Based on a mechanistic understanding of the factors affecting the growth of granules, a mathematical model of the granulation process has been developed. The model predicts the final granule size distribution based on the feed size distribution, the quantity of water added and physical properties of the feed. There was good agreement between the model and laboratory results for a wide range of ore types and feed size distributions. The model can be used to compare quantitatively the granulating ability of different ore blends, and to study the sensitivity of granulation to changes in the sinter feed mix.
External agitation in one form or the other, is an essential part of every steelmaking process. The nature of the agitation markedly influences the steelmaking operation. In this work, two separate consequences of gas bubble agitation viz. homogenisation of the bath and removal of dissolved oxygen, both of which are important to steelmakers, were studied. While the extent of homogenisation was investigated in a cold model set up, the variation in dissolved oxygen levels in the bath was determined in laboratory as well as in operating steelmaking furnaces. It was concluded that for identical volumes of gas injected into the bath, dispersed bubble agitation results in a distinctly shorter time of mixing than agitation induced by gas introduction through a single basal tuyere. The oxygen level of an un-deoxidised bath was found to decrease sharply at first and then increase gradually following agitation and a theoretical model ws developed to explain this variation.
A study was made on the mechanism of dust generation by investigation of dust behavior in a BOF with combined blowing. The results are summarized as follows: (1) BOF dust is generated through ''fumes'' condensing and mixing with ''burst bubble particles''. (2) The ratio of burst bubble particles in the dust is a little bit larger at the initial stage of blowing and decreases with the lapse of blowing time, whilst at the end of blowing, the ratio of fumes increases. Therefore, if there are any effective step for reducing the quantity of dust generation, they might be the formation of slag in an early time at the initial stage of blowing and the cool down of a hot spot from the middle stage of blowing.
Calcium-calcium fluoride melt was used to remove phosphorus from the ferro-chrome alloy (64.5 wt% Cr, 0.15 wt% P) during electro slag refining process. The effect of atmosphere and deoxidisers, viz. Al, Fe–Mo and misch metal were also studied during dephosphorisation reaction. The thermodynamic properties of Ca–CaF2 melt is calculated from a known phase diagram and these results are discussed in relation with the dephosphorisation reaction.
Experimental conditions of bubbling jets were chosen in the intermediate gas flow rate regime where the size and the shape of bubbles are mainly determined by nozzle size and gas flow rate. The velocity of liquid in bubbling jets were measured by making use of LDV (Laser Doppler Velocimeter). The radial and axial distributions of them were related to the behaviour of rising bubbles. The empirical expressions for the mean velocity and root mean square value of velocity fluctuation on the center-line were presented as functions of gas flow rate. Also, water jets in the same vessel were measured to confirm the applicability of LDV system and to clarify the effect of side wall on the confined jets.
The activity of Na2O in CaO-based slags has been measured employing a galvanic cell technique with a β-Al2O3 solid electrolyte. The iso-activity lines for Na2O were obtained over the liquidus composition range in the CaO–Na2O–SiO2 system at 1 400°C. The activity of Na2O in CaO–based slag is strongly controlled by the SiO2 content in slag and the activity coefficient of Na2O increases as the CaO content increases. The activity of Na2O in a 50%CaO–40%Al2O3–10%SiO2 (typical ladle slag composition) is extremely high. At a Na2O concentration of about 8 wt% in this slag, the activity of Na2O is nearly equal to that of 50wt%Na2O–SiO2 slag at the same temperature. The Richardson solution model fits the experimental data well and this model was used to compute the activity of CaO in these systems. The addition of Na2O significantly increases the activity of CaO.
A mathematical representation has been developed for the filling of cylindrical molds, using a bottom pouring arrangement. In the model allowance has been made for thermal natural convection, solidification and for the presence of the free surface. Turbulence was represented by assigning artificially enhanced parametric values to the viscosity and the thermal conductivity. The results have shown that the temperature profiles are markedly non-uniform, and that solidification would commence quite soon after the pouring process has been initiated. For the conditions considered, the free surface disturbances were not very great, although quite high free surface velocities were predicted by the model.
To improve creep rupture strength of a 30Cr-60Ni alloy which can be used for ultra super critical-pressure boiler tubes, the effects of Al and Ti additions on strength and microstructure were investigated. Creep rupture strength is improved by increasing Ti content in the range from 0.4 to 1.0 wt%. The most effective range lies in the addition of 0.8 to 1.0 wt% Ti with 0.4 wt% Al. These additions promote γ' phase formation at 700 and 750°C and the amount of γ' precipitation increases with Ti content. However, at 700°C excess Ti addition beyond 0.8 wt% causes carbide coagulation on grain boundaries and in grains which leads to the lowering of creep rupture strength. Accordingly, creep rupture strength is dependent not only on γ' precipitation but also on carbide coagulation.
The basic characteristics of pipe nozzle cooling with retaining water on a plate has been studied in a laboratory test by using a moving hot plate. The cooling ability of pipe nozzle flow changes with the amount of retaining water. It was found that maximum cooling ability can be obtained when the depth of retaining water is approximately 50 mm. The cooling ability with retaining water increases slightly as the nozzle is raised, while the cooling ability without retaining water decreases as the nozzle height increases. The influence of the cooling conditions, such as flow-type and plate temperature, on the cooling ability with retaining water was also investigated and the cooling ability of pipe nozzle flow was compared with that of slit nozzle flow with a large gap. It was found that the slit nozzle flow has less cooling efficiency than the pipe one in the high water flux, though no difference can be seen when the water flux is low.
Large scale migration of iron ions during oxidation of iron or reduction of iron oxides leads to porous products. It is mathematically proved that a porous magnetite is formed during the initial stages of solid state reduction of hematite by iron.
Electrical conductivity of synthetic high-alumina blast funcace slags was measured with graphite electrodes. Electrical conductivity of the melts increases with increasing temperature. It is also found to increase with the addition of MgO in the melt and with higher basicity ratio defined as (%CaO+0.7%MgO)/(0.94%SiO2+0.18%Al2O3). Activation energy for conduction has been found to decrease with the addition of MgO and increase with increasing Al2O3. Possible explanations for these observations have been suggested from the ionic point of view.