summer training report ntpc badarpur
TRANSCRIPT
SUMMER TRAINING REPORT ON BADARPUR
THERMAL POWER STATION
MADE BY:
DEEPAK BHAGAT 06415303710
NATIONAL POWER TRAINING
INSTITUTE
ACKNOWLEDGEMENTI would like to thank NTPC BADARPUR for providing me a golden opportunity to work with them. The support and the env i ronment prov ided to me dur ing my pro ject was more than what anyone would have expected. I am very grateful to Mrs. RACHNA BHAL (H.R.) who granted me the opportunity of working as a trainee at mechanical division of power engineering. I would also like to thanks Mr. MANMOHAN SINGH (DY.MANAGER), Mr. G.D SHARMA (TRAINING COORDINATOR) and my instructors of B.M.D., P.A.M., T.M.D. and divisions without them I would not be able to perform such a delightful job. And at last I would like to thanks all the people involve in the training that helped me in accomplishing it in such a wonderful way.
PREFACE
NTPC is one of the most important industries for producing the electricity. There are various divisions in NTPC for various branches like mechanical division, electrical division etc. The main objective of preparing this report has been to present the operations of BMD, PAM, TMD of mechanical division in a logical, innovative and manner. The basic theory presented in this report has been evolved out of simple and readily understood principles. A sincere effort has been made to maintain physical concepts in various operations. An effort has been made to give a balanced presentation of this report with the help of figures, different types of data and related suitable theories as well as concepts. Eventually, again I would like to thank BTPS.
DEEPAK BHAGAT B.TECH (P.E)
2ND YEAR Email:[email protected]
CONTENTS ABOUT N.T.P.C (NATIONAL THERMAL POWER CORPORATION)
•INTRODUCTION•POWER GENERATION• INSTALLED CAPACITY • NTPC POWER STATIONS IN INDIA
ABOUT B.T.P.S
(BADARPUR THERMAL POWER STATION)•INTRODUCTION •BASIC POWER PLANT
ABOUT BMD(BOILER MAINTENANCE DEPARTMENT)
•BOILER DESCRIPTION•FEED WATER & CONDENSATE CYCLE•COMBUSTION PRINCIPLE (TRIPLE T’S) •FURNACE & THEIR TYPE•BASICS OF FAN & DRAFT SYSTEM•PULVERISE (COAL IN TO PULVERISED COAL OUT)•BOILER AUXILIARIES
ABOUT PAM(PLANT AUXILIARY MAINTENANCE DEPARTMENT)
•THEORY OF CIRCULATION OF WATER • ASH HANDLING PLANT•CSP HOUSE• WATER TREATMENT PLANT• AIR COMPRESSER HOUSE•COOLING TOWER
ABOUT TMD (TURBINE MAINTENANCE DEPARTMENT)
•STEAM TURBINE THEORY •STEAM CYCLE•TURBINE CLASSIFICATION•TURBINE CYCLE•DESCRIPTION OF MAIN TURBINE•TURBINE AUXILLIARIES AND THEIR ARRANGEMENT
ABOUT OF NTPC
* INTRODUCTION
The year 1975 witnessed the birth of an organization that went on to achieve great feats in performance in a sector that was then, characterized largely
by lack of investment, severe supply shortages and operational practices that mad the commercial viability of the sector unsustainable. NTPC symbolized hop of the country suffering from crippling power black-outs, the Government of India, which was trying to pull an ailing, economy back on the track and he World Bank, which was supporting the country in many development initiatives. Thus, NTPC was created not only o redraw the power map of India but also excel in is performance and se benchmarks for others to follow. It succeeded on both counts.Today with an installed capacity of 39,174 MW, NTPC contributes one fourth of the Nations Power generation, with only one fifth of India total installed capacity. An ISO 9001:2000 Certified company, it is world world`s 10th largest power generation in the world, 3rd largest in the Asia. NTPC is #1 independent Power Producer (IPP) IN THE WORLD. Also it is 384th largest company in he world (FORBES 2011).It is one of the largest Indian companies in terms of market cap. The corporation recorded a generation of 222.07 billion unit (BUS) IN 2011-2012; through 16 coal based and 7 gas based power plant spread all over the country and also has 07 plants in joint venture. Rated as one of the best company to work for in India, it has developed into a multi-location and multi-fuel company over the past three decades.
Revenue 501.8852 billion (US$10.01 billion)(2009–10)
* POWER GENERATION
Presently, NTPC generates power from Coal and Gas. With an installed capacity of 39,174 MW, NTPC is the largest power generating major in the country. It has also diversified into hydro power, coal mining, power equipment manufacturing, oil and gas exploration, power trading and distribution. With an increasing presence in the power value chain, NTPC is well on its way to becoming an “Integrating Power Major.”
* INSTALLD CAPACITY
Be it the generating capacity or plant performance or operational efficiency, NTPC’s Installed Capacity and performance depicts the company’s outstanding performance across a number of parameters .NTPC OWNED NO. OF
PLANTSCAPACITY(MW)
COAL 16 30,855GAS/LIQUID FUEL 7 3,955 TOTAL 23 34,810OWNED BY JVsCOAL AND GAS 7 4,364
TOTAL 30 39,174
*POWER STATIONS IN INDIAGAS BASED:SR. NO.
PROJECT STATE INST. CAPACITY(MW)
1. NTPC ANTA RAJASTAN 413 2. NTPC AURAIYA UP 6523. NTPC KAWAS GUJARAT 645 4. NTPC DADRI UP 817 5. NTPC JHANOR GUJARAT 648 6. NTPC KAYAMKULAM KERALA 350 7. NTPC FARIDABAD HARYANA 430
TOTAL 3955
COAL BASED:SR. NO.
PROJECT STATE INST. CAPACITY
1. SINGRAULI SUPER THERMAL POWER STATION
UTTARP RADESH
2000
2., NTPC KORBACHHATTISGARH
2,600
3. NTPC RAMAGUNDAM ANDHRA PRADESH
2,600
4. FARAKKA SUPER THERMAL POWER STATION
WEST BENGAL 2,100
5. NTPC VINDHYACHAL MADHYA PRADESH
3,760
6. RIHAND THERMAL POWER STATION
UTTAR PRADESH
2,500
7. KAHALGAON SUPER THERMAL POWER STATION
BIHAR 2.340
8. NTPC DADRI UTTAR PRADESH
1,820
9. NTPC TALCHER KANIHA ORISSA 3,00010. FEROZE GANDHI UNCHAHAR
THERMAL POWER PLANTUTTAR PRADESH
1,050
11. TALCHER THERMAL POWER STATION
ORISSA 460
12. SIMHADRI SUPER THERMAL POWER PLANT
ANDHRA PRADESH
1,500
13. TANDA THERMAL POWER PLANT UTTAR PRADESH
440
14. BADARPUR THERMAL POWER PLANT
DELHI 705
15. SIPAT THERMAL POWER PLANT CHHATTISGARH 2,98016. NTPC ASSAM 750
BONGAIGAON (COMMISSIONING 2013 ONWARDS )
17. NTPC MOUDA (1 UNIT 500 MW IS COMMISSIONED IN APRIL 2012 )
MAHARASHTRA 1,000
18. RIHAND THERMAL POWER STATION (ERECTION PHASE)
UTTAR PRADESH
500
19. NTPC BARH (COMMISSIONING 2013 ONWARDS )
BIHAR 3,300
TOTAL 31,995
*ABOUT BTPS
*INTRODUCTION
The Badarpur Thermal Power Plant has an installed capacity of 705 MW. The main plant equipment was supplied by M/S. BHEL. The boiler of Stage - 1 (3×95) MW units are of CZECHOSOLOVAKIAN design and that of 210 MW units are of COMBUSTION ENGINEERING design. The Turbo-alternators, supplied by M/S BHEL, are of RUSSIAN design and Control and Instrumentation for Stage-1 (3×95) and Stage-2 units are mostly of RUSSIAN design and for Stage-3 are of KENT design and supplies by M/S Instrumentation Ltd., KOTA.
STAGE UNIT NUMBER INT. CAPACITY(MW0
DATE OF COMMISSIONING STATUS
First 1 95 July, 1973 RunningFirst 2 95 August, 1974 RunningFirst 3 95 March, 1975 RunningSecond
4 210 December, 1978 Running
Second
5 210 December, 1981 Running
*BASIC THERMAL POWER PLANT
In thermal generating plants, fuel is converted into thermal energy to heat water, making steam. The steam turns an engine (turbine), creating mechanical energy to run a generator. Magnets turn inside the generator, producing electric energy.Coal, oil and gas are used to make thermal electricity. They all work basically the same way (with a few exceptions: for example, in an oil- or gas-fired plant, fuel is piped to the boiler).
1. Coal supply — After haulers drop off the coal, a set of crushers and conveyors prepare and deliver the coal to the power plant. When the plant needs coal, coal “hoppers” crush coal to a few inches in size and conveyor belts bring the coal inside.
2. Coal pulveriser —the belts dump coal into a huge bin (pulveriser), which reduces the coal to a fine powder. Hot air from nearby fans blows the powdered coal into huge furnaces (boilers).
3. Boiler — The boiler walls are lined with many kilometres of pipe filled with water. As soon as the coal enters the boiler, it instantly catches fire and burns with high intensity (the temperatures inside the furnace may climb to 1,300° C). This heat quickly boils the water inside the pipes, changing it into steam.
4. Precipitators and stack — As the coal burns, it produces emissions (carbon dioxide, sulphur dioxide and nitrogen oxides) and ash. The gases, together with the lighter ash (fly ash), are vented from the boiler up the stack. Huge air filters called electrostatic precipitators remove nearly all the fly ash before it is released into the atmosphere. The heavier ash (bottom ash) collects in the bottom of the boilers and is removed.
5. Turbine and generator — Meanwhile, steam moves at high speed to the turbines, massive drums with hundreds of blades turned at an angle, like the blades of a fan. As jets of high-pressure steam emerge from the pipes, they propel the blades, causing the turbine to spin rapidly. A metal shaft connects the turbine to a generator. As the turbine turns, it causes an electro-magnet to turn inside coils of wire in the generator. The spinning magnet puts electrons in motion inside the wires, creating electricity.
6. Condensers and cooling water system — Next, the steam exits the turbines and passes over cool tubes in the condenser. The condensers capture the used steam and transform it back to water. The cooled water is then pumped back to the boiler to repeat the heating process. At the same time, water is piped from a reservoir or river to keep the condensers constantly cool. This cooling water, now warm from the heat exchange in the condensers, is released from the plant.
7. Water purification — To reduce corrosion, plants purify water for use in the boiler tubes. Wastewater is also treated and pumped out to holding ponds.
8. Ash systems — Ash is removed from the plant and hauled to disposal sites or ash lagoons. Ash is also sold for use in manufacturing cement.
9. Transformer and transmission lines — transformers increase the voltage of the electricity generated. Transmission lines then carry the electricity at high voltages from the plant to substations in cities and towns.
BOILER MAINTENANCE DEPARTMENT
*BOILER DESCRIPTION
TYPE: Natural circulation, Dry Bottom, Tangentially fired, Balanced Draft, Radiant Reheat type with direct fired pulverised coal system
DESIGNED FUEL: Indian Bituminous CoalFIXED CARBON
VOLATILE MATTER
MOISTURE ASH GRINDABILITY HIGH HEATING VALUE
38% 26% 8% 28%
55% 4860 Kcal/Kg
FURNACE: Fusion Welded Type
A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating application construction of boiler is mainly of steel, stainless steel and wrought iron. In live steam models copper or brass is often used. Historically copper was often used for fireboxes, because of its thermal conductivity. Cast iron is used for domestic water heaters. Although these are usually termed” boilers”, their purpose is to produce hot water, not steam, and so the run at low pressure and try to avoid actual boiling. Te brittleness of cast iron makes it impractical for steam pressure vessels. 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. The boiler includes the economizer, the steam drum, the chemical dosing equipment, and the furnace with its steam generating tubes and the super heater coils. Necessary safety valves are located at suitable points to avoid excessive boiler pressure. The air and flue gases path equipment include: forced draft (FD) fan, air pre heater (APH) boiler furnace, induced draft (ID) fan, fly ash collector (electrostatic precipitator or bag house) and the flue gas stack. Schematic diagram of typical coal-fired power plant steam generator
MAIN BOILER: AT 100% LOAD
• Evaporation 700t/hr • Feed water temperature 247°C• Feed water leaving economizer 276°C
STEAM TEMPERATUR:•Drum 341°C•Super heater outlet 540°C•Reheat inlet 332°C•Reheat outlet 540°C STEAM PRESSURE:•Drum design 158.20 kg/cm2
•Drum operating 149.70 kg/cm2
•Superheater outlet 137.00 kg/cm2
•Reheat inlet 26.35 kg/cm2
•Reheat outlet 24.50 kg/cm2
FUEL: COAL DESIGN WORST• Fixed carbon 38% • Volatile matter 26% • Moisture 8% • Grind ability 55 HGI • Hard grove 45%•Coal size to mill 20 mm OIL:• Calorific value of fuel oil 10,000 kcal/kg• Sulfur content 4.5% W/W• Moisture content 1.1% W/W •Sp. Weight 0.98 at 380C.
*FEEDWATER CYCLE
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 spinning steam 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 demineralises produces water so pure that it coincidentally becomes an electrical insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimetre. The makeup water in a 500 MW 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 travelling 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).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 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).] It is also dosed with pH control agents such as ammonia or morpholine to keep the residual acidity low and thus non-corrosive.
Deaerator → Boiler feed pump→ H.P. Heater-1→H.P.Heater-2→H.P. Heater-3 → Feedwater line → Economizer →Boiler drum→ Downcomer → Water walls
*CONDENSATE CYCLE
From low pressure turbine → Condenser → Condensate pump → Ejector → Gland steam cooler → GSC2 → LPH2 → LPH3 → LPH4 → Deaerator
*PRINCIPLES OF COMBUSTION
The primary function of oil and coal burning systems the process of steam generation is to provide controlled efficientconversation of the chemical energy of the fuel into heat energy which is then transferred to the heat absorbing surfaces of the steam generator. The combustion elements of a fuel consist of carbon, hydrogen and usually a small amount of sulphur. When combustion is properly completed the exhaust gases will contain, carbon dioxide, water vapour, sulphur dioxide and a large volume of Nitrogen, Combustion is brought about by combining carbon and hydrogen or hydrocarbons with the oxygen in air. When carbon burns completely, it results in the formation of a gas known as carbon dioxide. When carbon burns incompletely it forms carbon monoxide.The following factors in efficient combustion are usually referred to as "The three T’sTime:It will take a definite time to heat the fuel to its ignition temperature and having ignited, it will also take time to bum.Consequently sufficient time must be allowed for completecombustion of the fuel to take place in the chamber.Temperature: A fuel will not burn until it has reached its ignition temperature. The speed at which this temperature will be reached is increased by preheating the combustion air .The temperature of the
flame of the burning fuel may vary with the quantity of air used. Too much combustion air will lower the flame temperature and may cause unstable ignition.Turbulence: Turbulence is introduced to achieve a rapid relative motion between the air and the fuel particles. It is found that this produces a quick propagation of the flame and its rapid spread throughout the fuel/air mixture in the combustion chamber. Combustion efficiency: It varies with individual different grades of fuel within each boiler. The idea to be aimed at is the correct quantity of air together with good mixing of fuel and air to obtain the maximum heat release. Maximum combustion efficiency depends on•Design of the boiler.•Fuel used.•Skill in obtaining combustion with the minimum amount of excess air.
*TYPES OF FURNACE
P.F. FIRED DRY BOTTOM FURNACE:The tall rectangular radiant type furnace has now become a feature of modern dry bottom P.F. boiler. Indorsed height not only facilitates adequate natural circulation but also aids reduction of furnace exit gas temperature and hence less soot deposit in super heaters and reheater.
SLAG TYPE FURNACE:
Furnace of this type normally has two parts. Primary furnace is used for very high rate of combustion. Provision is to make molten slag and crush the granular form for easy disposal. As the ash has to flow from the primary furnace, coal having low melting temperature can only be used. To obtain high temperature inside the primary surface that will facilitate the easy flow of ash, very small but highly rated design is needed for primary furnace hence maintenance is needed.
OIL FIRED BOILER FURNACE:
Normally about 65% of furnace volume is enough for an oil-fired boiler as compared to the corresponding P.F. fired boiler. Oil-fired furnace is generally closed at the bottom, as there is no need to remove slag as in case of P.F. fired boiler. The bottom part will have small amount of slope to prevent film boiler building in the bottom tubes. If boiler has to design for both P.F. as well as oil, thefurnace has to be designed for coal, as otherwise higher heatloading with P.F. will cause slogging and high furnace exit gas temperature.
SPECIFICATIONS:FURNACE•Width 13.868 m •Height 42.797 m•Depth 10.592 m •Volume 5210 m3
BOILER DRUM Drum is of fusion-welded design with welded hemi-spherical dished ends. It is provided with stubs for welding all the connecting tubes i.e. down comers, risers, pipes, saturated steam outlet. The function of steam drum internals is to
separate the water from the steam generated in the furnace
walls and to reduce the dissolved solid contents of the steam below the prescribed limit of 1 ppm and also take care of the sudden change of steam demand for boiler. The secondary stage of two opposed banks of closely spaced thin corrugated sheets, which direct the steam and force the remaining generated water against the corrugated plates. Since the velocity is relatively low this water does not get picked up again but runs down the plates and off the second stage of the two steam outlets. From the secondary separators the steam flows upwards to the series of screen dryers, extending in layers across the length of the drum. These screens perform the final stage of separation.
WATER WALLS:Water flows to the water walls from the boiler drum by natural circulation. The front and the two side water walls constitute the main evaporation surface absorbing the bulk of radiant heat of the fuel burnt in the chamber. The front and rear walls are bent at the lower ends to form a water-cooled slag hopper. The upper part of the chamber is narrowed to achieve perfect mixing of combustion gases. The water walls tubes are connected to headers at the top and bottom. The rear water walls tubes at the top are grounded in four rows at a wider pitch forming the grid tubes.
REHEATER:Reheater is used to raise the temperature of steam from which a part of energy has been extracted in high- pressure turbine. This is another method of increasing the cycle efficiency. Reheating requires additional equipment I.e. Heating surface connecting boiler and turbine pipe safety equipment like safety valve, non-return valve, isolating valves, high pressure feed pump, etc. Reheater is composed to two sections namely front andrear pendant section which is located above the furnace arch between water-
cooled screen wall tubes and rear wall hanger tubes. Power plant furnaces may have a reheater section containing tubes heated by hot flue gases outside the tubes. Exhaust steam from the high pressure turbine is passed through these heated tubes to collect more energy before driving the intermediate and then low pressure turbines.
SUPERHEATER:The super heater is a heat exchanger in which heat is transferred to the saturated steam to increase its temperature. It raises the overall cycle efficiency. In addition, it reduces the moisture content in the last stages of the turbine and thus increases the turbine internal efficiency.
A super heater is a device found in steam boilers that is used to convert wet, saturated steam into dry steam. Super heaters are a very beneficial part of the steam cycle, because dry steam contains more thermal energy and increases the overall efficiency of the cycle. Not only that dry steam also is less likely to condense within the cylinders of a reciprocating engine or the casing of a steam turbine. Boiler super heaters can be found in three varieties: radiant super heaters, convection super heaters and separately fired super heaters.
Radiant super heaters are located directly within the combustion chamber of the boiler itself. This arrangement allows for the burner from the boiler to heat both the boiler tubing and the super heater tubes, making radiant superheaters highly effective devices. These are most commonly found in steam power plants and also were widely used in steam automobiles. In steam automobiles and power plant boilers alike, the superheater tubes — sometimes known as vaporizer coils — were located directly on top of the burner. Steam usually is run through the superheater after it has been admitted through the throttle.
ECONOMIZERThe function of an economizer in a steam generating unit is to absorb heat from the flue gases and add as asensible heat to the feed-water before the water enters theevaporation circuit of the boiler. Earlier economizer were introduced mainly to recover the heat available in flue gases that leaves the boiler and provision of this addition heating surface increases the efficiency of steamgenerators. In the modern boilers used for power generation feed-water heaters were used to increase the efficiency of turbine unit and feed-water temperature.
LOCATION AND MAINTENANCE:
It is usual to locate economizer ahead of air heater. Counter flow arrangement is normally selected so thatheating surface requirement is kept minimum for the same temperature drop in flue gas. Water flow is from bottom to top so that steam if any formed during the heat transfer can move along with water and the lock up steam which will cause overheating and failure of economizer tube. Manholes and adequate spacing between the banks of tubes are provided for inspection and maintenance works.
AIR PREHEATER Air preheater absorbs waste heat from the flue gases and transfers this heat to incoming cold air, by means of continuously rotating heat transfer element of specially formed metal plates. Thousands of these high efficiency elements are spaced and compactly arranged within 12 sections. Sloped compartments of a radially divided cylindrical shell called the rotor. The housing surrounding the rotor is provided with duct connecting both the ends and is adequately scaled by radial and circumferential scaling. Air Preheater Consists of:•Connecting plates
•Housing•Rotor •Heating surface elements•Bearings•Sector plates and Sealing arrangement SPECIFICATIONS • Number of air preheater per unit2
•Heater size 27-VI-(T)-74” casing•Approx heating surface 19000 m2 each•Rotor drive motor 15 H.P.•Speed reduct ion rat io 110:1 •Approx oil capacity 13 Gallons•Solenoid Value 110 V, A.C.
*Basics of Fans
The air we need for combustion in the furnace and the flue gas that we must imparting energy to the air/gas in the form of a boost in pressure. We overcome the losses through evacuate would not possible without using fans. A fan is capable of the system by means of this pressure boost. The boost is dependent on density at a given speed. The higher the temperature, the lower is the boost. Fan performance (Max. capability) is represented as volumes, pressure boost.
The basic information needed to select a fan is:•Air or Gas flow (Kg/hr).
•Density (function of temperature and pressure).•System, resistance (losses).
Classification of FansIn boiler practice, we meet the following types of fans.•Axial fans•Centrifugal (Radial) fans
Axial Fans
In this type the movement of air or gas is parallel to its exit of rotation. These fans are better suited to low resistance applications.
The axial flow fan uses the screw like action of a multipliedrotating shaft, or propeller, to move air or gas in a straight through path.
The axial flow fan uses the screw like action of a multipliedrotating shaft, or propeller, to move air or gas in a straight through path.
Centrifugal Fan
This fan moves gas or air perpendicular to the axis of rotation. There are advantages when the air must be moved in a system where the frictional resistance is relatively high.The blade wheel whirls air centrifugally between each pair of blades and forces it out peripherally at high velocity and high static pressure. More air is sucked in at the eye of the impeller. As the air leaves the revolving blade tips, part of its velocity is converted into additional static pressure by scroll shaped housing
There are three types of blades.•Backward curved blades.•Forward curved blades.•Radial blades.
*Draft System
Before a detailed study of industrial fans it is in the fitness of things to understand the various draft systems maintained by those fans.The terms draft denotes the difference between the atmospheric pressure and the pressure existing in the furnace. Depending upon the draft used, we have•Natural Draft
•Induced Draft•Forced Draft•Balanced Draft SystemNatural DraftIn natural draft units the pressure differentials are obtained have constructing tall chimneys so that vacuum is' created in the furnace Due to small pressure difference, air is admitted into the furnace. Induced DraftIn this system the air is admitted to natural pressure difference and the flue gases are taken out by means of induced Draft fans and the furnace is maintained under vacuum.Forced DraftA set of forced draft fans are made use of for supplying air to the furnace and so the furnace is pressurized. The flue gases are taken out due to the pressure difference between the furnace and the atmosphere.Balance DraftThere a set of induced and forced draft Fans are utilized in maintaining a vacuuming the furnace. Normally all the power stations utilize this draft system.
INDUSTRIAL FANS
Sr. no.
Description
Type No. of
boiler
Capacity m3/sec
Pressure mm
Temperature oC
KW Moor voltage kv
RPMM
A ID fan Axial impulse
type
2 230.9 387 150 1300
6.6 990
B FD fan Axial reaction
type
2 103.8 520.5 50 800 6.6 490
C PA fan Radial backward
curve
2 63.5 1345.5 50 1250
6.6 1485
I.D. Fan
The induced Draft Fans are generally of Axial -Impulse Type. Impeller nominal diameter is of the order of 2500 mm.The fan consists of the following sub-assemblies:•Suction Chamber •Inlet Vane Control•Impeller •Outlet Guide Vane Assembly
The outlet guides are fixed in between the case of the diffuser and the casing. These guide vanes serve to direct the flow axially and to stabilize the draft-flow
caused in theimpeller. These outlet blades are removable type from outside.During
operation of the fan itself these blades can be replaced one by one. Periodically the outlet blades can be removed one at a time to find out the extent of wear on the blade. If excessive wear is noticed the blade can be replaced by a new blade.
ID FAN LUBE OIL SYSTEM PUMP MOTOR FAN
TYPE-Gear type Power-0.5HP Capacity-5LPM Voltage-415v
Frequency-50C/S, 3 Inlet vane control Operating Press-2Kg/cm2 Speed-1380 RPMIV Relief Pr-7 Kg/cm2 Rated current-1.08 Amps
F.D Fan
The fan, normally of the same type as ID Fan, consists of the following components:*Silencer *Inlet bend*Fan housing*Impeller with blades and setting mechanism*Guide wheel casing with guide vanes and diffuser.The centrifugal and setting forces of the blades are taken up by the blade bearings. The blade shafts are placed in combined radial and axial antifriction bearings which are sealed off to the outside. The angle of-incidence of the blades may be adjusted during operation.The characteristic pressure volume curves of the fan may bechanged in a large range without essentially modifying theefficiency. The fan can then be easily adapted to changing operating conditions. The rotor is accommodated in cylindrical roller bearings and an inclined ball bearing at the drive side adsorbs the axial thrust. Lubrication and cooling these bearings is assured by a combined oil level and circulating lubrication system.
FD FAN LUB OIL SYSTEM Pump Motor Fan control
Type-Gear type Power-4KW Capacity79.2 LPM Voltage415V,
Variable pitch blade Frequency-50c/s, 3 control
Lub oil Pr. 0.8 to3ata Speed-1400 rpmRated Current-11Amp
Primary Air FanP.A. ran if flange mounted design, single stage suction, NDFV type, backward curved bladed radial fan operating on the principle of energy transformation due to centrifugal forces. Some amount of the velocity energy is converted to pressure energy in the spiral casing. The fan is driven at a constant speed and the flow is controlled by varying the angle of the inlet vane control. The Special feature of the fan is that is provided with inlet guide vane control with a positive and precise link mechanism.
PA FAN LUBE OIL SYSTEM PUMP MOTOR FAN
TYPE-Gear type Power-0.5HP Capacity-5LPM Voltage-415v
Frequency-50C/S, 3 Inlet Guide Vanes Operating Press-2Kg/cm2 Speed-1425 RPM control
Relief Pr-7 Kg/cm2 Rated current 1.2 Amps
*PULVERIZERA pulverizer is a mechanical device for the grinding of many different types of materials. For example, they are used to pulverize coal for combustion in the steam-generating furnaces of fossil fuel power plants.
Types of Pulverisers Ball and Tube MillsA ball mill is a pulverizer that consists of a horizontal rotating cylinder, up to three diameters in length \,containing a charge of tumbling or cascading steel balls, pebbles, or rods. A tube mill is a revolving cylinder of up to five diameters in length used for fine pulverization of ore, rock,
and other such materials; the material, mixed with water, is fed into the chamber from one end, and passes out the other end as slime.
TPCThis type of mill consists of two rings separated by a series of large balls. The lower ring rotates, while the upper ring presses down on the balls via a set of spring and adjuster assemblies. The material to be pulverized is introduced into the centre or side of the pulverizer (depending on the design) and is ground as the lower ring rotates causing the balls to orbit between the upper and lower rings. The pulverized material is carried out of the mill by the flow of air moving through it. The size of the pulverized particles released from the grinding section of the mill is determined by a classifiers separator.
MPS MillSimilar to the Ring and Ball Mill, this mill uses large "tires" to crush the coal.
These are usually found in utility plants.Bowl Mill
Similar to the MPS mill, it also uses tires to crush coal. There are two types, a deep bowl mill, and a shallow bowl mill. Advantage of pulverized coal •Efficient utilization of cheap and low grade coal•Flexibility to meet fluctuating load•Elevation of bending loser Chemicals in boiler water and erosion during blow down, particularly at the steam end. Any sign of corrosion or erosion indicates that a new glass is required. When testing the gauge glass steam connection, the water cock should be closed. When testing the gauge glass water connections, the steam cock pipe should be closed.
Gauge glass guards The gauge glass guard should be kept clean. When the guard is being
cleaned in place, or removed for cleaning, the gauge should be temporarily shut-off. Make sure there is a satisfactory water level before shutting off the gauge and take care not to touch or knock the gauge glass. After cleaning, and when the guard has been replaced, the gauge should be tested and the cocks set in the correct position.
COAL BUNKER
These are in process storage silos used for storing crushed coal from the coal handling system. Generally, these are made up of welded steel plates.' Normally, there are six such bunkers supplying coal of the corresponding mills. These are located on top of the mills so as to aid in gravity feeding of coal.
COAL FEEDER
Each mill is provided with a drag link chain/ rotary/ gravimetric feeder to transport raw coal from the bunker to the inlet chute, leading to mill at a desired rate.
MILLS
There are six mill (25% capacity each), for every 200 .MW unit, located adjacent to the furnace at '0' M level. These mills pulverize coal to the desired fineness to be fed to the furnace for combustion.
ELECTROSTATIC PRECIPITATOR
An electrostatic precipitator is a large, industrial emission-control unit. It is designed to trap and remove dust particles from the exhaust gas stream of an industrial process. In many industrial plants, particulate matter created in the industrial process is carried as dust in the hot exhaust gases. These dust-laden gases pass through
an electrostatic precipitator that collects most of the dust. Cleaned gas then passes out of the precipitator and through a stack to the atmosphere. Precipitators typically collect 99.9% or more of the dust from the gas stream.
Precipitators function by electrostatically charging the dust particles in the gas stream. The charged particles are then attracted to and deposited on plates or other collection devices. When enough dust has accumulated, the collectors are shaken to dislodge the dust, causing it to fall with the force of gravity to hoppers below. The dust is then removed by a conveyor system for disposal or recycling.Depending upon dust characteristics and the gas volume to be treated, there are many different sizes, types and designs of electrostatic precipitators. Very large power plants may actually have multiple precipitators for each unit.
PLANT AUXILIARY MAINTENANCE
DEPARTMENT
*WATER CIRCULATION SYSTEM
THEORY OF CIRCULATION
Water must flow through the heat absorption surface of the boiler in order that it is evaporated into steam. In drum type units (natural and controlled circulation)
the water is circulated from the drum through the generating circuits and then back to the drum where the steam is separated and directed to the super heater. The water leaves the drum through the down comers at a temperature
slightly below the saturation temperature. The flow through the furnace wall is at saturation temperature. Heat absorbed in water wall is latent heat of
vaporization creating a mixture of steam and water. The ratio of the weight of the water to the weight of the steam in the mixture leaving the heat absorption
surface is called
Types of boiler circulating system:•Natural circulation system•Controlled circulation system•Combines circulation system
NATURAL CIRCULATION SYSTEM
Water delivered to steam generator from feed heater is at a temperature well below the saturation value corresponding to that pressure. Entering first the economizer it isheated to about 30-40˚C below saturation temperature. Fromeconomizer the water enters the drum and thus joins the circulation system. Water entering the drum flows through the down comer and enters ring heater at the bottom. In the water walls a part
of the water is converted to steam and the mixture flows back to the drum. In the drum, the steam is separated, and sent to super heater for super heating and then sent to the high pressure turbine.Remaining water mixes with the incoming water from theeconomizer and the cycle is repeated .The circulation in this case takes place on the thermo-siphon principle. The down comers contain relatively cold water whereas the riser tubes contain a steam water mixture. Circulation takes place at such a rate that the driving force and the frictional resistance in water walls are balanced.As the pressure increases, the difference in density between water and steam reduces. Thus the hydrostatic head available will not be able to overcome the frictional resistance for a flow correspondingto the minimum requirement of cooling of water wall tubes.Therefore
natural circulation is limited to the boiler with drum operating pressure around 175 kg/cm².
CONTROLLED CIRCULATION SYSTEM
Beyond 80 kg/cm² of pressure, circulation is to be assisted with mechanical pumps to overcome the frictional losses. To regulate the flow through various tubes, orifice plates are used. This system is applicable in the high sub-critical regions (200 kg/cm²).
COMBINED CIRCULATION SYSTEM
Beyond the critical pressure, phase transformation is absent, and hence once through system is adopted. However, it has been found that even at super critical pressure, it is advantageous to recirculation the water through the furnace tubes and simplifies the start up procedure. A typical operating pressure for such a system is 260 kg/cm².
* ASH HANDLING PLANT
The ash produced in the boiler is transported to ash dump area by means of sluicing type hydraulic ash handling system, which consists of Bottom ash system, Ash water system and Ash slurry system.
Bottom ash system
In the bottom ash system the ash discharged from the furnace bottom is collected in two water compounded scraper through installed below bottom ash hoppers. The ash is continuously transported by means of the scraper chain conveyor onto the respective clinker grinders which reduce the lump sizes to the required fineness. The crushed ash from the bottom ash hopper from where the ash slurry is further transported to operation, the bottom ash can be discharged directly into the sluice channel through the bifurcating chute bypass the grinder. The position of the flap gate in the bifurcating chute bypasses the grinder. The position of the flap gate in the bifurcating chute is to be manually changed.
Fly ash system
The flushing apparatus are provided under E.P. hoppers, economizer hoppers, air preheaters, and stack hoppers. The fly ash gets mixed with flushing water and the resulting slurry drops into the ash sluice channel. Low pressure water is applied through thenozzle directing tangentially to the section of pipe to create turbulence and proper mixing of ash with water. For themaintenance of flushing apparatus plate valve is provided between apparatus and connecting tube.
Ash water system
High pressure water required for bottom ash hopper quenching nozzles, bottom ash hopper spraying, clinker grinder sealing scraper bars, cleaning nozzles, bottom ash hopper seal through flushing, economizer hopper flushing nozzles andsluicing trench jetting nozzles is tapped from the high pressure water ring mainly provided in the plant area. Low pressure water required for bottom ash hopper seal through make up, scraper conveyor make up, flushingapparatus jetting nozzles for all fly ash hoppers exceptingeconomizer hoppers, is trapped from low pressure water ringsmainly provided in the plant area.
Ash slurry system
Bottom ash and fly ash slurry of the system is sluiced up to ash pump along the channel with the acid of high pressure water jets located at suitable intervals along the channel.Slurry pump suction line consisting of reducing elbow with drainvalve, reducer and butterfly valve and portion of slurry pumpdelivery line consisting of butterfly valve, pipe & fitting has also been provided.
*CSPH(CONTROL STRUCTURE PUMP HOUSE)
The control system has following pumps:-•Chlorine pump-2(for chlorination of water)•HP pump-6(for boiling of water)•LP pump-3(for EP pump house)•Fire pump-(in case of fire breakdown)•TWS pump-3(for screening of water)•CRW pump-3(supply water for water treatment)This house is known as control house because amount of water to be supplied for treatment is controlled from this house with the help of these pumps. Generally 2 CRW pumps out of 3pumpsremains open similarly, 1 F , 2 LP,4 HP,1 TWS pumps remain so pen. If more water is needed then others pumps are opened.
*COMPRESSOR HOUSE
An air compressor is anything that increases the amount of air that is contained within a particular space. By packing in the air, the air pressure is increased. This creates a force that is useful for a variety of purposes, such as industrial, manufacturing, commercial and personal purposes. Stages
Another way to group air compressors is by the number of stages they have. A two-stage air compressor usually is used for heavy-duty use and offers a higher level of compression than smaller, single-stage air compressors. Two-stage air compressors can store air for future use and are more energy efficient because they produce more air per unit of horsepower than single-stage compressors. Also, less heat is generated in a two-stage compressor, which means that wear on the unit is reduced. Portable electric air compressors also are available for light-duty applications.
*WATER TREATMENT PLANT
As the types of boiler are not alike their working pressure and operating conditions vary and so do the types and methods of water treatment. Water treatment plants used in thermal power plants are designed to process the raw water to water with very lowin dissolved solids known as "dematerialized water". No doubt, this plant has to be engineered very carefully keeping in view the type of raw water to the thermal plant, its treatment costs and overall economics
Actually, the type of demineralization process chosen for a power station depends on three main factors:•The quality of the raw water.•The degree of de-ionization i.e. treated water quality•Selectivity of resins.Water treatment process which is generally made up of two sections:•Pre-treatment section•Demineralization section
Pre-treatment sectionPretreatment plant removes the suspended solids such as clay, silt, organic and inorganic matter, plants and other microscopic organism. The turbidity may be taken as of two types of suspended solids in water. Firstly, the separable solids and secondly the non separable solids (colloids). The coarsecomponents, such as sand, silt etc, can be removed from the water by simple sedimentation. Finer particles however, will not settle in any reasonable time and must be flocculated to produce the large particles which are settling able. Long term ability to remainsuspended in water is basically a function of both size and specificgravity. The settling rate of the colloidal and finely divided (approximately 001 to 1 micron) suspended matter is so slow that removing them from water by plain sedimentation is tank shavingordinary dimensions is impossible. Settling velocity of finelydivided and collide particles under gravity also are so small that ordinary sedimentation is not possible. It is necessary, therefore, to use procedures which agglomerate the small particles into larger aggregates, which have practical settling velocities. The term"Coagulation" and "flocculation" have been used indiscriminately to describe process of turbidity removal. "Coagulation" means to bring together the suspended particles. The process describes the effect produced by the addition of a chemical Al (SP) g to acolloidal dispersion resulting in particle destabilization by areduction of force tending to keep particles apart. Rapid mixing is important at this stage to obtain. Uniform dispersion of the chemical and to increase opportunity for particles to particle contact. This operation is done by flash mixer in thec1ariflocculator. Second stage of formation of settle able particlesfrom destabilized colloidal sized particles is termed a"flocculation". Here coagulated particles grow in size by attaching to each other. In contrast to coagulation where the primary force is electrostatic or intrinsic, "flocculation" occurs by chemical bridging. Flocculation is obtained by gentle and prolonged
mixingwhich converts the submicroscopic coagulated particle intodiscrete, visible & suspended particles. At this stage particles are large enough to settle rapidly under the influence of gravity anomaly be removedIf pre-treatment of the water is not done efficiently then consequences are as follows:•Si02 may escape with water which will increase the anion loading.•Organic matter may escape which may cause organic fouling in the anion exchanger beds. In the 'pre-treatment plant chlorine addition provision is normally made to combat organic contamination.•Cation loading may unnecessary increase due to addition of Ca (OH)2 in excess of calculated amount for raising the pH of the water for maximum floe formation and also AKOrDgmay precipitate out. If less than calculated amount of Ca (OH)2 is added, proper pH flocculation will not be obtained and silica escape to demineralization section will occur, thereby increasing load on anion bed.
DemineralizationThis filter water is now used for demineralising purpose and is fed to cation exchanger bed, but enroute being first dechlorinated, which is either done by passing through activated carbon filter or injecting along the flow of water, an equivalent amount of sodium sulphite through some stroke pumps. The residual chlorine which is- maintained in clarification plant to remove organic matter from raw water is now detrimental to action resin and must be eliminated before its entry to this bed.Normally, the typical scheme of demineralization up to the .mark against average surface water is three bed system with a provision of removing gaseous carbon dioxide from water before feeding to Anion Exchanger. Now, let us see, what happens actually in each bed when water is passed from one to another. Resins, which are built on synthetic matrix of a styrene divinely benzene copolymer, are manufactured in such a way that these have the ability to, exchange one ion for another, hold it temporarily in chemical combination and give it to a strong electrolytic solution. Suitable treatment is also given to them in such a way that a particular resin absorbs only a particular group of ions. Resins, when absorbing and releasing cationic portion of dissolved salts, is called cation, exchanger resin and when removing anionic portion is called anion exchanger resin. Preset trend is of employing 'strongly acidic cation exchanger resin and strongly basic anion exchanger resin in a DM Plant of modernthermal power station. We may see that the chemically activegroup in a cationic resin is SOx-H (normally represented by RH) and in an anionic resin the active group is either tertiary amine or quaternary ammonium group (normally the resin is represented by ROH.The water from the ex-cation contains carbonic acid also sufficiently, which is very weak acid difficult to be removed by strongly basic anion resin and causing hindrance to remove silicate ions from the bed. It is therefore a usual practice to remove carbonic acid before it is led to anion exchanger bed. The ex-cation water is trickled in fine streams from top of a tall tower packed with, rings, and compressed air is passed from the bottom. Carbonic acid breaks into C03 and water mechanically (Henry's Law) with the carbon dioxide escaping into theatmosphere. The water is accumulated in suitable storage tank below the tower, called degassed water dump from where the same is led to anion exchanger bed, using acid resistant pump. The ex-anion water is fed to the mixed bed exchanger containing both
cationic resin and anionic resin. This bed not only takes care of sodium slip from cation but also silica slip from anion exchanger very effectively. The final output fromthe mixed bed is Exira-ordinarily pure water having less than0.2/Mho conductivity 7.0 and silica content less than 0.02 pm. Any deviation from the above quality means that the resins in mixed bed are exhausted and need regeneration, regeneration of themixed bed first calls for suitable, back washing and settling, so that he two types of resins are separated from each other. Lighter anion resin rises to the top and the heavier cation resin settles to the bottom. Both the resins are then regenerated separately with alkali and acid, rinsed to the desired value and air mixed, to mix the resin again thoroughly. It is then put to final rinsing till the desired quality is obtained. It may be mentioned here that there are two types of strongly basic anion exchanger. Type II resins are slightly less basic than type I, but have higher regeneration efficiency than type I. Again as type II resins are unable to remove silica effectively, type I resins also have to be used for the purpose. As such, the general condition so far prevailing in India, is to employ type II resin in anion exchangers bed and type I resin in mixed bed (for the anionic portion).It is also a general convention to regenerate the above two resins under through fare system i.e. the caustic soda entering into mixed bed for regeneration, of type I anion resin, is utilized to regenerate type II resin in anion exchanger bed. The content of utilizing the above resin and mode of regeneration is now days being switched over from the economy to a higher cost so as to have more stringent quality control of the final D.M water.
PROCESS OF DEMINERALIZATION OF WATER
PUMP HOUSE CLARIFIER
FLASH MIXER (Adding PAC+CL2)
CLARIFIER STORAGE TANKTHROUGH
PUMPPRESSURE FILTER(REMOVE SMALL STONES)
ACTIVATED CARBON FILTER (REMOVE CL2)
WEAK ACID CATION (HCL USED)
DEGASSER(REMOVE CO2)
STROND ACID CATION
WEAK BASE ANION (NaOH USED)
STRONG BASE ANION
MIXED BED (REMOVE REMAINING CATION AND ANION)
DEMINRALISING WATER TANK (pH=7.00, CONDUCITIVTY<=0.1µ mho, TURBIDITY=NIL, SiO2< 20ppm
*INTERNAL TREATMENT
This final D.M effluent is then either led to hot well of the condenser directly as make up to boilers, or being stored in D.M. Water storage tanks first and then pumped for makeup purpose to boiler feed. There are five D.M.Tank: three tanks of 500 metric ton for three units Of 95 MW and other two of 600 metric ton for two units of 210 MW.The purpose of an internal water treatment program is:
1. To react with incoming feed water hardness and prevent it from precipitating on the boiler metal as scale
2. To condition any suspended matter such as hardness sludge in the boiler and make it non adherent to the boiler metal
3. To provide antifoam protection to permit a reasonable concentration of dissolved and suspended solids in the boiler water without foaming
4. To eliminate oxygen from the feed water5. To provide enough alkalinity to prevent boiler corrosion6. To prevent scaling and protect against corrosion in the steam-condensate
systems.
D.M.TANK
*COOLING TOWERThermal power plants use cooling towers to cool the circulating water used
for condenser cooling. Since water resources are limited, power plants have no other option but to adopt the closed cooling system with cooling towers. Read about the different types of cooling towers and their performance.
After air, water is the most important requirement for life on this planet. With fresh water resources depleting and increased population pressure, water sources have become very precious. The primary priority for fresh water is for human consumption and agriculture. Power plant requirements are only secondary. This necessitates the need for thermal power plants that require less water. Cooling Towers help by reusing the cooling water, making power plants economical and more environmentally friendly.
Cooling towers can be of two types.First is the natural draft-cooling tower with a large hyperbolic tower, which pulls in air due to the stack effect. Even though the capital costs are high, operating costs are less. This is because there is no fan to create the air flow.However, most commonly used is the Mechanical or forced cooling tower. A fan forces or sucks air through the cooling tower where the water falls through a packed heat transfer media. Operating costs are high for operating this, but they are simple and quick for construction.•The fans can be induced fan or forced draught fan.•The airflow can be parallel or cross flow to the water flow.Cooling towers work on the principle of psychometric properties of air. A part of the cooling water evaporates taking in Latent Heat from the water reducing its temperature. A properly sized Cooling tower can cool the incoming water to temperatures up to 3 °C more than the ambient wet bulb temperature. The relative humidity of the ambient air is an important deciding factor.
CROSS-FLOW COOLING COUNTER-FLOW COOLING
Design Tip: The main difference between counter-flow and cross-flow designs is that counter-flow towers are designed to a larger height than cross-flow towers, thus requiring more pumping power but requiring less tower area for a given capacity.Cooling Towers have one function:Remove heat from the water discharged from the condenser so that the water can be discharged to the river or recirculated and reused.
Losses in cooling Towers:The loss of water in a cooling tower is due to three different reasons and has to be made up during the operation. The makeup percentage in modern towers is around 1 %.•Evaporation loss. A part of the water evaporates; this is what creates the cooling effect. This depends on the ambient temperature and Relative humidity or the ambient wet bulb temperature.•Drift loss. The water particles carried away through the flowing air. Drift eliminators and detail design have reduced this largely. In modern towers, this could be in the range of 0.02 % of the water flow.•Blow down losses. The evaporated water leaves behind the salts, which over time accumulates increasing the TDS levels. This requires to be blow down occasionally. This constitutes a loss which has to be made up.
Biocides and chemical controls are required to eliminate bacterial growth and eliminate scales that are harmful and at the same time a performance reduction factor.
TURBINE MAINTENANCE DEPARTMENT
*STEAM TURBINE THEORY
OPERATING PRINCIPLES
A steam turbines two main parts are the cylinder and the rotor .As the steam passes through the fixed blades or nozzles it expands and its velocity increases.
The high-velocity jet of steam strikes the first set of moving blades. The kinetic energy of the steam changes into mechanical energy, causing the shaft to rotate. The steam then enters the next set of fixed blades and strikes the next row of moving blades. As the steam flows through the turbine, its pressure and temperature decreases, while its volume increases. The decrease in pressure and temperature occurs as the steam transmits .energy to the shaft and performs work. After passing through the last turbine stage, the steam exhausts into the condenser or process steam system.
The kinetic energy of the steam changes into mechanical erringly through the impact (impulse) or reaction of the steam against the blades.
STEAM CYCLE
The thermal (steam) power plant uses a dual (vapour +liquid) phase cycle. It is a closed cycle to enable the working fluid (water) to be used again and again. The cycle used is "Rankine Cycle" modified to include super heating of steam, regenerative feed water heating and reheating of steam. On large turbines, it becomes economic to increase thecycle efficiency by using reheat, which is a way of partiallyovercoming temperature limitations. By returning partially expanded steam to a reheat, the average temperature at which heat is added is increased and by expanding this reheated steam to theremaining stages of the turbine, the exhaust wetness isconsiderably less than it would otherwise be conversely, if the maximum tolerable wetness is allowed, the initial pressure of the steam can be appreciably increased.
TURBINE CLASSIFICATION:
Impulse Turbine: In Impulse Turbine steam expands in fixed nozzles. The high velocity steam from nozzles does work on moving blades which causes the shaft to rotate. The essential features of impulse turbine are that all pressure drops occur at nozzles and not on blades. A simple impulse turbine is not very efficient because it does not fully use the velocity of the steam. Many impulse turbines are velocity compounded. This means they have two or more sets of moving blades in each stage.Reaction Turbine: In this type of turbine pressure is reduced at both fixed & moving blades. Both fixed& moving blades act as nozzles. Work done by the impulse effect of steam due to reversals of direction of high velocity steam. The expansion of steam takes place on moving blades. A reaction turbine uses the "kickback" force of the steam as it leaves the moving blades and fixed blades have the same shape and act like nozzles. Thus, steam expands, loses pressure and increases in velocity as it passes through both sets of blades. All reaction turbines are pressure-compounded turbines.
COMPOUNDING:
Several problems occur if energy of steam is converted in single step & so compounding is done. Following are the types of compounded turbine:
• VELOCITY COMPOUNDED TURBINEThe velocity-compounded impulse turbine was first proposed by C.G. Curtis to solve the problems of a single-stage impulse turbine for use with high pressure and temperature steam. The Curtis stage turbine, as it came to be called, is composed of one stage of nozzles as the single-stage turbine, followed by two rows of moving blades instead of one. These two rows are separated by one row of fixed blades attached to the turbine stator, which has the function of redirecting the steam leaving the first row of moving blades to the second row of moving blades. A Curtis stage impulse turbine is shown in Fig. 23.1 with schematic pressure and absolute steam-velocity changes through the stage. In the Curtis stage, the total enthalpy drop and hence pressure drop occur in the nozzles so that the pressure remains constant in all three rows of blades.
Velocity is absorbed in two stages. In fixed (static) blade passage both pressure and velocity remain constant. Fixed blades are also called guide vanes. Velocity compounded stage is also called Curtis stage. The velocity diagram of the velocity-compound Impulse turbine is shown in Figure
The fixed blades are used to guide the outlet steam/gas from the previous stage in such a manner so as to smooth entry at the next stage is ensured.K, the blade velocity coefficient may be different in each row of blades
Work done =
End thrust =
The optimum velocity ratio will depend on number of stages and is given
by
• Work is not uniformly distributed (1st >2nd)
• The first stage in a large (power plant) turbine is velocity or pressure compounded impulse stage.
•PRESSURE COMPOUNDED TURBINEThis is basically a no. of single impulse turbines in series or on the same shaft.
The exhaust of first turbine enters the nozzle of the next turbine. Total pressure drop of steam does not take on first nozzle ring but divided equally on all of
them.
To alleviate the problem of high blade velocity in the single-stage impulse turbine, the total enthalpy drop through the nozzles of that turbine are simply divided up, essentially in an equal manner, among
many single-stage impulse turbines in series. Such a turbine is called a Rateau turbine , after its inventor. Thus the inlet steam velocities to each stage are essentially equal and due to a reduced Δh.
Figure Pressure-Compounded Impulse Turbine
Pressure drop - takes place in more than one row of nozzles and the increase in kinetic energy after each nozzle is held within limits. Usually convergent nozzles are used
We can write
where is carry over coefficient
REACTION TURBINE
A reaction turbine, therefore, is one that is constructed of rows of fixed and rows of moving blades. The fixed blades act as nozzles. The moving blades move as a result of the impulse of steam received (caused by change in momentum) and also as a result of expansion and acceleration of the steam relative to them. In other words, they also act as nozzles. The enthalpy drop per stage of one row fixed and one row moving blades is divided among them, often equally. Thus a blade with a 50 percent degree of reaction, or a 50 percent reaction stage, is one in which half the enthalpy drop of the stage occurs in the fixed blades and half in the moving blades. The pressure drops will not be equal, however. They are greater for the fixed blades and greater for the high-pressure than the low-pressure stages.The moving blades of a reaction turbine are easily distinguishable from those of an impulse turbine in that they are not symmetrical and, because they act partly as nozzles, have a shape similar to that of the fixed blades, although curved in the opposite direction. The schematic pressure line shows that pressure continuously drops through all rows of blades, fixed and moving. The absolute steam velocity changes within each stage as shown and repeats from stage to stage. Figure shows a typical velocity diagram for the reaction stage.
Figure: Three stages of reaction turbine indicating pressure and velocity distribution
Pressure and enthalpy drop both in the fixed blade or stator and in the moving blade or Rotor
Degree of Reaction =
or,
A very widely used design has half degree of reaction or 50% reaction and this is known as Parson's Turbine. This consists of symmetrical stator and rotor blades.
The velocity diagram of reaction blading
The velocity triangles are symmetrical and we have
Energy input per stage (unit mass flow per second)
From the inlet velocity triangle we have,
Work done (for unit mass flow per second)
Therefore, the Blade efficiency
Put then
For the maximum efficiency and we get
from which finally it yields
Figure: Velocity diagram for maximum efficiency
Absolute velocity of the outlet at this stage is axial. In this case, the energy transfer
can be found out by putting the value of in the expression for blade efficiency
is greater in reaction turbine. Energy input per stage is less, so there are more number of stages.
Stage Efficiency and Reheat factor
The Thermodynamic effect on the turbine efficiency can be best understood by considering a number of stages between two stages 1 and 2 as shown in Figure
Figure: Different stage of a steam turbine
The total expansion is divided into four stages of the same efficiency and pressure ratio.
The overall efficiency of expansion is . The actual work during the expansion from 1 to 2 is
or,
Reheat factor (R.F.)=
or,
R.F is 1.03 to 1.04
If remains same for all the stages or is the mean stage efficiency.
or,
We can see:
This makes the overall efficiency of the turbine greater than the individual stage efficiency. The effect depicted due to the thermodynamic effect called "reheat". This does not imply any heat transfer to the stages from outside. It is merely the reappearance of stage losses an increased enthalpy during the constant pressure heating (or reheating) processes AX, BY, CZ and D2.
•PRESSURE VELOCITY COMPOUNDED TURBINE
It is just the combination of the two compounding has the advantages of allowing bigger pressure drops in each stage &so fewer stages are necessary. Here for given pressure drop the turbine will be shorter length but diameter will be increased.
STEAM TURBINES MAY BE CLASSIFIED INTO DIFFERENT CATEGORIES DEPENDING ON THEIR CONSTRUCTION, THE PROCESS BY WHICH HEAT DROP IS ACHIEVED, THE INITIAL AND FINAL CONDITIONS OF STEAM USED AND THEIR INDUSTRIAL USAGE
. According to the direction of steam flow •Axial turbines•Radial turbinesAccording to the number of cylinder•Single - cylinder turbines.•Double- cylinder turbines.•Three-Cylinder turbines.•Four-Cylinder turbines.•Multi - Cylinder turbinesAccording to the steam conditions at inlet to turbines•Low-pressure turbines•Medium -pressure turbines•High-pressure•Turbines of very high pressures•Turbines of supercritical pressures According to their usage in industry •Turbines with constant speed of rotation primarily used for driving alternators.•Steam turbines with variable speed meant for driving turbo blowers, air circulators, pumps etc.•Turbines with variable speed: Turbines of this type are usually•employed in steamers, ships and railway locomotives (turbolocomotives)
MAIN TURBINE
The 210MW turbine is a tandem compounded type machine comprising of H.P. & I.P. cylinders. The H.P. turbine comprises of 12 stages the I.P. turbine has 11 stages & the L.P. has four stages of double flow. The H.P. & I.P. turbine rotor are rigidly compounded & the I.P. & the I.P. rotor by lens type semi flexible coupling. All the three rotors are aligned on five bearings of which the bearing no.2 is combined with thrust bearing. The main superheated steam branches off into two streams from the boiler and passes through the emergency stopvalve and control valve before entering, the governing wheelchamber of the H.P. turbine. After expanding in the 12 stages in the H.P. turbine the steam returned in the boiler for reheating.The reheated steam from the boiler enter I.P. turbine via interceptor valves and control valves and after expanding enters the L.P. turbine stage via 2 numbers of cross over pipes. In the L.P. stage the steam expands in axially opposite direction to counteract the trust and enters the condenser placeddirectly below the L.P. turbine. The cooling water flowingthroughout the condenser tubes condenses the steam and thecondensate collected in the hot well of the condenser. The condensate collected is pumped by means of 3*50% duty condensate pumps through L.P. heaters to deaerator from where the boiler feed pump delivers the water to boiler through H.P. heaters thus forming a closed cycle.
TURBINE CYCLE
Fresh steam from boiler is supplied to the turbine through the emergency stop valve. From the stop valves steam is supplied to control valves situated on H.P.
cylinders on the front bearing end. After expansion through 12 stages at the H.P. cylinder steam flows back to boiler for reheating and reheated steam
fromthe boiler cover to the intermediate pressure turbine trough two interceptor
valves and four control valves mounted on the I.P. turbine. After flowing trough I.P. turbine steam enters the middle part of the L.P. turbine through cross over pipes. In L.P. turbine the exhaust steam condenses in the surface condensers welded directly to the exhaust part of L.P. turbine. The selection of extraction
points and cold reheat pressure has been done with a view to achieve the highest efficiency. These are two extractions from H.P. turbine, four from I.P. turbine and one from L.P. turbine. Steam at 1.10 to 1.03 g/sq cm Abs is
supplied for the gland sealing. Steam for this purpose is obtained from deaerator through a collection where pressure of steam is regulated. From the condenser condensate is pumped with the help of 3*50% capacity condensate pumps to
deaerator through the low pressure regenerative equipments.
Feed water is pumped from deaerator to the boiler through the H.P. heaters by means of 3*50% capacity feed pumps connected before the
H.P. heaters.
*DESCRIPTION OF MAIN TURBINE
SPECIFICATION:TURBINE MAIN DATARated Power 210MWRated Speed 3000 rpm Rated Steam (Pressure) before ESV 130 Kg /̀cm2absRated Steam Temp. Before ESV 5350C Rated Steam pressure Before IV 27 Kg/cm2AbsRated Steam temp. Before IV 5350CRated Steam Flow 670 T/HrHPT Exhaust Pressure 27 Kg/cm2
HPT Exhaust Temperature 3270C Rated circulating water quantity 27000 m3
through condenser Condenser back pressure 0.09 Kg/cm2
Critical Speed 1585,1881, 2017&2489Rated condenser cooling water inlet 240C to 330C Temperature Rated condenser cooling water 1.0 to 1 Kg/cm2
Pressure Type of governing Hydro mechanical Nozzle type governing Type of turbine condensing, tandem compound Three cylinder, Horizontal Nos. of bearing 5 Nos.( for turbine side only &HPC front bearing is combined thrust & journal bearingBarring gear 3.4rpm, ac motor of 30kw, 730rpm, 50c/s,415v, 220:1 RatioLocation of anchor point of At the middle foundation frame of frontthe turbine exhaust part of the L.P. Cylinder
CONSTRUCTIONAL DETAILS:
H.P. CYLINDER: 12 stages (1st is governing stage) each stage Consists of a diaphragm & a set of moving Blades connected on a disc.
BODY: In two valves made of Creep Resistance(Cr-Mo-V) steel STUDS & NUTS: High Creep Resistance (Cr-Mo-V) steel Forgings NOZZLE & STEAM CHEST: 4 Nos (2 on Top & 2 on sides) made of High Creep
resisting (Cr-Mo-V)Steel casting I .P. CYLINDER: 11 stages BODY: 2 parts (a ) Pressure part made of Creep Resisting (Cr-Mo-V) steel
MAIN COMPONENTS OF TURBINE: EMERGENCY STOP VALVE
Steam from the boiler is supplied to the turbine through two emergency stop valves. The emergency stop valve operated by hydraulic servomotor shuts off steam supply to the turbine when the turbo set is tripped. The emergency stop valves connected tothe four control valves through four flexible loop pipes of Chromium-Molybdenum-Vanadium steel.
H.P. CYLINDERIt is made of creep resisting Cr-Mo-V steel casting made of two halves joined at the horizontal plane.The horizontal joint is secured with the help of stud sand nuts made of high creep resisting Cr-Mo-V steel forgings. To
ensure H.P. tightness the studs are tightened by heat to a predetermined temperature with the help of electric heater.
H.P. ROTOR
The H.P. rotor has discs integrally forged with the shaft sand is mechanical forming single Cr-Mo-V steel forging. A special process to prevent abnormal rotor deflection thermally stabilizes the rotor forging.
L.P. ROTORIt consists of shrunk fit discs on a shaft. The shaft is a forging of Cr-Mo-V steel
while the discs are of high strength Ni steel forging. The H.P. rotor is connected by rigid couplings whole the I.P rotor and L.P. rotor are connected by semi-flexible lens type coupling. The rotors are dynamically balanced to a very
precise degree.
TURBINE BEARINGS The three turbine rotors are supported on fine bearings. The second bearing from pedestal side is a combined radial thrust bearing while all others are journal bearings.
THRUST BEARINGSIt is Mitchell type with bearing surface distributed over a number of bearing
surfaces. They are pivoted in housing on the side of I.P. rotor thrust collar. During operation on oil film is forced between pads and thrust collar and there is
a no metal-to-metal contact. A second ring of pads on opposite side of thrust collar takes the axial thrust as may occur under abnormal conditions.
L.P. HEATERSTurbine is provided with non-controlled extractions which are utilized for heating the condensate from turbine bleedingsystem. There are four L.P. heaters. They are equipped withnecessary safety valves in steam space level indicator for visual
Mauges are present for measurement of steam pressure.
GLAND STEAM COOLER
Gland steam cooler has been provided to suck and cool the a i r s team mixture f rom the g land seats . I t employs a smal l ejector for which the working medium is steam of low parameters, which can be taken either from the deaerator or auxiliary source. The pressure and temperature of this steam should of this steam is retrieved to the fullest possible extent as the gland steam cooler is also interposed in the condensate heating cycle thereby improving overall efficiency of the cycle.
CONDENSATE PUMPS
The function of these pumps is to pumps out the condensate to the desecrator through ejectors, gland steam cooler, and L.P. heaters. These pumps have four stages and since the suction is at a negative pressure, special arrangements
have beenmade for providing sealing. This pump is rated generally for 160m3 hr. at a pressure 13.2 Kg/cm2.
*Feed Water System
The main equipments coming under this system are:•Boiler Feed Pump: Three per unit of 50% capacity each located in the '0' meter level in the TG bay.•High Pressure Heaters: Normally three in number and are situated in the TG bay.•Drip Pumps: Generally two in number of 100% capacity each situated beneath the LP heaters.•Turbine Lubricating Oil System: This consists of Main Oil Pump (MOP) Starting Oil Pump (SOP), AC standby oil pumps and emergency DC' oil pump and Jacking Oil Pump (JOP) (one each per unit).
BOILER FEED PUMPS
Boiler feed pump is used to feed water to steam generator boiler drum at desired pressure and temperature. Boiler feed pump extract water from de-aerator and feed it to the boiler drum via H.P heaters and economizer. It works with the steam extraction from Intermediate Pressure (I.P.) turbine exhaustThis pump is horizontal and of barrel design driven by an Electric motor through a hydraulic coupling. All the bearings of pump and motor are forced lubricated by a suitable oil lubricating system with adequate protection to trip the pump if the lubrication oil pressure falls below a preset value. The high-pressure boiler feed pump is very expensive machine which calls for a very careful operation and skilled maintenance. The safety in operation and efficiency of the feed pump depends largely on the reliable operation and maintenance. Operating staff must be able to find out the causes of defect at the very beginning which can be easily removed without endangering the operator of the power plant and also without the expensive dismantling of the high pressure feed pump. The feed pump consists of pump barrel, into which is mounted the inside stator together with rotor. The hydraulic part is enclosed by the high pressure cover along with the balancing device. The suction side of the barrel and the space in the high pressure cover behind the balancing device are enclosed by the low pressure covers along with the stuffing box casings. The bracketsof the radial bearing of the suction side and radial and thrust bearing of the discharge side are fixed to the low pressure covers.The entire pumps are mounted on a foundation frame. Thehydraulic coupling and two claws coupling with coupling guards are also delivered along with the pump. Water cooling and oil lubricating are provided with their accessories.
TURBINE DRIVEN BOILER FEED PUMP
The single cylinder turbine is of the axial flow type. The live steam flows through the emergency stop valve and then through the main Control Valves 5 nos. (Nozzle governing). These valves regulate the steam supply through the turbine in accordance with load requirements. The control valves are cylinder mounted on the turbine casing. The journal bearings supporting the turbine shaft are arranged in the two bearing blocks. The
front end -bearing block also houses the thrust bearing, which locates the turbine shaft and takes up "the axial forces”. There are 14 stages of reaction balding. The actuated by a lift bar which is raised or lowered via a lever system by the relay balancing piston is provided at the. Steam admission side to compensate the axial thrust to the maximum extent. Since the axial thrust varies with the load, the residual thrust is taken up by the thrust bearing. The leak off from the balancing piston is connected back to the turbine after 9th stage. The turbine is provided with hydraulic and electro-hydraulic governing system. A primary oil pump is used as a speed sensor for hydraulic governing and shall Probes are used as a speed sensor for electro hydraulic governing. Whenever steam is drawn from the cold reheat line or auxiliary supply, steam flow is controlled by auxiliary controlvalve. During this period the main control valves (4 nos.) will remain fully opened and the bypass valve across it will remain closed. (Bypass remains closed for a short period when change, over from IP steam to CRH takes place).The steam exhaust for the BFP- Turbine is connected to the main condenser and the turbine glands are sealed by gland steam.
HIGH PRESSURE HEATERS
These are regenerative feed water heaters operating athigh pressure and located by the side of turbine. These aregenerally vertical type and turbine bleed steam pipes are connected to them. HP heaters are connected in series on feed water side and by such arrangement, the feed water, after feed pump enters the HP heaters. The steam is supplied to these heaters form the bleed point of the turbine through motor operated valves. These heaters have a group bypass protection on the feed water side. In the event f tube rupture in any of the HPH and the level of the condensate rising to dangerous level, the group protection device diverts automatically the feed water directly to boiler, thus bypassing all the 3 H.P. heaters.Following fittings are generally provided on the HP heaters•Gauge glass for indicating the drain level.•Pressure gauge with three way cock.•Air Vent cock.•Safety valve shell side.•Seal pot.•Isolating valves.•High level alarm switch.
SPEED GOVERNOR
It is directly coupled to the turbine rotor through coupling and has been designed to maintain automatically the speed of the turbo set. It is located with the front pedestals.
LOAD LIMITER
Turbine is equipped with the load limiter used in special cases to limit the opening of valves by speed governor.
PURPOSE:
To limit the load rising beyond the set point, can be varied over the entire load range.TURBINE OIL LUBRICATING SYSTEM
This consists of main oil pump, starting oil pump emergency D.C. oil pump and each per unit.
TYPES OF VALVES USED AND MAINTAINED IN TMD•Gate Valve
•Regulating Valve
• Non-Return Valve
•Safety Valve
Valves are made of cast iron, cast steel, carbon steel, alloy steel. Cast iron valves: 0-150 0C temperature (used for water lines). Carbon steel valves: 150-4250C temperature (used for water/steam lines). Alloy steel valves: 425-5350C (used for steam lines)