coal based power station

1. Presenter : B.Narsaiah, M.E., JNTUHUCEJ
Unit 1 – Coal based Steam/Thermal
Power Plant
EE800OE: BASICS OF POWER PLANT
ENGINEERING (Open Elective - III)

2. EE800OE: BASICS OF POWER PLANT ENGINEERING (Open Elective -
III)
B.Tech. EEE IV Year II-Sem L T P C
3 0 0 3
Prerequisite: Power System-I
Course Objectives: To provide an overview of power plants and the
associated energy conversion issues
Course Outcomes: Upon completion of the course, the students can
understand the principles of operation for different power plants and their
economics
UNIT - I
Coal Based Thermal Power Plants: Basic Rankine cycle and its
modifications, layout of modern coal power plant, super critical boilers, FBC
boilers, turbines, condensers, steam and heating rates, subsystems of thermal
power plants, fuel and ash handling, draught system, feed water treatment,
binary cycles and cogeneration systems.

3. UNIT - III
Basics of Nuclear Energy Conversion: Layout and subsystems of nuclear power plants, Boiling
Water Reactor (BWR), Pressurized Water Reactor (PWR), CANDU Reactor, Pressurized Heavy
Water
Reactor (PHWR), Fast Breeder Reactors (FBR), gas cooled and liquid metal cooled reactors,
safety
measures for nuclear power plants.
UNIT - IV
Hydroelectric Power Plants: Classification, typical layout and components, principles of wind,
tidal,
solar PV and solar thermal, geothermal, biogas and fuel cell power systems
UNIT - V
Energy, Economic and Environmental Issues: Power tariffs, load distribution parameters, load
curve, capital and operating cost of different power plants, pollution control technologies
including waste
disposal options for coal and nuclear plants.
TEXT BOOKS:
1. Nag P.K., Power Plant Engineering, 3rd ed., Tata McGraw Hill, 2008.
2. El Wakil M.M., Power Plant Technology, Tata McGraw Hill, 2010.
REFERENCE BOOK:
1. Elliot T.C., Chen K and Swanekamp R.C., Power Plant Engineering, 2nd ed., McGraw Hill,
1998.

4. Thermal Power Plants in India
as on 31 Dec 2021

5. Introduction to thermal power plant
A steam power plant converts the chemical energy of the
fossil fuels (coal, oil, gas) into mechanical/electrical energy.
This is achieved by raising the steam in the boilers,
expanding it through the turbines and coupling the turbines
to the generators which convert mechanical energy to
electrical energy

6. The following two purposes can be served by a steam
power plant :
1. To produce electric power.
2. To produce steam for industrial purposes besides
producing electric power.
The steam may be used for varying purposes in the
industries such as textiles, food manufacture, paper mills,
sugar mills and refineries etc.

7. The steam power plants may be classified as follows :
1. Central stations.
2. Industrial power stations or captive power stations.
1. Central stations. The electrical energy available
from these stations is meant for general sale to the
customers who wish to purchase it.
Generally, these stations are condensing type where the
exhaust steam is discharged into a condenser instead of into
the atmosphere.
In the condenser the pressure is maintained below the
atmospheric pressure and the exhaust steam is condensed.
2. Industrial power stations or captive powerstations.
This type of power station is run by a
manufacturing company for its own use and its output is
not available for general sale.

8. RANKINE CYCLE., (STEAM POWER CYCLE)
□ 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 help of furnace. The high pressure steam in the
boiler expands in the turbine to produce shaft work. The
generator coupled with the turbine generates electric
power. Pv=mRT

9. Schematic representation and T-S diagram of Rankine cycle.
Process 3-4
First, the working fluid (water) is enter the pump at state 3 at
saturated liquid.
It is pumped (ideally isentropically) from low pressure to
high (operating) pressure of boiler by a pump to the state 4.
During this isentropic compression water temperature is slightly
increased.
Pumping requires a power input (either mechanical or
electrical).
The conservation of energy relation for pump is given as

10. Process 4-1
The high pressure compressed liquid enters a boiler at state 4 by
an external source.
It is heated at constant pressure to become a saturated vapour at
state l’.
Then the saturated vapour is superheated to state 1 through super
heater.
Common heat source for power plant systems are coal (or
other chemical energy), natural gas or nuclear power.
The conservation of energy relation for boiler is given as
Qin =m (h1 - h4)

11. Process 1 – 2:
The superheated vapour enter the turbine at state 1 and
expands through a turbine to generate power output.
Ideally, this expansion is isentropic and this decreases the
temperature and pressure of the vapour at state 2.
The conservation of energy relation for turbine is given as
Wturbine = m (h1 –h2)

12. Process 2 – 3:
The vapour then enters a condenser at state 2.
At this state, steam is a saturated liquid- vapour mixture
where it is cooled to become a saturated liquid at state 3.
This liquid then re- enters the pump and the cycle is
repeated.
The conservation of energy relation for condenser
is given as Qout = m (h2 – h3)
The exposed Rankine cycle can also prevent vapour
overheating, which reduces the amount of liquid condensed
after the expansion in the turbine.

13. Variables:
Qin- heat input rate (energy per unit
time) m= mass flow rate (mass per unit
time)
W- Mechanical power used by or
provided to the system (energy per
unit time)
 - thermodynamic efficiency of process (power used for
turbine per heat input) h1 , h2 , h3 and h4 - Specific Enthalpy of
fluid at specific points
Efficiency Calculation:
The thermodynamic efficiency of the cycle as the ratio of
net power output to heat input.
Wnet
 Wturbine  Wpump  or Qin  Qout 
  W / Q

14. Real Ranking Cycle (Non-ideal)
In a real Rankine cycle, the compression by the pump and
the expansion in the turbine are not isentropic.
In other words, these processes are non-reversible and
entropy is increased during the two process.
This increases the power required by the pump and
decreases the power generated by the turbine.
It also makes calculations more involved and difficult.

15. CONT.,

16. RANKINE CYCLE., (IMPROVISATIONS)
□ By increasing temperature of steam if it is super
heated condition. In addition to that the efficiency is also
improved by
a) By reheating steam in between 2 operating pressure
b) By adopting regeneration of steam
c) By using both reheat and regeneration

17. REHEAT CYCLE
□ In this ideal reheat cycle the expansion process
takes place in 2 stages.

18. CONT.,
□ In the first stage steam is expanded is entropically to an
intermediate pressure and sent back to the boiler where it is
reheated at constant pressure, usually to the inlet
temperature of the first turbine stage.
□ Steam expands is entropically in the second stage to
the condenser pressure, thus the total heat input and the
total turbine work output for a reheat cycle becomes.
Qin = Qprimary + Qreheat
= (h1
– h6
) + (h3
– h2
)
And Wturbine out = W turbine I + Wturbine II = (h1 – h2) + (h3 – h4) Ƞ
= WT
total / Qin
Total
□ The incorporation of the single reheat in a modern power
plant improves the cycle effectively by 4 to 5 percent by
increasing the average temperature at which heat is added
to the steam.

19. IDEAL REGENERATION CYCLE

20. CONT.,
□ The efficiency of any cycle can be improved by reducing
the heat rejection. The amount of heat to be rejected in the
condenser is reduced by partly supplying to the feed water
supplied to the boiler.
□ The feed water supplied to the boiler is passed through
the turbine caring in counter flow direction. The feed water
enters the turbine at 2 and is heated to saturated
temperature at inlet to the turbine.
□ The heat rejected by the steam in the expansion through
the turbine is equal to the heat gained by the feed water.

21. LAYOUT OF MODERN COAL POWER PLANT

23. MAIN CIRCUITS.,
The four main circuits are come across
in any thermal power plant layout are
□ Coal and Ash Circuit
□ Air and Gas Circuit
□ Feed Water and Steam Circuit
□ Cooling Water Circuit

24. COAL AND ASH CIRCUIT
□ Coal and Ash circuit in a thermal power plant layout
mainly takes care of feeding the boiler with coal from the
storage for combustion.
□ The ash that is generated during combustion is
collected at the back of the boiler and removed to the ash
storage by scrap conveyors.

25. Coal and ash circuit.
Coal arrives at the storage yard and after necessary
handling, passes on to the furnaces through the fuel
feeding device.
Ash resulting from combustion of coal collects at
the back of the boiler and is removed to the ash
storage yard through ash handling equipment.

26. AIR AND GAS CIRCUIT
□ Air from the atmosphere is directed into the
furnace through the air preheated by the action of a
forced draught fan or induced draught fan.
□ The dust from the air is removed before it enters
the combustion chamber of the thermal power plant
layout. The exhaust gases from the combustion
heat the air, which goes through a heat exchanger
and is finally let off into the environment.

27. Air and gas circuit.
Air is taken in from atmosphere through the action
of a forced or induced draught fan and passes on to
the furnace through the air
preheater, where it has been heated by the heat of
flue gases which pass to the chimney via the
preheater.
The flue gases after passing around boiler tubes
and superheater tubes in the furnace pass through a
dust catching device or precipitator, then through
the economiser, and finally through the air
preheater before being exhausted to the
atmosphere.

28. FEED WATER AND STEAM CIRCUIT
□ The steam produced in the boiler is supplied to the turbines to
generate power. The steam that is expelled by the prime mover in
the thermal power plant layout is then condensed in a condenser for
re-use in the boiler.
□ The condensed water is forced through a pump into the feed
water heaters where it is heated using the steam from different
points in the turbine.
□ To make up for the lost steam and water while passing through
the various components of the thermal power plant layout, feed
water is supplied through external sources.
□ Feed water is purified in a purifying plant to reduce the dissolve
salts that could scale the boiler tubes.

29. COOLING WATER CIRCUIT
□
The quantity of cooling water required to cool the steam in a
thermal power plant layout is significantly high and hence it is
supplied from a natural water source like a lake or a river.
□ After passing through screens that remove particles that can
plug the condenser tubes in a thermal power plant layout, it is
passed through the condenser where the steam is condensed.
□ The water is finally discharged back into the water source after
cooling. Cooling water circuit can also be a closed system where
the cooled water is sent through cooling towers for re-use in the
power plant.
□ The cooling water circulation in the condenser of a thermal
power plant layout helps in maintaining a low pressure in the
condenser all throughout.
All these circuits are integrated to form a thermal power plant layout
that generates electricity to meet our needs.

30. Advantages:
□ Fuel cost is cheap
□ Initial cost is lesser than hydro electric power plant.
□ Power generation does not depend on the natural
phenomena.
Disadvantages:
□ 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

31. The essential requirements of steam power station design
are :
1. Reliability
2. Minimum capital cost
3. Minimum operating and maintenance cost
4. Capacity to meet peak load effectively
5. Minimum losses of energy in transmission
6. Low cost of energy supplied to the consumers
7. Reserve capacity to meet future demands.
The above essential requirements depend to a large
extent on the following :
(i) Simplicity of design
(ii) Subdivision of plant and apparatus
(iii) Use of automatic equipment
(iv) Extensibility.

32. The following points should be taken into consideration
while selecting the site for a steam power station :
1. Availability of raw material
2. Nature of land
3. Cost of land
4. Availability of water
5. Transport facilities
6. Ash disposal facilities
7. Availability of labour
8. Size of the plant
9. Load centre
10. Public problems
11. Future extensions.

33. COMPONENTS OR PARTS OF THERMAL POWER
PLANT
□ River or Canal
□ Circulating Water Pump
□ Condenser
□ Heater
□ Economizer
□ Boiler
□ Super heater
□ Turbine
□ Generator

34. CONT.,
□ 1. River or Canal:
□ As we know Here a huge amount of water is present and it is
further used for the generation of electricity.
□ 2. Circulating Water Pump:
□ It circulates water from the river by the pump.
□ 3. Condenser:
□ The condenser presents here to cool the working fluid or we
can say to remove the heat from the water.
□ 4. Heater (Low or High Pressure):
□ As the name indicates a low or high-pressure heater
means that it increases or decreases the pressure of the
water.

35. □ 5. Economizer:
□ When water pressure gets increased there some amount of heat
generates and that heat sends from the economizer to the boiler.
Above Economizer, there Air preheater is present which work is to
heat the air and further that heated air is used in the boiler.
□ 6. Boiler:
□ Here Coal is burning which means that the heat is producing that
heats used to heat the water and the water changes its property and
then it sends to superheater, here it becomes steam with high
heated.
□ In the Boiler, there is two section
□ Coal storage and Coal Handling which works is to store the coal
and further used when needed.
□ Ash Handling and Ash Storage Plant which works is when coal is
burned the ash produced that ash goes to Ash storage.

36. □ 7. Super Heater:
□ Water heated with high temperature and it becomes
superheated here it becomes steam.
□ 8. Turbine:
□ The main function of the turbine is that when steam
strikes to the turbine the blade rotates and it converts the
Heat energy into mechanical energy.
□ 9. Generator:
□ Here the use of a generator, the mechanical energy is
converted into electrical energy that is electricity.

37. THERMAL POWER PLANT WORKING
□ Water from the river by the use of pump it circulates and that water is pressurized so
some amount of temperature is also generated.
□ And that water is sent to the Economiser.
□ From economizer, the water comes to the boiler where there is a huge amount of
temperature present because (from the air preheater and economizer and coal burning
in the boiler ) so there is a huge amount of heat present that heats the water and then
the heated water send to the superheater.
□ Here all the water is converted into steam because of high temperature.
□ That steam further sends to the turbine.
□ Turbine blades rotate heat energy is converted into mechanical energy. And that
mechanical energy is converted into electrical energy by the use of the generator.
□ Some amount of steam at the turbine comes to the condenser which is not further
used for the generation of electricity.
□ Here the temperature of the steam is reduced and then further the cycle will be
repeated.

38. BOILER CLASSIFICATION
□ The boilers are classified based on the various criteria :
□ • Based on the contents of fluid :-
- Fire tube Boilers
- Water Tube Boilers
□ • Based on applications:-
- Utility Boilers
- Industrial Boilers
- Marine Boilers
- Locomotive Boilers
• Based on Axis :-
- Horizontal Boiler
- Vertical Boilers

39. CONT.,
Based on the fuel :-
Coal
Wood
Gas
Diesel
• Based
on the
Pressure
:-
High
Pressur
e
Boilers
(P > 80
bar).
- M

40. WHY THE HIGH PRESSURE BOILER ?
□ Where 30 bar pressure & steam rate of 30 tones/hour is
required the fire tube boilers are preferred due to lower cost.
□ • In the power plant it is necessary to produce the steam at
high pressure , high rate and high efficiency.
□ • For the steam of 30 bar pressure & steam rate of
30 tones/hour is required then the water tube boilers
are preferred.
□ • Modern high pressure boilers are generate stem at the rate of
30 to 650 tones/hour and pressure upto 225 bar and temp. of
around 5500 C.
□ • To reduce the drum size.

41. ADVANTAGES OF HIGH PRESSURE BOILERS
□ Due to forced circulation of water, evaporative capacity
of the boiler is increased and size of drum is reduced.
□ • Due to high velocity of water, chances of scale
formation is reduced.
□ • Due to uniform heating there is less chances
of overheating.
□ • High Temp. and Pressure increases the plant
efficiency.
□ • The steam can be raised quickly to meet the
variable load.
□ • It is using modified draught system which leads to
reduction in the pollution.

42. DIFFERENT HIGH PRESSURE BOILERS
□ • La-Mont Boiler
□ • Benson Boiler
□ • Velox Boiler
□ • Loffler Boiler
□ • Schmidt-Hartmann Boiler
□ • Supercritical Boiler
□ • Supercharged Boiler
□ • fluidized bed combustion Boiler

43. LA-MONT BOILER

44. □ Specifications
□ • Pressure 120 bar .
□ • Temperature up to 5000 C or above.
□ • Steam production rate : 45 to 50 tones/hour. Difficulties
□ • The deposition of salt and sediments on the inner
surfaces of the water tubes ,which reduces the
heat transfer rate.
□ • There also formation of bubbling at the inner
surfaces of water tubes.

45. BENSON BOILER

46. □ Specifications
□ • It was discovered based on the argument of “If the
pressure of boiler is raised to the critical pressure of
(225 bar), the steam and water have same density .”
□ • So, The danger of bubble formation can be easily
eliminate.
□ • Temperature high up to 6500 C .
□ • Pressure 225 bar.
□ • Steam production rate : 150 tones/hour.
□ • Once through boiler.

47. □ Advantages
□ • It does not require drum it leads to the overall
weight up to 20% and also reduction in cost also. • At
the overload it can be operated economically by
changing pressure and temperature.
□ • There is no problem of bubbling.
□ • High steam generation rate. So, used for steam power
plant.

48. DISADVANTAGES
□ Salt deposition.
□ • Sediment on the inner surface of tube.
□ • Danger of over heating

49. LOEFFLER BOILER

50. SPECIFICATION
□ Forced circulation.
□ • Pressure 100 bar.
□ • Steam production rate : 100 tones/hour.

51. SUPER CRITICAL BOILERS
□ Supercritical steam generators (also known as Benson boilers)
are frequently used for the production of electric power.
□ They operate at “supercritical pressure". In contrast to a
"subcritical boiler", a supercritical steam generator operates at such a
high pressure (over 3,200 psi/22.06 MPa or 220.6 bar) that actual
boiling ceases to occur, and the boiler has no water - steam separation.
□ There is no generation of steam bubbles within the water, because
the pressure is above the "critical pressure" at which steam bubbles
can form.
□ It passes below the critical point as it does work in the high
pressure turbine and enters the generator's condenser.
□ This is more efficient, resulting in slightly less fuel use.
□ The term "boiler" should not be used for a supercritical pressure steam
generator, as no "boiling" actually occurs in this device.

52. SUPERCRITICAL BOILER

53. WORKING
□ The most recent method to produce economical
electric power is by the use of supercritical boiler in
the power plant.
□ • In the supercritical boiler working under the pressure
above critical pressure (221.2 bar), so the enthalpy of
evaporation is becomes zero. And at the temperature
of 3740 C. and the problems of bubbling is solved.
□ • The once through boiler is only type suited
to supercritical boiler.

54. ADVANTAGES:
□ Heat transfer rate is considerably high
□ It is possible to maintain more stable pressure level.
□ It is possible to achieve higher thermal efficiency
□ Erosion and corrosion are minimized due to the
absence of 2 phase mixture.

55. FLUIDIZED BED COMBUSTION BOILER
□ Fluidized bed combustion (FBC) is a combustion technology
used to burn solid fuels.
□ • In its most basic form, fuel particles are suspended in a hot,
bubbling fluidity bed of ash and other particulate materials
(sand, limestone etc.) through which jets of air are blown to
provide the oxygen required for combustion or gasification.
□ • The resultant fast and intimate mixing of gas and solids
promotes rapid heat transfer and chemical reactions within
the bed.
□ • FBC plants are capable of burning a variety of low-grade
solid fuels, including most types of coal and woody biomass,
at high efficiency and without the necessity for expensive fuel
preparation (e.g., pulverising).

56. PRINCIPLE OF FBC

58. ADVANTAGES
High thermal efficiency.
• Short commissioning and erection period.
• Efficient operation at temperatures down to 150° C ( i.e.
well below the ash fusion temperature).
• Reduced coal crushing etc. (pulverised coal is not
a necessity here).
• The system can respond rapidly to changes in load
demand, due to quick establishment of thermal
equilibrium between air and fuel particles in the bed.
• The operation of fluidized bed furnace at
lower temperature helps in reducing air
pollution.

59. DISADVANTAGES
□ There may be problem in distribution of coal
and dolomite.
□ • The direct contact of flue gases and tubes may
erosion.
□ • High pressure air is required.

60. ADVANTAGES AND DISADVANTAGES OF FLUIDIZED BED
COMBUSTION
□ FBC is being used exhaustively these days in all major power stations all
over the globe, owing to numerous advantages that it offers over the other
pre-dominant methods of combustion. Few of those are:-
□ High thermal efficiency.
□ Easy ash removal system, to be transferred for made cement.
□ Short commissioning and erection period.
□ Fully automated and thus ensures safe operation, even at extreme
temperatures.
□ Efficient operation at temperatures down to 150° C (i.e. well below the
ash fusion temperature).
□ Reduced coal crushing etc. (pulverised coal is not a necessity here).
□ The system can respond rapidly to changes in load demand, due to quick
establishment of thermal equilibrium between air and fuel particles in the
bed.

61. Introduction of turbines
The steam turbine is a prime mover in which the potential
energy of the steam is transformed into kinetic energy, and
latter in its turn is transformed into the mechanical energy
of rotation of the turbine shaft. The turbine shaft, directly
or with the help of a reduction gearing, is connected with
the driven mechanism. Depending on the type of the driven
mechanism a steam turbine may be utilised in most diverse
There are several ways in which the steam turbines may
be classified. The most important and common division
being with respect to the action of the steam, as :
(a) Impulse.
(b) Reaction.
(c) Combination of impulse and reaction.

62. TURBINES:
□ A turbine is a rotary mechanical device that extracts energy from
a fluid flow and converts it into useful work. The work produced
by a turbine can be used for generating electrical power when
combined with a generator or producing thrust, as in the case of jet
engines.
□ A turbine is a turbo machine with at least one moving part called a
rotor assembly, which is a shaft or drum with blades attached.
Moving fluid acts on the blades so that they move and impart
rotational energy to the rotor.

63. IMPULSE TURBINES:
□ Impulse turbines change the direction of flow of a high velocity fluid or gas
jet. The resulting impulse spins the turbine and leaves the fluid flow with
diminished kinetic energy.
□
□ There is no pressure change of the fluid or gas in the turbine blades, as in
the case of a steam or gas turbine, all the pressure drop takes place in the
stationary blades. Before reaching the turbine, the fluid's pressure head is
changed to velocity head by accelerating the fluid with a nozzle.
□
□ Pelton wheels and de Laval turbines use this process exclusively. Impulse
turbines do not require a pressure casement around the rotor since the fluid
jet is created by the nozzle prior to reaching the blades on the rotor.

64. Impulse turbine

65. □ Newton's second law describes the transfer of energy for
impulse turbines. Impulse turbines are most efficient for
use in cases where the flow is low and the inlet pressure
is high.

67. REACTION TURBINES:
□ Reaction turbines develop torque by reacting to the gas or fluid's
pressure or mass. The pressure of the gas or fluid changes as it
passes through the turbine rotor blades. A pressure casement is
needed to contain the working fluid as it acts on the turbine stages
or the turbine must be fully immersed in the fluid flow.
□ The casing contains and directs the working fluid and, for water
turbines, maintains the suction imparted by the draft tube. Francis
turbines and most steam turbines use this concept.
□ For compressible working fluids, multiple turbine stages are
usually used to harness the expanding gas efficiently. Newton's
third law describes the transfer of energy for reaction turbines.
Reaction turbines are better suited to higher flow velocities or
applications where the fluid head (upstream pressure) is low.

72. CONDENSERS:
□ In systems involving
heat
transfer, a condenser is a
device or unit used to condense a substance from
its gaseous to its liquid state, by cooling it. In so doing,
the latent heat is given up by the substance, and will
transfer to the condenser coolant.

73. □ Types of Condenser:
□ Surface condenser
□ Down flow surface condenser
□ Central flow surface condenser
□ Inverted flow surface condenser
□ Evaporative surface condenser
□ Regenerative surface condenser

74. □ Down flow surface condenser:
□ In Down flow surface condenser, steam enters on the top of
the condenser vessel and it comes down over the cooling
water pipes.
□ The steam as a result is condensed and the condensate is
extracted from the bottom by the condensate extraction pump.
The temperature of condensate gets decrease as it passes
downwards.
□ Also the partial pressure of steam decreases from top to
bottom of the steam condenser. The air exit is shielded from
the downstream of the condensate by means of buffle plate
and thus air is extracted with only a comparatively small
amount of water vapour.
□ As the air comes down, it is progressively cooled and
becomes denser and hence it is extracted room the lowest
convenient point.

75. □ Central flow surface condenser
□ In this type of surface condenser the suction pipe of the
air extraction pump is placed in center of the tubes
nest, this causes the condensate to flow radially
towards the center.
□ The condensate leaves at the bottom where the
condensate extraction pump is situated. The air is
withdrawn from the center of the nest of tubes.
□ This method is an improvement on the down flow type
as the steam is directed radially inward by a volute
casting around the tube nest it has thus access to the
whole periphery of the tubes.

76. □ Inverted flow surface condenser:
□ Here, the air extraction pump is situated at the top. The steam enters near
the bottom and goes upwards. The condensate extraction pump is situated
at the bottom of the condenser.
□ Evaporative surface condenser:
□ When the supply of cooling water is very limited, the evaporate type
steam condenser is used. In this condenser the exhaust steam is circulated
through a series of tubes and a thin film of cooling water is allowed to
flow over these tubes.
□ The condensed steam and wet air is extracted from the steam tube outlet
by means of wet air pump. A natural or force air flow helps rapid
evaporation of the film, which speeds up the condensation process.
□ The water which is not evaporated, collected in a water tray from which it
can be pumped back for reusing as cooling water. Evaporate type steam
condenser requires minimum cooling water. Only the makeup water
required to supply to compensate evaporation.

77. □ Regenerative surface condenser:
□ In regenerative surface condensers, the condensate is
heated by the use of regenerative method.
□ In that the condensate is passed through the exhaust
steam coming out from the turbine or engine. This
raises its temperature and it is used as the feed water for
the boiler.

78. □ STEAM & HEAT RATE:
□ Steam rate:
□ It is nothing but the rate of steam flow (kg/hr) required to
produce unit shaft output (1kw). Normally the capacity of steam
power plant is expressed in terms of steam rate.
□ Steam rate = 3600 / (WT
-WP
) (Kg/Kw-hr)
□
□
□ Heat rate:
□ The rate of heat input (Q1) required producing unit shaft
output (1kw)
□ Heat rate = 3600 Q / (WT
-WP
) (Kg/Kw-hr)
□ It is the amount of heat required by a power plant to produce 1
kwh of power. 1 kwh of power heat rate = (heat input (KJ/Sec) x
3600 S/L) / Net power Output in Kw Its unit is KJ/Kw.h

79. SUBSYSTEMS OF THERMAL POWER
PLANTS:
□ FUEL HANDLING SYSTEM:
□ Fuel handling system is a very important aspect in
power plant because supply of fuel in its suitable form
to the power plants.
□ Two Stages:
□ Out plant handling
□ In plant handling
□
□ Out plant handling:
□ It deals with the transportation of coal from coal mines
to the site of the power plant by road, rail and sea, etc.

81. □ Inplant handling:
□
□ i) Coal delivery
□ The coal from supply points is delivered by ships or boats to
power stations situated near to sea or river whereas coal is
supplied by rail or trucks to the power stations which are situated
away from sea or river. The transportation of coal by trucks is
used if the railway facilities are not available.
□
□ (ii) Unloading
□
□ The type of equipment to be used for unloading the coal received
at the power station depends on how coal is received at the power
station. If coal delivered by trucks, there is no need of unloading
device as the trucks may dump the coal to the outdoor storage.
Coal is easily handled if the lift trucks with scoop are used.

82. □ In case the coal is brought by railways wagons, ships or
boats, the unloading may be done by car shakes, rotary
car dumpers, cranes, grab buckets and coal accelerators.
Rotary car dumpers although costly are quite efficient
for unloading closed wagons.
□
□ (iii) Preparation
□ When the coal delivered is in the form of big lumps
and it is not of proper size, the preparation (sizing) of
coal can be achieved by crushers, breakers, sizers,
driers and magnetic separators.

83. □ (iv)Transfer
□ It consists of an endless belt moving over a pair of end drums
(rollers). At some distance a supporting roller is provided at the
centre. The belt is made up of rubber or canvas. Belt conveyor is
suitable for the transfer of coal over long distances. It is used in
medium and large power plants.
□ The initial cost of system is not high and power consumption is
also low. The inclination at which coal can be successfully elevated
by belt conveyor is about 20 .Average speed preferred than other
types.
□ After preparation coal is transferred to the dead storage by means
of the following systems.
□ 1. Belt conveyors
□ 2. Screw conveyors
□ 3. Bucket elevators
□ 4. Grab bucket elevators

85. BELT CONVEYOR

86. □ Figure shows a belt conveyor. It consists of an endless
belt moving over a pair of end drums (rollers). At some
distance a supporting roller is provided at the centre.
The belt is made up of rubber or canvas.
□ Belt conveyor is suitable for the transfer of coal over
long distances. It is used in medium and large power
plants. The initial cost of system is not high and power
consumption is also low. The inclination at which
coal can be successfully elevated by belt conveyor is
about 20 .Average speed preferred than other types.

87. SCREW CONVEYOR

88. □ It consists of an endless helicoids screw fitted to a
shaft (figure). The screw while rotating in a trough
transfers the coal from feeding end to the discharge
end.
□ This system is suitable, where coal is to be transferred
over shorter distance and space limitations exist. The
initial cost of the consumption is high and there is
considerable wear o screw. Rotation of screw varies
between 75-125 r.p.m

89. BUCKET ELEVATOR
It consists of buckets fixed to a chain (figure). The chain moves
over two wheels. The coal is carried by the bucket from bottom and
discharged at the top.

90. GRAB BUCKET ELEVATOR

91. □ It lifts and transfers coal on a single rail or track from
one point to the other. The coal lifted by grab buckets is
transferred to overhead bunker or storage. This system
requires less power for operation and requires
minimum maintenance.
□ The grab bucket conveyor can be used with crane or
tower as shown in figure. Although the initial cost of this
system is high but operating cost is less.

92. □ Outdoor Storage:
□ Outdoor storage or dead storage can be open space in one corner of the plant.
□ Its capacity can be six months or one year requirement of the plant.
□ Storage of coal gives protection against the interruption of coal supplies when there is delay
in transportation of coal or due to strikes in coal mines.
□ Coverage Storage:
□ Live Storage or coverage storage is a space provided in the plant near the boiler furnace to
meet one day requirement of the plant.
□ Live storage can be provided with buckers & coal bins.
□ Inplant Handling:
□ Handling of coal from live storage to firing equipment is known as inplant handling of
coal.
□ The equipments used for inplant handling are same as used for coal transfer.
□ Equipments from simple chutes for stoker firing to pulverized feeders, etc for pulverized fuel
firing are also included.
□ Weighing and measuring:
□ It is necessary to weigh the coal at the unloading point and the supply quantity to individual
boilers in order to run the plant in an economical manner.

93. □ ASH HANDLING:
□ It is an important aspect to be carefully undertaken in all
the coal fired steam power plant. The ash weighs upto 11
to 20% of the coal used to burn.
Types:
⚫ Mechanical System
⚫ Hydraulic System
⚫ Pneumatic System
⚫ Steam Jet System

94. MECHANICAL SYSTEM

95. □ In this system ash cooled by water seal falls on the belt
conveyor and is carried out continuously to the
bunker.
□ In this system, ash from the furnace grate falls into a
system of water possessing high velocity and is carried to
the sumps. It is generally used in large power plants.
□ Hydraulic system is of two types, namely, low pressure
hydraulic system used for intermittent ash disposal
figure. Figure shows hydraulic system.

96. □ Water-Jetting System
□ Water jetting of ash is shown in figure. In this method a
low pressure jet of water coming out of quenching
nozzle is used to cool the ash. The ash falls into trough
and is then removed.

97. PNEUMATIC SYSTEM
□ In this system ash from the boiler furnace outlet falls
into a crusher where a lager ash particles are crushed to
small sizes. The ash is then carried by a high velocity air
or steam to the point of delivery.
□ Air leaving the ash separator is passed through filter to
remove dust etc. So that the exhauster handles clean
air which will protect the blades of the exhauster.

99. □ DRAUGHT SYSTEM:
□ Because of the emission of large amount of flue gases and
other materials environment is polluted, thus to decrease the
environmental pollution some techniques and equipments are
used.
□ Generally Electrostatic precipitators and Draughts system is
used by coal gas plants to decrease the environment pollution.
Here we explain the brief about the Draught system.
□
□ Types:
□ Natural Draught
□ Artificial Draught

100. NATURAL DRAUGHT:
□ The natural draught is obtained with the use of tall chimney
which may be sufficient or insufficient to overcome the losses in
the system. Its usefulness depends upon the capacity of the
□ Plant and duct work.
□ This system of producing the draught is useful for small capacity
boilers and it does not play much important role in the present
high capacity thermal power plants.
□ A chimney is a vertical structure of masonry; brick, steel or
reinforced concrete built for the purpose of enclosing a column of
hot gases to produce the draught and discharge the gases high
enough which will prevent an air pollution the draught produced
by the chimney is due to the temperature difference of hot gases in
the chimney and cold air outside the chimney.
□ Consider the height of the chimney above the grate level is
‘H’. The pressure acting on the grate from the chimney side

101. ARTIFICIAL DRAUGHT
□ Forced draught:
□ In a forced draught system, a lower is installed near the base of
the boiler and air is forced to pass through the furnace, flues,
economizer, air-preheater and to the stack.
□ This draught system is known as positive draught or forced
draught system because the pressure of air throughout the system
is above atmospheric draught system or forced draught system
because the pressure of air throughout the system is above
atmospheric pressure and air is forced to flow through the system.
□ A stack or chimney is also used in this system but its function is to
discharge gases high in the atmosphere to prevent the
contamination.
□ It is not much significant for producing draught therefore height
of the chimney may not be very much.

103. INDUCED DRAUGHT:
□ In this system, the blower is located near the base of the
chimney instead of near the grate. The air is sucked in
the system by reducing the pressure through the system
below atmosphere. The induced draught fan sucks the
burned gases from the furnace and the pressure inside
the furnace is reduced below atmosphere and induces
the atmospheric air to flow through the furnace. The
action of the induced draught is similar to the action of
the chimney.

105. BALANCED DRAUGHT:
□ It is always preferable to use a combination of forced draught
and induced draught instead of using any one of these
system alone.
□ If the forced furnace is used alone, then the furnace cannot be
opened either for inspection or for firing because the high
pressure air inside the furnace will try to blow out suddenly
and there us every chance of blowing out the fire completely
and furnace stops.
□ If the induced draught is used alone, then also furnace cannot
be opened either for firing or inspection because the cold air
will try to rush into the furnace as the pressure inside the
furnace is below the atmospheric pressure.

106. FEED WATER TREATMENT:
□ Boilers, cooling towers and heat exchangers of the
power plant utilize water extremely. The physical
impurities are colour, turbidity, taste and odour and the
chemical impurities are acidity, minerals and dissolved
gases such as oxygen, ammonia etc.
□ Feed water be pretreated to remove impurities to control
deposition, carryover and corrosion in the boiler
systems.

107. WATER TREATMENT PROCESSES:
□ Filtration
□ Coagulation & flocculation
□ Chemical precipitation
□ Softening process with reaction of lime soda
□ Ion exchange
□ Deaeration of water
□ Reverse osmosis
□ Internal treatment of boiler feed water

108. □ Filtration:
□ To filter the suspended solid. The filtration process
removes or reduces all suspended solid impurities. The
rust, chemical particles, minerals, iron and silica are not
filtered put. They lead to severe scale formation, which is
difficult to clean and reduce boiler efficiency.

109. □ Coagulation & flocculation
□ If the suspended particles in water are so fine then the
cartridge filter are unable to remove them. The
important coagulants are alum, sodium aluminate, ferric
chloride and ferrous sulphate.
□ Coagulation, therefore involves neutralizing the
negative charges and providing a nucleus for the
suspended particles to adhere together. Flocculation is
the bridge together of coagulated particles.

110. □ Chemical precipitation
□ It is a process in which chemical added to react with
dissolved minerals in the water to produce a
relatively insoluble reaction product. It is used in
reducing dissolved hardness, alkalinity and silica.

111. SOFTENING PROCESS WITH REACTION OF LIME SODA
□ It is classified as hot or cold, depending on the
temperature of the water. In this method calculated
quantity of lime and soda is mixing with water at
temperature 80C to 150C. The hot process softeners
increase the rate of chemical reaction, increase
silica reduction and produce over all better quantity
water.
□ Particularly it reduces magnesium and coagulants help
remove silica in the softening process.

113. □ Ion exchange
□ Minerals dissolved in water from electrically charged
particles called ions. On exchange resin are 2 types.
□ Cation
□ Anion
□ Hard water is passed through the cation exchange bed which
removes the cations like ca2+ and mg2+ and equal amount
H+ ions are related from the bed to water. After dation
exchange bed the hard water is passed through the anion
exchange bed which removes the all anions like so42-, cl- etc
present in the water and equal amount.

114. DEAERATION OF WATER
□ The dissolved oxygen present in the water causes
corrosion in boiler shell. It should be removed before the
water is put in the boiler. Feed water deaeration
removes oxygen by heating the water with steam in a
deaerating heater.
□ Part of the steam is vented, carrying with it the
considerable quantity of the dissolved
oxygen.

115. REVERSE OSMOSIS
□ It was a semi-permeable membrane that allows ions to
pass from a high concentrated solution to a less
concentrated solution without allowing the reverse to
occur. It overcomes the osmotic pressure with a higher
artificial pressure to reverse the process and
concentrate the dissolved solids on one side of the
membrane.

116. INTERNAL TREATMENT OF BOILER FEED
WATER:
□ To react with incoming feed water harness and prevent it
from precipitating on the boiler metal as scale.
□ To condition any Suspended matter such as harness
sludge in the boiler and make it non ash event to the
boiler metal.
□ To eliminate oxygen from the feed water.
□ To prevent enough alkalinity to prevent boiler
corrosion.

117. COGENERATION SYSTEMS:
□ Cogeneration or combined heat and power (CHP) is the use of a heat
engine or power station to generate electricity and useful heat at the same
time. Trigeneration or combined cooling, heat and power (CCHP) refers to
the simultaneous generation of electricity and useful heating and cooling from
the combustion of a fuel or a solar heat collector.
□ Cogeneration is more thermally efficient use of fuel than electricity
generation alone. In separate production of electricity some energy must be
rejected as waste heat, but in cogeneration this thermal energy is put to good
use.
□ Combined heat and power (CHP) plants recover otherwise wasted thermal
energy for heating. This is also called combined heat and power district
heating (CHPDH). Small CHP plants are an example of decentralized
energy. By-product heat at moderate temperatures (100–180 °C) can also be
used in absorption refrigerators for cooling.

118. □ Types:
□ Gas turbine cogeneration system
□ Steam turbine cogeneration system
□ Reciprocating engine cogeneration system
□
□ Application:
□ Sugar industry
□ Cement industry
□ Steel industry
□ Ceramic industry

119. BINARY CYCLES:
□ No single fluid can meet all the requirements of vapour
power cycle.
□ Normally water is a good working fluid of vapour power
cycle.
□ But in high temperature range, there are few better fluids
available such as diphonyl ether (C6H5)2O, aluminum
bromide (al2 Br6) and mercury.
□ A binary vapor cycle is defined in thermodynamics as a
power cycle that is a combination of two cycles, one in a
high temperature region and the other in a lower
temperature region.

121. □ It is a simple Rankine cycle for mercury vapour.
□ Process
a – b = isentropic expansion of mercury in the turbine.
□ b – c = mercury condensation
□ c – d = feed pump
□ d – a = heat supplied to mercury
□ Process 1 – 2 – 3 - 4 – 5 – 6 = steam power cycle
□ Process 1 – 2 = isentropic expansion of steam at turbine
□ 2 – 3 = condensation
□ 3 – 4 = feed water
□ 4 – 5 = heating till it becomes a saturated liquid in
the economiser
□ 5 – 6 = hear added to boil the water to form saturated
vapour
□ 6 – 1 = the saturated steam is heated to form
superheated stream by external source

122. M = mass flow rate of mercury in the mercury cycle and the mass flow rate
of steam is 1 kg in steam power cycle.
The heat supplied in the mercury – steam power cycle
Q1
= m (ha
– hd
) + (h1
– h6
) + (h5
– h4
)
The heat rejected Q2
= h2
– h3
The mercury & steam turbine work,
WT
= m (ha
– hb
) + (h1
– h2
)
The pump work (WP
),
WP
= m (hd
– hc
) + (h4
– h3
)
Ƞ Binary Cycle = Q1 – Q2 / Q1 (or) WT – WP / Q1
Steam rate = 3600 / WT
– WP
Kg/KW.h
The energy balance of the mercury condenser –
steam boiler,
M(hb
– hc
) = (h6
– h5
)
M = h6 – h5 = (h6 – h5)
M = h6 – h5 / (hb – hc) kg
of mercury / kg of water
To vapourise 1Kg of water,