Landfill Gas to Power

Pioneers in Converting Landfill Methane to Electricity

EnviroWaste was the first operator in New Zealand to generate electricity from methane gas produced by waste in landfills. The landfill gas to energy (LFGTE) plants operated by EnviroWaste at Hampton Downs, Greenmount and Rosedale landfills in Auckland produce a peak of 8 megawatts of electricity, which is enough to supply up to 6,400 households.

Landfills produce large quantities of gas resulting from the natural decomposition of highly compacted refuse. The gas requires control and management for safety and environmental reasons and is extracted and flared on an ongoing basis.

At the Greenmount and Rosedale sites, the gas quantities and qualities proved to be sufficient to justify commercial utilisation, as opposed to simply being flared. Gas to energy generation plants were commissioned at both sites in 1992, employing state of the art design and construction technologies in what was the first venture of this type in New Zealand.

The project began as an unincorporated joint venture in 1990 between Northern Disposal Systems and the Auckland Electric Power Board to generate electricity. This is now a venture between EnviroWaste and Mighty River Power. Under the terms of the joint venture, EnviroWaste collects the gas, cleans and dries it and pipes it to generating plant on each site operated by Mighty River Power. Electricity generated at these sites is on-sold for distribution via the Vector network.

Greenmount and Rosedale between them employ nine gas engines which consume up to 7,000 cubic metres per hour of gas to produce a peak of 10MW of electricity. At peak production the combined sites produce enough electricity to supply almost 10,000 homes.

The production of gas within landfills is typically increases as refuse is placed and then peaks shortly after closure. This is followed by a slow decline over subsequent years. The commercial lifetime of a landfill gas field is typically 10 to 20 years from closure.

Studies at the Greenmount and Rosedale sites suggests they will continue to produce a commercial yield until at least 2010. Landfill gas extraction will continue at these sites beyond this time for environmental and safety reasons, however much of the utilisation plant and equipment will be able to be relocated to newer landfills if required.

EnviroWaste is proud of the role we played in developing innovative gas to energy technology. A new LFGTE plant at Hampton Downs landfill in Waikato will be up and running in 2009, and will generate enough electricity to supply all of the site's needs, as well as supply surplus energy into the national grid.