Unusual Feedstock Contaminants Continue to Surprise Refiners

Variability in feedstock characteristics result in oscillating plant run rates affecting equipment efficiencies, including compressors and pumps. For example, refiners in the U.S. Midwest continue reporting that paraffinic crudes from the Bakken and other shale regions destabilize asphaltenic crudes, such as the heavier bitumen crudes. Increased crude unit furnace fouling is also a problem from these destabilized feedstocks.

Plant diversity emphasis increasing beyond 2016.

While shale crudes may not have the same level of contaminants associated with heavy crudes, such as with their nickel and vanadium content, they are contaminated with production and hydraulic fracturing chemicals, such as barium and lead. Moreover, even though shale crudes are very low in sulfur-bearing compounds, they do contain H₂S. Tramp amines are left over in the drilling fluids and treatment programs that producers use to control H₂S at the wellhead and in the pipeline. Also, formulations used in the control of shale crude oil odor in transport (particularly by rail) eventually lead to increased overhead corrosion, beginning in the refinery’s desalter and CDU (i.e., amine hydrochloride salt induced corrosion).

Regardless of the problems encountered with combinations of heavy feed contaminants (e.g., Ni, N, Na, V, etc.), there is a site-specific solution for every FCC/HDT configuration where opportunity crudes, including LTOs, are being introduced. Considering the investment and changes required at the refinery’s front end (desalter and crude/vacuum unit), existing downstream thermal (e.g., delayed coker) and catalytic conversion processes can effectively be operated to meet market objectives, once these feedstock incompatibilities are resolved. One of these market objectives involves looking for ways to increase FCC unit middle distillate yield without incurring higher bottoms yield penalties, such as with LCOs. More detailed discussions concerning these operational challenges and incompatibility issues will be “roundtabled” at the May 2-6 RefComm® Galveston 2016 refining conference (www.refiningcommunity.com/refcomm-galveston-2016).

“Incompatibility issues” have become a cliché in the opportunity crude market. Just what type of incompatibilities to expect is key to making an additional $8 to $12/bbl (or higher) if the refiner quickly adjusts treating programs. For example, Nalco’s Sam Lordo recently noted that Bakken crude API gravity varies from 40 to 50, depending on where they are pulling it from. These crudes will lower interfacial tension when blended with asphaltenic crudes. Desalter operations must be carefully adjusted, according to Lordo, to control potential problems such as overhead corrosion, heater fouling (both organic and inorganic based fouling), etc. Other problems with these opportunity crudes, such as when combined with WCS, Eagle Ford and others, are a result of their high lead content, volatile phosphorous and other contaminants.

Understanding the causes of these problems are but the beginning to the challenges in finding cost effective solutions and maintaining unit run lengths that many refiners are extending to stabilize margins.