Physical Simulation of Bottom Blowing Stirring inside Smelting Reduction Vessel by Water Modeling

• Main Authors: Chau-Jeng Su, 蘇朝正
• Other Authors: Jaw-Min Chou
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/97449745232137483531

博士 === 義守大學 === 材料科學與工程學系博士班 === 98 === In order to increase the productivity, the gas bottom blowing technique has been applied to mix molten iron/slag inside the ironmaking smelter. The main function of the technique is to increase the interface area between slag and iron, then to enhance the rate of the smelting reduction. Dimensional analysis technique was used to intensify the similarity between the water model and the experimental smelting reduction vessel. Then, the water model experiments were conducted to investigate both the mixing time of the molten iron phase and the erosion of the bottom refractory lining around the tuyere tip inside smelting reduction vessel under different gas bottom-blowing conditions. In two experiments, the major parameters of gas bottom-blowing conditions were the gas flow rate(80~120NL/min), the inside diameter(6.0~15.0mm), the number(3~5pipes), and the placement of the bottom blowing tuyeres. Also, mixing time simulation work is used to simulate liquid iron this model is water, compressed air functions as the bottom-blowing gas, and KC1 was utilized as indicator in the iron mixing time test .Oil-pressed boric acid disks were used as specimens to simulate the refractory lining around the tuyere tip for refractory erosion test. For the mixing degree of molten iron/slag experiments, the major parameters of the gas bottom blowing were the inside diameter of tuyere, the total gas flow rate, the placement of the bottom blowing tuyeres. Also, water and spindle oil were selected to represent liquid iron and molten slag inside the smelter, respectively. And, thymol was used as the tracer of mass transfer between the two phases. Based on the mass transfer rate equation with the analyzed data of thymol concentration during experiments, the mixing degree could be distinguished for different blowing conditions. The result of research indicated that the important dimensionless groups for the similarity between the cold model and the ESRV are Modified Froude Number, Modified Weber Number, Reynolds Number, and Euler Number. The mixing time of molten iron phase experimental results indicate that in the cases of four tuyeres in the square-corner and triangle-corner-center placements, 10.0 mm tuyeres yield the shortest mixing time under different total gas flow rates. In the case of five tuyeres in the square-corner-center placement, 10.0 mm tuyeres also have the shortest mixing time under total gas flow rates of 400 NL/min and 500 NL/min. However, 12.5 mm tuyeres have the shortest mixing time under a total gas flow rate of 600 NL/min. In addition, in the case of three tuyeres in the triangle-corner placement, 12.5 mm tuyeres have the shortest mixing time under different total gas flow rates. When the gas flow rate per tuyere is 80 NL/min, the fewer the tuyeres, the shorter the mixing time. Depending on tuyere placement, some of the energy injected by the gas may be counteracted. In contrast, a tuyere placement without a center tuyere may yield better mixing effects. In experiments of the refractory erosion, it was indicated that the erosion rate of specimens around tuyere tip decreased with decreasing the bottom-blowing gas flow rate. The lowest erosion rate of boric acid specimens is at 10 mm inner diameter tuyeres in the case of four tuyeres in the square-corner placement. In all experiments except the above case, the lowest erosion rate of boric acid specimens was found at 15 mm inner diameter tuyere. The erosion rate of specimens around tuyere tip decreased with decreasing the number of the bottom blowing tuyere ranging from 3 to 5 tuyeres. It also was shown that the erosion rate of the triangle-corner-center placement case is lower than the square-corner placement case at the same bottom blowing condition. In the study of metal/slag mixing, it was found that the mixing degree at the case of 10.0 mm inner diameter tuyere was higher than other size tuyeres under the same gas flow rate via 4 tuyeres. And, the mixing degree increased with increasing the total gas flow rate. Additionally, the mixing degree in the case of 4 tuyeres in the square-corner placement was better than in the triangle-corner-center placement at the same tuyere size and total gas flow rate. In experiments of the refractory erosion behavior, it indicate that distribution of erosion surface can also be grouped into two characteristic zones, which are back-attack and cavitation erosion. In the back-attack phenomenon, back-attack pressure and frequency increased with an increase of total gas flow rate of the blown gas via reducing the tuyere size in the tuyere diameter range of 7.5 to 15.0mm. For the cavitation phenomenon, the pressure and frequency of shock wave or microjet increased with an increase of total gas flow rate of the blown gas via reducing the tuyere size. Also, the ersion model of the small tuyere size region(6.0mm and 7.5mm) is cavitation erosion, which made a serious result. It is concluded that the bottom blowing conditions for the shortest mixing time of molten iron phase, the lowest erosion rate of refractory lining and the best mixing efficiency are bottom blowing total gas flow rate at 480NL/min(120NL/min per tuyere), inner diameter of tuyere at 10.0mm and four bottom blowing tuyeres in the square-corner placement in the experiments conducted in this research.