STUDY OF THE BOILER IN THERMAL

POWER STATIONAT

NTPC RAMAGUNDAM

BY ANGARI ABHINAY

14675A0310

Under the guidance of

Mr. Y.VIJAY KUMAR, M.Tech,

Professor

Department of Mechanical Engineering

J.B. INSTITUTE OF ENGINEERING AND TECHNOLOGY

(UGC AUTONOMOUS)(Affiliated to Jawaharlal Nehru Technological University, Hyderabad, T.S)

Moinabad, Hyderabad-500075.

(2016-2017)

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ABSTRACT Thermal power plants are major area for the generation of power.

The combustion of coal is responsible for the generation of steam from

the water.

In thermal powerplant boiler plays a major role in power production.

In boiler water is converted in to steam using heat energy as

input source.

The combustion of coal is responsible for the generation of steam

from the water. There are many mountings&accessories supporting

the efficient functioning of the boiler.

This project deals with the study and applications of concepts and the

theories in the current industrial scenario by the study of boiler pressure

parts and firing systems.

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ABOUT THE ORGANISATION

NATIONAL THERMAL POWER CORPORATION, A public sector company, is the

major power utility generation over one fourth of the total thermal power of India. It was in

incorporated in the year 1975 to accelerate power development in the country. At present,

Govt. of India holds 89.5% of total equity shares of the company.

“NTPC Ltd., is the sixth largest & second efficient power utility in the world”.

As on date the capacity of NTPC 45,548MW through its

18coal based (40477MW)

7 gas based (4017.23MW) and

7 joint Venture Projects (1,054 MW).

Ramagundam super thermal power station is the current largest power station in South India.

it is the first ISO 14001 certified "Super Thermal Power Station" in India.

The NTPC at RSTPS generates 2600MW power through 3 units of 200 MW & 4 units of 500

MW used for domestic and industrial purpose in T.S & neighbor states.

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It is known for ages that when coal is burnt it release heat energy.

The same phenomenon chemically represented as:

C + O2 -- C02 + heat energy (395 KJ/ mole)

In the boiler, chemical energy of fuel is converted into thermal energy by heating water

and converting into steam. The steam produced in the boiler expands in the turbine.

In the turbine the thermal energy of the steam is converted into the kinetic energy

this motion of the turbine rotor is transmitted to generator in which mechanical energy is

converted into the electrical energy, which is transmitted to various load centers through

the transmission lines.

The energy conversion diagram can be shown as

CHEMICAL ENERGY THERMAL KINETIC ELECTRICAL

BOILER TURBINE GENERATOR

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The whole arrangement of the steam power station can be

divided into following stages:

Coal and Ash handling plant

Feed water supply

Steam Generating plant(BOILER)

Steam Turbine

Alternator or Generator

Cooling arrangement

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SCHEMATIC VIEW OF THERMAL POWER PLANT

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The Rankine cycle is an idealized thermodynamic cycle of a heat engine that converts heat into mechanical work. The heat is supplied externally to a closed loop, which usually uses water as the working fluid. The Rankine cycle, in the form of steam engines generates about 90% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants.

Simple rankine cycle consists of the following process:·

• Process 1-2: Adiabatic expansion of steam (in turbine)

• Process 2-3: Constant pressure heat rejection (in condenser)

• Process 3-4: Isentropic compression (in pump)

• Process 4-1: Heating at constant pressure (in boiler)

All the above processes are reversible in nature.

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Boiler or steam generator is the main part in the power generation process.

It is a closed vessel in which water is converted into steam with the help of

heat produced by the burning of coal in the presence of oxygen.

The pulverized coal from mills enter furnace through feeders due to

primary air from PA fans.

Now for the combustion of coal oxygen in atmospheric air is required and

this air is called secondary air. Secondary air is supplied by FD fans

(Forced Draft fans). This secondary air from FD fans is heated in

secondary air pre-heaters to improve combustion efficiency.

The Boiler structure consists of large number of tubes extending the full

height of the structure and the heat produced raises the temperature of

water circulating in them resulting in steam called saturated steam, this sent

to boiler drum where steam is separated from water. The stem separated is

heated in super heater and passed to high pressure cylinder of turbine.

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As we know basically two types of boilers are used, they are: fire tube & water tube boiler.

In RSTPS high pressure water tube boilers are used. There features are as follows:

Forced, induced and balanced draft provisions which help to improve the combustion efficiency.

Less tolerance for water quality calls for water treatment.

Higher thermal efficiency levels are possible.

In water tube boiler 70% of heat is transferres by Radiation.this is a faster way of heat transfer.

The steam is generated at a pressure between 80 bar to 300 bar and temperature of 450°C to 585°C with two super heaters in series. The use of such stream is very suitable for power generation. It increases thermal efficiency of the plant and reduces the moisture contents in low pressure stages of expansion in the turbine.

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Boiler components are classified as two typesI. Pressure partsII. Rotating machines In a steam generator the parts through which the feed water and

steam flows where the pressure of the system is more than atmospheric pressure are generally termed as boiler pressure parts

The pressure parts of boiler are as follows:• Water wall tubes• Economiser tubes• Superheater tubes• Reheater tubes• Downcomers• Headers• Boiler drum• Valves

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Coal mills

Fans

Forced draught fans

Induced draught fans

Primary air fans

Air preheaters

Pumps

Boiler feed pump

Condenser pump and circulation pump

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Almost all modern power boilers are equipped with water walls .In large boilers

water walls completely cover the interior surfaces of the furnace. Water walls

serves as the only means of heating and evaporating the feed water supplied to the

boiler from the economiser

Specifications Total number of tubes -- 1152

Heating Surface -- 1160 sq.mts

Material -- SA 210C

Outer diameter -- 51mm

Pitch -- 63.5mm

Designed thi -- 5.1mm

.

The function of boiler drum is to separate the water from the steam generated in the furnace

walls and to reduce the dissolved solid contents of the steam to below the prescribed limit of

1 ppm. The drum is located on the upper front of boiler.

Boiler drum is provided with welded stubs for connection of valves, various instruments,

down comers, return tubes, steam outlet tubes to primary super heaters, feed water tubes and

for the inlet of reagents and continuous drainage. The drum contains the diaphragms,

cyclones, scrubbers, steam separators, drilled tubes for feed water distribution, steam and

water sampling, system and the continuous blow down system.

Specifications of a 500MW Boiler Drum

Material -- SA-299

Length -- 26 m

Outer diameter -- 2.1 m

Inner diameter -- 1.8 m

Design pressure -- 204 MN/m2 (abs)

Operating pressure -- 192.5 MN/m2 (abs)

No. of cyclone separators -- 96

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1ST LEVEL IN THE BOILER DRUM

Boiler drum

↓ (through down comes)

Manifold

↓ (through three outlets)

Continuous circulation

↓

Boiler ring heads

↓

Water tubes

↓

Boiler drum

↓ (steam and water separate)

Steam enters LTSH

↓ (Attemperation)

Division panels

↓

Final super heaters

↓

High pressure turbine17

From H.P turbine through cold reheater

↓

Boiler

↓ (attemperation)

1st stage of reheater

↓

Final stage of reheater

↓

I.P turbine

↓

L.P turbine

↓ (condenser)

Hot well

↓

Condensate extraction pump

↓

L.P heater

↓

Deaerator

↓

Boiler feed pump→ H. P heater→ Economizer18

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Main steam flow -- 670,000 Kg/hr

Main steam pressure -- 187 MN/m2 (abs)

Main steam temperature -- 5400C

Reheat steam flow -- 580,000 Kg/hr

Reheat stem temperature -- 5400C

Reheat steam pressure -- 45 MN/m2 (abs)

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One of the most complex, critical, and vulnerable systems in fossil power generation nts is the boiler pressure components. Boiler pressure component failures have historically contributed to the highest percentage of lost availability. Failures have been related to :

Poor original design

Fabrication practices

Fuel changes

Operation

Maintenance

Chemical reactions

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Poor water quality. With increases in operating pressure, feedwater quality becomes

even more critical.

Coal quality. Using a different type of coal for emission or economic reasons has

adversely affected the capability, operability, and reliability of boiler and boiler

auxiliaries

Cycling operation. Many base-load-designed boilers have been placed into cycling

duty, which has a major impact on the boiler reliability as indicated by occurrences of

serious corrosion fatigue in water-touched circuitries, economizer inlet header shocking,

thick-wall header damages, and others.

NOx emission. Deep staging combustion for NOx reduction has produced serious

waterwall fire corrosion for high sulphur-coal firing, especially in supercritical units.

Age-ing. A large percentage of existing fossil-fired units are exceeding “design life”

without plans for retirement. These vintage units are carrying major loads in power

The boiler tubes are under high pressure and/or high-temperature conditions. They are

subject to potential degradation by a variety of mechanical and thermal stresses and

environmental attack on both the fluid and fireside. Mechanical components can fail due

to creep, fatigue, erosion, and corrosion

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Most coal fired power station boilers use pulverized coal, and many of the larger

industrial water tube boilers also use this pulverized fuel. This technology is well

developed, and there are thousands of units around the world, accounting for well

over 90% of coal fired capacity.

The coal is pulverized to a fine powder, so that less than 2% is +300 micro meter

(μm) and 70-75 % is below 75 microns.

The pulverized coal is blown with part of the combustion.

Air enters through 2 series of burner nozzles. Secondary and tertiary air may also

be added. Combustion takes place at temperatures from 1300-1700ºC, depending

largely on the coal grade. Particle residence time in the boiler is typically ₐ to 5

seconds, and the particles must be small enough for complete combustion to have

taken place during this time.This system has many advantages such as ability to fire

varying quality of coal, quick responses to changes in load, use of high pre-heat air

temperatures etc.

One of the most popular systems for firing pulverized coal is the tangential firing

using four burners corner to corner to create a fireball at the center of the furnace.

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Fuel Firing system can be broadly classified into direct firing system and

indirect firing or intermediate bunker system. Both the systems can use any

type of mill.

Direct Firing System:

n this type of firing system, controlled hot air from primary air pump carry

pulverized coal from mills which are operated depending on boiler loading and

coal stored in the bunker o coal burners of the combustion chambers.

Indirect Firing System:

In this type of firing system, controlled hot air from primary air pump carry

pulverized coal from mills which are operated independent of boiler loading

and coal stored in the bunker to coal burners of the combustion chambers using

cyclone type separators.

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There are four ways of firing the coal in furnace. They are:

Vertical firing

In vertical firing, a number of rectangular fan shaped nozzles are set across the width of the furnace

in an arc immediately under the boiler setting.

Front wall firing

Horizontal firing with the turbulent type of burner is set up usually in the front (front wall fired) o

r rear walls of the furnace.

Impact firing

This is the arrangement with the type of burner used with slag tap furnaces where

ash is kept in a molten state on the furnace floor and tapped of as and when

necessary.

Corner or tangential firing

Tangential firing is a method of firing a fuel to heat air, which is the most

Common one in thermal power stations. The flame envelope rotates ensuring

Thorough mixing within the furnace, providing complete combustion and uniform

heat distribution.

In RSTPS pilverised coal with tangential firing system is used.

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Power is an important infrastructure in developing countries. Power development in

India received a big boost with the dawn of National Thermal Power Corporation

Limited.

RSTPS is wll equipped with control systems for monitoring boilers, turbines and

other machinery.

Boiler feed pump control loop in RSTPS is manufactured by SIEMENS which

involves the measurement and maintenance of water level in the BFP through

pumps, controller, make-up valve, level transmitter and converters. Whose main

aim is to maintain the water level in the condenser so as to use the pressure and

heat of the water effectively to increase the efficiency of the system.

The plant is effectively and efficiently managed by various departments.

RSTPS has giving its importance in conserving coal and water by utilizing

advanced techniques to produce maximum energy without any wastage of input

sources.. NTPC Ramagundam is producing a qualitative power minimizing the

hazardous disposals.

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