Eskom announces stage 6 load-shedding — here’s the timetable
Eskom has announced that load-shedding will move to stage 6 at 21:00 on Tuesday, 10 January 2023.
It will continue until 05:00 on Wednesday, after which load-shedding will drop to stage 4 until 16:00.
“Stage 6 nightly load-shedding will then be implemented at 16:00–05:00 until further notice. Stage 4 load-shedding will be implemented at 05:00 – 16:00 daily until further notice,” Eskom said.
The state-owned power utility revealed seven generating units tripped on Tuesday, three of which were returned to service.
The return to service of three other units has been delayed.
“Unit 1 of Matla Power Station will be shut down tonight to repair a boiler tube leak,” said Eskom.
South Africa’s load-shedding schedule from Wednesday may be summarised as follows:
- 16:00–05:00 — Stage 6
- 05:00–16:00 — Stage 4
Why Eskom’s power plants keep failing
Wits Chemical and Metallurgical Engineering School head Professor Josias van der Merwe and postgraduate researcher K.G. Moloko recently published their findings on the underlying causes of the constant boiler tube failures at Eskom’s power plants.
Van der Merwe and Moloko found that the main culprit is sulphidation — a chemical process that degrades steel by forming brittle compounds of iron and sulphur.
They explain that two conditions must be present for this — there must be sulphur and a low concentration of oxygen, which lets the sulphur react with iron rather than being oxidised.
Unfortunately, eliminating or mitigating these chemical pre-conditions is not easy.
High sulphur content in the coal supplied to power plants is the root cause of the problem, but generally, lower-sulphur coal comes at a higher price.
If Eskom can’t buy higher-grade coal, Van der Merwe said another option is to use higher ratios of air to coal to reduce the rate at which this type of corrosion occurs.
However, this would result in increased emissions of nitrogen-oxide compounds, which have a range of adverse health effects and much higher global warming potential than CO2.
Wits Biomedical Engineering lecturer Neil Thomas Stacey explained that boilers are operated in conditions of restricted oxygen to prevent the formation of these compounds.
Stacey said this might be a trade-off that South Africa will have to accept as a stopgap to slow Eskom’s fleet’s deterioration while it hopefully finds a way to switch to higher-quality coal.
He said this task should be treated as a critical national priority.
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