POWER PLANT TRAINING PROGRAM

TURBINE BARRING GEAR / TURNING GEAR OPERATION


Hot turbine rotor and generator shaft is slowly rotated for uniformly cooing down rotor shafts to avoid distortion or bending. Also its operation is used when Turbine generator rotor is shut down for a prolonged period. In cold turbine periodic turning gear operation is used to rotate shaft position so that because of rotor weight hanging at bearings do not deform downwards at its centre of gravity.



Jack oil system

Turbine &Generator rotor is slightly lifted from its bearing position to reduce the starting torque requirement to rotate rotor at its initial running moment. A positive displacement pump of High pressure is used to supply oil to bearings to jack the rotor system.



Turbine Lube oil requirement

Turbine bearings are force lubricated system, in which lubricating oil is forced into the bearings to maintain lubrication requirement between static and rotating parts of bearings. Lubricating oil pump(s) are separately mounted to a lubricating oil tank which pumps oil to bearings and which is re circulated by suitable oil piping system, and its accessories. Hot oil after lubrication returns to tank which passes through a oil cooler to reduce oil temperature and again used in bearings. Suitable oil filters, suction filters, Oil injectors are the necessary arrangements to fulfill the systems certain needs of oil purifications, positive oil supply to pump suction, which is as discussed hereunder.

One oil pump (MOP) is either directly mounted or through gear arrangement at the turbine generator rotor system is used. When turbine attains its rated speed around 85% it started pumping lubricating oil in the system instead of the one placed outside(AOP), thus reducing power consumption.

As both these pump also supplies oil to Hydraulic speed control mechanism of Turbine to main Power frequency and in turn Generator Power Control system, these pumps Head development and Capacity delivered are bigger as compared to Emergency lubrication system pump(s)

Emergency Lubrication System

When in any case AC supply of the Force lubricating pump(AOP) is not available or any breakdown occurrence of the pumping unit another DC motor driven pump is used as Emergency Oil Pump which starts and starts supply of Lubricating Oil to bearings. This is an emergency measure and suitably incorporated in the system for automatic start







Over Head Oil Tank

This is also an emergency measure of Lube oil supply to bearings in which lubricating oil is continuously stored in a overhead mounted oil tank which can supply oil by gravity to bearings in case both pumps fails to supply lube oil in the rotating shaft.





Preparation of LUBE OIL SYSTEM prior to start of LUBE OIL CIRCUIT

1. Main oil tank is to be filled up with proper grade and quality of lube oil up to its optimum level as when Pump will be in service in can fill up Overhead Oil Tank also without shortfall of AOP or MOP pumping need.

2. Open Suction valve of AOP/MOP (if any)

3. Close Discharge Valve of AOP

4. Chose any one of the lube oil cooler for service by suitably opening of lube oil coolers inlet and outlet valve fully.

5. Choose any one of the duplex filter for service by suitably opening its inlet and outlet valve or changeover valve position.

6. Bearing inlet valves should be accurately opened for individual all bearings lube oil requirement, which varies.

7. Control Oil system is to be lined up by opening its isolation valve.

8 . Check all piping systems for any looseness, deformations, supporting system etc. thoroughly

9. Lineup Over head Oil tank system and its return piping circuit to bearings,

10. Open all pressure gauges impulse line, temperature gauges are working, Pressure , temperature transmitters , switches are properly working condition with all permissive, interlocks, protection circuit through DCS system.

11. Emergency Oil pump system DC Power, Battery system, Battery charger, Inverter, converter unit are healthy working condition.

10. Open Emergency DC Oil pump Suction valve

11. Close Emergency oil pump Discharge valve

12. Start Emergency Oil Pump

13. Open Discharge valve

14. After ensuring bearing oil flows are normal with pressure gauges are normal working , Pressure transmitter is showing Lube oil header pressure, Lube oil temperature are showing at local and DCS and no leakages are there, in the system.

15. Start AOP, and Open discharge valve

16. Oil header pressure will show through Local and DCS system

17. Check Overhead tank oil supply and its return.

17. All permissive are available except jack oil Pump pressure to start barring gear.

18. Line Jack oil pump discharge valves to bearings and pump discharge valve .

19. Jack Oil pump power supply is healthy

20. Start Jack oil Pump.

21. Ensure Barring Gear start permissive is available.

22. Slowly turn barring gear by hand wheel to engage its clutch mechanism and ensure Turbine freeness

23. Start barring gear, check barring current and record, Record Vibration and bearing oil pressure.

24. Main Oil temperature by adjusting cooling water supply to oil coolers. 42Deg C

TURBINE DETAILS

TURBINE BARRING GEAR / TURNING GEAR OPERATION


Hot turbine rotor and generator shaft is slowly rotated for uniformly cooing down rotor shafts to avoid distortion or bending. Also its operation is used when Turbine generator rotor is shut down for a prolonged period. Periodic turning gear operation is used to rotate shaft position so that because of rotor weight hanging at bearings do not deform downwards at its centre of gravity.



Jack oil system

Turbine &Generator rotor is slightly lifted from its bearing position to reduce the starting torque requirement to rotate rotor at its initial running moment. A positive displacement pump of High pressure is used to supply oil to bearings to jack the rotor system.



Turbine Lube oil requirement

Turbine bearings are force lubricated system, in which lubricating oil is forced into the bearings to maintain lubrication requirement between static and rotating parts of bearings. Lubricating oil pump(s) are separately mounted to a lubricating oil tank which pumps oil to bearings and which is re circulated by suitable oil piping system, and its accessories. Hot oil after lubrication returns to tank which passes through a oil cooler to reduce oil temperature and again used in bearings. Suitable oil filters, suction filters, Oil injectors are the necessary arrangements to fulfill the systems certain needs of oil purifications, positive oil supply to pump suction, which is as discussed hereunder.

One oil pump (MOP) is either directly mounted or through gear arrangement at the turbine generator rotor system is used. When turbine attains its rated speed around 85% it started pumping lubricating oil in the system instead of the one placed outside(AOP), thus reducing power consumption.

Emergency Lubrication System

When in any case AC supply of the Force lubricating pump is not available or any breakdown of the pumping unit another DC motor driven pump is used as Emergency Oil Pump which starts and starts supply of Lubricating Oil to bearings. This is an emergency measure and suitably incorporated in the system for automatic start

Over Head Oil Tank

This is also a emergency measure of Lube oil supply to bearings in which lubricating oil is continuously stored in a overhead mounted oil tank which can supply oil by gravity to bearings in case both pumps fails to supply lube oil in the rotating shaft.

Water treatment Water conditioning

Maintenance of internal and external surfaces of pressure part tubes/pipes in healthy conditions is essential to achieve high load factor and long life of any boiler. Deposition of insoluble material on internal surfaces of water and steam tubes/pipes influence heat transfer adversely and sometimes results in tube failure. Treatment of water should therefore be in its entirety that is from raw water to quality of steam in terms of impurities.


Working pressure of water and steam at different stages also significantly affect rate of reaction and solubility of chemicals used in water treatment. Higher operating pressure and temperature of boiler call for further stringent requirementand close limits of tolerance. Invariably water treatment system to ensure quality of water at feed water entry point as agreed and also take care of dosig appropriate chemicals at low pressure and high pressure in steam drum to ensure that impurities are within specified limits given in VGB or similar internationally accepted code.

Present day practice in water treatment technology suitable for the circofluid boilers generating steam at about 90 to 120 kg/cm2 G pressure and 500 deg C plus temperature is generally discussed in the following pages to serve as guidelines only.

Oxygen Corrosion Of Internal Surfaces

Carbon steel is protected by a fundamental iron water chemical reaction that forms a protective layer of magnetic iron oxide on the internal metal surfaces. A small amount of iron reacts with water unit to protective oxide film is formed. Once the film is established the film the reaction virtually stops and does not resume until the film is disturbed or removed. If the film is removed chemically or mechanically , the iron water reaction starts again to build up the protective oxide. This of course removes more iron the surface of the boiler parts and if allowed to continue will definitely thin the metal parts. It is therefore very important to maintain boiler water chemistry within close limits to prevent the chemical removal of the initial protective magnetic iron oxide film on the internal metal surfaces

The most common from of corrosion is that caused by the presence of oxygen in the water steam cycle. The most logical approach to the prevention of corrosion due to dissolved oxygen is to eliminate the entrance of oxygen to the cycle as far as possible and by expelling at the first opportunity the oxygen which has unavoidably entered the cycle.

The most common method of expelling oxygen is by de aerating the feed water from heaters to condensers.

HYDRAZINE HYDRATE AND SODIUM SULPHITE

Reation of Hydrazine with dissolved oxygen produces nitrogen and water. Even products of decomposition of hydrazine are volatile and tend to form , alkaline solutionswith water. This therefore donot increase dissolve solids content in boiler water. The reaction is of course dependant on hydrazine concentration , temperature and time. Due to the volatility of hydrazine and its decomposition at elevated temperature , only a small residual can be maintained I the boiler water. It is apparent that with this small quantity of hydrazine available only minute amounts of oxygen can be allowed to enter the boiler system.



Products of thermal decomposition at higher operating pressure of boiler are hydrogen sulphide and sulphur dioxide.. This will re dissolve at a point where condensation of steam occurs leading to acidic condition in water circuit. Hydrazine is therefore preferred as oxygen scavenger in the boiler operating in the region of 100 bars pressure.

pH Control of condensate feed water

in accordance with table 1 feed water pH should be controlled in the range of 8.5 to 9.5 to reduce iron and copper pickup in the condensate,feed water.

The most commonly used neutralizing chemicals used for controlling the pH of condensate water are Ammonia, Morpholine, Cyclohexamine, and hydrazine.

This chemicals are volatile alkalizers, which dissolved and distills with the steam and neutralize trace acids formed in the condensate. Hydrazine is included with the volatile alkalizers besides being an oxygen scavangers.It decomposes at the operating temperature of the boiler ito ammonia in accordance with the following reaction



2N2H4----------N2+H2+2NH3

Experience has shown that condensate pH, when using Hydrazine will stabilize in the range of 8.5-9.5 due to ammonia formation depending upon the residual of hydrazine maintained at the economizer inlet.

Proper pH control and selection of neutralizing chemical can only be determined by a critical study of the materials making up the condensate feed water system and on the basis of iron and copper concentration in the feed water system which would be indicative of the attackon these cycle materials.

I general a high pH due to ammonia concentration is considered more aggressive to copper bearing alloys but is more protective to carbo steel surfaces.



INTERNAL TREATMENT OF BOILER WATER

There are various methods for the internal treatment of boiler water. A blanket recommendation of any one method is not realistic. The final decision as to the type of treatment to be used in a particular boiler should be used on the raw water supply, history of condenser leakage, the percent of makeup required, the nature of the condensate returns, and other unique factors, A short summary of the recommended internal water treatment as follows

This type of treatment ivolves the addition of phosphates and caustic through the chemical feed ine to the steam drum. The caustic is added to the boiler water to maintain the pH in the range of 10.2- 11.2

The primary purpose of phosphate addition to boiler water is to precipitate the hardness constituents under the proper pH conditions. The calcium reacts with phosphates to precipitate calcium phosphate as hydroyapatite Ca10 (PO4)(OH)2. This is a flocculant tending to less adherent to boiler surfaces than simple tricalcium phosphate, which is precipitate below a pH of 10.2. also caustic reacts with magnesium to form magnesium hydroxide This precipitate is forme in presence to magnesium phosphate at a pH above 10.5 and is considered less adherent than magnesium phosphate.

At a higher pressure comparatively low phosphate residuals must be maintained in order to avoid appreciable phosphate hideout. Hideouts the term used to express the phenomenon of the partial disappearance of phosphate in the boiler wter upon increase in load and its reappearance upon load reduction. A change in phosphate concentration greater than 5 ppm as PO4 between high load and Low load is considered Hideout.