Page 230 - Chemical engineering design

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CHEMICAL ENGINEERING
So, total length for P calculation D 120 C 18.4 D 138.4m
138.4 1.98 2 2
P f D 8 ð 0.0032 998 ð D 277,247 N/m
3
25 ð 10 2
D 277 kN/m 2 5.3
Note: the two methods will not give exactly the same result. The method using velocity
heads is the more fundamentally correct approach, but the use of equivalent diameters is
easier to apply and sufficiently accurate for use in design calculations.

5.4.3. Power requirements for pumping liquids
To transport a liquid from one vessel to another through a pipeline, energy has to be
supplied to:
1. overcome the friction losses in the pipes;
2. overcome the miscellaneous losses in the pipe fittings (e.g. bends), valves, instru-
ments etc.;
3. overcome the losses in process equipment (e.g. heat exchangers);
4. overcome any difference in elevation from end to end of the pipe;
5. overcome any difference in pressure between the vessels at each end of the pipeline.
The total energy required can be calculated from the equation:
gz C P/ P f / W D 0 5.5
where W D work done, J/kg,
z D difference in elevations (z 1 z 2 ), m,
2
P D difference in system pressures (P 1 P 2 ), N/m ,
P f D pressure drop due to friction, including miscellaneous losses,
2
and equipment losses, (see section 5.4.2), N/m ,
3
D liquid density, kg/m ,
2
g D acceleration due to gravity, m/s .

P 2

Liquid
P 1 Level
Z 2
Vessel 2
Vessel 1
Z 1 Pump
Datum
Figure 5.8. Piping system