Natural gas/LP is used to produce CO2 in GREENHOUSES.
NEVER EVER attempt to do this in an occupied building.

Furthermore, this thread is getting weirder than weird-
You are trying to run a giant cash-crop cycle and then move?
Honestly the questions you are asking are making me think you don'thave anywhere near the expertise or experience to pull off something like this.
Start small.
Remember the parable about the greedy crow who gets his head stuck in the urn because he refuses to drop the GIANT mouthful of grapes?
You're biting off more than I think you are prepared to chew.