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FIGURE C-12
Pressure Drop per 100 ft of Duct (in. wc)
Max Inlet
BHP
4"
5"
Press
60 ppm NOx Level
200
1.00
1.4
0.4
250
1.00
2.1
0.6
300
1.25
3.1
0.9
350
1.25
4.2
1.2
400
1.25
5.5
1.6
450
1.25
7.0
2.0
500
1.50
2.5
550
1.50
3.0
600
1.50
3.6
700
1.50
4.9
750
1.50
5.6
800
1.50
6.4
900
2.00
8.1
1000
2.00
1100
2.00
1200
2.00
30 ppm NOx Level
200
1.00
250
1.00
300
1.25
350
1.25
400
1.25
450
1.25
500
1.50
550
1.50
600
1.50
700
1.50
750
1.50
800
1.50
900
2.00
1000
2.00
1100
2.00
1200
2.00
20 ppm NOx Level
200
1.00
250
1.00
300
1.25
350
1.25
400
1.25
450
1.25
500
1.50
550
1.50
600
1.50
700
1.50
750
1.50
800
1.50
900
2.00
1000
2.00
1100
2.00
1200
2.00
JBE(X) Manual
6"
8"
10"
12"
14"
16"
0.1
0.2
0.3
0.5
0.6
0.8
0.2
0.9
0.2
1.1
0.2
1.3
0.3
1.8
0.4
2.1
0.5
2.4
0.5
0.2
3.0
0.5
0.2
3.7
0.8
0.2
4.5
1.00
0.3
5.4
1.2
0.3
1.9
0.4
0.1
2.9
0.6
0.2
4.2
0.9
0.3
5.8
1.3
0.4
7.5
1.7
0.5
0.2
2.1
0.6
0.3
0.1
2.6
0.8
0.3
0.2
3.1
0.9
0.4
0.2
3.7
1.1
0.5
0.2
5.1
1.5
0.7
0.3
5.8
1.7
0.8
0.3
6.6
2.0
0.9
0.4
8.4
2.5
1.1
0.5
3.1
1.3
0.6
3.7
1.6
0.7
4.4
1.9
0.9
4.6
1.0
0.3
7.2
1.6
0.5
0.2
2.3
0.7
0.3
3.1
0.9
0.4
4.0
1.2
0.5
0.2
5.1
1.5
0.7
0.3
6.3
1.9
0.8
0.4
0.2
7.6
2.3
1.0
0.5
0.2
2.7
1.2
0.5
0.3
3.7
1.6
0.7
0.4
4.2
1.8
0.8
0.4
4.8
2.1
1.0
0.5
6.1
2.7
1.2
0.6
7.5
3.3
1.5
0.8
4.0
1.8
0.9
4.7
2.2
1.1
For example, consider the arrangement shown in Figure
C-13. There will be three standard 90 degree elbows and
22 feet of straight pipe. If 8" pipe is used, then the total
equivalent pipe length will be:
Equivalent Length = (3 x 17) + 22 = 73 ft.
If this is a 600 BHP 30 ppm system, then the maximum
ductpressure drop is 1.5". The calculated drop is:
Pressure drop = 73 ft. x (3.7"/100 ft) = 2.7"
which is higher than allowed. Adjusting the pipe to 10"
gives a new length of:
Length = (3 x 22) + 22 = 88 ft.
New pressure drop = 88 x (1.1"/100 ft.) = 0.97"
This pressure drop is good.
Changing to a 90 degree "T" as shown in the alternate:
Length = (2 x 22) + 52 + 22 = 118 ft.
New pressure drop is = 118 x (1.1"/100 ft) = 1.3"
This pressure drop is still good. Note the increase pressure
with the side outlet "T". The type of fittings used often has
a bigger impact on pressure drop than pipe size.
The design of the FGR duct must include the following
considerations:
a. Normally the duct would connect to the stack as
shown in Figure C-13, with a 45 degree cut facing
the flue gas flow and with the center of the cut
centered in the stack. The duct could be made to the
smoke box, but must still be located with the same 45º
cut facing the flue gas flow stream and with the center
of the cut in the center of the stream. Do not locate
in an area that does not have a high volume of flue
gas flow, or there may not be enough FGR available.
b. The duct should be routed in a manner that has the
minimum number of elbows and provides for normal
expansion and contraction of the piping. Long duct
runs can change length by over 1" and can put an
extreme load on the connecting points that could
cause component failures. The design must include
offsets that will allow for the required movement of
the piping without undue force on the burner or stack.
c. Duct expansion and contraction can be managed by
using two relatively long duct runs that are 90º
apposed to each other, similar to that shown in Figure
C-13. A small movement in the angle between these
two legs will provide the space needed to absorb the
expansion and contraction. The ends of the FGR duct
must be securely attached to allow this to work
properly, and prevent high loads from being applied to
the burner or stack.
d. A condensation drip leg must be provided upstream
of the FGR control valve and the FGR shutoff valve (if
used). There must be sufficient condensate drip legs
and catch space (volume of drip legs) to prevent the
condensation from flowing through the control valves
Page 25
Section C - Installation
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