Industrial training report of thermal power plant

I

A

Report of

Industrial Training

on

BOILER TURBINE & GENERATOR

(Operation & Maintenance)

Submitted By: - Submitted To: -

Ravinder Jangid Mr. Braj Gaur

Enroll No.: - PU216084 HOD ( Mech. Dept. )

Department of Mechanical Engineering

Pratap University, Chandwaji

Jaipur Rajasthan

II

PROJECT REPORT

On

Summer Training

In

PPGCL

(BARA, ALLAHABAD U.P.)

On

B.T.&G.

(O&M)

CERTIFICATE

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This is to certify that RAVINDER JANGID, S/O Mr. MALI RAM JANGID, B.Tech (Mechanical Engineering) from PRATAP UNIVERSITY, JAIPUR has successfully completed his Summer Training in PPGCL,Bara,Allahabad. His performance is good and up to the mark during the training.

Date:

(Signature)

Coordinator

ACKNOWLEDGEMENT

“….the beauty of destination is half veiled and the fragrance of success is half dull until the traces of all those enlightening the path are left to fly with the wind spreading word of thankfulness.

Keeping this in view, it would be unfair on my part if I don’t think the mentioned few. I express my

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sincere gratitude to

Mr. B.L. GAROO (consultant, P&A) who give me the opportunity to get training in such a recognized company. His guidance and knowledge help me to learn engineering in real sense. I also express my sincere thanks to the engineers and working staff of the accessories factory that excellently make me understand about the machines and mechanisms.

I am also very grateful to Mr. Braj Gaur (HOD, Mechanical Engineering, Pratap University), who extended his complete support for the training.

CONTENTS Page No.

1. Introduction and benefits of training vii

2. Vision, Mission, Target and challenges viii

3. About PPGCL ix

4. Basic Power Plant Cycle x

5. Boilers xi

V

6. Specification of boiler xiv

7. Turbine xxiii

8. Specification of turbine xxv

9. Generator xxvii

10. Specification of generator xxviii

11. Associated systems in power plant xxix

12. Ways to increase the efficiency of power plants xxxi

13. Losses during operation and maintenance of plant xxxiii

14. Conclusion xxxv

15. Bibliography xxxvi

List of Figures:-

Contents Page No.

Fig. 1- Modified Rankine Cycle x

Fig. 2- Cooling Tower xiv

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Fig. 3- Coal Roller xv

Fig. 4- Primary Boiler xxi

Fig. 5- Steam Turbine xxiii

Fig. 6- Electric Generator xxvii

Fig. 7- Effect of lowering of the condenser pressure on efficiency xxxii

Fig. 8- Effect of superheating the steam to high temperatures xxxii

Fig. 9- Effect of increasing boiler pressure to increase efficiency xxxiii

1.1 INTRODUCTION OF TRAINING

Training is the process of learning a sequence of programmed behaviour. It is the application of

knowledge. It gives people an awareness of the rules and procedure to guide their behaviours. It

attempts to improve their performance on the current job and prepare them for an intended job.

1.2 BENEFITS OF TRAINING

How training benefits the organization:

Leads to improved profitability and/or more positive attitudes toward profits orientation.

Improve the job knowledge and skills at all levels of the organization.

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Improve the morale of the workforce.

Helps people identify with organizational goals.

Helps create a better corporate image.

Fosters authenticity, openness and trust

Improve the relationship between the boss and subordinate.

Aids in organizational development.

Learn from the trainee

Helps prepare in guideline for work

Aids in understanding and carrying out organizational policies

Provides information for future needs and all areas of organization

Improves labour management relation

Organization gets more effective decision making and problem solving skills

Aids in development for promotion within

Aids in developing leadership skills, motivation, loyalty, better attitudes and other aspects

that successful workers and managers usually display.

Help keep cost in many areas, e.g. production, personnel distribution etc.

Develops a sense of responsibility in the organization for being competent and

knowledgeable.

2.1 VISION OF PPGCL

“To contribute significantly in strengthening India in the power sector and become the

world’s most valuable and reliant thermal power service providing company”

2.2 MISSION OF PPGCL

“To provide a world class distinguished service,focussed on adding value to the customers process,

whilst addressing customer`s needs in a professional and dynamic manner.”

2.3 TARGET AND CHALLENGES

2.3.1 [TARGET]

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The project is being built by Prayagraj Power Generation, a power generation subsidiary of the privately owned Jaypee Group, a major Indian infrastructure company with interests in Civil Engineering and Construction, Cement, Power, Real Estate, Expressways, Hospitality, Golf Courses and Education. According to Jaypee Group (2011), the project will be built in two Phases. Phase 1, comprising three 660 MW units, is slated to be commissioned in 2015. JPV bought the Prayagraj Power Generation Company, a special purpose project company created by the Uttar Pradesh Power Corporation to build the Bara project on a 'build, own, operate' basis.

According to the 2010/2011 annual report, the company was in possession of the 778 hectares needed for the project and had received the necessary environmental clearance, water linkage, and coal linkage. Boiler foundations were completed and other construction works was underway. Financial closure had been achieved.

According to the JP Power Ventures website (2014), Phase I is planned for completion by 2014. However, as of 2015 Phase I is under construction with Unit 1 planned for October 2015 and units 2-3 in 2016, according to the India Central Electrical Authority.

Phase II would comprise two 660 MW units. As of August 2015 phase II has yet to receive environmental permits, and appears to be deferred or abandoned.

.

2.3.2 [Challenge]

Both the Bara project and the nearby Karchana Thermal Power Project (now cancelled) have been the subject of local opposition and agitation. The Environmental Justice Atlas reported that protests at the Bara project in January 2011 damaged "police vehicles to protest against land acquisition policies." Additionally, protesters claimed one farmer was killed in police firing, a charge denied by the Uttar Pradesh government. It was reported in February 2011 that villagers ransacked and damaged property at the project site. The protesters had reportedly inflicted damage worth Rs 1 crore.

3. ABOUT THE COMPANY

Bara Thermal Power Project is 92.53% owned by Jaypee Group of Industries. The project is situated at Bara in Allahabad district of the state of Uttar Pradesh, India. The first phase of 1980 MW is expected to commence operations in 2014. The second phase of a 3300 MW thermal power plant is under construction. Some land owners, whose land was acquired for the project, were reportedly sitting on fast demanding better compensation for their agricultural land. The farmers claimed the company had promised job to one person of every family, whose land was being acquired, but it had not been fulfilled. Protesters went on a rampage damaging police vehicles to protest against land acquisition policies in January 2011. The agitators also alleged one farmer was killed in police firing, a charge denied by the Uttar Pradesh government. Protesters had damage worth Rs 1 crore to the company after they smashed computers, vehicles and damaged the mess and other facilities. The protesters are demanding jobs in the project and a rehabilitation allowance of Rs 62,500 which is given to labourers displaced by a project. Apprehending more trouble, the company shifted some of

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the equipment to nearby Madhya Pradesh.

BASIC DATA

o Name-Bara thermal power plant, Allahabad, Indiao Country-Indiao Province-Uttar Pradesho Site-Bara, Allahabado Accuracy of Location-MEDIUM regional level

SOURCE OF CONFLICT

Type of Conflict (1st level)-:

Fossil Fuels and Climate Justice/Energy

Type of Conflict (2nd level)-:

Water treatment and access to sanitation (access to sewage)OtherWater access rights and entitlementsLand acquisition conflictsThermal power plants

Specific Commodities-:

Coal Electricity

4. BASIC POWER PLANT CYCLE : RANKINE CYCLE

The Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 80% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants. It is named after William John Macquorn Rankine, a Scottish polymath. The Rankine cycle is the fundamental thermodynamic underpinning of the steam engine.

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5. BOILER : A boiler is the central or an important component of the thermal power plant which focuses on producing superheated steams that is used for running of the turbines which in turn is used for the generation of electricity. A boiler is a closed vessel in which the heat produced by the combustion of fuel is transferred to water for its conversation into steam of the desired temperature & pressure.

The heat-generating unit includes a furnace in which the fuel is burned. With the advantage of water-cooled furnace walls, super heaters, air heaters and economizers, the term steam generator was evolved as a better description of the apparatus.

Boilers may be classified on the basis of any of the following characteristics:

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Use Pressure Materials Size Tube Content Tube Shape and position Firing Heat Source Fuel Fluid Circulations Furnace position Furnace type General shape Trade name Special features

Use: The characteristics of the boiler vary according to the nature of service performed.

Customarily boiler is called either stationary or mobile. Large units used primarily for electric power generation are known as control station steam generator or utility plants.

Pressure: To provide safety control over construction features, all boilers must be constructed in accordance with the Boiler codes, which differentiates boiler as per their characteristics.

Materials: Selection of construction materials is controlled by boiler code material specifications. Power boilers are usually constructed of special steels.

Size: Rating code for boiler standardize the size and ratings of boilers based on heating surfaces. The same is verified by performance tests.

Tube Contents: In addition to ordinary shell type of boiler, there are two general steel boiler classifications, the fire tube and water tube boilers. Fire tube boiler is boilers with straight tubes that are surrounded by water and through which the products of combustion pass. Water tube boilers are those, in which the tubes themselves contain steam or water, the heat being applied to the outside surface.

Firing: The boiler may be a fired or unfired pressure vessel. In fired boilers, the heat applied is a product of fuel combustion. A non-fired boiler has a heat source other than combustion.

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Heat Source: The heat may be derived from (1) the combustion of fuel (2) the hot gasses of other chemical reactions (3) the utilization of nuclear energy.

Fuel: Boilers are often designated with respect to the fuel burned.

Fluid: The general concept of a boiler is that of a vessel to generate steam. A few utilities plants have installed mercury boilers.

Circulation: The majority of boilers operate with natural circulation. Some utilize positive circulation in which the operative fluid may be forced 'once through' or controlled with partial circulation.

Furnace Position: The boiler is an external combustion device in which the combustion takes place outside the region of boiling water. The relative location of the furnace to the boiler is indicated by the description of the furnace as being internally or externally fired.

Furnace type: The boiler may be described in terms of the furnace type.

General Shape: During the evaluation of the boiler as a heat producer, many new shapes and designs have appeared and these are widely recognized in the trade.

Trade Name: Many manufacturers coin their own name for each boiler and these names come into common usage as being descriptive of the boiler.

Special features: some times the type of boiler like differential firing and Tangential firing are described.

5.1 Categorization of Boilers:

Boilers are generally categorized as follows:

• Steel boilers

• Fire Tube type

• Water tube type

• Horizontal Straight tube

5.2 The main components of a boiler and their functions are given below:

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5.2.1 DRUM: It is a type of storage tank much higher placed than the level at which the boiler is placed, and it is also a place where water and steam are separated. First the drum is filled with water coming from the economizer, from where it is brought down with the help of down-comers, entering the bottom ring headers. From there they enter the riser, which are nothing but tubes that carries the water (which now is a liquid-vapor mixture), back to the drum. Now, the steam is sent to the super heaters while the saturated liquid water is again circulated through the down-comers and then subsequently through the risers till all the water in the drum turns into steam and passes to the next stage of heating that is superheating.

5.2.2 SUPER HEATERS: The steam from the boiler drum is then sent for superheating. This takes place in three stages. In the first stage, the steam is sent to a simple super heater, known as the low temperature super heaters (LTSH), after which the second stage consists of several divisional panels super heaters (DPSH). The final stage involves further heating in the Platen super heaters (PLSH), after which the steam is sent through the Main Steam (MS) piping for driving the turbine.

5.2.3 WATER WALLS: The water from the bottom ring header is then transferred to the water walls, where the first step in the formation of steam occurs by absorbing heat from the hot interior of the boiler where the coal is burned continuously. This saturated water steam mixture then enters the boiler drum.

5.2.4 ECONOMIZER: The economizer is a tube-shaped structure which contains water from the boiler feed pump. This water is heated up by the hot flue gases which pass through the economizer layout, which then enters the drum. The economizer is usually placed below the second pass of the boiler, below the Low Temperature Super heater. As the flue gases are being constantly produced due to the combustion of coal, the water in the economizer is being continuously being heated up, resulting in the formation of steam to a partial extent. Economizer tubes are supported in such a way that sagging, deflection & expansion will not occur at any condition of operation.

5.2.5 DEAERATOR: A deaerator is a device that is widely used for the removal of air and other dissolved gases from the feedwater to steam-generating boilers. In particular, dissolved oxygen in boiler feedwaters will cause serious corrosion damage in steam systems by attaching to the walls of metal piping and other metallic equipment and forming oxides (rust). Water also combines with any dissolved carbon dioxide to form carbonic acid that causes further corrosion. Most deaerators are designed to remove oxygen down to levels of 7 ppb by weight (0.005 cm³/L) or less.

5.3 SPECIFICATION OF BOILER IN PPGCL:

5.3.1 The boiler use in PPGCL is water tube boiler. There are some specification of water tube boiler.

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Fig 1. Cooling Tower at PPGCL

5.3.2 Boiler Auxiliaries:

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Fig 3. Coal Roller with conveyer belt

5.3.3 Main Parameters:

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5.4Coal Description:

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5.4.1 Flow

5.4.2 Temperature

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5.4.3 Pressures ( Steam & Water )

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5.4.4 Pressures & Drafts ( Air and Gas )

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5.4.5 Fuel

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Fig 4. Primary Boiler5.4.6 Mill and Burner Performance

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5.4.7 O2, CO2 ( Dry Vol. ) and Excess Air

5.4.8 Ambient Conditions

6.TURBINE: A turbine is a turbomachine with at least one moving part called a rotor assembly,

which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and

impart rotational energy to the rotor.

But in thermal power plant the turbine use as called steam turbine.

Steam Turbine: A steam turbine is a device which extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Sir Charles Parsons in 1884.

Because the turbine generates rotary motion, it is particularly suited to be used to drive an electrical generator – about 90% of all electricity generation in the United States (1996) is by use of steam turbines. The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency from the use of multiple stages in the expansion of the steam, which results in a closer approach to the ideal reversible expansion process.

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Fig 5. Steam Turbine in PPGCL

6.1 Types of Steam Turbine:

6.1.1 Impulse turbines: An impulse turbine has fixed nozzles that orient the steam flow into high speed jets. These jets contain significant kinetic energy, which is converted into shaft rotation by the bucket-like shaped rotor blades, as the steam jet changes direction. A pressure drop occurs across only the stationary blades, with a net increase in steam velocity across the stage. As the steam flows through the nozzle its pressure falls from inlet pressure to the exit pressure (atmospheric pressure, or more usually, the condenser vacuum). Due to this high ratio of expansion of steam, the steam leaves the nozzle with a very high velocity. The steam leaving the moving blades has a large portion of the maximum velocity of the steam when leaving the nozzle. The loss of energy due to this higher exit velocity is commonly called the carry over velocity or leaving loss.

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6.1.2 Reaction turbines: In the reaction turbine, the rotor blades themselves are arranged to form convergent nozzles. This type of turbine makes use of the reaction force produced as the steam accelerates through the nozzles formed by the rotor. Steam is directed onto the rotor by the fixed vanes of the stator. It leaves the stator as a jet that fills the entire circumference of the rotor. The steam then changes direction and increases its speed relative to the speed of the blades. A pressure drop occurs across both the stator and the rotor, with steam accelerating through the stator and decelerating through the rotor, with no net change in steam velocity across the stage but with a decrease in both pressure and temperature, reflecting the work performed in the driving of the rotor.

6.2 Operation and maintenance of steam turbine: Because of the high pressures used in the steam circuits and the materials used, steam turbines and their casings have high thermal inertia. When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with the steam turbine. Also, a turning gear is engaged when there is no steam to slowly rotate the turbine to ensure even heating to prevent uneven expansion. After first rotating the turbine by the turning gear, allowing time for the rotor to assume a straight plane (no bowing), then the turning gear is disengaged and steam is admitted to the turbine, first to the astern blades then to the ahead blades slowly rotating the turbine at 10–15 RPM (0.17–0.25 Hz) to slowly warm the turbine. The warm up procedure for large steam turbines may exceed ten hours.

During normal operation, rotor imbalance can lead to vibration, which, because of the high rotation velocities, could lead to a blade breaking away from the rotor and through the casing. To reduce this risk, considerable efforts are spent to balance the turbine. Also, turbines are run with high quality steam: either superheated (dry) steam, or saturated steam with a high dryness fraction. This prevents the rapid impingement and erosion of the blades which occurs when condensed water is blasted onto the blades (moisture carry over). Also, liquid water entering the blades may damage the thrust bearings for the turbine shaft. To prevent this, along with controls and baffles in the boilers to ensure high quality steam, condensate drains are installed in the steam piping leading to the turbine.

Maintenance requirements of modern steam turbines are simple and incur low costs (typically around $0.005 per kWh); their operational life often exceeds 50 years.

6.3 Specification of Steam Turbine in PPGCL:

6.3.1 Rating of Steam Turbine:

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6.3.2 Turbine, types:

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7. GENERATOR: An Electrical generator is a device that converts kinetic energy to electrical

energy, generally using electromagnetic induction. The task of converting the electrical energy into

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mechanical energy is accomplished by using a motor. The source of mechanical energy maybe water

falling through the turbine or steam turning a turbine (as is the case with thermal power plants).

There are several classifications for modern steam turbines. Steam turbines are used in our entire

major coal fired power stations to drive the generators or alternators, which produce electricity. The

turbines themselves are driven by steam generated in "boilers “or "steam generators" as they are

sometimes called. Electrical power stations use large steam turbines driving electric generators to

produce most (about 86%) of the world‟s electricity. These centralized stations are of two types:

fossil fuel power plants and nuclear power plants. The turbines used for electric power generation are

most often directly coupled to their-generators .As the generators must rotate at constant

synchronous speeds according to the frequency of the electric power system, the most common

speeds are 3000 r/min for 50 Hz systems, and 3600 r/min for 60 Hz systems. Most large nuclear sets

rotate at half those speeds, and have a 4-pole generator rather than the more common 2-pole one.

Fig 6. Electric Generator use in PPGCL

7.1 Specification of Generator:

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7.1.1 Rated Data and Outputs:

8. ASSOCIATED SYSTEMS IN A POWER PLANT :

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8.1 PA FANS: The primary air fans are used to carry the pulverized coal particles from the mills to the boiler. They are also used to maintain the coal-air temperature. The specifications of the PA fan used at the plant under investigation are: axial flow, double stage, reaction fan.

8.2 FD FANS: The forced draft fans, also known as the secondary air fans are used to provide the secondary air required for combustion, and to maintain the wind box differential pressure. Specifications of the FD fans are: axial flow, single stage, impulse fan.

8.3 ID FAN:( An induced fan ) The main purpose of an ID fan is to suck the flue gas through all the above mentioned equipments and to maintain the furnace pressure. ID fans use 1.41% of plant load for a 500 MW plant.

8.4 AIR PRE-HEATERS: Air pre-heaters are used to take heat from the flue gases and transfer it to the incoming air. They are of two types:

a) Regenerative b) Recuperative

8.5 ELECTROSTATIC PRECIPITATORS: They are used to separate the ash particles from the flue gases. In this the flue gas is allowed into the ESP, where there are several metallic plates placed at a certain distance from each other. When these gases enter, a very high potential difference is applied, which causes the gas particles to ionize and stick to the plates, whereas the ash particles fall down and are collected in a hopper attached to the bottom of the ESP. The flue gas is allowed to cool down and is then released to the ID fan to be sent to the chimney. 8.6 MILL: As the name suggests the coal particles are grinded into finer sized granules. The coal which is stored in the bunker is sent into the mill, through the conveyor belt which primarily controls the amount of coal required to be sent to the furnace. It on reaching a rotating bowl in the bottom encounters three grinding rolls which grinds it into fine powder form of approx. 200 meshes per square inch. the fine coal powder along with the heated air from the FD and PA fan is carried into the burner as pulverized coal while the trash particles are rejected through a reject system.

8.7 SEAL AIR FAN: The seal air fan is used near the mill to prevent the loss of any heat from the coal which is in a pulverized state and to protect the bearings from coal particle deposition.

8.8 WIND BOX: these acts as distributing media for supplying secondary/excess air to the furnace for combustion. These are generally located on the left and and right sides of the furnace while facing the chimney.

8.9 IGNITER FAN: Igniter fans which are 2 per boiler are used to supply air for cooling Igniters & combustion of igniter air fuel mixture.

8.10 CHIMNEY: These are tall RCC structures with single & multiple flues. Here, for I & II we

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have 1 chimney, for unit III there is 1 chimney & for units IV & V there is 1 chimney. So number of chimneys is 5 and the height of each is 275 metres.

8.11 COAL HANDLING PLANT: This part of the thermal power plant handles all the requirements of coal that needs to be supplied to the plant for the continuous generation of electricity. Coal is generally transported from coal mines ( mostly located in peninsular regions of India ) to Thermal power plant with the help of rail wagons. A Single rail wagon can handle upto 80 tons of coal( gross weight) . When these rail wagons reach the thermal plant the coal is unloaded with the help of wagon tipplers. A wagon tippler is actually a huge J shaped Link pinned at its top. Powerful motors are used to pull the ropes attached to an end which lets the wagon to rotate at an angle of 135 degree. The coal falls down due to action of gravity into the coal bunkers. Vibration motors then are used to induce the movement the coal through its way. as the coal reaches the hopper section of the bunker , it is taken away by conveyer belts to either the storage yard or to the assembly points where the coal gets distributed on different conveyers. Initially, the size of coal is taken as 250mm in size. The macro coal has to be converted into micro ( 25mm ) size coal for the actual combustion. This is attained by using high pressure crushers located at the coal handling plants. Here various metal are separated by various mechanisms. There are various paths through which a coal can go to boiler section. These paths are alternative such as A and B and only one is used at a time letting the other standby.

8.12 COAL BUNKER: These are in process storage used for storing crushed coal from the coal handling system. Generally, these are made up of welded steel plates. Normally, these are located on top of mills to aid in gravity feeding of coal. There are 10 such bunkers corresponding to each mill.

8.13 ASH HANDLING PLANT: The ash produced in boiler is transported to ash dump area by means of sluice type hydraulic ash handling system, which consists of:

8.13.1 Bottom Ash System: In the Bottom Ash system the ash slag discharged from the furnace bottom is collected in two water impounded scraper troughs installed below bottom ash hoppers. The ash is continuously, transported by means of the scraper chain conveyor, on to the respective clinker grinders which reduce the lump sizes to the required fineness.

8.13.2 Fly Ash System: In this system, Fly ash gets collected in these hoppers drop continuously to flushing apparatus where fly ash gets mixed with flushing water and the resulting slurry drops into the ash sluice channel. Low pressure water is applied through the nozzle directing tangentially to the section of pipe to create turbulence and proper mixing of ash with water.

8.13.3 Ash Water System: High pressure water required for B.A hopper quenching nozzles, B.A hopper`s window spraying, clinker grinder sealing scraper bars, cleaning nozzles B.A hopper seal through flushing, Economizer Hoppers` flushing nozzles and sluicing trench jetting nozzles is tapped from the high pressure water ring main provided in the plant area.

8.13.4 Ash Slurry System: Bottom Ash and Fly Ash slurry of the system is sluiced up to ash

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slurry pump along the channel with the aid oh high pressure water jets located at suitable intervals along the channel. Slurry pump section line consisting of reducing elbow with drain valve, reducer and butterfly valve and portion of slurry pump delivery line consisting of butterfly valve, Pipe and fitting has also been provided.

8.14 REHEATER: The function of reheater is to reheat the steam coming out from the high pressure turbine to a temperature of 540 degrees Celsius. It is composed of two sections: the rear pendant section is located above the furnace arc & the front pendant section is located between the rear water hanger tubes & the Platen superheater section.

8.15 BURNERS: There are total 20 pulverised coal burners for the boiler present here, & 10 of the burners provided in each side at every elevation named as A,B,C,D,E,F,G,H,J,K. There are oil burners present in every elevation to fire the fuel oil (LDO & HFO) during lightup.

9. Ways to increase the thermal efficiency of power plants:

The basic idea behind all the modifications to increase the thermal efficiency of a power cycle is the same: Increase the average temperature at which heat is transferred to the working fluid in the boiler, or decrease the average temperature at which heat is rejected from the working fluid in the condenser. That is, the average fluid temperature should be as high as possible during heat addition and as low as possible during heat rejection.

9.1 Lowering the Condenser Pressure (Lowers Tlow,avg): Steam exists as a saturated mixture in the condenser at the saturation temperature corresponding to the pressure inside the condenser. Therefore, lowering the operating pressure of the condenser automatically lowers the temperature of the steam, and thus the temperature at which heat is rejected. The effect of lowering the condenser pressure on the Rankine cycle efficiency is illustrated on a T-s diagram in Fig.1. For comparison purposes, the turbine inlet state is maintained the same. The colored area on this diagram represents the increase in net work output as a result of lowering the condenser pressure from P4 to P4’. The heat input requirements also increase (represented by the area under curve 2_-2), but this increase is very small. Thus the overall effect of lowering the condenser pressure is an increase in the thermal efficiency of the cycle.

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Fig 7. Effect of lowering of the condenser pressure on efficiency

9.2 Superheating the Steam to High Temperatures (Increases Thigh,avg): The average temperature at which heat is transferred to steam can be increased without increasing the boiler pressure by superheating the steam to high temperatures. The effect of superheating on the performance of vapor power cycles is illustrated on a T-s diagram in Fig.2. The colored area on this diagram represents the increase in the net work. The total area under the process curve 3-3_ represents the increase in the heat input. Thus both the net work and heat input increase as a result of superheating the steam to a higher temperature. The overall effect is an increase in thermal efficiency, however, since the average temperature at which heat is added increases.

Fig 8. Effect of superheating the steam to high temperatures

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9.3 Increasing the Boiler Pressure (Increases Thigh,avg): Another way of increasing the average temperature during the heat-addition process is to increase the operating pressure of the boiler, which automatically raises the temperature at which boiling takes place. This, in turn, raises the average temperature at which heat is transferred to the steam and thus raises the thermal efficiency of the cycle. The effect of increasing the boiler pressure on the performance of vapor power cycles is illustrated on a T-s diagram in Fig.3. Notice that for a fixed turbine inlet temperature, the cycle shifts to the left and the moisture content of steam at the turbine exit increases. This undesirable side effect can be corrected, however, by reheating the steam, as discussed in the next section.

Fig 9. Effect of increasing boiler pressure to increase efficiency

10. LOSSES DURING OPERATION & MAINTAINANCE OF PLANT:

10.1 SURFACE ROUGHNESS:

It increases friction & resistance. It can be due to Chemical deposits, Solid particle damage, Corrosion Pitting & Water erosion. As a thumb rule, surface roughness of about 0.05 mm can lead to a decrease in efficiency of 4%.

10.2 LEAKAGE LOSS:

a) Interstage Leakage b) Turbine end Gland Leakages c) About 2 - 7.5 kW is lost per stage if clearances are increased by 0.025 mm depending upon LP or HP stage.

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10.3 WETNESS LOSS:

A) Drag Loss: Due to difference in the velocities of the steam & water particles, water particles lag behind & can even take different trajectory leading to losses.

B) Sudden condensation can create shock disturbances & hence losses.

C) About 1% wetness leads to 1% loss in stage efficiency.

10.4 OFF DESIGN LOSSES:

a) Losses resulting due to turbine not operating with design terminal conditions. Change in Main Steam pressure & temperature.

b) Change in HRH pressure & temperature.

c) Condenser Back Pressure

d) Convergent-Divergent nozzles are more prone to Off Design losses then Convergent nozzles as shock formation is not there in convergent nozzles.

10.5 PARTIAL ADMISSION LOSSES:

A) In Impulse turbines, the controlling stage is fed with means of nozzle boxes, the control valves of which open or close sequentially.

B) At some partial load some nozzle boxes can be partially open / Completely closed.

C) Shock formation takes place as rotor blades at some time are full of steam & at some other moment, devoid of steam leading to considerable losses.

10.6 LOSS DUE TO EROSION OF LP LAST STAGE BLADES:

A) Erosion of the last stage blades leads to considerable loss of energy. Also, It is the least efficient stage.

B) Erosion in the 10% length of the blade leads to decrease in 0.1% of efficiency.

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CONCLUSION

All the minor & major sections in the thermal project had been visited & also

understood to the best of my knowledge. I believe that this training has made me well

versed with the various processes in the power plant. As far as I think there is a long

way to go till we use our newest of ever improving technologies to increase the

efficiency because the stocks of coal are dwindling and they are not going to last

forever. Its imperative that we start shouldering the burden together to see a shining

and sustainable future INDIA.

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Bibliography:

1. Wikipedia

2. http://indianexpress.com/article/cities/lucknow/no-more-dark-days/

3. External link of PPGCL

4. A text book of Power Plant Engineering by R K Rajput

5. http://www.cleanboiler.org/Eff_Improve/Primer/Boiler_Introduction.asp#Water_Tube_Boiler