Traditional Cooking Stoves: an overview of designs for improving them
1. A large number of people in the world still use wood as the main source of heat for cooking. Many of these people use ‘three stone’ open fires, and although these have the benefit of being very cheap to make, they are inefficient to use. In addition, Q1 cooking over an open fire exposes people to wood smoke, which irritates their eyes and lungs and makes them susceptible to respiratory diseases. There is also a risk of burns, as the fire has no protection around it. Finally, using wood for cooking contributes to deforestation, in particular around cities and towns, where the concentrated use of wood puts pressure on the surrounding land.
2. Improvements in stove design can bring a number of advantages. Improved stoves allow fuel to burn more efficiently, so getting more heat to the cooking pots, and reducing the amount of wood required to cook a meal. Typically they use between 25% and 60% less wood than open fires. Increased combustion also reduces the amount of smoke that is produced. Q2 Q8 People save time as they need to collect less firewood – a task which usually falls to women and children. The extra time allows women to take up other activities, including earning extra money, and allows children more time for education. Also, family members are reported to be more willing to help with the cooking once they have a smoke-free place in which to work.
3. There are various levels of improvement which can be made. Efficient wood combustion depends on an adequate supply of air reaching all the areas where the wood is burning. Q3 Hot gases tend to rise, creating a draught that draws in more air, so adding a Q12 chimney improves this draught. A Q13 grate to supply air under the fuel is a second improvement. The next step separates the combustion process from heat transfer to the cooking pots. For example, the ‘Rocket’ stove concept uses a vertical combustion chamber, where the wood burns in air, with a horizontal air and fuel inlet at the bottom. Q9 At the top of the combustion chamber, the hot gases are forced to flow through a narrow gap around the cooking pot, so that heat is transferred very efficiently to the pot.
The next improvement is to make sure that the hot gases are burned completely. This is achieved by enlarging the combustion chamber, and introducing a secondary supply of air to allow full combustion.
4. Depending on what they are made from, Q4 stoves can be more or less expensive to make. Steel or cast iron allows accurate manufacture of stove parts, but is expensive. Fired clay parts can be expensive, if they need to be made by trained potters, but are usually cheaper than steel. Mud is traditional for some stoves, but must be formed of the right mix of materials. Concrete can also be used for some stove parts as it can be cast into pre-determined shapes, but it is more expensive than mud. Natural waste, such as rice husk or wood ash, can be used to insulate the stoves and reduce heat loss.
5. Q10 Some stove designs use charcoal as their main fuel rather than wood. Q5 While charcoal is cleaner to burn than wood, and easier to transport and store, about 75% of the original energy in the wood is lost when charcoal is made. Other stoves use agricultural residues (nut shells, straw) as a fuel. Some stoves can use these in their loose form, but most rely on briquetting – compression of the loose material into denser blocks. Charcoal made from agricultural residues can also be bound into briquettes if a small proportion of clay is used as a binder.
6. Programmes to introduce improved stoves are rarely successful unless they fit with the preferred local cooking practices. For example, in Latin America, many people prefer a Lorena or block style wood-stove as they prefer to cook standing up. Q6 This type of stove is made of a solid block of material, with combustion and heat transfer chambers built into it, so the cooking pots and cooking plate are at waist height. In India, many people squat to cook, so the chula style is preferred. This is also a block style stove, but the cooking level is below knee height.
In parts of Africa, people tend to cook outside so prefer to use a jiko, a portable stove without a chimney. Traditionally, jikos use charcoal, but some can also burn wood. The combustion chamber has a pot support, so the pot can be placed directly above the combustion gases. In Asia, similar stoves are called bucket stoves. If such a stove is used indoors, smoke pollution can be reduced by placing it under a hood connected to a chimney.
7. There are over one hundred known organisations involved in the development and extension of improved stoves, in many different countries. However, since many stove programmes are in the informal sector, there is no central record of how many improved stoves have been constructed altogether. Q7 Some programmes have installed many thousands of stoves, while others are very local. Some operate subsidy schemes that allow people to afford improved stoves. Alternatively, programmes may train people to make their own stoves from local materials. Q11 The designs may not be quite as efficient as stoves made by technicians, but people can use and maintain their own stoves without relying too much on outside help. Finally, many stove programmes are part of wider rural development projects, offering improvements in health and economic status for rural people.