SEMINAR ON

1. SEMINAR ON STEAM TURBINE Presented By: Sandeep Kumar 8th Sem, Mechanical Engg. Regd. No. 0601222216

2. Introduction The invention of the reciprocating steam engine enabled man to convert the thermal energy of burning fuel to useful mechanical work, thus sparking the industrial revolution. As useful as it was, the reciprocating steam engine was still inefficient, cumbersome, had a very low power to weight ratio, and was a high maintenance piece of machinery. The development of the steam turbine was a vast improvement in all of these respects. The steam turbine led to applying many of the same principles of moving blades which ultimately led to the development of the gas turbine. All engineers should strive to learn as much as they can about the principles and features of steam and gas turbines. The vector analyses, detailed descriptions and illustrations are adapted and reproduced From publications of the U. S. Naval Institute, Power Magazine, and Marks Handbook for Mechanical Engineers. A rotor of a modern steam turbine, used in a power plant

3. Principles of operation • The motive power in a steam turbine is obtained by the rate of change in momentum of a high velocity jet of steam impinging on a curved blade which is free to rotate. • The steam from the boiler is expanded in a nozzle, resulting in the emission of a high velocity jet. This jet of steam impinges on the moving vanes or blades, mounted on a shaft. Here it undergoes a change of direction of motion which gives rise to a change in momentum and therefore a force. • Steam turbines are mostly 'axial flow' types; the steam flows over the blades in a direction Parallel to the axis of the wheel. 'Radial flow' types are rarely used. Classification of steam turbines Steam turbines can be classified in several different ways: 1. By details of stage design: Impulse or reaction. 2. By steam supply and exhaust conditions: Condensing, Non-condensing (back pressure), Automatic or controlled extraction, Mixed pressure (where there are two or more steam sources at different pressures), and Reheat (where steam is extracted at an intermediate stage, reheated in the boiler, and re-admitted at a lower turbine stage).

4. 3. By casing or shaft arrangement: Single casing, Tandem compound (two or more casings with the shaft coupled together in line), and Cross compound (two or more shafts not in line, and possibly at different RPM). 4. By number of exhaust stages in parallel: Two flow, four flow, six flow. 5. By direction of steam flow: Axial flow, radial flow, and tangential. 6. Single or multi-stage 7. By steam supply: Superheat or saturated. Any particular turbine may be classified by combinations of these classifications, e.g., tandem compound, three-casing, four-flow extraction turbine.A turbine stage consists of one set of stationary blades or nozzles and an adjacent set of moving blades or buckets. (The terms "blades" and "buckets" are nearly interchangeable. The term blade or blades will be used in this course for consistency). These stationary and rotating elements act together to allow the steam flow to do work on the rotor. The work is transmitted to the load through the shaft or shafts. Impulse turbine In impulse turbine, the drop in pressure of steam takes place only in nozzles and not in moving blades. This is obtained by making the blade passage of constant cross-sectional area.

5. Impulse-Reaction turbine In this type, the drop in pressure takes place in fixed nozzles as well as moving blades. The pressure drops suffered by steam while passing through the moving blades causes a further generation of kinetic energy within these blades, giving rise to reaction and add to the propelling force, which is applied through the rotor to the turbine shaft. The blade passage cross-sectional area is varied (converging type). The simple Impulse turbine It primarily consists of: a nozzle or a set of nozzles, a rotor mounted on a shaft, one set of moving blades attached to the rotor and a casing. A simple impulse turbine can be diagrammatically represented below. The uppermost portion of the diagram shows a longitudinal section through the upper half of the turbine, the middle portion shows the actual shape of the nozzle and blading, and the bottom portion shows the variation of absolute velocity and absolute pressure during the flow of steam through passage of nozzles and blades. Example: de-Laval turbine.

6. The main difference between impulse and reaction turbine lies in the way in which steam is expanded while it moves throw them In the former type,steam expands in the nozzle and its pressure doesn’t change as it moves over the blades while in the later types the steam expands continuously as it passes over the blades and thus there is a gradual fall in pressure during expansion Compounding of impulse turbine This is done to reduce the rotational speed of the impulse turbine to practical limits. (A rotor speed of 30,000 rpm is possible, which is pretty high for practical uses.) Compounding is achieved by using more than one set of nozzles, blades, rotors, in a series, keyed to a common shaft; so that either the steam pressure or the jet velocity is absorbed by the turbine in stages. Three main types of compounded impulse turbines are: a) Pressure compounded, b) velocity compounded and c) pressure and velocity compounded impulse turbines

7. Pressure compounded impulse turbine This involves splitting up of the whole pressure drop from the steam chest pressure to the condenser pressure into a series of smaller pressure drops across several stages of impulse turbine. The nozzles are fitted into a diaphragm locked in the casing. This diaphragm separates one wheel chamber from another. All rotors are mounted on the same shaft and the blades are attached on the rotor. Velocity compounded impulse turbine Velocity drop is arranged in many small drops through many moving rows of blades instead of a single row of moving blades. It consists of a nozzle or a set of nozzles and rows of moving blades attached to the rotor or the wheel and rows of fixed blades attached to the casing.

8. Pressure-velocity compounded impulse turbine This is a combination of pressure-velocity compounding.

9. Impulse-Reaction turbine This utilizes the principle of impulse and reaction. It is shown diagrammatically below: There are a number of rows of moving blades attached to the rotor and an equal number of fixed blades attached to the casing. The fixed blades are set in a reversed manner compared to the moving blades, and act as nozzles. Due to the row of fixed blades at the entrance, instead of nozzles, steam is admitted for the whole circumference and hence there is an all-round or complete admission.

10. The mode of operation of steam turbine Since it is a steam jet and no more a water jet who meets the turbine now, the laws of thermodynamics are to be observed now. The modern steam turbine is an action turbine (no reaction turbine), i.e. the steam jet meets from a being certain nozzle the freely turning impeller. There's a high pressure in front of the turbine, while behind it a low pressure is maintained, so there's a pressure gradient: Steam shoots through the turbine to the rear end. It delivers kinetic energy to the impeller and cools down thereby: The pressure sinks. Steam is produced in a steam boiler, which is heated in power stations by the burn of coal or gas or by atomic energy. Steam doesn't escape then, but after the passage through the turbine it is condensed in a condensor and then pushed back into the steam boiler again by a pump. This has the advantage that for example in nuclear power stations work- and cooling water are clearly separated

11. Diagram: 2-step steam turbine after Parsons (1883). This turbine possesses two impellers and an idler in the center

12. Multi-Level steam turbines In modern steam turbines not only one impeller is propelled, but several being in a series. Between them idlers are situated, which don't turn. The gas changes its direction passing an idler, in order to perform optimally work again in the next impeller. Turbines with several impellers are called multi-level. The principle was developed 1883 by Parsons. As you know, with the cooling gas expands. Therefore it is to be paid attention when building steam turbines to a further problem: With the number of passed impellers also the volume increases, which leads to a larger diameter of the impellers. Because of that, multi-level turbines are always conical. Fig. Coupled steam turbine

13. In power stations today, different types of turbines are used in a series, e.g. one high pressure -, two medium- and four low pressure turbines. This coupling leads to an excellent efficiency (over 40%), which is even better than the efficiency of large diesel engines. This characteristic and the relatively favorable production make the steam turbine competitionless in power stations. Coupled with a generator and fired by an atomic reactor, they produce enormously much electric current. The strongest steam turbines achieve today performances of more than 1000 megawatts. Advantages of Steam turbines: 01) Thermal Efficiency of a Steam Turbine is higher. 02) The Steam Turbine develops power at a uniform rate and hence does not required Flywheel 03) No internal lubrication is required for Steam Turbine as there is no rubbing parts inside 04) No heavy foundation is required for Turbine because of the perfect balancing of the different parts. 05) If the Steam Turbine is properly designed and constructed then it is the most durable Prime Mover 06) Much higher speed may be developed and a far grater range of speed is possible 07) In Steam Turbine no friction losses are there. 08) Steam Turbine are quite suitable for large Thermal Power Plant as they can be built in size from few Horse Power to over 200000 HP in singal unit.For more,please visit.

14. 09)Far fewer moving parts, hence potentially greater reliability. 10)Conventional piston steam locomotives give a varying, sinusoidal torque, making wheelslip much more likely when starting. 11)The side rods and valve gear of conventional steam locomotives create horizontal forces that cannot be fully balanced without substantially increasing the vertical forces on the track, known as hammer blow. Disadvantages of steam turbines 1) High efficiency is ordinarily obtained only at high speed (though some Swedish and UK locomotives were designed and built to operate with an efficiency equal to or better than that of piston engines under customary operating conditions). Gas turbine locomotives had similar problems, together with a range of other difficulties. 2) Peak efficiency can be reached only if the turbine exhausts into a near vacuum, generated by a surface condenser. These devices are heavy and cumbersome. 3) Turbines can rotate in only one direction. A reverse turbine must also be fitted for a direct-drive steam turbine locomotive to be able to move backwards

15. Conclusion The steam turbine is a prome mover in which the potential energy of steam is transformed into kinetic energy,and later in its turn is transferred into mechanical energy of the turbine shaft.so it is concluded that the steam turbine is very useful for mechanical work.

16. Reference R.K.Rajput. Google…Search---Steam Turbine. ^ "turbine." Encyclopedia Britannica. 2007. Encyclopedia Britannica Online. 18 July 2007 <http://www.britannica.com/eb/article-45691>. ^ P Keyser, A new look at Heron's 'steam engine', Arch. Hist. Exact Sci. 44 (2) (1992), 107-124. ^ Roberston, E and O'Connor. "Heron of Alexandria." MacTutor April 1999. 24 July 2007.<http://www-history.mcs.st-andrews.ac.uk/Biographies/Heron.html> ^Ahmad Y Hassan (1976). Taqi al-Din and Arabic Mechanical Engineering, p. 34-35. Institute for the History of Arabic Science, University of Aleppo.

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