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PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
THERMAL ENGGINEERING & GAS DYNAMICS
(ME404)
NOTES
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
UNIT-1
STEAM GENERATOR
DIFFERENT TYPES OF HIGH PRESSURE BOILER
1. LAMONT BOILER
A forced circulation boiler was introduced in 1925 by LA Mont. The
arrangement of water circulation and different components are shown
in below fig.
 Modern high pressure water tube boiler steam boiler working on
a forced circulation .The circulation of water is maintened by a
centrifugal pump driven by a steam turbine.
 It generate 45 to 50 tons /hr of superheated steam at a pressure
of 120 bar and at temperature of 500C
 The feed water from the hot well is goes through the economiser
into the steam separating drum. The feed water is heated by flue
gases. The circulating pump above the boiler pressure delivers
feed water to the evaporator.
 The mixture of water and steam from these tubes enter into the
boiler drum where steam is separated and is drawn off to the
superheater. The superheated steam thus passes to the
primemover (turbine) to run the engine.
LIMITATIONS:
 Formation of bubbles on the inner surface of the water tubes.
These bubbles reduce the heat flow and steam generation.
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
LAMONT BOILER
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
2. BENSON BOILER
In the lamount boiler, the main difficulty experienced is the formation and
attachment of bubbles on the inner surface of the heating tubes . The attached
bubbles on the inner surface of the heating tubes. The attached bubbles to the
tube surface reduce the heat flow and steam generation as it offers high
thermal resistance than water film.
BENSON BOILER
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
 Benson in 1922 argued that if the boiler pressure was raised to
critical pressure 212bar, the steam and water have the same
density and therefore the danger of bubbles formation can be
easily eliminated .
 The boiler too makes use of forced circulation and uses oil as
fuel. This boiler does not use any separating steam drum.
 The feed water after circulation through the economiser tubes
flow through the radient parallel tube section to evaporate
partly. The steam water mixture produced then moves to the
transit evaporator section where this mixture is converted into
the dry steam. The steam is now passed through the convective
superheater and finally supplied to the prime mover (turbine)
 Generating capacity 150 tons/hr, temperature 650C, Maximum
working pressure 500bar.
LIMITATIONS:
 Salt formation in the evaporator tubes. So removing of deposite salt is
required after required after each 400 working hours by special means.
 On evaporating tubes there is chance of corrosion.
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
3. LOEFFLER BOILER
In a benson boiler the major difficulty experienced is the deposition of salt and
sediment on the inner surfaces of the water tubes. The deposition reduces the
heat transfer and ultimately the generating capacity. This increases the danger
of over heating of tubes.
LOEFFLER BOILER

This boiler also makes use of forced circulation. The high pressure feed
pump draws water through the economiser and delivers it into the
evaporating drum. The steam circulating pump draws saturated steam
from the evaporating drum and passes it through radient and convective
superheater where steam is heated to required temperature.
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
 From the superheater about 30% of the superheated steam passes to
the turbine, the remaining 65% passing through the water in the
evaporating drum in order to evaporate feed water.
 Generating capacity 94.5 tonnes/hr and operating pressure at 140 bar.
ADVANTAGES:
 The salt deposited in the evaporator drum can be easily brushed
off by blowing off the water.
 There is no chance of corrosion.
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
PERFORMANCE OF BOILER:
EVAPORATIVE CAPACITY:
The evaporative capacity of a bolier may be expressed in terms of:
 Kg of steam/ hour
 Kg of steam/hr/m2 of heating surface
 Kg of steam/kg of fuel
EQUIVALENT EVAPORATION:
It is defined as the amount of water evaporated from water at 1000C to dry and
saturated steam at 1000 C at normal atmospheric pressure (1.0132 bar).
Heat required to evaporate Me kg of water = Me ( h – hf1)
Where Me = MS / Mf
Me = Equivalent mass
MS = Mass of water evaporated into steam
Mf = Mass of fuel
h= Enthalpy of steam at pressure p bar
hf1=Enthalpy of feed water at temperature t1 0C
Equivalent evaporation from the definition:
E = Me (h – hf1)/ 2257
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
FACTOR OF EVAPORATION:
It is defined as the ratio of heat received by 1kg of water under working
condition to that heat received by 1kg of water evaporated from and at 1000C
Fe = (h – hf1) / 2257
BOILER EFFICIENCY:
It is the ratio of heat actually used to produce steam to the heat supplied by the
furnace.
Boiler efficiency = MS ( h – hf1) /( MS ×CV)
Where
CV= Calorific value of fuel KJ/Kg of fuel
Numericals based on performance of Boiler:
1. A boiler produces 10 kg of steam per kg of fuel from feed water at 300C
at 9 bar absolute pressure . What is equivalent evaporation from and at
1000C per kg of fuel and factor of evaporation , if the steam is 0.9 dry.
Given: Me= 10 kg per kg of fuel
Temperature of feed water= 300C
Pressure of steam = 9bar
X = 0.9 ( 90% steam dry)
Formula used:
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
E = Me (h – hf1)/ 2257
Fe = (h – hf1) / 2257
SOL:
From steam table
At pressure base
AT P= 9bar, hf = 742.64KJ/kg,
hfg = 2029.5 KJ/kg ,
Using wet steam formula
h = hf + hfg
h= 742.64 + 2029.5×0.9
h= 2569.19 KJ/kg
E = Me (h – hf1)/ 2257
Equivalent Evaporation
E = 10 × (2569.19- 125.66)/ 2257
E= 10.83 Kg/kg of fuel
Factor Of Evaporation
Fe = (h – hf1) / 2257
Fe = (2569.19 – 125.66)/ 2257 =
x= 0.9
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
HEAT LOSSES IN BOILER PLANT
SYSTEMATIC REPRESENTATIONS OF HEAT RELEASE (Per kg of fuel based)
1. Heat supplied by fuel
Q Supplied= MS× CV KJ
Where,
Mf = Mass of fuel
CV= Calorific value fuel
2. Heat utilized to generate steam
Q1 = Me ( h- hf1) KJ
h= Enthalpy of steam
Where h = Enthalpy of steam
hf1= Enthalpy of feed water KJ/Kg
3. Heat lost in dry flue per kg of fuel
Q2 = MgCpg (Tg-Ta)
Where
Tg = Temperature of flue gases
Ta = Temperature of air entering to combustion chamber or temperature of
boiler room
Cpg =Mean specific heat of dry flue gasses
4. Heat lost in moisture present in fuel.
Assumed that the moisture is converted into superheated steam at
atmospheric pressure (1.013bar)
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
Q3 = Mm (hsup – hb)
Q3 = Mm (h +CP×(Tg-T) –hb)
Where,
Mm = Mass of moisture per kg of fuel
hb = Enthalpy of water at boiler house
t = Saturation temperature (100 OC )
5. Heat lost due to incomplete combustion of fuel
Q4 =(CO ×C× 24800)/ ( CO + CO) KJ/kg of fuel
6. Heat lost due to incomplete combustion of fuel
Q5 = Mf1 × C.V
Mf1 = Mass of unburnt fuel
7. Convection and Radiations
Q6 = Q Supplied – ( Q1 + Q2 + Q3 + Q4 + Q5)
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
HEAT BALANCE SHEET
Heat
Supplied
Heat
supplied by
fuel
KJ
Q Supplied=
MS× CV
Q Supplied
TOTAL
Heat Utilization
KJ
%
1.Heat supplied by
fuel
Q1
Q1/ Q Supplied×100
2.Heat utilized to
generate steam
Q2
Q2/ Q Supplied×100
3.Heat lost in dry
flue per kg of fuel
Q3
Q3/ Q Supplied×100
4.Heat lost in
moisture present in
fuel
5.Heat lost due to
incomplete
combustion of fuel
Q4
Q4/ Q Supplied×100
Q5
Q5/ Q Supplied×100
6.Convection and
Radiations
Q6
Q6/ Q Supplied×100
TOTAL
100%
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
DRAUGHT
The draught is one of the most essential systems of thermal power plant which
supplies required quantity of air for combustion and removes the burnt products
from the system.
To move the air through the fuel bed and to produce a flow of hot gases through
the boiler, economizer, preheater and chimney require a difference of
pressure.This difference of pressure for to maintaining the constant flow of air
and discharging the gases through the chimney to atmosphere is known as
draught
NATURAL DRAUGHT:
The draught produced by the boiler chimney is known as natural draught.The
natural draught is produced due to the difference in weight between the column
of hot gases inside the chimney and the weight of equal column of cold air
outside the chimney.
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
ARTIFICIAL DRAUGHT
Natural draught is not sufficient for high rate of fuel burning and it becomes
necessary to provide an artificial draught by some mechanical means. An
artificial draught may be produced by steam jet, fan or blower accordingly it is
known as mechanical draught.
The artificial draught is of two types:
1. Forced draught
2. Induced draught
FORCED DRAUGHT:
In a forced draught system, a blower is installed near the base of the boiler. This
draught system is known as positive draught system or forced draught system
because the pressure of air throughout the system is above atmospheric
pressure and air is forced to flow through the system.
PROF. P. P. PANDIT
9425773517
THERMAL ENGG & GAS DYNAMICS
MECHANICAL DEPARTMENT
GEC GROUP OF COLLEGE
FORCE DRAUGHT
INDUCED DRAUGHT:
In this system, the blower is located near the base of the chimney instead of
near the grate. The air is sucked in the system by reducingthe pressure through
the system below atmosphere.The action of the induced draught is similar to
the action of the chimney. The draught produced is independent of the
temperature of the hot gases therefore the gases may be discharged as cold as
possibleafter recovering as much heat as possible in air-preheater and
economiser.
INDUCED DRAUGHT