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.