3. CONSUMPTION PATTERNS OF WOOD FUELS

The consumption patterns of wood fuels in different rural processing activities depend on the location, type and scale of activity, raw materials, and the wood energy conversion system used. In the smaller-scale cottage and village activities, wood fuels are mostly supplied by women and the quality of wood fuel depends on local availability. The wood is converted into heat in simple kilns or furnaces for cooking, baking or drying purposes, or the fuel gases are used for smoking of products. In larger-scale village enterprises and rural industries, wood is purchased on a commercial base, the quality is controlled to a certain extent and the conversion system is technically more complicated. In some cases, wood is simply burnt to generate the necessary heat for processing a raw material, or the fuel gases from the combustion process are used for drying a certain crop either directly, as in rubber smoking, or indirectly with the aid of air-heat exchangers or more complicated boiler-radiator systems.

The consumption of wood fuels is dependent on fuel quality, the conversion system used, the raw material to be processed, the quality of the end-product, and the mode of operation. The specific use can vary from a low 0.1 kg/kg up to 15 kg/kg of the end-product, depending on the factors mentioned above. In order to get a clearer picture of consumption patterns of different wood fuels, the situation must be analysed relating to country, sector and industry. Unfortunately, the existing data on the consumption of wood fuels, is, however, incomplete, or is in many cases, more or less lacking.

The range of specific fuelwood consumption, as presented by Gordon (21) for the small cottage/village level and listed in the other background documents for the more formal rural industries, is summarized in Table 3.1. The figures given in the table are, in most cases, rather rough estimates and have not been thoroughly measured or investigated. In general, they have also been calculated backward from the total fuelwood consumption and production capacities and include big uncertainties, because the people in charge of operation are, in many cases, for some reason or other, not willing to reveal the actual amount of fuelwood consumed - not always even known - or of products manufactured.

To get true and more realistic values of the specific fuelwood consumption in different rural activities, it must be clearly defined, what, when, how and where to measure. In many cases, the average fuelwood consumption is not very easy to measure and it does not actually tell much about the efficiency of the wood fuel conversion system used.

This can only be measured or estimated by thorough monitoring of the fuel characteristics (especially the net heat value) and by calculating the theoretical amount of heat needed for a certain process. This also means that the quality of the end-product has to be analysed. The measurements should be performed in situ in the field during actual operation. In practice, this is, in most cases, impossible as it would require the availability of quite sophisticated measuring equipment, as for example, for determining the net heat value.

Although the total consumption amount of fuelwood over a longer period in proportion to the amount of the product processed or manufactured includes some deficiencies and uncertainties, it gives valuable data on the basis of which comparisons between countries and technologies, impact evaluations, policy and planning of intervention can be carried out.

In the following, some country-specific values of total fuelwood consumption in certain industries are given. Data for Sri Lanka as reported by Nanayakkara (16) are given in Table 3.2. The corresponding figures for Tanzania as reported by Mwandosya and Luhanga (39) are listed in Table 3.3.

In Thailand, some 250 000 m³ of fuelwood is consumed annually by the lime industry (10), and the corresponding estimate for the lime industry of Indonesia is 765 000 t/y (8). Koopmans has also estimated the wood fuel consumption in the brick and tile, coffee and cocoa industries of Indonesia. 384 000 t of wood is used by the brick industry and 222 000 t by the tile industry. For processing coffee some 30 000 t of wood fuels, and for processing cocoa 24 000 – 28 000 t of wood fuels are used annually.

The total amount of wood used by the tobacco industry of Malawi has been estimated to approximately 9 % of the total national consumption (13). The smallholder tea authorities of Malawi consume some 10 000 m³/y of wood fuels to dry 1 700 tons of tea, which is less than 5 % of the total national production.

Burne (20) reports that 1.9 million tons of fuelwood were used by rural cottage activities alone in Kenya in 1980, with another 540 000 tons of charcoal (equivalent wood weight), and UNDP/WB estimates that 83 % of fuel and charcoal used in Sudan industries is consumed by bakeries and brick factories. Velasquez (14) reports that the total wood fuel demand of the salt processing works of Nicaragua has dropped from 4 240 tons in 1981 to 81 tons in 1985. One of the main reasons for this drastic reduction is the difficulty with wood fuel supply, because of depleting forest resources, and this, in turn, has led to unfavourable wood fuel prices compared to other fuel alternatives - solar energy systems in the case of salt processing.