The influence of ball collision charging on carbon recovery of fly ash triboelectrostatic separation

The recovery of unburned carbon particles from fly ash by triboelectrostatic separation can realize energy conservation and solid waste recycling. Collision charging by metal ball has been proposed to enhance the particle charging and improve the unburned carbon recovery efficiency. It can increase the particle contact area, shorten the contact time, and improve the charge-mass ratio of particles. The charging model of ball collision was established. The collision charging process between particles and ball was simulated by CFD-DEM coupling method. The influence of ball material and gas velocity on the charge-mass ratio was studied, and that of gas velocity and voltage on separation was evaluated by experiments. The results showed that the collision charge between particles and metal ball was greater than that between particles. With the gas velocity of 30 m/s, Cu ball collisions obtained a relative maximum charge-mass ratio of 0.393nC/g and 0.275nC/g for carbon and ash particles, respectively. The reasonable experimental conditions were gas velocity of 20 m/s and voltage of 15kV. The loss on ignition of 14.3% and carbon recovery of 90.36% were obtained. Compared with the no-ball system, the ball collision improved the carbon recovery rate by 55.20%.