Advances in actuation

Actuators provide essential behind-the-scenes technology that aids automation of the water treatment process, writes Ian Sully.

For more than 100 years, actuators have played a critical supporting role to valve technology. Integrated into control systems and converting signals into mechanical motion, actuators are linked to control centres / monitoring consoles or rely on their own intelligent electronics.

Actuation technology's primary function is to control valves that, in water treatment applications, link to treatment plants or filtering systems.

Actuators are used for open/close valve applications to divert flow to different areas of the works to meet the utility's treatment requirements. Alternatively, where actuators are used in flow control duties, the actuator operates the valve in modulating mode, increasing or decreasing the amount of medium that passes through the valve into or out of the treatment plant.

Modulating duty actuators are able to precisely control the flow and are capable of a regulation frequency of up to 1,200 starts per hour, which converts to one movement every three seconds.

Reflecting wider technology trends, actuator design has evolved to lightweight, user-friendly designs comprising motor, gearbox and some form of limit and torque switching. The option of modular actuation solutions has further extended the application of actuators in the water sector with actuator components dove-tailing together to provide a mix-and-match solution.

The appeal of the new-generation actuators, and the evidence of their effectiveness, has resulted in a rapid uptake in their use. Today, it is rare to find a water treatment plant that does not use actuation technology.

The water industry has been pioneering in its acceptance of actuation technology - users in this sector have frequently been at the forefront of actuator applications, demonstrating to other industries the capabilities of the solutions.

Taking fieldbus technology as an example, WwTWs were early adopters of the digital systems introduced in the early 1990s, which provided a new level of sophistication for actuator solutions. New-generation bus technology removed the need for hard wiring and presented a simpler and more effective option that offered many benefits, including cost savings.

Traditionally, a 20-core multi cable had been connected to each actuator at the plant. But, with the digital option, a simple two-core cable could be used resulting in less cabling, providing significant cost reductions.

With just two wires instead of 20, commissioning has become easier with less chance of wiring errors.

Digital technology has also substantially increased the feedback of process information. Providing almost unlimited data feedback, the user can obtain precise information by adopting bus technologies relating to the site's processes.

A recent example of the adoption of Profibus technology in the water sector is with two major Southern Water contracts that will use digital actuation technology supplied by Auma.

Actuation development continues, and the functionality of actuators at wastewater treatment sites has been further extended in a technology initiative spearheaded by ITT Sanitaire. Its improved variant of the sequential batch reactor (SBR) is known as the Intermittent Cycle Extended Aeration System (ICEAS), where influent wastewater continually flows into the reactor.

A constant review of technology to respond to user needs is undertaken by ITT Sanitaire. And a recent advancement using actuators from SIPOS, a sister company to AUMA actuators, has been introduced to meet the variable speed requirements of the ICEAS decant operations at wastewater treatment plants.

In the SBR process, wastewater is added to a single batch reactor, and fluid is treated to remove undesirable components and discharged. A single batch reactor will fill, aerate and clarify wastewater. A number of reactors may be used in parallel to optimise performance. SBRs are established as a successful method of processing wastewater in a range of applications as they are suitable for large variations in flow conditions. As long as the flows and loads remain within the design parameters, SBRs produce sludges with excellent settling properties.

Owing to the continual flow of influent into the ICEAS SBR, control of the process is achieved through a simple time-based system. During the aeration phase, air is introduced via fine-bubble diffusers at the base of the tank to activate the sludge.

After a preset period, the air is turned off and the basin enters the settlement phase to allow the biologically treated particles or flocs to settle to the bottom before the clean, treated liquid is decanted from the top of the SBR during the decant phase. The ICEAS process is an enhanced variation of the standard SBR that enables the procedure to take place in a single basin, even during the settling and decant phases of the operating cycle. The solution is an automatic system that responds to flow and load variations, and according to the company it is easily expanded and produces a high-quality effluent.

In the last two decades, there have been major advancements in actuation technology in the design, data feedback, variable speed solutions and technological capabilities. Twenty years ago, actuators were basic mechanical devices consisting of little more than a motor and a few switches. Utility companies now benefit from compact, intelligent, multi-functional devices.

Users of actuators also have the option of sourcing modular solutions which meet the precise process requirements of the works' needs, while providing the flexibility for future adaptation.

With today's modular option, the efficiency of a water treatment works is increased as technology can evolve to meet changing requirements without down-time as any upgrades take place on site without having to replace the actuator.

Modular solutions look likely to become established as the preferred mode of operation, and advancements will be made through incorporation of intelligent communication technology.

Ian Sully is managing director
of Auma UK. T: 01275 871141

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