Vacuum systems design recommendations

The overall recommendation for the roller compaction system design that minimizes bypass is to employ a higher surface roughness or textured surface on the rolls, rolls oriented similar to vi or vii, and to conduct an assessment of vacuum deaeration. 

The most efficient way to prevent the liquid from an oil or mercury pressure gauge or bubbler from spilling into the rest of your vacuum system is to place a liquid trap between the liquid container and the vacuum system. The liquid trap design is fairly straightforward (see Fig. 7.36), and the installation of one is strongly recommended. 

Atmospheric and superatmospheric systems are usually designed for 5 to 25 percent vaporization (68, 356, 357, 372), with 20 to 25 percent being typical. For nonfouling vacuum systems, 50 percent vaporization has been recommended (181). 

Precondensers are recommended for any ejector system when the pressure conditions and coolant temperature will allow condensation of vapors, thus reducing the required design and operating load on the ejectors. This is usually the situation when operating a distillation column under vacuum. The overhead vapors are condensed in a unit designed to operate at top column pressure, with only the non-condensables and vapors remaining after condensation passing to the ejector system. 

Pressure drop. Packed towers are designed so that the pressure drop at any point in the tower does not exceed a recommended maximum value. Maximum pressure drop criteria for packed towers are listed in Table 8.4. For vacuum distillation, foaming systems, and where fan horsepower needs to be minimized, the pressure drop criteria frequently set tower diameter. 

It is recommended that pilot testing be used in developing design criteria for the site-specific conditions and MF/UF product selection. Both pressure-type MF/UF systems, where the membranes are encased in pressiue vessels, and vacuum-type systems, where the membrane are immersed in tanks open to atmosphere and use fUtrate/permeate pumps to create the driving force, may be used for seawater pretreatment. 

Vacuum-transferrable volatile materials (b.p. up to about 180-200 C) often encountered include (aside from those prepared as intermediates in the radiochemical laboratory) commercial building blocks such as [ C] methyl iodide and other low-molecular-weight carbon-14-labeled alkyl halides, methanol, ethanol, benzene, acetic and haloacetic acids, acetyl and haloacetyl chlorides and dimethylformamide. These compounds are most appropriately handled on vacuum manifolds in the same way as gases, but some may, with proper experimental design, be used without such systems. In the latter case, it is strongly recommended that safety measures be taken against the possibility of the release of volatile radioactivity. 

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