Bubble Disintegration And Dispersion In New Type Mechanical Stirring Injection Refine Equipment

This paper presents the new idea about desulfurization with in-situ mechanical stirring method on the basis of desulfurization by single blow grain magnesium and KR method, that is, the inner gases carry the magnesium vapor formed in-site in molten iron by magnesium-based desulfurization, bubble dispersed and disintegrated under the condition of mechanical stirring, thence improve the efficiency of desulfurization by single blow grain magnesium.It has been proved by research of Masamichi Sano that the bubble's dispersion and disintegration can not only boost the desulphurization efficiency but also increase the utilization rate of magnesium. Obviously, the bubble's dispersion and disintegration of magnesium vapor is the key problem in boosting the desulphurization efficiency and increasing the utilization rate of magnesium. Thus the research should be explored on bubble's dispersion and disintegration on the base of refining process and gas-liquid mass transfer. On the base of numerous documents and cold water model experimental result basing on principle of similitude. The influencing factors and interaction of bubble dispersion and disintegration have been studied from perspectives of image analysis, gas-liquid mass transfer, dimension analysis., uniform mixing time, bubble effectiveness, and numerical simulation. And the results pave the way for "the new idea about desulfurization with in-situ mechanical stirring method" in aspects of theoretical and experimental scientific basis.First, high speed camera, digital photograph and image processing technique are used to research on the influence law of the bubble dispersion and disintegration and gas-liquid absorption by the influence of impeller structure, rotation mode, nozzle structure, injection mode and gas flow rate. According to experimental and theoretical analysis, we can draw a conclusion:Vortex formed easily when centric stirring with unidirectional rotation, which leads to bubbles getting together around impeller shaft, bubble can not be dispersed widely. Forward-interrupt and forward-reverse rotation of the impeller can enhance the bubble disintegration and dispersion than forward rotation, the vortex formation is completely prevented. Eccentric stirring with unidirectional rotation is more effective than centric stirring for bubble disintegration and dispersion in liquid. The bubble disintegration is enhanced with increasing rotation speed and length of the impeller. in the cases of forward-interrupt and forward-reverse rotation mode. Under the same experimental condition, the bubble diameter expands with the enlarging nozzle diameter and decreasing with the number of nozzles.The deeper the nozzle immersion depth is, the wider the bubble dispersion is in the bath. The perforated blade impeller weakens the tangential flow and hence delays the vortex formation even under the forward rotation of the impeller, and also reduces the stirring power consumption. Meanwhile, the time for vortex formation using the perforated impeller can be prolonged 2 to 3 times longer than that using the non-perforated impeller. Therefore, the shift time of direction of the rotation in forward-reverse rotation can be longer using the perforated impeller. The impeller of large blade length and height with many holes can improve the bubble disintegration and dispersion. In the case of the perforated impeller, use of larger blade length and height is permissible.Second, on the basis of determining the impeller structure and rotation mode, combined with experimental research, applied dimensional analysis method and related the criterion equation on the various factors to the bubble sizes has been attained and is shown below:Furthermore, criterion equation on bubble size with gas flow rate,immersion depth and liquid height could be got separately by analyzing the influence of rotation speed, gas flow rate, immersion depth and the impact of liquid height on the average bubble diameter. The criterion equations as follows::(a)Effect of gas flow rate on bubble size:(b)Effect of immersion depth on bubble size:(c)Effect of liquid surface height on bubble sizeThird, this paper has studied various factors effecting on gas absorption process and volumetric mass transfer coefficient using the system of CO2-NaOH-H2O.The results show that high gas flow rate is beneficial to increase volumetric mass transfer coefficient in the bath, volumetric mass transfer coefficient and absorption efficiency of CO2 increase with the increasing rotation speed under the condition of eccentric stirring.With the gas injection mode of direct-blowing and side-blowing, bubble disperse quickly with mechanical stirring, which results in promoting complete reaction between CO2 and NaOH, and improving the mass transfer coefficient and absorption efficiency of CO2.Criterion equation on volumetric mass transfer coefficient and correlation number group have been related according to dimensional analysis principle.(a)forward-reverse rotation under centric stirring mode(b)forward rotation under centric stirring mode(c) forward-interrupt rotation under centric stirring mode (d) forward rotation under eccentric stirring modeGas holdup in gas injection stirring has been measured by instantaneous stop technology and pressure difference method. Mass transfer coefficient KL and surface renewal rate S with correlated condition were reckoned according to parameters of gas hold up,bubble size and volumetric mass transfer coefficient.Fourth, according to practical situation of Mg-based desulphurization, this paper has defined the formula of bubble effectiveness with low ratio of height to diameter, and derived the theoretical formulas on the bubble utilization rate relating to gas flow rate,bubble diameter and mass transfer coefficient. The calculated value of these formulas are shown to be in good agreement with experimental results, indicating the absorption rate can be treated as zero order reaction in the case of low ratio of height to diameter. But theoretical formula when the absorption rate treated as first order reaction is matched better than that when the absorption rate treated as zero order reaction.Theoretical formula when the absorption rate treated as zero order reactionTheoretical formula when the absorption rate treated as first order reactionFifth, conductivity method has been used to measure uniform mixing time. Influence of rotation mode, rotation speed, eccentric and centric stirring mode and gas flow rate on uniform mixing time have been researched respectively. The results show the uniform mixing time order are that forward-reverse rotation is better than forward-interrupt rotation and then forward rotation; Within the experiment, compared with low rotation speed, uniform mixing time is shorter at high rotation speed. The larger nozzle diameter is, the longer the uniform mixing time is; influence rules of rotation speed on uniform mixing time are the same in both eccentric stirring mode and centric stirring mode. No matter whether there is gas injection or not, uniform mixing time decreases with rotation speed increasing. Furthermore, uniform mixing time with mechanical stirring and injection gas is shorter than that of only injection gas at the same rotation speed.Finally, the flow patterns of single-phase flow and two-phase flow under mechanical stirring were simulated by FULENT and MIXSIM software, and compared with digital images at the same time. The simulation results of single-phase flow under mechanical stirring show that: Compared eccentric stirring with centric stirring, it was clearly that big vortex can be formed near impeller shaft when centric stirring mode, although vortex still exist when eccentric stirring, but the vortex deviated from shaft, and this mode can inhibit bubble accumulation. The simulation results of two-phase flow under mechanical stirring show that:under eccentric stirring mode, because vortex was smaller and deviated from shaft, this mode beneficial to bubble dispersion. The flow field in the bath was very disturbance under side blowing injection mode and two-phase flow eccentric stirring mode. Which has further improved bubble dispersion.