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After a few starts and restarts over the past few weeks, Royal Dutch Shell Plc was working to restart the heavy oil hydrocracking unit (HCU) at its 235,000 barrel per day (bpd) Convent, Louisiana, refinery, said sources familiar with plant operations.

The Convent refinery was restarting the 12,000 bpd isomerization unit May 15 after it tripped offline earlier in the day, the sources said in a Reuters report. The 45,000 bpd heavy oil hydrocracker, called the H-Oil Unit, was expected to remain shut for at least another two weeks before Shell decided late in the morning on May 15 to attempt a restart of the unit this week, the sources said.

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Officials later said the H-Oil Unit could return to production at full capacity by May 22 for the first time in nine months. No official word released as to if it was back in operation.

The H-Oil Unit has not run at full capacity since an Aug. 11, 2016 fire heavily damaged the hydrocracker.

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It ran at half capacity from late November to early March, when the HCU shut down in preparation to restart at full capacity once all the damage from the August blaze was repaired.

A fire broke out on the unit on March 18, requiring a further three weeks of repairs. As those repairs were nearing completion in early April, the decision was made to keep the H-Oil Unit shut for up to three months to repair cracks in welding revealed by X-ray photographs.

In late April, those plans were shelved and the hydrocracker was scheduled for restart the first week of May. The early May restart was halted to repair pinhole leaks.

The Convent refinery’s H-Oil unit is unique because it converts residual crude under high heat and pressure in the presence of hydrogen and a catalyst into motor fuel.

Most refineries send their residual crude to a coking unit to produce motor fuel feedstock and make petroleum coke, a coal substitute.

In April, Shell assumed sole ownership of refineries in Norco and Convent as part an agreement with Saudi Aramco to split up the assets of their Motiva joint venture. 

Maximizing production from the H-Oil Unit was the central reason Shell executives devised a plan to link up the Convent refinery with Shell’s 237,700 bpd refinery in Norco, Louisiana, 37 miles east. As part of that plan, Shell has weighed idling the gasoline-producing fluidic catalytic cracking unit (FCCU) at Convent to emphasize the hydrocracker’s production of diesel, which has become a lucrative export for Gulf Coast refiners.

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