Page 149 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Fluid Flow 133

Table 2-21 The suction pressure required at the vacuum pump (in
Criteria for Sizing Connecting Lines in Vacuum Service absolute pressure) is the actual process equipment operat-
ing pressure minus the pressure loss between the process
Vacuum pump Assumed flow velocity, ft/ s
equipment and the source of the vacuum. Note that absolute
Steam.jet: pressures must be used for these determinations and not
System pressure, torr gauge pressures. Also keep in mind that the absolute pres-
0.5-5 300 sure at the vacuum pump must always be a lower absolute
5-25 250
25-150 200 pressure than the absolute pressure at the process.
150--760 150
Liquid ring pump: Pipe Sizing for Non-Newtonian Flow
Single-stage" 100
Two-stage 150 Non-Newtonian fluids vary significantly in their prop-
Rotary piston: erties that control flow and pressure loss during flow from
Single-stage 50 the properties of Newtonian fluids. The key factors influ-
Two-stage 25 encing non-Newtonian fluids are their shear thinning or
Rotary vane.j thickening characteristics and time dependency of viscos-
Single-stage 200 ity on the stress in the fluid.
Two-stage 400 Most conventional chemical and petrochemical plants
Rotary blowers: do not process many, if any, non-Newtonian fluids. How-
Atmospheric discharge 50 ever, polymers, grease, heavy oils, cellulose compounds,
Discharging to backing pump 100
paints, fine chalk suspensions in water, some asphalts, and
�Assumes the pump features dual inlet connections and that an inlet other materials do exhibit one type or another of the
manifold will be used. characteristics of non-Newtonians, classified as:
+Based on rough vacuum process pumps. Use 25 ft/s for high vacuum
pumps.
By permission, Ryans.]. L. and Roper, D. L., Process Vacuum System Design • Bingham plastics
and Operation, McGraw-Hill Book Co. Inc., 1986 [18]. • Dilatant
• Pseudoplastic
• Yield pseudoplastics
of Figure 2-47, increase the pipe size and repeat the cal-
culations until an acceptable balance is obtained. For ini- Solving these classes of flow problems requires specific
tial estimates, the authors [ 18] recommend using 0.6 data on the fluid, which is often not in the public litera-
times the value obtained from Figure 2-4 7 for an accept- ture, or requires laboratory determinations using a rota-
able pressure loss between vessel and the pump. tional viscometer. The results do not allow use of the usual

1000
8
6

4
3 - ... -�
.. 2 - -Wui

� -�
ci J I � .
i �i---... es1gn as,s ""'"'�
·g 100
"ii 8 .
Miniin�rri
> 6 � � .......
..---
4 -�
3
Figure 2-46. Typical flow velocities for vacuum lines. 2 .
Note: 1 torr = 1.33 mb = 133.3 Pa. 1.0 ft/sec = 0.3048
rn/sec, By permission, Ryans, J. L. and Roper, D. L., 10
Process Vacuum System Design & Operation, McGraw- 1 2 3 466789 2 3 456789100 2 3 4 567891000
Hill Book Co., Inc., 1986 [18]. Pressure, torr