Physical Modeling and Optimization of Bottom Tuyere Configuration and Blowing Parameters in a Top and Bottom Combined Blowing Converter.код для вставкиСкачать
Dev. Chem. Eng. Mineral Process. I4(3/4), pp. 343-352, 2006. Physical Modeling and Optimization of Bottom Tuyere Configuration and Blowing Parameters in a Top and Bottom Combined Blowing Converter Liang-Cai Zhong*, Jun-Ying Chen', Zhe-Long Lei, Chen-Xi Ji, Ying-Xiong Zhu and Mao-Fa Jiang Department of Ferrous Metallurgy, Northeastern University, PO Box 312, Shenyang, Liaoning, P. R. China # Shaoguan Iron & Steel Co., Shaoguan 512123, P. R. China Optimizing experimentsfor the bottom tuyere configuration and blowing parameters of the 120 tonne top and bottom combined blowing converter at Shaoguan Iron & Steel Co. were carried out in a reduced-scale water model. Results showed that the former configuration with 6 bottom tuyeres in the converter was not suitable with bath stirring because of the two tuyeres arranged in 0.330 pitch circle which caused the cavity deformation and stirring energy loss. Ideal bath stirring in the converter was obtained by using a new arrangement with 4 bottom tuyeres, two being in 0.57D pitch circle and the other two in 0.420 pitch circle. The optimal blowing parameters of the converter with the new bottom tuyere configuration were 1.26 Nm3/h of bottom gasflow rate, 160 mm of top lance height, and 30.52 Nm3/hof top gas flow rate. Introduction The technology of top and bottom combined blowing is very important in oxygen-based steelmaking. In comparison with the process of top blowing converters, it has the benefits of smoother blowing procedure, lower iron oxides in end-point slag, higher iron yield, less alloy consumption, and easier production of low and ultra-low carbon steel [ 13. In top and bottom combined blowing converters, the bottom tuyere configuration has an significant influence on bath mixing, kinetics of slag-metal reactions, decarbonization rate, and splashing and spitting [2-4]. Roth et al. [ 5 ] studied the effects of bottom blowing in metallurgical reactors and found the best mixing results were obtained when eccentric tuyere configurations were applied. Paul and Ghosh  investigated mixing and mass transfer rates of slag-metal in top and * Authorfor correspondence (zhongIc@l26.com). 343 L . 4 . Zhong, J,-Y. Chen, Z.-L. Lei, C.-X.Ji, E-X.Zhu and M.-E Jiang bottom blown converters with water model experiments. Their results showed that bath mixing time decreases as the gas flow rate per tuyere is increased. Roth et al.  researched the fluid flow and mixing performance under different top lance tip, lance height, bottom nozzle arrangement and blowing rate in combined blowing experiments. They concluded that small amounts of bottom stirring gas have a great effect on bath mixing, and the mixing time decreases slightly with increasing bottom blowing rate. In the present work, the 120 tonne combined blowing converter of the Shaoguan Iron and Steel Co. was used as a prototype and its bottom tuyere configuration was optimized by physical modeling experiments. Based on the optimized bottom tuyere configuration, optimal parameters for the combined blowing process, such as top oxygen lance height, flow rate of top gas blowing and bottom gas injection, were determined. Experimental Details Figure 1 is a schematic of the experimental apparatus used for the physical modeling. A 1/10 reduced-scale model of the converter was made of 10 mm thick plexiglass. The dimensions of the prototype and the model are given in Figure 2. The diameters of the model converter mouth and body and the radius of the model bottom were determined by taking 200 mm lining corrosion in the prototype into account. Water and air were used to simulate molten steel, oxygen and bottom injection gas. The air was supplied by a compressor which pumped the air into a gas container. The air flow rate was controlled by rotameters. The top lance was fabricated from 22 mm diameter copper tube with a four-laval-hole nozzle, made of plexiglass, at one end. The included angle between each hole center line and the nozzle center line was 13". Bottom tuyeres were also made of 10 mm diameter, 20 mm long, plexiglass rod with one hollow end. Three holes (diameter 1 mm) were drilled at the other end of the rod. 50 mi of 4N NaCl solution was employed as a tracer for bath mixing time measurements. The tracer was added into the bath with a glass tube whose end was fixed, and immersed into a position 5 mm from the bath surface; a conductivity probe was placed at 180" From the tracer addition position at the bath bottom as shown in Figure 1. The probe was connected to a conductivity meter and the signals were recorded. The time when the bath conductivity reached 95% of the value corresponding to steady-state conditions was considered to be the bath mixing time. The dynamic similarity bemeen the model converter and the prototype was considered by using the modified Froude number. By letting the modified Froude number in the model be equal to that in the prototype, then: ...(1) where u is velocity of gas injected into the bath; p is density; L is characteristic length; g is gravity acceleration; and subscripts m for the model, p for prototype, I for liquid phase, and g for gas phase. Experimental conditions in this work are given in Table 1. 344 Physical Modeling and Optimization in a Blowing Converter U Figure 1. Schematic of the experimental apparatus 1. converter; 2. oxygen lance; 3. glass tube; 4. bottom tuyeres; 5. water; 6. conductwiry probe; ?.flow meter; 8. surge tank; 9. air compressor; 10. gas container; 11. conductiviry meter; 12. recorde,: t t (a) (b) Figure 2. Dimensions of the prototype (a) and the model (b). 345 L.-C. Zhong, J.-!I Chen, Z.-L. Lei, C.-X Ji, Y-X.Zhu and M.-E Jiang Parameter Top gas ow rate Qr(Nm /h) P Bottom gas rate QB (Nm3/W Top lance height hL (mm) Bath depth (mm) Prototype Model 22000,24000,26000,28000 27.98,30.52,33.07,35.61 360,504,720,1080,1440 0.42,0.59,0.84, 1.26,1.68 1400,1600,1800,2000 140,160,180,200 1300 130 The gas flow rates in the model were calculated from those in the prototype by: .*.(2) Q, = A2’QP where 1 is the geometrical similarity ratio. The pressure of gas was taken into consideration in the modeling experiments. The bottom tuyere configurations investigated in the experiments are shown in Figure 3. The mode M is the former bottom tuyere configuration. Three or four experiments for a group of particular operating conditions were carried out, and the mean value of the measured data was assumed to be the bath mixing time. Type A B C D E F G H I J K L M Bottom tuyere configuration 1346 3467 3567 2346 2356 3678 13458 34561 13451 13467 23456 123456 1346910 Vormer Wpe) Figure 3. Bottom tuyere configurations in the experiments. 346 Physical Modeling and Optimization in a Blowing Converter Results and Discussion Figure 4 shows the relationship between the bath mixing time and the different bottom tuyere configurations for top gas flow rates of 27.98 Nm3/h and 33.07 Nm3/h, top lance height of 180 mm, and bottom gas flow rate of 0.84 Nm3/h. The two horizontal lines in Figure 4 indicate the mixing time under the same conditions without bottom gas injection. It can be seen that the bath mixing time in the top and bottom combined blown converter is obviously lower than that in the top blown converter. The bottom tuyere configurations have a significant influence on the bath mixing time. From Figure 4 it is known that the bath mixing time of configuration F is the lowest obtained from all the configurations. Therefore, it can be concluded that the bottom tuyere configuration F is the best one in all the configurations investigated in the present work. Figure 4 also shows that the former bottom tuyere configuration (configuration M) has higher mixing time than most other configurations. The bath mixing time for the optimal bottom tuyere configuration can be reduced by about 36% when compared with that for the former configuration in the experimental conditions. The reason why the former bottom tuyere configuration has a higher mixing time is that there are two bottom tuyeres located in the 0.33D pitch circle, as seen in Figure 3 (configuration M). The location of the two bottom tuyeres is close to the central area of the vessel bottom so that the plumes from the two tuyeres deform the cavity formed by the top gas jet into an ‘00’shape. However, the cavity shape from configuration F is almost a regular circle as shown in Figure 5 . The two plumes from the two bottom tuyeres in the 0.33D pitch circle meet with the top gas jets in the bath, and such phenomenon decreases the stirring energy of bottom and top gases. As a result, the bath mixing time is longer for the former bottom tuyere configuration. This result agrees well with the conclusion obtained by Oymo and Guthrie [S] who suggested that the region between 0.2 and 0.35Din a circular arrangement of tuyeres for combined blowing should be avoided. It can be observed from the experiments that the bottom tuyere configuration F can causes re-circulating flows in the bath, not only in the vertical direction but also the horizontal direction. Such re-circulating flows are favorable to the bath stirring. In the other configurations, such re-circulating flows are not so strong. In most of the bottom tuyere configurations, differences in the bath mixing time between the two top gas flow rates is not evident in the same configuration, which indicates that bath stirring in combined blowing converters is mainly dependent upon bottom gas injection, not on the top gas jets. It can be seen in Figure 4 that the mixing time at the high top gas flow rate in the bottom tuyere configuration L is obviously longer than that at the low top gas flow rate. It is known from Figure 3 that configuration L is a symmetrical bottom tuyere arrangement. The re-circulating flows in the horizontal direction for this configuration are weakened by the higher top gas flow rate, which results in a longer mixing time. The influence of bottom gas flow rate and top lance height on bath mixing time, at different top gas flow rates, is presented in Figures 6 to 9 for configurations F and M. From these figures it can be seen that bath mixing time for configuration F is lower than that for configuration M under the blowing conditions investigated, especially at 347 L.-C. Zhong, J.-E Chen, Z.-L. Lei, (2.-X Ji, E-XZhuandM-F: Jiang h,=180 mm 27.98 Nm3/h To blown converter 70 Q, .-E 50 .-X 40 c 5 30 20 10 0 A B C D E F G H I J K L M Bottom tuyere configuration Figure 4. Bath mixing time in different bottom tuyere configurations. Figure 5. Cavity shape formedfrom confi urations Mand F at Qr=27.98 Nm3’h, hL=180 mm and Q8=0.84 Nm h. 5 348 Physical Modeling and Optimization in a Blowing Converter higher bottom gas flow rates. For the case of configuration M, usually the bath mixing time first increases at lower bottom gas flow rates. Then, it deceases at higher bottom gas flow rates. Such phenomena are associated with the bottom tuyere arrangement. In the range of lower bottom gas flow rate, the percentage of bottom gas momentum for bath stirring decreases when the bottom gas flow rate increase due to the momentum counteraction between top gas and bottom gas, as described above. Only when the bottom gas flow rate is larger than some critical value, does the bottom gas has enough momentum to stir the bath. Therefore it is concluded that the bottom tuyere configuration in top and bottom combined blowing converters is extremely important. If an unsuitable bottom tuyere configuration is employed, then bath stirring becomes aggravated. For configuration F, bath mixing time decreases at bottom gas flow rate from 0.4 Nm3/h to 1.26 Nm3/h and then does not change much at higher bottom gas flow rate. It is indicated that the bath stirring can be improved by increasing bottom gas flow rate for the bottom tuyere configuration F at low bottom blowing rate. However, when the bottom gas flow rate is larger than 1.26 Nm3/h, the effect of bottom gas flow rate on the bath mixing time is not remarkable. Among all the experimental conditions, the lowest bath mixing time is obtained at bottom gas flow rate of 1.26 Nm3/h, top lance height of 160 mm and top gas flow rate of 30.52 Nm3/h for configuration F. 80 Q,=27.98 Nm3/h 70 Q -0- 160 -v- 200 Configuration M 60 W ;. .-CX 50 2 40 30 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Bottom gas flow rate(Nm3k) Figure 6, Effect of bottom gas rate and top lance height on bath mixing time at Qr=27.98 Nm3/h. 349 L.-C. Zhong, J.-E Chen, Z,-L. Lei, C.-X.Ji, E X Zhu and M.-EJiang I " 80 Q,=30.52 Nm3/h -0- 140 -A- 180 -0- 160 -v- 200 70 Configuration M 2 60 hi .-E C :z - 50 lA3; ; -A. \ - W::. -5. 2 40 - b-L;-%.., T -2:- . Configuration F :*--- - z x z z = = s - - - = + ---- b----..:. 30 - * -. - n - = - = - - - - - 1 I 1 I I I I 0.8 0.6 0.4 Ihr I 1.0 1.2 I -0 1-0, I 1.4 c 1.6 Bottom gas flow rate(Nm3/h) Figure 7. Effect of bottom gas rate and top lance height on bath mixing time at Q ~ = 3 0 . 5 Nm3/h. 2 80 . Q,=33.07 Nm3/h -0- 140 70 -A- 180 9 60 hi .i .G 50 Configuration F -- 40 \ '0 30 l 0.4 . 1 0.6 . 1 0.8 * -V - -- -- :.= -- -- - -0 - -A -0:-------- 1 1.0 , 1 1.2 . 1 1.4 , 1 , 1.6 Bottom gas flow rate(Nm3/h) Figure 8. Effect of bottom gas rate and top lance height on bath mixing time at Q ~ = 3 3 . 0 Nm3/h. 7 350 Physical Modeling and Optimization in a Blowing Converter .* - -- 0-r2 40 - 0- -,-U'00.--=-<.-- --0zB - =- - - =- --- --- --- --- -0-0 - -- = z - - -v - - - - - - -- = - - - ------A .A- - - - - - n - - - - - - - - - - A - 0. L ~ - ;g ~ 30 I 1 . 1 . Configuration F I I , Figure 9. Efect of bottom gas rate and top lance height on bath mixing time at Qr=35. 61 Nm3/h. Conclusions Bottom tuyere configurations and blowing process parameters were optimized for the 120 tonne top and bottom combined blowing converter in a 1/10 reduced-scale water model. It was found that the former bottom tuyere configuration (configuration M) of the converter detracted from bath stirring, due to the two tuyeres located in the 0.33D pitch circle which caused the counteraction between the momentum of bottom gas and top gas jets. Among the bottom tuyere configurations investigated in the present work, configuration F had the lowest bath mixing time and was determined to be the ideal arrangement of bottom tuyeres. Bath mixing time decreased with an increase in bottom gas flow rate from 0.42 Nm3/h to 1.26 Nm3/h, and did not change significantly when the bottom gas flow rate is greater than 1.26 Nm3/h for configuration F. Strong bath stirring was achieved at a bottom gas flow rate of 1.26 Nm3/h, top lance height of 160 mm, and top gas flow rate of 30.52 Nm3/h, for a bottom tuyeres arrangement given by configuration F. References 1. Ishihara, S. 1982. Iron & Steelmaker, 9(3), 43-48. 2. Fiege, L., Schiel, V., Schroer, H., et al. 1983. Siahl u. Eisen, 103(4), 159-162. 3. Ajmani, S.K., and Chatterjee, A. 1996. Ironmaking Steelmaking, 23(4), 335-345. 4. Fabritius, T.M., Luomala, M., Virtanen, E., et al. 2002. ISlJInt., 42(8), 861-567. 35I L.-C. Zhong, J.-Y Chen, Z.-L. Lei, C.-X. Ji, Y-X Zhu andM.-F: Jiang 5 6 7 8 352 Roth, C , Peter, M , Schindler, M , et al 1995 Sfeel Res ,66(8), 325-330 Paul, S , and Ghosh, D 1986 Merall Trans, 17B,461-469 Roth. C , Peter, M , Schindler, M , et a1 1999 Sfeel Res ,70( 12), 502-507 Oymo, D and Guthrie, R I L 1984 Proc Mixed Gas Blowing 41h Process Technology Conference ISS/UME, Warrendale, Pennsylvania, USA, p 45 .