WATER AND STEAM SYSTEM

SYSTEMS REQUIRED IN WATER AND STEAM SYSTEM Boiler feed system Circulation system Boiler blow downs & drains Superheaters & Reheaters Steam temperature control Steam transfer lines and auxiliary steam system Boiler safety valves

BOILER FEED SYSTEM Closed loop system is adopted in this process. Boiler feed pump is part of this system. The feed loop starts from condenser hot well and ends in boiler drum. Condenser Dearator Drum This is the main feed system adopted in a closed loop cycle. Feed input quantity is regulated by using the correct flow and according to drum level & steam flow.

The main motive of a feed system is that to increase the pressure more than that of a boiler drum so as to produce water continuously. As temperature increases the pressure also increases subsequently to avoid vapour locking. Drum level is maintained for the continuous supply of water to the boiler. And ensuring the water is free from gases. Pressure rising is done from Deaerator to drum using BFP at 8kg/cm2 Temperature rise is done in deaerator by using the bleed steam from IPT stage NO.12. Now the outlet from the deaerator will be about 142 degree. Inlet to the drum will be around 338 to 349 degree centigrade.

INTERNAL TREATMENT Internal treatment is given both in thermal deaerator and also in chemical deaerator. In both the deaerator hydrazine hydrate is the main chemical used for the internal treatment for a deaeration process. It is dozed inside the deaerator to remove the 02 and other dissolved gases present in the water.

FEED SYSTEM ELEMENTS Main feed system cycle is as follows. 1.Deaerator 2.BFP 3.HP Heater 4.Feed water level control station 5.Economizer 6.Drum

FEED WATER FLOW MEASUREMENTS Feed water flow measurements are done by taking tapping from the HP heater feed lines in which nozzles are provided to it. And three tapping are taken at 22.5ML and connected to a transmitter to measure the followings 1. Drum level, 2. Pressure, 3. temperature.

FEED CONTROL STATION AND FEED CONTROL VALVE The feed control station is present at the 15ML using it the feed water is getting controlled to the inlet of the economizer. Pneumatic valves are placed to maintain the flow and to regulate the quantity of water flow to the boiler. Isolation valve is placed before and after of the control valve. water tapped for the De superheater is taken from the feed control station.

FEED WATER FLOW CONTROL The two main methods of flow control is that, 1. Single Element Control 2. Three Element Control Single element control is nothing but it is used during startups until load of 25% by throttling. Three element control is nothing but controlling the drum level, steam flow & feed water flow. Temperature and pressure indicators are tapped from the ms line. At low load operation the three element control valve full load line will be kept close. Alarm is provided in DCS for excessive difference in steam and water flow.

ECONOMIZER Economizer is located between the 76ML and 64ML in the furnace. It is made of non steaming type located at the lowest flue gas temperature flow. 224 tubes of economizer is divided into two sections consisting of 112 tubes each placed above and below in between 76ML to 64ML. Material of economiser tubes and headers are made of steel 15 Mo3. The heating surface of the economizer is around 11,547 square meter. Coils are arranged with a distance of 8mm between two tubes and coil travels from front to rear side.

CIRCULATION SYSTEM Continuous circulation is said to be the safe circulation process. Types; 1.Natural circulation 2.Forced circulation It is based on the thermo siphons principle in which the water with low density goes up through the up risers and the cold water stay back for the evaporation process. In TPS-II the natural circulation technique is adapted and the circulation takes place from water drum and ends with the steam drum. The circulation ratio is 1:7.

Number of tubes in every step of circulation process. 1. Down comers – 4 2. Bottom Headers – 12 3. Water wall coils – 688 4. Top Headers – 5 5. Raiser tubes – 112 These are the main places of circulation of water to get converted into steam.

BOILER DRUM The center line of the boiler drum is located at 89.3 ML. Length - 15M Thickness - 112mm OD – 1800mm The boiler drum is made of a material steel15NiCuMoNb5 Weight of about 77.133 tones Herd by a structural membrane at 89.3ML and it is supported by means of two heavy steel 20mm placed at 4.5ML.

STEAM AND WATER SEPARATOR The main thing is that the water and steam separation takes place in the cyclone separator. The water and steam mixture enters the drum through 112 riser tubes called as the wet chamber. Around 72 tubes are placed in the cyclone separator which is divided into 36 and 36 in front and rear sides. Separator has six sections in which six tubes are connected to each section. Vortex is placed in each tubes for the separation process.

DOWN COMERS AND DRAINS Down comers are placed at 35 ML 84 down comer pipes at 89.3ML are connected to the four main down comers. Two emergency drum drains and two normal drum drains are also placed. Feed water inlet from economizer to drum is connected through 22 pipes. Phosphate dozing line is also connected in it. CBD line is also taken from the drum to reduce the salt concentration in the water.

BOILER DRUM TAPPING 1.Feed water inlet to drum – 22 2.Down comers – 84 3.Riser tubes – 112 4.Saturated steam pipes – 30 5.Pressure tapping – 9 6.Emergency drum drains – 2 7.Drum drains – 2 8.CBD – 2 9.Phosphate dozing – 2 10.Water level – 2 11.Safety valve pipes – 2 12.Gauge glass connections – 12 13.N2 dozing - 2

EVAPORATOR There are 170(688) evaporator tubes comes and joins through down comers in all sides with out bending. The water walls are made of steel 15Mo3 Its is said to be membrane type water wall nothing but a thick steel type layer welded in between two tubes. Evaporator reduces radiation losses.

OPENINGS IN THE FURNACE 4 Oil burners 12 PF burners 6 Re suction ducts 36 WSB 42 SSB 36 man holes 12 peep holes 4 flame monitor 2 temperature probes

SUPER HEATING Rising the steam temperature above the saturation point. It can also be said as degree of super heat. The main types are radiant super heating(SH1) & convection type super heating(SH2&SH3). The super heating process raises the temperature of the steam from 353 degree to 540 degree centigrade. The saturated steam attains the maximum temperature as per the designed capacity. Super heater blow off it is nothing but the startup vent before commissioning HP and LP by pass.

SUPER HEATER ONE Inlet – 85ML Outlet - 40.8ML No. of Tubes – 224 (56 tubes in 4 sections) Air vent is connected at 93ML Enters the evaporator roof at 81ML It is made with a material called steam cooled tubes.

SUPER HEATER TWO Inlet – 56ML Outlet – 49.5ML No. of Tubes – 448 tubes Made with a material 13CrMo44 It is heated by using convection super heating process.

SUPER HEATER THREE Inlet – 43.2ML Outlet – 47.8ML No. Of tubes – 392 Made with a material 12Cr1MoV It is also a heated with convection heating process.

RE HEATER ONE Inlet – 65.2ML Outlet – 55ML No. of tubes – 784 Made with a material 13CrMo44. Outlet pressure from HPT is about 37kg/cm2 and outlet temperature is about 336 degree in which it is raised by using the reheating process.

RE HEATER TWO Inlet – 50.85ML Outlet – 46ML No. of tubes – 224 Made with the material 13CrMo44 And this is also used to reheat the steam to attain the temperature of about 540 degree.

DE SUPER HEATERS The de super heaters are also said to be attemptator which is used to control the steam temperature of super heaters and re heaters. It is located at 56ML (1A,1B) and 53.3ML (2A,2B). De super heater water lines are taken from the feed water control station at 15ML.

MAIN STEAM LINE The MS line is the inlet line to the HP Turbine. Temperature – 540 degree centigrade. Pressure – 150kg/cm2 Material made with is steelX20,CrMOV121 Steam flow is about 690 t/hr. Maximum velocity of about 43.73 m/sec MCR is about 656t/hr It is located at 43.72ML And comes down to the inlet of HPT at 13.5ML.

PRESSURE REDUSING AND DE SUPER HEATING(PRDS) It is located at 19ML. It is designed to withstand, 1.Temperature – 540 degrees 2.Pressure – 150kg/cm2 3.velocity – 18.28m/sec. And tapping to PRDS are from CRH,HRH,MS Line, ejector at 8ML,Auxiliary steam.

AUXILIARY BOILER Auxiliary boiler is a type of mini boiler which is used during commissioning period and during the start ups. It designed values are; 1.Pressure- 16 kg/cm2 2.Temperature – 230 degrees Auxiliary steam is also used to heat up the deaerator up to142 deg. And other initial heating up process.

CONTROL VALVES Safety valves present with a capacity as follows in out lets of super heaters and re heaters. Safety valves Relieving capacity T/hr Blow off Pressure kg/cm2 SH-50% 350 176 SH-10% 70 173 RH-50% 320 40

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