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18/02/2011
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Outokumpu Stainless is set to save £300,000 a year on fume extraction energy, thanks to the installation of four ABB variable speed drives.
 Its stainless steel plant in Sheffield operates a stainless melting and continuous casting (SMACC) facility, producing around 260,000 tonnes of steel a year in a mix of slab bloom and billet.
David Cobley, engineering manager for the SMACC facility, explains that the melt shop has an electric arc furnace, an argon oxygen decarburising vessel, a ladle arc furnace, a continuous slab/bloom casting machine and a continuous billet-casting machine – all generating dust and fumes.
Four extraction ducts on the plant lead to a common mixing chamber, from which air is extracted by four 1,200kW centrifugal extraction fans operating in parallel, he says.
Until last year, those fans were run by 11kV motors connected direct-on-line, with three running fixed-speed simultaneously and one assist. However, as they were becoming obsolete, along with their oil circuit breakers, Outokumpu decided to investigate variable speed drives.
ABB won the £1.6m contract to supply four 1.2 MW water-cooled drives – including the provision of motor bedplates, removal of old equipment, project management, integration of control equipment, a service contract and an extended 36 month warranty.
Pressure in the common mixing chamber is now kept at a constant negative -8 mbarg. Each extractor duct has its own damper, so, if a lot of dust is being produced, a damper opens wider under PLC control. A pressure sensor in the mixing chamber then feeds back to the PLC, which signals the drives to provide more extraction.
Cobley says the system now allows fume extraction to follow demand, saving an average of 18% on electrical energy – and leading to the projected £300,000 per year cost reduction – as well as helping Outokumpu Stainless to meet its environmental commitments by saving 5,000 tonnes of CO2.
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Author
Brian Tinham
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