POTENTIAL FOR CHEMICAL REACTION

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Tap-hole maintenance practice

For the tap-holes on a typical medium-scale smelter two types of maintenance practices exist: Scheduled maintenance and breakdown maintenance. Scheduled maintenance consists of tap-hole repair conducted with electrode paste. The electrode paste is heated in an oven and plugged into the tap-hole using a mudgun. The tap-hole/mudgun interface is also repaired to ensure proper connection between the mudgun and the tap-hole when plugging the tap-hole with clay. Once the tap-hole is repaired, the electrode paste is left to cure by heating it with an external heat source AND by tapping two taps through the other tap-hole. Breakdown maintenance is practiced in the case of a burn-through. A large section of damaged refractory, metal and slag is removed to a depth of 70 – 75 cm (preferably within the boundaries provided by the copper coolers) until undamaged refractory is reached where the cold ramming paste could tie-in. The area is boxed in and the cold ramming paste is rammed into position and cured. A tap-hole is then drilled through the paste using the tapping drill i.e. no spacer is utilised to form a tap-hole during ramming [30].

Research problem and questions

A commercial producer of SiMn – producing SiMn using the integrated process – found that tap- holes built from cold ramming paste during breakdown maintenance wore at a higher rate than the tapblock installed with the initial lining. In both instances the refractory materials were carbon- based. The producer wanted to obtain a better understanding of the cause of wear [30]. The goal of the study presented here was to determine to what extent chemical reaction between slag and refractory materials could be responsible for the wear observed. To reach the goal, the following research questions were addressed in the thesis: Question 1: When exposing carbon-based refractory material (ramming paste and carbon block) to SiMn slag or metal in the tap-hole, is chemical reaction between refractory and slag or refractory and metal a potential wear mechanism? Question 2: Is the choice in carbon-based refractory material important from a tap-hole refractory life perspective? Question 3: Having obtained answers to Question 1 and Question 2, what are the implications for the life of the tap-hole in a SiMn furnace? 1.8 Overview of chapters The three research questions are addressed in the following chapters: Chapter 2: A review of literature was conducted to obtain a better understanding of carbothermic SiMn reduction process, carbon-based refractory materials in general, wear mechanisms applicable to refractory materials and ways in which these wear mechanisms are studied. The chapter concludes with a review of the first research question. Chapter 3: Thermodynamic calculations were conducted as a first test of the argument that chemical reaction between refractory and slag or refractory and metal is a potential wear mechanism for carbon-based refractory material in the tap-hole. The chapter concludes with a statement on the requirement for experimental validation of these thermodynamic calculations. Chapter 4: Laboratory scale tests were conducted to support the results of the thermodynamic calculations conducted in Chapter 3. Synthetic SiMn slag and pure graphite were used as materials and an induction furnace as heat source. The chapter concludes with an introduction to the second research question which will be addressed in Chapter 5, Chapter 6 and Chapter 7 through further laboratory-scale experiments based on industrial SiMn slag and two commercial grades of refractory material: Carbon block and ramming paste. Chapter 5: Preparation and characterisation of the industrial SiMn slag and two commercial grades of refractory material are discussed and thermodynamic calculations repeated based on the chemical analysis obtained. The chapter concludes with a review of the second research question in terms of the results obtained for the industrial SiMn slag and two commercial grades of refractory material, and introduces the first set of laboratory-scale experiments: Wettability tests. Chapter 6: Wettability tests were conducted in which the wettability of the two commercial grades of refractory material by industrial (and in some instances synthetic) SiMn slag in both Ar-gas and CO-gas atmospheres at 1592°C were quantified. The chapter concludes with a review of both first and second research questions and an introduction to the second set of laboratory-scale experiments: Cup tests. Chapter 7: Cup tests were conducted in which the potential for chemical reaction between, and infiltration by, industrial SiMn slag and the two commercial grades of refractory material were investigated at 1400°C, 1500°C and 1600°C. The chapter concludes with a review of both first and second research questions and an introduction to the third research question to be addressed in Chapter 8 through the presentation of results of the excavation of the tap-hole of a 48 MVA SiMn furnace. Chapter 8: The excavation of the tap-hole of a 48 MVA SiMn furnace was reported and observations interpreted through thermodynamic and mass transfer calculations. Chapter 9: In the final chapter, the three research questions and their arguments are reviewed; conclusions and recommendations for further investigations made.

Literature review

Introduction

Chapter 1 introduced SiMn as alloy and SAF as the technology applied in the production of SiMn. Carbon-based refractory materials were introduced as tap-hole refractory material as was the need for improved understanding of tap-hole wear. Chapter 1 concluded by stating the purpose of the study (to determine to what extent chemical reaction between slag and refractory materials would be responsible for tap-hole refractory wear) and introducing three research questions. Chapter 2 reports on the literature study conducted to obtain a better understanding of carbothermic SiMn reduction process, carbon-based refractory materials in general, wear mechanisms applicable to refractory materials and ways in which these wear mechanisms are studied. The chapter concludes with a review of the first research question and an introduction to Chapter 3.

Carbothermic SiMn production process

Process overview

Figure 10 contains a typical cross-section of a SAF utilized to produce SiMn. Ore containing manganese and silicon oxides (Table 3) and carbon-based reductant are fed from the top of the furnace. The electrode tips are submerged in a burden of material and energy is transferred from the electrodes to the process through micro-arcing across a coke bed that floats on top of….

Table of Contents :

• CHEMICAL WEAR OF CARBON-BASED REFRACTORY MATERIALS IN A SILICOMANGANESE FURNACE TAP-HOLE
• ABSTRACT
• DECLARATION
• DEDICATION
• ACKNOWLEDGEMENTS
• TABLE OF CONTENTS
• LIST OF TABLES
• LIST OF FIGURES
• LIST OF EQUATIONS
• LIST OF ABBREVIATIONS
• 1 INTRODUCTION
  • 1.1 Manganese and its compounds
  • 1.2 Brief history of manganese ferroalloy production
  • 1.3 Commercial grades of manganese ferroalloy and their applications
  • 1.4 Industrial production of manganese ferroalloys
  • 1.5 Lining designs installed in industrial-scale SAFs producing SiMn
  • 1.5.1 Lining design principles
• 2 LITERATURE REVIEW
  • 2.1 Introduction
  • 2.2 Carbothermic SiMn production process
  • 2.2.1 Process overview
  • 2.2.2 Structure of carbon
  • 2.2.3 Carbon reactivity studies
  • 2.2.4 Wettability tests
  • 2.3 Carbon-based refractory materials
  • 2.3.1 Carbon in refractory materials
  • 2.3.2 Different types of carbon-based refractory materials
  • 2.3.3 Influence of thermal conductivity of carbon-based refractory materials
  • 2.4 Refractory wear mechanisms
  • 2.4.1 Different types of refractory wear mechanisms
  • 2.4.2 Development of carbon-based refractory materials in ironmaking
  • 2.4.3 Wear mechanisms in ironmaking blast furnace hearth
  • 2.4.4 Role of additives in carbon-based refractory material
• 3 POTENTIAL FOR CHEMICAL REACTION – PART A (CALCULATIONS)
  • 3.1 Introduction
  • 3.2 Method
  • 3.3 Results
  • 3.4 Discussion
  • 3.5 Conclusion
• 4 POTENTIAL FOR CHEMICAL REACTION – PART B (LABORATORY EXPERIMENTS)
  • 4.1 Introduction
  • 4.2 Method
  • 4.3 Results
  • 4.4 Discussion
  • 4.5 Conclusion
• 5 IMPORTANCE OF CHOICE IN REFRACTORY – PART A (CHARACTERISATION OF MATERIALS)
  • 5.1 Introduction
  • 5.2 Method
  • 5.3 Results
  • 5.4 Discussion
  • 5.5 Conclusion
• 6 IMPORTANCE OF CHOICE IN REFRACTORY– PART B (WETTABILITY TESTS)
  • 6.1 Introduction
  • 6.2 Method
  • 6.3 Results
  • 6.4 Discussion
  • 6.5 Conclusion
• 7 IMPORTANCE OF CHOICE IN REFRACTORY– PART C (CUP TESTS)
  • 7.1 Introduction
  • 7.2 Method
  • 7.3 Results
  • 7.4 Discussion
  • 7.5 Conclusion
• 8 IMPLICATIONS FOR THE LIFE OF THE TAP-HOLE IN A SIMN FURNACE
  • 8.1 Introduction
  • 8.2 Background
  • 8.3 Method
  • 8.4 Results

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