Question
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What type of flexibility can be built into a hydrocracker to quickly shift from naphtha to diesel output?
Feb-2025
Answers
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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
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