Development of a Direct Reduction (DR) Shaft Furnace Model for the Optimization of Direct Reduced Iron (DRI) Production = Development of a Direct Reduction (DR) Shaft Furnace Model for the Optimization of Direct Reduced Iron (DRI) Production

다국어 초록 (Multilingual Abstract)

Direct reduction (DR) is an ironmaking technique that converts iron ore into sponge iron, serving as a low-carbon alternative to the conventional blast furnace route. In 2024, global steel production via DR reached approximately 140.8 million metric tons (Mt), primarily driven by the widespread adoption of MIDREX and HYL technologies. The optimization of these DR shaft furnace processes is increasingly critical as the industry transitions towards H2-based iron production, aiming to further reduce carbon emissions and enhance process efficiency. A comprehensive process simulation model of DR systems becomes valuable for evaluating reduction kinetics, thermal behavior, and gas-solid interactions, thereby enabling process optimization and informed reactor design.

The objective of this study is to develop a unified, one-dimensional shaft furnace model for the direct reduction of iron ore, with the aim of introducing a more detailed and thermodynamically reliable chemical process compared to previous studies. The present PhD thesis consists of (i) a literature review of all available iron reduction models and numerical models of the shaft furnace, (ii) two newly developed numerical models for iron pellet reduction, (iii) a one-dimensional integrated shaft furnace model containing the pellet reduction model, validated with MIDREX and HYL industrial plant data, (iv) process optimization case studies, and (v) an analysis of DR plant operation considering the recycling of reducing gas from the shaft furnace and the reforming process.

In the literature review, all available models for iron ore reduction and shaft furnace in literature are collected and reviewed critically. Early studies focused on the reduction of individual pellets by H2, CO, or H2-CO mixed gas without considering a shaft furnace. Later studies addressed the simulation of the shaft furnace, typically in one or two dimensions. The iron ore (hematite) pellet reduction has been described by using the shrinking core model (SCM), zone model, grain model, and CFD based model. All available shaft furnace models focused on the MIDREX process, but only several of them included all three zones of the shaft furnace. No study on the HYL process operating at high pressure (about 10 atm) and high temperature (above 1100 0C) has been reported.

In the present study, both SCM and CFD based iron pellet reduction models were developed by considering all the complex chemical reaction kinetics of gas-solid and gas-gas reactions. It was demonstrated that no fitting parameters were needed for the present model to reproduce available experimental data on single pellet reduction under various CO-CO2-H2-H2O gas mixtures.

Subsequently, the integrated shaft furnace model (Finite Volume Method (FVM) based simulation) incorporating the iron pellet reduction models was introduced. In the shaft furnace model, all three zones of the furnace, namely the reduction, transition and cooling zone, were simultaneously and properly considered. The carburization reaction by methane cracking was also implemented. The present shaft furnace model was applied to both MIDREX and HYL processes. Plant data from both processes were successfully reproduced by using a single shaft furnace model without additional tuning parameters.

In the end of the thesis, various simulations were conducted using the present DR shaft furnace model in order to understand the chemical reactions and temperature evolution of iron pellets in the shaft furnace. Based on the results of the numerical simulations, optimal operating conditions for the DR shaft furnace were proposed.

목차 (Table of Contents)

• ABSTRACT I
• TABLE OF CONTENTS IV
• LIST OF TABLES X
• LIST OF FIGURES XII
• CHAPTER 1 INTRODUCTION 1
• 1.1 RESEARCH OBJECTIVE 1
• 1.2. THESIS ORGANIZATION 3
• 1.3. REFERENCES 6
• CHAPTER 2 REVIEW OF IRON ORE REDUCTION PROCESS 7
• ABSTRACT 7
• 2.1. THERMODYNAMICS OF IRON OXIDE REDUCTION 8
• 2.2. KINETICS OF IRON OXIDE REDUCTION 12
• 2.2.1 Reduction Degree 13
• 2.2.2 Metallization 13
• 2.3. GAS DIFFUSION 14
• 2.4 VISCOSITY 15
• 2.5. TORTUOSITY 16
• 2.6. WATER GAS SHIFT REACTION 17
• 2.7. METHANE REFORMING REACTION 18
• 2.8. METHANE CRACKING REACTION 19
• 2.9. BOUDARD REACTION 21
• 2.10. REFERENCES 26
• CHAPTER 3 REVIEW OF SINGLE PELLET MODELS 30
• ABSTRACT 30
• 3.1. INTRODUCTION 31
• 3.2. HOMOGENOUS MODEL 31
• 3.3. SHARP INTERFACE MODEL (SIM) OR SHRINKING CORE MODEL (SCM) 32
• 3.4. GRAIN MODEL 36
• 3.5. REFERENCES 40
• CHAPTER 4 REVIEW OF SHAFT FURNACE PROCESS FOR DRI PRODUCTION 45
• ABSTRACT 45
• 4.1. DIRECT REDUCTION SHAFT PROCESS 45
• 4.1.1. MIDREX Process 49
• 4.1.2. HYL Process 50
• 4.1.3. PERED Process 53
• 4.1.4. TYPICAL OPERATION 53
• 4.2. SHAFT FURNACE MODELS 54
• 4.2.1. Heat and Mass Transfer in shaft furnace 54
• 4.2.2. Models of Shaft furnaces 55
• 4.3. REFERENCES 59
• CHAPTER 5 REVIEW OF NUMERICAL METHODS 62
• ABSTRACT 62
• 5.1. VECTOR SPACES [1] 62
• 5.2. MATRICES [1] 63
• 5.2.1. Operations with Matrices [1] 64
• 5.2.2. Trace and Determinant of a Matrix [1] 66
• 5.2.3. Special Matrices [1] 67
• 5.2.4. Using Matrices to Describe Systems of Equations [2] 68
• 5.3 THE DISCRETIZATION PROCESS [2] 69
• 5.4 THE FINITE VOLUME METHOD [2] 71
• 5.5 THE FINITE VOLUME MESH [2] 72
• 5.5.1 Structured Grids [2] 73
• 5.5.2 Unstructured Grids [2] 73
• 5.6 SOLVING THE SYSTEM OF ALGEBRAIC EQUATIONS [2] 74
• 5.6.1 Direct or Gauss Elimination Method [2] 75
• 5.6.2 Iterative Methods [2] 77
• 5.7 UNDER-RELAXATION OF THE ALGEBRAIC EQUATIONS [2] 79
• 5.7.1 Explicit Under-Relaxation [2] 80
• 5.7.2 Implicit Under-Relaxation [2] 81
• 5.8 RESIDUALS AND SOLUTION CONVERGENCE [2] 82
• 5.8.1 Absolute Residual [2] 83
• 5.8.2 Maximum Residual [2] 83
• 5.8.3 Root-Mean Square Residual [2] 84
• 5.8.4 Scaled Residual [2] 84
• 5.9 REFERENCES: 86
• CHAPTER 6 ROOT FINDING ALGORITHMS 87
• ABSTRACT 87
• 6.1. INTRODUCTION 87
• 6.2. BRACKETING METHODS 88
• 6.2.1 Bisection Method 89
• 6.2.2 False Position (regula falsi) 90
• 6.3. ITERATIVE METHODS 91
• 6.3.1 Newton’s Method 92
• 6.3.2 Secant Method 93
• 6.3.3 Steffensen’s Method [5] 93
• 6.4. COMBINATION METHODS 94
• 6.4.1. Brent’s Method [6] 94
• 6.4.2. Ridder’s Method [7] 94
• 6.5 REFERENCES 95
• CHAPTER 7 SINGLE PELLET MODEL 96
• ABSTRACT 96
• 7.1. INTRODUCTION 96
• 7.2. MODEL #1: SHRINKING CORE MODEL (SCM) 97
• 7.2.1. Key assumptions of the SCM 97
• 7.2.2. Boundary conditions: flux balance equations at interface 99
• 7.2.3. Effective diffusivity of gas species in pellet 102
• 7.2.4. Reaction rates for reduction reactions 105
• 7.2.5. Carburization reaction 106
• 7.2.6. Validation of SCM 108
• 7.3. MODEL #2: NON-TOPOCHEMICAL MODEL (NTM) 111
• 7.3.1. Conservation of species 113
• 7.3.2 Effective diffusivity of gas species in pellet 114
• 7.3.3 Source term 116
• 7.3.4. Reaction rates 116
• 7.3.5 Boundary conditions 120
• 7.4. RESULTS AND DISCUSSION 120
• 7.4.1 Demonstration of viability as Dense or Porous model 120
• 7.4.2 Validation against Experimental data 122
• 7.4.3 Demonstration of Thermodynamic Consistency 124
• 7.4.4 Microstructurally aware model 127
• 7.5. COMPARISON OF SCM AND NTM 128
• 7.6 CONCLUSION 129
• 7.6. REFERENCES 133
• CHAPTER 8 INTEGRATED MODEL OF THE DIRECT REDUCTION (DR) SHAFT FURNACE 136
• ABSTRACT 136
• 8.1. INTRODUCTION 136
• 8.2. MATHEMATICAL MODEL 137
• 8.2.1 Overall Scheme of the model 137
• 8.2.2. Key Assumptions 140
• 8.2.3. Mass and Heat Balance Equations 141
• 8.3. RESULTS AND DISCUSSION 146
• 8.3.1. MIDREX shaft furnace simulation 146
• 8.3.2. HYL ENERGIRON process 156
• 8.4 GRID CONVERGENCE 159
• 8.4.1 Meshing 160
• 8.4.2 Grid Convergence Analysis 161
• 8.5. CONCLUSION 162
• 8.6. REFERENCES 168
• CHAPTER 9 CASE STUDIES FOR THE MIDREX AND HYL SHAFT FURNACE MODELS 170
• ABSTRACT 170
• 9.1. INTRODUCTION 170
• 9.2. GAS COMPOSITION 171
• 9.3. INPUT GAS TEMPERATURE 178
• 9.4. INPUT GAS FLOW-RATE 180
• 9.5. PELLET PRODUCTION RATE 182
• 9.6. REDUCTION ZONE HEIGHT 184
• 9.7. REDUCTION ZONE DIAMETER 184
• 9.8. CONCLUSION 186
• 9.9. REFERENCES 188
• CHAPTER 10 PLANT PROCESS SIMULATION: MIDREX PLANT INCLUDING SHAFT FURNACE AND REFORMERS 189
• ABSTRACT 189
• 10.1. INTRODUCTION 189
• 10.2. PYPROSIM SOFTWARE 191
• 10.2.1. Full Graphical Interface 193
• 10.2.2. Flowsheeting 193
• 10.2.3. Microsoft Excel for inputs and outputs 194
• 10.2.4. Reliable Thermodynamic databases 195
• 10.3. MIDREX PROCESS SIMULATION MODEL 195
• 10.4. RESULTS 198
• 10.5. CONCLUSION 200
• 10.5. REFERENCES 203
• CHAPTER 11 CONCLUSIONS AND FUTURE WORKS 206
• 11.1. SUMMARY 206
• 11.2. STATEMENT OF ORIGINALITY 208
• 11.3. SUGGESTIONS FOR FUTURE WORK 208
• ACKNOWLEDGEMENTS 210