Industrial furnaces / W. Trinks ... [et al.].

CONTENIDO
Excerpts from the Preface to the 5th Edition xv
Preface xvii
Brief Biographies of the Authors xix
No-Liability Statement xxi
1 INDUSTRIAL HEATING PROCESSES 1
1.1 Industrial Process Heating Furnaces 1
1.2 Classifications of Furnaces 7
1.2.1 Furnace Classification by Heat Source 7
1.2.2 Furnace Classification by Batch or Continuous, and by Method of Handling Material into, Through, and out of the Furnace 7
1.2.3 Furnace Classification by Fuel 16
1.2.4 Furnace Classification by Recirculation 18
1.2.5 Furnace Classification by Direct-Fired or Indirect-Fired 18
1.2.6 Classification by Furnace Use 20
1.2.7 Classification by Type of Heat Recovery 20
1.2.8 Other Furnace Type Classifications 21
1.3 Elements of Furnace Construction 22
1.4 Review Questions and Projects 23
2 HEAT TRANSFER IN INDUSTRIAL FURNACES 25
2.1 Heat Required for Load and Furnace 25
2.1.1 Heat Required for Heating and Melting Metals 25
2.1.2 Heat Required for Fusion (Vitrification) and Chemical Reaction 26
2.2 Flow of Heat Within the Charged Load 28
2.2.1 Thermal Conductivity and Difussion 28
2.2.2 Lag Time 30
2.3 Heat Transfer to the Charged Load Surface 31
2.3.1 Conduction Heat Transfer 33
2.3.2 Convection Heat Transfer 35
2.3.3 Radiation Between Solids 37
2.3.4 Radiation from Clear Flames and Gases 42
2.3.5 Radiation from Luminous Flames 46
2.4 Determining Furnace Gas Exit Temperature 53
2.4.1 Enhanced Heating 55
2.4.2 Pier Design 56
2.5 Thermal Interaction in Furnaces 57
2.5.1 Interacting Heat Transfer Modes 57
2.5.2 Evaluating Hydrogen Atmospheres for Better Heat Transfer 60
2.6 Temperature Uniformity 63
2.6.1 Effective Area for Heat Transfer 63
2.6.2 Gas Radiation Intensity 64
2.6.3 Solid Radiation Intensity 64
2.6.4 Movement of Gaseous Products of Combustion 64
2.6.5 Temperature Difference 65
2.7 Turndown 67
2.8 Review Questions and Project 67
3 HEATING CAPACITY OF BATCH FURNACES 71
3.1 Definition of Heating Capacity 71
3.2 Effect of Rate of Heat Liberation 71
3.3 Effect of Rate of Heat Absorption by the Load 77
3.3.1 Major Factors Affecting Furnace Capacity 77
3.4 Effect of Load Arrangement 79
3.4.1 Avoid Deep Layers 83
3.5 Effect of Load Thickness 84
3.6 Vertical Heating 85
3.7 Batch Indirect-Fired Furnaces 86
3.8 Batch Furnace Heating Capacity Practice 91
8.1 Batch Ovens and Low-Temperature Batch Furnaces 92
8.2 Drying and Preheating Molten Metal Containers 96
3.8.3 Low Temperature Melting Processes 98
3.8.4 Stack Annealing Furnaces 99
3.8.5 Midrange Heat Treat Furnaces 101
3.8.6 Copper and Its Alloys 102
3.8.7 High-Temperature Batch Furnaces, 1990 F to 2500 F 103
3.8.8 Batch Furnaces with Liquid Baths 108
3.9 Controlled Cooling in or After Batch Furnaces 113
3.10 Review Questions and Project 114
11 HEATING CAPACITY OF CONTINUOUS FURNACES 117
4.1 Continuous Furnaces Compared to Batch Furnaces 117
4.1.1 Prescriptions for Operating Flexibility 118
4.2 Continuous Dryers, Ovens, and Furnaces for 1400 F (760 C) 121
4.2.1 Explosion Hazards 121
4.2.2 Mass Transfer 122
4.2.3 Rotary Drum Dryers, Incinerators 122
4.2.4 Tower Dryers and Spray Dryers 124
4.2.5 Tunnel Ovens 124
4.2.6 Air Heaters 127
4.3 Continuous Midrange Furnaces, 1200 to 1800 F (650 to 980 C) 127
4.3.1 Conveyorized Tunnel Furnaces or Kilns 127
4.3.2 Roller-Hearth Ovens, Furnaces, and Kilns 129
4.3.3 Shuttle Car-Hearth Furnaces and Kilns 129
4.3.4 Sawtooth Walking Beams 130
4.3.5 Catenary Furnace Size 135
4.4 Sintering and Pelletizing Furnaces 137
4.4.1 Pelletizing 138
4.5 Axial Continuous Furnaces for Above 2000 F (1260 C) 139
4.5.1 Barrel Furnaces 139
4.5.2 Shaft Furnaces 142
4.5.3 Lim Kilns 142
4.5.4 Fluidized Beds 143
4.5.5 High-Temperature Rotary Drum Lime and Cement Klins 144
4.6 Continuous Furnaces for 1900 to 2500 F (1038 to 1370 C) 144
4.6.1 Factors Limiting Heating Capacity 144
4.6.2 Front-End-Fired ContinuOus Furnaces 152
4.6.3 Front-End-Firing, Top and Bottom 153
4.6.4 Side-Firing Reheat Furnaces 153
4.6.5 Pusher Hearths Are Limited by Buckling/Piling 155
4.6.6 Walking Conveying Furnaces 158
4.6.7 Continuous Furnace Heating Capacity Practice 160
4.6.8 Eight Ways to Raise Capacity in High-Temperature Continuous Furnaces 162
4.6.9 Slot Heat Losses from Rotary and Walking Hearth Furnaces 165
4.6.10 Soak Zone and Discharge (Dropout) Losses 166
4.7 Continuous Liquid Heating Furnaces 168
4.7.1 Continuous Liquid Bath Furnaces 168
4.7.2 Continuous Liquid Flow Furnaces 170
4.8 Review Questions and Projects 172
5 SAVING ENERGY IN INDUSTRIAL FURNACE SYSTEMS 175
5.1 Furnace Efficiency, Methods for Saving Heat 175
5.1.1 Flue Gas Exit Temperature 177
5.2 Heat Distribution in a Furnace 182
5.2.1 Concurrent Heat Release and Heat Transfer 182
5.2.2 Poc Gas Temperature History Through a Furnace 184
5.3 Furnace, Kiln, and Oven Heat Losses 185
5.3.1 Losses with Exiting Furnace Gases 185
5.3.2 Partial-Load Heating 187
5.3.3 Losses from Water Cooling 187
5.3.4 Losses to Containers, Conveyors, Trays, Rollers, Kiln Furniture, Piers, Supports, Spacers, Boxes, Packing for Atmosphere Protection, and Charging Equipment, Including Hand Tongs and Charging Machine Tongs 188
5.3.5 Losses Through Open Doors, Cracks, Slots, and Dropouts, plus Gap Losses from Walking Hearth, Walking Beam, Rotary, and Car-Hearth Furnaces 188
5.3.6 Wall Losses During Steady Operation 192
5.3.7 Wall Losses During Intermittent Operation 193
5.4 Heat Saving in Direct-Fired Low-Temperature Ovens 194
5.5 Saving Fuel in Batch Furnaces 195
5.6 Saving Fuel in Continuous Furnaces 196
5.6.1 Factors Affecting Flue Gas Exit Temperature 196
5.7 Effect of Load Thickness on Fuel Economy 197
5.8 Saving Fuel in Reheat Furnaces 198
5.8.1 Side-Fired Reheat Furnaces 198
5.8.2 Rotary Hearth Reheat Furnaces 198
5.9 Fuel Consumption Calculation 201
5.10 Fuel consumption Data for Various Furnace Types 202
5.11 Energy Conservation by Heat Recovery from Flue Gases 204
5.11.1 Preheating Cold Loads 204
5.11.2 Steam Generation in Waste Heat Boilers 209
5.11.3 Saving Fuel by Preheating Combustion Air 212
5.11.4 Oxy-Fuel Firing Saves Fuel, Improves Heat Transfer, and Lowers NOx 231
5.12 Energy Costs of Pollution Control 233
5.13 Review Questions, Problems, Project 238
6 OPERATION ANO CONTROL OF INDUSTRIAL FURNACES 243
6.1 Burner and Flame Types, Location 243
6.1.1 Side-Fired Box and Car-Bottom Furnaces 243
6.1.2 Side Firing In-and-Out Furnaces 244
6.1.3 Side Firing Reheat Furnaces 245
6.1.4 A Longitudinal Firing of Steel Reheat Furnaces 245
6.1.5 Roof Firing 245
6.2 Flame Fitting 246
6.2.1 Luminous Flames Versus Nonluminous Flames 246
6.2.2 Flame Types 247
6.2.3 Flame Profiles 247
6.3 Unwanted NOx Formation 247
6.4 Controls and Sensors: Care, Location, Zones 251
6.4.1 Rotary Hearth Furnaces 253
6.4.2 Zone Temperature in Car Furnaces 261
6.4.3 Melting Furnace Control 264
6.5 Air/Fuel Ratio Control 264
6.5.1 Air/Fuel Ratio Control Must Be Understood 264
6.5.2 Air/Fuel Ratio Is Crucial to Safety 265
6.5.3 Air/Fuel Ratio Affects Product Quality 270
6.5.4 Minimizing Scale 271
6.6 Furnace Pressure Control 272
6.6.1 Visualizing Furnace Pressure 272
6.6.2 Control and Compensating Pressure Tap Locations 273
6.6.3 Dampers for Furnace Pressure Control 276
6.7 Turndown Ratio 278
6.7.1 Turndown Devices 279
6.7.2 Turndown Ranges 280
6.8 Furnace Control Data Needs 281
6.9 Soaking Pit Heating Control 283
6.9.1 Heat-Soaking Ingots-Evolution of One- Way-Fired Pits 283
6.9.2 Problems with One-Way, Top-Fired Soak Pits 286
6.9.3 Heat-Soaking Slabs 288
6.10 Uniformity Control in Forge Furnaces 290
6.10.1 Temperature Control Above the Load(s) 290
6.10.2 Temperature Control Below the Load(s) 291
6.11 Continuous Reheat Furnace Control 293
6.11.1 Use More Zones, Shorter Zones 293
6.11.2 Suggested Control Arrangements 295
6.11.3 Effects of (and Strategies for Handling) Delays 301
6.12 Review Questions 306
7 GAS MOVEMENT IN INDUSTRIAL FURNACES 309
7.1 Laws of Gas Movement 309
7.1.1 Buoyancy 309
7.1.2 Fluid Friction, Velocity Head, Flow Induction 311
7.2 Furnace Pressure; Flue Port Size and Location 313
7.3 Flue and Stack Sizing, Location 319
7.3.1 The Long and Short of Stacks 319
7.3.2 Multiple Flues 320
7.4 Gas Circulatíon in Furnaces 322
7.4.1 Mechanical Circulation 322
7.4.2 Controled Burner Jet Direction, Timing, and Reach 323
7.4.3 Baffles and Bridgewalls 324
7.4.4 Impingement Heating 324
7.4.5 Load Positioning Relative to Burners, Walls, Hearth, Roofs, and Flues 326
7.4.6 Oxy-Fuel Firing Reduces Circulation 333
7.5 Circulation Can Cure Cold Bottoms 334
7.5.1 Enhanced Heating 334
7.6 Review Questions 337
8. CALCULATIONS/MAINTENANCE/QUALITY/SPECIFYING A FURNACE 341
8.1 Calculating Load Heating Curves 341
8.1.1 Sample Problem: Shannon Method for Temperature- Versus- Time Curves 343
8.1.2 Plotting the Furnace Temperature Profile, Zone by Zone on Figs. 8.6, 8.7, and 8.8 348
8.1.3 Plotting the Load Temperature Profile 357
8.1.4 Heat Balance-to Find Needed Fuel Inputs 366
8.2 Maintenance 378
8.2.1 Furnace Maintenance 378
8.2.2 Air Supply Equipment Maintenance 380
8.2.3 Recuperators and Dilution Air Supply Maintenance 380
8.2.4 Exhortations 381
8.3 Product Quality Problems 381
8.3.1 Oxidation, Scale, Slag, Dross 381
8.3.2 Decarburization 388
8.3.3 Burned Steel 389
8.3.4 Melting Metals 389
8.4 Specifying a Furnace 390
8.4.1 Furnace Fuel Requirement 390
8.4.2 Applying Burners 391
8.4.3 Furnace Specification Procedures 392
8.5 Review Questions and Project 396
9 MATERIALS IN INDUSTRIAL FURNACE CONSTRUCTION 397
9.1 Basic Elements of a Furnace 397
9.1.1 Information a Furnace Designer Needs to Know 397
9.2 Refractory Components for Walls, Roof, Hearth 398
9.2.1 Thermal and Physical Properties 398
9.2.2 Monolithic Refractories 400
9.2.3 Furnace Construction with Monolithic Refractories 403
9.2.4 Fiber Refractories 403
9.3 Ways in Which Refractories Fail 404
9.4 Insulations 405
9.5 Installation, Drying, Warm-Up, Repairs 406
9.6 Coatings, Mortars, Cements 407
9.7 Hearths, Skid Pipes, Hangers, Anchors 407
9.7.1 Hearths 408
9.7.2 Skid Pipe Protection 408
9.7.3 Hangers and Anchors 411
9.8 Water-Cooled Support Systems 414
9.9 Metals for Furnace Components 416
9.9.1 Cast Irons 417
9.9.2 Carbon Steels 418
9.9.3 Alloy Steels 420
9.10 Review Questions, Problem, Project 421
GLOSSARY 425
REFERENCES AND SUGGESTED READING 457
INDEX 461