Vacuum purging

Use seven minimum, perhaps use eight, for assurance that purging is complete. Note that the above relationships hold for vacuum purging. Keep in mind the relationships between high and low pressure of the system and use mmHg for pressure if more convenient. For sweep-through purging, see Ref. [29]. 

Unlike other methods, it is necessary to posttreat the product, either through vacuum purging or by allowing... 

Vacuum purging is the most common inerting procedure for vessels. This procedure is not used for large storage vessels because they are usually not designed for vacuums and usually can withstand a pressure of only a few inches of water. 

Use a vacuum purging technique to reduce the oxygen concentration within a 1000-gal vessel to 1 ppm. Determine the number of purges required and the total nitrogen used. The temperature is 75°F, and the vessel is originally charged with air under ambient conditions. A vacuum pump is used that reaches 20 mm Hg absolute, and the vacuum is subsequently relieved with pure nitrogen until the pressure returns to 1 atm absolute. 

One practical advantage of pressure purging versus vacuum purging is the potential for cycle time reductions. The pressurization process is much more rapid compared to the relatively slow process of developing a vacuum. Also, the capacity of vacuum systems decreases significantly as the absolute vacuum is decreased. Pressure purging, however, uses more inert gas. Therefore the best purging process is selected based on cost and performance. 

The number of purge cycles is j = 5.6. Thus six pressure purges are required, compared to four for the vacuum purge process. The quantity of nitrogen used for this inerting operation is determined using Equation 7-7 ... 

The purging cycles for an evacuate-first purge are shown in Figure 7-4. In this case the beginning of the cycle is defined as the end of the initial evacuation. The oxygen mole fraction at this point is the same as the initial mole fraction. Furthermore, the remaining cycles are identical to the vacuum purge operation and Equation 7-6 is directly applicable. However, the number of cycles / is the number of cycles after the initial evacuation. 

Equation 7-12 is used in place of Equation 7-6 for both pressure and vacuum purging. 

Determine the number of vacuum purges required to reduce a vessel s oxygen concentration from 21 % to 1 % if the nitrogen contains ... 

After weighing, the munitions are released to a four-unit vacuum purge station. Automatic vacuum/purge nozzles make a vacuum/pressure seal on top of the empty munitions, and a three-way automatic valve... 

Vacuum purge, as well as steam stripping, is used at the end of the cracking step (238). Air at about 45 p.s.i.g. is used for regeneration (130,260). This step is followed by another vacuum purge before placing the case back on stream (238). 

Vacuum Purging. The vessel is evacuated and then is increased to atmospheric pressure using the chosen inert gas. This procedure is repeated until the desired oxygen concentration is reached. The number of vacuum purges, n, required to achieve the desired LOC can be calculated by using the following equation ... 

It must further be observed that inertization is acknowledged as a protective measure only if it is continuously supervised by measurements. A vacuum purge inertization of an apparatus repeated once or twice without any subsequent supervision cannot be accepted as a preventive protecting measure. 

Table 7-2 Achievable degree of inertization by the vacuum purging method...

The low energy X-rays emitted by elements with atomic numbers less than sodium (Z < 11) are easily absorbed by air. Therefore most X-ray systems operate either under vacuum or purged with helium. The entire spectrometer, including the source, sample, optics, and most detectors are within the vacuum/purge chamber. Liquid samples cannot be analyzed under vacuum, so most systems permit the analyst to switch from a vacuum to a helium purge as needed, usually in less than 2 min. 

Chemical polynKrizations were carried out in 10 ml Schlenck tub. The tubes were treated with trimethylsilyl chloride, washed with three S ml portions of methanol, dried at 120 in a oven for 12 h, flame dried and kept in a desiccator to cool down to room temperature. In a glove bag maintained under nitrogen atmosphere the lactone mixture and the catalyst (0.1 molar solution in toluene, monomer to catalyst ratio was 1 2(X)) were transferred into the polymerization tube ami capped with a rubber septum. The tubes were degassed by several vacuum purge cycles to remove the solvent in the catalyst solution and then placed in an oil bath maintained at 120 for 12 h. At the end of die reaction period, the crude sample was collected to estimate the conversion and the contents of the tubes woe dissolved in chloroform (0.5 ml) and precipated in methanol (30 ml) by vigorous stirring and methanol decanted. The precipitate was further washed with methanol (2 X 20 ml). The polymer was dried in a vacuum oven at 40 °C for 24 h and GPC data were recorded. 

The polymerization ampules (10 mL) were treated with trimethylsilyl chloride, washed with three 5 mL portions of methanol, dried at 100 °C in an oven and flame-dried while being purged with dried argon. Monomers and Novozyme-435 were transferred into the ampule under inert nitrogen atmosphere. The ampule was degassed by several vacuum-purge cycles. 

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