Welsh Water is investing £200m to upgrade its water treatment works across Wales by 2015. This includes the water treatment plant at Cwellyn, where Rotork’s intelligent electric valve actuators have been installed to control the flow through a new state-of-the-art extension to the works.
The new plant at Cwellyn has been designed and built by Black & Veatch, one of Welsh Water’s asset management alliance partners for water supply capital investment schemes. The new treatment regime is designed to clarify the water before it enters the existing works in order to deal with changing raw water conditions and consistently meet all water quality standards. Rotork IQT direct drive quarter-turn intelligent electric actuators have been installed to operate butterfly valves controlling the flow of water throughout the new treatment plant.
Patrice Nadouce, mechanical engineer for Black & Veatch at Cwellyn, explained that Rotork was selected following a competitive bidding process. The selection criteria included value for money, reliability, low-cost of ownership and operator familiarity. All the Rotork IQT actuators are Profibus DP-enabled and linked to an existing distributed control system (DCS) on five two-wire bus networks. The operation of the plant is supervised by a SCADA system designed by Oasis Engineering.
Water from Llyn Cwellyn, some two kilometres distant, gravitates to the new treatment plant at a rate of up to 850m³/hr. The flow initially passes through inlet static mixers where coagulant is dosed to maximise the performance of the dissolved air flotation (DAF) process. The flow is divided into three identical DAF streams, which consist of one Flocculator followed by one DAF cell where particles in suspension are floated to the surface to form a sludge blanket.
The clarified water is then filtered through first stage rapid gravity filtration (RGF) before being pumped to the existing treatment works through ultra-violet disinfection to deactivate cryptosporidium.
The Rotork IQT actuators, including some modulating units, control all valve operations including the inlet works flow control, automatic desludging of the DAF cells, automatic backwashing of the RGF plant and the plant treating the effluent created by the clarification and filtration processes. The successful completion of the upgrade project at Cwellyn will safeguard the drinking water quality for 70,000 Dwr Cymru Welsh Water customers in the Caernarfon area.
