Coal Separation Research Articles

Performance optimization and parametric evaluation of coal deashing and desulfurization in a heavy-medium enhanced gravity field

ABSTRACT High-efficiency deashing and desulfurization of fine coal is an inevitable trend in the comprehensive utilization of coal resources. This work introducing heavy-medium into the enhanced gravity field to examine the effect of each parameter on the performance of fine coal separation. On this basis, the Response Surface Methodology (RSM) was conducted to study the influential significance of parameters, parametric interactions, and performance optimization of fine coal separation in the heavy-medium enhanced gravity field. The feed dosage and heavy-medium density influence the separation indexes obviously by changing the sorting environment, while the rotational frequency and recoil water pressure affect the separation effect apparently by adjusting the force on particles. The performance optimization results showed that the desired separation indexes – ηt of 81.11%, ηa of 80.00%, β of 44.93%, and λ of 44.76% can be obtained under the optimal combination of parameter levels – M of 27.23 g, ρ of 1.4 g/cm3, f of 30 Hz, and P of 0.03 Mpa. The verification experiments were carried out and the results were consistent with the results of performance optimization. The introduction of heavy-medium provides a new efficient way for the deashing and desulfurization of fine-grained high-sulfur coal in the enhanced gravity field.

Effective Separation of High-Ash Fine Coal Using Water Containing Positively Charged Nanobubbles and Polyaluminum Chloride.

The coal industry is facing the challenge of treating high-ash fine coal. In this study, we proposed an effective method to handle high-ash fine coal using water containing positively charged nanobubbles (PCNBs) and polyaluminum chloride (PAC). For comparison, normal nanobubble (NB) water was tested in parallel. Flotation results of a modeled high-ash fine coal showed that compared to the use of NBs alone, an enhanced combustible recovery with a simultaneous reduction in ash recovery was obtained when using water containing PCNBs and PAC. Particle size distribution together with particle video microscopy (PVM) and the degree of entrainment analysis were conducted to understand the underpinning mechanism. It was found that the presence of PCNBs intensified the aggregation of fine coal particles, which accounted for the boosted combustible recovery. It was interesting that PAC could disrupt coal flocs induced by NBs, leading to the release of trapped kaolinite particles with alleviated clay recovery by entrapment.

Study on Fluidization Characteristics of Magnetically Fluidized Beds for Microfine Particles

The bed pressure drop, minimum fluidized gas velocity, bed density, and bed expansion rate are important parameters characterizing the fluidization characteristics of gas-solid fluidized beds. By analyzing these parameters, the advantages and disadvantages of the fluidization state can be known. In this study, experiments were conducted to study the fluidization characteristics of a gas-solid magnetically fluidized bed for microfine particles by changing the magnetic field strength, magnetic field addition sequence, and static bed height. The experimental results show that when the magnetic field strength increased from 0 KA/m to 5 KA/m, the minimum fluidized gas velocity of particles increased from 4.42 cm/s to 10.32 cm/s, while the bed pressure drop first increased and then decreased. When the magnetic field strength is less than 3.4 KA/m, the microfine particles in the bed are mainly acted on by the airflow; while when the magnetic field strength is greater than 3.4 KA/m, the microfine particles are mainly dominated by the magnetic field. The magnetic field addition sequence affects the fluidization quality of microfine particles. The fluidized bed with ‘adding magnetic field first’ shows a more stable fluidization state than ‘adding magnetic field later’. Increasing of the static bed height reduces the bed expansion rate. The bed expansion rate is up to 112.5% at a static bed height of h0 = 40 mm and H = 5 KA/m. This will broaden the range of density regulation of a single magnetic particle and lay the advantage of gas-solid magnetically fluidized bed for microfine particles in the field of separation of fine coal.

Prediction of Cleaned Coal Yield and Distribution Rate in Coal Gravity Separation Based on the Modified Hyperbolic Tangent Model

Prediction of Cleaned Coal Yield and Distribution Rate in Coal Gravity Separation Based on the Modified Hyperbolic Tangent Model

Nonlinear Control of Refuse Discharge in a three-product Coal Jig

The paper presents the results of simulation tests of the dynamic characteristics of a three-product jig for coal separation and control systems for refuse discharge. The changes in the position of the stratified bed layers and the density of the separation layer in the product discharge zone as well as the static characteristics of the zone in two compartments of the jig were investigated. It was assumed that the main disturbance occurring in industrial systems are changes in the flow rate and the feed washability characteristics. The simulation model was verified in industrial tests in two coal preparation plants. An analysis of the effects of the control of the bottom product discharge system for nonlinear PI controllers and adaptive radiometric density meters with variable measurement time was carried out. The aim of control was to stabilize the density of the separation layer at the desired level. The parameters of the nonlinear PI controller depended on the direction of changes in the feed flow rate. The control effects were compared with linear control systems and meters with a constant measurement time commonly used in industry. Proposed system improves product quality and reduces product losses in waste compared to conventional systems.

Soil pollution of the Labin city area with polycyclic aromatic hydrocarbons derived from Raša coal mining and associated industries

The aim of this study was to determine the mass fraction of polycyclic aromatic hydrocarbons (PAHs) in the soil of the Labin city area (west Croatia) as a consequence of the pollution caused by centuries old Raša coal mining and associated metal processing and foundry industries. Samples of topsoil down to 10-cm depth, following the removal of plant cover, were collected, air-dried, and sieved to <2 mm. Afterwards, they were extracted, and PAH levels were measured by high performance liquid chromatography using a fluorescence detector with a varying wavelength of excitation and emission (HPLC/FLD). The results showed substantially elevated levels of PAHs across the study area. The soil pollution with PAHs increased in the direction towards the Raša Bay, where a former coal separation unit was in operation decades ago. The results demonstrated the presence of pyrolitic PAHs that resulted from Raša coal combustion at high temperatures in power plants, and unburnt coal-derived PAHs formed by Raša coal carbonization. This paper for the first time reports levels of PAHs in soil of the Labin city area, establishing them as higher than the values set by Croatian legislation. Therefore, this study clearly calls for immediate clean-up measures in order to solve the environmental pollution issue of the vulnerable local karst area.

Estimation of Bed Expansion and Separation Density of Gas–Solid Separation Fluidized Beds Using a Micron-Sized-Particle-Dense Medium

Coal is the dominant energy resource in China. With the Chinese policy of committing to reducing peak carbon dioxide emissions and achieving carbon neutrality, coal separation has recently become a hot topic, especially the fluidized separation of fine particles. In this study, micron-sized particles were introduced to ameliorate the properties of the traditional fluidized bed. The expansion characteristics of the micron-sized-particle-dense medium were explored. A bed expansion prediction model of the micron-sized-particle-dense medium was established, and the prediction error was about 10%, providing a theoretical basis for understanding the distribution characteristics of the bed. This model also helped predict the bed density in the presence of a micron-sized-particle-dense medium, and the prediction accuracy was between 85% and 92%, providing a theoretical basis for selecting and popularizing fluidized beds for industrial separation.

Separation of super clean coal with two-stage cyclones and related characteristics

ABSTRACT To recover super clean coal from raw coal slime of 28.53% ash, in this study, single factor experiment and response surface optimization experiment was used to design and optimize the design parameters of the two-stage cyclones for the separation and recovery of super clean coal. A quadratic mathematical model between the ash of super clean coal and the design parameters of the cyclones was established. Considering the minimum ash content as the optimization index, the following optimal experimental conditions were obtained: minimum ash content could reach 2.55%, which represented 5.35% recovery of the whole sample. The migration law of particles of different sizes, densities in classification and separation process, and the principle of preparation of super clean coal were explored under optimal conditions. Through the separation effect of the second-stage, overflow with particle size ≥ 0.125 mm could effectively recover super clean coal. However, the separation density was increased, and the separation effect was weakened when the particle was small. Therefore, to effectively recover super clean coal, sieving and desliming are necessary.

Contribution of friction to the heterocoagulation between coal surface and quartz particles studied by the particle vision and measurement (PVM)

The heterocoagulation between coal and micron-sized gangue particles is detrimental to the flotation separation of clean coal. Mineral heterocoagulation is usually inhibited by the adjustment of solution chemistry. But it is not explicit whether solution chemistry adjustment is universally suitable to inhibit heterocoagulation of gangue particles of different sizes, as the heterocoagulation mechanism may vary with the increase of particle size. In this work, the heterocoagulation between coal surface and quartz particles of different particle size was observed in turbulent flow field at acid and neutral pH by the in-situ particle vision and measurement (PVM) probe and was quantified via image processing. The observations indicated that the heterocoagulation between coal surface and fine quartz particles (D3,2 = 11 and 21 µm) was mitigated as pH varied from 3 to 7, however, the heterocoagulation between coal surface and coarse quartz particles (D3,2 = 31 µm) unexpectedly did not change with pH. The dependence of heterocoagulation on pH was different for fine and coarse quartz particles, indicating the variation of heterocoagulation mechanism. The heterocoagulation of fine quartz particles was regulated by the electrostatic double layer force in the framework of the DLVO theory, whereas the heterocoagulation of coarse quartz particles was mainly attributed to the non-DLVO force such as friction.

The role of polyvinylpyrrolidone in the selective separation of coal from quartz and kaolinite minerals

High-effective flotation of valuable coal resource from gangue is more challenging due to the increase of ultra-fine minerals in coal slime. Despite the use of novel flotation equipment and process strengthening regulation, the method of flocculation of coal or gangue particles to enhance selective separation draws increasing attention recently. The great potential in selective flocculation of particles makes the development of novel polymer flocculants a research hotspot in this field. Particularly, as a kind of polymeric reagent, polyvinylpyrrolidone (PVP) has great significance in clay aggregation/dispersion whereas there are few related researches in coal flotation. Thus, the effect of PVP on coal flotation was systematically investigated in this study by flotation tests and the measurements of zeta potential, turbidity, FBRM, and X-ray photoelectron spectroscopy. The results proved that PVP would be preferentially adsorbed on quartz and kaolinite surfaces rather than coal. The adsorption of PVP with low dosage induced the aggregation of quartz and kaolinite, as indicated by turbidity and FBRM results, while it basically made no difference on coal. It was discovered that the selective flocculation of quartz and kaolinite by PVP promoted the selectivity of flotation. This study furnishes a novel and feasible polymer flocculant to improve coal flotation efficiency. • PVP as a flotation regulator could reduce the ash content of clean coal. • PVP could improve flotation selectivity by flocculation of gangue particles. • PVP could adsorb preferentially on quartz and kaolinite than coal.

Particles movement behavior and apparent density in gas–solid fluidized bed as determined by an electronic dynamometer and electrical capacitance tomography

Fluidization technology is extensively applied in the field of wastewater treatment, the petroleum industry, and coal separation. In some industrial production processes, large particles exist in the fluidized bed. For the mentioned industrial applications, the prediction of the separation density is critical for discharging some large particles. Due to the existence of a defluidized hood above large particles, the theoretical analysis of the defluidized hood was conducted by combining the prediction correlation of the previous separation density. The main experiments were carried out to analyze the force acting on large particles. The electrical capacitance tomography (ECT) was employed to capture particles positions. It is founded that gas velocity has significant effects on the volume of the defluidized hood while bed height has slight effects on the volume of the defluidized hood. Moreover, the modified correlation of apparent separation density was developed for large particle density. The new model is in good agreement with the data both from the literature and this experiment.

Feasibility Study on TDS Intelligent Dry Separation of Large Particle Raw Coal in Xinzhuang Coal Preparation Plant

Feasibility Study on TDS Intelligent Dry Separation of Large Particle Raw Coal in Xinzhuang Coal Preparation Plant

Experimental study on separation of lumpish coal and gangue using X-ray

ABSTRACT The recognition of lumpish coal and gangue of different coal sorts was conducted using X-ray technique. Gas coal, fat coal and coking coal were used in this study, and the ash content was found to roughly increase linearly with the density independently of coal sort. Al2O3, SiO2, Fe2O3 and SO3 were detected to be the major oxides for the increase in ash content as the density increased. The gray value of coal was larger than that of gangue and decreased with the increase in thickness and density independently of coal sort and energy zone. The gray value in the high energy zone was found to overlap with that in the low energy zone. Material attribute value (R) was applied for estimating the accuracy of the recognition, and the highest accuracy was given at R = 1.3.

Structural difference of gas coal separation components and its effect on sulfur transformation during pyrolysis of high sulfur coal

Two gas coals were respectively separated into four components with different vitrinite content using ZnCl2 solution. The carbon structure, composition of coal macerals and minerals, and plastic layer behavior of separating components were characterized by nuclear magnetic resonance spectrometer (13C NMR), coal petrographic analyzer, X-ray fluorescence spectrometry (XRF) and Gieseler fluidity. Combining with X-ray photoelectron spectroscopy (XPS), effect of different gas coal separation components on sulfur transformation behavior during pyrolysis of high-sulfur coal and distribution of sulfur forms in coke was investigated. The results show that with increase of vitrinite content in gas coal, the relative ratio of aliphatic carbon in coal increases, and the release amount of volatiles increases during pyrolysis; hydrogen free radicals in volatiles promote decomposition of sulfur, stabilize sulfur free radicals in time and release as sulfur-containing gases, and thus sulfur content in coke is reduced. Low density components in gas coal have the largest maximum fluidity and widest plastic range, and stability of plastic layer is the best during co-pyrolysis with high sulfur coal. The basic minerals in gas coal are mainly enriched in high density components, which leads to increase of sulfide sulfur and sulfate sulfur in the coke. For utilization of gas coal in coal-blending pyrolysis, enrichment of vitrinite and selection of coals with easier removal of alkaline minerals are beneficial for reducing sulfur in coke.

Equipment Transformation and Application of Coal Gangue Separation and Transportation System

Equipment Transformation and Application of Coal Gangue Separation and Transportation System

Application of fractional factorial design for evaluating the separation performance of the screening machine

ABSTRACT Implementing the planned execution of experiments will optimize the resources and time of a newly developed process or equipment. In the present work, the screening machine is newly developed equipment designed for the separation of coal. The present work was carried out to evaluate the performance of separation efficiency of the screening machine using generalized and forward selection fractional factorial experimental design. Further, the present work will also determine the significance of each operational variable, such as moisture content, angle, and frequency, for increasing separation efficiency. A cube plot was developed from the experimental design, which shows the highest and lowest condition of separation efficiency for each level of the operational variables. Further, a Pareto chart was developed to evaluate the significant operational variable for the screening machine. The results of the generalized method and forward selection method of fractional design show that the moisture content was the most significant operational variable, followed by angle and frequency. The results also show that the screen blinding of a screening machine plays an important role in reducing the separation efficiency of a screening machine.

Extraction of clean coal from washery rejects and its effect on coking properties: an approach toward sustainable development

ABSTRACT Since coal washeries generate huge quantities of high-ash rejects as waste, effective utilization of coal rejects help in sustainable coal preparation. Out of different coal rejects, tailings from froth-flotation process can be a potential material for the extraction of clean coal due to its fine size, availability in the slurry form, presence of good carbon values, and better liberation properties. In the present study, three different methodologies i.e., chemical method, chemico-physical method, and physical method are explored to separate clean coal with >49.8% yield for their utilization in coke making process. The chemical method of demineralization by alkali-acid leaching shows a high clean coal yield of 65.4%; however, the alteration of vitrinite-group macerals makes it unsuitable for coke making process. Chemico-physical method of clean coal separation by hydrothermal extraction followed by density separation results in clean coal at 49.8% yield with an increase in vitrinite group macerals, which shows a positive impact on rheological and coking properties. The physical separation method by ultrafine grinding followed by density-gradient-centrifugation resulted in 58.2% of clean coal yield with coking properties similar to the clean coal obtained in conventional coal beneficiation plants. By adopting chemico-physical method and physical method of coal cleaning, the overall clean coal yield of the washery can be improved by >5.1%. Also, there is no deterioration in coke properties such as coke strength after reaction and coke reactivity index by using the prepared clean coal in coal blend.

A comparative study of trough profile and operating parameters performance in spiral concentrator

ABSTRACT Trough profile is an important structural parameter of the spiral concentrator. However, limited attention has been focused on the influence of trough profile on coal separation. In the present work, 21 sets of experiments were carried out to investigate the impact of operating parameters and trough profile on the separation performance. Results show that particles tend to transport outward with the increase of the flow rate and the solid concentration. The cut specific gravity of separation (SG50) increases with the flow rate and the solid concentration. The SG50 of the spiral concentrator with the synthetic curve is much lower than that of spiral concentrator with the ellipse or cubic parabola. Light particles prefer to be placed in the outer place of the spiral concentrator with the trough profile of ellipse. Heavy particles tend to report to the inner region of the spiral concentrator with the trough profile of cubic parabola. The spiral concentrator, with the trough profile of cubic parabola in inner place and the ellipse in outer place, is more desirable to separate the coal slime used in this paper. The findings of the present study are of great importance in trough profile optimization of the spiral concentrator.

Raman Spectroscopic Study on a CO2-CH4-N2 Mixed-Gas Hydrate System

Accurate determination of the characteristics of coal mine gas separation products is the key for gas separation applications based on hydrate technology. Gas hydrates are synthesized from gases with two types of compositions (CO2-CH4-N2). The separation products were analyzed by in situ Raman spectroscopy. The crystal structure of the mixed-gas hydrate was determined, and the cage occupancy and hydration index were calculated based on the various vibrational modes of the molecules according to the “loose cage-tight cage” model and the Raman band area ratio combined with the van der Waals-Platteeuw model. The results show that the two mixed-gas hydrate samples both have a type I structure. Large cages of mixed-gas hydrate are mostly occupied by guest molecules, with large cage occupancies of 98.57 and 98.52%; however, small cages are not easy to occupy, with small cage occupancies of 29.93 and 33.87%. The average cage occupancies of these two hydrates are 81.41 and 82.36%, and the stability of the crystal structure of the mixed-gas hydrate in the presence of 75% CO2 is better than that of the mixed-gas hydrate in the presence of 70% CO2. The hydration indices of the two hydrate gas samples are 7.14 and 6.98, which are greater than the theoretical value of structure l.

Study on the Fluidization Quality Characterization Method and Process Intensification of Fine Coal Separation in a Vibrated Dense Medium Fluidized Bed.

Uniform and stable bed density is the basis of efficient coal separation by a gas–solid dense medium fluidized bed. The traditional air dense medium fluidized bed (ADMFB) is a kind of bubbling bed. By introducing vibration energy, a vibrated dense medium fluidized bed (VDMFB) with uniform and stable bed density can be formed, where the bubble merger is suppressed, the gas–solid contact can is strengthened, and the fluidization quality is also improved. In this paper, the transfer process of vibration energy in a fluidized bed is studied in detail. By calculating the coherence of pressure signals induced by vibration energy and bubbles at different bed heights, the suppression effect of vibration energy on bubble merger is analyzed. The coefficient Rimp to quantitatively evaluate the improvement effect of vibration energy on the fluidization quality is proposed. The differences and incentives of density uniformity and stability in different height bed areas have been clarified under different vibration parameters and gas flow parameters. It is proposed that the optimal separation bed height area of VDMFB is about H = 40–150 mm. The separation effect of the ADMFB and the VDMFB on 1–6 mm fine coal was compared. The results show that, compared with the ADMFB, the VDMFB reduces the separation probable error, E, from 0.134 to 0.083 g/cm3, and the ash content of the clean coal is reduced from 18.83 to 14.97%. The vibration energy significantly improves the fluidization quality of the ADMFB and the separation effect of fine coal.