Steam Boilers

UNIT-VI

Alpha Breathing- (2 mins)

Three steps for alpha breathing 1. Breathe-in (as much as possible)2. Breathe-out (Slowly & Completely)3. Hold (as long as possible)(Repeat the three steps 8 times)

Evocation

Steam Boiler (or) Generator

• A boiler is a closed vessel which generates steam by transforming heat produced by burning of fuel to water.

• Heat energy is released by burning of fuel is transferred to the water in the boiler.

• The boiler converts water into steam at the required temperature and pressure.

Uses of steam

• Power generation

• Processing (like bleaching)

• Heating (residents and buildings in winter)

Primary requirements of steam boiler or generator

• It should be capable of generating the max. quantity of steam at required temp. and pressure at low fuel consumption.

• The water must be safely contained.

• Consists of safe working condition as per IBR (Indian Boiler Regulation).

Primary requirements of steam boiler or generator

• All parts and components are easily accessible for inspection and repair.

• The initial cost, installation cost and maintenance cost of the boiler should be low.

• It should be a light in weight and should not occupy more space.

Classification of boilers

• Horizontal, vertical and inclined (according to the axis of cell)• Fire tube and water tube (according to flow of water and hot gases)• Externally and internally fired (according to the position of the furnace)• Forced and natural circulation (according to circulation of water)• Stationary and portable

Classification of boilers

• Single tube and multi-tube(according to the number of fire tubes)• High and low pressure (according to pressure of steam generated)• Natural draught and forced draught(according to movement of air circulation)

Simple vertical boiler

• It is an internally fired vertical low pressure fire tube boiler.• It is one of the fire tube boiler.

• Parts of the boiler• Shell: It consist of steel plate. Cylindrical in form. Most of the shell is filled with water and remaining portion

is steam. Diameter – 1.5 m. height – 2 m

Simple vertical boiler

• Fire boxIt consist of grate on which the fuel is burnt.The ash from it falls into the ash pit.• Central flue tubeTo carry the hot flue gases.As it passes through the tube the heat is

transferred onto the surrounding water. • Fire holeCharging door (through which the coal is fed)

Simple vertical boiler • Pressure gaugeTo indicate the steam pressure• Water level indicatorTo show the level of water inside the shell• Steam safety valveIt act as safety valve when pressure inside the boiler exceeds it’s limit• ChimneyThe exhaust flue gases are let through it• Steam stop valveIt like as a tap when the steam is required it is opened and closed after use• Blow off cockThe impurities like sand, sediments are removed.

Boiler mountings

• They are fitted on the boiler cell.

• The boiler mountings are used for the safety of the boiler and for complete control of the steam generation process.

• They are the integral part of the boiler.

Boiler mountings

• Pressure gauge• Water level indicator• Steam safety valve• Steam stop valve• Fusible plug

Babcock and Wilcox boiler

• It is a water tube boiler.• It is horizontal externally fired natural

circulation type stationary high pressure boiler.

• Parts of the boilerBoiler shell, water tubes, uptake and down take

header, Grate, Furnace, Baffles, Super heater, Mud box, Damper, Inspection door.

Specifications of Babcock and Wilcox water tube boiler

• Diameter of drum – 1.5-2 m• Length – 6-10 m • Diameter of water tubes – 7.5-10.5 cm• Diameter of super heater tubes – 3.5-5.5 cm• Working pressure – 40 bar max.• Efficiency – 60-80 %

Working of Babcock and Wilcox water tube boiler

• Fuel • Coal is fed to the grate through the charging door• Flue gas circulation • From the combustion of fuel the flue gases are coming out

and move upwards.• Baffles are arranged in a manner to deflect the hot flue

gases.• So the gases are forced to move in the upward and

downward directions.• The purpose of deflecting gases is to provide the maximum

heating of water tubes.

Working of Babcock and Wilcox water tube boiler

• Water circulation • The portion of the water in the tubes is heated which are

above the furnace.• The heated water moves upward direction due to

decreased density and passes into the drum through the up take header.

• The steam is separated from water and it is in upper portion of the drum.

• The water enter into the tubes through the down take header.

• This cycle is repeated. It is known as natural circulation.

Working of Babcock and Wilcox water tube boiler

• Superheating• The superheater is placed b/w drum and water

tubes.• The steam that is collected it is passed through

the superheater and flows out of the boiler through the steam stop valve.

• Mud box• It is used to collect the impurities and sediments

in the water and it is removed by blow off cock.

Brain Activation: (2 mins)

Survey and Reading (15-18 mins)

Discussion: (9 mins)

Mindmap: (5 -7 mins)

Summary

Boiler systems are classified in a variety of ways. They can be classified according to the end use, such as foe heating, power generation or process requirements. Or they can be classified according to pressure, materials of construction, size tube contents (for example, waterside or fireside), firing, heat source or circulation.

Boilers are also distinguished by their method of fabrication. Accordingly, a boiler can be pack aged or field erected. Sometimes boilers are classified by their heat source. For example, they are often referred to as oil-fired, gas-fired, coal-fired, or solid fuel –fired boilers.

Firetube boilers consist of a series of straight tubes that are housed inside a water-filled outer shell. The tubes are arranged so that hot combustion gases flow through the tubes.

Firetube boilers are subdivided into three groups. Horizontal return tubular (HRT) boilers typically have horizontal, self-contained firetubes with a separate combustion chamber.

Assessment: (5 min)

• 1. Which of the following enters the super heater of a boiler ? • (A) Cold water • (B) Hot water • (C) Wet steam • (D) Super-heated steam. •

• 2. Which of the following is accessory of the boiler • (a) Air preheater • (b) Superheater • (c) Economiser • (d) All of the above

3. In water tube boiler (a) Water passes through the tubes surrounded by flames and hot gases (b) The flames and hot gases pass through the tubes surrounded by water (c) Forced circulatin takes place (d) None of these

4. Which of these statement is wrong (a) Locomotive boiler is a fire tube boiler (b) Water tube boilers are externally fired (c) Cochran is a fire tube boiler

5. Boiler means any closed vessel exceeding ____capacity (a) 22.7 litres (b) 227 litres (c) 0.227 litres (d) 227 kg

Higher Order Questions 1. Explain the working principle the Wilcox and La-Mont boiler.