[Case Study, May 2009] -- When Dalriada Water Limited, a consortium made up of AECOM Design Build (previously Earth Tech), Kelda Water Services and Farrans, won a 25 year contract to design, build, finance and operate a large proportion of the water treatment infrastructure for Northern Ireland Water, it enlisted Siemens to provide and maintain all equipment across the network.
The project was the first ever Public Private Partnership (PPP) offered by Northern Ireland Water and aimed to significantly enhance the quality of NI Water's public water supplies in line with stringent water standards set out by the European Union.
When Dalriada began planning for the contract, it was keen to find a solution that would provide the best balance between the initial installation costs and the total operational costs over the 25-year period.
The contract win means that Dalriada Water will be responsible for the water production for 25 years.
For this reason we needed to consider all possible costs from initial equipment and installation costs, through to operational and maintenance costs for the 25-year period.
The contract was a huge project for Dalriada and it needed to work with an equipment supplier who it knew it could trust to do the job well.
Siemens offered a fieldbus solution for use in the project. The configuration used involved both new and proven technologies, integrating ProfiNet and Profibus across the plant. Using the S7-400 controller allowed a Profinet ring to be installed around the plant, giving all the advantages of Industrial Ethernet at the Plant level, but with real-time capabilities and then links were installed down to Profibus which was used in local areas for remote I/O and motor control.
The fieldbus solution meant that the installation costs were reduced and as it included wireless communications, cabling requirements were reduced even further. In addition this made installation quicker and easier and less materials were used in providing a building to house the equipment as the building needed to be smaller..
The networked solution also allows for operators and engineers to access the site remotely, via SCADA software installed on to a laptop. This means that live data can be collected and viewed by the plant operator or engineer, on their laptop, wherever they may be. This remote access means that network monitoring can be carried out more quickly and for a lower cost, as it is not necessary for an operator to physically go into the plant in order to collect the data. This is a huge benefit for general plant monitoring, but also makes identifying any problems on the network far quicker and easier. When there is a problem, the operator will be alerted instantly as to where and what the problem is without physically needing to go into the plant to establish what is wrong.
Safety communications were also a big aspect of the Siemens solution. An S7-416F/PN Failsafe Controller and Failsafe ET200S Distributed I/O were installed, allowing Profisafe to be used for the safety communications. This allowed a single network to be installed for standard and safety communications around the plant, reducing engineering costs. In addition, the safety I/O was connected to go straight back to the PLC, meaning that faults could be identified more easily, improving safety.
The solution also provided a higher level of safety than is currently required by European standards. Where as current legislation means that SIL-2 is required, the solution installed by Siemens is at SIL-3 standard, in anticipation of future legislation changes.
Northern Ireland Water supplies 910 million liters of water a day and is responsible for 38,000km of water mains and sewers, along with 47 water treatment works and 918 wastewater treatment works. It supplies water to the entire population of Northern Ireland so it is important that its equipment is well maintained so that it can supply the best service for its customers.