dummy piston in steam turbine

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Immediately it touches the revolving surface the match flies off sideways. Smith, Michael Abbott. The other type of turbine, suggested by Giovanni Branca in 1629, is known as the impulse type. e. Mixed pressure turbine. &{ A review and discussion of the recurrent problems experienced by reaction turbines is also presented to explain the main operating challenges for these machines due to the fluid dynamic phenomena perturbing the off-design operation and increasing the mechanical component damages.

For this reason, a gearbox represents an additional potential failure mode. The first practical turbine was built at Gateshead, Co. Durham, in 1884. Increase steam friction 1, 2, 3, 4. 2. Another name for the rotor is the rotor assembly. Mr Parsonsbecame one of the founders of the power generation industry after he constructed an electrical generating set using a direct coupled steam turbine as the prime mover. Cutting. Parsonss original design was inefficient, running at 18,000 rpm and producing 7.5 kilowattsabout the power of a small household backup generator today. In the steam inlet pipe there is also a steam separator (normally, but not always) which separates water droplets from the steam flow by causing a rapid change of direction of travel; the rapid change in direction causes moisture droplets to coalesce on the interior separator body surfaces and then drain out of the separator base. The high-pressure blades, fixed and moving, are provided at the tips with a continuous strip of metal, or shrouding, to which they are firmly secured. Extensive monitoring and control systems ensure turbines can be operated within their design limits, in a safe and efficient manner. c. Extraction-bleeder. b. a. LP turbines that have this setup are designated double flow, or two flow, turbines. 5. Strong. b. c. Atomization of the fuel. Advantages of the steam turbine include: d. 0.757, convergent b. Blade seals. For further convenience, the modern Parsons turbine is usually arranged in three separate cylinders or casings - for high, intermediate and low pressures respectively. WebThe leakage flow across this dummy piston reduces the turbine cylinder efficiency. c. 2,3,5 a. c. Maintained constant regardless of turbine load. As steam passes over a reaction turbine blade, a reactionary force is created upon the blade and this causes the turbine rotor to rotate. Tandem Compound Steam Turbine Arrangement. a. Webdummy piston thereon, the turbine wheels or disks, the steam-supply pipe leading to the dummy piston to resist the end-thrust, and a valve controlling said steam-Supply Convert the kinetic energy of the steam into mechanical The arrows indicate the, The steam, on beginning to expand, attains a speed that increases faster than does the volume. e. Set at 45 degrees to the nozzle angle. The power developed by the flow in a reaction turbine is also given by the general Euler equation.

As a small pressure drop occurs across both the stator and the rotor, there is a series of continuous and smooth pressure drops throughout the turbine length. e. Allow the use of smaller turbines. Convert heat energy into kinetic energy. Exhaust steam may be 3.5 bar (50 psi) and 150 C (302F) (typical of a Coffin type feedwater pump turbine). Such a form of gland is impossible for the turbine shaft revolving at high speed, and a type known as a labyrinth gland is used, with knife edges similar to those on the shrouding, referred to above. Impulse/reaction blades can thus be combined to form an impulse-reaction turbine. Extraction Where pressure compounding is adopted, the rings of fixed blades are omitted, and for them are substituted sets of nozzles which provide a drop in pressure with an increase of velocity. The load of the turbine (generator, pump etc.) The blades are made of the finest quality stainless steel, as they have to withstand tremendous heat combined with mechanical stresses due not only to pressure, but to the centrifugal forces to which they are subjected when whirled round at high speed.

c. 2% For example: https://petrotechinc.com/how-does-a-steam-turbine-work, https://en.wikipedia.org/wiki/Steam_turbine, https://www.explainthatstuff.com/steam-turbines.html. In a set of turbine engines, the casings - high-, intermediate- and low-pressure - contain rotors that are bladed in groups. c. 1,3,4. You can read more on Propelling the Modern Ship, The Queen Marys Engines and, Compound Triple & Quadruple Expansion Engines. A pipe from some stage in the turbine provides steam to act on the dummy piston which is mounted on the turbine rotor (Figure 6.73). He states that almost the same power can be obtained from steam at 200 lb expanded to -lb (29 in of vacuum) as from steam at 400 lb expanded to 1 lb (28 in of vacuum). Greater power per unit size may be absorbed. d. A pressure increase in the nozzles. The turbine, however, has many advantages over the reciprocating engine in its use of the steam. How is the drum end cover with shaft installed in the rotor? endobj The turbine is encapsulated in a spiral-shaped casing having an inlet and an outlet. endobj e. One set of nozzles. In other words, they also act as nozzles (Figure 6.16). 0.757, convergent /Height 3408 2. It is important to constantly monitor the condenser condensate level, as too much condensate in the condenser hotwell may lead to several problems: Steam turbines are normally fitted with comprehensive monitoring and control systems. a. 6.14 it follows that the diagram efficiency of a reaction stage is. The effect of exit velocity and air angle on the utilization factor for a 50% reaction axial turbine stage. 1. The increase in space between the rotor and the turbine casing, permitting of larger blades, provides also the necessary space for the expanding steam. Carbon rings, when used for turbine shaft seal require: The blading of such turbines is arranged at either end to face the central steam supply. At speed below 2000 rev/mm Propeller and Kaplan turbines are similar in the head, flow rate, and physical appearance. /Subtype /Image A further advantage in the turbine is the use of large exhaust passages which are always open to the condenser. c. A force on the blades produced according to Newton's 2nd Law Thin high temperature gaskets. To allow for the effects of varying temperature conditions i.e. It is on this principle of reaction that most modem turbines depend for their operation, coupled, however, with the impulse action suggested by Giovanni Branca in 1629. WebTo counteract this force, steam is admitted to a dummy (balance) piston chamber at the low-pressure end of the rotor. e. Velocity, kinetic energy. 2nd 1. Thus, as previously noted, a reaction turbine is moved primarily by reactive force but also to some extent by direct impulse/thrust. Each blade must also be able to cope with the operational stresses placed upon it, these stresses include high temperature variations, high pressure variations, mechanical stresses from vibration, erosive effects of foreign object damage (water or rust particles etc. Reaction steam turbines often use _____ seals as part of the shroud with the seal clearances kept as small as possible. WebIf, in addition to the turbine stages, you allow the high-pressure steam to act on a dummy piston secured to the turbine shaft which has low (e.g. d. Carbon. High rotational speeds are required. 4. Hall Ph.D., in Fluid Mechanics and Thermodynamics of Turbomachinery (Seventh Edition), 2014. LABYRINTH PACKING to seal the turbine against the atmosphere is indicated here in section. The steam enters the blades at great speed and loaves them slowly compared with the speed o! Steam is exhausted to the LP turbine at around 6 bar (87 psi) at 165C (329F). Temperature. e. 1,2,3,4. /Width 2320 d. 1, 3. Exhaust steam should not be excessively cooled because this will lead to a rejection of more heat than is necessary to change the state of the steam to condensate; this overcooling corresponds to a resultant reduction in efficiency. Equation[2.42] shows that the effect on efficiency is relatively small for a wide range of blade speed ratios (0.61.3). d. 1,2,4 Condensers, also sometimes called surface condensers, are large heat exchangers used to cool exhaust steam back into condensate; they are usually installed directly beneath the turbine but may be installed axially in some instances.

b. /Type /Catalog c. Polytropic process. A dummy piston on a steam turbine is used to: The passage of steam through moving and fixed blades (F) is indicated by the horizontal arrows. c. Water seals. /Contents 4 0 R a. Prior to the steam admission valve there is normally an emergency trip valve which slams shut (closes quickly) in the event of a critical situation occurring. Steam enters the machine through the nozzles shown at the top in the direction of the oblique arrows, and impinges on the first row of moving blades (M) that move in the direction indicated by the horizontal arrows. Dummy piston arrangement on Parsons Turbines&Doubl End thrust is balanced removing need for dummy pistons or cylinders on reaction turbines . /Thumb 11 0 R The size and shape of the turbine rotor blade can then be designed to ensure its resultant velocity is half of the steam velocity for that particular row of blades. This type of combination leads to an excellent compromise: an all-impulse turbine would have a very low efficiency and an all-reaction turbine would have an excessive number of stages. Electrical generation. d. Turbine blade velocity equals one half the steam velocity. WebThe dummy piston uses steam pressure to push the entire turbine rotor assembly along the length of the shaft. Disc rotors made from a solid forging are: Constant supervision 2.

b. If using a steam turbine to drive/rotate a ships propeller, there needs to be some way of driving it astern (reverse direction). Turbine casings are split along the horizontal axis to form an upper and lower casing; the two casings are bolted together to form a split casing. >> For this reason, they are cast from a hard stellite material which is an alloy of cobalt, chrome, tungsten, and molybdenum. e. Increase. The rotor shaft and everything mounted to it (moving blades, rotor discs etc. a. Pressure. d. Allow the use of higher steam pressures. Another method often used in low pressure turbines is to make the turbine double flow. Materials at the given maximum temperature and under constant pressure continue to deform with very slowly increasing strain of the material; this phenomenon is called _____. The shaft of the turbine is coupled to the electrical generator that produces electricity, as shown in Fig.

Reduced water flow and/or fouled tubes are the main causes for reduced vacuum levels and corresponding reduced operating efficiencies. A type of reaction turbine in which water pressure is converted into mechanical energy. d. Tandem compound b. Stationary blades. b. Relieving pressure. Consequently, the casing material of an LP turbine can have lower mechanical strength; LP casings are often constructed from carbon steel. 2,3 Steam turbine diaphragms are hollow disc shaped objects that house a turbines stationary blades (fixed blades). /Length 9 0 R b. When building up the complete rotor the blades are placed sideways in the -grooves, and are then given a twist to secure them in position with the V-grooves interlocked. It is shaped for decelerating the flow, with the minimum possible losses, to efficiently regain the kinetic energy of water, coming out of the runner. Due to these centrifugal forces, LP turbines are very sensitive to overspeed situations. Correctly maintaining the relationship between steam velocity and blade velocity is achieved using pressure staging. It is quiet in operation. Diesel engines are favoured because they do not require the large supporting water and steam systems that steam turbines require. Register to licenses this file for a specified project. 3. Comparison of different types of turbines. These conditions apply only at the beginning of the. WebCondensing steam turbines are normally used to bridge the power deficit. 7 0 obj A firework, the well-known catherine-wheel, provides a good illustration of reaction. The velocity diagram of a 50% reaction is symmetrical, and, for the maximum utilization factor, the exit velocity (V2) must be axial. Least efficient. Be sure to check your spelling. 1 0 obj There is a big gap between those pioneer engines and modern turbines that are supplied with steam at a pressure of 400 lb per square inch, but the importance of the vacuum in the condenser still remains. Double flow turbines are primarily used to equalise the thrust load from the opposing turbines, which minimises the size of the thrust bearings that the LP turbine requires. 2. e. Is adjusted to provide minimum clearances on start up. For example, LP turbine rotor blades are considerably larger than HP turbine rotor blades, thus a LP cylinder has a much larger diameter than a HP cylinder. e. 3, 4. Some power plants operate for months without ever adjusting the steam throttling valves; this has led to valves sticking and failing to actuate when desired. This is overcome, however, by the use of a group of blading arranged for astern working which is attached to the rotor of one or more of the turbines comprising the set. The exhaust steam from the turbine can then be used for process requirements e.g. Eng., Ph.D., C.A. Reaction turbines are the turbines that use the pressure as well as the velocity of the moving water to rotate. c. 30-35% /Type /Page

The dummy piston annular area and the steam pressure are chosen to produce a force which exactly balances the end thrust from the reaction blading. Schematic of a reaction type turbine showing the distribution of the thermodynamic and fluid mechanic properties. Forces are balanced by the drum offering a greater surface area to the low pressure balancing d. Cross-compound. Unless coupled to a lower speed section of the gearbox (if applicable), the larger blades can be more susceptible to cracking. a. Summarize the functions of the primary organ systems in the human body. 2, 3, 4 In a condensing-bleeder turbine up to 2% of the total steam flow may be bled off. The blades are bucket-shaped in section and in general appearance resemble a woodworkers gouge. The utilization factor for a fixed nozzle angle will increase as the reaction approaches 100%. However, a gradual turbine stop would require a large amount of oil and a correspondingly large gravity tank. 2. Copyright 2023 Elsevier B.V. or its licensors or contributors. Rotational speed. d. 40-45% e. A velocity drop in the stationary blades. 3. BLADES OF A VELOCITY COMPOUNDED TURBINE are arranged as shown diagrammatically. For reaction less than zero, the rotor has a diffusing action. e. Reduced if load increases. 1. With steam rushing violently through the casing from one end to the other, the rotor is not only rotated; it would be pushed bodily forward as well if means were not adopted to prevent this.

d. 1,2,4. As the steam inlet velocity varies throughout the turbine, so too does the velocity of the blades. 36 Figure 6.3. Boyce, in Combined Cycle Systems for Near-Zero Emission Power Generation, 2012. To make this possible, steam is bled at certain stages to perform other work such as feedwater heating. a. Increase in steam velocity.

e. Soft packing between each ring. d. High pressure drops are required. a. Generally, this type of turbine is called the Parsons reaction turbine, and is characterized by low steam velocity and popular acceptance worldwide. The standard setup is to have the drive end of the turbine fixed and stationary whilst the opposite end is free to move axially. a. Frictional losses are maximized. There is therefore no contact between the moving and fixed portions except at the bearings. Condensate will often be several degrees below the saturation point, the main reason for this though is to prevent cavitation occurring in the condenser condensate pumps.

The hub is close to an impulse turbine. [ /PDF /Text /ImageC ] Their working principle is similar to the Francis turbine. /Pages 2 0 R Steam flow is controlled by hydraulic valves equipped with stellite discs/plugs and seats; the stellite layer lends the plugs and seats very hard erosion resistant properties. The steam accordingly passes through the first ring of fixed blades or nozzles and, with an increase of velocity and decrease of pressure, imparts an impulse to the first ring of moving blades. For a 50% reaction design, the similarity between various angles is 1=2 and 2=1.

a. Exhaust steam in a back-pressure turbine is not reduced to vacuum pressure, whereas a condenser turbine is. The working process of the Kaplan turbine is similar to the propeller-type turbine along with adjustable runner blades so that it can work smoothly at vortices and shocks during partial load conditions. << Nozzles are subject to very high temperatures and severe erosion conditions.

Centrifugal forces increase with the _____ of the speed. c. Two or more rows of stationary blades. What is the pH\mathrm{pH}pH at the equivalence point ? Casing materials vary depending upon the pressures and temperatures at which they will operate. In a reaction turbine: Rows of stationary blades alternating with rows of moving 3. c. Deformation Steam turbine casings/cylinders are cylindrical shaped constructions consisting of two halves. In an impulse turbine as the steam, passes through the moving blades the _____ drops but the _____ remains the same Instead of using steam to move pistons, it used steam to turn propeller-like blades, converting the thermal energy into rotational energy. Comparing Eqs. d. 2,3 Keep the rotor in an exact position in the casing. Diaphragms are constructed from carbon steel, or in some cases cast iron, which is machined and then welded into place. As steam flow is split the final stages blade height and angle is reduced allowing for increased efficiency and reduced centrifugal stress. Shipping Wonders of the World 2012-23 | Contents | Site Map | Contact Us | Cookie Policy, The modern marine steam turbine has been developed from the two main principles, reaction type and impulse type, invented respectively by Hero of Alexandria about AD 50 and by Giovanni Branca in 1629. 2, 4, 5 a. WebThe modern marine steam turbine has been developed from the two main principles, reaction type and impulse type, invented respectively by Hero of Alexandria about AD 50 In an impulse turbine the enthalpy of the steam as it passes through the stationary nozzles. the 50% reaction turbine has the highest efficiency of all of the various types of turbines. In the chapter Steam Turbine Engines was traced the story of the turbine over a period of nearly two thousand years. d. Vary. Place the letter of your choice in the space provided. a. One set of nozzles. Typical components damaged due to water ingress include the fixed blades, moving blades, and diaphragm labyrinth seals. In the impulse turbine the blade-section is crescent-shaped and the space between adjacent blades is symmetrical about its centre. b. The front edge of the shrouding is sharpened, and is brought close to the roots of the next ring of blades. \SCJ3E(yj"Z-eUbjzQQKHB}TedGRjMmDKj'PMJ"!&F/-dv]I=!2Bk3kgO,_ .oji[ ,~/~?vKq_LrZuD^6mB> |4CRg~NnLmuwrOLJ#OMIO 4u ~W,TktbPR7m'iClrxOa]4k`!gH$""""AU>;L"bhDE4o2an 8vLg[X +})M0 Maximum seal clearance. b. Pas plant. /Count 5 THE DE LAVAL NOZZLE is shown in detail in the top diagram. c. Too expensive to maintain. Regenerative condensers utilise exhaust steam to reheat condensate back to as close to saturation temperature as possible, without it changing state to steam. a.

b. c. Condensing-bleeder Low rotational speeds are required. b. Centrifugal. e. Decreases. The shroud is usually above a reaction of 50%. In a reaction turbine the steam pressure drops across both the fixed and moving blades while the steam's _____ rises in the fixed blades and drops in the moving blades. a. The shape and angle of the blades - for example, those of the first row of fixed blades - provide a series of openings that decrease in size in the direction of the steams flow. Residual d. Chromium-nickel-molybdenum Rotors for high outputs and high temperatures are generally made of _____ steels: 6.9 and 6.17, it may be concluded that the maximum power (work done per unit time) of an impulse stage is twice that of a 50% reaction stage. d. 10% When steam leaves the moving blades at zero absolute velocity: Large numbers of blade rings are used in the Parsons turbine so that the number of stages in which the pressure falls shall be as many as possible. The kinetic energy is regained by the conversion of water into suction head, thereby increasing the total pressure difference on the runner. of Motion.

In most designs, the reaction of the turbine varies from hub to shroud. d. 3,5 1. In the Parsons turbine, although it is described as being of the reaction type, the steam has an impulse action on the blading in addition to its use on the reaction principle. Although some contraction and expansion occurs radially, most occurs along the axial axis. Steam turbines have been mentioned in history as far back as the 1st century, but the modern steam turbine design was created in 1884 and is accredited to the engineer Charles Parsons. Increase the absolute velocity. A reaction turbine results in a long machine due to a large number of alternate rows of: Sometimes, if a single casing LP turbine design is not possible, two smaller double flow LP turbines may be used. Another outstanding feature of the Parsons turbine is the increase in size of the blades.

b. a. /Length 5 0 R d. Absolute velocity equals zero.

d. 2,3,4 a. 4. Cracking typically occurs at the blade root and fire tree attachments due to the large centrifugal forces they encounter during operation. END-TIGHTENED BLADES are clearly shown in this illustration. The labyrinth gland comprises a series of plain grooves in the rotor shaft. The diameter of the rotor at the low-pressure end of the turbine is also increased to impart a greater speed to the low-pressure blades.

The impulse turbine depends for its action on the behaviour of steam (under pressure) that is allowed to expand. Table 7.2. 1,2,3 c. Condensing-bleeder.

in along the shaft: e. 2,3,4, The efficiency of the Rankine cycle (steam plant) that utilizes a steam turbine is: Decrease.

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