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Wood Stoves & Global Warming

Danny | 19.11.2007 16:06 | Ecology | Technology

Most activists have sat around a camp fire at some point, or heated a kettle on a gas camp stove, or lit a burner. This is damaging our health and our environment. Wood smoke stays chemically active in the body 40 times longer than tobacco, and solid fuel particulates kill over 2 million people each year in the developing world. Any stove uses less fuel and produces less pollutants for the same amount of energy compared to an open fire. A properly designed stove uses up to 80 less fuel and produces a fraction of the pollutants.

Global Waming Impact by Stove Design

Fan Stove Operation

Global Warming by Stove-type

Fan Stove principle

Two months ago the Aprovecho Research Center released "A Laboratory Comparison of the Global Warming Potential of Six Categories of Biomass Cooking Stoves". [1] A close second in the report is a rocket stove with a skirt ( the skirt significantly improves efficiency of rocket stoves). There was a clear winner, a fan stove which exemplifies the perfect hybrid of lo-tech and hi-tech. It beat the rocket stove by better burning off the secondary, more potent greenhouse gases produced when burning wood

Fan stoves drive air up through the combustion stage, but also drive air heated by the stove back into the stove as air jets which combust the various gases that normally escape from an open wood fire. Even small stoves can reach temperatures in excess of 1000 celsius. These various gases are all more potent greenhouse gases than carbon dioxide, and only the fan stoves combust them. The stove that popularised fan stoves was the small Sierra Zip camping stove which is no longer produced. It received regularly excellent reviews as a camping stove capable of gas stove temperatures without the need to carry fuel - even twigs and leaves could fuel it. A slightly larger camping fan stove is the WoodGas burner, but it still fits in a backpack [2]. The small fan at the base of the stove can be powered by a battery or a solar cell. The fan stove used in the global warming report is a prototype from Philips, a slightly larger rip-off of the Wood Gas stove [3]. It does have one rather amazing new feature though, it has a thermoelectric generator using the heat from the burning wood to generate electricity for the fan - and this power can also feed LED lighting, radios, recharge batteries etc.

A thermoelectric generator produces an electric current from heat differences, like an electronic turbine but without moving parts. It is a solid state array of N and P type semiconductor material such as bismuth telluride. It is quite inefficent but placing one next to any heat source that was being fully utilised, such as built into the chimney of a stove, provides electrical power where none exists. You don't need a special stove to produce electricity, although these devices are new to the market and you may need to build your own kit. [4]

After playing around with different designs of stove, I know it is possible to mix and match the design principles - for instance a 'rocket-fan stove' if you will. I can't make a better stove than the Philips prototype yet but it isn't avilable for purchase either. I did learn one tip for supercharging the fan stoves. If you wrap spirals of 'fire rope' around the inner container then you can channel, slow down the air destined for the combustion zone. This makes the air hotter at that stage and greatly increases combustion stage temperature, thus reducing pollutants.

[1]