BOILERSfor POWER andPROCESSCRC_75365_FM.indd i 3/23/2009 7:32:28 PMCRC_75365_FM.indd ii 3/23/2009 7:32:29 PMCRC Press is an imprint of theTaylor & Francis Group, an informa businessBoca Raton London New YorkBOILERSfor POWER andPROCESSKumar RayaproluCRC_75365_FM.indd iii 3/23/2009 7:32:29 PMCRC PressTaylor & Francis Group6000 Broken Sound Parkway NW, Suite 300Boca Raton, FL 33487-2742 2009 by Taylor & Francis GroupCRC Press is an imprint of Taylor & Francis Group, an Informa businessNo claim to original U.S. Government worksPrinted in the United States of America on acid-free paper10 9 8 7 6 5 4 3 2 1International Standard Book Number-13: 978-1-4200-7537-3 (Ebook)This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the valid-ity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint.Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or uti-lized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopy-ing, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers.For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged.Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe.Visit the Taylor & Francis Web site athttp://www.taylorandfrancis.comand the CRC Press Web site athttp://www.crcpress.com vDedicationTo my late parents.To my father,a power engineer himself, for instilling within me this love for boilers.To my wife Usha, without whose gentle encouragement and active support, this project would not have been undertaken and my teenage daughters Ramya and Amulya, without whose software and data entry help, this book would not have seen the light of the day. It is for the manner all of them have cheerfully suffered the total neglect and deprivation imposed on them during the past two years that this book could be completed.CRC_75365_FM.indd v 3/23/2009 7:32:30 PMCRC_75365_FM.indd vi 3/23/2009 7:32:30 PMviiContentsList of Figures ................................................................................................................ xviiList of Tables ............................................................................................................... xxxiiiPreface .............................................................................................................................. xliAcknowledgments .......................................................................................................... xlvAuthor ........................................................................................................................... xlviiStructure of this Book ................................................................................................... xlixConversion of Units .......................................................................................................... lvPreamble ......................................................................................................................... lxiiiSection I: Boiler Fundamentals1 Boiler Basics ..............................................................................................................31.1 Introduction ................................................................................................................... 31.2 Classifcation of Boilers ................................................................................................ 31.2.1 Defnition of a Boiler......................................................................................... 31.2.2 Classifcation...................................................................................................... 31.3 Boiler Specifcations ..................................................................................................... 71.3.1 Steam Flow or Evaporation or Boiler Output................................................ 71.3.2 Types of Pressures ............................................................................................ 91.3.3 Outlet Temperatures ......................................................................................... 91.3.4 Feed Water Temperature ................................................................................ 101.3.5 Fuels .................................................................................................................. 101.4 Scope of Boiler Plant ................................................................................................... 111.4.1 Inputs and Outputs ......................................................................................... 111.4.2 Boiler Package .................................................................................................. 131.4.3 Boiler Island ..................................................................................................... 131.5 Heat Balance for Boiler Effciency ............................................................................ 141.5.1 Energy Balance in Boiler ................................................................................ 141.5.2 Boiler Effciency Calculations ....................................................................... 141.5.3 Effect of Ambient Conditions on Boiler Effciency and Design ............... 151.5.4 Breakup of Losses ........................................................................................... 161.5.5 Typical Effciency Calculation ....................................................................... 201.6 Performance Testing of Boilers ................................................................................. 201.6.1 InputOutput Method .................................................................................... 211.6.2 Heat Loss Method ........................................................................................... 211.6.3 Calculation of Effciency from Performance Test Results ......................... 231.6.4 New 1998 Boiler Performance Test Code ..................................................... 241.6.5 Performance Testing of Waste Heat Recovery Boilers ............................... 251.6.6 Performance Testing of Heat Recovery Steam Generators ....................... 251.7 Boiler Evaluation ......................................................................................................... 271.8 Boiler Design for Optimum Performance ............................................................... 281.8.1 Stack Loss Reduction ...................................................................................... 291.8.2 Unburnt Loss Reduction ................................................................................ 301.8.3 Radiation Loss Reduction .............................................................................. 30CRC_75365_FM.indd vii 3/23/2009 7:32:30 PM1.8.4 Fan Power Reduction ...................................................................................... 301.8.5 Feed Pump Power Reduction ........................................................................ 311.9 Designing to Boiler Codes ......................................................................................... 311.9.1 Basics of Boiler Pressure Part Design ........................................................... 341.10 Capturing Basic Design Data .................................................................................... 37Further Readings ................................................................................................................. 402 Heat and Flow ......................................................................................................... 412.1 Introduction ................................................................................................................. 412.2 Steam and Water Properties ..................................................................................... 412.2.1 Boiling/Evaporation ....................................................................................... 422.2.2 Laws for Steam and Water ............................................................................. 422.2.3 Density ............................................................................................................. 422.2.4 Heat Distribution at Various Pressure Levels ............................................ 432.2.5 Steam/Rankine Cycle .................................................................................... 432.2.6 Steam and Water Properties .......................................................................... 452.2.7 Mollier Chart or EnthalpyEntropy (Hs) Diagram ................................. 452.2.8 TemperatureEntropy (Ts) Diagram .......................................................... 452.3 Heat Transfer ............................................................................................................... 472.3.1 Heat Flow ......................................................................................................... 472.3.2 Conduction ...................................................................................................... 482.3.3 Convection ....................................................................................................... 502.3.4 Radiation .......................................................................................................... 552.3.5 Combined Heat Transfer ............................................................................... 562.3.6 Extended Surfaces ........................................................................................... 572.4 Fluid Flow .................................................................................................................... 592.4.1 Bernoullis Equation ....................................................................................... 602.4.2 Material Balance or Continuity Equation ................................................... 602.4.3 Flow through Nozzles and Orifces ............................................................. 602.4.4 Flow Coeffcients ............................................................................................. 612.4.5 Resistance to Flow in Pipes ........................................................................... 622.4.6 Air and Gas Duct Losses ............................................................................... 652.5 Circulation ................................................................................................................... 652.5.1 Principles of Circulation ................................................................................ 652.5.2 Flow in Vertical and Horizontal Tubes ........................................................ 652.5.3 Departure from Nucleate Boiling ................................................................ 662.5.4 Maintaining Nucleate Boiling ....................................................................... 672.5.5 Types of Circulation ....................................................................................... 702.5.6 Limits for Natural Circulation ...................................................................... 732.5.7 Circulation Systems for Subcritical and Supercritical Pressures ............. 742.5.8 Boiler Feed Pumps .......................................................................................... 752.6 Combustion ................................................................................................................. 782.6.1 Stages of Combustion ..................................................................................... 782.6.2 Combustion Chemistry ................................................................................. 792.6.3 Combustion Air .............................................................................................. 792.6.4 Heat of Combustion ........................................................................................ 802.6.5 Three Ts ............................................................................................................ 822.6.6 Adiabatic Flame Temperature ....................................................................... 822.6.7 Specifc Heats of Gas ...................................................................................... 822.6.8 Air and Gas Weights ...................................................................................... 82viii ContentsCRC_75365_FM.indd viii 3/23/2009 7:32:30 PM2.6.9 Flue Gas Analysis ........................................................................................... 872.6.10 Specifc Volume of Flue Gases....................................................................... 892.7 Thermodynamic Cycles ............................................................................................. 902.7.1 Carnot Cycle ..................................................................................................... 912.7.2 Rankine or Steam Cycle ................................................................................. 912.7.3 Brayton or Gas Turbine Cycle ........................................................................ 922.7.4 Combined Cycle .............................................................................................. 92Further Readings ........................................................................................................ 953 Fuels and Ash .......................................................................................................... 973.1 Introduction ................................................................................................................. 973.2 Solid Fuels .................................................................................................................... 983.2.1 Fossil Fuels ....................................................................................................... 983.2.2 Waste Fuels .................................................................................................... 1103.3 Liquid Fuels ............................................................................................................... 1203.3.1 Fuel Oils.......................................................................................................... 1203.4 Gaseous Fuels ............................................................................................................ 1253.4.1 Fossil Fuels ..................................................................................................... 1253.4.2 Waste or Manufactured Fuels ..................................................................... 1283.5 Ash .............................................................................................................................. 1323.5.1 Coal Ash ......................................................................................................... 1323.5.2 Oil Ash ............................................................................................................ 142Further Readings ...................................................................................................... 1434 Water Conditioning .............................................................................................. 1454.1 Introduction ............................................................................................................... 1454.2 Water and Boiler ....................................................................................................... 1454.2.1 Effects of Water on Boilers ........................................................................... 1464.2.2 Types of Water ............................................................................................... 1474.2.3 Water Treatment ............................................................................................ 1474.2.4 Impurities in Water ....................................................................................... 1484.2.5 Water Terminology ....................................................................................... 1484.3 Deaeration and O2 Scavenging ............................................................................... 1494.3.1 Deaeration ...................................................................................................... 1504.3.2 O2 Scavenging ............................................................................................... 1534.4 Water and Steam Conditioning .............................................................................. 1544.4.1 Feed Water ...................................................................................................... 1544.4.2 Boiler Water ................................................................................................... 1554.4.3 Boiler Water Conditioning ........................................................................... 1564.4.4 Sludge Conditioning ..................................................................................... 1584.4.5 Boiler Blowdown ........................................................................................... 1584.4.6 After-Boiler Protection ................................................................................. 1594.4.7 Chemical Dosing ........................................................................................... 1594.5 Carryover ................................................................................................................... 1614.5.1 Steam Separators ........................................................................................... 1624.5.2 Silica in Boiler Water .................................................................................... 1634.5.3 Loading of Steam Separators ...................................................................... 1634.5.4 Foaming and Priming .................................................................................. 1644.5.5 Steam Purity Measurement ......................................................................... 165Further Readings ...................................................................................................... 166Contents ixCRC_75365_FM.indd ix 3/23/2009 7:32:30 PM5 Boiler Materials .................................................................................................... 1675.1 Introduction ............................................................................................................... 1675.2 Boiler Parts................................................................................................................. 1675.3 Boiler Steels ............................................................................................................... 1685.3.1 Boiler Quality (BQ) Plates ............................................................................ 1695.3.2 Boiler Tubes ................................................................................................... 1705.3.3 Pipes ................................................................................................................ 1775.3.4 Pressure Castings and Forgings ................................................................. 1785.4 Structural Steels ........................................................................................................ 1825.4.1 Structural Quality Tubes and Pipes ........................................................... 1825.4.2 High-Temperature Castings ........................................................................ 1835.5 Fundamentals of Metallurgy .................................................................................. 1845.5.1 Classifcation of Steels .................................................................................. 1855.5.2 Effect of Alloying Elements on Steel Properties ...................................... 1895.5.3 Heat Treatment Processes ............................................................................ 1895.5.4 Certain Terms in Heat Treatment as Relevant to Boiler Steels ............... 1895.5.5 Corrosion ........................................................................................................ 1925.6 Properties of Steel in Brief ....................................................................................... 1955.6.1 Tensile Strength ............................................................................................. 1955.6.2 Hardness ........................................................................................................ 1965.6.3 Toughness ...................................................................................................... 1965.6.4 Fatigue Strength ............................................................................................ 1995.6.5 High-Temperature Properties ..................................................................... 2005.7 Bricks, Refractory, Insulation, and Lagging ......................................................... 2015.7.1 Refractories ..................................................................................................... 2015.7.2 Various Types of Refractories ...................................................................... 2035.7.3 Insulation ........................................................................................................ 2075.7.4 Lagging ........................................................................................................... 2085.8 Wear-Resistant Refractory Ceramic Materials ..................................................... 209Further Readings ...................................................................................................... 210Section II: Boiler Parts and Auxiliaries6 Heating Surfaces ................................................................................................... 2136.1 Introduction ............................................................................................................... 2136.2 Evaporator Surfaces .................................................................................................. 2146.2.1 Furnace ........................................................................................................... 2146.2.2 Boiler Bank (BB) ............................................................................................ 2226.3 Superheater and Reheater (SH and RH) ................................................................ 2276.3.1 Superheater (SH) ........................................................................................... 2276.3.2 Reheater (RH) ................................................................................................ 2286.3.3 Superheater and Reheater Design Principles............................................ 2286.3.4 Superheater and Reheater Classifcation ................................................... 2296.3.5 Tubes for Superheater and Reheater .......................................................... 2336.3.6 Tube Spacing and Gas Velocities ................................................................ 2356.3.7 Tube Metal Temperatures ............................................................................ 2366.3.8 Steam Temperature Control (STC) ............................................................. 2376.4 Back-End Equipment ................................................................................................ 2426.4.1 Airheater or Economizer? ............................................................................ 243x ContentsCRC_75365_FM.indd x 3/23/2009 7:32:30 PM6.4.2 Airheater versus Economizer ...................................................................... 2436.4.3 Airheater and Economizer Arrangements ................................................ 2446.5 Economizer ................................................................................................................ 2456.5.1 Classifcation .................................................................................................. 2466.5.2 Tube and Fin Materials ................................................................................ 2506.5.3 Operating Concerns in Economizers ......................................................... 2516.6 Airheater .................................................................................................................... 2536.6.1 Airheater Types ............................................................................................. 2536.6.2 TAH versus RAH .......................................................................................... 2556.6.3 Tubular Airheater ......................................................................................... 2556.6.4 Rotary Airheater ........................................................................................... 2596.6.5 Operational Concerns .................................................................................. 262Further Readings ...................................................................................................... 2657 Fabricated Parts ..................................................................................................... 2677.1 Introduction ............................................................................................................... 2677.2 Unheated Pressure Parts .......................................................................................... 2677.2.1 Steam and Water Drums .............................................................................. 2687.2.2 Downcomers, Supplies, and Risers ............................................................ 2767.2.3 Integral Piping ............................................................................................... 2787.3 Draft Plant Items ....................................................................................................... 2817.3.1 Flues, Ducts, Hoppers, and Casing ............................................................. 2827.3.2 Dampers ......................................................................................................... 2837.3.3 Expansion Joints ............................................................................................ 2867.3.4 Airfow Measuring Devices ......................................................................... 2867.4 Structure ..................................................................................................................... 2897.4.1 Site Conditions ............................................................................................... 2897.4.2 Loads to be Supported by Structure ........................................................... 2907.4.3 External Loads on Structure ........................................................................ 2907.4.4 Boiler Expansion and Guides ...................................................................... 2917.4.5 Hot and Cold Structures .............................................................................. 2927.4.6 Top, Middle, or Bottom Support .................................................................. 2987.4.7 Bolted or Welded Construction ................................................................... 2987.4.8 Rolled Beams or Built-Up Sections ............................................................. 299Further Readings ............................................................................................................... 2998 Boiler Auxiliaries ................................................................................................. 3018.1 Introduction ............................................................................................................... 3018.2 Fans ............................................................................................................................. 3018.2.1 Fans in Boiler Plant ....................................................................................... 3018.2.2 Salient Aspects of Fans ................................................................................ 3028.2.3 Types of Fans ................................................................................................. 3038.2.4 Centrifugal Fans ........................................................................................... 3058.2.5 Axial Fans ...................................................................................................... 3088.2.6 Fan Laws ........................................................................................................ 3108.2.7 Fan Selection .................................................................................................. 3118.2.8 Effciency and Power .................................................................................... 3148.2.9 Fan Control .................................................................................................... 3158.2.10 Construction Features .................................................................................. 3208.2.11 Two Modes of Fan Operation ...................................................................... 322Contents xiCRC_75365_FM.indd xi 3/23/2009 7:32:30 PM8.2.12 Single Set and Two Sets of Fans ................................................................ 3248.2.13 Fan Erosion and Protection ....................................................................... 3248.2.14 Boiler Fans .................................................................................................... 3258.3 Dust-Collecting Equipment .................................................................................... 3268.4 Mechanical Dust Collectors (MDCs) ..................................................................... 3288.4.1 Multiclones ..................................................................................................... 3288.4.2 Large-Diameter Cyclones ............................................................................ 3318.5 Dry Electrostatic Precipitator (ESP) ....................................................................... 3328.5.1 Operating Principle of an ESP ..................................................................... 3328.5.2 Components ................................................................................................... 3338.5.3 Features .......................................................................................................... 3338.5.4 Advantages .................................................................................................... 3388.5.5 Limitations ..................................................................................................... 3388.5.6 Performance Parameters .............................................................................. 3388.6 Fabric Filters (FFs) ..................................................................................................... 3418.6.1 Advantages of FF........................................................................................... 3428.6.2 Limitations of FF ........................................................................................... 3428.6.3 ESP versus FF ................................................................................................ 3438.6.4 Performance of FF ......................................................................................... 3438.6.5 Reverse Gas Filters ........................................................................................ 3448.6.6 Pulse Jet Filters .............................................................................................. 3448.6.7 RGF versus PJF .............................................................................................. 3458.6.8 Bags for FF ..................................................................................................... 3458.7 Wet Scrubbers (WSs) ................................................................................................ 3468.7.1 Advantages of WS ......................................................................................... 3468.7.2 Limitations of WS .......................................................................................... 3488.7.3 Application of WS ......................................................................................... 3488.7.4 Comparison of Different Dust Collectors by Performance ..................... 3488.8 Valves and Mountings ............................................................................................. 3498.8.1 Main Steam Stop Valve and Nonreturn Valve .......................................... 3508.8.2 Start-Up Vent Valves ..................................................................................... 3528.8.3 CBD and IBD Valves ..................................................................................... 3538.8.4 Safety Valves .................................................................................................. 3538.8.5 Drain and Vent Valves ................................................................................. 3568.8.6 Control Valves ............................................................................................... 3588.9 Soot Blowers .............................................................................................................. 3618.9.1 Working Principle of Soot Blowers ............................................................. 3628.9.2 Types and Locations of Soot Blowers ......................................................... 3638.9.3 Boiler Firing and Soot Blowers .................................................................... 3638.9.4 Steam versus Air ........................................................................................... 3658.9.5 Types of Blowers ............................................................................................ 3658.9.6 Rotary AH Cleaning ..................................................................................... 3698.9.7 Water Lancing ................................................................................................ 3698.9.8 SB Piping......................................................................................................... 3708.9.9 Acoustic or Sonic Soot Blowers ................................................................... 3708.10 Water-Level Indicators ............................................................................................. 3718.10.1 Direct Water-Level Indicators ...................................................................... 3728.10.2 Remote Water-Level Indicators .................................................................... 376Further Readings ............................................................................................................... 378xii ContentsCRC_75365_FM.indd xii 3/23/2009 7:32:30 PMSection III: Boilers and Firing9 Industrial and Utility Boilers ............................................................................. 3819.1 Water Tube Boilers for Industry and Power .......................................................... 3819.1.1 Characteristic Features of Industrial Boilers ............................................. 3819.1.2 Characteristic Features of Utility Boilers ................................................... 3829.2 Industrial Boilers ...................................................................................................... 3839.2.1 Boiler Classifcation by Firing ..................................................................... 3839.2.2 Classifcation by Number of Drums .......................................................... 3939.2.3 Balanced Draft and Pressurized Firing ..................................................... 3949.3 Utility Boilers ............................................................................................................ 3959.3.1 Small versus Large Utility Boilers .............................................................. 3959.3.2 Supercritical Boilers ...................................................................................... 3969.3.3 Boiler Designs for Utilities........................................................................... 4049.3.4 Features of Supercritical Boilers ................................................................. 4089.3.5 Drum-Type or Supercritical Boiler? ............................................................ 4159.3.6 Standard Plant Confgurations for Supercritical Boilers ......................... 416Further Readings ............................................................................................................... 41610 Burner Firing ......................................................................................................... 41710.1 Oil and Gas Firing .................................................................................................. 41710.2 Burners and Combustion....................................................................................... 41810.2.1 Burner Size ................................................................................................. 41810.2.2 Burner Turndown ..................................................................................... 41910.2.3 Air Registers .............................................................................................. 42010.2.4 Excess Air for Oil and Gas Firing ........................................................... 42110.2.5 Combustion of Oil and Gas in Circular Burners.................................. 42410.2.6 Atomizers ................................................................................................... 42510.2.7 Gas Burners ................................................................................................ 43210.2.8 Low NOx Burners ...................................................................................... 43510.2.9 Igniters ........................................................................................................ 43810.2.10 Flame Monitors .......................................................................................... 44010.3 Duct Burners ........................................................................................................... 44110.4 Burner Management and Safety System .............................................................44410.5 Oil- and Gas-Fired Boilers ..................................................................................... 44510.5.1 Package Boilers .......................................................................................... 44610.5.2 Field-Erected Modular Boilers ................................................................ 453Further Readings ............................................................................................................... 46111 Stoker Firing.......................................................................................................... 46311.1 Introduction ............................................................................................................. 46311.2 Mechanical Stokers ................................................................................................. 46311.2.1 Grates and Stokers ..................................................................................... 46611.2.2 CG versus TG ............................................................................................. 46611.2.3 Using Same Grate for Mass and Spreader Burning ............................. 46711.2.4 Moistening of Coal before Firing ............................................................ 46711.2.5 Clinker ........................................................................................................ 46711.2.6 Coal Segregation ....................................................................................... 46811.2.7 Coal Sizing ................................................................................................. 468Contents xiiiCRC_75365_FM.indd xiii 3/23/2009 7:32:31 PM11.3 Mass Burning .......................................................................................................... 47111.3.1 Chain or Traveling Grates with Gravity Feeding ................................. 47111.3.2 RG and PG Grates ..................................................................................... 47311.4 Spreader Burning .................................................................................................... 47511.4.1 Spreader Firing: CG and RG with Spreader Stokers ............................ 47511.4.2 Spreader Firing with Dumping Grates .................................................. 49211.5 Stoker-Fired Boilers ................................................................................................ 49511.5.1 Oil or Gas Firing in Stoker-Fired Boilers ............................................... 49711.5.2 Principles of Spreader Stoker-Fired Boiler Design ............................... 49811.5.3 Fuel Flexibility in Stokers ........................................................................ 50011.5.4 Biofuel Firing on Stokers .......................................................................... 501Further Readings ............................................................................................................... 50412 Fluidized Bed Combustion ................................................................................. 50512.1 Introduction ............................................................................................................. 50512.2 FBC Fundamentals ................................................................................................. 50612.2.1 Fluidization ................................................................................................ 50612.2.2 Desulfurization ......................................................................................... 50912.2.3 Denitrifcation ........................................................................................... 51012.3 FBC Process: Pros and Cons ................................................................................. 51112.3.1 Characteristics of FBC Boiler ................................................................... 51112.3.2 Advantages of FBC Boilers ...................................................................... 51212.3.3 Limitations of FBC Boilers ....................................................................... 51212.3.4 Thermal Effciency: Conventional versus FBC Boilers ........................ 51312.4 Bubbling Fluidized Bed Combustion .................................................................. 51412.4.1 Process ........................................................................................................ 51412.4.2 Underbed versus Overbed Feeding ....................................................... 51412.4.3 Bed Regulation for Part-Load Operation .............................................. 51712.4.4 Bed Coil ...................................................................................................... 51712.4.5 Deep versus Shallow Bed ........................................................................ 51812.4.6 Erosion in BFBC Boilers ........................................................................... 51912.4.7 Bed ............................................................................................................... 51912.4.8 Freeboard ................................................................................................... 52012.4.9 Ash Recirculation ...................................................................................... 52012.4.10 Air Nozzles ................................................................................................ 52112.4.11 Salient Process Parameters of BFBC Boilers ......................................... 52112.4.12 Applications ............................................................................................... 52112.4.13 BFBC Boiler Design Principles ................................................................ 52312.4.14 BFBC Boiler Designs ................................................................................. 52412.5 Circulating Fluidized Bed Combustion .............................................................. 52512.5.1 Process ........................................................................................................ 52512.5.2 Design Features of Classical or Hot Cyclone CFBC ............................. 53012.5.3 CFBC Boilers .............................................................................................. 53912.5.4 Cold Cyclone CFBC Boiler ....................................................................... 54212.5.5 No-Cyclone U-Beam CFBC Boilers ........................................................ 54912.6 Utility Circulating Fluidized Bed Combustion Range Boilers ........................ 55212.7 Ignifuid Boilers ...................................................................................................... 554Further Readings ............................................................................................................... 558xiv ContentsCRC_75365_FM.indd xiv 3/23/2009 7:32:31 PM13 Pulverized Fuel Firing ......................................................................................... 55913.1 Introduction ............................................................................................................. 55913.1.1 Main Features ............................................................................................ 55913.1.2 Advantages and Limitations ................................................................... 56113.2 Types of Firing ........................................................................................................ 56213.2.1 Indirect Firing ............................................................................................ 56213.2.2 Direct Firing .............................................................................................. 56313.3 Milling Plant ............................................................................................................ 56413.3.1 Suction and Pressurized Milling ............................................................ 56413.3.2 Feeders ........................................................................................................ 56513.3.3 Mills or Pulverizers .................................................................................. 56613.3.4 Coal Pipes ................................................................................................... 58713.4 Pulverized Firing Burners ..................................................................................... 58913.4.1 Burner Light-Up and Low Load .............................................................. 59013.4.2 Igniters ........................................................................................................ 59113.4.3 Flame Monitors and Burner Management System .............................. 59113.4.4 Burner Types .............................................................................................. 59113.4.5 Circular Burners ........................................................................................ 59113.4.6 Tangential Corner Burners ...................................................................... 59213.4.7 Circular versus Tangential Burners ....................................................... 59413.4.8 Vertical Down-Shot Burners .................................................................... 59413.4.9 Corner Firing ............................................................................................. 59613.4.10 Low NOx PF Burners ................................................................................ 59613.5 Pulverized Fuel Boilers .......................................................................................... 59813.5.1 Design Principles ...................................................................................... 59813.5.2 Fuel Flexibility ........................................................................................... 60213.5.3 Co-Firing of Fuels ..................................................................................... 60313.5.4 Boiler Turndown ....................................................................................... 60313.5.5 PF Boiler Layouts ...................................................................................... 60313.5.6 PF Boiler Designs ...................................................................................... 604Further Readings ............................................................................................................... 60914 Waste Gas Firing (Heat Recovery Steam Generators) ..................................... 61114.1 Introduction ............................................................................................................. 61114.2 Heat Recovery Steam Generators and Waste Heat Recovery Boilers .............. 61114.3 Gas Turbines ............................................................................................................ 61214.3.1 Gas Turbines for Power: Rapid Growth ................................................. 61314.3.2 Defnitions of Terms ................................................................................. 61414.3.3 Basics ........................................................................................................... 61514.3.4 Cycles .......................................................................................................... 61714.3.5 Types ........................................................................................................... 61914.3.6 Manufacturers ........................................................................................... 62014.3.7 Popular Models ......................................................................................... 62114.3.8 Characteristics ........................................................................................... 62314.3.9 Performance Enhancement ...................................................................... 62514.4 Heat Recovery Steam Generators ......................................................................... 62714.4.1 Conventional Boilers versus HRSGs ...................................................... 62714.4.2 Standardized HRSG Designs: Not Possible .......................................... 62814.4.3 Demanding Design ................................................................................... 629Contents xvCRC_75365_FM.indd xv 3/23/2009 7:32:31 PM14.4.4 Scope Issues ............................................................................................... 62914.4.5 Diverter Damper and Bypass Stack Assembly ..................................... 63014.4.6 Fired HRSGs .............................................................................................. 63014.4.7 Design Aspects .......................................................................................... 63114.4.8 Fins and Tubes ........................................................................................... 63514.4.9 Vertical and Horizontal HRSGs .............................................................. 64014.4.10 System Confgurations of Typical HRSGs ............................................. 64514.4.11 Once-Through Steam Generators (OTSGs) ............................................ 64514.4.12 Performance Testing ................................................................................. 64814.4.13 Layout of CCPP .......................................................................................... 648Further Readings ............................................................................................................... 650Glossary .......................................................................................................................... 651Appendix A: Boiler Calculations ................................................................................ 667A.1 Introduction .............................................................................................................. 667A.1.1 Combustion Calculations ........................................................................... 667A.1.2 Effciency Calculations ............................................................................... 675A.1.3 Firing Equipment Selection ........................................................................ 679A.1.4 Preliminary Furnace Calculations ............................................................ 680A.1.5 Draft Plant Calculations ............................................................................. 681A.1.6 Sizing of Valves and Mountings ................................................................ 686A.1.7 Sizing of Pumps ........................................................................................... 690A.1.8 Sizing of Control Valves ............................................................................. 692A.1.9 Sizing of Drives ............................................................................................ 693Further Readings ............................................................................................................... 695Appendix B: Table of Combustion Constants ........................................................... 697Appendix C: ASTM Standards Pertaining to Testing and Specification of Coals and Oils ........................................................................................ 701List of Calculations ....................................................................................................... 703List of Symbols .............................................................................................................. 705List of Acronyms ........................................................................................................... 707Design Guidelines ....................................................................................................... 711Fuel and Ash Data ......................................................................................................... 713Technology Comparisons ............................................................................................. 715Important Descriptions ................................................................................................ 717Index ................................................................................................................................ 719xvi ContentsCRC_75365_FM.indd xvi 3/23/2009 7:32:31 PMxviiList of Figures1.1 Range of smoke or flue tube shell boilers................................................................41.2 Range of steam generators along with approximate electric power equivalents. ................................................................................................................61.3 Drum-type RH utility boiler with ECON and AH as back-end equipment. ............................................................................................................... 121.4 Energy balance in a boiler plant. ........................................................................... 141.5 Radiation loss as per American Boiler Manufacturers Association (ABMA). .................................................................................................................... 181.6 Relative effectiveness of heating surfaces. ............................................................ 291.7 Allowable high-temperature stresses for selective pressure part materials as per ASME BPVC 2007. ......................................................................................... 372.1 Ts diagram of steam and water. ........................................................................... 432.2 Density variations of saturated water and steam with pressure ......................... 432.3 Workload of heating surfaces as the pressure increases ...................................... 442.4 Simplified schematic of a steam cycle in a power plant ...................................... 442.5 Hs or Mollier diagram in imperial units ............................................................. 452.6 Mollier chart in SI units. ......................................................................................... 462.7 Ts diagram for steam in British units. ................................................................. 462.8 Thermal conductivity (k) of air and flue gas at various temperatures. .............. 492.9 Thermal conductivity (k) of select boiler metals at high temperatures. ............. 502.10 Types of flow. ........................................................................................................... 512.11 Absolute viscosity of water. .................................................................................... 522.12 Absolute viscosity of steam .................................................................................... 532.13 Cross and longitudinal flows outside tubes and longitudinal flows through tubes. ......................................................................................................... 552.14 Graphical solution for LMTD ................................................................................. 582.15 Common fins. .......................................................................................................... 582.16 Types of fluids ......................................................................................................... 592.17 Friction factor (f) versus Reynolds number (Re). .................................................. 622.18 Relative roughnesses of pipe materials ................................................................. 632.19 Flow in vertical tubes. ............................................................................................. 66CRC_75365_FM.indd xvii 3/23/2009 7:32:31 PM2.20 Flow in horizontal tubes. ........................................................................................ 662.21 Departure from nucleate boiling............................................................................ 672.22 Rifled/ribbed tube................................................................................................... 67 2.23 Effect of ribbed tube on permissible steam quality to avoid DNB. ..................... 672.24 Relationship between SBV and SBW. ..................................................................... 682.25 Typical circulation ratios for single and bidrum boilers...................................... 692.26 Minimum percentage of SWH at various pressures............................................. 692.27 Types of circulation. ................................................................................................ 702.28 Typical natural circulation circuit ......................................................................... 722.29 Self-limiting characteristic of natural circulation ................................................ 722.30 Evaporation processes with (a) fixed and (b) variable SOPs. ............................... 742.31 Subcritical pressure evaporator systems ............................................................... 752.32 Supercritical pressure evaporator systems. ........................................................... 752.33 Cross-sectional view of a typical 10-stage radial ring section centrifugal pump......................................................................................................................... 782.34 Psychrometric chart in SI units .............................................................................. 802.35 Approximate mean specific heats of gases and steam. ........................................ 832.36 Combustion properties of solid fuels .................................................................... 852.37 Fuel oil combustion properties............................................................................... 862.38 Orsat analyzer. ......................................................................................................... 872.39 Percentage of CO2 in dry flue gas versus excess air ............................................. 882.40 Percentage of excess air versus flue gas in kilogram per kilogram (kg/kg) of fuel ....................................................................................................................... 892.41 Percentage of excess air versus air weight in kilogram per kilogram (kg/kg) of fuel ......................................................................................................... 892.42 Specific volume of flue gas at NTP conditions ..................................................... 902.43 Carnot cycle in diagrammatic form. ...................................................................... 912.44 Carnot cycle on Ts chart ....................................................................................... 912.45 Simplified steam cycle for power generation with condensing turbine. ............ 922.46 Simplified cogeneration cycle with back-pressure turbines. ............................... 932.47 Improvements in cycle efficiency due to feed water heating by regeneration. ............................................................................................................ 932.48 Brayton cycle on Ts diagram................................................................................. 942.49 Brayton cycle on PV diagram................................................................................ 942.50 Components of Brayton cycle. ................................................................................ 94xviii List of FiguresCRC_75365_FM.indd xviii 3/23/2009 7:32:31 PM2.51 Components of combined cycle. ............................................................................. 953.1 Proximate analyses and GCV of various classes of coals. ................................. 1003.2 Seylers classification of coal ................................................................................ 1003.3 Bases of coal analysis ............................................................................................ 1023.4 Coke profiles from swelling test .......................................................................... 1053.5 Behavior of coal on application of heat ............................................................... 1063.6 Typical lignites of the world ................................................................................. 1093.7 Variation of specific gravity of fuel oils with temperature................................ 1223.8 Variation of specific heat of fuel oils with temperature. .................................... 1233.9 Viscosity versus temperature chart for various liquid fuels ............................. 1243.10 Schematic of CO gas formation ............................................................................ 1313.11 Four stages of ash deformation temperatures. .................................................... 1343.12 Effects of iron compounds and reducing conditions on IADT .......................... 1353.13 (a) Special tubes and liners for wear resistance. (b) Tube arrangements for better wear life ........................................................................ 1383.14 Slagging and fouling zones in a PF boiler. .......................................................... 1393.15 Effect of slagging and fouling on furnace size and soot blower location ........ 1403.16 High-temperature sintered ash deposits. ............................................................ 1413.17 Low-temperature friable ash deposits downstream building upstream of the tube and decreasing with gas velocity. .................................... 1414.1 Failure due to oxygen pitting ............................................................................... 1504.2 Solubility levels of oxygen in water ..................................................................... 1504.3 Spray- and tray-type vertical deaerator without feed tank. .............................. 1514.4 Spray- and tray-type horizontal deaerator mounted on feed tank. .................. 1524.5 Schematic arrangement of a deaerator................................................................. 1524.6 Effectiveness of O2 scavengers ............................................................................. 1544.7 Operating regimes for coordinated and congruent treatments for pressures from 70 to 110 bar. ................................................................................ 1574.8 Chemical dosing in a boiler plant. ....................................................................... 1604.9 Dosing and measurement points. ........................................................................ 1604.10 Centrifugal steam separation. .............................................................................. 1624.11 Inertial steam separation. ..................................................................................... 1624.12 Permissible concentrations of silica in boiler water at various pressures and pH values. ...................................................................................... 1645.1 Effect of carbon percentage on steel properties. ................................................. 185List of Figures xixCRC_75365_FM.indd xix 3/23/2009 7:32:31 PM5.2 Classification of steel by carbon wt%. ................................................................. 1865.3 Classification of steel by deoxidation. ................................................................. 1875.4 Ironcarbon (FeC) diagram. ............................................................................... 1885.5 Hardening effects of various alloying elements dissolved in pure iron. ......... 1915.6 Heat treatment processes. ..................................................................................... 1925.7 Stressstrain relationship. .................................................................................... 1975.8 Comparisons of hardness scales .......................................................................... 1975.9 Mohs scale and its approximate equivalent hardness. ....................................... 1985.10 Typical Charpy and Izod impact test specimens. ............................................... 1995.11 Corrosion fatigue. .................................................................................................. 1995.12 Typical creep strains. ............................................................................................ 2006.1 Typical FEGT versus heat release graph for burner and grate firing. ............... 2166.2 (a) Tube and tile construction. (b) Tangent tube construction. (c) Membrane wall construction. .......................................................................... 2186.3 (a) Membrane panel. (b) Temperature variation in membrane strip. ................ 2196.4 Typical studded tube. ............................................................................................ 2216.5 Typical buckstay details. ....................................................................................... 2226.6 (a) Single-pass boiler bank in cross flow. (b) Two-pass boiler bank in longitudinal flow. .................................................................................................. 2236.7 Temperature profiles for boiler bank. .................................................................. 2246.8 Tube expander. ....................................................................................................... 2246.9 (a) Single-pass cross flow, (b) two-pass longitudinal flow, and (c) multipass longitudinal flow boiler banks ........................................................... 2266.10 (a) Counterflow, (b) parallel flow, and (c) and (d) mixed-flow surfaces. ........... 2296.11 Typical radiant and convective superheater. ....................................................... 2306.12 Radiant and convective superheater characteristics. ......................................... 2306.13 Two-loop arrangements with 1 to 4 tubes and loops. ........................................ 2316.14 Horizontal single-loop pendant. .......................................................................... 2326.15 Multiloop vertical pendant. .................................................................................. 2326.16 Supporting for horizontal sections. ..................................................................... 2326.17 Typical vertical platen. .......................................................................................... 2336.18 Typical horizontal platen. ..................................................................................... 2346.19 In-line and staggered arrangements of tubes. .................................................... 2346.20 Progressive narrowing of tube spacing with gas cooling. ................................. 235xx List of FiguresCRC_75365_FM.indd xx 3/23/2009 7:32:31 PM6.21 Steam crossover by header.................................................................................... 2376.22 Steam crossover by pipes. ..................................................................................... 2376.23 Effect of attemperator location on steam temperature rise................................ 2396.24 Spray attemperator. ............................................................................................... 2396.25 Drum attemperator ............................................................................................... 2406.26 Control by gas bypassing in boiler second pass. ................................................ 2416.27 Effect of gas recirculation on secondary superheater outlet temperatures. ......................................................................................................... 2416.28 (a) Economizer and airheater in sequence. (b) Economizer and airheater in zigzag arrangement. ......................................................................... 2446.29 (a) Single tube per loop. (b) Two tubes per loop ................................................. 2476.30 (a) Cast iron finned-tube economizer. (b) Cast iron gilled steel tube. (c) Helically finned tube ....................................................................................... 2486.31 Tubes with plate fins ............................................................................................. 2496.32 Gas flow over fin tubes. ........................................................................................ 2506.33 Longitudinal fin. ................................................................................................... 2506.34 Finned tube packaged ECON. .............................................................................. 2516.35 Long-flow vertical ECON. .................................................................................... 2516.36 Low-temperature corrosion limits (external) for CS economizer and airheater tubes for various fuels. ......................................................................... 2526.37 (a) Single-pass air and gas vertical tubular airheater in cross flow. (b) Three-pass gas and single-pass air vertical tubular airheater. (c) Two air and two gas vertical airheater. (d) One gas and two-pass air vertical tubular airheater. (e) Three gas and three air vertical tubular airheater in L-shape ................................................................................................................... 2576.38 (a) Single-pass tubular airheater with air in long flow. (b) Two-pass tubular airheater with air in long flow. ............................................................... 2586.39 (a) Single-pass gas and four-pass air horizontal tubular airheater. (b) Vertical tubular airheater and its parts. ......................................................... 2606.40 Moving RAH with (a) vertical shaft. (b) Horizontal shaft. (c) Corrugated packing. (d) Rotor sectors with corrugated packing. ......................................... 2616.41 Rotating hood rotary airheater. ............................................................................ 2636.42 Schematic arrangement of steam coil airheater. ................................................. 2646.43 Low-pressure economizer for airheater temperature control. ........................... 2646.44 (a) Wear pattern in VTAH. (b) Wear pattern over horizontal tubes. ................. 2657.1 Typical drum sizes and rows of steam separators. ............................................. 2707.2 Deflection baffles or baffle-type separator. ........................................................ 271List of Figures xxiCRC_75365_FM.indd xxi 3/23/2009 7:32:31 PM7.3 Cyclone or centrifugal separator. ......................................................................... 2727.4 Drum internals with two sets of vertical cyclones in a stubbed drum. ........... 2737.5 Drum internals with single set of horizontal cyclones in an expanded drum ....................................................................................................................... 2747.6 Three-flap louver damper with power cylinder actuator in closed position. .................................................................................................................. 2847.7 Leak tightness. ....................................................................................................... 2847.8 Guillotine damper in open condition. ................................................................. 2857.9 Diverter damper in boiler running condition. .................................................... 2857.10 Dampers and expansion joints in a typical pulverized fuel boiler. .................. 2877.11 Orifice plate ........................................................................................................... 2887.12 Two-sided venturimeter. ....................................................................................... 2887.13 Multiaerofoil .......................................................................................................... 2887.14 Typical thermal expansion of a top-supported two-pass boiler. ....................... 2927.15 Top-suspension rods in an industrial boiler. ...................................................... 2947.16 Typical suspension rods in a utility boiler. ......................................................... 2947.17 Drum slings ........................................................................................................... 2957.18 Intermediate cradle for roof tube support........................................................... 2967.19 Typical column arrangements. ............................................................................. 2977.20 Typical bracing patterns in a tower-type boiler. ................................................. 2977.21 Top, middle, and bottom supports for bidrum boilers. ...................................... 2988.1 Static and total pressures ...................................................................................... 3038.2 Fan and compressor cycles on PV diagram. ...................................................... 3038.3 Centrifugal fans. .................................................................................................... 3048.4 Propeller fan .......................................................................................................... 3048.5 Tube and vane axial fans ...................................................................................... 3058.6 Air velocity profiles .............................................................................................. 3068.7 Various blade shapes and static efficiencies ....................................................... 3068.8 Centrifugal fan with backward-curved blades ................................................... 3078.9 Centrifugal fan with radial blades ....................................................................... 3078.10 Centrifugal fans with forward-curved blades .................................................... 3088.11 Axial fans with variable blade angles ................................................................. 3088.12 Two-stage variable-speed axial fan ..................................................................... 3098.13 Comparison of various fan characteristics. ......................................................... 310xxii List of FiguresCRC_75365_FM.indd xxii 3/23/2009 7:32:32 PM8.14 System resistance versus fan curves .................................................................... 3128.15 Action of fan outlet damper ................................................................................. 3158.16 Action of inlet vane control .................................................................................. 3168.17 Typical curves for inlet vane control. .................................................................. 3178.18 Power transmission in hydraulic coupling. ......................................................... 3188.19 Load variation by scoop control. .......................................................................... 3188.20 Comparison of fan controls. ................................................................................. 3198.21 Overhung fan with single inlet and single width of impeller. .......................... 3208.22 Simply supported fans with single inlet and single width of impeller. ........... 3218.23 Double-inlet double-width fan. ............................................................................ 3218.24 Fan operation in series and parallel .................................................................... 3238.25 Comparison of fans in parallel operation ........................................................... 3238.26 Overview of various types of dust and collectors. ............................................. 3278.27 Large-diameter cyclone separators. ..................................................................... 3298.28 Small-diameter cyclones used in multiclones. .................................................... 3308.29 Multiclones. ............................................................................................................ 3308.30 Typical collection efficiency of multiclone. ......................................................... 3318.31 Volume/cell versus pressure drop. ...................................................................... 3328.32 Particle collection in an electrostatic precipitator. ............................................. 3338.33 Arrangement of dry electrostatic precipitator with top rapping ...................... 3348.34 Types of emitting electrodes ................................................................................ 3358.35 Electrodes and side rapping system .................................................................... 3368.36 Ash resistivity versus migration velocity. ........................................................... 3408.37 Variation of resistivity with sulfur and temperature. ........................................ 3408.38 Various fabric filters and their operation: (a) pulse jet filter, (b) reverse gas filter, and (c) shaker filter. ........................................................... 3428.39 Reverse gas filter. .................................................................................................. 3448.40 Pulse jet filter ......................................................................................................... 3458.41 Bags of pulse jet filter............................................................................................ 3468.42 Isometric view of Venturi scrubber ..................................................................... 3478.43 Schematic arrangement of Venturi scrubber ...................................................... 3478.44 (a) Typical parallel slide and (b) wedge gate valves. .......................................... 3518.45 Typical swing-check valve. ................................................................................... 3528.46 Piston check valve with dashpot. ......................................................................... 352List of Figures xxiiiCRC_75365_FM.indd xxiii 3/23/2009 7:32:32 PM8.47 Hand-operated globe valve. ................................................................................. 3538.48 Typical IBD valve. .................................................................................................. 3548.49 Spring-type safety valves with valve and disk in open and closed positions. ................................................................................................................ 3558.50 Drip pan and safety valve in discharge piping. ................................................. 3578.51 Flow versus lift for various types of trims.......................................................... 3588.52 Control valves with different trims. .................................................................... 3598.53 Pressure reduction and recovery in a flow stream. ............................................ 3598.54 Typical control valve and diaphragm actuator. .................................................. 3608.55 Three-way mixing and diverting valve. .............................................................. 3608.56 Integrated attemperator spray control valve. ...................................................... 3618.57 Soot blower locations in a large pulverized fuel boiler. ..................................... 3648.58 Typical wall blower/deslogger/short retractable. ............................................... 3658.59 Manually operated rotary soot blower. ............................................................... 3668.60 Lane and mass blowing. ....................................................................................... 3678.61 Fully retractable soot blower. ............................................................................... 3678.62 Soot blowing patterns for platens and pendants. ............................................... 3688.63 Rake-type soot blower for economizer and tubular airheater. .......................... 3698.64 Typical piping for soot blowers. ........................................................................... 3708.65 Wave generator and bell section of acoustic blower. .......................................... 3718.66 Tubular gauge glasses: (a) plain and (b) protected (up to 15 bar). .................. 3738.67 Reflex-type gauge glass (up to 32 bar). ............................................................. 3738.68 Affinity of water to glass. ..................................................................................... 3748.69 Transparent gauge and its action (up to 120 bar). ............................................ 3758.70 Bicolor gauge and action (up to 180 bar). ............................................................. 3758.71 Port-type bicolor gauge (up to 220 bar) ............................................................. 3768.72 Gauge glass combinations. ................................................................................... 3778.73 Schematic diagram of manometric gauge ........................................................... 3778.74 Schematic diagram of electronic remote water-level indicators along with probe .............................................................................................................. 3789.1 Horseshoe furnace with two cells ........................................................................ 3889.2 Horseshoe with water-cooled furnace. ................................................................ 3889.3 Grate casting with cleaning port.......................................................................... 3899.4 Pinhole grate assembly. ........................................................................................ 389xxiv List of FiguresCRC_75365_FM.indd xxiv 3/23/2009 7:32:32 PM9.5 Bidrum boiler with pinhole grates and fuel distributors. ................................. 3919.6 Inclined water-cooled grate for high-moisture biofuels .................................... 3929.7 Balanced draft and pressurized boilers. ............................................................. 3959.8 Typical draft-loss diagrams for pressurized and balanced draft boilers............................................................................................................ 3959.9 Sub- and supercritical cycles on Ts chart. ......................................................... 3979.10 Sub- and supercritical cycles. ............................................................................... 3979.11 Typical steam cycle of 1300 MW supercritical boiler on Ts diagram .............. 3989.12 Rise in plant efficiency over time. ....................................................................... 3989.13 Rise in cycle efficiency as steaming conditions improve. .................................. 3999.14 Effect of increased steaming conditions on fuel consumption. ........................ 4009.15 Reduction in specific CO2 generation, 19302000. .............................................. 4019.16 Load transients in drum and once-through boilers. .......................................... 4019.17 Typical hot, warm, and cold start-up times. ....................................................... 4029.18 Variable and sliding pressure operation. ............................................................ 4039.19 Auxiliary power of boiler feed pumps in fixed and sliding operations. .......... 4039.20 Two-pass opposed wall-fired boiler with divided gas flow in second pass and part vertical superheater and reheater. ................................................ 4059.21 Two-pass opposed fired boiler with single second pass with part vertical and part horizontal superheater and reheater. ................................................... 4069.22 Tower-type supercritical boiler with opposed firing and horizontal drainable superheater and reheater. .................................................................... 4079.23 Tube arrangement in a tower-type boiler. ........................................................... 4089.24 Modified tower-type boiler with two passes and horizontal drainable superheater and reheater. ..................................................................................... 4099.25 U-type down-shot firing. ...................................................................................... 4109.26 W-type down-shot firing. ..................................................................................... 4109.27 Spiral furnace tubes for supercritical boilers. .......