How do you calculate the work done & specific steam consumption of a back pressure steam turbine?

 

In back pressure turbines, steam just inters through HP valves & exists through exhaust, no any bleed or condensation is done.

The efficiency of the back pressure turbines is more as compared to condensate & condensate cum extraction steam turbines. However specific steam consumption of back pressure turbines is very less as compared to above both type of Turbines

 How do you calculate the work done per kg of steam?

 Let us assume 1 kg/sec of steam is entering into Turbine whose enthalpy is H1 kcal/kg & existing from turbine at enthalpy H2 kcal/kg

Then, work done per kg of steam is given as =(H1-H2) kcal/s

Or 4.18 X (H1-H2) KW, since 1 KJ/sec = 1 KW

 How do you calculate specific steam consumption of a back pressure Turbine?

 Specific steam consumption is defined as the amount of steam consumed to generate 1 KW of power

 SSC = 860 / (Difference in inlet & exhaust enthalpy)

 i.e 860 / (H1-H2)

 A back pressure turbine is operating at pressure & temperature 64 kg/cm2 and 490 deg C respectively, the exhaust steam at pressure 2 kg/cm2& temperature 140 deg C is being used for process.Calculate the work done and specific steam consumption?

 Enthalpy of inlet steam at pressure & temperature 64 kg/cm2 and 490 deg C  = 809 kcal/kg

 Enthalpy of inlet steam at pressure & temperature 2 kg/cm2 and 140 deg C  = 660 kcal/kg

 Work done = (809-660) = 149 kcal/sec

Or 4.18 X 149 = 622.82 kJ/kg or 622.82 KW

Specific steam consumption SSC = 860 / (Difference in inlet & exhaust enthalpy)

SSC = 860 / 149 = 5.78 kg/kw or MT/MW

 A back pressure turbine having inlet steam enthalpy and exhaust enthalpy 780 kcal/kg & 580 kcal/kg, then calculate the specific steam consumption of that Turbine?

 SSC = 860 / (Difference in inlet & exhaust enthalpy)

SSC = 860 / (780-580)

SSC =4.3 MT/MW

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Steam Turbine standard operating procedures (SOPs)

 

Lube oil system operation

Pre-checks

• Ensure lube oil tank level is normal
• Ensure lube oil pumps are healthy to operate
• Ensure lube filter & cooler are in service
• Ensure lube oil inlet and outlet valve provided at filters & coolers are open
• Ensure cooling water inlet & outlet valves provided for oil coolers are in closed condition
• Ensure suction & discharge valve of the pumps are in opened condition

Operation

• Start the oil pump (AOP)
• Ensure no abnormal sound & vibrations
• Observe the discharge pressure
• Ensure header pressure is normal, if not adjust with PRV or recirculation valve
• Check the oil filter DP, if high change over the filter
• Check overhead oil tank is getting filling
• Ensure lub oil is supplying to each bearing & adjust the oil pressure to each bearing as per desired requirement
• Maintain the oil temperature by adjusting cooling water inlet & outlet valves.

Note: Keep open cooling water inlet valve 100% open & adjust the temperature by adjusting outlet valve

• Ensure the over head oil tank is full
• Keep stand by lube oil pump & EOP ready

Barring gear operation

• Ensure lube oil system is in service and oil is circulating at the bearings at a desired pressure
• Ensure barring gear motor is healthy to start & its all interlocks are in place
• Engage the barring gear clutch
• Start the barring gear motor
• Observe the rotor is rotating at barring speed without increase in bearing vibrations & temperature
• Ensure there is no any abnormal sound

Cooling water system operation

Pre-checks

• Ensure the cooling tower level is normal
• Ensure cooling water pump is healthy to operate & their protections & interlocks are in place
• Ensure cooling water pump (MCWP) suction valve is open & discharge valve is closed
• Ensure all the field instruments are healthy & inline
• Ensure surface condenser inlet & outlet cooling water line valves are open
• Ensure Condenser water box vents are open
• Ensure cooling tower inlet cooling water line valves are open

 15-Emergencies in Power plant

Operation

• Start the pump from DCS at 70% RPM
• Open the discharge valve slowly
• Observe discharge pressure is increasing gradually
• Ensure the pump’s vibration & bearing temperatures are normal
• After venting air from condenser water box close the vent valves
• Observe cooling water is falling in cooling water
• Increase the pump’s speed as per requirement
• Note down cooling water inlet & outlet water temperature of condenser
• Start cooling tower fans one by one as per requirement

 SOP Lube oil & Oil cooler change over

Condensate system operation

• Ensure the hot well level is adequate. Otherwise make the hot well level with DM water
• Ensure the CEP is healthy & its all interlocks are in place
• Ensure pump’s suction & discharge valves are open
• Ensure ejector & gland sealing steam condenser inlet & outlet cooling water line valves are open
• Start the pump, ensure the water will flow from ejector & Gland steam condenser (GSC)
• Ensure gland steam outlet control valve to deaerator is close & cooling water is recirculating through recirculating control valve
• If the hot well level increases, then GSC discharge valve can be opened
• Once the Turbine comes into line,GSC outlet control valve should be kept in auto mode to maintain hot well level
• Vacuum pulling & Vacuum killing
• Pre-checks
• Ensure auxiliary steam is available at desired pressure and temperature
• Ensure vacuum breaker valve fitted on steam condenser is closed
• Ensure cooling water is circulating in the condenser and the turbine gland is charged fully at 0.1 kg/cm2
• Ensure live steam line to ejector steam lines drain are kept open
• Ensure Hogger & main ejectors steam and air valves are in closed condition

Vacuum pulling through hogger ejector

• Charge the main steam line to ejector steam & temperature control valve
• Ensure the rated pressure (10 kg/cm2) and temperature (220 deg C) for ejector vacuum pulling
• Once the rated parameters are reached open the steam valve of starting or hogger ejector
• Observe the steam is vented to the atmosphere
• Then open the ejector airline valve
• Observe vacuum inside the condenser increasing slowly and will reach 60 to 70% of rated vacuum within 20 minutes

SOP to put main ejector into line

• Ensure CEP is running
• Ensure cooling water inlet and outlet valves of main ejector which is to be taken into line
• Vent out air from water box of the ejector
• Then open the drain valve of inter condenser and after condenser of ejector
• Open the steam valve of after condenser ejector
• Open the steam valve of inter condenser ejector
• Observe the condensate is drained out from both the condensers
• Slowly open the air valve & observe the vacuum is increasing
• When vacuum reaches rated, then stop the hogger or starting ejector

Vacuum killing or Taking out of main ejector

• Close the air valve of the ejector
• Close the steam valve of inter condenser
• Close the steam valve of after condenser
• Close the drain valves of after & inter condensers
• Close the cooling water inlet & outlet valve once the ejector is cooled

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Power plant & Calculations

Turbine lube oil flushing procedure

 

Oil pipe lines cleaning & flushing:

Generally Steam Turbo Get machineries lube oil supply line & control oil lines are of stain less steel & return oil lines are of carbon steels. The oil pipelines fabricated at site are to be cleaned by acid pickling for CS pipelines and by Caustic Soda for SS pipelines.

Before acid pickling the pipes should be thoroughly flushed with air for removing of loose particles.

Acid pickling pipes should be dummied one end with rubber gasket and filled with acid of 5 to 8% of concentrated HCL acid and keep the pipes filled with acid for 24 hours, so that all loos metal particles will come out. There after remove the acid from pipes & clean the pipes thoroughly with water and neutralize with caustic soda.

Fill the 3 to 4% of concentrated caustic soda solution in the acid cleaned pipelines and keep the pipes for 24 hours, so that all acid contents gets neutralized.

Ensure the time between acid cleaning and soda wash should be kept minimal Also chemical solution should not exceed 60˚C. After that all soda washed pipes are thoroughly cleaned/rinsed with water and dry with Air, Lube oil (ISO VG 46) to be applied inside the pipelines to avoid rusting.

All the passivated pipelines are covered both the ends of pipes with plastics caps / lids so that no dust particles can enter inside. All passivated pipelines are to be fitted immediately in the original position and start the oil circulation / flushing.

Reference books for power plant O&M

Turbine oil flushing:

Pre-checks or requirements for oil flushing;

• Fire fighting system at MOT and STG area is ready to use.
• Main oil tank should clean thoroughly using sponge/Cloth, diesel and with compressed air
• Ensure AOP suction strainers are cleaned and boxed up properly
• Fill the Oil Tank with flushing oil of Grade ISO VG 46 (refer O&M Manual) through centrifuge by site suitable temporary flexible hose connection. Temporary hose connection one end is immersed in the oil barrel and another end is connected to oil centrifuge inlet point. Centrifuged oil should be send from oil centrifuge outlet to Main oil tank by permanent piping. Flushing oil should be same as per first fill oil. The detailed specification & makes are specified in the operation & Maintenance manual
• Ensure Main oil tank level should be > 65% or as per requirement in local level gauge
• Before start up the LOS system please ensures there is no bypass in protections of motors like-Over load, single phase preventer etc.
• All the Oil Pumps & Main oil tank fans are kept ready for operation. Ensure Emergency local Buttons of all the motors are released condition.
• MOT heaters should on. Also ensure Heaters to be cut of at 65 ˚C of MOT Oil temperature
• Ensure MOT Mist fans power supply panel are in charged condition and Mist fan kept ready to start
• Ensure Aux. Oil pump power supply panel is in charged condition kept ready to start.
• Ensure STG Barring gear motor, EOP motor & ACOP motors power supply is switched off condition.
• Ensure AOP pump suction and discharge Pressure Gauges are working and its isolation valves are in opened condition.
• Ensure any one of the Lube oil cooler is line up i.e the inlet 3 way valves is directed in one cooler only and cooler equalizing valve is in closed position. Also ensure corresponding lube oil cooler vents and drains are in closed condition
• Lube oil cooler inlet and outlet cooling water valves are in closed condition. Ensure cooling water to be charged up to isolation valves during flushing
• Ensure lube oil cooler inlet Pressure Gauge isolation valves are open. Also ensure All PTs (if applicable) isolation valve is closed condition during flushing to avoid entry of any foreign particles.
• Remove the original filter elements (625 mesh) from filters skid & put Temporary made filters element (perforated pipe and rolled with temporary filter screen having sizes start from 50 mesh and fastened by wire) to both filter shell.
• Ensure any one of the Lube oil filter is line up i.e. inlet 3 way valves are directed in single oil filter only and equalizing valve is in closed condition. Ensure Lube oil temporary filters are cleaned and box up properly. Ensure Lube Oil filter drains and vents are in closed condition. Ensure Lube Oil filter line inlet & outlet Pressure Gauges is working and its isolation valves are open.
• Ensure Lube oil header Pressure Gauge is working and its isolation valve is open and PT‟s isolation valves are closed condition during flushing to avoid entry of any foreign particles.
• Turbine front & Rear bearing pedestal flanges oil inlet to out let, Gear box flanges oil inlet to out let, Alternator Front & Rear bearing pedestal flanges oil inlet to out let should be bypassed during oil flushing by suitable temporary hose pipes.

Procedure:

Stage-1

• Start AOP & check any oil leakage from the pipe lines welding joints & flange joints
• Observe lube oil header pressure rising
• Monitor the lube oil circulating through bearings bypass hose pipes
• Observe AOP oil pressure regularly, if discharge pressure is decreasing it means that, pump’s suction strainer is jammed. So stop the pump, clean the strainer & again restart the AOP
• Observe the Lube oil filter DPs if it crosses 0.6 kg/c2 change over the filter to stand by filter
• Raise the lube oil temperature 55 to 65 ˚C by MOT heaters or Temporary heaters. Once the oil temperature raised 55 to 65 ˚C lightly hammer the line with mallet or soft hammer so that all the loose materials will come out with the oil.
• After duration of two to three hours, change over the filter to the stand by one and check for the cleanliness of the mesh and if required replace the same. These processes are to be repeated by changing the filters in line and also mesh if required at intervals of 2hrs, 4hrs, 8hrs durations..
• Every 4 hours reduce the oil temperature by raking lube oil cooler into line. This thermal shock will helpful for expansion & contraction of pipe lines thereby removing scale & clogged particles inside the pipe lines & other system.
• Once 50mesh cleared then change to 100mesh then 150mesh and then 200mesh.This process to be continued up to 200mesh cleanness. Once 200 meshes are cleared then follow the Stage -2 flushing.

SOP lube oil cooler & oil filter change over

Stage-2

• Remove top half of the bearings (Thrust, Front & Rear) of T u r b i n e Rotor and keep them at safe location-Clean the preservatives which applied in the rotor. Re-place the bearing caps and their housing/cover in its position and ensure that oil will not spill out during flushing.
• Turbine front and rear pedestal loop line (flexible hoses) to be removed and normalized the inlet and out let connections as per original. Ensure Loop will be continued in the gearbox & Alternator bearings which are bypassed with flexible hoses.
• Ensure the temporary made filters element filter screen having sizes start from 50 mesh.
• Repeat the procedure as per Oil flushing Stage -1 Continue flushing further till system is clear. Once 200 meshes are cleared Oil flushing is completed.

Stage-3

• Completely drain the oil from MOT, coolers, filters and piping system.
• Once the MOT is drained completely, open oil tank cleaning, Clean the tank internals using site suitable special wipers with long rod along with compressed air. After cleaning, fill fresh lube oil inside the tank, ensure that oil is sprayed throughout inside of the tank (Sprayer-site suitable hose connection). Once the oil fogging is over fix the oil cleaning door with oil gasket and apply the grease on the gasket before tightening the bolts.
• Remove the Turbine thrust, front & rear bottom half the bearings from respective pedestals by small amount of lifting the Turbine rotor (max 0.1mm only)
• Remove the Turbine thrust, front & rear bottom half the bearings from respective pedestals by small amount of lifting the Turbine rotor (max 0.1mm only)
• Completely disassemble and clean the Turbine thrust, front & rear bearings by petrol or site suitable cleaning medium. All bearings pads to be inspect. Clean/polish both top & bottom halves. Ensure their correct fitting. Clean the holes provided in Thrust Bearings Pads holder & Journal Bearing holes also
• Insert the Turbine thrust; front & rear bottom half of the bearings in the respective places. Rest the Turbine rotor on the bearings
• Assemble thrust, front & rear top half of the bearings in the respective places. Ensure required clearances as O&M Manual recommendations
• Position the bearing caps/cover and tightens the cap studs as per torque recommended
• Ensure all pumps (AOP, MOP, EOP & ACOPs) suction strainers are well cleaned and boxed up properly
• Ensure both filters skid temporary filters are removed and filter skid is thoroughly cleaned. Insert the original filters in the respective places.
• Main oil tank – Oil should be filled through centrifuge with first fill oil of OEM recommended Grade 

Do not use: Flushing oil for final filling of MOT, if required get it tested from authorized party or OEM.

• Ensure Loop lines (flexible hoses) to be removed in the gearbox & Alternator bearings and normalized the inlet and out let connections as per original
• Ensure all dummies are removed which installed in PRVs, MOP & EOP discharge piping, control oil line and trip oil line system.
• Ensure all field instruments are fitted properly & they are taken into line
• Take All PRV’s into line
• Ensure all flange joints are fitted correctly
• Ensure all interlocks are in line
• Start the AOP & circulate the lube oil throughout the system

 

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What do you mean by Turbine supervisory system???

 

What do you mean by Turbovisory or Turbine supervisory system?

Turbovisory or Turbine supervisory system is the monitoring of a Turbine. It supervises the condition of turbine and informs to an operating person. It also ensures the parameters do not exceed maximum allowable limit.

What is the significance of Turbine supervisory system?

Turbines are heavy & high speed machines, failures of machine lead into unrecoverable losses. So in case of any abnormality turbine should stop automatically. This is taken care by Turbine supervisory system.

What are the equipments or systems used in Turbine supervisory system?

Vibration probes: These probes are used for sensing shaft or bearing casing vibrations. Generally two probes are fitted at 90⁰ apart at X & Y-directions to measure the shaft vibrations. These vibrations are measured in microns, mills or mm/sec.

Speed probes: Speed sensors are generally Magnetic Pick up unit (MPU) type. These are fitted at teethed portion of turbine shaft for measurement. Generally 2 MPUs are used to measure the shaft speed, one for speed sensing & other for controlling.

Axial shift probes: This probe is fitted at the turbine front end to measure the axial displacement of shaft. Axial displacement probe of the shaft is generally set between +/- 0.4 to +/- 0.6 mm.

Read reference books for power plant O&M

Bearing temperature measuring sensors: These are used to sense the bearing metal temperature or bearing drain oil temperature. For measuring bearing metal temperature, RTD is inserted into drilled hole & touches the white metal & to measure the oil temperature RTD sensor touches the drain oil only.

Differential expansion probes: During abnormal operation conditions like quick start up, wrong SOP & uninform temperature distribution in casing & turbine rotor there could be the possibility of rubbing among turbine internals. To measure & monitor these gaps differential expansion probes are used & trips the turbine if these gaps increase beyond set values.

Casing temperature measuring sensors: Generally turbine casing thickness is very large around 150 mm &it depends on turbine operating parameters. So it is very much necessary of uniform distribution of temperature throughout the casing thickness.

And also the difference between top & bottom casing temperature of turbine should be very less.

Casing expansion measurement probes/sensors: These sensors are used to measure absolute expansion of casing. During startup &subsequent loading conditions turbine casing thermal expansion is must. Generally LVDTs are used for casing expansion measurement.

ESV opening indication: This is used to indicate the actual position of valves.

Eccentricity: This is very important supervision system. This is used to measure the mechanical bow. This may happen due to sudden trip of turbine & unavailability of barring device. Standstill position of turbine rotor for long time

Why do vacuum breaker valves are provided on steam condensers?

During tripping of turbine due to any of the above reasons like bearing vibration, temperature, axial shift, differential expansion etc, the vacuum breaker valve opens to bring down the turbine rotor speed to zero at the earliest time

 Read Power plant & Calculations

 Turbine oil flushing procedure

 

9-steps for Steam Turbine commissioning

 

1. What do you mean by Turbine commissioning?

Turbine commissioning is the process of start-up of newly installed Turbine auxiliaries & Turbine up to satisfactory level.

2. When and how do one shall conduct commissioning of Turbine?

Turbine & their auxiliaries are commissioned after proper install, checking & trials. And it is commissioned under the guidance of OEM (Original Equipment Manufacturer)

3. Write down the sequential steps involved in Turbine commissioning

• Steam blowing
• Oil flushing
• Cooling water system commissioning
• Evacuation or vacuum pulling system commissioning
• Condensate lines flushing
• Calibration of servomotor, interlocks checking
• Turbine rolling
• Over speed trip setting
• Synchronization & loading

4. Write down the various steps involved in steam blowing

• Hope Boiler is commissioned
• Steam blowing line is installed properly with required supports
• Start to increase Boiler pressure up to 40% of operating or 40 kg/cm2 whichever is lower
• Heat up the line by opening Boiler Main bypass valve, heat up is done at steam temperature around 400 deg C
• Blow the steam line from steam pressure 40 kg/cm2 to 25-20 kg/cm2
• Again steam line is cooled up to 100-150 deg C or 3 hours if main steam line from Boiler to Turbine is insulated & 1 hour if line is uninsulated
• Continue this process for around 20-30 blows
• Then put the target plate aluminium or steel & continue the blow
• Blowing is continued till

For Target Plate Made of Aluminum:

The piping considered clean if there are not more than 3 (Three) pitting of 0.5 mm to 1mm dia. in center area of 25 mm X 25 mm and shall not have any deformed edges. Besides this there shall be no pitting in the rim zone. Pitting below 0.5 mm may be ignored.

 For Target Plate Made of Stainless Steel:

The piping is considered clean if there are not more than five pitting of 0.1 mm dia to 0.5 mm dia. in centre area of 50 mm X 50 mm & shall not have any deformed edges. Pitting below 0.1 mm may be ignored

Then normalize the steam line

Connect main steam line flange to ESV (Ensure MS line flange & ESV flange’s prallelity is done)

What do you mean by Turbine supervisory system???

5. Write down the sequential steps for Steam line charging.

 Following steps shall be followed during steam line charging:

•  Ensure all the maintenance works related to steam lines are finished.
•  Ensure the clearance from process or Turbine side for charging the steam line.
• Ensure all the drain and trap valves are opened. 
• Slowly open the steam line bypass valve and allow for heat up of line.
• After ensuring line proper heat up, cracks open the main valve and allow for condensate drain.
• After ensuring no condensate in drain line, open the main valve gradually and observe the hammering. (If hammering occurs suddenly close the main valve). 
• After opening the valve 100%, wait till line stabilization. 
• After ensuring no condensate in drain lines, close all the drain valves

6. What is the significance of steam blowing?

Steam blowing allows power station boilers and pipelines to ensure that during normal operation no adhering material in the super heaters, reheaters, and steam pipelines will become dislodged, reach the turbine blades, and damage them. The steam blowing operation cleans all the debris in the super heater, reheater and the steam pipe line connecting the turbine.

7. What are the sequential steps involved in Turbine oil flushing?

Following are the steps

• Ensure OEM recommended oil is being selected for oil flushing
• Oil tank is filled with oil
• Flushing loops are prepared as per OEM recommendations
• Ensure return oil line is fitted with OEM recommended strainers
• Ensure oil centrifuge is in place & ready for operation
• Flush oil by starting lube oil pump & ensure oil is circulating through cooler
• Keep oil centrifuge ON with heater ON
• Maintain oil temperature up to 70 deg C for 4-5 hours
• Charge oil cooler & bring down the oil temperature up to 35-40 deg C
• Then hammer the oil lines to dislodge the sludge, bur or any other foreign materials
• Continue oil flushing till return line strainer is clean by 24 microns filter
• Oil flushing shall be deemed as completed, If Lube oil filter does not choke for more than 24 hours

8-What are the steps involved in cooling water system commissioning?

Following activities are involved in cooling water system commissioning

• Ensure all erection activities are completed on cooling water system
• Ensure all instruments are fitted on CW system
• Ensure cooling tower level is filled with required quality water
• Check the Cooling water pumps physical condition, if found ok take no load trial Or Ensure CW pumps are commissioned under the guidance of OEM
• Connect cooling water line with flushing line & leave to open areas (DO not connect return cooling water line to cooling tower)
• Then start the cooling water pumps & flush all the lines
• This activity shall be done -5 times & keep on making up cooling tower level every time

9-List down the sequential steps involved in condensate line flushing

• Condensate system consists of Condenser, CEP, Ejector, GSC
• Ensure all condensate system is ready for flushing
• Condensate line should be left open at deaerator floor
• Ensure hot well level is normal & provision is made to make up the level of hot well
• Ensure CEP is ready to start or CEP is commissioned under the guidance of OEM
• Then start CEP & flush the line
• This activity shall be dine for 8-10 times & every time up hot well level

10-What are the sequential steps for turbine rolling?

• Ensure Lube oil system is commissioned & is in service
• Ensure cooling water system is commissioned & is being charged
• Ensure condensate system is in service
• Ensure main steam line is charged as per standard process
• Vacuum pulling is done
• Reset turbine protections
• ESV opens & Turbine rolling is done s per OEM guidance

 

 Questions & Answers on steam blowing

 

 

 

 

 

18-Reasons for Turbine bearings vibration

 

1. Unbalance & Bend shaft:

Unbalance is the uneven distribution of body mass in rotating machine.

Machine unbalance & shat bend or bow lead to the bearing vibrations in radial direction

2. Miss alignment:

Miss alignment is non-coincidence of shaft centers of two rotating mating machines.

Miss alignment lead to axial vibrations of bearings

3. Looseness in turbine base bolts or foundation bolts leads to radial vibrations

4. More bearing clearance:

More clearance in journal bearings leads to radial vibrations

5. Rotor rubbing:

If Turbine rotor rubbing with any other stationary parts leads to more radial & axial vibrations. If it is rubbing radially then radial vibrations increase & if it is rubbing in axial direction then there will be more axial vibrations.

Read what do you mean by turbine supervisory system???

6. Seal rubbing:

Seal rubbing with rotating parts like rotor or blades to vibrations in horizontal directions.

This rubbing may due to improperly mounted seals or eccentricity of seals.

7. Distortions in foundations & casing:

Distortion & deflection of foundation include base frame and structure on which turbine is rested. In such cases bearing vibrations are most likely in radial direction & in axial direction. Also vibrations on base frame & on foundations show more.

Similarly bearings vibrations increase in radial direction due to casing distortion. Also casing vibrations show more.

8. Defective bearings:

Bearings vibrations are high in radial direction if bearing is defective in respect to pitting, wear, cracks & more clearance.

9. Inadequate Rigidity in bearing Pedestals:

Bearings start to vibrate in horizontal, vertical & axial directions if pedestal rigidity is less in horizontal, vertical & axial directions respectively.

10. Damage of thrust bearings

This leads to the vibrations of journal bearings in axial directions

11. Defects in coupling:

Coupling defects like more run out, looseness or crack also lead to turbine bearings vibrations

Defective couplings lead to bearings vibrations in both axial & radial directions.

12. High lube oil temperature:

High lube oil temperature causes decrease in viscosity of oil, which in turn reduces the oil film between journal & bearings leading to high vibrations in radial directions.

13. Contaminants in oil:

Lube oil containing burs & other foreign materials can also lead to high bearing vibrations

14. Lube oil & Control oil pipe line forces:

Improperly aligned & non stress relieved pipe lines lead to bearing vibrations. Oil lines not having expansion bellows may transfer vibrations from pump & lines to turbine bearings

Read Top 6-Power plant O&M books

15. Steam line forces & Aerodynamic forces:

Stresses in steam line, improperly supported steam lines transfer vibrations to turbine

16. Changes in steam parameters:

If the quality of steam changes for an example, reduced steam temperature, wet steam etc

17. Overloading the Turbine:

If the turbine is loaded beyond the allowable capacity for long time without consultation with OEM can certainly lead to bearings vibrations & subsequent failure.

18. Other probable reasons for bearings vibrations are

• Turbine resonance
• Operating the turbine in critical speed
• Wrong installation

Read Power plant & calculations for all such posts

Turbine oil flushing procedure

15-Emergencies in Power plant

Steam turbine, cold, warm & hot start up procedure

Turbine cold start up procedure

·         Check all turbine interlocks and protection of turbine.

·         Ensure MOT level normal.

·         Ensure DP across the Lube oil and Control oil filter is normal.

·         Start AOP and fill up the overhead tank up to normal level. Put the EOP in Auto mode.   Maintain the oil temperature within the range of 40 to 45 deg C by MOT heater on, if required. Cut off the MOT heater manually after getting 40 deg C. (Note: The minimum oil temperature for turbine start up is 25 deg C as per OEM manual). Keep stand by AOP in auto made.

·         After getting the above said temperature, start Vapour Extractor fan then start JOP. Ensure its normal discharge pressure i.e. 150 kg/cm2.

·         Put the TG on barring gear and at this speed, record vibrations & temperature at all bearing points.

·         Ensure TG runs on barring gear at least 1 hour prior to rolling. (Note: Prior to start up the steam turbine, the turning gear is operating for at least 25 minutes as per OEM manual).

• Ensure hot well level normal i.e. 850 mmwc. Start CEP and put the system in recirculation mode. If required, make up the hot well level normal by make up
• Control valve from surge tank. Put stand by CEP in auto mode. Keep Hot well control in auto mode.
• Ensure cooling tower fore bay water level normal i.e. 60% and start MCW pump to circulate the cooling water through the condenser. Ensure l/L, O/L valve of condenser and l/L valve of cooling tower opened before MCW pump starts.
• Adjust the I/L valve of cooling tower in such a way that, CW flow should not beyond the design value.
• Open all the drain 100 % of main steam line and keep warm up vent in minimum position and open MSSV bypass valve fully at main steam pressure of 60 kg/cm2 & temperature of 350 deg C.
• After ensured all condensate removed & colorless steam comes through drains, keep all the drains in crack position, then open main steam stop valve and close the by pass steam valve.
• Charge the PRDS of Ejector and gland sealing PRDS line; ensure ejector pressure is of 10 kg/cm2 and temperature of 325 deg C. Adjust the HP & LP side gland sealing pressure at 1.1 ata. Maintain the sealing steam temperature of 393 deg C at HP side and temperature of 250 deg C at LP side.
• Prior to pulling the vacuum, ensure vacuum breaker valve is closed. Then pull the vacuum through hugger ejector.
• After getting vacuum -0.7 kg/cm2 through hugger ejector, take the main ejector into service and keep both the ejector in parallel and ensure the vacuum of - 0.93 kg/cm2 through running ejector, keep the main ejector in running and slowly close hogger ejector air line and then close the steam line after ensuring vacuum stable after STG synchronized only.
• Ensure the Steam pressure at TG I/L is above 70 kg/cm2 (Alarm at 65 kg/cm2, Tripping at 52 kg/cm2), steam temperature at TG l/L is above 420 deg C (Alarm at 395 deg C, Tripping at 385 deg C), vacuum is above -0.7 kg/cm2 (Alarm at - 0.65 kg/cm2, Tripping at -0.5 kg/cm2). Acknowledge all the alarm in the annunciation panel/DCS and ensure all parameters are in healthy condition. Then reset the ESV of turbine through DCS to proceed for the rolling.
• Ensure ESV opened & control valves are at zero position after reset the ESV. Give run command in Woodward 505E and observe the speeding should be carried out according to start up curve, respecting the preceding standstill  (soaking) time (thermal condition of turbine).
• At every soaking period, record/check all the critical parameters with respect to speed as follows:

1.     Oil pressure & temperature

2.     Bearing metal temperature

3.     Main stream pressure & temperature

4.     Exhaust steam pressure & temperature

5.     Axial displacement

6.     Vibrations

What do you mean by turbo supervisory system???

• Ensure barring gear motor is switched off in auto as per interlock
•   If the oil temperature after oil cooler gets near to 48 deg C, adjust the cooling water O/L valve to maintain the oil temperature 49 deg C by keeping its I/L valve full open and ensure oil temperature should not below the 45 deg C.
• If we prefer the rolling in manual, follow the start up curves and raise the speed as per start up curves and record above mentioned parameters at every soaking period Note: Cross the Critical Speed range as fast as possible.
• Keep exhaust hood spray in auto mode. (Note: Do not allow exhaust steam temperature to exceed 105 deg C. Load Turbine or shut it off in case temperature keeps increasing.)
• Start synchronizing by excitation on and voltage build up, match the DG voltage and frequency with generator voltage and frequency. When frequency and voltage matches within tolerable limit and synchroscope LED glows and allow to close the breaker. Close the breaker and increase the load on TG as per load curve (i.e. Approximately 2% of its rated load in order to avoid the activation of reverse power relay) up to the rated load by pushing the corresponding keys on the WOODWARD GOVERNOR
• Adjust the Generator Air Cooler cooling water O/L valve to maintain the ‘Generator winding temperature by keeping its I/L valve full open.
• Close all the main steam line drains and vents.
• Start Remaining MCW pump and CT fan one by one to maintain the vacuum and exhaust temperature.
• As per interlocks, after getting the steam flow of 60 TPH or more than 60 TPH at TG I/L, QC NRV of both bleeds of 22 ata & 9 ata respectively and control extraction of 3 ata will be reset.
• Charge the Deaerator through control Extraction and ensure Deaerator pressure reaches at 1.5 kg/cm2 & temperature at 100 deg C at least.
• Charge both the HP heaters and ensure Feed Water is charged through HP heaters prior to charge steam side.

TURBINE WARM START UP PROCEDURE

When after a clearly detected tripping the causes is eliminated or when the turbine is shutdown intentionally, observe the following for standstill’s longer than 5 minutes up to max. 8 hours

Refer the Warm Startup Curve given by OEM

• Keep the live steam line up to the emergency stop valve pressurized and gland steam open unless turbine rests far longer than 60 minutes
• Pre-warming the control valve block is not required
• Open turbine drain(live steam)
• The oil unit remains in full operation: the turbine oil should not be cooled below 45 deg C
• Keep the turning gear in permanent operation
• In case of no-uniform cooling-down process of turbine and rotor or drop out of turning gear (in this case immediately all isolation valves and steam to the labyrinths), slight distortion may arise, probably within the design clearances. This occurs especially with turbine arrangements where the turbine is exposed to an air draft.
• In the case of a failure of turning gear motor or fall-out loss of electric power turn manually the turbine shaft by means of turning gear hand wheel each 5 minutes of must be turned manually at least 2 turns. If turning unexpectedly is not possible, at all circumstances do not apply undue force but let the turbine cool down.
• Observe the instructions given & check for smooth action of the turbine at speed increase when starting again. Only a completely uniform warmed up turbine rotor is in straight condition so that further acceleration may take place without any risk.

                 SOP FOR TURBINE HOT START UP

 Refer the Hot Startup Curve given by OEM

• Check the availability of import power and start DG set.
• Open the warm up vent and chest drains.
• Start AOP, MCW & CEP pumps.
• Maintain the hot well level 50% through make up
• Close the Vaccum breaker valve and restart the Vaccum pulling.
• Keep the barring gear motor in auto.
• Maintain the lube oil temperature 45 deg C.
• Check the overhead tank healthy condition.
• Check the availability of Vaccum, main steam pressure and temperature.
• Inform to higher officials about all parameters in healthy condition for rolling.
• Reset the turbine and give for rolling.
• Check the vibrations, bearing temperature and any abnormalities.
• After turbine attend 6800 RPM give clearance for synchronization.

 

 Read Boiler start up SOP

Read Steam turbine commissioning

 Turbine oil flushing procedure

 

 Vacuum pulling SOP