What will this "pressurized air at the molten pit" be used for?
In that service (whatever it is) what are the quality requirements (pressure, reliability, water levels, particle content, etc.)?
How much will be used at a time? (Maximum, minimum, average)?
How much can your current instrument air deliver at that location?
More generally, why do you think you have two independent sources of pressurized air at your plant that are called two different things with two different quality and reliability standards?
Here is some information on the requirements for liquid sulfur tanks. The quantity of air is enough that one would utilize a stand alone "blower" or "fan" utilizing atmospheric air for the application.
Utilization of plant air or instrument air would more than likely exceed the capacity of an "in plant" plant air / instrument air system.
