Coal Separation Research Articles

Dry beneficiation technology of coal with an air dense-medium fluidized bed

Dry beneficiation technology of coal with an air dense-medium fluidized bed commenced application lately in China. This paper analyzes the characteristics of gas-solids fluidized beds and basic principles of coal separation, and describes systems for coal dry beneficiation (including raw coal pre-treatment, coal separation, medium solids recovery, air supply and dust removing). Experiments on a 50MTPH air dense-medium fluidized bed system for the dry beneficiation of coal shows that a uniform and stable fluidized bed can be formed with magnetite powder or a mixture of magnetite powder and fine coal as medium solids. The separation performances of the separator were investigated and assessed in detailed. The results indicate that 50×6 mm coal can be separated effectively with an E P value of 0.05. The performance results of this technology are satisfactory.

Influence of pretreatment and activation conditions in the preparation of activated carbons from anthracite

The influence of pretreatment and activation conditions on anthracite activation was investigated. Separation of low ash coals by using dense media was conducted to obtain appropriate raw materials for activation. Activated carbons were produced from crushed and granule coals by physical activation (steam or CO2) and physical activation with chemical pretreatment in mild and strong conditions. Microporous activated carbons having a surface area of 900 m2/g were produced by steam activation from granules with 60% burn-off for 3 hrs of activation. Chemical pretreatment at the strong condition increased the surface area by 30% as compared with non-treated activated carbons. Chemical pretreatment, in general, affected activation degree, so pore volume increased by 20% and burn-off increased remarkably at the identical activation conditions. CO2 activation was proven to be an effective method for producing microporous activated carbons having an average pore diameter of 20 a.

Enhanced fine coal beneficiation using ultrasonic energy

Fine coal particles are difficult to separate effectively from liquids or other solids. Ultrasonic energy may be used to enhance the efficiency of the conventional fine-particle separation processes widely used in the coal and mineral industries. Flotation, settling and dew ate ring tests were conducted using several fine coal samples to study the effects of ultrasonic treatment on these processes. Process variables such as particle size, ultrasonic treatment time and solids concentration were investigated for their impacts on ultrasonic treatment effectiveness. The results obtained from this study showed that ultrasonic treatment is an effective approach for enhancing solid/solid separation in flotation and solid/liquid separation in sedimentation and dewatering of fine coal. SEM microphotographs demonstrate that ultrasonics cleaned particle surfaces, which is, in part, responsible for the observed improvement in fine coal separation processes.

AIR FLOW AND PARTICLE TRANSPORT IN A TRIBOELECTRIC COAL/ASH CLEANING SYSTEM-COUNTER FLOWING STRAIGHT DUCT DESIGN

ABSTRACT The process of triboelectric coal/ash cleaning is outlined and a new design for scale-up to industrial systems is described. A straight rectangular duct forms the mixing chamber and the main body of this triboelectric separator. To improve mixing and to generate a uniform concentration in the main electrostatic separator duct, the mixture enters the mixing box in the form of two opposing jets. The stress transport model of the FLUENT code is used for simulating the mean gas flow and to guide the overall design of the electrostatic coal/ash separator. The three-dimensional computational grid covers the mixing chamber with the opposing inlets and the upper part of the main separator duct. The gas flow field conditions including the directional intensities of turbulence are evaluated. The instantaneous fluctuating velocity field was simulated by a Gaussian filtered white noise model. A recently developed computational model for Lagrangian particle tracking is used to study the transport of particles from the inlets to the main body of the separator duct. The model accounts for the drag and lift forces acting on the particle, in addition to the Brownian motion and gravitational sedimentation effects. The particles are also dispersed by the action of the high level of turbulence that is generated in the mixing chamber. The computational results show that the new design generates roughly uniform flow conditions in the triboelectric separator duct. Furthermore, the larger 100 µm particles will have a more uniform distribution when compared with the smaller (40 µm) particles. The effect of the presence of an electric field perpendicular to the flow direction is also studied. It is shown that the charged particles are significantly deflected by the action of the electrostatic forces. As a result, the system could separate coal and ash particles that carry different charges. The simplicity and effectiveness of the straight duct separator makes it a prime candidate for scale-up for use in industrial applications for online coal beneficiation and separation of minerals from ash in combustion product.

00/01201 Efficiency promotion in separation of ultrafine coal

00/01201 Efficiency promotion in separation of ultrafine coal

Dynamic Modeling of Fine Coal Separations in a Hindered-bed Classifier

Hindered-bed classifiers have recently received significant attention for the potential of achieving effective density-based separations. Although the fundamental principles of hindered-bed classifiers are relatively simple, the complex interactions between the operating parameters provide a degree of difficulty that hinders the ability for on-line plant optimization. Thus, a dynamic population balance model was developed to evaluate and optimize the separation performance achievable on the basis of density by a hindered-bed classifier for the cleaning of fine coal. The steady-state results of the model include partition curves as a function of particle size and density as well as metallurgical data. A statistical comparison of the simulation results with those obtained from industrial units reveal a high level of accuracy with adjusted R2 values greater than 0.95. Simulation results indicate the potential for efficient density-based separations over a particle size range of 3:1.

Froth flotation: preparation of a laboratory standard

In evaluating the separation of coal from slurries of fine solids by froth flotation, it is necessary to work to a standard method to ensure that the procedure, on the same sample, can be repeated by others and the same results obtained. In a number of countries the standard procedure is produced and distributed by the International Standards Organisation (ISO) working through its member countries. In the preparation of a froth flotation standard, two different techniques from two countries (Australia and Great Britain) have been proposed. These procedures, known as the ‘tree’ and ‘release’ analyses respectively, differ in the laboratory technique and presentation of results. In order to assist in the debate of which of the procedures should be adopted as the basis for the International Standard, a short programme of comparative work was undertaken to evaluate the different methods. Samples of coal slurries from Australia, Great Britain and South Africa were evaluated using the Australian and British procedures. The work undertaken is described detailing the preparation of the samples, test procedures and differences between the two techniques. The results showed that the two techniques produced similar results with the ‘Release Analysis’ giving more detail at the cleaner (low ash) end of the curve and the ‘Tree Analysis’ more data for the middle (medium ash-higher yield) part of the curve. The results indicated that the technique chosen would be dependent upon the information required from the flotation analysis, i.e. the British ‘Release Analysis’ for the cleaner coal data and the Australian ‘Tree Analysis’ for higher ash fractions.

Evaluation of the Altair Centrifugal Jig for Fine Coal Separation

A significant effort has been made during the past decade to develop gravity separators for treating fine particles. As a result, several enhanced gravity separators have been developed and commercialized. The Altair Centrifugal Jig is an enhanced gravity separator that provides relatively efficient separations on +25 μm size fractions. An experimental program conducted on −600 μm coal found that the Altair Jig reduced the ash content of the 600×44 urn material from about 30% to 10% with an 86% combustible recovery value. The pulse water pressure, feed volumetric rate and ragging volume were found to be the key operating parameters affecting the separation performance indices obtained from the process. A low density cut point of 1.55 with a probable error value of 0.09 was indicative of the high process efficiency values achievable by the Altair Jig.

Centrifugal float–sink separation of fine Turkish coals in dense media

Zonguldak bituminous coal, Tunçbilek and Soma–Merkez lignites were each separated into two sub-fractions, coal rich and mineral matter rich, using a centrifugal float–sink separation technique in heavy media. An isopropyl alcohol (IPA)–carbon tetrachloride (CCl 4) mixture and a zinc chloride (ZnCl 2) solution, with a specific gravity of 1.40 g cm −3 at 25°C were used as dense medium liquids. The addition of surface active agents (Triton X-100 and Brij-35) to the zinc chloride solution improved the removal of minerals. The recovery and purity of the final product (float) obtained from the heavy media separation depend on such parameters as the density of the medium, rotor speed and centrifugation time. The separation efficiency of each coal differed significantly. Particle size distributions of the coals and their float and sink fractions were analysed using a Laser Particle Size Analyser. A Scanning Electron Microscope (SEM) was used to interpret the liberation of minerals from the coal particles.

98/01865 A preliminary investigation of dense-medium centrifugation for fine coal separations : Klima, M. S. et al. Proc. Int. Miner. Process. Congr., 19th, 1995, 2, 139–142

98/01865 A preliminary investigation of dense-medium centrifugation for fine coal separations : Klima, M. S. et al. Proc. Int. Miner. Process. Congr., 19th, 1995, 2, 139–142

98/00048 Apparatus and process for fluidized-bed drying and separation of coal

98/00048 Apparatus and process for fluidized-bed drying and separation of coal

97/04412 In-line coal cleaning. Triboelectrostatic separation of coal and mineral matter: Stencel, J. M. et al. DGMK Tagungsber., 1997, 9702, (Proceedings ICCS '97, Volume 1), 523–526

97/04412 In-line coal cleaning. Triboelectrostatic separation of coal and mineral matter: Stencel, J. M. et al. DGMK Tagungsber., 1997, 9702, (Proceedings ICCS '97, Volume 1), 523–526

The distribution of mineral matter in pulverised coal particles in relation to burnout behaviour

The presence of mineral matter in a pulverised coal particle may affect the behaviour of the particle during combustion, and could influence the level of unburnt carbon in ash experienced in power stations. This paper presents details of a computer-controlled scanning electron microscopy (CCSEM) method of characterising the mineral content of individual pulverised coal particles and describes the distribution of mineral matter in pulverised coal samples. The possible influences of the mineral matter distribution on levels of unburnt carbon are discussed in the light of burnout measurements for the same coal samples. Pulverised coal particles may be divided into three types on the basis of their mineral content: organic-rich particles, organic particles with included minerals, and excluded mineral particles. The relative proportions of these different particle types have been characterised for a suite of 18 power station coals from around the world. Organic-rich particles are the most abundant, and particles containing included minerals form a greater mass fraction of the coals than excluded mineral particles. The excluded mineral particles have a considerably finer size distribution than the particles containing organic material, and the organic-rich particles are generally slightly larger than the organic particles with included minerals. Ranking the coals by degree of mineral-organic association shows a strong separation of coals on a geographical basis. Australian and South African coals show higher levels of mineral-organic association than British and North American coals. Although there are a number of possible mechanisms by which included minerals might modify the combustion behaviour of pulverised coal particles, comparison between the mineral distribution and the combustion performance of these coals does not favour any particular mechanism for influencing levels of unburnt carbon.

A Density Gradient Centrifugation Method for Separation of Peat

The conditions necessary for a laboratory—scale separation of the premaceral constituents of peat (i.e., the precursor to coal) are investigated. The method used is an isopycnic density centrifugation (DGC) technique aimed at isolating pure premacerals. This method, which is based on known density differences of various macerals, has been used successfully in coal separations but never with peats. The technique involved grinding the peats in a planetary ball mill to an approximate 10 μm average particle size and conducting dispersion tests using NaCl, Ca(NO3)2, CsCl, and TBE as solvents coupled with numerous surfactants. The density gradient centrifugation technique was run with both an aqueous and organic gradient using plain milled peat, demineralized peat, and demineralized methylated peat. The best separations were achieved in a single run if the peat was demineralized and dispersed with a wetting agent in an organic gradient. Analytical-scale separations were used to choose the most responsive peat to be used in a preparative-scale separation. A low and high density weight fraction, analyzed by flash pyrolysis, revealed distinctly different chromatograms, indicating that the peat had reached a reasonable degree of separation. Four peats of differing constitution are reviewed.

97/02615 Use of a magnetic fluid-based process for coal separations

97/02615 Use of a magnetic fluid-based process for coal separations

Use of a magnetic fluid-based process for coal separations

The use of a laboratory-scale magnetic fluid-based separator for coal separations was examined. A Frantz laboratory magnetic separator was modified by fabricating new pole pieces of the appropriate geometry to provide the proper magnetic field gradients. Two separation chambers, which were constructed of Plexiglas, were designed to fit between the pole pieces. A commercially available, water-based, ferromagnetic fluid was used as the separating medium. The separating density was changed by varying the current intensity of the electromagnet coil. Both batch and continuous separations were made using 0.59 × 0.50-mm and 0.18 × 0.15-mm coal. The results are compared to those obtained using organic liquids.

96/05775 Triboelectric separation of coal from mineral impurities

Dissolved gaseous mercury (DGM) was studied in surface and deep waters of the Mediterranean Sea over the last 15 years during several oceanographic cruises on board the Italian research vessels Urania and Minerva Uno, covering the Western and Eastern Mediterranean Basins as well as Adriatic Sea as its northernmost part. DGM was measured together with other mercury species (RHg - reactive Hg, THg - total Hg, MeHg - monomethyl Hg and DMeHg - dimethylmercury), and with water quality parameters in coastal and open sea deep water profiles. DGM represents a considerable portion of THg (on average 20%) in Mediterranean waters. Spatial and seasonal variations of measured DGM concentrations were observed in different identified water masses. DGM was the highest in the northern Adriatic, the most polluted part of the Mediterranean Sea as a consequence of Hg mining in Idrija and heavy industry in northern Italy, and near the Gulf of Lion. Generally, average DGM concentration was higher in the West and East Mediterranean Deep Waters (WMDW and EMDW) and Levantine Intermediate Water (LIW) than in overlaying Modified Atlantic Water (MAW); however, it was the highest in N Adriatic Surface waters (NAdSW) and consequently in outflowing Adriatic Deep Waters (AdDW). In deep water profiles the portion of DGM typically increased at depths with oxygen minimum and then towards the bottom, especially in areas with strong tectonic activity (Alboran Sea, Strait of Sicily, Tyrrhenian Sea), indicating its bacterial and/or geotectonic origin. During oceanographic cruises in 2011 and 2015 in the Tyrrhenian Sea, novel methods for continuous DGM determination in surface waters (Wangberg and Gardfeldt, 2011, Begu et al., 2016) were applied and compared to the standard method, and showed good agreement.

96/03540 Distribution of rare and toxic elements according to the products by high gradient magnetic coal separation

96/03540 Distribution of rare and toxic elements according to the products by high gradient magnetic coal separation

Surface Energy and Induction Time of Fine Coals Treated with Various Levels of Dispersed Collector and Their Correlation to Flotation Responses

Separation of fine coal in froth flotation relies upon the wettability difference between the coal-rich and mineral-rich particles in the aqueous solution. Two methods were used to measure the wettability of six ranks of coal as well as coal samples treated with various levels of dispersed collector in aqueous solution. Wettability was determined by measuring the distribution of critical wetting surface tension, i.e., surface energy, using the film flotation technique and by measuring the induction time, i.e., bubble-particle attachment time, of the material. The wetting of coal particles is strongly dependent upon the coalification processes and can be affected by ash content. For anthracite coal with a high ash content, very high surface energy and intermediate induction time were measured, but intermediate floatability with a very good ash rejection was obtained. Sub-bituminous coal with low mineral inclusion was found to have a relatively low surface energy, and thus a high floatability, but very poor selectivity was observed, which was reflected in lengthened induction time. When dynamics of flotation behaviors are involved, flotation results can be better interpreted by induction time. For dispersed collector-treated coal samples, an increase in collector dispersion (i.e., a decrease in kerosene droplet size), by direct liquid collector mechanical agitation, ultrasonic energy emulsification, or atomization, caused decreases in surface energy and induction time and closely matched the increase of flotation recovery and selectivity. With similar particle density, mineral liberation conditions, and particle size, the induction time was found to be closely related to the mean critical surface tension for untreated coal samples and for HV-bituminous coal samples treated by various levels of dispersed collector.

Horizontal and Vertical Distribution of the Zebra Mussel (Dreissena polymorpha, Pallas) Larvae in the Modrac Reservoir, Bosnia and Herzegovina

AbstractIn the Modrac Reservoir, loaded with coal separation suspended material, rapid development of the zebra mussel (Dreissena polymorpha) took place from at least 1987. It is probably the first distinguished “infection” for this part of Balkan Peninsula, caused by this organism. Horizontal and vertical distribution of this mussel, at 15 different reservoir profiles, had been investigated.