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REPORT ON THEORITICAL ANALYSIS ON AFBC(ATMOSPHERIC FLUIDIZED BED COMBUSTION)
BOILER
Submitted by
CHHATRAVALA AMIT A. (080160119013)BARAIYA RAMESH P. (090163119002)
SANGANI JAYVANT B. (090163119101)
In fulfil lment for the award of the degreeof
BACHELOR OF ENGINEERING
In
MECHANICAL
GOVERNMENT ENGINEERING COLLEGE MODASA
Gujarat Technological University, Ahmedabad
December, 2011
Government Engineering College Modasa
Mechanical Engineering Department2012
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CERTIFICATE
Date: 25-4-2012
This is to certify that the dissertation entitled “Theoritical analysis
on AFBC(Atmospheric Fluidized Bed Combustion) Boiler” has been
carried out by BARAIYA RAMESH P. under my guidance in
fulfillment of the degree of Bachelor of Engineering in Mechanical
engineering (8th Semester) of Gujarat Technological University,
Ahmedabad during the academic year 2011-12.
Guides:Prof. R.J. Jani
Head of the Department
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Government Engineering College Modasa
Mechanical Engineering Department2012
CERTIFICATE
Date:25-4-2012
This is to certify that the dissertation entitled “Theoritical analysis
on AFBC(Atmospheric Fluidized Bed Combustion) Boiler” has been
carried out by CHHATRAVALA AMIT A. under my guidance in
fulfillment of the degree of Bachelor of Engineering in Mechanical
engineering (8th Semester) of Gujarat Technological University,
Ahmedabad during the academic year 2011-12.
Guides:
Prof. R.J. Jani
Head of the Department
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Government Engineering College ModasaMechanical Engineering Department
2012
CERTIFICATE
Date:25-4-2012
This is to certify that the dissertation entitled “Theoritical analysis
on AFBC(Atmospheric Fluidized Bed Combustion) Boiler” has been
carried out by SANGANI JAYVANT B. under my guidance in
fulfillment of the degree of Bachelor of Engineering in Mechanical
engineering (8th Semester) of Gujarat Technological University,
Ahmedabad during the academic year 2011-12.
Guides:
Prof. R.J. Jani
Head of the Department
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Table of content
Acknowledgement
Abstract
List of figure
Title of chapter
Chapter no 1. Introduction page
1.1 Introduction 10
1.2 Main components of plant 14
1.3 Rankine cycle and its analysis 15
Chapter no 2. Raw water treatment plant
2.1 D.M Plant Circuit 19
2.2 D.M.Plant 20
2.3 Deaerator 22
Chapter no.3 Coal handling plant
3.1 Coal Handling Process description 25
Chapter no. 4 Boiler
4.1 AFBC Boiler 28
4.2 Waste Heat Recovry Boiler 39
4.3 Boiler Specification 39
4.4 Boiler Safty 40
Chapter no 5 Boiler mountings and accesories
5.1 Mountings 41
5.2 Accessories 44
General Problems In boiler 56
Emegencies in Boiler 56
Do & Donts 58
Features & Benefits 60
Conclusion 61
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Acknowledgement
we are the students of government engineering college modasa, we has take industrial training in
varrasana ispat ltd at varrasana nearby gandhidham. when a good thing comes to end, memories
are left behind, in this regard, I amindebted to respected chairman S.P. Patel for giving us this
wonderful opportunity to a project in a organization, we are highly obliged to varrasana ispat ltd.
where we have done our summer training.we are thankful to S.P.Patel for giving us permission
for doing summer training.We are also thankful to Prof. R.J. Jani for supporting us throughout the
entire project.
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ABSTRACT
With teaching our knowledge become good, traning is developing our habbit.It
assure that technical studies cannot perform adroit without practical training. Hence
the practical training is exorbitant for engineering student. The actual objective of
plant training is to get all detail about organization and main enance about all
operation and procrss, which are caried out practical knowledge. Its inviting feature
is to learn industrial management and discipline. In this report of training we
include all the details related to our project as well as company.
In this report we have include AFBC boiler detail and try to get knowledge about
AFBC Boiler.
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List of figures
Fig no. fig. description page
1.1 Over View of plant 11
1.2 Physical layout of rankine cycle 15
2.1 D.M Plant 21
2.2 Deaerator 22
3.1 Grab Bucket Conveyer 28
4.1 AFBC Boiler 28
4.2 Mechanism of FBC 32
5.1 Boiler Mountings & Accesories 41
5.2 Economiser 46
5.3 Air-Preheater 47
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PREFACE
In developing economy that is ours, development inputs remain constant demand
necessitating use of resources. Electric by virtue of its being the most convenient form of inputs,has proved to be one of the most powerful vehicles for promoting economic well being of the
society through industrial growth.
Electric power has thus come to be considered as the most important input in the nation’s
endeavors towards industrialization as well as in attaining the growth rate that our development
plans aim to achieve. It is thus only natural that the per capita of electricity has come to be
considered as a measure of the country’s industrial accomplishment as also the standard of living
of the society.
The country has made tremendous progress in the field of electric power in the past three
decades. The installed capacity has steadily increased to 45000 MW. From this generation was
from coal fired power plant.
Indian has reserves of the order of 13000 million tones/ much of reserves is not of high
quality and contains appreciable amount of incombustible matter. It is only rational to utilize
these large reserves of coal by converting this primary source of energy to process and more
concentrated forms, which makes it easy for transportation and use. Conversion of electric power
is one such processing on which the country has rightly placed the emphasis upon.
Chapter 1
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INTRODUCTION
This section briefly describes the Boiler and various auxiliaries in the Boiler Room.
A boiler is an enclosed vessel that provides a means for combustion heat to be transferred to water until it becomes heated water or steam. The hot water or steam under pressure is then
usable for transferring the heat to a process. Water is a useful and inexpensive medium for
transferring heat to a process. When water at atmospheric pressure is boiled into steam its volume
increases about 1,600 times, producing a force that is almost as explosive as gunpowder. This
causes the boiler to be an equipment that must be treated with utmost care.
The boiler system comprises of: a feed water system, steam system and fuel system. The
feed water system provides water to the boiler and regulates it automatically to meet the steam
demand. Various valves provide access for maintenance and repair. The steam system collects
and controls the steam produced in the boiler. Steam is directed through a piping system to the
point of use. Throughout the system, steam pressure is regulated using valves and checked with
steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate
the necessary heat. The equipment required in the fuel system depends on the type of fuel used in
the system.
The water supplied to the boiler that is converted into steam is called feed water. The two
sources of feed water are: (1) Condensate or condensed steam returned from the processes and (2)
Makeup water (treated raw water) which must come from outside the boiler room and plant
processes. For higher boiler efficiencies, an economizer preheats the feed water using the waste
heat in the flue gas.
1.1) OVERVIEW OF THE PLANT
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1.1 Fig. captive power plant at Electrotherm ( AFBC type.)
OVERVIEW OF THE PLANT
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SR NO. NAME DESCRIPTION
1. Location Varrsana(gujarat)
2. Capacity 36MW
3. Fuel type Indonesian coal , char coal , lignite
4. Boiler type A.F.B.C & W.H.R.B
5. Nos. of boiler Four
6. Turbine Impuls reaction turbine
7. Condenser Surface type
8. Coling tower Cross flow Coling tower
- The power plant of ELECTROTHERM has a maximum generation capacity of 25MW
with the help of two Turbine each of 15MW capacity.
- Now the generator according to its principle converts the mechanical energy of rotational
into electrical energy which is varied according to use by the transformers.
- The coal to the boiler is supplied from the coal bunker with the help of the conveyor belt.
The coal is crushed in between crusher and is transferred to the boiler furnace, with a
requirement size. The size of the coal feed to the boiler should not be more than 6mm.
- Limestone is also added to lignite during feeding to furnace to control the Sox and NOx
emission.
- During this the primary air is supplied from the nozzles below bed and the secondary air is
supplied from the walls of furnace.
- Due to fluidization the flue gas and fly ash with unburnt particles goes to cyclone
separator. Now the fly ash below the 60-micron size is separate and flue gas goes to super
heater and unburnt particles are entered into the seal pot.
- One particle of the lignite recycles about 50,000 times, so it is obvious that the total
combustion of lignite takes place in furnace, so the efficiency is increased.
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- The ash product is of two types. They are bottom ash and fly ash. The fly ash is removed
by ESP and the bottom ash is removed by mechanical ash handling system.
1.2) THE MAIN COMPONENT OF A POWER PLANT :
Boiler
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Turbine
Alternator, generator
Coal handling system
Ash handling system
Condenser
Pumps Fans
Raw water treatment plant.
Cooling tower
1.3) RANKINE CYCLE AND ITS ANALYSIS
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Rankine cycle is the idealized cycle for steam power plants. This cycle is shown on p-v, t-
s, h-s, diagram in the below figures. It consists of following processes:
(A)Physical layout of the four main devices used in the Rankine cycle
The different process involved in rankine cycle is explained below:
Process 1-2: Water from the condenser at low pressure is pumped into the boiler at high
pressure. This process is reversible adiabatic.
Process 2-3: Water is converted into steam at constant pressure by the addition of heat in the
boiler.
Process 3-4: Reversible adiabatic expansion of steam in the steam turbine.
Process 4-1:Constant pressure heat rejection in the condenser to convert condensate in to water.
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1.3.1) THERMAL EFFICIENCY OF RANKINE CYCLE
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Consider one kg of working fluid, and applying first law to flow system to various
processes with the assumption of neglecting changes in potential and kinetic energy, we can
write,
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1.3.2) REASONS FOR COSIDERING RANKINE CYCLE AS AN IDEAL
CYCLE FOR STEAM POWER PLANT
1. It is very difficult to build a pump that will handle a mixture of liquid and vapor at state 1’
(refer T-s diagram) and deliver saturated liquid at state 2’. It is much easier to completely
condense the vapor and handle only liquid in the pump.
2. In the rankine cycle, the vapor may be superheated at constant pressure from 3 to 3” without
difficulty. In a Carnot cycle using superheated steam, the superheating will have to be done at
constant temperature along path 3-5. During this process, the pressure has to be dropped. This
means that heat is transferred to the vapor as it undergoes expansion doing work. This is
difficult to achieve in practice.
Chapter 2
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RAW WATER TREATMENT PLANT
2.1.) D.M. PLANT CIRCUIT
Raw water
D.M.F. (de-media filter)
U.F. membrance (ultra filter )
S.A.C. (stronge acid catayan )
Degasser tank
W.B.A (week base anayen )
S.B.A. (stronge base anayen )
M.B. (mix bed )
D.M. water tank
Boiler
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2.2) DEMINERALISATION PLANT (D.M. PLANT):-
Ion exchange units can be used to remove any charged (ionic) substance from water, but
are usually used to remove hardness and nitrate from groundwater. Water is pretreated to reduce
the suspended solids and total dissolved solids (TDS) load to the ion-exchange unit. Methods of
pretreatment include:
• Filtration,
• Coagulation and filtration,
• Cold lime with or without soda ash,
• Hot lime with or without soda ash,
• Evaporation or distillation,
• Electrodialysis,
• RO (reverse osmosis).
Ion exchange:-
Ion exchange effectively removes more than 90 percent of barium, cadmium, chromium
(III), silver, radium, nitrites, selenium, arsenic (V), chromium (VI), and nitrate. Ion exchange is
usually the best choice for small systems that need to remove radionuclides.
Procedure:-
Procedure for demineralization are given below,
- Water from filter are passed through the carbon filter and remove chlorine from it.
Cation exchanger:-
Water from carbon filter is passed from upper side the cation exchanger tank and
discharge from bottom outlet water in cation exchanger process with in tanks and remove the all
positive from the water.
Dessenger :-
To remove O2 & CO2 from water then fallen from top of dessenger And is given from
bottom of the dessenger, This remove CO2 from water.
Water base exchanger:-
Water is then passed through the water base anion exchanger to remove chlorine and ion
from it.
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D.M. pumps specifications
SR. NO. DESCRIPTION UNIT
1 Make Beacon weir Ltd.
2 No. of pumps Nos. 2 (1 working + 1 standby)
3 Water temperatureoC 45
4 Rated flow design m3 /hr 253
5 Head at design condition M 75
6 Rated speed Rpm 1470
2.3) DEAERATOR:-
A steam generating boiler requires that the boiler feed water should be devoid of air and
other dissolved gases, particularly corrosive ones, in order to avoid corrosion of the metal.
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DEARATOR SPECIFICATIONS
MAKE EAS system Hyderabad
QUANTITY One
TYPE Spray cum tray- counter flow
DEARATOR CAPACITY 150 TPH
OPERATING PRESSURE 1.5 kg/cm2
TEMP. OF INCOMING WATER 55 oc
TEMP. OF DEARATOR WATER 120 oc
DISSOLVED O2 IN WATER 0.005 ppm
NORMAL WATER LEEVEL +1125 mm
Generally, power stations use a deaerator to provide for the removal of air and other
dissolved gases from the boiler feedwater. A deaerator typically includes a vertical, domed
deaeration section mounted on top of a horizontal cylindrical vessel which serves as the deaerated
boiler feedwater storage tank.
There are many different designs for a deaerator and the designs will vary from onemanufacturer to another. The adjacent diagram depicts a typical conventional trayed deaerator. If
operated properly, most deaerator manufacturers will guarantee that oxygen in the deaerated
water will not exceed 7 ppb by weight (0.005 cm³/L).
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Chapter 3
COAL HANDLING PLANT
Coal handling system contains unloading, transferring, crushing and storage of coal and
finally supplying quantity to the boiler plant.
Properties:-
Coals are ranked according to their carbon content. Under mild conditions of heat and
pressure, the lowest rank coals were formed, consisting of brown coal and lignite. At higher
temperatures and pressures, sub-bituminous and bituminous coals were formed, and under very
high pressures, the highest rank coals, called anthracites, were formed. The anthracites contain
more than 92% carbon, 2–3% hydrogen together with oxygen, volatile matter and impurities.
Bituminous coal contains about 5% hydrogen and has a carbon content of 70–80%. The lowest
ranks of lignite and brown coal may have less than 50% carbon content. Sulfur is an important
impurity as it appears in combustion products as oxides of sulfur (SO2), which pollutes the
environment.
COAL SPECIFICATIONS
COAL MOISTUR
E
(%)
ASH
(%)
VOLATILE
MATTER
(%)
CARBON
(%)
CALORIFIC
VALUE
(kcal/kg)
SULPHURE
(%)
pet-coke 5-8 0.6 9-11 70-80 8200 0.65-0.80
Indonesian 10-12 3-10 38-40 40 5410 0.89
South African 9.59 23.67 22.9 44-55 4760 0.48
Chinese 8.08 12.83 29.3 49-79 6335 0.66
Australian 8.75 13.4 25.2 52-62 6348 0.70
High ash 8.22 31.79 25.8 34-45 4505 084
Lignite 30 15.20 30-34 23-30 3500-4000 -----
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3.1 COAL HANDLING PROCESS DESCRIPTION:
Coal handling process is mainly divided into three process according to the path of coal.
1. Staking
2. Direct bunkering
3. Reclaiming
1.) STAKING
In this process coal from the coal hopper is go to the belt conveyor 1.
On belt conveyor-1 one magnetic separator placed to separate the metal particles
from the coal.
Then coal is gone to the crusher and crushed in size of 5 to 6mm.
This crushed coal is gone to storage through the belt conveyor-5.
2.) DIRECT BUNKERING:
As given above process, coal come at crusher from hopper and after crushing the
coal in 5 to 6mm size is gone on belt conveyor-2 as requirement in boiler plant.
From belt conveyor-2 coal gone on belt conveyor-3.
On belt conveyor-3also one magnetic separator is placed to find out the metallic particle from coal.
Then coal is gone on the belt conveyor-4 from which coal is feed in bunker. This
process is called direct bunkering because coal from wagon trippler is directly
comes to the bunker.
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3.) RECLAIMING:
Process of transferring coal from storage to the coal bunker at boiler plant is called
reclaiming.
Coal storage from conveyor receiving hopper goes on the belt conveyor-6
On belt conveyor-6 magnetic pulley and magnetic separator are placed to separate
the magnetic particles.
Then this coal is gone on the belt conveyor-2, belt conveyor-3 and belt conveyor-4
and finally in bunker as direct bunkering.
STORAGE OF COAL
The purpose of coal storage is two fold, first fuel storage is an insurance against complete
shutdown of a power plant occurring from failure of normal supplies. Second, the storage permits
the choice of the date of purchase allowing the management to take advantages of seasonal
market condition. Storage of coal protects the plant failure in case of coal strikes, failure of the
transportation system and general coal storage of coal. Coal is undesirable, because its cost more
as there is risk of spontaneous combustion, possibility of loss and deterioration during storage,
interest on capital costs of coal lying dormant cost of insurance, cost required to protect the
storage coal deterioration and many others.
Fig.3.1grab bucket conveyor
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FUEL CIRCUIT
Pure coal
bunker
pocket feeder
drag chain feeder
P.A. Line
Furnace
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Chapter 4
BOILERS
Boiler is designed as a heart of TPS because it is the component in which due to burningof fuel, heat is produced which in turn is used to heat the water so as to produced steam, at rated
pressure which rotates the turbine rotor. The turbine is coupled with the generator, which
produced the electricity. Not only is this, the steam produces also utilized for the process.
4.1.) Atmospheric Fluidized Bed Combustion. (AFBC) Boiler
Fig:4.1 AFBC Boiler
4.1.1) Introduction to FBC Boilers
This section briefly describes the Boiler and various auxiliaries in the Boiler Room. A boiler
is an enclosed vessel that provides a means for combustion heat to be transferred to water
until it becomes heated water or steam. The hot water or steam under pressure is then usable
for transferring the heat to a process. Water is a useful and inexpensive medium for
transferring heat to a process. When water at atmospheric pressure is boiled into steam its
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volume increases about 1,600 times, producing a force that is almost as explosive as
gunpowder. This causes the boiler to be an equipment that must be treated with utmost care.
The boiler system comprises of: a feed water system, steam system and fuel system. The
feed water system provides water to the boiler and regulates it automatically to meet the steam
demand. Various valves provide access for maintenance and repair. The steam system collectsand controls the steam produced in the boiler. Steam is directed through a piping system to the
point of use. Throughout the system, steam pressure is regulated using valves and checked
with steam pressure gauges. The fuel system includes all equipment used to provide fuel to
generate the necessary heat. The equipment required in the fuel system depends on the type of
fuel used in the system.
The water supplied to the boiler that is converted into steam is called feed water. The two
sources of feed water are: (1) Condensate or condensed steam returned from the processes and
(2) Makeup water (treated raw water) which must come from outside the boiler room and
plant processes. For higher boiler efficiencies, an economizer preheats the feed water using
the waste heat in the flue gas.
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The traditional grate fuel firing systems have several limitations and hence are techno
economically unviable to meet the challenges of the future. FBC has emerged as a viable
alternative as it has significant advantages over conventional firing system. FBC offers multiple
benefits, such as: compact boiler design, flexibility with fuel used, higher combustion efficiency
and reduced emissions of noxious pollutants such as SOx and NOx. The fuels burnt in these
boilers include coal, washery rejects, rice husk, bagasse and other agricultural wastes. Thefluidized bed boilers have a wide capacity range- 0.5 T/hr to over 100 T/hr.
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WATER CRICUIT
Raw water
D.M.plant
Dearator
Feed pump
Economiser
Steam drum
Down chamber
Bed coil
Water wall
Riser tube
Steam drum
Primory superheater
Secondray superheater
Main steam line
Turbine
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4.1.2.) Mechanism of Fluidized Bed Combustion
When an evenly distributed air or gas is passed upward through a finely divided bed of
solid particles such as sand supported on a fine mesh, the particles remain undisturbed at low
velocities. As the air velocity is gradually increased, a stage is reached when the individual
particles are suspended in the air stream and the bed is called “ fluidized ”. With further increase inair velocity, there is bubble formation, vigorous turbulence, rapid mixing and formation of dense
defined bed surface. The bed of solid
particles exhibits the properties of a boiling liquid and assumes the appearance of a fluid –
“bubbling fluidized bed”. At higher velocities, bubbles disappear, and particles are blown out of
the bed. Therefore, some amounts of particles have to be re-circulated to maintain a stable system
and is called as “Atmospheric fluidized bed ". This principle of fluidization is illustrated in Figure.
Fig:4.2 Mechanism of FBC Boiler
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Fluidization depends largely on the particle size and the air velocity. The mean solids
velocity increases at a slower rate than does the gas velocity. The difference between the mean
solid velocity and mean gas velocity is called as slip velocity.
Maximum slip velocity between the solids and the gas is desirable for good heat transfer
and intimate contact. If sand particles in fluidized state are heated to the ignition temperatures of fuel (rice husk, coal or bagasse), and fuel is injected continuously into the bed, the fuel will burn
rapidly and the bed attains a uniform temperature.
The fluidized bed combustion (FBC) takes place at about 840°C to 950°C. Since this
temperature is much below the ash fusion temperature, melting of ash and associated problems
are avoided. The lower combustion temperature is achieved because of high coefficient of heat
transfer due to rapid mixing in the fluidized bed and effective extraction of heat from the bed
through in-bed heat transfer tubes and walls of the bed. The gas velocity is maintained between
minimum fluidization velocity and particle entrainment velocity. This ensures a stable operation
of the bed and avoids particle entrainment in the gas stream.
Any combustion process requires three “T”s - that is Time, Temperature and Turbulence.
In FBC, turbulence is promoted by fluidization. Improved mixing generates evenly distributed
heat at lower temperature. Residence time is many times higher than conventional grate firing.
Thus an FBC system releases heat more efficiently at lower temperatures. Since limestone can
also be used as particle bed (in case the fuel with sulphur content is used), control of SOx and
NOx emissions in the combustion chamber is achieved without any additional control equipment.
This is one of the major advantages over conventional boilers.
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AIR CIRCUIT
Atmospheric air
F.D. fan
F.D. header
Air box P.A. fan suction
Furnace P.A.fan
Furnace
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PROCESS AND PLANT STRUCTURE:-
The plant basically consist of two boiler, two electrostatic precipitator, one ID fan, one
primary air fan, one secondary air fan, and two hot gas generators and cyclones and siphons are
provided for circulating the ash.
FIG. Atmospheric Fluidized Bed Combustion System
AFBC is one of the most important types of FBC boilers as it can be used for variety of fuels
- such as agricultural residues like rice husk or bagasse and even low quality coal. This type of
boiler find use in industries where there is a possibility of having a combined heat and power
generation application.
In AFBC boilers the fuel is sized depending on the type of fuel ( in case of coal, the coal is
crushed to a size of 1 – 10 mm depending on the grade of coal) and the type of fuel feeding
system and is fed into the combustion chamber.
The atmospheric air, which acts as both the fluidization air and combustion air, is delivered at a
pressure and flows through the bed after being preheated by the exhaust flue gases. The velocity
of fluidizing air is in the range of 1.2 to 3.7 m /sec. The rate at which air is blown through the bed
determines the amount of fuel that can be reacted.
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Almost all AFBC/ bubbling bed boilers use in-bed evaporator tubes in the bed of limestone, sand
and fuel for extracting the heat from the bed to maintain the bed temperature. The bed depth is
usually 0.9 m to 1.5 m deep and the pressure drop averages about 1 inch of water per inch of bed
depth. Very little material leaves the bubbling bed – only about 2 to 4 kg of solids is recycled per
ton of fuel burned. Typical fluidized bed combustors of this type are shown in Figures 5 and 6.
The combustion gases pass over the super heater sections of the boiler, flow past the
economizer, the dust collectors and the air pre-heaters before being exhausted to atmosphere. The
main special feature of atmospheric fluidized bed combustion is the constraint imposed by the
relatively narrow temperature range within which the bed must
be operated. With coal, there is risk of clinker formation in the bed if the temperature exceeds
950°C and loss of combustion efficiency if the temperature falls below 800°C. For efficient
sulphur retention, the temperature should be in the range of 800°C to 850°C.
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4.2.) Waste Heat Recovery Boiler
Wherever the waste heat is available at medium or high temperatures, a waste
heat boiler can be installed economically.
Wherever the steam demand is more than the steam generated during waste heat,
auxiliary fuel burners are also used. If there is no direct use of steam, the steam
may be let down in a steam turbinegenerator set and power produced from it. It
is widely used in the heat recovery from exhaust gases from gas turbines and
diesel engines.
4.3.) BOILER SPECIFICATIONS
BOILER NO. AND NAME TYPE OF COAL USED STEAM PRE.AND QUANTITY,
TEMP.
A.F.B.C-1
Atmosperic Fluidized bed
combustion
Indonesian+ char Coal+
Lignit
65 TPH, 66.5 Kg/cm2, 4900 C
A.F.B.C-2
Atmosperic Fluidized bed
combustion
Indonesian+ char Coal+
Lignit
65 TPH, 66.5 Kg/cm2, 4900 C
W.H.R.B-1
West heat recovery boiler
___ 28 TPH, 66.5 Kg/cm2, 4900 C
W.H.R.B-2
West heat recovery boiler
___ 36 TPH, 66.5 Kg/cm2, 4900 C
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4.4) BOILER SAFETY
Historically, boilers were a source of many serious injuries and property destruction due to
poorly understood engineering principles. Thin and brittle metal shells can rupture, while poorly
welded or riveted seams could open up, leading to a violent eruption of the pressurized steam.
Collapsed or dislodged boiler tubes could also spray scalding-hot steam and smoke out of the air
intake and firing chute, injuring the firemen who loaded coal into the fire chamber. Extremely
large boilers providing hundreds of horsepower to operate factories could demolish entire
buildings.
A boiler that has a loss of feed water and is permitted to boil dry can be extremely
dangerous. If feed water is then sent into the empty boiler, the small cascade of incoming water
instantly boils on contact with the superheated metal shell and leads to a violent explosion thatcannot be controlled even by safety steam valves. Draining of the boiler could also occur if a leak
occurred in the steam supply lines that was larger than the make-up water supply could replace.
The Hartford Loop was invented in 1919 by the Hartford Steam Boiler and Insurance Company
as a method to help prevent this condition from occurring, and thereby reduce their insurance
claims.
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Chapter 5
BOILER MOUNTINGS AND ASSESORIES
5.1) Mountings:
Boiler mountings are the machine components that are mounted over the body of the
boiler itself for the safety of the boiler and for complete control of the process of steam
generation.
Various boiler mountings are as under:
1.) Safety valve
2.) Pressure gauge.
3) Fusible plug.
4) Steam stop valve
5) Feed check valve
6) Blow off cock
7) Man and mud holes.
8.) Water level indicators:
9.) Low- water cutoff:
10.) Bottom blow down valves:
11.) Surface blowdown line
12.) De-superheater tubes or bundles:
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1.) Safety valve:
It is used to relieve pressure and prevent possible explosion of a boiler.
2.) Pressure gauge:
Function: To record the steam pressure at which the steam is generated in the boiler. A
bourden pressure gauge in its simplest form consists of elliptical elastic tube bent into an arc. This bent up tube is called as BOURDEN’S tube. One end of tube gauge is fixed and connected to the
steam space in the boiler. The other end is connected to a sector through a link.
3.) Fusible plug:
Function: To extinguish fire in the event of water level in the boiler shell falling below a
certain specified limit. It protects fire tubes from burning when the level of the water in the water
shell falls abnormally low and the fire tube or crown plate which is normally submerged in the
water, gets exposed to steam space which may not be able to keep it cool. It is installed below
boiler's water level. When the water level in the shell falls below the top of the plug, the steam
cannot keep it cool and the fusible metal melts due to over heating. Thus the copper plug drops
down and is held within the gunmetal body by the ribs. Thus the steam space gets communicated
to the firebox and extinguishes the fire. Thus damage to fire box which could burn up is avoided.
By removing the gun metal plug and copper plug the fusible plug can be put in position again by
interposing the fusible metal usually lead or a metal alloy.
4.) Steam stop valve
A valve is a device that regulates the flow of a fluid (gases, fluidized solids, slurries, or
liquids) by opening, closing, or partially obstructing various passageways
Function: to shut off or regulate the flow of steam from the boiler to the steam pipe or
steam from the steam pipe to the engine. When the hand wheel is turned, the spindle which is
screwed through the nut is raised or lowered depending upon the sense of rotation of wheel. The
passage for flow of steam is set on opening of the valve.
5.) Feed check valve:
i) To allow the feed water to pass into the boiler.
ii) To prevent the back flow of water from the boiler in the event of the failure of the feed
pump.
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6.) Blow off cock.
Function: To drain out the water from the boiler for internal cleaning, inspection or other
purposes.
7.) Man and mud holes:
To allow men to enter inside the boiler for inspection and repair
8.) Water level indicators: They
show the operator the level of fluid in the boiler, also known as a sight glass, water gauge or
water column is provided.
9.) Low- water cutoff:
It is a mechanical means (usually a float switch) that is used to turn off the burner or shut
off fuel to the boiler to prevent it from running once the water goes below a certain point. If a
boiler is "dry-fired" (burned without water in it) it can cause rupture or catastrophic failure
10.) Bottom blow down valves:
They provide a means for removing solid particulates that condense and lay on the bottom
of a boiler. As the name implies, this valve is usually located directly on the bottom of the boiler,
and is occasionally opened to use the pressure in the boiler to push these particulates out.
11.) Surface blowdown line:
t provides a means for removing foam or other lightweight non-condensible substances that
tend to float on top of the water inside the boiler
12.) Desuperheater tubes or bundles:
A series of tubes or bundles of tubes in the water drum or the steam drum designed to cool
superheated steam. Thus is to supply auxiliary equipment that doesn't need, or may be damaged
by, dry steam.
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5.2) Accessories:
Boiler accessories are those components which are installed either inside or outside the
boiler to increase the efficiency of the plant and to help in the proper working of the plant.
Various boiler accessories are:
1) Air Preheater
2) Economizer
3) Superheater
1. Air preheater:
Waste heat recovery device in which the air to on its way to the furnace is heated utilizing
the heat of exhaust gases
2. Economiser:
Function: To recover some of the heat being carried over by exhaust gases (This heat is
used to raise the temperature of feed water supplied to the boiler.
3. Superheater :
To superheat the steam generated by boiler Super heaters are heat exchangers in which
heat is transferred to the saturated steam to increase its temperature.
Fossil fuel power plants can have a superheater and/or reheater section in the steamgenerating furnace. Nuclear-powered steam plants do not have such sections but produce steam at
essentially saturated conditions. In a fossil fuel plant, after the steam is conditioned by the drying
equipment inside the steam drum, it is piped from the upper drum area into tubes inside an area of
the furnace known as the superheater, which has
an elaborate set up of tubing where the steam vapor picks up more energy from hot flue gases
outside the tubing and its temperature is now superheated above the saturation temperature. The
superheated steam is then piped through the main steam lines to the valves before the high pressure turbine.
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ACCESSORIES:
1. Economiser
2. Superheater
3. Air pre-heater (APH)
4. Feed pump5. Eletrostasic precipitator (ESP)
6. Deaerator
7. Bed Ash Cooler
8. Drum
9. Mechanical Dust collect
ECONOMISER : An economiser is a device in which the waste heat of the flue gas is
utilized for heating the feed water.Economiser is generally of two types: independent and
integral type. Former is installed in chamber a part from the boiler setting. The chamber is
suited at the passage of flow of the gases from the boiler or boiler to chimney. Latter is
part of the boiler heating surface and is installed within the boiler setting.
SUPERHEATER:
The function of the superheater is to increase the temperature of the steam above its
saturation point.They are located in the path of the furnace gases so that heat is recovered
by the supreheater from the gases. They are two types of superheaters: convective and
radiant.
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Fig 5.2: Economiser
Fig 5.3: Super heater
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AIR PRE-HEATER: Air for combustion purposes may be preheated before it enter the
boiler furnace by passing it through banks of tubes placed in the flue leading from boiler to
the chimney. It thus uses some heat of leaving flue gases, that would otherwise passed to
waste.
Fig 5.4: Air preheater
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ELECTROSTATIC PRECIPIRATOR: An electrostatic precipitator (ESP), or electrostatic air
cleaner is a particulate collection device that removes particles from a flowing gas (such as air)
using the force of an induced electrostatic charge. Electrostatic precipitators are highly efficient
filtration devices that minimally impede the flow of gases through the device, and can easily
remove fine particulate matter such as dust and smoke
from the air stream. In contrast to wet scrubbers which apply energy directly to theflowing fluid medium, an ESP applies energy only to the particulate matter beingcollected and therefore is very efficient in its consumption of energy.
S.no Description UnitBHAVNAGA
R LIGNITE
KUTCH
LIGNIT
E
IMPORTE
D COAL
1. Design Gas Volume AM3/Sec 76.11 74.22 62.42. Temperature Deg cen. 150 150 1403. Dust Type Fly Ash Fly Ash Fly Ash4. Max. Inlet Dust loading GM/NM3 50 48 49
5.Outlet Emission (all fieldsin service)
MG/NM3 <50
8. Collection Area M3 8748
9. Specific Collection rates M2/m3/sec
114.93117.78140.19
10. No. of Gas passes 2811. Velocity through ESP M/Sec 0.5212. No. of Fields in Series 4 Electrical & 4 Mechanical13. Design Pressure Mmwc -420
14.Flange to Flange PressureDrop
Mmwc -28
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Fig 5.4: Electrostatic precipitator
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ESP SPECIFICATIONS
SR.
NO.
DESCRIPTION UNIT
1 Number of streams Nos. 1
2 Make Alstom Projects India Ltd.
3 Design flow of flue gases Nm3/sec 90
4 Temperature of flue gases oC 160
5 Dust loading at ESP inlet gm/Nm3 120
6 Dust loading at ESP outlet gm/Nm3 50
7 System pressure mm of WC (-)600
Through gas discharge theory, it is known that breakdown of non-uniform electric field (as
ESP electric field breakdown) are all due to the formation and extension of streamer.
Definition of streamer: In some parts in the gas, the formed mixing zone of positive and
negative ions which possesses high conductance passage is called as streamer. It is one of the gas
discharge ways (corona discharge and streamer discharge) of non-uniform electric field.
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is at the corona outer region and forms even more extricated electron avalanche(no Cause of
streamer formation: Normal negative corona is electron-avalanche-like extrication in corona zone.
However when the bared voltage of the ESP electric fields rises continually, the photon will be
discharged at the electron avalanche head as a result of the compounding of the positive and
negative ions or that the excitonic atom regains normal state. The generated electron extricated by
photon is entitled as photoelectron, which longer extricate through the high field intensity of thesharp electrode, while extricate through photoelectron), this even more extricated electron
avalanche converges with the avalanche head of the main electron avalanche and in some parts of
the gas of corona outer region forms mixing zone with high conductance of positive and negative
ions. The mixing zone is called as streamer. After streamer forms, by the effect of basic electric
field, the charges in streamer section are to part and go ahead the both ends of the section, hence
to weaken electric field in the streamer. Thus, although streamer occurs at the edge of the corona
zone, the potential from it to opposite electrode is almost the same with that to the sharp
electrode, because the interior electric field intensity of streamer is very weak (i.e. streamer
obtains the ability to transmit potential), which is equivalent to that the sharp electrode extends
forward and makes extrication develop at the depth of the electric field gap (corona outer region)
and results in breakdown (spark.) Thus, the breakdown course of ESP electric fields is finished in
three segments, i.e., corona zone electron avalanche (corona)-corona outer
region streamer-electric field breakdown. Therefore the formation of streamer is premonition of
electric field breakdown; it is also acceptable to say that the streamer formation is the sufficient
condition of electric field breakdown. As for conven- tional ESP with single zone and negative
corona, this kind of pre-breakdown streamer is unfavorable, in respect that streamer will speed up
discharge development and make breakdown voltage decrease. What is more important, streamer
formation makes cation
and positive dust charged by cation appear in corona outer region (in the streamer, the
appearance of cation at corona outer region will enhance DE ionization making the corona current
increase, streamer tend to develop and breakdown voltage fall. At the same time, as for the dust,
cation reduces the charge capacity of negatively charged
dust and even charges the dust positively to make positive corpuscles form at corona outer region
of the electric fields.) Whereas ESP with single zone and negative corona can not collect positive
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corpuscle dust charged by the cation in the streamer, therefore dust leakage rate increases, the
deposited dust layer on the corona wire will become thick, which brings the ESP operation
exacerbation.
At corona outer region of conventional ESP, cation and positive corpuscle dust charged by
cation also exist. One of the sources is before electric field breakdown gas discharges and forms
streamer, which is the mixing zone of the positive and negative ions. Its second source is cationand positive corpuscle dust charged by cation formed because of back corona. Its third source is
the carbon in the dust with much fly ash combustible substance, which tends to be charged
positively and form cation and positive corpuscle dust charged by cation. Since the cation and
positive corpuscle dust charged by cation exist at corona outer region, then these ions and dust
must have an escape hatch, therefore a sort of structure needs to be designed to collect them.
It is common knowledge that dust charge requires high corona current in the electric field,
while collection of charged dust requires high field intensity but not high current. Thereby, charge
and dust collection is contradictory at the corona current aspect. Especially for collection of high
specific resistance dust, too high current will give birth to highelectric field on the collected dust
layer and cones- quently result in dust layer gap breakdown, back corona and dust removal
efficiency drop. As against double-zone ESP, the charge zone and dust collection zone of the
double-zone electric field are structurally completely separated and is able to be intensified
respectively.
Through variant wire-plate tests, Longking has developed a new model of double-zone ESP -
mechanical and electronic multiplex double-zone ESP (hereinafter referred to as double- zone
ESP.). It is composed of charge zone structure of the conventional needle bared wire & flat plate
type BE plate and the dust collection zone structure of tube type auxiliary electrode & flat plate
type BE plate. These two structures is configured alternatively, each of which is energized by
independent power supply. Thus, charge and dust collection functions are intensified respectively
and forms a sort of mechanical and electronic multiplex structure. In no-load electric pressure
build-up test, no spark over appears in the fields composed of tube type auxiliary electrode and
flat
plate type BE plate with the gas passage spacing of 400 mm, when the electric field intensity
reach 4.2 kV/cm. During actual operation, its secondary voltage is able to reach 80 kV in general,
which intensifies enormously dust collection function.
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Electricity Consumption:-
The charge zone and collection zone of the double-zone ESP are energized separately by
independent HV power supply. The charge zone employs power supply according to conventional
plate current density. However, since in the collection zone the on-site operation voltage is very
high and the current is very low, when the gas passage spacing is 400mm, the voltage is chosen as80 kV. For the dust with not too high specific resistance, 90 kV level can be chosen; the plate
current density is general between 0.05 mA-0.08 mA/m2. Compared to conventional ESP fro
300MW unit, to reach the same dust removal efficiency, the double ESP can save 15%-18%
electricity consumption.
In double-zone electric fields, the wire-plate form of the charge zone is almost the same with
the conventional electric fields, which not only charges the dust, but also collect the negatively
charged dust. The collection zone is composed of the tube type auxiliary electrodes and ordinary
plate type CE plates, which possesses characteristics of high electric voltage, low current and
more uniform plate current density distribution.
The industrial application results show when collecting coal burnt boiler dust, the double-zone
ESP can be adaptable to comparatively wide scale of coal without back corona in the dust
collection zone and with more stable operation. Besides the dust removal efficiency, dust
migration speed and value-cost ratio are all higher than the conventional horizontal ESP. The last
but not the least, it can reduce the flue dust emission concentration below 50 mg/DNm3 thereby
to reduce the fine dust emission, which is favorable to protect atmosphere environment and
human health.
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FLUE GAS CIRCUIT
Furnace
Economiser
Air preheater
I.D. fan
Chimeny
5.6)Boiler efficiency
Thermal efficiency of a boiler is defined as “the percentage of (heat) energy input that is
effectively useful in the generated steam.”
This is also known as ‘input-output method’ due to the fact that it needs only the useful output
(steam) and the heat input (i.e. fuel) for evaluating the efficiency. This efficiency can be
evaluated using the formula:
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Parameters to be monitored for the calculation of boiler efficiency by direct method are:
Quantity of steam generated per hour (Q) in kg/hr.
Quantity of fuel used per hour (q) in
kg/hr.
The working pressure (in kg/cm2(g)) and superheat temperature (oC), if any
The temperature of feed water (oC)
Type of fuel and gross calorific value of the fuel (GCV) in kcal/kg of fuel
And where
hg – Enthalpy of saturated steam in kcal/kg of steam
hf – Enthalpy of feed water in kcal/kg of water
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GENERAL PROBLEMS IN POWER PLANT
EMERGENCY CASES REQUIREING SHUT DOWN OF BOILER:
Very high drum level
Fall in drum level
Pressure rise in boiler furnace
Flame failure
Both I.D & F.D. fans trip.
SHUT DOWN OF THE UNIT REQUIRING USE OF VACCUM BREAKER:
Abrupt increase in axial shift up to critical limits.
Rise in temperature of oil drum drain from seal and bearing.
Emission of sparks from rear seals of turbine
Sudden drop in turbine oil level and pressure.
OTHER EMERGENCIES IN BOILER
Water wall tube failure
Re-heater/super heater/economizer tube failure. High reheat steam temperature.
Steam pressure rise
Ignition of unburnt particles of coal in boiler flues.
Plugged air heater.
Slag in superheater
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Boiler water conductivity high.
Impulse steam
High smoke density.
Boiler flue gas temperature low.
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DO’S AND DONT ‘S:
DO’S:
1. Maintain all instruments and interlocks in good working condition.
2. Maintain the instrument air free from moisture and oily matters and the pressure asrecommended.
3. All dampers must be in smooth operating condition.
4. Maintain fuel as per the recommendation.
5. Use the bed material as per the specification.
6. Maintain bed chemistry as per the design limits.
7. Maintain feed and boiler water as per the design limits.
8. Use proper lubricants as per the manufacturer recommendation.
9. Clean all Ash hoppers, feed water and transfer pump suction strainers, Oil gun regularly.
10. Operate the boiler within the recommended operating limits and Maintain proper operation log sheets regularly.
11. Operation & Servicing of individual equipment should be done as per the manufacturer’sschedule.
12. Carry out regular cleaning of direct water level gauge glass on Feed water tank,
Deaerator and Boiler drum.
13. Keep the stand by auxiliaries ready for operation.
14. Chemical dosing systems as per recommendation.
15. Boiler surroundings and equipment must be properly illuminated.
16. Cleared the bed material immediately to make room for emergency.
17. Use genuine spares.
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DONT’S:
1. Don’t by pass any instruments and safety interlocks.
2. Don’t run the Boiler with furnace in pressurized condition.
3. Don’t throttle the feed water pump balancing leak off valve while the pump is inoperation.
4. Don’t operate the furnace wall header drain valves while the Boiler is in operation.
5. Don’t leave the furnace door open while the boiler is in operation.
6. Do not open the furnace manhole without the permission from control room.
7. Don’t leave the Instrument Control Panel unattended.
8. Don’t allow unauthorized persons to operate the boiler and associated equipment.
9. Avoid continuous operation of boiler at low loads (low back end temperature) to protecteconomizer and air preheater corrosion.
10. Do not dose chemicals into the boiler in batch wise, they should be done on a continuous basis.
11. Do not slump the in-between compartments, it must be from the last compartment.
Do not slump the start-up compartment
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FEATURES AND BENEFITS:
A) Two-stage particle separation system1. Greater than 99.8% particle collection efficiency2. Provides a means to control particle size distribution in furnace, which results in
improved carbon burnout, limestoneutilization, emissions and heat transfer 3. Reduces operating costs
B) All-internal primary solids recirculation(U- beam)1. Compact design requires 20-30% less building volume thancyclone-based CFBC
boilers — critical for repowering projects2. Lowers auxiliary power consumption compared with cyclone-based CFBC boilers
C) Low, uniform velocities at the furnace exitU-beam separators, and the super heater 1. Significantly reduces erosion in upper furnace andsuper heater compared with
cyclone designs2. To date, no U-beam erosion maintenance required in anyIR-CFBC unit3. No high-maintenance vortex fi nders or hot expansion joints;therefore, no
maintenance expenses for these items
D) No thick refractory due to elimination of hotcyclones and hot return legs1. Thin, cooled refractory places no restriction on boiler start-upor shut–down rate2. Significantly reduces need for refractory maintenance3. Virtually eliminates forced outages due to refractory failures4. Requires only 10 to 25% of the total refractory comparedwith hot cyclone CFBC
designsE) In-furnace heat transfer surface
1. Vertical, flat membraned tube panels within furnace performevaporative or superheat duty
2. Proven reliability and low maintenanceF) Unique primary air nozzles (bubble caps)
1. Reduces back sifting of solids during low-load operation
2. Reduces need for periodic cleaning of nozzles and primary airwindbox3. Minimises erosion inside nozzle caused by the re-entrainmentof back-sifted solids
G) Soot blowers not required upstream of MDC1. Eliminates steam consumption, maintenance costs and forcedoutages typically
associated with sootblowersH) Gravity fuel feed and fl y ash recycle system
1. Reduces maintenance, forced outages and auxiliary powerrequirements byeliminating the mechanical fuel injection andpneumatic fl y ash recycle systems
I) High turndown (up to 5:1) without auxiliary fuelsupport1. Allows wider load swings2. Reduces operating costs (no auxiliary fuel) during low–loadoperation
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CONCLUSION
After the study of the captive power generation the power plant as a whole and coal handling,
boiler and turbine, it becomes very clear that the boiler work in efficiency range of 60-75% and
the efficiency of the boiler depends upon the degree by which the heat recovered which is lost in
the intermediate stage of the steam and electricity generation.
Apart from the above conclusions a combined conclusion can be drawn that if the heat
loosed are kept at kept at minimum and better quality fuel is used which is hydrogen and moisture
content ( as these are the major causes of heat loss other then the dry gas loss). In the desired
quantities and good preventive maintenance can boost the overall station efficiency of the plant.