Biomass energy from mesquite shrubs

An improved design for a metal charcoal kiln can help to improve livelihoods, while also controlling a pervasive weed.

Metal kiln for producing charcoal from MesquiteProsopis, known as Mesquite in Sudan is a perennial woody plant, characterized by a strong root system, and with the ability to grow under a wide range of environmental conditions. In the 1970s and 1980s it was widely disseminated in Sudan for the purpose of addressing the problems of Sudan's arid and semi-arid areas, summarized as: fuel wood production; pods for fodder; soil stabilization; and as a means for stopping the desertification process. However there is great controversy surrounding the Mesquite shrub. When unmanaged, it often colonizes disturbed, eroded and over-grazed lands, forming dense impenetrable thickets alarming pastoralists, farmers and conservationists alike. Its spreading and growth are extremely difficult to control and it negatively affects Sudan's agriculture productivity.

Due to these reasons Sudan decided to declare Mesquite a noxious weed and launched a national program for its eradication. This is an audacious task as it continues to spread quickly into agricultural lands and irrigation canals. Therefore the purpose of this project is to introduce an alternative method for Mesquite control that can improve livelihoods through resource exploitation to produce charcoal using improved carbonization techniques (metal kilns).

The design came up with the idea of using the same metal kiln which helped design for carbonization of cotton stalk as part of the Biomass Technology Group at the Energy Research Institute in the 1980s.

It is actually quite similar in design to a MARK V metal kiln (a well known charcoal kiln) but of smaller volume and weight to allow for easy transportation by labor, with a volume of about 2 m. Its nominal carbonization efficiency is around 25 %, although this figure will depend on the skill of the operator. The metal kilns additional advantage over the normally used earth-mound kiln is that it enables fine charcoal to be made from the small branches of the Mesquite shrub.

To prove that this idea was feasible we conducted a training exercise with local charcoal producers to operate the kiln while simultaneously testing its efficiency with regards to Mesquite. Twenty charcoal producers were trained to use two identical metal kilns that were used for burning. The trainees participated with great enthusiasm and within a couple of hours of training they were comfortable with the kilns operation. Due to the fact that the wood originally put in the kiln was a little wet the carbonization process took four days, however this was reduced to one day after further testing. The output was very good producing 6 sacks of good quality coal.

The metal kiln could easily be fabricated locally at a low cost as it can be made from empty oil barrels which can be purchased in Kassala market. A manufacturing instruction list and technical drawings have been made to help with its dissemination. The charcoal makers were very happy with the metal kiln, particularly regarding ease of operation and the time it saved. The quality of charcoal was also reported superior to that produced from earth-mound kilns.

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This article first appeared in the April 2009 issue of Sharing, Practical Action Sudan's newsletter.
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