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After two hydrocracker cycles that were challenged by pressure drop, reliability issues and short cycle lengths, the technologists at the Total refinery in Normandy, France, asked Criterion Catalysts & Technologies (Criterion) and Shell Global Solutions to help resolve these issues.

The unit was not a Shell design but it was imperative that the refinery should address the root cause of its problems, as Total also needed to increase the hydrocracker capacity to produce more valuable middle distillates.

By working together, the three companies have been able to identify the issues that were causing the hydrocracker’s production downtime and improve its operability.

The hydrocracker, which was already the largest in Europe and can now process up to 10,000 tonnes per day, was built in 2007.

A single reactor configuration, it originally featured six catalyst beds.

The first four were to pretreat the feed to remove nitrogen, sulphur and aromatics, and the last two beds  hydrocracked the intermediate product into ultra-low-sulphur diesel, kerosene and naphtha.

About 50% of the hydrocracker feed is imported vacuum gas oil.

Theo Visser, Senior Technologist Hydrocracking, Criterion Catalyst & Technologies, explains that, because the quality of this is variable, the pretreatment sections are particularly important.

“A lower-quality vacuum gas oil can affect the  performance of the hydrocracking catalyst by accelerating its deactivation rate,” he says.

“We found that one reason why the unit could not achieve its target cycle length was because it was experiencing a high radial temperature spread over the pretreatment catalyst beds.

This is common when conventional distribution trays are used.

The combination of higher radial temperatures and the higher deactivation rate caused by the lower feed quality resulted in an unpredictable and hard to manage cycle length.

“Poor thermal distribution can also lead to hot spots in the cracking beds,” he continues.

“This can cause temperature runaways and change the yield  pattern, which means that the unit may make more gas compared with during normal temperature distribution.”

Edwin Maas, Principal Engineer, Shell Global Solutions, adds that there were further challenges.

Total’s original request was for Shell Global Solutions and Criterion to replace the reactor internals on a like-for-like basis.

However, closer inspection revealed several other aspects of the reactor’s design were limiting its performance.

For instance, the catalyst support grids had a very low net free area.

“The catalyst support grids were fouling extremely quickly because they were actually acting as filters,” Maas says.

“Moreover, we identified that beds two and three could be combined into one without affecting reliability.

This meant that because one set of interbed internals could be omitted there was the potential to load much more catalyst into the reactor, which would enhance capacity and cycle length,” he concludes.

By working together, the three companies have been able to identify the issues that were causing the hydrocracker’s production downtime and improve its operability.

After a series of technical discussions during which Shell Global Solutions and Criterion demonstrated why the unit was not achieving the desired performance and the potential value that could be captured, Total gave the go‑ahead to remove everything inside the vessel and completely rebuild it.

Shell Global Solutions provided the entire reactor internals system, which includes high-dispersion (HD) trays, a filter tray, ultra-flat quench interbed internals, catalyst support grids and a compact bottom basket.

While Visser was responsible for the technical performance of the catalyst, Maas was in charge of the reactor internals.

“We worked together to estimate the expected performance of the catalyst,” says Visser, “Shell Global Solutions’ HD trays offer superior distribution, which means you can utilise more catalyst.

It is good to have such in-depth interactions because there is a strong correlation between reactor internals and catalyst performance.”

“Safety is always our top priority at Shell, and the new reactor internals reflect this.

They have been equipped with very large, quick-to-open internal manways that offer easy and fast access to all the beds, which minimises the inert entry time.

This important safety feature will facilitate reduced shutdown time in future catalyst changeouts,” adds Maas.

The hydrocracker debottlenecking exercise was one element of Total’s RN 2012 project, a major $980 million upgrade programme of 13 projects to build, revamp or replace units.

This project was a response to the declining petroleum product consumption in Europe and the market’s shift away from gasoline and heating oil to diesel.

To install the internals, load the catalyst and start up the unit, Shell Global Solutions and Criterion had up to three people on the site for 30 days.

Elisabeth Vayssettes, Senior Account Executive, Criterion Catalyst & Technologies, project managed Shell Global Solutions and Criterion’s activities and dealt with the scheduling, permitting issues and risk assessments.

She explains that it was important to take into account the other projects that were being delivered across the refinery.

“RN 2012 was an enormous programme,” she says.

“At one point, there were up to 4,000 additional contractors on the site, which of course added an extra layer of complexity to what we were doing.”

Nevertheless, the project was delivered well within the schedule.

Total’s management was excited and has expressed its satisfaction.

Raphaël Le Gall, Manager Process Engineering, Total Raffinerie de Normandie, explains that the reactor internals’ installation and maintenance characteristics are highly significant for Total.

They have a boltless design and welding is not required, which facilitates fast installation and simplifies maintenance tasks.

“Shell installed them in 30% less time than we had scheduled,” he says.

“This will also be valuable at the end of the run, as it could help us to reduce the turnaround duration.

“We were keen to adopt Shell’s reactor internals because their performance in other hydrocrackers that we operate around the world has been impressive,” Le Gall adds.

“They have been the key to us increasing the cycle length, operability and reliability of the hydrocracker at Normandy.”