What does wet coal mean?

The Citizen (KZN) - - News -

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.

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