Effect Of Feeding Particles On Separating Fluidization And Its Separation Behavior

Air dense medium fluidized bed can achieve effective separation of-50+6 mm coal,but the significant density difference between airflow and heavy medium makes it difficult to form a homogeneous and stable fluidized bed,and it is determined by the nature of the fluidized medium.In addition,the feeding particles interference is also an important factor affecting the stability of fluidized bed,in view of this,it is necessary to study the effect of feeding particles on the bed characteristics.The dynamic characteristics of large particles directly determine the separation behavior of particles,thereby affecting the separation results.By changing different factors,the motion behavior and distribution of different particles were both studied.The pressure drop of narrow-range-size magnetite powder under different height to diameter ratios was measured,by drawing the pressure-drop-velocity fluidization characteristic curve,it was found that the critical fluidization velocity was basically constant with the increase of static bed height,however,the degree of expansion was changed.According to the mass ratios of each narrow-range-size in the wide,the relationship between the critical fluidization velocity and the proportion was obtained.The effect of material layer on upper bed fluidization characteristics was acquired using density spheres instead of coal particles.The influence of feeding particles on bed activity was investigated by means of many standard 13 mm intermediate density spheres(ensuring that the spheres were completely immersed in the bed),by comparing the volume of all feeding spheres and bed expansion,the "squeeze" characteristics of the feed to the emulsified phase was acquired.The position relationship of particles in two cases was established by using the height data measured in the fluidization and corresponding standing state.The narrow-range-size magnetite powder with unconspicuous stratification and grading was adopted,and the heavy medium particle concentration was not the same when the bed with different static bed heights were controlled in the critical fluidization state,the average floating velocity of the low density particles decreased with the increase of the heavy medium particle concentration,which indirectly reflected the change of bed fluid activity.High density steel spheres which are hard to be influenced by bubbles were used during the process of measurement,the force of testing spheres in the fluidized bed was analyzed theoretically by means of SF-3 dynamometer,the additional resultant force acting on particles with different sizes was deduced and then understood its variation at different fluidization numbers.The high-speed dynamic image analysis system was employed to analyze the bubble characteristics under different conditions,and then the appropriate bubble size calculation model was received.The correlation equation was established by the dimensionless value ? related with the diameters of bubbles and testing spheres at the additional resultant force F = 0.In order to evaluate the separation results of particles in the fluidized bed based on bed density using the axial distribution coefficient formula,the settling behavior of high density particles was tested by the segmentation test design method.The results indicated that finer heavy medium achieved optimum settling performance at larger fluidization number than coarser medium,while the effect of medium size on the collision of the feeding particles was less than that of bed viscosity.The effect of static bed height on separation performance was not obvious at low fluidization number,but the axial distribution coefficient decreased with the increasing of bed height when the fluidization number was more than 1.2.The time to achieve best settlement would be shortened with increasing feeding particle size.The backmixing degree was strengthened gradually with the increase of fluidization number,and larger medium size was beneficial to weaken the backmixing.It was difficult to separate each other when the density differences between the bed and tracer spheres was more than 0.3g/cm~3,and the ? value was almost constant with the increase of the fluidization number for each sphere whose density difference is less than 0.3g/cm~3.