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A Study of the Heat Flow in the Blast Furnace Hearth Lining

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A Study of the Heat Flow in the Blast Furnace Hearth Lining A Study of the Heat Flow in the Blast Furnace Hearth Lining Maria Swartling Doctoral Thesis Stockholm 2010 Department of Materials Science and Engineering Division of Applied Process Metallurgy Royal Institute of Technology SE-100 44 Stockholm Sweden Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm, framlägges för offentlig granskning för avläggande av Teknologie Doktorsexamen, fredagen den 11 juni 2010, kl. 13.00 i F3, Lindstedtsvägen 26, Kungliga Tekniska Högskolan, Stockholm. ISRN KTH/MSE- -10/31- -SE+APRMETU/AVH ISBN 978-91-7415-677-5 i Maria Swartling A Study of the Heat Flow in the Blast Furnace Hearth Lining KTH School of Industrial Engineering and Management Division of Applied Process Metallurgy Royal Institute of Technology SE-100 44 Stockholm Sweden ISRN KTH/MSE- -10/31- -SE+APRMETU/AVH ISBN 978-91-7415-677-5 © The Author ii To the memory of my mother iii ABSTRACT The aim of the present thesis was to study the heat flows in the blast furnace hearth lining by experimental measurements and numerical modeling. Thermocouple data from an operating furnace have been used throughout the work, to verify results and to develop methodologies to use the results in further studies. The hearth lining were divided into two zones based on the thermocouple readings: a region with regular temperature variations due to the tapping of the furnace, and another region with slow temperature variations. In an experimental study, the temperatures of the outer surfaces of the wall and bottom were measured and compared with lining temperature measured by thermocouples. Expressions to describe the outer surface temperature profiles were derived and used as input in a two-dimensional steady state heat transfer model. The aim of the study was to predict the lining temperature profiles in the region subjected to slow temperature variations. The methodology to calculate a steady state lining temperature profile was used as input to a three-dimensional model. The aim of the three-dimensional model was primarily to study the region with dynamic lining temperature variations caused by regular tappings. The study revealed that the replacement of original lining with tap clay has an effect when simulating the quasi-stationary temperature variations in the lining. The study initiated a more detailed study of the taphole region and the size and shape of the tap clay layer profile. It was concluded, that in order to make a more accurate heat transfer model of the blast furnace hearth, the presence of a skull build-up below the taphole, erosion above the taphole and the bath level variations must to be taken into consideration. v ACKNOWLEDGEMENTS I would like to express my sincere gratitude and appreciation to my supervisors Professor Pär Jönsson and Dr Anders Tilliander for believing in me and always encouraging me. I am very grateful for your constant support during my years at KTH. Special thanks to Bo Sundelin at SSAB Oxelösund for many valuable discussions and help, and to the personnel at Blast Furnace No. 2 for qualified help and assistance. I owe Professor Henrik Saxén at Åbo Academy a special gratitude; your support has not been underestimated in any way. Financial support from the Swedish Energy Agency, the Swedish Steel Producers Association and the committee JK21064, as well as grants from Gerhard von Hofstens and Axel Hultgrens foundations, are greatly acknowledged. Thanks to all my friends at the department of Materials Science and Engineering; I have truly enjoyed my time as a Ph.D. student in your company. We have shared many laughs and discussed every conceivable topic. There is no issue on local or global level that has not been discussed (some of them we have even solved!). I am also very grateful that I have had the possibility to work among people from all over the world. Special thanks to my friends in the A P´nR-team. To my father, brother and Johan: thank you for being there for me! A cold February morning I received a phone call telling me that my mother had lost her long fight against cancer. To my friends, colleagues and supervisors at KTH and Åbo Academy: I have truly experienced what it means when someone cares about you. If I could pay you back in any way, I would! Maria Swartling, Stockholm, May 2010 vii SUPPLEMENTS The present thesis is based on the following supplements: Supplement 1: Experimentally Determined Temperatures in Blast Furnace Hearth M. Swartling , B. Sundelin, A. Tilliander and P.G. Jönsson Ironmaking & Steelmaking, Vol. 37, No. 1, pp 21-26, 2010. Supplement 2: Heat Transfer Modelling of a Blast Furnace Hearth M. Swartling , B. Sundelin, A. Tilliander and P.G. Jönsson Steel Research International, Vol. 81, No. 3, pp 186-196, 2010. Supplement 3: Short-term Lining Temperature Changes During Tapping in a Blast Furnace M. Swartling , B. Sundelin, A. Tilliander and P.G. Jönsson Accepted for publication in Steel Research International, September 2010. Supplement 4: A Study of Dynamic Lining Temperature Variations in the Taphole Region of Blast Furnace M. Swartling , A.Tilliander, H. Saxén and P. G. Jönsson Submitted to Steel Research International, May 2010. ix The contributions by the author to the different supplements of the thesis: 1. Literature survey, experimental work, major part of the writing. 2. Literature survey, numerical calculations, major part of the writing. 3. Literature survey, numerical calculations, major part of the writing. 4. Literature survey, numerical calculations, major part of the writing. Parts of this work have been presented at the following conferences: Temperature measurements on Blast Furnace 2 at SSAB Oxelösund M.Swartling , B. Sundelin, A. Tilliander and P. Jönsson 3rd Nordic Conference for Young Scientists, May 2008, Helsinki, Finland. Heat transfer study on Blast Furnace 2 at SSAB Oxelösund M.Swartling , B. Sundelin, A. Tilliander and P. Jönsson 5th International Congress on the Science and Technology of Iron-making, October 2009, Shanghai, China. xi 1 INTRODUCTION 1 1.1 LITERATURE SURVEY 2 1.2 PRESENT WORK 4 2 PLANT DESCRIPTION 7 2.1 SSAB OXELÖSUND 7 2.2 DETAILS OF BLAST FURNACE NO. 2 7 2.2.1 HEARTH LINING MATERIALS 7 2.2.2 MONITORING OF TEMPERATURES 8 2.2.3 HEARTH COOLING CONDITIONS 9 2.3 CHARACTERIZATION OF THE STATE OF THE HEARTH 10 3 EXPERIMENTAL STUDY 11 4 MATHEMATICAL MODELS 13 4.1 TWO-DIMENSIONAL MODEL 13 4.1.1 COMPUTATIONAL DOMAIN 13 4.1.2 EQUATIONS 13 4.1.3 BOUNDARY CONDITIONS 14 4.1.4 CALCULATIONS PROCEDURE 14 4.2 THREE-DIMENSIONAL MODEL 15 4.2.1 COMPUTATIONAL DOMAIN 15 4.2.2 EQUATIONS 15 4.2.3 BOUNDARY CONDITIONS 16 4.2.4 CALCULATION PROCEDURE 17 4.2.5 MODIFICATION OF MODEL 17 4.3 LOGGING OF TEMPERATURES DURING CALCULATIONS 17 4.4 MATERIALS 18 5 RESULTS AND DISCUSSION 19 5.1 EVALUATION OF THERMOCOUPLE PROCESS DATA 19 5.1.1 LONG-TERM TEMPERATURE VARIATIONS 19 5.1.2 SHORT-TERM TEMPERATURE VARIATIONS 21 5.2 EXPERIMENTAL STUDY 22 5.2.1 WALL SURFACE TEMPERATURE 22 5.2.2 BOTTOM SURFACE TEMPERATURE 25 5.3 TWO-DIMENSIONAL STEADY STATE CALCULATIONS 26 xiii 5.4 THREE-DIMENSIONAL TRANSIENT CALCULATIONS 29 5.4.1 EFFECT OF TAP CLAY LAYER – A FIRST APPROACH 30 5.4.2 EFFECT OF TAP CLAY LAYER – DETAILED STUDY 31 5.4.3 SIMULATION BASED ON PROCESS DATA 36 5.5 THERMPCOUPLE POSITIONS 39 6 CONCLUSIONS 43 7 FUTURE WORK 47 8 REFERENCES 49 xiv 1 INTRODUCTION The blast furnace is an ironmaking process with a long history: the oldest known blast furnace in Sweden can be dated to the 12 th century. Research and engineering efforts to improve the process have presumably been going on since the first furnace was built. That has contributed to the fact that the blast furnace has maintained its unchallenged position as the dominating process in the ore-based steel production route. Throughout the years, large efforts have been put on finding ways to increase the productivity and extend the campaign length. The state of the hearth has by many been identified as the most important factor for a long campaign length. This lower region of the furnace is exposed to liquid iron and slag at high temperatures that could be in direct contact with the lining, causing erosion and corrosion of the lining material. The most aggressive environment is found in the region closest to the taphole. It is exposed to thermal stresses and liquid iron and slag at high flow rates. An increased productivity results in higher load on the furnace, which potentially can shorten the campaign length. To strive to optimize both these goals, it is important to carefully control the state of the hearth. Other challenges in blast furnace research are to reduce the coke rate and the amount of exhaust gases. The average coal consumption for the Swedish blast furnaces was 467 kg, based on statistics from 2009. [1] Hence, the Swedish domestic coal consumption for producing pig iron is close to the theoretically required amount. However, the coal consumption increases temporarily during unsteady blast furnace operation. Thus, to keep the total coke consumption at low levels, it is important to eliminate disturbances as far as possible. Accordingly, the ability to control the state of the hearth and maintain a steady operation, are two key issues in blast furnace practice. It is therefore of importance to understand the process and be able to interpret its behavior. The aim of the present thesis is to study the 1 heat flows in the blast furnace hearth lining, by experimental measurements and numerical modeling. Most blast furnaces are equipped with thermocouples, measuring lining temperature.
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