Text: Susanna Lidström
Scana Steel has raised efficiency levels and improved its environmental footprint at its forge in Björneborg, Sweden thanks to a range of oxyfuel technologies from Linde Group member AGA.
Steel production has a long tradition in Sweden’s Björneborg, where the first forge was built back in 1656. Now, some 350 years later, the forge is at the cutting edge of steel production thanks to a range of oxyfuel solutions implemented by current owner, Norwegian industrial group Scana, with the help of AGA.
Scana Steel Björneborg employees 350 people at its steel plant, forge, heat treatment facility and machine shop. In 1997, the company installed oxyfuel burners, followed by flameless combustion technology in 2005 and a new flue gas system in 2008 – since then the company has never looked back.
“Oxyfuel has given us the additional heat we need for the volumes in our furnaces,” says Hans Joelsson, Project Manager and former Forge and Maintenance Manager at Scana Steel Björneborg. “Without it we wouldn’t be where we are today.”
Forge manager Leif Näsman agrees. He explains that like many other companies in the steel industry, Björneborg has seen market demand leap in recent years. Its forge is running at full capacity to meet orders for the large rotationally symmetrical parts it specialises in. These include propeller axles for ships and rotor axles for wind power stations.
To make the parts, ingots weighing between 5 and 75 tons have to be heated from around 650°C to 1250°C in the forge. Before the installation of REBOX®, this process took place at a rate of 10 to 15 degrees per hour.
“When we installed the oxyfuel burners, we saw our heat rates leap to 50 degrees an hour in tests,” says Joelsson. “That equates to significant time and energy savings.”
Air contains nitrogen, which has to be heated during combustion. Oxyfuel technology uses pure oxygen for combustion instead of air, making it a more efficient process by eliminating the nitrogen ballast. Oxyfuel combustion also requires significantly less fuel than conventional technology, thus reducing carbon dioxide emissions.
Yet although oxyfuel burners use pure oxygen, they still generate a significant amount of nitric oxide emissions. This is because air still gets into the furnace, and once this comes into contact with the very hot flame generated by conventional oxyfuel combustion, it produces nitric oxides.
The forge in Björneborg has been using AGA’s flameless burners since 2005. The resulting flame is wider and diluted by furnace gases, producing a lower maximum flame temperature without impacting heating capabilities.
Pressure regulation is a key factor in reducing the risk of leakage and undesirable air intake. Switching from air to oxygen reduces flue gas streams by around 80 percent. When this happens, the flue gas ducts also have to be reduced proportionately to prevent low pressure sucking the heat out of the furnace and pulling in cold air. Scana Björneborg initially regulated this by throttling the flue ducts. In summer 2008, however, the company installed a completely new flue system from AGA.
“Previously, the flue gas ducts exited high up in the furnaces,” says Näsman. “With the new system we have moved them down so that they are now at hearth level. This makes it easier to maintain uniform pressure in the whole furnace, and it has cut fuel consumption by five to ten percent”.
To further reduce the risk of leaks, the company also replaced the hatch closing in one of the furnaces with a modern model from AGA.
“Our forge furnaces are from 1980 and are starting to show signs of wear,” says Näsman “Sealing is important to gain the full benefit of oxyfuel combustion”.