Nikhil kumar project report ON NTPC KANTI


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Nikhil kumar project report ON NTPC KANTI

  2. 2. NTPC-AT GLANCE Page 2 ACKNOWLEDGMENT It is my pleasure to be indebted to various people, who directlyor indirectly contributed in the development of this work and who influenced my thunking, behaviour, and acts during the course of study. I express my sincere gratitude to Sh.S.S.Jha,AGM (MM) and Sh.S. Chakarborty,officer HR for providing me an opportunity to undergo summer training at NTPS-KBUNL, Muzaffarpur. I am thankful to Sh. K.C. Tiwari, Dy. Sypdt. (MM) for his support, cooperation, and motivation provided to me during the training for constant inspiration, presence and blessings. I also extend my sincere appreciation to Sh. UmeshPrasad and Sh. Manoj Kumarfor their valuable suggestions and precious time in accomplishing my project report. Lastly, I would like to thank the Almighty and my Parents for their moral support and my Friends with whom I shared my day-to-day experience and receivedlots of suggestions that improved my quality of work. SUBMITTED BY:- NIKHIL KUMAR B.TECH. (5TH SEMESTER) MECHANICAL ENGINEERING NOIDA INSTITUTE OF ENGG. & TECH. UPTU,UNIVERSITY ROLL NO:-1213340118 BATCH:-2012-2016
  3. 3. NTPC-AT GLANCE Page 3 DECLARATION I, NIKHIL KUMAR, student of B.Tech. 5th semester,studying at NOIDA INSTITUTEOF ENGINEERING& TECHNOLOGY, GR. NOIDA (UPTU), hereby declare that the summer training report on “topic” submitted to NOIDA INSTITUTEOF ENGINEERING TECHNOLOGY,(GR. NOIDA)in partial fulfilment of degree of bachelor’s in technology with ME is the original work conducted by me. The information and data given in the report is authentic to the best of my knowledge. This summer training report is not being submitted to any other university for award of any degree, diploma and fellowship. SUBMITTED BY:- NIKHIL KUMAR B.TECH. (5TH SEMESTER) MECHANICAL ENGINEERING NOIDA INSTITUTE OF ENGG. & TECH. UPTU,UNIVERSITY ROLL NO:-1213340118 BATCH:-2012-2016
  4. 4. NTPC-AT GLANCE Page 4 ABSTRACT Any thermal power plant is converting the chemical energy of fossil fuel (coal) into electrical energy. The process involved for this conversion is based upon the Modified Rankine Cycle. The major components that are used to accomplish the modified rankine cycle are  Boiler feed pump,  The steam generator water walls (evaporator),  Steam generator super heaters,  Steam turbine,  Reheater,  Condenser,  Regenerative feed heaters etc. All components of a power generating cycle are vital and critical in operation. In Modified Rankine Cycle, the two most important aspects that is added are reheating & regenerative heating. By reheating we used to send the steamcoming from exhaust of the turbines back to the reheater of the boiler so that its enthalpy increases and more work can be done by this steamthe other purpose is to make steam dry so that no harm will be done to the blades of the turbine. In NTPC, Kanti, we have three turbines in Tandem coupling namely one H.P Turbine, one I.P Turbine & one L.P Turbine coupled with the generator to which is synchronized with the grid to produce electricityat 50Hz. In all my modesty, I wish to record here that a sincere attempt has been made for the presentation of this project report. I also trust that this study will not only prove to be of academic interest but also will be able to provide an insight into the area of technical management.
  5. 5. NTPC-AT GLANCE Page 5 CONTENT SL NO. DESCRIPTION PAGE NO. 1 An Over-View 6-7 2 Working Process 8 3 Process Of Generation Of Electricity 9-10 4 Generator 11 5 Transformer 12 6 Light Up Process 13 7 Coal Preparation ,Storage & Milling system 14-15 8 Boiler and Auxiliaries 16-22 9 Types Of Pump 23 10 Types Of Turbine 24-25 11 Types Of Cycle 26 12 Types Of Heater 26 13 Flame Scanners 27 14 Important Control Loops In A Thermal Power Plant 27-33 15 Unit Control Desk & Panels 33 16 Advantages Of Coal Based Thermal Power Plant 34 17 Disadvantages Of Coal Based Thermal Power Plant 34 18 References 35
  6. 6. NTPC-AT GLANCE Page 6 AN OVER-VIEW NTPC NTPC was set up in 7th November 1975, the MAHARATNA power giant today generates more than one fourth of the total power in the country, Ranked 5th largest power generating utility in the world, NTPC is the second most efficient in capacity utilization among the top ten thermal generating companies according to a survey conducted by Data Monitor, United kingdom. In a short span of two decades, NTPC has earned its prime status by setting up a total generating capacity of 22,249 MW. With 19.14% of India’s operating capacity,the company generates 26.7% of country electricitythrough its 13 coal and 7 gas based power plants spread all over the country. STATION AT GLANCE- Kanti Thermal Power Station is located in Kanti, Muzaffarpur,90 km away from Patna, the capital of the Indian state of Bihar.It is managed by the Kanti Bijlee Utpadan Nigam Ltd (KBUN),-a joint venture between NTPC and BSEB Patna.The majority shares of the Joint Venture Company is hold by NTPC,with NTPC 64.57% and BSEB 35.43%. First startedin 1985, Kanti Power Plant has an installed capacity of 110×2 MW. An additional capacity of 195×2 MW is being erectedand is due to be completed by December 2014.Bihar is the most power stricken state of India; and in the issue of uplifting our current nation, an excellent and clean 'Thermal Power station' is a necessity. Kanti thermal Power Plant came into existence in 1985 with the efforts of then MP of Muzaffarpur, GEORGE FERNANDES. To take over Muzaffarpur Thermal Power Station (2*110MW), a subsidiary company named ‘Vaishali Power Generating Company Limited (VPGCL)’ with NTPC on 06/09/2006,-contributing 51% of equity; and the balance equity was contributed by Bihar State ElectricityBoard. The company was rechristenedas ‘Kanti Bijlee Utpadan Nigam Limited’ on April 10, 2008.
  7. 7. NTPC-AT GLANCE Page 7
  8. 8. NTPC-AT GLANCE Page 8 WORKING PRINCIPLE Coal based thermal power plant works on the principal of Modified Rankine Cycle. • Process 1-2 • working fluid is pumped from low to high pressure. • Process 2-3 • high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a dry saturatedvapor. • Process 3-4 • The dry saturated vapor expands through a turbine, generating power. • Process 4-1 • The wet vapor then enters a condenser where it is condensed at a constant temperature to become a saturatedliquid. • Process 3-3’ • After the vapor has passed through H.P. it is reheated before passing through I.P. turbine. • this prevents the vapor from condensing during its expansion which can seriously damage the turbine blades, and improves the efficiency of the cycle
  9. 9. NTPC-AT GLANCE Page 9 PROCESS OF GENERATION OF ELECTRICITY NTPC, Kanti is a Thermal Power Plant. The functioning of every thermal power plant is based on the following processes: - 1. Coal To Steam. 2. Steam To Mechanical Power 3. Power Generation, Transmission & Distribution. STEP-1  Coal To Steam Coal and Water are primary inputs to a thermal power plant. This process of conversion of water to steam by using the heat energy produced by burning coal for producing heat takes place in the boiler and its auxiliaries.Coal burns in a furnace located at the bottom part of the boiler. Feed water is supplied to the boiler drum by boiler feed pumps, where water is heated and converted into saturatedsteam This is further superheated in the super heaters. STEP-2  Steam To Mechanical Power This is the most important process of a power plant. The superheated Steam produced in the boiler at high pressure and temperature is feed to the turbine. The steam expands in the turbine giving up heat energy, which is transformed into mechanical energy on turbine shaft. Thus, Mechanical power is obtained from the turbine shaft. TURBINE
  10. 10. NTPC-AT GLANCE Page 10 STEP-3 Power Generation, transmission & Distribution Mechanical power produced at the shaft of the turbine is used to rotate the rotor of an electrical generator that produces electric power. The electric power produced by the generator is boosted to a higher voltage by a generator transformer to reduce the transmission losses. This power at EHV i.e. 400 kV is transmitted and distributed by EHV transmission lines. Schematic Diagram of a Thermal power station RIVER
  11. 11. NTPC-AT GLANCE Page 11 GENERATOR Rating Active Output Continuous 110MW Rated Voltage 11000+/-5%V Rated Current 7220 A Power Factor 0.8 lagging Frequency 50 Hz Excitation System Static type Field current at rated output 1335 A Type of coolingsystem Hydrogen Cooled Hydrogen Pressure 2 Ata No. Of H₂ cooled elements 06 Coolingmedium for H₂ Soft water
  12. 12. NTPC-AT GLANCE Page 12 TRANSFORMER A transformer is an electrical device which works on the principle of mutual induction. The autotransformer used in power station. It has three windings primary, secondary and tertiary. The 220kv voltage is fed as input to primary by step down 132kv fed MTPS as input. The output of generator is step up to 220kv by using step up transformer or generating transformer. Three phase is fed to station transformer. There are two station transformer1 and 2 which is step down transformer. Here 220kv is step down to 6.6kv for internal purpose. This 6.6kv is step down to 415v for low rating motors. At generating transformer we are using lighting arrestor which protects G.T from lighting. This 220kv is given to grid substation. In grid substation we are using some protective system before distribution we have Bus isolator, SF6 breaker, Line isolator, CT, lightning arrestor. Similarly we have two unit auxiliary transformer UAT-1 and UAT- 2, which will step down voltage from 11kv to 6.6kv and it will supply to unit auxiliary board 1BA, 1BB. Similarly station transformer will supply to station board 9BA, 9BB. One unit is tie with other unit because during the failure of any one of the unit other unit will able to supply.
  13. 13. NTPC-AT GLANCE Page 13 LIGHT UP PROCESS • STEP-1 • A controlled quantity of crushed coal is fed to each bowl mill (pulveriser) by its respective feeders and primary air is supplied from the primary air fans which drives the coal as it is being pulverized and transports the pulverized coal through the coal piping system to the coal burner. • STEP-2 • The pulverized coal and air discharge from the coal burners is directed towards the centre of furnace to form fire ball. • STEP-3 • The secondary air heating system supplies secondary air for combustion in the furnace around the pulverized coal burners and through auxiliary air compartments ,directly adjacent to the coal burner compartments. • STEP-4 • Above a predictable minimum loading condition, the ignition becomes self- sustaining. Combustion is completed as the gases spiral up in the furnace.
  14. 14. NTPC-AT GLANCE Page 14 Components of Coal Fired Thermal Power Station:  Coal Preparation i)Fuel preparation system: In coal-firedpower stations, the raw feedcoal from the coal storage area is first crushed into small pieces and then conveyed to the coal feed hoppers at the boilers. The coal is next pulverized into a very fine powder, so that coal will undergo complete combustion during combustion process. 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. There are six mills located adjacent to the furnace at 0 m level .These mills pulverize coal to desired fineness to be fed to the furnace for combustion. The main structure of the pulverisering mill is fabricatedfrom mild steel in three cylindrical sections, the bottom section (the mill housing support )which support the entire unit and encloses the mill drive gear unit, a center section (the mill housing)that contains the rotary grinding element and upper section (the classifier housing )comprising an accommodate the gas loading cylinders of the mill loading gear .A platform around the upper section provide an access to an inspection door and to the top of the mill routine maintenance and is served by detachable ladder . The grinding element comprises of 3 rotatory rollers. Types of Pulverisers: Ball and Tube mills; Ring and Ball mills; MPS; Ball mill; Demolition. ii)Dryers: They are used in order to remove the excess moisture from coal mainly wetted during transport. As the presence of moisture will result in fall in efficiency due to incomplete combustion and also result in CO emission. iii)Magnetic separators: Coal which is brought may contain iron particles. These iron particles may result in wear and tear. The iron particles may include bolts, nuts wire fish plates etc. so these are unwanted and so are removed with the help of magnetic separators.
  15. 15. NTPC-AT GLANCE Page 15 The coal we finally get after these above process are transferred to the storage site. Purpose of fuel storage is two –  Fuel storage is insurance from failure of normal operating supplies to arrive.  Storage permits some choice of the date of purchase, allowing the purchaser to take advantage of seasonal market conditions. Storage of coal is primarily a matter of protection against the coal strikes, failure of the transportation system & general coal shortages. There are two types of storage: 1. Live Storage(boiler room storage): storage from which coal may be withdrawn to supply combustion equipment with little or no remanding is live storage. This storage consists of about 24 to 30 hrs. of coal requirements of the plant and is usually a covered storage in the plant near the boiler furnace. The live storage can be provided with bunkers & coal bins. Bunkers are enough capacity to store the requisite of coal. From bunkers coal is transferred to the boiler grates. 2. Dead storage- stored for future use. Mainly it is for longer period of time, and it is also mandatory to keep a backup of fuel for specified amount of days depending on the reputation of the company and its connectivity.There are many forms of storage some of which are – 1. Stacking the coal in heaps over available open ground areas. 2. As in (I). But placed under cover or alternativelyin bunkers. 3. Allocating special areas & surrounding these with high reinforced concerted retaking walls.
  16. 16. NTPC-AT GLANCE Page 16 BOILER AND AUXILIARIES A Boiler or steam generator essentially is a container into which water can be fed and steam can be taken out at desired pressure, temperature and flow. This calls for application of heat on the container. For that the boiler should have a facility to burn a fuel and release the heat. The functions of a boiler thus can be stated as:- 1. To convert chemical energy of the fuel into heat energy 2. To transfer this heat energy to water for evaporation as well to steam for superheating. Salient Features Of Boiler Plant:- 1. General a) Type of boiler Single drum tangentialfiring & reheattype. b) Type of fuelused Pulverized coal(MainFuel) Heavy oil& L.D.O. (for lightup & flame stabilization) c) No. of Mills 6 d) Type of Mills Pressurized type BowlMill e) Furnace Balanced draught f) P.A. Fans 2 nos. (each 60% capacity) g) F.D. Fans 2 nos. (each 60% capacity) h) I.D. Fans 3 nos. (one standby) (each 60% capacity) i) Air Heater 2 nos. j) Type of Air Heater Trisector regenerative k) Electrostatic Precipitator 1 nos.
  17. 17. NTPC-AT GLANCE Page 17 2. M.C.R. Parameter M.C.R. Value a) S.H. OutletSteam Flow 375 T/Hr b) R.H. Steam Flow 331 T/Hr c) Pressure atS.H. Outlet 141.5 Ata d) Temp. atS.H. Outlet 540ºC e) Pressure atR.H. Inlet 37 ata f) Pressure atR.H. Outlet 32.9 ata g) Temp. atR.H. Inlet 369ºC h) Temp. atR.H. Outlet 540ºC i) Pressure in Drum 148.69 ata j) Design Pressure 158.0 kg/cm k) Flue Gas temp. leaving Economiser 350ºC l)Flue Gas temp. Leaving Air Heater 142ºC m) Feed Water Temp. Before Economizer 235ºC The basic components of Boiler are: -  Furnace  Economiser  Air Preheater
  18. 18. NTPC-AT GLANCE Page 18  Super Heater  Reheater  Desuperheaters  Condenser  Cooling tower  Fan or draught system  Ash handling system • FURNACE A boiler furnace is the first pass of the boiler in which fuel is burned and from which the combustion products pass to the super heater and second pass of boiler. The combustion process is a continuous process, which takes place in first pass of the boiler and controlled by fuel input through coal feeders.It is a radiant type and water- cooled furnace and enclosure is made up of water wall. The furnace is open at the bottom to allow ash/clinkers to fall freelyinto the furnace bottom ash hopper (through a ‘furnace throat’), and at the top of its rear wall, above the arch, to allow hot gases to enter the rear gas pass. The basic requirements that a furnace must satisfyare: 1. Proper installation, operation and maintenance of fuel burning equipment. 2. Sufficient volume for combustion requirements. 3. Adequate refractories and insulation. • ECONOMISER It is locatedbelow the LPSH in the boiler and above pre heater. It is there to improve the efficiencyof boiler by extracting heat from flue gases to heat water and send it to boiler drum. Advantages of Economiser include 1) Fuel economy: – used to save fuel and increase overall efficiencyof boiler plant 2) Reducing size of boiler: – as the feed water is preheated in the economiser and enter boiler tube at elevatedtemperature. The heat transfer area required for evaporation reduced considerably.
  19. 19. NTPC-AT GLANCE Page 19  AIR PREHEATER The heat carried out with the flue gases coming out of economiser are further utilized for preheating the air before supplying to the combustion chamber. It is a necessary equipment for supply of hot air for drying the coal in pulverized fuel systems to facilitate grinding and satisfactorycombustion of fuel in the furnace • SUPERHEATER The steamgenerated by the boiler is usually wet or at the most dry saturatedbecause it is in direct contact with water.So, in order to get superheated steam,a device known as superheater has to be incorporated in the boiler. The function of the superheater system, is to accept dry saturatedsteam from the steam drum and to supply superheated steamat the specifiedfinal temperature of 540oC, by means of a series of heat transfer surfaces arrangedwithin the boiler gas passes. A superheater is a surface type heat exchanger generally located in the passage of hot flue gases. The dry saturatedsteam from the boiler drum flows inside the superheater tubes and the hot flue gases flows over the tubes and in this way its temperature is increasedat the same pressure. The super heater consists of three sections classifiedas primary super heater, secondary super heater and final super heater. In Kanti, there are 14 super heater coils which are divided into above different sections where temperature is increasedfrom approx. 340oC to 540oC  REHEATER 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 rerouted to go inside the reheater tubes to pickup more energy to go drive intermediate or lower pressure turbines. • DESUPERHEATERS A. Superheater Desuperheater The superheater desuperheater is fittedafter 10th coil to control the superheated
  20. 20. NTPC-AT GLANCE Page 20 steamat the specified terminal temperature of 540˚C. The maximum design temperature reduction at the superheater desuperheater is from 446˚C to 388˚C. B. Reheater Desuperheater The reheater desuperheater is only brought into use when the reheater outlet temperature rises above the normal temperature.  CONDENSER The condenser condenses the steam from the exhaust of the turbine into liquid to allow it to be pumped. If the condenser can be made cooler, the pressure of the exhaust steam is reduced and efficiencyof the cycle increases.The functions of a condenser are:- 1) To provide lowest economic heat rejection temperature for steam. 2) To convert exhaust steam to water for reserve thus saving on feed water requirement. 3) To introduce make up water. We normally use surface condenser although there is one direct contact condenser as well. In direct contact type exhaust steam is mixed with directly with D.M cooling water.  COOLING TOWER The cooling tower is a semi-enclosed device for evaporative cooling of water by contact with air. The hot water coming out from the condenser is fed to the tower on the top and allowed to tickle in form of thin sheets or drops. The air flows from bottom of the tower or perpendicular to the direction of water flow and then exhausts to the atmosphere after effective cooling. The cooling towers are of four types: - 1. Natural Draft cooling tower 2. Forced Draft cooling tower 3. Induced Draft cooling tower 4. Balanced Draft cooling tower
  21. 21. NTPC-AT GLANCE Page 21 • FAN OR DRAUGHTSYSTEM: In a boiler it is essential to supply a controlled amount of air to the furnace for effective combustion of fuel and to evacuate hot gases formed in the furnace through the various heat transfer area of the boiler. This can be done by using a chimney or mechanical device such as fans which acts as pump. i) Natural draught When the required flow of air and flue gas through a boiler can be obtained by the stack (chimney) alone, the system is called natural draught. When the gas within the stack is hot, its specific weight will be less than the cool air outside; therefore the unit pressure at the base of stack resulting from weight of the column of hot gas within the stack will be less than the column of extreme cool air. The difference in the pressure will cause a flow of gas through opening in base of stack. Also the chimney is form of nozzle, so the pressure at top is very small and gases flow from high pressure to low pressure at the top. ii) Mechanized draught There are 3 types of mechanized draught systems 1) Forced draught system 2) Induced draught system 3) Balanced draught system Forced draught: – In this system a fan called Forced draught fan is installed at the inlet of the boiler. This fan forces the atmospheric air through the boiler furnace and pushes out the hot gases from the furnace through superheater, reheater, economiser and air heater to stacks. Induced draught: – Here a fan called ID fan is provided at the outlet of boiler, that is, just before the chimney. This fan sucks hot gases from the furnace through the superheaters, economiser, reheater and discharges gas into the chimney. This results in the furnace pressure lower than atmosphere and affects the flow of air from outside to the furnace.
  22. 22. NTPC-AT GLANCE Page 22 Balanced draught:-In this system both FD fan and ID fan are provided. The FD fan is utilized to draw control quantity of air from atmosphere and force the same into furnace. The ID fan sucks the product of combustion from furnace and discharges into chimney. The point where draught is zero is calledbalancing point. • ASH HANDLING SYSTEM The disposal of ash from a large capacity power station is of same importance as ash is produced in large quantities. Ash handling is a major problem. i) Manual handling: While barrows are used for this. The ash is collected directly through the ash outlet door from the boiler into the container from manually. ii) Mechanical handling: Mechanical equipment is used for ash disposal, mainly bucket elevator, belt conveyer. Ash generated is 20% in the form of bottom ash and next 80% through flue gases, so calledFly ash and collectedin ESP. iii) Electrostatic precipitator: From air preheater this flue gases (mixed with ash) goes to ESP. The precipitator has plate banks (A-F) which are insulated from each other between which the flue gases are made to pass. The dust particles are ionized and attractedby charged electrodes.The electrodes are maintained at 60KV.
  23. 23. NTPC-AT GLANCE Page 23 TYPES OF PUMP 1. Condensate Extraction Pump (CEP) The function of Condensate extraction pumps is to pump out the condensate to the deaerator through, LP heaters.The steamfrom the LP cylinders exhausts into the condenser shells where it is constrained to flow across the water tubes, through which cooling water is circulated. There are two 100% duty extraction pumps, one remains in duty and one remains stand by. The thrust bearings in the driving motors have temperatures sensor, which can trip the motors automatically. The pump discharge the condensate to the LP heater system with a pressure increasedto approx. 18 kg/sq. cm from 70-75 mm of Hg. 2. Air Extraction Pump (AEP) The function of the air extraction pump is to raise and maintain the vacuum conditions in the turbine main condensers, and to remove air and other non-condensable gases vented to the condenser from various parts of the turbine and feedwater heating system. 3. Boiler Feed Pump (BFP) Boiler feed pump is the most critical component of a power plant. It is a rotary machine, which is coupled to a motor through variable speed coupling or turbo coupling. Feed water suppied to the boiler drum should have high pressure which is achieved when passed through boiler feed pump. Whenever the pressure of water is to be raised, BFP is used. The discharge pressure of a boiler feed pump is approx. 150 kg/sq. cm.
  24. 24. NTPC-AT GLANCE Page 24 TYPES OF TURBINE High pressureturbine • It is of single flow design with eight stages of blading. • Each stage has moving and stationary blades. • Superheated steam(at 1100⁰c) from boiler drum enters in to it. • Speed-3000rpm Intermediatepressureturbine • Double flow design with seven stages of blading on either side. • Each stage has moving and stationary blades. • Reheated steam(at 535⁰ c) from H.P turbine outlet enters in to it. • Speed-3000rpm Low pressureturbine • It is also of double flow design with 6 stages in front and rear flow paths. • Each stage has moving and stationary blades. • Stem out of I.P. turbine directly enters in to it. • Speed-3000rpm
  25. 25. NTPC-AT GLANCE Page 25  Salient Feature Of Turbine:- 1. General a) Type Of Turbine Reheat b) No. Of Cylinders 3 (HP,IP & LP) c) No. Of LP Heater 5 d) No. Of HP Heater 2 e) Deaerator 1 (Variable pressure type) f) No. Of Extraction pump 3 (one standby) g) No. Of BFP 2 (one standby) 2. M.C.R. Parameter M.C.R. Value a) Rated output 110 MW b) M.S. Pressure atH.P. turbine inlet 130 ata c) M.S. temp. atH.P. turbine inlet 535oC d) H.R.H. temp. atI.P. turbine inlet 535oC e) Turbine speed 3000 rpm f) Condenser Vacuum 0.1 kg/cm2 (abs) g) No. of Extraction 7 h) Quantity of cooling water 15,400 m3/hr
  26. 26. NTPC-AT GLANCE Page 26 TYPES OF CYCLE 1. Steam Cycle Drum↔ Steam Heater↔ High Pressure Turbine ↕ Intermediate Pressure Turbine↔ ReHeater ↕ Low Pressure Turbine↔Condenser 2. Water Cycle Hotwell↔ Condensate Extraction Pump ↔ Low Pressure Heater↔ Deaerator ↕ Drum↔ Economizer↔ High Pressure Heater↔Boiler Feed Pump 3. Flue Gas Cycle Furnace↔ Steam Heater↔ ReHeater↔ Economizer ↕ Chimney ↔Electrostatic Precipitator ↔ Air Preheater TYPES OF HEATER 1. High Pressure Heater (HPH) In the water cycle, temperature of feed water from BFP is increasedto approx. 130oC by heating it in HP heater. As the heating of the feed water in HP heater is done by the extra steamcoming out of the High Pressure Turbine(HPT) hence, it is named as High Pressure Heater(HPH). 2. Low Pressure Heater (LPH) In the water cycle, temperature of condensate from CEP is raised to approx. 80oC by heating it in LP heater. As the heating of the condensate in LP heater is done by the extra steam coming out of the Low Pressure Turbine(LPT) hence, it is named as Low Pressure Heater(LPH).
  27. 27. NTPC-AT GLANCE Page 27 FLAME SCANNERS In a flame there are three zones. 1.Visible zone 2. UV zone 3.Infrared zone The flame scanner consists of UV light sensitive tube and UV light sensitive element filled inside the tube on which 700 DC volt is supplied. Initially there is no contact between the two electrode on which 700 DC volt is supplied. As there is UV light sensitive element present inside the tube, it sacns the UV zone of the flame.When it scans the UV zone, the UV element present inside the tube conducts and the two electrode are in contact. Now, the supplied voltage is reduced to zero. Hence, whenever it scans the UV zone, the supplied voltage becomes 0V otherwise it is 700V. Therefore, on an average the scanner shows 400V – 450V which confirms the presence of flame inside the furnace. As there are two types of fuel which are the main source of burning. Hence, basically there are two types of flame scanners depending upon the fuel used. So, to sense the flame due to oil used in the furnace there are oil flame scanners and to sense the flame due to coal used are known as coal flame scanners. IMPORTANT CONTROL LOOPS IN A THERMAL POWER PLANT  Basic Block Diagram Of Any Closed Control Loop
  28. 28. NTPC-AT GLANCE Page 28 Process:The equipment whose present level, pressure and other values is to be measured is known as process. Set Point: The required value of parameter is set by the manual which is to be maintained in order to protect the process from damage. Measurement: The present value of parameter in process is measured here. Generally, capacitance type of measurement is used. Two tapping from the process, one at high pressure & other at low pressure, is taken and transmitted through isolating diaphragm and silicon oil fill fluid to a sensing diaphragm in the centre of the differential pressure cell.The sensing diaphragm deflects in response to differential pressure. The position of the sensing diaphragm is deflectedby capacitor plates on both sides of the sensing diaphragm. The differential capacitor between the sensing diaphragm and the capacitor plate is converted electronicallyto a 4-20 mA signal and transmittedto comparator. This measurement sometimes also known as transmitter. Comparator: It compares the signal between set point and measured value. If the two values differ from one another, an error signal is generated and sent to the controller. Controller: It is an electronic card which, according to the error signal sent by comparator, gives a current signal between 4-20 mA to final control element. Final Control Element: It is that portion of the loop which directly changes the value of the manipulated process variable and finally do some work to maintain the set point of the process. 1.Drum Level Control
  29. 29. NTPC-AT GLANCE Page 29 The required drum level is set at the set point. The present drum level is then measured which is done by capacitor type transmitter.Two tapping, one at the bottom in water while other at the top in steam, is made and allowed to flow to the transmitter.Since, the two elements are in different states,steamis condensed and collectedin a constant head unit (CHU) before going to the transmitter where the present drum level is measured and converted to current signal between 4-20 mA. This set value and measured value are then compared in a comparator and an error signal, if any, is generated and sent to controller which finally directs the final control element to control the drum level. Here, the final control element is a control valve through which a fluid passes that adjusts the size of the flow passage as directed by a signal from controller to modify the rate of flow of the fluid. Hence, the drum level is controlled. 2. D.P. Across Feed Control Station In order to maintain the linear characteristics of the feed regulating valves under different loads, the differential pressure(D.P.) control loops maintains a fixed differential across the regulating valves and BFP discharge pressure is varied by
  30. 30. NTPC-AT GLANCE Page 30 changing BFP motor speed through hydraulic scoop tube device which is the final control element here. The D.P. across feed station (comparator) is sensed and is fed to the controller. The controller are automatically adjusted as function of steam flow to achieve stable condition. The reserve Boiler Feed pump scoop tube automatically follows the running pump scoop tube and the changeover to the reserve BFP takes place with the scoop tube in the same position of the scoop tube. 3. Combustion Control The combustion control proposed for this boiler comprises of the following loops: a. Master pressure control b. Pulverized coal flow control c. Combustion air flow control d. Oxygen trimcontrol e. Mill temperature and air flow control a. MasterPressure Control The turbine throttle pressure which is a measure of turbine and boiler mismatch, is maintained by proper fuel and air flow control to the burners. Actual steam pressure at turbine inlet is measured and error against a set value is fed to the individual pulveriser control loop through controller. b. Flue Flow Control In order to maintain an air rich furnace, air flow demand signal is superimposed over total fuel flow signal through a high limiter unit. This way when master demand signal increases and if air flow is low, fuel flow is not straightaway increased. Instead, main demand signal first increases the air flow and only when demand signal is low as compared to air flow, tie selector unit in the fuel control loop increases the fuel flow. When the master demand calls for a reduction of combustion, fuel flow and air flow are reduced simultaneously with fuel flow leading air flow, thus ensuring always an air rich furnace. c. Combustion Air Flow Control
  31. 31. NTPC-AT GLANCE Page 31 Total air flow signal is fed to control and this controller output adjusts the FD fan vanes. Provision also exists to ensure a minimum air flow (30% of maximum) through a high signal selector. d. Oxygen Trim Control To ensure some percentage of excess air for optimum combustion, Oxygen trim control is employed. Oxygen contain in flue gas before air preheater is measured and error is fed to controller. A maximum/minimum limiter is introduced so that should the oxygen supply fall, a minimum disturbance is introduced in the flue/air control loop. e. Mill Temperature And Flow Control This control loop is envisaged to maintain constant air flow to the mills and also to maintain constant mill outlet temperature. Primary air flow and mill outlet temperature signals are measured and fed to the controller respectively.Output of the controllers are connected to each of the two error modules, the output of which are going to coal and hot air dampers through respective auto manual stations. The provision of variable air flow supply exists in the hardware supplied and shall be adopted on site,if required. 4. Furnace Draft Control The furnace draft is maintained by modulating the I D fan Hydraulic coupling (3 nos.). Furnace draft at combustion chamber outlet is measured and the error is fed to the controller. Output of this controller accordingly positions the vanes to maintain constant furnace pressure to improve the system dynamic response. An anticipator total air flow signal is alsoadded in the loop. 5.Primary Air Header Pressure Control A control loop always ensure sufficient PA to the pulveriser hot air duct at the set pressure and achieves the same by modulating the PA fan vanes (2 nos.).
  32. 32. NTPC-AT GLANCE Page 32 6. Superheat Steam Temperature Control The superheater steam temperature control system makes use of three parameters, secondary superheater outlet temperature,total steam flow and superheater inlet temperature. The final superheaters temperature error is fed to controllers which positin spray control valves left & right sides to maintain constant superheater outlet temperature. 7. Reheat Steam Temperature Control Reheat outlet steam temperature is maintained by tilting the burner to increase/decrease heat absorption in the reheat section of the boiler. Additional emergency reheat spray is used to maintain temp. when burner tilts are unable to reduce the temp. sufficiently. Left and right reheater temp. signals are averaged and fed to controller. Controller output is indexed with total steam flow signal and through an auto-manual station drives nozzle tilt drive. In case of differential reheater temp. difference above allowable limits, respective spray control valve left or right are used to bring balance in left and right side R.H. steamtemperatures. 8. BFP Minimum Flow Recirculation Control In order to ensure safetyof the pump against overheating, the minimum flow is to be maintained when the pump flow reduces below a preset limit. This is achieved by a reliable pneumatically operated minimum flow recirculationcontrol valve with built-in pressure breakdown device. The control envisaged is an on-off control, the operation of which is initiatedby a low range DP switch sensing the boiler feed pump flow. Whenever the flow falls below 100 T/hr., the minimum circulation valve is opened and when the flow increases above 200 T/hr., this valve is kept closed. Indication is provided on the UCB to indicate the operator the status of this valve by open-close position indication lamp. 9. Hotwell Level Control :-Hotwell level is maintained by recirculationof the condensate after steamjet air ejector through a level controller and split-range control valves. Any excess condensate is, therefore, fed to the deaerator.
  33. 33. NTPC-AT GLANCE Page 33 10. Deaerator High & Low Level Control The deaerator low level control acts on the condenser make-up control valve to add DM water in the hotwell and the high level control acts on the excess condensate to Unit condensate floating tank. Two separate control loops have been provided for the above. 11. Secondary Air Damper Controls The function of a secondary air damper control system is to distribute the secondary air from the windbox requirements. Electronic analog control system is used for this application. Duplicate transmitters of 4-20 mA dc output for Heavy oil and furnace/wind box differential pressure are used to improve system availability. The 4- 20 mA dc output from the control system is converted into pneumatic signal using E/P signal converter to position power cylinder operated dampers at all the elevations on four corners. Electric to pneumatic (E/P) signal converters are field mounted type. UNIT CONTROL DESK & PANELS The operation of each unit is envisaged from the central unit control room. It is located in the control bay at 9.0m TG floor. It is adequately illuminated and is centrallyair conditioned. For operational convenience, the control room front wall has complete glass paneling for TG hall view and the two double doors for entry from TG hall. The control board has a special profile with three sloping surfaces for mounting a large facias, instruments and controls. The automatic control station and drive contrl switches & Indications are located on the first sloping surface. The process indicators/recorders and ammeters are mounted on the second sloping surface and the alarm annunciation window facias are mounted on the top i.e. third sloping surface. The unit control board are arranged in logical operating sequence from the left to right starting with (i.)Air & Flue Gas, (ii.)Fuel oil, (iii)Bowl Mills, (iv)Steam & Feed water, (v)Regenerative System, (vi)Turbine and (vii) Generator.
  34. 34. NTPC-AT GLANCE Page 34 ADVANTAGES OF COAL BASED THERMAL POWER PLANT  They can respond to rapidly changing loads without difficulty  A portion of the steam generated can be used as a process steam in different industries  Steam engines and turbines can work under 25 % of overload continuously  Fuel used is cheaper  Cheaper in production cost in comparison with that of diesel power stations. DISADVANTAGES OF COAL BASED THERMAL POWER PLANT  Maintenance and operating costs are high  Long time required for erection and putting into action  A large quantity of water is required  Great difficulty experienced in coal handling  Presence of troubles due to smoke and heat in the plant  Unavailability of good quality coal  Maximum of heat energy lost  Problem of ash removing REFERENCES:
  35. 35. NTPC-AT GLANCE Page 35 ‘Modern power station practice-Volume-B. -Volume-C. ‘ Power plant Engg.’ By P.K.NAG Control & Instrumentation-Volumel Operation & Maintenance Manual (MTPS)-Volume H  Wikipedia   plant/