There are a quite a few licensed processes. It generally takes a special furnace and boiler design. The smallest ones typically run about 300000-400000 lb/hr of SH steam and burn 2000+ tons of sulfur per day. Most refineries do not produce enough sulfur to justify the cost, but if you are and you have a demand for several thousands tons of acid per day I am certain that you will generate some interest.
Try Chemetics or EnviroChem, for starters. There are several others that service the refining industry.