Q&A

(2014) Question 74: What are the main causes of vacuum jet ejector poor performance? What methods have you used to mitigate these issues?

Diagnosing poor vacuum jet ejector performance can be tricky.

(2014) Question 75: Do you draw liquid hydrocarbon from the overhead system in the vacuum tower after the pre-condenser? What is the operating temperature of the tower overhead? What issues do you observe?

At vacuum tower top temperatures over 135-150°F some material heavy enough to condense after the pre-condenser goes overhead. In units with extremely paraffinic feeds the hydrocarbon can form wax in the pre-condenser, leading to reduced heat transfer and higher vacuum tower pressures.

(2014) Question 76: What is considered industry Best Practices with respect to the control of thermal cracking in vacuum tower bottoms? If quench is not available, what other parameters do you monitor and control? How do you establish the target control points?

Thermal cracking of liquid in the vacuum tower bottoms depends upon time and temperature. The higher the temperature, the higher the cracking rate. The longer the residence time, the more cracking. The key to reduced cracking in the vacuum tower bottoms is to keep the bottoms temperature down and the residence time low.

(2014) Question 77: What operating procedures are do you use to mitigate/prevent coking issues in the vacuum tower from loss of wash oil pumps?

Wash oil loss can result in coking in either the wash oil delivery system or in the wash bed, or both. The best method is to prevent coking is to keep the wash oil in service. Auto-start of standby wash oil pumps, alternate wash oil supply sources (AGO), and putting pumps on critical service power supply are used.

(2014) Question 78: What economic issues do you consider when deciding how deep to cut heavy vacuum gas oil?

What economic issues do you consider when deciding how deep to cut heavy vacuum gas oil?

(2014) Question 79: What is your experience with respect to the use of trough distributors in vacuum wash zone service? Please address installation, reliability and performance.

What is your experience with respect to the use of trough distributors in vacuum wash zone service? Please address installation, reliability and performance.

(2011) Question 49: What criteria do you use to predict coke drum hot spots (leading to blowouts) during the cutting cycle? How do you modify your standard cutting procedure if you anticipate hot spots?

Coke drum hot spots can be difficult, if not impossible, to predict but there are operating practices that can help minimize the occurrence of coke drum hot spots/blowouts.

(2011) Question 50: What unique challenges do you consider when designing a safety instrumented system (SIS) for a delayed coker heater?

We are currently constructing two new delayed coker heaters at our El Dorado, Kansas facility. As part of this project, we have performed both a process hazard analysis (PHA) and a safety integrity level (SIL) evaluation.

(2011) Question 51: What are some steps that can be taken to minimize re-foaming while steaming to the fractionator? Are there ways to predict re-foaming tendencies of different crudes or coker feed properties?

After a Coke drum is taken offline, it is steam stripped with ‘little’ steam @ 2.5 t/hr for 30 minutes (28 ft drum) to main fractionator to recover volatile hydrocarbon material.

(2011) Question 52: What test methods do you use to predict desalter performance when switching to new crudes or a blend of several crudes?

Standard laboratory tests include salt, BS&W, gravity, viscosity, and filterable solids. The amount, and type of filterable solids can be the greatest factor to consider for interface emulsion resolution and predicting performance.

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