振动流化床中双组份湿润非球形颗粒的混合/分离特性研究

The development of the combined dry separation and drying of high-ash lignite in a vibrated gas-fluidized bed dryer is the basis of large-scale efficient upgrading technologies of the high-ash lignite. To master the distribution characteristics and mixing/separation mechanism of the binary mixtures of wet and non-spherical particles is the key issues of this technology. First of all, using the physical separation method of sieve and sink-float, the key morphological parameters of these lignites were obtained quantitatively by the microscopic image method and a series of stimulant coal / gangue particles were then prepared. Secondly, in a laboratory scale gas-vibro fluidized bed, the pressure drop, minimum fluidization velocity and flow pattern was investigated by recording pressure differential signals and fluidization images. Meanwhile, the mixing/segregation dynamics and kinetic characteristics of bubble rising, aggregation and splitting process were screened by a high-speed camera with dye tracer particles method. Moreover, the effect of particle properties and operating parameters on the fluidized behaviors, mixing/segregation dynamics and kinetic bubble characteristics were examined systematically. Finally, on the basis of multi-ball method, the contact model of wet and non-spherical particles was obtained and the movement behaviors of these special particles were then simulated by means of combined computational fluid dynamics and discrete element method (CFD-DEM) in a gas-vibro fluidized bed. According to these above data, the mixing/segregation mechanism was achieved.

振动流态化干燥分选联合脱除技术的开发是实现高灰褐煤大规模高效提质利用的基础，掌握褐煤这种双组份湿润非球形颗粒在振动流化床中的分布特性及混合/分离机理是该技术开发的关键。本项目采用筛分、浮沉的物理方法对褐煤进行分级与分离，通过显微图像法定量获得褐煤颗粒形貌特征的关键参数，并制备出反映这些参数的模拟精煤/矸石颗粒；以模拟颗粒体系为对象，在振动流化试验台上，通过压差计和高速摄像仪，分析床层压降、临界流化速度、流形等床层流化行为，利用高速摄像仪结合染色颗粒示踪方法，在线同步获得模拟颗粒的分布动力学特征及气泡上升、聚合以及分裂过程的详细信息，揭示颗粒混合/分离的宏观机理；在实验基础上，基于多球法建立非球形湿颗粒的离散元法接触模型，对双组份湿润非球形颗粒在振动流化床运动规律进行模拟，揭示颗粒混合/分离的微观机理。

本项目综合运用矿物加工学、流体力学、颗粒学等学科理论对振动流化床中双组份颗粒的混合/分离特性进行了研究，通过显微图像法定量获得褐煤颗粒形貌特征的关键参数，利用电子压差计分析振动流化床床层流化行为，利用高速摄像仪结合染色颗粒示踪方法，在线同步获得颗粒的分布动力学特征及气泡运动规律，在实验基础上，基于CFD-DEM方法对振动流化床中二元颗粒体系进行模拟，揭示颗粒混合/分离的作用机理，取得了以下重要进展：.（1）高灰褐煤中的矿物质具有大量异质结晶矿物，含氧官能团数量少，表面积小以及孔容积低，难以持水；随粒径减少，褐煤持水能力（内水和全水含量）显著降低；随粒度减小，灰分含量逐渐增大，此趋势与高阶煤情况截然相反。.（2）随褐煤湿含量、粒径和灰分减小，床层起始流化速度减小，流化后床层更稳定；随振幅增大和频率减小，起始流化速度增大，流化后床层不稳定；当气速较低时，振动对床层作用以密实为主，气速较高时，床层膨胀率变为正值。 .（3）随流化数N增大，分离效果先增强后减弱，N=1.1~1.2时具有最好分离效果；混合物的分离过程不仅按密度离析，颗粒还按粒级分层；振动参数对混合/分离行为有重要影响，外水含量对分离有显著抑制作用。.（4）颗粒物性、操作参数对气泡运动都有明显作用，当振动强度较大时，床面和气泡不稳定，气泡尺寸增大；颗粒粒度越小，振动的消泡作用越大。.（5）提出了适用于普通流化床、重介流化床及振动流化床的颗粒分离/混合区域相图，阐释了气泡驱动的浮升组分-沉降组分作用机理。 .（6）颗粒在N=0.8~0.9时，在振动（促进颗粒向床表面运动）和气流（迫使颗粒向床底部运动）协同作用下趋于一特殊混合状态，传热传质效应改善，干燥效果与高气速条件下（N=1.6）干燥效果接近，能高效低耗干燥褐煤。.项目研究可为振动流态化干燥分选联合脱除系统的设计、运行及参数优化提供依据，为实现高灰褐煤大规模高效提质利用奠定基础。