Q&A

(2017) Question 61: When performing catalyst evaluations and considering catalyst resistance to attrition about particulate matter (PM) emission requirements, what new or advanced attrition testing methods are you using to predict the performance of the new catalyst system? Are there third parties who can conduct a standard testing regime to multiple catalyst systems?

A number of operating factors influence catalyst losses from the regenerator that can lead to particulate matter (PM) emissions. These factors include: the number of fines present in the freshly added catalyst, the number of fines generated in the unit, the amount of catalyst transport to the cyclones by entrainment, and the cyclone performance.

(2017) Question 62: Do you know of factors that are likely to lead to deposit formation on power recovery turbine blades? Is there anything that can be done to prevent these deposits from laying down on the blades? Once the deposits have been formed, what are the consequences and is there any way to remove the deposits online?

Deposit formation is usually linked to catalyst depositing on the turbine blades. The deposits are mostly a function of catalyst loading of the inlet flue gas. An increase in catalyst loading could be due to several factors, including performance of the third-stage separator, loss in cyclone efficiency, change in catalyst attrition properties, excess fines in fresh catalyst, an increase in fresh catalyst additions, and/or an increase in flue gas rates due to higher air rates.

(2017) Question 63: Please explain the phenomenon known as “coke ratcheting” in the FCC reactor where equipment exposed to coking services elongates over time and heat cycles. Please provide details of actual examples of where this occurred and the impact to equipment operations and reliability.

Coke ratcheting occurs in hot-wall reactor/riser systems. When the system is at operating temperature, the parent metal expands more than the hex mesh lining does. This expansion creates small voids between the hex mesh biscuits that are large enough for hydrocarbon vapors to enter and come in contact with the parent metal. Coke forms in these voids.

(2017) Question 64: What are the risks and negative factors you see associated with processing slurry oil, either as slurry separator backwash or recycle, in the FCC reactor?

Slurry recycle and slurry separator backwash are two very different processes with varying objectives and negative impacts. Slurry recycle is typically done intentionally for the purpose of increasing coke make to help a unit that is short on heat balance. Such units are usually processing very light, sweet feeds and are unable to meet their processing objectives without additional heat input. Slurry separator backwash is required to remove the collected solids from the slurry filter/separator to ensure their efficient operation.

(2017) Question 65: What variables impact feedstock atomization in the FCC riser? What steps do you take to optimize the feed and catalyst mixing for proper vaporization and catalytic reaction?

Feedstock atomization typically comes down to the design and reliability of the feed injector. Obtaining good atomization of the feed is important for optimizing the performance of any FCC. Feedstock atomization facilitates the rapid and efficient vaporization of the feed inside the riser, which can then initiate the cracking reactions.

(2017) Question 66: In order to meet the pending MARPOL/IMO (International Convention for the Prevention of Pollution from Ships/International Maritime Organization) 0.5% sulfur fuel oil standards in 2020, what options do you have available to implement within FCC units to improve slurry quality, adjust yield, or find alternate dispositions, both within the overall facility and as a saleable product?

The FCC bottoms (decant oil or slurry bottoms), along with cycle oils, are often blended into internal and external fuel oils. With the lower sulfur regulation, high sulfur FCC bottoms will be a discounted stream based on sulfur content; and then further, on catalyst content.

(2017) Question 67: What strategies do you employ to optimize FCC plus hydrocracker operations? Do you process hydrocracker unconverted oil (UCO) in the FCC or FCC LCO/HCO in the hydrocracker?

FCC plus hydrocracker optimization covers several additional units including the reformers, H2 plants, sulfur plants, and LCO hydrotreaters (neat or mixed with other feeds). If the H2 plant and/or sulfur complex (including amine and sour water strippers) are constraining, then these constraints need to be considered in the optimization.

(2017) Question 68: What process and catalyst changes would you recommend for a refinery that is planning to process a percentage of resid in an FCC that typically runs gasoil?

One specific challenge related to catalyst in processing resid is achieving a proper balance of metals tolerance, catalyst activity, and bottoms upgrading. Recommendations on catalyst changes will be dependent on the quality and variability of the resid. It is critical to understand these parameters.

(2017) Question 69: What operational or other changes prompt evaluation and optimization of standpipe aeration? What do you monitor to ensure the standpipes remain fluidized across a range of conditions?

Standpipe aeration is something which has been studied and reported on since the inception of cat cracking. Some standpipes require no attention and may not even have any aeration provisions provided. Others may be so sensitive to changing conditions that adjusting aeration is a daily action. Standpipe design is the most important factor. They tend to be very sensitive to changing direction, such as going from vertical to slanted.

(2017) Question 70: Electrostatic precipitator (ESP) fines handling is often complicated by fluidization and mechanical integrity issues. How often do you experience these types of fines handling issues, and what are some of your Best Practices to successfully mitigate these issues? What are your Best Practices for safe fines withdrawal from the ESP?

Electrostatic precipitators (ESPs) represent an effective medium for particulate emissions control and are, therefore, commonly used within the FCC industry, especially in North America. Although ESPs are not designed to capture all of the catalyst particles present in the regenerator flue gas, they usually exhibit sufficient performance to successfully reduce the particulate content in the flue gas below 50 mg/Nm3. As the question suggests, fluidization and mechanical integrity issues can significantly hinder the withdrawal and handling activities of catalyst fines.

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

Q&A