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Basics in Process Design
Pressure in pipe systems
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Chemical Engineering Design,
Towler, Sinnott, 2013
Block flow diagrams
Calculate flows from mass and
energy balances
Rough sizing of equipment for
– storage
– preprocessing
– reaction
– separation,
– heat exchange
– transport
Instrumentation
Cost estimates
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Today
Factors influencing
pressure in pipes
Modelling
Local pressure
System curve
Typical questions
Example
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Factors influencing
pressure drop in pipes
Height difference, inlet and outlet pressure,
flow velocity
Pipe length, pipe diameter, surface roughness,
pipe fittings, configuration
Fluid density and viscosity
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Modelling
Draw a diagram of the pipe system
Divide the pipe system into logical sections
Note what is known and unknown (flow velocity/
inlet pressure/ outlet pressure/ pressure drop/
pipe length/ pipe diameter/ pipe parts/ height
differences/ densities/ viscosities/ pipe data ...
For each section:
– Outlet pressure = inlet pressure – pressure drop
2
2
1wpzzgpp pumpoutininout
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Local pressure
Pressure at each section boundary
Plotted against pipe length
Fluid might change phase if pressure too low → could change flow calculations
Can the pipe handle the pressure?
119
120
121
122
123
124
125
126
127
128
129
0 2 4 6 8 10 12
pipe length from inlet (m)
pre
ssu
re (
kP
a)
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System curve
Necessary pressure increase or
decrease in pipe system
for certain flows
Can be used with
pump curves or
valve curves
2
2
1wzzgppp outininoutpump
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Typical questions
inlet pressure, outlet pressure, pipe system and fluid properties → flow in pipe
flow, outlet pressure, pipe system and fluid properties → inlet pressure
flow, outlet pressure, inlet pressure and fluid properties → pipe system
Iterative solution – guess, calculate, check, guess better, calculate ....
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Flow velocity
0
20000
40000
60000
80000
100000
120000
140000
160000
180000
0 0,5 1 1,5 2 2,5 3 3,5 4 4,5 5
tota
l p
rice (€
)
flow velocity (m/s)
cost of
pumping
cost of pipe
total cost
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Example
Pump ammonia from synthesis to storage tank
Inlet pressure 3 bar, temperature -33 C
Outlet 30 m higher than inlet and 200 m away
Pipe size? Necessary pressure increase in
pump at different volume flows
Ammonia properties? Pipe roughness?
– http://www.peacesoftware.de/einigewerte/nh3_e.ht
ml
– http://www.engineeringtoolbox.com/ammonia-
d_971.html
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Questions?