Graf Spee had a oil conversion plant using steam
No. GS used diesel fuel from her bunkers, not heavy oil. The steam powered system of which you speak was the filtration systems for the diesel and lubricating oils. Fuel was pumped from the bunkers to settling tanks, and thence through mesh filters to remove larger solid particulates and bio contaminants. The partially filter fuel then went to the steam activated banks of centrifugal separators, that in essence polished the fuel, to use a modern term, by removing smaller particulates and water droplets. The cleaned fuel was then deposited in the day use tanks for the engines.