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)

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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.

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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.

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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.

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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

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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

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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

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Uniform Firing8

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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

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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

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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

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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

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Fired Heater Optimization33

• Two sides• Fluid side• Flue gas side

• Both side operations need to beoptimized

• Flue gas side is neglected, needsmore attention

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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

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Routine Inspection35

• Inspect firebox at regular intervals

• Inspect fireboxes using allobservation doors

• Check heater tubes

• Check burner flames

Bad flames

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Routine Inspection36

• Tube skin temperatures

• Heater fire box temperature

• Heater tube appearance

• Flame impingement

• Tube hangers

• Refractory

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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.