SUBMITTED TO: MR. ABDUL WAHEED (HEAD OF MECHANICAL DEPARTMENT)
SUBMITTED BY: HAMMAD NAEEM (B.Sc. MECHANICAL INTERNEE)
Fatima Sugar Mills Mi lls Limited Lim ited Fazal Garh,
Sanawan, Kot Adu, Adu, Distt. Muzaffargarh Muzaffargarh
Acknowledgement Acknowledgement I take this opportunity to express a deep sense of gratitude to M r . M ohamma ohammad d Asl Asl am Shi Shi f t I ncharge, ncharge, M r . Babar Babar Ri az, az, Shi f t En gine gin eer and M r . Yas Yasii r Shahi d Graduate Tr aine ain ee Engin eer , F atima Suga Sugarr M il ls L TD , for cordial support,
valuable information and guidance, which helped me in completing this task through various stages.
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Acknowledgement Acknowledgement I take this opportunity to express a deep sense of gratitude to M r . M ohamma ohammad d Asl Asl am Shi Shi f t I ncharge, ncharge, M r . Babar Babar Ri az, az, Shi f t En gine gin eer and M r . Yas Yasii r Shahi d Graduate Tr aine ain ee Engin eer , F atima Suga Sugarr M il ls L TD , for cordial support,
valuable information and guidance, which helped me in completing this task through various stages.
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(BACK PRESSURE TYPE)
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Fatima Sugar Mills Limited
Mills House Turbine Specification KKK steam turbine (AK Tiengesellschafft Kuhnle Kopp & Kaussch D-6710 Frankenthal) Number of Steam Turbines in Mills House = 5 Model type = CF5G5 Pressure type = Back pressure Output power = 650KW
Speed Minimum speed 750 RPM Maximum speed 1500 RPM
Inlet Steam Pressure
Minimum steam pressure 19.2 Kg/cm2 2
Normal steam pressure 21.5 Kg/cm
Maximum steam pressure 23.8 Kg/cm2
Outlet Steam Pressure
Minimum steam pressure 1.2 Kg/cm2 2
Normal steam pressure 1.45 Kg/cm
2
Maximum steam pressure 1.7 Kg/cm Trip speed = 1725 RPM Inlet Steam Temperature = 340 Outlet steam temperature = 170 Speed reduction system
1000 RPM to 140 RPM then 140 RPM to 6 RPM Page 3 of 31
Important Terms Q: What is Impulse Turbine? A: It involved striking of the blades by a stream or a jet of high pressure steam, which caused the blades of the turbine to rotate. The direction of the jet was perpendicular to the axis of the blade.
Q: What is Reaction Turbine? A: A power-generation prime mover utilizing the steady-flow principle of fluid acceleration, where nozzles are mounted on the moving element. Q: What is Steam or Water Hammering? A: Steam hammering is the sound that is heard as a pinging, rattling, or banging in a steam system under conditions of Start-up, shutdown, changing loads or even in few cases, steady state full load operation. Q: What Is Water Or Steam Hammering? A: Steam hammering is the sound that is heard as a pinging, rattling, or banging in a steam system under conditions of Start-up, shutdown, changing loads or even in few cases, steady state full load operation.
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Causes of steam hammering Steam hammering is the phenomenon which occurs in steam charging in the pipeline while there is a presence of condensate in the line. This is because of sudden drop in pressure of steam as it comes in contact of condensate.
This can also occur due to poor heating of steam network before the steam enters into the system. Piping network remains cool and as soon as the hot steam enters, condensation takes place and water gets accumulated in the lines forming a Slug. As the steam flow increases, steam carries the water with it and lot of momentum is created and it hammers the line loops with tremendous forces creating a lot of stress. Steam hammers can blow flange joints and can damage piping supports and even piping itself. Poor condensate drainage in pipeline leads to this steam hammering. Where air filled traps are used, these eventually become depleted of their trapped air over a long period of time through absorption into the water. This can be cured by shutting off the supply, opening taps at the highest and lowest locations to drain the system and then closing the taps and re-opening the supply. Effects of steam hammering The effect of steam hammering can result in following:
Cracking of steam traps and pressure gauges Page 5 of 31
Break pipe welds and even rupture piping systems Bend internal system mechanism Causes valve failure Cause heat exchanger equipment tube failures Failure of pipe supports. Prevention of steam hammering Steam hammering condition exists in a steam system where condensate coexists with generated steam or flash steam. Typical examples include heat exchangers, tracer lines, steam mains, condensate return lines and sometimes, pump discharge lines.
A common example of steam hammer occurs during start-up or energizing of a steam system. If the steam line is energized too quickly without proper warm up time and condensate created during the start-up is not properly removed; steam hammer will be the result. There are few design or system changes that can be implemented to prevent or eliminate steam hammering:
Ensure correct steam and condensate design. Have documented SOP’s (standard operation procedures) for steam system start-ups and shut downs. Proper training for plant personnel. Have installation standards for steam components. Correct condensate connections of branch lines to the main condensate header and entry only from the top of the header. Page 6 of 31
Use steam traps that are properly sized and appropriate for application. Use warm up vales as steam line isolation valves larger than 2 inch. Do not “crack open” large steam isolation valves. Check or repair the pipe insulation. It saves energy and reduces accumulation of condensate in the piping system
TUDY
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Introduction A steam turbine is a mechanical device that converts thermal energy in pressurized steam into useful mechanical work. A steam turbine is a h eat engine in which the energy of the steam is transformed into kinetic energy by expanding the steam through NOZZLE. This resultant kinetic energy is converted into force by impinging on rings of MOVING BLADES (which deflect the jets of steam) mounted on a rotating element called a ROTOR. A steam turbine may be utilized in process industries, Power plants and for transport. The steam turbine obtains its power from the change of momentum of a jet of steam flowing over curved vanes. The steam jet, in moving over the curved surface of the blade, exerts a pressure on the blade owing to its centrifugal force. This centrifugal pressure is exerted normal to the blade surface and acts along the whole length of the blade. The resultant of this centrifugal pressure, plus the effect of change of velocity, is the motive force on the blade.
Working Principle The steam energy is converted mechanical work by expansion through the turbine. The expansion takes place through a series of fixed blades (nozzles) and moving blades each row of fixed blades and moving blades is called a . The moving blades rotate on the central turbine rotor and the fixed blades stage are concentrically arranged within the circular turbine casing which is designed to withstand the steam pressure.
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Back pressure steam turbine cycle
Theory of Steam Turbines Steam turbines extract heat from steam and transform it into rotational energy by expanding the steam from high to low pressure, resulting in mechanical work. Small and intermediate-sized steam turbines are used for a wide range of applications, including power generation, drivers for mechanical services. When coupled with gears they can be used to drive fans, reciprocating compressors and other classes of low-speed machinery. The largest turbine applications are generator drives in utility and other central power stations. The turbines discussed in this manual are the low-pressure (LP) turbine. There are several components which are turbine casing houses and supports the turbine rotor, and bearings. The casing is cast in two halves and bolted together with a metal to metal fit. This metal to metal fit is initially sealed using a sealing compound vice a gasket. In the event of a steam leak around the edge of the casing, a groove is machined around the peripheral of the turbine casing. This groove is known as the gunning groove . The gunning groove provides the ability to inject a sealing compound for emergency sealing of the turbine casing.
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The turbine rotor is the rotating part of the engine and is constructed of chromium molybdenum (chromoly) steel . The rotor wheels , which are
mounted to the rotor shaft, carry the movin g blades . The non-movin g blades are attached to the tur bine casi ng . The moving blades are attached to the turbine rotor. Non-moving blades are attached directly to the turbine casing. Short str ips of m etal , shrouding , are attached to the outer edges of the blading. This
shrouding is used to assist in maintaining rigidity of the blades. In addition, there is minimal clearance between the shrouding and the turbine casing preventing steam from leaking around the outer edges of the turbine blading. In the gl and seal system , these seals prevent any steam from leaving the turbine casing and also prevent any air from entering the turbine casing and subsequently the main condenser.
Boiler feed water at is injected into the boiler.
Water is heated evaporated in the boiler. The resulting superheated steam at to i ncr ease its enth alpy and r educe moistur e .
Steam is expanded in the turbine to a lower pressure. A small portion of the steam thermal energy is used to drive a generator.
The steam turbine is cogeneration system when an application involves the sequential use of a single source of energy for both power generation and
useful thermal energy output. A topping cycle uses a back-pressure or extraction turbine as a pressurereducing valve. As high pressure steam is expanded to a lower pressure, the turbine generates shaft power.
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Steam Turbine Classification and Types Steam turbines are classified according to their fundamental operating Principles, some of which are:
Number of stages: single or multi stage
Number of valves: single or multi valve
Steam supply: saturated or superheated; single or multi pressure
Turbine stage design class: impulse or reaction
Steam exhaust conditions: condensing, non-condensing
Types of driven apparatus: mechanical drive or generator drive
More focus will now be on the singl e-stage, n on-condensing steam tur bin e as it was the preferred choice in this application. In a single-stage turbine, steam is accelerated through a nozzle and guided into the rotating blades on the turbine wheel to produce power. A single pressure drop occurs between the nozzle inlet and the exit for the last row of blades. Single-stage turbines are usually limited to sizes of a few th ousand hp . The single-stage design is simplicity, dependability and first low (kW ) or l ess cost. Steam turbines can be generally classi fi ed as ei ther condensing or Non - condensi ng (back-pr essur e) . A condensing tur bine oper ates wi th an exhaust pr essur e l ess than atmospheri c or vacuum pressur e. Because of the ver y low exhaust pr essur e, the pr essur e dr op thr ough the tur bine is gr eater and h ence
. This design adds increased mor e energy can be extr acted fr om the steam f low capital and operating cost. Non-condensin g (back-pr essur e) tur bines oper ate with an exhaust pr essur e equal to or i n excess of atmosphere. Exhaust steam is used for heating, process or other purposes. Because all of the unused steam in the power Page 11 of 31
generation process is passed on to the process application and, therefore, not wasted, mechanical efficiency is not a major concern.
Turbine Stage Design Class On the basis of operation, steam turbines can be classified as: Impulse turbine and reaction turbine.
Impulse Turbine The impulse turbine was one of the basic steam turbines. It involved striking of the blades by a stream or a jet of high pressure steam, which caused the blades of the turbine to rotate. The direction of the jet was perpendicular to the axis of the blade. It was realized that the impulse turbine was not very efficient and required high pressures, which is also quite difficult to maintain. The impulse turbine has nozzles that are fixed to convert the steam to high pressure steam before letting it strike the blades. KKK 650 KW of steam turbine contain 27 nozzles in which 8 nozzles are used for overload purpose.
Impulse Turbine Page 12 of 31
Reaction Turbine A reaction turbine also rotates its blades due to the impending pressurized steam, but the steam does not strike the blades perpendicular, as in an impulse turbine. The steam is directed to flow along the blades, thus causing the blades to rotate because of the reaction force more than the impulse force.
Reaction Turbine
Components of Steam Turbine Blades For starters, a simple turbine works just like a windmill. The blades are designed in such a way as to produce maximum rotational energy by directing the flow of the steam along its surface. So the primary component that goes into a steam turbine is its blades. The blades are made at specific angles in order to incorporate the net flow of steam over it in its favor. The steam turbine contain 180 blades of length 25mm each and are moving type.
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Nozzles In KKK steam turbine 27 nozzles are used in which 19 nozzles are worked as standard loading and 8 nozzles are used as overloading.
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Shafts The shaft is a power transmitting device and is used to transmit the rotational movement of the blades connected to it at one end via the rotor to the coupling, speed reducer or gear at the other end.
Turbine casings, bearing housings The steam turbine is surrounded by housing or an outer casing which contains the turbine and protects the device components from external influence and damage. It may also support the bearings on which the shafts rest to provide rigidity to the shaft. Usually split at the center horizontally, the casing parts are often bolted together for easy opening, checking and steam turbine maintenance, and are extremely sturdy and strong.
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Turbine casings are designed for disassembly, usually about the horizontal plane, the casing halves are secured in service by the bolted flange , as in Fig. below. Casing internals, including diaphragms, are split at the same plane, and remain attached to their upper or lower casing halves when the turbine is opened. The casing is usually steel, using all cast steel components, or, where appropriate, a mixture of castings and plate, welded together. Some auxiliary turbines have cast iron casings. Bearing housings are also split for disassembly
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Bearings There are two types of bearings used in steam turbine shaft following are. 1. Thrust Bearing 2. General Bearing (Sliding Contact Bearing)
Thr ust Beari ng A thrust bearing is used to guide or support the shaft which is subjected to a load along the axis of the shaft. Such type of bearings are mainly used in turbines and propeller shafts.
Sli ding Contact Beari ng In sliding contact bearings, the sliding takes place along the surfaces of contact between the moving element and the fixed element. The sliding contact bearings are also known as plain bearings.
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Governor The governor is a device used to regulate and control or govern the output of the steam turbine. This is done by means of control valves which control the steam flow into the turbine in the first place.
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Oil System A steam turbine has many of moving parts and all these parts not only have to move in high velocities, but also need to be protected from wear and tear over the years. This is done by effective lubrication by the oil system, which governs the pressure, flow and temperature of the turbine oil, the bearing oil and lubrication of other moving parts. Generally following oil pumps are used in KKK steam turbine.
Auxiliary pump turbine
Auxiliary pump gear box
Mechanical pump
Turbo pump
Auxiliary pump
The auxiliary oil pump has two functions 1. It operates during startup and shutdown when the turbine shaft is not rotating fast enough for the main oil pump to deliver the required pressure and flow. 2.
It acts as a standby lube oil pump in the event of a main oil pump failure
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Mechanical Pump Mechanical oil Pump The main oil pump is the one that delivers all the oil requirements for the turbine generator at high pressure during normal operation. It is direct-driven from the turbine shaft and may be located at either the turbine or generator end of the shaft
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Turbo pump This pump is used as stand by when auxiliary and mechanical pumps are malfunctioned. This pump is driven by steam and it contain rotating blades which is coupled with the pump.
Pipes The pipe is an all-important steam turbine component that brings the steam from the boiler to the turbine. This has to be done without loss in pressure, and at the same time, must be able to withstand all these pressures safely. The pipes should be easy to clean.
Start and Stop Valve This valve is hydraulically operated. The purpose of start and stop valve is to start the flow of steam when required and In case of emergency this valve is used of stop the flow of steam to turbine. Here reset knob use to reset the turbine after emergency.
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Throttle valve The throttle valve performs the functions of controlling the quantity of steam admitted to the turbine by throttling and acting as a quick-closing emergency valve (on some governors). It should always be closed by means of the manual trip device. The throttle valve should receive careful attention and all moving parts should be kept well lubricated.
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Steam Strainer A steam strainer should be installed in the main steam line to the turbine to prevent foreign particles from being carried into the turbine with the steam. It is therefore an important accessory. Steam strainers are normally installed ahead of and close to the throttle valve.
Overload Valve The purpose of overload valve is that when the load on the turbine is increase and turbine needs more steam to maintain the speed therefore this valve is engage to maintain the speed and load. This valve engage the overload steam nozzles.
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Expansion Bellows A bellow is made up of a series of one or more convolutions, with the shape of the convolution designed to withstand the internal pressures of the pipe, but flexible enough to accept the axial, lateral, and/or angular deflections. In simpler words, bellows are created in such a way that they can handle the pressure on the inside of the pipe. they should also be flexible enough to move either way. In most cases, expansion bellows are used to absorb movement and vibration in the process of transfer of high temperature commodities like steam, exhaust gases etc. However, expansion bellows are alsoused for other alternative purposes like noise absorption, anti-vibration, and building settlement. Expansion Bellows are auxiliary to any heavy duty, or high pressure processes
Tachometer Tachometer is an instrument used to measure the speed of the turbine in
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revolution per min RPM.
Pressure and Temperature Gauges Pressure and temperature gauges installed on steam turbine can be used to pending troubles. Thermometers on the oil inlet and discharge lines from a bearing will indicate a rise in temperature caused by a bearing that is dirty or out of adjustment, by an insufficient flow of oil. The normal temperature of a steam turbine bearing usually should not exceed 150 degrees. Fahrenheit.
Reverse Gearing Clutch When the mills rolls stop rotating due to increase in load on the steam turbine. Fibers of cane stuck into the mills which cause of stopping the steam turbine. To restart the steam turbine this element is used. This clutch contain a reversing motor which rotates the mills in reverse direction, after fibers of cane free from the mill, then steam turbine is start.
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Control panel Control panel contain all the operation features of the steam turbine including speed controlling, lubrication, rest, temperature, governor speed controlling, reverse direction of reverse gearing clutch etc.
Lubricating oil cooler This is used to cool the lubricating oil. This contains water pipes inside and heated oil is passed between the cooled water pipes which cool the oil.
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Operation and Maintenance of Steam Turbine When warming up a steam turbine for use, the main steam stop valves (after the boiler) have a bypass line to allow superheated steam to slowly bypass the valve and proceed to heat up the lines in the system along with the steam turbine. Also, a turning gear is engaged when there is no steam to the turbine to slowly rotate the turbine to ensure even heating to prevent uneven expansion. After first rotating the turbine by the turning gear, allowing time for the rotor to assume a straight plane (no bowing), then the turning gear is disengaged and steam is admitted to the turbine, first to the astern blades then to the ahead blades slowly rotating the turbine at 10 to 15 RPM to slowly warm the turbine. Problems with turbines are now rare and maintenance requirements are relatively small. Any imbalance of the rotor can lead to vibration, which in extreme cases can lead to a blade letting go and punching straight through the casing. It is, however, essential that the turbine be turned with dry steam - that is, superheated steam with a minimal liquid water content. If water gets into the steam and is blasted onto the blades (moisture carryover), rapid impingement and erosion of the blades can occur leading to imbalance and catastrophic failure. Also, water entering the blades will result in the destruction of the thrust bearing for the turbine shaft. To prevent this, along with controls and baffles in the boilers to ensure high quality steam, condensate drains are installed in the steam piping leading to the turbine.
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Over Speed Trip System In order to prevent the turbine unit accelerating to a dangerous speed an OVERSPEED TRIP GEAR IS FITTED. Over speed can be caused when the turbine load is suddenly lost. This should normally be controlled by the speed governor.
Process over Speed Trip System In addition to a speed control system, steam turbines is fitted with a shutdown system to prevent damage to the machine. In the event the speed governor fails to control the speed, the over speed trip actuates to shut down the machine. When shaft speed exceeds a desired safe level, generally 10% over speed, a latching device or oil dump mechanism is actuated to close a special emergency stop valve. This system is totally independent of the Mechanical system that is completely separate from the speed governing systems. A trip pin or plunger is mounted in the turbine shaft with its center of gravity slightly off center. In the event the speed regulating governor fails to Page 28 of 31
control the speed, the unbalanced plunger overcomes a spring force at a preset trip speed. As it moves outward, it strikes the trip-lever, causing release of a spring dump valve that releases the trip circuit oil pressure.
Losses Common to All Turbines Are Described Below 1. Loss of working substance. Loss of steam along the shaft through the shaft glands where the shaft penetrates the casing. 2. Work loss. Loss due to mechanical friction between moving parts. 3. Throttling loss. 4. Windage loss. This is caused by fluid friction as the turbine wheel and blades rotate through the surrounding steam. 5. Friction loss as the steam passes through nozzles and blading.
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Steam Turbine Troubleshooting Vibrations S.no Condition
1
2
3
4
5
6
Unbalance
Identifiable by
1. Uniform vibration throughout the turbine, decreasing slightly under load.
Poor alignment with driven equipment.
2. Variable vibration least noticeable at no load; becoming worse under load.
Poor or inadequate foundation.
3. Vibration of surrounding structure; constant vibration of turbine under all load conditions.
Loose parts
Internal rubbing
Steam troubles
4. localized vibrations with noise at start-up & shut-down.
5. localized vibrations with varying with turbine speed.
6. Unusual noise at the intake; failure of strainer.
Probable cause 1. Sprung shaft 2. Incorrectly located balance weights. 3. Displacements of balance weights. 4.corroded or eroded blades or buckets 5.Sediment in blades or buckets 6. Rotor unequally heated. 7. Broken blades or buckets. 1. Eccentric flexibility coupling 2. Driver & driven equipment not aligned properly at installation. 3. Piping strain on driver or driven equipment. 4. Foundation selected unequally.
1. Improper grouting. 2. Bed-plate not securely foundation.
1. Excessive bearing clearance. 2. Ball joint of bearing is loose. 3. Loose coupling or coupling bolts.
1. Rotating buckets coming in contact with stationary buckets. 2. Inadequate casing clearance. 3. Thrust bearing is worn. 1. Water coming in with steam. 2.Sediment in steam
Remedy 1. Replace shaft. 2. Relocate weights & balance rotor. 3. Balance rotor. 4. Replace worn blades or buckets. 5. Replace broken blades or buckets. 6. Clean blades or buckets. 7. Consult manufacturer.
1. Replace flexible coupling. 2. Realign driver with driven equipment’s as per manufacturer instructions. 3. Provide support for piping to relieve strain. 4. Solidify foundation; regrout if necessary.
1. Regrout bed-plate. 2. Tighten foundation bolts.
1. Machine off joints between bearing halves; replace bearing if necessary. 2. Add shims as required to tighten bearing; replace worn parts as required. 3. Tighten setscrews securing coupling to shaft; tighten coupling bolts. 1. Check clearance; adjust as required. 2. Check for chemical deposits; adjust bearings. 3. Replace thrust bearing. 1. Re-evaluate piping; install a separator ahead of the throttle valve. 2. Test steam for sediment, acid, or salt. Take corrective action.
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