Q&A

(2011) Question 69: What are the effects of a poorly insulated coke drum? What is a good way to assess coke drum insulation effectiveness? How can the benefits of new insulation be estimated?

Poor coke drum insulation impacts both the mechanical integrity and unit operation

(2011) Question 70: How do you monitor coke drum cutting water for fines content (test methods, frequency, time in cycle) and what is your trigger level for action to reduce fines content?

There are different methods to separate the fines in cutting water. In our latest Cokers, we have hydrocyclones, provided at the discharge of the reuse water pumps. The older cokers deploy clarifier.

(2011) Question 71: We have coker/cracked naphtha reboilers which foul on the shell side. How can we minimize the fouling? Are you practicing on-line cleaning in this service?

Coker debutanizer fouling is mainly caused by conversion of diolefins to form polymerization material. The polymerization material over time can turns into hard coke.

(2011) Question 72: When replacing coke drums with larger diameter drums, what process and operational changes do you expect?

In 2009, we completed a group of projects at El Dorado involving larger coke drums and a deep cut vacuum tower. The coke drum project limited the scope to drum replacement with minimal changes to the balance of the unit.

(2011) Question 73: What is your best practice for coke drum velocity to minimize coke carryover to the fractionator?

Coke drum velocity limit depends on the capability of the coker main fractionator and downstream equipment to handle entrained coke.

(2011) Question 74: Please discuss the pros and cons of the various coke drum level technologies.

The process conditions are highly fouling, high temperature, changing pressure and composition, and high velocity hydraulic decoking every cycle.

(2011) Question 75: What are the pros and cons of driving coke VCM (volatile combustible matter) to a low level? What are the lowest green coke VCM you have consistently achieved?

Volatile combustible material (VCM) is an important parameter of Petcoke. VCM is basically unconverted pitch in the coke. The metal and sulphur are controlled by the type of crudes processed, but VCM content of coke is mainly in the control of DCU operators.

(2017) Question 43: What is your experience with intermittent mud washing of single-stage and two-stage desalting? What are the advantages of continuous versus intermittent mud washing?

The primary purpose of a mud wash is to suspend and remove solids that have accumulated in the bottom of the desalter. Some desalting operations use the mud wash to remove solids (asphaltenes and oil-wetted inorganic solids including iron) that have accumulated in the interface of the desalter. The desalter level may be lowered to accomplish this goal in some of these operations.

(2017) Question 44: How do you monitor exchanger fouling? How do you use that information to justify additional work scope during unplanned shutdowns?

Exchanger monitoring software or spreadsheets that pull in refinery process data can be used to monitor fouling trends. Exchanger trains should be evaluated for fouling on a routine basis to provide historical references and trends to compare pre- and post-cleanings.

(2017) Question 46: What is your design service life of atmospheric tower overhead heat exchangers? How does that compare to actual service life? What do you do to better manage corrosion and improve reliability of these heat exchangers?

Heat exchangers are designed for heat recovery and only rarely for corrosion control. The designer’s tool for reliability is to use upgraded materials of construction. Over the years, those on our team have seen even Hastelloy C276 and titanium being used.

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