Dry Coal Separation Research Articles

On the separation mechanism of high vibration frequency compound dry separator and multi-parameter optimization

ABSTRACT Dry coal separation is the key technology for coal separation in arid and water-scarce areas. The content of −6 + 1 mm coal gradually increases, and the weak gravity affect of this part of coal restricts the separation effect, causing serious resource waste and environmental pollution. In this paper, a process intensification method for compound dry separation based on high-frequency vibration was proposed to improve the separation effect of fine coal. The kinematic characteristics of the bed surface with high-frequency vibration was captured by the three-channels acceleration sensor, and the motion trajectories of different regions on bed surface were reconstructed. The separation area was located at the front end of the vibrating bed, and the elliptical trajectory promoted the material to roll. However, the tail of the bed showed a linear trajectory, the main team to the transport of the material. And then the force characteristics of various density particles were studied by using spherical inertial sensors. Compared with low-density particle swarm, the collision between high-density particles was more obvious, causing serious loss of kinetic energy, which increased the motion difference of particles with different densities. Furthermore, the significance of the effects of vibration frequency, bed inclination and air velocity on the separation effect of −6 + 1 mm coal and the interaction between the factors were investigated. Furthermore, the influence of vibration frequency, inclination, and air velocity on the separation effect and the interaction among various factors were explored. The influence of frequency and inclination was more obvious than that of gas velocity. And then a mathematical model was established to predict the calorific value of clean coal. The results illustrated that at a vibration frequency of 37.52 Hz, a bed inclination angle of 13.69°, and an air velocity of 2.26 m/s, the calorific of product was increased from 4306 kcal/kg to 5868 kcal/kg, and the heat efficiency reached 90.18%. The results provide a referable way to realize the large-scale and high-efficiency dry separation of fine coal.

Mixing and migration rule of binary medium in vibrated dense medium fluidized bed for fine coal separation

The vibrated dense medium fluidized bed is an efficient waterless dry coal separation technology. In order to reduce the interference of the macroscopic migration of the entire bed with the coal settlement process, the material composition and diffusion behavior of the binary medium are studied. The results show that the maximum mass fraction of fine coal particles is 18% in the uniformly mixed binary medium. Bubbles and vibration are the main factors influencing the mixing process. At low vibration intensity and high gas velocity (f = 15 Hz, Uv = 15 cm/s), the fine coal particles rapidly rise and back mixing under the entrainment of a large number of bubbles. If the vibration frequency is increased to 25 Hz, the excessive kinetic energy causes the entire bed to flow circularly in the vertical direction, interfering with the normal settlement of coal. After reducing the gas velocity (f = 25 Hz, Uv = 11 cm/s), the fine coal particles in the wall region rise rapidly, which is mainly driven by the vibration, whereas the fine coal particles in the central region migrate upward at a relatively low velocity, dragged by the bubbles. The bed impact forces in the opposite directions differ slightly, which promotes the directional settlement of coal.

Hydrodynamics and subsequent separation of gas-solid separation fluidized bed with secondary air injection

Dry coal separation is mainly restricted by the spatial instability in the fluidized bed. Secondary air injection provides a new way to improve the bed stability. In this study, the hydrodynamics and separation operations of the fluidized bed under secondary air injection were investigated using a numerical simulation and experiment. The results show that secondary air injection changed the internal particle circulation mode: the particle flow-field appeared in the middle of the rising stream on both sidewalls, and the sidewall effect was eliminated, thus improving the fluidization quality of the bed. At the appropriate jet velocity (uj = 2.4 m/s), the minimum variance of bed density fluctuation was less than 0.127 g/cm3, further enhancing the bed stability. In addition, 6–50 mm coal was separated in the fluidized bed under secondary air injection. The lowest probable deviation E value was 0.06 g/cm3, which indicates a good separation performance.

Mathematical model of dry coal deshaling by using FGX vibrating air table

Dry coal separation process is a relatively new method for coal separation in Poland. First air separators which were used on bigger scale was in United States before Second World War in 1930s. Nowadays is widely used in China, United States, Russia and all those places where access to water is limited. Last year’s very popular become separation by using vibrating air tables FGX where beneficiation process use air suspension which separate heavier particles from light coal grains. This separation process depends on different parameters like preparation of feed and it parameters, grain size fraction, air supply etc.. This paper will describe what is it a dry coal separation, modern separation techniques and in the main part focus on creating mathematical model which will present the quality of using this kind of process for coal deshaling. Mathematical model will base on dependence between calorific value and ash content in the tested samples.

Dry coal beneficiation by the semi-industrial Air Dense Medium Fluidized Bed with binary mixtures of magnetite and fine coal particles

Air Dense Medium Fluidized Bed (ADMFB) is deemed to be one of the most efficient methods for dry coal beneficiation. In the present work, a semi-industrial ADMFB system in continuous operation was utilized to study the effects of operating gas velocity, feed coal size, and mixture composition of medium particles on the coal beneficiation in industrial practice. Binary mixtures of magnetite and fine coal particles were used as the medium material, and four different feed coal samples with the size ranges of −50 + 25, −25 + 13, −13 − 6, and −6 + 2 mm were tested individually. The experimental results showed that the influence of excess gas velocity on the dry coal separation is relatively small in the lower flow rates. The separation density and probable error increase with the decreasing of feed coal size, regardless of the type of feed coal. The separation density can be continually reduced by further increasing the fraction of fine coal in the medium material, with the compromise of the increased probable error. Moreover, the ash content and calorific value of −50 + 6 mm coarse coal can be effectively upgraded, but the beneficiation of −6 + 2 mm fine coal was less efficient.

Deash and mercury rejection of fine coal in air dense fluidized bed with shallow bed height

Due to the serious environmental problem, dry coal separation has become the hot research topic in the world. In the study, an air dense fluidized bed was used for reduction of ash content and mercury rejection with shallow bed heights. The results showed that pressure drop fluctuation was smallest when bed height was 100 mm. When fluidized gas velocity was 1.50 Umf, the ash content decreased to 9.65, 10.33, and 11.74% for −6 + 3, −3 + 2, and −2 + 1 mm samples; the yield of clean coal were 77.45, 81.52, and 83.65% for −6 + 3, −3 + 2, and −2 + 1 mm samples; the mercury content decreased to 0.47, 0.48, and 0.48 ppm for −6 + 3, −3 + 2, and −2 + 1 mm samples. The results indicated that an air gas-solid fluidized bed has satisfied separation performance on fine coal beneficiation with shallow bed height.

Effect of middling coal on separation efficiency in air dense gas–solid fluidized bed

ABSTRACT Dry coal separation using the air dense medium fluidized bed (ADMFB) is an effective method for the coal cleaning. The characteristic of feed coal would affect the fluidization behavior in the separation process. In this study, effect of middling coal 1 1 Middling coal: coal with density closing to separation density in the continuous production. on the pressure drop fluctuation, settling time of jetsam, and separation efficiency was investigated. Separation experiments with different amount of middling coal content were conducted. The results indicated that middling particles could increase the pressure drop fluctuation and decrease the separation efficiency. The middling particles could impede the falling of jetsam, increasing the jetsam settling time. With the increasing content of middling coal, probable error (E) had a slight tendency to increase from 0.057 to 0.072 g/cm3. The study provides theoretical support for decreasing the content of middling coal from the gas–solid fluidized bed separator in the continuous production to improve the coal separation efficiency.

A method to improve fluidization quality in gas–solid fluidized bed for fine coal beneficiation

Dry coal separation has become essential in China because it does not consume water and it reduces environmental pollution. In this study, a method for improving fluidization quality in a fluidized bed separator using a micropore sponge is proposed. The separator is used for fine coal beneficiation. The pressure drop across the distributor and bed fluidization characteristics were analyzed to evaluate fluidization quality. The beneficiation efficiency for fine coal was further investigated by using a laboratory-scale fluidized bed with and without a micropore sponge. With the sponge, the highest pressure drop fluctuation factor decreased from 0.23 to 0.16, indicating an improvement in density stability. The modified separation method reduced the ash content of a sample of fine coal from 23.83% to 10.70%. The probable error efficiency value E for −6+3mm coal was 0.12g/cm3, close to the efficiency error values reported for other dry-beneficiation techniques. The separation results show that using a sponge in the fluidized bed can readily improve the efficiency of fine coal beneficiation.

Flow pattern transition and coal beneficiation in gas solid fluidized bed with novel secondary distributor

Gas solid fluidized bed (GSFB) is an effective method of dry coal separation. In this study, porous sponge was introduced into a typical gas solid fluidized bed as secondary air distribution layer (PSFB) to stabilize the fluidized bed layer. The difference between PSFB and GSFB in flow pattern transition process was studied. Compared with GSFB, the minimum gas velocity and bed density fluctuation decreased while bed expansion ratio increased in PSFB. Furthermore, the distribution of bubble phase and emulsion phase were more homogeneous in PSFB. Under the operational conditions, the results of coal preparation in a PSFB showed that the ash content of clean coal was 10.25% .The probable error (E) was 0.095 g/cm3, indicating that PSFB could provide a novel way for a good performance of dry coking coal beneficiation.

Characteristic gas velocity and fluidization quality evaluation of vibrated dense medium fluidized bed for fine coal separation

In order to remove incombustible impurity minerals, a vibrated dense medium fluidized bed (VDMFB) can be adopted for fine coal dry separation, while Geldart B magnetite powder can serve as the medium. The influence of vibration on characteristic gas velocity in flow pattern transition stage was experimentally investigated at a vibration amplitude range of 0.5–4 mm and frequency range of 5–35 Hz. The experimental results demonstrate that at a low frequency (f < 10 Hz), the vibration effect results in a denser bed and a slightly smaller initial fluidization gas velocity. As the vibration frequency increases to a level similar to the bed’s natural frequency, the minimum fluidization gas velocity reduces sharply. The minimum fluidization gas velocity correlation in the VDMFB is obtained by means of theoretical deduction and experimental data fitting. Furthermore, a method is proposed for evaluating the effects of vibration on improving fluidization quality. Based on that, using the coal separation probable error Ep⩽0.1 as the evaluation index, a suitable effective operating gas velocity range for coal separation under different vibration parameters is determined. The ratio of the boundary operating gas velocity to Umfc is 0.67–2.28. Thus, a uniform and stable fluidization environment is provided for dry fine coal separation.

Performance Optimization of a New Air Table and Flip-flow Screen for Fine Particle Dry Separation

ABSTRACT The mining industry has seen increased efforts toward achieving dry mineral separation owing to current and projected water scarcity and environmental problems associated with conventional wet processing methods. Commercially available dry coal separation technologies such as air tables and air jigs have proven effective in cleaning only the +6.35 mm while the −6.35 mm comprised of coal and impurities is discarded or used without further cleaning. To address this issue, a new density-based dry separator named SIU Airtable was developed. The main objective of this study was to evaluate the fine coal (6.35 × 1 mm) dry cleaning performance of the developed air table. The study also sought to evaluate the dry screening performance of the Liwell flip-flow screen to achieve efficient size separations at 1 and 2 mm. Two different Illinois No. 6 coal samples were used to optimize the new air table by varying its operating variables. The analysis of separation efficiency showed similar trends for both coal samples based on the cut point density (SG50) and probable error (Ep). Additionally, separation efficiency was significantly higher for the 6.35 × 3.36 mm size fraction and reduced when the size range was broadened to 6.35 × 1 mm. Product coal ash of 13.8–14.5% and tailings ash of 52.9–59.7% were achieved from the feed ash of 31–36%. Screening experiments on the Liwell flip-flow screen showed an efficiency of 88.7% and 85.1% achieved for the 1-mm and 2-mm polyurethane panels, respectively.

Effect of the secondary air distribution layer on separation density in a dense-phase gas–solid fluidized bed

Dry coal separation has been the most significant process in the field of coal beneficiation to date, because of its special advantage of operation with no water consumption. Mineral dry separation research has received wide attention, particularly in countries and regions experiencing drought and water shortages. During the process of dense coal gas–solid fluidized bed beneficiation, the material is stratified according to its density; the high density material layer remains at the bed bottom, and thus the high density coarse particle bed becomes an important influencing factor in fluidized bed stability. In the steady fluidization stage, a small number of large radius bubbles are the direct cause of unsteady fluidization in the traditional fluidized bed. The dispersion effect of the secondary air distribution bed for air flow is mainly apparent in the gas region; when the particle size exceeds 13mm, the secondary air distribution bed has a synergistic effect on the density stability of the upper fluidized layer. When the particle size is small, especially when less than 6mm, particles will constantly move, accounting for instability of the secondary air distribution bed and distorting the stability of the upper fluidized bed. Under optimum operation conditions, the probable deviation E of gas–solid separation fluidized with a high density coarse particle layer can be as low as 0.085g/cm3.

Effect of feed characteristics on the fluidization of separating fluidized bed for dry coal separation

A separating fluidized bed (SFB) with magnetic powders as the heavy medium was used for dry coal separation. However, during the continuous separation process in the modularized dry coal separation system, the bed density under the coal inlets was found to fluctuate seriously. In this study, the effect of feed with different densities on the fluidization of the SFB was investigated using pressure time series and image analyses. The pressure measured at different bed heights severely fluctuated when particles run into the bed, and the bed surface sunk locally. After feeding, the SFB returned to the previous status, being a “separating fluidized bed”. However, for large particles, the stability of the SFB was severely damaged, and the “separating fluidized bed” acted as a “bubbling fluidized bed”, after feeding. Therefore, particles large enough to damage the stability of the SFB should not be fed into the bed.

Fine coal dry classification and separation

Coal is currently cleaned with a minimum of size reduction; fine particle processing, recovery and tailings disposal are major problems; and adequate water resources are not always available. Two-thirds of China’s coal is located in arid areas. Hence, dry separation provides an alternative approach. Of the dry coal separation methods available, air dense-medium fluidized beds have been used to separate 6- to 50-mm size coal efficiently. However, excessive bubbling and back mixing of the separated solids in the air-dense media fluidized bed results in a high lower size limit of 6 mm for the feed material, which affects the preparation efficiency. Based on a previous study of air-fluidized dense-media for 6- to 50-mm coal preparation, this paper presents methods and test results on the fine coal dry classification, electrostatic beneficiation of 0- to 0.5-mm coal and magnetically stabilized fluidized beds for separating 0.5- to 6-mm coal.

Fundamentals of a Magnetically Stabilized Fluidized Bed for Coal Separation

The performance of a magnetically stabilized fluidized bed is strongly affected by the properties of the air-fluidized dense medium, especially for the dry fine coal separation. The successful design and operation of a magnetically stabilized fluidized bed system for dry coal separation depend on the ability to accurately predict the fundamental properties of the fluidized bed, particularly the fluidized bed's rheological properties and density. These properties are controlled and modified by magnetic field intensity and medium composition. The composition variables include medium density, magnetite particle size distribution, particle shape, and level of contamination. Some of these fundamentals of a magnetically stabilized fluidized bed for dry coal separation are described in this paper.