Application of an Off-Gas Analysing System to Control Oxidation during Stainless Steelmaking in an EAF

During stainless steelmaking in the electric arc furnace at Deutsche Edelstahlwerke GmbH, oxygen is injected to oxidize unwanted tramp elements mainly carbon and silicon. Unfortunately the injected oxygen also oxidizes valuable elements such as chromium and iron, which causes an economical loss and has a negative environmental effect. Since the temperature and dilution techniques to minimise chromium oxidation are seldom applied in the electric arc furnace, a new strategy to minimise chromium oxidation has to be developed. This paper proposes a new strategy which involves the use of a continuous off-gas analysing system to minimise chromium oxidation by monitoring the oxidation products in the off-gas, i.e. CO and CO2. During stainless steelmaking in the electric arc furnace, for which initial carbon and silicon input cannot be precisely known due to imprecise scrap analysis, the installed off-gas analysing system should provide precise information concerning an efficient oxygen injection. This would then directly prevents excess chromium and iron oxidation. A continuous off-gas analysing system installed at Deutsche Edelstahlwerke GmbH delivers a promising result for future applications. During the plant trial, the efficiency of oxygen injection as well as the chromium and iron yields were increased.