02 January 2012
Medway Galvanising Company provides galvanising, powder coating, stripping and shot blasting services for all types of architectural and structural steel for customers in the South East of England. As part of its galvanising service, it processes up to 12,000 metric tonnes of steel a year, based on 24-hour production from Sunday to Saturday. Galvanising is carried out in the zinc dipping bath, which contains 145 metric tonnes of molten zinc at 450°C. An extraction system over the zinc dipping bath is used to extract the harmful fumes given off in the process. The fan on this extraction system was initially run at full speed for 24-hours a day, even when not needed.The new installation involves an ABB standard drive and a high efficiency 37 kW ABB motor. For most of the time, the motor runs at half speed, or 25 Hz. A limit switch detects when the crane carrying the components to be dipped is over the zinc bath, signalling the drive to ramp up the motor to full speed to achieve the maximum extraction rate. This maximum speed is required for between 10 and 20 minutes, depending on the weight of the component being dipped.Steve Lovelock, engineering manager for the plant explains more about the project: “We have always been keen to save as much energy as we can throughout the plant, and so in 2005 we started an energy saving project that resulted in us receiving climate change levy discounts. We identified the extraction fan motor as the largest energy user in the plant, and we wanted a solution that would improve its energy efficiency.”Mid Kent Electrical (MKE), an ABB Drives Alliance member, was approached for help in achieving the right solution. “We have worked with MKE for some time,” said Lovelock. “Not only are they local, but they provide a fast, quality service, rewinding our motors and carrying out all our pump maintenance with the fast turnarounds we need.”MKE installed an energy monitor on the application over a complete production week to determine its exact energy use. This showed that the motor would use just over 215 MWhr a year, at a total cost of around £20,000.Following this, an ABB variable-speed drive was fitted and the monitoring repeated. This showed that with the variable-speed drive in place, Medway Galvanising would achieve a reduction of just over 105 MWhr a year at a cost of around £9,800. This is an annual reduction in running costs of £10,200 and a cut in CO2 production of some 60 tonnes a year.“We estimated we could achieve a saving of around £8,500 so the actual savings we are making are even better and we are still getting the effective fume clearance we need. The fact that the motor is not working constantly flat out will also extend its life. We are currently conducting a motor management survey of other large energy using applications on the site so there could well be other uses for variable-speed drives in the plant,” concludes Lovelock.
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