Water Journal : Water Journal May 2011
resource recovery refereed paper 98 MAY 2011 water technical features Abstract In an Australian first, Western Water (Vic) partnered with Aquatec-Maxcon to design, supply and install a Capstone Micro-turbine at the Melton Recycled Water Treatment Plant to operate on anaerobically produced bio-gas. The single Capstone CR200 turbine can provide over 200kW of electrical power at the Melton Recycled Water Treatment Plant, along with 276kW of heat to enable the plant's digesters to work at optimum efficiency. A pre-treatment system ensures that the turbine is protected from silica deposition. Introduction Western Water is a Victorian water utility that services 135,000 people in the outer regions of Western Melbourne. One of Western Water's core corporate values is to operate sustainably and the organisation has committed to be carbon- neutral by 2017. The Melton Recycled Water Treatment Plant is a 10ML/day activated sludge treatment plant with tertiary lagoon treatment. It services the townships of Melton, Melton South, Toolern and Eynesbury with both Class C recycled water and Class A recycled water. The sludge treatment process at Melton Recycled Water Treatment Plant incorporates an anaerobic digester. Through Western Water's design and tender process different technologies for capturing bio-gas to produce energy were investigated. Aquatec-Maxcon's Capstone Micro-turbine technology was identified as providing the best present value. In an Australian first, Western Water partnered with Aquatec-Maxcon to design, supply and install a single Capstone CR200 turbine which can provide over 200kW of electrical power at the Melton Recycled Water Treatment Plant, along with 276kW of heat to make the plant's digesters work at optimum efficiency. Together, the combined heat and power produced has resulted in cuts in carbon dioxide emissions at the plant of 1800 equivalent tonnes per year. The implementation of this project represents a greenhouse gas emissions saving to Western Water of 8% of our total emissions and is a significant step towards carbon neutrality by 2017. Cogeneration Facility Anaerobic digester systems have been used for decades at municipal wastewater facilities and, more recently, have been used to process industrial and domestic wastes. These systems are designed to optimise the growth of the methane- forming (methanogenic) bacteria that generate CH4. Typically, using organic wastes as the major input, the systems produce biogas that contains 55% to 70% CH4 and 30% to 45% CO2. The Melton Recycled Water Treatment Plant utilises mesophilic anaerobic digestion operating at an elevated temperature of 35˚C to 38˚C. An external energy source is required to maintain this elevated temperature. Western Water operating staff have spent a number of years optimising and understanding how to get the best out of the anaerobic digester at the Melton Recycled Water Treatment Plant, and have proven that a well-maintained digester is able to produce methane levels of up to 70%. This increases the enthalpy value of the biogas above 25 MJ/m3, increasing the ability of a cogeneration system to produce more power and thermal output, and provides a higher value on this important resource. The conventional system adopted in Australia is a dual fuel diesel set, with the jacket cooling water used to warm the digester. However, Aquatec-Maxcon offered the alternative of a Capstone Micro-turbine. The model CR200 can produce 200kW of power with less than 100Nm3/hr of biogas. Secondly, an external heat recovery module working in combination with the exhaust from the Micro-turbine can deliver 200kW of thermal energy through cogeneration to supply the process heat requirements of the Recycled Water Treatment Plant. Figure 1 is a photograph of the facility. J Boan, R Howick, A Davey Australia's first application of Capstone Micro-turbine technology reduces greenhouse gas emissions COGENERATION BY A MICRO-TURBINE OPERATING ON BIOGAS Figure 1: Capstone Micro-turbine installation at Melton Recycled Water Treatment Plant.
Water Journal April 2011
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