AOD PRODUCTION HEAD -BOBILI

Job Description:

Argon oxygen decarburization (AOD) is a process primarily used in production of stainless steel and other high grade alloys such as silicon steels, tool steels, nickel-base alloys and cobalt-base alloys with oxidizable elements such as chromium and aluminum. AOD was invented in 1954 by the Lindé division of The Union Carbide Corporation, which became Praxair in 1992.

AOD converter is a pear shaped vessel usually lined with basic refractory lining. It has a removable, conical cover in place. The important feature of an AOD converter is that it is normally side blown. In case of those steel grades which can tolerate nitrogen, a mixture of oxygen and nitrogen can also be blown. As molten stainless steels do not generate foam, and most stainless steel refining processes are side or bottom-blown, the dimensions of a stainless refining converter are smaller than a comparable BOF (basic oxygen furnace) converter. Typical internal volumes of AOD converters are in the range 0.4 – 0.8 cum /metric ton bath weight.

For converters that tap into a ladle held by a crane, a sliced cone top section is often used. The slice portion allows the crane to come close to the converter mouth. Converters that tap into a ladle car usually have a BOF type concentric cone top section.

A high production shop typically has three interchangeable converters for 100 % availability of the process. At any given time, one of the converters is in the tiltable trunnion ring refining steel, a second newly lined converter is at a preheating station, and the third converter is at a reline station. The converter in the trunnion ring typically can be replaced with a preheated converter in less than an hour.

The AOD converter has tuyeres mounted in the sidewall or in the bottom. These tuyeres typically consist of a copper tube with a stainless steel outer tube. An annulus is formed between the copper and stainless tubes. Cooling gases blown through the outer annulus (shroud) form a metal or oxide accretion (called a mushroom) at the tuyere tip. This accretion protects the tuyere and surrounding refractory. Process gases of oxygen/inert mixtures blow through the inner annulus. Special designs exist for normalizing the flow in the annular gap. Tuyere size and number depend on specific process parameters. There are usually between two and nine tuyeres in an AOD vessel.

Sidewall mounted tuyeres are submerged while processing. When the vessel is rotated, the tuyeres are above the bath. At this point, the process gases can be shut off and a small cooling flow protects the tuyeres

Bottom blown converters have a variety of tuyere configurations depending on flow rates required. There are usually two to four tuyeres in the bottom.

A major modification of the AOD process involves the use of top blowing lance in addition to the side blowing tuyeres. The lance can be used to inject oxygen at desired blow rates to increase decarburization and/or post combustion. The top lance can also be designed for blowing mixed gases such as inert gas – oxygen mixtures. The installation of a lance and introduction of oxygen in the early stages of decarburization can reduce the time for a heat. The technology can be used to increase the productivity (tons/hour) of the steel melting shop. Most of the recent converter installations include the use of a top lance for blowing oxygen.

Another modification of the AOD process involves applying vacuum on the converter to reduce the consumption of argon and silicon as well as the process time when making low carbon grades. The modification is known as AOD-VCR.