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1. PROFILE OF THE ORGANIZATION

Neyveli Lignite Corporation Limited, a “Navratna” Government of India

Enterprise, under the administrative control of MOC has a chequered history

of achievements in the last 58 years since its inception in 1956. A pioneer

among the public sector undertakings in energy sector, NLC operates

Three Opencast Lignite Mines of total capacity of 28.5 Million Tonnes

per Annum at Neyveli and one open cast lignite Mine of capacity 2.1

Million Tonnes per Annum at Barsingsar, Rajasthan.

Three Thermal Power Stations with a total installed capacity of 2490

Mega Watt at Neyveli and one Thermal Power Station at Barsingsar,

Rajasthan with an installed capacity of 250 Mega Watt

All the Mines of NLC are ISO Certified for Quality Management System,

Environmental Management System and Occupational Health & Safety

Management System. All the Power stations of NLC are also ISO Certified

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for Quality Management System and Environmental Management System.

NLC‟s growth is sustained and its contribution to India‟s social and economic

development is significant.

1.1. MINE - I:

The lignite seam was first exposed in August 1961 and regular mining

of lignite commenced in May 1962. German excavation technology in open

cast mining, using Specialized Mining Equipment (SME) like Bucket Wheel

Excavators, Conveyors and Spreaders were used for the first time in the

country in Neyveli Mine-I. The capacity of this mine was 6.5 MT which met

the fuel requirement of TPS-I. The capacity was increased to 10.5MT of

lignite per annum from March 2003 under Mine-I expansion scheme and at

present meets the fuel requirement for generating power from TPS-I and TPS-

I Expansion.

Mine – I

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1.2. MINE - II:

In February, 1978 Government of India sanctioned the Second Lignite

Mine of capacity 4.7 MT of lignite per annum and in February `83,

Government of India sanctioned the expansion of Second Mine capacity from

4.7 Million Tonnes to 10.5 Million Tonnes. Unlike Mine-I, Mine-II had to

face problems in the excavation of sticky clayey soil during initial stage. The

method of mining and equipment used are similar to that of Mine-I. The seam

is the same as of Mine-I and is contiguous to it. The lignite seam in Mine-II

was first exposed in September 1984 and the excavation of lignite

commenced in March, 1985. GOI sanctioned the expansion of Mine-II from

10.5 MTPA to 15.0 MTPA of lignite in October 2004 with a cost of Rs.

2295.93 crore. Mine-II Expansion project was completed on 12th March

2010. The lignite excavated from Mine-II meets the fuel requirements of

Thermal Power Station-II and Thermal Power Station–II Expansion under

implementation.

Mine - II

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1.3. MINE-IA:

Government of India sanctioned the project Mine-I A of 3 million

tonnes of lignite per annum at a sanctioned cost of Rs. 1032.81 crores in

February'98. This project is mainly to meet the lignite requirement of M/s ST-

CMS for their power plant and also to utilize the balance lignite to the best

commercial advantage of NLC. The project was completed on 30th March

2003 within time and cost schedule.

Mine - IA

1.4. BARSINGSAR MINE:

GOI sanctioned implementation of Barsingsar mine with a capacity of

2.1 MTPA of lignite per annum at an estimated cost of Rs. 254.60 crore in

December 2004. Both overburden and lignite production has been outsourced.

Lignite excavation commenced on 23rd November 2009 and production

attained the rated capacity on 31st January 2010.

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Barsingsar Mine

1.5. THERMAL POWER STATION-I:

The 600 MW Neyveli Thermal Power Station-I in which the first unit

was synchronized in May'62 and the last unit in September'70 consists of six

units of 50 MW each and three units of 100 MW each. The Power generated

from Thermal Power Station-I after meeting NLC's requirements is fed into

Tamil Nadu Electricity Board which is the sole beneficiary. Due to the aging

of the equipments / high pressure parts, Life extension programme has been

approved by GOI in March 1992 with an estimated cost of Rs.315.23 crore

and was successfully completed in March‟99 thus extending the life by 15

years. The extended life also to be completed between 2009-2014. However

as per the request of TNEB, this power station is being operated after

conducting Residual Life Assessment (RLA) study. GOI has sanctioned a

2x500 MW Power Project (Neyveli New Thermal Power Plant – NNTPS) in

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June 2011 as replacement for existing TPS-I The Board of Directors of NLC

accorded approval to taper down the generation of TPS-I by 300 MW by

March 2015 or earlier and to close down the remaining units by September

2015 or earlier.

Thermal Power Station - I

1.6. THERMAL POWER STATION-II:

The 1470 MW Second Thermal Power Station consists of 7 units of

210 MW each. In February 1978, Government of India sanctioned the Second

Thermal Power Station of 630 MW capacity (3 X 210 MW) and in Feb.'83,

Government of India sanctioned the Second Thermal Power Station

Expansion from 630 MW to 1470 MW with addition of 4 units of 210 MW

each. The first 210 MW unit was synchronised in March 1986 and the last

unit (Unit-VII) was synchronized in June'93. The power generated from

Second Thermal Power Station after meeting the needs of Second Mine is

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shared by the Southern States viz., Tamil Nadu, Kerala, Karnataka, Andhra

Pradesh and Union Territory of Pondicherry.

Thermal Power Station - II

1.7. THERMAL POWER STATION-I Expansion:

Thermal Power Station-I has been expanded based on the additional

lignite available from Mine-I Expansion. The scheme was sanctioned by

Government of India in February 1996 with a sanctioned cost of Rs. 1590.58

Crores. The Unit-I was synchronised in October 2002 and Unit-II in July

2003. The power generated from this Thermal Power Station after meeting

the internal requirements is shared by the Southern States viz., Tamil Nadu,

Kerala, Karnataka, and Union Territory of Pondicherry.

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Thermal Power Station – I Expansion

1.8. BARSINGSAR THERMAL POWER STATION:

Government of India sanctioned the Barsingsar Thermal Power Station

250 MW (2 X 125 MW) in October 2004 with a latest cost of Rs. 1626.09

Crores. First Unit was synchronised on 27th October 2009 and second unit

was synchronized on 5th June 2010. Both the units could not be taken for

commercial operation due to teething trouble and stablisation problem. Both

the units were commissioned in December 2011 and January 2012.

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Barsingsar Thermal Power Station

1.9. PRODUCT OF NLC:

The main core activity of NLC is Lignite Excavation and power

generation using lignite excavated. NLC is having lignite mining units named

as Mine I, Mine II, Mine IA and Barsingsar Mine. Also raw lignite is being

sold to small scale industries to use it as fuel in their production activities.

MINES CAPACITY

MINE I 10.5 MT / A

MINE I A 3 MT / A

MINE II 15.0 MT / A

BARSINGSAR MINE 2.1 MT / A

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NLC is generating power in its Thermal Power Station I, Thermal

Power Station -II and in Thermal Power Station I Expansion. All the southern

states are beneficiaries of this power generation project. NLC is started

generating power in Barsingsar Power Station also.

THERMAL UNITS CAPACITY

TPS – I (06×50)+(03×100) 600 MW

TPS – II (07×210) 1470 MW

TPS - I EXPANSION (02×210) 420 MW

BARSINGSAR TPS (02×125) 250 MW

2. THERMAL POWER STATION-II:

Thermal power station – II has a total installed capacity of 1470 MW (7

units of each 210 MW capacity). The station was constructed in two stages,

Stage I comprising the first phase of three units and stage-II comprising the

second phase of four units. The total cost of the project including IDC worked

out to 2011.26 crores. The project is constructed on an area of 207 hectares.

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The steam generator and the Turbo Generators of phase – I were

supplied by Transelekto. Hungary in collaboration with EVT, GERMANY

ANDFRANCOTOSI, ITALY respectively. All the equipment‟s of phase – II

are of indigenous make except the Milling and Firing Technology for Steam

Generators from EVT, GERMANY. The power station is equipped with a

sophisticated instrumentation system.

The power station has been awarded the ISO 9001:2000 certificate for

Quality Management system, ISO 14001:2004 for Environmental

Management System and OHSAS – 18001: 2007 for Occupational Health and

Safety Assessment series.

As a Central Power Generating System, the Station caters to the power

needs of the Southern Region. The power allocation from the station to the

Southern States of Tamilnadu, Andhra Pradesh, Karnataka, Kerala and

Pondicherry and to NLC mines is based on Government of India guidelines

with changes in actual share notified from time to time. The fixed share of the

beneficiaries is as follows. The actual share will vary depending on the

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pattern of distribution of the unallocated part among the beneficiaries based

on their requisitioning.

Andhra Pradesh : 18.84%

Karnataka : 13.54%

Kerala : 10.41%

Tamilnadu : 30%

Pondicherry : 5.44%

NLC mines : 6.8%

Unallocated : 14.97%

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2.1. ISO CERTIFICATION:

All mine units and thermal power plants have obtained ISO

certification for Quality management system (ISO 9001:2000)

Environmental management system (ISO 14001:2004)

Occupational health and safety management system (OHSAS

18001:1999)

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3. INTRODUCTION:

3.1. THERMAL POWER PLANT:

In thermal power plant the important medium for producing

mechanical energy is steam. A thermal power plant continuously converts the

energy stored in fossil fuels (coal, lignite, oil, natural gas etc.). Steam has the

advantage that it can be raised from water which is available in abundance.

The thermal power stations are very much suitable where coal / lignite is

available in abundance. The pressure ranges from 250o C to 650

oC.

3.2. WORKING PRINCIPLE OF THERMAL POWER

PLANT:

The thermal power plant uses steam as the working fluid. Steam is

produced in a boiler using coal / lignite as fuel and used to drive the prime

mover (Steam Turbine).

The heat energy is converted into mechanical energy by the steam

turbine and that mechanical energy is used for generating power with the help

of generator.

The layout of the thermal power plant consists of four main circuits.

They are,

1. Coal / Lignite and ash circuit.

2. Air and flue gas circuit.

3. Water and steam circuit

4. Cooling water circuit.

3.3. COAL / LIGNITE AND ASH CIRCUIT:

This circuit consists of lignite storage, ash storage, lignite handling and

ash handling systems. The handling system consist of belt conveyors, screw

conveyors etc. Lignite from the storage yard is transferred to the boiler

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furnace by means of lignite handling equipment. Ash resulting from the

combustion of coal in the boiler furnace is removed to ash storage through

ash handling.

The Indian coal contains 30% to 40% of ash and a power plant of

100MW produces normally 20 to 25 tones of hot ash per hour.

3.4. AIR AND FLUE GAS CIRCUIT:

The circuit consists of air filter, air preheater, dust collector and

chimney. Air is taken from the atmosphere to the air preheater, the dust from

the air is removed by means of using air filter.

After combustion in the furnace, the flue gas which has sufficient

quantity of heat is passed around the boiler tubes, dust collector, economizer

and preheater before being exhausted to the atmosphere through the chimney.

By passing the flue gas around the economizer and air preheater, the water

and air are preheated before going to the boiler.

3.5. FEED WATER AND STEAM CIRCUIT:

This circuit consists of Boiler Feed Pump, boiler, turbine, and feed

heaters. The steam generated in the boiler passes through super heater and is

supplied to the steam turbine. The steam is expanded in the steam turbine

then passed to the condenser where it is condensed.

The condensate is heated in the HP and LP heaters using the steam

tapped from different points of the turbine. The feed water is passing through

the economizer, where it is further heated by means of flue gases. Using the

economizer, the feed water is supplied from external source to compensate

losses.

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3.6. COOLING WATER CIRCUIT:

This circuit consists of circulating water pump, condenser, cooling

water pumps and cooling tower. Abundant quantity of water is required for

condensing the steam in the condenser. Adequate water supply is available

from various sources like river or lake. If adequate quantity of water is not

available at plant sites, the warm water coming out from the condenser is

cooled in cooling tower and is recirculated again and again.

4. RANKINE CYCLE (THERMAL CYCLE):

Steam engine and steam turbines in which steam is used as working

medium follow Rankinecycle. This cycle can be carried out in four pieces of

equipment joint by pipes for conveying working medium as shown. The cycle

is represented on Pressure Volume P-V and S-T diagram as shown.

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4.1. REHEAT CYCLE:

In this cycle steam is extracted from a suitable point in the turbine and

reheated generally to the original temperature by flue gases. Reheating is

generally used when the pressure is high say above 100 kg/cm2. The various

advantages of reheating are as follows:

(i) It increases dryness fraction of steam at exhaust so that blade erosion

due to impact of water particles is reduced.

(ii) It increases thermal efficiency.

(iii) It increases the work done per kg of steam and this result in reduced

size of boiler.

The disadvantages of reheating are as follows:

(i) Cost of plant is increased due to the re-heater and its long connections.

(ii) It increases condenser capacity due to increased dryness fraction. First

turbine is high-pressure turbine and second turbine is low pressure

(L.P.) turbine. This cycle is shown on T-S (Temperature entropy)

diagram.

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4.2. REGENERATIVE CYCLE (FEED WATER HEATING):

The process of extracting steam from the turbine at certain points

during its expansion and using this steam for heating for feed water is known

as Regeneration or Bleeding of steam. The arrangement of bleeding the steam

at two stages is shown.

Regenerative Cycle

Reheat Regenerative Cycle

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5. PUMP:

Pump is one of the earliest inventions for the conversion of natural

energy in to useful work. The earliest forms of pumps were Persian wheels,

water wheels containing buckets. The best known of early pumps, the

Archimedean screw also persists into modern times. With the development of

technology and need for various applications had lead to the inventions of

modern day pumps. Perhaps most interesting, however is the fact that with all

the technological development which has occurred since ancient times

including the transformations from water power through other forms of

energy all the way to nuclear fission, the pumps remain probably the second

most common machine in use exceeded in numbers by electric motor.

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5.1. HOW PUMP WORKS:

A centrifugal pump converts the input power to kinetic energy in the

liquid by accelerating the liquid by a revolving device - an impeller. The most

common type is the volute pump. Fluid enters the pump through the eye of

the impeller which rotates at high speed. The fluid is accelerated radially

outward from the pump casing. A vacuum is created at the impellers eye that

continuously draws more fluid into the pump.

The energy created by the pump is kinetic energy according the

Bernoulli Equation. The energy transferred to the liquid corresponds to the

velocity at the edge or vane tip of the impeller. The faster the impeller

revolves or the bigger the impeller is, the higher will the velocity of the liquid

energy transferred to the liquid be. This is described by the Affinity Laws

5.2. AFFINITY LAWS:

The capacity, or amount of fluid pumped, varies directly with this number.

Example:

50 Cubic meters per hour x 0.5 = 25 Cubic meters per hour

The head varies by the square of the number.

Example: a 50 foot head x 4 (22) = 200 foot head

Or in metric, a 20 meter head x 0.25 ( 0.52 ) = 5 meter head

The horsepower required changes by the cube of the number.

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Example:

If a 12 kilowatt motor were required at 3000 rpm. and the speed is

decreased to 1500 the new kilowatts required would be: 12 x 0.125

(0.53) =1.5 kilowatts required for the lower rpm.

5.3. CENTRIFUGAL PUMPS:

Any pump which converts energy of a prime mover, such as a electric

motor, into velocity or pressure energy of a liquid or gas product being

pumped is termed as centrifugal pump.

In a centrifugal pump the product enters the suction eye of the pump at

the center of rotating impeller. As the impeller vane rotate, they transmit

motion to the incoming product, then leaves the impeller, collect in a pump

casing, and leave the pump under pressure through the pump discharge.

Centrifugal Pump – Sectional view

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Boiler Feed Pump is one among the centrifugal pumps available in thermal

power stations.

6. BOILER FEED PUMP (BFP):

The boiler feed pump is one of the most important pieces of equipment

in a steam power plant as seen in the above thermal cycle. The water capacity

of a boiler is only great enough to supply steam to the prime mover for a

period of a few minutes when operating at full load. This fact outlines the

extreme importance of an uninterrupted water supply to the, boiler. This is

why, when selecting boiler feed pumps, its performance record, installation

and operation must be considered prior to any commitment in order to insure

this uninterrupted flow of water to the boiler.

6.1. TWO BFP PUMPS:

In Thermal Power Station – II, Two types of Boiler Feed

Pumps are available for supplying feed water to boiler

Boiler Feed pump type 6WC137/C

Boiler Feed pump type FK 6D 30

Though both the above types are similar in construction, there are unique

design variations viz. stuffing box sealing, secondary sealing and minor

variations in the impeller size and speeds.

6.2. BOILER FEED PUMP TYPE FK 6D 30:

The FK 6D 30 type boiler feed pump is a six stage horizontal

centrifugal pump of the barrel casing design.

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The pump internals are designed as cartridge which can be easily

removed for maintenance without disturbing the suction and discharge piping

work or the alignment of the pump and the turbo coupling

The pump shaft is sealed at the drive end and non-drive end by

mechanical seals, each seal being flushed by water in a closed circuit and

which is circulated by the action of the seal rotating ring. This flushing water

is cooled by passing through a seal cooler, one per pump which is circulated

with demineralized cooling water. The rotating assembly is supported by

plain white metal lined journal bearings and axially located by a Glacier

double tilting pad thrust bearing.

6.3. TECHNICAL DATA:

Pump type : FK6D30

No of stages : 6

Direction of rotation viewed : Anti-clockwise On drive end

Liquid pumped : Boiler Feed Water

Sp.wt.at suction temp., (kg/m3) : 905.0

Suction temperature (OC) : 162.5

Differential head (m) : 2222

Design flow rate (m3/hr) : 420

Minimum recirculation flow (m3/hr) : 100

Efficiency (%) : 81

Speed rev/min : 5300

Power (kw) : 2840

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Sectional View of Boiler Feed Pump-FK 6D 30:

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7. DESCRIPTION FK 6D 30:

7.1. PUMP CASING:

The pump casing consists of a forgot steel barrel with welded suction,

discharge branches, interstage Lapping and mounting feet. The drive end of

the casing is closed by a suction guide which is entered from the non-drive

end of casing and is located by a spigot against the inner face of the casing. A

mild steel gasket is located between the suction guide‟s spigot and the casing

inner face to prevent the leakage between the barrel casing and suction

annulus. An „O‟ ring with backup ring is also fitted in a groove in the

periphery of the suction to prevent leakage. Leakage between the suction

annulus and the drive end of the pump casing is prevented by an „O‟ ring and

gasket located on an insert ring which is secondary to the pump casing by a

ring of studs and nuts. The non-drive end of the casing is closed by a

discharge cover is secured to a casing by a ring of studs, washers and nuts,

sealing being effected by an „O‟ ring located in a machine recess in the pump

casing. On each side of the casing, on its horizontal Centre line, are two feet

which are secured to the base plate pedestals by spacer pieces, washers and

holding down bolts, thus allowing for expansion. Transverse keys in the drive

end pump feet ad longitudinal keys under the casing transfer moments and

thrust to the base plate, while allowing the casing freedom to expand.

Provision is made on the pump casing for a drain connection and temperature

probes.

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Boiler Feed Pump Assembled

7.2. DISCHARGE COVER:

The discharge cover closes the non-drive end of the pump casing and

also forms the balance chamber which, in turn, is closed by the non-drive end

water jacket and mechanical seal housing. The discharge cover as a close fit

in the casing bore and is held in place by a ring of studs and units. A spring

disc is located between the last stage diffuser and the discharge cover balance

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drum bush to provide the force required to hold the ring section assembly in

place against the drive end of the barrel before start-up. Once running, the

discharge pressure assists the spring disc in holding the ring sections in place.

The last stage diffuser is free to slide over the balance drum bush which is

shrunk into the discharge cover bore to minimize the flow of liquid to the

balance chamber.

Two holes are drilled radially through the periphery of the discharge cover to

provide outlet connections through which the liquid from the balance

chamber is returned to the

Discharge Cover

pump suction piping and two similarly drilled holes are also provided in the

discharge cover for cooling water connections to the water jacket. The non-

drive end bearing housing is attached to a bearing bracket secured to the outer

face of the discharge cover by studs, nuts and dowel pins.

To assist in removing the cover, two tapped holes are provided on the

flange for the use of starting screw and a tapped hole is provided on top of the

cover for an eye-bolt.

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7.3. SUCTION GUIDE:

Suction Guide

The suction guide closes the drive end of the pump casing and forms

the suction annulus. As a section of the pump cartridge, the suction guide is

not secured to the pump casing but is held against an internal shoulder in the

casing by the ring section assembly, the discharge cover and the spring disc.

Like the discharge cover, the suction guide is closed by the drive end water

jacket and mechanical seal housing.

Two tapped holes are provided in the suction guide for cooling water

connections to the water jacket. The drive end bearing housing is attached to

a bearing bracket secured to the outer face of the suction guide by studs, nuts,

and dowel pins.

7.4. RING SECTION ASSEMBLY:

The ring section assembly consists of ring section which located one to

another by spigots and are secured to each other by socket head screws in

counter-bored holes, sealing being effected by metal to metal joint faces and

„O‟ rings with backup rings located in grooves in the ring section spigots.

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Diffusers are dowel and spigot located to the ring section and to the suction

guide, and the last stage diffuser is secured to the last stage ring section with

socket head screws in counter-bored holes, the screws being locked in

position by locking strips. Packing rings are shrunk in to the bores of the ring

section and diffuser and are secured by the pumped liquid between the stages.

Ring Sections

The ring section and diffusers from the transfer package from impeller

outlet of one stage of the pump to the impeller inlet of the next stage, and the

diffusers are designed to cover some of the kinetic energy of the product into

pressure energy

The first stage ring section is spigot and dowel located to the suction

guide and is secured in position by socket head screws in counter-bored holes.

At the non-drive end a dowel pin fitted to the discharge cover is located in a

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hole in the last stage diffuser and thus keeps the ring section assembly in its

correct position relative to the casing. A circular spring disc is located in the

last stage diffuser and over the inner end of the balance drum bush. A

shoulder on the balance drum bush bears against the spring disc and clamps

the ring section assembly and suction guide in position.

7.5. ROTATING ASSEMBLY:

The dynamically balanced rotating assembly consists of the shaft,

impeller, abutment rings, keys, and the rotating parts of the mechanical seal,

shaft nuts, balance drum, thrust collar and the pump half coupling.

Rotating Assembly

The shaft is chromium plated at each end where it is supported by the

journal bearings, and its diameter increases in increments from the non-drive

end towards the drive end to facilitate the fitting and removal of the impellers.

The impellers are of the single entry shrouded inlet type and are keyed

and shrunk onto the shaft, the keys, one per impeller, being alternately fitted

on diametrically opposite sides of the shaft to maintain the rotational balance.

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The hub of the each impeller butts against a split abutment ring fitted in a

groove in the shaft. The split ring is retained by an extension on the impeller

hub.

Diffuser Impeller

The balanced drum is keyed and shrunk onto the shaft and held in place

against the shaft location shoulder by the balance drum nut and lock-washer.

The inner end of the balance drum is recessed and the bore of the recess is a

close fit over the last stage impeller hub. The faces of the balance drum

incorporate a connection for oil injection to assist to removal of the drum and

tapped holes are provided for withdrawal purpose.

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Balancing Drum

The rotation parts of the mechanical seals are fitted to the shaft where it

passes through the seal housings. The seal sleeves are keyed to the shaft and

are clamped in position by seal sleeve nuts and lock nuts.

The thrust collar is keyed to the non-drive end of the shaft and is

secured against a shoulder on the shaft by the thrust collar nut locked by a

lock-washer.

The pump half coupling is located on the tapered end of the shaft by

the keys and it is secured by a coupling nut locked by a grub screw.

7.6. MECHANICAL SEALS:

The mechanical seals fitted at each end of the pump and each seal

comprises a seal body assembly secured to a seal housing which contains the

rotating components of the seal.

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Mechanical Seal

Each seal consists of a rotating tungsten carbide seat, mounted in a

carrier, running against a stationary carbon face. Contact between the face

and seat is maintained by the hydraulic pressure during running by the spring

pressure on the start-up. Any other possible leakage paths, within the seal

unit, are sealed with „O‟ rings and the stationary components are prevented

from rotating by keys or anti-rotation pins.

The seal is designed to recirculate the pumped product through a seal

cooler, to maintain an acceptable temperature in the region of the seal face.

7.7. JOURNAL AND THRUST BEARING:

The rotation assembly is supported at each end of the shaft by a white

metal lined journal bearing and the residual thrust is carried by a tilling pad

double thrust bearing mounted at the non-drive end of the pump.

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The journal bearing shells are mild steel, white metal lined, thin wall

type and are split on the horizontal plate through the shaft axis. Each bearings

is secured in a bearing housing and prevented from rotating by lugs locating

in recesses in the housing.

The thrust bearing is fitted in the non-drive end bearing housing and

has eight digit white metals lined tilting pads held in a split carrier ring

positioned on each side of the thrust collar. The carrier ring are prevented

from rotating with the shaft by the dowel pins in the each ring which engage

in slots in the bearing housing top half. The thrust pads are retained on the

carrier rings by special pads stops screwed into the rings.

A split floating oil sealing ring is located in a groove in the thrust

bearing housing to restrict the escape of lubricating oil from the thrust bearing

chamber. To ensure that the thrust bearing remains flooded, an orifice is filled

at the oil outlet.

Machined spacers are fitted behind the carrier rings to affect the axial

position setting of the rotation assembly on the original built. The bearings

are supplied with the lubricating oil from the forced lubrication oil system.

7.8. BEARING HOUSINGS:

The bearing housings in the form of cylindrical castings split on the

horizontal shaft axis.

The drive end bearing housing is secured to the bearing housing

brackets by bolts, nuts and washers and is radially located by dowel pins

fitted in the flange of the housing brackets. The journal bearing is located by

lugs in recesses in the bearing housing, and held by the top half bearing

housing, which is secured to the bottom half by studs and the nuts are

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Bearing Housing

located by dowel pins. Oil guards fitted in the groove at each end of the

bearing housing are dowel located and serve to prevent oil escaping from the

housing.

An air breath is screwed to the tapped hole in the top half bearing

housing are tapped hole is provided for a temperature gauge. Connections for

an oil inlet and an oil outlet are provided in the bottom half bearing housing.

The non-drive end bearing housing, which contains both the journal

and the thrust bearings, is secured to the bearing housing bracket by studs and

nuts. The top and bottoms halves of the bearing housings are secured together

by stud and nuts and located on dowel pins. Leakage of lubricant oil from the

non-drive end bearing housings prevented by the oil guard in the inboard side

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of the housing and by a bearing housing end cover with „O‟ ring, secured to

the outboard side of the housing by socket head screws.

7.9. HYDRAULIC BALANCE:

The rotating assembly is subject to varying forces due to the

differential pressure force acting on the impellers. The pump has therefore

been designed so that the shaft is kept it tension by the location of a balance

drum at the non-drive end, and is hydraulically balanced so that only a small

residual thrust remains, which is carried by the thrust bearing.

The main components of the hydraulic balancing arrangement are the

balance chamber in the discharge cover, the balance drum which is secured to

the shaft and the balance drum bush fitted in the bore of the discharge cover.

The thrust caused by the discharge pressure acting on the area outside each

impeller wear ring on the inlet side of the impeller is balanced by the same

pressure acting on an equal area on the outlet side of each impeller. The thrust

caused by the suction pressure acting on the area inside the wear ring on the

inlet side of each impeller is overcome by the much greater thrust caused by

the discharge pressure acting on an equivalent area on the outlet side of each

impeller. The resultant thrust force, due to the different pressures acting on

these equal areas, tends to move the rotating assembly towards the drive end

of the pump.

The thrust force will vary with the load on the pump but the hydraulic

balance arrangement will reduce its effect, enabling the residual thrust to be

taken by the tilting pad thrust bearing. This bearing has a double face so that

the surges in opposite directions which occur during the start-up period and

during transient conditions will be accommodated.

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7.10. THE HYDRAULIC BALANCE WORKING:

The pump product passes from the last stage of the pump between the

balance drum and the bush, and enters the balance chamber at a pressure

approximately equal to the suction pressure. Two ports in the discharge cover

allow the product to be piped back to the pump suction side. The pressure

differential across the balance drum is therefore equal to that across the

impellers. The cross-sectional area of the balance drum is sized to give a

small residual thrust towards the drive end of the pump.

7.11. FLEXIBLE COUPLING:

The flexible coupling between the hydraulic coupling and the pump

shafts consists of two hubs flexibly connected through laminated stainless

steel elements to a tubular spacer.

The element assemblies are secured to the flanges of the spacer and the

hubs by bolts and Nyloc nuts. The flanges of the hubs are drilled to clear the

overload washers fitted to the bolts which secure the flexible element to the

spacer. Similarly the flanges of the spacer are drilled to clear the overload

washers fitted to the bolts which secure the flexible elements to the hubs. The

coupling is thus above to accommodate a certain amount of misalignment

between the turbo coupling and pump shafts, to which the hubs are fitted.

8. These pumps are directly involved in the power generation

process,

Though power generation is a continuous process, the sustainability of

maintaining the generating unit‟s full load is affected by a number of factors

viz. Fuel quality & availability, Grid conditions, availability of auxiliary

equipments etc.

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The availability of these pumps is ensured by proper maintenance that

involves;

Inspection of equipments

Condition Monitoring

Preventive Maintenance

Failure analysis & recurrence prevention

9. COMMON FAILURES OF BOILER FEED PUMPS:

1. Pump does not deliver liquid

2. Insufficient capacity delivered.

3. Insufficient pressure developed

4. Pump loses prime after starting.

5. Pump requires excessive power.

6. Pump vibrates or is noisy at all flows.

7. Pump vibrates or is noisy at low flows.

8. Pump vibrates or is noisy at high flows.

9. Shaft oscillates axially.

10. Impeller vanes are eroded on visible side.

11. Impeller vanes are eroded on invisible side

12. Impeller vanes are eroded at discharge near center

13. Impeller vanes are eroded at discharge near shrouds or at shroud/vane

fillets

14. Impeller shrouds bowed out or fractured

15. Pump overheats and seizes.

16. Internal parts are corroded prematurely

17. Internal clearances wear too rapidly.

18. Axially split casing is cut through wire drawing.

19. Internal stationary joints are cut through wire drawing.

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20. Packed box sleeve scored

21. Packed box leaks excessively or packing has short life.

22. Mechanical seal leaks excessively.

23. Mechanical seal: damaged faces sleeve bellows.

24. Bearing have short life.

25. Coupling fails.

10. POSSIBLE CAUSES OF TROUBLES:

10.1. Suction troubles:

1. Pump not primed.

2. Pump suction pipe not completely filled with liquid.

3. Insufficient available NPSH

4. Excessive amount of air or gas in liquid.

5. Air pocket in suction line.

6. Air leak in suction line.

7. Air leaks into pump through stuffing boxes or through mechanical seal.

7a. Air in source of sealing liquid.

8. Water seal pipe plugged.

9. Seal cage improperly mounted in stuffing box.

10. Inlet or suction pipe insufficiently submerged.

11. Vortex formation at suction.

12. Pump operated with closed or partially closed suction valve.

13. Clogged suction strainer.

14. Obstruction in suction line.

15. Excessive friction loss in suction line.

16. Clogged impeller.

17. Suction elbow in plane parallel to shaft. (For double suction pumps)

18. Two elbows in suction piping at 900 to each other, creating swirl and

pre rotation. Suction of pump with too high a suction specific speed.

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10.2. Other Hydraulic problems:

1. Speed of pump too high.

2. Speed of pump too low.

3. Wrong direction of rotation.

4. Reserve mounting of double suction impeller.

5. Un-calibrated instruments.

6. Impeller diameter smaller than specified.

7. Impeller diameter larger than specified.

8. Impeller selection with abnormally high head coefficient.

9. Running the pump against a closed discharge valve without opening a

bypass.

10. Operating pump below recommended minimum flow.

11. Static head higher than shut off head.

12. Friction losses in discharge higher than calculated,

13. Total head of system higher than design of pump.

14. Total head of system lower than design of pump.

15. Running pump at too high a flow. (For low specific speed pumps).

16. Running pump at too low a flow. (For high specific speed pumps).

17. Leak off stuck check valve.

18. Too close a gap between impeller vanes and volute tongue or diffuser

vanes.

19. Parallel operation of pumps unsuitable for the purpose.

20. Specific gravity of liquid differs from design condition.

21. Viscosity of liquid differs from design condition.

22. Excessive wear at internal running clearances.

23. Obstruction in balancing device leak off line.

24. Transient at suction source. (Imbalance between pressure at surface of

liquid and vapour pressure at suction flange).

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10.3. Mechanical troubles general:

1. Foreign matter in impellers

2. Misalignment

3. Foundation insufficiently rigid.

4. Loose foundation bolts.

5. Loose pump or motor bolts.

6. Inadequate grouting of base plates.

7. Excessive piping force and moments on pump nozzles.

8. Improperly mounted expansion joints.

9. Starting the pump without proper warm up.

10. Mounting surface of internal fits.(at wearing rings impellers, shaft

sleeves, shaft nuts, bearing housings etc)

11. Bent shaft.

12. Rotor out of balance.

13. Parts loose on the shaft.

14. Shaft running off centre because of worn bearings.

15. Pump running at or near critical speed.

16. Too long shaft span or too small a shaft diameter.

17. Resonance between operating speed and natural frequency of

foundation, base plate or piping.

18. Rotating part rubbing on stationary part.

19. Incursion of hard solid particles into running clearances.

20. Improper casing gasket material.

21. Inadequate installation of gasket.

22. Inadequate tightening of casing bolts.

23. Pump materials not suitable for liquid handled.

24. Certain couplings lack lubrications.

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10.4. Mechanical troubles in sealing area:

1. Shaft or shaft sleeves worn or scored at packing.

2. Incorrect type of packing for operating condition.

3. Packing improperly installed.

4. Gland too tight, prevents flow of liquid to lubricate packing.

5. Excessive Clearance at bottom of stuffing box allows packing to be

forced into pump interior.

6. Dirt or grit in sealing liquid.

7. Failure to provide adequate cooling liquid to water cooled stuffing

boxes.

8. Incorrect type of mechanical seal for prevailing conditions.

9. Mechanical seal improperly installed

10.5. Mechanical troubles in bearings:

1. Excessive radial thrust in single volute pumps.

2. Excessive axial thrust caused by excessive wear at internal clearances

or by failure or, if used, excessive wears of balancing device.

3. Wrong grade of grease or oil.

4. Excessive grease or oil in antifriction bearing housings.

5. Lack of lubrication.

6. Improper installation of antifriction bearings such as damage during

installation, incorrect assembly of stacked bearings, use of unmatched

bearings as a pair, etc.

7. Dirt getting into bearing.

8. Moisture contaminating lubricant,

9. Excessive cooling of water cooled bearings

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11. CASE STUDIES:

The following are some of the failure encountered,

1. Shaft cut / shaft breakage.

2. Seal failure.

3. High vibration levels.

4. Seizure of rotating element.

11.1. CASE - 1

Shaft cut / shaft breakage:

Pump ID : 4C

Type : Shaft cut

The pump got failed when the unit is running at full load. The pump

cartridge was replaced with spare and put back into service within 7 shifts.

The failed cartridge was dismantled and the observations are;

1. Fretting corrosion noticed in the shaft at the thrust collar area.

2. Crack cut found in the thrust collar region

3. Ring section fixing screws found sheared.

4. „O‟ rings found to be hardened and broken.

Analysis:

Breaking of shaft at the thrust collar region being a recurring defect, it

had already been discussed with the pump designer M/s. BHEL, Hyderabad.

Excerpts of analysis:

In dynamic working conditions, machine parts may fail even at stresses

below the ultimate strength or yielding strength of material. The characteristic

of this sort of part failure is that the stresses are repeated many times, which

is so called fatigue failure. Fatigue failure starts with a micro crack, where the

crack is so small that is not visible with normal eyes Crack is extended from a

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point of discontinuity (such as change in cross-section, or a hole) on the part.

When the crack is created, the effect of stress concentration is increased;

hence the original micro crack is extended. While the cross-sectional area

under stress is decreased, stress gets increased until the failure happens at the

remaining cross section

The diameter of the shaft at the thrust collar portion is only 65 mm,

which is not sufficient to withstand the stress that is accumulated at the

shoulder area of the shaft.

Remedy:

Advised to replace the shaft with 70 mm diameter collar area shaft and

supplied a new shaft incorporating the changes.

After replacing the shaft with the improved one, the recurring defect got

nullified.

11.2. CASE - 2

Pump outage due to seal failure

Pump ID : 2B

Type : Labyrinth seal failure led to oil contamination

The pump got seized due to galling of labyrinth seal mating parts.

Analysis:

Labyrinth seal comprises a rotating shaft sleeve and a stationary

bushing. A close running clearance between these parts limits the seal

leakage. As the temperature of the medium to be sealed is over 1700 C, cold

water at a temperature of 490 C & 26 KSC pressure is admitted into the gap

between the seal parts to avoid flashing of the leakage water. This

temperature leads to stratification of fluid leading to greater thermal

expansion of the upper casing than the lower casing. This uneven expansion

causes seal parts to gall at times.

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Further the seal bushing fixing screws gets broken due to high

temperature difference, which causes disorientation of the bushing leading to

galling of mating parts.

Labyrinth seal failure leads to flashing of high temperature water which

contaminates the bearing oil and thus the failure of line & thrust bearing.

Remedy:

Replacing the labyrinth seal with the advanced mechanical seal will

eradicate this problem. Accordingly al the Boiler Feed Pumps have been

retrofitted with Mechanical seals. Since then recurrence of pump failure and

oil contamination due to seal failure is not encountered.

11.3. CASE - 3

Pump outage due to high vibration

Pump ID : 4A, 7C

Type : High Noise

Based on condition monitoring the pump was taken for overhaul. The

vibration amplitudes were observed to be more than 9 mm/sec. The vibration

analysis revealed that the predominant component occurs at a frequency of

70000 cpm to 90000 cpm, which indicates unbalance and internal

recirculation.

During overhaul the running clearances were found to have exceeded the

upper limit by over 1.5 times. The rotor unbalance also exceeded the

maximum limit.

Remedy:

All the wearing rings were replaced and the running clearances were

corrected as per the design value.

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The rotor unbalance was corrected to less than 2 grams in toto.

11.4. CASE - 4

Pump seizure

Pump ID : 4A, 7C

Type : Cavitation defect

Pump got tripped consequent to unit tripping.

Operation personnel informed that there was heavy mechanical seal

leak.

Local inspection indicated seal face opening.

Pump was drained and no free rotation found in the pump rotor.

Post trip parameters indicated that,

a) The pump had been started immediately after tripping.

b) Deaerator parameter indicates insufficient NPSH at the time of

restarting.

Pump was dismantled.

Observations:

2nd

stage diffuser wearing ring got broken into pieces.

1st stage diffuser found with effect of cavitation.

1st stage impeller got completely damaged at the neckside shroud inner

end and suction & discharge sides found connected through a 2 mm

hole of length 10 mm.

Remedy:

All the wearing rings replaced.

Rotor was balanced dynamically with a residual unbalance of 2 grams

at the right plane.

1st and 2

nd stage diffusers replaced with spare.

1st stage impeller replaced with spare.

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12. CONCLUSION:

This project provided us with an excellent opportunity and experience to

enlighten our knowledge with insight into the world of high speed pumping

system. Details of the study carried out in dismantling, the parts & its

functions, overhaul and failure analysis of Boiler Feed Pump is explained in

this report. The objective of this project was done as follows,

Analyzed the failures of Boiler Feed Pumps and suggested ways to

prevent recurrences.

Energy conservation was done by taking the pump for overhaul

based on condition monitoring i.e, on higher power consumption by

the pump.

Reduced O & M cost, by preventing failure recurrences.

We faced many issues and challenges during the entire study and

successfully overcame all the threat perceptions. Our sincerity, commitment,

hard work and proper guidance from our department made the project a huge

success and we were able to deliver the results as per our expectations.

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13. REFERENCES:

A. O & M Manual of Boiler Feed Pumps type FK 6D 30

B. History Register of Boiler Feed Pumps, Turbine Maintenance, Thermal

Station – II

C. Overhaul records of Boiler Feed Pumps

D. Fluid Mechanics and Hydraulic Machines – R.K.Bansal.

E. A Textbook of Thermal Engineering – R.S.Khurmi, J.K.Gupta.