Energy Sources and Power Plant

Structure1.1 Introduction

1.2 Different Forms of Energy

1.3 Energy Sources and their Availibility

1.4 Conventional Energy Sources

1.5 Non - Conventional Energy Sources

Learning ObjectivesAfter studying this unit, the student will be able to know the

• Different energy sources and their availability.

• Study of conventional and non-conventional energy sources.

1.1 IntroductionThe energy of a body is its capacity to do work. It is measured of the

total amount of work that the body can do.

Energy is the primary and most universal measureof all kinds of workby human beings and nature. Every thing what happens in the world is theexpression of flow of energy in one of its forms.

1UNIT

Energy Sources

Mechanical Engineering Technician2

1.2 Different Forms of EnergyThe different forms of energy are

1. Mechanical energy (Kinetic and potential)

2. Thermal or Heat energy

3. Chemical energy

4. Electrical energy

5. Nuclear energy

6. Electromagnetic energy

7. Gravitational energy

The S.I unit of energy is joule or K.J or Watt.Hour

1.2.1 Primary energy sourcesPrimary energy sources can be defined as sources which provide a net

supply of energy. The energy required to obtain these fuels is much less thanwhat they can produce by combustion or nuclear reaction. The supply of primaryfuels is limited. It becomes very essential to use these fuels sparingly.

Examples : Coal, Natural gas, Oil and Nuclear energy.

1.2.2 Secondary energy sourcesSecondary energy sources can be defined as sources which produce

no net energy. Though it may be necessary for the economy, these may not yieldnet energy.

Examples : Sun (Solar energy can be used by plants, solar cells, solar heaters and solar collectors), wind, water (Tides), etc..

1.3 Energy Sources and their AvailabilityToday every country draws its energy needs from a variety of sources.

We can broadly categorize these sources as commercial and non-commercial.The commercial sources include the fossil fuels (coal, oil and natural gas),hydroelectric power and nuclear power, while the non-commercial sources includewood, animal waste and agriculture wastes. In an industrialized country likeU.S.A., most of the energy requirements are met from commercial sources,while in an industrially less developed country like India, the use of commercialand non-commercial sources are about equal.

3Paper - I Energy Sources and Power plant

1.4 Conventional Energy SourcesConventional energy sources are

i. Fossil fuel energy

ii. Hydraulic energy

iii. Nuclear energy

1.4.1 Fossil Fuel EnergyCoal, petroleum and natural gas are called fossil fuel as these are formed

by the decomposition of the remains of dead plants and animals buried underthe earth for a long time.

These are non-renewable sources of energy which it will be exhaustedcan not be replenished in a short time. Their reserves are limited and areconsidered very precious. These should be used with care and caution.

These are also contributing to the global environmental pollution.

(a) Coal

Since the advent of industrialization coal has been the most commonsource of energy. In the last three decades, the world switched over from coalto oil as a major source of energy because it is simpler and cleaner to obtainuseful energy from oil.

Coal is a complex mixture of carbon, hydrogen and oxygen. Smallamount of nitrogen and sulphur compounds are also present in coal. It is mainlyavailable in Bihar, West Bengal, Orissa and Madhya Pradesh. The big coalmines are in our country at Jharia and Bokaro in Bihar and at Raniganj in WestBengal. It is considered as the back bone of the energy sector for its use inindustry, transportation and electric power generation.

Depending upon the carbon contents of coal, it is classified as follows.

Carbon content (%)

60

70

80

90

S. No.

1.

2.

3.

4.

Types of Coil

Peat

Lignite (Soft coal)

Bituminous (House hold coal)

Anthracite (Hard coal)


It is clear that peat is the most inferior quality of coal. Where as anthraciteis the most superior quality of coal. Bituminous is most commonly used in household and industry.

On strong heating, coal breaks upto produce coal gas, ammonia, coaltarand coke. Coke is 98% carbon, obtained after losing all its volatile constituentsduring destructive distillation of coal. It can be used as smoke free fuel.

(b) Petroleum

It is a dark coloured, viscous and foul smelling crude oil. The petroleummeans rock oil. It is normally found under the crust of earth trapped in rocks.The crude oil is a complex mixture of several solid liquid gaseous hydrocarbonsmixed with water, salt and earth particles. It is a natural product obtained fromoil wells.

Some of the crude oil producing locations in our country are

i. Ankaleshwar and kalol in Gujarat

ii. Rudrasagar and Lakwa in Assam

iii. Bombay high (Off-shore area)

The crude petroleum is refered by the process of fractional distillationto obtain more useful petroleum products. The crude petroleum is heated to atemperature of about 400 Degree Centigrade in a furnace and vapors thus formedare passed into a tall fractioning column from near its bottom. As the mixture ofhot vapours rises in the column, it starts getting cooled gradually.

The products obtained from crud petroleum as follows

i. Petroleum gas (Below 40 degree centigrade) used as LPG

ii. Petrol (40 to 170 degree centigrade) for light vehicles

iii. Kerosene (170 to 250 degree centigrade) for house hold and industrial use.

iv. Diesel oil (250 to 350 degree centigrade) for heavy vehicles .

v. Residential oil (Lubrication oil, Paraffin wax and Asphalt .

vi. Fuel oil (350 to 400 degree centigrade) for boilers and furnaces

(c ) Natural gas

It consists about 95% Methane and rest Ethane and propane. It occursdeep under the crust of the earth either alone or a long with oil above the petroleumdeposits. It is a product of petroleum mining.


The gas is available in Tripura, Jaisalmer, off-shore areas of Bombayhigh and in the Krishna and the Godavari delta. It is used as a domestic andindustrial fuel. The natural gas is now also available as CNG (Compressed NaturalGas) a substitution of petrol in automobiles.

1.4.2 Hydraulic EnergyIt is also called water power, which is developed by allowing water to

fall under the force of gravity. It is used almost exclusively for electric powergeneration. In fact the generation of water power on a large scale became possiblearound the beginning of the twentieth century only with the development of electricpower transmission prior to that, water plants (or) hydro electric plants wereusually of small capacities usual less than 100 KW.

Potential energy of water is converted into mechanical energy by usingprime mover known as hydraulic turbines. Water power is quite cheap wherewater is available in abundance. Although capital cost of hydro electric powerplants is higher as compared to other types of power plants but their operatingcost is quite low, as no fuel is required in this case.

The development rate of hydropower is still low, due to the following problems.

1. In developing a project, it will take about 6-10 years time for planning,investigation and construction..

2. High capital investment is needed, and some parts of the investmenthave to be derived from foreign sources.

3. There are growing problems on relocation of villages, involvedcompensation for damage, selecting the suitable resettlement area andenvironmental impact.

Because of long transmission line to the villages with low load factor, theelectric power will be available to the people in rural areas may not be economical.This leads to the development of mini or micro hydroelectric projects to supplythe electric power to remote areas. The importance of micro hydroelectric projectshave been observed in some parts of the country with availability of river flowthrough out the year.

In order to reduce the cost of development, several measures havebeen considered as follows .

i. Development of low cost turbines and generators.

ii. Participation of villages in the development and operation of the project..


iii. Using the appropriate technology and tolerable substandard requirement and project civil work component at the beginning stage.

1.4.3 Nuclear EnergyAccording to modern theories of atomic structure,matter consists of

minute particles known as atoms. Heavier unstable atoms such as Uranium(U235), Thorium (Th232) liberate large amount of heat energy. The energyreleased by the complete fission of 1 Kg of uranium, is equal to the heat energyobtained by burning 4500 tons of coal or 2200 tons of oil. The heat producedby nuclear fission of the atoms of fissionable material is utilized in special heatexchangers for the production of steam which is then used to drive turbogenerators as in the conventional power plants.

However there are some limitations in the use of nuclear energy..

i. High capital cost of nuclear power plants..

ii. Limited availability of raw materials..

iii. Difficulties associated with disposal of radio active waste and shortage of well trained personal to handle the nuclear power plants.

The uranium reserves in the world at present are small. These reservesare recoverable but are expensive.

The presently working power plants are

i. Tarapur atomic power station in Maharastra..

ii. Ranapratap sagar atomic power station near Kota in Rajasthan..

iii. Kalpakkam atomic power station near Chennai in Tamilnadu.

iv. Narora atomic power station in Utharapradesh. About 3% of the energy produced in India is obtained from nuclear power plants.

1.5 Non conventional Energy SourcesThe sources of energy which are being produced continuously in nature

and are in exhaustible are called renewable sources of energy or non-conventionalenergy.

Some of these sources are

i. Wind energy

ii. Tidal energy

iii. Solar energy


1.5.1 Wind energyWinds are caused because of two factors..

i. The absorption of solar energy on the earths surface and in the atmosphere..

ii. The rotation of the earth about its axis and its motion around the sun.

A wind mill converts the kinetic energy of moving air into mechanicalenergy that can be either used directly to run the machine ( or ) the generator toproduce electricity.

1.5.2 Tidal energyTides are generated primarily by the gravitational attraction between the

earth and the moon. They arise twice a day in mid-ocean. The tidal range is onlya meter.

Basically in a tidal power station water at high tide is first trapped in aartificial basin and then allowed to escape at low tide. The escaping water isused to drive water turbines, which is drive electrical generators.

1.5.3 Solar energyEnergy from the sun is called solar energy. The sun’s energy comes

from nuclear fusion reaction that take place deep in the sun. Hydrogen nucleusfuse into helium nucleus. The energy from these reactions flow out from the sunand escape into space.

Summary• Primary energy sources produce net energy.

• Secondary energy sources produce no net energy.

• Conventional energy sources are fossil fuel energy, hydraulic energy, nuclear energy.

• Coal is complex mixture of compounds of carbon, hydrogen and oxygen.

• Crude oil products are petroleum gas, petrol, kerosene, diesel, lubrication oil, paraffin wax, asphalt.

• Natural gas consists of 95% methane and rest ethane, propane.

• Potential energy of water is converted into mechanicalenergy by using prime mover is known as hydraulic turbine.


• Non-conventional energy sources are wind energy, tidal energy, solar energy.

Short Answer Type Questions1. Define energy and write its units.

2. Define primary energy sources and write its examples.

3. Define secondary energy sources and write its examples.

4. What are the different forms of energy ?

5. What are the compounds present in the coal ?

6. What products can obtain from crude oil ?

7. What are the conventional sources of energy ?

8. What are the non-conventional sources of energy ?

Long Answer Type Questions1. What are the conventional energy sources and explain briefly?

2. What are the non-conventional energy sources and explain briefly?

On Job TrainingIf it is possible visit nearest nuclear power plant.


2.2 Solar Constant

2.3 Solar Radiation at the Earth’s Surface

2.4 Instruments for Measuring Solar Radiation and Sun Shine

2.5 Solar Energy Utilisation - Basic Ideas about the Pre - Historic ways of Using Solar Energy

2.6 Solar Energy Applications

Learning ObjectivesAfter studying this unit, the student will be able to

• How to measure solar radiation and sun shine.

• Uses of solar collector.

• How to use solar energy.

2.1 IntroductionEnergy from the sun is called solar energy. The sun’s energy comes

from nuclear fusion reaction that takes place deep in the sun. Hydrogen nucleusfuse into Helium nucleus. The energy from these reactions flow out from the sunand escape into space.

2UNIT

Solar Energy


Solar energy is some times called radiant energy. these are differentkinds of radiant energy emitted by sun. The most important are light infraredrays. Ultra violet rays and X-rays.

The sun is a large sphere of very hot gases. It’s diameter is 1.39X106KM. While that of the earth is 1.27X104 KM. The mean distance betweenthe two is 1.5X108 KM. The beam radiation received from the sun on theearth is reflected into space, another 15% is absorbed by the earthatmosphere and the rest is absorbed by the earth’s surface. This absorbedradiation consists of light and infrared radiation without which the earthwould be barren.

All life on the earth depends on solar energy. Green plants make foodby mean of photosynthesis. Light is essential from in this process to takeplace. This light usually comes from sun. Animal get their food from plantsare by eating another animals that feed on plants. Plants and animals also needsome heat to stay alive. Thus plants are store houses of solar energy.

2.2 Solar constant“The rate at which solar energy arrives at the top of the atmosphere is

called solar constant. It is denoted by ISc “ . This is the amount of energyreceived in unit time on a unit area perpendicular to the sun’s direction atthe mean distance of the earth from the sun. Because of the sun’s distance andactivity very through out the year, the rate of arrival of solar radiation variesaccordingly.

The solar constant is thus an average from which the actual values veryup to 3% in either direction. The National Aeronautics and SpaceAdministration’s ( NASA ) standard value for the solar constant, expressed inthree common units are as follows.

i. 1.353 KW per Square meter

ii. 116.5 Langleys per hour (1 Langley being equal to 1Cal/cm2 of solar radiation received in one day).

iii. 429.2 Btu per Sqr. ft. per hour.

The distance between the earth and the sun varies a little through theyear. Because of this variation, the extra-terrestrial (out side the earth’satmosphere) flux also varies. The earth is closes to the sun in the summer andfarthest away in the winter. This variation in the intensity of solar radiation ( I )that reaches the earth. This can be approximated by the equation.


where ‘n’ is the day of the year

2.3 Solar Radiation at the Earth’s SurfaceThe solar radiation that penetrates the earth’s atmosphere and reaches

the surface differs in both amount and character from the radiation at the top ofthe atmosphere. In the first place part of the radiation is reflected back into thespace, especially by clouds.

Further more, the radiation entering the atmosphere is partly absorbedby molecules in the air. Oxygen and Ozone (O3) formed from oxygen, absorbnearly all the ultraviolet radiation and water vapour and carbondioxide absorbsome of the energy in the infrared range. In addition part of the solar radiationis scattered (i.e its direction has been changed) by droplets in clouds byatmosphere molecules and by dust particles.

Solar radiation that has not been absorbed or scattered and reachesthe ground directly from the sun is called “Direct radiation or Beam radiation”.

Fig 2.1 Solar Radiation at the Earth’s Surface

365I . = 1+0.033 Cos [360(n-2) ]

ISC = 1+0.033 Cos [360 X n]365

Reflected back into Surface

Reflected back by Surface Deffuse

Radiation

DeffuseScattering

Direct RadiationSurface of the Earth

Atmospheric Absorption (warning of air)


Diffuse radiation is that solar radiation received from the sun after itsdirection has been changed by reflection and scattering by the atmosphere.Because of the solar radiation is scattered in all directions in the atmosphere,diffuse radiation comes to the earth from all parts of the sky.

The sum of the beam radiation and diffuse radiation flux is called thetotal or global radiation.

2.4 Measuring Instruments for Solar Radiation and Sun shine

Solar radiation flux is usually measured with the help of a pyranometeror a Pyrheliometer, Sun shine recorder is used for measuring sunshine.

2.4.1 PyranometerA pyranometer is an instrument which measures either global or diffuse

radiation over a hemispherical field of view. A sketch of the instrument as installedfor the measurement of global radiation is shown in fig. 2.2 . Basically thepyranometer consists of a “black” surface with heats up when exposed to solarradiation. Its temperature increases until its rate of heat gain by solar radiationequals its rate of heat loss by convection, conduction and radiation.

The hot junctions of a thermopile are attached to the black surface.While the cold junctions are located in such a way that they don’t receive theradiation. As a result, an e.m.f. is generated. This e.m.f. which is usually in therange of 0 to 10 mV can be read, recorded or integrated over a period of timeand is a measure of the global radiation.

Fig 2.2 Pyranometer

21

3

456

7

1. Black Surface 2. - Glass Domes 3. - Glass Plate4. Three Leveling Screw 5. - Mounting Plate 6. - Grouted bolts 7. Platform


The pyranometer shown in fig. 2.2 is used common in India. It has itshot junctions arranged in the form of a circular disc of diameter 25mm and iscoated with a special black lacquer having a very high absorptivity in the solarwave length region. Two concentric hemispheres, 30 and 50mm in diameterrespectively made of optical glass having excellent transmission characteristicsare used to protect the disc surface from the weather. An accuracy of about +2% can be obtained with the instrument.

2.4.2 Sun Shine RecorderThe duration of bright sun shine in a day is measured by means of a sun

shine recorder shown in fig. 2.3. The sun’s rays are focused by a glass sphere topoint on a card strip held in a groove in a spherical bowl mounted concentricallywith the sphere. Whenever there is bright sun shine, the image formed is intenseenough to burn a spot on the card strip. Through the day the sun moves acrossthe sky, the image moves along the strip. Thus, a burnt space whose length isproportional to the duration of sun shine is obtained on the strip.

Fig 2.3 Sun Shine Recorder

1

2

43 5

1. Glass Sphere 2. Spherical bowl with Grooves 3. Marble base

4. Grouted bolts 5. Platform


2.5 Solar Energy utilization - Basic ideas about pre - historic way of using solar Energy

Energy is a common man’s daily commodity. The world energyconsumption in 1975 was 8002 million tons of coal equivalent and is expectedto shoot upto 27,400 million tons of coal equivalent in the year 2000. It isbecoming scarce day by day even then its demand is on the increase. Theincreased population has let to depilation of energy. The process of mankindhas influenced the subsequent exploitation of new source of energy from time totime.

The utilization of coal, the development of hydro electricity, the discoveryof oil and gas and the advents of nuclear energy or significantly mile stones inhuman history. Each new source brought about a performed change in the lifestyle of the people. Each new source supplemented the other.

The size of the balance of fossil fuels will be over within a hundredyears. Hence it is essential to tap the other sources of energy to supplement theexisting energy demands of all non-conventional energy source, solar energyholds the greatest promise as it is abundant, renewable and pollution free. Itscollection, storage on conversion is also easy. Hence world wide attention isnow focused on various methods of utilization of solar energy.

The solar energy that falls on India in one minute is enough to supply theenergy needs of our country for one day. Man has made very little use of thisenormous amount of solar energy that reaches the earth. He has used solarenergy indirectly, for many thousands of years. Wind mills which are driven bywind that results from infrared solar energy.

2.6 Solar Energy Applications1. Heating and cooling of residential building

2. Solar water heating.

3. Solar drying of agricultural and animal products.

4. Salt production by evaporation of sea water.

5. Solar cooking.

6. Solar engines for water pumping.

7. Solar refrigeration.

8. Solar electric power generation.

9. Solar photo voltaic cells, which can be used for electricity.


10. Solar furnaces.

2.6.1 Solar CollectorsA solar collector is a device for collecting solar radiation and transfer

the energy to a fluid passing in contact with it. Utilization of solar energy requiressolar collectors.

These are generally of two types.

i. Non-concentrating or Flat plate type solar collector.

ii. Concentrating or Focusing type solar collector.

The solar energy collector, with its associated absorber, is the essentialcomponent of any system for the conversion of solar radiation energy into moreusable form (Ex. Heat, Electricity). In the non-concentrating type, the collectorarea is the same as the absorber area. On the other hand, in concentratingcollectors, the area intercepting the solar radiation is greater.

By means of concentrating collectors, much higher temperatures can beobtained than with the non-concentrating type. They use many differentarrangements of mirrors and lenses to concentrate the sun’s rays on the boiler.This type shows better efficiency than the flat plate type. For the best efficiency,collectors should be mounted to face the sun as it moves through the sky.

i . Non -Concentrating or Flat plate solar Collector

Fig 2.4 Non - Concentrating Collector

Where temperature below about 900C are adequate, as they are forspace and service water heating flat plate collectors, which are of the non-

1 2

3

4

51. Transparent Cover 2. Cushion Support and seat for Glass3. Absorber Plate 4. Insulation 5.Heat Transport Fluid (in tubes)


concentrating type, and particularly convenient. They are made in rectangularpanels, from about 1.7 to 2.9 Sq.m in area and are relatively simple to constructand erect. Flat plates can collect and absorb both direct and diffuse radiations,they are consequently partially effective even on cloudy days when there is nodirect radiation.

ii. Concentrating or Focusing Type Solar Collector

This type of solar collector is a device to collect solar energy with highintensity of solar radiation on the energy absorbing surface. Such collectorsgenerally use optical system in the form of reflectors. A focusing collector is aspecial form of flat plate collector modified by introducing a reflecting surfacebetween the solar radiation and the absorber. In these collectors radiation fallingon a relatively large area is focused on to a receiver (or absorber) of considerablysmaller area. As a result of the energy concentration, fluids can be heated totemperatures of 5000oC or more.

Fig 2.5 Concentrator or Point Focus Collector

2.6.2 Solar CookerIn our country energy consumed for cooking shares a major portion of

the total energy consumed in a year. In villages 95% of the consumption goesonly to cooking. Variety of fuel like coal, kerosene, cooking gas, fire wood,dung cakes and agricultural waste are used. The energy crisis is affecting everyone. It is affecting the fuel bills for those who use it for heating the houses andcooking their food.

1 2

3

Solar

Radiat

ion

1. Reciever 2. Concentrator 3. Supporting Stand


The poor of the developing countries who have been using dry wood,picked up from the fields and forests as domestic fuel, have been affected intheir own way, due to scarcity of domestic fuel in the rural areas. At present firewood and cow dung cakes are the most important sources of fuel to cock food.Cow dung too precious to allowed to be used for burning and cooking.

It is very useful to improve the fertility of soil, it should be used inproper way. The supply of wood is also fast depleting because of theindiscriminate felling of trees in the rural areas and the denudation of forests.There is a rapid deterioration in the supply of these fossil fuels like coal, keroseneand cooking gas. The solution for the above problem is the harnessing of solarenergy for cooking purposes.

The most important is that the solar cooker is a great fuel saver. Thedepartment of new conventional energy source has calculated that a familyusing a solar cooker 275 days a year would save 800 Kg of fire wood or 65liters of kerosene. Similarly an industrial canteen or a hostel mess using thelarger community solar cooker for 20 to 25 people could save 400 Kgs of firewood or 335 liters of kerosene per year.

(a) Types of Solar Cooker

Basically there are three types of solar cooker

i. Flat plate box type solar cooker with or without reflector.

ii. Multireflector type solar cooker.

iii. Parabolic disc concentrator type solar cooker.

i. Flat plate box type solar cooker

This type of solar cooker is the simplest of all designs. This cookerallows solar radiation to enter through a double walled glass cover placed insidea blackened box which is well insulated and made air tight. Maximum no loadtemperature with a single reflector reaches upto 1600oC.

ii. Multi reflector type solar cooker

In multi reflector type, four square or triangular or rectangular reflectorsare mounted on the oven body. They all reflect the solar radiations into thecooking zone in which cooking utensils are placed.

Temperature obtained is the order of 2000oC. The maximum temperaturecan reach to 2500oC, if the compound cone reflector system is used.


iii. Parabolic disc concentrator type solar cooker

In parabolic disc concentrator type solar cooker, parallel sun’s rays aremade to reflect on a parabolic surface and concentrated on a focus on which theutensils for cooking are placed. The temperature of the order of 4500C can beobtained in which solar radiation are concentrated on to a focal point. Principleof operations of solar cooker is shown in Fig. 2.8.

Fig 2.6 Flate Plate box types Solar Cooker

Fig 2.7 Multi Refrtector type Solar Cooker

1 2

5 34

6

1. Rubber Packing 2. Glass Cover 3. Blackened Metal tray4. Cooking Utensils 5. Insulation 6. Wooden Frame

Solar Radiation

1

2

1. Reflector 2. Blackened Metal tray


Fig 2.8 Parabolic disc Concentrator type Solar Cooker

(b) . Constructional details and working principle of Box type solar cooke

Fig 2.9 Working Principle of box type Solar Cooker

The principle of operation of box type solar cooker is illustrated in fig.2.9. The solar rays penetrate through the glass covers and absorbed by ablackened metal tray kept inside the solar box. The solar radiation entering thebox are of short wavelength. Two glass covers are provided to minimize theheat loss. The loss due to convection is minimized by making the box air tight byproviding a rubber strip all around between the upper lid and the box. Insulatingmaterials like glass wool, saw dust or any other material is filled in the spacebetween blackened tray and outer cover of the box.

This minimizes heat loss due to conduction. With this type of cooker isplaced in the sun, the blackened surface starts absorbing sun rays and temperature

1

2

Sun’s Rays

1. Cooking Pot 2. Parabolic Mirror

1 2

6

345

1. Rubber Packing 2. Glass Cover 3. Blackened Metal tray4. Cooking utensils 5. Insulation 6. Wooden Frame


inside the box starts rising. The cooking pots, which are also blackened areplaced inside with food material, get heat energy and food will be cooked in acertain period of time depending upon the actual temperature attained inside.The temperature attained depends upon the intensity of solar radiation andmaterial of insulation provided.

The amount of solar radiation intensity can be increased by providedmirrors. The solar cooker is made up of inner and outer metal or wooden boxwith double glass sheet on it. Absorber tray or blackened tray is painted withsuitable black paint like black board paint. This paint should be dull in colourand can with stand the maximum temperature attained inside the cooker as wellas water vapour coming out of the cooking utensils.

Fig 2.10 Construction Details of box type Solar Cooker

The top cover contain 3mm thick two plain glasses fixed in wooden ormetal frame, keeping about 20mm distance between two. The entire top covercan be made tight with padlock hasp. Neoprene rubber sealing is providedaround the contact surfaces of the glass cover and hinged on one side of theglass frame.

A mechanism (guide for adjusting mirror) is provided to adjust the reflectorat different angles with the cooker box when the reflector is adjusted to shine inthe cooker box, 1150C to 1250C. Temperature is achieved inside the cookerbox. Addition of the reflector is useful in cooking earlier particularly in winter.

1

2

3

4

5

60 Cm

20 Cm

1. Reflecting Mirror 2. Guide for adjustment of Reflecting Mirror3. Glass Cover 4. Handle 5. Cooking Pots


The solar cooker is able to cook about 1.25Kg dry food materials,which is enough for a family of 5 to 7 persons. The total weight of the cooker isabout 22 Kgs. Over all dimensions of atypical model are 60X60X20cm height.

(c) Merits of solar cooker

Following are the some merits of a solar cooker

1. No attention is need during cooking as in other devices.

2. No fuel is required.

3. Negligible maintenance cost.

4. No pollution.

5. Vitamins of the food are not destroyed and food cooked is nutritive and delicious with natural taste.

6. No problem of over flowing of food.

(d) Limitations of solar cooker

1. One has to cook according to the sunshine, the menu has to be pre planed.

2. One can not cook at short notice and food can not be cooked in the night or during cloudy days.

3. It takes comparatively more time.

4. Chapattis are not cooked because high temperature for baking is required.

2.6.3 Solar water heaterIt is a device of producing heat water using solar energy. Solar water

heaters are one of the best options to be adapted in the developing country.Solar water heating systems are commercially produced in the country. Most ofthe systems available in India are designed to give water temperature from 600oCto 900oC. These are suitable for pre heating feed water to boiler and processingindustries and hot water application in hotels, bakeries, etc..

The term solar water heater includes conventional flat plate collectorwith either thermo syphon or forced circulation flow system. A solar water heaternormally consists of the following components.

i. A flat plate collector to absorb solar radiation and convert it into thermal energy.


ii. Storage tank to hold hot water for use and cold water for feeding the flat plate collector.

iii. Connecting pipes inlet and outlet for feeding cold water from the storage tank and taking hot water to the storage tank or point of use.

A diagram of a simple, small capacity, natural circulation system suitablefor domestic purpose is shown in fig. 2.11. The two main components of thestorage tank, the tank being located above the level of the collector. As water inthe collector is heated by solar energy, it flows automatically to the top of thewater tank and its place is taken by colder water from top of the tank. Wheneverthis is done, cold water automatically enters at the bottom. An auxiliary heatingsystem is provided for use on cloudy or rainy days.

Fig 2.11 Solar Water Heater

Typically, such system have capacities ranging from 100 to 200 litersand adequately supply the needs of a four or five persons. The temperature ofthe hot water delivery ranges from 500oC to 700oC. Solar water heating is agood example to illustrate one of the assets of the direct use of solar energy.This is the possibility of matching the temperature achieved in the heating devicewith the temperature required for use. As a result of this matching, thethermodynamic efficiency based on considerations of availability of energy canbe shown to be higher in the case of solar water heating system than a waterheating system using gas or electricity.

1

2

3

4

1. Hot Water for use 2. Insulated Storage tanks3. Cold Water for Feeding 4. Flat Plate Solar Collector


Solar water heaters of the natural circulation type were used fairly widelyfrom the beginning of the twentieth century till about 1940 until cheap oil andnatural gas became available. Now they are a being installed again. They are inwide spread use in countries like Israel, Australia and Japan.

2.6.4 Solar DistillationFresh water is necessity for the sustenance of life and also the key to

man’s prosperity. It is generally observed that arid, semi arid and coastal areaswhich are thinly populated and scattered, one or two family members are alwaysbusy in bringing fresh water from a long distance. In these areas solar energy isplentiful and can be used for converting saline water in to distilled water. Thepure water can be obtained by distillation in the simplest solar still, generallyknown as the “basin type solar still”.

Fig 2.12 Solar Distillation

Solar water still is shown schematically in Fig. 2.12, it consists of ablackened basin containing saline water at a shallow depth, over which is atransparent air tight cover that encloses completely the space above the basin. Ithas a roof shape. The cover which is usually glass may be of plastic, is slopedtowards a collection through. Solar radiation passes through the cover and isabsorbed and converted into heat in the black surface. Impure water in thebasin or tray is heated and the vapour produced is condensed to purified wateron the cooler interior of the roof. The transparent roof material, transmits nearlyall radiation falling on it and absorbs very little, hence it remains cool enough tocondense the water vapour. The condensed water flows down the sloping roofand is collected in troughs at the bottom. Saline water can be replaced in theoperation by either continuous operation or by batches.

1 2

3

456

1. Condensed Water drops 2. Transparent Cover 3. Filler4. Blackened Surface 5. Insulation 6. Over flow Line

WaterVopour

Impure Water


2.6.5 Solar water pumpingSolar pumping consists in utilizing the power generated by solar energy

for water pumping useful for irrigation.

Solar energy offers several features that make its utilization for irrigationpumping quite attractive. First, the greatest need for pumping occurs during thesummer months when solar radiation is greatest. Second, pumping can beintermittent to an extent. During periods of low solar radiation when pumpingdecreases, evaporation losses from crops are also low. Finally, relatively inexpensive pumped storage can be provided in the forms of bonds.

A number of recently constructed solar irrigation pump installations arenow operational. The major obstacle to increase use of solar irrigation systemsat this time is their relatively high capital cost. If the costs of solar pumps can besubstantially reduced and assuming that conventional fuel costs continue to rise,solar irrigation could become economical, and increased use of such systemsmight be anticipated in future.

The basic system consists of the following components

1. The solar collector.

2. The heat transport system.

3. Boiler or heat exchanger.

4. Heat engine.

5. Condenser.

6. Pump

The solar pump is not much different from a solar heat engine workingin a low temperature cycle. The sources of heat is the solar collector, and sink isthe water to be pumped. A typical solar powered water pumping system isshown in Fig. 2.13.

The primary components of the system are an array of flat plate collectorsand an Rankin engine with an organic fluid as the working substance. Duringoperation a heat transfer fluid (Pressurized water) flows through the collectorarrays. Depending upon the collector configuration, solar flux and the operatingconditions of engine, the fluid will be heated in the collector to a higher temperature,the solar energy which is thus converted to the thermal energy. The fluid (water)flows into a heat exchanger (boiler), due to temperature gradient, and comesback to the collector. This water yields its heat to an intermediate fluid in theboiler.


This fluid evaporates and expands in the engine before reaching thecondenser, where it condenses at low pressure. The condenser is cooled by thewater to be pumped. The fluid is then re injected in the boiler to close the cycle.The expansion engine or Rankin engine is coupled to the pump and it could ofcourse be coupled to an electric generation.

Fig 2.13 Solar Water Pumping

2.6.6 Electricity from solar EnergyElectricity energy is the most convenient form of energy. It is easy to

use, transport, control and transform into other forms of energy.

Modern society has an insatisfiable hunger for energy. This need forenergy will continue to increase as the newly developing countries become moreindustrialized and the mature nations increase their scope of mechanization. Tosatisfy this need, vast quantities of coal and petroleum products are required.More recently, the advent of nuclear energy has added vast quantities for futureneeds.

Although sun is the ultimate source of all the power which has at hisdisposal, the conversion of solar radiation directly into electrical power by somecheap and efficient means has been sought for several decades. Many differentmethods have been tried for this purpose but none of these could complete withconventional fossil fuel or hydro electric power plants.

1

2

3

4

5

6

7

89

10

sun

1. Ground Water 2. Condenser 3. Pump 4. Heat engine5. Feed Pump 6. Organic Fluid 7. Circulating Pump8. Hot Water 9. Solar Collector array 10. Heat exchanger


(a) Solar photo voltaic Effect

The direct conversion of solar energy into electrical energy by means ofthe photo voltaic effect, i.e. the conversion of light (or other electromagneticradiation) into electricity.

The photo voltaic effect is defined as the generation of the electromotiveforce as a result of the absorption of ionizing radiation. Energy conversion deviceswhich are used to convert sun light to electricity by the use of the photo voltaiceffects are called solar cells. A single converter cell is called a solar cell or, moregenerally, a photo voltaic cell, and combination of such cells, designed to increasethe electric power out put is called a solar module or solar array.

The photo voltaic effect can be observed in nature in a variety of materials,but the materials that have shown the best performance in sunlight. When photonsfrom the sun are absorbed in a semiconductor, they create free electrons withhigher energies than the electrons which provide the bonding in the basecrystal.

Once these electrons are created, there must be an electric field to inducethese electron higher energy electrons to flow out of the semi conductor to douseful work. The electric field in most solar cells is provided by a junction ofmaterials which have different electrical properties. The photo voltaic effect canbe described easily for p-n junction in a semi conductor.

Fig 2.14 Solar Photo Voltaic Cell

1. Positive Contact 2. Negative Contact 3. Metal Conductor4. Current Collection Grid (metal fingers) 5. Diffused Layer


To obtain a useful power output from photon interaction in a semiconductor three processes are required.

1. The photons have to be absorbed in the active part of the material and result in electrons being excited to a higher energy potential.

2. The electron hole charge carrier created by the absorption must be physically separated and moved to the edge of the cell.

3. The charge carries must be removed from the cell and delivered to a useful load before they loose their extra potential.

For completing the above processes, a solar cell consists of

1. Semi conductor in which electron hole pairs are created by absorption of incident solar radiation.

2. Region containing a drift field for charge separation.

3. Charge collecting front and back electrodes.

(b) Applications of solar photo voltaic system in rural areas

A variety of photo voltaic system configuration have been developedand deployed for rural applications such as drinking water supply, street lighting,irrigation water pumping and for operation of electronic equipment. Governmentof India is sponsoring a programme for popularizing solar lighting, solar waterpumping etc. by providing capital subsidies and concessional interest onborrowed capital.

Solar lighting

Electricity for lighting during night is one of the most convenient andpreferred form of energy. However in our country out of 6 lacks villages, 1 lakhvillages are still to be electrified. Even in electrified villages only a quarter ofhouse-holds have properconnection. Owing to power shortage in many stages,electricity supply situation in villages for lighting when it is most needed.

The bulk of rural house-holds in India, normally use kerosene lanternsfor meeting their lighting requirement. It is estimated that around 100 millionkerosene lanterns are used in India. These lanterns provided insufficient andpoor quality of light.

For village lighting three major system configuration are available

1. Domestic lighting system or solar lantern.

2. Pole mounted stand alone street lighting system.


3. Non-grid interactive centralized lighting system.

1. Solar lantern

Solar photo voltaic powered lights called lanterns Fig. 2.15 areconsidered to be alternative solution to village lighting needs. A typical solarlantern consists of small photo voltaic module, a lighting device, a high frequencyinvertor, battery charge controller and appropriate housing is connected to lanternthrough cable for charging a typical lanterns uses a 10 watt lamp. The expectedlife of the lamp is 3 to 5 years.

Storage battery is one crucial component in lantern, recombinantmaintenance free absorbed electrotype batteries are being used. The batteryhas a life of 3 to 5 years. Sealed nickel cadmium battery is a good optionconsidering their deep discharge characteristics.

It is important to have reliable electronics to operate the lamp andprovide suitable protection. A high frequency investor is being used to excitecompact fluorescent lamp and a charge controller which protect battery fromover charging.

Fig 2.15 Solar Lantern

2. Street lighting system

It is consists of two photo voltaic modules, mounting frame, 4m longpole, battery box, tubular type lead-acid battery, charge controller, investor andday light senses, Time module sensing is used to switch on lights on the eveningtime. It works for one fluorescent tube lights of 20 watts for whole night.


Fig 2.16 Solar Street Lighting System

Summary• The rate at which solar energy arrives at the top of the atmosphere is

called solar constant ISC .

• Solar radiation that has not been absorbed or scattered and reachesthe ground directly from the sun is called direct radiation or beam radiation.

• Diffuse radiation is that solar radiation received from the sun afterits direction has been changed by reflection and scattering by the atmosphere.

• The sum of the beam and diffuse radiation flux is referred to as total(or) global radiation.

• Solar radiation flux is usually measured with the help of a pyranometeror a pyrheliometer, sun shine recorder is used for measuring sun shine.

• Solar collectors are generally two types one is Nonconcentratingor flat plate solar collector another one is concentrating or focusing type solarcollector.

• Basically there are three design of solar cooker (i) Flat plate box typesolar cooker, (ii) Multi reflector type solar cooker,( iii) Parabolic discconcentrator type solar cooker.

• The term solar water heater includes conventional flat plate collectorwith either thermo syphon or forced circulation flow system.

• The solar pump is not much different from a solar heat engine working


in a low temperature cycle. The sources of heat is the solar collector and sink isthe water to be pumped.

• The direct conversion of solar energy into electrical energy by meansof the photo voltaic effect, that is the conversion of light into electricity.

Short Answer Type Questions1. Define solar constant.2. Define solar energy.3. What is diffuse radiation ?4. What is global radiation ?5. What are the instruments used for measuring solar radiation and sun

shine?6. What are the applications of solar energy ?7. What are the different types of solar cooker ?8. What are the advantages of a solar cooker ?9. What are the components of solar water heater ?10. What are the basic components of solar water pumping ?11. Define photo voltaic effect.12. What are the different applications of solar photo voltaic system in

rural area ?13. What are the different types of solar collector ?

Long Answer Type Questions

1. Explain Pyranometer with the help of neat sketch.2. Explain basic ideas about the Pre-historic ways of using solar energy.3. Explain solar collectors with the help of a neat sketch.4. Explain working principle and constructional details of box type solar

cooker.5. Explain briefly about solar water pumping with the help of neat sketch?.6. Describe briefly about photo voltaic system.7. Explain briefly about the applications of solar photo voltaic system in

rural areas.8. Explain briefly about solar water heaters with the aid of a neat sketch.

OJT / Project work1. Visit the Solar water heating plant.2. Visit the Solar lighting plant.


3.2 Classification of Wind Mills

3.3 Horizontal Wind Mills

3.4 Vertical Wind Mills

3.5 Advantages and Disadvantages of Energy

Learning ObjectivesAfter studying this unit, you will be able to know

• Known to convert kinetic energy of air into useful power.

• Classifications of wind mills and their working principles.

• Known the uses of using wind power.

3.1 IntroductionWinds are caused because of two factors

1. The absorption of solar energy on the earth’s surface and in the atmosphere.

2. The rotation of the earth about its axis and its motion around the sun.

3UNIT

Wind Energy


Because of these factors, alternate heating and cooling cycles occur,differences in pressure are obtained and the air is caused to move. The potentialenergy of wind as a source of power is large. This can be judged from the factthat energy available in the wind over the earth’s surface is estimated to be1.6X107 KW besides the energy available is free and clean.

The problem associated with utilizing wind energy are that

1. The energy is available in dilute form, because of this conversion machines have to be necessarily large.

2. The availability of the energy varies considerably over a day and with the seasons.

For this reason some means of storage have to be devised if a continuoussupply of power is required.

A wind mill converts the kinetic energy of moving air into mechanicalenergy that can be either used directly to run the machine or generator to produceelectricity.

3.2 Classifications of wind Mills

3.3 Horizontal wind Mills3.3.1 Horizontal axis single blade wind Mill

Horizontal axis propeller type arrangement, a long blade is mounted ona rigid hub shown in fig. 3.1. If extremely large blades are mounted on rigid hub,large blade root bending moments may occur due to tower shadow, gravity andsudden shifts in wind directions on a 200 fts long blade. Fatigue load may beenough to cause blade root failure.

To reduce rotor cost, use of single long blade centrifugally balanced by


a low cost counter weight. The relatively simple rotor hub consists of a UniversalJoint between the rotor shaft and blade allowing for blade. This type of hubdesign contains fewer parts and costs less.

Fig 3.1 Horizontal axis single blade wind Mill

3.3.2 Horizontal axis double blade wind Mill

Fig 3.2 Horizontal axis double blade wind Mill

1

2

3

4

5

Wind

1. Hub 2. Counter Weight 3. Composite blade4. Induction generator and gear box 5. Stand

Rotor

Wind Mill Head

Supporting Structure


Horizontal axis using two aerodynamic blades type arrangement,rotor drives through a step up gear box. The components are mounted ona bed plate which is mounted on a pinttle at the top of the tower. The two bladerotor is usually designed to be oriented down wind of the tower. The arrangementaxis wind mill is shown in Fig. 3.2

When the machine is operating its rotor blades are continuouslyflexed by unsteady aerodynamic, gravitational and inertial loads. If the bladesare metal, flexing reduces their fatigue life. The tower is also subjected to unsteadyload and dynamic interactions between the components of the machine towersystem can cause serious damage.

3.3.3 Horizontal axis Multiblade wind MillThis type of design for multi blades as shown in Fig. 3.3 made from

sheet metal or aluminium. The rotors have high strength to weight ratios andhave been known to service hours of freewheeling operation in 60 Km/Hr winds.They have good power coefficient, high starting torque and added advantageof simplicity and low cost.

Fig 3.3 Horizontal axis Multi blade wind Mill

3 .4 Vertical axis wind Mills3.4.1 Vertical axis darrieus Rotor wind Mill

This type was invented by G.J.M. Derrieus a French engineer in 1925.It has two or three thin, curved (egg beater) blades with airfoil cross section andconstant chord length shown in fig. 3.4 . Both ends of blades are attached to avertical shaft. Thus the force in the blade due to rotation is pure tension. Thisprovides a stiffness to help with stand the wind forces it experiences.


The blades can thus be made lighter than in the propeller type. Whenrotating, these airfoil blades provide a torque about the central shaft in responseto a wind stream. This shaft torque is being transmitted to a generator at thebase of the central shaft for power generation.

Darrrieus type rotors are lift devices, characterized by curved bladeswith air foil cross sections. They have relatively low solidity and low startingtorques, but high tip to wind speeds and relatively high power outputs per givenrotor weight and cost. Derrieus rotor can also be combined with varioustypes of auxiliary rotors to increase their starting torques. However such additionsincreased the weight and cost of the system, so trade-offs in thesecharacteristics must be considered in developing an optimum design.

Characteristics of Darrieus Rotor

i. No self starting

ii. High speed

iii. High efficiency

iv. Potentially low capital cost

Fig 3.4 Vertical axis darrieus Rotor wind Mill

1

2

3

4 5

6.5 Cm

1. Aero Foil blades (Catenary shape) 2. Guys3. Vertical shaft 4. Generator 5. Support Structure


3.4.2 Vertical axis savonius rotor wind MillPerhaps the simplest of the modern types of wind energy conversion

system is the Savonius rotor which works like a cup anemometer. This type wasinvented by S.J. Savonius in the year 1920. This machine has becomepopular since it requires relatively low velocity winds for operation.

It consists of two half cylinders facing opposite directions in sucha way as to have almost an S-shaped cross section shown in fig. 3.5 . Thesetwo semi circular drums are mounted on a vertical axis perpendicular to thewind direction with a gap at the axis between the two drums. Irrespective of thewind direction the rotor rotates such as to make the convex sides of the bucketshead into the wind. From the rotor shaft we can take power for use like waterpumping, battery charging, grain winnowing etc. However, instead of havingtwo edges together to make an S-shaped they overlap to leave a wide spacebetween the two inner edges, so that each of these edges is near the central axisof the opposite half cylinder. The main action of the wind is very simple, theforce of the wind is greater on the cupped face than on the rounded face. Indetail it is a bit more complicated.

The wind curving around the back side of the cupped face exerts areduced pressure much as the wind does over the top of an air foil and this helpsto drive the rotation. The wide slot between the two inner edges of the halfcylinders, lets the air whip around inside the forward moving cupped face, thuspushing both in the direction of the rotation.

Characteristics of Savonius Rotor

i. Self starting

ii. Low speed

iii. Low efficiency

Fig 3.5 Vertical axis Savonius rotor wind Energy(a) (b)


3.5 Advantages and Disadvantages of Wind Energy3.5.1 Advantages of wind Energy

i. The wind energy is free, inexhaustible and does not need transportation.

ii. Wind mills will be highly desirable and economical to the rural areas which are far from existing grids.

iii. Wind power can be used in combination with hydroelectric plants. Such that the water level in the reservoir can be maintained for longer periods.

iv. The major advantages of darrieus rotor design is that the rotor blades can accept the wind from any compass.

v. A savonius wind energy conversion system has a vertical axis whicheliminates the expensive power transmission system from the rotor to theaxis. Since it is a vertical axis machine it does not matter much about the winddirection. The machine performs even at low wind velocity ranges.

3.5.2 Disadvantages of Wind Energyi. Wind power is not consistent and steady, which makes the

complications in designing the whole plant.

ii. The wind is a very hazard one. Special and costly designs and controls are always required.

iii. The cost factor, which has restricted the development of wind power in large scale for feeding to the existing grid.

iv. It has low power coefficient.

v. Careful survey is necessary for plant location.

Summary• Winds are caused due to the absorption of solar energy on the earth’s

surface and in the atmosphere.

• Winds are caused due to the rotation of the earth its axis and its motion around the sun.

• A wind mill converts the kinetic energy of moving air into mechanical energy.

• The darrieus rotor has a slightly higher efficiency of 35% but is not self starting.


Short Answer Type Questions1. How the wind mills are classified.

2. What are the advantages of wind power ?

3. What are the disadvantages of wind power ?

4. What is the principle of wind mill ?

5. Which are the factors for wind flows on earth’s surface.

Long Answer Type Questions1. Explain briefly about the horizontal wind mills with neat sketch.

2. Explain briefly about vertical wind mills with neat sketch.

O.J.T / Project work

1. Visit the plants of wind mills.


4.2 History of Bio - gas

4.3 Process of Bio - gas generation

4.4 Raw Materials available for Bio - gas Fermentation

4.5 Selection of site for installation of a Bio - gas plant

4.6 Materials Required for for Construction of Bio - gas Plant.

4.7 Constructional details of Bio - gas Plant

4.8 Types of Bio - gas Plant


• Known to reuse of domestic wastes and agricultural wastes.

• Known wastes how to produce useful energy.

• Known to construct a bio gas plant.

4UNIT

Bio Energy


4.1 IntroductionBio gas is generated through a process of anaerobic digestion of

bio mass. Bio mass is organic matter produced by plants both terrestrial (thosegrown on land) and aquatic (those grown in water) and their derivatives.

Bio mass means organic matter and photo chemical approach toharness solar energy means harnessing of solar energy by photo synthesis. Solarenergy is stored in the form of chemical energy.

Hence, Solar energy —> Photosynthesis —> Bio mass —> Energy generation.

4 .2 History of bio -gasIn the field of an aerobic digestion of waste material India and China

are recognized world leaders. This practice is based upon an age-old traditionof composting human, animal and plant wastes to produce an organic fertilizer.In fact bio gas programme has been recognized for making available a clean andsoil conditioner all over the world. Since the 1920’s there have been sporadicattempts made to recover bio gas from sewage wastes and animal dung. A fewbio gas plants for sewage disposal and bio gas recovery were installed in Europeand the U.S.A. in 1920’s and 1930’s respectively.

Although the Chinese have been experimenting with bio gas since the1950’s and China had its first bio gas plant in 1936, yet it was reported only in1970’s in Sichvan. Mainly, there was a movement to extend the practice andreproduce the digester in a large way through the country wide.

The history of bio gas from cattle dung in India goes back to 1939 whenIndia Agricultural Research Institute (ARI) in New Delhi, was able to fermentcattle dung to produce methane.

Subsequently Proof. N.V. Joshi at poona patented a model of bio gasplant in 1945. Later on Jashbhai, J. Patel evolved a simple model called“Gramalaxmi” was patented it in the year 1951. Mean while J. Patel continuedhis efforts to simplify his earlier patented. Model, which resulted in thedevelopment of two chamber digester with central guide for free up and downmovement of steel gas holder. This design was accepted by the Khadi andVillage Industries Commission (KVIC) at bombay in India during 1962.Subsequently many Scientists, Engineers, Government, Semi-Government anddifferent social organisations contributed to the development of bio gastechnology.

The planning Research and Action Division (PRDA) of state planninginstitute, Government of Uttar Pradesh, Lucknow developed a cheap and


convenient model of bio gas in 1957 and called it Janata bio gas plant. Afterindependence the Ministry of Agriculture, Government of India was looking thebio gas programme related development and extension activities. KVIC andstate Government continued the programme in 1970-1980.

The national project on bio gas development was launched in 1980-1981 under Ministry of Agriculture. Currently Department of Non-conventionalEnergy Sources (DNES), the Ministry of power and Non-Conventional energyis also actively involved in supporting research and diffusion of bio gas technologyand many institutions and state agriculture universities are supporting researchprogramme on bio gas technology.

4.2.1 Bio gas CompositionsBio gas contains 55-70% methane, 30-45% carbon dioxide as well as

small quantities like N2, H2, H2S of some gases. It is lighter than the air and hasan ignition temperature of approximately 7000C. The temperature of the flameis 8700C. Its calorific value is approximately 4713 Kcal/m3.

4.2.2. Advantages of bio gas technology1. It provides a better and cheaper fuel for cooking, lighting, and power

generation.

2. It produce good quality, enriched manure to improve soil fertility.

3. It proves an effective and convenient way for sanitary disposal of human excreta, improving the hygienic conditions.

4. It generates social benefits such as reducing burden on forest formeeting cooking fuel by cutting of tree for fire wood, reduction in thedrudgery of women and children etc.

5. As a smoke less domestic fuel, it reduces the incidence of eye and lung diseases.

6. It also helps in generation of productive employment.

4.3. Process of bio gas generation4.3.1 Wet process(i) Anaerobic digestion

Bio gas is produced by the bacterial decomposition of wet sewagesludge, animal dung or green plants in the absence of oxygen. Feed stocks likewood shavings, straw and refuse may be used, but digestion takes much longer.The natural decay process ‘anaerobic decomposition’ can be speeded up by


using a thermally insulated, air tight tank with a stirrer unit and heating system.

The gas collects in the digester tank above the slurry and can be pipedoff continuously. At the optimum temperature (350C) complete decompositionof animal or human faces takes around 10 days. Gas yields depend critically onthe nature of the waste, pig manure is better than the cow dung or house holdrefuse. The residue left after digestion is valuable fertilizer. It is also rich in proteinand could be dried and used as animal feed supplement.

(ii ) Fermentation

As stated, ethanol or ethyl alcohol is produced by the fermentation ofsugar solution by natural yeast’s. After 30 hours of fermentation the brew or‘beer’ contains 6-10% alcohol and this can readily removed by distillation.Traditionally, the fibrous residues from plant crops like sugar cane bagassehave been burnt to provide the heat. Suitable feed stocks include crushed sugarcane, beet and fruit etc. sugar can also be manufactured from vegetable likemaize, wheat grain and potatoes starches and cellulose.

For example they must be ground or pulped and then cooked withenzymes to release the starch and convert it to fermentable sugars. Cellulosematerials like wood, paper waste or straw require harsher pre treatment,typically milling and hydrolysis with hot acid. One tone of sugar will produce upto 520 liters of alcohol, a tone of grain, 350 liters and a tone of wood anestimated 260 to 540 liters. After fermentation the residue from grains andother feed stuffs contains high protein content and is a useful cattle feedsupplement.

The hydrolysis and distillation steps require a high energy input forwoody feed stocks direct combustion or pyrolysis is probably more productiveat present, although steam treatment and new low energy enzymatic hydrolysistechniques are under development.

The energy requirement for distillation is also like to be cut dramatically.Alcohol can be separated from the beer by many methods which arenow under intensive development. These include solvent extraction, reverseosmosis molecular sieves and use of new desiccants for alcohol drying. It maysoon be possible to halve the energy required for alcohol production to producea greater net energy gain.

4.3.2 Dry process (Pyrolysis)A wide range of energy rich fuels can be produced by roasting dry

woody matter like straw and wood chips. The material is fed into a reactorvessel or retort in a pulverised or shredded form and heated in the absenceof air. As the temperature rises the cellulose and lignin break down to simpler


substances which are driven off leaving a char residue behind. This process hasbeen used for centuries to produce charcoal.

The end products of the reaction depend critically on the conditionsemployed, at lower temperatures around 5000C, organic liquid predominatewhilst at highest temperatures nearer 10000C combustible mixture of gasesresults.

4.4. Raw mater ials available for bio gas fer MentationFeed stock materials. The following organic matter rich feed stocks are

found feasible for their use as input materials for biogas production.

i. Animal wastes.

ii. Human wastes.

iii. Agricultural wastes.

iv. Waste of aquatic origin.

v. Industrial wastes.

4.4.1 Animal wastesCattle dung, urine, goat and poultry droppings, slaughter house wastes,

fish wastes, fetus wastes, leather and wood wastes, sericulture wastes elephantdung, piggery wastes etc.

4.4.2 Human wastesFeces, urine and other wastes emanating from human occupations.

4.4.3 Agricultural wastesAquatic and terrestrial weeds crop residue, stubbles of crop, sugar cane

trash, spoiled fodder, bagasse, tobacco wastes oilcakes fruit and vegetableprocessing wastes, press mud, cotton and textile wastes, spent coffee and teawastes.

4.4.4 Waste of aquatic originMarine plants, twigs, algae, water hyacinth and water weeds.

4.4.5. Industrial wastesSugar factory, tannery, paper etc.


4 .5 Selection of site for installation of a bio gas plantFollowing factors must be considered while selecting the site for a biogas plant.

1. Distance : The distance between the plant and site of gas consumption or kitchen should be less to minimize cost on gas pipe line and gas leakage. For a plant of capacity 2m3 the optimum distance is 10 m.

2. Minimum gradient : For conveying the gas a minimum gradient of 1% must be made available for the line.

3. Open Space : The sunlight should fall on the plants as temperature between 150oC to 300oC is essential for gas generation at good rate.

4. Water table : The plant is normally constructed underground for ease of charging the feed and unloading slurry requires less labour. In such cases care should be taken to prevent the seepage of water and plant should not be constructed if the water table is more than 10 ft. (3 m).

5. Seasonal run off : Proper care has to be taken to prevent the interference of run off water during the monsoon. Intercepting ditches or bunds may be constructed.

6. Distance from well : The seepage of fermented slurry may pollute the well water. Hence a minimum of 15 m should be maintained from the wells.

7. Space requirements : Sufficient space must be available for day to day operation and maintenance. As a guide line 10 to 12 m2 area is needed per 1 m3 of the gas.

8. Availability of water : Plenty of water must be available as the cow dung slurry with a solid concentration of 7% to 9% is used.

9. Source of cow dung/ materials for bio gas generation : The distance between the material for biogas generation and the gas plant site should be minimum to economics the transportation cost.


4.6 Materials required for the construction of bio gas plant

4 .7 Constructional details of bio gas plantFloating gas holder type

The construction techniques used in bio gas plant should be simple withlow demand of materials, low in cost and it should be easily known to mason.The standard requirement for bio gas plant construction is specially trained skilledmason to make it leak proof air tight. Otherwise, the chance of failure of theplant would be more.

1. Bricks

2. Cement

3. Sand

4. Steel for bigger size plant.

5. Concte

6. Reinforced concrete for larger tank.

7. Asbestos-cement pipes for inlet and outlet

8. Ferro-cement

9. Ferro-cementbricks

10. Plastic.

Good quality bricks preferablyMachine made first class bricks withuniform size and shape.

Pure port and land with noimpurities packed in polythenebags.

Fine and coarse with good quality.

Standard.

Hard with out any impurities.

Having good quality composition ofcement, sand and water.

Good qualities with no leakage andshould have uniform diameterand length as required.

Having few layers of iron wire meshplastered with diameter and length asrequired.

Outer wall of bricks, inner surfaceplastered with ferro-cement.

Fiber - glass reinforced plastics, PVC,polythene, etc.

S. Material Quality neededNo


(i) Lay out

The first step is to mark the lay out of the plant on selected andleveled site by marking the out line of the plant on the ground according torequired dimensions using accord stretched from the center.

Fig 4.1 Marking the out Line of the Plant

(ii) Excavation

Excavate with care so that the sides do not collapse. The deeper thepit, the more dangerous the excavation work becomes. Especially in sandysoil walls, the pit should be supported with a frame of bamboo poles. Theexcavated soil should be thrown at least half a meter away from the site so thatit does not fall in when the construction work is in progress. The diameter of thepit to be excavated, should be equal to the base diameter.

(iii) Floor

The bottom should be consolidated and leveled. If the bottom is muddyor soft and sandy, a layer of broken bricks or stones must be pounded in untilthe ground is firm. Bricks for the floor, including wall foundations are set on theiredge. This method gives sufficient strength. Where the ground condition is verybad concert or reinforced concrete should be used.

(iv) Side wall

A circular well should be constructed. It is essential to back fill betweenthe wall and the sides after every 30 Cm height with a piece of wood and wateradded to help compact the soil shown in Fig. 4.2 failure to properly ram theback fill will cause cracking in the walls.


Fig 4.2 Backfilling

(V) Partition wall

A partition wall is constructed to divide the circular well into two equalhalves in floating gas holder plants. It controls the flow of slurry. A half brick wallis enough. It is built upto the level of the top surface of the central guide frame orledge.

(vi) Inlet and Outlet pipes

These should be fixed slanting and inserted at an appropriate height inthe walls. There should not be any bends in the pipe as these cause blockage.The lower end of the inlet pipe is placed in about the center of the compartment.This position is not vital, but what is important bottom and dead patches ofunmoving slurry are not above to form the mouth of the pipe is about 30-35Cmabove the floor of the digester. This prevents any blockage of the inlet pipe andalso provides some volume in case stones, sands etc. get inside the plant andcollect over a period of time. The lower end of the outlet pipe is constructed ina similar way. The only difference is that the mouth of the pipe is set about 25-30Cm above the floor as it is less likely that stones, sands etc will come down tothis pipe.

The difference in the top level of inlet and outlet pipe should be at least0.45m to allow digested slurry to come out automatically when fresh slurry isadded.


Fig 4.3 Inlet and Outlet Pipes

(Vii) Plastering

The digester should be plastered from inside with 1: 3 mortar of cementand sand cured properly.

(viii) Slurry mixing tank

In order to mix dung and water thoroughly before feeding into the digester,a masonry tank is provided in the bio gas plant. The mixture of dung and wateris called slurry which is a substance used for biogas generation.

It may be provided with a mechanical or hand operated stirrer forpreparation of homogenous mixture. The bottom of the tank is given a slopeopposite to the direction of inlet chamber in order to prevent entry of sand or in-organic materials into the digester.

(ix) Compost pit

These can be dug in the ground or limed with masonry. Thevolume should be sufficient to receive the amount of slurry put in per day multipliedby the number of days required for emptying the pits.

(x) Placing of the gas holder

The guide frame is greased generally and then the gas holder is mounted

1

2

34

5

30 Cm

1. Inlet Pipe 2. Digester Wall 3. Supoprt Pillar

4. Foundation 5. Partition Wall


carefully without causing any tilting of the guide pipe and damage to the digesterwall.

(xi) Testing and operation

The digester portion should also be tested for water leaks. When theplant is found leak proof, it is ready to fed with dung slurry and for the productionof gas.

4.8 Types of bio gas plantThere are four types of bio gas plant these

i. Khadi and Village Industries Commission (KVIC)

ii. Pragathi design bio gas plant (Now we discouse about it) iii. Janata bio gas plant

iv. Deenbandhu bio gas plant

4.8.1 KVIC bio gas plantThe floating gas holder digester developed in India is of masonry

construction with gas holder made of M.S plates. The drum in the KVIC modelis the costliest component and its life is comparatively less.

Fig 4.4 KVIC bio gas Plant

1

23 4

5

6

7

8

1. Inlet Pipe 2. Mixing Pipe 3. Gas Holder 4. Gas Pipe5. Bio - gas (CH4+Co2) 6. Outlet 7. Slurry 8. Partition Wall


The design of KVIC plant was developed and perfected in India inthe year 1945. This was taken up propagation in the villages in the year 1962 byKhadi and Village Industries Commission at bombay. The design is available insize of 1 m3 to 140 m3 gas per day. In KVIC plant the gas is stored in mild steeldrum of storage capacity of 30-40% of plant size.

The plant consists of two parts. The digester, which is well containingthe animal waste in the form of a slurry and the dome, which floats the gas on theslurry and serves as the gas holder. The digester is normally below ground leveland two pipe lines lead to its bottom. One for feeding the animal waste slurryand the other for spent slurry called sludge to come out after it has underfermentation. It is worthy, nothing that the sludge to come out retains an excellentfertilizer it contains nitrogen, phosphorous and potassium.

A vertical partition wall divides it into two equal parts and serves todirect the flow of the slurry. The gas generation process occurs in two stages.In the first stage, the complex organic substance contained in the waste areacted upon by a certain kind of bacteria which produces methane and carbondioxide.

The calorific value of bio gas ranges from 1600 to 2500 KJ/m3. It isan excellent fuel for cooking and lighting. When compared with diesel it isalso be a very good fuel for compression, ignition engines and can save 70 to80 % of diesel.

4.8.2 Pragathi bio gas plantThe design has been developed by United Socio Economic

Development and Research Programme (UNDARP) pune, in order to have acheaper floating drum bio gas plant. In this design the depth of pit is less thanKVIC plant so that it can be constructed in hilly and high water table areas. Thecost of Pragathi plant is 20% less than KVIC plant. The design shown in fig.4.5, it indicates its different parts.

The foundation of this plant is of conical shape, with difference of onefeet between outer periphery and its center so as to reduce the earth and digesterwall work. It is constructed at the base of the pit with cement, sand andconcrete, keeping the site conditions in view so it the load due to weight ofslurry in the digester. The digester of pragathi plant start from the foundation indome shape there by reducing the constructional area, for same digester volume,thus reducing the cost of the plant. The wall thickness of digester is kept 75mmonly. Dome shape construction takes place upto a collar base, where acentral guide frame is provided. The digester wall above guide frame isconstructed in cylindrical shape.


Fig 4.5 Pragathi bio gas Plant

Partition wall is constructed in the digester for 4 m3 for bigger size plantso as to control the flow of slurry inside the digester. It divides digester in twoequal parts and separating inletand outlet portions. The inlet feeding is throughpipe, it is placed while construction digester wall. It is used for feeding slurry dailyinto the digester and generally its diameter is 100mm. The out let pipe is also100mm diameter and fixed while constructing digester wall. The asbestos cementpipes can be used for inlet and outlet pipes.

The guide frame is made of angle iron and steel pipe is embedded in thedigester wall at top of spherical portion of digester. The central guide pipe holdsgas holder which is also made of M.S sheet and angle iron. It floats up anddown along pipe depending on the quantity of gas in the drum.

Summary• Bio mass is organic matter produced by plants, both terrestrial and

aquatic.

• Bio gas is generated through a process of anaerobic digestion of bio mass.

• Bio gas contains 55 - 75 % methane and 30 - 45 % carbon dioxide as well as small quantities like N2, H2, H2S of some gases.

1. Mixing Pit 2. Inlet Pipe 3. Digester 4. Foundation5. Gas Storage 6. Out let Pipe 7. Mixing Pit

4


• Bio gas provides simultaneous dual benefits in terms of fuel for cooking and lighting as well as fertilizer.

• Bio gas burns efficiently without smoke or smell and eliminates the possibility of eye and lung diseases caused by smoke.

• Bio gas reduces the drudgery of women and children in terms ofproviding relief from the collection of fire wood and preparation of dungcakes.

• The gas can be used in dual engines, where upto 80% of the diesel can be replaced with bio gas.

• Utilization of waste materials in the plant not only improves thesanitarycondition of our village but also prevents deforestation and assures collegialand environmental balance.

Short Answer Type Questions1. Define bio gas energy.

2. What are the raw materials required for fermentation ?

3. What are the benefits of bio gas technology ?

4. What is bio mass ?

5. Write the percentage compositions of bio gas.

6. What is anaerobic digestion ?

7. What are the types of bio gas plant ?

Long Answer Type Questions1. Write the brief history of bio gas.

2. Explain briefly about the process of bio gas generation.

3. Explain briefly about the selection of site for installation of a bio gas plant.

4. Explain briefly about the material requirement for construction of bio gas plant.

5. Explain KVIC bio gas plant with the help of neat sketch.

6. Explain Pragathi design bio gas plant with the help of neat sketch.

OJT / Project work1. If available visit any type of bio gas plant.


5.2 Components of Tidal Power Plant

5.3 Classification of Tidal Power Plant

5.4 Working Principle of Tidal Power Plant

5.5 Advantages and Limitation of Tidal Power Plant


• Known to use tides from sea.

• Known to generate power from tidal energy.

5.1 IntroductionThe development of a nation is estimated from the total amount of energy

it produces and consumes in relation to its size and population. Human progresshas been judged from the way in which man has been able to develop andharness energy. What is tidal power? Tide is periodic rise and fall of the waterlevel of the sea. Tides occur due to the attraction of sea water by the moon.These tides can be used to produce electrical power which is known as tidalpower. When the water is above the mean sea level, it is called flood tide andwhen.

5UNIT

Tidal Energy


The level is below the mean level, it is called ebb tide. A dam isconstructed in such a way that a basin gets separated from the sea and adifference in the water level is obtained between the basin and sea. The constructedbasin is filled during high tide and emptied during low tide passing throughsluices and turbine respectively. The potential energy of the water stored in thebasin is used to drive the turbine which in turn generates electricity as it is directlycoupled to an alternator.

5.2 Components of Tidal Power PlantThere are three main components of a tidal power plant. That is

i. Dam or Barrage

ii. Sluice gate-ways from the basin to the sea and vice versa iii. Power house.

5.2.1 Dam or BarrageBarrage has been suggested as a more accurate term for tidal power

scheme, because it has only to with stand heads a fraction of the structure heightand stability problems are far more modest. Even though heads are small withtidal power cutoff. Tidal power barrages have to resist waves, whose shock canbe severe and where pressure changes continuously at its sides.

The barrage needs to provide channels in reinforced concrete for theturbines. To build these channels a temporary coffer dam is necessary but it isnow possible to built them on land. Tidal barrages require sites where thereis a sufficiently high tidal range to give a good head of water (The minimumuseful range is three meters). The best sites are bays and estuaries but watercan also be impounded behind bounded reservoir built between two points onthe same shore line.

The location of the barrage is important because the energy available isrelated to the size of trapped basin and to the square of the tidal range. Thenearer it is built to the mouth of bay for the larger basin but the small tidal range.A balance must also be struck between increased out put and increasedmaterial requirements and construction costs.

5.2.2 Sluice gate waysSluice gate ways are opened and closed regularly and frequently

for tidal power basins have to be filled and emptied. But heads are vary inheight. The gates must be opened and closed rapidly and this operationshould use a minimum of power. Leakage is tolerable for gates and barrages.Since we are dealing with sea water corrosion problems are actuate, they


have been very successfully solved by the catholic protection and where notpossible by paint. Gate structures can be floated as modular units into place.

Though, in existing plants, vertical lift gates have been used. Thetechnology is about ready to substitute a series of flap gates that operates bywater pressure. Flap gates are gates that are positioned so as to allow water into the holding basin and require no mechanical operation. The flap gates allowonly in the direction of the sea to basin. Hence, the basin level rises well aboveto sea level as ebb flow area is far less than flood flow area.

5.2.3 Power houseBecause of small heads only are available , large size turbines are needed.

Hence, the power house is also a large structure. Both the French and Sovietoperating plants use the bulb type of turbine, of the propeller type, with reversibleblades, bulbs have horizontal shafts coupled to a single generator. The cost perinstalled kilo watt drops with turbine size, and perhaps larger turbines might beinstalled in a future major tidal power plant.

5.3 Classification of Tidal Power PlantThe classification is represented with the help of a line diagram as given

below

5.4 Working Principle of Tidal Power PlantSome tidal power plants of Working principle are briefly explained below.

5.4.1 Working Principle of Single Basin one wayCycle Tidal power plant

In single basin one way cycle system, the generation is affected whenthe sea is at flood tide. The water of the sea is admitted into the basin over theturbines. As the flood tide period is over and the sea level starts falling again, the


generation is stopped. The basin is drained into the sea through the sluice ways.

Flood operation scheme needs larger size plant, operating for shorterperiod and hence less efficient as compared to ebb tide operation. The ebboperation plant will be of smaller size but will operate over a large period. Theaim and effort should be to obtain as long a period of operation as possible atthe beginning and finishing the work at the minimum operating head.

Fig 5.1 Single Basin one way Cycle Tidal Power Plant

Adjustable blade bulb turbines area specially suited for such operationsunder low and variable heads. All these turbines may be reversible which canwork as a pumps after the high tide, to increase the amount of water in thestorage lake, until the generation can start. this cycle requires a deeper reservoirso as to locate the sills of the sluice gates deeper and, thus requires greaterconstruction costs.

5.4.2 Working Principle of Single Basin two wayCycle Tidal power plant

The power generation is affected during the ebb as well as in floodtides. The direction of flow through the turbines during the ebb and flood tidesalternates, but the machine acts as a turbine for either direction of flow.In this method, the generation of power is accomplished both during emptyingand filling cycles. Both filling and emptying processes take place during shortperiods of time, the filling when the ocean is at high tide while the water in thebasin is at low tide level, the emptying when the ocean is at low tide and thebasin at high tide level.

The flow of water in both directions is used to drive a number of reversiblewater turbines, each driving an electrical generator. Electric power would thusbe generated during two short period during each tidal period. The powergeneration is also intermittent but generation period is increased compared withone way cycle.

Though two way cycle system has only short duration interruptions inthe turbine operation, yet a continuous generation of power coincide onlyoccasionally with periods of peak demand. These problems are solved to some

SluicesSea

TurbinesBasin of Estuary

Power Productions

MSL

MSL

KW

Basi

n Le

vel


extent in the two basin scheme described below. However, a fundamentaldrawback to all methods for generating tidal power is the variability in output caused by the variations in the tidal range.

Fig 5.2 Single Basin two way Cycle Tidal Power Plant

5.4.3 Working principle of single basin two wayCycle with pump storage tidal power plant

The Rance tidal power plant in France uses this type of arrangement. Inthis system, power generated both during flood and ebb tides. Complex machinescapable of generation power and pumping the water in either directions areused. A part of the energy produced is used for introducing the difference in thewater levels between the basin and the sea at any time of the tide and this isdone by pumping water into the basin up or down. The period of powerproduction with this system is much longer than the other two described earlier.The cycle of operation is shown in Fig. 5.3

Fig 5.3 Single Basin Two way Cycle with Pump Storage Tidal Power Plant

5.4.4 Working principle of simple double basin tidal power plantIt requires two separate adjacent basins. In one basin is called “upper

basin”, the water level is maintained above that, in other basin is called “lowerbasin”. Because there is always a head between upper and lower basins,electricity can be generated continuously, although at a variable rate. In thissystem turbines are located in between the two adjacent basins, while the sluicegates are as usual embodied in the dam across the mouths of the two estuaries.At the beginning of the flood tide, the turbines are shut down, the gates ofupper basin are opened and the lower.

SeaTidal Basin

TGi

MSL

MSL

Bas

in L

evel

KW

Sea

Tidal BasinBasin Level

Power Productions

PumpingMSL

MSL

TG

Bas

in L

evel

KW


Basin gates are closed. The upper basin is filled up while the lower basin isempty. As soon as the rising water level in upper basin provides sufficient differenceof head between the two basins, the turbines are started.

Fig 5.4 Simple Double Basin Tidal Power Plant

The water flows from upper basin to lower basin through the turbines,generating power. The power generation thus continues simultaneously withthe filling up the upper basin. At the flood tide when upper basin is full and thewater level is maximum, its sluice gates are closed. When the ebb tide level getslower than the water level of lower basin, its sluice gates are opened, where bythe water level in lower basin which was raising and reducing, the operatinghead, starts falling with the ebb. This process is continue until the head andwater level in upper basin is sufficient to run the turbines. This cycle repeats itselfwith the next flood tide. With this twin basin system, a longer and more continuousperiod of generation per day is possible.

5.4.5 Working principle of double basin with pump storage tidal power plant

This system also has twin basin. The operation of the two basin schemecan be controlled so that there is a continuous water flow from upper to lowerbasin. However since the water head between the basins varies during eachtidal cycle, as well as from day to day, so also does the power generated.

A part of energy produced is used for introducing the difference in thewater levels between the basin and the sea at any time of the tide and this isdone by pumping water into the basin up or down. The period of powerproduction with this system is much longer than the other one.

To pump water from the lower basin to the upper basin for increasedhead would then be available for tidal power generation at time of peak demand.This is very similar to pumped storage system in hydro electric power stations.


5.5 Advantages and Disadvantages of Tidal PlantAdvantages

1. Exploitation of tidal energy will in no case make demand for large area of valuable land because they are on bays.

2. It is free from pollution as it does not use any fuel.

3. It is much superior to hydro power plant as it is totally independent of rain which always fluctuates year to year. Therefore, there

is certainly of power supply the tide cycle is very definite.

4. As in every form of water power, this will also not produce any unhealthy waste like gases, ash, atomic refuse which entails heavy removal costs.

5. Tidal power is superior to conventional hydro power as the hydroplants are know for their large seasonal and yearly fluctuations in the outputof energy because they are entirely dependent upon the nature’s cycle ofrainfall, which is not the case with tidal as monthly certain power is assured.The tides are totally independent on nature’s cycle of rainfall.

6. Another notable advantages of tidal power is that it has a uniquecapacity to meet the peak power demand effectively when it works incombination with thermal or hydro electric system.

7. It can provide better recreational facilities to visitors and holiday

Disadvantages

1. These power plants can be developed only if natural sites are available.

2. As the sites are available on the bay which will be always far awayfrom the load centers. The power generated must be transported to longdistances. This increases the transportation cost.

3. The supply of power is not continuous as it depends upon thetiming of tides. Therefore some arrangements (double basin or double basinwith pump storage) must be made to supply the continuous power. This alsofurther increases the capital cost of the plant.

4. The capital cost of the plant (Rs. 5000/KW) is considerably large compared with conventional power plants (Hydro, Thermal).

5. Sedimentation and siltration of the basins are some of the added


problems with tidal power plants.

6. The navigation is obstructed.

7. It is interesting to note that the output of power from tidal plantvaries with lunar cycle, because the moon largely influences the tidal rhythm,where as our daily power requirement is directly related to solar cycle.

In addition to all the above mentioned limitations of tidal power, theutilization of tidal energy on small scale has not yet proved economical.

Summary• Tide is periodic rise and fall of the water level of the sea. Tides occur

due to the attraction of sea water by the moon. These tides can be used toproduce electrical power which is knownas tidal power.

• The power produced by a tidal plant depends mainly on the rangeof tide and the cubature of the tidal flow occurring in the estuary during atidal cycle which can be stored and utilized for power generation. Thecubature of the tidal flow not only depends on the tidal range but on the widthof estuary mouth.

• The site should not create interruption to the shipping traffic runningthrough the estuary other wise the cost of the plant will be increase as locksare to be provided.

• Silt index of the water of the estuary should be as small as possibleto avoid the siltation troubles. The siltation leads to reduction of the rangeof tides and reduces the power potential of the plant.

• The turbines, electric generators and other auxiliary equipments arethe main equipments of a power house.

• The function of dam to form a barrier between the sea and the basinor between one basin and other in case of multiple basins.

• The sluice ways are used either to fill the basin during the high tide orempty the basin during the low tide, as per operational requirement. These aregate controlled devices.

Short Answer Type Questions1. Define tidal energy.

2. What are the components of tidal power plant ?

3. What are the advantages of tidal power plant ?


4. What are the disadvantages of tidal power plant?

5. How to classify the tidal power plants?

6. What is the use of sluice gates in tidal power plant?

Long Answer Type Questions1. Explain briefly about single basin one way cycle and two way

cycle tidal power plants.

2. Explain briefly about double basin with and without pump storage tidal power plant.

3. Explain briefly about main components of tidal power plant.



6.2 Types of fuel cell

6.3 Components of fuel cell

6.4 Constructional details and working principle of Bocon’s fuel cell

6.5 Working principle of Aluminium and Oxygen fuel cell

6.6 Advantages and disadvantages of cuel cell

Learning ObjectivesAfter studying this unit, you will be able to know

• Known to convert the chemical energy to electrical energy

•Known to work the Bacon’s fuel cell

6.1 IntroductionFuel cells are efficient and quiet, operate on a variety of hydrocarbon

fuels and produce almost no objectionable emissions. The concept has beenproven in numerous small scale applications. The recent infusion of power costfrom fossil fuels may convert this promising device into a major source of electricpower generation.

6UNIT

Fuel Cells


A fuel cell (or combination of cells) capable of generating an electricalcurrent by converting the chemical energy of a fuel directly into electrical energy.

The electric Power Research Institute and United TechnologiesCorporation recently agreed to construct a 4.8 MW capacity plant, with aninvestment of 25 million dollars. It is predicted that if the fuel cell clears anumber of technical hurdles and proves financially viable, it could contribute20,000 MW power to the US grid by the end of 1985. This would save onebillion dollar in power generation costs and 100 million barrels of fuel oil annually.

6.2 Types of Fuel CellsAs per the fuel used the main types of fuel cells are

i. Hydrogen (H2) fuel cell.

ii. Hydrazine (N2H4) fuel cell.

iii. Hydrocarbon fuel cell.

iv. Alcohol (Methanol) fuel cell.

6.3 Components of Fuel CellThe present research work done in this area is to increase the efficiencies

or modify the design of the three major components of fuel cell power plant toincrease the overall efficiency of the system i.e processor, Electrolyte, Inverter.

6.3.1 ProcessorIt converts a hydrocarbon fuel into a hydrogen rich gas that can be

accepted by the cell. One of the main problems regarding fuel cell developmentis finding away to convert low grade fuel into H2 rich gas that has a minimumof impurities.

Material such as sulpher in fuel can adversely affect the fuel processor.Presently the research is directed to find a cell electrolyte that is moretolerant of fuel impurities. It is predicted that the developments in both processorand electrolyte will allow the use of standard fuel oil. The life of such aprocessor is presently limited to about 15,000 hours.

6.3.2 ElectrolyteInitial work has been done chiefly with phosphoric acid which has an

operating temperature of 1600oC to 2000oC. This electrolyte can give fuel cellsefficiency of 50%.

Next generation of fuel cells will use molten carbonate electrolyte.


Operating at a temperature of 5000oC to 7500oC, this material is more tolerantof fuel impurities and gives a fuel cell efficiency of 40 to 50%. Life for existingmolten carbonate fuel cell is about 10,000 hours. Solid oxide may be electrolyteof the third generation of fuel cells, which are probably 20 years away.

This electrolyte will give a fuel efficiency of 60% of better and will becompatible with many of the coal gasification processes.

6.3.3 InverterThe last element in the fuel cell power generation system which

converts DC current to AC current does not yet exist commercially in the sizesneeded for large scale power conversion. To date inverters with a capacity of20 to 40 KW are in limited use and some capable of 1.8 KW have been tested.Major research work is presently directed to develop the inverters of highcapacity.

6.4 Constructional Details and Working Principle of Bacon’s Fuel Cell

The first fuel cell was developed by Francis Bacon in 1959. It wasfuelled by Hydrogen and Oxygen gases and was chosen for Apollo mission.Fig. 6.1 illustrates the constructional details and working principle of Hydrogen-Oxygen fuel cell.

The Bacon’s fuel cell is filled with an alkaline electrolyte like potassiumhydroxide (KOH) or caustic potash in water. Water is bound by two specialnickel electrode plates. They are made out of porous metal into which electrolytepenetrates but not passes right through.

Fig 6.1 Bacon’s Fuel Cell

Electron Flow Load

ElectrolyteH2

02

02

H2

Water Heat


On to the other side of fuel electrode (Anode) hydrogen gas is fed atcontrolled pressure so that it does not pass After studying this chapter, you will beable to know high through the porous electrode plate but simply penetrates partlyinto the plate.

The oxygen gas is fed to the other side of Oxygen electrode (Cathode)in a similar way. In the process of these electrodes chemical reaction takesplace between gas and electrolyte. At hydrogen electrode H2+ moleculescombine with hydroxyl ions OH — from the electrolyte and release electrons.At the oxygen electrode O2 molecules capture electrons from the electrodemetal and combine with water molecules to make hydroxyl ions which dissolvein electrolyte.

The chemical reactions are as follows

At anode : 2 H2 + 4 OH ——> 4H2 + 2 O2 + 4e—

At cathode : O2 + 2 H2O + 4e ———> 4 OH—

If electrodes are connected outside the cell, the reactions will continue andcurrent flows through the circuit as long as H2 and O2 are supplied. To acceleratechemical reaction metal electrodes specially of platinum are used which act as catalyst.Bacon used nickel electrode which work very well at about 2000oC.

6 .5 Working principle of Aluminium and Oxygen Fuel cellIt is being developed by the Lawrence Livermore Laboratory in U.S.A.

mainly for electric vehicle propulsion. This cell is unusual in the respect that the metalaluminium is effectively the fuel which is consumed during operation and replaced asrequired. The aluminium (Al) forms the negative electrode of the cell, and oxygen(from air) is the positive electrode, the electrolyte is an aqueous solution of sodiumhydroxide. The overall cell reaction is symbolically.

Al + 3 O2 (air) + 3 H2O ——> Al (OH)3 4 4

( - ) ( + )

So, that aluminium, oxygen (from air) and water (from the electrolyte)combine to form aluminium hydroxide Al (OH)3. The aluminium (negative) electrodesare made of the metal containing a small amount of gallium and the air (positive)electrodes are carbon coated with an electro chemical catalyst possibly silver. Beforeentering the battery, the air is scrubbed to remove CO2. The operating temperatureof the battery is about 500C to 600C.


6.6 Advantages and Disadvantages of Fuel cellsAdvantages

1. Operation of fuel cell is quiet.

2. They have only a few mechanical components.

3. No atmospheric pollution.

4. No requirement of large volume of cooling water.

5. It can be used in residential areas.

6. It takes little time to go into operation.

7. It is compact and occupy less space.

8. It has high conversion efficiency (nearly 70%) because of direct conversion of chemical energy into electrical energy.

Disadvantages

1. It can be installed at use points, thus transmission losses.

2. It has high initial cost.

3. It has Low service life.

4. Its overall efficiency is 40 to 50%.

Summary• A fuel cell capable of generating an electric current by converting

the chemical energy of a fuel directly into electrical energy.

• Processor converts hydrocarbon fuel into a hydrogen rich gas that can be accepted by the cell.

• Inverter converts DC current to AC current.

Short Answer Type Questions1. What are the components of fuel cell ?

2. What is the use of inverter in fuel cell ?

3. Write the advantages of fuel cell.

4. Write the disadvantages of fuel cell.


Long Answer Type Questions1. Explain about constructional details and working principle of Bacon’s

fuel cell with neat sketch.

2. Explain about working principle of aluminium & oxygen fuel cell.

3. Explain briefly components of fuel cell.

OJT / Project work

Show and explain parts of fuel cell.

Mecahnical Engineering Technician68


7.2 Classification of Steam Boilers

7.3 Working Principle of Cochran Boiler

7.4 Working Principle of Babcock and Wilcox Boiler

Learning ObjectivesAfter studying this unit, the student will able to know

• Known to reduce the heat loss in power plants.

• Known to work the boilers.

7.1 IntroductionBoiler is a closed vessel in which the given fluid is heated and evaporated.

Steam boiler is one in which water is evaporated. It is why steam boiler is calledsteam generator. Large size steam boilers are usually called steam generatingplant.

1. Elements of boiler : Basic elements of boiler are shell, furnace, heating source, heating surface, steam space, mountings and accessories, etc.

2. Boiler mountings : The important boiler mountings are Pressure

7UNIT

Steam Boilers


gauge, water level indicator, safety valve, fusible plug, feed check valve, blowoff cock, stop valve, man hole etc.

3. Applications of boiler : Steam boilers find wide applications inroad rollers, pile driving machines, hoisting rigs, power hammers, heatingresidential or industrial buildings, sugar, chemical and textile industries,locomotives and ships.

7 .2 C lassifications of Steam BoilersThere are many classifications of steam boilers, yet the following are

important from the subject point of view.

1. According to the contents in the tube.

(a) Fire tube or smoke tube boiler.

(b) Water tube boiler.

2. According to the position of the furnace.

(a) Internally fire tube boiler.

(b) Externally fire tube boiler.

3. According to the axis of the shell.

(a) Vertical boiler.

(b) Horizontal boiler.

4. According to the number tubes.

(a) Single tube boiler.

(b) Multi tubular boiler.

5. According to the method of circulation of water and steam.

(a) Natural circulation boiler.

(b) Forced circulation boiler.

6. According to the use.

(a) Stationary boilers.

(b) Mobile boilers.

7. According to the pressure.

(a) Low pressure boiler.


(b) High pressure boiler.

7.3 Working Principle of Cochran BoilerCochran boiler is shown in Fig. 7.1 it is an improved form of simple

vertical boiler. It is a multi tubular boiler, vertical, fire tube boiler. It is internallyfired natural circulation boiler.

Fig 7.1 Cochran Boiler

Boiler may be coal fired or oil fired. In coal fired boiler, coal is fedthrough the fire door on to the grate. In oil fired boiler, grate is not necessary buta lining of fire brick is provided beneath the furnace. Fuel is burnt in the fire boxwhich has a convex, hemispherical dome as its roof. Number of fire tubes aremounted horizontally providing space all around them for water. Hot gases risingfrom the furnace get deflected by the dome shaped roof and pass through thechamber as shown by arrows. These hot gases flow through fire tubes and giveaway heat to surrounding water. Steam formed on evaporation ofwater iscollected at the top in steam space.

1

23

4

5

6

7

9 810

11

12

13

18

16

14

15

17

1.Grate 2. Fire door 3. Furnance (Fire box) 4. Fire Tubes5. Smoke box 6. Chimney 7. Exhaust to atmosphere 8. Steam stop Valve9. Safety Valve 10. Pressure gauge 11. Manhole 12. Water level Indicator13. Fusible Plug 14. Combustion Chamber 15. Fire brick Lining 16. Flu tube17. Feed check valve 18. Blow off valve (clock)


Finally the flue gases reach the smoke box and are discharged outinto atmosphere through the chimney.

Fire tubes are generally of 60 mm size and 165 in number. Thecombustion chamber is lined with fire bricks on the shell side. A manhole isprovided at the top to give access for an attender to clean the boiler periodically.Mountings such as pressure gauge, water level indicator, stop valve and fusibleplug are shown in figure.

7.4 Working principle of Babcock and Wilcox boilerFig. 7.2 illustrate the Babcock and Wilcox water tube boiler. It was

designed by George Babcock and Stephen Wilcox in 1868. It is a horizontal,externally fired, natural circulation type of stationary water tube boiler.

It consists of a large horizontal cylindrical drum 6 to 10 m long and 1 to2 m in diameter. From front and rear ends of the drum, connections are madewith uptake header and downtake header. The headers are joined by a largenumber of steel tubes of 100 mm diameter.

Fig 7.2 Bab Cock and Wilcox Boiler

The tubes are staggered in rows and are given an inclination of about150 to the horizontal. The furnace is located below the uptake header. The coalis fed through the fire door on to the grate and is fired. Hot gases flow as shownby arrows. Baffles are provided to deflect the hot flue gases so that the hot

SteamWater

Ash Rjt

1. Grate 2. Fire door 3. Furnance 4. Tubes5. Up take header 6. Feed Water inlet 7. Water level indicator8. Pressure guage 9. Safety valve 10. Drum 11. Stop valve12. Manhole 13. Down take header 14. Mud box15. Blow of valve 16. To chimney


gases travel a long way and cover large heating surface.Water circulation ismaintained by convective currents.

Water inside the tubes get heated. Hottest water and steam rise fromthe tubes to uptake header (due to less density) and then enter the boiler drum.The steam occupies steam space above water level. The cold water flows fromthe drum to the downtake header (or rear header) and thus the cycle is completed.The superheater remains initially flooded with water. When steam reaches workingpressure, it is drained and steam is fed to it. Hot gases flowing over the superheaterreheat the steam and steam gets superheated. It flows to a stop valve fitted atthe top of the drum.

Mounting such as water level indicator, pressure gauge and safety valveare shown in figure. At the bottom of a downtake header there is a mud boxwhich collects sediments and any foreign matter in water. This can be blown offperiodically through a blow off pipe. Boiler being suspended on steel girders, itis free from distortions due to thermal stresses. The inspection doors are providedfor attenders to enter the boiler room for repair work and cleaning. Evaporativecapacity of Babcock and Wilcox boiler ranges from 10,000 to 45,000 Kg/hrat 10 to 70 bar pressure and 450oC. This is extensively used in thermal powerplants.

Summary• Hot gases from furnace flow through tubes. Water remains or circulated

around tubes in fire tube boiler.

• Water flows inside the tubes. Hot gases or flames surround the tubes.

• Furnace is located inside the shell of the boiler in internally fired boilers.

• Furnace is located outside the boiler shell in externally fired boilers.

• In natural circulation steam boiler water in the boiler iscirculated by natural convection currents setup during the heating of water. In most of the steam boilers, there is a natural circulation of water.

• In forced circulation steam boilers, there is a forced circulation of water by a centrifugal pump driven by some xternal power. Use of forced circulation is made in high pressure boilers.

• The important boiler accessories are feed pump,economiser, superheater, air preheater, steam trap, steam separator, steam injector etc.


Short Answer Type Questions1. What are the basic elements of boiler ?

2. What is the fire tube boiler ?

3. What is the water tube boiler ?

Long Answer Type Questions1. Explain briefly about working principle of Cochran boiler.

2. Explain briefly about working principle of Babcock and Wilcox boiler.



8.2 Types of Noazzles

8.3 Application of Nozzles

8.4 Flow of Steam through Nozzles

Learning ObjectivesAfter study this unit, the student will be able to know

• Known to converts heat energy of steam into kinetic energy.

• Known Types of steam nozzles.

• Known the flow of steam through nozzles.

8.1 IntroductionA steam nozzle is a passage of varying cross-section, which converts

heat energy of steam into kinetic energy (the energy passed by the body byvirtue of its motion is called kinetic energy). During the first part of the nozzle,the steam increases its velocity. But in its later part, the steam gains more involume than in velocity. Since the mass of steam, passing through any sectionof the nozzle remains constant, the variation of steam pressure in the nozzledepends upon the velocity, specific volume and dryness fraction of steam.

8UNIT

Steam Nozzles


A well designed nozzle converts the heat energy of steam into kineticenergy with a minimum loss. The main use of steam nozzle in steam turbines, isto produce a jet of steam with a high velocity. The smallest section of the nozzleis called throat.

8.2 Types of Steam NozzlesThere are three types of steam nozzles.

(i) Convergent nozzle.

(ii) Divergent nozzle.

(iii) Convergent - divergent nozzle.

8.2.1 Convergent NozzleWhen the cross section of a nozzle decreases continuously from

entrance to exit, it is called a convergent nozzle as shown in Fig. 8.1

Fig 8.1 Convergent Nozzle

8.2.2 Divergent NozzleWhen the cross section of a nozzle increases continuously from entrance

to exit, it is called a divergent nozzle, as shown in Fig. 8.2

Fig 8.2 Divergent Nozzle

8.2.3 Convergent - divergent NozzleWhen the cross section of a nozzle first decreases from its entrance to

throat and then increases from its throat to exit, it is called a convergent -divergent nozzle as shown in Fig. 8.3 this type of nozzle is widely used now adays in various types of steam turbines.

Entry Exit

Entry Exit


Fig 8.3 Convergent - divergent Nozzle

8.3 Applications of Steam NozzlesSteam nozzles are extensively used in

(i) Steam and gas turbines to increase the kinetic energy of jet.

(ii) Injectors for pumping feed water to boiler.

(iii) For metering the flow of fluids.

(iv) Ejectors for removal of air from condenser.

8.4 Flow of Steam through NozzlesSteam enters the nozzle with a relatively small velocity and a high

initial pressure. The initial velocity is so small compared to exit velocity that itmay be neglected. Flow of steam is simply regarded as ‘adiabatic’. During theexpansion of steam no heat is supplied or rejected. As steam expands its velocityincreases, the heat energy of steam being converted to kinetic energy. Work isdone by increasing the kinetic energy of steam. At the end of expansion pressureis much lower than that at admission. This loss or drop in pressure results inenthalpy drop.

Hence the change of total heat of steam (enthalpy drop) must be equalto increase in kinetic energy. Expansion of steam is not a free expansion nor it isa throttling expansion, but is an isentropic or adiabatic expansion.

Adiabatic flow of steam through nozzles may be done in three ways.

(i) Frictionless adiabatic flow.

(ii) Frictional adiabatic flow.

(iii) Super saturated flow.

Entry Exit

6 to 150


8.4.1 Frictionless Adiabatic FlowIt is assumed that nozzle wall do not cause friction between them and

mass of system. Pure adiabatic expansion occurs from boiler pressure P1 toexit pressure P2 as shown in H - O mollier diagram Fig. 8.4

Fig 8.4 Frictionless in Nozzle (Mollier diagram)

8.4.2 Frictional Adiabatic FlowIt takes into account the friction produced between walls of the nozzle

and mass of steam. This frictional causes resistance to flow which is convertedinto heat. Steam at the end of expansion tends to condense, but the heat producedby friction tends to dry it, thus improving the value of dryness fraction at exitpressure. This is represented in Fig. 8.5 by 1-2’ line.

Fig 8.5 Effect of Friction in Nozzle

P1

P2 S 2

SupT

1

2

P1

P2

1

2

S

S


8.4.3 Super Saturated FlowIn the divergent portion of a convergent - divergent nozzle a phenomenon

called super saturation of steam occurs and hence it is called super saturatedflow. It is due to time lag in the condensing of the steam during expansion. Thevelocity of steam at throat section is high and further expansion in divergentportion takes place very rapidly. Theoretically speaking steam should condense(become wetter) because pressure falls during adiabatic expansion. Owingto the rapidity of expansion, the steam does not have time to condense. It remainsin an unnatural dry or super heated state. Such a flow is known as super heatedflow or metastable flow.

Fig 8.6 Super Saturated Expansion

Summary• A nozzle is passage of varying cross - section in which a fluid is

accelerated to high velocity.

• A well designed steam nozzle converts heat energy into kinetic energy with a minimum loss.

• The main use of steam nozzle in steam turbines, is to produce a jet of steam with a high velocity.

•The smallest section of the nozzle is called throat.

• There are three types of steam nozzles, they are convergent steam nozzle, divergent steam nozzle and convergent -divergent steam nozzle.

A

H

S

D D

B

G

C

Satline

Wilson line


Short Answer Type Questions1. What is a steam nozzle ?

2. What are the types of steam nozzles ?

3. What are the applications of steam nozzle ?

4. What is convergent nozzle ?

5. What is divergent nozzle ?

6. What is convergent - divergent nozzle ?

Long Answer Type Questions1. Explain briefly about the frictionless flow with the help of mollier

diagram.

2. Explain briefly about the frictional flow with the help of millier diagram.

3. Explain briefly about the super saturated steam flow in a nozzle.



9.2 Classification of steam turbines

9.3 Working principle of impulse turbine

9.4 Working principle of reaction turbine

9.5 Comparison between impulse turbine and reaction rurbine

9.6 Advantages and disadvantages of stream turbines

Learning ObjectivesAfter studying the unit, the student will be able to

• Know to convert heat energy to kinetic energy in the steam nozzle to mechanical energy.

• Know work the impulse turbine.

• Know work the Reaction turbine.

9.1 IntroductionTurbine is a prime mover. Steam turbine converts heat energy in steam

into mechanical energy in two stages. First heat energy is transformed into kineticenergy in the nozzle part of the turbine. This kinetic energy appears in theform ofhigh velocity of steam jet.

9UNIT

Steam Turbines


This is directed towards a wheel (rotor or runner) of a turbine carryingblades or vanes around its periphery. The kinetic energy in the steam jet istransformed into mechanical energy here. Mechanical energy manifests in theform of rotation of the wheel at high speed. The turbine shaft coupled to anelectric alternator (generator) enables the latter to produce electrical power.

9.2 Classification of Steam TurbineThe steam turbines may be classified into the following types.

1. According to the mode of steam action.

(a) Impulse turbine.

(b) Reaction turbine.

2. According to the direction of steam flow.

(a) Axial flow turbine.

(b) Radial flow turbine.

3. According to the exhaust condition of steam.

(a) Condensing turbine.

(b) Non-Condensing turbine.

4. According to the pressure of steam.

(a) High pressure turbine.

(b) Medium pressure turbine.

(c) Low pressure turbine.

5. According to the number of stages.

(a) Single stage turbine.

(b) Multi stage turbine.

9.3 Working Principle of Impulse TurbineDe-Laval turbine is the simplest form of a single stage impulse steam

turbine. Fig. 9.1 shows the half sectional view of an impulse turbine. Main partsof a De-Laval turbine are

(i) nozzle(ii) runner(iii) casing.


Fig 9.1 Impulse Turbine

The runner is a circular disc mounted on a horizontal shaft. Numberof blades are fixed uniformly on its periphery. The blades are symmetricallycurved and impact strength.

Casing that houses the runner is an air-tight metallic chamber.Nozzles are located around the inner periphery of the casing inclined at about200 to the wheel tangent. Steam issuing out of these nozzles strike the set ofblades at a number of points.

The smallest De-Laval wheel has a diameter of 125 mm and speed of30,000 r.p.m. It is suitable for low pressure steam supplies. Steam expandsdown to atmospheric pressure in the nozzle and pressure remains constantas it flows over the blades. The blades are made symmetrical with angleof about 300 at inlet and exit.

The power developed is about 3.7 KW and the blade speed isabout 220 m/s. The high speed of rotation will, for mechanical reasons,such as centrifugal force, stress etc., restrict the size of the wheel. It also needsa reduction gear box unit when coupled to an electrical generator to run themachine at practical speed limits.

To produce an impulsive force a high velocity jet should strike a blade.If series of blades are mounted on the wheel (rotor), each blade in turn receivesthe impulsive force resulting in high rotational speed. In impulse turbine the highvelocity jet is produced by expanding steam in a nozzle. Steam from the boiler isat high pressure and high temperature.

1. Shaft 2. Rotor 3. Blade 4. Casing


When steam expands in a nozzle, pressure drops followed by enthalpy(heat) drop. This heat energy is converted into kinetic energy whichappears in the form of high velocity steam jet. This jet or number of jets directedtowards a wheel with blades fixed on its periphery produces motive force.Steam flows over the blades and velocity gradually reduces. One conspiciousthing is that pressure remains constant as steam passes over the blades in theimpulse turbine and it is almost atmospheric.

9.4 Working principle of Reaction TurbineReaction turbine consists of ring of fixed blades followed by a ring

of moving blades. The fixed blades act as nozzles and allows a relativelysmall expansion of steam. Further expansion takes place in the moving blades.Thus in reaction turbine, steam expands continuously and consequently there is anincrease in specific volume as the expansion proceeds, which is accommodatedby an increase in the size of the blades.

As the steam expands through blades, relative velocity increases andthis increase in relative velocity a thrust or reaction force acts on the blades.This reaction force consists the driving force.

Examples of reaction turbine are Parson’s turbine and Ljungstorm turbine.

Fig 9.2 Reaction Turbine

Steam

A

F M

R s


9.5 Comparison between Impulse Turbine and Reaction ` Turbine S. No. Impulse turbine Reaction turbine

1.

2.

3.

4.

5.

6.

7.

9.6 Advantages and Disadvantages of Steam TurbineSteam turbines offer the following advantages over steam engines.

• Higher thermal efficiency.

• No reciprocating parts and hence heavy foundations are not required.

• Torque is uniform and does not need any flywheel.

The steam flows through thenozzles and impinges on themoving blades.

The steam impinges on thebuckets with kineticenergy.

The steam may or maynot be admitted over thecircumference.

The steam pressure remainsconstant durings its flowthrough the moving blades.

The relative velocity of steamwhile gliding over the bladesremains constant (assumingno friction)

The blades are symmetrical

The number of stagesrequired are less for the samepower developed

The steam flows firstthrough guide mechanism andthen through the movingblades.

The steam glides overmoving vanes withpressure and kineticenergy.

The steam must beadmitted over the wholecircumference.

The steam pressure isreduced during its flowthrough the moving blade.

The relative velocity of steamwhile gliding over the movingblades increases (no friction)

The blades are notsymmetrical

The number of stagesrequired are more for thesame power developed.


• No rubbing parts, no internal lubrication is required.• Higher speeds may be developed with greater speed range.• Can be directly coupled to high speed machines.• Governing is easy.• Less maintenance.• Requires less floor space for given output.• Exhaust steam is free from oil, hence condensate can berefused as

feed water.Disadvantages of steam turbine over steam engine.

• Steam turbines are not suitable where frequent stopping and starting necessary.

• Condenser must be provided to take advantage of greater range of expansion.Summary

• Steam turbine is a prime mover in which the heat energy in the steam is converted into kinetic energy and kinetic energy is absorbed by turbine blades.

• Steam turbine is used in stationary power plant and shippropellers.• It is also used for driving speed machines such as centrifugal pumps,

centrifugal blowers, centrifugal compressors, etc..• Steam turbines are mainly two types one is Impulseturbine and another

one is reaction turbine.• No lubrication is necessary inside the turbine.

Short Answers Type Questions1. How to classify the steam turbines?2. What are the advantages of steam turbines?3. What are the disadvantages of steam turbines?

Long Answers Type Questions1. Write the comparison between Impulse turbine and Reaction

turbine.

2. Explain briefly about Impulse steam turbine with neat sketch.

3. Explain briefly about Reaction steam turbine with neat sketch.



10.2 Classification of Steam condensers

10.3 Functions of Steam condenser

10.4 Advantages and disadvantages of Steam condenser

10.5 Comparison between Jet and Surface condenser

Learning ObjectivesAfter studying this unit, we will be able to know

• Importance of steam condenser in power plant

• Function of steam condenser

• Advantages of steam condenser

10.1 IntroductionA steam condenser is a closed vessel into which the steam is exhausted

and condensed after doing work in an engine cylinder or turbine. A steamcondenser has the following two objects

1. The primary object is to maintain a low pressure (below atmosphericpressure) so as to obtain the maximum possible energy from steam and thusto secure a high efficiency.

10UNIT

Steam Condenser


2. The secondary object is to supply pure feed water to the hot well, from where it is pumped back to the boiler.

Note : The low pressure is accompanied by low temperature and thusall condensers maintain a vacuum under normal conditions. The condensedsteam is called condensate. The temperature of condensate is higher on leavingthe condenser than that of circulating water at inlet. It is thus obvious, that thecondensate will have a considerable liquid heat.

10.2 Classifications of Steam CondensersCondensers are broadly classified into two types

1. Jet condenser.

2. Surface condenser.

10.2.1 Jet condenserThese are also called Mixing condensers and are further classified as

i. Low level parallel jet condensers.

ii. Low level counter flow jet condensers.

iii. High level (or Barometric) jet condensers. iv. Ejector condensers.

10.2.2 Surface CondenserThese are further classified as

i. Down flow (Two-pass) surface condensers.

ii. Central flow surface condensers.

iii. Regenerative surface condensers.

iv. Evaporative condensers.

v. Inverted type surface condensers.

10.3 Functions of Steam CondenserIn jet condenser exhaust steam from the prime mover and the cooling

water come directly into contact. Heat takes place quickly between them bydirect conduction. For effective cooling, water is introduced into the condensershell in a spray form.

When steam condenses into water, the mixture of this condensate andcooling water gravities down which is continuously with drawn using a extractionpump. In jet condensers recovery of condensate is not possible.


Forthat reason, the above mixture of fluids is not reused as boiler feedwater. This is the major draw back with jet condensers.

Fig 10.1 Parallel Flow jet Condenser

In a parallel flow jet condenser steam as well as cooling water,both enter the shell at top and the mixture is collected at the bottom. From hereit is with drawn into a hot well. Surplus condensate from the hot well gravitiesto cooling pond as shown in Fig. 10.1. Air is extracted by an air pump so as tomaintain required vacuum in the condenser.

10.4 Advantages and Disadvantages of Steam CondenserAdvantages

Following are the main advantages of incorporating a condenser in asteam power plant.

1. Steam in 2. To air Pump 3. Water Spray 4. Sheel

5. Perforated Tray 6. Condensate 7. Hot Water 8. Cooling Pond

9. Cold Water


1. It increases expansion ratio of steam, and thus increases efficiency of the plant.

2. It reduces back pressure of the steam, and thus more work can be obtained.

3. It reduces temperature of the exhaust steam, and thus more work can be obtained.

4. The reuse of condensate (i.e condensed steam) as feed water for boilers reduces the cost of power generation.

5. The temperature of condensate is higher than that of fresh water. Therefore the amount of heat supplied per kg of steam is reduced.

Disadvantages

Following are the disadvantages of steam condenser in a steam powerplant.

1. Vacuum rarely exceeds 650 mm of Hg.

2. High power is required for air pump.

3. Size is more bulky and condenser occupies more space.

4. High capital and maintenance cost.

10.5 Comparison between Jet and Surface CondenserS.No. Jet Condensor Surface Condenser

1. Cooling water and steam are mixed up.

2. Less suitable for high capacity plants.

3. Condensate is wasted.

4. It requires less quantity of circulating water.

5. The condensing plant is economical and simple.

6. Its maintenance cost is low.

7. More power is required for air pump and water pumping

Cooling water and steamare not m ixed up.

More suitable for high capacityplants.

Condensate is reused.

It requires a large quantity ofcirculating water.

The condensing plant is costly andcomplicated.

Its maintenance cost is high.

Less power is required for air pumpand water pumping.


Summary• Jet condenser requires less quantity of circulating water.

• In jet condenser more power is required for air pump and water pumping.

• Surface condenser requires a large quantity of circulating water.

• In surface condenser less power is required for air pump and water pumping.

Short Answer Type Questions1. What are the types of steam condensers?

2. What is the function of steam condenser?

3. Write the advantages and disadvantages of steam condenser?

Long Answer Type Questions1. Explain briefly the function of steam condenser with neat sketch.

2. Write the comparison between jet condenser and surface condenser.

Energy Sources and Power Plant

Documents

Transcript of Energy Sources and Power Plant