ISA BOILR CNTRL SYS-2010 Boiler Control Systems Engineering (Second Edition).pdf

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1、BOILER CONTROLSYSTEMS ENGINEERING,Second EditionBOILER CONTROLSYSTEMS ENGINEERING,Second EditionG. F. (Jerry) GilmanThe 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 informationby

2、the reader, both the author and the publisher disclaim any and all liability of any kindarising out of such use.The reader is expected to exercise sound professional judgment inusing any of the information presented in a particular application.Additionally, neither the author nor the publisher has i

3、nvestigated or considered the affect ofany patents on the ability of the reader to use any of the information in a particular applica-tion.The reader is responsible for reviewing any possible patents that may affect anyparticular use of the information presented.Any references to commercial products

4、 in the work are cited as examples only. Neither theauthor nor the publisher endorses any referenced commercial product.Any trademarks ortrade names referenced belong to the respective owner of the mark or name. Neither theauthor nor the publisher makes any representation regarding the availability

5、of any referencedcommercial product at any time.The manufacturers instructions on use of any commercialproduct must be followed at all times, even if in conflict with the information in this publi-cation.Copyright 2010 by International Society of Automation67 Alexander DriveP. O. Box 12277Research T

6、riangle Park, NC 27709All rights reserved.Printed in the United States of America10 9 8 7 6 5 4 3 2 ISBN 978-1-936007-20-2No part of this work may be reproduced, stored in a retrieval system, or transmitted in anyform or by any means, electronic, mechanical, photocopying, recording or otherwise, wit

7、houtthe prior written permission of the publisher.Library of Congress Cataloging-in-Publication DataGilman, G. F. (Jerry)Boiler control systems engineering / G.F. (Jerry) Gilman. - 2nd ed.p. cm.ISBN 978-1-936007-20-2 (pbk.)1. Steam-boilers-Automatic control. I.Title.TJ288.G527 2010621.194-dc22201002

8、2406About the AuthorJerry Gilmans career has spanned more than 37 years with Procter ISA84 Burner Man-agement System Working Group; and ISA77 Fossil Fuel Power Plant Standards.IIntroductionBoilers are a key power source for electrical generation in the United States and around theworld and for provi

9、ding heat in process industries and buildings. Regardless of the capacityor fuel, there are certain fundamental control systems required for boiler control. Large utilitysystems are more complex due to the number of burners and overall capacity and equipment.Although there are numerous ways to achie

10、ve control, the purpose is always the same tocontrol the firing of a boiler safely, reliably, and efficiently.One of the keys to good control is accurate measurement. If you cannot measure a processvariable, the variable cannot be controlled.This book addresses issues to consider whendefining transm

11、itter measurements and specifications.The characteristics and sizing of finalcontrol elements are also reviewed.This book is for anyone who works with boilers: utilities managers, power plant managers,controls systems engineers, maintenance technicians or operators.The information deals pri-marily w

12、ith water tube boilers with Induced Draft (ID) and Forced Draft (FD) fan(s) orboilers containing only FD fans. It can also apply to any fuel fired steam generator.Other books have been published on boiler control; however, they do not cover engineeringdetails on control systems and the setup of the

13、various control functions. Boiler Control Sys-tems Engineering provides specific examples of boiler control including configuration andtuning.The requirements as stated are based on the NFPA 85 Code 2007 Edition, and the followingISA standards:ANSI/ISA-77.41.01-2005 - Fossil Fuel Power Plant Boiler

14、Combustion ControlsANSI/ISA-77.42.01-1999 (R2006) - Fossil Fuel Power Plant Feedwater Control System(Drum-Type)ISA-TR77.42.02-2009 - Fossil Fuel Power Plant Compensated Differential Pressure BasedDrum Level MeasurementANSI/ISA-77.44.01-2007 - Fossil Fuel Plant-Steam Temperature Controls IIIDedicatio

15、nThe book is dedicated to my wife, Judy, and our children Jeff, Kelly,Tom, and Doug. Ourlove for one another has always been my greatest blessing.I want to thank my wife for her many hours of typing and proofreading assistance and ISA,particularly Susan Colwell, who has guided me through the publish

16、ing process andfor her many hours of assistance.A special thanks to Harold Wade for creating the new drawings.VTable of ContentsChapter 1 Boiler Fundamentals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1Basic Boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

17、 . . . . . . . . . . . . . . . . . 1Boiler Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Furnace . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Fans. . . . . . . . . . . . . . . . . . .

18、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Windbox . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Flue Gas Heat Exchangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Combusti

19、on Air Preheater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Economizer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Superheater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

20、. . . . . . . . 6Boiler Drums . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6Piping and Instrument Diagrams (P however, in utility plants the boiler is directly connected to the turbine. The firingdemand in industrial plants is based on header pressu

21、re or drum pressure. Utility plants controlthe firing rate on megawatt demand, or throttle pressure.The firing rate demand depends onthe particular system.FurnaceThe combustion chamber/furnace releases the heat and becomes the heat transfer system.Thereare three Ts required for combustion to take pl

22、ace in the furnace: time, temperature, and turbu-lence.The control of the furnace draft is required to maintain a negative pressure in the furnacein a balanced draft boiler.This pressure is defined by the boiler manufacturer. Negative 0.5 inchesis a common control point.The control set point may be

23、raised during inspection rounds from0.5 inches to 1.0 inches to minimize the possibility of flame coming out of inspection doors.Draftpressure control setting is defined by the boiler manufacturer and environmental equipment.FansFigure 1-2 illustrates the basic components of a coal-fired boiler.The

24、boiler consists of an ID(Induced Draft) fan and an FD (Forced Draft) fan. Large utility boilers may have two ID fansand two FD fans.The ID fan pulls air through the boiler producing a negative pressure in thefurnace, thus creating draft control.The FD fan pushes air for combustion through the boiler

25、.On utility boilers, FD fans normally supply secondary and overfire (tertiary air) with primaryair (PA) flow being supplied by the PA fans. Industrial boilers often have separate fans for thetertiary air as well.Due to the 1990 Clean Air Act amendments, there is often emission control equipment such

26、as precipitators, bag houses, and sulfur dioxide scrubbers on the discharge of boilers(Figure 1-3). If environmental equipment is added, booster ID fans may be required.The draftpressure control is defined by both the boiler manufacturer and environmental equipment.WindboxThe windbox distributes sec

27、ondary air to the burners.The windbox may have damper adjust-ments to create turbulence to improve combustion.Flue Gas Heat ExchangersTo reduce heat loss in the boiler flue gases and to improve boiler efficiency, heat exchangersare added to the boiler to recover heat and to cool the flue gases.2 Boi

28、ler Control Systems EngineeringBoiler Fundamentals 3FEEDERPULVERIZERPULVERIZED COAL WITH PRIMARY AIR (P.A.)FROM OTHER PULVERIZERSHOT AIR DAMPERCOLD AIR DAMPERHOT AIRSECONDARY AIRSECONDARYPRIMARYCOLD AIRCOLD AIRP.A. CONTROL DAMPERP.A. FANRAW COALAIR HEATERFEEDWATERFLUE GASESAMBIENTAIRTOTALAIRFD FANIN

29、LET VANESID FANINLET DAMPERSTEAM HEADERSTEAMFROMSECONDBOILERSTEAMFROM THIRDBOILERSTEAMTOPROCESSDESUPERHEATERSTEAM DRUMSPRAY WATER FROM FEEDWATER PUMPSUPERHEATERECONOMIZERFURNACEWINDBOXFigure 1-2 Boiler components. Source:Fisher Controls4 Boiler Control Systems EngineeringHEAT-THERMAL RISEPLUMEFUGITI

30、VE DUSTCOAL PILEWATER RUNOFFCOAL PILETURBINEBOILERCONDENSERCOOLINGTOWERCOOLINGTOWERBLOWDOWNBOTTOMASHHOPPERASHSCRAIRHEATERPRECIPITATORORBAGHOUSEFLYASHFGDSTACKFLUE GAS SO2NOxPARTICULATE VOC CO CO2OTHERFGDWATERFGD WASTE TREATMENTANDDEWATERING FGD BYPRODUCTGYPSUM OFLANDFILL SLUDGEASHSETTLING PONDNOISELA

31、NDFILLWATERSLUDGE/LANDFILLBLOWDOWNWATERCHEMICAL CLEANINGWASTE LIQUIDGAS SIDE WASHINGWASTE WATERNOTE: SCR-SELECTIVE CATALYTICREDUCTION DENOXSYSTEMFGD-FLUE GAS DESULFURIZATION SYSTEMB&W Steam its generation and Use 40th Edition.Figure 1-3 Typical power plant effluents and emissions.Combustion Air Preh

32、eaterThe combustion air preheater is one type of heat exchanger (Figure 1-4).As the flue gas leavesthe boiler, it passes through the combustion air preheater.The combustion air passes throughthe air preheater heat exchanger before being mixed with the fuel.Figure 1-4 Simple boiler plus combustion ai

33、r heater. Since the flue gas temperature is higher than the air temperature, heat is transferred from theflue gas to the combustion air via the convection heat transfer surface of the combustion airpreheater.This transfer of heat cools the flue gas and thus reduces its heat loss and reduces thetempe

34、rature of the air to the stack.The added heat in the combustion air entering the furnaceenhances the combustion process.This reduces the fuel requirement in an amount equal in heatvalue to the amount of heat that has been transferred in the combustion air preheater, thusimproving efficiency.By the u

35、se of an air preheater, approximately one percent of fuel is saved for each 40F rise inthe combustion air temperature.EconomizerAnother flue gas heat recovery method is through the use of an economizer. The economizerheats the feedwater to improve boiler efficiency and reduce heat loss to the stack.

36、 The increasedheat in the feedwater reduces the boilers requirement for fuel and combustion air. In the econ-omizer arrangement shown in Figure 1-5, the flue gas leaves the boiler and enters theeconomizer where it makes contact with the heat transfer surface, in the form of water tubes,through which

37、 the boiler feedwater flows. Since the flue gas is at a higher temperature thanthe water, the flue gas is cooled and the water temperature is increased. Cooling the flue gasreduces its heat loss in an amount equal to the increased heat in the feedwater to the boiler.Both types of heat exchangers are

38、 often used in large boilers.Boiler Fundamentals 5WATERFUELAIRBOILERAIRPREHEATERFLUE GASSTEAMAIR PREHEATER PURPOSE - PREHEAT COMBUSTION AIRAND ABSORB ADDITIONAL HEAT FROM FLUE GASWhen both an air preheater and an economizer are used,the normal practice consists of passingthe flue gases first through

39、 the economizer and then through the combustion air preheater(Figure 1-5). Utility boilers normally have economizers and air heaters.While economizers are used to recover heat from the flue gas, the use of Selective CatalyticReduction (SCR) requires flue gas temperatures above a specified minimum te

40、mperature tooperate.To extend the range of operation of the SCR,the economizer surface may be bypassedto raise flue gas temperatures at lower loads.Figure 1-5 Simple boiler with economizer and air heater.SuperheaterThe superheater provides additional heat to the steam to remove any moisture from the

41、 steam,thereby improving the quality of the steam (Figure 1-2). The dryness of the steam (in percent)is the determining factor of its quality.When there is no moisture in the steam, the quality is100 percent.Boiler DrumsThe boiler in Figure 1-2 does not have a lower drum. High pressure utility boile

42、rs used forpower generation have only an upper drum.Boilers may consist of an upper drum, or steam or water drum, and a lower drum, or muddrum. The mud drum terminology comes from the function of the lower drum. Althoughthe water is treated to eliminate dissolved solids, some solids always remain in

43、 the water.Thesesolids collect in the lower drum, and a drum blowdown is required to remove the solids thatcollect in the lower drum. The blowdown may be manual or automatic. If there is only anupper drum the blowdown is from the upper drum.6 Boiler Control Systems EngineeringBOILERFLUEGASFLUEGASIND

44、UCEDDRAFT FANINLETVANECONTROLINLETVANECONTROLWINDBOXFUELAIRAIRPREHEATERFORCEDDRAFT FANECONOMIZERFigure 1-6 has an upper and lower drum. Industrial plants commonly have both upper andlower drums. The heating of the tubes initiates a natural circulation of the water. In some large utility boilers, thi

45、s circulation is not sufficient and a pump is installed to produce therequired circulation.The circulation of the water creates a cooling effect to keep the tubesfrom overheating.Figure 1-6 Boiler drums.Piping and Instrument Diagrams (P&IDs)The purpose of P&IDs is to provide the design basis for the

46、 boiler and to provide the engi-neering requirements to identify the measurements and functions that are to be controlled.They are also used to define the number of inputs and outputs and the design basis check list(DBCL) that lists all of the instruments and functions.To further define the control

47、functions,utility plants generally utilize “SAMA”1functional diagram/symbol drawings to supplementthe P&IDs. Example of P&ID is shown in Figure 1-7.By identifying the required measurement and control functions and the I/O count, thememory requirements can be established. Memory and I/O capabilities

48、can be important inselecting a process control system (PCS) and/or logic system.Boiler Fundamentals 7STEAMSTEAMMUDDRUMFUELFURNACEFLAMEAIRGAS BAFFLESFLUE GASCIRCULATIONWATERCIRCULATESCLOCKWISE1SAMA PMC 22.1-1981 functional diagramming symbols have been adopted by ISA and are now included in ANSI/ISA-

49、5.1-2009.The controls system may consist of panel-mounted instruments, a distributed control system(DCS), logic system, or a combination.This also includes the amount of redundancy of bothmeasurement and final control elements.The numbering system will be based on the standard for the plant. The ISA and functional diagram/symbol letter identification is used by most companies. ISA and functional diagram/symbol identification letters are the same. (See ISA and functional diagram/symbol identificationtables in the Reference section for more information.) The numbering system will