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A Study on the Thermal State of Steelmaking Ladles
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling. (Micro-Modelling)ORCID iD: 0000-0002-6127-5812
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the present thesis a study on the thermal state of steelmaking ladles was undertaken. The transient hot wire method was verified for thermal conductivity measurements on metallurgical slags and applied to ladle slag measurements. Temperature measurements on ladles in an industrial environment were carried out. The emissivities of the outer and inner shells of steelmaking ladles were investigated. Two dynamic models were developed to predict the heat transfer and fluid flow in a preheating and teeming ladle. The gathered thermal conductivity values for ladle slag were used to study the effect of the slag layer on the top surface of the melt on heat transfer and fluid flow in a teeming ladle.

In the first stage, the transient hot-wire method was verified to measure the thermal conductivity of metallurgical slags at steelmaking temperatures. A numerical model was developed, cold model experiments were conducted and test measurements using a high temperature experimental setup were carried out. To minimize natural convection and to obtain more reliable measurements, the crucible diameter, the hot-wire diameter, the applied current, the position of the wire in the crucible and the cooling on the upper surface of the crucible were studied. Investigations into the choice of sheathing material of the circuit exposed to the slag were also made. It was found that only certain materials were suitable for slag measurements depending on slag composition and temperature. The electrical resistivity of the hot wire was measured to make the thermal conductivity calculation more reliable. The wire diameter also played a major role due to the heat generation per surface area. The thermal conductivity should be derived from the values measured during the first seconds. In this initial stage, the effect of the natural convection as a function of the wire position in the crucible, the cooling on the top surface and the diameter of the crucible are negligible. A compromise has to be made in choosing the electrical current, since higher current results in higher sensitivity but at the same time in more natural convection.

In the second stage, the thermal conductivities of four different ladle slags were measured at 1773 K, 1823 K, 1873 K and 1923 K using the transient hot wire method. Very good reproducibility was obtained. The thermal conductivity did not vary substantially with the variation of slag composition at 1873 K and 1923 K, at which the slag samples were all entirely liquid. The thermal conductivities were low. It was found that the precipitation of solid phase resulted in a considerable increase of thermal conductivity.

In the third stage, a two dimensional model was developed in order to predict the temperature distribution in the ladle wall during the preheating process. The model calculated the heat transfer and the velocity field in the gas phase inside the ladle as well as the heat transfer in the solid walls during the preheating process. Measurements of the temperature profiles in an industrial ladle were carried out using an infrared thermography. The measurements were made both inside and outside the ladle. The model predictions were found to be in reasonably good agreement with the measured temperatures. It was found that the preheating time could be minimized when the working lining became thinner. The effect ofthe distance between the lid and the ladle was also studied by the model. The results indicated that there was no significant temperature change on the upper side wall of the ladle. On the lower side wall and bottom the temperature changed slightly. The temperature difference in the lower part of the ladle could be explained by the larger flame distance from the bottom layer.

In the fourth stage, a two dimensional axisymmetric model was developed to predict the heat flux in a steelmaking ladle during the teeming process. The model predicts dynamically the flow fields in both the liquid phase and the gas phase along with the movement of the liquid upper surface. The model also predicts the temperature distributions in the liquid metal, gas phase and all layers in the ladle wall. Again, industrial measurements were performed using an infrared thermography, both inside the ladle after teeming and at the wall outside the ladle during the whole process sequence. The model predictions were found to be in agreement with the measured data. It was found that the heat transfer to the surrounding atmosphere and the conductivity of the highly insulating layer were the most important factors for the heat loss. The decrease of the thickness of the working lining was found to have limited effect on the total heat flux.

In the fifth and final stage, the effect of the slag layer on the top surface of the melt, on fluid flow and on heat transfer in a teeming ladle was investigated theoretically. The two dimensional axisymmetric model developed in the fourth stage was used. To predict the effect of the slag layer a stationary heat conduction boundary condition including thermal conductivity and slag layer thickness was employed. Different calculations with differing thermal conductivity values for the slag layer were carried out. The calculations showed that the effect of the slag layer was insignificant. This could be explained by the similarity of the thermal conductivity of slag and gas phase.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , 53 p.
Keyword [en]
steelmaking ladle, refractory, thermal conductivity, transient hot wire method, slag, peheating
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:kth:diva-103303ISBN: 978-91-7501-494-4 (print)OAI: oai:DiVA.org:kth-103303DiVA: diva2:559686
Public defence
2012-10-26, F3, Lindstedtvägen 26 Entreplan, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20121010

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2012-10-10Bibliographically approved
List of papers
1. Determination of Experimental Conditions for Applying Hot Wire Method to Thermal Conductivity of Slag
Open this publication in new window or tab >>Determination of Experimental Conditions for Applying Hot Wire Method to Thermal Conductivity of Slag
2013 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 84, no 7, 649-663 p.Article in journal (Refereed) Published
Abstract [en]

In order to apply the hot wire method for metallurgical slags at steelmaking temperatures, a numerical model was developed, cold model experiments were conducted and test measurements using a high temperature experimental setup were carried out. To minimize natural convection and obtain more reliable measurements, the crucible diameter, the hot-wire diameter, the applied current, the position of the wire in the crucible, and the cooling on the upper surface of the crucible were studied. Investigations into the choice of sheathing material of the circuit exposed to the slag were also made. It was found that only certain materials were suitable for slag measurements depending on slag composition and temperature. The electrical resistivity of the hot wire was measured to make the thermal conductivity calculation more reliable. The wire diameter also played a major role, because of the heat generation per surface area. The thermal conductivity should be derived from the values measured during the first seconds. In this initial stage, the effect of the natural convection as a function of the wire position in the crucible, the cooling on the top surface, and the diameter of the crucible are negligible. A compromise has to be made in choosing the electrical current, since higher current results in higher sensitivity but at the same time in more natural convection.

Keyword
thermal conductivity, molten slag, transient hot wire method, line source method
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103330 (URN)10.1002/srin.201200206 (DOI)000322366700004 ()2-s2.0-84879846565 (Scopus ID)
Note

QC 20130830. Updated from accepted to published.

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2017-12-07Bibliographically approved
2. Thermal Conductivity Measurements of Ladle Slag Using Transient Hot Wire Method
Open this publication in new window or tab >>Thermal Conductivity Measurements of Ladle Slag Using Transient Hot Wire Method
2013 (English)In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 44, no 1, 1-4 p.Article in journal (Refereed) Published
Abstract [en]

Thermal conductivities of four different ladle slags were measured at 1773 K, 1823 K, 1873 K, and 1923 K (1500 A degrees C, 1550 A degrees C, 1600 A degrees C, and 1650 A degrees C) using the transient hot wire method. Very good reproducibility was obtained. The thermal conductivity did not vary substantially with the variation of slag composition at 1873 K and 1923 K (1600 A degrees C and 1650 A degrees C), at which the slags were all entirely liquid. The thermal conductivities were low. It was found that the precipitation of solid phase resulted in considerable increase of thermal conductivity.

Keyword
Heat-Transfer, Steelmaking, Steel, Flow
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103331 (URN)10.1007/s11663-012-9773-9 (DOI)000314909000001 ()2-s2.0-84873990162 (Scopus ID)
Note

QC 20130320.  Updated from submitted to published.

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2017-12-07Bibliographically approved
3. Thermal Modelling of the Ladle Preheating Process
Open this publication in new window or tab >>Thermal Modelling of the Ladle Preheating Process
2011 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 82, no 12, 1425-1434 p.Article in journal (Refereed) Published
Abstract [en]

To predict the temperature distribution in the ladle wall during the preheating process a two dimensional model was developed. The model calculated the heat transfer and the velocity field in the gas phase inside the ladle as well as the heat transfer in the solid walls during the preheating process. Measurements of the temperature in an industrial lade were carried out using an infrared radiation (IR) camera. The measurements were made inside and outside the ladle. The model predictions were found to be in reasonably good agreement with the measured temperatures. It was found that the preheating time could be minimized when the working lining became thinner. The effect of the distance between the lid and the ladle was also studied by the model. The results indicated that there was no significant temperature change on the upper side wall of the ladle. On the lower side wall and bottom the temperature changed slightly. The temperature difference in the lower part of the ladle could be explained by the larger flame distance from the bottom layer.

Place, publisher, year, edition, pages
John Wiley & Sons, 2011
Keyword
Heat transfer, steel making ladle, refractory, preheating
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-67456 (URN)10.1002/srin.201100198 (DOI)000298303600011 ()2-s2.0-82755190791 (Scopus ID)
Note

QC 20120207

Available from: 2012-02-07 Created: 2012-01-27 Last updated: 2017-12-08Bibliographically approved
4. Fluid Flow and Heat Transfer in the Ladle during Teeming
Open this publication in new window or tab >>Fluid Flow and Heat Transfer in the Ladle during Teeming
2011 (English)In: Steel Research International, ISSN 1611-3683, E-ISSN 1869-344X, Vol. 82, no 7, 827-835 p.Article in journal (Refereed) Published
Abstract [en]

A two dimensional axisymmetric model was developed to predict the heat flux in a steelmaking ladle during the teeming process. The model predicts dynamically the flow fields in both liquid phase and gas phase along with the movement of the liquid upper surface. The model also predicts the temperature distributions in the liquid metal, gas phase and all layers in the ladle wall. Industrial measurements using infrared radiation camera inside the ladle after teeming and at the wall outside the ladle during the whole process were carried out. The model predictions were found to be in agreement with the measured data. It was found that the heat transfer to the surrounding atmosphere and the conductivity of the highly insulating layer were the most important factors for the heat loss. The decrease of the thickness of the working lining was found to have limited effect on the total heat flux.

Keyword
fluid flow, heat transfer, refractory, steelmaking ladle, teeming
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-37548 (URN)10.1002/srin.201000270 (DOI)000293266600010 ()2-s2.0-79959952664 (Scopus ID)
Note
QC 20110816Available from: 2011-08-16 Created: 2011-08-15 Last updated: 2017-12-08Bibliographically approved
5. The effect of the slag layer on fluid flow and heat transfer in a teeming ladle
Open this publication in new window or tab >>The effect of the slag layer on fluid flow and heat transfer in a teeming ladle
(English)Manuscript (preprint) (Other academic)
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-103333 (URN)
Note

QS 2012

Available from: 2012-10-10 Created: 2012-10-10 Last updated: 2012-10-10Bibliographically approved

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