Electrostatic Separation of Fine Particles in Vibrated Fluidized Beds
Very fine particles which cannot be fluidized by means of a flowing gas alone because of entrainment may be effectively individualized and retained in the bed through a combination of gas at low rate flow and mechanical vibrations of selected frequency and amplitude. A mixture of very fine particles may be fluidized and successfully separated and/or concentrated by means of electrostatic fields. Results are presented of a factorial experiment in which the conditions of temperature, humidity, and voltage were investigated for the separation of a (50-50 by weight) synthetic mixture of iron and glass powder of particle size ranging from 15-45¿m. A new and highly efficient particle collection mechanism is introduced, and mathematical models of the process are presented as part of the optimization work.
Electrostatic Separation of Particles Below 40 μm in a Dilute Phase Continuous Loop
Investigators at The University of Western Ontario, Canada have developed an apparatus for electrostatic separation of very fine particles. The dilute phase loop eliminates the entrainment problems generally associated with dry handling of particles below 40 ¿m. Results are presented for separation of two materials: 1) coal macerals; 2) carbon particles from fly ash.
Contact Charging Between a Borosilicate Glass and Nickel
The charging of borosilicate glass spheres rolling on clean nickel has been studied under controlled conditions of cleanliness, humidity, and gas pressure. Strong evidence indicates the process of charge transfer to be a type of contact electrification akin to that operating between two metals. The observed charging is, however, influenced by other factors. The amount of charge acquired increases with surface areas in contact and hence with distance rolled until other factors intervene. The rate of charging depends on rolling speed and surface conductivity of the borosilicate glass, while the maximum equilibrium charge depends on the pressure of the ambient gas. The gas pressure effect is shown to be caused by electrical discharge of the highly charged sections of the borosilicate glass to the metal, as suggested by E. W. B. Gill, and this causes a minimum equilibrium charge to occur about 1 mm air pressure, as observed by D. E. Debeau. The effect of transverse electrical fields reported by E. W. B. Gill ...