Analysis and application of maintenance strategies for Omnicane Thermal Energy Operations (St Aubin) Ltd

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i

Analysis and application of maintenance strategies for Omnicane Thermal Energy Operations

(St Aubin) Ltd

Jasbeersingh BUNDHOO Student ID: 800630A751

DSEE Mauritius

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ii Master of Science Thesis EGI 2012 – 102

MSC EKV920

Analysis and application of maintenance strategies for Omnicane Thermal Energy

Operations (St Aubin) Ltd

Jasbeersingh BUNDHOO

Approved

Date

Examiner

Name

Supervisor

Name

Commissioner Contact person

Abstract

Maintenance costs at Omnicane Thermal Energy Operations (St Aubin) Ltd contribute a significant part of the unit cost of electrical energy produced and affect the profitability of the power plant. Hence it is necessary and crucial to minimize maintenance costs by optimizing maintenance processes to make the plant more reliable and to run economically.

The total maintenance cost for OTEOSAL from year 2008 to 2011 is seen to be increasing and has even double from 2008 to 2011. The cost of external labor during operation has increased by nearly four times due to a lot of breakdown on different equipments and also the value of the spare parts store is seen to rise because many spare parts are bought at random in fear of having a shut down due to unavailability of spare parts. These excess expenses contribute to a loss in profitability. With a good maintenance strategy, the total maintenance cost can be reduced by about 30%.

Fault Tree Analysis (FTA) and Failure Mode Effect Analysis (FMEA) were done and allowed identifying critical equipments at the power plant and the Grate Stocker, one of the most important and critical equipment for the plant was selected to perform a Quantitative Analysis of the FTAs. The probability of failure for the Grate Stocker is seen to be 0.98 and has reliability as low as 0.02. Quantitative Analysis of FTA and Pareto Analysis will allow having the right quantity of spare parts at the right time without overstocking.

From this thesis, it can be said that combining different maintenance and management methods and

strategies based on FTA, FMEA and Pareto Analysis and all these well formalized and documented according to ISO 9001 will certainly allow the power plant to gain a lot like availability, reliability and even financially from maintenance and also will make OTEOSAL ready for new challenges appearing in the energy sector in Mauritius.

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Table of Figures and Tables

FIGURE 1.4-1 [A]BAR CHART REPRESENTING EVOLUTION OF TOTAL MAINTENANCE COST AND [B]CHART REPRESENTING EVOLUTION OF

THE VALUE OF THE SPARE PART STORE ... 2

FIGURE 2.1-1CONVEYOR IN THE COAL HANDLING PLANT ... 4

FIGURE 2.1-2 COAL HANDLING PLANT ... 4

FIGURE 2.1-3 COAL SPREADER AND FEEDER ... 5

FIGURE 2.1-4 TRAVELLING GRATE STOKER AND BOTTOM ASH CONVEYOR ... 6

FIGURE 2.1-6 COAL SPREADER AND FEEDER ... 9

FIGURE 2.1-7 DEMINERALISED WATER TREATMENT PLANT ... 10

FIGURE 2.1-8 TURBINE OPERATION DIAGRAM ... 11

FIGURE 2.1-9 CONDENSER ... 12

FIGURE 2.1-10COOLING TOWER ... 12

FIGURE 2.1-11 PROCESS DIAGRAM ... 13

FIGURE 2.3-1THE BATHTUB CURVE FOR PREVENTIVE MAINTENANCE (MOBLEY,R.K.,2002) ... 15

FIGURE 3.2-1PROCESS SCHEMATIC OF MAIN EQUIPMENTS AT OTEOSAL ... 29

FIGURE 4.3-1TWO REGULARLY USED FAULT TREE GATE SYMBOLS :(1)OR GATE;(2)AND GATE. ... 32

FIGURE 4.3-2TWO FREQUENTLY USED FAULT EVENT SYMBOLS:(1) CIRCLE;(2) RECTANGLE. ... 32

FIGURE 4.6-1 FTA FOR WHOLE POWER PLANT ... 35

FIGURE 4.6-2 FTA FOR COAL HANDLING PLANT ... 36

FIGURE 4.6-3 FTA FOR WATER TREATMENT PLANT ... 37

FIGURE 4.6-4 FTA FOR COMBUSTION AIR ... 38

FIGURE 4.6-5 FTA FOR FEED WATER ... 39

FIGURE 4.6-6 FTA FOR BOILER ... 40

FIGURE 4.6-7 FTA FOR STEAM DISTRIBUTION ... 41

FIGURE 4.6-8 FTA FOR WASTE DISPOSAL SYSTEM ... 42

FIGURE 4.6-9 FTA FOR TURBO-ALTERNATOR AND AUXILIARY EQUIPMENTS ... 43

FIGURE 4.6-10 FTA FOR INSTRUMENTATION AND CONTROL ... 44

FIGURE 4.6-11 FTA FOR COMPRESSED AIR ... 45

FIGURE 6.2-1 FTA FOR COAL SPREADER ... 57

FIGURE 6.2-2 FTA FOR COAL FEEDER ... 58

FIGURE 6.2-3 FTA FOR GEARBOX ... 58

FIGURE 6.2-4 FTA FOR DRIVE MOTOR ... 59

FIGURE 6.2-5 FTA FOR TRAVELLING GRATE ... 60

FIGURE 6.2-6FTA FOR GRATE STOCKER ... 61

FIGURE 6.5-1EXAMPLE OF PARETO CHART ... 68

FIGURE 6.5-2PARETO FOR DRIVING PART OF TRAVELLING GRATE FOR THE YEAR 2008 ... 69

FIGURE 6.5-5PARETO FOR MEAN FREQUENCY OF BREAKDOWN ... 70

FIGURE 6.5-6PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR DRIVING PARTS IN TRAVELLING GRATE ... 71

FIGURE 6.5-7PARETO FOR REAR DRIVING PART OF TRAVELLING GRATE FOR THE YEAR 2008... 72

FIGURE 6.5-10PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR REAR DRIVING PART OF TRAVELLING GRATE ... 73

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FIGURE 6.5-11PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR REAR DRIVING PARTS IN TRAVELLING GRATE ... 74

FIGURE 6.5-12PARETO FOR CHAIN ASSEMBLY PARTS OF TRAVELLING GRATE FOR THE YEAR 2008 ... 75

FIGURE 6.5-15 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR CHAIN ASSEMBLY PARTS OF TRAVELLING GRATE ... 76

FIGURE 6.5-16 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR CHAIN ASSEMBLY PARTS IN TRAVELLING GRATE ... 77

FIGURE 6.5-17 PARETO FOR FIXED PARTS OF TRAVELLING GRATE FOR THE YEAR 2008 ... 78

FIGURE 6.5-18 PARETO FOR FIXED PARTS OF TRAVELLING GRATE FOR THE YEAR 2009 ... 78

FIGURE 6.5-19 PARETO FOR FIXED PARTS OF TRAVELLING GRATE FOR THE YEAR... 79

FIGURE 6.5-20 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR FIXED PARTS OF TRAVELLING GRATE ... 79

FIGURE 6.5-21 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR FIXED PARTS IN TRAVELLING GRATE ... 80

FIGURE 6.5-22 PARETO FOR WHOLE TRAVELLING GRATE FOR THE YEAR 2008 ... 81

FIGURE 6.5-25 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR WHOLE OF TRAVELLING GRATE ... 82

FIGURE 6.5-26 PARETO FOR COAL FEEDER FOR THE YEAR 2008 ... 83

FIGURE 6.5-29 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR COAL FEEDER ... 85

FIGURE 6.5-30 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR COAL FEEDER ... 85

FIGURE 6.5-31 PARETO FOR COAL SPREADER FOR THE YEAR 2008 ... 86

FIGURE 6.5-34 PARETO OF MEAN FREQUENCY OF BREAKDOWN FOR COAL SPREADER ... 87

FIGURE 6.5-35 PIE CHART REPRESENTING MEAN FREQUENCY OF BREAKDOWN FOR COAL SPREADER ... 88

FIGURE 7.2-1 THE MAINTENANCE WORKFLOW (BSEN13460:2002,2002) ... 101

FIGURE 7.2-2INPUT/OUTPUT DOCUMENTS (BSEN13460:2002,2002)... 102

Tables TABLE 1.4—1EVOLUTION OF TOTAL MAINTENANCE COST ... 2

TABLE 3.2—1SUMMARY OF THE MAIN EQUIPMENTS WITH THEIR CONSTITUENT PARTS... 30

TABLE 5.5—1RANKING FOR SEVERITY ... 49

TABLE 5.6—1RANKING FOR OCCURRENCE OF FAILURES ... 50

TABLE 5.7—1 RANKING FOR DETECTION OF FAILURES ... 51

TABLE 5.9—1MAINTENANCE TASK ... 52

TABLE 5.10—1FMECATABLE FOR COAL HANDLING PLANT –TIPPER ... 53

TABLE 5.10—2 SUGGESTED MAINTENANCE STRATEGY AND RPN FOR COAL HANDLING PLANT –TIPPER ... 54

TABLE 5.11—1RPN RANGE ... 55

TABLE 5.12—1MAINTENANCE TASKS ... 55

TABLE 5.12—2 PERCENTAGE CONTRIBUTION OF RESPECTIVE MAINTENANCE TASK FOR BOTH ACTUAL &RCM STRATEGY. ... 56

TABLE 6.3—1 QUANTITATIVE ANALYSIS FOR THE FTA OF THE COAL SPREADER ... 64

TABLE 6.3—2 QUANTITATIVE ANALYSIS FOR THE FTA OF THE COAL FEEDER ... 65

TABLE 6.3—3QUANTITATIVE ANALYSIS FOR THE FTA OF THE TRAVELLING GRATE ... 66

TABLE 7.1—1 SHOWS GUIDELINES IN THE NORMATIVE PART FOR THE PREPARATORY PHASE.(BSEN13460:2002,2002) ... 90

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ix TABLE 7.1—2 SHOWS GUIDELINES / DOCUMENTS NEEDED WITHIN THE OPERATIONAL PHASE OF EQUIPMENT.(BSEN13460:2002,

2002) ... 94

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Nomenclature

CEB Central Electricity Board CBM Condition based maintenance

CM Corrective maintenance

CMMS Computer maintenance management system DMAIC Define, Measure, Analyze, Improve, Control DFSS Design for Six Sigma

ESP Electrostatic precipitator FMEA Failure Mode Effect Analysis

FF Fault-finding

FTA Fault Tree Analysis ID Fan Induced Draught Fan

ISO International Standard Organization

IPP Independent power producers

LCE Life Cycle Engineering LP Heater Low Pressure Heater MDC Mechanical dust collector MTTF Mean Time to Failure

OTEOSAL Omnicane Thermal Energy Operations (St Aubin) Ltd OEE Overall equipment effectiveness

PPA Power purchase agreement

PM Preventive maintenance

RCM Reliability Centered Maintenance

RPN Risk priority number

SCADA Supervisory Control and Data Acquisition

TD Time-directed

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Introduction

1.1 OTEOSAL

Omnicane Thermal Energy Operations Limited (OTEOSAL) is an 82 bar coal power plant of capacity 34.5 MW with a Condensing Extraction Steam Turbine system (CEST). Since the price of coal is very volatile on the international market, it is primordial that the optimum potential of electricity generation from coal is tapped and used sustainably. Also, as a result of the tougher competition brought on by future and new entrants into the power market in Mauritius, OTEOSAL must meet strong demands to reduce maintenance and repair costs if they are to gain the upper hand over the competition. Along with that, it is becoming increasingly necessary to guarantee plant reliability and economic efficiency.

Being used as a base load power plant, the reliability of OTEOSAL is crucial and this put a lot of stress on maintenance departments. Hence it is important to view maintenance as a positive activity and see it as a profit center instead of a cost center. A cost-center approach for maintenance is strictly concerned with adhering to the budget and decreasing expenses as much as possible whereas moving rapidly away from the conventional way and with the appropriate management method to optimize maintenance, the power plant can gain a lot like availability, reliability and even financially from maintenance.

1.2 Aim of Thesis

The aim of this thesis is to select and plan the maintenance strategies that will address the maintenance needs of the power plant at the least cost and also to determine the most critical components of the station based on Failure Mode Effect Analysis (FMEA). Also a critical equipment will be taken for a more in depth investigation using FTA (Fault Tree Analysis) and Pareto Analysis to see the potential failures of different constituent parts of the equipment. This will allow seeing the evolution of failures over the past years and will help to identify the recurrent failures on particular parts and will help to have the right and optimum spare parts without spending too much for unnecessary spare parts or putting into danger the power plant for not having the critical spare parts. Since the management of OTEOSAL wants the power plant to be an ISO9001 certified company in 2012 so as to be able to implement Quality Management Systems, maintenance strategies and guidelines will be proposed for OTEOSAL. The British Standard, BS EN13460:2002, 2002

“Maintenance – Documents for Maintenance” will be analyzed and adapted for OTEOSAL power plant.

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2 1.3 Objectives of Thesis

The outcomes expected from this thesis are to reduce maintenance cost and downtime losses of the steam power plant and increase profitability by adopting the proper maintenance strategies that ensure its reliable availability and thus, satisfy the maturing and growing electricity demand of the Mauritian economy.

1.4 Maintenance data for OTEOSAL

The total maintenance cost (in Mauritian Rupees) as in Table 1.1 for OTEOSAL from year 2008 to 2011 is seen to be increasing and has even double from 2008 to 2011. According to the people from the maintenance department, the cost of external labor during operation has increased by nearly four times due to a lot of breakdown on different equipments and has needed urgent intervention of external labor to prevent the power plant from shutting down. Also the value of the spare parts store is seen to rise (Figure 1.4-1 [B]) because many spare parts are bought at random in fear of having a shut down due to unavailability of spare parts. But these excess expenses on unnecessary spare parts prevent the power plant from using wisely its finance and also contribute to a loss in profitability. All this is due to a lack of a good maintenance strategy and knowledge of the criticalities and failure rates of particular equipments.

Table 1.4—1 Evolution of Total Maintenance Cost

2008 2009 2010 2011

Cost of Spare Parts used (Rs) 14,680,737.78 23,303,201.60 12,508,640.50 26,751,309.20 Cost of External Labour during operation (Rs) 2,985,074.87 4,543,213.92 7,195,333.01 12,818,026.67 Cost of External Labour during shut down (Rs) 4,028,727.77 4,609,677.35 8,674,446.14 5,034,165.81 Total Maintenance Cost (Rs) 21,694,540.42 32,456,092.87 28,378,419.65 44,603,501.68 Figure 1.4-1 [A] Bar Chart representing Evolution of total Maintenance Cost and [B] Chart representing Evolution of the value of the spare part store

[A] [B]

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2 Background and Literature Review

Omnicane Thermal Energy Operations St Aubin Limited

The power plant OTEOSAL (Omnicane Thermal Energy Operations (St Aubin) Limited) is found in Union Ducray, Rivière des Anguilles in the southern part of Mauritius and forms part of the independent power producers (IPP) in the island. Under a power purchase agreement (PPA), OTEOSAL sells the electricity generated to the CEB (Central Electricity Board) which is the governing body for power distribution in Mauritius. OTEOSAL is a consortium of Omnicane (65%), Séchilienne-SIDEC (25%), and the Sugar Investment Trust (15%). The PPA was signed in October 2005 and is guaranteed by the government. The boiler was supplier by Stein Industrie (now Alstom). The Turbine/Generator was supplied by Thermodyn and Jeumont. Water treatment system was from VWS Envig.

The company is under operation since November 2005 and almost 6 years later it continues to be a base load power plant.

2.1 Process Description

2.1.1 Coal Handling Plant

Bituminous coal is imported from South Africa and Mozambique and is stored at the port here in Mauritius.

Then trucks transport the coal (approximately 30 tons per truck) to the power plant. The coal is unloaded in a hydraulic auto-tipper where it is then sent on a vibrating table to be discharged on a conveyor. This first conveyor direct the coal through a vibrating screener where coal smaller than 25mm is allowed to proceed to the next conveyor. Coal bigger than 25mm is directed towards a crusher where the bigger coal is reduced to about 25mm and then allowed to proceed.

Under the screening and crushing plant, there are two conveyors, one conveyor can bring coal directly to the daily hopper to be then sent to the boiler or one conveyor can direct coal to a silo with storage capacity of 800 tons. Coal from the silo can be extracted with the aid of an extraction screw at night or during the week end and then be sent to the daily hopper. The daily hopper has a capacity of 200 tons and it supplies the coal feeders and spreaders which in turn supply the furnace in the boiler with coal.

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4 Figure 2.1-1 Conveyor in the Coal Handling

Plant

Figure 2.1-2 Coal Handling Plant

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2.1.2 Feeders and Spreaders

After the coal handling plant, the next step for coal is to pass through the coal feeders and spreaders. The boiler is equipped with four feeders and spreaders. The feeders are conveyors of about 1.5m long made of metal plates which push coal towards the spreaders. The feeders are powered by variable speed motors so as to be able to control the amount of coal to the boiler depending on the load.

The spreaders are metal elements rotating on a metal shaft where the speed can be controlled for an optimum projection. The spreaders project coal in the furnace of the boiler at a certain angle. The angle of projection is very important because the coal should be well spread on the travelling grate so as to be able to burn completely and prevent wastage of coal.

Figure 2.1-3 Coal Spreader and Feeder

2.1.3 Traveling Chain Grate

The furnace is equipped with a traveling chain grate stoker powered by a variable speed motor. The speed of the grate is around 7 m/hr so as to give coal enough time to burn completely. Also another function of the traveling grate is that combustion air enters the furnace form under the grate.

2.1.4 Bottom Ash

The traveling grate also help to unload the remaining bottom ash or slag on a conveyor immersed in water so as to cool down the hot bottom ash. Then the bottom ash is carried outside of the boiler to be loaded on trucks.

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6 Figure 2.1-4 Travelling Grate Stoker and Bottom ash conveyor

Travelling Grate

Botton Ash Conveyor

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2.1.5 Air preheater

Combustion air from the primary and part of the secondary air is channeled through an air preheater. This air preheater uses hot boiler water which comes from the economizers to preheat combustion air. The air temperature then varies from 80 °C to 120 °C

2.1.6 Primary and Secondary Air

The combustion of coal in the furnace is done by primary and secondary air. Primary air is obtained from a fan equipped with dampers so as to be able to control the amount of air entering the furnace. The primary air enters the furnace from under the traveling grate. Before entering the furnace, the primary air passes through an air pre-heater to be heated up to around 110 °C. The secondary air is also obtained from a fan equipped with dampers. For the secondary air, part of it is heated and part of the air is left at room temperature. Part of the heated air is injected in the boiler from under the spreaders in order to burn small particles of coal projected and the other part enters the furnace at the back of the boiler where this air is injected about 3 meters high in the furnace so as to complete combustion at this height. On the other hand, the unheated air is injected in front of the furnace just above the traveling grate.

2.1.7 Induced Draught Fan

The combustion of coal produces flue gas and this flue gas must be evacuated from the furnace. This is done by the induced draught fan which is driven by a variable speed motor and equipped with dampers. The ID Fan also keeps a slight depression in the furnace chamber to prevent flue gas from getting out of the furnace.

2.1.8 Re-injection of Fly Ash

As a result of coal combustion, there is a lot of fly ash produced and this fly ash is rich in unburned carbon.

The fly ash is taken away from the furnace by the action of the induced draught fan (ID Fan). Since fly ash is rich in unburned carbon and represents a useful source of energy, it is collected via a mechanical dust collector (MDC), channeled through pipes and rotating valves and then re-injected in the furnace with the aid of a blowing fan.

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8 Figure 2.1-5 Mechanical dust collector

2.1.9 Economizers

The flue gas duct is fitted with two finned tubes economizers and since after the mechanical dust collector (MDC) the temperature of the flue gas is around 450 °C, this source of heat is used to pre-heat boiler water.

The boiler water before the first economizer which is second in the flow of flue gas is about 110 °C and after the economizer it is around 170 °C. Then after the second economizer, the boiler water reaches around 230

°C. This heated water then passes through the air preheater as described before.

2.1.10 Electrostatic Precipitator and Fly Ash

The next step is to pass the flue gas through an electrostatic precipitator (ESP) in order to gather and convey all the fly ash into a silo. The fly ash is then channeled to trucks and transported away.

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9 Figure 2.1-5 Coal Spreader and Feeder

Mechanical Dust Collector

Economizer

Electrostatic Precipitator Boiler

Chimney

Secondary Air Fan

Primary Air Fan

Air Heater

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2.1.11 Boiler Water

The demineralised water plant generates the boiler water which is directed to the feed water tank. The demineralised water is then heated from the extracted steam at 3 bars from the turbine. The feed water tank provides the feed water pumps which propels water at 115 bars and this water passes via the economizers and finally to the boiler. Added to that, the flowrate of feed water to the boiler is about 128 m³/hr. The boiler is of water tube type. This type of boiler is used for the production of high pressure and superheated steam up to 160 bars and 500 ˚C. Water tube boilers consist of a series of the water tubes arranged inside a furnace in a number of possible configurations. These tubes receive water from the feed water tank and connect the lower drum to the upper drum. In the furnace where combustion takes place the heat is transferred mainly by radiation to tubes. Saturated steam is generated in the boiler and then goes through superheaters to come at 82 bars and 525 ˚C superheated. The superheated steam then passes into the turbine for expansion.

Figure 2.1-6 Demineralised Water Treatment Plant

2.1.12 Steam Turbine and Electric Generator

Superheated steam enters the turbine at 82 bars and is expanded to about 100 mbars. The amount of superheated steam at the inlet of the turbine is controlled by inlet valves which allow the optimum flow of steam in the turbine. The energy produced turns the turbine at 5000 rpm. Steam is extracted from the turbine at 2 stages. The first extracted steam is used to heat feedwater in the feedwater tank. The second extraction is to heat return condensate in a LP (Low Pressure) Heater (close feedwater heater). The steam turbine is coupled to a reduction gear where the speed of the turbine is reduced to 1500 rpm and the reduction gear is coupled to an electric generator to produce 34.5 MW net. The electric generator produces voltage at 11 KV and then is stepped up in transformers to 66KV to then be sent to the national grid.

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11 Figure 2.1-7 Turbine Operation Diagram

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2.1.13 Condenser and Cooling Tower

After expansion in the turbine, the saturated steam is cooled down in the condenser to around 80 ˚ C. The condenser is basically a shell and tube heat exchanger. The return condensate is then pumped back to the feedwater tank with the help of a centrifugal pump. The cooling of the saturated steam is done with the help of recirculating water at about 35 ˚ C in the condenser and this recirculated water is cooled down in the cooling tower. The cooling tower is an induced draught type making the use of fans to create the draught.

Figure 2.1-8 Condenser

Figure 2.1-9 Cooling Tower

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13 OTEOSAL – Process Diagram

Figure 2.1-10 Process Diagram

Ash Storage

Ash Handling Plant

Boiler Coal Handling Plant

Economiser

Superheater Air Preheater

Main Valve Generator National Grid

Aux. Power Plant Equipments

Condenser

Condensate extraction pump LP Heater

Feed Water Tank

& Dearator Boiler Feed

Water Pump

Cooling Tower

Sand Filters Circulating Water

Pump

Water Treatment Plant

Make up water

Flue gases Flue gases

Turbine

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14 2.2 Maintenance at OTEOSAL

Since OTEOSAL is operated as a base load power station, this put greater challenges to the maintenance teams so as to ensure high availabilities and reliabilities of the power plant. Also since Mauritius is an island deprived of natural resources like coal, a good maintenance management is important to ensure sustainability of the resources and meet the growing expectations from its sole client the CEB.

OTEOSAL and like many other coal power plants in Mauritius build their own maintenance management systems depending on their maintenance needs, their intuitive judgment and experiences and supported by recommendations of the manuals of the different equipments composing the power stations.

Most manufacturers of equipment recommend maintenance practices accompanying their equipment in the maintenance manuals. Their recommendations assume application and operation of equipment according to design conditions. In practice, equipment are rarely operated according to design. Overloading or underutilizing equipment and operating them in environmental conditions not always according to design conditions result in maintenance recommendations in the maintenance manual ineffective.

2.3 Maintenance Management Strategies and Methods

The maintenance cost in probably most industries is quite significant and therefore, an evolution in maintenance management has certainly been the driving force to reduce maintenance costs, improve productivity, the quality of work and ensure human, equipments and environmental safety.

The literature about the different maintenance methods is quite numerous. For this thesis, maintenance management methods like preventive maintenance (PM), condition based maintenance (CBM), corrective maintenance (CM) along with six sigma, lean maintenance and reliability centered maintenance (RCM) will be reviewed.

2.3.1 Preventive Maintenance

Preventive maintenance (PM) is a time based maintenance method in which the maintenance activities are planned and scheduled based on predetermined counter intervals in order to prevent breakdowns and failures from occurring (Clety, 2008). The book ‘applied reliability centered maintenance’ (Jim August, 1999) defines PM as any scheduled preventive tasks intended to reduce the probability of failure of equipment. Also a

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15 preventive maintenance (PM) approach is to prevent the problems associated with CM so as to get rid of the waste and decrease asset life cycle costs.

PM tasks are carried out to avoid failure, to detect initial failure, or to determine hidden failure (Smith, 1993).

This results in three types of PM task:

(1) time-directed (TD);

(2) CBM; and (3) fault-finding (FF).

A TD task may refer to the replacement of a component, in which case it is an suitable choice only when the hazard rate is an increasing function of age (i.e. new items are better than old ones in terms of probability of imminent failure or other measures of usefulness), and the cost of a preventive replacement is considerably less than the cost of a failure and its associated repair (Mann et al., 1995).

A CBM task is carried out to notice early failures long before their occurrence. CBM uses condition monitoring techniques to find out whether a problem exists in equipment, how severe the problem is, and how long the equipment can run before failure; or to detect and identify specific components (e.g. gear sets, bearings) in the equipment that are deteriorating (i.e. the failure mode) .

An FF task is carried out at a fixed plan decided in advance to verify the health conditions of rarely used items such as protective devices and standby units.

The aim of PM is to enhance equipment performance and reliability by preventing failure of equipment. PM is commonly used where equipment failure is age related or where the equipment failure rates follow what is called bath-tub curve. (Figure 2.3-1)

Figure 2.3-1 The bathtub curve for preventive maintenance (Mobley, R.K., 2002)

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16 The different tasks that are performed in a PM include inspections, adjustments, tests, calibrations, rebuilding and replacements of parts.

By adopting PM, the objectives and benefits are (Clety, 2008):

• Improved system reliability.

• Decreased cost of replacement.

• Decreased system downtime.

• Better spares inventory management.

However, for the good running of a PM system, a list of tools, spare parts and instruments required should be available. A procedure to record the measurements to be made should also be present. Emphasis should also be made on the limits or ranges for the parameters to be measured.

Required safety procedures such as isolation and locking out must also be available.

In order to be able to organize a PM strategy, recommendations in maintenance manuals from equipment suppliers should be available along with the knowledge of the different persons working in the maintenance teams.

As all maintenance systems, advantages and disadvantages do exist as are discussed below. The performance of PM has many advantages including increase in equipment availability, performed as convenient, balanced workload, increase in production revenue, consistency in quality, reduction in need for standby equipment, stimulation in preaction instead of reaction, reduction in parts inventory, improved safety and easy availability of scheduled resources. Whereas, some disadvantages of PM are: exposing equipment to possible damage, using a greater number of parts, increases in initial costs, failures in new parts/components, and demands more frequent access to equipments. (B.S Dhillon, 2002)

2.3.2 Condition based maintenance

CBM Systems or Predictive Maintenance (PdM) methods are an extension of preventive maintenance and have been proved to minimize the cost of maintenance, improve operational safety and reduce the frequency and severity of in-service machine failures. The basic theory of condition monitoring is to know the deteriorating condition of a machine component, well in advance of a breakdown.

Condition based maintenance is a set of maintenance actions based on the evidence of need for maintenance obtained from real time assessment of equipment condition obtained from embedded sensors and external

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17 tests and measurement taken by portable equipment. (Michael V Brown, 2003). Also, Predictive maintenance (PdM) involves comparing the trends of measured physical parameters against known engineering limits for the purpose of detecting, analyzing and correcting problems before failure occurs

There are varieties of critical equipments in power plants. These components require routine inspection to ensure their integrity. The purpose of the inspection is to identify any degradation in the integrity of the systems during their service life and to provide an early warning in order that remedial action can be taken before failure occurs. Assessing the condition is necessary to optimize inspection and maintenance schedules, so as to be able to make decisions and to avoid unplanned outages.

To maintain an efficiently power plant and avoid failure of critical equipments, it is necessary to maintain the critical parts of these equipments. The effect of planned maintenance is depending upon the methods used for maintenance. The combination of corrective, preventative and condition based maintenance is primordial for critical equipments. This type of maintenance policy and strategy will improve performance of power plants through the availability of critical equipments.

CBM is system that strives to identify faults before they become critical which enables accurate planning of PMs. With CBM, the different critical equipments are assessed while in operation and a decision is made as to whether they need maintenance or not and if so, when it should be done to prevent failures. Assessments can be of all kind ranging from like simple visual inspection or fully automated system to sense, receive and process performance data, monitor, diagnose and predict failure.

Condition monitoring techniques and their applications to a power plant

Vibration monitoring measures the frequency and amplitude of vibrations which are mainly caused by misalignment, rotational imbalance, wear and improper installation of equipment, and looseness of assembled parts. Vibrations are undesirable because they lead to damage and the eventual failure of the equipments.

Vibration monitoring and analysis are important means to detect future failures in rotation machines and can be used to prevent costly failures.

In oil analysis, samples of lubricating, hydraulic, or dielectric oil are examined at frequent periods to determine the quality and metal contents of the oil. If these measurements show that the oil quality has deteriorated to an intolerable level, it will be substituted to guarantee adequate operation of the equipments.

The analysis comprises of spectrographic techniques and diagnostic procedures to examine the elements contained in the oil sample. The state of health of the machine can also be revealed by scrutinizing the size, shape, quantity and composition of wear particles in the oil samples.

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18 Ultrasonic technology is also used in CBM because ultrasonic apparatus are sensitive to high-frequency sounds. These high-frequency sounds are inaudible to the human ear and therefore ultrasonic apparatus distinguishes them from lower-frequency sounds and mechanical vibration. Machine friction and stress produce distinctive sounds in the upper ultrasonic range and changes in these friction and stress waves can indicate deteriorating conditions for a particular equipment. An ultrasonic apparatus can differentiate normal wear from abnormal wear, physical damage, imbalance conditions and lubrication problems. Therefore this give sufficient time to prepare for maintenance and helps in spare part management.

Infrared Thermography is also widely used in power plants to detect heat signature created by faulty mechanical equipment, high electrical resistance or high current flow in electrical systems.

2.3.3 Corrective Maintenance

Corrective maintenance (CM), also known as breakdown maintenance, is done to bring back an equipment in a state of working condition after a failure has occurred. The logic of run-to-failure management is easy and direct.

A plant using run-to-failure management does not spend any money on maintenance until a machine or system break down. However, few plants use a true run-to-failure management philosophy. In almost all instances, plants carry out basic preventive tasks (i.e., lubrication and machine adjustments) even in a run-to- failure environment. The major expenses linked with this type of maintenance management are:

• High spare parts inventory costs.

• High overtime labor costs.

• High machine downtime.

• Low production availability.

2.3.4 Reliability-centered maintenance (RCM)

In a reliability-centered maintenance (RCM) process, systematically all of the functions and functional failures of assets should be identified. This process also identifies all likely causes for these failures. Then RCM proceeds to identify the effects of these likely failure modes and to identify in what way those effects matter.

Once it has gathered this information, the RCM process then selects the most appropriate asset management policy. (L.R. Higgins, 2008)

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19 On the other hand, Reliability centered maintenance (RCM) magazine provides the following definition of RCM: “a process used to determine the maintenance requirements of any physical asset in its operating context.”

Basically, RCM methodology deals with some key issues not dealt with by other maintenance programs and it is aware that all equipment in a facility is not of equal importance to either the process or facility safety. Also it recognizes that equipment design and operation differs and that different equipment will have a higher probability to undergo failures from different degradation mechanisms than others.

RCM also approaches the structuring of a maintenance program recognizing that a facility does not have unlimited financial and personnel resources and that the use of both need to be prioritized and optimized.

Hence, RCM is a systematic approach to evaluate a facility’s equipment and resources to best combine the two and result in a high degree of facility reliability and cost-effectiveness.

Some advantages and disadvantages of RCM are:

Advantages

• Can be the most efficient maintenance program.

• Lower costs by eliminating unnecessary maintenance or overhauls.

• Minimize frequency of overhauls.

• Reduced probability of sudden equipment failures.

• Able to focus maintenance activities on critical components.

• Increased component reliability.

• Incorporates root cause analysis.

Disadvantages

• Can have significant startup cost, training, equipment, etc.

• Savings potential not readily seen by management

The procedure involves asking questions on the following subjects in a RCM:

• The functions and related performance standards of an item in its present working condition.

• Possible ways in which the item may fail to carry out its required tasks.

• Causes of each functional failure.

• Events that follow each failure.

• Significance of each failure.

• Measures to prevent failure.

• Corrective measures that may be taken if there is no appropriate preventive step.

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20 RCM Process

The RCM process takes place first during the equipment design and development stage, when it is used to develop maintenance plans. During product process and use, these plans are then revised based on field experience. The following two criteria are keys to the maintenance plans:

• Parts that are not critical to safety. In this case, preventive maintenance tasks should be chosen that will decrease the ownership life cycle cost.

• Parts that are critical to safety. In this case, preventive maintenance actions should be chosen that will help to prevent reliability or safety from reducing to an undesirable stage, or will help to decrease the ownership life cycle cost. It is through the preventive maintenance program that initial failures are identified and corrected, the probability of failure is decreased, hidden failures are detected, and the cost-effectiveness of the maintenance program is improved.

RCM methodology

The RCM methodology is completely described in four unique features:

• Safeguard functions.

• Detect failure modes that can make the functions fail.

• Prioritize function need (via failure modes).

• Select applicable and effective PM tasks for the high priority failure modes.

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21 RCM Procedure (Kelly, 1997)

Figure 9: RCM Procedure

1. SYSTEM DEFINITION System partitioning

Functional/ Reliability Block Diagram Analysis Data Acquisition

2. IDENTIFICATION OF MSI’s Fault Tree Analysis

Maintenance Cost Pareto Analysis

3. IDENTIFICATION OF SIGNIFICANT FAILURE MODES

Failure Modes, Effect and Criticality Analysis

6. IMPLEMENTATION, COLLECTION AND ANALYSIS OF IN-SERVICE DATA

5. SCHEDULING

4. SELECTION OF MAINTENANCE TASKS

Decision Tree Analysis

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22 The basic RCM process is composed of the following steps:

1. Identify important items with respect to maintenance.

Usually, maintenance important items are identified using techniques such as failure, mode, effects, and criticality analysis (FMECA) and fault tree analysis (FTA).

2. Obtain appropriate failure data.

In determining occurrence probabilities and assessing criticality, the availability of data on part failure rate, operator error probability, and inspection efficiency is essential. These types of data come from field experience, generic failure databanks, etc.

3. Develop fault tree analysis data.

Probabilities of occurrence of fault events— basic, intermediate, and top events are calculated as per combinatorial properties of the logic elements in the fault tree analysis.

4. Apply decision logic to critical failure modes.

The decision logic is designed to lead, by asking standard assessment questions, to the most desirable preventive maintenance task combinations. The same logic is applied to each crucial mode of failure of each maintenance-important item.

5. Classify maintenance requirements.

Maintenance requirements are categorized into three classifications: on-condition maintenance requirements, condition-monitoring maintenance requirements, and hard-time maintenance requirements.

6. Implement RCM decisions.

Task frequencies and intervals are set as part of the overall maintenance strategy or plan.

7. Apply sustaining-engineering on the basis of field experience.

Once the system/equipment start operating, the real-life data begin to accumulate. At that time, one of the most urgent steps is to re-evaluate all RCM-associated default decisions.

RCM Components

The four major components of RCM are: corrective maintenance, preventive maintenance, predictive testing and inspection, and proactive maintenance.

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23 Industries can benefit a lot from RCM in various ways as enumerated below:

• Traceability. The information, assumptions and reasoning that led to all maintenance policy decisions are fully documented. Hence, subsequent plant reliability can be periodically audited maintenance experience reviewed and strategy updated (where necessary) on a rational basis.

• Rationalism. By identifying unnecessary preventive work unachievable maintenance workload is eliminated.

• Cost saving. Overall workload is reduced due to a general shift from away from time-based preventive works towards condition-based work. Hence, a reduction in spares holding.

• Plant improvement. Re-design eliminates recurrent failures or poor maintainability‘s.

• Education. The whole exercise raises the workforce‘s overall level of skill and technical knowledge. Moreover, the actual existence of a RCM regime will itself tend to attract better-skilled personnel in maintenance.

2.3.5 Lean Maintenance

Lean Maintenance means reliability and reduced need for maintenance troubleshooting and repairs. Also Lean Maintenance comes from protecting against the real causes of equipment downtime and not just their symptoms. (Howard C. Cooper, 2002)

On his part, Ricky Smith of Life Cycle Engineering (LCE) defines lean maintenance as ‘a proactive maintenance operation employing planned and scheduled maintenance activities through total productive maintenance practices using maintenance strategies developed through application of reliability centered maintenance (RCM) decision logic and practiced by empowered (self-directed) action teams using the 5S process, weekly Kaizen improvement events, and autonomous maintenance together with multi-skilled, maintenance technician-performed maintenance through the committed use of their work order system and their computer managed maintenance system (CMMS) or enterprise asset management system’ (Ricky Smith, 2004).

The key elements of a lean maintenance method can be summarized as described below (Clety, 2008 and Ricky Smith, 2004):

• Proactive maintenance means that lean maintenance uses PM and CBM strategies to prevent and predict failure instead of reacting to it.

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24

• Planned and scheduled means that the maintenance activities are documented in such a way that the required activities, labour needs, spare parts and time needed to complete the tasks are known in advance. By being scheduled, the maintenance activities are prioritized and assigned a designated action time.

• Application of RCM decision logic means lean maintenance tasks are optimized.

• Self empowered teams’ means lean teams are designed so that a maintenance team has all the skills required to execute all the tasks within the team.

• Application of 5S: sort (remove unwanted items), straighten (organize), scrub (clean), standardize (make routine), spread (expand to other areas).

• Kaizen means that lean focuses on continuous evaluation and improvement of the maintenance processes in terms of time, resources use and quality of work.

In his article ‘lean principles’ Jerry Kilpatrick classifies the benefits of lean maintenance into three types (Jerry Kilpatrick, 2003):

1. Operational gains– reduced lead time, increase productivity, reduced inventory and improved quality.

2. Administrative improvements – reduced paperwork, reduced staffing, reduced process errors, streamlined customer care, cost reduction, job standardization.

3. Strategic gains in achieving overall company goals.

Kishan Bagadia in the white paper from Infor global solutions identifies four areas that can benefit from lean maintenance as optimization of spare parts inventory management, achieving quality preventive maintenance through better management, cross training of staff for multi-skilled task force and a continuous improvement drive in the maintenance spectrum.

2.3.6 Six Sigma

According to Stan Grabill, a certified Six Sigma expert (Black Belt) writing for Maintenance Technology’s Viewpoint column, Six Sigma focuses on reducing variation in a business’ internal processes using a rigorously structured, statistical approach that is tied to business results.

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25 He also states that Six Sigma for asset dependability reduces the variation in design, procurement, installation, operation, reliability, and maintainability of equipment assets in order to provide predictable performance at optimal cost of ownership.

Stan Grabill thinks of Six Sigma as root cause variation analysis, where a different set of tools is used to identify sources of variation and determine a means to mitigate “bad” variation and control “good” variation to enhance output productivity. The reason to do this highly structured methodology is to reap the business benefits of reducing variation, which results in break-through productivity improvements. (Stan Grabill, 2001) Originated by Motorola, Six Sigma took hold in a big way in the early 1990s. The focus was reducing variation in manufacturing processes.

Six Sigma does not create new tools but uses existing ones. The main methodologies of Six Sigma are Define, Measure, Analyze, Improve, Control (DMAIC) and Design for Six Sigma (DFSS).

DMAIC (Robson Quinello, 2003)

Robson Quinello explains that to apply Six Sigma in maintenance, work groups that have a good understanding of preventive maintenance techniques in addition to a strong leadership commitment should be first found.

The methodology is divided into five distinct phases:

• Phase D (Define). Establish the objectives of the department and identify the critical-for-quality processes. In this phase, leaders, planners, maintenance staff, need to work together to set departments goals.

• Phase M (Measure). After teams have made their choices, the indexes, data collection plan, and analysis method can be chosen. Some common indexes include frequency of preventive maintenance, frequency of predictive maintenance, productivity, number of corrective occurrences, maintenance costs, downtime, pulse survey, overall equipment effectiveness (OEE), etc.

• Phase A (Analyze). Teams will use analysis graphs (Pareto, scatter, run chart, box plots, etc.) to visualize trends and to search for root causes.

• Phase I (Improve). An action plan and failure mode and effects analysis (FMEA) can help in the action definition to improve the performance of the chosen indexes.

• Phase C (Control). Teams will outline a plan to retain the gains after the conclusion of the project.

The finance department can assist in investment calculations, profits, ROI, etc.

Analysis and application of maintenance strategies for Omnicane Thermal Energy Operations (St Aubin) Ltd