| In the metallurgical industry, gas injection technology, as an effective approach to improve the metallurgical effect and efficiency, is gradually applied to various metallurgical reactors and has received a considerable attention over the years. In order to improve sufficiently the reaction efficiency between bubble and metallurgical melt, the fine bubbles need to be created and uniformly distributed in the molten pool to increase the gas-liquid interfacial area, which in turn enhance the efficiency of gas-liquid mass transfer. Therefore, the studies of bubble behavior and related hydrodynamic in metallurgical melts are critical for optimizing the reactors structure, blowing mode and operating parameters during the actual metallurgical process.In this paper, for the interaction between bubble and melt in our self-developed new technology including in-situ desulfurization of hot metal pretreatment with mechanical-gas injection coupled stirred and bottom blown copper smelter, the CFD software Fluent 12.0 combining the user defined function (UDF) was adopted to establish the mathematical model. The numerical simulation and physical simulation were combined to investigate the gas-liquid two phases flow, mixing efficiency, bubble size distribution and gas-liquid mass transfer behaviors in the gas injection-mechanical coupled stirred system of hot metal pretreatment and the injection system of bottom blown copper smelter, which laid a theoretical foundation for the further industrial popularization. The main contents and results obtained are as follows:1. For the gas injection-mechanical coupled stirred system of hot metal pretreatment, a water model and a CFD-PBM coupled mathematical model were established according to the similarity principle, computational fluid dynamics and other relevant theories. The influence of nine bubble coalescence and breakage models on the predicted bubble size distribution was studied and compared with the measured results of water model experiments, a reasonable bubble coalescence and breakage model and corrected parameter were proposed. In addition, the impacts of different impeller location, shape and rotation speed, and the gas flow rate on the gas-liquid two phases flow, mixing time, bubble size and gas-liquid mass transport were investigated by water models and numerical simulation. The results were shown as follows:(1) For the different bubble coalescence-breakage model, the predicted bubble size distribution in bath with Luo-Lehr model and Luo-Laakkonen model was more consistent with measured results than that with other models, and the Luo-Laakkonen model was chosen to calculate the bubble diameter distribution since the computationally efficient with Laakkonen model is higher than that with Lehr model. Furthermore, the model parameter R was presented to modify the Luo-Laakkonen model for fitting the measured data, and as the R of 0.5 was adopted, the predicted results agreed well with the measured date.(2) As the impeller was moved from the center toward the side wall, the bubbles distribution area was enlarged gradually, the gas total volume θ in the bath first decreased and then increased, the bubble size decreased, and the total mass transport rate parameter ξ between gas and liquid increased gradually. When the impeller eccentricity was 0.4, both the maximum of gas total volume and total mass transport rate parameter were achieved, and the 0 and ξwere 1.19L and 1.65×10-4m3/s, respectively. In addition, the average mixing time with impeller eccentricity of 0.4 was 12.3s, which was shorter 22.6s than that with central impeller. Overall, the eccentric pattern had significant advantages with respect to the center pattern, and the impeller eccentricity of 0.4 was recommended.(3) Compared with conventional VB impeller, although the mixing efficiency with SSB-D impeller was slightly lower, the innovative impeller could enlarge gas distribution area in molten pool, and a downwards back flow was formed above the impeller, which avoided bubble rising rapidly and increased gas residence time. In this way, the utilization of gas was improved. For the present system, the predicted gas total volume in bath with SSB-D impeller was 0.29L more than that with VB impeller, and had an increase of 32.2%. Thus the SSB-D impeller was recommended.(4) Increasing of rotation rate of impeller and gas flow rate would reduce bubble size, but increase the total bubble volume 0 and total mass transfer parameterξbetween gas and liquid phases. In addition, the mixing time also decreased by increasing rotation rate. When rotation rate was over 200rpm and gas flow rate was over 2.0Nm3/h, further more, increase on rotation rate and gas flow rate would have insignificant impacts. Meanwhile, the excessive gas flow rate would reduce the mixing efficiency in bath, therefore, the rotation rate range of 200rpm, and gas flow rate of 2.0 Nm3/h were recommended.(5) Compared with the traditional industrial VB propeller, when the optimized stirring-blowing mode was adopted in industrial hot molten bath, the mixing time prolonged 2.4s, but the gas total volume θ increased by 20.2%, which was 0.25m3, and total mass transfer parameter ξ, between gas and liquid increased by 10.3%, which was 0.06m3/s.2. In the injection system of bottom blown copper smelter, a water model and a CFD-PBM coupled mathematical model were established according to the similarity principle, computational fluid dynamics and other relevant theories. Based on the corresponding results of numerical simulation and experimental data, impacts of the number of nozzle the arrangements and gas flow rate on the gas-liquid flow, mixing efficiency, bubble micronization and mass transfer between gas and liquid phases were investigated. The results indicated that:(1) When the nozzles of group A and B were located near the center of the bath bottom, namely Odeg and 7deg, the gas total volume θ and total mass transport rate parameter ξ were larger in the whole bath, but the mixing efficiency was very low. With the increase of nozzle arrangement angle, the mixing time gradually decreased. But when the nozzle angle arrangement of group A and B exceeded 21deg respectively, the distance of bubble traveling from nozzle to liquid surface was shortened, which reduced the total gas volume and total mass transfer rate. Therefore, based on the comparison of the predicted result with different nozzle arrangement, the nozzle angles of group A and B arrangement at 7deg and 14deg were recommended.(2) With the increase of the number of nozzle and gas flow rate, a better bubble distribution was achieved, and total bubble volume θ and the total mass transfer parameter ξ increased. However, excessive increasing the number of nozzle would decrease the mixing efficiency, and the growing trend tended to be negligible when the gas flow rate was over 18.8 Nm3/h. Based on the comprehensive consideration, the number nozzle of 13, and gas flow rate of 18.8 Nm3/h were recommended. Correspondingly, the gas total volume θ was 7.2L, the mixing time was 241.8s, and the total mass transfer parameterξ was 3.78 ×10-4m3/s.(3) In the actual industrial oxygen bottom blowing copper smelting, compared with the existing industrial nozzle arrangement, when the optimized blowing mode was adopted, the gas total volume θ increased by 7.7%, the total mass transfer parameter ξ between gas and liquid increased by 18.1%, and the mixing time decreased by 73.2s, which indicated that the optimized scheme had more advantages than the existing industrial blowing mode.In short, the mathematical models established in this paper could accurately describe the bubble behaviors in the two different kinds of metallurgical melt above. The results of the study contribute to the optimization of the structure of the existing reactors, blowing mode and technical parameters, which lay the theoretical foundation for the further industrial popularization for these two independent technologies. |
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