ME2403 POWER PLANT ENGINEERING L T P C 3 0 0 3 …

ME 2403 POWER PLANT ENGINEERING VII/IV MECHANICAL ENGINEERING

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ME2403 POWER PLANT ENGINEERING L T P C3 0 0 3

OBJECTIVE: To understand the various components, operations and applications of different types

of power plants

UNIT I INTRODUCTION TO POWER PLANTS AND BOILERS 9

Layout of Steam , Hydel , Diesel , MHD, Nuclear and Gas turbine Power PlantsCombined Power cycles – comparison and selection , Load duration Curves Steam boilersand cycles – High pressure and Super Critical Boilers – Fluidised Bed Boilers

UNIT II STEAM POWER PLANT 9

Fuel and ash handling, Combustion Eq u ip me n t for burning coal, Mechanical Stokers.Pulveriser, Electrostatic Precipitator, Draught- Different Types, Surface condensertypes, cooling Towers

UNIT III NUCLEAR AND HYDEL POWER PLANTS 9

Nuclear Energy-Fission, Fusion Reaction, Types of Reactors, Pressurized water reactor,Boiling water reactor, Waste disposal and safety Hydel Power plant- EssentialElements, Selection of turbines, governing of Turbines- Micro hydel developments

UNIT IV DIESEL AND GAS TURBINE POWER PLANT 9

Types of diesel plants, components, Selection of Engine type, applications-Gas turbine powerplant- Fuels- Gas turbine material – open and closed cycles- reheating – Regeneration andintercooling – combines cycle

UNIT V OTHER POWER PLANTS AND ECONOMICS OF POWER PLANTS 9

Geo thermal- OTEC- tidel- Pumped storage –Solar central receiver system Cost of electricEnergy- Fixed and operating costs-Energy rates- Types tariffs- Economics of load sharing,comparison of various power plants.

TEXT BOOKS:

1. Arora S.C and Domkundwar S, “A Course in Power Plant Engineering”, DhanpatRai, 2001

2. Nag P.K,”Power Plant Engineering”. Third edition Tata McGraw- Hill ,2007

REFERENCES:

1. EI-Wakil M.M, Power “Plant Technology,” Tata McGraw-Hill 19842. K.K.Ramalingam , “ Power Plant Engineering “, Scitech Publications, 20023. G.R,Nagpal , “Power Plant Engineering”, Khanna Publishers 19984. G.D.Rai, “Introduction to Power Plant technology” Khanna Publishers, 1995


iv

CONTENT

UNIT NO. TITLE PAGENO.

1 INTRODUCTION TO POWER PLANTS AND BOILERS

1.1 Steam Power Plants 1

1.2hydel Power Plants 3

1.3 Diesel Power Plants 5

1.4 Nuclear Power Plants 8

1.5 Gas Turbine Power Plants 11

1.6 Magneto Hydro Dynamic (MHD) Power Plants 15

1.7 Combined Power Cycles 17

1.8 Load Duration Curve 18

1.9 Boilers 19

1.10. Fluidised Bed Combustion (FBC) 25

2 STEAM POWER PLANT

2.1 Steam Power Plant 27

2.1.1 Fuel Handling System 27

2.1.2pulverized Coal Storage 30

2.2 Ash Handling System: 32

2.3 Draught 35

2.4 Surface Condenser 39

2.5 Cooling Towers 41


v

3 NUCLEAR AND HYDEL POWER PLANTS

3.1 Nuclear And Hydel Power Plants 43

3.1.1Fission Energy 43

3.1.2 Chain Reaction 44

3.1.3 Main Components Of Nuclear Power Plants 44

3.2 Boiling Water Reactor (BWR) 46

3.3 CANDU Type Reactor 47

3.4 Fast Breeder Reactor 48

3.5 Waste Disposal 49

3.6 HYDEL Power Plant 50

3.6.1. Classification Of Hydro-Power Plants 52

4 DIESEL AND GAS TURBINE POWER PLANT

4.1 Diesel Engine Power Plant System 56

4.3 Gas Turbine Power Plant 57

4.3.1 Layout Of Gas Turbine Power Plant 58

4.4 Working Of Gas Turbine Cycle With Regenerator 60

4.5 Working Of Gas Turbine Cycle With Inter Cooling 61

5OTHER POWER PLANTS AND ECONOMICS OF

POWER PLANTS

5.1 Geo-Thermal Power Plant 63

5.2 Tidal Power Plants 64

5.3 Tidal Power Plants 65

5.4 Solar Power Plant 66

5.5 Ocean Thermal Energy Conversion 69

5.6 Pumped Storage 70

5.7 Tariffs 71

5.8 Economics Of Power Plants 71

5.9 Load Duration Curve 72


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1 M.MANIKANDAN-AP/MECHN 2014-2015

UNIT-I

INTRODUCTION TO POWER PLANTS AND BOILERS

1.1 STEAM POWER PLANTS:

A thermal power station is a power plant in which the prime mover is steam driven.

Water is heated, turns into steam and spins a steam turbine which drives an electrical generator.

After it passes through the turbine, the steam is condensed in a condenser and recycled to where

it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal

power stations is due to the different fuel sources. Some prefer to use the term energy center

because such facilities convert forms of heat energy into electricity. Some thermal power plants

also deliver heat energy for industrial purposes, for district heating, or for desalination of water

as well as delivering electrical power. A large proportion of CO2 is produced by the worlds

fossil fired thermal power plants; efforts to reduce these outputs are various and widespread.

LAYOUT OF STEAM POWER PLANT:

The four main circuits one would come across in any thermal power plant layout are- Coal and Ash Circuit- Air and Gas Circuit- Feed Water and Steam Circuit- Cooling Water Circuit



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Coal and Ash Circuit

Coal and Ash circuit in a thermal power plant layout mainly takes care of feeding the

boiler with coal from the storage for combustion. The ash that is generated during combustion

is collected at the back of the boiler and removed to the ash storage by scrap conveyors. The

combustion in the Coal and Ash circuit is controlled by regulating the speed and the quality of

coal entering the grate and the damper openings.

Air and Gas Circuit

Air from the atmosphere is directed into the furnace through the air preheated by the

action of a forced draught fan or induced draught fan. The dust from the air is removed before

it enters the combustion chamber of the thermal power plant layout. The exhaust gases from

the combustion heat the air, which goes through a heat exchanger and is finally let off into the

environment.

Feed Water and Steam Circuit

The steam produced in the boiler is supplied to the turbines to generate power. The

steam that is expelled by the prime mover in the thermal power plant layout is then condensed

in a condenser for re-use in the boiler. The condensed water is forced through a pump into the

feed water heaters where it is heated using the steam from different points in the turbine. To

make up for the lost steam and water while passing through the various components of the

thermal power plant layout, feed water is supplied through external sources. Feed water is

purified in a purifying plant to reduce the dissolve salts that could scale the boiler tubes.

Cooling Water Circuit

The quantity of cooling water required to cool the steam in a thermal power plant layout

is significantly high and hence it is supplied from a natural water source like a lake or a river.

After passing through screens that remove particles that can plug the condenser tubes in a

thermal power plant layout, it is passed through the condenser where the steam is condensed.

The water is finally discharged back into the water source after cooling. Cooling water circuit

can also be a closed system where the cooled water is sent through cooling towers for re-use in

the power plant. The cooling water circulation in the condenser of a thermal power plant layout

helps in maintaining a low pressure in the condenser all throughout.

All these circuits are integrated to form a thermal power plant layout that generates

electricity to meet our needs.



Advantages

Generation of power is continuous.

Initial cost low compared to hydel plant.

Less space required.

This can be located near the load centre so that the transmission losses are reduced.

It can respond to rapidly changing loads.

Disadvantages

Long time required for installation.

Transportation and handling of fuels major difficulty.

Efficiency of plant is less.

Power generation cost is high compared to hydel power plant.

Maintenance cost is high.

1.2HYDEL POWER PLANTS

Hydroelectric power plants convert the hydraulic potential energy from water into

electrical energy. Such plants are suitable were water with suitable head are available. The

layout covered in this article is just a simple one and only cover the important parts of

hydroelectric plant.

LAYOUT OF HYDEL POWER PLANT:



(1) Dam

Dams are structures built over rivers to stop the water flow and form a reservoir. The

reservoir stores the water flowing down the river. This water is diverted to turbines in power

stations. The dams collect water during the rainy season and stores it, thus allowing for a steady

flow through the turbines throughout the year. Dams are also used for controlling floods and

irrigation. The dams should be water-tight and should be able to withstand the pressure exerted

by the water on it. There are different types of dams such as arch dams, gravity dams and

buttress dams. The height of water in the dam is called head race.

(2) Spillway

A spillway as the name suggests could be called as a way for spilling of water from

dams. It is used to provide for the release of flood water from a dam. It is used to prevent over

toping of the dams which could result in damage or failure of dams. Spillways could be

controlled type or uncontrolled type. The uncontrolled types start releasing water upon water

rising above a particular level. But in case of the controlled type, regulation of flow is possible.

(3) Penstock and Tunnels

Penstocks are pipes which carry water from the reservoir to the turbines inside power

station. They are usually made of steel and are equipped with gate systems. Water under high

pressure flows through the penstock. A tunnel serves the same purpose as a penstock. It is used

when an obstruction is present between the dam and power station such as a mountain.

(4) Surge Tank

Surge tanks are tanks connected to the water conductor system. It serves the purpose of

reducing water hammering in pipes which can cause damage to pipes. The sudden surges of

water in penstock is taken by the surge tank, and when the water requirements increase, it

supplies the collected water thereby regulating water flow and pressure inside the penstock.

(5) Power Station

Power station contains a turbine coupled to a generator. The water brought to the power

station rotates the vanes of the turbine producing torque and rotation of turbine shaft. This

rotational torque is transferred to the generator and is converted into electricity.



The used water is released through the tail race. The difference between head race and

tail race is called gross head and by subtracting the frictional losses we get the net head

available to the turbine for generation of electricity.

Advantages

Water the working fluid is natural and available plenty.

Life of the plant is very long.

Running cost and maintenance are very low.

Highly reliable.

Running cost is low.

Maintenance and operation costs are very less.

No fuel transport problem.

No ash disposal problem.

Disadvantages

Initial cost of plant is very high.

Power generation depends on quantity of water available which depends on rainfall.

Transmission losses are very high.

More time is required for erection.

1.3 DIESEL POWER PLANTS

Diesel power plants produce power from a diesel engine. Diesel electric plants in the

range of 2 to 50 MW capacities are used as central stations for small electric supply networks

and used as a standby to hydroelectric or thermal plants where continuous power supply is

needed. Diesel power plant is not economical compared to other power plants.

The diesel power plants are cheaply used in the fields mentioned below.

1. Mobile electric plants

2. Standby units

3. Emergency power plants

4. Starting stations of existing plants

5. Central power station etc.



LAYOUT OF DIESEL POWER PLANT:

Figure shows the arrangements of the engine and its auxiliaries in a diesel power plant.

The major components of the diesel power plant are:

1) Engine

Engine is the heart of a diesel power plant. Engine is directly connected through a gear box to

the generator. Generally two-stroke engines are used for power generation. Now a days,

advanced super & turbo charged high speed engines are available for power production.

2) Air supply system

Air inlet is arranged outside the engine room. Air from the atmosphere is filtered by air filter

and conveyed to the inlet manifold of engine. In large plants supercharger/turbocharger is used

for increasing the pressure of input air which increases the power output.

3) Exhaust System

This includes the silencers and connecting ducts. The heat content of the exhaust gas is utilized

in a turbine in a turbocharger to compress the air input to the engine.

4) Fuel System

Fuel is stored in a tank from where it flows to the fuel pump through a filter. Fuel is injected to

the engine as per the load requirement.



5) Cooling system

This system includes water circulating pumps, cooling towers, water filter etc. Cooling water

is circulated through the engine block to keep the temperature of the engine in the safe range.

6) Lubricating system

Lubrication system includes the air pumps, oil tanks, filters, coolers and pipe lines. Lubricant

is given to reduce friction of moving parts and reduce the wear and tear of the engine parts.

7) Starting System

There are three commonly used starting systems, they are;1) A petrol driven auxiliary engine2) Use of electric motors.3) Use of compressed air from an air compressor at a pressure of 20 Kg/cm.

8) Governing system

The function of a governing system is to maintain the speed of the engine constant irrespective

of load on the plant. This is done by varying fuel supply to the engine according to load.

Advantages

Diesel power plants can be quickly installed and commissioned.

Quick starting.

Requires minimum labour.

Plant is smaller, operate at high efficiency and simple compared to steam power plant.

It can be located near to load centres.

Disadvantages

Capacity of plant is low.

Fuel, repair and maintenance cost are high.

Life of plant is low compared to steam power plant.

Lubrication costs are very high.

Not guaranteed for operation under continuous overloads.

Noise is a serious problem in diesel power plant.

Diesel power plant cannot be constructed for large scale.



1.4 NUCLEAR POWER PLANTS

Nuclear power is the use of sustained or controlled nuclear fission to generate heat

and do useful work. Nuclear Electric Plants, Nuclear Ships and Submarines use controlled

nuclear energy to heat water and produce steam, while in space, nuclear energy decays naturally

in a radioisotope thermoelectric generator. Scientists are experimenting with fusion energy for

future generation, but these experiments do not currently generate useful energy.

Nuclear power provides about 6% of the world's energy and 13–14% of the world's

electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear

generated electricity.

Also, more than 150 naval vessels using nuclear propulsion have been built. Just as

many conventional thermal power stations generate electricity by harnessing the thermal

energy released from burning fossil fuels, nuclear power plants convert the energy released

from the nucleus of an atom, typically via nuclear fission.

LAYOUT OF NUCLEAR POWER PLANT:



NUCLEAR REACTOR

A nuclear reactor is an apparatus in which heat is produced due to nuclear fission chain

reaction. Fig. shows the various parts of reactor, which are as follows:

1. Nuclear Fuel

2. Moderator

3. Control Rods

4. Reflector

5. Reactors Vessel

6. Biological Shielding

7. Coolant.

1. Nuclear Fuel

Nuclear reactor

Fuel of a nuclear reactor should be fissionable material which can be defined as an

element or isotope whose nuclei can be caused to undergo nuclear fission by nuclear

bombardment and to produce a fission chain reaction. It can be one or all of the following U233,

U235 and Pu239.

Natural uranium found in earth crust contains three isotopes namely U234, U235 and U238

and their average percentage is as follows:

U238 - 99.3%

U235 - 0.7%

U234 - Trace



2. Moderator

In the chain reaction the neutrons produced are fast moving neutrons. These fast moving

neutrons are far less effective in causing the fission of U235 and try to escape from the reactor.

To improve the utilization of these neutrons their speed is reduced. It is done by colliding them

with the nuclei of other material which is lighter, does not capture the neutrons but scatters

them. Each such collision causes loss of energy, and the speed of the fast moving neutrons is

reduced. Such material is called Moderator. The slow neutrons (Thermal Neutrons) so

produced are easily captured by the nuclear fuel and the chain reaction proceeds smoothly.

Graphite, heavy water and beryllium are generally used as moderator

3. Control Rods

The Control and operation of a nuclear reactor is quite different from a fossil fuelled (coal or

oil fired) furnace. The energy produced in the reactor due to fission of nuclear fuel during chain

reaction is so much that if it is not controlled properly the entire core and surrounding structure

may melt and radioactive fission products may come out of the reactor thus making it

uninhabitable. This implies that we should have some means to control the power of reactor.

This is done by means of control rods.

Control rods in the cylindrical or sheet form are made of boron or cadmium. These rods

can be moved in and out of the holes in the reactor core assembly. Their insertion absorbs more

neutrons and damps down the reaction and their withdrawal absorbs less neutrons. Thus power

of reaction is controlled by shifting control rods which may be done manually or automatically.

4. Reflector

The neutrons produced during the fission process will be partly absorbed by the fuel

rods, moderator, coolant or structural material etc. Neutrons left unabsorbed will try to leave

the reactor core never to return to it and will be lost. Such losses should be minimized. It is

done by surrounding the reactor core by a material called reflector which will send the neutrons

back into the core. The returned neutrons can then cause more fission and improve the neutrons

economy of' the reactor.

Generally the reflector is made up of graphite and beryllium.

5. Reactor Vessel

It is a. strong walled container housing the cure of the power reactor. It contains

moderator, reflector, thermal shielding and control rods.



6. Biological Shielding

Shielding the radioactive zones in the reactor roan possible radiation hazard is essential

to protect, the operating men from the harmful effects. During fission of nuclear fuel, alpha

particles, beta particles, deadly gamma rays and neutrons are produced. Out of these gamma

rays are of main significance. A protection must be provided against them. Thick layers of lead

or concrete are provided round the reactor for stopping the gamma rays. Thick layers of metals

or plastics are sufficient to stop the alpha and beta particles.

7. Coolant

Coolant flows through and around the reactor core. It is used to transfer the large

amount of heat produced in the reactor due to fission of the nuclear fuel during chain reaction.

The coolant either transfers its heat to another medium or if the coolant used is water it takes

up the heat and gets converted into steam in the reactor which is directly sent to the turbine.

Advantages

Need less space.

Fuel consumption is small, hence transportation and storage charges are low.

Well suited for large power demands.

Less work men required.

Disadvantages

Capital cost very high.

Radioactive wastes, if not disposed properly have adverse effect on environment.

Maintenance cost high.

1.5 GAS TURBINE POWER PLANTS

A gas turbine, also called a combustion turbine, is a type of internal combustion engine.

It has an upstream rotating compressor coupled to a downstream turbine, and a combustion

chamber in-between.

Energy is added to the gas stream in the combustor, where fuel is mixed with air and

ignited. In the high pressure environment of the combustor, combustion of the fuel increases

the temperature. The products of the combustion are forced into the turbine section. There, the

high velocity and volume of the gas flow is directed through a nozzle over the turbine's blades,

spinning the turbine which powers the compressor and, for some turbines, drives their

mechanical output. The energy given up to the turbine comes from the reduction in the

temperature and pressure of the exhaust gas.



LAYOUT OF GAS TURBINE POWER PLANT

The gas turbine power plants which are used in electric power industry are classified into two

groups as per the cycle of operation.

(1) Open cycle gas turbine.

(2) Closed cycle gas turbine.

Open cycle gas turbine

1- Atmospheric Air

2- Compressed Atmospheric Air

3- Fuel air mixture after compression

4- Exhaust gases.

The heated gases coming out of combustion chamber are then passed to the turbine where

it expands doing mechanical work. Part of the power developed by the turbine is utilized in

driving the compressor and other accessories and remaining is used for power generation.

Since ambient air enters into the compressor and gases coming out of turbine are exhausted

into the atmosphere, the working medium must be replaced continuously. This type of cycle is

known as open cycle gas turbine plant and is mainly used in majority of gas turbine power

plants as it has many inherent advantages.

Advantages

1. Warm-up time is very less.

2. Low weight and size.

3. Almost any hydrocarbon fuels can be used.

4. Open cycle plants occupy comparatively little space.

6. Very economical when compared to other plants.

7. Independent of separate cooling medium.



Disadvantages

1. The part load efficiency of the open cycle plant decreases rapidly as the considerable

percentage of power developed by the turbine is used to drive the compressor.

2. The system is sensitive to the component efficiency; particularly that of compressor.

3. The open cycle plant is sensitive to changes in the atmospheric air temperature, pressure and

humidity.

3. The open-cycle gas turbine plant has high air rate compared to the other cycles.

4. It is essential that the dust should be prevented from entering into the compressor.

5. The deposition of the carbon and ash on the turbine blades is not at all desirable as it also

reduces the efficiency of the turbine.

Closed cycle gas turbine

1- Low Pressure Working Fluid @ Low temperature

2- High Pressure Working Fluid

3- Fuel + Working Fluid mixture @ High Pressure and Temperature

4- Low Pressure Working Fluid @ Temperature T4 < Temperature T3

In closed cycle gas turbine plant, the working fluid (air or any other suitable gas) coming

out from compressor is heated in a heater by an external source at constant pressure.

The high temperature and high-pressure air coming out from the external heater is passed

through the gas turbine. The fluid coming out from the turbine is cooled to its original

temperature in the cooler using external cooling source before passing to the compressor.



The working fluid is continuously used in the system without its change of phase and the

required heat is given to the working fluid in the heat exchanger.

Advantages

1. The closed cycle plant is not sensitive to changes in the atmospheric air temperature, pressure

and humidity.

2. The closed cycle avoids erosion of the turbine blades due to the contaminated gases and

fouling of compressor blades due to dust.

3. The need for filtration of the incoming air which is a severe problem in open cycle plant is

completely eliminated.

4. Load variation is usually obtained by varying the absolute pressure and mass flow of the

circulating medium, while the pressure ratio, the temperatures and the air velocities remain

almost constant.

5. The density of the working medium can be maintained high by increasing internal pressure

range, therefore, the compressor and turbine are smaller for their rated output. The high density

of the working fluid further increases the heat transfer properties in the heat exchanger.

6. As indirect heating is used in closed cycle plant, the inferior oil or solid fuel can be used in

the furnace and these fuels can be used more economically because these are available in

abundance.

8. The maintenance cost is low and reliability is high due to longer useful life.

Disadvantages

1. The system is dependent on external means as considerable quantity of cooling water is

required in the pre-cooler.

2. Higher internal pressures involve complicated design of all components and high quality

material is required which increases the cost of the plant.

3. The response to the load variations is poor compared to the open-cycle plant.

4. It requires very big heat-exchangers as the heating of workings fluid is done indirectly.



1.6 MAGNETO HYDRO DYNAMIC (MHD) POWER PLANTS

MHD power generation is a new system of electric power generation which is said to

be of high efficiency and low pollution. In advanced countries MHD generator are widely used

but in developing countries like India it is still under construction. This construction work is in

progress at Tiruchirapalli in Tamilnadu under joint efforts of BARC (Bhabha Atomic Research

Centre), BHEL, Associated Cement Corporation and Russian technologists.

As its name implies, magneto-hydro-dynamic (MHD) is concerned with the flow of

conducting fluid in presence of magnetic and electric field. This fluid may be gas at elevated

temperature or liquid metal like sodium or potassium.

A MHD generator is a device for converting heat energy of fuel directly into electric

energy without a conventional electric generator. The basic difference between conventional

generator and MHD generator is in the nature of conductor.

Principle of MHD Power Generation

When an electric conductor moves across a magnetic field; an emf is induced in it,

which produced an electric current. This is the principle of the conventional generator also,

where the conductors consists of copper strips.

In MHD generator the solid conductors are replaced by a gaseous conductor; i.e.an

ionized gas. If such gas is passed at high velocity through a powerful magnetic field, a current

is generated and can extract by placing electrodes in a suitable position in the stream.













































LAYOUT OF MHD POWER PLANT

A MHD conversion is known as direct energy conversion because it produces

electricity directly from heat source without the necessity of the additional stage of steam

generation as in a steam power plant. An ionized gas is employed as a conducting field.

Ionization is produced either by thermal means i.e. by an elevated temperature or by seeding

with substance like cesium or potassium vapour which ionize at relatively low temperature.

The atom of seed element split off electrons. The presence of negatively charge

electrons make the carrier gas an electrical conductor.

Advantages

1. Large amount of power is generated.

2. No moving parts, so more reliable.

3. Closed cycle system produces power, free of pollution.

4. Ability to reach its full power as soon as started.

5. Size of the plant is considerably small.

6. Low overall operation cost.

7. Better utilization of fuel.

Disadvantages

1. Needs very large magnets (high expensive).

2. Very high friction and heat transfer losses.

3. It suffers from the reverse flow of electrons through the conducting fluids around the ends

of the magnetic field.











Advantages








Disadvantages















Advantages








Disadvantages







1.7 COMBINED POWER CYCLES

In electric power generation a combined cycle is an assembly of heat engines that work

in tandem off the same source of heat, converting it into mechanical energy, which in turn

usually drives electrical generators. The principle is that the exhaust of one heat engine is used

as the heat source for another, thus extracting more useful energy from the heat, increasing the

system's overall efficiency. This works because heat engines are only able to use a portion of

the energy their fuel generates (usually less than 50%).

The objective of this approach is to use all of the heat energy in a power system at the different

temperature levels at which it becomes available to produce work, or steam, or the heating of

air or water, thereby rejecting a minimum of energy waste. The best approach is the use of

combined cycles. There may be various combinations of the combined cycles depending upon

the place or country requirements. Even nuclear power plant may be used in the combined

cycles.

GT-ST Combined Power plants

It has been found that a considerable amount of heat energy goes as a waste with the

exhaust of the gas turbine. This energy must be utilized. The complete use of the energy

available to a system is called the total energy approach. The remaining heat (e.g., hot exhaust

fumes) from combustion is generally wasted. Combining two or more thermodynamic cycle’s

results in improved overall efficiency, reducing fuel costs. In stationary power plants, a

successful, common combination is the Brayton cycle (in the form of a turbine burning natural

gas or synthesis gas from coal) and the Rankine cycle (in the form of a steam power plant).

Multiple stage turbine or steam cylinders are also common.



ST-MHD Combined Power plants

1.8 LOAD DURATION CURVE

The load demand on a power system is governed by the consumers and for a system

supplying industrial and domestic consumers, it varies within wide limits. This variation of

load can be considered as daily, weekly, monthly or yearly. Such load curves are termed as

“Chronological load Curves”.

If the ordinates of the chronological load curves are arranged in the descending order

of magnitude with the highest ordinates on left, a new type of load curve known as “load

duration curve” is obtained. If any point is taken on this curve then the abscissa of this point

will show the number of hours per year during which the load exceeds the value denoted by its

ordinate.

The lower part of the curve consisting of the loads which are to be supplied for almost

the whole number of hours in a year, represents the “Base Load”, while the upperpart,

comprising loads which are required for relatively few hours per year, represents the “Peak

Load”.



1.9 BOILERS

Boiler is an apparatus to produce steam. Thermal energy released by combustion of fuel is

transferred to water, which vaporizes and gets converted into steam at the desired temperature

and pressure.

The steam produced is used for:

Producing mechanical work by expanding it in steam engine or steam turbine.

Heating the residential and industrial buildings.

Performing certain processes in the sugar mills, chemical and textile industries.

Boiler is a closed vessel in which water is converted into steam by the application of heat.

Usually boilers are coal or oil fired.

A boiler should fulfil the following requirements;

Safety. The boiler should be safe under operating conditions.

Accessibility. The various parts of the boiler should be accessible for repair and

maintenance.

Capacity. The boiler should be capable of supplying steam according to the

requirements.

Efficiency. To permit efficient operation, the boiler should be able to absorb a

maximum amount of heat produced due to burning of fuel in the furnace.

It should be simple in construction and its maintenance cost should be low.

Its initial cost should be low.

The boiler should have no joints exposed to flames.

The boiler should be capable of quick starting and loading.

The performance of a boiler may be measured in terms of its evaporative capacity also



called power of a boiler. It is defined as the amount of water evaporated or steam produced

is in kg per hour. It may also be expressed in kg per kg of fuel burnt.

1.9.1Classification of Boilers

The boilers can be classified according to the following criteria.

According to flow of water and hot gases.

1. Water tube.

2. Fire tube.

In water tube boilers, water circulates through the tubes and hot products of combustion

flow over these tubes. In fire tube boiler the hot products of combustion pass through the

tubes, which are surrounded, by water.

Fire tube boilers have low initial cost, and are more compacts. But they are more likely

to explosion, water volume is large and due to poor circulation they cannot meet quickly the

change in steam demand. For the same output the outer shell of fire tube boilers is much larger

than the shell of water-tube boiler. Water tube boilers require less weight of metal for a given

size, are less liable to explosion, produce higher pressure, are accessible and can response

quickly to change in steam demand.

Tubes and drums of water-tube boilers are smaller than that of fire-tube boilers and due

to smaller size of drum higher pressure can be used easily. Water-tube boilers require lesser

floor space. The efficiency of water-tube boilers is more.

According to position of furnace.

(i) Internally fired (ii) Externally fired

In internally fired boilers the grate combustion chamber are enclosed within the boiler shell

whereas in case of extremely fired boilers and furnace and grate are separated from the boiler

shell.

According to the position of principle axis.

(i) Vertical (ii) Horizontal (iii) Inclined.

According to application.

(i) Stationary (ii) Mobile, (Marine, Locomotive).

According to the circulating water.

(i) Natural circulation (ii) Forced circulation.

According to steam pressure.

(i) Low pressure (ii) Medium pressure (iii) Higher pressure.



1.9.2 HIGH PRESSURE BOILERS

A boiler is a closed vessel in which water or other fluid is heated. The heated or

vaporized fluid exits the boiler for use in various processes or heating applications.

In all modern power plants, high pressure boilers (> 100 bar) are universally used as

they offer the following advantages. In order to obtain efficient operation and high capacity,

forced circulation of water through boiler tubes is found helpful.

1. The efficiency and the capacity of the plant can be increased as reduced quantity of steam is

required for the same power generation if high pressure steam is used.

2. The forced circulation of water through boiler tubes provides freedom in the arrangement of

furnace and water walls, in addition to the reduction in the heat exchange area.

3. The tendency of scale formation is reduced due to high velocity of water.

4. The danger of overheating is reduced as all the parts are uniformly heated.

5. The differential expansion is reduced due to uniform temperature and this reduces the

possibility of gas and air leakages.

Superheater operation is similar to that of the coils on an air conditioning unit, although

for a different purpose. The steam piping is directed through the flue gas path in the boiler

furnace. The temperature in this area is typically between 1,300–1,600 degrees Celsius. While

the temperature of the steam in the superheater rises, the pressure of the steam does not. Almost

all the steam superheater systems are designed to remove droplets entrained in the steam to

prevent damage to the turbine blading and associated piping.

1.9.2.1LA-MONT BOILER

It is a forced circulation- water tube boiler which was first introduced in 1925 by La

Mont.

The feed water from hot well is supplied to a storage and separating drum (boiler) through theeconomizer. Most of the sensible heat is supplied to the feed water passing through theeconomizer



The feed water from hot well is supplied to a storage and separating drum (boiler)

through the economizer. Most of the sensible heat is supplied to the feed water passing through

the economizer. A pump circulates the water at a rate 8 to 10 times the mass of steam

evaporated. This water is circulated through the evaporator tubes and the part of the vapour is

separated in the separator drum. The large quantity of water circulated (10 times that of

evaporation) prevents the tubes from being overheated.

The centrifugal pump delivers the water to the headers at a pressure of 2.5 bar above

the drum pressure. The distribution headers distribute the water through the nozzle into the

evaporator. The steam separated in the boiler is further passed through the super-heater.

To secure a uniform flow of feed water through each of the parallel boiler circuits a

choke is fitted entrance to each circuit. These boilers have been built to generate 45 to 50 tons

of superheated steam at a pressure of 120 bar and temperature of 500°C.

Important Components

1. Steam separating drum – The feed water from the hot well is stored in the drum. The

steam is separated from water in the drum and the steam is usually collected at the top

of the drum.



2. Circulating pump – Water from the steam separating drum is drawn by a circulating

pump and it circulates water through the evaporator tubes. Pump circulates water at a

rate of 8-10 times the mass of steam evaporated. Forced circulation is necessary to

prevent the overheating of tubes.

3. Distribution header – The distribution header distributes the water through the nozzle

into the evaporator.

4. Radiant evaporator – Water from the drum first enters the radiant evaporator through

the pump and header. The water is heated by the radiation heat from the combustion

chamber. In radiant evaporator, the hot flue gases do not pass over the water tubes.

5. Convective evaporator – The mixture of water and steam coming out from the radiant

evaporator enters the convective evaporator tubes. The hot flue gases passing over the

evaporator tubes transfer a large portion of heat to the water by convection. Thus, water

becomes steam and the steam enters to the steam separating drum.

6. Superheater – The steam from the steam separating drum enters the superheater tubes

where it is superheated by the hot flue gases passing over them. The superheated steam

then enters the steam turbine to develop power.

7. Economiser – The waste hot flue gases pass through the economiser where feed water

is pre-heated. By pre-heating the feed water, the amount of fuel required to convert

water into steam is reduced.

8. Air pre-heater – The hot flue gases then passes through the air pre-heater where the

air required for combustion is pre-heated.

Advantages

1. La-Mont boilers can generate 45 to 50 tons of superheated steam at a pressure of 120

bar and temperature of 500°C.

2. Drum is of small size.

3. Tendency of scale formation is eliminated due to forced circulation of water.

Disadvantages

1. Bubbles are formed on the inside of the water tubes and this bubbles reduce the heat

transfer rate.

2. Initial and operating costs are high.

3. Maintenance costs are very high.

1.9.3BENSON BOILER (SUPERCRITICAL BOILER)

The main difficulty experienced in the La Mont boiler is the formation and attachment

of bubbles on the inner surfaces of the heating tubes. The attached bubbles reduce the heat flow



and steam generation as it offers higher thermal resistance compared to water film. Benson of

siemens- West Germany in 1922 argued that if the boiler pressure was raised to critical pressure

(225 atm.), the steam and water would have the same density and therefore the danger of bubble

formation can be completely removed.


1. Economiser – The feed water from the well passes through the economiser where it is

pre-heated by the pre-heat of exhaust hot flue gases.

2. Radiant evaporator – The feed water after circulation through the economiser flows

through the radiant evaporator tubes. Water is heated up by the radiation heat from the

combustion chamber. Here, part of the water is converted to steam directly.




becomes steam in the convective evaporator.

4. Superheater – The steam from the convective evaporator enters the superheater tubes

where it is superheated by the hot flue gases passing over them. The superheated steam

then enters the steam turbine to develop power.



5. Air pre-heater – The hot flue gases then passes through the air pre-heater where the

air required for combustion is pre-heated.

Advantages

1. As there is no drum, the total weight of Benson boiler is 20% less than other boilers.

This reduces the cost of the boiler.

2. Floor space requirements of Benson boiler are very less.

3. Transportation of Benson boiler parts and its erection is very easy as there are no drums.

4. Natural circulation boilers require expansion joints in pipes but the pipes in Benson

boilers are welded.

Disadvantages

1. As the Benson boiler operates at high pressure and temperature, special alloy materials

are required.


3. This is more efficient, resulting in slightly less fuel use.

1.10. FLUIDISED BED COMBUSTION (FBC)

Burning of pulverised coal has some problems such as particle size of coal used in

pulverized firing is limited to 70-100 microns, the pulverised fuel fired furnances designed to

burn a particular cannot be used other type of coal with same efficiency, the generation of high

temp. about (1650 C)in the furnace creates number of problems like slag formation on super

heater, evaporation of alkali metals in ash and its deposition on heat transfer surfaces, formation

of SO2 and NOX in large amount.

Fluidised Bed combustion system can burn any fuel including low grade coals (evencontaining 70% ash), oil, gas or municipal waste. Improved desulphurisation and low NOXemission are its main characteristics. The fuel and inert material dolomite are fed on adistribution plate and air is supplied from the bottom of distribution plate. The air is suppliedat high velocity so that solid feed material remains in suspension condition during burning.

The heat produced is used to heat water flowing through the tube and convert water into

steam. During burning SO2 formed is absorbed by the dolomite and thus prevents its escape

with the exhaust gases. The molten slag is tapped from the top surface of the bed. The bed

temperature is nearly 800-9000C which is ideal for sulphur retention addition of limestone or

dolomite to the bed brings down SO2 emission level to about 15% of that in conventional firing

methods.



Various advantages of FBC system are as follows:

1. FBC system can use any type of low grade fuel including municipal wastes and

therefore is a cheaper method of power generation.

2. It is easier to control the amount of SO2 and NOX, formed during burning. Low

emission of SO2 and NOX will help in controlling the undesirable effects of SO2

and NOX. During combustion. SO2 emission is nearly 15% of that in conventional

firing methods.

3. There is a saving of about 10% in operating cost and 15% in the capital cost of the

power plant.

4. The size of coal used has pronounced effect on the operation and performance of

FBC system. The particle size preferred is 6 to 13 mm but even 50 mm size coal

can also be used in this system.

The major portion of the coal available in India is of low quality, high ash content and

low calorific value. The traditional grate fuel firing systems have got limitations and are

techno-economically unviable to meet the challenges of future. Fluidized bed combustion has

emerged as a viable alternative and has significant advantages over conventional firing system

and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion

efficiency and reduced emission of noxious pollutants such as SOx and NOx.



UNIT II STEAM POWER PLANT

2.1 STEAM POWER PLANT

Coal needs to be stored at various stages of the preparation process, and conveyed aroundthe CPP facilities. Coal handling is part of the larger field of bulkMaterial handling, and is a complex and vital part of the CPP.

2.1.1 FUEL HANDLING SYSTEM

Coal delivery equipment is one of the major components of plant cost. The various steps involved incoal handling are as follows:

1. Coal delivery.2. Unloading3. Preparation4. Transfer5. Outdoor storage6. Covered storage7. Implant handling8. Weighing and measuring9. Feeding the coal into furnace



i) Coal deliveryThe coal from supply points is delivered by ships or boats to power stations situated near to sea or

river whereas coal is supplied by rail or trucks to the power stations which are situated away from sea orriver. The transportation of coal by trucks is used if the railway facilities are not available.ii) Unloading

The type of equipment to be used for unloading the coal received at the power station depends onhow coal is received at the power station. If coal delivered by trucks, there is no need of unloading deviceas the trucks may dump the coal to the outdoor storage. Coal is easily handled if the lift trucks withscoop are used. In case the coal is brought by railways wagons, ships or boats, the unloading may bedone by car shakes, rotary car dumpers, cranes, grab buckets and coal accelerators. Rotary car dumpersalthough costly are quite efficient for unloading closed wagons.(iii) Preparation

When the coal delivered is in the form of big lumps and it is not of proper size, thepreparation (sizing) of coal can be achieved by crushers, breakers, sizers, driers and magnetic separators.

iv)TransferAfter preparation coal is transferred to the dead storage by means of the following systems.

1. Belt conveyors2. Screw conveyors3. Bucket elevators4. Grab bucket elevators5. Skip hoists6. Flight conveyor

Belt Conveyor

Figure shows a belt conveyor. It consists of an endless belt moving over a pair of end drums(rollers). At some distance a supporting roller is provided at the centre. The belt is made up of rubber orcanvas. Belt conveyor is suitable for the transfer of coal over long distances. It is used in medium and largepower plants. The initial cost of system is not high and power consumption is also low. The inclination atwhich coal can be successfully elevated by belt conveyor is about 20. Average speed preferred than othertypes.



2. Screw ConveyorIt consists of an endless helicoid screw fitted to a shaft (figure). The screw while rotating in a trough

transfers the coal from feeding end to the discharge end.This system is suitable, where coal is to be transferred over shorter distance and space limitations

exist.The initial cost of the consumption is high and there is considerable wear o screw. Rotation ofscrew varies between 75-125 r.p.m

3. Bucket elevator

It consists of buckets fixed to a chain (figure). The chain moves over two wheels. The coal iscarried by the bucket from bottom and discharged at the top.

4. Grab bucket elevatorIt lifts and transfers coal on a single rail or track from one point to the other. The coal lifted by grab

buckets is transferred to overhead bunker or storage. This system requires less power for operation andrequires minimum maintenance.

The grab bucket conveyor can be used with crane or tower as shown in figure . Although theinitial cost of this system is high but operating cost is less.



Storage of CoalIt is desirable that sufficient quantity of coal should be stored.Storage of coal gives protection

against the interruption of coal supplies when there is delay in transportation of coal or due to strike in coalmines. Also when the prices are low, the coal can be purchased and stored for future use.

The amount of coal to be stored depends on the availability of space for storage, transportationfacilities, the amount of coal that will whether away and nearness to coal mines of the power station. Usuallycoal required for one month operation of power plant is stored in case of power stations is situated at longerdistance from the collieries whereas coal need for about 15 days is stored in case of power station situatednear to collieries. Storage of coal for longer periods is not advantageous because it blocks the capital andresults in deterioration of the quality of coal.

2.1.2PULVERIZED COAL STORAGE

Periodically a power plant may encounter the situation where coal must be stored for sometimes in abunker, for instance during a plant shut down. The bunker, fires can occur in dormant pulverized coal fromspontaneous heating within 6 day of loading. This time can be extended to 13 days when a blanket ofCO2 is piped into the top of the bunker. The perfect sealing of the bunker from air leakage can extend thestorage time as two months or more. The coal in the bunker can be stored as long as six months byexpelling air from above the coal with the use of CO2 and then blanketing of all sources of air. Acontrol system used for storing the pulverized fuel in bunker is shown in figure.



Pulverized Fuel Handling System:Two methods are in general use to feed the pulverized fuel to the combustion chamber of the power

plant. First is ‘Unit System’ and second is ‘Central or Bin System ‘.

In unit system, each burner of the plant is fired by one or more pulverizers connected to the burners,while in the central system, the fuel is pulverized in the central plant and then disturbed to each furnacewith the help of high pressure air current. Each type of fuel handling system consists of crushers,magnetic separators, driers, pulverizing mills, storage bins, conveyors and feeders.

2.1.3 Ball MillA line diagram of ball mill using two classifiers is shown in figure. It consists of a slowly rotating

drum which is partly filled with steel balls. Raw coal from feeders is supplied to the classifiers fromwhere it moves to the drum by means of a screw conveyor. As the drum rotates the coal get pulverizeddue to the combine impact between coal and steel balls. Hot air is introduced into the drum. The powderedcoal is picked up by the air and the coal air mixture enters the classifiers, where sharp changes in thedirection of the mixture throw out the oversized coal particles. The over-sized particles are returned to thedrum. The coal air mixture from the classifier moves to the exhauster fan and then it is supplied to theburners.



2.1.3 Ball And Race MillsIn this mill the coal passes between the rotating elements again and again until it has been

pulverized to desired degree of fineness. The coal is crushed between two moving surfaces, namely,balls and races. The upper stationary race and lower rotating race driven by a worm and gear hold the ballsbetween them. The raw coal supplied falls on the inner side of the races. The moving balls and races catchcoal between them to crush it to a powder. The necessary force needed for crushing is applied with thehelp of springs. The hot air supplied picks up the coal dust as it flows between the balls and races and thenenters the classifier. Where oversized coal particles are returned for further grinding.

2.2 ASH HANDLING SYSTEM:Boilers burning pulverized coal (PC) have bottom furnaces. The large ash particles are

collected under the furnace in a water-filled ash hopper, Fly ash is collected in dust collectors with either anelectrostatic precipitator or a baghouse. A PC boiler generates approximately 80% fly ash and 20%bottom ash. Ash must be collected and transported from various points of the plants as shown in figure.Pyrites, which are the rejects from the pulverizers, are disposed of with the bottom ash system. Three majorfactors should be considered for ash disposal systems.

1. Plant site2. Fuel source3. Environmental regulationNeeds for water and land are important considerations for many ash handling systems. Ash

quantities to be disposed of depend on the king of fuel source. Ash storage and disposal sites are guided byenvironmental regulations.



2.2.1 Ash Handling Equipment:

Mechanical means are required for the disposal of ash. The handling equipment should performthe following functions: 1. Capital investment, operating and maintenance charges of the equipment shouldbe low. 2. It should be able to handle large quantities of ash. 3. Clinkers, shoot, dust etc. create troubles.Theequipment should be able to handle them smoothly.4. The equipment used should remove the ashfrom the furnace, load it to the conveying system to deliver the ash to dumping site or storage andfinally it should have means to dispose of the stored ash. 5. The equipment should be corrosion and wearresistant.



Hydraulic SystemIn this system, ash from the furnace grate falls into a system of water possessing high velocity and is

carried to the sumps. It is generally used in large power plants. Hydraulic system is of two types, namely,low pressure hydraulic system used for intermittent ash disposal figure. Figure shows hydraulic system.

Water-Jetting SystemWater jetting of ash is shown in figure. In this method a low pressure jet of water coming out of

quenching nozzle is used to cool the ash. The ash falls into trough and is then removed.

Pneumatic System

In this system ash from the boiler furnace outlet falls into a crusher where a lager ash particles arecrushed to small sizes. The ash is then carried by a high velocity air or steam to the point of delivery. Airleaving the ash separator is passed through filter to remove dust etc. So that the exhauster handles cleanair which will protect the blades of the exhauster.



Mechanical system

Figure shows a mechanical ash handling system.In this system ash cooled by water seal falls on the belt conveyor and is carried out continuously to

the bunker.

2.3 DRAUGHT:Draught is defined as the difference between absolute gas pressure at any point in a gas flow

passage and the ambient (same elevation) atmospheric pressure. . Draught is achieved by small pressuredifference which causes the flow of air or gas to take place. It is measured in milimetre (mm) or water.The purpose of draught is as follows:

i) To supply required amount of air to the furnace for the combustion of fuelThe amount of fuel that can be burnt per square root of grate area depends upon the quantityof air circulated through fuel bed.

ii) To remove the gaseous products of combustion.



2.3.1 Classification of DRAUGHT

Artificial Draught

If the draught is produced by steam jet or fan it is known as artificial draught

Steam jet Draught:

It employs steam to produce the draughtMechanical draught

It employs fan or blowers to produce the draught.

Induced draught

The flue is drawn (sucked) through the system by a fan or steam jet

Forced draught

The air is forced into system by a blower or steam jet.

Natural Draught:

Natural draught system employs a tall chimney as shown in figure. The chimney is a verticaltubular masonry structure or reinforced concrete. It is constructed for enclosing a column of exhaust gasesto produce the draught. It discharges the gases high enough to prevent air pollution. The draught isproduced by this tall chimney due to temperature difference of hot gases in the chimney and coldexternal air outside the chimney.



Artificial Draught

It has been seen that the draught produced by chimney is affected by the atmospheric conditions.It has no flexibility, poor efficiency and tall chimney is required. In most of the modern

power plants, the draught used must be independence of atmospheric condition, and it must have greaterflexibility (control) to take the fluctuating loads on the plant.

Today’s large steam power plants requiring 20 thousand tons of steam per hour would be impossibleto run without the aid of draft fans. A chimney of an reasonable height would be incapable of

developing enough draft to remove the tremendous volume of air and gases (400 × 103 m3 to 800 × 103

m3 per minutes). The further advantage of fans is to reduce the height of the chimney needed.

The draught required in actual power plant is sufficiently high (300 mm of water) and to meet highdraught requirements, some other system must be used, known as artificial draught. The artificialdraught is produced by a fan and it is known as fan (mechanical) draught. Mechanical draught ispreferred for central power stations.

Forced Draught

In a forced draught system, a blower is installed near the base of the boiler and air is forced to passthrough the furnace, flues, economizer, air-preheater and to the stack.This draught system is known as positive draught system or forced draught system because the pressureand air is forced to flow through the system.

The arrangement of the system is shown in figure. A stack or chimney is also in this system as shown infigure but its function is to discharge gases high in the atmosphere to prevent the contamination. It is notmuch significant for producing draught therefore height of the chimney may not be very much



Induced Draught:

In this system, the blower is located near the base of the chimney instead of near the grate. The air issucked in the system by reducing the pressure through the system below atmosphere. The induced draughtfan sucks the burned gases from the furnace and the pressure inside the furnace is reduced belowatmosphere and induces the atmospheric air to flow through the furnace. The action of the induceddraught is similar to the action of the chimney. The draught produced is independent of the temperatureof the hot gases therefore the gases may be discharged as cold as possible after recovering asmuch heat as possible in air-preheater and economizer.

Balanced Draught:

It is always preferable to use a combination of forced draught and induced draught instead of forcedor induced draught alone. If the forced draught is used alone, then the furnace cannot be opened either forfiring or inspection because the high pressure air inside the furnace will try to blow out suddenly and thereis every chance of blowing out the fire completely and furnace stops.

If the induced draught is used alone, then also furnace cannot be opened either for firing orinspection because the cold air will try to rush into the furnace as the pressure inside the furnace is belowatmospheric pressure. This reduces the effective draught and dilutes the combustion.



2.4 SURFACE CONDENSER:

In surface condensers there is no direct contact between the steam and cooling water and thecondensate can be re-used in the boiler. In such a condenser even impure water can be used for coolingpurpose whereas the cooling water must be pure in jet condensers.Although the capital cost and thespace needed is more in surface condensers but it is justified b the saving in running cost and increase inefficiency of plant achieved by using this condenser.Depending upon the position of condensateextraction pump, flow of condensate and arrangement of tubes the surface condensers may be classified asfollows:

1. Down flow condenser2. Central flow condenser3. Evaporative condenser

1. Down flow condenser

Figure shows a sectional view of down flow condenser. Steam enters at the top and flowsdownward. The water flowing through the tubes in one direction lower half comes out in the oppositedirection in the upper half. In this type of condenser, the cooling water and exhaust steam do not comein direct contact with each other as in case of jet condensers.



This is generally used where large quantities of inferior water are available and better quantity offeed water to the boiler must be used most economically. The arrangement of the surface condenser is shownin figure. It consists of cast iron air- tight cylindrical shell closed at each end as shown in figure. A numberof water tubes are fixed in the tube plates which are located between each cover head and shell.

2. Central flow condenser.

Figure shows a central flow condenser. In this condenser the steam passages are all around theperiphery of the shell. Air is pumped away from the centre of the condenser. The condensate movesradially towards the centre of the tube next. Some of the exhaust steam which moving towards thecentre meets the under cooled condensate and pre-heats it thus reducing under cooling.

3. Evaporative condenser

In this condenser steam to be condensed in passed through a series of tubes and the cooling waterfalls over these tubes in the form of spray. A steam of air flows over the tubes to increase evaporation ofcooling water which further increases the condensation of steam.

These condensers are more preferable where acute shortage of cooling water exists. Thearrangement of the condenser is shown in figure. Water is sprayed through the nozzles over the pipecarrying exhaust steam and forms a thin film over it. The air is drawn over the surface of the



2.5 COOLING TOWERS

In the power industry, energy in the form of heat is transformed to energy in the form of electricity.Unfortunately, t h i s t r a n s f o r m a t i o n i s n o t a c c o m p l i s h e d o n a o n e -to-one ratio. Althoughdesigners continuously seek newer and better ways to improve overall system efficiency,considerably more units of heat must be input that are realized as equivalent units of electric output.System equilibrium requires that this excess heat be dissipated ultimately to the atmosphere.



In an increasing number of cases, because of qualitative and quantitative restrictionsregarding the use of natural waterways, plant make use of a closed circuit system typical ofthat depicted in figure. As shown, the system’s dependence on the river is limited to therequirement for a supply of makeup water and, perhaps, as a point of discharge of blow down.In these cases, the entire heat loads are dissipated by cooling towers, at the variety, applicationand operation of which are the subject of this chapter.



UNIT III NUCLEAR AND HYDEL POWER PLANTS

3.1 NUCLEAR AND HYDEL POWER PLANTS

A nuclear power plant is similar to a conventional steam power plant except how thatenergy is evolved. The heat is produced in the nuclear power plant by fission, whereas insteam and gas turbine plants, the heat is produced by combustion in the furnace. Thenuclear reactor acts as a furnace where nuclear energy is evolved by splitting or fissioning ofthe nucleus of fissionable material like Uranium U-235. It is claimed that 1 kg U-235 canproduce as much heat energy that can be produced by burning 4500 tones of high grade coal or1700 tons of oil.

3.1.1Fission energy

Nuclear energy is divided from splitting (or) fissioning of the nucleus offissionable material like Uranium U-235. Uranium has several isotopes (Isotopes areatoms of the same element having different atomic masses) such as U-234, U-235 and U-238.Of the several isotopes, U-235 is the most unstable isotope, which is easily fissionable andhence used as fuel in an atomic reactor.

When a neutron enters the nucleus of an unstable U-235, the nucleus splits into twoequal fragments (Krypton and Barium) and also releases 2.5 fast moving neutrons with a

velocity of 1.5×107 m/sec and along with this produces a large amount of energy, nearly200 million electron- volts. This is called nuclear fission.

3.1.2 Chain reaction

The neutrons released during fission are very fast and can be made to initiate the fissionof other nuclei of U-235, thus causing a chain reaction. When a large number offission occurs, enormous amount of heat is generated, which is used to produce steam.

The chain reaction under controlled conditions can release extremely largeamount ofenergy causing “atomic explosion” Energy released in chain reaction,according to Einstein law is



E = mc2

Where E = Energy liberated (J)m= Mass (kg)

c = Velocity of light (3 × 108 m/sec).Out of 2.5 neutrons released in fission of each nucleus of U-235, one neutron is used to

sustain the chain reaction, about 0.9 neutron is captured by U-238, which gets converted intofissionable material Pu-239 and about 0.6 neutron is partially absorbed by control rodmaterials, coolant and moderator.

3.1.3 Fusion energy

Energy is produced in the sun and stars by continuous fusion reactions in which fournuclei of hydrogen fuse in a series of reactions involving other particles that continually appear

and disappear in the course of the reaction, such as He3, nitrogen, carbon, and othernuclei, but culminating in one nucleus of helium of two positrons.

To cause fusion, it is necessary to accelerate the positively charged unclei to highkinetic energies, in order to overcome electrical repulsive forces, by raising their temperature tohundreds of millions of degrees resulting in plasma. The plasma must be prevented fromcontacting the walls of the container, and must be confined for a period of time (of the order of asecond) at a minimum density. Fusion reactions are called thermonuclear because very hightemperatures are required to trigger and sustain them.

3.1.3 Main components of nuclear power plants:

i) Moderators

In any chain reaction, the neutrons produced are fast moving neutrons. These are

less effective in causing fission of U235 and they try to escape from the reactor. It is thusimplicit that speed of these neutrons must be reduced if their effectiveness is carrying outfission is to be increased. This is done by making these neutrons collide with lighter nuclei ofother materials, which does not absorb these neutrons but simply scatter them. Eachcollision causes loss of energy and thus the speed of neutrons is reduced. Such a material iscalled a ‘Moderator’. The neutrons thus slowed down are easily captured by the fuel elementat the chain reaction proceeds slowly.ii) Reflectors

Some of the neutrons produced during fission will be partly absorbed by the fuelelements, moderator, coolant and other materials. The remaining neutrons will try toescape from the reactor and will be lost. Such losses are minimized by surrounding (lining)the reactor core with a material called a reflector which will reflect the neutrons back tothe core.They improve the neutron economy. Economy: Graphite, Beryllium.



.

iii) Shielding

During Nuclear fission particles and neutrons are also produced. They are harmfulto human life. Therefore it is necessary to shield the reactor with thick layers of lead, orconcrete to protect both the operating personnel as well as environment from radiation hazards.

iv) Cladding

In order to prevent the contamination of the coolant by fission products, the fuelelement is covered with a protective coating. This is known as cladding.

Control rods are used to control the reaction to prevent it from becoming violent.They control the reaction by absorbing neutrons. These rods are made of boron orcadmium. Whenever the reaction needs to be stopped, the rods are fully inserted and placedagainst their seats and when the reaction is to be started the rods are pulled out.

v) Coolant

The main purpose of the coolant in the reactor is to transfer the heat produced insidethe reactor. The same heat carried by the coolant is used in the heat exchanger for furtherutilization in the power generation.

Some of the desirable properties of good coolant are listed below1. It must not absorb the neutrons.2. It must have high chemical and radiation stability3. It must be non-corrosive.4. It must have high boiling point (if liquid) and low melting point (if solid)5. It must be non-oxidising and non-toxic.

The above-mentioned properties are essential to keep the reactor core in safe conditionas well as for the better functioning of the content.

6. It must also have high density, low viscosity, high conductivity and high specificheat. These properties are essential for better heat transfer and low pumping power.

vi) Nuclear reactor

A nuclear reactor may be regarded as a substitute for the boiler fire box of a steampower plant. Heat is produced in the reactor due to nuclear fission of the fuel U235

vii) Radiation hazards and Shieldings

The reactor is a source of intense radioactivity. These radiations are very harmful tohuman life. It requires strong control to ensure that this radioactivity is not released into theatmosphere to avoid atmospheric pollution. A thick concrete shielding and a pressure vesselare provided to prevent the escape of these radiations to atmosphere



vii) Steam generator

The steam generator is fed with feed water which is converted into steam by the heat ofthe hot coolant. The purpose of the coolant is to transfer the heat generated in the reactorcore and use it for steam generation. Ordinary water or heavy water is a common coolant.

viii) Turbine

The steam produced in the steam generator is passed to the turbine and work is doneby the expansion of steam in the turbine.

ix) Coolant pump and Feed pump

The steam from the turbine flows to the condenser where cooling water iscirculated. Coolant pump and feed pump are provided to maintain the flow of coolantand feed water respectively.

3.2 BOILING WATER REACTOR (BWR)

Figure shows a simplified BWR. Light water, which acts as the coolant andmoderator, passes through the core where boiling takes place in the upper part of the core.The wet steam then passes through a bank of moisture separators and steam dryers in theupper part of the pressure vessel. The water that is not vaporized to steam is recirculatedthrough the core with the entering feed water using two recirculation pumps coupled to jetpumps (usually 10 to 12 per recirculation pump). The steam leaving the top of the pressurevessel is at saturated conditions of 7.2 MPa and 278C.



The BWR reactor core, like that in a PWR, consists of a large number of fuel rodshoused in fuel assemblies in a nearly cylindrical arrangement. Each fuel assembly containsan 8×8 or 9×9 square array of 64 or 81 fuel rods (typically two of the fuel rods contain waterrather than fuel) surrounded by a square Zircaloy channel box to ensure no coolant crossflow inthe core. The fuell rods are similar to the PWR rods, although larger in diameter. Each fuelrod is a zirconium alloy- clad tube containing pellets of slightly enriched uranium dioxide (2%to 5% U-235) stacked end-to- end. The reactor is controlled by control rods housed ina cross-shaped, or cruciform, arrangement called a control element. The control elementsenter from the bottom of the reactor and move in spaces between the fuel assemblies.

The BWR reactor core is housed in a pressure vessel that is larger than that of a PWR.A typical BWR pressure vessel, which also houses the reactor core, moisture separators, andsteam dryers, has a diameter of 6.4 m, with a height of 22 m. Since a BWR operators ata nominal pressure of 6.9 MPa, its pressure vessel is thinner that that of a PWR.

3.3 CANDU Type Reactor(CANDU – Canadium, Deutrium, Uranium).

These reactors are more economically to those nations which do not produce enricheduranium as the enrichment of uranium is very costly. In this type of reactors, the natural

uranium (0.7% U235) is used as fuel and heavy water as moderator.This type of reactor was first designed and developed in Canada. The first heavy

water reactor in Canada using heavy water as coolant and moderator of 200 MW capacity with29.1% thermal efficiency was established at Douglas (Ontario known as Douglas powerstation.



The coolant heavy water is passed through the fuel pressure tubes and heat-exchanger.The heavy water is circulated in the primary circuit in the same way as with a PWR and thesteam is raised in the secondary circuit transferring the heat in the heat exchanger to theordinary water.

The control of the reactor is achieved by varying the moderator level in the reactor and,therefore, control rods are not required. For rapid shutdown purpose, the moderator canbe dumped through a very large area into a tank provided below the reactor.

3.4 FAST BREEDER REACTOR

Figure shows a fast breeder reactor system. In this reactor the core containing U235

in surrounded by a blanket (a layer of fertile material placed outside the core) of fertile material

U238. In this reactor no moderator is used. The fast moving neutrons liberated due to fission of

U235 are absorbed by U238 which gets converted into fissionable material Pu239

which is capable of sustaining chain reaction. Thus this reactor is important because it

breeds fissionable material from fertile material U238 available in large quantities.

Like sodium graphite nuclear reactor this reactor also uses two liquid metal coolantcircuits. Liquid sodium is used as primary coolant when circulated through the tubes ofintermediate heat exchange transfers its heat to secondary coolant sodium potassium alloy.The secondary coolant while flowing through the tubes of steam generator transfers its heat tofeed water



Fast breeder reactors are better than conventional reactors both from the point of viewof safety and thermal efficiency. For India which already is fast advancing towards selfreliance in the field of nuclear power technology, the fast breeder reactor becomes inescapablein view of the massive reserves of thorium and the finite limits of its uranium resources.

The research and development efforts in the fast breeder reactor technology will haveto be stepped up considerably if nuclear power generation is to make any impact on thecountry’s total energy needs in the not too distant future.

3.5 WASTE DISPOSAL:

Waste disposal problem is common in every industry. Wastes from atomicenergy installations are radioactive, create radioactive hazard and require strong control toensure that radioactivity is not released into the atmosphere to avoid atmospheric pollution.

The wastes produced in a nuclear power plant may be in the form of liquid, gas orsolid and each is treated in a different manner:

1. Liquid Waste

The disposal of liquid wastes is done in two ways:

i) Dilution

The liquid wastes are diluted with large quantities of water and then released into theground. This method suffers from the drawback that there is a chance ofcontamination of underground water if the dilution factor is not adequate.

ii) Concentration to small volumes and storage

When the dilution of radioactive liquid wastes is not desirable due to amount or natureof isotopes, the liquid wastes are concentrated to small volumes and stored in undergroundtanks. The tanks should be of assured long term strength and leakage of liquid from the tanksshould not take place otherwise leakage or contents, from the tanks may lead to



significant underground water contamination.

2. Gaseous Waste

Gaseous wastes can most easily result in atmospheric pollution.Gaseous wastesare generally diluted with air, passed through filters and then released to atmosphere throughlarge stacks (chimneys).

3. Solid Waste

Solid wastes consist of scrap material or discorded objects contaminated withradioactivematter. These wastes if combustible are burnt and the radio active matter.

These wastes if concrete, are drummed and shipped for burial. Non-combustiblesolid wastes, are always buried deep in the ground.

3.6 HYDEL POWER PLANT

Introduction

Hydro-electric power plant utilizes the potential energy of water stored in a dambuilt across the river. The potential energy of water is used to run water turbine to which theelectric generator is coupled. The mechanical energy available at the shaft of the turbine isconverted into electrical energy means of the generator.

ELEMENTS OF HYDEL POWER PLANT

The schematic representation of a hydro-electric power plant is shown in figure.

i) Water reservoir

Continuous availability of water is the basic necessity for a hydro-electric lant.Watercollected from catchment area during rainy season is stored in the reservoir. Water surface inthe storage reservoir us known as head race.

ii) Dam

The function of a dam is to increase the height of water level behind it which ultimatelyincreases the reservoir capacity. The dam also helps to increase the working heat of the powerplant.

iii) Spillway

Water after a certain level in the reservoir overflows through spillway without allowingthe increase in water level in the reservoir during rainy season



iv) Pressure tunnel

It carries water from the reservoir to surge tank.

v) Penstock

Water from surge tank is taken to the turbine by means of penstocks, made up ofreinforced concrete pipes or steel.



vi) Surge tank

There is sudden increase of pressure in the penstock due to sudden backflow of water,as load on the turbine is reduced. The sudden rise of pressure in the penstock is known aswater hammer. The surge tank is introduced between the dam and the power house tokeep in reducing the sudden rise of pressure in the penstock. Otherwise penstock will bedamaged by the water hammer.

vii) Water turbine

Water through the penstock enters into the turbine through and inlet valve. Primemovers which are in common use are Pelton turbine, Francis turbine and Kaplan turbine. Thepotential energy of water entering the turbine is converted into mechanical energy. Themechanical energy available at the turbine shaft is used to run the electric generator. Thewater is then discharged through the draft tube.

Viii) Tail race

Tail race is a water way to lead the water discharged from the turbine to the river.The water held in the tail race is called tail race water level.

x) Step-up transformer

Its function is to raise the voltage generated at the generator terminatingbefore transmitting the power to consumers.

xi) Power house

The power house accommodates the turbine, generator, transformer and control room.

3.6.1. Classification of Hydro-Power plants

Hydro-plants are classified according to the head of water under which they work.

When the operating head of water exceeds 70 metres, the plant is known as “highhead power plant”. Pelton turbine is used as prime mover in such power plants.When the head of water ranges from 15 to 70 metres then the power plant is known as“medium head plant”. It uses Francis turbine.When the head is less than 15 metres the plant is named as “low head plant”.It usesFrancis or Kaplan turbine as prime mover.



3.6.2 Pelton Wheel

This is a commonly used impulse type of turbine. It is named after an Americanengineer Lester. A. Pelton (1829-1908), who developed this turbine. The Pelton wheel issuitable for very high heads and it requires a lesser quantity of water.A pelton wheel isshown in figure.It consists of a runner, buckets, a nozzle, a guide mechanism, a hydraulicbrake and casing.

3.6.3 Runner and BucketsThe runner is a circular disc. It consists of a number of semi-ellipsoidal buckets

evenlyspaced around its periphery. The buckets are divided into two hemi-spherical cupsby a sharp- edged ridge known as a splitter. This arrangement avoids the axial thrust andend thrust on bearings.(The axial thrusts being equal and opposite, neutralize eachother).Generally, the buckets are bolted to the periphery of the runner. In some cases, to theperiphery of the runner. In some cases, the buckets and the wheel are cast integral as onepiece. In the case of the bolted type, broken or damaged buckets can be replacedconomically. For low heads, the bucket is made of case iron and for high heads, they aremade of bronze or stainless steel to withstand heavy impact.

Nozzle and Guide



mechanism:

A nozzle is fitted to the end of the penstock near the turbine. The nozzle is providedwith a conical needle or spears to regulate the quantity of water coming out of the nozzle,thereby control the speed of the runner. The spear may be operated manually by a hand wheel(for small units) or automatically by a governing mechanism (for larger units).

Hydraulic brake:

When the turbine has to be brought to rest by closing the inlet valve of the turbine, therunner generally takes a very long time to come to rest due to its inertia.To bring it torest quickly, a small brake nozzle is provided. This nozzle is opened and it directs a jet ofwater at the back of the buckets. This acts as a brake to bring revolving runner quickly to rest.

Working principle

The water is conveyed to the power house from the head race throughpenstocks.The nozzle is fitted to the end of the penstock (power house end) delivers a highvelocity water jet into the bucket. One or more jets of water are arranged to impinge on thebuckets tangentially. The impact of water jet on the bucket causes the wheel to rotate, thusproducing mechanical work. An electric generator is coupled to the runner shaft andmechanical energy is converted into electrical power.

After leaving the turbine wheel, water falls into the tail race. The Pelton wheel islocated above the tail race so that, the buckets do not splash the tail race water.

3.6.4 PELTON WHEEL



The velocity of jet, velocity of wheel and the jet ratio (the ratio of pitch circle diameterof runner and jet diameter) are restricted in the case of a single jet Pelton wheel. Hence, asingle jet Pelton wheel cannot develop high power. However the power can be increased byarranging more than one jet (usually 2, 3, 4 or 6) spaced evenly around the same runner.

The maximum number of jets with a single runner is six.Sometimes, for increasing the power, a number of runners mounted on a common shaft

may be used. In certain cases, a combination of the above two systems may be preferred.

3.6.5. FRANCIS TURBINE

Reaction turbines operate under pressure of water. Only a part of the total head ofwater is converted into a kinetic head before it reaches the runner. The watercompletely fills all the passages in the runner (turbine runs full). Water enters the wheeldue to the head of water at inlet and flows through the vanes. When flowing throughthe vanes, both the pressure and velocity change. The water leaves the turbine to the tailrace at a reduced pressure and velocity.



UNIT IV DIESEL AND GAS TURBINE POWER PLANT

4.1 DIESEL ENGINE POWER PLANT SYSTEMS

The diesel engine power plant consists of the following auxiliary systems:

4.1.1Fuel Supply System

It consists of fuel tank for the storage of fuel, fuel filters and pumps to transfer andinject the fuel. The fuel oil may be supplied at the plant site by trucks, rail, road, tank, cars,etc.

4.1.2 Air Intake and Exhaust System

It consists of pipe for the supply of air and exhaust of the gases. Filters areprovided to remove dust etc. from the incoming air. In the exhaust system silencer is providedto reduce the noise.

Filters may be of dry type (made up of cloth, felt, glass, wool etc.) or oil bath type. Inoil bath type of filters the air is swept over or through a bath of oil in order that the particles ofdust get coated. The duties of the air intake systems are as follows:

i) To clean the air intake supply.ii) To silence the intake air.

iii) To supply air for super charging.

The intake system must cause a minimum pressure loss to avoid reducing enginecapacity and raising the specific fuel consumption. Filters must be cleaned periodically toprevent pressure losses from clogging. Silencers must be used on some systems to reduce highvelocity air noises.

3. Cooling Systems

This system provides a proper amount of water circulation all around the engines tokeep the temperature at reasonable level. Pumps are used to discharge the water inside and thehot water leaving the jacket is cooled in cooling ponds or other devices and is recirculatedagain.

4. Lubrication System

Lubrication is essential to reduce friction and wear of the rubbing parts.Itincludes lubricating oil tank, pumps, filters and lubricating oil cooler.



5. Starting System

For the initial starting of engine the various devices used are compressed air,battery, electric motor or self-starter. The auxiliary equipment of diesel engine power plant.

4.2. Diesel Generator

A diesel generator is the combination of a diesel engine with an electrical

generator (often called an alternator) to generate electric energy. Diesel generating sets are

used in places without connection to the power grid or as emergency power-supply if

the grid fails. Small portable diesel generators range from about 1 kVA to 10 kVA may be

used as power supplies on construction sites, or asauxiliary power for vehicles such as

mobile homes.

4.3 GAS TURBINE POWER PLANT:

A gas turbine, also called a combustion turbine, is a type of internal combustionengine. It has an upstream rotating compressor coupled to a downstream turbine,and acombustion chamber in-between. Energy is added to the gas stream in the combustor, wherefuel is mixed with air and ignited. In the high pressure environment of the combustor,combustion of the fuel increases the temperature. The products of the combustion are forcedinto the turbine section.



There, the high velocity and volume of the gas flow is directed through a nozzleover the turbine's blades, spinning the turbine which powers the compressor and, for someturbines, drives their mechanical output. The energy given up to the turbine comes fromthe reduction in the temperature and pressure of the exhaust gas.

Theory of operation

Gasses passing through an ideal a gas turbine undergo three thermodynamicprocesses. These are isentropic compression, isobaric (constant pressure)combustion and isentropic expansion. Together these make up the Brayton cycle.

In a practical gas turbine, gasses are first accelerated in either a centrifugal or radialcompressor. These gasses are then slowed using a diverging nozzle known as a diffuser, theseprocess increase the pressure and temperature of the flow. In an ideal system this is isentropic.However, in practice energy is lost to heat, due to friction and turbulence. Gasses then passfrom the diffuser to a combustion chamber, or similar device, where heat is added. In an idealsystem this occurs at constant pressure (isobaric heat addition). As there is no change inpressure the specific volume of the gasses increases.

4.3.1 LAYOUT OF GAS TURBINE POWER PLANT

The gas turbine power plants which are used in electric power industry are classified into

two groups as per the cycle of operation.

(1) Open cycle gas turbine.

(2) Closed cycle gas turbine.

4.3.2. Open cycle gas turbine

1- Atmospheric Air



4- Exhaust gases.

The heated gases coming out of combustion chamber are then passed to the turbine where

it expands doing mechanical work. Part of the power developed by the turbine is utilized in

driving the compressor and other accessories and remaining is used for power generation.

Since ambient air enters into the compressor and gases coming out of turbine are exhausted

into the atmosphere, the working medium must be replaced continuously. This type of cycle is

known as open cycle gas turbine plant and is mainly used in majority of gas turbine power

plants as it has many inherent advantages.



4.3.3. Closed cycle gas turbine power plant

In this, the compressed air from the compressor is heated in a heat exchanger (air

heater) by some external source of heat (coal or oil) at constant pressure. Then the high

pressure hot gases expand passing through the turbine and mechanical power is developed.

The exhaust gas is then cooled to its original temperature in a cooler before passing into the

compressor again.

The main difference between the open and closed cycles is that the working fluid is

continuously replaced in open cycle whereas it is used again and again in a closed cycle. The

open cycle plant is much lighter than the closed cycle. Hence it is widely used.







In closed cycle gas turbine plant, the working fluid (air or any other suitable gas) coming

out from compressor is heated in a heater by an external source at constant pressure.

The high temperature and high-pressure air coming out from the external heater is passed

through the gas turbine. The fluid coming out from the turbine is cooled to its original

temperature in the cooler using external cooling source before passing to the compressor.The

working fluid is continuously used in the system without its change of phase and the required

heat is given to the working fluid in the heat exchanger

4.4 WORKING OF GAS TURBINE CYCLE WITH REGENERATOR

In earlier discussion it is seen that for the maximization of specific work output the gas

turbine exhaust temperature should be equal to compressor exhaust temperature. The turbine

exhaust temperature is normally much above the ambient temperature.

Thus their exist potential for tapping the heat energy getting lost to surroundings with

exhaust gases. Here it is devised to use this potential by means of a heat exchanger called

regenerator, which shall preheat the air leaving compressor before entering the combustion

chamber, thereby reducing the amount of fuel to be burnt inside combustion chamber

(combustor).

Regenerative air standard gas turbine cycles shown ahead in figure (a) has a regenerator(counter flow heat exchanger) through which the hot turbine exhaust gas andcomparatively cooler air coming from compressor flow in opposite directions



This shows an obvious improvement in cycle thermal efficiency as every thing else

remains same. Network produced per unit mass flow is not altered by the use of regenerator.

4.5 WORKING OF GAS TURBINE CYCLE WITH INTER COOLING

Net work output from gas turbine cycle can also be increased by reducingnegative work i.e., compressor work. Multistage of compression process with intercooling inbetween is one of the approaches for reducing compression work. It is based on the fact thatfor a fixed compression ratio is higher is the inlet temperature higher shall be compressionwork requirement and vice- versa.

Thermodynamic processes involved in multistage inter cooled compression are shownin figure.First stage compression occurs in low pressure compressor (LPC) and

compressed air leaving LPC at ‘2’ is sent to intercooler where temperature of compressed airis lowered down to state 3 at constant pressure. Schematic for inter cooled gas turbine cycle



In case of perfect inter cooling the temperature after inter cooling is brought down toambient temperature i.e., temperature at 3 and 1 are same. Intercooler is a kind of heatexchanger where heat is picked up from high temperature compressed air. The amount ofcompression work saved due to inter cooling is obvious from p-V diagram and shown byarea 2342’. Area 2342’ gives the amount of work saved due to inter cooling betweencompressions.

Some large compressors have several stages of compression with inter cooling betweenstages. Use of multistage compression with inter cooling in a gas turbine power plantincreases the network produced because of reduction in compressor work. Inter cooledcompression results in reduced temperature at the end of final compression

T-S diagram for gas turbine cycle with intercooling



UNIT V OTHER POWER PLANTS AND ECONOMICS OF POWER PLANTS

5.1 GEO-THERMAL POWER PLANT

It is also a thermal power plant, but the steam required for power generation is availablenaturally in some part of the earth below the earth surface. According to various theoriesearth has a molten core. The fact that volcanic action taken place in many places on the surfaceof earth supports these theories

Steam well

Pipes are embedded at places of fresh volcanic action called steam wells, where themolten internal mass of earth vents to the atmospheric with very high temperatures. Bysending water through embedded pipes, steam is raised from the underground steamstorage wells to the ground level.

Separator

The steam is then passed through the separator where most of the dirt and sand carriedby the steam are removed.



Turbine

The steam from the separator is passed through steam drum and is used to run theturbine which in turn drives the generator.The exhaust steam from the turbine iscondensed.The condensate is pumped into the earth to absorb the ground heat again and to getconverted into steam.

5.2 TIDAL POWER PLANTS

PrincipleTide or wave is periodic rise and fall of water level of the sea.Tides occur due to

the attraction of sea water by the moon. Tides contain large amount of potential energy whichis used for power generation. When the water is above the mean sea level, it is called floodtide. When the water level is below the mean level it is called ebb tide.

Working

The arrangement of this system is shown in figure. The ocean tides rise and fall andwater can be stored during the rise period and it can be discharged during fall. A dam isconstructed separating the tidal basin from the sea and a difference in water level isobtained between the basin and sea.

During high tide period, water flows from the sea into the tidal basin through the waterturbine.The height of tide is above that of tidal basin.Hence the turbine unit operates andgenerates power, as it is directly coupled to a generator.



5.3 TIDAL POWER PLANTS

1. Single basin-one-way cycle

This is the simplest form of tidal power plant. In this system a basin is allowed to getfilled during flood tide and during the ebb tide, the water flows from the basin to the seapassing through the turbine and generates power. The power is available for a short durationebb tide.

2. Single-basin two-way cycle

In this arrangement, power is generated both during flood tide as well as ebb tide also.The power generation is also intermittent but generation period is increased compared withone-way cycle. However, the peak obtained is less than the one-way cycle. The arrangementof the basin and the power cycle is shown in figure.

3. Single – basin two-way cycle with pump storageIn this system, power is generated both during flood and ebb tides. Complex

machines capable of generating power and pumping the water in either directions are used. Apart of the energy produced is used for introducing the difference in the water levels betweenthe basin and sea at any time of the tide and this is done by pumping water into the basin up ordown. The period of power production with this system is much longer than the other twodescribed earlier. The cycle of operation is shown in figure.



4. Double basin type

In this arrangement, the turbine is set up between the basins as shown in figure. Onebasin is intermittently filled tide and other is intermittently drained by the ebb tide. Therefore,a small capacity but continuous power is made available with this system as shown in figure.The main disadvantages of this system are that 50% of the potential energy is sacrificed inintroducing the variation in the water levels of the two basins.

5. Double basin with pumping

In this case, off peak power from the base load plant in a interconnectedtransmission system is used either to pump the water up the high basin. Net energy gain ispossible with such a system if the pumping head is lower than the basin-to-basin turbinegenerating

5.4 SOLAR POWER PLANT

Figure shows a solar power plant with a low temperature solar engine using heated waterfrom flat plate solar collector and Butane as the working fluid. This was developed to liftwater for irrigation purposes



1. Solar collectorsa) Flat plate collector

Figure: Flat plate collector Figure: Cylindrical parabolic concentratorcollector



In a flat plate collector (figure), the radiation energy of the sun falls on a flat surfacecoated with black paint having high absorbing capacity. It is placed facing the generaldirection of the sun. The materials used for the plate may be copper, steel aluminium. Thethickness of the plate is 1 to 2 mm. Tubing of copper is provided in thermal contact with theplate.

Heat is transferred from the absorbed plate to water which is circulated in the coppertubes through the flat plate collection.

Thermal insulation is provided behind the absorber plate to prevent heat losses from therear surface. Insulating material is generally fibre glass or mineral wool. The front cover ismade up of glass and it is transparent to the incoming solar radiations.

b) Cylindrical parabolic concentrator collector

Concentrator collectors (figure) are of reflecting type utilizing mirrors. Thereflecting surface may be parabolic mirror. The solar energy falling on the collector surface isreflected and focused along a line where the absorber tube is located. As large quantity ofenergy falling on the collector surface is collected over a small surface, the temperature of theabsorber fluid is very much higher than in flat plate collector.

c) Butane boiler

The water heated in flat plate solar collector to 80Cis used for boiling butane at highpressure in the butane boiler. Boiling point of butane is about 50C.

d) Turbine

The butane vapour generated at high pressure in the boiler is used to run thevapour turbine which drives the electrical generator.

The vapour coming out of the turbine at low pressure is condensed in a condenser usingwater. The condensed liquid butane is fed back to the butane boiler using feed pump.Tower concept for power generation

The tower concept consists of an array of plane mirrors or heliostats which areindividually controlled to reflect radiations from the sun into a boiler mounted on a 500 metreshigh tower. Steam in generated in the boiler, which may attain a temperature upto2000K. Electricity is generated by passing steam through the turbine coupled to a generator.



5.5 OCEAN THERMAL ENERGY CONVERSION

The ocean and seas constitute about 70% of the earth’s surface area and hencethey represent a large storage reservoir of the solar energy. In tropical waters, thesurface water temperature is about 27Cand at 1 km directly below, the temperature is about4C. The reservoir of surface water may be considered a heat source and the reservoir of coldwater (1 km below) is considered a heat sink. The concept of ocean thermal energy conversionis based on the utilization of temperature difference between the heat source and the sink in aheat engine to generate power.

The temperature gradient present in the ocean is utilized in a heat engine togenerate power. This is called OTEC. Since the temperature gradient is very small, even inthe tropical region, OTEC systems have very low efficiencies and very high capital costs.There are two basic designs for OTEC systems.

1. Open cycle or Claude cycle.2. Closed cycle or Anderson cycle.

Open cycle or Claude cycle

In this cycle, the seawater plays a multiple role of a heat source, working fluid, coolantand heat sink. Warm surface water enters an evaporator where the water is flash evaporated tosteam under particle vacuum. Low pressure is maintained in the evaporator by a vacuumpump. The low pressure so maintained removes the non-condensable gases from theevaporator. The steam and water mixture from evaporator then enters a turbine, driving it thusgenerating electricity. The exhaust from the turbine is mixed with cold water from deepocean in a direct contact condenser and is discharged to the ocean. The cycle is then repeated.Since the condensate is discharged to the ocean, the cycle is called ‘open’.

Flash evaporation

In the evaporator the pressure is maintained at a value (0.0317 bar) slightly lower thanthe saturation pressure of warm surface water at 27C (0.0356 bar). Hence, when the surfacewater enters the evaporator, it gets ‘superheated’. This super heated water undergoes “volumeboiling” causing the water to partially flash to steam.



Closed OTEC cycle

Here, a separate working fluid such as ammonia, propane or Freon is used in additionto water. The warm surface water is pumped to a boiler by a pump. This warm water givesup its heat to the secondary working fluid thereby losing its energy and is discharged back tothe surface of the ocean. The vapours of the secondary working fluid generated in the boiler,drive a turbine generating power. The exhaust from the turbine is cooled in a surfacecondenser by using cold deep seawater, and is then circulated back to the boiler by a pump.

5.6 PUMPED STORAGE:

Pumped-storage hydroelectricity is a type of hydroelectric power generation used bysome power plants for load balancing. The method stores energy in the form of water,pumped from a lower elevation reservoir to a higher elevation. Low-cost off- peak electricpower is used to run the pumps. During periods of high electrical demand, the stored water isreleased through turbines. Although the losses of the pumping process makes the plant a netconsumer of energy overall, the system increases revenue by selling more electricity duringperiods of peak demand, when electricity prices are highest. Pumped storage is the largest-capacity form of grid energy storage now available.



5.7 TARIFFS:

In economic terms, electricity (both power and energy) is a commodity capable ofbeing bought, sold and traded. An electricity market is a system for effecting purchases,through bids to buy; sales, through offers to sell; and short-term trades, generally in the formof financial or obligation swaps. Bids and offers use supply and demand principles to set theprice. Long-term trades are contracts similar to power purchase agreements and generallyconsidered private bi-lateral transactions between counterparties

5.8 ECONOMICS OF POWER PLANTS

Fixed cost includes the following cost.

1. Cost of land 2. Cost of building

3. Cost of equipment 4. Cost of installati6n

5. Interest 6. Depreciation cost

7. Insurance 8. Management cost

Operating cost includes the following cost.

1. Cost of fuel 2. Cost of operating labour,

3. Cost of maintenance labors and materials.

4. Cost of supplier like

Water for feeding boilers, for condenser and for general use.

Lubrication oil and, grease.

Water treatment chemicals.



Depreciation cost

Depreciation cost is the amount to be set aside per year from the income of the plant to

meet the depreciation caused by the age of service, wear and tear of the machinery and

equipments. Depreciation amount collected every year helps in replacing and repairing the

equipment.

5.9 LOAD DURATION CURVE

The load demand on a power system is governed by the consumers and for a system

supplying industrial and domestic consumers, it varies within wide limits. This variation of

load can be considered as daily, weekly, monthly or yearly. Such load curves are termed as

“Chronological load Curves”. If the ordinates of the chronological load curves are arranged

in the descending order of magnitude with the highest ordinates on left, a new type of load

curve known as “load duration curve” is obtained. If any point is taken on this curve then the

abscissa of this point will show the number of hours per year during which the load exceeds the

value denoted by its ordinate. The lower part of the curve consisting of the loads which are to

be supplied for almost the whole number of hours in a year, represents the “Base Load”, while

the upperpart, comprising loads which are required for relatively few hours per year, represents

the “Peak Load”.


73 M.MANIKANDAN-AP/MECH 2014-2015

ME2403 POWERPLANTENGINEERING

UNIT - I - INTRODUCTION OF POWERPLANTS AND BOILERS

Part-A(2 Marks)

1. Name the four major circuits in steam power plant.

Coal and ash circuit

Air and flue gas circuit

Feed water and steam circuit

Cooling water circuit

2. What is the use of surge tank? (Nov/Dec 2005)

The surge tank is used to provide better regulation of water pressure in the system. The

surge tank controls the water when the load on the turbine decreases and supplies water when

the load on the turbine increases. Thus, surge tank controls the pressure variations resulting

from the rapid changes in water flow in penstock and hence prevents water hammer.

3. Explain about penstock?

The pipe between surge tank and prime mover is known as penstock. It is

designed to withstand high pressure. It is made up of reinforced concrete. In very cold areas,

the penstock is buried to prevent ice formation and to reduce the expansion joints.

4. What are the types of power plants? ( May 2011)

1. Thermal Power Plant 2. Diesel Power Plant

3. Nuclear Power Plant 4. Hydel Power Plant

5. Steam Power Plant 6. Gas Power Plant

7. M.H.D. Power Plant

5. What consists of lubrication system in diesel engine power plant?

The lubrication system consists of oil pumps, oil tanks, filters, coolers and connecting

pipes. The purpose of the lubrication is to reduce the friction of moving parts and also pipes to

reduce the wear and tear of moving parts.



6. What is the purpose of intercooler in gas turbine power plant? (Nov/Dec 2011)

Since the power required to compress the air is less in isothermal process it is required

to maintain the, temperature of air constant as far as possible. Hence the air leaving the L.P.

compressor is cooled by intercooler and then passed to the H.P compressor.

15. What is the purpose of Draught? (Apr 2011)

(i) To supply required amount of air to the furnace for the combustion of fuel. The amount

of fuel can be burnt per square foot of grate depends upon the quantity of air circulated

through fuel bed.

(ii) To remove the gaseous products of combustion.

8. Write about Benson boiler? State some important advantages of Benson boiler?

Benson boiler is the high pressure, vertical fire tube boiler. This boiler has no drum and

is ~designed to operate at critical pressure of 225 bar. Benson boiler has no drum. So the total

weight of the Benson boiler is reduced by-20%, when compared to other boilers.

o The erection of Benson boiler is easier and quicker.

9. Define load curve? (Nov/Dec 2009)

Load curve is a graphical representation between load in kW and time in hours. It.

shows variati6n of load at the power station. The area under the load curve -represents

the energy generated in a particular period.

10. Explain Reheat cycle?

If the dryness fraction of steam leaving the turbine is less than 0.88, then, corrosion and

erosion of turbine blades occur. To avoid this situation, reheat is used. In the reheat cycle, the

expansion of steam takes place in one (or) more-turbines. Steam is expanded in the HP turbine

first, and then it is reheated. The reheated steam is again expanded in. the LP turbine.

11. What are the important advantages of Re-heating? (Nov/Dec 2005)

Due to reheating, network done increases

Heat supply increases

Thermal efficiency increases

Due to reheating, the turbine exit dryness fraction increases so moisture decreases - so

blade erosion becomes minimum - so life of the turbine will be increased.



12. Define bleeding in steam power plant?

Assume I kg of steam is expanded in the turbine. Before complete amount of steam -is

expanded, some amount of steam (m kg) is -extracted ' Extracting the steam in the turbine

before exhaust is called bleeding. This bled steam is used to heat the feed water.

13. Explain the term Regeneration & advantages of Regeneration cycle?

Regeneration means heating the feed water by steam taken from the turbine. The steam

is exhausted (bled) from the turbine at several locations before exhaust and is supplied to

regenerator (feed water heater) to heat the feed water.

Advantages of Regeneration cycle

Heat supplied to boiler becomes reduced

Thermal efficiency is increased since the average temperature of heat addition to the

cycle is increased.

Due to bleeding in the turbine, erosion of turbine due to moisture is reduced.

14.. Define the term waste heat recovery?

Waste heat is the heat which is not at all used and exhausted out as a waste product.

Waste heat is normally available from the industry in the form of process steam and water at

high temperature. Also, the waste heat is discharged with the exhaust gases in so many

industries. This heat can be recovered for useful purpose. This process is known-as waste heat

recovery.

15. What are the waste materials, which can be used for fuel for power generation?

(Nov/Dec 2004)

Municipal waste

Industrial waste

Paper waste

Rubber waste.



PART –B

1. Draw and Explain the working of thermal power plant? (Apr 2005)

The four main circuits one would come across in any thermal power plant layout are

- Coal and Ash Circuit

- Air and Gas Circuit

- Feed Water and Steam Circuit

- Cooling Water Circuit.

Coal and Ash Circuit

Coal and Ash circuit in a thermal power plant layout mainly takes care of feeding

the boiler with coal from the storage for combustion. The ash that is generated during

combustion is collected at the back of the boiler and removed to the ash storage by scrap

conveyors. The combustion in the Coal and Ash circuit is controlled by regulating the speed

and the quality of coal entering the grate and the damper openings.

Air and Gas Circuit

Air from the atmosphere is directed into the furnace through the air preheated by the

action of a forced draught fan or induced draught fan. The dust from the air is removed

before it enters the combustion chamber of the thermal power plant layout. The exhaust

gases from the combustion heat the air, which goes through a heat exchanger and is finally

let off into the environment.

Feed Water and Steam Circuit

The steam produced in the boiler is supplied to the turbines to generate power.

The steam that is expelled by the prime mover in the thermal power plant layout is then

condensed in a condenser for re-use in the boiler. The condensed water is forced through a

pump into the feed water heaters where it is heated using the steam from different points in

the turbine. To make up for the lost steam and water while passing through the various

components of the thermal power plant layout, feed water is supplied through external

sources.



Cooling Water Circuit

The quantity of cooling water required to cool the steam in a thermal power plant layout

is significantly high and hence it is supplied from a natural water source like a lake or a

river. After passing through screens that remove particles that can plug the condenser tubes

in a thermal power plant layout, it is passed through the condenser where the steam is

condensed. The water is finally discharged back into the water source after cooling. Cooling

water circuit can also be a closed system where the cooled water is sent through cooling

towers for re-use in the power plant. The cooling water circulation in the condenser of a

thermal power plant layout helps in maintaining a low pressure in the condenser all

throughout.

All these circuits are integrated to form a thermal power plant layout that generates

electricity to meet our needs.

Figure: Layout of a steam power plant.



2. Draw and explain the working of magneto hydro dynamic (MHD) power plants

(Nov/Dec 2004)


be of high efficiency and low pollution. In advanced countries MHD generator are widely

used but in developing countries like India it is still under construction. This construction

work is in progress at Tiruchirapalli in Tamilnadu under joint efforts of BARC (Bhabha

Atomic Research Centre), BHEL, Associated Cement Corporation and Russian

technologists.











(Nov/Dec 2004)






technologists.











(Nov/Dec 2004)






technologists.














ionized gas. If such gas is passed at high velocity through a powerful magnetic field, a

current is generated and can extract by placing electrodes in a suitable position in the stream.





Ionization is produced either by thermal means i.e. by an elevated temperature or by

seeding with substance like cesium or potassium vapour which ionize at relatively low

temperature.

















temperature.

















temperature.





3. Draw and explain the working of combined power cycles

In electric power generation a combined cycle is an assembly of heat engines that

work in tandem off the same source of heat, converting it into mechanical energy, which in

turn usually drives electrical generators. The principle is that the exhaust of one heat engine

is used as the heat source for another, thus extracting more useful energy from the heat,

increasing the system's overall efficiency. This works because heat engines are only able to

use a portion of the energy their fuel generates (usually less than 50%).

The objective of this approach is to use all of the heat energy in a power system at the

different temperature levels at which it becomes available to produce work, or steam, or the

heating of air or water, thereby rejecting a minimum of energy waste. The best approach is

the use of combined cycles. There may be various combinations of the combined cycles

depending upon the place or country requirements. Even nuclear power plant may be used in

the combined cycles.

GT-ST Combined Power plants

It has been found that a considerable amount of heat energy goes as a waste with the

exhaust of the gas turbine. This energy must be utilized. The complete use of the energy

available to a system is called the total energy approach. The remaining heat (e.g., hot

exhaust fumes) from combustion is generally wasted. Combining two or more

thermodynamic cycle’s results in improved overall efficiency, reducing fuel costs. In

stationary power plants, a successful, common combination is the Brayton cycle (in the form

of a turbine burning natural gas or synthesis gas from coal) and the Rankine cycle (in the

form of a steam power plant). Multiple stage turbine or steam cylinders are also common.



ST-MHD Combined Power plants

4. A. Draw and explain the working of boilers, B. Classification of Boilers and C. High pressure

boilers. (Nov/Dec 2009)

Boiler is an apparatus to produce steam. Thermal energy released by combustion of fuel is

transferred to water, which vaporizes and gets converted into steam at the desired temperature and

pressure.

The steam produced is used for:

Producing mechanical work by expanding it in steam engine or steam turbine.

Heating the residential and industrial buildings.

Performing certain processes in the sugar mills, chemical and textile industries.

Boiler is a closed vessel in which water is converted into steam by the application of heat.

Usually boilers are coal or oil fired. A boiler should fulfill the following requirements;

Safety. The boiler should be safe under operating conditions.

Accessibility. The various parts of the boiler should be accessible for repair and

maintenance.



Capacity. The boiler should be capable of supplying steam according to the

requirements.

Efficiency. To permit efficient operation, the boiler should be able to absorb a

maximum amount of heat produced due to burning of fuel in the furnace.

It should be simple in construction and its maintenance cost should be low.

Its initial cost should be low.

The boiler should have no joints exposed to flames.

The boiler should be capable of quick starting and loading.

The performance of a boiler may be measured in terms of its evaporative capacity also called

power of a boiler. It is defined as the amount of water evaporated or steam produced is in kg per

hour. It may also be expressed in kg per kg of fuel burnt.

B.Classification of Boilers

The boilers can be classified according to the following criteria.

According to flow of water and hot gases.

1. Water tube.

2. Fire tube.

In water tube boilers, water circulates through the tubes and hot products of combustion flow

over these tubes. In fire tube boiler the hot products of combustion pass through the tubes, which are

surrounded, by water.

Fire tube boilers have low initial cost, and are more compacts. But they are more likely to

explosion, water volume is large and due to poor circulation they cannot meet quickly the change in

steam demand. For the same output the outer shell of fire tube boilers is much larger than the shell

of water-tube boiler. Water tube boilers require less weight of metal for a given size, are less liable

to explosion, produce higher pressure, are accessible and can response quickly to change in steam

demand.

Tubes and drums of water-tube boilers are smaller than that of fire-tube boilers and due to

smaller size of drum higher pressure can be used easily. Water-tube boilers require lesser floor

space. The efficiency of water-tube boilers is more.



1. According to position of furnace.

(i) Internally fired (ii) Externally fired

2. According to the position of principle axis. (i) Vertical (ii) Horizontal (iii) Inclined.

3. According to application.

(i) Stationary (ii) Mobile, (Marine, Locomotive).

4. According to the circulating water.

(i) Natural circulation (ii) Forced circulation.

5. According to steam pressure.

(i) Low pressure (ii) Medium pressure (iii) Higher pressure.

C. High pressure boilers

A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized

fluid exits the boiler for use in various processes or heating applications.

In all modern power plants, high pressure boilers (> 100 bar) are universally used as they

offer the following advantages. In order to obtain efficient operation and high capacity, forced

circulation of water through boiler tubes is found helpful.

1. The efficiency and the capacity of the plant can be increased as reduced quantity of steam is

required for the same power generation if high pressure steam is used.

2. The forced circulation of water through boiler tubes provides freedom in the arrangement of

furnace and water walls, in addition to the reduction in the heat exchange area.

3. The tendency of scale formation is reduced due to high velocity of water.

4. The danger of overheating is reduced as all the parts are uniformly heated.

5. The differential expansion is reduced due to uniform temperature and this reduces the possibility

of gas and air leakages.

Superheater operation is similar to that of the coils on an air conditioning unit, although for a

different purpose. The steam piping is directed through the flue gas path in the boiler furnace. The

temperature in this area is typically between 1,300–1,600 degrees Celsius.

While the temperature of the steam in the superheater rises, the pressure of the steam does

not. Almost all the steam superheater systems are designed to remove droplets entrained in the

steam to prevent damage to the turbine blading and associated piping.



5. Draw and explain the working of la-Mont boiler (Nov/Dec 2005)

It is a forced circulation- water tube boiler which was first introduced in 1925 by La Mont

The feed water from hot well is supplied to a storage and separating drum (boiler) through

the economizer. Most of the sensible heat is supplied to the feed water passing through the

economizer. A pump circulates the water at a rate 8 to 10 times the mass of steam evaporated. This

water is circulated through the evaporator tubes and the part of the vapour is separated in the

separator drum. The large quantity of water circulated (10 times that of evaporation) prevents the

tubes from being overheated.

The centrifugal pump delivers the water to the headers at a pressure of 2.5 bar above the

drum pressure. The distribution headers distribute the water through the nozzle into the evaporator.

The steam separated in the boiler is further passed through the super-heater.To secure a uniform

flow of feed water through each of the parallel boiler circuits a choke is fitted entrance to each

circuit. These boilers have been built to generate 45 to 50 tons of superheated steam at a pressure of

120 bar and temperature of 500°C.




1. Steam separating drum – The feed water from the hot well is stored in the drum. The steam

is separated from water in the drum and the steam is usually collected at the top of the drum.

2. Circulating pump – Water from the steam separating drum is drawn by a circulating pump

and it circulates water through the evaporator tubes. Pump circulates water at a rate of 8-10

times the mass of steam evaporated. Forced circulation is necessary to prevent the

overheating of tubes.

3. Distribution header – The distribution header distributes the water through the nozzle into

the evaporator.

4. Radiant evaporator – Water from the drum first enters the radiant evaporator through the

pump and header. The water is heated by the radiation heat from the combustion chamber. In

radiant evaporator, the hot flue gases do not pass over the water tubes.




becomes steam and the steam enters to the steam separating drum.

6. Superheater – The steam from the steam separating drum enters the superheater tubes where

it is superheated by the hot flue gases passing over them. The superheated steam then enters

the steam turbine to develop power.

7. Economiser – The waste hot flue gases pass through the economiser where feed water is pre-

heated. By pre-heating the feed water, the amount of fuel required to convert water into

steam is reduced.

8. Air pre-heater – The hot flue gases then passes through the air pre-heater where the air

required for combustion is pre-heated.

Advantages

1. La-Mont boilers can generate 45 to 50 tons of superheated steam at a pressure of 120 bar and

temperature of 500°C.

2. Drum is of small size.

3. Tendency of scale formation is eliminated due to forced circulation of water.



Disadvantages

1. Bubbles are formed on the inside of the water tubes and bubbles reduce the heat transfer rate.

2. Initial and operating costs are high.


6. Draw and explain the working of Benson Boiler (Supercritical Boiler) (Apr 2004)

The main difficulty experienced in the La Mont boiler is the formation and attachment of

bubbles on the inner surfaces of the heating tubes. The attached bubbles reduce the heat flow and

steam generation as it offers higher thermal resistance compared to water film. Benson of siemens-

West Germany in 1922 argued that if the boiler pressure was raised to critical pressure (225 atm.),

the steam and water would have the same density and therefore the danger of bubble formation can

be completely removed.


1. Economiser – The feed water from the well passes through the economiser where it is pre-

heated by the pre-heat of exhaust hot flue gases.

2. Radiant evaporator – The feed water after circulation through the economiser flows through

the radiant evaporator tubes. Water is heated up by the radiation heat from the combustion

chamber. Here, part of the water is converted to steam directly.



evaporator tubes transfer a large portion of heat to the water by convection.

4. Superheater – The steam from the convective evaporator enters the superheater tubes where

it is superheated by the hot flue gases passing over them. The superheated steam then enters

the steam turbine to develop power.

5. Air pre-heater – The hot flue gases then passes through the air pre-heater where the air

required for combustion is pre-heated.



Advantages

1. As there is no drum, the total weight of Benson boiler is 20% less than other boilers.

This reduces the cost of the boiler.

2. Floor space requirements of Benson boiler are very less.

3. Transportation of Benson boiler parts and its erection is very easy as there are no drums.

4. Natural circulation boilers require expansion joints in pipes but the pipes in Benson boilers

are welded.

Disadvantages

1. As the Benson boiler operates at high pressure and temperature, special alloy materials are

required.


3. This is more efficient, resulting in slightly less fuel use.

The term "boiler" should not be used for a supercritical pressure steam generator, as no

"boiling" actually occurs in this device.



7. Draw and explain the working of Fluidised Bed Combustion (FBC) (Nov/Dec 2005)

Burning of pulverised coal has some problems such as particle size of coal used in

pulverized firing is limited to 70-100 microns, the pulverised fuel fired furnaces designed to burn a

particular cannot be used other type of coal with same efficiency, the generation of high temp. about

(1650 C)in the furnace creates number of problems like slag formation on super heater, evaporation

of alkali metals in ash and its deposition on heat transfer surfaces, formation of SO2 and NOX in

large amount.

Fluidised Bed combustion system can burn any fuel including low grade coals (even

containing 70% ash), oil, gas or municipal waste. Improved desulphurisation and low NOX

emission are its main characteristics. The fuel and inert material dolomite are fed on a distribution

plate and air is supplied from the bottom of distribution plate. The air is supplied at high velocity so

that solid feed material remains in suspension condition during burning.

The heat produced is used to heat water flowing through the tube and convert water into

steam. During burning SO2 formed is absorbed by the dolomite and thus prevents its escape with the

exhaust gases. The molten slag is tapped from the top surface of the bed.



The bed temperature is nearly 800-9000C which is ideal for sulphur retention addition of

limestone or dolomite to the bed brings down SO2 emission level to about 15% of that in

conventional firing methods

Various advantages of FBC system are as follows:

1. FBC system can use any type of low grade fuel including municipal wastes and

therefore is a cheaper method of power generation.

2. It is easier to control the amount of SO2 and NOX, formed during burning. Low

emission of SO2 and NOX will help in controlling the undesirable effects of SO2 and

NOX. During combustion. SO2 emission is nearly 15% of that in conventional firing

methods.

3. There is a saving of about 10% in operating cost and 15% in the capital cost of the power

plant.

4. The size of coal used has pronounced effect on the operation and performance of FBC

system. The particle size preferred is 6 to 13 mm but even 50 mm size coal can also be

used in this system.



UNIT - II - STEAM POWER PLANT

PART –A

1. Write about out plant handling?

Out plant handling includes the handling of coalmine to the thermal power plant. These

handlings are outside the plant in the following ways.

Transportation by sea (or) river

Transportation by rail

Transportation by road

Transportation of coal by pipeline.

2. Write about inplant handling of-coal? (Apr 2011)

In order to handle large quantity of coal inside the plant, some mechanical handling systems

are provided f6r smooth, easy and better controlled operation. The inplant coal handling is divided,

into following categories.

Coal unloading

Coal preparation

Coal transfer

Coal storage

3. Why the preparation of coal is necessary?

The coal from coal nines cannot be directly fed into the furnace. Proper preparation of coal

should be done before feeding the coal to the furnace. In the coal preparation, the coal passes through

the different equipments like 1. Crushers 2.Sizers 3.Driers and Magnetic Separators.

4. Name the different types of coal transforming equipments?

1. Belt conveyors 2. Screw conveyors 3. Bucket elevators 4. Grab bucket elevators 5. Skip

hoists 6. Flight conveyors. The coal transfer starts by carrying of coal from-unloading point to the

storage site.

5. Write the classification of Mechanical Stokers? (Apr 2010)

1. Travelling grate stoker 2. Chain grate stoker

3. Spreader stoker 4. Vibrating grate Stoker

5. Underfeed stoker.



6. Define draught, what is the use of draught in thermal power plants?

Draught is defined as a small pressure difference required between the fuel bed (furnace) and

outside air to maintain constant flow of air and to discharge the gases through chimney to the

atmosphere. Draught can be obtained by chimney, fan, steam jet (or) -air jet (or) combination of these.

The uses are

To supply required quantity of air to the furnace for combustion of fuel.

To draw the combustion products through the system.

To remove burnt products from the system

7. Why the balanced draught system is preferred than other system?

In the induced draught system, when the furnace is opened for firing, the cold air enters the

furnace and dilate the combustion. In the forced draught system, when the furnace is opened for firing,

the high pressure air will try to blow out suddenly and furnace may stop. Hence the furnace cannot be

opened for firing (q) inspection in both, systems. Balanced draught, which is a combination of

induced and forced draught, is used to overcome the above stated difficulties.

8. Define forced draft and induced draft cooling towers

If the fan is located at the bottom of the tower and air is blown by the fan up through the

descending water it is called as forced draft cooling towers. If the fan is located at the top of the tower

and air enters through the louvers located on the tower’s side and drawn up and discharge through the

fan casing, it is called as induced draft.

9. What is the working principle of Cooling Towers? (Nov/Dec 2013)

The hot water is sprayed from the top of the tower, while the air is made to flow from the

bottom of the tower to the top. This air cools the hot water in the cooling tower. Air vaporises a small

percentage of water, there by cooling the remaining water. The air absorbs the heat and leaves at the

top of the tower and cooled water leaves at the bottom and recirculated to the condenser.



10. How the atmospheric (or) natural draught cooling towers- are classified?

In atmospheric (or) natural cooling towers, the natural air provides the required Cooling

without the use of fans. This is classified into three types.

1. Natural draft spray filled towers

2. Natural draft packed type towers.'

3. Hyperbolic cooling towers

11. How mechanical draft cooling towers are classified? (Nov/Dec 2011)

Mechanical draft cooling tower is classified into three types

1. Forced draft tower.

2. Induced draft counter flow tower

3. Induced draft cross flow tower.

12. Write the classification of Ash handling system? (Dec 2009)

1. Hydraulic system,

2. Pneumatic system

3. Mechanical system

13. What are the Ash discharge equipments? (Apr 2008)

1. Rail road cars

2. Motors truck

3. Barge

13. List the different types of components (or) systems used in steam (or) thermal power plant?

1. Coal handling system. 2. Ash handling system.

3. Boiler 4. Prime mover

5. Draught system.

a. Induced Draught b. Forced Draught



14. What are the merits of thermal power plants? (Dec 2008)

Merits (Advantages) of Thermal Power Plant:

1. The unit capacity of thermal power plant is more. The cost of unitdecreaseswith the

increase in unit capacity

2. Life of the plant is more (25-30 years) as compared to diesel plant(2-5 years)

3. Repair and maintenance cost is low when compared with diesel plant

4. Initial cost of the plant is lessthan nuclearplants

5. Suitable for varying load conditions.

15. What are the Demerits of thermal power plants? Demerits of thermal Power Plants:

1. Thermal plant are less efficient than diesel plants

2. Starting up the plant and briningintoservice takes more time

3. Cooling water required is more

4. Space required is more.

PART B

1. Explain the working of Surface condensers with advantages and disadvantages?a) Down flow b) Central flow c) E v a p o r a t i v e ( D e c 2 0 1 4 )

Surface Condenser:

In surface condensers there is no direct contact between the steam and cooling water and

the condensate can be re-used in the boiler. In such a condenser even impure water can be used

for cooling purpose whereas the cooling water must be pure in jet condensers.

Although the capital cost and the space needed is more in surface condensers but it is

justified b the saving in running cost and increase in efficiency of plant achieved by using this

condenser. Depending upon the position of condensate extraction pump, flow of condensate and

arrangement of tubes the surface condensers may be classified as follows:

1. Down flow condenser

2. Central flow condenser




1. Down flow condenser:

Figure: Sectional views of down flow condenser.

Figure shows a sectional view of down flow condenser. Steam enters at the top and flows

downward. The water flowing through the tubes in one direction lower half comes out in the

opposite direction in the upper half. In this type of condenser, the cooling water and exhaust

steam do not come in direct contact with each other as in case of jet condensers. This is generally

used where large quantities of inferior water are available and better quantity of feed water to the

boiler must be used most economically.

The arrangement of the surface condenser is shown in figure. It consists of cast iron air-

tight cylindrical shell closed at each end as shown in figure. A number of water tubes are fixed in

the tube plates which are located between each cover head and shell.



Figure: Surface The exhaust steam from the prime mover enters at the top of the condenser

and surrounds the condenser tubes through which cooling water is circulated under force.

The steam gets condensed as it comes in contact with cold surface of the tubes. The cooling

water flows in one direction through the first set of the tubes situated in the lower half of condenser

and returns in the opposite direction through the second set of the condenser is discharged into

the river or pond. The condensed steam is taken out from the condenser by a separate extraction

pump and air is removed by an air pump.

2. Central flow condenser.

Figure shows a central flow condenser. In this condenser the steam passages are all around

the periphery of the shell. Air is pumped away from the centre of the condenser. The condensate

moves radially towards the centre of the tube next. Some of the exhaust steam which moving

towards the centre meets the under cooled condensate and pre-heats it thus reducing under cooling.

Figure: Central flow condenser


In this condenser steam to be condensed in passed through a series of tubes and the cooling

water falls over these tubes in the form of spray. A steam of air flows over the tubes to increase

evaporation of cooling water which further increases the condensation of steam



These condensers are more preferable where acute shortage of cooling water exists. The

arrangement of the condenser is shown in figure. Water is sprayed through the nozzles over the pipe

carrying exhaust steam and forms a thin film over it. The air is drawn over the surface of the coil

with the help of induced fan as shown in figure. The air passing over the coil carries the water from

the surface of condenser coil in the form of vapour.

The latent heat required for the evaporation of water vapour is taken from the water film

formed on the condenser coil and drops the temperature of the water film and this helps for heat

transfer from the steam to the water. This mode of heat transfer reduces the cooling water

requirement of the condenser to 10% of the requirement of surface condensers. The water particles

carried with air due to high velocity of air are removed with the help of eliminator as shown in

the figure. The make-up water (water vapour and water particles carried with air) is supplied

from outside source.



2. Draw and explain construction and working principle of cooling towers. And explain one –

Through system, closed circuit system. (Apr 2006)

Introduction

In the power industry, energy in the form of heat is transformed to energy in the form of

electricity. Unfortunately, this transformation is not accomplished on a one-to-one ratio.

Although designers continuously seek newer and better ways to improve overall system

efficiency, considerably more units of heat must be input that are realized as equivalent units of

electric output. System equilibrium requires that this excess heat be dissipated ultimately to the

atmosphere.

The traditional vehicle used to transport the lion’s share of this waste heat to atmospheric is

water, using the principle of evaporation as the primary mechanism of heat transfer.Where

available and ecologically acceptable, water from rivers, lakes, or oceans is often used on a once-

through bases, schematically shown in figure. Taken from the river, water absorbs heat from the

steam condenser and returns to the river (at an elevated temperature) downstream from its point of

extraction.



In an increasing number of cases, because of qualitative and quantitative restrictions regarding

the use of natural waterways, plant make use of a closed circuit system typical of that depicted in

figure. As shown, the system’s dependence on the river is limited to the requirement for a supply of

makeup water and, perhaps, as a point of discharge of blow down. In these cases, the entire heat

loads are dissipated by cooling towers, at the variety, application and operation of which are the

subject of this chapter

3. Draw and Explain the various steps involved in coal handling? (Apr 2011, 09)

Fuel Handling System

Coal delivery equipment is one of the major components of plant cost. The various steps

involved in coal handling are as follows:

1. Coal delivery.

2. Unloading

3. Preparation

4. Transfer

5. Outdoor storage

6. Covered storage

7. Inplant handling

8. Weighing and measuring

9. Feeding the coal into furnace.



Figure: Steps involved in fuel handling systemi) Coal delivery

The coal from supply points is delivered by ships or boats to power stations situated near

to sea or river whereas coal is supplied by rail or trucks to the power stations which are situated

away from sea or river. The transportation of coal by trucks is used if the railway facilities are not

available.

ii) Unloading

The type of equipment to be used for unloading the coal received at the power station

depends on how coal is received at the power station. If coal delivered by trucks, there is no need

of unloading device as the trucks may dump the coal to the outdoor storage. Coal is

easily handled if the lift trucks with scoop are used. In case the coal is brought by railways

wagons, ships or boats, the unloading may be done by car shakes, rotary car dumpers, cranes, grab

buckets and coal accelerators. Rotary car dumpers although costly are quite efficient for unloading

closed wagons.



(iii) Preparation

When the coal delivered is in the form of big lumps and it is not of proper size, the

preparation (sizing) of coal can be achieved by crushers, breakers, sizers, driers and magnetic

separators.

iv)Transfer

After preparation coal is transferred to the dead storage by means of the following systems.

1. Belt conveyors

2. Screw conveyors

3. Bucket elevators

4. Grab bucket elevators

5. Skip hoists

6. Flight conveyor

v).Storage of Coal

It is desirable that sufficient quantity of coal should be stored. Storage of coal gives

protection against the interruption of coal supplies when there is delay in transportation of coal or due

to strike in coal mines. Also when the prices are low, the coal can be purchased and stored for future

use. The amount of coal to be stored depends on the availability of space for storage,

transportation facilities, the amount of coal that will whether away and nearness to coal mines of the

power station.

Usually coal required for one month operation of power plant is stored in case of power

stations are situated at longer distance from the collieries whereas coal need for about 15 days is

stored in case of power station situated near to collieries. Storage of coal for longer periods is not

advantageous because it blocks the capital and results in deterioration of the quality of coal

4. Write short notes of pulverized coal handing system? Pulverized Fuel Handling System:

(Dec 2009)

Periodically a power plant may encounter the situation where coal must be stored for

sometimes in a bunker, for instance during a plant shut down. The bunker, fires can occur in dormant

pulverized coal from spontaneous heating within 6 day of loading. This time can be extended to

13 days when a blanket of CO2 is piped into the top of the bunker.



The perfect sealing of the bunker from air leakage can extend the storage time as two months

or more. The coal in the bunker can be stored as long as six months by expelling air from above

the coal with the use of CO2 and then blanketing of all sources of air. A control system used for

storing the pulverized fuel in bunker is shown in figure.



In this mill the coal passes between the rotating elements again and again until it

has been pulverized to desired degree of fineness.The coal is crushed between two

moving surfaces, namely, balls and races. The upper stationary race and lower rotating

race driven by a worm and gear hold the balls between them. The raw coal supplied falls

on the inner side of the races. The moving balls and races catch coal between them to

crush it to a powder. The necessary force needed for crushing is applied with the help

of springs. The hot air supplied picks up the coal dust as it flows between the balls and

races and then enters the classifier. Where oversized coal particles are returned for

further grinding.Where as the coal particles of required size are discharged from the

top of classifier.

5. Explain the Layout of Ash handling system (Apr 2010)

Ash Handling System:

Boilers burning pulverized coal (PC) have bottom furnaces.The large ash

particles are collected under the furnace in a water-filled ash hopper, Fly ash is collected in

dust collectors with either an electrostatic precipitator or a baghouse. A PC boiler

generates approximately 80% fly ash and 20% bottom ash. Ash must be collected and

transported from various points of the plants as shown in figure. Pyrites, which are the

rejects from the pulverizers, are disposed of with the bottom ash system. Three major

factors should be considered for ash disposal systems.

1. Plant site

2. Fuel source

3. Environmental regulation

Needs for water and land are important considerations for many ash handling

systems.Ash quantities to be disposed of depend on the king of fuel source. Ash storage

and disposal sites are guided by environmental regulations.

The sluice conveyor system is the most widely used for bottom ash handling, while

the hydraulic vaccum conveyor (figure) is the most frequently used for fly systems.



Figure: Layout of ash collection and transportation

Figure: Layout of ash handling system.



Bottom and slag may be used as filling material for road construction. Fly ash can

partly replace cement for making concrete. Bricks can be made with fly ash. These

are durable and strong.

6. Write short notes of Ash handling Equipment

Ash Handling Equipment:

Mechanical means are required for the disposal of ash. The handling equipment

should perform the following functions:

1. Capital investment, operating and maintenance charges of the equipment should be low.

2. It should be able to handle large quantities of ash.

3. Clinkers, shoot, dust etc. create troubles. The equipment should be able to handle

them smoothly.

4.The equipment used should remove the ash from the furnace, load it to the

conveying system to deliver the ash to dumping site or storage and finally it should

have means to dispose of the stored ash.

5. The equipment should be corrosion and wear resistant.

Figure: Ash handling equipment



7. Draw and Explain the a) Forced Draught, b) Induced Draught, c) Balanced Draught

Artificial Draught (Dec 2014)

It has been seen that the draught produced by chimney is affected by the

atmospheric conditions. It has no flexibility, poor efficiency and tall chimney is

required. In most of the modern power plants, the draught used must be independence of

atmospheric condition, and it must have greater flexibility (control) to take the fluctuating

loads on the plant.

Today’s large steam power plants requiring 20 thousand tons of steam per hour

would be impossible to run without the aid of draft fans. A chimney of an reasonable

height would be incapable of developing enough draft to remove the tremendous volume

of air and gases (400 ×103 m3 to 800 × 103 m3 per minutes). The further advantage of

fans is to reduce the height of the chimney needed. The draught required in actual power

plant is sufficiently high (300 mm of water) and to meet high draught requirements, some

other system must be used, known as artificial draught. The artificial draught is

produced by a fan and it is known as fan (mechanical) draught. Mechanical draught

is preferred for central power stations.

Forced DraughtIn a forced draught system, a blower is installed near the base of the boiler and air is

forced to pass through the furnace, flues, economizer, air-preheater and to the

stack.This draught system is known as positive draught system or forced draught system

because the pressure and air is forced to flow through the system. The arrangement of

the system is shown in figure. A stack or chimney is also in this system as shown in

figure but its function is to discharge gases high in the atmosphere to prevent the

contamination. It is not much significant for producing draught therefore height of the

chimney may not be very much.

Figure: Forced draught



Induced Draught:

In this system, the blower is located near the base of the chimney instead of near the

grate. The air is sucked in the system by reducing the pressure through the system below

atmosphere. The induced draught fan sucks the burned gases from the furnace and the

pressure inside the furnace is reduced below atmosphere and induces the atmospheric

air to flow through the furnace. The action of the induced draught is similar to the action

of the chimney. The draught produced is independent of the temperature of the hot

gases therefore the gases may be discharged as cold as possible after recovering as

much heat as possible in air-preheater and economizer.

This draught is used generally when economizer and air-preheater are incorporated

in the system. The fan should be located at such a place that the temperature of the gas

handled by the fan is lowest. The chimney is also used in this system and its function is

similar as mentioned in forced draught but total draught produced in induced draught

system is the sum of the draughts produced by the fan and chimney. The arrangement of

the system is shown in figure.

Figure: Induced draught

Balanced Draught:

It is always preferable to use a combination of forced draught and induced draught

instead of forced or induced draught alone.

If the forced draught is used alone, then the furnace cannot be opened either for

firing or inspection because the high pressure air inside the furnace will try to blow out

suddenly and there is every chance of blowing out the fire completely and furnace stops.



If the induced draught is used alone, then also furnace cannot be opened either for

firing or inspection because the cold air will try to rush into the furnace as the pressure

inside the furnace is below atmospheric pressure. This reduces the effective draught and

dilutes the combustion.

To overcome both the difficulties mentioned above either using forced draught or

induced draught alone, a balanced draught is always preferred. The balanced draught is a

combination of forced and induced draught. The forced draught overcomes the resistance

of the fuel bed there fore sufficient air is supplied to the fuel bed for proper and complete

combustion. The induced draught fan removes the gases from the furnace maintaining the

pressure in the furnace just below atmosphere. This helps to prevent the blow – off of

flames when the doors are opened as the leakage of air is inwards.



UNIT III NUCLEAR AND HYDEL POWERPLANTS

Part-A (2 Marks)

1. Define Fission? (Dec 2014)

Fission is the process that occurs when a neutron collides with the nucleus of certain

of heavy atoms, causing the original nucleus to split into two or more unequal

fragments which carry-off most of the energy of fission as kinetic energy.This process

is accompanied by the emission of neutrons and gamma rays.

2. Define nuclear fusion? (Dec 2009)Nuclear fusion is the process of combining or fusing two lighter nuclei into a stable

and heavier nuclide. In this case large amount of energy is released because mass of

the product nucleus is less than the masses of the two nuclei which are fused.

3. Write the types of nuclear radiations?

The five types of nuclear radiations are :

(i) Gamma rays (or photons) : electromagnetic radiation.

(ii) Neutrons : uncharged particles, mass approximately 1.

(iii) Protons : + 1 charged particles, mass approximately 1.

(iv) Alpha particles : helium nuclei, charge + 2, mass 4.

(v) Beta particles : electrons (charge – 1), positrons (charge + 1), mass very small.

4. Define Nuclear Reactor?

A nuclear reactor is an apparatus in which nuclear fission is produced is the form of

a controlled self-sustaining chain reaction.

5. Write the Essential components of a nuclear reactor? (May/June 2009)

Essential components of a nuclear reactor are:

(i) Reactor core (ii) Reflector

(iii) Control mechanism (iv) Moderator

(v) Coolants (vi) Measuring instruments

(vii) Shielding.



6. What are the factors are consider to selecting the site for Nuclear power plant?

Following factors should be considered while selecting the site for a nuclear

power plant: (i) Proximity to load centre

(ii) Population distribution (iii) Land use

(iv) Meteorology (v) Geology

(vi) Seismology (vii) Hydrology

7. What are the advantages of nuclear power plant?

1. It can be easily adopted where water and coal resources are not available.

2. The Nuclear power plant requires very small quantity of fuel. Hence fuel transport

cost is less.

3. Space requirement is very less compared to other power plant of equal capacity.

4. It is not affected by adverse weather condition.

8. Define Surge tank? (Nov/Dec 2005)

A surge tank is a small reservoir or tank in which the water level rises or falls to

reduce the pressure swings so that they are not transmitted in full to a closed circuit.

9. Write the purpose of Draft tube? (Nov/Dec 2004)

A draft tube serves the following two purposes:

1. It allows the turbine to be set above tail-water level, without loss of

head, to facilitate inspection and maintenance.

2. It regains, by diffuser action, the major portion of the kinetic energy

delivered to it from the runner

10. What is the Element of Hydel Power Plant?

Elements of Hydel Power Plant: (Nov/Dec 2009)

1. Water reservoir, 2. Dam, 3. Spillway,

4. Pressure tunnel,5. Penstock, 6. Surge tank,

7. Water turbine,8. Draft tube, 9. Tail race,

10. Step-up transformer,11. Power house.



11. Write the Advantages of Hydro-electric power plants?

1. Water is a renewable source of energy. Water which is the operating

fluid, is neither consumed nor converted into something else,

2. Water is the cheapest source of energy because it exists as a free gift of nature.

The fuels needed for the thermal, diesel and nuclear plants are exhaustible and

expensive.

3. There is no ash disposal problem as in the case of thermal power plant.

12. Define Governing Mechanism? (Nov/Dec 2006)

When the load on the turbine changes, the speed may also change. (i.e., without load

the speed increases and with over load, the speed decreases). Hence, the speed of the

runner must be maintained constant to have a constant speed of generator. This is

done by controlling the quantity of water flowing on the runner according to the load

variations. This speed regulation is known as governing and it is usually done

automatically by a governor.

13. Define Francis water turbine?

The modern Francis water turbine is an inward mixed flow reaction turbine. It

operates under medium heads and also requires medium quantity of water.

14. Write the advantages of small Hydro-power plant (SHP)?

a) Readily accessible source of renewable energy,

b) Can be installed making use of water head as low as 2 m and above,

c) Does not involve setting up of large dams,

d) Least polluting.

15. Differentiate propeller and Kaplan turbine?

In the propeller turbine the runner blades are fixed and non-adjustable. In Kaplan

turbine, which is a modification of propeller turbine the runner blades are adjustable and

can be rotated about the pivots fixed to the boss of the runner.



Part-B (16 Marks)

1. Write short notes

(a) Fission Energy (b) Chain Reaction (c) Fusion Energy (Nov/Dec 2014)

A nuclear power plant is similar to a conventional steam power plant except how

that energy is evolved. The heat is produced in the nuclear power plant by fission, whereas

in steam and gas turbine plants, the heat is produced by combustion in the furnace. The

nuclear reactor acts as a furnace where nuclear energy is evolved by splitting or fissioning

of the nucleus of fissionable material like Uranium U-235. It is claimed that 1 kg U-235

can produce as much heat energy that can be produced by burning 4500 tones of high grade

coal or 1700 tons of oil.

Fission energy

Figure: Nuclear fission

Nuclear energy is divided from splitting (or) fissioning of the nucleus of

fissionable material like Uranium U-235. Uranium has several isotopes (Isotopes are

atoms of the same element having different atomic masses) such as U-234, U-235 and U-

238. Of the several isotopes, U-235 is the most unstable isotope, which is easily fissionable

and hence used as fuel in an atomic reactor.

When a neutron enters the nucleus of an unstable U-235, the nucleus splits into two

equal fragments (Krypton and Barium) and also releases 2.5 fast moving neutrons with

a velocity of 1.5×107 m/sec and along with this produces a large amount of energy,

nearly 200 million electron- volts. This is called nuclear fission.



1. Chain reaction

The neutrons released during fission are very fast and can be made to initiate the

fission of other nuclei of U-235, thus causing a chain reaction.When a large number

of fission occurs, enormous amount of heat is generated, which is used to produce steam.

The chain reaction under controlled conditions can release extremely large amount

of energy causing “atomic explosion”

Energy released in chain reaction, according to Einstein law is

E = mc2

Where E = Energy liberated (J), m= Mass (kg),

c = Velocity of light (3 × 108 m/sec).

Out of 2.5 neutrons released in fission of each nucleus of U-235, one neutron is used

to sustain the chain reaction, about 0.9 neutron is captured by U-238, which gets converted

into fissionable material Pu-239 and about 0.6 neutron is partially absorbed by control rod

materials, coolant and moderator. If thorium is used in the reactor core, it gets converted to

fissionable material U-233. Thorium 232 + Neutron U-233 Pr-239 and U-233 so

produced are fissionable materials are called secondary fuels. They can be used as

nuclear fuels. U-238 and Th-232 are called fertile materials.

2. Fusion energy

Energy is produced in the sun and stars by continuous fusion reactions in which four

nuclei of hydrogen fuse in a series of reactions involving other particles that continually

appear and disappear in the course of the reaction, such as He3, nitrogen, carbon,

and other nuclei, but culminating in one nucleus of helium of two positrons.To cause

fusion, it is necessary to accelerate the positively charged unclei to high kinetic

energies, in order to overcome electrical repulsive forces, by raising their temperature to

hundreds of millions of degrees resulting in plasma. The plasma must be prevented

from contacting the walls of the container, and must be confined for a period of time (of

the order of a second) at a minimum density. Fusion reactions are called thermonuclear

because very high temperatures are required to trigger and sustain them. Table lists the

possible fusion reactions and the energies produced by them. n, p, D, and T are the

symbols for the neutron, proton, deuterium (H2), and tritium (H3), respectively.



2. Draw and explain the construction and working principle of Pressurized Water

Reactor (PWR)?

Pressurized Water Reactor (PWR): (Nov/Dec 2013)

Working principle:

A nuclear power plant differs from a conventional steam power plant only in the

steam generating part. There is no change in the turbo-alternator and the condensing

system.

The nuclear fuel which is at present in commercial use is Uranium. Heat energy

evolved by the fission reaction of one kg of U235 can produce as much energy as can be

produced by burning 4500 tons of high grade coal.

Uranium exists in the isotopic form of U235 which is unstable. When a neutron

enters the nucleus of U235, the nucleus splits into two equal fragments and also releases

2.5 fast moving neutrons with a velocity of 1.5 × 107 metres / sec producing a large

amount of energy, nearly 200 millions electron-volts. This is called “nuclear fission”.

Chain reaction

The neutrons released during the fission can be made to fission other nuclei of

U235 causing a “chain reaction. A chain reaction produces enormous amount of heat,

which is used to produce steam”.

The chain reaction under uncontrolled conditions can release extremely large

amounts of energy causing “atomic explosion”.

Figure: Nuclear fission.



Energy liberated in chain reaction, according to Einstein Law, is E = mc2, where E =

energy liberated, m = mass in grams, c = speed of light = 3 1010 cm/sec. Out of 2.5

neutrons released in fission of each nuclei of U235, one neutron is used to sustain the chain

reaction, 0.9 neutron is converted into fissionable material Pu239 and 0.6 neutron is

absorbed by control rod and coolant moderator.

Function of the moderator is to reduce the energy of neutrons evolved during fission

in order to maintain the chain reaction. The moderators which are commonly used

are ordinary water and heavy water.

Main components of nuclear power plants:

i) Moderators

In any chain reaction, the neutrons produced are fast moving neutrons. These

are less effective in causing fission of U235 and they try to escape from the reactor. It is

thus implicit that speed of these neutrons must be reduced if their effectiveness is carrying

out fission is to be increased. This is done by making these neutrons collide with lighter

nuclei of other materials, which does not absorb these neutrons but simply scatter

them. Each collision causes loss of energy and thus the speed of neutrons is reduced.

Such a material is called a ‘Moderator’. The neutrons thus slowed down are easily

captured by the fuel element at the chain reaction proceeds slowly.

ii) Reflectors

Some of the neutrons produced during fission will be partly absorbed by the fuel

elements, moderator, coolant and other materials.The remaining neutrons will try to

escape from the reactor and will be lost. Such losses are minimized by surrounding

(lining) the reactor core with a material called a reflector which will reflect the neutrons

back to the core. They improve the neutron economy. Economy: Graphite, Beryllium.

iii) Shielding

During Nuclear fission , , particles and neutrons are also produced. They

are harmful to human life. Therefore it is necessary to shield the reactor with thick layers

of lead, or concrete to protect both the operating personnel as well as environment from

radiation hazards.



iv) Cladding

In order to prevent the contamination of the coolant by fission products, the fuel

element is covered with a protective coating. This is known as cladding.

Control rods are used to control the reaction to prevent it from becoming violent.

They control the reaction by absorbing neutrons. These rods are made of boron

or cadmium. Whenever the reaction needs to be stopped, the rods are fully inserted and

placed against their seats and when the reaction is to be started the rods are pulled out.

v) Coolant

The main purpose of the coolant in the reactor is to transfer the heat produced inside

the reactor. The same heat carried by the coolant is used in the heat exchanger for further

utilization in the power generation.

Some of the desirable properties of good coolant are listed below

1. It must not absorb the neutrons.

2. It must have high chemical and radiation stability

3. It must be non-corrosive.

4. It must have high boiling point (if liquid) and low melting point (if solid)

5. It must be non-oxidising and non-toxic.

The above-mentioned properties are essential to keep the reactor core in safe

Condition as well as for the better functioning of the content.

6. It must also have high density, low viscosity, high conductivity and high

specific heat. These properties are essential for better heat transfer and low pumping

power.

The water, heavy water, gas (He, CO2), a metal in liquid form (Na) and an

organic liquid are used as coolants.

The coolant not only carries large amounts of heat from the core but also keeps

the fuel assemblies at a safe temperature to avoid their melting and destruction.



.

vi) Nuclear reactor

A nuclear reactor may be regarded as a substitute for the boiler fire box of a steam

power

plant. Heat is produced in the reactor due to nuclear fission of the fuel U235The heat

liberated in

the reactor is taken up by the coolant circulating through the core. Hot coolant leaves the

reactor at top and flows into the steam generator (boiler).

Radiation hazards and Shieldings

The reactor is a source of intense radioactivity. These radiations are very harmful to

human life. It requires strong control to ensure that this radioactivity is not released into

the atmosphere to avoid atmospheric pollution. A thick concrete shielding and a pressure

vessel are provided to prevent the escape of these radiations to atmosphere

Figure : Nuclear Power Plant (PWR)

vii) Steam generator

The steam generator is fed with feed water which is converted into steam by the

heat of the hot coolant. The purpose of the coolant is to transfer the heat generated in

the reactor core and use it for steam generation. Ordinary water or heavy water is a

common coolant.



viii) Turbine

The steam produced in the steam generator is passed to the turbine and work is

done by the expansion of steam in the turbine.

ix) Coolant pump and Feed pump

The steam from the turbine flows to the condenser where cooling water is

circulated. Coolant pump and feed pump are provided to maintain the flow of

coolant and feed water respectively.

3. Draw and explain construction and working principle of Boiling Water Reactor

(BWR)?(June 2012)

Figure shows a simplified BWR. Light water, which acts as the coolant and

moderator, passes through the core where boiling takes place in the upper part of the

core. The wet steam then passes through a bank of moisture separators and steam dryers

in the upper part of the pressure vessel. The water that is not vaporized to steam is

recirculated through the core with the entering feed water using two recirculation pumps

coupled to jet pumps (usually 10 to 12 per recirculation pump). The steam leaving the top

of the pressure vessel is at saturated conditions of7.2 MPa and 278C.

The steam then expands through a turbine coupled to an electrical generator.

Aftercondensing to liquid in the condenser, the liquid is returned to the reactors as

feedwater. Prior to entering the reactor, the feed water is preheated in several stages of

feedwater heaters.The balance of plant systems (Example: Turbine generator, feedwater

heaters) are similar for both PWR and BWRs.

The BWR reactor core, like that in a PWR, consists of a large number of fuel rods housed in

fuel assemblies in a nearly cylindrical arrangement. Each fuel assembly contains an 8×8

or 9×9 square array of 64 or 81 fuel rods (typically two of the fuel rods contain water rather

than fuel) surrounded by a square Zircaloy channel box to ensure no coolant crossflow in the

core. The fuel rods are similar to the PWR rods, although larger in diameter. Each fuel rod

is a zirconium alloy- clad tube containing pellets of slightly enriched uranium dioxide (2% to

5% U-235) stacked end-to- end.



Figure: Schematic for a boiling water reactor.

The reactor is controlled by control rods housed in a cross-shaped, or

cruciform, arrangement called a control element. The control elements enter from the

bottom of the reactor and move in spaces between the fuel assemblies.

The BWR reactor core is housed in a pressure vessel that is larger than that of a

PWR. A typical BWR pressure vessel, which also houses the reactor core, moisture

separators, and steam dryers, has a diameter of 6.4 m, with a height of 22 m.Since a

BWR operators at a nominal pressure of 6.9 MPa, its pressure vessel is thinner that that of

a PWR.

4. Draw and explain construction and working principle of Heavy Water

Cooled Reactor (HWR) (or) CANDU Type Reactor (CANDU – Canadium, Deutrium,

Uranium). (June 2012)

These reactors are more economically to those nations which do not produce enriched

uranium as the enrichment of uranium is very costly. In this type of reactors, the natural

uranium (0.7% U235) is used as fuel and heavy water as moderator.



This type of reactor was first designed and developed in Canada. The first

heavy water reactor in Canada using heavy water as coolant and moderator of 200 MW

capacity with 29.1% thermal efficiency was established at Douglas (Ontario known as

Douglas power station.The arrangement of the different components of CANDU type

reactor is shown in figure.

Figure: Douglas-point candu type heavy water moderated and cooled nuclear

reactor power plant

The coolant heavy water is passed through the fuel pressure tubes and heat-

exchanger. The heavy water is circulated in the primary circuit in the same way as with a

PWR and the steam is raised in the secondary circuit transferring the heat in the heat

exchanger to the ordinary water.

The control of the reactor is achieved by varying the moderator level in the reactor

and, therefore, control rods are not required.For rapid shutdown purpose, the

moderator can be dumped through a very large area into a tank provided below the reactor.



5. Draw and explain the Fast Breeder Reactor?

Figure shows a fast breeder reactor system. In this reactor the core containing

U235 in surrounded by a blanket (a layer of fertile material placed outside the core) of

fertile material U238. In this reactor no moderator is used. The fast moving neutrons

liberated due to fission of U235 are absorbed by U238 which gets converted into

fissionable material Pu239 which is capable of sustaining chain reaction. Thus this

reactor is important because it breeds fissionable material from fertile material U238

available in large quantities. Like sodium graphite nuclear reactor this reactor also uses

two liquid metal coolant circuits. Liquid sodium is used as primary coolant when

circulated through the tubes of intermediate heat exchange transfers its heat to secondary

coolant sodium potassium alloy. The secondary coolant while flowing through the tubes of

steam generator transfers its heat to feed water. Fast breeder reactors are better than

conventional reactors both from the point of view of safety and thermal efficiency. For

India which already is fast advancing towards self reliance in the field of nuclear power

technology, the fast breeder reactor becomes inescapable in view of the massive reserves

of thorium and the finite limits of its uraniumresources.The research and development

efforts in the fast breeder reactor technology will have to be stepped up considerably if

nuclear power generation is to make any impact on the country’s total energy needs in the

not too distant future.

Figure: Fast breeder reactor.



5. Draw the Layout diagram of Hydro Power Plant and also explain the

components and working of Hydro power plant? (Nov/Dec 2012)

Introduction

Hydro-electric power plant utilizes the potential energy of water stored in a

dam built across the river. The potential energy of water is used to run water turbine to

which the electric generator is coupled. The mechanical energy available at the shaft of the

turbine is converted into electrical energy means of the generator.

ELEMENTS OF HYDEL POWER PLANT

The schematic representation of a hydro-electric power plant is shown in figure.

i) Water reservoir

Continuous availability of water is the basic necessity for a hydro-electric

plant.Water collected from catchment area during rainy season is stored in the reservoir.

Water surface in the storage reservoir us known as head race.

ii) Dam

The function of a dam is to increase the height of water level behind it which

ultimately increases the reservoir capacity. The dam also helps to increase the working

heat of the power plant.

Figure: Layout of hydro-electric power plant.



iii) Spillway

Water after a certain level in the reservoir overflows through spillway without

allowing the increase in water level in the reservoir during rainy season

v) Pressure tunnel

It carries water from the reservoir to surge tank.

v) Penstock

Water from surge tank is taken to the turbine by means of penstocks, made up of

reinforced concrete pipes or steel.

vi) Surge tank

There is sudden increase of pressure in the penstock due to sudden backflow of

water, as load on the turbine is reduced. The sudden rise of pressure in the penstock is

known as water hammer. The surge tank is introduced between the dam and the

power house to keep in reducing the sudden rise of pressure in the penstock. Otherwise

penstock will be damaged by the water hammer.

vii) Water turbine

Water through the penstock enters into the turbine through and inlet valve. Prime

movers which are in common use are Pelton turbine, Francis turbine and Kaplan turbine.

The potential energy of water entering the turbine is converted into mechanical energy.

The mechanical energy available at the turbine shaft is used to run the electric generator.

The water is then discharged through the draft tube.

viii) Draft tube

It is connected to the outlet of the turbine. It allows the turbine to be placed over

tail race level.

ix) Tail race

Tail race is a water way to lead the water discharged from the turbine to the

river. The water held in the tail race is called tail race water level.

x) Step-up transformer

Its function is to raise the voltage generated at the generator terminating

before transmitting the power to consumers.



xi) Power house

The power house accommodates the turbine, generator, transformer and control

room.

Classification of Hydro-Power plants

Hydro-plants are classified according to the head of water under which they work.

When the operating head of water exceeds 70 metres, the plant is known as “high

head power plant”. Pelton turbine is used as prime mover in such power plants. When the

head of water ranges from 15 to 70 metres then the power plant is known as “medium

head plant”. It uses Francis turbine. When the head is less than 15 metres the plant is

named as “low head plant”.It uses Francis or Kaplan turbine as prime mover.

6. Draw and Explain Pelton wheel?

Pelton Wheel

This is a commonly used impulse type of turbine. It is named after an American

engineer Lester. A. Pelton (1829-1908), who developed this turbine. The Pelton wheel is

suitable for very high heads and it requires a lesser quantity of water. A pelton wheel is shown in figure. It consists of a runner, buckets, a nozzle, a guide mechanism, a hydraulic brake and casing.

Figure: Peloton wheel Runner and Buckets



The runner is a circular disc. It consists of a number of semi-ellipsoidal buckets

evenly spaced around its periphery. The buckets are divided into two hemi-spherical cups

by a sharp- edged ridge known as a splitter.

This arrangement avoids the axial thrust and end thrust on bearings. (The axial

thrusts being equal and opposite, neutralize each other).Generally, the buckets are

bolted to the periphery of the runner.

In some cases, to the periphery of the runner. In some cases, the buckets and the

wheel are cast integral as one piece. In the case of the bolted type, broken or damaged

buckets can be replaced economically. For low heads, the bucket is made of case

iron and for high heads, they are made of bronze or stainless steel to withstand heavy

impact.

Nozzle and Guide mechanism:

A nozzle is fitted to the end of the penstock near the turbine. The nozzle is provided

with a conical needle or spear to regulate the quantity of water coming out of the nozzle,

thereby control the speed of the runner. The spear may be operated manually by a hand

wheel (for small units) or automatically by a governing mechanism (for larger units).

Figure: Bucket of pelton wheel.

Hydraulic brake:

When the turbine has to be brought to rest by closing the inlet valve of the turbine,

the runner generally takes a very long time to come to rest due to its inertia. To

bring it to rest quickly, a small brake nozzle is provided. This nozzle is opened and it

directs a jet of water at the back of the buckets. This acts as a brake to bring revolving

runner quickly to rest.



Casing

The casing is made up of cast-Iron or fabricated steel plates. It is provided for the

following purposes:

1. To prevent splashing of water,

2. To lead the water to the tail race and

3. To act as a safeguard (cover) against any accidents.

Working principle

The water is conveyed to the power house from the head race through

penstocks. The nozzle is fitted to the end of the penstock (power house end) delivers a high

velocity water jet into the bucket. One or more jets of water are arranged to impinge on the

buckets tangentially. The impact of water jet on the bucket causes the wheel to rotate, thus

producing mechanical work. An electric generator is coupled to the runner shaft and

mechanical energy is converted into electrical power.

After leaving the turbine wheel, water falls into the tail race. The Pelton wheel is

located above the tail race so that, the buckets do not splash the tail race water.



UNIT IV DIESEL AND GASTURBINEPOWERPLANT

Part-A (2 Marks)

1. What is the essential component of diesel power plants? (Nov/Dec 2012)

Essential components of a diesel power plant are:

(i) Engine (ii)Air intake system

(iii)Exhaust system (iv)Fuel system

(v) Cooling system (vi) Lubrication system

(vii) Engine starting system (viii) Governing system.

2. List the various Liquid Cooling Systems?

In liquid cooling following methods are used for circulating the water around the

cylinder and cylinder head:

(i) Thermo-system cooling

(ii) Forced or pump cooling

(iii) Cooling with thermostatic regulator

(iv) Pressurized cooling

(v) Evaporative cooling.

3. What is the purpose of super charging? (Nov/Dec 2008)

The purpose of supercharging is to raise the volumetric efficiency above that value

which can be obtained by normal aspiration.

4. Define Flywheel?

It is a heavy wheel mounted on the crankshaft. It stores the excess energy delivered

by the engine during power stroke and supplies the energy needed during other strokes.

Thus it keeps the fluctuations in the crankshaft speed within desired limits.

5. Write the Disadvantages of over cooling of the Engine?

1) Engine starting is difficult,

2) Over-cooling reduces the overall efficiency of the system,

3) At low temperatures, corrosion assumes considerable magnitude that it may reduce the

life of various components.



6. Write the function of Lubrication? (Nov/Dec 2007)

a. To reduce the wear and tear between the moving parts and thereby

increasing the life of the engine.

b. The lubricating oil acts as a seal, i.e., it prevents the high pressure gases

in thecombustion chamber from entering the crankcase

c. To cool the surfaces.

7. What are the classifications of Lubrication system?

Classification of Lubrication System:

Some of the lubricating systems used for IC engines are:

i) Wet sump lubricating system,

ii) ii) Mist lubricating system.

Wet sump lubricating system can be further classified as,

i) Splash type lubricating system,

ii) Pressure feed lubricating system.

8. Define – open cycle gas turbine? (Nov/Dec 2004)

In the open cycle gas turbine, air is drawn into the compressor from atmosphere and

is compressed. The compressed air is heated by directly burning the fuel in the air at

constant pressure in the combustion chamber. Then the high pressure hot gases expand in

the turbine and mechanical power is developed.

9. Define – closed cycle gas turbine?

In this, the compressed air from the compressor is heated in a heat exchange (air




compressor again.

10. Write the few fuels for Gas turbine and why these fuels are use for gas turbine?

Natural gas, last furnace gas, produce gas, coal gas and solid fuels distillate

oils and residual oils paraffins used in gas turbine and methane, ethane, propane,

octane.



Important properties to be considered while selecting the fuel for gas turbine are as

follows:

1) Volatility 2) Combustion products,

3) Energy contents, 4) Lubricating properties, 5) Availability.

11. Write the major field of application of gas turbines?

The major fields of application of gas turbines are:

i) Aviation

ii) Power generation

iii) Oil and gas industry

iv) Marine propulsion.

12. Define Gas turbine plant and write the working medium of this gas turbine?

A gas turbine plant may be defined as one “in which the principal prime-mover is of

the turbine type and the working medium is a permanent gas”.

13. What are the components of gas turbine plant? (Nov/Dec 2004)

A simple gas turbine plant consists of the following:

i) Turbine ii) Compressor iii) Combustor iv) Auxiliaries

.A modified plant may have in addition and intercooler, a regenerator, a repeater etc.

14. What are the methods to improving the thermal efficiency in open cycle gas turbine

plant?

Methods for improvement of thermal efficiency of open cycle gas turbine plant are :

i) Inter cooling

ii) Reheating

iii) Regeneration



15. Define turbo charging in combined gas turbine and diesel cycles?

In the combined cycle, the exhaust gas from the diesel engine is expanded in

the turbine, which is coupled with compressor which supplies pressurized air to the diesel

engine. This increases diesel engine output. This arrangement is known as turbo charging.

PART – B

1. Explain the working of gas turbine cycle with regenerator. (Nov/Dec 2011)

In earlier discussion it is seen that for the maximization of specific work output the

gas turbine exhaust temperature should be equal to compressor exhaust temperature. The

turbine exhaust temperature is normally much above the ambient temperature.

Thus their exist potential for tapping the heat energy getting lost to surroundings

with exhaust gases. Here it is devised to use this potential by means of a heat exchanger

called regenerator, which shall preheat the air leaving compressor before entering the

combustion chamber, thereby reducing the amount of fuel to be burnt inside combustion

chamber (combustor).

Regenerative air standard gas turbine cycles shown ahead in figure (a) has a

regenerator (counter flow heat exchanger) through which the hot turbine exhaust gas

and comparatively cooler air coming from compressor flow in opposite directions.

Under ideal conditions, no frictional pressure drop occurs in either fluid stream

while turbine exhaust gas gets cooled from 4 to 4’ while compressed air is heated from 2 to

2’. Assuming regenerator effectiveness as 100% the temperature rise from 2 – 2’ and drop

from 4 to 4’ is shown on T-S diagram.

This shows an obvious improvement in cycle thermal efficiency as every thing else

remains same. Network produced per unit mass flow is not altered by the use of

regenerator.



Figure: Regenerative air standard gas turbine cycle.

3. Explain the working of gas turbine cycle with inter cooling.

Net work output from gas turbine cycle can also be increased by reducing

negative work i.e., compressor work. Multistage of compression process with intercooling

in between is one of the approaches for reducing compression work. It is based on the fact

that for a fixed compression ratio is higher is the inlet temperature higher shall be

compression work requirement and vice- versa. Schematic for inter cooled gas turbine

cycle is give in figure.

Thermodynamic processes involved in multistage inter cooled compression are

shown in figure. First stage compression occurs in low pressure compressor (LPC)

and compressed air leaving LPC at ‘2’ is sent to intercooler where temperature of

compressed air is lowered down to state 3 at constant pressure.

In case of perfect intercooling the temperature after intercooling is brought down

to ambient temperature i.e., temperature at 3 and 1 are same. Intercooler is a kind of heat

exchanger where heat is picked up from high temperature compressed air. The amount of

compression work saved due to intercooling is obvious from p-V diagram and shown

by area 2342’. Area 2342’ gives the amount of work saved due to intercooling between

compressions.



Figure: Gas turbine cycle with intercooling

Figure : Intercooled compression

Some large compressors have several stages of compression with intercooling

between stages. Use of multistage compression with intercooling in a gas turbine power

plant increases the network produced because of reduction in compressor work. Inter

cooled compression results in reduced temperature at the end of final compression.

T-S diagram for gas turbine cycle with intercooling shows that in the absence of

intercooling within same pressure limits the state at the end of compression would be 2’

while with perfect intercooling this state is at 4 i.e., T2’ > T4. The reduced temperature

at compressor exits leads to additional heat requirement in combustion chamber i.e., more

amount of fuel is to be burnt for attaining certain inlet temperature as compared to

simple cycle without intercooling.



Figure: T-S diagram for gas turbine cycle with intercooling

Thus intercooled cycle thermal efficiency may not increase with intercooling because

of simultaneous increase in heat addition requirement.

The lower temperature at compressor exit enhances the potential for regeneration so

when intercooling is used in conjunction with regeneration an appreciable increase in

thermal efficiency can result.

Net work output in gas turbine cycle with intercooling;

Wnet, intercool = m{(h5 – h6) – (h4 – h3) – (h2 – h1)}

Wnet, intercool = m cp {(T5 – T6) – (T4 – T3) – (T2 – T1)}

4. Draw and Explain the construction and working principle of Open cycle gas

turbine power plant? (Apr 2011)

In the open cycle gas turbine, air is drawn into the compressor from atmosphere and

is compressed. The compressed air is heated by directly burning the fuel in the air at

constant pressure in the combustion chamber. Then the high pressure hot gases expand in

the turbine and mechanical power is developed.

Part of the power developed by the turbine (about 66%) is used for driving the

compressor. The remaining is available as useful output. The working fluid, air and

fuel, must be replaced continuously as they are exhausted into the atmosphere. Thus the

entire flow comes from the atmosphere and is returned to the atmosphere.



LAYOUT OF GAS TURBINE POWER PLANT

The gas turbine power plants which are used in electric power industry are classified

into two groups as per the cycle of operation.

(1) Open cycle gas turbine. (2) Closed cycle gas turbine.

1. Open cycle gas turbine

1- Atmospheric Air



4- Exhaust gases.

The heated gases coming out of combustion chamber are then passed to the turbine

where it expands doing mechanical work. Part of the power developed by the turbine is

utilized in driving the compressor and other accessories and remaining is used for power

generation.

Since ambient air enters into the compressor and gases coming out of turbine are

exhausted into the atmosphere, the working medium must be replaced continuously. This

type of cycle is known as open cycle gas turbine plant and is mainly used in majority of gas

turbine power plants as it has many inherent advantages.



5. Draw and explain the construction and working principle of closed cycle gas

turbine power plant? (Apr 2011)

In this, the compressed air from the compressor is heated in a heat exchanger (air




compressor again.

The main difference between the open and closed cycles is that the working fluid is

continuously replaced in open cycle whereas it is used again and again in a closed cycle.

The open cycle plant is much lighter than the closed cycle. Hence it is widely used.

Closed cycle gas turbine







In closed cycle gas turbine plant, the working fluid (air or any other suitable gas)

coming out from compressor is heated in a heater by an external source at constant

pressure.

The high temperature and high-pressure air coming out from the external heater is

passed through the gas turbine. The fluid coming out from the turbine is cooled to its

original temperature in the cooler using external cooling source before passing to the

compressor.The working fluid is continuously used in the system without its change of

phase and the required heat is given to the working fluid in the heat exchanger

6. Draw and explain the construction and working principle of layout of diesel power

plant: (May 2008)

Figure shows the arrangements of the engine and its auxiliaries in a diesel power

plant.



The major components of the diesel power plant are:

1) Engine

Engine is the heart of a diesel power plant. Engine is directly connected through a gear box

to the generator. Generally two-stroke engines are used for power generation. Now a days,

advanced super & turbo charged high speed engines are available for power production.

2) Air supply system

Air inlet is arranged outside the engine room. Air from the atmosphere is filtered by

air filter and conveyed to the inlet manifold of engine. In large plants

supercharger/turbocharger is used for increasing the pressure of input air which increases

the power output.

3) Exhaust System

This includes the silencers and connecting ducts. The heat content of the exhaust gas is

utilized in a turbine in a turbocharger to compress the air input to the engine.

4) Fuel System

Fuel is stored in a tank from where it flows to the fuel pump through a filter. Fuel is

injected to the engine as per the load requirement.

5) Cooling system

This system includes water circulating pumps, cooling towers, water filter etc. Cooling

water is circulated through the engine block to keep the temperature of the engine in the

safe range.

6) Lubricating system

Lubrication system includes the air pumps, oil tanks, filters, coolers and pipe lines.

Lubricant is given to reduce friction of moving parts and reduce the wear and tear of the

engine parts.

7) Starting System

There are three commonly used starting systems, they are;

1) A petrol driven auxiliary engine

2) Use of electric motors.

3) Use of compressed air from an air compressor at a pressure of 20 Kg/cm.



UNIT V OTHER POWERPLANTS AND ECONOMICS OF POWERPLANTS`

Part-A(2 Marks)

1. List the non – conventional energy sources?

The various non-conventional energy sources are as follows:

Ocean thermal energy conversion

Tidal energy

Geothermal energy

Hydrogen energy

Fuel cells

Magneto-hydrodynamics generator

Thermionic converter

Thermo-electric power.

2. Write the advantages of non – conventional Energy sources? Advantages of non-

conventional energy sources:

The leading advantages of non-conventional energy sources are:

1. They do not pollute the atmosphere

2. They are available in large quantities.

3. They are well suited for decentralized use.

3. Write the characteristic’s of wind energy?

1. Wind-power systems do not pollute the atmosphere.

2. Fuel provision and transport are not required in wind-power systems.

3. Wind energy is a renewable source of energy.

4. Wind energy when produced on small scale is cheaper, but competitive with

conventional power generating systems when produced on a large scale.

Wind energy entails following short comings/problems:

1. It is fluctuating in nature.

2. Due to its irregularity it needs storage devices.

3. Wind power generating systems produce ample noise.



4. What are the advantages and limitation of Tidal power generation?

Advantages:

1. Tidal power is completely independent of the precipitation (rain) and its

uncertainty besides being inexhaustible.

2. Large area of valuable land is not required.

3. When a tidal power plant works in combination with thermal or hydro-electric

system peak power demand can be effectively met with.

4. Tidal power generation is free from pollution.

Limitations:

1. Due to variation in tidal range the output is not uniform.

2. Since the turbines have to work on a wide range of head variation (due to

variable tidal range) the plant efficiency is affected.

3. There is a fear of machinery being corroded due to corrosive sea water.

4. It is difficult to carry out construction in sea.

5. As compared to other sources of energy, the tidal power plant is costly.

6. Sedimentation and silteration of basins are the problems associated with tidal power

plants.

7. The power transmission cost is high because the tidal power plants are located

away from load centers.

5. Write the advantages of MHD systems? (Nov/Dec 2011)

1. More reliable since there are no moving parts.

2. In MHD system the efficiency can be about 50% (still higher expected) as

compared to less than 40% for most efficient steam plants.

3. Power produced is free of pollution.

4. As soon as it is started it can reach the full power level.

5. The size of plant is considerably smaller than conventional fossil fuel plants.

6. Less overall operational cost.

7. The capital cost of MHD plants is comparable to those of conventional steam plants.


9. Suitable for peak power generation and emergency service.



6. Write the advantages of OTEC? (May 2011)

1. Ocean is an infinite heat reservoir which receives solar incidence throughout the

year.

2. Energy is freely available

Write the disadvantages of OTEC? (May 2010)

1. Efficiency is very low, about 2.5%, as compared to 30 - 40% efficiency for

conventional power plants.

2. Capital cost is very high

7. Define – Tidal power plant?

The tidal power plants are generally classified on the basis of the number of basins

used for power generations. They are further subdivided as one-way or two-way system as

per the cycle of operation for power generation.

8. Write the application of geothermal energy? (Nov/Dec 2013)

The following are the three main applications of the steam and hot water from

the wet geothermal reservoirs:

1. Generation of electric power.

2. Space heating for buildings.

3. Industrial process heat.

The major benefit of geothermal energy is its varied application and versatility.

9. What are the Advantages and disadvantages of Geothermal Energy over

other Energy forms?

Advantages of geothermal process:

1. Geothermal energy is cheaper.

2. It is versatile in its use.

3. It is the least polluting as compared to other conventional energy sources.

4. It is amenable for multiple uses from a single resources

5. Geothermal power plants have the highest annual load factors of 85 percent to 90

per cent compared to 45 per cent to 50 per cent for fossil fuel plants.

6. It delivers greater amount of net energy from its system as compared to other

alternative or conventional systems.



Disadvantages:

1. Low overall power production efficiency (about 15% as compared to 35% to 40%

for fossil fuel plants).

2. Drilling operation is noisy.

3. Large areas are needed for exploitation of geo-thermal energy.

4. The withdrawal of large amounts of steam or water from a hydro-thermal

reservoir may result in surface subsidence or settlement.

10. Define demand factor?

Demand factor is defined as the ratio of maximum demand to connected load.

Connected load is the sum of ratings in kW of equipment installed in the

consumer's premises.

Maximum demand is the maximum load, which a consumer uses at any time.

11. Define load curve? (Nov/Dec 2011)

Load curve is a graphical representation between load in kW and time in hours. It.

shows variati6n of load at the power station. The area under the load curve -represents the

energy generated in a particular period.

12. Define load factor? (May 2013)

Load factor is defined as the ratio of average load to the peak load (or) maximum

demand.

13. What includes fixed cost? (May2012)

Fixed cost includes the following cost.

1. Cost of land 2. Cost of building

3. Cost of equipment 4. Cost of installati6n

5. Interest 6. Depreciation cost

7. Insurance 8. Management cost



14. What includes operating cost?

Operating cost includes the following cost.

1. Cost of fuel 2. Cost of operating labour,

3. Cost of maintenance labours and materials.

4. Cost of supplier like

Water for feeding boilers, for condenser and for general use.

Lubrication oil and, grease.

Water treatment chemicals.

15. What is the need of depreciation cost?

Depreciation cost is the amount to be set aside per year from the income of the plant

to meet the depreciation caused by the age of service, wear and tear of the machinery and

equipments. Depreciation amount collected every year helps in replacing and repairing the

equipment.

Part-B (16 Marks)

1. Explain the construction and working principle of solar power plant? (May 2013)

Figure shows a solar power plant with a low temperature solar engine using heated

water from flat plate solar collector and Butane as the working fluid. This was developed

to lift water for irrigation purposes. In a flat plate collector (figure), the radiation energy of

the sun falls on a flat surface coated with black paint having high absorbing capacity.

It is placed facing the general direction of the sun. The materials used for the plate

may be copper, steel aluminium. The thickness of the plate is 1 to 2 mm. Tubing of

copper is provided in thermal contact with the plate. Heat is transferred from the absorbed

plate to water which is circulated in the copper tubes through the flat plate collection.

Thermal insulation is provided behind the absorber plate to prevent heat losses from the

rear surface. Insulating material is generally fiber glass or mineral wool. The front cover is

made up of glass and it is transparent to the incoming solar radiations.



Figure : Solar power plant

SOLAR COLLECTORS

a) Flat plate collector

Figure: Flat plate collector Figure: Cylindrical parabolic concentrator

collector



b) Cylindrical parabolic concentrator collector

Concentrator collectors (figure) are of reflecting type utilizing mirrors.The

reflecting surface may be parabolic mirror. The solar energy falling on the collector surface

is reflected and focused along a line where the absorber tube is located. As large quantity

of energy falling on the collector surface is collected over a small surface, the temperature

of the absorber fluid is very much higher than in flat plate collector.

While flat place collectors may be used to heat water upto 80C (low temperature),

the concentrating type of collectors are designed to heat water to medium and high

temperature ranges.

c) Butane boiler

The water heated in flat plate solar collector to 80C is used for boiling butane at

high pressure in the butane boiler. Boiling point of butane is about 50C.

d) Turbine

The butane vapour generated at high pressure in the boiler is used to run the

vapour turbine which drives the electrical generator.

The vapour coming out of the turbine at low pressure is condensed in a condenser

using water. The condensed liquid butane is fed back to the butane boiler using feed pump.

Tower concept for power generation

The tower concept consists of an array of plane mirrors or heliostats which are

individually controlled to reflect radiations from the sun into a boiler mounted on a 500

meters high tower. Steam in generated in the boiler, which may attain a temperature

upto 2000K. Electricity is generated by passing steam through the turbine coupled to a

generator.

Figure: Tower concept for power generation.



2. Draw and Explain two basic design of OCEAN THERMAL ENERGY

CONVERSION (OTEC) (OR) Draw and Explain the

(1) Open cycle (or) Claude cycle.

(2) Closed cycle (or) Anderson cycle.

The ocean and seas constitute about 70% of the earth’s surface area and

hence they represent a large storage reservoir of the solar energy. In tropical

waters, the surface water temperature is about 27C and at 1 km directly below, the

temperature is about 4C. The reservoir of surface water may be considered a heat source

and the reservoir of cold water (1 km below) is considered a heat sink. The concept of

ocean thermal energy conversion is based on the utilization of temperature difference

between the heat source and the sink in a heat engine to generate power.

The temperature gradient present in the ocean is utilized in a heat engine to

generate power. This is called OTEC. Since the temperature gradient is very small, even

in the tropical region, OTEC systems have very low efficiencies and very high capital costs.

There are two basic designs for OTEC systems.

1. Open cycle or Claude cycle.

2. Closed cycle or Anderson cycle.

Open cycle or Claude cycle

In this cycle, the seawater plays a multiple role of a heat source, working fluid,

coolant and heat sink. Warm surface water enters an evaporator where the water is flash

evaporated to steam under particle vacuum. Low pressure is maintained in the evaporator

by a vacuum pump. The low pressure so maintained removes the non-condensable gases

from the evaporator.

The steam and water mixture from evaporator then enters a turbine, driving it

thus generating electricity. The exhaust from the turbine is mixed with cold water

from deep ocean in a direct contact condenser and is discharged to the ocean. The

cycle is then repeated. Since the condensate is discharged to the ocean, the cycle is

called ‘open’.



Flash evaporation

In the evaporator the pressure is maintained at a value (0.0317 bar) slightly lower

than the saturation pressure of warm surface water at 27C (0.0356 bar). Hence, when the

surface water enters the evaporator, it gets ‘superheated’. This super heated water

undergoes “volume boiling” causing the water to partially flash to steam.

Figure: TEC open cycle. Closed OTEC

Here, a separate working fluid such as ammonia, propane or Freon is used in

addition to water. The warm surface water is pumped to a boiler by a pump.

This warm water gives up its heat to the secondary working fluid thereby losing

its energy and is discharged back to the surface of the ocean. The vapors of the secondary

working fluid generated in the boiler, drive a turbine generating power. The exhaust from

the turbine is cooled in a surface condenser by using cold deep seawater, and is then

circulated back to the boiler by a pump.

Figure: OTEC – closed cycle



Advantages of OTEC

1. Ocean is an infinite heat reservoir which receives solar incidence throughout the

year.

2. Energy is freely available.

Disadvantage of OTEC

1. Efficiency is very low, about 2.5%, as compared to 30-40% efficiency for

conventional power plants.

2. Capital cost is very high.

2. Explain the construction and working principle of Tidal power plants? (Dec 2005)

Principle

Tide or wave is periodic rise and fall of water level of the sea.Tides occur due

to the attraction of sea water by the moon. Tides contain large amount of potential energy

which is used for power generation. When the water is above the mean sea level, it is

called flood tide. When the water level is below the mean level it is called ebb tide.

Working

The arrangement of this system is shown in figure. The ocean tides rise and fall and

water can be stored during the rise period and it can be discharged during fall.

A dam is constructed separating the tidal basin from the sea and a difference in

water level is obtained between the basin and sea. During high tide period, water flows

from the sea into the tidal basin through the water turbine.The height of tide is above that

of tidal basin.Hence the turbine unit operates and generates power, as it is directly

coupled to a generator.

During low tide period, water flows from tidal basin to sea, as the water level in the

basin is more than that of the tide in the sea. During this period also, the flowing water

rotates the turbine and generator power.



Figure: High tide

Figure: Low tide

The generation of power stops only when the sea level and the tidal basin level are

equal. For the generation of power economically using this source of energy requires

some minimum tide height and suitable site. Kislaya power plant of 250 MW capacity in

Russia and Rance power plant in France are the only examples of this type of power plant.

Advantages of tidal power plants.

1. It is free from pollution as it does not use any fuel.

2. It is superior to hydro-power plant as it is totally independent of rain.

3. It improves the possibility of fish farming in the tidal basins and it can provide

recreational to visitors and holiday makers.



Disadvantages

1. Tidal power plants can be developed only if natural sites are available on

the bay.

2. As the sites are available on the bays which are always far away from load

centres, the power generated has to be transmitted to long distances. This increases

the transmission cost and transmission losses.

4. Draw and Explain the working of 5 – different tidal power plants? (Nov/Dec 2011)

The tidal power plants are generally classified on the basis of the number of basins

used for the power generation. They are further subdivided as one-way or two-way

system as per the cycle of operation for power generation.

The classification is represented with the help of a line diagram as given below.

Working of different tidal power plants

1. Single basin-one-way cycle

This is the simplest form of tidal power plant. In this system a basin is allowed to

get filled during flood tide and during the ebb tide, the water flows from the basin to the sea

passing through the turbine and generates power. The power is available for a short

duration ebb tide.



Figure: (a) Tidal region before construction of the power plant and tidal variation

Figure: (b) Single basin, one –way tidal power plant

Figure (a) shows a single tide basin before the construction, of dam and

figure (b) shows the diagrammatic representation of a dam at the mouth of the basin and

power generating during the falling tide.

2. Single-basin two-way cycle

In this arrangement, power is generated both during flood tide as well as ebb tide

also. The power generation is also intermittent but generation period is increased compared

with one-way cycle. However, the peak obtained is less than the one-way cycle. The

arrangement of the basin and the power cycle is shown in figure.

Figure: Single –basin two-way tidal power plant



The main difficulty with this arrangement, the same turbine must be used as prime

mover as ebb and tide flows pass through the turbine in opposite directions. Variable pitch

turbine and dual rotation generator are used of such scheme.

3. Single – basin two-way cycle with pump storage

In this system, power is generated both during flood and ebb tides. Complex

machines capable of generating power and pumping the water in either directions are used.

A part of the energy produced is used for introducing the difference in the water levels

between the basin and sea at any time of the tide and this is done by pumping water into the

basin up or down. The period of power production with this system is much longer than

the other two described earlier. The cycle of operation is shown in figure.

Figure: Single-basin, two-way tidal plant coupled with pump storage system.

4. Double basin type

In this arrangement, the turbine is set up between the basins as shown in figure.

One basin is intermittently filled tide and other is intermittently drained by the ebb tide.

Therefore, a small capacity but continuous power is made available with this system as

shown in figure. The main disadvantages of this system are that 50% of the potential

energy is sacrificed in introducing the variation in the water levels of the two basins.

Figure: Double basin, one-way tidal plant.



Double basin with pumping

In this case, off peak power from the base load plant in a interconnected

transmission system is used either to pump the water up the high basin. Net energy gain is

possible with such a system if the pumping head is lower than the basin-to-basin turbine

generating head.

5. Explain the geothermal power plant?

It is also a thermal power plant, but the steam required for power generation is

available naturally in some part of the earth below the earth surface. According to

various theories earth has a molten core. The fact that volcanic action taken place in many

places on the surface of earth supports these theories.

Steam well

Pipes are embedded at places of fresh volcanic action called steam wells, where the

molten internal mass of earth vents to the atmospheric with very high temperatures. By

sending water through embedded pipes, steam is raised from the underground steam

storage wells to the ground level.

Separator

The steam is then passed through the separator where most of the dirt and sand

carried by the steam are removed.

Figure: Geo-thermal power plant



Turbine

The steam from the separator is passed through steam drum and is used to run the

turbine which in turn drives the generator.The exhaust steam from the turbine is

condensed.The condensate is pumped into the earth to absorb the ground heat again and to

get converted into steam.

Location of the plant, installation of equipment like control unit etc., within the

source of heat and the cost of drilling deep wells as deep as 15,000 metres are some of the

difficulties commonly encountered.

6. Explain the load duration curve (Nov/Dec 2012)

The load demand on a power system is governed by the consumers and for a

system supplying industrial and domestic consumers, it varies within wide limits. This

variation of load can be considered as daily, weekly, monthly or yearly. Such load curves

are termed as “Chronological load Curves”. If the ordinates of the chronological load

curves are arranged in the descending order of magnitude with the highest ordinates on left,

a new type of load curve known as “load duration curve” is obtained. If any point is taken

on this curve then the abscissa of this point will show the number of hours per year during

which the load exceeds the value denoted by its ordinate. The lower part of the curve

consisting of the loads which are to be supplied for almost the whole number of hours in a

year, represents the “Base Load”, while the upperpart, comprising loads which are required

for relatively few hours per year, represents the “Peak Load”.

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