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A stainless steel plant in Sheffield is set to save GBP300,000 a year on its fume extraction energy costs thanks to the installation of four ABB variable-speed drives.

Outokumpu Stainless operates a Stainless Melting and Continuous Casting (SMACC) facility at its Sheffield site, producing around 260,000 tonnes of stainless steel a year in a mixture of slab bloom and billet.

The SMACC melting shop is equipped with an Electric Arc Furnace (EAF), an Argon Oxygen Decarburising (AOD) vessel, a Ladle Arc Furnace (LAF), a continuous slab/bloom casting machine and a continuous billet-casting machine.

All these processes generate large quantities of fumes and dust, requiring an efficient extraction system.

This is based on four extraction ducts, leading to a common mixing chamber.

From here, the air is extracted by four 1,200kW centrifugal extraction fans operating in parallel.

Built in 1977, the plant was using the original equipment installed at the time – fans run by 11kV motors connected direct-on-line.

These fans were no longer in production and the oil circuit breakers they used were becoming expensive to replace.

The demand for extraction was governed by the melt shop production and therefore the amount of fumes produced.

Three of the four motors were usually run simultaneously and could supply the extraction needed at full power, but if the fume levels decreased, the motors could not follow demand as they would still be running at full speed.

Outokumpu decided to investigate the potential for using variable speed drives to run the extraction system.

Following a competitive tender process, ABB won the contract to supply four 1.2MW water-cooled variable-speed drives.

The GBP1.6m contract included the supply of four motor bedplates, removal of old equipment, a service contract, project management, integration of control equipment and an extended 36-month warranty.

The pressure in the common mixing chamber is kept at a constant negative value of -8 mbarg.

Each extractor duct has its own damper.

If a lot of dust is being produced, a damper will be opened wider by the PLC.

A pressure sensor in the mixing chamber feeds a signal back to the PLC, which commands the drives to provide more extraction to maintain the required negative pressure.

Installed in summer 2010, the system now allows fume extraction to match demand, saving an average of 18 per cent on electrical energy use over the previous DOL method.

This is set to cut energy costs for the application by GBP300,000 a year, as well as helping Outokumpu Stainless to meet its environmental commitments by saving 5,000 tonnes of CO2 per annum.

ABB Automation Tech – Drives and Motors

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