干法重介质流化床煤炭颗粒受力特性与分选研究

Investigation on force characteristics and separation of coal in dry dense medium fluidized bed

近年来,干法重介质流化床分选技术的快速发展为世界干旱缺水地区的煤炭洁净分选提质提供了一条有效途径。在干法重介质流化床中,上升气流驱动加重质颗粒流化形成具有似流体性质的气固两相流床层,营造了适合煤炭分选的均匀稳定的流态化环境。入选煤炭颗粒在床层中迁移、浮沉,受到自身重力、气流曳力、介质阻力、床层浮力等综合作用按密度进行分选。煤颗粒物性特征、床层密度分布、流化床操作参数等是影响煤颗粒受力特征、沉降特性及分选效果的关键因素。重点研究了加重质颗粒在流化过程中的迁移过程和床层密度空间分布规律,定量评估了床层密度的均匀稳定性;研究了颗粒粒度、密度、浸没深度与流化气速对入选煤炭颗粒受力特性的影响规律,采用响应面分析方法对比了不同影响因素的扰动规律与影响程度,建立了表征各影响因素与煤炭颗粒综合受力关系的关联式;确定了入选煤颗粒各密度组分的迁移路径与稳定分布区域。研究结果表明,以磁铁矿粉(0.300~0.074 mm,2.36 g/cm^(3))与玻璃微粉(0.300~0.074 mm,1.14 g/cm^(3))组成二元加重质作为流化介质颗粒,可形成密度均匀的气固流化床层,二元加重质颗粒混合均匀稳定,床层密度波动控制在±0.01 g/cm^(3)以内;各主要影响因素对入选颗粒受力影响显著性程度依次为粒径、浸没深度、流化气速;入选煤颗粒给入床层后,各密度组分快速松散、沉降、分层,分选时间≤8 s,高于床层密度的煤颗粒快速下沉,沉降于床高40 mm以下区域;低于床层密度的煤颗粒沿床层表面附近区域松散、横向迁移,分布在床高160 mm以上区域;中间密度颗粒松散、沉降并行,整体分布于45 mm床高以上的床层区域。

In recent years,the development of dry separation technology of air dense medium fluidized bed(ADMFB)provides an effective way for clean coal processing in arid and water deficient areas of the world.In the dry heavy medium fluidized bed,the updraft drives the fluidization of dense medium to form a gas-solid two-phase flow bed with pseudo-fluid properties,which creates a uniform and stable fluidization environment suitable for coal separation.The coal particles migrate,float and sink in the bed,and are separated according to density under the comprehensive action of gravity,air drag,medium resistance,bed buoyancy and other forces.The characteristics of coal particles,bed density distribution and operation parameters of fluidized bed are the critical factors affecting the suffering force,settlement characteristics and separation effect of coal particles.Therefore,the migration process of dense particles in the fluidization process and the spatial distribution of bed density were studied.The uniformity and stability of bed density were quantitatively evaluated.The influence of particle size,density,immersion depth and gas velocity on the force properties of coal particles was studied.The response surface method was used to compare the disturbance law and influence degree of different factors.The correlation between the influencing factors and the com⁃prehensive force of coal particles was established.The migration path and stable distribution area of each density component of coal particles with different densities were determined.The results show that the ADMFB with uniform density can be formed by using magnetite powder(0.300-0.074 mm,2.36 g/cm^(3))and glass powder(0.300-0.074 mm,1.14 g/cm^(3))as the binary medium.The binary dense particles are mixed evenly and stably.The bed density fluctuation can be controlled within±0.01 g/cm^(3).The significant degree of the main influencing factors on the force of the selected particles is in the order of particle size,immersion depth and gas velocity.After coal parti⁃cles are fed into the bed,the density components are rapidly loosened,settled and stratified.The separation time is less than or equal to 8 s.The coal particles with density higher than bed sank rapidly and settled in the area below the bed height of 40 mm.The coal particles with density lower than the bed are loose and migrate laterally along the area near the bed surface,and are distributed in the area above 160 mm.The middle density particles are loose and settled,which are distributed in the bed area above 45 mm.