A mathematical model has been developed to explain the effect of the number of nozzles on recirculation flow rate in the RH process. Experimental data from water modeling were employed to validate the mathematical model. The experimental data included the velocity fields measured with a particle image velocimetry technique and mixing time. The multiphase model volume of fluid was employed to allow a more realistic representation of the free surface in the vacuum chamber while injected argon bubbles were treated as discrete phase particles and modeled using the discrete phase model. Interfacial forces between bubbles and liquid phase were considered, including the lift force. The simulations carried out with the mathematical model involved changes in the gas flow rate from 12 to 36 L/min and a number of nozzles from 4 to 8. The results indicated a logarithmic increment in the recirculation rate as the gas flow rate increased and also corresponded with an exponential decrease in mixing time. The plume area and liquid velocities resulting from individual nozzles were computed. A maximum optimum recirculation rate was defined based on a mechanism proposed to explain the effect of gas flow rate and the number of nozzles on the recirculation rate.

Investigation on the Effect of Nozzle Number on the Recirculation Rate and Mixing Time in the RH Process Using VOF + DPM Model

A physical model of a ladle degassing operation was developed to simulate the reactions at rising bubbles and at the free surface. Carbon dioxide desorption from a sodium hydroxide solution was used to simulate the liquid-phase diffusion-controlled decarburization of liquid steel. It was found that under reduced pressure, the reactions were faster than attributable to solely the increase in volumetric flow rate. It was possible to separate the reactions with the bubbles from the free surface reactions; 20 to 40 pct of the reactions occurred at the free surface, depending on injection conditions. The free surface desorption rate depended on the gas flow rate and the number of injectors. The mass transfer coefficients to the bubbles were in reasonable agreement with previous work. Plume bending was observed when small bubbles were influenced by the bulk liquid flow patterns.

Modeling of gas-liquid reactions in ladle metallurgy: Part I. Physical modeling

A physical model based on similarity principles has been constructed for simulating the RH degasser of Companhia Siderurgica de Tubarao (CST), Vitoria, ES, Brazil. The influence of gas injection through nozzles in the upleg with simultaneous bottom injection of gas, as well as the influence of nozzle blockage, on the circulation rate has been investigated. In addition, mathematical relationships for mixing characteristics in the process have been evaluated.

Fluid flow and mixing characteristics in RH degasser of Companhia Siderúrgica de Tubarão, and influence of bottom gas injection and nozzle blockage through physical modelling study

The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operating conditions. According to the apparent decarburization rate constant (KC) calculated by the carbon content in the samples taken from the hot melt in a ladle at an interval of 1–2 min, it is observed that the total decarburization reaction period in RH can be divided into the quick decarburization period and the stagnant decarburization period, which is quite different from the traditional one with three stages. In this study, the average apparent decarburization rate constant during the quick decarburization period is 0.306 min−1, and that of the stagnant period is 0.072 min−1. Increasing the initial carbon content and enhancing the exhausting capacity can increase the apparent decarburization rate constant in the quick decarburization period. The decarburization reaction comes into the stagnant decarburization period when the carbon content in molten steel is less than 14×10−6 after 10 min of decarburization.

Decarburization rate of RH refining for ultra low carbon steel

Phosphorus removal in basic oxygen steelmaking is a significant problem for integrated steelmakers. Phosphorus removal is required due to its deleterious effect on the mechanical properties of stee...

/pdf/a-review-of-phosphorus-partition-relations-for-use-in-basic-4an05zb7yh.pdf

A review of phosphorus partition relations for use in basic oxygen steelmaking

Fundamental experiments were carried out in order to accelerate the vacuum decarburization rate in low carbon range. As the results, it became clear that enlargement of interfacial area was more efficient than increase in overall mass transfer coefficient. One of the most practical methods to enlarge interfacial area was Ar injection into molten steel. Effect of Ar injection on decarburization rate was investigated in the 150 kg VIF. Ar injection was effective on decarburization rate, and the apparent decarburization rate constant with a two-holed nozzle was larger than that with a one-holed nozzle. Next, effect of Ar injection into a vacuum vessel of RH was investigated with a water model. CO2 desorption rate was measured to simulate decarburization rate. Gas injection nozzles were settled at the lowest part of the side wall in the vacuum vessel. The number of nozzles was 1, 8, or 16. An experiment without gas injection was also carried out as a reference. Gas injection into the vacuum vessel was effective on the CO2 desorption rate. In particular, increase in the number of nozzles was more effective at a constant total gas flow rate.Finally, plant trials were carried out. Configuration of the nozzles was the same as the case of 8 nozzles in the water model. Gas flow rate into the snorkel for circulation was 2 500 NI/min. Gas flow rate into the vacuum vessel was 800 NImin. Inner diameter of the nozzles was 2 mmφ. As the result, it became possible to decrease the carbon content from 200 to 10 ppm within 10 min.Interfacial area with Ar injection was evaluated to be 1.6 times larger than that without Ar injection.

Acceleration of Decarburization in RH Vacuum Degassing Process

https://www.jstage.jst.go.jp/article/tetsutohagane1955/77/10/77_10_1641/_pdf

Experiment of Phosphorus and Oxygen Distribution between CaO-SiO2 MgO-FetO Slag and Liquid Steel and Estimation of Phosphorus Content at End Point of Top and Bottom Blowing Converter

Dephosphorization experiments under oxidizing condition were carried out to develop an inexpensive flux for the chromium-containing iron with a large dephosphorizing capacity. Among various halides tried in CaO-halide-Cr2O3 systems, NaF and BaF2 are superior to others in their dephosphorization performance for chromium-containing iron though the fluxes are not inexpensive. From view points of both the dephosphorization ability and the flux cost, CaF2 was selected among halides and BaO was added in order to contrive their compatibility. In the CaO-BaO-CaF2-Cr2O3 system, various composition was tried and the composition was optimized. As the result, 90% of maximum dephosphorization degree was obtained with 100g of flux per kilogram of the metal at 2% C and 15% Cr.Effect of carbon content and chromium content in the metal on dephosphorization was investigated with this CaO-BaO-CaF2-Cr2O3 flux. As the result, it became possible to dephosphorize the iron with wider range of carbon (0.2 to 4% C) and chromium (15 to 22% Cr) contents. It was revealed that coexistence of calcium, barium, and sodium as cation was effective in dephosphorization. Fluorine as an anion was more effective in dephosphorization than chlorine.

Dephosphorization of Chromium-containing Iron with Various Oxide-Halide Fluxes

PURPOSE:To carry out dephosphorization in high efficiency at low cost without causing Cr losses by oxidation, by adding a CaCO3-NaF type flux to the Cr- containing molten iron CONSTITUTION:The CaCO3-NaF type flux containing CaCO3 and NaF is added to the Cr-containing molten iron to remove the phosphorus in the molten iron As the means of incorporating the flux, charging of the flux onto the molten iron, blowing of the flux into the molten iron by use of a nonoxidizing gas as a carrier gas, ie, injection method, or another method is used

Shigeru Inoue

Papers

Acceleration of Decarburization in RH Vacuum Degassing Process

Experiment of Phosphorus and Oxygen Distribution between CaO-SiO2 MgO-FetO Slag and Liquid Steel and Estimation of Phosphorus Content at End Point of Top and Bottom Blowing Converter

Dephosphorization of Chromium-containing Iron with Various Oxide-Halide Fluxes

Dephosphorizing method of chromium-containing molten iron