High pressure boiler

Chapter No. 2- High
Pressure Boiler
(Fluidized Bed Boiler, Indian
Boiler Regulation Act 1920)
Babasaheb Phadtare Poly. (DME) Prof. Kokare A.Y.
Dnyan, Kala, Krida and Krishi Prathisthan’s

Unit No.2- High Pressure
Boiler
CO b- Select High Pressure
Boiler for Power Generation
capacity of Plants.

- A boiler is a closed vessel in which
water or other fluid is heated.
- The heated or vaporized fluid exist the
boiler for use in various Process or
Heating applications or for Power
generation.
- In Steam Power Plant, typically called
Thermal Power Plant, water is heated to get
steam for Power generation.
What is Boiler?

- A boiler is called a high-pressure boiler
when it operates with a steam pressure
above 80 bars.
- The modern high pressure boiler:
Steam capacities – 30 to 650 tons/hour
and above
Pressure – up to 160 bar
Maximum steam temperature – 540 °C

Types of High Pressure Boiler
(1) La-Mont boiler
(2) Loeffler boiler
(3) Benson boiler
(4) Schmidt-Hartman boiler
(5) Velox boiler

Unique Feature of High
Pressure Boiler
- Method of water circulation: Forced
circulation, using pump
- Types of Turbine: Water Tube Boilers, with
flow through several sets of parallel system
of turbine – to reduce pressure loss
occurring in single tube system and to
have better control over quality of steam.

- Improve method of heating:
 Saving of heat by evaporation of water above
critical pressure of steam.
 Heating of water by mixing with superheated
steam, to give high heat transfer coefficients.
Increase in overall heat transfer coefficients
by increasing water velocity inside the tube and
increasing gas velocity above sonic velocity.
- Compactness: Large number of small size tubes
and number of pass are used which increases the
heat transfer area, hence size and weight of
boiler is reduced.

Advantages of High Pressure
Boiler over Conventional Boiler
 Due to forced circulation of water, evaporative
capacity of boiler is increased and size of drum
is reduced.
 Smaller diameter tube are used, which increases
heat transfer rate and reduce fuel consumption.
 Pressurised combustion is used which increases
the rate of firing of fuel thus increasing the rate
of heat release.

 These boiler is compact and hence less floor
space is required.
 Due to high velocity of water through tubes,
the scale formation tendency is eliminated.
 Due to uniform heating of all parts, there is
less chances of overheating.
 High pressure and temperature of steam
lead to increase the plant efficiency.
 The steam can be raised quickly to meet
the variable load.
 A very rapid start from cold is possible.

La-Mont Boiler
Types of boiler: Water
tube, forced
circulation, High
Pressure boiler
Steam Generating
Capacity: 45 to 50
tones/hour
Pressure: 120 atm.
Temp.: 500 °C

Principle: This boiler works on basic principle of
forced circulation maintained by steam driven
Centrifugal pump.
- If the water is circulate by a pump inside the tube, the
heat transfer rate from gas to the water is increase.
- Various part of boiler:
 Economizer
 Centrifugal pump
 Evaporator tube
 Grate
 Furnace
 Super heater
 Water steam separator drum
 Air preheaterBabasaheb Phadtare Poly. (DME) Prof. Kokare A.Y.

Working:
A feed pump forces the water into the
economizer where the temperature of water is
increases. This water forced into the
evaporator tube by using centrifugal pump
driven by steam turbine. Water passes 10-15
times into the evaporator tube. The mixture
of saturated steam and water is formed
inside the tube.
 This mixture sends to the steam separator
drum which is outside the boiler. Steam from
the separator sends

to the economizer, where the saturated steam
converts into superheated steam. The water
again sends to the economizer where it again
passes by the evaporator tubes.
 The air from the air preheater enter into the
furnace where fuel burn. The fuel gases first
heat the evaporator tube then passes by the
super heater.
 These gases from the super heater again use
to preheat the air into air preheater before
exhaust into atmosphere.

- Difficulties:
 The deposition of salt and sediments on the
inner surfaces of the water tubes, which
reduces the heat transfer rate.
 There also formation of bubbling at the inner
surfaces of water tube. It leads to increase the
heat flow resistance.
- Advantages:
 High Pressure Boiler
 Flexible in design
 Easily start
 Higher heat transfer rate
 Reassemble in natural circulation

Benson Boiler
Type of boiler: High
Pressure, Forced
circulation, Once
through and Water
tube boiler.
Principle: This boiler
works on the basic
principle of critical
pressure of water.

Advantages:
 The benson boiler does not use water- steam separator,
which reduce the total cost of boiler.
 This boiler can transport easily from one station to
another.
 It is economical and have higher efficiency.
 This boiler can use over the pressure above
350 bar without changing evaporator.
 This can be start easily and can reach its maximum
load capacity within 10 minutes.
- Disadvantages:
 Danger of overheating
 Salt deposition and sediment on the
 inner surface of water tube. inner surface of water tube.

Loeffler Boiler
Type of boiler: High Pressure,
Forced circulation, Water tube
boiler , Generating Capacity: 100
tones/hour Pressure: 140 bar
Principle: This boiler working
principle is to evaporate the feed
water by the use of superheated
steam from the super heater.

Advantages:
 The evaporator tubes in this boiler carries
superheated steam, therefore there is no salt
deposition on the surface of tubes.
 Compact in design.
 High steam generating capacity.
 Suitable for marine application.
Disadvantages:
 Bubbles are formed at inner surface of tube,
which reduce the heat transfer rate.
 Evaporating drum is use, which
increase the cost of boiler.

Schmidt-Hartmann
Boiler
Pressure in primary
circuit: 100 bar
Pressure in
secondary circuit: 60 bar
In this boiler, working
operation is similar to
an electric transformer.
 Two pressures are
used to effect an
interchange of
energy.

- Advantages:
 Any deposits in evaporator drum due to impure water
can simply brushed off by remove the submerged tube as
of the drum or by blowing off water.
 As it can use impure water there is no necessity of
water softening plant eventually reduces cost.
 It can utilize impure water for creation of steam.
- Disadvantages:
 Evaporating drum is use which increase size
of plant by cost.
 Due to deposits in evaporator drum because of
impure water plant has to stop often for cleaning.

Velox Boiler
Principle: When the
velocity of the gas is
greater than the speed
of sound, its heat is
transfer rate is also
increase. So more heat
is transfer from gas to
water as compare when
the heat transfer at
the subsonic speed.

Advantages:
 This boiler has high heat transfer rate.
 It has great flexibility.
 It is compact in design.
 It is easy to control. It is fully automatic.
 It has thermal efficiency about 90-95%
Disadvantages:
 Need extra ground as of horizontal
construction.
 Fuel oil burning power station lies in the high
cost of fuel.
 It can only operate on liquid or gaseous fuels.

Ramsin Boiler
Principle: One through
boiler.
Forced circulation.

Advantages:
 This boiler has high heat transfer rate.
 It has great flexibility.
 It is compact in design.
 It is easy to control. It is fully automatic.
Disadvantages:
 Fuel oil burning power station lies in the high
cost of fuel.

FBC BOILER
FLUDIZED BED COMBUSTION BOILER

INTRODUCTION
In 1921, the first fluidized bed being used
successfully in Germany.
Fluidized bed combustion has emerged as a feasible
alternative and has significant advantages over
conventional firing system and offers multiple benefits –
compact boiler design, fuel flexibility, higher combustion
efficiency and reduced emission of noxious pollutants
such as SOx and NOx.
The fuels burnt in these boilers include coal, washery
rejects, rice husk, wood chips & other agricultural
wastes.
The fluidized bed boilers have a wide capacity
range0.5 T/hr to over 100 T/hr.

MECHANISM
Fluidization of solids
Sand particles resting on a mesh
(left) become fluidized when air is blown
through (right) and take on the
appearance and some of the properties
of a boiling fluid.
Granular solids remain in layers when
one is poured on to another (left), but
rapid mixing occurs on fluidization
(right).
A bed of stationary particles supports
objects whatever their density (left). On
fluidization, an object of lower density
(the green ball) floats while the higher
density (red ball) sinks.
In a bed of stationary particles (left),
heat is transferred slowly and there are
big differences in temperature. In a
fluidised bed (right), rapid mixing
ensures uniformity of temperature.

CHARACTERISTICS OF FLUDIZED BED
Fluidization depends largely on the particle size and the air
velocity.
Combustion process requires the three “T”s that is Time,
Temperature and Turbulence. In FBC, turbulence is promoted
by fluidization.
If sand particles in a fluidized state is heated to the ignition
temperatures of coal, the coal will burn rapidly and bed attains
a uniform temperature.
The fluidized bed combustion (FBC) takes place at about
840OC to 950OC. Since this temperature is much below the ash
fusion temperature, melting of ash and associated problems are
avoided.
The lower combustion temperature is achieved because of
high coefficient of heat transfer due to rapid mixing in the
fluidized bed.
Limestone is used as particle bed, control of sulphur dioxide
and nitrogen oxide emissions in the combustion chamber.

Types of Fluidized Bed Combustion Boilers
There are three basic types of fluidized bed
combustion boilers:
1. Atmospheric classic Fluidized Bed Combustion
System (AFBC)
2. Atmospheric circulating (fast) Fluidized Bed
Combustion system(CFBC)
3. Pressurized Fluidized Bed Combustion System
(PFBC).

1.AFBC / Bubbling Bed
• Coal is crushed to a size of 1 –
10 mm depending on the rank
of coal.
• The atmospheric air, which acts
as both the fluidization air and
combustion air.
• The velocity of fluidizing air is
ranges from 1.2 to 3.7 m /sec.
• Almost all AFBC/ bubbling bed
boilers use in-bed evaporator
for extracting the heat from
the bed to maintain the bed
temperature.
• The bed depth is 0.9 m to 1.5
m deep.

1. FUEL FEEDING SYSTEM
For feeding fuel, sorbents like
limestone , usually two
methods are followed: under
bed pneumatic feeding and
over-bed feeding. Under Bed
Pneumatic Feeding If the fuel
is coal, it is crushed to 1-6 mm
size and pneumatically
transported from feed hopper
to the combustor through a
feed pipe piercing the
distributor.

Over-Bed Feeding
The crushed coal, 6-10 mm size is
conveyed
from coal bunker to a spreader by a
screw conveyor.
The spreader distributes the coal over
the surface
of the bed uniformly.
This type of fuel feeding system
accepts over size
fuel also and eliminates transport
lines,
when compared to under-bed feeding
system

2. Air Distributor
Purpose is to introduce the
fluidizing air through the bed
cross section, keeping the
solid particles in constant
motion.
The distributor, is
constructed from metal plate
having a number nozzles or
nozzles with bubble caps .
The distributor plate is
protected from high
temperature of the furnace by:
i) Refractory Lining ii) A Static
Layer of the Bed Material iii)
Water Cooled Tubes.

3. Bed & In-Bed Heat
Transfer Surface:
a ) Bed The bed material can
be sand, ash, crushed refractory
or limestone, with an average
size of about 1 mm. Depending
on the bed height these are of
two types: shallow bed and deep
bed.
b) In-Bed Heat Transfer Surface
In a fluidized in-bed heat
transfer process, it is necessary
to transfer heat between the bed
material and an immersed
surface, which could be that of a
tube bundle, or a coil. The heat
exchanger orientation can be
horizontal, vertical or inclined.

4. Ash Handling
System
a) Bottom ash removal
b) In the FBC boilers, the
bottom ash constitutes
roughly 30 - 40 % of the
total ash, the rest being
the fly ash.
c) Ash from the boiler
furnace outlet falls into the
crusher, where large ash
particle is crushed to small
size. Finally ash is carried
by high velocity air to
delivery point.

b) Fly ash removal
The amount of fly ash to be handled
in FBC boiler is relatively very high,
when compared to conventional
boilers.
Fly ash carried away by the flue gas
is removed in number of stages;
firstly in convection section, then
from the bottom of air
preheater/economizer and finally a
major portion is removed in dust
collectors.
The types of dust collectors used are
cyclone, bag filters, electrostatic
precipitators (ESP’s) .
To diminish the SOx, recycling of fly
ash is practiced in some of the units.

2. Circulating Fluidized
Bed Combustion
(CFBC)
Taller boiler structure Coal
is crushed to a size of 6 –
12 mm depending on the
rank of coal. The fluidizing
velocity in circulating beds
ranges from 3.7 to 9
m/sec. Combustion
efficiency as high as
99.5%.

3.Pressurised Fluid Bed
Combustion
Combined cycle i.e Rankine &
Brayton cycle using steam & gas
turbine. Operating temp. & pressure
is 860OC & 16-18 bars.
The fuel is fed along with the sorbent
and is maintained in fluidized
condition in the pressurized
combustion chamber.
The pressurized flue gases are
cleaned off & are expanded into a
gas turbine. In addition, the excess
air requirements of the boiler are
met by the gas turbine compressor.
Power generated by steam cycle and
that generated by gas turbine which
is of the order of 80:20

Advantages of FBC boiler over
Conventional boiler:
1. High Efficiency. Combustion efficiency of over 95%
Overall operating efficiency is 84%
2. Fuel Flexibility.
3. Ability to Burn Low Grade Fuel.
4.Pollution Control. SOx formation is minimised by
addition of limestone for high sulphur coals. CaCO3
(solid) + SO2 (gas) → CaSO3 (solid) + CO2 (gas)
SO3 + CaCO3 = CaSO3 + CO3 Low combustion
temperature eliminates NOx formation. NOx
formation takes place around1500o C
5. Easier Ash Removal – No Clinker Formation
6. Simple Operation, Quick Start-Up

7. No Slagging in the Furnace-No Soot Blowing
8. Provisions of Automatic Coal and Ash Handling
System
9. Provision of Automatic Ignition System
10.High Reliability and low maintenance costs.
Disadvantages of FBC boiler over
Conventional boiler:
1. The only disadvantage is that, a large amount of
power will be required to lift up the silica surface.
So motor of force draft fan will b twice bigger than
that of other conventional system.
2. System required 50% more Dolomite and
limestone.
3. Erosion problem cause and Problem associate with
distribution of coal and dolomite.

Sr.
No
Comparison Aspect Water Tube
Boiler
Fire Tube
Boiler
1. Contents in tube Water Hot gases
2. Pressure of steam generated 165 bar (high) 24.5 bar (low)
3. Rate of steam generated High Low
4. Floor area Less More
5. Overall Efficiency 90 % (High) 75% (Low)
6. Direction of water circulation Well defined Not Definite dir
7. Operating cost High Less
8. Bursting chances Less More
9. Construction Complex Simple
10
.
Application, Ex. Large power plant
High press. boiler
Small plant,
Cochran,
Lancashire

Sr.
No
Comparison Aspect Conventional
Boiler
Once Through
Boiler
1. Sub-critical or supercritical Both Sub-critical
2. Orientation of boiler tube Generally Vertical Generally Spiral
3. Efficiency at Part load High Poor
4. Circulation ratio One Four
5. Requirement of Circulation
pump
No even at high
pressure
Required for High
Pressure
6. Uniform of water flow Uniform Not Uniform
7. Provision of blow down Not due to absence
of drum
Yes
8. Need of monitoring temp. temp. of tube
monitor avoid
overheating
Not required due
to mixture of
water and steam
at saturated
condition
9. Start-up time Low High

INDIAN BOILER
REGULATION ACT (IBR)

INDIAN BOILER REGULATION ACT (IBR)
 Regulations Act 1920". It is an Act of Law: "It
governs the manufacture, installation, operation
and maintenance of Steam Boilers".
 To prevent hazards and explosions, some rules and
regulations were introduced as mandatory to follow
by industrial sectors.
 In India, IBR Act was established, which specified
that, a Government Inspector would be responsible
and would have to certify all steam boilers as
'suitable from the safety point of view.
 Every part of IBR approved steam system has to be
manufactured, installed, tested, operated and
maintained under the watchful eye of local
inspector. Every customer, who runs an IBR boiler,
must carry out an annual IBR inspection in

presence of an IBR The local BR office is a state
government department and maintains satellite
offices close to each inspector.
 In the IBR act, a steam boiler is defined as, "a
vessel containing greater than 22.5 liters of water,
which is IBR Boiler and IBR System.
 An IBR license is required to manufacture steam
equipment
 This is a factory approval, even before, the company
starts manufacturing valve or pipe etc. This license
is also given to workshops, where adequate
infrastructure for pressurized joint welding and
testing is available. The product drawing is
submitted for provisional IBR approval along with
the necessary fees paid. Once the approval is
received, raw materials have to be purchased from
IBR approved vendors.

 The inspector has to be called to inspect and
approve the material before manufacturing, Before
commencing manufacture of a boiler or boiler
component, every manufacturer shall engage an
procedures as specified by IBR. Inspecting
Authority for carrying out inspection at various
stages of manufacture as per I.B.R. regulations.
The Inspecting Authority shall follow necessary
procedure for inspection and certification of boiler
or If inspector finds the boiler or the boiler
component conforming to the standards prescribed
by boiler component.
 Regulations, he/she shall issue a 'certificate of
approval' and stamp the boiler or boiler component.
But, if inspector finds the boiler or boiler
component not conforming to the standards
prescribed by regulations, then 'certificate of

 refuse' has to be issued for non-conformance.
Provided that, no certificate shall be refused unless
the Inspecting Authority had informed the
manufacturer to carry out necessary modifications
or rectifications. But, if inspecting Authority finds
that, inspite of giving necessary action.
Conditions for Repairing Boiler and Boiler
Component:
1.No person shall repair any boiler or boiler
component or both, unless he has necessary
facilities for repairs, in the premises.
2.Design &drawings of boiler or boiler components
should be confirming to the 'IBR‘ regulations.
3.The materials, mountings and fittings used in the
repair of such IBR approved boiler or boiler
component should conform to the regulations.

4. Person (engaged in welding) has a "Welder
certificate" issued by a Competent Authority.
Report of Accidents:
 Accident in "Boiler Act" is defined as, "an explosion
of a boiler or steam pipe or any damage to a boiler
or steam pipe" If any accident occurs due to a
boiler or boiler component, the owner shall report
the same in writing to the Inspector within twenty-
four hours.
 Every such report shall contain a true description
regarding nature of accident, damage to the boiler
or to the boiler component or injury to any person.
The report must specify all details, so that,
inspector can judge the severity of the accident.
Every person shall be bound to answer truly to the
best of his knowledge and answer every question
put to him in writing by the Inspector.

Renewal of Certificate:
 The owner of any boiler, which is not registered
under IBR, may submit application to the Inspector
along with documents as prescribed by regulations
to obtain certificate of registration.
 Every such application shall be accompanied by the
prescribed fee paid. The Inspector shall fix a date
(within thirty days or a specified period from the
date of receipt), for the examination of boiler.
 certificate authorizing the use of a boiler is ceased
after expiry of the granted period or when any
accident occurs to the boiler, or when the boiler is
to be shifted from one place to other.

Penalties for Illegal Use of Boiler:
 Any owner of a boiler, who uses the boiler either without
certificate of approval, shall be punishable with fine up to one
lakh rupees, or in the case of a continuing offence, along with
fine, additional one thousand rupees per day may be charged
after the first day of conviction. authority may be punished.
 Also if any person, who has transferred boiler from one state
to another without reporting to competent authority may
punished. The owner is liable to punish, if he makes any
structural changes, addition or renewal in IBR system without
obtaining prior sanction of the Chief Inspector, or fails to
report about an accident.
Provisions under Boiler Act for Remedial Measure:
1. Prohibitions of use of unregistered or uncertified
boiler
2. Renewal of certificate from time to time.
3. Modification and Renewal to boiler.
4. Modification or changes in steam pipes.

Maintenance Procedure For Major Components
Of High Pressure And Fbc Boilers
• Maintenance of high pressure and FBC boilers can
be done in two stages:
(A) Boiler inspection:
• The boilers are required to be tested regularly as
per Indian Boilers Act. Before inspection, boiler
should be made empty and all manhole doors, caps,
mud drums, fire bars, front end bridge plates, oil
burners etc. should be removed and boiler should be
cleaned. All tubes, smoke boxes and external flues
should be cleaned and checked. All the steam and
water connections should be disconnected and then, it
should be made ready for conducting the following
tests:.

(a) Hydraulic Test: This test is conducted to find out
leakages in steam boiler. For this test, the mountings
should be fitted tightly except the safety valves. The
openings of the safety valves should be closed. All the
joints should be made tight and leak-proof. Boiler
should be filled with water and inspector's gauges
should be fitted to the boiler. Generally, the boilers
are tested at a pressure equal to twice the working
pressure of the boiler. During this test, no part of
boiler should deflect.
(b) Steam Test: This test is conducted to check
whether the safety valves operate properly to relieve
the steam, when the steam pressure inside the boiler
exceeds the rated pressure. This operation is tested
keeping the feed valve and steam stop valve closed.

(B) Boiler Maintenance:
1. The combustion equipment should be so adjusted
that, the temperature in the furnace does not follow:
exceed the designed value. The air supply to the
furnace should be in correct proportion.
2. The water level in the boiler should not be allowed
to fall beyond the minimum level.
3. The temperature should change slowly and
uniformly in the various parts of the boiler. Rapid
changes in temperature lead to unequal expansion.
4. The water used for steam generation should be
free from scale forming impurities, because the
scale deposited on tube and boiler shell does not
allow the heat transfer to take place effectively and
sometimes causes over heating of tubes and boiler
shell, which may result in failure of tubes
and boiler explosion.

5. Soot and ash deposited in tubes on gas side should
be removed regularly
6. Bearings of pumps, stokers, pulverizes and fans
etc., should be lubricated regularly.
7. Oil or scale in the tubes is undesirable. Hence, such
tubes should be traced or located to solve
the problem.
8. All stays should be in even tension and they should
be properly adjusted.
9. The tube leakage is caused due to extreme
overheating of tubes as it is exposed to high
temperature. The boiler should be stopped, when
such leakage is noted and it must be immediately
repaired.

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