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FCCU Constraints

I would classify an FCCU or an RFCCU as under-utilized with two very different and distinct definitions. The first definition of an under-utilized FCCU/RFCCU is based upon the unit as a stand-alone entity. I do not necessarily consider the unit under-utilized if it is not at maximum feed throughput/rate or at maximum conversion. The true test of the definition for an under-utilized unit is if the unit is constrained.

  1. main air blower (MAB);
  2. wet gas compressor (WGC);
  3. hydraulically on catalyst circulation or slide valve;
  4. main fractionator bottoms (MFB) heat removal capacity;
  5. main fractionator overhead (MFO) cooling/condensing capacity;
  6. hydraulically in the vapor recovery unit (VRU) area?

Shaw S&W integrated FCCU complexIf the unit is not constrained, then the unit can be considered under-utilized unless it comes into conflict with the second definition. The second definition is if the refinery is constrained in such a manner that the FCCU/RFCCU is not operating at one or more of its constraints.  If the refinery is operating in such a manner that it is uneconomical or unable to push the FCCU/RFCCU to a constraint, then I do not “punish” the FCCU/RFCCU, as this condition is beyond the control on the FCCU/RFCCU operations and/or technical team.  There have been many circumstances where the refinery has cut crude runs either for economical reasons or due to one or more processing unit problems or issues.  Anything that is “beyond the control” of the FCCU/RFCCU team should not count against them.

It is the duty of the FCCU/RFCCU operations and technical team to always look for ideas/solutions in order to maximize the profitability of their unit; which usually means push the unit to multiple constraints.  However, the team also needs to understand the place that their unit has in the over-all scheme of the refinery.  There may be times when the FCCU/RFCCU may need to be under-utilized for the greater economic good of the entire refining complex.

– K.P.

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Posted by: Paul R Orlowski

Paul Orlowski is General Manager for the Refining Community which includes,,, Resid Hydrocracking and SDA. They consult at refineries around the world. They've hosted 36 technical conferences around the globe, trained 1,000's and completed very beneficial consulting and troubleshooting projects. Paul co-founded Inc in 1998 with Gary Pitman. Evan Hyde later joined the team. Besides being an educator and software applications engineer, he worked 18 years at ARCO and BP refineries near Seattle, WA USA. Previously he worked for Science Applications International Corporation and Dealer Information Systems. In 2019 look for #RefComm Galveston Coking | CatCracking | Resid Hydrocracking and RefComm® Rotterdam Coking | CatCracking. In 2020 Galveston; Gdansk, Poland and Rio de Janeiro, Brazil and Singapore.