Getting power from refuse

Landfill gas generation is a growing industry in New Zealand among small generators. One tonne of household rubbish can produce up to 200 cubic metres of gas made up of up to 60 percent of productive methane for running generators.

Despite the fact this sector gets no incentive or encouragement from the Government, New Zealand’s landfills are already collectively producing over 20MW of electricity. Landfill gas generation will increase as new projects come online. One of the newer projects is the Hampton Downs Landfill south of Auckland operated by EnviroWaste Services.

Built on 386 hectares of ex-farmland, the capacity of the Hampton Downs Landfill is 30 million cubic metres and it is consented for 25 years, with 21 years remaining.

About one million tonnes of refuse from the Auckland and Hamilton areas was received into the site before there was sufficient gas for generation. The gas was flared before two Waukesha APG1000 units, each generating 1000kW, were installed at the site. The engines are made in Wisconsin, USA and distributed in New Zealand by Entec Services.  

With a 48 litre cubic capacity, V16 configuration, turbocharged and inter-cooled, these engines are engineered into a container module in New Zealand by Entec. The enclosed module comprises the engine/generator set, a control/switchgear panel, ventilation fans, exhaust system and dump heat radiator. The finished product is a self-contained, “plug and play” power station.

Operating since 1982, the company specialises in equipment and back-up service for biogas power generation applications such as digester gas and landfill gas.

Engine manufacturer, Dresser Waukesha has only recently launched this high-tech 1MW rated machine and Bob Weston, general manager of Entec Services, says the company has enjoyed very good initial success with containerising and customising the engine in New Zealand.

“Our local, innovative angle is the way in which we have packaged these engines into standard shipping containers (we’re not unique in that, but we have some nice features).

“This combination of our packaging and the new engine has led us into our first export job, packaging one of these units for a large pig farm in Philippines (a climate change project), plus we’ve also had orders from two local landfill sites.”

One of the main criteria in its equipment packaging design has been to ensure access and serviceability for good long-term maintenance, he says.

“Our 26 years maintaining these things has taught us some tricks on how best to look after them.”

As the Hampton Downs Landfill builds up, EnviroWaste plans to increase generation by one or two megawatts of generation per year.

There are currently 32 landfill gas extraction points on the site drawing 2500 cubic metres of gas an hour (made up of 58 percent methane) Current gas modelling suggests gas production will eventually reach 20,000 cubic metres an hour, therefore generation could reach a maximum output of 40MW, says EnviroWaste Services, national manager - post collections, Chris Lobb.   

Project power is sold to Meridian through an 11kV line under the Waikato river that was installed by Counties Power.

Lobb agrees with other landfill operators that landfill generation margins are ‘thin’ and payback periods long.

Nor do they enjoy the sort of incentives doled out by overseas governments to encourage development. Successive governments in New Zealand have offered no incentives for using methane for generation which, under our National Environment Standards (NES), can be simply flared off, while costs go up. A Waste Levy of $10 a tonne is added to fill from July this year, which could result in less organics in the waste stream and a reduction in LFG generation rates.

“Landfill gas is a resource that needs to be responsibly utilised rather than just flared,” iterates Lobb. “Currently there is no monetary incentive from the Government to utilise LFG and turn it into electricity or useful heat.”

Worse. There are several smaller landfills around the country that are not captured under the requirements of the NES and the landfill gas is not even collected at these sites, he says.

“EnviroWaste has recommended to the Government that the current NES threshold be revisited to capture these landfills.  We would really like to see the Government provide more tangible support to the landfill gas sector to make the utilisation of gas at such sites viable.”