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.