Page 237 - Chemical engineering design

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PIPING AND INSTRUMENTATION
The total length of the pipeline from the rail tanker outlet to the pump inlet is 50 m.
The vertical distance from the tank outlet to the pump inlet is 10 m. Commercial steel
piping, 50 mm internal diameter, is used.
Miscellaneous friction losses due to the tanker outlet constriction and the pipe fittings
in the inlet piping, are equivalent to 1000 equivalent pipe diameters. The vapour pressure
2
of chlorine at the maximum temperature reached at the pump is 685 kN/m and its density
3
2
and viscosity, 1286 kg/m and 0.364 mNm s. The pressure in the tanker is 7 bara.
Solution
Friction losses

Miscellaneous losses D 1000 ð 50 ð 10 3 D 50 m of pipe
Total length of inlet piping D 50 C 50 D 100 m
Relative roughness, e/d D 0.046/50 D 0.001
3 2 3 2
Pipe cross-sectional area D 50 ð 10 D 1.96 ð 10 m
4
16,000 1 1
Velocity, u D ð ð D 1.76 m/s
3600 1.96 ð 10 3 1286
1286 ð 1.76 ð 50 ð 10 3 5
Reynolds number D D 3.1 ð 10 5.4
0.364 ð 10 3
Friction factor from Figure 5.7, f D 0.00225
100 1.76 2 2
P f D 8 ð 0.00225 ð 1286 ð D 71,703 N/m 5.3
3
50 ð 10 2
7 ð 10 5 71.703 685 ð 10 3
NPSH D C 10 5.7
1286 ð 9.8 1286 ð 9.8 1286 ð 9.8
D 55.5 C 10 5.7 54.4 D 5.4m

5.4.7. Pump and other shaft seals
A seal must be made where a rotating shaft passes through the casing of a pump, or the
wall of a vessel. The seal must serve several functions:

1. To keep the liquid contained.
2. To prevent ingress of incompatible fluids, such as air.
3. To prevent escape of flammable or toxic materials.

Packed glands
The simplest, and oldest, form of seal is the packed gland, or stuffing box, Figure 5.12.
Its applications range from: sealing the stems of the water taps in every home, to proving
the seal on industrial pumps, agitator and valve shafts.