Supersonic injection has become a widely-used way to decarburize steel in the EAF using O2. Air Liquide, through an extensive research and development program, has developed the ALARC-JET to help steelmaker optimize its use of oxygen in the EAF. Results of theoretical studies, confirmed by a sophisticated experimental program and long-term industrial test are: 1. The geometric design of the nozzle is the most important parameter to create a regular jet with minimized turbulence, thus allowing to increase the jet's coherency length. To achieve this, design of the converging-diverging nozzle must include very specific parameters. Conventional supersonic nozzles being used in the steel industry do not incorporate in their design the specific parameters to create an adapted jet. 2. Quality of manufacturing, especially inner surface quality is also a key factor to prevent from creating any disturbance of the supersonic gas flow at the exit. 3. The coherent zone of the jet is defined as the length of the potential core flow, that is to say the region in which the axial velocity is constant and supersonic. 4. An innovative formula is proposed to calculate and predict the coherency length of the jet. The validity of this formula has been confirmed with an extensive 3D-modeling study. This formula is very useful to quickly select nozzle design and operation parameters for a specific application required by a steelmaker. 5. According to this formula, the key parameters are: a / upstream pressure of the jet, b/ ambient temperature and c/ gas flow-rate. In industrial conditions, theoretical optimized coherency length can vary from 1,3 m up to 1,8 m for oxygen flow rate of 2500 Nm3/h to 4500 Nm3/h. During decarburization process, the ambient conditions are very favorable to increase the coherency length. Temperatures of 1900 K have been measured. Coherency length under these conditions is 3 to 4 times the coherency length in room temperature conditions. ALARC-JET is made of a range of supersonic oxygen injectors with enhanced properties for Electric Arc Furnaces. ALARC-JET injectors can be located in EAF walls, in combination with or without burners, depending on location and whether or not there are existing devices at a given location. ALARC-JET technology is especially attractive for all oxygen injection technologies retrofits operation. ALARC-JET efficiency has been shown on a 165-ton furnace, on which only one injector installed in November 1999 has the tap-to-tap time by 0,5 to 1,5 minutes. The extreme simplicity of ALARC-JET design ensures it has maximum reliability for decarburazing. Additional implementations are in process, in several BOF plants (converters and secondary metallurgy) as well as in non-ferrous converters.
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