ENHANCING CAPACITY UTILIZATION OF COAL FIRED POWER PLANT THROUGH BETTER OPERATION AND MAINTENANCE PRACTICES

TO ACHIVE ENERGY EFFICIENCY

Pandurang S Jalkote, Anup Ghosh & Rajendra Nandi Dahanu Thermal Power Station, Reliance Infrastructure Ltd., Dahanu

Phone: +919325119746, E-mail: Pandurang.Jalkote@relianceada.com,

ABSTRACT : This paper describes the capacity enhancement of coal fired power plants with through operational optimization, control techniques and better maintenance practices The philosophy of “Prevention is Better than Cure” is dealt in detail to improve the Plant load factor (PLF) of plant. The energy conservation measures are also implemented in improving the plant performance and are enumerated in this paper.

1.0 INTRODUCTION

The Indian power sector is highly dependent on thermal power generation i.e., 64.6 % of total generation. The power generation by coal forms about 53.4 % of total energy generation. The coal is fissile fuel which is a finite source of energy and is going to be exhausted. The Indian power sector has alarmed to reduce the energy loss and conserve the energy to reduce the huge gap between supply and demand (energy deficit of 10 % and peak demand shortage of about 12 %). Therefore, it is essential to generate the power with energy efficiently and Dahanu Thermal Power Station (DTPS) is committed to generate power with energy efficiently. DTPS had taken up lot of initiatives in conserving the energy while generating the power. The performance improvement of individual thermal power generating units will help in achieving

• Increased power generation and there by reducing the demand supply gap • Reduction in power generation cost and thereby improving the competitiveness of Indian industry • Reduction in Green house gas emissions and Global warming

Reliance Infrastructure Limited is a fully integrated utility engaged in the generation, transmission and distribution of electricity. It ranks among India’s top listed private companies on all major financial parameters, including assets, sales, profits and market capitalization. Dahanu TPS is Reliance Infrastructure Ltd.’s single largest power generating facility. It is a 500 MW (2 X 250 MW) coal based thermal power station situated approximately 120 kms North of Mumbai on the western seacoast. The power plant was commissioned in 1995 and has been constantly upgraded to maintain its technological edge. It is the first generating utility in the country to be certified as ISO 9001 and ISO 14001 for its Quality Management System and Environmental Management system respectively. The health and safety of the employee is given utmost importance at DTPS and the plant is also certified as OHSAS 18001 as well as SA-8000 for Social Accountability. The DTPS is a first utility in Thermal power plants in India which was certified as BS EN 16001 for Energy Management System. One of the key contributors to this is the continuously improving Operation & Maintenance practice. The present shape of maintenance management practices has been evolved over a period of 10 years of striving towards excellence. This paper showcases the typical organization of operation & maintenance setup at DTPS and the maintenance philosophy being followed. Organization wide SAP as a part of maintenance management system, efficiently performs day-to-day asset management functions. Reviews & monitoring at daily, weekly & monthly frequencies ensure effective implementation of maintenance strategies

2.0 APPROCH FOR CAPACITY UTILISATION

• Best operation and maintenance practices. • Maximum capacity utilization without violating the critical equipment parameters. • System implementations. • Regular monitoring and control. • Regular energy and system audits. • Use of new technologies. • Use of break through quality tools. • Knowledge sharing in different national and international forums. • Most important factor is to create awareness regarding energy conservation.

The performance improvement of the power generating units was taken up in the following areas:

• Safety • Availability • Reliability • Output • Efficiency • Cost • Environment protection

3.0 MAINTENANCE PHILOSOPHY Maintenance is largely viewed as a cost-center, an evil, insurance, a disaster repairing function. But Maintenance at DTPS is perceived as an opportunity to improve reliability and availability of the equipments and of the unit as a whole. Maintenance is used as a tool to maximize generation level and minimize cost, instead of just attending the equipment defects. 3.1 Methodology The maintenance methodologies include Preventive Maintenance, Corrective or Reactive Maintenance, Predictive Maintenance, Proactive Maintenance and Maintenance Prevention techniques in an integrated manner to increase the probability that equipment will function with desired operating parameters over its life cycle with minimum maintenance. These different maintenance strategies are proactively deployed to avoid breakdowns, premature equipment malfunctions and to increase response times to recover from failure, in order to effect improvements in overall plant availability. Appropriate selection of right maintenance strategy to deal with each situation, is based on maintenance requirements supported by sound technical and economic justification. The flow chart below demonstrates the various methods.

3.1.1 Corrective maintenance

Normally corrective maintenance for minor defects, inconsequential, for redundant equipments are requested through work requests. However any defect leading to failure of equipment to function in normal way is highly undesirable. This type of maintenance becomes Breakdown. Percentage of breakdown to total work orders is an indicator of maintenance performance in general. Every effort is taken to minimize this. Minor defects do appear and helps in minimizing equipment failure & improving performance. 3.1.2 Preventive Maintenance

The preventive maintenance program is the key to any attempt to improve the maintenance performance. It reduces the amount of reactive maintenance to a level that allows other practices to be effective. This is achieved by having plans/schedules for equipment to carry out standard maintenance activities such as lubrication tasks, replacement of worn out parts, checking of blockages and oil levels etc. The preventive maintenance schedules are designed to strike a measured balance between achieving high equipment reliability through considerable lowering of failures and optimizing equipment down time that inevitably results from planned preventive maintenance. Systematic or scheduled maintenance, such as lubrication or replacement is done at regular intervals. 3.1.3 Predictive Maintenance The predictive maintenance uses an array of condition monitoring techniques to initiate the preventive action (like replacement of part or even small corrections like re-alignment of coupling), exactly when it is needed. Predictive maintenance helps in identifying the minute changes in equipment behavior, on account of any component degradation or any abnormal operating condition, which might lead to equipment failure. Various techniques are used to monitor the condition of almost all the equipments. Condition Monitoring describes a range of key technique used in Predictive Maintenance Engineering.

• Vibration Monitoring • Lubricant analysis • Motor current signature analysis • Dissolved gas analysis • Wear debris analysis • Noise • Magnetic particle inspection (MPI) • ELCID Test • Thermography • NDT

The application of Condition Monitoring program has specific advantages such as

• Reduction in unplanned outages. • Extension of plant life. • Better deployment of maintenance crew. • Advance planning in procurement of spares. • Reduction in secondary damages. • Increase in productivity.

A combination of traditional & latest techniques for monitoring equipment health delivers highest figures for availability & equipment performance. The monitoring schedules are followed by a dedicated Condition Monitoring Team and weekly / monthly reports hence generated are reviewed.

3.1.4 Proactive Maintenance Proactive maintenance uses analytical tools and techniques such as RCA, FMEA, Risk Assessment etc, to eliminate, minimize or avoid stress condition on equipment. It works by carefully considering following questions:

• What does the system or equipment do; • What is its function? • What functional failures are likely to occur? • What are the likely consequences of these functional failures? • What can be done to reduce the probability of the failure, identify the onset of failure, or reduce

the consequences of the failure? These tools are discussed in detail in later parts of this paper.

3.2 Maintenance Prevention Maintenance prevention is the most crucial, most costly & a long term maintenance strategy, as It involves techno-economic considerations. It is used for equipments with very high failure rates involving costly maintenance & high downtimes. 3.3 Preventing Failure Every equipment item has a resistance to or margin to failure. Using equipment subjects it to stress that can result in failure when the stress exceeds the resistance to failure. Stress is dependent on use and may be highly variable. It may increase, decrease, or remain constant with use or time.

4.0 MONITORING AND CONTROL The operation and maintenance performance is monitored through various reviews & reports 4.1 Daily Planning Meeting Daily maintenance review is pivotal in monitoring O&M performance, ensuring the implementation of the policies in day-to-day functioning of the plant. All department heads gather in the morning to address all the issues related to the Operation & Maintenance, which is chaired by O&M head. Reviews & monitoring in DPM (Daily Planning Meeting) ensure the healthy operation of the plant. Following are the points of regular discussions. • Daily Generation Report: Daily generation report includes all operational parameters of the plant.

Plant Load Factor (PLF), Availability, Units Generated, Auxiliary Power Consumption, Specific Coal Consumption, Specific Oil Consumption, Fuel Stock Positions, etc are given on daily, monthly & cumulative yearly basis. Any abnormal deviation in the performance is discussed, including the reasons and immediate corrective action & remedial measures for future.

• Daily Maintenance Report: This report shows the maintenance performance at a glance on daily,

monthly & yearly basis. Maintenance work status figures out the quantum of maintenance carried out during the day in

terms of Work orders raised & attended, Clearance permits issued & cancelled and monthly work completion. It also shows the percentage of planned maintenance to unplanned maintenance.

Maintenance Targets Status shows the status of all the maintenance performance indicators, namely Non-availability of Unit, Loss of Generation and Tripping of Unit on account of equipment under performance, Oil Consumption due to maintenance problems, Auxiliary Power Consumption and Maintenance Cost. All the maintenance departments namely Mechanical,

Electrical, Control & Instrumentation, Civil & Coal Handling Plant are given target figures against each parameter. This daily review keeps maintenance aware of the current performance and further improving them.

Equipment Status shows all major equipment under maintenance for the day. Critical equipments, which are down or under maintenance for more than 7 days & 15 days are also listed to keep the plant management informed. Critical work orders, Equipment with abnormal parameters (detected through condition monitoring) or any other information affecting plant performance is given.

• Daily Defect Report: All new and pending defects pertaining to all maintenance departments appear

in Defect Review Report. These are reviewed, planned, scheduled & rescheduled. Inter departmental coordination & issues resolution is also catered. These defects are tagged as Corrective, Predictive, Modification, ES (requiring Equipment Shutdown), US (requiring Unit Shutdown), CS (requiring Station Shutdown) and Miscellaneous, as decided.

4.2 Daily Energy Deviation Report

DTPS monitoring all HT auxiliaries’ energy consumption very closely by using in house developed software in excel. This report can help to operation and maintenance engineers to take a decision for operation and maintenance of individual equipment in view of energy efficiency and conservation. Any deviation observed will be taken as a FIR (Non Conformity) and CA/PA will be taken for the same. This report can influence the scheduled maintenance and changeover of stand by equipments. The decision will be taken by all O&M personals during daily planning meeting.

4.3 FIR notification for Energy/Process/Safety/Fire/Environment Deviation

DTPS follow the FIR system for not meeting the targets for its energy, process, safety, environment, fire and human and CA/PA to be prepared to avoid the recurrence of the same.

4.4 Corrective and Preventive Action (CA/PA):

DTPS taking CA/PA for non conformity products which were raised through FIR system. 4.5 Improvement Plans DTPS taking improvement plans for Energy, Process, Safety, Environment, Fire and Health. The source for improvement plans are.

a. Participation in national and international seminars/Workshops/Award functions. b. Visit to different plants in India and aboard. c. Discussion with vendors and suppliers. d. Discussion among cross functional teams. e. Outcome of CA/PA f. Suggestions from individual employee.

5.0 Unit Overhauling Strategy “Failing to plan is planning to fail”. That is why Long Term Maintenance Plan at DTPS imbibes the actions undertaken by management to establish the vision, goals, objectives, and performance expectations for the shutdown. It allows for consistent improvement in execution strategy and provides a forum for communication among team members to ensure that all anticipated problems or issues related to the shutdown are resolved. The planning is done in view of the following:

• Reduction in shutdown period.

• Work Estimation

• Resource Planning

• Accident free overhaul

The planning requires assessment of the maintenance activities of both corrective as well as preventive nature, to keep the plant and its auxiliaries fit and performing, without any significant downgrading of the overall equipment effectiveness, till the next schedule overhaul.

5.1 Scope of work – It is assessed from the experience gained through running the unit, the pre outage survey and thorough efficiency tests. The assessment is also benefited from the experience of previous major and minor overhauls of both the Units. Following are the measures that ensure the completion of unit overhauling in minimum time.

5.2 Learning from past to beat the surprises - We have tried to learn from the experiences from the previous overhauls. This has helped to anticipate the surprises that arise during the overhaul.

5.3 Selected & Motivated Contracting Participants - The contracting agencies have a vital bearing on the quality and timely completion of the work. The contract conditions are made stringent and fine-tuned to include penalty, safety & incentive clauses. A lucrative incentive to the major overhaul agencies is also included in the contract terms & conditions, to keep them motivated.

5.4 Tools Tackles & Moving Equipments- The required T & Ps such as welding machines, cutting sets etc are placed such that these can be operated all across the area. The requirement of TIL, Hydra etc is evaluated prior to the overhaul and activities are scheduled accordingly to conveniently share these resources. Backup arrangements are also kept ready for any unforeseen requirement.

5.5 Relevance of Infrastructure - Availability of the required infrastructure including housing, food, safety, first-aid, transportation etc is ensured. These small issues may hamper the work progress, if not taken care of properly.

5.6 Safety and Environment - Ensuring a good work environment and safety & security of the man and machine on work, is of utmost importance for the timely success of the overhaul. All employees and contract people use personal protective equipments during overhaul. During overhaul, Fire fighting people are deputed round the clock at various locations to avoid any incidence fire.

5.7 Use of IT Tools -The overhauling plans are implemented using various planning & scheduling tools of SAP and professional project management software like Primavera.

6.0 PLANT PERFORMANCE DTPS is able to operate the plant to generate power in the range of 262 (PLF: 104.8 %) to 270 MW (PLF: 108.0 %) by using the margins provided for each individual equipments, better quality of coal and operating the generator at near unity power factor. The main parameters that affect the life of auxiliary equipment are current, winding temperature and bearing temperature. All these parameters are collected from the hourly past data from HMI report of DTPS for all twelve months to consider all seasons. Table 1 gives the plant performance of DTPS power plant.

PERFORMANCE INDICES PREVIOUS BEST

F.Y 2003-04

F.Y 2004-05

F.Y 2005-06

F.Y 2006-07

F.Y 2007-08

F.Y 2008-09

F.Y 2009-10

F.Y 2010-11

GENERATION (MUS) 4481 4407 4439 4323 4458 4459 4423 4481 4424

PLF (%) 101.79 100.34 101.35 98.7 101.79 101.53 100.99 102.33 101

AVAILABILITY (%) 97.18 96.84 96.88 94.71 96.79 96.7 96.31 97.18 96.48

LOADING FACTOR (%) 105.30 103.61 104.61 104.22 105.17 104.99 104.86 105.3 104.69

AUX. POWER CONSUMPTION(%) 7.34 7.34 7.53 7.59 7.64 7.67 7.71 7.6 7.37

SP. OIL CONSUMPTION (ML/KWH) 0.11 0.115 0.13 0.18 0.11 0.13 0.13 0.14 0.192

SP. COAL CONSUMPTION(KG/KWH) - 0.526 0.531 0.534 0.533 0.544 0.575 0.581 0.626

DM MAKE UP (%) 0.22 0.39 0.37 0.38 0.24 0.22 0.24 0.32 0.42

TOTAL OUTAGE(Nos.) 6 6 14 17 8 8 12 8 10

HEAT RATE (KCAL/KWH) 2261 2268 2261 2286 2278 2279 2300 2288 2282

TRIPPINGS/ 1000 HRS RUNNING HOURS 0.056 0.117 0.412 0.301 0.177 0.176 0.355 0.176 0.056

DAHANU THERMAL POWER STATION (2 X250 MW) FINANCIAL YEARWISE PERFORMANCE REPORT

Efficiency DepartmentCommitted To Enhance Value To Operations

6.1 Turbine, Generator and Boiler: DTPS carried out detailed joint study with OEM for loading of Boiler and Turbine. According to guidelines of study DTPS loading the machine without violating the said parameters like steam flow should not exceed >780 T/hr, Generator current should not exceed > 10290Amp. Boiler designed for steam flow of 805T/Hr capacity. For loading of turbine 105% the maximum steam flow noted was 778 T hr. and generator current noted 9820Amp.

Table 1: Plant performance of DTPS

Generator Current in Amp at Load between 260 to 265 MW

Main Steam Flow in T/hr at Load between 260 to 265 MW

6.2 Boiler Feed pumps There are two Boiler Feed Pumps (BFP) of 9000 kW. One BFP motor is powered from UAT bus and other is powered from station bus. One pump will be continuously working and other will be stand-by. The Booster pumps are mounted on the same shaft of main pump. The feed water flow is controlled by scoop coupling. Figure 1 gives the variation of BFP current with plant load. The current rating of BFP is 922 A and the maximum current recorded at a plant load of 271 MW was 774.83 A. The currents are not exceeded the design current rating of BFP motors. The performance of these BFPs are quite good and the better performance of individual equipment had enhanced the overall capacity of plant. Figure 2 shows the variation of winding temperature of BFP motors with plant load for past one year. The BFP motor winding temperatures are in the range of 92.77 – 95.71 oC and are well within the permissible limit of 105 oC or 75 oC above the ambient temperature. The performance of cooling system of BFP is good and heat removal capacity is also quite good. The bearing temperatures of BFP are also analyzed for a period of one year. The BFP pump and motor bearing temperatures are in the range of 55.43 – 62.34 oC and are well within the permissible limit.

 

6.3 Condensate Extraction Pumps (CEP) There are two Condensate Extraction Pumps (CEP) of 700 kW. One pump will be continuously working and second will be stand-by. CEP 1A is provided with Variable frequency drives (VFD). Figure 3 gives the variation of CEP current with plant load. CEP 1A motor is provided with variable frequency drives. The current rating of CEP is 71.2 A and the maximum current recorded at a plant load of 271 MW was 62.21 A. The currents are not exceeded the design current rating of CEP motors. The performance of these CEPs are quite good and the better performance of individual equipment will enhance the overall capacity of plant.

Figure 4 shows the variation of winding temperature of CEP motors with plant load for one year. The CEP winding temperatures are in the range of 87.65 – 92.29 oC and are well within the permissible limit of 105 oC or 75 oC above the ambient temperature. The performance of cooling system of CEP is good and heat removal capacity is also quite good. The bearing temperatures of CEP are also analyzed for a period of one year. The CEP pump and motor bearing temperatures are in the range of 39.54 – 53.21 oC and are well within the permissible limit. 5.4 Induced Draft Fans (IDF) There are two Induced Draft Fans (IDF) of 1850 kW and both fans will be working continuously. The performance Test is conducted on ID fans during the energy audit study. Figure 5 gives the variation of IDF motor current with plant load. The current rating of IDF motors is 205.5 A and the maximum current recorded at a plant load of 271 MW was 190.31 A. The currents are not exceeded the design current rating of IDF motors. The performances of these IDFs are quite good and the better performance of individual equipment enhanced the overall capacity of plant. Figure 6 shows the variation of winding temperature of ID fan motors with plant load for past one year. The IDF winding temperatures

 

are in the range of 85.21 – 96.89 oC and are well within the permissible limit of 105 oC or 75 oC above the ambient temperature. The performance of cooling system of IDF is good and heat removal capacity is also quite good. The bearing temperatures of IDF are also analyzed for a period of one year. The IDF fan and motor bearing temperatures are in the range of 46.55 – 68.56 oC and are well within the permissible limit. 5.5 Forced Draft Fans (FDF) There are two numbers of 725 kW FD fans and both fans will be working continuously. Figure 7 gives the variation of FDF motor current with plant load. The current rating of FDF motors is 80 A and the maximum current recorded at a plant load of 271 MW was 51.36 A. The currents are not exceeded the design current rating of FDF motors. The performance of these fans are quite good and the better performance of these individual equipments enhanced the overall capacity of plant. Figure 8 shows the variation of winding temperature of FD fan motors with plant load for past one year. The FDF winding temperatures are in the range of 72.02 – 76.03 oC and are well within the permissible limit of 105 oC or 75 oC above the ambient temperature. The performance of cooling system of FDF is good and heat removal capacity is

also quite good. The bearing temperatures of FDF are also analyzed for a period of one year. The FDF fan and motor bearing temperatures are in the range of 49.25 – 91.80 oC and are well within the permissible limit. 5.7 Primary Air Fans (PAF) There are two Primary Air fans of 1350 kW to provide the primary air to mills. Figure 9 gives the variation of PAF motor current with plant load for both units. The current rating of PAF motors is 140 A and the maximum current recorded at a plant load of 271 MW was 114.25 A. The currents are not exceeded the design current rating of PAF motors. The performance of these fans are quite good and the better performance of these individual equipments will enhance the overall capacity of plant. Figure 10 shows the variation of winding temperature of PA fan motors with plant load for past one year. The PAF winding temperatures

 

are in the range of 63.72 – 84.86 oC and are well within the permissible limit of 105 oC or 75 oC above the ambient temperature. The performance of cooling system of PAF is good and heat removal capacity is also quite good. The bearing temperatures of PAF are also analyzed for a period of one year. The PAF fan and motor bearing temperatures are in the range of 44.92 – 80.89 oC and are well within the permissible limit. 5.8 Mills There are three Mills of 2300 kW, Ball Tube mill BBD 4772, two mills will be working continuously and third mill will be stand-by to meet 100 % MCR load. Each mill is provided with two output coal pipes to provide coal to each elevation. The coal-air mixture temperature is maintained by varying the hot air and cold air flow to mills. Figure 11 gives the variation of Mill motor current with plant load. The current rating of Mill motors is 260.6 A and the maximum current recorded at a plant load of 271 MW was 194.68 A. The currents are not exceeded the design current rating of Mill motors. The performance of these mills are quite good and the better performance of these individual equipments will enhance the overall capacity of plant. Figure 12 shows the variation of winding temperature of Mill motors with plant load for past one year. The Mill motor winding temperatures are in the range of 62.74 – 72.27 oC and are well within the permissible limit of 105 oC or 75 oC above the ambient temperature. The performance of cooling system of mills is good and heat removal capacity is also quite good. The bearing temperatures of Mills are also analyzed for a period of one year. The Mills and motor bearing temperatures are in the range of 44.92 – 63.97 oC and are well within the permissible limit.

7.0 CONCULSIONS The main conclusions are:

As Dahanu Thermal Power Station shown a path to Indian Thermal Power Sector that, we can generate more than 100% Plant Load Factor without compromising the life of machines.

By operating units at maximum capacity without violating the design parameters of individual equipments, it will help to reduce the gap between demand and supply of electricity and conserve energy.

Considering the national present average Plant Load Factor (PLF) of 74.8% and around 350 sets of 210 & 250 MW units, by enhancing Plant Load Factor from 74.8 % to 95% and considering 97 % plant availability, we can able to generate 1,26,450 MU’s more electricity, which will help for nation building.

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