ee2252-power plant engineering

PRCET/EEE/IV SEMESTER/EE2252-POWER PLANT ENGINEERING/NOTES

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DEPARTMENT OF EEE

II YEAR / IV SEMESTER

EE2252- POWER PLANT ENGINEERING

e-Content

PONNAIYAH RAMAJAYAM COLLEGE

OF ENGINEERING & TECHNOLOGY Thanjavur – 613403


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EE2252 POWER PLANT ENGINEERING L T P C

3 1 0 4 AIM: Expose the students to basics of various power plants so that they will have the comprehensive idea of power system operation. OBJECTIVE: To become familiar with operation of various power plants. UNIT I - THERMAL POWER PLANTS Basic thermodynamic cycles, various components of steam power plant-layout-pulverized coal burners- Fluidized bed combustion-coal handling systems-ash handling systems- Forced draft and induced draft fans- Boilers-feed pumps-super heater- regenerator-condenser- dearearators-cooling tower UNIT II - HYDRO ELECTRIC POWER PLANTS Layout-dams-selection of water turbines-types-pumped storage hydel plants UNIT III - NUCLEAR POWER PLANTS Principles of nuclear energy- Fission reactions-nuclear reactor-nuclear power plants UNIT IV - GAS AND DIESEL POWER PLANTS Types, open and closed cycle gas turbine, work output & thermal efficiency, methods to improve performance-reheating, intercoolings, regeneration-advantage and disadvantages- Diesel engine power plant-component and layout UNIT V NON-CONVENTIONAL POWER GENERATION Solar energy collectors, OTEC, wind power plants, tidal power plants and geothermal resources, fuel cell, MHD power generation-principle, thermoelectric power generation, thermionic power generation L = 45 T = 15 TOTAL = 60 PERIODS TEXT BOOKS 1. A Course in Power Plant Engineering by Arora and Domkundwar, Dhanpat Rai and Co. Pvt. Ltd., New Delhi. 2. Power Plant Engineering by P.K. Nag, Tata McGraw Hill, Second Edition , Fourth reprint 2003. REFERENCES 1.Power station Engineering and Economy by Bernhardt G.A.Skrotzki and William A.Vopat- Tata McGraw Hill Publishing Company Ltd., New Delhi, 20th reprint 2002. 2. An introduction to power plant technology by G.D. Rai-Khanna Publishers, Delhi- 110 005. 3. Power Plant Technology, M.M. El-Wakil McGraw Hill 1984.


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UNIT I - THERMAL POWER PLANTS

INTRODUCTION :

In this lesson a brief idea of a modern power system is outlined. As consumers, we

use electricity for various purposes such as:

1. Lighting, heating, cooling and other domestic electrical appliances used in home.

2. Street lighting, flood lighting of sporting arena, office building lighting, powering PCs

etc.

3. Irrigating vast agricultural lands using pumps and operating cold storages for various

agricultural products.

4. Running motors, furnaces of various kinds, in industries.

5. Running locomotives (electric trains) of railways. BASIC IDEA OF POWER GENERATION:

Prior to the discovery of Faraday‟s Laws of electromagnetic discussion, electrical power

was available from batteries with limited voltage and current levels. Although complicated in

construction, D.C generators were developed first to generate power in bulk. However, due to

limitation of the D.C machine to generate voltage beyond few hundred volts, it was not

economical to transmit large amount of power over a long distance. For a given amount of

power, the current magnitude (I = P/V), hence section of the copper conductor will be large.

Thus generation, transmission and distribution of d.c power were restricted to area of few

kilometer radius with no interconnections between generating plants. Therefore, area specific

generating stations along with its distribution networks had to be used.

CHANGEOVER FROM D.C TO A.C:

In later half of eighties, in nineteenth century, it was proposed to have a power system

with 3-phase, 50 Hz A.C generation, and transmission and distribution networks. Once a.c

system was adopted, transmission of large power (MW) at higher transmission voltage becomes

a reality by using transformers. Level of voltage could be changed virtually to any other desired

level with transformers – which were hitherto impossible with D.C system. Nicola Tesla

suggested that constructional simpler electrical motors (induction motors, without the complexity

of commutates segments of D.C motors) operating from 3-phase a.c supply could be

manufactured. In fact, his arguments in favor of A.C supply system own the debate on switching

over from D.C to A.C system.

VARIOUS COMPONENTS OF STEAM POWER PLANT AND LAYOUT:

We have seen in the previous section that to generate voltage at 50 Hz we have to run the

generator at some fixed rpm by some external agency. A turbine is used to rotate the generator.


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Turbine may be of two types, namely steam turbine and water turbine. In a thermal power station

coal is burnt to produce steam which in turn, drives the steam turbine hence the generator (turbo

set). In figure 2.2 the elementary features of a thermal power plant is shown.

In a thermal power plant coil is burnt to produce high temperature and high pressure steam in

a boiler. The steam is passed through a steam turbine to produce rotational motion. The

generator, mechanically coupled to the turbine, thus rotates producing electricity. Chemical

energy stored in coal after a couple of transformations produces electrical energy at the generator

terminals as depicted in the figure. Thus proximity of a generating station nearer to a coal reserve

and water sources will be most economical as the cost of transporting coal gets reduced. In our

country coal is available in abundance and naturally thermal power plants are most popular.

However, these plants pollute the atmosphere because of burning of coals.

Stringent conditions (such as use of more chimney heights along with the compulsory use of

electrostatic precipitator) are put by regulatory authorities to see that the effects of pollution is

minimized. A large amount of ash is produced every day in a thermal plant and effective

handling of the ash adds to the running cost of the plant. Nonetheless 57% of the generation in

out country is from thermal plants. The speed of alternator used in thermal plants is 3000 rpm

which means 2-pole alternators are used in such plants.

SUBSTATIONS:

Substations are the places where the level of voltage undergoes change with the help of

transformers. Apart from transformers a substation will house switches (called circuit breakers),

meters, relays for protection and other control equipment. Broadly speaking, a big substation will

receive power through incoming lines at some voltage (say 400 kV) changes level of voltage

(say to 132 kV) using a transformer and then directs it out wards through outgoing lines.

Pictorially such a typical power system is shown in figure 2.6 in a short of block diagram. At the

lowest voltage level of 400 V, generally 3-phase, 4-wire system is adopted for domestic

connections. The fourth wire is called the neutral wire (N) which is taken out from the common

point of the star connected secondary of the 6 kV/400 V distribution transformer.

SOME IMPORTANT COMPONENTS / EQUIPMENTS IN SUBSTATION:

As told earlier, the function of a substation is to receive power at some voltage through

incoming lines and transmit it at some other voltage through outgoing lines. So the most

important equipment in a substation is transformer(s). However, for flexibility of operation and

protection transformer and lines additional equipments are necessary


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PRCET/EEE/IV SEMESTER/EE2252-POWER PLANT

ENGINEERING/NOTES

Suppose the transformer goes out of order and maintenance work is to be carried

out. Naturally the transformer must be isolated from the incoming as well as from the

outgoing lines by using special type of heavy duty (high voltage, high current) switches

called circuit breakers. Thus a circuit breaker may be closed or opened manually

(functionally somewhat similar to switching on or off a fan or a light whenever desired with

the help of a ordinary switch in your house) in substation whenever desired. However

unlike a ordinary switch, a circuit breaker must also operate (i.e., become opened)

automatically whenever a fault occurs or overloading takes place in a feeder or line. To

achieve this, we must have a current sensing device called CT (current transformer) in each

line. A CT simply steps down the large current to a proportional small secondary current.

Primary of the CT is connected in series with the line. A 1000 A/5 A CT will step down the

current by a factor of 200. So if primary current happens to be 800 A, secondary current of

the CT will be 4 A.

Suppose the rated current of the line is 1000 A, and due to any reason if current in

the line exceeds this limit we want to operate the circuit breaker automatically for

disconnection.

The basic scheme is presented to achieve this. The secondary current of the CT is fed to the

relay coil of an over current relay. Here we are not going into constructional and

operational details of a over current relay but try to tell how it functions. Depending upon

the strength of the current in the coil, an ultimately an electromagnetic torque acts on an

aluminum disc restrained by a spring. Spring tension is so adjusted that for normal current,

the disc does not move. However, if current exceeds the normal value, torque produced will

overcome the spring tension to rotate the disc about a vertical spindle to which a long arm is

attached. To the arm a copper strip is attached as shown figure 2.8. Thus the arm too will

move whenever the disk moves

The relay has a pair of normally opened (NO) contacts 1 & 2. Thus, there will exist

open circuit between 1 & 2 with normal current in the power line. However, during fault

condition in the line or overloading, the arm moves in the anticlockwise direction till it

closes the terminals 1 & 2 with the help of the copper strip attached to the arm as explained

pictorially in the figure 2.8. This short circuit between 1 & 2 completes a circuit comprising

of a battery and the trip coil of the circuit breaker. The opening and closing of the main


ENGINEERING/NOTES

contacts of the circuit breaker depends on whether its trip coil is energized or not. It is

interesting to note that trip circuit supply is to be made independent of the A.C supply

derived from the power system we want to protect. For this reason, we expect batteries

along with battery charger to be present in a substation.

Apart from above there will be other types of protective relays and various meters

indicating current, voltage, power etc. To measure and indicate the high voltage (say 6 kV)

of the line, the voltage is stepped down to a safe value (say 110V) by transformer called

potential transformer

(PT). Across the secondary of the PT, MI type indicating voltmeter is connected. For

example a voltage rating of a PT could be 6000 V/110 V. Similarly, across the secondary

we can connect a low range ammeter to indicate the line current.

DISTRIBUTION SYSTEM:

Till now we have learnt how power at somewhat high voltage (say 33 kV) is received in

a substation situated near load center (a big city). The loads of a big city are primarily

residential complexes, offices, schools, hotels, street lighting etc. These types of consumers

are called LT (low tension) consumers. Apart from this there may be medium and small

scale industries located in the outskirts of the city. LT consumers are to be supplied with

single phase, 220 V, 40 Hz. We shall discuss here how this is achieved in the substation

receiving power at 33 kV

Power receive at a 33 kV substation is first stepped down to 6 kV and with the help of

underground cables (called feeder lines), power flow is directed to different directions of

the city. At the last level, step down transformers are used to step down the voltage form 6

kV to 400 V. These transformers are called distribution transformers with 400 V, star


ENGINEERING/NOTES

connected secondary. You must have noticed such transformers mounted on poles in cities

beside the roads. These are called pole mounted substations. From the secondary of these

transformers 4 terminals (R, Y, B and N) come out. N is called the neutral and taken out

from the common point of star connected secondary. Voltage between any two phases (i.e.,

R-Y, Y-B and B-R) is 400 V and between any

phase and neutral . Residential buildings are supplied with single phase 230V, 50Hz. So

individual are to be supplied with any one of the phases and neutral. Supply authority tries

to see that the loads remain evenly balanced among the phases as far as possible. Which

means roughly one third of the consumers will be supplied from R-N, next one third from

Y-N and the remaining one third from B-N. The distribution of power from the pole

mounted substation can be done either by (1) overhead lines (bare conductors) or by (2)

underground cables. Use of overhead lines although cheap, is often accident prone and also

theft of power by hooking from the lines takes place. Although costly, in big cities and

thickly populated areas underground cables for distribution of power, are used.

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.

Purpose of Draught.

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.

To remove the gaseous products of combustion

Classification of Draught

The following flow chart gives the classification of draughts


ENGINEERING/NOTES

Artificial draught

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

Induced draught

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

Forced draught

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

Merits of Natural Draught

No external power is required for creating the draught

Air pollution is prevented since the flue gases are discharged at a higher

level

Maintenance cost is practically nil since there are no mechanical parts

Its has longer life,

Capital cost is less than that of an artificial draught.

De-merits of Natural Draught

Maximum pressure available for producing draught by the chimney is less,

Flue gases have to be discharged at higher temperature since draught increases

with the increase in temperature of flue gases.

Heat cannot be extracted from the fluid gases for economizer, superheater, air pre-

heater, etc. Since the effective draught will be reduced if the temperature of the

flue gases is decreased

Merits of steam Jet draught

This system is very simple and cheap in cost,

Low grade fuel can be used

Space required is less

De-merits at steam jet draught


ENGINEERING/NOTES

o It can be operated only when the steam is raised

o The draught produced is very low

Condenser

A condenser is a device in which the steam is condensed by cooling it

with water. The condensed steam is known as condensate.

Essential elements of a steam condensing plant

o A closed vessel in which the steam is condensed.

o A pump to deliver condensed steam to the hot well from the condenser.

o A dry air-pump to remove air and other non-condensable gases,

o A feed pump to deliver water to the boiler from hot well.

Sub division of jet condensers

Low level counter flow jet condenser

High level (or) Barometric jet condenser

Ejector condenser.

Surface condenser

Down flow condenser

Central flow condenser

Evaporative condenser

Advantages of surface condenser

The condensate can be used as boiler feed water

Cooling water of even poor quality can be used because the cooling water

does not come in direct contact with steam

High vacuum (about 73.5 cm of Hg) can be obtained in the surface

condenser. This increases the thermal efficiency of the plant

Disadvantages of surface condenser

The capital cost is more,

The maintenance cost and running cost of this condenser is high,

It is bulky and requires more space.

Heat saving devices used in a thermal power plant

Air pre heater

Economizer

Thermal power plant

Layout of steam power plant:

Introduction: Steam is an important medium for producing mechanical energy. Steam

is used to drive steam engines and steam turbines. Steam has the following

advantages.

1. Steam can be raised quickly from water which is available in plenty.

2. It does not react much with materials of the equipment used in power plants.

3. It is stable at temperatures required in the plant.

Equipment of a Steam Power Plant:


ENGINEERING/NOTES

A steam power plant must have the following equipment.

1. A furnace for burning the fuel.

2. A steam generator or boiler for steam generation.

3. A power unit like an engine or turbine to convert heat energy into mechanical

energy.

4. A generator to convert mechanical energy into electrical energy.

5. Piping system to carry steam and water.

Figure: shows a schematic layout of a steam power plant. The working of a steam

power plant can be explained in four circuits.

1. Fuel (coal) and ash circuit

2. Air and flue gas circuit

3. Feed water and steam flow circuit

4. Cooling water flow circuit

1. Coal and Ash circuit: This includes coal delivery, preparation, coal handling, boiler furnace,

ash handling and ash storage. The coal from coal mines is delivered by ships, rail

or by trucks to the power station. This coal is sized by crushers, breakers etc.

The sized coal is then stored in coal storage (stock yard). From the stock yard,

the coal is transferred to the boiler furnace by means of conveyors, elevators etc.

The coal is burnt in the boiler furnace and ash is formed by burning of coal,

Ash coming out of the furnace will be too hot, dusty and accompanied by

some poisonous gases. The ash is transferred to ash storage. Usually, the ash is

quenched to reduced temperature corrosion and dust content.

There are different methods employed for the disposal of ash. They are

hydraulic system, water jetting, ash sluice ways, pneumatic system etc. In large

power plants hydraulic system is used. In this system, ash falls from furnace grate

into high velocity water stream. It is then carried to the slumps. A line diagram of

coal and ash circuit is shown separately in figure.


ENGINEERING/NOTES

Figure: Layout of a steam power plant

2. Water and Steam circuit

It consists of feed pump, economizer, boiler drum, super heater, turbine

condenser etc. Feed water is pumped to the economizer from the hot well. This

water is preheated by the flue gases in the economizer. This preheated water is

then supplied to the boiler drum. Heat is transferred to the water by the burning

of coal. Due to this, water is converted into steam.

Figure: Fuel (coal) and ash circuit


ENGINEERING/NOTES

The steam raised in boiler is passed through a super heater. It is

superheated by the flue gases. The superheated steam is then expanded in a

turbine to do work. The turbine drives a generator to produce electric power.

The expanded (exhaust) steam is then passed through the condenser. In the

condenser, the steam is condensed into water and recirculated. A line diagram of

water and steam circuit is shown separately in figure.

Figure: Water and Steam circuit

3. Air and Flue gas circuit It consists of forced draught fan, air pre heater, boiler furnace, super

heater, economizer, dust collector, induced draught fan, chimney etc. Air is taken

from the atmosphere by the action of a forced draught fan. It is passed through

an air pre-heater. The air is pre-heated by the flue gases in the pre-heater. This

pre-heated air is supplied to the furnace to aid the combustion of fuel. Due to

combustion of fuel, hot gases (flue gases) are formed.


ENGINEERING/NOTES

Figure: Air and flue gas circuit

The flue gases from the furnace pass over boiler tubes and super heater

tubes. (In boiler, wet steam is generated and in super heater the wet steam is

superheated by the flue gases.) Then the flue gases pass through economizer to

heat the feed water. After that, it passes through the air pre-heater to pre-heat the

incoming air. It is then passed through a dust catching device (dust collector).

Finally, it is exhausted to the atmosphere through chimney. A line diagram of air

and flue gas circuit is shown separately in figure.

4. Cooling water circuit: The circuit includes a pump, condenser, cooling tower etc. the exhaust

steam from the turbine is condensed in condenser. In the condenser, cold water

is circulated to condense the steam into water. The steam is condensed by losing

its latent heat to the circulating cold water.

Figure: Cooling water current

Thus the circulating water is heated. This hot water is then taken to a

cooling tower, In cooling tower, the water is sprayed in the form of droplets

through nozzles. The atmospheric air enters the cooling tower from the openings

provided at the bottom of the tower. This air removes heat from water. Cooled

water is collected in a pond (known as cooling pond). This cold water is again

circulated through the pump, condenser and cooling tower. Thus the cycle is

repeated again and again. Some amount of water may be lost during the

circulation due to vaporization etc. Hence, make up water is added to the pond by

means of a pump. This water is obtained from a river or lake. A line diagram of

cooling water circuit is shown in figure separately.

Merits (Advantages) of a Thermal Power Plant


ENGINEERING/NOTES

1. The unit capacity of a thermal power plant is more. The cost of unit

decreases with 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 less than nuclear plants.

5. Suitable for varying load conditions.

6. No harmful radioactive wastes are produced as in the case of nuclear plant.

7. Unskilled operators can operate the plant.

8. The power generation does not depend on water storage.

9. There are no transmission losses since they are located near load centres.

Demerits of thermal power plants

1. Thermal plant are less efficient than diesel plants

2. Starting up the plant and bringing into service takes more time.

3. Cooling water required is more.

4. Space required is more

5. Storage required for the fuel is more

6. Ash handling is a big problem.

7. Not economical in areas which are remote from coal fields

8. Fuel transportation, handling and storage charges are more

9. Number of persons for operating the plant is more than that of

nuclear plants. This increases operation cost.

10. For large units, the capital cost is more. Initial expenditure on structural

materials, piping, storage mechanisms is more

The type of Basic Boilers thermodynamic cycles and process of the Rankine cycle

BOILER CYCLES In general, two important area of application for thermodynamics are:

1. Power generation

2. Refregeration

Both are accomplished by systems that operate in thermodynamic cycles such as:

a. Power cycles: Systems used to produce net power output and are often called

engines.

b. Refrigeration cycles: Systems used to produce refregeration effects are

called refregerators (or) heat pumps.

Cycles can further be categorized as (depending on the phase of the working fluid)

1. Gas Power cycles In this cycle working fluid remains in the gaseous phase throughout the entire

cycles.

2. Vapour power cycles In this case, the working fluid exists in the vapour phase during one part of

the cycle and in the liquid phase during another part.

Vapour power cycles can be categorized as


ENGINEERING/NOTES

a. Carnot cycle

b. Rankine cycle

c. Reheat cycle

d. Regenerative cycle

e. Binary vapour cycle

Steam cycles (Ranking cycle) The Rankine cycle is a thermodynamic cycle. Like other

thermodynamic cycle, the maximum efficiency of the Ranking cycle is given by

calculating the maximum efficiency of the carnot cycle.

Process of the Rankine Cycle

Figure: Schematic representation and T-S diagram of Rankine

cycle.

There are four processes in the Rankine cycle, each changing the state of the

working fluid.

These states are identified by number in the diagram above.

Process 3-4: First, the working fluid (water) is enter the pump at state 3 at saturated

liquid and it is pumped (ideally isentropically) from low pressure to high


ENGINEERING/NOTES

(operating) pressure of boiler by a pump to the state 4. During this isentropic

compression water temperature is slightly increased. Pumping requires a power

input (for example, mechanical or electrical). The conservation of energy

relation for pump is given as

Wpump = m (h4 - h3)

Process 4-1: The high pressure compressed liquid enters a boiler at state 4 where it is

heated at constant pressure by an external heat source to become a saturated

vapour at statel‟ which in turn superheated to state 1 through super heater.

Common heat source for power plant systems are coal (or other chemical

energy), natural gas, or nuclear power. The conservation of energy relation for

boiler is given as

Qin =m (h1 - h4)

Process 1 – 2: The superheated vapour enter the turbine at state 1 and expands

through a turbine to generate power output. Ideally, this expansion is isentropic.

This decreases the temperature and

pressure of the vapour at state 2. The conservation of energy relation for

turbine is given as

Wturbine = m (h1 –h2)

Process 2 – 3: The vapour then enters a condenser at state 2. At this state, steam is a

saturated liquid- vapour mixture where it is cooled to become a saturated liquid

at state 3. This liquid then re- enters the pump and the cycle is repeated. The

conservation of energy relation for condenser is given as

Qout = m (h2 – h3)

The exposed Rankine cycle can also prevent vapour overheating, which reduces

the amount of liquid condensed after the expansion in the turbine

Regenerative Ranking Cycle

The regenerative Ranking cycle is so named because after emerging

from the condenser (possibly as a sub cooled liquid) the working fluid heated by

steam tapped from the hot portion of the cycle and fed in to Open Feed Water

Heater(OFWH). This increases the average temperature of heat addition which in

turn increases the thermodynamics efficiency of the cycle.


ENGINEERING/NOTES

Principles of Fluidized Bed

Combustion Operation:

A fluidized bed is composed of fuel (coal, coke, biomass, etc.,) and bed

material (ash, sand, and/or sorbent) contained within an atmospheric or

pressurized vessel. The bed fluidized when air or other gas flows upward at

a velocity sufficient to expand the bed. The process is illustrated in figure. At

low fluidizing velocities (0.9 to 3 m/s). relatively high solids densities are

maintained in the bed and only a small fraction of the solids are entrained from

the bed. A fluidized bed that is operated in this velocity range is refered to as a

bubbling fluidized bed (BFB). A schematic of a typical BFB combustor is

illustrated in figure.

Figure: Basic fluid bed Systems


ENGINEERING/NOTES

Figure: Atmospheric bubbling bed combustor:

As the fluidizing velocity is increased, smaller particles are entrained in the

gas stream and transported out of the bed. The bed surface, well-defined for a

BFB combustor becomes more diffuse and solids densities are reduced in the bed.

A fluidized bed that is operated at velocities in the range of 4 to 7 m/s is referred to

as a circulated fluidized bed, or CFB. A schematic of a typical CFB combustor is

illustrated in figure

Figure: Circulating bed combustor.

Advantages of fluidized bed combustion The advantages of FBC in comparison to conventional pulverized coal-fueled

units can be summarized as follows:

1. SO2 can be removed in the combustion process by adding limestone to

the fluidized bed, eliminating the need for an external desulfurization

process.

2. Fluidized bed boilers are inherently fuel flexible and, with proper design

provision, can burn a variety of fuels.

3. Combustion FBC units takes place at temperatures below the ash fusion


ENGINEERING/NOTES

temperature of most fuels. Consequently, tendencies for slagging and

fouling are reduced with FBC.

4. Because of the reduced combustion temperature, NOx emissions are

inherently low.

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

system

i) 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


ENGINEERING/NOTES

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.

a. Belt conveyors

b. Screw conveyors

c. Bucket elevato

d. Grab bucket elevators

e. Skip hoists

f. Flight conveyor

Belt Conveyor

Figure: 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 or canvas. Belt conveyor is


ENGINEERING/NOTES

suitable for the transfer of coal over long distances. It is used in medium and

large power plants. The initial cost of system is not high and power

consumption is also low. The inclination at which coal can be successfully elevated

by belt conveyor is about 20. Average speed preferred than other types.

Advantages of belt conveyor

1. Its operation is smooth and clean

2. It requires less power as compared to other types of systems

3. Large quantities of coal can be discharged quickly and continuously.

4. Material can be transported on moderate inclines.

2. Screw Conveyor It 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.

Figure: Screw

conveyor

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 of screw 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 is carried by the bucket from bottom and discharged at the top.


ENGINEERING/NOTES

Figure: Bucket elevator

4. Grab bucket elevator It 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 and requires minimum maintenance.

The grab bucket conveyor can be used with crane or tower as shown in

figure . Although the initial cost of this system is high but operating cost is less.

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.

pulverized coal storage in Bunker


ENGINEERING/NOTES

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.

Figure : Control system used for storing the pulverized coal with the

use of CO.

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 furnace with 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.


ENGINEERING/NOTES

Figure: Pulverized coal handling plant showing all required equipment for

unit and central system The arrangement of different equipment required in both systems is shown

in figure. With the help of a block diagram.

The coal received by the plant from the mine may vary widely in sizes. It


ENGINEERING/NOTES

is necessary to make the coal of uniform size before passing the pulverizer for

efficient grinding. The coal received from the mine is passed through a

preliminary crusher to reduce the size to allowable limit (30 mm). The crushed

coal is further passed over magnetic separator which removes pyrites and tramp

iron. The further equipment through which coal is passed before passing to

pulverizer are already shown in figure

Ball Mill pulverizing A 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 from where it moves to the drum

by means of a screw conveyor. As the drum rotates the coal get pulverized due to

the combine impact between coal and steel balls. Hot air is introduced into the

drum. The powdered coal is picked up by the air and the coal air mixture enters

the classifiers, where sharp changes in the direction of the mixture throw out the

oversized coal particles. The over-sized particles are returned to the drum. The

coal air mixture from the classifier moves to the exhauster fan and then it is

supplied to the burners

Figure: Ball

mill

Ball and Race Mills pulverizing Figure: shows a ball and race mill


ENGINEERING/NOTES

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.

Advantages:

i) Lower capital cost

ii) Lower power consumption

iii) Less space required.

iv) Less weight

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.


ENGINEERING/NOTES

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

Hydraulic System

In 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.

In this method water at sufficient pressure is used to take away the ash to sump.

Where water and ash are separated. The ash is then transferred to the dump site in

wagons, rail cars to

trucks. The loading of ash may be through a belt conveyor, grab buckets. If there is

an ash basement with ash hopper the ash can fall, directly in ash car or conveying system

Water-Jetting System


ENGINEERING/NOTES

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

out of quenching nozzle is used 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 are crushed to small sizes. The ash is then carried by

a high velocity air or steam to the point of delivery. Air leaving the ash

separator is passed through filter to remove dust etc. So that the exhauster

handles clean air which will protect the blades of the exhauster.

Classification of boilers:

The steam boilers are classified according to the following conditions

1. According to the relative position of water and hot gases

a. Fire tube boiler [Cochran Boiler]

b. Water tube boiler [ Babcock – Wilcox Boiler]

2. According to the axis of shell

a. Vertical boiler [Cochran Boiler]

b. Horizontal boiler [Lancashire Boiler]

3. According to the position of boiler

a. Internally fired boiler [ all fire tube boilers] [Cochran Boilers]

b. Externally fired boiler [ all water tube boilers] [Babcock and Wilcox


ENGINEERING/NOTES

Boilers]

4. According to the pressure developed

a. Low pressure boiler [Pressure less than 80 bar]

b. High pressure boiler [Pressure greater than 80 bar]

5. According to the method of water circulation

a. Natural circulation [all low pressure boilers] [ Cochran Boiler]

b. Forced circulation [all high pressure boilers] [ LaMont Boiler]

6. According to the use of the boiler

a. Stationary boiler [Cochran Boiler]

b. Mobile boiler [Locomotive Boiler]

7. According to the number of drums

a. Single Drum

b. Multi Drum

8. According to the nature of draught

a. Natural Draught

b. Forced Draught

Difference between water tube and fire tube boilers

S.No Fire tube boiler Water tube boiler

1. Hot flue gases flow inside the tubes Water flows inside the tubes.

2. Evaporation takes place slowly. Evaporation takes place quickly.

3. Failure in water supply may not Failure in water supply may overheat

overheat the boiler. the boiler.

4. Removal of impurities is difficult. Removal of impurities is easy.

5. The failure of fire tube (explosion), The failure of water tube does not cause

causes a very serious problem. any serious problem.

6. Here the furnace is fitted inside the Here the furnace is fitted outside the

water space. water tube.

7. Inspection is not easy. Inspection is easy.

8. Efficiency is less. Efficiency is high.

9. Construction and design is rigid, Construction and design is complex.

compact and simple.

Cochran Boiler:

The Cochran boiler is one of the most popular type of vertical, multi

tubular, fire tube boilers. Figure shows the Cochran boiler which is made in

sizes up to 2.75 metre diameter and

metre height. It has an evaporative capacity of 3640 kg of steam per hour

when burning 568 kg of coal per hour, for working pressure of 20 bar.


ENGINEERING/NOTES

Locomotive boiler:

The locomotive boiler is a horizontal fire tube boiler having an internal

firebox.


ENGINEERING/NOTES

It consists of a cylindrical shell having a rectangular firebox at one end a

smoke box at the other end. The firebox forms the chamber within which the

fuel is burnt on the grate which is supported in the firebox at the bottom. The

firebox is connected to the smoke box by a number of horizontal smoke tubes.

The hot gases from the furnace pass through these tubes into the smoke box and

are then discharged from the furnace pass through these tubes into the smoke box

and are then discharged from the short chimney. The grate of the boiler is

inclinded. A steam dome is placed on the top of the shell and in front of the

firebox. A stop valve called the regulator is placed in the steam dome. The

steam is taken from the elevated dome to the engine cylinder so that it contains

as few water particles as possible. The steam pipe from the regulator leads to a

superheater placed in the smoke box and from the superheater, the steam is sent to

the cylinder by pipes passing out from the smoke box to the cylinder. The

necessary draught is obtained by the steam exhausted from the engine cylinder

which is discharged through the blast pipe placed in the smoke box to the

chimney. A movable cap is attached to the mouth of blast orifice. A steam

blower is also provided for use when the steam supply to the engine is shut – off.

Advantages of locomotive boilers:

a. Compactness

b. High steaming capacity

c. Portability

d. Fair economy

Disadvantages of locomotive boilers:

a. Large flat surface requires sufficient supporting.

b. Corrosion in the water legs.

c. It is difficult to clean inside.

Lancashire boiler:

It is a stationary, fire tube, internally fired boiler. The size is

approximately from 7 – 9 metres in length and 2 – 3 metres in diameter.

Description:

It consists of

1. Cylindrical shell

2. Furnace tubes bottom flue and side flues

3. Grate

4. Fire bridge

5. Dampers

Cylindrical shell:

It is placed in horizontal position over a brick work. It is partly filled up


ENGINEERING/NOTES

with water. The water level inside the shell is well above the furnace tubes.

Furnace tubes, bottom flue and Side flues:

Two large internal furnace tubes (flue tubes) extend from one end to the

other end of the shell. The flues are built up of ordinary bricks lined with fire

bricks. One bottom flue and two side flues are formed by the brick setting, as

shown in the figure.

Grate:

The grate is provided at the front end of the main flue tubes. Coal is

fed to the grate through the fire hole.

Fire bridge:

A brickwork fire bridge is provided at the end of the grate to prevent the flow of

coal and ash particles into the interior of the furnace (flue) tubes. Otherwise

the coal and ash particles carried with gases form deposits on the interior of the

tubes and prevents the heat transfer to the water.

Dampers:

Dampers in the form of sliding doors are placed at the end of the side

flues to control the flow of gases from side flues to the chimney flue.

Working:

Coal is fed to the grate through the fire hole and is burnt. The hot gases

leaving the grate move along the furnace (flue) tubes up to the back end of the

shell and then in the downward direction to the bottom flue. The bottom of the

shell is thus first heated.

The hot gases, passing through the bottom flue, travel up to the front

end of the boiler, where they divide into two streams and pass to the side flues.

This makes the two sides of the

B o i l e r shell to become heated. Passing along the two side flues, the hot gases

travel up

to the backend of the boiler to the chimney flue. They are then discharged into

the atmosphere through the chimney.

With the help of this arrangement of flow passages of the hot gases, the

bottom of the shell is first heated and then its sides. The heat is transferred to

water through the surfaces of the two flue tubes (which remain in water) and the

bottom and sides of the shell.

This arrangement of flues increases the heating surface of the boiler to a large

extent.

Dampers control the flow of hot gases and regulated the combustion rate as

well as stream generation rate.

The boiler is fitted with necessary mountings. Pressure gauge and water level

indicator are provided at the front. Safety valve, steam stop valve, low water and

high steam safetly valve and man – hole are provided on the top of the shell.

High steam low water safety valve:

It is a combination of two valves. One is lever safety valve, which blows –


ENGINEERING/NOTES

off steam when the working pressure of steam exceeds. The second valve

operates by blowing – off the steam when the water level falls below the normal

level.

Blow – off cock:

It is situated beneath the front portion of the shell for the removal of mud

and sediments. It is also used to empty the water in the boiler during inspection.

Fusible plug:

It is provided on the top of the main flues just above the grate. It prevents

the overheating of the boiler tubes by extinguishing the fire when the water level

falls below a particular level. A low water level alarm is mounted in the boiler to

give a warning when the water level falls below the present value.

Salient features:

1. The arrangement of flues in this boiler increase the heating surface of the

shell to a large extent.

2. It is suitable where a large reserve of steam and hot water is needed.

3. Its maintenance is easy.

4. Superheater can be easily incorporated into the system at the end of the

main flue tubes. Thus overall efficiency of the boiler can be increased.

Water tube Boilers:

Babcock and Wilcox boiler:

It is a water tube boiler used in steam power plants. In this, water is


ENGINEERING/NOTES

circulated inside the tubes and hot gases flow over the tubes.

Description:

The Babcock and Wilcox boiler consists of

1. Steam and water drum (Boiler shell)

2. Water tubes

3. Uptake – header and down – comer

4. Grate

5. Furnace

6. Baffles

7. Superheater

8. Mud box

9. Inspection doors

10. Damper

1. Steam and Water drum (Boiler Shell) One half of the drum which is horizontal is filled up with water and steam

remains on the other half. It is about 8 metres in length and 2 metres in diameter.

2. Water tubes Water tubes are placed between the drum and the furnace in an inclined

position (at an angle of 100 to 150) to promote water circulation. These tubes are

connected to the uptake – header and the down – comer as shown.

3. Uptake – Header and Down – comer (or Down take – Header) The drum is connected at one end to the uptake – header by short tubes

and at the other end to the down – comer by long tubes.


ENGINEERING/NOTES

Figure: Babcock and Wilcox boiler

Grate:

Coal is fed to the grate through the fire door.

Furnace:

Furnace is kept below the uptake – header.

Baffles:

The fire – brick baffles, two in number, are provided to deflect the hot flue

gases.

Superheater:

The boiler is fitted with a superheater tube which is placed just under the

drum and above the water tubes.

Mud box:

Mud box is provided at the bottom end of the down – comer. The mud or

sediments in the water are collected in the mud box and it is blown – off time by

means of a blow – off cock.

Inspection doors:

Inspection doors are provided for cleaning and inspection of the boiler.

Working principle:

Coal is fed to grate through the fire door and is burnt.

Flow of flue gases:

The hot flue gases rise up ward and pass across the left – side portion of

the water tubes. The baffles deflect the flue gases and hence the flue gases travel

in a zig – zag manner (i.e., the hot gases are deflected by the baffles to move in

the upward direction, then downward and again in the upward direction) over

the water tubes and along the superheater. The flue gases finally escape to the

atmosphere through the chimneA continuous circulation of water from the drum to

the water tubes and water tubes to the drum is thus maintained. The circulation

of water is maintained by convective currents and is known as “natural

circulation

Economizer:

Function:

An economizer pre – heats (raise the temperature) the feed water by the

exhaust flue gases. This pre – heated water is supplied to the boiler from the

economizer

Location:

An economizer is placed in the path of the flue gases in between the boiler and the

air pre – heater or chimney


ENGINEERING/NOTES

Construction:

An economizer used in modern high pressure boilers is shown by a line

sketch. It consists of a series of vertical tubes. These tubes are hydraulically

pressed into the top and bottom headers. The bottom header is connected to

feed pump. Top header is connected to the water space of the boiler. It is

provided with a safety valve which opens when water pressure exceeds a certain

limit. To keep the surface of the tubes clean from soot and ash deposits,

scrapers are provided in the tubes. These scrapers are slowly moved up and down

to clean the surfaces of the tubes. The action of adjacent pairs of scraper is in

opposite direction. i.e., when one scraper moves up, the other moves down.

Economizers may be parallel or counter-flow types. When the gas flow and

water

flow are in the same direction, it is called parallel flow economizer. In

counter-flow, the gas flow and water flow are in opposite direction.

Fig. Economizer

Working

The feed water is pumped to the bottom header and this water is carried to

the top header through a number of vertical tubes. Hot flue gases are allowed to

pass over the external surface of the tubes. The feed water which flows upward in

the tubes is thus heated by the flue gases. This pre-heated water is supplied to the

boiler.

Advantages

1. Feed water to the boiler is supplied at high temperature. Hence heat

required in the boiler is less. Thus fuel consumption is less.

2. Thermal efficiency of the plant is increased.

3. Life of boiler is increased.

4. Loss of heat in flue gases is reduced.

Steaming capacity is increased

Air pre-heater Function

Air pre-heater pre-heats (increases the temperature) the air supply to the


ENGINEERING/NOTES

furnace with the help of hot the gases.

Location

It is installed between the economizer and the chimney.

Construction

A tubular type air pre-heater is shown in figure. It consists of a large

number of tubes. Flue gases pass through the tube. Air flows over the tubes.

Baffles are provided to pass the air number of times over the tubes. A soot

hopper is provided at the bottom to collect the soot

Figure: Air pre-heater

Working

Hot flue gases pass through the tubes of air pre-heater after leaving the

boiler or economizer. Atmospheric air is allowed to pass over these tubes. Air

and flue gases flow in opposite directions. Baffles are provided in the air pre-

heater and the air passes number of times over the tubes. Heat is absorbed by the

air from the flue gases. This pre-heater air is supplied to the furnace to air

combustion

Advantages

1. Boiler efficiency is increased.


ENGINEERING/NOTES

2. Evaporative rate is increased.

3. Combustion is accelerated with less soot, smoke and ash.

4. Low grade and inferior quality fuels can be used.

Superheater

Function

It superheats the steam generated by the boiler and increases the temperature

steam above saturation temperature at constant pressure.

Location

Superheaters are placed in the path of flue gases to recover some of their

heat. In bigger installations, the superheaters are placed in an independently

fired furnace. Such superheaters are called separately fired or portable

superheaters.

There are many types of superheaters. A combination type of radiant and

convective superheater is shown in figure. Both these superheaters are arranged in

series in the path of flue gases. Radiant superheater receives heat from the burning

fuel by radiation process. Convective superheater is placed adjacent to the furnace

wall in the path of flue gases. It receives heat by convection.

Working

Steam stop valve is opened. The steam (wet or dry) from the evaporator

drum is passed through the superheater tubes. First the steam is passed through the

radiant superheater and then to the convective superheater. The steam is heated

when it passes through these superheaters and converted into superheated steam.

This superheated steam is supplied to the turbine through a valve.

Applications

This type of superheaters are used in modern high pressure boilers.


ENGINEERING/NOTES

Advantages of superheated steam (super heaters)

1. Work output is increased for the same quantity of steam.

2. Loss due to condensation of steam in the steam engine and is the

steam mains is minimized.

3. Capacity of the plant is increased.

4. Thermal efficiency is increased since the temperature of superheated

steam is high

Injector Function

An injector lifts and forces water into a boiler which is operating under

pressure.

Construction

In consists of a converging nozzle, mixing chamber, divergent tube, steam

valve and a non- return valve. A steam injector is shown in figure.

Working

The steam passes through the converging nozzle through a valve. Steam

expands through the nozzle. The pressure drops and consequently velocity of

steam increases. This steam mixes with water in the mixing chamber. In the

mixing chamber steam condenses and vacuum is created. Due to this vacuum,

more water is sucked into the mixing chamber. The jet water enters divergent

tube. In the divergent tube kinetic energy of water is converted into pressure

energy. Due to this increased pressure, feed water is forced into the boiler through

feed check valve.

Figure: Steam injector

Application

They are commonly used in vertical and locomotive boilers.

3. Feed pump Function: It delivers feed water into the boiler drum

Location

It is placed in between boiler and water supply source (hot well).


ENGINEERING/NOTES

Construction

The feed pumps used may be of reciprocating type or rotary type

(centrifugal pump). The reciprocating pump may use plunger or piston. It is

driven by a steam engine or electric motor. The piston rod of the steam engine is

connected directly with the piston rod of the pump (figure).

Working

When the piston moves to the right, vacuum is created in the left side of

the piston. The water from the hot well is forced into the cylinder through the

left side suction valve. When the piston returns (moves to the left), vacuum is

created in the right side of the piston. The liquid from the well is sucked into

the cylinder through the right side suction valve. At the same time, the liquid in

the left side of the piston is forced out through the left side delivery valve into

the delivery pipe. The operations are repeated. During each stroke, suction takes

place on one side of the water is delivered continuously in the boiler.

Figure: Feed pump

(reciprocating type).

4. Steam

Sepeartors It separates water particles from steam before it is supplied to a steam

engine or turbine.

Thus it prevents the damaging of turbine blades due to moisture present in steam

Location: It is located in the supply line near the turbine or engine

Construction

There are different types of steam separators. A separator with baffle

plates is shown in figure. It consists of a cylindrical vessel. The vessel is fitted

with baffle plates. A water gauge is fitted to indicate the water collected in the

separator to drain away to separated water.

Working

The steam is allowed into the separator. The steam strikes the baffle plates

and the direction of the flow is changed. As a result, heavier water particles in

steam falls down to the bottom of the separator. The separated steam is free

from water particles. It is passed to the turbine or engine through the outlet pipe.


ENGINEERING/NOTES

5.Steam Seperator Steam trap In any steam system, water may be formed due to partial

condensation of steam in the piping system. This may cause water hammer and

reduction in efficiency. A steam trap removes the condensed water, without allowing

the steam to escape out.


ENGINEERING/NOTES

UNIT II HYDRO POWER PLANT

LAYOUT – DAM:

In a hydel power station, water head is used to drive water turbine coupled to the

generator. Water head may be available in hilly region naturally in the form of water

reservoir (lakes etc.) at the hill tops. The potential energy of water can be used to drive the

turbo generator set installed at the base of the hills through piping called pen stock. Water

head may also be created artificially by constructing dams on a suitable river. In contrast to

a thermal plant, hydel power plants are eco-friendly, neat and clean as no fuel is to be burnt

to produce electricity. While running cost of such plants are low, the initial installation cost

is rather high compared to a thermal plants due to massive civil construction necessary.

Also sites to be selected for such plants depend upon natural availability of water reservoirs

at hill tops or availability of suitable rivers for constructing dams. Water turbines generally

operate at low rpm, so number of poles of the alternator is high. For example a 20-pole

alternator the rpm of the turbine is only 300 rpm.

Up stream

water level

Water head

Dam H 3-phase A.C

Electric power

Water

Generator

Turbine

Discharge of water

in down stream

Potential energy Kinetic

Electrical

of water

energy

energy


ENGINEERING/NOTES

Basic components of a hydel generating unit.

Dam

A dam is a barrier to confine or raise water for storage or diversion to create a hydraulic

head

WATER TURBINE SELECTION:

A turbine converts energy in the form of falling water into rotating shaft power. The

selection of the best turbine for any particular hydro site depends on the site characteristics,

the dominant ones being the head and flow available. Selection also depends on the desired

running speed of the generator or other device loading the turbine. Other considerations

such as whether the turbine is expected to produce power under part-flow conditions, also

play an important role in the selection. All turbines have a power-speed characteristic.

They will tend to run most efficiently at a particular speed, head and flow combination.

A turbine design speed is largely determined by the head under which it operates.

Turbines can be classified as high head, medium head or low head machines. Turbines are

also divided by their principle way of operating and can be either impulse or reaction

turbines.

The rotating element (called `runner') of a reaction turbine is fully immersed in

water and is enclosed in a pressure casing. The runner blades are profiled so that pressure

differences across them impose lift forces, like those on aircraft wings, which cause the

runner to rotate.

In contrast, an impulse turbine runner operates in air, driven by a jet (or jets) of

water. Here the water remains at atmospheric pressure before and after making contact

with the runner blades. In this case a nozzle converts the pressurised low velocity water

into a high speed jet. The runner blades deflect the jet so as to maximise the change of

momentum of the water and thus maximising the force on the blades.

Impulse turbines are usually cheaper then reaction turbines because there is no need

for a specialist pressure casing, nor for carefully engineered clearances. However, they

are only suitable for relatively high heads.


ENGINEERING/NOTES

IMPULSE TURBINES:

Impulse turbines are generally more suitable for micro-hydro applications compared

with reaction turbines because they have the following advantages:

greater tolerance of sand and other particles in the water,

better access to working parts,

no pressure seals around the shaft,

easier to fabricate and maintain,

better part-flow efficiency.

The major disadvantage of impulse turbines is that they are mostly unsuitable for

low-head sites because of their low specific speeds. The crossflow, Turgo and multi-jet

Pelton are suitable at medium heads.

A Pelton turbine consists of a set of specially shaped buckets mounted on a

periphery of a circular disc. It is turned by jets of water which are discharged from one or

more nozzles and strike the buckets. The buckets are split into two halves so that the

central area does not act as a dead spot incapable of deflecting water away from the

oncoming jet. The cutaway on the lower lip allows the following bucket to move further

before cutting off the jet propelling the bucket ahead of it and also permits a smoother

entrance of the bucket into the jet. (see diagrams below)

The Pelton bucket is designed to deflect the jet through 165 degrees (not 180

degrees) which is the maximum angle possible without the return jet interfering with the

following bucket for the oncoming jet.


ENGINEERING/NOTES

RUNNER OF A PELTON TURBINE


ENGINEERING/NOTES

In large scale hydro installation Pelton turbines are normally only considered for

heads above 150 m, but for micro-hydro applications Pelton turbines can be used

effectively at heads down to about 20 m. Pelton turbines are not used at lower heads

because their rotational speeds become very slow and the runner required is very large and

unwieldy. If runner size and low speed do not pose a problem for a particular installation,

then a Pelton turbine can be used efficiently with fairly low heads. If a higher running

speed and smaller runner are required then there are two further options:

REACTION TURBINES:

The reaction turbines considered here are the Francis turbine and the propeller

turbine. A special case of the propeller turbine is the Kaplan. In all these cases, specific

speed is high, i.e. reaction turbines rotate faster than impulse turbines given the same head

and flow conditions. This has the very important consequences in that a reaction turbine

can often be coupled directly to an alternator without requiring a speed-increasing drive

system. Some manufacturers make combined turbine-generator sets of this sort. Significant

cost savings are made in eliminating the drive and the maintenance of the hydro unit is very

much simpler. The Francis turbine is suitable for medium heads, while the propeller is more

suitable for low heads.

On the whole, reaction turbines require more sophisticated fabrication than impulse

turbines because they involve the use of larger and more intricately profiled blades together

with carefully profiled casings.

Francis turbines can either be volute-cased or open-flume machines. The spiral

casing is tapered to distribute water uniformly around the entire perimeter of the runner and

the guide vanes feed the water into the runner at the correct angle. The runner blades are

profiled in a complex manner and direct the water so that it exits axially from the centre of

the runner. In doing so, the water imparts most of its pressure energy to the runner before

leaving the turbine via a draft tube.

The Francis turbine is generally fitted with adjustable guide vanes. These regulate

the water flow as it enters the runner and are usually linked to a governing system which

matches flow to turbine loading in the same way as a spear valve or deflector plate in a

Pelton turbine. When the flow is reduced the efficiency of the turbine falls away.


ENGINEERING/NOTES

PROPELLER TURBINE:

The basic propeller turbine consists of a propeller, similar to a ship's propeller, fitted

inside a continuation of the penstock tube. The turbine shaft passes out of the tube at the

point where the tube changes direction. The propeller usually has three to six blades, three

in the case of very low head units and the water flow is regulated by static blades or swivel

gates ("wicket gates") just upstream of the propeller. This kind of propeller turbine is

known as a fixed blade axial flow turbine because the pitch angle of the rotor blades cannot

be changed. The part-flow efficiency of fixed-blade propeller turbines tend to be very poor.


ENGINEERING/NOTES

KAPLAN TURBINE:

Large scale hydro sites make use of more sophisticated versions of the propeller

turbines. Varying the pitch of the propeller blades together with wicket gate adjustment,

enables reasonable efficiency to be maintained under part flow conditions. Such turbines

are known as variable pitch or Kaplan turbines.

Centrifugal pumps can be used as turbines by passing water through them in

reverse. Research is currently being done to enable the performance of pumps as turbines to

be predicated more accurately.

Elements of Hydel Power Plant:


ENGINEERING/NOTES

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,Power house

Advantages of Hydro-electric power plants Water is a renewable source of energy. Water which is the

operating fluid, is neither consumed nor converted into something else,

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.

There is no ash disposal problem as in the case of thermal power plant.

Hydraulic turbines are classified as follows:

1) According to the head and quantity of water available,

2) According to the name of the originator,

3) According to the action of water on the moving blades,

4) According to the direction of flow of water in the runner,

5) According to the disposition of the turbine shaft,

According to the specific speed N

Comparison of Impulse and reaction turbine

S.No Impulse turbine Reaction turbine 1. Head: The machine is suitable for

high installation. (H=100 + 200 m).

The machines can be used for medium

heads (H=50 to 500 m) and low heads (less

than 50 m) 2. Nature of input energy to the

runner: The nozzle converts the

entire hydraulic energy into kinetic

energy before water strikes the

runner.

The head is usually inadequate to produce high

velocity jet. Hence water is supplied to the

runner in the forms of both pressure and

kinetic energy.

3. Method of energy transfer:

The buckets of the runner are so

shaped that they extract almost all the

kinetic energy of the jet.

The wicket gates accelerate the flow a little

and direct the water to runner vanes to

which energies of water are transferred.

4. Operating pressure: The turbine works under atmospheric

pressure. Which is the difference

between the inlet and exit points of

the runner.

The runner works is a closed system under the

action of reaction pressure.


ENGINEERING/NOTES

5. Admission of water to the wheel:

Only a few buckets comprising a

part of the wheel are exposed to the

water jet.

The entire circumference of the wheel

receives water and all passages between the

runner blades are always full of water.

6. Discharge: They are essential

low discharge turbines.

Since power is a product of head and weight

of the rate of flow, these turbines consume

large quantities of water in order to develop

a reasonable power under a relatively low

head. 7. Speed of operation: The speed

are invariably high.

Although the specific speeds of these

turbines is high, their actual running speeds

are comparatively low.

8. Size : These are generally small size. The turbines sizes is much larger than impulse

wheels, in order to accommodate heavy

discharge.

9. Casing: It prevents splashing of

water. It has no hydraulic function to

serve.

The spiral casing has an important role to

play; it distributes water under the available

pressure uniformly around the periphery of the

runner.

10. Turbine setting: The head

between the wheel and race is lost.

The draft tube ensures that the head of water below tail race level is not lost.

ADVANTAGES OF WATER TURBINES

ENVIRONMENTAL BENEFITS:

Environmentalists are quick to point out that water turbines produce no carbon as

they generate power. Not only do they not emit carbon, but they do not react chemically

with the water at all; no water is destroyed in the process of creating electricity. While some

critics point out that turbines may alter fish migrations, there are a number of turbines that

operate like waterwheels, which do not affect any wildlife.

RELIABILITY:

The greatest advantage of water turbines is their reliability. The tidal nature of

oceans and the steady flow of rivers means power can be produced around the clock, while

wind turbines remain motionless on calm days. Their blades continue to turn on cloudy

days that prohibit solar panels from harvesting the energy of protons, as well as after the

sun goes down in the evening. The amount of water flowing through a river is nearly

always predictable, allowing their gearboxes to keep the speed of the blades at a safe and


ENGINEERING/NOTES

productive level. Even in shoreline areas, jetties can be constructed to regulate the flow of

water.

POTENTIAL:

According to green-trust.org, only 2,400 of the country's 80,000 dams are equipped to

generate hydroelectricity. This means much of the construction necessary for large-scale

hydroelectric production has already been completed, and only a retrofit is necessary to

begin to produce power. As fossil fuels become more scarce, engineers have been working

to find sources of power, such as the Gulf Stream and various river deltas, where long-term

solutions can be developed.

PUMPED STORAGE HYDEL PLANT :

Pumped-storage hydroelectricity (PSH) is a type of hydroelectric power

generation used by some power plants for load balancing. The method stores energy in the

form of potential energy of water, pumped from a lower elevation reservoir to a higher

elevation. Low-cost off-peak electric power is used to run the pumps. During periods of

high electrical demand, the stored water is released through turbines to produce electric

power. Although the losses of the pumping process makes the plant a net consumer of

energy overall, the system increases revenue by selling more electricity during periods

of peak demand, when electricity prices are highest.

Pumped storage is the largest-capacity form of grid energy storage available, and, as

of March 2012, the Electric Power Research Institute (EPRI) reports that PSH accounts for

more than 99% of bulk storage capacity worldwide, representing around

127,000MW.[1]

PSH reported energy efficiency varies in practice between 70% and

80%,[1][2][3][4]

with some claiming up to 87%

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ENGINEERING/NOTES

At times of low electrical demand, excess generation capacity is used to pump water

into the higher reservoir. When there is higher demand, water is released back into the

lower reservoir through a turbine, generating electricity. Reversible turbine/generator

assemblies act as pump and turbine (usually a Francis turbine design). Nearly all facilities

use the height difference between two natural bodies of water or artificial reservoirs. Pure

pumped-storage plants just shift the water between reservoirs, while the "pump-back"

approach is a combination of pumped storage and conventional hydroelectric plants that use

natural stream-flow. Plants that do not use pumped-storage are referred to as conventional

hydroelectric plants; conventional hydroelectric plants that have significant storage capacity

may be able to play a similar role in the electrical grid as pumped storage, by deferring

output until needed.

Taking into account evaporation losses from the exposed water surface and

conversion losses, approximately 70% to 85% of the electrical energy used to pump the

water into the elevated reservoir can be regained.[6]

The technique is currently the most

cost-effective means of storing large amounts of electrical energy on an operating basis, but

capital costs and the presence of appropriate geography are critical decision factors.

The relatively low energy density of pumped storage systems requires either a very

large body of water or a large variation in height. For example, 1000 kilograms of water

(1 cubic meter) at the top of a 100 meter tower has a potential energy of about

0.272 kW·h (capable of raising the temperature of the same amount of water by only 0.23

Celsius = 0.42 Fahrenheit). The only way to store a significant amount of energy is by

having a large body of water located on a hill relatively near, but as high as possible above,

a second body of water. In some places this occurs naturally, in others one or both bodies of


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http://en.wikipedia.org/wiki/Cubic_meter

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ENGINEERING/NOTES

water have been man-made. Projects in which both reservoirs are artificial and in which no

natural waterways are involved are commonly referred to as "closed loop".

This system may be economical because it flattens out load variations on the power

grid, permitting thermal power stations such as coal-fired plants and nuclear power

plants and renewable energy power plants that provide base-load electricity to continue

operating at peak efficiency

(Base load power plants), while reducing the need for "peaking" power plants that

use the same fuels as many base load thermal plants, gas and oil, but have been designed for

flexibility rather than maximal thermal efficiency. However, capital costs for purpose-built

hydro storage are relatively high.

Along with energy management, pumped storage systems help control electrical

network frequency and provide reserve generation. Thermal plants are much less able to

respond to sudden changes in electrical demand, potentially causing frequency

and voltage instability. Pumped storage plants, like other hydroelectric plants, can respond

to load changes within seconds.

The first use of pumped storage was in the 1890s in Italy and Switzerland. In the

1930s reversible hydroelectric turbines became available. These turbines could operate as

both turbine-generators and in reverse as electric motor driven pumps. The latest in large-

scale engineering technology are variable speed machines for greater efficiency. These

machines generate in synchronization with the network frequency, but

operate asynchronously (independent of the network frequency) as motor-pumps.

The first use of pumped-storage in the United States was in 1930 by the Connecticut

Electric and Power Company, using a large reservoir located near New Milford,

Connecticut, pumping water from the Houstatonic River to the storage reservoir 230 feet

above.[7]

A new use for pumped storage is to level the fluctuating output of intermittent

energy sources. The pumped storage provides a load at times of high electricity output and

low electricity demand, enabling additional system peak capacity. In certain

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http://en.wikipedia.org/wiki/Switzerland

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http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity#cite_note-7

http://en.wikipedia.org/wiki/Intermittent_energy_source




ENGINEERING/NOTES

jurisdictions, electricity prices may be close to zero or occasionally negative (Ontario in

early September, 2006), on occasions that there is more electrical generation than load

available to absorb it; although at present this is rarely due to wind alone, increased wind

generation may increase the likelihood of such occurrences. It is particularly likely that

pumped storage will become especially important as a balance for very large

scale photovoltaic generation

UNIT III - NUCLEAR POWER PLANTS

NUCLEAR PLANT – LAYOUT:

As coal reserve is not unlimited, there is natural threat to thermal power plants based

on coal. It is estimated that within next 30 to 40 years, coal reserve will exhaust if it is

consumed at the present rate. Nuclear power plants are thought to be the solution for bulk

power generation. At present the installed capacity of unclear power plant is about 4300

MW and expected to expand further in our country. The present day atomic power plants

work on the principle of nuclear fission of 235

U. In the natural uranium, 235

U constitutes

only 0.72% and remaining parts is constituted by 99.27% of 238

U and only about 0.05% of

234U. The concentration of

235U may be increased to 90% by gas diffusion process to obtain

enriched 235

U. When 235

U is bombarded by neutrons a lot of heat energy along with

additional neutrons are produced.

These new neutrons further bombard 235

U producing more heat and more neutrons.

Thus a chain reaction sets up. However this reaction is allowed to take place in a controlled

manner inside a closed chamber called nuclear reactor. To ensure sustainable chain

reaction, moderator and control rods are used. Moderators such as heavy water (deuterium)

or very pure carbon 12

C are used to reduce the speed of neutrons. To control the number

neutrons, control rods made of cadmium or boron steel are inserted inside the reactor. The

control rods can absorb neutrons. If we want to decrease the number neutrons, the control

rods are lowered down further and vice versa. The heat generated inside the reactor is taken

out of the chamber with the help of a coolant such as liquid sodium or some gaseous fluids.

The coolant gives up the heat to water in heat exchanger to convert it to steam as shown in

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ENGINEERING/NOTES

figure 2.4. The steam then drives the turbo set and the exhaust steam from the turbine is

cooled and fed back to the heat exchanger with the help of water feed pump. Calculation

shows that to produce 1000 MW of electrical power in coal based thermal plant, about 6

106 Kg of coal is to be burnt daily while for the same amount of power, only about 2.5 Kg

of 235

U is to be used per day in a nuclear power stations.

Coolant

Control rods

Steam

3-phase A.C

Electric

power

Reactor

Ex

ch

an

ger

Turbin

e Generator

Fuel

H e a t

rods

Exhausted

steam

Moderator

from turbine

Condenser

Coolant

Water feed

pump

circulating

pump

Nuclear power generation.

The initial investment required to install a nuclear power station is quite high but

running cost is low. Although, nuclear plants produce electricity without causing air

pollution, it remains a dormant source of radiation hazards due to leakage in the reactor.

Also the used fuel rods are to be carefully handled and disposed off as they still remain

radioactive.

The reserve of 235

U is also limited and can not last longer if its consumption continues


ENGINEERING/NOTES

at the present rate. Naturally search for alternative fissionable material continues. For

example, plutonium (239

Pu) and (233

U) are fissionable. Although they are not directly

available. Absorbing neutrons, 238

U gets converted to fissionable plutonium 239

Pu in the

atomic reactor described above. The used fuel rods can be further processed to extract 239

Pu

from it indirectly increasing the availability of fissionable fuel. Effort is also on to convert

thorium into fissionable 233

U. Incidentally, India has very large reserve of thorium in the

world.

Total approximate generation capacity and Contribution by thermal, hydel and nuclear

generation in our country are given below.

Method of generation in MW % contribution

Thermal 77 340 69.4

Hydel 29 800 26.74

Nuclear 2 720 3.85

Total generation 1 11 440 -

PRINCIPLES OF NUCLEAR ENERGY:

FISSION REACTION AND FUSION REACTION:

NUCLEAR FUSION:

nuclear reaction in which two or more atomic nuclei collide at very high speed and

join to form a new type of atomic nucleus (e.g. The energy that the Sun emits into space is

produced by nuclear reactions that happen in its core due to the collision of hydrogen nuclei

and the formation of helium nuclei). During this process, matter is not conserved because

some of the mass of the fusing nuclei is converted to photons which are released through a

cycle that even our sun uses. Fusion is the process that powers active stars.

The fusion of two nuclei with lower masses than iron (which, along with nickel, has

the largest binding energy per nucleon) generally releases energy, while the fusion of nuclei

heavier than iron absorbs energy. The opposite is true for the reverse process, nuclear

fission. This means that fusion generally occurs for lighter elements only, and likewise, that

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ENGINEERING/NOTES

fission normally occurs only for heavier elements. There are extreme astrophysical events

that can lead to short periods of fusion with heavier nuclei

NUCLEAR FISSION:

Nuclear fission is either a nuclear

reaction or a radioactive decay process

in which the nucleus of an atom splits

into smaller parts (lighter nuclei), often producing

free neutrons and photons (in the form of gamma rays), and releasing a very large amount

of energy, even by the energetic standards of radioactive decay. The two nuclei produced

are most often of comparable but slightly different sizes, typically with a mass ratio of

products of about 3 to 2, for common fissile isotopes.[1][2]

Most fissions are binary fissions

(producing two charged fragments), but occasionally (2 to 4 times per 1000

events), three positively charged fragments are produced, in a ternary fission. The smallest

of these fragments in ternary processes ranges in size from a proton to an argon nucleus.

Fission as encountered in the modern world is usually a deliberately produced man-

made nuclear reaction induced by a neutron. It is less commonly encountered as a natural

form of spontaneous radioactive decay (not requiring a neutron), occurring especially in

very high-mass-number isotopes. The unpredictable composition of the products (which

vary in a broad probabilistic and somewhat chaotic manner) distinguishes fission from

purely quantum-tunneling processes such as proton emission, alpha decay and cluster

decay, which give the same products each time.

Nuclear fission of heavy elements was discovered in 1938

by Meitner, Hahn and Frisch, and named by analogy with biological fission of living cells.

It is an exothermic reaction which can release large amounts of energy both

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ENGINEERING/NOTES

as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk

material where fission takes place). In order for fission to produce energy, the total binding

energy of the resulting elements must be greater than that of the starting element. Fission is

a form of nuclear transmutation because the resulting fragments are not the same element as

the original atom.

Nuclear fission produces energy for nuclear power and to drive the explosion

of nuclear weapons. Both uses are possible because certain substances called nuclear

fuels undergo fission when struck by fission neutrons, and in turn emit neutrons when they

break apart. This makes possible a self-sustaining nuclear chain reaction that releases

energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in

a nuclear weapon.

The amount of free energy contained in nuclear fuel is millions of times the amount

of free energy contained in a similar mass of chemical fuel such as gasoline, making

nuclear fission a very dense source of energy. The products of nuclear fission, however, are

on average far more radioactive than the heavy elements which are normally fissioned as

fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem.

Concerns over nuclear waste accumulation and over the destructive potential of nuclear

weapons may counterbalance the desirable qualities of fission as an energy source, and give

rise to ongoing political debate over nuclear power.

Nuclear fission of heavy elements was discovered in 1938

by Meitner, Hahn and Frisch, and named by analogy with biological fission of living cells.

It is an exothermic reaction which can release large amounts of energy both

as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk

material where fission takes place). In order for fission to produce energy, the total binding

energy of the resulting elements must be greater than that of the starting element. Fission is

a form of nuclear transmutation because the resulting fragments are not the same element as

the original atom.

Nuclear fission produces energy for nuclear power and to drive the explosion

of nuclear weapons. Both uses are possible because certain substances called nuclear

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ENGINEERING/NOTES

fuels undergo fission when struck by fission neutrons, and in turn emit neutrons when they

break apart. This makes possible a self-sustaining nuclear chain reaction that releases

energy at a controlled rate in a nuclear reactor or at a very rapid uncontrolled rate in

a nuclear weapon.

The amount of free energy contained in nuclear fuel is millions of times the amount

of free energy contained in a similar mass of chemical fuel such as gasoline, making

nuclear fission a very dense source of energy. The products of nuclear fission, however, are

on average far more radioactive than the heavy elements which are normally fissioned as

fuel, and remain so for significant amounts of time, giving rise to a nuclear waste problem.

Concerns over nuclear waste accumulation and over the destructive potential of nuclear

weapons may counterbalance the desirable qualities fission as an energy source, and give

rise to ongoing political debate over nuclear power.

NUCLEAR REACTOR:

A nuclear reactor is a device to initiate and control a sustained nuclear chain

reaction. Nuclear reactors are used at nuclear power plants for generating electricity and

in propulsion of ships. Heat from nuclear fission is passed to a working fluid (water or gas),

which runs through turbines. These either drive a ship's propellers or turn electrical

generators. Nuclear generated steam in principle can be used for industrial process heat or

for district heating. Some reactors are used to produce isotopes

for medical and industrial use, or for production of plutonium for weapons

COMPONENTS OF A NUCLEAR REACTOR:

There are several components common to most types of reactors:

FUEL:

Uranium is the basic fuel. Usually pellets of uranium oxide (UO2) are arranged in

tubes to form fuel rods. The rods are arranged into fuel assemblies in the reactor core.

MODERATOR:

Material in the core which slows down the neutrons released from fission so that

they cause more fission. It is usually water, but may be heavy water or graphite.

CONTROL RODS:

These are made with neutron-absorbing material such as cadmium, hafnium or

boron, and are inserted or withdrawn from the core to control the rate of reaction, or to halt


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ENGINEERING/NOTES

it. In some PWR reactors, special control rods are used to enable the core to sustain a low

level of power efficiently.

COOLANT:

A fluid circulating through the core so as to transfer the heat from it. In light water

reactors the water moderator functions also as primary coolant. Except in BWRs, there is

secondary coolant circuit where the water becomes steam. (see also later section on

primary coolant characteristics).

PRESSURE VESSEL OR PRESSURE TUBES:

Usually a robust steel vessel containing the reactor core and moderator/coolant, but

it may be a series of tubes holding the fuel and conveying the coolant through the

surrounding moderator.

Part of the cooling system where the high-pressure primary coolant bringing heat

from the reactor is used to make steam for the turbine, in a secondary circuit. Essentially a

heat exchanger like a motor car radiator*. Reactors may have up to four 'loops', each with a

steam generator.

CONTAINMENT:

The structure around the reactor and associated steam generators which is designed

to protect it from outside intrusion and to protect those outside from the effects of radiation

in case of any serious malfunction inside. It is typically a metre-thick concrete and steel

structure.

REACTIVITY CONTROL:

The power output of the reactor is adjusted by controlling how many neutrons are

able to create more fissions.

Control rods that are made of a neutron poison are used to absorb neutrons.

Absorbing more neutrons in a control rod means that there are fewer neutrons available to

cause fission, so pushing the control rod deeper into the reactor will reduce its power

output, and extracting the control rod will increase it.

At the first level of control in all nuclear reactors, a process of delayed

neutron emission by a number of neutron-rich fission isotopes is an important physical

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ENGINEERING/NOTES

process. These delayed neutrons account for about 0.65% of the total neutrons produced in

fission, with the remainder (termed "prompt neutrons") released immediately upon fission.

The fission products which produce delayed neutrons have half lives for

their decay by neutron emission that range from milliseconds to as long as several minutes.

Keeping the reactor in the zone of chain-reactivity where delayed neutrons are necessary to

achieve a critical mass state, allows time for mechanical devices or human operators to have

time to control a chain reaction in "real time"; otherwise the time between achievement

of criticality and nuclear meltdown as a result of an exponential power surge from the

normal nuclear chain reaction, would be too short to allow for intervention.

In some reactors, the coolant also acts as a neutron moderator. A moderator

increases the power of the reactor by causing the fast neutrons that are released from fission

to lose energy and become thermal neutrons. Thermal neutrons are more likely than fast

neutrons to cause fission, so

more neutron moderation means more power output from the reactors. If the coolant

is a moderator, then temperature changes can affect the density of the coolant/moderator

and therefore change power output. A higher temperature coolant would be less dense, and

therefore a less effective moderator.

In other reactors the coolant acts as a poison by absorbing neutrons in the same way

that the control rods do. In these reactors power output can be increased by heating the

coolant, which makes it a less dense poison. Nuclear reactors generally have automatic and

manual systems to scram the reactor in an emergency shutdown. These systems insert large

amounts of poison (often boron in the form of boric acid) into the reactor to shut the fission

reaction down if unsafe conditions are detected or anticipated.[6]

Most types of reactors are sensitive to a process variously known as xenon

poisoning, or the iodine pit. Xenon-135 produced in the fission process acts as a "neutron

poison" that absorbs neutrons and therefore tends to shut the reactor down. Xenon-135

accumulation can be controlled by keeping power levels high enough to destroy it as fast as

it is produced. Fission also produces iodine-135, which in turn decays (with a half-life of

under seven hours) to new xenon-135. When the reactor is shut down, iodine-135 continues

http://en.wikipedia.org/wiki/Prompt_neutron


http://en.wikipedia.org/wiki/Neutron_emission

http://en.wikipedia.org/wiki/Critical_mass

http://en.wikipedia.org/wiki/Critical_mass_(nuclear)

http://en.wikipedia.org/wiki/Nuclear_meltdown

http://en.wikipedia.org/wiki/Coolant

http://en.wikipedia.org/wiki/Neutron_moderator

http://en.wikipedia.org/wiki/Thermal_neutron

http://en.wikipedia.org/wiki/Fast_neutron



http://en.wikipedia.org/wiki/Scram

http://en.wikipedia.org/wiki/Boron

http://en.wikipedia.org/wiki/Boric_acid

http://en.wikipedia.org/wiki/Nuclear_reactor#cite_note-TOURISTRP-6

http://en.wikipedia.org/wiki/Iodine_pit

http://en.wikipedia.org/wiki/Xenon-135




http://en.wikipedia.org/wiki/Iodine-135


ENGINEERING/NOTES

to decay to xenon-135, making restarting the reactor more difficult for a day or two. This

temporary state is the "iodine pit." If the reactor has sufficient extra reactivity capacity, it

can be restarted. As the extra xenon-135 is transmuted to xenon-136 which is not a neutron

poison, within a few hours the reactor experiences a "xenon burn off (power) transient".

Control rods must be further inserted to replace the neutron absorption of the lost xenon-

135. Failure to properly follow such a procedure was a key step in the Chernobyl disaster.

Reactors used in nuclear marine propulsion (especially nuclear submarines) often

cannot be run at continuous power around the clock in the same way that land-based power

reactors are normally run, and in addition often need to have a very long core life

without refueling. For this reason many designs use highly enriched uranium but

incorporate burnable neutron poison directly into the fuel rods.[7]

This allows the reactor to

be constructed with a high excess of fissionable material, which is nevertheless made

relatively more safe early in the reactor's fuel burn-cycle by the presence of the neutron-

absorbing material which is later replaced by naturally produced long-lived neutron poisons

(far longer-lived than xenon-135) which gradually accumulate over the fuel load's operating

life.

Figure : Nuclear Power Plant




http://en.wikipedia.org/wiki/Chernobyl_disaster

http://en.wikipedia.org/wiki/Nuclear_marine_propulsion

http://en.wikipedia.org/wiki/Nuclear_submarine

http://en.wikipedia.org/wiki/Reactor_refueling

http://en.wikipedia.org/wiki/Nuclear_reactor#cite_note-7


ENGINEERING/NOTES

ELECTRICAL POWER GENERATION:

The energy released in the fission process generates heat, some of which can be

converted into usable energy. A common method of harnessing this thermal energy is to use

it to boil water to produce pressurized steam which will then drive a steam turbine that

generates electricity.

UNIT

IV - GAS AND DIESEL POWER PLANTS

Heat engine

Any type of engine or machine which derives heat energy from the

combustion of fuel or any other source and converts this energy into mechanical

work is termed as a heat engine.

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.

Commonly used fuel injection system in a diesel power station:

Common-rail injection system

Individual pump injection system

Distribution system.

OPEN AND CLOSED CYCLE:

http://en.wikipedia.org/wiki/Thermal_energy

http://en.wikipedia.org/wiki/Steam_turbine


ENGINEERING/NOTES

A closed-cycle gas turbine is a turbine that uses a gas (e.g.

air, nitrogen, helium, argon,[1][2]

etc.) for the working fluid as part of a closed

thermodynamic system. Heat is supplied from an external source.[3]

Such re circulating

turbines follow the Brayton cycle. The initial patent for a closed-cycle gas turbine was

issued in 1935 and they were first used commercially in 1939.[3]

Seven CCGT units were

built in Switzerland and Germany by 1978.[2]

Historically, CCGTs found most use

as external combustion engines"with fuels such as bituminous coal, brown coal and blast

furnace gas" but were superseded by open cycle gas turbines using clean-burning fuels (e.g.

"gas or light oil"), especially in highly-efficient combined cycle systems.[3]

Air-based

CCGT systems have demonstrated very high availability and reliability.[6]

The most notable

helium-based system thus far was Oberhausen 2, a 50megawatt cogeneration plant that

operated from 1975 to 1987 in Germany.

GAS TURBINE:

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.

The basic operation of the gas turbine is similar to the of the steam power

plant except that air is used instead of water. Fresh atmospheric air flows through

a compressor that brings it to higher pressure. Energy is then added by spraying fuel into


http://en.wikipedia.org/wiki/Nitrogen

http://en.wikipedia.org/wiki/Helium

http://en.wikipedia.org/wiki/Argon

http://en.wikipedia.org/wiki/Closed-cycle_gas_turbine#cite_note-1



http://en.wikipedia.org/wiki/Working_fluid

http://en.wikipedia.org/wiki/Thermodynamic_system#Closed_system



http://en.wikipedia.org/wiki/Closed-cycle_gas_turbine#cite_note-HUF-3

http://en.wikipedia.org/wiki/Brayton_cycle

http://en.wikipedia.org/wiki/Patent


http://en.wikipedia.org/wiki/Switzerland

http://en.wikipedia.org/wiki/Germany

http://en.wikipedia.org/wiki/Closed-cycle_gas_turbine#cite_note-Schleicher-2

http://en.wikipedia.org/wiki/External_combustion_engine

http://en.wikipedia.org/wiki/Bituminous_coal

http://en.wikipedia.org/wiki/Brown_coal

http://en.wikipedia.org/wiki/Blast_furnace_gas



http://en.wikipedia.org/wiki/Gas_turbine

http://en.wikipedia.org/wiki/Natural_gas

http://en.wikipedia.org/wiki/Fuel_oil

http://en.wikipedia.org/wiki/Combined_cycle


http://en.wikipedia.org/wiki/High_availability


http://en.wikipedia.org/wiki/Megawatt

http://en.wikipedia.org/wiki/Cogeneration

http://en.wikipedia.org/wiki/Internal_combustion_engine



http://en.wikipedia.org/wiki/Gas_compressor


http://en.wikipedia.org/wiki/Combustion_chamber

http://en.wikipedia.org/wiki/Steam_power_plant



http://en.wikipedia.org/wiki/Compressor



ENGINEERING/NOTES

the air and igniting it so the combustion generates a high-temperature flow. This high

temperature high-pressure gas enters a turbine, where it expands down to the exhaust

pressure, producing a shaft work output in the process. The turbine shaft work is used to

drive the compressor and other devices such as an electric generator that may be coupled to

the shaft. The energy that is not used for shaft work comes out in the exhaust gases, so these

have either a high temperature or a high velocity. The purpose of the gas turbine determines

the design so that the most desirable energy form is maximized. Gas turbines are used to

power aircrafts, trains, ships, electrical generators, or even tanks. Gas turbines are also used

in many liquid propellant rockets, the gas turbines are used to power a turbo pump to permit

the use of lightweight, low pressure tanks, which saves considerable dry mass.

TURBO PROP ENGINES:

A turboprop engine is a type of turbine engine which drives an external aircraft

propeller using a reduction gear. Turboprop engines are generally used on small subsonic

aircraft, but some large military and civil aircraft, such as the Airbus A400M, Lockheed L-

188 Electra , have also used turboprop power.

AERODERIVATIVE GAS TURBINES:

Aero derivatives are also used in electrical power generation due to their ability to

be shut down, and handle load changes more quickly than industrial machines. They are

also used in the marine industry to reduce weight. The General Electric LM2500, General

Electric LM6000, Rolls-Royce RB211 and Rolls-Royce Avon are common models of this

type of machine.

AMATEUR GAS TURBINES:

Increasing numbers of gas turbines are being used or even constructed by amateurs.

In its most straightforward form, these are commercial turbines acquired through

military surplus or scrap yard sales, then operated for display as part of the hobby of engine

collecting.[9][10]

In its most extreme form, amateurs have even rebuilt engines beyond

professional repair and then used them to compete for the Land Speed Record.

The simplest form of self-constructed gas turbine employs an

automotive turbocharger as the core component. A combustion chamber is fabricated and

plumbed between the compressor and turbine sections.

http://en.wikipedia.org/wiki/Electric_generator

http://en.wikipedia.org/wiki/Exhaust_gases

http://en.wikipedia.org/wiki/Aircraft

http://en.wikipedia.org/wiki/Train

http://en.wikipedia.org/wiki/Ship


http://en.wikipedia.org/wiki/Tank

http://en.wikipedia.org/wiki/Rocket#Propellant

http://en.wikipedia.org/wiki/Turbopump

http://en.wikipedia.org/wiki/Turboprop

http://en.wikipedia.org/wiki/Airbus_A400M

http://en.wikipedia.org/wiki/Lockheed_L-188_Electra

http://en.wikipedia.org/wiki/Lockheed_L-188_Electra

http://en.wikipedia.org/wiki/General_Electric_LM2500




http://en.wikipedia.org/wiki/Rolls-Royce_RB211

http://en.wikipedia.org/wiki/Rolls-Royce_Avon

http://en.wikipedia.org/wiki/Gas_turbine#cite_note-latexiron-9



http://en.wikipedia.org/wiki/Green_Monster_(car)

http://en.wikipedia.org/wiki/Turbocharger


ENGINEERING/NOTES

More sophisticated turbojets are also built, where their thrust and light weight are

sufficient to power large model aircraft. The Schreckling design constructs the entire engine

from raw materials, including the fabrication of a centrifugal compressor wheel from

plywood, epoxy and wrapped carbon fiber strands.

Several small companies now manufacture small turbines and parts for the amateur.

Most turbojet-powered model aircraft are now using these commercial and semi-

commercial micro turbines, rather than a Schreckling-like home-build.

ADVANTAGES OF GAS POWER PLANT:

1.The three most obvious pros of using natural gas as a fuel to power your generators is that

it is cleaner, less expensive than other non-renewable fuels, and is considerably efficient.

2. In comparison to oil and coal, the emissions of sulfur, nitrogen, and carbon dioxide (a

greenhouse gas) are considerably lower. Hence, natural gas is one of the cleanest fossil

fuels when it burns.

3.Another advantage of natural gas generators is that natural gas does not produce a

pungent odor, which is fairly common in generators powered by oil or diesel.

4. Natural gas generators are also effective in reducing costs when used to power homes.

This is because electricity from the main utility source is a far more expensive alternative.

5. Apart from being cleaner and cheaper, natural gas is also readily available in large cities

since it is delivered directly through pipelines. Hence, when using natural gas powered

generators, storage of fuel becomes redundant.

DISADVANTAGES:

1. When it comes to the cons of natural gas generators, one of its advantages can also be

regarded as a disadvantage. Since natural gas need not be stored as it is supplied through

gas pipelines, at times of natural calamities the supply of natural gas is disrupted. You may

find yourself facing a lack of fuel when you need to operate your generator the most.

2. Apart from this, natural gas is extremely explosive and can be a serious fire hazard

should the pipeline burst.

3. In comparison to diesel generators, natural gas generators are:

4.More expensive to run

5. Emit more carbon dioxide, which is a greenhouse gas.

http://en.wikipedia.org/wiki/Kurt_Schreckling


ENGINEERING/NOTES

COMBINED LAYOUT OF GAS AND DIESEL POWER PLANT:

ENGINE STRATING SYSTEM:

This includes air compressor and starting air tank. The function of this system is to

start the engine from cold supplying compressed air.

FUEL SYSTEM:

Pump draws diesel from storage tank and supplies it to the small day tank through

the filter. Day tank supplies the daily fuel need of engine. The day tan is usually placed high

so that diesel flows to engine under gravity.

Diesel is again filtered before being injected into the engine by the fuel injection pump. The

fuel is supplied to the engine according to the load on the plant.

AIR INTAKE SYSTEM:

Air filters are used to remove dust from the incoming air. Air filters may be dry

type, which is made up of felt, wool or cloth. In oil bath type filters, the sir is swept over a

bath of oil so that dust particles get coated.

EXHAUST SYSTEM:

In the exhaust system, silencer (muffler) is provide to reduce the noise.

ENGINE COOLING SYSTEM:

The temperature of burning gases in the engine cylinder is the order of 1500 to

2000‟C. to keep the temperature at the reasonable level, water is circulated inside the

engine in water jackets which are passage around the cylinder, piston, combustion chamber


ENGINEERING/NOTES

etc. hot water leaving the jacket is sent to heat exchanger. Raw water is made to flow

through the heat exchanger, where it takes up the

heat of jacket water. It is then cooled in the cooling tower and re circulates again.

ENGINE LUBRICATION SYSTEM:

It includes lubricating oil tank, oil pump and cooler. Lubrication is essential to

reduce friction and wear of engine parts such as cylinder walls and piston.

Lubricating oil which gets heated due to friction of moving parts is cooled before

recirculation. The cooling water used in the engine is used for cooling the lubricant also.

ADVANTAGES OF DIESEL POWER PLANT:

1. Plant layout is simple. Hence it can be quickly installed and commissioned, while the

erection and starting of a steam power plant or hydro-plant takes a fairly long time.

2. Quick starting and easy pick-up of loads are possible in a very short time.

3. Location of the plant is near the load center.

4. The load operation is easy and requires minimum labors.

5. Efficiency at part loads does not fall so much as that of a steam plant.

6. Fuel handling is easier and no problem of ash disposal exists.

7. The plant is smaller in size than steam power plant for same capacity.

8. Diesel plants operate at high overall efficiency than steam.

DISADVANTAGES OF DIESEL POWER PLANT:

1. Plant capacity is limited to about 50 MW of power.

2. Diesel fuel is much more expensive than coal.

3. The maintenance and lubrication costs are high.

4. Diesel engines are not guaranteed for operation under continuous, while steam can work

under 25% of overload continuously.


ENGINEERING/NOTES

UNIT V NON-CONVENTIONAL POWER GENERATION

TIDE

The periodic rise and fall of the water level of sea which are carried

by the action of sun and moon on water of the earth is called the tide. In a

single basin arrangement power can be generated only intermittently.

THE CONSISTENCIES OF ‘SOLAR FARM’ AND ‘SOLAR TOWER’

The solar farm consists of a whole field covered with parabolic

trough concentrators and a ‘solar tower’ consists of a central receiver on a

tower and a whole field of tracking. SEE BECK EFFECT

‚If two dissimilar materials are joined to form a loop and the two

junctions maintained at different temperatures, an e.m.f. will be set up

around the loop‛. This is called Seeback effect.

WORKING PRINCIPLE OF THERMIONIC


ENGINEERING/NOTES

A thermionic converter works because of the phenomenon of

‘thermionic emission’.

PHOTO VOLTAIC EFFECT

‘Photovoltaic effect’ is defined as the generation of an

electromotive force as a result of absorption of ionizing radiation. MHD – generator:

‘MHD generator’ is a device which converts heat energy of a fuel

directly into electrical energy without a conventional electric generator. FUEL CELL’

A ‘fuel cell’ is an electrochemical device in which the chemical energy

of a conventional fuel is converted directly and efficiently into low voltage,

direct current electrical energy.

The various non-conventional energy sources are as follows:

Solar energy

Wind energy

Energy from biomass and biogas

Ocean thermal energy conversion

Tidal energy

Geothermal energy

Hydrogen energy

Fuel cells

Magneto-hydrodynamics generator

Thermionic converter

Thermo-electric power.

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.


ENGINEERING/NOTES

THE TYPES OF WIND MILLS

1. Multiple blade type

2. Savonius type

3. Darrieus type

SOLAR ENERGY COLLECTORS:

Solar energy, radiant light and heat from the sun, has been harnessed by humans

since ancient times using a range of ever-evolving technologies. Solar energy technologies

include solar heating, solar photo voltaic, solar thermal electricity, solar

architecture and artificial photosynthesis, which can make considerable contributions to

solving some of the most urgent energy problems the world now faces.

Solar technologies are broadly characterized as either passive solar or active

solar depending on the way they capture, convert and distribute solar energy. Active solar

techniques include the use of photovoltaic panels and solar thermal collectors to harness the

energy. Passive solar techniques include orienting a building to the Sun, selecting materials

with favorable thermal mass or light dispersing properties, and designing spaces

that naturally circulate air.

Solar collectors can be used in a large variety of applications. The main areas of

applications include:

1. Solar water heating, which includes thermosyphon, integrated collector storage

systems, air systems, direct circulation and indirect water heating systems.

2. Solar space heating systems, which includes both water and air systems.

3. Solar refrigeration, which includes both adsorption and absorption systems.

4. Industrial process heat systems, which include both low temperature (air and water

based) applications and solar steam generation systems.

5. Solar desalination systems, which include both direct (solar stills) and indirect

systems (conventional desalination equipment powered by solar collectors).

6. Solar thermal power generation systems, which include the parabolic trough

systems, the power tower or central receiver systems and the parabolic dish systems

(dish / Stirling engine).

http://en.wikipedia.org/wiki/Light


http://en.wikipedia.org/wiki/Sun

http://en.wikipedia.org/wiki/Ancient_history

http://en.wikipedia.org/wiki/Solar_heating

http://en.wikipedia.org/wiki/Solar_photovoltaics

http://en.wikipedia.org/wiki/Solar_thermal_electricity

http://en.wikipedia.org/wiki/Solar_architecture



http://en.wikipedia.org/wiki/Artificial_photosynthesis

http://en.wikipedia.org/wiki/Passive_solar

http://en.wikipedia.org/wiki/Active_solar



http://en.wikipedia.org/wiki/Solar_thermal_energy

http://en.wikipedia.org/wiki/Thermal_mass

http://en.wikipedia.org/wiki/Ventilation_(architecture)


ENGINEERING/NOTES

OCEAN THERMAL ENERGY CONVERSION (OTEC)

It uses the temperature difference between cooler deep and warmer shallow or

surface ocean waters to run a heat engine and produce useful work, usually in the form of

electricity. However, the temperature differential is small and this impacts the economic

feasibility of ocean thermal energy for electricity generation.

The most commonly used heat cycle for OTEC is the Rankine cycle using a low-

pressure turbine. Systems may be either closed-cycle or open-cycle. Closed-cycle engines

use a working fluids that are typically thought of as refrigerants such as ammonia or R-

134a. Open-cycle engines use vapour from the seawater itself as the working fluid.

OTEC can also supply quantities of cold water as a by-product. This can be used for

air conditioning and refrigeration and the fertile deep ocean water can feed biological

technologies. Another by-product is fresh water distilled from the sea.

Demonstration plants were first constructed in the 1880s and continue to be built,

but no large-scale commercial plants are in operation.

CLOSED SYSTEM:

Closed-cycle systems use fluid with a low boiling point, such as ammonia, to power

a turbine to generate electricity. Warm surface seawater is pumped through a heat

exchanger to vaporize the fluid. The expanding vapor turns the turbo-generator. Cold water,

pumped through a second heat exchanger, condenses the vapor into a liquid, which is then

recycled through the system.

In 1979, the Natural Energy Laboratory and several private-sector partners

developed the "mini OTEC" experiment, which achieved the first successful at-sea

production of net electrical power from closed-cycle OTEC.[12]

The mini OTEC vessel was

moored 1.5 miles (2.4 km) off the Hawaiian coast and produced enough net electricity to

illuminate the ship's light bulbs and run its computers and television.

OPEN SYSTEM:

Open-cycle OTEC uses warm surface water directly to make electricity. Placing

warm seawater in a low-pressure container causes it to boil. In some schemes, the

http://en.wikipedia.org/wiki/Ocean

http://en.wikipedia.org/wiki/Heat_engine

http://en.wikipedia.org/wiki/Rankine_cycle

http://en.wikipedia.org/wiki/Refrigerant

http://en.wikipedia.org/wiki/Ammonia

http://en.wikipedia.org/wiki/R-134a

http://en.wikipedia.org/wiki/R-134a

http://en.wikipedia.org/wiki/Seawater



http://en.wikipedia.org/wiki/Seawater

http://en.wikipedia.org/wiki/Heat_exchanger



http://en.wikipedia.org/wiki/Ocean_thermal_energy_conversion#cite_note-mini-otec-12


ENGINEERING/NOTES

expanding steam drives a low-pressure turbine attached to an electrical generator. The

steam, which has left its salt and other contaminants in the low-pressure container, is

pure fresh water. It is condensed into a liquid by exposure to cold temperatures from deep-

ocean water. This method produces desalinized fresh water, suitable for drinking

water or irrigation.

In other schemes, the rising steam is used in a gas lift technique of lifting water to

significant heights. Depending on the embodiment, such steam lift pump techniques

generate power from a hydroelectric turbine either before or after the pump is used.

In 1984, the Solar Energy Research Institute (now the National Renewable Energy

Laboratory) developed a vertical-spout evaporator to convert warm seawater into low-

pressure steam for open-cycle plants. Conversion efficiencies were as high as 97% for

seawater-to-steam conversion (overall efficiency using a vertical-spout evaporator would

still only be a few per cent). In May 1993, an open-cycle OTEC plant at Keahole Point,

Hawaii, produced 50,000 watts of electricity during a net power-producing experiment.

This broke the record of 40 kW set by a Japanese system in 1982.

HYBRID SYSTEM:

A hybrid cycle combines the features of the closed- and open-cycle systems. In a

hybrid, warm seawater enters a vacuum chamber and is flash-evaporated, similar to the

open-cycle evaporation process. The steam vaporizes the ammonia working fluid of a

closed-cycle loop on the other side of an ammonia vaporizer. The vaporized fluid then

drives a turbine to produce electricity. The steam condenses within the heat exchanger and

provides desalinated water.

WIND POWER PLANT:

Wind power is the conversion of wind energy into a useful form of energy, such as

using wind turbines to make electrical power, windmills for mechanical power, wind pumps

for water pumping or drainage, or sails to propel ships.

Large wind farms consist of hundreds of individual wind turbines which are

connected to the electric power transmission network. Offshore wind farms can harness

more frequent and powerful winds than are available to land-based installations and have

http://en.wikipedia.org/wiki/Steam


http://en.wikipedia.org/wiki/Salt

http://en.wikipedia.org/wiki/Fresh_water

http://en.wikipedia.org/wiki/Desalinization

http://en.wikipedia.org/wiki/Drinking_water



http://en.wikipedia.org/wiki/Irrigation

http://en.wikipedia.org/wiki/Gas_lift

http://en.wikipedia.org/wiki/Mist_lift

http://en.wikipedia.org/wiki/Water_turbine

http://en.wikipedia.org/wiki/National_Renewable_Energy_Laboratory



http://en.wikipedia.org/wiki/Watt


http://en.wikipedia.org/wiki/Desalination

http://en.wikipedia.org/wiki/Wind


http://en.wikipedia.org/wiki/Wind_turbine

http://en.wikipedia.org/wiki/Electrical_power

http://en.wikipedia.org/wiki/Windmill

http://en.wikipedia.org/wiki/Water_pumping

http://en.wikipedia.org/wiki/Drainage

http://en.wikipedia.org/wiki/Sail

http://en.wikipedia.org/wiki/Wind_farm

http://en.wikipedia.org/wiki/Wind_turbine

http://en.wikipedia.org/wiki/Electric_power_transmission


ENGINEERING/NOTES

less visual impact on the landscape but construction costs are considerably higher.

Furthermore, offshore poses problems when

considering accessibility for maintenance issues. Small onshore wind facilities are used to

provide electricity to isolated locations and utility companies increasingly buy surplus

electricity produced by small domestic wind turbines.

Wind power, as an alternative to fossil fuels, is plentiful, renewable, widely

distributed, clean, produces no greenhouse gas emissions during operation and uses little

land. The effects on the environment are generally less problematic than those from other

power sources. As of 2011, Denmark is generating more than a quarter of its electricity

from wind and 83 countries around the world are using wind power on a commercial

basis. In 2010 wind energy production was over 2.5% of total worldwide electricity usage,

and growing rapidly at more than 25% per annum. The monetary cost per unit of energy

produced is similar to the cost for new coal and natural gas installations.

Wind power is very consistent from year to year but has significant variation over

shorter time scales. The intermittency of wind seldom creates problems when used to

supply up to 20% of total electricity demand, but as the proportion increases, a need to

upgrade the grid, and a lowered ability to supplant conventional production can occur.

Power management techniques such as having excess capacity storage, geographically

distributed turbines, dis patchable backing sources, storage such as pumped-storage

hydroelectricity, exporting and importing power to neighboring areas or reducing demand

when wind production is low, can greatly mitigate these problems. In addition, weather

forecasting permits the electricity network to be readied for the predictable variations in

production that occur.

Types of Wind Machines

Wind machines (aerogenerators) are generally classified as follows:

1. Horizontal axis wind machines.

2. Vertical axis wind machines.

Horizontal axis wind machines. Figure shows a schematic arrangement of

horizontal axis machine. Although the common wind turbine with horizontal axis

is simple in principle yet the design of a complete system, especially a large

http://en.wikipedia.org/wiki/Net_metering



http://en.wikipedia.org/wiki/Fossil_fuel

http://en.wikipedia.org/wiki/Renewable_energy

http://en.wikipedia.org/wiki/Sustainable_energy

http://en.wikipedia.org/wiki/Greenhouse_gas

http://en.wikipedia.org/wiki/Environmental_impact_of_wind_power

http://en.wikipedia.org/wiki/Intermittent_power_sources

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity

http://en.wikipedia.org/wiki/Weather_forecast




ENGINEERING/NOTES

one that would produce electric power economically, is complex. It is of

paramount importance‟s that the components like rotor, transmission, generator

and tower should not only be as efficient as possible but they must also function

effectively in combination.

Figure: Horizontal axis wind machine.

Vertical axis wind machines. Figure shows vertical axis type wind machine.

One of the main advantages of vertical axis rotors is that they do not have to be

turned into the windstream as the wind direction changes. Because their

operation is independent of wind direction, vertical axis machine are called

panemones


ENGINEERING/NOTES

Figure: Vertical axis wind machine

Magneto Hydro Dynamic (MHD) Generator

Magnetohydrodynamics (MHD) is power generation technology in which

the electric generator is static (nonrotating) equipment. In the MHD concept, a

fluid conductor flows through a static magnetic field, resulting in a dc electric

flow perpendicular to the magnetic filed. MHD/steam combined cycle power

plants have the potential for very low heat rates (in the range of 6,500 Btu/kWh).

So2 and NOx emission levels from MHD plants are projected to be very low.

GEOTHERMAL ENERGY:

Geothermal energy is thermal energy generated and stored in the Earth. Thermal

energy is the energy that determines the temperature of matter. The Geothermal energy of

the Earth's crust originates from the original formation of the planet (20%) and

from radioactive decay of minerals (80%).[1][2]

The geothermal gradient, which is the

difference in temperature between the core of the planet and its surface, drives a continuous

conduction of thermal energy in the form of heat from the core to the surface. The

adjective geothermal originates from the Greek roots γη (ge), meaning earth, and

(thermos), meaning hot.


http://en.wikipedia.org/wiki/Temperature


http://en.wikipedia.org/wiki/Geothermal_energy#cite_note-ucsusa-1



http://en.wikipedia.org/wiki/Geothermal_gradient



ENGINEERING/NOTES

At the core of the Earth, thermal energy is created by radioactive decay and

temperatures may reach over 5000 degrees Celsius (9,000 degrees Fahrenheit). Heat

conducts from the core to surrounding cooler rock. The high temperature and pressure

cause some rock to melt, creating magma convection upward since it is lighter than the

solid rock. The magma heats rock and water in the crust, sometimes up to 370 degrees

Celsius (700 degrees Fahrenheit).

The Earth's geothermal resources are theoretically more than adequate to supply

humanity's energy needs, but only a very small fraction may be profitably exploited.

Drilling and exploration for deep resources is very expensive. Forecasts for the future of

geothermal power depend on assumptions

about technology, energy prices, subsidies, and interest rates. Pilot programs like EWEB's

customer opt in Green Power Program show that customers would be willing to pay a little

more for a renewable energy source like geothermal. But as a result of government assisted

research and industry experience, the cost of generating geothermal power has decreased by

25% over the past two decades. In 2001, geothermal energy cost between two and ten cents

per kwh.

A geothermal power plant uses its geothermal activity to generate power. This type

of natural energy production is extremely environmentally friendly and used in many

geothermal hot spots around the globe.

To harness the energy, deep holes are drilled into the earth (much like when drilling

for oil) until a significant geothermal hot spot is found.

When the heat source has been discovered, a pipe is attached deep down inside the

hole which allows hot steam from deep within the earth crust to rise up to the surface.

The pressurized steam is then channeled into a turbine which begins to turn under

the large force of the steam. This turbine is linked to the generator and so the generator also


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ENGINEERING/NOTES

begins to turn, generating electricity. We then pump cold water down a new pipe which is

heated by the earth and then sent back up the first pipe to repeat the process.

The main problems with geothermal energy is that firstly, you must not pump too

much cold water into the earth, as this could could cool the rocks too much, resulting in

your geothermal heat source cooling down. secondly, geothermal power plants must be

careful of escaping gases from deep within the earth.

We suggest if you would like to learn more on this topic, you take a look at

our advantages of geothermal energy, and our disadvantages of geothermal energy articles.

A very good way of thinking about geothermal energy is remembering that all our

continents lie on molten rock deep within the earth, this rock produces tremendous levels of

heat that we are able to extract, just think of your nation lying on a bed of fire.

Geothermal power is one of the most renewable energy sources that exists on our

planet today, the earth will contain this heat for our lifetime. If this heat disappears, our

planet will become too cold to survive on.

MHD POWER GENERATION:

The MHD (magnetohydrodynamic) generator transforms thermal energy and kinetic

energy directly into electricity. MHD generators are different from traditional electric

generators in that they operate at high temperatures without moving parts. MHD was

developed because the hot exhaust gas of an MHD generator can heat the boilers of

a steam power plant, increasing overall efficiency. MHD was developed as a topping

cycle to increase the efficiency of electric generation, especially when

burning coal or natural gas. MHD dynamos are the complement of MHD propulsors, which

have been applied to pump liquid metals and in several experimental ship engines.

An MHD generator, like a conventional generator, relies on moving a conductor

through a magnetic field to generate electric current. The MHD generator uses hot

http://www.clean-energy-ideas.com/articles/advantages_of_geothermal_energy.html

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conductive plasma as the moving conductor. The mechanical dynamo, in contrast, uses the

motion of mechanical devices to accomplish this. MHD generators are technically practical

for fossil fuels, but have been overtaken by other, less expensive technologies, such as

combined cycles in which a gas turbine's or molten carbonate fuel cell's exhaust

heats steam for steam turbine.

Natural MHD dynamos are an active area of research in plasma physics and are of

great interest to the geophysics and astrophysics communities, since the magnetic fields of

the earth and sun are produced by these natural dynamos.

MHD concept

The fundamental MHD concept is illustrated in figure. The fluid

conductor is typically an ionized flue gas resulting from combustion of

coal or another fossil fuel. Potassium carbonate, called ‚seed,‛ is injected

during the combustion process to increase fluid conductivity. The fluid

temperature is typically about 2,480C to 2,650C.

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ENGINEERING/NOTES

Figure: Basic magnetohydrodynamic concept

The conductive fluid flows through the magnetic fields, inducing an

electric field by the Faraday effect. The electric field is orthogonal to both

the fluid velocity and magnetic field vectors. As a result, a potential difference

is developed between the two walls of the duch as shown in figure. The direct

current (dc) generated is converted to alternating current (ac) by a solid-state

inverter.

CONSTRUCTION AND WORKING PRINCIPLE

The planned application of the MHD concept for utility scale electric power

generation uses MHD as a topping cycle combined with a steam bottoming cycle,

as shown in figure. The topping cycle consists of the coal combustor, nozzle,

MHD channel, magnet, power conditioning equipment (inverter) and a diffuser.

The bottoming cycle consists of a heat recovery/seed recovery unit, a particulate

removal system, a steam turbine-generator system, cycle compressor, seed

regeneration plant, and for some concepts, an oxygen plant.

The combustor burns coal to produce a uniform product gas with a high

electrical conductivity (about 10 mho/m). A typical MHD plant requires

combustion gases of about 2,650C at a pressure of 5 to 10 atmospheres. The

goal is to remove a large portion (50% to 70%) of the slag (molten ash) formed in

the combustion process in the combustor. High ash carryover inhabits efficient

seed recovery later in the process. Oxygen enriched air is used as the oxidant to

achieve high flue gas temperatures.

Commercial-scale MHD plants will use superconducting magnets. Magnetic

fields must be in the range of 4.5 to 6 tesla. To achieve superconducting

properties, the magnets must be cooled to about 4K.


ENGINEERING/NOTES

Figure: Layout of coal-fueled magnetohydrodynamics system.

In addition to converting direct current to alternating current, the

power conditioning system consolidates power from the electrode pairs and

controls the electric field and current. Commercial power conditioning systems

will use existing line-

commutated solid state inverter technology.

The diffuser is the transition between the topping cycle and the

bottoming cycle. The diffuser reduces the velocity of the hot gases from the

MHD channel, partially converting kinetic energy into static pressure.

The heat recovery/seed recovery unit consists of radiative and

convective heat transfer surfaces to generate and super heat steam. It also

removes slag and the seed from the flue gas. In addition, the heat recovery/seed

recovery preheats the oxidant supply NO2 control may be achieved within the

recovery unit by a second stage of combustion. The first stage of combustion

within the MHD combustor is conducted in a fuel-rich environment. The second

stage of combustion within the recovery unit takes place at a temperature above

1.540C with a residence time and cooling rate such that NOX decomposes into

N2 and O2.

Control of SOX is intrinsic with the removal of the potassium seed from

the flue gas. The potassium seed combines with the sulfur to form potassium

sulfate, which condenses and is removed downstream by the particulate

removal system. The recovered potassium sulfate is converted to potassium seed


ENGINEERING/NOTES

in the seed regeneration unit.

Thermo Electric Conversion System:

The quest for a reliable, silent, energy converted with no moving parts that

transforms heat to electrical power has led engineers to reconsider a set of

phenomena called the Thermoelectric effects. These effects, known for over a

hundred years, have permitted the development of small, self contained electrical

power sources

Seebeck (thermoelectric) effect:

The German Scientist Seebeck (in 1822) discovered that if two dissimilar material

are joined to form a loop and the two junctions maintained at different temperatures, and

e.m.f will be set up around the loop. The magnitude of e.m.f. will be E = T where T is

the temperature difference between the two junctions and is the Seebeck co-efficient.

This effect has long been used in thermocouples to measure temperatures

THERMO ELECTRIC AND THERMIONIC POWER GENERATORS:

Thermoelectric generators (also called See beck generators) are devices which

convert heat (temperature differences) directly into electrical energy, using a phenomenon

called the "See beck effect" (or "thermoelectric effect"). Their typical efficiencies are

around 5-8%. Older See beck-based devices used bimetallic junctions and were bulky.

More recent devices use semiconductor p-n junctions made from bismuth

telluride (Bi2Te3), lead telluride (PbTe), calcium manganese oxide, or combinations there

of, depending on temperature.

These are solid state devices and unlike dynamos have no moving parts, with the

occasional exception of a fan or pump.

Radioisotope thermoelectric generators can provide electric power for

spacecraft. Automotive thermoelectric generators are proposed to recover usable energy

from automobile waste heat.

A thermionic converter consists of a hot electrode which thermionically

emits electrons over a potential energy barrier to a cooler electrode, producing a useful

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ENGINEERING/NOTES

electric power output. Cesium vapor is used to optimize the electrode work functions and

provide an ion supply (by surface contact ionization or electron impact ionization in a

plasma) to neutralize the electron space charge.

Thermionic power converter also called thermionic generator, thermionic power

generator, or thermoelectric engine, any of a class of devices that convert heat directly into

electricity using thermionic emission rather than first changing it to some other form of

energy. A thermionic power converter has two electrodes. One of these is raised to a

sufficiently high temperature to become a thermionic electron emitter, or “hot plate.” The

other electrode, called a collector because it receives the emitted electrons, is operated at a

significantly lower temperature.

The space between the electrodes is sometimes a vacuum but is normally filled with

a vapor or gas at low pressure. The thermal energy may be supplied by chemical, solar, or

nuclear sources. Thermionic converters are solid-state devices with no moving parts. They

can be designed for high reliability and long service life. Thus, thermionic converters have

been used in many spacecraft. Emission of electrons from a hot plate is analogous to the

liberation of steam particles when water is heated.

These emitted electrons flow toward the collector, and the circuit can be completed

by interconnecting the two electrodes by an external load. Part of the thermal energy that is

supplied to liberate the electrons is converted directly into electrical energy, while some of

the thermal energy heats the collector and must be removed.

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

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http://www.britannica.com/EBchecked/topic/183035/electrode

http://www.britannica.com/EBchecked/topic/1067729/solid-state-device

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