Power from the People

17 Jul 2008Archived News Energetics in the News

Published: Business Review Weekly - by Kate Burgess - Gilles Walgenwitz; Principal Consultant Energetics Pty Ltd talks about the work he did with Sydney Water on co-generation.

 

The enormous cost of treating raw sewage is being offset by extracting mehtane gas from the waste and turning it into clean energy to run the treatment plant.

Imagine if a processing plant could power itself for no cost from its own raw materials - and even better, if that raw material was already the most unwanted of all waste.

At its North head waste water treatment plant, Sydney Water captures methane gas from city sewage piped to the plant for treatment and uses it to generate power for the entire process of treating waste water.

North head has big power needs: waste water arriving there has to be pumped 60 metres up a cliff face before processing can begin, a lift that uses a lot of electricity.

With a new system, the quivalent of three truckloads of effluent a day is put through a digester to extract the methane to fuel the giant motor which drives the generators powering the plant.

Another source of free power will be tapped when Sydney Water completes the second half of its North Head renewable energy projecty. Treated water will be dropped back down the slope through a hydro-power turbine, on its way to the deep ocean outfall 3.7 kilometres off the coast.

"It's all about harvesting the energy," plant manager Tony Williamson says. "We are reclaiming the energy we expended getting the untreated effluent up the hill."

The self-sufficiency is timely too, he says. "Energy prices are going up. We've tried to renegotiate our electricity contract with Origin Energy but because of the recent drought in Queensland we were unable to get the same rates as we used to."

Williamson adds: "In 2009 we will be able to run a 3.5-megawatt pump and be energy neutral."

The project, which was jointly planned and executed between WorleyParsons, consultant Energetics and Sydney Water, takes advantage of a process used to treat waste water called anaerobic digestion to produce the gas.

The sludge is maintained at a temperature of 35-37 degrees inside the digester to produce a biogas which is 60 per cent methane. The gas then fuels a 20-cylinder internal combustion engine to run the alternators. Waste heat from the engine's cooling water and exhaust are used to help keep the digester at the right temperature, so nothing is wasted.

Before this "co-generation system" was developed, the effluent was put through a centrifuge and four truckloads a day were transported to local farms. Now only one truckload of sludge is left behind.

Sydney Water has eight renewable energy projects under way which will generate 10 per cent of the company's power needs when they are finished. The company has pledged to reach carbon neutrality by 2020. The company's Malabar and Cronulla sewage treatement plants already have similar co-generation systems to that of North Head, and five more are under development at other sewage treatment plants around the city.

In a further low-emission power project, a hydro-power plant at Prospect in the city's west will use water flowing through the Sydney Water network to generate 20,000 megawatt hours a year when it opens in 2009. Biogas-fired co-generation plants such as those in Sydney are also operating in Melbourne and Brisbane.

The gensis of the North Head project goes back to 2003 when a pre-feasibility study was carried out. A cost estimate for a range of options was calculated by WorleyParsons before the anaerobic digesters and biogas generation system was decided on.

Energetics then worked out what the cost benefits would be, including the cost of electricity, the cost of green commodities produced, such as carbon offsets, and the amount of power that could be sold to the grid.

Energetics consultant Gilles Walgenwitz says that the project "has not only avoided the cost of electricity and reduced the use of coal-fired power, but green commodities are also created. Currently, renewable energy credits are worth $50 a tonne".

When green commodities have been created, Walgenwitz says, producers need to decide whether to sell them on the market as renewable energy certificates or keep them to offset emissions as part of a carbon neutrality strategy.

North Head uses all of the power it produces. However, Sydney Water's energy manager, Daniel Cooper, says that the facility has gone through the process of connecting itself to the grid.

This means that the power utility has to check that the generator can feed power to the grid without causing any damage and that transformers and other equipment meet the standards of the utility.

Cooper says that co-generation projects bigger than five megawatts need a higher level of approval to connect to the grid.

However, even the relatively small methane co-generation at North Head will pay for itself, he says. "They have got returns, they are commerical products, and they are not pies in the sky. That's what makes them good: we've gone with real rates of return that actually make a difference.

 

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