The supply of ten SEW-Eurodrive DRN motors with MC-series gearboxes for the aerators at a local wastewater treatment plant represents the first project success for the company’s new IE3-rated motors since their release into South Africa last year. MechChem Africa talks to head of projects, Rudi Swanepoel.
SEW-Eurodrive has recently completed a delivery of ten customised aerator drive systems destined for a wastewater treatment plant being upgraded in Meyerton. “Springing from our core agitator gearbox business, we were approached by an OEM for wastewater treatment, management systems and services that was handling the upgrade on behalf of the water board,” says Swanepoel.
Having designed the wet-end of the aeration system, the OEM contracted SEW-Eurodrive for the supply of the drive ends of these systems, each consisting of a vertically hung MC-series gearbox coupled to a DRN motor.
Aeration is the critical stage of the activated sludge treatment process, a process that oxidises biological matter and removes nutrients such as nitrogen and phosphorus. Aeration supplies the oxygen required to accelerate sludge activation. “Simply put, an impeller is used to churn up the surface and bubble air into the wastewater,” Swanepoel explains.
Surface aerator impeller vanes are used to pull wastewater up from the tank and discharge it horizontally outside of the impeller rim. A liquid plume is created that maximises the contact area between the air and the water, causing air and oxygen to be continuously mixed, dissolved and circulated through the wastewater being treated.
“We supplied gearboxes from our mixer and agitator (MC) range, coupled to the motors. Ten drive systems in total were supplied, six with 45 kW DRN motors and four with 55 kW motors,” Swanepoel says.
The MC gearbox range is purpose built for mixing, agitating and aerating applications. “Our portfolio of high-torque and robust industrial gear units is designed to meet the most rigorous torque and shock-loading requirements,” says Swanepoel.
Large axial and radial forces occur along the impeller shaft during these processes and SEW-Eurodrive has overcome this problem with its extended bearing distance (EBD) design. This extends the life of the bearings within the gearbox and prevents the need for oversized gearboxes or additional support bearings.
“We design our gearboxes for a bearing life of 100 000 hours, which is just short of 10 years of operation. Thermal ratings are also excellent. We don’t get overheating, particularly on the MC range, even under high ambient temperatures,” Swanepoel adds.
For surface aeration applications the MC gearbox is installed vertically above the tank, but for mixing or agitation use, these units can also be installed horizontally (on the side of the tank) or under the tank in special cases, and both left and right output shaft positions are possible.