- Title
- Slag splashing dynamics in basic oxygen steelmaking furnace - a fundamental study on the coating formation by molten droplets
- Creator
- Chowdhury, Raju
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Wearing of the inner refractory lining of the Basic Oxygen Steelmaking (BOS) furnace is a known problem in the steelmaking industry which occurs due to a combination of chemical, mechanical, and thermal attacks. It reduces the effective life span of the BOS refractories, leading to an increase in the cost per tonne of steel. As a remedy, it is essential to deploy some workable strategies to prolong the useful life of the furnace. Splashing of retained slag in BOS systems by blowing an inert gas is an effective technique which can be utilised to form a protective coating layer on the furnace lining. Interaction of gas jet with slag phase generates numerous slag droplets of different sizes which then deposit on the refractory wall and solidify to form a coating. The present research aims at investigating the potential coating formation behaviour in an industrial scale BOS furnace by slag splashing with a specific focus on the underlying coating formation mechanism in a single molten droplet–solid surface system. Utilising commercial steel plant data, a Computational Fluid Dynamics (CFD) model of the BOS system was developed, and the model was utilised to simulate two main scenarios – a usual oxygen injection operation to determine the wear prone zones inside the furnace and a slag splashing operation with inert gas injection from both furnace top and bottom. A sensitivity analysis was performed to determine the effect of three main parameters – design of the gas injection lance (number of holes on lance), lance location relative to the furnace floor and the initial slag mass in the furnace. CFD modelling showed that for a fixed gas flow rate, a 6-hole lance design produced more coated surface area compared to a 5-hole design. However, the lance design was noted to have no significant effect when the retained slag quantity in the furnace was doubled. The coating formation mechanism involving impact of a molten droplet on a solid surface was separately studied. Experiments were performed comprising both normal and oblique impact of a single molten droplet (Weber number, We < 150) using high-speed imaging. For normal impact, two distinct outcomes were noted – (1) rebound and (2) disintegration demarcated by a critical Weber number. The maximum droplet coated area and droplet spreading time were found to have a non-linear dependency on the Weber number. It was shown that in all cases, solidification time was almost twice the droplet oscillation time. Both times however decreased with the increase of Weber number. The droplet impact dynamics and coating behaviour however were observed to be quite different in the oblique impact case. Five distinct outcomes were noted – (1) rebound, (2) disintegration, (3) partial rebound, (4) rivulet, and (5) combine effect of spreading and detachment depending on the impact Weber number and impact angle. The maximum coated area decreased with decreasing impact angle for the same Weber number. A theoretical scaling law was established to predict the droplet spreading time on inclined surface which agreed well with the experimental data. Coating efficiency was quantified based on the utilisation of the initial droplet mass in coating formation and found to be highly dependent on the impact angle. A recovery type exponential profile was used to describe the coating kinetics. The solidification time was also found to decrease with decreasing impact angle and increasing Weber number. Two regime maps were developed to determine coating efficiency and dominant mode of spreading (non-solidification or solidification restricted) corresponding to an impact outcome as a function of the impact angle and droplet Weber number. A 3D CFD model was also developed based on the volume of fluid (VOF) approach and enthalpy-porosity solidification sub-model to predict the coating formation behaviour in a single molten droplet-flat surface system for both normal and oblique impact. The CFD model predicted the transient deformation behaviour of the droplet quite reasonably well compared to the experiment for both cases with a maximum deviation ~ 17%. As an alternative to the solidification effect, a viscosity model was developed to predict the transient coating behaviour of molten droplet-solid surface interactions for the normal impact case. The model predicted maximum coated area agreed well with the experimental result at We 70 with a deviation 16%.
- Subject
- molten droplet; droplet-surface interaction; oscillation time; gas-jet interactions; lining wear; slag coating; Weber number; spreading time.; coating area; solidification time; basic Oxygen Steelmaking; slag splashing; main blowing; CFD modelling
- Identifier
- http://hdl.handle.net/1959.13/1473307
- Identifier
- uon:48993
- Rights
- Copyright 2023 Raju Chowdhury
- Language
- eng
- Full Text
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| View Details Download | ATTACHMENT01 | Thesis | 12 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 532 KB | Adobe Acrobat PDF | View Details Download |