Coal plays a predominant role in the national economy of South Africa and indeed in the region of Southern Africa. This source is the life blood of progress and development and, with this, job creation and life enhancement. However, the quantities of good-quality coals remaining in the major mining areas in the country are fast dwindling owing in part to the limited reserves of such coal and to the extraction of the best quality seams for the increasing export trade. The cost of extracting, beneficiating, and transporting the lower quality coals from distant coal basins is beyond the bounds of economic reality at current prices and with current technology.
The situation therefore arises that South Africa's future domestic economic growth depends upon the use of the poorer quality coals that will remain once the better quality coals have been fully exploited. This remainder will include materials that have been discarded into stockpiles on the land's surface over many decades as a result of the intense beneficiating procedures that have been required to meet the rigorous standards demanded for export quality products.
The viability of using the poorer quality coals remaining in the country, both underground and in stockpiles in the most technologically, economically, and environmentally friendly manner is therefore becoming the most important issue facing the domestic and industrial market in the country. These challenges pertain specifically to the metallurgical, manufacturing, mining, and independent energy-generating sectors of the community. The exceptions to this scenario may be found in Eskom, the region's major power-generating utility, and Sasol, the largest coal petrochemical-producing industry, both in the country and in the world at large. Geared for low- quality coals, Sasol produces over 40 percent of the country's petrol and diesel requirements and over 200 major primary chemical products used, for example, in the plastics, explosives, fertilizer, metallurgical, and chemical industries and for a host of manufacturing industries such as textiles. Similarly, Eskom has developed relatively unique methodologies for the use of low-quality coals in their generating stations, nationwide, and in so doing is also currently developing a nationwide electrification strategy into all rural districts and into a continentwide electricity reticulation system.
For the above reasons, South Africa is currently embarking on strategies to enhance coal-quality characterization and developing more efficient methods of exploration, extraction, beneficiation, and utilization with improved clean coal technologies that will lead to more efficient use of the available reserves and better environmental control. Recent national alignment with the Kyoto Protocol has engendered new perspectives in the latter issues and has provided added impetus for the latter developments.
However, the tasks listed above need to be considered in terms of other associated issues endemic to the region, namely, social customs, unemployment, poverty, and economic disadvantage. Unlike other first-world regions, these issues must be factored into the entire coal, carbon, and energy scenarios in the subcontinent. The increasing importance of natural gas in the region is an additional factor that will in time become increasingly important in the energy economy of the region. For the present, however, coal remains the primary source of energy and economic development and, for this reason, the primary target of national and regional research and economic and policy development.
Coal plays a predominant role in the national economy of South Africa and in the Southern African region. It is estimated that coal provides about 77 percent of South Africa's primary energy requirements (Van der Riet and Begg, 2001), the remaining being largely derived from imported crude oil. South Africa has very limited reserves of oil and natural gas, and, with coal reserves that are estimated to last several hundred years at current consumption rates, it is clear that coal will remain the primary energy resource in this country. In 2000, South Africa's total saleable coal production was approximately 221 million tonnes of mainly bituminous coal. Local sales are estimated at 154 million tonnes worth R 8,563 billion (Department of Minerals and Energy, 2000); Eskom's electric power stations and the Sasol synthetic fuels and chemicals complexes are the main consumers. Beneficiated coal exports of 70 million tonnes in 2000 are worth an estimated R 11,082 billion. The South Africa economy therefore relies heavily on the coal industry, which in turn provides progress, development, job creation, and life enhancement.
Although mining activities create much-needed employment opportunities and economic growth, there are important local and global issues to acknowledge and address. The quantities of better quality coals remaining in the major mining areas in the country are fast dwindling owing in part to the limited reserves of such coal and to the extraction of the best-quality seams for the increasing export trade. The cost of extracting, beneficiating, and transporting the lower quality coals from distant coal basins is not economic at current prices and with current technology. The mining activities also impact the surrounding environment, and these impacts need to be understood, managed, mitigated, and beneficially exploited where possible.
This paper aims at addressing those issues that are most pressing for the South African coal industry, with reference to some initiatives already underway to address these problems.
The distribution of coalfields in the Southern African region is shown in figure 1 (reproduced from Anhaeusser,1986); the black areas in figure 1 indicate viable coal reserves. Nineteen coalfields are recognized in South Africa, with several more in neighboring countries to the north, east, and west. A total of about 54 mines were in production during 2000 (Department of Minerals and Energy, 2000), with approximately 90 percent of the total coal production coming from mines in the Witbank, Highveld, and Mpumalanga coalfields. The predominant coal type is bituminous, and in general the coal rank increases from west to east, with limited reserves of anthracite and low volatile bituminous coal located in the easternmost coalfields.
Figure 1. Coalfields in the Southern African region (from Anhaeusser, 1986). |
Reserve estimates are often conflicting, and government initiatives to estimate reserves have had limited success owing to extensive private ownership. South Africa's total coal reserves are estimated at 39.2 billion tones; assuming some growth in the local and export coal markets, it is estimated that this reserve will last approximately 140 to 150 years (Prevost, 1998), although other estimates are more optimistic, exceeding 200 years (Horsfall, 1993; Van der Riet and Begg, 2001). Some coalfields are estimated to be depleted much sooner; the Witbank reserve, for example, estimated to last only another 72 years, is the main source of South Africa's export coal (Department of Minerals and Energy, 2000).
Export coal is primarily produced from the No. 2 coal seam in the Witbank coalfield. This field has been mined extensively for more than 100 years and is nearing its limit as previously indicated. It is estimated that coal exports will probably peak at 75 million tonnes by 2010, after which they are expected to decline (fig. 2). The coal is beneficiated by dense medium separation to reach low ash yields that are competitive on the world market. The result is the generation of large quantities of discard material, generally containing useful carbon that is not utilized owing to global market demands for low-ash coal. It is estimated that 1 billion tonnes of discard material is currently available on the surface, with another 68 million tonnes being added annually (Department of Minerals and Energy, personal communication, 2001).
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Figure 2. South African coal export volumes (data from G. Esterhuizen, Sasol Coal (Pty) Ltd). |
National (local) coal consumption figures are shown in figure 3. Over the last 20 years coal consumption in South Africa doubled from about 100 million tonnes per year to 200 million tonnes per year. Eskom and Sasol are the major consumers of coal for power, fuel, and chemical production, and account for almost 140 million tonnes of coal consumed per year in South Africa. Important to note is that both Sasol and Eskom utilize low-grade coal that is not acceptable to the export market. The availability of high-quality coking coal for the metallurgical industry is limited, and estimated figures indicate that only 3 percent of South Africa's coal reserves are of metallurgical quality. Domestic coal consumption is mainly for heating and cooking requirements in the poorer informal housing communities of South Africa (to be discussed below).
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Figure 3. Local coal consumption in South Africa (data from G. Esterhuizen, Sasol Coal (Pty) Ltd). |
Statistics on South Africa's power generating capacity are shown in figure 4. It is clear that coal is the primary energy source for power generation, and this scenario will remain largely unchanged in the near future owing to economic considerations. At present, Eskom has excess power generating capacity, which will be reduced by a growing economy.
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Figure 4. Power-generating capacity in South Africa (data from G. Esterhuizen, Sasol Coal (Pty) Ltd). |
There are two main drivers for technological development pertaining to the coal utilization. These are, firstly, issues related to the optimum utilization of the limited coal reserves and, secondly, issues related to environmental pressures. The environmental aspects to consider are numerous and diverse, ranging from mining practices to emissions and the effect not only on the environment but also on human and animal health. Although the emphasis over the last two decades had been on NOx and SOx emissions, it is now swinging towards the issues of mine water quality, submicron particulate matter, harmful trace-element emissions, volatile organic components (VOC's), and CO2 emissions.
In view of the limited reserves of high-quality coal remaining in South Africa, the viability of using the poorer quality coals remaining in the country, both underground and in stockpiles, in the most technologically, economically, and environmentally efficient manner is therefore becoming the most important issue facing the domestic and industrial market in the country. These issues pertain specifically to the metallurgical, manufacturing, mining, and independent energy-generating sectors of the community.
The exceptions to this scenario may be found in Eskom, the region's major power-generating utility, and Sasol, the world's largest synthetic fuels and petrochemical producing industry. Both Eskom and the Sasol processes are geared for utilizing low-quality coals, where the ash content of the coal may exceed 30 percent. Sasol produces over 40 percent of the country's petrol and diesel requirements and over 200 major primary chemical products. These are used. for example. in the plastics, explosives, fertilizer, metallurgical, and chemical industries and for a host of manufacturing industries such as textiles.
Similarly, Eskom has developed relatively unique methodologies for the use of low-quality coals in their power-generating stations. In so doing, Eskom is also currently introducing a nationwide electrification strategy into all rural districts and into a continentwide electricity reticulation system. An alternative technology to conventional pulverized coal combustion being considered by Eskom is fluidized bed combustion (FBC) (Van der Riet and Begg, 2001). With this technology, coals can be utilized that are problematic for conventional pulverized fuel combustion owing to various undesirable characteristics (for example high ash content and low reactivity). The FBC technology thus offers much more flexibility with regards to coal-quality characteristics. Although the FBC technology is considered mature, there are at present no FBC power plants in South Africa. In addition to the high flexibility that the technology offers with regards to coal quality, it also offers other "Clean Coal Technology" advantages, such as lower NOx emissions and, possibly, SO2 emission reductions by in situ removal of these gases with sorbents such as limestone. A pre-feasibility study was conducted by Eskom from 1996 to 1997, and the technical feasibility and favorable economics led to a full feasibility study from 1998 to 2000, which was jointly funded by the government, Eskom, and two mining companies. The techno-economic feasibility study and the fuel and sorbent evaluation have now been successfully completed and show that the project has no insurmountable technical hurdles. A strategic environmental assessment (SEA) was also undertaken and highlighted the typical advantages of such a concept. The project is now going through the strategic and commercial phases (Van der Riet and Begg, 2001).
The lack of reliable coal-reserve estimates is a point of concern and needs to be addressed. Some implications of this are that new reserves must be explored primarily to establish reliable reserve estimates but, more importantly, to provide data for techno-economical evaluations and feasibility studies for future exploration. Research and development efforts have to be focused toward the development of techniques to extract reserves that are not readily accessible by today's mining practices. Existing operations must strive toward the maximum extraction of coal, because it is unlikely that coal that is left behind can ever be mined at a later stage in an economically feasible way. Pillar extraction projects in the Witbank coalfield are part of an initiative to maximize coal extraction and extend the limited lifetime of this reserve. Another initiative is COALTECH 2020, which is a task team that was established to investigate the coal resources and remaining reserves in the Witbank coalfield and to develop new initiatives to extend the life of the mines in the area.
Estimates for discard coal production have been given before, and it is estimated that approximately 60 percent of the 1 billion tonnes of available discard material contains energy that can be recovered by existing and new technologies (information obtained from Department of Minerals and Energy). At the Department of Minerals and Energy, a project is currently underway to address the discard issue; completion of the first phase of the project is expected by January 2002 with the establishment of a national inventory for discard coal in South Africa. The FBC technology discussed earlier also offers an opportunity for power generation from the vast reserve of discard material available in South Africa (Van der Riet and Begg, 2001).
Coal-handling operations always generate fine coal; although certain processes are not affected by fine coal generation (for example, pulverized coal combustion), other are. In the Sasol process, for example, approximately 70 percent of the total coal consumption is gasified to produce synthesis gas, whereas the other 30 percent is a finer coal fraction (typically less than 6 mm top size) that is not suited for gasification by the Sasol-Lurgi fixed bed gasifiers and is thus used for steam and electric power generation. The balance between coarse and fine coal is important and, if not managed correctly, may lead to an excess of fine coal, with an associated cost and environmental consequences. Stockpiling of fine coal is only practiced as a last resort but is unfortunately required from time to time. Research into the briquetting and agglomeration of fine coal proved these solutions to be technically feasible, but unattractive economics have prevented implementation.
The gasification of fine coal by alternative technologies is another feasible solution, and a number of studies have been conducted to assess the economics. Owing to the limited volume of fine coal to be gasified, the economics of scale cannot be exploited, which leads to a significantly higher synthesis gas cost and unfavorable economics. Currently, Sasol exchanges excess fine coal for coarse coal from another coal producer. Although not the most cost effective way of addressing the fine coal issue owing to the high transport costs, it does prevent the land disposal (stockpiling) of fine coal. This is an excellent example of the collaboration that is required between all coal producers and users in South Africa to make optimum use of the limited coal reserves.
Extensive utilization of fine coal for combustion and gasification is often limited by the high moisture content of fine coal. Solutions must be found for drying fine coal in an economically viable way, and a number of such investigations are under way in South Africa.
Water quality in the vicinity of mining operations is of concern to all those exploiting coal and is not unique to the South African situation. Geological disturbances caused by coal extraction result in an increase in the influx and a degradation in the quality of any water passing through the mine workings. The main mechanism of water contamination is acid rock drainage at exposed coal surfaces and the dissolution (leaching) of chemical constituents from these exposed surfaces. This process is driven by the microbially mediated oxidation of pyritic material in the coal and associated rock. The extent of contamination is affected by the water's being in contact with the coal remaining on the mining horizon for long periods of time before it is removed to the surface or handled elsewhere.
The excessive cost of end-of-pipe treatment has pointed to the need to address the water issue by reducing the generation of water at its source. Most large mines have water management plans, including water balances, giving relatively accurate projections of future mine water production. Currently, the factors influencing the management and control of water ingress into the mine workings and its subsequent chemical decay are being investigated by Sasol, and detailed models are being prepared to assist with future planning. The information generated will be incorporated into an appropriate mine planning tool.
Opportunities for reusing mine water, such as the utilization of mine water as cooling water, are being extensively explored by Sasol. Although technically feasible, pre-softening of the water is required, and extensive pilot tests are being conducted to determine the most suitable chemical treatment program. Sasol is cofunding an industry-sponsored mine water irrigation research project, and trials are being carried out at Secunda. The salinity of the mine water and soil types in the area largely restrict the large-scale implementation of mine water irrigation schemes, but it may be a viable technology for application in niche circumstances. Mine water treatment through desalination is conducted by Sasol at Secunda, where surplus mine water is being upgraded for reuse through an electrodialysis desalination process. A coproduct of desalination is a brine stream that needs to be handled. An evaporator crystalizer is being built to accommodate this brine stream, which has to date been accommodated in the ash-handling system or rerouted to the feed dam. Finding effective brine-handling solutions remains a high-priority area for research.
With an integrated approach to mine water management, the negative impacts associated with mine water can be turned into opportunities. Furthermore, mine water management needs to have a trans- mine boundary approach, inasmuch as it is becoming ever more apparent that these complex issues need to be addressed on a regional basis.
Depending on the particular process, trace elements present in coal may report in a variety of process effluent and product streams. There is currently no legislation addressing gaseous trace-element emissions in South Africa. In the future, however, it is to be expected that both the local and international community will enforce much stricter legislation on all emissions. South Africa is no longer isolated from the rest of the world, and non-compliance in South Africa to international legislation may result in tax levies being imposed if South African products are put on the international market. Nationwide mercury controls are expected by 2005 to 2007 (Van der Riet and Begg, 2001), and legislation of other trace elements is expected to follow.
For these reasons, the quantification of trace-element levels in coal and their concentrations in process products, effluents, and emissions are of high importance to the South African coal-consuming industry. Both Eskom and Sasol have embarked on projects to quantify the trace-element emission levels in their combustion and gasification processes. Suitable analytical laboratories that can deal with the complexities of trace elements in coal are limited in South Africa, and those laboratories that have some expertise are geared toward metallurgical and catalytic applications. Eskom is the exception and has done substantial amounts of trace-element analyses, looking at the total pathway from combustion to emission. Although there will be local collaboration between Eskom and Sasol on trace elements, it must be kept in mind that the combustion and gasification processes are distinctly different in nature, because trace elements are released in an oxidizing atmosphere during combustion versus a reducing atmosphere during gasification. The speciation (that is, oxidation state) and degree of release from the coal are expected to be substantially different for the two processes. Mercury is a good example. During combustion, volatile mercuric components are produced and are emitted with the flue gas, as opposed to gasification, where mercury is reduced to Hg0 that is scrubbed during the gas cooling and cleaning steps.
In view of the limited local expertise and analytical facilities, it is believed that international collaboration is of utmost importance. For Sasol, which competes with chemicals on the international market, confidentiality and intellectual property are issues that understandably have to be considered.
The greenhouse effect of ever increasing global CO2 emissions is by now largely accepted. The Kyoto protocol may have far-reaching implications for all those relying on coal and is of particular concern for South Africa, which has very limited oil and gas reserves. The most abundant co-product produced during coal gasification is greenhouse gas CO2, and Sasol has put much emphasis on better understanding the thermodynamics and process parameters that dictate the carbon distribution of products during synthesis gas production through coal gasification. Significant improvements in carbon utilization to lower CO2 emissions can be obtained by either switching to or co-feeding additional feedstock with a higher H/C ratio. Owing to a combination of economic, environmental, and strategic reasons, Sasol has decided to convert from coal to natural gas as primary feedstock for the Sasolburg plant, which currently consumes about 6 million tons of coal per year. Natural gas is to be supplied by pipeline from Mozambique and is scheduled to reach Sasolburg by 2004. All coal gasification activities in Sasolburg are likely to be phased out after 2004, and only a small amount of coal will be used for steam and power generation. However, studies are being conducted and research and development work is being done to investigate the possibility of continued utilization of some of the gasification facilities to gasify mixtures of coal, biomass, and other carbon-rich waste feedstocks. A small volume of natural gas will also be fed to the Secunda plants, although coal will remain the main feedstock for these plants. The known gas reserves off the Mozambican coast are insufficient to supply the Secunda plants with a sustainable source of natural gas. For the same reason it is unlikely that coal-burning power plants in South Africa will change over to natural gas.
The trend toward natural gas and away from coal poses a serious threat to a developing country like South Africa, which relies heavily on coal for economic growth. Although local consumption of coal by the two main consumers, Eskom and Sasol, is expected to remain fairly constant, coal exports may be seriously affected by global trends toward alternative energy sources.
The ultimate solution for dealing with CO2 is to sequester (store) CO2 in deep underground or undersea aquifers. Unfortunately, local CO2 production is too far removed from South Africa's deep coastal waters and transport would be too expensive. Underground storage is theoretically considered an option for South Africa but is also expected to have unfavourable economics (Van der Riet and Begg, 2001). No CO2 sequestration research projects have yet been undertaken in South Africa, and. to the authors' knowledge, no companies in South Africa are actively involved in global collaborative research on this topic, mainly because of the high costs involved. The issue nevertheless remains pressing, and South Africa will be followers looking toward the international community for ground-breaking progress.
Everyone who has visited South Africa during winter time will be aware of the air-quality problems the country experiences because of domestic coal usage in the poor and informal housing sector. Despite the fact that electricity is available to the larger informal housing areas, many of these people are unemployed and poor and simply cannot afford electricity and therefore rely heavily on coal for domestic purposes. It is estimated that approximately 1.5 million of the poorer households in the central industrialized areas of South Africa are still dependent on coal as a basic fuel for cooking and heating. Coal is burned in open appliances and stoves, often without suitable chimneys, causing widespread respiratory illnesses.
An important challenge facing South Africa, at least in the near term, is to provide a cleaner burning fuel with the same characteristics as coal at an affordable price for poor households. The reason for concentrating on the fuel is that the relatively well developed distribution channels and existing appliances can be used. The Department of Minerals and Energy (DME) is part of a collaborative activity for low-smoke fuel and appliances for coal combustion in South African domestic conditions (C. Grobbelaar, Department of Minerals and Energy, personal communication, 2001).
The issue of coal education in South Africa is perhaps the Achilles heal of the coal industry in this country. Coal and its related processes are often regarded as "dirty" or old-age technology by the younger generation of scientists, and there is a reluctance to pursue coal research as a career of expertise. Formal semester-long courses in coal-related subjects are unlikely to be continued after 2000, mainly owing to dwindling student numbers, lack of industrial support, and restructuring of university courses because of economic pressures (Pinheiro, 1999). A fundamental knowledge and understanding of coal properties and their effect on process performance and economics are lacking and need to be addressed. Optimal use of South Africa's coal reserves cannot be achieved without scientists and engineers equipped with at least a basic understanding of coal. Accreditation and professional training will require the establishment of formal education and training at all levels in the near future (Pinheiro, 1999).
Although it is accepted that coal will play a major role in the economic growth and well-being of South Africa for many years to come, the South African coal-based industry faces many technical, economic, social, and environmental challenges. International pressure on environmental issues is expected to increase, and South Africa will have to follow suit to remain a competitive global player in the coal and derived products industry. South Africa requires a growth rate in excess of 6 percent in order to meet its developmental requirements over the next decade (Pinheiro, 1999), and coal can make a significant contribution to this objective. Optimal utilization of limited coal resources is of utmost importance but cannot be achieved without the human resources skilled in the fundamental requirements of the coal industry. To quote: "Without learning there can be no vision, and without vision, no innovation" (Pinheiro, 1999).
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Horsfall, D.W., 1993, Coal preparation and usage: coal preparation for management, vol. 1, chapter 5: Coal Publications (Pty), Ltd.
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