Physical Simulation Of RH Vacuum Refining Process For Injection Parameters Optimization

RH vacuum refining process and equipment has got steady development withthe improvement of metallurgical function and the need for low Carbon and lowSulfur in high performance clean steel since it was invented. As one of the importantaspects,the top lance blowing process(powder) in the RH refining equipment haseffectively solved the problem of deep decarburization and deep desulphurization inhigh purity steel which was difficult to achieve by conventional process.But in thetop lance blowing process,the desulfurization efficiency was unstable and the slagdeposition caused by vacuum spray was hard because the process parameters are notideal.Compared to the top lance blowing process, the side blowing in the lowergroove avoid the spray produced by top lance blowing process,morover,it could usethe full depth of the molten steel to refine which is helpful to improve the powderutilization rate and refining efficiency,but it got little practical application due to thecomplexity of the process.A physical model was build in this article patterned after the300t RH-PTBequipment in a certain plant and the similarity ratio was1:6.5. The model was usedto optimize the process parameters that influence flow and mixture,thus reduce thevacuum spray and improve the injection efficiency in the top lance blowing and sideblowing process.The key influencing factors and mechanism was also exploredwhich could provide theoretical basis for the optimization of key parameters’ designin the RH top and bottom groove side spray equipment and operation processparameters.The results show that:(1)The pre-pumping mode in initial RH vacuum treatment has a big effect onthe vacuum spray.In prior to production,the vacuum could be pumped,when theliquid height in the vacuum chamber was67.8mm and the top lance height was307.7~462mm,the vacuum spray could be inhibited effectively. Lifting gas didn’tshow an obvious effect on vacuum spray. It was considered that the spray caused bythe promotion of large amount of gas produced during degassing reaction in liquidsteel to liquid droplet could not be reflected under the water model in this paper. Inorder to avoid the entrainment of bubbles in the liquid steel in the vacuum chamberto drop tube,which affect the effective circulation flow,the liquid height in thevacuum chamber shouldn’t be lower than60mm(390mm in the factory).(2) Circulation flow rate is increasing with the growth of lift gas flow rate, top lance gas flow rate, and liquid level of the vacuum chamber, while reducing alongwith the height top lance level growth. It can be used as "saturation value" ofimproving the circulation flow rate when lift gas flow rate reaches to1.21m3/h.When the top lance height is less than153.8mm, it’s needed to reduce lift gas flowrate and top lance gas flow rate; however, when the height is greater than461.5mm,the change of top lance gas flow rate is not obvious to molten steel, it means thatmolten steel flow rate is mainly affected by the gas lift. To ensure the efficientcirculation flow of liquid steel and prevent spillage of vacuum chamber at the sametime, the suitable height of top lance is in range of307.7.7~461.5mm.(3) Mixing time is decreasing with the growth of the lift gas flow rate, vacuumchamber liquid level, the top lance flow rate, and height level of the top lance. Theshortest mixing time is51s, while under the condition of307.7.7mm top lance height,73.8mm vacuum chamber liquid level, and1.12m3/h lift gas flow rate. When the toplance height is greater than307.7.7mm, in order to achieve rapid mixing of liquidsteel, the vacuum chamber liquid level should be increased, and reducing the toplance flow rate, increasing lift gas flow rate to1.21m3/h.(4) In the2#and4#lateral blowing nozzle position, Airflow erosion of vacuuminner wall is lighter during blowing, and mixing effect is better, but the blowingmixing effect of4#lateral blowing nozzle is much better than2#with the highestcirculation flow rate of264L/min. Circulation flow rate of4#lateral blowing nozzleis19L/min greater than2#, when the lateral injection flowrate reaches to3.91m3/h.But2#lateral blowing nozzle can insure that he injection powder could make gooduse of a longer liquid steel trip, it can improve the utilization rate of powder.(5) Injection efficiency comparison between top lance and the lower groove sideInjection:1) Splash phenomenon was not founded when increasing the gas injection, liftgas flow rate and vacuum degree during the injection process at each side of thenozzle position;2)At top lance injection, mixing efficiency is main affected by top lance flowrate, circulation flow amount can reach267L/min by the use of4.09m3/h high toplance ga flow rate, which is31.5%higher than2.98m3/h;4#injection position sideis optimal, mixing efficiency is mainly influenced by gas lift, circulation flow rate264L/min when the lift gas flow rate is1.21m3/h, improved38.9%while comparedwith0.84m3/h; the both shortest mixing time are51s, but top lance injection cycle flow rate is slightly greater than lower slot-side injection, lower slot injection modehave an advantage from the point of view of energy efficiency.3)Under this water model condition, it is unable to impersonate vacuummutation, which caused by large amounts of gas during the field decarburizationreaction, so whether it is a top lance or lower slot side injection, the vacuumchamber and liquid level changes have no obvious influence to circulation flow rateand mixing time in this experiment.