A FCC typically creates an extra 10-15 percent in yield (product volume/feed volume) due to the cracking taking place. As you reduce cracking you’re losing volume and total barrels of value… typically olefins and LPG. While the value of natural gas is in the gutter these days, free volume still carries a large incentive.

Reducing cracking also means you’re deconverting LCO into cat bottoms. While cycle oil prices follow closely with diesel prices, cat bottoms prices are closer in parity to fuel oil – more specifically carbon black. There’s often a large spread between LCO and HCO value, so make sure you’re not losing more there than you’re gaining with the gas to diesel spread.

There may be more effective ways of increasing LCO

Have you thought about recycling bottoms to the reactor? Cat bottoms is typically one of the lower value products a refinery has. If you’re willing to sacrifice volume growth and have some available air, why not make LCO out of bottoms instead of gasoline?

Reconsider where you’re running on ecat activity or even think about reformulating your fresh catalyst. There may be an option to maintain riser temperature but spend a little less on catalyst while you make more LCO.

Even if it comes out of the reactor as LCO will it leave the fractionators as LCO? Are there diesel molecules that you’re not currently capturing?

Is your FCC fractionator capable of handling the extra LCO? Or is it just going to drop down into bottoms putting you right back where you started?  Some sites may even want to consider adding a cat bottoms stripper to recover every possible LCO molecule.

In an ideal world, LCO and HCO draw streams should be constrained by quality specs for you to feel happy that you are maximizing LCO recovery:

• Minimize LCO flash to maximize as much FCC gasoline undercut into diesel
• Maximize LCO 90% to increase distillate molecules recovered from HCO
• Minimize HCO API to ensure that distillate molecules have been recovered from HCO

Don’t forget to keep downstream unit operability in mind!  Since LCO often requires additional hydroprocessing, ensure that LCO optimization does not adversely affect catalyst runlength or the refinery hydrogen balance. 

At the end of the day, there are many reasons why refineries should focus on maximizing LCO production in today’s economics.  The simple truth is that this is a challenging problem that requires considerable evaluation. Whether LCO is used as fuel oil cutter or incremental diesel hydrotreater feed, there are high margins at stake.