Effect of Froude Number on Submerged Gas Blowing Characteristics

• The submerged gas jet generated by a plasma generator is an important part of the IronArc processwhere it is used to provide the heat for melting, inject reducing compounds to the melt, and forstirring of the reactor. Therefore, accurate predictions of the gas plume from the plasma generatorare required to enable process control. Submerged gas side-blowing with high temperature gas andlarge density differences between superheated gas and liquid slag as is present in the IronArcprocess has not been studied previously to the authors knowledge. The flow behavior of gas in a compressible and incompressible system was investigated at an ambient temperature in the water-air system, and at a high temperature in the IronArc system. The simulation results were compared to verifying experiments in the water-air system and established empirical equations to predict the penetration length. The simulations in the air-water system were found to replicate the experimental behavior using both the incompressible and compressible models with only small deviations of 7-8 %. However, at higher temperatures as is present in theIronArc system the compressible simulations were required to replicate the varying density in the injected gas as it changes temperature when in contact with the liquid. It was found that there is a soft lower requirement for the Froude number of the gas blowing to produce a jetting behavior and allow accurate prediction of the penetration length by the empiricalequation. For gas blowing below the required Froude number the gas will form large pulsating bubbles instead of a steady jet, which makes the empirical equation severely underpredict the penetration length. The large pulsating bubbles also expand backwards from the inlet and may cause back-attack on the refractory wall.The lower limit for the Froude number was found to be approximately 300 for the studied IronArc system, at this point the empirical equation is quite accurate but the flow is still partly unstable. It was also found that the Froude number limit is system dependent and may be based on the density ratio between gas and liquid or the viscosity of the liquid. The amplitude of the pulsing for gasblowing below the Froude number limit is also expected to be dependent on the bath height and the density ratio. For submerged blowing applications it is important to ensure sufficiently high Froude numbers of the gas blowing if the gas penetration length is to be stable as a jet and predictable by the empirical equation.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

Nyckelord

compressible flow

incompressible flow

IronArc

OpenFOAM

modified FroudeNumber

submerged gas blowing

gas jetting

Metallurgical process science

Metallurgisk processvetenskap

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