Dry coal beneficiation has played a vital role during the initial stage of coal cleaning in recent years. Successful utilization of a gas–solid fluidized bed for >6 mm coal cleaning motivates scholars to explore the possibility of fine coal cleaning using dry beneficiation methods. In this study, pulsed flow was introduced into a fluidized bed to optimize bubble behavior, thus improving the density stability. The equation of minimum fluidization velocity (U_mfp) in a gas-vibro fluidized bed for coal preparation was investigated theoretically. An equation has been proposed for predicting U_mfp while considering changes in the friction coefficient (C_f) in the gas-vibro fluidized bed. Based on two-phase theory, the correlation of bed density was determined by analyzing the bubble behavior in the gas-vibro fluidized bed. The theoretical bed density was then compared with experimental data of the bed density and separation density. The predicted bed density in monodisperse and binary dense medium systems was found to be consistent with the experimental results. Overall, the equation of bed density is suitable for estimating the separation density in the gas-vibro fluidized bed.

With China already committed to peak carbon dioxide emissions before 2030 and aiming at achieving carbon neutrality before 2060, coal separation has recently become a hot research topic, in particular, gas–solid fluidized separation technology has attracted significant research attention. Coal particles with size of +10 mm can be separated efficiently via currently used technologies; nonetheless, specific scientific problems of fine coal separation still need to be systematically explored. In this study, combined with the properties of coal particles, a density model of fine coal in fluidized bed separation process was proposed. The separation effect was found to be better with the increase of feeding coal particle size, in particular, the coal particles with size larger than 5 mm underwent effective separation. The results reveal that the drag force of the fine coal separation process is an important factor restricting the separation efficiency. Fluidization theories, such as pressure drop, gas–solid two-phase model, and particle sedimentation theory could explain that with the decrease in the feeding coal particle size from 10 mm, the probable error E value increases from 0.105 to 0.355 g/cm³, the misplaced material content M increases from 5.48% to 16.13%, and the lower limit of the separation is controlled at 5 mm. This helps to enhance the processing capacity and increase the separation granularity range of the fluidized bed.

Gas-solid fluidized bed is an effective dry method for beneficiation of −6mm fine coal, belonging to Geldart D particle. Due to the density difference of concentrates and gangue in the raw coal, the bed can remove gangue through segregation of binary particles. The core problem is how to reduce the bubble coalescence and improve segregation degree in the bed. In this study, glass beads and plastic beads were selected to simulate high-density and low-density particles in pulsed gas-solid bed (PGFB). And different pulsation frequencies (f = 0–7 Hz) and gas velocities (N = 1.1–1.7) were selected in this work. The results showed that gas velocity and pulsation frequency played important role on particle segregation and mixing behavior. The segregation index reached the maximum value at pulsation frequency f = 3.49 Hz and gas velocity N = 1.3 when h = 80 mm, indicating pulsed gas-solid fluidized bed can effectively separate particles of different densities. With the increase of bed height, the standard deviation of separation index decreases, and the optimal frequency moves to the low frequency region. This work provides guidance for the study of segregation and mixing behavior of Geldart D binary particles in pulsed fluidized bed.

Coal is the dominant energy resource in China. With the Chinese policy of committing to reducing peak carbon dioxide emissions and achieving carbon neutrality, coal separation has recently become a hot topic, especially the fluidized separation of fine particles. In this study, micron-sized particles were introduced to ameliorate the properties of the traditional fluidized bed. The expansion characteristics of the micron-sized-particle-dense medium were explored. A bed expansion prediction model of the micron-sized-particle-dense medium was established, and the prediction error was about 10%, providing a theoretical basis for understanding the distribution characteristics of the bed. This model also helped predict the bed density in the presence of a micron-sized-particle-dense medium, and the prediction accuracy was between 85% and 92%, providing a theoretical basis for selecting and popularizing fluidized beds for industrial separation.