Q&A

(2017) Question 54: What recent innovations have you made to instrumentation that has application in FCC units?

For level measurement, guided-wave radar level instruments have been gaining popularity and been successfully applied in numerous services, especially for interface levels. Nuclear-type level instruments have been more or less accepted in other processing units in refineries and have made their way into the FCCU for severe services, such as main fractionator bottoms level, and for hopper levels.

(2017) Question 73: Gasoline octanes continue to have a high value for many refineries. What fractionation strategies do you apply to increase gasoline octane? What rules of thumb do you apply for estimating changes in octane with gasoline endpoint adjustments?

RVP and endpoint both have a minor effect on gasoline octane. With other operating parameter changes and repeatability of octane results in the lab (+/- 0.5 RON), it is difficult to quantify small changes in octane caused by fractionation changes. Literature suggests that for every 1.5 psi RVP increase, RON will increase 0.3. We have very little data to support the literature, because the octane and RVP value of mixed C4s is much greater as alkylate than on the frontend of FCC gasoline.

(2017) Question 74: How do you mitigate aqueous corrosion in the main fractionator overhead and gas concentration unit? What contaminants do you test for in the sour water, and what limits do you impose? What are your concerns with using stripped sour water as waterwash?

Over the last six years, there have been a number of questions related to different aspects of overhead and gas concentration unit corrosion management, including design recommendations. For completion of the Answer Book, here is a brief summary of the topics covered.

(2017) Question 75: What are your Best Practices in design and operation to achieve positive isolation of slurry/HCO equipment?

Technip’s practice is to specify gate valves with flushing connections at the base of the seat. To ensure positive isolation, the flushing connection can be used to remove any sediments that may be impact the contact of the gate with the seat. Another option is to orient the valve stem off of vertical in order to move the final seating location away from the low point, therefore reducing the chances of sediment to accumulate there.

(2017) Question 34: What are your current protocols, practices, and concerns for using wireless communication between field instruments and the control room? Would wireless communication be acceptable for monitoring only, or is control allowed as well?

Technology continues to progress in this field. Since 2011, we have had guidance that allows some usage of wireless instrumentation, but this technology is limited based on application.

(2017) Question 35: What are your major parameters and mechanisms that affect coker furnace fouling? Are there known effects from some specific crude properties? What are typical fouling rates, and how can they be minimized?

The major factors affecting coker furnace fouling fall onto three key areas: mechanical, operations, and feed.

(2017) Question 36: What are your primary indicators that a coker furnace spall is complete? What steps do you take to optimize the efficiency of spalling?

Delayed coker furnace spalls are performed to remove the buildup of coke on the inner walls of the furnace tubes in order to improve furnace heat transfer and maintain unit throughput and efficiency. As furnace spalls require coker and sometimes refinery crude rate reductions, they should be planned and communicated effectively to the refinery’s Planning Department to ensure that crude and product inventories are managed appropriately.

(2017) Question 37: What programs have you implemented to improve reliability and life of the coke drums including inspection and maintenance?

The refining industry is continuously experiencing coke drum problems and failures due to low cycle fatigue. The two main problems caused by the cyclical operation of coke drums are shell bulging and shell/skirt circumferential weld-seam cracking.

(2017) Question 38: How do you monitor coke drum overhead lines to determine when cleaning is required? What cleaning techniques are effective and which are ineffective?

Higher pressure drop reduces gasoil yields in the coker fractionator and profitability for the refinery. Establish graphs that demonstrate the relationship between pressure drop and yield loss and make them visible to the organization.

(2017) Question 39: What procedures and techniques are you currently using to monitor and control cyanide corrosion on coker overhead circuit and light ends units?

Cyanide corrosion is a hydrogen permeation phenomenon on steel that tends to cause cracking, commonly at high stress zones, and possible blistering on “dirty” base steel. Finding cyanide in an overhead circuit does not mean there is a problem.

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