Q&A

Question 16: In your experience, are there documented cases of organic chlorides coming in with certain crudes? If so, what is their impact on hydrotreating units?

In researching this question with our corrosion experts, they identified this as a mature issue that has been well documented in NACE publications and international symposiums. These papers identify multiple cases of organic chlorides coming in with specific crude oils.

(2010) Question 17: What are the best practices to manage ammonium chloride fouling ? What methods are used to set wash intervals? What are the potential pitfalls?

It is not unusual that NH3, H2S, and HCl are all present in the reactor effluent stream. Since ammonium chloride (NH4Cl), and ammonium bisulfide (NH4HS) form above the dew point of water, water is injected in reactor effluent train, upstream of the effluent air cooler.

(2010) Question 18: What are your key strategies to maximize the heavy diesel barrels in the diesel pool without cracking? Do you consider blending and dewaxing etc. to meet product specifications?

Generally maximizing heavy diesel barrels in the total refinery diesel pool would be based on distillation cut points the diesel processing units, mainly crude atmospheric columns. The objective is to maximize barrels by increasing distillation cut points up to distillation cut point maximum or to product quality specifications.

(2010) Question 19: In your experience, what are the effects on ULSD hydrotreaters when FCC operation is adjusted to maximize diesel?

There are a number of approaches to maximize the diesel yield from FCC units, such as catalyst optimization, process modifications, and changing the FCC product cut points. These approaches can be used independently or in combination - the ultimate objective being to maximize the production of light-cycle oil (LCO) from the FCC unit for subsequent conversion to diesel.

(2010) Question 20: How do refiners quantify the impact of sodium on hydroprocessing units, specifically those processing either residuum or VGO feeds?

Sodium generally enters a hydrotreater due to upstream addition of caustic soda or desalter operational problems. Feed sodium content of more than 3-5 ppm should be avoided. Sodium has a significant deactivation effect; 1-3 %wt results in a 50% loss of catalyst activity.

(2010) Question 23: The liquid recycle rate to a second stage of a hydrocracker can shift conversion, light end yields, cycle length and/or the required temperature to achieve a desired conversion. What strategies do you employ to reach optimum conditions

In two-stage hydrocracking design there are several variables that need to be balanced for optimum performance. Desired product yields or selectivity can be affected by conversion per pass in each stage. Lower conversion per pass is desirable to maximize heavier product selectivity.

(2010) Question 25: Besides high reactor temperatures and flow maldistribution, what are other causes of high gas and LPG yields in a hydrocracker have you experienced?

Hydrocrackers typically process heavy gas oils into distillate-range material. The gas oils are catalytically cracked at high pressures in the presence of hydrocracking catalyst and hydrogen. The reaction is exothermic and consumes a relatively large quantity of hydrogen. High gas and LPG yields would be generally undesirable in a properly operating hydrocracker.

(2010) Question 30: What process parameters can affect alkylate T90? What are the critical variables you monitor in both sulfuric and HF units? Discuss processing schemes, feed impacts and operating variables.

The type of feed is very significant for T90. Amylenes make alkylate with higher T90 in both sulfuric and HF units. Propylene generally makes lower T90 than butylene in HF units. However, with sulfuric-catalyzed technologies, propylene can increase T90 as discussed below.

(2010) Question 31: In your experience, when sampling the HF Alky iso-recycle stream, how and where is the sample neutralized prior to analysis? Can this approach be used for online GC analysis as well?

The isobutane recycle sample can be neutralized at the sample location using a chamber filled with alumina or KOH pellets. If using a KOH chamber, it is best to add a filter downstream to filter out any fines.

(2010) Question 32: In your experience, what contributes to Monel denickelification in the HF Acid Regenerator circuit? What are the potential problems associated with this?

Oxygen is a major cause of monel denickelfication. Oxygen can enter the circuit during loading operations. Care should be taken to avoid pressuring air contained within loading pipes/hoses into the unit.

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