Southern Landfill
Electricity Generation Plant
To read the press release about this project click here.
Converting landfill gas to energy involves the use of extracted landfill gas as the fuel source for an internal combustion engine coupled to an electricity generator. Landfill gas is produced as a result of microbial action on organic material in the waste (biodegradation) and to a far lesser extent from chemical and physical processes acting on non-organic material.
The Southern Landfill gas collection and extraction system was originally installed in 1995, by Nova Gas in conjunction with Wellington City Council, and is being expanded as Stage 3 of the landfill develops. The system involves linked vertical and horizontal gas collection wells sunk through the landfill area with blowers connected to the collection system to extract the gas out of the landfill. A membrane cap prevents the escape of this odourous and environmentally harmful gas from the landfill.
Currently there is a sufficient supply of landfill gas for Bay of Plenty Energy to run a generator that will produce 1,000 kW of electricity that is fed into the local distribution network. The electricity generated is sufficient to meet the electricity demands of approximately 1000 homes.
Depending on future waste volumes received, and the content of the waste, there may be sufficient gas to enable installation of additional generation units in years to come.
Key Facts:
Landfill Gas: Typically consists of methane (60%), carbon dioxide (35%), nitrogen (3%), oxygen (0.2 %) and other trace elements.
Methane is a greenhouse gas 20 times more harmful (by volume) to the environment than carbon dioxide.
Landfill gas volumes: Currently, approximately 4.8 million cubic metres of landfill gas is collected annually and destroyed. Landfill gas volumes are expected to increase.
Generator rated capacity: 1,065 kW
Generation volumes: 8 GWh of electricity annually - enough to meet the demands of around 1000 average households.
Converting landfill gas to electricity
Landfill gas collection system: Nova Energy, Wellington's gas specialists, own and operate the landfill gas extraction and collection system in conjunction with Wellington City Council. The system captures odourous and environmentally harmful landfill gas before it escapes to the atmosphere. The gas is carried via a pipeline to the electricity generation plant.
Electricity generation plant: Owned and operated by Bay of Plenty Energy, the generation plant utilises landfill gas to produce electricity. Methane, a significant greenhouse gas and the predominant component of landfill gas, and other odourous components are destroyed during the process.
- Landfill - Layers of waste break down and release landfill gas.
- Membrane cap - Prevents the release of odourous and environmentally harmful landfill gas from the surface of the landfill.
- Gas well and collection system - Vertical and horizontal gas wells installed progressively in the landfill are used to collect gases produced from the decomposing waste.
- Extraction blower - The blower connected to the gas collection system is used to extract landfill gas by creating negative pressure in the landfill around the gas wells.
- Generation plant - Internal gas combustion engine coupled to an electricity generation unit produces electricity from the landfill gas.
- Gas flare - Used to combust landfill gas when the generation plant is taken out of service or following an increase in landfill gas production.
- Electrical connection - Electricity produced is supplied to the local power network.
