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Coal experts search for ways to cut emissions
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12th February 2007
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South Africa is a coal-loving country.We have received it in abundance and, making use of this act of geological generosity, have figured out how to turn low-quality coal into the world's cheapest electricity, while exporting the good stuff to countries abroad, fattening a few coffers along the way.

Unfortunately, though, rising global emissions have been steadily turning the boardroom darling into the environmentalists' miscreant.

This international pressure has forced everyone in the coal club to search actively for better ways to use the fossil fuel, especially as inherently cleaner fuels, such as nuclear energy and renewable energy, have been courting governments with far sweeter-sounding promises.

Now coal experts worldwide - South Africans included - are working towards using coal more efficiently, and with less environmental consequence, which could, once again, make it the more desirable energy option.

Clean coal?
Coal currently provides about 68% of South Africa's primary energy needs, and about 92% of the country's electricity is generated by coal-fired power stations, owned by parastatal Eskom. (Internationally, 36% of the world's electricity is generated by coal.)

These power stations burn more than 100-million tons of coal each year.

A proposed new power station - in two phases, namely Project Alpha and Project Charlie - will provide an additional 4 500 MW, adding to the coal burnt into the atmosphere.

Building this station is a matter of urgency, as Eskom is currently experiencing a severe demand squeeze, skirting ever closer to maximum capacity.

Although the quantity of emissions the country's coal-fired power stations generate is not publicised, Eskom has put an internal target on the table of reducing particulate emission (such as fly ash) over a five-year period to an average of 0,28kg/MWh - meaning current emission levels are higher. A 1998 figure for Eskom particulate emissions is given as 0,40kg/MWh.

Typical emissions generated by a coal-fired power station include carbon dioxide, sulphur, ash and nitrogen oxides (NOx).

Owing to environmental pressures and slowly-diminishing coal resources, Eskom has been keeping an eagle eye on so-called clean-coal technologies for more than a decade now, implementing some smaller-scale interventions in its existing plants, and seeking opportunities to do so on a larger scale in all its proposed new plants.

But, is something like 'clean-coal' even possible? After all, coal has always been something of a dirty word.

Clean-coal technologies (CCTs) are aimed at using coal for power generation in more environmentally acceptable and economically viable ways, explains Eskom Resources and Strategy corporate specialist Chris Gross.

Innovative technologies achieving this have already been developed, he explains.

These include processes that can be applied before, during and after combustion. There are two basic approaches associated with CCTs.

One is to develop more thermally efficient systems that use less coal to generate the same amount of power with an associated reduction in emissions.

The other is to enhance and develop new methods to effectively clean the emissions in an affordable manner.

(Perhaps here just a quick, simplistic note on how Eskom uses coal to generate electricity. The process starts when coal is pulverised in mills into a fine powder, from where it is blown into boilers. Owing to the heat in the boiler, the coal particles combust and burn to generate heat, turning water into steam. This steam is used to activate a turbine. This turbine activates a generator. The generator produces electricity.)

Coal is here to stay - for a while, anyway
It is vital for South Africa to investigate CCTs, as coal is still the country's most abundant energy resource, and the least expensive.

“There are a few outcomes that appear indisputable and that need to be addressed in the context of a sustainable energy future for South Africa,” says Gross. “Coal has repeatedly emerged as an electricity-generation fuel that South Africa cannot ignore, and it will be a major part of our generation mix for the next 50 years.”

The country has significant reserves of coal, he notes. Some of this is high-quality coal, suitable for export, but much is of low quality and, fortunately, relatively low cost, suitable for little else than power generation.

(Gross notes that a number of CCTs can be applied to the low-quality coal Eskom uses for power generation.)

However, every technology has environmental implications and, in the case of coal, these relate primarily to emissions, significant water use and ash production, says Gross, so it would be prudent to deal with these effectively.

He notes that Eskom does currently employ some CCTs at its power stations - even though not of the zero-degree emission variety, which is proposed to be the ultimate in clean-coal technology.

Eskom's current efforts include controlling particulates using a variety of technologies, such as fabric filters, electrostatic precipitators, SO3 injection and skew flow electrostatic precipitators.

Fabric filler plants have, for example, been installed at Majuba, Arnot, Hendrina and Duvha power stations to improve particulate removal.

There is also a concerted effort aimed at implementing much more advanced CCTs in Eskom's proposed new plants, says Gross.

“Eskom has an active research and development programme that is committed to introducing CCT options into its supply-side options.

“An extensive research and collaboration programme is assessing the short-, medium-and long-term options to inform decision-making on new and existing power stations. The technologies being reviewed for consideration include supercritical pulverised-fuel power plant, fluidised-bed combustion, integrated-gasification combined-cycle power plant (IGCC), underground-coal gasification (UCG), flue-gas desulphurisation, advanced low-NOx burner, reburn and cofire NOx reduction strategies.

“Technologies to manage emissions from coal plants are adapted to fit specific existing plant, and are planned ahead for new plant, while new technologies, such as carbon capture and storage, are continually being assessed for future power stations.”

Gross says advanced CCTs will play an important role in South Africa's future.

“These technologies signal a quantum leap in addressing sustainability challenges, and allow coal to compete on an equitable basis with other energy carriers.”

UCG is an Eskom CCT project that is advancing steadily. In fact, it is currently the subject of a pilot project at Majuba power station.

Gross describes the potential of this project as “enormous”. “If successful, this technology has the potential to revolutionise the South African energy sector.”

The ultimate aim of the UCG project is to construct a 1 200-MW commercial facility should it prove viable to supply syngas to the nearby Majuba for cofiring with coal.

UCG is a process whereby underground coal is converted on site into a combustible gas, which can be used as a fuel for power gener-ation. This is done by igniting the coal in a created cavity underground, and maintaining the combustion by injecting air or oxygen, and/or steam through one of two boreholes - resulting in pressurised gas which can be tapped. This has the advantage of obviating the need for coal-mining, transportation, preparation, the gasification train, and ash transportation and disposal.

If the Majuba study proves that UCG is indeed feasible, it could be applied to other Eskom sites. Even more importantly, if UCG technology can be applied to the 45-billion tons of coal on Eskom's books that cannot be mined economically, the parastatal can produce an additional 350 GW of electricity using a clean- coal technology.

Government has already communicated that it hopes to soon have a power station using combined-cycle technology (termed UCG-IGCC), which is a combination of coal and gas, such as would be the case at Majuba.

If this is, indeed, Majuba, is not known. Combined-cycle technology has the potential of being one of the most efficient coal-based generating technologies, and exceeds, or compares with emerging IGCC developments on a global level, says Gross.

CCT does not come cheaply, though and this in a country with one of its biggest competitive advantages being the low cost of electricity. One only has to realise the number of international companies that have set up smelters locally to realise that electricity is big business for South Africa.

“As part of the current review of Eskom's options for the future, the cost of electricity is one of its primary focuses,” says Gross.

“Eskom is tracking the implementation of CCTs around the world, and their associated costs.

“As with most technologies, cost decreases and development costs are recovered as the use of the particular technology increases. “However, it is not always feasible to wait for these costs to reduce significantly.

“The cost of introducing CCTs will have to be balanced against the long-term benefits.

“In all cases, every effort will be made to keep the cost of electricity as low as possible.”

Department of Minerals and Energy (DME) coal and hydrocarbons chief mineral economist Xavier Prevost says it is not yet clear what cost increases the use of CCTs will spell, but that it may be between 200% and 300%.

He notes, though, that South Africa's electricity will still be cheap compared to international standards, especially as most countries are working towards implementing clean technologies of some kind, which means their generation costs will also rise.

Eskom's CCT development process is part of an international effort to develop CCTs.

South Africa is, in fact, a member of the International Energy Agency (IEA) implementing agreement on Clean Coal Science (CCS).

The IEA is an energy forum of 25 countries, taking joint measures to “meet oil supply emergencies”. The CCS has a particular focus on CCT research, and on sharing research results.

South Africa joined in 2003, says Prevost, in a decision driven by the DME.

The thinking was that if South Africa continues using and exporting coal, it would need to develop CCTs, as the country is set to introduce emission limits in the near future, he explains.

It goes even further than that, though. Prevost says South Africa is almost fully dependent on coal for its energy needs, with this situation likely to continue into the future.

“The environmental issues of such an extensive use of coal need to receive attention, or South Africa's emissions will somehow be penalised by its European Union trade partners.”

Prevost says the CCTs implemented by Eskom to date are not yet the real thing in terms of what is possible, and that full-scale CCT implementation will probably be seen in South Africa only after the first of Eskom's new coal-fired plants is completed, which is between 2012 and 2015.

This means that the urgency to build generation capacity by the embattled power producer will probably see projects Alpha and Charlie not featuring CCT technology on the scale possible were there fewer time constraints.

As far as international research is concerned, one large-scale attempt to implement CCTs is the FutureGen project.

Four US sites have already been shortlisted for a prototype plant, billed to be a “coal-fuelled, near-zero emissions power plant”.

The FutureGen alliance is an international nonprofit consortium that includes some of the largest coal producers and users in the world, including a few well-known faces, such as Anglo American, BHP Billiton, Rio Tinto Energy America, and Xstrata Coal. The alliance is partnering the US Department of Energy to design and construct the FutureGen plant.

Some of the arguments behind this project are that coal is an affordable, abundant and reliable fuel source, which can also act as a source of hydrogen, thereby reducing the growing pressure on the demand for natural gas and oil.

Edited by: Irma Venter


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