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(2011) Question 68: What is a typical duration of online spalling of the coker furnace? What are the guidelines on maximum steam velocity during online spall?

Prima facie, the spalling operation is dovetailed with the coke drum cycle. We try to avoid continuing with the online spall during the changeover operation. This is to eliminate any chances of foam-over or coke carryover to fractionators.

(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.

(2011) Question 76: What can cause exothermic reactions in propylene driers and guard beds and how can these reactions be prevented?

As introduction, Propylene Recovery Units downstream of FCC units typically consist of a C3/C4 Splitter, a Deethanizer and a C3 Splitter in series.

(2011) Question 77: How prevalent is the use of low slide valve dP override control in modern FCCU DCS systems and can the over-ride be considered an "independent protection layer" (IPL) when conducting a layer of protection analysis (LOPA) to protect against a pressure reversal scenario?

The panel concluded that 100% of the FCC units in their respective companies used the low slide valve dP over-ride to protect against reversals.

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