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


How to calculate steam & water pipe line size???

 









What are the factors needed to calculate steam & water pipe line sizes?

Quantity of maximum & minimum flow through the line

Pressure & temperature of the fluid

Pressure drop allowed

Velocity of the fluid in pipe

Density & specific volume of the fluid

How do you measure the steam flow through the pipe?

Steam flow is measured with the help of orifice plate, flow nozzles etc

How do you measure the water flow through the pipe?

Water flow is measured with the help of orifice plate, vortex meter, Rota meter & turbine meters installed in pipe lines.

What is the importance for calculating pipe line size for particular fluid flow?

To provide correct required flow

To avoid pressure drop of fluid

To avoid starvation

Why the velocity is the important factor while calculating the line size?

Flow = Area of the pipe X Velocity

By looking at the above relation, velocity is the critical & important parameters, as miss judgment of velocity may lead to wrong result.

Fluid having high pressure will be having high velocity & hence require lesser pipe line size & vice versa

And also fluid having lower density will be having high velocity & hence lesser pipe size and vice versa

What are the assumed velocity for various fluids flow?

Velocity of water at the suction of pump = 0.7 to 0.9 m/sec

Feed water flow at pressure 87 kg/cm2 = 2 to 4 m/sec

Saturated steam = 25 to 50 m/sec

Super-heated steam = 30 to 70 m/sec

What will happen if a 6” pipe line carrying hot water at the rate of 100 TPH suddenly contracts to 4”?

Following shall be observed

Velocity in the pipe will increase suddenly

Head or pressure loss will occur

Energy required to pump the water will increase

What are the factors that can cause the pressure drop in a pipe line?

Friction factor of pipe (pipe internal wall roughness)

Length of the pipe

Diameter of the pipe (size of the pipe)

Velocity of fluid in the pipe line

Pipe line fittings like valves, bend, tee etc. present in the pipe line

What are the effects of over sizing the pipe lines?

The cost of pipe lines & related fittings like valves, bend, Tee etc. will increase accordingly

Higher installation cost including pipe line supports & insulations

For higher sized steam pipe lines more condensate will tend to form & hence more number of steam traps are required

For higher sized steam pipe lines, there is more possibility of carryover wet steam to end user

More heat loss due to more exposed heat/hot surface area

What are the effects of under sizing the pipe lines?

For under sized pipe lines low pressure will be available for end user

In steam lines more pressure drop may cause starvation in pipe lines

Chance of erosion

Chance of water hammer & noise

Calculations:

1. Calculate the pipe line size required to pump 100 m3/hr of water at pressure 85 kgg/cm2 to the Boiler.

As discussed in the above theory part, velocity of the feed water at pressure 85 kg/cm2 is around 3 m/sec

Then flow, Q = Area of pipe line in M2 X Velocity in meter

(100/3600) m3/sec = (3.142 X D2/4) X 3 m/sec

D = 0.108 m = 108 mm

Looking at the above value, the pipe line size required should have internal diameter 108mm.

Then pipe line size = Pipe ID + 2 X thickness

For feed water pipe line having above pressure needs minimum 80 schedule, so refer carbon steel pipe line chart & select the required schedule & thickness.

2. Calculate the main steam pipe line size required for connecting Boiler out let steam to distribution header. Maximum steam flow is 125 TPH at pressure 110 kg/cm2 & temperature 540 deg C, assume velocity of steam in pipe line is 52 m/sec

Steam flow = 125 TPH = 125000 kg/hr

Density of steam at pressure 110 kg/cm2 & 540 deg C = 32 kg/m3...Refer steam table

Steam flow in m3/sec = 1250000 / (32 X 3600) = 1.08 m3/sec

We have,

Q = AV

1.08 = A X 52

A = 0.02 M2

A = 3.142 X D2/4

0.02 = 3.142 X D2/4

D = 0.159mm = 160 mm

So need pipe line of internal diameter 150 mm

Note: Outer diameter of the pipe line is standard, need to select schedule based on operating pressure & temperature to get desired line size.

3-Calculate the velocity of 55 TPH saturated steam flowing in 500 NB pipe line at pressure 1.7 kg/cm2 & 135 deg C

Density of steam at pressure 1.7kg/cm2 & temperature = 1.5 kg/m3

Steam flow in m3/sec = 55 X 1000 / (1.5 X 3600) = 10.18 m3/sec

We have,

Q = AV

10.18 = (3.142 X 0.92/4) X V

V = 15.99 m/sec

Following are the various cases taken as case study for pipe line size

 Case-1

Pressure (kg/cm2)

2.7

Temperature (deg c)

135

Density (kg/m3)

1.4

Flow TPH

135

Flow M3/sec

26.79

Line size-mm

800

Area M2

0.50

Velocity m/sec

53.28

 Case-2

Pressure (kg/cm2)

2.7

Temperature (deg c)

135

Density (kg/m3)

1.4

Flow TPH

160

Flow M3/sec

31.75

Line size-mm

900

Area M2

0.64

Velocity m/sec

49.9

 Case-3

Pressure (kg/cm2)

2.7

Temperature (deg c)

135

Density (kg/m3)

1.4

Flow TPH

80

Flow M3/sec

15.87

Line size-mm

600

Area M2

0.28

Velocity m/sec

56.13

 Case-4

Pressure (kg/cm2)

2.7

Temperature (deg c)

135

Density (kg/m3)

1.4

Flow TPH

40

Flow M3/sec

7.94

Line size-mm

450

Area M2

0.16

Velocity m/sec

49.90

 

 Read Power plant and calculations for all such articles

 

 

How do you calculate the attemperator water consumption in Boilers?

 












1-What do you mean by attemperation?

Attemperation is a method employed for controlling the super-heated steam temperature

Attemperators are used to control the main steam (super-heated steam) temperature in Boilers.

2-What are the two basic types of attemperators?

Spray type attemperator

Surface type attemperator

3-What is the main differences between attemperator & Desuper heaters?

Sl No.

Attemperator

Desuper heater

 

 

 

1

An attemperator controls steam temperature

 

Desuperheater removes whatever superheat there is in steam and reduces the temperature to a point at or nearly at saturation temperature

 

 

 

 

2

Attemperators are generally found in and/or associated with boiler steam, in zones where too high temperature affects something downstream of that point

 

Desuperheaters are used for downstream use of saturated steam

 

 

3

Outlet of the attemperation will be superheated steam only

 

Outlet of desuperheater will be saturated steam

 

 

4

Used in super-heated lines

 

Used in MP or LP steam lines

 

 Read top-6-Power plant O&M books

4-What type of attemperation method is used in modern high pressure boilers?

In modern high pressure boilers variable nozzle and spray type attemperators are generally used

5-What is the percentage of attmepration used in High pressure Boilers?

Generally varies from 8 to 15%

 6-What is the reason behind using stainless steel sleeve inside the attemperator header?

Generally SS sleeves are fitted inside the attemperator header, this sleeve performs following functions.

 

Acts as a thermal barrier, separates hot and cold working elements to mitigate the intensity of thermal cycles experienced by critical components.

Protects steam pipe from thermal shock, helps to improve secondary atomization.

 

7-What precautions should be taken during attemperator liner or sleeve design?

  •  Minimum length of straight pipe upstream of the liner should be three times the pipe diameter.
  • Length of the liner downstream from the spray nozzles should be between 3 and 6 ft, depending on the particular installation.
  • Length of straight pipe downstream of the liner should allow a residence time of 0.067 second for spray water to evaporate before the first elbow.
  • Location of the temperature sensor should be at a distance downstream of the liner that allows 0.2 seconds of residence time to ensure complete mixing of the evaporated water and superheated steam. However, if the mass flow of spray water is greater than 15% of the mass flow of superheated steam, the residence time should be increased to 0.3 seconds.

 8-What factors are considered for designing attemperator?

Following factors are considered:

  • Feed water pressure, flow rate, and temperature at the spray water control valve during various load conditions
  • Locations of temperature sensors at the upstream & downstream ends
  • Water chemistry
  • Residence time of steam & water mixture for sensing temperature at downstream end
  • Type of attemperator spray nozzle
  • Rate of atomization & size of droplets

9-What is the distance of temperature sensors from attemperator spray nozzles?

For proper controlling of steam temperature, the upstream & downstream distance of sensors should be minimum of 5D & 20D respectively for straight pipe, where D is the diameter of attemperator header

 How do you calculate the Attemperator water consumption?

1. An attemperator is used to control the 95 TPH super-heated steam temperature from 425 deg C to 395 deg C by using 110 deg C feed water. Consider the main steam & feed water pressure 87kg/cm2 & 100 kg/cm2 respectively. Calculate the quantity of attemperator water

Given data,

Mass of steam, Ms = 95 TPH

Enthalpy of steam before attemperation at pressure 87 kg/cm2 & temperature 425 deg C, H1 = 762.41 kcal/kg.

Enthalpy of steam after attemperation at pressure 87 kg/cm2 & temperature 395 deg C, H2 = 741.81 kcal/kg

Feed water enthalpy at temperature 110 deg C, Hf = 111.65 kcal/kg

For calculation of attemperator water Mw

We have the relation,

Heat lost by the super-heated steam = Heat gained by the feed water

Ms X (H1-H2) = Mw X (H2-Hf)

95 X (762.41-741.81) = Mw X (741.81-111.65)

Mw = 3.1 TPH

2. A 125 TPH Boiler having variable type attemperator control valve for controlling main steam temperature from 495 deg C to 425 deg C at pressure 67 kg/cm2. The feed water is used for attemperation is 105 deg C, calculate the quantity of water required for de-superheating.

In the above example, Boiler feed pump having head 1000 meter & efficiency 62% supplies attemperator water, then calculate the extra power consumption for attemperation. Consider motor efficiency 95%

Given data,

Mass of steam, Ms = 125 TPH

Enthalpy of steam before attemperation at pressure 67 kg/cm2 & temperature 495 deg C, H1 = 812 kcal/kg.

Enthalpy of steam after attemperation at pressure 87 kg/cm2 & temperature 425 deg C, H2 = 771 kcal/kg

Feed water enthalpy at temperature 105 deg C, Hf = 106 kcal/kg

For calculation of attemperator water Mw

We have the relation,

Heat lost by the super-heated steam = Heat gained by the feed water

Ms X (H1-H2) = Mw X (H2-Hf)

125 X (812-771) = Mw X (771-106)

Mw = 7.7 TPH

For calculation of power required for pumping 7.7 TPH of water, we have

Motor input power = Flow in m3/sec X Total head X Density of water X 9.81 / 1000 X Pump efficiency X Motor efficiency)

Density of attemperator water at temperature 105 deg C = 960 kg/m3

Attemperator flow in m3/sec = 7.7 X 1000 X / (960 X 3600) =0.022 m3/sec

Now,

Motor power = 0.0022 X 1000 X 960 X 9.81 / (1000 X 0.62 X 0.95)

Motor power = 35.17 KW


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Power plant & Calculations

What do you mean by Regenerative system in power plants???

 

Thermal power plants efficiency is in the range of 30 to 40%, the improvement of thermal cycle efficiency can be done either by increasing the inlet steam pressure & temperature or decreasing the turbine exhaust pressure. But improvement of Boiler parameters & decreasing exhaust pressure lead to increase in cost & also have limitations related to metallurgy & risk.

Another way is to increase the thermal efficiency is by using regenerative cycle. This cycle is more efficient than Rankine cycle.

What do you mean by Regenerative process or cycle???

In this process, steam is extracted from turbine at one or more points during steam expansion. This pressure is high, medium & low. Steam after some expansion cycle gets feed water heating ability. Such extracted steam is utilized to heat the feed water going to the Boilers nearer to its saturation temperature. Heating the Boiler feed water temperature ultimately increases the overall thermal efficiency.

How does the increase in feed water temperature increase the overall thermal efficiency??

Increase in feed water temperature at economizer inlet reduces the work done by boiler to generate the steam & hence consumes less fuel. As a thumb rule, on every 6-7 degree C rise in feed water temperature reduces Boiler fuel consumption by 1%.

What are the advantages of Regenerative cycle???

Regenerative cycle helps to increase in power plant thermal efficiency

Amount of steam condensed in steam condenser per KW decreases

Cooling water consumption decreases

Condenser size reduces

Auxiliary power consumption of cooling system reduces

Heat rate of the plant drastically reduces

Due to less fuel consumption load on fuel handling, fuel feeding & Boiler fans decreases & hence saving in plant auxiliary power consumption.

What are the major disadvantages of Regenerative cycle or process?

There are no much disadvantages except the requirement of HP, LP heaters, relating piping & controlling equipments.

What are the major parts of Regenerative cycle?

HP heaters, LP heaters & Deaerator.

What are the HP heaters?

HP heaters are the shell & tube type of heat exchangers situated between Boiler feed pumps & economizer.

The main design purpose of the HP heater is to heat the feed water coming from Boiler feed pump.

 

Why the name HP heater?

Because it I situated in high pressure zone that is at Boiler feed pump discharge feed water circuit

What are the heat transfer areas present in HP heaters?

Main heat transfer zones are

De-super heating zone

Condensing zone

Sub-cooling zone

What is the function of de-super heating zone in HP heaters?

It is separate heat exchanger placed within the shell, its main function is to remove the super heat from extracted steam

What is the function of sub-cooling zone in HP heaters?

It is another separate counter flow heat exchanger placed within the HP heater shell, its main function is to sub cool the condensate formed in condensing zone

What are LP heaters & where they are placed?

The condensate formed in the surface condenser is pre heated to elevated temperature before it goes to deaerator are called LP heaters.

LP heaters are placed between deaerator & ejector or CEP

LP heaters are also having 3 zones as like HP heaters

Why the name LP heater?

LP heaters are placed at low pressure zone from CEP to deaerator hence called LP heaters

Schematic diagram of power plant regenerative system

 














How do you prove that, regenerative cycle will increase the thermal power plant efficiency?

This can be explained by taking an example

Sl No.

Particular

UOM

Boiler-1

Boiler-2

1

Boiler steam generation

TPH

100

100

2

Steam pressure

Kg/cm2

87

87

3

Steam temperature

Deg C

515

515

4

Boiler efficiency

%

69

69

5

Fuel GCV

Kcal/kg

4300

4300

6

HP heater available

YES/NO

Yes

No

7

Feed water temperature at economizer inlet

Deg C

160

110

 

Looking at the above example, both boilers seem to be safe, except Boiler-1 has HP heater that is feed water heater & Boiler-2 has no HP heater.

Based on this we shall calculate fuel consumption of both the Boilers.

Enthalpy of steam at above parameters Hg = 818 kcal/kg

Enthalpy of feed water at temperature 110 deg C, Hf1 = 111kcal/kg

Enthalpy of feed water at temperature 160 deg C, Hf2 = 162kcal/kg

Now we shall calculate the fuel consumption of Boiler-1

Boiler1 = Steam flow X (Steam enthalpy-Feed water enthalpy) / (Fuel GCV X Boiler efficiency)

Boiler 1 =100 X (818-160) / (4300 X 0.69)

Boiler 1 fuel consumption = 22.17 TPH

Boiler2 = Steam flow X (Steam enthalpy-Feed water enthalpy) / (Fuel GCV X Boiler efficiency)

Boiler 2=100 X (818-110) / (4300 X 0.69)

Boiler 2 fuel consumption = 23.86 TPH

Looking at the fuel consumption of both the Boilers, Boiler 1 consumes less fuel as it has HP heater & hence more feed water temperature than Boiler-2

 Less fuel consumption in the sense less heat rate & less heat rate is nothing but more efficiency of the plant

 

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