a new approach to improving heater efficiency
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A new approach to improving heater efficiency
Ashutosh Garg, Furnace Improvements
1www.heatflux.com
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TROUBLESHOOTING
REVA
MPIN
GTRA
ININ
G
FIS
FIG. 1
Feed In Feed Out
450 °F 600 °F
Radiant SectionConvection Section
1,650 °FFlue gas
750 °FFlue gas
3,200 °FFlue gas
1,650 °FFlue gas
500 °F
Typical Fired HeaterFluid------ Convection section Radiant section
2www.heatflux.com
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TROUBLESHOOTING
REVA
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Conventional Approach to Efficiency Improvement
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Feed Out
450 °F600 °F
Radiant SectionConvection Section
1,650 °FFlue gas
900 °FFlue gas
3,200 °FFlue gas
1,650 °FFlue gas
500 °F
Flue gas
Flue gas
900 °F
600 °F
AdditionalConvection
Section
Additional Heat Transfer Surface in Convection Section
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TROUBLESHOOTING
REVA
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Split flow Fired Heater
Feed In Feed Out
450 °F 600 °FRadiant Section
ConvectionSection - I
1,650 °FFlue gas 3,200 °FFlue gas
1,650 °FFlue gas
500 °F
ConvectionSection- II
900 °FFlue gas
Flue gas
Flue gas
Split Flow in Split Flow out450 °F 600 °F
600 °F
4www.heatflux.com
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TROUBLESHOOTING
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www.heatflux.com 5
Typical Reformer Heater
Process heated in radiant section
Parallel passes, high volume, low pressure drop
Convection-Waste Heat Recovery ( HC reboiler or steam generation service)
Process Feed In Process Feed Out
Waste HeatRecovery Unit
1,600°F
750°F
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Split Flow Reformer Heater
Process fluid split into two streams
Main flow is heated through radiant section
Split flow is heated in the convection section.
Fluid mixed together at the radiant outlet
ProcessFeed In
ProcessFeed Out
Split Flow in
Split Flow Out
Waste HeatRecovery Unit
1,600°F
1,100°F
600°F
6www.heatflux.com
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TROUBLESHOOTING
REVA
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www.heatflux.com 7
Case Studies
Citgo Corpus Christi No. 4 Platformer Heater
Valero Texas City No. 2 Platformer Heater and NHT heaters (Reboilers)
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Citgo, Corpus ChristiNo. 4 Platformer Heater
Objective:Improve Efficiency
Stack temperature was 1100 F
No steam generation No air preheater
8www.heatflux.com
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Current Heater Operation
Parameter Units Operating Value
Total Heater Duty
MMBtu/hr
158.10
Radiant Heat Duty
MMBtu/hr
120.19
Convection Heat Duty
MMBtu/hr
37.91
Firing Rate MMBtu/hr
229.20
Efficiency % 68.989www.heatflux.com
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Flow Scheme - Before Revamp#4 Platformer Heater
StackStackStackStabilizerBtms
StabilizerBtms
Stripper Btms
Stripper Btms
To Plat. RX To Plat. RX
From Plat. RX.To Plat. RX
From Plat. RX
Stripper Btms
From Plat.RX
To Plat. RX
Stripper Btms
BURNERS
10www.heatflux.com
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Existing #4 Platformer Heater
INLET OUTLET INLET OUTLET INLET OUTLET
INLET
OUTLET
CONVECTION
SECTION
STACK
DAMPER
STACK
DAMPER
STACK
11www.heatflux.com
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StackStackStack
#1 In
#1 Out
In
#2 In
#2 Out
#3 InOut
In Out
#4 Out
#4 In
#3 Out
Proposed Conventional Design
High Pressure Drop
12www.heatflux.com
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Conventional Design with Series Flow
FUTURE ROWS
REBOILER COIL
PROCESS COIL
STACK
INLET
OUTLET
INLET
OUTLET
INLET/ OUTLET
INLET/ OUTLET
OUTLET OUTLET OUTLET
OUTLET
RADIANT
SECTION
CONVECTION
SECTION
13www.heatflux.com
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Comparison of Pressure Drop at 22,000 BPD
Pressure Drop, psi
Original Design
Series flow Design
Cell 1 3.1 4.5
Cell 2 3.3 4.6
Cell 3 1.2 2.5
Cell 4 1.1 2.3
Total 8.7 13.9
14www.heatflux.com
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TROUBLESHOOTING
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Disadvantages
Higher pressure dropsLarge Size pipingLarge Convection SectionsHigher costs
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FIS Split Flow* Scheme
StackStackStack
Burners
#1 In
#1 Out
In
#2 In
#2 Out
#3 In
#3 Out
#4 In
#4 Out
In
Out
Out
* Split flow - US Patent
16www.heatflux.com
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FIS Split flow * design- Proposed
INLET INLET
INLET
INLETOUTLETOUTLET OUTLET
OUTLET
DAMPERDAMPER DAMPER
REBOILERCOIL
PROCESSCOIL
STACKSTACKSTACK
CONVECTION
SECTION
RADIANT
SECTION
* Patented.17www.heatflux.com
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Comparison (Cell 1) Parameters at 22,000 BPD
Parameter Original Design
Split flow Design
Pressure Drop, psi 3.1 2.1
Firebox temperature, F
1,615 1,551
Radiant flux, Btu/hr ft2
19,823 15,047
Radiant tube metal temp, F
1,151 1,120
Firing rate, MMBtu/hr 116.35 82.65 18www.heatflux.com
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#4 Platformer Heater Data Comparison
Item Units Before Revamp
After Revamp
Capacity BPD 18,500 24,000
Heat Duty MM Btu/hr
158.0 194.5
Heat Release
MM Btu/hr
234 225
Efficiency % 67.50 86.60
Stack Temp.
°F 1,092 478
Fuel MSCFH 244 242.8
Fuel Savings
$/annum 5.8 Million**Based on $6.0 / MM Btu
19www.heatflux.com
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#4 Platformer Heater Before and After Revamp
20www.heatflux.com
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Case Study-2
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TROUBLESHOOTING
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FISPlatformer Heaters - Existing
Common Convection section with H-18/H-19 and H-23
Process heating-all Radiant
Steam Generation in Convection
Common Stack
Natural Draft
22www.heatflux.com
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Platformer Heaters (H-20/21/22)
Parameter Units Original Design
Total Heater Duty MMBtu/hr 155.98
Radiant Heat Duty MMBtu/hr 74.09
Convection Heat Duty MMBtu/hr 81.89
Radiant Fuel Efficiency % 54.2
23www.heatflux.com
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TROUBLESHOOTING
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Plan View of heater
24www.heatflux.com
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Convection Section
Steam Generator Bank Steam Superheater
Bank BFW Preheater Bank Steam Generation:
73,669 lbs/hr@464 psig
14 tubes per row Eighteen rows Two future rows
25www.heatflux.com
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H-18- Hydrotreater Charge Heater
Duty-11.97 MMBtu/hr All Radiant Single pass 5 burners 24 tubes P9 metallurgy 8“ NPS tubes 16” spacing Efficiency -55%
26www.heatflux.com
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H-19 Hydrotreater Stripper Reboiler
Duty-18.45 MMBtu/hr All Radiant Four passes 5 burners 56 tubes CS 4” NPS tubes 8” spacing Efficiency -54%
27www.heatflux.com
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TROUBLESHOOTING
REVA
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H-23 Depropanizer Reboiler
Duty- 15.15 MMBtu/hr All Radiant Two pass 6 burners 52 tubes CS 4” NPS tubes 8” spacing Duty- 56%
28www.heatflux.com
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Field Survey
High draft in all the radiant cellsBurners flame spread outVery high fuel gas pressuresBowed tubes in H-21/H-22Stack dampers are fully openHigh excess Oxygen in all the cellsBurner registers practically closed
29www.heatflux.com
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Operating Data Simulation Results
Convection section was in bad state Fins are burnt out / fouled Steam superheater temperature is 40 F
lower than design Thermal Efficiency is 78-81% compared
to 88% design. Stack temperature is higher by almost
275 F. Stack temperature ~ 675 F
30www.heatflux.com
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Conventional Scheme
Waste heat recovery( with new convection section retubed in
kind) It would not have
solved any of the problems linked to over firing of the heaters
Description Units Design
Stack temperature °F 404
BFW flow rate Lb/hr 94,000
SSH flow rate Lb/hr 92,120
SSH temperature °F 623
Steam pressure psig 472
31www.heatflux.com
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Split Flow Scheme
H-20/H-21/H-22 Limit radiant heat flux to 15,000 Btu/hr ft2 Shift the balance duty to convection section
H-18/H-19/H-23 Limit heat flux to 8,000-9,000 Btu/hr ft2 Limit the firing to design rate Limit the volumetric heat release to 10000
Btu/ft3 Shift the balance duty to convection section
32www.heatflux.com
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Valero Proposed Revamp – Split Flow Scheme
33www.heatflux.com
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Split Flow for H-20/H-21
H-20- 3 Bare RowsH-21- 2 Finned Rows
34www.heatflux.com
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H-18/H-19/ H-23 Revamping Options
H-18/H-19/H-23 Heaters All Radiant Heaters Design Efficiency- Low -51-53% Operating Efficiency- 42-52% High Draft Very tight design
35www.heatflux.com
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H-18/H-19/H-23 Revamping Options
Do nothing High firing rates, firing limitation Existing burners may not handle
Add convection sections on each heater Good option Expensive
Add heat transfer surface in main convection Two rows Economical
36www.heatflux.com
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TROUBLESHOOTING
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Valero Proposed Revamp – Split Flow Scheme
37www.heatflux.com
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H-18/H-19/H-23 Split Flow
H-18- 8 tubesH-19-12 tubesH-23- 8 tubesTotal- 2 rows of tubes
38www.heatflux.com
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Split flow Convection Section
Heat Recovery Sequence H-20 H-21 H-18 / H-19 / H-23 Steam
Superheating Steam Generation BFW Preheating
Total no. of rows – 20
Convection section dimensions unchanged
39www.heatflux.com
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Proposed Split Flow Revamp
Advantages Lower Pressure drop in all heaters Reduce Heat Flux – 15,000 Btu /hr ft2 Lower Firing Rate – 203 MMBtu /hr Lower Volumetric Heat Release More efficient system - 88% No civil works
40www.heatflux.com
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Split flow – Control Scheme
Balancing of heat transfer and pressure drop by:Variable resistance (butterfly control
valve)Split stream outlet temperature
control by adjusting convection section flow
41www.heatflux.com
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Advantages of FIS Split flow scheme
Lower pressure drop (process)Lower firing rateLower fire box temperaturesLower radiant heat fluxesLower tube metal temperaturesLesser turnaround timeLower installation cost
42www.heatflux.com
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Thank you very much
Questions and comments are welcome
43www.heatflux.com