It added that 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,” Eskom said.
“Specific steam flow conditions are prescribed to achieve a minimum velocity and disturbance factors inside the various elements of the boiler. Steam is generated by the boiler itself, operating with lower than normal temperatures and pressures, and with fans and some coal burners fully functional.”
It also stated that the steam is delivered in short blasts, typically for 10 to 20 minutes at a time and that 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 into the path of the steam exhaust,” Eskom added.
It further emphasised that each of the remaining steps requires critical assessment of the inherent risks to both safety of people and the equipment integrity before proceeding.
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“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,” the utility said.
“On the basis of the above, a management decision was taken to proceed with the reinstatement of the pipework and that should enable to send steam to the turbine whilst implementing the mitigating strategies.”