Dr Jaspal Singh, Chief Engineer, Guru Angad Dev Veterinary and Animal Sciences University, Ludhiana
In India, the major source of power generation is thermal energy. Over 65% of electric power is made by thermal plants in India. The country has a huge store of coal (about 170 billion tons) – the fifth largest in the world. A thermal power plant converts the thermal energy of coal into electrical energy. Coal is burnt in a boiler that converts water into steam. The growth of steam in the turbine produces mechanical power that drives the generator coupled to the turbine.
Though the thermal power plants contribute most to the generation of power in any nation, they are going to be closed due to their inability to meet the emission guidelines. The Central Pollution Control Board (CPCB) has given warnings to shut down plants that are old and whose carbon outflow levels are high. The land so emptied could be put to an elective use.
In enormous urban communities with population of over one million, clean air is a concern. The administration proposes to support expressions that are figuring and actualizing plans to guarantee cleaner air in urban areas of over one million. The increasing demand of electricity leads to increase in the number of solar plants as these plants do not produce pollution as compared to thermal power plants in which coal is the major source used for production of electricity. In fact, there are plenty of options to choose from for energy generation. While fossil fuels are still the most common, solar thermal power is gaining popularity. One of the main advantages of solar power is that it is economical and more efficient. With its ability to store energy to be used at one’s discretion, this power source is adaptable and less wasteful.
Uses of Fly Ash – a by-product of thermal power plants
Thermal power plants produce fly ash in which coal is used as a fuel for the generation of electricity. The utilization of fly ash is as follows:
- About 40–70% fly ash is used in building bricks which are environment friendly and economically viable.
- Use of fly ash in the manufacture of distemper has replaced white cement. Fly ash distemper is used for interior surfaces with satisfactory performance. This would decrease the cost of production of distemper by 50%.
- Fly ash-based ceramics provide superior resistance against abrasion.
- In developed countries, ready-mix concrete is quite popular; but in India, it utilizes less than 5% of total cement consumption. Recently, the application of ready-mixed concrete has grown at a rapid rate. Several ingredients and quality parameters are strictly controlled in ready-mix concrete, which is not so possible in concrete production at site and it may accommodate higher quantity of fly ash.
- Fly ash used in road construction saves surface soil, avoiding formation of low lying areas. Fly ash is also used for stabilizing and constructing the sub-base or base, for filling purposes etc. The use of concrete with fly ash (10–20% by wt.) is quite cost effective and enhances the performance of rigid pavement. The mixture of soil with fly ash and lime enhances California Bearing Ratio (CBR) to 84.6%.
- As an engineering material, the properties of fly ash are somewhat unique. For the construction of embankments, soils are used; but fly ash has a large uniformity coefficient due to clay-sized particles. The properties that affect fly ash use in embankments include compaction characteristics, grain size distribution, shear strength, compressibility, permeability, and frost susceptibility.
The schematic line diagram of thermal power plant is shown in Fig.1.
The whole arrangement can be divided into the following stages:
- Coal and dust handling arrangement
- Steam generating plant
- Steam turbine
- Alternator generator
- Feed water
- Cooling arrangement
Figure 1: Schematic Line Diagram of thermal power plant
Coal and Dust Handling Arrangement
The coal is transported to the power station by road or rail and is put away in the coal stockpiling plant. From the coal stockpiling plant, coal is conveyed to the coal handling plant where it is crushed into tiny pieces to increase its surface area. The squashed coal is sustained to the boiler by belt transports. The coal is burnt in the boiler and the ash produced (after complete combustion of coal) is removed to the ash handling plant and then delivered to the ash storage plant for disposal. The expulsion of the cinder from the boiler is vital for legitimate consuming of coal.
Steam Generating Plant
The steam generating plant comprises of a boiler for the production of steam and other supporting gear for the utilisation of flue gases.
The function of boiler is to generate steam at the desired pressure and temperature by transferring heat produced by burning of fuel in a furnace to convert water into steam. The flue gases produced from the boiler pass through the superheater, economiser, air preheater and then are finally exhausted in the atmosphere through the chimney.
The steam delivered in the boiler is commonly wet and is gone through a superheater where it is dried and superheated. Superheating gives two main advantages. Firstly, the overall efficiency is expanded. Furthermore, a lot of build-up in the last phases of turbine, which would cause sharp edge consumption, is neglected. The superheated steam from the superheater is nourished to steam turbine through the principle valve.
An economiser is basically a feed water heater and derives heat from flue gases for this purpose. The feed water is fed to the economiser before supplying to the boiler. The economiser extracts a part of heat of flue gases to increase the feed water temperature. This use of economizer results in saving coal consumption and higher boiler efficiency.
An air preheater increases the temperature of the air provided 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 preheater before providing to the boiler furnace. The air preheater separates heat from flue gases and increases the temperature of air utilized for coal ignition. The important advantages of preheating the air are increased thermal efficiency and increased steam capacity per square metre of boiler surface.
The dry and superheated steam from the superheater is sustained to the steam turbine through main valve. The heat energy of steam when passing over the blades of turbine is converted into mechanical energy. After giving heat energy to the turbine, the steam is exhausted to the condenser which condenses the exhausted steam by means of cold water circulation.
The steam turbine is coupled to an alternator. The alternator converts mechanical energy of turbine into electrical energy. The electrical output from the alternator is delivered to the bus bars through transformer, circuit breakers and isolators.
The condensate from the condenser is used as feed water to the boiler. Some water may be lost in the cycle which is suitably made up from external source. The feed water on its way to the boiler is heated by water heaters and economiser. This helps in raising the overall efficiency of the plant.
To improve the efficiency of the plant, the steam exhausted from the turbine is condensed by means of a condenser. Water is drawn from a natural source of supply such as a river, canal or lake and is circulated through the condenser. The circulating water takes up the heat of the exhausted steam and it becomes hot. This hot water coming out from the condenser is discharged at a suitable location down the river. In case, the availability of water from the source of supply is not assured throughout the year, cooling towers are used. During the scarcity of water in the river, hot water from the condenser is passed on to the cooling towers where it is cooled. The cold water from the cooling tower is reused in the condenser.
Advantages of Thermal Power Plants
- Initial cost of thermal plants is very less.
- The fuel is quite cheap which is generally coal.
- The cost of generation is lesser than that of the diesel power station.
- Running cost is more as compared to hydroelectric plant
- Due to the large amount of production of smoke and flue gases, the atmosphere is getting polluted.
Fly ash flows into Sutlej; third incident in two years
The leakage of contaminated water from Guru Gobind Singh Super Thermal Plant, Ropar (GGSSTP) polluted the Sutlej river which in turn posing a threat to environment in the region. Hundreds of tonnes of ash produced by the plant everyday that was initially mixed with water, then through the pipes it had been dropped into the 3 ash sites together with different stages –
- Stage 1 dyke (350 acres)
- Stage 2 dyke (400 acres)
- Stage 3 dyke (225 acres)
The leakage continues to appear due to carelessness and lack of routine check of the dykes. Moreover, the flow of ash content was above the approved limit. This water percolates down to the ground water thereby polluting the drinking water and nearby agricultural land. The villagers were not being able to use the water of Sutlej River for different purposes. They had to take their animals to the contaminated water for drinking. Because they had no other option but soon the leakage of contaminated water was controlled.
Rise in pollution, Bathinda suffers
It is well known fact that Bathinda is an industrial town in which Guru Nanak Dev Thermal Power Plant (GNDTP) has been set up. Due to this, the nearby water resources, mainly ground water, starts polluting to a large extent. The disposal of waste from thermal power plants is a bigger issue, which we have been facing from generation to generation. If proper procedure is not followed for disposal of waste, then it will contaminate the ground water. Also, people living in areas near the plants come into contact with severe diseases due to the raining of coal ash.
The management has failed to bring the quality of ash contents emitted from it under control and make it environment friendly. Due to some renovations, the emission of fly ash was less than the prescribed limit which is 300 mg fly ash particles per cubic meter. Thereby, it was declared that Bathinda as a protected city. It was also added that the dumping of fly ash can be reduced by supplying fly ash free of cost to the Gujarat Ambuja, and was also provided for earth filling and other purposes.
Half of India’s coal fired plants fail to comply with emission norms
Around 80% industrial emissions which contain harmful gases such as sulphur and nitrous oxide from thermal power plants are responsible for the smog and acid rain. According to the analysis by Reuters and private industries, it is a well known fact that people are facing problems of clean and fresh air due to the generation of smog from the thermal power plants. Most thermal power plants have failed to meet the emission standards. This negligence comes to the headlines at a time when cities are battling hazardous levels of pollution according to the Air Quality Index. So, it is pertinent to reduce the emission of harmful gases from thermal power plants and meet the emission standards set up by the government.
The most commonly used material in thermal power plants is coal, but today, the coal available is of low quality as it contains large amounts of ash. Consumption of enormous quantity of coal in thermal power plant has created many adverse effects on the surroundings, resulting in world global climate change and fly ash management problem. Thermal power plants primarily based on coal are one of the major causes of pollution which leads to an adverse impact on the environment as well as on human health. So, it is essential to protect our environment by proper disposal of fly ash.
It is better to explore all reasonable applications for ash utilization. Fly ash can be utilized as a partial replacement of cement in concrete which has the same properties as that of cement. It can also be used as a fertilizer as it modifies the properties of soil, thereby improving the yield. Numerous government and non-government bodies are operating in the field of utilization of ash for construction of roads and embankments. Utilization of fly ash gives good result in almost every aspect, including strength, economic feasibility, and environmental friendliness. Today, solar energy plants are gaining more attention due to their higher efficiency and economic viability compared to thermal power plants.
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