Dry Coal Beneficiation Research Articles

Fluidization Characteristics of a Gas-Paigeite-Powder Bed to be Utilized for Dry Coal Beneficiation

The physical properties of paigeite powder were investigated and the characteristics of a gas-solid fluidized bed using the powder were studied. The intent was to expand the choice of medium solids appropriate for fluidized bed dry coal beneficiation. Experimental results show that paigeite powder has a low density, a high saturation magnetization, and a small coercivity. Under suitable technical and operating conditions the fluidization performance of paigeite powder with either a narrow, or a specified wide, size range is good. A gas-paigeite fluidized bed, formed from 0.074–0.3 mm paigeite, was used to separate 6–13 mm, hard-to-wash coal at a separating density of 1.5 g/cm3. The ash content of this coal was reduced from 22.37% to 9.88%, with a clean coal recovery of 60.64% and a probable error, E, value of 0.075 g/cm3. This indicates good separation performance of the fluidized bed.

Modularized dry coal beneficiation technique based on gas-solid fluidized bed

A 40–60 t/h modularized dry coal beneficiation process with a novel method to control the bed was designed around a gas-solid fluidized bed separator. Furthermore, the hydrodynamics of medium-solids consisting of wide-size-range magnetite powder (0.3–0.06 mm) and <1 mm fine coal were numerically studied. The simulation results show that the fluidization performance of the wide-size-range medium-solid bed is good. The separation performance of the modularized system was then investigated in detail using a mixture of <0.3 mm magnetite powder (mass fraction of 0.3–0.06 mm particles is 91.38 %) and <1 mm fine coal as solid media. The experimental results show that at separation densities of 1.33 g/cm3 or 1.61 g/cm3, 50–6 mm coal can be separated effectively with probable error, E, values of 0.05 g/cm3 and 0.06 g/cm3, respectively. This technique is beneficial for saving water resources and for the clean utilization of coal.

Beneficiation of high-ash, Indian non-coking coal by dry jigging

Indian coals, which are of Gondwana origin, contain high amounts of mineral matter, wherein the extraneous material was intimately mixed in the coal matrix during the formation stage, causing a high level of impurity in the run-of-mine (ROM) material. These coals possess difficult to very difficult washability characteristics. Beneficiation of high-ash non-coking coals of India has become the prerequisite for improving the overall economics and efficiency of power generation. The use of dry cleaning systems in India for beneficiation of non-coking coals has gaining renewed interest recently. The benefit of the dry beneficiation process is to exploit the given resources while providing a more reliable and consistent quality fuel with a low operating cost. M/S Allmineral has introduced a technique for the dry beneficiation of coal, which is being tried in India for the treatment of high-ash non-coking coals. The first commercial air jig of 50 t/hr capacity was installed and commissioned to beneficiate high-ash coals of 40 × 5 mm feed with an ash content of 40%; a clean coal product of 33% ash was produced and is being used for a sponge iron plant.

The Effect of Vibration on Dry Coal Beneficiation in the Reflux Classifier

This article examines the application of dry beneficiation technology to the separation of coal and mineral matter in a novel air-fluidized bed. The Reflux Classifier (RC) is an innovative design that incorporates an inclined zone above a conventional fluidized bed to achieve increased segregation rates and a higher throughput than separators with an equivalent footprint. In this study, the effectiveness of magnetite and sand as dense media for the separation of coal in an air-fluidized RC was evaluated. The effect of vibration on the separations obtained using both these media was also examined. The coal separation results are reported and compared with coal washability data.

Experimental and numerical simulation studies of the fluidization characteristics of a separating gas–solid fluidized bed

Gas–solid fluidized bed separation expands the choices of highly efficient dry coal beneficiation methods. The hydrodynamics of 0.3–0.15 mm large Geldart B magnetite powder were studied using a combination of experimental and numerical methods to optimize the design of the solid medium used in the fluidized bed. The results show that the Syamlal–O'Brien drag model is suitable for simulating the bed and it is verified that simulated and experimental results are consistent with each other. If the static bed height is no more than 300 mm then the bed height has minimal effect on the fluidization characteristics. As the superficial gas velocity increases the bed activity is improved. However, at the same time the uniformity and stability of the bed drop. Therefore, the gas velocity should be adjusted to no more than 2.0 U mf. The density of the Geldart B bed is uniform and stable, which indicates a relatively high fluidization quality. Furthermore, compounded medium solids consisting of < 0.3 mm magnetite powder with a 0.3–0.15 mm particle content of 65.25% and < 1 mm fine coal were used in a pilot gas–solid fluidized bed of 5–10 ton/h capacity. The pilot bed was used to separate 50–6 mm coal. This test resulted in the coal ash content being reduced from 23.74% to 11.79% with a probable error, E, of 0.07 g/cm 3 and a recovery efficiency of 98.26%. This indicates that the bed has good separating performance. Nevertheless, to increase the applicability of the separating bed a further study emphasizing a decrease in the lower size limit of the magnetite powder should be performed.

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.

Fine coal preparation using novel tribo-electrostatic separator

Dry coal beneficiation has been examined by tribo-electrostatic method using Indian thermal coal sample from Ramagundam coal mines. The process of tribo-electric coal/ash cleaning is carried out with a newly built cylindrical fluidised bed tribo-charger with internal baffles, made up of copper metal. The charge transfer in coal maceral and mineral particles after repeated contact with copper plate tribo-charger is measured. Separation of particles in an electrostatic separator according to the polarity of particle charge generated during tribo-electrification is discussed with respect to gas flow rate and residence time in fluidised bed tribo-charger and the applied electric field. The coal and mineral particles charge with positive and negative polarities respectively. The magnitude of particles charge found to be relatively high illustrating greater efficiency of contact electrification in fluidised bed tribo-charger. The separation results with −300 μm size fraction of coal containing 43% ash showed that the ash content can be reduced to 18% and 33% with an yield of about 30% and 67%, respectively. These results are comparable to the maximum separation efficiency curve of washability studies on this coal sample. Since the ash percentage of coal particles collected in the bins close to positive and negative electrodes are about 70% and 20%, a better yield with low ash content can be accomplished on recycling the material.

Density-dependent separation of dry fine coal in a vibrated fluidized bed

The main purpose of coal separation is to reduce ash, sulfur, mercury and other mineral contaminants in the coal to increase the calorific value and benefit the environment. Dry coal beneficiation has obvious advantages over the wet process although the latter is currently the predominant method in use throughout the world. A vibrated fluidized bed was constructed for separating dry fine coal particles from unwanted gangue particles. An experimental investigation of vibrational energy transmission, and the interaction between vibration and gas flow, was performed. The motivation for these experiments was a theoretical development of the principles involved in forming a dense-media vibrated fluidized bed (DMVFB). The mechanism of bubble breaking by vibration is discussed. A formula for calculating the critical vibration frequency at which bubbles can be efficiently broken and bubble formation restrained is proposed. The experimental results demonstrate that the density of a dense-media vibrated fluidized bed is uniform, with a maximum relative error of 1.68% under optimal technological and operating conditions. The < 6 mm fine coal was efficiently separated with a probable error E value of 0.07 t/m 3. A lower limit of separation of 0.5 mm was achieved. The DMVFB separation efficiency is higher than wet jig with E value of 0.11 t/m 3.

Low Density Dry Coal Beneficiation Using an Air Dense Medium Fluidized Bed

Abstract For the production of low ash content clean coal, separation at low density is required for some raw coals. Based on analyzing the fluidizing characteristics of magnetic pearls with a specific size distribution and formation mechanism of a microbubble fluidized bed, optimal technological and operating parameters suitable for low density coal separation were determined. The experimental results show that an air dense medium fluidized bed with low density can be formed using magnetic pearls as medium solids, which can efficiently beneficiate coal of 6–50 mm size with a probable error E p value of 0.05 at a separating density of 1.44 g/cm 3 .

DRY BENEFICIATION OF COAL—A REVIEW

Coal continues to play a major role in the economic development of a country, especially in metallurgical industries and conventional power generation plants. For effective utilization of high ash coals, it is necessary to beneficiate them. The wet beneficiation process for coal cleaning is currently the predominant method of purification of coal in the world. However, dry beneficiation of coal has obvious advantages over wet processes. The dry processes for coal are based on the physical properties of coal and its associated mineral matters. Different types of equipment for dry beneficiation have been developed, based on the exploitation of physical properties such as density, size, shape, magnetic susceptibility, and electrical conductivity. This article presents a summary assessment of different technologies and their performance in the beneficiation process of high ash coals with particular reference to Indian thermal coals. The literature on sorting, air jigs, magnetic separation, air-dense medium fluidized bed separation, and electrostatic separation is summarized and discussed.

Development of coal dry beneficiation with air-dense medium fluidized bed in china

In China more than two-thirds of available coal reserves are in arid areas, where, to beneficiate the run-of-mine coal, there is not enough water resource required by conventional processing. Developing efficient dry beneficiation technology is of great significance for efficient coal utilization in China, notably the clean coal technology (CCT). The dry coal beneficiation technology with air-dense medium fluidized bed utilizes air-solid suspension as beneficiating medium whose density is consistent for beneficiation, similar in principle to the wet dense medium beneficiation using liquid-solid suspension as separating medium. The heavy portion in feedstock whose density is higher than the density of the fluidized bed will sink, whereas the lighter portion will float, thus stratifying the feed materials according to their density. In order to obtain efficient dry separation in air-dense medium fluidized bed, stable fluidization with well dispersed micro-bubbles must be achieved to ensure low viscosity and high fluidity. The pure buoyancy of beneficiation materials plays a main role in fluidized bed, and the displaced distribution effect should be restrained. The displaced distribution effects include viscosity displaced distribution effect and movement displaced distribution effect. The former is caused by viscosity of the fluidized bed. It decreases with increasing air flow velocity. Movement displaced distribution effect will be large when air flow rate is too low or too high. If medium particle size distribution and air flow are well controlled, both displaced distribution effects could be controlled effectively. A beneficiation displaced distribution model may be used to optimize beneficiation of feedstock with a wide particle size distribution and multiple components in the fluidized bed. The rheological characteristics of fluidized beds were studied using the falling sphere method. Experimental results indicated that the fluidized bed behaves as a Bingham fluid. The plastic viscosity and yield stress can be obtained by measurement of the terminal settling velocity of spheres and linear regression of the experimental data. Both plastic viscosity and yield stress increase with increasing size of the fluidized particles. The drag coefficient can be calculated with favorable agreement with experimental data. The first dry coal beneficiation plant with air-dense medium fluidized bed was established by CUMT with an output of 320000 t·a −1 and a probable error E p value up to 0.05 was achieved. The plant was accepted by the Chinese government in June, 1994. Since then, new applications have been found including a 700000 t·a −1 dry coal beneficiation plant put up for commercial testing. To realize coal dry beneficiation of full size range of 300∼0 mm, further research on dry coal beneficiation of different size fractions has been under way at the Mineral Processing Research Center of CUMT, leading to the following results: • Dry beneficiation technology with a vibrated air-dense medium fluidized bed for fine coal of size fraction 6∼0.5 mm Ash content was reduced from 16.57% to 8.35%, with yield up to 80.20% and E p value up to 0.065. • Coal dry beneficiation technology with a deep air-dense medium fluidized bed for >50 mm coal An E p value up to 0.02 was achieved. This technology is of great value for waste removal from 300∼50 mm large feedstock, especially for big surface mines in China. • Coal triboelectric cleaning technology for <1 mm pulverized Coal Coal is comminuted down to 320 mesh (0.043 mm) to fully liberate the embedded minerals, yielding an ultra-low ash coal (less than 2%). Currently a pilot system with triboelectric cleaning has successfully passed technical appraisal. • Three-product beneficiation technology with dual-density fluidized bed This technology yields three products: clean coal, middling and tailing, with the following typical results: E p value of 0.06∼0.09 for the upper layer with a density of 1.5∼1.54 g·cm −3 and E p value of 0.09∼0.11 for the lower layer with density of 1.84∼1.9 g·cm −3.

Coal dry beneficiation technology in china: the state-of-the-art

In China, coal is the major source of energy and its leading role in energy consumption would not change in the next 50 years. Coal preparation is the essential component of Clean Coal Technology. In China more than two-thirds of available coal reserves are in arid areas, which results in the unfeasibility with conventional wet processing for coal preparation. The uniqueness of dry coal beneficiation technology with air-dense medium fluidized bed is discussed in this paper and a detailed survey of the current status of theoretical study, commercial application and development of the new technology is given in this paper.

Formation of Double-Density Fluidized Bed and Application in Dry Coal Beneficiation

Currently utilized separators with air-dense medium fluidized bed can only produce two products with single-separating density. Two separators must be employed in series to generate three products, which leads to the complication of the technical system and on increase in construction investment and operation costs. Moreover, they are difficult to operate continuously owing to the problems of preparation and recovery of dense media. The double-density fluidized bed forms two separating areas with different densities in a fluidized cascade. In each separation area, the bed density is uniform and meets the needs for three-product separation of coal. Therefore, the coal can be separated into three products according to density. In this paper, the fluidized behavior of binary dense media was experimentally studied in different bed structure. The segregation and mixing process of binary dense media was analyzed. By use of the proper operation conditions and the specially designed bed structures, a double-density fluidized bed was formed for three-product separation of coal.

Development of Dry Beneficiation of Coal in China

This article discusses the status and function of coal preparation in Clean Coal Technology (CCT), the characteristics of different dry beneficiation technologies, and the uniqueness of dry coal beneficiation technology with air-dense medium fluidized bed. This new technology required devoted major efforts to develop and is 'a high efficiency dry beneficiation process.

Dry beneficiation of Slovakian coal

In the present work, the pressure leaching of low-grade wolframite concentrate (33.61 wt% WO3) with average particle size of 62 μm obtained from Chahpalang mine located in the Yazd province of Iran was studied. The Effects of temperature, time and Na2CO3/WO3 weight ratio on tungsten leaching efficiency were evaluated by Response Surface Method (RSM) and Central Composite Design (CCD). The predictions of statistical model showed that the leaching temperature has the major effect on tungsten leaching efficiency with respect to other leaching factors. Increasing the temperature up to 210 °C lead to the increase of tungsten leaching efficiency while resulted in decreasing of leaching efficiency from 210 °C to 230 °C. Optimum conditions by utilizing desirability function follows: 202–208 °C temperature, 3.0–3.7 h, 3.68–4.27 Na2CO3/WO3 weight ratios. The experimental results showed that a leaching efficiency of > 95% under these optimum leaching conditions can be obtained.

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.

Dry beneficiation of Slovakian coal

The dry beneficiation of three types of Slovakian brown coal, namely Ci'gel, Handlova', and Nova'ky coal was conducted via triboelectrostatic separation. Three different types of separators—parallel plate, cylindrical and louvered plate—were used for this study. It was found that a parallel plate separator could reduce the ash contents of Ci'gel and Handlova' coals. The poor quality of separation for the Nova'ky coal studied is probably due to the particle–particle interactions and surface oxidation states of the coal.

Rheology of gas–solid fluidized bed

Coal dry beneficiation with gas–solid fluidized beds belongs to dry dense medium separation. It is important for us to study the rheological behaviors of gas–solid fluidized beds. In this paper, the viscosity of fluidized beds was measured by the solid-settling experiments. The rheological characteristics of fluidized beds can be described with Bingham fluid model. The effective viscosity of fluidized beds can be calculated. The plastic viscosity and yield stress of fluidized beds can be obtained by linear regression analysis of the experimental data. The calculated results agree with the experimental data well.

99/03506 Mechanism and application of coal dry beneficiation with air-dense medium fluidized bed: Wei, L. J. Cent. South Univ. Technol., 1998, 5, (2), 100–103

A thermodynamic analysis of the fluidized bed drying process of large particles is performed to optimize the input and output conditions. Energy and exergy models were used for the study. The effects of the hydrodynamic and thermodynamic conditions such as the inlet air temperature, the fluidization velocity and the initial moisture content on the energy efficiency and the exergy efficiency were analyzed. The analysis was carried out using two different materials, wheat and corn. It was observed that the thermodynamic efficiency of the fluidized bed dryer was the lowest at the end of the drying process in conjunction with the moisture removal rate. The inlet air temperature has a strong effect on thermodynamic efficiency for wheat, but for corn, where the diffusion coefficient depends on the temperature and the moisture content of particles, an increase in the drying air temperature did not result in an increase of the efficiency. Furthermore, the energy and exergy efficiencies showed higher values for particles with high initial moisture content while the effect of gas velocity varied depending on the particles. A good agreement was achieved between the model predictions and the available experimental results.

Mechanism and application of coal dry beneficiation with air-dense medium fluidized bed

The mechanism of beneficiation with air-dense fluidized bed has been theoretically studied in the paper. Focusing attention on the misplacing resources in separation process, the misplacing effects are divided into two parts called respectively as misplacing effect of viscosity and misplacing effect of motion. The proposed separation theory can reasonably explain the results of separation in different fluidization states. Experimental results in pilot and commercial plants showed that the air-dense medium fluidized bed is a high efficiency dry cleaning technique. The dynamic stability of fluidized bed density is directly affected by the variation of fine coal content in fluidized bed and can be controlled in expected range through measurement of fluidized bed density and adjusting of splitflow rate. With air-dense medium fluidized bed, various coals of size 50–6 mm can be efficiently beneficiated. The separation density can be adjusted between 1.2–2.2 g/cm3, and the probable error Ep value is about 0.06.