NPTI (SR) Scheme Tracing Report TSII

A Scheme Tracing Report For Partial Fulfilment Of Post Graduation Diploma In Thermal Power Plant Engineering From NPTI (SR), Neyveli

Submitted To:

Submitted By:

Vinay & Rishiraj

Chhattisgarh Lions

(Assistant Directors) 1

INTRODUCTION Introduction:In thermal power plant very high quantity of fuel is fired in steam generating system. During this process large quantity of heat is carried by exhaust gases it self. The heat carried by the exhaust gas is nearly 75x106 kcal for 100MW unit. In order to avoid such loss economizers are installed in flue gas path. By increasing the temperature of feed water passing through economizer by utilizing the furnace exhaust gas the quantity of heat given to generate per kg of steam in the boiler is mechanized. So boiler accessories improve the boiler efficiency and also total efficiency of the power plant is increased as explained below. From the above process we clearly under stood that the feed water is heated to raise its temperature corresponding to the boiler drum pressure .this is the constant pressure is taking place in an economizer.

Accessories:The following are the boiler accessories 1. Feed pump 2. Economiser 3. Air preheater 4. Superheater and reaheter 5. Steam trap To increase the efficacy of the boiler the proper working of boiler accessories should help. The economizer is one of the mach pressure part in the boiler accessories. Three routes are there:Route1:- if any problem in stacker system the meshes loaded is diverted to boiler bunker. Route2:- one steam for stage1 and one for stage 2. Eccentric disc screen:-coal size less than 8 mm pass through it other wisesend it to roller crusher for making it to less than 8 mm. 2

Belt way switch: - To avoid leave out small line out is controlled by roller but if the line out is more than this switch trip the conveyor. Speed monitoring switch:-1000t/h in normal condition nthe normal speed reduces actuator fault occur i.e. motor over load. -

For 7 unit 3500t/day lignite- 1470MW Maximum yard capacity-2lakh/tones depend upon heap position. 1ton coal=1MW

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1. CIRCULATING WATER SYSTEM

INTRODUCTION: In the thermal cycle, the condenser is a “Heat Sink” where the unutilized heat energy is rejected. The heat rejection takes place in the condenser when the condensation of exhaust steam of turbine is effected by the transfer of latent heat of the condensation of the circulating water. The system in which water fed to a condenser carries the heat rejected at the condenser to the cooling tower and operates in a closed cycle, named as Circulating Water System. In Thermal Power Station II/Stage II, a separate circulating water pump house is erected at the western end of the power house to meet the circulating water requirements of the four 210MW units.

FUNCTIONS OF CIRCULATING WATER SYSTEM: The primary function of the circulating water system is to effect the condensation of exhaust steam of turbine by the removal of its latent heat of condensation in the condenser. It also serves for other purposes as follows:     

To cool the auxiliary cooling water in water to water heat exchangers. To cool the lubricating oil in the lub oil coolers of turbo-generator. To cool the seal oil in the seal oil coolers of generator. To supply the water for the disposal of ash. To meet the water requirements of fire service and multi fire systems.

DESCRIPTION OF THE SYSTEM  The circulating water pumps are of single stage, vertical, mixed flow pumps of each capacity 16,500 M3/hr at the deliver pressure of 1.5 KSC.  The general arrangement of the circulating water system is shown in figure (1). The circulating water pump house has totally 12 circulating water pumps.  Two pumps are needed to supply circulating water for each unit. Two additional pumps are intended to be stand-by for all four units.  The cold circulating water flowing from the basin of cooling towers is diverted to a place or storage called “FOREBAY”. From the forebay, the circulating water is supplied to all the suction pits of the circulating water pumps. 4

5

 There are totally 12 suction pits out of which 11 pits are for 11 pumps and the 12 th one is for fire pumps. The forebay water level is to be maintained at an adequate level, since low level will lead to starvation of circulating water pumps and tripping of the unit on “Condenser low vacuum”.  The pump will also get damaged. The water level in the forebay is maintained between +5 and +10 divisions in scale provided. Two standby circulating water pumps are located in between the pairs of pumps of each unit.  The delivery of each pump is supplied through a steel pipe with a butterfly discharge valve. The pump is connected to the discharge piping through an expansion joint so that the vibration and shock, if any, are not affecting the piping.  A pair of discharge pipes of the pumps joins to a concrete tunnel of diameter 2.66m. This tunnel, called as cold water tunnel, takes the cold water to condenser of single unit. The same tunnel can also get water from the stand by pump which is common for two units.  In the discharge pipe of each pump, an automatic air releasing cum vacuum breaker valve is provided. In the cold water tunnels, the manholes with the provision of air vents are provided near by the pump house and the units.  The cold water tunnel nearby the turbine hall divides into two separate channels to supply water for both water boxes of the condenser. The condenser is of divided water box type with two passes of water.  Two steel pipes from intake channels join the sides of the water boxes to provide top side entry of eater. After making two passes inside the condenser, the water leaves through two outlet steel pipes from the bottom of the water boxes to join with two out-take concrete channels.  The two passes of the water are interconnected at rear chambers. The water boxes and rear chambers are provided with air vents and drains. Both inlet and outlet pipes join with the water boxes through the expansion joints. Butterfly isolation valves are provided at inlets and outlets of both water boxes.  From the condenser ‘A’ side intake channel, the circulating water is drawn by auxiliary circulating water booster pumps to boost up and supply circulating water for cooling auxiliary water in water to water heat exchangers. The hot circulating water returning from the heat exchangers joins with outtake channel of ‘A’ side.  From the condenser ‘B’ side intake channel. The circulating water is drawn by lub oil cooler booster pumps to supply the cooling water of about 300 M3/hr to lub oil coolers of turbine and seal oil coolers of generators. The hot water returning from the above coolers is utilized for disposal of ash. 6

 Apart from the above water supply to ash disposal pump house, a direct line from the outtake channel of condenser ‘B’ side is also there to supply water at a maximum rate of 900 M3/hr. The hot water outtake channel from the condenser joins with a common hot water tunnel outside the turbine hall.  This single hot water tunnel of diameter 2.66m carries the hot circulating water up to the cooling tower. Man holes with provision of air vents are provided in these hot water tunnels also. Two steel pipes from the hot water tunnel finally take the hot water to both sections of distribution system of natural draught cooling tower.  The up-riser valves are provided in both these pipes for isolation purpose. The hot water is cooled by the incoming natural air in the cooling tower and the cold circulating water flows to the fore bay through open channel. Filter screens are provided at the outlets of the basin to filter debris.

MAKE UP WATER FOR CIRCULATING WATER SYSTEM In the closed cycle of circulating water system, the water losses occur at number of points. Since the principle of cooling the hot water at the cooling tower is of evaporative cooling, the water evaporated is a loss in the system. The finer particles of water are carried along with up going natural air. This loss is known as the drift loss. Apart from the above, the water utilized for the disposal of ash, fire service etc. are not recovered and hence constitute a loss. In order to meet the water requirements for making up the loss, an artificial lake of capacity 17, 08,605 m3 is located in the north west of the power house. It receives its water supply from Mines II through two pipe lines. From the lake, the make up water is added in the fore bay by gravity valve has both inlet and outlet isolation valves and a bypass valve also. All the valves are butterfly valves. The same make up line can also receive the water directly from the two make up lines (from Mines II) supplying the water to the lake. The storage capacity of the lake is sufficient for 6 days for all seven units (both stages of TS-II).

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TECHNICAL DATA AND SPECIFICATIONS OF CIRULATING WATER PUMP 1. Total number of pumps 2. No. of pumps required for each unit 3. No. of pumps as stand by 4. Type of the pump 5. Design Capacity 6. No. stages 7. Total head 8. Shut off head 9. Speed 10. (i). Provision to take up the end thrust of pump rotor (ii). Provision for cooling the Oil in the oil bath of thrust & guide bearing (iii). Sources of cooling water

-

-

A tapping from the pump’s discharge. 35 litters/min. 2 KSC.

11. Number of line shafts

-

5.

12. Type of line shaft coupling

-

Flame rigid.

13. Efficiency

-

86%

14. Diameter & thickness of discharge pipe

-

1600mm X 12mm.

15. Type of pump

-

Motor coupling – Flexible.

-

46.36 M. 36.25 M.

-

8.8 M.

-

12.8 M

-

1 M.

(iv). Required quantity (v). Required pressure

-

12 2 3( for all 4 units) vertical mixed flow type 18,500 M3/hr one. 24 M of water column. 45 M of water column. 494 rpm. vertical, tilting pad & guide bearing at pump top with ail bath lubrication. by water flowing through coil in the oil bath

LEVELS  Top of intermediate floor level.  Top of sump floor level.  Depth of tip of the suction bell from the top of the intermediate floor.  Depth of tip of the suction bell from the top of the operating floor.  Distance between the tip of the suction bell and the sump floor.

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FOREBAY WATER LEVELS Water level

Indication of scale

Absolute level

Maximum level

+18 division

45.75 M

Normal level

0 division

43.95 M

Low level

-10 division

42.95 M.

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2. WATER TREATMENT PLANT The main objective of water treatment plant is to produce a boiler feed water. so that there shall be 1. Should not form scale formation in the boiler. 2. Should not corrode the boiler. 3. Should not cause priming, foaming in the boiler. 4. Should lower the blowdown requirement and increase the boiler efficiency. The main impurities in the water can be broadly classified 1. suspended particles: Such as clay, slit, organic matter and inorganic matter. this commonly known as turbidity. It cab deposit on the heating surface and causes clogging. this is also known as fouling. 2. dissolved solids: Ca and Mg  Ca and Mg salts present in water cause hardness.  Ca and Mg salts are present in water in the form of bicarbonates and carbonates known as temporary hardness.  Hardness is associated with chloride and sulphate is known as permanent hardness. Iron: Dissolved iron commonly found in ferrous form. When water contain iron comes in contact with air, Ferrous iron converted into ferric hydroxide. it is insoluble in water and precipitate out to give the water reddish brown color. it deposits in pipes bends etc and reduces area causing foaming. 3. Dissolved gases: O2:It is present in surface water in dissolved form in varying concentration depend upon water temperature. It causes corrosion and pitting of water lines in boiler. Co2: Co2 lowers pH.it will make corrosion.

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4.Other impurities: The presence of silica in water,it causes corrosion in the turbine blades.the process involved in DM wateris ion exchange pressure sand filter process. It contains crushed gravels and pebbles.it is used to filter the sand ash in the water. Cation ion exchanger- Ca, Mg, Na, K Anion ion exchanger-HCO3, cl2, so4, Si02 Cation filter-T-42 +ve charged-cx-g Anion filter-A-36 -ve charged-A-27 Mixed bed exchanger: Some traces of iron is removed in mixed bed exchanger. Stage-II, TPS-II  Anion and cation filter can be removed after 2300 m3 and replaced with new one.  Mixed bed exchanger can be removed after 27000 m3 and replace with new one. Regeneration: 5% of HCL, 5% of NaOH. Cation resin: R (Na, Mg, Ca) +HCl→ RH +NaCl MgCl2 + CaCl

(removed by R)

Anion resin: R(Cl,SO4) + NaOH → ROH + Na2SO4 NaCl Degasser tower → used to Co2 present in water. Effluent pit: The drain of NaOH and HCl during regeneration process is sent to pit. Treating chemicals in pit, afterwards send out according to TNPCB. HCl + NaOH → NaCl + H20 11

3. SEAL OIL SYSTEM Purpose of sealing for generator: Sealing is provided to avoid flow of hydrogen from generator to atmosphere. Sealing process can be divided into two processes: 1. Sealing process 2. Drain process a. Air side and b. Hydrogen side

Sealing process: Ring type sealing with single flow type. Source of seal oil: SOT, SOST

Seal oil tank (SOT): 

Located at zero meter level.



Contains a float operated valve to maintain level.



Vacuum pump is provided below SOT to remove vacuum.



Three (3) pumps are used to pump the oil from SOT to generator.

Detail of pump: DC SOP – 1 no.

AC SOP – 2 no.



5.6 Kw

4.85 Kw



220V DC

415V A.C



Class F insulation

10.6 amp



960 rpm

945 rpm

 Only one will be in service  The discharge of pump forms common header  These will produce the pressure of about 8ksc.  Each pump having recirculation line and it is connected from header. 12

Oil cooler: 

Two (2) nos. (1W+1S) with duplex filters



Across the filter, differential pressure is maintained.



The discharge is connected to flow meter.

Differential pressure regulator (DPR) A+B: Control the pressure of oil as to 1.5 ksc above the hydrogen pressure in generator. Impulse signal for A  Hydrogen side drain air pressure  Oil pressure at the outlet of filter  From recirculation line of the pumps Impulse signal for B:  Governor oil pressure  Oil pressure at the outlet of duplex filter  Hydrogen side drain air pressure Anyone of the DPR is in service and control the flow of oil to generator Flow meter: From the duplex filter, oil flows to flowmeter in 2 branches. One side of the oil for turbine end. Another side oil for generator slipping end. Pressure of oil at generator: Normally hydrogen pressure is maintained at 3.5 ksc. So oil will be around 4 to 5ksc. In TS-II, they are maintaining at 4.5 Ksc oil pressure.

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4. Lignite handling system Three routes are there: Route1: If any problem in stacker system, the mines loaded diverted to boiler bunker. Route2: From mines to stack yard. Route3: One steam for stage1 and one for stage2. Eccentric Disc screen: Coal size less than 8mm pass through it otherwise send it to roller crusher for making it to less than 8mm. Scrapper Conveyor: Provided below the shuttle conveyor, belt conveyor carring lignite split inside this conveyor take care of this. Beltway switch: To avoid line out. Small lineout is controlled by roller but if the line out is more than this switch trip the conveyor. Speed monitoring Switch: 1000T/hr in normal condition, the normal speed reduces accusation fault occur i.e. motor over load.  For 7 unit 35000 T/Day lignite - 1470  Maximum yard capacity = 2Lakh/Tones depend upon heap position.  1 Ton coal=1Mw.

Lignite Flow: Stock Yard Detail: Capacity of stockyard

- 200000 Tons

Closed Area

- 20000 Tons

Open Area

- 130000 Tons

No. of Stacker

- 02

No. of Reclaimer

- 02

Maximum height of separator -13.2M

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Conveyor Specification: Belt width

- 1.8M

Capacity

- 2.8T/hr

No. of metal detector

- 06

No. of magnetic separator

- 02

Screens: -

80mm lignite directly full from screen to shuttle conveyor. 80mm size is rejected by screen send to crusher.

Stacker: It is a rail mounted trapper is located on conveyor and capable of spread the lignite at 2800T/hr. This also slowing with the help of slowing mechanism involved in it. Reclaimer: There are two reclaimer which moves on the rail with stock piles. The conveyor capacity is 2800T/hr. In junction forward lignite from stock poles are directed to conveyor TA and TB. Magnetic separators are provided to remove Ferrous metal present in lignite. Crusher: The lignite size above 80mm are transferred to crusher for further crushing. The crushing taken by roller rotated in clockwise direction and they are driven by separate motors Shuttle Conveyor: The outlet of crusher is discharged to hopper and to the belt 12a or 12b by using the concerned shuttle conveyor we are able to fill the bunker. Each bunker is divided into six stages. one will be kept empty. Shuttle conveyor is the conveyor we can move it in forward and backward direction. Junction Tower: In this tower lignite either from mine or stockyard can be directed to stage1 or stage2 or both.

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The parallel conveyor K1A and K1B from crusher house can be direct to load the stage1 or stage2 with the help of shuttle conveyor. Magnetic Separator: Two magnetic separator placed in the conveyor before the crusher house used to separate the foreign (Iron) particles from lignite. It separate up to 20kg of Iron electro magnet is used here. Crusher House: Height of crusher house – 38.5M The coal from mines and stock yard has to pass through crusher house before reaching to the bunker for mill operation. Here the big particles that will be sufficient for mill to take it pulverized form. Crusher consists of 2drum, 2flywheel, 2motors and pin arrangement. Capacity of unit (crusher) – 1800T/hr Speed of motor – 119 to 126 rpm After starting flywheel rotates for (30-40 sec) and engaged with drum. After 40 sec. we have to engage roller with turn by small pin arrangement. Roller protection: If the roller of the crusher become overload then pin gets detached the shear off from roller shaft in order to protect the crusher to become over loaded. Scrapper: Chain Scrapper – Used for cleaning floor and shuttle conveyor. Rotary Scraper – It is used to clean conveyor. Function of LHS: 1. 2. 3. 4.

To receive the lignite from mines. To stock filling the lignite. To crush the lignite. To supply the lignite to unit boiler bunker.

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Metal Detector: There are two metal detector before the crusher and 1 metal detector after the crusher to detect the Iron metals more than 20kg. It has a sand bag which falls in the exact position of foreign particles and tends to shut down i.e. trip the conveyor. Then the foreign metal particle is removed manually. Safety Protection: Pull cord and pull core are used to stop the conveyor due to the emergency condition. AMVWSS (automatic medium velocity water spray system). If any fire in conveyor it detects and spray the water. It also tends to stop the conveyor. If any heavy Iron particles come means metal detector details and trip the conveyor. Specification of lignite: Calorific value Brawn coal

- 2599 kJ/kg - since its colour is in chocolate brawn

Moisture content - 50-60% Volatile matter

- 24-27%

Ash content

- 4%

Fixed carbon

- 19.4%

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5. OIL HANDLING SYSTEM

FUEL OIL: Auxiliary Oil Secondary Oil 18

MAIN FUEL: Lignite OIL USED AS LDO: Light Diesel Oil, Warmed up Oil, Pour Point-18 C, Carbon 86%, Calorific Value-10400Kj/Kg, Ash- 0.1%, Used for lignite up at boiler, Atomising agent- air Firing through 20 ML oil burners OIL USED AS LSHS: Low Sulpher Heavy Stroke Oil available from Indian crude oil Sulpher Content- 0.05 to 0.1 %, High Calorific Value- 10600Kj/Kg, Used for flame stabilization and to meet rapid load increase Pour Point- 66C, Fire Point- 132C Atomising Agent- Steam from AST OIL FIRING: Through four oil burners TRACE HEATING: Heating at pipe line at LSHS to avoid solidifying at low Temperature by pegging steam from 16 ATA sream. LDO DECANTING: two LDO storage tanks, each having 100 m3 capacity. Both tanks are interconnected OIL PUMPS: all are screw pumps provided with pressure relief valve DECANDING: Oil tanker connected to decanding header. Open the air vent to remove air inside the pipe line. Once the line filled with air closed. Total =2 pumps-1 service& 1 reserve. Decanding pump capacity 13.5 kg/min, pressure- 4.5 Ksc Both lines provided with filter. LDO PRESSURING: Common suction header for both tanks Filter -250m provided with differential indicator, 19

Pressuring pump- 32 Ksc, Cap- 11.1 kl/hr Pressure control valve for recirculation at oil burner not in Service DRAIN TANK: To collect the drain of oil from filter pump etc & is pumped to oil Tank LSHS FLUSHING: To wash the LSHS pipelines by LDO to avoid condensing inside the pipe when not in use for long period. LSHS PRESSURING: 2 tanks, cap-1900 m3 .bottom oil tank provided with floor heating coils (by steam at 1600C) SUCTION HEATER: to heat the oil at suction at pumps. FUEL OIL SUPPLY: 2pumps, 2 filters. One set working &another standby. Filter -500m,duplex filter provided with diff. pr indicator, colour indicator PUMPS: Double cutting screw pumps. 32ksc, 30 kl/hr provided with pressure relief valve setting at 32ksc SECONDARY HEATER: oil heated upto 1300C in stage II at pump house stage I, 16mlevel RECIRCULATION VALVE: To recirculate the oil where not used pr at 28 ksc oil recirculated to oil tank FLOROMETER: provided in the oil line to know the exact consumption of the oil. ATOMISING: For the atomisingat 100 ksc service air is used.For the atomization of LSHS steam from AST header is used. OILPRESSURE: Always should be less than attemperation steam temp upto 800C oil burners will be in service. Oil burner capacity 4 T/hr To take a first mill in service min. 3 oil burner should be in service.

UV SCANNER: ultra violet Scanner is provided to know the flame of oil burner. 20

6. BOILER PRESSURE PARTS

In a typical high pressure boiler have the following high pressure part region. 1. Economiser 2. Boiler Drum 3. Water Wall System 4. Super heater 5. Reheater

Economiser 

Economiser here one of the heat recovery devices here on the first passes of the Tower Type boiler.



Economiser is the last component from the first pass of the flue gas path.



Here the sensible heat is alone increased where it receives feed water from BFP to Boiler Drum via Economiser. Here the Economiser is Non-Steaming type



The tubes are arranged inline manner which can be effectively cleaned



Ash hopper at the bottom of economiser made up of Diameter (38 to 53 mm)



Separate Air vents are provided for the economiser



Economiser-2 will be of parallel flow to avoid steaming

Economiser Failure The economiser Failure takes place by overheating (Temp over 400 degree Celsius) and Water starvation, corrosion and erosion Economiser Recirculation System Tapping from one of the Down comer with NRV and isolating valve connected to the Economiser Inlet. This performed when during start up.

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Drum Internals 

Capacity: 690 T/Hr



ASME Code: SA 515 – 70



Internal Diameter :1676 mm



Wall thickness: 131 mm



Weight : 123 tones



Totally Down comers : 84 (21 * 4)



Total number of Turbo separators : 72 (36 * 2)



Total safety values = 3 ( Spring Loaded)

Safety value Set Pressure 

SV1 180 KSC



SV2183.6 KSC



SV3185.6 KSC

When this set pressure exceeds, it will automatically vent out the steam. Hydra Step Instrument which monitors the level of water and steam in Boiler drum. This instrument made by Schlumberger. Drum metal temperature is monitored and measured by the 3 pairs of thermo pads. Drum Level, Pressure Level are separately monitored The drum consists of the following important components 1. 2. 3. 4. 5.

Feed header Chemical Dozing Line EBD,CBD line Turbo Separators Anti vortex spider

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1. Feed Header: Feed header which receives water from the economiser-2, which is immersed in the bottom of the drum, has rows of feed nozzles, which supply water to drum. 2. Chemical Dozing Line: Dozing Pump of (Reciprocating type) is used to doze tri sodium phosphate to prevent in forming of scales and sludge’s. 3. EBD and CBD Line Normal Water Level is maintained below the drum center line. (245 +/- 50 mm) EBD line If water flow exceeds the normal water Level, the possibility of carry over to take place blown down by EBD line. Which is connected to EBD Expander (Flash Tank???) CBD Line Continuous Feed water sampling is done to ensure contamination / TDS are within the limits. The CBD line is connected to the CBD Expander. 4. Turbo separators A very important component inside the drum which separates the steam from the steam water mixture. Primary Separator It is guided by reversing hoods which serves as baffle plates welded, get connected to the turbo separator. Secondary Separator Steam enters the spinner blades in which water is separated from steam Mesh dryers Finally the steam is passed through the mesh dryers where the steam is completely separated. The outlet form the drum is dry saturated steam, with 170 Kg/cm2 and temperature is around (360-370 degree Celsius) Anti vortex Spider :To prevent the Water hammering, water outlet is provided with vortex Inhibitor (At Down comer). 23

Water wall System In TS-2 Membrane type Water wall is used. Tube material will be made by low carbon steel + 0.5 % of Molybdenum for better stress value. Water wall system is well insulated by Mineral wool Blankets The water wall will be completely exposed to the furnace zone. For support of water walls Buck stay Beam is provided Perpendicular to the water wall system. Forces Caused in water walls are transmitted via Buck stay Beams. Bottom Ring Header Bottom ring header is like stream reservoir where the down comers and up risers will be directed from the Bottom Ring header. This will be partly inside the furnace and partly outside Gooseneck (Bending of the tubes will be provided for 60% of the tubes. 30% of Tubes will be straight connected to up risers. Boiler Expansion The Entire boiler is hanging because from No load to Rated MCR load Boiler will be expanding in the downward direction. The Expansion of the Boiler from the normal Bench marking Index is 214 mm.

Super Heaters It is to eliminate the condensation of steam early stages of Turbine. Material Used Generally Ferrite, Pearlite and very limited amount of austenitic steels are chosen for the super heater. In Tower type Boiler (BHEL) – Three super heaters are arranged SH1, SH2- will be counter Flow SH3- Parallel Flow (LMTD and Metallurgical Limitations)

24

25

Desuper Heating stations are provided to control temperature before the entry of the H.P Turbine. Design Aspects Minimum Pressure drop. Low metal temperature. According Ideal Gas Equation the volume is constant in the system. The steam coming from the Boiler Drum is dry saturated having residual moisture is removed in super heating section. Drains and air vents for the super heaters are provided separately. The pressure lost in the Super heater not more than 10% drum operating pressure. The pressure loss in the system is due to back pressure

Super heater Spray Control Station 

Super heater spray control station maintains the constant outlet temperature of super heater between (535-540 degree Celsius).



When overheating occurs de superheating are employed between two consecutive super heaters.



The steam for atomizing feed water is taken from the AST steam header at 16 KSC, 230 degree Celsius.



35-40 T/hr of feed water is required for the desuperheating purpose.



Feed water taken from the feed control station pressure is 17 KSC.



Since SH3 is parallel flow crossover is done in the 3rd stage for the Desuperheating.

Desuperheating process 

Spray Nozzle is provided (Venturi section) Thermal sleeve on downstream of the spray nozzle.



Water is atomized by steam and sprayed directly into superheated steam, such that decreasing the steam quality (Dryness Fraction)

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Reheaters 

Reheaters are provided to avoid Pre condensing and pitting and corrosion side the turbine.



Same material as such of the S.H tubes.



The temperature has to be attained to 540 degree Celsius. And pressure of 37 KSC is maintained to IP turbine Inlet.



RH1 Counter Flow



RH2Parallel Flow



Separate air vents are provided for the reheaters



Reheaters Spray Control station:



One desuperheating station will be provided which is crossed to each other since RH-6 is parallel flow.



Atomizing Steam is taken from the (CRH) Line of pressure of 37 KSC and temperature of 340 Degree Celsius is maintained.



Here feed water is taken from the third stage of BFP pressure of 70-75 KSC.



Water and steam get mixed in Venturi Nozzle and directed to the steam for decreasing the steam for decreasing steam quality.

Normally very less Temperature is reduced in Desuperheating stations. Normally Feed water is maintained at 30-40 T/hr.

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7. Switch Yard A switchyard control room regulates the power flow. In NLC/TPS-II, two different systems are adopted for transmission i.e. 230 kV system (stage-II) and 400 kV system (stage-II). It is out-door type switchyard. Each unit has a Control Room with elaborate protection, interlock and control circuits and instruments. Data Acquisition System (DAS) is employed in Stage-I where as Distributed Digital Control System (DDCS) is available for Stage-II units. On 230 KV there are 10 feeders: Perambalur (1),

Thiruvarur (1),

Pondicherry (1),

Attur (1),

Mine-I (2),

Mine-II (2),

Tie lines to Thermal Power Station-I (2)

On 400 KV side there are 5 feeders: Salem (2),

Chennai (1),

Trichy (2).

Lay-Out Transformer yard is next to the turbine hall, so that generator terminals and step-up transformer are been connected with short bus duct. Switch yard is next to the transformer yard, for easy connection between unit step-up transformer and switch yard. Total 13 bays in the 400 kV yard Total 23 bays in the 230 kV yard Bus system Bus –I, Bus- II and Transfer Bus

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Transformers Generating TransformerGT-I, GT-II, GT-III

(Stage-1)

GT-IV, GT-V, GT-VI, GT-VII

(Stage-2)

Station transformer- ST-1, ST-2 Interconnecting Transformer- ICT-1, ICT-2

CONNECTION DIAGRAMOF GENERATOR AND FEEDER TO A GRID GENERATOR

B/T

BC

FEEDER BUS 1 BUS 2 TRANSFER BUS

89A

89B

89TRA

89TRB

89TRC

89A

89B

89A

89B

89D

89D BC

GB

FB

89C

89C

GT UAT

UAT

GENERATOR

FEEDER

29

230 kV Switch yard Circuit breaker

BHEL make Type- HLR 245/2502E Rated Current- 2500A Both MOCB and SF6 Circuit breakers are used. Minimum Oil circuit Breaker

It has 2 breaking contact per phase. Breaking contacts are mounted over posts. Each breaking unit is vertically sealed, consists of container with an arc control device. Each breaking unit is provided with grading capacitors (1250 pf). The space above the oil is filled with N2 at a pressure of 7.5 kg/cm2. Purpose of N2 is to get high velocity oil jet during opening time. Approximate quantity of oil is 100 kg/unit

Operation Of MOCB

MOCB is operated with a motor operated spring mechanism. The operating device is connected with the open mechanism of the breaking unit thermo push rod system line gears and operation insulator. During closing, the spring gets charged and during opening spring get released. Operating Time

Closing Speed: 8 to 9.2 m / s Opening speed: 6.8 to 7.8 m/s Closing Time = 130 ms Tripping time=35+-5 sec

30

Current Transformer

For current measurement and protection during fault condition CT Details

BHEL Make No of secondary- 5 Ratio- 1200-800-1600 Amps CT’s consists of

Steel tanks, Porcelain insulator mounted on the top of the tank and top chamber mounted on the top of the insulator. Tank is filled with oil. Above the oil space is filled with N2. Capacitor voltage transformer

For wave trapping, voltage measurement and protection purpose

CVT Details

MYS INS India Ltd/Bangalore make Type CVC/245/1050 Intermediate voltage 20 kV Total O/P simultaneously 925VA O/P max 1000 MVA at 50oC Lightening Arrestor

It works on the conductivity action of the gap between the conducting elements of the surge. It is used to protect the line from lightening.

31

Wave Trap

It is used to create a communication between two stations. This type of communication is called POWER LINE CARRIER COMMUNICATION. Insulators

Rated 245 kV Three type are used  245 kV, 1600A,40 A double breaker with single earth switch supported by 9 spark insulators used as bus insulators.  Same as above with single earth switch & w/o earth switch.  Insulators are provided with 3 phase, 4.5 V motor with necdesory gear. Motor provided with HRC fuse and can overload relay. Isolators

Center rotating double break isolator are used.

32

33

400 kV Switch Yard Circuit breaker

SF6 Circuit breakers are used at 6.5 kg/cm2 Rated current- 2000A Rated short circuit current- 40 kV/sec Rated making current 100 kA (peak) Isolators

Bus isolator- Pantograph Type Line isolator- Single Break type, operated by motor.

Preparation of hydraulic oil systems a. Open all the air venting screws, PRV b. Fill aero shell fluid-4 through 60 micron filter c. Start the oil pump and priming of the pump d. Close venting screws and PRV e. Check priming pressure of Nitrogen in accumulator f. Venting of oil at accumulator inlet and at drive assemblies of all 3 poles g. Connect standard pressure gauge h. Check for a. General Lock out (i) Closing Lock out (ii) Auto reclosure lock out (iii) Pump on and off pressures i. Check for any oil leaks in pipe lines,in pilot valve/ main valve j. Topping up of oil 34

Preparation of SF6 gas system 1. Charging of filters 2. Making density monitor operational 3. Evacuation of the CB up to 20mbar 4. Filling of SF6 gas up to 1bar 5. Connect the standard pressure gauge 6. Filling SF6 gas up to lock out pressure 7. Check for vanishing/appearance of lock out signal 8. Continue filling SF6 gas till loss of gas pressure 9. Check for vanishing / appearance of loss of gas signal 10. Check for SF6 gas leak test with detector 11. Dew point measurement

35

36

8. STEAM TO SEALS Objective: The objective of this system is to safeguard the Labyrinth sealing, reduce the steam leakage out of it & proper utilization of it.

Process During Startup:  During startup condition steam from the AST header is supplied to the steam header through AS10 and MAW10 servo valve for initial heat up of all the lines.  In this situation the system is run for sometime unless and Until the CRH line gets the pressure above the AST header.  AST header steam pressure is 17 KSC and temperature is 270˚C.  After 30% load the steam from of HPT & IPT seal box is taken to maintain the steam header pressure.

Steam Supply And Extraction Points From Both Sides Of Turbines:  Point 1: From point 1 the steam will go to CRH line. This is carrying steam at pressure of 37 KSC and its Temperature 340˚C.  Point 2: From point 2 the steam will go to exhaust of IPT. It is carrying steam at pressure of 7 Ksc.  Point 3: At point 3 the steam will enter from steam header. It is carrying steam at pressure of 0.01 Ksc.  Point 4: From point 4 all escaped steam will go to gland steam condenser (GSC). The pressure over here is maintained at vacuum but the steam is sucked as the GSC is having vacuum extraction fan. HPT: In HPT we are having four different extraction points i.e. points 1,2,3 & 4 on inlet & 2,3 & 4 on out let. IPT: IPT is only provided with point 3 and point 4 on both sides. LPT: LPT is also provided with point 3 and point 4. The steam pressure coming out from point 4 is at 0.1033 atm. 37

Always the pressure of steam in the steam header is maintained at 10 milli bar (0.01 Ksc) with help of three valves MAW 10, MAW 50, and BY-PASS valve. Function Of Above Mentioned Valves:  MAW 10: This valve opens when the steam header pressure comes below 0.01 Ksc.  MAW 50: The function of this valve is relief the pressure of steam header above 0.01 Ksc.  BY-PASS VALVE: If the labyrinth ring sealing is damaged then excess steam coming out of point 1 will overload the steam header above the working pressure of MAW 50 valve. So in this condition to safeguard the MAW 50, By-Pass valve of steam header is open to the condenser.  During normal running conditions steam header pressure is maintained by getting stream from HP & IP turbines seal box.  CRH acts as the first stand by to seal box & AST is the second stand by for the steam header.  When the steam header pressure raises above 0.01 KSC then steam is relieved to the condenser.  We are having 2 HPT control valves and 2 IPT control valves and all the leakage steam from all these valves is supplied to the steam header.  During initial startup when the steam from AST header is supplied to steam header of steam to seal system it goes through 2 points 1. Drain to Flash Box 2. 2. Drain to atmosphere. Function Of Drain To Flash Box 2: If any moisture is accumulated in this above mentioned line it is drained to the Flash Box (FB) 2 by opening (DR 119 valve). Function Of Drain to Atmosphere: If any problem is there is there in the drain to FB 2, then the moisture is drained to atmosphere directly.

38

10.MAKEUP WATER SYSTEM

INTRODUCTION 

Makeup water, which is de-mineralized water (DM-water), is used to compensate the tank levels in the condensate and feed water path.



The main source for the makeup water system is DM water tank which is located in water treatment plant.

DESCRIPTION

CONDENSATE STORAGE TANK 

Makeup water system originates from the condensate storage tank. This serves as an initial part of the system.



There are two storage tanks each of capacity 500 and height of 10metres. The water from the DM tank is stored in the condensate storage tank. .



The water from both the tanks is given to the common header, which is maintained at a pressure of 1ksc.

CONDENSATE TRANSFER PUMP 

The water from the tank header is passed through condensate transfer pumps. There are 3 condensate transfer pumps out of which one pump will be in service and the other two pumps are standby.



Two non-return valves (NRV) are placed in the path, one present before the pump and the other present after the pump. If all the 3 pumps are not in working condition, two by-pass paths are provided with NRV’s for uninterrupted water supply to the common header.



The discharge pressure of the CT pumps is 9ksc.

39

CONNECTIONS IN THE COMMON HEADER

STATOR WATER TANK 

The stator winding of the generator is supplied with DM water from the expansion tank for cooling purpose. The expansion tank is supplied with DM water by stator water tank.



The stator water tank is connected to the common header through a NRV and a motor operated valve with level switch (DM-28).



The capacity of the stator tank is 5 27metre from the zero metre.

.The stator water tank is placed at a level of

AUXILIARY COOLING WATER OVER HEAD TANK 

The DM water supply to RAPH, SCAPH, ABG, oil cooling in bearing, H2 cooling in generator is obtained from auxiliary cooling water over head tank.



The DM water is supplied to the ACW O/H tank from the common header through a NRV and a motor operated valve (DM-26).



The capacity of ACW O/H tank is 15

.

DEAERATOR 

The dissolved non-condensable gases in the condensate are removed in the deaerator by direct mixing of steam with the condensate. The gases are removed through the air vent.



The deaerator is supplied with water from the common header through a NRV and motor operated valve (DM-20).The water temperature in deaerator is maintained at 120°c.



The water pressure in the deaerator is maintained at 8ksc. The capacity of the deaerator is 130

. The deaerator is placed at the level of 27metre.

SURGE TANK 

The water level in the deaerator is maintained at 1585mmwc with the help of surge tank. The water makeup is done in the hot well to maintain the level in the deaerator. 40



During initial startup DM water is supplied to the deaerator from the common header through NRV motor operated valve (DM-20).



During normal condition the level in the deaerator is maintained by adding water to the hot well from the surge tank. If the water level in the deaerator goes high the condensate is re-circulated to the surge tank using the valves CD23 & CD60.



If the CT pump or CD64, CD66 are not in working condition, the DM 6 valve automatically open and supplies water to the hot well. Thus DM-6 is used as emergency valve.

41

11.STATOR WATER COOLING SYSTEM

STATOR WATER COOLING: To absorb the heat generated in the stator winding.

WATER USED: D.M Water is used for stator cooling.  To avoid scale formation.  To avoid chemical reaction with stator winding material.

D.M WATER: First be free from all other component. Conductivity must be below 0.5 micro mho/cm.

EXPANSION TANK:  Provided at on higher elevation than generator.  2 m3 capacity material tank.  Inside the tank vacuum of 200-300mm of height column in maintained.  Vacuum in provided to remove the any gas distilled from the D.M water.  Two number of A.C pumps are provides to keep the tank always in vaccum.  Expansion tank can be filled by operating the value DM 28.  Feed water comes from DM Tank(make up)

VACCUM PUMP:  Discharge 51 m³/hr  2 nos; 1 in working; 1 standby. 42

 Vacuum 750 mm of height column for maximum level.  Speed 2850 rpm.

VACCUM PUMP MOTOR: Rated Power 2.2 KW

Speed 2860 rpm

Voltage 415 V

Freq 50 Hz

Current 4.6 A

STATOR WATER PUMPS: o From the expansion tank DM water is taken by stator pumps. o Provided at 0 meter level. o One is standby; one is working condition.

S.W.P. MOTOR: Rated Power 9.3 KW Voltage 415 V Current 19 Amp Speed 3000 rpm Freq 50 Hz

43

WATER COOLER:  Cooling of pressurized water take place in cooler.  From the cooler water flows trough the filter where all the impurities of water are removed.  2 Nos. of filters.

MAGNETIC FILTERS: Magnetic filter is provided in the line to remove all the magnetic particles in the water.

GAS TRAP:  Provided to remove the hydrogen gas if any exerted to the D.M water.  Provided at turbine side.

WATER PRESSURE:  Stator water pressure maintaining at 3.3 ksc. & H2 pr = 3.5ksc.  Flow rate 27-30 m³/hr  At full load a temp. difference at 10-15ºC can be expected between inlet hydrogen & outlet water.

PURITY OF DM WATER:  Conductivity 75 k ohm.cm.

TEFLON TUBES: Are used for inter connecting the winding for water flow.

44

FLOAT OPERATED VALVE: For automatic maintaining of normal D.M water level in the expansion tank

POLISHING UNIT: For purification of primary coolant  About 10% of primary coolant is passed through polishing unit.

45

WORKING OF STATOR WATER COOLING SYSTEM: The cooling water from the expansion tank is circulated by two 100% duty A.C motor driven centrifugal pump. Pumps are electrically interlocked between each other. Two 100% duty coolers are provided for cooling the distillate. Cold distillate temp. is measured and when it rises above 45ºC alarm signal appears. Two water filters are provided in system after coolers in the addition to water filters, magnetic filters also have been provided to catch any magnetic particles coming in circulation. After, it has been passed through the windings and thus cooling them. Water is sprayed back into expansion tank. From the tank again it is circulated in the system by pumps. Normal level is maintained in the expansion tank by means of make up water regulated by float operated valve. Any gas entrapped in the stator winding cooling distillate, is removed by maintaining a vacuum of 200-300 mm Hg column inside the expansion tank. Adequate instrumentation and interlocking are provided in the system for its efficient and reliable operation.

46

12.FUEL FIRING SYSTEM

1.The firing system in TS-2 is tangentially fired system and it is a single flame concept 2.Maximum temperature of the furnace=980 centigrade 3.Maximum flame temp in the active burning zone such as to prevent the water slagging 4.WATER SLAGGING: Water slagging is the phenomena of deposition of flue gas particles (ash particles)over the water walls which lead to the disturbance in the transfer of heat from the flue gas to the water walls 5.SOOT BLOWERS: There are four types of soot blowers for removing the soot from the water walls ,super heaters and reheaters a).WATER LANCER: (i)Water lancer is a type of soot blower to remove the deposition of the ash particles over the waterwall tubes and the water lancer are PLC programme (ii)Two motor drive standard on a BHEL wall deslagger is the unique two motor drive design one electric motor extends and retracts the suvivel tube a full 305mm in a quick of 3 seconds (iii)The high speed traverse motion not only saves valuable time between wall blower sequence but it also quickly removes the suvivel tube from the high temp zone when the blowing stops (iv)The second motor rotates the suvivel tube for effective cleaning (v)Traverse motion=3sec,Rotary motion=84sec (vi)Radius to which water lancer can clean the soot is about 2.5m to 2.8m and it is a single nozzle arrangement b).STEAM SOOTBLOWERS: (i)Steam soot blower is used to remove the soot deposition over the superheaters reheaters

and

(ii)Long Retractable: 1.It is provided with a long shaft since it has a long flow path with the two nozzle arrangement 2.It is provided in the superheaters and reheaters 47

c) Short Retractable:  It is provided with a short shaft since it has a short flow path with the two nozzle arrangement  It is provided in the economizer

6. NUMBER OF SOOT BLOWERS: (i)Water Lancer: Front+rear=32,Left+Right=24,Totally=56 (ii)Air heater(rotary)=2(It is provided in the air heaters) (iii)Steam sootblower: 1.Long Retractable=30 2.Half Retractable=4 7. 1 mill used for 2 burners and the burners are designed with 10 degree downward inclined 8.

12 vertical burners are used for 6 mills

9. SOOT BLOWER PUMPS: (i)Two centrifugal pumps are present at the zero meter level (ii) the water soot blowers take water from the service water and the pressure is about 3.5ksc 10.FORMATION OF ASH DEPOSITS IN THE FURNACE: (I)Fused ash (or) Slag: This can occur on the furnace walls and other surfaces exposed to high gas temp and this is due to entrainment of fused ash and slag in the combustion steam (ii)Sintered Ash: In the convection surfaces the temp of the gas will be very much less than the ash softening temp,formation deposits in this place is said to be sintered ash and this mainly gets settled in the superheaters and reheaters (iii)Fly Ash: In the cooler parts powdery fly ash deposits .These deposits cause corrosion due to its deposits cause corrosion due to its acidic nature in the low temp areas 11. Secondary hot air is feeded through proper air duct to the lignite burners 12.Pulverized lignite velocity=12-14 m/sec 48

13.Secondary hot air velocity=33-38m/sec 14. RESUCTION DUCT: (i) It is present at 38 m level (ii)Flue gas from the boiler pressurize it while pulverizing the coal at the same time (iii) Pressurized flue gas carries the pf to the burners (iv)Number of resuction duct =6(front=2,left=1,rear=2,right=1) 15.PRIMARY AIR: for temperature control

Hot air from the air heater is mixed with the flue gas before the mill

16.SINGLE FLAME CONCEPT:The single flame envelope is produced by providing interaction interaction between all streams of air and fuel introduced into the furnace 16.APRON CONVEYORS: (i) Extracts lignite jointly feed to conveyor belt and it is arranged downstream and it directs lignite to the chute (ii)Lignite from the apron conveyors spread lignite to six belt conveyor which is a closed one 17. Maximum steam capacity of boiler can be provided by 5mills and 1 mills can be in standby 18. Maximum mill capacity =62tonnes/hr;Maximum moisture content in the lignite =55% 19. 40% of the load can be carried out without support from heavy furnace oil(HFO) 20.Mill oil flow rate =11 tonnes/hr and one oil burner can supply 4 tonnes/hr burners to start the 1 mill

so we need 3 oil

21.DAMPER LIGNITE:Allows lignite according to need required. 22.Flue gas temperature at the SH3 should not go beyond 930 centrigrade because the marcosite material present in the lignite comes out at this temp which gets settled on the waterwall tubes and puncture the tubes 23.Mill outlet temperature should not go beyond 250centigrade 24. Three plate belt feeders for 1 bunker 25.Total ignition energy=Inherent ignition energy+auxillary ignition energy 49

TURN DOWN RATIO: Normal firing equipment is designed to perform efficiently for range of fuel flow OIL BURNER =2t/hr : 0.5t/hr 4

:

1

LIGNITE BURNER = 100% : 40% 2.5

: 1

27. Upto 40% of lignite oil support is needed to maintain flame stability 28.For purging inside the furnace the pressure required is 16 ksc and for atomizing the pressure required is (10-12 ksc) 29.During the time of starting HFO can take upto 30% of the load and LDO can take upto 7.5% of the load 30.Pressure inside the furnace is about (-250 to 150)centigrade 31. 2% to 3% of the unburnt particles fall in the after burnt grade (ABG)for recirculation of the unburnt particles 32.SCANNERS: A) ULTRA VIOLET SCANNERS: (i)Scanner head is located near the burner consists of ultraviolet tube (ii) The special glass envelope has a low attenuation for the Ultra violet rays and the tube is filled with the helium gas at low pressure and pure tungsten electrodes are placed inside the tube (iii) It is used to measure the performance of the flame B) INFRA RED SCANNERS: (i)This scanner is used to measure the performance of the mill (ii) The flame controller in conjunction with the flame detector monitors coal, oil, gas , flames selectively near the infrared spectral range (iii)The flame monitoing circuit is sensitive only to the evaluation of the flicker frequency and not to the steady infrared radiation from the combustion chamber and glowing boiler wall refractory

50

(iv) It is insensitive to daylight ,the system consists of an infrared light receiver located near the burner and the control unit. C) VISIBLE LIGHT SCANNERS: (i)This flame scanner is an optical scanner utilizing a fibre optic light guide (ii)It recognizes particular characteristics of visible light radiated from the furnace flames 33.IGNITORS:

HIGH ENERGY ELECTRIC ARC IGNITORS: (i)

the HEA ignitor effectively eliminates dependence on these fuels by igniting heavy oil and L.S.H.S directly

(ii)

The HEA ignition system consists of a high energy arc ignitor,an oil compartment capable of producing a stable flame at all loads,a flame detecting a system sensitive only to its associated guns, a control system to co-ordinate all the components and provide for unit safety

(iii)

The ignitor is a self - contained electrical discharge device for producing a high intensity sparkUse of high resistance transformer to produce a full wave charging circuit and to control spark rate enables the sealed power supply unit to store maximum energy through insulated cables to the ignitor tip on a very short time in terms of micro second

51

13.6.6kv, 0.4kv& DC system

Generator output is15.75kv is step in the GT to 400KV and is feed to the double bus bar with transfer bus arrangement. This supply of 15.75KVis also used to drive in house load. In house load application is designed for two rating 6.6KV and 0.4KV. There are UAT is unit auxiliary transformer to step down the 15.75KV to 6.6KV and then to 0.4KV for each UST i.e. UST – A & UST-B of 6.6kv and UAT i.e. UAT-A&UAT-B of 0.4KV. During startup when separator is not feeding power is required to operate the auxiliary which is obtained from grid through station transformer. When unit is synchronized with the grid the supply from the grid is cut and generator output is sufficient to feed home load. Dc system is used to feed the artificial load where grid power cannot be obtained. 6.6 KVloads:- Unit service transformer. - Mills - FD fans - Esp. Transformer - ID fan - Condensate extraction pump. - Boiler feed pump.

0.4KVloads:- ID fans- boiler coiling air. - RAPH - turning gear -supply to ups. - Auxiliary oil pump. -slag conveyor 52

DC supply goes:-scanner air cooling fan. -feeder - Stator water cooling. -RAPH DC supply -CT pump - seal oil system

53

14.DEAERATOR AND ITS CONNECTIONS

FUNCTIONS OF DEAERATOR: 

Deaerator of feed water i.e, removal of non-condensable gases.Ex:-O2,CO2,NH3.etc.



Heating of feed water(Regenerative Feed Heating)



To act as a Feed water storage tank of B.F.P. & to provide NPSH to it.

WORKING PRINCIPLE: Basically Deaerator works on following TWO principles: 

HENRY’S LAW:

It states that, ‘’the mass of gas with definite mass of liquid which will dissolve in definite temperature is directly proportional to partial pressure of gases in the liquid”.i.e. P=(Pw+Po2+Pco2+Pnh3). 

DALTON’S LAW OF PARTIAL PRESSURE:

It states that ‘’the pressure of container having mixture of gas and vapour is the sum of partial pressure of vapour and partial pressure of gas.”



So, from the above two statements it is clear that, the solubility of gases decreases with the increase in solution temperature or decrease in pressure.



This holds good for any gas with in close limits which does not react with the solvent



But we cannot go for pressure reduction for deaeration as nearly all our equipments work on +ve pressure. so we increase temperature of water for deaeration

DESCRIPTION OF DEAERATOR:

The deaerator we generally use is of combined spray & tray type. It consists of two elements i.e, a feed water storage tank & a deaerating header.



The feed water storage tank is horizontal cylindrical vessel with dished ends at either end and the horizontal deaerating header is connected at the upper part of the feed water storage tank. 54

55

STORAGE TANK: 

It is made of Boiler quality shell.



It has got 3 supports at bottom , centre one is fixed and the other two at both sides are roller support to expand upto 8m during thermal expansion on both sides.



It has 2 safety relief valves and 2 man holes on either sides for internal inspection.



While the main condensate is led into the deaerating header, the heating cum deaerating steam enters Deaerator through storage tank and deaerating header.



The storage tank contains a steam header below water level(normal)to supply heating steam through it.



The BFP suction line connected to it, has an anti vortex spider to prevent BFP cavitation.



It has also some connection like HPH 5&6 drain condensate, BFP circulation, CBD tank steam and steam inlets like turbine extractions, CRH & pegging steam. It has two deaerator drains, two level switches on either sides.

DEAERATING HEADER: 

The deaerator header is a steel shell mounted on feed water storage tank.it comprises of a water distributor with spray nozzles and trays.



In order to increase efficiency of the deaerator ,the area of contact and also the duration of contact between the main condensate and deaerating steam are increased by breaking main condensate into fine particles(in the form of spray)also making the condensate flow down through perforated trays.



The main condensate which is pre heated in three number of LPHS, is making its entry into deaerator at the top of D.H., then the condensate sprayed through 40 number of spray nozzles provided distributor.



The condensate sprayed over two stacks of perforated trays. Each stack has five number trays in it. The deaerating steam admitted at the storage tank rises up in a counter flow direction at the header. Most of the steam quantity is recovered as feed water on condensation. The remaining quantity of steam along with air removed the deaerating header through deaerating vents. By this main condensate is also heated before it goes to storage tank.



Tray removal doors are provided on either side. 56

DEAERATOR CONNECTIONS: (1)STEAM INLETS: (a)NORMAL SOURCE OF STEAM:

During normal running condition the steam source is 4th extraction or IP exhaust.

(b)1st stand by source of steam(CRH Steam): 

The CRH acts as the 1st stand by. It comes through a pressure control station comprising of an electric motor driven isolation valve & pneumatic control valve



The deaerator can also get steam from CRH when turbine is not running and boiler in service. It gets the steam with the help of HP & LP by pass system. (C)2nd Stage by source of steam(Pegging or auxiliary steam):-



during initial start up and emergency If both 4th extraction & CRH steam fails , steam comes through pressure control station (PCV-1).



All the above three source of steam are connected to a junction with NRVs and four safety valves are also provided.

(2) PRE HEATING STEAM FROM AST: 

Initial preheating of feed water in the storage tank can be done by AST header steam.

(3) CBD TANK STEAM to THE STORAGE TANK: 

The CBD water is high pressure and temperature and consequently has high enthalpy. Roughly one third of it is flashed into steam in CBD flash tank at a higher pressure then deaerator and sent to the storage tank through a gate valve and NRV.



The two-third of CBD comes to IBD where further flashing into steam is done and the rest is led to the drainage.



So the above arrangement not only reduces the amount of makeup water but also utilizes the enthalpy of CBD water.

(4) SHELL VENTS OF HPH 5&6 TO THE DEAERATOR HEADER: 

The non condensable gases which come to the HPH, reduces the heat transfer rate and oxygen of it corrodes the tubes of it.



The non condensable gases with little amount of steam is thus sent to the deaerator through isolation valves and NRVs to extract heat out of it. 57

WATER INLETS TO DEAERATOR 1) MAIN CONDENSATE AFTER LPH: 

The main condensate coming from three LPH is admitted to the top of deaerating header, where it is sprayed and it flows to the storage tank through perforated trays kept in stacks.

2) INITIAL FILLING FROM CST: 

During unit start up initial filling is done by city pump, which supplies DM water from CST through a motor driven isolation valve(DM 20).

3) BFP RECIRCULATION LINES (3): 

The BFP recirculation lines are connected to storage tank with NRV, manually operated gate valve and an orifice in each line. There are three such lines in BFP.

4) DRAIN CONDENSATE FROM HPH 5&6: 

Drain condensate from HPH 5&6 are connected to storage tank through level control stations with pneumatic level control valve and a motor driven bypass valve.



The drain condensate helps in pre heating the feed water.

 WATER OUTLETS FROM DEAERATOR 1) FEED WATER SUCTION HEADER TO BFP: 

The BFP suction line is taken from the bottom of the storage tank at one end and hydrazine hydrate dozing is done at the other end.



In the BFP suction line anti vortex spider is provided ,which acts as a BFP protection .

2) DEAERATOR OVERFLOW LINE: 

Deaerator overflow line is at the end of storage tank and it is connected to blow down tank with automatic control valve.

3) DEAERATOR DRAINS: 

Two drain valves are provided on both sides of storage tank .These lines are again interconnected before overflow valve, which is connected to blow down tank.

58

STEAM OUTLETS FROM DEAERATOR 

Four air vents are provided to remove the non condensable gases from the deaerator header as given below



One air vent with motorized valve



One air vent with hand operated valve.



Two nos of vents with an orifice in each line without any valve

Technical Data: Design Data: 1)

Type

2)

Layout

:

Spray and Tray

Deaerating Header

:

Horizontal (Top ).

Deaerator storage tank

:

Horizontal (Bottom ).

3)

Code followed in the designand fabrication :ASME Sec VIII Division I (1986 ).

4.

Design and Test parameters for header and storage tank :

5.

6.

Design pressure

:

7.4 Kg / cm2 and full vacuum.

Design temperature

:

250 o C.

Test pressure

:

11.1 Kg / cm2 (1.5 design pressure)

Test temperature

:

Room temperature.

Dry weight

:

65 tonnes

Operating weight

:

197 tonnes.

Flooded weight

:

262 tonnes.

Weight of the deaerator :

Deaerator support: Distance between the centre and the roller support: 7500 mm. Expansion rollers

:

provided at both ends.

59

7.

Elevation: Deaerator floor

:

27.0 M.

Deaerator centre line

:

29.22 M

Diameter

:

2400 mm.

Length

:

5800 mm.

Material

:

Stainless steel.

Number

:

40

Deaerating Header: 1)

2)

Dimensions :

Spray nozzles:

3)

Number of vertical stacks

:

2.

4)

Number of trays in each stack

:

5.

5)

Main condensate pipes connecting header and storage tank

6)

:

Steam pipe connecting header and storage tank :

2 Nos. (Left and Right ). 1 No. ( at the Centre ).

Storage Tank: 1)

Capacity

2)

Overall dimensions ( OD x Length ) mm

3)

:

130 m3.

:

3500 x 21400.

Safety valve : (i)

Set pressure

:

7 Kg / cm2 (g).

(ii)

Relieving Capacity

:

40,000 Kg / hr . of saturated steam.

(iii)

Number

:

2.

60

Thermal Data: 1. Mode of operation of deaerator

:

Variable Pressure

:

0.005 cc / liter.

3. Operating pressure

:

6.6 ata (at 100 % MCR).

4. Minimum pegging pressure

:

1.5 ata.

5. Operating temperature

:

161.9 o C (at 100 % MCR).

6. Normal source of steam for Deaeration

:

IVth Extraction steam of Turbine.

Pressure

:

7.2 ata.

Temperature

:

319.4 o C.

Saturation temperature

:

165.3 o C

Degree of superheat

:

154 o C.

ii)

Enthalphy of steam

:

740.5 Kcal / Kg.

iii)

Steam flow

:

35.18 T/ hr.

iv)

Tapping point of extraction

: IP cylinder outlet. (from cross around pipes) (after 45 stages).

8.

Water Parameters:

2. Limit down to which oxygen is removed

i)

Parameter at the point of extraction:

Main condensate

Feed water

(at inlet)

(at outlet) 162.8

1. Enthalpy (Kcal / Kg)

:

121.3

2. Temperature (o C)

:

120.8

3. Pressure

:

8.5 ata

6.5 ata

4. Flow

:

530 T / hr

660 T / hr.

`

161.9

61

8.

Terminal Temperature Difference oC (TTD)

:

=(Saturation Temperature of extracted steam – Out going feed water temperature) deg C. 9.

=

3.9

IV th Extraction steam parameters at lower loads:

Presssure (ata)

Flow (T / hr)

1. 80 % load

:

5.86

27.64

2. 60 % load

:

4.54

19.55

62