Research progress and outlook of efficient dry separation of fine coal

DUAN Chenlong; XU Yangfan; ZHANG Bo; DONG Liang; ZHOU Enhui; WANG Weinan; PAN Miao; ZHOU Chenyang

doi:10.13225/j.cnki.jccs.YG25.1244

Abstract：As the primary energy source in China,coal plays a crucial role in national energy security.More than two-thirds of coal reserves are distributed in arid and water-scarce regions.Low-quality coal accounts for approximately 40％of total resources.With the widespread application of fully mechanized mining,the production of fine coal(＜6 mm)has increased to more than 40％of raw coal.Although dry separation technologies for ≥6 mm coarse coal have achieved stable industrial application in several mining areas,the separation accuracy for＜6 mm fine coal remains limited.In addi-tion,hydraulic fracturing and water spraying for dust suppression during mining substantially increase the moisture con-tent of raw coal(above 15％),leading to pronounced particle agglomeration.These factors highlight the need to develop effective dry separation theories and technologies for moist and low-quality fine coal.The performance constraints of gas-solid fluidized separation and vibration-air synergistic separation technologies that have been utilized in industrial applica-tions are examined.Based on flow responses,interface formation mechanisms,and equipment adaptability under condi-tions of moist low-quality fine coal,several key scientific questions are summarized.These include density-stratification regulation and multiscale flow coupling in gas-solid fluidized separation,controllable construction of stable force fields for vibration-air synergistic separation of low-quality fine coal,and nonequilibrium thermos-hydrodynamic coupling mechan-isms governing moisture removal from wet particles.The numerical simulations and theoretical models from experimental studies are synthesized,concerning fine dense-medium gas-solid fluidized separation,vibration-air synergistic separation,fluidized-bed drying,and transient steam flash drying.For fine dense-medium gas-solid fluidized beds,findings related to bed expansion,pressure fluctuations,bubble dynamics,and electrical capacitance tomography(ECT)are summarized with corresponding flow-regime criteria,density-control correlations,and quantitative instability indicators.For vibration-air-flow synergistic separation,the researches are reviewed on vibration acceleration responses,the evolution of surging struc-tures,three-dimensional particle dynamics,interface formation behavior,and parameter combinations involving high-fre-quency vibration and stepped air distribution.For drying processes,studies on liquid-bridge mechanics,heat and mass transfer under vibration-airflow coupling,nonequilibrium thermodynamic drying models,and the energy distribution and moisture-migration characteristics during saturated-steam pressurization followed by rapid depressurization are synthes-ized.Building on these findings,the processes of drying,dry screening,and dry separation are reorganized to summarize and discuss an integrated"Drying-Dry screening-Dry separation"beneficiation approach for＜6 mm fine coal.In this scheme,moderate drying reduces liquid-bridge adhesion,dry screening forms a narrow size-fraction feed,and gas-solid fluidized or vibration-airflow synergistic separators accomplish dry separation,thereby expanding the applicability of dry beneficiation to a broader range of coal types and particle sizes.Overall,existed studies have established a preliminary foundation in multiscale coupling mechanisms,quantitative characterization of flow stability,and integrated design of dry-ing and separation.The further progress is needed in multiphysics coupling under complex operating conditions,intelli-gent monitoring and adaptive control,and the integration of dry beneficiation with waste-heat recovery and carbon-reduc-tion objectives.That provides references for future research and process optimization related to the efficient dry upgrading of fine coal.