Principle
The principle of the desulphurisation process is as follows:-
A ladle of liquid steel is transferred by car or turntable to the desulphurisation station. In this position, the ladle is covered by a hood which is designed to capture and extract the fume generated during the process, and, at the same time, minimise contact between the surface of the steel and the atmosphere.
For effective desulphurisation, the amount of slag carry-over from the furnace or convertor is minimised, and a basic synthetic slag is added to the ladle surface.
Desulphurisation is achieved by the deep injection of a mixture of elements including lime-fluorspar and calcium bearing compounds such as calcium silicide or calcium itself. These materials are injected through an immersed lance as fine powder, using argon as a carrier gas.
Sulphur dissolved in the liquid steel combines with calcium in the injected materials to form calcium sulphide, which floats up into the top slag.
The combination of the reaction between sulphur in the liquid steel and both the injected materials and the top slag is effective in producing extremely low residual sulphur levels of less than 10 ppm.
To achieve good results, the steel must be fully killed, with very low residual oxygen levels. The top slag must be within a fairly narrow compositional range, with very low levels of reducible oxides such as FeO, MnO and P2O5.
Process
The furnace or convertor slag is held back during tapping, as far as possible, or removed by deslagging after tap. The residual tapping slag is treated with aluminium pellets to reduce any remaining reducible oxides.
Synthetic slag is added to bring the top slag composition within the required range for effective desulphurisation.
The ladle is located in the treatment station, and then sealed as far as possible by a ladle cover. The ladle cover serves two functions, the first being to capture and remove fume generated during the process. The fume is removed by a duct which connects the ladle cover to a fabric filter duct cleaning unit. The second function of the ladle cover is to minimise atmospheric contact with the surface of the steel, which would cause oxidation and nitrogen pick up. For this reason, the ladle cover design is relatively sophisticated.
Fluxing of the ladle top slag is done by argon stirring, either by top lance or bottom porous plug. When the top slag is in the required condition, desulphurisation by injection begins.
A lime-fluospar mixture, which may be prefused, is injected into the steel through an immersed lance. Argon is used as a carrier gas. To increase the effectiveness, the lance tip is close to the bottom of the ladle. Calcium compounds are also injected, either in combination with lime-spar (co-injection) or separately (mono or sequential injection).
The amount of reagent injected is obviously dependant on the initial sulphur level and final required level. Calcium is also used to modify the shape of the remaining sulphides.
Both the total amount and the rate of injection are predetermined and controlled.
At the end of the injection, the lance is automatically retracted, and a sample is taken. The ladle cover is then raised and the ladle removed.
The principle of the desulphurisation process is as follows:-
A ladle of liquid steel is transferred by car or turntable to the desulphurisation station. In this position, the ladle is covered by a hood which is designed to capture and extract the fume generated during the process, and, at the same time, minimise contact between the surface of the steel and the atmosphere.
For effective desulphurisation, the amount of slag carry-over from the furnace or convertor is minimised, and a basic synthetic slag is added to the ladle surface.
Desulphurisation is achieved by the deep injection of a mixture of elements including lime-fluorspar and calcium bearing compounds such as calcium silicide or calcium itself. These materials are injected through an immersed lance as fine powder, using argon as a carrier gas.
Sulphur dissolved in the liquid steel combines with calcium in the injected materials to form calcium sulphide, which floats up into the top slag.
The combination of the reaction between sulphur in the liquid steel and both the injected materials and the top slag is effective in producing extremely low residual sulphur levels of less than 10 ppm.
To achieve good results, the steel must be fully killed, with very low residual oxygen levels. The top slag must be within a fairly narrow compositional range, with very low levels of reducible oxides such as FeO, MnO and P2O5.
Process
The furnace or convertor slag is held back during tapping, as far as possible, or removed by deslagging after tap. The residual tapping slag is treated with aluminium pellets to reduce any remaining reducible oxides.
Synthetic slag is added to bring the top slag composition within the required range for effective desulphurisation.
The ladle is located in the treatment station, and then sealed as far as possible by a ladle cover. The ladle cover serves two functions, the first being to capture and remove fume generated during the process. The fume is removed by a duct which connects the ladle cover to a fabric filter duct cleaning unit. The second function of the ladle cover is to minimise atmospheric contact with the surface of the steel, which would cause oxidation and nitrogen pick up. For this reason, the ladle cover design is relatively sophisticated.
Fluxing of the ladle top slag is done by argon stirring, either by top lance or bottom porous plug. When the top slag is in the required condition, desulphurisation by injection begins.
A lime-fluospar mixture, which may be prefused, is injected into the steel through an immersed lance. Argon is used as a carrier gas. To increase the effectiveness, the lance tip is close to the bottom of the ladle. Calcium compounds are also injected, either in combination with lime-spar (co-injection) or separately (mono or sequential injection).
The amount of reagent injected is obviously dependant on the initial sulphur level and final required level. Calcium is also used to modify the shape of the remaining sulphides.
Both the total amount and the rate of injection are predetermined and controlled.
At the end of the injection, the lance is automatically retracted, and a sample is taken. The ladle cover is then raised and the ladle removed.
Great! thanks for the heads up. It's really nice to get a lot of updates online though. I would love to share my experiences on metal steel as well. I hope to see updates soon. Nice post!
ReplyDeletemetal
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