Cleaning processes still under way at power station

MALALANE – Eskom has warned that more load-shedding can be expected as of next week. This can largely be attributed to the reopening of schools and businesses.
According to Eskom the power system is expected to come under severe strain, with a medium to high risk of load-shedding.

However, measures will only be taken as a last resort in order to protect the power system from a total collapse.
The parastatal also said the Medupi Power Station has also not been switched on yet due to certain technical cleaning processes which were still underway.

According to Eskom, the first unit of the power station is close until synchronisation can take place.
However, the only step necessary before finally admitting steam to the turbine is to clean the boiler and associated pipework from all scale, welding residue and contaminants, arising from the construction process.

Initially, cleaning is done by means of chemical flushing, which removes all major contaminants as well as any foreign objects, but this is followed by a process known as steam blow through. Specific steam-flow conditions are prescribed to achieve minimum velocity and disturbance factors inside the various elements of the boiler.

In principle, steam is generated by the boiler itself, operating in lower than normal temperatures and pressures, and with fans and some coal burners fully functional. It is delivered in short blasts, typically for 10 to 20 minutes at a time. So far, a number of steam blows have been performed.

Once the steam flow and disturbance factors reach optimum levels, cleanliness of the steam is determined by measuring the number of microscopic impacts on steel plates, placed in the path of the steam exhaust.

Eskom has previously indicated that while the commissioning process towards the synchronisation is at an advanced stage, each of the remaining steps requires critical assessment of the inherent safety risks to people and the equipment integrity before proceeding to stage.

A team of Eskom experts has evaluated the risks in proceeding to restore pipework to the turbine.

While specified cleanliness levels have not been completely reached, a full technical risk analysis has been performed, which clearly shows that the consequences of admitting steam, which is not quite clean enough are only slightly accelerated erosion of the high-pressure or intermediate-pressure turbine blades and possibly valve seats, during the first few days of operation.

Thereafter, stable, reliable and predictable operating conditions will be achieved.
To further reduce the already low risk, Eskom has developed a set of robust-mitigating actions which involve regular internal inspection, bringing maintenance intervals forward, typically to within a year or so of operation.

On the basis of the above, a management decision was taken to proceed with the reinstatement of the pipework and that should enable it to send steam to the turbine while implementing the mitigating strategies.

Load-shedding schedules can be accessed on Eskom’s website, however, at this point the company has confirmed that it is not currently load-shedding.