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Bioenery and Timber

Ever since humans lit their first camp-fires, wood has been a major source of bioenergy. Indeed, even today it constitutes 38% of home heating in New Zealand.

Wood for Heating

A good woodburner can produce some 10-20 kW of heat (the output of an electric heater may be 2 KW, and even a heat-pump may only produce 6 kW) and can be up to 85% efficient, as opposed to open fires which lose 80-90% of their energy potential up the chimney.

A new and fast-expanding trend in home heating involves wood-pellet burners. Pellets are made from compressed sawdust and shavings, and have a number of benefits including continuous and adjustable heat, reduced maintenance and reduced air pollution.

There is a pilot programme to replace coal-using boilers in schools with pellets, and this could soon be extended to hospitals and hotels, and to industries such as dairy factories, cement works, meat works, and food processing plants.

Environmental issues are important. Biofuels are deemed to be carbon-neutral, in that their emissions can be seen as recycled atmospheric carbon rather than new additions. Wood has very little ash (about 1%) but, unlike ash from coal, this is a useful fertiliser. There is very little smoke from a good wood-burner or pellet-burner, and emissions from wood – unlike from coal – contain almost no sulphur.

Most of the industrial use of wood residues is by the timber processing sector, which is already 66% self-sufficient in energy. After the logs have been removed from landings (ie harvesting sites), considerable residue remains. Only a quarter of this is used, and it would benefit the forest grower if even more was taken away. As well as this resource potentially available on the landings, there is also the possibility of extracting residues from the forest cutover (ie away from the landings and around the tree stumps).

Wood for Liquid Fuels

There are exciting possibilities in the energy potential of wood apart from its direct use for heating. Wood can be made to generate electricity or, more interestingly, it can be converted to liquid fuels. These are second-generation biofuels. The first-generation of biofuel was rightly criticised because it took good land out of food production, or else resulted in the destruction of native tropical forests, but with our own wood-based biofuels New Zealand could be self-sufficient without harming the environment or affecting food supplies.

The Crown Research Institute, Scion, is currently exploring ethanol production from wood and estimates that a harvest of only 125,000 ha per year would meet all New Zealand’s requirements for both heat and transport fuels. Assuming a 30-year rotation this implies a doubling of our existing forest area.

But ethanol production is only one of the ways to convert wood: also being investigated elsewhere are technologies for gasification, pyrolysis and even for dissolving the wood under high temperatures and pressures.