Frictional Ignitions Potentials Map for South African Coal Mines

Cynodon dactylon outperformed Themeda triandra and Hyparrhenia hirta, reaching 100 per cent survival and cover at all three trial sites by 2007 with or without fertiliser. Acacia sieberana reached 97 per cent survival at Kleinkopje Colliery but grew poorly at Optimum and Syferfontein. Planting plugs suits slopes too steep for a planter machine and buffers against pasture grass intrusion.

A compound dry cleaning machine de-stoned low grade raw coal without using water, but separation efficiency was low, with high relative density cut points and EPM values in the order of 0.3. Misplaced material was heavy and coal below 6 mm reported to product almost indiscriminately. The unit is cheap to buy and run, needs only crushing to 50 mm, and gives high throughput.

Nine bituminous coals from the Witbank, Waterberg and Soutpansberg coalfields all formed compacts without a binder, and the process worked better with coking coals. Reactive maceral content, free swelling index and Hardgrove grindability index governed briquette strength, with ash and kaolinite contents also contributing to bonding. Briquetting pressure, feed moisture and particle size distribution controlled the outcome.