Q&A

(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 95: What are the key wash nozzle design criteria for an effective FCC main column overhead water wash system? Please discuss the effectiveness of using hollow-cone versus full-cone and the spray angle direction - up flow versus co-current flow?

What are the key wash nozzle design criteria for an effective FCC main column overhead water wash system? Please discuss the effectiveness of using hollow-cone versus full-cone and the spray angle direction - up flow versus co-current flow?

(2014) Question 96: What are the different methods you employ to increase C3 recovery? What are your typical C3 recovery improvements for these various methods?

What are the different methods you employ to increase C3 recovery? What are your typical C3 recovery improvements for these various methods?

(2014) Question 97: What is your optimal pH for wet gas scrubber water and how is this maintained? What are the implications of too high or too low pH?

The optimum pH for a wet gas scrubber treating FCC flue gas is 6.9 to 7.1. This pH is maintained by the controlled addition of sodium hydroxide.

(2014) Question 98: What are the options for removing catalyst fines from the main fractionator bottoms product? Which, ifany, can reduce the ash content to 50 ppm or less?

Slurry oil catalyst fines Settling Aid chemistries have been used for many years in this type of application. Electrostatic precipitators and filtration equipment is also available for minimization of ash content in slurry oil.

(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?

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