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fired heater operation1.pdf
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Fired Heater Operation
Coping everyday with furnaces
www.heatflux.com 11/5/2009
PRE-STARTUP BROAD GUIDELINES (BUT NOT LIMITED TO FOLLOWING)
Heater & the area around it, Platforms, Walkways must be in clean condition.
Flammable materials should be removed from firebox prior to start-up.
Check peepholes, Explosion doors and header boxes for their conditions.
All valves in the FG/FO systems, all burner valves should be checked to ensure theiroperability and are closed.
All damper mechanism to be tested for their operability. Main Stack damper to bepositioned fully opened.
Ensure all Instrumnets to put in right place and are in good condition. Stroke check allcontrol valves, Check all emergency SDVs. Check ID Fan, FD Fans, APH for theirreadiness.
(NOTE: FOLLOW VENDOR GUIDELINES FOR DETAILS)
www.heatflux.com 11/5/2009
START-UP (BROAD GUIDELINES BUT NOT LIMITED TO THE FOLLOWING)
Purge the heater before light up to remove flammable vapours in the furnace.
Remove blinds from main fuel lines with all burner valves closed. Open main valve inthe line to gas header. Drain condensate from the FG KOD under supervision.Establish FO circulation.
Ignite pilot burners immediately after purging operation is completed. Monitorfurnace box and arch temperature. If the pilot go out, purge the firebox and relight.
Establish process stream flows through all the passes. Verify flow.
Check heater interlocks during cold circulation and rectify/record.
Light up main burners, check flame pattern, burner conditions & balance firing. Checkall flows, draft and temperature readings. Visually observe the furnace box forflame conditions.
NOTE: Follow Vendor guidelines for detailed Start-up activities.
www.heatflux.com 11/5/2009
NORMAL SHUT DOWN (BROAD GUIDELINES BUT NOT LIMITED TO THE FOLLOWING) Reduce the charge flow rate gradually to heater turndown condition.
Reduce heat input gradually as per guidelines. This reduction in flow and temperaturetakes several hours.
Put the unit under Circulation. Shut-off all the burners. Continue circulation to cool downthe unit.
When heater is cooled down sufficiently, stop circulation and Flush out the coil withsteam.
When fuel input is reduced some burners need to be shut off to maintain adequatefuel press to prevent flasck or flameout.
Flush out the oil burners with steam.
Open the sight doors, access doors and stack damper for cooling the heater. Formanentry ensure positive isolation of heater.
NOTE: Follow Vendor guidelines for detailed Start-up activities.
www.heatflux.com 11/5/2009
NORMAL OPERATIONAL CHECKS OF FURNACE: Check load carrying columns for deflection and corrosion.
Check ladders and platforms foe corroded areas.
Check all explosions doors and sight doors for tight closer.
Check tube coils for sagging, bowing buldging or discoloration.
Check convection coil for external fouling.
Check tube support for cracks, looseness, corrosion or oxidation.
Check burner firing for stable flame & uniform firing condition.
Check oil gun for drip-back.
Check for noticeable heater vibration as a result of burner mal-operation.
Check that fans donot cause undue vibration & fans are properly lubricated.
Check soot blower condition and maintain them healthy.
Check burner register for ease of adjustment. Shut off unused burners.
Check refractory conditions. Check damper for ease of adjustment.
Check that draft gauges are operable and negative pressure exits.
www.heatflux.com 11/5/2009
Requirements for Good Operation
2
• Reliable operating parameters• Good combustion• Equal flow distribution
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Good Operation Consists of
3
• Uniform heat distribution in firebox
• Draft and excess air control
• Fluid pass balancing
• Firebox inspection
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Uniform Heat Distribution
4
• Use equal amount of fuel and air to all burners• Natural draft - all registers open equally• Forced draft - all dampers fully open
• Unused burners - shut off the registers
Case StudyCrude Heater Tuning
5
• Natural Draft Crude Heater• Horizontal tube• Up-fired burners• 11 burners
www.heatflux.com 11/5/2009
Fuel gaspressu re,psig
Fuel
gas
flow
, MSC
FD6
Fuel Gas Flow and PressureBefore & After Tuning
3440
3420
3400
3380
3360
3340
3320
3300
3280
20
18
16
14
12
10
8Flue Gas Flow,MSCFD 6
4Fuel GasPressure, psig 2
3260 011:15 AM 11:30 AM11:45 AM12:00 PM 12:45 PM 1:00 PM 1:15 PM 1:30 PM
www.heatflux.com 11/5/2009
TSk
in,°
F
Tube Skin TempBefore & After Tuning the Heater
7
760
740
720
700
680
660
640
620
600
58011:15 AM 11:30 AM 11:45 AM 12:00 PM 12:45 PM 1:00 PM 1:15 PM 1:30 PM
www.heatflux.com 11/5/2009
Draft/ Excess O2 Control9
• Target 2-3% O2.
• Target draft?
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Draft Control12
• Controlled by stack damper• Stack damper
• Control valve controlling the upstream arch draft
• In heaters with induced draft fan, it is the induced draftfan which controls the draft• Suction damper• Variable speed
www.heatflux.com 11/5/2009
Heater Draft Profiles13
BURNERS -.70 -.60 -.50 -.40 -.30 -.20 -.10 0 -.10 -.20
Furnace Pressure- "WC
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Draft Control and Excess Air Adjustment14
• Do not use the stack damper or burner air register aloneto adjust the draft or excess air.
• Use both to obtain proper draft and excess air value.
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Draft Control15
PIC
Draft
ProcessFluidHeater
Fuel gasControl Valve Burners
O pen P eep D o o rs
C h eck F lam e P attern /16 Im p ing em en t
N oB ad Flam es?H azy Fire B o x
Step 1C hecking flam es
Yes
Increase Airflow
Is flam eO .K ?
Yes
N o
- Shutdow n B urn er- C lean B u rn er- L igh t up
- R ech eck flam e- P attern /
Im pin gem ent
G ood flam e
Step 1 (Continued...)
17 Good Flame
Check Arch Draft
Check Excess Oxygen
Close allPeepdoors
Step 2- Checking "Arch Draft"
Read Arch Draft
18
O.K. LowIs Draft
O.K?
High
Decrease StackDamper Opening
Increase StackDamper Opening
Check flamecharacteristics
(See fig.1)
Check ExcessOxygen
(See fig.3)
Arch Draft = 0.1"WC
Step 3- Checking "Excess Oxygen"
Read ExcessOxygen
19
O.K. Is ExcessOxygen
O.K?
Low
High
Close Air DuctDamper
Open Air DuctDamper
Check flamecharacteristics
(See fig.1)
Check Arch Draft(See fig.2)
Excess O2 at target
Stack Damper /Air DamperAdjustment Guide
20
Oxygen Level Draft Value Adjustment RequiredHigh Close stack damper
Low Open stack damper
High Close air damper
Low Open air damper
Stack Damper21
• Closing will have the following effects:• Reduced oxygen in the flue gas• Decreased draft at the radiant arch• Firebox temperature will increase• Stack temperature will go down• Increased radiant heat transfer• Decreased convective heat transfer• Increased heater efficiency
Draft Measurement and Control22
• Draft is an essential measurement of any fired heater.
• Measurement required at following places:• Radiant Floor• Radiant Arch• Convection Outlet• Upstream and Downstream of Damper
Draft/Excess Air Control Limitation23
• Physical condition of burners• Burner tiles• Air registers
• Condition of stack damper• Struck
• Air leakage in the furnace
Draft/Excess O2 Control24
• Good reliable oxygen and carbon monoxide analyzer• Good and reliable draft gauges• Good air registers• Good stack damper• Good operating practices• Trained operators
Recommended Draft/Excess O2 Levels25
• Gas firing 10 %-15% excess air• Oil firing 15 %-20% excess air• Keep on increasing excess air till you get no CO and
Combustibles and also good flames• Above excess air values are for natural draft. For true
forced draft burners, the values can be lower.• Draft- maintain 0.1” WC draft at arch
Excess O2 Control26
• Flame size• Flame shape• Flame impingement• After combustion
Air Leakage28
• Air can enter from a number of places:• Peepholes• Header box doors• Unused burners
Air Leakage29
• Peepholes, header box doors, openings• Unused / off burner• Does not mix with fuel• Does not help the combustion• Absorbs heat• All combustion air through
• ‘ON’ burners
1. Air register position - Equally open
30 2. Only 3 out of 5 burners are fired
StackDamper
O2 Analyser
Draft @ arch-0.1"WC
Air leakage
Air register
Air
Fuel gas Fuel gas Fuel gas Fuel gas Fuel gas
www.heatflux.com 11/5/2009
Air Leakage/ Oxygen Measurement31
• Check excess Oxygen in flue gases leaving the arch
• Check excess Oxygen in flue gases leaving theconvection section
• Check excess Oxygen in the flue gases after airpreheater in balanced draft system
www.heatflux.com 11/5/2009
Minimize Air Leakage32
• All burner registers closed if not inservice
• All peepholes closed
• All header box doors closed
• All tube guide openings in heaterfloor plugged
www.heatflux.com 11/5/2009
Fired Heater Optimization33
• Two sides• Fluid side• Flue gas side
• Both side operations need to beoptimized
• Flue gas side is neglected, needsmore attention
www.heatflux.com 11/5/2009
What Can Operation Do?34
• Maintain equal flow through all passes• Good guideline is to keep within +- 10%
• Watch pressure drop across each pass• Downstream of control valve and orifice• At heater inlet and outlets
• Watch control valves opening• If any parameter is abnormal, investigate
www.heatflux.com 11/5/2009
Routine Inspection35
• Inspect firebox at regular intervals
• Inspect fireboxes using allobservation doors
• Check heater tubes
• Check burner flames
Bad flames
www.heatflux.com 11/5/2009
Routine Inspection36
• Tube skin temperatures
• Heater fire box temperature
• Heater tube appearance
• Flame impingement
• Tube hangers
• Refractory
www.heatflux.com 11/5/2009
Furnace Bogging37
• Fired heater starves for air
• Develops positive pressure in the firebox.
• Overfire the fired heater
• DO NOT OPERATE FIRED HEATERS AT POSITIVEPRESSURE AT ANY TIME.