Sugarcane resources in southern Africa
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Francis Johnson examines the
use of sugarcane as a renewable energy resource in southern Africa.
The author is a Research Fellow in the Sustainable Energy Programme at the Stockholm Environment Institute in Sweden. |
The sugarcane plant offers one of the most cost-effective renewable resources among those renewable energy options that are readily available in developing countries. It is a highly efficient converter of solar energy and, in fact, has the highest energy-to-volume ratio among energy crops. It is a highly diversified resource, offering alternatives for production of food, feed, fibre and energy. Such flexibility is valuable in the developing world where fluctuations in commodity prices and weather conditions can cause severe economic hardships.
As a biomass energy resource, sugarcane is among the most ideal of feedstocks in terms of efficiency and flexibility, providing gaseous, liquid and solid fuels. Owing to climatic factors, sugarcane is found predominantly in the developing world and, as such, represents a valuable tool in the simultaneous search for sustainable energy sources and new development alternatives. It offers the potential for climate change mitigation through substitution for fossil fuels without the need for excessive subsidies or expensive infrastructure development.
In this article, a brief overview is provided of the sugarcane resource and its role in supporting climate-friendly sustainable development, with special reference to the opportunities in southern Africa.
The sugarcane plant, a large perennial tropical grass, is the main source of processed sucrose, or white refined sugar, found on so many kitchen tables around the world. Sugarcane grows in tall stalks (six to ten feet) with a considerable amount of leaves surrounding the stalks, which have the function of assimilating carbon dioxide through photosynthesis. The leaves, along with the tops of the stalks, are either burnt or cut off at harvest time, and hence are sometimes referred to as ‘cane trash.’
At the sugar mill, the cane stalks are shredded and crushed to extract the cane juice while the fibrous outer residue, known as bagasse, is sent to the boiler to provide steam and electricity for the mill.
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Bagasse accumulating at a sugar factory. Photo: F Johnson. |
Even with today’s inefficient boilers, excess bagasse accumulates at sugar factories, posing fire hazards as well as representing great opportunity costs as a readily available and renewable resource.
The installation of efficient cogeneration systems can increase the energy output of the factory to roughly ten times today’s typical level, thereby freeing up 90 per cent of the energy produced for sale to industries or to the electricity grid.
The fibre content and chemical composition of bagasse has also led to its increased use in industrial applications such as particleboard, pulp production and various chemical industries. The proteins and sugars in cane by-products, especially molasses and bagasse, have long made them popular in agricultural applications to make animal feed.
Many of these applications are particularly valuable in developing countries due to population pressures, the need for rural development and dwindling supplies of forest-based biomass. At the same time, expansion of a renewable energy resource found mainly in developing countries has obvious appeal for international efforts to reduce carbon dioxide emissions.
In addition to bagasse, molasses has long been another important by-product of sugar production, being used to make a variety of products, such as animal feeds, alcohols and fertilizers. Alternatively, cane could be sent to a distillery capable of fermenting the cane juice directly into ethanol, as is common in Brazil, where the government initiated an ethanol programme in the wake of the oil crises of the 1970s.
Just as is the case in the sugar mill, bagasse provides the bulk of the energy inputs for the distillery. The organic wastewater stream from ethanol production, known as vinasse, can be used as fertilizer or it can be converted to methane gas through anaerobic digestion. The transportation fleets used in sugar factories and ethanol distilleries in Brazil have in some cases been powered by methane gas.
The sugar industry has faced a number of competitive pressures in recent years, due to such factors as saturated demand in industrialized countries, competition from other sweeteners and low and/or fluctuating sugar prices. These difficulties have increased economic incentives for sugar producers to diversify their product portfolio by investing in other applications in the energy, industrial and agricultural sectors.
Production of fuels and electricity has naturally been an attractive option for an energy-rich crop like sugarcane. A number of countries such as India and Mauritius have made significant investments in advanced bagasse cogeneration systems. But the diversification of sugar companies and expansion of cane energy systems have been slowed somewhat by a number of barriers, including the lack of regulations for independent power producers and the continued price supports for sugar production around the world.
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Sugar cane production in selected countries in southern Africa, 1996-97. |
The energy potential of sugar cane resources is related to the quantity of cane that is harvested and sent to the sugar factory. Cane production is shown for 1996-97 in the figure above for selected southern African countries.
Not surprisingly, the largest producer by far is South Africa. Mauritius, Swaziland and Zimbabwe also produce significant quantities, when one considers their size and level of industrialization in comparison to South Africa. Sugar factories in Zambia, Tanzania and Malawi are fairly small, but have been in continuous operation for many years. Production in Mozambique has been depressed due to the civil war, but, with the end of the war and the new economic opportunities, it is expected that the industry in Mozambique will be expanding significantly in coming years.
The current cane resource in southern Africa of approximately 40 million tonnes of cane per year can also be translated into energy terms. In the case of electricity production, the installation of state-of-the-art cogeneration systems would translate into about 550 GWh of electricity. In the case of ethanol production, this cane, if used as a direct feedstock for ethanol production, would amount to over three billion litres of ethanol. These amounts are not large by world standards. But by African standards, they represent a significant expansion of the domestic resource base and could lead to the displacement of five to ten per cent of gasoline demand and four to eight per cent of electricity demand in the region. If one takes into account the possibilities to expand cane output through modernization of facilities, the contribution could be much higher.
The world’s major cane sugar producers, including India and Brazil, have initiated investments in modern cogeneration facilities at sugar mills that produce electricity at commercially competitive rates. Detailed studies, such as the 1998 Global Environment Facility report, Using Area-Specific Cost Analysis to Identify Low Incremental-Cost Renewable Energy Options: a Case Study of Cogeneration in the State of Sao Paulo, have shown that such cogeneration plants offer a cost-effective distributed resource to poorer rural areas.
The use of bagasse briquettes is receiving attention in those areas plagued by fuelwood scarcity and deforestation. The making of charcoal fines from bagasse could also be attractive because of the implications for more sustainable industries and because the direct substitution for coal and/or forest resources can result in significant environmental benefits.
The African country that has come the furthest in bagasse utilization is Mauritius, where modern efficient Condensing Extraction Steam Turbines at sugar mills produce a significant share of the island’s electricity. This particular method is explained in detail by Revin Beeharry in a 1996 issue of Biomass and Bioenergy entitled Extended Sugarcane Biomass Utilization for Exportable Electricity Production in Mauritius.
One down side to the plants in Mauritius is the fact that these plants run on bagasse only during the six to seven month harvest season, and run on coal the remainder of the year. Techniques and methods for bagasse storage should be considered so that the plants can be operated on biomass year-round.
In most other African countries, excess bagasse is either not utilized at all or it is burned in extremely inefficient boilers.
A study in Tanzania found that cogeneration facilities for bagasse and cane trash could be run at competitive prices. Mohamed Gabra and Bjorn Kjellstrom outlined a method for this in their 1995 working paper, A Pre-Feasibility Assessment of the Potential of Cane Residues for Cogeneration in the Sugar Industry.
A study in Zambia, focusing on a proposed future site in Northern Province, found that cogeneration units like those found in Mauritius could provide power to the grid at competitive prices.
A study at the Nakambala sugar mill in Zambia found that the production and sale of bagasse briquettes appeared to be economically viable and useful as a domestic fuel source for the local community. Julius Kaoma described this study in his 1997 report, Bagasse Char Development Project, which was undertaken on behalf of Zambia Sugar PLC.
The production of ethanol has been viewed as a valuable means of saving foreign exchange in developing countries while at the same time providing local and global environmental benefits.
The Brazilian ethanol programme remains, in effect, the world’s largest carbon reduction programme. The Zimbabwe ethanol programme and the Malawi ethanol programme have in some respects achieved similar successes on a much smaller scale.
But ethanol has been plagued by a number of economic difficulties due to low oil prices and the regional dependencies of ethanol markets. There are also a number of operational issues related to the existing oil-based infrastructure that have made ethanol a difficult option to introduce in developing countries.
Deborah Cornland explained the various issues needing further and detailed consideration in her 1996 paper, Alcohol as an Alternative Transportation Fuel: Operational Issues in Developing Countries, undertaken for the Stockholm Environment Institute.
Among the most promising approaches for optimal utilization of sugar cane resources from an economic perspective is that of flexible production strategies, under which the quantity of sugar produced can be lowered and the quantity of ethanol increased, or vice versa, depending on the prevailing prices. A modest tax on fossil fuels or similar incentives could improve the market outlook for ethanol.
The introduction of ethanol would bring a wide variety of environmental benefits. In addition to climate mitigation and reduction of local pollutants, it can serve as an octane enhancer that might speed the phase-out of leaded gasoline in African countries. The health benefit of removing lead would be of great value in and of itself.
The economic and environmental attractiveness of sugarcane as a renewable energy resource and the variety of options for increasing use of cane by-products and co-products could one day lead to sugar becoming the by-product rather than the main product.
Further information
Francis Johnson, Sustainable Energy Programme, Stockholm Environment Institute, Box 2142, 103 14 Stockholm, Sweden. Fax: +46-8-7230348. Email: francis.johnson@sei.se. Web: www.sei.se.