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close this bookBoiling Point No. 26 - December 1991 (ITDG Boiling Point, 1991)
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View the documentStove Technology Transfer
View the documentDoes Anyone Need to Design a ''New'' Stove?
View the documentLimits of Technology Transfer
View the documentA Single Pot for the Pacific
View the documentImproved Stove Promotion in Three Indian States
View the documentTechnology Transfer - The KCJ
View the documentTraining for Technology Transfer
View the documentGATE/GTZ NEWS
View the documentSolar Cooking of Traditional Foods in Western Africa
View the documentSri Lanka's Rural Stove Programme
View the documentStove Building & Dissemination in Developing Countries
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A Single Pot for the Pacific

Institutional Stoves from BEST

Reproduced from GLOW, Vol 1, June 1991

Many schools, hospitals, prisons, hotels and commercial cooking establishments in developing countries rely on wood as their primary source of energy for cooking food, baking, heating water and sterilizing. But often the heating is carried out over inefficient and smoky open fires or simple stoves that burn wood or charcoal. Gas and electricity is often still too expensive and out of reach.

Increasing rates of deforestation have resulted in demand exceeding supply and thus large increases in the price of wood. In Kenya, many schools with 400 pupils now, on average, spend $3000 per year on fuel for cooking.

In some areas, as wood becomes scarce, schools resort to burning residues. This leads to an increase of toxic emissions. Health authorities are concerned about the decrease in hygiene and safety in the kitchen and are looking for solutions to the problem.

Over the past 4 years, Biomass Energy Services and Technology (BEST) has worked with researchers, entrepreneurs and extension of ficers in developing and developed countries to meet the needs of such institutions.

In the Pacific island nations of Vanuatu and the Solomon Islands, architects at Gazzard Sheldon have been designing schools to be as energy-efficient as possible. The criteria for their stoves included the following:

· long life and low maintenance requirement
· should be able to be repaired locally
· easy to light and quick to heat, will stay hot over night
· can boil 180 litres of water in under 60 minutes
· smokeless in the kitchen
· use a pot with a 200 litre capacity, easy to stir and remove
· cost less than US$3.000 delivered to the school.

During the design phase, materials were selected, design calculations were carried out and a prototype built and tested. Modifications were made and a production model was built. After further tests, another 11 stoves were built for tests in the field.

Material Selection

To ensure a long life, ease of cleaning and maintenance, the designers chose to make the pot and casing from stainless steel.

The inner walls are lined with insulating refractory material to ensure heat retention and quick heating to operating temperature. The firebox is lined with tough firebrick to withstand abrasion from the wood and the grate is made of 6mm mild steel angle. This steel is available in the Pacific Islands and can be easily obtained when the grate wears out (after about 5-10 years). The doors are made of mild steel plate and lined on the inside with stainless steel. The handles for the door and air controls are made from stainless rod.

Configuration

To ensure that the cooks can easily stir the food, the maximum height of the stove is no more than 1 meter. At an offset of 60 degrees the cooks can easily load the wood into the stove without touching the hot chimney. Two doors are fitted to the stove. Wood is fed through the top door. Secondary air enters into the firebox through two jets that are placed in the middle of the top door. A sliding door controls the amount of air entering. The bottom door allows the ash to be removed and the primary air to enter. It can be fully opened for maximum output and for ash removal, half open for simmering and closed for very slow cooking.

Design work was carried out on a range of pot sizes, resulting in a pot size of 750mm die with a depth of 500mm. A bronze tap is fitted to the bottom to allow hot water to be easily removed and for the pot to be cleaned.

The use of secondary air and a properly sized grate ensures that, once the stove is operating, it is nearly smokeless. Time for boiling 150 litres of wateris approximately 35 minutes with a thermal efficiency of about 45% (5-10 times more than an open fire).

If the unique air control system is used properly, the cook needs only to stoke the fire 2-3 times. At the end of each day the air holes are closed and the stove will remain hot, producing 40°C hot water overnight. This can be used to make the morning tea or for bathing.

Table 1: Stove Specifications

Pot capacity

200 litres

Pot diameter

750 mm

Height

1000 mm

Width

900 mm

Grate area

23 m2

Approximate weight

100 kg

Chimney diameter

20 cm

Stove Tests

A series of water boiling tests were carried out to determine the operating characteristics and the thermal efficiency of the stove. Eucalyptus wood, diameter 6 cm and length 45 cm, with an average moisture content of 25% was used for the experiments. The pot was filled with 185 litres of water and then brought to a boil. The primary and secondary air ports were adjusted so the water was kept just boiling. The weight of the wood used and the time to bring the water to boil were recorded. The time when the water went off the boil and the wood used at this stage were also noted. The pattern of boiling in the pot was also noted to determine if some areas were obtaining more heat than others. If one area was receiving more heat then more bubbles would form on the bottom and the side walls in this region. The results are summarized in the table 2 below.


The lnstitutional One-Pot Stove from BEST

It can be seen that the performance of this stove is dependent on the heat output. If the fire is carefully controlled, then an efficiency of 47.7% can be achieved. If the cooks are in a hurry to bring the water to boil, the efficiency can be as low as 35.6%. Under all operating conditions, water will boil in less than 60 minutes. The stove needs to be stoked 3 to 4 times to bring the water to boil, after which there is sufficient retained heat in the walls and charcoal to keep the food simmering for another hour.

Table 2: Summary of Test Results

Stove

Output Boil Simmer Efficiency

Boil

Overall

Time

Time

Boil

Overall

kw

kw

Mins

Mins

%

%

47.3

23.6

57

65

37.0

47.7

51.1

27.2

52

66

33.4

39.2

55.6

33.7

48

68

29.3

35.6

Conclusion

The performance and acceptability of the stove will be monitored at the schools over the next year and improvements made. Further research work will be undertaken to reduce the cost and improve the durability of the stove.