Purging techniques

The best purge method is to evacuate the system and then fill the system with an inert gas such as nitrogen. 

Second best is to run nitrogen through the system until all contaminants are expelled and replaced with nitrogen. 

No matter what method is used to purge, the purge process should be repeated at least six times. 

Purging can be done from 2 to 20 psi, though purging can be done at any pressure desired, as long as the system will allow and contain the pressure. 

Consider nitrogen purging a fundamental and necessary task for operating a hydrogen system. 

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Michael LC, Erickson MD, Parks SP, et al. 1980. Volatile environmental pollutants in biological matrices with a headspace purge technique. Anal Chem 52 1836-1841. 

M.90 (sediment/water, initial-final values of 5-100 d contact time, gas-purge technique-HPLC/fluo., ten Hulscher et al. 2003)... 

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. 

Use the sweep-through purging technique to reduce the concentration of toluene from an initial 20% to 1 % in a room with a volume of 25,000 ft3. Assume that the room is purged with air at a rate of 6 room volumes per hour. How long will it take to complete this purge process ... 

Modern leak detectors are being more frequently equipped with oil-free vacuum systems, the so-called dry leak detectors (UL 200 dry, UL 500 dry). Here the problem of gas being dissolved in oil does not occur but similar purging techniques will nonetheless be employed. 

Low-flow minimal drawdown or micro-purge technique... 

Remove the pump from the well. (If not sampling with a bailer, go to Step 5 of low-flow micro-purge technique, described below in Chapter 3.6.2.4.)... 

Closing or capping machine Shroud or purge technique Blanketing or purging Undetermined... 

Fig. 11-2. Comparison of sorption-kinetic data for chlorinated benzenes obtained using the gas-purge technique. Figure was taken from Brusseau et al., (1990a).

Unusual circumstances, however, may defeat any of these gas-purging techniques. It should also be remembered that batteries generate a significant amount of explosive gas during the maintenance procedure, and therefore maintenance should always be performed in a well-ventilated shop. 

To receive alloys, there are additional purification and alloying procedures. Raw A1 is purified from metallic and gaseous admixtures and fi-om sodium and calcium by a gas purging technique. Aluminium goes through the launders to the degassing unit and then to the direct chill mold. 

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