Dynamic Characteristics And Stability Of Vibrating Fluidized Bed

The0~6mm level fine-grained coal content of raw coal gradually increase with theextensive application of fully mechanized mining, and directly accessing to marketwithout any processing of fine coal cause serious waste of resources in most dry area,thus, the research on a simple, reliable, and efficient separation technology andequipment for fine coal is significance and urgent. The vibrating energy is introducedinto the traditional fluidized bed to develop a vibrating fluidized bed (VFB) dryseparation technology, which provides a uniform and stable fluidized bed layer and aneffective way for fine coal dry separation. However, stable vibration environment is theguarantee of good separation performance. So far, relevant research about vibrationcharacteristics of VFB and fluidization characteristics under the condition of complexvibration nearly remains blank. According to the basic movement characteristics of thevibrating machine and the basic process of granular material’s fluidization, this thesispresents a study on the fluidization characteristics under the condition of liner andswing composite vibration and dynamic characteristics of simplified VFB mechanicsmodel, providing theoretical reference for the industrialization and large-scale sizeVFB.According to the separation principle of fine coal VFB dry separation machine andcharacteristics of vibration device, a novel structure of VFB is proposed, the basicparameters of VFB are determined, the preliminary process parameters of VFB areselected and system design of the VFB is completed.Experimental study is carried out to study the fluidization characteristics of VFBunder the condition of linear and swing complex vibration. The VFB testing platformwith linear and swing complex motion is designed. The basic process of densitystratification and back mixing under the disturbance condition are analyzed by using thehigh-speed dynamic system. The single-factor experiment is conducted with testingfactor of vibration frequency, vibration intensity and swing disturbance conditions,respectively, from which the conclusions are found out that better separation efficiencybrought out under conditions of low and medium frequency vibration while nostratification brought out under the condition of high-frequency vibration, big bubblesand a wide range of circulation are formed inside the bed under the swing disturbancecondition, leading the stratified materials back mixed and keeping the phase differencebetween vertical motion and swing motion around zero degree can effectively avoid theoccurrence of a wide range of circulation. The motion equations of VFB simplified model are established using Lagrangeequation. An approximate solution of the motion equations and the average equation offirst order derived system are obtained through the multiple scales method. Freevibration characteristics of non-resonance conditions and1:1:2:2internal resonanceconditions are analyzed. Under the resonance condition, both response amplitude andfrequency of coefficient of first order derived system vary with the change of initialconditions, and there exists a phenomenon of energy exchange between the vertical andswing motion. Stability of the system is analyzed with first method of Lyapunov,finding out that many factors of instability exist under the resonance condition. Theresonance condition should be avoided when the VFB is designed.The high speed dynamic system is used to verify that the in-plane vibration systemwith double rotors can achieve synchronized movement with0°and180°phasedifference. Under the condition of self-synchronization, the forced vibrationcharacteristics of this system are revealed. The forced response of system under bothnon-resonant and main resonance conditions are solved, and stability of the system isanalyzed by the first method of Lyapunov. Considering higher order terms of swingmotion, the frequency response equations under the condition of main resonance areobtained by using multiple scales method, and significant swing causing shifted peak ofthe frequency response curve is found out, so that the stable region shrink or evendisappear.Modal analysis and dynamic response experiment are conducted on the VFB pilotplant testing device. Experimental modal analysis is used to obtain the first six ordernatural frequency of VFB. Based on modal experimental analysis, the dynamicresponses of loaded and unloaded VFB are acquired, the time domain and frequencydomain signals in the starting, stopping and steady state operating period are obtained.Testing results indicate that there may be frequency-doubled oscillation and chaoticmotion nearby the resonance region of starting and stopping period, and a certain degreeof swing motion in the steady state operation period along the bed width direction.Eliminating swing motion and avoiding resonance are the basic conditions to guaranteethe good fluidization environment.