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REFINING DEVELOPMENTS md Xd r-1 4ZLCme.

Novel 'control' scheme optimizes operations and reliability h.-of combustion unitsI F. RODR~GUEZ,E. TOVA, M. MORALES,M. A. PORTILLA and L. CANADA~,NERCO,Seville, Spain; and J. L. VtZCA(N0, CEPSA, Process Engineering, Huelva, Spain

Improve efficiency of furnacesand boilers "9%.$2

Nw technologies enable optimizing combustion pro-cesses for hydrocarbon processing facilities. Economicand environmental drivers require improving operatingefficiency while mitigating emissions of carbon dioxide (COX),nitrogen oxide (NOJ, carbon monoxide (CO) and paniculates."Smoother" operations increase the safety for combustion units.In the following case history, a Spanish refiner applies a novelcombustion control technology to the crude oil furnace. Thearticle describes the overall technologicalapproachand the latest

Recently, considerableattention has been directed to wmbus-tion adjustments for efficiencyoptimizationand emissionslimita-tion. Neverrheless, the cost-effectivenessof these adjustments islimired by mentioned restrictions over wmbustion monitoringand control.This gives rise to the erroneous decision to upgradethe burner systemwithoutfirsrattempring o optimizethe presentcombustionsystem.This situationis evenmore relevant in scenarioswith highvari-abiity in fuelproperties, loadingprofiles andlor burner arrange-

rerulrr, regarding combustion efficiency improvement (overall ment.. for inultiburncrsystems.lnthesecases, unwnuolled com-CO: emissions reduction) and p d c l effects in NO, emissions bustion conditiomm3y formopcraton to apply "too w~crvauvc"control, through the implementation of a novel combustion boiler settingsand to move away from optimum tnning.control technology to a crude oil furnace of a Spanish refinery.Project goals included reduced C02 nd NO, emissionswith Controlledfurnace technology. Efficiencyand emissionsbetter reliability. (NO., CO, CO,, panicles, S O , etc.) in industrial furnaces and

boilen depend %ely on the correct distribution of fuel and airBackground. Combustion improvement offers the greatest supplies to the combustion process. Moreover, inappropriate fuel1. - - -p o t e n d for economicsavingsregarding the operation oTindus- air ratios on critical locatiok severely impact important furnacetrial boilers and furnaces. Nevertheless, the wmbustion process is parameters (Fig. 1).Therefore,strictercombustion controlsareaopaque from the operator'spoint ofview. For thisoperaung unit, function to b&ce the combustionprocess.fuel costs are the greatest operaringexpense;yet, how rhis fuel sutilized remains unclear.

Despitethe economicand environmental importanceof com-bustion processes, these operations involve a low level of moni-coringand control.These processes aregoverned by a fewglobalmiables suchasa rm oxygen (02) or process streamyields, withno direct control of wmbustion conditions.Furnace or boiler operations are supported by standardizedproceduresand operatorexperience, rather than byeffective onlineinformationand optimizedflame control. Moreover, in most casesof multiburner application, standard monitoring applied forglobal excess0, control in the combustion unit does not rep-resent the true average excess O2 d u e at the furnace level, thusintroducing a critical restriction when trying to optimizetuning . ,of combustion conditions.

This situation heavily contrastswith the current sute-of-the-art level of most industrial processes, in which comprehensivemonitoring and advanced control systems ensure process safety,plant availability and maximum efficiency. It is surprising that ..a chemical process such as combustion,with an impressiveeca-nomic and environmental impactworldwide, stillrelies on nearlyarchaic controls.

optimization operating criteria for HPI furnaces and,A " -

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REPORT I REFINING DEVELOPMENTS

timized Combustiinling fo r optimizatiiI balanced slrategiescombustion:ontrolled furnace

MaXlmum NO,and efficiencycontml usingimplementedcapabilities,gic diagram fo r controlled furnace approach.

Combustion optimization technology& n the adequatedosed-loop control of local combustion conditions, promoringwhat is called a "controlled furnace" (Fig. 2). This controlledopemion is a critical factor m ensure he maximum bendits ofcombustion ~ a ~ i a b l e sdjusrment whose tuning directly impamunit efficiency and NOF ormation.The conrrollcd tiunaa approach enables individual optimi-zation for any single burner. RewloTotal optimization of thecombustion process.This application i m p m unit &ciencyandr e d m C O or NO , emissionsby applying sp&c op t i nk t i onmregies inmultiburner systems.Comequendy, this approach is both a costzffective alterna-tive m impluoylting com&shn-systun modifications@ m e tsubstitution)andis an additional improvementmol if& m&fiations are finally installed. Also, insding this technology toan existingcombustion unit requiresminimum modificauons toexisringequipment and a s h o w shutdown to install the wod-ated new elements.As shown in Fig. 3, controlled furnace conditions inwlve anintegtaced approach and require:Advanced monitoring technologiesN o d regulation systemsforcombustion opcimizadonExpert s o h or optimized combusdoncond.Advanced monitoring tschnofoilies. Monitoring in-fnmacz pombwtion conditians enable sde~e~o~ingccurate&-bustion ~surveillance hidris essen~alo implement conuolled-f b a c e conditions.L o c a - h moniterhgguides the opsratot m obtain themost adequate Nniog f o ~ny individual burner. Such actionsfacilitate the totaloptjmizationof the combusion unit. Iniprovedoperations iwease unir operatingefficiency and mitigarcs emis-sions aswell asprovide a safer, more reliable and flexible unitoperation.Also, in-furnacx monitoring t&ologies aid in identifyinghidden&or boiler malfunctions that can in- C O lev-els, even though.the unit isworking under correct combunionconditions. Also, suchmonitoring&leg adjustingflame geom-88 1 SEFIEMEER 2009 HYDROCARBONPROCESYNG

Operating points of controlled furnace approach to' nntimiln rnmh~#r+inn I

enies, ideneng the o p r i m ~ n u m b af a& burners for eachoperating load, meamring flame stabiliv, and/or reducing NO,generadon. Particular applications of this techtrology indude:r D i r e a assessmentofLoeal combustion conditions at any

furnacearea, nor l i t e d by exisringfurnace viewing ports.t Correct determination of actualexcesssair levels within the!barn , which Eadlitatesidendfyingpossible airleakages,aswellas, safe implementation of combustion optimization srrategies.* Supenririonof realcombustion conditions: scenariosof load@don and fuel proputywuiations to support the decision-making process on chc number and location of active burnersfor each logding, optirnking cxcess-air levels for each load, andidendying maintenance probluns.

S&CC and runing of combusdon conditionsfor sce-narioswith sificant fuelpmperty variations.* Conno1 ool for managingNOxreductionwhilemaintain-ing an adequate conuol ofsafety limitsfw oiler regulations.Also, controlled furnaceconditionscanenhance omplemen-tary combustion monitoring capabilities:Pyrometers grid to determine furnace temperaturedistributionOnline measurementof fud and air flowraps. . .Gasarussrons monimring.Th e scope of the monitoring approach is to be decided foreachcast according o plantdesign,o p t i o n c h a n cm i c s andperformance objecrim.Nwelregulationsystemsforcombustion. Implement-ing controlled furnaceconditionsinvolves, nmost caw, etterbo&r tnningcdpabilities. Betterboiler operations caninvolveoneor a combination of the following conditions:Automation of existing manual regulations from th ewnuol roomImplementation of other fuel and air M a t i o n dampersa n d d v e s

r Modification in the design of adsringburners t o increasetheir tuning potential.By applying these o p t i n g conditions, existing regulationcapabilities are improved as if new burners, i,e., low-NO, burn-ers (LNB) were installed. When further NO, reductions are

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REFINING DEVELOPMENTS REPORTdemanded, these regulation systems are totally complemenraryto more substantialplant modifications(such asLNB or wind-box redesign.)Expert software optimizes combustion control.Controlled-furnace conditionsareestablishedin dosed-loopcon-trol scenariosbyinregratingthe previously described monitoringand regulation,capabilities with advanced combustion controlsystems, which are configuredfor each specificapplication.Thisintegrationallows applying combusrion oprimization strategieswith the maximum reliabiliryand profitability.Main f e a m of these strategies are implementedwithin anappropriateexpert combustion control design that establishesasubordinaremanner to the combustionunit master control. Bothcontrolsystemsdo not interfere, as the expertcombustioncontrolwill only affect adjustmentsnot related to the unit master control.The expen systemisconf'lguredindividuallyforeach combustionunit duough specificcombustiontests. 11 Disagreement between 02figuresdetected by the originalCarehistory.The followingexamplediscusses thecombustion O2monitoringsystem (averaged figureswithin the 3.5%-4.5%opdmizationproject of a direct-firedheater ro the crude oil unit interval) and the more accurate values resulting from completeat a Spanishrefmery. This furnace is equippedwith 32 horizontal controlled furnace approach (with average O2 levels of 1% tooiland-gasburnersplaced in two opposite 3.5%+). Manual measurements carriedrows. A refractory division waJl is located out ar furnace exit sections demonstratein the middle of the furnace for bending . and emissions in the full agreement between the averagedthe flames and defining two independent industrial urnacesdepend measurementsfrom tbe mplementedsys-in-furnace areas. tem and global furnace excessOz levels.For thebase caseof the furnace,moni- On thecorrectdistributionof Therefore, the existingmonitoring sys-toringoftheincomingcombustionairwas tem does not represent the cod excwO2carried out by an O2probe placed in the fuel and air supplies to the levels in this furnace. Fumhennore, thecenter of the east sidewall. Two manual global excess O2 moliitoringis not com-&aft regdating dampers, located at north combustion process. parable, in prms ofcombusion opdmiza-andsouthfurnacechimneys,werewd for tion potential, with valuable informationoverall cornbusr~onir control. Burnerswere also equipped wilh prov~dudhe advancemonitoringsystem.manual primary and secondary air regulation capabilirics. 11 1. k , a consequence from itcms I and 11, the high exccss0,New optimization.The scope of the optimizationstudy ofthecrude unit furnace serdedusing controlled furnace conditions.Thisapproach isaimed at attainingoptimized hrnace efficiencyscenarios,while coveringeverypossible operatingsituationvia:An in-furnace monitoring system to characterize the mm-bustion process at each individual burner.Automation of the air-regulationdampers in both rows ofthe multibumers;optimized flame tuning and furnace stadcs viabetter control of the furnace draft.A controlapproach and an expertsystemfor the dosed-loopcontrol of the total process.Processbaselinecharacterization.The combustion fur-nace baseline isdeterminedby a thoroughtectingcampaign usingnew monitoringand regulatingcapabilities.Tbis testingcampaignis designed to cover all possible furnace operating scenarios interms ofdutyrequiremenu, name and proportionsof fuelsused,burners in service, etc.Results of rhis combustion diagnosis forthe furnace base case are:I. Identify important imbalances between individual burn-ers. Measured differenw above 3.5% in excess O2 levels (andwen higher foruncontrolled globalO2 eduction scenarios) limit$fdency optimizationefforts throughuncontrolledcombustiontuningstrategies that generate unsustainable CO levels. (Fig. 4shows the baseline operation.)

and minimumCO levels at the furnaceourlet sectionwere mea-sured (Fig. 4). HighNO, genemtion associatedwith O2 evels isalso produced The averaged furnaceO2 alues measured by thelocal in-fumace monitoring system ranged between 5%-7%.Controlled-furnace system performance.Followingthe installationof improved combustion control strategies via acontrolled-fumace approach, adear evolution of excessO2 evels,recorded by the local in-furnace monitoring system, could beo b d rom thebaseline operation to the controlledoperation(Fi.). The resulting final O2average values were around 2%(frominitialaverage values around 5?&7%).Final combusrionconditionsvia the controlledfurnacestrate-gies enabled safer, sustainable (negligibleCO levels), homoge-neous and efidenr combustionscenarios. The controlledfumaceconditionswere reached viaappropriateglobaland individualairregulations tuning carriedout by the expert combustioncontrolsystem followinga fully automated process.The reported 3%-5% ~ c e s s 2minimizationwas coupledto agas temperaturereductionandd t e d n anw e dM onsumpdon savingsabove 5%.An equivalent reductionwas obtained forCO2and SOx emissions. Results nduded in Fig. 4 show a dearreduction in the resultsdispersion forconmlled operation.The controlled operation enables identifying burner mal-functions.These types of malfunctionscan remain hidden whenconventionalmonitoring is applied. Burner malfunction iden-

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SPECIALREPORT

Applicabilityof controlled iurhaec approach furconven t hna l and low-NO. burner aooiicationr I

- Improved unit combustionaciency resulting in fuel con-sumptionsavings above 5% (withequivalentCOZ nd SO, emis-sion reductions).

Simultaneousreductionsin total NO, emission (cph) up to450?50% (resulting in NO, emissions levels ranging 300 mg/Nm3-350 mg/Nm3, referred to 3% Oz).

Controlof unburnt fuel and CO emissionsyields negligibleC O levels even for the most stringent low-excess-air scenarios(avemgeexcessOzis approximately2%).

Applying the controlled-furnaceapproachto the crudeoilfur-nacecand t n improved combustionconrrolh t ostershigherunit reliability, safer operation and reductions in maintenancecosts. Crucial information for preventive maintenanceaction isobtainedby immediatelyidentifyingb u m &aions (beforemajor failuresor damagesare produced) and by continuouscon-trol of CO or unbumt fuel, which arealso associatedwith f o u h-and cokedepositsscenarios.

The potential of this optimization strategy is significantlytification is an essential tool for a cost-effective burner mainte- increased under scenarios of variable fuel supplies or operation..nance program. Result: Optimized maintenance schedules can loads, where combustion unlt operators are otherwise totallybe achieved via a controlled furnace approach. "blind" to the changesoccurring n the combustion process.This

approachisa cost&ctive alternativeandlor a valuable comple-Improve combustion.When facing combustionoptimila- mentary tool to larger-scale combustion system retrofits, whichdon challenges, such asefficiency improvementandlor emissions would neewarily lead to combustionfacil~ues ith morecomplexreduction (NO,, CO, COz or particles), the conuolled fiunace designs and greater needs for surveillanceand control (Fig. 5).approach can providean advanrageousalternative,and isan essen- In addition, the important parallel reductions in NO, emis-tial complement, to large-scale combustioninstallations. Benefiuj sions achievablethrough controlled-furnace applicationscouldfrom such applicationsinclude: make it feasible, from an environmentalpoint of view, and espe-

3 YDROCARBOrVPROCESSING - ding montl.., gazinefor stayingconnectedto the hydrocarbon pmcessing in dust^^. published since 1922,HYDROCARBONPROCESSINGorovides owrationalandtechnical information to1 imorove ~ l an teliabilii. orofi&bbllitv, saf&and end-~roductaualitv.Theditors.ofHYDROU~RBONR&ESSING bring yo;~*st -hai lrnowledgeonthe latestaclvancesintechnokgiesand tedmicalatidcr ohelpyoudoyourjobmoreeffectively.lovember2009: PlantSafehandEnvironmentSafetysystemsfaci~it~com~liance,lobal security issues- Flare svstems. design. manaaement maintenance- -. Emissionscontrol valves,vessels, pumps, pipingI eamber20M):PbntDesignand EngineeringProject management. CAD/CAMLaserscanninganuary2010:Gas ProcessingDevelopmentrSulfur removal technologies- Liquefiednatural gas (LNG) and gas-to-liquid(a)dvancesCatalystdevelopments

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