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
Vertical tube cylindrical heater
• Most common type refinery heaters.
• Vertical radiant tubes and horizontal
• 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
• Heat duty up to 40 MM K cal/hr.
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.
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.
Inverted wicket type
• Horizontal firing.
• Single or double firing.
• In situ hydro testing not possible.
• Eg. CCR
Helical coil heater
small heat duties up to 15 mm kcal/hr.
Not used in refineries.
Classification based on firing.
• Side fired -One side / both side.
• Bottom fired
• Top fired.
• Side fired Bottom fired Top fired 9
Classification based on fuel
• Gas firing
• Oil firing
• Combination firing
Gas firing Oil firing Oil + Gas firing
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.
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
• Draft is controlled by stack damper or by ID fan.
• Ideal draft in a natural draft furnace is -1 mm wc.
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
• Low air flow through burners , low
excess air [ in natural draft]
• Pressurization of heater.
• 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.
• 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.
Excess Air = 100 x (20.9%) / (20.9% -O2m%) - 100%
Where O2 m% = The measured value of oxygen in the exhaust.
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%
• 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.
• Bare tubes at the bottom of the convection section shields the studded tubes from direct
• 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
• Soot blowing area.
• Absorbs 60-80% of total duty.
• Radiation contribution -90%
• Tubes are in Vertical or Horizontal.
• 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.
Parts / 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
• Duct: conduit for air or flue gas
• Anchor / Tieback/ Jagger : a metallic or refractory material that holds refractory
• Ceramic wool / Refractory bricks : Insulators
• SOB : Shut off Blind./guillotine blind : single blade isolation of air ducts in a
heater , like blind.
Parts / 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
• Target wall/ reradiating wall: Vertical refractory brick which is exposed to direct flame
impingement on one or both sides.- mainly in DCU heaters.
• 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.
• Bare Tubes.
• Tubes with extended surface.
• Segmented fins
Bare tubes Studded tubes Fins Segmented fins
Tubes with extended surface
• Most commonly used in gas
• Soot deposit chance is more.
• Easy to fabricate.
• Less pressure drop.
• More prone to damage.
• Higher heat transfer rate than
• Higher pressure drop.
• Rarely used in refinery.
Tubes with extended surface
• Used for oil firing /combination firing case.
• Easier to clean.
• Costlier than fins.
• Horizontal tubes –maximum 25m due to construction /handling
• Vertical tubes- maxi. 18m due to limit large variation in the
longitudinal heat flux distribution.
• Convection area -Normally all tubes are horizontally.
• 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.
• 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.
Classification based on fuel
• Fuel gas burner.
• Fuel oil burner.
• Combination burner.
Classification based on draft
• Natural draft.
• Forced draft
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.
Raw gas/ oil burner
• Can fire fuel oil fuel gas or combination.
• Typical turn down ratio 3:1 [oil] and 5:1 [ gas ]
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
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
• Primary air to initiate combustion.
• Secondary air to complete the combustion
and maintain flame shape.
• Tertiary air to control the flame outer
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.
New technology next generation Ultra Nox burner
• Nox less than 10 ppm
• Employ combination of staged air, staged fuel, flue gas recirculation methods.
• Total heat absorbed divided by the total input of heat derived from the combustion of
fuel only. [Lower heating value basis.]
• 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
Total heat input – Stack losses – Radiation heat losses
Efficiency = X 100
Total heat input
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.
11 . Heater body red hot / paint damage due to over heat
12 . Refractory damage.
13 . Flame flash back.
14 . Flame lift off [ high draft, high fuel gas pressure, atomizing steam / fuel oil
15 . After burning or secondary combustion.[ re- ignition CO in convection
16 . Pilot burner tip damages
17 . Flue gas / combustion air leakages through burner plenum chamber.
18 . Pilot lite off.
19 . Skin temp raise
20 . Arch temp raise 39mcj
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 pressure
29 . Hot spots on tubes.
30 . Flue gas leaks through air ducts.
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 condition
35 . 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% normal
39 . Draft/ arch pressure.
40 .Combustion air damper, opening. hot spot ,flame back up.
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 conditions
46 . 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.
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.
61 . Soot blower steam valve conditions
62 . 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
67 . Convection outlet temperature reading
68 . Radiation outlet individual pass out let temperature.
69 . COT.
70 . Box purging steam any passing.
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
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.
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.
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.
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]
• To be done after heater long shut down work or refractory work .
• Controlled fire inside the furnace and steam inside the tubes .
problems - reasons
Internal tube corrosion sulphur and naphthenic acid corrosion
External tube corrosion metal oxidation, and by H2S04
Erosion High velocity with solids, impingement on
Polythionic acid corrosion [ for steel tubes]
on tube outside.
In hydro cracking /hydrode-sulphurisation
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
Coking on fuel oil gun / oil dripping High viscosity , poor atomization ,
improper gun guide tube fitting.
problems - reasons
Flame lift off high draft
Back fire High arch pressure, burner coking , burner
tip damage , block inside burner chamber
Flame impingement on tubes Burner tip coking , tip damage ,poor
Sparkling flame Condensate in atomizing steam
Over bright flame [ combination firing ] More excess air
Smoky flame High fuel firing pressure , low combustion
air , poor atomizing , and burner coking
High arch pressure Over firing , stack damper/ ID problem ,
burner coke purging
problems - reasons
High arch temperature Over firing , flame lift off , high gas firing
pressure , secondary combustion .
Pulsating fire [ alternately ignite and goes
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
Tube support damage Flame impingement , hammering of tubes
high temp oxidation ,
problems - 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
Refractory damages , flue gas entry inside
the refractory bed gaps .
Pass flow control valve / flow failure Closely monitor individual pass outlet
temp , put c/v in MAN mode or open b/p
Fuel oil trip Rectify the problem and start oil firing
Fuel gas trip Rectify the problem and restart firing
Heater 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 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 ]
Crude 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
Crude 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.