delayed coker fired heaters

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Delayed Coker Fired HeaterDesign and Operations

Sim RomeroRio Oil & Gas 201013-16 September 2010 Riocentro Convention Center Rio de Janeiro, Brazil

Como Conquistar a Liderana de Mercado Na Nova Dcada

IBP2714_10 2010 KBC Advanced Technologies plc. All Rights Reserved.

Heater Design and Operations 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)PROPRIETARY INFORMATION 2

Heater Design and OperationsWhy Do Coker Heater Foul - ChemistryThermal Cracking Is Both Cracking And PolymerizationcrackingVacuum Resid or other coker feeds1000


Liquids0 500

Coke1500 2000 2500 3000

Boiling Point, F

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 fluxDelayed coker furnace fouling is a complex function of the thermal kineticsPROPRIETARY INFORMATION 3

Heater Design and OperationsWhy Do Coker Heater Foul - Feed Quality Issues Asphaltene and concarbon content are strong indicators of fouling rates

Asphaltene content increases exponentially as the API gravity decreasesFeed quality is primary factor affecting heater run lengthPROPRIETARY INFORMATION 4

Heater Design and OperationsWhy Do Coker Heater Foul - Operating ConditionsTube Skin Temperature

Heat Flux

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

Q = Surface x HeatArea Flux

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

High Heat Flux and Low Velocities Increase Tube Fouling/CokingPROPRIETARY INFORMATION 5

Heater Design and OperationsWhy Do Coker Heater Foul - Operating ConditionsClean 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



Heater Design and OperationsWhy Do Coker Heater Foul - ContaminatesSalts, iron oxides, oxygen and other contaminates can accelerate heater fouling at times acting like a catalyst to coking in the heater tubes Typical Coke In Furnace Tube AnalysisSample Date Moisture (as received, %) Ash (%) 3/24/2005 10.4 38.49 3/24/2005 7.05 37.57 3/24/2005 7.3 35.55 10/4/2005 1.66 17.39 10/4/2005 1.8 27.34

Analysis of AshSilicon (dry, ppm) Iron (dry, ppm) Vanadium (dry, ppm) Nickel (dry, ppm) Aluminum (dry, ppm) Calcium (dry, ppm) Sodium (dry, ppm) Magnesium (dry, ppm) 10,270 241,100 1,699 1,023 251 7,799 5,439 2,764 15,240 169,400 2,140 1,607 111 12,230 7,227 3,196 14,190 272,700 1,760 1,393 2,385 9,225 3,954 2,107 5,623 301,900 19,910 15,880 2,645 10,130 7,004 842 4,551 312,000 8,577 3,037 2,506 15,910 19,800 3,519

Crude Unit Desalter Performance Significantly Affects The Delayed Coker Heater7 PROPRIETARY INFORMATION

Heater Design and OperationsDesign Parameters To Mitigate Coking In The Heater TubesSingle vs. Double Fired Heater TubesFor an average heat flux of 10,000 BTU/Hr/SqFt the peak flux on the tube will be

18,000 BTU/Hr/SqFt

12,000 BTU/Hr/SqF t

Single Fired Tube

Uneven flux distribution peak to average heat flux is about 1.8

Double Fired Tube

Even flux distribution peak to average heat flux is about 1.2

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 limitedPROPRIETARY INFORMATION 8

Heater Design and OperationsHigher 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 velocitiesIncreased velocity steam will help reduce coke fouling but at a cost (drum solids carry over, tower flooding, sour water etc)PROPRIETARY INFORMATION 9

Heater Design and OperationsDesign & 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 coilPROPRIETARY INFORMATION 10

Heater Design and OperationsDesign & Operating Parameters Tube Metallurgy Tube metallurgy 9 Chrome vs. SS 347 SS Sch 80 tubes design temperature limit is much higher ~1400F The higher temperature limit may not be possible if you spall because o f the coke thickness at temperature higher than 1300F 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 ratesSS 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 spallingPROPRIETARY INFORMATION 11

Heater Design and OperationsDesign & 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 ~75F 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 1stBecause of the severe coking issue in a delayed coker heater the O2 levels should be relaxed to 5% to 8%PROPRIETARY INFORMATION 12

Heater Design and OperationsDesign & 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 processStraight run out of heater short thermowell longer thermowell First 90 bend out of heater

Badly installed thermowells can significantly effect heater performance13

Heater Design and OperationsOperating Parameters Heater Outlet Temperature 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 specsThe objective is to deliver sufficient heat to the coke drums the drum inlet should be about 890F to 900FPROPRIETARY INFORMATION 14

Heater Design and Operations 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 600-800 o 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 l


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