Study on tribocharge characteristics and triboelectric separation of fly ash from circulating fluidized-bed boiler

Removal of unburnt carbon from fly ash is the prerequisite for comprehensive utilization of fly ash, and triboelectric separation is an effective method for use in this respect. In order to determine tribocharge charactristics of fly ash and the optimum separation conditions, the fly ash produced by the circulating fluidized-bed boiler is selected as the object of study. Based on results of analysis of physiochemical property and mineralogical characteristics of the fly ash, test on tribocharge characteristics of coke and the main components in fly ash(SiO₂,CaO,CaSO₄) is conducted using stainless steel, copper, aluminum and PVC as friction materials. The effect of carbon removal that can be obtained through triboelectric separation, with an aim to explore the law governing the effect on carbon removal efficiency produced by feed rate, airflow rate and voltage. The operating parameters involved in the separation process are then optimized using the Box-Behnken response surface method. As revealed by test result, a best result can be expected in separation of coke and the main components in fly ash with the use of PVC as the friction material; the loss on ignition of fly ash shows the tendency of first going up and then dropping down with the increase of airflow rate, and tends to gradually fall with increase of airflow rate, the rise of voltage is beneficial to decrease of loss ignition of fly ash, among the three operating parameters, the airflow rate can exert the most noticeable impact on loss on ignition of fly ash; when separation is made under the optimum operating conditions with an airflow rate of 70 m³/h, a voltage of 20 kV and a feed rate of 10.8 kg/h, the loss on ignition of fly ash can be reduced to a lowest level of 8.45%. The results of the study made in the paper may serve as a valuable reference for optimization of the carbon removal process using this separation method under industrial conditions.