Page 144 - 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
2
LlPTr = LlPc<I> crr = (0.0254) (1.31) 2 = 0.0438 psi/ft follow), and ( d) the lower limit for application of the
method is
6. Fe= 0.00967 (Wm) 05 /v1'· 7
= 0.00967 (19,494)0.5/(2ll)0.7 W/d 7 20 (2-125)
= 0.032

Vertical elevation pressure drop component: where Wis the flow rate in lbs/hr and d is the inside pipe
diameter in inches. If the above ratio is less than 20, the
= n h fcpdl44 = [(3) (10) + (]) (50)] (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.
LlPTPh = (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- LlP vac (FICDICTI) + (F2CD2CT2) (2- 126)
terns in several different sizes of lines. P1

where LlP,,.c = pressure drop, in. water/100 ft of pipe
Table 2-20
Two-Phase Flow Example Pt = initial pressure, inches mercury absolute
F 1 = base friction factor, Figure 2-43
Horizontal Flow Pattern F 2 = base friction factor, Figure 2-43
Eleva-
Strati- tion Gy, 1 = temperature correction factor, Figure 2-43
Pipe I.D. Annular tied Wave Factor, Ft./sec ..
Inches Psi/Ft. Psi/Ft. Psi/Ft. F. Gas Ve!. � = temperature correction factor, Figure 2-43
3.068 0.0438 0.000367 0.131 0.032 210.9 CD! = diameter correction factor, Figure 2-43
4.026 0.0110 0.000243 0.0336 0.0465 122.5 Cn 2 = diameter correction factor, Figure 2-43
6.065 0.00128 0.000131 0.00434 0.0826 53.9
7.981 0.00027 0.000087 0.00110 0.121 31.1
10.020 0.000062 0.000062 0.00035 0.166 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
atmospheric pressure to some level between atmospheric F1 = 0.0155
barometer and absolute vacuum (which cannot be F2 = 0.07l
attained in an absolute value in the real world), but is CDI = 0.96
used for a reference of measurement. In most situations, C02 = 0.96
a vacuum is created by pumping air out of the container Cn = 1.5
(pipe, vessels) and thereby lowering the pressure. See Fig-
ure 2-1 to distinguish between vacuum gauge and vacuum � = 1.67
absolute. LlP,.,.c = [(0.0155) (0.96) (1.5) + (0.071) (0.96) (l.67)]/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.