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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:	How can the LPG levels in dry gas be controlled in FCC plants?
Keywords:	lpg,dry,gas
Answer:	LPG (C3's and C4's) in the dry gas are normally controlled by the operation of the primary absorber. Operationally, increasing the lean oil rate to the absorber should decrease the LPG in the dry gas. If the unit has recycle lean oil from the debutanizer then this can be increased. If there is no recycle lean oil, then decreasing the main fractionator overhead accumulator temperature or increasing its pressure would increase the amount of liquid condensed and thus the lean oil rate to the primary absorber. Decreasing the stripping rate in the stripper (deethanizer) will also decrease the C3's and C4's lost to dry gas. The limit to this option is normally the build up of non-condensables in the debutanizer overhead drum. Modifications that would increase the recovery of C3 and C4 material (and thus decrease the loss) would include the addtion of intercoolers on the primary absorber or chilled water systems to cool the lean oil to the absorber. Other modifications may also be possible depending on the configuration of the current gas plant.