Q&A

(2010) Question 32: In your experience, what contributes to Monel denickelification in the HF Acid Regenerator circuit? What are the potential problems associated with this?

Oxygen is a major cause of monel denickelfication. Oxygen can enter the circuit during loading operations. Care should be taken to avoid pressuring air contained within loading pipes/hoses into the unit.

(2010) Question 33: How do refiners avoid De-isobutanizer (DIB) column/reboiler fouling in sulfuric acid alkylation? What process conditions on the column do you use to detect this fouling? What process modifications do you take to minimize the impact of this fouling?

Fouling in the DIB column is almost always caused by salt deposits. These salts are typically sodium sulfate and sodium sulfite but can also contain calcium or magnesium if the effluent treating water is not demineralized. If these water-soluble salts are present in the DIB feed, the water will evaporate once inside the column leaving the solids behind.

(2010) Question 74: Please discuss how yield data can be used to identify hardware issues. What hardware issues can you address to fix dry gas and benzene production?

There are several examples of how yield data can be used to identify hardware issues in the FCCU. For example, a decrease in cat to oil and/or catalyst circulation (which leads to a decrease in overall conversion and liquid yield) can be the result of a high regenerator dense bed temperature at constant process conditions. Several mechanical/hardware issues can contribute to higher regenerator temperatures.

(2010) Question 75: What have refiners done to mitigate or eliminate coke buildup in reactors? How do you monitor and vary feed quality, reactor severity, catalyst formulation and other variables to impact coke formation. How does feed distributor operation and design impact reactor coke buildup?

A lot of coke formation can occur during start-ups and shutdowns and upsets of the unit. During start-up, it is important to make sure that all the reactor internals are hot and at operating temperature before introducing oil. If the temperature is too low, the hydrocarbon will condense and form coke. It is also desirable to initially start-up during the first few hours without resid in the feed so there are less chances of heavy hydrocarbon condensing in cold spots.

(2010) Question 76: How can you tell if spent catalyst stripping is "good"? We don't believe our hydrogen on coke results

From the equation it’s easy to see that inerts can be minimized by reducing catalyst circulation rate or increasing the catalyst density in the standpipe. Reducing the catalyst circulation will linearly reduce the amount of inerts.

(2010) Question 77: How do you minimize the entrainment of inerts from the regenerator which eventually enter the fuel gas system and sulfur recovery units reducing available capacity?

In the Shaw RFCC, we utilize a withdrawal well design that allows the catalyst to deaerate before it enters the RCSP. The withdrawal well achieves a very high catalyst density at a stable flux. It can also help the pressure balance.

(2010) Question 79: Backwash containing catalyst fines collected by main column bottoms hydrocyclones, filters or electrostatic precipitators are normally routed back to the FCC reactor riser. In your experience, how does the recycle of catalyst fines in main column bottoms impact particulate emissions from the FCCU?

The distribution of pumparound duties in the Main Fractionator dictates th amount of LCO recovery from the bottom's product. The primary handle to adjust LCO production is the pumparound duty below the LCO section (slurry pumparound or slurry and HCO pumparounds in towers with an), not the LCO pumparound.

(2010) Question 80: What best practices do you recommend to improve LCO recovery? Do changes in LCO pump around affect LCO recovery? What are common challenges?

There has been a lot of work and discussion on LCO maximization at the FCCU and there is plenty of literature on different options for LCO recovery. This will be a general overview of available options to refiners and some challenges recently experienced at Coffeyville.

(2010) Question 81: Refiners operating FCCUs producing high levels of propylene have seen different or excessive product contaminants when compared to a less severe operation. In your experience, how has this impacted gasoline or LPG treating unit? What specific contaminants have you identified? What impact have you seen in amine color, consumption, or foaming tendency? What actions have you taken that have mitigated or prevented treating unit issues?

The answer to this question depends on what is considered high levels of propylene and what is the method to achieve it. If the additional propylene is produced by the addition of ZSM-5 to a standard operation, then I would not expect to see additional effects of contaminants. However, if the propylene production is increased through higher severity, ROT, bottoms cracking, etc., then there will be additional contaminant issues.

(2010) Question 82: Immediately after startup of the FCCU, we experienced a hot spot in the regenerator dome and flue gas system. Do you know of any "on the run" acceptable mitigations? Should steam and/or water sprays be applied to the impacted area? Are there reliable analytical techniques to determine if and when the unit should be shutdown for repairs?

Hot Spots are an unfortunate but common problem in cold walled FCC converter vessels and transfer lines. Hot Spots which are not treated can lead to several undesirable effects to the steel envelope. Most refiners typically mitigate these effects by applying steam to the localized hot area.

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