A renewable source of fuel

Derek Earl

Derek Earl is a British forester with extensive experience in management, who has made a special study of the economics of the forest as a source of energy. Information in this article is from his book Forest energy and economic development (Oxford, Clarendon Press, 1975).

To obtain fuel from forests does not mean that forests have to be "mined" to extinction. Forests can be managed for the production of firewood and charcoal on a permanent, renewable basis. The author examines the use of fuel wood and charcoal in the world and recommends it in particular for countries with underutilized land and labour.

The chemical reactions which produce heat from all conventional fuels are the same; the energy is produced from the exothermic oxidation of carbon and hydrogen. The only differences are related to the varying amounts of carbon and hydrogen per unit weight of fuel or to the state of the fuel, i.e., liquid, solid or gas. The energy value of a fuel is expressed as the number of calories released when one gram of it is burnt completely. (One large calorie is the quantity of heat required to raise the temperature of one kilogram of water one degree centigrade, and one small calorie is the amount required to raise the temperature of one gram of water one degree centigrade.) For large-scale fuel-planning purposes, fuel resources are sometimes expressed in coal equivalent (CE) - the energy equivalent to that contained in one ton of coal.

TUNISIANS WEIGH CHARCOAL worth growing

The most important factor influencing the value of wood as a fuel is its high initial moisture content. Dry wood is preferable to wet wood for two reasons: it has an increased calorific value, and handling and transport costs are reduced.

Wood to be used as a primary fuel or for conversion to charcoal should be allowed to dry until the moisture content falls to about 30% (dry weight basis) which takes from two to six months, depending upon the climate.

In the forest, fuelwood is measured in stacks, i.e., by volume, to facilitate checking and assessment of payment for the forest workers. As a factor input in industry, fuelwood is usually accounted for by weight. There can be considerable discrepancies between the expected and actual weight of wood in a stack because of changes in moisture content and in the expected and actual solid volume content which may be affected by the dimensions of the individual pieces of wood it contains. A stack consisting of large-diameter wood contains more solid volume than one containing small-diameter wood. The length of the individual pieces and the incidence of knots and crookedness also affect the solid volume content. The solid volume content of a stere (stacked cubic metre) ranges from 0.80 to 0.55 cubic metre; thus a stack made up of the latter will contain only 69% of the energy content of a stack of the former. The relationship between stacked and solid volume contents of various categories of fuelwood should be established and drying curves prepared before large-scale operations are undertaken.

Apart from domestic application, wood may be used to provide heat in many industries, for example: brick works, distilleries, jaggeries, potteries., sugar refineries, tile works, handmade paper works, tobacco factories and tea factories.

Wood can provide steam for mechanical energy in saw mills, locomotives and boats and may be used to generate electricity for many purposes.

The disadvantages associated with the use of fuelwood of low calorific value can be eliminated if the demand is such that it will bear the higher costs of conversion to charcoal, which has about twice the heat content of a similar weight of wood.

Charcoal techniques

Fuelwood and charcoal can result in big foreign exchange savings

Charcoal is produced by a partial chemical reduction of wood under controlled conditions. The yield of charcoal by weight is usually about 20% to 30% of the dry weight of the wood used, and the yield by volume is about 50 % The techniques range from simply covering burning wood with soil and turf to the use of very sophisticated automatic retorts and furnaces. In countries with surplus manpower and plentiful forest resources, the use of portable steel kilns to make charcoal offers a low-cost investment opportunity.

1. Traditional crude brick charcoal oven in Argentina

The two most important raw material sources for charcoal are roundwood and residues, the former being the more abundant.

Roundwood can be grown in plantations or may be a subsidiary product in other forestry or land-clearing schemes. The trunks and branches of softwoods and hardwoods and the stems of palms can all usually be converted to charcoal.

Residues often contain a high proportion of bark, and the resultant charcoal is suitable for general fuel purposes. Carbonized bark is crushed and briquetted in Japan and the United States, and finds a ready market in both countries.

2. A simple earth kiln near a logging site uses residue. Later it will be fertile ground for a tree nursery.

The physical and chemical properties of charcoal depend upon those of the original material from which it is made and on the carbonization process. Most users prefer charcoal which does not break easily, can be ignited readily and will continue to emit heat for a long time. Traders often mix different charcoals together to obtain an acceptable quality for domestic use.

3. A portable metal kiln loaded with wood from undesirable species

The economic benefits which may be derived from the managed use of forest energy resources can be divided into the following categories: direct, indirect and intangible.

1. Direct benefits. The most obvious direct benefit is that obtained from home production of a valuable fuel. Equally important is the effect which fuelwood and charcoal production may have in reducing the costs of silvicultural operations, which therefore increases the total profitability of forest resources.

2. Indirect benefits. Provision of employment is a benefit, not only because of the extra production obtained from the more efficient use of the human resource but also because of the possibility of collecting taxes for government projects which will in turn generate more employment. A large portion of the money obtained from sales of fuelwood and charcoal in the towns returns to the workers in the country. This acts as a useful distributive effect upon national income which is usually weighted unfairly in favour of the urban worker. As there is less income differential between the upper and lower echelons in forest-based enterprises than in industries which often have to rely upon highly qualified personnel, there is an improvement in the vertical distribution of money. The use of forest fuel for domestic cooking and industrial purposes often represents an unappreciated enormous saving in foreign exchange. If sufficient capital and technical skill are available, fuelwood may be converted to charcoal in qualities and quantities suitable for export. A charcoal industry will stimulate local firms to manufacture carbonization equipment, and encourage factories to expand their activities with the use of local fuel (linkage effects) Finally, charcoal is a smokeless fuel which will not add to the pollution problems of the larger cities.

3. Intangible benefits. These are difficult to quantify, but include such benefits as the encouragement of self-reliance, conservation of the wand's fossil fuel resources, reduction of waste, creation of a dynamic rural environment, improvement of facilities for recreation and beautification of the countryside.

4. Smoke stacks are fitted to a kiln developed by the Uganda Forest Dept. It converts 100 cubic metres of otherwise wasted wood to 6000 kilograms of char coal in a month.

Table 1 Comparative fuel energy values

Fuel	Calories
Paraffin	10.4
Fuel oil	9.8
Charcoal	7.1
Coal (good quality bituminous)	6.9
Wood (air dry)	3.5

SOURCE: author.

The designated forests of the world, according to FAO, cover about 3800 million hectares, out of a total land area of about 14900 million hectares. The forest resource is estimated to contain 312000 million cubic metres of saw timber and an amount at least equal to that in the form of branch-wood and unmerchantable trees. The estimated increment of this growing stock, its distribution by forest type and the amount produced and utilized in different regions are shown in Table 2.

Table 2 The world's renewable forest energy resource

Forest type	Area ha	Annual increment of wood per ha		Total increment wood
	X 106	m3	tons	m3 X 109	tons X 109	tons CE X 109
Cool coniferous	800	4.1	3.0	3.3	2.4	1.4
Temperate mixed	800	5.5	4.0	4.4	3.2	1.9
Warm temperate	200	5.5	4.0	1.1	0.8	0.5
Equatorial rain	500	8.3	6.0	4.1	3.0	1.8
Tropical moist deciduous	500	6.9	5.0	3.5	2.5	1.5
Dry	1000	1.4	1.0	1.4	1.0	0.6
Totals and means	3800	5.3	3.8	17.8	12.9	7.7

SOURCE: Oxford economic atlas and the author.

Lost energy

Natural forests are in dynamic equilibrium, with incremental energy gains balancing losses. Forest management aims at converting potential into effective utilizable increment by organizing cutting and regeneration to take place in accordance with ecological principles.

Table 3 Utilization of the world's incremental forest energy resource

	Growing stock	Increment	User for industrial purposes	Used for fuel	Total consumption	Unused increment	Unused increment
m3 X 109							in tons CE X109
Developed countries	242	8.8	1.1	0.3	1.4	7.4	3.2
Developing countries¹	382	9.0	0.2	0.8	1.0	8.0	3.5
Totals	624	17.8	1.3	1.1	2.4	15.4	6.7

SOURCE: FAO and the author.

¹ Defined as those with annual per caput incomes of less than US$500.

At present, approximately only 13% of the world's estimated forest increment of 7600 million tons of CE is harvested - 7% for industrial purposes and 6 percent for fuel (see Table 3). The balance of 6700 million tons of CE (87%) is dispersed and lost to space as heat through biological degradation and fire (Table 4).

Table 4 Comparative fuel prices:

Relative price indexes of fuels compared on the same calorific value basis in five different areas, with fuelwood taken as the standard¹

Fuel	E. Africa (1970)	India (1973)	Nepal (1973)		U.K. (1973)
			Katmandu	Terai towns
Fuelwood	1.0	1.0	1.0	1.0	1.0
Charcoal	1.6	1.1	0.8	0.7	3.5
Coal	-	0.7	0.8	0.9	0.5
Fuel oil	2.0	-		-	0.7
Paraffin	4.0	1.5	1.6	1.6	0.7-1.0
Electricity	8.9	9.3	28.5	9.3	4.1
Butane	19.8	-	-	-	15.4

SOURCE: author.

¹ It should be noted that the prices of a particular fuel are not comparable between areas.

² Domestic.

The impediments to fuller utilization of this fuel source are technical, economic and, to some extent, institutional. The technical problems are mostly associated with fuelwood's low thermal capacity to bulk ratio. Economic difficulties occur because of the high costs involved in gathering and transporting the raw material. Institutional handicaps are chiefly those associated with the belief that the use of fuelwood is primitive and should be discouraged.

The technical and economic problems can be solved by, for example, locating industries near forests which are managed to provide a sustained fuelwood supply, or converting fuelwood to charcoal to avoid high transport costs.

Charcoal as fuel Advantages It is almost smokeless when burnt and produces a fire-bed from which a high proportion of the energy is emitted as radiant heat. It can be ground and used with standard equipment in pulverized fuel firing. The calorific value is similar to that of high quality coal. It acts as a strong reducing agent when heated. It has many industrial uses. Disadvantages Its low bulk density necessitates special transporting and storage. It is rather fragile and is easily broken during handling or by compression. This can be a disadvantage if lump fuel is especially required. As with all fuels with a high carbon content, care has to be taken during combustion to ensure that there is free circulation of air because of the danger of carbon monoxide poisoning.

Wood as fuel Advantages In many countries it is the cheapest fuel available, not only per ton but also per unit of heat. When properly dried it burns safely and easily so that semiskilled labour can soon be taught to use it with economy. Skilled labour is needed, however, when the latest, highly efficient types of furnace are used. No special storage facilities are required apart from open space. Disadvantages It is a labour-intensive fuel, which makes it expensive in regions where wages are high. Without properly organized management the forests become quickly depleted. Its use requires organization and cooperation with forest departments and other land users. Regular supplies may be uneven in quality, but this can be minimized with good control. The calorific value is lower than that of fossil fuels. A large stacking space is required near the place of use.

Table 5 Energy consumption in developing countries in 1970

Commercial sources	Forest sources	Total
million tons CE
613	403	1016

SOURCE: UN Statistical Yearbook and FAO

Table 6 Charcoal consumption trend as seen in Uganda

Year	Home produced tons	No. men on production	Imported tons
1962/63	200	15	22000
1964/65	1200	84	27000
1966/67	6000	270	29500
1968/69	21500	1400	30000
1970/71	58535	3660	17000

SOURCE: Forestry Department of Uganda.

Table 7 Tropical forests compared

Estimated production per hectare from conversion operations

Forest type	Fuelwood	Charcoal (portable kilns)	Charcoal (earth kilns)
	tons
Rain	120	30.0	15.00
Tropical deciduous	50	12.5	6.25
Mean	85	21.3	10.63

SOURCE: author.

Table 8 Fuel and energy compared

Estimated production of fuel from conversion operations on 100000 hectares of tropical forest

Fuel operation	Million tons		Million tons CE
	max.	min.	max.	min.
Fuelwood	12.0	5.0	6.0	2.5
Charcoal (portable kilns)	3.0	1.3	3.1	1.3
Charcoal (earth kilns)	1.5	0.6	1.5	0.6

SOURCE: author.

Table 9 Labour

Labour requirements for the production of fuel from the conversion of 100000 hectares of forest

Fuel operation	Man-days per ha		Man-days per tons CE	Total man-years (200 days) in thousands
	max.	min.		max.	min.
Fuelwood	120	50	2.0	60	25
Charcoal (portable kilns)	210	88	7.0	105	44
Charcoal (earth kilns)	308	128	20.5	154	64

SOURCE: author.

YOUNG WOOD GATHERER wood lots needed'

Where are the fuelwood statistics? World consumption of energy from wood is in fact greater than that from hydroelectric schemes, nuclear power and geothermal sources combined, but statistics about this subject are rare. The FAO Yearbook of forest products regularly contains world fuelwood and charcoal figures as part of annual data on production and trade in forest products. The latest edition brings these figures up to 1973 and the edition scheduled to appear in 1976 will have them up to 1974. The United Nations Statistical yearbook, which deals extensively with energy consumption throughout the world, does not include fuelwood and charcoal, and should therefore be used together with the latest edition of the FAO Yearbook of forest products.

Institutional attitudes which have, until now, encouraged the substitution of finite energy stocks for indigenous renewable energy supplies will change under the pressure of necessity, but such changes can be accelerated by the adoption of economic criteria which take into account the needs of a changing world fuel situation.

The energy crisis as it affects developing countries has tended to be overlooked because of their comparatively low consumption of commercial energy, i.e., less than 10% of the world's total consumption in 1970.

Many tropical developing countries have vast underdeveloped forests which could very easily be managed to produce fuel rapidly for industrial purposes as well as continuing to meet much of domestic needs. It should be noted that about 80% of the households in developing countries now use fuelwood or charcoal for domestic purposes. Developing countries are estimated to contain about 500 million hectares of rain forest, 500 million hectares of tropical, moist deciduous forest and 1.000 million hectares of dry forest. The unused increment of 3500 million tons of CE in tropical developing countries amounts to 51% of the world's forest increment, and is more than three times their present total energy consumption, and about half the world's commercial energy consumption of 6847 million tons of CE in 1970.

Labour source

In developing countries the human resource is generally underutilized, and labour can usually be withdrawn from subsistence agriculture with a net gain to the economy as a whole. Evidence from Uganda shows that the active participation of the Forest Department in promoting a charcoal industry by means of organized courses, demonstrations and research increased employment opportunities and created new wealth (see Table 6).

From experience gained in rain and deciduous forests in both Africa and Asia it is estimated that the placing of only 10% of these forests under systematic management would be sufficient to produce enough fuel, from unmerchantable wood made available in the conversion process, to sustain a 5 % annual growth in total energy consumption in developing countries for more than two decades.

The estimated labour requirements for the preparation of wood and char coal from these conversion operations are shown in Tables 7-9.

It is estimated that the conversion of 100000 hectares of tropical forest (assuming an average yield of 85 tons per hectare) each year would provide fuelwood equivalent to 4.2 million tons of coal and jobs for 42500 men. If the fuelwood were to be converted to charcoal the manpower input would be even greater.

Forest energy sources are vital for most developing countries. This fact is often ignored by planners where the conversion of forest land to other use is deemed to be a necessary ingredient of economic growth.

The suggestion put forward in this paper is that the increased production of fuel from forests, provided it is well managed, is not only necessary for basic survival but is also likely to help solve the problem of finding enough fuel for economic development.

The utilization of wood fuel and charcoal can either be tied in with the improvement of timber production in tropical forests, by suitable cultural operations, or can become part of a programme of reforestation with fast-growing species capable of providing fuel increments of several tons of CE per hectare per annum.

The work has special significance for developing countries with underutilized land and labour resources, and could well be assisted by technical aid from outside agencies.

Projects aimed at increasing the fund of renewable energy supplies deserve a higher priority than they have hitherto been granted.