Lephalale — Mogol Post enquired at Eskom’s Media Desk about the “short” boilers and design flaws which were trumpeted in national media.
At the question whether they can confirm that at least “12,5 m” should be added to each boiler, Eskom’s representative said theoretically increasing the furnace height will reduce the furnace exit gas temperature, however, the exact increase in height is not confirmed. “Increasing the furnace height practically is not economical post boiler construction. The boiler will therefore not be corrected by 12,5 m during the outage, as this is unfeasible”.
What is the impact of the current furnace size? The impact is that less heat is absorbed in the furnace compared to the current design, thus leading to higher furnace exhaust gas temperatures. The higher furnace exhaust gas temperature increases the convective surfaces heat absorption, therefore requiring additional spray water to control the reheater and superheater temperatures for the steam turbines.
According to Eskom, there are however agreed solutions for the boiler to address the issues through an integrated approach being implemented during the outage on Medupi Unit 3. The solutions include various modifications to the milling plant equipment, the modification to the reheater to reduce the spray water requirements, the modifications to the inlet flow and pulsing system of the Pulse Jet Fabric Filter Plant, modifications to the Gas Air Heater and erosion protection modifications to the air ducting and dampers. Also, further boiler process optimization work will be conducted once Medupi unit 3 returns to service, including boiler performance verification testing. During this period, all parameters affecting boiler performance, including coal quality, will be monitored.
What impact will it have on load shedding and the overall power situation in SA?
“We are doing everything we can to avoid or minimize stage of load shedding. Our planned maintenance has increased to an average of more than 5 000 MW capacity at any given time, from just under 3 000 MW of infrastructure in the past. This includes all planned shutdowns, including this one.
Why is there only now realized that the boilers have flaws?
Eskom has known about the theoretical furnace height increase for a long time, however as this is not economically feasible, Eskom considered other alternatives. Eskom continuously seeks solutions to design faults and technical problems, and as such, solutions will be implemented as and when they are found to be effective. Certain defects only manifest after extended periods of operation of plant under all conditions.
How long will it take until completion?
The current Medupi Unit 3 outage is scheduled to take 75 days and is expected to return to service by April 2020.
Eskom, however, confirmed that fixing design flaws is not necessarily an opportunity to create local jobs.