Planning Ahead for Effective Canadian Crude Processing
Heavy conventional and bitumen-based crudes from Canada represent a significant volume increase in feedstocks for North American refineries, as production and transportation infrastructure is developed. Some shipments of these feedstocks have already been processed in Gulf Coast refineries. But aside from existing heavy Canadian crude processors, many refiners may not yet recognize the full scope of these feedstocks or the complex processing challenges they pose in terms of desalting, corrosion, fouling and wastewater operations. This paper, based on extensive Baker Petrolite experience, suggests that successful processing will depend on implementing a combination of treatment “best practices,” which have already been proven on these feedstocks.
The Coming Boom in Production and Processing
Refineries in the U.S. Midwest, the Great Lakes, the Rockies and Canada already process a variety of crude feedstocks from Alberta and Saskatchewan (often denoted as Western Canadian Sedimentary Basin, or WCSB, crudes). These include conventional heavy Canadian crudes and synthetic crudes from the oil sands bitumen upgraders in Alberta.
More recently, diluted bitumens (dilbit) from in-situ steamassisted gravity drainage or cyclic steam stimulation production, and combinations of bitumens and synthetic crudes (synbit and syndilbit) are also being produced.
Continued growth in these feed streams is antipated, world oil prices notwithstanding. Production and transportation strategies are driven by producers’ need for expanded export capacity, economic sources of diluents, and U.S. refineries’ need to maintain diversified sources of supply.
In one “moderate growth case,” total WCSB oil production is projected to increase to almost 3.3 MMBPD in 2020 from about 2.4 MMBPD in 2008. Also, current and future pipeline projects will allow this increased WCSB production to reach the U.S. Gulf Coast, the Atlantic Coast, Southern Illinois/Ohio, Oklahoma/ Kansas and ports in British Columbia.
This category’s wide variety of feedstocks exhibits fundamentally different characteristics. In fact, “the composition and contaminant levels of bitumen-derived crudes does not make them an easy replacement for conventional crudes, especially since most existing refineries have limited capacity to accept poorer quality feedstocks.” The impacts of these streams on profitable refinery operations will be significant. However, there is still considerable industry uncertainty about exactly when and how these feedstocks will find their way into the U.S. and overseas markets.
Understanding the New Feedstreams
In the future, actual WCSB uptake will depend on many factors. Key variables include the rate of WCSB production increases, capacity and actual completion dates of pipeline projects, competing crude pricing, diluent availability and pipeline tariffs imposed.
Market acceptance of Canadian feedstocks is a function of pricing, chemical and physical properties, and the speed and extent of refinery project investments to allow processing of these feedstocks. Most heavy, sour WCSB feedstocks will be shipped to refineries already configured for these types of crudes, i.e., those with sour coking configurations.
Most of these facilities are on the Gulf Coast, which are already processing heavy, sour and high-total acid number (TAN) crudes from Venezuela, Brazil and Mexico. Most lighter, lower-sulfur feedstocks (synthetic crudes) are expected to be shipped to the low- to medium-sulfur refineries in the Mid-Continent, Midwest and Great Lakes regions of the U.S. Upon completion of pipeline projects to coastal British Colombia, higher volumes of WCSB crudes will be available for the West Coast market. Heavy, sour feedstocks should be processed at the refineries in California, which are already configured for heavy, sour, high-TAN crudes. Other WCSB grades would be suitable for the low- to medium-sulfur crude units in California and Puget Sound refineries.
Several refineries have already initiated or announced projects designed to increase WCSB processing capability, but understanding which refineries are the best candidates to receive these feedstocks is important. The specific processing challenges posed by these feedstocks depend on the physical and chemical characteristics of the feedstocks, their behavior when blended with other crudes, and the configurations and capabilities of the refineries’ process units.
WCSB Crudes: Direct Processing Challenges
Athabasca bitumens are high in sulfur, nitrogen, CCR, metals and TAN.
This assay suggests that heavy, sour, high-TAN diluted bitumens and blends will present several processing problems for refiners. Synthetic crudes tend to have high, heavy vacuum gas-oil yield; lighter distillates are high in aromatics and produce straightrun diesels with very low cetane numbers.
Refinery Constraints and Modifications for Oil Sands Crude Processsing
The most challenging WCSB feedstocks, from the standpoint of crude unit operations, are the heavier crudes that contain high levels of filterable solids, unstable asphaltenes or difficult-to-remove chloride salts due to thermal stressing of the hydrocarbon during production. Since the filterable solids, asphaltenes, and salts are concentrated in bottoms fractions, the more difficult feedstocks tend to be:
- Heavy, conventionally produced crude oils
- Thermally produced oil sands bitumens diluted with lighter hydrocarbons or synthetic crudes to meet pipeline gravity and viscosity specifications
Most heavy feedstocks exported from Western Canada range from 19-22° API, which creates additional desalter challenges due to resulting higher crude blend viscosities. However, there are also lower-density crudes coming from this region that can be problematic, owing to their high-filterable solids contents.
Typical desalter problems include effluent water with high oil and solids content (and subsequent problems at the wastewater treating plant), poor desalting efficiency, uncontrollable emulsions, and basic sediment and water (BS&W) carryover into desalted crude. Effective wastewater treatment is another key factor in solving the complex treatment challenge.
The same feedstocks that cause desalter problems can also cause crude unit distillation column overhead corrosion problems due to the higher chloride loadings caused by lower desalter performance. Thermally produced bitumens from the Athabasca oil sands deposits may also be high TAN, which can cause upgrader or refinery high-temperature naphthenic acid corrosion problems in the crude unit atmospheric and vacuum distillation systems. They can also contribute to crude unit distillation tower overhead corrosion problems, as high TANs promote salt hydrolysis to hydrogen chloride and can thermally degrade to form lower molecular-weight organic acids. These acids can increase both unit neutralizer demand and overhead system corrosion potential.
The high solids contents and unstable asphaltenes in these crudes can increase crude preheat exchanger and atmospheric and vacuum column heater fouling. Increased heater fouling can also be experienced in downstream delayed coker units. Most 100% synthetic crudes will cause minimal crude unit processing problems, as they do not contain any unconverted bottoms (bitumen) fractions. Their lower sulfur, nitrogen and TAN contents also prevent most downstream unit problems.
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