By far, the most pulverised fuel ash, commonly known as fly ash, comes from coal-fired power stations operated by ESKOM.
Coal is mined from a quarry and transported to power stations where it is stockpiled into different grades. The coal is milled in large mills into a fine powder, whereafter it is blown through a series of pre-heaters into a furnace where it burns at +- 1400 degrees Celsius.
After the burning process, the leftover coarse material is discarded at the bottom of the furnace known as ‘bottoms ash’ and stockpiled in waste dumps, while the leftover finer material is drawn through particle filtration equipment. This fine material is retained while the flue gasses are released into the atmosphere.
The fine, burnt coal particles captured in the filtration equipment are deposited into bunkers or holding bins and accessed as unclassified fly ash. Sephaku Cement has access to at least 1.1 million tons anually and has branded this as Hard Ash (see graph below).