Introduction to Thermal Power Plant
The Role of Thermal Power Plant in the Modern Power Generation Scenario
The development of thermal power plant in any country depends upon the available resources in that country. The hydro-power plant totally depends on the natural availability of the site and the hydrological cycle. The new sites cannot be created manually for hydropower plants.
The development of nuclear power requires high investment and technology. Many tinies, hydro-power plant suffers if the drought comes even once during a decade and the complete progress of the nation stops. The calamity of rain drought on power industry has been experienced in many states in the country.
To overcome this difficulty, it is necessary to develop thermal power plants in the country which are very much suitable for baseload plants. The coal resources in India account for about 5.7% of the proven reserves in the world.
The geological reserves of coal in India are 193.8 billion tonnes. The thermal power sector contributing nearly about 66% of installed capacity in India. The coal production in the country is increasing at the rate of 4.6% every year and new plants are set in many parts of the country to increase the power production to meet the demand to increase the per capita income of the country. Due to increased power generation –
- Countries income can be increased.
- Standard of living can be increased.
- Reducing the unemployment
- Development in all the sectors.
- Development in new technology.
- GDP of the country can be increased.
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The layout of the Modern Thermal Power Plant
The general layout of the thermal power plant as shown in the figure and it consists of the following four circuits:
- Coal and ash circuit
- Ash and gas circuit
- Feedwater and steam flow circuit
- Cooling water circuit.
The above circuits consist of:
- Coal storage.
- Coal handling plant.
- Ash storage and ash handling plant.
- High-pressure boiler.
- Boiler accessories such as Air pre-heater, economiser, superheater and feed water supply unit.
- Condenser and condensate extraction pump.
- Cooling tower and water circulating pump.
- Draught system.
- Boiler chimney.
Working of Thermal Power Plant
Coal received in the coal storage yard of the power station is transferred in the furnace by coal handling unit. The heat generated due to burning of coal is used in converting water included 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. The pressure decreases after some work done in the turbine. Steam after leaving the turbine pass through the condenser which maintains the low pressure at the exhaust of the turbine.
The pressure of the steam in the condenser depends on the flow rate and temperature of the cooling water flow, and on the effectiveness of the air removal equipment. Water circulating through the condenser may be taken from the various sources such as river, lake or sea.
If a sufficient amount of water is not available, the hot water coming out of the condenser can be cooled in cooling towers and circulated through the condenser again. Bled steam taken from the turbine at extraction points is sent to low pressure and high-pressure water heaters.
The air taken from the environment is first passed through the air preheater, where it is heated by exhaust gases. The hot air then passes through the furnace. The exhaust gases flow through the dust collector and then through the economiser, air pre-heater and finally, they are exhausted to the atmosphere through the chimney.
Factors for Selection of Site for Thermal Power Plant
Following factors are to be considered for the selection of site:
1. Availability of Coal
The coal should be available in sufficient quantity nearer to the plant at low cost.
2. Ash Disposal Facilities
There must be sufficient space to dispose of a large quantity of ash.
3. Space Requirement
Sufficient land should be available for the construction of the plant at low cost with future expansion scope.
4. Nature of land
The site for the plant should have good bearing capacity to withstand the dead load of the plant.
5. Availability of water
A large quantity of water should be available for drinking, condensing, for disposal of ash and as feedwater at low cost throughout the year nearer to the site.
6. Transportation facilities
The site should be connected by suitable transportation lines such as road and rail to bring the machinery, coal etc.
7. Availability of labour
The cheap and large number of labours should be available at the proposed site as a large number of labours are is required during the construction of the plant.
8. Public problem
The site should be away from the towns to avoid the nuisance from smoke, fly ash, etc.
9. Nearness to the load centre
The site should be nearer to the load centre to reduce the transmission cost and losses.
- The initial cost of the plant
- The nature and magnitude of load to be handled.
- The necessity of future expansion of the plant.
Materials Required for Thermal Power Plant
Following basic materials are essentially required by the thermal power plant:
- Cooling water.
- Water for ash disposal.
The feed water is the water circulated through a closed circuit of the power plant which is further converted into steam in the boiler. For example, a plant of 100 MW capacity may require nearly 500 tons of water per hour to be circulated through the system
The coal is required for converting the feed water into the steam in the boiler. A sufficient quantity of coal is required. So that the plant should run without any stoppage due to the coal shortage. Nearly 1500 tons/day coal is required for 100 MW capacity plant generating 5 kg/kWh of steam.
3. Cooling water
The cooling water is required for condensing the steam coming out from the turbines. Nearly 25000 tons/hr quantity of water is required for a 100 MW plant.
4. Water for ash disposal
The large quantity of water is required for disposing of the ash. Nearly 5 kg of water is required per kg of ash disposal.
5. SO2 (Low Sulfur contains coal)
We should always be required to have low sulfur content coal because on burning such coal generates SO2 and it is highly poisonous to human and animal health and as well as for the crops. Nearly 1.8 tons/hr amount of SO2 is coming out by burning the coal containing sulfur up to 1 to 1.5% in 100 MW capacity plant. This SO2 should be properly removed from the exhaust gases through improved technology.
Air is required for the combustion of the fuel as well as required for cooling the water in the cooling tower. Nearly 1200 tons of air per hour for 100 MW capacity plant, in addition to this nearly 25000 tons of air per hour is to be required for circulating in the cooling tower.
Types of Fuels Utilized in Thermal Power Plant
Following are the types of fuels utilised in thermal power plant :
- Natural gas
- Geothermal energy
- Nuclear fuel
- Waste heat from industrial process
- Biomass – These plants are fuelled by waste from sugarcane, landfill methane and municipal waste, etc.
- Solar heat
- Blast furnace gas.
Advantages of Thermal Power Plants
Following are the advantages of thermal power plants:
- Fuel cost of the thermal power plant is relatively low.
- Thermal energy can be produced everywhere in the world.
- The heat production system is simple compared to other systems.
- The overall system is cost-effective.
- Easy mechanism.
- Same heat could be reused.
- Easier maintenance of the power station.
- Use of water is prominent here, therefore any places with ample of water is a perfect location for installing a thermal power plant.
- These plants require comparatively small space to be installed.
- Its construction cost is cheaper due to the nearness of urban areas.
- These plants are completed within a few years.
- They are generally located near the urban areas.
- Scope of expansion is unlimited.
- These are located in a place where the displacement of people is minimum.
- They can be located near the consuming centres.
- The cost-benefit ratio is always better than the hydel power plant.
Disadvantages of Thermal Power Plant
Following are the disadvantages of thermal power plant:
- The raw materials used are exhaustible resources,
- The ability of these plants depends on the quality of coal.
- High maintenance cost.
- High production of CO2 in the atmosphere.
- Exhaust gases harm outside the environment badly.
- Low overall efficiency.
- Thermal engines require a huge amount of lubricating oil that is very expensive.
- Nuclear thermal power plant demands an excessive amount of water for cooling purpose.
- Coal type thermal power plant requires a larger duration before it supplies the generated power to the grid.
- This type of power station is ultimately responsible for the rise in seawater level.
- Shorter life span.
- It is very difficult to maintain the optimum supply for a long period.
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