Page 102 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

86 Applied Process Design for Chemical and Petrochemical Plants

Summation: Pressure drop = i:'.P = 0.00001799 Kp Q2/d 4 (2-52)
= 0.00001799 (52.48) ( 48.6)
K = [4.38 + 7.45* + 3.94 + 0.175* + l.O] = 16.941 (350)2/ ( 4.026) 4
i:'.P = 21.2 psi friction pressure loss only
*Threaded, from Table 2-2. (no elevation change)
For fittings:
Alternate Calculation Basis for Piping System Friction
Head Loss: Liquids
16.941 (4.292)
Lhen, h = Kv /2g = = 4.84 ft kerosene Pressure loss in a piping system (not including the
2
2(32. 2)
tanks, heat exchangers, distillation columns, etc.) is usu-
Total friction loss for discharge side pump due to fric- ally expressed in units of feet of flowing fluid, or the equiua-
tion: lent converted to pounds per square inch. Some published
pressure loss data is expressed as per 100 equioalent feet of
h = 11.64 + 4.84 = 16.48 ft fluid kerosene the size pipe being used or estimated.
hr= L'ip = 16.48/((2.31)/(0.81)) = 5.77 psi
Equivalent Feet Concept for Valves, Fittings, Etc.
Example 2-2: Laminar Flow Through Piping System
With pipe of any specified size as the basis, the total
A heavy weight oil, No. 5 fuel oil, is to be pumped footage of straight pipe in a system is just the measured
through 350 ft or existing 4-in. Schedule 40 pipe at 350 length (totaled).
gpm. Oil data: For fittings, valves, etc., in the same system, these can
be expressed as equivalent straight pipe, then added to the
Temperature = 100°F straight pipe described above, to arrive at a total equiva-
Viscosity = 150 cp lent straight length of pipe of the specific size in question.
Sp Gr= 0.78 = 48.6 lb/cu ft Figure 2-20 presents equivalent lengths of straight pipe
Pipe I.D. = 4.026 in. = 0.3355 ft (feet) for various pipe system components. For example,
a standard threaded 6-inch 90° elbow is equivalent to
Reynolds number= 50.6 Qp/(dµ) adding 17 feet of straight pipe to the system. This 17 feet
= 50.6 [ (350) ( 48.6) I ( 4.026) (150) l is additive to the lengths of nominal 6-inch straight pipe
= 1425 (2-50) in the system (dotted line). However, there is an impor-
tant consideration in the use of this chart, i.e., use only for
Flow is <2000, therefore, flow of viscous or laminar sys- threaded or screwed pipe/fittings, and only for sizes
tem consists or friction factor, fT, for 4-in. pipe = 0.017 under 2-inch nominal size. It is not practical in current
(Table 2-2). industry practice to thread a process or utility system
much greater in nominal diameter than 2 inches. For spe-
1 gate valve= K = 8 fr = 8 (0.017) = 0.136, (Table 2-2) cial situations, the larger sizes can be used, but from a
3 90° = K = 20 fr = 20 (0.017) = 0.345 handling standpoint, sizes greater than 3 inches or 4 inch-
1 90° = RID = 5; 5/D = 0.00045 (Figure 2-11); K = es are not practical.
0.1 (Figure 2-13A) For pipe sizes greater than 2 inches nominal, industry
1 pipe entrance to tank projecting inward, K = 0.78 practice is to weld the pipe and fittings into one continu-
(Table 2-2) ous system, and then use flanged or special bolted con-
For 350 ft pipe, K = f (L/D) = 0.0449 (350/0.3355) = nections for attaching the valves, orifices, and connec-
51.12 tions to vessels or other equipment: For special lethal,
[For f, see calculations below] high pressure, and steam power plant high tempera-
ture/high pressure utility systems, even the valves and
f = 64/Rc connections to vessels are welded into the system (See
f = 64/1425 = 0.0449 (2-17) ASME and Ai'\TSI Codes). For these situations of about 1 �-
inch to 2-inch nominal pipe size and larger, use Figure 2-
Total K values =51.12 + 0.78 + 0.1 + 0.136 + 0.345 = 21 to determine the equivalent pipe lengths for these fit-
52.48 tings, valves, etc. For example, a 45° welding elbow, or an
open 6-inch gate valve (see line on chart) have an equiva-
Velocity v, = 0.4.-08 Qld2 = 0.408 (350)/ ( 4.026) 2 lent length of 6-inch pipe of four feet (straight), which is
= 8.8 ft/sec (2-51) an addition to the actual straight pipe in the system. In