Chimney design

In these slides, I include design requirements for the chimney and its procedure.
I wish it would be helpful for your knowledge.

1. POWER PLANT ENGINEERING
Chimney Design

2. The Industrialchimneyis a tall structure used to ventilate or
exhaust off all gases generated during theCombustion of
Fuel.
Tall, slender and generally with circular cross-sections.
INTRODUCTION

3. Elevate harmful gases emitted from factories so as to keep
the surrounding atmosphere as clean as possible.
Helps keep the health of the workers as well as surrounding
city clean as much as possible
NEED OF A CHIMNEY

4. Based on number of flues
a)Single flue (each boiler will have an independent
chimney)
b)Multi flue (Single chimney serves more than one
boiler; more flues are housed inside a common
concrete windshield)
CLASSIFICATION OF INDUSTRIAL CHIMNEY

5. Based on material of construction
a)Concrete (Chimney); Reinforced/Pre-stressed
b)Steel (stack)
c)Brick
Concrete or RCC type selected or preferred over brick.
CLASSIFICATION OF INDUSTRIAL CHIMNEY

7. Based on lining
a)With Lining : Lined chimneys/stacks
b)Without lining :Unlined chimneys/stacks
CLASSIFICATION OF INDUSTRIAL CHIMNEY

8. Based on structural support
a)Guyed stacks (used in steel stacks for deflection control)
b)Self supporting (cantilever structures)
CLASSIFICATION OF INDUSTRIAL CHIMNEY

9. Steel chimneys are ideally suited for process work where a
short heat-up period and low thermal capacity are required.
Steel chimneys are also economical, for height up to 45m.
STEEL CHIMNEY

10. Volume of flue gas
Temperature of flue gas at entry point
Exit velocity required
Composition of flue gas
HOW BIG A CHIMNEY DO I REQUIRE?

11. Terrain category 1 –Exposed open terrain with few or no
obstructions and if any then height about 1.5 m.
Terrain category 2 –Open terrain with well scattered
obstructions of height 1.5m –10m.
Terrain category 3 –Terrain with closely spaced obstruction
having size of 10m.
Terrain category 4 –Terrain with numerous large high closely
spaced obstruction.
TERRAIN CATEGORIES

12. Initial data
Height of chimney = 72m
Diameter of chimney = 3m
Soil Capacity = 200 KN/m
2
Thickness of fire brick lining = 100 mm
Topography at the site is almost flat
Location is of terrain category 2.
DESIGN OF SELF SUPPORTED CHIMNEY

13. Basic Dimension of Chimney
Total height of Chimney = 72 m
Height of Flared portion = (1/3)x H=
Diameter of Cylindrical portion = 3m
Diameter of Flared Portion = 1.6 x Dia. of Cylinder
= 1.6 x 3 = 4.8 m
DESIGN OF SELF SUPPORTED CHIMNEY

14. Computation of wind Pressure
Design wind Speed(Vz) at z m Height
Vz= Vb. K1 . K2 . K3
Vb= Basic wind speed at site = 47 m/s
K1 = Risk Factor = 1.0 ( For general building & Structure)
K3 = Topography Factor = 1.0
K2 = Terrain Roughness & structure size Factor
DESIGN OF SELF SUPPORTED CHIMNEY

15. DESIGN OF SELF SUPPORTED CHIMNEY
Class A -Height less than 20 m
Class B -Height Between 20 to 50 m
Class C-Height greater than 50 m

16. Computation of wind Pressure
Vz= Vb. K1 . K2 . K3
Vz= 47 x 1 x 1 x K2 = 47 K2
Wind Pressure
Pz= ½ x ρx Vz
2
For Air ρ= 1.2 Kg/m
3
Pz= 0.6 x 47K2
Wind Force
Fz= k x pzx (D x Δz)
k = Shape Factor = 0.7
Δz = 8 m
DESIGN OF SELF SUPPORTED CHIMNEY

18. DESIGN OF SELF SUPPORTED CHIMNEY

19. Design of Chimney Shell
Stress due to chimney weight
Weight(W) = ρx V = ρx A x h
Stress = Force / Area = ρAh / A =ρh
= 78.5(h) KN/m
2
fs= 0.0785(h) KN/mm
2
Stress due to weight of lining fl= 0.002 h/t N/mm
2
Stress due to wind fw= 0.004 x Mw / (Πx d
2
x t ) N/mm
2
DESIGN OF SELF SUPPORTED CHIMNEY

20. Design of Chimney Shell
Minimum thickness for chimney = 6 mm
For corrosion life thickness = 4 mm
Total thickness = 6 + 4 = 10 mm
DESIGN OF SELF SUPPORTED CHIMNEY

21. DESIGN OF SELF SUPPORTED CHIMNEY

22. Design of Chimney Shell
(Section X1-X1)
h = 8 m, D = 3 m, M
wxx1= 113 .892 KN.m
Effective t = 6 mm
D/t = 3000/6 = 500 and h/D = 8/3 = 2.67
σ
c .Ƞ= 58 N/mm
2
(For comprissiblestress Ƞ= 1)
σ
t .Ƞ= 0.6 fy. Ƞ(For tensile stress Ƞ= 0.7)(fy= 250 for Fe
250)
σ
t = 105 N/mm
2
fs= 0.63 N/mm
2
fl = 2.67 N/mm
2
fw=2.69 N/mm
2
fc= fs+ fl + fw= 5.99 N/mm
2
< 58 N/mm
2
(safe)
Ft = fw–fs= 2.06 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

23. Design of Chimney Shell
(Section X2-X2)
h = 16 m, D = 3 m, M
wxx2= 453.32 KN.m
Effective t = 6 mm
D/t = 3000/6 = 500 and h/D = 16/3 = 5.33
σ
c = 58 N/mm
2
σ
t = 105 N/mm
2
fs= 1.26 N/mm
2
fl = 5.33 N/mm
2
fw=10.69 N/mm
2
fc= fs+ fl + fw= 17.28 N/mm
2
< 58 N/mm
2
(safe)
Ft = fw–fs= 9.43 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

24. Design of Chimney Shell
(Section X3-X3)
h = 24 m, D = 3 m, M
wxx3= 1013.82 KN.m
Effective t = 6 mm
D/t = 3000/6 = 500 and h/D = 24/3 = 8
σ
c = 58 N/mm
2
σ
t = 105 N/mm
2
fs= 1.88 N/mm
2
fl = 8 N/mm
2
fw= 23.9 N/mm
2
fc= fs+ fl + fw= 33.79 N/mm
2
< 58 N/mm
2
(safe)
Ft = fw–fs= 22.02 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

25. Design of Chimney Shell
(Section X4-X4)
h = 32 m, D = 3 m, M
wxx4= 1790.34 KN.m
Effective t = 6 mm
D/t = 3000/6 = 500 and h/D = 32/3 = 10.67
σ
c = 58 N/mm
2
σ
t = 105 N/mm
2
fs= 2.51 N/mm
2
fl = 10.67 N/mm
2
fw= 42.20 N/mm
2
fc= fs+ fl + fw= 55.39 N/mm
2
< 58 N/mm
2
(safe)
Ft = fw–fs= 39.7 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

26. Design of Chimney Shell
(Section X5-X5)
h = 40 m, D = 3 m, M
wxx5= 2775.43 KN.m
Effective t = 6 mm
D/t = 3000/6 = 500 and h/D = 40/3 = 13.33
σ
c = 58 N/mm
2
σ
t = 105 N/mm
2
fs= 3.14 N/mm
2
fl = 13.33 N/mm
2
fw=65.44 N/mm
2
fc= fs+ fl + fw= 81.91 N/mm
2
< 58 N/mm
2
(Unsafe)
So we need to Incresethickness 10 to 12 mm
DESIGN OF SELF SUPPORTED CHIMNEY

27. Design of Chimney Shell
(Section X5-X5)(Conti…)
h = 40 m, D = 3 m, M
wxx5= 2775.43 KN.m
Effective t = 8 mm
D/t = 3000/8 = 375 and h/D = 40/3 = 13.33
σ
c = 74 N/mm
2
σ
t = 105 N/mm
2
fs= 3.14 N/mm
2
fl = 10 N/mm
2
fw= 49.08 N/mm
2
fc= fs+ fl + fw= 62.22 N/mm
2
< 74 N/mm
2
(safe)
Ft = fw–fs= 45.94 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

28. Design of Chimney Shell
(Section X6-X6)
h = 48 m, D = 3 m, M
wxx6= 3959.94 KN.m
Increase thickness 12 to 16 mm, Effective t = 12 mm
D/t = 3000/12 = 250 and h/D = 48/3 = 16
σ
c = 99 N/mm
2
σ
t = 105 N/mm
2
fs= 3.77 N/mm
2
fl = 8 N/mm
2
fw= 46.68 N/mm
2
fc= fs+ fl + fw= 58.45 N/mm
2
< 99 N/mm
2
(safe)
Ft = fw–fs= 42.91 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

29. Design of Chimney Shell
(Section X7-X7)
h = 56 m, D = 3.6 m, M
wxx7= 5343.03 KN.m
Effective t = 12 mm
D/t = 3600/12 = 300 and h/D = 56/3.6 = 18.67
σ
c = 87 N/mm
2
σ
t = 105 N/mm
2
fs= 4.4 N/mm
2
fl = 9.33 N/mm
2
fw= 43.74 N/mm
2
fc= fs+ fl + fw= 57.74 N/mm
2
< 87 N/mm
2
(safe)
Ft = fw–fs= 39.34 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

30. Design of Chimney Shell
(Section X8-X8)
h = 64 m, D = 4.2 m, M
wxx8= 6937.55 KN.m
Effective t = 12 mm
D/t = 4200/12 = 350 and h/D = 64/4.2 = 15.24
σ
c = 78 N/mm
2
σ
t = 105 N/mm
2
fs= 5.02 N/mm
2
fl = 10.67 N/mm
2
fw= 41.73 N/mm
2
fc= fs+ fl + fw= 57.42 N/mm
2
< 87 N/mm
2
(safe)
Ft = fw–fs= 36.71 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

31. Design of Chimney Shell
(Section X9-X9)
h = 72 m, D = 4.8 m, M
wxx9= 8757.93 KN.m
Effective t = 12 mm
D/t = 4800/12 = 400 and h/D = 72/4.8 = 15
σ
c = 70 N/mm
2
σ
t = 105 N/mm
2
fs= 5.65 N/mm
2
fl = 12 N/mm
2
fw= 40.33 N/mm
2
fc= fs+ fl + fw= 57.98 N/mm
2
< 70 N/mm
2
(safe)
Ft = fw–fs= 34.68 N/mm
2
< 105 N/mm
2
(safe)
DESIGN OF SELF SUPPORTED CHIMNEY

32. Calculation of Actual Weight
Weight of Shell = Density x Volume of section 1 to 9
= 771.806 KN
Weight of liner = Density x Volume of section 1 to 9
= 1447.646 KN
( Density of Brick Work = 20 KN/m
3
)
( Thickness of lining = 100 mm)
Total Weight = 2219.452 KN
Increase Weight by 5% for lap, Platform, Ladder etc.
Total Weight = 2330 KN
DESIGN OF SELF SUPPORTED CHIMNEY

33. Design of base Plate
Maximum Compressive Force per unit circumference
length
Fc= (Ws + Wl)/(Π. D
c) + 4 Mw/(Π. D
c
2
)
= 638.49 N/mm
Allowable bearing Stress σ
c= 4 N/mm
2
Width = 638.49/4 = 159.4 mm ≈ 160 mm
DESIGN OF SELF SUPPORTED CHIMNEY

34. Design of Anchor Bolt
Maximum Uplift force per unit length of circumference
F
t = 4 Mw/(Π. D
c
2
) –Ws/(Π. D
c) = 674.8 N/mm
As per Is code Overturning moment Mw Should be 1.5 times
from stability consideration
Assume 36 mm dia. anchor bolt
Area = Π/4 .d
2
= Π/4 .(36)
2
= 1017.87 mm
2
Take Permissible tensile strength = 120 N/mm
2
Strength of each bolt = 1017.87 x 120 = 122.144 KN
Spacing of Anchor bolt = 122.144 x 1000/674.8 =181 mm
DESIGN OF SELF SUPPORTED CHIMNEY