10d Troubleshooting Crude Heaters

Training Services

Troubleshooting  Crude and Vacuum  Heaters

FH/10-1

Crude Heaters

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Most Important Heater in refinery  –

Affects entire refinery

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Large energy consumption

Very forgiving  –

Two phase flow-high heat transfer

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Low pressure operation

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Tube leak not dangerous

FH/10-2

Crude Column

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Arab Light Crude

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61% volume lift

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Heat input is 423 Btu/lb or 128,000 Btu/BBL.

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Crude Exchange Train 55% Heat Input ($0.21/BBL)

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Crude Heater 45% Heat Input($0.17/BBL) FH/10-3

World Class Crude Heaters 

Air Preheat with 92.5% fuel efficiency

FH/10-4

 Ras Tanura Crude  Exchange Train •World Class 550°F • Vertical crude-ovhd exchange • Flash Drum to control vapor pressure at heater control valve • Exchanger Bypass valves for cleaning FH/10-5 EXC-Roo-09

Crude Heater Coking Problems

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Benchmark- 6” tubes-200MV @ 10,000 Flux rate  –

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High Flux Rate with low pass flow causes coking

Outlet Temperature Range 640°F-735°F  –

Cracking initiates around 700°F

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Low coking potential @ 640-680°F

Low pass Flow  –

Limit pass balancing to 10%

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Clear heater passes during power failure

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Monitor pass P and % control valve opening

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Flash Drum Vaporization- 5-10% maximum FH/10-6

Crude Heater Coking Problems

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Asphaltene Precipitation

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Salt Precipitation

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High Oil Film Temperature

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Local Overheating

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Improper Pass Purging  –

-emergency shutdown

FH/10-7

Crude Heater Coking Problems 

Asphaltene Precipitation  –

Opportunity Crudes

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Crude Blending Incompatibility

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Exchanger Fouling in last two services

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Loss of Inlet Temp > (7 C/year) •

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Benchmark-Heater Inlet 260 C (500 F)

Solutions  –

Crude Compatibility Testing •

Soluble Solutions(www.SolubleSolutions.com)

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Phone:908-470-0847

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Spriref Spings

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Exchanger Bypassses and On-line Cleaning FH/10-8

Crude Desalter 

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Operates 121°C (250°F)

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Removes salts in crude

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Removes some Filterable Solids

FH/10-9

Crude Heater Coking Problems 

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Salt Precipitation  –

Poor Desalting

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Caustic Injection

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Loss of Inlet Temp > (7 C/year)

Solutions (Optimize Desalter)  –

(90% efficiency per stage)

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4-6% water wash rate(water quality)

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1/3 water to upsteam exchanger train

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Demulsifier 4-8 ppm

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Mix Valve P Optimization(typical 0.5 bar)

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Acidic Ph

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Limit caustic injection(3-5ppm) with 30 ppm Cl in ovhd water

FH/10-10

Crude Heater Coking Problems

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Asphaltene Precipitation  –

Opportunity Crudes

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Crude Blending Incompatibility

Salt Precipitation  –

Poor Desalting

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Caustic Injection

High Oil Film Temperature  –

High Flux-low mass velocity design

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Outlet temperatures around 388°C (730°F)

FH/10-11

Crude Heater Coking Problems 

High Oil Film Temperature  –

High Flux-low mass velocity design •

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(150 lb/sec-ft2 @ 12,000 Btu/h-ft2)

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Outlet temperatures around 388 C (730°F)

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Skin Temp Rise > (12 C/year)

Solutions  –

decrease number of passes(expensive)

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1-2% condensate injection to heater inlet

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potential column flooding

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water disposal

frequent pig cleaning

FH/10-12

Crude Tube Deposit  

Typically 85% organic -15% inorganic deposit

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LOI Test for % organic

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4 mm thickness gives 50-60°C TWT rise

FH/10-13

Crude Tube Deposit  

Oil Fired Heater

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Light color is ash deposit

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Dark color is 7-10 mm coke in tube

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Ash Deposit melt around 670°C(1240°F)

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Coke caused by not clearing oil from pass during power failure

FH/10-14

Crude Heater Tube Failures 

Local Hot Spot- Internal Coke Deposit-External Pitting

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Replace at 3-5% diameter growth

FH/10-15

Crude Heater Tube Failure

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Leaking Tube

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Most Failures Caused by Flame Impingement

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Poor Burner Maintenance

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Control O2 Level high enough to keep flames off the tubes

FH/10-16

Crude Heater Shock Tube Failure 

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Often the hottest tube in the heater Flame Impingement Problems

FH/10-17

 Poor Low NOx Burner Retrofit 

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Flames Are Too Long for 20 foot(6 m) Firebox Height

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Flame Height Should be 50% of Firebox Height

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High BWT

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Hot Roof Supports

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Poor Revamp

FH/10-18

 Burner Problems 

Burner Problems cause most tube failures

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Burners are in bad condition

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New Burners are recommended

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Oil and steam should have flexible hose connections

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Hard piping have oil gun at wrong height

FH/10-19

Crude Heaters

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Flames Are Proper Height

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Flame Height Should be 50% of Firebox Height

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Good Heater Design

FH/10-20

Vacuum Unit  

700- 760°F Flash Zone

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20- 100 mm Hg Flash Zone

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Higher Temperatures, more coking potential

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Wet, Dry, Damp Units

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Minimize transfer line

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Heater located minimum

∆P

distance from column

FH/10-21

 Deep Cut Operations

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1100°F (593°C) Cut Point

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Low Flash Zone-20-30 mmHg

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Heater Outlet-800 F(426 °C)

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Steam Injection  –

0.5 wt% to heater

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1.0 wt% to column boot

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Low Transfer Line Pressure Drop

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Low Radiant Flux Rate

FH/10-22

Vacuum Column Transfer Line 

Design for 2-4 psi

∆P

to give 15-35°F rise at heater

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Minimize flow disturbances(erosion-corrosion problems)

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Thermal Expansion Concerns

FH/10-23

Vacuum Heaters

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Benchmark- 4-6” tubes-250MV @ 8,000 Flux rate  –

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Outlet Tube 8’-10”

Outlet Temperature Range 735°F-800°F  –

Cracking problems around 11,000 flux

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High coking potential @ 800°F

Pass Balancing  –

Limit pass balancing to 10%

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Clear heater passes during power failure

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Monitor pass P and % control valve opening

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Steam Injection-0.5 wt% FH/10-24

Vacuum Heater  

Modern Vertical Tube design minimizes hot residence time

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Accommodates new low NOx burners better

FH/10-25

Vacuum Heater Crossover Lines 

Liquid Phase until the last few tubes

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Local TI gives convection duty

FH/10-26

Vacuum Heater  

Increase tube diameter at point of vaporization to minimize temperature rise

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Steam injection at vaporization point

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Sonic velocity (380-420 fps)

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Locate Large outlet tube in cold location

FH/10-27

Vacuum Heater  

0.5 wt% steam injection at point of vaporization to reduce temperature peaking

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Removeable pipe spool on outlet for tube pigging

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Swing elbow for decoking

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Outlet TI on each outlet

FH/10-28

Cracking Monitoring  (Ejector Off-Gas&Ovhd Drum Liquid)

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Normal 0.15 Wt% Dry Gas

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Normal 0.4 Wt% Naphtha

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Normal 1.0 Wt% Distillate

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Maximum 0.3 Wt% Dry Gas

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Maximum 0.75 Wt% Naphtha

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Maximum 2.0 Wt% Distillate

FH/10-29