The owners of Diamond Green Diesel are evaluating an expansion that would double the capacity of its Norco refinery to 550 million gallons of renewable diesel fuel per year.

Darling Ingredients Inc. and Valero Energy Corp. already are expanding annual production capacity at Norco from 160 million gallons to 275 million gallons of renewable diesel made from recycled animal fat, used cooking oil and other feedstocks. That $190 million project is targeted for completion in second-quarter 2018.

The companies said Tuesday they will initiate an engineering and construction cost review to analyze an additional expansion for a potential startup in the first half of 2021. A final decision on the proposed project is expected in 2018, based on results of the review as well as the status of government regulations, the companies said. The proposed expansion would be built on property owned by Valero.

The Diamond Green facility is adjacent to Valero’s St. Charles refinery, which is connected to a major pipeline.

The companies said they anticipate growing demand for renewable diesel because of the Renewable Fuel Standard and global low-carbon fuel markets.

"Diamond Green Diesel has proven to be a tremendous success and we acknowledge Valero's engineering excellence as the key," said Randall C. Stuewe, chairman and chief executive officer of Darling Ingredients Inc. "Our partnership through DGD has created a sustainable and efficient process of converting Darling's feedstocks into high-quality biofuels to meet the needs of our customers around the world."

Darling, of Irving, Texas, supplies the feedstock for the plant, which includes recycled animal fat and used cooking oil. Diamond Green Diesel's product is compatible with petroleum-based diesel and can be mixed into Valero’s general diesel fuel supply to produce a biodiesel fuel that meets low-carbon fuel standards.

Darling is the world's largest publicly traded developer and producer of sustainable natural ingredients from edible and inedible bio-nutrients, creating a range of ingredients and specialty products for customers in the pharmaceutical, food, pet food, feed, technical, fuel, bioenergy and fertilizer industries.

Valero Energy Corp., through its subsidiaries, manufactures and markets transportation fuels and other petrochemical products internationally. The Fortune 50 company, based in San Antonio, Texas, has 15 petroleum refineries and 11 ethanol plants.