delayed coker fired heaters

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© 2010 KBC Advanced Technologies plc. All Rights Reserved. Delayed Coker Fired Heater Design and Operations Sim Romero Rio Oil & Gas 2010 13-16 September 2010 Riocentro Convention Center Rio de Janeiro, Brazil IBP2714_10 Como Conquistar a Liderança de Mercado Na Nova Década

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Page 1: Delayed Coker Fired Heaters

© 2010 KBC Advanced Technologies plc. All Rights Reserved.

Delayed Coker Fired HeaterDesign and OperationsSim Romero

Rio Oil & Gas 201013-16 September 2010

Riocentro Convention CenterRio de Janeiro, Brazil

IBP2714_10

Como Conquistar aLiderança de Mercado

Na Nova Década

Page 2: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 2

The fired heater is the key piece of equipment in the delayed coker - delivering the correct thermal conditions to drive cracking and coking reactions

The objective is to keep the heater from coking or fouling as long as possible and still get the result needed Sufficient heat is needed to drive thermal

cracking and polymerization reactions in the coker

High heater outlet result in less coke and more liquid products – incremental gas oil is of very poor quality

Low heater outlet temperature result in several coke drum operating problems (foaming, hot spots etc…)

Page 3: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 3

Why Do Coker Heater Foul - ChemistryThermal Cracking Is Both Cracking And Polymerization

The polymerization or coking kinetics are a function of;

• Feed quality (i.e. asphaltenes, concarbon, sulfur etc…)• Feed contaminates (i.e. sodium, iron oxides/sulfides, general

inorganic solids)• Heater operating conditions – time at temperature and heat flux

0 500 1000 1500 2000 2500 3000Boiling Point, °F

CokeLiquids

Vacuum Resid or

other coker feeds

cracking polymerization

Delayed coker furnace fouling is a complex function of the thermal kinetics

Page 4: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 4

Why Do Coker Heater Foul - Feed Quality Issues

Feed quality is primary factor affecting heater run length

Asphaltene content increases exponentially as the API gravity decreases

Asphaltene and concarbon content are strong indicators of fouling rates

Page 5: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 5

Why Do Coker Heater Foul - Operating Conditions

The coke thickness acts as an insulation to heat transfer causing the tube wall temperature to increase.

Q =

Coke formation occurs at the boundary layer where the velocity is low and the temperature is high.

High Heat Flux and Low Velocities Increase Tube Fouling/Coking

Tube Skin Temperature

Heat Flux

Surface Area

Heat Flux

x

Page 6: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 6

Why Do Coker Heater Foul - Operating Conditions

Clean ConditionsOutside Tube Wall Temperature Slightly Greater Than Boundary Layer Temperature - Thermal Resistance Due To Metal Wall

Fouled ConditionsOutside Tube Wall Temperature Significantly Greater Than Boundary Layer Temperature -Thermal Resistance Due To Metal Wall And More Importantly The Coke Deposited On The Tube

Page 7: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION7

Why Do Coker Heater Foul - Contaminates Salts, iron oxides, oxygen and other contaminates can accelerate heater fouling – at times acting like a catalyst to coking in the heater tubes

Sample Date 3/24/2005 3/24/2005 3/24/2005 10/4/2005 10/4/2005

Moisture (as received, %) 10.4 7.05 7.3 1.66 1.8

Ash (%) 38.49 37.57 35.55 17.39 27.34

Analysis of AshSilicon (dry, ppm) 10,270 15,240 14,190 5,623 4,551

Iron (dry, ppm) 241,100 169,400 272,700 301,900 312,000

Vanadium (dry, ppm) 1,699 2,140 1,760 19,910 8,577

Nickel (dry, ppm) 1,023 1,607 1,393 15,880 3,037

Aluminum (dry, ppm) 251 111 2,385 2,645 2,506

Calcium (dry, ppm) 7,799 12,230 9,225 10,130 15,910

Sodium (dry, ppm) 5,439 7,227 3,954 7,004 19,800

Magnesium (dry, ppm) 2,764 3,196 2,107 842 3,519

Crude Unit Desalter Performance Significantly Affects The Delayed Coker Heater

Typical Coke In Furnace Tube Analysis

Page 8: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION8

Design Parameters To Mitigate Coking In The Heater Tubes

SingleFired Tube

DoubleFired Tube

Uneven flux distributionpeak to average heat flux is about 1.8

Even flux distributionpeak to average heat flux is about 1.2

Single vs. Double Fired Heater Tubes

For an average heat flux of

10,000 BTU/Hr/SqFtthe peak flux on the

tube will be

18,000 BTU/Hr/SqFt

12,000 BTU/Hr/SqF

t

Double fired heater design reduces the peak flux and allows for higher average flux rates – the average flux should, in a new design, still be limited

Page 9: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 9

Higher velocities – velocity steam • Helps to reduce fouling by

removing coke as it form in the tubes

• Improves the heat transfer rate in the boundary layer

• Reduces the residence time in the heater

Higher velocities – velocity steam• Increased sour water• Increased pressure drop thru heater• Increased tower loading• Increased drum and flash zone velocities

Increased velocity steam will help reduce coke fouling but at a cost (drum solids carry over, tower flooding, sour water etc…)

Page 10: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 10

Design & Operating Parameters – Firebox Flame impingement will rapidly foul the

affected area Ultralow NOx burners have very small fuel

orifices at the burner tip and will plug with time The fuel should be filtered with a fuel gas

coalescer The fuel gas line from the coalescer to the

burners should SS Steam trace the fuel gas line – especially

in cold climates

In a retrofit the box height needs to be reviewed - ultralow NOx burner extend the flame and can cause flame impingement

Flame impingement can rapidly foul the heater coil

Page 11: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 11

Design & Operating Parameters – Tube Metallurgy Tube metallurgy – 9 Chrome vs. SS 347 SS Sch 80 tubes design temperature limit is much higher ~1400ºF The higher temperature limit may not be possible if you spall because o

f the coke thickness at temperature higher than 1300ºF The coefficient of expansion is much greater than 9 Chrome, which can

be good for spalling but can cause problems with uneven tube growth or shrinkage and keeping the tubes from moving off their supports

SS can significantly reduce scale on the outside of the tube External tube ceramic coating

Effective in reducing scale Can shift the heat load away from high heat flux and high tube wall

temperature zones Will slightly increase firing rates SS tubes are a good replacement for 9 Chrome but some of the perceived

benefits of longer runs may not be possible due to excessively thick coke in the coil and the difficulty this presents for spalling

Page 12: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 12

Design & Operating Parameters – Firebox Oxygen Control

O2 levels can be controlled too closely (less than 3%) – run higher O2(greater than 5%) will help reduce fouling by lowering the tube wall temperature Higher O2 will shifts heat to convection section and reduces radiant

flux rates Higher O2 will lower peak by lowering the tube wall temperature Increasing the O2 from ~3% to ~8% will lower the tube wall

temperature by ~75ºF Multiple O2 analyzers are needed in a typical fire box

Air preheat systems Good way to improve efficiency but are costly Startup procedures need to be well thought out with air preheat

systems – generally start with the on natural draft 1st

Because of the severe coking issue in a delayed coker heater the O2 levels should be relaxed to 5% to 8%

Page 13: Delayed Coker Fired Heaters

Heater Design and Operations

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Design & Operating Parameters – Temperature Of The Heater Outlet

Location of Thermowell Perpendicular to pipe location results in a short thermowell and can

lead to errors in measurements Poor insulation around the TW can cause poor measurements Return bend location gives better performance Decoking methods need to be considered with the location of the

thermal wells Metallurgy or special hardening should be required to prevent erosion Some locations are using the process temperature two to four tubes

back in the process

Badly installed thermowells can significantly effect heater performance short thermowell longer thermowell

Straight run out of heater

First 90º bend out of heater

Page 14: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION 14

Operating Parameters – Heater Outlet Temperature

The objective is to deliver sufficient heat to the coke drums – the drum inlet should be about 890ºF to 900ºF

The outlet temperature can vary depending on: Feedstock – paraffinic feeds require more heat due to increased cracking Lighter boiling point distribution in feed will vaporize in the transfer line

and enter the drum cooler High pressure drops in the transfer line will increase vaporization in the

transfer line and enter the drum cooler – also create high backpressure and lower velocities in the heater coil

Heat loss in the transfer line and coke drums will require added heater outlet temperatures

What should the outlet be set to Enough to avoid problems in the drum – foaming, excessively soft coke

and hot spots Enough to meet coke quality specifications i.e. anode coke VCM specs

Page 15: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION

Steam-Air Decoking Difficult and labor intensive – must watch air/steam ratio to prevent overheating the

tubes with accelerated combustion Not practices as much Requires a heater/unit shut down Can cause damage to the tubes if the tubes are overheated – carburization of tubes Requires some spalling to remove the bulk of the coke before the actual air burn

Pigging or mechanical coke removal Very easy for operations – contracted work Requires heater/unit shut down Can work inside heater box simultaneously (but not common) Can damage the tube if the pig metal studs are improperly used

o Tungsten carbide has a Brinell hardness of 600-800o Most furnace tube materials, will have a Brinell hardness of 150-225

Online Spalling Can be difficult initially – operation needs to walk through the process carefully –

detailed MOC Does not require unit shutdown Every effective in removing coke in the lower radiant section of the heater – not

effective for removing inorganic solids in the convection section of the heater Risk of plugging the coil if the spall is done too aggressively and/or if there is too

much coke in the tubes – ¼ “ is a good maximum thickness Return bend in the heater and 90º bend directly outside the heater need to be thicker

to prevent erosion from spalling coke

General practice is to online spall and pig decoke when the opportunity arises

Page 16: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION

Fouling rates and monitoring heater operations Design should be for less than 1.5ºF/day Greater than 3ºF/day implies an operational

problem or excessively high heat flux 3ºF/days = 3 month run 1.5 º/day = 6 month run

Use a linear regression to filter out variables Infrared scans should be done to verify or check

tube metal skin temperatures

Operating Practices - Heater Tubes And Unit Monitoring

Provides a way to estimate decoking schedule Shows abnormal operations or feed quality

Sudden changes in sodium content Fire box problems Measure the effectiveness of increased

steam velocity Measure the effectiveness of shifting O2

levels

General practice is to online spall and pig decoke when the opportunity arises

Page 17: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION

Fire box startup problems Auto ignition systems - keep the operator safely away from the box on startup Forced draft systems – go to natural draft 1st then latter switch to forced draft O2 level controls – avoid O2 level optimization until after startup

Circulation or putting the unit into by-pass requires lowering the outlet temperature significantly Burners will need to be cut out and sometimes pilots The outlet temperature must be kept below 700ºF or lower to prevent polymerization

Frequent (per shift min.) visual inspection of the heater is required regardless of the degree of instrumentation

Loss of flow requires immediate steam purging Automate the purge system on loss of flow After a loss of flow event, operate with a higher than normal velocity steam rates to

remove newly deposited coker. This should not be done on a full drum especially if the coke drum was filled cold

The coke drum can not be filled with low heater outlet temperatures for extended periods of time – this will cause foaming and a possible foam over.

Operating Practices – Safety Issues

Page 18: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION

Acoustic pyrometry is a relatively new technology for measuring gas temperature in a furnace. This method involves determining the temperature of flue gas by measuring the speed of sound waves as they pass through the gas.A detailed mapping of the gas temperature is possible with a matrix of sound transmitters and receivers.

DCS

Acoustic pyrometry provides a continuous monitoring of the heat flux in the fire box

Recent Innovations In Coker Fired Heaters – Acoustic Pyrometry

Page 19: Delayed Coker Fired Heaters

Heater Design and Operations

PROPRIETARY INFORMATION

Recent Innovations In Coker Fired Heaters – Flow MetersWedge Meter

Better reliability - large diaphragm pressure taps Similar accuracy to an orifice plate Fewer solid plugging issues

Sonic Meter New technology very low maintenance and good reliability No obstruction in flow path Pressure drop equal to an equivalent length of straight pipe Unaffected by changes in temperature, density or viscosity Corrosion/erosion -resistant Accuracy about 1% of flow rate

Coriolis Meter New technology some maintenance and startup issues Good reliability Excellent accuracy- better than +/-0.1% with an turndown rate more than 100:1.

The Coriolis meter can also be used to measure the fluid density.

A great man once said “if you can’t measure it, you can’t manage it”

Page 20: Delayed Coker Fired Heaters

PROPRIETARY INFORMATION

Muito ObrigadoSim Romero

KBC Advanced Technologies, Inc.+1 832 494 0441

[email protected]

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