This document provides an introduction to steam generators and boilers. It discusses the origin and impact of steam on science and technology. It describes the working principles of fire tube and water tube boilers. The key components and classifications of boilers are explained. The document also covers boiler efficiency, capacity, pressure, mountings, accessories and their functions. High pressure boilers and their types are discussed. The fuels used for steam generation and the analysis and grading of coal are summarized. Finally, the necessity and requirements of an effective coal handling system are outlined.

1. UNIT-I
Introduction to Steam Generators
By
Pramod Kathamore
Energy Conversion– I

2. Steam, The origin of Scientific & Industrial Civilization.
• Trace the origin of steam.
• Think about the impact of Steam on Science.
• Enumerate the impact of steam on Technology.
• Appreciate the role of steam in industrial world.
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3. Science of Cooking Methods
Camp fire
Wood Stove Gas Stove
Micro Wave
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4. Science of Lighting
Wick lamp
Gas Lamp
Electric Lamp
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5. Science of Motive Power : Land
Horse Cart
Steam Wagon
Car
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6. Science of Motive Power : Sea
Man power Ship
Steam Engine Ship
Steamer
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7. Science of Motive Power : Air
Propeller aircraft
Turbojet Aircraft
Supersonic
aircraft
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8. Origin of Steam : Basis of Scientific &
Technological Research
• Denis Papin, while working at Huygens and of Boyle, started to be
interested in the vapor.
• Several geniuses of science tried before him to try out an unspecified
machine which would run on the vapor, but their efforts were useless.
• It is into 1707 that Denis Papin made his first great realization: the
boat with vapor.
• This superb invention brought much controversy near the boatmen,
who destroyed the ship.
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9. The Steam Machines were in industrial use since 1712.
Establishment of the first and second laws of thermodynamics by Clausius, Kelvin
et al., occurred in 1855!!!
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10. 1.1 Steam Fundamentals:
Steam is uniquely adapted, by its availability
and advantageous properties, for use in industrial and
heating processes and in power cycles.
The fundamentals of the steam generating process
and the core technologies upon which performance
and equipment design are based are described in this
Chapter.
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11. What is Steam?
Steam is an invisible gas that's generated
by heating water to a temperature that brings it to the
boiling point. When this happens, water changes its
physical state and vaporizes, turning from a liquid into
a gas.
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12. How the Energy of Steam Is Used ?
The uses for steam are many and varied.
Like : 1. Power Generation
2. Industrial Process
3. Heating
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13. What is a Boiler?
A boiler is a closed vessel in which steam is produced from water by
combustion of fuel.
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14. How a Boiler works:
 Water is pumped into the boiler at operating pressure
 Heat of flue gases vaporizes water to form steam
 Steam formed is passed into steam space above the water space
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15. Applications of steam generators (Boilers)
 The steam generators or boilers are integral components of steam
turbines which are used as prime movers to drive generators to produce
electricity in all thermal and nuclear power plants.
 These are used in the industry for example in heating systems or for
cement production, textiles.
 These are used to produce distilled water for medicines,
pharmaceuticals and other usage.
 The boilers are used in cold countries for heating large buildings, in
agriculture as well for soil steaming.
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16. 1.2 Boiler classification:
1. Tube content:
(i) Fire tube boiler and (ii) water tube boiler
2. Axis of shell:
(i) Horizontal, (ii) vertical, (iii) inclined
3. Location of furnace:
(i) Externally fired, (ii) internally fired
4. Method of circulation:
(i) Natural, (ii) forced
5. Mobility: (i) Stationary, (ii) portable
6. Usage: (i) Packaged, (ii) unpackaged
7. Pressure: (i) High, (ii) low
8. Tubes: (i) Single-tube, (ii) Multi-tube
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17. 1.3 How a Fire Tube Boiler works:
• Hot flue gases are fed through the tubes.
• Tubes are surrounded by water.
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19. 1.3.1 Cochran Boiler (A Fire Tube Boiler):
Fig: Cochran Boiler
 Vertical mulititubular
 Efficiency 70 - 75%
 Low initial cost
 Suitable for fluctuating loads
 20 kg/hr to 3000 kg/hr
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20. 1.3.2 Locomotive Fire-Tube Boiler
Uses:
• It is mainly used in locomotives though it may also be used for
stationary power service where semi portability is desired.
Working:
• Path of Flue Gas
• Path of Steam Flow
• Draft System: artificial draft has to the created to drive out the
burnt gases.
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21. Locomotive Fire-Tube Boiler
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22. Advantages
• The compactness,
• high steaming capacity,
• Mobility
• low cost of installation.
Weaknesses
• Corrosion in the water legs,
• not capable of meeting very high overloads,
• joint leakages,
• sluggishness of water circulation
• limited maximum steam pressure of 20 bars are the weaknesses in this boiler.
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23. 1.4 How a Water Tube Boiler works:
 Small parallel tubes contain water connected to drum with the header
 Gases pass outside tubes containing water
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24. Invented by George Herman Babcock and Stephen Wilcox in 1967
Babcock and Wilcox Boiler
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25. 4.1 Babcock and Wilcox Boiler ( A Water Tube Boiler ):
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26. Comparison of Fire tube and water tube boilers
Criterion Fire Tube Water tube
1. Flow of hot gases
and water
Gases in tubes surrounded by
water
Outside Water in tubes and gases flow outside
2. Location of
furnace
Internal External
3. Floor area for
given output
Large Small
4. Capacity 10000 kg/hr 50000 kg/hr
5. Evaporation Slow Fast
6. Pressure range 15 to 20 bar 170 to 200 bar
7. Efficiency 80% 92%
8. Safety Large water content and low
steam so better safety
Small water content and large steam generation.
Needs expert attention.
9. Explosion Lesser risk due to lower P Higher risk due to higher P
10. Application Not suitable for large power plant Suitable
11. Skill Less More
12. Water Treatment No Yes
13. Construction Difficult Simple
14. Shell Diameter More Less
15. Transportation Difficult Simple
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27. Boiler Efficiency :
Boiler efficiency is the ratio of the quantity of heat utilized actually by the water and
steam to the quantity of heat supplied, i.e.
 Boiler efficiency = Heat actually absorbed by the water and steam / quantity of heat
supplied
Boiler Capacity:
Boiler capacity is defined as the amount of steam a particular boiler can supply per
hour usually expressed in kg (of steam)/hr or tons/day.
Boiler Pressure:
The designated operating pressure of a boiler at which it can safely deliver the steam at
its rated capacity.
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28. Components of a steam generator (Boiler)
• Boiler drum, tubes, furnace
• Boiler mountings
• Boiler Accessories
Boiler mountings are devices which are required for proper operation, safety
and control of the boiler.
Examples are water level indicator (WLI), pressure gauges (PGs), steam stop
valve, safety valves, fusible plug, feed-check valve, blow-off cock, manhole and
Mud hole, etc.
Boiler accessories are devices which are used to increase the efficiency of a
boiler.
Examples are air preheater, economizer, superheater, feed pump or injector,
baffles, etc.
1.6 Boiler Mountings And Accessories
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29. Boiler mountings
Water Level Indicator
Water level indicator: This is required to
indicate the safety level of water inside
the boiler shell.
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30. Bourdon Tube Pressure Gauge
Pressure gauge: This is required to indicate
the steam pressure inside the boiler shell.
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31. Fusible Plug
Fusible plug: This is required to stop the
boiler if the boiler gets dry to prevent
damage to the boiler. It is a metallic plug
installed in the water pathway. If the
boiler temperature exceeds a safe value,
it melts and allows shell water to pass
through extinguish the furnace
fire.
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32. Lever Safety Valve
Safety valves: These are required to release
the internal boiler pressure if the pressure
exceeds a predetermined safety level.
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33. Boiler Accessories:
Economizer and Superheater
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34. Functions of Boiler accessories:
Air preheater: This is usually used to utilize the waste heat of the chimney
to preheat the furnace air thus increasing the boiler efficiency.
Economizer: This is usually used to utilize the waste heat of the chimney to
preheat
the boiler feed water thus increasing the boiler efficiency.
Superheater: This is usually used to utilize the waste heat to dry and/or
superheat the steam leaving the boiler on the delivery side, thus increasing
the steam quality and boiler efficiency.
Baffles: These are built inside the boilers. These baffles significantly increase
the efficiency by helping feed water in extracting heat from the flue gas.
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35. High Pressure Boiler
Types of High Pressure Boiler
1) Lamont boiler,
2) Benson boiler,
3) Loeffler boiler,
4) Babcock and Wilcox boiler
• A boiler is called a high pressure boiler when it operates with a steam
pressure above 80bar.
• The high-pressure boilers are widely used for power generation in
thermal power plants.
Features of High pressure Boilers
1. Forced circulation of water
2. Large number of small diameter tubes
3. Higher steam pressure and temperature
4. Improved mode of heat transfer and heating
5. Pressurized combustion
6. Compactness
7. High efficiency
8. Once through construction
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36. PramodKathamore

37. The source of heat for a boiler is combustion of any of several fuels, such as
wood, coal, oil, or natural gas. Nuclear fission is also used as a heat source
for generating steam.
B) Fuels for Steam Generators
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38. Gradation
As per the Colliery Control Rule 2004, Coal Controller Organisation (CCO) is
the statutory body under Government of India who regulates the
classification/categorisation/grading of coal mined in India.
Different categories / qualities of coal are being produced by Coal India
Limited. They are mainly
(i) non-coking coal where grading is based on Gross Heat content
(ii) Coking Coal where grading is based on ash % and
(iii) Semi coking coal and weakly coking coal where grading is based on ash
and moisture %.
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39. Grade
of
Coal
Range of Gross Calorific Value
In Kilo Calories
Grade
of Coal
Range of Gross Calorific Value
In Kilo Calories
G1 Greater than 7000 G2 Greater than 6700 and Less than 7000
G3 Greater than 6400 and Less than 6700 G4 Greater than 6100 and Less than 6400
G5 Greater than 5800 and Less than 6100 G6 Greater than 5500 and Less than 5800
G7 Greater than 5200 and Less than 5500 G8 Greater than 4900 and Less than 5200
G9 Greater than 4600 and Less than 4900 G10 Greater than 4300 and Less than 4600
G11 Greater than 4000 and Less than 4300 G12 Greater than 3700 and Less than 4000
G13 Greater than 3400 and Less than 3700 G14 Greater than 3100 and Less than 3400
G15 Greater than 2800 and Less than 3100 G16 Greater than 2500 and Less than 2800
G17 Greater than 2200 and Less than 2500
1) Non-Coking Coal
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40. Grade Ash Content ( %)
Steel – I Upto 15
Steel- II Exceeding 15 and upto 18
Washery. I Exceeding 18 and upto 21
Washery. II Exceeding 21 and upto 24
Washery. III Exceeding 24 and upto 28
Washery. IV Exceeding 28 and upto 35
2) Coking Coal
3) Semi Coking and Weakly Coking Coal
Grade Ash + Moisture Content ( %)
Semi Coking-I Not Exceeding 19 %
Semi Coking –II Exceeding 19 % but not exceeding 24 %
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41. ANALYSIS OF COAL
• To decide the Quality of Coal
• To determine the percentage of various constituents
present in coal which directly affect the calorific value of
coal.
• To Specify its use for particular purpose.
• To Calculate air requirement for complete combustion
• To decide price of coal.
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42. Analysis of Coal
o To measure the particular physical and chemical properties of coals.
o There are two methods to analyse coal
1)The proximate analysis
• Determines only the Moisture, volatile matter, ash and fixed carbon
percentages
• It can be determined with a simple apparatus.
2) The ultimate analysis
• determines all coal component elements (C, N, H, S, solid or gaseous )
• It is useful in determining the quantity of air required for combustion and the
volume , composition of the combustion gases.
• These information are required for the calculation of flame temperature and
the flue duct design etc.
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43. Proximity Analysis
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44. 1. Measurement of moisture
The analysis of coal determines the following aspects:
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45. 2. Measurement of volatile matter
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46. 3. Measurement of Ash
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47. 4. Fixed carbon
o The fixed carbon gives a rough estimate of the heating value of coal.
o It consists of maximum carbon but also contains some hydrogen, oxygen,
sulphur and nitrogen not driven off with the gases.
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48. Summary
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49. PramodKathamore

50. PramodKathamore

51. PramodKathamore

52. Ultimate Analysis
1) Carbon Content: A small Sample of coal is burnt in presence
of enough oxygen.
• The fuel gas is obtained & it is passed through a tube of
known weight of KOH, Where Co2 get observed.
Wt of % C =12 X ΔW
44 X W1
Where,
12=Weight of Carbon
44=Weight of KOH (Potassium hydroxide)
ΔW=Increase in Weight of KOH
W1=Weight of Sample
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53. 2) Hydrogen Content: The Fuel gas is passed through a tube
containing Cacl2 which absorbs water Vapour.
ΔW=Increase in Weight of Cacl2
3) Nitrogen Content: Coal sample is treated concentric H2SO4 .
Then the solution is allowed to stand still until a clear solution
obtained. Solution is treated with KOH (Excess). Ammonia is
liberated and is observed and measured:
Wt. of % H = 2 X ΔW
18 X W1
Wt. of % N = NXVX14
1000 X W1
Where, Weight of NH4OH NXV
1000
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54. 4) Sulpher Content: Coal sample is heated under High
temperature & Pressure until all S is converted into H2SO4 and
Collected. After Washing, Washing are treated with BaCl2 which
react to form BaSO4 then it Precipitated and measure.
5) Oxygen Content:
Wt. of % O= 100- wt.( C+ H + N + S )
Wt. of % S = 32 X ΔW
233 X W1
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55. NECESSITY OF COAL HANDLING SYSTEM
 A 600MW Power Plant handles about 7200 tons of coals per day.
 Coal handlings are to be flexible, reliable & capable of handling large
quantities in less time than even before.
 Coal plays a vital role in electricity generation worldwide. Coal-fired
power plants currently fuel 61% of global electricity.
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56. REQUIREMENT OF GOOD COAL HANDLING PLANT
 It should have minimum maintenance
 It should be simple.
 It should be reliable
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57. COAL HANDLING SYSTEM
Coal Delivery
Unloading
Transfer
Outdoor Storage
Covered Storage
Inplant Handling
Weighing
Furnace Firing
Preparation / Weighing
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58. Coal Transportation
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59. UNLOAD OF COAL AT SITE
 Unload from Rail cars
 Unloading from Ships
 Unloading equipment.
 Self unloading ship.
oUnloading from trucks (lifting trucks)
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60. RAIL CAR UNLOADING
 Rail car unloading by means of
Rotary Drum
o Rail Car unloading featuring
bottom dump by unloading bridge.
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61. TRANSPORTATION BYPIPELINE
Ultra-high-molecular-weight polyethylene
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62. TRANSPORTATION THROUGH ROPE & BELT
CONVEYORS
 Transfer of coal by rope, belt & conveyor is also used if the distance between
the mines & power station is less than 10 km.
 Conveying capacity id 600 tonnes per hour. The line is 270 meters long, with
a vertical rise of 23 meters. It eliminated 115,000 truck journeys.
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63. COAL WEIGHING
 All of our train weighing systems involves "Load Cell" technology which is
the only genuinely recognized method of long term accurate & reliable
train weighing & uses the exact principal as weighbridges, truck scales &
every other general scale is based upon.(onboard coal weighing)
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64. COAL STORAGE
 Storage of coal is undesirable because it costs more as there is,
 Risk of spontaneous combustion.
 Weathering.
 Possibility of loss deterioration during storage.
 Interest on capital cost of coal lying dormant.
 Cost of protecting the stored coal from deteriorating & so on.
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65. PURPOSE OF STORAGE OF COAL
 To store the coal for a period of 30 – 80 days so that plant is never required
to be shut-down.
 Storage of coal allows the purchaser to take the advantage of seasonal
market fluctuation in prices of coal.
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66. OUTDOOR STORAGE (DEAD STORAGE)
 The coal is usually kept on ground in the form of pile exposed to
outside weather.
 The coal is required to be protected from deterioration & weathering
 This is a long term storage i.e.10% of annual consumption.
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67. CLOSED OR LIVE STORAGE
 In the closed or live storage the coal is stored for one or two days
requirement of the power plant.
 This storage is used for the purpose of supplying the coal to the
combustion equipment with negligible handling
 The coal is usually stored in the vertical cylinder bunkers or coal bins.
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68. INPLANT COAL HANDLING
 The In-Plant coal handling system deals
with feeding of coal from live storage to
the furnace.
 It includes various equipment's for
transfer of coal like belt conveyor, screw
conveyor etc. & the equipment needed
to weigh the quantity of coal for feed.
 In case of pulverized coal firing system, it
requires large no. of equipment’s like
pulverized mills, feeders, weighing
machine, hoppers & automatic scales.
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69. POINTS TO REMEMBER.
 Simple & sound, requiring minimum Operations & transportation.
 No double handling of coal in plant.
 Handling unit should be centralized to facilitate inspection & maintenance.
 Electric motors can be used as driver of mechanism.
 Working parts should be enclosed to avoid abrasion & corrosion.
 System should be able to supply required quantity of coal as per demand.
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70. COAL PREPARATION
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71. VIBRATING SEPARATOR
 Size of vibrating separator is fitted after crusher to screen the
coal crushed below set size.
 Oversized coal is returned to crusher for further proper crushing.
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72. TRANSFER OF COAL.
1. Belt conveyors.
2. Screw conveyors.
3. Bucket elevators.
4. Grab bucket elevators.
5. Flight conveyors or scrapers.
6. Skip hoist.
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73. BELT CONVEYORS
 It consist of endless belt of suitable material running over pair of end
drums supported at regular interval by series of rollers(idler).
 Max Inclination: 20degree.
 Running Speed: 400-500 RPM.
 Transport Capacity: 50-100ton/hour over long distance
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74. BELT CONVEYORS (CONT.)
Advantages
1. Low cost & power consumption.
2. Smooth & clean operation.
3. Cheap maintenance.
4. Controlled rate of coal transfer.
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75. SCREW CONVEYORS
 It is used for shorter distance(30m).
 Totally enclosed from atmosphere.
 Coal dust can also be transferred easily.
 Diameter: 15-50cm.
 Speed: 70-120rpm.
 Transfer Capacity: 100tons/hour.
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76. SCREW CONVEYORS
 Advantages
1. Cheap
2. Requires small space, simple & tight.
3. Dust tight.
 Disadvantages
1. High power consumption per ton of coal transfer
2. Wear and tear of screw is high. Shorter life
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77. BUCKET ELEVATOR
 Coal is lifted vertical or near
vertical direction.
 It carries the buckets fixed to
a chain.
 Buckets are loaded with coal
at bottom & discharges at the
top.
Limitation:
 The lift of coal is limited to about 30m.
 Inclination is limited to 60 degree with horizontal
 Transfer Capacity: 60 tons/hour.
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78. BUCKET ELEVATOR
 Coal is lifted vertical or near
vertical direction.
 It carries the buckets fixed to
a chain.
 Buckets are loaded with coal
at bottom & discharges at the
top.
Limitation:
 The lift of coal is limited to about 30m.
 Inclination is limited to 60 degree with horizontal
 Transfer Capacity: 60 tons/hour.
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79. BUCKET ELEVATOR
 Coal is lifted vertical or near
vertical direction.
 It carries the buckets fixed to
a chain.
 Buckets are loaded with coal
at bottom & discharges at the
top.
Limitation:
 The lift of coal is limited to about 30m.
 Inclination is limited to 60 degree with horizontal
 Transfer Capacity: 60 tons/hour.
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80. BUCKET ELEVATOR
 Coal is lifted vertical or near
vertical direction.
 It carries the buckets fixed to
a chain.
 Buckets are loaded with coal
at bottom & discharges at the
top.
Limitation:
 The lift of coal is limited to about 30m.
 Inclination is limited to 60 degree with horizontal
 Transfer Capacity: 60 tons/hour.
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81. GRAB BUCKET ELEVATOR
 It lifts & transfer coal on a single rail or track from one point to
the other.
 It can be used with crane or tower.
 Transfer Capacity: 50 tons/hour
Advantages:
1. Requires less power for operation and minimum maintenance.
2. Used when other arrangements are not possible.
3. Lesser operating cost.
4. Disadvantages:
1. Initial cost is high.
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82. ASH HANDLING EQUIPMENT
Mechanical means are required for the disposal of ash. The handling equipment should
perform the following functions:
(1) Capital investment, operating and maintenance charges of the equipment
should be low.
(2) It should be able to handle large quantities of ash.
(3) Clinkers, soot, dust etc. create troubles, the equipment should be able to
handle them smoothly.
(4) The equipment used should remove the ash from the furnace, load it to the
conveying system
to deliver the ash to a dumping site or storage and finally it should have means to
dispose of the stored ash.
(5) The equipment should be corrosion and wear resistant.
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83. General layout of ash handling and dust collection system
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84. The commonly used ash handling systems are as follows
(i) Hydraulic system
(ii) pneumatic system
(iii) Mechanical system
(iv) Water Jetting
(v) Ash Sluice Ways and Ash Sump System
Hydraulic System
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85. Pneumatic System
• In this system, ash from the boiler furnace outlet falls into a crusher
where larger ash particles are crushed to small sizes.
• The ash is then carried by a high velocity air or steam to the point of
delivery.
• Air leaving the ash separator is passed through filter to remove dust etc.
so that the exhauster handles clean air which will protect the blades of
the exhauster.
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86. Mechanical Ash Handling
In this system ash cooled by water seal falls on the belt conveyor and is carried out
continuously to the bunker.
The ash is then removed to the dumping site from the ash bunker with the help of
trucks.
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87. FLUIDISED BED COMBUSTION (FBC)
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88. TYPES OF FBC SYSTEMS
FBC systems are of following types :
(i) Atmospheric FBC system : Circulating Fluidized Bed Combustion
(CFBC).
(a) Over feed system
(b) Under feed system.
(ii) Pressurised FBC system (Bubbling Fluidized Bed Combustion (BFBC)
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89. • In this system the pressure inside the bed is atmospheric.
• Fig. shows commercial circulation FBC system. The solid fuel is made to enter the
furnace from the side of walls.
• The Low Velocity (LV), Medium Velocity (MV) and High Velocity (HV) air is
supplied at different points along the sloping surface of the distribution ash is
collected from the ash port.
• The burning is efficient because of high lateral turbulence.
(i) Atmospheric FBC system :
Circulating Fluidized Bed
Combustion (CFBC).
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90. (ii) Pressurised FBC system.
(Bubbling Fluidized Bed Combustion (BFBC)
In this system pressurised air is used for fluidisation and
combustion.
This system : the following advantages:
(a)High burning rates.
(b)Improved desulphurisation and low NO, emission.
(c)Considerable reduction in cost.
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91. “Fluidized bed combustion (FBC) is a combustion technology used to burn solid fuels.”
Bubbling Fluidized Bed Type Combustion
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92. Various advantages of FBC system are as follows:
(i) FBC system can use any type of low grade fuel including municipal
wastes and therefore is a cheaper method of power generation.
(ii) It is easier to control the amount of SO2 and NOX, formed during
burning. Low emission of SO2 and NOX. will help in controlling the
undesirable effects of SO2 and NOX. during combustion. SO2 emission is
nearly 15% of that in conventional firing methods.
(iii) There is a saving of about 10% in operating cost and 15% in the capital
cost of the power plant.
(iv) The size of coal used has pronounced effect on the operation and
performance of FBC system. The particle size preferred is 6 to 13 mm but
even 50 mm size coal can also be used in this system.
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