Details about industrial chimney

1. A Design project submitted in partial fulfillment of the
requirement for the award of the degree of
BACHELOR of engineering
IN
CIVIL ENGINEERING
SUBMITTED BY
BASITH AHAMED ( 113012103018)
MANISH KUMAR MANDAL (113012103056)
MOHAMED SALIM (113012103062)
UNDER THE GUIDANCE OF
Mr. MANOJ KUMAR ,ME
(DEPARTMENT OF CIVIL ENGINEERING )
VELTECH HIGHTECH DR.RANGARAJAN DR.SAKUNTHALA ENGINEERING
COLLEGE,AVADI

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INDUSTRIAL CHIMNEYS

3. AIM
 To design industrial chimney which
includes RCC chimney.

4. CHIMNEY OVERVIEW
 In many industries chimneys are required to leave hot
waste gases at great heights.
 They are used mostly in thermal power plant eg, coal
based thermal power plant, because of high amount of
waste gases it lets out.
 In order to avoid pollution on ground surface chimneys are
designed very height.
 RC chimneys are becoming more and more popular
because of economy in construction and maintenance.
maintenance cost of steel chimney is high and also brick
chimneys become too bulky and costly when height of
chimney is more than 30m.

5. OBJECTIVES
 To analyze and design industrial RCC
chimney.
 To construct a stable superstructure
considering in mind various load
considerations.
 To decide the size and structural parameters
governing the chimney.

6. SCOPE
 To design chimney to sustain the stresses
due to self-weight, wind load, temperature
variations and also seismic effect.
 To extend the durability and longevity of
the structure.

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INDUSTRIAL CHIMNEYS
1. DEFINITION OF CHIMNEY
Chimneys are tall and slender structures which are
used to discharge waste/flue gases at higher elevation
with sufficient exit velocity such that the gases and
suspended solids (ash) are dispersed into the
atmosphere over a defined spread such that their
concentration, on reaching the ground is with in
acceptable limits specified by Pollution Control
Regulatory Authorities.
In a coal based power plant, flue gases from each
boiler are fed to a chimney, for dispersion into
atmosphere.

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INDUSTRIAL CHIMNEY
3. CLASSIFICATION OF CHIMNEYS
a) Based on number of flues
 Single flue (each boiler will have an independent chimney)
 Multi flue (Single chimney serves more than one boiler; more
flues are housed inside a common concrete windshield)
b) Based on material of construction
 Concrete (Chimney); Reinforced/Pre-stressed
 Steel (stack)
c) Based on structural support
 Guyed stacks (used in steel stacks for deflection control)
 Self supporting (cantilever structures)
d) Based on lining
 With Lining : Lined chimneys/stacks
 Without lining :Unlined chimneys/stacks

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INDUSTRIAL CHIMNEYS
5. DESIGN LOADS
 Dead Loads (weight of chimney shell & lining)
 Wind Loads (as per IS:875; Part-3)
 Seismic Loads (as per IS;1893)
 Temperature Loads (depends on flue gas temperature)
Note: wind and seismic loads are not considered to act simultaneously
as both are environmental loads
6. LOAD COMBINATIONS
 Dead load + Wind load
 Dead load + Seismic load
 Dead load + Temperature load
 Dead load + Wind load + Temperature load
 Dead load + Seismic load + Temperature load

10. PARTS OF RCC CHIMNEY
 RC SHELL
 BRICK LINING
 AIR GAP
 RC BRACKET
 COALTAR LINING

11. RCC CHIMNEY
• RCC chimneys of height 50-100m are
commonly used.
• The outer diameter of chimney maybe
kept constant throughout or may be
linearly varied. Also thickness of concrete
shell maybe varied in steps or linearly.
• The concrete chimneys are provided with
lining of 100-150mm thick fire bricks ,so
as to reduce temperature stresses in
concrete shells.

12. TYPES OF RCC CHIMNEYS

13. Continue….
 The fire brick lining is supported by
reinforced concrete brackets provided at
regular intervals of 4-6m.
 Thickness of shell wall is kept to a min of
200mm at top and is increased to 300-
400mm at bottom depending upon height of
chimney.
 an air gap of 80-150mm is provided
between concrete shell and rick lining to
reduce temperature gradient.

14. DESIGN FACTORS
 RCC chimneys are to be designed to sustain
the stresses due to :
 1. self-weight
 2. wind load
 3. temperature variation.
Wind load depends upon various
factors like nature of terrain, wind velocity in
the zone, height of building. it depends upon
shape of structure. shape factor is one has to
multiply wind pressure in the area to get
design wind pressure on the structure.

15. SHAPE FACTOR FOR WIND
LOAD CALCULATION

16. RELIABILITY OF CONCRETE OVER
BRICK:
 Brick chimneys are not suitable because
they are restricted to limited height and
and require huge foundations
 Concrete chimneys are suitable for
cases where the temperature difference
between the outer shell and inner lining
is 400 degrees.
 In case of the temperature rising above
400 degrees, an additional layer of brick
lining and an air gap is provided to take
care of the increased temperature
gradient.

17. Continue..
 Inside temperature is higher compared to
outer side. this causes differential
expansion and hence stresses are induced
in RC wall in both horizontal and vertical
directions.

18. Continue…
 Vertical steel is provided to resist
bending moment due to wind.
 Horizontal steel is provided to take
care of the horizontal shear and
reduce the effect of temperature
gradient.

19. Wind pressure:
 Wind obviously causes obstruction to
anything in its way. The intensity of
wind pressure depends on wind
velocity which in turn depends on the
elevation above the ground. IS875
specifies wind pressure at various
heights as given below:

20. WIND PRESSURE FOR VARYING ELEVATION
ABOVE GROUND LEVEL

21. SHAPE FACTORS FOR
VARIOUS SIZES OF CHIMNEY:

22. STRESSES IN CHIMNEY SHAFT DUE
TO SELF-WEIGHT AND WIND:
 Purpose of analysis of stresses due to
self weight and wind, it is assumed
that the steel reinforcement is
replaced by a thin steel cylinder and it
is located at the centre of the
thickness.
 It is assumed that variation of stresses
in the thickness of the shell is small
and total compressive or tensile stress
may be taken acting on the centre line
of the shell thickness.

23. STRESSES IN HORIZONTAL REINFORCEMENT
DUE TO WIND SHEAR:
 Horizontal reinforcement is provided in
the form of hoops which resists the
horizontal shear due to wind.
Stress in steel, (t) is given by,
T= (P*S)/2AɸD1
 P – horizontal shear force
 S- pitch (mm)
 Aɸ -horizontal reinforcement
 D1- distance between reinforcement on
both sides

24. STRESSES DUE TO
TEMPERATURE DIFFERENCE:
 Because of the high temperature
difference in flue gases there is large
temperature gradient.
 The fall of temperature through the
concrete shall cause severe stresses.
 To reduce the temperature stresses,
10cm thick fire brick lining is provided,
spaced slightly away from the concrete
shell so that air gap of 8-10 cm wide is
available between the two. The lining is
supported at every 5-7m.

25. COMBINED EFFECT OF SELF LOAD,
WIND, TEMPERATURE:
We have to consider 2 sections of
chimney:
 Leeward side
 Windward side

26.  The leeward side of the chimney is
the compressive zone in which the
compressive stress due to self load
and wind has uniform value
throughout the shell thickness.
 The windward side is the tension
zone. Due to self-load and wind, the
whole concrete shell on the windward
side is in tension which is completely
borne by steel having stress t1.

27. TEMPERATURE STRESS IN HORIZONTAL
REINFORCEMENT
 The inner surface is prevented from
expansion and is therefore subjected
to compressive stress due to
temperature gradient, while the outer
surface expands more than its natural
expansion and is subjected to tensile
stress. Since the horizontal
reinforcement are located in the outer
face, it is subjected to tensile stress.

28. INTERNAL LININGS
Acid Resistant
Fire Bricks
Coal-tar applied
to Inner
surface of
Concrete shell to
close shrinkage
cracks and as
protection to
concrete

29. Autocad drawings of chimney

30. Elevation of chimney

31. Elevation continued..

32. Continued..

33. Plan of chimney

34. Plan continued..

35. Plan continued..

36. FOUNDATION
 Generally circular raft foundations are provided.
 Pile foundations are also common.
 Diameter and thickness of raft foundation is governed
by combined vertical loads and wind / seismic loads.
 Stability factors govern the design,
 F.O.S (overturning) > 1.5
 F.O.S (sliding) > 1.5
 Foundations are taken deeper to get additional soil
weight on raft to assist stability.
 Gross bearing pressure under footing should be
compressive i.e. “loss of contact” is to be avoided or
limited to a maximum of 1/6 of raft diameter.

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Following two methods are very common:
 Jump form
 Slip form
Jump Form: Construction is in stages of about 1.5 to
3.0m lifts
Slip form: Continuous construction
Formwork keeps moving upward at low
speed as the concreting continues.
Eg. DHOKA System (from Austria)
METHOD OF CONSTRUCTION

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REFERENCES
1. IS: 4998 – Criteria for Design of Reinforced Concrete
Chimneys
2. IS: 6533 - Code of Practice for Design and
Construction of Steel Chimneys
3. Tall Chimneys- Design & Construction by S.N.
Manohar, Tata McGraw-Hill Publishing Company
Limited.
4. Hand Book of Concrete Engineering, edited by Mark
Fintel, CBS Publishers & Distributors