Festo is combining measurement, control and regulation technology with pneumatic actuators and valve terminal blocks, along with its Aquatronics training capability, to supply customised automation solutions for water and wastewater treatment. MechTech talks to Durban-based industry segment specialist for water & wastewater at Festo, Strini Perumal.
“Globally we have been automating water treatment plants for many years, and for the past few years we have been growing our water offering in the southern and South African market,” begins Perumal. “A key focus for us is providing complete turnkey solutions for municipalities, water utilities and industrial treatment plants,” he adds.
“South Africa has many manual system, where operators need to open and closer valves using wheels and levers. Festo provides fully automated systems, which offer much better control of water or wastewater treatment processes and deliver better and more consistent water quality. Equally important, though, is maintenance and these systems have built-in diagnostics and are designed for easy plug-and-play maintenance,” he tells MechTech.
“In partnership with water infrastructure contractors, we provide turnkey installation packages for water service providers with all media valves, pneumatic actuators, controls and up to the SCADA and software for the main control room – and we are able to optimise an automation solution regardless of the plant’s size or location,” Perumal assures.
Describing the needs of a typical municipal treatment plant for potable water, he says that water is generally pumped into the plant from a river into a raw water reservoir. From there it is first chemically treated (pre-chlorination) to minimise algae growth, before being aerated for the removal of dissolved solids.
The water is then treated with clarifying agents or flocculants, which cause tiny dispersed particles called colloids to coagulate onto larger ones. “The treated water is then slowly mixed before being passed into a clarifier tank, where the heavier particles sink forming a sludge at the bottom of the tank, while the clear water is tapped off over a weir at the top.
The clear water then passes into filter beds, typically gravity-fed sand beds that remove the remaining fine solid particles. “Between cycles, though, these beds are cleaned, via a backwash process,” Perumal point out. The filtered water is again dosed to remove any remaining bacteria and then transferred to storage reservoirs as potable water.
“At every stage of this process, valves are used to control the process flow. Valve actuators open and close these valves. This used to be done manually, but we are now able to automate every part of the process, from level control to dosing management and back purging,” Perumal explains.
There are two technologies available for automating valve actuation, electrical or pneumatic actuation. “Based on extensive research by Festo, we have found pneumatic actuation to be far more economical than electrical. Pneumatic systems need a compressor, air driers and filtration units, which have to be piped through to the valves and actuators, while electrical systems only need power. But electrical systems are more expensive and they need specialised technicians to manage them. They also need more complicated programming, since they are continuously variable devices,” he says, adding that, “pneumatic valve actuators are much easier to manage. All they need is two air lines into each valve.”
Perumal argues that cost comparisons need to be evaluated over time. “While pneumatic actuation systems are often believed to use a lot of compressed air, this is not really the case. Once a valve has been opened, it stays open, without consuming additional air, so very little is actually consumed. We use compressed air storage tanks across the plant, and once these have reached system pressure, the supply compressor can shut down.
“But the air that is used needs to be properly cleaned and dried. In the past, we have found that operators haven’t been properly draining and cleaning out their filters. This causes condensation to accumulate in the airlines, which eventually damages the actuators,” he explains.
“In response, we have automated the draining of the filters on the compressors. This enables operators to realise even better long-term cost savings. Instead of having to send a technician to drain the filters, we have automatic dump valves on timers that will ensure that these filters are adequately drained,” he adds.
Festo has an agreement with compressor suppliers to incorporate these dryers as part of an integrated compressor solution. “Also, with these compressors, we offer maintenance contracts to service compressors during our warranty periods,” he says.
On a component level, Festo offers an extensive range of valves and actuators with unique features to improve product life. “On butterfly valves, for example, the rubber seats can leak. A traditional valve, which is often controlling the flow of dirty or chemically dosed water, fluid can leak though the valve stem and into the actuator itself, eventually causing damage and shortening the valve life.
“Festo has a safety relief system on its actuators to automatically purge any leakage, safeguarding the actuator and prolonging its life,” Perumal says, adding that these particular valves can operate for between 20 add 50 million cycles. “Festo also provides service kits for all of its actuators and service agreements can be also be adopted to further improve reliability.”
A cornerstone of lowering costs is the simplicity and maintainability of pneumatic systems over electrical equivalents. “We believe that pneumatics offers better solutions for South Africa in terms of long term operational and maintenance costs, largely due to the system’s simplicity.
“Conventionally, where a pneumatic valve was connected to an actuator, each valve would have its air supply and electrical power and control cabling routed back via a thick conduit though junction boxes to a centralised filter bank and back to the main control room. Now, we can use valve terminal block technology in decentralised Festo panels to significantly reduce the complexity and amount of piping and cabling,” Perumal says.
“From a decentralised panel, which includes its own filter unit, we can control a number of nearby valves. And between the panel and the valve actuators, we need only connect one pneumatic pipe and an electrical feedback cable.
“Communication between each distributed panel and the centralised SCADA control system is achieved via a Fieldbus connectivity such as Profibus, Ethernet or DeviceNet or any other single cable protocol. This system also enables self-diagnostics. If a coil, valve or actuator fails to reach the position required, this is immediately diagnosed and an alarm signal is sent to the main SCADA to direct the operator to the problem point. So faultfinding is easy and much more immediate, significantly reducing downtime,” he tells MechTech.
Valve terminal blocks consist of all the solenoids, pneumatic valves and input/output signal sensor – ultrasonic level sensors, temperatures probes, valve position sensors, etc. The sensors are all wired into the valve terminal block in the distributed panel, from where ‘intelligent signals’ are sent to the central controller. And the distributed panels are IP65 protects from dust, moisture and sunlight.
“Panels are easy to access. LEDs are used to detect problems and, to replace a single valve-slice of a terminal block, all you need to do is to isolate the main pressure into the panel, remove two screws on the faulty terminal and replace it with a new one,” says Perumal.
Festo is currently involved with a rural project that involves remote monitoring and control. “At a water treatment plant in northern KwaZulu-Natal, we are installing an automated plant and SCADA system that will allow the water treatment plant and the pump station to be managed from one central point. Using the CPX-MPA valve terminal block, which has its own built-in PLC and wireless communication system, operators have full control functionality and faultfinding capability from the remote control and monitoring office.
In addition, for small rural treatment plants using borehole water, for example, Festo has a solution for containerised water treatment. “These systems have all the required water treatment processes packaged into a transportable container. This removes the need for any civil construction onsite, making it an ideal rural solution, particularly if coupled with remote control and monitoring,” suggests Perumal.
“We are a complete solutions provider in the automatic water treatment space,” he concludes. “This is a differentiator for us. We even offer the operator training courses at several different level through the globally developed Aquatronics courses.”