Modelling of slag emulsification and slag reduction in CAS-OB process

Abstract Composition Adjustment by Sealed argon bubbling – Oxygen Blowing (CAS-OB) process is a ladle treatment process that was developed for chemical heating and alloying of steel. The main stages of the process are heating, (possible) alloying and reduction of slag. The CAS-OB process aims for homogenization and control of the composition and temperature of steel. In this dissertation, a mathematical reaction model was developed for the slag reduction stage of the CAS-OB process. Slag reduction is carried out by applying vigorous bottom stirring from porous plugs at the bottom of the ladle. Due to the bottom stirring a circular steel flow is induced which disrupts top slag layer and due to shear stress at the steel-slag interface small slag droplets are detached. This induces an immense increase in the interfacial area between steel and slag which provides favourable conditions for the reduction reactions. In order to model reduction reactions, a sub-model for describing the interfacial area was needed. For this the slag droplet formation was studied using computational fluid dynamics (CFD) and based on these studies, a sub-model for droplet formation was developed. The model for the reduction stage of the CAS-OB process takes into account not only the reaction during the reduction but also the heat transfer between the phases, ladle and surroundings. The reduction stage model was validated using validation data obtained from the CAS-OB station of the SSAB Raahe steel plant in Finland. It was concluded that the model was able to predict steel and slag compositions as well as the steel temperature very well.Tiivistelmä CAS-OB -prosessi on sulametallurgiassa käytettävä senkkakäsittelyprosessi, joka on kehitetty teräksen kemialliseen lämmittäseen ja seostukseen. CAS-OB-prosessin pääprosessivaiheet ovat lämmitysvaihe, mahdollinen seostusvaihe ja kuonan pelkistysvaihe. CAS-OB -prosessilla tavoitellaan teräksen koostumuksen homogenisointiin ja lämpötilan kontrollointiin. Tässä tutkimuksessa kehitettiin matemaattinen reaktiomalli CAS-OB -prosessin kuonan pelkistysvaiheen kuvaamiseen. Kuonan pelkistys tapahtuu senkan pohjassa olevien huuhtelutiilien avulla suoritettavan voimakkaan kaasuhuuhtelun avulla. Pohjahuuhtelu aiheuttaa kiertävän teräsvirtauksen senkassa. Teräsvirtaus irrottaa teräksen päällä olevasta kuonakerroksesta pisaroita ja kuonan ja teräksen välinen reaktiopinta-ala kasvaa voimakkaasti. Tämä tarjoaa suotuisat olosuhteet pelkistysreaktiolle senkassa. Pelkistysreaktioiden mallintamiseksi tässä työssä kehitettiin CFD-simulaatioiden avulla alimalli, jonka avulla voidaan kuvata teräksen ja kuonan välisen pinta-alan suuruutta. Pelkistysvaiheen mallissa huomioidaan reaktioiden lisäksi myös systeemissä tapahtuva lämmösiirto. Pelkistysmalli validoitiin mittausdatalla, joka hankittiin SSAB Raahen terässulaton CAS-OB -asemalla järjestetyssä validointikampanjassa. Tutkimuksessa havaittiin, että malli kykenee hyvin ennustamaan teräksen ja kuonan koostumuksen sekä teräksen lämpötilan

Added value for forest industry for metals producing and processing integrates (FOR&MET):project report of University of Oulu

Preface This report covers the studies related to biochar characterization and use in blast furnace injection. The research was carried out by Processing Metallurgy Research Unit (University of Oulu) as part of the Added Value for Forest Industry for Metals Producing and Process Integrates (FOR&MET) project. University of Oulu and Technical Research Centre of Finland (VTT) were the research partners in the project. The activities of Technical Research Centre of Finland have been reported in a separate report. We would like to sincerely thank Business Finland for financing the project. We would also like to acknowledge the project partners from industry — SSAB Raahe, Finnpulp Oy, St1 Biofuels Oy and Valmet — for very valuable cooperation and discussion during the project

A review of pyrolysis technologies and the effect of process parameters on biocarbon properties

Abstract Biomass-based solutions have been discussed as having the potential to replace fossil-based solutions in the iron and steel industry. To produce the biocarbon required in these processes, thermochemical treatment, pyrolysis, typically takes place. There are various ways to produce biocarbon, alongside other products, which are called pyrolysis oil and pyrolysis gas. These conversion methods can be divided into conventional and non-conventional methods. In this paper, those techniques and technologies to produce biocarbon are summarized and reviewed. Additionally, the effect of different process parameters and their effect on biocarbon yield and properties are summarized. The process parameters considered were final pyrolysis temperature, heating rate, reaction atmosphere, pressure, catalyst, use of binders, and particle size. Finally, the effect of different reactor configurations is discussed. Understanding the combination of these methods, technology parameters, and reactor configurations will help to produce biocarbon with the desired quality and highest yield possible

A thermogravimetric analysis of lignin char combustion

Abstract Understanding the combustion behavior is the basic requirement for a new resource to be used as an alternative fuel for the industrial design of the future plants. In this article, thermogravimetric analysis (TGA) of lignin char combustion in different heating rates (5, 10 and 15 °C/min) was investigated. Extracted combustion indices showed increased weight loss rate, peak temperature and burnout temperature but no change in ignition temperature for all samples when the heating rate increased. Lignin chars containing higher volatile material illustrated higher combustibility through the low ignition and burnout temperatures. Kinetic parameters of lignin combustion were also obtained by the Coat-Redfern method in the first-order kinetic model. High combustibility of high volatile sample (L300: vol%=41) was also confirmed by its low activation energy which was 46.68 compared to 150.34 for L500 (vol%=18) and 174.37 kJ/mol for L650 (vol%=5.1). The pre-exponential factor was also measured to be 2.61E-01, 8.15E+06 and 1.21E+08 min-1for L300, L500 and L650 respectively

A CFD and experimental investigation of slag eye in gas stirred ladle

Abstract In ladle metallurgy, gas stirring and behavior of the slag layer are very important for the quality of the steel. When gas is injected through a nozzle located at the bottom of the ladle into the metal bath, the gas jet exiting the nozzle breaks up into gas bubbles. The rising bubbles break the slag layer and create a slag eye. In this paper, the behavior of the slag eye area for different gas flow rates is been investigated through experimental measurements and CFD simulations. A 1/5-scale water model of 150 ton-ladle was deployed for the experimental measurements and for studying the effect of gas flow rate on the slag eye diameter. The physical modelling results show that the slag eye area changes from 20 to 182 cm2 when the gas flow rate increases from 1.5 to 15NL/min. The dimensionless area of the open eye was found to be in agreement with earlier studies. The simulations were carried out in the commercial CFD code ANSYS Fluent with mesh generation in ANSYS Workbench. The numerical model developed is based on the Eulerian Multiphase Volume of Fluid (VOF) approach and employs standard 𝑘−𝜀 turbulence model for solving the turbulent liquid flow induced by bubble-liquid interaction. The simulation results of slag eye area showed a good agreement when compared to experimental results measured

Modeling of the effect of the gas flow rate on the fluid flow and open‐eye formation in a water model of a steelmaking ladle

Abstract In ladle metallurgy of steelmaking, the role of gas injection into the metal bath is been studied to a great extent as it improves the quality of steel. The size of the open‐eye is associated with higher emulsification of top slag, which intensifies metal–slag reactions, and information about the position and size of the open‐eye is important for effective alloying practice. Moreover, the open‐eye has an effect on the energy balance since it increases heat losses. In this work, experimental measurements and numerical simulations are performed to study the effect gas flow rate on the formation of the open‐eye in a steelmaking ladle. A one‐fifth scale water model is constructed for studying gas injection with single and dual plug configurations. For the numerical modeling, the Multiphase Volume of Fluid (VOF) model is used for simulating the system including the behavior of the slag layer. The physical modeling results show that the open‐eye area changes from 9.22 to 198.34 cm2 when the gas flow rate varies from 0.75 to 15 SLM using a single plug. The effect of the number of plugs on the open‐eye area for the same range of flow rates mentioned above is also studied. The two open‐eye areas generated due to the gas injected through the dual plugs change from 37.59 to 231.1 cm2 when the gas flow rate is increased from 0.75 to 7.5 SLM for each plug in the physical modeling. The numerical simulation results of the open‐eye area are found to be in good agreement with the experimental data obtained from the water model. During the gas stirring process, the slag layer is deformed such that the thickness of the slag becomes thick near to the wall and thin near the slag eye at high gas flow rates. In dual plug system, the two open‐eyes tends to merge and form a huge open‐eye at high flow rates that suits for better alloying purposes. The high‐flow velocity near the surface, which could damage the ladle refractory, tends to be reduced in dual plug system when compared to single plug system

Numerical study of multiphase flows in a ladle for different closure models

Abstract Computational Fluid Dynamics (CFD) modelling is increasingly being used for studying various metallurgical processes. In secondary steelmaking, gas stirring is used in ladles to enhance the mixing of the steel. This work aims at numerical study to investigate the effect of different closure models on of the flow analysis in a two-phase gas-stirred ladle. The study represents a cylindrical geometry, in which liquid Wood’s metal represents the liquid metal phase and nitrogen gas is injected through nozzle located centrically or eccentrically at the bottom of the vessel. Three-dimensional CFD simulations were carried out using the commercial software package ANSYS FLUENT using Euler-Euler multi-phase model. To study the influence of turbulence models on the accuracy of the CFD analysis, three different models Standard k-ε, k-ω and Reynolds Stress Model (RSM) were employed. Furthermore, four different gas flow rates (100, 200, 500 and 800 cm3/s) were used for studying the effect of gas flow rates on the flow velocities. The simulation results were compared with the available experimental data of the liquid velocity profiles, volume fraction of gas and turbulent kinetic energy at different heights in the ladle. The RSM model showed a good accuracy of results when compared to experimental results, but it requires more computational time when compared to other turbulence models. The simulation results using the liquid Wood’s metal/nitrogen system were compared to water/air and liquid steel/argon systems to check the effect of material properties on the flow velocities in the ladle. The results provide useful guidelines for numerical modelling of fluid flows in steelmaking ladles and suggest that the RSM turbulence model is better suited for studying gas injection in metallurgical ladles than k-ε or k-ω models

Physical and CFD modeling of the effect of top layer properties on the formation of open‐eye in gas‐stirred ladles with single and dual‐plugs

Abstract In secondary steelmaking, the optimal size and position of open‐eye is important for effective alloying practice. In the current work, the effect of the top layer thickness and density on the formation of open‐eye in a gas stirred ladle was investigated. A one‐fifth scale water model of 150‐ton ladle was established with single and dual plug configurations for the physical modeling measurements. Air, water and three different oils were used to simulate the argon, liquid steel and slag in the water model, respectively. A transient Computational Fluid Dynamics (CFD) model based on Eulerian Volume of Fluid (VOF) approach was developed for numerical modeling of the fluid flow behavior. The physical modeling results show that the relative open‐eye area decreases from 46.7 to 5.6% when top layer thickness was increased from 0.75 to 7.5 cm using a gas flow rate of 7.5 NL min−1. The effect of the number of plugs on the open‐eye area for the same range of top layer thickness mentioned above was also studied. The relative open‐eye area generated due to the gas injection through the dual plugs decreased from 49.9 to 5.8%. To study the effect of top layer properties, rapeseed oil, castor oil and paraffin oil were employed for studying the effect of density and dynamic viscosity on the open‐eye formation. The results revealed that a larger open‐eye is formed when the density is increased. Furthermore, it was found out that the density of the upper phase dominates the open‐eye formation while dynamic viscosity has only minor effect. The results obtained from numerical simulations and physical modeling were found to be in good agreement