• To know the basic knowledge about steam power plant
• To know the working principle of steam power plant
• To know the equipment used in steam power plant
• To know principle of steam power plant design
• To know cost about steam power plant and their layout
• To know environment control for steam power plant
• To know advantages and disadvantages of steam power
The steam engine is a heat engine converting heat energy to
work. The conversion is performed by a cycle of processes.
Heat created externally by pump is transferred to water in a
steam generating unit or boiler. The steam carries energy to
the expander (engine), part of the heat energy is converted to
mechanical energy, which is work. The steam leaves the
expander and is condensed back to water at condenser,
rejecting some heat energy. This is known as an external
combustion engine. These processes must conform to the
First Law of Thermodynamics expressed in the General
Energy Equation. This cycle is called the Rankine cycle and is
the accepted standard of comparison for steam plants today
6. Essentials of steam power plant
A steam power plant must have following equipment :
• A furnace to burn the fuel.
• Steam generator or boiler containing water. Heat
generated in the furnace is utilized to convert water into
• Main power unit such as an engine or turbine to use the
heat energy of steam and perform work.
• Piping system to convey steam and water.
7. In addition to the above equipment the plant requires
various auxiliaries and accessories depending upon the
availability of water, fuel and the service for which the
plant is intended.
The flow sheet of a thermal power plant consists of the
following four main circuits :
• Feed water and steam flow circuit.
• Coal and ash circuit.
• Air and gas circuit.
• Cooling water circuit.
8. 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 systems and components used in steam power plant
are as follows :
• High pressure boiler
• Prime mover
• Condensers and cooling towers
• Coal handling system
• Ash and dust handling system
• Draught system
• Feed water purification plant
• Pumping system
• Air preheater, economizer, super heater, feed heaters.
11. • Figure shows a 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 upon flow
rate and temperature of cooling water and on effectiveness of air
removal equipment. Water circulating through the condenser may be
taken from the various sources such as river, lake or sea. If sufficient
quantity of water is not available the hot water coming out of the
condenser may be cooled in cooling towers and circulated again
through the condenser. Bled steam taken from the turbine at suitable
extraction points is sent to low pressure and high pressure water
12. Steam condensing system consists of the
• Cooling water
• Cooling tower
• Hot well
• Condenser cooling water pump
• Condenser air extraction pump
Steam is used in a wide range of industries. Common applications for steam
are, for example, steam heated processes in plants and factories and steam
driven turbines in electric power plants, but the uses of steam in industry
extend far beyond this.
Here are some typical applications for steam in industry:
For higher production of electricity, Steam power plant is better than diesel
15. Principle of steam power plant
Working fluid cycle steam power plant is a closed cycle, which uses the
same fluid repeatedly. First, the water is filled into the boiler to fill the
entire surface area of heat transfer. In the boiler water is heated by
the hot gases of combustion fuel with air so that turned into vapor
• Steam produced by boiler with pressure and temperature are
directed to do work on the turbine to produce mechanical power in
the form of rotation.
• The former steam out of the turbine, and then flowed into the
condenser to be cooled with cooling water that turned to water.
Condensate water is then used again as boiler feed water. Thus the
cycle goes on and repeats.
16. Rotation of turbine is used to turn a generator that is
coupled directly to the turbine. So when the turbine
rotates, the generator output terminals generate
electricity. Although working fluid cycle is a closed cycle,
but the amount of water in the cycle would decrease.
The reduction is due to the leakage of water either
intentional or unintentional. steam power plant working
on rankine cycle
19. There are four processes in the Rankine cycle. These
states are identified by numbers (in brown) in the above
• Process 1-2: The working fluid is pumped from low to
high pressure. As the fluid is a liquid at this stage, the
pump requires little input energy.
• Process 2-3: The high pressure liquid enters a boiler
where it is heated at constant pressure by an external
heat source to become a dry saturated vapour. The input
energy required can be easily calculated using mollier
diagram or h-s chart or enthalpy-entropy chart also
known as steam tables.
20. • Process 3-4: The dry saturated vapour expands through
a turbine, generating power. This decreases the
temperature and pressure of the vapour, and some
condensation may occur. The output in this process can
be easily calculated using the Enthalpy-entropy chart or
the steam tables.
• Process 4-1: The wet vapour then enters
a condenser where it is condensed at a constant
pressure to become a saturated liquid
21. • In an ideal Rankine cycle the pump and turbine would be isentropic, i.e., the
pump and turbine would generate no entropy and hence maximize the net
work output. Processes 1-2 and 3-4 would be represented by vertical lines
on the T-S diagram and more closely resemble that of the Carnot cycle. The
Rankine cycle shown here prevents the vapor ending up in the superheat
region after the expansion in the turbine, 
which reduces the energy
removed by the condensers.
• The actual vapor power cycle differs from the ideal Rankine cycle because
of irreversibilities in the inherent components caused by fluid friction and
heat loss to the surroundings; fluid friction causes pressure drops in the
boiler, the condenser, and the piping between the components, and as a
result the steam leaves the boiler at a lower pressure; heat loss reduces the
net work output, thus heat addition to the steam in the boiler is required to
maintain the same level of net work output.
22. Essential equipments
1. Cooling tower.
2. Cooling water pump.
3. Transmission line (3-phase).
4. Unit transformer (3-phase).
5. Electric generator (3-phase).
6. Low pressure turbine.
7. Condensate extraction pump.
9. Intermediate pressure turbine.
10. Steam governor valve.
11. High pressure turbine.
A deaerator is a device that is widely used for the
removal of oxygen and other dissolved gases from
the feed water to steam-generating boilers. In particular,
dissolved oxygen in boiler feed waters will cause serious
corrosion damage in steam systems by attaching to the
walls of metal piping and other metallic equipment and
forming oxides (rust). Dissolved carbon
dioxide combines with water to form carbonic acid that
causes further corrosion. Most deaerators are designed
to remove oxygen down to levels of 7 ppb by weight
(0.005 cm³/L) or less as well as essentially eliminating
27. • There are two basic types of deaerators, the tray-type
and the spray-type:
• The tray-type (also called the cascade-type) includes a
vertical domed deaeration section mounted on top of a
horizontal cylindrical vessel which serves as the
deaerated boiler feed water storage tank.
• The spray-type consists only of a horizontal (or vertical)
cylindrical vessel which serves as both the deaeration
section and the boiler feedwater storage tank.
Economizers are mechanical devices intended to reduce
energy consumption, or to perform useful function such
as preheating a fluid. The term economizer is used for
other purposes as well. Boiler, power plant, heating,
ventilating, and air conditioning uses are discussed in
this article. In simple terms, an economizer is a heat
A precipitator is a filtration device that removes fine particles, like dust
and smoke, from a flowing gas using the force of an
induced electrostatic charge minimally impeding the flow of gases
through the unit.
30. Chimney stack
• A chimney is a structure which provides ventilation for hot flue
gases or smoke from a boiler, stove, furnace or fireplace to the
outside atmosphere. Chimneys are typically vertical, or as near as
possible to vertical, to ensure that the gases flow smoothly, drawing
air into the combustion in what is known as the stack, or chimney,
effect. The space inside a chimney is called a flue. Chimneys may
be found in buildings, steam locomotives and ships. In the United
States, the term smokestack is also used when referring
to locomotive chimneys or ship chimneys, and the term funnel can
also be used.
• The world's tallest chimney, of GRES-
2 inEkibastuz, Kazakhstan(419.7 metres)
35. The condensed water is then passed by a condensate pump (7) to a deaerator
(12), then pumped by feed water pump (28) and pre-warmed, first in a feed
heater (13) powered by steam drawn from the high pressure set, and then in
the economiser (23), before being returned to the boiler drum. The cooling
water from the condensor is sprayed inside a cooling tower (1), creating a
highly visible plume of water vapor, before being pumped back to the
condensor (8) in cooling water cycle. The three turbine sets are sometimes
coupled on the same shaft as the three-phase electrical generator (5) which
generates an intermediate level voltage (typically 20-25 kV). This is stepped
up by the unit transformer (4) to a voltage more suitable for transmission
(typically 250-500 kV) and is sent out onto the three-phase transmission
system (3). Exhaust gas from the boiler is drawn by the induced draft fan
(26) through an electrostatic precipitator (25) and is then vented through the
chimney stack (27).
36. Principle of steam power
The essential principles of steam power plant design are as
• Low capital cost
• Low operating and maintenance cost
• High thermal efficiency
• A simple design
37. The power plant should be designed such that it
can be expanded if required. It should be simple
in design. Use of automatic equipment is desired
to reduce the labor cost. Heat recovery devices
should be used wherever possible. Total
capacity of the plant should be subdivided into
four or five generating units so that during
reduced load periods some of the units may be
38. Factors affecting steam power plant
The various factors which affect the design of a
steam power plant are as follows:
• Steam pressure and temperature
• Capacity of power plant
• Ratings of generating units
• Thermodynamic cycle
• Voltage generation
39. The trend is towards using higher pressure and
temperatures of steam. This improves the thermal
efficiency. The capacity of the plant can be determined
by studying the load duration curve and anticipated
future load demand. The size of turbo-generator
depends on the following:
• Rate of growth of load
• Availability of condensing water
• Space available
40. Large type turbo generator sets should be used.
• The voltage of generation is usually 11kV, though 22kV
and 33 kV are also used. In central power plants water
tube boilers are commonly used. The type of fuel used in
a boiler will influence the design and efficiency of the
boiler plant considerably.
41. The steam power plants needs a lot of space for
• Storing the fuel
• Elaborated arrangements for fuel handling
• Ash handling
• Lay out of high-pressure boilers
• Steam turbines
• Control switch boards
• Cooling water arrangements
42. In steam power plant the A.C. generators are driven by
turbines with condensing arrangement at a high vacuum
of about 73.3 cm Hg . The size of the generating set may
vary between 10MW to 500MW or even higher. Modern
generators are 2 pole with 3000 R.P.M. as speed and
50 cycle per second as frequency.
The energy efficiency of a conventional thermal power
station, considered salable energy produced as a
percent of the heating value of the fuel consumed, is
typically 33% to 48%. As with all heat
engines, their efficiency is limited, and governed by the
laws of thermodynamics. By comparison,
most hydropower stations in the United States are about
90 percent efficient in converting the energy of falling
water into electricity.
44. The energy of a thermal not utilized in power production
must leave the plant in the form of heat to the
environment. This waste heat can go through
a condenser and be disposed of with cooling water or
in cooling towers. If the waste heat is instead utilized
for district heating, it is called co-generation. An
important class of thermal power station are associated
with desalination facilities; these are typically found in
desert countries with large supplies of natural gas and in
these plants, freshwater production and electricity are
equally important co-products.
45. The Carnot efficiency dictates that higher efficiencies can
be attained by increasing the temperature of the steam.
Sub-critical fossil fuel power plants can achieve 36–40%
efficiency. Super critical designs have efficiencies in the
low to mid 40% range, with new "ultra critical" designs
using pressures of 4400 psi (30.3 MPa) and multiple
stage reheat reaching about 48% efficiency. Above
the critical point for water of 705 °F (374 °C) and 3212
psi (22.06 MPa), there is no phase transition from water
to steam, but only a gradual decrease in density
46. Currently most of the nuclear power plants must operate
below the temperatures and pressures that coal-fired
plants do, since the pressurized vessel is very large and
contains the entire bundle of nuclear fuel rods. The size
of the reactor limits the pressure that can be reached.
This, in turn, limits their thermodynamic efficiency to 30–
32%. Some advanced reactor designs being studied,
such as the very high temperature reactor, advanced
gas-cooled reactor and supercritical water reactor, would
operate at temperatures and pressures similar to current
coal plants, producing comparable thermodynamic
47. The overall efficiency of steam power plants
depends upon the efficiency of boiler , turbine
and alternator. The heat produced due to the
burning of coal is not fully utilized for generating
electrical energy because there are heat losses
in the boiler turbine and mechanical and
electrical losses in the turbine. The overall
thermal efficiency of steam power station is
given by the following relation:
49. Cost of steam power plant:
In recent days vast improvements have been made in
generating electric power from steam. About 0.45 kg of
coal is need to produce 1kWh of electricity. It is
observed that larger capacity power plants can utilize the
thermal energy more efficiency than the smaller capacity
plant. In the design of a thermal power station future
availability of coal and its price has to be taken into
A steam power station may cost about TK 1600 per kW of
capacity. A typical sub-division of investment cost of a
steam power station is as follows:
51. The investment cost include the following costs:
• Costs of land
• Cost of building
• Cost of mechanical and electrical equipment and their
Conditions affecting the investment depend on a number of
• Characteristics of the site
• Size and number of power generating units
• Fuel storing and fuel handling methods
52. Plant Layout:
Here show the layout of power plant. The turbine room
should be sufficiently wide to accommodate various
auxiliaries. In boiler room enough space should be left
for repairs and maintenance. Various equipment should
be so placed that access to all the parts is easy
54. Basic arrangements of various equipments used in power station differ
from station to station. The following factors should be considered while
installing various components.
• All similar items such as turbines, boiler, transformer, bunker bays and
other mechanical and electrical components are arranged in parallel
lines and at right angles rows individual boiler turbo-generator,
• Chimneys should be erected independently of the station building with
chimney serving two or more boilers.
• Main flue, draft fans and outdoor precipitators should be located behind
the boiler house.
• Circulating water supply , coal supply to bunkers and lifting equipment
should be properly placed.
• Outdoor generator and unit transformers should be in front of the
55. Modern steam power station
Central steam power station of larger capacities use higher
boiler pressure with super-heated steam as the super
heated steam contains more heat energy than saturated
steam at the same pressure and provides more energy
to the turbine for conversion into electric energy. They
use large capacity boiler , and improved methods of coal
firing such as stoker firing or pulverized coal firing. The
coal used is of good quality as low grade coal such as
those having high ash contents ( about 18-20% and
above) and higher moisture contents (about 30% or
more) are not
56. preferred. High ash contents in coal reduce the heating
value of coal and more labour is required for the removal
of ash from the furnace . Ash with low fusing , or melting
temperatures forms clinkers when subjected to high
temperatures of fuel bed. The clinkers so formed
interfere with the movement of fuel on the stokers. The
coal to be burnt on hand fired grates and on the stokers
should have a minimum of about 4 to 6% of ash.
Moisture also reduces the heat value of coal. Coals with
7 to 12% moisture are generally burnt on chain grate and
travelling grate stokers. Coal analysis is done to know its
57. Thermal power station in Bangladesh:
A thermal power station is a power plant in which the prime
mover is steam driven. Water is heated, turns into steam and
spins asteam turbine which drives an electrical generator.
After it passes through the turbine, the steam is condensed in
a condenser and recycled to where it was heated; this is
known as a Rankine cycle. The greatest variation in the
design of thermal power stations is due to the different fossil
fuel resources generally used to heat the water. Some prefer
to use the term energy center because such facilities convert
forms of heat energy into electrical energy. Certain thermal
power plants also are designed to produce heat energy for
58. purposes of district heating, or desalination of
water, in addition to generating electrical power.
Globally, fossil fueled thermal power plants
produce a large part of man-made
CO2 emissions to the atmosphere, and efforts to
reduce these are varied and widespread.
In Bangladesh, Barapukuria Power Station which
is coal fired power plant and capacity is about
59. Environmental control
Fuel burnt in at thermal power plants contain harmful
impurities which are ejected into the environment as
gaseous and solid components of combustible products
and can adversely affect the atmosphere and water.
Toxic substances contained in the flue gases discharge
from chimneys of thermal power plants can produce
harmful effects on the whole of complex of living nature.
60. The flue gases may contain the following:
• Oxides of carbon and hydrogen
• Fly ash
• Solid particles of unburnt fuel
• Oxides of sulphur and nitrogen
Thermal power plants consume more than 1/3 of all the
fuels produced and thus can significantly affect the local
environment and the whole of bio-shepre comprising the
atmospheric layer near the earth’s surface and upper
layers of soil and water basins.
61. Advantages and disadvantages
• The fuel used is quite cheap.
• Less initial cost as compared to other generating plants.
• It can beinstalled at any place iirespective of the
existence of coal. The coal can be transported to the site
of the plant by rail or road.
• It require less space as compared to Hydro power
• Cost of generation is less than that of diesel power
• It pollutes the atmosphere due to production of large
amount of smoke and fumes.
• It is costlier in running cost as compared to Hydro
63. Present situation in Bangladesh:
At present , Barapukuria Power Station which is coal fired and
produced electricity about 250 MW. There are several oil and
gas fired power plant among them largest one is Ghorasal
and produced electricity about 950 MW and Ashuganj power
station is also largest power station which produce electricity
about 638 MW . Bangladesh have lots of gas resources.
That’s why there have many gas turbine powered power
plants.There are one hydroelectric power plants which
produced electricity about 230MW and having five turbine.
Ruppur Nuclear Power Plant is a proposed 2,000 MW nuclear
power plant. Planned to go into operation by 2020, it will be
the country's first nuclear power plant.
Steam power plants are located at the water and coal
available places. Steam is utilized to run the turbines, in
turn gives the power to generator and generator
produces the electricity, the electricity is utilized for
lighting, running the industries, for lighting of offices,
schools, etc. Boiler is an important component of the
power plants, it produces the steam.