Operator Training Simulator in Ammonia Plants: Increase Safety, … · 2018. 8. 22. · duction performance increase of each ... It was quite a very simple calculation to be done

2011 [33] AMMONIA TECHNICAL MANUAL

Operator Training Simulator in Ammonia Plants: Increase Safety, Decrease Cost and Strengthen

Competitiveness

This paper presents the first year experience gathered about an advanced safety simulation process

successfully implemented at the two ammonia plants of SKW Stickstoffwerke Piesteritz GmbH in

Piesteritz, Germany. In the past, operation safety at ammonia plants has mainly been personally taught

and passed through generations of experienced operators to new ones. But what happens when a big

part of the experienced operators retire and when disturbances and plant upsets become rare? What is

the cost for the ammonia production business when the operator readiness to react to these upsets

weakens due to lack of practice? This paper describes how an operator training simulator (OTS)

implemented at the SKW ammonia plant revolutionizes the whole safety concept. The OTS enables

SKW to excellently train the operators to provide them with all skills to properly react in real-time to all

operation scenarios and especially during plant upsets. This ensures efficient risk management and

significantly reduces the number of unscheduled shut-downs. This in turn results in significant

economic benefits to the company allowing it to considerably strengthen its competitiveness.

Klaus Schübel

SKW Stickstoffwerke Piesteritz GmbH, Wittenberg, Germany

Norbert Ringer, Kisnaduth Kesore

Süd-Chemie AG, Munich, Germany

Marco Lanteri, Massimiliano Morniroli

APC Tech, Milan, Italy

Gregor Fernholz

Invensys Operations Management, Düsseldorf, Germany

Introduction

hat is the value of an Operator Train-

ing Simulator (OTS) in an ammonia

plant when the plant has been oper-

ated more or less safely according to the industry

standard for many years? This is an example of

the philosophical category called the unity of op-

posites. The challenges of maintaining a high

level of safety in the plant is that without distur-

bances or upsets in the plant the operators lack

the opportunity to get on-the-job training for ex-

actly these scenarios. Consequently, the

W

332011 AMMONIA TECHNICAL MANUAL


smoother the operation, the more the operators

will forget how to react in critical situations.

This is exactly what this paper addresses: giving

a very practical and proven answer to the above

dilemma through the implementation of an Op-

erator Training Simulator (OTS).

The production cost of ammonia is dominated

worldwide by its energy consumption. In com-

parison to this the personnel costs are negligible.

However, the qualification of the operators

strongly impacts the costs since approximately

30 % of the plant failures can be traced back to

them. Therefore, this paper demonstrates how

the problem of experience loss of the operators

due to replacement by a new generation of opera-

tors is solved at the SKW Stickstoffwerke Pi-

esteritz’ ammonia plant.

The safety process training represents one of the

most important tools in ammonia producing

plants to ensure safe and smooth operation of the

production plant and to provide the operators

with practical skills and readiness for emergency

situations. SKW has operated two NH3 plants

with a capacity of 1650 (metric) tons per day

each for more than 35 years. In the next five

years about 30 percent of the operators will retire

and will have to be replaced. This loss of experi-

enced operators and the need for maintaining a

highly skilled workforce by transferring knowl-

edge from the experienced operators to the ones

to be newly employed were the main decision

criteria for SKW to kick-off an Operator Train-

ing Simulator (OTS) project in 2008. This OTS

has successfully gone into operation in April

2010.

The OTS is based on Invensys Operations Man-

agements (IOM) software platform DYNSIM™

and was implemented by IOM’s OTS engineer-

ing team in close co-operation between SKW

Piesteritz and Süd-Chemie. This OTS enables

SKW Piesteritz to provide its operators with

best-in-class training and to empower them to

react reliably and reproducibly in the most effec-

tive way in cases of emergencies.

Catalytic technology plays a very crucial role in

the safety management as every deviation from

the optimized operational parameters can se-

verely impact the safety of the plant because of

its high pressure and temperature regime. More-

over, deviations from the optimal operation con-

ditions can be very large during failures poten-

tially leading to both irreversible physical and

economic damages to the plant. Süd-Chemie has

a long-lasting rich experience related to all kinds

of ammonia synthesis catalytic technologies.

Without doubt, besides its input about the han-

dling, operation and emergency measures linked

with the catalytic processes, the thermodynamics

and kinetics programs delivered by Süd-Chemie

are crucial components of the overall OTS sys-

tem at SKW’s ammonia plant.

This paper describes how the partnership among

the ammonia producer SKW Stickstoffwerke Pi-

esteritz GmbH, the catalytic technology supplier

Süd-Chemie and the automation and simulation

solutions provider Invensys Operations Man-

agement has been translated into a tailored Op-

erator Training Simulator and successfully im-

plemented at the ammonia plant, significantly

increasing the operations safety and also bring-

ing large economic benefits by avoiding plant

trips in case of any disturbances.

Training offered through the OTS can provide

the operators with a very high qualification level

to properly react in standard operation as well as

under stress during plant upsets with great confi-

dence, capabilities and readiness skills. It also

helps to overcome the problems of experience

loss linked with the operators generation change

in the control room. Finally, the OTS will deliver

very strong economic benefits and will support

the business sustainability in today’s world.

34 2011AMMONIA TECHNICAL MANUAL

2011

SKW Stickstoffwerke (SKW) and their Ammonia Production

SKW has operated since 1974/75 as a p

complex for the production of urea-

lizers. It consists of:

- 2 ammonia trains (2x 1650 mt/d)

- 3 urea production units (4000 mt/d)

- 1 mix-fertilizer plant (700 mt/d)

- 1 nitric acid plant (500 mt/d)

- 3 liquid fertilizer plants (2000 mt/d

The plant produces ammonia in two

the Kellogg process. The production of ammonia

started in 1974 and 1975, respectively, each with

a daily capacity of 1360 mt/d. Natural gas serves

as feed, which is supplied through a European

wide distribution network of natural gas coming

from different sources/countries. At the end of

the eighties there was a complex revamp of both

plants. The most important results were the pr

duction performance increase of each

1650 mt/d at a reduced natural gas consumption

of about 10 % and the change of the conventio

al automation system into a modern DCS.

Evaluation of the Production Situation at SKW in 2006

Till 2006 both ammonia plants were operated

with high productivity and good economics. The

failures occurrence was in line with the general

situation at other ammonia productions. SKW

was benchmarked in the first quarter among the

European fertilizers producers. Every two years

the plant was closed for the planned shut

This results in an on-stream factor of

95 %. However, there were still important re

sons for carrying out detailed investigations in

order to remain a competitive ammonia producer

in the market also in the future.

At the time of the start of operation of the plant

in the early seventies young, specialized techni

al staffs and university graduates were mainly

recruited. The inevitable personnel reduction in

[35] AMMONIA TECHNICAL MANUAL

SKW Stickstoffwerke (SKW) and

since 1974/75 as a plant

-based ferti-

2 ammonia trains (2x 1650 mt/d)

3 urea production units (4000 mt/d)

3 liquid fertilizer plants (2000 mt/d)

The plant produces ammonia in two lines using

rocess. The production of ammonia

started in 1974 and 1975, respectively, each with

a daily capacity of 1360 mt/d. Natural gas serves

as feed, which is supplied through a European-

of natural gas coming

from different sources/countries. At the end of

the eighties there was a complex revamp of both

. The most important results were the pro-

duction performance increase of each plant to

atural gas consumption

of about 10 % and the change of the convention-

al automation system into a modern DCS.

Evaluation of the Production Situation at

Till 2006 both ammonia plants were operated

with high productivity and good economics. The

ailures occurrence was in line with the general

situation at other ammonia productions. SKW

was benchmarked in the first quarter among the

Every two years

the plant was closed for the planned shut-down.

stream factor of about

%. However, there were still important rea-

sons for carrying out detailed investigations in

order to remain a competitive ammonia producer

time of the start of operation of the plant

specialized technic-

al staffs and university graduates were mainly

personnel reduction in

the nineties resulted in a situation where very

little new staff could be employed.

quence from this practice was that the average

age of the employees in the ammonia production

at SKW in 2006 was around 47 years (

Fig. 1).

Fig.1. Age structure of the employees at the SKW

ammonia production in 2006

It was quite a very simple calculation to be done

to know when which staff at which position

would be required to be replaced. On an average

in Germany, every employee at the industry r

tires at the age of 62. Based on this fact and

comparing to the operators age situation, the next

personnel demand till 2016 w

proposed (Fig. 2).

Fig. 2. Necessary personnel replacement till 2016

AMMONIA TECHNICAL MANUAL

the nineties resulted in a situation where very

new staff could be employed. The conse-

ice was that the average

age of the employees in the ammonia production

at SKW in 2006 was around 47 years (see

Fig.1. Age structure of the employees at the SKW

It was quite a very simple calculation to be done

w when which staff at which position

would be required to be replaced. On an average

in Germany, every employee at the industry re-

tires at the age of 62. Based on this fact and

comparing to the operators age situation, the next

personnel demand till 2016 was calculated and

Fig. 2. Necessary personnel replacement till 2016



The first and main conclusion from the above

investigation revealed that the experience level in

2016 would be halved (see Fig. 3).

Fig. 3. Experience with perspective

But this was only considered to be one important

aspect. The analysis has also shown that because

of the very scarce disturbance occurrence (on an

average of 1.5 emergency shut-downs per year

per train) and the continuously increasing cycle

time for the planned shut-downs, the operators

would be permanently having lesser practical

experience for managing failures situations and

shut-downs. Some of them did not even expe-

rienced trip conditions/situations for 10 years or

more. This means that the readiness by these op-

erators to deal with critical situations in the early

years of their careers is more and more lost.

Thus, SKW was confronted with the task to find

a way how personnel replacement could be effi-

ciently realized in a cost-effective manner and in

high quality, simultaneously minimizing the

danger from a higher number of failures occur-

rences caused by weakening readiness skills of

the operators.

Managing the Transition from Ex-perienced to New Operators

At SKW the retiring operator and the newly

hired will team up during a defined transition

period. New staff usually start working and gath-

ering experience in the field. After an appropriate

examination, the operator is transferred to the

control room. According to our experience a new

operator with standard qualification needs up to

three years in an ammonia plant before taking

the position as a self-responsible operator in the

control room. The training concept of teaming up

a new operator with an experienced one during

this training period has a significant impact on

the wage costs, because the same position in the

shift is filled with two operators. After a tho-

rough analysis directed towards the possibility to

reduce this cost, SKW concluded to implement

an Operator Training System (OTS). Through

this tool we aim to decrease the qualifying period

by at least one year.

Further investigation through experience ex-

change with other ammonia producer who were

already using an OTS in their plants, have also

shown that the experience lost over a longer time

interval, caused by low possibility of getting

trained how to manage critical situations, could

be significantly improved through an OTS.

The successful application of an OTS as a solu-

tion to the above problems bring with it a very

significant cost saving. With a cost-benefit anal-

ysis showing a ROI of shorter than 4 years, the

management at SKW decided to acquire and im-

plement an OTS for the ammonia plant.

The time factor determining the start of the

project was the replacement of the DCS (an-

nounced by SKW’s supplier partner) which was

planned for 2009. It was revealed that the supply

of the new DCS and the OTS should, in a mea-

ningful way, be done from “one“ hand so as to

avoid additional expenses. This, in turn, created

some delay in the start but eventually an agree-

ment was signed with the company Invensys in

March 2008 for the replacement of the DCS of

both ammonia trains and for the supply of the

OTS for the ammonia plant number 2. The new

DCS of the ammonia plant 2 was successfully

taken into operation in September 2009.


2011

Operator Training Simulation

The Concept

Operator Training Simulators (OTS) are co

puter based training systems where operators are

put in an environment resembling the real pr

duction plant (Fig 4).

Fig 4: Mapping of the components in the real plant

to the components of an OTS

All items of the real plant relevant to the oper

tion of the plant are represented in the OTS by an

adequate simulation component:

• The plant with its equipment is replaced by a

dynamic process simulator acting as a virtual

plant.

• The control systems with all control applic

tions of the real plant are represented by a

simulation (sometimes called “emulation”).

• A Human-Machine-Interface (HMI) that e

ables the operator to operate the virtual plant

as the operator console in the control room.

Requirements from the Plant OwnerOperator´s Point of View.

A key aspect to the success of OTS applications

is to make the training experience for

tor as close to real life a possible – the difference

between the OTS and the real plant should be

minimal to ensure efficient training, especially

for safety critical aspects. Therefore key r

quirements for SKW’s OTS are:


Operator Training Simulation

Operator Training Simulators (OTS) are com-

puter based training systems where operators are

bling the real pro-

: Mapping of the components in the real plant

All items of the real plant relevant to the opera-

tion of the plant are represented in the OTS by an

plant with its equipment is replaced by a

dynamic process simulator acting as a virtual

The control systems with all control applica-

tions of the real plant are represented by a

simulation (sometimes called “emulation”).

(HMI) that en-

ables the operator to operate the virtual plant

as the operator console in the control room.

wner /

A key aspect to the success of OTS applications

is to make the training experience for the opera-

the difference

between the OTS and the real plant should be

minimal to ensure efficient training, especially

for safety critical aspects. Therefore key re-

• A highly accurate dynami

that behaves exactly like the real plant, esp

cially in those areas considered to be critical

in terms of the safe operation of the plant.

Only if the model behaves exactly as the real

plant the operator will accept this as “his”

plant. And only if the model behaves like the

real plant the right behaviour will be pra

ticed during the training.

• The OTS should be used both for the field

operators and those in the control room. The

system should be adequately equipped to

train two control room and one field operator

at the same time.

• An exact representation of the control sy

tems. They need to behave exactly as the

control applications in the real plant. A

“similar” behaviour is not good enough

needs to be an exact replica in

tails and use of the actual DCS software as

well as the independent emergency shut

down system of the ammonia plant.

• The HMI for the operator in the OTS needs

to be identical to the operator stations in the

control room. The HMI needs to have ident

cal displays showing the same information

with the same interaction options for the o

erator. A crucial part of the training is that

the operator learns how to access the impo

tant information quickly and how to immed

ately implement the required steps on the o

erator console.

• Easy maintenance of the system to support

the adjustment and fine-

changes in the ammonia plant or the control

system.

• Easy-to-use graphical user interface (GUI)

that integrates the instructor station and the

engineer working place for the required mo

ifications tasks.

Operator Training Simulator (OTS) System Architecture

Based on the above requirements the key cha

lenges for building an OTS are twofold:


A highly accurate dynamic process model

that behaves exactly like the real plant, espe-

cially in those areas considered to be critical

in terms of the safe operation of the plant.

Only if the model behaves exactly as the real

plant the operator will accept this as “his”

only if the model behaves like the

real plant the right behaviour will be prac-

ticed during the training.

The OTS should be used both for the field

operators and those in the control room. The

system should be adequately equipped to

and one field operator

An exact representation of the control sys-

tems. They need to behave exactly as the

control applications in the real plant. A

“similar” behaviour is not good enough – it

needs to be an exact replica in the minute de-

tails and use of the actual DCS software as

well as the independent emergency shut-

down system of the ammonia plant.

The HMI for the operator in the OTS needs

to the operator stations in the

control room. The HMI needs to have identi-

plays showing the same information

with the same interaction options for the op-

erator. A crucial part of the training is that

the operator learns how to access the impor-

tant information quickly and how to immedi-

ately implement the required steps on the op-

Easy maintenance of the system to support

-tuning of the OTS to

changes in the ammonia plant or the control

use graphical user interface (GUI)

that integrates the instructor station and the

king place for the required mod-

Training Simulator (OTS) – the

Based on the above requirements the key chal-

lenges for building an OTS are twofold:



• Developing a software infrastructure that

supports the implementation of the three core

components (process simulation, control

simulation, operator HMI) with the required

accuracy.

• Developing and implementing the process

simulation model, control applications and

the operator HMI.

Invensys Operations Management’s (IOM)

DYNSIM™ platform is a process modelling and

simulation environment supporting all activities

from dynamic simulation for engineering pur-

poses to full-scale operator training. DYNSIM is

based on the SIM4ME architecture (Fig. 5) that

supports the integration of control applications

with a process simulation to form an OTS.

Each component is connected to the SIM4ME

simulation executive as a so called “engine”. The

SIM4ME simulation executive

• Manages the data between the different ap-

plications of the system,

• Synchronizes these applications and

• Controls the overall execution of the OTS via

the graphical user interface (GUI) of the in-

structor station.

Fig. 5. The DYNSIM system architecture for the

OTS.

For the SKW ammonia OTS the high-fidelity

process model is running in several DYNSIM

engines representing the virtual plant of the OTS.

The control system of the real plant consists of

an IOM Foxboro I/A DCS and an IOM Triconex

Tricon ESD. IOM’s OTS solution provides simu-

lation components for both applications: FSIM

Plus for the I/A DCS and TRISIM Plus for the

Tricon ESD. FSIM Plus and TRISIM Plus run

the same software code as the real hardware and

support the download of the control databases

from the Foxboro and Triconex engineering en-

vironment in the simulation without any modifi-

cation making sure that the simulation behaves

exactly as the real hardware and the real control

applications. Moreover, FSIM Plus fully sup-

ports the functionality of the Foxboro operator

consoles so that the HMI for the operator is iden-

tical to the operator consoles in the control room.

This solution exactly matches the respective re-

quirements as outlined in the previous paragraph.

The Challenges of Operating an Ammonia Plant.

In order to illustrate the challenges of operating

an ammonia plant and to highlight the necessity

of proper training this section shows a couple of

real-life examples from the operation of the

plant. Because the reactors are one of the most

complex and most difficult to operate units in the

plant, the reactors were analyzed in very detail.

In case of failures, the automatic emergency

shut-down system mainly cares for the safe shut-

down of the reactors and thus, damages could be

avoided. During start-ups and shut-downs the

possible field of influence of the operator is

however, larger and can due to wrong manipula-

tions results into time delays and also specific

equipment damages before the Triconex ESD

brings the ammonia plant into a safe operational

situation.

The ammonia synthesis at the SKW plant is cha-

racterized by a 2-step process. The fresh gas is

reacted in the fresh gas reactor through a single

GUI

DCS

FSIM Plus

Excel®

Engine

DYNSIMEngine

PLC/ESDTRISIM

Plus

3rd PartyEngine

GUI

SIM4ME

GUI

DCS

FSIM Plus

DCS

FSIM Plus

Excel®

Engine

Excel®

Engine

DYNSIMEngineDYNSIMEngine

PLC/ESDTRISIM

Plus

PLC/ESDTRISIM

Plus

3rd PartyEngine3rd PartyEngine

GUIGUI

SIM4ME



pass up to a 22 % ammonia yield mixture. This is

equivalent to approximately 35 % of the total

production. Due to the presence of a very low

inert gas concentration here, a very high yield is

reached in this reactor. This places higher and

stricter demands on to the catalyst during start-up

processes and also highest attention from the op-

erators.

For this reaction step, both ammonia plants use

the wustite-type iron catalyst AmoMax-10 from

Süd-Chemie, which has proved to be extremely

stable for the harsh conditions mentioned before.

The partly reacted fresh gas is put back to syn-

thesis process and is led to the synthesis cycle

there. Here the rest 65% of the ammonia is pro-

duced with the help of a big volume of catalyst.

Case Study 1: Start-of-Operation/ Reduc-tion of the Main Ammonia Reactor

For this reaction step there is need for external

quantity of heat, which is delivered by a natural

gas fired start-up pre-heater. The pre-heater is

equipped with four burners each of which is

lighted with a pilot burner.

Fig. 6. Example of a bad night shift

According to the existing legal regulations there

is an automatic emergency shut-down process in

place. It comes very close to the case that during

the heating up operation there is a failure of one

burner. This results in an interruption of the heat-

ing-up/reduction process. The impact of this in-

terruption strongly depends on the experience of

the operator if and how much time is lost until

the process could be continued. Fig. 6 shows a

particularly bad night shift.

Case Study 2: Start-up of Main Ammonia Reactor

It is not unusual that during small up-sets in the

ammonia synthesis loop (e.g., malfunction of the

instrumentation) fresh synthesis gas is again fed

to the ammonia synthesis reactors after a short

time. Very often the catalyst still has the neces-

sary high temperature to potentially achieve high

conversion rates especially in the case of the low

feed rates even at relatively lower pressures. This

would, according to design, lead to an increase in

of the exit temperature, which can reach the de-

sign value of the reactor piping. The operator is

left with the only option to immediately shut

down the synthesis losing even more valuable

time. Experienced operators master this chal-

lenge by balancing gas quantities, pressure and

temperatures saving valuable time (Fig. 7).

Fig. 7. Start Up of the main ammonia reactor

Such scenarios can be extensively trained

through the OTS. It allows to significantly better

control difficult situations.


2011

Süd-Chemie´s High Performance Catalytic Technology and its Dnamic & Kinetic Models

As demonstrated in the previous section the o

eration of the reactors is a challenging task. To

better understand the behaviour of the reactor a

detailed analysis of the thermodynamics and r

action kinetics is give.

The New Ammonia Synthesis Catalyst AmoMax-10®

Süd-Chemie´s highly active wustite type catalyst

AmoMax-10® has been proved to very succes

fully withstand all the severe conditions and a

rupt changes which are common during amm

nia synthesis. The second-to-none activity co

bined with the outstanding stability of this cat

lyst has set new standards for ammonia catalyst

in the industry. Fig. 8 proves the excellent the

mal stability of the AmoMax-10®

550°C. The activity (ammonia concentration in

outlet gas) was measured at 425°C. The result

shown here also reveal that even at this high

temperature the catalyst´s deactivation is very

slow, implying in a longer life time.

Fig. 8. Excellent high tacticity and thermal stability

of AmoMax® -10 compared to traditional magnetite

catalysts

The Ammonia Synthesis Reaction

Ammonia synthesis reaction is an exothermic,

equilibrium reaction, produced from a stoich


Chemie´s High Performance Catalytic Technology and its Dy-

As demonstrated in the previous section the op-

eration of the reactors is a challenging task. To

better understand the behaviour of the reactor a

detailed analysis of the thermodynamics and re-

sis Catalyst

Chemie´s highly active wustite type catalyst

has been proved to very success-

fully withstand all the severe conditions and ab-

rupt changes which are common during ammo-

none activity com-

with the outstanding stability of this cata-

for ammonia catalyst

Fig. 8 proves the excellent ther-

stressed at

550°C. The activity (ammonia concentration in

outlet gas) was measured at 425°C. The result

shown here also reveal that even at this high

temperature the catalyst´s deactivation is very

and thermal stability

compared to traditional magnetite

Reaction

reaction is an exothermic,

equilibrium reaction, produced from a stoichi-

ometric mixture of hydrogen and nitrogen and

promoted by an iron catalyst:

3�H2 + N2 �

This is the only reaction that occurs and no side

reactions are present.

Reaction rate equation and parameters was pr

vided by the catalyst vendor Süd

their AmoMax®-10 catalyst used by SKW in

their ammonia synthesis reactors.

point of view very accurate

models are required which exactly describes all

the changes and consequences form the catalytic

point of view. Here, Süd-Chem

a very exact model for the AmoMax

has been directly used in the OTS dealing with

the reactors system.

The equation rate is function of temperature,

pressure and molar fractions:

Where fi is the fugacity of the component

which can be written in terms of fugacity coeff

cients ∏i as:

The fugacity coefficient itself is calculated by a

correlation developed by Süd

Reactor Configuration

In the plant two ammonia reactors are present:

105-DA (fresh gas reactor) and

reactor) which are slightly different in terms of

the arrangement of the flow paths and heat e

change. Fig. 9 illustrates the complex flow pa

tern of the fresh gas reactor 105

example for an ammonia reactor where a co

plex reactor structure ensures optimal operation


mixture of hydrogen and nitrogen and

promoted by an iron catalyst:

2�NH3

This is the only reaction that occurs and no side

Reaction rate equation and parameters was pro-

vided by the catalyst vendor Süd-Chemie for

10 catalyst used by SKW in

their ammonia synthesis reactors. From the OTS

accurate dynamic and kinetic

models are required which exactly describes all

the changes and consequences form the catalytic

Chemie has worked out

a very exact model for the AmoMax-10®, which

has been directly used in the OTS dealing with

The equation rate is function of temperature,

pressure and molar fractions:

is the fugacity of the component i,

which can be written in terms of fugacity coeffi-

The fugacity coefficient itself is calculated by a

correlation developed by Süd-Chemie.

In the plant two ammonia reactors are present:

DA (fresh gas reactor) and 105-D (main

reactor) which are slightly different in terms of

the arrangement of the flow paths and heat ex-

illustrates the complex flow pat-

tern of the fresh gas reactor 105-DA. This is one

example for an ammonia reactor where a com-

tor structure ensures optimal operation



conditions using a specific combination of feed

flows and locations and heat transfer in the reac-

tor. In the fresh gas reactor the feed is preheated

in two embedded exchangers (WT1 and WT2),

flows inside the inner tube of the reactor (heat

transfer here is negligible) and then from the top

to the bottom reacts in the four catalyst beds: af-

ter the first two beds the reacted gas is quenched

to favor the reaction in the next bed. After the

third and fourth beds the reacted gas is used for

heating up the fresh gas in the heat exchangers

WT1 and WT2. Afterwards the gas is fed to the

two heat exchangers 123-CA and 123-CB and

then exits through the mantel side, for cooling

down the pressure shell.

The main reactor uses the conventional 4-bed

Kellogg quench concept. The overall combina-

tion of these two reactors makes the start-up and

operation of the reactor system a challenging

task and requires highly skilled operators.

Fig. 9. Reactor 105-DA: flow path has been highlighted (Magenta: feed and quench streams, Red: reacting

flows, Black: reacted flow exiting from the reactor)



Operator Training Simulator – Model Implementation

The process model

Invensys Operations Management and SKW

collaborated closely in the development of the

model structure required for the OTS. The proc-

ess model for the simulator covers around 30

process sections, including:

• Primary and secondary reformers.

• High and low temperature converters.

• CO2 absorption.

• Methanation.

• Synthesis gas compression.

• Fresh gas reactor ammonia.

• Main reactor ammonia.

• Ammonia refrigeration system

• Steam system.

• Utilities.

Different levels of the model accuracy were de-

fined to ensure that the model behaves sufficient-

ly realistically in the different parts of the plant

for the training purposes. Most units of the plant

were modeled with a high degree of accuracy

and level of detail. In units less relevant for the

training the requirements for the accuracy of the

model were relaxed. Although it might be desir-

able to model each aspect of the plant in the

highest possible accuracy the impact on the

project is obvious: Over-specifying the require-

ments results in additional investment in devel-

oping the OTS without adding benefits with re-

spect to the goals defined for the OTS and poten-

tially deteriorating the performance of the OTS

by overburdening the computer hardware with

unnecessary calculation and communication ac-

tivities. Therefore the decision on the required

level of accuracy was made based on the key

question: Is the model quality chosen satisfactory

enough for the qualification /training of the oper-

ator? For some specific equipments there were

naturally, very strict requirements imposed. That

mainly concerned the equipments where due to

the lacking of practical training /formation no

running optimal plant operation could be guaran-

teed or in failure situations and during start-ups

and shut-downs during critical situations or there

is loss of precious time to be taken into account.

The Reactor Model

Due to the complex nature of the synthesis of

ammonia the process model for the synthesis re-

actors was developed in close cooperation be-

tween IOM, Süd-Chemie and SKW Piesteritz

based on the reaction kinetics and thermodynam-

ics provided by Süd-Chemie (see previous sec-

tion) and the operational experience from SKW

Piesteritz.

Developing the reactor model for the ammonia

synthesis is a challenging task:

Complex reaction kinetics and thermodynamics.

Complex reactor design with multiple feeds,

quenches, integrated heat-exchange.

DYNSIM’s modeling capabilities address all is-

sues:

It handles reaction kinetics even of high com-

plexity like the kinetic developed by Süd-

Chemie for the ammonia synthesis.

It supports rigorous thermodynamic calculation

and supports user-added functions to e.g. calcu-

late fugacity coefficients provided by the user for

the kinetics.

It allows to create reactor models for a complex

reactor geometries and flow patterns by using

flexible, rigorous reactor building blocks. This

way the real geometry and flow patterns are

mapped in a reactor model.

The structure of the model of reactor 105-DA is

shown in Fig. 10. Comparing the structure of the

model to the structure of the real reactor (Fig. 9):

Each sub-section of the reactor catalyst beds

(acting as a reactor and as a heat exchanger), in-


2011

ternal heat exchanger, internal flow patterns, feed

and quench positions are represented in the mo

el matching the real reactor structure to the stru

ture in the model. Including the accurate therm

Fig. 10. Reactor 105-DA: DYNSIM model (reactor section only).

Process Model Validation

The process model was validated in the full o

eration regime of the plant from cold conditions

to full operation including the start

shut down. The accuracy of the model was tested

based on nearly 1000 reference values ens

that this model acting as the virtual plant is an

accurate representation of the real plant in all o


ternal heat exchanger, internal flow patterns, feed

and quench positions are represented in the mod-

el matching the real reactor structure to the struc-

e accurate thermo-

dynamics and detailed reaction kinetics provided

by Süd-Chemie in this structure results in a hig

ly accurate model.

DA: DYNSIM model (reactor section only).

The process model was validated in the full op-

eration regime of the plant from cold conditions

to full operation including the start-up and the

shut down. The accuracy of the model was tested

based on nearly 1000 reference values ensuring

that this model acting as the virtual plant is an

accurate representation of the real plant in all op-

eration modes relevant for the operator training.

The model was validate during

ceptance Test, Pre Factory Acceptance Test and

of course, also in Factory Acceptance Test and

Site Acceptance Test with

experienced operators, process engineers and

technology experts of SKW ensuring that the

OTS fully matches SKW’s requirements.


dynamics and detailed reaction kinetics provided

Chemie in this structure results in a high-

eration modes relevant for the operator training.

The model was validate during the Model Ac-

tance Test, Pre Factory Acceptance Test and

also in Factory Acceptance Test and

Site Acceptance Test with the participation of

experienced operators, process engineers and

technology experts of SKW ensuring that the

OTS fully matches SKW’s requirements.



A Training Scenario Example - Re-sults.

The capability of the OTS is demonstrated on a

typical scenario in the real plant. The scenario

considers the case of the start-up of the main re-

actor 105-D (Fig. 11).

Fig. 11. Scenario considering the case of the start-

up of the main reactor 105-D

The furnace 102-B is used to heat up the syngas

going to the reactor. The test was conducted with

fresh catalyst so it is already active at lower tem-

peratures (below 300°C). During the start up, the

beds are heated up slowly: The hottest bed is the

1st while the coldest is the 4

th. When the reaction

starts, the temperature gradient is steeper and

there is no need for a further increase of the fuel

gas flow to the furnace. Since the reaction is exo-

thermic, the reactor is able to produce enough

heat to sustain the reaction once the reaction

kicks-in, and the pre-heater is then stopped.

Quench flows are regulated by the operator in

order to keep under control the temperatures of

the beds to avoid overheating, till reaching stable

conditions.

As outlined in the section on the challenges to

operate the reactor this is a complex operation.

Thus, this illustrates that the high-fidelity OTS is

an adequate training tool for even the most com-

plex units and operation procedures.

The OTS. One Year in Operation

The Organisation of the Training

After installation of OTS, we also installed an

updated Foxboro command system on the OTS,

since January 2011 we have carried out training

for the control room operators and the field op-

erators as per our schedule of the previously

agreed plan. After some discussions the follow-

ing organisation was set-up:

1. An OTS-Team for the operation of the

simulator was set-up. The following per-

sons were chosen to make up the team: a

coordinator (Senior Process Engineer), a

main instructor (experienced control room

operator) and a process engineer (responsi-

ble for Model-Adaptation).

This team will work together for the next

one or two years in order to fine-tune the

simulator model, specially to match as

closely as possible plant dynamics.

2. The training was carried out at two levels.

a) The instructor trains, in agreement with

the shift manager, the present early

shift, preferably 2 staffs. During this

time, of course, the plant situation must

be observed.

b) In every shift an experienced staff is

trained as a shift instructor. Depending

on the personnel situation, as such, dur-

ing the early and late shifts and on

weekends, certain instructions are exe-

cuted. The training, its content and the

occurring problems are documented.

Through this practice, the OTS team

gets a number of tips about the neces-

sary adaptation of the model to the real

plant.

3. Changes to the model are made after hav-

ing agreement with the OTS Team. The

documentation occurs in a configuration

book.



Till now we have already carried out more than

600 hours of training through our instructors.

An Example from the last Month

Evaluation of Plant Hick-ups

On 16 February 2011 we observed a malfunction

of the kickback valve of the recirculation stage of

the synthesis gas compressor. This valve opened

in 3 seconds from 0 to 100%. The shift present

took 2 minutes to figure out the malfunction.

The first alarm came out from the NH3 refrigera-

tion system, the compressor hit the surge-limit.

After 3 minutes the valve was manually closed.

Through the rapid reaction of the operator we

could avoid a plant trip. And immediately in the

following shift, this failure was replayed on our

simulator. Also the OTS team compared the re-

action of the OTS with that of the real plant. The

most dominating parameters behaved according

to the real plant. The discrepancies observed, es-

pecially in the dynamics, were quickly elimi-

nated.

Conclusions

The OTS project has been executed in very close

collaboration between the ammonia producer

SKW Stickstoffwerke Piesteritz GmbH , the cat-

alytic technology supplier Süd-Chemie and the

automation and simulation solutions provider

Invensys Operations Management. The project

was very successfully completed in April 2010

with the performance test of the OTS.

Under the lead of the OTS Team, with a main

instructor and four shift instructors as team

members, a continuous training program has

been executed since December 2010. Through

this practice, a 24 hours usage of the simulator

could be sustained.

The training process is permanently adapted to

the rising demand. Specially, the realization of

training documentations poses a big challenge to

the OTS team and will still cost us some time.

The fine-tuning of the simulator models, in par-

ticular with respect to the dynamics compared to

the real ammonia plant, is the main focus point

of the OTS team task at the present. We want to

especially highlight that the acceptance of the

simulator by the operators has increased signifi-

cantly.

The successful deployment of the OTS and the

first results from training is the first step in suc-

cessfully managing the difficult task of the oper-

ator generation change and the problems of

maintaining the skills of the operators. Maintain-

ing this qualification is crucial to keep the high

level of plant safety, reliability of availability.

The first experience gathered with this advanced

simulation process clearly demonstrates how ef-

fectively it helped us not only to avoid tripping

of our two plants but also how to very rapidly we

now can react to upsets and solve any upsets

with confidence which all could have led to safe-

ty issues and economic drawbacks.



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Operator Training Simulator in Ammonia Plants: Increase Safety, … · 2018. 8. 22. · duction performance increase of each ... It was quite a very simple calculation to be done