Analysis and evaluation on pressure fluctuations in air dense medium fluidized bed

Pressure fluctuations contribute to the instability of separation process in air dense medium fluidized bed, which provides a high motivation for further study of underlying mechanisms. Reasons for generation and propagation of pressure fluctuations in the air dense medium fluidized bed have been discussed.Drift rate and collision rate of particles were employed to deduce the correlation between voidage and pressure fluctuations. Simultaneously, a dynamic pressure fluctuation measuring and analysis system was established. Based on frequency domain analysis and wavelet analysis, collected signals were disassembled and analyzed. Results show gradually intensive motion of particles increases magnitudes of signal components with lower frequencies. As a result of violent particle motion, the magnitude of real pressure signal's frequency experienced an increase as air velocity increased moderately. Wavelet analysis keeps edge features of the real signal and eliminates the noise efficaciously. The frequency of denoised signal is closed to that of pressure signal identified in frequency domain analysis.

Numerical simulation and experimental verification of bubble size distribution in an air dense medium fluidized bed

Bubble size distribution is the basic apparent performance and obvious characteristics in the air dense medium fluidized bed (ADMFB). The approaches of numerical simulation and experimental verification were combined to conduct the further research on the bubble generation and movement behavior. The results show that ADMFB could display favorable expanded characteristics after steady fluidization. With different particle size distributions of magnetite powder as medium solids, we selected an appropriate prediction model for the mean bubble diameter in ADMFB. The comparison results indicate that the mean bubble diameters along the bed heights are 35 mm < D b < 66 mm and 40 mm < D b < 69 mm with the magnetite powder of 0.3 mm+0.15mm and 0.15mm+0.074mm, respectively. The prediction model provides good agreements with the experimental and simulation data. Based on the optimal operating gas velocity distribution, the mixture of magnetite powder and <1mm fine coal as medium solids were utilized to carry out the separation experiment on 6-50mm raw coal. The results show that an optimal separation density d P of 1.73g/cm 3 with a probable error E of 0.07g/cm 3 and a recovery efficiency of 99.97% is achieved, which indicates good separation performance by applying ADMFB.

Effects of sintered metal distributor on fluidization quality of the air dense medium fluidized bed

Dry coal beneficiation using an air dense medium fluidized bed (ADMFB) requires the formation of a sta- ble and uniform bed from the dense medium. Others have shown that the structure and geometric parameters of the air distributor have a significant influence on the experimentally observed fluidization quality. In this study we used a sintered metal distributor (SMD) in the ADMFB separator and study its effect on the fluidization quality. The results show that for the same open area ratio (OAR), a smaller aper- ture in the SMD will provide improved fluidization quality. If aperture size is held constant bigger open area ratios result in improved fluidization quality. And, the fluidization quality also improves when the pressure drop across the SMD increases. A model relating distributor pressure drop and the geometric parameters of the SMD is also proposed.

RESEARCH ON DENSITY STABILITY OF AIRDENSE MEDIUM FLUIDIZED BED

In this paper on the basis of studying the distribution of fine Coal in the dense medAn fluidised bed. the optimai size range of fine coal, which constitutes a fluidized bed together with the dense medium, has been found. In the separating process the fine coal will continuously aeeumulate in fluidized bed, thus inevitably reducing the density of the bed.In order to keep bed density stable, the authors adopted such measures as split-now of used medium and complement of fresb dense medium.The experiment results in both lab and pilot systems of the air-dense medium fluidized bed show that these measures are effective and satisfactory. Then authors also have estabinbed some relative dynamic mathematical models for it.

The Forming-Mechanism and Role of Creativity Thinking in Dry Coal Beneficiation of Coal with Air-Dense Medium Fluidized Bed

In this paper, the authors point out that the Creativity is an inevitable request in solving engineering and technological problems and that the coal beneficiation technology with air dense medium fluidized bed is a result of reversal thinking, and its forming mechanism is the use of other things for reference and the transplantation.

DRY CLEANING OF COAL WITH AIR DENSE MEDIUM FLUIDIZED BED

This paper deals with the experimental study of dry cleaning of coal with air dense medium fluidized bed. This technique opens up an efficient way of coal separation for vast areas in the country where water resources are in short supply or coals tend to slime seriously in wet process. Tests show that it can separate any kind of coal (6--50mm) efficiently. The probable error E, can reach 0.05--0.08. The separating density can be adjusted in the range of 1.0--2.0 g/cm^3. This technique brings about enormous economic benifits.

Separation density prediction of geldart A^(-)dense medium in gas-solid fluidized bed coal beneficiators

Gas-solid Fluidized Bed Coal Beneficiator(GFBCB)process is a crucial dry coal beneficiation fluidization technology.The work employs the GFBCB process alongside a novel Geldart A^(-)dense medium,consisting of Geldart A magnetite particles and Geldart C ultrafine coal,to separate small-size separated objects in the GFBCB.The effects of various operational conditions,including the volume fraction of ultrafine coal,the gas velocity,the separated objects size,and the separation time,were investigated on the GFBCB's separation performance.The results indicated that the probable error for 6∼3 mm separated objects could be controlled within 0.10 g/cm^(3).Compared to the traditional Geldart B/D dense medium,the Geldart A/A^(-)dense medium exhibited better size-dependent separation performance with an overall probable error 0.04∼0.12 g/cm^(3).Moreover,it achieved a similar separation accuracy to the Geldart B/D dense medium fluidized bed with different external energy for the small-size object beneficiation.The work furthermore validated a separation density prediction model based on theoretical derivation,available for both Geldart B/D dense medium and Geldart A/A^(-)dense medium at different operational conditions.

Fluidization stability and periodic fluctuations in gas–solid separation fluidized bed using Geldart A dense medium

Gas–solid separation fluidized bed is a typical method for coal separation without water utilization.Geldart A particles is also considered as the ideal dense medium to strengthen separation efficiency.Fluidization stability reflects the bed pressure fluctuations and the distribution of bubble and emulsion phases,affecting the separation performance.And the main frequency of pressure fluctuations can directly reflect the degree of pressure fluctuations.Therefore,the detailed fluidization stability is analyzed combined the method of standard deviation of pressure fluctuations,power spectral density,etc.,for Geldart A particles.The results showed that maintaining an appropriate gas velocity resulted in an average bed pressure of around 2000 Pa.The main frequency is mainly concentrated around 1–1.5 Hz.Finally,a prediction model of the main frequency of pressure fluctuations is established,and the error can be controlled within±0.15.The investigation further proved the stable fluidization of Geldart A particles and provides a method for predicting the main frequency of pressure fluctuations in the gas–solid separation fluidized bed.

Dense Pellicular Agarose-Glass Beads for Expanded Bed Application: Flow Hydrodynamics and Solid Phase Classifications

Two dense pellicular agarose-glass matrices of different sizes and densities, i.e., AG-S and AG-L, have been characterized for their bed expansion behavior, flow hydrodynamics and particle classifications in an expanded bed system. A 26 mm ID column with side ports was used for sampling the liquid-solid suspension during expanded bed operations. Measurements of the collected solid phase at different column positions yielded the particle size and density distribution data. It was found that the composite matrices showed particle size as well as density classifications along the column axis, i.e., both the size and density of each matrix decreased with increasing the axial bed height. Their axial classifications were expressed by a correlation related to both the particle size and density as a function of the dimensionless axial bed height. The correlation was found to fairly describe the solid phase classifications in the expanded bed system. Moreover, it can also be applied to other two commercial solid matrices designed for expanded bed applications.

Progress in developments of dry coal beneficiation

China’s energy supply heavily relies on coal and China’s coal resource and water resource has a reverse distribution.The problem of water shortages restricts the applications of wet coal beneficiation technologies in drought regions.The present situation highlights the significance and urgency of developing dry beneficiation technologies of coal.Besides,other countries that produce large amounts of coal also encounter serious problem of lack of water for coal beneficiation,such as American,Australia,Canada,South Africa,Turkey and India.Thus,dry coal beneficiation becomes the research hot-points in the field of coal cleaning worldwide in recent years.This paper systematically reviewed the promising research efforts on dry coal beneficiation reported in literature in last 5 years and discussed the progress in developments of dry coal beneficiation worldwide.Finally,we also elaborated the prospects and the challenges of the development of dry coal beneficiation.

Comparison of coal separation characteristics based on different separating approaches in dry coal beneficiation flowsheet

The separation characteristic of raw coal from Luoyang mining area, China, was investigated by applying a dry coal beneficiation flowsheet with the dense medium gas-solid fluidized bed as main separating equipment. The experimental and simulation results indicate that the dense medium gas-solid fluidized bed can provide uniform distribution and stable fluctuation of bed densities at various heights. Two types of different separating approaches were compared using the dry coal beneficiation flowsheet. Compared with obtaining cleaning coal in the first stage of the flowsheet, a higher yield of the cleaning coal and better separation efficiency can be achieved when discharging gangue in the first stage. Finally, the results indicate that 64.86% pure cleaning coal with an ash content of 11.77% and 13.53% middlings were obtained, and 21.61% gangue was removed in two successive separation stages with the probable errors of 0.05 and 0.07 g/cm3, respectively.

Prediction of medium-to-coal ratio effect in a dense medium cyclone by using both traditional and coarse-grained CFD-DEM models

Dense medium cyclone(DMC)is the working horse in coal industry.In practice,it is usually operated under constant pressure and the operational conditions(mainly medium-to-coal(M:C)ratio and oper-ational pressure)need to be adjusted according to coal washability data(mainly coal particle size and density distributions).Nonetheless,until now it is still not well understood how the M:C ratio would affect the performance of DMCs especially under the practical conditions.In this work,the effect of M:C ratio is for the first time numerically studied under conditions similar to plant operation by using both tra-ditional and coarse-grained(CG)combined approach of computational fluid dynamics(CFD)and discrete element method(DEM),called as traditional CFD-DEM and CG CFD-DEM,in which the flow of coal par-ticles is modelled by DEM or CG DEM which applies Newton's laws of motion to individual particles and that of medium flow by the conventional CFD which solves the local-averaged Navier-Stokes equations,allowing consideration of particle-fluid mutual interaction and particle-particle collisions.Moreover,impulse and momentum connection law is used to achieve energy conservation between traditional CFD-DEM and CG CFD-DEM.It is found that under constant pressure,the M:C ratio affects DMC perfor-mance significantly.The specific effect depends on coal washability or coal type.Under extremely low M:C ratio,the phenomenon that high-quality coal product is misplaced to reject is successfully repro-duced,which has been observed in plants in Australian coal industry and called as"low-density tail".Moreover,strategies are proposed to mitigate the"low-density tail"phenomenon based on the model.

Evaluation of Mayer curve validity on feed blending at the Zarand coal washery plant

The coal processing methods used at the Zarand coal washery plant are the heavy medium bath,jigs,and flotation.The coal-containing materials that are fed to the plant are acquired from different mines,and they have different washability properties.In this paper,the validity of Mayer curve (M-curve),the conventional method for determining coal washability,was evaluated on blending of raw coals that are fed to the plant.Washability curves were prepared for the hand-blended samples and compared with the washability predicted by the Mayer curves.Different samples from different seams and mines were blended by hand in 50:50 ratios,and sink and float tests were performed;the resulting washability curves were in good agreement with the washability curves predicted using the Mayer method for the same blending ratio.This work resulted in the preparation of the optimum plant feed that can be achieved from the blending of different coal samples to produce the best plant yield at a given ash content.