Biofuel: Jatropha
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Introduction
Jatropha is a feedstock for biofuels. Jatropha curcas is a non-edible seeds bearing tree. The tree can grow in dry, arid land (e.g. marginal, low-fertility land) but is sensitive to humidity (e.g. flooding). As Jatropha curcas is not browsed by animals, it is traditionally often used as a natural fence.
Jatropha Growing
Correct pruning is vital to achieve high yields. Ideally, stems are pruned just above the ground to achieve bush-like plants with many branches. A good plant should have bunches of Jatropha fruits at every end of a branch. In the first years, patience is needed: Jatropha bushes need about 4 to 5 years until full production capacity is reached. Achievable yields then can reach 4 to 5 tons per ha per year.
When planted in a plantation, 1,300 plants can be found in 1 ha (2.5 meters between the planys, 3 meters between the rows). Then, 3.8 kg seeds/year/plant should be reached in theory. Yet, single bushes cannot be compared to bushes in plantations that easily (e.g. lower access to minerals, etc.), so the yield per tree will probably be a bit lower.
When starting a jatropha plantation with the aim to produce oil for electricity generation, potential land use conflicts with food cropping must be avoided.
Jatropha Products
Jatropha Oil
Jatropha oil is a plant oil with some similar physical and chemical properties to diesel, which is why it is possible to run diesel engines on jatropha oil after some adaptations. The oil content of jatropha seeds is around 30-35%, so around 3 kg of seeds deliver one liter of oil.
- calorific content: Jatropha oil has a 7% lower calorific content than diesel. A greater quantity of Jatropha oil is needed when switching from diesel to jatropha oil.
- viscosity: Jatropha has a higher viscosity than fossil-fuel based diesel. Hence, at lower temperatures (in ares with colder climates) this can cause problems when running a diesel engines, especially during the start-up phase when both the engine and the fuel are relativly cool. More stress is put on the fuel pump, the filter and injectors. By installing heating coils around the fuel lines, this problem can be mitigated.
Jatropha Oil Extraction
Before extraction, the seeds are is usually dried and cleaned. Cleaning the seed is to eliminate foreign material that may damage the oil extraction machine, while heating the seeds by leaving them in the sun or by roasting them gently for ten minutes, improving oil extraction efficiency of the hand expellers. Oil extraction can be done by both hand and machine. Traditional oil extraction methods are highly labour intensive, requiring some 12 hours to produce one litre of oil. The process requires roasting the seed kernels, pounding them to a paste, adding water and boiling, and then separating the oil by skimming and filtering.
Seed Cake
Being rich in nitrogen, the seed cake of the oil extraction process is good excellent source of nutrients and can be applied as an organic fertilizer.
Also, the seed cake is a good feeding material for biogas plants.
Others
Jatropha is also used to grow mushrooms and to produce soap.
Power Generation and Rural Electrification based on Jatropha Oil
Oil from Jatropha seeds can be used to fuel diesel generators adapted to be operted with vegetable oils. The oil is usually filtered through a cloth before poured into the generator.
In rural electrification projects, which are (partly) based on jatropha oil, different models of jatropha supply (or a mix of the below) exist:
- large privately (e.g. by a company) planations ==> easy to administer, danger of plant deseases
- large or scattered community owned plantations ==> very difficult to organize and maintain, challenge of logitics but easier control over growing techniques
- scattered small holder plantations ==> challenge of logistics maintenance and growing
- small holder/household intercropping and fencing ==> lower yields, sometime contradictory goals (large bushes for fencing, lower yields, more difficult to collect seeds).
Experiences from Cambodia
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Further Reading
For further information see Electricity Generation from Vegetable Oil.
www.jatropha-alliance.org and its Jatropha Handbook
Fact Foundation Jatropha Handbook
