Not a lot to it. You find fry places that will give you the oil. You heat it to remove the water and filter it to remove contaminants. If heated to 180F it can be used just like diesel without any chemical conversion. You cn also use it in a furnace.

So what kind of system do you need to remove all the particles from the oil like food etc.?

I thought you had to use a small home made refinery?

What about the used motor oil, what is the process for that?

Google Franze oil filter.