Hydrocracker revamp lifts product flexibility
How an innovative moving bed technology enabled a major refinery to improve residue conversion and crude flexibility.
JOHN BARIC and COEN HODES
Shell Catalysts & Technologies
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The refining sector is once again in a transition period. The International Maritime Organization’s 2020 fuel sulphur mandate has introduced a need for significant changes in a refinery’s management of its fuel oil pool; demand for gasoline and diesel continues to decline in some regions; and there is continuous pressure to sustain margins, especially as new capacity comes on-stream in Asia and the Middle East.
Consequently, two key objectives have emerged: the need to reduce fuel oil production and to increase margins. To reduce fuel oil production, refiners with an abundance of capital could consider investing in the technologies that provide the highest conversion levels, such as slurry hydrocracking or ebullated bed residue hydrocracking, but these will be out of reach for most.
The combination of solvent deasphalting (SDA) and deasphalted oil (DAO) hydrocracking offers one of the lowest capital cost options for residue conversion, especially compared with slurry hydrocracking. The depth of extraction depends on the crude and the technology, which needs to handle high contaminant feedstocks.
Although this combination is considered a relatively new option, it has been applied at several sites over the last decade. Traditionally, DAO had to be processed in a fluidised catalytic cracking (FCC) unit because of its high metals and Conradson carbon residue (CCR) content, but can now be processed in a hydrocracking unit (HCU) with a modern, well-designed catalyst system featuring a demetallisation catalyst followed by pretreat and cracking catalysts.
To increase margins, many refiners are shifting away from the traditional Middle Eastern crude mix to incorporate lower-priced heavy crudes from Mexico, Canada, or Venezuela.
However, compared with traditional grades, such crudes can present substantial challenges because they typically have a high total acid number and high aromatics, metals, and nitrogen contents.
A high sulphur content is relatively easy to manage with today’s high activity catalyst systems; however, metals such as nickel and vanadium are extremely difficult to remove. The amount of lower-priced crude that can be processed is often limited by the performance of the refinery hydrocracker or residue hydroprocessing unit.
Other refiners want to take advantage of their hub location and invest in revamps to enable increased flexibility for their bulk crude diet. This enables the refinery to take advantage of short-term fluctuations in crude pricing, and increases the refinery’s economic robustness against longer term market disruption and trends.
Studies by Shell Catalysts & Technologies have shown that refiners with full flexibility to take crudes of differing qualities from several supply regions can also capture margin benefits of up to $0.5/bbl compared with those that have a restricted feed diet. This could unlock a total value of up to $31.5 million if applied to 90% of the core diet of a typical 200000 b/d refinery.
Shell Hycon MB technology can be used as a revamp option to remove constraints in the downstream hydrocrackers and residue hydroprocessing units, and enable the desired crude flexibility.
About the unit being revamped
Pernis’s Hycon unit started up in 1989 and was designed to enable the processing of high metals vacuum residue (VR) feeds from crudes such as Maya. This produced vacuum gasoil (VGO) for a high conversion FCC unit and a modest, but low sulphur residue stream for low sulphur fuel oil.
Key to its operation were the three moving bed reactors in which the hydrodemetallisation catalysts were continuously replenished to maintain a consistent activity level without deactivation over time (see Figure 1). The unit consistently achieved two-year cycles, whilst processing 100% VR feeds.
Fast forward to 2018 and the market had changed. The site’s management needed to reduce exposure to the forthcoming changes in bunker fuel specifications and also saw value in increasing crude flexibility.
Pernis’s response was to install a new SDA unit, to revamp the gasification unit, and to repurpose the Hycon unit by changing its mode of operation from VR hydrocracking to DAO hydrocracking. The unit now predominantly produces on-specification Euro 5 diesel.
As the new feed to the unit had lower levels of contaminants, especially metals, only the single moving bed lead reactor was necessary for demetallisation. Consequently, two of the moving bed reactors were converted to fixed bed mode (see Figure 2).
The key to the project has been the ability of Shell Hycon MB technology to remove metals from heavy DAO feed, which can severely limit the performance of an HCU.
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