Apr-2015

Fine-tuning for maximum diesel (TIA)

Sweden’s largest refiner, Preem AB, expects optimum performance from all elements of its refinery, which is one of the most modern in Europe.

Tereas Brod
Criterion Catalysts & Technologies:

Article Summary

Consequently, the company went to the market for new reactor internals when it discovered there was scope to improve the catalyst utilisation in its hydrocracker and maximise diesel yield.

Preem operates a single-stage, two reactor, 142 bar, 53 000 b/d hydrocracker at its 220 000 b/d Preemraff Lysekil facility. Studies showed, however, that only about 85% of the two reactors’ catalyst volume was being utilised owing to thermal maldistribution. Thermal maldistribution in pretreatment and cracking reactors is a common issue that can cause performance limiting hot spots and dry areas. In an effort to boost catalyst utilisation, Preem’s technologists called on catalyst vendors to suggest their best catalyst option and reactor internals to solve this problem. The proposed catalysts were then tested competitively, back to back, at an independent pilot plant testing laboratory. After successful testing, Shell Global Solutions’ reactor internals and catalysts offered through Criterion Catalysts & Technologies (Criterion) were selected and implemented at Preem’s refinery during a 2013 shutdown.

Shell’s internals include high dispersion (HD) trays, which provide ultra-uniform vapour-liquid distribution and excellent thermal distribution; ultra-flat quench (UFQ) interbed internals for uniform process and quench mixing at the interbeds; catalyst support grids for improved catalyst retention and better fouling handling; and a skirt to raise the HD tray and provide more catalyst volume.

Installing the new internals has led to a 10% increase in the amount of catalyst that can be loaded into the reactor and, because of the improved dispersion, nearly 100% of the catalyst is now being used. The quick to open and close design also means that the time spent on any future maintenance of the new reactor internals will be less, which means more on-stream days for the hydrocracker. Criterion also provided its most active and stable pretreatment catalyst, Centera DN-3620 Z-2513, which offers outstanding selectivity for middle distillates; and guard beds and grading to protect the pretreatment catalyst from fouling. The catalyst and the internals are already improving performance and helping Preem to run its hydrocracker at a higher conversion rate. “The results so far are all in line with Criterion’s catalyst offer and the pilot plant tests. They are not due only to the internals, although we do have an excellent temperature profile in all four beds. The internals ensure that we can benefit from the new, improved catalyst throughout the cycle,” says Mats Hörnfelt, Senior Process Engineer with Preemraff Lysekil. “The advantage of the catalyst is its selectivity towards diesel with lower yields of fuel gas and naphtha, which were limiting the throughput of the last cycle. This enables us to run at a higher conversion within the maximum fuel gas and naphtha make. In fact, we are close to the maximum rundown of diesel at a lower feed rate, which is very valuable when you are importing hydrocracker feed.”

Since start-up of the catalysts, Criterion has continued to support Preem with continuous monitoring and technical services to ensure that the catalysts function as predicted and that the hydrocracker performs to its full potential over the long term.

This short case study originally appeared in PTQ's Technology In Action feature - Q2 2015 issue.
For more infomation, please contact Teresa.Brod@CRI-Criterion.com