Lecture notes Power plant Engineering

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LECTURER NOTES ON EE2252 POWER PLANT ENGINEERING II YEAR /IV SEMESTER EEE ACADEMIC YEAR 2012-2013 EE2252 POWER PLANT ENGINEERING SYLLABUS 3 1 0 4 AIM Expose the students to basics of various power plants so that they will have the comprehensive idea of power system operation. OBJECTIVES To become familiar with operation of various power plants. 1 THERMAL POWER PLANTS 1Basic thermodynamic cycles, various components of steam power plant- layoutpulverized coal burners- Fluidized bed combustion-coal handling systems- ash handling systems- Forced draft and induced draft fans- Boilers-feed pumps- super heaterregenerator-condenser- dearearators-cooling tower 2 HYDRO ELECTRIC POWER PLANTS Layout-dams-selection of water turbines-types-pumped storage hydel plants 3 NUCLEAR POWER PLANTS Principles of nuclear energy- Fission reactions-nuclear reactor-nuclear power plants 4 GAS AND DIESEL POWER PLANTS Types, open and closed cycle gas turbine, work output & thermal efficiency, methods to improve performance-reheating, intercoolings, regeneration- advantage and disadvantages- Diesel engine power plant-component and layout 5 NON-CONVENTIONAL POWER GENERATION Solar energy collectors, OTEC, wind power plants, tidal power plants and geothermal resources, fuel cell, MHD power generation-principle, thermoelectric power generation,thermionic power generation TEXT BOOKS A Course in Power Plant Engineering by Arora and Domkundwar, Dhanpat Rai and Co.Pvt.Ltd., New Delhi. Power Plant Engineering by P.K. Nag, Tata McGraw Hill, Second Edition , Fourth reprint 2003. REFERENCES() Power station Engineering and Economy by Bernhardt G.A.Skrotzki and William A. Vopat- Tata McGraw Hill Publishing Company Ltd., New Delhi, 20th reprint 2002. 2An introduction to power plant technology by G.D. Rai-Khanna Publishers, Delhi-  005.  Power Plant Technology, M.M. El-Wakil McGraw Hill 1984. EE2252 POWER PLANT ENGINEERING UNIT-I INTRODUCTION TO POWER PLANTS AND BOILERS STEAM POWER PLANT: 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 electricity. 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 CO is produced by the worlds fossil fired thermal 2 power plants; efforts to reduce these outputs are various and widespread. 3The four main circuits one would come across in any thermal power plant layout are -Coal andAshCircuit -AirandGasCircuit Feed Water and Steam Circuit Cooling Water Circuit Coal and Ash Circuit Coal and Ash circuit in a thermal power plant layout mainly takes care of feeding the boiler with coal from the storage for combustion. The ash that is generated during combustion is collected at the back of the boiler and removed to the ash storage by scrap conveyors. The combustion in the Coal and Ash circuit is controlled by regulating the speed and the quality of coal entering the grate and the damper openings. Air and Gas Circuit Air from the atmosphere is directed into the furnace through the air preheated by the action of a forced draught fan or induced draught fan. The dust from the air is removed 4before it enters the combustion chamber of the thermal power plant layout. The exhaust gases from the combustion heat the air, which goes through a heat exchanger and is finally let off into the environment. Feed Water and Steam Circuit The steam produced in the boiler is supplied to the turbines to generate power. The steam that is expelled by the prime mover in the thermal power plant layout is then condensed in a condenser for re-use in the boiler. The condensed water is forced through a pump into the feed water heaters where it is heated using the steam from different points in the turbine. To make up for the lost steam and water while passing through the various components of the thermal power plant layout, feed water is supplied through external sources. Feed water is purified in a purifying plant to reduce the dissolve salts that could scale the boiler tubes. Cooling Water Circuit The quantity of cooling water required to cool the steam in a thermal power plant layout is significantly high and hence it is supplied from a natural water source like a lake or a river. After passing through screens that remove particles that can plug the condenser tubes in a thermal power plant layout, it is passed through the condenser where the steam is condensed. The water is finally discharged back into the water source after cooling. Cooling water circuit can also be a closed system where the cooled water is sent through cooling towers for re-use in the power plant. The cooling water circulation in the condenser of a thermal power plant layout helps in maintaining a low pressure in the condenser all throughout. All these circuits are integrated to form a thermal power plant layout that generates electricity to meet our needs. LAYOUT OF HYDEL POWER PLANT: 5Hydroelectric power plants convert the hydraulic potential energy from water into electrical energy. Such plants are suitable were water with suitable head are available. The layout covered in this article is just a simple one and only cover the important parts of hydroelectric plant.The different parts of a hydroelectric power plant are (1) Dam Dams are structures built over rivers to stop the water flow and form a reservoir.The reservoir stores the water flowing down the river. This water is diverted to turbines in 6power stations. The dams collect water during the rainy season and stores it, thus allowing for a steady flow through the turbines throughout the year. Dams are also used for controlling floods and irrigation. The dams should be water-tight and should be able to withstand the pressure exerted by the water on it. There are different types of dams such as arch dams, gravity dams and buttress dams. The height of water in the dam is called head race. (2) Spillway A spillway as the name suggests could be called as a way for spilling of water from dams. It is used to provide for the release of flood water from a dam. It is used to prevent over toping of the dams which could result in damage or failure of dams. Spillways could be controlled type or uncontrolled type. The uncontrolled types start releasing water upon water rising above a particular level. But in case of the controlled type, regulation of flow is possible. (3) Penstock and Tunnel Penstocks are pipes which carry water from the reservoir to the turbines inside power station. They are usually made of steel and are equipped with gate systems.Water under high pressure flows through the penstock. A tunnel serves the same purpose as a penstock. It is used when an obstruction is present between the dam and power station such as a mountain. (4) Surge Tank Surge tanks are tanks connected to the water conductor system. It serves the purpose of reducing water hammering in pipes which can cause damage to pipes. The sudden surges of water in penstock is taken by the surge tank, and when the water requirements increase, it supplies the collected water thereby regulating water flow and pressure inside the penstock. 7(5) Power Station Power station contains a turbine coupled to a generator. The water brought to the power station rotates the vanes of the turbine producing torque and rotation of turbine shaft. This rotational torque is transfered to the generator and is converted into electricity. The used water is released through the tail race. The difference between head race and tail race is called gross head and by subtracting the frictional losses we get the net head available to the turbine for generation of electricity. DIESEL POWER PLANT Diesel power plants produce power from a diesel engine. Diesel electric plants in the range of 2 to 50 MW capacities are used as central stations for small electric supply networks and used as a standby to hydro electric or thermal plants where continuous power supply is needed. Diesel power plant is not economical compared to other power plants. The diesel power plants are cheaply used in the fields mentioned below.Peak load plants  Mobile electric plants  Standby units  Emergency power plants  Starting stations of existing plants  Central power station etc. General Layout of Diesel power plants 8General Layout of Diesel power plants Figure shows the arrangements of the engine and its auxiliaries in a diesel power plant. The major components of the plant are: a) Engine Engine is the heart of a diesel power plant. Engine is directly connected through a gear box to the generator. Generally two-stroke engines are used for power generation. Now a 9days, advanced super & turbo charged high speed engines are available for power production. b) Air supply system Air inlet is arranged outside the engine room. Air from the atmosphere is filtered by air filter and conveyed to the inlet manifold of engine. In large plants supercharger/turbocharger is used for increasing the pressure of input air which increases the power output. c) Exhaust System This includes the silencers and connecting ducts. The heat content of the exhaust gas is utilized in a turbine in a turbocharger to compress the air input to the engine. d) Fuel System Fuel is stored in a tank from where it flows to the fuel pump through a filter. Fuel is injected to the engine as per the load requirement. e) Cooling system This system includes water circulating pumps, cooling towers, water filter etc. Cooling water is circulated through the engine block to keep the temperature of the engine in the safe range. f) Lubricating system Lubrication system includes the air pumps, oil tanks, filters, coolers and pipe lines. Lubricant is given to reduce friction of moving parts and reduce the wear and tear of the engine parts. g) Starting System There are three commonly used starting systems, they are;  A petrol driven auxiliary engine,  Use of electric motors, 103)Use of compressed air from an air compressor at a pressure of 20 Kg/cm‖ h) Governing system The function of a governing system is to maintain the speed of the engine constant irrespective of load on the plant. This is done by varying fuel supply to the engine according to load. Advantages of diesel power plants  More efficient than thermal plant  Design, Layout etc are simple and cheap  Part load efficiency is very high  It can be started quickly  Simple & easy maintenance  No problem with fuel & dust handling  It can be located in the heart of town  Less cooling water required. Disadvantages  There is a limitation for size of a diesel engine  Life of plant is comparatively less  Noise pollution is very high  Repair cost is very high  High lubrication cost NUCLEAR POWER PLANT: 11Nuclear power is the use of sustained Nuclear fission to generate heat and do useful work. Nuclear Electric Plants, Nuclear Ships and Submarines use controlled nuclear energy to heat water and produce steam, while in space, nuclear energy decays naturally in a radioisotope thermoelectric generator. Scientists are experimenting with fusion energy for future generation, but these experiments do not currently generate useful energy. Nuclear power provides about 6% of the world's energy and 13–14% of the world's electricity, with the U.S., France, and Japan together accounting for about 50% of nuclear generated electricity. Also, more than 150 naval vessels using nuclear propulsion have been built. Just as many conventional thermal power stations generate electricity by harnessing the thermal energy released from burning fossil fuels, nuclear power plants convert the energy released from the nucleus of an atom, typically via nuclear fission. Nuclear reactor technology When a relatively large fissile atomic nucleus (usually uranium-235 or plutonium-239) absorbs a neutron, a fission of the atom often results. Fission splits the atom into two or more smaller nuclei with kinetic energy (known as fission products) 59 and also releases gamma radiation and free neutrons. A portion of these neutrons may later be absorbed by other fissile atoms and create more fissions, which release more neutrons, and so on. This nuclear chain reaction can be controlled by using neutron poisons and neutron moderators to change the portion of neutrons that will go on to cause more 60 fissions. Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if unsafe conditions are detected. 12Three nuclear powered ships, (top to bottom) nuclear cruisers USS Bainbridge and USS Long Beach with USS Enterprise the first nuclear powered aircraft carrier in 1964. Crew 2 members are spelling out Einstein's mass-energy equivalence formula E = mc on the flight deck. There are many different reactor designs, utilizing different fuels and coolants and incorporating different control schemes. Some of these designs have been engineered to meet a specific need. Reactors for nuclear submarines and large naval ships, for example, commonly use highly enriched uranium as a fuel. This fuel choice increases the reactor's power density and extends the usable life of the nuclear fuel load, but is more expensive and a greater risk to nuclear proliferation than some of the other nuclear fuels. A number of new designs for nuclear power generation, collectively known as the Generation IV reactors, are the subject of active research and may be used for practical power generation in the future. Many of these new designs specifically attempt to make fission reactors cleaner, safer and/or less of a risk to the proliferation of nuclear weapons. Passively safe plants (such as the ESBWR) are available to be builtand other designs that are believed to be nearly fool-proof are being pursued. Fusion reactors, which may be viable in the future, diminish or eliminate many of the risks associated with nuclear fission. There are trades to be made between safety, economic and technical properties of different reactor designs for particular applications. Historically these decisions were often made in private by scientists, regulators and engineers, but this may be considered problematic, and since Chernobyl and Three Mile Island, many involved now consider informed consent and morality should be primary considerations. Cooling system A cooling system removes heat from the reactor core and transports it to another area of the plant, where the thermal energy can be harnessed to produce electricity or to do other useful work. Typically the hot coolant will be used as a heat source for a boiler, and the pressurized steam from that boiler will power one or more steam turbine 13driven electrical generators. Flexibility of nuclear power plants It is often claimed that nuclear stations are inflexible in their output, implying that other forms of energy would be required to meet peak demand. While that is true for the vast majority of reactors, this is no longer true of at least some modern designs. Nuclear plants are routinely used in load following mode on a large scale in France. Unit A at the German Biblis Nuclear Power Plant is designed to in- and decrease his output 15 % per minute between 40 and 100 % of it's nominal power. Boiling water reactors normally have load-following capability, implemented by varying the recirculation water flow. GASS TURBINE POWER PLANT: A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between. Energy is added to the gas stream in the combustor, where fuel is mixed with air and ignited. In the high pressure environment of the combustor, combustion of the fuel increases the temperature. The products of the combustion are forced into the turbine section. There, the high velocity and volume of the gas flow is directed through a nozzle over the turbine's blades, spinning the turbine which powers the compressor and, for some turbines, drives their mechanical output. The energy given up to the turbine comes from the reduction in the temperature and pressure of the exhaust gas. COMBINED POWER CYCLES: In electric power generation a combined cycle is an assembly of heat engines that work in tandem off the same source of heat, converting it into mechanical energy, which in turn 14usually drives electrical generators. The principle is that the exhaust of one heat engine is used as the heat source for another, thus extracting more useful energy from the heat, increasing the system's overall efficiency. This works because heat engines are only able to use a portion of the energy their fuel generates (usually less than 50%). The remaining heat (e.g., hot exhaust fumes) from combustion is generally wasted. Combining two or more thermodynamic cycles results in improved overall efficiency, reducing fuel costs. In stationary power plants, a successful, common combination is the Brayton cycle (in the form of a turbine burning natural gas or synthesis gas from coal) and the Rankine cycle (in the form of a steam power plant). Multiple stage turbine or steam cylinders are also common. LOAD DURATION CURVE: A load duration curve (LDC) is used in electric power generation to illustrate the relationship between generating capacity requirements and capacity utilization. A LDC is similar to a load curve but the demand data is ordered in descending order of magnitude, rather than chronologically. The LDC curve shows the capacity utilization requirements for each increment of load. The height of each slice is a measure of capacity, and the width of each slice is a measure of the utilization rate or capacity factor. The product of the two is a measure of electrical energy (e.g. kilowatthours). HIGH PRESSURE BOILERS: 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. Most boilers produce steam to be used at saturation temperature; that is, saturated steam. Superheated steam boilers vaporize the water and then further heat the steam in a superheater. This provides steam at much higher temperature, but can decrease the overall thermal efficiency of the steam generating plant because the higher steam temperature requires a higher flue gas exhaust temperature. There are several ways to 15circumvent this problem, typically by providing an economizer that heats the feed water, a combustion air heater in the hot flue gas exhaust path, or both. There are advantages to superheated steam that may, and often will, increase overall efficiency of both steam generation and its utilisation: gains in input temperature to a turbine should outweigh any cost in additional boiler complication and expense. There may also be practical limitations in using wet steam, as entrained condensation droplets will damage turbine blades. Superheated steam presents unique safety concerns because, if any system component fails and allows steam to escape, the high pressure and temperature can cause serious, instantaneous harm to anyone in its path. Since the escaping steam will initially be completely superheated vapor, detection can be difficult, although the intense heat and sound from such a leak clearly indicates its presence. Superheater operation is similar to that of the coils on an air conditioning unit, although for a different purpose. The steam piping is directed through the flue gas path in the boiler furnace. The temperature in this area is typically between 1,300–1,600 degrees Celsius. Some superheaters are radiant type; that is, they absorb heat by radiation. Others are convection type, absorbing heat from a fluid. Some are a combination of the two types. Through either method, the extreme heat in the flue gas path will also heat the superheater steam piping and the steam within. While the temperature of the steam in the superheater rises, the pressure of the steam does not: the turbine or moving pistons offer a continuously expanding space and the pressure remains the same as that of the boiler. Almost all steam superheater system designs remove droplets entrained in the steam to prevent damage to the turbine blading and associated piping. SUPERCRITICAL BOILER: Supercritical steam generators (also known as Benson boilers) are frequently used for the production of electric power. They operate at "supercritical pressure". In contrast to a "subcritical boiler", a supercritical steam generator operates at such a high pressure (over 3,200 psi/22.06 MPa or 220.6 bar) that actual boiling ceases to occur, and 16the boiler has no water - steam separation. There is no generation of steam bubbles within the water, because the pressure is above the "critical pressure" at which steam bubbles can form. It passes below the critical point as it does work in the high pressure turbine and enters the generator's condenser. This is more efficient, resulting in slightly less fuel use. The term "boiler" should not be used for a supercritical pressure steam generator, as no "boiling" actually occurs in this device. FLUIDIZED BED BOILERS: The major portion of the coal available in India is of low quality, high ash content and low calorific value. The traditional grate fuel firing systems have got limitations and are techno-economically unviable to meet the challenges of future. Fluidized bed combustion has emerged as a viable alternative and has significant advantages over conventional firing system and offers multiple benefits – compact boiler design, fuel flexibility, higher combustion efficiency and reduced emission of noxious pollutants such as SOx and NOx. The fuels burnt in these boilers include coal, washery rejects, rice husk, bagasse & other agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr. UNIT-II STEAM POWER PLANT Coal needs to be stored at various stages of the preparation process, and conveyed around the CPP facilities. Coal handling is part of the larger field of bulk material handling, and is a complex and vital part of the CPP. Stockpiles Stockpiles provide surge capacity to various parts of the CPP. ROM coal is delivered with large variations in production rate of tonnes per hour (tph). A ROM stockpile is used to allow the washplant to be fed coal at lower, constant rate. A 17simple stockpile is formed by machinery dumping coal into a pile, either from dump trucks, pushed into heaps with bulldozers or from conveyor booms. More controlled stockpiles are formed using stackers to form piles along the length of a conveyor, and reclaimers to retrieve the coal when required for product loading, etc. Taller and wider stockpiles reduce the land area required to store a set tonnage of coal. Larger coal stockpiles have a reduced rate of heat lost, leading to a higher risk of spontaneous combustion. Stacking Travelling, lugging boom stackers that straddle a feed conveyor are commonly used to create coal stockpiles. Reclaiming Tunnel conveyors can be fed by a continuous slot hopper or bunker beneath the stockpile to reclaim material. Front-end loaders and bulldozers can be used to push the coal into feeders. Sometimes front-end loaders are the only means of reclaiming coal from the stockpile. This has a low up-front capital cost, but much higher operating costs, measured in dollars per tonne handled. High-capacity stockpiles are commonly reclaimed using bucket-wheel reclaimers. These can achieve very high rates ASH HANDLING SYSTEMS: Ash Handling Systems is the none / un combusted portion or residue, after taking combustion of any solid fuel. Solid fuel is usually coal. And any coal contains some non combustible portion which is called ash. Content of that coal. There are different types of ashes. Bottom ash 18fly ash. Bottom ash is the residue which remains in the solid form at the bottom and fly ash is the light particle which goes out along with exhaust gases, and usually they are collected in chimneys. Taking their so formed ash away from the Plant / Boiler is called – "ASH HANDLING SYSTEM" This is done in either Mechanical conveying Pneumatic conveying Mechanical system requires conveyors, and Pneumatic system requires – compressed air to carry out the ash. Ash Handling Systems Bulk Material Handling Systems Conveyors And Material Handling Equipments Process Equipments And Storage Equipments Portable Handling Equipments Rotary Equipments Pneumatic Conveying Systems Magnetic Equipments Vibratory Equipments Spares Overhead Bag Handling Systems 19COMBUSTION EQUIPMENTS: Combustion control options range from electro / mechanical through to full microprocessor control systems to match both application and customer needs. Cochran supply an extensive range of fuel handling equipment to complement and help ensure that the optimum performance from the combustion and control equipment is maintained. Fuel handling equipment includes gas boosters, oil pumping and heating stations, fuel metering and instrumentation packages are available to match individual installation requirements. STOCKERS: A mechanical stoker is a device which feeds coal into the firebox of a boiler. It is standard equipment on large stationary boilers and was also fitted to large steam locomotives to ease the burden of the fireman. The locomotive type has a screw conveyor (driven by an auxiliary steam engine) which feeds the coal into the firebox. The coal is then distributed across the grate by steam jets, controlled by the fireman. Power stations usually use pulverized coal-fired boilers. PULVERISER: A pulverizer or grinder is a mechanical device for the grinding of many different types of materials. For example, they are used to pulverize coal for combustion in the steam- generating furnaces of fossil fuel power plants. Types of pulverizers Ball and tube mills A ball mill is a pulverizer that consists of a horizontal rotating cylinder, up to three diameters in length, containing a charge of tumbling or cascading steel balls, pebbles, or rods. 20

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