Making water treatment processes more efficient

Bauer Gear Motor has teamed up with pump manufacturer Allweiler to reduce the energy usage of eccentric screw pumps installed at the Stendal wastewater treatment plant in Germany, by fitting highly efficient permanent magnet synchronous motors (PMSMs).

The wastewater treatment plant at Stendal is aiming to be entirely energy self-sufficient by 2025. The site has a biogas production facility which provides low carbon energy from waste. Sludge produced from treating wastewater is pumped into storage tanks then transferred to the biogas plant.

To reduce reliance on the grid and grow the percentage of operations supported by low carbon energy, operators at the plant began assessing equipment improvements to achieve this. The eccentric screw pumps were quickly identified as an area for enhancement.

Eccentric screw pumps are used to transport the large amounts of sludge generated during wastewater treatment. However, continuous operation requires a large quantity of energy. Furthermore, pumps often work at low speeds, which can result in the motors powering them operating inefficiently. With the stated aim of self-sufficiency in energy, Stendal wastewater treatment plant operators wanted to enhance the efficiency of these pumps to reduce overall energy demands. Luckily, a proven solution was ready and available to plant operators.

Bauer PMSMs feature an efficient rotor design matched to optimised permanent magnets, which the company says offer a distinct performance and efficiency advantage over traditional designs. There are no heat losses from the rotor, with total losses down by 25%. Operators typically benefit from consistent motor efficiency improvements of over 10% when compared to other drives. Bauer PMSMs are available to meet IE3, IE4 and even IE5 efficiency standards according to IEC TS 60034-30-2.

A key advantage for PMSMs in eccentric screw pump applications is that they deliver high torque at low speeds with increased efficiency. At Stendal, the pumps typically run at around 25 Hz to reduce wear and provide a performance reserve for high volumes of water – a frequency at which an asynchronous motor would have to be oversized to deliver the desired torque figure, resulting in energy inefficiency. However, due to inherent characteristics under partial load, PMSMs can deliver full torque at this speed with a smaller motor size. High torque is available from start-up too, ideal for pumping applications. Furthermore, operators can expect energy savings of more than 30% when under partial load compared to asynchronous motors.

For Stendal, Allweiler specified Series AE2E Eccentric Screw Pumps, a popular choice in wastewater applications due to the ability to handle highly viscous or aggressive liquids that contain solids or fibres. These were coupled to Bauer BG30 Helical-Series gears with PMSMs and installed in the cellar of the pumping house at the facility.

The benefits to the facility of moving to Allweiler pumps powered by Bauer helical PMSM geared motors have been illustrated by the data, as Micheal Riske, head of wastewater/water department at Stendal discovered: “We operated two identical pumps alternately with a PMSM and an IE3 asynchronous motor for a month each, comparing electricity demand and primary sludge pumping. The pump with the PMSM installed was found to have consumed 24% less energy.”

The low power consumption of the drives at Stendal ensured that ROI was achieved after only three months – this while reducing power consumption, enhancing performance and taking a large stride in switching to low carbon energy at the site.