Steam Turbines

Presentation about steam turbines including how is it work, parts, operations

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  1. Amir Ayad
    Presentation about steam turbines including how is it work, parts, operations
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    Steam Turbines
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    • 1. Steam Turbines Egyptian Propylene and Polypropylene Company. PDH Plant. Eng.Amir Ayad
    • 2. Introduction • We classify as turbo-machines all those devices in which energy is transferred either to or from, a continuously flowing fluid by the dynamic action of one or more moving blade rows the word turbo or turbines is of Latin origin and implies that which spins or whirls around. • Essentially, a rotating blade row or rotor changes the stagnation enthalpy of the fluid moving through it by either doing positive (compressors & pumps) or negative work (turbines), depending upon the effect required of the machine. These enthalpy changes are intimately linked with the pressure changes occurring simultaneously in the fluid.
    • 3. TURBOMACHINES Turbines, compressors and fans are all members of the same family of machines called turbo-machines. A turbo-machine is a power or heat-generating machine, which employs the dynamic action of a rotating element, the rotor; the action of the rotor changes the energy level of the continuously flowing fluid through the turbo-machine. Two main categories of turbo-machine are identified: • Absorb power to increase the fluid pressure or head (ducted fans, compressors and pumps). • Produce power by expanding fluid to a lower pressure or head (hydraulic, steam and gas turbines).
    • 4. TURBOMACHINES Turbine Compressor Pumps
    • 5. Types of Turbines Hydraulic Gas Turbine Steam Turbine Turbine
    • 6. Hydraulic Turbines • A water turbine is a rotary engine that takes energy from moving water. • Flowing water is directed on to the blades of a turbine runner, creating a force on the blades. • Since the runner is spinning, the force acts through a distance (force acting through a distance is the definition of work). • In this way, energy is transferred from the water flow to the turbine. • Used to generate electricity from the energy of water.
    • 7. Hydraulic Turbines
    • 8. Gas Turbine • 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. • The compressor, which draws air into the engine, pressurizes it, and feeds it to the combustion chamber at speeds of hundreds of miles per hour. • The combustion system, typically made up of a ring of fuel injectors that inject a steady stream of fuel into combustion chambers where it mixes with the air. The mixture is burned at temperatures of more than 2000 degrees F. The combustion produces a high temperature, high pressure gas stream that enters and expands through the turbine section.
    • 9. Gas Turbine • The turbine is an intricate array of alternate stationary and rotating aerofoil-section blades. As hot combustion gas expands through the turbine, it spins the rotating blades. • The rotating blades perform a dual function they drive the compressor to draw more pressurized air into the combustion section, and they spin a generator to produce electricity. • This high-temperature high-pressure gas enters a turbine, where it expands down to the exhaust pressure, producing a shaft work output in the process. • The turbine shaft work is used to drive the compressor and other devices such as an electric generator that may be coupled to the shaft.
    • 10. Gas Turbine • The energy that is not used for shaft work comes out in the exhaust gases, so these have either a high temperature or a high velocity. • these gases can sometimes be used directly, they are more often passed to a heat recovery boiler for the production of hot water or steam. Where the site’s heat requirement exceeds the heat available in the exhaust gases, or is variable, a burner can be incorporated in the ducting between the turbine and the heat recovery boiler to increase the temperature of the exhaust gases and improve the heat output of the plant. • Gas turbines are used to power aircraft, trains, ships, electrical generators, or even tanks • Gas turbines accept most commercial fuels, such as petrol, natural gas, propane, diesel, and kerosene as well as renewable fuels such as biodiesel and biogas. • Gas turbine, may be spinning at 100,000 to 500,000 rpm.
    • 11. Gas Turbine
    • 12. Thermodynamic Theory • In an ideal gas turbine, gases undergo three thermodynamic processes: 1. an isentropic compression, 2. an isobaric (constant pressure) combustion 3. an isentropic expansion. Together, these make up the Brayton cycle. • In a practical gas turbine, mechanical energy is irreversibly transformed into heat when gases are compressed (in either a centrifugal or axial compressor), due to internal friction and turbulence. • Passage through the combustion chamber, where heat is added and the specific volume of the gases increases, is accompanied by a slight loss in pressure. During expansion amidst the stator and rotor blades of the turbine, irreversible energy transformation once again occurs
    • 13. Brayton Cycle • Ideal Brayton cycle: 1. isentropic process - ambient air is drawn into the compressor, where it is pressurized. 2. isobaric process - the compressed air then runs through a combustion chamber, where fuel is burned, heating that air—a constant-pressure process, since the chamber is open to flow in and out. 3. isentropic process - the heated, pressurized air then gives up its energy, expanding through a turbine (or series of turbines). Some of the work extracted by the turbine is used to drive the compressor. 4. isobaric process - heat rejection (in the atmosphere).
    • 14. Brayton Cycle
    • 15. Steam Turbines What's Steam Turbine? • The steam turbine is a prime mover in which the potential energy of steam is transformed into kinetic energy and the latter in its turn is transformed into the mechanical energy of rotation of the turbine shaft. • The turbine shaft, directly, or with the help of a reduction gearing, is connected with the driven mechanism which can be generator or a compressor.
    • 17. Steam Turbines The simplest single-disc steam turbine consists of the following parts • Shaft. • Disc with moving blades • Fixed blades on its periphery. • Expansion nozzle. • The shaft along with the disc mounted upon it comprises the most important part of the turbine and is known as the rotor, which is housed in the turbine casing. • The journals of the shaft are placed in bearings, which are located in the base of the turbine casing
    • 18. Steam Turbines
    • 19. Steam Turbines Theory of Working: • In turbines of these types the expansion of the steam is achieved from its initial pressure to its final one in a single nozzle or a group of nozzles situated in the turbine stator and placed in front of the blades of the rotating disc. • The decrease of steam pressure in the nozzles is accompanied by a decrease of its heat content; this decrease of heat content achieved in the nozzles subsequently accounts for the increase in the velocity of the steam issuing from the nozzles. • The energy velocity of the steam jets exerts an impulse force on the blades and performs mechanical work on the shaft of the turbine rotor.
    • 20. Steam Turbines
    • 21. Steam turbine is based upon Rankine cycle
    • 22. Rankine cycle • 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 vapour. • Process 3-4: The dry saturated vapour expands through a turbine, generating power. This decreases the temperature and pressure of the vapour, 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 vapour then enters a condenser where it is condensed at a constant pressure to become a saturated liquid. • 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. • Rankine cycle shown here prevents the vapor ending up in the superheat region after the expansion in the turbine, which reduces the energy removed by the condensers.
    • 23. Rankine cycle T-S diagram
    • 24. • An ideal Rankine cycle operates between pressures of 30 kPa and 6 MPa. The temperature of the steam at the inlet of the turbine is 550°C. Find the net work for the cycle and the thermal efficiency. • Wnet=Wturbine-Wpump OR Qin-Qout • Thermal efficiency hth=Wnet/Qin • Net work done is converted into power output of turbine.
    • 25. Steam Turbines Classification Steam Turbine Flow Direction Axial Radial Way of energy conversion & type of blading Impulse Reaction Type of Compounding Pressure compounding Velocity compounding Pressure- Velocity compounding Exhausting condition Condensing Extraction Backpressure Reheat No.of stages Single Multi Inlet Pressure Low Medium High
    • 26. Flow Directions Axial Flow turbine • The great majority of turbines, especially those of high power are axial flow. • In such turbines the steam flows in direction parallel to the axis of the shaft leaves the turbine in the same direction. • The most preferred turbine for electricity generation as several cylinders can be coupled together to achieve a turbine with greater output.
    • 27. Axial Flow Turbines
    • 28. Flow Directions Radial flow • In a radial flow turbine the steam enters the turbine in the direction of its radius and leaves it in the direction of the axis of the shaft. • Not preferred for electricity generation and employed for small outputs such as driving pumps.
    • 29. Flow Directions
    • 30. Way of Energy Conversion 1) way of energy conversion - impulse turbines - reaction turbines
    • 31. Types of Blade • The heat energy contained within the steam that passes through a turbine must be converted into mechanical energy to achieve this depends on the shape of the turbine blades. The two basic blade shapes are: 1- Impulse 2- Reaction
    • 32. Impulse Turbine • Impulse working on the principle of high pressure steam hitting against moving blades. • Pressure drop only occurs at the nozzles in the turbine. • In an impulse turbine, the fluid is forced to hit the turbine at high speed (due to change of potential energy to kinetic energy at the nozzles). • They are generally installed in the higher pressure sections of the turbine where the specific volume of steam is low. • Blades are usually symmetrical have entrance and exit angles 20. • Blades are short and have constant cross section area.
    • 35. Impulse Turbine NOZZLE STEAM CHEST ROTOR
    • 37. Reaction Turbine • The principle of pure reaction turbine is that all energy stored within the steam is converted to mechanical energy by reaction of the jet of steam as it expands at the blades of the rotor. • In a reaction turbine the steam expands when passing across fixed blades where pressure drop occurs and velocity increase. • When passing to moving blades both pressure and velocity decreases (work extraction). STEAM CHEST ROTOR
    • 38. Comparison Impulse Reaction Pressure drop occurs in both fixed and rotating blades. Enthalpy changed into kinetic energy in both stationary and moving blades There is change in both pressure and velocity as the steam flows through the moving blades. Whole pressure drop occurs at the fixed blades. Whole enthalpy is changed into kinetic energy in the nozzle There is no change in the pressure of the steam as it passes through the moving blades. There is change only in the velocity of the steam flow.
    • 39. Impulse Stage • An impulse stage consists of stationary blades forming nozzles through which steam expands, increasing velocity as a result of decreasing pressure. • The steam then strikes the rotating blades and performs work on them, which in turn decreases velocity (kinetic energy)of the steam. • The steam then passes through another set of stationery blades which turn it back to original direction and increases the velocity again through nozzle action.
    • 40. Reaction Stage • In the reaction turbine both the moving and fixed blades are designed to act like nozzles. • As steam passes through the non-moving blades, no work is exerted pressure will decrease and velocity will increase. • In the moving blades are designed to act like nozzles velocity and pressure will decrease due to wok being extracted from the steam.
    • 41. Way of compounding • Compounding of steam turbines is the method in which energy from the steam is extracted in a number of stages rather than a single stage in a turbine. • A compounded steam turbine has multiple stages i.e. it has more than one set of nozzles and rotors, in series, keyed to the shaft or fixed to the casing, so that either the steam pressure or the jet velocity is absorbed by the turbine in number of stages. • The steam produced in the boiler has very high enthalpy. In all turbines the blade velocity is directly proportional to the velocity of the steam passing over the blade.
    • 42. Why it’s required ? • Now, if the entire energy of the steam is extracted in one stage, i.e. if the steam is expanded from the boiler pressure to the condenser pressure in a single stage, then its velocity will be very high. • Hence the velocity of the rotor (to which the blades are keyed) can reach to about 30,000 rpm, which is pretty high for practical uses because of very high vibration. • Moreover at such high speeds the centrifugal forces are immense, which can damage the structure. Hence, compounding is needed. • The high velocity which is used for impulse turbine just strikes on single ring of rotor that cause wastage of steam ranges 10% to 12%. To overcome the wastage of steam compounding of steam turbine is used.
    • 43. Pressure Compounding impulse turbine • The pressure compounded Impulse turbine is also called as Rateau turbine, after its inventor. This is used to solve the problem of high blade velocity in the single-stage impulse turbine. • It consists of alternate rings of nozzles and turbine blades. The nozzles are fitted to the casing and the blades are keyed to the turbine shaft. • In this type of compounding the steam is expanded in a number of stages, instead of just one (nozzle) in the velocity compounding. It is done by the fixed blades which act as nozzles. The steam expands equally in all rows of fixed blade. • The steam coming from the boiler is fed to the first set of fixed blades i.e. the nozzle ring. The steam is partially expanded in the nozzle ring. Hence, there is a partial decrease in pressure of the incoming steam. This leads to an increase in the velocity of the steam. Therefore the pressure decreases and velocity increases partially in the nozzle.
    • 44. Pressure Compounding impulse turbine • This is then passed over the set of moving blades. As the steam flows over the moving blades nearly all its velocity is absorbed. However, the pressure remains constant during this process. • After this it is passed into the nozzle ring and is again partially expanded. Then it is fed into the next set of moving blades, and this process is repeated until the condenser pressure is reached. • It is a three stage pressure compounded impulse turbine. Each stage consists of one ring of fixed blades, which act as nozzles, and one ring of moving blades. As shown in the figure pressure drop takes place in the nozzles and is distributed in many stage
    • 45. Pressure Compounding impulse turbine
    • 46. Velocity Compounding impulse turbine • The velocity compounded Impulse turbine was first proposed by C G Curtis to solve the problem of single stage Impulse turbine for use of high pressure and temperature steam.The rings of moving blades are separated by rings of fixed blades. The moving blades are keyed to the turbine shaft and the fixed blades are fixed to the casing. The high pressure steam coming from the boiler is expanded in the nozzle first. The Nozzle converts the pressure energy of the steam into kinetic energy. It is interesting to note that the total enthalpy drop and hence the pressure drop occurs in the nozzle. Hence, the pressure thereafter remains constant. • This high velocity steam is directed on to the first set (ring) of moving blades. As the steam flows over the blades, due the shape of the blades, it imparts some of its momentum to the blades and losses some velocity. Only a part of the high kinetic energy is absorbed by these blades. The remainder is exhausted on to the next ring of fixed blade. • The function of the fixed blades is to redirect the steam leaving from the first ring moving blades to the second ring of moving blades. There is no change in the velocity of the steam as it passes through the fixed blades. The steam then enters the next ring of moving blades; this process is repeated until practically all the energy of the steam has been absorbed.
    • 47. Velocity Compounding impulse turbine
    • 48. Pressure-Velocity compounded Impulse Turbine • It is a combination of the above two types of compounding. The total pressure drop of the steam is divided into a number of stages. Each stage consists of rings of fixed and moving blades. Each set of rings of moving blades is separated by a single ring of fixed blades. In each stage there is one ring of fixed blades and 3-4 rings of moving blades. Each stage acts as a velocity compounded impulse turbine. • The fixed blades act as nozzles. The steam coming from the boiler is passed to the first ring of fixed blades, where it gets partially expanded. The pressure partially decreases and the velocity rises correspondingly. The velocity is absorbed by the following rings of moving blades until it reaches the next ring of fixed blades and the whole process is repeated once again.
    • 49. Exhaust Utilization 1. Condensing Turbine • In this type of turbine steam with pressure (42 bar) and temperature (400C) enters where pressure drop is occurred in first stage impulse turbine. • Then expands in reaction turbine and exhaust with lower pressure than atmospheric pressure. • The cooling water condenses the steam turbine exhaust in the condenser creating the condenser vacuum by using ejector or small compressor (vacuum pump). • This type is used to get only mechanical energy and not to use the exhaust steam ماكنة حمل Load machine البخار المكثف صمام التحكم بكمية جريان البخار دخول البخار steam inlet ريشة ثابتة )التوجيهية( ريش متحركة
    • 50. Condensing turbine
    • 51. Exhaust Utilization 2. Extraction Turbine • In this turbine steam is withdrawal from one or tow stages at a certain pressure for using at plant processing such as heating also called (bleeder turbines). • This type used for having a steam with a certain pressure to be used in other process. صمام التحكم بكمية جريان البخار دخول البخار steam inlet Load machine صمام التحكم ريش متحركة ريش ثابتة سحب البخار من مرحلة وسطية لتلبية متطلبات أخرى خروج بخار مكثف
    • 52. Extraction Turbine
    • 53. Exhaust Utilization 3. Backpressure Turbine • Non condensing turbine which exhausts it’s steam to industrial process or facility steam which used in another process. ماكنة حمل Load machine البخار المكثف فوق الضغط الجوي 1 ضغط جوي bar > صمام التحكم بكمية جريان البخار دخول البخار steam inlet ريش ثابتة )التوجيهية( ريش متحركة Back Pressure Turbine مخطط توربين بخاري البخار المكثف أعلى من الضغط الجوي
    • 54. Backpressure Turbine
    • 55. Reheat Turbine • Reheat turbines are also used almost exclusively in electrical power plants. • In a reheat turbine, steam flow exits from a high pressure section of the turbine and is returned to the boiler where additional superheat is added. • The steam then goes back into an intermediate pressure section of the turbine and continues its expansion.
    • 56. 116MT01 Condensing turbine with a backpressure extraction Extraction MP steam to drive LP chamber MP steam LP steam to condenser LP chamber Balance line HP steam
    • 57. 118MT01 a backpressure turbine charging MP & LP to headers HP steam MP steam LP steam
    • 58. What is a stage in a steam turbine? • In an impulse turbine, the stage is a set of moving blades behind the nozzle. • In a reaction turbine, each row of blades is called a "stage. • " A single Curtis stage may consist of two or more rows of moving blade.
    • 59. Number of stages & Inlet Pressure • Single stage • Multi-stage • High pressure (p> 6,5MPa) • Intermediate pressure(2,5MPa
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