Q&A

(2012) Question 84: What measures can be taken to reduce the residence time in the FCC main fractionator to offset slurry circuit fouling? What basis is used to determine the residence time in the main fractionator bottoms?

I would like to start with a little background on bottoms coke to present some clarity on the basis for my answer to this question. Bottoms coke sources could come from multiple places. But to address the question with respect to residence time, our impression was that we are mostly looking at the thermal cracking and decomposition reactions in the main fractionator bottoms as opposed to asphaltene precipitation or reactor transfer line coke generation and carryover.

(2012) Question 85: What is the state-of-the-art design used to minimize the impact of coke in the FCCU main fractionator bottoms and remove coke from the bottoms draw and circulating circuit?

In general, reducing fractionator bottoms coking starts with an optimum slurry system design to minimize the column residence time and bottoms temperature. We typically target around 680°F in the bottoms. This design should include the fractionator soft area, as well as the entire slurry exchangers train.

(2012) Question 87: What is typical light cycle oil/fractionator bottoms distillation overlaps, and what can be done to improve separations to increase LCO recovery?

The distillation overlap of LCO bottoms product varies somewhat. In our experience, it is in the range of 20ºF to 60ºF. We also have a few units that report distillation overlaps.

(2012) Question 88: What is the variation in fresh catalyst chemical and physical properties for your refineries? How do you determine acceptable tolerances for your fresh catalyst quality control?

There are large numbers of chemical and physical properties that can be measured. I am really just going to focus on the ones that are most typical. First of all, in the metals’ category will be the sodium, alumina, and rare earth.

Find the answer to your technical question in AFPM's extensive Q&A database.

Q&A

(2012) Question 84: What measures can be taken to reduce the residence time in the FCC main fractionator to offset slurry circuit fouling? What basis is used to determine the residence time in the main fractionator bottoms?

(2012) Question 85: What is the state-of-the-art design used to minimize the impact of coke in the FCCU main fractionator bottoms and remove coke from the bottoms draw and circulating circuit?

(2012) Question 87: What is typical light cycle oil/fractionator bottoms distillation overlaps, and what can be done to improve separations to increase LCO recovery?

(2012) Question 88: What is the variation in fresh catalyst chemical and physical properties for your refineries? How do you determine acceptable tolerances for your fresh catalyst quality control?