Pumping stations are essential for water treatment. You’re probably thinking that this is unfortunate, as these systems, which circulate massive amounts of water through the various treatment and purification stages, are prone to failure and consume a great deal of energy. Festo has developed a safe and energy-efficient automation solution for these ‘problematic cases’, which has proven itself around the world hundreds of times over. The check valves are the key here. You won’t need these at all if you are using a Festo solution.
The tirelessly running pumps in a wastewater treatment plant circulate enormous amounts of water. This requires massive machines – and their energy consumption is equally massive. Unsurprisingly, the energy consumed by wastewater treatment plants accounts for up to 20% of municipal electricity costs. A large part of this is due to pressurisation, while the pumping stations are the second cost driver. This is particularly the case when outdated technology is used, especially when several pumps are running at the same time. And when you have to have other pumps on standby for reasons of redundancy.
It is clear that energy-efficient processes are needed and are thus increasingly in demand. We know from experience that most systems offer a huge potential for saving energy. Let’s look at a conventional pumping station first. Or you can skip straight to the Festo solution .
Even nowadays, the pumping stations of many wastewater and water treatment plants are protected in a conventional way by mechanical check valves. In general, check valves are meant to prevent the backflow of water should the pump come to a standstill. But the solution that uses mechanical check valves has several disadvantages. Above all, it is prone to failure and is inefficient.
The main problem is that a check valve, because of the valve disc, acts as a form of resistance to the pump’s performance that it must first overcome. This requires more energy than would really be necessary. Even worse, a check valve impacts operational safety. When the pump comes to a standstill, a gas bubble created by microorganisms is formed that prevents the pump from automatically starting back up. This means that the check valve must first be activated manually so that the gas bubble can escape and the pump can start.
What’s more, in the long run, closing check valves can also create water hammer, which causes the piping systems to vibrate. This makes damage to the pipes more likely. And there is a further factor that shortens the service life of the whole system: check valves are prone to leaks. And these leakages and backflows are difficult to detect. Once the damage has become visible, it’s often not just the check valve that needs to be replaced; in the worst case, you will also have to replace the entire pump.
Instead of mechanical check valves, Festo offers a reliable and energy-efficient solution for pumping stations: automated gate valves with pneumatic linear actuators. The process valves are connected via a centralised or decentralised PLC.
An important argument in favour of pneumatically automated knife gate valves is that the pump no longer has to work against the flow resistance generated by the check valve. The energy savings that this generates for the pump are far greater than the energy required for the additional controller and for generating the compressed air.
The NAMUR valves, which are controlled by a centralised or decentralised PLC and mounted directly on the linear actuator, ensure that the knife gate valves open and close at the same time as the pump. If unwanted cavitation does occur, the gas bubbles escape immediately when the gate valve is opened so that pump operation is not compromised. And there no longer is a risk of water hammer in the piping system thanks to the controlled closing function. Furthermore, there is less wear on the automated knife gate valve and a tighter seal, which significantly extends the service life of the system.
Even in the event of a power failure, your system remains reliable and moves into a safe position; if there is a voltage drop, a compressed air reservoir automatically springs into action for the compressor. Pneumatic actuators have three emergency functions: open, close, stop. This means that the process valves are guaranteed to function correctly in any situation.
Automated gate valves with pneumatic linear actuators from Festo offer a number of concrete benefits:
To date, Festo has successfully implemented the described solution in over 100 water treatment and more than 200 wastewater treatment plants. For example, at the Sindelfingen wastewater treatment plant. The plant treats the wastewater generated by roughly 250,000 residents in southern Germany. In the pumping station, which feeds the wastewater from the primary settlement tank for biological treatment, there are six centrifugal pumps, each with a power consumption of 90 kW and a pumping capacity of up to 500 l/s at a discharge head of 8 to 9 m. Depending on the volume of wastewater, up to five of these pumps are in operation at any one time. One pump is for redundancy purposes.
Prior to the upgrade, the check valves had to be kept open at all times, but this reduced the flow rate by up to 10%. In addition, the free flow cross section was reduced, and the piping system suffered from water hammer when the check valve closed.
Since we completely replaced the check valves and their functionality by pneumatically automating the existing knife gate valves, the same pump flow rate has been achieved with significantly less energy. The Sindelfingen wastewater treatment plant now saves almost 90,000 kWh of power per year. This corresponds to 2% of the wastewater treatment plant’s total energy requirements and represents an annual saving of over 11,000 euros. The municipal authority invested 25,000 euros in this solution. If you do the maths, you’ll see just how quickly Festo automation pays for itself.