Notes on non-household energy needs which might be met by wood fuels, and on alternative sources of renewable energy for meeting theme needs
Russell deLucia
Fuelwood and other traditional fuel requirements are not associated only with domestic users, Not only are there existing uses of fuelwood in the agricultural, commercial, and industrial sectors, there is also the potential for dramatically increasing requirements in these sectors, and in addition there is an opportunity to increase the efficiency of current uses in these sectors as well as in the domestic sector. At the same time, these more concentrated uses provide opportunities for viable substitution of wood fuels by other renewable sources of energy such as wind, biogas, and solar.
In addition to embodied energy in inputs such as fertilizer, energy requirements for agriculture and industry can be divided between demands for shaft power and demands for process heat* This division for rural industries is shown in Table IV-1. Firewood and charcoal can be used to meet these requirements, but there are other sources which are also suitable, as indicated in the same table. In some survey efforts it may be necessary to explore the nature of these demands in detail, since for all of these there are technologies that allow for providing for these demands with wood fuel, and it may be necessary to determine whether this or some other energy form is most appropriate.
All industries can make use of shaft power for materials handling and preliminary processing of raw materials, but only certain industries such as textiles, crop processing, metal and woodworking use shaft power in the primary production activity. The amount of shaft power required depends on the scale of production and the extent to which an industry is run off a central source of power or separately powered machines.
Electric motors have played an increasing role in providing shaft power, especially for portable equipment and small horsepower machines. Studies in India and Taiwan (SIETI, 1976; Samuel, n.d.) indicate that in initial stages of development the use of shaft power in small industries is in areas characterized by relatively small loads per enterprise. In a more developed economy, such as Taiwan, the connected load increases. Where electricity is not available, diesel engines can be used for small horsepower requirements and steam engines or direct hydro-power can be used for larger power requirements. Despite these options, rural industries, by and large, operate on manual power. There is considerable latent demand for shaft power to increase labour productivity and to improve product quality, but this demand is not realized primarily because of lack of finance, and in many areas lack of electricity. Energization of industry is usually associated with the replacement of labour with capital, although in most rural industries the increase in labour productivity will increase the returns to labour and shift and perhaps reduce the skill requirements.
Shaft power needs are of critical importance in agriculture. The energy requirements for agricultural production are considerable and include fertilizers, agrochemicals, human and animal labour as well as fuels for mechanization, pumping and other activities. Many of these have implicit shaft power needs. Although these activities can be performed by manual or animal labour, there are advantages to mechanizing them and this requires shaft power. These advantages include the ability to meet peak manpower demands, specifically during ploughing, planting, weeding, harvesting and threshing, and to provide water from greater depths and in greater quantities.
The installed shaft power and amount of energy required for cultivating a hectare of land varies with the crop, the soil condition, and the method and cycle of agriculture. For agriculture energy requirements, as for domestic energy requirements, it is not easy to generalize1 about energy and power requirements. However, a limited amount of data has been collected on local requirements, some of which is presented in Table IV-2.
1 FAO in the work undertaken in-preparing its study Agriculture: Toward 2000 has developed estimates of the energy requirements for the production of most major crops under various production regimes. These are summarised in Table 4.6 of that publication (FAO, 1981:71); more detailed information may be obtained from the Global Perspective Studies Unit, Economic and Social Policy Department. FAO Rome.
Table IV-1 - Industrial and agricultural energy uses
|
Activity |
Energy |
Firewood, Charcoal |
Substitutes |
|
Planting and Cultivating |
Shaft power |
With gasifier |
Commercial liquid and gas fuels, biogas |
|
Pumping |
Shaft power |
With gasifier and/or electricity |
Commercial liquid and gas fuels, biogas, solar, hydro-wind, central grid, compressed air |
|
Harvesting |
Shaft power |
With gasifier |
Commercial liquid and gas fuels |
|
Drying |
Process heat |
Direct combustion, process steam |
Solar, biogas, agricultural wastes, commercial fuels |
|
Killing |
Shaft power |
With gasifier engine or electricity |
Agricultural residues, commercial liquid and gas fuels, wind central grid, hydro-electric, biogas, water wheels |
|
Cooking, Baking |
Process heat |
Direct combustion, process steam |
Commercial fuels, solar, biogas, agricultural residues, geothermal, cogeneration |
|
Woodworking |
Shaft power |
Electrification, process steam |
Commercial fuels, wood wastes, central grid, biogas |
|
Metalworking |
Shaft power |
Gasification, process steam, electrification |
Commercial fuels, hydro-electric, central grid, biogas, water wheels, wind |
|
Forging, Smelting |
Process heat |
Charcoal by direct combustion |
Oil, gas, coke |
|
Bricks, Cement |
Process heat |
Direct combustion |
Agricultural residues, commercial liquid and gas fuels, geothermal, cogeneration |
|
Mineral processing |
Process heat |
Direct combustion |
Commercial fuels, agricultural residues |
|
Shaft power |
Gasification, electrification, central steam |
Commercial fuels, hydro-electric, central grid, hydro, biogas |
With mechanized cultivation using small tillers or tractors, the amount of energy required for land preparation can range from 150 to 1050 horsepower-hours per hectare. The higher values are associated with the cultivation of high-yielding varieties. The amount of shaft power required can range from under ten horsepower for a small hand tractor to over a hundred horsepower for a large tractor. The fuel required to provide this energy ranges from 1.4 to 10 gigajoules per hectare, assuming an overall conversion efficiency of 28%. (35% for the engine and 20% mechanical losses). The requirements for installed shaft power and energy for irrigation vary even more than for cultivation, due to differences in the availability of rainfall, surface and ground water. From Table IV-2 a broad range of demand from 150 to over 2000 horsepower-hours can be deduced assuming that the irrigation is provided from wells using pumpsets. These pumpsets can range from 1 to over 50 HP. The amount of energy required pan be less than 150 horsepower-hours where gravity systems are used, or where shallow wells provide sufficient water. The amount of energy needed can be reduced through careful application, an extreme example of which is the use of drip agriculture which has been used increasingly in the Levant.
The demand for fuels to operate threshing and transport equipment can be better measured in terms of tons processed and ton-kilometres travelled. The fuel requirements for a rice milling operation are on the order of 2 litres of diesel fuel per ton and the requirements for transportation are on the order of 2-2-5 litres of diesel fuel per ton-kilometres.
For all four activities - land preparation, irrigation, milling and transport available technologies exist which utilize renewable fuels. Irrigation and milling require stationary shaft power, while the others require moveable shaft power. The latter can be provided through the use of liquid fuels produced from biomass or gasifier/engine driven tractors. The former can be provided not only from biomass converted to gaseous or liquid fuels, but also from water, solar, geothermal, and wind power (and of course human and animal power).
The small industries that are the primary consumers of fuels for heat generation are the brick and lime kilns, crop driers, blacksmith forges, commercial ovens and stoves, and pottery kilns. Fuels used include wood fuels, agricultural and forestry residues, coal, oil, and, in some oases, electricity, The fuel requirements vary over a wide range because of differences in the firing temperature, the thermal efficiency of the conversion unit, the physical characteristics of the raw materials and the type of product. An indication of the range of energy demand is shown in Table IV-3.
For most processes the fuel consumption rates vary by at least ± 50% from the median. The lower consumption rates are generally not associated with a specific fuel type, but the ability to control the feed rate for different fuels is important. The reduction in fuel consumption has been achieved through the use of continuous processing rather than batch processing. The latter has large losses associated with heating and cooling the walls of the processing unit. Other reductions in fuel consumption have been achieved by improving the insulation, using downdraft convection flow, and recycling the exhausted process heat to preheat the input materials
The evolution of technology for generating process heat can be roughly divided into four phases: 1) temporary, earth pit or mound units; 2) permanent, updraft, batch fed units; 3) semi-continuous, down or horizontal draft units with sequential or movable firing and preheating, and 4) continuous, forced convection, moving products units with recycled waste heat. Each subsequent phase requires greater investment in fixed capital production levels which are intermediate in scale between the transport-dependent urban factories and the village-limited rural enterprises.
Table IV-2 Energy requirements for agriculture
|
Location |
Crop |
Activity |
Requirement* (Hp-hr/ha) |
Notes |
Source |
|
Up India |
HYV Rice |
Land prep |
576 |
Tractor |
Singh & Singh |
|
HYV Wheat |
Land prep |
1069 |
|
|
|
|
We Bengal, |
Rice |
Field Prep** |
216+ |
8HP/Tiller |
Indian Institute of Technology (IIT) |
|
Wheat |
Field prep |
200 |
8HP/Tiller |
IIT |
|
|
Asia |
Rice |
Cultivation Irrigation |
6 |
Traditional |
Kuether, et al. |
|
Philippines |
Rice |
Cultivation |
160 |
Transition |
FAO |
|
USA |
Rice |
Irrigation |
2730 |
Modern |
|
|
Punjab |
Rice |
Irrigation |
4.4 |
|
Singh and Miglani |
|
Sri Lanka |
Rice |
Ploughing, twice |
146 |
|
|
* Amount in horsepower hours per hectare; assume .2 lit/hp-hr and efficiency of drive train equal to 30 percent yielding net .25 lit/hp-hr.
** Includes nursery raising.
Table IV-3 - Sample energy requirements for small industries
Table IV-3 - Sample energy requirements for small industries (Continued)
|
*Assume coal |
29.0 MJ/kg |
|
|
wood 14.5 MJ/kg |
|
|
oil 42.5 MJ/kg |
Several conversion technologies using renewable energy sources are being developed which are both complementary to and competitive with fuelwood and charcoal in some of the applications discussed above. Information on the applicability of several old and new energy technologies in specific and uses is summarized in Table IV-4.
Biogas is one of the technologies that clearly warrants consideration. Biogas plants are in operation in many countries, particularly in Asia, and the technology has the potential for meeting some of the energy requirements of rural areas. The important technical problems are to develop and refine low-cost designs based on local materials, to provide for gas storage requirements and to raise the productivity of the biological system in cold areas, and to deal with factors (toxics, pH, etc.) affecting digester functioning. Economic problems are associated with costs of the systems, breakdowns and repairs, and the difficulties in establishing a system for the inputs, an well as the biogas outputs where community systems are established. Fuel supply problems include availability of domestic animals. The institutional and social implications of the introduction of biogas plants must be carefully studied because evidence indicates that its benefits tend to accrue to the larger farmers (Bhatia, 1979) at the expense of the poor who previously collected the dung for their own uses
Small-scale hydro-power is being increasingly introduced or reintroduced where the necessary generators and turbines are within the country's manufacturing capability. The primary problem with hydro-power in the limited availability of falling water with sufficient flow and head throughout a years A secondary problem is the need for trained personnel to operate and maintain a hydro-power system including its power take-off equipment.
Wind power is also being introduced or reintroduced in a number of countries. A number of designs have been developed to produce power from winds which fluctuate in velocity and directions High-torque and high-speed designs have been introduced, many of which can be locally fabricated and easily maintained, The major problem with wind power devices in the unreliability of supply. Locations such as the coastal areas of Thailand can be selected to ensure a relatively continuous supply of wind, but the demands for energy are not usually located in the same areas One solution to the problem of varying wind supply is the conversion of the kinetic energy to potential energy in batteries, elevated water storage, or other mediums. However, this storage adds considerably to the cost and introduces conversion losses.
Another source of energy which in constrained by the availability of supply is solar energy. Passive solar heating can provide hot water and solar concentrators can produce high temperature process heat, but only when there in adequate solar radiation. The introduction of solar cookers has been hindered by a number of factors. Industrial processes are generally dependent on having a supply of energy available as and when needed. Solar drying has been used only in situations where the drying activity was not part of a continuous activity, or where an adequate inventory could be maintained as a buffer against overcast skies.
The generation of electricity using photovoltaics faces the same problem of variation of supply of solar radiation. A product of the space age, some investigations suggest that the rapidly decreasing unit cost of photovoltaics may soon make it competitive, The relative compatibility of this technology with small systems (no real economies of goals) suggests that it may ultimately hold promise for many of the world's small farms, but thin remains to be proven.
Gasifiers and other controlled combustion technologies using wood, charcoal and other materials are being rediscovered and improved for meeting both direct fire and shaft power requirements, the latter when coupled with an engines These technologies have economic potential when applied to agriculture and rural industries as well an to large-scale needs.
Table IV-4 New and old technologies to meet village energy requirements
Table IV-4 New and old technologies to meet village energy requirements (Continued)
Table IV-4 New and old technologies to meet village energy
requirements (Continued)
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