Gasoline Machines in a Diesel Ruled World | RefinerLink

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Gasoline Machines in a Diesel Ruled World

By Ralph Laurel

Jun 14, 2015

Tips on FCC process optimization in a distillate driven world.


Refinery Cat Cracking used to being the center of attention. People have ooh’ed and aaah’ed at them for decades as they’ve taken gasoil molecules and churned out large quantities of gasoline. Cars were happy, refineries were happy, and a whole generation of Cat Cracking experts went around trying to figure out how to increase gasoline yields and optimize the unit.


So what happens now? If you haven’t heard, diesel will be King. Everyone has gone out and become fuel efficient and now gasoline is being generated out of corn instead of gasoil.


The appetite for maximizing diesel yield will continue to grow and poor Cat Crackers, with their experts, will take a bit of a back seat.



That is, unless we start looking at them in a bit of different light and optimize them to the new set of rules that has been set for us.



Catalyst Reformulation


What was an optimal catalyst five years ago may no longer be optimal today. Regular catalyst evaluations can help you structure Cat Cracker product yields specifically for your refinery and your market.


Not only will a focus on FCC catalyst reformulation help optimize yields but it will optimize operational expenses as well. Yes, we all have heard about rare earth prices, so catalyst expense is indeed a big focus area.



It’s critical that the catalyst vendors are aware of the main objectives you’re trying to accomplish in your FCC catalyst reformulation effort. Working closely with the catalyst vendors will pay out in the end.


This proves true whether the intent is to generate better quality cycle oil for your diesel hydrotreater, or minimize bottoms make.

Recycle Streams


Don’t be afraid to try something new. Things that weren’t even close to economic in the past may all of a sudden be big money makers. Recycling cycle oil or Cat Cracker bottoms will create a big air demand and reduce overall product volume but may still be economic depending on product pricing.


If the uplift between cycle oil and bottoms is huge and the difference between naphtha and cycle oil is smaller, it might make sense to recycle bottoms to make more cycle oil. Economics for each site will be different but the point is, evaluate everything.

Regenerated Catalyst Optimization


That's right, you heard me. I’m not talking about your favorite variable, FCC Riser Top Temperature. I’m asking you to look at the other vessel sitting next to the reactor.



If you’re not trying to constantly shove rate through the unit (more on this to come), I suggest you optimize the temperature of the catalyst in your FCC Regenerator. Lower catalyst temperatures will increase Cat to Oil ratio and provide improved yields.


More catalyst for every barrel of oil will help drive more of the desired reactions. This should be an easy move if you’re not operating to an air constraint. And if you are limited by air demand, it’s possible that a reduction in Riser Top Temperature may be a worthy sacrifice for higher Cat to Oil ratios.


Another reason many refiners choose to operate the catalyst temperature higher than needed is over concerns of high coke on regenerated catalyst. If that’s the case, check with your catalyst vendor about what levels of coke the catalyst can withstand. The newer generation of catalysts may be able to get as high as 0.4 wt% coke without having significant impacts on product yields. 

Rate versus Yields


Maximizing Cat Cracking rate historically had been a norm. It may be time to challenge that norm the economics haven’t been carefully vetted. Increased FCC rate beyond a certain point almost always comes at a cost of yields.


Once the rate increases to a point where the Cat to Oil ratio drops, you’re probably sacrificing yields. Make sure that the marginal barrel is being evaluated correctly and that marginal yields are being used to calculate the economics.


Once an air limit is reached, the marginal yields on a refinery FCC typically tail spin to the point where the last barrel is producing close to 50-60% cycle oil and bottoms. It’s hard to justify extra rate with yields like that.



So with the new set of conditions the market has given, it only makes sense to redefine our optimal operating points. Even if diesel is King, refinery Cat Cracking can still play a vital role in keeping your refinery profitable.

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  • Rick Manner :   Alternate feeds and products are also emerging options for FCCUs . Higherseverity and Light Naphtha feed to produce olefins is a possibility. Biomass or other waste as feeds are possibilities. An FCCU is not the preferred coice to make diesel because LCCO has a very low cetane # and would require significant additional hydrotreating to saturate the aromatics. Short term there is some room for LCCO to replace higher quality diesel boiling range streams as fuel oil cutter stock. In some refineries additional LCCO and slurry production has relatively high value because it frees up higher quality cutter stocks that can be blended into diesel more easily than LCCO FCCUs are being replaced by Hydrocrackers as the preferred way to upgrade VGO. Many older units are likely to be shut down when significant repairs are required. Others may be re-purposed to produce olefins or to operate with novel feedstocks and of course many will continue to produce gasoline and alkylation plant feed.

    Jun 21, 2015

  • Mark Edwards :   When using LCO as feeds to ULSD units, Cetane improvement deltas experienced across ULSD units can be calibrated approximately by using LCO Cetane values calculated in FCC Kinetic Models ULSD product Cetanes from lab measurements are then used to then back-calculate approximate but unknown Cetane improvement effects across ULSD units experienced by Crude unit and purchased high sulfur diesel streams that are then directed as feeds to ULSD units. This is needed and can be approximated using LP runs and some actual plant lab data. This avoids the technical challenge of determining Cetane improvement effects by ULSD unit using ULSD reaction information, which may not be available at all or may be available but not in a timely manner. This may allow quick determination if Cetane improvement may meet the requirements of Cetane for export from America to Europe. If you have multiple FCCs it may also help you determine options for running LCO from different units in a different manner, depending on piping options.

    Jun 21, 2015

  • Nelmo Fernandes :   LCO is a distressed refinery stream with limited future disposition options without further significant upgrading. Refiners will have to consider investments in technology to upgrade the LCO to higher value transportation fuels as they prepare for clean fuels production and increased market demand in the future. I think that a hydrotreating unit for ULSD is the best usually option if you have hydrogen enough.

    Jun 21, 2015

  • Rick Manner :   It will take a lot of H2 and probably noble metal catalyst to turn significant amounts of LCCO into ULSD. gradually replacing Cat Cracking with Hydrocracking is probably a better route but there have been some LCCO Aromatic saturation units built in the past and there will probably be a few more built in the future.

    Jun 23, 2015

  • Nelmo Fernandes :   Considering the cetane number a high severity hydrotreating unit for ULSD will increase this parameter by 6 to 8 points. There will be a reduction in the density of the product as well.

    Jun 23, 2015

  • Rick Manner :   LCCO can have a Cetane number as low as 20. It can by upgraded by 5 to 10 numbers with conventional ULSD hydrotreating and blended off with higher Cetane material or it can be upgraded by 20 or more Cetane numbers in a low temperature noble metal reactor (after preteating to remove S and N) or it can be upgraded pretty well in a Hydrocracker.

    Jun 24, 2015

  • Prateek Gupta :   Light Cycle Oil (LCO) has very high in aromatic content and low Cetane number while having same distillation range. LCO can be upgraded through conventional high severity hydrotreater followed by novel metal catalyst to boost cetane and USLD diesel by decreasing density and saturating the aromatic content. There are some noble process offered in industry like Unisar.

    Jun 24, 2015

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