| American Fuel & Petrochemical Manufacturers

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.

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.

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.

Question 73: What levels of distillate boiling range material do you include in the FCC feeds? Discuss the yield and heat balance implications of varying the feed distillate content. What equipment/technology options do you employ to minimize the distillate levels

Question 72: With advance controls on the FCCU and gas plants, what are refiners doing to train new operators and keep their experienced operators sharp and ready to handle FCCU upsets and emergencies? Are refiners using simulators to help with the training and retraining?

Sunoco employs Dynamic Matrix Control (DMC) on all the FCC gas plants and DMC on reactor and regenerator systems. One FCC has a complete process training simulator, and we are in the process of installing simulators on all of our FCC’s.

Question 71: For the main column, "tri lines" can be utilized to monitor bottoms level. When other level instruments are being verified or have failed, what are the best operating and safety practices being employed to verify the level? What do refiners use to monitor and control level in the bottom of the main column?

For the main column, "tri lines" can be utilized to monitor bottoms level. When other level instruments are being verified or have failed, what are the best operating and safety practices being employed to verify the level? What do refiners use to monitor and control level in the bottom of the main column?

Question 70: How can you minimize the possibility of ignition and fire in the structured packing of main fractionators after they are opened for maintenance? Do you use chemicals to improve this procedure?

Zyme-flow products have been used in our past FCC turnarounds to mitigate pyrophoric compounds as well as decrease the amount of time to hydrocarbon free the main fractionator and associated pumparound circuits.

Question 69: What do you see as the critical considerations for wash bed design in high C-factor vacuum columns? How does one determine bed type, depth, and appropriate wash oil distributor design?

A new vacuum column will typically be designed for a C-factor of 0.36 ft/sec above the wash zone which is normally the section with the highest vapor velocity. A high C-factor situation (say above 0.43) would then involve an existing unit operating well above its original design point.

Question 68: Do you see any benefit in continuing to steam strip crude tower distillate cuts since these side streams require further processing in down stream hydrotreaters?

We have observed definite benefits to steam stripping the distillate cuts and have been working to determine whether the benefit is worth the cost. The main purpose for distillate side strippers is to control product flash with a secondary purpose of lifting lighter material and affecting the product cuts.

Question 67: Have you experienced coking or other fouling of reboilers in naphtha distillation service (splitter, debutanizer, etc.)? If so, what operational or design changes did you implement to eliminate this problem?

Two types of fouling are common in naphtha reboilers. The first type of fouling is generated as a result of the more reactive cracked stock hydrocarbons and is typically seen only in units like Cokers or FCCUs with a cracking process. The second type of fouling is a more complicated issue related to the presence of sulfides in the naphtha and can be seen in straight run units like the Atmospheric Crude.

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