thermal power plant

1. Electric Power Generation Transmission and
Distribution
Dr. Muhammad Farasat Abbas
Assistant Professor | Electrical Power Engineering
U.S.-Pak Center for Advanced Studies in Energy (USPCAS-E)
National University of Sciences and Technology (NUST)
farasat.abbas@uspcase.nust.edu.pk
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2. Structure of Power Systems
• Basic structure of power system
• Generation, Transmission and Distribution
• Generation, 11kV, 33kV
• Why not to generate high voltage at the first place to avoid transformer? Cooling, insulation,
material
• Transmission is cheaper at higher voltages, more power will be transferred, 500kV
• Higher the voltage lower the losses
• Sub-transmission to large consumer you can have generation here too.
• Primary (11kV), secondary distribution (440/220V)
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3. Structure of Power System
• HVDC long distance, back to back connection, two AC systems working on different frequencies
can only be connected through HVDC
• Primary or feeder voltage 11kV
• Secondary or consumer voltage 440V three phase, 220 V single phase
• Different kinds of consumers (domestic, industrial, commercial) would be there, electric utility is
obligated to supply energy of your own choice.
• System design, plan and operation
cost
Reliable
economic Pollution
loss
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4. Structure of Power System
• Regional grids National grid  International grid (SAARC countries)
• Divide the whole country into different regions so that they can be interconnected
• Regional grids strongly interconnected form a national grid
• Whole of Europe is a national grid
• Site of a power plant
• Thermal Hydro (least flexible)  water Nuclear  flexible
• Interconnection, surpluses to scarce area
technical
Economical
environmental
political
coal
load
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5. Advantages and Disadvantages of interconnected Power
System
• Advantages
• Use of older plants
• Economical operation
• Increase the reliability of power supply
• Exchange of peak load
• Increase the diversity factor
• Reduce capital and operating cost
• Disadvantages
• Expensive tie line
• Expensive circuit breaker
• Synchronization problem
• Metering and instrumentation
• Voltage control
• Frequency control
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6. Generating station
• Bulk electric power needs to be generated to meet the bulk load demands
• Bulk electric power is produced by special plants called, generating stations, power plants
• Employs a prime mover coupled to an alternator for the production of electric power
• Prime mover, steam turbine, water turbine etc.. Converts energy from some other form to
mechanical energy
• Alternator then converts the mechanical energy into electrical energy
• Electric energy produced is than transmitted and distributed with the help of conductors
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7. Conventional sources- Thermal
• Only three conventional sources, Thermal (coal, gas, oil), Hydro, Nuclear (fission, fusion)
• A generating station which converts heat energy of coal combustion into electrical energy is
known as a steam power station.
• Basically works on Rankine Cycle
• Steam is produced in the boiler by utilizing the heat of coal combustion
• Steam is than expanded in the prime mover (steam turbine)
• The steam turbine drives the alternator which converts mechanical energy into electrical energy
• This type of power generation is suitable where coal and water are available in abundance
• Fuel (coal) is cheap
• Less capital cost compared with other
generating stations
• Can be installed at any place
• Requires less space compared with hydro
• Cost of generation is lesser than that of the
diesel
• Pollutes the atmosphere
• Running cost is more than that of hydro
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8. Schematic
• Coal and Ash Handling Arrangement
• Coal is transported to the power station by road or
rail and is stored in the coal storage plant
• Why to store coal? To protect against coal strikes,
failure of transportation system and general coal
shortage
• From coal storage to coal handling plant where it is
pulverized
• Why to pulverize the coal? Rapid combustion,
surface exposure,
• Pulverized coal is then fed to the boiler by belt
conveyers
• The coal is burnt in the boiler* and ash is produced
after the complete combustion which is than
removed from ash handling plant and delivered to
ash storage plant
• Electrostatic precipitator
• From storage plant to where?, waste management,
road filling, buildings,
*Design of a boiler/burner is itself a research topic.
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9. Schematic of Coal Fired Steam Plant
• The removal of the ash is necessary for proper burning of coal.
• 100 MW station operating at 50% load factor (average load /max peak
load) may burn about 20,000 tons of coal per month and ash produced
may be of 10-15% of coal fired
• 50-60% operating cost consists of fuel purchasing and its handling.
• Steam generating plant
• Boiler and auxiliary equipment
• Heat of combustion of coal is utilized to convert water into steam at
high temperature and pressure
• The flue gases (CO2, NOx, SOx, etc.) from the boiler are exhausted into
the atmosphere through chimney, passing through super heater,
economizer and air-preheater.
• These flue gases affects environment, human, vegetables, combine
with water (acid is formed), acid rain
• The steam produced in the boiler is wet and is passed through the
super heater (90 bars @450 0C) where it is dried (steam temperature
increased above that of boiling point of water).
• Two principle benefits of super heating; 1)overall efficiency increased
[dry steam contains more thermal energy] 2) too much condensation
(conversion of gas/vapor to liquid) is avoided
• Superheated steam is then fed to steam turbine through main valve.
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10. Schematic of Coal Fired Steam Plant
• Feed water is fed into the economizer before it is fed to boiler
• ofEconomizer is essentially a feed water heater
• Air pre-heater increased the temperature air supplied for
coal burning by deriving heat from flue gases
• Air is drawn from the atmosphere by a forced draught fan and
is passed through air pre-heater before supplying to the boiler
furnace.
• Steam Turbine
• The dry and superheated steam from the super heater is fed
to the steam turbine through main valve.
• Heat energy of steam passing over the blades of turbine is
converted into mechanical energy
• After giving heat energy to turbine, steam is exhausted to the
condenser
• Alternator
• Turbine is coupled with alternator which converts mechanical
energy into electrical energy which is then delivered to the
bus bar through transformer, circuit breaker and isolator
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11. Schematic of Coal Fired Steam Plant
• Feed Water: The condensate from the
condenser is used as feed water to the boiler
• Some water may be lost which is
compensated from external source
• Cooling arrangement
• Steam exhausted from the turbine is
condensed by means of condenser
• Water is drawn from a natural resources
(river, canal, ) and is circulated through
condenser
• Water coming out of condenser is discharged
into suitable location in river
• During the scarcity of water in river, hot water
from the condenser is passed on the cooling
towers where it is cooled which is then
reused in the condenser
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12. • higher the temp. higher the pressure, more efficiency
• Larger the size of unit better it is. World’s practice
• Large units consumes less fuel, less pollution,
• Only advantages having large units?
• Suddenly large unit is not available will put the system in shock
• 10% cap
• 6720MW, Tuoketuo Power Station, which country
• 1320MW
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13. • Ways to reduce pollution due to thermal power plants
• Min. emission dispatch, minimize the emission and forget about the cost
• Fluidized bed boiler
• Cogeneration, simultaneous generation of heat and power
• Industrial use and space heating
• Chemicals, paper, textile, food, petroleum refining
• Wheeling and banking of electric power
• Wheeling of power: Four/five industry together install a power plant and forget about govt.
supplied power
• Take power from you in Islamabad and give you power in Multan: Banking
• Primary aim to generate power secondary aim is heat is called Topping cycle
• Primary aim is to get heat first and if there is any waste heat generate power from it.
• Acid rain and greenhouse effect, thanks to so called progress.
• You can minimize, can’t make it zero.
• Solar energy has zero pollution?
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14. Choice of site for steam power stations
• Supply of fuel, should be near the coal mines to minimize the transportation cost
• Availability of water, huge amount of water is required for condenser, therefore plant should be
located near canal, river to ensure the continuous supply of water
• Transportation facilities, plant should be well connected with other parts of the country
• Cost and type of land, plant should be installed where land is cheap and can be extended,
bearing capacity of the ground should be adequate so that the heavy equipment should be
installed
• Near to load center, to reduce the transmission cost
• Distance from populated area, smoke and fumes pollute the surrounding areas therefore plant
should be located at a considerable distance from the populated areas
• There is no place where you can find all these factors in favour.
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15. Efficiency
• The overall efficiency of steam power station is low i.e. 29%
because of two reasons
• 1. huge amount of heat is lost in the condenser
• 2. heat losses occur at various stages of the plant
• Heat loss in the condenser can not be avoided. Because
heat energy can not be converted into mechanical energy
without any temperature difference
• Greater the temperature difference, greater the heat
energy will be converted into mechanical energy
• Thermal efficiency,
• η𝑡ℎ𝑒𝑟𝑛𝑎𝑙 =
𝐻𝑒𝑎𝑡 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑜𝑓 𝑚𝑒𝑐ℎ.𝑒𝑛𝑒𝑟𝑔𝑦
𝑡𝑟𝑎𝑛𝑠𝑚𝑖𝑡𝑡𝑒𝑑 𝑡𝑜 𝑡𝑢𝑟𝑏𝑖𝑛𝑒 𝑠ℎ𝑎𝑓𝑡
𝐻𝑒𝑎𝑡 𝑜𝑓 𝑐𝑜𝑎𝑙 𝑐𝑜𝑚𝑏𝑢𝑠𝑡𝑖𝑜𝑛
• Thermal efficiency of modern steam power station is 30%.
• If 100 calories of heat is supplied by coal combustion, then
mechanical energy equivalent of 30 calories will be
available at the turbine shaft and rest is lost.
• More than 50% of total heat of combustion is lost in the
condenser
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Turning heat into electricity, thermoelectric devices
are made from the materials that can convert a
temperature difference into electricity without
requiring any moving parts. The phenomena is
reversible, apply the electricity to thermoelectric
device and it can produce a temperature difference.
Today thermoelectric devices are only used for low
power applications, but scientists are hopping to
design more powerful thermoelectric devices
Topological materials which have unique electronic
properties
There has been little understanding as to how
electrons in such topological materials would travel in
response to temperature differences in order to
produce thermoelectric effect
*If interested, read MIT research articles on it.

16. Efficiency, contd..
• Overall efficiency, the ratio of heat equivalent of electrical output to the heat combustion of coal
is known as overall efficiency of steam power station
• η𝑜𝑣𝑒𝑟𝑎𝑙𝑙 =
𝐻𝑒𝑎𝑡 𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑜𝑓 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑜𝑢𝑡𝑝𝑢𝑡
𝐻𝑒𝑎𝑡 𝑜𝑓 𝑐𝑜𝑎𝑙 𝑐𝑜𝑚𝑏𝑢𝑠𝑡𝑖𝑜𝑛
• The overall efficiency of a steam power station is 29%
• Overall efficiency is less than the thermal efficiency why??
• Overall efficiency= Thermal efficiency × Electrical efficiency
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17. Equipment of Steam Power Station
• Steam generating equipment [boiler, boiler furnace, super-heater, economizer, air pre-heater]
• Condenser [Jet condenser, surface condenser]
• Prime mover [Impulse turbines, reaction turbines]
• Water treatment plant
• Electrical equipment [alternators transformers, switchgear]
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18. Equipment of Steam Power Station
• Concerned with the generation of superheated steam and includes boiler, boiler furnace, super heater,
economizer, air pre-heater
• Boiler, closed vessel in which water is converted into steam by utilizing the heat of coal combustion
• 1- Water tube boilers [water flow through the tubes and the hot gases of combustion flow over these
tubes], smaller size, less space, higher working pressure, universally used
• 2- Fire tube boilers [hot products of combustion pass through the tubes surrounded by water]
• Boiler Furnace, chamber in which fuel is burnt to liberate the heat energy, walls made of refractory
materials such as fire clay, silica, kaolin etc. These materials have the property to resist the change of
shape, weight, or physical properties at higher temperatures.
• (1) Plain refractory walls, (2) Hollow refractory walls, (3) water walls
• Refectory materials may get damaged at higher temperatures.
• Super heater, superheats the steam to increase the overall efficiency of the plant, A superheater
consists of a group of tubes made of special alloy steels
• 1.Radiant super-heater, 2.convection super-heater (disadv)
• 1Temperature of super-heater falls with increase in steam output in radiant type
• 2Temperature of super-heater increases with the increase in steam output
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19. • Prime mover converts steam energy into mechanical energy
• 1-impulse turbines 2-reaction turbines
• 1.Steam expands completely over fixed blades and pressure over the moving blades remain
constant
• 2.Steam expands partially over the fixed blades and remaining expansion takes place during its
flow over the moving bladed.
• Water treatment plant, boiler needs clean and soft water for longer life but water from river has
impurities
• The suspended impurities are removed through sedimentation, coagulation and filtration
• Electrical equipment, alternator, transformer, switchgear
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Equipment of Steam Power Station

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21. 1- Overall efficiency=20%, Coal burnt=0.6kg per kWh, Calculate calorific value?
2- max demand=20000kW, load factor=40%, boiler efficiency=85%, turbine efficiency=90%, coal
consumption=0.9kg/kWh, cost of 1 ton of coal = 300 RS, calculate thermal efficiency and coal bill
per anum?
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