Page 142 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

128 Applied Process Design for Chemical and Petrochemical Plants

5. Two-phase flow for horizontal flows: lent flow, (b) sub-atmosphere pressure, (c) pressure drop
is limited to 10% of the final pressure (see comment to
APTP = APGQ‘GT~ = (0.0254) (1.31)2 = 0.0438 psi/ft follow), and (d) the lower limit for application of the
method is
6. F, = 0.00967 (Wm)0.3/v0.7
= 0.00967 ( 19,494)0.5/(211)0.7 W/d7 20 (2-125)
= 0.032

Vertical elevation pressure drop component: where W is the flow rate in Ibs/hr and d is the inside pipe
diameter in inches. If the above ratio is less than 20, the
= n h F,pL/144 = [(3) (10) + (1) (SO)] (0.032) (63)/144 flow is “streamlined” and the data does not apply.
= 1.125 psi total If the pressure drop is greater than 10% of the final
pressure, the pipe length can be divided into sections and
Total: the calculations made for each section, maintaining the
same criteria of (c) and (d) above.
APph = (0.0438) (358) + 1.125
= 16.7 psi, total for pipe line
Method [54]
Because these calculations are somewhat uncertain
due to lack of exact correlations, it is best to calculate The method solves the equation (see Figure 2-43)
pressure drop for other flow patterns, and apply a gener-
ous safety factor to the results.
Table 2-20 gives calculated results for other flow pat- (2 - 126)
terns in several different sizes of lines.

where AP”,, = pressure drop, in. water/100 ft of pipe
Table 2-20
Two-Phase Flow Example p1 = initial pressure, inches mercury absolute
Fl = base friction factor, Figure 2-43
Pipe I.D. 1 Annular 1 Strati- I 1 Eleva- 1 I CT1 = temperature correction factor, Figure 2-43
1 Horizoytal Flow Pattern
F, = base friction factor, Figure 2-43
fied 1 Wave 1 ‘$”.”
Factor, Ft./sec..
CT2 = temperature correction factor, Figure 2-43
Inches
Psi/Ft.
Psi/Ft.
Psi/Ft.
4.026 1 0.0110 1 0.0002431 0.0336 1 :::si5 1 I-- Gas Vel. CDl = diameter correction factor, Figure 2-43
I
I
I
I
0.000367 0.131
210.9
3.068
0.0438
1 0.000062 I 0.000062 1 0.00035 I 0.166 I 31.1
53.9
6.065 0.00128 0.000131 0.00434 0.0826 122.5 C,, = diameter correction factor, Figure 2-43
0.121
0.000087 0.00110
0.00027
19.7
Example 2-17: Line Sizing for Vacuum Conditions
Determine the proper line size for a 350 equivalent
feet vacuum jet suction line drawing air at 350”F, at a rate
Pressure Drop in Vacuum Systems of 255 lbs/hr with an initial pressure at the source of 0.6
in. Hg. Abs. Assume 10-in. pipe reading Figure 2-43. Note:
Vacuum in process systems refers to an absolute pressure watch scales carefully.
that is less than or below the local barometric pressure at
the location. It is a measure of the degree of removal of F, = 0.0155
atmospheric pressure to some level between atmospheric
barometer and absolute vacuum (which cannot be F, = 0.071
attained in an absolute value in the real world), but is CD1 = 0.96
used for a reference of measurement. In most situations, CDz = 0.96
a vacuum is created by pumping air out of the container CT1 = 1.5
(pipe, vessels) and thereby lowering the pressure. See Fig-
ure 2-1 to distinguish between vacuum gauge and vacuum CT2 = 1.67
absolute. APmc = [(0.0155) (0.96) (1.5) + (0.071) (0.96) (1.67)1/0.6
This method [54] is for applications involving air or = (0.02232 + 0.1138)/0.6
steam in cylindrical piping under conditions of (a) turbu- = 0.2269 in. water/100 ft.