Page 113 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Fluid Flow 99

Example 2-6: Water Hammer Pressure Development 1. From Table 2-4, selected velocity = 6 fps.

An 8-inch process pipe for transferring 2000 GPM of Estimated pipe diameter, d = (0.408 Q/V)'/~
methanol of Sp Gr = 0.75 from the manufacturing plant = [ (0.408) 25/61 'I2 = 1.3 inch
site to a user plant location is 2,000 feet long, and the liq-
uid is flowing at 10.8 ft/sec. Try 1X-inch (i.d. = 1.61), since 1%-inch (i.d. =
Maximum pressui-e developed (preliminary solution) 1.38) is not stocked in every plant. If it is an accept-
when an emergency control valve suddenly closes: able plant pipe size, then it should be considered
and checked, as it would probably be as good pres-
sure drop-wise as the 1Minch. The support of 1%-
inch pipe may require shorter support spans than
the 1Xinch. Most plants prefer a minimum of 1%
Since methanol has many properties similar to water: inch valves on pressure vessels, tanks, etc. The valves
at the vessels should be 1% inch even though the
a, = 4660/(1 + Qs B,)l12 pipe might be 1% inch The control valve system of
= 4660/[1 -r 0.01 (24.7x)]1/2 = 4175 ft/sec gate and globe valves could very well be 1% inch. For
this example, use lMinch pipe, Schedule 40:
Tor 8-inch std pipe, = 7.981/0.322 = 24.78
2 Linear length of straight pipe, E = 254 ft.
Time interval for pressure wave travel: 3. Equivalent lengths of fittings, valves, etc.

ts = 2L/a, = 2 (2000)/4175 = 0.95 sec (2-71) Estimated q. Feet
Fittings Type (from Figure 2-20)
If the shutoff time for the valve (or a pump) is less than
0.95 seconds, the watter hammer pressure will be: 10 1%'-90" Elbows 4' (10) = 40
8 1V-Tees 3' (8) = 24
4 lY-Gate Valves 1' (4) = 4
hwh = 4175 (10.8)/32.2 = 1400 ft of methanol 68 fi. Use 75 ft.
= (1400)/[(2.31)/0.73)] = 454 psi hydraulic shock

Then total pressure on the pipe system 4. No expansion or contraction losses (except control
valve).
5. Pressure drop allowance assumed for orifice plate =
= 454 + (existing pressure from process/or pump)
5 psig.
This pressure level would most 1.ikely rupture an 8-inch Control valve loss will be by difference, trying to
Sch. 40 pipe^ For a imore exact solution, refer to specialty maintain minimum 60% of pipe friction loss as min-
articles on the subject. imum drop through valve, but usually not less than
10 psi.
Example 2-7: Pipe Elow System With Liquid of Specific
Gravity Other Than Water 6. Reynolds number, & = 50.6 (2-49)
= 50.6 (25) C0.93 (62.3)]/
This is illustrated1 by line size sheet, Figure 2-28. (1.61) (0.91)
= 50,025 (turbulent)
Figure 2-29 represents a liquid reactor system discharg-
ing crude product similar to glycoll through a flow control 7. From Figure 2-11, &/d = 0.0012 for 1Kinch steel pipe.
valve and orifice into a storage tank. The reactor is at 350
psig and 280°F with the liquid of 0.93 specific gravity and From Figure 2-3, at R, = 50,025, read f = 0.021
0.91 centipoise viscosity. There is essentially no flashing of
liquid across the control valve.
8. Pressure drop per 100 feet of pipe:
Flow rate: 1 P ,000 1Whr AF'/100' = 0.0216 fp Q2/d5 (2-72)
GPM actual = 11,000/(60) (8.33) (0.93) = 23.7 = 0.0216 (0.021) (62.3) (0.93) (25)2/(1.61)5
Design rate = 23.;' (1.05) = 25 gpm = 1.52 psi/100 ft equivalent