Study On Bubble Characteristics Of Bottom Injection At Elevated Pressures

Bubble behavior is one of the most important phenomena in hot metal pretreatment process by Mg injection. The desulfurization rate is determined by the reaction rate of Mg bubble with the liquid in the bath. The more decentralized and fine of the bubbles are, the better the desulfurization results are. However, magnesium-based desulfurizer is expensive, so how to improve the utilization of magnesium is becoming the current problems to be solved. Based on this, to provide a certain extent theoretical and practical guidance by optimizing magnesium injection and improving the utilization of magnesium metal, bubble characteristics of bottom blowing at elevated pressures were studied.In this thesis,400mm-height pressurized bath was studied, and establishing a set of test device by double probes and corresponding software. During the experiment, the bubble frequency and the local gas holdup were mainly investigated. Finally, the flow field in the bath and mixing time with certain gas flow rates were numerically simulated. The main conclusions were shown as follows:(1) The flow rates had significant impact on the bubble frequency and gas holdup. With the increasing of the flow rates, the gas holdup and bubble frequency were increased significantly; with the increasing of pressure, bubble frequency and gas holdup were also increased; the influence of pressure on the local gas holdup under low flow rates was significantly lager than high flow rates;(2) In the radial direction, the bubble frequency increased with the increasing of the flow rates; in the place far from the center of the pool, the bubble frequency and gas holdup increasd with the increase of the axial height; while in the place near the center of the pool, bubble frequency and gas holdup decreased with the increase of the axial height;(3) The bubble frequency and gas holdup gradually reduced with the increase in orifice diameter. In small gas flow rates, such change is particularly evident when the orifice diameter increased from 1mm to 3mm;(4) There was a critical point on the relationship between gas volume and mixing time. Before the critical point, with increase of gas flow rate, the mixing time became shorter. After the critical point, the mixing time did not change significantly with the increase of gas flow rate. Among all the orifices, the flow rate at the critical point is 0.15m3/h;(5) With the same diameter orifice, the bottom gas only increased the liquid flow velocity in the bath, but did not change the flowing pattern, and the characteristics of the flow field remained the same;(6) The cycle center was at about 0.5H-0.80H from the bottom and stayed unchanged under different bottom blowing gas rates. With the gas flow increasing, the absolute velocity of the liquid had increased, while the cycle center position remained unchanged.