Unit 3

Hydraulic Turbines & Pumps

3.1 Introduction, Classification, Construction details and working of Pelton Wheel, Francis and Kaplan turbines, Specific speed (Definition and significance only)

Pelton wheel turbine:

Pelton Turbine is a Tangential flow impulse turbine in which the pressure energy of water is converted into kinetic energy to form high speed water jet and this jet strikes the wheel tangentially to make it rotate. It is also called as Pelton Wheel.

• The turbine capable of working under the high potential head of water is the Pelton Wheel Turbine which works on the head greater than 300 m.
• The runner consists of a circular disc with a suitable number of double semi-ellipsoidal cups known as buckets which are evenly spaced around its Periphery.
• One or more nozzles are mounted so that, each directs a jet along the tangent to the circle through the centres of the buckets called the Pitch Circle.
• A casing is provided only to prevent the splashing of water and for discharging the water to the tailrace.

Parts and Their Functions of Pelton Turbine

Different parts and their functions of Pelton turbine are as follows.

1. Nozzle and Flow Regulating Arrangement
2. Runner and Buckets
3. Casing
4. Braking Jet

Fig 1: Parts of Pelton Turbine

The water from source is transferred through penstock to which end a nozzle is provided. Using this nozzle the high speed water jet can be formed. To control the water jet from nozzle, a movable needle spear is arranged inside the nozzle.

The spear will move backward and forward in axial direction. When it is moved forward the flow will reduce or stopped and when it is moved backward the flow will increase.

2.       Runner and Buckets

A Pelton turbine consists of a runner, which is a circular disc on the periphery of which a number of buckets are mounted with equal spacing between them. The buckets mounted are either doubling hemispherical or double ellipsoidal shaped..

Runner and Buckets of Pelton Wheel

A dividing wall called splitter is provided for each bucket which separates the bucket into two equal parts. The buckets are generally made of cast iron or stainless steel or bronze depending upon the head of inlet of Pelton turbine

3. Casing

The whole arrangement of runner and buckets, inlet and braking jets are covered by the Casing. Casing of Pelton turbine does not perform any hydraulic actions but prevents the splashing of water while working and also helps the water to discharge to the tail race.

Pelton Turbine Model With Casing

4. Braking Jet

Braking jet is used to stop the running wheel when it is not working. This situation arises when the nozzle inlet is closed with the help of spear then the water jet is stopped on the buckets. But Due to inertia, the runner will not stop revolving even after complete closure of inlet nozzle.

To stop this, a brake nozzle is provided as shown in figure . The brake nozzle directs the jet of water on the back of buckets to stop the wheel. The jet directed by brake nozzle is called braking jet.

Working principle of pelton wheel:

Let’s understand by the figure or layout of the hydropower plant, The water is stored at the high head. From there it comes through the penstock and reaches the nozzle of the Pelton turbine. The nozzle increases the kinetic energy of the water and directs the water in the form of the jet.

Now, the jet of water from the nozzle strikes the buckets (vanes) of the runner. So that the runner rotates at very high speed and the quantity of water striking the vanes or buckets is controlled by the spear present inside the nozzle and then the main important process is the generator is attached to the shaft of the runner which converts the mechanical energy (rotational energy) of the runner into an electrical energy.

Water flows from the nozzle with high kinetic energy along the tangent to the path of the runner and when the jet of water comes in contact with the bucket, it exerts a force on the bucket called as Impulse force.

In order to control the quantity of water striking the runner, the nozzle fitted at the end of penstock is provided with a spear or needle fixed to the end of a rod.

In this process, the momentum of the water is transferred to the turbine. The impulse force produced due to this momentum of water causes the turbine to rotate.

The double Semi ellipsoidal buckets split the water jet into two halves which helps in balancing the wheel(runner). This ensures a smooth transfer of the fluid jet to the turbine wheel.

For maximum power and efficiency, the turbine is designed such that, the water Jet velocity is twice the velocity of the bucket.

Advantages of Pelton Wheel:

These are some advantages of Pelton Wheel Turbine:

• The Pelton turbine is the most efficient of hydro turbines.
• It operates with a very flat efficiency curve
• Each bucket splits the water jet in half, thus balancing the side-load forces or thrust on the wheel and thus the bearings.
• It operates on the high head and low discharge.
• It has a tangential flow which means that it can have either axial flow or radial flow.
• Pelton wheel turbine is very easy to assemble.
• There is no cavitation because water jet strikes only a specific portion of the runner.
• It has fewer parts as compared to Francis’s turbine which has both fixed vanes and guided vanes.
• The overall efficiency of the Pelton turbine is high.
• Pelton wheel turbines, both first law and the second law of motion are applied.
• The main advantages are that In this turbine, the whole process of water jet striking and leaving for the runner takes place at atmospheric pressure.

Disadvantages of Pelton Wheel:

And these are some disadvantages of Pelton Wheel Turbine:

• The efficiency decrease very quickly with time.
• The Turbine size runner, generator and powerhouse required is large.
• The variation in the operating head is difficult to control because of high heads.

Application:

Pelton turbine is used in the hydroelectric power plant where the water available at high head i.e. 150 m to 2000 m or even more. In hydroelectric power plant, it is used to drive the generator attached to it and the generator generates the mechanical energy of the turbine into electrical energy.

The Efficiency of the Impulse or Pelton wheel Turbine:

The term “efficiency” is defined as the ratio of work done to the energy supplied.

a)     Hydraulic Efficiency:

It is the ratio of power generated by the runner of the turbine to the water-energy supplied to the bucket of the runner.

The expression is also written as:

Here H is a Net head developed by the water at the inlet, and it can find out by this equation:

b)    Mechanical Efficiency:

It is defined as the power available at the shaft to the power produced by the runner.

c)     Volumetric Efficiency:

It is a ratio of the actual quantity of water on the runner blades per second to the net quantity of water supplied by the jet to the turbine per second is known as volumetric efficiency.

Where Q= Water that actually striking on the runner & Delta Q= Amount of water discharged after striking.

d)    Overall Efficiency:

It is defined as a ratio of the power available at the shaft to the net power available at the base of the nozzle.

e)     Mathematical Formula of Pelton Wheel:

The formula of Calculating Specific Speed of a Pelton Wheel (Where ns=Specific Speed)

f)       Calculation of Torque on the Runner:

T = F(D/2) = p.Q.D (Vi-u)

Where,

p = density

Q= Volume rate of flow of fluid

D= Wheel dia.

F= Force

T= torque of the runner

g)    The formula of Flow Ratio:

It is the ratio of Velocity of flow at inlet to the energy head at the inlet

h)    The Formula of Speed Ratio:

It is the ratio of Peripheral velocity to the energy head at the inlet

i)       The formula of Peripheral velocity:

In the case of Pelton Wheel, the velocity at the inlet (U1) is equal to the velocity of the outlet (U2)

j)       Calculation of Power:

The power P = Fu = T.w where w is the angular velocity of the wheel.

Kaplan turbine:

Kaplan Turbine is an axial reaction flow turbine and has adjustable blades.

If water flows parallel to the axis of the rotation of the shaft, the turbine is known as the axial flow turbine.  And if the head of the inlet of the turbine is the sum of pressure energy and kinetic energy during the flow of water through a runner a part of pressure energy is converted into kinetic energy, the turbine is known as reaction turbine.For the axial flow reaction turbine, the shaft of the turbine is vertical.The lower end of the shaft is made larger which is known a hub or boss.

The vanes are fixed on the hub and hence hub acts as a runner for axial flow reaction turbine.It was developed in 1913 by the Austrian professor Viktor Kaplan.The Kaplan turbine was an evolution of the Francis turbine.

Its invention allowed efficient power production in the low head application that was not possible with Francis turbine.Kaplan turbine is now widely used throughout the world for high-flow, low head power production.

The Kaplan turbine is an axial flow reaction turbine because the water is moving in the axial direction.

Operating parameters of Kaplan Turbine

Head: 10 m to 70 m

RPM: 54.5 to 429

Power output: 5 MW to 200 MW

Runner diameter: 2 m to 11 m

Main Parts of Kaplan Turbine:

A Kaplan Turbine is consisted of:

1. Scroll casing,
2. Guide vane mechanism,
3. Hub with vanes or runner of the turbine, and
4. Draft tube.

The scroll casing is a spiral type of casing that decreases the cross-section area. First, the water from the penstocks enters the scroll casing and then moves to the guide vanes. From the guide vanes, the water turns through 90° and flows axially through the runner.

The scroll casing protects the runner, runner blades, guide vanes and other internal parts of the turbine from external damage to the turbine.

This is the only controlling part of the whole turbine which opens and closes depending upon the demand of power requirement, the more power output requirements, it opens wider to allow more water to hit the blades of the rotor.

And when low power output requires, it closes to cease the flow of water.When the guide vanes are absent then the turbine cannot work efficiently and so that the efficiency of the turbine decreases.

The term “Runner” in the Kaplan turbine plays an important role. The runner is the rotating part of the turbine in which helps in the production of electricity.The shaft is connected to the shaft of the generator.The runner of this turbine has a large boss on which its blades are attached and the blades of the runner are adjustable to an optimum angle of attack for maximum power output.

The blades of the Kaplan turbine have twist along its length.Twist along its length in the Kaplan turbine is provided because to have always the optimum angle of strike for all cross-section of blades and hence to achieve greater efficiency of the turbine.

At the exit of the runner of Reaction Turbine, the pressure available here is generally less than the atmospheric pressure.The water at the exit cannot be directly discharged to the tailrace.A tube or pipe is gradually increasing area and this is used for discharging water from the exit of the turbine to the tailrace.

So, the increasing area of the tube or pipe is called a Draft tube. One end of the draft tube is connected to the runner outlet and the other end is submerged below the level of water in the tail-race.

The main important point is that the Draft tube is used only in the Reaction turbine.

There are 4 types of draft tube:

• Simple Elbow Draft Tube
• Elbow with the varying cross-section
• Moody Spreading Draft Tube.
• Conical Diffuser or Divergent Draft Tube

Working Principle of the Kaplan Turbine:

Kaplan turbine is an axial flow reaction turbine. So the working fluid changes the pressure as it moves across the turbine and gives energy.Power recapitulates from both the Hydrostatic head and kinetic energy of the following water.

From the penstock, the water is coming to enter into the casing. Here flow pressure is not lost because the shape of casing is designed in such a way that it does not lose the flow.From the casing, the water is entering into the guide vane. Here rotor is attached so the water comes with much pressure and hence it rotates the runner.

From the runner, the water enters into draft tube here pressure and kinetic energy decreases. The remaining kinetic energy gets converted into pressure energy and hence increases the pressure of water.Further rotation of the turbine is used to rotate the shaft of a generator and further used for the generation or production of electricity.

Advantages of the Kaplan Turbine:

• This turbine work more efficiently at low water head and high flow rates as compared with other turbines.
• This is smaller in size.
• The efficiency of the Kaplan turbine is very high as compares with other types of hydraulic turbines.
• The Kaplan turbine is easy to construct and
• The space requirement is less.

Disadvantages of Kaplan Turbine:

• The position of the shaft is only in the vertical direction.
• A large flow rate must be required.
• The main disadvantages are the cavitation process. Which occurs due to pressure drops in the draft tube.
• The use of the draft tube and proper material generally stainless steel for the runner blades may reduce the cavitation problem to a greater extent.

Applications of Kaplan Turbine:

• Kaplan turbines are widely used throughout the world for electric power production. They cover the lowest head hydro sites and are especially suited for high flow conditions.
• Inexpensive micro turbines are manufactured for individual power production with as little as two feet of head.
• Large Kaplan turbines are individually designed for each site to operate at the highest possible efficiency, typically over 90%. 
• They are very expensive to design, manufacture and install but operate for decades.

Francis turbine:

The Francis turbine is a mixed flow reaction turbine. This turbine is used for medium heads with medium discharge. Water enters the runner and flows towards the centre of the wheel in the radial direction and leaves parallel to the axis of the turbine.

Turbines are subdivided into impulse and reaction machines. In the impulse turbines, the total head available is converted into the kinetic energy.In the reaction turbines, only some part of the available total head of the fluid is converted into kinetic energy so that the fluid entering the runner has pressure energy as well as kinetic energy. The pressure energy is then converted into kinetic energy in the runner.

The Francis turbine is a type of reaction turbine that was developed by James B. Francis. Francis turbines are the most common water turbine in use today. They operate in a water head from 40 to 600 m and are primarily used for electrical power production. The electric generators which most often use this type of turbine have a power output which generally ranges just a few kilowatts up to 800 MW

Parts Of Francis Turbine

Francis turbine consists mainly of the following parts

a) Spiral or scroll casing – 

It is a closed passage whose cross-sectional area gradually decreases along the flow direction. The area is maximum at the inlet and nearly zero at the outlet.

b) Guide mechanism –

Guides vanes direct the water onto the runner at an angle appropriate to the design. The driving force on the runner is both due to impulse and reaction effects. The number if a runner blade usually varies between 16 and 24.

c) Runner and turbine main Shaft:

d) Draft tube:

It is a gradually expanding tube which discharges the water passing through the runner to the tailrace.

e) Penstock:

It is the large pipe which conveys water from the upstream of the reservoir to the turbine runner.

Spiral casing or scroll Casing:

The casing of the Francis turbine is designed in a  spiral form with a  gradually increasing area. Most of these machines have vertical shafts although some smaller machines of this type have a horizontal shaft. The fluid enters from the penstock (pipeline leading to the turbine from the reservoir at high altitude) to a spiral casing that surrounds the runner.

This casing is known as scroll casing or volute. The cross-sectional area of this casing decreases uniformly along the circumference to keep the fluid velocity constant in magnitude along its path towards the stay vane. This is so because the rate of flow along the fluid path in the volute decreases due to continuous entry of the fluid to the runner through the openings of the stay vanes.

The casing is made of cast steel, plate steel, concrete, or concrete and steel depending upon the pressure to which it is subjected. Out of these a plate steel scroll casing is commonly provided for turbines operating under 30 m or higher heads.

The advantages of this design are

i) Smooth and even distribution of water around the runner.

Ii) Loss of head due to the formation of eddies is avoided.

Iii) The efficiency of the flow of water to the turbine is increased.

In big units stay vanes are provided which direct the water to the guide vanes. The casing is also provided with inspection holes and a pressure gauge connection.

The selection of material for the casing depends upon the head of water to be supplied

For a head up to 30 meters —concrete is used.

For a head from 30 to 60 meters —    welded rolled steel plates are used.

For a head of above 90 meters.    — Cast steel is used.

Guide Mechanism

It consists of a stationary circular wheel all around the runner of the turbine. The stationary guide vanes are fixed on the guide mechanism. The guide vanes allow the water to strike the vanes fixed on the runner without shock at the inlet.

The guide vanes (also called as wicket gates) are fixed between two rings. This arrangement is in the form of a wheel and called a guide wheel. Each vane can be rotated about its pivot canter.

The opening between the vanes can be increased or decreased by adjusting the guide wheel.  The guide wheel is adjusted by the regulating shaft which is operated by a governor. The guide blades rest on pivoted on a ring and can be rotated by the rotation of the ring, whose movement is controlled by the governor. In this way the area of blade passage is changed to vary the flow rate of water according to the load so that the speed can be maintained constant. The variation of area between guide blades is illustrated in Figure

The guide mechanism provides the required quantity of water to the runner depending upon the load conditions.  The guide vanes are in general made of cast steel.

Guide Mechanism For Francis Turbine

Runner and Turbine Main Shaft: 

Runner is a circular wheel on which a series of radial curved vanes are fixed. The surfaces of the vanes are made very smooth. The radial curved vans are so shaped that the water enters and leaves the runner without shocks.The flow in the runner of a modern Francis turbine is partly radial and partly axial.

The runners may be classified as

i) Slow

Ii) Medium

Iii) Fast

The runner may be cast in one piece or made of separate steel plates welded together.  The runner made of CI for small output, cast steel, or stainless steel or bronze for large output. The runner blades should be carefully finished with a high degree of accuracy.The runner may be keyed to the shaft which may be vertical or horizontal. The shaft is made of steel and is forged it is provided with a collar for transmitting the axial thrust.

Draft Tube: 

The pressure at the exit of the runner of a reaction turbine is generally less than atmospheric pressure. The water at the exit cannot be directly discharged to the tailrace. A tube or pipe of the gradually increasing area is used for discharging water from the exit of the turbine to the tailrace. This tube of increasing area is called the draft tube

The water after doing work on the runner passes on to the tall race through a tube called a draft tube.It is made of riveted steel plate or pipe or a concrete tunnel.The cross-section of the tube increases gradually towards the outlet. The draft tube connects the runner exit to the tailrace.This tube should be drowned approximately 1 meter below the tailrace water level.

Function of draft tube –

i) To decrease the pressure at the runner exit to a value less than atmospheric pressure and thereby increase the effective working head.
ii) To recover a part of electric energy into pressure head at the exit of the draft tube. This enables easy discharge to the atmosphere.

Types of draft tube:

i. Conical draft tube
ii. Simple elbow draft tube
iii. Moody spreading draft tube
iv. Elbow draft tube with circular cross-section at inlet and rectangular at outlet

(1) Conical Draft Tubes—

This is known as a tapered draft tube and used in all reaction turbines where conditions permit. It is preferred for low specific speed and Francis turbine. The maximum cone angle is 8° (a = 40°). The hydraulic efficiency is 90%.

(2) Simple Elbow Tubes-

The elbow type draft tube is often preferred in most of the power plants. If the tube is large in diameter; ‘it may be necessary to make the horizontal portion of some other section. A common form of section used is over or rectangular. It has low efficiency of around 60%.

(3) Moody Spreading Tubes-

This tube is used to reduce the whirling action of discharge water when the turbine runs at high speed under low head conditions. The draft tube has an efficiency of around 85%.

(4) Elbow with circular inlet and rectangular outlet—

This tube has circular cross-section at the inlet and rectangular section at the outlet. The change from the circular section to the rectangular section takes place in the bend from the vertical leg to the horizontal leg. The efficiency is about 85%.

Working of Francis turbine:

First, the water is allowed to enter into the spiral casing of the turbine, which guides the water through the stay vanes and guide vanes. The spiral case is kept here in decreasing diameter so that to maintain the flow pressure.

The stay vanes being stationary at their place removes the swirls from the water, which are generated due to flow through the spiral casing and tries it to make the flow of water more linear to be deflected by adjustable guide vanes.

The angle of guide vanes determines the angle of strikes of water at the runner blades thus make sure the output of the turbine. The runner blades are stationary and can-not pitch or change their angle. In short, the guide vane controls the power output of a turbine.

The performance and efficiency of the Francis turbine are dependent on the design of the runner blades.

In a Francis turbine, the runner blades are divided into two parts. The lower half is made in the shape of a small bucket so that it uses the impulse action of water to rotate the turbine.

The other or you can say the upper part of the blades uses the reaction force of water flowing through it. Thus, runner blades make use of both pressure energy and kinetic energy of water and rotate the runner most efficiently.

The water which is coming out of runner blades would lack both the kinetic energy and pressure energy, so we use the draft tube to recover the pressure as it advances towards tailrace, but still, we cannot recover the pressure to that extent that we can stop air to enter into the runner housing thus causing cavitation.

Efficiencies of Francis Turbine:

Hydraulic efficiency:

It is the ratio of work done on the wheel to the head of water (or energy) supplied to the turbine.

Mechanical efficiency:

It is a ratio of actual work available at the turbine to the energy imparted to the wheel.

Overall efficiency:

It is the measure of the performance of a turbine and the ratio of power produced by the turbine to the energy supplied to the turbine.

Blade efficiency:

Let’s see the velocity triangle of an Ideal Francis Turbine:

The formula of Power developed:

Degree of Reaction:

Advantage of Francis Turbine:

1. The difference in the operating head can be extra simply controlled in Francis turbine than in the Pelton wheel turbine.
2. The ratio of utmost and least operating head can even be two in the case of Francis Turbine.
3. The mechanical efficiency of the Pelton wheel decreases faster by wear than Francis turbine.
4. Francis turbine variation in operating head can be more simply controlled.
5. No head failure occurs still at the low discharge of water.

6. The size of the runner and generator is small.

7. Small changes in efficiency over time.

8. Operating head can be utilized even when the variation in tail water level is relatively large when compared to the total head.

Disadvantage of Francis Turbine:

1. The water which is not dirt-free can cause extremely rapid wear in high head Francis turbine.
2. As spiral casing is stranded, the runner is not simply available. Therefore dismantle is hard.
3. The repair and inspection is much harder reasonably.
4. Cavitation is an ever-present hazard.
5. Current losses are certain

6. Head 50 percent lower can be a harmful effect on the efficiency as well as cavitation danger becomes more serious.

Applications of Francis Turbine:

1. This is the most efficient hydraulic turbine.
2. Large Francis turbine is individually designed for the site to operate at the highest possible efficiency, typically over 90%. 
3. Francis type units cover a wide head range, from 20 to 700 M and their output varies from a few kilowatts 200 megawatt. 
4. In addition to electrical products and they may also be used for pumped storage; Where is Reservoir is filled by the turbine (acting as a pump) during low power demand, and then reversed and used to generate power during peak demand. 
5. Francis turbine may be designed for a wide range of heads and flows. This, along with their high efficiency, has made them the most widely used turbine in the world.

3.2 Classification of water pumps, working of centrifugal pumps and reciprocating pumps (Theory of working principles only)

Centrifugal pump is a hydraulic machine which converts mechanical energy into hydraulic energy by the use of centrifugal force acting on the fluid. These are the most popular and commonly used type of pumps for the transfer of fluids from low level to high level. Its is used in places like agriculture, municipal (water and wastewater plants), industrial, power generation plants, petroleum, mining, chemical, pharmaceutical and many others.

Pumps are the mechanical devices that convert mechanical energy into hydraulic energy. They are generally used to raise the water or other fluids from lower elevation to higher elevation. So pumps are generally classified into centrifugal pump and positive displacement pump. Centrifugal pumps are non- positive displacement pumps. They work on the principle of centrifugal action.

The Main parts of Centrifugal Pump are:

1. Impeller

It is a wheel or rotor which is provided with a series of backward curved blades or vanes. It is mounded on the shaft which is coupled to an external source of energy which imparts the liquid energy to the impeller there by making it to rotate.

Fig 2: Open, Semi Enclosed and Enclosed Impeller.

Impellers are divided into following types,:

a) Based on direction of flow:

1)  Axial-flow: – the fluid maintains significant axial-flow direction components from the inlet to outlet of the rotor.

2)  Radial-flow: – the flow across the blades involves a substantial radial-flow component at the rotor inlet, outlet and both.

3) Mixed-flow: – there may be significant axial and radial flow velocity components for the flow through the rotor row.

b) Based on suction type:

1)  Single suction: – liquid inlet on one side.

2)  Double suction: – liquid inlet to the impeller symmetrically from both sides.

c) Based on mechanical construction:

1) Closed: – shrouds or sidewall is enclosing the vanes.

2) Open: – no shrouds or wall to enclose the vanes.

3) Semi–open or vortex type.

2. Casing

It is a pipe which is connected at the upper end to the inlet of the pump to the centre of impeller which is commonly known as eye. The double end reaction pump consists of two suction pipe connected to the eye from both sides. The lower end dips into liquid in to lift. The lower end is fitted in to foot valve and strainer.

Fig 3: Main Components of Centrifugal Pump.

Commonly three types of casing are used in centrifugal pump are –

1) Volute casing: – It is spiral type of casing in which area of flow increase gradually. The increase in area of flow decreases the velocity of flow and increases the pressure of water.

2) Vortex casing: – if a circular chamber is introduced between casing and the impeller, the casing is known as vortex casing.

3) Casing with guide blades: – the impeller is surrounded by a series of guide blades mounted on a ring know as diffuser.

3. Delivery Pipe

It is a pipe which is connected at its lower end to the out let of the pump and it delivers the liquid to the required height. Near the outlet of the pump on the delivery pipe, a valve is provided which controls the flow from the pump into delivery pipe.

4. Suction Pipe with Foot Valve and Strainer

Suction pipe is connected with the inlet of the impeller and the other end is dipped into the sump of water. At the water end, it consists of foot value and strainer. The foot valve is a one way valve that opens in the upward direction. The strainer is used to filter the unwanted particle present in the water to prevent the centrifugal pump from blockage.

Working of Centrifugal Pump:

Water is drawn into the pump from the source of supply through a short length of pipe (suction pipe). Impeller rotates; it spins the liquid sitting in the cavities between the vanes outwards and provides centrifugal acceleration with the kinetic energy.

This kinetic energy of a liquid coming out an impeller is harnessed by creating a resistance to flow. The first resistance is created by the pump volute (casing) that catches the liquid and shows it down.

In the discharge nozzle, the liquid further decelerates and its velocity is converted to pressure according to BERNOULLI’S PRINCIPAL.

Working of a Centrifugal Pump

Let us understand in detail, how a Centrifugal pump works. Centrifugal pumps are used to induce flow or raise a liquid from a low level to a high level. These pumps work on a very simple mechanism. A centrifugal pump converts rotational energy, often from a motor, to energy in a moving fluid.

The two main parts that are responsible for the conversion of energy are the impeller and the casing. The impeller is the rotating part of the pump and the casing is the airtight passage which surrounds the impeller. In a centrifugal pump, fluid enters into the casing, falls on the impeller blades at the eye of the impeller, and is whirled tangentially and radially outward until it leaves the impeller into the diffuser part of the casing. While passing through the impeller, the fluid is gaining both velocity and pressure

Efficiency of centrifugal pump:-

The efficiency of a centrifugal pump can be defined as the ratio of the output power (water) to the input power (shaft). It can be demonstrated by using the following equation.

Ef = PW / PS

Where,

Ef is efficiency

Pw is the water power

Ps is the shaft power

Some other efficiencyis given below:

1. Mechanical efficiency: – It is ratio of the impeller power to the shaft power.
2. Hydraulic efficiency: – It is ratio of the monomeric head to the Euler head.
3. Volumetric efficiency:- It is ratio of the actual to the theoretical discharge.
4. Overall efficiency: – It is ratio of the water power to the shaft power.

Applications of Centrifugal Pumps:

The fact that centrifugal pumps are the most popular choice for fluid movement makes them a strong contender for many applications.They are used across numerous industries. Supplying water, boosting pressure, pumping water for domestic requirements, assisting fire protection systems, hot water circulation, sewage drainage and regulating boiler water are among the most common applications. Outlined below are some of the major sectors that make use of these pumps:

1. Oil & Energy - pumping crude oil, slurry, mud; used by refineries, power generation plants
2. Industrial & Fire Protection Industry - Heating and ventilation, boiler feed applications, air conditioning, pressure boosting, fire protection sprinkler systems.
3. Waste Management, Agriculture & Manufacturing - Wastewater processing plants, municipal industry, drainage, gas processing, irrigation, and flood protection
4. Pharmaceutical, Chemical & Food Industries - paints, hydrocarbons, petrochemical, cellulose, sugar refining, food and beverage production
5. Various industries (Manufacturing, Industrial, Chemicals, Pharmaceutical, Food Production, Aerospace etc.) - for the purposes of cryogenics and refrigerants.

Advantages of Centrifugal Pumps

The centrifugal pumps advantages include the following.

a)     These pumps do not include drive seals that reduce leakage risk.

b)    These pumps are used to pump out harmful and risky fluids.

c)     These pumps have magnetic coupling that can be damaged simply in overload situations as well as protects the pump from external forces.

d)    The motor and pump are separated from each other so heat transfer is impossible from the motor to pump.

e)     These pumps generate low friction.

Disadvantages of Centrifugal Pumps

The centrifugal pumps disadvantages include the following.

a)     The energy loss can be occurred due to the coupling that generates some magnetic resistance.

b)    Once the intense load occurs, possibilities are there for the coupling fall.

c)     If fluids with ferrous particles are pumped out, then rust occurs & over the time pumps stops working.

d)    When the flow of liquid is less through the pump, then the overheating can occur

Reciprocating pumps:

Reciprocating pump is a positive displacement pump where certain volume of liquid is collected in enclosed volume and is discharged using pressure to the required application. Reciprocating pumps are more suitable for low volumes of flow at high pressures.

It is very important part of the ships machinery and any other industry which is present in the world. High pressure is the main characteristic of this pump and this high pressure output are being used in places like starting of the engine or you can say the building of pressure in the fluids.

But there are used in limited application because they require lot of maintenance. These pumps are positive displacements pumps and that is the reason they do not require any type of priming for their functioning in the starting period of the pump.

Parts of Reciprocating Pump:

The Parts of Reciprocating Pump are as follows.

1. Water Sump
2. Strainer
3. Suction Pipe
4. Suction Valve
5. Cylinder
6. Piston and Piston rod
7. Crank and Connecting rod
8. Delivery valve
9. Delivery pipe

The explanation for the parts of reciprocating pump is as follows.

1. Water Sump:

It is the source of water. From the sump, water is to be transported to the delivery pipes by the usage of the piston.

II.            Strainer:

It acts as a mesh that can screen all the dirt, dust particles, etc. from the sump. If there is no strainer, then the dirt or dust also enters into the cylinder which can jam the region and affects the working of the pump.

III.            Suction Pipe:

The main function of the suction pipe is to collect the water from the sump and send it to the cylinder via a suction valve. The suction pipe connects the water sump and the cylinder.

IV.            Suction Valve:

It is a non-return valve which means it can take the fluid from the suction pipe and send it to the cylinder but cannot reverse the water back to it. In the sense, the flow is unidirectional.

This valve opens only during the suction of fluid and closes when there is a discharge of fluid to outside.

V.            Cylinder:

It is a hollow cylinder made of cast iron or steel alloy and it consists of the arrangement of piston and piston rod.

VI.            Piston and Piston rod:

For suction, the piston moves back inside the cylinder and for discharging of fluid, the piston moves in the forward direction.

The Piston rod helps the piston to move in a linear direction i.e. either the forward or the backward directions.

VII.            Crank and Connecting rod:

For rotation, the crank is connected to the power source like engine, motor, etc. whereas the connecting rod acts as an intermediate between the crank and piston for the conversion of rotary motion into linear motion.

VIII.            Delivery Pipe:

The function of the delivery pipe is to deliver the water to the desired location from the cylinder.

IX.            Delivery valve:

Similar to the suction valve, a delivery valve is also a Non-return valve. During suction, the delivery valve closes because the suction valve is in opening condition and during Discharge, the suction valve is closed and the delivery valve is opened to transfer the fluid.

Working Principle of Reciprocating Pump:

When the power supply is given to the reciprocating pump, the crank rotates through an electric motor.The angle made by the crank is responsible for the movement of the piston inside the cylinder. By referring to the above diagram, the piston moves towards the extreme left of the cylinder when the crank meets position A i.e. θ=0.

Similarly, the piston moves towards the extreme right of the cylinder when the crank meets the position C i.e. θ=180.

A partial vacuum in the cylinder takes place when the piston movement is towards the right extreme position i.e. (θ=0 to θ=180.) and that makes the liquid enter into the suction pipe.This is due to the presence of atmospheric pressure on the sump liquid which is quite less than the pressure inside the cylinder. Therefore, due to the difference in pressure, the water enters into the cylinder through a non-return valve.

The water which stays in the volume of the cylinder has to be sent to the discharge pipe via discharge valve and this can be done when the crank is rotating from C to A i.e. (θ=180 to θ=360) which moves the piston in the forward direction.Due to the movement of the piston in a forward direction, the pressure increases inside the cylinder which is greater than the atmospheric pressure.

This results in the opening of the delivery valve and closing of the suction valve.Once the water comes into the delivery valve, it cannot move back to the cylinder because it is a unidirectional valve or non-return valve.

From there, it enters into the delivery pipe so that it can be sent to the required position.Therefore, in this way, the water is sucked and discharged from the sump to the desired location through the piston inside the cylinder.

Reciprocating Pump Advantages:

Reciprocating Pump Disadvantages:

1. Flow is not consistent, so we have to fit a bottle at equally ends.

2. Flow is extremely less and cannot use for high flow process.

3. High wear and tear, so need lot maintenance.

4. Early price is much more in this pump.

5. Additional heavy and large in shape.

6. Low discharging capacity

7. The maintenance cost is very high due to the presence of a large number of parts.

8. The initial cost of this pump is high.

9. Viscous fluids are difficult to pump.

Applications of Reciprocating Pump:

Power plants:

3.3 Hydro-electric power plants

Hydroelectric power is developed from hydroelectric power plant or hydroelectric power station. It develops hydroelectricity to utilize the potential energy of water. In hydroelectric power plant, water is stored in a dam called hydroelectric dam which is located upper level from the ground especially any hilly areas. Water head is created by construction the dam across any river or lake.

This type of water head store huge potential energy. The water fall into water turbine and the potential energy of water is converted into kinetic energy. This kinetic energy is converted into mechanical energy at the turbine shaft. A hydroelectric generator or alternator is coupled with turbine shaft to convert mechanical energy into electrical energy.

The power P is developed-

Here,

W = Specific weight of water in kg/m3

Q = Rate of flow of water in m3/s

H = Height of fall or head in meters

η = Overall efficiency of operation

Hydroelectric power plant is becoming very popular nowadays to full feel rapid increasing demand of electric power day by day. Every country is trying to develop more Hydro Electric Power Station to full fill their demand for electricity. In other hand fossils, fuels (coal, oil, and gas) are limited stock in the world and these fuels are expensive. So hydroelectricity may be a good alternative electrical source. So in a single word we can say, a generating Station which utilizes the potential energy of high-level water for the generating of electrical energy is known as hydropower plant or hydroelectric power plant.

Constituents of a hydro-electric plant

The constituents of hydro-electric power station can be divided mainly into three categories 1) hydraulic structure 2) water turbines 3) electrical equipment.

Hydraulic structure:

Hydraulic structure of hydro-electric power station includes a dam, spillways, head works, surge tank, and penstock.

1) Dam: 

The place where the water can be store and creates water head. Dams are mostly built of concrete or stone masonry, the type and arrangement depend on the location of the site. The type of dam also depends on the foundation condition, local material, and transportation available. The dam should not be very expensive.

2) Spillways: 

There are times when the water head exceeds the storage capacity of the reservoir. Such situation can affect the whole process. In order to discharge the surplus water from the storage area into the river downstream. A concrete path constructed alongside the dam called spillways is used to drain the excess water.

3) Headwork’s:

The headwork’s consist of the diversion structures at the head of an intake. It controls the flow of water into and through headwork’s should be as smooth as possible to avoid heat loss.

4) Surge tank: 

When the open conduit is used to carry water to the turbine it requires no protection but when the closed conduit is used it needs protection to limit the pressure in the conduit. For this reason, a surge tank is used for closed conduit. The surge tank is a small reservoir or tank in which water level rises or falls to reduce the pressure.

5) Penstock: 

Penstocks are open or closed conduits which carry water to the turbines. They are mostly made of reinforced concrete or steel.

Water turbines:

Those devices which convert water’s kinetic energy into mechanical energy are called water turbines. There are so many turbines used to generate mechanical effort.1) impulse turbines 2) reaction turbines.

Reaction turbine has two types 1) Francis turbines 2) Kaplan turbines

Electrical equipment: 

Every power station consists of different electrical types of equipment. There are so many types of equipment can be used for example alternator, exciter, Dc batteries, relays, circuit breakers, measuring devices, controlling devices, electrical motors etc.

WORKING PRINCIPLE OF HYDROELECTRIC POWER PLANT

Working principle of hydroelectric power plant depends on the conversion of hydraulic energy into electrical energy. To get this hydroelectricity, hydroelectric power plant needs some arrangements for proper working and efficiency. The block diagram of hydroelectric power plant is shown below:
 

Hydroelectric power station needs huge amount of water at sufficient head all the time. So a hydroelectric dam is constructed across the river or lake.an artificial storage reservoir where water is stored, is placed back side of the dam. This reservoir creates sufficient water head. A pressure tunnel is placed in between the reservoir to valve house and water is coming from reservoir to penstock via this tunnel. An automatic controlling sluice valve is placed in valve house and it controls water flow to the power station and the letter cuts off supply of water in case the penstock bursts. Penstock is a huge steel pipe in which water is taken from valve house to turbine. A surge tank is also provided just before the valve house for better regulation of water pressure in the system. Now water turbine converts hydraulic energy into mechanical energy and an alternator which is couple to the water turbine converts this mechanical energy into electrical energy.

Site selection criteria

1. Water Availability:

Main fuel of this plant is water. So, such plant should be located nearer to river, canal etc. where sufficient water is available all the time.

2.     Water Storage:

Storage of water in a suitable reservoir or dam has to be placed by a careful geological study of the area to get the maximum advantage of that water. Dam should be located across the river to get continuous water supply throughout the year especially in a dry season. The storage capacity of dam can be determined by hydrograph or mass curve or using analytical method. Adequate facilities of erection a dam and storage of water are two important matters for site selection of hydroelectric power plant.

3.     Water Head:

It is an important point for site selection of hydroelectric power plant. Water head is directly related to the cost of generation of electric power. If effective head is increased, water storage has to be reduced as well as capital cost of the plant is reduced.

4.     Distance from the load center:

Since it is located away from the load center, more transmission line is required to supply the power. To avoid the line loss and economical power supply, distance of such plant should need more attention.

5.     Transportation Facilities:

Good transportation facilities must be available to any hydroelectric power plant, so that necessary equipment should be reached easily.

6.     Availability of land:

Hydroelectric power plant needs enough space. It should be kept in mind that land cost must be cheap.

 Advantage and disadvantage

ADVANTAGES & DISADVANTAGES OF HYDROELECTRIC POWER PLANT

Advantages

There are lots of advantages in Hydroelectric Power Plant:

1. Since water is the main source of energy, so no fossil fuels are required.

2. This plant is neat and clean and no smoke or as disposal is required.

3. It is the cheapest operating and maintenance cost as compared to the other power plants because water is freely available in the world.

4. It is very reliable, robust and has a longer life app rocks 45 to 60 years.

5. This plant can start instantly.

6. It can start hydroelectric power with fluctuating load demand.

7. The efficiency does not fall at the age of this plant.

8. There is no standby loss in this plant.

9. At the initial time of construction highly skilled engineers are required and after that only few experience persons can run the plant.

10. This plant also serves to help in irrigation and Flood control etc.

11. Since this plants are located remote area so land is available and competitively cheaper rates.

Disadvantages

There are some Disadvantages in hydro power plant:

1. Such plant requires large area

2. High construction cost is required due to construction of dam.

3. When experience skilled engineers are required to build this plant

4. Scenes such plant is located as from the load areas, long transmission line is required to transmit this hydroelectric power.

5. It doesn't supply constant hydroelectricity due to the availability of water. In transition, power supply is most affected.

3.4 Thermal power plants

Thermal energy is the major source of power generation in India. More than 60% of electric power is produced by steam plants in India. India has large deposit of coal (about 170 billion tonnes), 5th largest in world. Indian coals are classified as A-G grade coals.

In Steam power plants, the heat of combustion of fossil fuels is utilized by the boilers to raise steam at high pressure and temperature. The steam so produced is used in driving the steam turbines or sometimes steam engines couples to generators and thus in generating electrical energy.

Steam turbines or steam engines used in steam power plants not only act as prime movers but also as drives for auxiliary equipment, such as pumps, stokers fans etc.  Steam power plants may be installed either to generate electrical energy only or generate electrical energy along with generation of steam for industrial purposes such as in paper mills, textile mills, sugar mills and refineries, chemical works, plastic manufacture, food manufacture etc.

The steam for process purposes is extracted from a certain section of turbine and the remaining steam is allowed to expand in the turbine. Alternatively the exhaust steam may be used for process purposes.  Thermal stations can be private industrial plants and central station

Components of Coal Fired Thermal Power Station:

         Coal Preparation

In coal-fired power stations, the raw feed coal from the coal storage area is first crushed into small pieces and then conveyed to the coal feed hoppers at the boilers. The coal is next pulverized into a very fine powder, so that coal will undergo complete combustion during combustion process.

Pulverizer is a mechanical device for the grinding of many different types of materials. For example, they are used to pulverize coal for combustion in the steam-generating furnaces of fossil fuel power plants.

Types of Pulverisers: Ball and Tube mills; Ring and Ball mills; MPS; Ball mill; Demolition.

They are used in order to remove the excess moisture from coal mainly wetted during transport. As the presence of moisture will result in fall in efficiency due to incomplete combustion and also result in CO emission. 

Coal which is brought may contain iron particles. These iron particles may result in wear and tear. The iron particles may include bolts, nuts wire fish plates etc.

So these are unwanted and so are removed with the help of  magnetic separators.

The coal we finally get after these above process are transferred to the storage site.

Purpose of fuel storage –

• Fuel storage is insurance from failure of normal operating supplies to arrive.
• Storage permits some choice of the date of purchase, allowing the purchaser to take advantage of seasonal market conditions. Storage of coal is primarily a matter of protection against the coal strikes, failure of the transportation system & general coal shortages.

There are two types of storage:

1. Live Storage (boiler room storage): storage from which coal may be withdrawn to supply combustion equipment with little or no remanding is live storage. This storage consists of about 24 to 30 hours of coal requirements of the plant and is usually a covered storage in the plant near the boiler furnace. The live storage can be provided with bunkers & coal bins. Bunkers are enough capacity to store the requisite of coal. From bunkers coal is transferred to the boiler grates.
2. Dead storage- stored for future use. Mainly it is for longer period of time, and it is also mandatory to keep a backup of fuel for specified amount of days depending on the reputation of the company and its connectivity. There are many forms of storage some of which are –
   1. Stacking the coal in heaps over available open ground areas.
   2. As in (I). But placed under cover or alternatively in bunkers.
   3. Allocating special areas & surrounding these with high reinforced concerted retaking walls.

         Boiler and auxiliaries

A Boiler or steam generator essentially is a container into which water can be fed and steam can be taken out at desired pressure, temperature and flow. This calls for application of heat on the container. For that the boiler should have a facility to burn a fuel and release the heat. The functions of a boiler thus can be stated as:-

1. To convert chemical energy of the fuel into heat energy
2. To transfer this heat energy to water for evaporation as well to steam for superheating.

The basic components of Boiler are: -

1. Furnace and Burners
2. Steam and Superheating

a. Low temperature super heater

b. Platen super heater

c. Final super heater

         Economiser

It is located below the LPSH in the boiler and above pre heater. It is there to improve the efficiency of boiler by extracting heat from flue gases to heat water and send it to boiler drum.

Advantages of Economiser include

1) Fuel economy: – used to save fuel and increase overall efficiency of boiler plant.

2) Reducing size of boiler: – as the feed water is preheated in the economiser and enter boiler tube at elevated temperature. The heat transfer area required for evaporation reduced considerably.

         Air Preheater

The heat carried out with the flue gases coming out of economiser are further utilized for preheating the air before supplying to the combustion chamber. It is necessary equipment for supply of hot air for drying the coal in pulverized fuel systems to facilitate grinding and satisfactory combustion of fuel in the furnace.

         Reheater

Power plant furnaces may have a reheater section containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the reheater tubes to pick up more energy to go drive intermediate or lower pressure turbines.

         Steam turbines

Steam turbines have been used predominantly as prime mover in all thermal power stations. The steam turbines are mainly divided into two groups: -

1. Impulse turbine
2. Impulse-reaction turbine

The turbine generator consists of a series of steam turbines interconnected to each other and a generator on a common shaft. There is a high pressure turbine at one end, followed by an intermediate pressure turbine, two low pressure turbines, and the generator. The steam at high temperature (536 ‘c to 540 ‘c) and pressure (140 to 170 kg/cm2) is expanded in the turbine.

         Condenser

The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases. 

The functions of a condenser are:-

1) To provide lowest economic heat rejection temperature for steam.

2) To convert exhaust steam to water for reserve thus saving on feed water requirement.

3)  To introduce make up water.

We normally use surface condenser although there is one direct contact condenser as well. In direct contact type exhaust steam is mixed with directly with D.M cooling water.

         Boiler feed pump

Boiler feed pump is a multi-stage pump provided for pumping feed water to economiser. BFP is the biggest auxiliary equipment after Boiler and Turbine. It consumes about 4 to 5 % of total electricity generation.

         Cooling tower

The cooling tower is a semi-enclosed device for evaporative cooling of water by contact with air. The hot water coming out from the condenser is fed to the tower on the top and allowed to tickle in form of thin sheets or drops. The air flows from bottom of the tower or perpendicular to the direction of water flow and then exhausts to the atmosphere after effective cooling.

The cooling towers are of four types: -

1. Natural Draft cooling tower

2. Forced Draft cooling tower

3. Induced Draft cooling tower

4. Balanced Draft cooling tower

         Fan or draught system

In a boiler it is essential to supply a controlled amount of air to the furnace for effective combustion of fuel and to evacuate hot gases formed in the furnace through the various heat transfer area of the boiler. This can be done by using a chimney or mechanical device such as fans which acts as pump.

i) Natural draught 

When the required flow of air and flue gas through a boiler can be obtained by the stack (chimney) alone, the system is called natural draught. When the gas within the stack is hot, its specific weight will be less than the cool air outside; therefore the unit pressure at the base of stack resulting from weight of the column of hot gas within the stack will be less than the column of extreme cool air. The difference in the pressure will cause a flow of gas through opening in base of stack. Also the chimney is form of nozzle, so the pressure at top is very small and gases flow from high pressure to low pressure at the top.

Ii) Mechanized draught

There are 3 types of mechanized draught systems

1)   Forced draught system

2)   Induced draught system

3)   Balanced draught system

1) Forced draught: – In this system a fan called Forced draught fan is installed at the inlet of the boiler. This fan forces the atmospheric air through the boiler furnace and pushes out the hot gases from the furnace through super heater, reheater, economiser and air heater to stacks.

2) Induced draught: – Here a fan called ID fan is provided at the outlet of boiler, that is, just before the chimney. This fan sucks hot gases from the furnace through the superheaters, economiser, reheater and discharges gas into the chimney. This results in the furnace pressure lower than atmosphere and affects the flow of air from outside to the furnace.

3) Balanced draught:-In this system both FD fan and ID fan are provided. The FD fan is utilized to draw control quantity of air from atmosphere and force the same into furnace. The ID fan sucks the product of combustion from furnace and discharges into chimney. The point where draught is zero is called balancing point.

         Ash handling system

The disposal of ash from a large capacity power station is of same importance as ash is produced in large quantities. Ash handling is a major problem.

i) Manual handling: While barrows are used for this. The ash is collected directly through the ash outlet door from the boiler into the container from manually.

Ii) Mechanical handling: Mechanical equipment is used for ash disposal, mainly bucket elevator, belt conveyer. Ash generated is 20% in the form of bottom ash and next 80% through flue gases, so called Fly ash and collected in ESP.

Iii) Electrostatic precipitator: From air preheater this flue gases (mixed with ash) goes to ESP. The precipitator has plate banks (A-F) which are insulated from each other between which the flue gases are made to pass. The dust particles are ionized and attracted by charged electrodes. The electrodes are maintained at 60KV.Hammering is done to the plates so that fly ash comes down and collect at the bottom. The fly ash is dry form is used in cement manufacture.

         Generator

Generator or Alternator is the electrical end of a turbo-generator set. It is generally known as the piece of equipment that converts the mechanical energy of turbine into electricity. The generation of electricity is based on the principle of electromagnetic induction.

Sites selection criteria

The site of the thermal power plant is chosen with some specific conditions. The condition that must be fulfilled to build a thermal power is explained as below.

• Availability of Coal

A huge amount of coal is required for the generation of electrical energy. The thermal power station of 400 MW capacities requires 5000 to 6000 tons of coal per day. Therefore, thermal power stations should be located near to the coal mines to minimize the transportation cost.

• Ash Disposal Facilities

Ash produced after burning the coal is about 20 to 40% of the weight of the coal i.e. 1500 to 2000 tons per day. Thus, it becomes a more serious problem as it comes out in hot conditions and is highly corrosive. Therefore, there must be sufficient space available for the disposal of a large quantity of ash.

• Space Requirement

Space required for thermal power station is quite large for plant equipment, coal storage, ash disposal, staff colony, etc. The land available for the thermal power station must be available at low cost and with sufficient bearing capacity to withstand the load of machinery.

• Availability of Water

As the secondary requirement of the thermal power station is water.

The water is required for two purposes, firstly for conversation into steam for steam turbine and secondly for a condenser. Hence such power plants should be located near to the water resource such as river, lake, or canal.

• Transportation Facility

Power station should have the transportation facility such that as road and rail for transportation of material and machinery.

• Away from Populated Area

The thermal power station produces smoke and fumes by burning a huge amount of coal. This pollutes the atmosphere. Hence plants should be located at a considerable distance from the populated area.

• Near to the Load Center

Power stations should be located near to the load center to minimize the cost transmission system to transfer the electricity.

Environmental aspects for Site Selection of Thermal Power Plant

      Air Pollution

Particulate meters SO2, NO2, and CO2 are emitted from the combustion of fuels in a thermal Power plant. If the uncontrolled, these affect humans, vegetation, buildings, and monuments, aquatic forest ecosystem.

The emission of large quantities of SO2 and NO2 from Thermal power plant may result in Acid-rain problems.

      Waste Water Discharge

The large wastewater streams from Thermal power plant are cooling water below down, which can be either recycled or discharged to a surface water body, and then its chemical quality gets affected. Associated waste heat can impact ambient water temperature which in turn can radically alter aquatic plant and animal communities.

Other effluents from a Thermal power plant, like wastewater from de-mineralized backwash and resin regenerator wastewater, ash transport water and runoff from  ash piles and sites, trace metals, acids and other chemicals in various combinations in the effluents, oil spills, etc. harm water quality.

      Land Degradation

The thermal power stations are generally located on the non-forest land and do not involve much resettlement and rehabilitation problems.

However, its effects due to stack emission, etc. on flora and fauna, agricultural and other land have to be studied for any element percolation to groundwater through ash disposal in ash ponds are the serious effects of thermal power stations.

      Noise Pollution

Some areas inside the plant will have noisy equipment such as crushers, belt conveyors, fans, pumps, milling plants, compressors, boiler, turbine, etc. Various measures to reduce the noise generation and exposure of workers to high noise levels in the plant area include silencers of fans, compressors, steam safety valves, etc., using noise absorbent materials, providing noise barriers for various areas, noise-proof control rooms.

Advantage and disadvantage

Advantages The advantages of thermal power plants are listed below.

• The thermal power station has less initial cost as compared to the hydro-electric generating station.
• It requires less space as compared to the hydro power plant.
• The fuel cost is less as compared to a gas power plant.
• It can be installed at any location irrespective of coal mines. Coal can be transported to the site by road and rail.
• The huge amount of power can be generated by the thermal power station.

DisadvantagesThe disadvantages of thermal power plants are listed below.

• The running cost of the thermal power station is more as compared to the hydro generating station.
• It pollutes the atmosphere due to the production of a large amount of smoke and fumes.
• Maintenance cost is more.
• A skilled person is required for the Erection and Maintenance of the power station.
• Starting time is quite high (6 to 7 hours from the cold condition). Hence not suitable for peak loads.
• The overall efficiency of the thermal power station is very low (about 29%).

• Unavailability of good quality coal
• Maximum of  heat  energy lost
• Problem of ash removing

3.5 Nuclear power plants

The heat energy in the nuclear power plant can be generated through a nuclear reaction or nuclear fission. The heavy elements of nuclear fission are Uranium/Thorium is carried out within a special device called a nuclear reactor. A huge amount of energy can be generated because of nuclear fission. The rest parts within the nuclear, as well as conventional thermal plants, are the same. The fission of 1 Kg Uranium generates heat energy which is equal to the energy generated through 4500 tons of high-grade coal. This significantly decreases the fuel transportation cost, so it is a major benefit of these plants. Worldwide, there are huge deposits of fuels existing; therefore, these plants can supply electrical energy continuously for hundreds of years. Nuclear power plants generate 10% of the electricity from the whole electricity in the world.

The power plant that is used to warm the water to generate steam, then this steam can be used for rotating huge turbines for generating electricity. These plants use the heat to warm the water which is generated by nuclear fission. So the atoms in the nuclear fission will split into different smaller atoms for generating energy.

Nuclear Power Plant Working Principle

In the power plant, the fission takes place in the reactor and the middle of the reactor is known as the core that includes uranium fuel, and this can be formed into pellets of ceramic. Every pellet generates 150 gallons of oil energy. The total energy generated from the pellets is stacked in metal fuel rods. A bunch of these rods is known as a fuel assembly and a reactor core includes several fuel assemblies.

During nuclear fission, the heat can be generated within the core of the reactor. This heat can be used to warm the water into steam so that turbine blades can be activated. Once the turbine blades activated then they drive the generators to make electricity. In a power plant, a cooling tower is available to cool the steam into the water otherwise they use the water from different resources. Finally, the cooled water can be reused to generate steam.

Components of Nuclear Power Plant

In the above nuclear power plant block diagram, there are different components which include the following.

1) Nuclear Reactor

In a power plant, a nuclear reactor is an essential component like a heat source that includes the fuel & its reaction of nuclear chain including the waste products of nuclear. The nuclear fuel used in the nuclear reactor is Uranium & its reactions are heat generated in a reactor. Then, this heat can be transferred to the coolant of the reactor to generate heat to all the parts in the power plant.

There are different types of nuclear reactors that are used in the manufacturing of plutonium, ships, satellites & aircraft for research as well as medical purposes. The power plant includes not only includes the reactor and also includes turbines, generators, cooling towers, a variety of safety systems.

2) Steam Generation

In all the power plants, the production of steam is general; however, the way of generating will change. Most of the plants use water reactors by using two loops of rotating water to generate steam. The primary loop carries very hot water for heating an exchange once water at a low-pressure is circulated, then it warms the water to generate the steam to transmit to the turbine section.

3) Generator & Turbine

Once the steam is generated, then it travels with high pressures to speed up the turbine. The rotating of the turbines can be used to rotate an electric generator for generating electricity that is transmitted to the electrical grid.

4) Cooling Towers

In a nuclear power plant, the most essential part is a cooling tower which is used to reduce the heat of the water. Please refer to this link to know more about what is a cooling tower – components, construction & applications

Working of Nuclear Power Plant

The elements like Uranium or Thorium are sued nuclear fission reaction of a nuclear reactor. Because of this fission, a huge amount of heat energy can be generated and it is transmitted to the coolant reactor. Here, the coolant is nothing but water, liquid metal otherwise gas. The water is heated to flow in a heat exchanger so that it changes into high-temperature steam. Then the steam which is produced is permitted to make a steam turbine run. Again the steam can be changed back into the coolant & recycled to use for the heat exchanger. So, the turbine and alternator are connected to produce electricity. By using a transformer, the electricity which is produced can be increased to use in long-distance communication.

PWR and BWR

Site Selection for Nuclear Power Plant

The selection of the site for nuclear PowerPoint can be done by considering the technical requirement. The arrangement and working of a nuclear power plant mainly depend on the characteristics of the site.
While designing the plant, the risks from the site must be considered. The plant design has to handle with tremendous natural occurrence & human-induced actions, without damaging the operational security of the plant.

Each site has to give needed necessities like discarded and decay heat sinks, power supply availability, excellent communications and efficient crisis management, etc. For a power plant, the estimate of the site typically occupies different stages like selection, characterization, pre-operational, and operational.

The purpose of characterisation of any particular area during the site selection stage is to determine the suitability of particular site for setting up a Nuclear Power Project (NPP). In this stage, geological, geo-morphological and geo-technical aspects are considered and regions or areas are usually identified that are excluded from further consideration. Subsurface information for this stage is usually obtained from current and historical documents, field reconnaissance, including geological surveys. In the recent past, remote sensing played great role in obtaining detailed and accurate information with minimum effort within least possible time frame. For a nuclear power plant, site evaluation typically involves the following stages, 

a. Selection stage: One or more preferred candidate sites are selected after investigation of a large region, rejection of unsuitable sites, and screening and comparison of the remaining sites.

b. Characterization stage: This stage is further subdivided into:

• Verification-In which the suitability of the site to host a nuclear power plant is verified mainly according to predefined site exclusion criteria;

• Confirmation-In which the characteristics of the site necessary for the purposes of analysis and detailed design are determined.

c. Pre-operational stage: Studies and investigations from the previous stages are continued to refine the assessment of site characteristics. Data obtained from site allow a final assessment of simulation models used in the ultimate design of foundation and superstructure as well.

d. Operational stage: Selected investigations are pursued over the lifetime of the plant, to ensure that the variation of engineering properties are not varying significantly during the operating life of the plan

Advantages and disadvantages

Advantages

The advantages of nuclear power plants include the following.

Disadvantages

The disadvantages of nuclear power plants include the following.

Applications

The applications of nuclear power plants include the following.

Nuclear energy is used in different industries all over the world for desalination of ocean water, production of hydrogen, district cooling/heating, the removal of tertiary oil resources & used in heat processapplications like cogeneration, conversion of coal to liquids & help in the chemical feedstock synthesis.

3.6 Diesel power plants

By the end of the nineteenth century there mountains of useless coal dust had piled up in the Ruhr valley in Germany, and Rudolf Diesel started to work to develop an engine that would burn coal dust. The attempts to design such an engine failed, but in 1892, Diesel was issued a patent for a proposed system in which air would be so greatly compressed that the temperature would far exceed the ignition temperature of an oil fuel. Ever since, internal combustion engines have been providing shaft power. There are basically two main types of diesel power plants combustion engines categorized by the type of fuel used: gasoline or diesel.

The vast majority of those engines power automobiles, but they have been also used for ships, boats, agricultural processing machinery, and many other industrial applications. During the last quarter of the twentieth century abundant fossil fuel production and distribution made possible commercial application of diesel-powered electricity generation for several applications. In addition, hybrid schemes were deployed to integrate and complement intermittent distributed generation systems. Diesel-based low power generation consists basically of a diesel engine coupled to an electric power generator and a field-exciting generator. The arrangement isvery compact, it goes online in a very short lead time, requires only routine maintenance, and is easily available through practicing professionals in mechanical workshops and garages. Diesel engines have some disadvantages: They are noisy, polluting, driven economically by fuel costs (and thus captive to world politics), require fuel storage close to the power plant, and require logistics and infrastructure for transportation. Figure depicts a typical arrangement of a small diesel engine–powered plant. Since a conventional synchronous generator is used, special attention to frequency and synchronization is required.

3.7 Wind mills

Wind energy is a form of solar energy. Wind energy (or wind power) describes the process by which wind is used to generate electricity. Wind turbines convert the kinetic energy in the wind into mechanical power. A generator can convert mechanical power into electricity. Mechanical power can also be utilized directly for specific tasks such as pumping water.

Wind is caused by the uneven heating of the atmosphere by the sun, variations in the earth's surface and rotation of the earth. Mountains, bodies of water, and vegetation all influence wind flow patterns.

Wind turbines convert the energy in wind to electricity by rotating propeller-like blades around a rotor. The rotor turns the drive shaft, which turns an electric generator. Three key factors affect the amount of energy a turbine can harness from the wind: wind speed, air density, and swept area.

Equation for Wind Power

P = ½ (pAV3)

P= density

Wind speed

The amount of energy in the wind varies with the cube of the wind speed, in other words, if the wind speed doubles, there is eight times more energy in the wind ( 23 = 2 x 2 x 2 = 8).Small changes in wind speed have a large impact on the amount of power available in the wind.

Density of the air

The more dense the air, the more energy received by the turbine. Air density varies with elevation and temperature. Air is less dense at higher elevations than at sea level, and warm air is less dense than cold air. All else being equal, turbines will produce more power at lower elevations and in locations with cooler average temperatures.

Swept area of the turbine

The larger the swept area (the size of the area through which the rotor spins), the more power the turbine can capture from the wind. Since swept area is A = pi x r2where r = radius of the rotor, a small increase in blade length results in a larger increase in the power available to the turbine.

Wind energy benefits

1)     Renewable energy

2)     Inexhaustible

3)     Not pollutant

4)     Reduces the use of fossil fuels

5)     Reduces energy imports

6)     Creates wealth and local employment

7)     Contributes to sustainable development

3.8 Solar energy (Working principles using schematic representations only)

The Sun is the biggest source of renewable energy for the Earth. The fact is that even though the earth receives only a part of the energy generated by the Sun (i.e. Solar energy), that part of solar energy is also tremendously huge. The Earth receives solar energy in the form of light and heat. But in today's world, the words 'power' and 'energy' are leaned more towards 'electricity'. This article explains how electricity is harvested from the solar energy and how it is utilized.
 

How Solar Power Works?

Electrical energy can be harvested from solar power by means of either photovoltaic or concentrated solar power systems.

Photovoltaic (PV)

Photovoltaic directly convert solar energy into electricity. They work on the principle of the photovoltaic effect. When certain materials are exposed to light, they absorb photons and release free electrons. This phenomenon is called as the photoelectric effect. Photovoltaic effect is a method of producing direct current electricity based on the principle of the photoelectric effect.

Based on the principle of photovoltaic effect, solar cells or photovoltaic cells are made. They convert sunlight into direct current (DC) electricity. But, a single photovoltaic cell does not produce enough amount of electricity. Therefore, a number of photovoltaic cells are mounted on a supporting frame and are electrically connected to each other to form a photovoltaic module or solar panel. Commonly available solar panels range from several hundred watts (say 100 watts) up to few kilowatts (ever heard of a 5kW solar panel?). They are available in different sizes and different price ranges. Solar panels or modules are designed to supply electric power at a certain voltage (say 12v), but the current they produce is directly dependent on the incident light. As of now it is clear that photovoltaic modules produce DC electricity. But, for most of the times we require AC power and, hence, solar power system consists of an inverter too.

Photovoltaic Solar Power System

According to the requirement of power, multiple photovoltaic modules are electrically connected together to form a PV array and to achieve more power. There are different types of PV systems according to their implementation.

• PV direct systems: These systems supply the load only when the Sun is shining. There is no storage of power generated and, hence, batteries are absent. An inverter may or may not be used depending on the type of load.
• Off-grid systems: This type of system is commonly used at locations where power from the grid is not available or not reliable. An off-grid solar power system is not connected to any electric grid. It consists solar panel arrays, storage batteries and inverter circuits.
• Grid connected systems: These solar power systems are tied with grids so that the excess required power can be accessed from the grid. They may or may not be backed by batteries.

Concentrated Solar Power

As the name suggest, in this type of solar power system, sun rays are concentrated (focused) on a small area by placing mirrors or lenses over a large area. Due to this, a huge amount of heat is generated at the focused area. This heat can be used to heat up the working fluid which can further drive the steam turbine. There are different types of technologies that are based on the concentrated solar power to produce electricity. Some of them are - parabolic trough, Stirling dish, solar power tower etc. The following schematic shows how a solar power tower works.