Human settlements

Renewable energy

Biomass 03: A new source of energy emerges from a prickly problem

Renewable Energy Commercialisation in Australia, Australian Greenhouse Office, 2003
NOTE: The status of these projects will have changed since the time of publication, and project contacts may also have changed.

A feasibility study has identified potential for a sustainable supply of renewable energy for remote areas of northern Australia by converting chipped mimosa weed using an advanced hot briquetting technique.

Biomass Energy Services and Technology Pty Ltd (BEST) and the Northern Territory Department of Primary Industries and Fisheries received a $200,000 grant under the Renewable Energy Industry Program to evaluate the economic and technical feasibility of converting the environmentally damaging Mimosa pigra (prickly mimosa) into renewable energy.

The consortium set out to establish whether the mimosa could be used to simultaneously provide cheaper electricity in remote areas (replacing reliance on diesel fuel), provide weed control and reduce the emission of greenhouse gases. The consortium also saw the prospect for the development of a significant export industry for the technologies.

Significant areas of northern Australian grazing country are now at peril from the spread of imported noxious weeds. The Northern Territory, Queensland and New South Wales governments currently spend $5 million per annum on weed control.

In the Northern Territory prickly mimosa is a serious problem forming dense, inaccessible and unproductive shrubland that has a serious impact on river systems and grassland flood plains. Substantial resources are required to prevent it from spreading onto surrounding wetlands, including the world heritage listed Kakadu National Park. Control of the mimosa has involved spraying to defoliate it and then 'rolling over' by pulling it with a chain between several bulldozers. The resultant material is then dried and set on fire, which produces carbon dioxide.

Prickly mimosa

The two-year feasibility study investigated both a sustainable location and development of a commercially viable technology. The dense infestation of the Northern Territory's Adelaide River region indicates that there is a sufficient mass of mimosa in that area to fuel a biomass electricity generation plant.

For the stage of the study following the bulldozing of the mimosa, a local landholder collected and chipped a tonne of the material, which was then sent to BEST's facility near Gosford in New South Wales. There it was hammer milled, partially pyrolysed and formed into briquettes using an advanced hot briquetting technique.

The BEST research focused on the hot briquetting technology to create durable briquettes that could be used in a suitable biomass gasifier to generate good-quality producer gas. BEST carried out trials using its downdraft gasifier to prove that the briquettes would make a convenient fuel source for gasification and the gas generated would be suitable for power generation.

The Northern Territory Power and Water Corporation (PAWC) could use the combustible gas produced from the mimosa in a gas engine or gas turbine to generate electricity. Suitable biomass sources like mimosa, as a form of stored solar energy, can provide an acceptable energy source for utilities.

The successful completion of this project has been instrumental in PAWC's plans to construct a 350kW prototype biomass energy generation system. On average the prototype unit would produce around 10MWh per day. In CO2 terms this would amount to a daily expenditure saving of around six tonnes in addition to eliminating the greenhouse emissions that are currently produced from burning the mimosa.

In addition to the prospects for sustainable energy generation, the feasibility study also offers potential breakthrough technology for dealing with other serious noxious weed infestations that are generating major problems for large areas of the pastoral industry in western Queensland and northern New South Wales. The same approach offers the prospect for exporting the technology to parts of Asia that are also experiencing significant problems with prickly mimosa.

For more information please contact

Dr Stephen Joseph
Biomass Energy Services and Technology Pty Ltd
56 Gindurra Road
Somersby NSW 2250
Tel (02) 4340 4911
Fax (02) 4340 4878

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