Page 399 - APPLIED PROCESS DESIGN FOR CHEMICAL AND PETROCHEMICAL PLANTS, Volume 1, 3rd Edition

Ejectors and Mechanical Vacuum Systems 367

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SYSTEM VOLUME-CUBIC FEET MAXIMUM AIR LEAKAGE VALUES FOR .,....
COMMERCIALLY TIGHT SYSTEMS
Notes:
1.) The air leakage rates indicated are guidelines only. In actual field practice, the air
leakage may be significantly larger or smaller depending upon the condition of seat-
ing, maintenance factors, and application.
2.) For comparison purposes, alternate methods of air leakage estimation may be used.

Figure 6-21. Maximum air leakage values for commercially tight systems. Reprinted by permission [11 ].

or the alternate method using Table 6-7 may be checked, The saturation pressure corresponds to a temperature
or even multiplied by 2 or 3. of79° - 7.5°F = 71.5°F, based on condenser-ejector design
practice. The pressure from steam tables= 0.78 in. Hg abs.
The water vapor to saturate tl1e air going to the ejector is:
Example 6-9: Ejector Load For Steam Surface
Condenser pv
w' = 0.62 - = (0.62) (0.78)/(l - 0.78) (6- 8)
\' p
a
= 2.19 lbs water vapor/lb air
A surface condenser condensing the steam from a
process turbine drive operates at 1.0 in. Hg abs. The con- From Table 6-6 the recommended dry air SCFM = 5.0
densing load is 85,000 lbs/hr steam. What is the capacity The equivalent
of the ejector?
lbs/hr = (5.0) (60) (0.075 lb/ cu ft) = 22.5
The temperature of the condensing steam at 1.0 in. Hg Total water vapor= (2.19) (22.5) = 49.4 lbs/hr
is 79°F (from steam-tables). Total vapor mixture to ejector = 49.4 + 22.5 = 71.9 lbs/hr