No abstract

Steelmaking converter vessels do not usually wear evenly. Often, the higher wear rate in the trunnion area determines the lining life of the vessel. On the other hand, major skull growth may occur in other parts. In order to ensure consistent BOF performance, maintaining the vessel geometry by selective slag coating is important. Since selective slag splashing is difficult to perform by conventional oxygen lance, the effect of e.g. plugging one or two lance nozzles on the amount and direction of splashing was investigated by physical model experiments. Furthermore, the model was used to predict the influence of lance height, lance position, bottom blowing configuration and liquid viscosity on splashing behaviour. Lowering the lance increased the rate of splashing to a certain lance height beyond which it decreased. Similar behaviour was found to apply also to the slag wash coating mechanism. At low lance distance, plugging one lance nozzle increased the amount of splashing on charge pad and trunnion areas and decreased on slag hole side. Generally, bottom blowing increased the amount of slag drops considerably. Positioning of bottom stirring plugs had a clear effect on the direction of splashes.

Due to the different nature of the required measurements, two separate water models were utilised. Both models have the same geometry and dimensions; scaled down to 1 : 7. The operational and geometrical parameters of the physical model and the prototype are presented in Table 1. Figure 1 shows the location of bottom nozzles for 3, 4 and 5 nozzle arrangements. The two lance positions used in splashing and oscillation studies are also displayed in the same figure. Measurement of Splashing and SpittingSplashing and spitting behaviour in the combined blown converter vessel was studied with the new method, which is previously described elsewhere in more detail. 17) Since the whole model wall is perforated, the experimental set-up enables studying overall splashing distribution on the model wall. Spitting is referred to as water droplets collected from the mouth of the converter model by an absorbent cloth. Measurement of Mixing TimeThe experimental apparatus and auxiliary instruments for ISIJ International, Vol. 44 (2004) The blowing behaviour of the BOF is affected in many ways by the behaviour of molten bath. Bottom blowing and its interaction with top blowing have a strong influence on splashing and spitting behaviour, bath homogenisation and bath oscillation. Therefore, three selected bottom nozzle configurations were studied by physical modelling, and the results were compared regarding splashing, homogenisation and oscillation of the bath. According to model tests, bottom nozzle positioning has a great influence on the amount and direction of splashing and spitting. Moreover, at lower lance gaps, the direction of splashes was changed because of bath oscillation. At low lance gap, when type A oscillation is dominant, correlation between the degree of overlap and stability of the bath was found. The bigger the degree of overlap, the more unstable the system as far as type A oscillation and splashing is concerned. The amplitude and oscillation frequency of the bath changed as a function of lance height. Blowing through bottom nozzles prevented the onset of so called type A oscillation. Bottom nozzle configuration of three nozzles resulted in shortest mixing time, lowest total splashing on model walls and longest starting time of type A oscillation.

Wear of refractory lining, skulling of converter cone and metal losses were studied by splashing and spitting measurements in physical model during combined blowing. The aim of the present study was to determine the effect of the bottom nozzle arrangement and lance height as far as on harmful splashing and spitting in combined blowing converter are considered. The investigation has concentrated mainly on the initial period of blowing.According to the model tests, total splashing on the converter walls increases as a function of number of bottom nozzles (with increase of total gas flow rate) both initial and final period of blowing. At the initial period of blowing, combined blowing produces maximum measured total splashing and large reaction area as a form of droplets. The nozzles arranged at the centre of the vessel increase metal losses and skulling of the converter cone especially with lowered lance height. The introduction of outside of lance cavities arranged bottom nozzles decreases metal losses and skulling of converter cone compared to the top lance blowing at final period of blowing. The usage of high lance height and several bottom nozzles accelerate wear of the refractory, especially at the knuckle area and charge pad area. It is possible to reduce splashing to the knuckle areas with certain lance gaps by positioning bottom nozzles directly between the cavity and knuckle area with remarkable (approximately 30-40 %) overlap.

The amount of iron droplets ejected in the BOF affects on metallic yield, refactory wear and the progress of decarburisation. The purpose of this study was to investigate the effect of lance height, lance nozzle angle, lance position, top gas flow rate, bottom blowing and foamy slag on splashing and spitting. A new cold model method for investigating the effects of above-mentioned parameters on the location and quantity of liquid splashed on the walls of the model was utilised. According to the model tests, reduction of the nozzle angle increased the total amount of splashing and spitting considerably. Consequently, reduced productivity due to an increase in metal losses, skulling of the cone and converter mouth and further increased time for skull removal is expected. Introduction of bottom blowing increased splashing significantly on lower parts of the vessel. Lance position has an effect on total amount of splashing when bottom blowing is used. The presence of even minor foam layer on water surface reduced the amount of total splashing significantly.KEY WORDS: BOF; steelmaking; splashing; spitting; physical model.In order to clarify the interaction of the lance jet cavity with bottom blowing plume, experiments were first conducted with a very simple water model. 16) For the splashing studies in the BOF, more sophisticated model was developed. 17) In the present paper, the effect of lance height, lance nozzle angle, top gas flow rate, bottom blowing and foamy slag on the amount and direction of the splashing is investigated. Furthermore, the effect of various blowing parameters on the wear of refractory lining, on metal losses and on skulling of the cone is discussed. Experimental Set-upTo simulate splashing in the steelmaking converter, three-dimensional water model apparatus was set up and scaled down to the 1 : 9 of the actual process. The cylindrical vessel was made of an acrylic glass and has an inner diameter of 487 mm and a height of 809 mm. The geometrical and operational parameters for both the model and the converter are summarized in Table 1. A more detailed description of the apparatus is given elsewhere. 17)Special feature of the model was that the wall is perforated; altogether 60 holes in four rows around the wall. When all the parameters were set for the test compressed air was blown through the lance to splash the liquid. Splashed water then fell to the certain hole and was further guided through the tube into a corresponding bottle where water gradually accumulated during the blow. The rate of splash was measured by weighing the amount of liquid collected during the blow in each of the 60 bottles. The weight was divided by blowing time and area of corresponding hole.The model lance tip was made of stainless steel. Converging-diverging or de Laval nozzles were used for blowing air; their specifications are given in Table 1. A collectible textile was used at the mouth of the model in order to estimate the amount of liquid ejected outside. The weight of the water obtained from the textile will b...