Experience with a Simulator forTraining Ammonia Plant Operators

A computer-based simulator was used for training operators, priorto the start-up of a new fertilizer complex which includes a 1,350-MTPD ammonia plant, two 1,100-MTPD urea plants, and a steamand power generation plant with two 18-MW gas turbines. Thesimulator offered many benefits, which can be used for continuededucation of operators and engineering studies.

S. ManiIndian Farmers Fertilizer Coop Ltd., Aonla Project, India

S. K. ShoorCombustion Engineering Simeon, Inc., Bloomfield, NJ

Hans S. PedersenHaldor Topsoe A/S, Denmark

INTRODUCTION

The Indian Farmers FertilizerCooperative Limited (IFFCO) Aonlaproject, consists of a 1350 MTPDammonia plant based on Haldor TopsoeA/S technology, two 1100 MTPD ureaplants based on Snamprogettitechnology, and a steam and powerplant with two 18 MW gas turbines(see Figure 1). The plant uses amodern distributed control system(DCS) supplied by CombustionEngineering's subsidiary, ProcessAutomation Business, Inc.

In 1986, the management of IFFCO wasfaced with the question of operatortraining for its Aonla facility.After weighing various options, itwas concluded that a trainingsimulator which duplicates thedynamic behavior of the plant wouldbest serve the training needs atAnola. It was recognized that theconventional approach of using theactual plant for operator trainingwas highly restrictive. With such anapproach, the operators cannot startup and shut down the plant or respondto abnormal events repeatedly.Similarly, in-plant training does notpermit the operators to recreate anoperating problem and try alternativeapproaches to solving it.

The training simulator, whichincludes completely interactive andintegrated models for ammonia, urea,and steam/power plants, was suppliedby Combustion Engineering Simeon(Simeon) of Bloomfield, New Jersey.The simulator is the first of itskind in the Indian fertilizerindustry.

At the time of this writing, theplant was at the initial stages ofcommissioning and the simulator wasbeing used extensively for operatortraining, as well as for checkout ofoperating procedures and the controlsystem.

PLANT DESCRIPTION

Ammonia

The ammonia plant has a capacity of1350 MTPD and is based on HaldorTopsoe A/S technology. The plantuses well known processing stepswhich are summarized below (seeFigure 2):

Natural Gas Desulfurization

- Primary and Secondary Reforming

Shift Conversion

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CO2 Removal by Benfield System

Methanation

- Synthesis Gas Compression andAmmonia Synthesis

Refrigeration and ProductRecovery

- Steam System.

Urea

The urea plants are based onSnamprogetti process in which ammoniaacts as a stripping agent and assistsin the decomposition of carbamate(see Figure 3).

The major process steps of the ureaplant are summarized below:

Feed Compression/Pumping

urea Synthesis

- Carbamate Decomposition andRecycle

- Evaporation

Prilling

Waste Water Treating.

Steam/Power Generation

The steam and power generation plantconsists of the following systems(see Figure 4):

Boiler feedwater

- Service boiler which generatessteam at 115 kg/cm2g

Heat recovery boilers which alsogenerate steam at 115 kg/cm2g fromturbine exhaust gas

- Two gas turbines with a capacityof 18 MW each

Steam distribution systemconsisting of HP, MP, and LPheaders.

NEED FOR SIMULATOR TRAINING

A modern fertilizer plant is a highlyintegrated and interactive processfacility where a problem or upsetexperienced in one area of the plantimpacts the operation of other areas.An effective training program whichpermits the operating personnel todevelop an understanding of theseinteractions so that they cancorrectly respond to various upsetsis considered a key to successfuloperation. Faulty operation coulddamage equipment and imperil theplant and the personnel.

Ammonia-urea production is energyintensive. Improper operation oftenresults in excessive energy usage.Further, because this is a capitalintensive plant, it is necessary tocommission and stabilize theoperation at full capacity as quicklyas possible. The traditionaltraining approach in which operatorsgain the necessary skills throughactual operation over a long period

of time is, therefore, an expensiveproposition. At Aonla, even thoughmost operators had previousexperience, few were exposed to thesame technology. Therefore, plant-specific training was necessary forpreparing the operators forsuccessful plant startup andoperation.

Conventional training emphasizesclassroom lectures followed byinplant training for experiencedoperators. However, there arelimitations to that approach:

- Trainee does not get a good feelfor operating the plant since hecannot change the operatingparameters and learn cause andeffect relationships.

Training is at best limited toactual situations that arise inthe plant during the trainingperiod.

Training for handlingemergencies, startup, andshutdowns are difficult.

Concept of learning by doing is

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not possible since mistakescannot be tolerated in a runningplant.

Computerized simulator trainingovercomes these limitations. Theability to create realistic trainingsituations without the risk ofdamaging or upsetting the actualplant facilities is a great advantageof the simulator.

Recognizing operator training as animportant requirement for efficientand safe plant operations, IFFCOacquired a computerized trainingsimulator for its Aonla project.

SIMULATOR HARDWARE

A simulation computer, an instructorstation, and operator stationsconstitute the hardware of thesimulation system (see Figure 5).

The simulation computer is a MicroVAXII system with 9 MB memory, a 456 MBfixed disk, a 90 MB cartridge tape,a VT220 console, and an LA120printer.

The instructor station consists of anAydin monitor, a standard keyboard,and an LAI20 printer. The instructorstation provides various trainingfeatures that allow the instructor tocontrol the training exercise andmonitor the process conditions andthe trainee's actions.

The operator station comprises a CRT-based emulation station and TaylorMOD 30 XL intelligent single-loopdigital control instruments mountedon a panel. The MOD 30 panelconsists of dual indicators,controllers, recorders, annunciators,multi-point digital indicators, andpushbuttons.

In this arrangement, all controlleractions and meter indications areexecuted by the simulation computer.Although the actual plant uses a verylarge panel with many controllers,the simulator includes only one partof the panel sufficient to operateone section of the plant at a giventime, say, the ammonia synthesisloop. The rest of the plant isoperated and controlled from the

emulated station. This type oftrainee station is cost-effective andalso allows the trainee to understandand respond to all the . interactionsamong various sections of the plant.

SIMULATOR SOFTWARE

A customized ammonia plant model wasdeveloped for simulator-basedtraining. The model simulates 150 ofthe important control loops.Emphasis is on the simulation ofcontrol room operations. inaddition, the following models weredeveloped: a semi-customized • ureaplant (40 loops) , a generic steam andpower plant, a two-stage centrifugalcompressor, and operationfundamentals.

Ammonia Model

This is a completely interactive andcomprehensive model of a 1350 MTPDammonia plant and was developedjointly by Simeon and Haldor TopsoeA/S. The model is customized to theprocess flow sheet being adopted byIFFCO's Aonla project. Processcontrol schemes, trip system, andcritical standby equipment aresimulated.

The ammonia model simulates primarilycontrol room operations. However,realistic training cannot be givenunless selected field operations arealso simulated. This is achievedthrough the use of remote functionscontrolled by the instructor. Acritical training requirement is theneed to train operators to handleemergencies due to equipment andinstrument failures. Therefore, aset of malfunctions are programmedwhich can be introduced by theinstructor and corrected by thetrainee.

i

The malfunctions simulate the failureof rotating equipment, partial andtotal loss of the utilities supply(such as cooling water and electrical

power), spurious trips resulting frominstrument faults, instrumentfailures, and tube leaks in criticalexchangers and the reformer tubes.

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Urea Model

The urea model is based onSnamprogetti process and is also afully integrated dynamicrepresentation of the plant. Itconsiders the interactions of varioussections of the plant as they affecteach other through changes in theoperating parameters. The modelincludes all major control loops andinstruments, as well as typicalupsets and failures in the form ofinstructor-initiated malfunctions.

Steam/Power Generation Model

The steam and power generation modeldynamically simulates the operationof a boiler feedwater system, autility boiler, a cogeneration systemincorporating a gas turbine, and aheat recovery boiler.

Standard Models

The standard models of basic unitoperations consisting of a mixingtank, exchanger, pumps and a boilerare included so that the newoperators with little or no plantexperience can familiarize themselveswith the basic processing principles.

MODEL DEVELOPMENT

The process models were developedusing Simeon's proprietary GEPURS™(GEneral Purpose Realtime Software)software. Some custom-designedalgorithms were also incorporated tomodel the plant (such as, forexample, the Topsoe S-200 radial flowammonia converter). GEPURS, a block-structured language, simulates theprocess dynamically and in real time.

Algorithms are selected from astandard math or process algorithmlibrary to simulate variouscomponents of a process flow sheet bymeans of blocks. Physical,thermodynamic, and processcoefficients are included in theblocks to match the actual processparameters. The blocks are thenlinked together in their logicalsequence to simulate the flow sheetand then are activated to simulatethe process being modeled. Theseactivities can be carried out onlineand interactively. Adding new blocks

and changing blocks does not requirecoding or recompilation. After theplant startup, IFFCO engineers willbe able to tune and modify the modelas required to adhere to physicalchanges in the plant or to conform tosubtle dynamic responses of the plantwhich may differ from those of themodel.

SIMULATOR OPERATION

The operation of the simulator issimple and is achieved through menu-dri,ven commands. The instructorstation allows the instructor to loadvarious models and associated initialconditions. The instructor can startor stop a model, generate an eventlog, and take snapshots at apredetermined interval. He can alsoreplay the snapshots to recreateevents, and he can monitor theprocess through multi-trend displays.He can introduce malfunctions, createscenarios for various trainingsituations, and play those scenariosand save intermediate processconditions for starting from the samepoint at a later time. Theinstructor also takes the role of afield operator when he responds torequests from the trainees to operatefield controls through the use ofremote functions.

The instructor station can beconverted by a software command intoan engineering development stationfor monitoring internal modelparameters, changing the model, andfine-tuning the model's dynamicbehavior.

The trainee controls the processthrough a generic emulated stationusing CRT displays, or through MOD 30panelboard instruments. All controlfunctions are performed by thesimulation computer by means ofsoftware. Group displays, overviews,alarm summaries, alarm details,process graphics displays, trenddisplays and other display facilitiesare available.

OPERATING EXPERIENCE

All IFFCO shift engineers weretrained as instructors using thesimulator. Both instructors andtrainees learned the mechanics of

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operating the keyboards in a shorttime. Four training sessions,lasting about two hours each, wereadequate to make them familiar withkeyboard operations.

At the time of this writing, thesimulator had been in full operationfor only a short time. Exercises onstartup/shutdown, steady-stateoperation, changing the plant load,and stabilizing the processparameters at various load conditionshad been carried out. Otherexercises had included operatorresponse to perturbations in the fuelgas, feed gas, and steam systems.During various exercises, operatorshad become familiar with the processcontrol schemes and normal operatingparameters.

Insights had been gained into thekind of operating practice requiredunder special circumstances. Onesuch instance relates to the fuelflow to the primary reformer.Besides NG, the primary reformer atIFFCO's Aonla project uses purge gas,and any surplus synthesis gas asfeed. The NG fuel flow is underpressure control. During plantupsets, startups, and shutdowns, thefuel mix changes. Although the NGfuel flow is maintained underpressure control, the temperatureresponse of the reformer changesbecause of change in the calorificvalue of the fuel mix. When thetrainees encountered this situationthey recognized the need to changethe set point of the NG pressurecontroller or to switch to manualcontrol to maintain the reformerfurnace operation. In fact, a goodidea of the changes in the set pointneeded for various mix of fuels wasgathered by simulating appropriateconditions.

Training for malfunction response isone area where simulator trainingprovides an excellent benefit byenhancing the plant's safety andreliability. This is expected to bea highly useful exercise for both newand experienced operators.

The simulator's performance has beenvalidated with the design data. Asmore operating experience becomesavailable, a more rigorous validation

of the simulator response vis-a-visactual plant behavior will be carriedout.

If the simulator is to remain auseful tool, the model must undergomodifications when modifications aremade to the actual plant. After ashort GEPURS training course, IFFCOengineers are now able to tune andchange the model. This ability willkeep the model current in comingyears.

CONCLUSION

The simulator is an advanced trainingtool with excellent capabilities forproviding hands-on experience in atrue-to-life environment. It isequally useful for training newoperators and for refresher trainingof experienced operators. It isespecially valuable for trainingoperating personnel on faultdiagnosis and developing appropriatecorrective strategies to minimizeprocess upsets, thereby improving thereliability and safety of the plant.The dynamic simulator is also ofsignificant benefit in carrying outprocess studies to evaluatealternative process control schemesand operating parameters.Computerized simulator training wasintroduced to the Indian fertilizerindustry at the IFFCO Aonla project,and valuable experience is beinggained on this new trainingtechnology.

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NATURAL GAS

WATER

AMMONIA

PLANT

AMMONIA

CARBON DIOXIDE

STEAM

POWER

UREA

PLANT

UREA

STEAM/POWER

PLANT CONDENSATE

Figure!. IFFCOAonlaproject.

NATURAL QAS

AMMONIA PRODUCT

Figure 2. Ammonia plant processes.

Figure 3. Urea plant processes.

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HP STEAM

NATURALGAS

WATER

Figure 4. Steam/power plant systems.

INSTRUCTORSTATION

COMPUTERCOMPLEX

OPERATORSTATION

SYSTEM•-PRINTER -

INSTRUCTOR CONSOLESYSTEM CONSOLE & PRINTER

OPERATOR CRT'S & KEYBOARDS

fcn-.PRWTER

LOGGING PRINTER

• » MB MEMORY

• 456 MB DISK

• 16 COMMUNICATIONS PORTS

• 90 MB TAPE CARTRIDGE

i!ID

MICROVAX II CPU

-AMMONIA MODEL

-UREA MODEL

-STEAM «POWER MODEL

• UTILITY BOILER MODEL

- FUNDAMENTALS MODEL

SOFTWARE

PANELBOARD

• 32 MOD 30 XL CONTROLLERS

• « DUAL INDICATORS

• 32 ANNUNCIATORS

• 40 BACKLfT SWITCHES

• 82- PEN RECORDERS

• 2 DIGITAL METERS W/40 SELECTOR SWITCHES

Figure 5. IFFCO simulator system.

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Photo 1, Training session in progress.

2. Simulator control panel—Taylor MOD 30.

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DISCUSSIONT. CHALLAND, The M. W. Kellogg Company, Houston,TX: Would you tell me what the delivery time wasfrom ordering the simulator to its receipt on site? Whatwas the approximate cost?

S. MAN!, IFFCO, New Delhi, India: Delivery time waseight months and the cost was approximately$700,000.

M. APPL, BASF Aktiengesellschaft, Ludwigshafen,West Germany: Is your simulation just displayingschematically the interdependencies and the func-tions, or is it a real picture of your plant, in whichreal time simulation can be done? Are there realvolumes of reactors, holdups, kinetics, status of activityof the various catalysts, etc. incorporated? How highis the fidelity of that simulation? Can you really showin real time the development of events? For example,'let the air compressor trip. Is it possible to see howthe plant situation deteriorates until finally the wholeplant will trip?

MANI: The simulator is based on actual data sheetsand actual process flow diagrams.

APPL: In addition tp the schematic sequence of theprocess flow diagram, to what extent are the realdimensions of vessels and reactors with holdups andvolumes and so on incorporated to your model?

MANI: It takes actual dimensions of the equipment,of the reactors, catalysts, etc. At 100% normaloperating conditions, simulated process value will bet 2% of the actual process values. When you activatea trip the way the simulation process behaves willbe similar to the actual process. However, actualvalues of process parameters and their simulatedvalue during such a condition requires to be validated.

So far, validation has been done only with referenceto design values.

APPL: So it's no problem, for example, to feed in adifferent activity for the catalyst? If it is aging?

MANI: Yes, it can be done.

J.E. JARVAN, Haldor Topsoe A/S, Lynby, Denmark:I have a comment about Dr. Appl's question on kinetics.The process simulator contains a kinetic model forthe ammonia synthesis converter, which we deve-loped, and it has a very good fidelity for simulatingthe ammonia synthesis converter and you can alsodetermine the activity of the catalyst.

W. ARMSTRONG, CIL Inc., Courtright, Canada: Whenyou were describing your training area, you stated youhad a Mod 30 control panel operating in parallel withthe TDC 2000 console, and then you referred to aTaylor Mod System which is also a distributed controlsystem. What is the present plant control system?

MANI: The present plant control system is a Mod 30.We are also simultaneously in the first phase ofoperation in Mod 300 and maybe in another six toeight months it will be a Mod 300. Both are availablein the plant. TDC 2000 is available only on the simulator.Actual plant does not have a TDC system.

G.G. GONZALEZ, Petroquimica de Venezuela, S.A.,Venezuela: In your simulator system, do you believeyou could change the instructor's station into a backupoperator station in case of operator station failure?

MANI: We have two operator stations. You cannot havea system without an instructor station. However, anyterminal can be configured as either instructor oroperator station.

GONZALEZ: Thank you.

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