Turning landfill gas into energy at Puwera Landfill

Middleton Group worked with Pacific Energy on a unique 1.56MW landfill gas generator project (above) at Puwera Landfill, near the city of Whangārei in northern Aotearoa New Zealand. The gas produced by landfill decomposition was fed into an engine (pictured) and the energy produced sent directly to Golden Bay Cement in Portland, several kilometres distant, via a new 11kV cross-country line.

The project, undertaken by landfill owner Northland Waste and its joint-venture partner, Whangarei District Council, aimed to make better use of the gas than simply flaring it into the atmosphere to mitigate the climate-damaging effects of methane release. Northland Waste Engineering Lead Nate Holland-Kearins says that as the energy value of methane is significant, “using this recovered resource to our best of our ability was considered the right thing to do to”.

Pacific Energy Director Perry Hutchinson, who engaged Middleton Group to provide electrical engineering services, said that the project was unique in that the 11kV line connected directly into Golden Bay Cement’s embedded network, bypassing the local distribution system and thus reducing pressure on it. Pacific Energy oversaw technical delivery and coordination across multiple project elements. Middleton Group provided a range of services, including protection design, high voltage and earthing design services, fibre-based intertripping integration with Golden Bay Cement, site-specific earthing design, stakeholder engagement and switchgear procurement.

At Middleton Group, Engineer Chloe Gordon took the lead, working primarily with Rajendra Vaidya. Amajith Wanigasinghe and Praveen Gunaratne assisted on earthing design. Perry describes Middleton Group’s engineering support as “first-class. They responded flexibly to changes, took on additional scope seamlessly, and maintained a consistently high standard of work throughout.”

Nate says that these sorts of gas-to-energy projects are relatively rare in Aotearoa New Zealand, partly due to the relatively low population density and because there are few landfills of the scale to undertake such a project. He believes that Puwera now has the largest single gas-fired engine in the country – “other engines operating at landfills tend to be smaller but more numerous”. Nate adds that the joint venture is also the first in the country to invest in pre-treatment of the landfill gas prior to injection into the engine for sustainability reasons. “Gas-fired engines operating on landfills typically suffer from extreme corrosion due to the highly acidic nature of the gas,” he says. Historically, similar projects overcome this problem by installing multiple engines in parallel to achieve redundancy. “We viewed this as wasteful, so invested in pre-treatment of the gas instead to protect the engine and hopefully extend its life.”

Perry says that the Puwera project represents “a strong step toward sustainable energy solutions and showcases what’s possible when great minds come together.” The team that Pacific Energy assembled also included Mahurangi Electrical, Ventia, Tyree NZ LTD, HV Power, Arthur D Riley & Co Ltd, Powerpro, Manufactured Switchgear Ltd,  Infrastructure Asset Management Systems Ltd and Eneraque Renewables.

• See a walk-through of the project here, taken by Perry Hutchinson.