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.

Characteristics of fluidization and dry-beneficiation of a wide-size-range medium-solids fluidized bed

Wide-size-range medium-solids are used in a modularized coal beneficiation demonstration system with a gas-solid fluidized bed. The characteristics of fluidization and dry-beneficiation of the medium solids were studied. The numerical simulation results show that 0.15–0.06 mm fine magnetite powder can decrease the disturbances caused by the bubbles. This is beneficial to the uniformity of the gas-solid interactions and thus to the uniformity and stability of the bed density and height. The experimental results show that, with an increase in the fine coal content in medium solids, both the fluidization quality and the beneficiation performance of the bed decreased gradually. When the fine coal content was no more than 13%, a relatively high superficial gas velocity increased the beneficiation efficiency. When the content was more than 13%, part of the fine coal was separated, leading to product layers. The separation efficiency was therefore gradually decreased. The models for predicting the bed density standard deviation and the probable error, E, value were both proposed. The E value can reach to 0.04–0.07 g/cm^3 under the optimized experimental parameters. This work provides a foundation for the adjustment of the bed density and the separation performance of the modularized 40–60 ton per hour dry coalbeneficiation industrial system.

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.

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.