The document discusses improvements to coker heaters critical for converting heavy feedstock in refineries to valuable products like gasoline and diesel fuel. It outlines design parameters, operating issues, and proposes a new radiant coil re-tubing design to enhance performance and reduce overheating. Future upgrades to the convection section are suggested to further optimize heater efficiency in a planned revamping around 2026.

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Improving Performance of Coker Heaters
Ashutosh Garg
Furnace Improvements
Sugar Land, TX

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Coker Heaters
 Most critical heaters in the refineries
 Objective: Heavy feedstock is converted to higher value products, such as
gasoline, diesel fuel, LPG, and petroleum coke
 Delayed coking is an endothermic reaction with the heater supplying heat
 Coking in Tubes:
 Pressure drop goes up
 Tube metal temperatures go up
 The rate of coke deposition determine Coker heater run length
 Coke removal by steam spalling/pigging (1-4 days lost)
 Any shutdown for coke removal causes production loss
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Coker Heater Typical Design Parameters
 Inlet temperature
 500-600°F
 Outlet temperature
 900-950°F
 Coil Pressure Drop
 350-450 Psi (EOR)
 Condensate Flow Rate
 0.5–1% of heater feed
 Average Heat Flux
 < 10,000 Btu/hr.ft2 (Single
Fired)
 Mass velocity
 350-550 lb/sec.ft2
 Cold oil velocity
 around 6-10 ft/s
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Coker Heater
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 Twin Cell Box Type Heater
 Natural Draft Operation
 Horizontal Tube Arrangement
 Central Bridgewall
 Gas fired floor mounted Burners
 Process, SSH and SG Coils in
Convection Section
 Self- supported stack on top of
Convection Section
Existing Coker Heater
PROCESS COIL
4 BARE ROWS
SG COIL
7 FINNED ROWS
SSH COIL
2 FINNED TUBES
PROCESS COIL
7 FINNED ROWS
#1 #2
CELL-1 CELL-2
#1
#1
#2
#2
#4
#4#3

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Existing Coker Radiant Section
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Stack
Flue Gas Offtake Ducts
Convection Section
Platforms
Radiant Header Boxes (New)
Radiant Arch (New)
Coker Heater
(Isometric View)
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Coker Heater Operating Issues
Coking
 Frequent decoking requirement (every year)
 Short tube life around 5-6 years
Overheating and flame impingement on roof tubes
 Longer flame lengths
 Low roof tubes elevation
 Firing Imbalance
 Higher firing in outer cells by almost 30%
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Existing Geometry for CFD
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Burner 1 Burner 2
Cell 1
Zone 1 Zone 2
Inner cell
tubes
Outer cell tubes
No. of burners in
CFD model: 6
Design heat release
per burner: 3.0
MMBtu/hr

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Flue Gas Flow and Temperature Profile
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 Higher
velocity flue
gas is
observed on
the inner side
 Higher flue
gas
temperature
observed near
the inner cell
tubes
Existing Design
[°F]
[ft/s]

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Radiant Heat Flux Profile
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 Radiant heat flux for
inner cell tubes is
higher as compared to
the outer cell tubes
Existing Design
Inner Tubes Outer Tubes
[Btu/hr.ft2]

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Flue Gas Temperature around Tubes
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[°F]
Inner Tubes Outer Tubes
 Flue gas temperatures around
inner cell tubes and outer cell
tubes are significantly
different
Existing Design

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[°F]
Flue Gas Flow and Temperature Profile
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 High flue gas temperature and
velocity is reduced for the inner
tubes
Existing Operating[ft/s]

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Radiant Heat Flux
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Inner Tubes Outer Tubes
 Radiant heat flux is
similar for inner and
outer tubes for
operating case
Existing Operating
[Btu/hr.ft2]

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Flue Gas Temperature around Tubes
Inner Tubes
Existing Operating
[°F]
Outer Tubes
 Clearly, the difference in
flue gas temperatures around
inner and outer cell tubes
have reduced significantly as
compared to the design case
 This reduction is because
inner cells were fired at 30%
lower firing rate than outer
cells
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Design = 12 Psi
Average = 17.58 Psi
10
13
16
18
21
24
15-May-14 8-Jan-15 2-Sep-15 26-Apr-16 19-Dec-16 14-Aug-17
Pressure,(Psi)
TIME
Fuel Gas Pressure
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West Outer Cell West Center Cell
Design = 12 Psi
Average = 12.45 Psi
6
9
12
14
17
20
15-May-14 8-Jan-15 2-Sep-15 26-Apr-16 19-Dec-16 14-Aug-17
Pressure,(Psi)
TIME
Fuel gas pressure in outer cell is almost 40% higher than the fuel gas
pressure in inner cells

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1
(Pass
inlet)
5
10
31
(Pass
outlet)
800
810
820
830
840
850
860
870
880
890
900
1 2 3 4 5 6 7 8 9 10 11-15
TubeMetalTemperature,ºF
Tube No(s).
Operating: Inner Tubes
Operating: Outer Tubes
0.6°F
1.5°F
4.2°F
5.2°F
4.8°F
5.8°F
6.8°F
6.8°F
7.6°F
5.6°F
7.5°F
800
810
820
830
840
850
860
870
880
890
900
1 2 3 4 5 6 7 8 9 10 11-15
TubeMetalTemperature,ºF
Tube No(s).
Design: Inner Tubes
Design: Outer Tubes2.9°F
7.7°F
13.4°F
15.7°F
17.9°F
16.9°F
17.1°F
15.3°F
16.8°F
14.5°F
16.4°F
TMT Comparison with Existing Design
TMT difference between the inner and outer tubes has decreased
for each of the tubes for the operating case where inner cell
burners fire 30% lower than the outer cell burners
Existing Design Existing Operating

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Flue Gas Temperature Profile
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Operating Case
For operating case flue
gas temperature in the
inner cell has reduced
[°F]
Design Case

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Radiant Heat Flux Profile
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Design Case Operating Case
Radiant tubes heat flux
for inner tubes has
been reduced for the
operating case
[Btu/hr.ft2]

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Radiant Re-Tubing Proposed Options
(Design TMTs)
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The design tube metal temperature comparison for existing and proposed
options at design pressure of 215 psig:
Case Tube Details Material
Design
TMT, °F
Limiting
Design Metal
Temp, °F
Existing 3.5” NPS Sch 80 9 Cr-1Mo 1,240
1,300
Proposed Option-1
4” OD, 0.4” MWT
9 Cr-1Mo 1,285
Proposed Option-2 SS347H 1,500 1,500
Proposed Option-3
(Finalized Option)
4.25” OD, 0.5”
MWT
9 Cr-1Mo 1,300 1,300

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Radiant Coil Re-Tubing
 No. of radiant tubes: 62 per box
 Tube size: 4” OD, Sch 80
 Heat transfer area: 7,770 ft2
 Tube material: 9 Cr
 Coker Mass Velocity-295 lbs/s ft2
 Pressure drop-210 psi
 Total radiant tubes: 66 per box
 Addition of 4 new radiant tubes
 2 tubes installed at outlet and 2
at roof
 Tube size: 4.25” OD, 0.5” MWT
 Heat transfer area: 8,880 ft2
 Tube material: 9 Cr
 Coker Mass Velocity-347 lbs/s ft2
 Pressure Drop- 242 psi
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Existing Design Proposed Design
Radiant heat transfer area increased by 15% in the heater

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Revamped Heater Radiant Section
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Existing & Proposed Design
of Radiant Section
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New Radiant Tubes
(Each Cell)
New Radiant Tubes
(Each Cell)
ProposedExisting
CELL-1 CELL-2
#1
#1
#2
#2
#4
#4#3
#1 #2 #4#3
CELL-1 CELL-2

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Velocity Vectors
 Flue gas velocity near inner
tubes is very high and getting
deflected downward
 Flue gas velocity is shifted
downward with addition of baffle
 Roof tubes are away from flue gas
Adding refractory baffle at the top further improves the flue gas recirculation pattern
Existing Proposed Case with
Baffle
Proposed Case
[ft/s]

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Flue Gas Temperature Contours
Addition of refractory baffle further increased the distance of hot flue gas with
respect to roof tubes
 High temperature flue gas is
touching the inner roof tubes
 Shifting roof tubes reduces chances of
flame impingement / coking issues
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[°F]
Existing Proposed Case with
Baffle
Proposed Case

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Radiant Tube Heat Flux (Arch)
Maximum heat flux on roof tubes is reduced by ~4,200 Btu/hr.ft2
Proposed Case
Heat Flux 18,651 Btu/hr.ft2 Heat Flux 14,443 Btu/hr.ft2
Existing
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[Btu/hr.ft2]

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5,000
9,000
13,000
17,000
21,000
25,000
0 5 10 15 20 25 30
RadiantHeatFlux,Btu/hr-ft2
Radiant Tube No.
Comparison of Radiant Heat Flux
Existing
Proposed Case
Roof
Tubes
Wall
Tubes
Tube wise comparison of heat flux shows considerable reduction for roof tubes
Radiant Heat Flux – Inner Tubes
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Existing vs Proposed Design
Parameters Units Existing Proposed
Total Heat Duty MMBtu/hr 125.1 126.8
Process Heat Duty MMBtu/hr 112.1 114.2
Charge Flow Rate lb/hr 263,000 326,953
Outlet Temperature °F 950 935
Bridge Wall Temperature °F 1,620 1,552
Radiant Heat Duty MMBtu/hr 77.7 79.3
Radiant Heat Transfer Area ft2 7,770 8,880
Average / Maximum Radiant Heat Flux Btu/hr/ft2 10,000 / 17,000 8,932 / 15,184
Fluid Mass Velocity in Radiant Section lb/sec/ft2 295.9 431.0
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Future Revamping
 The convection section needs upgrading. Feed outlet
temperature from convection section is 650-660F as
compared to design of 710F.
 The flue gas temperature approach to the coker feed is
around 250-300 F and can be reduced significantly.
 Convection upgrade will substantially help the coker heater
further.
 Future revamping window opens up around 2026
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Thank you very much
 Questions and Comments are Welcome
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