ArcelorMittal Riverdale maintenance manager, Ken DeGroote, is rotating the coupling by hand and looking for buildup of debris on cooling fans of the newly-installed adjustable speed drive

As an alternative to a variable frequency drive, ArcelorMittal Riverdale saves energy and increases reliability through the installation of an adjustable speed drive with permanent magnet torque transfer.

The action of starting up a motor creates stress on the coupling and shaft. Over time, repeated stress can cause a failure. This was the case on a precipitator at the Riverdale plant. A precipitator removes dust and fine particles from gas.

“We needed a way to soft start the motors for the fans,” said Ken DeGroote, BOF maintenance manager. “We also wanted to stop or at least slow down the fan speed, so we could clean the hoppers without totally shutting down the motor.”

DeGroote investigated medium voltage soft starts, VFDs, fluid couplings, gear reducers, belt drives and changing from medium voltage to 480 volts. While any of these might work, none provided a good return on investment.

“I started looking at different variable couplings – some of Nikola Tesla’s work – and came across the idea to use magnets for coupling purposes. I contacted MagnaDrive Corporation and found a solution,” said DeGroote.

The couplings were installed during Riverdale’s annual outage. Immediate benefits included the reduced starting torque and energy savings.

“We were pleasantly surprised to see how quickly the starting amps came down after reaching full motor speed. With the old system, the high amps would be sustained for about 22 seconds as the fan got up to speed. Now it takes only two seconds and the starting amps are much lower.”

The switch to the magnet system has improved production by reducing failures. Crews are able to clean hoppers without the delay of shutting down the motor. The plant has reduced its energy consumption and the return on investment came in under 1.3 years.