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Case Studies - Mining

NZ Steel

Case Study: Lime and Steel Production

Product Sector: Industrial-Steel Production

Location: Glenbrook Steel Mill, New Zealand

Products: Burnt Lime, Limestone Chip and Hydrated Lime

Source/ Interviewee: New Zealand Steel-Connal Holmes, Principal Technologist, Steelmaking

 

Introducing New Zealand Steel

  • New Zealand Steel Limited is NZ’s sole producer of flat rolled steel products for the construction, manufacturing and agricultural industries
  • Using locally-sourced iron sand, NZ Steel produces around 620,000 tonnes of steel each year
  • The company is committed to being a world-class steelmaker, and exports about 60% of its steel output

The challenge: Securing top grade lime products to produce top grade steel

  • New Zealand Steel operates a fully-integrated steel mill at Glenbrook, about 60 kilometres south of Auckland
  • Crushed burnt lime transferred by pneumatic line of the steelmaking furnace, to generate slag to remove impurities from the steel
  • According to NZ Steel’s Principal Technologist, Steelmaking, Connal Holmes: “We need a very high grade limestone to produce the burnt lime – we can not have excessive levels of impurities like silica, which would cause wear on our transfer system.” The other specific requirement is the size of the lime; it cannot be larger than 1mm or it will not fluidise and inject via the tuyere [or nozzle] to the furnace interior. “We also use lump burnt lime at the ladle treatment station to create the slag that we want. We add limestone chip to the furnace as a coolant, and we use hydrated lime as a water treatment for pH control.”

Why Graymont?

  • Product quality/quality control

Graymont carries out routine chemical analysis and sizing checks to ensure that finely ground calcium oxide is supplied within tight standards that is required by New Zealand Steel.

  • A great relationship

“We have good communication and a very open way of talking with McDonald’s (now Graymont) . We have regular meetings, plant familiarisation visits to each other's operations and very few issues" says Connal. 

  • Long association

The two businesses share a long history.When McDonald’s relocated to the Waikato in the 1960s, it coincided with the opening of the Glenbrook mill.
“We’ve worked with McDonald’s ever since both our businesses began in the 1960s,” says Connal. “It’s a mutually beneficial relationship.”