Boiler Control Systems Engineering

Chapter 1 Boiler Fundamentals 1
Basic Boilers 1
Boiler Components 2
Furnace 2
Fans 2
Windbox 2
Flue Gas Heat Exchangers 2
Combustion Air Preheater 5
Economizer 5
Superheater 6
Boiler Drums 6
Piping and Instrument Diagrams (P&IDs) 7
Design Basis Check List 8

Chapter 2 Control of Boilers 11
Control Strategies 11
Bumpless Transfer 11
Simple Feedback Control 11
Feedforward plus Feedback Control 12
Cascade Control 13
Ratio Control 14
Feedforward Control 14
Controller Tuning 15
Determining Gain, Reset, and Derivative 17
Gain vs Proportional Band (PB) 19
Controller Actions 19
Controller Actions Setup 22
The Effects on Tuning 22
Calibration Effect on Gain 22
Transmitters 22
Redundancy 23
Interlock Circuitry 23
Final Control Elements 24

Chapter 3 Furnace Draft 25
Pressure Fired Boilers 25
Balanced Draft Boiler Fans 26
Furnace Pressure Control 26
Summer 30

Chapter 4 Feedwater 35
Once-Through Boilers 35
Drum Level Feedwater Control 36
Transmitters 41
Shrink and Swell 42
Single Element Level Control 44
Two Element Level Control 44
Three Element Level Control 48
Control System Configuration 48
Summer 48

Chapter 5 Coal Fired Boilers 51
Pulverized Coal Fired Boilers 51
Raw Coal and Feeder 54
Stoker Boilers 56
Cyclone Boiler 56
Graphics: Pulverizer Coal Boiler 59

Chapter 6 Fuel and Air Control 67
Fuel and Air Control Gas Oil 72
Fuel and Air Control Characterization 74
Excess Air to Oxygen 76
Multiple Fuel Control 77
Oxygen (O2) Trim Control 78
Multiple Boilers 80

Chapter 7 Steam Temperature 81
Three Element Level Control 83

Chapter 8 Burner Management Systems 91
Burner Management System (BMS) Control 91
NFPA 85 Code 2007 91
Boiler Control and Operating Documentation 92
Combustion Control 92
Purge Control 93
Requirement for Independence of Control (Hardware/Software) 94
Flame Detection 95
Flame Monitoring and Tripping System (Multiple Burner Boilers) 96
Flame Tripping Validation 97
Examples of Permissive Starting Logic and Protective Tripping Logic 109

Chapter 9 Environment 111
NOx and NOx Control 111
Excess Air to Oxygen 113
Boiler Efficiency Computations 115
Input/Output Example 115

Chapter 10 Control Valve Sizing 117
Valve Characteristics 117
Valve Characteristic Graph 118
Recommended Velocities 118
Valve Sizing for Different Control Media 119
Control Valve Sizing Calculations 119
Gas Valve Sizing 120

Chapter 11 Steam Temperature Control 123
Purpose 123
Introduction 123
Principles and Methods of Transient Superheat Steam 124
Temperature Control
NOx Control 126
Redundancy 126
Reset Windup Prevention 126
Advanced Steam Temperature Control 127
Acronyms 129

Appendix A 131
Appendix B 141
Appendix C 179
Appendix D 181

Bibliography 187
References 189
Kraft Pulp Mill 195
Index 197