steam power plant

BABA HIRA SINGH BHATTAL INSTITUTE OF

ENGINEERING AND TECHNOLOGY LEHRAGAGA-

148031 DISTT.SANGRUR (Pb.)

By :-

Rakesh kumar

Assistant professor

Electrical Engineering Department.

Essentials of Steam Power Plant Equipment

A 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.

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 components used in steam

power plant

(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.

Types of steam Generators

Horizontal vertical or inclined.

Fire tube or water tube.

Externally fired or internally fired.

Forced circulation and natural circulation.

High pressure or low pressure boiler.

Dalton’s law

The partial pressure pressure of eachconstituent is that pressure which the gaswould exert if it occupied alone that volumeoccupied by the mixture at the sametemperature.

Factors that should be considered while

selecting the boiler

Working pressure and quality of steamrequired.

Steam generation rate.

Floor area available.

The portable load factor.

Erection facilities.

Properties of good steam generators

It should be absolutely reliable.

It should occupy minimum space.

It should be light in weight.

Capable of quick starting.

Erection of boiler should be simple.

Steam Power Plants are Classified as

1. By fuel.

2. By prime mover.

3. By cooling tower.

Steam Power Plants are also Classified as;

Central stations; the electrical energy available from

these stations is meant for sale to the consumers who

wish to purchase it.

Industrial/ captive power stations; this type of

power station is run by the manufacturing company for

its own use and its output is not available for general

sale.

Jet condenser; low manufacturing cost. Low

upkeeps, requires small floor space and more

auxiliary power required.

surface condenser; high manufacturing

cost. high upkeeps, requires large floor space and

less auxiliary power required.

Feed water heating improves overall plant

efficiency.

Quantity of steam produced by the boiler is

increase.

Thermal stress due to cold water entering the

boiler drum are avoided.

Chance of boiler corrosion are decrease.

Dust collectors are Classified as;

Mechanical dust collectors;(a) Wet type(scrubbers).

Spray type, packed type and impingement type.

(b) Dry type.

Gravitational separators, cyclone separators,

electrical dust collectors;Rod type and plate type.

DIFFERENT TYPES OF BOILERS USED IN

STEAM POWER PLANTS

horizontal, vertical or inclined.

fire tube and water tube .

Externally or internally fired.

Forced or natural circulation.

High pressure or low pressure.

Stationary or portable.

Single-tube and multi-tube.

Working diagram Thermal

power station.

C

saturated water

hot gases

SteamTurbine

Gen

compressedwater

superheated steam

Condenser

Pump

cooling watersaturatedsteam

Steam Generator(Boiler / Furnace)

Steam Turbine Power Plant

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 uponflow rate and temperature of cooling water andon effectiveness of air removal equipment.

Water circulating through the condenser may betaken from the various sources such as river, lakeor sea. If sufficient quantity of water is notavailable the hot water coming out of thecondenser may be cooled in cooling towers andcirculated again through the condenser.

Bled steam taken from the turbine at suitableextraction points is sent to low pressure and highpressure water heaters.

Air taken from the atmosphere is firstpassed through the air pre-heater, where it isheated by flue gases. The hot air then passesthrough the furnace.

The flue gases after passing over boiler andsuperheater tubes, flow through the dustcollector and then through economiser, airpre-heater and finally they are exhausted tothe atmosphere through the chimney.

Disadvantage of steam power plant

Maintenance and operating cost are high.

Long time required for erection and putting into

action .

Large quantity of water is required.

Great difficulty experienced in coal handling .

Efficiency decreases rapidly below about 75

percent load.

Mechanical equipment in Thermal

power station.

BOILER

ECONOMISER

TURBINE

SUPER HEATER

AIR PREHEATER

CONDENSER

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.

Advantages of superheated steam

Capacity to do work is increased without

increasing its pressure.

High temperature of super heated steam

results in an increase in thermal efficiency.

Heat losses due to condensation of stem on

cylinder walls are avoided to a great extent.

Does not produce corrosion effect on

turbine.

Superheater

It is a heating device.

It is used to raise temp of steam at const

pressure.

It removes even last traces of moisture.

Classification of super heater

Convection.

Radiation.

Combination of convection and radiation.

Reheater

The function of reheater is 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.

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.

Condenser

The 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.

Functions of Condensers

The main purposes of the condenser are to

condense the exhaust steam from the turbine

for reuse in the cycle and to maximize turbine

efficiency by maintaining proper vacuum.

As the operating pressure of the condenser is

lowered (vacuum is increased), the enthalpy

drop of the expanding steam in the turbine will

also increase. This will increase the amount of

available work from the turbine (electrical

output).

Cooling Tower

The 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.

Cooling Towers have one function :

Remove heat from the water discharged

from the condenser so that the water can be

discharged to the river or re-circulated and

reused.

A cooling tower extracts heat from water by

evaporation. In an evaporative cooling

tower, a small portion of the water being

cooled is allowed to evaporate into a moving

air stream to provide significant cooling to

the rest of that water stream.

Cooling Towers are commonly used to

provide lower than ambient water

temperatures and are more cost effective and

energy efficient than most other alternatives.

The smallest cooling towers are structured for

only a few litres of water per minute while the

largest cooling towers may handle upwards of

thousands of litres per minute. The pipes are

obviously much larger to accommodate this

much water in the larger towers and can

range up to 12 inches in diameter.

Advantages of regenerative cycle

Improve overall plant efficiency.

Protect boiler corrosion.

Avoid the thermal stresses due to cold water

entering the boiler .

Increased the quantity of steam produced by

boiler.

Function of economizer

To extract a part of heat from the fuel gas

coming out of the boiler.

To use heat for heating feed water to the

boiler.

To increases the efficiency of boiler.

The 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.

Air Pre-heater

The 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.

Advantages of mechanical handling

Higher reliability.

Less labour required.

Operation is easy and smooth.

Economical for large capacity plant.

Losses in transport are minimised.

Easily started.

Disadvantages of mechanical handling

Need continuous maintenance and repair.

Capital cost of plant is increased.

Working diagram Thermal

power station.

Side view Thermal power station.

C

saturated water

Gen

compressedwater

superheated steam

cooling water

Pump

SteamTurbine

Condenser

Steam Generator

Steam Turbine Power Plant

saturatedsteam

hot gases

Heat

Workout

Total

Workin

in

Total

Loss???

Where???

R. Shanthini 15 Aug 2010

According to the 2nd Law of Thermodynamics

when heat is converted into work, part of the heat energy must be wasted

Power generation

type

Unit size

(MW)

Energy wasted

(MW)

Diesel engine 10 - 30 7 – 22

Gas Turbine 50 - 100 36 – 78

Steam Turbine 200 - 800 120 – 560

Combined (ST & GT) 300 - 600 150 – 380

Nuclear (BWR & PWR) 500 - 1100 330 – 760

The Simple Ideal Rankine Cycle9-1

© The McGraw-Hill Companies, Inc.,1998

How can We Increase the Efficiency of the

Rankine cycle?

Rankine cycle efficiency can be increased by

increasing average temperature at which

heat is transferred to the working fluid in

the boiler or decreasing the average

temperature at which heat is rejected from

the working fluid in the condenser. That is,

the average fluid temperature should be as

high as possible during heat addition and as

low as possible during heat rejection.

The three ways by which efficiency of the

Rankine cycle can be increased are :

(a) Lowering the condenser pressure.

(b) Superheating the steam to high

temperatures.

(c) Increasing the boiler pressure.

• The thermal efficiency of the Rankine cyclecan be increased by increasing the averagetemperature at which heat is added to theworking fluid and/or by decreasing theaverage temperature at which heat isrejected to the cooling medium. The averagetemperature during heat rejection can bedecreased by lowering the turbine exitpressure.

Consequently, the condenser pressure of most

vapor power plants is well below the

atmospheric pressure. The average

temperature during heat addition can be

increased by raising the boiler pressure or by

superheating the fluid to high temperatures.

There is a limit to the degree of superheating,

however, since the fluid temperature is not

allowed to exceed a metallurgically safe value.

• Superheating has the added advantage of

decreasing the moisture content of the steam at

the turbine exit. Lowering the exhaust pressure

or raising the boiler pressure, however, increases

the moisture content. To take advantage of the

improved efficiencies at higher boiler pressures

and lower condenser pressures, steam is usually

reheated after expanding partially in the high-

pressure turbine.

This is done by extracting the steam after

partial extraction in the high-pressure

turbine, sending it back to the boiler where

it is reheated at constant pressure, and

returning it to the low-pressure turbine for

complete expansion to the condenser

pressure.

The average temperature during the reheatprocess, and thus the thermal efficiency ofthe cycle, can be increased by increasing thenumber of expansion and reheat stages. Asthe number of stages is increased, theexpansion and reheat processes approach anisothermal process at maximumtemperature. Reheating also decreases themoisture content at the turbine exit.

•Another way of increasing the thermal

efficiency of the Rankine cycle is by

regeneration. During a regeneration process,

liquid water (feed water) leaving the pump

is heated by some steam bled off the turbine

at some intermediate pressure in devices

called feed water heaters.

The two streams are mixed in open

feed water heaters, and the mixture

leaves as a saturated liquid at the

heater pressure. In closed feed water

heaters, heat is transferred from the

steam to the feed water without mixing.

•The production of more than one useful

form of energy (such as process heat and

electric power) from the same energy source

is called cogeneration. Cogeneration plants

produce electric power while meeting the

process heat requirements of certain

industrial processes.

This way, more of the energy

transferred to the fluid in the boiler

is utilized for a useful purpose. The

faction of energy that is used for

either process heat or power

generation is called the utilization

factor of the cogeneration plant.

•The overall thermal efficiency of a power

plant can be increased by using binary

cycles or combined cycles. A binary cycle

is composed of two separate cycles, one at

high temperatures (topping cycle) and the

other at relatively low temperatures.

The most common combined cycle is the gas-steam combined cycle where a gas-turbinecycle operates at the high-temperature rangeand a steam-turbine cycle at the low-temperature range. Steam is heated by thehigh-temperature exhaust gases leaving thegas turbine. Combined cycles have a higherthermal efficiency than the steam- or gas-turbine cycles operating alone.

Selection of plant site

The selection of plant site for thermal power

plant compared with hydro-power plant is

more difficult as it involves number of

factors to be considered for its economic

justification.

A few important factors to be considered for

the selection of thermal power plants.

Selection of plant site

AVAILABILITY OF COAL.

Huge quantity of coal is required for large thermal plants.

ASH DISPOSAL FACILITIES.

SPACE REQUIREMENT.

NATURE OF LAND.

AVAILABILITY OF WATER.

Selection of plant site

TRANSPORT FACILITYIES.

AVAILABILITY OF LABOUR.

PUBLIC PROBLEMS.

SIZE OF THE PLANT.

Nowadays, the environment protection has

become a crucial problem and the

authorities are requested to set increasingly

more stringent limits , one of which is the

emissions from the industrial plants of solid

particulate and other gaseous pollutants.

ABOUT ELECTROSTATIC

PRECIPITATOR

ABOUT ELECTROSTATIC PRECIPITATOR

Electrostatic precipitator (ESP) is a widely

used device in so many different domains

to remove the pollutant particulates,

especially in industrial plants.

What is ESP

HOW ESP WORKS

Generally, the processes of

electrostatic precipitator are known as

three main stages: particle charging,

transport and collection.

Main process of ESP

Schematic of wire-plate ESP

Schematic of wire-plate electrostatic

precipitator

Mechanism of ESP

Mechanism of electrostatic precipitator

PROCESS OF Particle charging

Particle charging is the first and

foremost beginning in processes.

As the voltage applied on precipitator

reach threshold value, the space inside

divided into ionization region and drift

region.

The electric field magnitude around the

negative electrode is so strong that the

electrons escape from molecule.

Under the influence of electric field, the positive

ions move towards the corona, while the

negative ions and electrons towards the

collecting plates.

Particle transport

In the moving way, under the influence of

electric field, negative ions cohere and charge the

particles, make the particles be forced towards

collecting-plate.

Particle collection

As soon as the particles reach the plate,

they will be neutralized and packed by

the succeeded ones subsequently. The

continuous process happens, as a result,

particles are collected on the collecting

plate.

72

What is a Boiler?

Introduction

• Vessel that heats water to become hot water

or steam

• At atmospheric pressure water volume

increases 1,600 times

• Hot water or steam used to transfer heat to a

process

The boiler is a rectangular furnaceabout 50 feet (15 m) on a side and 130 feet

(40 m) tall. Its walls are made of a web of

high pressure steel tubes about 2.3 inches

(58 mm) in diameter.

A boiler should fulfill the following requirements

(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.

Introduction

BURNERWATER

SOURCE

BRINE

SOFTENERSCHEMICAL FEED

FUELBLOW DOWN

SEPARATOR

VENT

VENTEXHAUST GASSTEAM TO

PROCESS

STACK DEAERATOR

PUMPS

Figure: Schematic overview of a boiler room

BOILER

ECO-

NOMI-

ZER

Types of Boilers

1. Fire Tube Boiler

2. Water Tube Boiler

3. Packaged Boiler

4. Fluidized Bed (FBC) Boiler

5. Stoker Fired Boiler

6. Pulverized Fuel Boiler

7. Waste Heat Boiler

8. Thermic Fluid Heater (not a boiler!)

What Type of Boilers Are There?

The boilers can be classified according to the

following criteria.

According to flow of water and hot

gases :

(a) Water tube

(b) Fire tube.

Type of Boilers

1. Fire Tube Boiler

• Relatively small steam

capacities (12,000 kg/hour)

• Low to medium steam

pressures (18 kg/cm2)

• Operates with oil, gas or solid

fuels

Type of Boilers

2. Water Tube Boiler

• Used for high steam demand

and pressure requirements

• Capacity range of 4,500 –

120,000 kg/hour

• Combustion efficiency

enhanced by induced draft

provisions

• Lower tolerance for water

quality and needs water

treatment plant

3. Packaged Boiler

Oil

Burner

To

Chimney

• Comes in complete package

• Features

• High heat transfer

• Faster evaporation

• Good convective heat

transfer

• Good combustion efficiency

• High thermal efficiency

• Classified based on number of

passes

Working of power plant

Pulverized coal is air-blown into the

furnace from fuel nozzles at the four

corners and it rapidly burns, forming a

large fireball at the center. The thermal

radiation of the fireball heats the water

that circulates through the boiler tubes near

the boiler perimeter.

The water circulation rate in the boiler

is three to four times the throughput and

is typically driven by pumps. As the

water in the boiler circulates it absorbs

heat and changes into steam at 700 °F

(371 °C) and 3,200 psi

The water enters the boiler through a

section in the convection pass called the

economizer. From the economizer it

passes to the steam drum. Once the

water enters the steam drum it goes down

to the lower inlet water wall headers.

From the inlet headers the water rises

through the water walls and is eventually

turned into steam due to the heat being

generated by the burners located on the

front and rear water walls (typically). As

the water is turned into steam/vapor in the

water walls, the steam/vapor once again

enters the steam drum.

The steam/vapor is passed through a series of

steam and water separators and then dryers

inside the steam drum.

The steam separators and dryers remove

water droplets from the steam and the cycle

through the water walls is repeated. This process

is known as natural circulation.

super heater

Fossil fuel power plants can have a super

heater and/or re-heater section in the steam

generating furnace. In a fossil fuel plant,

after the steam is conditioned by the drying

equipment inside the steam drum, it is piped

from the upper drum area into tubes inside

an area of the furnace known as the super

heater,

which has an elaborate set up of tubing where

the steam vapor picks up more energy from

hot flue gases outside the tubing and its

temperature is now superheated above the

saturation temperature. The superheated

steam is then piped through the main steam

lines to the valves before the high pressure

turbine.

CondenserThe 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 cycleincreases.

For best efficiency, the temperature in the

condenser must be kept as low as

practical in order to achieve the lowest

possible pressure in the condensing

steam.

Since the condenser temperature can almost

always be kept significantly below 100 °C

where the vapor pressure of water is much

less than atmospheric pressure, the condenser

generally works under vacuum. Thus leaks

of non-condensible air into the closed loop

must be prevented.

The condenser generally uses either

circulating cooling water from a cooling

tower to reject waste heat to the

atmosphere, or once-through water from a

river, lake or ocean.

The condenser tubes are made of brass

or stainless steel to resist corrosion

from either side. Nevertheless they may

become internally fouled during operation

by bacteria or algae in the cooling water or

by mineral scaling, all of which inhibit heat

transfer and reduce thermodynamic

efficiency.

Many plants include an automatic

cleaning system that circulates sponge

rubber balls through the tubes to scrub

them clean without the need to take the

system off-line.

Re heater

Power plant furnaces may have a re heater

section containing tubes heated by hot flue

gases outside the tubes. Exhaust steam from

the high pressure turbine is rerouted to go

inside the re heater tubes to pickup more

energy to go drive intermediate or lower

pressure turbines.

Non –toxic dust

Sulphurous anhydride

Carbon monoxide

Nitrogen dioxide

Soot (fly ash)

Hydrogen sulphide

Pollution can be define as the contamination of soil,

air and water with undesirable amount of material and

heat.

Main pollutants from a power system

Acid rain; the rain which contain acid as its

constituents, brings all the acid down from high above the environment.

Contaminant; it is the another name of pollution. It is undesirable substances which may be physical, chemical or biological.

Pollutant; these are undesirable substances

present in the environment these can be NO2, SO2, CO2,smoke,salt, bacteria.

Lot of heat is injected into biosphere from

thermal power plant, through exhaust gases

and waste water. The major problem is the

effect of discharge of large quantity of

heated wasted water into natural water

basins. Hot water raises the temperature

and disturbs the natural ecological balance

Bad effects of thermal pollution

Greater reliability of supply to the consumers.

Avoid complete shut down.

The overall cost of energy per unit of an

interconnected system is less.

There is a more effective use of transmission

line facilities.

Less capital investment required.

Less expenses on supervision, operation and

maintenance.

Advantages of combined operation of plants

Due to limited generating capacity diesel

power stations is not suitable for base load

plants.

Nuclear power stations is not suitable for

peak load plants.

Incremental rate curve shows that as

output power increases, cost of plant

also increases.