Power stations designed to handle wet coal – expert
Although embattled power utility Eskom earlier in the year said no load-shedding could be expected over the festive holiday period, citizens, like elsewhere in the country, were shocked when unprecedented stage 6 load-shedding was unexpectedly implemented on Monday
ZULULANDERS left without power for hours every day are fuming as load-shedding continues.
Although embattled power utility Eskom earlier in the year said no load-shedding could be expected over the festive holiday period, citizens, like elsewhere in the country, were shocked when unprecedented stage 6 load-shedding was unexpectedly implemented on Monday.
Apart from the usual maintenance problems and unexpected unit breakdowns, the need for the drastic cuts has mostly been attributed to ongoing problems with wet coal.
Speaking to the ZO, North-West University professor of chemical and mineral engineering, Quentin Campbell, explained the chemical challenges of wet coal and why it posed a threat to electricity supply.
‘Wet coal is like wet braai wood. Apart from the fact that it burns with difficulty, it is also very energy inefficient,’ Campbell said.
‘A significant amount of energy from the combustion of coal is first used to ‘boil away’ excess moisture. Only after that the energy is used to generate steam, and hence electrical energy.
‘The result of this is that a lower fraction of the available coal energy is eventually usefully converted. Incidentally, another consequence is that more carbon dioxide is produced for lower electrical output.’
However, power stations have been designed to handle such challenges.
‘Eskom usually has a contract with coal suppliers stipulating that the coal moisture should be between 8 and 10 per cent.
‘They can easily handle this since our power stations were designed for it.
‘During wet periods, they may experience a lower energy output per tonne of coal, but normally their so-called ‘reserve margin’ of surplus energy on the grid will adsorb this,’ Campbell explained.
‘Our current problems result from the fact that this margin of surplus energy is extremely low, and any reduced electricity output will spill over to load-shedding.
‘This is not necessarily the wet coal causing the problems, but rather localized flooding at power stations interfering with conveyor belts, trucks and loaders. So we cannot blame wet coal for all the problems. They have been handling it successfully for many years.’
South Africans, having never experienced load-shedding higher than stage 4, were panicked by what stage 6 meant as most municipal schedules ended at stage 4.
As Eskom explained, the load-shedding schedule goes up to stage eight, with stages 6 and 7 respectively shedding 6 000MW and 7 000MW.
Stage 6 means that load-shedding frequency is doubled from stage 3 and will run over four days for four hours per power cut.
Should load-shedding reach stage 8, 8 000MW will be shed from the grid and residents could experience power cuts of up to six times a day or 12 hours.
According to an Eskom statement, the probability of load-shedding remains high for the week
‘We remind customers that load-shedding, regardless of the stage, is no cause for alarm as the system is being effectively controlled.
‘Load-shedding is a responsible act and a highly controlled process implemented to protect the country from a national blackout.’
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