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Stahl Gerafingen Restarts Siemens-Upgraded Finger-Shaft EAF

04/21/2008 - Stahl Gerafingen restarts their finger-shaft electric arc furnace following an extensive upgrade by Siemens Metals Technologies to increase productivity and reduce emissions.

Stahl Gerafingen AG, Switzerland, (part of the Beltrame Group) recently restarted their modernized finger-shaft electric arc furnace. The objective of the modernization, carried out by Siemens Metals Technologies, was to increase productivity and to reduce the emissions of the steelworks, which is located in the midst of the town of Gerlafingen. Contractual performance parameters were met within the first week of operation week.
 

Siemens Metals Technologies’ shaft furnace allows scrap to be preheated in a shaft installed above the EAF using the latent as well as chemical heat of the EAF off-gas. This innovative, energy-saving solution allows a facility to significantly reduce its electrical energy consumption and tap-to-tap times.
 
At Stahl Gerlafingen, special scrap-retaining "fingers" suspend the scrap within the shaft where it is preheated for the next charge. After the liquid steel has been tapped, the fingers open downwards and the first charge of preheated scrap drops into the EAF shell.
 
When the first charge of preheated scrap is charged into the furnace, a second scrap basket is immediately charged into the emptied shaft. As the scrap inside the EAF shell melts, scrap within the shaft gradually descends.
 
Once there is enough room in the shaft, the fingers are closed again and the first scrap charge for the next heat is loaded. This process allows 100% of the entire scrap charge to be efficiently preheated.
For the upgrade, the EAF was equipped with a new shaft, including scrap-retaining fingers for the scrap preheating, an improved off-gas exhaust system, and an optimized charging process. The capacity of the modernized furnace was increased considerably and the availability of the plant exceeded 98% within a few weeks after commissioning.

 
Siemens’ project scope for the modernization comprised the engineering, supply and installation of a new shaft and furnace equipment. This included the roof of the EAF vessel, the shaft-support structure, the shaft itself, the scrap-retaining fingers within the shaft, and a shaft-roof slide gate. Siemens also developed and supplied a tighter off-gas exhaust system equipped with a movable collar for better dilution-air infiltration, and a newly designed scrap-basket-guidance and -positioning system to improve scrap charging into the shaft and minimize spillage. Siemens also upgraded the hydraulic, automation and visualization systems for the finger-shaft EAF, which it had originally supplied to the company in 1996.
 
The furnace has a tapping weight of 80 tonnes of steel. Following the modernization, tap-to-tap times were shortened by more than two minutes, primarily due to the more efficient and faster charging of scrap into the shaft, improved scrap preheating, and the optimized off-gas flow within the shaft. Natural gas consumption for post-combustion could be reduced by more than 6% due to the enhanced off-gas control system and reduced dilution-air intake. The tighter shaft design and faster scrap-charging system also helped to significantly reduce emissions to the surrounding steel bay. Finally, the design of the shaft top and funnel together with exact scrap-bucket positioning for charging means less scrap spillage and potential damage outside the shaft, reducing downtime and maintenance.
 
With Siemens Metals Technologies’ shaft furnace, scrap is preheated in a shaft installed above the EAF using the latent as well as chemical heat of the EAF off-gas. This process makes possible significant reductions in a facility’s electrical energy consumption and tap-to-tap times.
 
At Stahl Gerlafingen, special scrap-retaining "fingers" suspend the scrap within the shaft where it is preheated for the next charge. After the liquid steel has been tapped, the fingers open downwards and the first charge of preheated scrap drops into the EAF shell. When the first charge of preheated scrap is charged into the furnace, a second scrap basket is immediately charged into the emptied shaft. As the scrap inside the EAF shell melts, scrap within the shaft gradually descends. Once there is enough room in the shaft, the fingers are closed again and the first scrap charge for the next heat is loaded. This process allows 100% of the entire scrap charge to be efficiently preheated.
 
Stahl Gerlafingen, the leading Swiss supplier of reinforcing steel products, produces steel for the construction industry as well as for the machine and vehicle construction industry from scrap which is sold as structural and reinforcing steel, steel mats and accessories, flat steel bars, universal plate and rolled wire.
 
The Siemens Industry Sector (Erlangen, Germany) is a leading supplier of production, transportation and building systems. The Sector comprises six Divisions: Building Technologies, Industry Automation, Industry Solutions, Mobility, Drive Technologies and Osram. In fiscal 2007 (ended September 30), Siemens Industry generated sales of approximately EUR40 billion (pro forma, unconsolidated) with around 209,000 employees worldwide.
 
With the business activities of Siemens VAI Metal Technologies, (Linz, Austria), Siemens Water Technologies (Warrendale, Pa.), and Industry Technologies, (Erlangen, Germany), the Siemens Industry Solutions Division (Erlangen, Germany) is one of the world's leading solution and service providers for industrial and infrastructure facilities. Using its own products, systems and process technologies, Industry Solutions develops and builds plants for end customers, commissions them and provides support during their entire life cycle.