Profibus network-enabled Rotork IQT intelligent electric actuators have been installed to operate butterfly and plug valves on new pipework at a sewage membrane treatment plant. The upgrade involves increasing the number of membrane packs in each tank to 36, increasing the treatment capacity without exceeding the confines of the existing works' footprint. Automation of the treatment process also enables it to run with increased efficiency and reduced energy consumption.On each of the membrane plants, the Rotork IQT actuators operate inlet isolation and outlet modulating valves for the sewage, together with air, sodium hypochlorite and wash water-injection valves. Additional IQT actuators control the permeate isolation valves used for automated sequential flushing to maintain membrane efficiency. In total, 51 actuators are installed on each tank to provide automatic sequencing of the sewage treatment, membrane cleaning and backwashing processes. 14 Profibus-DP two-wire networks link the actuators to PLCs in the site's central MCC. These are controlled by a PLC and SCADA system written by Wessex Water's automation team.
The control PLC is a twin CPU configuration, with one dedicated to the control and monitoring of more than 300 actuators, while the other runs the automation process, resulting in the collection of control, status and full diagnostic data from each actuator, without any PLC speed or memory limitations. Diagnostic information is available, locally at the valve or nearby HMI, on the site SCADA system and at the regional operation centre at Bath. Running costs are expected to reduce due to more effective control of the plant.
