EE09 502 PSGTD ASSIGNMENT: SUBMITTED BY: ATHULVINOY.P.P

NO: 41

1. Write detailed notes on a) conventional sources of energy b) non-conventional sources of energy.

NON-CONVENTIONALThe contemporary non-conventional sources of energy like wind, tidal, solar etc. were theconventional sources until James Watt invented the steam engine in the eighteenth century.In fact, the New World was explored by man using wind-powered ships only. The nonconventionalsources are available free of cost, are pollution-free and inexhaustible. Man hasused these sources for many centuries in propelling ships, driving windmills for grinding cornand pumping water, etc. Because of the poor technologies then existing, the cost of harnessingenergy from these sources was quite high. Also because of uncertainty of period of availabilityand the difficulty of transporting this form of energy, to the place of its use are some of thefactors which came in the way of its adoption or development. The use of fossil fuels andnuclear energy replaced totally the non-conventional methods because of inherent advantagesof transportation and certainty of availability; however these have polluted the atmosphere toa great extent. In fact, it is feared that nuclear energy may prove to be quite hazardous in caseit is not properly controlled.In 1973 the Arab nations placed an embargo on petroleum. People began to realise thatthe fossil fuels are not going to last longer and that remaining reserves should be conserved forthe petro-chemical industry. But unfortunately, both nuclear and coal energy pose seriousenvironmental problems. The combustion of coal may upset the planets heat balance. Theproduction of carbondioxide and sulphurdioxide may adversely affect the ability of the planetto produce food for its people. Coal is also a valuable petro-chemical and from long term pointof view it is undesirable to burn coal for generation of electricity. The major difficulty withnuclear energy is waste disposal and accidental leakage (e.g. leakage at Chernobyl nuclearpower plant).As a result of these problems, it was decided by almost all the countries to develop andharness the non-conventional sources of energy, even though they are relatively costlier ascompared to fossil-fuel sources. It is hoped that with advancement in technology and moreresearch in the field of development of non-conventional sources of energy, these sources mayprove to be cost-effective as well. The future of wind, solar, tidal and other energy sources isbright and these will play an important role in the world energy scenario.The following sections have been devoted to the study of some of the important nonconventionalsources of energy.

TIDAL POWER

Tidal or lunar energy as it is sometimes called, has been known to mankind since timeimmemorial. Various devices, particularly the mills were operated using tidal power. In thepast water supply of London was pumped to a water tower by a mill operated by the tidalpower (which consisted of a large paddle wheel, mounted on a raft and fastened between two of

the piers of old London Bridge). The tidal power has been used to irrigate fields in Germanyand to saw firewood in Canada.Tides are caused by the combined gravitational forces of Sun and Moon on the waters ofthe revolving Earth. When the gravitational forces due to the Sun and the Moon add together,tides of maximum range, called spring tides, are obtained. On the other hand, when the twoforces oppose each other, tides of minimum range, called neap tides, are obtained. In one yearthere are approximately 705 full tidal cycles

Basic SchemesIt has been suggested, that for harnessing tidal power effectively the most practicablemethod is the basin system. Here a portion of the sea is enclosed behind a dam or dams andwater is allowed to run through turbines, as the tide subsides.The power available from a given head of water varies as the square of the head andsince the head varies with the tidal range, the power available at different sites from tidalenergy shows very wide variation. Various tidal basin systems have, therefore, been evolved,in order to overcome this wide variation in availability of tidal power.Single Basin SystemThe simplest scheme for developing tidal power is the single basin arrangement, inwhich a single basin of constant area is provided with sluices (gates), large enough to admitthe tide, so that the loss of head is small. The level of water in the basin is the same as that ofthe tide outside. When the tides are high, water is stored in the basin and sluice gates areclosed. When the tides are falling, sluices are opened to allow water to go through the turbineto generate power. A head of water is obviously required for the turbine to generate water.This continues to generate power till the level of the falling tides coincides with the level of thenext rising tide. Two Basin SystemAn improvement over the single basin system is the two-basin system. In this system, aconstant and continuous output is maintained by suitable adjustment of the turbine valves tosuit the head under which these turbines are operating.A two-basin system regulates power output of an individual tide but it cannot take careof the great difference in outputs between spring and neap tides. This system, therefore, providesa partial solution to the problem, of getting a steady output of power from a tidal scheme.This disadvantage can be overcome by the joint operation of tidal power and pumpedstorage plant. During the period when the tidal power plant is producing more energy thanrequired, the pumped storage plant utilizes the surplus power for pumping water to the upperreservoir. When the output of the tidal power plant is low, the pumped storage plant generateselectric power and feeds it to the system. This arrangement, even though technically feasible,is much more expensive, as it calls for higher installed capacity for meeting a particular load.This basic principle of joint operation of tidal power with steam plant, is also possiblewhen it is connected to a grid. In this case, whenever tidal power is available, the output of thesteam plant will be reduced by that extent which leads to saving in fuel and reduced wear andtear of steam plant. This operation requires the capacity of steam power plant to be equal tothat of tidal power plant and makes the overall cost of power obtained from such a combinedscheme very high. In the system shown in Fig. 1.1, the two basins close to each other, operatealternatively. One basin generates power when the tide is rising (basin getting filled up) andthe other basin generates power while the tide is falling (basin getting emptied). The twobasins may have a common power house or may have separate power house for each basin. Inboth the cases, the power can be generated continuously. The system could be thought of as acombination of two single basin systems, in which one is generating power during tiding cycle,and the other is generating power during emptyingThe major disadvantage of this single basin scheme is that it gives intermittent supplyof power, varying considerably over the period of operation. It is for this reason that the tidalpower has not been developed on a large scale. Also with this scheme, only about 50 per cent oftidal energy is available.

Cooperating double basin system. This scheme consists of two basins, at different elevationconnected through turbine. The sluices in the high and low level basin communicate with seawater directly as shown in Fig. 1.2. The high level basin sluices are called the inlet sluices andthe low level as outlet sluices. The basic operation of the scheme is as follows.

Turbines for Tidal PowerTidal power plants operate using a rapidly varying head of water and, therefore, theirturbines must have high efficiency at varying head. The Kaplan type of water turbine operatesquite favourably under these conditions. The propeller type of turbine is also suitable becausethe angle of the blades can be altered to obtain maximum efficiency while water is falling.A compact reversible horizontal turbine has been developed by French Engineer whichacts with equal efficiency both as a pump and as a turbine. The bulb-type turbine (Fig. 1.3)consists of a steel shell completely enclosing the generator which is coupled to the turbinerunner. The turbine is mounted in a tube within the structure of the barrage, the whole machinebeing submerged at all times.

More than fifty sites have been identified in the world for possible generation of tidalpower. As more and more technological advancement take place, even more sites could beidentified for tidal power development. Some of the important sites are:(i) La Rance (France), (ii) Severn Barrage (UK), (iii) White sea (USSR), (iv) Passamaquoddy(USA), (v) Gulf of Cambey (India) and (vi) Gulf of Kutch (India).The maximum tidal range in the Gulf of Cambey is about 10.8 m and is quite attractivefor a tidal plant. However, the silt charge of the Gulf of Cambey is relatively high and needs acloser study for further development.The Gulf of Kutch has a maximum spring tide of 7.5 m and the silt charge is relativelylow.

WIND POWERIntroductionThe wind wheel, like the water wheel, has been used by man for a long time for grinding cornand pumping water. Ancient seamen used wind power to sail their ships. With the developmentof the fossil fuelled and hydro-electric plants, there was decline in the use of wind power due to

the less cost involved in the new methods. Another difficulty with wind power was the problemof energy storage. The energy could not be made available, on demands, due to uncertainties ofwind. Due to these two reasons, no further attempt was made to develop wind power for largescale power generation.In recent years, however, as a result of energy crisis in the world, it has been decided toinvestigate all possible means of developing power, as alternatives to fuel fired plants. Thewind could supply a significant portion of the worlds energy demand. An estimate by anAmerican Professor indicates the potentialities of wind power. According to him about 350,000wind mills each rated for about 1250 KW to 2200 KW could develop power of the order of190,000 MW. With the advancement in the knowledge of aero-dynamics it has been possible tobuild larger and more efficient wind power plants. A typical example is the 1250 KW installationat Grandpas Knol in U.S.A. Whereas some success has been achieved in developing small andmedium size plants, the prospects of large scale generation i.e., 1 MW or above are not, as yetvery encouraging.

Characteristics of Wind PowerWind as a source of energy is plentiful, inexhaustible and pollution free but it has the

disadvantage that the degree and period of its availability are uncertain. Also, movement oflarge volumes of air is required, to produce even a moderate amount of power. As a result, thewind power must be used as and when it is available, in contrast to conventional methodswhere energy can be drawn upon when required. Wind power, therefore, is regarded as ameans of saving fuel, by injection of power into an electrical grid, or run wind power plant inconjunction with a pumped storage plant.The power that can be theoretically obtained from the wind, is proportional to the cubeof its velocity and thus high wind velocities are most important. The power developed usingthis law, in atmospheric condition where the density of air is 1.2014 kg/cu metre, is given asPower developed = 13.14 106 A V 3 KWwhere A is the swept area in sq. metre and V the wind velocity in Km/hr. The energy developedis affected by :The Altitude of the SiteThe velocity of the wind increases with the altitude. In general, the higher the windwheel is placed above ground, the greater will be wind power available.Velocity Duration CurveThe variation of velocity of wind over the period affects the power output, e.g., let thevelocity over the first hour be 30 kmph and the next hour be 20 kmph. The energy developed isproportional to 303 + 203 = 35,000. On the other hand, if we assume average velocity duringthese two hours of 25 kmph, the power developed is proportional to 2 253 = 33250. Thus, therelation between the actual energy available, and that available from a steady wind of averagevelocity, varies considerably and depends on the shape of the velocity-duration curve for theperiod of generation.The wind speeds, between which a wind wheel generator operates, are limited. A certainminimum wind velocity is required to overcome frictional and other losses of the machine and,

on the other hand, it would be uneconomical to design a plant for very high velocity windwhich would occur only for a small period over the year. Therefore, the machine must bedesigned for a rated wind velocity, for which the output is maximum. Typical wind velocitiesfor some sites may range between 30 kmph to 45 kmph.The rated wind velocity, for which a plant is designed substantially affects the specificoutput (K whr generated per annum per KW installed capacity) and also the cost of construction.If the rated velocity is low, the specific output is high as full output will be generated for arelatively longer duration of the year, whereas if the rated velocity is high, the converse will betrue. But with low rated wind velocity, a larger diameter wheel will be required for a given KWrating, which in turn increases the cost of the plant. Economic development of wind power,therefore, requires selection of sites where high specific outputs are compatible with reasonablecost of construction of plant. It is, therefore, necessary to obtain wind velocity duration curvefor a particular site and to know the output of the machine for varying wind velocities. Themaximum efficiency of the wind power plant is found not to exceed 40%.

Design of Wind WheelsSeveral types of wind wheels have been used but the advantage of propeller rotatingabout a horizontal shaft, in a plane perpendicular to the direction of the wind make it the mostlikely type to realise economic generation on a large scale. A propeller consisting of two orthree blades (with an aerofoil section) and capable of running at the high speeds is likely to bethe most efficient. Present technology has been able to build systems with 60 m long blades, ontowers as high as 305 m. A large tower system, to support many small rotor-generator units,can also be built.Wind pressure rotates the wind vanes or propellers attached to a shaft. The revolvingshaft rotates the rotor of a generator, through a mechanism of gears couplings etc. Thus,electricity is generated.The wind power plants can be operated in combination with steam or hydro power station,which will lead to saving in fuel and increase in firm capacity, respectively of these plants.Wind energy can prove to be a potential source of energy for solving the energy problem.It can certainly go a long way to supply pollution-free energy to millions of people, living in thevillages all over the world.The economic viability of wind mills is better in situations where conventionaltransmission costs are extremely high (because of inaccessiability and small load) or wherecontinuous availability of supply is not essential so that only a limited amount of storage onstandby power need be provided.

GEOTHERMAL POWER

IntroductionMany geothermal power plants are operating throughout the world. Although larger geothermalpower plants are in operation in America today, it is to the credit of the Italians that the firstimpressive breakthrough in geothermal power exploitation was achieved. The oldest geothermal

power station is near Larderello in Italy, which has an installed capacity of 380 MW. InNewzealand geothermal power accounts for 40% of the total installed capacity, whereas inItaly it accounts for 6%.It is a common knowledge that the earths interior is made of a hot fluid called magma.The outer crust of the earth has an average thickness of 32 Km and below that, is the magma.The average increase in temperature with depth of the earth is 1C for every 35 to 40 metredepth. At a depth of 3 to 4 Kms, water boils up and at a depth of about 15 Kms, the temperatureis, in the range of 1000C to 1200C. If the magma finds its way through the weak spots of theearths crust, it results into a volcano. At times, due to certain reasons the surface waterpenetrates into the crust, where it turns into steam, due to intense heat, and comes out in theform of springs or geysers. Moveover, the molten magma also contains water, which it releasesin the form of steam, which could be utilized for electric power generation.

Principle of OperationVarious types of cycles have been suggested for geothermal power generation. Only twoimportant ones, which are being used in practice, are discussed here.Indirect Condensing CycleWhile developing Larderello power plant, it was thought, that geothermal steam maycorrode the turbines. Therefore, an indirect system was adopted, which involved the use of aheat exchanger by means of which clean steam was raised from contaminated natural steam(Fig. 1.4). In spite of the fact that about 15% to 20% of the steam power potential had to besacrificed in the heat exchanger, the cycle was considered economical, because of the recoveryof minerals and non-condensible gases from the new steam.With the advancement in metallurgy technology and the declining economic attractionsof mineral extraction, through this process, this cycle has been rendered obsolete.Direct Non-Condensing CycleThis is the simplest, cheapest and most widely used geothermal cycle. Bore steam, eitherdirect from dry bores, or after separation (using centrifugal separator) from wet bores, is simplypassed through a turbine and exhausted to atmosphere

layers of the earth. It has been suggested that water should be pumped into artificial volcaniccraters and then turned into useful steam.Like hydro power stations, geothermal power plants are unattended and do not needfull time supervision. Since the units are unattended, the warning alarm can be transmitted tothe attended station where appropriate action can be taken.If a well has been shut down, it requires several hours to get it upto rated flow to clearit of water and debris. Some more time is required to warm up the steam collection systempiping the drain condensate from it. No attempt should be made to fast start ups as it resultsin damage to the turbine blades. Steam temperature and steam line drains should be closelymonitored, for any indication of water. If there is any possibility of water coming alongwiththe steam, the unit should be tripped to prevent damage to the turbine. Rated turbine throttlepressure is maintained by connecting sufficient number of wells to the supply line of a unit.Whenever a unit trips, the steam should be released to the atmosphere. If a unit is to be shut

down for a long time, the wells should also be shut down.It is important that a systematic schedule of preventive maintenance be observed atthese plants. A rigidly planned periodic maintenance schedule must be adhered to. Units shouldbe inspected every three years. An adequate stock of spare partsespecially the turbine bladesmust be maintained. With proper maintenance, it is possible to operate these plants at veryhigh annual plant load factor of the order of 90% or even more.

MAGNETO HYDRO DYNAMIC (MHD) GENERATIONIntroductionIn the conventional steam power plants, the heat released by combustion of fuel istransformed into the internal energy of steam. The temperature and pressure of steam increasein the process. The steam turbine, then, converts steam energy into mechanical energy, whichdrives a generator. This way, the mechanical energy is converted into electric energy. Therepeated conversion of various forms of energy involves losses and, hence, the overall efficiency

The direct conversion of heat to electricity would enable the industry to use the fuel resourcesmore efficiently. MHD generation is one form of energy technology, wherein direct conversionof heat into electric energy has been devised. The technological development in the field ofplasma physics and metallurgy etc. and other branches of science and technology has made itpossible for this kind of direct transformation of energy.An ionized gas is used as conducting medium in the MHD generator. The gas can bemade electrically conducting when it is maintained at least at a temperature of 2000C. Thisfact does not allow MHD generation from being used in the entire temperature range from3000 K to 300 K. It is therefore, thought beneficial that MHD generators be used in conjunctionwith steam operated thermal plants utilising the heat of the gas leaving the MHD ducts. Thecombined operation of MHD generators alongwith the conventional thermal plant, will raisethe overall efficiency to nearly 60%, thereby lot of saving in the fuel cost will result.

Principle of Operation of MHD GeneratorThe basic principle of operation is based on Faradays law of electro magnetic induction,which states an e.m.f. is induced in a conductor moving in magnetic field. The conductor maybe a soild, liquid or a gaseous one. The study of the dynamics of an electrically conducting fluidinteracting with a magnetic field, is called magneto hydro dynamics.In this method (Fig. 1.9) gases at about 2500C are passed through the MHD duct acrosswhich a strong magnetic field has been applied. Since the gases are hot, and partly ionizedthey form an electrically conducting conductor moving in the magnetic field. An e.m.f. (directcurrent)is thus induced, which can be collected at suitable electrodes.

SOLAR ENERGYIntroductionSun is the primary source of energy. The earth receives 1.6 1018 units of energy from

the Sun annually, which is 20,000 times the requirement of mankind on the earth. Some of thesolar energy causes evaporation of water, leading to rains and creation of rivers etc. Some of it is utilized in photosynthesis which is essential for sustenance of life on earth. Man has tried,from time immemorial, to harness this infinite source of energy, but has been able to tap onlya negligibly small fraction of this energy, till today.

Solar Power PlantIt is known that only a small fraction of the energy radiated by the Sun reaches theEarth. It would, therefore, be an attractive proposition, if energy could be received from outsidethe atmosphere and then transmitted to the earth. A man-made satellite revolving around theearth will receive energy for all the 24 hours and will not be affected by the weather conditions.Fig. 1.12 shows the arrangement and general view of a solar power plant, carried by aman-made satellite. The solar cell panels to be installed on the satellite may vary in area from

16 to 100 sq km according to the plant capacity. The solar cells arranged in space would generated.c. electric power and transmit it by means of microwaves (of about 10 cm. wave length),using a transmitting antenna. Microwave transmission may be at 2 to 3 GHz, as this keeps thelosses at minimum. On the earth, this energy will be converted into high voltage d.c. orcommercial frequency electric power.The diameter of transmitting antenna would be around 1 km and that of the receivingantenna, 7 to 10 Kms. The effeciency of transmission is estimated to be in the range of 55 to75%. The overall efficiency, with the present technology, is around 25% but is likely to go upto60% in the near future.The solar cells operate on the principle of photo electricity i.e., electrons are liberatedfrom the surface of a body when light is incident on it. Backed by semi-conductor technology, itis now possible to utilize the phenomenon of photo-electricity.It is known that if an n-type semi-conductor is brought in contact with a p-type material,a contact potential difference is set-up at the junction (Schottky effect), due to diffusion ofelectrons. When the p-type material is exposed to light, its electrons get excited, by the photonsof light, and pass into the n-type semi-conductor. Thus, an electric current is generated in aclosed circuit. The pn junction silicon solar cells have emerged as the most important source oflong duration power supply necessary for space vehicles. These cells are actuated by both,direct Sun rays and diffuse light. The efficiency of silicon solar cells increases with decreasingtemperature. In cold weather the decreased luminous flux is compensated for, by higherefficiency. The efficiency of these solar cells varies from 15 to 20%.Although the energy from the Sun is available free of cost, the cost of fabrication andinstallation of systems, for utilization of solar energy, is often too high to be economicallyviable. In order to make solar installations economically attractive, plastic materials are beingincreasingly used for the fabrication of various components of the system.The efficiency of solar heating/cooling installation depends on the efficiency of collectionof solar energy and its transfer to the working fluid (e.g. water, air etc.). There are two mainclasses of collectors. The flat plate collector is best suited for low and intermediate temperatureapplications (4060, 80120C) which include water heating for buildings, air heating andsmall industrial applications like agricultural drying etc. The concentrating collectors areusually employed for power generation and industrial process heating.

Solar ConcentratorsSolar concentrators are the collection devices which increase the flux on the absorbersurface as compared to the flux impinging on the concentrator surface. Optical concentrationis achieved by the use of reflecting refracting elements, positioned to concentrate the incidentflux onto a suitable absorber. Due to the apparent motion of the Sun, the concentrating surface,whether reflecting or refracting, will not be in a position to redirect the sun rays onto theabsorber, throughout the day if both the concentrator surface, and absorber are stationary.Ideally, the total system consisting of mirrors or lenses and the absorber should follow theSuns apparent motion so that the Sun rays are always captured by the absorber. In general, asolar concentrator consists of the following:(i) a focussing device;

(ii) a blackened metallic absorber provided with a transparent cover; and

(iii) a tracking device for continuously following the Sun.Temperatures as high as 3000C can be achieved with such devices and they findapplications in both photo-thermal and photo-voltaic conversion of solar energy. The use ofsolar concentrators has the following advantages:(i) Increased energy delivery temperature, facilitating their dynamic match betweentemperature level and the task.(ii) Improved thermal efficiency due to reduced heat loss area.(iii) Reduced cost due to replacement of large quantities of expensive hardware materialfor constructing flat plate solar collector systems, by less expensive reflecting and/orrefracting element and a smaller absorber tube.(iv) Increased number of thermal storage options at elevated temperatures, therebyreducing the storage cost.Parameters Characterising Solar ConcentratorsSeveral terms as used to specify concentrating collectors. These are:(i) The aperture area is that plane area through which the incident solar flux is accepted.It is defined by the physical extremities of the concentrator.(ii) The acceptance angle defines the limit to which the incident ray path may deviate,from the normal drawn to the aperture plane, and still reach the absorber.(iii) The absorber area is the total area that receives the concentrated radiation. It is thearea from which useful energy can be removed.(iv) Geometrical concentration ratio or the radiation balance concentration ratio is definedas the ratio of the aperture area to the absorber area.(v) The optical efficiency is defined as the ratio of the energy, absorbed by the absorber,to the energy, incident on the aperture.(vi) The thermal efficiency is defined as the ratio of the useful energy delivered to theenergy incident on the aperture.Solar concentrators may be classified as point focus or line focus system. Point focussystems have circular symmetry and are generally used when high concentration is requiredas in the case of solar furnaces and central tower receiver systems. Line focus systems havecylindrical symmetry and generally used when medium concentration is sufficient to providethe desired operating temperature.A solar concentrator consists of the following components:(i) A reflecting or refracting surface, (ii) An absorbing surface i.e., an absorber, (iii) Afluid flow system to carry away the heat, (iv) a cover around the absorber, (v) Insulation for theunirradiated portion of the absorber and (vi) A self supporting structural capability and welladjusted tracking mechanism.Flat Plate CollectorThe schematics of a flat plate collector are shown in Fig. 1.13. It usually consists of fivemain components viz(i) an absorber plate (metallic or plastic),(ii) tubes or pipes for conducting or directing the heat transfer fluid,(iii) one or more covers,(iv) insulation to minimise the downward heat loss from the absorbing plate,(v) casing which encloses the foregoing components and keeps them free of dust andmoisture and also reduces the thermal losses.Generally flat plate collectors are framed sandwich structures, mounted on roofs orsloping walls. In most of these collectors, the absorber element is made of a metal such asgalvanised iron, aluminium, copper etc. and the cover is usually of glass of 4 mm thickness.The back of the absorber is insulated with glass wool, asbestos wool or some other insulatingmaterial. The casing, enclosing all the components of the collector is either made of wood orsome light metal like aluminium. The cost, with such meterials, is rather too high to beacceptable for common use. As the temperatures needed for space heating are rather low,plastics are being considered as potential material for fabrication of various components of theflat, plate collector. This would make solar energy systems comparable with other energysystems.

CONVENTIONAL SOURCESHydro Station

The water wheel, as developed in the early part of 19th century, played an importantrole in converting water power into mechanical power. With the invention of steam engines,the use of water wheel began to decrease and larger steam engines were developed. Steamengines possessed the advantage of mobility, allowing power to be produced, where it wasrequired and also that of flexibility in its application.It was only later with the discovery of conversion of mechanical energy into electricenergy, and transmission of electric energy being the most efficient method of transportingenergy from one place to another, that water wheel was revived. The modern water turbine, isbeing built in single unit of more than 200 MW. Also, the concept multipurpose project, inwhich the production of power is included as one of several uses (flood control, navigation,irrigation, water for domestic and industrial purpose, etc.), has led to the development of siteswhich otherwise could not be harnessed economically for power alone. The capital investment

per KW is much higher in case of hydro power as compared to thermal power. This is becausein order to store water at sufficient head, it is essential to construct a dam which is a costlyaffair. However, the running cost of hydro electric energy is much less as no fuel is used.Water power differs fundamentally from thermal power in that it represents aninexhaustible source of energy which is continually replenished by the direct agency of theSun; whereas thermal power represents chemical energy which has been created and storedwithin the earths crust during past geological ages. The use of chemical energy is thus equivalentto the consumption of capital as the replacement is not so easy. Another important differencebetween the two is that whereas water power can be developed only where it is present innature, thermal power (liquid or solid fuel) can be transported for use from one place to another

Water is the cheapest source of power. The energyof water utilized for hydro power generation may be kinetic orpotential. The kinetic energy of water is its energy in motion and isa function of mass and velocity while the potential energy is afunction of the difference in level of water between two points, calledthe head. In either case continuous availability of water is a basicnecessity. For this purpose water collected in natural lakes orreservoirs at high altitudes may be utilized or water may be artificiallystored by constructing dams, across flowing streams. In order togenerate energy by this method economically, ample quantity ofwater at sufficient potential (head) must be available. Moreover thepast history of the place of location of the plant must be known, inorder to estimate the minimum and maximum quantity of waterthat can be made available for the purpose of power generation. Thepotential energy is converted into mechanical energy. Hydraulicturbines convert the potential energy of water into mechanical energy.The mechanical energy developed by the turbine is used in runningthe electric generator which is directly coupled to the shaft of the turbine.

The main elements ofhydro electric power plant are:1. Catchment area and water reservoir.2. Dam and the intake.3. Inlet water ways.

4. Power house and equipment.5. The tail race.1. Catchment area and water reservoir. The area behindthe dam, which collects rain water, drains into a stream or river, iscalled catchment area. Water collected from catchment area is storedin a reservoir, behind the dam. The purpose of the reservoir is tostore the water during rainy season and supply it during dry season.Water surface in the storage reservoir is known as head race levelor simply head race. A reservoir can be either natural or artificial. Anatural reservoir is a lake in high mountains and an artificial reservoiris made by constructing a dam across the river. Water held in upstreamreservoir is called storage whereas water behind the dam at theplant is called pondalJe.2. Dam and the Intake. A dam is a structure of masonryearth and/or rock fill built across a river. It has two functions:(a) to provide the head of water,(b) to create storage or pondage,Many times high dams are built only to provide the necessaryhead to the power plants. Concrete and masonry dams are quitepopular and are made as :(i) solid gravity dam(ii) the buttress dam(iii) the arched damThe topography of the site and the foundation considerationsmainly govern the type of the dam to be selected. A narrow deepgorge is best bridged with a concrete or masonry dam whereas anearth dam best suits a wide valley. The basic requirements of adam are economy and safety. The dam foundation must provide fordam stability under different forces and supports its weight. Thefoundation should be sufficiently impervious to prevent seepage ofwater under the dam.The intake house includes the head works, which are thestructure at the intake of conduits, tunnels or flumes. There arebooms screens or trash racks, sluices for by passing debries andgates or valves for controlling the water flow. Ice and floating logare prevented by booms, which divert them to a bypass chute. Trashrack is made up of steel bars and is placed across the intake toprevent the debries from going into the intake. Gates and valvescontrol the rate of water flow entering the intake. Gates dischargeexcess water during flood duration. Gates are of the followingtypes;Radial gates, sluice gates, wheeled gates, plain sliding gates,crest gates, rolling or drum gates etc.The various types of valves used are needle valve and butterflyvalves.3. Inlet water ways. Inlet water ways are the passagesthrough which water is conveyed from the dam to the power house.It includes canal, penstock (closed pipe) or tunnel, flume, forewayand also surge tank.Tunnel is made by cutting the mountains where canal or pipeline can not be used due to topography. Tunneling provides a directand a short route for the water passages.Penstocks. Water may be conveyed to turbines through openconduits or closed pressure pipes called penstocks made ofreinforcedconcrete or steel. It is desirable that the penstock should be sloppingtowards the power house and its grade is adjusted as per thetopography. Penstocks usually are not covered and placed as exposedpipes, which facilitates easy maintenance and repair. When there isdanger from slides of snow, rock, earth etc. covered penstocks areused. The thickness of the penstrok increases as working pressureor head of the water increases. A large diameter of penstock giveslesser friction loss. Long penstocks are manufactured in sectionstogether by welding or rivetting, the welded joints give less frictionloss.Surge Tanks. These are additional storage spaces near thepower unit, usually provided in high head or medium head plantswhen there is considerable distance between the water source andthe power unit, needs a long penstock. The surge tank furnishes;space for holding water during load rejection by the turbine and forfurnishing additional water when the load on the turbine increases.

There is sudden increase of pressure in the penstock due to suddendecrease in the rate of water flow to the turbine when the load onthe generator decreases, then due to action of governor, the gatesadmitting water to the turbines are suddenly closed, this causessudden rise of pressure in the penstock above normal due to reducedload on generator, which is known as water hammer. Surge tankrelieves water hammer pressures when the penstock under conditionsof sudden changes in condition of water flow. Thus, the surge tankserves to regulate the flow of water through the conveyance system,to relieve water hammer pressures, and to improve performance ofthe machines by providing better speed regulation. Several designsof surge tanks have been adopted in power stations, the importantconsiderations being the amount of water to be stored, the amountof pressure to be relieved of, and the space available at the site ofconstruction.Forebay. The water carried by the power canals is distributedto various penstocks leading to the turbine, through the forebay,also known as the head pond. Water is temporarily stored in theforebay , in the event of a rejection of load by the turbine and thereis withdrawal from it when the load is increased. Thus, the forebayalso acts as a sort of regulating reservoir. This can be considered asnaturally provided surge tank as it does the work of surge tank.The head pond or foreway is created at the end of the power canalby widening it into the form of a small basin, which can store somewater for sadden demands of the turbine.Spillways. These structures provide for discharge of the surpluswater from the storage reservoir into the river on the down streamside of the dam. It includes the gate and control gearing. Spillway isconsidered a safety device for a dam, which acts as a safely valve,which has the capacity to discharge major floods without damage tothe dam. It keeps the reservoir level below the predeterminedmaximum level.There are several designs of spillways, such as the simplespillway, the side channel spillway, the siphon spillway etc. Theparticular type selected for a construction depends upon topographical,geological and hydrological conditions at the site. Maintenance costof spillways may also be an important consideration in selection ofthe type.4. Power House and Equipments. The power house is abuilding in which the turbines, alternators and the auxiliary plantare housed. Here conversion of energy of water to electrical energytakes place. The power house consists of two main parts, a substructureto support the hydraulic and electrical equipment and super structureto house and protect these equipments. The superstructure mostlyis a building, housing an operating equipments. The generatingunits and exciters are usually located on the ground floor. The turbinesare placed just below the floor level if they rotate on vertical axis.These turbines which rotate on a horizontal axis are placed on theground floor along side the generator. Following are some of themain equipments provided in a power house:(i) Prime movers (turbines) coupled with generators.(ii) Turbine governors.(iii) Relief valve for penstock fittings.(iv) Gate valves.(v) Water circulating pumps.(vi) Flow measuring devices.(vii) Air ducts.(viii) Transformers.(ix) Reactors.(x) Switch board equipment and instruments.(xi) Oil circuit breakers.(xii) Low tension and high tension bus bar.(xiii) Cranes.(xiv) Shops and offices.The turbines which are in common use are Pelton turbine,Francis turbine, Kaplan turbine and Propeller turbines.5. Tail Race and Outlet Water Way.:Tail race is a passagefor discharging the water leaving the turbine into the river and incertain cases, the water from. the tail race can be pumped back intothe original reservoir. Water after doing work on turbine runner

passes through the draft tube to tail race. The water held in the tail

race is called as tail race water level. The draft tube is a essentialpart of reaction turbine installation. It is a diverging passage fromthe point of runner exit down to the tail race. It is so shaped todecelerate the flow with a minimum loss so that the remainingkinetic energy of water coming out of the runner is efficientlyregained by converting into suction head, thereby increasing thetotal pressure difference on the runner. Thus a draft tube has twomain functions: It permits the establishment of negative head below therunner and so makes it possible to set the turbine above the tailrace level, where it is more easily accessible and yet does not causea sacrifice in head.(ii) Its diverging passage converts a large portion of the velocityenergy rejected from the runner into useful pressure head, therebyincreasing the efficiency of the turbine.

Major advantages of hydro stations may be summed up asfollows:1. The plant is highly reliable and its operation andmaintenance charges are very low.2. It is quick starting and can be brought on load within fewminutes, and the load can be increased rapidly.3. Hydro stations are able to respond to rapidly changingloads without loss of efficiency.4. The plant has no standby losses.5. The efficiency of the plant does not change with age, whereasthere is considerable reduction in efficiency of thermal as well asnuclear power plant with age.6. The plant and associated civil engineering structures havea long life.7. Less labour is required to operate the plant, much of theplant is under automatic control.8. In this case no nuisance of smoke, exhaust gases, soot etc.exists.9. It uses non-wasting natural source, i.e. water power.10. Cost of land is not a problem, as the hydro stations aresituated away from the developed areas.11. The cost of generation of energy varies with little withthe time.12. The machines used in hydel plants are more robust andgenerally run at low speeds (300 to 400 rpm) where the machinesused in thermal plants run at a speed of 3000 to 4000 r.p.m. Due tolow speed and temperature, there are no complications of specialalloys required for construction.13. It can be made multipurpose so as to give additionaladvantages of irrigation and flood control

disadvantages.1. Initial cost of the plant including the cost of dam is high.2. Hydro-station has special requirement of site which usuallyis an isolated area with difficult access.3. Power generation by the hydro-plant is only dependenton the quality of water available, which in turn depends on rain.During the dry year, the power production may be curtailed or evendiscontinued. This availability of power from such plants is notmuch reliable.4. The site of hydro relectric station is selected on the basisof water availability at economical head. Such sites are usuallyaway from the load centres. The transmission of power from powerstation to the load centre requires long transmission lines. Thissubstantially increases the capital expenditure and also there isloss of power in such transmissions.5. It takes long time for its construction as compared to thermal plants

Steam Power Plant

Essentials of Steam Power Plant EquipmentA steam power plant must have following equipment :(a) A furnace to burn the fuel.(b) Steam generator or boiler containing water. Heat generated in the furnace is utilized to convert water into steam.(c) Main power unit such as an engine or turbine to use the heat energy of steam and perform work.(d) Piping system to convey steam and water.In addition to the above equipment the plant requires various auxiliaries and accessories depending upon the availability of water, fuel and the service for which the plant is intended.The flow sheet of a thermal power plant consists of the following four main circuits :(a) Feed water and steam flow circuit.(b) Coal and ash circuit.(c) Air and gas circuit.(d) Cooling water circuit.A steam power plant using steam as working substance works basically on Rankine cycle.Steam is generated in a boiler, expanded in the prime mover and condensed in the condenser and fed into the boiler again.The different types of systems and components used in steam power plant are as follows :(a) High pressure boiler(b) Prime mover(c) Condensers and cooling towers(d) Coal handling system(e) Ash and dust handling system(f) Draught system(g) Feed water purification plant(h) Pumping system(i) Air preheater, economizer, super heater, feed heaters.Figure 2.11 shows a schematic arrangement of equipment of a steam power station. Coal received in coal storage yard of power station is transferred in the furnace by coal handling unit. Heat produced due to burning of coal is utilized in converting water contained in boiler drum intosteam at suitable pressure and temperature. The steam generated is passed through the superheater. Superheated steam then flows through the turbine. After doing work in the turbine the pressure of steam is reduced. Steam leaving the turbine passes through the condenser which is maintained the low pressure of steam at the exhaust of turbine. Steam pressure in the condenser depends upon flow rate and temperature of cooling water and on effectiveness of air removal equipment. Water circulating through the condenser may be taken from the various sources such as river, lake or sea. If sufficient quantity of water is not available the hot water coming out of the condenser may be cooled in cooling towers and circulated again through the condenser. Bled steam taken from the turbine at suitable extraction points is sent to low pressure and highpressure water heaters.Air taken from the atmosphere is first passed through the air pre-heater, where it is heated by flue gases. The hot air then passes through the furnace. The flue gases after passing over boiler and superheater tubes, flow through the dust collector and then through economiser, air pre-heater and finally they are exhausted to the atmosphere through the chimney.Steam condensing system consists of the following :(a) Condenser(b) Cooling water

(c) Cooling tower(d) Hot well(e) Condenser cooling water pump(f) Condensate air extraction pump(g) Air extraction pump(h) Boiler feed pump(i) Make up water pump.2 ClassificationBoiler is an apparatus to produce steam. Thermal energy released by combustion of fuel is transferred to water, which vaporizes and gets converted into steam at the desired temperature and pressure.The steam produced is used for :(a) Producing mechanical work by expanding it in steam engine or steam turbine.(b) Heating the residential and industrial buildings.(c) Performing certain processes in the sugar mills, chemical and textile industries.Boiler is a closed vessel in which water is converted into steam by the application of heat. Usually boilers are coal or oil fired.

(a) Safety : The boiler should be safe under operating conditions.(b) Accessibility : The various parts of the boiler should be accessible for repair and maintenance.(c) Capacity : The boiler should be capable of supplying steam according to the requirements.(d) Efficiency : To permit efficient operation, the boiler should be able to absorb a maximum amount of heat produced due to burning of fuel in the furnace.(e) It should be simple in construction and its maintenance cost should be low.(f) Its initial cost should be low.(g) The boiler should have no joints exposed to flames.(h) The boiler should be capable of quick starting and loading.2.3.3 Types of BoilersThe boilers can be classified according to the following criteria.According to flow of water and hot gases :(a) Water tube(b) Fire tube.In water tube boilers, water circulates through the tubes and hot products of combustion flow over these tubes. In fire tube boiler the hot products of combustion pass through the tubes, which are surrounded, by water. Fire tube boilers have low initial cost, and are more compacts. But they are more likely to explosion, water volume is large and due to poor circulation they cannot meet quickly the change in steam demand. For the same output the outer shell of fire tube boilers is much larger than the shell of water-tube boiler. Water tube boilers require less weight of metal for a given size, are less liable to explosion, produce higher pressure, are accessible and can respond quickly to change in steam demand. Tubes and drums of water-tube boilers are smaller than that of fire-tube boilers and due to smaller size of drum higher pressure can be used easily. Water-tube boilers require lesser floor space. The efficiency of water-tube boilers is more.Water tube boilers are classified as follows :Horizontal Straight Tube Boilers(a) Longitudinal drum(b) Cross-drum.Bent Tube Boilers(a) Two drum(b) Three drum(c) Low head three drum(d) Four drum.Cyclone Fired BoilersVarious advantages of water tube boilers are as follows :(a) High pressure can be obtained.(b) Heating surface is large. Therefore steam can be generated easily.(c) Large heating surface can be obtained by use of large number of tubes.(d) Because of high movement of water in the tubes the rate of heat transfer becomes large resulting into a greater efficiency.

External Furnace(a) Horizontal return tubular(b) Short fire box(c) Compact.Internal FurnaceHorizontal Tubular(a) Short firebox(b) Locomotive(c) Compact(d) Scotch.Vertical Tubular(a) Straight vertical shell, vertical tube(b) Cochran (vertical shell) horizontal tube.Various advantages of fire tube boilers are as follows :(a) Low cost

(b) Fluctuations of steam demand can be met easily(c) It is compact in size.According to position of furnace :(a) Internally fired(b) Externally firedIn internally fired boilers the grate combustion chamber are enclosed within the boiler shell whereas in case of extremely fired boilers and furnaceand grate are separated from the boiler shell.According to the position of principle axis :(a) Vertical(b) Horizontal(c) Inclined.According to application :(a) Stationary(b) Mobile, (Marine, Locomotive).According to the circulating water :(a) Natural circulation(b) Forced circulation.According to steam pressure :(a) Low pressure(b) Medium pressure(c) Higher pressure. Major Components and Their FunctionsEconomizerThe economizer is a feed water heater, deriving heat from the flue gases. The justifiable cost of the economizer depends on the total gain in efficiency. In turn this depends on the flue gas temperature leaving the boiler and the feed water inlet temperature. A typical return bend type economizer is shown in the Figure.

Air Pre-heaterThe flue gases coming out of the economizer is used to preheat the air before supplying it to the combustion chamber. An increase in air temperature of 20 degrees can be achieved by this method. The pre heated air is used for combustion and also to dry the crushed coal before pulverizing.Soot BlowersThe fuel used in thermal power plants causes soot and this is deposited on the boiler tubes, economizer tubes, air pre heaters, etc. This drastically reduces the amount of heat transfer of the heat exchangers. Soot blowers control the formation of soot and reduce its corrosive effects. The types of soot blowers are fixed type, which may be further classified into lane type and mass type depending upon the type of spray and nozzle used. The other type of soot blower is the retractable soot blower. The advantages are that they are placed far away from the high temperature zone, they concentrate the cleaning through a single large nozzle rather than many small nozzles and there is no concern of nozzle arrangement with respect to the boiler tubes.CondenserThe use of a condenser in a power plant is to improve the efficiency of the power plant by decreasing the exhaust pressure of the steam below atmosphere. Another advantage of the condenser is that the steam condensed may be recovered to provide a source of good pure feed water to the boiler and reduce the water softening capacity to a considerable extent. A condenser is one of the essential components of a power plant.Cooling TowerThe importance of the cooling tower is felt when the cooling water from the condenser has to be cooled. The cooling water after condensing the steam becomes hot and it has to be cooled as it belongs to a closed system. The Cooling towers do the job of decreasing the temperature of the cooling water after condensing the steam in the condenser.The type of cooling tower used in the Columbia Power Plant was an Inline Induced Draft Cross Flow Tower. This tower provides a horizontal air flow as the water falls down the tower in the form of small droplets. The fan centered at the top of units draws air through two cells that are paired to a suction chamber partitioned beneath the fan. The outstanding feature of this tower is lower air static pressure loss as there is less resistance to air flow. The evaporation and effective cooling of air is greater when the air outside is warmer and dryer than when it is cold and already saturated.SuperheaterThe superheater consists of a superheater header and superheater elements. Steam from the main steam pipe arrives at the saturated steam chamber of the superheater header and is fed into the superheater elements. Superheated steam arrives back at the superheated steam chamber of the superheater header and is fed into the steam pipe to the cylinders. Superheated steam is more expansive.ReheaterThe reheater functions similar to the superheater in that it serves to elevate the steam temperature. Primary steam is supplied to the high pressure turbine. After passing through the high pressure turbine, the steam is returned to the steam generator for reheating (in a reheater) after which it is sent to the low pressure turbine. A second reheat cycle may also be provided.Advantages of steam power plant:1. Initial investment is low2. Power plant can be located near load center, so transmission cost and losses are considerably reduced.3. Commissioning of thermal power plant requires less period of time4. Feed water heaters are provided to heat the feed water supplied to boiler by which overall efficiency of plant can be increased.

Disadvantages of steam power plant:

1. Life and efficiency of steam power plant is less when compared to Hydel power plant2. Transportation of fuel is major problem

3. Cost of power generation is more than hydro power4. Air pollution is major problem5. Coal may be exhausted by gradual use.

Diesel power plantA generating station in which diesel engine is used as the prime mover for the generation of electrical energy is known as diesel power station.In a diesel power station, diesel engine is used as the prime mover. The diesel burns inside the engine and the products of this combustion act as the working fluid to produce mechanical energy. The diesel engine drives alternator which converts mechanical energy into electrical energy. As the generation cost is considerable due to high price of diesel, therefore, such power stations are only used to produce small power.Although steam power stations and hydro-electric plants are invariably used to generate bulk power at cheaper costs, yet diesel power stations arefinding favour at places where demand of power is less, sufficient quantity of coal and water is not available and the transportation facilities are inadequate. This plants are also standby sets for continuity of supply to important points such as hospitals, radio stations, cinema houses and telephone exchanges.Advantages

(a) The design and layout of the plant are quite simple.(b) It occupies less space as the number and size of the auxiliaries is small.(c) It can be located at any place.(d) It can be started quickly and it can pickup load in a short time.(e) There are no standby losses.(f) It requires less quantity of water for cooling.(g) The overall cost is much less than that of steam power station of same capacity.(h) The thermal efficiency of the plant is higher than that of a steam power station.(i) It requires less operating staff.

Disadvantages(a) The plant has high running charges as the fuel (diesel) used is costly.(b) The plant doesnt work satisfactorily under overload conditions for a longer period.(c) The plant can only generate small power.(d) The cost of lubrication is generally high.(e) The maintenances charges are generally high

ESSENTIAL ELEMENTS OF DIESEL POWER PLANT

Fuel Supply System

It consists of storage tank, strainers, fuel transfer pump and all day fuel tank. The fuel oil is supplied at the plant site by rail or road. The oil is stored in the storage tank. From the storage tank, oil is pumped to smaller all day tank at daily or short intervals. From this tank, fuel oil is passed through strainers to remove suspended impurities. The clean oil is injected into the engine by fuel injection pump.Air Intake SystemThis system supplies necessary air to the engine for fuel combustion. It consists of pipes for the supply of fresh air to the engine manifold. Filters are provided to remove dust particles from air which may act as abrasive in the engine cylinder.Because a diesel engine requires close tolerances to achieve its compression ratio, and because most diesel engines are either turbocharged or supercharged, the air entering the engine must be clean, free of debris, and as cool as possible. Also, to improve a turbocharged or supercharged engines efficiency, the compressed air must be cooled after being compressed. The air intake system is designed to perform these tasks. Air intake systems are usually one of two types, wet or dry. In a wet filter intake system, as shown in the Figure 4.1, the air is sucked or bubbled through a housing that holds a bath of oil such that the dirt in the air is removed by the oil in the filter. The air then flows through a screen-type material to ensure any entrained oil is removed from the air. In a dry filter system, paper, cloth, or a metal screen material is used to catch and trapdirt before it enters the engine. In addition to cleaning the air, the intake system is usually designed to intake fresh air from as far away from the engine as practicable, usually just outside of the engines building or enclosure. This provides the engine with a supply of air that has not been heated by the engines own waste heat. The reason for ensuring that an engine's air supply is as cool as possible is that cool air is denser than hot air. This means that, per unit volume, cool air has more oxygen than hot air.Thus, cool air provides more oxygen per cylinder charge than less dense, hot air. More oxygen means a more efficient fuel burn and more power

After being filtered, the air is routed by the intake system into the engine's intake manifold or air box. The manifold or air box is the component that directs the fresh air to each of the engines intake valves or ports. If the engine is turbocharged or supercharged, the fresh air will be compressed with a blower and possibly cooled before entering the intake manifold or air box. The intake system also serves to reduce the air flownoise.Exhaust SystemThis system leads the engine exhaust gas outside the building and discharges it into atmosphere. A silencer is usually incorporated in the system to reduce the noise level.The exhaust system of a diesel engine performs three functions. First, the exhaust system routes the spent combustion gasses away from the engine, where they are diluted by the atmosphere. This keeps the area around the engine habitable. Second, the exhaust system confines and routes the gases to the turbocharger, if used. Third, the exhaust system allows mufflers to be used to reduce the engine noise.Cooling SystemThe heat released by the burning of fuel in the engine cylinder is partially converted into work. The remainder part of the heat passes through the cylinder wall, piston, rings etc. and may cause damage to system. In order to keep the temperature of the engine parts within the safe operating limits, cooling is provided. The cooling system consists of a water source, pump and cooling towers. The pump circulates water through cylinder and head jacket. The water takes away heat form the engine and it becomes hot. The hot water is cooled by cooling towers and re circulated for cooling.Lubricating SystemThe system minimises the wear of rubbing surfaces of the engine. It comprises of lubricating oil tank, pump, filter and oil cooler. The lubrication oil is drawn from the lubricating oil tank by the pump and is passed through filter to remove impurities .The clean lubrication oil is delivered to the points which require lubrication. The oil coolers incorporated in the system keep the temperature of the oil low.

An internal combustion engine would not run for even a few minutes if the moving parts were allowed to make metal-to-metal contact. The heat generated due to the tremendous amounts of friction would melt the metals, leading to the destruction of the engine. To prevent this, all moving parts ride on a thin film of oil that is pumped between all the moving parts of the engine. The oil serves two purposes. One purpose is to lubricate the bearing surfaces. The other purpose is to cool the bearings by absorbing the friction- generated heat. The flow of oil to the moving parts is accomplished by the engine's internal lubricating system.

Oil is accumulated and stored in the engine's oil pan where one or more oil pumps take suction and pump the oil through one or more oil filters asshown in the figure. The filters clean the oil and remove any metal that the oil has picked up due to wear. The cleaned oil then flows up into the engine's oil galleries. A pressure relief valve(s) maintains oil pressure in the galleries and returns oil to the oil pan upon high pressure. The oil galleries distribute the oil to all the bearing surfaces in the engine. Once the oil has cooled and lubricated the bearing surfaces, it flows out of the bearing and gravity-flows back into the oil pan. In medium to large diesel engines, the oil is also cooled before being distributed into the block. This is accomplished by either internal or external oil cooler. The lubrication system also supplies oil to the engines governor.Engine Starting SystemThis is an arrangement to rotate the engine initially, while starting, until firing starts and the unit runs with its own power. Small sets are started manually by handles but for larger units, compressed air is used for starting. In the latter case, air at high pressure is admitted to a few of the cylinders, making them to act as reciprocating air motors to turn over the engine shaft. The fuel is admitted to the remaining cylinders which makes the engine to start under its own power.Starting Circuits

Diesel engines have as many different types of starting circuits as there are types, sizes, and manufacturers of diesel engines. Commonly, they canbe started by air motors, electric motors, hydraulic motors, and manually. The start circuit can be a simple manual start pushbutton, or a complex auto-start circuit. But in almost all cases the following events must occur for the starting engine to start.(a) The start signal is sent to the starting motor. The air, electric, or hydraulic motor, will engage the engines flywheel.(b) The starting motor will crank the engine. The starting motor will spin the engine at a high enough rpm to allow the engines compression to ignite the fuel and start the engine running.(c) The engine will then accelerate to idle speed. When the starter motor is overdriven by the running motor it will disengage the flywheel.Because a diesel engine relies on compression heat to ignite the fuel, a cold engine can rob enough heat from the gasses that the compressed air falls below the ignition temperature of the fuel. To help overcome this condition, some engines (usually small to medium sized engines) have glow plugs. Glow plugs are located in the cylinder head of the combustion chamber and use electricity to heat up the electrode at the top of the glow plug. The heat added by the glow plug is sufficient to help ignite the fuel in the cold engine. Once the engine is running, the glow plugs are turned off and the heat of combustion is sufficient to heat the block and keep the engine running. Larger engines usually heat the block and/or have powerful starting motors that are able to spin the engine long enough to allow the compression heat to fire the engine. Some large engines use air start manifolds that inject compressed air into the cylinders which rotates the engine during the start sequence.

Nuclear Reactor

Nuclear reactors, which produce heat by splitting uranium atoms,do the same job as conventional power producing equipment inthe generation ofelectricity they produce heat to convert waterinto steam, which spins a turbine or generator to make electricity.Instead of coal, oil or natural gas,Canadian nuclear reactors usenatural uranium for fuel. But the uranium is not burned. Uraniumatoms make heat by splitting the technical term is fissioning

ProductFission makes Heat When a neutron (a tiny sub-atomic particlethat is one of the components of almost allatoms) strikes an atom of uranium, theuranium atom splits into two lighter atoms(which are called fission products) andreleases heat at the same time. The fis-sioning process also releases from one tothree more neutrons that can split other ura-nium atoms. This is the beginning of a "chainreaction" in which more and more uranium atomsare split, releasing more and more neutrons(and heat).In a power reactor, the chain reaction istightly controlled to produce only theamount of heat needed to generate amount of electricity.

Heat makes Steam The fission process generates a huge amount of heat. Inorder to be useful, the heat has to be moved to boilers tomake steam. Ina reactor, heavy water does thisjob. It is pumped constantly through the fuel channels inthe reactor and takes the heat from the fuel bundles upto boilers above the reactor. In the boilers the heatedheavy water heats up ordinary water to make steam. Thesteam is piped out of the boilers and over to the turbinehall where it drives the huge turbines/generators thatmake the electricity we use.

Creating A Chain ReactionCanadian reactors use fuel made of natural uranium. Like uranium in the ground, almost all of the uranium in

fuel is U-238. This is the common form of theelement. The ore also contains tiny amounts (0.7%) of U-235, an unstable isotope of uranium that fissions spon-taneously thats why Geiger counters react to ore-car-rying rock. The fact that U-235 atoms fission sponta neously makes it possible to get a controlled chain reac-tion going inside the mass of fuel in the reactor. But nochain reaction can take place in this fuel unless threeconditions are all satisfied at the same time:several tons of fuel are present;the tubes containing the fuel are stacked in a specialarrangement, neither too close together, nor too farapart; and,a material called a "moderator" surrounds the fuel.The moderator slows, or moderates, the speed of theneutrons resulting from the fission so they are more like-ly to collide with, and split, more uranium atoms. Themoderator in Canadian reactors is heavy water which isvery efficient at slowing down neutrons while notabsorbing too many of them. Heavy water is 10% heav-ier than ordinary water because it incorporates a heavyform of hydrogen called deuterium.

Reactor FuelNatural uranium fuel for Ontario Power Generationsreactors is first formed into ceramic pellets and thensealed into metal tubes. Thetubes are assembled intofuel bundles weighing about 22 kilograms each. Onebundle produces the same amount of heat as 400tonnes of coal.

2. write detailed notes on powerplant economics. ans:

In all fields of industry economics plays an important role. In power plant engineering economics of power system use certain well established techniques for choosing the most suitable system. The power plant design must be made on the basis of most economical condition and not on themost efficient condition as the profit is the main basis in the design of the plant and its effectiveness is measured financially. The main purpose ofdesign and operation of the plant is to bring the cost of energy produced to minimum. Among many factors, the efficiency of the plant is one of the factors that determines the energy cost. In majority of cases, unfortunately, the most thermally efficient plant is not economic one.

Connected Load The connected load on any system, or part of a system, is the combined continuous rating of all the receiving apparatus on consumers premises, which is connected to the system, or part of the system, under consideration.Demand The demand of an installation or system is the load that is drawn from the source of supply at the receiving terminals averaged over a suitable and specified interval of time. Demand is expressed in kilowatts (kW), kilovolt-amperes (kVA), amperes (A), or other suitable units.Maximum Demand or Peak Load The maximum demand of an installation or system is the greatest of all the demands that have occurred during a given period. It is determined by measurement, according to specifications, over a prescribed interval of time.Demand Factor The demand factor of any system, or part of a system, is the ratio of maximum demand of the system, a part of the system, to the total connected load of the system, or of the part of the system, under consideration. Expressing the definition mathematically, Maximum demand Demand factor = Connected loadLand Factor The load factor is the ratio of the average power to the maximum demand. In each case, the interval of maximum load and the period over which the average is taken should be definitely specified, such as a half-hour monthly load factor. The proper interval and period are usually dependent upon local conditions and upon the purpose for which the load factor is to be used. Expressing the definition mathematically, Average load Load factor = Maximum demandDiversity Factor The diversity factor of any system, or part of a system, is the ratio of the maximum power demands of the subdivisions of the system, or part of a system, to the maximum demand of the whole system, or part of the system, under consideration, measured at the point of supply. Expressing the definition mathematically, Sum of individual maximum demands Diversity factor = Maximum demand of entire groupUtilisation Factor The utilisation factor is defined as the ratio of the maximum generator demand to the generator capacity.Plant Capacity Factor It is defined as the ratio of actual energy produced in kilowatt hours (kWh) to the maximum possible energy that could have been produced during the same period. Expressing the definition mathematically,Plant capacity factor = E/ (C t )

Plant Economy where, E = Energy produced (kWh) in a given period,C = Capacity of the plant in kW, andt = Total number of hours in the given period.Plant Use Factor It is defined as the ratio of energy produced in a given time to the maximum possible energy that could have been produced during the actual number of hours the plant was in operation. Expressing the definition mathematically,. Plant use factor = E /C t'.where, t' = Actual number of hours the plant has been in operation

Types of Loads Residential Load This type of load includes domestic lights, power needed for domestic appliances such as radios, television, water heaters, refrigerators, electric cookers and small motors for pumping water.Commercial Load It includes lighting for shops, advertisements and electrical appliances used in shops and restaurants, etc.Industrial Load

It consists of load demand of various industries.Municipal Load It consists of street lighting, power required for water supply and drainage purposes.Irrigation Load This type of load includes electrical power needed for pumps driven by electric motors to supply water to fields.Traction Load It includes terms, cars, trolley, buses and railways .

Load Curve A load curve (or load graph) is a graphic record showing the power demands for every instant during a certain time interval. Such a record may cover 1 hour, in which case it would be an hourly load graph; 24 hours, in which case it would be a daily load graph; a month in which case it would be a monthly load graph; or a year (7860 hours), in which case it would be a yearly load graph. The following points are worth noting :(i) The area under the load curve represents the energy generated in the period considered.(ii) The area under the curve divided by the total number of hours gives the average load on the power station.(iii) The peak load indicated by the load curve/graph represents the maximum demand of the power station.Significance of Load Curves 1. Load curves give full information about the incoming and help to decide the installed capacity of the power station and to decide the economical sizes of various generating units. 2.These curves also help to estimate the generating cost and to decide the operating schedule of the power station, i.e. the sequence in which different units should be ru

Straight line depreciation:

3. What is a steam power station? Discuss its advantages disadvantages.Ans:

Essentials of Steam Power Plant EquipmentA steam power plant must have following equipment :(a) A furnace to burn the fuel.(b) Steam generator or boiler containing water. Heat generated in the furnace is utilized to convert water into steam.(c) Main power unit such as an engine or turbine to use the heat energy of steam and perform work.(d) Piping system to convey steam and water.In addition to the above equipment the plant requires various auxiliaries and accessories depending upon the availability of water, fuel and the service for which the plant is intended.The flow sheet of a thermal power plant consists of the following four main circuits :(a) Feed water and steam flow circuit.(b) Coal and ash circuit.(c) Air and gas circuit.(d) Cooling water circuit.A steam power plant using steam as working substance works basically on Rankine cycle.Steam is generated in a boiler, expanded in the prime mover and condensed in the condenser and fed into the boiler again.The different types of systems and components used in steam power plant are as follows :(a) High pressure boiler(b) Prime mover(c) Condensers and cooling towers(d) Coal handling system(e) Ash and dust handling system(f) Draught system(g) Feed water purification plant(h) Pumping system(i) Air preheater, economizer, super heater, feed heaters.Figure 2.11 shows a schematic arrangement of equipment of a steam power station. Coal received in coal storage yard of power station is transferred in the furnace by coal handling unit. Heat produced due to burning of coal is utilized in converting water contained in boiler drum

into steam at suitable pressure and temperature. The steam generated is passed through the superheater. Superheated steam then flows through the turbine. After doing work in the turbine the pressure of steam is reduced. Steam leaving the turbine passes through the condenser which is maintained the low pressure of steam at the exhaust of turbine. Steam pressure in the condenser depends upon flow rate and temperature of cooling water and on effectiveness of air removal equipment. Water circulating through the condenser may be taken from the various sources such as river, lake or sea. If sufficient quantity of water is not available the hot water coming out of the condenser may be cooled in cooling towers and circulated again through the condenser. Bled steam taken from the turbine at suitable extraction points is sent to low pressure and high pressure water heaters.Air taken from the atmosphere is first passed through the air pre-heater, where it is heated by flue gases. The hot air then passes through the furnace. The flue gases after passing over boiler and superheater tubes, flow through the dust collector and then through economiser, air pre-heater and finally they are exhausted to the atmosphere through the chimney.Steam condensing system consists of the following :(a) Condenser(b) Cooling water(c) Cooling tower(d) Hot well(e) Condenser cooling water pump(f) Condensate air extraction pump(g) Air extraction pump(h) Boiler feed pump(i) Make up water pump.2 ClassificationBoiler is an apparatus to produce steam. Thermal energy released by combustion of fuel is transferred to water, which vaporizes and gets converted into steam at the desired temperature and pressure.The steam produced is used for :(a) Producing mechanical work by expanding it in steam engine or steam turbine.(b) Heating the residential and industrial buildings.(c) Performing certain processes in the sugar mills, chemical and textile industries.Boiler is a closed vessel in which water is converted into steam by the application of heat. Usually boilers are coal or oil fired.

(a) Safety : The boiler should be safe under operating conditions.(b) Accessibility : The various parts of the boiler should be accessible for repair and maintenance.(c) Capacity : The boiler should be capable of supplying steam according to the requirements.(d) Efficiency : To permit efficient operation, the boiler should be able to absorb a maximum amount of heat produced due to burning of fuel in the furnace.(e) It should be simple in construction and its maintenance cost should be low.(f) Its initial cost should be low.(g) The boiler should have no joints exposed to flames.(h) The boiler should be capable of quick starting and loading.2.3.3 Types of BoilersThe boilers can be classified according to the following criteria.According to flow of water and hot gases :(a) Water tube(b) Fire tube.In water tube boilers, water circulates through the tubes and hot products of combustion flow over these tubes. In fire tube boiler the hot products of combustion pass through the tubes, which are surrounded, by water. Fire tube boilers have low initial cost, and are more compacts. But they are more likely to explosion, water volume is large and due to poor circulation they cannot meet quickly the change in steam demand. For the same output the outer shell of fire tube boilers is much larger than the shell of water-tube boiler. Water tube boilers require less weight of metal for a given size, are less liable to explosion, produce higher pressure, are accessible and can respond quickly to change in steam demand. Tubes and drums of water-tube boilers are smaller than that of fire-tube boilers and due to smaller size of drum higher pressure can be used easily. Water-tube boilers require lesser floor space. The efficiency of water-tube boilers is more.Water tube boilers are classified as follows :Horizontal Straight Tube Boilers(a) Longitudinal drum(b) Cross-drum.Bent Tube Boilers(a) Two drum(b) Three drum(c) Low head three drum(d) Four drum.Cyclone Fired BoilersVarious advantages of water tube boilers are as follows :(a) High pressure can be obtained.(b) Heating surface is large. Therefore steam can be generated easily.(c) Large heating surface can be obtained by use of large number of tubes.(d) Because of high movement of water in the tubes the rate of heat transfer becomes large resulting into a greater efficiency.

External Furnace(a) Horizontal return tubular(b) Short fire box(c) Compact.Internal FurnaceHorizontal Tubular(a) Short firebox(b) Locomotive(c) Compact(d) Scotch.Vertical Tubular(a) Straight vertical shell, vertical tube(b) Cochran (vertical shell) horizontal tube.Various advantages of fire tube boilers are as follows :(a) Low cost(b) Fluctuations of steam demand can be met easily(c) It is compact in size.According to position of furnace :(a) Internally fired(b) Externally firedIn internally fired boilers the grate combustion chamber are enclosed within the boiler shell whereas in case of extremely fired boilers and furnace and grate are separated from the boiler shell.According to the position of principle axis :(a) Vertical(b) Horizontal(c) Inclined.According to application :(a) Stationary(b) Mobile, (Marine, Locomotive).According to the circulating water :(a) Natural circulation(b) Forced circulation.According to steam pressure :(a) Low pressure(b) Medium pressure(c) Higher pressure. Major Components and Their FunctionsEconomizerThe economizer is a feed water heater, deriving heat from the flue gases. The justifiable cost of the economizer depends on the total gain in efficiency. In turn this depends on the flue gas temperature leaving the boiler and the feed water inlet temperature. A typical return bend type economizer is shown in the Figure.

Air Pre-heaterThe flue gases coming out of the economizer is used to preheat the air before supplying it to the combustion chamber. An increase in air temperature of 20 degrees can be achieved by this method. The pre heated air is used for combustion and also to dry the crushed coal before pulverizing.Soot BlowersThe fuel used in thermal power plants causes soot and this is deposited on the boiler tubes, economizer tubes, air pre heaters, etc. This drastically reduces the amount of heat transfer of the heat exchangers. Soot blowers control the formation of soot and reduce its corrosive effects. The types of soot blowers are fixed type, which may be further classified into lane type and mass type depending upon the type of sprayand nozzle used. The other type of soot blower is the retractable soot blower. The advantages are that they are placed far away from the high temperature zone, they concentrate the cleaning through a single large nozzle rather than many small nozzles and there is no concern of nozzle arrangement with respect to the boiler tubes.CondenserThe use of a condenser in a power plant is to improve the efficiency of the power plant by decreasing the exhaust pressure of the steam below atmosphere. Another advantage of the condenser is that the steam condensed may be recovered to provide a source of good pure feed water to the boiler and reduce the water softening capacity to a considerable extent. A condenser is one of the essential components of a power plant.Cooling TowerThe importance of the cooling tower is felt when the cooling water from the condenser has to be cooled. The cooling water after condensing the steam becomes hot and it has to be cooled as it belongs to a closed system. The Cooling towers do the job of decreasing the temperature of the cooling water after condensing the steam in the condenser.The type of cooling tower used in the Columbia Power Plant was an Inline Induced Draft Cross Flow Tower. This tower provides a horizontal air flow as the water falls down the tower in the form of small droplets. The fan centered at the top of units draws air through two cells that are

paired to a suction chamber partitioned beneath the fan. The outstanding feature of this tower is lower air static pressure loss as there is less resistance to air flow. The evaporation and effective cooling of air is greater when the air outside is warmer and dryer than when it is cold and already saturated.SuperheaterThe superheater consists of a superheater header and superheater elements. Steam from the main steam pipe arrives at the saturated steam chamber of the superheater header and is fed into the superheater elements. Superheated steam arrives back at the superheated steam chamber of the superheater header and is fed into the steam pipe to the cylinders. Superheated steam is more expansive.ReheaterThe reheater functions similar to the superheater in that it serves to elevate the steam temperature. Primary steam is supplied to the high pressure turbine. After passing through the high pressure turbine, the steam is returned to the steam generator for reheating (in a reheater) after which it is sent to the low pressure turbine. A second reheat cycle may also be provided.Advantages of steam power plant:1. Initial investment is low2. Power plant can be located near load center, so transmission cost and losses are considerably reduced.3. Commissioning of thermal power plant requires less period of time4. Feed water heaters are provided to heat the feed water supplied to boiler by which overall efficiency of plant can be increased.

Disadvantages of steam power plant:

1. Life and efficiency of steam power plant is less when compared to Hydel power plant2. Transportation of fuel is major problem3. Cost of power generation is more than hydro power4. Air pollution is major problem5. Coal may be exhausted by gradual use.

4. Draw a neat schematic diagram of a hydroelectric power plant and explain thefunctions of various parts.

Introduction: Water is the cheapest source of power. The energyof water utilized for hydro power generation may be kinetic orpotential. The kinetic energy of water is its energy in motion and isa function of mass and velocity while the potential energy is afunction of the difference in level of water between two points, calledthe head. In either case continuous availability of water is a basicnecessity. For this purpose water collected in natural lakes orreservoirs at high altitudes may be utilized or water may be artificiallystored by constructing dams, across flowing streams. In order togenerate energy by this method economically, ample quantity ofwater at sufficient potential (head) must be available. Moreover thepast history of the place of location of the plant must be known, inorder to estimate the minimum and maximum quantity of waterthat can be made available for the purpose of power generation. Thepotential energy is converted into mechanical energy. Hydraulic

turbines convert the potential energy of water into mechanical energy.The mechanical energy developed by the turbine is used in runningthe electric generator which is directly coupled to the shaft of the turbine.

The main elements ofhydro electric power plant are:1. Catchment area and water reservoir.2. Dam and the intake.3. Inlet water ways.4. Power house and equipment.5. The tail race.1. Catchment area and water reservoir. The area behindthe dam, which collects rain water, drains into a stream or river, iscalled catchment area. Water collected from catchment area is storedin a reservoir, behind the dam. The purpose of the reservoir is tostore the water during rainy season and supply it during dry season.Water surface in the storage reservoir is known as head race levelor simply head race. A reservoir can be either natural or artificial. Anatural reservoir is a lake in high mountains and an artificial reservoiris made by constructing a dam across the river. Water held in upstreamreservoir is called storage whereas water behind the dam at theplant is called pondalJe.2. Dam and the Intake. A dam is a structure of masonryearth and/or rock fill built across a river. It has two functions:(a) to provide the head of water,(b) to create storage or pondage,Many times high dams are built only to provide the necessaryhead to the power plants. Concrete and masonry dams are quitepopular and are made as :(i) solid gravity dam(ii) the buttress dam(iii) the arched damThe topography of the site and the foundation considerationsmainly govern the type of the dam to be selected. A narrow deepgorge is best bridged with a concrete or masonry dam whereas anearth dam best suits a wide valley. The basic requirements of adam are economy and safety. The dam foundation must provide fordam stability under different forces and supports its weight. Thefoundation should be sufficiently impervious to prevent seepage ofwater under the dam.The intake house includes the head works, which are thestructure at the intake of conduits, tunnels or flumes. There arebooms screens or trash racks, sluices for by passing debries andgates or valves for controlling the water flow. Ice and floating logare prevented by booms, which divert them to a bypass chute. Trashrack is made up of steel bars and is placed across the inta