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Proven control on £17m water works

Proven control on £17m water works The Dee Valley Water (DVW) project to build a new water treatment works at its Llwyn Onn site in North Wales, has now been completed. The £17m project was officially opened in March and is controlled by a Mitsubishi Electric system redundant, Q series modular PLC solution.

The new works provides DVW with the capacity to produce 47,000m3 of drinking water per day for Wrexham and the surrounding area. In addition to the standard treatment processes, Llwyn Onn also includes an automated processing system for removing manganese, a mineral that occurs naturally in the surface water of the DVW area.

With so many people depending on a continued supply of clean water the process for selecting a reliable automation control system for the entire works was particularly stringent. In all, four automation providers, including Mitsubishi, submitted proposals which were scrutinised by DVW and the main project contractor Black and Veatch, before the preferred Mitsubishi solution was chosen.

The majority of the subcontract supply chain for this project has been sourced from the north Wales area, including the system integrator, Tycon Automation. Tycon has an extensive knowledge of the Mitsubishi product range, and was perfectly positioned to provide the integration for what is a large and complex site control solution.
The water treatment process consists of dissolved air flotation (DAF) clarification, granular activated carbon (GAC) filtration followed by rapid gravity filtration (RGF) and a chlorine contact tank before being pumped to a storage tank - from where it is fed into the distribution network. Although this is not the conventional process order, it is an arrangement that has been designed to work in this area, which has the additional issue of manganese to deal with.

A crucial aspect to the control system was the use of a full dual redundant PLC system. Complete with its own CPU, the secondary system is fully wired-in and tested, increasing the system reliability by mirroring the primary CPU so that in the unlikely event of a failure of the main CPU, power supply or base unit, the secondary system can take over within 21 milliseconds from the same control point.

Andrew Robertson, Technical Director at Tycon, says: "There were elements in the contract specification which in our opinion meant it suited the Mitsubishi hardware. Dee Valley Water were looking for a fully redundant system. They could see that we had achieved this before with a very reliable fully redundant architecture on a larger system installed on the Isle of Man, which we arranged for them to visit, it meant that we could meet both the performance targets and the price point set for this project.
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