Q&A

(2014) Question 90: What is the most profitable way to schedule the FCC and associated catalytic naphtha hydrotreater turnarounds? Are there benefits in synchronizing the shutdown of these units?

What is the most profitable way to schedule the FCC and associated catalytic naphtha hydrotreater turnarounds? Are there benefits in synchronizing the shutdown of these units?

(2014) Question 91: What are the characteristics of FCC catalyst to minimize particulate emissions at the stack?

While there are several operational and mechanical factors that can influence a unit’s particulate emissions, the question asks specifically about the FCC catalyst; as such, the following discussion will address characteristics of fresh catalyst only.

(2014) Question 92 What is the impact of high iron you have seen in some tight oil feeds? What level of Fe on the equilibrium catalyst causes problems, and what are the typical symptoms? What changes to FCC units hardware, catalyst and operation have you implemented to manage Fe poisoning? What is the impact of other uncommon contaminants such as K, Ca and Mg?

Tight oil feeds generally have high levels of iron and calcium present in them. Iron can have a negative effect on catalyst performance. While particulate tramp iron from rusting refinery equipment does not have a significant detrimental effect on catalyst, finely dispersed iron particles in feed (either as organic compounds or as colloidal inorganic particles) can deposit on the catalyst surface, reducing its effectiveness.

(2014) Question 93: What is your process safety concerns in withdrawing equilibrium catalyst from the FCC regenerator? How do you manage catalyst transfer piping and spent catalyst hopper temperatures? What materials of construction are appropriate (or inappropriate) for these services?

What is your process safety concerns in withdrawing equilibrium catalyst from the FCC regenerator? How do you manage catalyst transfer piping and spent catalyst hopper temperatures? What materials of construction are appropriate (or inappropriate) for these services?

(2014) Question 94: To reduce the risk of igniting the gas mixture in the electrostatic precipitator (ESP), we are considering safety interlocks for de-energizing the ESP when carbon monoxide content gets too high. Please share your experience regarding (a) setting an appropriate trip point, (b) other interlocks to consider, and (c) advantages over operating procedures.

Automatic trip points should be set so that the CO gas concentration is well below the Lower Explosive Limit (LEL). Consideration should also be given to adding interlocks to trip the ESP based on high concentrations of methane, especially if the ESP is downstream of a CO Boiler or if there are other potential sources of fuel gas/natural gas to the ESP (even during upset conditions).

(2014) Question 99: We are struggling with high afterburn in the regenerator. What hardware changes (spent catalyst distributor, air distributor, etc.) have you implemented to improve afterburn? What commercial experience exists using computational fluid dynamics (CFD) to resolve such issues?

CFD has been successfully used to predict afterburn in FCC regenerators. A published example was presented as part of the CFD Case Studies workshop at the 2012 AFPM Cat Cracker Seminar.

(2014) Question 100: How do Nitrogen compounds distribute in the product streams of FCC Units? What effect does riser severity and feed properties have on this distribution?

How do Nitrogen compounds distribute in the product streams of FCC Units? What effect does riser severity and feed properties have on this distribution?

(2014) Question 101: What factors influence butylene selectivity in the FCC LPG? What is the relative role of feedstocks, catalysts, additives, and operating conditions?

A number of factors influence butylene selectivity in the FCC LPG stream. Figure 1 summarizes the fundamentals of butylene selectivity and maximization.

(2014) Question 102: What benefits have you realized by installing packing in their FCC strippers? How did this equipment impact your catalyst circulation and unit pressure balance?

What benefits have you realized by installing packing in their FCC strippers? How did this equipment impact your catalyst circulation and unit pressure balance?

(2014) Question 103: We increased reactor severity and noticed an increase in oxygenates in LPG and sour water. Can you explain the mechanism by which phenols and other oxygenates form in the riser?

Since increasing reactor severity will result in an increase in catalyst circulation, it is likely that the increased oxygenate production being observed is from the higher catalyst circulation which is increasing the entrained molecular oxygen carryover to the riser.

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

Q&A