Water. Desalination + reuse
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PROJECTS of the project to a joint venture between Thiess and Degr��mont (TDJV). The operations and maintenance (O&M) component was contracted to a joint venture between Degr��mont and Thiess Services. Water Supply System Treated water quality objectives and process treatment ��� The project���s treated water objectives meet some of the highest water quality standards in Australia and the world. In order to achieve the contract performance requirements, the plant is based on a well proven two-pass RO process and a high level of redundancy of critical equipment and systems. Caustic soda dosing on the RO second pass provides the necessary additional removal of boron to meet the target specification of 0.5 mg/L. To protect the RO membranes, the seawater is collected 1.1 km from the shore in water approximately 20 m deep. It is pretreated through enhanced coagulation and filtration on anthracite/sand dual media pressurized filters (DMPF) followed by 5 micron nominal cartridge safety filtration. Treated water quality objectives are finally met after a potabilisation treatment including remineralisation (CO2 and lime water), dosing of fluorosilicic acid and sodium hypochlorite, and storage in two 35,000 m3 baffled tanks to ensure the disinfection process. System configuration ��� The modularity of the pretreatment selected and the RO Tunnelling and offshore activities - Figure 3a: View of the first of the two TBMs; Figure 3b: View of the jack-up barge off the desalination plant construction site. PROJECTS technology are well adapted to any plant size. However, to optimise the plant availability and necessary equipment or system redundancy, the main processes (pretreatment and RO) are split into three 50 million m3/y independent streams, each one having the capacity of the Perth Seawater Desalination Plant (2006, 45 million m3/y). Each stream is composed of five dedicated feed pumps, 24 DMPFs, 14 cartridge filters, nine first-pass RO trains and eight second-pass RO trains. A layout of the desalination plant is presented in Figure 2, including the seawater lift-pumping station, the three parallel streams, the treated water storage tanks, the pumping station to deliver desalinated water through the transfer pipeline, and the common facilities for a total of 29 buildings. The plant���s common structures are designed for the final plant capacity of 200 million m3/y: l Two 4 m-dia tunnels (for a combined length of 2.6 km) built under the seabed to ensure seawater supply and brine discharge back to the sea through a 1 million m3/d brine diffusion system. Intake and outlet tunnels have been built using two 91 m-long 500 t tunnel boring machines (TBMs) supplied from Germany (Figure 3a). Each TBM was equipped with a 4.8 m-dia cutter head, capable of 4.9 rotations per minute. The tunnels are lined with more than 11,000 pre-cast concrete segments forming a watertight concrete tunnel l The underwater connections have been constructed by drilling vertical pits to the tunnel and using precast concrete risers and diffusers, installed from a 250 t jack-up barge (mobile off-shore working platform supplied from The Netherlands) (Figure 3b). l A 1.5 million m3/d seawater lift pumping station l Two 35,000 m3 storage tanks based on soft bladder technology. The storage tanks provide the buffer volume to feed the treated water pumping station and the contact time to meet the disinfection requirement l An 84 km 1.93 m diameter mild steel cement lined pipeline. It includes seven delivery points to allow water authorities to connect to the plant���s water supply, from an outlet immediately adjacent to the desalination plant, to the last point | 18 | Desalination & Water Reuse | November-December 2012 Figure 2: VDP RO plant layout 84 km away (Figure 4). It is a ���twoway��� pipeline so that if required, water can be supplied in the opposite direction from Cardinia Reservoir to Western Port and South Gippsland customers. The pipeline is fed by a main transfer pumping station located at the plant and the desalinated water is boosted by a second pumping station 74 km from the plant l An 87 km 220 kV AC power supply comprising three separate cables in conduits, buried in an underground trench within the same easement as the pipeline. The power supply follows largely the same path as the pipeline. Underground power was the state government���s preferred power source for the project as it has the least impact on the landowners, farmers and other people living and working in the area. Energy - The plant is designed for optimal energy efficiency with the overall process designed for minimal energy consumption. Key design features to maximise energy efficiency include the ability to operate individual streams at their optimum efficiency point, equipment selection, use of isobaric pressure-exchange energy-recovery devices, optimised RO design, use of the latest low-energy membranes, gravity flow of the brine stream to the outfall and energy-efficient buildings. The energy requirements of the plant and pipeline will be fully offset by renewable energy through the purchase of Renewable Energy Certificates (RECs) to be supplied by AGL from its overall portfolio of renewable energy assets, including from new wind farms being built in Western Victoria. VDP START-UP AND PROGRESS In the 36 months since the construction began on the Victorian Desalination Project ��� one of the largest infrastructure projects undertaken in Australia in recent Figure 4: Transfer pipeline route and a view of the pipeline construction site during pipe laying. years ��� a great deal has been achieved; from an empty paddock in September 2009 to October 2012 when the complex construction project is now in the home stretch (Table 1). The project was originally contracted to tight deadlines ��� 27 months from financial close to 150 million m3 of water being produced and 33 months to completion of commissioning. Ironically, Victoria has experienced adverse weather conditions, including significant rainfall, since construction began. While progress in some areas has been delayed as a result (although the plant will be at full production by the end of 2012), the urgency for the desalination plant to top up Melbourne���s water supplies following 12 years of drought has been reduced. Engineering and construction achievements to date have been significant: more than 17 million man-hours have been worked, with no serious injury; and the five projects have now been completed. Construction of the two underground tunnels and of associated marine works was finished in 2011. The tunnels have been successfully filled with seawater in February this year and commissioning of the marine structures and tunnels has been completed. The 84 km, 1.93 m-dia transfer pipeline that will provide water to the communities throughout Melbourne, South Gippsland and Westernport as required is also completed. Hydro testing of the pipeline was finished before Christmas 2011. The two pumping stations have been fully commissioned and tested, including the surge mitigation system. The transfer system is currently delivery drinking water to Cardinia reservoir, supplied by the first stream. Another major achievement of the project is the completion of the 87 km underground power cable. The longest 220 kV HVAC underground power cable of its type in the world has been successfully built and energised in January 2012. The power from Melbourne grid supplies the two 22 kV transformers located on site, energising the 29 plant buildings. The RO building construction is completed, the 55,000 RO membranes are installed and the last of the 3 streams is under commissioning. Stream 1 performance and reliability tests are completed and plant operations have started at the end of September. The full O&M team was on board during the precommissioning activities, going through theoretical and practical training and preparing the operation phase. Operators have been mobilised for the commissioning, in order to assist the commissioning team to operate the plant, acquiring a detailed knowledge of plant and equipment, participating in trouble shooting and manual/automatic operation of the plant and its sub-systems. This approach ensures a smooth transition between commissioning and the start of the 27-year operation period. Back outdoors, the largest green roof in the southern hemisphere, covering more than 26,000 m2, has been planted out with around 100,000 indigenous plants, blending the building in the surrounding natural landscape, a key feature of the design and which, along with the size of the plant, distinguishes it from all other desalination projects in Australia and around the world. The last key milestone consist of the test of the streams 2 and 3, and the final reliability test at full production capacity. CONCLUSION The Victorian Desalination Project is one of the most complex construction projects to have been undertaken in Australia in recent years. As at October 2012, two streams (66% of the plant) are operating and are delivering desalinated water to Cardinia Reservoir and Melbourne supply system. The last one is under final commissioning and testing for an operation starting mid November. By the end of 2012 this state of theart facility will be at full production and Melburnians will have access to a reliable, high quality, rainfall independent water source.l COMPONENT WORkfORCE More than 17 million man hours worked to date. No significant injury. INTAkE ANd OUTfALL TUNNELS 1.2 km intake tunnel and 1.5 km outfall tunnel completed, filled with seawater and commissioned. In operation. TRANSfER PIPELINE 84 km pipeline completed, hydro-tested and process tested, including full surge system protection test. Operational and delivering drinking water. UNdERgROUNd POWER CAbLE 87 km - longest underground power cable in the world ��� completed, energised and in operation. dESALINATION PLANT COMMISSIONINg Commissioning of 2/3 of the plant completed, involving 80 specialists and more than 200,000 tests. REgULATORY APPROVAL On-going commissioning activities under Section 30A of the EPA act. Operation & Maintenance Environmental Management Plan approved by the Minister for Environment and Climate Change. gREEN ROOf The largest green roof in the southern hemisphere, covering more than 26,000 m2 is planted with around 100,000 indigenous plants. dELIVERY Of ThE fIRST dRINkINg WATER ��� ACTIVITY STATUS Following Stream 1 performance tests, the first drinking water was delivered to Cardinia reservoir and Victorian people in September 2012. Table 1: Progress Check List November-December 2012 | Desalination & Water Reuse | 19 |