BASIC CIVIL AND MECHANICAL ENGINEERING
(Power Plant Engineering, Pumps and Turbines)
Steam Power Plant
Steam is used to drive steam engines and steam turbines due to the following reasons:
- Steam can be raised quickly from water
- It does not react much with materials.
- It is stable at temperatures required in the plant
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.
DIAGRAM WILL BE THERE IN NOTES
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:
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.
• 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 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.
• 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%