|Boiling Point No. 20 - December 1989 (ITDG - ITDG, 1989, 40 p.)|
By H. Johannes, Gadjak Mada University, Yogyakarta, Indonesia
This paper describes how low grade biomass such as dry leaves, grass, weeds, twigs and stalks can be converted into briquettes and burnt very efficiently in a simple stove.
'Energy Efficient Stoves That Burn Biochar And Biosmoke Only And Can Save The World's Forests'
Conversion of Biomass To Biochar
Biochar, or char from biomass, can be obtained as follows. Put a 20cm layer of coarse dry biomass, like leaves, grasses, weeds, twigs and stalks, in a 200 litre drum with a 25cm mouth opening in its top plate, and fire it. The evolving smoke will expel air from the drum and prevent it from re-entering, hence the biomass in the drum cannot be oxidised to ash, but can only be pyrolysed to biochar. Biomass is added gradually into the drum and occasionally stirred with a stick. When the Biochar obtained fills one third of the drum then it is extinguished with water and stored. 10 kg dry biomass will give 3kg dry biochar.
Briquetting of Biochar
To use the biochar in stoves it should be briquetted. No binder needs to be added because the biochar's own tar can function as a binder. No briquetting machine needs to be used. One merely pounds moist Biochar in a mortar to a sticky dough and mould the dough manually into briquettes. Two types of briquettes should be made, ball briguettes can be moulded by compressing the dough between one's handpalms. Contained briquettes with a combustion well could be moulded in a containing vessel using a thin stick. A cylindrical pipe in the vessel's centre which is later on withdrawn will form the well. Its diameter could be 6-8 cm. The dough should contain as little water as possible for the briquettes to dry faster and to have a greater density, hardness and strength.
Fig 1 - Contained biochar - biomass briquette stove
Contained briquettes take a long time to dry, hence they should be dried artificially by burning twigs in their wells. Ball briquettes should be burned in the wells of contained briquettes because then energy losses through conduction, convection and radiation will be minimal. They constitute the main energy providing fuel and should be added regularly into the combustion well so that the contained briquette can last longer. Ball briquettes should be moulded in different sizes from 4-10 cm to accommodate the changing diameter of the wells. They can be dried in the sun within 3-7 days and should preferably be made from pure biochar.
Biochar-biomass Briquettes And Biosmoke
Contained briquettes can be made from pure biochar, but to save biochar they should preferably be made of a mixture of biochar and particulate biomass, like ricehusks, coffee-husks, peat, sawdust, choir dust, leaflets, leaf powder and dung. Two volumes of biochar and one volume of particulate biomass are moistened, pounded into a sticky dough and moulded into contained briquettes. The water content of the dough should also be minimal. When the biochar-biomass briquette is burned, the biomass in it will give off smoke, but the smoke will burn off in the briquette's well. Biosmoke contains eight combustible components, namely methanol, acetic acid, acetone, tar, carbon monoxide, hydrogen gas, methane and carbon particles. In passing through the incandescent char layer in the wall of the briquette's well and coming in contact with heated air and the glowing surfaces of ball briquettes, all these components will be converted to producer gas CO+H2 that will burn to CO + H20 giving off heat. Even the non-combustible components water vapour and carbon dioxide in the smoke in passing the incandescent layer of char will change to producer gas and burn off. Biochar-biomass briquette stoves are smoke burning energy efficient stoves. An energy efficient stove may be defined as a stove that burns all its fuel to carbon dioxide and water vapour much as a human body does.
Smoky briquettes like dung cakes and peat sods can be made smokeless by mixing them with biochar. In India, each year 73 million tons of cow dung are burned for cooking and heating. Many other countries like Bangladesh, Transkei, Lesotho, use cattle dung as a fuel. The dung stoves give off a thick acrid smoke (Ref:1). They waste energy and pollute the environment. Moulding cattle dung in contained biochar-dung briquettes and burning ball briquettes in their wells will give energy efficient biosmoke burning stoves. Peat stoves are also smoky, but biochar-peat briquette stoves will be smokeless, smell-less, energy efficient stoves. With this new technology, the LDC's may use their peat deposits to substitute fuelwood and save forests. Fifty one LDC's have a peat deposit of more than 36.7 million hectares with a thickness of more than 40 cm (Ref:2) . With an average thickness of one metre and a water content of 90% they may have more than 36.7 billion tons absolute dry peat, which at present is practically unused for fuel.
Contained Briquette Stoves
Figure 1 shows a fired clay stove with a contained biochar-biomass briquette in it and 4 biochar ball briquettes in its well. The dimensions are shown in the figure. The stove has 13 holes of 13mm diameter near the centre of its floor and it has an ash compartment that can be closed. In the upper layer of the contained briquette a groove is made of 26cm diameter, 2cm wide, and 4cm deep. This groove is filled with moist sand. When the mouth of a tin of 26cm diameter is stuck in this groove after the ash compartment has been closed, then the stove will be extinguished. When a contained briquette will be moulded in a drum of 30cm diameter and 40cm height, then 13 holes of 13mm diamter should be punched in its floor and a 4cm thick insulating and protecting layer is laid on it. As insulating material one can use a mortar of 1 cement and 6 lime or ricehusk ash. The side walls themselves are protected and insulated by the biochar-biomass briquette. The briquette itself should not be burned completely because the fire will corrode the side walls. If the well has reached a diameter of 24cm, then the stove should be extinguished and the briquette remoulded. Two or three of these stoves can be used in turn. They are small enough to be used in the kitchen, but also large enough to be used in home industries like in the production of palm sugar or in the distillation of essential oils.
Charcoal fines which at present are thrown away by charcoal makers and charcoal sellers can be briquetted without adding glue in the same way as briquetting charcoal.
Fuelwood is scarce and expensive, while billions of tons of biomass like leaves, grasses, weeds, vegetable wastes, peat and dung are wasted, unutilised or underutilized. Energy efficient stoves that burn biochar and biosmoke only can by E G Krishna Rao easily be constructed. They do not need fuelwood at all and can save forests while cleaning the environment. The use of biochar stoves does not impoverish the soil because the energy and carbon do not come from the soil. The energy comes from the sun and the carbon comes from the air and is returned to the air at the burning. The cooking pan can he seated on a U-shaped 1cm thick iron rod.
1. Foley, Gerald and Patricia Mose, 1983, Improved Cooking
Stoves in Developing Countries, Earthscan,
2.Muranen, K, 1987, Transfer and Adaption of Peat Technology to Tropical Countries, Symposium on Tropical Peat and Peatlands for Development, Yogyakarta, Indonesia.
Letter to Editor
While biomass stoves are the main thrust to improve the quality of life of the rural masses. I feel more could be done if we work on a wider canvas including solar energy. You may think that such developments are too high technical, but technologies can be developed on the principle of heat pipes. Building a tracking solar collector need not be too complicated and the technicians at grass root levels could be trained to handle the techniques should suitable hardware be developed.
With the heat pipe, a pressure type, steam cooker seems possible. The Brace Institute device was a non-tracking, flat plate collector but with a tracking solar concentrator, which need not be too mechanically complicated, a steam pressure cooker can be developed.
You perhaps know that the Government of India has succeeded in introducing advanced types of solar cookers in some parts of India, particularly in the arid regions. If the technology could be brought down to the grass root level, the rural areas which stand at the interface of man's technology and nature's technology. The population drift to the towns could be counteracted since the ruralite also could boast of a high tech area within his reach.
What Else Does ITDG Do?
Interest Increase in Hydro as Rural Power Source
ITDG is assisting local NGOs and engineering companies in Peru to develop the potential of micro hydro as an alternative power source in remote Andean Communities.
The first three Pelton turbines have been maufactured by two Lima engineering companies and the first Electronic Load Controller (ELC) has been assembled under licence from the UK manufacturer. A 50kW installation at 5,000 feet in the Ceja de Sela of Cuzco, has completed its first full year of operation, powering a carpentry and welding workshop, bakery and various other small machines, in addition to providing lighting. The unit has already been used for training and is acting as the focus for interest in other parts of the Yanatile and Yavero area.
A demonstration project, using a small SkW hydro system, is being established at a village nearby to supply mechanical power for cassava processing. Households at the village are widely dispersed, making electricity generation impractical. Instead, the unit will be used to charge 12V car batteries used in individual houses for lighting.
The 15-year-old micro hydro system in one Lima province community at 10,000 feet in the Andes has been renovated and upgraded using an ELC. Improvements to the channel and river defences are continuing and the turbine, reconditioned in Lima will be ready for commissioning shortly. The system is to be used for a women's textile project and the community also has plans for a small carpentry workshop.
Wider interest in micro hydro technology for Peru has been stimulated by a successful seminar for local NGOs on hydro energy and rural development.
Each edition Boiling Point now carries a detailed profile of an improved stove being promoted in one or more countries. These profiles are reproduced from lTDG's "Improved Wood, Waste and Charcoal Burning Stoves". If any readers have improved the design or construction of any of these stoves we should like to hear from them and publish details. A free copy of the manual will be sent for any details of improvements published.