MechChem Africa March 2017

MechChem Africa

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March 2017

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Products and industry news

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EW-Eurodrive has recently

completed a delivery of ten cus-

tomised aerator drive systems

destined for a wastewater treat-

ment plant being upgraded in Meyerton.

“Springing fromour core agitator gearbox

business, wewere approachedby anOEM

for wastewater treatment, management

systems and services that was handling

the upgrade on behalf of thewater 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

verticallyhungMC-seriesgearboxcoupled

to a DRN IEC motor.

Aeration is the critical stage of the

activated sludge treatment process, a

process that oxidisesbiologicalmatter 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.

Aerator drives

and the single source advantage

SEW-Eurodrive recently supplied ten of its DRN IEC motors directly coupled to MC-series gearboxes for the

aerators at a local wastewater treatment plant.

The supply of ten SEW-Eurodrive DRN IEC 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.

Surface aerator impeller vanes are

used to pull wastewater up from the tank

anddischarge it horizontallyoutsideof the

impeller rim. A liquidplume 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 IEC

motors and four with 55 kW motors,”

Swanepoel says.

TheMCgearbox range is purpose built

for mixing, agitating and aerating applica-

tions. “Our portfolio of high-torque and

robust industrial gear units is designed to

meet themost rigorous torque and shock-

loading requirements,” says Swanepoel.

Large axial and radial forces occur

along the impeller shaft during these pro-

cesses and SEW-Eurodrive has overcome

this problem with its extended bearing

distance (EBD) design. This extends the

life of the bearingswithin the gearbox and

prevents theneed for oversizedgearboxes

or additional support bearings.

“Wedesignour gearboxes for abearing

life of 100000hours, 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 horizon-

tally (on the side of the tank) or under the

tank in special cases, and both left and

right output shaft positions are possible.

SEW-Eurodrive uses a calculation

program designed specifically to select a

gearbox suitable for the application. “We

use this program to determine whether a

gearbox selection is adequate, based on

the calculated torques, loads and bending

moments. This is particularly important

when it comes to aerators and mixers. So

these are not off-the-shelf products, but

have been selected specifically for the

system in question,” he says.

Swanepoeltells

MechChemAfrica

about

gear ratios used for theMeyertonaeration

project: “The 45 kWunits are fittedwith a

gearbox with a 32.22 reduction to rotate

the impeller at around 46 rpm from the

four pole, 1 470 rpmasynchronousmotor

speed,” Swanepoel responds, adding that

the more powerful 55 kW units turn the

impeller a little slower at 41 rpm from a

higher ratio gearbox (35.78).

“The impeller speeds and gearbox

torques are all very carefully selected so

that the impellers can continuously sup-

ply the optimum quantity of oxygen to

the process. Too little oxygen slows the