A study of rotary tribo-electrostatic separation of South African fine coal

This article presents an experimental study of rotary tribo-electrostatic separation (RTS) as an alternative approach for beneficiating steam coal mainly used in South African power plants. An RTS with an octagonal charger developed at the University of Kentucky, USA has been used in beneficiating two types of South African coals containing nearly 37% and 32% ash, respectively. System parameters, such as applied charger potential, separation chamber voltage, rotation speed of the copper-plated rotor, and splitter distances were investigated for their effects on the separation performance. It was found that better separation was observed at 5000rpm rotation speed, no applied potential to the charger, and 25KV separation voltage. The RTS process reduced the ash content of the -177m coal fraction by nearly 14.9% for the Klipfontein coal and 12.2% for the Liketh Townlands coal, with corresponding combustible recovery values of 10.7% and 8.9%, respectively. Total sulphur content was also reduced from 2.1% to 0.9% for the Klipfontein coal and from 2.8% to 0.4% for the Liketh Townlands coal at corresponding combustible recovery values of 5.7% and 8.9%, respectively. The x-ray diffraction analysis of the cleaned-coal samples confirmed a reduction in the mineral content with an improvement in the organic composition for both coal samples.