(Bloomberg) — In a sign of changing times, a U.S. oil refining company is converting one of its plants into a producer of clean fuel.HollyFrontier Corp.’s Cheyenne refinery will stop using crude oil and be repurposed to pump out renewable diesel, which is typically made from soybean oil, recycled cooking oil and animal fats. That’s after processing margins plummeted on the collapse in fuel demand due to Covid-19-related lockdowns. Besides, the old facility’s maintenance costs were “uncompetitive,” and the government is promoting cleaner fuel production.It’s the latest example of how the traditional fossil fuel industry is changing amid rising calls […]