Structurally required? I-beam support under stair opening header
2x8s aren't adequate for floor joists by modern standards, let alone for beams (even doubled). Someone probably added the steel beam and post due to floor bounce or sag. My former home had something nearly identical underneath where a fireplace was added. 

I'd either leave it in place or bolster the doubled 2x8s that are along the duct with additional support in other ways:


Add another beam underneath them.
Replace them with a 3-1/2" laminated beam of the appropriate height (consult an engineer).
Add a post to halve the span. This would require adequate footing structure, of course.