| American Fuel & Petrochemical Manufacturers

Question 47: What correlations do you use to predict cracked gas make in a vacuum tower from atmospheric tower bottoms based on feedstock properties and heater outlet temperature?

In the past, vacuum towers’ flash zones have operating at or below atmospheric tower flash zone temperatures. These units relied on the vacuum to increase heavy gasoil yields from the atmospheric resid without running the risk of thermal cracking associated with higher temperatures.

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.

Question 45: What are your typical consequences and probable sources of fuel gas fouling? What are your respective solutions?

Fuel gas fouling in refineries is an ongoing problem and is typically the result of many years of corrosion due to moisture in the fuel gas system. These systems are typically saturated with water vapor due to the amine scrubbing that is used to remove H2S, and water may drop out as a liquid in low velocity areas or in areas with inadequate insulation.

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 Exchanger trains should be evaluated for fouling on a routine basis to provide historical references and trends to compare pre- and post-cleanings.

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.

Question 42: What water sources are you using for desalter waterwash, and what are the advantages and disadvantages of each? What role does desalter waterwash source and injection location play in desalter performance?

Over the years, we have established several Best Practices concerning desalter wash water rates, quality, injection locations, and sources that – when utilized – help ensure optimum crude oil desalting.

Question 41: What are some of your operating practices used to mitigate incursion of water slugs in crude feed from tankage? Are there any early warning devices or procedures currently being used successfully?

Plugs of water are problematic, in terms of causing desalting and crude column upsets. Pockets of water can form in the tank due to the characteristics of the crude. The primary defense is to minimize water in crude oil; but with current upstream practices, we know water will enter in with the crude. Having systems in place to reduce, mitigate, and handle water intrusion is important to maintain stable crude unit operations.

Question 40: What crude properties and process conditions are you monitoring as part of a crude slate change?

Crude quality should be compared against similar crudes already approved for processing at the refinery. Obtain crude samples, when possible, to confirm the properties listed in the assay. Ensure that sufficient sample volume (three to five quarts is recommended) to pre-test for crude compatibility with other crudes in your tank farm.

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.

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.