| 1. |
- Ek, Mattias
(författare)
-
A study of some aspects of gas-slag-metal interactions : Towards dynamic process model and control
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis deals with the development of a new type of dynamic model for metallurgical reactors. It also covers some of the theoretical aspects of steelmaking that is necessary to include in such an application. The thesis consists of modeling work, high temperature experiments and cold model experiments.Two different aspects of slags in the oxygen steelmaking were investigated. In the first study, slag samples were equilibrated with copper at 1923K in order to study their capacities in capturing phosphorous. Some of the samples were liquid-solid mixtures. The solid phases in these samples were identified by SEM analysis. The identified phases were found to agree well with Thermocalc calculations while the amount of solid fractions didn’t. The phosphorous distribution between the different phases was examined. The phosphate capacities of the samples were evaluated. The MgO content didn’t show any appreciable impact on the phosphate capacity. Furthermore the activities of FeO in the liquid slag samples were calculated and were found to deviate positively from ideality. In the second study the foaming height of CaO-SiO2-FeO slags by the reaction with hot metal was investigated. It was found that the foaming height increased with increasing FeO content up to 20-25%. The foaming height was seen to decrease with increased viscosity. The present results indicated that simply using foaming index for converter slag might lead to wrong conclusion.Simulation experiments using cold model at room temperature were conducted. Cold model experiments were carried out in order to study the penetration depth due to an impinging gas jet on the surface of a liquid metal. The liquid alloy Ga-In-Sn was used to simulate steel. And an HCl solution was used to simulate the slag. A comparison with predictions of existing models was made and a new model parameter was suggested. The observation of the movement of metal droplets generated by the gas jet was also made. The low velocity of droplets suggested that the turbulent viscosity played important role and the droplets could have long resident time in the slag.Furthermore a study of the effect of gas flow rate on homogenization and inclusion removal in a gas stirred ladle was carried out. Both industrial trials and cold model experiments were conducted. As an auxiliary tool CFD was used to predict the mixing times and was found to agree well with both the model experiments and industrial data. The increase of flow rate of inert gas would not improve the mixing substantially at higher flow rates. The water model study showed also that the gas flow rate had negligible effect on the rate of inclusion removal. Both the experiments and CFD calculation strongly suggested that low gas flow rate should be applied in the ladle treatment.Lastly a new approach to a dynamic process model of 300 ton BOF converter was made. The main feature was to utilize the velocity vectors obtained by CFD simulation. In the standalone model, the steel melt domain was sliced into 1000 cells. Based on the imported velocity vectors from the CFD calculation, the mass transfer of carbon and phosphorus was calculated taking into account the slag metal reactions. The mass exchange between slag and metal was considered to be dominated by the metal droplet formation due to oxygen jet. The convergence of the model calculation and the promising comparison between the model prediction and the industrial data strongly suggested that the proposed approach would be a powerful tool in dynamic process control. However, more precise descriptions of other process aspects need to be included before the model can be practically employed in a dynamic controlling system.
|
|
| 2. |
- Malmberg, Donald
(författare)
-
Innovative Contact Free Sensors for Metallurgical Process Control
- 2003
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The steel- and metal industry has an extensive production processing comprising many different process steps of solid, gaseous and liquid nature. Thus it is obvious that a number of different measurement technologies must be used to collect and evaluate key physical parameters which are necessary to control the production processes. In this respect, the software to monitor the processes have, during the past decade, undergone extensive improvement whilst the sensors reading off the instantaneous process status have not and are still afflicted with severe drawbacks.This situation, in combination with increased demands on energy savings and rules regarding reduction of green house gas emission (the Kyoto protocol), has created incentives for the development and implementation of new technologies to monitor and control production processes in the steel and metal industry.The objectives in this thesis are to develop and evaluate sensor technology that can be used for in-situ on line analysis of metallurgical processes.The work is divided into:- To test and evaluate microwave technology for on line slag analysis.- To design, develop and evaluate microwave sensors for off gas analysis.- To evaluate laser sensors for simultaneous analysis of the process environment in metallurgical processes with emphasis on measuring the oxygen concentration and temperature in a steel reheating furnaceDuring the work on slag a broad band antenna was used for the microwave investigations on solid and liquid slag. The results show that it is possible to evaluate a refractive index for both solid and liquid slag. The results also show that there is a weak correlation between the refractive index for liquid slag and slag basicity.Trials on off gases from a pilot process as well as a full scale metallurgical production processes have been performed with microwave technology. The instrument used for the microwave trials has been developed from individual components. The results show that it is possible to use the technology for process analysis however the data collected regarding individual spectral lines still remain to be correlated to known molecular frequencies.Laser technology for gas analysis is a known technology in many different industrial applications. However, using the technology in steel and metal production processes requires that the technology must be adapted to the environment specific to those processes. Trials on a pilot process has been performed to find a suitable set of O2 absorption line parameters to be used during the forthcoming trials of full scale production processes. The outcome of these trials clearly show that the TDLAS technology can be used successfully on reheating furnaces but have a limited application potential on the LD converter process as well as the EAF.The benefit of the presented work will on production scale contribute to a lowered emission of green house gases, lowered energy consumption and an improved production yield.
|
|
| 3. |
- Martinsson, Johan
(författare)
-
A Study of the Behavior of Foaming Slag in Steelmaking
- 2018
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis presents a fundamental study on some aspects regarding foaming slag. In today’s society, the requirements on environmental impact and energy consumption are increasing. It is essential for the steel industry to better understand the fundamentals of their processes to be able to develop both the process but also process control to reach the demands. In this work, the basic BOF furnace is the main focus, even though foaming slag may also occur in some electric arc furnaces. The BOF is a chaotic process with the purpose to decarburize and dephosphorize hot metal from the blast furnace. The foaming slag plays a profound role in the kinetics of the reactions, maintains the temperature in the furnace and protects the lining material of the furnace.The first part of the thesis includes a study of the structure of different foams and some viscosity measurements. Both room temperature and high temperature experiments are conducted. It is shown that the apparent viscosity of a foam is not only depending on the dynamic viscosity of the liquid phase and the gas fraction of the foam, but also the surface tension of the liquid and the bubbles size of the foam. The foam appears to show a shear thinning non-Newtonian behavior with apparent viscosities up to 5 times as high as for the pure liquid. The reason is found in the structure of the foams.The behavior of particles falling through foams generated from different sugar solutions is studied in the second part of the thesis. The particle behavior differs a lot depending on the size and density of the particle, and the viscosity and surface tension of the liquid phase. Some particles get stuck in the foam, some heavy particles fall through the foam crushing the bubbles in its path, and some particles fall slowly in a zick-zack pattern towards the bottom. The residence time is also measured, and a semi-empirical model is developed to describe the apparent velocity of the particles falling in a zick-zack pattern.The decarburization is the source of the foam in the furnace, and is studied in the third part of the thesis. Pig iron is dropped into liquid slag and the reaction rate is studied by quenching of samples at different times. Small droplets are decarburized faster than big droplets, and the incubation time of the reaction is found to play a big role in the decarburization process for different slag compositions.ivThe last part of the thesis is a comparison of lime dissolution in liquid versus foaming BOF slags. The controlling dissolution mechanism in liquid slag is the removal of interfacial layers of calcium silicates. In the foam on the other hand, the contact area between liquid slag and lime seem to be the controlling mechanism. In total, the rate seem to be similar in some liquid and foaming slag compositions while in others, the lime is dissociated into small pieces in the foaming slag due to the chaotic environment in the experiment.
|
|
| 4. |
- Millman, Stuart, et al.
(författare)
-
Radio-wave inferometry for BOS slag control
- 2001
-
Rapport (refereegranskat)abstract
- The aim of the project is to use radio-wave interferometry to determine the BOF slag and metal heights in both a quiescent and a blowing BOS convertor. The hydrodynamics of the slag/metal emulsion and 1, 2 and possibly 3D representations of slag and metal movements during the blowing phase will be made. Process factors such as vessel shape, lance movements, bath agitation, flux/ore additions and fume generation will be considered.
|
|
| 5. |
- Wang, Huijun, 1988-
(författare)
-
A Study on the Reaction between MgO Based Refractories and Slag-Towards the Development of Carbon-free Lining Material
- 2017
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In present thesis, the fundamental studies on the reaction between MgO based refractories and slag were undertaken for the development of a carbon-free bonding MgO lining material. Alumina was selected as a potential binder material. Due to MgO-Al2O3 chemical reaction, the developed refractory was bonded by MgO·Al2O3 spinel phase. To begin with, an investigation of the dissolution process of dense MgO and MgO·Al2O3 spinel in liquid slag was carried out. To obtain reliable information for dissolution study, a new experimental method was therefore developed. In this method, a cylinder was rotating centrally in a special designed container with a quatrefoil profile. This method also showed a good reliability in revealing the dissolution mechanism by quenching the whole reaction system. The experimental results showed that the dissolution process of MgO and spinel was controlled by both mass transfer and chemical reaction. It was found that the rapid dissolution of spinel was mainly because of its larger driving force. To improve the resistance against slag penetration, two aspects were studied to develop carbon-free MgO refractory. First, colloidal alumina was used and the effect of its addition into MgO matrix was investigated. The use of colloidal alumina was to form bonding products in the grain boundary of MgO. The results showed that the alumina addition greatly improved the resistance of MgO based refractory against slag penetration in comparison with the decarburized MgO-carbon refractory. It was found that the improvement of resistance was mainly related to the spinel-slag reaction products of CaO·Al2O3 and CaO·MgO·Al2O3 solid phases at the grain boundaries. Second, the effect of particle size distribution on the penetration resistance of MgO was investigated. The most profound improvement against the slag penetration was obtained by using a proper particle size distribution. The results highlighted the importance of considering the refractory structure. Experiments were undertaken to investigate the dissolution mechanism of different types of MgO based refractories in liquid slag. It was observed that the dissolution of spinel bonded MgO refractory was much slower than the decarburized MgO-carbon refractory. The primary dissolution in spinel bonded MgO refractory occurred at the slag-penetrated layer, and the removal of this layer by peeling off enhanced the dissolution rate rapidly.
|
|
