Mar 042009

Last night I attended the most recent of the public lectures in the Australian Academy of Science’s series “Australia’s Renewable Energy Future”. Dr Steve Schuck, Manager of Bioenergy Australia, spoke about biomass as a renewable energy source. His presentation slides are available, and are worth looking at if you want more details.

Bioenergy is chemical energy stored in biological systems. an obvious example is wood, which can be burned for heat (for example). Burning biomass like this does release carbon into the atmosphere, but it is carbon which has only recenly been captured from the atmosphere through photosynthesis. This is fundamentally different from fossil fuels, which release carbon that has been out of circulation in the biosphere for a long time.

Bioenergy makes up about 11% of the global energy consumption. Systems range from internal wood combusting fireplaces used for heating individual homes, all the way to massive powerstations that supply electricity and heat to cities. One of the largest biomass-capable powerstations in the world is the Avedøre-2 power plant in Copenhagen, which is able to “supply district heat to about 180,000 homes and provide electricity consumption for 800,000 households.”

Power stations like this are often designed to burn fuels like wood pellets (compacted sawmill waste), as well as straw and other dry bio waste forms. In fact, some of these power stations can operate on 100% coal, 100% biomass, or any mix in between! Burning dry biomass in these sort of power plants makes for very cheap clean energy, because the infrastructure essentially exists already.

It is also possible to produce liquid and gas fuels directly from biomass. Ethanol and biodiesel are well-known examples of this. Australia produces about 170 MW of landfill gas energy each year, which is simply harvesting the gasses given off by domestic waste in landfills. This gas may be used to produce electricity, but it can be used directly; 15 000 vehicles run on biogas in Sweden – including busses and even a train!

I’m particularly excited by projects such as the Camillia anaerobic digester, a large commercial venture in Sydney. It is situated close to the Sydney fresh food markets, and is designed to recover energy and fertiliser from 51,000 tonnes/year of food wastes from supermarkets, restaurants and food industries. The facility generates approximately 3.0 MW of electrical energy while utilising the waste heat to produce high quality organic fertiliser.

This fertiliser is a good illustration that bioenergy is not just an energy system; the waste from using “waste” to generate energy is rarely useless. Burning wood produces much less ash than burning coal, and wood ash is non-toxic (unlike coal). Ash from wood furnaces can be used to enrich soils, and can even be sprayed back into the forests that supply the original fuel.

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