同轴旋转磁场对重介质旋流器切向速度和分选效果的调控机制研究

A new conceive of centrifugally accelerating magnetic powder to improve separation effect in dense-medium cyclone by applying rotating magnetic field is proposed. It employs coaxial rotating magnetic field outside cyclone and is characterized by double driven feedings involving pressure and magnetic force, and compound force field involving centrifugal force and magnetic force as well. By the numerical modeling of both flow field and magnetic field, the measurement of particle movement characteristics, and the separation experiments of cyclones, equation set that describes the force and the movement of magnetic particle is expected to be established, and the inherent law of rotating magnetic field affecting the slurry flow and density distribution inside cyclone is to be uncovered. The influence rule of factors including the position of rotating magnetic field, the characteristics of magnetic poles, the intensity of magnetic field, and the rotating speed on the centrifugal intensity, the density distribution and the coal preparation effect is to be studied employing mono-factor experiment and response surface methodology. Then multi-factor mathematical model for the separation of dense-medium cyclone controlled by rotating magnetic field is to be constructed. Moreover, an energy efficiency model of magnetic force driving is to be established by comparing the energy consumption of ordinary pressure feeding with pressure-magnetic feeding. Finally, the combination way of rotating magnetic field and static magnetic field is to be optimized to further improve on-line density regulation and control for dense-medium cyclone. The results of this research are significant for improving the separation efficiency and the auto-regulation level of dense-medium cyclone, decreasing energy consumption, and promoting the development of coal preparation as well.

以旋流器外配置同轴旋转磁场为手段，以压力和磁力双重驱动给料、离心力与磁力复合力场分选为特色，提出了利用旋转磁场对磁铁矿粉作加重质的重介质旋流器实施离心加速和分选效果调控的新构想。通过流场与磁场数值模拟、颗粒运动特性测试与旋流器分选试验相结合的研究方法，建立磁铁矿粉在旋转磁场中的受力与运动方程组，揭示旋转磁场影响重介质旋流器内矿浆流场和密度场的内在规律；通过单因素试验和多因素响应曲面法，研究旋转磁场的位置、磁极特性、磁场强度、旋转速度等因素对旋流器内离心强度、密度分布及其选煤效果的影响规律，构建旋转磁场下重介质旋流器分选效果的多因素数学模型；通过常压给料与压力磁力双给料的能耗对比，建立磁力驱动能效模型；优化旋转磁场与静态磁场的组合方式，进一步完善重介质旋流器密度在线调控的技术手段。本项研究成果，对提高重介质旋流器分选效果和自动调节技术水平、降低能耗、促进选煤技术发展具有重要意义。

为寻找重介旋流器选煤在线调控新途径，提高其智能化调控水平，研制了顶盖型、筒体型、锥体型、底流型同轴旋转磁场旋流器，构建了同轴旋转磁场重介旋流器分选系统。通过入料流量与压力、底流、溢流密度的变化，研究了旋转磁场对重介旋流器速度场、压力场、密度场的影响。采用数值模拟与分选试验相结合的方法，确定了N-S对称布置为最佳永磁极布置方式。详细研究了磁场位置、磁极数、磁场强度、旋转速度、旋转方向等参数对旋流器分选效果的影响，发现锥体中段旋转磁场分选效果最佳。在此施加静态磁场可同时降低精煤与尾煤灰分，磁场旋转方向与矿浆入料方向一致时精煤与尾煤灰分均高于静态磁场时的精煤与尾煤灰分，相反时的精煤灰分均低于静态磁场时的精煤灰分或基本持平，尾煤灰分均高于静态磁场时的尾煤灰分或基本持平。在旋流器锥体中段，磁场逆矿浆运动方向旋转时既能降低重介旋流器选煤的分选密度又能提高分选精度。旋转磁场降低分选密度的原因在于对重介质施加了向下的磁分力，提高分选精度的原因在于密实磁环对煤颗粒的水跃松散作用和反转磁场对矿浆的加速作用。将高场强旋转磁场置于底流口处，由于磁铁矿粉吸附在底流口处，缩小了底流口的尺寸进而使分选密度提高。锥体与底流口旋转磁场相结合，形成了旋转磁场调控重介旋流器分选效果的完整机制。以示踪、高速摄像为主要手段，研究了旋转磁场作用下磁性颗粒的运动和堆积特性规律，发现了磁性颗粒被旋转磁场反向驱动这一重要现象，提出了反向驱动的机理模型。采用多种方式，对旋转磁场的加速效能进行了研究，得到了旋转磁场可调控重介旋流器分选效果但不足以驱动磁性悬浮液高速流动的结论，但旋转磁场的反向弱驱动作用启发项目组研制出新型螺旋磁分离器，对磁铁矿具有良好的精选效果。本项目研究成果，对提高重介旋流器分选效果和自动调节技术水平、促进选煤技术发展、研制新型磁选设备具有重要意义。