Process Steam Systems: A Practical Guide for Operators, Maintainers, Designers, and Educators

Carey Merritt has over 30 years’ experience designing, operating, and maintaining process steam systems. He has designed over 200 process steam systems in a wide variety of industries and countries, including ­Australia, Canada, and China.

Preface xi  

Acknowledgments xiii

 List of Examples xv

List of Tables xvii

1 Steam: a Heat Transfer Fluid 1

Why Steam? 1

Steam Is Safe and Flexible 2

Steam Is Easy to Control 2

The Concept of Steam Formation: Boiling 3

Pressure and Boiling 4

The Ideal Gas Law 6

2 The Development of Boiler Safety 9

How It All Began 9

The Consequences of Development 10

Development of Asme Code 12

Future of Steam 13

3 Understanding Heat Transfer 15

Radiation-Type Heat Transfer 15

Conduction-Type Heat Transfer 18

Convection-Type Heat Transfer 21

The Heat Transfer Equations 23

The Overall Heat Transfer Coefficient (U) 23

mean Temperature Difference (ΔT M) 25

ΔT m for a Steam Boiler 26

ΔT m for a Steam to Process Fluid Heat Exchanger 27

Surface Area (m) 27

Heat Flux 30

4 Steam Formation, Accumulation, and Condensation 31

The Boiling Process 31

Steaming 32

Latent and Sensible Heat Versus Pressure 34

Condensation of Steam 34

The Formation of Flash Steam 36

Steam Accumulation and Storage 38

5 Steam Quality: It Matters 41

Why Steam Quality Is Important 42

Poor Steam Quality Causes and Cures 42

Steam Classifications 45

Measuring Steam Quality 47

Superheated Steam 48

6 The Steam System Design 53

Steam System Types 53

The Process Steam System: An Overview 55

7 The Steam Generator 59

The Ideal Steam Generator 60

Steam Generator Types 62

Fossil Fuel-Fired Boilers 62

Solid Fuel-Fired Boilers 68

Electric Boilers 70

Unfired Steam Generators 73

Heat Recovery Steam Generators 74

8 Boiler Operation and Trim 75

The Packaged Boiler Concept 76

Fuel Delivery and Combustion Systems 83

Low Emissions 91

Multiple Boiler Sequencing 94

9 The Steam Delivery System 97

Steam Flow 97

Steam Distribution Piping 98

Control Valves 111

Steam Accumulation 116

Steam Filtration 120

Sensors and Meters 122

Steam Metering 123

Stop and Safety Valves 123

10 The Condensate Recovery System 129

Condensate Line Sizing 131

Steam Trap Applications 134

Thermostatic Group 134

Mechanical Group 134

Thermodynamic Group 134

Thermostatic Steam Trap Group 134

Mechanical Group 136

Thermodynamic Group 139

Flash Steam Utilization 142

How to Size Flash Tanks and Vent Lines 143

Condensate Collection 146

Electric Condensate Return System 146

Pressure Motive Condensate Pump 148

Pressure Motive Pump Installation Requirements 148

Pumped Condensate Return Line Installation 151

Surge Tank Application 152

11 The Feed Water System 153

Feed Water Deaeration 153

The Elimination of Dissolved Gases 154

Feed Water Tanks 156

Feed Water Tank Sizing 158

Feed Water Pumps 160

Feed Water Pump Sizing 164

Feed Water Piping 166

Feed Water-Surge Tank Controls 168

12 Steam System Chemistry Control 169

Basic Water Chemistry 169

Scale Control 171

Fouling Control 174

Corrosion Control 175

Boiler Blowdown 178

Best Operating Practices for Boiler Blowdown 179

Automatic Versus Manual Blowdown Controls 179

Determining Blowdown Rate 180

Chemical Feed Systems 181

Chemistry Limits 183

Steam System Metallurgy 183

13 Mechanical Room Considerations 187

Codes and Standards 187

Steam Load Profile 190

Steam System Performance Considerations 192

Environmental Considerations 194

Boiler Room Utilities 200

14 Steam System Applications 207

Low-Pressure Steam with High Condensate Returns 209

High-Pressure Steam with High Condensate Returns 210

High- or Low-Pressure Steam with Little or No Returns 212

High-Pressure or Superheated Steam with Condensate Returns 214

Multiple Boiler Installations 215

Steam for Hot Water Generation 217

Other Miscellaneous Steam-Use Application Designs 219

15 Specialized Steam Equipment 223

Back Pressure Turbine 223

Steam Hydro Heater 225

Steam Superheaters 226

Steam Dump Mufflers 229

Jacketed Kettles 230

Sterilizers 230

Reboilers 231

16 Steam System Efficiency/Sustainability 233

The System Heat Balance 233

Boiler Heat Balance 234

Boiler Efficiency 234

Steam System Efficiency 239

Boiler Internal Cleanliness 244

Steam Delivery System Efficiency 245

Condensate and Feed Water System Efficiency 246

Biomass Fuel Water Content Reduction 248

17 Shutdown, Startup, Inspection, and Maintenance 249

Shutdown and Startup Practices 249

Boiler Safety Checks 251

Maintenance and Inspection Practices 253

Inspections 255

Boil Out and Layup Practices 257

18 Troubleshooting and Commissioning Basics 261

Startup Versus Commissioning 261

Approach to Troubleshooting 262

Don’t Play the Blame Game 262

Precommissioning 263

19 Commissioning and Troubleshooting the Steam Generator 265

Determining Boiler Input, Output, and Efficiency 265

Boiler Performance Test 267

Commissioning the Boiler Burner Controls 269

Commissioning the Boiler Pressure Control System 269

Commissioning the Boiler Level Control System 270

Commissioning the Boiler Blowdown Controls 270

Steam Boiler Troubleshooting 270

20 Commissioning and Troubleshooting the Steam Delivery System 279

Steam Distribution Piping 279

Control Valves 280

Steam Piping Venting 281

Condensate Trapping/Draining 281

Troubleshooting the Steam Delivery System 281

21 Commissioning and Troubleshooting the Condensate and Feed Water System 283

Condensate Collection 283

Feed Water System 285

Troubleshooting the Condensate and Feed Water Systems 285

22 Commissioning and Troubleshooting the Water Treatment Equipment 289

Setting Up the Water Treatment Systems 289

Troubleshooting Water Treatment System Problems 290

23 Sample Problem Sets 293

Appendix A References and Reference Information 297

Appendix B Operations, Maintenance, and Inspection Guidance 313

Appendix C Steam System Design and Commissioning Guidance 323

Appendix D Problem Set Answers 331

Index341