boiloers and its mountings 4

8/13/2019 Boiloers and Its Mountings 4

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STEAM BOILERS,

MOUNTINGS

&ACCESSORIES


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STEAM BOILERS, MOUNTINGS & ACCESSORIES

STEAM GENERATOR/BOILER


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The equipment used forproducing and transferring

steam is calledSteam generators/

Boilers.


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Classification of

Boilers


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Classification of Boilers:Boilers may be classified according to the following-

1. Relative position of Hot gases and Water

a) Fire tube boiler:

The hot gases passes through the tubes that aresurrounded by water. Fire tube boilers are also known bycertain common names-

i) chocran Boiler


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b) Water tube Boiler:

The water passes through the tubes and the hot gases

produced by combustion of fuel, flow outside. This

type of Boilers designated by the following

common names:

i) Babcock and Wilcox Boiler (straight but inclined

tubes which connect the headers).ii) Stirling Boiler (multitubular boiler having bent

tubes that connect boiler drums to headers).


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FIRE TUBE BOILER


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Fire tube boiler

Cochran Boiler

Simple vertical boiler

Suitable for small plantsrequire small quantity ofsteam.

Size = 1 m Dia. x 2 m high

(evaporation 20kg/hr.) Size = 3 m Dia. x 6 m high

(evaporation 3000kg/hr.)

Heating surface= 10 to 25times of grate area

Steam pressure= upto 20 bar

Efficiency = 70 to 75%


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WATER TUBE BOILERS


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BABCOCK & WILCOX BOILERS


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BABCOCK & WILCOX BOILERS

(Capacity and utility)

Evaporative capacity ranges from 20000 to 40000

kg/hrOperative pressure ranges from 11.5 to 17.5 bar.

Steam formed from such boilers are primarily used

to run steam turbines and generate electric power.


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COMPARISION

Between

WATER

TUBE&

FIRE TUBE

BOILERS

WATER TUBE FIRE TUBE

Water passes through water

tubes.

Hot gases passes through

tubes.

steam capacity (high speed) Steam capacity (Slow speed)

Complexity in design requires

quick examination by skilled

hands.

Simple & rigid construction

hence greater reliability & low

operating cost.

Operating pressure up to 200

bar.

Pressure ranges from 17.5 bar

to 24.5 bar

Evaporation rate ranges from

20,000 to 50,000kg/hr.

Evaporation rate 900kg/hr.

Increased heating surface area. Low heating surface area.

Low water to steam ratio Large water to steam ratio

Bigger in size, suitable for large

power plants

Smaller in size, used only for

small power plants

Transportation and installation

is easy due to handling of

dismentaled parts

Transportation and installation

is difficult due to large size of

shell.

Externally fired boilers, furnace

size can be varied.

Internally fired boilers, furnace

size can not be varied.

Requires more floor area Requires less floor area


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ESSENTIALS OF A GOOD

BOILER

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ESSENTIALS OF A GOOD BOILER

1. Steam generation capability should be at:

a) Required pressure

b) Required quality

c) Fast speed

d) Minimum fuel consumption

2. Economic :

a) Low initial costb) Low installation cost

c) Low operating cost

d) Low maintenance cost


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ESSENTIALS OF A GOOD BOILER

3. Construction:

a) Light in weight

b) Less amount of brick work

c) Occupy small floor area

4.Quick starting.

5.Capable to meet fluctuating demand of steam

supply.

6. Easy availability of spare parts


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BOILER MOUNTINGS AND

ACCESSORIES

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Boiler Mountings:

The necessary devices installed or mounted for the

safety of boiler and its cont ro l are called boiler

mountings.


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Boiler Accessories:The devices which are installed in the boiler for their

eff ic ient operat ion and smooth work ing are called

Boiler Accessories.


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Boiler Mountings for safety:

1. water level indicators

2. safety valves.3. Combined high steam and low water safety valve.

4. Fusible plug.


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Boiler Mountings for control:

1. Pressure gauge

2. Junction or stop valve3. Feed check valve

4. Blow-off cock

5. Man hole and mud hole


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Boiler Accessories for efficient operation:

1. Water heating devices.

2. Water feeding devices.

3. Super heater4. Economizer

5. Air preheater


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BOILER MOUNTINGS


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BOILER MOUNTINGS

1. WATER LEVEL INDICATOR


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BOILER MOUNTINGS

2. PRESSURE GAUGE(Bourdons)

a) Records gauge pressure

b) Elliptical spring tube is also called

Bourdon tube and is made up of

special quality Bronze.

c) Plug (P) is provided for cleaning the

siphon tube.

d) Siphon is filled with cold water to

prevent the hot steam entering into

the bourdon tube and spring tube

remains comparatively cool.


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SAFETY VALVES

LEVER SAFETY VALVE Dead Weight safety valve


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SAFETY VALVES

SPRING LOADED SAFETYVALVE

HIGH STEAM AND LOW WATERSAFETY VALVE


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JUNCTION VALVE:

The valve placed directly on a boiler in order to regulate thesteam supply from boiler to steam pipe is called the

Junction Valve.

STOP VALVE:

The valve used to regulate the steam supply from the

steam pipe to the prime mover (steam engine or steam

turbine) is called Stop Valve.


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JUNCTION VALVE


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FEED CHECK VALVE

1. Feed check valve

works as NRV

(Non- return

valve).2. Prevents the back

flow of water from

the boiler when

the feed waterpump is either not

working or in case

of its failure.


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BLOW-OFF COCK


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FUSIBLE PLUG

Plugs P and R

are made up ofGun Metal.

Plug S is madeup of Copper.

Plug R is screwedto the plug P.

Plug S is lockedinto plug R by a

metal like tin orlead.


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MANHOLE

This is provided at suitable position on the boiler

shell so that the man can enter into boiler shell

for inspection, maintenance and repairs. This

hole is usually made in elliptical shape of the

size convenient for a man to enter through thishole. The opening is closed by steam tight cover.


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STEAM TRAPSteam trap is used to collect and automatically

drain away the water resulted from partial

condensation of steam without steam to escape

with this condensate through a valve. The valve

after draining the condensate is closed. Is presses

the leakage of steam from the trap.

,


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ANTIPRIMING PIPE

It is attached below the stop valve to avoid the water

particles being carried away along with steam. It has

closed pipe with closed ends of 1m and 2m length. The

top side of the pipe has perforations. When the steam

passes through it, due to inertia effect, the moisture of

steam falls into the pipe and the steam with reduced

moisture passes into the stop valve.


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BOILER ACESSORIES

The devices used to improve theperformance and operation of theboilers are called boiler accessories.Main accessories used are:


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BOILER ACCESSORIES

WATER HEATING DEVICES

Used to heat the feed water

before it is fed to boiler with

the help of steam of a steam

engine.

Heating of feed water can be

carried out either by:

1. Open Heater- Direct mixing

2. Closed heater- Indirectconvection

WATER FEEDING

DEVICES

Used to supply water while the

boiler is in operation. Thesedevices include the use of feed

pumps either reciprocating type or

centrifugal type.

SUPER HEATERS


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SUPER HEATERS


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ECONOMISER

AIR PREHEATER


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AIR PREHEATER

High Pressure Boilers


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High Pressure BoilersA boiler which generates steam at a pressure of 85

kgf/sq.cm or above is termed as ahigh pressure

boiler. The present tendency is towards the use ofhigh pressure boilers in power plants.

The modern high pressure boilers used for power

generation have capacities of 40 to 1600 tonnes/hr ofsuperheated steam with a pressure upto 210

kgf/sq.cm and a temperature of about 650C.

Water tube boilers are generally preferred for highpressure and high output whereas fire tube boilers for

low pressure and low output.

Advantages of high pressure boilers


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Advantages of high pressure boilers

Method of water circulation

In high pressure boilers, water circulation is made with the help of a centrifugal

pump which forces water through the boiler tubes. This is called forcedcirculation

of water. Forced circulation increases the rate of heat transfer and hence increases

the steam generating capacity of boilers.

Size of drums

The high pressure boilers are characterized by the use of very small steam

separating drums or by the complete absence of any drum.

Type and arrangement of tubes

The heat of combustion is utilized more efficiently by the use of small diameter and

light weight tubes in large numbers. To avoid large resistance to the flow of water ,

the high pressure boilers have a parallel set of arrangement of tubes.


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Efficiency

The efficiency of the power plant is increased up to

40%, by using high pressure superheated steam. Also

steam can be raised quickly after the boiler is fired.

Scale formation

The tendency of scale formation is eliminated due to the

high velocity of water through the boiler tubes.

Cost of electricity

Since efficiency of the plant is increased by using highpressure boilers, the cost of electricity production is

reduced.

La Mont Boiler


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La Mont Boiler

This is a modern high pressure

boiler(water tube type steam boilers)

working on forced circulation system.
http://mechanical-engineering-info.blogspot.in/2012/03/modern-high-pressure-boilers.htmlhttp://mechanical-engineering-info.blogspot.in/2012/03/modern-high-pressure-boilers.htmlhttp://mechanical-engineering-info.blogspot.in/2012/03/modern-high-pressure-boilers.htmlhttp://mechanical-engineering-info.blogspot.in/2012/03/modern-high-pressure-boilers.html


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La Mont Boiler

The capacity of la-mont boiler is about 50 Tonnes/hr of

superheated steam at a pressure of 170 kgf/sq.cm. and at a

temperature of 500 C.

Loeffler Boiler


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Loeffler Boiler

The novel feature of the Loeffler

Boiler is to evaporate water solely

by means of superheated steam. Thefurnace heat is supplied only to

economiser and superheater. In other

words, steam is used as a heat

absorbing medium.

The major difficulty experienced in

La-Mont boiler is deposition of salt

and sediment on the inner surfaces

of water tubes. The deposition

reduces the heat transfer, ultimately,

the generating capacity. This

difficulty was solved in Loeffler

boiler by preventing the flow of

water into the boiler tubes.

Loeffler Boiler


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Loeffler Boiler

Capacity of the Loeffler boiler is about 100 Tonnes/Hr of

superheated steam generated at a pressure of 140 kgf/sq.cm

and at a temperature of 500C.

Benson Boiler


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Benson Boiler The presence of steam bubbles in contact with the surface of tubes seriously impairs heat

transmission from the flue gases to water. By rising the boiler pressure to the critical pressure

of steam (225 kgf/sq.cm.), this difficulty is overcome, as suggested by Mark Benson in 1922.

At the critical pressure water and steam have the same density and no bubbles are formed.

Working principle of Benson Boiler:

This boiler has a unique characteristic of absence of steam separating drum. The entire

process of heating, steam generation and superheating is done in a single continuous tube.

Radiant evaporator

The feed water from the economiser flows into the radiant evaporator with radiant parallel

tube sections. The radiant evaporator receives heat from the burning fuel through radiation

process and majority of water is converted into steam in it.

Convection Evaporator

The remaining water is evaporated in the convection evaporator, absorbing the heat from the

hot gases by convection. Thus the saturated high pressure steam at a pressure of 210 kg/sq.cmis produced.

Convection superheater

The saturated steam is now passed through the convection superheater where the saturated

steam os superheated to 650C. The radiant evaporator, the convection evaporater and the

convection superheater are all arranged in the path of the flue gases.

Benson Boiler Cont


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Benson Boiler Cont

Capacity of benson boiler is about 150 tonnnes/hr at a pressure of 210

kgf/sq.cm. and at a temperature of 650C. (Efficiency may be improved by

running the boiler at a pressure slightly lower than the critical pressure).


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Velox Boiler

This boiler can generate a pressure of about 84 kg/cm2


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Pipe Fitting is the occupation of installing orrepairing piping or tubing systems that

convey liquid, gas, and occasionally solid

materials. This work involves selecting and

preparing pipe or tubing, joining it togetherby various means, and the location and

repair of leaks.

V i fitti


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Various fittings

Thread fittings

Pipe or tube fittings

Connectors


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Lagging

Insulation used to prevent heatdiffusion, as from a steam pipe.


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Performance of boilers

Evaporative capacityEquivalent of Evaporation

Factor of evaporation

Boiler efficiency

boiloers and its mountings 4

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