Integration of Air and Gas Flow Paths

1
Integration of Air and Gas Flow Paths

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Establish a Continuity from the Beginning to the
End.
2
A General Layout of Steam Generator
3
Air and Gas flow diagram
4
Fluid flows in A Rotary Regenerator
5
Development of Air Flow Circuits
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Draft Required to Establish Air Flow
Flue as out
Air in
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Natural Draft
Zref
pA pref Dp
Tgas
Tatm
B
A
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Natural Draft

• Natural Draft across the furnace,
• Dpnat pA pB

• The difference in pressure will drive the
  exhaust.
• Natural draft establishes the furnace breathing
  by
• Continuous exhalation of flue gas
• Continuous inhalation of fresh air.
• The amount of flow is limited by the strength of
  the draft.

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Mechanical (Artificial)Draft Induced Draft
Essential when Natural Draft cannot generate
required amount of breathing through various
obstructions.
pA patm ratm g Hchimney
Hchimney
pB pfan,s
Tatm
B
B
A
Tgas
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Mechanical (Artificial)Draft Forced Draft
Hchimney
pB patm rgas g Hchimney
pA pfan
Tgas
Tatm
B
A
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Mechanical (Artifical)Draft Balanced Draft
Hchimney
pB pfan,s
pA pfan.b
B
Tatm
A
B
Tgas
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Balanced Draught System
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Resistance to Air Gas Flow Through Steam
Generator System
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ve
-ve
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210 MW POWER PLANT SG
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Pressure drop in Air and Gas Duct Systems

• Mechanical Energy equation pressure drop across
  a flow passage
•  

 
Frictional resistance along flow path
where f coefficient of friction L
length of the duct, m ddl equivalent
diameter of the duct, m ? density of
air or gas calculated at the mean gas
temperature, kg/m3 u cross section
average velocity of air or gas in the duct, m/sec
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Equivalent diameter for rectangular duct is given
as
where a and b are sides of the duct, mm.   The
coefficient of friction for flow through tubes
can be approximated as shown below,
for 5000 lt Relt108, 10-6lt (k/ddl)lt0.01
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Minor Losses Calculation of Local pressure
drops   where ?p local pressure
drop K local resistance factor, r density
of air or gas at the position of the pressure
drop calculated, kg/m3 u velocity of air
through the fittings m/s.
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Pressure drop across a burner
pa K 1.5 for tangential burner 3.0
for swirl burner
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Pressure drop across heating surfaces
Pressure drop across tube bundles  
Inline arrangement K n K0 Where n number
of tube rows along the flow direction K0 loss
coefficient for one row of tubes K0 depends on
s1 s1/d, s2 s2/d , F (s1 - d )
Where s1 is lateral pitch s2 is
longitudinal pitch If s1 lt s2 K0 1.52
(s1 1) 0.5 F 0.2 Re 0.2
If s1 gt s2 K0 0.32 (s1 1) 0.5 (F
0.9) 0.2 Re 0.2/F  
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Staggered Arrangement The loss coefficient is
obtained as K K0 (n1) Where K0 is the
coefficient of frictional resistance of one row
of tubes
K0 depends on s1 s1/d, F (s1 - d ) / (s2l
- d ) Where s2 l is the diagonal tube pitch
given by s2 l v ( 0.25 s12 s22)
and K0 can be written as, K0 Cs
Re-0.27 Cs is design parameter of the staggered
banks
S1
S2
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  For 0.17 lt F lt 1.7 and s1 gt 2.0, Cs
3.2 If s1 lt 2.0,then Cs given as Cs 3.2
(4.6 2.7 F)(2 - s1) For F 1.7 5.2,
Cs 0.44(F1)2
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Pressure drop through rotary air heater
Corrugated plate-corrugated setting plate
Re gt 2.8 x 103 f 0.78 Re-0.25
Re lt 2.8 x 103 f 5.7 Re-0.5
Corrugated plate- plane setting plate Re gt 1.4
x 103 f 0.6 Re-0.25 Re lt 1.4 x 103
f 33 Re-0.8 Plane plate- plane setting
plate Re gt 1.4 x 103 f 0. 33 Re-0.25 Re
lt 1.4 x 103 f 90/ Re
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Ash Collectors

• Following Table is used to estimate the pressure
  drop in Ash collectors.
• Cyclone 15 20 m/s 70 90 500 1000 Pa
• ESP 1 2 m/s 99 100 200 Pa

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Pressure Drop through Stack
where ?pst stack pressure drop, Pa f
friction factor Lst height of the chimney,
m D diamter of the chimney , m Kc resistance
factor at the stack outlet ? gas
density in the stack, kg/m3 uc gas
velocity at the chimney outlet, m/s