ME6701 POWER PLANT ENGINEERING/ EEE DEPT/R SENTHI KUMAR VEL TECH HIGH TECH DR. RANGARAJAN DR.SAKUNTHALA ENGINEERING COLLEGE

ME6701 POWER PLANT ENGINEERING/ EEE DEPT/R SENTHI KUMAR VEL TECH HIGH TECH DR. RANGARAJAN DR.SAKUNTHALA ENGINEERING COLLEGE

UNIT-1 COAL BASED THERMAL POWER PLANTS

PART-A

1. What are the types of power plants?

1. Thermal Power Plant

2. Diesel Power Plant

3. Nuclear Power Plant

4. Hydel Power Plant

5. Steam Power Plant

6. Gas Power Plant

7. Wind Power Plant

8. Geo Thermal

9. Bio – Gas

10. M.H.D. Power Plant

2. What are the flow circuits of a thermal Power Plant?

1. Coal and ash circuits.

2. Air and Gas

3. Feed water and steam

4. Cooling and water circuits

3. List the different types of components (or) systems used in steam (or) thermal power plant?

1. Coal handling system.

2. Ash handling system.

3. Boiler

4. Prime mover

5. Draught system.

a. Induced Draught

b. Forced Draught 4.What are the merits of thermal power plants? 1.The unit capacity of thermal power plant is more. 2.The cost of unit decreases with the increase in unit capacity

3. Life of the plant is more (25-30 years) as compared to diesel plant (2-5 years)

4. Repair and maintenance cost is low when compared with diesel plant

5. Initial cost of the plant is less than nuclear plants

6. Suitable for varying load conditions.

5. What are the Demerits of thermal power plants?

Demerits of thermal Power Plants:

1. Thermal plant are less efficient than diesel plants

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

3. Cooling water required is more

4. Space required is more.

6. What are the various steps involved in coal handling system?

1. coal delivery

ME6701 POWER PLANT ENGINEERING/ EEE DEPT/R SENTHI KUMAR VEL TECH HIGH TECH DR. RANGARAJAN DR.SAKUNTHALA ENGINEERING COLLEGE

ME6701 POWER PLANT ENGINEERING/ EEE DEPT/R SENTHI KUMAR VEL TECH HIGH TECH DR. RANGARAJAN DR.SAKUNTHALA ENGINEERING COLLEGE

2. Unloading,

3. Preparation

4. Transfer

5. Outdoor storage

6. Covered storage

7. In-Plant handling

8. Weighing and measuring

9. Feeding the coal into furnace

7. After coal preparation, How the coal transfer?

1. Belt conveyors

2. Screw conveyors

3. Bucket elevation

4. Grab bucket elevators

5. Skip hoists

6. Flight conveyor.

8. Write the 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.

9.Write the classification of Mechanical Stokers?

1. Travelling grate stoker

2. Chain grate stoker

3. Spreader stoker

4. Vibrating grate Stoker

5. Underfeed stoker.

10.What are the three major factor consider for ash disposal system?

a. Plant site

b.Fuel source

c.Environmental regulation

11. Write the classification of Ash handling system?

1. Hydraulic system,

2. Pneumatic system

3. Mechanical system

12. What are the Ash discharge equipments?

1. Rail road cars

2. Motors truck

3. Barge

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13. Define 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.

14. What are the purpose of Draught.

(i) To supply required amount of air to the furnace for the combustion of fuel. The amount of fuel can be burnt per square foot of grate depends upon the quantity of air circulated through fuel bed.

(ii) To remove the gaseous products of combustion.

15.Define Condenser? A condenser is a device in which the steam is condensed by cooling it with water. The condensed steam is known as condensate.

16.Write the essential elements of a steam condensing plant?

1. A closed vessel in which the steam is condensed.

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

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

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

17.What are the sub division of jet condensers?

1.Low level counter flow jet condenser

2.High level (or) Barometric jet condenser

3.Ejector condenser.

18.Write the surface condenser?

1. Down flow condenser

2. Central flow condenser

3. Evaporative condenser

19.Write the advantages of surface condenser?

a. The condensate can be used as boiler feed water b. Cooling water of even poor quality can be used because the cooling water does not come

in direct contact with steam c. High vacuum (about 73.5 cm of Hg) can be obtained in the surface condenser. This

increases the thermal efficiency of the plant.

20.Write the De-merits of Natural Draught?

a. Maximum pressure available for producing draught by the chimney is less, b. Flue gases have to be discharged at higher temperature since draught increases with

the increase in temperature of flue gases. c. 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 .

21.Write the disadvantages of surface condenser?

1. The capital cost is more,

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

3. It is bulky and requires more space.

22.Name any two heat saving devices used in a thermal power plant?

i. Air pre heater ii. Economizer

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PART-B

I.Working of thermal power plant

Layout of steam power plant:

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:

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.

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 temperaturecorrosion 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.

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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.

Fuel (coal) and ash circuit

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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.

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.

Air and flue gas circuit

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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.

Cooling water circuit

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

Merits (Advantages) of a Thermal Power Plant

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 plant.

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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.

II.Type of Basic Boilers thermodynamic cycles 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

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 a

a. Carnot cycle

b. Rankine cycle

c. Reheat cycle

d. Regenerative cycle

e. Binary vapour cycle

Steam cycles (Rankine 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.

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Process of the Rankine Cycle

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.

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 (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 Qs =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

andpressure 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 QR = m (h2 – h3)

Description

Rankine cycles describe the operation of steam heat engines commonly found in power generation plants. In such vapour power plants, power is generated by alternatively vaporizingand condensing a working fluid (in many cases water, although refrigerants such as ammonia may also be used.)

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The working fluid in a Rankine cycle follows a closed loop and is re-used constantly. Water vapour seen billowing from power plants is evaporating cooling water, not working fluid. (NB: steam is invisible until it comes in contact with cool, saturated air, at which point it condenses and forms the white billowy clouds seen leaving cooling towers).

Variables

QS- heat supplied (energy per unit time)

m= mass flow rate (mass per unit time)

W- Mechanical power used by or provided to the system (energy per unit time)

- thermodynamic efficiency of the process (power used for turbine per heat input, unitless).

The thermodynamic efficiency of the cycle as the ratio of net power output to heat input.

Wnet Wturbine Wpump or Qs QR

Wnet / QS

Real Rankine Cycle variation of Basic Rankine Cycle

Real Ranking Cycle (Non-ideal)

In a real Rankine cycle, the

compression by the pump and the expansion in the turbine

are not isentropic. In other words, these processes are non-

reversible and entropy is increased during the two process

(indicated in the figure). This somewhat increases the power

required by the pump and decreases the power generated by

the turbine. It also makes calculations more involved and

difficult.

Rankine cycle with reheat

Schematic diagram and T-S diagram of Rankine cycle with reheat

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In this variation, two turbines work in series. The first accepts vapour from the boiler at high

pressure. After the vapour has passed through the first turbine, it re-enters the boiler and is reheated before passing through a second, lower pressure turbine. Among other advantages, this

prevents the vapour from condensing during its expansion which can seriously damage the turbine blades.

III. Explain a) Regenerative Ranking Cycle b) Binary Vapour 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.

Binary Vapour Cycle:Generally water is used a working fluid in vapour power cycle as it is found

to be better than any other fluid, but it is far from being the ideal one. The binary cycle is an

attempt to overcome some of the shortcomings of water and to approach the ideal working fluid

by using two fluids. The most important desirable characteristics of the working fluid suitable for

vapour cycles are

a .A high critical temperature and a safe maximum pressure.

b. Low- triple point temperature

c. Condenser pressure is not too low.

d. high enthalpy of vaporization

e. High thermal conductivity

f. It must be readily available, inexpensive

inert and non-toxic.

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Mercury-steam binary vapour cycle &T-S Diagram

Therefore it can be concluded that no single working fluids may have desirable

requirements of working fluid. Different working fluids may have different attractive feature in

them, but not all. In such cases two vapour cycles operating on two different working fluids are

put together, one is high temperature region and the other in low temperature region and the

arrangement is called binary vapour cycle.

The layout of mercury-steam binary vapour cycle is shown in figure. Along with the

depiction of T-S diagram figure. Since mercury having high critical temperature (898C) and low

critical pressure (180 bar) which makes a suitable working fluid will act as high temperature cycle

(toppling cycle) and steam cycle will act as low temperature cycle.

Here mercury vapour are generated in mercury boiler and sent for expansion in mercury

turbine and expanded fluid leaves turbine to condenser. In condenser, the water is used for

extracting heat from the mercury so as to condensate it. The amount water entering mercury

condenser. The mercury condenser also act as steam boiler for super heating of heat liberated

during condensation of mercury is too large to evaporate the water entering of seam an auxiliary

boiler may be employed or superheating may be realized in the mercury boiler itself.

IV. Types of pulverised coal firing system

a. Unit system (or) Direct System

b. Bin (or) Central system

c. Semi direct firing system.

Pulverized Coal Firing System: Pulverised coal firing is done by two systems:

i) Unit system or Direct System.

ii) Bin or Central system

Unit System: In this system, the raw coal from the coal bunker drops on to the feeder.

Unit System

Hot air is passed through coal in the factor to dry the coal. The coal is then transferred to the

pulverising mill where it is pulverised. Primary air is supplied to the mill, by the fan. The mixture

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of pulverized coal and primary air then flows to burner where secondary air is added. The unit

system is so called from the fact that each burner or a burner group and pulverized constitute a

unit.

Advantages:

1. The system is simple and cheaper than the central system

2. There is direct control of combustion from the pulverizing mill.

3. Coal transportation system is simple.

Central or Bin System: Crushed coal from the raw coal bunker is fed by gravity to a dryer where

hot air is passed through the coal to dry it. The dryer may use waste flue gasses, preheated air or

bleeder steam as drying agent. The dry coal is then transferred to the pulverizing mill. The

pulverized coal obtained is transferred to the pulverized coal bunker (bin). The transporting air is

separated from the coal in the cyclone separator. The primary air is mixed with the coal at the

feeder and the mixture is supplied to the burner.

Advantages

1. The pulverizing mill grinds the coal at a steady rate irrespective of boiler feed.

2. There is always some coal in reserve. Thus any occasional breakdown in the coal supply will not affect the coal feed to the burner.

3. For a given boiler capacity pulverizing mill of small capacity will be required as compared

to unit system.

Disadvantages

1. The initial cost of the system is high

2. Coal transport system is quite

complicated

3. The system requires more space.

Central or Bin system

IV.Fluidized Bed Boilers

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.

Advantages of fluidized bed combustion

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 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.

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Classification of Fluidized Bed Combustion:

1. Atmospheric fluidized Bed Combustion (AFBC)

a. Bubbling fluidized bed combustors

b. Circulating fluidized

2.Pressurized Fluidized Bed Combustin (PFBC)

1.8 Atmospheric Fluidized Bed Combustion (AFBC)

Bubbling fluidized bed combustor

A typical BFB arrangement is illustrated schematically in figure. Fuel and sorbent are

introduced either above or below the fluidized bed. (Overbed feed is illustrated.) The bed

consisting of about 97% limestone or inert material and 3% burning fuel, is suspended by hot

primary air entering the bottom of the combustion chamber. The bed temperature is controlled

by heat transfer tubes immersed in the bed and by varying the quantity of coal in the bed. As

the coal particle size decreases, as a result of either combustion or attrition, the particles are

elutriated from the bed and carried out the combustor. A portion of the particles elutriated

from the bed are collected by a cyclone (or multiclone) collector down-stream of the

convection pass and returned to the bed to improve combustion efficiency.

Secondary air can be added above the bed to improve combustion efficiency and to achieve staged combustion , thus lowering NOx emissions. Most of the early BFBs used tubular air heaters to minimize air leakage that could occur as a result of relatively high primary air pressures required to suspend the bed. Recent designs have included regenerative type air heaters.

Circulating fluidized bed combustor:A typical CFB arrangement is illustrated schematically in

figure. In a CFB, primary air is introduced into the lower portion of the combustor, where the

heavy bed material is fluidized and retained. The upper portion of the combustor contains the less

dense material that is entrained from the bed. Secondary air typically is introduced at higher levels

in the combustor to ensure complete combustion and to reduce NOx emissions.

.

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Atmospheric circulating bed combustor.

The flue gas, after removal of more than 99% of the entrained solids in the cyclone or particle separator, exists the cyclone or separator to a convection pass. The convection pass designs are similar to those used with unconvectional coal-fueled units, and contain economizer, superheat, and reheat surface as required by the application.

Pressurized fluidized Bed combustion

PFBC turbocharged arrangement

The PFBC unit is classified as either turbocharged or combined cycle units. In turbocharged

arrangements (figure) combustion gas from the PEBC boiler is cooled to approximately 394 C and

is used to drive a gas turbine. The gas turbine drives an air compressor, and there is little, if any, net gas turbine output. Electricity is produced by a turbine generator driven by steam generated in

the PFBC boiler.

VI.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

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7. Inplant handling

8. Weighing and measuring

9. Feeding the coal into furnace.

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(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 coal by trucks is used if the railway

facilities are not available.

(ii) Unloading:The type of equipment to be used for unloading the coal received at the power

station. depends on how coal is received at the power station. If coal delivered by trucks, there is

no need of unloading device as the trucks may dump the coal to the outdoor storage. Coal is easily

handled if the lift trucks with scoop are used. In case the coal is brought by railways wagons, ships

or boats, the unloading may be done by car shakes, rotary car dumpers, cranes, grab buckets and

coal accelerators. Rotary car dumpers although costly are quite efficient for unloading closed

wagons.

(iii) Preparation:When the coal delivered is in the form of big lumps and it is not of proper size,

the preparation (sizing) of coal can be achieved by crushers, breakers, sizers, driers and magnetic

separators.

iv)Transfer:After preparation coal is transferred to the dead storage by means of the following

systems.

1. Belt conveyors

2. Screw conveyors

3. Bucket elevators

4. Grab bucket elevators

5. Skip hoists

6. Flight conveyor

1.11 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 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

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2. Screw Conveyor: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.

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.

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 handing system and 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.

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The coal received by the plant from the mine may vary widely in sizes. It 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) Ball and Race 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.

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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:

Lower capital cost,Lower power consumption,Less space required,Less weight

VII.Ash Handling System:

Boilers burning pulverized coal (PC) have bottom furnaces. The large ash particles are collected

under the furnace in a water-filled ash hopper, Fly ash is collected in dust collectors with either an electrostatic precipitator or a baghouse. A PC boiler generates approximately 80% fly ash and 20%

bottom ash. Ash must be collected and transported from various points of the plants as shown in

figure. Pyrites, which are the rejects from the pulverizers, are disposed of with the bottom ash system. Three major factors should be considered for ash disposal systems

1. Plant site

2. Fuel source

3. Environmental regulation

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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.

Ash Handling Equipment:

Mechanical means are required for the disposal of ash. The handling equipment should perform

the following functions: 1. Capital investment, operating and maintenance charges of the

equipment should be low. 2. It should be able to handle large quantities of ash. 3. Clinkers, shoot,

dust etc. create troubles. The equipment should be able to handle them smoothly. 4. The equipment

used should remove the ash from the furnace, load it to the conveying system to deliver the ash to

dumping site or storage and finally it should have means to dispose of the stored ash. 5. The

equipment should be corrosion and wear resistant.

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.

Mechanical system:In this system ash cooled by water seal falls on the belt conveyor and is carried

out continuously to the bunker. The ash is then removed to the dumping site from the ash banker

with the help of trucks.

22

VIII. Draught and types of Draught.

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

flow passage and the ambient (same elevation) atmospheric pressure. Draught is plus if Patm < Pgas

and it is minus Patm > Pgas. Draught is achieved by small pressure difference which causes the flow

of air or gas to take place. It is measured in milimetre (mm) or water.

The purpose of draught is as follows:

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

The amount of fuel that can be burnt per square root of grate area depends upon the quantity of air circulated through fuel bed.

ii) To remove the gaseous products of combustion.

Classification of DRAUGHT:

Natural Draught :If only chimney is used to produce the draught, it is called natural draught.

Natural draught system is used only in small capacity boilers and it is not used in high capacity thermal plants.

23

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

Mechanical draught:It employs fan or blowers to produce the draught.

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

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

a)Forced Draught b) Induced Draught c) Balanced Draught

Forced Draught:In a forced draught system, a blower is installed near the base of the boiler and air

is forced to pass through the furnace, flues, economizer, air-preheater and to the stack. This

draught system is known as positive draught system or forced draught system because the

pressure and air is forced to flow through the system. The arrangement of the system is shown in

figure. A stack or chimney is also in this system as shown in figure but its function is to discharge

gases high in the atmosphere to prevent the contamination. It is not much significant for producing

draught therefore height of the chimney may not be very much.

Induced Draught:In this system, the blower is located near the base of the chimney instead of

near the grate. The air is sucked in the system by reducing the pressure through the system

below atmosphere. The induced draught fan sucks the burned gases from the furnace and the

pressure inside the furnace is reduced below atmosphere and induces the atmospheric air to

flow through the furnace. The action of the induced draught is similar to the action of the

chimney. The draught produced is independent of the temperature of the hot gases .

24

Balanced Draught:It is always preferable to use a combination of forced draught and induced

draught instead of forced or induced draught alone.If the forced draught is used alone, then the

furnace cannot be opened either for firing or inspection because the high pressure air inside the

furnace will try to blow out suddenly and there is every chance of blowing out the fire completely

and furnace stops.

Compare Forced and Induced Draught?

S. No Forced Draught Induced Draught

1. The size and power required by The size and power required by I.D.

the F.D. fan is less. fan is more.

2. Volume of gas handled is less. Volume of gas handled is more.

Water cooled bearings are not Water cooled bearings are required to

required. withstand high temperature flue gas.

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Unit II – Diesel, Gas Turbines and Combined cycle Power Plants

1.Gas Turbine Power plant

A gas turbine power plant may be defined as one “in which the principal prime mover is of the turbine type

and the working medium is a permanent gas”.

A simple gas turbine plant consists of the following:

1. compressor 2. Intercooler 3. Regenerator 4. Combustion chamber 5. Gas turbine 6.Reheating unit

Compressor:

In gas turbine plant, the axial and centrifugal flow compressors are used. In most of the gas turbine power

plant, two compressors are used. One is low pressure compressor and the other is high pressure compressor. In low

pressure compressor, the atmospheric air is drawn into the compressor through the filter. The major part of the

power developed by the turbine (about 66%) is used to run the compressor. This low pressure air goes to the high

pressure compressor through the intercooler. Then the high pressure air goes into the regenerator.

2. Intercooler:

The intercooler is used to reduce the work of the compressor and it is placed in between the high pressure

and low pressure compressor. Intercoolers are generally used when the pressure ratio is very high. The energy

required to compress the air is proportional to the air temperature at inlet. The cooling of compressed air in

intercooler is generally done by water.

3. Regenerator:

Regenerators are used to preheat the air which is entering into the combustion chamber to reduce the fuel

consumption and to increase the efficiency. His is done by the heat of the hot exhaust gases coming out of the

turbine.

4. Combustion chambers

Hot air from regenerator flows to the combustion chambers and the fuel like coal, natural gas or kerosene

are injected into the combustion chamber. After the fuel injection, the combustion takes place. This high pressure,

high temperature products of combustion are passed through the turbine.

Fig.1.3 Layout of Gas turbine power plant

5. Gas turbine

Two types of gas turbines are used in gas turbine plant.

- High pressure turbine

- Low pressure turbine

1. High Pressure turbine

In the beginning, the starting motor runs the compressor shaft. The burnt gases (product of combustion)

expand through the high pressure turbine. It is important to note that when the turbine shaft rotates it in fact drives

the compressor shaft which is couples to it. Now, the high pressure turbine runs the compressor and the starting

motor is stopped. About 66% of the power developed by the turbine is used to run the compressor and only 34% of

the power developed is used to generate electric power.

2. Low pressure turbine

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The purpose of the low pressure turbine is to produce electric power. The shaft of the LPT is coupled with

the generator. The burnt fuel (gases) after leaving the HPT is again sent to a combustion chamber where it further

undergoes combustion. Even if there is any left out unburnt fuel from the previous turbine it gets fully burnt in the

combustion chamber. The burnt gases run the low pressure turbine (LPT). The shaft of the turbine is directly

coupled with the generator for producing electricity. The exhaust hot gases after leaving the LPT passes through the

regenerator before exhausted through the chimney into the atmosphere. The heat from the hot gases is used to

preheat the air leaving the HPC before it enters the combustion chamber. This preheating of the air improves the

efficiency of the combustion chamber.

Working of Gas Turbine Power plant

The working of gas turbine plant is shown in fig.1.3. The atmosphere air is drawn into the low pressure

compressor through the air filter and it is compressed.

The compressed low pressure air goes into the high pressure compressor through the intercooler. Here, the

heat of the compressed air is removed. Then the high pressure compressed air goes into the combustion chamber

through the regenerator. In the combustion chamber, the fuel is added to the compressed air and the combustion of

the fuel takes place.

The product of the combustion goes into the high pressure turbine. The exhaust of the high pressure turbine

goes to another combustion chamber and the additional fuel is added and it goes to the low pressure turbine.

After the expansion in the low pressure turbine, the exhaust is used to heat the high pressure air coming to

the combustion chamber through the regenerator. After that, the exhaust goes to the atmosphere.

Advantages of Gas turbine power plant:

- For a gas turbine plant, Natural gas is a very suitable fuel. It would be ideal to install gas turbine plants near

the site where natural gas is readily available.

- Gas turbine plants can work economically for short running hours.

- Storage of fuel requires less area and handling is easy.

- Gas turbine plant is small and compact in size as compared to steam power plants.

- It can be started quickly and can be put on load in a very short time.

- The cost of maintenance is less.

- It is simple in construction. There is no need for boiler, condenser and other accessories as in the case of

steam power plants.

- The gas turbine can operate at high speed since there are no reciprocating parts

- Cheaper fuel such as kerosene, paraffin, benzene and powdered coal (cheaper than petrol and diesel) can be

used.

- Gas turbine plants can be used in water scarcity areas

- Less pollution and less water is required.

Disadvantages of gas turbine power plant:

- 66% of the power developed is used to drive the compressor; the gas turbine unit has a low thermal

efficiency

- The running speed of the gas turbine is in the range of (40, 000 to 1, 00,000 rpm) and the operating

temperature is as high as 2000 0C, for this reason special metals and alloys have to be used for the various

parts of the turbine.

- Special cooling methods are required for cooling the turbine blades.

- It is difficult to start a gas turbine as compared to a diesel engine in a diesel power plant

- The life of a gas turbine plant is upto 10 years, after which its efficiency decreases to less than 10 percent.

Applications of gas turbine power plant:

- To drive generators and supply loads in steam, diesel or hydro plants

- To work as combination plants with conventional steam boilers

- Thermal process industries

- Petro chemical industries

- Power generation (used for peak load and as stand by unit)

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- Aircraft and ships for their propulsion. They are not suitable for automobiles because of their very high

speeds.

Classification of Gas Turbine

Gas turbines may be broadly classified as:

Open cycle gas turbine Closed cycle gas turbine

Open cycle gas turbine

In the open cycle gas turbine, fig.1.4, air is drawn into the compressor from the atmosphere. The

compressed air is heated by directly burning the fuel in the air at constant pressure inside the combustion chamber.

The high pressure hot gases from the combustion chamber drive the turbine and the power is developed when the

turbine shaft rotates.

Gas turbines are not self starting. A starting motor drives the compressor till fuel is injected inside the

combustion chamber, once the turbine starts gaining speed the starting motor is disengaged.

Part of the power developed by the gas turbine (about 60%) is used to drive the compressor and the

remaining is used to drive a generator or other machinery.

Open cycle gas turbine

In the open cycle, system, the working fluid i.e. air and the fuel must be replaced continuously as they are

exhausted into the atmosphere. Thus the entire flow comes from the atmosphere and is returned to the atmosphere,

hence it is called “open cycle”.

Closed cycle gas turbine

In this the compressed air from the atmosphere is heated in air heater (heat exchanger). Heat is added to the air

heater from some external source (oil or coal) at constant pressure. High pressure working fluid expands through the

turbine and power is developed. The exhaust working fluid is cooled in a pre cooler before the same fluid is sent into

the compressor again.

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Closed cycle gas turbine

S.no Closed Cycle Gas Turbine Open Cycle Gas Turbine

1.

In this first the air is compressed in the

compressor and then heated

in a heating chamber. As the air is heated by an

external source, so the amount of the gas remains

same.

Here the compressed air is heated in the combustion

chamber. So the

products of combustion gets mixed with the heated

air and hence the amount of

gas does not remain same.

2.

In closed cycle gas turbine, the gas that comes out

from the gas

turbine passes into the cooling chamber.

In open cycle, the gases coming out from the gas

turbine is exhausted

in the atmosphere.

3. The working fluid is circulated continuously. The working fluid is replaced continuously.

4.

Any other fluid that possesses better

thermodynamic properties like helium

can be used. Here only air can be used as the working fluid.

5.

No earlier wear of the turbine blades, because the

enclosed gas does

not gets contaminated while flowing through the

heating chamber,

Earlier wear of turbine blades, as the air form the

atmosphere enters the

combustion chamber it gets contaminated.

6.

It is best suited for the stationary installation and

marine uses

because the air from the turbine is cooled by the

circulating water.

It is best suited for the moving vehicle because the

air from the

turbine is discharged into the atmosphere.

7.

The maintenance cost of this type of turbine is

high. Its maintenance cost is low.

8. More mass of installation per kW.

Less mass of installation per

kW.

2.Layout of Diesel Power plant

The essential components of diesel power plant are

- Diesel engine

- Air filter and super charger

- Engine starting system

- Fuel system

- Lubrication system

- Cooling system

- Governing system

- Exhaust system

Diesel engine:

This is the main component of a diesel power plant. The engines are classified as two stroke engine and four stroke

engines. Engines are generally directly coupled to the generator for developing power. In diesel engines, air

admitted into the cylinder is compressed. At the end of compression stroke, fuel is injected. The fuel is burned and

the burning gases expand and do work on the piston. The shaft of the engine is directly coupled to the generator.

After the combustion, the burned gases are exhausted to the atmosphere.

Air filter and supercharger

The air filter is used to remove the dust from the air which is taken by the engine. Air filters may be of dry type,

which is made up of felt, wool or cloth. In oil bath type of filters, the air is swept over a bath of oil so that dust

particles get coated. The function of the supercharger is to increase the pressure of the air supplied to the engine and

thereby the power of the engine is increased.

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Engine starting system

Diesel engine used in diesel power plants is not self starting. Engine starting system includes air compressor and

starting air tank. This is used to start the engine in cold conditions by supplying the air.

Fuel system

It includes the storage tank, fuel pump, fuel transfer pump, strainers and heaters. Pump draws diesel from

the storage tank and supplies it to the small day tank through the filter.

Day tank supplies the daily fuel need for the engine. The day tank 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 injection

system performs the following functions.

- Filter the fuel

- Meter the correct quantity of the fuel to be injected

- Time the injection process

- Regulate the fuel supply

- Secure fine atomization of fuel oil

- Distribute the atomized fuel properly in the combustion; chamber.

- The fuel is supplied to the engine according to the load on the plant.

Lubrication system It includes oil pumps, oil tanks, coolers and pipes. It is used to reduce the friction of moving

parts and reduce wear and tear of the engine parts such as cylinder walls and piston. Lubrication oil which gets

heated due to the friction of the moving parts is cooled before recirculation.

In the lubrication system the oil is pumped from the lubricating oil tank through the oil cooler where the oil is cooled

by the cold water entering the engine. The hot oil after cooling the moving parts return to the lubricating oil tank.

Cooling system The temperature of the burning fuel inside the engine cylinder is in the order of 15000 C to 20000 C.

In order to lower this temperature, water is circulated around the engine. The water envelopes (water jacket) the

engine, the heat from the cylinder, piston, combustion chamber etc, is carried by the circulating water. The hot water

leaving the jacket is passed through the heat exchanger. The heat from the heat exchanger is carried away by the raw

water circulated through the heat exchanger and is cooled in the cooling tower.

Governing system It is used to regulate the speed of the engine. This is done by varying the fuel supply according

to the engine load.

Exhaust system The exhaust gases coming out of the engine is very noisy. In order to reduce the noise a silencer

(muffler) is used.

Air intake system:

An intake or (for aircraft) inlet is an opening on a car or aircraft body capturing air for operation of

an internal combustion engine. Because the modern ground vehicle internal combustion engine is in essence a

powerful air pump, like the exhaust system on an engine, the intake must be carefully engineered and tuned to

provide the greatest efficiency and power. An ideal intake system should increase the velocity of the air until it

travels into the combustion chamber, while minimizing turbulence and restriction of flow. However, in aircraft,

particularly supersonic aircraft, the purpose of the intake is to slow and increase the pressure of the air.

Exhaust System:

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An exhaust system is usually piping used to guide reaction exhaust gases away from a

controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and

includes one or more exhaust pipes. Depending on the overall system design, the exhaust gas may flow through one

or more of:

- Cylinder head and exhaust manifold

- A turbocharger to increase engine power.

- A catalytic converter to reduce air pollution.

- A muffler (North America) / silencer (UK/India), to reduce noise.

Common rail injection System:

Common rail direct fuel injection is a direct fuel injection system for diesel engines. On diesel engines, it

features a high-pressure (over 100 bar or 10 MPa or 1,500 psi) fuel rail feeding individual solenoid valves, as

opposed to a low-pressure fuel pump feeding unit injectors (or pump nozzles). Third-generation common rail diesels

now feature piezoelectric injectors for increased precision, with fuel pressures up to 2,500 bar (250 MPa;

36,000 psi). In petrol engines, it is used in Gasoline direct injection (GDI) engine technology.

Individual pumps injection system:

Distributer System:

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A distributor is an enclosed rotating shaft used in spark-ignition internal combustion engines that have

mechanically-timed ignition. The distributor's main function is to route secondary, or high voltage, current from

the ignition coil to the spark plugs in the correct firing order, and for the correct amount of time. Except

in magneto systems, the distributor also houses a mechanical or inductive breaker switch to open and close the

ignition coil's primary circuit.

Cooling System:

Cooling system, apparatus employed to keep the temperature of a structure or device from exceeding limits

imposed by needs of safety and efficiency. If overheated, the oil in a mechanical transmission loses its lubricating

capacity, while the fluid in a hydraulic coupling or converter leaks under the pressure created. In an electric motor,

overheating causes deterioration of the insulation. The pistons in an overheated internal-combustion engine may

seize (stick) in the cylinders. Cooling systems are employed in automobiles, industrial plant machinery, nuclear

reactors, and many other types of machinery. (For a treatment of cooling systems used in buildings, see air-

conditioning.)

1. Air cooling 2. Liquid cooling

Air Cooling:

Air cooling is a method of dissipating heat. It works by expanding the surface area or increasing the flow of

air over the object to be cooled, or both. An example of the former is to add cooling fins to the surface of the object,

either by making them integral or by attaching them tightly to the object's surface (to ensure efficient heat transfer).

In the case of the latter, it is done by using a fan blowing air into or onto the object one wants to cool. The addition

of fins to a heat sink increases its total surface area, resulting in greater cooling effectiveness. In all cases, the air has

to be cooler than the object or surface from which it is expected to remove heat. This is due to the second law of

thermodynamics, which states that heat will only move spontaneously from a hot reservoir (the heat sink) to a cold

reservoir (the air).

Liquid Cooling:

1. Single circuit cooling System 2. Double circuit cooling system

Single circuit cooling System:

Single-circuit cooling system is used to cool down process and devices which have within a certain period

of time a constant cooling water flow. Normally such cooling systems are used for production lines which function

with ON/OFF regime as a whole. Pumps, which ensure water flow, pump cold water from the cooling water pool

and they supply it to the consumers. The water heated by the consumers is directed to cooling towers to be cooled

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again. Cooled water is then directed back to cooling water pools. In open system of cooling towers a part of energy

is transmitted by means of heat transfer from water into the air, one part is released through evaporation. That kind

of cooling systems is used, when temperature of cooled cooling water is some degrees higher than the one of the wet

bulb thermometer. Due to a constant evaporation, when water is released from the system in the form of water

vapour, the concentration of other substances is rising, which is also called condensed water.

Double circuit cooling System:

Double Circuit Cooling Coils : We are Double Circuit Cooling Coils used widely in heavy industries

including marine motor vessels. These are designed to offer the optimum level of heating and cooling levels desired.

Further, our range of cooling coils are designed to maximize heat transfer, within the constraints of air pressure drop

across the cooling coil.

Types of lubrication System:

1. Wet sump lubrication system 2. Dry sump lubrication system. 3. Mist sump lubrication system.

Wet sump lubrication system:

A wet sump is a lubricating oil management design for piston engines which uses the crankcase as a built-

in reservoir for oil, as opposed to an external or secondary reservoir used in a dry sump design. Piston engines are

lubricated by oil which is pumped into various bearings, and thereafter allowed to drain to the base of the engine

under gravity. In most production automobiles and motorcycles, which use a wet sump system, the oil is collected in

a 3 to 10 litres (0.66 to 2.20 imp gal; 0.79 to 2.64 US gal) capacity pan at the base of the engine, known as

the sump or oil pan, where it is pumped back up to the bearings by the oil pump, internal to the engine.

Dry sump lubrication system:

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A dry-sump system is a method to manage the lubricating motor oil in four-stroke and large two-

stroke piston driven internal combustion engines. The dry-sump system uses two or more oil pumps and a separate

oil reservoir, as opposed to a conventional wet-sump system, which uses only the main sump (U.S.: oil pan) below

the engine and a single pump. A dry-sump engine requires a pressure relief valve to regulate negative pressure inside

the engine, so internal seals are not inverted.

Engines are both lubricated and cooled by oil that circulates throughout the engine, feeding

various bearings and other moving parts and then draining, via gravity, into the sump at the base of the engine. In

the wet-sump system of most production automobile engines, a pump collects this oil from the sump and directly

circulates it back through the engine. In a dry-sump, the oil still falls to the base of the engine, however instead of

collecting in a reservoir-style oil sump, it falls into a much shallower sump, where one or more scavenge pumps

draw it away and transfer it to a (usually external) reservoir, where it is both cooled and de-aerated before being re

circulated through the engine by a pressure pump. Dry-sump designs frequently mount the pressure pump and

scavenge pumps on a common crankshaft, so that one pulley at the front of the system can run as many pumps as the

engine design requires. It is common practice to have one scavenge pump per crankcase section, however in the case

of inverted engines (aircraft engine) it is necessary to employ separate scavenge pumps for each cylinder bank.

Therefore, an inverted V engine would have a minimum of two scavenge pumps and a pressure pump in the

pump stack.

Mist sump lubrication system:

Oil mist lubrication oils are applied to rolling element (antifriction) bearings as an oil mist. Neither oil

rings nor constant level lubricators are used in pumps and drivers connected to plant-wide oil mist systems. Oil mist

is an atomized amount of oil carried or suspended in a volume of pressurized dry air. The oil mist, actually a ratio of

one volume of oil suspended or carried in 200,000 volumes of clean, dry air, moves in a piping system (header). The

point of origin is usually a mixing valve (the oil mist generator), connected to this header. Branch lines often feed oil

mist to hundreds of rolling elements in the many pumps and drivers connected to a plant-wide system.

At standstill, or while on standby, pump and driver bearings are preserved by the surrounding oil mist,

which exists in the bearing housing space at a pressure just barely higher than ambient. These pump and driver

bearings are lubricated from the time when atomized oil globules join (or wet out) to become larger oil droplets.

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This joining-into-large-droplets starts whenever the equipment shafts rotate, which is when small globules come into

contact with each other and start coating the bearing elements.

Working of Diesel Power Plant

The air and fuel mixture act as a working medium in diesel engine power plant. The atmosphere air enters

inside the combustion chamber during the suction stroke and the fuel is injected through the injection pump. The air

and fuel is mixed inside the engine and the charge is ignited due to high compression inside the engine cylinder. The

basic principle in diesel engine is that, the thermal energy is converted into mechanical energy and this mechanical

energy is converted into electrical energy to produce the power by using generator or alternator.

Applications of Diesel Engines in Power Field:

The diesel electric power plants are chiefly used in the following field.

Peak load plant: Diesel plants can be used in combination with thermal or hydro-plants as peak load units. They can

be easily started or stopped at a short notice to meet the peak demand.

Mobile plant: Diesel plants mounted on trailers can be used for temporary or emergency purposes such as for

supplying power to large civil engineering works.

Standby unit: If the main unit fails or cannot cope up with the demand, a diesel plant can supply the necessary

power. For example, if water available in a hydro-plant is not adequately available due to less rainfall, the diesel

station can operate in parallel to generate the short fall in power.

Emergency plant: During power interruption in a vital unit like a key industrial plant or a hospital, a diesel electric

plant can be used to generate the needed power.

Nursery station: In the absence of main grid, a diesel plant can be installed to supply power in a small town. In

course of time, when electricity from the main grid becomes available in the town, the diesel unit can be shifted to

some other area which needs power on a small scale. Such a diesel plant is called a "nursery station".

Starting stations: Diesel units can be used to run the auxiliaries (like FD and ID fans, BFP, etc.) for starting a large

steam power plant.

Central stations: Diesel electric plants can be used as central station where the capacity required is small

LAYOUT DIESEL POWER PLANT

Advantages of diesel power plant:

- It is easy to design and install these electric stations.

- They are easily available in standard capacities.

- They can respond to load changes without much difficulty.

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- There are less standby losses.

- They occupy less space.

- They can be started and stopped quickly.

- They require less cooling water.

- Capital cost is less.

- Less operating and supervising staff required.

- High efficiency of energy conversion from fuel to electricity.

- Efficiency at part loads is also higher.

- Less of civil engineering work is required.

- They can be located near the load centre.

- There is no ash handling problem.

Disadvantages in installing diesel units for power generation

- High operating cost.

- High maintenance and lubrication cost.

- Capacity is restricted. Cannot be of very big size.

- Noise problem.

- Cannot supply overload.

- Unhygienic emissions.

3.Combined Cycle Power Plants

Combined Gas turbine and steam power plants

Combined gas and steam (COGAS) is the name given to marine compound power plants

comprising gas and steam turbines, the latter being driven by steam generated using the heat from the exhaust of the

gas turbines. In this way, some of the otherwise lost energy can be reclaimed and the specific fuel consumption of

the plant can be decreased. Large (land-based) electric power plants built using this combined cycle can reach

conversion efficiencies of over 60%.

If the turbines do not drive a propeller shafts directly and instead a turbo-electric transmission is used, the

system is also known as COGES.

COGAS differs from many other combined marine propulsion systems in that it is not intended to operate

on one system alone. While this is possible, it will not operate efficiently this way, as with Combined diesel and

gas systems when run solely on diesel engines. Especially COGAS should not be confused with Combined steam

and gas (COSAG) power plants, which employ traditional, oil-fired boilers for steam turbine propulsion for normal

cruising, and supplement this with gas turbines for faster reaction times and higher dash speed.

COGAS has been proposed as upgrade for ships that use gas turbines as their main (or only) engines, e.g.

in COGOG or COGAG mode, such as the class destroyers, but currently no naval ship uses this concept. However

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some modern cruise ships are equipped with COGES and other ships of her class use turbo-electric plants with

two General Electric LM2500+ gas turbines and one steam-turbine.

BMW is currently researching combined gas and steam for automotive use, using their turbo

steamer system. This uses the waste heat of combustion from the exhaust and turns it into steam to produce torque

which is input into the crankshaft.

The gas turbine is one of the most efficient one for the conversion of gas fuels to mechanical power or

electricity. The use of distillate liquid fuels, usually diesel, is also common as alternate fuels.

More recently, as simple cycle efficiencies have improved and as natural gas prices have fallen, gas

turbines have been more widely adopted for base load power generation, especially in combined cycle mode, where

waste heat is recovered in waste heat boilers, and the steam used to produce additional electricity.

The advantages of combined gas-steam cycles may be summarized as follows:

1. High overall plant efficiency

2. Low investment costs

3. Small amount of water required

4. Great operating flexibility

5. Phased installation

6. Simplicity of operation

7. Low environmental impact

8. Advantages for cogenerations of heat and electricity

4.INTEGRATED GASIFICATION COMBINED CYCLE (IGCC)

An integrated gasification combined cycle (IGCC) is a technology that uses a high pressure gasifier to

turn coal and other carbon based fuels into pressurized gas synthesis gas . It can then remove impurities from the

syngas prior to the power generation cycle. Some of these pollutants, such as sulfur, can be turned into re-usable

byproducts through the Claus process. This results in lower emissions of sulfur dioxide, particulates, mercury, and in

some cases carbon dioxide. With additional process equipment, a water-gas shift reaction can increase gasification

efficiency and reduce carbon monoxide emissions by converting it to carbon dioxide. The resulting carbon dioxide

from the shift reaction can be separated, compressed, and stored through sequestration. Excess heat from the primary

combustion and syngas fired generation is then passed to a steam cycle, similar to a combined cycle gas turbine.

This process results in improved thermodynamic efficiency compared to conventional pulverized coal combustion.

The gasification process can produce syngas from a wide variety of carbon-containing feed stocks, such as

high-sulfur coal, heavy petroleum residues, and biomass. The plant is called integrated because (1) the syngas

produced in the gasification section is used as fuel for the gas turbine in the combined cycle and (2) the steam

produced by the syngas coolers in the gasification section is used by the steam turbine in the combined cycle. In this

example the syngas produced is used as fuel in a gas turbine which produces electrical power. In a normal combined

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cycle, so-called "waste heat" from the gas turbine exhaust is used in a Heat Recovery Steam Generator (HRSG) to

make steam for the steam turbine cycle. An IGCC plant improves the overall process efficiency by adding the

higher-temperature steam produced by the gasification process to the steam turbine cycle. This steam is then used in

steam turbines to produce additional electrical power.

IGCC plants are advantageous in comparison to conventional coal power plants due to their high thermal

efficiency, low non-carbon greenhouse gas emissions, and capability to process low grade coal. The disadvantages

include higher capital and maintenance costs, and the amount of CO2 released without pre-combustion capture.

Advantages of IGCC:

1. They use less coal than conventional power plants to given same output.

2. They are very clean and highly efficient.

3. Sulphur and other emissions are reduced.

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PART – A

1. Define Isotopes and isotones

Those pairs of atoms which have the same atomic number and hence similar chemical

properties but different atomic mass number are called isotopes.Those atoms whose nuclei

have the same number of neutrons are called isotones.

2. Define Radioactivity?

The phenomenon of spontaneous emission of powerful radiations exhibited by heavy

element is called radioactivity. The radioactivity may be natural or artificial.

3. Write the types of Nuclear radiations?

The five types of nuclear radiations are

(i) Gamma rays (or photons) : electromagnetic radiation.

(ii) Neutrons : uncharged particles, mass approximately 1.

(iii) Protons : + 1 charged particles, mass approximately 1.

(iv) Alpha particles : helium nuclei, charge + 2, mass 4.

(v) Beta particles : electrons (charge – 1), positrons (charge + 1), mass very small.

4. Define Fertile Materials? It has been found that some materials are not fissionable by themselves but they can be converted to the fissionable materials, these are known as fertile materials. 5. Define Fission?

Fission is the process that occurs when a neutron collides with the nucleus of certain of heavy atoms, causing the original nucleus to split into two or more unequal fragments which carry-off most of the energy of fission as kinetic energy. This process is accompanied by the emission of neutrons and gamma rays.

6. Define chain reaction?

A chain reaction is that process in which the number of neutrons keeps on multiplying rapidly (in

geometrical progression) during fission till whole the fissionable material is disintegrated. The

multiplication or reproduction factor (K) is given by

K= No. of neutrons in any particular generation

No. of neutrons in the preceding generation

If K > 1, chain reaction will continue and if K < 1, chain reaction cannot be maintained.

7. Define Nuclear fusion?

Nuclear fusion is the process of combining or fusing two lighter nuclei into a stable and heavier

nuclide. In this case large amount of energy is released because mass of the product nucleus is less

than the masses of the two nuclei which are fused.

8. Write the Essential components of a nuclear reactor?

(i) Reactor core

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(ii) Reflector

(iii) Control mechanism

(iv) Moderator

(v) Coolants

(vi) Measuring instruments

(vii) Shielding.

9.Mention some important reactors

(i) Pressurized water reactor (PWR)

(ii) Boiling water reactor (BWR)

(iii) Gas-cooled reactor

(iv) Liquid metal-cooled reactor

(v) Breeder reactor.

10.What are the factors are consider to selecting the site for Nuclear power plant?

(i) Proximity to load centre

(ii) Population distribution

(iii) Land use

(iv) Meteorology

(v) Geology

(vi) Seismology

(vii) Hydrology

11.What are the advantages of nuclear power plant?

1. It can be easily adopted where water and coal resources are not available.

2. The Nuclear power plant requires very small quantity of fuel. Hence fuel transport cost is less.

3. Space requirement is very less compared to other power plant of equal capacity.

4. It is not affected by adverse weather condition.

12.Mention any 3 fast breeder reactors?

1. Liquid Metal

2. Helium

3. Carbon dioxide

13.Write the effects of Nuclear radiation?

1. Ionization

2. Displacement

3. Absorption

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PART – B

I short notes (a) Fission Energy (b) Chain Reaction (c) Fusion Energy

A nuclear power plant is similar to a conventional steam power plant except how that energy is

evolved. The heat is produced in the nuclear power plant by fission, whereas in steam and gas turbine plants, the heat is produced by combustion in the furnace. The nuclear reactor acts as a

furnace where nuclear energy is evolved by splitting or fissioning of the nucleus of fissionable

material like Uranium U-235. It is claimed that 1 kg U-235 can produce as much heat energy that

can be produced by burning 4500 tones of high grade coal or 1700 tons of oil.

a.Fission energy

Nuclear energy is divided from splitting (or) fissioning of the nucleus of fissionable material

like Uranium U-235. Uranium has several isotopes (Isotopes are atoms of the same element having

different atomic masses) such as U-234, U-235 and U-238. Of the several isotopes, U-235 is the most

unstable isotope, which is easily fissionable and hence used as fuel in an atomic reactor.

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

1.5×107 m/sec and along with this produces a large amount of energy, nearly 200 million electro-volts. This is called nuclear fission.

b. Chain reaction

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

The chain reaction under controlled conditions can release extremely large amount of energy causing ‚atomic explosion

Energy released in chain reaction, according to Einstein law is

E = mc2

Where E = Energy liberated (J)

m= Mass (kg)

c = Velocity of light (3 × 108 m/sec).

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Out of 2.5 neutrons released in fission of each nucleus of U-235, one neutron is used to sustain the

chain reaction, about 0.9 neutron is captured by U-238, which gets converted into fissionable material Pu-239 and about 0.6 neutron is partially absorbed by control rod materials, coolant and moderator.If thorium is used in the reactor core, it gets converted to fissionable material U-233.

Thorium 232 + Neutron U-233

Pr-239 and U-233 so produced are fissionable materials are called secondary fuels. They can be used as nuclear fuels. U-238 and Th-232 are called fertile materials.

2. Fusion energy

Energy is produced in the sun and stars by continuous fusion reactions in which four nuclei of

hydrogen fuse in a series of reactions involving other particles that continually appear and

disappear in the course of the reaction, such as He3, nitrogen, carbon, and other nuclei, but

culminating in one nucleus of helium of two positrons.

41 H 1 21 e 4 0

2 He

To cause fusion, it is necessary to accelerate the positively charged unclei to high kinetic

energies, in order to overcome electrical repulsive forces, by raising their temperature to hundreds

of millions of degrees resulting in plasma. The plasma must be prevented from contacting the

walls of the container, and must be confined for a period of time (of the order of a second) at a

minimum density. Fusion reactions are called thermonuclear because very high temperatures are required to trigger and sustain them. Table lists the possible fusion reactions and the energies

produced by them. n, p, D, and T are the symbols for the neutron, proton, deuterium (H2), and

tritium (H3), respectively.

Number

Fusion reaction Energy perreaction

MeV

Reactants Products

1 D + D T + p 4

2 D + D He3 + n 3.2

3 T + D He4 + n 17.6

4 He3 + D He4 + p 18.3

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Many problems have to be solved before an artificially made fusion reactor becomes a reality. The most important of these are the difficulty in generating and maintaining high temperatures and the instabilities in the medium (plasma), the conversion of fusion energy to electricity, and many other problems of an operational nature.

II.construction and working principle of Pressurized Water(PWR)

Working principle:

A nuclear power plant differs from a conventional steam power plant only in the steam generating part. There is no change in the turbo-alternator and the condensing system.The nuclear fuel which is at present in commercial use is Uranium. Heat energy evolved by the fission reaction of one kg

of U235 can produce as much energy as can be produced by burning 4500 tons of high grade coal.

Uranium exists in the isotopic form of U235 which is unstable. When a neutron enters the nucleus of

U235, the nucleus splits into two equal fragments and also releases 2.5 fast moving neutrons with a

velocity of 1.5 × 107 metres / sec producing a large amount of energy, nearly 200 millions electron-volts. This is called ‚nuclear fission‛.

III.Block diagram of Nuclear power plant and write few advantages and disadvantages.

Main components of nuclear power plants:

i) Moderators

In any chain reaction, the neutrons produced are fast moving neutrons. These are less effective in causing fission of U235 and they try to escape from the reactor. It is thus implicit that speed of

these neutrons must be reduced if their effectiveness is carrying out fission is to be increased. This

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is done by making these neutrons collide with lighter nuclei of other materials, which does not

absorb these neutrons but simply scatter them. Each collision causes loss of energy and thus the speed of neutrons is reduced. Such a material is called a ‘Moderator’. The neutrons thus slowed

down are easily captured by the fuel element at the chain reaction proceeds slowly

ii) Reflectors

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

iii) Shielding

During Nuclear fission , , particles and neutrons are also produced. They are harmful to

human life. Therefore it is necessary to shield the reactor with thick layers of lead, or concrete to

protect both the operating personnel as well as environment from radiation hazards.

iv) Cladding

In order to prevent the contamination of the coolant by fission products, the fuel element is covered with a protective coating. This is known as cladding.Control rods are used to control the reaction to prevent it from becoming violent. They control the reaction by absorbing neutrons. These rods are made of boron or cadmium. Whenever the reaction needs to be stopped, the rods are fully inserted and placed against their seats and when the reaction is to be started the rods are pulled out.

v) Coolant

The main purpose of the coolant in the reactor is to transfer the heat produced inside the reactor. The same heat carried by the coolant is used in the heat exchanger for further utilization in the power generation.Some of the desirable properties of good coolant are listed below

1. It must not absorb the neutrons.

2. It must have high chemical and radiation stability

3. It must be non-corrosive.

4. It must have high boiling point (if liquid) and low melting point (if solid)

5. It must be non-oxidising and non-toxic.

vi) Nuclear reactor

A nuclear reactor may be regarded as a substitute for the boiler fire box of a steam power

plant. Heat is produced in the reactor due to nuclear fission of the fuel U235 The heat liberated in the reactor is taken up by the coolant circulating through the core. Hot coolant leaves the reactor at top and flows into the steam generator (boiler).

Radiation hazards and Shieldings

The reactor is a source of intense radioactivity. These radiations are very harmful to human life. It

requires strong control to ensure that this radioactivity is not released into the atmosphere to avoid

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atmospheric pollution. A thick concrete shielding and a pressure vessel are provided to prevent the

escape of these radiations to atmosphere

vii) Steam generator

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

viii) Turbine

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

ix) Coolant pump and Feed pump

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

Advantages of nuclear power plant

1. It can be easily adopted where water and coal resources are not available.

2. The nuclear power plant requires very small quantity of fuel. Hence fuel transportation cost is less.

3. Space requirement is less compared to other power plants of equal capacity.

4. It is not affected by adverse weather conditions.

5. Fuel storage facilities are not needed as in the case of the thermal power plant.

6. Nuclear power plants will converse the fossils fuels (coal, petroleum) for other energy needs.

7. Number of workmen required at nuclear plant is far less than thermal plant.

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8. It does not require large quantity of water.

Disadvantages

1. Radioactive wastes, if not disposed of carefully, have adverse effect on the health of workmen and the population surrounding the plant.

2. It is not suitable for varying load condition.

3. It requires well-trained personnel.

4. It requires high initial cost compared to hydro or thermal power plants.

IV.construction and working principle of Boiling Water Reactor (BWR)

Figure shows a simplified BWR. Light water, which acts as the coolant and moderator, passes

through the core where boiling takes place in the upper part of the core. The wet steam then passes

through a bank of moisture separators and steam dryers in the upper part of the pressure vessel.

The water that is not vaporized to steam is recirculated through the core with the entering feed

water using two recirculation pumps coupled to jet pumps (usually 10 to 12 per recirculation

pump). The steam leaving the top of the pressure vessel is at saturated conditions of 7.2 MPa and

278C.

The steam then expands through a turbine coupled to an electrical generator. After

condensing to liquid in the condenser, the liquid is returned to the reactors as feedwater. Prior to

entering the reactor, the feedwater is preheated in several stages of feedwater heaters. The balance

of plant systems (Example: Turbine generator, feedwater heaters) are similar for both PWR and

BWRs.

The BWR reactor core, like that in a PWR, consists of a large number of fuel rods housed in fuel

assemblies in a nearly cylindrical arrangement. Each fuel assembly contains an 8×8 or 9×9 square

array of 64 or 81 fuel rods (typically two of the fuel rods contain water rather than fuel)

surrounded by a square Zircaloy channel box to ensure no coolant crossflow in the core. The fuell

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rods are similar to the PWR rods, although larger in diameter. Each fuel rod is a zirconium alloy-

clad tube containing pellets of slightly enriched uranium dioxide (2% to 5% U-235) stacked end-to-

end. The reactor is controlled by control rods housed in a cross-shaped, or cruciform, arrangement

called a control element. The control elements enter from the bottom of the reactor and move in

spaces between the fuel assemblies.

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

V. construction and working principle of Heavy Water Cooled Reactor (HWR) (or) CANDU Type Reactor (CANDU – Canadium, Deutrium, Uranium).

These reactors are more economically to those nations which do not produce enriched uranium as

the enrichment of uranium is very costly. In this type of reactors, the natural uranium (0.7% U235) is used as fuel and heavy water as moderator.

This type of reactor was first designed and developed in Canada. The first heavy water reactor in Canada using heavy water as coolant and moderator of 200 MW capacity with 29.1% thermal efficiency was established at Douglas (Ontario known as Douglas power station. The arrangement of the different components of CANDU type reactor is shown in figure

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

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

Advantages and disadvantages of HWR (or) CANDU type Reactor.

Advantages

1. The major advantage of this reactor is that the fuel need not be enriched.

2. The reactor vessel may be built to withstand low pressure, therefore, the cost of the vessel is less.

3. No control rods are required, therefore, control is much easier than other types.

The moderator can be kept at low temperature which increases its effectiveness in slowing-

down neutrons.

5. Heavy water being a very good moderator, this type of reactor has higher multiplication factor and low fuel consumption.

6. A shorter period is required for the site construction compared with PWR and BWR.

Disadvantages

1. The cost of heavy water is extremely high (Rs. 300/kg).

2. The leakage is a major problem as there are two mechanically sealed closures per fuel channel. Canadian designs generally are based or recovering high proportion of heavy water leakages as absolute leak-tightness cannot be assured.

3. Very high standard of design, manufacture inspection and maintenance are required.

4. The power density is considerably low (9.7 kW/litre) compared with PWR and BWR, therefore, the reactor size is extremely large.

Even though CANDU-type reactors look promising in future, light water reactors all over the world proved more efficient than heavy water and in fact only 36 out of 529 power reactors in the world are based on heavy water.

VI. Sodium Graphite Reactor (SGA)? Sodium Graphite

Reactor (SGR):The reactor shown in figure uses two liquid metal coolants. Liquid sodium (Na)

serves as the primary coolant and an alloy of sodium potassium (NaK) as the secondary coolant.

Sodium melts at 208C and boils at 885C. This enables to achieve high outlet coolant temperature

in the reactor at moderate pressure nearly atmospheric which can be utilized in producing steam

of high temperature, thereby increasing the efficiency of the plant. Steam at temperature as high as

540C has been obtained by this system. This shows that by using liquid sodium as coolant more

electrical power can be generated for a given quantity of the fuel burn up.

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Secondly low pressure in the primary and secondary coolant circuits, permits the use of less

expensive pressure vessel and pipes etc. Further sodium can transfer its heat very easily. The only

disadvantage in this system is that sodium becomes radioactive while passing through the core

and reacts chemically with water. So it is not used directly to transfer its heat to the feed water, but

a secondary coolant is used. Primary coolant while passing through the tubes of intermediate heat

exchanges (I.H.X) transfers its heat to the secondary coolant. The secondary coolant then flows

through the tubes of steam generator and passes on its heat to the feed water. Graphite is used as

heat transfer media have certain advantages of using liquids used for heat transfer purposes. The

various advantages of using liquid metals as heat transfer media are that they have relatively low

melting points and combine high densities with low vapour pressure at high temperatures as well

as with large thermal conductivities.

VII. Fast Breeder Reactor

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

by a blanket (a layer of fertile material placed outside the core) of fertile material U238. In this

reactor no moderator is used. The fast moving neutrons liberated due to fission of U235 are

absorbed by U238 which gets converted into fissionable material Pu239 which is capable of sustaining chain reaction. Thus this reactor is important because it breeds fissionable material from

fertile material U238 available in large quantities. Like sodium graphite nuclear reactor this reactor also uses two liquid metal coolant circuits. Liquid sodium is used as primary coolant when circulated through the tubes of intermediate heat exchange transfers its heat to secondary coolant sodium potassium alloy. The secondary coolant while flowing through the tubes of steam generator transfers its heat to feed water.

Fast breeder reactors are better than conventional reactors both from the point of view of safety

and thermal efficiency. For India which already is fast advancing towards self reliance in the field

of nuclear power technology, the fast breeder reactor becomes inescapable in view of the massive

reserves of thorium and the finite limits of its uranium resources. The research and development

efforts in the fast breeder reactor technology will have to be stepped up considerably if nuclear

power generation is to make any impact on the country’s total energy needs in the not too distant

future.

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The commonly used coolants for fast breeder reactors are as follows:

i) Liquid metal (Na or NaK).

ii) Helium (He)

iii) carbon dioxide.

Sodium has the following advantages:

i) It has very low absorption cross-sectional area.

ii) It possesses good heat transfer properties at high temperature and low pressure. It does not react on any of the structural materials used in primary circuits.

VIII.Safety Measures carried out in Nuclear Power Plant Safety for Nuclear power plants:

Nuclear power plants should be located far away from the populated area to avoid the radioactive hazard. A nuclear reactor produces and particles, neutrons and - quanta which can disturb the normal functioning of living organisms. Nuclear power plants involve radiation leaks, health hazard to workers and community, and negative effect on surrounding forests.

At nuclear power plants there are three main sources of radioactive contamination of air.

1. Fission of nuclei of nuclear fuels. 2. The second source is due to the effect of neutron fluxes on the heat carrier in the primary

cooling system and on the ambient air.

3. Third source of air contamination is damage of shells of fuel elements. This calls for special safety measures for a nuclear power plant. Some of the safety measures are as follows.

1. Nuclear power plant should be located away from human habitation.

2. Quality of construction should be of required standards.

3. Waste water from nuclear power plant should be purified. The water purification plants must have efficiency of water purification and satisfy rigid requirements as regards the volume of radioactive wastes disposed to burial.

4. An atomic power plant should have an extensive ventilation system. The main purpose of this ventilation system is to maintain the concentration of all radioactive impurities in the air below the permissible concentrations.

5. An exclusion zone of 1.6 km radius around the plant should be provided where no public habitation is permitted.

6. The safety system of the plant should be such as to enable safe shut down of the reactor whenever required.

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UNIT IV POWER FROM RENEWABLE ENERGY

PART-A

1. Differentiate propeller and Kaplan turbine? In the propeller turbine the runner blades are fixed and non-adjustable. In Kaplan turbine,

which is a modification of propeller turbine the runner blades are adjustable and can be rotated about the pivots fixed to the boss of the runner. 2.What are the Element of Hydel Power Plant?

1. Water reservoir,

2. Dam,

3. Spillway,

4. Pressure tunnel,

5. Penstock,

6. Surge tank,

7. Water turbine,

8. Draft tube,

9. Tail race.

3.Write the Advantages of Hydro-electric power plants? 1. Water is a renewable source of energy. Water which is the operating fluid, is neither

consumed nor converted into something else, 2. Water is the cheapest source of energy because it exists as a free gift of nature. The fuels

needed for the thermal, diesel and nuclear plants are exhaustible and expensive.

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

4.Write the classification of Hydro turbines?

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,

6. According to the specific speed N.

5.Define Governing Mechanism?

When the load on the turbine changes, the speed may also change. (i.e., without load the speed

increases and with over load, the speed decreases). Hence, the speed of the runner must be

maintained constant to have a constant speed of generator. This is done by controlling the quantity

of water flowing on the runner according to the load variations. This speed regulation is known as

governing and it is usually done automatically by a governor.

6.What are the functions of draft tubes?

1.Increase in efficiency,

2.Negative head.

7.Write the two types of Draft tubes?

1) Conical or divergent draft tube,

2) Elbow type draft tube,

3) Hydracone or Moody spreading draft tube.

8.Define Kaplan turbine?

The Kaplan turbine is an axial flow reaction turbine. It is suitable for relatively low heads.

Hence, it requires a large quantity of water to develop high power. It operates in an entirely.

9.Define Tide?

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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.

10.Write a short notes on 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.

11. List the non – conventional energy sources?

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.

12. Write the advantages of non – conventional Energy sources?

1. They are available in large quantities.

2. They are well suited for decentralized use.

13.Write the characteristic’s of wind energy?

1. Wind-power systems do not pollute the atmosphere.

2. Fuel provision and transport are not required in wind-power systems.

3. Wind energy is a renewable source of energy. 4. Wind energy when produced on small scale is cheaper, but competitive with conventional

power generating systems when produced on a large scale.

14.Write the application of fuel cell?

1. Domestic use.

2. Automotive vehicles

3. Central power stations.

4. Special applications.

15.Define – Tidal power plant

The tidal power plants are generally classified on the basis of the number of basins used for power generations. They are further subdivided as one-way or two-way system as per the cycle of operation for power generation.

16.Write the application of geothermal energy?

1.Generation of electric power.

2.Space heating for buildings.

3. Industrial process heat

17.What are the five general categories of geothermal sources?

1. Hydrothermal convective systems

Vapour – dominated or dry steam fields.

Liquid – dominated system or wet steam fields.

Hot – water fields.

2. Geopressure resources.

3. Petro-thermal or hot dry rocks (HDR)

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4. Magma resources

5. Valcanoes.

18.Write the advantages of small Hydro-power plant (SHP)?

1. Readily accessible source of renewable energy,

2. Can be installed making use of water head as low as 2 m and above,

3. Does not involve setting up of large dams,

4. Least polluting.

PART-B

I.Construction and working principle of pumped storage plants

Pumped storage plants are employed at the places where the quantity of water available for power generation is inadequate. Here the water passing through the turbines is store in ‘tail

race pond’. During low load periods this water is pumped back to the head reservoir using the

extra energy available. This water can be again used for generating power during peak load

periods. Pumping of water may be done seasonally or daily depending upon the conditions of the

site and the nature of the load on the plant.Such plants are usually interconnected with steam or diesel engine pants so that off peak capacity of interconnecting stations is used in pumping water

and the same is used during peak load periods. Of course, the energy available from the quantity

of water pumped water the power available is reduced on account of losses occurring in prime movers. Advantages:

1. There is substantial increase in peak load capacity of the plant at comparatively low capital cost.

2. Due to load comparable to rated load on the plant, the operating efficiency of the

plant is high. 3. There is an improvement in the load factor of the plant.

4. The energy available during peak load periods is higher than that of during off peak

periods so that inspite of losses incurred in pumping there is over-all gain.

5. Load on the hydro-electric plant remains uniform.

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6. The hydro-electric plant becomes partly independent of the stream flow conditions.

Under pump storage projects almost 70 percent power used in pumping the water can be

recovered. In this field the use of ‚Reversible Turbine Pump‛ units is also worth noting. These units

can be used as turbine while generating power and as pump while pumping water to storage. The

generator in this case works as motor during reverse operation. The efficiency in such case is high

and almost the same in both the operations. With the use of reversible turbine pump sets,

additional capital investment on pump and its motor can be saved and the scheme can be worked

more economically.

II.Compare Impulse and reaction turbines

S.No Impulse turbine Reaction turbine

1. Head: The machine is suitable for high The machines can be used for medium heads

installation. (H=100 + 200 m). (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 The head is usually inadequate to produce high

hydraulic energy into kinetic energy velocity jet. Hence water is supplied to the

before water strikes the runner. runner in the forms of both pressure and

kinetic energy.

3. Method of energy transfer:

The buckets of the runner are so The wicket gates accelerate the flow a little and

shaped that they extract almost all the direct the water to runner vanes to which

kinetic energy of the jet. energies of water are transferred.

4. Operating pressure:

The turbine works under atmospheric The runner works is a closed system under the

pressure. Which is the difference action of reaction pressure.

between the inlet and exit points of

the runner.

5. Admission of water to the wheel: The entire circumference of the wheel receives

Only a few buckets comprising a part water and all passages between the runner

of the wheel are exposed to the water blades are always full of water.

jet.

6. Discharge: They are essential low Since power is a product of head and weight of

discharge turbines. 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 Although the specific speeds of these turbines

invariably high. 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. The spiral casing has an important role to play;

It has no hydraulic function to serve. it distributes water under the available

pressure uniformly around the periphery of the

runner.

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10. Turbine setting: The head between The draft tube ensures that the head of water

the wheel and race is lost. below tail race level is not lost.

11. Maximum efficiency: The highest The maximum efficiency (=95%) of design

efficiency (=88%) is less than that of output is higher than that of impulse wheels.

reaction turbine.

12. Part load operation: From about 20% With the exception of a Kaplan turbine, all

to 100% of design output, the reaction turbines give poor part load

efficiency remains nearly the same. performance i.e., appreciably low efficiency at

Hence the machine is ideal for less than design output.

generating small loads over long

periods of time.

13. Cavitation: These machine are not Runner blades and draft tube invariably

susceptible to cavitation. undergo cavitation on damage.

14. Civil engineering works: Civil works Civil works are more expensive on account of

like excavation and concreting are spiral casing and draft tube.

much simpler and economical.

III.Hydel Power plant

Hydro-electric plants: This type of plant makes use of energy of water stored at an elevation arid

allowed to drop to a lower level. The electric generator is driven by a turbine through which the

water from the pond is made to work.

A hydro-electric plant comprises of the turbines, governing gear, coolant circulators etc. The

operation of such a plant is usually much simpler than that of a steam, diesel or gas powered

plant.

In hydro-electric plants energy of water is utilized to move the turbines which in turn run the

electric generators. The energy of water utilized for power generation may be kinetic or potential.

The kinetic energy of water is its energy in motion and is a function of mass and velocity while the

potential energy is a function of the difference in level/head of water between two points.

The main parts of the hydel power plant are

Reservoir:The function or purpose of reservoir is to store the water during rainy season and

supply the same during dry season. This is in simple, water storage area.

Dam:The function of dam is to increase the height of the water level (increase in the potential

energy) behind it which ultimately increases the reservoir capacity. The dam also helps in

increasing the working head of the power plant. Dams are generally built to provide necessary

head to the power plant.

Trash Rack:The water intake from the dam or from the forebay are provided with trash rack. The

main function of trash rack is to prevent the entry of any debris which may damage the wicket

gates and turbine runners or choke-up the nozzles of impulse turbine. During winter season when

water forms ice, to prevent the ice from clinging to the trash racks, they are often heated

electrically. Sometimes air bubbling system is provided in the vicinity of the trash racks which

brings warmer water to the surface of the trash racks.

Forebay: The function of forebay is to act as regulating reservoir temporarily storing water when

the load on the plant is reduced and to provide water for initial increment of an increasing load

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while water in the canal is being accelerated. In many cases, the canal itself is large enough to

absorb the flow variations. In short, forebay is naturally provided for storage of water to absorb

any flow variations if exist. This can be considered as naturally provided surge tank as it does the

function of the surge tank. The forebay is always provided with some type of outlet structure to

direct water to penstock depending upon the local conditions.

Surge Tank:The main function of surge tank is to reduce the water hammering effect. When there

is a sudden increase of pressure in the penstock which can be due sudden decrease in the load

demand on the generator. When there is sudden decrease in the load, the turbine gates admitting

water to the turbine closes suddenly owing to the action of the governor. This sudden rise in the

pressure in the penstock will cause the positive water hammering effect. This may lead to burst of

the penstock because of high pressures.

A surge tank is introduced in the system between dam and the power house nearest. Surge tank

is a tank provided to absorb any water surges caused in the penstok due to sudden loading and

unloading of the generator. When the velocity of the water in the penstock decreases due to

closing of turbine valves, the water level in the surge tank increases and fluctuating up and down

till its motion is damped out by the friction. Similarly when the water accelerates in the penstock,

water is provided by the surge tank for acceleration. Surge tank water level falls down and

fluctuates up and down absorbing the surges.

Penstock:Penstock is a pipe between the surge tank and the prime-mover. The structural design of

the penstock is same as for any other pipe expect it has to bear high pressure on the inside surface

during sudden decease in the load and increase in the load. Penstocks are made of steel through

reinforced concrete. Penstocks are usually equipped with the head gates at the inlet which can be

closed during the repair of the penstocks, A sufficient water head should be provided above the

penstock entrance in the forebay or surge tank to avoid the formation of vortices which may carry

air in to the penstock and resulting in lower turbine blade efficiency.

Spillway:The function of spillway is to provide safety of the dam. Spillway should have the

capacity to discharge major floods without damage to the dam and at the same time keeps the

reservoir levels below some predetermined maximum level.

Power House:A power house consists of two main parts, a sub-structure to support the hydraulic

and electrical equipment and a superstructure to house and protect this equipment.

The superstructure of most power plants is the buildings that house all the operating equipment.

The generating unit and the exciter is located in the ground floor. The turbines which rotate on

vertical axis are placed below the floor level while those rotating on a horizontal axis are placed on

the ground floor alongside of the generator.

Prime movers or Hydro Turbines:The main function of prime movers or hydro turbines is to

convert the kinetic energy of the water in to the mechanical energy to produce the electric power.

The prime movers which are in common use are pelton wheel, francis turbine and kaplan

turbines.

Draft tube:The draft tube is a part of the reaction turbine. The draft tube is a diverging discharge

passage connecting the running with tailrace. It is shaped to decelerate the flow with a minimum

loss so that the remaining kinetic energy of the water coming out of the runner is efficiently

regained by converting into suction head., thereby increasing the total pressure difference on the

runner. This regain of kinetic energy of the water coming out from the reaction turbine is the

primary function of the draft tube. The regain of static suction head in case where the runner is

located above the tail water level is the secondary purpose of the draft tube.

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IV.Working of different tidal power plants

1. Single basin-one-way cycle:This is the simplest form of tidal power plant. In this system a basin

is allowed to get filled during flood tide and during the ebb tide, the water flows from the basin to

the sea passing through the turbine and generates power. The power is available for a short

duration ebb tide.

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Figure: (a) Tidal region before construction of the power plant and tidal variation

Figure: (b) Single basin, one –way tidal power plant

Figure (a) shows a single tide basin before the construction, of dam and figure (b) shows the diagrammatic representation of a dam at the mouth of the basin and power generating during the falling tide.

2. Single-basin two-way cycle

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

Figure: Single –basin two-way tidal power plant

The main difficulty with this arrangement, the same turbine must be used as prime mover as ebb and tide flows pass through the turbine in opposite directions. Variable pitch turbine and dual rotation generator are used of such scheme.

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3. Single – basin two-way cycle with pump storage

In this system, power is generated both during flood and ebb tides. Complex machines

capable of generating power and pumping the water in either directions are used. A part of

the energy produced is used for introducing the difference in the water levels between the

basin and sea at any time of the tide and this is done by pumping water into the basin up or

down. The period of power production with this system is much longer than the other two

described earlier

Figure: Single-basin, two-way tidal plant coupled with pump storage system.

4. Double basin type

In this arrangement, the turbine is set up between the basins as shown in figure. One basin is

intermittently filled tide and other is intermittently drained by the ebb tide. Therefore, a small

capacity but continuous power is made available with this system as shown in figure. The main

disadvantages of this system are that 50% of the potential energy is sacrificed in introducing the

variation in the water levels of the two basins.

Figure: Double basin, one-way tidal plant.

V.Wind-Electric Generating power plant

The main parts of the Wind power plant are

1.Wind turbine or rotor.

2.Wind mill head – it houses speed increaser, drive shaft, clutch, coupling etc.

3. Electric generator.

4.Supporting structure. The most important component is the rotor. For an effective utilization, all components should be properly designed and matched with the rest of the components.

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(i) The wind mill head performs the following functions It supports the rotor housing and the

rotor bearings. (ii) It also houses any control mechanism incorporated like changing the pitch of the blades for safety devices and tail vane to orient the rotor to face the wind, the latter is facilitated by

mounting it on the top of the supporting structure on suitable bearings.

Wind-Electric generating power plant

The wind turbine may be located either unwind or downwind of the power. In the unwind

location the wind encounters the turbine before reaching the tower. Downwind rotors are

generally preferred especially for the large aerogenerators.

The supporting structure is designed to withstand the wind load during gusts. Its type and height is related to cost and transmission system incorporated. Horizontal axis wind turbines are mounted on towers so as to be above the level of turbulence and other ground related effects.

Types of Wind Machines

1. Wind machines (aerogenerators) are generally classified as follows: 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 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.

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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.

Vertical axis wind machine.

VI. Fuel cell with Schematic diagram

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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. One of the chief

advantages of such a device is that because the conversion, atleast in theory, can be carried out

isothermally, the Carnot limitation on efficiency does not apply. A fuel cell is often described as

primary battery in which the fuel and oxidizer are stores external to the battery and fed to it as

needed. The fuel gas diffuses through the anode and is oxidized, thus releasing electrons to the

external circuit; the oxidizer diffuses through the cathode and is reduced by the electrons that have

come from the anode by way of the external circuitThe fuel cell is a device that keeps the fuel

molecules from mixing with the oxidizer molecules, permitting, however, the transfer of electrons

by a metallic path that may contain a load.Of the available fuels, hydrogen has so far given the

most promising results, although cells consuming coal, oil or natural gas would be economically

much more useful for large scale applications.

Schematic of a fuel cell.

Some of the possible reactions are :

Hydrogen/oxygen 1.23 V 2H2 + O2 2 H2O

Hydrazine 1.56 V N2H4 + O2 2H2O + N2

Carbon (coal) 1.02 V C + O2 CO2

Methane 1.05 V CH4 + 2O2 CO2 + 2H2O

Hydrogen-oxygen cell :

The hydrogen-oxygen devices shown in figure is typical of fuel cells. It has three chambers

separated by two porous electrodes, the anode and the cathode. The middle chamber between the

electrodes is filled with a strong solution of potassium hydroxide. The surfaces of the electrodes are

chemically treated to repel the electrolyte, so that there is minimum leakage of potassium hydroxide into the outer chambers. The gases diffuse through the electrodes, undergoing reactions

are show below: 4KOH 4K+ + f(OH)-

Anode: 2H2 + 4 (OH)- 4H2O + 4e-

Cathode: O2 + 2H2O + 4e- 4 (OH)-

Cell reaction 2H2 + O2 2H2O

The water formed is drawn off from the side. The electrolyte provides the (OH)- ions needed for the reaction, and remains unchanged at the end, since these ions are regenerated. The electrons

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liberated at the anode find their way to the cathode through the external circuit. This transfer is equivalent to the flow of a current from the cathode to the anode.

Such cells when properly designed and operated, have an open circuit voltage of about 1.1 volt. Unfortunately, their life is limited since the water formed continuously dilutes the electrolyte. Fuel efficiencies as high as 60%-70% may be obtained.

VII.SOLAR CENTRAL RECIVER SYSTEM:

The solar power tower (also known as 'central tower' power plants or 'heliostat' power plants or power towers) is a type of solar furnace using a tower to receive the focused sunlight. It uses an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). Concentrated solar thermal is seen as one viable solution for renewable, pollution free energy production with currently available technology. Early designs used these focused rays to heat water, and used the resulting steam to power a turbine. Newer designs using liquid sodium has been demonstrated, and systems using molten salts (40% potassium nitrate, 60% sodium nitrate) as the working fluids are now in operation. These working fluids have high heat capacity, which can be used to store the energy before using it to boil water to drive turbines. These designs allow power to be generated when the sun is not shining.

1. Central receiver system: The central receiver at the top of the tower has a heat absorbing surface

by which the heat-transport fluid is heated. There are two basicreceiver configurations have been

proposed. They are:

a) cavity receiver type

b) External receiver pipe type

In the Cavity type, pipe line, the solar radiation reflected by the heliostats enters through an

aperture at the bottom of the cavity.

In the external receiver pipe type, the absorber surface are on the exterior of a roughly cylindrical

structure.

2. Heat conversion sub system: Liquid water under pressure enters the receiver absorbs the heat

energy, and leaves as superheated steam. Typical steam conditions might be a temperature of

5000C and a pressure of about 100atm. The steam is piped to ground level where it drives a

conventional turbine generator system.

3. The heat storage device: Short steam storage of heat can be provided by fire bricks, ceramic

oxides, fused salts, sulphur. The choice of a conventional storagematerial is determined by its

energy density, thermal conductivity, corrosion characteristic, cost and convenience of use, as well

as by the operating temperature of the working fluid.

4.Mirrors: The flat mirror surface can be manufactured by metallization of float glass or flexible

plastic sheets. The mirror must be steerable. The glass mirrors would not be capable of

withstanding the wind loads that often occur in arid lands without any supporting structure.

Working: - The inclining solar radiation is focused to a central receiver or a boiler mounted on a

tall tower using thousands of plane reflectors which are steerable about two axes and are called

heliostats. Fig. below shows a schematic arrangement of a central receiver heliostat array

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VIII.Geothermal power plant

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

Steam well

Pipes are embedded at places of fresh volcanic action called steam wells, where the molten internal mass of earth vents to the atmospheric with very high temperatures. By sending water through embedded pipes, steam is raised from the underground steam storage wells to the ground level. Separator The steam is then passed through the separator where most of the dirt and sand carried by the steam are removed.

Turbine

The steam from the separator is passed through steam drum and is used to run the turbine which

in turn drives the generator. The exhaust steam from the turbine is condensed. The condensate is

pumped into the earth to absorb the ground heat again and to get converted into steam. Location of the plant, installation of equipment like control unit etc., within the source of

heat and the cost of drilling deep wells as deep as 15,000 metres are some of the difficulties commonly encountered.

IX.PHOTOVOLTAIC SYSTEM & SOLAR COLLECTORS

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A photovoltaic system, also PV system or solar power system, is a power system designed to

supply usable solar powerby means of photovoltaics. It consists of an arrangement of several

components, including solar panels to absorb and convert sunlight into electricity, a solar

inverter to change the electric current from DC to AC, as well as mounting, cabling, and other

electrical accessories to set up a working system. It may also use a solar tracking system to

improve the system's overall performance and include an integrated battery solution, as prices for

storage devices are expected to decline. Strictly speaking, a solar array only encompasses the

ensemble of solar panels, the visible part of the PV system, and does not include all the other

hardware, often summarized as balance of system (BOS). Moreover, PV systems convert light

directly into electricity and shouldn't be confused with other technologies, such as concentrated

solar power or solar thermal, used for heating and cooling.

Distributed (Parabolic) Collector System Power Plant. The second type is the distributed collector

system. It is also called solar farm power plant as a number of solar modules consisting of

parabolic trough solar collectors are interconnected. This system uses a series of specially

designed ‘Trough’ collectors which have an absorber tube running along their length. Large

arrays of these collectors are coupled to provide high temperature water for driving a steam

turbine. Such power stations can produce many megawatts (MW) of electricity, but are confined

to areas where there is ample solar insulation.

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UNIT V ENERGY, ECONOMIC AND ENVIRONMENTAL ISSUES OF POWER PLANTS

PART-A

1.Define demand factor

It is the ratio of of actual maximum demand on the system to the total connected demand of

the system,

Demand factor = actual maximum demand / total connected demand

2. Define load factor and capacity factor

Load factor: - It is the ratio of average load over a given time interval to the peak load during

the same time interval

Capacity factor or plant capacity factor: It is the ratio of actual energy produced in kilowatt

hour(kWh) to the maximum possible energy that could have been produced during the same period.

3.Illustrate the significance of load curve

This curve gives full information about the incoming load and helps to decide the installed

capacity of the power station. It is als useful to decide the economical sizes of various generating units

4.Discuss the tariff

The tariff is the rate at which the electrical energy is sold. There are various types of tariffs

followed in the market

The general energy rate or tariff can be given by the following equation

E = Ax + By + C

5. Calculate the cost of electricity

A power plant should provide a reliable supply of electricity at minimum cost to the

consumers / customers. The cost of electricity may be determined by the following: Fixed cost or

capital cost and Operating costs. the total cost of energy produced is the sum total of fixed charges and

operating charges.

Total cost = Fixed costs + Operating costs

6. Express the two part tariff

When the rate of electrical energy is charged on the basis of maximum demand of the

consumer and the units consumed it is called two-part tariff.

7. What is fixed costs in a power plant.

It is the cost required for the installation of the complete power plant. This cost includes

1.The cost of land, equipments, buildings, transmission and distribution lines cost of planning and designing the plant and many others . 2.Interest, 3.Depreciation cost, 4.Insurance,

5.Management costs, etc 8. Define load curve?

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

load at the power station. The area under the load curve -represents the energy generated in a particular

period.

9.List down the nuclear waste disposal methods?

a. Geological Disposal b. Reprocessing c. Transmutation d. Space Disposal

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10. What is the need of depreciation cost? Depreciation cost is the amount to be set aside per year from the income of the plant to meet the

depreciation caused by the age of service, wear and tear of the machinery and equipments. Depreciation

amount collected every year helps in replacing and repairing the equipment.

11.Define base load and peak load power plants

The load below which the demand never falls and is supplied 100% of the time. The power

plant used to supply base loads are called base load power plants. The peak load is the load which

occurs at the top portion of the load curve. The power plants which are used to supply peak loads are

called as peak load power plants. The peaking load occurs for about 15% of the time

I.Types of Tariffs

The various forms used for changing the consumers as per their energy consumed and maximum

demand are discussed below.

1.Flat demand rate: In this type of charging, the charging depends only on the connected load and fixed

number of hours of use per month or year.

This can be given by the following equation - E = Ax

The notations are taken as; discussed above. This rate expresses the charge per unit of demand (kW) of the

consumer. Here no metering equipments and manpower are required for charging. In this system, the

consumer can theoretically use any amount of energy upto that consumed by all connected loads. The unit

energy cost decreases progressively with an increased energy usage. The variation in total cost and unit cost

are shown in fig. above

Straight line meter rate:

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This type of charging depends upon the amount of total consumed by the consumer. The bill charge is directly

proportional to the energy consumed by the consumer.This can be represented by the following equation.

E = By

:

2.Block-meter rate:

In previous straight line meter rate the unit charge is same for all magnitudes of energy consumption.

The increased consumption spreads the item of fixed charge over a greater number of units of energy

Therefore, the price of energy should decrease with an increase in consumption. The block meter rate is used

to overcome this difficulty.

This method of charging is represented by the equation.

E = B1y1 + B2y2 + B3y3 + …….

Where, B3 < B2 < B1 and \

(y1 + y2 + y3 +……) = y (total energy consumption)

The level of y1 , y2 , y3 …… is decided by the government to recover the capital cost, In is system, the rate of

unit charge decrease with increase in consumption of energy as shown in fig above

3.Hopkinson demand rate of Two-part tariff:

This method of charging depends upon the maximum demand and energy consumption. This method

of charging is represented by the equation E = A + By

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In this method two meters are required to record the maximum demand and the energy consumption of the

consumer. This method is generally used for the industrial consumers. The variation in total cost with respect

to the total energy consumption taking x as parameter is shown in fig above.

4.Doherty rate or three part tariff:

This method is proposed by Henry L. Doherty. In this method of charging, the consumer has to pay

some fixed amount in addition to the charges for maximum demand and energy consumed. The fixed amount

to be charged depends upon the occasional increase in prices and wage charges of the workers etc.

This method of charging is expressed by the equation.- x = Ax + By + C

This Doherty method of charging is most commonly used in Tamilnadu and all over India. In this method the

customers are discouraged to use more power when the generating capacity is less than the actual demand.

For example, for the first 50kW-hr units the charging rate is fixed as, say, Rs. 2.5/Kw-hr and if it exceeds than

this charge is rapidly increased as Rs. 3.5/kW-hr for next 100 kW-hr units (i.e from 51Kw-hr to 150kW-hr) .

this method is unfair to the customer, but very common in India and many developing nations

.

II.Nuclear waste disposal methods

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According to the amount and type of radioactivity in them, nuclear waste materials can generally be classified

under two categories – a) low level nuclear waste and b) high level nuclear waste.

a) Low level nuclear waste: usually includes material used to handle the highly radioactive parts of nuclear

reactors (i.e. cooling water pipes and radiation suits) and waste from medical procedures involving radioactive

treatments or x-rays. Low-level waste is comparatively easy to dispose of. The level of radioactivity and the

half-life of the radioactive isotopes in low-level waste are relatively small. Storing the waste for a period of 10

to 50 years will allow most of the radioactive isotopes in low-level waste to decay, at which point the waste

can be disposed of as normal refuse.

Low-level nuclear waste is generated from hospitals, laboratories and industry, as well as the nuclear fuel

cycle. It comprises paper, rags, tools, clothing, filters etc., which contain small amounts of mostly short-lived

radioactivity. It is not dangerous to handle, but must be disposed of more carefully than normal garbage.

Some low-level waste viz., resins, chemical sludges and reactor components, as well as contaminated

materials from reactor decommissioning may require special shielding before disposal. Low-level nuclear

waste is usually buried in shallow landfill sites. To reduce its volume, it is often compacted or incinerated (in

a closed container) before disposal. Worldwide it comprises 97% of the volume but only 5% of the

radioactivity of all nuclear waste.

b) High level nuclear waste: may be the spent fuel itself, or the principal waste from reprocessing this. It

is generally material from the core of a nuclear reactor or nuclear weapon. This waste includes uranium,

plutonium, and other highly radioactive elements formed during fission. Most of the radioisotopes in high

level waste emit large amounts of radiation and have extremely long half-lives (some longer than 100,000

years) requiring long time periods before the waste will settle to safe levels of radioactivity. While only 3%

of the volume of all radwaste, it holds 95% of the radioactivity. It contains the highly radioactive fission

products and some heavy elements with long-lived radioactivity. It generates a considerable amount of heat

and requires cooling, as well as special shielding during handling and transport. If the spent fuel is

reprocessed, the separated waste is vitrified by incorporating it into borosilicate (Pyrex) glass, which is sealed

inside stainless steel canisters for eventual disposal deep underground.

As can be readily appreciated from the foregoing, disposal of the high level nuclear waste is more problematic

than the low level one. This article describes some of the methods that can/are being undertaken for dealing

with this problem. The methods of nuclear waste disposal include:

1. Short Term Storage

2. Long Term Storage

3. Transmutation.

1. Short Term Storage of Nuclear Waste

Radioactive material decays in an exponential fashion. Short-term storage will reduce the radioactivity of

spent nuclear fuel significantly. A ten-year storage can bring a 100 times decrease in radioactivity. A further

reduction of radioactive emissions, similar to that of the first 10 years, would take another 100 years of

storage. Storing the waste for at least 10 years is recommended. The reduction in radioactivity during short-

term storage makes handling and shipment of the waste much easier. After short term storage the waste will

be sent for transmutation or long-term storage.

2. Long Term Storage for High Level Radioactive Waste

While there are methods of significantly reducing the amount of high-level radioactive waste, some (or all)

high level radioactive waste must end its journey in long-term storage. Because "long term" refers to a period

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of thousands of years, security of the radioactive waste must be assured over geologic time periods. The waste

must not be allowed to escape to the outside environment by any foreseeable accident, malicious action, or

geological activity. This includes accidental uncovering, removal by groups intending to use the radioactive

material in a harmful manner, leeching of the waste into the water supply, and exposure from earthquake or

other geological activity. In addition, this security must be maintained over a period of time during which, not

only will the designers of the storage area die, but also the host country will, in all likelihood, see different

political regimes. Civilization has undergone tremendous changes in the last 3000 years since the Egyptian

Empire, yet some high level radioactive waste will take over 20,000 years to decay to safe levels.

Posing further difficulty is the fact that some of this waste is plutonium, and other actinide elements, produced

as byproducts of uranium fission. These elements are not only highly radioactive, but highly poisonous as

well. The toxicity of plutonium is among the highest of any element known.

Areas currently being evaluated for long-term storage of nuclear waste are:

a) Space

b) Under the sea bed, and

c) Large stable geologic formations on land.

Long-term storage on land seems to be the favorite of most countries.

a) Disposal of Nuclear Waste in Space

Outer space is the most appropriate long-term storage option for high-level nuclear waste. This would

ensure it’s safe removal from humans regardless of the activities of nature or man on earth. Anybody

accidentally stumbling upon this waste would be at a lesser risk as they would be using radioactive shielding

for space travel. Delivery of the waste into space has a crippling drawback -- the rocket used to deliver the

waste into space would need to provide enough power to escape the earth’s gravity. This is necessary for two

reasons: a) to leave the waste in orbit creates space garbage that is likely to reenter the earth’s environment at

some time due to collision with satellites and other orbiting waste or spacecraft; and b) the large delivery

rocket would be expensive and an accident during launch could have catastrophic results. Space disposal

therefore, will not be a viable option until space travel is considerably safer and less expensive.

b) Storage of Radioactive Waste in the Sea Bed A possibility for long-term storage on the earth is burial in the seabed. The rock formations in the seabed

are generally more stable than those on land reducing the risk of exposure due to seismic activity. Apart

from this, there is little groundwater circulation under the seabed, reducing the possibility of radioactive

material contaminating ground water available for human consumption. The greatest appeal of under

sea burial is also its greatest drawback. The enormous cost and difficulty of excavating the waste would

likely prevent accidental or malicious disturbing of the waste. This cost is also keeping us from burying

the waste at sea.

c) Long Term Storage of Radioactive Waste on Land

Long term storage in tectonically stable rock formations on land is the most likely solution for high-level

radioactive waste. The radioactive material may be vitrified[1]1 and buried in caverns, created in a large

rock formation. When use of the storage area is complete, it would be sealed again with stone. While still

extremely expensive, and considerably unsafe, this is the most viable storage option currently

available. Using methods that reduce the amount of radioactive waste could further enhance safety levels.

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While most countries should not only be able to find suitably safe sites in stable geological formations,

they should also demonstrate this safety so as to create public confidence. This is best achieved where

there is simple geology.

3. Transmutation

Transmutation is the transformation of one element into another. The goal of transmutation, in radioactive

waste disposal, is to transmute long half-life, highly radioactive elements, into shorter half-life, less-

radioactive elements. There are two methods currently proposed for the transmutation of high-level

radioactive waste are:

a) fast consumer reactors, and

b) hybrid reactors.

a) Fast Consumer Reactors

Fast consumer reactors are merely variations of fast breeder reactors. These reactors take the plutonium

created by nuclear reactors as byproduct, or as fuel for nuclear weapons and "consume" it. This process leaves

uranium and other less dangerous radioactive waste. As an added benefit, the isotopes of the elements created

as byproducts generally have shorter half-lives than the initial plutonium used as fuel.

b) Transmutation with a Hybrid Nuclear Reactor

Hybrid nuclear reactors promise near complete transmutation of almost any high level radioactive waste. The

general process is to produce a sub-critical nuclear reactor (i.e. the nuclear reactions would stop under normal

conditions) and bombard the reactor fuel with neutrons. The neutrons break apart the large radioactive

elements, releasing energy. This energy is used to power the neutron source needed to start the fission

reaction. There will be some high level radioactive waste produced (generally parts of the neutron source) but

in comparison to the amount of radioactive waste consumed, this will be minimal. This high level waste will

need to be placed in long-term storage.

III.Load curves and Load duration curves

1.Load curve: - it is the graphical representation showing the power demand for every instant during a

certain time period. It is drawn between load in kW and time in hours, if it is plotted for one hour, it is

called as hourly load curve and if the time considered is of 24 hours then it is called daily load curve,

and if plotted for one year(8760 hours) , then it is annual load curve. The area under the load curve

represents the energy generated in the period considered. If we divide the area under the curve by the

total number of hours, then it will give the average load on the power station. The peak load indicated

by the load curve represents the maximum demand of the power station.

Load

(kW

)

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12 3 6 9 12 3 6 9 12 AM PM

Typical daily Load curve

This curve gives full information about the incoming load and helps to decide the installed capacity of the power station. It is als useful to decide the economical sizes of various generating units.

1.Load duration curve: - this curve represents the re-arrangement of all the load elements of load curve in order of decreasing magnitude. This curve is derived from load curve.

6 9 12 3 6 9 12 3 6 AM PM AM

(a) Daily Load curve

A typical daily load curve for a power station is shown above. It may be observed that the maximum load is 40kW from

6 pm to 9 pm . Similarly other loads are plotted in decreasing order in figure (b) and this is called load duration curve.

It may be observed that the area under the both curves is equal and represents the total energy delivered by

generation station. Load duration curve gives a clear analysis about generating power economically

40

24

9

6 4

Load

(kW

)

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6 9 12 3 6 9 12 3 6 AM PM AM

(b) Load duration curve

IV. Pollution control methods in thermal power plants

Modern pollution control devices

a. Electrostatic precipitators

b. Cyclone dust collectors

c. Spray type wet scrubbers

d. Fluidised bed combustion

a.Electrostatic precipitators

In electrostatic precipitators, dust particles are seperated from the flue gases by electrostatic

attraction. It involves two operations ,one is charging of dust particles and the other is

collection of dust Particles In the charging section ,dust particles are collected on the collector

electrodes. The electrostatic field exerts a force on the dust particles and they are driven

towards the collecting electrodes at the bottom .Then the filtered air is given outside

b. Cyclone dust collectors

40

24

9

6 4

Load

(kW

)

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The flue gases carrying dust particles enter tangentially into a conical shell with high velocity.

A whirling motion is imparted to the gas within the shell. Due to this heavier particles are

thrown to the sides and fall down They are collected from the bottom of the dust collector. The

gas is then passed through a secondary chamber. In the secondary chamber dust particles if any

, are Seperated The cleaned gas goes out of the chamber.

c. Water spray type wet scrubber

The fumes smokes and soluble gases such as SO2 and H2S in the flue gases can be removed by

using wet type mechanical scrubbers. The flue gas carrying dust particles is passed through the

bottom of the scrubber. The liquid is sprayed through the spray nozzles. The liquid particles

mix with the dust particles and the mixture is collected from the bottom of the scrubber.

Eliminators are provided at the outlet to avoid escaping of liquid. The cleaned gas goes out of

the scrubber.

d.Fluidised bed combustion

It is a new technique to reduce the emission of sulphur di-oxide and oxides of nitrogen. In the

Fluidised bed system, lime stone or dolomite is used as bed material. The lime stone reacts

with so2 in flue gases from the bottom of the bed. Another advantage of using Fluidised bed is

stabilization of combustion at 700 to 900 C .This temperature is well below the ash can be

tapped from the bottom of the bed. The low combustion temperature also reduces the formation

of oxides of nitrogen.

Thermal power generation plant plays an vital role in electric power generation all over the

world which is an important non-renewable source of energy which uses fossil fuels as an

important fuel. This case study discusses about modern pollution control technologies for

power generation, which may provide adequate solutions to the problems faced in controlling

pollution. By identifying the necessary reasons for pollution and by developing new

technologies can overcome sufficient amount of pollution rate. Hazardous air pollutants

emission characteristics from coal and oil fired thermal power plants have been studied in

order to control pollution. Another cause is the use of water as coolant by power plants and by

manufacturers which causes increase in temperature, decreases oxygen supply, and affects

ecosystem composition. Alternatively power plants can be designed or refitted to be more

efficient and to produce less waste. For India’s bright future in power generation and

sustainable environment, new methods and technology must be improved for the well being of

the society