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close this bookBoiling Point No. 33 - May 1994 Number 33 (ITDG - ITDG, 1994, 36 p.)
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Zimbabwe's 'Sloven' woodstove

by Makhosi Khumalo, Friends Rural Service Centre, PO Box 708, Bulawayo, Zimbabwe.

HLEKWENI is a Zimbabwe NGO providing training to rural people in a wide range of activities such as agriculture, building and carpentry metalwork, early childhood education and care, women's courses and appropriate technologies including domestic cooking stove and oven construction.

The Stoven now being produced by Hlekweni combines a three-pot stove with an oven as shown below It is a brick structure with a 5mm steel top plate and a steel grate. The Stoven is produced for domestic use and for sale to institutions and small commercial cooking businesses. It is designed to suit Zimbabwe's rural population which relies on wood fuel for cooking, heating and lighting. The fuelwood supply which has been the salvation of the rural population is now diminishing at an alarming rate, and so a fuel saving stove is urgently needed. The stove needs to provide all the facilities and benefits available from an open three-stone fire but to have a lower fuel consumption and produce less smoke.

The Stoven provides these facilities and saves 45% of the fuel used by a three-stone fire. It will burn wood, dung, maize cobs, sawdust and other combustible biomass. Because of its chimney, it does not pollute indoor air. It costs around US$25, which is less than the commercial stoves which cost from US$30. The Stovens have not yet been widely promoted because of lack of project funds, but since production started in 1989, 490 have been sold. leave no air spaces. The moulded cake is then pushed out carefully and dried in the open air.


Figure

It takes 375g of cowdung (wet weight) and 125g of waste to make one fuel cake. After drying, the weight will have reduced to around 250g. At an ambient temperature of 30 to 33°C the drying process takes seven days to complete. The dried cake, being compacted, can then be stacked conveniently.

When ready to use, the dried cake is inserted into the stove that has been used as the mould and is lit at the centre. The flame should be regulated with a log of firewood, fed through the side hole. The cake burns from the inside with a blue flame, emitting very little smoke. One cake will burn steadily for about five and a half hours.

The thermal efficiency of a stove burning this dried fuel cake is 38% compared with 12% for a stove using conventional flat dung cakes. The cylindrical fuel wall acts as insulation and reduces the loss of heat through conduction.

For a family of six, a day's cooking can be completed using only one fuel cake. To put out the flame, the log of wood is pulled out, and a little water is sprinkled on the inner side of the cake. The ash residue from beneath the stove is soft and clean and can be used for cleaning utensils. Very little soot is deposited on the sides of the cooking pots. Fuel cakes also help to prevent the accidents that occur when the flames rise above the top of a conventional stove.

Comments from users include: 'there is no smoke while burning'; 'it burns like a kerosene stove'; 'the exertion needed for cooking is reduced'; 'the fuel can be stored conveniently'; and 'rubbish from around the house becomes usable'. The negative aspects reported centred around the amount of time needed for the cake to dry. Overall, the technology proved to be sound and acceptable.