| Boiling Point No. 08 - December 1985 |
By Wclaw Micuta, Vice-President and
Director of the Bellerive Foundation, Geneva.
There seems to be general agreement among people working on the problem of fuel-efficient stoves that renewed efforts should be made to design, test and promote simple, low-priced metal braziers to replace those currently prevalent in developing countries. Whilst considerably improving fuel-efficiency, the new designs should aim to preserve the principal advantages of the traditional models they are intended to supersede. Many of these such as the "Jikos" of East Africa or the "Feu Malgache" in French speaking parts of Africa, are very popular - particularly in urban areas where households are not usually equipped with separate kitchens. Instead, cooking is commenced outside and the brazier is only brought into the living quarters when the charcoal is burning well and the initial smoke has diminished. The brazier thereafter provides heat and light and generally serves as the focal point of family life.
The popularity of charcoal for cooking grew when there was an ample supply of firewood. In those circumstances its use could be justified. Nowadays, however, in the face of critical de-forestation it is essential to examine strategies whereby its use may be gradually phased out in favour of fuels which are not only less wasteful and expensive but also easier for the consumer to employ. To start charcoal glowing demands time and effort - particularly if it is of poor quality. Worse still, the possibilities for regulating power are limited to the point of being virtually non-existent. As a result, it takes a long time to bring food to the boil and it is then difficult to arrange for gentle simmering.
If women were given the opportunity to compare the use of the two fuels in modern braziers there is little doubt that they would follow suit and opt for firewood.
With this in mind, Mr. Emil Haas and I developed a series of braziers including that featured in the present article. As with the other models in the series , the "miha" is 'universal' and may he fired with either wood or charcoal as well as with alternative fuels such as kerosene, biogas or bottled gas. It may be cheaply produced in any rudimentarily-equipped local workshop and is simple and comfortable to use. The model has one disadvantage in that it is designed for use with only one size of cooking pot. For this reason Mr. Haas and I have recently developed a new model which can be used with two sizes of pot without significant loss of heat energy. This model will be fully described in a future article.
Basically the Miha consists of a single metal sheet cylinder 1.0 mm thick.
The brazier is equipped with a metal sheet door providing for primary and secondary pre-heated air. A half-moon shaped platform, on which the pots will sit, is riveted to the inner walls of the stove. As the platform is exposed to intensive heat, it is preferable to make it out of 2.0 mm sheet. Unlike other models in the series, the Miha is not fitted with a permanent ring on its top surface. Instead, a lip is hammered around the top of the stove walls to provide greater strength and durability. The lip should be 1.5 cm wide so as to ensure the correct space between the pot and the stove walls. When standardized cooking pots are used, the rim of the pot sits on the lip and closes the stove from above. The stove may, however, also be used successfully with locally-available pots. In this case, it is advisable to use a mobile ring equipped with handles so as to increase user comfort.
The fire-box consists of a basket supported on three legs. The grate is adjustable and should be placed at the base of the basket for burning wood-waste. The top position is reserved for cooking on charcoal or in conjunction with gas and kerosene burners.
An alternative design for the basket takes the form of an open cone with two different grids. This arrangement offers two additional advantages. Firstly, when wood is being used, it ensures that the pieces fall automatically into the correct position within the fire-box and, secondly the form of the cone provides for an improved concentration of heat around the base of the pot.
Manufacturing the cone presents no major difficulties if local craftsmen are provided with a template. It may be noted that on the model shown below the distance between the base of the stove and the Orate is 105 mm. There is no reason why this space could not be reduced to 60 mm, thus economising some sheet metal. However, the extra space was specifically requested by users in Kenya so as to make it possible to roast corn cobs or other food below the grate.
The use of a basket as a fire-box has several advantages. It is easy and inexpensive to produce and, as air is able to enter from all sides with the door open, it is relatively easy to start combustion. Thereafter, with the door closed, the regulation of combustion is greatly facilitated and even with charcoal a fair degree of control is possible. The position of the basket (see Figure 2) means that it is separated from the stove walls by a layer of air. This, acting as a natural insulator, greatly diminishes the loss of heat from the stove by radiation and goes a long way to compensating for the fact that the stove, unlike others in the series, is made with a single rather than double skin. Thus, during operation the temperature of the outer walls of the stove around the basket does not normally surpass 200° C. The upper part of the stove is cooled even further by the contents of the pot to around 150
C. The temperature of the gases in the chimney should be in the region of 100-120° C at the height of normal cooking.
The basic designs of the Miha, which may be constructed from recycled metal sheet, are presented in Figures 1, 2 and 3. Rivets are used for assembly so as to facilitate manufacture in any local workshop. The weight of the brazier illustrated is 6.7 kg. The basic cost elements are approximately 7 kg of metal sheet and one to two person/day's labour - depending on the skill and organisation of the workers. The manufacturing time could, of course, be considerably reduced in larger-scale production.
During field tests, the Miha has proved popular with users and has been readily accepted particularly by those communities accustomed to using portable metal braziers. As with all promotion of new stove designs, the main problems are likely to be connected with low-cost production, quality control and correct use.
The pot is placed deep in the stove so as to enable heating from below and around the sides. At an ambient temperature of about 20°C, it has proved possible to bring five litres of water to the boil in 12 to 14 minutes using less than 50 grams of wood per litre of water boiled(2)
The test results given are based on the provisional international standards established at the Arlington meeting in December 1982 and adopted by Mr. Frans Sulilatu during previous independent testing of Bellerive stoves(3).
Somewhat improved results could be obtained if the stoves were supplied with efficient, standardised cooking pots. Past experience in Europe has proved conclusively the value of such pots in the interests of achieving fuel economies and the reader is referred to the author's publication "MODERN STOVES FOR ALL"(4) for a more detailed consideration of this problem.
The other models in the series are presented in the author's publications "MODERN STOVES FOR ALL" (1985 - ITDG Publications, 9 King Street, London WC2E 8HW) and "STOVES TO SAVE OUR FORESTS" (Independent tests conducted on Bellerive stoves by Mr. Frans Sulilatu - 1985 - Bellerive Foundation, PO. Pox 6, 1211 Geneva 3).
(2) Measured immediately after-the water was boiled.
(3) See: "Stoves to save our forests" op. cit.
(4) op. cit.
Fuel efficiency rate (FER) in % 41
Max power output (kW)4.0
Min power output (kW)1.8
Initial amount of water (kg)5.0
Wood consumption at max power output (kg) 0.385
Wood consumption for the duration of the test (kg) 0.910
Specific wood consumption at max power (SWC) 0.077
SWC for the duration of the test 0.274