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)

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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

Read Generator and Turbine inter tripping

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

 

 

 

 

 

14 unknowns you must know in Boilers

 1-How do you decide Right hand side & Left hand side of a Boiler?

Boiler front is decided based on boiler outlet duct.

If you stand by facing towards boiler out let duct, then the most front part of you is deemed as Boiler front , next to that is boiler rear & LHS & RHS side of you is deemed as Boiler left hand side & right hand side.

2-Why in Some HP boilers drums are aligned at an angle 2 to 4⁰ towards right or left?

Drum slanting side depends on the connection of CBD line. If CBD line is connected at LHS side of the drum then the drum is slanted towards LHS side that is it is made down by an angle 2 to 4^0. This is because to avoid the blow down of excess water throughout the drum length & for such drums CBD line is extended for only for short distance only .And also it is been ensured that all the sludge will collect at slant position only.

3-How it is been decided that RHS or LHS safety valve of steam drum is set at higher pressure?

It is decided based on the slanting angle of steam, drums & CBD line connection.

If drum is aligned horizontally then you can set any side of the Safety valve at higher pressure as there is uniform spreading of sludge in drum.

Whereas if drum is slanted (made down)towards right or left from where CBD line is connected then it is needed to set that side safety valve at higher pressure to avoid carryover of sludge into the safety valve if t blows first. Such sludge will deposit on safety valves disc & seat which again leads into leakages & wrong operation related issues. So safety valve of such location is always set at higher pressure.

4-Why thickness of steam drum dish end is somewhat lesser than other area

Because dish end has spherical shape, so there develop hoop or circumferential stresses & on the other part of the drum longitudinal stress.

 For Hoop stresses

σc =  Pd/2tη

Thickness t = Pd/(2 ησ)

& For longitudinal stresses σl = Pd/4tη

Thickness t = Pd/(4 ησ)

Where P = Pressure acting & d is internal diameter of the drum

Based on above relations thickness for spherical part of the drum that is dish end, the thickness is lesser than other part of the drum.

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5-Why the start up vent is used in Boilers?

Start up vent is used for

• To provide minimum steam flow from the boiler during start up, shutdown & sudden load cut off
• It is used to manual relieve of excess pressure
• Used to give excess flow for temperature rising during start up or partial loads
• Used to take excess load on boilers during peak load test

6-Why the super heater safety valve is set at lower pressure than drum safety valve

If drum safety valves set at lower pressure, then there will be very less or no steam flow to super heaters.

In order to save super heater coils from starvation due to no flow of steam during steam blow from drum safety valves, the super heater safety valves are always set at lower pressure than drum safety.

7-Why LHS/RHS water wall panels expand more (towards down) than front & rear water wall panels?

Side water panels are usually straight hence expansion readings show more value  where as front & rear water wall panel will have bends.

8-Why pressure gauges fitted at boiler firing floors show more pressure than actual (that of fitted at steam drum EL.level)

Pressure gauges show 2 to 3 kg/cm2 higher pressure due to addition of hydraulic head in PG impulse line laid from actual location to firing floor

9-Why there is a pressure difference between main steam line pressure & drum pressure?

Main steam line pressure shows lower pressure than drum pressure due to pressure loss in super heater coils. And this pressure difference increases as the number of super heater coils & steam flow increase.

10-Why do high pressure Boilers have higher efficiency & lower fuel consumption?

Because:

1-High pressure boilers have higher  saturation temperature

2-High pressure boilers have higher feed water temperature at economiser inlet

3-High pressure boiler have lower enthalpy of evaporation (latent heat)will be less

H = Hf + Hfg + Cps x (Tsup-Tsat) -

Where,

Hf = Enthalpy of liquid at operating pressure

Hfg = Latent heat

Tsup = Suepr heated steam temperature

Tsat = Saturated temperature of steam

Example:What amount of heat would be required to produce 5000 kg of steam at a pressure of 65 kg/cm2 and temperature 485 °C from water at temperature 175 °C?

Steam pressure P = 65 kg/cm2

Steam temperature Tsup = 485 °C

At above parameters, saturated temperature Ts = 282.7 °C

hf = 298.82 kcal/kg, hfg = 364.47 kcal/kg

Now, enthalpy of 1 kg of superheated steam

Hsup= hf + hfg + Cps (Tsup - Ts)

hsup = 298.82 + 364.47 + 0.5 X (485 - 282.7)

hsup = 764.44 kcal/kg

Amount of heat already associated with 1 kg of water = 1 X 1 X (175 – 0) X 175 kcal/kg

Therefore net heat to be supplied per kg is 764.44 – 175 = 589.44 kcal/kg

11-Why there is more CO in flue gas?

More CO in flue gas is due to improper combustion, that is due to

• Less excess air
• In adequate turbulent
• Lower furnace/bed temperature
• Higher FC in fuel

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12-Why Does boiler furnace pressure fluctuate?

• Interrupted fuel flow
• Leakage in boiler pressure parts
• Furnace combustion controller not working properly
• Malfunctioning of fans pneumatic dampers
• Higher moisture in fuel

13-Why there is more NOX in flue gas?

• Higher NOx is due to
• Higher bed temperature or furnace temperature
• Higher excess air
• More N2 in fuel

14-Why there is no Temperature gauge (TG) is fitted on steam drum of any Boiler?
In steam dream the phase of water is at saturated state, so no any necessary of providing TG. However temperature gauges are provided at drum inlet feed water line & drum outlet saturated line.

In some drums whose thickness is > 100 mm, there you may find thermo couples for measuring skit temperature. So in order to avoid  weakening of steam drums due to making number of drill holes for unnecessary instruments, the TG is not generally provided for drums.

For example if  drum PG showing  pressure 110 kg/cm2, then its temperature will be around 320 deg c. (Refer steam table for saturation temperature). And generally not used in any calculation or performance analysis, if required one can refer steam tables for saturated water

The temperature gauge or thermo couple provided at the drum outlet lines is used during plant start up.

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50-Interview questions & answers on centrifugal pumps

 

1. What are the centrifugal pumps?

Centrifugal pumps are the mechanical devices which pump or transport various fluids by converting their rotational kinetic energy into hydrodynamic energy.

2. Why the name centrifugal pump?

A centrifugal pump uses centrifugal force

3. Where the centrifugal pumps find applications in power plants? 

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• Boiler feed water pump 
• Auxiliary & main cooling water pumps 
• Raw water transfer pumps  
• Condensate extraction pump,  
• Deaerator & feed water tank make up pumps 
• Firefighting water pumps 
• UF & RO feed water pumps 
• MGF feed pump 
• Degassed water transfer pumps 
• Sometimes lube & control oil pumps 

4. How do you specify the centrifugal pumps? 

Centrifugal pumps are specified as bellow 

• Flow in M3/Hr or M3/sec 
• Head or discharge pressure in meter or bar or kg/cm2 
• Shutoff head 

5.What are the various parts of centrifugal pumps? 

Centrifugal pumps have following parts 

• Pump casing or diffuser 
• Impeller 
• Wear ring 
• Shaft 
• Lantern ring 
• Stuffing box 
• Inlet vertex 
• Mechanical seal or gland packing 
• Shaft sleeve 
• Bearings 

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6.What are the energy conversions take place in centrifugal pumps 

In centrifugal pumps hydraulic energy is being converted into kinetic energy  

7.What types of reducers are used at pump suction & discharge ends? 

Suction side: Eccentric type & Discharge side: Concentric 

8.What are the two main types of centrifugal pumps?

Axial flow & Radial flow

9.What is the function of impeller in centrifugal pumps?

It converts kinetic energy of pump into hydrodynamic energy by rotary motion

10.What is the function of pump casing?

Casing converts velocity head from impeller into pressure head & also guides the flow to the discharge end.

11. What are the types of pump casing?

Volute & diffusers are two different types of pump casing

12. What do you mean by volute?

A volute is a spiral-like geometry with an increasing through-flow area, reducing the velocity of the fluid and increasing the static pressure

13. What are the different types of volutes?

Single volute & Double volute

15. Write down the working principle of centrifugal pumps

In centrifugal pumps, fluid enters the impeller through inlet eye & exists along the circumference between the vanes of impeller. This impeller is connected to shaft & in turn to motor, this rotary motion of the impeller converts kinetic energy of the fluid into hydrodynamic energy.

16.What are the types of impellers?

Open impeller: As its name suggests, an open impeller has vanes that are open on both sides without any protective shroud. These are structurally weak.

These are used for low flow & low head applications. Generally used for pump solids or sludge. These require much NPSH.

Semi open impeller: Semi-open impellers have a back-wall shroud that adds mechanical strength to the vanes.

Closed impeller: Are very robust & require low NPSH

Impellers are also classified as single suction & Double suction

17.What are the rotary & stationary parts of the pumps?

Rotary parts:

• Shaft
• Impeller
• Shaft sleeve
• Bearings

Stationary Parts

• Pump casing
• Gland packing or mechanical seal
• Lantern ring

18.Why eccentric reducers are used at pump suction side? 

To avoid air locking & cavitation eccentric reducers are used at suction side 

19. What do you mean by the NPSH in pumps? 

It is the net positive head required at pump suction to avoid cavitation 

20. What do you understand by the term cavitation? 

Cavitation is the formation & collapsing of vapor bubbles at pump’s suction 

21. How the cavitation does affect the pump’s life? 

• Cavitation causes 
• Vibrations in pump 
• Damage of impellers 
• Heavy noise 

22. What are the factors considered for centrifugal pumps design? 

• Flow required 
• NPSH available & NPSH required 
• Total head 
• Pump efficiency 
• Fluid used 

23. What are the materials used for pump casing? 

Generally cast steel or cast iron are used for single stage centrifugal pumps 

24. What are the materials used for Impellers? 

Impellers are made up of cast iron, gun metal & stain less steel 

25. What is the function of wear ring? 

As the name indicates it protects the wear & tear of impeller 

26. What do you mean by static suction head in pump?

Therefore, the static suction head is the vertical distance from the center line of the pump to the free level of the liquid to be pumped.

27. What do you mean by static suction head in pump?

Static discharge head is the vertical distance between the pump centerline and the point of free discharge or the surface of the liquid in the discharge tank.

28. What do you mean by total static head?

Total static head is the vertical distance between the free level of the source of supply and the point of free discharge or the free surface of the discharge liquid.

29. What do you mean by total head?

It is total dynamic discharge head plus total dynamic suction head

Note: If source water level is below the pump center line, then

Total head = Discharge head Suction lift

If source Water level is above the pump suction line, then

Total head = Discharge head-Suction head

30. What are the problems associated with centrifugal pumps? 

Following are the common problems associated with pumps 

• Low discharge pressure 
• Low delivery 
• Cavitation 
• High vibrations 
• Pump seize 
• Over load 
• More suction lift 
• Air locking & No priming 

 31. What are the reasons for no delivery or no discharge in centrifugal pumps?

•  Probable reasons are
• Air lock in pump suction
• Suction valve closed
• Low tank level
• 32. What are the reasons for low delivery?
• Suction valve partially opened
• Reverse rotation of pump
• Low speed of pump
• Suction strainer is chocked

 33. What are the reasons for over load of pump?

•  More flow
• High speed
• Reverse rotation of pump
• Pump discharge kept open to atmosphere
• Internal friction in impeller & wear ring or impeller & casing
• More tightened gland packing
• No lubricant in bearing or bearing seized

 34. What are the potential reasons for pump vibrations?

•  Overloading of pump
• Reverse rotation of pump
• Impeller rubbing inside the casing
• Misalignment
• Damaged bearing
• Shaft run out
• Shaft imbalance

 35. Too much noise coming from pump inside, what does this mean?

•  Air lock in pump
• Overloading of pump
• Pump discharge line is less than actual required
• Cavitation
• No lubricant in bearings

 36. What are the common mistakes done during pump installation?

• Choosing poor foundation
• Note: Pump foundation weight should be 3 to 4 times the pump weight
• Lesser size suction pipe line
• Lesser size discharge pipe line
• Interchanging concentric & eccentric reducers

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37. What are the safety protections & interlocks given for a centrifugal pumps?

• Over load
• Low load
• High bearing vibrations
• High bearing temperature
• High suction DP
• Source water level low

38. How do you increase the head & flow of pump by modifying impeller size?

By increasing the impeller diameter head & flow can be increased

By increasing the impeller width flow can be increased

 39. What are the reasons for reduction of pump efficiency?

• Operating the pump at lower capacity
• Operating the pump at higher load
• Throttling the discharge valve
• Increase in impeller & wearing clearance
• Lower suction head
• High suction lift

Calculation part

 40. How do you calculate NPSHA?

 NPSHA is Net positive suction available

NPSHA = Atmospheric pressure + static head - vapor pressure - pressure loss in the suction piping - pressure loss due to the suction strainer.

 41. A centrifugal pump of rated capacity 75 M3/Hr & total head 35 meter is supplying water to fill a tank in 2 hours, calculate the total power consumption. Consider pump & motor efficiency 50% & 85% respectively

 Power consumption = Pump flow in m3/sec X Pump total head in meter X fluid density X g / (1000 X Pump eff. X Motor eff)

Power consumption = (75/3600) X 35 m X 1000 kg/m3 X 9.81m/s2 / (1000 X 0.5 X 0.85)

Power consumption = 16.83 KWH

Power consumption in 2 hours = 16.83 X 2 = 33.66 KW

 42. A centrifugal pump having hydraulic power 22 KWH, discharge & suction head 55m & 12m respectively

Calculate the pump flow in m3/hr, assume density of water 990 kg/m3

Pump flow = Pump hydraulic power X 1000 / (Pump total head X density of fluid kg/m3 X 9.81 m/s2)

Pump flow = 22 X 1000 /( (55-12) X 990 X 9.81)

Pump flow = 0.052 m3/sec

Pump flow in M3/hr = 0.052 X 3600 = 189.6 M3/hr

 43. A centrifugal pump having hydraulic power 15KWH & pump efficiency 65% calculate the pump shaft power

 Pump shaft power = Pump hydraulic power / Pump efficiency = 15 / 0.65 = 23 KW

 44. A centrifugal pump produces flow 20M3/hr (Q1) flow at rated speed 1500 RPM (N1) , then calculate the flow of pump at 1000 RPM(N2)

 We have pump affinity law

 Q1/Q2 = N1/N2

20 / Q2 = 1500 / 1000

Q2 = 13.33 M3/hr

45. A centrifugal pump consumes power of 25KW (P1) at speed of 1500 RPM (N1), after reducing certain RPM its power consumption reduces by 5 KW (P2), calculate that speed

 We have pump affinity law

 P1/P2 = (N1/N2)3

25 / 5 = (1500 / N2)3

N2 = 877.2 RPM

 46. A centrifugal pump produces 150 m (H1) head at 3000 RPM (N1), calculate the head produced if its speed reduced to 50%

We have pump affinity law

H1 / H2 = (N1/N2)2

N2 = N1 X 50% = 3000 X 0.5 = 1500 RPM

150 / H2 = (3000 / 1500)2

H2 = 37.5 meter

47. A centrifugal pump having impeller diameter 250 mm produces flow 250 M3/hr, calculate the diameter of impeller to produce flow 300 M3/hr

We have

Q1 / Q2 = D1 / D2

250 / 300 = 0.250 / D2

D2 = 0.35 m = 350 mm

48. A centrifugal pump having impeller diameter 300 mm produces 250 m head & what could be the diameter if we want to reduce the head by 30m

Reduced head = 250 – 30 = 220 m

We have

H1 / H2 = (D1/D2)2

250 / 220 = (300 / D2)2

D2 = 281.4 mm

49. A centrifugal pump having impeller diameter 150 mm (D1) consumes 15 kw (P1), what is the size of impeller if we want reduce power by 4 KW

P2 = P1-4 = 15-4 = 11 KW

We have

P1 / P2 = (D1 / D2)3

15 / 11 = (150 / D2)3

D2 = 135.2mm

 

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