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The crude oils that Petrobras processes at its 11 refineries in Brazil are among the most difficult to process in the world.

The predominant crude oil is Marlim, which is produced offshore Brazil, is heavy and highly naphthenic, and has a low API (19).

Marlim’s sulphur content is relatively low (0.78%), but its elevated nitrogen content presented Petrobras’s refineries with a serious challenge when the country tightened its fuel specifications.

Although Brazil’s clean fuels journey has lagged behind the USA and Europe, the country introduced specifications equivalent to Euro V (10-ppm sulphur in diesel) at the beginning of 2013.

In addition, the naphthenic crude characteristics translate to high density and a low cetane number for diesel streams in comparison with other crude sources, which makes it even more challenging to meet Euro V diesel quality.

Silvio José Vieira Machado, Senior Consultant, Hydroprocessing Technology at Petrobras, explains what the crude’s characteristics mean for the country’s refineries.

“In diesel hydrotreating units in ultra-low-sulphur-diesel (ULSD) service in many other parts of the world, the sulphur content is the principal  challenge,” he says.

“But for us, it is the nitrogen content. The nitrogen levels in our crude oils are among the highest in the world, which means that the cracked feedstock components in the light cycle oil from the fluidised catalytic cracker and the delayed coker streams are also high in nitrogen.

“This is a problem,” Machado continues, “because high nitrogen content inhibits desulphurisation and the aromatic hydrogenation that is necessary for the additional density reduction and cetane number improvement to meet Euro V specifications. Consequently, it is extremely difficult to achieve the high conversion levels that are necessary to produce 10‑ppm sulphur diesel.

Furthermore, the more stringent cetane and density specifications present an additional challenge owing to the high level of (aromatics) cracked stocks we process.”

At the same time as responding to Brazil’s new cleaner fuel specifications, it also became vital for Petrobras to increase its refining capacity.

Brazil has one of the highest rates of growth in demand in the world for transportation fuels and Petrobras, the country’s only refiner, was striving to satisfy the growing demand for domestic fuel and to become an exporter.

Petrobras’s response included a plan to revamp an existing, moderate-pressure diesel hydrotreater at its Paulínia refinery (REPLAN) for ULSD service.

The unit, which has two reactors in series, was originally designed to produce 500-ppm sulphur diesel at a feed rate of 5,000 cubic metres a day.

Petrobras’s objectives were to revamp the unit to produce 10-ppm sulphur diesel and to increase its capacity.

Another benefit is that the timeline of the revamp project was much less than it would have been to build a new unit, having been installed in less than two years from the time of first evaluation.

Technologists from the refinery and Petrobras’s technology arm joined forces with catalyst and process experts from Shell Global Solutions and Criterion Catalysts & Technologies (Criterion) to investigate solutions.

The team found a way to achieve the objectives, which was a drop-in solution that involved using Shell Global Solutions advanced reactor internals in combination with the new state-of-the-art catalyst CENTERA™ DN-3630 from Criterion.

“CENTERA DN-3630 is a fabulous catalyst in terms of activity and stability,” says Machado, “and the reactor internals are designed to increase the reactor utilisation.

By using these together, we have been able to meet the ULSD specification.

In addition, we have been able to debottleneck the unit to make more diesel.

This enabled us to increase the loaded catalyst volume by 19% without increasing the total reactor volume, which helped to increase the unit’s capacity to 6,000 cubic metres a day.

Another benefit is that the timeline of the revamp project was much less than it would have been to build a new unit, having been installed in less than two years from the time of first evaluation.

All the modifications were also completed in the normal turnaround period of just over a month.”

“Petrobras had a need to modify its units cost-effectively to make cleaner fuels,” adds Sal Torrisi, Director of Strategic Accounts, Criterion Catalysts &  Technologies.

“Of course, this is not a unique story, but what makes it distinctive is the fact that they are also processing the most difficult feeds in the world.

“To increase its refining capacity and meet its clean fuels mandate, Petrobras has been building big, high-powered units while simultaneously revamping existing units,” says Geraldo Márcio Diniz Santos, REDUC Refinery Optimisation Manager, Petrobras.

“These revamps have significantly reduced the required investment because their capital cost is about 5–20% that of the grassroots units.”

Torrisi is quick to add, however, that a revamp is by no means a simple procedure.

“It is difficult to squeeze more out of an established asset and it calls for a lot of expertise in different disciplines, but, as Petrobras has demonstrated with these projects, revamps can be extremely effective solutions,” he says.

Petrobras management deemed the REPLAN project a major success and the organisation subsequently rolled out the same approach to revamping diesel  hydrotreaters at its refineries in Duque de Caxias (REDUC), and at its Presidente Bernardes refinery (RPBC) in Cubatão.

Both locations were also able to increase capacity by about 20% while meeting the more stringent sulphur specification.

“These revamp projects have enabled the units to produce more diesel at a much higher quality specification while using our difficult domestic feedstock,”  Diniz Santos concludes.

“And in each case, the capital required was a fraction of that required for an equivalent grassroots unit.

They have been extremely valuable and cost-effective solutions.”