【作者】 宋树磊；

【导师】 赵跃民；

【作者基本信息】 中国矿业大学 ， 矿物加工工程， 2009， 博士

【摘要】 空气重介流化床是一项高效干法选煤技术,可以成功处理50～6mm级粗粒煤的分选,但是由于气泡的存在而引起加重质一定程度的返混,所以分选粒度下限较高,无法满足<6mm煤炭的高效分选要求。通过引入磁场能量使空气重介流化床成为磁稳定流化床,可减小甚至消除流化床中的气泡,从而改善流态化质量,甚至达到气固散式流态化,是解决<6mm级细粒煤炭的高效干法分选方法。本论文主要研究了加重质的物理化学性质及其在磁稳定流化床中的流化特性;磁稳定流化床的消泡机理及密度稳定性;磁稳定流化床的屈服应力、表观粘度和流动性等流变学性质;颗粒在磁稳定流化床中的运动机理,建立了颗粒运动的动力学方程;错流磁稳定流化床中以模拟颗粒和<6mm细粒煤的分选实验。磁铁矿粉、磁珠和硼铁矿粉三种加重质的物理化学性质的研究表明三种加重质都是强磁性物质,有一定的强度、耐磨性和抗氧化性,可以作为空气重介质磁稳定流化床的分选介质。加重质的流化特性说明,初始流化速度Umf与磁场强度无关,而起始鼓泡速度Umb、颗粒带出速度Ut、稳定操作速度范围以及床层膨胀率随着磁场强度的增大而增大。外加磁场使磁性介质形成磁链是磁稳定流化床消除气泡的主要原因。密度稳定性研究表明磁稳定流化床的床层压力波动极小,始终处于稳定状态,且密度分布均匀;而普通流化床的压力波动较为明显,密度分布不均匀。拉板法测量磁稳定流化床屈服应力的研究表明屈服应力随床层深度的增加而变大,随磁场强度的增大而变大,随流化气速的增大而减小。同一磁性介质的不同粒级形成的磁稳定流化床的屈服应力随着介质粒度的减小而变大。落球法测量表观粘度的研究表明表观粘度随流化速度的增大减小,随磁场强度的增大而增大。借助Design-Expert试验设计软件对屈服应力和表观粘度进行正交试验,通过方差分析寻找显著影响因素,并得到了屈服应力和表观粘度的公式。错流磁稳定流化床的流动性实验表明增大床体倾角和流化气速使流动性增强,增大介质流量、磁场强度使流动性降低。并探讨了错流磁稳定流化床拟流体的本构关系。利用颗粒高速动态分析系统研究颗粒沉降的试验表明颗粒在磁稳定流化床中所受到的阻力可分为二部分:运动阻力和磁稳定流化床的屈服力,且屈服力对颗粒的作用非常大。基于以上的受力分析建立了颗粒沉降的动力学方程。在自行设计研制的错流磁稳定流化床分选模型机中研究了直径为4~4.5mm模拟颗粒和<6mm细粒煤的分选。模拟颗粒的分选实验重点研究了磁场强度和流化气速对分选效果的影响,为<6mm细粒煤的分选探索最佳的操作条件。<6mm细粒煤中-6+3mm、-3+1mm和-1+0.5mm三个粒级以及-6+0.5mm混合粒级细粒煤进行了分选,结果表明:错流磁稳定流化床可以实现-6+0.5mm粒级细粒煤的分选,分选结果的可能偏差Ep=0.068~0.095g/cm3。更多还原

【Abstract】 Air Dense Medium Fluidized Bed is a highly effective technique for dry coal separation, which can separate successfully the coarse coal of 50~6mm. This technology can not satisfy the highly effective separation of fine coal of <6mm, however, because the bubbling turbulence that exists in the bed can cause a certain extent of intermixing of the medium, so the lower limit of the separation size is rather high. By introducing the magnetic field energy to the Air Dense Medium Fluidized Beds and making them be Magnetically Stabilized Fluidized Beds (MSBs), the bubbles will be minished or even eliminated. The fluidization quality of the fluidized bed will be improved, even the air-solid dispersive fluidization can be achieved. The MSB is a highly effective separation technique for the fine coal of <6mm.Research contents of this dissertation mainly involve physical and chemical properties of the mediums and fluidization properties of the mediums in the MSBs; mechanism of eliminating the bubbles and stability of the density in the MSBs; rheological properties like yield stress, apparent viscosity and the flowability of the MSBs; motion mechanism of the particles in the MSBs and building of the dynamics equation of the partiticles’motion; separation tests of model particles and fine coal of <6mm in the Crossflow Magnetically Stabilized Fluidized Beds (Crossflow MSBs).Physical and chemical properties of magnetic powder, magnetic beads and paigeite ore powder indicate that the three mediums are all ferromagnetic matter, with relative strength, abrasion resistance and antioxygenic properties, so they can be the separation mediums of the Air Dense Medium MSBs. Fluidization properties of the mediums in the MSBs show that initial fluidization velocity Umf is independent of the magnetic field intensity, while the initial bubbling velocity Umb, particle entrainment velocity Ut,the scope of stably operating velocity and bed expanding rate all increase with the augmentation of the magnetic field intensity. The major reason of the eliminating bubbles in the MSBs is that applied magnetic field makes the magnetic mediums be magnetic chains. Stability of density of the MSBs indicates that the pressure fluctuation of the bed is very small, the bed is always in the stable state and the density distributes uniformly. On the contrary, the pressure fluctuation of the ordinary fluidized beds is very obviously and the density distributes uneven.Measuring the yield stress of the MSBS by Drawing Plate show that the yield stress increases with the augment of the bed depths, increases with the augment of the magnetic field intensity, while decreases with the augment of the air velocity. The yield stress in the MSBs formed by various sizes of one magnetic medium increases with the decreasing of the size of the medium. Study of apparent viscosity of the MSBs by Falling Sphere indicate that the apparent viscosity decreases with the increasing of the air velocity, and increases with the increasing of the magnetic field intensity. Factorial experiment design was carried on by dint of Design-Expert software for studying the yield stress and apparent viscosity. By variance analysis finding the remarkably influential factors, thereout the equations of the yield stress and the apparent viscosity were obtained. The flowability of the Crossflow MSBs indicates that increasing the bed obliquity and the air velocity the flowability increases, while the flowability decreases when the solids throughput and the magnetic field intensity increase. The constitutive relation of the Crossflow MSBs was discussed in this dissertation.Settling tests of particles studied by MEMRECAM Ci3 High-speed Dynamic Analysis System show that the resistances on the particle in the MSBs can be divided into two parts: motion resistance and yield force. The yield force on the particle is very great. Based on the aforementioned analysis of the forces the dynamics equation was established.Separation tests of model particles of 4~4.5mm and fine coal of <6mm in Crossflow MSBs designed and developed by the author were done. Magnetic field intensity and air velocity were studied during the separation tests of model particles to seek after the optimal operating conditions of fine coal of <6mm. Three parts of -6+3mm, -3+1mm and -1+0.5mm of fine coal of <6mm and fine coal of -6+0.5mm were separated respectively. The results of the separation tests show that the Crossflow MSBs can achieve successfully the separation of fine coal of -6+0.5mm. The Ep values of these tests are in the range of 0.068~0.095g/cm3.更多还原