This document discusses combustion processes in steam power plants. It describes the properties of different fuels like coal and their combustion characteristics. It explains different types of combustion equipment for solid, liquid and gaseous fuels. For solid fuels, it discusses hand firing and various types of stoker firing methods. It also covers pulverized fuel firing systems. For liquid and gaseous fuels, it explains injection and evaporation systems. The document further discusses draught systems, chimneys, forced and balanced draught. It concludes with describing smoke and dust removal methods like mechanical and electrical dust collectors and cyclone separators.

1. ANNAMACHARYA INSTITUTE OF TECHNOLOGY &
SCIENCES::RAJAMPET
(AUTONOMOUS)
DEPARTMENT OF MECHANICAL ENGINEERING
Steam power plant –Combustion Process
Prepared by B Venkatesh

2. Properties of Coal:
1. Energy Content
2. Sulphur Content
3. Burning Characteristics
4. Grind ability
5. Weather ability
6. Ash Softening Temp.,

3. Combustion Equipment's:
1. Solid Fuel Fired
2. Liquid Fuel Fired
3. Gaseous Fuel Fired

4. Combustion Equipment for Solid fuel
selection consideration:
1. Initial cost of the equipment
2. Sufficient combustion Space
3. Area of the grate (Over which fuel burns)
4. Operating cost
5. Minimum smoke nuisance
6. Flexibility of operation
7. Arrangement for through mixing of air with fuel for efficient combustion

5. 1 Hand fired
A Solid fuel fired 2 Stoker fired a Overfeed Stoker
b Underfeed Stoker
3 Pulverised fuel fired a Unit System
b central System
c Combination of Unit & Centra

6. 1 Injection System
B Liquid fuel fired 2 Evaporation System
3 Combination of 1 &2

7. 1 Atmospheric Pressure System
C Gaseous Fuel Fired
2 High Pressure System

8. HAND FIRING
Various Types of Hand Fired Grates
This is a simple method of firing coal
into the furnace. It requires no capital
investment. It is used for smaller plants.
This method of fuel firing is
discontinuous process, and there is a
limit to the size of furnace which can be
efficiently fired by this method.

9. Hand fired furnaces are simple in design and can burn the fuel successfully but they have
some disadvantages also mentioned below:
(i) The efficiency of a hand fired furnace is low.
(ii) Attending to furnace requires hard manual labour.
(iii) Study process of fuel feed is not maintained.

11. Principle of Overfeed Stoker:

13. Types of Overfeed Stoker:
These Over feed stokers are used for large capacity boiler
installation where the coal is burnt with pulverisation
1. Travelling grate stoker:
(A) Chain grate type
(B) Bar grate type
2. Spreader Stoker
Note: Pulverised fuel firing system the coal is reduce to a fine powder
with the help of grinding mill and then projected into the combustion
chamber with the help of hot air current

14. Speed: 15 cm to 50 cm per min

27. Equipments for Central and Unit System.

28. Chimney:-
The most common method to achieve this difference in pressure, the draught, is to
provide a chimney. Chimney is a tall hollow structure, which creates the required draught
due to difference in pressure from the ground level to some altitude in the atmosphere.
1.Chimneys are made of steel, bricks or concrete.
2.Brick and concrete chimneys are generally used as they have a longer life.
3.The average life of concrete chimneys is about 50 years.
4.The life of steel chimneys is about 25 years, which depends upon the maintenance and
care taken to prevent corrosion.
5.Chimneys ere provided with lightning conductor to protect from thunder lightning and
aircraft warning light as they are at higher altitudes.

29. Draught (or Draft) system:-
1.Draught systems are essential for flue gas propagation.
2.Flue gas propagation is the process of movement of the hot gases from the combustion
chamber through boiler pipes, economizer, air pre-heater and finally to the chimney.
3.The function of draught is to supply required quantity of air for combustion, propagate
the flues and remove the flues from the system.
4.A difference in pressure is required to move the air through the fuel bed to produce a
flow of hot gases i.e., propagation of the flue gases through the boiler, economizer, pre
heater and to the chimney by overcoming the pressure losses in the system.
5.This difference in pressure required maintaining a constant flow of air, through the
boiler systems and finally to discharge the hot flues to the atmosphere through chimney
is termed the draught

30. Draught Classification

31. Chimney Height

33. Forced Draught

34. Balanced Draught

36. Cooling Towers

37. Wet type:-
a)Natural draught cooling tower:-
The height of the cooling tower ranges from 50 m to 80 m, with base diameter up to 40 m
.

38. Forced draught cooling tower

39. Dry type:-
a) Direct type

40. Indirect dry cooling tower with a open type condenser

48. SMOKE AND DUST REMOVAL
The disposal smoke to the atmosphere is not desirable due to the following reasons :
1. A smoky atmosphere is less healthful than smoke free air.
2. Smoke is produced due to incomplete combustion of coal. This will create a big
economic loss due to loss of heating value of coal.
3. In a smoky atmosphere lower standards of cleanliness are prevalent. Buildings,
clothings, furniture etc. becomes dirty due to smoke. Smoke corrodes the metals and
darkens the paints.
In coal fed furnaces the products of combustion contain particles of solid matter
floating in suspension. This may be smoke or dust. The production of smoke indicates that
combustion conditions are faulty and amount of smoke produced can be reduced by
improving the furnace design.
TYPES OF DUST COLLECTORS
The various types of dust collectors are as follows :
1. Mechanical dust collectors.
2. Electrical dust collectors.

49. Mechanical dust collectors

50. Cyclone Separator:

51. Electrical dust collectors

64. References:
1.Power Plant Engineering, C. Elanchezhian, L. Saravanakumar, B. Vijaya RamnathI.K. International Publishing House Pvt. Limited, 2007
2.Power Plant Engineering, A. K. Raja, New Age International,2006
3.Power Plant Engineering, P. K. Nag, McGraw-Hill Educatio,2014
4.A Textbook of Power Plant Engineering Fifth Edition (English, Paperback, Rajput R K),2016