Impact of bitumen feeds on the FCCU: part I
The impact of processing bitumen-derived feeds on FCC operations and product yields is assessed, and the capital investments required to process varying quantities of bitumen feeds are discussed
Keith A Couch, James P Glavin and Aaron O Johnson
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Refining rates worldwide have been steadily increasing since 1997. Many refiners have pushed existing assets to maximum throughput and utilisation. To accommodate additional growth, the refining industry has seen an extensive amount of investment in recent years, especially in the Middle East and Asia. Many of the new refinery and crude expansions are world-scale, in the range of 350–
600 000 bpsd, and are being constructed at an incredible pace. Several will be realised in less than three years from their start date. In addition to leveraging economies of scale, they utilise state-of-the-art designs, equipment and controls for greater energy efficiency and reduced Opex. They are highly integrated with both aromatics and petrochemicals production to maximise value of upgrading, and provide greater flexibility to move with the market. However, with projects costing in the range of $6–12 billion, these advantages come at a hefty price tag that most US refiners are not expected to match.
As these projects start to come on-stream in 2008, US refiners will begin to feel the economic impact. One of the ways in which they will maintain a competitive position is to maximise the use of lower-cost opportunity crudes, such as Canadian oil sands bitumen-derived crude.
According to one company that operates both oil sands production and refining assets, the difference in upgrading oil sands-derived bitumen at a Midwest refinery instead of Alberta is approximately $3.50 per barrel.1 With this type of cost advantage, there is little doubt that many US refiners will look to increase their diet of Canadian bitumen in the near future.
Supply and composition
The primary importers of Canadian bitumen-derived crude oil to the US have historically been refiners in the Rocky Mountain states (PADD IV) and Midwest (PADD II). Wider use has been limited primarily by a lack of pipeline infrastructure to support an economically broader distribution. With numerous market pressures compelling refiners to consider increasing their diet of opportunity crudes, pipeline companies are actively working to upgrade their distribution capabilities by expanding mainlines to the US. Pipeline extensions to the East Coast (PADD I) and Gulf Coast (PADD III) are projected to be in service between 2010 and 2011, and to the West Coast of British Columbia for Pacific Ocean transport to both California (Southern PADD V) and the Far East between 2012 and 2014.
In 2007, Enbridge presented its understanding of Canadian export production growth and the associated pipeline capacity necessary to keep a pace with the capacity increase.2 The historical and long-range production forecasts are shown Figure 1.
Figure 1 shows that the production of Canadian bitumen-derived crudes is expected to reach 3.0 MM bpsd by 2015, which would constitute nearly 30% of the total imported crude volume processed in the US.
There has been a large number of heavy crudes historically marketed from Western Canada, which have varied widely in their assay properties. In an effort to provide a crude oil with consistent properties, a unique and standardised blend of synthetic crude, diluent and bitumen (SynDilBit) was developed by EnCana, Talisman, Canadian Natural Resources Limited (CNRL) and Petro-Canada, and has been marketed under the name of Western Canadian Select (WCS) since January 2005. WCS has essentially become the benchmark product from Western Canada, and is the crude basis on which refiners have most recently focused enquires to UOP regarding the impact that processing Canadian bitumen will have on their refinery and, more specifically, their FCC operation.
The blend specifications for WCS meet an API gravity of 19–22°, carbon residue of 7–9 wt%, sulphur of 2.8–3.2 wt%, and a total acid number (TAN) of 0.7–1.0 mg KOH/g. The resultant crude composition for WCS compared to a standard crude such as West Texas Intermediate (WTI) shows that WCS has three times more residual material than WTI, 50% more VGO, half the distillate and half of the naphtha (Figure 2).
In addition to the composition differences between WCS and more conventional crudes, the resulting VGO qualities are substantially different (Table 1).
While many refiners have invested to take advantage of processing heavier and sourer crudes, bitumen processing presents additional challenges. The FCC unit is the primary conversion unit for most US refineries, and is typically integrated with upstream hydrotreating and downstream alkylation and reforming units. As the crude composition changes with additional bitumen processing, the material balance around the FCCU changes substantially due to both the quality and volume of the feed. Bitumen-derived feeds have more VGO per barrel of crude, but come with the penalty of lower hydrogen and API gravity, and higher sulphur and nitrogen, as demonstrated in Table 1.
Understanding the impacts associated with each of these characteristics presents technical challenges that are critical when considering which investments are needed to achieve the highest overall product margin.
FCC feedstock can range from 15°–45° API, but is typically in the range of 20–25° API. Any API gravity change is due to a change in boiling range, crude type or both. If the API gravity decreases because the feedstock is less saturated (ie, more aromatic and less paraffinic, as is the case with processing bitumen feeds), the following changes can be expected:
- The feedstock will not crack as readily at the same reactor temperature and conversion will decrease
- At a constant conversion, there will be a lower gasoline yield, with a slightly higher octane
- Products will be more olefinic.
Characterisation factor (UOP K)
The UOP K is a characterisation factor that relates boiling point to specific gravity and provides a rough indication as to the quantities of paraffins or aromatics present in the FCC feedstock. The UOP K factor is given by:
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