Coker design achieves cycle times, throughput needs at ... - CB&I

P r o c e s s i n gCoker design achieves cycle times,throughput needs at Kansas refineryDon MulraneyArt StefaniCB&IHoustonCoby StewartFrontier El Dorado RefiningEl Dorado, Kan.RefiningOver the last few years, FrontierRefining’s plant in El Dorado, Kan., hasundergone a major refinery reconfigurationto facilitate processing a greaterproportion of very heavy crudes. TheThis view shows the completed Frontier El Dorado coker alongside an existingcoking structure (Fig. 1).project added a new vacuum unit andrevamped several existing units for processingthe heavier crude oil feed.These modifications produced significantconstraints on the coker unit, dueto the lack of sufficient coke-drum volume.Frontier evaluated running shorterdrum cycles, but review of the drum’svapor velocity indicated severe foamingand carryover would likely result.In addition, coke-drum reliabilitywas decreasing because of frequentdrum cracks. Frontier evaluated severaloptions for repairingthe existingdrums, but mostwere deemedunacceptable dueto the extendedunit downtime thatwould have beenrequired to completethe work.CB&I had beenadvising Frontieron these drumevaluations, includingthe anticipatedcoke make increase.Frontier and CB&Iconcluded the existingcoke drumsshould be replacedwith larger drums.Scopeof projectIn 2006, CB&Iwas contractedto evaluate theexisting coker todetermine its suitabilityto processthe new feed. Withthe exception of the coker feed preheattrain, blowdown steam condensing, andthe larger coke drums, the existing unitwas capable of handling the new feedcomposition.CB&I and Frontier set the cokedrum’s size based upon the new feedand Frontier’s expected future expansioncapacity: 26 ft diameter and 70ft. It was determined that the existingcoke drum’s piping and valving wouldbe acceptable for the new capacity,which set the scope of the new cokedrum’s structure as follows:• Two new vertical plate cokedrums.• New foundation and elevatedtable top.• Steel structure.• Ruhrpumpen decoking system andnew jet pump.• DeltaValve automated bottom andtop unheading devices.• Piping, valving, and controls to tiethe new drums into the existing cokedrum isolation system.The new structures and remote cuttingbuildings can be seen alongsidethe existing drums in Fig. 1. In addition,Frontier elected to install a cokehandling and conveying system througha separate arrangement.FeaturesThe Frontier structure design continuedthe focus on operator safetyand a low-maintenance installation.One consideration of the design approachwas to minimize the time forthe operator to be on the structureduring the coke cutting part of thecycle. The heavier feedstock to be processedby this unit is a known shotcokeproducer and therefore subjectto blowouts. For this reason, removalof operating personnel from theBased on a presentation to the 2009 NPRA AnnualMeeting, San Antonio, Mar. 22-24, 2009.Reprinted with revisions to format, from the August 3, 2009 edition of OIL & GAS JOURNALCopyright 2009 by PennWell Corporation

showed that the T-Rex configurationhas lower stress levels for the criticalcharge-and-quench thermal cycles. TheT-Rex design was used on the Frontiercoker project to take advantage of thereliability improvement (Fig. 3).The T-Rex design was used on the Frontier coker project to take advantage of the reliability improvement(Fig. 3).Shown are the open design and monorail system of the bottom unheading valve (Fig. 4).was performed on the T-Rex design,the results of which were comparedto those for the conventional designconfiguration. This was a transientthermal analysis to establish the modeltemperature profile over the load cycletime history.The results of the thermal load testsDelta valve unheadingThe bottom unheading device hassubstantially improved delayed-cokerdesign and safety. By creating a completelysealed connection from the bottomof the coke drum down throughthe discharge chute, the unheadingdevice isolates personnel, equipment,and the environment from exposureto hydrocarbons, hot coke, water, andsteam.With the addition of the bottom unheadingdevice, the following benefitsare realized:• Substantial savings in time, up to2 hr, to implement the unheading andreheading portions of the decokingcycle.• Reduced operating and maintenanceexpenses.• Fewer coke-drum operators.• Operators are not required to beon the structure when the drum headsare removed.• The bottom DeltaValve device alsohas throttling capability so as not tooverwhelm the primary crushing andtransportation systems.• The deck design provides substantialopen area that benefits operatorsafety and ease of maintenance.For the Frontier project, the bottomunheading device is supported by adual-purpose monorail system. Whilethe primary function is to support theweight of the unheading valve, themonorails were extended to allow theremoval of the unheading valve fromthe unit without the need of any assistancecrane. Fig. 4 shows the opendesign and monorail system of the bottomunheading valve.The traditional approach to topunheading, as with bottom unheading,was labor intensive. The operatorsworking on the top head were exposedto upsets within the coke drum expel-

P r o c e s s i n gFig. 5 shows the camera display for the operator.Fig. 6 shows the containment dome with the drillstem parked.ling hot steam, fumes, and coke. Withthe top head of the Frontier cokerconnected to the containment domethat is vented to a more remote location,operators’ exposure to coke-drumupsets is reduced.Remote cuttingThe remote cutting shelter consistsof two buildings, one containing thecontrol panels and camera monitorsfor the operator to unhead and decokethe drum and a second to house theinput/output panels, variable frequencydrives, and programmablelogic controller. The operator shelteris centered facing the chutes to allowoperators to observe the coke leavingthe drum.The interior of the cutting shelterconsists of two sets of panels, one foreach drum, controlling the decokingequipment. The cutting shelter alsohouses the DeltaValve top and bottomcontrol panels. Also included are readoutsfor coke-drum acoustics and vibrationthat the operator uses to determinewhen the coke drum’s wall is reached,as well as the camera system located onthe structure.The camera system consists of fourtilt-and-pan cameras operated from thecutting shelter. These cameras have lowlight, zoom, and panning capabilities ifrequired by the location.Two of the cameras are mountednear grade to provide views where thecoke chutes are located. These camerasprovide two additional angles toprevent a loss of line-of-sight in caseof heavy steam in one direction due tothe prevailing winds. A third camera isin the top unheading deck to providegeneral monitoring of the area as wellas the location of the cutting tool andthe rotation of the drill stem.The fourth camera is about halfway up the derrick structure with theprimary function of providing a viewof the rotation of the hoist cable. Fig.5 shows the camera display for theoperator.Auto-switch cutting toolThe auto-switch cutting tool allowsthe operator to switch from boringmode to cutting mode without needingto remove the cutting tool from thedrum. The switch is done by cyclingthe pressure to the cutting tool.Properly used, this enhances operatorsafety by not requiring operatorpresence on the structure with a fullcoke drum open to the environment.This operation is performed veryquickly, thereby providing time for usein other steps in the decoking cycle.

Containment domeThe cutting tool floating containmentdome has several advantages:• Self alignment of the drillstemguide to centerline of the derrick tocompensate for any banana effect. Thisreduces the potential for a stuck tooldue to cutting tool/drillstem channeling.• Centering of drillstem guide withdampening springs to reduce the impactfrom blowouts.• A permanent parking place for thedrillstem and cutting tool when thedrum is in the coking cycle. The stemdoes not have to be tied off when notin use.• The dome acts as a venting chamberfor fumes that are expelled whenthe top head is opened and to dissipateheat during the coking cycle. The domeis vented to a more remote location.• Containment for coke pieces thatare expelled during a blowout.Fig. 6 shows the containment domewith the drillstem parked. The line fromthe side of the dome is the vent, whichis directed to a remote location. Thedome itself is mounted directly on thetop DeltaValve unheading device.DecokingThe decoking system supplied byRuhrpumpen is a totally electronic controlsystem that is electrically powered.The hoist and drill stem drive are bothelectric-motor driven. This eliminatesthe intermediate step of a hydraulicpower unit or pneumatic-driven equipment.The electric-drive electronic-controlnature of the system facilitates theability to control the decoking systemremotely. Also included in the system isThe authorsDonald D. Mulraney (DMulraney@CBI.com)is currentlyvice-president for downstreamtechnology services with CB&ILummus, Houston. Previously,he was vice-president of processand technology with Howe-Baker Engineers. With CB&I,Mulraney is responsible fordeveloping refining and petrochemical projects, especiallyfor unique technologies and businesses. Heholds BS and MS degrees in chemical engineeringfrom the University of Texas at Austin.a stem free-fall arrestor.Since its start-up in mid-2008, theFrontier El Dorado delayed coker hasachieved its desired design cycle timesand is capable of additional throughput.✦Coby W. Stewart is currentlymanager for maintenance andreliability at Frontier Refining’sEl Dorado, Kan., refinery.Previously, he spent more than28 years in construction, turnaround,and maintenance in theoil and natural gas, petrochemical,and refining industries.Stewart holds degrees from Texas State TechnicalCollege and LeTourneau University.Arthur N. Stefani is currentlyvice-president of delayedcoking with CB&I Lummus,Houston. His responsibilitiesinclude working with clients todevelop coking projects, as wellas ensuring that the technicalcontent of all EPC delayed cokingprojects meets the highestindustry standards. He has held technical managementpositions with all prominent delayed-cokinglicensors. Stefani holds a BS in chemical engineeringfrom Manhattan College, New York City.