1- Power Plant Engineering

8/10/2019 1- Power Plant Engineering

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Electrical Power Plant Engineering

Dr. Fouad Zaro

Assistant Professor

Electrical Engineering Department

Palestine Polytechnic University


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Useful Definitions

Energy is the ability to perform work.

Energy cannot be created or destroyed but can be converted from one

form to another.

examples,

chemical energy in fossil fuels can be converted into electrical energy.

Electrical energy in turn can be converted into useful work in the form of heat,

light, and motion.

Energy measured in watt seconds or joules, traditionally in the electric

power industry, kWh, MWh, GWh, TWh

Example, A 100 watt light bulb consumes 2,400 Wh (or 2.4 kWh) of energy

in 24 hours.

2Electrical Power Plants


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Poweris the rate at which energy is flowing or work is being done.

power = energy / time

power loss is equal to

Loss in a transmission line can be reduced by increasing the transmissionvoltage, which allows the current to be reduced for the same amount ofpower transmitted.

Long transmission lines employ high voltage. High-voltage lines havedrawbacks, including the need to maintain larger clearances to maintainsafety.

Workis the amount of energy transferred by a force acting through adistance (units : N.m)

W = F . d

Useful Definitions

2

LossP RI



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Classification of power plant

Methods of general classification of electricity generation power plant are

as follows :

1. Status

2. Fuel type

3. Capacity4. Operation

5. Prime mover



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I. Status

Conventional Non Conventional

Steam turbine PP Wind energy PP

Steam engine PP

Geothermal energy

Diesel PP Ocean thermal energy

Gas turbine PP Wave & tidal wave

Hydro-electric PP Solar energy

Nuclear PP

Biogas & biomass energy



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II. Fuel Type

1. Heat engine

Where mechanical power is produced by heat engine, which transfer

thermal energy from combustion of fuel to rotational mechanical energy

2. Nuclear PP

Nuclear reactors heat is used to generate steam and thus operates steam

turbine

3. Fossil fuel

Where natural gas fired plant may be used in steam turbine or gas turbine

4. Geothermal power

Steam is extracted from hot underground source.

5. Renewable energy

Waste, biomass, wind power, solar energy .. etc



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III. Capacity

Power plant can be classified according to its capacity :

1. Small power plant :

producing less than (5 MW)

2. Medium capacity plant :

production capacity lies in the range of (5100) MW

3. High capacity plant :

Have production range of (1011000) MW

4. Super capacity plant :

Exceeds (1000) MW power production level



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IV. Operation1. Base load plant

Used to meet the base power needs of the system. Run continuously throughout the year

except when they have to be shut down for repair and maintenance.

Must be reliable and economical to operate.

These Nuclear and coal plants, generally, Because of their low fuel costs. However, They are

expensive to build and have slow ramp ratesthat is, their output power can be changed only

slowly (on the order of hours).

2. Intermediate load

operate for extended periods of time

They have the ability to vary their output more quickly than base load units.

These Combined-cycle gas turbine plants and older thermal generating units.

3. Peak load

Used in a small fraction of time operate only when the system power demand is close to itspeak.

They have to be able to start and stop quickly, but they run only for a small number of hours in

a year.

Gas turbine and hydroelectric plants with reservoirs are generally used as peaking units.

Gas turbines are the least expensive to build but have high operating costs.



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Remarks

Large generating units generally are located outside densely populated

areas, and the power they produce has to be transported to load centers.

generating units produce three-phase ac voltage at the level of a few to a

few tens of kV.

To reduce power losses during onward transmission, this voltage isimmediately converted to a few hundred kV using a transformer.

All the generators on a single ac system are synchronized.

In addition to the main large generating units, the system typically also has

some distributed generation, including combined heat and power units.

The small generating units, generally operate at lower voltages and areconnected at the distribution system level.

Small generating units, such as solar photovoltaic arrays, may be single-

phase.



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Remarks

Electric power systems are predominantly ac, although a few select

sections are dc.

Ac is preferred because it allows voltage levels to be changed with ease

using a transformer.

The voltage level of a dc system also can be changed, but doing sorequires more sophisticated and expensive equipment using power

electronics technology.

DC can be advantageous when energy has to be transmitted over long

distances.

Dc also is used to connect ac systems that operate at different frequencies.

or systems with identical frequencies that are not synchronized.

Synchronized systems are at the same frequency and have a specific phase

difference between their voltages.



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Three-phase ac has multiple advantages over single-phase ac

1. Requiring less conducting material in the transmission lines.

2. Allowing the total instantaneous power flowing from the generator

to be constant.


Remarks


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Thermal Power Plant

Electrical Power Plants 14


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Thermal Power Plant

THERMAL POWER PLANT:

Steam Power Plant,

Diesel Power Plant,

Gas Turbine Power Plant, Nuclear Power Plants

because these convert heat into electric energy.



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A typical Thermal Power Station Operates on a Cycle


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A typical Thermal Power Station Operates on a Cycle



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Steam Prime Mover The prime movers to be used for generating electricity could be

o diesel engine,

o steam engine,

o steam turbines,

o gas turbines,

o

water turbine. The prime mover convert the natural resources of energy into

power or electricity.

Presently, the steam turbine has totally replaced steam engine.

The steam is generated in a boiler and is then expanded in theturbine.

The output of the steam turbine is utilized to run the generator.



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Boiler

Purpose:To produce steam under pressure

Types:

1. Fire Tube Boiler:Hot gases of combustion are inside the tubesand the tubes are surrounded by water.

2. Water Tube Boiler:Water is inside the tube and hot gases are

outside the tube.

B il


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Boiler


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Fire Tube Boiler


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Water Tube Boiler


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Steam Condensers

Thermal efficiency of a closed cycle power developing system using steam

as working fluid and working on Carnot cycle is given by an expression

The efficiency of the steam plant is considerably increased by the use of a

condenser.

The maximum temperature T1 of the steam supplied to a steam prime

mover is limited by material considerations.

The temperature T2 (temperature at which heat is rejected) can be

reduced to the atmospheric temperature if the exhaust of the steam takes

place below atmospheric pressure. If the exhaust is at atmosphericpressure, the heat rejection is at 100C.

Low exhaust pressure is necessary to obtain low exhaust temperature. But

the steam cannot be exhausted to the atmosphere if it is expanded in the

engine or turbine to a pressure lower than the atmospheric pressure.


1

21

T

T


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Steam Condensers

A condenser is a closed vessel in which steam is condensed by

abstracting the heat and where the pressure is maintained below

atmospheric pressure.

The steam condenser is one of the essential components of allmodern steam power plants.

Steam condenser are of two types:

1. Surface condenser.2. Jet condenser.



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Cooling Tower Remove heat from the water discharged from the condenser so that the water

can be discharged to the river or recirculated and reused.

Some power plants, usually located on lakes or rivers, use cooling towers as a

method of cooling the circulating water (the third non-radioactive cycle) that

has been heated in the condenser.

During colder months and fish non-spawning periods, the discharge from the

condenser may be directed to the river. Recirculation of the water back to the

inlet to the condenser occurs during certain fish sensitive times of the year(e.g. spring, summer, fall) so that only a limited amount of water from the

plant condenser may be discharged to the lake or river.

It is important to note that the heat transferred in a condenser may heat the

circulating water as much as 40 degrees Fahrenheit (F).

In some cases, power plants may have restrictions that prevent dischargingwater to the river at more than 90 degrees F. In other cases, they may have

limits of no more than 5 degrees F difference between intake and discharge

(averaged over a 24 hour period).

When Cooling Towers are used, plant efficiency usually drops. One reason is

that the Cooling Tower pumps (and fans, if used) consume a lot of power.Electrical Power Plants 29


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Types of Cooling Towers

1. Mechanical Draft Towers


Mechanical draft Cooling Towers have long piping runs that spray the water

downward. Large fans pull air across the dropping water to remove the heat.

As the water drops downward onto the "fill" or slats in the cooling tower, the

drops break up into a finer spray.


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2. Natural Draft Towers

Natural draft towers are typically about

400 ft (120 m) high, depending on the

differential pressure between the cold

outside air and the hot humid air on the

inside of the tower as the driving force.

No fans are used.

Whether the natural or mechanical drafttowers are used depends on climatic and

operating requirement conditions.


Types of Cooling Towers


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Superheater

Device used to remove the traces of moisture from saturatedsteam leaving boiler tubes.

It also increase the temperature above saturationtemperature


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Rankine Cycle



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Rankine Reheat Cycle



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Gas Turbine



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Combined Cycle Gas Turbine (CCGT)



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