4 ways to reduce energy use in mixing applications

With rising energy prices, wastewater treatment plants and industrial facilities are taking a closer look at how they can reduce energy use in their mixing operations. Mixing is an energy-intensive process, but advances in mixer design and technology are showing that mixer energy consumption can be significantly reduced – by as much as 50% in some cases.

To get an idea of how much energy mixing uses, it is estimated that mixing consumes between 5 to 10% of the world’s total electric power. In wastewater treatment plants, mixing can use 5 to 20% of the plant’s total energy consumption, but can also sometimes be used to reduce the far larger aeration energy by substantial amounts. Reducing energy use can not only lower operating costs, but also contribute to more sustainable operations.

Here are four ways that public utilities and industrial facilities can improve efficiency and reduce energy use in mixing applications. These recommendations are based on Xylem’s 60 years of experience in developing mixers for wastewater treatment and other processes, as well as over 300,000 installations of Flygt mixers worldwide.

1. Proper mixer sizing

A mixer's size generally refers to its physical dimensions and capacity to handle a specific volume of fluid. In some processes, particularly wastewater treatment, larger mixer sizes have traditionally been selected to handle peak conditions, such as maximum flow or maximum load. The thinking is that selecting larger mixer sizes will avoid the risk of undermixing, however, this practice often wastes energy and could result in suboptimal processes, such as overmixing. 

Instead of using oversized and overpowered mixers, operators should consider upgrading to more modern mixers that can change speeds and use high-efficiency motors. It’s also important to remember that more input power (the energy the mixer uses) does not necessarily lead to better mixing. Instead, optimal mixing should be based on how much thrust the mixer produces divided by the power it consumes. This will give you a much more accurate understanding of a mixer’s energy efficiency.

2. Variable speed submersible mixers

To solve the problem of overmixing or undermixing, submersible mixers can be connected to external variable frequency drives (VFDs) or use drives integrated with the mixer’s submerged motor. With this type of adaptive mixing, the mixer’s speed is adjusted so that the required output (thrust) matches changing conditions. The result is greater flexibility to address changing conditions and less energy use.

Xylem’s Flygt adaptive mixers, for example, can adjust to actual process conditions and reduce energy consumption by up to 50%. In 2015, Flygt introduced the first mixer to provide variable speed mixing without using an external, tank-side variable frequency drive. This integrated drive technology is predesigned and pre-optimized for its motor, eliminating the complicated installation process of matching the external VFD with the mixer’s motor.

3. Optimized propeller design

When looking to reduce energy consumption, several features of a mixer’s propeller are particularly important. The shape of propeller blades, for example, should be designed to minimize resistance while maximizing thrust. The propeller diameter should also be sized for the specific application, as this ensures effective mixing while keeping power within permissible limits and ensuring an optimal hydraulic environment for the mixer.

Self-cleaning blade designs are also important, as debris build-up can require more energy use to overcome resistance. Flygt’s signature banana-blade propellers, for example, have a backswept, self-cleaning design that provides energy-efficient, non-clogging performance.

First launched in 1984, the banana-blade propellers have been have continuously improved over 40 years to ensure maximum thrust with minimal energy consumption.

Flygt also designs propellers with materials that resist wear and corrosion, including reinforced polyurethane, stainless steel, hard iron and duplex steel, to ensure continued efficiency over time.

4. Upgrading to IE3 or IE4 motors

Upgrading to mixers that use energy-efficient motors can significantly reduce energy consumption and operating expenses. The International Electrotechnical Commission (IEC) sets specific standards for electrical motors, defining the energy efficiency of a motor based on how much energy is lost between consumption and output. For example, IE1 motors are about 88% efficient, IE3 motors are nearly 94% efficient, and IE4 motors exceed 96% efficiency. Upgrading from IE1 to IE3 or IE4 motors, therefore, can yield substantial energy savings.

Modern Flygt mixers have robust and high-efficient drive units with IE3 and IE4 motors, helping operators meet energy-efficiency requirements. For even more energy savings, Flygt’s adaptive mixers have IE4-equivalent permanent magnet motors that can produce the equal amount of thrust as a standard compact mixer’s direct drive motor with up to 50% less energy input.

Ready to reduce your energy consumption?

Xylem’s experts can help you design the most energy-efficient solution for your mixing application. We offer a broad range of mixers that deliver the best performance for the least lifecycle cost.