Q & A > Question Details
Clarified Oil (CLO) is coming from bottom of fractionator in FCC. Does it relate to catalyst-oil circulation and catalyst properties? How can we reduce the CLO quantity from main fractionator bottom?
01/03/2011 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
Increasing the severity of cracking can decrease your CLO make, however what slurry oil you do make will then be more concentrated, and also having higher solids content with respect to ash & FCC catalyst fines in the MCB bottoms. So to do that does also mean your CLO treatment becomes more difficult. (same amount of cat fines in small quantity of CLO plus sometimes higher asphatene & dienne content as well).
Of course utilising a lighter FCC feed will also reduce your slurry oil make, but there is margin advantages in using the heavier feedstocks and that trend is continuing.
18/02/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
Increased conversion means, in general, less bottoms product. Any combination of variables that increase conversion will reduce bottoms yield. Two of those variables are riser outlet temperature (ROT) and cat to oil ratio (Cat/Oil). Also, bottoms cracking additives in the catalyst will have a similar result (See the current issue of PTQ, article by Albemarle).
18/02/2011 A: Alan Goelzer, Jacobs Consultancy, alan.goelzer@jacobs.com
Fluid catalytic cracking always yields Dusty FCC Slurry Oil & FCC Heavy Cycle Oil [combined nominal 350C to 525C with catalyst fines = 0.1-0.2 wt% before special filtration]. These 350C+ distillates are an integral part of the co-product spectrum within the FCC riser reactor effluent vapours. When operating at higher FCC riser outlet temperatures [say 530C to 545C], yield of 350C+ SLO + HCO will reflect weight percent higher carbon number PNA cores within the cat feed plus natural polymerization of some light olefins.
The Am3/hr flow of FCC slurry oil to the quench zone [preferably using alloy grid packings] and the Am3/hr flow of FCC heavy cycle oil within the HCO pump-around zone should reflect "high wetting flux' principles and steam generator tubeside velocity criteria and should NOT be directly related to net draws of SLO + HCO.
If the catalyst content in the FCC Slurry Oil is above 0.2 wt% and FCC SLO + HCO make is with the 3 wt% to 8 wt% range, then riser terminator & reactor cyclones & reactor stripper & regenerator cyclones may be "worn out" or poorly conceived.
Some refiners choose to recycle FCC SLO + HCO with cat feed in order to reduce net make. But, be aware that upwards of one-third of FCC SLO + HCO recycled can become "additional coke". VGO FCC Units are in particular "not good cokers".