Wastewater Pumping - Combining a Drive

With the launch of Flygt Experior, Xylem will introduce an extended range of Adaptive N pumps, available on all N pumps between 1.3 and 7.4 kilowatts (kW), or 2.2 and 11 horsepower (HP).

Adaptive N-technology allows the pump impeller to move axially upward when necessary to permit bulky materials or tough debris to pass through smoothly, significantly reducing stress on the shaft, seals and bearings.

"Flygt Experior builds on the premise that to achieve the highest possible reliability, efficiency and simplicity, three fundamental functions – hydraulics, motors and controls – all have to be optimised and able to work seamlessly together,” said Anders Fredriksen, head of Xylem’s wastewater transport business area.

Flygt Experior’s SmartRun intelligent controls enable the pumping system to be preprogrammed and pre-set to handle any wastewater handling situation, making it very easy to automate, install and operate. The SmartRun controls optimise energy use and can reduce energy consumption by an estimated 30% compared to conventional on/off systems.

CONTROLS FOR WASTEWATER PUMPING

Today there are generally two types of controls for wastewater pumping systems. Conventional on/off controls, which are simple to use but give limited opportunities to optimise functionality, and variable frequency drives which provide more fine-tuning possibilities but can be complicated to install and difficult to optimise. SmartRun solves this issue by combining the advanced functionality of a drive with a simple intuitive interface.

"While the internal functions are multifaceted, the interface is simple to operate,” added Fredriksen.

Flygt Experior is available with motors up to 70kW, or 105HP, optimised for wastewater pumping applications, including some models featuring a Line Started Permanent Magnet, or LSPM design.

All of the new motors comply with international Premium Efficiency Standard (IEC 60034- 30), commonly referred to as IE3.

With the LSPM technology, the Flygt motors supersede the nominal standard by up to 4%.

The LSPM design – said to be the world’s first for a wastewater pump – was first introduced in a Flygt compact mixer in 2009.

LSPM motors combine the efficiency of a synchronous permanent magnet motor with the direct on-line starting of an induction motor. They do this by combining a permanent magnet rotor for a better motor efficiency during synchronous running with an induction motor squirrel cage rotor to permit motor starting by direct coupling to power source.

Consequential challenges associated with this type of motor include higher cost, extra manufacturing burden and the transient and synchronisation behaviour.

THE ADAPTIVE N-IMPELLER

First introduced just under three years ago, this anti-clog impeller technology for wastewater pumps significantly reduces maintenance and energy costs. Adaptive N builds on technology originally introduced in 1997.

The problem with conventional impellers is the gradual build-up of stringy material. Over time, the passage in the impeller narrows, reducing the amount of water it can pump. So, as the impeller gradually clogs up, efficiency drops. In contrast, pumps equipped with the N-technique sustains efficiency at the original rated level.

The secret behind the N-technique is the combination of a swept-back leading edge and a relief groove in the volute. The leading edge on most impellers is axial. This is the ideal shape for rags and other long stringy material to wrap themselves around. To avoid this problem, the leading edges of the impeller were flattened and swept back to sweep solids from the centre to the perimeter of the inlet, enabling easy flow of detritus, virtually eliminating clogging under the most difficult of conditions.

To help really stubborn material pass through the impeller, the impeller can rise momentarily, axially upwards enabling very large debris to pass the impeller. After passage of the debris, the N-impeller immediately returns to the normal operating position in close proximity to the volute insert ring. A ‘relief groove means that, as the impeller turns, rags are forced into this spiral-shaped groove. The combined action helps to tug material from the impeller into the volute where it is free to be pumped away.

This impeller is now available for small Flygt N-series pumps. Using a Flygt N-pump with its adaptive Nimpeller also gives around 25% energy savings.