Dense Medium Fluidized Bed Separator Research Articles

Semi-industrial experimental research on the influence of moisture on air dense medium fluidized bed separation

This paper conducted a semi-industrial experimental study on the influence of moisture on air heavy medium fluidized bed separation. The research results show that with the increase of coal moisture, the separation accuracy of the separator decreases. When the coal external water is 6.83%, it is difficult to effectively sort the coal; with the increase of the sorting time, the medium moisture will increase slightly; the medium consumption of clean coal and gangue products increases with the increase of the coal external water; when the water exceeds 3%, the media consumption has an almost linear relationship with the external water content; the media with agglomeration or excessive water content is not suitable for direct use as a sorting media and needs to be dried.

The process optimization for separation performance and fluidization stability based on air dense-medium fluidized bed

Dry mineral separation methods are based on the pseudo-fluid properties of two-phase gas-solid fluidization during the air dense medium fluidized bed separation. In this paper, the air dense medium fluidized bed separation method was introduced for coal deashing. In order to better understand the impact of separation performance of air dense medium fluidized bed, the uniform stability of fluidized bed on separation performance the factors (fluidization number (N), height-to-diameter ratio (λ) and feeding volume fraction (γ)) were varied. The process optimization of these three factors was investigated. The results showed that the fluidization number was the main factor reflect on fluidized characteristics. The separation efficiency achieved the optimal value when the feeding volume fraction reached 13%. The segregation stabilized at 0.90–0.95, with the possible deviation ranged from 0.10 to 0.15. Further, the yield of cleaned coal is 78.5–80%, and ash content reduced by 75–78%. The dense medium fluidized bed can achieve efficient deashing of coal. Highlights Factors to influence the uniform stability of fluidization within ADMFB. The Process optimization for separation performance was conducted. Synthesizing the separation test results get formulas about feeding volume fraction y and feed rate q. The yield of the cleaned coal is around 80% while its ash decreased to 10%.

Separation performance of coal in an air dense medium fluidized bed at varying feeding positions

Coal preparation is the basis and prerequisite for clean coal utilization. Air dense medium fluidized bed separation (ADMFB) technique demonstrated good separation performance for coal cleaning. Feeding position remarkably affects separation performance of ADMFB. In this work, we studied how feed height, separating time and gas velocity influence fluidization. Bubble behavior and separation process of the coal in ADMFB were investigated using pressure measuring system and image analysis. Ash separation degree (Sash) was used to evaluate separation performance of ADMFB. Research results showed that separation performance was satisfactory when the material was fed from the upper or middle position, and it was poor when the material was fed from the bottom position. Materials needed certain period of time to complete the sink-float process. Sash values increased and then stabilized as separation time increased. Sufficient loosening of the materials was the key factor for the highly efficient separation. Gas velocity increase helped materials to loosen, and it also destroyed bridging and smuggling. Thus, the overall separation performance improved, while, excessive gas speed was unfavorable. At h∗ = 0.75, t = 5 min and N = 1.8, ADMFB showed excellent separation performance, and its corresponding Sash value reached maximum value equal to 1.07.

Statistical Analysis of Coal Beneficiation Performance in a Continuous Air Dense Medium Fluidized Bed Separator

ABSTRACTIn this study, the performance of a continuous air dense medium fluidized bed (ADMFB) separator is investigated for coal beneficiation. The full factorial experimental design method is used to study the effect of superficial air velocity (U), bed length (T), and bed height (H) on the clean-coal ash content, organic material recovery, and overall system separation efficiency. Optimum operating conditions are determined and followed by the effect of feed particle size on separation quality. Statistical analysis of the results revealed that H had no significant effect on product ash content while U and T had negative effects. A reduction in ash content from 19% to 10% was obtained once full bed length was utilized. The increase of all parameters had a negative effect on organic material recovery, while recovery was always above 88%. The only significant mutual interaction was found to be between T and H with even more effectiveness than U on the recovery. Separation efficiency increased by increasing the bed length and reached 20% once full bed length was utilized. The optimum operating condition was determined to be at U = 19.5 cm/s, T = full bed length, and H = 15 cm. It was observed that feeding finer particles deteriorated the beneficiation process.

Application of response surface methodology for parametric evaluation of air dense medium fluidized bed separator used for coal cleaning

An air dense medium fluidized bed separator is an efficient dry process for the removal of undesirable gangue material from run-of-mine coal. Its cleaning performance depends on a variety of operating parameters that are interrelated in unknown, complex ways. A literature review showed that these parameters’ effects had been experimentally investigated using a traditional one-variable-at-a-time approach, which is highly inefficient and sometimes misleading because many of the parameters often interact with each other to alter the overall equipment performance. Also, it is realized that the interrelationship among these parameters can have a significant effect on equipmentperformance. Therefore, to correctly evaluate the effects of individual parameters as well as their interactional effects on the separation performance of an air dense medium fluidized bed, we conducted a scientific study based on response surface methodology. Empirical modelsfor two key response variables, namely; product ash and combustible recovery, were developed and subsequently used for identifying an appropriate operating region to achieve optimum separation performance. Furthermore, the optimum performances predicted from the empirical models were validated against experimental data. Preliminary results show a strong interaction among the operating parameters investigated in this test program.

Influence of medium particle size on the separation performance of an air dense medium fluidized bed separator for coal cleaning

Synopsis Dry beneficiation of coal by air dense medium fluidized bed is an emerging trend. It is widely believed that the particle size of the medium has a significant effect on the separation efficiency. This investigation demonstrates that medium particle size has a major effect on separation efficiency. Experimental results show that different size fractions of the same feed respond differently to the same size fraction of medium solids. Furthermore, a particular size fraction of feed coal responds differently with different size fractions of medium solids. The E p values and overall metallurgical performance parameters, obtained from experimental results, clearly indicate the superior performance of an air dense medium fluidized bed separator when using –150+106 µm magnetite powder as the fluidizing medium. These observations reinforce the importance of sizing the medium particle size for the air dense medium fluidized bed.

Prediction of the position of coal particles in an air dense medium fluidized bed system

An air dense medium fluidized bed separator (ADMFBS) is used for dry beneficiation of coal using ultra-fine magnetite particles as a pseudo-fluid medium. In this process, the coal particle gains additional weight due to coating on its surface and deposition at dead zone area by fine magnetite particles. Hence, the effective density of coal particle increases and the position of coal particle changes accordingly. In this work, an attempt was made to predict the position of coal particle in non-bubbling condition dense medium fluidized bed system. Coal particles of different shape such as cubical, rectangular prism, spherical and triangular prism with different projected area and density were used. The results show that the position of coal particle in air dense medium fluidized bed follows descending order with respect to the increase of density, projected area of coal particle and different shapes (i.e., triangular prism, cubical, rectangular prism and spherical). Empirical mathematical correlations were developed to predict the position of coal particle.

Optimization Process of an Air Dense Medium Fluidized Bed Separator for Treating High-Ash Non-coking Indian Coal

The performance of an air dense medium fluidized bed separator, used for coal cleaning, is significantly affected by the operating process parameters. Proper estimation of these parameters is of great importance from both operational and control standpoints. The existing literature reveals that the optimum operating range for these parameters has been experimentally determined by pursuing a traditional “one variable at a time approach” which fails to consider parameter interactions and sometimes misleading, especially when the behavior of two process parameters changes as a function of a third parameter. It is realized that the interrelationship among these process parameters have a significant effect on the overall performance of this separator. In this study, a detailed investigation is carried out to examine the interdependencies among these parameters and their interactional effect on the separation performance of an air dense medium fluidized bed separator. Response surface methodology is used for this purpose and empirical models for two key response parameters, namely, product ash content and combustible recovery, are developed. These empirical models are utilized to establish the new levels of the parameters to achieve the optimum performance of the equipment and subsequently these model predictions are validated against the experimental results. Preliminary results show a strong interaction among some operating parameters.

Study on particle dynamics in different cross sectional shapes of air dense medium fluidized bed separator

Dry coal washing is gaining popularity on account of its ability to produce clean coal without the use of water which is becoming to be a costly resource for beneficiation. Air dense medium fluidized bed separation (ADMFBS) is one of the dry beneficiation techniques which is used for cleaning of coal. Fine magnetite particles are used as medium to make pseudo-fluid by fluidization method. The effectiveness of ADMFBS depends on stability of the fluidized bed. In the present work, an attempt has been made to study the stability characteristics of different cross-sectional shapes of fluidized bed having same cross-sectional area. Different indicators like fluidization index, particulate expansion function, pressure drop of bed and distributor, minimum fluidization and bubbling velocities were used to characterize the stability of fluidized bed. The effect of different operating and design parameters on the homogeneity and stability of the fluidized bed was studied. It was observed that cross sectional shape of the fluidized bed column has a significant effect on the stability of the bed. Moreover, rectangular cross-sectional shape provides better stability properties compared to square or circular shape.

Characteristics of Minimum Fluidization Velocity for Magnetite Powder used in an Air Dense Medium Fluidized Bed for Coal Beneficiation

AbstractAccurate determination of minimum fluidization velocity of medium particle is essential for proper designing and operation of an Air Dense Medium Fluidized Bed Separator for coal beneficiation. Significantly different values of minimum fluidization velocity have been obtained from different available correlations. So, it is necessary to develop a suitable correlation for this specific purpose. In this study, the minimum fluidization velocities of different size magnetite powders are investigated in a 15 cm diameter fluidized bed. Three correlations are derived from the fundamental principles for the theoretical prediction of these minimum fluidization velocities. The adequacy and reliability of each of these correlations is tested by adopting a statistical analysis approach and the most suitable correlation is selected. The predictive capability of this selected correlation is verified by using the data available in the literature. The results show that this new correlation is in very well agreement with these experimental data and shown to be applicable for practical purpose. Moreover, this study reveals that the correlation developed from the basic particle properties and bed characteristics can predict more accurate results.

Influence of Coal Feed Size on the Performance of Air Dense Medium Fluidized Bed Separator Used for Coal Beneficiation

In gravity separation operation, the probability of a coal particle to appear in the product stream or in the refuse stream is a strong function of its size. Improper selection of feed size may lead to significant reduction in efficiency of the separation unit. Available literature conforms that the separation efficiency of an air dense medium fluidized bed separator, which is a gravity separation operation, decreases with feed coal size, but determination of appropriate feed size range, for efficient operation of this separator, still remains as a challenge. In this paper, the effect of feed size on the separation performance is investigated and an attempt has been made to quantify the optimum size range over which the separator can operate satisfactorily. The performance of the equipment is evaluated in two steps, namely, sharpness of separation affected by the washing unit and the efficiency of the washing operation. Predictive model equations are also proposed for describing the relation between sharpness of separation and feed size. Four Indian coal samples of different washability characteristics are considered for this investigation. Preliminary results show that the air dense medium fluidized bed separator performance is quite satisfactory for the feed coal within the 50–15 mm size range.

Stability Study of an Air Dense Medium Fluidized Bed Separator for Beneficiation of High-Ash Indian Coal

Indian high ash noncoking coal contains a substantial quantity of near-gravity materials (NGM). The presence of NGM needs beneficiation in dense medium separation process. Air dense medium fluidized bed separator (ADMFBS) uses the magnetite medium to improve the separation efficiency of beneficiation of high NGM coal. Stability of the particulate fluidized bed in this system is the essential prerequisite for the separation of heavy and light particles. In this study, the characterization of medium and particulate fluidized bed was assessed to maintain the nonbubbling condition. Stability of the fluidized bed was characterized by different expressions like fluidization index, particulate expansion function, Froude number of particle, Reynolds number of particle, and pressure drop ratio using the minimum fluidization velocity, minimum bubbling velocity, pressure drop of distributor and bed, bed porosity, air viscosity, aspect ratio, density of air, and density of medium. It was found that the fluidization indexes of this system for different experimental runs are around 1 to 2. The system was scaled up from laboratory to pilot scale, having a feed throughput capacity of 600 kg/hr. Indian high ash noncoking coal at particular size (−25 + 6 mm) was used in continuous operation. The partition number was calculated based on washability data of product and reject. The Ep and imperfection value for the pilot-scale ADMFBS was found to be 0.12 and 0.071, respectively.

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.

Potential of Air Dense Medium Fluidized Bed Separation of Mineral Matter for Mercury Rejection from Alberta Sub-Bituminous Coal

In this study, three basic conditions for efficient dry separation of mineral matter from coal by an air dense medium fluidized bed (ADMFB) separator were assessed. The optimal fluidization air velocity for ADMFB separation was found to be insensitive to particle sizes of feed examined. The suitability of using an ADMFB separation to co-reject mercury with mineral matter was demonstrated. A strong linear relationship between mercury content and mineral matter content was confirmed for two of the three actively mined seams of this sub-bituminous coal. Following ADMFB separation, the linear fit of mercury rejection and ash rejection led to a coefficient of determination ranging from 0.98 to 0.86. In one of the coal seams studied, a mercury rejection of 58% and a mineral matter rejection of 60% were achievable at a total combustible recovery of 87% at optimized fluidization air velocity.

An Investigation on Mercury Association in an Alberta Sub-bituminous Coal

There are various mercury species in nature. Understanding mercury association with coal components could play a critical role in controlling mercury emission from coal utilization. In this study, an Alberta sub-bituminous coal was fractionated into various size and density fractions. The mercury and sulfur contents in each fraction were determined. To identify mercury association with coal components, the fractionated coal samples before and after low-temperature ashing were characterized by an X-ray diffractometer. Our study showed a clear correlation between the mercury and ash contents of coal. Such a relation was not observed between the mercury and sulfur contents. The potential to remove mercury prior to coal utilization by ash rejection using an air dense medium fluidized bed separator was demonstrated. At a combustible recovery of 81%, an ash rejection of 55% was achieved, leading to a mercury rejection of 56%.

Fine Coal Beneficiation using an Air Dense Medium Fluidized Bed

The potential of using Air Dense Medium Fluidized Bed (ADMFB) separation for cleaning sub-bituminous coal was investigated. The effect of operating parameters such as the fluidizing air velocity and medium particle size on separation efficiency was determined with coal of various size fractions. Good separation efficiencies with raw coal in the 6 to 1 mm size fraction were achieved. Partition curves showed an E p value of 0.03 for coal in 5.6 to 3.35 mm size fraction. For the 1.00 to 0.42 mm size fraction, the separation efficiency deteriorated to an E p value of 0.10. To achieve an optimum separation efficiency, a separation medium with a narrow and distinct size fraction is needed to allow a superficial gas velocity sufficiently high to create a pseudo fluid medium bed while sufficiently low to avoid back mixing of fine coal and lifting of fine size mineral matter during fluidization.