IMPROVEMENT OF SERBIAN POWER PLANTS TE NT A AND TE NT B BASED ON ALSTOM ECO RAM TM 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 Page 1 of 18
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 Page 2 of 18
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. Joint Team Customer Operation Maintenance Plant data Team Technology (incl. R&D) Service Worldwide experience 1+1>2 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. Integrated Study to Improve Plant Profitability Balance of plant Turbine/Generator Boiler Electrical Environmental I&C Design Operation Maintenance Goal Increase of power output More flexible operation Increase of availability Reduction of maintenance cost - Systematic investigation of the plant - Picture 2 Integrated systematic investigation of the power plant as a whole Page 3 of 18
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. Project Set-up Customer Operation Maintenance engineering Service International Experience Steering Committee -Contract, -Definition of targets, -Boundary Conditions Phase 1 Phase 2 Plant assessment and appr. evaluation GO / NOGO Analysis of potentials Solutions Implementation plan Implementation 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. Page 4 of 18
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. Customer Country Power Station/ Unit Output Main Fuel Order Year Status Phase 1 Phase 2 Vattenfall Europe Generation (VE-G) Germany Jänschwalde 6 x 500 Lignite 2001 Finalised DSK Germany EVA Ibbenbüren 27 Mining Gas 2003 Finalised Hidrocantabrico Spain Abono 1 350 2003 Finalised RWE Power Germany Neurath E 600 Lignite 2003 Finalised VE-G Germany Schwarze Pumpe 2 x 800 Lignite 2004 Finalised E.on UK United Kingdom Ironbridge 2 x 500 2006 Finalised Energy Randers Denmark Randers CHP 49 e + 105 th / Wood 2006 Finalised EPS Serbia TE NT A6 308,5 Lignite 2006 Finalised Start November 2007 British Energy United Kingdom Eggborough 4 x 500 2006 Finalised Start September 2007 EPS Serbia TE NT B2 620 Lignite 2007 Finalised Start November 2007 EPS Serbia TE KO B 2 x 348,5 Lignite 2008 Start February 2008 Picture 4 ECO RAM references Page 5 of 18
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 2003 STEP C Finalised Vattenfall Heat Germany HKW Berlin- Mitte 400 th Gas / Oil 2004 STEP C Finalised Tavanir Iran Bandar Abbas 4 x 320 Oil / Gas 2004 STEP S Finalised VE-G Germany Jänschwalde / Boxberg 8 x 500 Lignite 2005 STEP L Finalised EnBW Germany Heilbronn 7 750 2005 STEP C Finalised RWE Germany BASF 3 x 200 ESKOM South Africa Matla 6 x 600 Gas / Oil 2005 STEP R Finalised 2005 STEP C Finalised STEAG SaarEnergie Germany Weiher 680 2006 STEP W Finalised DONG Denmark Studstrup 4 350 2006 STEP R Finalised ESKOM South Africa Kendal 6 x 730 2006 STEP C Finalised E.on Germany Franken 426 Gas / Oil 2006 STEP C Finalised Page 6 of 18
Customer Country Power Station/ Unit Output Main Fuel Order Year STEP x Status RWE Germany BASF 3 x 200 Gas / Oil 2006 STEP R Finalised DONG Denmark Esbjerg 417 EnBW Germany Heilbronn 7 750 2006 STEP C Finalised 2006 STEP C Finalised ESKOM South Africa Matimba 6 x 670 ESKOM South Africa Lethabo 6 x 620 ESKOM South Africa Tutuka 6 x 610 ESKOM South Africa Duvha 6 x 600 ESKOM South Africa Majuba 6 x 660 ESKOM South Africa Kriel 6 x 500 2007 STEP C Finalised 2007 STEP C Finalised 2007 STEP C Finalised 2007 STEP C Finalised 2007 STEP C Finalised 2007 STEP C Finalised EPS Serbia TE NT A4 308,5 Lignite 2007 STEP C Finalised Hidrocantabrico Spain Abono 1 350 SNET France Gardanne 868 2007 STEP C Finalised 2007 STEP W Finalised Vattenfall Heat Germany HKW Berlin- Mitte 400 th Gas / Oil 2008 STEP C Start September 2008 EnBW Germany Marbach 55 + 265 DELTA Australia Vales Point 2 x 660 Gas / Oil 2008 STEP C Finalised 2008 STEP S Finalised CGTEE Brazil Presidente Medici 2 x 63 2008 STEP S Finalised Picture 5 STEP x references Page 7 of 18
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 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 Page 8 of 18
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. Page 9 of 18
5. Example 1 Optimisation of steam generator area Optimisation of Steam generator and Air Heater 5 6 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 2 1 3 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. Page 10 of 18
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 Height [m] (-) 0 (+) Hot Gas (>1000 C) Primary Air (~300 C) Combustion Chamber Burner Lignite (Feeder) Pressure [mbar] Beater Wheel Mill with Classifier Picture 8 Circuit lignite firing with beater wheel mill Page 11 of 18
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. Page 12 of 18
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: - 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. Page 13 of 18
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. Energy optimisation of ESP Installation of dust emission measurement and connection with the control cubicles and installation of new control equipment Control cubicles High Tension Rectifier Dust emission measuring 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. Page 14 of 18
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 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. Page 15 of 18
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, 1 x 305 and 3 x 308,5. 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 - Boiler feed pump Sulzer, France - Main transformer Minel, Serbia Unit No. 6 - Steam generator Rafako, Poland based on a Sulzer license - Steam turbine and generator ALSTOM, France - Boiler feed pump Sulzer, France - Main transformer Minel, Serbia The units are running in base load operation mode. Page 16 of 18
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. Page 17 of 18
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 Page 18 of 18