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On the Study of a Liquid Steel Sampling Process
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Process Metallurgy.
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The liquid steel sampling method is one of the commonly used procedures in monitoring the steelmaking process. Besides it can be used for analyzing the dissolved alloys, hydrogen content and oxygen content, it can be also employed to monitor the inclusion characteristics at the steelmakings. Here, a crucial point is that the steel sampler should be filled and the metal solidifies without changing the inclusion characteristics. Therefore, the objective of this work is to fundamentally understand the liquid steel sampling process by means of analyzing and modeling the two-phase flow during the sampler filling process, and verifying the mathematical model by using the experimental data.

The present dissertation presents an experimental and theoretical study of the filling process of both the lollipop-shaped sampler and the rectangular-shaped sampler. Firstly, a physical modeling by using a water model has been carried out to fundamentally investigate the flow pattern inside the sampler vessels during its filling. The flow patterns were obtained by a PIV system. Then, a mathematical model has been built to theoretically understand the phenomena. The commercial CFD code was used. Here, different turbulence model have been compared between the realizable k-ε turbulence model and Wilcox k-ω turbulence model. It concludes that the Wilcox k-ω turbulence model agrees well with the PIV measurements.HH

Thus, the preferred it was further employed to predict the turbulent flow inside the production lollipop-shaped sampler fillings. It is important to find that the average collision volume in the production steel sampler without solidification at filling is about 30 times higher than that in a ladle furnace.

In the end, the whole sampling system was modeled. The initial solidification during the filling was taken into account. Focus was on the influence of the initial solidification on the inclusion concentrations. A discrete phase model was used to simulate the movement of inclusions in the liquid steel. Some selected different sized primary inclusions that exist in the ladles at a steelmaking process were simulated.

The same method of studying the filling procedure of the lollipop-shaped sampler was further applied to comprehensively investigate the rectangular-shaped sampler.

Place, publisher, year, edition, pages
Stockholm: KTH , 2010. , 47 p.
National Category
Metallurgy and Metallic Materials Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-24385ISBN: 978-91-7415-704-8 (print)OAI: oai:DiVA.org:kth-24385DiVA: diva2:349410
Public defence
2010-09-17, Salongen KTHB, Osquars Backe 31,KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100908Available from: 2010-09-08 Created: 2010-09-07 Last updated: 2012-02-24Bibliographically approved
List of papers
1. Physical modeling of a sampler filling for molten steel
Open this publication in new window or tab >>Physical modeling of a sampler filling for molten steel
2009 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 49, no 10, 1522-1529 p.Article in journal (Refereed) Published
Abstract [en]

In recent years, much attention has been paid to determining not only the composition, but also the inclusion characteristics from liquid steel samples extracted from a ladle or a tundish. Here, a crucial point is that the steel sampler is filled and solidified without changing the inclusion characteristics that exist at steel making temperatures. Therefore, one of the first steps to investigate is the flow pattern inside samplers during filling in order to obtain a more in-depth knowledge of the sampling process. In this paper, this is done using physical modeling of a lollipop-shaped sampler. More specifically, particle image velocimetry was employed to capture the flow field and calculate the velocity vectors during the entire experiment. The filling rate at the pin part of the sampler was varied during the experiments. It was found that due to the geometry change at the transition from the inlet pin to the body part of the sampler, the flow is very chaotic at the initial filling stage. Furthermore, vortexes are formed in the water sampler vessel during all the fillings and the height of the vortex center varies with the filling rate. Overall, it was found that the flow patterns in the lollipop-shaped sampler vessel can be characterized into three distinct flow regions: the upper vortexes region, the lower horizontal flow region and the middle nozzle flow region.

Keyword
Flow pattern, Physical modeling, PIV, Sampler, Vortex
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24398 (URN)10.2355/isijinternational.49.1522 (DOI)000271176100009 ()2-s2.0-73949145212 (Scopus ID)
Note
QC 20100907. Tidigare titel “Physical Modeling of a Sampler Filling”.Available from: 2010-09-07 Created: 2010-09-07 Last updated: 2017-12-12Bibliographically approved
2. Mathematical Modelling of Water Sampler Filling
Open this publication in new window or tab >>Mathematical Modelling of Water Sampler Filling
2010 (English)In: Steel Research International, ISSN 1611-3683, Vol. 81, no 2, 112-122 p.Article in journal (Refereed) Published
Abstract [en]

Steel samples taken from ladles or tundishes during the steel making process can be of significant importance when monitoring the inclusion size and distribution. In order to preserve the original size and distributions of inclusions in the extracted samples, it is important to avoid their collisions and coagulations inside samplers during filling. Thus, it is necessary to investigate the flow during a sampling process to make sure that this is minimized. In addition, it is important to study the turbulence characteristics, since it is known to influence the inclusion growth. This study presents mathematical modelling of sampler filling using water as a media and experimental results for verification. The study focuses on a lollipop-shaped sampler since it is one of the most common in the industry. The sampler is filled from an inlet pin located at the bottom centre of the main body. In addition, two different turbulence models, the realizable k-ε model and Wilcox k-ω model, were used to study the flow pattern in the sampler. The predictions were compared to experimental results obtained by Particle Image Velocimetry (PIV) measurements. It was found that the flow field predictions using the Wilcox k-ω model agreed best with the flow field obtained by PIV measurements. Furthermore, it was illustrated that the Wilcox k-ω model can be used for predictions of the different flow regions as well as the positions of the centres of vortexes which are located near the free surface. Thus, it is concluded that the Wilcox k-ω model can be used in the future to predict the filling of steel samplers.

Keyword
sampler, filling, simulation, flow pattern, turbulence, vortex, Wilcox k-ω model
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24413 (URN)10.1002/srin.200900085 (DOI)000275142400004 ()2-s2.0-77949430978 (Scopus ID)
Note
QC 20100907Available from: 2010-09-07 Created: 2010-09-07 Last updated: 2011-11-06Bibliographically approved
3. Simulation of the Filling of a Liquid Steel Sampler
Open this publication in new window or tab >>Simulation of the Filling of a Liquid Steel Sampler
2010 (English)In: Steel Research International, ISSN 1611-3683, Vol. 81, no 9, 749-758 p.Article in journal (Refereed) Published
Abstract [en]

Steel samples extracted from the ladle furnace in liquid state are vital to monitor the steel making process in the iron & steel industries. The main function of the steel sample is to exam whether the steel is at the aimed composition for elements that dissolve in steel. In addition, more interest is arising to determine the inclusion characteristics in steel samples, in order to monitor the development throughout the process. However, the molten steel sampling is a process involving multi-phenomena such as a high temperature, a fast solidification, reoxidation of steel and a highly turbulent flow pattern. Therefore, mathematical simulations have been carried out to fundamentally study the sampler filling process. The Wilcox k-ω turbulence model was employed to predict the turbulent flow. The calculated results show that flow patterns inside the sampler can be classified into three distinct flow regions: the vortex flow region close to the free surface, the lower horizontal flow region and the middle vertical flow region. From the flow and turbulence data, the inclusion particle collision volume rate was calculated to study the influence of turbulent flow on the inclusion growth in the sampler during fillings. It is shown that the collision volume in the sampler is much higher than that found in the ladle furnace, where the steel sampling normally takes place. This is due to the high turbulence energy dissipation rate in the samplers compared to the ladles.

Keyword
steel sampler, simulations, turbulent flow, Wilcox k-ω turbulence model, turbulence energy dissipation rate, collision volume
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24415 (URN)10.1002/srin.201000107 (DOI)000281912200008 ()2-s2.0-77956585289 (Scopus ID)
Note
QC 20100907Available from: 2010-09-07 Created: 2010-09-07 Last updated: 2011-11-06Bibliographically approved
4. Simulation of the Steel Sampling Process
Open this publication in new window or tab >>Simulation of the Steel Sampling Process
2010 (English)In: ISIJ International, ISSN 0915-1559, E-ISSN 1347-5460, Vol. 50, no 12Article in journal (Refereed) Published
Abstract [en]

This work presents a theoretical study of the liquid steel sampling process in the iron &steel industry. As a continuous research with the previous work, the initial solidification duringthe sampler filling was taken into account. The liquid steel sampling procedure, which ismainly used to monitor whether the steel is at the correct composition during the steelmaking,can also be applied to examine the inclusion size characteristics. Focus was on the influence ofthe initial solidification on the inclusion concentrations. The whole sampling system wasmodeled in order to obtain a simulation result which is realistic from an industrial perspective.Argon-protected sampling was the focus in the simulations. A discrete phase model was usedto simulate the movement of inclusions in the liquid steel. Inclusions were injected from theinlet pin of the lollipop-shaped sampler. Some selected different sized primary inclusions thatexist in the ladles during a steelmaking process were simulated. The conclusion from this workis that turbulent flow patterns within the sampler mold will change because of the spaceshrinkage due to the solidification. This, in turn, will also affect the inclusion dispersions. Itconcludes that the preferred position for detecting inclusions is the bottom region, except thebottom surface. It estimates that the mean deviation between the calculated result and the initialconcentration for all inclusions in these regions is within 10%.

Keyword
liquid steel sampling, sampler, solidification, flow fields, CFD, mathematical modeling, Wilcox k-ω turbulence model, inclusion concentration
Identifiers
urn:nbn:se:kth:diva-24416 (URN)000285666400004 ()2-s2.0-79952044944 (Scopus ID)
Note
QC 20100907Available from: 2010-09-07 Created: 2010-09-07 Last updated: 2017-12-12Bibliographically approved
5. An Experimental and Numerical Study of theFilling of a Steel Sampler
Open this publication in new window or tab >>An Experimental and Numerical Study of theFilling of a Steel Sampler
(English)Manuscript (preprint) (Other academic)
Abstract [en]

During the steelmaking process, it is important to understand the origin, types and nature ofinclusions. After an initial period of heating, mixing and chemical reactions in an electric arcfurnace and some crucial processes in a ladle, taking liquid steel samples in the ladle is a criticalstep in monitoring the inclusion population. This paper presents a study of filling of a steelsampler process as well as the primary inclusion dispersions inside a steel sample. To betterunderstand the influence of filling on the inclusion populations, physical modelings of waterfilling in a rectangular-shaped vessel have been carried out to study flow fields. The flow fieldswere obtained by a Particle Image Velocimetry. Thereafter, simulation of water samplers havebeen done to mathematically study the flow fields. The physical modeling data were used forverification of the model predictions, including the selection of the most appropriate turbulencemodel. Finally, simulations of the filling of liquid steel were carried out for a rectangular-shapedsampler, which is used in the laboratory.

Keyword
steel sampler, filling, flow pattern, vortex, PIV, turbulent flow, Wilcox k-ω model, inclusions
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-24420 (URN)KTH/MSE--10/35--SE+APRMETU/ART (ISRN)
Note
QC 20100908Available from: 2010-09-08 Created: 2010-09-08 Last updated: 2010-09-08Bibliographically approved

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