A new approach to improving heater efficiency

A new approach to improving heater efficiency

Ashutosh Garg, Furnace Improvements

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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

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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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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

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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

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

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Case Studies

Citgo Corpus Christi No. 4 Platformer Heater

Valero Texas City No. 2 Platformer Heater and NHT heaters (Reboilers)

Citgo, Corpus ChristiNo. 4 Platformer Heater

Objective:Improve Efficiency

Stack temperature was 1100 F

No steam generation No air preheater

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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

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

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Existing #4 Platformer Heater

INLET OUTLET INLET OUTLET INLET OUTLET

INLET

OUTLET

CONVECTION

SECTION

STACK

DAMPER

STACK

DAMPER

STACK

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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

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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

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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

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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

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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

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

#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

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#4 Platformer Heater Before and After Revamp

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Case Study-2

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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

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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

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Plan View of heater

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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

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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%

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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%

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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%

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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

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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

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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

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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

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Valero Proposed Revamp – Split Flow Scheme

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Split Flow for H-20/H-21

H-20- 3 Bare RowsH-21- 2 Finned Rows

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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

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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

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Valero Proposed Revamp – Split Flow Scheme

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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

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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

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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

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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

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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

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Thank you very much

Questions and comments are welcome

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