Rotork IQPro intelligent electric actuators with Profibus two-wire digital control provide an adaptable, reliable and economical solution for automated valve monitoring and control. Two recent projects undertaken by Wessex Water serve to illustrate the benefits of adopting Profibus-enabled Rotork actuators for automated valve control in new-build schemes and modernization programs in existing plants.
SCADA screen at Maundown, monitoring the operation of rapid gravity filters.
CASE STUDY: MAUNDOWN WATER TREATMENT PLANT
Maundown water treatment plant was originally built in the 1960s and first extended in the early 1970s. The site has recently been entirely redeveloped to further improve the quality of drinking water, upgrade the water treatment facilities and meet the increased demand for water from the 200,000 customers served in central Somerset.
More than two hundred Rotork intelligent electric valve actuators have been installed throughout the £25 million ($38 million) project at Maundown. Under PLC control, Profibus-enabled Rotork IQ and IQT electric actuators operate penstocks and butterfly valves to control the flow of water and sequential backwashing operations throughout the new state-of-the-art treatment plant, comprising raw water screening, dissolved air flotation, rapid gravity filtration and granular activated carbon treatment followed by chlorine contact tanks. As well as increasing the treatment capacity to 82.4 MI/D, the improved treatment processes overcome taste and odor problems caused by increased algal blooms in the local water sources resulting from changing weather patterns.
HMI screen at Maundown. The Rotork actuators can be interrogated, monitored and controlled at these stations.
ANTICIPATING DEMAND
Swanage sewage treatment works utilizes the latest membrane bioreactor technology to produce high quality effluent that exceeds EU standards and is cleaner than the sea into which it is discharged. The site treats sewage for a population of around 10,000 which can more than double when the area is busy with holiday visitors. A major plant upgrade at the site has introduced automation and energy saving measures, while increasing the size of the membrane treatment plant to provide spare capacity for future demand. Following preliminary screening and grit removal, sewage enters Kubota membrane plants installed in six large tanks for biological treatment and disinfection.
The upgrade involved doubling the number of membrane plants in each tank to thirty-six thus considerably increasing the treatment capacity without exceeding the confines of the existing works’ footprint. Automation of the treatment process has also enabled it to run with increased efficiency and reduced energy consumption.
Central to the upgrade, Profibus-enabled Rotork IQT actuators have been installed to operate butterfly and plug valves on new pipework throughout the plant. On each of the membrane plants, the Rotork actuators operate inlet isolation and outlet modulating valves for the sewage, together with air, sodium hypochlorite and wash water injection valves. Other IQT actuators control permeate isolation valves used for automated sequential flushing to maintain membrane efficiency. In total fifty-one actuators are installed on each tank to provide automatic sequencing of the sewage treatment, membrane cleaning and backwashing processes.
HMI screen at Swanage, displaying actuator status.
ACTUATORS AT WORK
At both sites, the Rotork actuators are linked on Profibus-DP two-wire networks to PLCs in motor control centers. These are controlled by a PLC and SCADA system written by Wessex Water’s in-house Automation Team. The control PLC is a twin CPU (Central Processing Unit) configuration, with one dedicated to the control and monitoring of the actuators whilst the other runs the complex 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, stored in the actuators’ data loggers, is available locally at the valve, on nearby HMIs, on site SCADA systems and remotely at Wessex Water’s regional operation center at Bath, some sixty miles from both sites. Remote diagnosis is recognized by Wessex Water as a cost effective method of maintenance and service as it enables the right operational staff to be sent to a site when required. Diagnostics also allow the plant to run with increased efficiency by ensuring that maintenance is only performed when it is absolutely necessary, ruling out the need for over-cautious routine maintenance schedules.
IQT actuators controlling the backwashing sequences on the membrane plants at Swanage.
SOPHISTICATED BUT SIMPLE
The sophisticated control benefits provided by Rotork IQPro actuation technology combine with Rotork’s mechanical design features to deliver long term low cost of ownership, optimum reliability and maximum plant availability. Among these features, the double-sealed, IP68 watertight and temporarily submersible enclosure ensures that the actuator will operate reliably in the most challenging environments. “Non-intrusive” set-up and commissioning technology eliminates the need to remove the actuator’s electrical covers on-site once the electric connections are made in the separately sealed terminal compartment.
With the high level of process automation enabled by the Rotork actuators comes the added benefit of process integrity auditability, together with highly reliable and accurate process control. The effective use of Profibus technology has allowed significant installation savings in cabling, terminations, PLC hardware and labor. As a further assistance to maintenance, the actuators utilize Rotork’s “bumpless” Profibus interface module, enabling individual motorized valves to be disconnected without disrupting communication with other devices on the network.
Profibus-DP V1 enabled Rotork IQT intelligent electric valve actuators control the air supply to the new activated sludge plant (ASP) at Weston-super-Mare STW.
CASE STUDY: WESSEX WATER
Rotork flow control equipment has been installed throughout a major water industry AMP5 environmental improvement project at a sewage treatment works serving Somerset’s largest tourist resort on the southwest coast of England.
The upgrade project at Weston-super-Mare STW has been performed by a partnership made up of the Halcrow Group, Dean and Dyball Civil Engineering, Nomenca and Wessex Engineering and Construction Services. The Rotork equipment was supplied in accordance with the Framework Agreement that the company holds with Wessex Water.
This IQ3 unit, the latest version of Rotork’s intelligent actuation product range, drives through Rotork IB gearboxes and extension drive shafts to control the position of the two outlet modulating penstocks on the site’s new ultraviolet disinfection plant.
HIGH STANDARDS
Wessex Water has invested heavily at the site to achieve improved bathing water quality for the resort of Weston-super-Mare. The improvements will ensure that the site can cope with increased population and continues to comply with standards set by the Environment Agency. The work has been completed ahead of the revised Bathing Water Directive, which comes into force in 2015 and introduces more stringent water quality standards.
A new process plant has been constructed to improve secondary treatment by the replacement of submerged biological contactors with an efficient and reliable four-channel activated sludge plant (ASP), combined with increased final settlement capacity. This enables the newly installed ultraviolet disinfection plant to achieve better microbial reduction and meet strict consent levels in the final effluent. The upgraded site is designed to deliver a flow to full treatment (FFT) rate of 16,642 gallons per minute (1050 liters per second).
Additional work on the site has involved the introduction of storm settlement tanks with a capacity of over 23,000 tons (21,000 tonnes) to assist the reduction of over-spills in combination with a separate program to remove surface water flows into the area’s foul sewer network.
Rotork IB gearboxes are installed for the manual operation of isolating valves at site locations including the pumping stations.
SUPERIOR CONTROL
Rotork’s scope of supply for flow control in the project encompasses IQ multi-turn and IQT quarter-turn intelligent electric actuators and IB manual gearboxes for motorized and hand operated valves and penstocks throughout the new works. All electric actuators are Profibus-DP V1 network enabled and centrally controlled by a SCADA system designed by the Wessex Water Automation Team. The use of Profibus technology, a standard feature of Wessex Water’s automation programs, delivers significant savings in cabling, terminations, PLC hardware, and labor.
The SCADA system runs the automated processes and collects control, status and diagnostic data from each actuator. This information is available on the site and at Wessex Water’s regional operation center at Bath, where remote diagnostics has proved to be a cost effective method of maintenance and service by identifying the right operational staff to be sent to site if required. ■
_________________________________________________________________________
ABOUT THE AUTHOR
Mike Heuseveldt is the marketing coordinator for Rotork Controls, Inc. and can be reached at 585.247.2304 ext. 10268, or by email at mike.heuseveldt@rotork.com. For more information, visit www.rotork.com.
_________________________________________________________________________
MODERN PUMPING TODAY, August 2013
Did you enjoy this article?
Subscribe to the FREE Digital Edition of Modern Pumping Today Magazine!
Keep Control, Keep it Clean
