Mastodon Power plant and calculations

Top-14 reasons for Boiler Tubes failure

 

        What are the potential reasons for Boiler Tube failure??

Following are the direct causes for Boiler tubes or pressure parts failure.

1-Operation of the Boiler at higher pressure:

Boiler pressure parts are designed to operate at particular pressure for continuous operation. If they are being operated at higher pressure than recommended, leads to failure of pressure parts may be at welding joints or even at plain surfaces.

Boiler pressure parts lose their strength as they become older and older.

As per IBR-7, Boiler operating pressure should be reduced by 5% after 25 years of operation. That is A boiler operating at 109 kg/cm2 pressure should be operated at 103.55 kg/cm2 after 25 years.

Boiler operating pressure reduction chart

Age of the Boiler (From the date of first use in years

25

35

45

50

60

70

80

90

100

% of reduction in working pressure

5

10

15

20

30

40

50

60

70

 

2-Operation of the Boiler at higher temperature:

Operation of the Boilers at Higher temperatures can cause metallurgical weakening of the tubes, leading to deformation, cracking, or rupture. Continuous exposure to high temperatures causes creep, where the metal elongates and loses strength over time.

Rapid or excessive temperature variations cause thermal expansion and contraction, leading to cracks. Operation of the Boilers at higher temperature can also increase internal scaling.

3-Pressure parts or tubes internal scaling:














Poor quality of DM water can lead to internal scaling, this internal scaling of tubes results into poor heat transfer subsequently overheating and tube failure.

Calcium, Magnesium & silica present in water if not treated well can form hard scales on pressure parts internal surfaces.

Operation of the High Boiler at lower pH (< 8) for long time eventually leads filure of pressure parts.

In sugar-based cogeneration plants, there is the chance of entering sugar traces in process return condensate. Due to this, pH of feed water drops ( up to 6) quickly and result into tube failures.

Operation of the high-pressure Boiler at pH around 5 to 6 results into tubes failure in just 3 to 5 hours.

4-Over heating of tubes:

Over heating of pressure parts due to wrongly set burners, air and internal scaling, poor water circulation & soot build up leads into tubes failure.

5-Erosion of tubes:































Erosion of pressure parts is mainly due to high flue gas velocity, bed materials in case of AFBC & CFBC boilers and even due to high velocity of steam and water.

So, ensuring right flue gas velocity at various locations of the Boiler is Vital to take care of erosion of pressure parts.

In case of AFBC & CFBC Boilers, bed coils (Evaporator & Super heaters) and water wall tubes erode due to bubbling beds.

Wrongly designed economiser, evaporators tubes and super heaters coils may suffer from erosion due to high velocity of water and steam. Usually, steam/ water velocity increases due to under sized tubes/coil or operation of the Boiler at over load.

Velocity of the fluid increases as the size of the tubes decreases.

Velocity (m/sec) = Flow (m3/sec) / Area (m2)

Based on above relation, velocity of the fluid increases as the Area of the tubes/pressure parts decreases and Flow increases.

Read>>>Boiler interview questions & Answers

6-Fatigue Failure:

Repeated thermal and mechanical stress due to frequent start up and shutdown cycles, frequent load variation leads to thermal shocks & failure of pressure parts.

7-Chemical cleaning of The Boilers internals:

Excessive use of chemicals especially acids during Boiler chemicals cleaning leads to Pressure parts failure during operation.

8-Stress & corrosion cracking:

Tubes fail due to corrosion, corrosion is mainly due to low pH, dissolved oxygen and other impurities in water which lead to pitting and weakening of the tubes. If Boilers are being operated in such conditions pressure parts go into failure.

9-Poor welding joints:

If welding joints quality is poor i.e if No standard welding procedure was followed during installation stages the joints fails upon small variation load or during abnormal operations.

Joints fail in following cases;

1-Poor welding techniques followed

Read>>>>> What is the significance of post weld and Pre-weld heat treatments (PWHTs)?

2-Poor skill of welder

3-Selecting wrong electrodes etc

4-Wet atmospheric condition

10-Poor operations:

What are the poor operation methods which lead to failure of pressure parts>>>>>??

Boiler pressure parts failure largely depends on Boiler operation skills of the operators.

Pressure parts may fail in following poor operation techniques

1-Not following Boiler start up procedures

2- Not following Boiler shut down procedures

3-Quick start-up of the Boiler, not following the Boiler start up curve

4-Not operating the vents & drains as per requirement or SOP

5-Sudden load variation

6-Operating the Boiler by ‘Bypassing the Boiler protections & Interlocks’.

7-Not providing minimum circulation steam to Boiler during start-ups, shut downs or even in case of ab normal operations.

Not knowing the function of ‘start up vent’ is the main reason for super heater coils failure during Boiler shut downs or low load operations.

Start up vent is used to provide minimum required flow to the Boilers during start-ups, which helps in cooling the super heater coils during No load operations

8-Operating the Boiler on low drum levels or not taking the quick shut downs if there is no water flow into the Boiler.

9-Wrong operation of attemperator. Sudden opening and closing of attemperator valves lead to thermal shocks in super heaters.

10-Operating the Boiler at higher drum levels. Operating the boiler at higher drum levels leads to carryover of wet steam or water into super heaters, which leads to thermal shock & tubes failure.

11-Giving water wall bottom headers blow down at high steam rate: This leads the starvation of water wall tubes.

12-Wrongly set safety valves & higher blow down percentage of safety valves:

In a Boiler, if drum safety valves pop up frequently before popping up of super heater safety valves, then it leads to the starvation of super heater coils and even failure.

12-Hydrogen damage:








Reaction between steel and water at high temperatures produces atomic hydrogen, which diffuses into the metal & leads to embrittlement and cracking, resulting in a fish mouth rupture.

13-Un even thermal expansion of pressure parts:

Un even of thermal expansion of Boiler tubes due to not following Boiler start up curves & start-up/Shut down procedures or restriction to thermal expansion lead to cracks or failure of joints of pressure parts.

 

Read>>>Why does the thermal expansion occur in Boilers??

14-Metallurgical defects:

Poor quality of metals used for manufacturing of Boiler pressure parts lead to failure of pressure parts during operation.

What are the main reasons for Boiler tubes ‘fish mouth’ opening??
























Fish mouth openings are catastrophic failures in Boilers, It’s a type of rupture where the tube bursts open, resembling a fish's mouth. This failure is highly dangerous and usually indicates severe operational or maintenance issues. The main reasons for a fish mouth opening in boiler tubes are:

Following are the major reasons for Boiler tubes ‘fish mouth’ opening.

1-Short term over heating: Occurs due to localized overheating when tubes are exposed to direct flame or high temperatures without sufficient cooling

2-Internal scaling

3-Operation of the Boiler with low water level

4-Starvation of super heater coils & water wall tubes

5-Hydrogen damage

6-Erosion of pressure parts, mostly in case of AFBC & CFBC Boilers.

7-Operation of the Boiler at higher pressure & Temperature than recommended.

8-Over heating.


Read more>>>>power plant and calculations

 

How to calculate the specific fuel consumption of Power plant??





Specific Fuel Consumption (SFC) in Power Plants refers to the amount of fuel required to generate a unit of energy output. It is a key performance metric used to assess the efficiency of different power generation systems.

Specific fuel consumption (SFC)= Fuel consumption in kg/hr / Power generation in Kwh

Specific fuel consumption (SFC)= Specific steam consumption (SSC) / Steam to fuel ratio (SFR)

Factors affecting the Specific fuel consumption:

1-Steam consumption of the Turbine: Higher steam consumption of steam Turbine leads to more Specific fuel consumption (SFC).

2-Main steam parameters like pressure & temperature: Should be always on higher side but within design limit.

3-Boiler efficiency: High efficiency boilers consumer lesser fuel and hence Specific fuel consumption (SFC) will be on lower side.

4-Turbine efficiency: High efficiency Turbines will have higher out put on lesser input, hence Specific fuel consumption (SFC) of such Turbines is LESS

5-Fuel type & quality: High GCV fuel firing power plants will have lesser Specific fuel consumption (SFC).

6-Boiler operator competency: Efficient Operation of the Boiler, Turbine and other power plant equipment depends on the skill & competency of the operators.

7-Plant load factor: Operation of the Power plant units on higher loads or optimised loads leads to lower Specific fuel consumption (SFC) & Vice Versa, that is operation of plant on partial loads results into more fuel consumption and hence leads in more Specific fuel consumption (SFC).

8-Atmospheric conditions: Atmospheric conditions like temperature, pressure & humidity play a very vital role on achieving best efficiency of power plant equipment.

Specific fuel consumption (SFC) is also termed in terms of heat rate.

Heat rate = Energy consumed in kcal/ Power generation

It is measured in terms of kcal/kwh

Specific fuel consumption (SFC) is different for different fuels, fuels having higher heating value or calorific value will have lesser Specific fuel consumption (SFC) & fuels having lower calorific value will have higher specific fuel consumption.

It’s always recommended that Specific fuel consumption (SFC) should LESS.

Power plants having lesser Specific fuel consumption (SFC) are in more profit.

How to calculate the specific fuel consumption???

Specific steam consumption (SSC) is the amount of steam consumed by Turbine is always lesser to achieve lesser Specific fuel consumption (SFC). It’s measured in kg/kwh or MT/MW.

Similarly, Stam to fuel ratio (SFR) is the amount of steam generated on burning 1 MT or 1 Kg of fuel. It’s measured in kg/kg or MT/MT.

Examples:

1-Calculate the specific steam consumption of a 50 MW thermal power plant, which consumes around 960 MT of coal to generate 1200 MW power.

Given data,

Power generation = 1200 MW

Fuel consumed = 960 MT

Specific fuel consumption (SFC)= Fuel consumption in kg/hr / Power generation in Kwh

Specific fuel consumption (SFC)= 960/1200 =0.8 kg/kwh or 0.8 MT/MW

2-A 225 MW Thermal power plant’s steam turbines Specific steam consumption (SSC) is 3.5 MT/MW and it’s Boiler’s Steam to fuel ratio (SFR) is 4.5. Calculate the specific steam consumption of that plant

Given data,

Specific steam consumption (SSC) = 3.5

Stam to fuel ratio (SFR) = 4.5

Specific fuel consumption (SFC)= Specific steam consumption (SSC) / Steam to fuel ratio (SFR)

Specific fuel consumption (SFC)= 3.5/4.5 =0.78 Kg/kwh or 0.78 MT/MW

3-A Boiler consumes 25 MT of bio mass to generate 55 MT of steam per hour at pressure 67 kg/cm2 and temperature 490 deg C, which is used to run the 12 MW condensing Turbine. What would be the specific fuel consumption of this plant?

Given data,

Fuel consumption = 25 MT

Steam generated = 50 TPH

Power generation = 12 MW

Steam to fuel ratio (SFR) = Steam generated per hour / Fuel consumed per hour

Steam to fuel ratio (SFR) = 55 / 25 =2.2

Specific steam consumption (SSC) = Steam consumption by Turbine TPH / Power generated in MW

Specific steam consumption (SSC) = 50 / 12

Specific steam consumption (SSC) = 4.16 MT/MW

Specific fuel consumption (SFC)= Specific steam consumption (SSC) / Steam to fuel ratio (SFR)

Specific fuel consumption (SFC)= 4.16 / 2.2 =1.89 MT/MW


Read more on>>>power plant and calculations

12-troubleshooting guide for Boiler Feed Pumps (BFP)


 

                           








                       12-troubleshooting guide for Boiler Feed Pumps

SL No.

Problem

Root cause

Remedy/Action to be taken

 

 

 

 

 

 

 

  

 

1

 

 

 

 

 

 

 

 

 

High bearing vibrations

 

What are the reasons for high bearing vibration in Boiler feed pump (BFP)

More clearance in bearing

Maintain bearing clearance within the limit as recommended by OEM

Contaminants/burs in oil

Replace the oil

Pump operation in re circulation mode for long time.

Operate the pump at the flow > 30% of rated capacity

Pump should not be operated more than 30 min in recirculation mode

Miss alignment for axial vibrations

Check & correct the alignment

Looseness in foundation bolt or coupling bolts for vertical vibrations

Tighten the bolts

Imbalance for horizontal vibrations

Check & conduct balancing test at OEM shop

Over load operation

Operate the Turbine at or within its maximum capacity

Looseness in impeller

Inspect the pump thoroughly & rectify the errors in impeller fitment

Malfunction of the vibration sensor

Get confirm the high bearing vibrations are due to malfunction, if confirmed ensure tightness of all connections.

 

 

 

 

 

 

2

 

 

 

 

 

 

High bearing temperature (Journal)

 

What are the reasons for high bearing temperature in BFP?

Low lube oil level

Check for any leakages, if there arrest the leakages

Top up the oil.

High lube oil temperature

Check for cooling water flow, remove the blockages if any.

Over load operation

Operate the pump at or within rated flow

Less clearance in bearing

Maintain bearing clearance within the limit as recommended by OEM

Malfunction of the temperature sensor

Get confirm the high bearing vibrations are due to malfunction, if confirmed ensure tightness of all connections.

 

 

 

 

    3

 

 

 

 

Cavitation/abnormal sound

 

What are the reasons for cavitation in Pumps?

Low suction pressure

Check the reason for low suction pressure & Normalise

High feed water temperature at pump’s suction

Reduce the steam flow to deaerator & maintain the suction temperature as pre-design pressure. If pump suction pressure is low, it may reach the vapour temperature leading into steam formation inn pump.

Low deaerator level

Normalise the deaerator flow by increasing make up water or process return condensate.

Low deaerator operating pressure

Increase & maintain the Deaerator pressure as per rated pressure

Low suction water

1.Check for suction valve throttling & increase the suction water flow

2.Check for clogging of pump strainer due to any foreign materials.

High flow

Reduce the flow & maintain as per OEM design.

 

 

 

 

 

 

    4

 

 

 

 

 

 

More Balance leak off pressure

 

What is the reason for more balance leak off pressure in BFP?

Worn out balance discs

Inspect & replace the discs

More clearance in balance & counter balance discs

Inspect & adjust the clearance as per OEM manual

More suction pressure

Maintain the suction pressure as per OEM recommended

Blocked balance leak off pressure impulse line

Check & clear the line

Read>>>Boiler feed pumps SOP

Higher pump discharge pressure

Maintain the discharge pressure as per OEM recommended

High discharge flow

Maintain the discharge flow as per OEM recommended

Faulty pressure gauge

Replace the pressure gauge

 

 

 

 

 

 

 

    5

 

 

 

 

 

Low Balance leak off pressure

 

What is the reason for less balance leak off pressure in BFP?

Less clearance in balance & counter balance discs

Inspect & adjust the clearance as per OEM manual

Improperly fitted balance discs

Inspect & adjust the clearance as per OEM manual

Low suction pressure

Check & increase the suction pressure

Low discharge pressure

Check & ensure the correct discharge pressure

Leakages in balance leak off line

Arrest the leakages

Faulty pressure gauge

Replace the pressure gauge

 

 

 

 

 

 

   6

 

 

 

 

 

 

Pump overheating

 

What is the reason for pump over heating?

High feed water temperature

Maintain the feed water temperature as per design

Operating the pump at higher flow

Optimise the discharge flow

Operating the pump at flow < 30% of rated

1.Increase the flow beyond 30%

2.Do not operate the pump with discharge valve closed for long time.

Low suction flow

Check the strainer & clean

Check the suction valve & ensure it’s open 100%

Cavitation

Ensure suction pressure & temperature are as per design

Bearing failure

Replace the bearing or maintain the clearance

Continuous operation of the pump

Follow pump change over schedule.

 Boiler feed pumps SOP

Internal rubbing due to improper thermal expansion

1.Ensure uniform expansion of pump.

 

2.Do not start pump as soon as hot water induced into it. Allow it for some times for uniform thermal expansion.

 

 

 

 

 

 

 

 

 

 

 

 

 

   7

 

 

 

 

 

 

 

 

 

 

 

 

 

Journal bearing failure

 

What is the reason for BFP pump bearing failure??




No lubrication

1.Ensure proper oil level.

2.Follow lubrication & lubricant replacement schedule.

Insufficient cooling & operation of the pump at higher bearing temperatures

1.Ensure bearing temperature is in the range of 50 to 70 deg C.

2.Ensure proper cooling water is flowing in & out of the bearing cooling jacket.

Operating the pump at lower speed for long time

Ensure the pump will be operated at speed >80% to ensure proper splitting of lubricant oil to bearing liners

Starting of the pump at lower speed

Always start the pump at speed reference > 50%

Ensure pump will attain its 50% speed (1500 rpm) in initial 10-12 seconds, this will protect the bearing from lack of lubrication at initial lower speed.

Frequent start & stop of the pump

Ensure pump will not be started or stopped frequently

Starting of the pump with discharge valve opened

Never start the pump with discharge valve open to avoid sudden jerk load to the pump, which not only damages the bearing even harms pumps internals, coupling & motor

Stopping of the pump with discharge valve opened

Never stop the pump with discharge valve open to avoid sudden jerk load to the pump, which not only damages the bearing even harms pumps internals, coupling & motor

Boiler feed pump SOP

 

 

 

    8

 

 

 

Insufficient discharge flow or pressure

 

What is the reason for low discharge or low discharge pressure from Boiler feed pump?

 

Pump is running on partial load or lesser speed

Increase the speed

Discharge valve throttled

Ensure 100% opening of the discharge valve

Suction valve throttled

Ensure 100% opening of the suction valve

Air lock

Ensure proper priming of the pump. Keep open drain/vent provided at suction strainer for 3 sec.

ARC (Automatic recirculation) valve stuck or passing

Servicing of the ARC valve

 

 

 

    9

 

 

Frequent tripping of pump during start up

 

Why does the pump trip during start up?

Discharge valve Open

Close the discharge valve & start the pump

Pump jam

1.Ensure proper lubrication

2.Ensure uniform thermal expansion

Electrical related problems

Check at Motor & Panel side and rectify the identified problems

  

 

 

 

  10

 

 

 

Excessive Noise & Vibration

 

What are the reasons for excessive noise & vibrations in pumps?

Cavitation in pump

Ensure suction pressure & temperatures are normal

 

Pump air lock

Ensure proper priming of the pump

Bearing damage/worn out

Inspect and replace if needed

Internal rubbing

Inspect & replace damaged internals

Pipe lines vibrations

Inspect supports & rectify if required

 

 

 

 

  11

 

 

 

 

Mechanical seal leakage/Gland leakage

 

What are the reasons for Mechanical seal failure in pumps?

Improper installation

Check & reinstall the seals

Seals parts damaged

Check the root cause & replace the damaged parts

Frequent start & stop of the pump

Ensure pump will not be started or stopped frequently

Worn out shaft sleeve

Replace the sleeve

Jerk loads on seals

Ensure discharge valve is closed before starting or stopping of the pump

 

 

 

 

  12

 

 

 

 

Pump consuming more power

 

What are the reasons for more power consumption by Boiler feed pumps?

Automatic Recirculation Valve (ARC) passing

Get done the overhauling of valve

Bearing friction

Maintain required clearance in bearing

Internal rubbing

Replace the worn-out parts

Lesser efficiency of coupling & motor

Replace the worn-out couplings

Verify motor load & efficiency

Higher flow

Ensure pump is delivering flow as per design

Lower pump efficiency

1-Check pump hydraulic power

2-Check fluid temperature & suction pressure and ensure both are as per design.

3-Ensure pump’s discharge pressure is as per design

 











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