THERMAL POWER PLANTS.doc (Size: 1.34 MB / Downloads: 228)
Due to the growth in population and industrial growth the demand for power is increasing in the country by leaps and bounds. But the power production through hydro-electric projects and through nuclear power projects is not keeping pace with the demand. Thermal power offers a ray of hope in this scenario. Power development is the key to the economic development. The per capita consumption of electricity in the country also increased from 15 kWh in 1950 to about 338 kWh in 1997 -98, which is about 23 times. However this is very small compared to the developed world. Still about 15% of the villages are not electrified. The quality and quantity of electricity supply is also very poor.
Coal based thermal power stations are presently the mainstay of power development and this is likely to be so in the immediate future also, considering the present status of the projects and various constraints in development of hydro and nuclear power. There are several advantages as well as disadvantages for thermal power generation. However the advantages overweigh the disadvantages. The thermal power is the only ray of hope for the country.
India’s largest power company, NTPC was set up in 1975 to accelerate power development in India. NTPC is emerging as a diversified power major with presence in the entire value chain of the power generation business. Apart from power generation, which is the mainstay of the company, NTPC has already ventured into consultancy, power trading, ash utilization and coal mining. NTPC needs to be encouraged in all possible manner not only to increase the thermal power production but also to increase its efficiency by adopting latest technological innovations.
Ultra Mega Power projects (UMPP) are a series of ambitious power projects planned by the Government of India. With India being a country of chronic power deficits, the Government of India has planned to provide 'power for all' by the end of the eleventh plan (by 2012). This would entail the creation of an additional capacity of at least 100,000 MW by 2012. The Ultra Mega Power projects, each with a capacity of 4000 megawatts or above, are being developed with the aim of bridging this gap. Already some UMPP’s are under implementation at Saasan-(Reliance Energy), Mundra-(TATA power), Kudagi-(NTPC) etc.
Hitachi has recently developed products and services for advanced support for maintenance and preservation through the use of IT (information technology) and network technology, going beyond what has previously been available. This technological innovation needs to be adopted by the existing as well as forth coming power plants not only to increase the efficiency of power production but also to increase the life of the power plants.
The per capita availability and consumption of electricity is very less in the country as compared to the developed world. The rapid economic growth and the resultant increased standard of living of the population calls for huge increase in supply of power. The growing population as well as rapidly expanding industry also demands for a huge supply of power. In this context increasing thermal power production assumes great significance in the country.
The power sector has registered significant progress since the process of planned development of the economy began in 1950. Hydro -power and coal based thermal power have been the main sources of generating electricity. Nuclear power development is at slower pace, which was introduced, in late sixties. The concept of operating power systems on a regional basis crossing the political boundaries of states was introduced in the early sixties. In spite of the overall development that has taken place, the power supply industry has been under constant pressure to bridge the gap between supply and demand.
A thermal power station is a power plant in which the prime mover is steam driven. Water is heated, turns into steam and spins a steam turbine which drives an electrical generator. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated; this is known as a Rankine cycle. The greatest variation in the design of thermal power stations is due to the different fuel sources. Some prefer to use the term energy center because such facilities convert forms of heat energy into electrical energy. Some thermal power plants also deliver heat energy for industrial purposes, for district heating, or for desalination of water as well as delivering electrical power. A large proportion of CO2 is produced by the worlds fossil fired thermal power plants; efforts to reduce these outputs are various and widespread.
Almost all coal, nuclear, geothermal, solar thermal electric, and waste incineration plants, as well as many natural gas power plants are thermal. Natural gas is frequently combusted in gas turbines as well as boilers. The waste heat from a gas turbine can be used to raise steam, in a combined cycle plant that improves overall efficiency. Power plants burning coal, oil, or natural gas are often referred to collectively as fossil-fuel power plants. Some biomass-fueled thermal power plants have appeared also. Non-nuclear thermal power plants, particularly fossil-fueled plants, which do not use co-generation are sometimes referred to as conventional power plants.
Reciprocating steam engines have been used for mechanical power sources since the 18th Century, with notable improvements being made by James Watt. The very first commercial central electrical generating stations in the Pearl Street Station, New York and the Holborn Viaduct power station, London, in 1882, also used reciprocating steam engines. The development of the steam turbine allowed larger and more efficient central generating stations to be built. By 1892 it was considered as an alternative to reciprocating engines Turbines offered higher speeds, more compact machinery, and stable speed regulation allowing for parallel synchronous operation of generators on a common bus. Turbines entirely replaced reciprocating engines in large central stations after about 1905. The largest reciprocating engine-generator sets ever built were completed in 1901 for the Manhattan Elevated Railway. Each of seventeen units weighed about 500 tons and was rated 6000 kilowatts; a contemporary turbine-set of similar rating would have weighed about 20% as much.
The energy efficiency of a conventional thermal power station, considered as salable energy (in MW) produced at the plant, is typically 33% to 48% efficient. This efficiency is limited as all heat engines are governed by the laws of thermodynamics . The rest of the energy must leave the plant in the form of heat. This waste heat can go through a condenser and be disposed of with cooling water or in cooling towers. If the waste heat is instead utilized for district heating, it is called co-generation. An important class of thermal power station are associated with desalination facilities; these are typically found in desert countries with large supplies of natural gas and in these plants, freshwater production and electricity are equally important co-products.
1.3 Growth of Indian Power Sector
Power development is the key to the economic development. The power Sector has been receiving adequate priority ever since the process of planned development began in 1950. The Power Sector has been getting 18-20% of the total Public Sector outlay in initial plan periods. Remarkable growth and progress have led to extensive use of electricity in all the sectors of economy in the successive five years plans. Over the years (since 1950) the installed capacity of Power Plants (Utilities) has increased to 89090 MW (31.3.98) from meagre 1713 MW in 1950, registering a 52d fold increase in 48 years. Similarly, the electricity generation increased from about 5.1 billion units to 420 Billion units – 82 fold increase. The per capita consumption of electricity in the country also increased from 15 kWh in 1950 to about 338 kWh in 1997 -98, which is about 23 times. In the field of Rural Electrification and pump set energisation, country has made a tremendous progress. About 85% of the villages have been electrified except far-flung areas in North Eastern states, where it is difficult to extend the grid supply.
1.4 Development of Coal Based Generation
Coal based thermal power stations are presently the mainstay of power development and this is likely to be so in the immediate future also, considering the present status of the projects and various constraints in development of hydro and nuclear power. As per the present estimates, the coal reserves in the country are the order of 202 billion tones with the bulk of the reserves lying in the Eastern Region states of Bihar, Orissa and West Bengal. Of the coal produced about 70% is consumed in the power sector. Presently, about 200 Million Tonnes of coal is consumed yearly in the power sector and this requirement would continue to increase in the coming years. The Planning Commission in the 9th plan document has projected a coal demand in the country for end of 11th plan (2011-12) of 775 MT and production of 672 MT leaving a gap of about 103 MT. It is estimated that the demand for coal by the power sector is likely to be substantially in excess of the production by the end of Ninth and Tenth Plan periods. This demand would need to be met by importing coal and augmenting domestic coal producing capability. Both the options would require special efforts and policy measures. The Government had taken a major step in opening up coal mining to the private sector. It is hoped that substantial private participation would give a boost to the domestic production. Besides quantity, the quality of Indian coal has been a major problem and concern for the power supply industry. With ash content of coals being in the range of 30-50%, the beneficiation of coal assumes special significance. Establishment of washeries therefore assumes a great importance and country has t o address this problem seriously. So far the power sector has relied primarily on railways for coal transportation. However, there are considerable constraints in this area and other modes of transport, viz. shipping, rail-cum-sea route for coastal projects will have to be examined on case to case basis. Keeping in view the problems of fly ash and the high ash content coal, the desirable option would be to develop large pit head coal projects and transmit the power to the load centers. Only Washed Coal should be transported to load centre stations and washery rejects may be utilized through fluidized bed boilers in power stations at the pit head itself.
WORKING OF THERMAL POWER PLANT
2.1 Diagram of a typical coal fired thermal power station
2.2 Block Diagram
2.3 Working of Thermal power plant
1.3.1 Feedwater heater
A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler. Preheating the feed water reduces the irreversibility involved in steam generation and therefore improves the thermodynamic efficiency of the system. This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feed water is introduced back into the steam cycle.
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.
2.3.3 Steam condensing
The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiency of the cycle increases.
2.3.4 Electrical Generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy.
2.3.5 Steam Turbine
A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion.
1. The fuel used is quite cheap.
2. Less initial cost as compared to other generating plants.
3. It can be installed at any place irrespective of the existence of coal. The coal can be transported to the site of the plant by rail or road.
4. It requires less space as compared to Hydro power plants.
5. Cost of generation is less than that of diesel power plants.
6. They can be located very conveniently near the load centers.
7. Does not require shielding like required in nuclear power plant
8. Unlike nuclear power plants whose power production method is difficult, for thermal power plants it is easy.
9. Transmission costs are reduced as they can be set up near the industry.
10. The portion of steam generated can be used as process steam in different industries.
11. Steam engines and turbines can work under 25%of overload capacity.
12. Able to respond changing loads without difficulty.
1. It pollutes the atmosphere due to production of large amount of smoke and fumes.
2. Large amounts of water are required.
3. Takes long time to be erected and put into action.
4. Maintenance and operating costs are high.
5. With increase in pressure and temperature, the cost of plant increases.
6. Troubles from smoke and heat from the plant, disposal of ash.
ENVIRONMENTAL IMPACT OF THERMAL POWER STATIONS
Thermal Power Stations in India, where poor quality of coal is used, add to environmental degradation problems through gaseous emissions, particulate matter, fly ash and bottom ash. Growth of manufacturing industries, in public sector as well as in private sector has further aggravated the situation by deteriorating the ambient air quality. Ash content being in abundance in Indian coal, problem of fly ash and bottom ash disposal increase day by day. The fly ash generated in thermal power station causes many hazardous diseases like Asthma, Tuberculosis etc.
3.1 Air pollution
Initially, perceptions of objectionable effects of air pollutants were limited to those easily detected like odour, soiling of surfaces and smoke stacks. Later, it was the concern over long term/chronic effects that led to the identification of six criteria pollutants. These six criteria pollutants are sulphur di-oxide (SO2), Carbon Mono-oxide (CO), Nitrogen oxide (NO2), Ozone (O3), suspended particulates and non-methane hydrocarbons (NMHC) now referred to as volatile organic compounds (VOC). There is substantial evidence linking them to health effects at high concentrations. Three of them namely O3, SO2 and NO2 are also known phytotoxicants (toxic to vegetation). In the later part Lead (Pb) was added to that list.
3.2 Nitrogen Oxide (NOx)
Most of the NOx is emitted as NO which is oxidised to NO2 in the atmosphere. All combustion processes are sources of NOx at the high temperature generated in the combustion process. Formation of NOX may be due to thermal NOx which is the result of oxidation of nitrogen in the air due to fuel NOx which is due to nitrogen present in the fuel. Some of NO2 will be converted to NO3 in the presence of 02. In general, higher the combustion temperature the higher NOx is produced. Some of NOxis oxidised to NO3, an essential ingredient of acid precipitation and fog. In addition, NO2 absorbs visible light and in high concentrations can contribute to a brownish discoloration of the atmosphere.
3.3 Sulphur Oxide
The combustion of sulphur containing fossil fuels, especially coal is the primary source of SOx. About 97 to 99% of SOx emitted from combustion sources is in the form of Sulphur Di-oxide which is a criteria pollutant, the remainder is mostly SO3, which in the presence of atmospheric water is transformed into Sulphuric Acid at higher concentrations, produce deleterious effects on the respiratory system. In addition, SO2 is phytotoxicant.
3.4 Water pollution
Water pollution refers to any change in natural waters that may impair further use of the water, caused by the introduction of organic or inorganic substances or a change in temperature of the water. In thermal power stations the source of water is either river, lake, pond or sea where from water is usually taken. There is possibility of water being contaminated from the source itself. Further contamination or pollution could be added by the pollutants of thermal power plant waste as inorganic or organic compounds.
3.5 Land degradation
The thermal power stations are generally located on the non-forest land and do not involve much Resettlement and Rehabilitation problems. However it's effects due to stack emission etc, on flora and fauna, wild life sanctuaries and human life etc. have to be studied for any adverse effects. One of the serious effects of thermal power stations is land requirement for ash disposal and hazardous elements percolation to ground water through ash disposal in ash ponds. Due to enormous quantity of ash content in India coal, approximately 1 Acre per MW of installed thermal capacity is required for ash disposal. According to the studies carried out by International consultants if this trend continues, by the year 2014 -2015, 1000 sq. km of land should be required for ash disposal only.
3.6 Noise pollution
Some areas inside the plant will have noisy equipments such as crushers, belt conveyors, fans, pumps, milling plant, compressors, boiler, turbine etc. Various measures taken to reduce the noise generation and exposure of workers to high noise levels in the plant area will generally include:
i) Silencers of fans, compressors, steam safety valves etc.
ii) Using noise absorbent materials.
iii) Providing noise barriers for various areas.
iv) Noise proof control rooms.
v) Pro vision of green belt around the plant will further reduce noise levels.