PACE Zenith Awards 2013: Best Fieldbus Implementation category sponsored by BECKHOFF Automation
Winner: BlochTech, WorleyParsons and Profibus Association of Australia
Project: Southern Seawater Desalination Plant
BlochTech, WorleyParsons and Profibus Association of Australia led the implementation of Fieldbus technology at the Southern Seawater Desalination Plant (SSDP).
The SSDP, located in Binningup is Western Australia’s second seawater desalination plant and is owned by the Water Corporation, the main provider of water, wastewater and drainage services in Western Australia.
Winner of the 2012 Global Water Award for ‘Desalination Plant of the Year’, the SSDP is a seawater reverse osmosis based plant, widely recognised around the world as the technology of choice for the desalination of sea and brackish water.
The second desalination plant built by the Water Corporation, SSDP was designed to be constructed in 2 phases, Stage 1 being commissioned in August 2011. It delivers water to the Integrated Water Supply System that supplies over 1.7 million people in Perth. Stage 2 was ordered to commence before Stage 1 was even completed and is currently being commissioned.
From past experience, the Water Corporation was aware that a major greenfields water treatment plant would deliver significant benefits from the application of high speed networking technologies.
Aside from the installation benefits of reducing the significant amount of point to point cabling employed by analogue technologies, Fieldbus application and the deployment of smart devices would deliver enhanced data availability to the plant operator, information that is needed for advanced automation functions such as control, monitoring and supervision.
Water Corporation decided to adopt Fieldbus technology, specifically Profibus PA and Profibus DP for all water treatment and desalination plants. High availability was a key requirement for the Water Corporation, so redundancy throughout the entire process and mechanical design a priority when evaluating and planning the SSDP’s network design.
Whilst Worley Parson successfully won the tender to design the Control System, in practice the initial design is usually followed by consultation and design modifications with the System integrators – BlochTech – whose responsibility was to program the design and make it work.
In consultation with BlochTech, the Siemens PCS7 control platform was selected. This includes the SIMATIC PDM (Process Device Manager), a cross-vendor tool based on EDD technology and used for configuring, managing and commissioning intelligent field devices.
Steven Sischy (R), Managing Director, BECKHOFF congratulates the winner Trevor Bloch of BlochTech.
The greater level of redundancy required by the client highlighted the need for greater segregation and therefore a greater number of controllers. During the design stage typical questions to consider included the number of controllers required to manage individual process areas.
Also considered were the location and size of the controllers, whether the controllers selected be big enough and have enough bandwidth to communicate with all the devices, and the number of smart devices which would be required to monitor each process area.
For most desalination plants the major processes required to deliver potable water are: Intake, Pre-treatment, RO, Post-treatment (potabilisation) and Waste Treatment.
The finalised design stipulated five controllers, located in the Seawater Intake, inb Microfiltration/Waste (pre-treatment and waste treatment), RO Bank A & Auxiliaries, RO Bank B, and finally in Post Treatment.
Worley Parsons and BlochTech then set about addressing the electrical issues, specifically, how best to optimise the performance of each cable run so as to maintain connectivity while not compromising the accuracy of the data gathered.
From past experience with DCS application in the Perth Seawater desalination plant, it was decided that a DCS would be the preferred control system, rather than a PLC/HMI implementation. The large quantity of the I/O meant that the benefits of an integrated development environment would offer significant savings in time.
Performing remote set-up and maintenance of devices over fieldbus was a recognised benefit of Profibus application, perhaps more so on Profibus-PA through the use of either DDL or FDT/DTM interfaces. Being able to centrally manage deployment of instrumentation saved significant time in the integration and commissioning.
In order to access the full information potential of smart devices, the PCS7 Maintenance Station add-on was used on the control system, which provided a portal from the HMI to access status and configuration data via the PDM application (which is based on acyclic communications and therefore does not impact real-time operations).
Unlike the Perth Desalination plant where one company was appointed ‘most preferred instrumentation supplier’, a decision was made to identify the major instrument categories and choose ‘best in class’, ensuring at the same time, their Profibus interfaces were certified.
Instruments selected included: flow meters from Krohne; pressure devices from Yokogawa; level devices from Vega; temperature from Moore Industries; and water analysis from Hachs, a German company. Profibus PA segment couplers were also supplied by Moore Industries.
By choosing Profibus PA, the companies allowed themselves greater design flexibility in their implementation. While Profibus PA only has one speed, it offers a greater variety of topology layouts for field installation. And the spur lengths allowable are a little bit longer making it a bit more workable in the field.
As Profibus DP was used to capture the control and switch gear type of equipment such as VSDs and motor starters and some of the packaged equipment with internal PLCs, the implementers requested a Profibus DP interface.
In the short term, the implementation of Profibus PA and Profibus DP significantly reduced their cabling costs and the time required to install and commissioning hundreds of process instruments, sensors and actuators throughout the plant.
But more importantly, Profibus provided access to a wide range of process information that would enable their plant operators to initiate predictive maintenance checks, troubleshooting, more efficient plant asset management and it gave the plant operators the ability to perform detailed diagnostic evaluations on instruments or control issues and then decide what action is required.
The 2013 PACE Zenith Best Fieldbus Implementation Awards are sponsored by BECKHOFF Automation.
Read more: BECKHOFF Automation sees 2013 as a rewarding year for the automation industry
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