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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 would be the effect of cracking about 10 % atmospheric gas oils blended with vacuum gas oils in the Fluidized Catalytic Cracking Unit (FCCU)?
Keywords:	fccu,fcc,cracking,atmospheric,gas,oils,vacuum,fluidized,catalytic,cracking,unit
Answer:	If by 'atmospheric gas oil' you are referencing material boiling below 344 ⁰C, then addition of this material to the FCC will generally cause an increase in catalyst circulation, a decrease in regenerator temperature and an increase in over all conversion. Much of this effect is due to heat balance considerations. The lighter gas oils generally do not produce sufficient coke to supply the heat necessary to vaporize them and raise them to reactor temperature. Thus, the unit heat balance forces higher conversions to produce the necessary coke from the heavier gas oils. The atmospheric gas oil does crack, but not to the extent of the heavier materials. It also tends to produce a lower octane cat naphtha. It is not uncommon to find this material in FCC feed, though it is more often the result of poor separation in the crude unit rather than a conscious operating decision. Since many of the effects are heat balance related, they are difficult to predict without a well tuned FCC model. If a model is used, it is essential that it correctly predicts the effect of conversion and cat/oil on coke yield.