Boiler and Its Auxilliaries
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Transcript of Boiler and Its Auxilliaries
IN-PLANT TRAININGPROJECT REPORT
ON
Submitted by
1. Banpreet Singh Sodhi2. Charan kumar3. Shrikant Singh4. Satish 5. Ashish Gadkari
N ATIONAL P OWER T RAINING I NSTITUTE
NAGPUR
KTPS UNIT DETAILS: Present capacity:1080MW
U.No.
Inst.Capacity in MW
DeratedCapacity
Date of Commi.
Make
Boiler T.G.
1 2 3 4 5 6 7
120
120
120
120
200
210
210
115
115
115
115
200
210
210
03.06.1974
24.03.1975
03.03.1976
22.07.1976
15.07.1978
30.03.1982
13.01.1983
ABL
ABL
ABL
ABL
CE
Through BHEL--do—--do--
Zamech
Zamech
Zamech
Zamech
Russian
Russian
Russian
THE TWO STAGES IN KTPS:-
Stage 1:
Unit1-115 MW
Unit 2-115 MW
Unit 3-115 MW
Unit 4-115 MW
Stage 2:
Unit 5-210MW
Unit 6-210MW
Unit7-210MW
SCENARIO OF POWER INDUSTRY IN INDIA
Indian electricity act:
The first supply undertaking in the country was sponsored by a company in the year 1896 which constructed a small generating station at Surat in Gujarat. The electricity legislation was first made in India in 1887 based on English framework, which was modified time-to-time. Then after independence this act was reinforced by the provisions of Indian (supply) Act 1948. Recently government has enacted Electricity Act, 2003, which replaces all above acts.
Growth of Power Industry:
The growth of installed capacity since independence till year 2003 is shown in fig. below.
In 1947 when India became independent the installed capacity was merely 1364 MW.
Out of these 63% was contributed by private companies and balance 37% by govt.
undertakings. About 78% power was generated from oil.
After 1955 the electricity boards were performed by State Governments and most of the
small private powers generating companies were merged into these boards.
The real growth of power industry started from 1960 onwards and jumped up
exponentially from 1970 onwards. This is because of the large scale industrialization
taking place in process industries and textile sector.
The major break through in the power industry was achieved in 1975 with the
formation of National Thermal Power Corporation (NTPC) and National Hydro
Electric Power Corporation (NHPC), the Central Government PSUs.
The remarkable rise of installed capacity took place after 1990 due to opening of utility
power generation sector to private companies. Similarly thrust was given to install
captive power plants by power intensive industries (cement, steel, textile etc.). the
licensing policy was further liberalized.
The present installed capacity is about 108000 MW, inclusive of generation by all
sectors.
The share of NTPC is almost 22000MW.
SECTOR WISE BREAK-UP
Figure below shows the break-up of installed capacity sector-wise. As shown in the figure,
the majority of power generation in India i.e. 67% is contributed by coal, fired thermal
power stations. The hydro power stations contribute only 21% against the potential of
84000MW. The nuclear power generation, which is at present 3%, may rise to about 8% by
the year 2010.
Highlights of Power position
Peak load demand :120000 MW
Present Power Generation :105000 MW
Peak Power Deficit :15%
Average Plant Load Factor on all India basis :64%
Resources Potential in India for Power Generation
Coal reserves :84000 Million Tons
Lignite :5000 Million Tons
Crude oil :84000 MW
Hydro :728 Million Tons
Natural gas :686 Billion Tons
Uranium :6700 Tons
Thorium :363000 Tons
Solar + Wind :20000 MW
Biomass :6000 MW
BOILER AND ITS AUXILLIARIES
1. Principles of steam generation.
2. Boiler drum.
3. Water wall tubes.
4. Super heaters.
5. Reheaters.
6. Economizers.
7. Electro-static precipitators.
8. Coal mill (bowl type).
9. Air pre heaters.
10. ID fan.
11. FD fan.
12. Chimney.
13. PA fan.
14. Wind box.
15. Soot blowers.
PRINCIPLES OF STEAM GENERATION.
Steam generation is the process of converting water into steam, a vapor
exhibiting the properties of a gas by application of heat. Heating water
at any pressure eventually will cause it to boil and steam will be
released.
For effecting steam generation, it is essential to transfer heat from a
source to the water. Heat in boilers is transferred by all of the following
modes during combustion:
1. Conduction
2. Convection
3. Radiation
A boiler, which provides steam of large quantity, must have sufficient
heating surface. The heating surfaces are in the form of round tubes.
Through these tubes placed in heating zones, water or steam will be
circulated to receive sensible heat, latent heat and superheat.
A boiler will have number of circuits of heating surfaces such as
economizer, water walls, boiler bank, super-heater and re-heater for
efficiently transferring the heat of combustion to the water and steam.
They may absorb heat either by radiation, convection or both.
BOILER DURM AND ITS INTERNALS.
In the erection of a power boiler, the lifting of the boiler drum is the first
mile stone activity.
Functions of the boiler:
(a). Separation of saturated steam from the steam-water mixture
produced by the evaporating tubes.
(b). Mixing feed water from economizer and water separated from
steam-water mixture, and re-circulate through the evaporating tubes.
(c). Carrying out blow down for reduction of boiler water salt
concentration.
(d). Treatment of boiler water by chemicals.
As the quantity of water contained in the drum below the water level is
relatively small compared to the total steam output, the function of
water storage in the drum is not significant.
The boiler drum is generally made of carbon steel; located at the top of
the boiler. The higher elevation at which the drum is located provides
the necessary head for circulation and facilitates the natural circulation
in the evaporating tubes of the boiler. INTERNALS:- Inside the boiler
drum a number of fittings are installed to carryout various functions.
Following components together are termed as drum internals.
Feed header
Anti vortex spider or vortex inhibitors
Steam separators
Steam dryers or scrubbers
C.B.D. line
E.B.D. line
Chemical dozing line
WATER WALL TUBES
Evaporator tubes, called as the water walls running from bottom ring
header to riser tubes, line the furnace walls from inside. The water walls
absorb the heat from fire ball by radiation due to which temperature of
flue gases is restricted below ash fusion temperature to prohibit the
melting of fly ash. Also the temperature of furnace walls is brought down
to evaporation temperature by water cooling effect and so the refractory
thickness is reduced drastically.
SUPER HEATERS
The steam separated and given out by the boiler drum is only in dry
saturated condition. For many applications, especially for running a
turbine, on efficiency aspects the steam must be in superheated
condition. To meet this requirement the boilers are provided with
separate tube circuits in the flue gas path. These heat transfer areas are
termed as super heaters. When the saturated steam from the drum is
circulated through the tubes of super heaters the steam temperature
increases.
REHEATERS.
Re haters are provided only in boilers supplying steam to large capacity
steam turbines (capacity more than 100Mwe). Like super heaters, re
heaters are also heating surfaces in the flue gas path meant for heating
the steam. The difference is, in re heaters the steam brought back at
low pressure from the turbine is heated to a higher temperature before
returning back to the turbine. This is required for improving cycle
efficiency.
ECONOMISER.
Economizers are provided in the boilers to improve the efficiency of the
boiler by extracting the heat from flue gases and add it as either
sensible heat alone or sensible heat and latent heat to feed water before
the water enters the evaporating surface of the boiler.
ADVANTAGES:- Provision of economizer in a boiler brings in two major
advantages .
1. As the economizer recovers the heat in the flue gas that leaves
the boiler and transfer to working fluid there will be savings in fuel
consumption.
2. As the feed water is preheated in the economizer and enters the
boiler tubes at an elevated temperature (near to saturation
temperature) the heat transfer area required for the evaporation
surface required will be reduced considerably. As such the size of
boiler will also be reduced.
ELECTRO STATIC PRECIPITATOR
WORKING PRINCIPLE:- The principles upon which an electrostatic
precipitator operates are that the dust laden gases pass into a chamber
where the individual particles of dust are given an electric charge by
absorption of free ions from a high voltage DC ionising field. Electric forces
cause a stream of ions to pass from the discharge electrodes to the
collecting electrodes and the particles of dust entrained in the gas are
deflected out of the gas stream into the collected surfaces where they are
retained either by electrical or molecular attraction. They are removed by
an intermittent blow usually referred as rapping. This causes the dust
particles to drop into dust hoppers situated below the collecting electrodes.
DESCRIPTION:- The electrostatic precipitator essentially consist of two sets
of electrodes, one in form of thin wires called discharge or emitting
electrodes and other set called collecting electrodes in form of pipes or
plates. The emitting electrodes are placed in centre of pipes or midway
between two plates and are connected usually to negative polarity of high
voltage DC source of order 25-100 kV. The collecting electrodes are
connected to the positive of source and grounded.
COAL MILL.
Coal mill (bowl type) is a vertical spindle medium mill. In a bowl mill the
coal is pulverized between a disc called bowl rotated by the drive assembly
and rollers kept above the disc loaded by springs or pneumatic or hydraulic
loading devices. The coal mill works under pressure, to prevent the entry of
dust laden air to the gear box a sealing arrangement is provided. The mill
has three grinding roll assemblies called roller journal assemblies.
ADVANTGES : low power consumption
Reliability, Min. maintenance
Ability to handle wide range of coals.
AIR HEATERS
Air heater is an important boiler auxiliary, which primarily preheats the
combustion air for rapid and efficient combustion in the furnace. The air
heater recovers the waste heat from the outgoing flue gas of a boiler and
transfers the same to the combustion air. In an utility boiler the flue gas
leaves the economizer at a temperature of around 380degree C. as every
55 degree drop in the flue gas temperature improves the boiler efficiency
by about 2.5%, having an air heater in the downstream of economizer the
boiler efficiency is considerably improved. Further the air heater may also
be used for heating the air to dry the coal in the pulverizing plant .
INDUCED DRAFT FAN
Induced draft fans evacuate combustion products from the boiler furnace
by creating the negative pressure to establish a slight suction in the
furnace (usually 5-10 mm). these fans must have enough capacity to
accommodate any infiltration caused by the negative pressure in the
equipment downstream of the furnace and by any seal leakage in air
heaters.
As ID fans are now typically located downstream of any particulate removal
system they are relatively clean service fan. Since ID fans have to
compensate for heavy pressure drop of flue gas across boiler contour, the
power requirement is very high and it is the boiler auxiliary, which
consumes maximum ower. As such high efficiency fans are demanded for
this application. The airfoil radial fans, which have efficiencies of more than
88% and can, have capacities greater than 1.6 lakh m3 /min. the airfoil
blade shape minimizes turbulence and noise. The blades and centre plates
may also be fitted with wear plates and replaceable nose section for
greater wear life.
FORCED DRAFT FAN
Forced draft fans supply air necessary for fuel combustion and must be
sized to handle the stoichiometric air plus the excess needed for proper
burning of the specific fuel. In addition, they provide air to make up for air
heater leakage and for some sealing air requirements. FD fans supply the
total airflow except when an atmospheric suction primary air fan is used.
FD fans operate in the cleanest environment associated with a boiler and
are generally the quietist and most efficient fans in the power plant. They
are particularly well suited for high speed operation. radial aerofoil or
variable pitch axial fans are preferred for FD service.
PRIMARY AIR FAN
These are the large high pressure fans which supply the air needed to dry
and transport coal either directly from the coal mills to the furnace or to the
intermediate bunker. These fans may be located before or after the milling
equipment. The most common applications are cold primary air fans, hot
primary air fans and pulverizer exhauster fans.
CHIMNEY
Though in natural circulation boilers, the Chimney creates the draught in
the boiler, in large boilers where mechanized draught system is adopted
the function of a Chimney is largely limited to discharge flue gases to the
atmosphere at such height and velocity that the concentration of pollutants
is kept within acceptable limits at ground level. The pollutants exiting from
the chimney must first clear the area of turbulent air created by the wind
around the chimney top. To ensure this height of the chimney is sufficiently
high above the boiler house or near by buildings and the gases are emitted
with sufficient upward velocity. Generally the height of the chimney is
decided based on the concentration of pollutants in the flue gas, emission
standards, wind velocity, location of the plant etc.
WIND BOX
The wind box assembly is installed at each corner of the furnace in a
tangentially fired system. The wind box is vertically divided into number of
compartments which are provided with coal nozzles, air nozzles and fuel oil
nozzles alternately.
SOOT BLOWERS
Soot blowers are the devices, which admit the blowing medium over the
heating surfaces. Soot blowers are made according to the surface they
have to clean. The soot blowers for water walls are called wall blowers or
deslaggers. Long retracts and half retracts are used for super heaters, re-
heaters and economizers. Rotary air heaters are provided swivel blowers.
The exact mechanism of a blower depends on the manufacturer.
BOILER CONSTRUCTION
HISTORY OF BOILERS:
Boiler means any closed vessel exceeding 22.75 liters in capacity used for steam generation under pressure. The first Boiler was developed in 1725 & it’s working pressure was6 to 10 kg/cm2 and was called Wagon Boiler.
TYPES OF BOILERS:
There are two types of Boilers :
1) Fire tube boilers (Carnish & Lauchashire blrs.) developed in the year 1844
2) Water tube boilers developed in the year 1873.
Water tube Boilers are used in Thermal Bower stations. These are sub divided according to water circulation
1) Natural circulation :
Drum to down comers to ring main header to waterwall tubes & back to drum. Due to difference in density of water and steam this type ofcirculation takes place.
2) Forced circulation :
As operating pressure of the boiler approaches to the criticalpressure, additional pumps are required to install in down comers, because at thispressure there is no appreciable density difference between water and steam to have anatural circulation of water.
According to working pressure the Boiler, Boilers are classified as:
1) Drum type sub critical pressure boiler: When working pressure of the boiler is between130 kg/cm2 and 180 kg/cm2, the boiler is called as, “Drum type sub critical pressureboiler”.
2) Critical pressure Boilers : When boiler working pressure is 221.2 kg/cm2, it is termed as,“Critical pressure Boilers”.
3) Super critical or drum less once through boilers: When boiler working pressure is 240kg/cm2, it is called as, “Super critical”.
All modern Boilers are top slung from steel structures. From the beams a series ofslings take up the boiler loads. Approximately suspended weight of one 210 MW boiler is 3640metric tones. Height of Boiler is about 64 meters and Boiler drum is at a height of 52 metersfrom the ground.
Boiler design consideration :
Following factors are taken into consideration for designingthe modern boiler.
1) Lowest capital cost, ease of construction, simplicity, safety, good working condition,ease of maintenance.
2) Efficient operation, effective baffling for heat transfer, well insulated casings, ability todeliver pure steam with effective drum internals to generate steam of fuall capacity.
3) Availability of auxiliaries.
Period of constructions :
In India the Boiler is being constructed in three years i.e. 36 months.
References:
NPTI manual
Encarta
Wikipedia search
www.mahagenco.com
THANK YOU.