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What type of flexibility can be built into a hydrocracker to quickly shift from naphtha to diesel output?

Feb-2025

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James Esteban, Unicat Catalyst Technologies, James.Esteban@unicatcatalyst.com

In the ever-evolving landscape of hydroprocessing, the ability to adapt operations swiftly is paramount for refiners aiming to optimise production and meet market demands. A well-designed graded bed system, particularly utilising Unicat’s Advanced Filtration System (AFS) and MagAFS technologies, is essential for enhancing the operational flexibility of hydrocrackers. These systems not only optimise catalyst performance but also ensure that refiners can respond effectively to changing product requirements, such as shifting from naphtha to diesel output.

The design of the catalyst bed is fundamental to the efficiency and longevity of hydrocracking operations. AFS technology provides a unique solution by offering high available void space and optimised flow channels, mitigating pressure drop, which is critical in maintaining consistent reactor performance. The AFS allows for uniform distribution of reactants, ensuring that the catalyst operates at peak efficiency throughout its lifecycle.

Refineries utilising AFS have reported significant improvements in operational metrics. For instance, one facility experienced a 150% increase in cycle length compared to traditional grading systems, leading to reduced downtime and enhanced profitability. This extended cycle life translates to lower operational costs and improved throughput, allowing refiners to maximise output without compromising product quality.

Hydrocracker flexibility
The flexibility built into hydrocracker operations through advanced catalyst systems like AFS and MagAFS is multifaceted. The ability to quickly adjust operational parameters allows refiners to optimise yields based on real-time market conditions. When transitioning from naphtha to diesel production, the graded bed system can accommodate changes in feed composition and processing conditions without significant downtime. In one case, a refinery successfully shifted its output from naphtha to diesel within a matter of hours, thanks to the rapid response capabilities enabled by the AFS. This adaptability not only meets immediate market demands but also positions the refinery to capitalise on price fluctuations, enhancing overall profitability.

Integration of demetalisation catalysts within the AFS framework enhances the ability to process a wider range of feedstocks. By effectively removing contaminants such as metals, these catalysts prolong the life of the primary hydrocracking catalysts and facilitate smoother transitions between different product outputs. Facilities employing Unicat’s demetalisation and grading catalysts have reported a minimum of a 30% reduction in catalyst replacement frequency, significantly lowering maintenance costs and improving operational efficiency. This reduction in downtime and/or process unit utilisation is crucial for maintaining continuous production and meeting customer demands.

Significant demetalisation of the feed to the hydrocracker using MagAFS is seen in commercial operations on naphtha (light coal tar). This process has successfully demonstrated the removal of up to 98% total solids and 60-100% various metals in the feed steam, as shown in Table 1.

Although vanadium is not shown in the tested liquid stream, the mass susceptibility (magnetising characteristic) of V₂O₃ (1,976 x 10-6 c.g.s. unit) is much higher than that of NiO (600 x 10-6 c.g.s. unit). Therefore, V₂O₃ is easier than NiO to be removed by MagAFS.

In conclusion, the implementation of a well-designed graded bed system using AFS and MagAFS technologies is vital for enhancing the flexibility of hydrocracker operations. By ensuring optimal catalyst performance and facilitating quick adjustments in production outputs, these systems empower refiners to confidently navigate the complexities of the market effectively. The commercial performance results underscore the tangible benefits of these technologies, demonstrating that refiners can achieve longer run lengths, lower pressure drops, and improved profitability. As industry continues to evolve, the importance of such innovative solutions will only grow, positioning refiners to meet both economic and environmental challenges head-on.

Jan-2025
Peter Nymann, Topsoe, pan@topsoe

In general, changes to the operation of a hydrocracker should never be made quickly due to safety concerns. It is possible to operate a hydrocracker in ‘swing mode’ where the product objectives switch between maximising middle distillates (MDs) and maximising naphtha. This requires a margin in the operating temperature of the catalyst, so it should be a medium-to-high activity hydrocracking catalyst. If the unit is operated in recycle mode, maximum (‘max’) MD is favoured, and changing to once-through operation will lead to a switch to a higher naphtha production rate.

High-activity catalyst may be installed in the latter part of the hydrocracking reactor, and the temperature profile may be changed from ‘equal-outlet’ to ‘ascending’ to move more conversion to the more active catalyst with a higher naphtha selectivity. The change in temperature profile may be amplified in case the unit has several reactors, and a heat exchanger is installed between the two last reactors so that the high-activity hydrocracking catalyst can be operated colder during max MD production and hotter during maximum naphtha production campaigns.

It is important to check that the fractionation section, especially the overhead section and light ends recovery sections, can handle higher amounts of light material inadvertently being produced during maximum naphtha production if the unit normally produces max MD. It should also be checked if the unit is able to provide the necessary lift of light material during max MD production in case normal operation is max naphtha. Hydrocrackers are, in general, very flexible, and a full range of catalysts from max MD to max naphtha production may be applied with the right expertise and safety considerations.

Jan-2025
Heather Gilligan, Imubit, heather.gilligan@imubit.com

Closed-loop artificial intelligence optimisation (AIO) technologies, such as manipulated available handles (for example, reactor temperature and fractionator targets), drive towards a pre-computed optimal product mix based on a provided price set. This can occur for a single-unit or multi-unit system. The AIO model looks at economic objectives and constraints, manipulating the handles to the optimal position to maximise the profit of the unit or the system as a whole.

Moving from naphtha mode to diesel mode can have two transition points. The first is deconverting the tower to maximise naphtha into the diesel cut, often to a flash constraint, once diesel is the more valued product. However, reducing conversion/reactor temperatures to make more diesel frequently comes with a loss of liquid value gain, so diesel needs to have an even greater price advantage over naphtha before reducing reactor temperatures becomes attractive.

Imubit’s AIO models are built on deep neural networks that ‘learn’ the nonlinear liquid volume gain and conversion curves associated with changing the reactor temperatures. This occurs not just at a single point in time but across the catalyst cycle as the catalyst deactivates, so the reactor stays optimised whether this transition occurs with fresh catalyst or just before the next changeout.

Jan-2025