1、THE CONTROL OF BOILERS 2nd Edition SAM G. DUKELOW ISA-1be Inslnlmentatlon, Systems, and AuIomaDon Society The information presented in this pUblication is for the general education of the reader. Because neither the author nor the publisher has any control over the use of the information by the read
2、er, both the author and the publisher disclaim any and all liability of any kind arising out of such use. The reader is expected to exercise sound professional judgment in using any of the information presented in a particular application. Additionally, neither the author nor the publisher have inve
3、stigated or considered the effect of any patents on the ability of the reader to use any of the information in a particular application. The reader is responsible for reviewing any possible patents that may affect any particular use of the information presented. Any references to commercial products
4、 in the work are cited as examples only. Neither the author nor the publisher endorses any referenced commercial product. Any trademarks or trade names referenced belong to the respective owner of the mark or name. Neither the author nor the publisher makes any representation regarding the availabil
5、ity of any referenced commercial product at any time. The manufacturers instructions on use of any commercial product must be followed at all times, eveR if in conflict with the information in this publication. THE CONTROL OF BOILERS Copyright 1991 by ISA - The Instrumentation, Systems, and Automati
6、on Society 67 Alexander Drive P.O. Box 12277 Researc h Triangle Park, NC 27709 All rights reserved. Printed in the United States of America. 1098765 ISBN 1-55617-330-X We would like to thank the many suppliers who provided material for this book, and we regret any we may have inadvertently failed to
7、 credit for an illustration. On notification we shall insert a correction in any subsequent printings. Some material herein has previously appeared in Improving Boiler Efficiency by Sam G. Dukelow, produced by Kansas State University and distributed by ISA. For information on corporate or group disc
8、ounts for this book, e-mail: bulksalesisa.org. Library of Congress Cataloging-in-Publication Data Dukelow, Sam G., 1917-The control of boilers/Sam G. Dukelow. - 2,d ed. p. cm. Includes bibliographical references and index. ISBN 1-55617-330-X 1. Steam-boilers - Automatic control. 1. Title. TJ288.D781
9、991 621.1 83-dc20 91-31399 CIP Dedication To my New Orleans son Bill, who helped to complete this book by continually asking, “Is your book done yet?“ Contents Chapter Page Section 1 Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1-1 Content and Objectives . . .
10、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1-2 Boiler Control Objectives. 2 1-3 Control System Diagramming . . 3 1-4 Boiler Control Application in Historical Perspective. 4 Section 2 Boiler Basics and the Steaming Process. 15 2-1 The Basic Steaming Process 15 2-2 The Bas
11、ic Boiler 15 2-3 Heat Recovery from the Flue Gases. 17 2-4 Boiler Types and Classifications. 21 2-5 Firetube Boilers. 22 2-6 Watertube Drum Boilers. 26 2-7 Watertube Once-Through Boilers 32 Section 3 Performance and Input-Output Relationships. 35 3-1 Capacity and Performance 35 3-2 Input Related to
12、Output 35 3-3 Mass and Energy Balances Involved 36 3-4 Efficiency Calculation Methods 38 3-5 Boiler Control - The Process of Managing the Energy and Mass Balances. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 Sec
13、tion 4 Basic Control Loops and Their System Interconnection . . 41 4-1 Simple Feedback Control . 41 4-2 Feedforward-Plus-Feedback Control 44 4-3 Cascade Control 46 4-4 Ratio Control 46 4-5 Some Fundamentals of Control System Application and Design. 47 4-6 Process Dynamics - Control Response 48 4-7 P
14、rocess Factors That Affect the Control System or Loop Application 48 Section 5 Combustion of Fuels, Excess Air, and Products of Combustion 49 5-1 Gaseous Fuels-Their Handling and Preparation 49 5-2 Liquid Fuels-Their Handling and Preparation 50 5-3 Solid Fuels-Their Handling and Preparation for Firi
15、ng. 55 5-4 Handling and Delivery of Solid Fuels. 56 5-5 Fuel Mixtures-Coal-Oil, Coal-Water 58 5-6 Physical Combustion Requirements. 59 5-7 Combustion Chemistry and Products of Combustion. . . . . . . . . . . . . . . . . . . 61 5-8 Theoretical Air Requirements and Relationship to Heat of Combustion.
16、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 5-9 The Requirement for Excess Combustion Air. 67 Section 6 Efficiency Calculations 73 6-1 Input-Output or Direct Method . 73 6-2 Heat Loss or Indirect Method 75 v Cha
17、pter Page Section 7 The Steam Supply System 87 7 -1 Saturated Steam Moisture Elimination 87 7-2 Steam Supply Systems. 88 7-3 Heat Energy and Water Storage 89 Section 8 Firing Rate Demand for Industrial Boilers. 93 8-1 Relationships. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
18、 . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 8-2 Linking the Steam Pressure Change to Changes in Firing Rate 93 8-3 Steam Presssure or Steam Flow Feedback Control . . . 96 8-4 Feedforward-plus-Feedback-Steam Flow plus Steam Pressure 99 8-5 Load Sharing of Multiple Boilers 103 8-6 Automa
19、tic Compensation for the Number and Size of Boilers Participating. 104 8-7 Preallocation of Boiler Load Based on Test Results. . 107 8-8 Energy Management by Boiler Load Allocation on a Least Cost Basis . . . . 107 8-9 Energy Management Involving Cogeneration Networks. 109 Section 9 Firing Rate Dema
20、nd for Utility Boilers. 115 9-1 Matching Firing Rate Demand to Electrical Load (Boiler-Turbine Coordination) 116 9-2 Boiler Load Measurement. 118 9-3 Unit Load Demand Development. . 121 9-4 Boiler Following-Firing Rate Demand Development. 123 9-5 Turbine Following-Throttle Pressure Control with the
21、Turbine Valves 129 9-6 Boiler-Turbine Coordinated Contro!. . . . . 133 9-7 Sliding or Variable Pressure Control 136 9-8 Heat Rate Optimization with Sliding Pressure Control. 137 9-9 Digital Interlock and Tracking Control Modes 137 Section 10 Main Steam and Reheat Steam Temperature Control . 139 10-1
22、 Temperature vs. Boiler Load 139 10-2 Mechanisms for Control of Superheat Temperature. 139 10-3 Basic Steam Temperature Control Strategies. 144 10-4 Steam Temperature and Reheat Temperature Control Strategies 147 10-5 A Reheat Temperature Control Arrangement for a Combustion Engineering Boiler 149 1
23、0-6 The Corresponding Superheat Temperature Control for the Combustion Engineering Boiler 152 10-7 Spray Water Sources-Steam and Water Flow Measurements . 154 10-8 Interactions. 156 10-9 Pumping and Firing Rate for Once-Through Boilers 156 10-10 Steam Temperature Control for Once-Through Boilers . 1
24、60 Section 11 Boiler and Unit Interlocks. 165 11-1 Applicable Codes . 165 11-2 Logic Diagramming for Motor Starting and Trip Protection. 165 11-3 Digital Interlocks within the Control System. 173 11-4 Classification of Trip Interlocks Relative to Potential Consequence 174 11-5 Limits and Runbacks .
25、176 VI Chapter Page Section 12 Feedwater Supply and Boiler Water Circulation Systems 177 12-1 The Basic System. 177 12-2 Heating and Deaeration 177 12-3 The Boiler Feedwater Pump. 180 12-4 The Flow Regulation System. 181 12-5 Shrink and Swell and Boiler Water Circulation 183 12-6 Feedwater Chemical
26、Balance and Control of Boiler Blowdown. 187 Section 13 Feedwater Control Systems 189 13-1 Measurement and Indication of Boiler Drum Level 189 13-2 Feedwater Control Objectives. . . . . . . 191 13-3 Single-Element Feedwater Control . . . 194 13-4 Two-Element Feedwater Control. . . 198 13-5 Three-Elem
27、ent Feedwater Control 202 13-6 Control Refinements and Special Control Problems . 204 13-7 Control of Feedwater for Once-Through Boilers. 207 Section 14 Boiler Draft Systems . 211 14-1 Draft Losses in Boilers . 211 14-2 Natural Draft and Forced Draft. 212 14-3 Pressure-Fired Boilers 213 14-4 Balance
28、d Draft Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215 14-5 Dampers and Damper Control Devices 216 14-6 Draft and Air Flow Control Using Variable-Speed Fan. 221 14-7 Minimum Air Flow. 224 Section 15 Measurement and Control of Furnace Draft. 227 15-1 Measurement o
29、f Furnace Draft . . . . 229 15-2 Furnace Draft Control Using Simple Feedback Control 229 15-3 Furnace Draft Control Using Feedforward-plus-Feedback Control 230 15-4 Furnace Draft Control Using Push-Pull Feedforward-plus-Feedback Control. . . 231 15-5 Protection Against Implosion 233 Section 16 Measu
30、rement and Control of Combustion Air Flow plus Related Functions. 239 16-1 Differential Pressure Measurement of Air Flow 239 16-2 Non-Inferential Measurement of Air Flow 244 16-3 Control of Air Flow. 246 16-4 Flue Gas Dew Point ControL 249 16-5 Soot Blowing. 253 Section 17 Flue Gas Analysis Trimming
31、 of Combustion Control Systems. 255 17 -1 Useful Flue Gas Analyses 255 17-2 Methods of Flue Gas Analysis 256 17 -3 Pros and Cons of Measurement Methods and Gases Selected for Measurement. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
32、. . 260 17-4 Flue Gas Analysis vs. Boiler Load. 262 17-5 PPM CO vs. PPM Total Combustible Gases . 264 17 -6 Control Applications Used for Flue Gas Analysis Trimming 265 17-7 Limiting Factors in Reducing Excess Air . . . . . 272 vii Chapter Page Section 18 Fluid Fuel Burners for Gas, Oil, and Coal. 2
33、75 18-1 Burners for Gaseous Fuel 275 18-2 Pulverized Coal Burners 279 18-3 Fuel Oil Burners . 282 Section 19 Solid Fuel Burning Systems 291 19-1 Types and Classification of Stokers 291 19-2 Special Stoker Control Problems 297 Section 20 Burner Management and Flame Safety Interlocks for Gas- and Flui
34、d-Fired Boilers. 299 20-1 Basic Cause of Furnace Explosions 299 20-2 Boiler Purge Logic 301 20-3 Ignitor Header Valve Management. 393 20-4 Main Gas Header Valve Management . 303 20-5 Gas Burner Management Logic. 304 20-6 Main Fuel Trip. 307 20-7 Degree of Burner Automation. . . . . . . . . . . . . .
35、 . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 20-8 Reliability of Interlock Circuitry. . . . . . . . . . . . . . . . . . . . . . . . . . . . 308 Section 21 Combustion Control for Liquid and Gaseous Fuel Boilers . 311 21-1 Single-Point Positioning Control 311 21-2 Parallel Positioning Co
36、ntrol 315 21-3 Metering Control Systems 317 21-4 Effects of Fuel Btu Variation 328 Section 22 Pulverized Coal and Cyclone Coal Burning Systems. 333 22-1 The Coal Feeder. 333 22-2 The Pulverizer and Classifier 336 22-3 The Primary Air Fan or Exhauster Fan and the Coal Drying System. 338 22-4 Pulveriz
37、er Control Systems 341 22-5 Compartmented Windbox Pulverized Coal Boilers 350 22-6 Start-up and Management of Pulverizers and Their Burners. 352 22-7 The Cyclone Furnace. 355 22-8 Start-Up and Management of Cyclone Furnaces. 358 Section 23 Combustion Control for Cyclone and Pulverized Coal-Fired Boi
38、lers “ . . . . . . . . . . . . . . . . . . 359 23-1 Coal Btu Compensation 359 23-2 The Use of Multiple Pulverizers 362 23-3 The Combustion Control System for Pulverized Coal as a Single Fuel 363 23-4 Pulverized Coal in Combination with Liquid or Gaseous Fuels. 364 23-5 Compartmented Windbox Pulveriz
39、ed Coal Control Systems. 367 23-6 Control Systems for Cyclone Furnace Boilers 369 Section 24 Combustion Control for Stoker-Fired Boilers. 373 24-1 Parallel Positioning Control System for Stoker-Fired Boilers 373 24-2 Inferential Measurement of Combustion Conditions in Boilers 375 24-3 Parallel Posit
40、ioning Control System with Steam Flow/ Air Flow Readjustment. 376 24-4 Series Ratio Control Systems for Stoker-Fired Boilers 379 viii Chapter Page 24-5 Applying Flue Gas Analysis Trim Control to Stoker-Fired Boilers. . . . . 381 24-6 Combustion Control for Combination of Stoker and Liquid or Gaseous
41、 Fuel Firing. 383 24-7 NFPA Purging and Interlock Requirements for Stoker-Fired Boilers. 386 Section 25 Atmospheric Fluidized-Bed Boilers. 389 25-1 Bubbling Bed Fluidized-Bed Boilers. 390 25-2 Circulating Bed Fluidized-Bed Boilers. 392 25-3 NFPA Requirements for Atmospheric Fluidized-Bed Combustion
42、System Boilers . 395 Section 26 Control System Complexity and Future Directions for Boiler Control 397 26-1 Complex Control Systems for Electric Utility Boilers Using Embedded Process Models. 397 26-2 Improving Control Precision and Stability without Process Modeling. . . . . . . . . . . . . . . . .
43、 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 26-3 Artificial Intelligence and Expert Systems. 402 26-4 A General Observation Relative to Boiler Modeling 402 26-5 General Observations Relative to Boiler Control Application 404 Index 407 ix ) o
44、 x Preface to Second Edition Five years have passed since the first edition of this book, and I have continued to learn as I have become older and wiser. In the third paragraph of the preface to the first edition, I implied that what I have done in this second edition was impossible. I want to eat t
45、hose words. The cartoon by Gus Shaw on the opposite page tells the story. During his work with Bailey Meter Co. (prior to Bailey Controls Co.), Gus made several great cartoons on this theme. A complete study of “The Control of Boilers“ must include the “starting up“ phase of the process. One of the
46、purposes of this edition is to include some basic information on that digital phase of the operation in addition to the modulating “on-line“ operation covered in the orig inal edition. This results in the sections and subsections covering interlocks, burner start-up and man agement, and the manageme
47、nt of the start-up and operation of pulverizers and other fuel burning equipment. Along with this is the recognition of applicable safety codes of the Na tional Fire Protection Association (NFPA). Another purpose of this edition is the extension of the on-line“ aspects of boiler control into the are
48、na of the larger-capacity electric utility boilers. The results of this are new sections covering the firing rate demand for utility boilers and steam temperature control. The section covering furnace pressure control has been expanded to include implosion protection. The section covering the contro
49、l of pulverized coal firing has been expanded to include cyclone furnaces and their control and the compartmented windbox boiler and its control. And, as I said above, I have become older and wiser in the past five years. My ASME membership card now says 51 years, my ISA membership card says 42 years, and I have had time to rethink some the things I thought I already knew. In this last five years my work has taken me to installations involving chain grate stokers, pulverized coal-fired boilers, gas-fired boilers, the steam power cycle of a nuclear breeder reactor, and p
