48 HYDROCARBON ENGINEERING SEPTEMBER 2002 C atalytic reforming continues to have a significant impact on refinery profitability as it is still the key source of much of the high octane blendstock and hydrogen produced in the refining industry. Despite ever tightening legislation governing the aromatics content of gasoline, emphasis on catalytic reforming is likely to increase as demand grows substantially for hydrogen used in the production of low sulfur fuels. Depending on the specific refinery configuration, regio- nal legislation or seasonal demand, the operator will be required to optimise the reforming unit in many different ways. These operating targets may include limiting aromat- ics content of gasoline, increasing hydrogen production, increasing reformate yield or increasing aromatics produc- tion for petrochemical use. In addition, each unit has its own equipment limitations, leading to a unique optimisation sce- nario for the individual refinery. Despite the presence of unique local demands and constraints, the universally recog- nised primary control variable in reforming operations is reformate research octane number (RON). RON charac- terises unit severity and impacts on a whole range of other unit parameters that include product yield patterns, reactor temperatures, catalyst deactivation and product composition. Traditional approaches to severity control Reforming units provide significant advanced control oppor- tunities because of the high value attached to reformate octane and hydrogen, expensive operating costs and com- plex multivariable process interactions. The primary control loop, in almost all cases, maximises feed throughput while honouring the minimum octane target to maximise octane- barrels for the unit. This is achieved while maintaining heater, coking rate and hydraulic constraints to obtain the maximum unit profitability. Severity control is provided by feedback from a measured or inferred octane, that in turn adjusts the weighted average inlet temperatures (WAIT). Conventional RON measurement Reformate RON is therefore a key measurement in any cat- alytic reformer control scheme and is usually obtained by one of the following methods: Inferred models: an online RON model can be construct- ed as a function of operating variables that can include feedrate, operating temperatures and feed PONA analy- sis. The RON model is usually updated online, based upon periodic lab analysis of the reformate itself. Lab analysis: in the absence of inferred online property models, many unit operators carry out offline sampling and analysis for RON measurement. This usually involves analysing routine or test run reformate sam- ples on the octane engine of the refinery laboratory. Traditional online NIR analysers: in the early 1990s, refiners started to implement near infrared (NIR) analy- sers on catalytic reformers for rapid online RON mea- surement. This technology promised to solve many of the problems associated with traditional laboratory engine analyses. The improvement in analytical speed and data quality would allow improved control, leading to tighter approaches to operating targets. In addition, the technique was capable of multi stream and multi property application. However, for the catalytic reformer operator, there are a number of problems associated with these conventional methods of RON measurement. What are the issues? Inferred octane models: inferred models commonly require large data sets to describe the operating range of the process and properties of interest. This data col- lection is time consuming and, even after implementa- tion, the model may require frequent maintenance and intervention to adapt the training set to current operat- ing scenarios. In addition, laboratory octane engine analysis is still necessary, as the model requires peri- odic updates using real lab data. Laboratory octane engine analysis: RON measurement via laboratory engine analysis can be imprecise and too slow for optimum control when sampling time and the test itself are taken into account. Also, the analysis is only carried out once or twice a day, which is too infre- quent for optimum control purposes. Making process decisions on the basis of engine results is therefore dif- ficult for the process engineer, since precise, timely information is seldom available. Traditional online NIR octane analysers: many NIR implementations on catalytic reformers have failed to deliver pre project expectations and benefits for a num- ber of reasons. Similar to the problems associated with inferred property models, the traditional NIR analyser requires a large number of local calibration samples, to allow refinery specific prediction models to be built before the system can be implemented. Furthermore, the analyser commonly requires frequent model updates to allow the current operating envelope to be calibrated into the original prediction database. Lastly, after hard- ware maintenance, many spectrometers require re-cali- bration as instrument responses have changed and the Reforming reformate octane measurement Jim Kelly,ABB Bomem, Canada, describes the benefits of turnkey reformate octane analysis.
Transcript
48 HYDROCARBON ENGINEERING SEPTEMBER 2002
Catalytic reforming continues to have a significantimpact on refinery profitability as it is still the keysource of much of the high octane blendstock and
hydrogen produced in the refining industry. Despite evertightening legislation governing the aromatics content ofgasoline, emphasis on catalytic reforming is likely toincrease as demand grows substantially for hydrogen usedin the production of low sulfur fuels.
Depending on the specific refinery configuration, regio-nal legislation or seasonal demand, the operator will berequired to optimise the reforming unit in many differentways. These operating targets may include limiting aromat-ics content of gasoline, increasing hydrogen production,increasing reformate yield or increasing aromatics produc-tion for petrochemical use. In addition, each unit has its ownequipment limitations, leading to a unique optimisation sce-nario for the individual refinery. Despite the presence ofunique local demands and constraints, the universally recog-nised primary control variable in reforming operations isreformate research octane number (RON). RON charac-terises unit severity and impacts on a whole range of otherunit parameters that include product yield patterns, reactortemperatures, catalyst deactivation and product composition.
Traditional approaches to severitycontrol Reforming units provide significant advanced control oppor-tunities because of the high value attached to reformateoctane and hydrogen, expensive operating costs and com-plex multivariable process interactions. The primary controlloop, in almost all cases, maximises feed throughput whilehonouring the minimum octane target to maximise octane-barrels for the unit. This is achieved while maintaining heater,coking rate and hydraulic constraints to obtain the maximumunit profitability. Severity control is provided by feedbackfrom a measured or inferred octane, that in turn adjusts theweighted average inlet temperatures (WAIT).
Conventional RON measurementReformate RON is therefore a key measurement in any cat-alytic reformer control scheme and is usually obtained byone of the following methods:
� Inferred models: an online RON model can be construct-ed as a function of operating variables that can includefeedrate, operating temperatures and feed PONA analy-sis. The RON model is usually updated online, basedupon periodic lab analysis of the reformate itself.
� Lab analysis: in the absence of inferred online propertymodels, many unit operators carry out offline sampling
and analysis for RON measurement. This usuallyinvolves analysing routine or test run reformate sam-ples on the octane engine of the refinery laboratory.
� Traditional online NIR analysers: in the early 1990s,refiners started to implement near infrared (NIR) analy-sers on catalytic reformers for rapid online RON mea-surement. This technology promised to solve many ofthe problems associated with traditional laboratoryengine analyses. The improvement in analytical speedand data quality would allow improved control, leadingto tighter approaches to operating targets. In addition,the technique was capable of multi stream and multiproperty application.
However, for the catalytic reformer operator, there are anumber of problems associated with these conventionalmethods of RON measurement.
What are the issues?� Inferred octane models: inferred models commonly
require large data sets to describe the operating rangeof the process and properties of interest. This data col-lection is time consuming and, even after implementa-tion, the model may require frequent maintenance andintervention to adapt the training set to current operat-ing scenarios. In addition, laboratory octane engineanalysis is still necessary, as the model requires peri-odic updates using real lab data.
� Laboratory octane engine analysis: RON measurementvia laboratory engine analysis can be imprecise and tooslow for optimum control when sampling time and thetest itself are taken into account. Also, the analysis isonly carried out once or twice a day, which is too infre-quent for optimum control purposes. Making processdecisions on the basis of engine results is therefore dif-ficult for the process engineer, since precise, timelyinformation is seldom available.
� Traditional online NIR octane analysers: many NIRimplementations on catalytic reformers have failed todeliver pre project expectations and benefits for a num-ber of reasons. Similar to the problems associated withinferred property models, the traditional NIR analyserrequires a large number of local calibration samples, toallow refinery specific prediction models to be builtbefore the system can be implemented. Furthermore,the analyser commonly requires frequent model updatesto allow the current operating envelope to be calibratedinto the original prediction database. Lastly, after hard-ware maintenance, many spectrometers require re-cali-bration as instrument responses have changed and the
Reforming reformateoctane measurement
Jim Kelly,ABB Bomem, Canada, describes the benefits of turnkey reformate octane analysis.
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original calibration set is notimmediately applicable afterservice intervention.
How can the operator of a catalytic reforming unit obtainfast, precise RON measurement and avoid theproblems highlighted above?The CatReformir from ABBBomem is a proven solution to thetraditional difficulties associatedwith reformate RON measure-ment. It is the only NIR analyserproviding turnkey reformate RONmeasurement to the refiningindustry. More detail is provided inthe opposite panel.
What other reformate propertiescan be measured ?The turnkey RON capability can besupplemented by other valuablereformate quality parameters. Thereal time availability of benzeneand aromatics content allows theoperator to modify unit operation tomeet either legislated fuel qualityor petrochemical product targets.Knowledge of reformate RVP per-mits stabiliser column control.
The universal turnkey RONmodel is supplemented by ABBBomem ‘Starter Models’, whichcontain extensive sample databas-es for MON, aromatics, RVP, andbenzene. For specific refinery use,the starter models only requirefine-tuning using local client sup-plied reference data. 10 samplesprovide adequate local reformatecharacteristics to create completemodels for these other properties.
What other streams can be characterised?
Reformer feedThe influence of feed compositionon catalytic reforming operationsis significant. Reformer feed qua-lity varies for many reasons:
� Ever changing crude feedsimpact straight run naphthaquality.
� Imported ‘opportunity’ naph-thas are processed from vary-ing sources.
� Naphthas from cracking orcoking processes vary due toprocessing changes and theirimpact is significant even atlow feedrates.
� Cut points within naphtha split-ters vary as the overall reform-
HYDROCARBON ENGINEERING SEPTEMBER 2002 49
CatReformirThe CatReformir is an NIR based analyser that is precalibrated for turnkey reformateRON measurement over the severity range 86 – 103. � Available in lab, at line or process analyser configurations (Figures 1 & 2). � Allows the operator to gain all the benefits of NIR technology without the tradi-
tional problems and costs associated with data collection and model maintenance. � Operation for RON measurement with NIR technology is covered under multiple patents.� The robust nature of ABB Bomem technology also guaran-
tees that the prediction capability is unaffected by systemhardware maintenance.
� The precalibrated severity envelope covers normal gaso-line operating regimes while allowing octane trackingduring startup operations. Real time reformate RON analysis is now available,
turnkey and risk free.
A brief history ABB Bomem is a leader in refining industry NIR applications with over 200 project installations. These projects have resulted in significant experience and understanding of refinery blendstock quality and analysis. The widespread use of reformate in blendingmeans that the company has collected over 6000 samplesthat have been used to create a RON prediction model, whichcovers the CatReformir operating envelope of 86 – 103 octane. This database includes data from semi-regenerative, cyclic and continuous catalyst regeneration unitsoperating across all major refining regions using local naph-thas and with catalysts from all major vendors and licensors.
How can a universal NIR model for reformate RON be created?Every single ABB Bomem analyser has identical spectroscopic response. This stab-ility allows the transfer of calibrations from one analyser to another without the needfor re-calibration. This unique capability then allows the use of 6000 reformate calibra-tion samples, collected across multiple refineries, in any newrefinery reformate application. The combination of the com-pany’s spectrometer stability and vast database of reformatesamples has allowed the capture of basically all the RONvariations found in reformates over the severity range 86 – 103. This universal, turnkey model has encapsulatedthe RON characteristics of reformates produced using vari-ous process designs, feedstocks and catalyst combinations.
How good is the performance ?A test of this turnkey RON capability was carried out in a trial at a US West Coast refinery.93 local reformate samples were collected over the severity range 96 – 100.8 RON. Enginetests were performed to provide data for the creation of a local RON prediction model. Thismodel was then tested on the original samples and found to pre-dict the engine values within an error of 0.18 RON. This is a suc-cessful performance given the reproducibility of the engine itself.The CatReformir was then used to predict the same samplesand was found to predict the engine values within an error of0.20 RON with a nearly zero bias of 0.01. It is important to notethat no local sampleshad been included in theCatReformir model andso the universal modelwas truly being testedon blind samples.
ConclusionThe difference in performance comparing the local refinery model and the CatReformiruniversal RON model is 0.02 RON. Statistically, there is no difference between themodels given the NIR instrument repeatability. The CatReformir model was proven tobe statistically equivalent to a locally produced NIR model created from 93 samplesanalysed on a single instrument. These results are typical of those experienced atother refineries. This demonstrates that the CatReformir RON model, based on datacollected from a significant number of global refineries, can indeed be used for turnkeyreformate analysis in a new refinery.
Table 1. CatReformir performance test – US West Coast refineryLocal NIR Model Turnkey CatReformir model
Severity range (RON) 96 – 100.8 86 - 103NIR to engine RON 0.18 0.2reproducibility
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ing/isom complex is optimised.
Feed naphthas are commonly defined by hydrocarbonfamily (P,N,A) and distillation characteristics. The distillationcharacteristics are important as light feeds result in higherreactor temperatures, shorter run lengths and more ben-zene in the product. Higher end points usually result inaccelerated catalyst coking while naphthenic feeds givemuch higher yield than paraffinic feeds.
The operator can optimise the significant effects of feedquality changes by adding feed analysis capability to thebase CatReformir product. This includes additional sam-pling capability for the process analyser and models forparaffins, naphthenes, aromatics and distillation character-istics of reformer feed. The analysis of both reformer feedand product can be achieved on one instrument with eachstream available on a two minute cycle.
IsomerateMany refiners process full range naphtha in a combinedreforming/isomerisation complex. The operations of thesetwo units are closely tied and optimisation is usually carriedout considering both units as part of a single operatingcomplex. By adjusting naphtha fractionation, the refiner canincrease overall throughput of the complex and increasereformate or hydrogen yields. The maximum octane-barrelscan be achieved by an overall optimisation approach to thenaphtha complex. These different operating scenarios areideally implemented by rapid online characterisation of
reformate and isomerate.The operator can optimise the overall naphtha complex
by adding isomerate analysis capability to the baseCatReformir product. This includes additional samplingcapability for the process analyser and models for RONand MON. ABB Bomem has an extensive sample databasefor RON and MON of isomerate. The models are close tobeing universal and only require fine tuning locally withapproximately 10 samples. The analyses of both reformateand isomerate can be achieved on one instrument witheach stream available on a two minute cycle.
What are the benefits?Real time, turnkey RON analysis allows the operator of aCatalytic Reformer to:
� Maximise octane-barrels by optimum real time severitycontrol.
� Optimise run lengths of semi-regenerative units bytighter severity control.
� Minimise RON variation and reduce operating costs bytighter WAIT control.
� Reach optimum Tsor faster with rapid RON measurement. � Manage feed supply interruptions affecting severity.� Maintain product RON throughout the coking cycle.� Evaluate catalyst performance at vendor test condi-
tions.� Track product quality during bed changeovers for cyclic
reformers.� Optimise hydrogen production by tight severity control. � Track product quality during contaminant break-
throughs and process upsets.� Provide feed forward reformate octane data to the refin-
ery blender.� Optimise reformer/isom complex to maximise profitability.� Optimise product quality during varying seasonal
demands. � Optimise product quality during crude swings and
opportunity feed processing.� Maximise overall refinery octane barrels for multiple
reformer operation.� Optimise the petrochemical/refinery interface for chem-
ical feedstock reformers.
Catalytic reforming continues to have a significantimpact on refinery profitability despite ever tightening legis-lation governing the aromatics content of gasoline. Realtime, turnkey RON measurement can significantly assistthe operator in meeting the production and legislativedemands placed upon the catalytic reformer in this complexoperating environment.
Enquiry no: 26
50 HYDROCARBON ENGINEERING SEPTEMBER 2002
Figure 2. Lab/atline CatReformir.
Figure 1. Online CatReformir.
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The only NIR analyzer providing turnkey reformate RON measurement.
Reformate RON measurement is important inany catalytic reforming operation. The problemis that conventional methods have limitations.Problem solved.
ABB Bomem’s CatReformir provides fast,accurate on-line reformate RON measurement –without the need for local calibration. Validatedwith 6,000 reformate samples collected acrossmultiple refineries, CatReformir is the only NIRanalyzer that can offer a hassle-free, turnkey
approach. CatReformir is the proven solutionwith the versatility to extend measurementproperties to include MON, aromatics, RVP,benzene and more, including other streamssuch as reformer feed and isomerate.
With the predominant NIR technology position in the global petroleum refining market, ABB Bomem has already installed over160 projects in partnership with many of theworld’s pre-eminent refiners. Optimize yourcatalytic reforming operations with CatReformirand turn conventional problems into turnkeysolutions.
Introducing ABB Bomem’s CatReformir:the hassle-free solution you simply plug inand turn on.
