Basics of Steam Engineering which is used in a fabricated line in a .ppsx.ppt

08/26/2024
Cheema Boilers Limited
1

INTRODUCTION
TO
BOILERS
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Boiler is a vessel which produces steam at more than 1
Kgcm² and temperature 100° C.
Boiler designs are governed by Indian Boiler
Regulations 1923 laws.
Inspection agencies control & implement this law to
ensure safety to the public.
Vessel upto 25 Ltr capacity and below 1Kgcm² is not
covered under IBR Act.
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Use of steam : Utility for Power Or Process
Assembly :Shop assembled/Site assembled
Nature of support : Bottom /Top supported
Steam condition: Saturated/Superheated
Firing system : Oil/ Gas fired
Solid fuel fired fixed grate, Dumping grate,
Reciprocating grate, Traveling grate
Pulverized fuel fired, Fluidized bed, AFBC and CFBC
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Fire tube boilers
Water tube boilers
Fire cum Water tube boilers
Heat source : Coal, Oil, Gas, Bio-Mass, Waste heat
Construction : Bi-drum, Single drum, Multi-drum,
Shell & Tube
Installation : Out door / In door
Circulation : Natural / Forced/Once throw
Draft: natural/forced/induced/balanced
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Super Heater Coil
Membrane
Membrane
Bank Tubes

Boiler parameters
Capacity, Steam outlet pressure , Steam outlet
temperature , Feed water inlet temperature
Fuel characteristics
Boiler efficiency
Ambient conditions
Other statutory and auxiliary stipulations
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Ambient temperature
Relative humidity
Site elevation
Seismic zone
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Boiler efficiency = Heat Output / Heat Input
i.e.
Steam Enthalpy x Steam Output
Fuel Input x Fuel Enthalpy
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

Dry flue gas loss : Enthalpy difference between flue gas
leaving boiler and ambient air multiplied by dry flue
gas quantity
Fuel moisture loss : Heat taken by the fuel moisture to
become water vapour
Moisture due to combustion of hydrogen loss : Every
unit of hydrogen in fuel produces 9 units of moisture.
Heat taken by this moisture to become water vapour
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Contd…..

Air moisture loss : enthalpy difference in
moisture brought in by combustion air
between flue gas temperature and ambient
temperature
Unburnt carbon loss : heat lost due to
incomplete combustion of carbon in fuel
Unaccounted losses : small losses which can
not be accurately calculated like heat loss in
blow down water , heat going with ash , heat
loss by radiation from boiler openings etc.
Radiation loss : heat loss from boiler external
surface to atmosphere
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Contd…..

Considerations
 Initial cost vs. Running fuel cost
 Energy conservation
 Waste fuel utilization
Governing factors
 Excess air
 Flue gas outlet temp.
 Moisture and hydrogen content in fuel
 Ambient temperature and moisture
 Completeness of combustion
 Effectiveness of insulation
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NCV means Net Calorific Value
GCV means Gross Calorific Value
Boiler efficiency on NCV is equals to
Boiler efficiency on GCV x GCV/NCV
The difference in efficiency is the heat loss due moisture
in fuel
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Three types of heat is added to feed water in
the boiler to convert the same to steam.
Sensible heat up to boiling point.
Latent heat to convert liquid phase water to
vapour phase steam.
Sensible heat addition to raise the steam
temperature from saturation to the desired
super heat temperature.
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Water boils at its saturation temperature.
Boiling temperature of water at ambient
condition in sea level is 100°C.
Boiling temperature increases with pressure.
Latent heat decreases with pressure.
From & At 100°C means only latent heat of
evaporation of water to be calculated i.e.
540KCal/Kg of water.
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Furnace – In this fuel is burnt and heat is released. The
absorption of heat by radiation & convention is done here.
Super heater – The steam is super heated above saturation
temperature in this part.
Boiler banks or Evaporator – Part of sensible heat & latent heat
is added in this zone.
Economizer – Sensible heat is added to water to take it close to
saturation temperature.
Air heater – Heat from hot flue gases is observed by incoming
combustion air in this part to increase the efficiency &
combustion.
Steam drum : Steam from steam-water mixture from furnace
& evaporator is separated here.
Water drum: Holds enough water volume to protect boiler
furnace tubes in the event of boiler trip.
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By the major type of heat receipt
- Radiant super heater
- Convective super heater
By orientation
- Horizontal , fully drainable
-Vertical , non- drainable
By arrangement
- In-line
- staggered
By flow of gas and steam
- Parallal flow
- Counter flow
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By orientation
- Horizontal
- Vertical
By arrangement
- In-line
- staggered
Type of tube
- Plain tube
- Finned tube
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Steaming
economizers will
cause hammering
hence it is
recommended to
keep the
temperature 20°C
below saturation
temperature of
particular boiler.

Tubular air heaters
- Heat exchange across tubes from gas to air
- Air heater is stationary
- Used for industrial boilers
Rotating air heaters
- Elements heated and cooled by the gas and air
respectively as it moves through them
- Continuously rotating
- More compact for large size boilers
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Boiler feed pumps :
 Sustains boiler pressure by pumping against operating
pressure.
 Failure of feed pump results in boiler trip & hence
standby essential.
 Multi-stage centrifugal pumps are generally used.
 Normally driven by electric motor. Steam turbine
drive can be used.
 Flow control is by outlet control valve.
 To save power variable speed drives are also used.
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Contd…..

Fans :
 Provides combustion air.
 Evacuates flue gas to chimney.
 Generally centrifugal fans are used.
 Axial fans may be used in large boilers for FD fan.
 Normally driven by electric motor. Steam turbine
drive can be used.
 Normally controlled by inlet guide vane/
damper.
 To save power variable speed drives are used.
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Contd…..

Mechanical Dust Collector.
- Can be single or multi-cyclone.
- Dust collection efficiency between 90% to 95%.
- Dust separates due to centrifugal action.
- Good for large particle sizes.
- Draft loss around 75-100 mmwc.
Wet Scrubbers :
- Uses moisture to capture dust.
- Used in boilers using low ash fuels like bagasse.
- Water is an essential pre-requisite.
- Draft loss 75 to 100 mmwc.
- Converts air pollution to water pollution.
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Contd…..

Electro-static precipitators:
 Ionizes the gases and dust captured on the cathodes
 Efficiency as high as 99.9%
 Can capture finer dust
 Draft loss only 25 mmwc
 High voltage used as elements to be electrically charged
 Used for large solid fuel fired boilers and cement plants
Bag filters :
 Uses cloth as filters
 Generally used in low erosive dust
 Efficiency above 99.9%
 High draft loss 75 to 150 mmwc and hence high ID fan power
consumption
 Bags needs frequent maintenance and replacement
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Contd…..

Natural circulation
Forced circulation
Assisted forced circulation
Once through boilers
What does good circulation do ?
Essential to protect the furnace tubes from over
heating failure.
To keep the evaporation in the nucleate boiling
range.
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Nucleate boiling :
 Lower heat flux.
 Ensures that always water is in touch with heating
surface and thus ensures good cooling.
 Boundary layer heat transfer co-efficient higher and
temperature drop across boundary layer larger.
Film boiling :
 Very high heat flux.
 Steam in touch with heating surface & hence cooling
is poor.
 Boundary layer heat transfer co-efficient lower and
lower temperature drop across the boundary layer.
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Motive force for natural circulation is the density
difference between the water and water steam
mixture.
This is high at low pressures and low in high pressure
boilers due to the behavior of steam and water
densities with pressure.
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C + O2 CO2 + Heat
2H2 + O2 2H2O + Heat
S +O2 SO2 + Heat
I kg of C requires 2.667 kg of Oxygen
1 kg of H2 requires 8 kgs of Oxygen
1 kg of Sulphur requires 1 kg of Oxygen
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Stoichiometric air is the quantity of air
theoretically required to complete the
combustion of fuel.
Practically stoichiometric air quantity is
not sufficient to complete the
combustion due to fuel particle size and
homogeneity of fuel and air is not good.
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Excess air is the quantum of air that is
required over and above
stoichiometric air quantity to have
satisfactory completion of combustion.
Solid fuels require more excess air
than liquid fuels.
Liquid fuels require more excess air
than gaseous fuels.
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Fixed grate / Reciprocating grate: 40-50 %
Dumping grate : 35-40 %
Traveling grate : 35%
Traveling grate with spreader stoker : 30-35 %
Fluidized bed : 20-25 %
Pulverized fuel firing : 20%
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Pressure jet burners : 15 - 20%
Steam/air atomized burners : 10 - 15%
Rotary cup burners : 10 - 15%
Gas burners – natural gas : 5 - 10%
Gas burners – low calorie gases : 10 - 15%
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Hope you have understood the basics of steam engineering.
THANKS FOR YOUR
CONCENTRATION
08/26/2024
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Basics of Steam Engineering which is used in a fabricated line in a .ppsx.ppt

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Basics of Steam Engineering which is used in a fabricated line in a .ppsx.ppt