Saturday, July 9, 2011

Rocket stoves: a better burn

UPDATE: This has turned out to be one of the more popular posts on my blog. Since I posted it, I've found that the most innovative rocket stoves on the market are sold by Biolite, which can not only cook your dinner but charge your mobile phone as well, using minimal fuel. New Yorkers who had them found biolites especially handy when the power was knocked out during Superstorm Sandy.

Last night I made a pot of tea for my guests. To boil the water, I burned a handful of twigs and small sticks I gathered from under the trees at the back of my small urban backyard. It took less than ten minutes to bring the water to a rolling boil.

Something might strike you as odd in the preceding paragraph (I mean, besides the fact that I would be using a fire to boil water for guests - like most people, I do have a kettle at my house). The odd thing is how little fuel and how little time I needed to boil enough water for four cups of tea. If you've ever tried to boil a pot of water over a campfire, you'll know you can't do it with kindling alone, and certainly not so quickly. I was able to do so using my new toy, a rocket stove.

The rocket stove uses a simple design principle to channel large amounts of heat from small amounts of fuel. You take a vertical, metal cylinder (like a piece of stove pipe or an empty paint can with the lid off) and insulate it (e.g. by surrounding it with bricks, or a clay-straw mix, or even another, larger diameter steel tube with the gap between them sealed to make an air chamber). The vertical tube is the fire chamber. You then make a vertical hole into the side of the fire chamber and insert another metal tube (like a soup can with the end cut off). You need to divide this horizontal tube into an upper and lower half, such as by making slits in the side and inserting a sardine tin lid. The top half is the fuel chute, the lower half the air intake.

Voila, you've got a rocket stove. Light a piece of paper, drop it down the top of the fire chamber, and stick some dried grass or twigs into the fuel chute. You'll quickly see flames come shooting out the top of the fire chamber. Set a pot on top of the cans and off you go (first put a metal fork or something across the top so that the pot doesn't smother the fire). Insert more stick and grass as needed. Rocket stoves come in various shapes and sizes; click here to see more. All of them produce the same effect: the fuel burns hot and efficiently, and the heat is channeled directly to the base of the pot or pan. Compare this with campfire cooking, where you need to burn several pieces of firewood and get a good bed of coals before you're ready to cook.

Rocket stoves are spreading across developing countries, especially in dryland regions where wood fuel is scarce. The reality is that the world's poorest typically can not afford electricity or fossil fuels, and so they must rely on biomass-based fuels (i.e. wood, charcoal, dried animal dung) for cooking and heating. This places tremendous pressure on forests in many countries. It also places tremendous pressure on families to gather fuel, especially women, to whom this task most often falls. As easily accessible biomass fuel sources become scarcer around settlements, women must travel ever farther and be away from home for longer, which consumes time that could be better spent doing other tasks. In some situations, such as for women living in refugee camps, traveling to gather fuel puts their personal security at risk. By adopting a simple and easily made cooking implement like the rocket stove that uses so little fuel, the lives of the poorest of the poor are made a little less difficult.

Here in North America, not many people have heard about rocket stoves, and fewer still own one. Those who do consist primarily of campers and survivalists. You'll find many internet testimonials to rocket stoves along the lines of, "when the s*** hits the fan, you'll want to own this stove". I'm not a survivalist, and if it really did hit the fan, I probably wouldn't last too long. But I suppose I would last longer than before I bought the stove, because the half-dozen Manitoba maples at the back of my yard provide enough fallen twigs and branches to keep that stove cooking meals on an indefinite basis. In case you're interested, here's the one I bought, and I assure you, it works exactly as advertised.

Canadians don't worry much about where our cooking fuel comes from, we flick a switch or push a button to start our electric or natural gas stoves/ovens, slow cookers, kettles and the like. When we do cook outside, it's most often on a propane grill (a relatively small % of the population uses charcoal grills). In other words, 99% of the meals cooked in Canada are powered by fossil fuels or electricity (here in Ontario, more than half our electricity is generated by nuclear and coal, not exactly the most environmentally benign sources).

In a country where there's so much biomass, moving surface water, wind and sunshine, it's a shame we rely so heavily on fossil and nuclear to make a simple cup of tea. In Ontario and other provinces, there are initiatives to increase the amount of energy supplied to the electrical grid by alternative sources. There are a variety of challenges, from the up-front costs to the need to persuade an odd but vocal portion of the population who try to block wind turbine installations because they are unsightly.* In the meantime, energy demands keep going up, up, up.

Don't get me wrong, I'm not now about to conclude that every Canadian household should get or make a rocket stove and cook all its meals on it (although you'd have a lot of fun if you did). The rocket stove is simply a reminder of how an ounce of innovation is worth a pound of fuel. Through smart design, the amount of energy needed to cook a meal is shrunk to a tiny fraction of other options, and the cost of cooking is shrunk to virtually zero in dollar terms and environmental terms. How many other smart, sustainable technologies are we not adopting as we cling to old, wasteful habits?

*For the life of me, I've never understood this. I've never met anyone who would say the following, much more ubiquitous examples of built infrastructure to be attractive: telephone poles, traffic lights, highway billboards, high-voltage transmission towers, apartment blocks, divided highways, off-ramps, fast-food outlets, strip malls, warehouses... And yet people get worked up about the sight of a wind turbine on the horizon? It's beyond me.


Anonymous said...

Excellent and very useful, I'm going to build one. However, I won't use soup-cans or paint-cans because they can both produce very hazardous fumes, including dioxin, the most toxic substance known to date which comes from burning plastics, including the plastics that line canned food today and paint cans. The heat from combustion will leave those in the environment and/or the people nearby. An old paint can that has been used is also not a good idea for a whole host of other noxious reasons. I might suggest recycling those tins and instead getting some stove-pipe or even some cast-off duct material from a contractor (it is also very cheap at home-depot). That stuff is not coated and is made of galvanized metal and shouldn't produce noxious fumes which would ruin an otherwise good tea-party. Cheers. Mike

Robert McLeman said...

You're right, an insulated piece of L-shaped stove pipe would be a much better way to go. It seems to me a rocket stove-type design would be ideal for people who like to tap a few maple trees on their property to make syrup.

NM said...

It would seem this design has inspired a method of efficient home heating:

Slow combustion heaters said...

Sunshine is a major source of energy.The need of time is to make certain arrangements to avail this source of energy.

William35453 said...

Heating galvanized metal gives off zinc fumes that cause neurological damage and the " zinc shakes ", unless the metal is first burned in a fire outside and downwind to drive the zinc off.

William35453 said...

Heating galvanized metal gives off zinc fumes that cause neurological damage and the " zinc shakes ", unless the metal is first burned in a fire outside and downwind to drive the zinc off.