Cat Cracking Logo

LCO Quench and FCCU Rx Outlet Temp

We are determining yields at different Rx Outlet Temperatures (ROTs). The unit’s procedures call for an LCO quench once the ROT reaches 1010F. Last week, the operators tried to put in CatCracker Rx Outlet Temperaturethe LCO but found the nozzles were plugged. There is steam going to the nozzles, so I’m not sure exactly how they got plugged. The current discussion between everyone is whether or not we should keep going with the test run.
I wanted to make sure the LCO quench was more for process optimization rather than equipment constraints. I always heard that the quench is to keep the process material from cracking once it leaves the Ramshorn. The original plan is for an ROT of 1020F. Do you see any negatives from continuing to raise ROT?


  1. It is OK/safe to proceed with the FCCU Rx Outlet Temp (ROT) test run.
  2. The LCO quench is for yield optimization.
  3. The LCO quench does not have any impact on the metallurgy or mechanical integrity.
  4. From a metallurgy/integrity point-of-view, the Rx is good up to 1050F; but, let’s use 1025F just to err on the side of safety.

Also, the unit volume balance for your unit process conditions should be 110-112 vol%.
The 97+% wt. balance and the 107+% vol. balance suggests that either one or both of the LPG flow-meters C3 and C4 are off.

Leave a Reply

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.