关键词: 气固流化床, 静电压, 摩擦起电, 双极带电, 料位

Abstract:

An on-line measurement technique, which consisted of electrostatic probe, signal transmitter and data acquisition systems, was developed to study the electrostatic characteristics in gas-solid fluidized beds.By measuring the electrostatic potential at different bed heights, it was found that the electric field inside the bed was non-uniform.The axial profiles of electrostatic potential were Z-shaped, and the voltage polarity would reverse near the interface between dense and dilute phases.The heights where voltage polarity reversal happened would increase with the increase of gas velocity and static bed level.Comparing the fluidization of particles with different sizes, it was discovered that the polarity reversal would change significantly when there was an obvious interface between dense and dilute phases, and the converse was not true.Subsequently, the principle on bipolar charging of different sizes fluidizing particles was presented.Work function, surface structure, selective adsorption of contaminants and surface energy were all dependent on the particle size, which resulted in finer and coarser particles charged reversely, consequently influencing the electrostatic potential profile in fluidized beds.A new method to determine bed level based on the characteristics of electrostatic potential in fluidized beds was proposed.The results showed that bed level could be successfully predicted with the maximum relative error 4.08% and the mean relative error 2.02% with the method in this work.The novel electrostatic approach to measuring the bed level in gas-solid fluidized bed could replace the γ-ray method in the future, and could monitor electrostatic potential in the bed and bed level simultaneously.

Key words: 气固流化床, 静电压, 摩擦起电, 双极带电, 料位