Advanced Process Control for Ultra-deep-hydrodesulfurization Using Exasmoc R3 and Exarqe R3 33ADVANCED PROCESS CONTROL FORULTRA-DEEP-HYDRODESULFURIZATIONUSING Exasmoc R3 AND Exarqe R3IKEGAYA Yoshihiro *1 TERASHIMA Nobuhiko *1 KHOO Lena Bee Yean *1Advanced process control in the PCS (Process Control System) market is akey technology to glean the greatest profit from the existing equipment in the plant.TheAdvancedprocesscontrolcanbeeasilyappliedtoin-serviceprocessesandhelpsstabilizeandoptimizeoperationstakingprocessrestrictionsintoconsideration.The Exasmoc (a multivariable model predictive control package) and Exarqe(arobustqualityestimatorpackage)releasedin2000havebeeninoperationinmany DCS (Distributed Control System) or PLC (Programmable Logic Controller)systems.Recently,ExasmocR3andExarqeR3whichincorporateenhancedalgorithmshavebeennewlydevelopedtorealizeoperationsforlarge-scaleandcritical control processes.Hence, these two packages are strongly recommended foradoptionintheultra-deep-hydrodesulfurizationprocesswhichisnowunderconsideration by world-wide oil refinery plants.ThispaperintroducesanexampleofthefunctionsofExasmocR3andExarqe R3, which are recommended for use in high-level advanced process control.*1 Industrial Automation Systems Business DivisionINTRODUCTIONYokogawahasformedanalliancewithShellGlobalSolutions International B.V. (SGSI) for advanced processcontrolandhasbeenjointlydevelopingrelatedproductssincethen.As part of this collaborative work, we commercialized theExasmoc*multivariablemodelpredictivecontrolpackageandthe Exarqe* robust quality estimator package in 2000, which areusedtocontrolDCSandPLCsystemsbasedonSGSIsmultivariablepredictivecontrolandqualityestimationalgorithmsnamely,SMOC*(ShellMultivariableOptimizingController) and RQE* (Robust Quality Estimator).Recently worldwide efforts have been intensifying to regulatesulfur concentration in fuel oil from an environmental viewpoint.Sulfuroxidesnotonlyproduceacidrainbutalsosignificantlydeterioratetheefficiencyandservicinglifeoffilteringsystemswhichremovechemicalsharmfultohealthfromvehicularexhaust gas.Japan is obliged to provide light oil that emits sulfuroxides of 50 ppm or less, a tenth the current limit, by the end of2004,withfurtherplanstoreducetheemissionto10ppmorlower in the future.To meet these new standards, world-wide oilrefineries including those located in Japan have been consideringtheuseofultra-deep-hydrodesulfurizationprocesses.Whilehigher-performancecatalystsandprocessesthemselveshavebeenstudied,advancedcontrolsystemsthatcanhandleever-restrictingreactionconditionshavealsobeensought.TheExasmoc R3 and Exarqe R3 were developed in response to thesemarket needs.34 Yokogawa Technical Report English Edition, No. 37 (2004)HistoricaltrendFuturetrendNEW FUNCTIONS OF Exasmoc R3 AND Exarqe R3Byincorporatingseveralnewfunctions,ExasmocR3andExarqeR3implementadvancedcontrolofultra-deep-hydrodesulfurization processes as well as can be used for multi-purpose, large-scale processes.ExasmocR3MultivariableModelPredictiveControlPackageThe Exasmoc package performs on-line multivariable modelpredictivecontrol,whereacontrollerisequippedwithinternaldynamicbehaviormodelsofprocessesandgivesprocessesoptimum manipulated inputs after predicting their next step.Thismethodisparticularlyeffectiveatstabilizingoroptimizingprocesses that are susceptible to disturbance, time delay, inverseresponse,andinterferencefromotherprocesses.TheExasmocR3 offers the following additional functions: Large-scale system control Priority-based control Trend predictionThepreviousversionsofExasmoccouldnotbeusedforethyleneplantsorotherlarge-scaleprocessesthatrequireanenormousnumberofinputsandoutputs.TheExasmocR3,however, has a two-level structure consisting of a main controllerandsub-controllersasshowninFigure1,whichenablestheoverallprocesstobedividedintogroupsthatarecomprisedofcontrol variables and manipulated variables.Sub-controllersperformmultivariablemodelpredictivecontrol on a group basis.The main controller determines if thecurrentprocessstatusallowsforcontrolworkbytakingrestrictiveconditionsintoaccountandperformsoptimizingoperationsforeachsub-controller.Itthenprovidesthesub-controllers with the optimum setting ranges for control variables.Asthesub-controllerscanoperateatdifferentcontrolintervalswith each other, the Exasmoc R3 can be adopted for a large-scaleprocessinwhichfast-intervalgroupsandslow-intervalgroupscoexist.A priority ranging from 1 to 100 can be specified for controlvariables,facilitatingflexiblecontrolaccordingtotheirimportance.TheExasmocR3sHMI(HumanMachineInterface)displaysrelationshipsbetweenthevariablesinavisually easy-to-understand tree format as shown in Figure 2.OptimizingFunctionMain ControllerSub-controllerProcess 1 Process 2SMOCControllerMultivariableModel PredictiveControl 1MultivariableModel PredictiveControl 2MultivariableModel PredictiveControl 3Figure 1Two-level Structured ControllerFigure 2Exasmoc R3 Operation and Monitoring Screen Figure 3Predicted TrendAdvanced Process Control for Ultra-deep-hydrodesulfurization Using Exasmoc R3 and Exarqe R3 35The Exasmoc R3 can also display trends of predicted processvariables.Thisfunctioncompilespredicteddataandhistoricaldata which the Exasmoc outputs periodically, and then displaystheirchangesintrendgraphs.Thesimultaneousdisplayofchangesinbothtypesofdataneablestochronologicallygraspprocesstrendsataglance,therebyprovidingoperatorswithaccurateinformationforchoosingcontroloperations.Figure3showsascreenexampleofthetrendfunctionillustratingpredicted data and historical data.In the graph in Figure 3, a border between the predicted andhistorical trends is indicated by dashed lines, which represent thecurrent time and show the past data on the left with the future dataon the right.The future data as predicted data is repeatedly re-calculated by the Exasmoc R3 at regular intervals.Exarqe R3 Robust Quality Estimator PackageTheExarqepackagesperformon-linequalityestimationinrealtimeandcanalsobeusedassoftwaresensors.Qualityestimation means inferring properties or qualities that cannot bemeasured directly, such as freezing points and the concentrationofimpurities,frommeasurableprocessvaluesthatinfluenceflow, temperature, and other properties.With other types of on-lineanalysesorlaboratoryanalyses,therearetimedelaysbetween the sampling and measuring of the target object, and thusreflectingtheresultantestimatedpropertyvaluesincontrolisdifficult to optimize the system operation.On the other hand, astheExarqeestimatespropertyvaluesinaconsistent,realtimemanner,theyareaccurateenoughtobeusedastheestimatedcurrentprocessvaluesforcontrollingthesystem.ThenewExarqe R3 also offers the following additional functions: Multi-point quality estimation Computing BlendingThe Exarqe R3 enables estimation of multiple qualities in aquality estimator application, and a multi-stage quality estimatormodel, with which a predicted quality is subsequently used as aninput to estimate another quality (see Figure 4), can be realizedwithasingleapplication.Althoughbuildingsuchamodelpreviouslyrequiredconsideringtheconnectiontimingbetweentherelevantqualityestimators,theExarqeR3overcamethisproblembyintegratingtheactionsthatareassociatedwithaquality estimator application.FurthermoretheExarqeR3implementsblendingfunctionsthatareapracticalapplicationofthequalityestimatorfunctionandthatmakepossibleestimationofintegratedqualities(tankqualityestimation)andtankqualitycontrolusingtheestimatedintegratedqualities.Otherbuilt-infunctionsarealsoavailable,includingthedefinitioncapabilityofarbitraryoperationalexpressions and SGSIs unique, abundant blending expressions.IncombinationwiththeExasmocR3,theExarqeR3achievesvarioustypesofblendingcontroldependingontheapplication.Nextchapterdescribesanultra-deep-hydrodesulfurizationprocess,whichisanexampleofadvancedcontrolattainedbymaking the most of the aforementioned new functions.APPLICATION OF ADVANCED CONTROL TOTHE ULTRA-DEEP-HYDRODESULFURIZATIONPROCESSCombining the functions of the Exasmoc R3 and the ExarqeR3facilitatesadvancedcontrolofanultra-deep-hydrodesulfurization process as follows.Figure 5 shows a system configuration example where feedoils1to3withdifferentsulfurconcentrationsareblendedataspecified ratio; sulfur content is reduced from the mixture usinghydrodesulfurizationequipment;andthenaproperlyadjustedamount of additives are added to output the final product (whichislightoilinthisexample)withinatargetedrangeofsulfurconcentration.Inthissystem,theExarqeestimatesthesulfurconcentrationoftheintermediateproductinrealtimeafterthehydrodesulfurization treatment, based on various data such as thepre-analyzedindividualingredientsofthefeedoilsandtheFigure 4Multi-point Quality EstimationRQE ApplicationProcess Value 1Process Value 5Process Value 4Process Value 3Process Value 2QualityEstimator 3QualityEstimator 2QualityEstimator 1Predicted Quality 2Predicted Quality 1Predicted Quality 336 Yokogawa Technical Report English Edition, No. 37 (2004)additives,andprocess-relateddataincludingtheblendingratioand temperature.The Exasmoc controls the reaction temperatureand blending ratio according to actual process measurements andthe estimated qualities through the Exarqe, to make sure that thefinal product is consistently within the targeted quality range.Asmeasuringsulfurconcentrationusingconventionalanalyzers including gas chromatographs takes a certain amount oftime,thesemethodsarelikelytogenerateagapbetweentheestimatedandactualqualitiesduetotimedelayswhenthemeasurementresultsarereflectedontheprocess,resultinginafinal product that does not satisfy the required specifications, orthatisofexcessivequalitycausedbyexcessivelyprotectivesystemsettingsagainstpossibledeterioration.Ingeneralitconsumes more energy to manufacture a product with excessivequality,andaccordinglycostsmore.Asasolutiontothesechallenges,wedevelopedahighlyefficientcontrolsystemthatcanstablyoutputproductsthatmeettherequiredspecificationsbyanarrowmargin,throughExarqeR3sreal-timequalityestimationandExasmocR3smultivariablemodelpredictivecontrol.This control system has another advantage in that it canmanufactureproductswithtargetedqualityinacontinuousprocessandthusdoesnotrequireatemporarytankthatstoresintermediate products halfway through the process.Overall, thissystem can achieve massive cost reductions by cutting an annualmaintenance cost of approximately 100 million yen per tank andother costs.CONCLUSIONThe Exasmoc and the Exarqe are advanced control packagesthatamalgamateYokogawasextensiveexperienceinthePCSfield and SGSIs sophisticated technology for oil refining.It isFigure 5Advanced Control Example of Ultra-deep-hydrodesulfurization Processimperativeforenterprisestoreducecostsbyoperatingplantsefficiently,andadvancedcontrolisexpectedtosignificantlycontribute to this area.Combining the Exasmoc and the Exarqeenablesprocessqualitiestobestabilizedinrealtime,anachievementthathasneverbeenrealizedwithon-lineorlaboratoryanalyzers.Thetwopackageshavealreadybeenintroducedtoavarietyofprocessing,suchasoilandpetrochemicalaswellasgasandethylene,andarehighlyevaluated on the site.Ultra-deep-hydrodesulfurizationisknowntoinvolvemanycostandtechnologicaldifficulties,anditsapplicationhasbeenwidely studied in various fields.We believe that the Exasmoc R3andtheExarqeR3whichincorporateSGSIscomprehensivepractical knowledge of this technique can play an important rolein yielding good results.We will continue to upgrade the Exasmoc and the Exarqe tonurture them as the mainstays of Yokogawas advanced controlbusiness,aswellastofurtherincreaseouractualresultsandexpertise in the relevant solutions.REFERENCE(1) TerashimaNobuhiko,TakatsuHaruo,OkadaKenji,ExasmocMultivariableModelPredictiveOptimizingController,YokogawaTechnicalReport,Vol.45,No.3,2001, pp. 35-40 (in Japanese)* ExasmocandExarqearetrademarksofYokogawaElectricCorporation.* SMOCandRQEaretrademarksofShellGlobalSolutionsInternational B.V.ExarqeFeed Oil 1Feed Oil 2Feed Oil 3AdditivesProductTankExasmocHDS Unit