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MAN B&W
15.05
Page 1 of 3
MAN Diesel
MAN B&W MC/MCC, ME/MEC/MEGI/ME-B engines
198 40 949.3
Calculation of Exhaust Gas BackPressure
Exhaust gas velocity (v)
In a pipe with diameter D the exhaust gas velocity is:
v =
M
__
ρ
x
4
_____
π
x D
2
in m/s
Pressure losses in pipes (
Δ
p)
For a pipe element, like a bend etc., with the resist-
ance coefficient
ζ
, the corresponding pressure
loss is:
Δ
p =
ζ
x ½
ρ
v
2
x
1
___
9.81
in mm WC
where the expression after
ζ
is the dynamic pres-
sure of the flow in the pipe.
The friction losses in the straight pipes may, as a
guidance, be estimated as :
1 mm WC per 1 diameter length
whereas the positive influence of the updraught
in the vertical pipe is normally negligible.
Pressure losses across components (
Δ
p)
The pressure loss
Δ
p across silencer, exhaust
gas boiler, spark arrester, rain water trap, etc., to
be measured/ stated as shown in Fig. 15.05.01 (at
specified MCR) is normally given by the relevant
manufacturer.
Total backpressure (
Δ
p
M
)
The total backpressure, measured/stated as the stat-
ic pressure in the pipe after the turbocharger, is then:
Δ
p
M
=
Σ Δ
p
where
Δ
p incorporates all pipe elements and
components etc. as described:
Δ
p
M
has to be lower than 350 mm WC.
(At design stage it is recommended to use max.
300 mm WC in order to have some margin for
fouling).
The exhaust gas back pressure after the turbo
charger(s) depends on the total pressure drop in
the exhaust gas piping system.
The components, exhaust gas boiler, silencer, and
spark arrester, if fitted, usually contribute with a
major part of the dynamic pressure drop through
the entire exhaust gas piping system.
The components mentioned are to be specified
so that the sum of the dynamic pressure drop
through the different components should, if pos-
sible, approach 200 mm WC at an exhaust gas
flow volume corresponding to the specified MCR
at tropical ambient conditions. Then there will be
a pressure drop of 100 mm WC for distribution
among the remaining piping system.
Fig. 15.05.01 shows some guidelines regarding
resistance coefficients and backpressure loss
calculations which can be used, if the maker’s
data for backpressure is not available at an early
stage of the project.
The pressure loss calculations have to be based
on the actual exhaust gas amount and tempera-
ture valid for specified MCR. Some general formu-
las and definitions are given in the following.
Exhaust gas data
M: exhaust gas amount at specified MCR in kg/sec.
T: exhaust gas temperature at specified MCR in °C
Please note that the actual exhaust gas tempera-
ture is different before and after the boiler. The
exhaust gas data valid after the turbocharger may
be found in Chapter 6.
Mass density of exhaust gas (
ρ
)
ρ ≅
1.293 x
273
______
273 + T
x 1.015 in kg/m
3
The factor 1.015 refers to the average backpres-
sure of 150 mm WC (0.015 bar) in the exhaust gas
system.
Summary of Contents for S65ME-C8.2-GI-TII
Page 4: ......
Page 10: ......
Page 11: ...MAN B W MAN Diesel Engine Design 1...
Page 12: ......
Page 29: ...MAN B W MAN Diesel Engine Layout and Load Diagrams SFOC 2...
Page 30: ......
Page 53: ...MAN B W MAN Diesel Turbocharger Selection Exhaust Gas By pass 3...
Page 54: ......
Page 58: ......
Page 59: ...MAN B W MAN Diesel Electricity Production 4...
Page 60: ......
Page 100: ......
Page 101: ...MAN B W MAN Diesel Installation Aspects 5...
Page 102: ......
Page 136: ......
Page 145: ...MAN B W MAN Diesel List of Capacities Pumps Coolers Exhaust Gas 6...
Page 146: ......
Page 164: ......
Page 165: ...MAN B W MAN Diesel Fuel 7...
Page 166: ......
Page 186: ......
Page 207: ...MAN B W MAN Diesel Lubricating Oil 8...
Page 208: ......
Page 228: ......
Page 229: ...MAN B W MAN Diesel Cylinder Lubrication 9...
Page 230: ......
Page 239: ...MAN B W MAN Diesel Piston Rod Stuf ng Box Drain Oil 10...
Page 240: ......
Page 242: ......
Page 243: ...MAN B W MAN Diesel Central Cooling Water System 11...
Page 244: ......
Page 249: ...MAN B W MAN Diesel Seawater Cooling System 12...
Page 250: ......
Page 262: ......
Page 263: ...MAN B W MAN Diesel Starting and Control Air 13...
Page 264: ......
Page 269: ...MAN B W MAN Diesel Scavenge Air 14...
Page 270: ......
Page 281: ...MAN B W MAN Diesel Exhaust Gas 15...
Page 282: ......
Page 295: ...MAN B W MAN Diesel Engine Control System 16...
Page 296: ......
Page 316: ......
Page 317: ...MAN B W MAN Diesel Vibration Aspects 17...
Page 318: ......
Page 332: ......
Page 333: ...MAN B W MAN Diesel Monitoring Systems and Instrumentation 18...
Page 334: ......
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Page 360: ......
Page 361: ...MAN B W MAN Diesel Dispatch Pattern Testing Spares and Tools 19...
Page 362: ......
Page 368: ......
Page 380: ......
Page 381: ...MAN B W MAN Diesel Project Support and Documentation 20...
Page 382: ......
Page 391: ...MAN B W MAN Diesel Appendix A...
Page 392: ......