What kind of flue is this?

Hi Everyone,
I'm renovating a 1975 vintage house and have a 30' vertical flue from a gas fireplace that I need to deal with. The flue is ~16" in outside diameter and ~6" interior (double walled) and apparently the space between the inner and outer walls is filled with tightly packed fiberglass. There is a nearly illegible label that says in part "... 123 starter section".
Can anyone tell me the name of this type of flue so I can figure out how much it weighs, how the sections are joined, etc? I'm removing the gas fireplace and want to decomission the flue as easily as possible, but it is resting on top of the stove insert with no other visible means of support. It was lifted into place with a crane as one piece into a woodframed chase on the side of the house. I want to frame in some sort of permanent support and cut the bottom section out, then seal the flue. I don't want to mess with the roof cap or anything else, if possible.
Any info or ideas would be appreciated.
Thanks, Mitch
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