Q&A

Question 83: What is your experience with regenerator cyclone refractory hex steel failure due to oxidation/corrosion? Do you observe a relationship between these failures and feed sulfur content or refractory type?

The other mode of failure can be the erosion of the CFN holding flanges and cone, which could potentially result in leaking flue gas and catalyst to atmosphere. In either case, a shutdown may be needed if expander blade deposits and expander vibration become unmanageable or the CFN boxes kept on eroding.

(2010) Question 84: Please describe the function of the critical flow nozzle in relation to the operation of a third stage separator. What are the key process/operations/maintenance considerations you associate with the performance of the nozzle? Can poor performance result in a unit shutdown?

The critical flow nozzle (CFN) is located on the underflow line of the Third Stage Separator (TSS). The purpose of the critical flow nozzle is to continuously help blow down cat fines separated in the TSS. The nozzle is normally designed for 2-4% flue gas and designed to take the same pressure drop as the Expander.

(2010) Question 85: What is the typical range that you employ for iron content on FCC equilibrium catalyst? What methods are available to determine how iron is accumulated on the catalyst surface? How does the distribution of iron on the catalyst surface impact the FCC operation, yield structure and emissions?

There are several methods available to quantify iron contamination on catalyst. Scanning Electron Microscopy (SEM) pictures are a valuable means to qualitatively assess iron laydown morphology on the catalyst particle.

(2010) Question 86: In your experience, what are catalyst best practices to shift FCC yields rapidly between gasoline and diesel maximization and then back again? Many catalyst suppliers are recommending blended catalyst systems. Do you believe this catalyst/additive blending is the best approach?

Co-catalysts are a new product category providing the refiner with the flexibility to change the product slate of the FCC without changing the FCC catalyst. Changing between a maximum gasoline co-catalyst and a maximum LCO co-catalyst will allow the refiner to rapidly capture the most favorable economics at all times – maximizing FCC profitability. Co-catalysts are added to the base catalyst to rapidly change the core performance of the FCC.

(2010) Question 87: In your experience, how does catalyst activity affect the catalyst's coke selectivity and the FCCU's delta coke? How are the coke selectivity and delta coke related? Lastly, discuss how to determine the proper activity to maximize conversion.

When designing an FCC catalyst, one must consider coke selectivity, delta coke and total coke yield. Coke selectivity is the relative coke-making tendency of the catalyst, or in other words, a catalyst with good coke selectivity produces higher conversion per unit of coke make than the reference catalyst.

(2010) Question 88: What options exist for the disposition of FCC equilibrium catalyst and fines? For refineries processing residual feedstocks, what are the limitations on the contaminate levels for the various disposal options?

E-cat and ESP hopper fines are either send to a cement kiln or land filled. Fines captured by the Wet Gas Scrubber are also land filled. Metals limits are normally for leachable metals as measured by the TCLP (Toxicity Characteristic Leaching Procedure) testing, as opposed to total metals in the catalyst.

(2010) Question 89: In shifting from partial burn to full burn in a side by side unit, what has been your observed impact on the NOx emissions? What is necessary to achieve 20 ppm NOx?

Several Grace customers successfully operate with NOx emissions less than 20 ppm in full combustion without the use of NOx removal hardware in the flue gas circuit.

(2010) Question 90: Does any refiner use an on-line particulate emissions (PM) analyzer to measure PM concentration and/or particle size distribution in the flue gas? Are any of these analyzers using continuous emission monitoring systems (CEMS)? How reliable and accurate have these systems been?

Sunoco currently has a particulate matter (PM) analyzer in one location on the stack of a Wet Gas Scrubber. It is there to measure Filterable PM only, not particle size distribution. This was installed as a requirement of a local environmental permit.

(2010) Question 91: Assuming the FCCU already has a third stage separator, what are the various options you consider for further reduction of particulate emissions (PM) and what is the expected level of PM to be achieved?

The first thing to consider is the fourth stage collector. For designs that re-introduce the collected fines downstream of the expander, a fourth stage collector with fines removal and filter on the TSS underflow gas will aid in reducing PM.

(2019) Question 33: What downstream processing issues have been associated with the overfeed of NaOH at the crude unit?

Caustic is injected with the crude charge on some units to reduce chlorides in the crude overhead system and impact the salting and corrosion potential.

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