Fine Coal Beneficiation Research Articles

Fine Coal Dewatering Using High Airflow

Fluidized bed drying is currently receiving much attention as a dewatering option after the beneficiation of fine coal. Apart from concerns about safety and combustion, the operating costs can be high if very high gas or air temperatures are used. The aim of this study was to investigate the removal of moisture from fine coal by using air at a lower temperature (25°C − 40°C) within a controlled environment by lowering the relative humidity of air. It was firstly proven that fluidization has a major advantage over normal static beds when allowed to reach equilibrium. Hereafter, several parameters that influence the dewatering rate and final moisture content were tested, from which it was concluded that the relative humidity of air acts as the largest driving force for dewatering. It was, therefore, shown that this is a viable technology for the dewatering of fine coal.

Modeling of Free and Hindered Settling Conditions for Fine Coal Beneficiation Through a Falcon Concentrator

In this study, the free and hindered settling conditions for coal-shale-clay separation through a Falcon concentrator were determined experimentally using response surface methodology. The model parameters consisted of the separation efficiency and ash content of the concentrate and tailings. Based on the model with the highest response, free settling conditions dominated at centrifugal forces below 100 g and at solid concentrations of up to 30%–35%, especially for coarser particle sizes of 300 µm. These results revealed that, for effective fine coal beneficiation through a Falcon concentrator, the solid concentration should be maintained higher than 30%–35% (with a maximum of 45%–50%) to create hindered settling conditions because separation under these conditions is achieved based on specific gravity. The best results were obtained at a solid concentration of 50%. This finding was interesting because separations through enhanced gravity separators were achieved under conditions similar to separations performed in autogenous media.

Fine coal dry beneficiation using autogenous medium in a vibrated fluidized bed

Dry beneficiation of fine coal (−6mm) using autogenous medium in a vibrated fluidized bed has been studied. The results show that in the particulate bed of fine coal, most of −1+0.5mm size fractions of coal and a small portion of −0.5mm size fraction of coal having high ash content contribute to the formation of an autogenous medium bed. This provides a favorable fluidization environment for the stratification process of fine coal particles depending on their density difference. The main operational parameters including superficial air velocity, vibration frequency and amplitude, initial bed height and separating time all have significant influences on the stratification performance of the particulate bed of fine coal. The batch separation results of Wuhai fine coal in an autogenous medium vibrated fluidized bed show that the separation efficiency, i.e. the probable error E, is 0.14, indicating that dry beneficiation of fine coal using an autogenous medium vibrated fluidized bed is a promising technique for coal cleaning in dry regions.

Segregation and Process Features in a Teeter Bed Separator as Revealed by High-Speed Videography and Image Processing

Gravity concentration in a liquid fluidized bed floatex density separator (FDS) was investigated through high-speed videography and image analysis. Process performance in terms of yield and grade of the product for fine coal beneficiation in the FDS was established experimentally. The feed coal (−1.18 mm) with 36% ash was enriched to 24% ash at a mass yield of 65%. Coarsest underflow with a d50 of 700 μm was obtained at 5.8 kPa bed pressure, 120 kg/h feed rate, and 12 lpm teeter water flow. The lowest SG50 of 1.62 was obtained at 5.4 kPa, 15 lpm, and 80 kg/h. At 9 lpm water flow, steady state was achieved in 400 sec when the voidage and suspension density distributions became constant. From the suspension density distribution, the SG50, 1.69 under this set of conditions, was estimated with reasonable accuracy. Increase in teeter water was shown to increase the time required for attaining steady state. It was established that particle size distribution at the bottom of the bed in the column offers a good indication of the separation performance. The influences of the operating variables on the axial steady state profile of the suspension density and voidage were also established. Image analysis is shown to be quite useful in collecting quantitative transient and steady state data that may be difficult to obtain otherwise. The process performances were adequately described using such transient and steady state observations.

Analysis of separation response of Kelsey centrifugal jig in processing fine coal

Beneficiation of fine coal of size 300×150μm was investigated in a laboratory Kelsey jig. A number of process variables were studied while others were kept constant. Silica sand of size −1.68+0.85mm was used as ragging material to prevent pegging of the internal screen. The thickness of the ragging bed was established to be most crucial in controlling the separation. Rotational speed significantly affected the porosity of the ragging bed and particle momentum which had a contrasting influence on process performance. Pulsation rate determined bed dilation and misplacement of heavier particles. A slip velocity based estimation of the particle momentum indicated that the passage of particles in the intermediate momentum region to the overflow or underflow determined the performance. In a single pass through the Kelsey jig an absolute 7% reduction in the ash content was achieved at over 55% yield. A thicker bed depth was found to facilitate rejection of high ash materials. Models were developed for the response parameters and optimization performed. Operating regimes were identified for roughing or cleaning application of the Kelsey jig for optimum performance. It was established that Kelsey jig could be effective in fine coal cleaning if operated in a controlled manner.

Beneficiation of Fine Coal Using the Air Table

The increased mechanization in the underground coal-mining industry has increased the volume of fine size coal and waste (refuse) in the mined coal. Processing of run-of-mine (ROM) coal is generally done using water away from mine and in some cases the coal has to be transported a long distance to the preparation plant. Dry processing of coal can be economical as it will not utilize water and no dewatering or drying of the product will be required. The goal of this study was to develop a dry separation process for processing of coal finer than 6.3 mm . The coal sample from a mine located in Western Kentucky was used for the study. Statistical design experiments were conducted to assess the effects of operating parameters of the dry separator on product yield for a given ash content. Tests conducted with 6.3 × 3.35 mm (and 3.35 × 1.4 mm size fractions showed that the air table was able to reduce the ash from 27% to 10%–12% ash with a clean coal yield of 75%–80%. The ash rejection was about 77%–80% with a combustible recovery of around 95% indicating excellent separation efficiency. The pyritic sulfur rejection was 43%. The heat content of the 6.3 × 1.4 mm (1/4 inch × 14 mesh) coal fraction increased from 23997 kJ/kg to 29595 kJ/kg. The pyritic sulfur was reduced by about 33% with a product yield above 80%.

Development of Air Dense Medium Fluidized Bed Technology For Dry Beneficiation of Coal – A Review

Wet processing of coal requires a large quantity of water. Waste generated from wet process ties up a significant amount of water and land. The slurry ponds also pose serious problems in case of dam breakage. Dry beneficiation of coal offers a better alternative approach for cleaning coal. An overview on the development of separation technology for beneficiation of coal using dense medium fluidized bed system is described. A theory of the dry separation relevant to coal beneficiation by density difference has been highlighted. This paper summarizes past and present development of different designs and operational features of a counter-current cascade fluidization (CCFC) system and air dense medium fluidized bed separator (ADMFBS) based on their separation efficiency for different sizes of coal at different scales of operation. For fine coal beneficiation, magnetically stabilized bed improves the separation efficiency by preventing the back mixing of the separated solids.

Coal-Fine Beneficiation Studies of a Bench-Scale Water-Only Cyclone Using Artificial Neural Network

Coal fines generated in Indian coal preparation plants account for 25%–30% of run-of-mine (ROM) coal. Coal cleaning is receiving increasingly greater attention of process engineers in view of the increase in amounts to be handled as well as the difficult washability characteristics of high-ash-content Indian coals. Froth flotation is usually practiced in Indian coal washeries for washing the coals to bring down their ash content to acceptable limits. Because of the supply of feed coal from multiple sources, their different characteristics and composition, viz., varying mineralogy and ash content, presence of microfines, and their varying oxidation levels, the fine coal circuits, more often than not, fail to deliver consistent product quality and desired yields. Water-only cyclones have been used in most of the western countries for treating coal and mineral fines below 3 mm. However, the industrial use of these cyclones in India has not yet been put to practice in the coal-washing industry; the primary reason for this being that their design is unsuitable for high-ash content coals and therefore needs to be suitably modified according to the feed material characteristics. Highlighted in the present paper are the results of a case study of beneficiation of high-ash fine coal, using a water-only cyclone. The influence of two of the critical design variables, viz., cyclone length and solid concentration, on which the cyclone performance and the process yield (%) depend to a great extent, is described. Further, based on the experimental data of a water-only cyclone of varying lengths used for below a 3 mm coal beneficiation study, an attempt has also been made to develop a three-layer feed-forward artificial neural network (ANN) model, which is inherently trained using an error-back propagation algorithm. The results evince that the predictions from the ANN model are in good qualitative and quantitative agreement with the experimental observations, thereby validating the applicability and accuracy of the developed ANN model.

STUDY OF A LABORATORY-SCALE FROTH FLOTATION PROCESS USING ARTIFICIAL NEURAL NETWORKS

A three-layer feed-forward artificial neural network (ANN) model, trained using the error back propagation algorithm, has been established to simulate the froth flotation process for the beneficiation of coal fines. The network model validates the experimentally observed qualitative and quantitative trends. The optimal model parameters in terms of network weights have been estimated and can be used to compute the parameters of the coal flotation process over wide-ranging experimental conditions.

A study of a multistage column for fine coal beneficiation

A novel dual-axis microgyroscope fabricated by a surface micromachining process is developed. A 7.0-μm thick polysilicon layer deposited by LPCVD (Low Pressure Chemical Vapor Deposition) is used for the vibrating structure. The microgyroscope is based on the angular vibration of the four plates with closed-loop rate detection. The comb-driven rotational body tilts to each input-axis parallel to the substrate and the tilting motion is sensed with capacitance change between the bottom electrode and the structure. The two tilting modes enable the sensor to detect two-input axis angular rate simultaneously within a single-chip. In particular, the structure utilizes a simple force-balancing torsional torque which does not need another top electrode layer to reduce the intrinsic non-linearity of a capacitance-type sensor. The vibrating structure is strongly damped by air, so the gyroscope is tested in a high vacuum chamber for a high quality factor with hybrid signal-conditioning integrated circuit. The experiment resulted in a noise equivalent signal of 0.1°/s.

Biochemical removal of HAP precursors from coal — INEEL slurry column testing

A combined physical/biochemical process for the precombustion removal of 13 inorganic hazardous air pollutant (HAP) precursors, i.e., Sb, As, Be, Cd, Cr, Cl, Co, F, Pb, Hg, Mn, Ni and Se, from coal was tested. Biochemical processes for removal of HAP precursors from coal potentially offer advantages of deeper cleaning, more specificity and less coal loss. The slurry column is a second-generation process for the beneficiation of fine (60-mesh × 10µm) coal by a combination of physical separation of mineral matter and biooxidation of pyrite. Sixty-seven percent removal of pyrite from a 60-mesh Pittsburgh #8 coal was achieved at a 35% (w/w) slurry concentration and a five-day reactor residence time. Ninety percent of the heating value of the feed coal was recovered. Among the HAP precursors of most concern, over half of the Se, As and Hg were removed from the feed coal. From 40% to 70% of most HAP precursors were removed from the feed coal. Hg in the feed coal was reduced from 0.12 to 0.054 µg/g in the product coal, while waste coal contained 0.24 µ/g.

A Study of a Multistage Column for Fine Coal Beneficiation

A novel multistage column has been successfully developed for fine coal beneficiation. This new column uses vortex-inducing contactors as stages to enhance the separation process. This paper presents an experimental study of the beneficiation characteristics or such a multistage column in terms of recovery rate, heating value recovery and impurity rejection. The paper also discusses the effects of dosage on the column performance. The results are compared with those obtained from the conventional column (without vortex-inducing contactors).

97/04390 Beneficiation of coal fines toward clean ecological fuels: Sciazko, M. et al. DGMK Tagungsber., 1997, 9702, (Proceedings ICCS '97, Volume 1), 539–542

97/04390 Beneficiation of coal fines toward clean ecological fuels: Sciazko, M. et al. DGMK Tagungsber., 1997, 9702, (Proceedings ICCS '97, Volume 1), 539–542

The slurry-column coal beneficiation process

The slurry column is a second-generation process developed at the Idaho National Engineering Laboratory (INEL) for the beneficiation of fine (60 mesh × 10 μm) coal by a combination of the physical separation of mineral matter and the biooxidation of pyrite. The bioreactor is a slurry-type airlift, specifically designed to allow the large liberated inclusions of pyrite and other insoluble minerals to settle out. They are transferred to a similar reactor, called the rougher/propagator, that gives a second stage of physical separation, as well as the longer residence time for the biodegradation of the large pyritic inclusions and the associated bacterial growth. The bioreactors operate in sequenching-batch mode, and also serve as settlers for coal/water separation when the air is turned off. This separation allows counter-current flow of coal and water, which minimizes the volumes of water consumed and wastewater generated. The complete flow sheet incorporates two-stage washing to remove sulfate and bacteria from the product coal, and recycle of bacteria into the process to inoculate the feed coal. A description of the process illustrates some general principles applicable to the optimum design of any coal bioprocess.

97/03502 Economical beneficiation of fine coal by using Reichert spiral and its application to Turkish coals

In this study, the possibility of applying Reichert spiral to Turkish coals is discussed. In the first part of the study, nine coal samples, six of them are lignite and one bituminous coal, collected from seven different locations of Turkey, have been studied. Their {open_quotes}Density Histograms{close_quotes} and {open_quotes}Optimum Separation Densities{close_quotes} were investigated. In the second part of the study, pilot scale experiments were carried out with Mark 10 type of Reichert spiral with six helical turns, on the coal samples taken from Zonguldak, the only bituminous coal area in Turkey, and the characteristic Turkish lignite. The results of the pilot scale experiments were compared to that of the known properties of the Reichert spiral.

97/01604 Belt separation system using composition for extruded belt with good wear resistance

This paper presents the results of an investigation of the performance of a number of different flotation cell technologies for the beneficiation of fine coal. The work was conducted on-site at the Grootegeluk Colliery in the northern Transvaal province of South Africa, using a pilot-scale conventional column cell, a pilot-scale Jameson-type cell, and an air-sparged hydrocyclone (ASH). In addition, characterisation and conventional batch flotation tests were conducted in the laboratory in the Department of Chemical Engineering at the University of Cape Town.All three units tested on-site demonstrated improved selectivity compared to conventional subaeration flotation. In the column cell, optimum performance could only be achieved at very low throughputs. Substantial losses of coal occured in the coarser size fractions. The Jameson-type cell was able to operate effectively at about double the throughput of the column cell at similar recoveries. Coal recovery in the coarser size fractions was still poor, but better than that of the column cell. The ASH was characterised by a very high throughput, more than 150 times that of the column cell on the basis of solids capacity per unit cross-sectional area. However, the ASH required more than three times the reagent dosage of the other two units to achieve this. The ASH performed particularly well in the recovery of the coarser size fractions, but was less effective than the other cells on the finer size fractions.Overall, the best performance for this application was that of the Jameson cell, owing to its higher capacity in comparison to the column cell. The high reagent requirement of the ASH makes this technology uneconomic in this application.

Morphological analysis and modelling of fine coal filter cake microstructure

The microstructure of fine coal filter cakes governs their formation rate and dewaterability, which are both critical to the efficient beneficiation of fine coal. However, the principles by which the microstructure influences the transport properties of filter cakes are not well understood, partly due to the difficulty in obtaining information about the three-dimensional morphology of their pore structure. The paper describes an example of application of the Boolean model that leads to a straightforward and realistic quantification of the three-dimensional microstructure of fine coal filter cakes. Such a model is extremely attractive, for (1) it relies on well-established random set theory, (2) its characterisation involves standard image analysis of polished sections, and (3) no empiricism is involved. Although the model was found to be ideally suited to the characterisation of fine coal filter cakes, the flexibility of its underlying theory makes it an excellent candidate for quantifying other porous media. Such a model not only permits easy access to the three-dimensional details of porous media, but also holds promise for assisting in predicting the transport properties of porous media because of its realism. Subsequent publications will discuss applications of the model to obtain three-dimensional computer simulations of filter cakes, and to predict single-phase permeability of filter cakes.

Mechanism of fine coal flotation using insoluble collectors in the presence of frothers.

This paper deals with the application of froth flotation techniques to the beneficiation of fine waste coal of El-Maghara colliery. Different reagent systems of oily collector-frother were investigated. The main object of this study is to investigate the feasibility of recovering the combustible matter from waste fine coal. The attention is also paid to highlight the oily collector-frother interaction.

95/05629 A further investigation of the novel multi-stage agitated column for fine coal beneficiation

The interaction between sulfide-ion species and smithsonite surfaces and its response to flotation performance were investigated by means of microflotation experiments, surface-adsorption tests, zeta-potential determination, and X-ray photoelectron spectroscopy (XPS) analysis. The microflotation experiments results indicated that addition of Na2S elicited a positive effect on the smithsonite floatability within an appropriate concentration range (<7.5 × 10−4 mol/L), otherwise it showed an obvious negative influence. The surface adsorption tests showed that a significant difference in amounts of sulfide-ion species retained in the pulp solutions was exhibited after smithsonite samples were sulfidized with different concentrations of Na2S. The negativity of the zeta-potential increased with increasing Na2S concentration but decreased under alkaline conditions after adding NaAX. The XPS analysis results revealed that zinc sulfide species formed on the smithsonite surface after sulfidization, and its contents increased with increasing Na2S concentration. Moreover, the sulfidization product formed on the mineral surface was composed of monosulfide and polysulfide, and polysulfide played an important role in the sulfidization flotation of smithsonite. These results demonstrated that excess Na2S concentrations could enhance smithsonite sulfidization but could inhibit the adsorption of collector onto the sulfidized smithsonite surfaces due to the abundant sulfide-ion species retained in the pulp suspension.

95/01208 An on-site evaluation of different flotation technologies for fine coal beneficiation

95/01208 An on-site evaluation of different flotation technologies for fine coal beneficiation