Fundamental Study Of Air Dense Medium Magnetically Stabilized Fluidized Beds For Fine Coal Separation

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.