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Lanco amarkantak power ltd korba mechanical vocational training report 1 haxxo24 i~i

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Lanco amarkantak power ltd korba mechanical vocational training report 1 haxxo24 i~i

Lanco amarkantak power ltd korba mechanical vocational training report 1 haxxo24 i~i

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  • 1. LANCO PROJECT CHHATTISGARH INDIA A Project Report on the Partial Fulfillment of Vocational Training on TURBINE & GENERATOR DEC Guided By:- Submitted By:- Mr.K.D.N. Singh
  • 2. ACKNOWLEDGEMENT The project bears imprints of many people. I take this opportunity to express my gratitude to all those people who have been instrumental in the successful completion of this project. I would like to show my greatest appreciation to Mr. K.D.N.Singh (HOD Turbine).I can’t say thank you enough for their tremendous support and help. I feel motivated and encouraged every time I attend their meeting. Without their encouragement and guidance this project would not have materialized. I would like to convey my special Thanks and gratitude to Mr.Sudip Banerjee –Officer HR, for his consistent support and guidance during the three weeks of vocational training. . The guidance and support received from all the TG team members of Lanco infratech Ltd., including Mr. Milind Bhajan & Mr. Vinit Pradhan was vital for the success of the project. I am thankful for their constant support and help.
  • 3. INTRODUCTION LANCO Power Ltd (LPL) is further setting up 2x660 MW Coal based power project near Pathadi - Saragbundia villages on the Champa - Korba State Highway in Chhattisgarh, India. The commissioning schedule of 36 months for Unit III and 40 Months for Unit IV categorizes these as fast track projects. Upon attaining the required statutory clearances for Unit 3, the implementation of the project with supercritical technology started from 1 January 2010 as the zero date. Letter of Acceptance for the supply of coal has been obtained for the third unit and Long Term Coal linkage has been obtained for fourth unit. Power Finance Corporation, the lead lender for the project has already appraised the project and the project is well poised to achieve financial closure shortly. The ultimate capacity of the LANCO Power Plant after completion of Phase IV would be around 1920 MW. |~| Contact CORPORATE OFFICE LANCO Power Ltd Plot No. 397, Phase-III, Udyog Vihar, Gurgaon - 122016 Haryana - India. Tel : +91-124 - 4741000/01/02/03 Fax : +91-124 - 4741024 Email: lapl@lancogroup.com PROJECT OFFICE LANCO Thermal Power Station Village-Pathadi,P.O-Tilkeja Dist.- Korba Chhattisgarh-495 674, India Tel : 07759 279238,279123 Fax : 07759 279370 email : lapl@lancogroup.com MISSION Development of society through entrepreneurship. VISION Most admired integrated infrastructure enterprise.
  • 4. INDEX Content 1. Thermal Power Plant 2. History 3. Principal of Power Plant 4. Efficiency 5. Boiler Steam Cycle 6. Feed Water heating & Deaerations 7. Super Heater 8. Re-Heater 9. Air Path 10.Turbine 11.Types Of Turbine 12.Uses Of Turbine 13.Theory Of Operation 14.Condenser 15.Electrical Generator
  • 5. Thermal power station 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 termenergy center because such facilities convert forms of heat energy into electricity [1] . 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 part of human CO2emissions comes from fossil fueled thermal power plants; efforts to reduce these outputs are various and widespread. History 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 [2] 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. [3] |~| Efficiency The energy efficiency of a conventional thermal power station, considered as salable energy as a percent of the heating value of the fuel consumed, is typically 33% to 48%. 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 incooling 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.
  • 6. A Rankine cycle with a two-stage steam turbine and a single feed water heater. 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 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, high cost, and poor heat transfer properties, have ruled out mercury as a working fluid. Above the critical point for water of 705 °F (374 °C) and 3212 psi (22.06 MPa), there is no phase transition from water to steam, but only a gradual decrease in density. Boiling does not occur and it is not possible to remove impurities via steam separation. In this case a super critical steam plant is required to utilize the increased thermodynamic efficiency by operating at higher temperatures. These plants, also called once-through plants because boiler water does not circulate multiple times, require additional water purification steps to ensure that any impurities picked up during the cycle will be removed. This purification takes the form of high pressure ion exchange units called condensate polishers between the
  • 7. steam condenser and the feed water heaters. Sub-critical fossil fuel power plants can achieve 36–40% efficiency. Super critical designs have efficiencies in the low to mid 40% range, with new "ultra critical" designs using pressures of 4400 psi (30.3 MPa) and dual stage reheat reaching about 48% efficiency. Current nuclear power plants operate below the temperatures and pressures that coal-fired plants do. This limits their thermodynamic efficiency to 30–32%. Some advanced reactor designs being studied, such as the Very high temperature reactor, Advanced gas-cooled reactor andSuper critical water reactor, would operate at temperatures and pressures similar to current coal plants, producing comparable thermodynamic efficiency. Boiler and steam cycle In fossil-fueled power plants, steam generator refers to a furnace that burns the fossil fuel to boil water to generate steam. In the nuclear plant field, steam generator refers to a specific type of large heat exchanger used in a pressurized water reactor (PWR) to thermally connect the primary (reactor plant) and secondary (steam plant) systems, which generates steam. In a nuclear reactor called aboiling water reactor (BWR), water is boiled to generate steam directly in the reactor itself and there are no units called steam generators. In some industrial settings, there can also be steam-producing heat exchangers called heat recovery steam generators (HRSG) which utilize heat from some industrial process. The steam generating boiler has to produce steam at the high purity, pressure and temperature required for the steam turbine that drives the electrical generator. Geothermal plants need no boiler since they use naturally occurring steam sources. Heat exchangers may be used where the geothermal steam is very corrosive or contains excessive suspended solids. A fossil fuel steam generator includes an economizer, a steam drum, and the furnace with its steam generating tubes and super heater coils. Necessary safety valves are located at suitable points to avoid excessive boiler pressure. The air and flue gas path equipment include: forced draft (FD) fan, Air Preheater (AP), boiler furnace, induced draft (ID) fan, fly ash collectors (electrostatic precipitator or baghouse) and the flue gas stack.|~|
  • 8. Feed water heating and deaeration The feed water used in the steam boiler is a means of transferring heat energy from the burning fuel to the mechanical energy of the spinningsteam turbine. The total feed water consists of recirculated condensate water and purified makeup water. Because the metallic materials it contacts are subject to corrosion at high temperatures and pressures, the makeup water is highly purified before use. A system of water softeners and ion exchange demineralizers produces water so pure that it coincidentally becomes an electrical insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimeter. The makeup water in a 500 MWe plant amounts to perhaps 20 US gallons per minute (1.25 L/s) to offset the small losses from steam leaks in the system. The feed water cycle begins with condensate water being pumped out of the condenser after traveling through the steam turbines. The condensate flow rate at full load in a 500 MW plant is about 6,000 US gallons per minute (400 L/s). Diagram of boiler feed water deaerator (with vertical, domed aeration section and horizontal water storage section The water flows through a series of six or seven intermediate feed water heaters, heated up at each point with steam extracted from an appropriate duct on the turbines and gaining temperature at each stage. Typically, the condensate plus the makeup water then flows through a deaerator [7][8] that removes dissolved air from the water, further purifying and reducing its corrosiveness. The water may be dosed following this point with hydrazine, a chemical that removes the remaining oxygen in the water to below 5 parts per billion (ppb). [vague] It is also dosed with pH control agents such as ammonia or morpholine to keep the residual acidity low and thus non-corrosive.
  • 9. Super heater Fossil fuel power plants can have a super heater and/or re-heater section in the steam generating furnace. In a fossil fuel plant, after the steam is conditioned by the drying equipment inside the steam drum, it is piped from the upper drum area into tubes inside an area of the furnace known as the super heater, which has an elaborate set up of tubing where the steam vapor picks up more energy from hot flue gases outside the tubing and its temperature is now superheated above the saturation temperature. The superheated steam is then piped through the main steam lines to the valves before the high pressure turbine. Nuclear-powered steam plants do not have such sections but produce steam at essentially saturated conditions. Experimental nuclear plants were equipped with fossil-fired super heaters in an attempt to improve overall plant operating cost. Re heater Power plant furnaces may have a re heater section containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high pressure turbine is rerouted to go inside the re heater tubes to pickup more energy to go drive intermediate or lower pressure turbines. Air path External fans are provided to give sufficient air for combustion. The forced draft fan takes air from the atmosphere and, first warming it in the air preheater for better combustion, injects it via the air nozzles on the furnace wall. The induced draft fan assists the FD fan by drawing out combustible gases from the furnace, maintaining a slightly negative pressure in the furnace to avoid backfiring through any opening.
  • 10. TURBINE A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work. The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and water wheels. Gas, steam, and water turbines usually have a casing around the blades that contains and controls the working fluid. Credit for invention of the steam turbine is given both to the British engineer Sir Charles Parsons (1854–1931), for invention of the reaction turbine and to Swedish engineer Gustaf de Laval (1845–1913), for invention of the impulse turbine. Modern steam turbines frequently employ both reaction and impulse in the same unit, typically varying the degree of reaction and impulse from the blade root to its periphery. A device similar to a turbine but operating in reverse, i.e., driven, is a compressor or pump. Theaxial compressor in many gas turbine engines is a common example. Here again, both reaction and impulse are employed and again, in modern axial compressors, the degree of reaction and impulse typically vary from the blade root to its periphery. Claude Burdin coined the term from the Latin turbo, or vortex, during an 1828 engineering competition. Benoit Fourneyron, a student of Claude Burdin, built the first practical water turbine.|~|
  • 11. TYPES OF TURBINE  Steam turbines are used for the generation of electricity in thermal power plants, such as plants using coal, fuel oil or nuclear power. They were once used to directly drive mechanical devices such as ships' propellers (e.g. the Turbinia), but most such applications now use reduction gears or an intermediate electrical step, where the turbine is used to generate electricity, which then powers an electric motorconnected to the mechanical load. Turbo electric ship machinery was particularly popular in the period immediately before and during WWII, primarily due to a lack of sufficient gear- cutting facilities in US and UK shipyards.  Gas turbines are sometimes referred to as turbine engines. Such engines usually feature an inlet, fan, compressor, combustor and nozzle (possibly other assemblies) in addition to one or more turbines.  Transonic turbine. The gasflow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a transonic turbine the gasflow becomes supersonic as it exits the nozzle guide vanes, although the downstream velocities normally become subsonic. Transonic turbines operate at a higher pressure ratio than normal but are usually less efficient and uncommon.  Contra-rotating turbines. With axial turbines, some efficiency advantage can be obtained if a downstream turbine rotates in the opposite direction to an upstream unit. However, the complication can be counter-productive. A contra-rotating steam turbine, usually known as the Ljungström turbine, was originally invented by Swedish Engineer Fredrik Ljungström (1875–1964), in Stockholm and in partnership with his brother Birger Ljungström he obtained a patent in 1894. The design is essentially a multi-stage radial turbine (or pair of 'nested' turbine rotors) offering great efficiency, four times as large heat drop per stage as in the reaction (Parsons) turbine, extremely compact design and the type met particular success in backpressure power plants. However, contrary to other designs, large steam volumes are handled with difficulty and only a combination with axial flow turbines (DUREX) admits the turbine to be built for power greater than ca 50 MW. In marine applications only about 50 turbo-electric units were ordered (of which a considerable amount were finally sold to land plants) during 1917-19, and during 1920-22 a few turbo-mechanic not very successful units were sold. [1] Only a few turbo-electric marine plants were still in use in the late 1960s (ss Ragne, ss Regin) while most land plants remain in use 2010.
  • 12.  Statorless turbine. Multi-stage turbines have a set of static (meaning stationary) inlet guide vanes that direct the gasflow onto the rotating rotor blades. In a statorless turbine the gasflow exiting an upstream rotor impinges onto a downstream rotor without an intermediate set of stator vanes (that rearrange the pressure/velocity energy levels of the flow) being encountered.  Ceramic turbine. Conventional high-pressure turbine blades (and vanes) are made from nickel based alloys and often utilise intricate internal air-cooling passages to prevent the metal from overheating. In recent years, experimental ceramic blades have been manufactured and tested in gas turbines, with a view to increasing Rotor Inlet Temperatures and/or, possibly, eliminating aircooling. Ceramic blades are more brittle than their metallic counterparts, and carry a greater risk of catastrophic blade failure. This has tended to limit their use in jet engines and gas turbines, to the stator (stationary) blades.  Shrouded turbine. Many turbine rotor blades have shrouding at the top, which interlocks with that of adjacent blades, to increase damping and thereby reduce blade flutter. In large land-based electricity generation steam turbines, the shrouding is often complemented, especially in the long blades of a low-pressure turbine, with lacing wires. These wires pass through holes drilled in the blades at suitable distances from the blade root and are usually brazed to the blades at the point where they pass through. Lacing wires reduce blade flutter in the central part of the blades. The introduction of lacing wires substantially reduces the instances of blade failure in large or low-pressure turbines.  Shroudless turbine. Modern practice is, wherever possible, to eliminate the rotor shrouding, thus reducing the centrifugal load on the blade and the cooling requirements.  Bladeless turbine uses the boundary layer effect and not a fluid impinging upon the blades as in a conventional turbine.  Water turbines  Pelton turbine, a type of impulse water turbine.  Francis turbine, a type of widely used water turbine.  Kaplan turbine, a variation of the Francis Turbine.  Wind turbine. These normally operate as a single stage without nozzle and interstage guide vanes. An exception is the Éolienne Bollée, which has a stator and a rotor, thus being a true turbine.
  • 13. Uses of turbines Almost all electrical power on Earth is produced with a turbine of some type. Very high efficiency steam turbines harness about 40% of the thermal energy, with the rest exhausted as waste heat. Most jet engines rely on turbines to supply mechanical work from their working fluid and fuel as do all nuclear ships and power plants. Turbines are often part of a larger machine. A gas turbine, for example, may refer to an internal combustion machine that contains a turbine, ducts, compressor, combustor, heat-exchanger, fan and (in the case of one designed to produce electricity) an alternator. Combustion turbines and steam turbines may be connected to machinery such as pumps and compressors, or may be used for propulsion of ships, usually through an intermediate gearbox to reduce rotary speed. Reciprocating piston engines such as aircraft engines can use a turbine powered by their exhaust to drive an intake-air compressor, a configuration known as a turbocharger (turbine supercharger) or, colloquially, a "turbo". Turbines can have very high power density (i.e. the ratio of power to weight, or power to volume). This is because of their ability to operate at very high speeds. The Space Shuttle's main engines use turbopumps (machines consisting of a pump driven by a turbine engine) to feed the propellants (liquid oxygen and liquid hydrogen) into the engine's combustion chamber. The liquid hydrogen turbopump is slightly larger than an automobile engine (weighing approximately 700 lb) and produces nearly 70,000 hp (52.2 MW). Turboexpanders are widely used as sources of refrigeration in industrial processes. Wikimedia Commons has media related to: Turbine Military jet engines,as branch of gas turbines, have recently been used as primary flight controller in post- stall flight using jet deflections that are also called thrust vectoring [7]. The U.S. FAA has also conducted a study about civilizing such thrust vectoring systems to recover jetliners from catastrophes.
  • 14. Theory of operation A working fluid contains potential energy (pressure head) and kinetic energy(velocity head). The fluid may be compressible or incompressible. Several physical principles are employed by turbines to collect this energy: Impulse turbines These turbines change the direction of flow of a high velocity fluid or gas jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. There is no pressure change of the fluid or gas in the turbine blades (the moving blades), as in the case of a steam or gas turbine, all the pressure drop takes place in the stationary blades (the nozzles). Before reaching the turbine, the fluid's pressure head is changed to velocity head by accelerating the fluid with a nozzle. Pelton wheels and de Laval turbines use this process exclusively. Impulse turbines do not require a pressure casement around the rotor since the fluid jet is created by the nozzle prior to reaching the blading on the rotor. Newton's second law describes the transfer of energy for impulse turbines. Reaction turbines These turbines develop torque by reacting to the gas or fluid's pressure or mass. The pressure of the gas or fluid changes as it passes through the turbine rotor blades. A pressure casement is
  • 15. needed to contain the working fluid as it acts on the turbine stage(s) or the turbine must be fully immersed in the fluid flow (such as with wind turbines). The casing contains and directs the working fluid and, for water turbines, maintains the suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages are usually used to harness the expanding gas efficiently. Newton's third law describes the transfer of energy for reaction turbines. In the case of steam turbines, such as would be used for marine applications or for land-based electricity generation, a Parsons type reaction turbine would require approximately double the number of blade rows as a de Laval type impulse turbine, for the same degree of thermal energy conversion. Whilst this makes the Parsons turbine much longer and heavier, the overall efficiency of a reaction turbine is slightly higher than the equivalent impulse turbine for the same thermal energy conversion. Steam turbines and later, gas turbines developed continually during the 20th Century, continue to do so and in practice, modern turbine designs use both reaction and impulse concepts to varying degrees whenever possible. Wind turbines use an airfoil to generate lift from the moving fluid and impart it to the rotor (this is a form of reaction). Wind turbines also gain some energy from the impulse of the wind, by deflecting it at an angle. Crossflow turbines are designed as an impulse machine, with a nozzle, but in low head applications maintain some efficiency through reaction, like a traditional water wheel. Turbines with multiple stages may utilize either reaction or impulse blading at high pressure. Steam Turbines were traditionally more impulse but continue to move towards reaction designs similar to those used in Gas Turbines. At low pressure the operating fluid medium expands in volume for small reductions in pressure. Under these conditions (termed Low Pressure Turbines) blading becomes strictly a reaction type design with the base of the blade solely impulse. The reason is due to the effect of the rotation speed for each blade. As the volume increases, the blade height increases, and the base of the blade spins at a slower speed relative to the tip. This change in speed forces a designer to change from impulse at the base, to a high reaction style tip. Classical turbine design methods were developed in the mid 19th century. Vector analysis related the fluid flow with turbine shape and rotation. Graphical calculation methods were used at first. Formulae for the basic dimensions of turbine parts are well documented and a highly efficient machine can be reliably designed for any fluid flow condition. Some of the calculations are empirical or 'rule of thumb' formulae, and others are based on classical mechanics. As with most engineering calculations, simplifying assumptions were made.|~|
  • 16. Velocity triangles can be used to calculate the basic performance of a turbine stage. Gas exits the stationary turbine nozzle guide vanes at absolute velocity Va1. The rotor rotates at velocity U. Relative to the rotor, the velocity of the gas as it impinges on the rotor entrance is Vr1. The gas is turned by the rotor and exits, relative to the rotor, at velocity Vr2. However, in absolute terms the rotor exit velocity is Va2. The velocity triangles are constructed using these various velocity vectors. Velocity triangles can be constructed at any section through the blading (for example: hub , tip, midsection and so on) but are usually shown at the mean stage radius. Mean performance for the stage can be calculated from the velocity triangles, at this radius, using the Euler equation: Hence: where: specific enthalpy drop across stage turbine entry total (or stagnation) temperature turbine rotor peripheral velocity change in whirl velocity The turbine pressure ratio is a function of and the turbine efficiency. Modern turbine design carries the calculations further. Computational fluid dynamics dispenses with many of the simplifying assumptions used to derive classical formulas and computer software facilitates optimization. These tools have led to steady improvements in turbine design over the last forty years.
  • 17. Condenser  Condenser (heat transfer), a device or unit used to condense vapor into liquid. More specific articles on some types include:  Air coil used in HVAC refrigeration systems  Condenser (laboratory), a range of laboratory glassware used to remove heat from fluids  Steam locomotive condensing apparatus  Surface condenser, a heat exchanger installed in steam-electric power stations to condense turbine exhaust steam into water  Condenser (optics), in classical optics gathers visible light and directs it onto a projection lens  Condenser (microscope), a group of lenses mounted below the stage of an optical microscope to concentrate light  Capacitor, formerly called a condenser, an electrical device that can store energy  Condenser microphone, a device that converts sound waves into an electrical signal  Steam locomotive condensing apparatus, a condenser fitted to steam locomotives for use in tunnels and to increase range  Synchronous condenser, a rotating machine similar to a motor, used to control AC power flow in electric power transmission Electric generator In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electrons in the windings to flow through the externalelectrical circuit. It is somewhat analogous to a water pump, which creates a flow of water but does not create the water inside. Thesource of mechanical energy may be a reciprocating or turbinesteam engine, water falling through a turbine or waterwheel, aninternal combustion engine, a wind turbine, a hand crank,compressed air or any other source of mechanical energy.
  • 18. Early 20th century alternator made inBudapest, Hungary, in the power generating hall of a hydroelectric station Early Ganz Generator in Zwevegem,West Flanders, Belgium The reverse conversion of electrical energy into mechanical energy is done by an electric motor, and motors and generators have many similarities. In fact many motors can be mechanically driven to generate electricity, and very frequently make acceptable generators.
  • 19. What We Learn In Our Vocational Training At Lanco During our vocational Training at Lanco (EPC). We are with Turbine Team & Here we got opportunity to learn following things: 1. Setup of Turbine Deck 2. Strength Checking By UT 3. Setup of Condenser Foundation 4. Centre Line Marking 5. Blue Matching of Foundation Plates 1. SETUP OF TURBINE DECK Turbine deck consists of three floors a) Ground Floor b)First Floor or Massinne Floor c) Second Floor or Operating Floor 2. Strength checking by UT It is done to check the strength of the foundation. It can show the air bubbles between the concrete through waves. It is measure done to prevent the foundation from being collapsed.
  • 20. PRINCIPAL OF POWER PLANT
  • 21. Rankine cycle The Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 80% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants. It is named after William John Macquorn Rankine, a Scottish polymath. The Rankine cycle is the fundamental thermodynamic underpinning of the steam engine Description Physical layout of the four main devices used in the Rankine cycle A Rankine cycle describes a model of steam-operated heat engine most commonly found in power generation plants. Common heat sources for power plants using the Rankine cycle are the combustion of coal, natural gas and oil, and nuclear fission. The Rankine cycle is sometimes referred to as a practical Carnot cyclebecause, when an efficient turbine is used, the TS diagram begins to resemble the Carnot cycle. The main difference is that heat addition (in the boiler) and rejection (in the condenser) are isobaric in the Rankine cycle and isothermal in the theoretical Carnot cycle. A pump is used to pressurize the working fluid received from the condenser as a liquid instead of as a gas. All of the energy in pumping the working fluid through the complete cycle is lost, as is all of the energy of vaporization of the working fluid in the boiler. This energy is lost to the cycle in that no condensation takes place in the turbine; all of the vaporization energy is rejected from the cycle through the condenser. But pumping the working fluid through the cycle as a liquid requires a very small fraction of the energy needed to transport it as compared to compressing the working fluid as a gas in a compressor (as in the Carnot cycle).
  • 22. The efficiency of a Rankine cycle is usually limited by the working fluid. Without the pressure reaching super critical levels for the working fluid, the temperature range the cycle can operate over is quite small: turbine entry temperatures are typically 565°C (the creep limit of stainless steel) and condenser temperatures are around 30°C. This gives a theoretical Carnot efficiency of about 63% compared with an actual efficiency of 42% for a modern coal-fired power station. This low turbine entry temperature (compared with a gas turbine) is why the Rankine cycle is often used as a bottoming cycle in combined-cycle gas turbine power stations. The working fluid in a Rankine cycle follows a closed loop and is reused constantly. The water vapor with entrained droplets often seen billowing from power stations is generated by the cooling systems (not from the closed-loop Rankine power cycle) and represents the waste energy heat (pumping and vaporization) that could not be converted to useful work in the turbine. Note that cooling towers operate using the latent heat of vaporization of the cooling fluid. The white billowing clouds that form in cooling tower operation are the result of water droplets that are entrained in the cooling tower airflow; they are not, as commonly thought, steam. While many substances could be used in the Rankine cycle, water is usually the fluid of choice due to its favorable properties, such as nontoxic and unreactive chemistry, abundance, and low cost, as well as its thermodynamic properties. One of the principal advantages the Rankine cycle holds over others is that during the compression stage relatively little work is required to drive the pump, the working fluid being in its liquid phase at this point. By condensing the fluid, the work required by the pump consumes only 1% to 3% of the turbine power and contributes to a much higher efficiency for a real cycle. The benefit of this is lost somewhat due to the lower heat addition temperature. Gas turbines, for instance, have turbine entry temperatures approaching 1500°C. Nonetheless, the efficiencies of actual large steam cycles and large modern gas turbines are fairly well matched. [edit]The four processes in the Rankine cycle
  • 23. Ts diagram of a typical Rankine cycle operating between pressures of 0.06bar and 50bar There are four processes in the Rankine cycle. These states are identified by numbers (in brown) in the diagram above.  Process 1-2: The working fluid is pumped from low to high pressure, as the fluid is a liquid at this stage the pump requires little input energy.  Process 2-3: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturated vapor. The input energy required can be easily calculated usingmollier diagram or h-s chart orenthalpy-entropy chart also known as steam tables.  Process 3-4: The dry saturated vapor expands through a turbine, generating power. This decreases the temperature and pressure of the vapor, and some condensation may occur. The output in this process can be easily calculated using the Enthalpy-entropy chart or the steam tables.  Process 4-1: The wet vapor then enters a condenser where it is condensed at a constant temperature to become a saturated liquid.
  • 24. In an ideal Rankine cycle the pump and turbine would be isentropic, i.e., the pump and turbine would generate no entropy and hence maximize the net work output. Processes 1-2 and 3-4 would be represented by vertical lines on the T-S diagram and more closely resemble that of the Carnot cycle. The Rankine cycle shown here prevents the vapor ending up in the superheat region after the expansion in the turbine, [1] which reduces the energy removed by the condensers.|~|