| Using water modeling method, the fluid and mixing characteristics under the different operating modes in RH process have been investigated. A water model of 1/5 linear scale for a 90t multifunction RH degasser has been designed, fabricated and established. The circulation rate has been determined directly with a new method. The mixing time of molten steel in the ladle has been measured with conductivity method. The influence of the main technological and structural parameters was examined. The fluid flow pattern and flow field in the ladle were demonstrated, observed and analyzed. The results indicated that the circulation rate of molten steel in the unit can be estimated by the following equation: Ql=0.0333Qs0.26D0.69D0.80 (t/min), where Qg-gas flow rate (NL/min), Du and Dd-up- and down-snorkel inner diameter(cm); the relation between mixing time and stirring power density is obtained to be m 0.50. The residence time distribution curve in the RH model obtained by tracer response showed that three circulation cycles are at lest needed for complete mixing of the liquid steel in the RH unit.The mass transfer characteristics between powder particles and liquid steel in the RH-PTB (Powder Top Blowing) refining have been investigated on this model. The sodium chloride powder with analytical purity was used as the flux for blowing. The mass transfer coefficient in liquid steel (k) was determined under the conditions of RH-PTB. The effects of the main technological and structural parameters were examined. It may be concluded that under the conditions of the present work, k increases with increasing Qg, Du, Q1, and dp, and decreases with an increase of Dd. Its value is in the range of (1.36~7.30) 10-4m/s. Thefollowing dimensionless relationships were obtained:The desulphurization process by powder injection and blowing in RH refining of molten steel and its mechanism have been considered and analyzed. Based on the two-resistance mass transfer theory and the mass balance of sulphur in the system, a kinetic model for the process has been developed. The related parameters of the model have been reasonably determined. Modeling and calculations for the process by injecting and blowing the lime based powder flux under the assumed operating modes in a RH degasser of 300t capacity have been carried out using the model. The corresponding circulation rate and the powder injection and blowing rate were taken as 100t/min and 150kg/min, respectively. The initial contents of sulphur and the amounts of powder injection and blowing were respectively assumed to be 70, 60, 50, 40, 30, 20 10-4 mass % and 10, 8, 6, 5, 4, 3kg/t-steel. The total treatment time for desulphurization under each mode was set up to be 24min that is equivalent to eight circulation cycles of liquid steel to be treated. The results showed that the predictions made by this model are in good agreement with some data from industrial experiments and production practice. By injecting and blowing the lime-based powder flux (85%lime(CaO)+15% fluorite(CaF2)) of 3~5kg/t-steel with the totaltreatment time of 12~20min, it is possible to decrease the sulphur content in molten steel to an ultra-low level below (5~10)x10-4mass% from (60~80)xl0 -4mass%. Intensifying the powder injection and blowing operation and increasing the circulation rate of liquid steel may effectively raise the rate of the process in RH refining.On the basis of mass and momentum balance, a mathematical model to simulate the refining process in a 90t multifunction RH unit has been proposed and presented. The contributions of three decarburization sites (the up-snorkel zone, the droplets and molten steel bath in the vacuum chamber) were simultaneously considered. It is demonstrated that for the RH and RH-KTB refining processes, the calculated results agree well with some plant data. The contribution of up-snorkel zone is 10.47% -1.62% of the overall amount of decarburization, 37.44%~37.92% for the droplets in the vacuum chamber and 50.52%~52.09% for the vacuum chamber bath. The effectiveness of d...
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