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How to convert PPMw (by weight) to PPMv(Volume) for H2S & moisture(H2O) in gas mixture?
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Submitted Chris Haslego, Nov 21 2011 11:21 AM | Last updated Nov 21 2011 01:29 PM

Category:	Plant Basics
Question:	What are the most common methods of gas purging a vessel?
Keywords:	purge,purging,gas,methods,vacuum,pressure,sweep,through,syphon
Answer:	The four (4) most common methods of batch gas purging are:syphon, vacuum, pressure, and sweep-throughSyphon purging involves filling the vessel with liquid (product or water) and then the gas purge is introduced into the vapor space and the liquid is drained. The purge gas volume is equal to the volume of the vessel.Vacuum purging is perhaps the most common method for purging vessel rated for the needed vacuum condition. Vacuum is drawn on the vessel and then purge gas is used to relieve the vessel to atmospheric pressure. This proceed is often repeated until an acceptable level of a component (usually oxygen) is reached. The acceptable level will determine the number of cycles that will be necessary.Pressure purging involves the introduction of the purge gas under pressure to dilute the component gas. Then the vessel is relieved to atmosphere (or other treatment device depending on the gas component to be diluted). Then additional pressure cycles can be executed to reach the desired component level.Sweep-through purging is common used for vessels that are not rated for sufficient pressure or vacuum conditions. Purge gas enters one connections and is simultaneously withdrawn from another connection until the component level is within acceptable limits.Reference: CEP Magazine, February 2001