Energy production

Domestic firewood use

Public opinion is that some species provide substantially better firewood than do other species. In fact all hardwoods and softwoods provide similar amounts of heat in the oven-dry condition, with hardwoods 19 MJ/kg and softwoods 21 MJ/kg. The higher value for softwoods is because of the higher resin content. Note: hardwoods are flowering plants or angiosperms, and softwoods are cone-bearing plants or conifers.

The important factor is the moisture content of the wood. Oven-dry, as referred to above, means that all moisture has been removed from the wood. In practice, air-dry is the usual situation. If actual moisture content is higher than air-dry moisture content, then heat is wasted in driving off water.

For example, green jarrah wood generally has a moisture content of about 80 per cent, which reduces available heat to 9.5 MJ/kg. Further information is given in a Technical Advisory Note.

Charcoal production

In Western Australia Simcoa Operations Pty Ltd has been producing high quality charcoal for silicon refining at its Kemerton plant. Jarrah is the major species used because it gives an ash-free product. The plant takes about 65 000 tonnes of residue logs (either logs from the forest floor, logs that are identified as below sawlog quality after trees are felled, or thinnings) and a similar quantity of sawmill dockings each year. The quality of charcoal from other species is inferior to jarrah charcoal.

Note: there is an incorrect public perception that good quality logs are used for charcoal production. At a 2000 auction held at Simcoa, sawmillers were prepared to bid for less than 10 per cent of the logs because of the low quality. Craftsmen can inspect the log stockpile at any time and buy logs from Simcoa for personal use.

Bioenergy

With increasing concern about the generation of greenhouse gases when fossil fuels are used for energy production, there is increasing interest in growing trees for bioenergy production. In Western Australia, this has particular application for towns currently outside the Western Power grid and relying on diesel generators for energy production.

The heat available from hardwoods, e.g. eucalypts, is 19 MJ/kg of completely dry wood. Heat generated is used to power gas turbines that generate electricity. The process is very clean in comparison to burning fossil fuels.