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Safeguarding Wellington’s water supplies

When the Greater Wellington Regional Council wanted to improve the reliability and operational flexibility of its Te Marua water treatment plant, it chose a ControlLogix process automation control solution from Rockwell Automation.

The reliable provision of clean water is essential for any large population. In the modern age, the pressure has never been higher for water authorities to be able to consistently meet variable consumer demands with safe, dependable water supplies. It is now commonplace for water treatment plants to run autonomously and, for this to be effective, a reliable process control system is needed to supervise plant activities. Through the 1980s, distributed control system (DCS) architectures were widely used to manage these processes. However, many of these systems are now reaching the end of their design lives, and consequently suffer from declining availability of spares, and waning access to technical assistance.

This was the situation faced by the Te Marua Water Treatment Plant in New Zealand. Functioning in parallel with two additional water treatment facilities, Te Marua supplies up to 50 per cent of Wellington city’s annual water consumption. The three plants are owned and operated by the Greater Wellington Regional Council (GWRC), and were all facing increasing problems sourcing spare parts and expertise for their legacy operating systems. In addressing the issue, GWRC decided to upgrade the 22-year-old DCS system at Te Marua to an Allen-Bradley ControlLogix programmable automation controller (PAC) from Rockwell Automation.

Standardised solution

At the Te Marua water treatment plant, ControlLogix process automation control solutions were installed from Rockwell Automation.

According to GWRC Control Systems Development Technician, Philip Wilkie, the legacy DCS system had reached the end of its technical and commercial life. “Getting spare parts was an increasing problem, but the biggest risk was that there were progressively fewer specialists in New Zealand who could support the system,” he says. “A major fault onsite had the potential to seriously jeopardise the water supply for Wellington. We gravely needed an alternative process control solution with a ready supply of parts, and a good level of support.”

In addition to these requirements, the GWRC was looking for a solution that would be compatible with the existing human machine interface (HMI), which provides a common graphics package system-wide across the entire water distribution network. Moreover, it needed to be compatible with other reporting systems being run by the council, and provide a platform that could support future improvements and innovations. “We had reached a dead-end with the old system. We could not expand or develop the functionality as we were unable to efficiently write new code for the system,” says Wilkie. “With three plants each running a different control system, our goal was to bring these into line on a common process automation platform.”

The Allen-Bradley ControlLogix solution from Rockwell Automation proved an obvious choice. “It was the only option to meet all requirements for the three different plants,” says Wilkie. “ControlLogix has the most extensive control capabilities, and is—quite simply—the best automation platform in its class.”

The solution implemented is based on a redundant pair of ControlLogix processors, which are linked to the HMI/data network via Ethernet. “ControlLogix is rapidly emerging as an industry standard PAC for Water and Waste Water treatment plants in New Zealand,” says Rockwell Automation Industry Manager for New Zealand, Prasad Nory. “Furthermore, it is widely used across a broad spectrum of process control applications in industry, which means there is a great deal of expertise in the marketplace with these systems.”

Simultaneous operation
As the Te Marua treatment works cannot be taken offline for more than 12 hours without impacting Wellington’s water supply, it was essential to keep the existing plant running while the new control system was installed. “We decided to install the ControlLogix platform between the legacy DCS and the I/O it was controlling,” Wilkie explains. “This means that when the DCS directed a pump to run, for example, it actually instructed the ControlLogix system to carry out the function. The beauty of this set-up was that it allowed us to transition control one element at a time, and test each function of the new system as we progressed.”

Once the new hardware was installed, and all connections between the legacy DCS system, ControlLogix and the I/O thoroughly tested, it was possible to systematically turn off the DCS supervision to each element in turn. This was conducted in a live environment with no need for downtime.

As part of the upgrade, 40 peripheral programmable logic controllers (PLCs) were removed, and their functions assumed by ControlLogix. Additionally, 400 analogue and 4000 digital I/O points were also replaced using a combination of Allen-Bradley FLEX I/O and POINT I/O, linked to ControlLogix via a fully media-redundant ControlNet network. “One of the huge benefits of POINT I/O is that it is sufficiently compact to allow it to be squeezed into the cabinets alongside the legacy I/O,” says Nory. “This reduced the complexity of migrating control to POINT I/O, and helped significantly in maintaining the uptime of the system throughout the transition period.”

Successful switchover

Jeremy McKibbin of GWRC inspects the installation of the Rockwell Automation ControlLogix system.

Once the control functions for the valves, motors and pumps had been transferred to ControlLogix, the procedural functions—such as the dosing, filtering, sequencing and backwashing were also brought across from the DCS, one element at a time. The last stage was to transfer control of the main site inlet valve, and a range of chlorine instruments. This final cutover involved a plant shutdown of just four hours. In total, the transition of plant automation control from DCS to ControlLogix was accomplished in six months.

“I’ve been involved in a number of similar upgrades, and this has run the smoothest,” says Wilkie. “ControlLogix is extremely intuitive to use and program, and this enabled us to complete the whole project in-house, for a small fraction of the cost that it would have been if we had employed a third-party systems integrator.”

The advantages provided by ControlLogix were not limited to the transition phase. The system is inherently more reliable, and if faults do occur, they are easier to rectify. “Parts sourcing is simple and quick compared to the DCS,” says Wilkie. “The system support and industry expertise available for ControlLogix is also phenomenal. Having configured this system in-house, our own knowledge of the system is extremely good, and this gives us a much greater sense of ownership over it.”

The plant is now easier and more intuitive to operate, and provides a platform from which improvements can be made more readily. Energy and chemical costs onsite have already been reduced by an estimated 15 per cent, and greater familiarity by site personnel has allowed more functionality and performance to be leveraged from the system. For example, backwash time of the filters has been reduced from four to two hours, and maximum production capacity has potentially increased from 100 to 120 mega-litres per day.

Ongoing savings
Further enhancements are already underway at Te Marua—made possible by ControlLogix. As part of GWRC’s ‘water information system’, FactoryTalk Historian data-collection software and FactoryTalk VantagePoint data-reporting software from Rockwell Automation are currently being installed onsite. These will improve the delivery of documentation required by the council—especially Drinking Water Standard reports.

“We have many requirements onsite for data collection and reporting,” says Wilkie. “Until now, we have spent a great deal of time and resources on manually preparing reports. Now, with FactoryTalk Historian and FactoryTalk VantagePoint, we will be able to capture the data and prepare reports easily in a fraction of the time. We are expecting to save as much here in operational expenses, as we have with the process control improvements.”

The move to a ControlLogix platform has also opened the doors for incorporating advanced process control into the plant’s operations—especially with chemical dosing. One of the principal coagulants used onsite is Aluminium sulphate, and while the facility is already running a world-class system for ‘alum dosing’, Wilkie believes advanced process control offers the scope to further refine this.

“We are currently using an on-line spectrophotometer to monitor raw water quality and provide real-time prediction of the exact amount of alum required based on the measured concentration and type of organics in the raw water,” Willkie says. “Traditional, feedback methodology often results in under - over-dosing. We anticipate usage reductions of alum—our biggest chemical cost on site—by as much as 20 per cent as a result of this new technology. The advanced ControlLogix platform we are now running will allow us to take full advantage of this information to ensure we are eliminating organics in the treated water to exactly the level desired.”

The upgrade to ControlLogix at Te Marua has been a resounding success, bringing new levels of reliability, functionality and controllability to the plant. “We are using this project as a template for upgrades at other water treatment works, and have already implemented the same PAC platform at our Waterloo plant,” Wilkie says. “The future of Wellington’s water supply is now assured by ControlLogix.”