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| Wednesday, 17 March 2004 |
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Energy use in the production of Tea by Rohan H. Wickramasinghe, Institute for Tropical Environmental Studies
A notable area of concern is the energy supply for the production of tea both due to the considerable demand for this input as well as the importance of this crop to the nation. The account which follows highlights some areas of interest in connection with the supply of energy in the context of the production of tea. Manufacture of Tea Tea Flavour The flavour of tea depends, in part, on the control of the manufacturing process and the conditions in which it is conducted. For instance, too much withering or rolling, over-fermentation or under-firing can have adverse effects on quality while exposure of the leaf to flue gases during manufacture may lead to a tainted flavour. Energy Inputs The cultivation and manufacture of tea entails a considerable use of energy and this is being investigated at the TRI, Talawakelle. Energy inputs take the form of fuelwood, furnace oil, kerosene, petrol, diesel, electricity and fertiliser. The use of petrol and diesel (for running vehicles) and the energy component of fertiliser will not be treated in detail here. Energy (as specified above) is required for two purposes on a tea estate: . For the operation of the factory . For the domestic needs of the resident employees and for offices, temples and health centres A study reported by van der Knyff in 1987 noted that made tea for the year amounted to 211.3 million kg and that around 1.7 million workers were employed on the plantations. The energy consumption in the production processes and for domestic and related needs were as follows: . Processes: Fuelwood (404 mn kg, 5.5 mn GJ), oil (13.1 mn L, 0.58 mn GJ), electricity (160.8 mn kwh, 0.58 mn GJ) and fertiliser (128.8 mn kg, 1.9 mn GJ) . Domestic and related uses: Fuelwood (1000 mn kg, 13.5 mn GJ) and kerosene (48 mn L, 1.7 mn GJ) The tea industry in Sri Lanka is the principal consumer of electricity and of fuelwood (33 per cent of the consumption of the country's industries) and a major user of oil. The withering process is the major user of electricity component. Improvements could be made in the efficiency of energy use in the factory. Tea manufacture consumes energy mainly in the following stages: . Withering (heat and motive power, i.e. fans) Lw-grown teas require longer withering periods and more heat input during withering than high-growns. Fuelwood is more easily procured by low and mid-country estates due to that resulting from rubber replanting programmes, while up-country estates are more likely to use oil-fired heaters. However, fuelwood may also be obtained from felling of jungles illegally by contractors for supply to tea estates. Due to concern over the rapid diminution of the jungles and the increasing scarcity and expense of fuelwood, tea plantations have been strongly advised to establish fuelwood coupes on at least 10 percent of their lands. It has also been suggested that conversion to oil-fired burners would not only reduce dependence on fuelwood but also improve the quality of the product by facilitating better control of the process. However, precautions need to be taken to ensure the flue gas emissions, e.g. resulting from burning high-sulphur oil, do not harm the product, machinery or plantations. Wood-fired furnaces may have poor efficiencies due to a variety of reasons. Fuelwood consumption is around 0.5 to 2 kg per kg made tea according to different workers etc. Once relevant factor is the use of insufficiently dried fuelwood. freshly cut wood may contain 50 per cent moisture and it is usually recommended that wood be left to dry for at least three months under covered conditions to bring this down to 15 per cent. N.G.P. Jayatunge has recommended that firewood should be cut into pieces of not more than 35 x 15 cm to facilitate improving the efficiency of the air heaters. Energy audits have found that 22 MJ of thermal energy is used in producing 1 kg of tea. Electricity is a source of energy for both factory and domestic (and support service) needs. Van der Knyff reported in 1987 that in one plantation studied, electricity consumption during tea manufacture was 0.43 kWh/kg made tea and that for domestic use was 0.08 kWh/kg made tea. The ITDG Report of 1998 noted estimates of regional differences of electricity consumption as follows: . high-grown: 0.9 to 0.95 kWh/kg made tea In earlier years, electricity requirements for tea factories were met by diesel generators or around 400 to 600 'run-of-the-river' mini-/micro-hydro units (Pelton wheels). However, with availability of low cost and reliable national grid electricity in the late 1960s these were mostly abandoned and fell into disuse and only about 60 units remained in use. With the rising cost and supply problems of grid electricity the rehabilitation and construction of mini-/micro-hydro units have for some years been increasingly looked upon with favour. The ITDG Report gives detailed studies of several scenarios where the tea sector electricity demand is met with supplies from the national grid together with that generated using microhydro and biomass technologies. The considerable avoidable costs calculated considered economic aspects as well as the environmental components of pollution and soil erosion. The study notes the losses due to spoilage of tea during grid failures. These avoidable costs as at July 1998 will need to be re-evaluated taking into account relevant increases which have taken place. Hopes that gasification of biomass to producer gas could be a useful source of energy for the tea industry have not yet been realised. Other advances with regard to research in the energy sector include: . Improvements leading to savings of thermal energy . Tapping solar energy by using flat plate collectors for domestic hot water and for generation of part of the hot air required for drying leaf. While solar energy could be used to heat air from 32 to 92 degrees C, it may be used operationally to preheat the air to 50 or 60 degrees C followed by the use of firewood or oil to achieve a working temperature of 95 degrees C. Preliminary data showed a cost saving of about 34 per cent for the drying operation. . Saving of energy by varying the airflow through the leafbed during withering. For the withering process, the difference between wet bulb and dry bulb temperatures should be maintained as close as possible in the range of 1.5 to 3 degrees C. (I am grateful to Dr. W.W.D. Modder, formerly Director, Tea Research Institute of Sri Lanka, for helpful discussions and making available the facilities of the TRI for this study, which was suggested to me by Dr. C.G.U. Uragoda. I thank also Ravi Algama and P.G. Joseph for discussions and Mrs. Vasantha and her staff at the TRI Library, Talawakelle for help.) |
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Produced by Lake House |
Sri Lanka is experiencing energy shortages partly due to delays in
bringing in coal-fired thermal power and other non-traditional sources and
partly due to increases in demand.
