UNIT:1

COAL BASED THERMAL

POWER PLANTS
 INTRODUCTION
• A steam power plant converts the chemical energy of the fossil fuels
(coal, gas, oil) into mechanical / electrical energy.
• In steam power cycle the most common working substance is water
• The steam power cycle continuously converts heat energy into shaft work
• The heat transferred to the water to produce steam in the boiler with the
help of furnace
• The high pressure steam in the boiler expands in the turbine to produce
the shaft work
• The generator coupled with the turbine generates electric power
THERMAL POWER STATIONS IN
TAMILNADU
Power station Location Installed capacity (MW)
North chennai TPS Athipattu 630
Ennore TPS Ennore 450
Mettur TPS Mettur dam 840
Tuticorin TPS Turicorin 1050
Neyveli TPS-1 Neyveli 1020
Neyveli TPS-2 Neyveli 1470
Neyveli zero unit Neyveli 250
 THE IMPORTANT STEAM POWER
CYCLES
• Carnot cycle
• Rankine cycle
• Reheat cycle
• Regenerative cycle
• Binary vapour cycle
• Combined cycle
RANKINE CYCLE
 IMPROVISATIONS OF RANKINE
CYCLE
Increasing the temperature at which takes place in the boiler
(Increasing the boiler pressure)
Decreasing the temperature at which the condensate process takes
place (Reducing the back pressure)
By increasing temperature of steam if it is in super heated condition
In addition to that the efficiency is also improved by
1. By reheating steam in between 2 operating pressure
2. By adopting regeneration of steam
3. By using both reheat & regeneration
THE REHEAT CYCLE
REGENERATIVE CYCLE
 CLASSIFICATION OF POWER PLANTS

•
LAYOUT OF STEAM POWER PLANT
 The layout of steam power plant has the following circuits

Fuel (Coal) and ash circuit

Air and flue gas circuit

Feed water and steam flow circuit

Cooling water flow circuit.

 ADVANTAGES OF THERMAL POWER PLANT

They respond rapidly to the load variations without difficulty

Can be located very conveniently near the load centre
Transmission cost is reduced, as they are situated near the load
centre
Steam engines & turbines can work under a over load of 25%
continuously
Less space is required compared to hydel power plants
Cheaper in production and initial cost composed to diesel power
stations
 DISADVANTAGES OF THERMAL POWER PLANT

Fuel used is a fossil fuel and hence may be exhausted by gradual use

Efficiency of the plant decreases with time

Life is hardly less than that of hydro power plant

Air pollution is a major problem in thermal power plant

Transportation of fuel and ash disposal are the major difficulties in
steam power plant

Power generation cost is high

It can not be used as a peak load plant, as its part load efficiency
decreases very rapidly with decreasing load
 HOW ITS WORKS:-

How Thermal Power Station Works, by OcS (www.octavesim_com).mp4

How a thermal power plant works.mp4
 STEAM BOILER

Boiler is a high quality steel made closed vessel

Steam generating unit

Generates steam at high pressure and high temperature

Chemical energy of the fuel is converted into heat energy

In common practice high pressure boilers are most commonly used
 HIGH PRESSURE BOILER

• Modern features HPB:-

Method of water circulation

Arrangement of drums and tubing

Improved methods of heating

 SUPERCRITICAL BOILERS
• Boilers are usually designed for high working pressure for steam generating plants.

• Large number of steam generating plants are designed to work between the range of 125 atm
and 510 °C to 300 atm and 660 °C.

• These types of steam generators are basically categorised into sub-critical and super critical
boilers.

• Once through boilers are the only type suited to supercritical operation (above 221.2 atm for
the steam) because the latent heat of vapourization at and above the critical pressure is 0

• It is a common practice that super critical boilers are employed when the capacity of the
plant is above 300 MW
 ADVANTAGES OF SUPER CRITICAL BOILERS

• Heat transfer rate is considerably high

• It is possible to maintain more stable pressure level

• The problems of erosion and corrosion are minimized due to the absence of two phase
mixture
• It is possible to achieve high thermal efficiency ( about 40 to 42%)

• Greater case in operation and flexibility makes the unit more adaptable for load
fluctuations
• It can be used to generate peak loads by changing the operating pressure
LA-MOUNT BOILER

• The pump circulates water

equals to 8 to 10 times the
mass of steam evaporated
• The capacity of this boiler is
about 45 to 50 tonnes per hour
of super heated steam at a
pressure of 130 bar at 540°C
Advantages Disadvantages

• Light in weight • Salts and sediments are deposited on the

• Less number of drum required inner surfaces of the water tubes

• Quick starting in even cold conditions

• High evaporation rate

• Absence of scaling trouble in the pipes

LOEFFLER BOILER
• The major difficulty
experienced in lamount
boiler is the deposition of
salt and sediment on the
inner surface of the water
tubes
• In super heater the steam
is heated to the required
temperature of about
500°C
• The capacity of this boiler
is about 100 tonnes per
hour of super heated
steam at a pressure of 150
bar at about 500°C
ADVANTAGES

• It can carry higher salt concentrations than any other boiler type

• System is more compact and can be transported easily

BENSON BOILER

• The major drawback in lamount

and other high pressure boilers is
the formation of steam bubbles
in contact with the tube surface
• This drawback is overcome by
benson boiler in which the boiler
pressure is raised to critical
pressure (221.2 bar)
• The capacity of this boiler is
about 150 tonnes per hour of
super heated steam at a pressure
of 210 bar at about 650°C
Advantages Disadvantages
• The total weight of the boiler is 20% less than other boilers due to the
absence of drum. This also reduces the cost of the boiler
• Boiler is compact • Deposition of salt and sediments in th tubes
• Transportation of boiler parts is easy as the majority of the parts are carried surfaces
to the site without pre assembly
• High safety
• Difficult to clean the tubes
• Benson boiler can be started very quickly within 15 minutes because the • Tubes are subjected to corrosion
welded joints
• Benson boiler is an once through boiler as there is no drum and hence the • Tubes may get overheated, if the water flow
feed water enters at one end discharged at the other end as superheated is insufficient
steam
• Circulation pumps and down comers are absent

• Since there is no pressure limit, supercritical pressure may be employed

• No bubble formation and hence high heat transfer rate

• The furnace walls of the boiler can be more efficiently protected by using
small dia and close pitched tubes
 PULVERIZED FUEL FIRING TECHNIQUE
• Pulverized fuel firing means the coal is burned in its finely powdered form

The drawbacks are

• The furnace design of pulverized fuel firing system is based on particular of coal and
cannot be used for other type fuel with the same efficiency and safety

• Coal particle size is limited (to 70 – 100 µ) by furnace temperature, volatile method of
fuel, ash content etc., So, large investments are needed in preparing equipments and its
maintenance with considerable effort for achieving such sizes

• The coal particles could be steadily easily ignited only when the furnace temperature is in
the order of 1700°C, which is very difficult to maintain at part loads as the temperature
drops
• High furnace operating temperature increases the amount of NOx and the removal of SO2 needs a
very expensive flue gas scrubbing system

• High furnace operating temperature cause subsequent corrosion and erosion on boiler parts even
with in 30-35% ash content coal is used. So, high ash content and low grade fuels cannot be used

FLUIDIZED BED BOILERS

• Coal upto 12 mm particle size even with 70% ash content can be burned efficiently

• Particle size can be extended upto 50 mm

• The rating of FBB goes even upto 150 tonnes per hour at a pressure of 150 bar and at a
temperature of 400°C
FLUIDIZED BED COMBUSTION (FBC) SYSTEM
• Usually, the coal is fed into the
furnace when the bed temperature has
reached about 650°C
• To avoid clinker formation and the
emission of some undesirable
substances, bed temperature should
be controlled to 950°C or below
 ADVANTAGES
• FBC system offers more flexibility to handle wide variety of fuels including high ash content coals, low rank fuels, domestic and
industrial waste
• Lower and uniform bed operating temperature avoids the formation of clinker and emission of clinker and emission of some
undesirable substances like NOx

• Vigorous mixing of coal particles and air makes it possible to use the excess air as very low as 10 to 15%

• High heat transfer rate between the particle and the heat transfer tubes immersed in the bed due to good rapid mixing and efficient
combustion. This leads to appreciable size reduction of boiler and hence the weight

• Incorporating limestone (or) dolomite in the bed material reduces the SO 2 emission level to 15% of that in conventional firing
systems
• No ash fusion takes place as the furnace temperature is below 950°C which is well below the ash fusion temperature, 1100°C.
This low combustion temperature reduces the fouling and corrosion of heat transfer tubes
• High combustion efficiency (99%) due to very high heat transfer rates

• System is fast enough to respond for changes in load demand

• Usage of FBC system saves 10% operating cost and 15% capital cost

• Volatilization of ash constituents like alkali metals are minimised and hence ash particles are soft and non abrasive
 CLASSIFICATION OF FLUIDIZED BED BOILER (FBB)

• Atmospheric Fluidized Bed Combustor (AFBC)

 Bubbling Fluidized Bed Boiler
 Circulating Fluidized Bed Boiler
• Pressurized Fluidized Bed Combustor (PFBC)
 Pressurized bubbling fluidized bed combustor (PBFBC)
 Pressurized circulating fluidized bed combustor (PCFBC)
ATMOSPHERIC BUBBLING FLUIDIZED BED BOILER

• Bubbling Bed
• Crushed coal – 6 to 20 mm
• This boiler 10 to 15 times higher
volumetric heat release rate and 2 to
3 times higher surface heat transfer
rate than a conventional boiler
CIRCULATING FLUIDIZED BED BOILER
• Drawbacks
 Alternative fuels may flew off the bed
 The other heavy materials and incombustible
stack at the bottom of the bed may block the
distributor
• To over come this,
 Providing sloping distributor plate to give an air
slide effect
 Providing non uniform fluidizing velocities over
the bed
 Benting one of the FBC walls over the bed to
contain the light particles
PRESSURIZED FLUID COMBUSTION
• The bed is operated under pressure by
supplying the compressed air at pressure of
upto 10 bar
• The velocity may be around 1m/s which is
much lower than ABFBC (1.3 – 3.5 m/s) due
to the use of pressurized air
 ADVANTAGES OF FBC

• The unit size is small hence the capital costs are reduced
• Responds rapidly to changes in load demand
• Fouling and corrosion of tubes is reduced
• The cost of coal crushing is reduced
• Pollution is controlled
• Combustion temperature can be controlled accurately
 Turbines - introduction

• During the early days, the heat energy is converted into useful
mechanical work by means of steam engine
• But nowadays, steam turbines are employed for this purpose
• A steam turbine is a prime mover, in which the PE (heat) of the steam
is converted into the useful mechanical work by transforming first it
into KE & then into useful mechanical work in the form of rotary
motion due to the gradual change of momentum of the steam
 MAIN CIRCUITS
• Coal and ash circuit
• Air and gas circuit
• Feed water and steam circuit
• Cooling water circuit
 UNIT:1
COAL BASED THERMAL POWER PLANTS

Power plant engineering deals with the study of energy, its sources
and utilization of energy for power generation.

The power is generated by prime movers (example- Hydraulic

turbines, steam turbines, diesel engines).
 ENERGY

Energy may be defined as the capacity to do work.

Energy exists in various forms, such as Mechanical Energy, thermal

energy, electrical energy, solar energy etc.

Electricity is the only form of energy, which is easy to produce, easy

to transport, easy to use and easy to control.

The utilization of energy is an indication of the growth of the nation.

 POWER
Power is the rate doing work, which equals energy per time. Energy is thus
required to produce power.
We need energy to run power plants to generate electricity. We need power to
run our appliances, and heat our homes.
Without energy we would not have electricity.
Electricity is the most convenient and versatile form of energy
consumption of electricity in the country is an indicator of productivity and
growth.
1 Watt = 1 joule per second
1 Kilowatt = 1,000 Watts
1 Megawatt = 1,000 kilowatts = 1 horsepower
LAYOUT OF HYDEL POWER PLANT
Main components of Hydel power plant:-
• Water reservoir • Penstock
• Dam • Spill way
• Catchment area • Water turbine
• Trash rack • Draft
• Fore bay
• Surge tank
 ADVANTAGES
• Operating and running cost lower than thermal power plant

• Water is a renewable source of energy and free of cost

• No pollution

• Plant can be started with in matter of minutes

• It requires less supervising staff

• Its useful life is very high and its efficiency

 DISADVANTAGES

• Capital cost is considerably high

• Power generation depends upon availability of water

• Its takes long time for construction and commissioning

 HOW ITS WORKS:-

Hydroelectric Power Plant Working Animation.mp4 Hydroelectric Documentary.mp4

LAYOUT OF DIESEL POWER PLANT
Main components of Diesel power plant:-
 Diesel Engine
 Air intake system
 Exhaust gas System
 Fuel supply System
 Engine Starting System
 Lubricating system
 Engine Cooling system
 Governing system
 ADVANTAGES
 More efficient than thermal plant
 Design, Layout is simple and cheap
 Part load efficiency is very high
 It can be started quickly
 Simple & easy maintenance
 No problem with fuel & dust handling
 It can be located in the heart of town
 Less cooling water required.
 DISADVANTAGES
There is a limitation for size of a diesel engine

Life of plant is comparatively less

Noise pollution is very high

Repair cost is very high

High lubrication cost

 APPLICATIONS
 Higher thermal efficiency, diesel power plants are most welcome in
industries where power requirement is small.

They can be used as a Peak load plants in combination with some

other plants.

 Suitable for mobile power generation in industries.

 It can be used under emergency service

 Power cut in industries, now-a-days can over come only by installing

the generating sets.
NUCLEAR FISSION REACTION
 FISSION REACTION

• The process of releasing chromous amount of energy by breaking up

of heavy nuclei of intermediate atomic number is known as fission.

• When a heavy nucleus of an unstable uranium atom is bombarded with

high energy neutrons, it splits into two equal fragments of more or less
of equal mass and also releases 2 to 3 neutrons per fission. This is
known as nuclear fission.
 NUCLEAR CHAIN REACTION

• The neutrons released during the fission cause further fission reaction
with other nuclei of uranium and thus chain reaction is maintained
under favourable conditions.

• This chain reaction may be either in controlled condition or in

uncontrolled condition.
LAYOUT OF NUCLEAR POWER PLANT
 Essential components of nuclear power plant:-
Nuclear reactor
Fuel
Moderator
Control rods
reactor vessel
Shielding coolant
Coolant
 Steam generating unit
 Steam turbine
 ADVANTAGES
• More economical when as compared with thermal power plant.

• No ash disposal problems.

• Low capital cost in bigger unit sizes.

• Less space is required.

• Process is highly reliable.

• It consumes less quantity of fuel.

 DISADVANTAGES
• High initial and maintenance cost.

• Well trained person required for operation.

• Radio active wastes may affect the workers health and surroundings.

• Disposal of radioactive waste is a major problem faced in nuclear

power plants.
LAYOUT OF GAS TURBINE POWER PLANT
 Essential components of Gas turbine power plant:-
• Air compressor

• Intercooler

• Regenerator

• Combustion chamber

• Gas turbine
 ADVANTAGES
• Gas turbine plants can work economically for short running hours.
• Storage of fuel requires less area and handling is easy.
• Gas turbine plant is small and compact in size as compared to steam
power plants.
• It can be started quickly and can be put on load in a very short time.
• The cost of maintenance is less.
• It is simple in construction. There is no need for boiler, condenser and
other accessories as in the case of steam power plants.
• Less pollution and less water is required.
 DISADVANTAGES
• 66% of the power developed is used to drive the compressor; the gas
turbine unit has a low thermal efficiency

• Special cooling methods are required for cooling the turbine blades.

• It is difficult to start a gas turbine as compared to a diesel engine in a

diesel power plant

• The life of a gas turbine plant is upto 10 years, after which its
efficiency decreases to less than 10 percent.
COMBINED POWER CYCLES
 ADVANTAGES
• Higher thermal efficiency

• In the event of power failure at one power plant, operation can be

continued by feeding the other plants there avoiding complete
shutdown.

• Operation is simple as they are fully automised

• It operates at less smoke and hence eco-friendly

 SELECTION OF POWER PLANT
General considerations:-
Distance from load centre

Site selection

Availability of water

Foundations conditions

Accessibility of site

Overall plant cost

Time period for power generation

Efficiency and capacity of the plant

 SELECTION OF POWER PLANT
Specific considerations:-

Ash disposal facilities for thermal power plant

Storage of water with required head for Hydel power plant

Fuel transportation for diesel and thermal plants

Waste disposal from nuclear power plants

Safeguard against earthquake for nuclear plants

 LOAD CURVE
• Load curve is the graphical representation showing the load demand
for every instant during a particular time interval.

• The load demanded noticed according to the consumer requirement

during particular period can be categorized into Base load, Average
load and peak load.

• This curve is called hourly load curve, if the load is plotted in hourly
basis.
 LOAD CURVE
100

90
90

Peak load
80
80

70 68
65

60
Load,MW

50 48
46
40 40

Average load
40

30 28
25
22
20

10
10

0
0 1 2 3 4 5 6 7 8 9 10 11 12
Base Load
TIME in months
 LOAD DURATION CURVE
20

18

16

14
Load in MW

12
20
10

8
12 11
6 10
4
7 6
2

0
6am-9am 9am-12pm 12pm-3pm 3pm-6pm 6pm-12am 12am-6am

Time in hours
MAGNETO HYDRO DYNAMIC POWER PLANT
Open cycle MHD plant with steam plant
Closed cycle MHD power plant
Liquid metal system
 UNIT-II
STEAM POWER PLANT
• Fuel handling system

1. Out plant handling

2. In plant handling
 OUT PLANT HANDLING
Transportation by road (lorries)

Transportation by rail

Transportation by sea or river (ships)

Transportation by ropeways (less than 10 km distance)

Transportation by pipelines
 IN PLANT HANDLING
• Coal delivery
• Unloading
• Preparation
• Transfer
• Outdoor storage (dead storage)
• Covered storage (live storage)
• In plant handling
• Weighting and measuring
• Furnace firing
COAL PREPARATION
 COAL TRANSFER

Belt conveyors

Screw conveyors

Bucket elevators

Grab bucket elevators

Belt conveyors
Screw conveyors
Bucket elevators
Grap bucket elevators
 ASH HANDLING
Mechanical system

Hydraulic system

Pneumatic system

Steamjet system