Powering Sydney Water's carbon neutral future

24 Jul 2008Archived News Energetics in the News

Published: Eco Generation - Energetics Pty Ltd is quoted as a firm working on the biogas and hydroelectricity projects with Sydney Water.

 

Suppling drinking water to, and processing seage from, over four million customers is an energy intensive exercise. As one of NSW's largest energy users, Sydney Water has undertaken a major renewable energy project involving cogeneration plants and hydroelectric generators that promises to substantially cut emissions.

Over the last year, Sydney Water has consumber almost 400 gigawatt hours (GWh) of electricity - representing almost one per cent of the total energy consumed in the state.

Sydney Water has recognised the importance of acting early to eliminate the impact of carbon emissions generated from energy and electricity consumed by its operations and made a commitment last year to make its operations carbon neutral by 2020.

The ambitious plan will ultimately eliminate or offset over 400,000 tonnes of carbon dioxide each year - equivalent to taking 100,000 cars off the road. The first milestone on this path will be to cut emissions by 60 per cent by 2012.

Zoning in on renewable energy projects

To achieve this lofty aim, Sydney Water required a diverse portfolio of renewable energy solutions and energy effiency projects. The company is large network of interconnected plants, which presented it with a renage of very different options for energy generation.

Using its access to water and wastewater resources, Sydney Water has pursued cogeneration and hydroeletricity projects. The cogeneration facilities will convert biogas, which is a product of the wastewater treatment process, into electricity and heat that used for the on-site digesters, while the hydroelectricity projects will capture energy from the flows of water and wastewater travelling through a shaft or pipeline.

Scoping work by engineering firm WorleyParsons in consultation with Energetics, revealed that many potential biogas and hydroelectricity projects could be developed, with eight projects being selected as being cost-effective.

Cogeneration facilities

Sydney Water has given the go-ahead for installation of five cogeneration facilities at sewage treatment plants in Bondi, Glenfield, Liverpool, Warriewood and Wollongong. These projects will run alongside three cogeneration plants already operating at Malabar, Cronulla and the recently-installed project at the North Head Sewage Treatment Plant.

Hydroelectric generators

The company has also started design works on the installation of hydroelectric generators being installed at the North Head sewage treatement plant, Woronora Water Filtration Plant and Prospect Reservoir.

When built, the Prospect Hydrogeneration Project will become Sydney Water's largest renewable energy project, producing around 20,000 megawatt hours (MWh) annually.

In addition, the cogeneration facility at the Warriewood sewage treatment plant, Woronora pipeline and North Head sewage treatment plant will be supported by the NSW Government's Climate Change Fund.

In total, $45 million has been committed to the project, which will be completed by the end of February 2009. Combined with existing biogas cogeneration engines, Sydney Water will generate around 80 GWh of renewable energy annually, offsetting 80,000 tonnes of carbon dioxide.

Combining hydroelectricity and cogeneration at North Head

Of Sydney Water's entire network, the North Head sewage treatment plant uses the most amount of energy - accounting for 13 per cent of corporation-wide energy use. The site is also considered somewhat unique, perched on the northern headland of Sydney Harbour within the boundary of Sydney Harbour National Park, which makes it an even more challenging project.

Most of the energy used by the North Head sewage treatment plant is associated with pumping up sewage onto the headland for treatment. Sewage flows in at sea level under gravity, and is then pumped 50 metres up onto the headland for treatment. A bank of six 3 MW pumps contributes substantially to the site's energy use of 48 GWh per annum.

This unique location, coupled with the second-largest sewage flow of Sydney Water plants, makes the site an excellent option for two seperate energy generation projects.

Initial design was based on the use of a 1.2 MW generator, using existing deep ocean outfall connections and found to generate approximately 10 GWh annually. Using existing connections proved a major limiting factor. Therefore detailed desgin consequently involved construction of a new connection to the deep ocean outfall in order to cater for average dry weather flow. With a 2 MW generator, the detailed design phase was likely to annually generate 12 GWh.

The large sewage flow makes the site an excellent candidate for biogas production using the new anaerobic digesters. This project proved cost-effective with the installation of a 1.4 MW Jenbacher cogeneration engine, which is capable of producing 8.5 GWh annually - approximately 18 per cent of the site load. The cogeneration plant is operating, with final commissioning tests due soon.

The second energy generation option being pursued at North Head is the hydraulic potential of the treated sewage on the way out to sea. Some of the principal design considerations invgolved ensuring that effluent flow was maxmised, that plant operation was not compromised and harvesting as much value from teh energy generated.

Presently the treated sewage falls down a drop shaft then out to sea via the deep-ocean outfall. WorleyParsons engineers designed a novel solution to utilise this resource, one of the world's first hydropower generators designed to run on treated sewage.

Designing the North Head hydroelectric project

Having been in operation for over 30 years, the hydroelectric potential of the North Head plant had been previously studied. However, the final decision to proceed was encouraged by a change in Sydney Water management philosophy, which approved new feasibility studies.

WorleyParsons and Energetics' initial study of the North Head hydroelectric project indicated that 1.5 MW of electricity could be generated from a hydroelectic turbine operating at 330 ML/day of dry weather flow.

In the first study, a plant arrangement was proposed utilising an inclined raised bore from the sedimentation tank outlet penstocks to the pump floor chamber adjacent to the deep ocean outfall inlet.

WorleyParsons engineers, in consultation with Sydney Water staff, considered various options for plant arrangement including:

  • Installing a retractable turbine in the existing drop shaft that could be withdrawn from teh flow when not in use
  • Installing a new drop shaft from teh surface to the motor floor creating a new parallel flow for the hydro
  • Installing an additional effluent discharge pipeline from the surface to the motor floor creating a new parallel flow path for the hydro.

The second option (a new drop shaft) was selected and forms the basis of the preferred design concept as shown in Figure 1. Detailed design has been completed on the hydrogenation plant, and engineering is on schedule for start of operations by the end of the year.

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