I hope to provide 'food for thought' as much as supporting firewood and condemning the consumption of fossil fuels.
One tonne of air-seasoned wood releases 16 gigajoules (GJ) of heat when burned; see Wikipedia. At the time of writing a tonne of firewood sold for around Aud$160 in Adelaide, South Australia. For comparitive energy costs see Energy cost calculator.
BackgroundUntil the Industrial Revolution firewood was mankind's main source of heat. It was also used for the production of charcoal which then was used to smelt metallic ores and to work iron and steel.
Fossil fuels can be obtained in greater quantities than firewood, and petroleum, being a liquid, is more convenient to use as a fuel. However, there are three great problems associated with burning fossil fuels:
Modern stoves are designed to produce little smoke if used properly. Some stoves have a calalytic 'after-burner', a ceramic honeycomb in which smoke and other particles are consumed.
It is at least theoretically possible to efficiently burn wood in large
facilities that could then provide heat to whole communities via piped
hot water; so minimizing smoke and avoiding the consumption of fossil fuels
and the net production of greenhouse carbon-dioxide.
Wood contains minerals such as phosphorus that are valuable plant nutrients. Phosphorus is already being removed from rural land and dumped in city sewers via cropping; this removal of nutrients from soil is unsustainable.
While carbon-dioxide is also produced by burning wood, it is reabsorbed by growing the trees that produce replacement wood. So long as the net amount of wood in the world remains constant, no net carbon-dioxide is released into the atmosphere by burning firewood.
However, if the firewood is not burned completely, if there is insufficient flow of air in the stove where the wood is being burned, or if the wood is not sufficiently dried before burning, gasses such as methane can be generated.
For more information on this problem see Australian wood heaters currently increase global warming and health costs, an article in ScienceDirect written by Dorothy L. Robinson.
A significant factor is that where home heating is most needed - at high latitudes - people are wealthier and are generally able to use petroleum for heating. Where people are forced to gather and use firewood by poverty - in the third world - there is less need for home heating because most third world nations are in the tropics.
To change from petroleum heating to wood heating in rich nations would
require a huge consumption of firewood.
overpopulation, and production of greenhouse gas and smoke.
The collection of firewood, reducing it to a convenient size for consumption in the home, and finally carting it from where it is collected to where it can be burned, involve considerable exercise.
By comparison, there is little or no exercise in the use of electricity, gas or liquid fuel for heating.
RocketFew people in Australia (and, I suspect, the developed world generally) use firewood for water heating. A good wood-fired water-heater is available from 'The Center for Appropriate Technology' in Alice Springs, Australia. Loosely called 'The Rocket' for its appearance, it is made out of a recycled 80kg liquefied gas cylinder. It heats enough water for two generous showers in 30 to 40 minutes (starting from water at about 5 degrees Celsius).
If you were to get the water temperature up to around boiling point I would think there would be enough for four generous showers in winter. Of course if you keep the fire going you could have a shower about every 15 minutes. About 7kg of firewood is sufficient to heat the water to showering temperature in winter.
The cost, as of July 2002, is about $550 plus whatever it costs you to arrange transport.
I later placed a steel drum over the rocket and stuffed non-flammable insulation between the water heater and the drum.
Of course a 200L drum is not built to take much internal pressure, so care must be taken to not burst it. A drum bursting due to the water boiling inside it would be very dangerous.
This type of water heater has been used in the station (outback) country of
Australia for many years. The fire must be kept going for about
two hours to heat the water.
Wood cooking stoves do often seem to be combined with water heating.
I have read, and can believe from my own experience, that about 0.2 ha of land, 0.4 ha at a maximum, is sufficient to grow enough trees to supply a household with firewood. This assumes that firewood is the main source of space and water heating. It is based on a 500 mm annual rainfall and 25 years experience with growing native trees in Australia and the use of firewood.
A litre of methanol, when burned, yields about 45% as much energy as a litre of petroleum, and ethanol yields about 68% as much energy as petroleum; see Energy units.
Tore Högnäs wrote a page on the efficient production of liquid fuel from wood, it was, but is no longer, available from www.confor.org.uk/timber_transport/.
Below is a quote from this page:
"The production of wood liquid fuel is based on rapid pyrolysis. Crushed wood is heated in an airborne bed reactor to 500-600 ºC for some seconds, which leads to a separation of gas, liquid and solid material. The gas is liquefied by rapid cooling. The process is efficient: 60-70 % of the dry weight of the wood is transformed into liquid. The product is a liquid and not tar since it contents 20 % water. The energy content for wood liquid fuel is about half of that for normal mineral oil. The product cannot be mixed with mineral oil.
Is there a lot of difference between growing and burning firewood and growing vegetables and fruit, or for that matter cereals and other crops? The carbon in all comes from and goes back into the atmosphere.
There are environmental problems in all technologies (I’m a strong supporter of wind power but I have to accept that the glass reinforced blades are very difficult to recycle.)
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