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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:	Refining
Question:	What technologies are commonly employed to purify hydrogen from a reforming unit?
Keywords:	v1i8,hydrogen,purify,purity,purification,separation,reforming,reformer
Answer:	There are three (3) commonly used technologies to purify hydrogen from reformers. The determination of which one to use depends on a number of factors.If the hydrogen must be 99% by volume pure, then Pressure Swing Adsorption (PSA) is the most common choice. The other two technologies are rarely capable of this purity. Instead, they're generally able to reach 95-98% by volume purity.If the purity required is in the range of 95-98% by volume and the feed gas is at a pressure of 2-5 times that required for the product hydrogen stream, then membrane separation can be employed. Obviously the pressure loss in such a system is substantial.If the feed gas stream contains substantial byproducts that are to be recovered and a hydrogen purity of 95-98% by volume is acceptable, then a cryogenic unit is a good choice. Byproducts can be recovered from PSA unit off-gases but the low pressure at which this stream is available often make byproduct recover uneconomical.Another consideration is the capacity of the product hydrogen stream. PSA units are built for 5-100 MMscfd of hydrogen. PSA units and cryogenic units have excellent economies of scale for large capacities. Membrane units are generally a better option for smaller capacities.Reference: Hydrocarbon Processing Magazine, February 2003