At approximately 09:45AM on Sunday the 23rd October 2022 while Kusile unit 1 was on a forced outage, the flue duct experienced a structural failure on the horizontal rubber expansion joint, as well as on the rubber expansion joint at the 55m level.
Eskom reports that it is currently expecting to operate temporary stacks on the three Kusile units – which have been inoperable since October 23 when the Unit 1 flue duct failed in a way that also compromised the Unit 2 and 3 flue ducts – for about a year while permanent remediation works are carried out.
The temporary stacks will bypass the flue-gas desulphurisation (FGD) system and Eskom is, therefore, preparing to seek an exemption from the Department of Forestry, Fisheries and the Environment (DFFE) in order to allow it to operate the units without using the air-pollution control system.
The DFFE tells Engineering News that no formal exemption request has yet been received from the State-owned utility which, for its part, says the request will be submitted once the project scope and project details are finalised.
The DFFE also gave no indication as to how long it would take to consider the application, saying only that the “processes to be undertaken to consider the exemption request will be informed by the nature of the request from Eskom when the department is ultimately approached”.
Eskom has already started making the case for moving ahead with the construction of the temporary stacks that bypass the FGD on the basis that the project will shave about a year off the time it would otherwise take to return the units to service and would, thus, help it in reducing the intensity of loadshedding.
The three units are able to produce 2 160 MW of electricity and their unavailability is currently adding about two stages of loadshedding every time Eskom implements rotational cuts. Loadshedding affected 208 days in 2022 and has been implemented every day since the start of 2023, at times at Stage 6.
“The current plan is to bypass the FGD until the permanent remediation of units 1, 2 and 3 flues is completed.
“[We are] currently anticipating running the temporary flues for a duration of approximately one year before the final solution will be ready,” Eskom said in response to emailed questions from Engineering News.
Should it secure the exemption, the first temporary stack construction will take about ten months from environmental authorisation, with stacks 2 and 3 becoming available at one-month intervals thereafter.
The temporary stacks will be designed, constructed and commissioned by Concor and preparatory work by Concor is reportedly already in progress.
Eskom says it is unable to provide a cost estimate for the temporary stacks, stating that the exact costing will be confirmed only once the detailed designs are available.
The utility’s current “rough” cost estimate for the permanent remediation solution, which will be implemented in parallel to the temporary stacks, is R240-million and will be funded as an operational rather than a capital cost.
Therefore, Eskom insists that the estimated total cost to complete Kusile remains R233.4-billion; a figure that is said to include interest during construction.
Besides returning units 1, 2 and 3 to service, Eskom is currently estimating that Unit 5, the commissioning of which was delayed by a gas-heater fire also in October, will be synchronised to the grid in July or August and that Unit 6 will be completed by May 2024.
Currently only Unit 4 is operational at Kusile, where there have also been serious boiler design problems and where Eskom has been struggling to operate the FGD units, which are unique to its coal fleet in South Africa.
The boiler design problems have been attributed to “creative tendering”, while the Kusile project has been shown, including during evidence presented at the Zondo Commission, to have been seriously affected by corruption.
The Unit 1 flue duct failure has been attributed partly to the boiler design, which is 16 m too short and has resulted in high exhaust gas temperatures and air velocities, as well as a high buildup of slurry material.
This, together with inadequate monitoring of the flue, caused the bend on the Unit 1 flue to collapse because of excessive weight imposed on the common support platform structure.
The adjacent Unit 2 and 3 flue duct bends, located inside the same 220-m chimney as the Unit 1 flue, were also compromised rendering all three units inoperable. The chimney functions as a windshield for the three flues.
“With the information that is currently available, the internals of the windshield will need to be made safe [and] this will be done by retaining the concrete windshield and repairing the flues and the 151 m level platform,” Eskom says.
“The lobsters for all units will likely need to be replaced and the platform at the 55 m level will need to be rebuilt.
“It is anticipated that the entire process will take approximately 24 months.”
These remediation works, which will need to be carried out slowly to ensure that there is no catastrophic failure of the chimney, will be performed in parallel to the construction of the temporary stacks.
“Lessons learnt are being considered for future operations, including units 4, 5 & 6 and Eskom is currently in negotiations with the original equipment manufacturer for a technical support contract.”