Study on feasibility of charcoal production from Commiphora species and Terminalia orbicularis

Abstract

This study was carried out within Sosoma Ranching Cooperative Society located in the southeastern corner of Mwingi District. The ranch, which is 126,000 Ha, is not inhabited except for a few squatters and a small stock of cattle owned by the owners. There is some harvesting of Melia volkensii for timber and charcoal conversion within the ranch. The vegetation is very similar to that found in other semi-arid areas dominated by thorny trees and shrubs with very little ground cover. The dominant trees include Commiphora baluensis, C. africana, C. campestris, Terminalia orbicularis, Lannea triphylla, Acacia senegal, A. tortilis, A. mellifera and Delonix elata. The shrubs include Boscia coriaceae, Combretum sp. Premna oligotricha, Grewia villosa, G. bicolor, Erythrochlamys spectabilis and Lippia kituiensis. The woody climbers are represented by Entada leptostachya and Thunbergia guerkeana. Annual herbs including grasses and some sedges dominate the ground cover. Grasses include Aristida adscensioni, Heteropogon contortus and Sporobolus fimbriatus. The common sedge is Kyllinga alba. The society has a rather ambitious 5-year plan (2001- 2005), which includes fencing the rangeland, improving the beef cattle breed, constructing ten water dams or boreholes, cutting service roads, constructing cattle dips and demarcating the rangeland. However, the society lacks adequate resources to implement the plan. Despite the small stock of animals (due to cattle rustlers), the pasture is not enough due to the heavy canopy during the rainy season. Therefore, interventions by DFDP/INRMU (District Forest Development Program/ Integrated Natural Resources Management in Ukambani) planned to open up the woodland (by selective cutting of tress) to increase the pasture. The Kenya Forestry Research Institute (KEFRI) was contracted to conduct a survey of the area and make an inventory of the vegetation. They were also contracted to convert the felled tree species into charcoal using improved earth mound kilns. The selected species were Commiphora africana, Commiphora baluensis, Commiphora campestris and Terminalia orbicularis. These ordinarily are not used for making charcoal, and thus the study was to investigate the optimal kilning process for these species. A follow up study on the vegetation recovery will be done to see the effects of the selective felling of trees and charcoal burning. The following activities were then carried out. 1. Review the local uses of woodlands in general, and Commiphora species in particular, by the local communities of Mwingi. 2. Description of the trial area where trees were cut and the kilns established, before and after the felling, in view of an eventual follow-up study on vegetation recovery. The description was related to tree and shrub, and grass species composition, density and biomass. 3. Determination of the energy and selected wood working characteristics of Commiphora species and other alternative species Terminalia orbicularis for charcoal production. 4. Establishment of optimal kilning process for the three Commiphora species, separate and together, and in a mixture with some other species (especially Terminalia orbicularis) in view of producing commercially acceptable charcoal. Kiln types to be used; Improved earth, Casamance and “Subri Trench”. 5. Investigate marketing aspects of the produced charcoal: acceptability to the average consumer. 6. Execute an economic analysis of the charcoal production. Looking at the costs of the inputs and outputs (product). The cutting of the trees was carried out for two purposes. The first purpose was to obtain some wood material for testing the different kilns for making charcoal. Secondly, the trees were cut and measured to facilitate determining the volume of wood cut from the plot as well as providing data for development of volume functions for these species. A total of 124 plant species in 94 genera distributed in 37 families were recorded as the most common plants comprising the vegetation in and around the project site. The trees and shrubs are described giving the local names and uses. A list of herbs including grasses is also given. To determine the tree and shrub composition in the ranch, a plot of one hectare was selected and its boundaries marked. A total of 42 tree and shrub species were documented within the study plot. Among these 13 of them (31%) were trees while the rest were shrubs (67%) and climbers (2%). The inventory of C. baluensis before felling was estimated at 150 trees per hectare with an average volume of 0.4670 m3 per tree. Though these are interim results, this implied that the study plot had approximately 70.05 m3 of C. baluensis. The Terminalia orbicularis were estimated at 30 trees per hectare and with an average volume of 0.2467 m3, the wood volume in the plot was approximately 7.40 m3. The population of C. africana was quite low estimated at 15 trees per hectare. With a mean volume of 0.4267 m3, the estimated volume per hectare was 6.40 m3. The effect of the Commiphora and Terminalia species on the pasture development in the dry areas has been thought to be negative. In the past, removal of trees in the ranch has been carried out basically to obtain some specific wood products. No concerted efforts have been put in place to establish how much of the tree cover should be removed to deliberately improve the pasture. Close follow up of this work will in future guide the ranch managers on how much of the tree cover will be removed to obtain some wood products such as charcoal, timber and poles while at the same time improving the pastures. Before carbonisation, the energy and various wood characteristics of Terminalia orbicularis and the three Commiphora species were established. Terminalia orbicularis and Commiphora africana wood gave calorific values of 5.1 KJ and 4.8 respectively. Most of the Commiphora species were found to be unsuitable for timber production because of their difficulty to saw on a bandsaw and their lack of a straight bole. It was therefore recommended that Terminalia orbicularis and Commiphora africana are more suitable for charcoal production than for timber. The three Commiphora species, Terminalia orbicularis and a mixture of all the species were carbonised using four kiln types (improved earth kiln, casamance, subri trench and the traditional earth kiln) in an effort to determine the optimum kilning process. These species were felled and crosscut into 1 m lengths (other than those for the casamance kiln which were cut into 0.5 m lengths) six months prior to the carbonising activity to enable drying. Three replicate stacks of 2 m3 each were set up. While carbonising several parameters were recorded; the time taken to arrange the wood and the number of people used, time taken to cover the wood mound with grass/soil and the number of people used, the time taken to completely close the kiln and the length of the carbonisation process. The recovery rates obtained varied greatly while carbonising the various species. However, the highest recovery rate achieved within each kiln type, other than the traditional earth, was above 20%. The highest achieved was 24% with the improved earth kiln. It was noted that the high recovery rates were achieved while carbonising Commiphora baluensis (for both Improved earth and Casamance Kilns). It was noted too that most bags of charcoal were produced from this species (Commiphora baluensis) in all the kiln types (other than the traditional kiln which only used the mixed species) and the most number of bags (37 bags from 30 m3 of wood) were from the casamance kiln. It was not easy to clearly determine the optimum kilning process because of the climatic factors that affected the processes. These were the lack of wind and when it was there, its non-unidirectional direction. This especially affected the results of the subri trench. The other factor was the heavy rain that poured on a couple of days in the middle of the kilning exercise thus interfering with the carbonisation process. The wet soil affected the cooling process in that the soil was not loose enough as needed to prevent burning of the charcoal. This therefore, caused over burning of the charcoal especially with the subri trench. The only species that was not affected by this rainfall was the Commiphora baluensis, which incidentally gave the highest recovery rates (using improved earth and casamance kiln) because most of the replicates had been carbonised before the rain fell. However, from the results obtained, the casamance kiln yielded most bags of charcoal (37 bags; ten bags more than the improved earth kiln). It is important to note that averagely the wood for the casamance was drier than all the other wood. This could have been because the wood was only 0.5 m in length while for the other kilns they were all 1 m long. It was noted that the total weight of wood carbonised using the Casamance kiln was 6.8% and 21.4% more than that of improved earth kiln and Subri trench respectively. However, what is clear is that the traditional earth kiln gives lower recovery rates than the other improvements of the earth mound kilns Once the charcoal was produced, its energy values were determined. The moisture content, volatile matter, ash content, fixed carbon and calorific value of charcoal from each species and each kiln type were determined. Generally the moisture content of the charcoal samples from each tree species was within the range of a good quality charcoal. In general, the volatile matter was within the known range for charcoal (5-40%). However, it was slightly higher than 30%, which is the limit for a good commercial charcoal. It was highest with the mixed species charcoal, which was 37%. The ash content from the samples was slightly on the higher side, as a good quality charcoal should average 3%. The fixed carbon content was within the required range for charcoal, which is 50-95%. However, it was generally on the lower side as the tested samples generally averaged between 52-56%. The calorific values were all comparable to other charcoal from other species, which averaged between 6.5 – 7.1 Kcal; the highest value being from the mixed species. Burning tests were carried out to test the charcoal from each species type by boiling a fixed mass of water (1.5 litre) using a known mass of charcoal (A filled 2kg tin) under standardised conditions. The time taken to light the charcoal, time taken to bring the water to boil and time taken for the charcoal to go off/extinguish was recorded. Other characteristics such as whether the burning charcoal produced sparks, produced smoke, had a smell and whether the ash disintegrated or remained as a solid form on cooling and the amount of ash produced were also noted. The Terminalia orbicularis took the longest time to light (close to 10 minutes), the longest time to bring the water to boil (more than 16 minutes) and the longest time to go off. Commiphora africana took the shortest time (just less than 3 minutes) to be ignited, and the mixed species took the shortest time to bring the water to boil (8.5 minutes) and Commiphora campestris went off in the shortest time (just less than 28 minutes). These observations are supported by literature where higher density species take longer to ignite, take longer to bring the water to boil and give off a steady heat for long before going off. All the samples produced smoke when burning, with Terminalia orbicularis producing an irritating smell. This could be because of the high volatile matter in the charcoal. Terminalia orbicularis produced the most amount of ash, about 4-5 times more than the other species. This means the wood has a high mineral matter, such as clay, silica and calcium and magnesium oxides. These energy tests indicated that no one species had all the desirable characteristics of a charcoal. However for quick cooking or heating the less dense species (Commiphora campestris and C. africana) and the charcoal from the mixed species may be preferable. The mixed charcoal species took the shortest time to bring the water to boil and took longer to go off than the other Commiphora species. Interestingly the average calorific value was highest with the charcoal from the mixed species. Where cooking must be done slowly over a long period (simmering or keeping food warm) the Terminalia orbicularis which maintained a steady heat (please note that this species gave the lowest calorific value) for a longer time may be better. This species (Terminalia orbicularis) also had the highest ash content, which is basically inorganic matter, and thus would explain why it gave out steady heat for a longer period than the other species. To determine the marketability of the produced charcoal, it was introduced in the marketing system through consumers and charcoal traders who then gave their comments through a questionnaire. Marketing was done in a rural set-up and major urban centres (Nairobi and Thika). Results of marketing showed that most charcoal consumers bought charcoal based on its weight (52%) and the type of tree species (37%) used. The highest percentage (56%) buying charcoal based on weight was from urban consumers. This was because of the higher population and thus higher demand. Majority (48%) of peri-urban consumers bought charcoal based on the tree species used. Perhaps this could be because they usually can identify the species from which the charcoal was made from. The level of acceptability for Commiphora charcoal was average with the highest level of acceptability coming from low-income urban consumers followed by consumers in rural areas. It is therefore, recommended that marketing of Commiphora charcoal should be done in the low-income estates in urban areas like Nairobi and Thika. Also, promotional meetings to be carried out in rural areas to create awareness over the good attributes of Commiphora charcoal to help tap the existing demand in rural areas. The highly preferred charcoal by consumers was charcoal made from Terminalia orbicularis followed by Commiphora baluensis and mixed tree species. The least preferred was Commiphora campestris. It is therefore, recommended that Terminalia orbicularis and Commiphora baluensis can be utilised for charcoal making while Commiphora campestris and C. africana used for other purposes like fencing. However, production of charcoal from mixed tree species should be encouraged to help utilise less preferred tree species like Commiphora campestris for charcoal making. On the aspect of price, majority of consumers were willing either to buy Commiphora charcoal at a price lower or at most the same price as conventional charcoal. It is recommended that Commiphora charcoal can be sold at prices lower than those being offered for charcoal from conventional charcoal tree species at the initial stages of introduction in the market. Finally, the packaging of Commiphora charcoal can be clearly labelled with weight of its content, tree species used and place of origin to help reduce confusion with consumers. Lastly, the economic analysis was carried out to determine the most optimum kilning method using the data collected during the carbonisation process of the wood. This data included, type of tree species, volume of wood used, time taken for each operation and number of people involved, materials, equipment and tools used, length of carbonisation, man-day rates applied and the amount of charcoal produced. To determine the efficiency of the different charcoal making methods, cost/output ratios were established. The most efficient production methodology was the one with the least cost per unit of charcoal produced. The recommendation for the best method took into consideration additional factors like, labour availability, skills required, and the environmental and social factors. The cheapest method for producing charcoal was the casamance kiln (Ksh. 79.23/ bag) followed by the improved earth kiln (Ksh. 101.44/ bag). The most expensive method was the subri trench almost five times (Ksh. 388.04/ bag) more than the casamance kiln. The high cost observed when using the subri trench arose from the use of iron sheets that accounted for over 80% of the total cost. The highest costs in the kilning methods were the labour costs. Such labour costs vary with seasons whereby they are at the peak during the cropping seasons and lowest during the off-seasons (when no activities are done on the farms). To reduce the production costs perhaps charcoal could be produced during the periods when there are few or no on-farm activities to get cheap labour. The inclusion of the marketing costs had a bigger impact on the overall costs for charcoal. The major marketing cost component was the transport cost. This raised the cost to Ksh 145.64/bag and Ksh 177.31/bag for those produced from the casamance kiln and improved earth kiln respectively. It is recommended that marketing of Commiphora charcoal can be done at the points of production i.e. the buyers/charcoal dealers should be encouraged to collect the charcoal from the production points.