Q&A

(2011) Question 5: What are the pros and cons of motor vs. steam turbine drives for hydrotreater and hydrocracker recycle compressors?

The nature of the hydroprocessing unit is such that a wide range of molecular weights are possible for the recycle gas from nitrogen at start-up to hydrogen with increased light ends during normal operation. While the treat gas requirements are pre-determined, quench gas demands vary during normal operation with varying chemical hydrogen uptakes and emergency situations.

(2011) Question 6: Organic chloride in feed streams to hydroprocessing units is becoming more prominent. Chloride measurement is very important to define correct unit metallurgy; however, measurement is difficult. One of the issues related to accurate analysis of the feed is the impact of feed nitrogen and sulfur on chloride measurement. What test methods are you currently using in light of high nitrogen and sulfur in the feed to give accurate chloride results?

For measuring chloride in feed stream, some of our refineries use an instrument based on Monochromatic Wavelength Dispersive X-Ray Fluorescence (MWD XRF), for which nitrogen and sulfur offer no interference. The instrument measures total chloride, whether organic or inorganic. The relevant ASTM method is D7536.

(2011) Question 57: What is your best practice and expected efficiency in removal of calcium napthanates in higher calcium crudes? Has anyone experienced severe fouling in downstream unit equipment (i.e., Vacuum Heater, Coker heater) when processing high calcium crudes? What are the concerns when processing resid containing high Calcium content?

We have extensive experience removing calcium and other metals from crude oils, with over 20 successful applications removing contaminants spanning the last 8 years.

(2011) Question 58: Some crudes contain fine particles which result in poor desalting and/or high sludge generation. How are you managing this? Are there specific strategies for treating desalter brine separately (ahead of the wastewater plant)?

Along the lines of Ron’s last point on secondary treatment of brine, some refineries have installed diversion tanks to receive the effluent water when the mud wash is being used.

(2011) Question 59: What are revamp best practices to minimize fouling in crude preheat trains? What services are typically the most difficult? What exchanger technologies have proven most successful?

What are revamp best practices to minimize fouling in crude preheat trains? What services are typically the most difficult? What exchanger technologies have proven most successful?

(2011) Question 60: Assuming good desalting, what are the common / best practices, control ranges and testing frequency of overhead boot water for chlorides - with and without caustic injection?

While general limits are assigned for overhead chloride levels, the reality is that these are simple rules of thumb and should not be relied on to provide satisfactory corrosion control for most systems.

(2011) Question 61: What test methods identify acids (other than HCl) in crude tower overhead water?

What test methods identify acids (other than HCl) in crude tower overhead water?

(2011) Question 62: What options do you use to manage or mitigate high carboxylic acids/TAN in jet/kerosene?

What options do you use to manage or mitigate high carboxylic acids/TAN in jet/kerosene?

(2011) Question 63 What is your refinery's first stage vacuum ejector configuration (single or parallel, idle/standby or all in service)? How do you evaluate your ejector system to determine if it is properly sized and performing optimally? Have you made any modifications to reduce steam consumption?

Typically, vacuum unit ejector systems have three ejector stages in series. Large crude vacuum units have multiple three-stage ejector system in parallel.

(2011) Question 64: What are the impacts on coker operation (yields, capacity, energy, coke quality) of excess VGO (1000F-) in the feed?

Our El Dorado facility has transitioned from a 950o F HVGO/VTB cut point coker feed to a +1075 F while maintaining a fairly constant feed rate to the delayed coker unit. Our experience has seen coke and off-gas yield increase while HCGO yield decreases.

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