Effects of gas injection with multihole orifices in upleg snorkel on bubble behaviour and decarburisation rate during RH refining

Physical model experiments have been conducted to investigate the effects of multihole orifices in the upleg snorkel on bubble behaviour and decarburisation rate during Ruhrstahl–Heraeus refining. Bubble behaviour was recorded by a high speed video camera and a volumetric mass transfer coefficient kA/V was used to evaluate the decarburisation rate. Measurement of the volumetric mass transfer coefficient kA/V was made by means of the CO₂ desorption from a NaOH solution. Pictures of bubble behaviour show that gas bubbles are generated separately from the multihole orifice in the low region of gas flowrate, but they tend to coalesce at high gas flowrate. It was demonstrated that kA/V increases with increasing gas flowrate and decreasing orifice hole diameter. In the low region of gas flowrate, kA/V for multihole orifices is larger than that for one-hole orifices. In this case, kA/V increases as the number of holes increases, and the hole distance of orifice has little effect on kA/V. However, in the high region of gas flowrate, kA/V for multihole orifices is lower than that for one-hole orifices, and kA/V decreases with the increase in orifice interhole distance. It was found that there exists a critical gas flowrate, above which kA/V for multihole orifices is lower than that for one-hole orifices. This critical value increases with increasing hole distance and hole number. Some explanations were also made in terms of bubble behaviour.