Maximising mixing: is it time to look beyond motor efficiency?
Against a backdrop of rising energy costs and tighter sustainability goals, maximising mixing efficiency is critical. Traditionally, the spotlight has been on motor efficiency to boost performance but this overlooks the influence of other key factors at play. Hanna Do, Global Product Manager at Xylem explains why it’s important to look beyond IE motor ratings and the primary considerations for selecting a submersible mixer.
Effective wastewater treatment relies heavily on proper mixing. It plays a vital role in keeping solids suspended, reducing sediment build-up and facilitates biological nutrient removal. Yet while mixing is central to the effective running of a plant, it is energy-intensive. Getting the right mixing solution, that delivers performance and efficiency gains, is therefore business critical.
Rethinking motor efficiency
When selecting a mixer, historically it has been common practice to look at motor efficiency – and it’s easy to see why. Mandatory efficiency classes for electric motors have become more widespread, especially in the European Union. All electric motors in the EU between 75kW and 200kW had to meet the IE4 efficiency-class requirements by July 2023.
Mechanical power is only one aspect of mixing efficiency though. It’s crucial to look at the overall energy efficiency of the mixer. This broader perspective has a far more significant effect on both operating expenses and energy consumption than solely focusing on the motor’s efficiency. In fact, our studies show that hydraulics contribute to as much as 80% of the mixer’s total energy efficiency.
An example of this is the Flygt 4530 hybrid mixer. It has an IE3 equivalent motor but what sets it apart is its highly efficient hydraulic design, due to its 1.2m stainless steel propeller. This is also the case with the Flygt 4230, which has an IE4 equivalent motor and is available with either the 770mm or 1.2m stainless steel propeller.
To achieve the best mixing efficiency, you therefore need to evaluate the entire mixing system design – including the placement of the mixer, effectiveness of the hydraulics, the characteristics of the material being mixed, and the mechanical power involved.
Get retrofitting
Enhanced mixer efficiency isn’t limited to new installations. Retrofitting existing mixer systems offers a straightforward and affordable way to take advantage of technological improvements. Many plants have successfully modernised their older installations by incorporating IE3 motors. As an example, customers have replaced their high-speed mixers with a Flygt 4530 hybrid mixer or Flygt 4230 adaptive mixer if they want an adaptive option to improve the efficiency of their plant. The Flygt 4530 and 4230 can easily replace high speed compact mixers as they are able to fit onto the same guide bar.
A case in point
When a wastewater treatment plant near Florence, Italy, needed to replace a set of mixers, Flygt 4530 was the clear choice to retrofit with. The Publiacqua treatment plant, which handles more than 65 million cubic meters of wastewater annually, found the hybrid mixer was the stand-out winner in operational efficiency in all 24 tanks tested. This was thanks to its larger propeller and lower speed of rotation. Compared to a direct-drive, compact high-speed mixer, the Flygt 4530 can reduce energy use by up to 50%.
The bigger picture
Whether you’re installing a new mixer or need to upgrade your existing system, focusing on motor efficiency alone won’t deliver the benefits that are critical to operational success. It’s time to rethink mixer efficiency and look at the bigger picture to maximise operational gains and cost savings.