Power plants using circulating fluidised bed (CFB) technology have not gained momentum in South Africa’s power generation landscape, despite experiencing increased uptake internationally and “demonstrating various benefits”, says coal advocacy organisation FFF Carbon director Professor emeritus Rosemary Falcon.

While CFB technology was available prior to the development of State-owned power utility Eskom’s Medupi power station in Limpopo and Kusile power station in Mpumalanga – construction of which started in May 2007 and April 2008, respectively – CFB technology was not selected as a combustion technology largely owing to CFB units being considered too small for Eskom’s required boiler size, says University of the Witwatersrand senior researcher Professor Samson Bada.

In addition, FFF Carbon chairperson Tumi Kgomo adds that, at the time, Eskom only adopted technologies with an established market track record.

Given that technology adoption approval processes and waiting for peer power utilities to prove a technology can take many years, Kgomo points out that Eskom is typically significantly behind other technology adopters, effectively adopting a technology at a point at which it is almost obsolete and at a time when power station developers have already likely moved on to a second generation of suitable applicable technologies.

Apart from Eskom, Falcon explains that there have been attempts by South African mining, metallurgical and manufacturing operators to introduce industrial-sized CFB-enabled boilers. However, she notes that these attempts were blocked by environmental legal challenges.

One such example, she points out, is a thermal coal business unit of a major mining company in South Africa, whereby a 150 MW CFB-enabled three-boiler power station was proposed, with the miner being the sole off-taker for all the electricity produced by the power plant.

The miner intended to carry the power purchase agreement on its balance sheet as a $1-billion finance lease. However, the project encountered financial and legal challenges.

Falcon explains that, at the time of industry’s attempts to roll out CFB technology, it was difficult to demonstrate that CFB technology can be a “clean” coal technology “without local proof, despite ample proof shown in other countries”.

While South Africa has lagged in adopting CFB technology in its power stations, Falcon points out that CFB installations have gained “strong momentum” globally, such as in China, India and Indonesia, alongside new CFB-enabled plants being built in Botswana, Zimbabwe, Mozambique and Zambia.

By doing so, these countries can use all grades of coal as a fuel-to-power source in a more efficient and “cleaner” manner which, in turn, is able to support economic growth and ensure stable energy supply, says Falcon.

Leveraging CFB Technology
While Falcon acknowledges that CFB solutions are marginally more expensive to build, she says the technology has proved to be cheaper to operate.

CFB technolgy benefits include negating the need to crush coal as fine as that required by pulverised power stations, being able to use poor-grade discard coal and to co-fire biomass and other waste products.

Further, Falcon notes that the technology produces low nitrogen oxide emissions and embedded sulphur oxide (SOx) capture which avoids the need for large back-end nitrogen oxides (NOx) and SOx scrubbers. These benefits, she adds, are all achieved through low-temperature combustion.

Kgomo adds the CFB solutions also enable by-product creation. Rather than sequestering captured SOx, SOx can be converted into sulphuric acid through a relatively simple process, he says.

“Sequestering a portion and converting another portion into usable products solves a disposal problem and creates a resource at the same time,” says Kgomo, noting that South Africa typically imports about one-million tonnes of sulphuric acid a year for metallurgical, defence and agricultural uses, while Eskom itself uses about 250 000 t a year to demineralise boiler water.

While acknowledging that the yield of sulfuric acid depends on the elemental composition of the coal used, which is specified by the boiler operator, Kgomo proposes that adopting CFB technology would enable Eskom to offset some of its sulfuric acid demand by capturing SOx internally.  

He adds that NOx can be used to provide fertilisers while carbon dioxide can be targeted in for high value carbon products including carbon nanotubes, carbon fibre and activated carbon.