What does wet coal mean?
Eskom has 13 coal-fired power stations, all with various requirements for coal.
They all can use wet coal – when it is roughly the size of a large potato.
“The coal is pulverised in huge mills into a fine powder before it is blown into huge kettles, called boilers,” the Eskom website states.
“Due to the heat, the coal particles combust and burn to generate heat to turn water into steam.” The problem is when coal arrives at the crusher as mud, it cannot be moved by the blowers, much like a blocked fuel injector on a car that has to atomise the fuel before it can combust.
“There was wet coal at 10 units causing loss of generation,” energy expert Ted Blom said. “Normally when you buy coal, you would stipulate no more than 10% fine. I’m guessing people are buying up to 50% fine, which means there is a lot of money going into someone’s pocket.”
The temperature of the coal entering a boiler furnace is ±90ºC. “The reason for having the coal at such a high temperature is to ensure combustion takes place in the shortest possible time. When the coal is removed through a blast of hot air, if the coal is too wet, the drying out is ineffective and has a negative effect on the combustion. The heat required to evaporate the moisture is greater than the boiler design allows,” Eskom stated.