Industrial and process furnaces : Principles, design and operation

Industrial and Process Furnaces

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Industrial and Process

Furnaces

Principles, Design and Operation

Peter Mullinger

Associate Professor, School of Chemical Engineering

University of Adelaide, South Australia

Barrie Jenkins

Consulting Engineer, High Wycombe, Bucks, UK

AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD

PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO

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Butterworth-Heinemann is an imprint of Elsevier

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First edition 2008

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08 09 10 11 12 10 9 8 7 6 5 4 3 2 1

To the late Frank David Moles, who showed us a better way of

thinking about furnaces, especially those where the product is

directly heated by the flame.

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Contents

Foreword xvii

Preface xix

Acknowledgements xxi

List of Figures xxiii

List of Tables xxxi

Chapter 1 Introduction 1

1.1 What is a furnace? 3

1.1.1 Furnace outline 4

1.1.2 Furnace classification 5

1.1.3 Principle objectives of furnace designers and operators 5

1.2 Where are furnaces used? Brief review of current furnace applications

and technology 7

1.2.1 Ceramics, brick making and pottery 7

1.2.2 Cement and lime 8

1.2.3 Glass making 11

1.2.4 Metal ore smelting 13

1.2.5 Metal refining 16

1.2.6 Flash and fluid bed furnaces 18

1.2.7 Metal physical processing 20

1.2.8 Incinerators and resource recovery furnaces 24

1.2.9 Furnaces with reducing atmospheres 24

1.2.10 Oil refining and petrochemical furnaces 25

1.3 Drivers for improved efficiency 28

1.4 Concluding remarks 29

References 29

Chapter 2 The combustion process 31

2.1 Simple combustion chemistry 32

2.1.1 The complete oxidation of carbon 32

2.1.2 The complete oxidation of hydrogen 32

2.1.3 The incomplete oxidation of carbon 33

2.1.4 The oxidation of carbon monoxide 33

2.2 Combustion calculations 33

2.3 Chemical reaction kinetics 36

2.3.1 Types of reactions 37

2.3.2 Reaction rate theory 38

viii Contents

2.3.3 Reaction rate behaviour 40

2.3.4 Burning droplets and particles 43

2.4 The physics of combustion 47

2.4.1 The role of primary air 50

2.4.2 The role of swirl flows 56

2.4.3 Turbulence in jets 57

2.4.4 Secondary flow aerodynamics 59

2.4.5 Effect of excess air on fuel consumption 61

2.4.6 Multiple burner installations 62

Nomenclature 63

References 64

Chapter 3 Fuels for furnaces 67

3.1 Gaseous fuels 69

3.1.1 Properties of natural gas 69

3.1.2 Manufactured gas 69

3.1.3 Wobbe number or index 71

3.1.4 Flammability limits 72

Calculation of the flammable limits for mixtures

of gases 72

Influence of temperature and pressure on the limits 73

3.1.5 Flame radiation from gaseous fuels 75

3.2 Liquid fuels 75

3.3 Solid fuels 77

3.3.1 Ash 79

3.4 Waste fuels 79

3.5 Choice of fuel 80

3.5.1 Furnace performance 81

Heat transfer 81

Furnace atmosphere 83

Flexibility of operation 83

Effect of ash 84

Refractory life 84

Fuel cost and security of supply 85

Fuel handling system capital and running costs 85

3.6 Safety 86

3.7 Emissions 86

Nomenclature 86

References 87

Solid fuel bibliography 88

Chapter 4 An introduction to heat transfer in furnaces 89

4.1 Conduction 90

4.1.1 Steady state conduction 91

4.1.2 Transient conduction 93

Analytical approach 93

Numerical approach 96

4.2 Convection 100

4.2.1 Dimensional analysis 101

4.2.2 Application to convective heat transfer 102

4.2.3 Evaluating convective heat transfer coefficients 104

4.2.4 High temperature convective heat transfer 108

4.3 Radiation 113

4.3.1 Physical basics of radiative exchange 114

4.3.2 Emissivity and absorptivity 117

4.3.3 View factors 121

Equivalent grey surface 126

4.3.4 Mean beam length 127

4.4 Electrical heating 128

4.4.1 Resistance heating 128

Direct resistance heating 129

Indirect resistance heating 129

4.4.2 Arc heating 129

Electrode devices 130

Electrodeless devices 131

4.4.3 Induction heating 132

4.4.4 Dielectric heating 133

4.4.5 Infrared heating 133

Nomenclature 134

References 136

Appendix 4A Tables of emissivity data 137

Chapter 5 Flames and burners for furnaces 141

5.1 Types of flame 142

5.1.1 Premixed flames 143

5.1.2 Turbulent jet diffusion flames 145

5.1.3 Heterogeneous combustion 145

Atomisation of liquid fuels and pulverisation of coal 146

The importance of drop and particle size 148

5.2 Function of a burner and basics of burner design 152

5.2.1 The essential importance of heat flux profiles 154

5.2.2 Flame stabilisation 155

5.3 Gas burners 158

5.3.1 Premixed burners 158

Effect of excess air (mixture ratio) on flame temperature 160

Radiant wall burners 161

Use of premix burners in low NOx applications 162

Safety issues with premix burners 162

Size limitations 165

Contents ix

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5.3.2 Turbulent jet diffusion burners 165

5.3.3 Precessing jet diffusion burners 167

5.4 Oil burners 168

5.4.1 Turndown 171

5.4.2 Atomisers 172

Pressure jet atomisers 173

Twin fluid atomisers 176

5.5 Pulverised coal burners 179

5.6 Furnace aerodynamics 182

Burner and furnace air flow patterns 184

5.6.1 Single burner systems 184

Package burner installations 185

Rotary kilns and driers, etc. 185

5.6.2 Multiple burner systems 186

5.6.3 Combustion air duct design 188

5.6.4 Common windbox and plenum design 192

5.7 Combustion system scaling 193

5.7.1 Example of combustion system scaling 194

5.8 Furnace noise 196

5.8.1 Combustion roar 198

5.8.2 Nozzle and turbulent jet noise 198

5.8.3 Fan noise 199

5.8.4 Pipe and valve noise 199

5.8.5 Furnace noise attenuation 200

5.8.6 Combustion driven oscillations 201

Nomenclature 204

References 205

Chapter 6 Combustion and heat transfer modelling 209

6.1 Physical modelling 211

6.1.1 Thring-Newby parameter 214

6.1.2 Craya-Curtet parameter 214

6.1.3 Becker throttle factor 215

6.1.4 Curtet number 215

6.1.5 Relationship between scaling parameters 216

6.1.6 Determining the required model flows 216

6.1.7 Applying the scaling parameter 216

6.1.8 Applying a post-measurement correction 217

6.2 Mathematical modelling 217

6.2.1 Simple well-stirred furnace models 219

6.2.2 Long furnace models 227

6.2.3 Two- and three-dimensional zone models 229

6.2.4 Computational fluid dynamics models 233

Gridding of CFD models 235

Convergence of CFD models 237

6.2.5 Particle drag in combustion systems 237

6.3 Application of modelling to furnace design 238

Nomenclature 239

References 241

Chapter 7 Fuel handling systems 243

7.1 Gas valve trains 244

7.1.1 Safety shutoff systems 245

Double block and bleed 246

Leak testing and proving 246

7.2 Fuel oil handling systems 246

7.2.1 Storage, pumping and heating 247

7.2.2 Oil valve trains 249

7.3 Pulverised coal handling and firing systems 251

7.3.1 Raw coal bunkers and feeders 252

7.3.2 Coal grinding and drying 253

Coal drying characteristics 253

7.3.3 Coal mills 254

Ball mills 255

Vertical spindle mills 257

High speed mills 258

7.3.4 Coal mill grinding capacity 260

Coal fineness 261

Coal dryness 262

7.3.5 Pulverised coal grinding and firing systems 262

Direct and indirect firing systems 262

Direct firing 263

Semi-direct firing 263

Indirect firing 263

Semi-indirect firing 263

7.3.6 Coal system drying capacity 266

7.3.7 Coal firing system fans 270

7.3.8 Fine coal storage 271

7.3.9 Fine coal feeding and conveying 274

Volumetric feeders 275

Mass flow feeders 276

7.3.10 Pulverised coal conveying 278

7.4 Waste fuel handling 280

7.4.1 Waste gas fuel handling 281

7.4.2 Waste liquid fuel handling 282

7.4.3 Solids waste fuel handling 282

Size distribution 282

7.4.4 Environmental benefits and health hazards of

waste fuel utilisation 283

Nomenclature 284

References 284

Applicable codes and standards 285

Contents xi

xii Contents

Chapter 8 Furnace control and safety 287

8.1 Process control 288

8.1.1 Basic furnace control strategies 289

Control of product temperature 289

Fuzzy logic and rule-based systems 290

8.2 Furnace instrumentation 290

8.2.1 Temperature measurement 290

8.2.2 Heat input measurement 295

Flow measurement of liquid and gaseous fuels 295

Calorific value measurement 296

Solid fuels 296

8.2.3 Determination of excess air 297

8.3 Flue gas analysis 300

8.3.1 Extractive gas sampling systems and analysers 302

Sample probe installation 302

Cold gas extractive systems 305

Hot wet gas extractive systems 305

Dilution extractive systems 306

8.3.2 In-situ systems 306

Dust monitors 307

Oxygen analysers 308

Cross-duct analysers 309

8.4 Combustion control 312

8.5 Ensuring furnace safety 313

8.5.1 Risk factors in furnace operation 313

8.5.2 Furnace start-up 314

Critical time for ignition during furnace start-up 316

8.5.3 Operation with insufficient combustion air 317

Corrective action for unintentional sub-stoichiometric operation 318

8.5.4 Flame quenching 318

8.5.5 Eliminating ignition sources 319

8.6 Burner management systems 319

8.6.1 Safety requirements for burner management systems 320

8.6.2 False trips 322

8.6.3 Achieving acceptable safety standards with programmable

logic controller burner management systems 323

8.6.4 Choosing an appropriate safety integrity level 324

8.6.5 Determining the safety integrity level of the BMS system 326

8.6.6 Flame detectors 329

Nomenclature 332

References 332

Certification and testing organisations 333

Chapter 9 Furnace efficiency 335

9.1 Furnace performance charts 338

9.2 Mass and energy balances 341

9.2.1 On-site measurement 342

Flue gas sampling and analysis 344

Calibration and errors in plant instrumentation 345

9.2.2 Constructing mass and energy balances 346

9.3 Energy conversion 358

9.3.1 Low and high grade heat 360

9.3.2 Exergy and pinch point analysis 362

9.4 Heat recovery equipment 363

9.4.1 Recuperative heat exchangers 364

9.4.2 Regenerative heat exchangers 366

9.4.3 General heat exchanger design procedure 368

9.5 Identifying efficiency improvements 369

Nomenclature 372

References 372

Chapter 10 Emissions and environmental impact 375

10.1 Formation of carbon monoxide 377

10.2 Formation of nitrogen oxides 378

10.2.1 Thermal NOx formation 379

10.2.2 Fuel NOx formation 381

10.2.3 Prompt NOx formation 382

10.2.4 NOx modelling 384

10.3 Formation of sulphur oxides 385

10.4 Formation of intermediate combustion products 386

10.4.1 Volatile organic compounds (VOCs) 386

10.4.2 Polycyclic aromatic hydrocarbons (PAH) 386

10.4.3 PCBs, dioxins and furans 387

10.5 Particulate emissions 390

10.5.1 Formation of soot 390

10.5.2 Formation and composition of fuel ash 393

10.5.3 Non-combustible volatile cycles 394

10.6 Environmental control of emissions 396

10.6.1 Prevention and abatement of emissions 397

Pre-flame control 397

In-flame control 399

End-of-pipe control 405

10.6.2 Dispersion modelling 408

References409

Chapter 11 Furnace construction and materials 413

11.1 Basic performance requirements of the furnace structure 414

11.2 Basic construction methods 415

11.2.1 Brick lining 417

11.2.2 Monolithic linings 419

Castable refractory 419

Contents xiii

xiv Contents

Traditional installation of castable refractory 420

Installation of castable refractory by gunning 421

Drying and curing of cast and gunned refractory 423

Mouldable and rammable refractories 424

11.2.3 Furnace steelwork 425

11.2.4 Furnace roof construction 426

11.2.5 Furnace cooling systems 428

11.3 Practical engineering considerations in the use of refractories 431

11.4 Ceramic refractory materials 433

11.4.1 Testing of refractories 434

11.4.2 Properties and uses of refractories 435

Silica and siliceous refractories 435

Alumina and aluminous refractories 435

Chromite/magnesite/alumina refractories 436

Dolomite refractories 437

Zircon and zirconia refractories 437

Carbon refractories 438

Insulating refractories 438

11.5 Heat resisting and refractory metals 438

11.5.1 Effect of elevated temperature on metal properties 439

11.5.2 High temperature alloys 441

Service temperature 442

Intergranular corrosion 442

Proprietary high nickel alloys 443

11.6 Practical engineering considerations in the use of high

temperature metals 443

11.7 Concluding remarks 444

References 445

Selection of relevant standards 445

Advisory organisations 446

Appendix 11A General properties of selected refractory materials 447

Chapter 12 Furnace design methods 455

12.1 Introduction 456

12.1.1 Design constraints 458

12.1.2 Cost of design changes 459

12.2 Conceptual design 459

12.2.1 Process functions 460

Straight-through furnace system 464

Separation furnace system 464

Combining furnace with downstream separation 464

Combining and separation furnace system 464

12.2.2 Defining the physical and chemical changes 464

12.2.3 Preliminary mass and energy balances 466