The plant, in the northern Chinese port city of Tianjin, will also undergo retooling work to allow it to produce more lower-sulphur refined products, including marine bunker fuel that meets new global emission rules, said the official with direct knowledge of the matter. He declined to be named as he's not authorized to speak to media.

Sinopec Tianjin Petrochemical Corp will shut down the 12.5 million tonnes per year (tpy), or 250,000 barrels per day, refinery from early May through early July.

The overhaul will cut crude throughput this year by some 2 million tonnes, or roughly 16% from the 2019 production level, the source added.

The complex will also switch off its entire ethylene facilities for maintenance, including a one million tpy plant and a 200,000 tpy facility, said the source. The larger facility is a joint venture with Saudi Basic Industries Corp.

Sinopec Corp did not immediately respond to emails seeking comment.

The company is adding secondary units -- including a residue desulphurizer (RDS) and hydrotreating facilities for gasoline and diesel -- to an existing crude distillation unit able to process 50,000 barrels of crude oil a day.

"The Tianjin plant is following many other Sinopec refineries that are equipped with RDS facilities," said the source, adding that the revamp is due for completion in October.

After the retooling, the plant will mothball an aging coking unit making high-sulphur petroleum coke for which demand has been shrinking due to environmental reasons.

By Chen Aizhu