Desalination plant adopts unique instrument design

Among the Perth Seawater Desalination Plant’s numerous accolades are top awards for construction excellence and project management which it won earlier this year. At the heart of the plant is a sophisticated and future-proofed instrumentation and control strategy that has helped make the project a model for other desalination plants being considered — not only within Australia but also worldwide. This strategy also propelled the plant to a win in the recent Zenith Awards, where it won Best Automation Project 2007.

The seeds of success for this Water Corporation project were sown way back in 2005, when the project was put out to tender. Endress+Hauser Australia was closely involved with the two joint ventures (JVs) even at the project bidding phase. The company’s Profibus expertise, comprehensive instrument range, competitive pricing and global presence were no doubt deciding factors that led to its involvement even at that early stage. The MDJV consortium that eventually won the Perth desalination project included the major European company Degrémont, considered a world leader in water treatment and desalination plants. Endress+Hauser was appointed the preferred instrumentation supplier and automation design partner and also tasked with the installation and commissioning of all process instruments at the plant.

For the Perth desalination plant situated at Kwinana, WA, Endress+Hauser worked with Degrémont’s Australian office to lay the groundwork for the system design. Degrémont subsequently opted to do the bulk of the detailed design at its office in Spain.

For over eight months, Endress+Hauser’s Spanish office worked closely with its counterparts in Australia and, drawing on its Profibus expertise, developed the detailed instrumentation design with Degrémont. Endress+Hauser supplied all flow, pressure, level and temperature devices as well as a vast selection of water analysis instruments.

The Perth desalination plant’s superior design philosophy was evident in the built-in redundancy for important measurements such as pH/ORP, conductivity, residual chlorine and turbidity. Two sets of instruments were installed in parallel at critical stages to ensure that, even in the case of instrument failure, the water produced retained the desired high levels of purity and quality. In most cases, the Endress+Hauser Profibus PA-powered Liquiline transmitters with Memosens technology were used — significantly reducing future maintenance costs.

As with most major projects, this one would have its share of teething problems during implementation, so Endress+Hauser was given the commissioning contract as well as ensuring the installation was correctly done. In doing so, Endress+Hauser was able to extend the warranty on all instruments. In general, commissioning went smoothly.

During the implementation stage, the project threw up a host of unique challenges for the instrumentation team. The electromagnetic flowmeters, for example, were affected by eddy currents flowing through the water in the GRP (glass reinforced plastic) inlet pipes, caused by the electromagnetic interference from the pumps. Magmeters require a stable magnetic field without outside interference for best operation. GRP pipes cannot easily be earthed and this led to electromagnetic interference in the water in the pipework. Using steel pipes in the process was not an option due to corrosion by the salt water, so Endress+Hauser installed high-quality steel earth rings between the flanges to provide solid grounding and eliminate the electromagnetic interference.

For the commissioning and troubleshooting of the instruments, Endress+Hauser proposed the use of the ‘open’ FDT/DTM technology embedded in its Fieldcare commissioning and troubleshooting software management tool. Not only did this future-proof the plant, it also enabled smoother commissioning, troubleshooting and start-up. The operators subsequently incorporated Endress+Hauser’s W@M (Web-based Asset Management) technology to manage all of their instrument assets.

The 45-gigalitre per annum Perth Desalination Plant has been up and running since November 2006 and has set the benchmark for similar plants in Australia in the future. The designers have implemented the latest automation and instrumentation technologies which will future-proof the plant, reduce maintenance and operating costs, and ensure high-quality potable water for the Perth community.

Endress+Hauser Australia Pty Ltd
www.au.endress.com