/ Cleaner cookstoves help save lives, put more money in people’s pockets and protect precious forests
Cooking shouldn’t kill. But 3 billion people cook on open fires and
dirty cookstoves that use charcoal, wood or animal dung, exposing
them to toxic smoke. Cleverly designed cleaner cookstoves
improve people’s health by emitting less smoke. By using less fuel,
they ease the burden of the women and girls who gather wood,
also helping protect forests and cut greenhouse gas emissions.
Open fires are smoky and inefficient: the wood does not burn completely, and much of the heat produced does not reach the food. A simple stove cuts heat losses by burning the wood in an enclosed chamber and directing the hot combustion gases to the cooking pots, and sometimes uses a chimney to take smoke away from the cook. However, many stoves still burn fuel inefficiently and produce smoke, and much of the heat is lost because of poor insulation.
Combustion or burning of wood is an exothermic (heat-releasing) chemical reaction between organic compounds in the wood and oxygen in the air. As the wood heats up it releases a mixture of volatile vapours and gases, leaving behind a solid, carbon-rich char. For efficient burning, enough air must continue to reach both the gas, which contain about three quarters of the energy content of the wood, and the char.
Smoke is mostly the result of incomplete combustion. It contains unburned gases including carbon monoxide, methane, aldehydes and organic acids, many of which are harmful. It also contains small particles or ‘particulates’ of both organic material (soot) and inorganic material (ash).
Many people in developing countries, particularly in towns and cities, cook on charcoal rather than wood. Charcoal weighs less for a given heat output, so is easier to transport and store and it burns with a very hot flame. Cooking with charcoal increases the overall use of wood, because charcoal production usually wastes more than two thirds of the energy in the wood.
Different designs of stoves and construction materials are popular in different parts of the world, all of which can be improved. The main ways of doing so are:
Improved burning of both the solid fuel and the hot gases, so that less fuel is needed and less smoke is produced. The best way to improve burning is to raise the wood onto a grate so that air can flow underneath, and design the combustion chamber carefully so that enough air reaches all the burning areas
Better insulation of the combustion chamber, and direction of hot gases around the cooking pot or hotplate, so as not to waste heat
Removal of any remaining smoke from the kitchen area to reduce health effects. A simple chimney on a well-designed stove can both remove smoke from the home and also improve combustion by increasing air flow through the stove
Advanced stoves, called semi-gasifiers, separate the combustion of solid fuel and gases, each with its own air supply. The latest designs control air flow with a small fan, which can improve efficiency. Their main benefit is to significantly reduce smoke production: there is growing international concern about the health impacts of cooking smoke.
How different types of improved stoves work and are used
An improved stove needs to be technically well-designed, affordable and durable. But above all the cook has to like it and want to use it. Neither the cook nor the environment benefit if the supposedly ‘improved’ stove is not used, and there have been many examples of failed stove programmes. Successful NGO and business-led programmes to develop and introduce improved stoves work closely with potential users to find out what they really want.
Improved stand-up stoves
Women in Honduras usually cook standing up indoors, using a fire or simple block stove on a raised platform. Ashden Award winners AHDESA and TWP worked with women in Tegucigalpa to develop the Justa stove. This is built on a raised platform in the kitchen, using bricks. It has a steel hotplate at waist height where tortillas can be cooked and pots can simmer at the same time. The combustion chamber uses the ‘Rocket’ design, in which the wood is placed on a grate in a horizontal chamber.