1.1. Developing a fuelwood and charcoal energy policy
1.2. The energy balance concept
1.3. Calculating an energy balance
1.4. Unit processes of charcoal production
The first step a country must take in seeking to guarantee an adequate supply of fuelwood and charcoal for its citizens is the development of a national fuelwood and charcoal energy policy. Such a policy must be national in scope since the allocation of resources needed to satisfy fuelwood requirements calls for action on the national level. (4)
A national fuelwood policy must also be interlocked with a national energy policy covering the whole field of energy use, singe fuelwood supply cannot be expanded without corresponding inputs of liquid fuels' electricity etc. Nevertheless it is possible as a first step to begin with fuelwood and charcoal and other fuels used for domestic purposes in significant quantities.
The typical energy budget of a developing country relies heavily on fuelwood and charcoal for domestic cooking and heating.
In drawing up a fuelwood energy policy the three major aspects to be considered are:
- The present size and characteristics of the wood resource and its future development.- The present consumption pattern of fuelwood and charcoal and probable future development.
- How the present supply is produced and distributed and what the possibilities are for its rationalisation and improvement.
The world consumption of fuelwood per caput, including charcoal, was estimated in 1978 at 0.37 m³. However, in the developed world the per caput usage was only 0.13 m³, compared to 0.46 m³ in the developing world. Developed countries have a high per caput usage of energy as a whole, of which wood is a minor component; developing countries have a low per caput energy input, most of which consists of wood and charcoal.
Table 1 taken from the UN Conference on New and Renewable Sources of Energy (Third Session 1981) shows the relative importance of fuelwood in various regions of the world. (30)
As a starting point it is useful to prepare a series of projections of the present and future consumption pattern which can be derived fairly easily from available population data and typical per caput requirements. From this one can estimate quite quickly the rate at which wood must be being harvested and the area of forest worked over and probably destroyed each year. From a knowledge of the distribution of the forest areas contributing to production and the main areas of consumption one can fairly easily make a sketch of the main distribution network and probable quantities which must be flowing into the various markets. At this stage various "grey areas" in the image will begin to appear and surveys can be planned to provide the necessary data to clarify the picture.
Table 1. Fuelwood in World Energy Consumption in 1978
|
|
Population |
Total fuelwood a/ |
Consumption per capita |
Energy equivalent of fuelwood b/ |
Commercial energy c/ |
Fuelwood (percentage of total) d/ |
|
|
(millions) |
(millions of m³) |
(m³) |
(millions of gigajoules) |
% |
|||
|
World |
4 258 |
1 566 |
0.37 |
14 720 |
256 594 |
5.4 |
|
|
Developed world |
1 147 |
145 |
0.13 |
1 363 |
205 115 |
0.7 |
|
|
|
- Market economies |
775 |
54 |
0.07 |
508 |
145 148 |
0.3 |
|
|
- Centrally planned economies |
372 |
91 |
0.24 |
855 |
59 967 |
1.4 |
|
Developing world |
3 111 |
1 421 |
0.46 |
13 357 |
51 479 |
20.6 |
|
|
|
- Africa |
415 |
353 |
0.85 |
3 318 |
2 415 |
57.9 |
|
|
of which least developed countries |
138 |
163 |
1.18 |
1 532 |
255 |
85.7 |
|
|
- Asia |
2 347 |
796 |
0.34 |
7 478 |
37 558 |
16.6 |
|
|
of which |
|
|
|
|
|
|
|
|
least developed countries |
130 |
34 |
0.26 |
319 |
180 |
63.9 |
|
|
Centrally planned economies |
1 010 |
220 |
0.22 |
2 068 |
24 048 |
7.9 |
|
|
- Latin America |
349 |
272 |
0.78 |
2 557 |
11 306 |
18.4 |
a/ Includes wood for charcoal
b/ IM³ = 9.4 gigajoules
c/ IMT coal = 29.3 gigajoules
d/ Not including other sources of non-commercial energy important in some regions
In this preliminary stage of planning it is useful to remember that the per caput fuelwood requirement in the various developing countries is more uniform than one would expect. Most of the developing countries are situated in the tropics and hence are subject to fairly uniform temperature regimes. The exceptions are high mountains and plateaux but, an a country level, these differences are not usually serious and the same figures for the whole population can be used as a first estimate.
The basic per caput consumption can be taken as 1200 kg of 30 percent moisture content fuelwood per annum. This figure applies to traditionally low efficiency stoves and cooking fires. High efficiency stoves can reduce this figure to 450 kg. Charcoal consumption ranges from about 60 kg to about 120 kg per caput per year and for preliminary planning purposes a figure of 100 kg can be used, convertible as follows: the production of 100 kg of charcoal requires about 700 kg dry wood taking into account transport losses. The heat content of charcoal fines of 100 kg of charcoal is equivalent to that of about 300 kg of air dry wood. From these figures it is clear that it pays to encourage the use of high efficiency stoves burning dry wood but that it is better to burn charcoal rather than wood in traditional, low efficiency stoves and open fires. Open fires and poorly designed stoves may have a thermal efficiency as low as three to five percent. A typical charcoal "pot" has a thermal efficiency of 23-28 percent. (See chapter II). There are also savings on transport costs with charcoal.
Whatever strategy is chosen will affect the projected production and consumption plan worked out for the years ahead and exert a major influence on forest management policy.
The following conversion factors will be useful in preparing energy balances:
Table 2
|
Typical per capita fuelwood consumption range for domestic purposes in developing countries. (Actual figures depend on local climate, supply, traditions, etc.) |
0.5 m³ to 2.0 m³ | |
|
Amount of fuelwood used in producing one ton (1 000 kg) of charcoal |
7 to 11 m³ (solid) | |
|
Yield of fuelwood obtainable by clearing | ||
|
|
(a) Tropical high forest |
80-100 m³/ha |
|
|
(b) Savannah forest |
20-45 m³/ha |
|
|
(c) Eucalyptus plantation forest (12-15 years old) of good quality. (Yield of plantations depends entirely on growth rate achieved. Actual inventory is needed to make firm yield predictions) |
80-200 m³/ha |
|
Annual yield of well-managed eucalyptus plantations on good sites (12-20 year rotation) (Mean Annual Increment: MAI) |
14-20 m³/ha | |
|
1 ton (1 000 kg) of charcoal when burned has an energy output equivalent to: | ||
|
|
(a) Fuel oil |
0.55 tons |
|
|
(b) Electric power, if used to produce heat |
7 260 kWH |
|
|
(c) Bituminous (hard) coal |
0.83 tons |
|
|
(d) Dry wood (15 percent moisture content) |
1.65 tons |
|
|
(e) Green wood (say 60 percent moisture content) |
2.5 tons |
The next step in developing a fuelwood strategy is to estimate total fuelwood and charcoal consumption for the base year and then construct a tabulation which will show the annual requirement keeping in step with the projected increase in population for a period of about twenty years. This is usually long enough to stabilise the production/consumption situation.
By inserting into the table the harvested yields of fuelwood per hectare typical of the various production zones, the amount of forest to be worked over each year in the future may be quantified.
Various prospects will now begin to emerge. In the case of countries with small population density and large remaining areas of forest, it will usually be found that their prospects appear good. The forest area needed will be adequate and it should even be possible to dedicate forest production zones of sufficient size to yield on a continuing basis the required quantity of charcoal even though these natural forests may have a rather low mean annual increment (MAI) under any feasible management system. However, an implicit assumption must be made that population growth can be stabilised; otherwise no forest resource, however, large, can meet future demand.
In the case of countries with greater population density and less endowed with forests, the available forest area will usually be found to be inadequate to supply future fuelwood and charcoal needs, unless radical steps are taken to bring the situation under control.
Formulating plans to overcome these serious problems requires specialist knowledge and experience. All relevant factors, both technical and social, must be taken into account.
The principal options open to the developing country facing this situation are:
- Better management, or introduction of management where none now exists, of the forested areas may be sufficient to raise yields to a point where natural regrowth will solve the problem.- High yield forest plantations, frequently of eucalyptus species, may be established permitting sufficient wood to be generated quickly enough to catch up with demand and overcome the problem. However, specialist help and good planning are needed. Plantation sites must be carefully chosen taking into account soil fertility, rainfall, location in relation to consumption centres, and the practicality of permanently dedicating the land for forest purposes.
Usually there is a conflict with the need to use the land to grow food for an expanding population and, under these conditions, the social factors governing the survival and growth of forest plantations in the midst of subsistence agricultural zones become of dominant importance.
High yielding plantations can easily show an MAI per hectare over ten to twelve year rotations of twenty or more cubic metres of wood. This compares with effective MAI's of natural unmanaged forest of around two or three cubic metres. However, it must be stressed that high yields of plantations are not achieved without investment in good land, good management and maybe also fertilizers. (11)
The rate of consumption of wood can also be slowed down by improved methods of charcoal production and distribution and by increasing the efficiency of wood-burning stoves. Sometimes traditional fuel-gathering methods due to inadequate tools result in large quantities of large diameter logs and branchwood being unharvested and left to rot.
A hypothetical fuelwood energy balance for a region is calculated below showing the method used and indicating key factors where collection of more accurate data may be necessary to develop a more precise picture.
Fuelwood Energy Balance
|
Region |
'X' |
|
Total area |
5 600 km² |
|
Arable land |
620 km² |
|
Undulating forested land |
3 400 km² |
|
Steep mountain, lakes, rivers and urban areas |
(2 - (3 + 4)) = 1 580 km² |
|
Population |
80 600 of which 9 000 estimated to be urban |
|
Estimated rate of population growth |
2.1% per annum |
|
Preliminary estimated annual per caput fuelwood use (taken from table 2) |
0.8 m³/pc./yr. (solid) |
|
Estimated charcoal sales in townships of zone |
110 000 kg |
|
Volume of fuelwood exported from region (estimated) |
nil |
|
Weight of charcoal exported from region (calculated from transport tax documents) |
35 000 kg |
|
Volume of fuelwood imported into zone |
nil |
|
Volume of charcoal imported into zone (calculated from transport tax documents |
7 400 kg |
From the above data a preliminary woodfuel energy balance for the region can be drawn up. This is based on production and imports being considered as input, and consumption and exports being considered as output. Thus, the annual fuelwood balance is as follows:
Inputs
1) Wood used to produce charcoal
|
Total charcoal production |
+ 110 000 kg sales |
|
- 7 400 kg imports |
|
|
+ 35 000 kg exports |
|
|
Net charcoal production |
137 000 kg |
Assuming that fuelwood to charcoal conversion efficiency is 5 to 1 by weight on an oven dry wood basis.If density of green fuelwood is 750 kg/m³ (solid) and moisture content is 40%, then each m³ of green wood contains 750 x 100/140 = 535 kg of oven dry wood equivalent to 535/5 = 107 kg charcoal.
To produce 137 000 kg of charcoal needs: 1 286 m³ of fuelwood or 964 485 kg of wet fuelwood. This is equivalent to a conversion ratio on a wet wood basis of about 7 to 1.
2) Amount of wood harvested or used directly as fuel and to make charcoal is:
|
a) used to make charcoal |
1 280 m³ |
|
b) used as fuelwood by rural dwellers |
80 600 x 1.2 = 96 720 m³ assuming per caput fuel wood use of 1.2 m³ and a rural population of 80 600. |
|
Total: |
98 000 m³ of green wood per year |
The estimate of present annual fuelwood usage in the region enables us to estimate the forest areas used each year for fuelwood and predict, in conjunction with estimates of population growth, the amount of forest of various types needed to satisfy a growing population's fuel needs. Using the above calculations the result is not likely to be precise. Where these calculations show that the region could be facing fuelwood deficits, it is then necessary to try to improve the accuracy of the figure to arrive at a more precise estimate of the adequacy or otherwise of the forest resources and take the necessary action to improve the supply situation.
When a figure for annual fuelwood consumption has been estimated, it is possible to calculate the effect of a fuelwood harvest of this dimension on the forest resources of the region. One must also take into account population growth rate. It is also reasonable to base production on a forward period of about twenty years since plantation resources take about this time to reach maximum yield and the effects of some form of management of neglected natural forests may well require ten to twenty years to show results. If the population remained static we could calculate as follows:
Hectares of prime high forest used up for woodfuel at a yield of 80 m³ per ha (98 000/80) = 1 225 ha per year. If the area of prime forest available for fuelwood is known, then the number of years over which supply can be maintained can be calculated. Likewise, if savannah or plantations are to be used, then the area needed each year can be similarly calculated.
As a rule, fuelwood and charcoal are produced from out-over and degraded forests and it is instructive to calculate what area must be put under management to maintain indefinitely such a system. Normally unmanaged but supervised cut-over high forest can maintain a mean annual increment of 2-4 m³ per ha per annum, if the rotation age of the forest is set at forty years, then a yield of 80 m³ of wood for charcoal per hectare can be expected. Population growth means an increase in the area to be harvested each year and the total area to be set aside to obtain a rotation of, say, forty years must take this into account. Using the figures for an initial wood requirement of 1 225 ha/yr, and an assumed population growth rate of 2.1%, then an area of 75 617 hectares of prime forest must be reserved for a forty year rotation. A larger area must be harvested each year to supply the increasing population.
The forest area above was conveniently calculated using the "amortization fund" equation of compound interest. This formula is as follows:
where
FV = final value (in area of forest)
PMT = area to be harvested in first year
i = rate of growth of population as %/100
n = number of years considered.
The area needed will, however, continue to rise if population growth continues and problems of forest availability must eventually arise. In cases where large areas of unexploited forest are not available, the problem becomes more complex singe out-over forest must be harvested at a lower and varying yield. The level of out should allow regeneration within, say, forty years to a normal forest yielding a out for fuelwood and charcoal of 80 m³ per ha. Setting up such management involves difficult relationship problems of a community to its forests and galls for specialist help which cannot be covered here. The object of the present study is to point out the implications of maintaining a continuing supply of fuelwood and charcoal and how to go about estimating the magnitude of the forest resource required. Higher forest productivity per area and improved efficiency in fuelwood use and charcoal production slow down the arrival of the resource crisis.
1.4.1. What is charcoal?
1.4.2. Unit processes of charcoal-making
Charcoal ready for use by the consumer implies a certain sequence of steps in a production chain, all of which are important and all of which must be carried out in the correct order. They have varying incidence on production cost. Noting these differences enables the importance of each step or unit process to be assessed so that attention may be concentrated on the most costly links of the production chain.
Charcoal is the solid residue remaining when wood is "carbonised" or "pyrolysed" under controlled conditions in a closed space such as a charcoal kiln. Control is exercised over the entry of air during the pyrolysis or carbonisation process so that the wood does not merely burn away to ashes, as in a conventional fire, but decomposes chemically to form charcoal.
Air is not really required in the pyrolysis process. In fact, advanced technological methods of charcoal production do not allow any air to be admitted, resulting in a higher yield, since no extra wood is burned with the air and control of quality is facilitated.
The pyrolysis process, once started, continues by itself and gives off considerable heat. However, this pyrolysis or thermal decomposition of the cellulose and lignin of which the wood is composed does not start until the wood is raised to a temperature of about 300° Celsius.
In the traditional charcoal kiln or pit some of the wood loaded into the kiln is burned to dry the wood and raise the temperature of the whole of the wood charge, so that pyrolysis starts and continues to completion by itself. The wood burned in this way is lost. By contrast, the success of sophisticated continuous retorts in producing high yields of quality charcoal is due to the ingenious way in which they make use of the heat of pyrolysis, normally wasted, to raise the temperature of the incoming wood so that pyrolysis is accomplished without burning additional wood, although some heat impact is needed to make up for heat losses through the walls and other parts of the equipment. The combustible wood gas given off by the carbonising wood can be burned to provide this heat and to dry the wood. All carbonising systems give higher efficiency when fed with dry wood, since removal of water from wood needs large inputs of heat energy.
The pyrolysis process produces charcoal which consists mainly of carbon, together with a small amount of tarry residues, the ash contained in the original wood, combustible gases, tars, a number of chemicals mainly acetic acid and methanol - and a large amount of water which is given off as vapour from the drying and pyrolytic decomposition of the wood.
When pyrolysis is completed the charcoal, having arrived at a temperature of about 500° Celsius, is allowed to cool down without access of air; it is then safe to unload and it is ready for use.
The overwhelming bulk of the world's charcoal is still produced by the simple process briefly described above. It wastefully burns part of the wood charge to produce initial heat and does not recover any of the by-products or the heat given off by the pyrolysis process.
Other woody materials such as nut shells and bark are sometimes used to produce charcoal. Wood is, however, the preferred and most widely available material for charcoal production. Many agricultural residues can also produce charcoal by pyrolysis but such charcoal is produced as a fine powder which usually must be briquetted at extra cost for most charcoal uses. In any case, encouraging the wider use of crop residues for charcoal-making or even as fuel is generally an unwise agricultural practice, although the burning of sugar cane bagasse to provide heat in sugar production and the burning of cornstalks and coarse grasses as domestic fuel in some regions do provide an overall benefit where carried out as part of a rational agricultural policy.
On the grounds of availability, properties of the finished charcoal, and sound ecological principles, wood remains the preferred and most widely used raw material and there appears to be no reason why this should change in the future.
Charcoal-making can be divided into several stages or unit operation. They are:
Growing the fuelwood
Wood harvesting
Drying and preparation of wood for carbonisation
Carbonising the wood to charcoal
Screening, storage and transport to warehouse or distribution point.
Production costs can also be conveniently analysed by using the following "cost centres" which show more clearly the merits of the various systems:
- The cost of fuelwood placed at the side of the kiln, pit or retort, including financial costs.
- Carbonisation labour costs, including loading and unloading.
- Cost of transport of charcoal to major markets or distribution points.
- Cost of working capital.
- Fixed investment costs of the pits, kilns or retorts.
All costs are expressed on the same unit basis, i.e. per ton of charcoal delivered, so that their relative importance is clear. An extract of studies made by FAO gives the following broad picture. (3)
Where traditional clay brick kilns and a savannah forest yielding about 40 m³ of wood per ha are used, the following unit costs apply (expressed as a percentage of the cost of delivered charcoal):
|
Cost of wood at kiln |
60% |
|
Kiln labour costs |
9% |
|
Working capital costs |
3.5% |
|
Fixed investment costs |
1.5% |
|
Transport costs of charcoal |
26% |
|
|
100% |
The importance of wood harvesting and charcoal transport costs is evident. Together they amount to 86% of costs.
Charcoal-making needs other auxiliary raw materials and inputs which must not be forgotten. Kilns require clay for sealing and making slurry for cooling and bricks which should wherever possible be made near the charcoal-making site. Earth pits and clamps require earth of suitable texture and significant amounts of straw and leaves and branches. Metal kilns require sand and gas welding and cutting supplies and sheet steel for repairs. All charcoal processes need a certain amount of water for cooling fire extinction and making clay slurry. Above all, the whole process requires nowadays a certain input of liquid fuels for wood growing and harvesting, transport of wood and charcoal and miscellaneous transport of personnel and servicing of equipment, etc. All the above are basic to a successful charcoal operation. Further factors which cannot be overlooked are food supplies, housing and other infrastructure for workers and provision of fodder where draught animals are used for transport. If the charcoal is not handled in bulk, then costs of packaging must be added.
The technical aspects of the unit operations of charcoal-making are covered in later chapters. Some information on cost control and economies related to charcoal-making is also included.
