|Boiling Point No. 19 - August 1989 (ITDG, 1989, 36 p.)|
Each edition of Boiling Point now carries a detailed profile of an improved stove being promoted in one or more countries. These profiles are reproduced from ITDG'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.
No. 3: Noflie - Shielded fire
One-pot chimneyless stoves (also known as shielded fires) are the simplest of the stove types and seem to be the most direct progression from the three- stone fireplace. High, consistent, field performance figures have been obtained from them. Some of these stoves have been used in Asia and Africa for many years. They are usually portable, are relatively low cost and can often operate over a wider variety of power outputs and at high efficiencies.
Grates significantly improve the performance of every stove to which they have been added, with the exception of the Louga-type stove. The addition of a grate to a shielded fire is one of the simplest effective improvements that can be made. Tests carried out on the simple stove shown gave efficiencies of 22-25% at 3-4kW in Sri Lanka and Nepal (Stewart 1981, 1983).
Grates bring in air directly underneath the wood and charcoal and promote better mixing of fuel gases and air. The optimum percentage of grate opening depends on the area of secondary air holes and the size of the doorway.
Cylindrical or cone-shaped fireboxes are used for stoves with a grate. The cone shape design helps keep the grate covered with charcoal.
When the firebox height is too small for the fire, combustion will be suppressed and there will he considerable smoke and charcoal build-up. When the firebox height is too large, combustion will he more complete but heat transfer will he less effective.
The Noflie stoves are made in three sizes (to suit three pot sizes) and according to two different designs - the newer cylindrical design is cheaper to make. They are made from oil barrel steel and the medium size is 33cm wide x 27cm high and weighs 3.7kg. There is a firebox, grate and pot supports welded onto an outer shell. The firebox entrance has a door and there are two handles. The medium-size stoves cost $6 for the straight-walled design and $7.50 for the cone-shaped type.
History and Field Experience
Initial design and test work was carried out in The Gambia by the Department of Community Development and ITDG (Joseph and Loose, 1983). It was then tested and optimized in the UK. The stove designs were taken to The Gambia where they were further modified by ITDG and the local stoves technical team, so that they could burn a mix of briquettes and wood and be more easily made by the local craftsmen. In the field tests that followed thorough laboratory testing, the new users were initially sceptical about the ability of such a small stove to cook quickly, but were soon impressed by the speed, fuel efficiency and relative smokelessness. The stove was given its name - the 'Fourno Noflie' - which literally means 'a stove where you can be at ease' or 'a stove that is easy and simple to operate'. After a positive response to the first 50 stoves in use, 4()0 more were built for use in an expanded field test early in 1984. Some 2,000-3,000 stoves were built in extended field trials in Banjul, Greater Banjul and smaller towns.
Construction, Installation and Maintenance
The steel pieces for the stove are cut out of old oil barrels using templates and then welded together. The stoves are portable, but when used on sand it is important to check that the primary air holes and grate do not become clogged. Repairs to sections that rust away can be made by local metal workers.
Use of the Stove
The stove can burn briquettes, briquettes and wood, or wood alone. The door is made to allow just three pieces of chopped wood to fit inside. The power output is controlled by the amount of fuel in the firebox. The door can be shut to improve the burning of the briquettes or small pieces of wood.