Thermal Power Generation Report


Published on

Published in: Education, Technology, Business
No Downloads
Total views
On SlideShare
From Embeds
Number of Embeds
Embeds 0
No embeds

No notes for slide

Thermal Power Generation Report

  1. 1. 1 SEMINAR REPORT ON “THERMAL POWER GENERATION” Submitted By MANISH KUMAR (4NM09EE031) Under the guidance of RAGHAVENDRA PRABHU Lecturer Seminar Report Submitted to Department of Electrical and Electronics, NMAM Institute of Technology, Nitte DEPARTMENT OF ELECTRICAL AND ELECTRONICS
  2. 2. 2 1. Introduction 2. Literature Review 2.1 Need for thermal power generation 2.2 Theory 2.3 Basic Definitions 3. Functional partitioning of the Seminar 3.1 By fuel 3.2 By prime mover 4. Methodology/Working Principle 4.1 Detailed process of power generation in a thermal power plant 4.2 Efficiency 5. Analysis 5.1 Advantages 5.2 Disadvantages 6. Conclusions References
  3. 3. 3 1. INTRODUCTION Electricity is a convenient form of energy. Thermal power plants convert the energy in coal to Electricity 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 either drives an electrical generator or does some other work. After it passes through the turbine, the steam is condensed in a condenser and recycled to where it was heated. Almost all coal, nuclear as well as many natural gas power plants are thermal. In thermal power stations, mechanical power is produced by a heat engine that transforms thermal energy often from combustion of a fuel into rotational energy. Most thermal power stations produce steam, and these are sometimes called steam power stations. Therefore, there is always heat lost to the environment. Electric power plants typically use three-phase or single-phase electrical generators to produce alternating current (AC) electric power at a frequency of 50 Hz or 60 Hz depending on its location in the world. 2. Literature Review 2.1 Need for thermal power generation  Scarcity of water resources: Water resources are not abundantly available and are geographically unevenly distributed. Thus hydel power plants cannot be installed with ease and are limited to certain locations.  Widely available alternate flues: Many alternate fuels such as coal, diesel, nuclear fuels, geo-thermal energy sources, solar-energy and biomass fuels can be used to generate power using steam cycles.  Maintenance: Once installed, these require less maintenance costs and on repairs.  Coal is abundant: Coal is available in excess quantities in India and is rich form of energy available at relatively lower cost.  Working fluid remains within the system, and need not be replaced every time thus simplifies the process.
  4. 4. 4 2.2 Theory Coal the primary energy source consists mainly of Carbon. During the combustion process the Carbon in the coal combines with Oxygen in the air to produce Carbon dioxide producing heat. The high heating value, the energy available in the coal, is in the range of 10500 kJ/kg to 27000 kJ/kg. For example, consider a coal with a high heating value of 20000 kJ/kg. Theoretically this is equivalent to 5.56 kwhr of electrical energy. Can we get all of this as electric power? No. In practice the effective conversion is only around one third of the theoretically possible value. 2.3 Basic Definitions Steam is vaporized water and can be produced at 100’C at standard atmosphere. Steam most often refers to the visible white mist that condenses above boiling water as the hot vapor mixes with the cooler air. A turbine is a rotary engine that extracts energy from a fluid or air flow and converts it into useful work. An electric generator is a device that converts mechanical energy to electrical energy. A generator forces electrons in the windings to flow through the external electrical circuit. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside. A boiler or steam generator is used wherever a source of steam is required. The form and size depends on the application: mobile steam engines, portable engines and steam-powered road vehicles typically use a smaller boiler that forms an integral part of the vehicle. 3. Functional partitioning of the Seminar Thermal power plants are classified by the type of fuel and the type of prime mover Installed. 3.1 By fuel  Nuclear power plants use a nuclear reactor's heat to operate a steam turbine generator.  Geothermal power plants use steam extracted from hot underground rocks.
  5. 5. 5  Biomass Fuelled Power Plants may be fuelled by waste from sugar cane, municipal solid waste, landfill methane, or other forms of biomass.  Solar thermal electric plants use sunlight to boil water, which turns the generator. 3.2 By prime mover  Steam turbine plants use the dynamic pressure generated by expanding steam to turn the blades of a turbine  Gas turbine plants use the dynamic pressure from flowing gases (air and combustion products) to directly operate the turbine.  Combined cycle plants have both a gas turbine fired by natural gas, and a steam boiler and steam turbine which use the hot exhaust gas from the gas turbine to produce electricity  Reciprocating engines are used to provide power for isolated communities and are frequently used for small cogeneration plants. Hospitals, office buildings, industrial plants, and other critical facilities also use them to provide backup power in case of a power outage. 4. Methodology/Working Principle In a thermal power plant, one of coal, oil or natural gas is used to heat the boiler to convert the water into steam. The steam is used to turn a turbine, which is connected to a generator. When the turbine turns, electricity is generated and given as output by the generator, which is then supplied to the consumers through high-voltage power lines. 4.1 Detailed process of power generation in a thermal power plant:  Water intake: Firstly, water is taken into the boiler through a water source. If water is available in a plenty in the region, then the source is an open pond or river. If water is scarce, then it is recycled and the same water is used over and over again.  Boiler heating: The boiler is heated with the help of oil, coal or natural gas. A furnace is used to heat the fuel and supply the heat produced to the boiler. The increase in temperature helps in the transformation of water into steam.  Steam Turbine: The steam generated in the boiler is sent through a steam turbine. The turbine has blades that rotate when high velocity steam flows across them. This rotation of turbine blades is used to generate electricity.
  6. 6. 6  Generator: A generator is connected to the steam turbine. When the turbine rotates, the generator produces electricity which is then passed on to the power distribution systems.  Special mountings: There is some other equipment like the economizer and air pre- heater. An economizer uses the heat from the exhaust gases to heat the feed water. An air pre-heater heats the air sent into the combustion chamber to improve the efficiency of the combustion process.  Ash collection system: There is a separate residue and ash collection system in place to collect all the waste materials from the combustion process and to prevent them from escaping into the atmosphere. Typical thermal efficiency for electrical generators in the electricity industry is around 33% for coal and oil-fired plants, and up to 50% for combined-cycle gas-fired plants. 4.2 Efficiency Power is energy per unit time. The power output or capacity of an electric plant can be expressed in units of megawatts electric (MWe). The electric efficiency of a conventional thermal power station, considered as saleable energy produced at the plant bus bars as a percent of the heating value of the fuel consumed, is typically 33% to 48% efficient. 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 cogeneration. Since the efficiency of the plant is fundamentally limited by the ratio of the absolute temperatures of the steam at turbine input and output, efficiency improvements require use of higher temperature and therefore higher pressure steam. Historically, other working fluids such as mercury have been experimentally used in a mercury vapor turbine power plant, since these can attain higher temperatures than water at lower working pressures. However, the obvious hazards of toxicity, and poor heat transfer properties, have ruled out mercury as a working fluid.
  7. 7. 7 5. Analysis The first process of energy conversion is the combustion where the potential energy in coal is converted to heat energy. The efficiency of this conversion is around 90 %. Why?  Due to practical limitations in heat transfer, all the heat produced by combustion is not transferred to the water; some is lost to the atmosphere as hot gases.  The coal contains moisture. Also coal contains a small percent of Hydrogen, which also gets converted to moisture during combustion. In the furnace, moisture vaporizes taking latent heat from the combustion heat and exits the boiler along with the hot gases.  Improper combustion of coal, hot ash discharged from the boiler and radiation are some of the other losses. The second stage of conversion is the thermodynamic stage. The heat from combustion is transferred to the water to produce steam. The energy of the steam is converted to mechanical rotation of the turbine. The steam is then condensed to water and pumped back into the boiler for re-use. This stage works on the principle of the Rankine cycle. For plants operating with steam at subcritical pressures (less than 221 bar) and steam temperatures of 570 °C, the Rankine cycle efficiency is around 43 %. For the state of the art plants running at greater than supercritical pressure and steam temperatures near to 600 °C, the efficiency is around 47 %. Water content can reduce to 13% 50 years experience and reliable!  The steam is condensed for re-use. During this process the latent heat of condensation is lost to the cooling water. This is the major loss and is almost 40 % of the energy input.  Losses in the turbine blades and exit losses at turbine end are some of the other losses.  The Rankine cycle efficiency is dictated by the maximum temperature of steam that can be admitted into the turbine. Due to metallurgical constraints steam temperatures are at present limited to slightly more than 600 °C. The third stage converts the mechanical rotation to Electricity in a generator. Copper, magnetic and mechanical losses account for 5 % loss in the Generator. Another 3 % is lost in the step-up transformer which makes the power ready for transmission to the consumer. To operate the power plant it is required to run various auxiliary equipment like fans, pumps. The power to operate these auxiliaries has to come from the power plant itself. For large power plants around 6 % of the generator output is used for internal consumption. This brings the overall efficiency of the power plant to around 33.5 %. This means we get only 1.9 kwhr of electrical energy from one kg of coal instead of the 5.56 kwhr that is theoretically available in the coal.
  8. 8. 8 The efficiency or inefficiency of power plants is something that we have to live with for the present till technology finds a way out. 5.1 Advantages  The fuel used is quite cheap.  Less initial cost as compared to other generating plants.  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.  It requires less space as compared to Hydro power plants.  Cost of generation is less than that of diesel power plants.  This plants can be quickly installed and commissioned and can be loaded when compare to hydel power plant.  It can meet sudden changes in the load without much difficulty controlling operation to increase steam generation.  Coal is less costlier than diesel.  Maintenance and lubrication cost is lower. 5.2 Disadvantages  It pollutes the atmosphere due to production of large amount of smoke and fumes.  It is costlier in running cost as compared to hydroelectric plants.  However, this could create more jobs for a lot of people thus increasing in a good way our current economic situation which by is failing miserably.  Over all capital investment is very high on account of turbines, condensers, boilers etc. maintenance cost is also high on lubrication, fuel handling, fuel processing.  It requires comparatively more space and more skilled operating staff as the operations are complex and required precise execution.  A large number of circuits makes the design complex.  Starting of a thermal power plant takes fairly long time as the boiler operation and steam generation process are not rapid and instantaneous.
  9. 9. 9 6. Conclusions At present, thermal power generation accounts for approximately 70% of the total amount of electricity produced around the world. However, thermal power generation, which uses fossil fuels, causes more CO2 emissions than other power generation methods. In order to reduce CO2emissions per unit power produced, Toshiba Group is developing next-generation thermal power technologies aimed at improving plant efficiency and commercializing the CO2 capture and storage system. To improve the efficiency of thermal power generation, it is of vital importance that the temperature of the steam or gas used to rotate the turbines is raised. Toshiba Group is working on the development of ultra-high-temperature materials and cooling technologies in order to commercialize an A-USC system (Advanced Ultra-Super Critical steam turbine system) more efficient than previous models, which is designed to increase steam temperature from 600°C to above the 700°C mark.
  10. 10. 10 7. Technical References 1. British Electricity International (1991).Modern Power Station Practice: incorporating modern power system practice (3rd Edition (12 volume set) ed.). Pergamon. ISBN 0-08- 040510-X. 2. Babcock & Wilcox Co. (2005).Steam: Its Generation and Use (41st edition ed.). ISBN 0- 9634570-0-4. 3. Thomas C. Elliott, Kao Chen, Robert Swanekamp (coauthors) (1997).Standard Handbook of Power plant Engineering (2nd edition ed.). McGraw-Hill Professional. ISBN 0-07-019435-1. 4. Air Pollution Control Orientation Course from website of the Air Pollution Training Institute Air Pollution Control Orientation Course from website of the Air Pollution Training Institute 5. First and second lectures by S. Banerjee on "Thermal Power Plants"