Q&A

(2016) Question 61: How many inside/outside operators staff your FCC plant? What other processes are included in their scope of responsibility?

[United Refining Company (URC)] Our FCC unit has five operators per shift. Typically, two people are inside running the DCS (distributed control system) and board-mounted controls while the other three are doing rounds in the unit.

(2016) Question 62: We have run a full-burn FCCU for many years. We are considering processing more resid and operating in a partial CO combustion mode. What is a carbon runaway, and how can it be addressed?

A carbon runaway or “snowball” occurs in an FCC that is operating in partial CO combustion mode and very high CO levels. In the runaway situation, the carbon on regenerated catalyst (CRC) rises to levels such that additional coke that is laid down on the catalyst cannot be burned from the catalyst in the regenerator, causing the CRC to continue rising like a snowball that gets bigger and bigger as it rolls down a hill.

(2016) Question 63: What are your current methods used for regenerator cyclone temperature control? Do you use water sprays or steam injection?

In the early days of FCC, the normal bed and dilute-phase operating temperatures –being less than 1100°F –did not support CO combustion. These units operated with high levels of carbon on catalyst and about 10 vol% CO in the flue gas with almost no excess oxygen in the flue gas.

(2016) Question 64: What are your typical operating guidelines to prevent compressor surge episodes? How closely do your FCCU operators approach the actual surge line of a compressor before adjusting operation?

[United Refining Company (URC)] The unit engineer/compressor manufacturer should be able to provide guidelines to prevent surge episodes. These guidelines may include safe windows of operation for air rates, discharge pressures, and discharge temperatures.

(2016) Question 65: Please comment on which FCC feed types you are currently processing and what chemicals you are using for gas plant corrosion prevention. Is waterwashing sufficient to sustain adequate unit reliability?

Our refinery typically runs Western Canadian Crudes, SYN, and some conventional heavy crudes.

(2016) Question 66: In your experience, how does changing the feed cutpoints impact FCC conversion and product yields? How does the LP (liquefied petroleum) determine where to make these cutpoints?

Deeper cuts will not have as high a conversion as will lighter cuts. For example, an FCC charge API gravity of 22 may have a conversion of 83%, while a lighter gravity of 23 will show conversion one point higher at 84%.

(2015) Question 29: What are the likely causes for temperature excursion events in a hydrogen plant?

Hydrogen plant temperature excursions are possible in several of the catalyst vessels and are usually observed in association with the water/gas shift reaction. During normal operation, the high, medium, and low temperature shift reactors display an exothermic reaction.

(2015) Question 30: What factors influence your decision to conduct air versus inert reactor entry for catalyst changeout? For, what methods do you use to avoid stress corrosion cracking?

For us to enter a reactor that is under an inert atmosphere, the conditions need to warrant it, such as when there are large amounts of pyrophoric material still present, when a specific job is required, an old catalyst needs to be vacuumed out for sampling purposes, or if there is filtration material on top that requires removal in order to allow the catalyst below to dump freely.

(2015) Question 31: What are your current safe practices for sour water monitoring? What are your preferred analytical methods/sampling frequency used to measure NH3/NH4HS (ammonia/ammonium bisulfide)?

The primary concern with sour water sampling is exposing operators to H2S and ammonia, which will evolve off the liquid as it is collected into the sample bottle. Typically, most of our plants would take an approach of ensuring that the operator pulling the sample was in supplied air.

(2015) Question 32: What is your suggested minimum temperature required to achieve adequate metals removal in the demetalization (demet) catalyst to protect primary treating catalyst in FCC and hydrocracker pretreaters?

The suggested minimum reactor temperature required for adequate metals removal is going to be metals specific. For silicon, the temperature is definitely greater than 570°F; and for nickel and vanadium, we suggest greater than 600°F. Now higher reactor temperatures may be required for adequate removal, depending on the space velocity through the metal-strapping catalyst and whether or not there may be a tolerance issue with the primary treating catalyst.

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