Q&A

(2018) Question 25: Coke drum integrity can be compromised due to the use of feed side entry devices. What is your experience with drum roundness upon inspection?

Coke drum integrity is typically dominated by low cycle fatigue. Imposed stresses due to thermal gradients during drum warming, water quenching and the contraction of the drum while full of coke can result in stresses higher than the yield stress of the coke drum metal.

(2018) Question 26: How do you monitor furnace convection section fouling? What mitigation steps do you implement?

Monitoring the flue gas temperature leaving the process convection section is a simple method of tracking the heat transfer in the convection section. The excess air needs to be taken into consideration as a higher O2 concentration will shift heat transfer into the convection section and causes the total quantity of flue gas to increase.

(2018) Question 27: What is your experience with chemical treatment to reduce furnace coking?

For conventional fouling, which is the result of asphaltene destabilization due to temperature, chemical treatment programs have not been effective for Coker heaters. For premature asphaltene precipitation due to resid compatibility concerns, chemical treatment programs have been effective in reducing or eliminating fouling.

(2018) Question 28: What are your best practices around initial crude oil qualifications? Upon receipt, what are your best practices for continuous inspection/receiving crude oil at a plant?

Once they have located these crudes, our economic/planning group will utilize the assay of the crude to evaluate this crude using our linear program (LP). This will generate the possible net back for processing the crude.

Question 29: How are crudes with high filterable solids crude managed to mitigate their impact on the operation? What levels of solids do you see and how are they measured?

Several major refiners have begun to use a water wash step at the end of the D4807 test to determine the actual non-water-soluble filterable solids. This method is more reflective of actual solids contained in the crude.

(2018) Question 30: When injecting wash water upstream of the cold train in a 2-stage system, do you use fresh wash water or brine water from the 2nd stage desalter?

For two stage desalting, injecting all the fresh wash water upstream of the second stage desalter provides the opportunity to use the lowest salt water on partially desalted crude which should result in the lowest level of salt in the desalted crude oil. Water from the second stage desalter is then used to provide wash water for the first stage. This water is typically split between being injected upstream of the exchanger train and upstream of the mix valve for the first stage desalter.

(2018) Question 34: What is considered your practical limit on TAN (Total Acid Number) of blended crude diet before monitoring, treatment, or metallurgy upgrades should be considered to avoid naphthenic acid corrosion issues?

Understanding the mechanism of naphthenic acid corrosion, we model the hot circuits looking at the potential TAN of the stream, metallurgy and fluid velocity within the circuit. Once this has been done, we evaluate the options, if the corrosion potential is high enough.

(2018) Question 35: For deep cut vacuum tower designs what is your experience with heater coking and typical run lengths? Are you using on-line cleaning (like coker heater spalling)?

For a properly designed vacuum heater, it should be possible for the heater to last the entire run between cycle ending turnarounds without having to decoke the heater. This requires the heater to have been designed with the appropriate heat flux and mass flux rates.

(2018) Question 36: How do you manage the potential negative impacts of H2S Scavengers in imported coker feed?

How do you manage the potential negative impacts of H2S Scavengers in imported coker feed?

(2018) Question 37: Do you extend the time between de-coking the furnace by cutting coil outlet temperature or cutting furnace charge? How often are spallings done in coker furnaces? What is the temperature recovery after spalling?

Heater fouling is dependent on several variables that include the process film temperature, residence time at temperature and coke precursor concentration. I like to target a coke drum outlet temperature of 825°F before quench injection, which normally requires a Coker heater outlet temperature of 925°F.

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