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IIP201Study of Corrosion in Boilers

Guru Govind Singh Super Thermal PlantPresentation By:

Sajeed Mahaboob2011ME1111

Supervised By:

Er. Tarun SharmaAsst. Executive Engineer, GGSSTP, PSPCL

13-10-2015

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Introduction

• Location – Rupnagar, Punjab, IndiaAbout 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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Salient features of GGSSTP1.   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

4Typical power plant layout

https://en.wikipedia.org/wiki/Super_thermal_power_station13-10-2015

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Main Parts of the Plant

• Coal Handling• D-M Water Plant• Boiler• Turbine• Generator • Transformer• Ash handling• Switchyard• Control room13-10-2015

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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 intomechanical work.

https://en.wikipedia.org/wiki/Rankine_cycle13-10-2015

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Internship

• Our internship was based on the understanding the working of following departments:

1. Feeder Section 2. Boiler Section3. Fly Ash Section

• The project assigned to us was ‘Study of different reasons of corrosion in the boiler’

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Coal Handling

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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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Overview of coal handling plant

http://www.pspcl.in/docs/gurugobind.htm13-10-2015

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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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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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W/T Drive System

www.slideshare.net/shrikant.khating/coal-handling-plant-chp

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Layout

www.slideshare.net/shrikant.khating/coal-handling-plant-chp

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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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16http://www.paulsengineering.com/double-roll-crusher-555231.html

Double Roll Crusher

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Rotary Breaker Crusher

http://terrasource.com/equipment/bradford-breakers-by-pennsylvania-crusher-brand13-10-2015

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Impact Crusher

http://minyu.com/content/products.php?act=detail&c_id=1813-10-2015

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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 rpmInput coal size is 25 mm while output is 65-75 micronCrushing of coal by replaceable bull ring segment and grinding rolls

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Raw Coal Feeders (Continued…)

• Speed reduction by two method :single stage worm & worm wheel setPlanetary 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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XRP 803 mill

XRP 803: It stands for X - Frequency of power supply (50 cycles /sec) R - Raymond, the inventor of bowl mills. P - Pressurized type, with primary air fan coming before the mill 80 - Diameter of mill in inches 3 - No. of rollers in the mill

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HP 08

HP 08: It stands for: H -High Performance mills P - Pressurized type, with primary air fan coming before the mill

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Boilers

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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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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.13-10-2015

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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 stagesi. Sensible heat additionii. Latent heat additioniii.Superheating

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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

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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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Sensible Heat Addition

• Feed Water PumpPumps the water at high pressure into the boiler from the feed water tank.

• Pre-HeatingFeed water heaters, using extracted steam from the turbine, adds a part of the sensible heat even before the water enters the boiler.

• EconomiserEconomiser is the Set of coils made from steel tubes located in the tail end of a boiler.

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http://www.brighthubengineering.com/power-plants/24054-how-does-a-power-plant-boiler-work-combustion-system/

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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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http://www.brighthubengineering.com/power-plants/24054-how-does-a-power-plant-boiler-work-combustion-system/

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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/

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Dry Fly Ash

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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. 13-10-2015

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ProjectCorrosion In Boilers

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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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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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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 Compounds2. 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_corrosion13-10-2015

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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-Corrosion

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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

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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_cracking13-10-2015

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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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Prevention of Corrosion

• Feed Water Treatment• Aeration• Deaeration• Ion Exchange• Chemical Treatment

• Protective layers in Boilers

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Concerned Images

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Concerned Images

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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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Thank You13-10-2015