RH DEGASSER | Rheinstahl Heinrich degasser

Recirculation Degassing | RH Degassing

In this process of degassing molten steel is allowed to circulation in free vacuum chamber continuously by special arrangements.

Introduction :

RH degassing technology is developed by Rheinstahl Heinrich from hattingen, Germany. In which a cylindrical refractory lined shell with two snorkel is designed such that steel is raised in one leg and fall back in to the ladle after degassing through the other leg.

RH Snorkel
RH Snorkel

RH Construction :

● Cylindrical shell is lined with fire bricks in the upper portion and alumina bricks in the lower portion in order to sustain high temperature. The legs are lined with alumina refractory. A lifter gas argon is injected at the inlet snorkel in order to increase the molten steel velocity entering in to inlet snorkel.

● The inlet snorkel is equipped with nos. Of gas injection pipes which is arranged in the lower section and equally distribued around the circumference. Top side of the cylindrical shell is provided with exhaust, alloy addition chute and control room.

RH Operation :

● Cylindrical chamber is heated to the desired temp in between 900℃ to 1500℃ in different plants. The chamber is lowered in to molten steel up to a desired level.
RH degassing
RH Degassing

● The chamber is evacuated so that molten steel begins to rise in the chamber. Lifter gas is introduced. This gas expands and creates a buoyant force to increase the speed of molten steel rising in to the inlet snorkel.

● Before degassing both snorkel are sufficiently immersed in to the liquid steel. The inert gas usually argon is started in the gas pipe of the inlet snorkel before dipped in metal. Argon acts as a lifter gas to increase the molten steel velocity which is entering in to the inlet snorkel.

● After achieving the required immersion depth of the snorkel, the reaction of vessel evacuated. Liquid steel circulation depends on the geometry of the equipment like snorkel diameter, radius of equipment and the position and number of lift gas tuyeres used.

● Molten steel in to the chamber is degassed and flows back through the other snorkel in to the ladle. This degassed steel is slightly cooler than steel in the ladle. Buoyancy force created by density difference (density of cooler liquid steel is greater than hot steel) stirs the bath.

● Rate of circulation of molten steel in cylindrical chamber controls the degassing. Circulation rate depends upon amount of lifter gas and the degree of vacuum. Alloy addition can be made at the end of degassing depending on the superheat.

DH Degassing :

In DH Degassing a small amount of 10 - 15% of the total mass of steel is degassed at a time. The process is repeated until required level of degassing is achieved. The arrangement of vessel and the ladle is similar to RH. DH has one cylindrical snorkel and also has heating facility.

● The DH chamber is equipped with heating facility, alloying addition arrangements and exhaust system, bottom of the cylindrical vessel is provided with a snorkel which can be dipped in to molten steel. The upper portion of the vessel is lined with the fireclay and the lower portion with the alumina bricks, snorkel is lined with high quality alumina bricks. The length of the snorkel is sufficiently large to realized the effect of the atmospheric pressure on rise of steel in the snorkel.

Operation :

DH vessel is pre heated and lowered in the ladle so that snorkel tip dips belows the molten steel surfaces.

1. The evacuated chamber is moved up and down so that the steel enters the chamber.

2. The chamber is moved for 50 to 60 times with a cycle time of 20 seconds.

3. Adequate degassing is possible in 20 to 30 cycle.
4. A layer of slag is kept in the ladle to minimize heat losses.

5. The DH degassing unit can operate with lower superheats compared with RH  since DH unit has heating facility.

Advantages :

1. Heat losses are relatively low.
2. Alloys addition can be adjusted more closely.
3. Small vacuum pumping capacity is adequate since smaller volume is to be evaluated as compared with ladle to ladle or stream degassing.

References :
1. Modern Steel Making :  Dr R.H. Tupkary and V.R. Tupkary.
2. Ironmaking and Steelmaking Theory an d Practice : A. Ghosh and A. Chatterjee
3. Steel Making : A.K.Chakravorty

4. Sr. Professors from IIT's & BPUT. (INDIA)

Author :
Subir Kumar Sahu

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