anna university of technology second semester BCM power plant engineering notes




Unit III
(Power Plant Engineering, Pumps and Turbines)

Steam Power Plant
                    Steam is used to drive steam engines and steam turbines due to the following reasons:
  1. Steam can be raised quickly from water
  2. It does not react much with materials.
  3. It is stable at temperatures required in the plant
Layout of Steam Power Plant:
The layout of steam power plant has the following circuits:
  1. Fuel (Coal) and ash circuit
  2. Air and flue gas circuit
  3. Feed water and steam flow circuit
  4. Cooling water flow circuit.


Coal and Ash Circuit:
         Coal from mines is delivered by ships, rails or trucks to the power station.
          Coal received at coal yard.
         Coal is sized by crushers, breakers etc.,
         The sized coal is stored in coal storage.
         From stock yard, the coal is transferred to the boiler furnace by means of conveyors, elevators etc.,
          The coal is burnt in the boiler and ash is formed.
         Ash coming out of the furnace will be too hot, dusty and accompanied by poisonous gases.
          The ash is transferred to the ash storage.
         Generally the ash will be quenched to reduce the temperature and the dust content.

Air and Flue Gas Circuit:
         Air is taken from the atmosphere by the action of FD fan.
          It is passed through an air pre heater
          The air is preheated by the flue gases in the pre heater.
          This preheated air is supplied to the furnace to aid the combustion of fuel.
         Due to the combustion of fuel the flue gases are formed.
          The flue gases from the furnace pass over the boiler tubes and super heater tubes.
          Then the flue gases pass through economiser to heat the feed water.
          After that it passes through a dust collector.
 It is then exhausted to atmosphere through chimney

Water and Steam Circuit:
Layout of Steam Power Plant
Water and Steam Circuit:
          The water is preheated by the flue gases in the economiser.
          This preheated water is then supplied to the boiler drum.
          Heat is transferred to the water by the burning of the coal.
          Due to this, water is converted into the steam.
          The steam raised in boiler is passed through a super heater.
         It is superheated by the flue gases.
          The turbine drives generator to produce electric power.
          The expanded steam is then passed through the condenser.
         In the condenser, steam is condensed into water the re circulated.

Cooling Water Circuit:
         The exhaust steam from the turbine is condensed in the condenser.
          In the condenser, the cold water is circulated to condense the steam into water.
         The steam is condensed by loosing its latent heat to the circulating the cold water.
         Hence the cold water gets heated.
          This hot water is then taken to a cooling tower.
          In cooling tower the water is sprayed in the form of droplets through nozzles.
         The atmospheric air enters the cooling tower from the openings provided at the bottom of the tower.
          This cold water is again circulated through the pump, condenser and the cooling
         Some amount of water may be lost during circulation.
          Hence make up water is added to the pond by means of a pump

Layout  of Steam ( Thermal) Power Plant
Energy Conversion Process:
Chemical Energy  (Fuel/Coal)
Heat Energy   (Boiler)
Mechanical Energy  (Turbine)
Electrical Energy     ( Generator)
Advantages of Steam Power Plant (Thermal plant)
         Life of plant is more (25-30 years ) compared to Diesel plant (2-5 years)
          Repair and maintenance cost is low when compared to diesel plant.
          Initial cost is less compared to nuclear plant.
          Suitable for varying load conditions.
          No radio active harmful wastes are produced
          Unskilled operators can operate the plant.
          The power generation does not depend on the water storage.
          There are no transmission losses, as they are located near load centres.
Disadvantages of thermal power plant:
         Less efficient than diesel plants.
          Starting up and bringing into service takes more time.
         Cooling water required is more.
          Space required is more.
          Storage required for the fuel is more.
          Ash handling is a big problem
          Not economical in areas which are remote from coal fields.
          Manpower required is more.
          For large units, the capital cost is more.
List down the factors to be considered for selection of site for thermal power plant:
Availability of coal:
         A thermal plant of 400M, capacity requires nearly 6000 tons of coal every day.
         Power plant should be located near coal mines.
Ash Disposal Facilities:
         Ash comes out in hot condition and handling is difficult.
 The ash can be disposed into sea or river.

Water Availability :
          Water consumption is more as feed water into boiler, condenser and for ash disposal.
          Water is required for drinking purpose.
          Hence plant should be located near water source.
Transport Facility :
          Railway lines or other mode of transport for bringing heavy machineries for installation also for bringing coal.
Public Problems:
          The plant should be far away from residential area to avoid nuisance from smoke, fly ash and noise.
Nature of Land :
          Many power plants have failed due to weak foundations.
          Land (soil) should have good bearing capacity to withstand dead load of plant.
Thermal power plants in Tamil Nadu:
Explain about the pollution caused by Thermal Power Plant (Steam Power Plant):
         Main pollutants from thermal plants are SO2, CO2, CO as minute particles such as fly ash.
         SO2 causes suffocation, irritation to throat and eyes and respiratory for people. It destroys crop.
         CO is a poisonous gas.
          Dust particles cause respiratory troubles like cough, cold, sneezing etc.,
Thermal Pollution:
          Thermal plants produce 40 millions kJ of heat to the environment through condenser water and exhaust gases.
          Thermal pollution of atmosphere can be reduced using the low grade energy exhausted steam.
Noise Pollution:
          The sources of noise in a power plant are turbo alternators, fans and power transformers.
          Sound proofing can be done to reduce the noise.
Gas Power Plant
         A gas power plant uses gas turbine as the prime mover for generating electricity.
          It uses natural gas or kerosene or benzene as fuel.
          Gas plant can produce only limited amount of the electricity.
         Efficiency of the plant is only 35%
         Generally a gas plant is expensive to operate.
         Hence it is usually installed with steam power plant in closed combined cycle.
         It is generally used in combination with steam/thermal power plant during peak load
          When the gas power plant is combined with thermal/steam power plant efficiency of the plant is up to 60% - 70%

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