ELE 2303 Power Generation and Transmission CLO1 PDF

8/15/2021 ELE 2303: Power Generation and Transmission CLO1 : Describe the layout of common electrical power generation plants 1  Power Generation and Transmission ELE 2303...

8/15/2021 ELE 2303: Power Generation and Transmission CLO1 : Describe the layout of common electrical power generation plants 1  Power Generation and Transmission ELE 2303 CLO1 Describe the layout of common electrical power generation plants 1.1 Describe the layout of common electrical power generation plants. 1.2 Explain the demand of base - power stations, intermediate - power stations, and peak- generation power stations. 1.3 Describe the layout of gas-turbine, hydropower, nuclear, solar and wind power generation plants 1.4 Identify the size, efficiency, availability and capital of generation for electrical power generation plants with focus on the common types in UAE 1.5 Explain the theory of operation and construction of thermal power station and describe the main parts with their function in the station Energy Definition Energy is the ability to do work and can be on different forms such as Heat, Light, Motion, Electrical, chemical and gravitational. Some of world energy resources are limited and some are unlimited. The limited energy resources should be wisely. The problems associated with the use of large quantities of energy are:  Depletion of reserves  Pollution and environmental degradation  High financial cost  Security of supply Electrical Energy Electrical energy is the most favorite energy form because it is clean and easy to be converted into other energy forms. Some of world energy resources are limited and some are unlimited. During this course, we will talk about Electrical form. Electric Energy Generation is a process of converting other forms (such as Wind chemical, etc…) into Electrical Energy. While we may have losses, the system efficiency is the ability to minimize the losses. World Energy Consumption  World Energy Consumption Energy production by fuel, 1980-2035 (quadrillion Btu) Conservation of Energy Using less energy can be accomplished in different ways: 1.Technical Methods: Developing more efficient processes to achieve present conditions with less energy input. 2. Adaptation of lifestyle and habits : Energy consumption could be reduced if individuals adopt different lifestyles. 3. Develop "Renewable" resources  Sources for Energy Energy Energy Nuclear Fossil Renewable Fuels Fission Fusion Coal Oil Gas Peat Geothermal Direct Tidal Indirect Solar Solar Wind Wave Hydro Biomass Power Definition Power is defined as the rate of producing /consuming energy. Why Electrical Energy? 1. Convenient: Easily converted to other forms: heat, mechanical, etc… 2. Easily controlled. 3. Flexible: Can be easily transmitted at long distances and within micro seconds (μs). 4. Relatively efficient. 5. Environmentally friendly. Electrical Power is need all around the worlds. So, there is a need to be transmit from place to place. This process is called Electric Power Transmission Power Distribution: Let each consumer to use as needed. be transmit from place to place. This process is called Electric Power Transmission Power Systems Main Components and Function Modern power systems are made up of three distinct and distant components: 1- Generation 2- Transmission 3- Distribution The function of a power system is to meet the energy demand of the residential, commercial and industrial consumers connected to it, safely and reliably. A Typical Electrical Power System The Structure of a Power System A power system, no matter how small, consists of the following parts:  Generation plants  Transmission system  Substations to convert between different voltage levels  Distribution system reaching all customers  1.2 Explain the demand of base - power stations, intermediate - power stations, and peak- generation power stations.  BASE LOAD, INTERMEDIATE LOAD AND PEAK LOAD Base Load: This is the load demanded 100% of the time Peak Load: This is the load that is demanded for a brief intervals during the day. Intermediate Load: The area between the peak load and the base load is the intermediate load POWER STATION TYPES 1.3 Describe the layout of gas-turbine, hydropower, nuclear, solar and wind power generation plants Common Electrical Power Generation Plants There are FOUR basic types of generating stations: Thermal generating stations Hydropower generating stations Nuclear generating stations Renewable Energy THERMAL (STEAM) POWER STATIONS Traditional thermal power plants: also called combustion power plants, they operate with energy produced by a steam boiler fueled by coal, natural gas, heating oil, as well as by biomass. https://www.engie.com/en/activities/thermal-energy/thermal- power-stations Gas Turbines  Expansion phase: Thermal energy is converted to mechanical energy as the hot expanding gases from the combustor turn the turbine rotor. Pressure and temperature decrease while volume increases through the expansion phase.  Exhaust phase: Hot exhaust gases are ducted through exhaust ducts to the atmosphere. Pressure, temperature and volume remain the same through the exhaust phase.  Combustion Chamber: The combustion chamber mixes fuel with compressed air and ignites the mixture.  Turbine: Hot gases from the combustion chamber are used to do work by driving loads such as electrical generators. Gas Turbine Operation  Energy is released when compressed air is mixed with fuel and ignited in the combustion chamber.  The gases are passed through a nozzle onto the turbine blades, generating thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure.  Energy is extracted in the form of shaft power, and used to power aircraft, trains, ships & electrical generators. Gas Turbine Operation  GE LM2500 GAS TURBINE Air Inlet Section Combustion Turbine Section Section Compressor 22 GAS TURBINE MAIN COMPONENT 23  BRAYTON CYCLE – GAS TURBINE CYCLE The Brayton cycle or Joule Cycle is made up of four internally reversible processes: 1-2 Compression 2-3 Heat addition 3-4 Expansion 4-1 Heat rejection 24  BRAYTON CYCLE – GAS TURBINE CYCLE The Brayton cycle is made up of four internally reversible processes: 1-2 Isentropic (constant entropy) compression (in a compressor) 2-3 Constant-pressure heat addition 3-4 Isentropic expansion (in a turbine) Pressure vs. Volume 4-1 Constant-pressure heat rejection Temperature vs. Entropy 25 OVERALL THERMAL EFFICIENCY  Useful Work = Energy released in turbine minus energy absorbed by compressor.  The compressor requires typically approximately 30% - 50% of the energy released by the turbine.  Typical overall thermal efficiency of a combustion turbine is 20% - 40%. 26 OVERALL THERMAL EFFICIENCY where r is the compression ratio, and temperatures are in Kelvin. 27 EXAMPLE 1 A gas turbine has a pressure ratio of 6:1. The inlet temperature to the compressor is 10˚C. The outlet temperature from the compressor is 199.4˚C. The inlet temperature to the turbine is 950˚C. Find: a) The gas turbine thermal efficiency. b) The outlet temperature from the turbine. c) The net output power if the inlet heat power is 150.8 MW. 28 EXAMPLE 1 A gas turbine has a pressure ratio of 6:1. The inlet temperature to the compressor is 10˚C. The outlet temperature from the compressor is 199.4˚C. The inlet temperature to the turbine is 950˚C. Find: a) The gas turbine cycle thermal efficiency. 29 EXAMPLE 1 A gas turbine has a pressure ratio of 6:1. The inlet temperature to the compressor is 10˚C. The outlet temperature from the compressor is 199.4˚C. The inlet temperature to the turbine is 950˚C. Find: a) The gas turbine thermal efficiency. b) The outlet temperature from the turbine. 30 EXAMPLE 1 A gas turbine has a pressure ratio of 6:1. The inlet temperature to the compressor is 10˚C. The outlet temperature from the compressor is 199.4˚C. The inlet temperature to the turbine is 950˚C. Find: a) The gas turbine thermal efficiency. b) The outlet temperature from the turbine. T1 = 10+273 = 283 K T2 = 199.4+273 = 472.4 K T3 = 950+273 = 1223 K  T4 = 733.36 K = 460.36 ˚C. 31 EXAMPLE 1 A gas turbine has a pressure ratio of 6:1. The inlet temperature to the compressor is 10˚C. The outlet temperature from the compressor is 199.4˚C. The inlet temperature to the turbine is 950˚C. Find: a) The gas turbine thermal efficiency. b) The outlet temperature from the turbine. T4 = 733.36 K = 460.36 ˚C. c) The net output power if the inlet heat power is 150.8 MW. Qin = 150.8 MW  Pnet = 60.32 MW 32 EXAMPLE 2 Calculate the thermal efficiency of a gas turbine if the net output power is 42 MW when the inlet heat energy is 120 MW. 33 HYDROELECTRIC POWER STATIONS Hydroelectric power plants use no fuel! They use the kinetic energy of falling water. Water is collected behind high dams, and when released it strikes the blades of the turbine, causing it to rotate. This will cause the generator, which is coupled to the turbine, to rotate and generate electricity. As coal, oil and uranium are becoming more expensive, hydro plants are becoming more popular. Hydroelectric Power Stations Hydroelectric Power Stations Advantages of Hydropower Stations  Water is used as the source of fuel, which cheaper and easily available  No smoke, no ashes or atmospheric pollution.  Running charges are small.  Availability time is very small which makes hydro electric power plants suitable for peak power station duties.  In addition to electrical energy generation, such stations help in flood control and irrigation. Disadvantages of Hydro Electric Power Stations  High initial cost, mainly used for dam construction  Climate dependent  Fish killing  High cost of transmission since hydro electric power plants are built well away from load centers. YouTube Video: https://youtu.be/q8HmRLCgDAI Wind Turbine Wind Energy Wind energy comes from a series of energy transformations from solar energy (radiation) to wind energy (kinetic). Land heats up faster than water does, but also loses heat faster (inland vs. coast). These differences in air temperature across the globe can create wind! But turbines can’t extract all of the kinetic energy of the wind. Why not? If this was the case the air would stop as soon as it passed through the blades and no other wind would be able to pass through. Wind Energy According to Betz Law you cannot capture more than 59.3% (2/3) of wind’s energy (Betz, 1919). maximum ratio of P/P0 = 2/3 is found at v2/v1 ≈ 1/3. Ideally you want the turbine to slow the wind down by 2/3 of its original speed. Wind Turbine Power Wind turbines are not 100% efficient: power = efficiency ∙ max power extracted 1 P = η ρAv 3 2 2 1 3 d  = η ρv π   2 2 1 P = ηρv 3πd 2 8 where d is the diameter of the circle covered by the rotor. Wind Turbine Power Local wind speed is also an important factor since: power α (wind speed)3 power α (blade diameter)2 The local wind speed should be, on average, at least 7 m/s at 25 m above the earth’s surface in order to make harnessing wind from it worthwhile. Wind Turbine Power The power produced by a wind turbine depends on: rotor area air density wind speed Example: A wind turbine has a blade circle diameter of 35 m and is operating with a wind speed of 15 m/s. If the energy conversion efficiency is 90% and the density of air is 1.2 kg/m3, calculate the average power output of the turbine. 𝑃𝑃 = 0.125 × 0.9 × 1.2 × 153 × 3.14 × 352 = 1752561.5 𝑊𝑊 = 1.75 × 106 𝑊𝑊 = 1.75 𝑀𝑀𝑀𝑀 Wind Turbine How does Wind turbine Works: https://www.youtube.com/watch?v=qSWm_nprfqE&t=45s  ENVIRONMENT IMPACTS Noise Pollution Noise pollution is one of the biggest disadvantages of a wind turbine. Wildlife Impact The force of the blades high up in the air may not seem powerful to you, yet they are more than capable of harming wildlife. ADVANTAGES OF WIND TURBINES  Easy to install  The wind is free and with modern technology it can be captured efficiently.  Once the wind turbine is built the energy it produces does not cause green house gases or other pollutants.  Although wind turbines can be very tall each takes up only a small plot of land. This means that the land below can still be used. This is especially the case in agricultural areas as farming can still continue.  Remote areas that are not connected to the electricity power grid can use wind turbines to produce their own supply. DISADVANTAGEAS OF WIND TURBINES  The strength of the wind is not constant and it varies from zero to storm force. This means that wind turbines do not produce the same amount of electricity all the time. There will be times when they produce no electricity at all.  Wind turbines are noisy.  Large wind farms are needed to provide entire communities with enough electricity. For example, the largest single turbine available today can only provide enough electricity for 475 homes, when running at full capacity. How many would be needed for a town of 100 000 people? Nuclear Energy – The Basics Just as ‘chemical’ fuel is needed for thermal power stations, nuclear fuel is needed for nuclear power stations Nuclear fuel is the material that is 'consumed' by the fission process to produce nuclear energy, just as chemical fuel is burned for energy. Uranium is the nuclear fuel needed for nuclear power stations The production of energy in nuclear reactors is from the 'fission' or splitting of the U-235 atoms Nuclear Power Stations – The fission process 51 NUCLEAR POWER STATIONS – THE FISSION PROCESS  A chain reaction is a process in which neutrons released in fission produce an additional fission in at least one further nucleus. This nucleus in turn produces neutrons, and the process is repeated. The process may be controlled (nuclear power) or uncontrolled (nuclear weapons)  Although two to three neutrons are produced for every fission, not all of these neutrons are available for continuing the fission reaction. If the conditions are such that the neutrons are lost at a faster rate than they are formed by fission, the chain reaction will not be self-sustaining. At the point where the chain reaction can become self-sustaining, this is referred to as critical mass 52 LIGHT WATER REACTORS (LWR)  The family of nuclear reactors known as light water reactors (LWR), cooled and moderated using ordinary water, tend to be simpler and cheaper to build than other types of nuclear reactor, and are well known to have excellent safety and stability characteristics. Due to these factors, they make up the vast majority of civil nuclear reactors in service throughout the world. LWRs can be subdivided into the following categories:  Pressurized water reactors (PWRs),  Boiling water reactors (BWRs) 53 PRESSURIZED WATER REACTOR – BLOCK DIAGRAM 54 BOILING WATER REACTOR – BLOCK DIAGRAM 55 SOLAR (PHOTOVOLTAIC) ENERGY 56 Solar Energy Levels on the Earth Surface 24 hour/365 day mean solar radiation received at the surface, in W/m2. It oscillates between a maximum of 275 W/m2 in the deserts of the Middle East, to a low of 75 W/m2 for misty isles in the Arctic. 57 Electricity from the Sun Using Photovoltaic Panels 58 What Happen in the Solar Cell Photons in sunlight hit the solar panel and are absorbed by semiconducting materials, such as silicon—creating a dc V-I source to extract energy from. An array of solar panels converts solar energy into a usable amount of DC electricity. Power Electronics Inverters convert the DC to mains AC to supply loads or feed the grid How the PV Solar System Works: https://www.youtube.com/watch?v=xKxrkht7CpY 59  Solar System Configurations Depending on the arrangement of system components, solar systems can be: Stand-Alone Systems Grid-Connected Systems 60 Construction of Solar Systems – Stand Alone System Sun Solar Panel Batteries Inverter Electric Panel Household Loads 61 Construction of Solar Systems – Grid-Connected System Sun Solar Panel Batteries (Low Capacity) Inverter Electric Grid Electric Panel Household Loads 62  Solar System Configurations Stand-alone Systems: – Systems meet all electrical need of installation – No connection to conventional power grid – Goal = Installation is Self Sufficient Grid-Connected Systems: – System meets some or all of electrical demand – Requires connection to power grid – Goal = Minimum import from grid 63  Stand Alone System – The Merits  Advantages:  Suitable for remote locations  Alternative source during power failures  Disadvantages: Requires much more powerful system Designed for worst-case scenario Must produce more power than average consumption Significantly more expensive Could run out of power in bad weather conditions 64  Grid-Connected System – The Merits oAdvantages:  System does not have to cover all electrical needs at all times  Requires less surface area for panels  Less expensive Needs small battery bank oDisadvantages:  Does not prevent extended grid power failures 65  Sub-outcome 1.4 Identify the size, efficiency, availability and capital of generation for electrical power generation plants with focus on the common types in UAE  Power Generation in the UAE The generation, transmission, and distribution of electricity in the UAE are dominated by four water and power authorities. Three of these authorities are owned by the governments of the Emirates of Abu Dhabi, Dubai, and Sharjah, whereas the authority that operates in the smaller northern emirates is federally controlled. These state-owned authorities serve as the exclusive purchasers and distributors of electricity in the respective emirates. The four major utility authorities are: 1- Abu Dhabi Department of Energy (DoE): The largest producer of water and power for the Emirate of Abu Dhabi (previously known as Abu Dhabi Water and Electricity Authority-ADWEA). 2- Dubai Electricity and Water Authority (DEWA): The second largest water and power generation, transmission, and distribution authority covering the Emirate of Dubai. Power Generation in the UAE 3- Sharjah Electricity and Water Authority (SEWA): Responsible for the generation, transmission and distribution of electricity in the Emirate of Sharjah. 4- Federal Electricity and Water Authority (FEWA): Responsible for the generation, transmission, and distribution of electricity in the Northern Emirates of Ajman, Umm Al Quwain, Fujairah and Ras Al Khaimah. The UAE is planning to add nuclear, renewable, and coal-fired electricity generating capacity to accommodate rising demand, but the country currently relies primarily on natural gas, with oil playing a secondary role. The UAE began liberalizing electricity markets in 2015 to support the national economy, lower consumption, and protect the environment. In 2018, there were over 27 gigawatts (GW) of installed capacity to generate electricity across the seven emirates utilizing natural gas. The UAE aims to increase clean energy power generation to 27% by 2021. The country’s energy consumption has slowed in recent years compared to the jumps in 2014 and 2015, but demand continues to increase in line with population and economic growth. Power Generation in the UAE As per the UAE State of Energy Report 2019, Dubai has the highest customer growth in the country, increasing 28% in 2017. Dubai is working to diversify its energy mix to increase electricity from renewable energy sources to 25%. According to the 2017 energy report, Dubai’s electricity sources were: 1- Gas turbines: 73%. 2- Steam turbines: 25%. 3- Renewable energy: 2%. In Sharjah, SEWA has embarked on improving and expanding its electricity transmission and distribution network on a large scale due to the increased demands in electricity and energy. Currently, the electricity used to power the emirate comes from Abu Dhabi. Power Generation in the UAE Installed Capacity of Electricity Generation Plants by Authority 2013 – 2017 (Megawatts) Authority 2013 2014 2015 2016 2017 DoE 14,383 15,546 15,546 15,220 16,622 DEWA 9,656 9,656 9,656 10,000 10,200 SEWA 2,895 2,894 2,840 2,838 2,846 FEWA 924 733 703 703 703 Total 27,858 28, 829 28, 745 28,761 30,371 Power Generation in the UAE Gross Generated Electricity by Authority 2014 – 2018 (Gigawatt hour) Authority 2014 2015 2016 2017 2018 DoE 70,847 79,768 80,527 83,006 84,182 DEWA 39,599 42,006 43,092 45,162 45,961 SEWA 5,683 5,433 5,685 5,899 5,272 FEWA 399 158 293 486 582 Total 116,528 127,365 129,596 134,553 135,997 Power Generation in the UAE Power Generation in the UAE The power capacity in the UAE is predicted to reach approximately 32 GW in 2030 as shown in the figure below:  Sub-outcome 1.5 1.5 Explain the theory of operation and construction of thermal power station and describe the main parts with their function in the station THERMAL (STEAM) POWER STATIONS How Thermal Power Stations Work, YouTube Link: https://www.youtube.com/watch?v=IdPTuwKEfmA THERMAL (STEAM) POWER STATIONS Thermal power stations convert water into steam at high pressure. Thermal Power stations are usually fueled by coal, natural gas, heating oil, nuclear energy and biomass. The generated steam is used to rotate a high speed steam turbines that are coupled with generators. The generators, which are coupled to the steam turbines, will rotate and generate electrical energy. This type of power station is widely used around the world. THERMAL (STEAM) POWER STATIONS THERMAL (STEAM) POWER STATIONS Because of the abundance of fuel (coal, oil & gas), this kind of power station can be used to produce large amounts of electrical energy. In most countries these power stations are used as base load power stations. This is because steam power stations are slow to start and cannot be used to cater for peak loads that generally occur for a short duration. These power stations (together with nuclear power stations) are kept running very close to full efficiency for 24 hours a day (unless they are being maintained). STEAM POWER STATION SCHEMATIC ARRANGEMENT Figure 1 DESCRIPTION OF THERMAL PLANT THERMAL (STEAM) POWER STATIONS Figure 2 THERMAL (STEAM) POWER STATIONS MAJOR PARTS THERMAL (STEAM) POWER STATIONS MAJOR PARTS Why Steam? Steam is used in the generation of electrical energy and is also used widely to provide process heating. Steam has many performance advantages that make it indispensable, such as:  Low toxicity  Ease of transportability  High efficiency  High heat capacity  Low cost with respect to other alternatives. FOSSIL-FUELLED THERMAL POWER PLANT SYSTEM Layout of thermal plant, an example of which is shown in Figures 1 & 2, can be easily understood by dividing the plant components into four main processes. 1- Coal and ash process. 2- Air and gas process. 3- Feed water and steam circuit. 4- Cooling water process. THERMAL STATION MAIN OPERATION PHASES 1- Coal and ash circuit – Description:  Coal arrives at storage yard (14)  Coal is directed in to the coal hopper (15)  In case of pulversing, coal is pulverized (broken up) (16) and then goes to the fuel burners.  Ash resulting from combustion of coal gets collected at the ash hopper (18) and is removed to ash storage yard by ash handling equipment. THERMAL STATION MAIN OPERATION PHASES The Pulveriser – Description:  The coal is put in the boiler after pulverization. A pulveriser is a device for grinding coal for combustion in a furnace in a power plant.  Pulverizing coal for a boiler is a very important factor in overall cycle efficiency. There are many types of pulverisers available, but proper selection will ensure consistent boiler and cycle efficiency.  Pulverized coal is the most efficient way of using coal in a steam generator. The coal is ground so that about 70% will pass through 200 mesh (0.075 mm) and 99 % will pass through 50 mesh (0.300 mm). THERMAL STATION MAIN OPERATION PHASES 2- Air and gas circuit - Description:  Air is taken in from the atmosphere (22) through forced draught or induced draught fans (20) and passes to the furnace through air preheater (24), where it is heated by the flue gases which pass to the chimney via the preheater.  The hot gases of combustion first flow through the boiler tubes, and superheater tubes (19) in the furnace then through the economizer (23) and then finally through the air preheater (24) and get discharged through the chimney (27) to the atmosphere. THERMAL STATION MAIN OPERATION PHASES 3- Feed water and steam circuit - Description:  Feed water flowing into the boiler is first preheated in the economizer (23), which recovers part of heat from the flue gases flowing from the furnace to the chimney (27) on its way to the atmosphere. This increases the efficiency of the plant as less heat must be supplied to the boiler.  The condensate leaving the condenser (8) is first heated in closed water heaters THERMAL STATION MAIN OPERATION PHASES 3- Feed water and steam circuit – Description (Cont.):  he bled steam from the turbine is used to heat the feed water in the heaters. In the boiler drum and tubes (17), water circulates due to natural circulation.  Wet steam from the drum is further heated in the superheater (19).  Steam then expands in the turbine (11) and produces power. From there it is exhausted to the condenser (8).  The condensate is collected in hot well. Then it goes to feed water heaters, economizer (23) and to the boiler. Make up water is added in the condenser after purification. THERMAL STATION MAIN OPERATION PHASES 4- Cooling Water Circuit:  The condenser (8) requires cooling water to condense the exhaust steam. The water is cooled in cooling towers (1) or in cooling ponds and reused again and again. Some make up cooling water is added in the circuit. THE CONDENSER  Steamfrom the exhaust of the turbine is taken into the condenser so that it is turned into water to allow it to be pumped. Figure 3 shows a typical water-cooled condenser. THE CONDENSER  The condenser is made of a shell to contain the inlet steam and tubes in which cooling water is circulated.  The exhaust steam from the low pressure stage of the turbine enters the shell where it is cooled and converted to water by flowing over the tubes as shown in Figure 3.  The condenser generally uses either circulating cooling water from a cooling tower to reject waste heat to the atmosphere, or once-through water from a river, lake, or ocean. THE BOILER - This is a large structure containing the burner and the furnace. The furnace is surrounded by large number of tubes (in water tube boilers) in which water is circulated at all times by pump P1. - In coal fired power plants, pulverized coal is prepared in the pulverizer (16) and is air-blown into the furnace from fuel nozzles at the four corners of the furnace and it burns rapidly, creating a large fireball at the center of the furnace. - The thermal radiation of the fireball heats the water that circulates through the boiler tubes near the boiler perimeter. - As the water in the boiler circulates it absorbs heat and changes into steam at a temperature of about 400 °C THE SUPERHEATER  In this super heater, the steam is superheated to about 500 °C before it is allowed into the turbine.  The super heater has an elaborate set up of tubes where the steam absorbs more energy from the hot flue gases surrounding the super heater tubing and its temperature is now superheated above the saturation temperature.  The superheated steam is then passed to the high pressure stage of the turbine. ADVANTAGES AND DISADVANTAGES OF THERMAL POWER PLANTS Advantages  They can be located very conveniently near the load centers.  Does not require shielding like required in nuclear power plants.  Unlike nuclear power plants whose power production method is difficult, for thermal power plants it is easy if compared.  Transmission costs are reduced as they can be set up near the industry.  The portion of steam generated can be used as process steam in different industries such as water desalination.  Steam engines and turbines can work under 25% of overload capacity.  Able to respond to changing loads without difficulty. ADVANTAGES AND DISADVANTAGES OF THERMAL POWER PLANTS Disadvantages:  Large amounts of water are required.  Great difficulties experienced in coal handling and disposal of ash.  Takes long time to be erected and put into action.  Maintenance and operating costs are high.  With increase in pressure and temperature, the cost of plant increases.  Troubles from smoke and heat from the plant. STEAM TURBINES How Steam Turbines Work: YouTube Link: https://www.youtube.com/watch?v=SPg7hOxFItI STEAM TURBINES A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern equivalent was invented by Sir Charles Parsons in 1884.  By far the most widely used and most powerful turbines are those driven by steam. Until the 1960s essentially all steam used in turbine cycles was raised in boilers burning fossil fuels (coal, oil, and gas) or, in minor quantities, certain waste products.  However, modern turbine technology includes nuclear steam plants as well as production of steam supplies from other sources. PRINCIPLE OF OPERATION OF A STEAM TURBINE  A steam turbine uses steam to rotate its blades. The rotary motion of the blades is used to rotate the armature of the generator, and the movement of the armature in a magnetic field results in the production of a current (electricity) in the armature!  Heat energy from a thermal power plant or a nuclear power plant is used to boil water, and convert it into steam at high pressure. This high pressure steam is directed to the turbine blades thus causing the blades to rotate!  Figures 4 & 5 shows the operation of the steam turbine. STEAM TURBINE OPERATION Figure 4 STEAM TURBINE OPERATION Figure 5 THERMAL POWER PLANT EFFICIENCY  The efficiency of thermal generating stations is always low because of the inherent low efficiency of the turbines.  The maximum efficiency of any machine that converts heat energy into mechanical energy is given by the equation: T2 η = (1 − ) ×100 where, T1 η is the efficiency T1 = Temperature of the gas entering the turbine (in Kelvin) T2 = Temperature of the gas leaving the turbine (in Kelvin) THERMAL POWER PLANT EFFICIENCY  Inmost thermal generating stations the gas is steam. In order to obtain a high efficiency, the quotient T2/T1 should be as small as possible.  However, temperature T2 cannot be lower the ambient temperature, which is usually about 20 ͦ C. As a result, T2 cannot be less than T2 = 20 + 273 = 293 K THERMAL POWER PLANT EFFICIENCY  This means that to obtain high efficiency, T1 should be as high as possible. The problem is that we cannot use temperatures above those that steel and other metals can safely withstand, bearing in mind the corresponding high steam pressures.  It turns out that the highest feasible temperature T1 is about 550 ͦ C. As a result, T1 = 550 ͦ + 273 ͦ = 823 K  It follows that the maximum possible efficiency of a turbine driven by steam that enters at 823 K and exits at 293 K is THERMAL POWER PLANT EFFICIENCY  Due to other losses, some of the most efficient steam turbines have efficiencies of 45%. This means that 65% of the thermal energy is lost during the thermal-to-mechanical conversion process.  The enormous loss of heat and how to dispose of it represents one of the major aspects of a thermal generating station. THERMAL POWER PLANT EFFICIENCY Example: Find the thermal power plant efficiency if the input steam temperature to the turbine is 700 K, and the output steam temperature from the turbine is 77 o C?