475 %, 0.044740 %, and 0.044585 %, respectively.

Study on dissociation characteristics and enhanced gravity separation of coking coal middlings

ABSTRACT This work innovatively introduced EGS technology into the re-separation process of coking coal middlings based on the dissociation characteristics. The EGS separation characteristics were compared with conventional FF and a novel pre-desliming EGS technology was proposed to achieve clean and efficient separation of coking coal middlings. The density composition and washability of the coking coal middlings crushed under the upper limit size of 6, 3, 1, and 0.5 mm show that the dissociation of the coking coal middlings has been basically completed when crushing to −0.5 mm. The clean coal ash can be reduced to 13.37% with a yield of 42.46% through the pre-desliming EGS technology. The optimal combustible recovery of 71.84% and ash removal rate of 81.36% can be obtained by EGS and pre-desliming EGS methods, respectively, which indicates the superiority of EGS compared to conventional FF. The pre-desliming EGS technology has already demonstrated its great potential in the re-separation of coking coal middlings with the advantages of low-cost, no-pollution and high-efficiency.

Separation performance of –0.5 mm fine coal in enhanced gravity field before and after desliming

ABSTRACT This study focused on the separation performance of a typical high-ash coal with high-mud content in the enhanced gravity field from the viewpoint of desliming. After necessity analysis of desliming, the EGS results of fine coal before and after desliming were examined. The EGS separation indicators and products were analyzed, and its separation characteristics were compared with FF and STS. The EGS results are unsatisfactory without desliming, and the sorting effect of −0.045 mm PS is inferior to other PSs. After desliming, the EGS performance of fine coal has been improved obviously. The optimal η a of 97.93%, η t of 85.99%, η c of 90.50%, and η d of 34.67% can be obtained through adjusting RF and RWP. In terms of deashing effect, FF > EGS > STS, but EGS can obtain the lowest clean coal ash of 3.02%, which reflects its advantages of preparing ultra-low ash coal. In terms of desulfurization effect, EGS > STS > FF. EGS is a clean and efficient method on fine coal deashing and desulfurization, and pre-desliming can significantly improve its separation performance. Pre-desliming EGS technology provides a new way for the sorting of fine coal with high-mud content.

Studies on low-grade coking coal characterisation, flotation response and process optimisation

ABSTRACT The work illustrates the physico-chemical, petrographic characteristics and flotation response of low-grade oxidized coking coal containing 39.5% ash. The maceral composition, surface oxidation, and particle liberation are the factors that affect coal flotation. The oxidized coal requires more collectors than the freshly ground coal. The flotation process modeling and optimization of −0.5 mm coal fraction was carried out using response methodology and central composite rotatable design (CCRD). The diesel, MIBC, and sodium hexametaphosphate are used as collectors, frothers, and depressants to maximize the coal grade, yield, and combustible recovery. At an optimum dosage of 1.35 kg/ton collector, 0.2 kg/ton frother, and 0.5 kg/ton depressant, it is possible to achieve 11.3% ash-clean coal with a 50.72% yield from 39% feed ash coal. The ash, yield, and combustible recovery model prediction matched well with the experimental results. The R2 of the ash, yield and combustible recovery model are 0.9676, 0.9662, and 0.9692, respectively. The work highlights that Indian coal can upgrade for metallurgical use using a flotation process.

Application of a water injection hydrocyclone on fine coal enhanced gravity separation

ABSTRACT This study introduced Krebs hydrocyclone into fine coal EGS process, examined the ultrafine classification effect of Krebs hydrocyclone by single-factor tests and orthogonal tests, and evaluated the fine coal EGS effect after ultrafine classification. Besides, the flow field characteristics in Krebs hydrocyclone were explored by simulation. The optimal grading efficiency of the verification test is 91.32%, and the content of ultrafine particles can be reduced to 1.01%, which prove the excellent ultrafine classification effect of Krebs hydrocyclone. The optimal combustible recovery and ash removal rate are 94.29% and 98.52%, respectively, and when the clean coal ash drops below 10%, the combustible recovery is more than 80%, which reveal that the sorting indexes of fine coal EGS after ultrafine classification are much better than that of unclassified coal. Both the static pressure and velocity in Krebs hydrocyclone have good symmetry and certain regularity. Due to the use of water as a separation medium, the introduction of Krebs hydrocyclone in the fine coal EGS process provides an effective and prospective approach for the industrial application of enhanced gravity separators in the fine coal washing process, especially in the face of increasingly serious environmental problems.

Recovery of clean coking coal from difficult-to-wash low volatile coking coal fines of Jharia coalfield by multi gravity separator

ABSTRACT Multi-gravity separator (MGS) is a centrifugal gravity separator deployed for beneficiation of fine particles with relatively low concentration. It is for the first time that a statistical tool was engaged to evaluate effects of the most influencing process variables and their actual impact upon the performance of MGS with respect to its potential to clean the difficult-to-wash low volatile coking (LVC) coal fines. Characteristics of LVC coal sample were analyzed and discussed in terms of physical properties, petrographic composition, washability, XRD and SEM analysis. Three different feed sizes such as – 500 μm, – 250 μm and – 150 μm were used for assessing the separation mechanism and efficacy of MGS along with three different process variables such as drum speed, shaking amplitude and wash water rate to study and ascertain the most efficient experimental design for obtaining optimal result. Results revealed that drum speed and feed size turned out to be most significant parameters for reduction of ash concentration. In design of experiments, clean coal ash, combustible recovery and separation efficiency were considered as response functions. Material balance for MGS unraveled that about 74% clean coal produced with 10% ash reduction from the feed ash of 32.8% could be achieved in single stage, in optimized process conditions.

Interactions between Mg2+-doped kaolinite and coal: Insights from DFT calculation and flotation

In order to explore the micro-influence mechanism of clay surface/interface property differences on coal slime flotation based on impurity defects, the influence mechanism of Mg2+ doping on the microscopic interactions between particles of kaolinite and coal is preliminarily discussed by using DFT (density functional theory) and flotation. DFT results showed that different coal structural units adsorption on Mg(II)_K (Mg2+-doped kaolinite) surface mainly through electrostatic attraction, and the coal structural units can be stably adsorbed on Mg(II)_K surface in the case of competitive adsorption with H2O. When coal structural units and H2O competed for adsorption on Mg(II)_K surface, H2O promoted the adsorption of coal structural units on Mg(II)_K surface. Flotation results showed that with the increase of kaolinite mass percentage in mixed minerals, the clean coal yield significantly decreased, and the clean coal ash firstly decreased and then increased. The influence mechanism of Mg2+ doping on the interaction between kaolinite and coal was that Mg2+ doping significantly enhanced the interaction between Mg(II)_K surface and coal structural unit. The results revealed the complex interaction between fine particles in coal slime, paving the way for its efficient selective separation.

Study on the modification of the coarse coal-slime separation process in Lv-jiatuo coal preparation plant

ABSTRACT A modification coarse coal-slime separation process used three-stage cone water-only cyclones (TWOCs) as the main separating equipment was designed and evaluated for Lv-jiatuo coking-coal preparation plant. Laboratory experiment was performed to guide the parameters determination of the industrialness TWOC. The industrialess TWOC is expanded five times according to the equal proportion of the laboratory TWOC. The stability of the modification system is obviously higher than that of the original system, the optimal parameters combination of the industrialness TWOC was determined as 500 mm cylinder height, 225 mm vortex finder, 267 mm insertion-depth of the vortex finder and 0.08 MPa feed pressure. After the modification, the clean-coal ash decreases from about 13.00% to 11.45%, the separation density (δ50) and possibility deviation (EP) value of the TWOC are 1.49 and 0.085 g/cm3, respectively. Plant’s yearly profit increases 13.54 million Chinese yuan (CNY), the static investment recovery period is 0.22 years.

Studies on Washability Characteristics of Low-Volatile Indian Coking Coal by Differential Crushing

The effect of differential crushing on liberation characteristics has been studied for a low volatile coking coal of Indian origin through washability studies. Two parameters, namely “Index of Washability” (IW) and “Near Gravity Material Index” (NGMI), are used to describe the ease of washability. The ROM Coal is crushed to four different top sizes namely, 75mm, 25mm, 13mm and 6mm.On the basis of calculated IW it is observed that relative ease of washability increases with decrease in top size. From calculated IW values it may be said that this coal can be economically beneficiated using gravity process after crushing to -6mm size. From the calculated NGMI values, the critical specific gravities have been estimated and the values for crushing to -75 mm, -25mm, -13mm and -6 mm are 1.65, 1.68, 1.53 and 1.58 respectively. These critical specific gravity values suggest the separation at this specific gravity range is most difficult task using gravity methods. From NGMI analysis, it may be said that the NGMI values for coals crushed to -25 mm & -6mm are identical (≈ 0.18) at 17% clean coal ash content. This suggests that with similar degree of difficulty, clean coal of 17% ash can be produced from these two different crushing sizes. In order to increase the yield for the clean coal of 17% ash, the decision on blending these two size coals may need to be taken.

Alkanes-esters mixed collector enhanced low rank coal flotation: Interfacial interaction between oil drop and coal particle

The interaction between oil collector drop and coal particle is important for low-rank coal (LRC) flotation. This paper investigated such interactions using dodecane (D), ethyl esters (E) and dodecane-esters mixed collector (MC). Measurements of oil drop-coal induction time and detachment force were conducted at a mesoscopic scale. The micro adsorption mechanism of oil collectors was revealed by wetting heats and FTIR measurements. Flotation results showed MC, especially dodecane-ethyl laurate, obtained high yield and low ash clean coal. There was a shorter induction time and higher adhesion strength between LRC particle and MC drop. The wetting heat of MC was greater than the sum of wetting heat of the two single collectors. FTIR analysis indicated that D validly adsorbed to the methyl or aromatic groups, and E bonded with the oxygen-containing groups. The macro flotation results was well interpreted by the interfacial interaction of collector-coal at the mesoscopic and micro scales.

Study on deashing and desulphurization of coal with heavy medium in enhanced gravity field

ABSTRACT This study carried out component sulfur composition analysis, electron probe microscopic analysis, and particle size and density composition analysis of coal samples from a coal preparation plant in Liupanshui. The influence of various factors on the indexes of clean coal products under different separation medium conditions by enhanced gravity separation technology, including water medium (WM), magnet powder suspension (MPS), and zinc chloride solution (ZCS), is discussed. The results show that the addition of MPS or ZCS has an obvious improvement on coal deashing and desulfurization compared with the WM separation, especially the separation effect of ZCS, which is better than that of MPS because of better uniformity and stability of ZCS. The addition of MPS or ZCS can help the materials stratify strictly according to the density to enhance the sorting function. The clean coal ash and sulfur content are reduced to 13.24% and 2.51%, while the combustible recovery and desulfurization efficiency are up to 71.46% and 49.27%, respectively, under the optimal condition.

Integrated process for coal chemical demineralization and spent caustic regeneration- A pilot scale study

Indian coal washing plants face tremendous pressure in maintaining clean coal yield and handling the rejects. Conventional coal washing plants generate clean coal with 15–18% ash content and 35–50% yield by several physical beneficiation techniques. Handling and disposal of the rest of 50% reject is an environmental concern and hence, alternate processes for utilization of high-ash washery rejects are of high importance. In this work, the chemical demineralization process is explored at a pilot scale to produce the low ash clean coal from different washery rejects. 44.6%–67.8% demineralization is achieved with the single-stage alkali-acid leaching process and 68.4%–78.3% by multi-stage leaching at optimum operating conditions. However, the economics of the process depends on the regeneration of the spent alkali solution. Therefore, a two-step methodology for spent-alkali regeneration is developed. In the first step, carbonation of spent-alkali with CO2 separates almost >95% of the silica and alumina impurities. In the second step, 89.2% caustic soda is recovered by causticization using quick lime.