Wheels of steel turn from gold to platinum

Magnetto get top award

Award

Details

The Magnetto-Topy team receive the award for energy saving. From left to right; Magnetto-Topy’s Dave Pound, Operations Manager and Phil Smith, Maintenance Service Administrator; Steve Ruddell, General Manager Drives and Motors, ABB: Brian Dick Managing Director, Sentridge Control.

In addition, there was a significant reduction in pump noise, which will help the former Dunlop company meet new health and safety levels set at 80dbA.

The cooling tower drives have replaced star-delta switching which turned the pumps on or off. Under the previous arrangements, the pumps were left running at full speed on 50Hz, regardless of production needs.

With the drives fitted, Magnetto-Topy has been able to reduce the running speed on one pump, rated at 55 kW, to 35 Hz, resulting in a 53% energy saving. On three other pumps the running speed is reduced to between 40 to 45 Hz, reducing energy consumption between 33 and 46%.

Steve Ruddell, general manager for ABB’s drives and motors comments: “The energy saving achievements of Magnetto-Topy, while significant, only scratch the surface of what can be achieved. If this company can save over 1,000 MWh of energy on seven pumps and fans just think what UK industry could be saving collectively. The figures are mind blowing. And with industry out to cut costs wherever possible, what easier win is there than taking a hard look at your electricity bill.”

Dave Pound, Operations Manager at Magnetto-Topy comments: “We have a very proactive policy to reduce our energy consumption. But variable speed drives are different to the usual measures like switching off lights etc. With drives you know it is going to work from the moment they are switched on and you walk away, unlike some other measures, where you need the involvement of people to remember to switch off lights.”

More savings achieved

Magnetto-Topy is achieving unprecedented energy savings by applying closed loop control to an existing variable speed drive installation. The original installation saved the company some £23,000 per year in energy. But an additional 50% energy saving has now been achieved by applying closed loop flow control, using water temperature as the control variable.

Platinum results

A PID controller is inserted within the control loop so that the loop can be tuned to ensure stable and accurate control with good response times. Because the PID controller is built into the ABB drive, the benefits of closed loop control can be realized without the additional expense of external control equipment.

A PID (Proportional-Integral-Derivative) controller is a universal type of controller that helps eliminate any error and improve steady state performance, as well as improve dynamic performance.

Magnetto-Topy use four drives, rated from 37 to 55 kW, on water pumps within four cooling towers that supply water to the wheel making process. Before installing variable speed drives, the company used star-delta switching which turned the pumps on or off. Thus, the pumps were left running at full speed on 50Hz.

With drives fitted, the company can reduce the running speed on a 55 kW pump to 35Hz, resulting in a 53% energy saving.

A further assessment showed that by applying closed loop control, the energy consumption could be reduced by an additional 50%. But Magnetto-Topy was cautious about further slowing the pumps, because of the risk presented by legionella bacteria, which can spawn in cooling towers. To prevent this, a continuous water flow is essential.

Along with water flow, the water temperature needs to be maintained at a maximum of 20º C to prevent the growth of legionella bacteria. Changing the water flow rate can also affect the water temperature.

So the system was tuned for these worse case conditions, which normally only occur during the summer, when the water temperature reaches its 20º C maximum. But during the winter months when the water temperature is naturally cooler, there is an opportunity to slow the pumps down even further. This is where PID control comes in.

A transducer is placed into the water tank and this feeds the temperature measurement back to the drive. So at 20º C, the drive is running at 40 Hz. As the temperature drops to 13º degrees C and below, the drive runs at 25 Hz. As the temperature of the water rises, the pump speeds up and allows more water to cascade over the cooling tower.

“The result is that with PID control, the energy bill has been halved yet again,” says Phil Smith, Maintenance Service Administrator. "PID control is a compensatory control method. Without it we have to cater for the worse case which means running pumps at 40Hz, which is the summer setting."

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