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Pikesh Jain 1
AMBUJA CEMENT LTD.
RABARIYAWAS
TRAINING REPORT ON GENERATION, TRANSMISSION &
DISTRIBUTION OF
ELECTRICAL POWER Submitted in partial fulfillment for the award of the degree of
Bachelor of Technology
In
Electrical Engineering
2013-14
Submitted to: Submitted By:
Dept. of Electrical Engineering Mr. Pikesh Jain
B. Tech. 4th year,
7thsem.
Electrical Engineering,
JECRC Jaipur
Pikesh Jain 2
Acknowledgement
I am thankful to Mr. S.N. Jhanwar Sir (Head, EE Dept.) under whose guidance
I have timely completed the report.
It is my proud privilege to express my profound sense of gratitude to Mr.
Sachin Singhal (HEAD, Power Plant) for his constant guidance and
encouragement throughout the training period.
I am indebted to Mr. Jai singh Shekhawat (Section head, Powerplant),Mr R.P
tak(asst. manager) for sharing their vast experience as well as providing me
with priceless study materials and photographs.
I also express my deep gratitude to Mr. Ritesh Dhuria,Mr. Grijesh, Mr. Mohd.
Arif, Mr.Ashok Sharma, Mr. Praveen Sharma, Mr. Mukesh Saxena, Mr. Sujeet
for sharing their knowledge patiently.
I am also thankful to Mr. Mangu Singh Shekhawat, Mr. Anil Sharma for
providing all facilities and ensuring all my requirements were attended to.
I will now conclude by thanking my parents, without whose care and
assurance, I would not have been able to accomplish this.
Pikesh Jain
Pikesh Jain 3
Preface
Practical knowledge means the visualization of the knowledge, which we
read in books. For this we perform experiments and get observations.
Practical knowledge is very important in every field. One must be familiar
with the problems related to that field so that he may solve them and
became successful person.
After achieving the proper goal of life an Engineer has to enter in
professional life. According to this life he has to serve an industry, may be
public or private sector or self-own. For the efficient work in the field he must
be well aware of practical knowledge as well as theoretical knowledge.
To be a good Engineer, one must be aware of the industrial environment &
must know about management, working in industry, labor problems etc., so
he can tackle them successfully.
Due to all the above reasons & to bridge the gap between theory and
practical, our engineering curriculum provides a practical training course of
30 days. During this period a student in industry and gets all type of
experience and knowledge about the working and maintenance of various
types of machinery.
I have undergone by 30 days of training ( after III yr.) at AMBUJA CEMENT LTD.
RABARIYAWAS. This report has been prepared on the basis of the knowledge
which I acquired during my 30 days (01-06-2013 to 030-06-2013) training at
Captive power plant.
Pikesh Jain 4
Introduction of Power Plant
Power plant is a process unit where by means of consumption of energy from
various fuels (i.e. coal, compressed gas, and nuclear energy, hydro) energy is
created and by which electricity is generated.
In Rabriyawas, we have two thermal power plants:
1. 15 MW
2. 18.7 MW
In these power plants we are using F-grade coal, Lignite, Pet coke & biomass
as fuel.
The steam is produced with the help of Atmospheric Fluidized bed
combustion Boiler having a pressure & temperature of 65Kg/sq.cm & 495 +/-
5 deg. C respectively.
This pressurized steam is then used to run a Turbine which in turn rotates the
Generator & produces the power.
Pikesh Jain 5
Various Circuits of Thermal
Power Plant
The thermal power plant can be divided into following circuits :-
1. Coal & Ash Handling Circuit:
This circuit describes the total loading of coal and how it is used for
burning in boiler, there handling and conversion into fly ash and how fly
ash handling is done.
2. Air & Flue Gas Circuit
This circuit describes the uses of atmospheric air in the process of power
generation. How air intake is done and how it is converted in the flue
gas.
3. Water & Steam Circuit
This circuit describes the uses of water in the plant. It also describes the
importance of water in thermal power plant and its conversion in to
steam. Use of the steam in power generation process.
4. Steam Condensing Circuit.
This circuit describes the conversion of steam into the water. This circuit
is used where there is scarcity of water. This circuit also reduces the
wasting of water as the cycle is the closed cycle.
Pikesh Jain 6
Description of Thermal Power
Plant: 15 MW
COAL & ASH HANDLING CIRCUIT :
COAL CIRCUIT:
In Rabriyawas unit, various type of coals are brought by the road
transportation. The trucks are emptied with the help of Coal Tippler, from
where it is feeded to a Reciprocating Feeder and is supplied to YC-1 belt.
A stacker is provided on YC-1 belt which is used for stacking the coal when
the Bunker levels are full.
The coal from the pile is reclaimed with the help of loader and feed to belt
no. YC2. The coal from YC1 & YC2 is fed to BC1 belt. As shown in the chart
The further sequence of the coal handling is as follows:
BC1 BC2 BC7 BC4 VIBRATING SCREEN CRUSHER VIBRATING
SCREEN 2 BC3 BC5 BC6A & BC6B
There is one metal separator near the tail pulley of BC2. From BC2 the
material is feed to vibrating screen, this contain two meshes of size 50 sq mm
and 9X 12 mm sq. The material which can pass through this screens will
directly fed to BC3 and rest will go to the crusher.
After this the coal is crushed into the hammer crusher.
Again the crushed coal passes through the vibrating screen2, where the mess
size is 9X12 mm sq.
The size of the coal is -6mm. this coal is fed to belt no. BC3 and from here it is
fed into the bunker via BC5, BC6A and BC6B.
The coal above 6mm size is consider as reject and fed again into the crusher
via BC7, BC4, BC1 and BC2.
From bunker, the coal is fed to the furnace through pocket feeder.
In this way the coal is feed to the furnace from the coal yard.
Pikesh Jain 7
ASH CIRCUIT:
After the coal is burnt, the ash is formed. This ash is carried with the Flue gases
and sticks to the economizer tubes, Air preheater tubes & ESP plates.
This ash is extracted from the economizer tubes, Air preheater tubes & ESP
plates by soot blowers and is conveyed to the fly ash Silos with the help of
compressed air.
AIR & FLUE GAS CIRCUIT :
In this plant we have two Induce Draft fan, Forced Draft fan, and Primary Air
fans for air & flue gas circuit.
F.D. fan takes the air from the atmosphere and is fed to the Air preheater.
In Air preheater the fresh air gets heat from the flue gases & thus becomes
hot i.e. it attain a temperature of about 140 deg C. 30% of this hot air is then
fed to the P.A. fan . The primary air from P.A. fan is used for conveying coal to
the furnace, while the remaining hot air i.e. secondary air is used for fluidizing
the bed.
The used air in the furnace is known as the Flue gas. This flue gases consist of
fly ash as well as high heat it have a temperature of approx 291.1 deg C.
therefore for utilizing this heat energy we passes it through the economizer (to
raise the temperature of feed water), Air Preheater (to raise the temperature
of fresh air), ESP (to collect dust & fine particles in order to decrease the
pollution rate).
As this hot flue gas is passing through the economizer it heat the incoming
feed water. The exhaust flue gas from the economizer has sufficient heat i.e
of temperature 226 deg C. As mentioned that this hot gas is used for heating
the fresh air while its passage through the APH.
While its flow through the ESP, fly ash are separated. And it is exhausted in the
atmosphere with a temperature of around 130 deg C.
In order to maintain a proper flow of flue gases from the furnace, a device is
needed for creating the suction and it is accomplished by the I.D. fan i.e.
induced draft fan.
Pikesh Jain 8
I.D. fan create the suction in the system and that take off the flue gases and
exhaust it into atmosphere via chimney.
WATER & STEAM CIRCUIT :
Water required for the various processes in this plant is obtained from the
under ground sources like bore wells. This water contains many impurities &
Minerals
Presence of impurities in feed water can causes scaling, corrosion and
problem related to the material.
The impurities present in the feed water can be categories as:
a) SUSPENDED SOLID
Suspended solid present in water are clay , silt, organic matter and micro-
organism.
Effect :- Scaling, deposition and it also accelerate corrosion.
b) DISSOLVED SOLID
Dissolved solid includes
i) calcium salt: calcium carbonate, calcium sulphate etc.
ii) magnesium salt: magnesium carbonate, magnesium sulphate
etc.
iii) sodium salt: sodium carbonate, sodium bicarbonate etc.
Presence of these minerals can caused temporary and permanent
hardness
Temporary hardness: this is caused by the presence of the calcium
sulphate and magnesium salt.
Permanent hardness: this is caused by the presence of the calcium
sulphate and magnesium salt.
Effects: it has a greater effect on scale deposition
c) DISSOLVED GASES
Pikesh Jain 9
Dissolved gases includes oxygen, carbondioxide and hydrogen
sulphate etc.
Effect:- It has invariably influence on corrosion.
PROCESS OF DEMINERALIZATION OF FEED WATER
The sequences by which we perform the demineralization is as follows
1. Water sources
the water source generally we are using is ground water.
2. Raw water tank
after pumping the ground water, we store this water in raw water tank.
From here, the water is divide in two part i.e. for cement plant and
power plant.
3. Raw water pump
two pump of centrifugal type are used for carring the water from the
raw water tank for processing in power plant.
This pump has a max flow of 12 cu. M / hr with a pressure of 4 kg/cu cm
4. Chlorination by hypo chloride dosing
chlorination is done to prevent fouling micro-organisms
chlorine gas is dosed in solution upto 1-3 ppm.
5. Multi Grade Filter (MGF)
it is 3 in no.(one operating at a time)
remove turbidity and suspended particle
it have steel vertical rubber line pressure vessel, 2 grade of silica
quartz for charging
water passes from top to bottom while in operation
MGF unit gets isolated when pressure drop across bed is
increases from 0.8 to 1 kg/cu cm
6. Activated Carbon Filter (ACF)
it is 2 in no.
Pikesh Jain 10
purpose- dechlorination, removal of color, odour and
organics
construction- steel vertical rubber line vessel. On top it has
distributor and at bottom it has plate type strainer.
Charging- granular activated carbon made of coconut shells
and supported by layer of siles and peeble.
Recharging – pressure exceed 0.8 – 1 kg/ cu cm
7. Sodium Metabisulfate dosing system(SMBS)
it is 1 in no.
Purpose- remove free chlorine
It effect the process of R.O. i.e effecting the R.O. membrane
8. Acid dosing system
it is 2 in no.
to avoid scaling because it filtered water contain
bicarbonate and CO3.
Hence dosing is done by HCl to make ph between 5-6
9. SHMP dosing system(sodium hexa meta biphosphate)
To remove hardness salt of calcium and magnesium
To improve quality of RO
10. Micron Cartilage Filter
It is two in no.
Used to remove particle upto the size of 5 micron
One MCF has 8 cartilage of cylindrical shape
11. High Pressure Pump
it is used to increase pressure which is needed for carrying RO
process i.e.12-16kg/sq.cm
12. Desalination by reverse osmosis
it is 2 in no.
it is used for removing solid particle
it has the efficiency of 97%
13. Degasification system
purpose- remove free carbon dioxide
system consist of
o degasses tower
o degasses air blower
o degassed water tank
14. Mixed bed polisher unit with regeneration system(MB)
Pikesh Jain 11
R.O. water contain many cation and anion
To remove this we used the M.B. system.
It contain the bed of resin of cation and anion exchanger
Regeneration- In codirection of flow with 5% HCl and NaOH.
15. PH correction dosing system
R.O. water has ph between 6.0-6.5
It is more acidic in nature and it cause corrosion .
So we have to increase ph
It is done by morphine dosing system. This increase the ph to
8.5
In this way water is ready to use in the plant.
The D.M. water is fed into the deaerator where the dissolved oxygen is
removed from the water.
The boiler feed pump, pumps all the incoming or stored water in the tank to
the boiler drum via economizer with a operating pressure of 86.9 kg/sq.cm.
Pikesh Jain 12
While passing through the economizer it get heated to a temperature of
225.6 deg C, with the help of flue gasses.
This warm water is feed to the boiler drum. From here it goes in the furnace for
further heating. With the help of down comer line the water passes through
the water tube and get start converting in the steam.
The saturated steam formed is separated in the boiler drum and pas through
the primary super heater where it attains a temperature of 453.5 deg C
After primary super heater there is a provision of cooling down the
temperature of steam by desuperheater.
Desuperheater make the superheat steam to a temperature of 374.7 deg C.
In desuperheater there is a spray of water which lower the temperature of
superheated steam.
After this, it passes through a radiant superheater, where the steam is heated
to a temperature of about of 472.5 deg C
This super heated steam is finally pass to the turbine for generation of
electricity having a pressure of 64.2 kg/sq.cm and temperature of 472.5 deg
C.
From turbine, the steam is extracted only at one place i.e. for deaerator.
The steam at the end of turbine is extracted at a pressure of 0.2 kg/cm.sq
and temperature of 60.3 kg/cm sq.
As this power plant runs on a closed circuit phenomenon. Therefore the
steam is condensed with the help of air cooled condenser.
The condensing of steam is explained in next section.
Pikesh Jain 13
STEAM CONDENSING CIRCUIT :
The steam once used to run the turbine losses it’s pressure but contains some
amount of temperature which can be used in various ways.
The steam from turbine enters into the Air Cooled Condenser where the
steam gets condensed into water by losing heat to the atmosphere.
The condensed water from the ACC goes to condenser tank from where it is
feed into VSC, GSC & deaerator through condensate extraction pump.
A part of the steam is extracted from the main steam line for gland sealing
and is given to vent steam condenser(VSC) & gland steam condenser(GSC).
In these condensers this steam losses heat to the condensate water & makes
it warmer while this steam gets condensed into water.
This condensed water is then supplied to the waste heat recovery system
where it gains heat from the exhaust gases of the Kiln and gets warmer.
This warmer water is then feed into the deaerater and the cycle repeats.
Temperature at various points:
Temperature and pressure after CEP (Condensate Extraction Pump): 13.5 to
14 kg/sq.cm and 50 deg C
Temperature after ejector: 60 deg C
Temperature after VSC (Vent Steam Condenser): 70 deg C
Temperature after GSC(Gland Steam Condenser): 82 deg C
Temperature after WHR(Waste Heat Recovery):120 deg C
At 120 deg C the water is fed again to the deaerator and the cycle repeats.
Pikesh Jain 14
Description of Thermal Power
Plant-2: 18.7 MW
COAL & ASH HANDLING CIRCUIT :
For this unit of Rabriyawas , the coal handling system is as similar as the that
of unit-1. The only difference lie is that after the vibrating screen the coal goes
on to the belt BC8 instead of BC3 .
Here the flow of coal is as follows:
BC1 BC2 VIBRATING SCREEN CRUSHER VIBRATING SCREEN 2
BC8 BC8ABC9BC10BC 11A
And the number of bunker is 2 with five hopper, with a capacity of 220 tons.
The conveying of coal and discharging of fly ash is similar to that of unit1.
Pikesh Jain 15
AIR & FLUE GAS CIRCUIT :
In this plant we have only one Induce Draft fan, Forced draft fan, Primary Air
fans for air & flue gas circuit.
All the process are same as that of unit-1.
F.D. fan takes the air from the atmosphere and is fed to the Air preheater.
In Air preheater the fresh air gets heat from the flue gases & thus becomes
hot i.e. it attain a temperature of about 140 deg C. 30% of this hot air is then
fed to the P.A. fan . The primary air from P.A. fan is used for conveying coal to
the furnace, while the remaining hot air i.e. secondary air is used for fluidizing
the bed.
The used air in the furnace is known as the Flue gas. This flue gases consist of
fly ash as well as high heat it have a temperature of approx 291.1 deg C.
therefore for utilizing this heat energy we passes it through the economizer
(to raise the temperature of feed water) , Air Preheater(to raise the
temperature of fresh air), ESP (to collect dust & fine particles in order to
decrease the pollution rate).
As this hot flue gas is passing through the economizer it heat the incoming
feed water. the exhaust flue gases from the economizer has sufficient heat
i.e. of temperature 226 deg C. As mentioned that this hot gas is used for
heating the fresh air while its passage through the APH.
While its flow through the ESP, fly ash are separated. And it is exhausted in the
atmosphere with a temperature of around 130 deg C.
In order to maintain a proper flow of flue gases from the furnace, a device is
needed for creating the suction and it is accomplished by the I.D. fan i.e.
induced draft fan.
I.D. fan create the suction in the system and that take off the flue gases and
exhaust it into atmosphere via chimney.
Pikesh Jain 16
WATER & STEAM CIRCUIT :
The D.M. water is fed into the deaerator where the dissolved oxygen is
removed form the water. The water level in the deaerator tank is maintained
at 1956 mm
The boiler feed pump, pumps all the incoming or stored water in the tank to
the boiler drum via economizer with a operating pressure of 84.3 kg/sq.cm.
While passing through the economizer it has initial temperature of 175 deg C
and get heated to a temperature of 282.6 deg C, with the help of flue gasses.
This warm water is feed to the boiler drum. From here it goes in the furnace for
further heating. With the help of down comer line the water passes through
the water tube and get start converting in the steam.
The saturated steam formed is separated in the boiler drum and pass through
the convective superheated where it is attain a temperature of 475.5 deg C
After convective super heater there is a provision of cooling down the
temperature of steam and i.e. by desuperheater.
Desuperheater makes the superheated steam to a temperature of 374.7 deg
C. In desuperheater there is a spray of water which lower the temperature of
superheated steam.
After this, it passes through a radiant superheater-1, where the steam get
more superheated by radiant method of heat transfer.
Again there is desuperheater for lowering the steam temperature.
And after this it passes through the radiant superheater-2, where it attains the
temperature and pressure according to the load.
Pikesh Jain 17
This super heated steam is finally pass to the turbine for generation of
electricity having a pressure of 64.2 kg/sq.cm and temperature of 472.5 deg
C.
STEAM CONDENSING CIRCUIT :
From turbine, the steam is extracted from three places that are:
3. to HP heater,
4. to Deaerator,
5. to LP heater,
and the final one is the main extraction line.
HP HEATER
The first extraction of steam from the turbine has a pressure and temperature
of 13.34 kg/cm sq and 321.36 deg C respectively. This steam is condensed by
the water coming from the deaerator via BFP and this condensed steam is
fed to the flash tank and deaerator. On the other hand, the water(139.66 deg
C) from deaerator get heated to a temperature of 190.04 deg C and this
water is fed to the economizer.
SPECIFICATION OF HP HEATER
SHELL SIDE TUBE SIDE
DESIGN PRESSURE 24 kg/cm.sq 120 kg/cm.sq
Pikesh Jain 18
DESIGN TEMPERATURE 215 kg/cm.sq 235 kg/cm.sq
SURFACE AREA 85 m sq
WEIGHT 7300 kg
DEAERATOR:
The second extraction is for the deaerator which is done at the temperature
and pressure of 335.9 deg C and 6.18 kg/cm sq.
This steam is used for the process of deaeration of incoming water, going to
the boiler. The deaerated water is stored in the deaeration tank. The
deaerator tank level is maintained at 13 75 mm.
This water is extracted from the tank by BFP and passed to the HP heater from
where it goes to boiler.
LP HEATER
The steam extracted from the turbine in the third stage is fed into the LP heater at
pressure and temperature of about 1.18kg/sq.cm and 129.90 deg C. This steam is
condensed with the help of cold water coming from the GSC. The condensed
steam is passed to the hot well via drain cooler. On the other hand, the condensed
water (61.48 deg C) from GSC get heated to a temperature of 108.17deg.C and
fed to the deaerator.
Pikesh Jain 19
SPECIFICATION OF LP HEATER
SHELL SIDE TUBE SIDE
DESIGN PRESSURE 3.5 kg/ sq.cm 20 kg/sq.cm
DESIGN TEMPERATURE 150 C 150 C
SURFACE AREA 75 sq.m
WEIGHT 4000 kg
TYPE U-Tube Horizontal
Pikesh Jain 20
Main Components Of Thermal
Power Plant
BOILER
The type of boiler in ACL Rabriyavas is of atmospheric fluidized bed combustion
type.
FLUIDISED BED COMBUSTION
FLUIDISED BED
When air or gas is passed through an inert bed of solid particle such as sand
supported on a fine mesh, the air initially will seek a path of least resistance and
pass upward through the sand. Which further increase in the velocity, the air
bubbles through the bed and particle attains a state of high turbulence. In such
condition the bed assumes the appearance of a fluid and exhibits the properties
associated with the fluid and hence the name fluidized bed.
MECHANISM OF FLUIDISED BED COMBUSTION
The sand in a fluidized state , is heated to the ignition temperature of the fuel and
the fuel is injected continuously into the bed, the fuel will burn rapidly and the bed
attains a uniform temperature due to effective burning. This, in short, is called
fluidized bed combustion.
Thus it is essential that temperature of bed temperature should be atleast equal to
ignition temperature of fuel and it will never be allowed to approach ash fusion
temperature (1050 deg C to 1150 deg C) to avoid melting of ash. This is achieved
by extracting heat from the bed by conductive and convective heat transfer
through tubes used in the bed.
Pikesh Jain 21
If velocity is to low, fluidization will not occur & if the gas velocity becomes too high,
the particles will be fed in the gas stream and lost. Hence to sustain stable
operation of the bed, it must be ensured that the velocity is maintained between
minimum fluidization velocity and particles entrainment velocity.
ADVANTAGES OF FBC BOILERS
The Considerable reduction in boiler size is possible due to high heat transfer
rate over a small heat transfer immersed in the bed.
Low combustion temperature of the order of 750 – 900 deg C facilitates
burning of coal with low ash fusion temperature, prevents NOx formation,
reduces high temperature corrosion and erosion, and minimizes
accumulation of harmful deposits due to low volatilization alkali components.
Such sulphur coals can be burnt efficiently without much generation of SOx
by feeding limestone continuously with the fuel.
These unit can be designed to burn a variety of fuels including low grade
coals like floatation slimes and periphery rejects without much sacrifice in
operation efficiency, because only about 1% by weight of carbon content in
the bed can sustain the fluidized bed combustion.
The formation of sticky deposits on the fire side of the tubes because of
lowering temperature by sodium components in ash is avoided due to low
bed temperatures.
Lower coal crushing cost due to higher particle size.
Using FBC, the plant efficiency goes to 80%
Pikesh Jain 22
STARTING OF ALL INDIVIDUAL EQUIPMENT:
The sequence of starting of the equipments is as follows:
1. check water level gauge for water in shell/drum
2. start the ID fan
3. start the FD fan
4. start the PA fan
Pikesh Jain 23
5. start the fuel feeding
Starting the ID fan
Before starting the fan close the damper on the suction side of the fan. If the fan
is started with damper in partially open condition, the fan may trip due to
overload or the fuses may get blown off. The fan may also fail to start, if the
water level in the drum is less then the trip level.
Starting of FD fan
It is to be carried out similar to that of ID fan by keeping the inlet damper close.
FD fan can be started only if the ID fan is running.
Starting of PA fan
PA fan should be started after the ID and FD fan have been started.
Starting of the fuel feeder
In FBC boiler, the fuel should not be fed when the bed material is cold and bed
temperature is less than 600 deg C in case of coal as fuel.
Hence before taking the trial run of the feeder care should be taken so that fuel
does not enter the furnace during the trial run.
This can be done in two ways:
The fuel between the gate and the feeder can removed after closing
fuel chute gate before taking the trial run.
The chain can be removed and the system can be checked upto the
output shaft of gear box.
Starting of Feed Pumps:
Ensure that the suction valve is open and water is available in the tank. Also ensure
that the valve in the min. recirculation line is open and the discharge valve or the
feed control valve including the bypass valve is closed. Then start the feed pump. Do
not close the suction valve, when the pump is running. The min. recirculation valve to
be opened at the time of starting the pump and immediately closed, after outlet
valve is open. Do not run the feed pump without suction filter. During normal running
of boiler the pump can be started/stopped with discharge valve open, since the
feed line is under pressurized condition.
Pikesh Jain 24
BOILER LIGHT UP:
The light up is done using charcoal and diesel as explained below:
A fixed quantity of dry charcoal is spread uniformly over the startup compartment
A fixed quantity of diesel mixed charcoal is spread uniformly over the dry charcoal
The fire is initiated using a burner.
Further by proper air flow control fire can be spread and the heat released by the
charcoal is utilized to heat the bed material to a temp above the ignition temp of
the fuel
In the process of preheating bed material the required fluidization velocity is
maintained in the bed by suitably opening the FD fan inlet damper
Further the fuel feed rate is adjusted to maintain a bed temp of 800 to 850 deg C
The charcoal of size below 15mm shall not be accounted for the above quantity
Keep the ID fan damper open at the time of lighting up. This would reduce the
possibility of furnaces puff.
Initiate the fire busing no. of swab. Throw the swab in such a way that fire spread
uniformly over the entire surface.
The lighting of the boiler is to be done with the help of charcoal and diesel. The light up is
to be done only for a single compartment. After stabilizing with a single compartment fire
is transferred to the other compartment as per the procedure explain separately.
COMPARTMENTAL TRANSFER
The start up with one compartment is recommended for the following reasons:
1) Gradual loading of pressure parts
2) Reduction of charcoal for startup
3) Load variation
The compartment transfer means activating a static compartment of the furnace
adjacent to the activated compartment. This is done just by admitting the fluidizing air
to the compartment to be activated and mixing the cold material with hot material of
the operating compartment.
Before activating a static compartment the air flow in the fluidizing compartment shall
be increased to 120% of the MCR air flow, and a fuel feed rate should be
correspondingly increase to maintain the bed temp of 900 degC.
Pikesh Jain 25
Now open a compartment air damper of the adjacent compartment which is to be
activated. The cold bed material in this compartment would begin to mix up with hot
bed material in the operating compartment. The bed temp in new compartment
would begin to rise.
The bed temperature in operating compartment shall be once again brought up to
900 deg C before another attempt is made.
By following the process of mixing the bed material of the compartment to be
activated with that of the operating compartment, on one or many attempts, the
activation can be completed. The bed temperature of any compartment shall be
brought to at least 600 deg C before fuel feeding is commenced.
The primary air line in the new compartment shall be opened and the fuel feeding
can be commenced and the bed temperature shall be brought to 800 deg C MCR
fluidizing air flow condition. Care shall be taken not to drop the temperature of the
operating compartment below 600 deg C in the process of activating adjacent
compartment.
If by mistake, the temperature of the operating compartment drops below 600 deg C
it becomes necessary to raise the temperature using charcoal.
NORMAL OPERATION
LOAD CONTROL:
The steam generation needs to be matched with that of demand to avoid venting of
the steam. If the steam drawn from the boiler is less compared to the steam generated
and then the pressure would rise and thus resulting in the lifting of the safety valve.
Frequent lifting of safety valve will damage the safety valve seat. Steam generation
can be varied by slumping compartments or by varying the fluidization air flow or by
varying the bed temperature or by varying the bed height.
Load variation of 70% to 100% may be obtained by varying the bed temperature. The
bed temperature can be reduced to 700 degC and can be increased to 900 degC
based on demand. For this purpose the fuel feed rate needs to be varied. Further
turndown is also possible by reducing the fluidization air flow but not to the extent of
defluidization of the bed. In such case the air flow through primary air line should never
be reduced. Only the fluidizing air flow should be reduced. Further load controlling is
done by slumping the compartment. The compartment can be slumped only from
either end of the bed. in case of three compartment only first or third compartment is
to be slumped before the middle compartment is slumped.
Pikesh Jain 26
Slumping of the compartment is to be done as explained here. Bring down the fuel
rate to minimum and switch off the feeder. Wait till the bottom bed temp comes
around 850 deg C and then closed the fluidizing air damper of the compartment.
Then closed the fuel transport air line damper. When the fluidizing air through a
compartment is cut off, the air through the other compartment could increase. This air
flow shall be adjusted by throttling inlet damper of FD fan. Further draft in the furnace
shall be adjusted by throttling of ID fan inlet damper.
Reactivation of the compartment shall be done in the following sequences. Open the
fuel transport air line valve first and ensure the required air pressure is available in the
PA fan header. If the line is chocked, chokes shall be removed by use the drain gate,
of the fuel transport line. Then open the fluidizing air damper and set the FD fan inlet
damper for the required flow. If the bed temp is above 600deg C fuel feed shall be
initiated and the bed temp shall be brought to the required operating temperature.
SLUMPING SEQUENCE
After running all the compartment at least once, the following philosophy shall be
adopted for meeting the load throw off.
75% LOAD
75% load can be achieved either by operating all the compartments under
reduced bed temperature. When the steam demand comes down to around 75%,
then the air flow has to be correspondingly reduced. To prevent the bed
temperature from shooting up. Fuel feed rate also has to be reduced thereby
reducing the total heat input to the boiler. Thus the reduced steam demand can
be met.
Alternatively 75% Load can be met by slumping compartment 1 or 2 and reducing
the air flow to the level specified for remaining compartments operation. During
slumping of a compartment proper sequence has to be followed as given below
1. stop the fuel feeder of the compartment to be slump
2. after two min stop the air flow to the compartment to be slump
3. reduce the air flow to the specified level for five compartment operation
it is not advisable to keep particular compartment slump for a long duration. Hence
it is suggested to activate the slump compartment after certain interval and slump
the other compartment
60% LOAD
Pikesh Jain 27
60% MCR load can be achieved by slumping one compartments and reducing the
air flow and fuel feed rate. A lower bed temperature than 900 degC may have to
be maintained by adjusting the fuel feed rate to meet the steam demand.
50% LOAD
50% MCR load can be achieved with 3 compartments. With this combustion,
though the steam flow can be matched, there may be a shortfall in superheated
steam temperature when the feed water temperature is more than 105 deg C. in
this arrangement one FD fan can be stopped in 15 MW plant. If compartments 3, 4
&6 or 4,5 & 6 are run then superheated steam temperature can be achieved .
however both the FD fan have to be operated.
40 % LOAD
40 %MCR load can be achieved by keeping the 3 compartments in operation
(indicated for 50 % MCR operation) and reducing the air flow and fuel feed rate.
However at high feed water temperature there will be shortfall in superheated
steam temperature while only 3 compartments are in operation.
IMPORTANT NOTE
1. During cold start compartment which are having the bed superheated
should be activated only after stabilizing other compartment or after ensuring
that 30% MCR steam is generated or vented.
2. During hot restart, if the compartments which are not lighted directly by
burners, have to be restarted after a long gap it is preferable to cool down
the entire bed and start from compartment 1 & 2 to avoid overheating of
bed super heater coil.
ASH REMOVAL
The ash should be drained from all collecting point. Failure to remove the gas will
result in choking of the flue gas path.
BOILER TRIPING DUE TO POWER CUT
In this case immediately close the inlet dampers of the FD, ID fan. In the event of power
availability and if the boiler is required to be started immediately switch on the fan.
Establishing the air flow and start fuel feeding. Otherwise if the boiler is to be boxed up,
close the main steam stop valve. Close the compartment damper also.
INGRESS OF FOREIGN MATTER IN FUEL:
Pikesh Jain 28
Ingress of cotton waste, cloth, coconut shell etc. will block the fuel flow from the chute
into the feeder. This is indicated by the drop in bed temperature provided the fed rate
of feeder is not increased.
The above mentioned problem can be eliminated if a screen is provided in the fuel
handling system.
At times it may so happen that the foreign matter may block the fuel transport line
when there is no air flow in the fuel transport line, the bed material from the bed enter
the fuel fed nozzle leads to choking of the line. The choking should be removed by
slumping the bed and by opening the drain gates.
NORMAL SHUT DOWN TO COLD
During shut down of boiler to the cold condition, the following steps are followed:
Reduce the fuel feed rate
Stop the fuel feeder
Maintain the same air flow to cool the bed faster
For slow cooling:
In this condition switch off the FD, ID fan when the bed temperature fall below 500
deg.C
For fast cooling
In this condition, keep the fan open till the temperature come down to 100 deg C
In both condition the blow down valve should be open.
NORMAL SHUT DOWN TO HOT STAND BY:
If boiler has to be put on standby for several hour like 2hrs, then following procedure has
to follows:
Switch off the fuel feeder
Switch off the FD, PA and ID fan
Do not reduce boiler pressure line. Keep the boiler pressure at desired pressure at
which it can withstand by closing main steam valve.
Pikesh Jain 29
HOT RESTART OF BOILER
For starting the boiler from standby, then following operation has to be followed:
Open the air vent and fluidizing air damper
Open FD, PA damper
Start ID, FD & PA fan
Start the fuel feeder
SPECIFICATION OF BOILER
MAKE Cethar Vessel Pvt. Ltd
TYPE Single Drum Water Tube Boiler(FBC)
CAPACITY 80 TPH
PRESSURE 65 kg/cm.sq
TEMPERATURE 495+/-10 deg. C
FUEL FIRING Coal
FEEDER TYPE Drag Chain(new plant) and Pocket
Feeder(old plant)
BED SIZE 5105 X 8950 mm sq
EXPANDED BED HEIGHT 998 mm
HEAT INPUT 68027637 Kcal/hr
EXISTING BOILER HEATING SURFACE
AREA
2285 m sq
BOILER DRUM
Boiler drum is the equipment used for storing the water as well as for separation
of steam from water.
Pikesh Jain 30
Water from the economizer is fed into the boiler drum. Through down comer tubes
it is fed in the furnace via water tubes, where this water start converting in the steam
and start rising in the boiler drum via riser tube. In this way, steam is produced. Now
the saturated steam is separated from the water by turbo separator and fed to the
convective superheater for superheating of the steam.
SPECIFICATION OF BOILER DRUM
MAKE Cethar Vessel Pvt. Ltd.
CAPACITY 80,000 kg/hr
MAX. WORKING PRESSURE 78 kg/cm.sq
SUPERHEAT OUTLET PRESSURE 66 kg/cm.sq
SUPERHEAT OUTLET TEMPERATURE 495+/-5 deg. C
BURNER
Burners play an important role in the combustion process i.e. during the cold
startup. It is used for burning the fuel to light up the boiler. The burner have
following characteristics:
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Make Wesman
Application Startup of boiler
Fuel Light diesel oil(LDO)
Type Air atomized
Oil through out 20 lt/hr
Oil pressure 3 kg/sq cm
Atomizing air pressure 800 mmWC
Combustion Air pressure 400 mmwc
Fixing arrangement Inclined
Combustion air temperature 40 deg C
Furnace back pressure -5 mmWC
Type of ignition Manual
Type of atomization By air
Location Furnace refractory wall
FANS:
In power plant, HA series fans are used which have been designed for medium and
heavy duty application.
The fan are available with backward curve, backward inline and straight radial
blade.
These fans are of single inlet and single width type.
Static Parts Of The Fans:
1. Casing: single or impart casing is provided with inspection door, drain plug
and sealing plates
2. Inlet Cone: it is space from where the air enter
3. Pedestal
Rotating Parts Of The Fans:
1. Impeller: it is made of high tensile steel and mounted on the main shaft.
2. Shaft fitted with bearing and housing
3. Flexible coupling with guard
4. Cooling disc with guard, if required.
Accessories of Fans:
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1. Flexible connections: it is provided between the fan and the ducts. It protect
fan from the damage caused due to expansion in the duct system. If fan is
mounted on anti vibration mounting then this connection must be provided
in order to have complete vibration isolation.
2. Cooling Disc: it is mounted on fan shaft. It is supplied incase the air or gas
temperature handle by the fans exceed 100 degC. Cooling is made up of
halves.
Additional Accessories & Features:
Inlet multi louver damper
Inlet guide vane
Inlet box
Sound absorber
Vibration isolator
Damper actuator
Bearing temperature indicator
Vibration monitor
Shock pulse monitor.
In plant we have three types of fans for operation, namely:
INDUCED DRAFT(ID) FAN
FORCED DRAFT (FD) FAN
PRIMARY AIR (PA) FAN
Specifications of these fans are as follows:
FD FAN :
The purpose of force draft fan is feed the air in the system. The specification
of this fan is given below
Type Centrifugal
Medium Ambient Air
Flow cu.m/sec 17.4
Pressure mmWC 835
Temperatue degC 40
Type of drive Direct coupled
Speed 1480 rpm
Casing orientation ACW-10(FD-1)
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CW-2(FD-2)
Motor rating 200kw/270 hp
Motor make ABB
Bearing 22226EK/C3
Bearing make SKF
Coupling A236
PA FAN:
The function of primary air fan is to feed the air for carrying the coal to the
furnace. The specification of this fan is given below:
Type Centrifugal
Medium Hot air
Flow 3.23 cu.m/sec
Pressure 715mmWC
Temperature 150 degC
Type of drive Direct coupled
Speed 2940 rpm
Casing orientation ACW-10 (PA-1)
CW-2(PA-2)
Motor rating 37 kw/50 hp
Motor make ABB
Bearing 22226EK/C3
Bearing make SKF
Coupling A236
TURBINE
FUNCTION
The function of the turbine is to drive an A.C. generator at a speed of 3000 R.P.M.
CONSTRUCTION OF TURBINE
The principle component part of the outer casing of the turbine are front section,
the exhaust section and middle section whose length depends on required no. of
stages
The front and the middle section are made up of cast steel and are single casing.
The welded exhaust section is bolted to the middle section.
Pikesh Jain 34
The outer casing is horizontally split and the top and bottom halves are held
together by a bolted flange.
FRONT SECTION
The front section can be subdivided into 3 parts:-
1. The Admission
2. The Control Valve Chest
3. The Front Bearing
The Admission:-
It incorporates a horizontally split inner casing in order to achieve a good efficiency
and simultaneously reduce the pressure on the outer casing. The inner casing is
supported in the outer casing so that it is free to expand in all the directions. In the
inner casing there are four nozzle groups which admit the steam to the control
stage & then into the wheel chamber of the inner casing.
There are sealing strips in the inner casing which mess with sealing strips in the
turbine rotor to form a labyrinth seal in which there are no physical contact. The
main steam enters the inner casing through inlet connections bolted to the outer
casing. In addition to the four nozzle groups there is an extra bypass inlet
connection for the direct admission of the initial steam into the wheel chamber of
the inner casing.
Steam Flow:-The steam passes through two inlet branches, emergency stop valves
of the control valve chest. When these control valves lift, the steam flows into the inner
casing. The inlet connections of the initial steam lines run towards the middle of the
turbine, which means that at first the steam flows away from the exhaust section. The
exhaust steam cools the inner wall of the casing admission section so that it cannot be
heated to the temp. of the initial steam by either the inlet connection or the radiated
heat from the inlet section of the inner casing.
Then the steam flows into the middle portion and then to the exhaust portion after
expanding to the condenser pressure.
Thrust Balance:-
The axial thrust produced in the moving blades is balanced by the dummy piston
near the nozzle chambers. The leakage steam from the dummy piston flows directly
from the labyrinth seal to the second drum stages in the middle portion whose
direction of flow is opposite to that of the first drum stages.
Since the dia of the dummy piston can not be normally made as large as really
necessary. A second piston Is provided near the front gland bush. It is exposed to
Pikesh Jain 35
the pressure of the steam after the inner casing. The leakage steam from this large
piston has already given up the power in the first drum stages which reduces the
loss of efficiency.
Control Valve Chest
The characteristic feature of this range of turbine are the control valve chest
placed at the side of the turbine. This reduces the overall height and allow the outer
casing to the symmetrical in the radial section. Also there is no contact between
initial steam and the outer casing.
Each control valve chest contain an emergency stop valve and two or three
control valve.
Since the casing admission has four inlet connection for the nozzle group and one
for the bypass in to wheel chamber and the control valve chest on the one side of
the turbine has three control valve and that on the other two valve. Whenever
there is no bypass valve, both the valve chest shall have two control valve each.
Each control valve chest has its own actuator which operates the 2 or 3 control
valve stems through a lever. Each control valve has a separate packed steam
gland.
The body of the emergency stop valve for each group of the control valve is
welded to the control valve chest. The hydraulic part of the emergency stop valve
incorporating the actuating piston is flange mounted on the valve body.
The emergency stop valve is the main shut off device b/w the steam supply system
and the turbine. A drop in pressure in the trip oil circuit causes the valve to interrupt
the steam supply to the turbine very rapidly.
Front Bearing
It comprises the pedestal, bearing housing and the main oil pump.
The pedestal support the front paw as well as the bearing housing. This
construction safely avoid any tilting of the bearing house as a result of thermal
movement of the outer casing.
The bearing housing is aligned parallel to are the turbine axis on a centralizing key in
the pedestal. This guide permits free movement in the axial direction and is aligned
transversely by adjusting devices. The bearing housing is freely supported on
adjusting devices in the pedestals. It is constrained by stud to prevent lifting. This
Pikesh Jain 36
stud allow clearance of few hundredth of mm b/w the bearing housing and the
pedestal in the vertical direction in order to ensure unrestricted sliding. The sliding
surface of the adjusting devices are coated with a special sliding substances.
The main oil pump is driven directly from the turbine rotor through an oil lubricated
toothed coupling. The pump is mounted solidly on the bearing pedestal. This means
that the toothed coupling accommodates any displacement b/w the turbine rotor
and pump shaft due to thermal expansion of the turbine casing.
MIDDLE SECTION
It provides space for blading after balanced piston gland to exhaust portion.
Turbine Rotor And Bearing
The turbine rotor is a single forging incorporating the thrust bearing collar and
coupling flange. It is supported in two pressure lubricated journal bearings. The
bearing have a shaft lift oil system which enables the rotor to be raised from
contact with the bearings while at rest. This ensures minimum wear during start up
and permit warming up and cooling down at low revolutions. The thrust bearing is of
the double sided type with tilting segmental pads. It locates the rotor relative to the
casing and absorbs any residual steam from the balding. It also formed the fixed
point of the rotor in the front bearing housing which means that , as the
temperature of the turbine casing rises, the rotor is carried forward by the bearing
housing. Since the rotor temp rises at the same time causing expansion, the end
result for the coupling flange at the rear of the rotor is only a small movement
relative to a fixed point of the turbine.
Casing Shaft Gland
Where the rotor shaft penetrates the turbine casing the internal steam space is
sealed to the atm. By the gland bushes. These bushes have caulked in sealing strip
which mesh with similar strips caulked in to the shaft to form a sealing in which there
is no metal to metal contact.
The rows of sealing strip from a labyrinth gland which drives its sealing effect from
the conversion of pressure energy into kinetic energy with subsequent conversion of
heat through the eddying of flow. The pressure is reduced to the point where , at
the final row of strip, there is only a very small excess pressure remaining. Most of the
leakage steam is bleed off from the center of the gland bush & therefore only a
very small portion of the total steam reaches the vapour pipe at the end of gland
bush and escapes to the atmosphere.
Blading
Pikesh Jain 37
The turbine contains fixed and moving blades.
Two different types of moving blades are used: impulse blades for the control stage
& reaction blades for the drum balding.
A control stage is needed if nozzle group control of the steam flow is employed. It
must be an impulse stage because of the possible use of partial admission.
The nozzles of the control stage are machined and mounted in slots in the inner
casing; therefore they can be changed individually if necessary.
The moving blades of the control stage are also machined and have a twin lug
straddle root with integral shrouding.
Apart from the last three rows the moving blades employed of the drum balding
have inverted T roots & integral shrouding. The inverted T roots are inserted into
grooves in the rotor and caulked with sectional strip to secure them. The roots of the
blades are sized so that when the blades lined up they produce passage of the
required size without the need for spacers. A gate blade fills the point of entry to the
groove so that there is no gap in the ring of blades nor any sudden change in the
pitch. The gate blade is secured to the rotor by grub screws.
Unlike the remainder of the drum balding, the moving blades of the last 3 rows have
no shrouding. The third from last rows has inverted T roots. The last row have twisted
moving blades which have been drop forged. These blades have fir tree roots
which are inserted into appropriate grooves in the rotor.
Blade Tip Sealing
The radial tip clearance of all fixed and moving blades with shrouding is several
mm. Therefore stationary & moving parts cannot come into contact with each
other even when distortion of the rotor & casing occurs. The large radial clearance
is sealed by shrouding in order to keep the power losses due to tip losses to
minimum.
In the case of the fixed blades the sealing strips are caulked into the turbine rotor
and for the moving blade, into the guide blade carrier. The thin sealing strips leave
only a few tenths of a mm. clearance b/w the shrouding & the rotor, guide blade
carrier. If the sealing strips touch, the amount of heat generated is so slight that no
dangerous distortion of the guide blade carrier of rotor can result.
Guide Blade Carrier
Function
Pikesh Jain 38
Its function is to support the fixed guide blades in the turbine. The use of guide
blade carriers enables damage guide blades to be changed without having to
dismantle the bottom half of the outer casing & its pipe work connections.
Construction
The guide blade carrier is of horizontally split design with a bolted flange. it is
supported and located axially in the outer casing by the means of a circumferential
groove which engages with a cast projection.
The paws of the bottom half of the carriers are supported in recesses in the bottoms
half of the outer casing. Adjusting devices enable it to lined up level with the turbine
axis. Side alignment is provided by an eccentric pin which engages in a slot in the
bottom half of the outer casing at right angles to the joint faces.
The support surfaces of the carrier paw and the eccentric pin lie in symmetrical
planes in order to prevent any distortion arising from thermal expansion.
Steam Labyrinth Gland
Purpose
The packing gland shell carries on the periphery of the inner surface caulked in
sealing strip which together with the edges of the corresponding sealing strips of
comb like projection on the rotor shaft, are forming a seal without mechanical
contact b/w the moving rotor and stationary turbine casing.
A seal of the labyrinth type act on the principle of transforming potential energy
into kinetic energy and subsequently dissipating the kinetic energy by the formation
of eddies.
Packing glands for sealing against Positive Pressure
With packing glands intended for sealing against a higher pressure prevailing in the
turbine casing, the major part of the leak steam flow will be exhausted from the
middle section of the gland shell. Only a very small part of the leak steam flow is
thus allowed to penetrate into the collecting groove provided at the downstream
end of the gland from where it will escape via the gland steam stack into the
atmosphere.
A disk shaped annular fin on the turbine shaft, which extends into the collecting
groove, aspirates air by centrifugal action from the atmospheric end of the packing
gland and delivers it into the gland steam stack. This is an effective means for
preventing the sealing steam which may be leaking out of the packing gland from
blowing against adjacent bearing sections and heating them up.
Packing glands for sealing against Negative Pressure
Pikesh Jain 39
Packing glands for sealing against negative pressure reigning in the turbine casing
have to block the penetration of air into the casing. The respective passage of the
packing gland, instead of serving for sucking off leak steam, will be connected to a
steam supply of slight positive pressure. The flow of this sealing steam will be split into
two parts. One part of the steam goes into the turbine casing, other to the gland
steam stack from where it escapes into the atmosphere. This latter part of the leak
steam prevents the penetration of air into the portion of packing gland, which is
situated b/w the gland steam stack and the sealing steam connection.
CONDENSATE DRAIN
Condensate accumulating in those passages of the packing gland, where the
gland steam is flowing, will be effectively drained through a hole drilled at lowest
point of the gland.
STEAM STRAINERS
Functions:
Steam strainers are initiated in the main steam lines and in the reheat lines from the
boiler to protect the admission elements of the HP and the LP turbines from foreign
objects which could be picked up in the boiler or associated piping.
Construction:
the strainer is made of corrugated strip wound on a frame. This design offers a high
degree of resistance even to particles impenging at high velocity. The frame
consists of two rings and number of rods welded b/w the rings. The rods additionally
braced by reinforcing rings welded inside them. The strainer is designed for a single
direction of flow the outside inwards. For longer strainers the screen is made up of
several parts.
The end turns of the corrugated strip are then tacked to the T section intermediate
rings. The maximum mesh size of the strainer which is determined by the height of
that corrugation is 1.6 mm. the effective area is made at least 3 times the cross
section area of the pipe. The strainer may be used for both initial commission of the
turbine and for regular operation.
CONTROL VALVES
Function:
the control valves are opened and closed in order to adjust the throughput of
steam to give the required power out put from the turbine. Depending upon the
power requirement the control valves are opened or closed in the specific
sequence. The valve seats are in the form of diffusers in order to keep flow losses to
a minimum.
Pikesh Jain 40
Construction:
The steam chest contains a valve cross bar in which the actual control valve are
suspended loosely. The cross bar is connected to the arm through two stems and
the pivoted links. The arm is operated by the actuator which is flexibly mounted on
the bracket attached to the steam chest.
The steam chest has two bonnets in which the valve stems are guided by two rings.
The rings also form the top and bottom stem glands.
Each stem head is loaded by a compression spring, so that the control valves are
held closed when the turbine is stationary.
Operation:
when the turbine is at rest the springs keep the cross bar in its lowest position and
the cons of the control valves are forced on to their seats by the pressure of steam.
A control pulse from the governor causes the actuator to pull the arm downwards,
thus raising the stems and lifting the cross bar. The valves then lift in a sequence
determined by the different lengths of the spacer bushes in the cross bar.
GOVERNING SYSTEM
Introduction:
The turbo generator set is equipped with electro hydraulic governing system. The
system offers the advantages of electronic methods for measurement and signal
processing and use of hydraulic devices for control of large positioning drives.
The advantages of this combination are
Better integration capability
High quality steady state and dynamic response
Facility for implementation of complicated function.
The signal processing, control function and inter locks are incorporated in the
electronic controlled cubicle, which is placed in the control room. An electro
hydraulic converter provides the link b/w electronic and hydraulic section.
Electro hydraulic turbine controller: Controls speed, load and inlet pressure.
Additionally the system incorporates protective devices like emergency trip device,
emergency stop valve, remote trip solenoid valve, over speed governor, thrust
bearing safety device.
Purpose:
Starting a turbine from the control room requires, remote control of the emergency
trip gear. Such control will be achieved by the following devices:
1) Solenoid valve
Pikesh Jain 41
2) An automatically control switch with interlocking mechanism which will block
the switch in open position.
Operation:
After the starting device has been brought into the starting position the solenoid
valve will be moved through the action of the control switch. This will allow pressure
oil to flow via the solenoid valve to the auxiliary piston of the emergency trip gear.
The described position of the control elements allows the building up of the system
oil pressure in the emergency tripping and starting oil circuits, thus enabling the
emergency trip gear to hold itself in the operating position. To the extent as these
pressures arising , the pressure switch is going to be actuated.
SPECIFICATION OF TURBINE
TYPE NK-40/56-3
MAX OUTPUT POWER 18.7 MW
DESIGN RATING 19.6 MW
SPEED 7700 rpm
INITIAL STEAM PRESSURE 64 ata
PREMISSIBLE DEVIATION IN PRESSURE 67.3 ata
INTIAL STEAM TEMPERATURE 490 C
PESSURE AT HP WHEEL CHAMBER 47 ata
EXHAUST PRESSURE 0.2 ata
PROTECTIVE EQUIPMENTS FOR TURBINE
Types:
1) Emergency Stop Valve:
Purpose:
The emergency stop valve serve as the principal shutting off device b/w steam
system and turbine. Under ordinary operating as well as under emergency
conditions it causes instantaneous interruption of the steam supply to the turbine.
The emergency stop valve is horizontally mounted to the steam chest of the outer
turbine casing ; it consists of steam section and an oil section with hydraulic servo
cylinder.
Pikesh Jain 42
Mode of operation:
Steam Section
Live steam, after having passed through strainer, arrives at valve cone which has
been provided with a relief cone owing to its considerably smaller area in
comparison to the area of the main cone, the relief help in reducing the forces
when the emergency stop valve is been opened, because it tends to balance the
pressure differential existing b/w the upstream and the downstream side of the main
cone. a bushing in the valve hub carrying a knife edge which acts as an additional
seal for the space behind the valve hub against the pressure of the live steam as
long as emergency stop valve is opened. In this way , the lost steam, which
otherwise may leak out along the valve steam is precluded all the time stop valve
remain in the open position. In closed position any leak steam which happened to
seep out b/w valve stem and the bushing will be drained off through the line the
major part of the steam pressure force acting upon the valve hub is transmitted
directly to the outer casing surrounding the steam section of the stop valve.
2) Speed Monitoring:
Function:
Convenience of operation or local site condition of a turbine plant sometimes
warrant the accurate measuring of remote reading of the turbine speed. To this
effect, the speed will be measured by electromagnetic pick up which does not
require mechanical contact with rotating part. This signal may also be used as input
for supplementary governor and control equipment.
Operation:
when the perforated disc rotating the front of the pick up this produces a frequency
proportional to the speed of turbine rotor. The pick up frequency is converted into
the speed proportional current in a converter and measured on an indicating
instrument.
3) Vibration Monitoring:
Function:
Vibration of turbine, originates from the rotor and is transmitted to the external
bearing housings through the bearing oil fill which has both spring and damping
effect.
When measuring the absolute bearing housing vibration, only secondary effect of
the vibrations is detected. The vibration can be measured at the surface of housing
can only give a general indication of the vibration behavior of a turbine. The
measurement do not have the same validity as measurement of the shaft vibration
Pikesh Jain 43
because the rotating mass is usually relatively small compared with the stationary
mass and the vibration is not transmitted fully.
Vibration measurement directly from the rotor of the turbine has proved in practices
to be the best form of the monitoring. By connecting dotted line or continuous line
recorders to the output of measuring device it is possible to connected to detect
changes in the vibration level which provide an early warning of damage.
For simple monitoring measurement of the vibration (peak value) in the one
direction can be adequate depending upon the specified requirement. For
complete acquisition of the vibration behavior according to VDI 2059 it is usually
necessary to provide 2 sensors at 90degree to each other at each measuring point.
SHAFT VIBRATION (PEAK TO PEAK) IN MICRONS
OPERATING
PARAMETER (micron)
INTERLOCK
PARAMETER (micron)
TURBINE
Front A VYX101
Front B VYX101B
29.7
34.4
170
170
Rear A VYX102
Rear B VYX102B
35.2
46.2
170
170
GEAR BOX
HSS A VYX103
HSS B VYX103B
5.6
6.0
160
160
LSS A VYX104
LSS B VYX104B
26.3
23.1
160
160
GENERATOR
FRONT A VYX105
FRONT B VYX105B
44.1
53.9
200
200
REAR A VYX106
REAR B VYX106B
48.8
50.3
200
200
LUBE OIL SYSTEM
A satisfactory & continuous supply of oil is essential for the safe & reliable running of
a turbine & its driven equipments.
The Oil supply system includes the following equipments:-
MAIN OIL TANK:- Housing the oil volume required for lubricating oil & governing
system.
Pikesh Jain 44
LUBE OIL PUMPS:- It is a single stage centrifugal pump driven by A.C. motor. The
pump delivers the total oil required for the governing & lubricating oil systems.
EMERGENCY OIL PUMPS:- During coasting down of turbine when lube oil pump
is not available lubricating oil is provided by emergency oil pump. It is operated
by a D.C. source.
OVERHEAD OIL TANK:- When emergency oil pump also fails as a last option to
protect bearing, an overhead oil tank is provided. This tank is kept at an
elevation so that oil flows through gravity.
TWIN OIL COOLERS:- The heat absorbed in the bearing is dissipated in the oil
cooler which is of shell & tube design. The system consists of two oil coolers
each of 100% capacity.
DUPLEX TYPE OIL FILTERS:- The Duplex type oil filter with disposable cartridge type
with filtration of 10 microns is provided to supply clean oil to the bearings.
Adjustable bearing oil throttles, which permit adjustment in the oil quantity
required for respective bearings.
OIL VAPOUR EXTRACTION FANS:- To remove oil vapors settled over the oil
surface in oil tank.
TURNING DEVICE:-
During turbine start up & shut down operations the rotor has to be turned. If a hot
turbine is shut down & the turbine rotor is not turned, distortion of the rotor will
occur after sometime & of high significance. If any immediate restart is required
the resultant eccentricity of the rotor can cause serious damage to the blade tip
sealing or to the blade themselves due to rubbing. In addition, the excessive
vibration due to unbalance of the rotor can lead to wearing of the bearings.
During the turning operation an A.C. motor drives the turning gear. For starting
turning operation, the Clutch has to be engaged manually when shaft train is in
standstill condition. As the turbine picks up the speed, the shaft train tends to
overtake the turning drive, the clutch is disengaged automatically.
The turning gear is provided on extension of input shaft of gear box. The turning
gear is also provided with hand wheel to turn the rotor when A.C. power is not
available.
Pikesh Jain 45
JACKING OIL SYSTEM:-
Function:-
Before a turbine is started up the shaft journals are in contact with the white metal
of the bearings due to its own weight.
In order to prevent the metal to metal contact b/w journal & bearing shell during
startup & shut down, which is damaging in the long term, an oil pocket machined
into the bottom shell of the journal bearing is supplied with oil under high pressure.
This lifts the shafting system slightly & it floats on a film of oil. Now the break away
torque (frictional torque required to overcome the metal to metal contact during
starting) depends on shear stress in the oil film, so the torque exerted by the turning
gear is less and hence the oil required for lifting the shaft is less.
TURBINE INTEGRAL STEAM FLOW SYSTEM
Live Steam System: The turbine is supplied with live steam from a steam source of
64 ata , 490 deg C.
During start up steam is admitted steadily for warming up the live steam piping
upto the turbine. During this period steam is vented to the atmosphere. Any
condensate formed shall be drained initially through the drain valves.
Turbine: The steam from live steam system is admitted into the turbine through
emergency stop valve and governing valves. The balance piston leak off line is
connected to second extraction line to deaerator.
Turbine Extraction System:
The turbine is a single cylinder machine with 3 uncontrolled extractions:
1) HP heater
2) Deaerator
3) LP heater
Power assisted check valves are provided one in each line, to prevent back flow of
the steam and causing over speeding of turbine. The valves are hooked up to the
turbine governing system to make them close with every trip of the turbine.
Extraction Drain System:
All the extraction lines are provided with drain points to drain condensate during
warming up of the pipes, during heated out conditions and during turbine trip
conditions.
It is recommended to keep all the drain valves open up to 10% of block load on
turbine to avoid any accumulation of drain in the piping. This drain valve shall be
Pikesh Jain 46
closed after attainment of above conditions. The drains upstream of extraction NRV
are connected to condenser surge pipe and downstream drains connected to
drain flash tank.
GLAND SEALING SYSTEM:
It is necessary to seal the gland steam of condensing turbine to maintain the
vacuums in turbine and condensing system. The vacuum in the system is
maintained by supplying steam at 1.1 ata . Through a source of 11 ata, 350 deg. C
continuously to turbine glands.
The pressure controller is set at 1.1 kg/cm2 and the steam is supplied from the
auxiliary steam header to gland steam header through the control valve.
Chimney Steam:
The steam from turbine gland is evacuated to gland steam condenser. This shall
prevent steam oozing out from the gland and heating the bearing pedestals. 2
ejectors are mounted on the GSC for evacuation.
Exhaust Hood Spray System:
It may necessary to run the turbine in no load condition for prolonged periods.
During this period, the exhausted hood temperature will rise beyond safe limits,
especially from material strength point of view. Hence it is necessary to limit the
exhaust hood temperature by cooling the exhaust steam by spraying condensate
through spray nozzle fitted in the exhaust. The spray water is taken from condensate
extraction discharge. The spray water is supplied to spray nozzle via a solenoid
operated valve. This valve opens automatically by means of the temperature
switch mounted on the exhaust hood whenever temp. exceeds the preset limit.
Whenever the temp. return to a safe limit the solenoid valve closes automatically.
Thus stopping the spray water supply.
Turbine Drain: The drain from all spaces of turbine which are under vacuum during
start up are connected to condenser. The drains are led to drain pot to air cooled
condenser.
The drains should be connected to drain manifold in the correct sequence i.e. the
drain from HP spaces must be farthest from the drain pot of ACC and followed by
the drain from the LP spaces. The pipeline riding from the turbine main steam stop
valve should be drained to atmosphere. The inlet of the drain to the surge pipe must
be at the min. of the 250 mm above the maximum water level in the drain pot.
Vacuum Breaking System:
In case of turbine trip (for reason of low lubricating oil pressure) vacuum is broken in
the condenser by admitting atmospheric air into the condenser through a motor
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operated valve that opens in such case. This is provided to shorten the coasting
down time. The valve is sealed with condenser water against ingress of air into the
condenser during normal running of set.
STARTING AND SHUTDOWN
The stating operation may have an impact influence on the possible curtailment of
turbine life because major thermal and mechanical stresses will be experienced in
the course of starting. This hazard may be particularly enhanced with start from the
cold. The most favorable condition can therefore be expected when the
temperature of the live steam during the starting period can be matched as closely
as possible to the actual temperature of the turbine. For starting a cold turbine or
one which has cold down to below 230 deg C , it is recommended to use the live
steam temperature to the casing temperature as the limit set by the requirement
after boiler or of the elements of the entire turbine will permit. However the
temperature of the live steam must exceed by at least 30 deg C the saturation
temperature of the steam at the chosen live steam pressure.
Oil Supply
The oil pump employed for starting should have been switched on some time
before in order to carry out the preparatory starting operation that can be
performed during standstill, the check for proper function of governor system and
also to achieve a certain pre warming of the oil.
Where a hydraulic jacking pump is provided for lifting the rotor off its bearing, it
should be taken into operation by opening the respective valves in the pressure oil
live as soon as turbine have achieved a speed of 80 – 120 rpm the jacking oil pump
can be switched of again.
Condensing System
The cooling water supply for the condenser should be taking into operation in
accordance to the local requirement of the site.
It is to ensure that all other element requiring water for cooling can be supplied with
cooling water as and when necessary.
Open the delivery valve fully. Open the maximum flow valve to the condenser to
the extent permitting the steady and adequate circulation of condensate. Start the
water level regulating system of the condenser. Also make sure that the collected
amount of condensate is returned to the feed water tank after passing such
intermediate apparatus like economizer, deaerator etc.
Pikesh Jain 48
Start the air extraction system in order to ensure the proper evacuation of the
condenser.
Opening the Live Steam Valve:
After through draining on the line ahead of the live steam valve, open that valve so
that live steam line up to the turbine will gradually be pressurized and warmed up.
If the live steam valve is equipped with the bypass, this should be opened first in
order to relieve the pressure on the valve.
In order to achieve satisfactory evacuation of the condensing system, steam must
be admitted to the shaft seal at a pressure exceeding the atmospheric by about 6
mbar. This prevents air from entering into the turbine casing along the rotor shaft.
Open the suction valve 1 to 2 turns and the seal steam valve to the point where
light wisps of steam emerge at the steam vents.
Opening of Emergency Stop Valve:
After having sufficiently drained the live steam line, turn the hand wheel of the
starting device in the opening direction. This will cause trip oil pressure to build up
behind the piston disc of the emergency stop valve. Check the oil pressure
prevailing in the space behind the piston, the condition at which the emergency
stop valve begins to open. The movement, the emergency stop valve, starts with its
opening movement, pause either further turning the starting device hand wheel
until the oil pressure behind the piston has definitely collapsed. Only after having
made sure that this has been the base, open the starting device to max. position to
open the emergency stop valve fully. Next, through electronic governor speed raise
push button built secondary oil pressure and speed start increasing.
Bringing the Turbine up to the Speed:
The turbine will be brought up to speed through further raising of speed reference
in electronic governor in accordance with the instruction of the test report and
while paying particular attention to the prohibited speed ranges and to smooth
running behavior of the entire machine set.
Automatic Oil Pumps Control:
When the auxiliary oil pump is not operating, make sure that automatic oil pump
control continues to be switched on. In the event of failure of the main oil pump, it
Pikesh Jain 49
will ensure that following a major drop in the system oil pressure, the existing auxiliary
oil pump will take over the supply immediately and maintain it at the required level.
Oil Cooling:
If the temperature of the oil cooler outlet exceeds 40 deg C, the cooling water inlet
valve has to be open to the point at which a constant oil temperature of 45 deg C
is maintained.
The oil outlet temp at the individual turbine bearing are not identical and may vary
enter a range of 50 deg to 65 deg for an inlet temp of 45 deg C.
If a temperature of 120 deg C is reached the turbine must be shut down
immediately.
UNLOADING THE TURBINE:
Regular Unloading:
For unloading the turbine, the hand wheel of the speeder gear has to be turned
slowly in the counter clockwise direction. This should result in a continuous decrease
of secondary oil pressure so that the control valves are going to close. The possible
effect of the unloading operation on the boiler control, on other auxiliary apparatus
and on turbine dependent element of the power plant should be taken into
account as far as possible. Prior to unloading all personnel involved has to be
contact and mutual understanding be reached about the measure to be taken.
Unloading after a Disturbance:
In this case the machine may be shut down by releasing the automatic trip gear,
regardless of its actual load.
Closing the Valves for Uncontrolled Extraction: Where uncontrolled extraction is
provided, make sure that at decreasing load the extraction valve will not be closed
before secondary oil pressure has dropped below the assigned value.
In case of spontaneous unloading, all extraction valves are going to close
simultaneously, even if the ESV remains open. The extraction valve can also be
closed by arranging small hand wheel on the change over valve, to be turned
clockwise. Subsequently the main hand wheel should be turned into the stop. Under
no circumstances the main hand wheel be forcibly tighten because this would risk
the entire valve mechanism.
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Opening the Drains
In installation equipped with extraction stop valve, the drain provided in the lines
b/w these valve and the turbine have to be opened immediately after the
extraction stop valve are closed, if it is intended to operate the turbine plant in that
condition for some time. All supplementary shutting off the device in the extraction
lines have to be closed.
Extraction Pressure Regulator:
Where an extraction pressure regulator is installed and the turbine is to be operated
at low load for a prolonged period, the regulator has to set to the zero extraction.
This will eliminate possible fluttering in the governing system. Such instabilities may
arise from the fact that the extraction pressure regulator attempts to maintain the
pressure at the extraction point constant.
DEAERATOR
DM water used for thermal power plant as heating fluid contains dissolved gases
(mainly oxygen and co2). These gases attack on metals at a high temperature
causing corrosion. So it is important to remove all these dissolved gasses before
using in boiler. This is achieved by heating the water at its saturation temperature.
The unit used for removing there dissolved gases is called deaerator.
In addition to removal of dissolved gases in feed water, the other functions of
deaerator are as follows.
1. It acts as surge tank to meet varied demand of boiler.
2. It increases the NPSH of feed water pump.
3. It forms a part of the regenerative cycle.
PRINCIPLE OF OPERATION
If the partial pressure of dissolved gases can be reduced by any method, then the
dissolved gas will escape from the water. Based on the principle the water is heated
up to its saturation temperature by using oxygen free steam. Steam also acts as a
carrier medium to carry the liberated gases to atmosphere.
DESCRIPTION: From the principle of deaeration it is clear that heating of feed water
and scrubbing of water have to take place in the shortest possible time to achieve
optimum deaeration. For this purpose the feed water is broken in droplets to
increase the contact area and to facilitate better heat exchange and fast
deaeration.
Pikesh Jain 51
The deaerator supplied is a tray cum spray type. It comprises of
a) A Deaerating header b) A Storage tank.
The condensate enters the deaerating header. Deaerating header comprises of
number of nozzles and trays stacked one above the other. The trays are sieve type.
Condensate collected in the tray trickles down to the next tray. Likewise flows to the
bottom most tray and then into storage tank.
Steam enters storage tank at one end travels over feed water and enter the
deaerating header. The steam heats up the condensate flowing downward and
apart of a steam is condensed back during this process. Remaining steam gas is
vented to atmosphere. The condensate is collected in the storage tank provided
below the deaerating header. The storage water in the storage tank and the
system control helps meeting varying demand of boiler.
VENT STEAM CONDENSER
The gland steam which vents from gland finally to atmosphere is called vent steam.
This vent steam is discharged either through chimney to atmosphere or it can be
discharged to a heat exchanger which is called vent steam condenser (VSC).
VSC is a shell and tube type heat exchanger. Condensate flows through the tube
while vent steam after releasing heat condenses at shell side. The inlet condensate
temperature increases taking the heat of steam and by this way it forms a part of
regenerative cycle.
CONSTRUCTION
VSC is fitted with the following mounting and fitting.
1. steam line and ejectors
2. vent steam line
3. condensate inlet and outlet line
4. level gauge and level switches
5. drip drain line with trap
6. pressure gauge in shell side
7. temperature gauges in condensate inlet/outlet line and drip drain line
OPERATION
Condensate from CEP discharge flows through the tube while the vent steam
condenses outside the tube. The drip thus formed is discharge at surged pipe
through trap. The non condensable gas which remains in the condensate is
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discharge to atmosphere by vapor extraction fan. Due to any leakage in
condenser, the GS condenser can be bypassed from condensate. In that case the
vent steam can be discharged directly to atmosphere.
GLAND STEAM CONDENSER
INTRODUCTION
It is a shell and tube heat exchanger. Gland leak off steam is gradually over
pressurized due to the gradual load. To maintain the gland steam pressure the
excess steam is condensed in the gland steam condenser. During lower load or any
tube leakage GSC can be bypass and gland steam can be dumped into the
condenser after desuperheating.
CONSTRUCTION
The GSC comprises mainly shell, tubes, water box. The shell is made of boiler quality
carbon steel. The GSC is fitted with the following fitting and mountings and
connections
1. condensate inlet outlet line connection
2. steam inlet connection
3. drip drain connection
4. level gauge connection
5. level switch
6. pressure indicator in shell side
7. temperature gauges in i/l and o/l condensate line and drip drain line
EVACUATION SYSTEM
(STEAM JET AIR EJECTOR)
Heat transfer action in surface condenser is impaired by the non condensable gas
which mixes with the film of condensate on the tube surface.
The source of air and other non condensable gases may come with the steam or
leakage through turbine gland. Air ingress is a serious factor and should be kept
down as much as possible. Since it is not possible to eliminate it entirely,
Pikesh Jain 53
arrangements are made for continuously drawing it out of the condenser and
compress it up to atm. Pressure where it can be released.
The steam jet air ejector is widely used to continuously draw the non condensable
gases from the surface condenser.
The steam jet air ejector used for evacuation may be categories into following type:
1. hogging or starting ejector
2. main or running ejector
HOGGING EJECTOR
It is used for quick evacuation of the condenser from atm. Pressure to around 0.6
kg/m.sq by 30 min before putting main ejector in line.
It is essentially consist of
1. steam nozzle
2. mixing chamber
3. diffuser
The ejector work on the principle of conversion of pressure energy into kinetic
energy in an expansion nozzle.
The steam air mixture from condenser is sucked mainly by viscous drag of high
velocity of steam jet. The resultant K.E. of the mixture is converted into the pressure
energy in a diffuser and finally let out to the atmosphere.
No ejector condenser is provided for hogger ejector.
MAIN EJECTOR
The main ejector is used for holding the vacuum in the condenser. The suction air
and vapour mixture is compressed into atmospheric pressure in two stages and
finally vented to the atmosphere.
Ejector condensers are provided at the end of each stage to condense the steam
in the mixture. The cooling medium for ejector condenser is condensate from CEP.
The condensate of the motive steam is drain to the flash tank or condenser through
U-leg and steam traps.
Generally two sets of ejector are supplied for the purpose. While one set is in service
the other set is kept as a stand by.
Pikesh Jain 54
AIR COOLED CONDENSER
Air cooled condenser is a finned tube condenser cooled by forced draft air.
Exhaust steam from turbine exchanges heat to the air and gets condensed.
ACC is used in those places where there is scarcity of water needed for cooling the
turbine exhaust steam.
The ACC provided for the power plant to serve the following function
1. to condensate the turbine exhaust steam
2. to deaerate the air from the condensate
ACC has three modules. Each modules is having two cooling fans. Two modules
from the condensing zone and the other module which is placed in between the
condensing zone is called the dephlegmator zone.
ACC is constructed in two number of A type frame. Each frame consists of 20
number of condensing and 4 no. of dephlegmator tube bundle. In the condensing
tube bundle the exhaust steam coming out from turbine get condensed whereas
air line for ejector has been tapped from dephlegmator tube bundle.
Each frame is connected with a steam header fixed at the apex and two
condensate headers at the bottom. Steam from apex header enters the
condensing zone through the tube bundle and after getting condensed the
condensate is collected at tube bottom condensate header.
The cooling medium that is air which is supplied by the FD fan flow crosswise to the
tube bundles.
Each tube bundles is fabricated from fine tube and arranged in triangular pitch for
better heat transfer. A frame structured ACC has the following advantages
1. Because of inclined tube bundle the condensate drainage is easier
2. Because of entry steam header is at the apex the steam distribution is
optimum.
3. Pressure drop across cooling tower is very less
Pikesh Jain 55
BOILER FEED PUMP.
These pumps are horizontal, multistage centrifugal
pumps designed for boiler feed and other high pressure applications.
The pumps are suitable for pumping clean liquid. This liquid is pumped with a liquid
velocity up to 2 m/s in the suction pipe and up to 3 m/s in the discharge pipe.
Specifications:
Medium delivered Boiler feed water
Capacity 48.7 cu.m/hr
Minimum capacity 12 cu.m/hr
Differential head 900 m
Differential pressure 79.7 bar
Suction pressure 8.7 bar
Discharge pressure 88.4 bar
Pumping temperature 164 deg C
Pump input 161.6 kw
Speed 2975 rpm
Impeller diameter 218 mm
Lubricating
Oil ISO VG 46
Oil temperature >40-65 deg C
Cooling
Cooling water 0.3 cu.m/hr
Pressure normal/max 2/10 bar
Temp outlet max. 40 deg
Allowable working
pressure
Suction side : 20 bar
Discharge side: 120 bar
Allowable working
temp
185° C
OTHER AUXILIARIES
ECONOMIZER
In boilers, economizers are heat exchange devices that heat fluids, usually water, up to
but not normally beyond the boiling point of that fluid. Economizers are so named
because they can make use of the enthalpy in fluid streams that are hot, but not hot
Pikesh Jain 56
enough to be used in a boiler, thereby recovering more useful enthalpy and improving
the boiler's efficiency. They are a device fitted to a boiler which saves energy by using the
exhaust gases from the boiler to preheat the cold water used to fill it (the feed water).
In thermal power plant, water passes through an economizer, then to a boiler and then to
a superheater. The economizer also prevents flooding of the boiler with liquid water that is
too cold to be boiled given the flow rates and design of the boiler.
A common application of economizers in steam power plants is to capture the waste
heat from boiler stack gases (flue gas) and transfer it to the boiler feed water. This raises
the temperature of the boiler feed water thus lowering the needed energy input, in turn
reducing the firing rates to accomplish the rated boiler output. Economizers lower stack
temperatures which may cause condensation of acidic combustion gases and serious
equipment corrosion damage if care is not taken in their design and material selection.
AIR PREHEATER
An air preheater is a device designed to heat air before another process with the primary
objective of increasing the thermal efficiency of the process.
The purpose of the air preheater is to recover the heat from the boiler flue gas which
increases the thermal efficiency of the boiler by reducing the useful heat lost in the flue
gas. As a consequence, the flue gases are also sent to the flue gas stack (or chimney) at
a lower temperature, allowing simplified design of the ducting and the flue gas stack. It
also allows control over the temperature of gases leaving the stack (to meet emissions
regulations, for example).
ELECTROSTATIC PRECIPITATOR
It consists of a steel air tight chamber housing the collecting and discharge electrodes.
The discharge electrodes are usually suspended from the top through support insulators.
Collecting electrodes are connected to ground and emitting electrodes are supplied with
a high negative voltage, in KV. Raping system periodically cleans the dust is collected on
the collecting electrodes. Dust is collected in trough type hoppers before they are
discharge pneumatically or through their combination of rotary air lock valve and dust
Pikesh Jain 57
conveying system. Inlet and outlet cones ensure gradual drop in velocity till it retains the
design velocity on reaching the collecting plates.
Gas distribution plates at the inlet and outlet ensures uniform gas distribution across the
length and width of ESP. collecting electrodes are usually spaced at 300mm or 400mm.
Emitting electrodes are of various types:
Some type of sharp point, which are corona generating sources.
Sections or fields to reduce the effect of electrical disturbance called sparking of
ESP
There are 2-3 fields in series for smaller quantity of gas.
5- 7 field in series for larger quantity of gas
Rapping which is usually either top rapping using MIGI rappers or side rappers using
rotating hammers driven by geared motors.
Inlet field naturally collects more dust as compared to outlet field.
In three field ESP
Inlet field collect 80% dust,
Second field collect 16% dust,
Third field collect 4% dust.
Inlet rappers are cleaned faster as compared to outlet rappers. Current increases as we
go from inlet field to outlet field and voltage reduces from inlet field to outlet field.
SPECIFICATION: ESP
Gas volume Am³/ hr 147024 Am³ / hr
Operating temperature 150 ° C
Operating pressure - 170 mmWC
Design pressure - 225 mmWC
Design temperature 250 ° C
Inlet dust load 48.29 gm / Nm³
Outlet dust concentration 30 mgm / Nm³ with all fields
operation
100 mgm / Nm³ with one TR set out
of service
Pressure drop across ESP 25-30MMwc
No of gas chamber 19 no.
Collecting surface spacing 400mm
Total no. of field 4
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DISCHARGE ELECTRODE
Type Rigid pipe & spiker
Material IS 513
Total no of electrodes 684 no
COLLECTING ELECTRODES
Material IS 513
No of electrodes per field 20 nos
Collecting electrodes 7.3’+9’(40+40)nos
Total no of electrodes 80
CE to CE spacing 400mm
RAPPING ARRANGEMENT
Type MIGI
No of collecting electrodes rapper 40nos
No of discharge electrode rapper 16nos
Rapper controller type PLC based
HOPPER
Type Pyramid
No of hopper 4
SILENCER
While steam blowing (for wet steam) the steam is exhausted in the atmosphere with a
very high velocity via a small duct and this result in generation of very high noise. To have
a control on this, we are using silencer. Silencer is a device that is used for decreasing the
noise level of the blowing off steam
The silencer used have following characteristics:
Application Steam line start up vent
Medium Superheated steam
Flow 24000 kg/hrs
Steam pressure 68 kg/sq.cm
Temperature 495+/-10 deg C
Sound level <85db at 1m distance of silencer
No. of inlet 1
Position Vertical
Materials (internal) Stainless steel (304)
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GENERATOR
ELECTRICAL DATA
Output rating 23375 KVA
Rated voltage 11 KV
Rated frequency 50 -5 % to +3% Hz
Rated current 2045 amp
Power factor 0.8 over excited
Rated speed 1500 rpm
Type of duty Continuous duty
Excitation method Brushless excitation
Full load excitation voltage 151.0 V
Full load excitation current 476.0 amp
Phase sequence ABC for clockwise rotating field
Insulation class for windings Stator F
Rotor F
MECHANICAL DATA
Type of construction Horizontal, foot mounted with two
bearings
Protection class IP54
Machine suitable for Installation indoor
Direction of rotation Clockwise rotation
Moment of inertia (GD^2 / 4) 1400 kg per sq mtr approx
Brush holders Qty type
Earthing brush Qty 2 type – grate
Size : 10* 20* 25
Bearings Size 315 dia lubrication : closed
circuit oil content 74 cub dm per
min
Pikesh Jain 60
: lube DIN CL 32
OIL 51517
Rate of oil required for
bearings at an oil
TS 37 DM^3 Per min
Temperature rise of 10 deg C ES 37 DM^3 Per min
Maximum oil pressure at
bearing inlet
0.6 Bar
VENTILATION DATA
VENTILATION Generator closed circuit air
cooling
Cooling air flow rate 19 cubic mtr per sec
Intake air temperature 42 deg C
Pressure drop on air side
mm of water cold
15
Altitude above sea level Above 1000
AIR COOLERS
Heat duty 510 kw
Quantity of cooling
water
100 cu. m ./ hr
Air outlet temperature 39 deg C
Cooling water inlet
temperature
32 deg C
Pressure drop on air side 15 mm of WCL
Pressure drop on water
side
7 m of WCL
Tube material Adm. Brass
Fin material Copper
No. of elements 5 +1
BRUSHLESS EXCITER
Type EAR 60/9- 15/16 -2
Serial no. 10738
Year of manufacture 2007
Continuous duty
Output rating 130 kw
Rated voltage 210 V
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Rated current 620 amp
Rated exciter voltage 29.6 V
Rated exciter current 10.74 amp
Type of construction Horizontal shaft
Overhang type
Degree of protection IP 54
Speed 1500 rpm
Direction of rotation
viewed from drive end
Clockwise rotation
Ventilation Tapped from generator
MACHINE TYPE
TYPE TALL 1240-12N-15
synchronous generator
Rating 23375 KVA
Power factor 0.8 lag
Speed 1500 rpm
Voltage stator 11 KV
Current stator 2045 amp
Frequency 50 Hz
Type of construction Horizontal shaft, foot
mounted with two bearings
Degree of protection
machine
IP54
WEIGHTS
Stator of generator 240000 Kg
Rotor of generator 17600 Kg
Base frame 5800 Kg
Generator weight with
brushless exciter
50600 Kg
Max. transport weight 506000 Kg
Brushless Excitation Type of machine Ear 80/9 –
15/16
Type of protection IP54
Auxiliary exciter Type of machine Ear 11/16 –
15/16
Type of protection IP54
BRUSHLESS EXCITATION
Main exciter Type EAR 80/9 – 15/16 -2
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S1 / 10s
Degree of protection
Voltage
Current
Output
Excitation
IP54
210/ 295 V
620/868 amp
130/ 255 Kw
29.6V / 10.74 amp
Weights Rotor
Stator
Pilot exciter
Total weight
1050 Kg
350 Kg
131 Kg
1530 Kg
Pilot exciter Type EAP 11/16 -15/6
Degree of protection
Voltage
Current
Output
IP54
221 V
3.94 V
1.5 KVA
DESCRIPTION OF MACHINE CONSTRUCTION
ROTOR
The rotor consists of the shaft, the rotor core, the field winding, the damper winding,
the fans, the slip rings or the rotor of the brushless exciter.
The shaft transmits the torque to the machine. The rotor is carried by two bearings.
The field winding is inserted in the slot group of the rotor core, connected and linked
to the terminals of the direct coupled exciter by lead runs through the bore in the
shaft. The bars of the damper winding are driven into the slots at the periphery of the
core and are connected to an end disc at the other end.
STATOR
The stator consists of the yoke core and the stator winding and parts of the enclosure.
The stator is secured to the base frame by means of holding down bolts with washers.
The slots of the stator core accommodate a double layer coil winding. The terminals
ABC are installed in a terminal board. Their location is selected to suit the conditions
at the suite the conditions at the site. The star point leads Ao Bo Co can be arranged
in the form of an open star point inside the outer casing. Certain machines have the
winding end leads connected to a terminal board at the lower part of the stator.
BEARINGS
The rotor runs in two floating type guide bearings, designed as pedestal bearings,
with forced oil and the bearings are of the self aligning type. The non drive end
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bearing pedestal is secured to the base frame and insulated from the later. All the
connections are arranged to prevent short circuiting of the insulation.
ENCLOSURE
The enclosure consists of the inner and outer compartments. The inner compartments
comprise the winding shields which from an annular enclosure of the end turns of the
stator winding and are also used as air guides.
The outer enclosure is designed as required for the particular degree of the
protection, as indicating in the dimension drawing or in “Terminal data”. The
ventilating circuit is of the double ended symmetrical arrangement.
EXCITATION: Depending on the service conditions involved, the synchronous
machine may be excited from a THYRIPART excitation system, a rotating exciter e.g
brushless excitation system or another external excitation system.
In this case a brushless exciter is employed, the excitation power is supplied to the
field circuit through rotating rectifier, and through brushless and slip rings with all the
other excitation systems.
BASE FRAME
The base frame carries the stator, the bottom section of the outer casing, the sleeve
bearings and the exciter. The base frame transmits the forces occurring the machine
to the foundation.
Depending on the mounting conditions at the site, the base frame is installed on
soleplates by means of anchoring bolts.
ACCESSORIES
The fixing accessories include shims and leveling plates. Various instruments e.g for
measuring pressure and temperature, fittings, space heaters and anchoring
accessories.
THERMAL PROTECTION STATOR WINDING
The description of the stator winding is monitored by resistance thermometer
embedded in the stator winding to protect the winding against thermal overloads.
Thermal overloading means a prolonged excess temperature which may destroy the
winding insulation or considerably reduce the life of the insulation.
If the winding temperature at the points reaches or exceeds the permissible limit
value, an alarm signal is given or the machine shut down automatically, depending
on the temperature attained.
The bifilar thermometer resistor is wound on a core covered with a glass fibre tape
and potted in cast resin, and thus has a high mechanical strength. The temperature
sensors are installed in separators of the stator winding.
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BRUSHLESS EXCITER
CONSTRUCTION
The exciter is brushless and takes the form of a stationary field generator. Its rotor is
mounted on the overhang of main machine shaft end. The stator may be fixed either
to be base frame of the main machine or to a separate steel or concrete foundation.
A permanent magnet three phase pilot exciter driven directly by the common
shafting or a static auxiliary excitation unit is used for exciting the field of the
stationary field generator via a voltage regulator. The three phase current flowing in
the rotor winding is rectified by silicon diodes in the rotating rectifier and fed into the
field winding of the main machine.
ROTOR
The rotor is fitted on the shaft extension of the main machine and locked to it in the
circumferential direction by parallel keys which are capable of accepting shock
loads caused by short circuit in the main machine without being over stressed.
The rotor hub is of welded construction and carried the laminated core which is
compressed axially by means of a clamping ring welded to the hub.
ROTOR WINDING
The three phase rotor winding inserted in the slots of the laminated core is connected
in the star. It is a two layer winding to insulation of class F. The end leads of the
individual windings are on the A end and connected to the U, V, W and neutral bus
rings arranged at the same end. Both winding overhangs are bound with heat setting
glass-fiber tapes to afford protection against centrifugal forces.
RECTIFIER
It comprise of 6 diodes assemblies and the protection circuit. The code assemblies
each consist of a light metal heat sink with integrally formed cooling fans containing
one end disc type diode secured by means of a clamping plate. A contact face
provided on the A side of each heat sink is connected by means of links to the
appropriate bus ring on the three phase side.
Diode assemblies situated on the opposite sides of the rotor spider have opposite
polarities. The dc bus rings carry the protective varistors are screwed to the B end of
the rotor spider by means of insulating mounts. The two bus rings are connected to
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the excitation cable, which are lead through the insulated hollow shaft of the main
machine.
VARISTORS
To protect the rectifier bridge against over voltages occurring during starting or
during fault conditions, a non linear resistor is provided. This protective resistor consists
of 12 varistor discs parallel connected between the positive and negative bus rings.
The varistor discs are clamped between the bus rings by means of insulated screws.
STATOR
The stator frame of the brushless exciter consists of a roller yoke ring with welded on
mounting feet. The pole pieces carrying the exciter winding are bolted to the inside
of the yoke ring. The coils would on the pole pieces are of insulted copper wore and
the impregnated with resin. They are connected in series in such a way that the leads
of the north poles are crossed over while those of the south poles are uncrossed. The
excitation winding end leads are led to the terminal box which is screwed to the
outside of the stator frame and contains the terminal block. The terminal box is fitted
with the two cable glands for the entry of the external connections. An earthing
terminal is provided on the stator frame at the point below the terminal box.
The stator frame of the B.L. exciter is fixed by means of hexagon bolts to either the base
frame of the machine or independent of the machine on separate foundation blocks
anchored in the concrete. Taper dowels are used for locating the exciter.
END SHIELDS
Depending on the degree of protection of the machine, these end shields have
either ventilating slots or welded on connection pieces for ventilating ducts.
The end shield on the A end is of the split type construction and has a split sealing ring
screwed to its inner diameter and embracing the sleeve of the rotor hub with title
clearance.
The end shield on the B end of the exciter is unsplit.
VENTILATION
The B.L. exciter uses closed circuit cooling the air inlet being on the A end and the
outlet on the B end. The stator spider is provided with the openings, permitting the
passage of cooling air past the rectifier heat sinks and also over the bus ring together
with the varistor and the carrier storage effect circuit.
To intensify the cooling air circulation, an additional fan impeller can be screwed
onto the end clamping ring. With open machines the cooling air flows through inlet &
outlet slots provided in the end shields.
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With enclosed machine, the end shields are provided with the welded-on
connecting pieces which permit the installation of ducts that may be connected to
the cooling circuit of the main machine, if required.
The connecting pieces may alternatively be designed so as to be connected via
gaskets with the air passages in the base frame supporting the main machine thus
integrating the cooling circuit of the B.L. exciter with that of the main machine.
MAINTENANCE
The brushless exciter requires only a minimum of maintenance. The machine should
be inspected for the dust deposits at the suitable intervals and to remove them,
specially in the region of the heat sinks. A suitable method is blowing out with the
compressed air at a pressure not exceeding 4 bars after first removing the end shield.
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SINGLE LINE DIAGRAM
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SEQUENCE OF EQUIPMENTS IN SWITCHYARD ARE AS :
Lightning arrestor
Isolator 1
Current transformer 1
Potential transformer
Circuit breaker cb 1
Isolator 2
Isolator 3
Current transformer
Circuit breaker cb 2
Lightning arrestor
Transformer
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VARIOUS EQUIPMENTS IN SWITCHYARD
1. ISOLATOR :
It differentiates the electrical equipment from the main line during fault
condition.
RATING: 132 KV 800 AMP
Motor 0.5 HP
Current ckt voltage 110 V dc
Rating of motor 3 phase 514 V ac
Heater voltage 240 V ac
Auxiliary contacts no. 6
2. CIRCUIT BREAKER :
Circuit breaker is an electromagnetic devices that opens a circuit
automatically when current exceeds a predetermined value.
It consists of current carrying contacts called electrodes which, under
predetermined conditions, separate to interrupt the circuit.
An arc is struck between them when the contacts are separated.
This arc is extinguished either by lengthening the arc or splitting the arc.
RATING : 145 KV Normal current 1250 KV
Lightning impulse withstand voltage 650 KV
Switching impulse withstand voltage 650 KV
S.C breaking current 31.5 amp
Line charging current 50 amp
Short time withstand current and duration 31.5 KA & 3 sec
3. LIGHTNING ARRESTOR :
A lightning arrestor or surge diverters is a device that that is connected
between line and earth, i.e., in parallel with the equipment to be
protected.
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When a traveling waves reaches the diverter, it sparks over at a certain
prefixed voltage and provides a conducting path of relatively low
impedance between the line and ground.
The surge impedance of the line restricts the amplitude of current flowing to
ground.
4. TRANSFORMER :
This step downs the incoming 132 KV voltage into 66 KV and feds into the
grid bus line.
RATING : KVA 22500 / 28000
Volts at no load HV 13.2 KV
LV 6.6 KV
Amperes HV 98.4 / 122.5
LV 1883 / 2343
Types of cooling ONAN / ONAF
5. CURRENT TRANSFORMER:
This is used for measuring the high current from the line.
This measures the current the high voltage side of transformer during on
load condition.
6. REACTORS :
Reactors are used to limit the short circuit current flowing to a safe
value.
They consist of large coils of high self inductance and very low
resistance.
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Conclusion:
The training at Ambuja Captive Power Plant was very helpful to me. It has improved my
theoretical and practical concept of electrical power generation, transmission &
distribution and also improvised my knowledge about protection of various electrical
equipments. This training also helped me in understanding the importance of Safety while
working.
So the training was more than helpful to me understanding every aspect related to
“Generation, Transmission and Distribution of Electrical Energy “
References
1. B.R. Gupta
2. J.B. Gupta
3. Manuals of Ambuja Captive Power Plant
