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IMPROVEMENT OF SERBIAN POWER

PLANTS TE NT A AND TE NT B BASED

ON ALSTOM ECO|RAMTM STUDY

PERFORMED

Authors:

Dirk Renjewski, ALSTOM Power Service

GmbH, Germany

Vladimir Bozinovic, Thermal Power Plants

Nikola Tesla Ltd., Serbia

Peter Stegelitz, ALSTOM Power Service

GmbH, Germany

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1. Abstract

In 2006 ALSTOM was awarded a contract for a study for increase of power output,

efficiency and availability on the Power Plant TE NT A, unit 6. In a second contract was

performed a study for the unit 4 in the same plant focussing just on power output and

efficiency. A third contract for the Power Plant TE NT B, unit 2 was given by EPS in 2007

with the same aims. Both plants are lignite fired.

Forming a joint team of EPS and ALSTOM the three units have been assessed and areas for

potential improvements have been defined. The potential improvements are mainly focused

on:

- Increase of unit power output based on increased main steam generation in the boiler and

modernisation of steam turbines

- Increase of unit efficiency based on improvements in Ljungstroem type air preheater,

electrostatic precipitator, boiler feed pump and steam turbine

- Increase of availability based on a change in maintenance strategy

- Necessary adoptions and modernisations of other equipment like alternator, pulverisers,

pumps, fans, piping etc. in order to meet the requirements of an increased power output.

In a first phase after the assessment the jointly defined potentials have been elaborated

conceptually and the economic effects have been defined. Based on those economic effects

several potentials have been selected for further elaboration in detail.

It has been defined, that the unit power output can be increased in the range of 10 % mainly

based on the increased steam generation in the boiler while the efficiency increase is be

mainly based on steam turbine modernisations and improvements in the equipment as

mentioned above.

The approach used by EPS and ALSTOM in this study and the further project execution is of

wide interest for other power plant owners as it can be easily used and grant improvements in

power plant output, efficiency and availability.

2. ECORAM™

ECORAM is a tool developed by ALSTOM for detailed analysis of plant design, operation

and maintenance of a unit. Based on a systematic investigation of the plant as a whole and

considering most modern design approach ideas for increase of power output, increase of

operational flexibility, increase of availability, reduction of maintenance cost, reduction of

environmental impact are generated. By this the customer of ALSTOM is selecting the goal

to be reached. The customer provides the current operation data, the information regarding

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availability and maintenance as well as the basic economic figures for a rough economic

analysis of the ideas developed during the project; ALSTOM provides the necessary

benchmark data and the plant engineering know-how. The whole project is performed by a

joint team of customer and ALSTOM.

Picture 1 – Joint team Customer – ALSTOM

In a first phase the plant conception is analysed, the customer experience in operation and

maintenance is evaluated and based on the future operational requirements the gap is defined.

By this approach are developed ideas for improvements, which are conceptually designed,

determined and evaluated the effects and respective costs of modifications.

Picture 2 – Integrated systematic investigation of the power plant as a whole

• Technology (incl. R&D)

• Service

• Worldwide experience

• Operation

• Maintenance

• Plant data

Team

11++11>>22

Joint Team

Customer

• Increase of power output

• More flexible operation

• Increase of availability

• Reduction of maintenance cost

Goal

Balance of plant

Turbine/Generator

Boiler

Electrical

Environmental

I&C

Design Operation

Maintenance

-- SSyysstteemmaattiicc iinnvveessttiiggaattiioonn ooff tthhee ppllaanntt --

Integrated Study to Improve Plant Profitability

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In a second phase economic feasible ideas as per customer selection are further detailed up to

basic engineering level including economic comparison with alternative solutions,

determination of implementation times spans. As a result the customer will get an investment

plan for unit modernisation.

Picture 3 – General project set-up

The implementation of identified measures can be done by the customer alone or together

with an external partner or ALSTOM ECORAM team acting in such a case as consultant of

customer.

Project Set-up

Customer • Operation

• Maintenance

• engineering

• Service

• International Experience

Implementation

Plant assessment and appr. evaluation

Analysis of potentials

Solutions

Implementation plan

Phase 1

Phase 2

GO / NOGO

Steering Committee

-Contract, -Definition of targets, -Boundary

Conditions

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The ECO|RAM product family was started to be developed in the year 2000. Since that time

several projects have been performed. The next picture shows the reference list as per August

2008.

Status Customer Country Power Station/

Unit

Output Main Fuel

Order Year

Phase 1 Phase 2

Vattenfall Europe Generation (VE-G)

Germany Jänschwalde 6 x 500 MW

Lignite 2001 Finalised

DSK Germany EVA Ibbenbüren

27 MW Mining Gas

2003 Finalised

Hidrocantabrico Spain Abono 1 350 MW Hard Coal

2003 Finalised

RWE Power Germany Neurath E 600 MW Lignite 2003 Finalised

VE-G Germany Schwarze Pumpe

2 x 800 MW

Lignite 2004 Finalised

E.on UK United Kingdom

Ironbridge 2 x 500 MW

Hard Coal

2006 Finalised

Energy Randers Denmark Randers CHP

49 MWe + 105 MWth

Coal / Wood

2006 Finalised

EPS Serbia TE NT A6 308,5 MW Lignite 2006 Finalised Start November

2007

British Energy United Kingdom

Eggborough 4 x 500 MW

Hard Coal

2006 Finalised Start September

2007

EPS Serbia TE NT B2 620 MW Lignite 2007 Finalised Start November

2007

EPS Serbia TE KO B 2 x 348,5 MW

Lignite 2008 Start February

2008

Picture 4 – ECO|RAM references

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During the execution of several ECO|RAM projects it was found that in some cases the

ECO|RAM is too large to find a solution for the certain problems in plant operation and

maintenance. That’s why a new product group called STEP|x was developed. The generic

approach to such projects is the same as for ECO|RAM but as the project is fixed on the

solution of a more single problem like just output increase or increase of some equipment

capacity etc. the projects can become much smaller and faster to be done.

Currently the STEP|x product family consists of:

STEP|C Capacity/ Flexibility Increase

STEP|L Lifetime Extension

STEP|R System Re-Design

STEP|S Plant Status (Due Diligence)

STEP|W Water Chemistry/ Water Management

Customer Country Power Station/ Unit

Output Main Fuel

Order Year

STEP|x Status

ESKOM South Africa Arnot 6 x 350 MW

Hard Coal

2003 STEP|C Finalised

Vattenfall Heat Germany HKW Berlin-Mitte

400 MWth Gas / Oil


Tavanir Iran Bandar Abbas 4 x 320 MW

Oil / Gas

2004 STEP|S Finalised

VE-G Germany Jänschwalde / Boxberg

8 x 500 MW

Lignite 2005 STEP|L Finalised

EnBW Germany Heilbronn 7 750 MW Hard Coal


RWE Germany BASF 3 x 200 MW

Gas / Oil

2005 STEP|R Finalised

ESKOM South Africa Matla 6 x 600 MW

Hard Coal


STEAG SaarEnergie

Germany Weiher 680 MW Hard Coal

2006 STEP|W Finalised

DONG Denmark Studstrup 4 350 MW Hard Coal


ESKOM South Africa Kendal 6 x 730 MW

Hard Coal


E.on Germany Franken 426 MW Gas / Oil


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Customer Country Power

Station/ Unit Output Main

Fuel Order Year

STEP|x Status

RWE Germany BASF 3 x 200 MW

Gas / Oil


DONG Denmark Esbjerg 417 MW Hard Coal


EnBW Germany Heilbronn 7 750 MW Hard Coal


ESKOM South Africa Matimba 6 x 670 MW

Hard Coal


ESKOM South Africa Lethabo 6 x 620 MW

Hard Coal


ESKOM South Africa Tutuka 6 x 610 MW

Hard Coal


ESKOM South Africa Duvha 6 x 600 MW

Hard Coal


ESKOM South Africa Majuba 6 x 660 MW

Hard Coal


ESKOM South Africa Kriel 6 x 500 MW

Hard Coal


EPS Serbia TE NT A4 308,5 MW Lignite 2007 STEP|C Finalised

Hidrocantabrico Spain Abono 1 350 MW Hard Coal


SNET France Gardanne 868 MW Hard Coal

2007 STEP|W Finalised

Vattenfall Heat Germany HKW Berlin-Mitte

400 MWth Gas / Oil

2008 STEP|C Start September

2008

EnBW Germany Marbach 55 MW + 265 MW

Gas / Oil


DELTA Australia Vales Point 2 x 660 MW

Hard Coal


CGTEE Brazil Presidente Medici

2 x 63 MW Hard Coal


Picture 5 – STEP|x references

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3. Basic situation at TE NT B

Picture 6 – Power Plant Nikola Tesla B

The power plant Nikola Tesla B owned by Electric Power Industry of Serbia (EPS) is located

at the town of Obrenovac approximately 40 kilometres southwest of Belgrade.

The power plant consists of two identical units with a rated electrical output of 618,4 MW

each. The steam generators installed are capable to burn lignite fuel from Vreoci and

Tamnava mines. Main and auxiliary cooling water cycles are of open type mainly. Original

suppliers of major equipment are:

- Steam generator Rafako, Poland based on a Sulzer license

- Steam turbine and generator BBC, Switzerland

- Boiler feed pump Sulzer, France

- Main transformer Minel, Serbia

The units are running in base load operation mode.

4. Site assessment

As part of the co-operation between EPS and ALSTOM it was agreed to perform a two week

site assessment in order to get an overview about the current operation and maintenance

conditions of the units. Therefore by EPS was completed a questionnaire before assessment

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start and during the assessment interviews regarding all operation and maintenance questions

have been performed.

It was found during the assessment that the boiler operation represents the most non-reliable

part of the unit. The reasons for this circumstances are mainly seen in big fluctuations in coal

quality as delivered from the mines to the power plant in regard of heating value range from

6,0 MJ/kg up to 9,3 MJ/kg and particle size resulting in damages based on corrosion and

erosion on the several heating surfaces as well as lack of pulveriser capacity from time to

time. Furthermore it was found that the fresh air flow through the Ljungstroem type air

preheater is just 70 % and the other 30 % of fresh air for burning is false air.

During the site assessment 25 ideas have been developed. They have been grouped into:

- Power output increase Boiler feed pump capacity

Pulveriser capacity

Boiler improvements in order to reach increase steam

flows

Cooling water flow increase through auxiliary condenser

Increase of steam turbine swallowing capacity in order to

meet increased steam flows from boiler

- Unit efficiency increase Improve of pulveriser operation

Reduction of hot gas recirculation

Improve Ljungstroem type air preheater sealing

Energy optimisation and improved control system of

Electrostatic precipitator

In the following two examples the major interest is laid on the power output increase.

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5. Example 1 – Optimisation of steam generator area

Picture 7 – Optimisation of steam generator and air preheater

As determined during the site assessment the steam generator is in general capable for a 10 %

main and reheat steam output increase. To reach this it is necessary to bring the steam

generator back to the original design conditions including an improved sealing of the furnace

and the Ljungstroem type air preheater.

The bottleneck for the output increase in this area is seen in the capacity of the beater wheel

mills. In general - the beater wheel mill as hearth of a lignite firing system is determining

directly the power output of the boiler. Based on the function of the mill acting like a radial

fan, the mill sucks the hot flue gases required for coal drying and transport out of the

combustion chamber independently. In the same time the lignite is pulverised to a predefined

fineness of the coal dust. The basic processes drying, pulverising and dust transport –

ventilation – are linked together in a way that a system analysis is mandatory.

Optimisation of Steam generator and Air Heater

1

2

3

4

1 – High leakage rate across air heater 2 – High leakage rate in the boiler area 3 – Low amount of combustion air 4 – Low amount of secondary air at

burners 5 - High damage rate of heating surfaces 6 – Limits for a 110 % load operation

5 6

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The picture 8 shows in a schematic manner the circuit of the system beater wheel mill

consisting of:

- Recirculation duct

- Mill

- Classifier

- Dust piping

- Burner

- Combustion chamber

Picture 8 – Circuit lignite firing with beater wheel mill

Com

bust

ion

Cha

mbe

r

Burner

Primary Air (~300°C)Hot Gas

(>1000°C)

Lignite(Feeder)

Beater Wheel Mill with Classifier

Height [m]

Pressure [mbar]

(-) 0 (+)

Com

bust

ion

Cha

mbe

r

Burner


(>1000°C)

Lignite(Feeder)


Height [m]

Pressure [mbar]

(-) 0 (+)

Com

bust

ion

Cha

mbe

r

Burner


(>1000°C)

Lignite(Feeder)


Height [m]

Pressure [mbar]

(-) 0 (+)Height [m]

Pressure [mbar]

(-) 0 (+)Height [m]

Pressure [mbar]

(-) 0 (+)

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System parts Pressure loss Pressure win Pressure build up

(1) Recirculation duct X

(2) Mill door X

(3) Combustion chamber X

(4) Burner and pulverised coal duct

X X

(5) Classifier X X

Summary PL + PW = (6) Mill – Beater Wheel

Table 1 – Rough system analysis

The picture shows that changes on the single components of the system (dimensions, shape,

baffles etc.) are changing the requirements on the power output of the mill itself. The same

applies if the coal quality is changed and/ or the coal quality range width is widened.

The following reasons can reduce the output of the beater wheel mill system:

- Pressure loss

- Wear or maintenance strategy

- Maintenance quality

- False or uncontrolled air

- Improper measurement instruments or insufficient number thereof installed

- Overloading by fuel

In order to define the fuel quality depending system optimum in regard of fuel amount and

efficiency/ economy the following should be performed:

- Detailed assessment of the system

- Process analysis

- Mill measuring based on mill test operation

- Detailed fuel analysis including determination of pulverising capabilities in a beater wheel

mill

- Assessment of maintenance approach and quality

- Theoretical simulation.

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After the first estimation and after the implementation of the measures as mentioned below,

the capability of the plant components are likely to be sufficient in order to achieve the

requested targets of the mill process:

- Coal – homogenisation (decreased range of heat value variations), reduction of xylite

parts, coal – ONLINE - analysis as an active control value etc.

- Intense decrease of leakage resulting in improvement of combustion, temperature control,

flow etc.

- Decrease of pressure loss in the mill

- Optimisation of the coal distribution

- Increase of the control ability of the mill (new control curves, more and/ or modern

measurement equipment)

- Use of wear-material with higher life time

- Optimisation of the maintenance and repair

- Adaptation of the pulverized fuel ducts and the firing system

6. Example 2 - Increase swallowing capacity of steam turbine

Picture 9 – New HP-Turbine blade path

On turbine and generator side the HP-turbine represents a bottleneck. The currently installed

HP-turbine is not capable to cover the increased main steam flow without increase in main

steam pressure. Therefore it is necessary to redesign the steam path of this turbine.

It was performed additionally an analysis of the other equipment in the water-steam-cycle in

order to determine other systems to be modified, e.g. alternator and condensate extraction

pumps.

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7. Example 3 – Energy optimisation of Electrostatic precipitator

The currently installed ESP control is trying to introduce as much energy as possible into the

system and therefore to remove the maximum possible amount of dust.

It is proposed to install a different control system as the recent experience with different

lignite fuel types has shown that there will be no any further decrease of dust emissions upon

certain strength of the electric field. The proposed system performs automatic self

optimisation of the power input in relation to the required dust emission level. By this power

savings in the range of up to 80 % can be realised without an important change of the emitted

dust level.

Picture 10 – Energy optimisation of ESP

8. Example 4 – Change in maintenance strategy

The currently used in TE NT B maintenance strategy is based on performing major overhauls

every 8 years with a usual 120 days period, medium overhaul every 3 years – 45 days period

planned - and minor overhauls each year for a time span of 30 days. This maintenance

strategy is reflecting the pure preventive maintenance approach and does not fit to current

needs in Serbian electric power grid suffering a lack of electricity.

Installation of dust emission measurement and connection with the control cubicles and installation of new control equipment

Energy optimisation of ESP

Control cubiclesHigh Tension

Rectifier Dust emission

measuring

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In order to improve the maintenance strategy it is recommended to perform intensive

technical and social competency based training for operation and maintenance staff on all

levels and to provide them with modern computerised maintenance management systems.

After performing those measures it is possible to change the maintenance strategy to a more

predictive type one in one of the following two alternatives:

Major overhaul every 8 years for a 73 days period

Medium overhaul every 4 years for a 44 days period

Minor overhaul every year for a 9 days period

Or

Major overhaul every 6 years for an 86 days period

Medium overhaul every 6 years for a 60 days period

No minor overhaul as the equipment will be maintained during unplanned shutdowns only.

For this an unplanned unavailability of the unit per year should be considered. As the major

reason for unplanned shutdown of the unit is seen in boiler area no change compared to

today’s situation in unavailability is expected.

The installation of new or modernised/ retrofitted equipment in the power plant gives the

additional chance to increase the time span between two overhauls. E.g. for ALSTOM steam

turbines the maintenance recommendation shows a time span of 100000 equivalent operation

hours between two major overhauls.

9. Summary TE NT B

The study performed show that it will be possible to increase the power output of each unit in

TE NT B by 49 MW without major investments required. A further output increase is

possible based on new IP- and LP-turbine design but is requiring major changes in the

alternator and therefore higher investments.

By this the steam generator is not overloaded – the material limits are used to a higher extend

only.

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10. TE NT A

The power plant Nikola Tesla A owned by Electric Power Industry of Serbia (EPS) is located

at the town of Obrenovac approximately 30 kilometres southwest of Belgrade.

The power plant consists of six units with a rated electrical output of 2 x 210 MW, 1 x 305

MW and 3 x 308,5 MW.

The steam generators installed are capable to burn lignite fuel from Vreoci and Tamnava

mines. Main and auxiliary cooling water cycles are of open type mainly.

The unit analysed have been No. 4 and No. 6. Original suppliers of major equipment are –

Unit No. 4

- Steam generator Tlmace, Slovakia based on a Babcock license

- Steam turbine and generator ALSTOM, France



Unit No. 6

- Steam generator Rafako, Poland based on a Sulzer license

- Steam turbine and generator ALSTOM, France



The units are running in base load operation mode.

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Picture 11 – Power Plant Nikola Tesla A

It was determined by the assessment and further home office elaborations that on both units

the steam production from the steam generator can be increased by 10 % as well as for TE

NT B. This was taken as basic point for the further elaborations.

On unit A4 the maximum achievable power output is limited by the alternator design to a

maximum of 386 MVA while on unit A6 this value is 405 MVA – both based on stator

cooling water flow and hydrogen pressure increase to a technically reasonable and economic

extend.

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As EPS is considering the installation of an additional district heating extraction from the

power plant, the study recommended using for this the unit A4. On unit A6 it was

recommended to use the maximum permissible power output increase. In order to reach this

it was proposed to perform the following activities:

- Steam generator Extended major overhaul

- Beater wheel mills system Improve operation

- Steam turbine Retrofit of all turbine parts

- Alternator Increase of stator cooling water flow and hydrogen

pressure after major overhaul

- Boiler feed pump Replacement of pump cartridge

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