3.1. Key factors in harvesting and transport
3.2. Laying out a charcoal production area
3.3. Equipment for harvesting and transport
Getting the fuelwood from the tree in the forest to the side of the carbonisation kiln or pit is the most costly operation in commercial charcoal production and requires good organization to keep costs under control. The operation is similar to pulpwood harvesting but, typically, is much less capital intensive. A four to sixfold weight reduction occurs when wood is carbonised. Therefore the guiding rule in wood harvesting is to keep the transport distance from stump to carbonisation point as short as possible, allowing the finished charcoal to be transported the greater distance. How short the distance can be depends on the carbonisation technology. There is a trade-off between the fuelwood transport distance and the cost/yield of the carbonisation process. At one end of the scale there are the pit and the portable metal kiln technologies which need a minimum harvest transport distance. At the other end of the scale are the technologically complex, capital intensive, large rinsing gas retorts and the multiple hearth furnace systems which are fixed installations. They imply relatively long transport distances for fuelwood. Brick kilns having a life of several years imply an intermediate distance for fuelwood transport. The fuelwood transport distance associated with brick kilns and high technology retorts and furnaces depends on the fuelwood yield of the forest and the expected life of the equipment for carbonisation. Retorts which may last thirty years or more require a large block of forest so that they can be supplied with wood at the minimum haul distance during their useful life, Brick kilns having a life of about five years, require sufficient forest to maintain fuelwood supply for this period before increased transport costs require the kilns to be moved to a new area.
Harvesting and transport can be analysed by breaking the process down into 'unit operations' and treating the 'unit operations' as cost centres to determine their influence on total costs. The 'unit operations' in harvesting are:
- Roading the forest compartment and defining the coupes or harvesting units of the compartment.- Felling and bucking to required lengths; splitting may be required.
- Primary transport to secondary collection point.
- Drying of fuelwood in the forest.
- Secondary transport to the carbonisation unit.
- Drying and storage of wood at the charcoal-making centre.
The above processes can be further subdivided or some operations may be combined and others omitted in particular cases.
In the above unit operations the only two which are significantly influenced by the distance between the charcoal production centre and the logging site are the primary and secondary transport of fuelwood. In the case of fully portable systems, i.e. pits, earth mounds and metal kilns, secondary transport is eliminated and primary transport remains more or less constant. For brick kilns it is different. Primary transport can be held constant, if desired, by laying out the forest area with a closely spaced access road network which reduces primary transport to a practical minimum. Flat areas, easy to road, suit this approach. Rough terrain may make it worthwhile to increase the primary transport leg somewhat to reduce roading costs. Experience and accurate costing will indicate the best compromise. Changes in one unit operation usually influence another. In charcoal-making it is not that transport of fuelwood is simply a cost but that some costs are worth incurring in fuelwood transport in order to reap the overall benefits of producing charcoal in organised centres at some distance from the point of wood harvesting.
When fixed brick kilns are used - unlike mobile systems - it is necessary to allocate in advance a certain area of forest to sustain the operation over its economic life. Alternatively, an area of forest may be available and it is necessary to calculate how it can best be turned into charcoal using a fixed kiln system, (3, 32, 33). The calculations indicate the basic parameters. Experience will permit judgement as to how changes can be made to accommodate the local situation and still allow profitable operation. (See Fig. 1).
Fig. 1. Fuelwood Harvesting System Layout (One 900 ha unit)
The following data is needed:
- A map of the forest available.- Data on the forest types and locations within the area and, for each type, an estimated or measured volume of fuelwood per hectare. The data should be checked from the air and on the ground to show that it is fairly reliable. Often information on fuelwood yields from the forest owner - government or private - is very optimistic and may ignore the slow, imperceptible removal of forest resources by the local people over the years.
- Data on the brick kilns to be used: useful life in years; true capacity in cubic metres of wood; typical charcoal yield per burn; number of days for a complete kiln cycle from loading to unloading.
- Number of kilns which can be operated by a team (usually two or three men).
- Number of weeks per year during which charcoal can be produced, allowing for holidays, rainy season, harvest time, and so on. The number of kilns at a production centre should always be the optimum number to efficiently occupy the operating crew, or a whole number multiple of the optimum number, i.e. 10, 20, 30, and so on.
Assume the following data as an example of calculation
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Kiln module = 10 kilns |
2 man crew |
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Kiln cycle = 9 days |
6 day working week except for kiln supervision on seventh day |
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Kiln capacity = 16 m³ producing 4 tons of charcoal per burn |
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Kiln life = 5 years |
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Working year = 40 weeks |
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Forest area available = Total area 580 ha (type 1 - 310 ha; type 2 - 270 ha) |
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Fuelwood yield per ha = Type 1 - 40 m³/ha (type 2 - 31 m³/ha) |
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Calculation:
Number of working days/yr. = 40 x 6 = 240 days
kiln cycle effectively is 10 days, including rest day
Production from 10 kiln: 24 cycles from first kiln, plus 23 cycles from other nine, since they are not reloaded at the end of the year.
Total production = 4 x 24 + 4 x 23 x 9 = 924 tons of charcoal per year
Fuelwood needed = 16 x 24 + 16 x 23 x 9 = 3 696 m³ per year
For 5 year kiln life needs 18 480 m³
Forest area available is
310 ha of type 1 at 40 m³/ha and
270 ha of type 2 at 31 m³/ha
Type 1 forest can produce 310 x 40 = 12 400 m³
Therefore, type 2 must produce: 18 400-12 400 = 6 080 m³
But type 2 can produce 8 370 m³, giving an excess of 2 290 m³ which is sufficient for 27 weeks extra operation in the sixth year.
Therefore one module or battery of kilns with some repairs will convert this block of forest to charcoal in five years and 27 weeks of operation.
The siting of the battery must now be decided and an estimate made of the average haulage distance.
The site for a kiln battery may often be determined by local site factors, such as drainage, water supply, location of access roads, settlements, etc. If these factors permit, the battery should be placed in the "centre of mass" of the forest area. Theoretically, this can be calculated from inventory data but, in practice, because the data on wood distribution by forest type is of low accuracy, refined calculations are hardly worthwhile. The best that can be done is to consider possible sites for the battery on the basis of their practical acceptability and then choose the one which is closest to the apparent "centre of mass" of the timber of the area. This location is always towards or within the most densely forested area.
When the location for the battery has been decided the average secondary transport distance can be estimated using the existing road system or after a roading system has been determined. This minimizes the ton/kilometre figure for secondary transport. The road system to link up with primary fuelwood transport usually consists of simple parallel tracks separated by a distance chosen to obtain the optimum balance between roading cost and cost of primary transport from the stump to the logging track. A separation of 500 metres to give an average primary transport distance of 100 to 150 metres is normal practice.
A diagram of the road layout usually favoured on flat or undulating terrain is shown in figure 1.
In the example the forest area was 580 ha and was adequately stocked. Providing it is reasonably square the average haulage distance will be roughly 1.8 to 2 km for the whole of the operating period. This is well within normal practice with brick kilns.
If the estimated average haulage distance because of the shape of the block, e.g. long and narrow, is excessive, then it may be necessary to consider moving the kiln battery after a few years to a new site to reduce haulage distance. In this case haulage cost savings are traded off against the cost of dismantling and rebuilding the kilns. There are many options. Profitable operations require close attention to all costs and close study of the experience of successful operators.
3.3.1. Felling and block preparation
3.3.2. Drying of fuelwood
3.3.3. The role of Government in maintaining forest productivity.
3.3.4. Description of a fuelwood harvesting operation.
Harvesting and transport of fuelwood is usually labour-intensive since low cost labour is available in most charcoal making operations. Animal power has yielded to mechanical in long distance secondary transport but otherwise it still plays an important role.
Axes and handsaws are still used to some extent but chainsaws have almost replaced them. Productivity is so much higher and yet their capital cost is tolerable in commercial operations. Axes are still useful where pits or brick kilns are used, as longer length fuelwood can be used. However, with steel kilns which require short blocks for easy loading, use of chainsaws nowadays is almost essential. Short wood dries out quicker and in humid rain forests this is a great advantage. Chain-saws make this possible. With chainsaws, the operator needs to be involved, at least to a certain extent, in the ownership of the saw, otherwise maintenance costs can become prohibitive.
Splitting of large diameter blocks where needed for steel kilns is best done with wedges and hammers assisted with large diameter blocks by chainsawing along the grain to provide an opening for the wedge. Hydraulic splitting machines have been used to reduce large diameter blocks so that they can be carbonised, in metal kilns. Results have been good but capital and maintenance costs in commercial operations have not yet been proven to be acceptable. Chainsaws compared to axes usually give a marked increase in the yield of wood per ha, because a chainsaw cut wastes less wood in useless chips than an axe and large diameter deformed logs, etc., are easily reduced to blocks with a power chainsaw. Axemen tend to bypass these difficult logs. This results in a lower yield. In some situations it is possible to combine axes and chainsaws quite successfully on the same area.
Blocks are either cut at the stump or from the log at the side of the road. The best method depends on the type of forest and terrain. Flat savannah type forests with large heavily branched irregular growth trees are best cut into blocks at the stump. Plantation eucalyptus stems or long straight trees growing in dense undergrowth favour cutting into blocks at the roadside. It is not common to transport whole logs to the charcoal production centre since this needs heavy equipment to load and transport and there are no advantages over block cutting in the forest, except where automated block cutting and splitting from large trees may be used, e.g. where rinsing gas retorts are installed. Drying out of blocks and measurement of volume may be simplified at roadside. Air circulation and hence drying rates are usually better at the roadside than in the forest itself. Carts drawn by mules, donkeys or oxen may be used to bring blocks or short-length wood to the roadside. Farm tractors are suitable for snigging logs to roadside. Wheel tractors with trailers can be used to collect blockwood at the stump where the terrain is suitable. Whatever system is used, the objective remains the same - delivery of dry blocks ready for carbonising at the side of the kiln at minimum cost. Only careful studies can determine the best method in each instance.
Measurement of the wood is done at stump or at roadside. The usual system is to pile the wood in a frame which contains one stere (a stacked cubic metre). After measuring, stacks of wood are usually paint marked and transported to the charcoal centre. Allowance must be made for loss of volume when wood blocks dry.
Drying fuelwood has a big influence on charcoal yield. The drier the wood the less fuel is used up inside the carbonising equipment, be it pit, kiln or whatever, in evaporating moisture. The free water in the wood is lost to the air fairly rapidly once the wood is cut into short blocks. Moisture content at felling may be say, 60%. After stacking three months moisture content may be reduced to 30-35%. Further drying is slow. Large diameter blocks of dense hardwood may take more than a year to reach 20%.
During drying there is a loss of weight which makes transport easier and cheaper. One ton of wood at 60% moisture content after drying to 30% moisture content will weigh only 812 kg, a loss of about 2 %. Also, while drying, some species may shed their bark. This is an advantage as bark makes only fragile, high ash charcoal of little commercial value. During drying, wood can rot and be attacked by insects; this is rapid in the humid tropical forest. Therefore, the drying time must be controlled to ensure the maximum drying out occurs quickly before deterioration of the wood.
Good practice in tropical wet forests is to cut the blocks short, pile them carefully and, if possible, off the ground, on scrap wood and in a place which gets plenty of sun and wind. About one or two months is often the maximum drying time allowable in humid tropical forest before severe deterioration occurs. This depends on local conditions species, and season of the year. A certain stock of dry wood is always needed to balance kiln and forest operations. This wood stock, usually about two months' supply, should be built up to a maximum in the dry period at clearings in the forest and at the kilns, and allowed to run down during the wet season. Species which show little degradation should be favoured if possible and stock should be held at those locations having a proven record of fast drying conditions.
In dry type forests, safe drying times of up to one year are not unknown with durable species but one must balance the drying benefit against the capital tied up in the drying stock. Sound dry dead trees should also be harvested for charcoal wherever possible. They give a good yield of charcoal and cost less to transport per unit of charcoal production. The gain in transporting and carbonising air dry wood over green wood is striking. There is a twofold gain. First, one avoids transport of useless water, second, the yield of charcoal from dry wood is high since less of the wood has to be burned up inside the kiln to dry out the remainder so that it will carbonise. For example, 1 000 kg of green wood, after a few weeks drying, may have a moisture content of 50%. It can be expected to yield about 180 kg of charcoal of 80% fixed carbon content. On the other hand, using dry wood of 15% moisture content only, 520 kg must be transported to yield the same amount of charcoal (180 kg). There is a saving of wood substance as well as a saving in useless transport. Green wood dries slowly, especially when it is merely cross-cut into blocks and not split as well. Wood moisture content is one of the most serious limiting factors in the economics of charcoal-making.
An experiment on drying cross-cut blocks of old growth Australian eucalyptus wood for charcoal gave the following results:
Length of blocks: 25 cms.
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Drying time in stack |
1 week |
6 months |
12 months |
18 months |
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Moisture content % |
54.4% |
31.6% |
21.6% |
15.9% |
These results indicate the value of some months of drying. While drying in a humid environment, however, the wood also deteriorates due to fungus and insect attack. The problem of drying fuelwood economically in the humid tropical forests which are today being called upon more and more to provide charcoal remains largely unsolved. It represents a serious waste of wood resource and a significant cost in fuelwood supply.
Problems of drying also affect fuelwood produced in plantations. Fortunately most eucalyptus plantation areas are not as humid as the tropical high forest.
The foundation of the charcoal industry is the fuelwood production from a nation's forests. Most forests are nominally under some kind of government control in practically all countries nowadays. Governments can play a critical part in ensuring the present and future productivity of their forests by the management policies they apply to them. They should actively concern themselves with the fuelwood logging process to see that regeneration of the forest takes place properly. They should safeguard the forests against fires and illegal wood cutting. They should assist the development of plantations for fuelwood and should provide credits for extraction machinery and for road building to ensure that the maximum permissible yield of fuelwood is obtained from the forest without damaging its powers to regenerate. Fuelwood gathering for charcoal is not usually regarded as a high prestige occupation. But nowadays it is one of the most significant activities carried on in the forests of the developing world and no government can afford, in the long run, to ignore it or treat it with contempt.
To aid understanding of the practical details of a fuelwood harvesting system a brief description is given of a system to harvest sufficient wood to produce 10,000 tons/year of charcoal from humid tropical forest. (32).
Basic Data
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Wood requirement |
40 000 tons per year over 5 years |
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Nominal labour cost for calculations |
US$ 10.00 per man/day. |
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Area available: |
3 600 ha divided into four 900 ha blocks each containing a charcoal centre or battern of 14 half orange kilns. |
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Terrain: |
flat to undulating; uniform stacking of mixed species fuelwood. |
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Roading: |
Logging track only without consolidation; 3 m wide cleared by hand with axe and cutlass. |
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Roading rate: |
30 m of road per man/day at US$ 10.00 per day = $24 000. |
Operations for 4 charcoal batteries
- a) Felling with chainsaws: trees are felled; no bucking is done at stump.Chainsaws needed: 4
Labour needed: 8- b) Hauling logs with farm tractor to roadsides
Average distance of haul: - 375 m
Average yield per tractors - 2.5 t/trip or 60 t/dayTractors needed: 2
Labour needed: 4- c) Bucking with chainsaw at roadside:
No. of chainsaws needed: 8
Labour needed: 12- d) Transport of firewood from c) to battery, with farm tractor and trailers:
Average transport distance: 1,500 m
Equipment: 1 tractor and 2 trailers of 10 ton capacity each.
Production per day per unit: 40-50 tons/day depending on haul distance
For 40,000 ton/year firewood following are needed: 3 tractors and 6 trailers (3 units)
Labour: 3 drivers and 9 loaders = 12
Costing for 40 000 tons of wood per year:
Labour rate including overheads: US$ 10.00 per man/day.
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Operation |
No. of Men |
Annual Cost Labour |
Machines |
Total |
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a |
8 |
24 000 |
4 000 |
28 000 |
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b |
4 |
12 000 |
30 000 |
42 000 |
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c |
12 |
36 000 |
7 000 |
43 000 |
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d |
12 |
36 000 |
46 000 |
82 000 |
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Total: |
36 |
108 000 |
87 000 |
195 000 |
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Roading cost = $24 000 for 5 years = $4 800 per year... |
4 800 | |||
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199 800 | |||
Basic cost per ton of wood delivered to side of kiln = $4.99Supervision and management costs have not been calculated but could be allowed at 10% of wood cost per ton = $0.49
Total cost per ton of wood at kiln = $5.50
No allowance has been made for any infrastructural costs or stumpage.
The above costing should be regarded as indicative of the relative cost and labour productivity of the various operations in harvesting.
