On August 10, Austria-based giant engineering and plantmaking company Siemens VAI Metals Technologies (Siemens VAI) announced its replacement and restarting, within a period of just three weeks, of AOD (automatic overdrive) stainless steel converters at German stainless steel producer ThyssenKrupp Nirosta in Krefeld, a company of German industrial conglomerate ThyssenKrupp Steel AG.
According to a statement released by Siemens VAI, in the course of a modernization project at ThyssenKrupp Nirosta the engineering giant has replaced two existing stationary AOD vessels and started up two new exchange-type AOD converters, including auxiliary equipment. All installation work up until the converter startups in the spring of 2009 was carried out within a period of only three weeks, minimizing production downtime. Following the fulfillment of the guarantee performance figures, a final acceptance certificate was issued by ThyssenKrupp Nirosta.
Meanwhile, in another statement released by ThyssenKrupp, Harald Behmenburg, head of operations at the Krefeld steel mill, said, "The converter vessels are now enclosed. The dust and gases arising during charging or tapping the heat are now collected more effectively. The air is extensively filtered before it is released back into the atmosphere. That enables us to sustainably reduce diffuse dust emissions."
The produced steel grades comprise mostly high quality austenitic chromium-nickel grades used for a wide range of flat steel applications, said Siemens VAI.
In the stainless steel industry, special converters are used to make steel from a carbon-rich primary heat produced in an electric arc furnace. The molten metal is poured into the converter and oxygen or a mixture of oxygen and nitrogen or argon is added. In the converter the undesirable carbon in the steel burns off and passes into the flue gas, while chromium - the element that makes stainless steel stainless - remains in the molten metal. The flue gas is extracted and filtered.