fuel burner & firebox operation & control

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  • Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

    Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramcos employees.Any material contained in this document which is not already in the publicdomain may not be copied, reproduced, sold, given, or disclosed to thirdparties, or otherwise used in whole, or in part, without the written permissionof the Vice President, Engineering Services, Saudi Aramco.

    Chapter : Vessels For additional information on this subject, contactFile Reference: MEX10405 R.K. Khanna

    Engineering EncyclopediaSaudi Aramco DeskTop Standards

    Fuel Burner And Firebox Operation And Control

  • Engineering Encyclopedia Vessels

    Fuel Burner And Firebox Operation And Control

    Saudi Aramco DeskTop Standards

    Contents Pages

    FUELS AND BURNERS.....................................................................................................1

    Fuel Options..............................................................................................................1

    Burners.....................................................................................................................1

    Burner Components.......................................................................................2

    Gas Burners...................................................................................................4

    Oil Burners....................................................................................................8

    Combination Gas and Oil Burners..................................................................9

    Forced Draft Burners.....................................................................................9

    Emissions Control.........................................................................................10

    FUEL SYSTEMS................................................................................................................16

    Fuel Gas Systems.....................................................................................................16

    Components..................................................................................................16

    Controls........................................................................................................20

    Fuel Oil Systems.......................................................................................................21

    Components..................................................................................................21

    Controls........................................................................................................26

    Effects on Boiler and Process Heater (Furnace) Design...........................................26

    MAJOR CONCERNS AND GUIDELINES FOR FIREBOX OPERATION........................27

    Major Concerns........................................................................................................27

    Flame Characteristics and Patterns................................................................27

    Typical Draft Profile.....................................................................................28

    Optimum Operation for Excess Air...............................................................29

    Operating Guidelines for Natural Draft Furnaces......................................................29

    GLOSSARY........................................................................................................................30

  • Engineering Encyclopedia Vessels

    Fuel Burner And Firebox Operation And Control

    Saudi Aramco DeskTop Standards

    Table of Figures Pages

    Figure 1. Typical Natural-Draft Oil/Gas Burners.......................................................2

    Figure 2. Pilot Burner...............................................................................................4

    Figure 3. John Zink Burner Capacities......................................................................7

    Figure 4. Typical Fuel Oil Burner.............................................................................8

    Figure 5. Forced-Draft Boiler Combination Burner..................................................10

    Figure 6. Typical LowNOx Burner..........................................................................12

    Figure 7. AVC LowNOx Burner..............................................................................13

    Figure 8. LowNOx Burner with Flue Gas Recirculation...........................................14

    Figure 9. Flue/Fuel Gas Mixture..............................................................................15

    Figure 10. Typical Gas Burner System (Automatic Startup).....................................17

    Figure 11. Typical Gas Burner System (Supervised Manual Startup)........................18

    Figure 12. Pilot Gas System.....................................................................................19

    Figure 13. Orifice Flow...........................................................................................20

    Figure 14. Fuel Oil System......................................................................................22

    Figure 15. RT Liquid Fuel System...........................................................................23

    Figure 16. Typical Oil Burner System (Automatic Startup)......................................24

    Figure 17. Typical Oil Burner System (Supervised Manual).....................................25

    Figure 18. Furnace Natural Draft Profile..................................................................28

    Figure 19. Optimum Excess Air for a Fired Heater..................................................29

  • Engineering Encyclopedia Vessels

    Fuel Burner And Firebox Operation And Control

    Saudi Aramco DeskTop Standards 1

    FUELS AND BURNERS

    Fuel Options

    The fuel options include gas and oil. Gas can include natural gas and/or a refinery or gas plantfuel gas. The refinery or gas plant fuel gas includes natural gas and make gas from the processes,and usually has a higher heating value than dry natural gas. Oil can be No. 6 fuel oil, bunker fueloil, resids, or crude oil. It is almost always more economical to burn fuel oil and resids than toburn crude oil.

    Burners

    Burners are mechanical devices for mixing fuel and air for combustion. The main functions ofburners are:

    To provide and mix the proper quantities of fuel and air.

    To provide a stable flame.

    To release heat in the desired pattern.

    Burners and their combustion control systems must produce satisfactory combustion over therange of expected operating conditions (fuel compositions and firing rates). Burners are expectedto be reliable and to meet these requirements with reasonable initial cost and maintenanceexpense.

    Failure of burners to perform any of these functions adequately can lead to inefficient combustionand/or poor flame patterns. This can lead to localized overheating and damage to furnace orboiler components, resulting in increased maintenance costs. This damage can also cause apremature shutdown due to failure (or impending failure) of critical components such as tubes,tube supports, or the refractory lining.

    Burners are available in two general types: natural-draft and forced-draft. Either type can be usedfor burning gas or liquid fuels alone, or both fuels in combination.

    Natural-draft burners are used in all Saudi Aramco process heaters.

    Forced-draft burners are used in all boilers. Forced-draft burners may also be used inprocess heaters (furnaces). At this time, none of Saudi Aramco's process heaters useforced-draft burners.

  • Engineering Encyclopedia Vessels

    Fuel Burner And Firebox Operation And Control

    Saudi Aramco DeskTop Standards 2

    Burner Components

    Burners consist of the following main components illustrated in Figure 1. Figure 1 shows typicalnatural-draft burners.

    Spider Head

    SecondaryAir Register

    Pilot

    Fuel/PrimaryAir Mixer

    Fuel Gas Connectiona b

    c

    With permission from the John Zink Co.

    Figure 1. Typical Natural-Draft Oil/Gas Burners

    Air Register - Air enters the burner through the air register. Air flow can be controlled byadjusting the size of the openings in the register. For natural-draft burners, the most commontype of air register consists of fixed and moveable concentric cylinders, each with slots.

  • Engineering Encyclopedia Vessels

    Fuel Burner And Firebox Operation And Control

    Saudi Aramco DeskTop Standards 3

    Plenum Chamber - The air register in some burners is located inside a plenum chamber, whichusually serves all the burners in the furnace or boiler. In boilers, the plenum chamber is called awindbox. The plenum chamber can serve several purposes:

    Reduces noise emissions from the burners. Reduces wind effects on natural-draft burners. Permits combustion air supply from a single source, such as a fan. Enables total air flow to the furnace or boiler to be controlled at one point.

    Fuel System - This consists of manifolds and piping to deliver the fuel to the burner tips. Thefuel passes through one or more openings in the tips, which act as restriction orifices. The fuel isinjected into, and mixes with, the airstream. Various types of burner tips are used, dependingupon the type of fuel and the flame pattern desired.

    Refractory Burner Tile - This is located at the burner exit. T

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