properties of steam: numerical - engineeringduniya.comengineeringduniya.com/slide_folder/first...

MADHWESH N., Faculty, Dept. of Mech & Mfg. Engg. 1

Steam Boilers Definition of a Boiler

Boiler is defined as a closed metallic vessel in which the water is converted into steam above the atmospheric pressure by the application of heat generated by the combustion of fuels.

Function of a Boiler

The function of a boiler is to generate & supply the steam at the required constant pressure with its quality either dry, wet or superheated.

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MADHWESH N, Faculty, Dept. of Mech & Mfg. Engg. 2

Classification of Boiler 1. According to the axis of the shell:

a. Horizontal boiler b. Vertical boiler c. Inclined boiler

2. According to the application a. Stationary boiler b. Mobile boiler

3. According to the location of the furnace a. Internally fired boiler b. Externally fired boiler

SHELL Furnace SHELL

Furnace


4. According to the type of fuel used a. Solid fueled boiler

b. Liquid fueled boiler

c. Gaseous fueled boiler

5. According to the method of circulation of water a. Natural circulation boiler (circulation of water due to

difference in temperature)

b. Forced circulation boiler (pumps are used)

6. According to the flow of water and flue gases a. Fire tube boilers

b. Water tube boilers


Fire Tube Boiler:

The hot flue gases are led

through a tube or a nest of

tubes around which the

water circulates.

Example:

Lancashire boiler, Locomotive

boiler, Cochran boiler.

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Water Tube Boiler:

The water circulates inside

the tubes while the hot

gases are passed around

them externally.

Example:

Babcock and Wilcox boiler

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1. Safety valve

2. Man hole 3. Steam pipe

4. Steam stop valve

5. Safety valve 6. Pressure gauge

7. Feed check valve 8. Water gauge

9. Blow off valve

10.Fusible plug

Lancashire boiler

B: Bottom central channel D: Dampers S: Side channels

C: Chimney E: Fire grate F :Flue tube K: Main channel


It is a horizontal, stationary, internally fired, natural

circulation, fire tube boiler.

By using this boiler, we can get steam up to a pressure of

15 bar.

Application:

It is widely used in sugar mills and chemical industries.

Lancashire boiler (Fire tube boiler)


Construction:

It consists of a horizontal cylindrical shell placed on a

brick setting.

2 large fire tubes of diameter 0.4 times that of boiler

shell are fitted inside the boiler shell & throughout the

boiler length.

In each of these fire tube 2 furnace grates are provided

at their front end.

The closed space below the grate is Ash pit.


The brick setting is designed to provide an enclosed

chamber for each of the flue tubes at the rear end of the

boiler shell, which are connected to the bottom central

channel which in turn connected to the side channels 1 &

2 at their front end.

2 side channels are connected at their rear ends to a

common rear passage which is connected to chimney.


The boiler shell is filled with water ¾ th of its volume

which will submerges both the flue tubes.

The remaining space above the surface of water in the

boiler shell is called steam space.


In the 1st run, the heat transfer takes place from the hot

gases to water through the walls of the flue tubes.

In the 2nd run, the heat transfer takes place from the hot

gases to water through the bottom portion of the boiler

shell.

In the 3rd run, the heat transfer takes place from the hot

gases to water through the portion of the boiler shell

exposed to side channel.


Babcock and Wilcox boiler A: Water tubes B: Uptake header C: Down take header D: Boiler drum E: Steel Caps F: Mud Box G: Dampers H: Doors J: Chain grate stoker K: Furnace door L: M: Lower junction box N: Upper junction box. O: Stop valve connection

P: Stop valve, Q: Safety valve, R: Water-level indicator, S: Super heater,

T: Pressure gauge, V: Feed check valve, W: Baffles, X: Blow off valve

R D

E

F

G H J K

L

N

M

O

P Q

s

T

V

W

X


Babcock & Wilcox boiler (Water tube boiler)

It is a horizontal, stationary, externally fired, natural

circulation, water tube boiler.

By using this boiler, we can get steam up to a pressure of 75 80 bar.

Application:

It is widely used in thermal power stations.


Construction:

It mainly consists of 4 parts

Boiler drum

Water tubes

Chain grate stoker

Super heater

Boiler drum rests on iron channels.

A number of inclined water tubes at a very low inclination

are connected at right angles to the end boxes called

headers.


The water tubes are arranged in a number of vertical rows, each row consisting of 4 to 5 tubes.

There will be a number of such vertical rows one behind the other.

Each row of such inclined water tubes are connected to one set of 2 headers.

Header shown at the right end of the water tube is called down take header and the other shown at the left end of the water tubes is called uptake header. Each set of header is in turn connected to the boiler drum, with one set of inclined tubes.


A mud box is provided just below the down take header.

Any sediments or impurities collected in the mud box are blown off from time to time through the blow off pipe.


Function of chain grate stoker:

If we use low quality coal, then the speed can be adjusted and hence the time for coal to reach from front end to rear end can be increased. Hence there will be effective burning of the fuel.


Water circuit in the boiler


Path of flue gases


Circulation of Water


Superheating of the steam


Advantages of Water Tube Boilers over Fire Tube Boilers

1. Steam can be raised more quickly

2. Steam at higher pressures can be produced

3. Higher rate of evaporation

4. Sediment deposition is less

5. Suitable for any type of fuel and method of firing

6. Failure of one of the water tube will not affect the working of boiler

7. Occupies less Space 8. Easy maintenance.


Disadvantages of Water Tube Boilers over Fire Tube Boilers

1. Not suitable for ordinary / impure water

2. Not suitable for mobile application

3. High initial cost and hence not economical


Differences / Comparison

High Low Rate of steam production

High ( Max. up to 75 bar)

Low (Max. up to 15 bar)

Operating pressure

Externally fired Internally fired Mode of firing

Water inside the tubes and hot gases surround the tubes

Hot gases inside the tubes and water is poured from outside

Flow of water & hot gases

Water tube Fire tube Particulars


Differences / Comparison

Small for given capacity

Large for given capacity

Shell diameter

Essential Not essential Treatment of water

Not safe, due to high pressure

Safe, due to low pressure

Safety

Ideally suitable for power generation plants.

Suitable for chemical & sugar industries & not for power generation

Applications Water tube Fire tube Particulars


Boiler Mountings and Accessories

BOILER MOUNTINGS, are required

To have complete control over the steam generation,

Measurement of some of the important steam properties,

To provide safety to the boiler. Manhole 8

Fusible plug 7

Feed check valve 6

Blow-off valve 5

Steam stop valve 4

Safety valves 3

Pressure gauge 2 Water level indicators 1


BOILER ACCESSORIES are required to improve the efficiency of steam power plant.

Steam trap 6

Steam separator 5

Feed pump 4

Super heater 3

Air preheater 2

Economizer 1


Functions of Boiler Mountings Water Level Indicator:

It is used to indicate the level of water inside the boiler drum.

Pressure Gauge: It is used to indicate the pressure of steam inside the boiler

drum.

Safety Valves: It suddenly blows off the excess steam from the boiler drum.

Steam Stop Valve: It is used to regulate the flow of steam from the boiler drum.


Feed Check Valve: It supplies the additional water, when the level of water

inside the boiler drum falls. Blow off Valve:

It is used to remove periodically the sediments & also used to empty water in the boiler when required.

Fusible Plug: It is used to extinguish the fire in the furnace of the boiler

when the water level falls below the normal level.

Manhole: It is an opening in the boiler shell through which a man can

go in for periodic inspection and cleaning.


Functions of Boiler Accessories Economizer:

It is a device, in which the waste heat of the flue gases is utilized for preheating the feed water.

Air preheater: It is a device, in which the waste heat of the flue gases is

utilized for preheating the air supplied for the combustion of the fuel in the furnace.

Super heater: It is used to increase the temperature of the steam above

the saturation temperature.


Steam Separator:

It separates the water particles from the steam flowing in

the pipe lines.

Steam trap:

It is used to drain off the condensed water accumulating

in the steam pipe lines while at the same time the high

pressure steam does not escape out of it.

Feed Pump:

It is used to force the feed water at higher pressure into

the boilers.


Differences between Boiler mountings & Accessories

Boiler mountings Boiler accessories It is mandatory (compulsion to use)

It is optional

It speaks about safety It speaks about efficiency & economy

These are fitted directly on the boiler drum

These are not fitted directly on the boiler drum

It is used to measure some of the important properties

It is used to improve some of the important properties


Simple Vertical Boiler

S Shell

C Chimney

M Manhole

H Hand hole

T Cross-tube

F Fire hole

B Fire box

G Grate

A Ashpan


It is a vertical, stationary, internally fired, natural circulation, fire tube boiler.

By using this boiler, we can get steam up to a pressure of 7 bar.

The fire box is placed at the bottom of shell

The grate is provided at the bottom of the fire box.

The ash pan is provided beneath the grate.

The fire box is fitted with two or more inclined cross tubes to increase the heating surface and to improve the circulation of water.

Hand holes H are provided in the shell opposite to the ends of each cross-tube for cleaning the tubes.


The coal is introduced over the grate G, where the fuel is

burnt, through the fire hole F.

The manhole is provided on the upper portion of the shell

to enable a man to enter into the shell to attend the

inspection and repair works.

The boiler shell is filled with 3/4th of its volume with water

which will submerge the fire box completely.

The remaining space above the surface of water in the

boiler shell is steam space.


The hot gases are directly passed through the fire box.

Hot gases transfer their heat to water through the entire

heated wall surface of the fire box.

The heat is also transferred from the hot gases through

the walls of the tubes to the water circulating in it.


Cochran Boiler


It is a vertical, stationary, internally fired, natural

circulation, fire tube boiler.



It consists of a cylindrical shell and firebox.

The shell and firebox are both hemispherical; the hemispherical crown of the boiler shell gives maximum space and strength to withstand the pressure of steam inside the boiler.

The hemispherical crown of the firebox is also advantageous for resisting intense heat. The firebox and the combustion chamber are connected through a short pipe.

The flue gases from the combustion chamber flow to the smoke box through a number of tubes.


The gases from the smoke box escape to the atmosphere through the chimney.

The combustion chamber is lined with firebricks to withstand intense heat.

A manhole near the top of the crown on the shell is provided for cleaning.

At the bottom of the firebox, there is a grate and the coal is fed in through the fire hole, which is kept closed by a fire door.


Locomotive Boiler


It is a horizontal, stationary or mobile, internally fired,

natural circulation, fire tube boiler.


Application:

It is generally used in railway engines and road rollers.

It consists of 3 main parts: fire box, boiler shell and smoke box.


The firebox which forms the furnace is constructed by

extending the boiler shell downward from the sides at its

rear end.

The annular space left in between the furnace wall and

the downward extension of the boiler shell is also

connected with the water space in the barrel.

The hot gases rising from the grate are deflected by the

fire brick arch which ensures more uniform proper

heating because the deflected hot gases come in contact

with the entire heating surface of the fire box.


Boiler shell accommodates a large number of flue tubes which connect the furnace with the smoke box.

The flue tubes are made of 2 sizes.

Superheater tubes are inserted into the large diameter flue tubes.

The steam dome located at the top of the cylindrical shell is meant to collect the dry steam.

The smoke box is connected to the boiler barrel at its front end.

A superheater header which distributes the steam to the superheater tubes.


The chimney located at the top of smoke box is made very shorter inorder to avoid its striking with the tunnels and underbridge when the locomotive passes through the tunnels and below the underbridge.

The smoke box door provided at its front end facilitates cleaning inside the smoke box.

properties of steam: numerical - engineeringduniya.comengineeringduniya.com/slide_folder/first...

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