Water Journal : Water Journal May 2011
resource recovery refereed paper technical features 102 MAY 2011 water Gas Approvals There were also significant challenges related to the application of hazardous area principles and the application of ventilation in accordance with AS (IEC) 60079.10. All equipment required an AGA or equivalent certification in accordance with NFPA 497 (Classification of Flammable Liquids, Gases or Vapours) and of Hazardous (Classified) Locations for Electrical Installations. However, the cogeneration plant is made up of a number of overseas technologies with foreign accreditation which are not often applicable to local standards. These items had to be approved by a local hazard area assessor and Energy Safe Victoria, and required minor modification to achieve local safety standards, or additional costs to certify the equipment to local AusEX code. The cogeneration plant was designated as a Zone 2 Hazardous Area, and a number of issues had to be addressed with the operating staff, such as: • Adequate equipment spacing away from combustion sources, using the regulatory standards; • Adequate maintenance access and gas containment during shutdowns and servicing of gas pre-treatment equipment; • Self-venting of combustible gases during plant shutdown and sufficient draining, sampling and purging of the equipment to operate the system efficiently. Lessons Learnt There were a number of key lessons learnt, including: 1. Although this was the first use of Capstone Micro-turbines at a recycled water treatment plant, the turbines are competitive and, in Western Water's application at Melton Recycled Water Treatment Plant, they were the optimal choice. 2. A life cycle assessment was a critical tool used by Western Water to decide on appropriate technologies, particularly when there were multiple technologies available in the market place with different characteristics. In this case, maintenance cost and availability became the critical factor. 3. It is important to understand the quality of the various components within the biogas feeding into the turbine. Extensive testing, although costly, can help mitigate this risk and allow better understanding of the necessary requirements for pre-treatment. 4. The operator and designer need to work closely together through the issues of hazardous area assessment and gas regulations to reach a point where the operators fully understand the risks of working safely with equipment operating on biogas. 5. A base load of not less than 100kW was necessary to ensure the generator was able to operate in an efficient manner without an extensive number of stops and starts. 6. There were challenges in ensuring that a reverse power situation back to the network grid did not occur and this required extensive discussions with the power authority. Any such facility operating in island mode will cause the power authority to be concerned about protection of their network infrastructure. 7. Western Water has proven that a well maintained digester should be able to produce methane levels up to 70%. Western Water operating personnel have spent a number of years optimising and understanding how to get the best out of the anaerobic digester at Surbiton Park. This has meant that biogas has an even higher value as a resource. 8. The control system needs to be significantly robust to ensure stable operation of the turbine equipment in comparison to varying gas production from the holding tank and anaerobic digester. 9. The combined heat and power produced has resulted in cuts in carbon dioxide emissions at the plant of 1800 equivalent tonnes per year. This is certainly a win for the environment, and has proven that biogas can provide a renewable source of energy. Western Water believes the facility will provide a platform for future installations at other recycled water plants across Australia. Conclusion This was Australia's first application of Capstone Micro-turbine technology operating from biogas produced at a Recycled Water Treatment Plant. Plant managers from Western Water predict that savings realised from the on-site generation of electrical and thermal power, plus the "green" incentives offered by the government, will justify the installation of a second CR200 system in 2010 and ultimately a third one as gas availability increases. Through careful consideration of the available technologies Western Water has reduced its greenhouse gas emissions by 8% and is moving towards carbon neutrality by 2017. The Authors Justin Boan (email: justin. email@example.com. au) is a Project Manager with Western Water, Sunbury, Victoria. Ron Howick (email: ronh@ aquatecmaxcon.com.au) is the National Manager of Standard Products for Aquatec-Maxcon, Ipswich, Queensland. Anthony Davey (email: anthonyd@aquatecmaxcon. com.au) is a branch manager with Aquatec-Maxcon, Melbourne, Victoria. Figure 10: Gas pre-treatment consists of a gas booster and siloxane adsorption vessels.
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