Study On Sound-assisted Fluidization Characteristics Of Fine Particles

Silicon nitride is a sort of ceramic material of excellent performance and has diverse preparations of its powder, of which the technology to generate silicon nitride powder directly through combustion in fluidized bed is more feasible to industrialize and be used in large scale.Due to the tiny size of raw silicon powder, phenomena such as plug flow, channeling, and agglomeration are easy to occur during the fluidizing procedure, deteriorating the quality of fluidization. To improve the fluidization quality, sound assist method to enhance fluidization was proposed.This paper is dedicated to study the fluidization characteristics of silicon powder in the fluidized bed of acoustic field through Cold state experiments. It consists of three parts:(1) Status quo to improve the quality of fine particles flow at home and abroad was reviewed, and the characteristics of various methods was analyzed. Sound field stands out to be the most suitable for preparation of silicon nitride powder owing to its unconstrained admit to the fluidized material, simple structure, and the distinct effect. Through the progress of sound assist fluidization, behaviors of different sound field parameters could be understood.(2) A device designed for the sound strengthen CFB Cold experiment was built, including fluidized bed body, a sound system and sound testing, pressure testing system. Experiments taken have studied the effect on fluidization quality for particles brought forth by acoustic parameters such as sound pressure level, sound frequency, sound wave and physical parameters such as bed height, particle size and so on.Following conclusions were derived from these experiments: 1. the critical flow rate was hardly affected by the bed height; 2. the critical flow rate declined when the sound pressure level increased; 3. there is a threshold frequency, above which the critical flow rate was almost not influenced, while abrupt drop can be observed under the frequency; 4. compared to triangle wave and square wave, sine wave has better effect; 5. acoustic field could help to fiuidize group C which is difficult to fluidize under normal state and would significantly decrease the critical flow rate of group A which is easy to fluidize.Comprehensive comparison showed that the best sound parameters for the test are 140 dB, 100 Hz, sine wave.(3) According to the energy balance model, the formula for calculating the critical fluidization rate of fine particles could be derived, which is applicable for group A with a wide frequency range, and the critical flow rate under different temperature could be predicted.This paper aims at the fundamental disciplines the sound field imposed on the critical fluidization rate. It has provided the basis for research on direct nitridation of silicon in fluidized bed, furthermore laying the foundation for research and application of sound field fluidization.