A boiler is a combination of systems and equipment in which chemical energy is converted into thermal energy, which is then transferred to working fluid, so as to convert it into steam at high temperature and pressure. Corrosion is a relevant problem caused by water in boilers. Corrosion can be of widely varying origin and nature due to the action of dissolved oxygen, to corrosion currents set up as a result of heterogeneities on metal surfaces, or to the iron being directly attacked by the water. While basic corrosion in boilers may be primarily due to reaction of the metal with oxygen, other factors such as stresses, acid conditions, and specific chemical corrodents may have an important influence and produce different forms of attack.

1. IIP201
Study of Corrosion in Boilers
Guru Govind Singh Super Thermal Plant
Presentation By:
Sajeed Mahaboob
2011ME1111
Supervised By:
Er. Tarun Sharma
Asst. Executive Engineer, GGSSTP, PSPCL
13-10-2015 1

2. Introduction
• Location – Rupnagar, Punjab, India
About 50 km from Chandigarh on Chandigarh-Nangal highway NH-
21 near Ghanauli railway station.
• Super Thermal Plant?
• What was the need of a power plant?
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3. Salient features of GGSSTP
1. No. of Houses 6
2. No. of Units 6
3. Total Generator Capacity 6×210 MW = 1260 MW
4. Source of Water Supply From Nangal Hydel Channel
5. Fuel used Coal from coal fields of Bihar, West Bengal &
Madhya Pradesh
6. Turbine 210 MW 3 Cylinder mixed flow tandem coupled
3000 rpm BHEL make.
7. Generator 247 MVA, 15.75 KV, 9050 A at 0.82 lag, 50 Hz,
double star two pole
8. Total energy contribution annually 6942 MUs
9. Cost per unit Rs. 1.8413-10-2015 3

4. Typical power plant layout
https://en.wikipedia.org/wiki/Super_thermal_power_station
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5. Main Parts of the Plant
• Coal Handling
• D-M Water Plant
• Boiler
• Turbine
• Generator
• Transformer
• Ash handling
• Switchyard
• Control room
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6. Working principle
• Coal based thermal power plant works on the principal of Modified
Rankine Cycle.
• The Rankine cycle is a model
that is used to predict the
performance of steam engines.
• The Rankine cycle is an idealised
thermodynamic cycle of a heat
engine that converts heat into
mechanical work.
https://en.wikipedia.org/wiki/Rankine_cycle13-10-2015 6

7. Internship
• Our internship was based on the understanding the working of
following departments:
1. Feeder Section
2. Boiler Section
3. Fly Ash Section
• The project assigned to us was ‘Study of different reasons of corrosion
in the boiler’
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8. Coal Handling
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9. Coal Feeder Section
• Coal consumption for one unit per day - 3000 ton
• Each raw coalbunker has capacity of 680 tons
• Total 6 units in the coal feeder section
• XRP 803 mills (4)
• HP 08 mills (2)
• Each unit has 6 bowl mills (total 36)
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10. Overview of coal handling plant
http://www.pspcl.in/docs/gurugobind.htm
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11. Coal handling plant functions
• Unloading of coal wagons.
• Reclaiming of crushed and uncrushed coal.
• Coal crushing.
• Removal of unwanted particular from the coal.
• Coal feeding to the raw coalbunkers of running units.
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12. Wagon Tippler
• A rake is a train containing about 58-60 wagons.
• Each wagon contains about 58 tons of coal.
• Equipment's Used
• Water Sprinkler System
• Dust Extraction System
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13. W/T Drive System
www.slideshare.net/shrikant.khating/coal-handling-plant-chp
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14. Layout
www.slideshare.net/shrikant.khating/coal-handling-plant-chp
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15. Crush House
Two Stage Crushing System is used in Plant.
Primary Crusher (Double Roll Crusher)
Secondary Crusher (Rotary Breaker Crusher and Impact Crusher)
W / T
DRCR RBCR Impact
250 mm 80 mm
600 mm
20-25 mm
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16. http://www.paulsengineering.com/double-roll-crusher-555231.html
Double Roll Crusher
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17. Rotary Breaker Crusher
http://terrasource.com/equipment/bradford-breakers-by-pennsylvania-crusher-brand
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18. Impact Crusher
http://minyu.com/content/products.php?act=detail&c_id=1813-10-2015 18

19. Raw Coal Feeders (Bowl Mill)
• Coal is pulverized in the bowl mill (grounded to a powder form).
• Two types
XRP 803 mills (4)
HP 08 mills (2)
• The basic features of Bowl Mill (Pulveriser) supplied by BHEL are:
Medium speed range of 40 to 60 rpm
Input coal size is 25 mm while output is 65-75 micron
Crushing of coal by replaceable bull ring segment and grinding rolls
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20. Raw Coal Feeders (Continued…)
• Speed reduction by two method :
single stage worm & worm wheel set
Planetary Gear Box
• Working Principle :
• Raw coal gets ground between the grinding rolls and bull ring
segments installed on the revolving Bowl.
Springs exert necessary pressure on rolls for grinding.
• Hot air through the mill picks up the lighter particles and takes
them through the classifier(also removes coal moisture)
Fine coal air mixture leaves the mill and enters the fuel piping
system.
• Tramp iron pieces which are not required to grind, leave the Bowl
due to centrifugal force and are removed through the reject removal
system.
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21. XRP 803 mill
XRP803:
Itstands for
X - Frequency of power supply (50 cycles /sec)
R - Raymond,theinventor of bowl mills.
P- Pressurizedtype, withprimary air fancomingbeforethemill
80- Diameter of mill ininches
3- No. of rollers inthemill
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22. HP 08
HP08:
Itstandsfor:
H-HighPerformancemills
P-Pressurizedtype,withprimaryairfancomingbeforethemill
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23. Boilers
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24. BM1-Boiler Maintenance Section
• A boiler is a combination of systems and equipment in which chemical
energy is converted into thermal energy, which is then transferred to
working fluid, so as to convert it into steam at high temperature and
pressure.
• In GGSSTP,
6 boilers for 6 units. Each boiler is a 210 MW Radiant Reheat, Natural
Circulation, Single drum, Semi-outdoor, Dry bottom, Water Tube and
designed for coal as principle fuel.
• HFO firing capacity is equivalent to 22.5% boiler Maximum
Continuous Rating.
• Four burners are capable for 7.5% boiler MCR heat input
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25. Continued…
• The complete furnace section is of fusion welded wall type, arranged
as a gas and pressure tight envelop.
• The extended sidewall section (where re-heaters are located) is
covered with water-cooled fin welded walls.
• The maximum flue gas velocity in the pressure part system is limited
to 10-12 m/sec at 100% boiler MCR load.
• All headers are located outside the gas path, except for the
economizer inlet header; intermediate headers and LTSH inlet header
are located in the low gas temperature section.
• Two re-heaters and de-super heaters are provided at the inlet of the re-
heater for emergency control of final reheated steam.
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26. Working of a Power Plant Boiler
• Boiler in a power plant has two functions.
i. The Combustion system
ii. Water and steam system
• Conversion of Water to Steam evolves in three stages
i. Sensible heat addition
ii. Latent heat addition
iii.Superheating
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27. Coal Flow In a Boiler
• Air carries the dry coal powder from the pulverisers to the burners in
the boiler furnace.
• In the burners the coal powder is mixed with the required amount of
Combustion air and burned in the furnace.
http://www.brighthubengineering.com/power-plants/24054-how-does-a-power-plant-boiler-work-combustion-system/13-10-2015 27

28. Boiler’s Components (Coal to Heat)
• Air system
• Forced Draft Fan
• Air Heater
• Primary Air Fan
• flue gas system
• Induced Draft Fan
• Electrostatic Precipitators
• Stack
• Balanced Draft
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29. Sensible Heat Addition
• Feed Water Pump
Pumps the water at high pressure into the boiler from the feed water
tank.
• Pre-Heating
Feed water heaters, using extracted steam from the turbine, adds a part of
the sensible heat even before the water enters the boiler.
• Economiser
Economiser is the Set of coils made from steel tubes located in the tail end
of a boiler.
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30. http://www.brighthubengineering.com/power-plants/24054-how-does-a-power-plant-boiler-work-combustion-system/
13-10-2015 30

31. Latent Heat Addition
• Drum
• A large cylindrical vessel that functions as the storage and feeding
point for water and the collection point for water and steam mixture.
• Largest and most important pressure part in the boiler.
• Water Walls
• Water filled tubes that form the walls of the furnace.
• Water Walls get the water from the ‘downcomers’
• Lower density than the water in the downcomers.
• This density difference creates a circulation of water from the drum,
through the downcomers, water walls and back to the drum.
• Steam collects at the upper half of the drum
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32. http://www.brighthubengineering.com/power-plants/24054-how-does-a-power-plant-boiler-work-combustion-system/
13-10-2015 32

33. Super Heater/Re-Heater
Furnace (1156C)
Platen SH (1026C)
Reheater (920C)
Final SH (666C)
LTSH (346C)
Economizer (140C)
APH
ESP
Induced Daft Fan
Chimney.
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http://www.brighthubengineering.com/power-plants/24054-how-does-a-power-plant-boiler-work-combustion-system/

34. Dry Fly Ash
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35. Dry Fly Ash Section
• The plant obtains 64 tons per hour ash in one unit.
• The ash is collected in an intermediate silo.
• The ash then moves down to stage called DV-1 into six different
containers. The containers in DV-1 have a secondary pipe which is
used to suck anything inside it into the silo a few seconds before the
ash is released into the container to ensure that a large pressure
difference between the silo and the container.
• The ash then moves to stage DV-2. This stage also has a container
only smaller than DV-1 but the process is same.
• After DV-2, the final stage is DV-3 when the ash is transferred from
DV-2 containers to nearby cement factories.
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36. Project
Corrosion In Boilers
13-10-2015 36

37. Introduction
In coal based thermal power plant, following type of corrosion are
possible:
• Water/gas/acid corrosion
• High Temperature corrosion
• Low Temperature corrosion
• Oil ash corrosion
• Stress corrosion
• Fatigue corrosion
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38. Water/Gas/Acid Corrosion
• This is basically a low temperature corrosion but it is caused by the presence of
gas or steam drops and acids present in the flowing water.
• Basically, Corrosion’s origin varies widely but it is mainly caused due to the
action of dissolved oxygen, and corrosion currents set up as a result of
heterogeneities on metal surfaces, or to the iron being directly attacked by the
water.
• Low make up feed water pH can cause serious acid attack on metal surfaces in the
pre-boiler and boiler system. Feed water can also become acidic from
contamination of the system.
• Acidic corrosion can also be caused by chemical cleaning operations (overheating
of the cleaning solution, excessive exposure of metal to cleaning agent, high
cleaning agent concentration).
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39. High Temperature Corrosion
• This is usually take place in parts which usually come in the contact of hot gas
containing certain contaminants like:
1. Vanadium Compounds
2. Sulphate Compounds
• These compounds can form compounds during
combustion having a low melting point.
• These liquid melted salts are strongly corrosive for
stainless steel and other alloys normally inert
against the corrosion and high temperatures.
https://en.wikipedia.org/wiki/High-temperature_corrosion
13-10-2015 39

40. Low Temperature Corrosion
• Using fuels with sulphur in steam generating units yields a potential hazard of
sulphur corrosion at the cold end of the boiler.
• Sulphur in the fuel is oxidized chiefly to sulphur dioxide (SO2) during
combustion. Some sulphur trioxide (SO3) is also formed, and combines with water
to form sulphuric acid, which condenses on and attacks low temperature boiler
surfaces.
http://www.chec.kt.dtu.dk/Our-Research/Facilities/Experimental-Facilities-within-CHEC/Low-Temperature-Corrosion13-10-2015 40

41. Oil Ash Corrosion
• All fossil fuels, with the possible exception of natural gas, contain constituents
that will promote corrosion on the fire side of boiler components.
• Fly-ash and soot-blower are not by themselves corrosive, but both remove the
protective iron-oxide layer.
• The cleaned steel is then exposed to the high temperature flue-gas environment,
and an oxide film reforms.
http://hghouston.com/our-services/corrosion-control.aspx13-10-2015 41

42. Stress Corrosion
• Stress corrosion may result in either inter-crystalline or trans-granular cracking of
carbon steel. It is caused by a combination of metal stress and the presence of a
corrosive.
http://www.qualitymarineservices.net/other_corrosion.htmlhttps://en.wikipedia.org/wiki/Stress_corrosion_cracking
13-10-2015 42

43. Fatigue Corrosion
• Corrosion fatigue is fatigue in a corrosive environment.
• It is the mechanical degradation of a material under the joint action
of corrosion and cyclic loading.
• More highly stressed parts of tubes (such as bends, or at other areas
close to supports) may be the most vulnerable.
• Additional thermal stresses could be imposed on the end tubes from
the boiler frames.
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44. Prevention of Corrosion
• Feed Water Treatment
• Aeration
• Deaeration
• Ion Exchange
• Chemical Treatment
• Protective layers in Boilers
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45. Concerned Images
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46. Concerned Images
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47. References
• V. Chawla, A. Chawla, D. Puri, S. Prakash, P. Gurbuxani and B. Sidhu (2011) "Hot Corrosion & Erosion Problems in Coal
Based Power Plants in India and Possible Solutions – A Review," Journal of Minerals and Materials Characterization and
Engineering, Vol. 10, No. 4, pp. 367-386.
• Patel, R.D. and Patel, I. J. (2015) 'A Review paper on Erosion and Corrosion behavior of Coal combustion chamber',
International Journal for Innovative Research in Science and Technology, Vol. 1, No. 7, pp. 72-76.
• Boiler. (2015, August 3). Retrieved from https://en.wikipedia.org/wiki/Boiler
• Air preheater. (2015, May 16). Retrieved from https://en.wikipedia.org/wiki/Air_preheater
• http://www.brighthubengineering.com/power-plants/24054-how-does-a-power-plant-boiler-work-combustion-system/
• https://en.wikipedia.org/wiki/Super_thermal_power_station
• http://www.pspcl.in/docs/gurugobind.htm
• http://www.qualitymarineservices.net/other_corrosion.html
• http://hghouston.com/our-services/corrosion-control.aspx
• http://www.chec.kt.dtu.dk/Our-Research/Facilities/Experimental-Facilities-within-CHEC/Low-Temperature-Corrosion
• http://www.brighthubengineering.com/power-plants/24054-how-does-a-power-plant-boiler-work-combustion-system/
• www.slideshare.net/shrikant.khating/coal-handling-plant-chp
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