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SAFETY TALK
FIRED HEATERS M.C JOMON
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Kochi Refinery
HEATER
Heater is used to raise the temperature of a process fluid from lower temperature to higher temperature.
Services in Refinery
• Fractionation: Crude, Vacuum, Reboilers.• Thermal cracking: DCU , Visbreaker, Hydrocracker.• Catalytic cracking: Reformer, CCR.• Reaction: Hydrotreater
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Kochi Refinery
HEATER
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Kochi Refinery
HEATERTypes
Vertical tube cylindrical heater• Most common type refinery heaters.• Vertical radiant tubes and horizontal convection tubes.• Smallest plot area required.• Tubes expand vertically.• Less number of tube supports. One at top and one guide at the bottom for each tube.• Not preferably used for highly vaporizing services.• Heat duty up to 40 MM K cal/hr.
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Kochi Refinery
HEATERTypes
Horizontal box type[ single shell/ twin shell ]• Heat duty from 20-125 MM Kcal/hr.• Horizontal radiant/convection tubes.• Requires large plot area.• Choice of having heater outlet at the radiant section bottom or top.• Large number of tube supports required.• 20-25% costlier than vertical heater.• Used in crude vacuum coker heaters.
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Kochi Refinery
HEATERTypes
Arbor or wicket type heater [for very low pressure drop [ .2-.3 kg/cm2]
• Tubes are like inverted U shape.• All vapour flow. Non coking services.• Low pressure heaters.• Heat duties of 17.5-100 MM Kcal/hr. eg. CCR , • Bottom manifold.• Free draining.• Can be combination firing because of bottom firing.
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Kochi Refinery
HEATERTypes
Inverted wicket type
• Horizontal firing.• Single or double firing.• In situ hydro testing not possible.• Eg. CCR
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Kochi Refinery
HEATERTypes
Helical coil heater
small heat duties up to 15 mm kcal/hr.
Not used in refineries.
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Kochi Refinery
HEATERTypes
Classification based on firing.
• Side fired -One side / both side.• Bottom fired• Top fired.
• Side fired Bottom fired Top fired 9
Kochi Refinery
HEATERTypes
Classification based on fuel• Gas firing• Oil firing• Combination firing
Gas firing Oil firing Oil + Gas firing
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Kochi Refinery
HEATERTypes
Classification based on Draft
• Natural Draft-
• Forced Draft - using F.D fan
• Induced Draft – using I.D fan and drop out doors.
• Balanced Draft – using F.D and I.D fans.
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Kochi Refinery
HEATER
Draft
Draft is the difference in pressure which causes the flow of air into the furnace and flue gases through the heater. The pressure differential is caused by the difference in densities of the flue gas in the heater and stack and the air surrounding the furnace.
• Positive draft means flue gas pressure is below ambient pressure.• Negative draft means fluid pressure is above ambient pressure at the same
elevation.• Draft is controlled by stack damper or by ID fan.• Ideal draft in a natural draft furnace is -1 mm wc.
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Kochi Refinery
HEATER
Impact of higher draft
• Taller flame• Flame lift –off• High air flow through burners[ in
natural draft burners only]• Air leakages thru joints of heater
body/ explosion door/peepholes.• Excess air more.
Impact of lower draft
• Damaging heater structure.• Flame or hot air leakage to
atmosphere• Low air flow through burners , low
excess air [ in natural draft]• Pressurization of heater.
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Kochi Refinery
HEATER
Complete Combustion• Complete combustion occurs when 100% of the energy in the fuel is extracted There must be
enough air in the combustion chamber for complete combustion to occur.
• The combustion process is extremely dependent on time, temperature, and turbulence.
Excess Air • In order to ensure complete combustion, combustion chambers are Fired with excess air.
• Excess air increases the amount of oxygen and nitrogen entering the flame increasing the probability that oxygen will find and react with the fuel. [ Nox formation ]
• Addition of excess air greatly lowers the formation of CO.
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Kochi Refinery
HEATER
Excess Air = 100 x (20.9%) / (20.9% -O2m%) - 100%
Where O2 m% = The measured value of oxygen in the exhaust.
Examples:
When O2m% = 5%
Then: excess air = 100 x (20.9%) / (20.9%-5%) - 100% = 100 x (20.9%) / (15.9%) - 100% = 100 x (1.31) - 100%
excess air = 31%
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Kochi Refinery
HEATER sections
• Convection section.
• Radiant section
• Header box: internally insulated structural compartment separated from the flue gas stream which is used to enclose a number of headers or manifolds.
• Stack
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Kochi Refinery
HEATER sections
Convection section• Bare tubes at the bottom of the convection section shields the studded tubes from direct
radiation.• Normally 3 rows. Absorbs remaining 40-20% of total duty.• Core bells to prevent flue gas by passing around tubes.• May have additional waste heat recovery coils or super heating coils for efficiency
improvement.• Soot blowing area.
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Kochi Refinery
HEATER sections
Radiant section
• Absorbs 60-80% of total duty.• Radiation contribution -90%• Tubes are in Vertical or Horizontal.
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Kochi Refinery
HEATERParts/ terminology
• Bridge wall : Wall separating two adjacent heater zones.
• Arch: Flat or sloped portion of the radiant section opposite the floor.
• Damper: A device for regulating the flow of air or flue gas.
• Pilot : Small burner that provides the ignition source for the mail burner
• Atomizer : Device used to reduce a liquid fuel to fine mist using steam.
• Breeching: Heater section that where the flue gases are collected after the last convection coil for transmission to the stack or the outlet duct.
• Jump over: Inter connecting pipe work within a heater coil section.
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Kochi Refinery
HEATERParts / terminology
• Louver damper: Damper consists of several blades [ Combustion air Control]
• Corbel : Projection from refractory surface generally used to prevent flue gas bypassing the tubes in the convection section. if they
are triangular pitch.• Duct: conduit for air or flue gas
• Anchor / Tieback/ Jagger : a metallic or refractory material that holds refractory or insulation.
• Ceramic wool / Refractory bricks : Insulators
• SOB : Shut off Blind./guillotine blind : single blade isolation of air ducts in a heater , like blind.
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Kochi Refinery
HEATERParts / terminology
• Pass: flow streams: Flow circuits consisting of one or more tubes in parallel.
• Plenum wind box: Chamber surrounding the burner that is used to distribute air to the burners or reduce combustion noise.
• Primary air: Portion of the total air that first mixes with fuel.
• Setting loss: Radiation loss: heat lost to the surroundings from the casing of the heater and the ducts and auxiliary equipment's.
• Secondary air: Air supplied to the fuel to supplement primary air.
• Shield section/ shock section: Tubes that shield the remaining convection section tubes from direct radiation.
• Target wall/ reradiating wall: Vertical refractory brick which is exposed to direct flame impingement on one or both
sides.- mainly in DCU heaters. 21
Kochi Refinery
HEATERParts terminology
• Tube guide: Device used with vertical tubes to restrict horizontal movement while allowing the tube to expand horizontally while firing.
• Tube supports: Device used to support tubes.
• Tube retainer: Device used to retain horizontal radiant tubes from lifting off the intermediate tube supports during operation
• Vapour barrier: Metallic foil placed between layers of refractory as a barrier to flue gas flow.
• Soot blower: device used to remove soot or deposits.
• Strake/spoiler: metal attachment to a stack that prevent the formation of vortices that can cause wind induced vibration.
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Kochi Refinery
HEATERTUBES
• Bare Tubes.• Tubes with extended surface.
• Fins• Studs• Segmented fins
Bare tubes Studded tubes Fins Segmented fins
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Kochi Refinery
HEATER Tubes with extended surface
Solid fins.
• Most commonly used in gas firing heaters.
• Soot deposit chance is more.• Easy to fabricate.• Less pressure drop.
Segmented fins
• More prone to damage.• Higher heat transfer rate than
solid fins.• Higher pressure drop.• Rarely used in refinery.
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Kochi Refinery
HEATERTubes with extended surface
Studded tubes
• Used for oil firing /combination firing case.• Easier to clean.• Strong.• Costlier than fins.
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Kochi Refinery
HEATERTUBES
• Horizontal tubes –maximum 25m due to construction /handling problems.
• Vertical tubes- maxi. 18m due to limit large variation in the longitudinal heat flux distribution.
• Convection area -Normally all tubes are horizontally.
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Kochi Refinery
HEATERTube Metallurgies
• Carbon steel:- Reboiler, steam generator, super heater, hot oil etc.
• 5 Cr/ 9cr :- Crude, Vacuum ,Visbreaker, DCU.
• SS316L/317L:- Crude with high TAN. Vacuum with high TAN.
• SS347H:- Hydrotreter ,Hydrocracker, and Hydrogen.
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Kochi Refinery
HEATERSoot blower
Soot blowers.
• Soot blower remove the soot from the studded tubes in convection section.• Dry MP steam is used.• After soot blowing flue gas temperature leaving convection section increases.• Soot blower frequency is depended on the fuel used.• In case of Fuel oil case daily is recommendable.
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Kochi Refinery
HEATER Burner
Burners
Classification based on fuel• Fuel gas burner.• Fuel oil burner.• Combination burner.
Classification based on draft
•Natural draft.•Forced draft
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Kochi Refinery
HEATER Burners
Classification based on fuel air mixing
• Premix gas burner• Raw gas/oil burner.• Staged fuel burner• Staged air burner. Low Nox Burners.• Flue gas recirculation burner.
Classification based on NOx emission.
• Low NOx burner [ less than 50 ppm]• Ultra NOx burner. 20-50 ppm• Next generation or new technology burner -less than 10 ppm.
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HEATERBurners
Raw gas/ oil burner
• Can fire fuel oil fuel gas or combination.• Typical turn down ratio 3:1 [oil] and 5:1 [ gas ]
31mcj
HEATERBURNERS
Staged Fuel Burners
• Low Nox burner [ 40 ppm vd]• Typically 30% primary fuel and• 70% secondary fuel• High excess air in primary tip reduces flame temperature.• Low O2 in secondary tip results in longer combustion time
32mcj
HEATERBURNERS
Staged Air Burner
• Low Nox burner - [50-70 ppm vd]• More effective with combination firing.• Air is split into 2-3 zones to slow the combustion• Primary air to initiate combustion.• Secondary air to complete the combustion and maintain flame shape.• Tertiary air to control the flame outer temperature.
33mcj
HEATERBURNERS
Flue Gas Recirculation Burner
• Ultra Nox burner [ 25- 30 ppm]• A part of flue gas is circulated back into the flame to dilute air/fuel mixture.• Delayed combustion as well as cooler flame.• Very large spacing required between burners And burners are bigger in size.• Very tall flames.
34mcj
HEATERBURNERS
New technology next generation Ultra Nox burner
• Nox less than 10 ppm• Employ combination of staged air, staged fuel, flue gas recirculation methods.
35mcj
HEATEROur fuel specifications
Fuel oilLHV 9500-10000Viscosity @ 185oc 19-23 cstSulphur .4-.7 %N2 2000ppmNa 90-170ppmVa 2.5 ppmCCR 14-19 %C/H ratio 8.1 -8.3Nickel 36-52ppm
Fuel GasLHV 9000
H2S 300ppm
H2 15-20 %
C1 25.3%
C2 19.6%
C4 4%
C5 .2%
C6 Nil
mcj 36
HEATEREfficiency
Fuel efficiency• Total heat absorbed divided by the total input of heat derived from the combustion of fuel
only. [Lower heating value basis.]
Thermal efficiency• Total heat absorbed divided by the total input of heat derived from the combustion of fuel plus
sensible heats from air fuel and any atomizing medium.
• The heat absorbed is equal to the total heat input minus the total heat losses from the system.
Total heat input – Stack losses – Radiation heat losses Efficiency = X 100 Total heat input
37mcj
HEATERChecking
1. Tube external corrosion ,tube crack , colour change, bend.2. Arch area refractory damage.3. Bottom refractory damage, refractory bulging, bottom body bulging.4. Flame impingements on tubes.5. Coking on oil/ gas burners.6. Atomization of fuel oil.7. Fuel oil temperature/ viscosity.8. Tube over heating by flame impingement/ coking/ low coil flow.9. Tube support / retainer damages.
38mcj
HEATERChecking
11 . Heater body red hot / paint damage due to over heat12 . Refractory damage.13 . Flame flash back.14 . Flame lift off [ high draft, high fuel gas pressure, atomizing steam / fuel oil
Dp more]15 . After burning or secondary combustion.[ re- ignition CO in convection
section ]16 . Pilot burner tip damages17 . Flue gas / combustion air leakages through burner plenum chamber.18 . Pilot lite off.19 . Skin temp raise20 . Arch temp raise
39mcj
HEATERChecking
21 . Stack temp high/low.22 . Fuel oil/ gas leaks.23 . Incomplete combustion [ black smoke ]24 . More excess air [ over bright flame, and white smoke on stack]25 . Intermittent flame/ flame height more.26 . Condensate in atomizing steam[ sparkling flame].27 . Condensate in fuel gas.28 . High fuel oil/ gas firing pressure29 . Hot spots on tubes.30 . Flue gas leaks through air ducts.
40mcj
HEATERChecking
31 . Check fuel oil pressure temp and flow , and steam tracing.32 . Ensure atomizing steam pressure, and condensate free.33 . Skin temperature- normal value 450- 4800C
34 . Stack damper condition35 . Air leaks[ open doors ,bolts joints]36 . Burner flame shape height , smoke.37 . Abnormal flue gas temperature in convection section.38 . O2 level in stack- 2-3% normal39 . Draft/ arch pressure.40 .Combustion air damper, opening. hot spot ,flame back up.
41mcj
HEATERChecking
41 . Individual burner valve opening [ should not be pinched]42 . Individual burner air damper opening [ should be same for all burners]43 . Fuel oil viscosity, return header flow, steam tracing.44 . Dp of atomizing steam / fuel oil.45 . Burner tile conditions46 . Abnormal noise, whistling sound.47 . Flue gas temperature at APH inlet and outlet.48 . ID suction temperature.49 .Fluid coupling loading/ VFD . rpm indication.50 . Bearing cooling water temperature/ flow.
42mcj
HEATERChecking
51 . Any abnormal sound/ vibration on coil jump over.
52 . Coil jump over supports ,coil outlet supports outside heater.
53 . Convection inlet flange leak, pressure reading.
54 . Igniter working condition.
55 . ID , FD motor amperages.
56 . Leakages through ID, FD , and ducts.
57 .ID, FD inlet outlet damper opening.
58 Clogging of FD inlet filter.
59 . ID suction pressure.
60 . ID, FD bearing temperature, vibration, sound.
43mcj
HEATERChecking
61 . Soot blower steam valve conditions62 . Soot blowing steam condensate traps.63 . Soot blower poppet valve opening / closing/ passing.64 . Soot blower shaft condition after soot blowing[ retract or not]65 . Damage of castable refractory after soot blowing.66 . Pilot conditions, pilot air register condition, any flame flash back through pilot.67 . Convection outlet temperature reading68 . Radiation outlet individual pass out let temperature.69 . COT.70 . Box purging steam any passing.
44mcj
HEATERChecking
71 . Peep hole damages, glass damages, rope damages etc.72 . Atomizing steam, fuel oil, gas valves passing/ gland leaks/wheel damages.73. Lp gas burner status. Lp gas flame arrestor dp. Lp gas pressure.74 . Hot well gas burner conditions. Flame arrestor dp, line plugging, condensate
carryover etc.75 . Hot well gas knock out drum level.76 . Fuel gas knock out drum level.77 . Fuel gas c/v SDV status, opening, gland leaks, SDV solenoid valve.78 . Fuel oil c/v SDV supply and return status.79 . Fuel header PCV opening [ supply/ return tie up].80 . Fuel oil heater steam/ condensate flow, temperature.
45mcj
HEATERChecking
81 . Fuel oil supply return header pressures at battery limit.82 . Oil leakages through oil guns.83 . Any abnormal fuel gas/ flue gas smell near heater.84 . Leakages through SOBs.85 . Any instrument air leaks, near c/v s stack dampers.86 . Stack damper openings.87 . Acid corroded spots on the body.88 . Explosion door opening.89 . Analyzers readings.90 . Insulation damages.
46mcj
HEATERChecking
91 . Heat resistant paint damage on heater body.92 . Heater body red hot bulging.93 . Velocity steam dryness.94 . Any abnormal vibration of coils due to velocity steam.95 . Radiation out let/ swing elbow flange leaks.96 . Oil soaking in insulation while start up after shut down.97 . Heater transfer line flange [ at column nozzle ] leak. 98 . Pass control valve openings, gland leak, coil pressure.99 . Emergency steam to be closed while heater starting.100 . Ensure plant air line blinds.101 . Ensure coil minimum flow.
47mcj
HEATERDecoking
Thermal decoking : Using air and steam inside tubes , controlled firing in heater. [ It take more time, chance to tube metallurgy damage]
Mechanical decoking : Using water with pigs inside the tubes.
On line Spalling : Steam inside tube and firing in heater. One individual pass can be done on line. Coke removed by thermal shock. [ only in DCU heater]
48mcj
HEATERdry out
• To be done after heater long shut down work or refractory work .• Controlled fire inside the furnace and steam inside the tubes .
49mcj
HEATERproblems - reasons
Internal tube corrosion sulphur and naphthenic acid corrosionExternal tube corrosion metal oxidation, and by H2S04Erosion High velocity with solids, impingement on
fitting
Polythionic acid corrosion [ for steel tubes]on tube outside.
In hydro cracking /hydrode-sulphurisation heaters only.
Creep rupture damage Due to high tube temp [ skin]Hot spot / tube bulging Due to coking inside tube , flame
impingement , and by low coil flow /velocity.
Coking on fuel oil gun / oil dripping High viscosity , poor atomization , improper gun guide tube fitting.
50mcj
HEATERproblems - reasons
Flame lift off high draftBack fire High arch pressure, burner coking , burner
tip damage , block inside burner chamberFlame impingement on tubes Burner tip coking , tip damage ,poor
atomizing .Sparkling flame Condensate in atomizing steamOver bright flame [ combination firing ] More excess airSmoky flame High fuel firing pressure , low combustion
air , poor atomizing , and burner cokingHigh arch pressure Over firing , stack damper/ ID problem ,
burner coke purging
51mcj
HEATERproblems - reasons
High arch temperature Over firing , flame lift off , high gas firing pressure , secondary combustion .
Pulsating fire [ alternately ignite and goes out]
Lack of air and low draft
Excess smoke on stack Incomplete combustion , burner coking , poor atomizing , burner tip damage , less combustion air , and heater tube failure
Burner tile damage Due to sodium Vandate corrosion , Tube coloure change Ash burning , coking inside tube , flame
impingement
Tube support damage Flame impingement , hammering of tubes high temp oxidation ,
52mcj
HEATERproblems - reasons
Tube sheet damage in convection section After burning , If Na, Va in fuel oil is more corrosion chance is more.
Refractory damages High arch temp, improper dry out , thermal shock due to fast temperature raise, soot blowing steam condensate , poor casting .
Hot spot / acid corroded holes on heater body
Refractory damages , flue gas entry inside the refractory bed gaps .
mcj 53
HEATER
mcj 54
EMERGENCIES ACTIONSPass flow control valve / flow failure Closely monitor individual pass outlet
temp , put c/v in MAN mode or open b/p b/v.
Fuel oil trip Rectify the problem and start oil firingFuel gas trip Rectify the problem and restart firingHeater total trip Restart after rectifying problem , ensure
proper coil flow , and furnace draft , and ensure pilot flame .
Heater tube failure shut down the heater from remote emergency switch , cut the coil flow, open emergency coil steam,
DO NOT
mcj 55
• Do not run heater with by passed interlocks • Do not pinch individual burners• Do not keep different openings in individual air louvers • In case of tube failure do not admit air into heater , use steam only • Do not run heater with fully closed stack damper
Use proper PPE s [ gloves , thermal protecting face shields ]
HEATERCrude heater start up after shut down
• Purge Fuel gas line with N2.• Reset FG / pilot SOVs and charge fuel gas.• Flush fuel oil lines to CBD , Reset supply /return SDV s.• Establish fuel oil circulation in supply and return headers.• Purge individual oil lines up to oil gun [ to a drum ] and insert oil guns.• Line up all instruments.• Start cold oil circulation inside heater coils.• Wide open stack damper and box purge heater with steam [ 20
minutes].ensure draft.
56mcj
HEATERCrude heater start up after shut down
• Start FD fan , open combustion air louvers, and purge heater with air.• Lite the pilot burners.• Lite FG burners. [ never lite from the adjacent burner]• Purge the FO burner with steam.• After gun purging open FO atomizing steam, then slowly open fuel oil and
adjust the flame.• After stabilizing start ID fan , and kept stack damper opening minimum .• Control arch pressure using ID fan speed, and stack damper opening.
57mcj
Thank Youmc jomon 58
