Page 99 - Applied Process Design for Chemical and Petrochemical Plants Volume I

86 Applied Process Design for Chemical and Petrochemical Plants

Summation: Pressure drop = AP = 0.00001799 Kp Q2/d4 (2-52)
= 0.00001799 (52.48) (48.6)
K = [4.38 + 7.45" + 3.94 + 0.175" + 1.01 = 16.941 (350)*/ (4.026)4
AP = 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

then, h = Kv"2g = 16.941 (4'292 ) = 4.84 ft kerosene Pressure loss in a piping system (not including the
2(32.2)
tanks, heat exchangers, distillation columns, etc.) is usu-
Total friction loss for discharge side pump due to fiic- ally expressed in units of feet offlowingfluid, or the equiva-
tion: lent converted to pounds per square inch. Some published
pressure loss data is expressed as per 100 equivalentfeet of
the size pipe being used or estimated.
h = 11.64 + 4.84 = 16.48 ft fluid kerosene
hf = Ap = 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
footage of straight pipe in a system is just the measured
A heavy weight oil, No. 5 fuel oil, is to be pumped
through 350 ft of existing 4in. 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/(dp) adding 17 feet of straight pipe to the system. This 17 feet
= 50.6 [ (350) (48.6)/(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 of friction factor, fT, for 4in. 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 fT = 8 (0.017) = 0.136, (Table 2-2) cial situations, the larger sizes can be used, but from a
3 90" = K = 20 fT = 20 (0.017) = 0.345 handling standpoint, sizes greater than 3 inches or 4 inch-
1 90" = R/D = 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/& connections to vessels are welded into the system (See
f = 64/1425 = 0.0449 (2-1 7) ASME and ANSI Codes). For these situations of about 1%-
inch to 2-inch nominal pipe size and larger, use Figure 2-

Total Kvalues =51.12 + 0.7'8 + 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-
Velocityv, = 0.408 Q/d2 = 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