| In recent years, with a boom of automobile industry in China, it has become the world’s largest producer and consumer. To meet demands, it is urgent to develop new technologies to produce automotive sheet in the energy-saving and environmental care. RH is a core device for producing the high-quality and low-carbon sheets. At present, the basic theory research of RH process is still insufficient. It is necessary to analysis the fluid behavior in perspective of chemical reactor within large RH equipment. The results will be much significance on building the gas-liquid distribution spectrum with the changes of production conditions, providing the visualization technique of RH process and laying a solid theoretical foundation for developing the technology of fast decarburization.In this paper, from the prototype of300t RH, the flow behavior was studied by water modeling in laboratory; the decarburization process was investigated by CO2-NaOH solution simulation; the two-phase flow patter was measured by high-speed camera. Combined theoretical research and industrial test, four aspects were illustrated in detail as following:the evaluation index of flow behavior in RH reactor; the effect of the liquid level in RH vacuum and flow behavior of two-phase flow; the bubble behavior and two-phase flow in upleg; the mechanism of decarburization process and the fast decarburization technology.The modeling of fluid flow and the evaluation index of flow behavior in the RH reactor showed that:the steel level and gas behavior are determinant of molten steel flow. The mixing degree of liquid in the ladle decreased with rising of liquid level in vacuum chamber. When the liquid level is higher than a certain value, the circulation flow rate and the mixing time were not applicable for evaluating the whole RH process. The liquid resident time was the most important indicator to evaluate the process and it should be firstly considered to evaluate the fluid behavior during RH process.The study on the effect of the liquid level in RH vacuum and flow behavior of two-phase flow showed that:for the300t RH, when the height of liquid level in vacuum chamber is from300mm to480mm, two-phase flow in vacuum chamber is in transition flow pattern and the resident time can reach the peak with less liquid spattering, the reaction zone of decarburization is in whole vacuum chamber. In the actual process, the optimal pattern in favor of decarburization is that:with the increasing decarburization time, molten steel rapidly transforms from boiling pattern to transition pattern, and then kept the TP until the end of the decarburization during practical RH process, and it is best to control the steel level in vacuum chamber near the critical point between transition pattern and wave pattern.Bubble behavior and the gas-liquid flow in upleg were analyzed by simulation experiments and the following conclusions obtained:in the actual production of300t RH, when the injection gas is less than100m3·h-1, the concentrated injection mode can enhance the void fraction in upleg and the resident time of bubble is more than5s; when the gas injection is from100m3·h-1to260m3·h-1, the concentrated gas injection mode is better than other modes and the resident time of bubbles is longer than the theoretical time of bubbles forming and growing, and the void fraction is near the saturated value. In a word, the condition accelerating the mass transfer and reaction rate is that:the apparent rate of gas is between7.50×10-2m·s-1and1.20×10-1m·s-1and the liquid level in vacuum chamber is from240mm to360mm.The study of decarburization mechanism showed that:when the length of snorkels is1.65m and the immersion depth is0.45m, in the first2min after the start of decarburization, the surface of Ar bubbles is the main decarburization site and the splash droplets also provide the reaction site; in the2min to8min. C-O reaction and CO bubbles is the key to rapid decarburization; in the last8min, C-O reaction is main occurred at the surface of vacuum chamber. Furthermore, in the first6min, decarburization rate is mainly influenced by the pressure of vacuum chamber. Then after the first6min, the depth of reaction is the key factors and final carbon content is decided by both reaction depth and gas rate after8min.By means of physical simulation in combination with industry experimentation, the validated technology of fast decarburization for300t RH is obtained as follow:when Ar gas is injected in the upleg, the concentrated injection mode is recommended; the effective injection mode is to take the chamber pressure down to67Pa in8.5min and for the gas volume to be less than10m3in the first4min after the reaction begins; the apparent rate of gas is between7.50×10-2m·s-1and1.20×10-1m·s-1; the liquid level in vacuum chamber is from300mm to360mm and the highest level is no more than480mm. |
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