One of the first things you notice as you approach the Kusile power plant from the main highway are the two stacks rising high above the partially built plant. The next thing you notice as you circle around the plant are the curious air-cooled condensers that sit on top of stilts high above the ground, and the sheer number of them – it looks like an ancient Greek edifice, as you can see from the photograph below. The use of air cooling to condense the steam from the turbines is not new, but has been refined by Eskom over the years as an effective measure to conserve water in a water stressed region. The height of the air-cooled condensers is needed to avoid the recirculation of heated air and allow the entry of colder air more effectively.
Security is tight at the plant, with everyone (visitors and workers alike) being breathalysed on entry and exit, as well as having to pass through airport-type security. The first of six units (each 800 MW) is now operating, but it is still very much a construction site. When fully built, Kusile will be one of the world’s largest coal-fired power plants. The plant uses supercritical technology and will have a net efficiency of 37.5% (lower heating value). While this seems low, the plant performance is compensated by the impressive water conserving air cooled system, which is the main reason for the lower efficiency.
Environmental pollution control includes pulse jet fabric filters, which remove 99.9% of particulate matter (PM). As there is currently no market for the fly ash, it will go into a 10 year ash dump; but there is no shortage of space due to the vast area that surrounds Kusile. Low NOx burners (configured for opposed firing in staggered rows) allow NOx emission limits to be met. Kusile is the first power plant in South Africa to be fitted with wet flue gas desulphurisation (FGD) technology. The FGD system uses a limestone slurry sorbent, which is prepared on-site. The FGD wastewater is treated and then reused to conserve water.
Kusile power plant
The design coal for the plant has a 0.8% sulphur content, but the FGD system allows coals as high as 1.6% sulphur to be fired. There is no market, as yet, for the gypsum that is produced as a by product. This is partly due to the vast quantities that will be generated and there is a risk of flooding the construction materials market too soon. Nevertheless, Eskom expects to develop a market for some of the gypsum in the future. In the meantime, the gypsum will be co-disposed with the fly ash.
Enough coal will be stocked to supply the plant for 40 days. It will be stored in compacted stockpiles to avoid dust formation affecting the surrounding farmland. The total project cost is 156 billion rand, of which 116 billion rand has so far been spent. Nearly 20,000 workers are currently employed in building the remaining units. Kusile will no doubt be an impressive showcase for large-scale dry-cooled power plants in the future.